Structural and tectonic evolution of the Acatlan Complex, southern

Mexico: Its role in the collisional history of Laurentia

and Gondwana

Ricardo Vega-Granillo,1 Thierry Calmus,2 Diana Meza-Figueroa,1 Joaquın Ruiz,3

Oscar Talavera-Mendoza,4 and Margarita Lopez-Martınez5

Received 24 May 2007; revised 22 January 2009; accepted 10 March 2009; published 25 July 2009.

[1] Correlation of deformational phases and thermalevents in the Acatlan Complex permits definition ofnine major tectonic events. Seven events are related tothe evolution of the Iapetus and Rheic oceans. By theEarly Ordovician, the Xayacatlan suite of Laurentianaffinity was metamorphosed to eclogite facies andexhumed before colliding with the El Rodeo suite.From the Late Ordovician to Silurian, the UpperOrdovician Ixcamilpa suite with peri-Gondwananaffinity was metamorphosed to blueschist facies,exhumed, and subsequently was overthrust by theXayacatlan–El Rodeo block. Part of the Esperanzasuite is an Early Silurian intra-Iapetian continental arcthat collided with and subducted beneath continentalcrust, generating a Silurian eclogitic event. By the LateDevonian, collision of the three high P/T suites closedthe Iapetus Ocean. The resulting composite terrain wasthrust over the Gondwana-bordering Cosoltepec suiteto close the Rheic Ocean. During the earliestMississippian, the collision of the Acatlan Complexand the Oaxaca terrane uplifted and deformed thecomposite terrane. By the Early Permian, depositionof the Chazumba suite occurred in a pull-apart basin.A latest Early Permian event produced thrust shearzones with N–S directed shortening. During theMiddle Jurassic, plume rise caused regional doming,magmatism and amphibolite facies metamorphism.During the Late Cretaceous–Paleogene, folds andthrust faults overprint the Acatlan Complex. Mostevents in the Acatlan Complex correlate with events inthe Appalachian chain, suggesting that the AcatlanComplex was located near the Appalachians until theJurassic when it was displaced by the Gulf of Mexico

opening. Citation: Vega-Granillo, R., T. Calmus, D. Meza-Figueroa, J. Ruiz, O. Talavera-Mendoza, and M. Lopez-Martınez(2009), Structural and tectonic evolution of the Acatlan Complex,southern Mexico: Its role in the collisional history of Laurentiaand Gondwana, Tectonics, 28, TC4008, doi:10.1029/2007TC002159.

1. Introduction

[2] The Acatlan Complex basement of the Mixtecoterrane contains the largest exposure of eclogites, high-Pgarnet amphibolites, blueschists and eclogitized granitoidsof Paleozoic age in Mexico. In a strict sense, the Mixtecoterrane must be considered a superterrane composed ofthrust sheets containing Mesoproterozoic to Paleozoic pet-rotectonic suites with Laurentian, Gondwanan and mixedaffinities, which were mostly juxtaposed during the Paleo-zoic [Talavera-Mendoza et al., 2005]. The Mixteco super-terrane must have been transported to its present locationafter Triassic time to avoid overlap with South Americancrust during the assembly of the Pangean supercontinent[e.g., Pindell, 1985, 1994]. Therefore, geologic, structuraland metamorphic correlations of this exotic terrane requirethe further consideration of regions beyond presently adja-cent areas.[3] The present body of work establishes the character-

istics of each deformation phase in the main tectonostrati-graphic assemblages of the Acatlan Complex. Fabrics revealcomplex deformation histories, and together with previousmetamorphism information and P-T paths, allow the recon-struction of orogenic cycles. This survey proposes a newmodel for the tectonic evolution of the Acatlan Complexand a comparison with tectonic events in the PaleozoicAppalachian orogen.

2. Geological Setting

[4] The Acatlan Complex is a tectonic pile of sevenmajor thrust sheets, each one with a particular lithologicalassemblage and a distinctive tectonothermal evolution.However, many issues concerning the general frameworkand evolution of the Acatlan Complex remain controversialand lack consensus [e.g., Ortega-Gutierrez et al., 1999;Talavera-Mendoza et al., 2005, 2006; Nance et al., 2006;Murphy et al., 2006]. Each thrust sheet including differentmetamorphic rock types is defined here as a suite, andcorresponds to an allochtonous nappe (Figures 1 and 2).

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1Departamento de Geologıa, Universidad de Sonora, Hermosillo,Mexico.

2Estacion Regional del Noroeste, Instituto de Geologıa, UniversidadNacional Autonoma de Mexico, Hermosillo, Mexico.

3Department of Geosciences, University of Arizona, Tucson, Arizona,USA.

4Unidad Academica de Ciencias de la Tierra, Universidad Autonoma deGuerrero, Taxco, Mexico.

5Departamento de Geologıa, CICESE, Ensenada, Mexico.

Copyright 2009 by the American Geophysical Union.0278-7407/09/2007TC002159$12.00

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[5] The Acatlan Complex is divided into seven majorsuites (Figure 2). The Tecolapa suite located in the westernarea of the complex (Figure 1) consists of megacrysticgranitoids and tonalitic gneisses of Mesoproterozoic age(1165 ± 30 to 1042 ± 50 Ma; U-Pb) [Campa-Uranga et al.,2002; Talavera-Mendoza et al., 2005].[6] The Xayacatlan suite consists of meter-thick alternat-

ing layers of oceanic metabasites and clastic metasediments,with minor felsic flows or dikes, all of which metamorphosedto eclogite and epidote-amphibolite facies. Serpentinizedultramafic bodies in or near the basal thrust are consideredpart of this suite [Carballido-Sanchez and Delgado-Argote,1989; Ortega-Gutierrez, 1993]. Eclogites of the Xayacatlansuite have geochemical and isotopic characteristics similar to

MORB [Yanez et al., 1991; Meza-Figueroa et al., 2003]. Themetasediments have a maximum age of!870Ma (Figure 3a)and a suggested although arguable Laurentian derivation[Talavera-Mendoza et al., 2005]. Lower-Middle Ordoviciangranite and leucogranite transect and engulf xenoliths of thehigh-P rocks [Talavera-Mendoza et al., 2005; Vega-Granilloet al., 2007] postdating the eclogitic event of the Xayacatlansuite.[7] The El Rodeo suite consists of interlayered metavol-

canics, quartzites and schists, with a low P/T greenschistfacies metamorphism [Vega-Granillo et al., 2007]. This unitwas formerly included as part of the Xayacatlan or Tecomateformations [Ortega-Gutierrez, 1978; Ramırez-Espinosa,2001]. Geochemical and isotopic data suggest an intra-arc

Figure 1. Geologic map of the Acatlan Complex (modified from Ramırez-Espinosa [2001]). Faultnumber indicates the chronology of thrusting.

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rift setting for the El Rodeo suite [Ramırez-Espinosa, 2001].The Lower Ordovician granites also intrude the greenschistfacies rocks of the El Rodeo suite [Talavera-Mendoza et al.,2005].[8] The Ixcamilpa suite, located in the central western

part of the complex, consists of interlayered metabasites andmetapelites with minor metachert beds, all of which meta-morphosed to blueschist facies [Talavera-Mendoza et al.,2002; Vega-Granillo et al., 2007]. This suite had beenmapped as part of the Xayacatlan suite [Ortega-Gutierrezet al., 1999; Ramırez-Espinosa, 2001]. The Ixamilpa suitehas a Late Ordovician (!477 Ma) maximum depositionalage based on U-Pb detrital zircon data, and the main detritalzircon age clusters are between 477 and 708 Ma (Figure 3b)[Talavera-Mendoza et al., 2005]. The spectrum of detritalzircon ages suggests a provenance from both an EarlyOrdovician arc and a peri-Gondwanan terrane similar tothe Avalon, Carolina or Suwannee terranes [e.g., Nance,1990; Wortman et al., 2000; Ingle et al., 2003].[9] The Esperanza Granitoids term was formerly applied

to igneous or metamorphosed granitic rocks [Ortega-Gutierrez, 1978] regardless of their age, metamorphism orgeochemical character. The Esperanza suite term is used forhigh-P metamorphic rocks whose protoliths are sedimen-tary rocks, porphyritic granites and mafic dikes [Talavera-

