ARTICLE IN PRESS

www.elsevier.com/locate/jsames

Journal of South American Earth Sciences xxx (2008) xxx–xxx

Time constraints on the Famatinian and Achalian structuralevolution of the basement of the Sierra de San Luis

(Eastern Sierras Pampeanas, Argentina)

Andre Steenken a,*, Siegfried Siegesmund b, Klaus Wemmer b, Monica G. Lopez de Luchi c

a Universidade de Sao Paulo, Instituto de Geociencias, Departamento de Mineralogia e Geotectonica, Rua do Lago,

562, Cidade Universitaria, CEP 05508-080, Sao Paulo, SP, Brazilb Geoscience Centre of the University of Gottingen, University Gottingen, 37077 Gottingen, Goldschmidtstr. 3, Germany

c Instituto de Geocronologıa y Geologıa Isotopica, Pabellon INGEIS, Ciudad Universitaria, C1428EHA, Buenos Aires, Argentina

Abstract

Geochronological data pertaining to the structural evolution of the Sierra de San Luis provide important insights into the geodynamichistory along the southwestern margin of Gondwana. In the Pringles metamorphic complex, metamorphic fabrics (S1) were affected bytwo folding events (D2 and D3) related to the Ordovician approach of the Cuyania terrane. Contemporary formations of high-tempera-ture shear zones record a prominent east-side-up displacement. Resumption of compression due to the Achalian collision with the Chile-nia terrane was accommodated by the reactivation of the Famatinian high-temperature shear zones in greenschist facies conditions. K–Ar Ms ages point to their activity up to the Early Carboniferous. The post-Pampean structural evolution of the Pringles metamorphiccomplex is supported by new Sm–Nd and 207Pb/206Pb data, which agree with previously proposed early Cambrian sedimentation of thepsammopelitic precursors. A Sm–Nd mineral isochron, together with published SHRIMP U–Pb zircon ages, bracket the emplacement ofmafic and ultramafic intrusions that control the granulite facies metamorphism between 506 and 478 Ma. A late Cambrian emplacementof the crustal-derived Paso del Rey pluton is suggested by a 207Pb/206Pb zircon age at 491 ± 19 Ma. The syn-D2 emplacement of thesegranitoids indicates that the D1 to D2 structural evolution predates the generally assumed Middle Ordovician accretion of the Precord-illera/Cuyania terrane. K–Ar Hbl, Ms, and Bt ages and some Rb–Sr mica data record the cooling after the Famatinian metamorphicpeak. Ms ages from large Ms booklets suggest a common cooling of the basement of the sierra at approximately 445 Ma, whereas nor-mal-sized muscovites from gneissic rocks (K–Ar ages of �380 Ma) indicate slow cooling of the Pringles metamorphic complex withrespect to the other basement domains. K–Ar Bt ages between 360 and 340 Ma capture cooling below approximately 300 �C of the base-ment. Differential cooling is interpreted to reflect the Achalian tectonic cycle as an event separate from the Famatinian process.� 2007 Elsevier Ltd. All rights reserved.

Keywords: Eastern Sierras Pampeanas; Sierra de San Luis; Famatinian and Achalian cycles; Structural evolution; Geochronology

1. Introduction

The Eastern Pampean ranges (Sierras Pampeanas Orien-tales of Argentina) constitute a polyphase deformed, lateProterozoic to early Palaeozoic basement outcropping incentral Argentina. The three episodes of their deforma-

0895-9811/$ - see front matter � 2007 Elsevier Ltd. All rights reserved.

doi:10.1016/j.jsames.2007.05.002

* Corresponding author. Tel.: +55 11 3091 4216; fax: +55 11 3091 4295.E-mail address: asteenken@igc.usp.br (A. Steenken).

Please cite this article in press as: Steenken, A. et al., Time constrainSci. (2007), doi:10.1016/j.jsames.2007.05.002

tional history, the early Cambrian (540–510 Ma), lateCambrian–Ordovician (500–440 Ma), and Devonian(420–350 Ma), are referred to as the Pampean, Famatinian,and Achalian cycles (e.g., Ramos et al., 1986; Sims et al.,1997, 1998; Rapela et al., 1998a,b; Stuart-Smith et al.,1999; Siegesmund et al., 2004; Steenken et al., 2004). Theyrelate to the accretion of different terranes integrated to theproto-Andean margin of Gondwana.

Different models have been invoked to explain the tec-tonometamorphic evolution in the Famatinian belt of the

ts on the Famatinian and Achalian structural ..., J. S. Am. Earth

2 A. Steenken et al. / Journal of South American Earth Sciences xxx (2008) xxx–xxx

ARTICLE IN PRESS

Eastern Sierras Pampeanas, considered to record theapproach of the Precordillera/Cuyania terrane during theEarly–Middle Ordovician (Astini, 1996; Thomas and Astini,1996, 2003; Rapela et al., 1999; Pankhurst et al., 2000; Ace-nolaza and Toselli, 2000; Acenolaza et al., 2002; Astini andDavila, 2004; Dahlquist and Galindo, 2004).

The Sierra de San Luis (32�100, 33�200S/65�150,66�200W), the southwesternmost tip of the Eastern Pam-pean Ranges (Fig. 1), represents an excellent location foranalysing the Ordovician–Devonian events, because of itslocation between the Pampean orogen and the Precordi-llera or larger Cuyania terrane (Ramos et al., 1986; Ramos,1995). Metamorphism and granitoids cover this time span,and different crustal sections are exposed (Kilmurray andDalla Salda, 1977; Hack, 1987; Lopez de Luchi, 1987,1996; Ortiz Suarez, 1988, 1996; Brogioni, 1993; Llambıaset al., 1996a, 1998; von Gosen and Prozzi, 1996, 1998; Simset al., 1998; Lopez de Luchi et al., 1999, 2000; Hauzenber-ger et al., 2001; Steenken et al., 2004). Cambrian sedimen-tation has been recognised in parts of the basement (Simset al., 1998; Sollner et al., 2000), reinforcing the idea of alocal, entirely post-Pampean evolution.

Fig. 1. Simplified compilation of the geology of the Eastern Sierras Pampeashowing the main basement provinces (Sierras de Cordoba, Sierra de Chepesbasement of southwestern Gondwana. Ages of the metasedimentary sequence

Please cite this article in press as: Steenken, A. et al., Time constrainSci. (2007), doi:10.1016/j.jsames.2007.05.002

The relative timing of fabric elements within the base-ment domains of the Sierra de San Luis previously has beenconsidered (e.g., Kilmurray, 1981, 1982; Lopez de Luchi,1986; von Gosen and Prozzi, 1996; von Gosen and Prozzi,1998; Gosen, 1998a,b; Gonzalez and Llambıas 1998; Lopezde Luchi and Cerredo, 2001; Gonzalez et al., 2002a,b; Satoet al., 2003a; Whitmeyer and Simpson, 2004). Nevertheless,the relation between the high-grade metamorphic rocks ofthe Pringles metamorphic complex (PMC; Fig. 2) and itslow-grade metamorphic envelope remains a matter of dis-cussion (cf. von Gosen and Prozzi, 1998; Sims et al.,1998; Steenken, 2002; Chernicoff and Ramos, 2003; OrtizSuarez and Casquet, 2005). Differences in the deforma-tional record led to a series of models explaining the timingof deposition of the metasedimentary precursors of thePMC (Sims et al., 1997, 1998; von Gosen and Prozzi,1998; Lopez de Luchi et al., 2003; Steenken et al., 2004).

This paper presents detailed structural observations andSm–Nd and 207Pb/206Pb data about the intrusive rocks toprovide the absolute timing of fabric elements within thePMC and its low-grade metamorphic envelope (Fig. 2).Thirty new K–Ar ages of Hbl, Ms, and Bt document the

nas (van Gosen and Prozzi, 1998; Martino, 2003; Steenken et al., 2004),, and Sierra de San Luis) that constitute the Late Proterozoic–Palaeozoics refer to the assumed timing of peak metamorphism.

ts on the Famatinian and Achalian structural ..., J. S. Am. Earth

Fig. 2. Schematic geological map of the southwestern Sierra de San Luis (van Gosen and Prozzi, 1998; Sims et al., 1998; Steenken et al., 2004). Names ofthe different basement domains are indicated following the suggestion of Sims et al. (1997). For further references, see Fig. 9. Pole figures (equal areaprojections, lower hemisphere) show structural linear and planar fabrics mostly recorded along three WNW-ESE-trending profiles (black dots). Numbersrefer to the most important Ordovician intrusives: (1) Rıo de la Carpa granite, (2) northern and southern stock of Paso del Rey granites, (3) Rıo Clarogranite, (4) Gasparillo tonalite, (5) Las Verbenas tonalite, (6) Bemberg tonalite.

A. Steenken et al. / Journal of South American Earth Sciences xxx (2008) xxx–xxx 3

ARTICLE IN PRESS

cooling history of the different basement domains of thesierra. The results are critically evaluated in light of previ-ously published data. The combination of structural obser-vations with geochronological results may help elucidatethe Famatinian–Achalian history recorded by themetasedimentary basement rocks and intruding granitoids.A better understanding of the geodynamic evolution of theSierra de San Luis allows for substantiation of a geody-

Please cite this article in press as: Steenken, A. et al., Time constrainSci. (2007), doi:10.1016/j.jsames.2007.05.002

namic scenario for the early Palaeozoic accretional historywest of the Rıo de La Plata Craton.

2. Geological setting

The NNE-trending, predominantly metaclastic base-ment domains of the Sierra de San Luis are consideredon the basis of their dissimilar structural record as the

ts on the Famatinian and Achalian structural ..., J. S. Am. Earth

4 A. Steenken et al. / Journal of South American Earth Sciences xxx (2008) xxx–xxx

ARTICLE IN PRESS

Nogolı metamorphic complex in the west, followed to theeast by the Pringles and Conlara metamorphic complexes(Fig. 2, Sims et al., 1997), though von Gosen and Prozzi(1996) divide the Sierra de San Luis into a Western Base-ment Complex that is largely coincident with the Nogolımetamorphic complex (Sims et al., 1997) and an EasternBasement Complex roughly coincident with the PMC.According to von Gosen and Prozzi (1996), the EasternBasement Complex constitutes a polyphase deformed,high-grade metamorphic basement covered by amedium-grade metamorphic mica-schist group and itslow-grade metamorphic equivalents, namely, the San LuisFormation (Fig. 2, Prozzi and Ramos, 1988). Early–Middle Ordovician quartz-dioritic to granitic intrusionsare parallel to the fabrics of their hosts in all domains(Ortiz Suarez et al., 1992; Sims et al., 1997; von Gosen,1998a; Llambıas et al., 1998; Lopez de Luchi et al.,2007). Mafic and minor ultramafic rocks along the wes-tern realm of the PMC are of intrusive origin (Bonorino,1961; Kilmurray and Villar, 1981; Hauzenberger et al.,1996; Brogioni, 2001), whereas within the Nogolı andConlara metamorphic complexes, a volcanic origin hasbeen considered (Delakowitz et al., 1991; Gonzalezet al., 2002b). A Devonian generation of granodioriticto syenogranitic voluminous batholiths shows syn- topostkinematic relations with their host (e.g., Llambıaset al., 1998; Siegesmund et al., 2004).

The metamorphic basement of the Nogolı metamorphiccomplex comprises (1) a supracrustal association (metape-lites, metaquartzites, and mafic–ultramafic metavolcanicrocks with minor banded iron formations, marbles, andcalc-silicates) and (2) ortho- and paragneisses, migmatites,and orthoamphibolites intruded by monzonites and gran-ites (Sims et al., 1997, 1998; Gonzalez, 2000).

A pre-Famatinian structural evolution of this basementcomplex has been proposed (Llambıas et al., 1996b; Gon-zalez and Llambıas, 1998; von Gosen and Prozzi, 1998;Gonzalez et al., 2004). Von Gosen and Prozzi (1998) recog-nise three pre-Famatinian deformation events within theNogolı metamorphic complex. Peak metamorphic condi-tions are indicated by Bt–Ms–Grt–Cd–Sil (abbreviationsfollow Kretz, 1983). Compelling geochronological evidenceof pre-Famatinian evolution is scarce. A Sm–Nd WR iso-chron at 1.5 Ga in the mafic and ultramafic metavolcanitescan be interpreted as either the crystallisation age or theage of differenciation of these rocks from the mantle (Satoet al., 2001a, 2003b). Vujovich and Ostera (2003) present aconventional U–Pb zircon discordia at 554 ± 5 Ma for adeformed crustal derived Bt–Kfs orthogneiss. U–Pb mona-zite ages for a Sil–Grt paragneiss at 458 ± 3 Ma (conven-tional) and 470 ± 15 Ma (electron microprobe) wereconsidered a Famatinian D4 event related to the peak ofpressure and the formation of penetrative NNE–SSW-trending structures, equivalent to D2 in the PMC (Gon-zalez et al., 2002a).