Mendoza et al., 2005; Vega-Granillo et al., 2007]. SilurianU-Pb ages ranging from 442 ± 5 to 440 ± 14 Ma [Ortega-Gutierrez et al., 1999; Talavera-Mendoza et al., 2005;Vega-Granillo et al., 2007], are interpreted as magmaticcrystallization ages of the typical Esperanza augen gneisses.Geochemical data from granitoids indicate a peraluminouscharacter and a calc-alkaline continental arc signature[Ramırez-Espinosa, 2001]. Weber et al. [1997] includehigh-grade metasediments such as garnet mica schist,quartzites and paragneisses (Figure 4g) in the formerEsperanza Granitoids. Field relationships reveal that LowerSilurian granite intrudes and engulfs xenoliths of thesemetasediments [Vega-Granillo, 2006]. The detrital zirconage plot from metasedimentary rocks of the Esperanza Suite(Figure 3c) has a younger detrital zircon cluster of !719 Maand larger clusters of Mesoproterozoic (1244–917 Ma) age[Vega-Granillo, 2006; Murphy et al., 2006]. On the basis ofthe detrital age plot, Murphy et al. [2006] suggest aGondwanan affinity for the Esperanza metasediments. Basicdikes crosscutting the metasedimentary rocks and the augengneisses, are tholeiites with continental-rift-type geochem-istry [Murphy et al., 2006], an interpretation supported bygeologic relationships. The Esperanza suite was metamor-phosed to medium-T eclogite facies during an Early LateSilurian collisional event [Ortega-Gutierrez et al., 1999;

Figure 2. Tectonic chart of Acatlan Complex.

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Vega-Granillo et al., 2007]. Upper Devonian (!370 Ma,U-Pb zircon) granites and leucogranites [Vega-Granillo etal., 2007] intrude the augen gneisses so pervasively thatthey are included in the Esperanza suite, despite of notdisplay eclogite facies assemblages [Vega-Granillo, 2006].An Upper Devonian porphyritic granite known as the LaNoria Granite also intrudes the El Rodeo suite [Yanez et al.,1991].[10] The Cosoltepec suite comprising up to 70% of the

Acatlan Complex outcrops (Figure 1) consists of interlay-ered quartzite and phyllite with minor volcaniclastic bedsand isolated tectonic slices of pillow basalts of oceanicaffinity [Ramırez-Espinosa, 2001], all of which are meta-

morphosed to greenschist facies. The maximum reliabledepositional age for this suite is Early Middle Devonian(!410–394 Ma). Detrital zircon ages suggest depositionalong the northern margin of South America [Talavera-Mendoza et al., 2005], although the basement of theCosoltepec suite is unknown. The Totoltepec Stock is anisolated trondhjemitic body of Early Permian age (287 ±2 Ma; U-Pb zircon) [Yanez et al., 1991; Keppie et al.,2004a], and crops out in the NE region where thrustingconceals its intrusive margins [Malone et al., 2002].[11] The Chazumba suite cropping out in the eastern

region of the complex includes the former Chazumba andMagdalena formations of Ortega-Gutierrez [1978]. TheChazumba suite is the lower structural unit of the AcatlanComplex and consists of a thick succession of pelitic-psammitic schists with metabasites interlayered near to thebase. The detrital zircon age plot of the Chazumba suiteindicates a maximum Leonardian depositional age (!275 Ma)and suggests a provenance from Laurentian and Gondwanansources [Talavera-Mendoza et al., 2005]. The Chazumbasuite was metamorphosed to upper amphibolite facies,migmatized and intruded by leucogranites and two-micagranites [Figueroa-Salguero, 2003; Salgado-Souto, 2004]during the Middle Jurassic (175 Ma to 163 Ma; U-Pb, Rb-Sr,Ar-Ar) [Ruiz-Castellanos, 1979; Yanez et al., 1991; Keppieet al., 2004a; Talavera-Mendoza et al., 2005].[12] The Acatlan Complex is depositionally overlain by an

Upper Devonian to Lower Permian sedimentary sequence,which crops out as isolated erosion remnants [Flores deDios and Buitron-Sanchez, 1982; Brunner, 1987; Villasenoret al., 1987; Enciso de la Vega, 1988; Ramırez-Espinosa etal., 2000; Vachard et al., 2000; Vachard and Flores de Dios,2002]. The Patlanoaya Formation [Villasenor et al., 1987]remains as the most complete section of that sequence. TheTecomate Formation that is overprinted by greenschistfacies dynamic metamorphism [Vega-Granillo, 2006] wasformerly considered as a separate regional metamorphosedunit of the Acatlan Complex. However, this unit containsEarly Permian (Kungurian) fossils [Keppie et al., 2004b;Vega-Granillo, 2006], and can be correlated with part of theunmetamorphosed Patlanoaya Formation.

3. The 40Ar/39Ar Geochronology

3.1. Analytical Methods

[13] Three new 40Ar/39Ar analyses were performed at theGeochronology Laboratory of the Departamento de Geo-

Figure 3. Cumulative plots of detrital zircon U/Pb ages,from (a) Xayacatlan suite; (b) Ixcamilpa suite [Talavera-Mendoza et al., 2005]; and (c) Esperanza suite [Vega-Granillo et al., 2007].

Figure 4. (a) Photography and (b) interpretative sketch of a garnet amphibolite exposure of the Xayacatlan suite. InFigure 4b, three foliations (S2XA " S4XA) and two phases of superposed isoclinal folding with axial planar foliations (S3XAand S4XA) are recognized. (c) Photography of exposure and (d) interpretative sketch of superposed folding (F2ER " F4ER)in quartzite from El Rodeo suite. F2ER is an isoclinal folding of the S1ER foliation and L1ER lineation. (e) Photography of aMid-Ordovician (461 Ma) leucogranite with xenoliths of Xayacatlan rocks. A mylonitic foliation in the leucogranite (S/C0)is oblique respect to a S3XA foliation in xenoliths. Some xenoliths are microfaulted during the mylonitic event.(f) Subisoclinal folding of the mylonitic foliation in Mid-Ordovician leucogranite. (g) Esperanza suite garnet micaschistwith a quartz-feldespathic vein emplaced along S1ES. The rock is isoclinally folded, and an axial planar coarse-grainedfoliation S2ES is developed. (h) Esperanza suite high-grade augen gneiss with folding of mantled K-feldspar porphyroclasts.Folds are related to a second mylonitic foliation S2ES, which commonly transpose S1ES.

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Figure 4

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logıa, CICESE. Two instruments were used for the argonisotope analyses, a laser extraction system on line with aVG5400 mass spectrometer for single grain experiments,while the bulk sample analyses were conducted with anMS-10 mass spectrometer equipped with a ModificationsLtd., Ta furnace. The samples were irradiated in the U-enriched research reactor of the University of McMaster inHamilton, Canada. As irradiation monitors, TCR-2 (splitG93) sanidine (27.87 ± 0.04 Ma) and internal standardCATAV 7–4 (88.54 ± 0.39 Ma) were irradiated alongsidethe samples. The argon isotopes were corrected for blank,mass discrimination, neutron interference reactions, radio-active decay of 37Ar and 39Ar and atmospheric contami-nation. The analytical precision is reported as two standarddeviations (1s). The decay constants recommended bySteiger and Jager [1977], were used in the argon datareduction procedures. The error in the plateau, integratedand isochron ages includes the scatter in the irradiationmonitors. The equations reported by York et al. [2004] wereused in all straight line fitting routines of the argon datareduction. The samples were step heated with the laserextraction system, the Ta furnace, or both.

3.2. Results

[14] The rocks dated in this work are metabasite andmuscovite-chlorite schist from the El Rodeo suite andgranitic pegmatite crosscutting the Esperanza suite. Agedata and sample location are displayed in the Table 1.Amphibole from a metabasite of the El Rodeo suite (sampleRAC-8) yielded a Late Mississippian 320 ± 13 Ma age

(Figure 5a). Fine-grained white mica from mica-chloriteschist (sample ACA-71) of the El Rodeo suite yielded aMiddle Mississippian 327 ± 2 Ma age, coeval within errorto the age obtained from the amphibole (Figure 5b). Thethird geochronologic study was performed on >2 cm mus-covite crystals from an undeformed granitic pegmatite(sample RAC-188) that crosscuts the high-grade gneissesof the Esperanza suite. These large muscovite crystals yieldan Early Mississippian 347 ± 3 Ma age (Figure 5c).