The PMC consists of paragneisses, mica schists, migma-tites, and amphibolites. A penetrative, NNE-trending D2

Please cite this article in press as: Steenken, A. et al., Time constrainSci. (2007), doi:10.1016/j.jsames.2007.05.002

foliation is associated with the development of the peakmetamorphic assemblage (M2) of Pl–Kfs–Grt–Bt–Sil ± Cd(von Gosen and Prozzi, 1998). Granulite facies paragneses,resulting from the emplacement of mafic and ultramaficintrusions along the NNE-trending belt in the westernrealm of the complex, are considered as M2-G: 740–790 �C and 5.7–6.4 kbar (Hauzenberger et al., 2001). TheP-T path shows near isobaric heating. During cooling,the formation (reactivation?) of mylonitic shear zones inthe western part of the PMC (La Arenilla mylonite belt;Ortiz Suarez et al., 1992) retrogrades most of the granulitefacies rocks at amphibolite facies conditions (M3-A; Hau-zenberger et al., 2001).

The metamorphic evolution of the PMC is constrainedby dating of felsic and mafic rocks. Sims et al. (1998) calcu-late, for the Grt–Bt–Sil gneisses, a SHRIMP U–Pb age of452 ± 12 Ma in monazite, supported by four additional zir-con rim analyses at approximately 460 Ma. These ages areinterpreted to mark the end of granulite facies metamor-phism. Igneous rocks, yielding SHRIMP U–Pb zircon agesof 484 ± 7 Ma in an orthogneiss and 478 ± 6 Ma in a felsicsegregation within the mafic rocks, suggest an Early Ordo-vician metamorphic peak.

von Gosen and Prozzi (1998a,b) consider the San LuisFormation and the mica-schist group part of one continu-ous crustal section that forms the metamorphic equivalentof the Puncoviscana Formation (Jezek et al., 1985). Theseauthors suggest that the high-grade rocks of the EasternBasement Complex were uplifted against the mica-schistgroup (medium-grade gneisses). Two deformational eventshave been recognised (von Gosen and Prozzi, 1998): tightfolds with a well-developed NNE-trending axial planecleavage (D1) and later discrete shear zones separated bydomains of open refolding and crenulation cleavage (D2).The latter cleavage is considered the result of continuousWNW–ESE, post-Famatinian compression. These defor-mations correspond to the D2 and D3 history of the high-grade metamorphic rocks of the Eastern Basement Com-plex. In contrast to the proposed interval of erosion ofthe high-grade metamorphic basement of the PMC, fol-lowed by deposition of low-grade units, Sims et al. (1997,1998) and Steenken et al. (2004) suggest the sedimentaryprecursors of the entire medium- to high-grade metamor-phic sequence were deposited in a post-Pampean exten-sional setting.

The main rock types of the Conlara metamorphic com-plex are gneisses, migmatites, banded schists, and scarceamphibolites (Kilmurray, 1981, 1982; Kilmurray and DallaSalda, 1977; Ortiz Suarez, 1988, 1996; Lopez de Luchi,1996; Lopez de Luchi et al., 2003). The metamorphic para-geneses of the gneisses and schists are restricted to Pl–Bt ± Ms ± Grt. Four deformational events have beenrecognised (Lopez de Luchi and Cerredo, 2001). At leastD3 affects the (pre?-) Famatinian granitoids that intrudedthe complex as either large plutons (e.g., El Penon granite;Llaneza and Ortız Suarez, 2000; Steenken et al., 2005a) orsheet-like stocks similar to the Rıo de La Carpa granite

ts on the Famatinian and Achalian structural ..., J. S. Am. Earth

A. Steenken et al. / Journal of South American Earth Sciences xxx (2008) xxx–xxx 5

ARTICLE IN PRESS

(Llambıas et al., 1991). Along the highly inclined Rıo Guz-man shear zone, the Conlara metamorphic complex isuplifted and sinistrally displaced against the eastern beltof phyllites (Sims et al., 1997; von Gosen and Prozzi,1998; von Gosen 1998a,b; Steenken, 2002).

3. Structural data pertaining to the Pringles metamorphic

complex

Detailed structural mappings were carried out along E–W-trending profiles that constitute the southern part of thePMC (sensu Sims et al., 1997) to unravel the relative timingof fabric elements (Fig. 2).

The metamorphic grade ranges from greenschist faciesin the realm of the two belts of the San Luis Formationto granulite facies in the vicinity of the mafic to ultramaficintrusions. The low-grade metapsammopelitic end mem-bers of this metamorphic sequence are characterised bymineral paragenesis of Pl–Bt–Ms ± Grt. Centimetre to afew decimetre wide calc-silicates appear as boudinagedand zoned lenses. The core of these lenses shows a mineralassemblage of Qtz–Pl–Czs–Grt–Hbl–Ms, suggesting uppergreenschist facies metamorphism (Bucher and Frey, 1994).Within the amphibolite facies metapelites, staurolitebecomes stable with biotite, muscovite, and garnet(Fig. 6c), whereas at higher metamorphic grades, sillima-nite appears at the expense of muscovite (cf. M2-G; Hau-zenberger et al., 2001). Widespread migmatisation isassociated with granulite facies metamorphism. In situ

melting is indicated by the lack of Ms in the high-grademetamorphic (Bt–Grt–Sil ± Cd) melanosome layers(Fig. 3a), whereas in the medium-grade gneisses, an injec-tion origin for the leucosomes is favoured. A minimummelting temperature of approximately 750 �C (e.g., Bucherand Frey, 1994) is indicated by the granodioritic composi-tion (Qtz–Ffs–Pl–Bt ± Grt) of newly formed melts (Steen-ken et al., 2005b).

3.1. Mica-schist group

The low- to medium-grade metasedimentary successionof the mica-schist group is characterised by close interlay-ers of tightly D2-folded gneisses and schists. Its first meta-morphic planar fabric (S1), indicated by Bt–Ms, issubparallel to the sedimentary layering. The origin of theS1 foliation is presumably the result of increasing tempera-tures in an extensional setting and indicated by the boudi-nage of the competent decimetre-thick calc-silicate layersobserved in the D2 fold hinges. The distribution of D2 foldaxes along an ESE-inclined great circle points to theirsheath fold geometry (Figs. 2 and 3b). The SE-plungingstretching lineation (L2) is parallel to the cone axes of thesheaths. L2 is marked by both the linear arrangement ofMs–Bt within the metapsammites and staurolite in thepelitic sequences. Locally, an older mineral lineation (L1)with shallow inclination probably related to the D1 eventis observed.

Please cite this article in press as: Steenken, A. et al., Time constrainSci. (2007), doi:10.1016/j.jsames.2007.05.002

In the west of the PMC, the crosscutting relationshipbetween the S1 and S2 planar fabrics (Fig. 3e) allows thereconstruction of WNW-inclined fold axial planes. Theintersection of the foliation planes led to a pronouncedcrenulation of the previous layering. The NNE–NE–/SSW–SW-trending crenulation lineation is generally shal-low plunging. To the west, the D2 fold limbs enclose moreacute angles with S2 fabrics. Within the gneissic layers, theS2 fabrics are characterised by the new growth of Bt ± Ms,which crosscuts the earlier metamorphic banding.

Small granitic injections of approximately 1-cm widthare ubiquitous within this medium-grade unit. Their foldpattern seems unrelated to the local D2 fold pattern.Because these granitic veins could have intruded the previ-ous metamorphic pile at any angles, the fold pattern can beexplained by the initial orientations of these veins. In addi-tion, the contrasting fold patterns might originate in therheological contrast between the fine-grained gneisses andthe medium-grained melt injections, as indicated by theptygmatic fold geometry (Fig. 3c and d). Randomly ori-ented injections are observed within the gneisses only;within the schist sequences, melt injections are parallel tothe penetrative S1 foliation. The differential behaviour isattributed to rheological contrasts and does not necessarilyimply an extensional setting for the intrusion of thesemelts. Von Gosen and Prozzi (1998) suggest an extensionalsetting based on the unconformity between lithologicalcontacts and planar fabrics.

Large Ordovician pegmatites are up to a few decametreswide. The structural relation of the largest pegmatites withthe gneissic host is difficult to establish because they behaveas rigid bodies during deformation and bear only marginaldeformation. Observed contacts are parallel to the penetra-tive S2 foliation. A few decimetre-wide dykes indicate thatthese pegmatites intruded the host parallel to any preexist-ing planar fabric, because they were tightly folded duringD2 (Fig. 3f). The interference of D2 structures with opento tight D3 folds is indicated by refolded pegmatite layers(Fig. 4a).

3.2. Medium- to high-grade metamorphic succession

Within the PMC, S2 becomes the dominant planar fab-ric element. Relative time constraints are provided by iso-clinally folded granitic and pegmatitic injections thatwere emplaced parallel to S1. During D3, these folds wererefolded by open to tight folds (Fig. 4b). The D3 fold axesgenerally strike NNE–SSW with a variable but moderateplunge (Figs. 2 and 4c). Locally along the eastern realmof the PMC, the migmatites exhibit a new foliation plane(S3). The ENE vergence of axial planes increases to the eastof the PMC. Steep fold axes indicate the D2 sheath foldgeometry. The L2 stretching lineation is within the dip-direction of the S2 planar fabrics and locally indicated bysillimanite needles.

Relicts of an older structural evolution were notobserved, which argues against the proposed pre-Famatin-

ts on the Famatinian and Achalian structural ..., J. S. Am. Earth

Fig. 3. (a) Migmatite of the PMC. Melt segregations are lined with thick melanosome layers largely composed of Bt–Sil ± Grt. (b) Intensely undulatingfold hinges within medium-grade gneisses denoting the D2 sheath fold geometry. (c and d) Ptygmatic folding of melt injections, the result of largerheological differences between the melts and their gneissic host. (e) S1/S2 cross-cutting relationship. (f) Tight D2 fold in a pegmatite vein in the medium-grade successions.

6 A. Steenken et al. / Journal of South American Earth Sciences xxx (2008) xxx–xxx

ARTICLE IN PRESS

ian structural evolution of the PMC suggested by vonGosen and Prozzi (1998) on the basis of a comparison ofthe structural record of the Western Basement Complexwith relict fabrics in the migmatites of the PMC.

Detailed mappings of the limits between the high- andmedium-grade metamorphic rocks were performed. Thewestern transition between the high-grade metamorphicrocks and the mica schists is controlled by the high-tempera-ture La Arenilla shear zone (Fig. 2). The zone of micaschists between La Escalerilla and the shear-zone is charac-terised by Pl–Ms–Bt–Grt ± St ± Sil ± Chl, whereas withinthe La Arenilla shear zone, Ms + St + Qtz are replaced byGrt + Sil + Bt. No major shear zone-controlled transitionbetween the high-grade metamorphic rocks and the easternbelt of the mica-schist group was found. A continuousdecrease of the metamorphic temperature is indicated bythe gradual replacement of sillimanite by muscovite, asporphyroblasts either overgrowing the foliation or defining

Please cite this article in press as: Steenken, A. et al., Time constrainSci. (2007), doi:10.1016/j.jsames.2007.05.002

the S2 penetrative foliation together with biotite, whichsuggests a prograde metamorphic sequence. Sims et al.(1997) report that the boundary between the medium-and high-grade rocks of the complex is transitional andmarked by pegmatites. In accordance with observationsby von Gosen (1998a), no major discontinuity was foundbetween the medium-grade mica-schist group and the phyl-litic rocks of the San Luis Formation, though the latterseem to lack a second folding phase.

3.3. Famatinian intrusions

The medium- to high-grade metamorphic rocks of thePMC provide the host for many granodioritic to graniticintrusions (e.g., Paso del Rey granite, Fig. 2) that wereconsidered synorogenic with respect to the main phaseof the Famatinian orogeny (Llambıas et al., 1998; Satoet al., 2003b). Contacts of these intrusions with the coun-

ts on the Famatinian and Achalian structural ..., J. S. Am. Earth

Fig. 4. (a and a0) Open refolding (D3) of an isoclinal D2 fold of a metre-wide pegmatite. (b and b0) D3 folds within medium- to high-grade metamorphicgneisses. Relict isoclinal folds of granodioritic injections are the result of D2. (c) Interlayering of migmatites and granodiorites within the PMC. D3 foldaxes shallowly plunge to the NNE or SSW. (d) d-type quartz mobilisation within phyllites of the western belt of the San Luis Formation, documentingeast-side up kinematics.

A. Steenken et al. / Journal of South American Earth Sciences xxx (2008) xxx–xxx 7

ARTICLE IN PRESS

try rock are parallel to the penetrative S2 fabrics, as hasbeen described previously by von Gosen (1998a), whoconsiders that within the mica-schist group, this foliationrepresents S1. Microstructures record a continuum frommagmatic to high-temperature solid-state fabrics. The lat-ter partially obliterate the magmatic fabric. Small shearbands formed on biotite and quartz domains. Subgrain

Please cite this article in press as: Steenken, A. et al., Time constrainSci. (2007), doi:10.1016/j.jsames.2007.05.002

formation in plagioclase, together with myrmekitegrowth at the expense of K–feldspar, suggests tempera-tures during the deformation of 400–500 �C (Simpsonand Wintsch, 1989). A similar temperature array mightbe assigned to the metamorphic growth of pinkish gar-nets that overgrow the previous fabric. Small granodio-ritic dykes that are coeval with the larger intrusives

ts on the Famatinian and Achalian structural ..., J. S. Am. Earth

8 A. Steenken et al. / Journal of South American Earth Sciences xxx (2008) xxx–xxx

ARTICLE IN PRESS

were isoclinally folded during D2, whereas D3 led toopen refold structures (Fig. 4a and b).