4. Structural Analysis of the Acatlan Complex

[15] The deformation history of the Acatlan Complex isdefined through detailed field study of mesoscopic struc-tures combined with microtectonic studies of about 350 thinsections. The StereoNett program (J. Duyster, StereoNett,Version 2.46, 2000, http://homepage.ruhr-uni-bochum.de/Johannes.P.Duyster/stereo/stereo1.htm) is used to analyzeand display the structural data. In this section, we use lettersD for deformation phase, S for foliation, M for metamorphicevent, and F for folding phase. Each suite underwent

Table 1. Location of 39Ar/40Ar Dated Samples

Sample Age Coordinates UTM

ACA-71 327 ± 2 E14 578254 2056208RAC-8 320 ± 13 E14 577745 2056175RAC-188 347 ± 2.6 E14 580071 2038791

Figure 5. The 40Ar/39Ar spectra for (a) mica schist and (b) metabasite from the El Rodeo suite.(c) Unmetamorphosed pegmatite intruding the Esperanza Suite.

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6.

Interpretativechartofthetectonic

eventsin

theAcatlan

Complex.

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separate tectonic events until they were progressivelyjuxtaposed. Therefore, a single sequential numbering cannotbe used for the deformation phases in all the suites. Instead,sequential numbering is used for deformation phases in eachsuite. Additionally, the following subscripts are used: XAfor Xayacatlan suite; ER for El Rodeo suite; OL for Mid-Ordovician leucogranite and granite; IX for Ixcamilpa suite;ES for Esperanza suite; CO for Cosoltepec suite; LN for LaNoria Granite; CH for Chazumba suite; OT for El OtateFormation, and TE for Tecomate Formation. The sequence ofdeformational metamorphic events is displayed in Figure 6.

4.1. Structural Framework

[16] The largest structures of the Acatlan Complex aretwo regional domes, the Ayu and Ahuatempan domes, andseveral large-scale folds (Figure 7). The domes influence thestrike of the contacts between units as far as 50 km away

from their centers. The Chazumba suite cropping out in thecore of the Ayu dome underwent a Mid-Jurassic thermalevent evidenced by regional metamorphism, migmatizationand leucogranite intrusion.[17] Large-scale folds with !10 km wavelength are the

most conspicuous structures of the Acatlan Complex (crosssection in Figure 1). The upper structural units, includingthe Ixcamilpa, Xayacatlan, Tecolapa, Esperanza and ElRodeo suites, crop out in the synclinoriums, whereas theCosoltepec suite crops out in the anticlinoriums. Variation inthe trend of major fold axes (Figure 7) may be due to thedomes acting as buttresses during the Late Cretaceouscompression. The Jurassic-Cretaceous sedimentary rocksoverlying the Acatlan complex display the same pattern oflarge folds [e.g., Cerca et al., 2007].[18] Major thrust faults juxtapose the suites of the Acatlan

Complex (Figures 1 and 2). Along one of the main faults,the high-P Ixcamilpa and Xayacatlan suites are thrust over

Figure 7. Megastructures in the Acatlan Complex include the Ayu and Ahuatempan domes, and largewavelength anticlinoriums and synclinoriums. The Papalutla fault is the western limit of the AcatlanComplex exposures. Abbreviations: TE, Tecolapa suite; XA, Xayacatlan suite; ER, El Rodeo suite; IX,Ixcamilpa suite; ES, Esperanza suite; CO, Cosoltepec suite; CH, Chazumba suite; DG, Late Devoniangranite; TG, Totoltepec granite; PG, Lower Permian granite; OG, Middle Ordovician Teticic granite.

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the lower P/T Cosoltepec suite [e.g., Ortega-Gutierrez et al.,1999; Ramırez-Espinosa, 2001]. The structural contactbetween these main blocks occurs throughout the AcatlanComplex exposures, although there is not a distinctive shearzone along that contact. The Ixcamilpa suite crops out as atectonic slice between the Cosoltepec suite below and the

Xayacatlan suite above. Either the low P/T El Rodeo or thehigh P/T Esperanza suites are thrust over the Xayacatlansuite as in the Piaxtla and eastern Mimilulco regions(Figures 1 and 7). During a younger event, the LowerPermian Totoltepec pluton was thrust over the Lower Perm-ian sedimentary cover, and the Cosoltepec suite was thrustover the Chazumba suite. Ages of all these deformationalevents will be discussed in the tectonic evolution section.

4.2. Detailed Structures and Microtectonics of the MainMetamorphic Suites4.2.1. Deformation of the Xayacatlan Suite[19] The Xayacatlan suite displays up to three foliations in

some outcrops. Additionally, isoclinal to subisoclinal foldsand overprinted folds are common in that suite (Figures 4aand 4b). The oldest deformational phase D1XA in the Xaya-catlan suite created amicroscopic foliation S1XA preserved asan internal foliation within poikiloblasts (Figure 8a). Garnetscommonly display helicitic folds of S1XA. A second meta-morphic deformation event D2-M2XA created coarse-grainedeclogite facies paragenesis, oriented along a pervasive S2XAfoliation (Figure 9d) oblique with regard to S1XA. Theeclogite assemblage includes omphacite, garnet, zoisite, phen-gite, barroisite, quartz, and rutile; garnet amphibolite displaysthe same assemblage but with albite instead of omphacite.[20] During a third M3XA metamorphic event, Mg-

hornblende, albite, clinopyroxene, pargasite, hastingsite,biotite, ilmenite and titanite crystallized as reaction rimsaround the high-P phases. This mineral assemblage isrelated to pressure diminution and temperature increasingand indicates a transition to epidote-amphibolite facies[Vega-Granillo et al., 2007]. Isoclinal folding of S2XAand its respective axial surface foliation S3XA evidence athird deformation phase D3XA related to the M3XA event(Figures 4a, 4b, 6, and 9e).[21] A fourth spaced mylonitic foliation S4XA with

N10!W to N20!E strikes mostly transposes older foliations

Figure 8. Sketches of the first foliations in Xayacatlan(Figure 8a) and Ixcamilpa suites (Figure 8b). (a) Internalfoliation Si1XA made by epidote, phengite, chlorite, andtitanite within albite poikiloblasts; the second coarse-grained foliation S2XA is related to the eclogite faciesmetamorphism. (b) Albite poikiloblast with two internalfoliations Si1IX and Si2IX. The second foliation is parallel tothe external coarse-grained foliation S2IX related toblueschist facies metamorphism.

Figure 9. Sketches of the first four foliations in a chloritoid-garnet micaschist of the Xayacatlan suite.(a) Developing of a fine-grained foliation S1XA. (b) Growth of chloritoid and (c) garnet poikiloblasts thatinclude the S1XA foliation. (d) Recrystallization produces a coarse-grained eclogitic foliation S2XA.(e) Isoclinal folding of S2XA and developing of a S3XA axial planar foliation transposing S2XA. (f) Foldingof S3XA related to a spaced crenulation cleavage S4XA.

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in the Xayacatlan suite, being the predominant foliation ofthat suite (Figures 4a and 4b). Fold axes trending fromN20!W to N20!E and ductile slickenside striations (asdefined by Lin et al. [2007]) trending from E–W toN80!W are ascribed to the same phase (Figures 6 and 9).Although younger low-grade cleavages overprint the Xaya-catlan suite, they are not easily discernible from the fourthcleavage.4.2.2. Deformation of the El Rodeo Suite[22] Microtectonic studies in the El Rodeo suite reveal at

least four foliations in some rocks (Figure 10). However,generally only two foliations can be easily discriminated inthe field. Additionally, some exposures display three over-printing folding phases subsequent to S1ER (Figures 4cand 4d). The first deformation phase D1ER imprinted onthe El Rodeo rocks produced a fine-grained foliation S1ER(Figures 10a and 10b) and thin compositional layering. Asecond deformation phase D2ER caused folding of the S1ERfoliation and development of an axial surface foliation S2ER(Figure 10c) transposing the first foliation. The seconddeformation phase also produced ductile slickenside stria-tions in some quartzites. In turn, a third deformation phaseD3ER folded the S2ER foliation and created an axial surfacefoliation S3ER. Finally, a fourth deformation phase D4ERfolded the S3ER foliation and produced a millimeter-spacedpressure solution crenulation cleavage S4ER (Figure 10d)parallel to the axial surfaces of microscopic and mesoscopicfolds.[23] Although subsequent deformation phases overprint

and usually transpose the older structures in the Xayacatlanand El Rodeo suites, both suites share fold axes trendingN40!W to N80!W (Figure 11), which are indiscernible inany other suite of the Acatlan Complex. These fold axesindicate shortening with a N50!–70!E azimuth.4.2.3. Deformation of Lower-Middle OrdovicianLeucogranite[24] Lower-Middle Ordovician granite and leucogranite

intrude and engulf xenoliths of the Xayacatlan (Figure 4e)and El Rodeo suites. These granites locally display a

mylonitic foliation S1OL (Figure 4e), which is isoclinallyfolded by a later F2OL phase (Figure 4f). The myloniticfoliation S1OL in the leucogranite is nearly parallel to theS4XA and S2ER foliations; hence, the three foliations areascribed to the same deformation phase.4.2.4. Deformation of the Ixcamilpa Suite[25] Two fine-grained foliations Si1IX–Si2IX (Figure 8b)

trapped within poikiloblasts record the older deformationphases in the Ixcamilpa suite. Zoisite and opaque inclusionswithin poikiloblasts of metabasites define the Si1IX internalcleavage. Glaucophane, zoisite and titanite lineated inclu-sions define the Si2IX cleavage, which is parallel to acoarse-grained external foliation S2IX (Figure 8) definedby preferred orientation and elongation of glaucophane,albite and clinozoisite poikiloblasts. A third deformationphase D1IX created a spaced mylonitic foliation indicated bya shear band cleavage S/C0. Chlorite, pistachite, calcite andtitanite, as well as reaction rims of winchite and barroisitearound glaucophane, form a third mineral assemblage M3IXrelated to the D3IX phase. Thermobarometry in the amphi-bole-plagioclase minerals of the M3IX event indicates tem-perature increasing and pressure decreasing [Vega-Granilloet al., 2007], producing the transition from blueschist toepidote-amphibolite facies. Microtectonic hints of youngerdeformation phases overprinting the Ixcamilpa suite occurbut are difficult to discern from the third phase.4.2.5. Deformation in the Esperanza Suite[26] The sedimentary, granitic, and basic protoliths of

the Esperanza suite were metamorphosed to !800!C and>16 kbar [Vega-Granillo et al., 2007], typical conditions ofmedium-T eclogites (as defined by Cuthbert and Carswell[1990]). Eclogitic metamorphism mostly obliterated anymineral or fabric vestige of the prograde path in theEsperanza suite. A ubiquitous coarse-grained foliationS1ES (Figures 4g and 4h) related to eclogite facies eventM1ES is the first recognizable deformation phase D1ES inrocks of the Esperanza suite. The eclogitic event trans-formed the granite into high-grade mylonitic garnet augengneiss and the original K-feldspar megacrysts to mantled

Figure 10. (a) Sketch of a greenschist of the El Rodeo Suite, four foliations can be recognized each onerelated with isoclinal folding and greenschist to subgreenschist facies metamorphic events. (b–e)Sketches interpreting the deformational metamorphic events in the El Rodeo metabasite.

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porphyroclasts (Figure 4h). In some places, intense defor-mation created striped gneisses. Mafic dikes are metamor-phosed to mildly foliated eclogite and garnet-Mg-taramitegranofels that display a mesoscopic pinch-and-swell struc-ture. Ductile slickenside striations and stretching lineationof the D1ES phase are poorly preserved in all the rocks,likely due to further static recrystallization. However,uncommon ductile slickenside striations and mantled por-phyroclasts from augen gneisses suggest an E–W move-ment direction and top to the W shear sense. U-Pb(monazite) [Ortega-Gutierrez et al., 1999] and 40Ar/39Ar(amphibole) geochronology [Vega-Granillo et al., 2007]indicate a Early Late Silurian !430–418 Ma age for thiseclogitic event.[27] The Esperanza suite underwent an almost isothermal

decompression after the eclogitic metamorphism [Vega-Granillo et al., 2007]. That change generated partial meltingof metasediments expressed as local migmatization andintrusion of leucogranites (Figure 4g). Stromatic migmatiteswith ptygmatic folding are locally developed in metapelites.Veinlets and pegmatitic pods of albite-quartz-phengiteoccur in the eclogite. A leucogranite yields a 372 ± 8 Maage (U-Pb, zircon), indistinguishable from a 374 ± 2 Ma age(40Ar/39Ar) [Vega-Granillo et al., 2007] obtained from aphengite pod in eclogite.[28] The Upper Devonian leucogranite displays both a

well-developed penetrative mylonitic foliation and ductileslickenside striations formed in medium to high-gradeconditions as indicated by dynamic recrystallization of K-feldspar. The deformational phase producing the first foli-ation in the leucogranite created an overprinting myloniticfoliation S2ES in the eclogitized metasediments and augengneisses of the Esperanza suite (Figures 4g and 4h). ThatS2ES foliation mostly transposes the first foliation S1ES inaugen gneisses and mica schists of the Esperanza suite insuch a way that the first deformation phase D1ES only canbe discerned in uncommon areas of low strain, either as acrenulated foliation, folding of mantled porphyroclasts(Figure 4h), or intrafolial folds. Well-developed ductileslickenside striations in leucogranite trend mainly N80!–90!W (Figure 11). Leucogranite dikes display mesoscopicisoclinal to tight folds and the fold axes of that F2ES phasetrend N70!–90!W. The similarity of trends among the foldaxes and the ductile slickenside striations suggests that thefolds are oblique folds developed in the leucogranite by theD2ES phase. Mantled porphyroclasts and S/C0-type shearband cleavage (as defined by Passchier and Trouw [1998])indicate a top to the W shear sense.[29] A third deformation phase D3ES created mesoscopic

subisoclinal folds in the Esperanza suite. Locally, a low-grade cleavage parallel to the axial surfaces of the F3ESfolds is developed. The D3ES phase also yielded discreteshear zones along which low-grade dynamic metamorphismM3ES generated ultramylonites. The M3ES inhomogeneousmetamorphism produced quartz elongation, chlorite crystal-lization, and pressure solution. Fold axes with trendsbetween N50!–70!E and NW vergence (Figure 11) areascribed to the D3ES deformation phase, as are ductileslickenside striations with N30!–60!W trends.

[30] Close folds F4ES with N70!–90!W trending axesdefine the fourth deformation phase D4ES in the Esperanzasuite. An inhomogeneous mylonitic foliation related togreenschist facies metamorphism, and poorly developedductile slickenside striations L4ES trending N to N40!W,are also ascribed to that fourth deformation phase D4ES(Figure 11). An S/C0-type shear band cleavage formed byD4ES indicates a top to the S shear sense.