The emplacement of tonalitic to granodioritic meltswithin the nonmetamorphic sediments of the San Luis For-mation has been suggested (Sims et al., 1997; von Gosenand Prozzi, 1998; von Gosen, 1998a,b). In contrast, smalltonalitic veins were injected parallel to the first foliationof the phyllites, which indicates that the magma ascentwas controlled by the first deformation of the San LuisFormation. A syndeformational emplacement of theseintrusions is indicated by recrystallised quartz ribbonsand kinked biotites suggesting upper greenschist facies con-ditions (Lopez de Luchi et al., 2007).

3.4. Mylonites

In the eastern Sierra de San Luis, the prominent RıoGuzman shear zone (Sims et al., 1997) controls the limitbetween the Conlara metamorphic complex and the SanLuis Formation. In addition to field observations, its con-tinuity and NNE-trending orientation is well documentedby satellite images. Mylonitic foliations are steeply inclinedto either the ESE or WNW, with a pronounced stretchinglineation close to the dip direction. This shear zone accom-modates the vertical displacement between the Conlarametamorphic complex and the San Luis Formation ingreenschist facies conditions. An oblique shear componentoverprinting the steep linear fabric varies from sinistral todextral (Fig. 5).

Within the PMC, the La Arenilla shear zone follows thebelt of mafic intrusions (Fig. 5). In the south, it compen-sates for the transition from the medium-grade metasedi-ments of the PMC to the granulite facies gneisses.Further to the north in the area of La Carolina, a seriesof smaller mylonitic belts is observed, which is consistentwith previous mappings (von Gosen, 1998b) that show afanning of the mylonitic belt in the north. This shear zoneaffects the metasedimentary rocks as well as the Ordovicianand Devonian intrusives with differential intensity.

The NNE-trending, steeply inclined mylonitic foliationis superimposed on the regional S2 fabric. The stretchinglineation (L2) is generally close to the dip direction of thefoliation. Meso- and microstructures indicate a top-to-the-west displacement of the eastern basement units (Figs.4d and 6a).

Few mylonites that cut the S2 fabrics at an acute anglecan be traced for a few decametres only. Kinematic indica-tors in combination with a subhorizontal stretching linea-tion of an NE–SW-striking mylonite indicate a dextralsense of displacement. A subhorizontal lineation also canbe detected within the NNE–SSW-trending mylonite belts.This second lineation is characterised by a linear arrange-ment of recrystallised, fine-grained muscovite. Scarce S-Cfabrics within few mica-rich layers point to sinistral dis-placement. These two sets of transpressive strike-slip planesare interpreted as antithetic faults related to a late-stage(Devonian) reactivation of the shear zone.

Please cite this article in press as: Steenken, A. et al., Time constrainSci. (2007), doi:10.1016/j.jsames.2007.05.002

Maximum temperatures during the beginning of mylo-nite formation are indicated by the alteration of granulitefacies paragenesis at higher amphibolite facies conditions(Fig. 6b). Newly grown prismatic sillimanite traces the lin-ear fabric within the migmatites. Snowball-textured garnetsdenote their syntectonic growth. Mylonitic pegmatiteslocally show elongated K–feldspar crystals. Subgrain rota-tion recrystallisation of K–feldspar crystals is indicated bycore-mantle structures. The absence of flame-perthite in therims of the relict grains, as well as the local growth ofasymmetric myrmekite in the pressure shadow of K–feld-spar r-klasts, denotes minimum temperatures of higherthan 500 �C (Fig. 6d; Simpson and Wintsch, 1989; Vidalet al., 1980; Olsen and Kohlstedt, 1985; Tullis and Yund,1991). Chessboard patterns in quartz grains indicate tem-peratures above the a–b transition at approximately550 �C (Mainprice et al., 1986; Kruhl, 1996).

Along the western border of the La Arenilla shear zone,temperatures during mylonitisation correspond to green-schist facies conditions. Plagioclase crystals are passivelyrotated in a matrix of recrystallised quartz. Quartz texturesof all mylonites show straight and high-angle grain bound-aries, pointing to a period of static annealing of textures.Thus, temperatures above 300 �C are indicated for theend of ductile deformation.

The margin of the La Escalerilla pluton is heteroge-neously affected by a variable, high-temperature sub-soli-dus deformation that decreases toward the centre andwestern margin of the pluton, where magmatic to sub-mag-matic microstructures, such as intracrystalline fractureswithin plagioclase filled with residual melt (Bouchezet al., 1992), are preserved. The outermost margin of thepluton exhibits a high-temperature, ultra-mylonitic lamina-tion. Anhedral plagioclase crystals show intense unduloseextinction. Grain boundary migration recrystallisationbetween neighbouring plagioclases (Fig. 6e) indicatesdeformation temperatures of more than 500 �C (Tullisand Yund, 1991). The stretching lineation is locally subhori-zontal, whereas in the neighbouring country rocks, a mod-erately to steeply SE-plunging lineation develops. Theappearance of subhorizontal lineations is restricted to myl-onite zones discordant to the penetrative S2 foliation andone mylonitic belt bordering a belt of Ordovician tonaliticto granodioritic plutons that intruded the limit between thewestern belt of the San Luis Formation and the Nogolımetamorphic complex. They indicate sinistral displacementbetween the basement domains during the Devonian.

4. Geochronology

To provide an absolute time scale for the structural evo-lution of the Sierra de San Luis, different geochronologicalmethods have been utilised. Extensive K–Ar data on Hbl,Ms, and Bt document the cooling history of the differentbasement domains. Sm–Nd mineral isochrons and207Pb/206Pb zircon evaporation experiments on three sam-ples provide insight into the intrusive history of the

ts on the Famatinian and Achalian structural ..., J. S. Am. Earth

Fig. 5. Compilation of recorded mylonitic planar fabrics and appropriate displacement vectors (Hoppener, 1955). Most observed fabrics record an east-side-up displacement with a minor sinistral component, with the exception of the mylonitic shear zones investigated within the Nogolı metamorphiccomplex or its eastern border with the Pringles metamorphic complex, where a local west-over-east displacement is observed. Samples of the labelledlocalities are subject to geochronological dating (see Figs. 2 and 9).

A. Steenken et al. / Journal of South American Earth Sciences xxx (2008) xxx–xxx 9

ARTICLE IN PRESS

PMC. Results were critically evaluated with regard to pre-viously established data.

4.1. Analytical methods

207Pb/206Pb zircon evaporation experiments were carriedout at the University of Adelaide (Australia) using the Pbevaporation technique, following the method outlined by

Please cite this article in press as: Steenken, A. et al., Time constrainSci. (2007), doi:10.1016/j.jsames.2007.05.002

Kober (1986, 1987). During direct evaporation, a zircongrain is stepwise heated, causing the initial release of Pbfrom cracks, exterior surfaces, metamict, and non-latticedomains of the grain. Pb from intact core domains isreleased at higher temperatures and condensed onto anopposing filament. Subsequent heating of the opposing fila-ment reevaporates and ionises this Pb for measurement.Isotope ratios were measured using a secondary electron

ts on the Famatinian and Achalian structural ..., J. S. Am. Earth

Fig. 6. (a) Mylonitic fabric within high-grade metamorphic gneisses (width of view �10 mm). (b) Preserved granulite facies microlithon in an amphibolitefacies mylonite (A 56-01) (width of view �16 mm). (c) Amphibolite facies paragenesis of a mica schist (A 42-02) in western PMC. The rotated garnetsuggests syndeformational growth (width of view �12 mm). (d) Ultramylonitic sample from a pegmatite of the La Arenilla mylonite belt. Mylonitisationled to the formation of K-feldspar core mantle structures. Recrystallised tails bear K-feldspar subgrains formed by subgrain rotation recrystallisation. Therelict feldspar clasts marginally lack perthitic exsolution lamellae (width of view �16 mm, upper image). (e) Grain boundary migration recrystallisationfeature of feldspars in the mylonitic margin of the La Escalerilla pluton (width of view �2 mm). (f) Statically recrystallised Pl–Bt fabric in a migmatite ofthe Nogolı metamorphic complex (A 39-01) (width of view �5.5 mm). (g) SEM cathodoluminescent image of analysed zircons of the Paso del Rey granite(A 02-02) showing polyphase growing structure. Envelopes are generally dark with minor zoning.

10 A. Steenken et al. / Journal of South American Earth Sciences xxx (2008) xxx–xxx

ARTICLE IN PRESS

multiplier. Analysis of the plating yields 208Pb/206Pb,204Pb/206Pb, and 207Pb/206Pb ratios (Table 1). The207Pb/206Pb ratios are used to calculate the ages, followingcorrections for common Pb, estimated from 204Pb/206Pbratios (Stacey and Kramers, 1975).

Please cite this article in press as: Steenken, A. et al., Time constrainSci. (2007), doi:10.1016/j.jsames.2007.05.002

Two samples from the (ultra-)mafic intrusions in thewestern realm of the PMC were subjected to Sm–Nd min-eral isochron dating. The Nd isotopic data were obtainedusing a ThermoFinnigan Triton mass spectrometer in staticmode at the Geoscience Centre of the University of Gottin-

ts on the Famatinian and Achalian structural ..., J. S. Am. Earth

Tab

le1

Pb

iso

top

ed

ata

fro

mth

eP

aso

del

Rey

gran

ite

of

the

Pri

ngl

esm

etam

orp

hic

com

ple

x(P

MC

)

Sam

ple

A02

-02

208P

b/2

06P

b±

2r(%

)204P

b/2

06P

b±

2r(%

)207P

b/2

06P

b±

2r(%

)U

nco

rrec

ted

age

±2r

Co

mm

on

Pb

corr

ecte

dS

tep

Age

±2r

207P

b/2

06P

b*

14/A

02-0

2/73

0.05

1549

12.0

0.00

0282

6.0

0.06

0114

48.

360

717

10.

0560

026

452

181

14/A

02-0

2/98

0.11

9205

0.9

0.00

0060

54.

60.

0593

862

0.8

581

180.

0585

075

548

2014

/A02

-02/

850.

0996

731.

90.

0000

993

4.4

0.05

8471

0.8

547

160.

0570

249

492

1914

/A02

-02/

080.

1137

82.

00.

0000

796

8.0

0.06

0206

1.7

611

360.

0590

503

568

3915

/A02

-02/

080.

2115

386.

30.

0001

4416

.70.

0619

214

1.9

671

410.

0598

322

597

54

A. Steenken et al. / Journal of South American Earth Sciences xxx (2008) xxx–xxx 11

ARTICLE IN PRESS

Please cite this article in press as: Steenken, A. et al., Time constrainSci. (2007), doi:10.1016/j.jsames.2007.05.002

gen (GZG, Germany). Detailed analytical procedure forthe Nd isotopic measurements are the same as thosereported in Steenken et al. (2004). Nd isotopic ratios werecorrected for mass fractionation relative to146Nd/144Nd = 0.7219. The La Jolla standard yields143Nd/144Nd = 0.511840 ± 0.000003 (2r). Total procedureblanks were consistently below 150 ppg for Nd. Sm–Ndisochron calculations use the regression program Isoplot/Ex (Ludwig, 2003). 143Nd/144Nd ratios are reported withtheir 2r internal precision, plus the uncertainties resultingfrom the spike correction (Table 2).

An extensive study of the cooling history of all basementdomains of the Sierra de San Luis was carried out by K–Ardating of micas and few amphiboles at the GZG. For min-eral enrichment, the grain fraction between 125 mm and350 mm was processed by magnetic separation and handpicking. The purity of the mineral separates is >99%. Puri-fied micas were grounded in pure alcohol to remove alteredrims that might have suffered a loss of Ar or K. The Ar iso-topic composition was measured in a Pyrex glass extractionand purification line coupled with a VG 1200 C noble gasmass spectrometer operating in static mode. The amount ofradiogenic 40Ar* was determined by the isotope dilutionmethod using a highly enriched 38Ar spike (Schumacher,1975). The spike is calibrated against the biotite standardHD-B1 (Fuhrmann et al., 1987). The age calculations arebased on the constants recommended by the IUGS, quotedin Steiger and Jager (1977). Potassium was determined induplicate by flame photometry using an Eppendorf Elex63/61. The samples were dissolved in a mixture of HFand HNO3, according to the technique of Heinrichs andHerrmann (1990). CsCl and LiCl were added as an ionisa-tion buffer and internal standard, respectively. The analyti-cal error for the K–Ar age calculations is 95% confidencelevel (2r) (Table 3). The analytical procedure at GZGhas been described in great detail by Wemmer (1991) andsuccessfully applied during recent studies (e.g., Siegesmundet al., 2004; Buttner et al., 2005).

4.2. 207Pb/206Pb evaporation results

Zircons were separated from sample A 02-02 of thenorthern body of the Paso del Rey granite (Fig. 5) withinthe PMC. This sheet-like intrusion was chosen as represen-tative due to the large mineralogical and geochemical simi-larities it shares with other granitoids of the PMC (Lopezde Luchi et al., 2007), as well as their comparable micro-structures and structural integration in the metapsam-mopelitic host. The sample exhibits a gneissic planarfabric, indicated by the arrangement of plagioclase andbiotite crystals parallel to S2 of the host rock. This penetra-tive foliation is most prominent within the fine-graineddomains of the intrusion. Microstructures attest to a sub-solidus origin of the planar fabric. A few probably meta-morphic garnets overgrow the planar fabric.

The analysed zircons of sample A 02-02 are subhedraland show a complex growth structure (Fig. 6g). Cathodo-

ts on the Famatinian and Achalian structural ..., J. S. Am. Earth

12 A. Steenken et al. / Journal of South American Earth Sciences xxx (2008) xxx–xxx

ARTICLE IN PRESS

luminescent imaging reveals overgrowths on host crystalsof various forms, presumably inherited grains. The over-growths have a low CL response but an inner zone ofhigher response (lower U), which probably reflects continu-ous crystallisation during changing conditions and mag-matic compositions rather than two different overgrowths.

Evaporation experiments reveal 207Pb/206Pb age spectraranging from approximately 597 ± 54 Ma to 491 ± 19 Ma(Fig. 7). The lower limit is interpreted to reflect the mag-matically grown zircon rims during the emplacement ofthe pluton. Studies show that the revealed age frequencyspectra of the evaporation technique resemble results fromSHRIMP U–Pb dating (e.g., Foden et al., 1999), whichimplies that the older time increments reflect the age mem-ory of inherited detrital zircon cores. This time interval,though consistent with the inherited age spectra for thegranulite facies gneisses of the PMC (Sims et al., 1998),does not fit the typically observed Gondwanan detritalage spectra, because Mesoproterozoic and Early Protero-zoic increments are lacking.

4.3. Sm–Nd mineral isochrons

Both analysed samples belong to the belt of mafic andultramafic intrusions in the western realm of the PMC.Sample A 01-02 was taken from the interior part of a Pl–Am-bearing diorite with well-preserved magmatic textures(Fig. 5). Rock-forming crystals lack any internal deforma-tion. In addition to WR powder, plagioclase and amphi-bole separates were subjected to Sm–Nd analytics. Theresults define an isochron of 506 ± 19 Ma, regarded asthe crystallisation age of the diorite (Fig. 8a).

The second sample (A 08-02) belongs to the margin of ameta-ultramafic rock (Fig. 5), structurally concordantwithin the surrounding high-grade metamorphic gneissesand migmatites. Microstructural observations reveal awell-defined planar and linear fabric defined by thearrangement of subhedral amphibole and pyroxene crys-tals. Few amphibole long axes deviate from the penetrativetexture. Interstitials of the amphibole–pyroxene frameworkare filled with plagioclase. Deformation within plagioclaseis indicated by wedge-shaped twinning lamellae. Garnetsappear in equilibrium with the metamorphic texture. Athree-point model 1 isochron (Ludwig, 2003) on Grt–Hbl–WR yields an age of 434 ± 12 Ma (Fig. 8b), whichis related to the regional cooling of the basement.

Table 2Nd systematic of the two analysed (ultra-)mafic intrusions in the Pringles met

Sample Rock type Sm (ppm) Nd (p

A 01-02 - Pl undeformed mafic rock 0.08 0.48A 01-02 - Am 2.23 6.58A 01-02 - WR 1.89 5.68

A 08-02 - Grt syn-D2 ultra-mafic rock 6.2 10.2A 08-02 - Am 19.2 63.5A 08-02 - WR 8.11 25.6

Please cite this article in press as: Steenken, A. et al., Time constrainSci. (2007), doi:10.1016/j.jsames.2007.05.002

4.4. K–Ar Ms, Bt, and Hbl data

Thirty new K–Ar ages are presented for the differentmetamorphic domains of the Sierra de San Luis. Mergingthese results with previous data (Table 3, Steenken et al.,2003, 2004) provides a more accurate reconstruction ofthe post-Famatinian history of the basement complexesof the sierra. K–Ar mineral ages were complementarilytested by Rb–Sr mica dating and 40Ar/39Ar step-heatingin one amphibole separate. The results of the differentmethods are compiled in Table 3.

Three amphibole separates were gained from (ultra-)-mafic rocks. Sample A 37-01 was taken from ultramaficrocks associated with the late Cambrian Rıo Claro graniteof the Nogolı metamorphic complex (von Gosen et al.,2002). Sample A 45-01 belongs to a minor dyke in thePMC north of Paso del Rey (Fig. 9). One amphibolite sam-ple (A 52-01) is interlayered in the migmatic rocks of thePMC east of La Carolina. K–Ar analyses for the formertwo amphibole separates yield ages of 464 ± 14 Ma and454 ± 18 Ma. An age of 411 ± 10 Ma is obtained for theamphibolite (A 52-01) (Fig. 9). An Ar–Ar step-heatinganalysis on the last sample yields a well-defined plateauage of 416 ± 2 Ma, indistinguishable within error fromthe K–Ar analysis. An interpretation of these ages mustconsider variations in the closure temperature, generallyassumed to be approximately 580 �C (Kamber et al.,1995). The retentivity of amphiboles for 40Ar* is affectedby many factors, such as structure and chemical composi-tion of the minerals (McDougall and Harrison, 1999).Lower retentivity for 40Ar*, and therefore a notably low-ered closing temperature, can be caused by inclusions ofphyllosilicates (Onstott and Peacock, 1987) or exsolutionof cummingtonite (Harrison and Fitz Gerald, 1986).

A first survey of the K–Ar data suggests a wide diversityof cooling ages, not only among the basement domains butalso within each domain, which may be partly explained bythe emplacement of magmatic rocks during the Achaliantectonic cycle, as recorded by muscovites from undeformedpegmatite veins that yield ages of approximately 400 Ma(Fig. 9).

The scatter in K–Ar Ms ages for the different metamor-phic domains, including the Ordovician intrusives, variesbetween 447 and 349 Ma. Part of this variation relates tolarge differences in the size of the analysed minerals. Thedependence of the closure temperature on the grain size

amorphic complex (PMC)

pm) 147Sm/144Nd 143Nd/144Nd ± 2r eNd (T0)

0.09482 0.512568 12 �1.40.20476 0.512930 8 5.70.20085 0.512925 11 5.4

0.36782 0.513308 12 13.10.18313 0.512799 8 2.90.19140 0.512799 8 3.5

ts on the Famatinian and Achalian structural ..., J. S. Am. Earth

Table 3Compilation of obtained K–Ar ages of muscovites, biotites, and amphiboles and comparison with Ar–Ar amphibole and Rb–Sr mica data

Rock Type Sample Mineral K2O (wt. %) 40Ar* (nl/g)STP 40Ar* (%) K/Ar-Age (Ma) ±2r Rb/Sr-Age (Ma) ±2r** Ar/Ar-Age (Ma) ±2r

Nogolı metamorphic complex

Ultramafic rock (Rıo Claro) A 37-01 Hbl 0.93 15.81 91.83 464.7 13.7Pegmatite A 35-01 Ms (booklet) 10.41 167.18 96.35 439.7 9.1Mylonitic Rıo Claro granite A 36-01 Ms 11.02 140.61 95.85 357.7 8.2Pegmatite A 38-01 Ms (booklet) 10.46 168.75 98.01 441.5 9.3Migmatite A 39-01 Ms 10.61 158.28 98.6 411.8 6.9 458.8 9.6

Bt 10.07 152.61 97.07 417.6 10.3 422.2 8.9El Realito granodiorite A 61-01 Bt 9.76 124.47 98.66 357.5 20.6Ms-Bt gneiss A 06-02 Ms 10.62 161.94 97.87 419.9 9.7

Ms (OG)*** 10.69 171.88 98.45 440.2 9.2Ms-Bt gneiss A 13-02 Ms 9.66 120.23 95.69 349.7 10.0

Ms (OG)*** 9.65 122.59 99.33 356.3 7.9Ms-Bt-Grt leucomonzogranite A 14-02 Ms 10.95 135.82 98.88 348.6 9.6

Bt 8.74 130.11 97.85 411.0 9.2

Pringles metamorphic complex (PMC)

Ultramafic rock (Paso de Rey) A 45-01 Hbl 0.18 3.00 87.14 453.9 17.6Amphibolite (La Carolina) A 52-01 Hbl 0.43 6.32 96.43 410.9 9.9 415.6 2.2Paso del Rey granite-northern stock G 10-01 Ms 10.50 149.60 97.01 395.2 8.6Pegmatite A 2-01 Ms 10.66 157.31 98.13 407.8 8.3

Bt 9.83 135.24 96.08 382.9 8.0Granitoid A 3-01 Bt 9.76 120.33 98.16 346.7 7.1Ms-Bt-Grt gneiss A 4-01 Ms 10.27 140.57 97.45 381.2 8.0

Bt 9.44 106.31 99.12 319.2 6.7Bt-Grt gneiss A 5-01 Bt 9.89 135.88 98.31 382.5 9.2Pegmatite A 6-01 Ms 10.82 154.01 97.37 394.8 8.1

Bt 8.81 97.70 95.36 314.7 6.7Pegmatite A 10-01 Ms (booklet) 10.45 166.86 98.51 437.5 9.5Pegmatite A 15-01 Ms 10.51 155.36 96.26 408.4 8.6Las Verbenas tonalite A 40-01 Bt 9.57 127.10 98.72 370.9 7.9Bemberg tonalite A 43-01 Bt 9.12 117.37 98.05 360.5 7.5Bt-Grt-Sil mylonite A 56-01 Bt 9.78 146.70 99.00 413.8 10.3Cerro de la Torre pegmatite A 78-01 Ms (booklet) 10.32 156.01 95.53 416.7 9.1Paso del Rey granite-northern stock A 83-01 Bt 9.67 129.31 96.99 373.2 7.8 371.5 7.8Ms-Bt-Grt gneiss A 16-02 Ms 9.24 126.52 98.09 381.3 9.3Paso del Rey granite-southern stock A 17-02 Ms 10.75 151.77 98.07 391.9 8.4Ms-Bt-St-Grt schist A 42-03 Ms 8.73 118.52 97.56 378.4 11.0 363.3 7.6

Bt 8.75 119.15 99.02 379.4 8.9 373.7 7.8Mylonitic Ms fraction of peg. A 06-01 A 44-03 Ms 10.69 139.57 99.17 365.2 8.2 404.2 8.5

Conlara metamorphic complex

Pegmatite A 18-01 Ms (booklet) 10.70 170.97 91.21 437.8 9.0Los Alanices leucogranite A 20-01 Ms 10.84 165.39 98.90 420.1 9.2Banded schist A 21-01 Bt n.d. - 394.2 8.3Pegmatite A 22-01 Ms (booklet) 10.26 167.76 97.21 446.8 9.2

Bt 9.42 125.32 97.29 371.5 8.5Banded schist A 23-01 Ms 9.97 156.86 97.07 431.8 6.2 439.1 9.2

Bt 8.81 105.23 95.26 336.9 8.4 334.0 7.0(continued on next page)

A.

Steen

ken

eta

l./Jo

urn

al

of

So

uth

Am

erican

Ea

rthS

ciences

xx

x(

20

08

)x

xx

–x

xx

13

AR

TIC

LE

INP

RE

SS

Please

citeth

isarticle

inp

ressas:

Steen

ken

,A

.et

al.,T

ime

con

straints

on

the

Fam

atinian

and

Ach

alianstru

ctural

...,J.

S.

Am

.E

arthS

ci.(2007),

do

i:10.1016/j.jsames.2007.05.002

Table

3(c

onti

nu

ed)

Ro

ckT

ype

Sam

ple

Min

eral

K2O

(wt.

%)

40A

r*(n

l/g)

ST

P40A

r*(%

)K

/Ar-

Age

(Ma)

±2r

Rb

/Sr-

Age

(Ma)

±2r

**

Ar/

Ar-

Age

(Ma)

±2r

Ban

ded

sch

ist

A25

-01

Bt

9.47

132.

0098

.29

375.

18.

6M

s-B

tgn

eiss

A27

-01

Bt

9.53

117.

6198

.73

347.

07.

2E

lP

eno

ngr

anit

eA

59-0

1M

s(b

oo

kle

t)10

.64

170.

3498

.38

438.

59.

9B

and

edsc

his

tA

61-0

4B

t9.

3913

3.82

99.2

639

5.3

9.1

Peg

mat

ite

A63

-04

Ms

(bo

ok

let)

10.6

617

4.77

95.8

844

7.9

10.7

Dev

onia

nin

trusi

ons

Myl

on

itic

apli

te(L

aE

scal

eril

lap

luto

n)

A8-

01M

s10

.87

139.

4995

.07

359.

68.

0

El

Ho

rnit

ogr

anit

eA

26-0

1B

t9.

3811

4.08

98.2

534

2.5

7.0

Peg

mat

ite

(Las

Ch

acra

s-P

otr

eril

los

bat

ho

lith

)A

29-0

1M

s(b

oo

kle

t)10

.97

135.