4.2.6. Deformation in the Cosoltepec Suite[31] The first deformation phase D1CO in the Cosoltepec

suite yielded a microscopic fine-grained continuous cleavageS1CO in quartzites, also defined in metavolcanics as aninternal foliation within albite poikiloblasts. A second defor-mation phase D2CO produced a fine-grained, millimeter-spaced schistosity S2CO, which is better developed in phyl-lites than quartzites. The S2CO foliation is the most visibleand penetrative fabric in the Cosoltepec suite (Figures 12aand 12b), and is indicated by preferred orientation of mus-covite, albite, quartz and chlorite in metasediments, plusactinolite and titanite in the uncommon metavolcanic layers.These assemblages formed by the M2CO event are typical ofgreenschist facies. Both, the predominant N20!W–N10!Estrikes of the S2CO foliation planes and the uncommonN80!W–N80!E trends of ductile slickenside striations mea-sured over the S2CO planes indicate a WNW–ESE shorten-ing direction for D2CO phase (Figure 11).[32] The third deformation phase D3CO in the Cosoltepec

suite is defined by mesoscopic to microscopic subisoclinaland isoclinal folding of the S2CO foliation and by aninhomogeneous axial surface cleavage S3CO (Figures 12aand 12b). The centimeter-spaced S3CO cleavage is mainlycreated by pressure solution as evidenced by concentrationof opaque and micaceous minerals along the cleavageplanes. Common steeply dipping brittle reverse faults areascribed to the D3CO deformation phase. The S3CO cleavageusually strikes !N30!E and dips more than 75! SE or NW,indicating a WNW–ESE shortening direction (Figure 11).[33] The fourth deformation phase D4CO in the Cosolte-

pec suite produced structures like those of the D3CO phase,both in metamorphic grade and cleavage spacing; therefore,it is difficult to discern D3CO from D4CO structures based ontheir physical appearance, except in scarce outcrops whereboth structures remain visible (Figures 12a and 12b). TheS3CO and S4CO cleavages must have originated in sub-greenschist facies conditions because no new mineralscrystallized along them. Pressure solution related to D4COlocally produced centimeter-thick black layers parallel toS4CO, which can be confused with slate beds. The S4COcleavage renders N to N50!E strikes and subhorizontal dips,and it is parallel to the axial surfaces of the F4CO folds.Folds formed by the F4CO phase vary from tight to isoclinalin phyllites, and from close to open in quartzites. Most ofthese folds are recumbent or overturned with a NW ver-gence. Refolded folds created by superposition of F4COover F3CO folds are relatively common and display a type 3fold interference pattern [Ramsay and Huber, 1987]. Foldaxes forming the major cluster in the Cosoltepec suite areascribed to the fourth deformation phase and have trends of

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Figure 11. Contoured (1% area) stereonets of foliation poles, fold axes, and ductile slickensidestriations for the Xayacatlan, El Rodeo, Esperanza, and Cosoltepec suites. An interpretation of thedeformation phases causing these structures is included on the right.

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N10!–50!E and plunges lesser than 20! to NE or SW(Figure 11). Common subhorizontal curved thrust faults andscarce striations with N50!–80!W trends are attributed tothe D4CO phase.4.2.7. Deformation in the La Noria Granite[34] The La Noria Granite is a coarse-grained two-mica

granite with K-feldspar phenocrysts, that yields a Late

Devonian age (371 ± 34 Ma, U-Pb zircon) [Yanez et al.,1991]. This granite was formerly included in the EsperanzaGranitoids [Yanez et al., 1991] but separated by its youngerage [Ortega-Gutierrez et al., 1999]. Additionally, La NoriaGranite lacks the eclogitic metamorphism of the Esperanzagneisses. Near the town of La Noria, the granite retains agranular texture that grades into a mylonitic fabric to the

Figure 12. (a) Photography of phyllites from the Cosoltepec suite, three cleavages may be recognized,the latter two related with folding events. (b) Sketch from Figure 12a. (c) Photography of the UpperDevonian La Noria Granite, a protomylonitic granite with elongated K-feldspar porphyroclasts. (d) Thinsection photography of a metalimestone of the Lower Permian Tecomate Formation. A microfaultedcalcite intraclast can be seen in the center. (e) Photography of subisoclinal folds in the El Otate Formationrocks. (f) Sketch of a slate thin section from the El Otate Formation. A very fine grained foliation S1EOand a second spaced foliation S2EO are displayed, both developed under very low grade conditions.

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east (Figure 12c). The mylonitic deformation is related to alow-T greenschist facies hydrothermal metamorphism,which produced sericite and chlorite from feldspars andbiotite, respectively. The mylonitic foliation displays N10!–40!W strikes and NE dips, while ductile slickenside stria-tions are mainly horizontal. S/C0-type cleavage in the granitemylonite indicates a top to S shear sense. Thus, the singlefoliation recognized in the La Noria Granite was originatedalong a shear zone with a NNW–SSE movement directionand top to the S shear sense.4.2.8. Deformation of the Chazumba Suite[35] In the eastern region of the Acatlan Complex, the

Cosoltepec suite is thrust over the Chazumba suite. Bothsuites display a regional foliation with general E–W strikeand N dip. Two deformation phases D1CH–D2CH, each onerelated to greenschist to upper amphibolite metamorphicevents [Figueroa-Salguero, 2003; Salgado-Souto, 2004],imprint the Chazumba rocks. Metamorphic minerals, leuco-somes of migmatites and granitic dikes, yield Mid-Jurassicages (175–162 Ma) [Ruiz-Castellanos, 1979; Yanez et al.,1991; Keppie et al., 2004a; Talavera-Mendoza et al., 2005].In the higher-T zone, recrystallization and deformationrelated to the second tectonic event obliterated the firstfoliation S1CH.4.2.9. Deformation of the Acatlan ComplexSedimentary Cover[36] The Patlanoaya Formation is the most complete

Paleozoic sedimentary sequence deposited in nonconformityover the Acatlan Complex (Figure 1) [Brunner, 1987;Villasenor et al., 1987]. The lower beds, which containlatest Devonian (Famennian) fossils [Vachard and Flores deDios, 2002], are overlain by conglomerate beds with clastsof porphyritic granite and metamorphic rocks. A platformsequence of sandstones and limestones overlying the con-glomerate contain fossils dated from the Early Mississippian(Kinderhookian) to the Early Permian (Leonardian)[Brunner, 1987; Villasenor et al., 1987; Vachard et al.,2000; Vachard and Flores de Dios, 2002]. Originally, theUpper Devonian beds were included in the PatlanoayaFormation [Vachard and Flores de Dios, 2002]; however,these beds display isoclinal folding (Figure 12e) and twoslaty cleavages (Figure 12f) formed by pressure solution, asevidenced by truncated layering and concentration ofopaque minerals in dark seams. Since the Carboniferous-Permian beds do not display isoclinal folding or cleavage,and the conglomerate overlies the Famennian beds on anangular unconformity, the Devonian beds must be separatedfrom the Patlanoaya Formation. The name El Otate Forma-tion, proposed by Hernandez-Suarez and Morales-Martınez[2002] for slightly metamorphosed beds of El Otate Creek,can be used to name this unit. Scarce fold axial surfacesmeasured indicate !N–S shortening deformation D1EO inthe El Otate Formation, but a more systematic study isrequired to precisely define the orientation of that deforma-tion phase.[37] The Tecomate Formation was formerly considered

part of the Acatlan Complex, but its lithology and EarlyPermian fossils indicate that the unit is part of the Patla-noaya Formation. South of the town of Acatlan (Figure 1),

the Tecomate Formation is thrust over the El Rodeo suite,which in turn, is thrust over the Xayacatlan suite. The mainstructure of the Tecomate Formation is a fine-grainedmylonitic foliation (Figure 12d) striking N0!–20!W, whichis related to horizontal ductile slickenside striations. Gra-nitic conglomerate clasts are stretched parallel to the stria-tions. Minerals of the phyllonites, slight recrystallization ofcalcite and widespread pressure solution cleavages indicategreenschist facies metamorphism related to the myloniticdeformation. Thus, dynamic metamorphism occurred in theTecomate Formation after Early Permian time, along a shearzone with a NNW–SSE movement direction. S/C0-typecleavage indicates a top to the S shear sense. Afterward,large-scale folds with axes trending N0!–20!W bent themylonitic foliation.