7897

.42

348.

07.

5

Bt

9.54

121.

3198

.14

356.

67.

4P

egm

atit

eA

44-0

1M

s(b

oo

kle

t)10

.57

153.

6097

.89

402.

28.

2A

pli

te(L

aE

scal

eril

lap

luto

n)

A23

-02

Ms

10.6

815

1.27

98.3

439

3.1

8.9

Peg

mat

ite

A28

-02

Ms

(bo

ok

let)

10.3

415

0.10

96.4

040

1.9

8.9

Peg

mat

ite

(La

Esc

aler

illa

plu

ton

)A

36-0

3M

s(b

oo

kle

t)10

.59

143.

8497

.04

378.

58.

8

Qu

ote

der

ror

com

pli

esw

ith

95%

of

con

fid

ence

leve

l(2

r).

Ar

iso

top

icab

un

dan

ce:

40A

r:99

.600

0%;

38A

r:0.

0630

%;

36A

r:0.

3370

%.

Sp

ike

iso

top

icco

mp

osi

tio

n:

40A

r:0.

0099

980%

;38A

r:99

.989

0000

%;

36A

r:0.

0009

998%

.D

ecay

con

stan

ts(1

year�

1):

ke:

5.81

0E-1

1;kb

- :4.

962E

-10;

k to

t:5.

543E

-10.

Po

tass

ium

40K

:0.

0116

70%

;K

2O

/K:

0.83

02.

Sta

nd

ard

tem

per

atu

rep

ress

ure

(ST

P)

0�C

;76

0m

mH

g;n

orm

alat

mo

sph

ere

(DIN

1343

);27

3.15

K;

1013

.25

mb

ar.

Mo

lar

volu

me;

(ml)

:22

413.

8.A

tom

icw

eigh

t(g

mo

l�1):

totA

r:39

.947

7;40A

r:39

.962

4;to

tK:

39.1

027.

*R

adio

gen

icar

gon

.**

2rer

ror

of

Rb

–Sr

ages

,as

sum

edto

be

±2%

.***

Lar

ged

isco

rdan

tM

scr

ysta

ls(>

1cm

ind

iam

eter

).

Fig. 7. Results from zircon evaporation experiments for sample A02-02from the northern body of the Paso del Rey granite. The indicated agespectra can be interpreted as the result of age inheritance of relict zirconcores. The age from the outermost rim is probably the best approximationof the crystallisation age.

14 A. Steenken et al. / Journal of South American Earth Sciences xxx (2008) xxx–xxx

ARTICLE IN PRESS

Please cite this article in press as: Steenken, A. et al., Time constrainSci. (2007), doi:10.1016/j.jsames.2007.05.002

of the mica is of minor importance when ‘‘normal” fine- tocoarse-grained rocks are considered (McDougall and Har-rison, 1999). However, in the case of Ms booklets of peg-matitic grain size, the effective diffusion lengths of Ar lossare high, implying effective closure temperatures signifi-cantly above the commonly accepted values (cf. Buttneret al., 2005). This effect might be enhanced by the lack ofpervasive deformation of the hosting pegmatite or recrys-tallisation of the booklets. The importance of recrystallisa-tion has been addressed by Villa (1998), who proposes aclosure temperature as high as 500 �C for nonrecrystallisedwhite mica. A similar effect is expected for biotitecrystals.

Differences in the retentivity between differently sizedmicas were tested for two samples of the Nogolı metamor-phic complex that bear large muscovite plates discordantto the planar fabric (Table 3; samples A 06-02 and A 13-02). Results show that the larger crystals yield up to 20 Maolder ages than the corresponding fine-grained muscovites(Table 3).

Separating the ages for the Ms booklets that confine therange to 447–395 Ma from the entire age spectra, coolingbelow the 350–420 �C temperature interval (Blanckenburget al., 1989) is well defined for the different domains. Theage of the Ms booklets corresponds to their individual sizefrom approximately 1 to 15-cm diameter. In the Conlarametamorphic complex, cooling took place between 440and 420 Ma, comparable with the northern portion of theNogolı metamorphic complex. The PMC is characterisedby younger K–Ar Ms ages between 410 and 380 Ma. Theyoungest K–Ar Ms ages at approximately 350 Ma appearwithin the southern portion of the Nogolı metamorphiccomplex. K–Ar Ms ages from mylonitic shear zone sampleseast and west of the PMC cover the range 379–358 Ma(Fig. 10). The ages of the mylonites accord with previouslypublished data (Sims et al., 1998).

K–Ar Bt ages encompass a wide range between 418 and337 Ma. The ages older 382 Ma are obtained from nonre-crystallised biotites (Fig. 6f) and pegmatitic Bt booklets.Two ages of 315 Ma and 319 Ma are considered the result

ts on the Famatinian and Achalian structural ..., J. S. Am. Earth

Fig. 8. Sm–Nd isochrons for (a) a undeformed dioritic sample and (b) a highly deformed sample from a garnet-bearing ultramafic rock. In the first case,the age is interpreted to reflect the timing of crystallisation, whereas in the latter case, it must be related to cooling after peak metamorphism.

A. Steenken et al. / Journal of South American Earth Sciences xxx (2008) xxx–xxx 15

ARTICLE IN PRESS

of a localised reactivation of the basement that led to Arloss in the biotites (Fig. 11).

To provide further constraints on the cooling paths ofthe basement domains, Rb–Sr mica-WR isochrons werecalculated (Table 3). Because of the higher closure tem-perature interval of 500 ± 50 �C (Steiger and Jager,1977) for the Rb–Sr system in muscovites, analysedsamples should yield higher ages than those obtainedby the K–Ar method, as is the case for all samples withthe exception of the Ms–Bt–Grt–St schist A 42-03 (Table3, cf. Fig. 10), which yields a slightly younger Rb–Sr ageof 363 Ma. This age relates to the La Arenilla shearzone. In case of the calculated Rb–Sr Bt–WR isochrones,no significant derivation from the appropriate K–Ar Btage is noted (Table 3).

5. Discussion

5.1. Timing of fabrics, metamorphism, and magmatism

The relative timing of the structural evolution of thePMC must be based on absolute time markers providedby different geochronological methods to integrate thedeformational history in the proto-Andean evolution ofGondwana.

Our structural data, combined with new and publishedgeochronological results, suggest that the central basementcomplex of the Sierra de San Luis, the PMC, encompassesnot only magmatic units and medium- to high-grademetasediments but also the San Luis Formation. Simset al. (1998) suggest that the latter succession was depositedafter the extensional collapse of the Famatinian orogen.Remapping the transition between the medium- to high-grade metamorphic rocks and the lower-grade metamor-phic successions of the San Luis Formation does not reveala structural discordance, though the low-grade metamor-phic rocks seem to lack part of the deformation history.A maximum age for the structural evolution of the meta-psammopelites of the PMC and the low-grade metamor-phic rocks of the San Luis Formation is given by U–Pbzircon data. SHRIMP U–Pb analyses of detrital zircons

Please cite this article in press as: Steenken, A. et al., Time constrainSci. (2007), doi:10.1016/j.jsames.2007.05.002

from the high-grade metamorphic gneisses (Sims et al.,1998) and conventional zircon data of dacitic dikes withinthe lower-grade successions (Sollner et al., 2000) denote toan early Cambrian (�530 Ma) deposition of the entiremetasedimentary succession. According to Sims et al.(1998), the medium- to high-grade metasediments derivedfrom the nearby Pampean orogen and were deposited ina backarc setting. Steenken et al. (2004) propose that theentire metamorphic pile of the PMC was deposited in abackarc developed within the former foreland of the Pam-pean orogen. The closure of this backarc, probably relatedto the approaching Precordillera/Cuyania terrane, led tothe first deformation within the lowermost deposits whilesedimentation continued on top. The medium- to high-grade metamorphic rocks are characterised by the develop-ment of two metamorphic foliations folded and refoldedduring D2 and D3, in support of the hypothesis that bothsequences form a single crustal section with a progrademetamorphic record.

Magmatic activity within this crustal section startedwith the emplacement of mafic and ultramafic intrusionsat 506 ± 19 Ma, as indicated by the Sm–Nd mineral iso-chron for sample A 01-02 (Fig. 8). This age is slightly youn-ger than SHRIMP U–Pb zircon ages of approximately 480Ma for felsic segregations and associated granodiorites(Sims et al., 1998). These ages define the metamorphic peakin the Pringles and Nogolı metamorphic complexes. Theend of this high-temperature period (i.e., granulite faciesmetamorphism) is constrained to between 470 and452 Ma by conventional and SHRIMP U–Pb monazitedating (Sims et al., 1998; Gonzalez et al., 2002a; Satoet al., 2003a). Our new results of 454 Ma from K–Ar Hbland 459 Ma from Rb–Sr Ms dating match the lower limitof this period. A Rb–Sr Ms age of 439 Ma for a gneissicsample (A 23-01) from the Conlara metamorphic complex(Table 1) suggests the entire basement of the Sierra de SanLuis underwent a uniform post-Famatinian evolution.Debatable, however, is the meaning of the Ar–Ar amphi-bole age of 416 ± 2 Ma. Assuming the K–Ar system isundisturbed, which seems confirmed by the well-definedplateau age from the Ar–Ar step-heating experiments, this

ts on the Famatinian and Achalian structural ..., J. S. Am. Earth

Fig. 9. Geological map of the Sierra de San Luis (see Fig. 2). Interpreted results of K–Ar Ms and Hbl analyses (in Ma) from this work, as well as Steenkenet al. (2003, 2004), (*1) Siegesmund et al., 2004. (*2) Lopez de Luchi et al., 2004).

16 A. Steenken et al. / Journal of South American Earth Sciences xxx (2008) xxx–xxx

ARTICLE IN PRESS

Please cite this article in press as: Steenken, A. et al., Time constraints on the Famatinian and Achalian structural ..., J. S. Am. EarthSci. (2007), doi:10.1016/j.jsames.2007.05.002

Fig. 10. Southwestern sector of the Sierra de San Luis, showing the K–ArMs and Bt (in Ma) ages of mylonitic shear zone samples (this work;Steenken et al., 2003, 2004. (*3) Sato et al., 2001a. (*4) Sims et al., 1998).

A. Steenken et al. / Journal of South American Earth Sciences xxx (2008) xxx–xxx 17

ARTICLE IN PRESS

age would reflect cooling below 580 �C. However, the clo-sure temperature of amphiboles may be highly variablewith respect to structure and composition. With the previ-ously noted closure temperature, the data suggest that thewestern realm of the PMC underwent a differential coolinghistory than the eastern region. The persistence of high-grade metamorphic conditions also is recorded by theSm–Nd mineral isochron of sample A 08-02 at434 ± 12 Ma, probably reflecting cooling of the ultra-maficrock.

Granodioritic to granitic crustal derived intrusions arefound in all basement domains. Llambıas et al. (1991) pres-ent a Rb–Sr WR errorchron of 454 ± 21 Ma for the south-ern Paso del Rey and Rıo de La Carpa intrusions that wascast in doubt by conventional U–Pb single zircon discordiaof 608 ± 26 Ma for the southern Paso del Rey granite (vonGosen et al., 2002). The analysed zircons are highly discor-dant, making its interpretation in terms of magma crystal-lisation arguable. New insights into the intrusive history ofthe Sierra de San Luis is provided by the 207Pb/206Pb zirconcrystallisation age at 491 ± 19 Ma for the northern Pasodel Rey granite (Fig. 9), which suggests exclusively post-Pampean history of the PMC (Sims et al., 1997; Steenkenet al., 2004). The oldest time increments at 597 ± 54 Ma(Table 1) are consistent with the age presented by vonGosen et al. (2002) and indicate an inherited source compo-nent within the zircons of this crustal derived intrusion.

Please cite this article in press as: Steenken, A. et al., Time constrainSci. (2007), doi:10.1016/j.jsames.2007.05.002

Similar U–Pb ages at 490 ± 15 Ma were calculated fromnear-concordant zircons for the Rıo Claro granite (vonGosen et al., 2002) that intruded the Nogolı metamorphiccomplex and at 497 ± 8 Ma for the El Penon granite withinthe Conlara metamorphic complex (Steenken et al., 2005a).

The Paso del Rey granite is concordant with the pene-trative S2 foliation of its country rock. Microstructuresrecord a continuum from magmatic to high-temperaturesolid-state fabrics, which suggest a synkinematic emplace-ment. Small granodioritic dykes associated with the mainintrusives were isoclinally folded during D2, and D3 ledto open fold structures (Fig. 4a and b). Consequently, thecrystallisation age of 491 ± 19 Ma defines the maximumage of the S2 fabric in the medium- to high-grade metamor-phic rocks. On the basis of the conformity of the intrusivecontacts and the penetrative foliation, von Gosen (1998a)argues that the granitoids were emplaced within unde-formed sediments. However, a sheet-like intrusion parallelto any anisotropy in a compressive environment would ful-fil the concordance between contacts and foliation.