5. Discussion: Tectonic Evolution of theAcatlan Complex

5.1. Early Ordovician Event (Pre-478 Ma): Subductionof the Xayacatlan Suite and Collision With theTecolapa–El Rodeo Arc

[38] The first two deformational phases in the Xayacatlansuite D1XA and D2XA are ascribed to the earlier and laterstages of the subduction of oceanic lithosphere until low-Teclogite facies conditions (609–491!C and 13–12 kbar)were reached [Meza-Figueroa et al., 2003; Vega-Granillo etal., 2007] (Figure 6). This tectonic event, one of the oldestrecorded in the Acatlan Complex [Vega-Granillo et al.,2007], probably occurred under a continental fragmentseparated from the Laurentian margin (Figure 13a)corresponding to the Tecolapa suite [Talavera-Mendoza etal., 2005]. Later, the Xayacatlan suite was exhumed andsubsequently overthrust by the El Rodeo and Tecolapasuites (Figure 13b). This tectonic juxtaposition (block 1 inFigure 6) yielded the third deformational metamorphicD3XA–M3XA event in the Xayacatlan suite and the firstD1ER–M1ER event in the El Rodeo suite. Afterward,Lower-Middle Ordovician 478–461 Ma (U-Pb zircon)two mica granite and leucogranite intruded the Xayacatlanand El Rodeo suites and the thrust fault between them,engulfing xenoliths of the high-P rocks (Figures 4e and 13c)[Talavera-Mendoza et al., 2005; Vega-Granillo, 2006].Thus, these granites constrain the time of metamorphismand tectonic amalgamation of the Xayacatlan, El Rodeo andTecolapa suites.[39] The Taconic phase in New England, the Humberian

phase in western Newfoundland and the Grampian phase inthe Scottish Highlands are nearly coeval with the EarlyOrdovician collision of the Xayacatlan and the El Rodeosuites. All these events are attributed to the collisionbetween Laurentia and a peripheral magmatic arc[McKerrow et al., 2000]. The Penobscotian phase is acoeval event but caused by collision between an intra-Iapetian magmatic arc and the Ganderia terrane [McKerrowet al., 2000]. The detrital zircon ages from the Xayacatlansuite suggest a Laurentian provenance [Talavera-Mendoza

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Figure 13. Interpretative sketches for the tectonic evolution of the Acatlan Complex.

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Figure 13. (continued)

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et al., 2005]; consequently, the correlation with the Taconicphase seems more feasible.

5.2. Late Ordovician-Silurian Event: Subduction of theIxcamilpa Suite

[40] The Ixcamilpa suite protolith was formed during theLate Ordovician within an intra-Iapetian basin (Figures 13cand 13d) receiving sediments from an Early Ordovician arcand a peri-Gondwanan terrane as suggested by its detritalzircon age plot [Talavera-Mendoza et al., 2005, 2006]. Thefirst two tectonic phases in the Ixcamilpa suite are relatedto the initial and final stages of a subduction process(Figure 13e), during which the Ixcamilpa protolith wasburied to !25 km depth and metamorphosed to blueschistfacies (200–390!C and 6–9 kbar) [Vega-Granillo et al.,2007]. The third tectonic event S3IX–M3IX caused theexhumation of the Ixcamilpa suite and subsequent over-thrusting by the Xayacatlan–El Rodeo–Tecolapa block(block 2 in Figure 6 and Figure 13e). Ixcamilpa lithologyand overprinting fabrics are similar to those of the Xaya-catlan suite excepting the metamorphic grade. However,the Ixcamilpa rocks contain a larger detrital zircon clusterof Early Ordovician age (!477 Ma, U-Pb) (Figure 3b)[Talavera-Mendoza et al., 2005], precluding correlationeither with the Xayacatlan suite or with its Early Ordovicianeclogitic metamorphism. Moreover, detrital zircon popula-tions of the Xayacatlan and Ixcamilpa suites are different(Figures 3a and 3b), indicating derivation from dissimilarsources. The time of deformation and metamorphism in theIxcamilpa suite is poorly constrained. Fine-grained phen-gites from blueschists yield a Late Mississippian 40Ar/39Arage (323 ± 6 Ma) [Vega-Granillo et al., 2007], but this agedoes not conclusively define the age of the high-P event as itmay represent a younger thermal event. Thrusting of theEsperanza suite over the Ixcamilpa suite during the LateDevonian may constrain the blueschist metamorphism ofthe Ixcamilpa suite to sometime during the Lower Ordovi-cian to Silurian.[41] As mentioned above, detrital zircon ages suggest an

intra-Iapetian origin for the Ixcamilpa suite. The NewBrunswick Complex in the Northern Appalachians has asimilar depositional tectonic setting, metamorphic faciesand age of tectonic events [van Staal et al., 1990; vanStaal, 1994] to those proposed for the Ixcamilpa suite. Thetectonic event including the subduction of the Ixcamilpasuite and the collision with the Xayacatlan–El Rodeo–Tecolapa block (Figure 6) may be correlated with theSalinic event in the Northern Appalachians, which isattributed to the collision of the Ganderia terrane againstthe Notre Dame Arc during the Silurian, which closed themain Iapetus Ocean [van Staal et al., 1990].

5.3. Early to Late Silurian Event (!430–418 Ma):Subduction of the Esperanza Suite

[42] During the Early Silurian, a calc-alkaline granitebatholith intruded clastic sedimentary rocks (Figure 13e).Basaltic rocks with continental rift geochemical affinity[Murphy et al., 2006] intruded the granite and its host rocks[Vega-Granillo, 2006]. These rocks forming the Esperanza

suite were buried (Figure 13f) and metamorphosed tomedium-T eclogite facies [Vega-Granillo et al., 2007].The first deformation phase D1ES recognized in the Esper-anza rocks is related to prograde eclogite facies metamor-phism M1ES. Uncommon ductile slickenside striations fromaugen gneisses suggest E–W movement direction, andmantled porphyroclasts indicate top to the W shear sense.Amphibole crystals from eclogite yield an Early Silurianage (430 ± 5 Ma, 40Ar/39Ar) [Vega-Granillo et al., 2007],coeval within errors with a 418 ± 18 Ma U-Pb monazite agefrom augen gneiss [Ortega-Gutierrez et al., 1999], indicat-ing an Early Late Silurian age for eclogitic metamorphism.However, latest Devonian–Early Mississippian ages(!360–345 Ma, U-Pb zircon) (M. Elıas-Herrera et al.,New geochronological and stratigraphic data related to thePaleozoic evolution of the high-P Piaxtla Group, AcatlanComplex, southern Mexico, paper presented at IV ReunionNacional de Ciencias de la Tierra, Sociedad GeologicaMexicana, Queretaro, Mexico, 2004) derived from zirconovergrowths in augen gneisses also are interpreted as theage range of the eclogitic event [Murphy et al., 2006].[43] Some authors have correlated the metamorphic rocks

of the Xayacatlan suite with some parts of the Esperanzasuite [e.g., Murphy et al., 2006]. However, the compositeblock of the Xayacatlan, El Rodeo and Ixcamilpa suites failto display fabric, mineralogical or geochronological evi-dence of the Silurian event imprinted in the Esperanza suite,implying these two blocks remained separated during Silu-rian time (Figure 13f). In addition, Silurian granites havenot been observed intruding the Xayacatlan–El Rodeocomposite block. Furthermore, field relationships demon-strate the Xayacatlan suite is composed of interlayeredvolcanic flows and sediments; whereas in the Esperanzasuite, mafic dikes crosscut sedimentary rocks and the LowerSilurian granites. Also, the Early Ordovician age for thehigh-P event in the Xayacatlan suite and the Early LateSilurian age for the high-P event in the Esperanza suitepreclude correlation of these events as has been proposed[Ortega-Gutierrez, 1978; Ortega-Gutierrez et al., 1999;Murphy et al., 2006]. Additionally, medium-T eclogites likethose of the Esperanza suite have been interpreted asresulting from continental subduction [e.g., Ernst, 1977;Cuthbert and Carswell, 1990; Putis et al., 2002; Puelles etal., 2005; Shervais et al., 2003], whereas low-T eclogiteslike those in the Xayacatlan suite are typically attributed tooceanic subduction [e.g., Schliestedt, 1990]. On that basis,an Early-Late Silurian continental subduction (Figure 13f)created the eclogitic assemblages and the first foliation ofthe Esperanza suite. That event is clearly distinct from theEarly Ordovician eclogitic metamorphism in the Xayacatlansuite.[44] Magmatic rocks with the same age, lithology, and

geochemical affinities, like those in the Esperanza suiteexist in the northern Appalachian in two different tectonicsettings. One is the Notre Dame Subzone [Whalen et al.,2006], which corresponds to a Laurentian peripheral arc; theother is the Kingston terrane, which is a magmatic arclocated between Ganderia and Avalonia [Barr et al., 2002].The Kingston terrane in southern New Brunswick com-