Tonalitic to granodioritic plutons appear in the San LuisFormation and Nogolı metamorphic complex. Their crys-tallisation ages are well confined by SHRIMP and conven-tional U–Pb zircon dating to 477–468 Ma (Stuart-Smithet al., 1999; Sato et al., 2003a, 2004). In case of the SanLuis Formation, an emplacement mode similar to that ofthe crustal derived granites within undeformed sedimentshas been proposed (Sims et al., 1997; von Gosen and Pro-zzi, 1998; von Gosen, 1998a,b), in contrast with the obser-vation of small tonalitic veins injected parallel to the firstaxial plane foliation of the phyllites, which suggests theirsynkinematic emplacement during the first deformationof the host (i.e., D2 of the high-grade metamorphic rocks).

In summary, the timing of the development of D2 struc-tures (i.e., D1 of the San Luis Formation) is constrained bythe age of the Paso del Rey granite at 491 Ma and the ton-alitic plutons that have a minimum age of 468 Ma. A sim-ilar time for the fabric development has been suggested forthe metasediments of the Sierra de Chepes (Dahlquist andBaldo, 1996). The peak metamorphic conditions associatedwith the D2 fabric result from the contemporaneousemplacement of mafic and ultramafic units between 506and 478 Ma. The exact timing of D3 open folds remainsunsolved, whether the latest stage of the Famatinian defor-mation prior to 440 Ma or a separate event during the sub-sequent Achalian tectonic cycle.

5.2. Differential cooling

The high density of K–Ar and Rb–Sr mica data pro-vided for the different basement domains enables a fairreconstruction of the differential cooling history of the dif-ferent basement domains after their respective metamor-phic peak conditions (cf. Steenken et al., 2003, 2004). Thereported ages match, to a large extent, previous data (Gal-liski and Linares, 1999; Sosa et al., 2002; for a review, seeSato et al., 2003b), though Cambrian-Early Ordovician

ts on the Famatinian and Achalian structural ..., J. S. Am. Earth

Fig. 11. Compilation and interpretation of K–Ar Bt cooling ages for Sierra de San Luis (see Figs. 9 and 10). Unexpectedly high K–Ar Bt ages relate to theeffective diffusion lengths of Ar in Bt booklet and static recrystallisation of biotite at medium- to high-grade metamorphism. Minor late-stage reactivationof the basement led to the alteration of biotites resulting in ages of �315 Ma.

18 A. Steenken et al. / Journal of South American Earth Sciences xxx (2008) xxx–xxx

ARTICLE IN PRESS

Please cite this article in press as: Steenken, A. et al., Time constraints on the Famatinian and Achalian structural ..., J. S. Am. EarthSci. (2007), doi:10.1016/j.jsames.2007.05.002

A. Steenken et al. / Journal of South American Earth Sciences xxx (2008) xxx–xxx 19

ARTICLE IN PRESS

K–Ar Ms cooling ages are not confirmed. The high ana-lytical errors of the previous data (usually more than20 Ma) impede a clear-cut evaluation of their meaningfor the temperature development of the Sierra de San Luis.

The oldest K–Ar Ms ages of approximately 445 Magained from pegmatitic Ms booklets document a common,postmetamorphic cooling history of all basement domains,as it is further supported by the Rb–Sr Ms data obtainedfor two samples of the Conlara and Nogolı metamorphiccomplexes. Subsequent cooling recorded by normal-sizedmuscovites and biotites is asymptotic in most areas of theSierra de San Luis. Deviations of some ages from theempirically constructed cooling paths (Fig. 12) relate touncertainties in the isotopic closure behaviour of the largebut differently sized Ms booklets. The only exception tothese asymptotic cooling paths seems to occur in the south-ern section of the Nogolı metamorphic complex, which ischaracterised by K–Ar Ms ages of approximately350 Ma. Thus far, the limited data prevent a detailed dis-cussion of the significance of this variation, because pub-lished (Sato et al., 2001b) and our new K–Ar Bt dataindicate an earlier cooling of the basement at 410 Ma(Fig. 12). A possible reason for the inversion of K–ArMs and Bt ages relates to the lack of recrystallisationwithin those biotites that were equilibrated at amphibolitefacies conditions, leading to a significant higher closuretemperature (cf. Villa, 1998).

In comparing the cooling paths of the three metamor-phic domains, slight differences appear. The Conlara andnorthern portion of the Nogolı metamorphic complexesrecord cooling below the K–Ar Ms closure temperatureinterval of 420–350 �C at approximately 420 Ma. K–ArMs ages in the PMC are between 400 and 380 Ma. Up to445 Ma old Ms booklets are interpreted to document thedecelerated cooling history of this domain (Fig. 13).

Fig. 12. Empirically constrained cooling paths for basement domains of the Sbooklets and normal-sized muscovites. (U–Pb ages: Pringles, Sims et al., 19Simpson, 2004).

Please cite this article in press as: Steenken, A. et al., Time constrainSci. (2007), doi:10.1016/j.jsames.2007.05.002

Differences in the K–Ar Bt ages within the two easterncomplexes, which document cooling between approxi-mately 360 and 380 Ma, are less pronounced. In contrast,K–Ar Bt ages in the Nogolı metamorphic complex are asold as 418 Ma (Fig. 13). Such a high age was obtainedwithin the PMC only for a high-temperature mylonite fromthe La Arenilla shear zone. Because the grain size of theseparated micas corresponds to micas preserved withinthe granulite facies microlithons of the mylonite, it canbe argued that the lack of recrystallisation during green-schist facies conditions causes an unexpectedly high closuretemperature.

In comparing the cooling history of the Conlara andPringles metamorphic complexes, it appears that their rela-tive positions changed during their individual exhumationhistory (Fig. 13). Consequently, the polarity of vertical dis-placement across the Rıo Guzman shear zone changed dur-ing the Devonian, as is confirmed by variable structuralindications that reveal locally dextral displacement withan oblique W-side up component. The individual post-Famatinian temperature development of the basementdomains emphasises the Achalian tectonic cycle is a sepa-rate event, likely related to the accretion of the Chilenia ter-rane (Sims et al., 1998; Astini and Thomas, 1999;Siegesmund et al., 2004). Nevertheless, Sato et al. (2003a)further the idea of Llambıas et al. (1998), who considerthe Devonian granitoids a consequence of post-Famatinianorogenic uplift.

K–Ar dating includes five mylonites of the La Arenillamylonite belt to constrain an upper limit for the displace-ment (Fig. 10). The data complement previous work bySims et al. (1998), who present three Ar–Ar Ms ages forthe La Arenilla and Rıo Guzman shear zones. The rangeof 380–350 Ma indicates that displacement along bothmajor shear zones was active during this interval

ierra de San Luis. Note different closure temperatures assigned to the Ms98; Nogoli, Gonzalez et al., 2002a; Conlara, Gromet in Whitmeyer and

ts on the Famatinian and Achalian structural ..., J. S. Am. Earth

Fig. 13. Compilation of K–Ar muscovite and biotite cooling ages withapproximate distance to the major La Arenilla and Rıo Guzman shearzones (see Fig. 9). The large Ms and Bt booklets and nonrecrystallisedbiotites are shown by tall symbols. K–Ar Ms ages of normal-sizedminerals indicate the postmetamorphic cooling history of the PMCdecelerated with respect to neighbouring complexes (grey fields showcooling below the closure temperature interval of 350–420 �C). K–Ar Btages document uniform cooling of the eastern basement domains.Differential reactivation of the basement complexes during the Silurodev-onian result from the separated Achalian tectonic cycle.

20 A. Steenken et al. / Journal of South American Earth Sciences xxx (2008) xxx–xxx

ARTICLE IN PRESS

(Fig. 10). The interval is in agreement with scarce mylonitedating in the Nogolı metamorphic complex (Sato et al.,2001b). Microstructures of the mylonitic gneisses andschists of the La Arenilla mylonite belt indicate a well-developed planar fabric characterised by the lineararrangement of biotite and muscovite. In addition todynamic quartz recrystallisation, quartz textures are fre-quently characterised by high-angle grain boundaries thatpoint to a static annealing after mylonitisation ceased.Quartz grains show limited internal stress. Therefore base-ment temperatures were still within the lower limit of duc-tile quartz deformation of approximately 300 �C (Hirthand Tullis, 1992) by the end of mylonitisation in the earlyCarboniferous.

6. Conclusion

The combination of structural observations and geo-chronological data reconstructs a geodynamic scenariofor the Sierra de San Luis within an absolute time frame.This scenario relates to the approach and accretion oftwo crustal fragments integrated in the southwestern mar-gin of Gondwana: the Precordillera/Cuyania and Chileniaterranes. The results highlight the tectonomagmatic andmetamorphic evolution.

Please cite this article in press as: Steenken, A. et al., Time constrainSci. (2007), doi:10.1016/j.jsames.2007.05.002

Geochronological constraints provided by U–Pb datingof detrital zircons for the high-grade metasediments of thePMC (Sims et al., 1998) and U–Pb dating of zircons fromdacitic dikes in the mica-schist group and San Luis Forma-tion (Sollner et al., 2000) suggest a single early Cambrianperiod of sedimentation.

According to the structural development of the entiresequence of the central basement domain of the Sierra deSan Luis, the onset of orthogonal compression in thehigh-grade metamorphic rocks was contemporaneous withthe deposition of younger sediments on top of thesequence. This scenario relates to the opening and subse-quent closure of a backarc basin in proximity to the Pam-pean orogen.

The initiation of granulite facies metamorphism due tothe contact heat of mafic and ultramafic intrusions isconfined to the middle Cambrian (�506 Ma), closely fol-lowed by the emplacement of crustal derived granitoids,such as the northern stock of the Paso del Rey graniteat 491 Ma, parallel to the S1 foliation of the countryrock.

The inferred syn-D2 emplacement of those granitoidsindicates that the D1 to D2 (i.e., D1 of the San Luis Forma-tion) structural evolution predates the generally assumedMiddle-Ordovician accretion of the Precordillera/Cuyaniaterrane.

Refolding (D3) of the tight to isoclinal D2 folds is poorlyconstrained but occurred prior to the cooling of the base-ment below the closure temperature for the K–Ar Bt sys-tem at approximately 380 Ma. Therefore, it might berelated to the approach of the Chilenia terrane.

On the basis of K–Ar Hbl, Ms, and Bt data, a detailedcooling history of the entire basement complex is high-lighted, emphasising the Achalian tectonic cycle as a sepa-rate event, as indicated by the differential displacementbetween the Conlara and Pringles metamorphic complexes.The K–Ar Ms and Bt cooling ages show that final west-side-up movements along the Rıo Guzman shear zonesuperimpose initial east-side-up displacement. The base-ment complexes had not reached similar crustal levels bythe Late Devonian.

Acknowledgments

We are grateful to the DAAD–ANTORCHAS programand the German Science Foundation (DFG) Grant Si 438/16-1, which funds our research project in central Argen-tina. A. St. thanks the DFG for research scholarship STE1036/1-1. Zircon evaporation experiments were kindly car-ried out by B. Kober (Adelaide, Australia). B.T. Hansen(GZG, Germany) kindly supported the analysis of the Srand Nd isotope systematics. The quality of the manuscriptwas significantly improved by careful readings by V. Ra-mos and R.D. Martino (Argentina). P.D. Gonzalez(Argentina) and an anonymous reviewer assisted in a com-prehensive revision of the manuscript, which we gratefullyacknowledge.

ts on the Famatinian and Achalian structural ..., J. S. Am. Earth

A. Steenken et al. / Journal of South American Earth Sciences xxx (2008) xxx–xxx 21

ARTICLE IN PRESS

References

Acenolaza, F.G., Toselli, A., 2000. Argentine Precordillera. Allochtho-nous or autochthonous Gondwanic?. Zentralblatt fur Geologie undPalaontolologie 1999. 743–756.

Acenolaza, F.G., Miller, H., Toselli, A.J., 2002. Proterozoic-early Paleo-zoic evolution in western South America-A discussion. Tectonophysics354, 121–137.

Astini, R.A., 1996. Las fases diastroficas del Paleozoico medio en laPrecordillera del oeste argentino-evidencias estratigraficas. XIII Cong-reso Geologico Argentino y III Congreso de Exploracion de Hidro-carburos. Actas 5, 509–526.

Astini, R.A., Thomas W.A., 1999. Origin and evolution of the Precordilleraof western Argentina: a drifted Laurentian orphan. In: Ramos, V.A.,Keppie, J.D. (Eds.), Laurentia-Gondwana connections before PangeaSpecial Papers of the Geological Society of America 336, pp. 1–20.

Astini, R.A., Davila, F.M., 2004. Ordovician back-arc foreland andOcloyic thrust belt development on the western Gondwana margin as aresponse to Precordillera terrane accretion. Tectonics 23. doi:10.1029/2003TC00162.

Blanckenburg, v.F., Villa, I.M., Baur, H., Morteani, G., Steiger, R.H.,1989. Time calibration of a PT-path from the Western TauernWindow, Eastern Alps: the problem of closure temperatures. Contri-butions to Mineralogy and Petrology 101, 1–11.

Bonorino, F.G., 1961. Petrologia de Algunos Cuerpos Basicos de SanLuis. Revista de la Asociacion Geologıa Argentina 16, 61–106.

Bouchez, J.L., Delas, C., Gleizes, G., Nedelec, A., Cuney, M., 1992.Submagmatic microfractures in granites. Geology (Boulder) 20, 35–38.

Brogioni, N., 1993. El Batolito de Las Chacras-Piedras Coloradas,Provincia de San Luis. Geocronologıa y ambiente tectonico. XIICongreso Geologico Argentino y II Congreso de Exploracion deHidrocarburos. Actas 4, 54–60.

Brogioni, N., 2001. Geologıa de los cuerpos Virorco y El Fierro, fajamafica-ultramafica del borde oriental de la sierra de San Luis. Revistade la Asociacion Geologica Argentina 56, 281–292.

Bucher, K., Frey, M., 1994. Petrogenesis of Metamorphic Rocks, sixth ed.Springer-Verlag, Berlin, pp. 318.

Buttner, S.H., Glodny, J., Lucassen, F., Wemmer, K., Erdmann, S.,Handler, R., Franz, G., 2005. Ordovician metamorphism and pluto-nism in the Sierra de Quilmes metamorphic complex: Implications forthe tectonic setting of the northern Sierras Pampeanas (NW Argen-tina). Lithos 83, 143–181.

Chernicoff, C.J., Ramos, V.A., 2003. El basamento de la sierra de SanLuis: Nuevas evidencias magneticas y sus implicancias tectonicas.Revista de la Asociacion Geologıa Argentina 58, 511–524.

Dahlquist, J.A., Baldo, E.G., 1996. Metamorfismo y deformacionfamatinianos en la Sierra de Chepes. 13 Congreso Geologico Argen-tino y 3 Congreso de Exploracion de Hidrocarburos. Actas 5, 393–409.

Dahlquist, J.A., Galindo, C., 2004. Geoquımica isotopica de los granitoidsde la sierra de Chepes: un modelo geotectonico y termal, implicacionespara el orogeno famatiniano. Revista de la Asociacion GeologıaArgentina 59, 57–69.

Delakowitz, B., Holl, R., Hack, M., Brodtkorb, M., Stark, H., 1991.Geological and geochemical studies of the Sierra del Morro Oeste (SanLuis Province, Argentina): meta-sediments and metavolcanics from aprobable bach-arc setting. Journal of South American Earth Sciences4, 189–200.

Harrison, T.M., Fitz Gerald, J.D., 1986. Exsolution in hornblende and itsconsequences for40 Ar/39 Ar age spectra and closing temperature.Geochimica et Cosmochimca Acta 50, 247–253.

Foden, J., Sandiford, M., Dougherty, P.J., Williams, I., 1999. Geochem-istry and geochronology of the Rathjen Gneiss; implications for theearly tectonic evolution of the Delamerian Orogen. Australien Journalof Earth Sciences 46, 377–389.

Fuhrmann, U., Lippolt, H.J., Hess, J.C., 1987. Examination of someproposed K–Ar standards:40 Ar/39 Ar analyses and conventional K–Ar-Data. Chemical Geology (Isotope Geoscience Section) 66, 41–51.

Please cite this article in press as: Steenken, A. et al., Time constrainSci. (2007), doi:10.1016/j.jsames.2007.05.002

Galliski, M.A., Linares, E., 1999. New K–Ar muscovite ages from graniticpegmatites of the Pampean Pegmatite Province. II. South AmericanSymposium on Isotope Geology Extended Abstracts, 63–67.

Gonzalez, P., 2000. Banded Iron Formation del basamento pre-Famatin-iano de San Luis: primer registro en Argentina, in: I. Schalamuk,M.K., de Brodtkorb and R., Etcheverry (Eds.), Mineralogıa yMetalogenia 2000. Publication 6, pp. 191–198.

Gonzalez, P., Llambıas, E., 1998. Estructura interna de las metamorfitaspre-Famatinianas y su relacion con la deformacion del Paleozoicoinferior en el area de Gasparillo, San Luis, Argentina X CongresoLatinoamericano de Geologıa. Actas 2, 421–426.

Gonzalez, P.D., Sato, A.M., Basei, M.A.S., Vlach, S., Llambıas, E.J.,2002a. Structure, metamorphism and age of the Pampean-Famatinianorogenies in the western Sierra de San Luis. 15 Congreso GeologicoArgentino, Actas 15, 6 pp. (CD edition).

Gonzalez, P.D., Sato, A.M., Llambıas, E.J., 2002b. The komatiites andassociated mafic to ultramafic metavolcanic rocks of western Sierra deSan Luis. 15 Congreso Geologico Argentino, Actas 15, 4 pp. (CDedition).

Gonzalez, P.D., Sato, A.M., Llambıas, E.J., Basei, M.A.S., Vlach, S.R.F.,2004. Early Paleozoic structural and metamorphic evolution ofwestern Sierra de San Luis (Argentina), in relation to CuyaniaAccretion. Gondwana Research 7, 1157–1170.

Gosen, v.W., 1998a. The phyllite and micaschist group with associatedintrusions in the Sierra de San Luis (Sierras Pampeanas/Argentina);structural and metamorphic relations. Journal of South AmericanEarth Sciences 11, 79–109.

Gosen, v.W., 1998b. Transpressive deformation in the southwestern partof the Sierra de San Luis (Sierras Pampeanas, Argentina). Journal ofSouth American Earth Sciences 11, 233–264.

Gosen, v.W., Prozzi, C., 1996. Geology, structure and metamorphism inthe area south of La Carolina (Sierra de San Luis, Argentina). 13Congreso Geologico Argentino y 3 Congreso de Exploracion deHidrocarburos. Actas 2, 301–314.

Gosen v.W., Prozzi, C., 1998. Structural evolution of the Sierra de SanLuis (Eastern Sierras Pampeanas, Argentina); implications for theProto-Andean margin of Gondwana. In: Pankhurst, R.J., Rapela,C.W. (Eds.), The proto-Andean margin of Gondwana GeologicalSociety of London, Special Publications 142, pp. 235–258.

Gosen, v.W., Loske, W., Prozzi, C., 2002. New isotopic dating of intrusiverocks in the Sierra de San Luis (Argentina): implications for thegeodynamic history of the Eastern Sierras Pampeanas. Journal ofSouth American Earth Sciences 15, 237–250.

Hack, M., 1987. Geologisch-geochemisch-lagerstatten-kundliche Unter-suchungen zur Genese von Wolfram Lagerstatten in der Pampa delTamboreo, Provinz San Luis, Argentinien. Munchner Geowissens-chaftliche Abhandlungen (B) 1, 1–108.

Hauzenberger, C.A., Mogessie, A., Hoinkes, G., Felfernig, A., Bjerg,E.A., Kostadinoff, J., 1996. Platinum group minerals from the LasAguilas Ultramafic Unit, San Luis Province, Argentina. Mitteilungender osterreichischen Mineralogischen Gesellschaft 141, 157–159.

Hauzenberger, C.A., Mogessie, A., Hoinkes, G., Felfernig, A., Bjerg,E.A., Kostadinoff, J., Delphino, S., Dimieri, L., 2001. Metamorphicevolution of the Sierras de San Luis, Argentina; granulite faciesmetamorphism related to mafic intrusions. Mineralogy and Petrology71, 95–126.

Heinrichs, H., Herrmann, A.G., 1990. Praktikum der AnalytischenGeochemie. Springer-Verlag, Berlin, pp. 669.

Hirth, G., Tullis, J., 1992. Dislocation creep regimes in quartz aggregates.Journal of Structural Geology 14, 145–159.

Hoppener, R., 1955. Tektonik im Rheinischen Schiefergebirge. EineEinfuhrung. Geologische Rundschau 44, 26–58.

Jezek, P., Willner, A.O., Acenolaza, F.G., Miller, H., 1985. ThePuncoviscana trough - a large basin of Late Precambrian age on thePacific edge of the Brazilian shield. Geologische Rundschau 74, 573–584.

Kamber, B.S., Kramer, J.D., Napier, R., Cliff, R.A., Rollinson, R.H.,1995. The Triangle Shearzone, Zimbabwe, rewisted: new data docu-

ts on the Famatinian and Achalian structural ..., J. S. Am. Earth

22 A. Steenken et al. / Journal of South American Earth Sciences xxx (2008) xxx–xxx

ARTICLE IN PRESS

ment an important event at 2.0 Ga in the Limpopo Belt. PrecambrianResearch 70, 191–213.

Kilmurray, J.O., 1981. Petrologıa metamorfica y aspectos estructurales delas formaciones comprendidas entre la Toma y el Rıo Quinto. Sierra deSan Luis. Revista de la Asociacion Argentina de Mineralogıa,Petrologıa y Sedimentologıa 12, 31–45.

Kilmurray, J.O., 1982. Estructura y petrologıa de la region de Trapiche,Dique La Florida, provincia de San Luis, Argentina 5. CongresoLatinamericano de Geologıa 2, 239–249.

Kilmurray, J.O., Dalla Salda, L.H., 1977. Caracteres estructurales ypetrologicos de la region central y sur de la Sierra de San Luis. Obradel Centenario del Museo de La Plata 4, 167–178.

Kilmurray, J.O., Villar, L., 1981. El basamento de la Sierra de San Luis ysu petrologıa. In: Yrigoyen, M. (Ed.), Geologıa y recursos minerales dela provincia de San Luis. Relatorio 8 Congreso Geologico Argentino,pp. 33–54.

Kober, B., 1986. Whole-grain evaporation for207 Pb/206 Pb investigationson single zircons using a double filament thermal ion source.Contributions to Mineralogy and Petrology 93, 482–490.

Kober, B., 1987. Single-zircon evaporation combined with Pb+ emitterbedding for207 Pb/206 Pb-age investigations using thermal ion massspectrometry, and implications to zirconology. Contributions toMineralogy and Petrology 96, 63–71.

Kretz, R., 1983. Symbols for rock-forming minerals. American Mineral-ogist 68, 277–279.

Kruhl, J.H., 1996. Prism- and basal-plane parallel subgrain boundaries inquartz; a microstructural geothermobarometer. Journal of Metamor-phic Geololgy 14, 581–589.

Llambıas, E., Cingolani, C., Varela, R., Prozzi, C., Ortız Suarez, A.,Caminos, R., Toselli, A., Saavedra, J., 1991. Leucogranodioritassincinematicas ordovicicas en la Sierra de San Luis, RepublicaArgentina. VI Congreso geologıco chileno Resumenes expandidos,187–191.

Llambıas, E.J., Quenardelle, S., Ortız Suarez, A., Prozzi, C., 1996a.Granitoides sin-cinematicos de la Sierra Central de San Luis. XIIICongreso Geologıco Argentino; III Congreso de Exploracion deHidrocarburos. Actas 5, 487–496.

Llambıas, E.J., Sato, A.M., Prozzi, C., Sanchez, V., 1996b. Los pendantsde gneises en el Pluton Gasparillo: evidencia de un metamorfismo pre-Famatiniano en las Sierras de San Luis. XIII Congreso GeologıcoArgentino; III Congreso de Exploracion de Hidrocarburos. Actas 5,369–376.

Llambıas, E.J., Sato, A.M., Ortız Suarez, A., Prozzi, C., 1998. Thegranitoids of the Sierra de San Luis. In: Pankhurst, R.J., Rapela, C.W.(Eds.), The proto-Andean margin of Gondwana Geological Society ofLondon, Special Publications 142, pp. 325–341.

Llaneza, G., Ortız Suarez, A.E., 2000. Geologıa y petrografıa del granitoEl Penon (Provincia de San Luis) y su relacion con el metamorfismo yla deformacion. IX Congreso Geologico Chileno. Actas 1, 639–643.

Lopez de Luchi, M.G., 1986. Geologıa y Petrologıa del basamento de laSierra de San Luis, Region del Batolito de Renca. Doctoral Thesis.Universidad de Buenos Aires, Argentina, 374 pp.

Lopez de Luchi, M.G., 1987. Caracterizacion geologica y geoquimica delPluton La Tapera y del Batolito de Renca, Sierra de San Luis, RepublicaArgentina. X Congreso Geologico Argentino. Actas 4, 84–88.

Lopez de Luchi, M.G., 1996. Enclaves en un batolito postectonico;petrologia de los enclaves microgranulares del batolito de Renca,Sierras Pampeanas, San Luis. Revista de la Asociacion GeologıaArgentina 51, 131–146.

Lopez de Luchi, M.G., Cerredo, M.E., 2001. Submagmatic and solid-statemicrostructures in La Tapera pluton. San Luis, Argentina. Publicaci-ones Especiales de la Asociacion Geologıa Argentina Serie D 5, 121–126.

Lopez de Luchi, M.G., Cerredo, M.E., Rossello, E.A., 1999. Protholithsof a metasedimentary sequence; a case study on the lower PaleozoicPacific margin of western Gondwana. Geological Society of AmericaAbstracts with Programs 31, 298–299.