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prises Early Silurian arc volcanic and intrusive rocks,(442–435 Ma) [Doig et al., 1990; Barr et al., 2002].Numerous sheeted mafic dikes intrude the arc rocks of theKingston belt, suggesting an extensional arc [e.g., Nanceand Dallmeyer, 1993; McLeod et al., 2001]. Thus, thepetrology, geochronology and tectonic settings of the King-ston terrane and the Esperanza suite are startling similar.The detrital zircon plot from the Esperanza metasediments(Figure 3c) remains inconclusive in discriminating a Gond-wanan or Laurentian provenance, although Murphy et al.[2006] suggest a Gondwanan affinity. The clastic characterof the host rock of the Esperanza granite and the continentalrift affinity of mafic dikes traversing these rocks, point to anorigin within a continental block. Such a block may besimilar to Ganderia, although the ages of the detrital zirconsin the Esperanza metasediments (Figure 3c) fail to matchthose observed in Ganderia [e.g., van Staal et al., 2004].[45] Metamorphic conditions like those of the Esperanza

suite are reported from the Carolina terrane in the SouthernAppalachian by Shervais et al. [2003]. Shervais et al.[2003] regard the eclogitic metamorphism in the Carolinaterrane as formed by continental collision of two separateperi-Gondwanan terranes. That metamorphism is ascribedeither to a Neoproterozoic–Early Cambrian (!575–535Ma)event or to a Late Ordovician–Early Silurian event [Shervaiset al., 2003]. The latter time span is similar to that definedby the eclogitic event in the Esperanza suite. The Silurianeclogitic event in the Esperanza suite is coeval with theSalinic event in the northern Appalachian. The Salinic eventis related to the Ganderia-Avalonia collision zone, althoughnot restricted to that zone [van Staal, 2007].[46] A Late Silurian tectonic event also occurred in the

Colombian and Venezuelan Andes. There, the detritalsequence of the Silgara Formation with Silurian fossils[Rıos et al., 2003] was deformed, metamorphosed toamphibolite facies, and thrust over the metamorphosedMesoproterozoic crust before deposition of Lower Devonianbeds [Forero Suarez, 1990]. Thus, the subduction of theEsperanza block may have been caused either by a trans-pressional collision between Laurentia and Gondwana asproposed by Dalziel et al. [1994], or between two peri-Gondwanan terranes located in the boundary of the Iapetusand Rheic oceans as suggested by Shervais et al. [2003].The second option is depicted in Figure 13f.

5.4. Late Devonian Event (!374 Ma): Uplift of theEsperanza Suite

[47] Thermobarometry indicates that an almost isother-mal pressure decline from 16 to 9 kbar follows the eclogiticmetamorphism in the Esperanza suite [Vega-Granillo et al.,2007], causing the transition from eclogite to amphibolitefacies. That transition generated partial melting evidencedby sparse migmatitic metasediments and intrusion of leu-cogranites (Figures 4g and 13h). A Late Devonian age of372 ± 8 Ma (U-Pb zircon) from leucogranite is coeval with a374 ± 2 Ma (40Ar/39Ar, phengite) age from a pod in eclogite[Vega-Granillo et al., 2007]. Zircon overgrowths in augengneisses yielding latest Devonian–Middle Mississippianages !360–345 Ma (U-Pb zircon [Elıas-Herrera and

Ortega-Gutierrez, 2002]) may be related with the migma-tization event following the eclogitic metamorphism, insteadof the peak eclogitic metamorphism as previously consid-ered [e.g., Murphy et al., 2006]. However, that age rangecoincides with the age of fossils in the Patlanoaya Forma-tion, which it can be contradictory and further analysis anddiscussion is required. Deposition of the Famennian ElOtate beds and the Kinderhookian to Leonardian Patlanoayabeds over the metamorphosed suites of the Acatlan Com-plex indicates that by the Late Devonian and afterward thecomplex was exposed, which prevents that the high-Pmetamorphism of the Esperanza suite could be occurringat the same time as suggested by Murphy et al. [2006].[48] A granite pegmatite crosscutting the Esperanza suite

high-grade gneisses yields an Early Mississippian age of347 ± 3 Ma (40Ar/39Ar white mica, this work). Thatpegmatite lacks of the HP metamorphism and deformationof the host gneisses; therefore, it postdates the eclogiticevent in that suite, supporting an older age for that event.The Esperanza suite uplift may be related to erosion and/ortectonic thinning of an overthickened crust and the con-comitant isostatic compensation (Figure 13g).[49] Field relationships in the Piaxtla and eastern Patla-

noaya regions indicate the Esperanza suite is thrust over theXayacatlan–El Rodeo–Tecolapa and Ixcamilpa block(block 3 in Figure 6 and Figure 13h) along an E–W directedthrust with top to the W shear sense. Mylonitic deformationof both Mid-Ordovician and Upper Devonian leucogranitesintruding the Xayacatlan and Esperanza suites, respectively(Figure 4e), are ascribed to that compressive event (Figure 6).Other structures related to the same event are (1) the fourthfoliation S4XA in the Xayacatlan suite; (2) the secondfoliation S2ER in the El Rodeo suite; and (3) folds with!N–S axes and ductile slickenside striations with !E–Wtrends in both the El Rodeo and Xayacatlan suites (Figures 6and 11). The Esperanza over Xayacatlan–El Rodeo thrust-ing must be coeval or subsequent to the Late Devonianemplacement of leucogranites in the Esperanza suite andpredates deposition of the Famennian El Otate beds. EarlyMiddle Devonian ages (416 ± 12 Ma and 386 ± 22 Ma;Sm-Nd Grt-WR) reported from eclogites of the Xayacatlansuite [Yanez et al., 1991] probably date a thermal eventproduced by the thrusting of the Esperanza suite, instead ofthe subduction-related eclogitic event as interpreted byYanez et al. [1991].[50] The thrusting event described above is nearly coeval

with a mid-Devonian tectonic-metamorphic event known asthe Acadian phase, which occurred throughout the northernAppalachians and Europe [McKerrow, 1988]. Although theNorthern Appalachian Acadian orogeny is difficult to tracethrough the central and southern Appalachian, Rast andSkehan [1993] discuss some evidence of its imprint in theseregions.[51] In Figures 13f and 13g we suggest that a collision

with a peri-Gondwanan terrane caused the Esperanza blockfirst to descend along a subduction zone and subsequentlyuplift to collide with the Early Ordovician block composedof the Xayacatlan, El Rodeo, and Ixcamilpa suites. Althoughrocks of Neoproterozoic age have not been found in the

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Acatlan Complex they are present in the Chiapas Massif ofthe SW Maya terrane [Schaaf et al., 2002]. Therefore, wepropose that either oblique subduction or strike-slip faultingparallel to the topographic belt laterally displaced theproposed peri-Gondwanan terrane (Figure 13i). In thenorthern Appalachians, evidence exists for dextral strike-slip movement following the Avalon terrane collision withLaurentia [Dalziel et al., 1994; Keppie, 1993; van Staal andde Roo, 1995].