Lopez de Luchi, M.G., Rapalini, A., Rossello, E.A., Geuna, S., 2000.Rock fabric and magnetostructure constraints on the emplacement of

Please cite this article in press as: Steenken, A. et al., Time constrainSci. (2007), doi:10.1016/j.jsames.2007.05.002

the Renca Batholith Sierra de San Luis, Argentina. UnderstandingPlanet Earth; searching for a sustainable future. Abstracts of the 15thAustralian geological convention 59, p. 313.

Lopez de Luchi, M.G., Cerredo, M.E., Siegesmund, S., Steenken, A.,Wemmer, K., 2003. Provenance and tectonic setting of the protolithsof the metamorphic complexes of Sierra de San Luis. Revista de laAsociacion Geologıa Argentina 58, 525–540.

Lopez de Luchi, M.G., Rapalini, A.E., Siegesmund, S., Steenken, A.,2004. Application of magnetic fabrics to the emplacement and tectonichistory of Devonian granitoids in Central Argentina. GeologicalSociety of London, Special Publications 238, pp. 447–474.

Lopez de Luchi, M., Siegesmund, S., Wemmer, K., Steenken, A.,Naumann, R., 2007. Geochemical constraints on the petrogenesis ofthe Palaeozoic granitoids of the Sierra de San Luis, Sierras Pampeanas,Argentina. Journal of South American Earth Sciences.

Ludwig, K.R., 2003. Isoplot/Ex version 3.00: A Geochronological Toolkitfor Microsoft Excel. Berkeley Geochronology Center Special Publica-tion 4, 1-73.

Mainprice, D., Bouchez, J.L., Blumenfeld, P., Tubia, J.M., 1986.Dominant c slip in naturally deformed quartz; implications fordramatic plastic softening at high temperature. Geology (Boulder)14, 819–822.

Martino, R.D., 2003. Las fajas de deformacion ductil de las SierrasPampeanas de Cordoba: una resena general. Revista de la AsociacionGeologia Argentina 58, 549–571.

McDougall, I., Harrison, T.M., 1999. Geochronology and thermochro-nology by the40 Ar/40 Ar method, second ed. Oxford University Press,Oxford, pp. 269.

Olsen, T.S., Kohlstedt, D.L., 1985. Natural deformation and recrystalli-zation of some intermediate plagioclase feldspars. Tectonophysics 111,107–131.

Onstott, T.C., Peacock, M.W., 1987. Argon retentivity of hornblendes: afield experiment in a slowly cooled metamorphic terrane. Geochimicaet Cosmochimica Acta 51, 2891–2903.

Ortiz Suarez, A.E., 1988. El basamento de Las Aguadas, Provincia de SanLuis. Revista de la Asocicacion Argentina de Mineralogıa. Petrologıa ySedimentologıa 19, 13–24.

Ortiz Suarez, A.E., 1996. Geologia y petrografia de los intrusivos de LasAguadas, Provincia de San Luis. Revista de la Asociacion GeologıaArgentina 51, 321–330.

Ortiz Suarez, A.E., Casquet, C., 2005. Inversion metamorfica en elorogeno Famatiniano de la Sierra de San Luis, Argentina. Geogaceta38, 231–234.

Ortiz Suarez, A.E., Prozzi, C., Llambıas, E.J., 1992. Geologıa de la partesur de la Sierra de San Luis y granitoides asociados, Argentina.Estudios Geologicos 48, 269–277.

Pankhurst, R.J., Rapela, C.W., Fanning, C.M., 2000. Age and origin ofcoeval TTG, I- and S-type granites in the Famatinian belt of NWArgentina. Transactions of the Royal Society of Edinburgh. EarthSciences 91, 151–168.

Prozzi, C., Ramos, G., 1988. La Formacion San Luis. Primeras Jornadasde Trabajo de Sierras Pampeanas, Abstracts 1, Universidad Nacionalde San Luis, San Luis 24–26 Aug.

Ramos, V.A., 1995. Sudamerica: Un mosaico de continents y oceanos.Ciencias Hoy 6, 24–29.

Ramos, V.A., Jordan, T.E., Allmendinger, R.W., Mpodozis, C., Kay,S.M., Cortes, J.M., Palma, M., 1986. Paleozoic terranes of the centralArgentine-Chilean Andes. Tectonics 5, 855–880.

Rapela, C.W., Pankhurst, R.J., Casquet, C., Baldo, E., Saavedra, J.,Galindo, C., Fanning, C.M., 1998a. The Pampean Orogeny of thesouthern proto-Andes; Cambrian continental collision in the Sierras deCordoba. In: Pankhurst R.J., Rapela, C.W. (Eds.), The proto-Andeanmargin of Gondwana Geological Society of London, Special Publica-tions 142, pp. 181–217.

Rapela, C.W., Pankhurst, R.J., Casquet, C., Baldo, E., Saave-dra, J., Galindo, C., 1998b. Early evolution of the Proto-Andean margin of South America. Geology (Boulder) 26,707–710.

ts on the Famatinian and Achalian structural ..., J. S. Am. Earth

A. Steenken et al. / Journal of South American Earth Sciences xxx (2008) xxx–xxx 23

ARTICLE IN PRESS

Rapela, C.W., Pankhurst, R.J., Casquet, C., Dahlquist, J.A., Fanning,C.M., 1999. U–Pb SHRIMP ages of Famatinian granites: newconstrains on the timing, origin and tectonic setting of I- and S-typemagmas in an ensialic arc. II South American Symposium on IsotopeGeologyExtended Abstracts, 264–267.

Sato, A.M., Gonzalez, P.D., Sato, K., 2001a. First indication ofMesoproterozoic age from the western basement of Sierra de SanLuis, Argentina. III South American Symposium on Isotope Geo-logyExtended Abstracts, 64–67.

Sato, A.M., Gonzalez, P.D., Petronilho, L.A., Llambıas, E.J., Varela, R.,Basei, M.A.S., 2001b. Sm–Nd, Rb–Sr, and K–Ar age constraints of theEl Molle and Barroso plutons, western Sierra de San Luis, Argentina.III South American Symposium on Isotope Geology, ExtendedAbstracts, pp. 620–623.

Sato, A.M., Gonzalez, P.D., Basei, M.A.S., Passarelli, C.R., Tickyj, H.,Ponce, J.M., 2003a. The Famatinian granitoids of southwestern Sierrade San Luis, Argentina. IV South American Symposium on IsotopeGeology, Short Papers, pp. 290–293.

Sato, A.M., Gonzalez, P.D., Llambıas, E.J., 2003b. Evolution of theFamatinian Orogen in the Sierra de San Luis: arc magmatism,deformation, and low to high-grade metamorphism. Revista de laAsociacion Geologıa Argentina 58, 487–504.

Sato, A.M., Gonzalez, P.D., Basei, M.A.S., Passarelli, C.R., Sato, K.,Vlach, S., Varela, R. Llambıas, E.J., 2004. The Famatinian Orogeny ofwestern Sierra de San Luis, Argentina. Simposio 40 anos degeocronologıa no Brasil. Boletim de resumos, p. 83.

Schumacher, E., 1975. Herstellung von 99,9997% 38Ar fur die 40K/40ArGeochronologie. Geochronologia Chimica 24, 441–442.

Siegesmund, S., Steenken, A., Lopez de Luchi, M.G., Wemmer, K., 2004.The Las Chacras-Potrerillos Batholith: Structural evidences on itsemplacement and timing of the Intrusion. International Journal ofEarth Sc iences 93, 23–43.

Simpson, C., Wintsch, R.P., 1989. Evidence for deformation-induced K-feldspar replacement by myrmekite. Journal of Metamorphic Geology7, 261–275.

Sims, J.P., Skirrow, R.G., Stuart-Smith, P.G., Lyons, P., 1997. Informegeologico y metalogenetico de las Sierras de San Luis y Comechin-gones (provincias de San Luis y Cordoba), 1:250000. 148 pp.SEGEMAR, Buenos Aires.

Sims, J.P., Ireland, T.R., Camacho, A., Lyons, P., Pieters, P.E., Skirrow,R.G., Stuart, S.P.G., Miro, R., 1998. U–Pb, Th-Pb and Ar-Argeochronology from the southern Sierras Pampeanas, Argentina;implications for the Palaeozoic tectonic evolution of the westernGondwana margin. In: Pankhurst, R.J., Rapela, C.W. (Eds.), Theproto-Andean margin of Gondwana Geological Society of London,Special Publications 142, pp. 251–281.

Sollner, F., de Brodtkorb, M.K., Miller, H., Pezzutti, N.E., Fernandez,R.R., 2000. U–Pb zircon ages of metavolcanic rocks from the Sierra deSan Luis, Argentina. Revista de la Asociacion Geologıa Argentina 55,15–22.

Sosa, G.M., Augsburger, M.S., Pedregosa, J.C., 2002. Columbite-groupminerals from rare-metal granitic pegmatites of the Sierra de San Luis,Argentina. European Journal of Mineralogy 14, 627–636.

Stacey, J.S., Kramers, J.D., 1975. Approximation of terrestrial leadisotope evolution by a two stage model. Earth and Planetary ScienceLetters 26, 207–221.

Please cite this article in press as: Steenken, A. et al., Time constrainSci. (2007), doi:10.1016/j.jsames.2007.05.002

Steenken, A., Lopez de Luchi, M.G., Siegesmund, S., Wemmer, K., 2002.An insight into the structural evolution of the Sierra de San Luis(southeastern Sierras Pampeanas, Argentina); a progress report. XVCongreso Geologico Argentino, Actas 15, 6 pp. (CD edition).

Steenken, A., Wemmer, K., Lopez de Luchi, M.G., Siegesmund, S., 2003.The cooling history of the basement complex of the Sierra de San Luis(Eastern Sierras Pampeanas/Argentina) and its implication for Fam-atinian vs. Achalian events based on K/Ar-Geochronology. IV SouthAmerican Symposium on Isotope Geology, Short Papers, pp. 117–120.

Steenken, A., Lopez de Luchi, M.G., Siegesmund, S., Wemmer, K.,Pawlig, S., 2004. Crustal provenance and cooling of the basementcomplexes of the Sierra de San Luis: An insight into the tectonichistory of the proto-Andean margin of Gondwana. GondwanaResearch 7, 1171–1195.

Steenken, A., Lopez de Luchi, M.G., Martino, R.D., Siegesmund, S.,Wemmer, K., 2005a. SHRIMP dating of the El Penon granite: a timemarker at the turning point between the Pampean and Famatiniancycles within the Conlara Metamorphic Complex (Sierra de San Luis;Argentina)?16th Congreso Geologico Argentino. Actas 1, 889–896.

Steenken, A., Lopez de Luchi, M.G., Siegesmund, S., Wemmer, K., 2005b.The thermal impact by the accommodation of mafic melts within thecentral basement complex of the Sierra de San Luis: constraints fromnumeric modelling. 16 Congreso Geologico Argentino. Actas 1, 265–272.

Steiger, R.H., Jager, E., 1977. Subcommission on geochronology;convention on the use of decay constants in geo- and cosmochronol-ogy. Earth and Planetary Science Letters 36, 359–362.

Stuart-Smith, P.G., Camacho, A., Sims, J.P., Skirrow, R.G., Lyons, P.,Pieters, P.E., Black, L.P., Miro, R., 1999. Uranium-lead dating offelsic magmatic cycles in the southern Sierras Pampeanas, Argentina;implications for the tectonic development of the proto-AndeanGondwana margin. In: Ramos, V.A., Keppie, J.D. (Eds.), Laurentia-Gondwana connections before Pangea Special Papers of the Geolog-ical Society of America 336, pp. 87–114.

Thomas, W.A., Astini, R.A., 1996. The Argentine Precordillera; a travelerfrom the Ouachita Embayment of North American Laurentia. Science273, 752–757.

Thomas, W., Astini, R., 2003. Ordovician accretion of the ArgentinePrecordillera terrane to Gondwana: a review. Journal of SouthAmerican Earth Sciences 16, 67–79.

Tullis, J., Yund, R.A., 1991. Diffuse creep in feldspar aggregates;experimental evidence. Journal of Structural Geology 13, 987–1000.

Vidal, J.L., Kubin, L., Debat, P., Soula, J.C., 1980. Deformation anddynamic recrystallization of K feldspar augen in orthogneiss fromMontagne Noire, Occitania, southern France. Lithos 13, 247–255.

Villa, I.M., 1998. Isotopic closure. Terra Nova 10, 42–47.Vujovich, G.I., Ostera, H.A., 2003. Evidence of the Pampean cycle in the

basement of the northwestern sector of the Sierra de San Luis. Revistade la Asociacion Geologıa Argentina 58, 541–548.

Wemmer, K., 1991. K/Ar-Altersdatierungsmoglichkeiten fur retrogradeDeformationsprozesse im sproden und duktilen Bereich - Beispiele ausder KTB-Vorbohrung (Oberpfalz) und dem Bereich der InsubrischenLinie (N-Italien). Gottinger Arbeiten zur Geologie und Palaontologie51, 1–61.

Whitmeyer, S.J., Simpson, C., 2004. Regional deformation of the Sierra deSan Luis, Argentina: Implications for the Paleozoic development ofwestern Gondwana. Tectonics 23. doi:10.1029/2003TC00154.

ts on the Famatinian and Achalian structural ..., J. S. Am. Earth