5.5. Late Devonian Event (Post-374–Pre-359 Ma):Collision With the Gondwanan Cosoltepec Suite

[52] After the Middle Devonian, the composite blockformed by the Xayacatlan, Ixcamilpa, Esperanza, El Rodeoand Tecolapa suites, was thrust over the Gondwana affinityCosoltepec suite (block 4 in Figure 6 and Figure 13k) asindicated by geological mapping (Figures 1 and 7). Thepredominant N20!W to N10!E strikes of the S2CO foliationplanes and scarce N80!E–!N80!W trends of ductile slick-enside striations in the Cosoltepec suite (Figure 11) indi-cates an E–W shortening direction for the compressiveevent causing the thrust. The sense of motion remainsundefined, although some mantled porphyroclasts in thinultramylonites crosscutting the Esperanza suite rocks sug-gest a top to E shear sense. The timing for the juxtapositionof the high P/T suites over the Cosoltepec suite is subject ofdebate. The thrusting may create a piggyback basin wherethe relatively deep-water sedimentary sequence of El OtateFormation with Famennian fossils was deposited. Thus, thethrusting event must postdate the Late Devonian leucograniteemplacement and predate deposition of the El Otate For-mation. The paleontological content of sedimentary unitsoverlying the Grenvillian granulitic basement in Oaxaca andCiudad Victoria areas provides additional evidence of theproximity of the Laurentia and Gondwana continents by theMississippian. Whereas the Lower Ordovician and Siluriansedimentary sequences only contain fossils of Gondwananaffinity [Pantoja-Alor, 1993; Stewart et al., 1999], theMississippian to Lower Permian beds contain fossils ofmixed Laurentian and Gondwanan affinities [Stewart etal., 1999].[53] In a regional context, the closing of the Rheic Ocean

culminated with the thrusting of the high P/T block formedby the Xayacatlan, Ixcamilpa, and Esperanza suites, overthe Cosoltepec suite. The subduction related to the closureof the Rheic Ocean is inferred to have been west dipping(Figure 13j), because no magmatic arc was emplaced on theCosoltepec suite, whereas Upper Devonian granites cut thehigh P/T block. A west dipping subduction is compatiblewith some interpretations in the Southern and NorthernAppalachian [e.g., Hatcher, 1987; Ziegler, 1988; Scotese,2001], but some paleogeographic reconstructions proposesoutheastern subduction direction in the Ouachita region[e.g., Loomis et al., 1994; R. Blakey, Sedimentation, tec-tonics, and paleogeography of the North Atlantic region,2007, http://jan.ucc.nau.edu/!rcb7/340Nat.jpg]. In theAppalachians, Acadian postmetamorphic plutons range inage from 388 to 371 Ma [Loiselle et al., 1983]; therefore,they are coeval with granites from the Acatlan Complex,

including La Noria Granite and leucogranites of the Esper-anza suite (371–372 Ma) [Yanez et al., 1991; Vega-Granilloet al., 2007]. In the northern Appalachians, the term Neo-acadian orogeny was introduced by Robinson et al. [1998]to encompass Middle Devonian to Early Carboniferousdeformation and metamorphism in southern New England.The Neoacadian orogeny is coeval with the docking andorogenesis of the Meguma terrane in Canada [Hicks et al.,1999; Keppie et al., 2002].

5.6. Devonian-Mississippian Boundary Event: Collisionof a Gondwanan Block

[54] A compressive tectonic event created the last twovery low grade deformation phases D3CO–D4CO in theCosoltepec suite. Structural analysis in the Cosoltepec suiteindicates a N50!–80!W shortening direction for the D3CO–D4CO phases (Figure 11), and the common mesoscopicfolds have a NW vergence. Structures related to the sameevent include (1) two phases of isoclinal to tight foldingF3ER–F4ER in the El Rodeo suite (Figures 4c and 4d) withfold axes trending N50!–80!E, and their respective axialplanar cleavages; (2) a minor group of fold axes trendingN30!–50!E in the Xayacatlan suite; (3) isoclinal folding ofMid-Ordovician leucogranite dikes (Figure 4f); and (4) tightfolds and two very low grade cleavages in slates of the ElOtate Formation (Figures 12e and 12f). The Devonian-Mississippian boundary event is also evidenced by the thickconglomerate separating the Kinderhookian-Leonardianbeds of the Patlanoaya Formation from the underlyingFamennian beds of the El Otate Formation. That conglom-erate contains clasts of metamorphic rocks and granitesderived from the Acatlan Complex, and it overlies inangular unconformity the folded beds of the El OtateFormation.[55] Phengites from the high P/T suites were dated with

the 40Ar/39Ar method by Vega-Granillo et al. [2007].Eclogite and mica schist from the Xayacatlan suite in thePiaxtla and Mimilulco regions yield Middle Mississippianages of 336 ± 6 Ma and 336 ± 4 Ma respectively. Ablueschist from the Ixcamilpa region yields a Late Missis-sippian age of 323 ± 12 Ma. A mica schist from themetasedimentary sequence of the Esperanza suite yields aMiddle Mississippian age of 345 ± 2 Ma. Furthermore,phengite from a Mid-Ordovician 461 Ma (U-Pb zircon)leucogranite dike [Talavera-Mendoza et al., 2005] intrudingthe Xayacatlan suite yields a 335 ± 2 Ma (40Ar/39Ar) age[Vega-Granillo et al., 2007]. The Mid-Late Mississippian327 ± 2 Ma and 320 ± 13 Ma ages obtained from El Rodeosuite (40Ar/39Ar, phengite and amphibole, this work), aswell as the 347 Ma age (40Ar/39Ar, white mica, this work)from an undeformed granite pegmatite crosscutting theEsperanza gneisses also indicates a Mississippian event.These 40Ar/39Ar ages ranging from 347 to 318 Ma mayrepresent the interval during which the Acatlan Complexwas progressively raised and cooled below phengite closuretemperature of 350 ± 50!C [Geyh and Schleicher, 1990].Yanez et al. [1991] report similar Mid-Late Mississippian332–318 Ma (Rb-Sr muscovite) ages for the Xayacatlansuite rocks. Therefore, a tectonic compressive event occurred

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at the Devonian-Mississippian boundary, producing defor-mation and gradual exhumation of the Acatlan Complex, aswell as the angular unconformity between the El OtateFormation and the Patlanoaya Formation. The Devonian-Mississippian boundary event may result from the collisionof the Gondwana-related Oaxaca terrane with the AcatlanComplex (block 5 in Figure 6 and Figure 13l). That eventreversed the sense of movement of the Late Devonian eventthat caused the thrusting of the high-P suites over theCosoltepec suite. In a wider context, a Late Mississippian(!325–320 Ma) compression-related uplift, similar to thatoccurred in the Acatlan Complex, also occurred in thesouthern Appalachians [Hatcher, 2004].

5.7. Lower Permian Event (!275–270): DextralStrike-Slip Movement and Compression

[56] The eastern boundary of the Acatlan Complex withthe Mesoproterozoic granulitic Oaxaca terrane is regardedas an Early Permian !N–S dextral strike-slip fault [Elıas-Herrera and Ortega-Gutierrez, 2002]. Red beds of theMatzitzi Formation with fossils attributed to the Leonardian[Weber and Cevallos-Fernandez, 1994] overlap the tectonicboundary between the Acatlan Complex and the Oaxacaterrane [Elıas-Herrera and Ortega-Gutierrez, 2002]. Thetime of strike-slip faulting is constrained by the 275 ± 1 Ma(U-Pb, zircon) age of leucosomes in syntectonic migmatites[Elıas-Herrera and Ortega-Gutierrez, 2002] and the Leo-nardian deposition of the Matzitzi Formation. On the basisof the detrital zircon ages, the Chazumba suite depositionbegan about the same time (!275 Ma) [Talavera-Mendozaet al., 2005]. These observations suggest that the Chazumbasuite may have been deposited in a pull-apart-type basin(Figure 13n) created by dextral lateral movement betweenthe Acatlan Complex and the Oaxaca terrane. The detritalzircon ages in the Chazumba suite indicate zircon sourcesare both the Acatlan Complex and the Oaxaca terrane[Talavera-Mendoza et al., 2005], supporting the pull-apartbasin hypothesis.[57] Hatcher [2002] mentions an Early Permian dextral

shear with !NE40!SW strike in the southern Appalachians.In a wider context, Muttoni et al. [2003] propose that!ENE–WSW dextral strike-slip displacement betweenLaurentia and Gondwana occurred in the Early Permian.The dextral displacement in the Appalachian chain and theAcatlan Complex may be related to the same regionaltectonic event. To make this correlation plausible, ananticlockwise rotation about 40! for the Acatlan Complexis required to have occurred since the Early Permian.[58] Mylonitic deformation with !N–S ductile slicken-

side striations related to greenschist facies metamorphismlocally overprints the Tecomate Formation; the La NoriaGranite [Vega-Granillo, 2006], the Totoltepec pluton[Malone et al., 2002], the Esperanza suite [Weber et al.,1997; Vega-Granillo, 2006], and the Xayacatlan, El Rodeoand Cosoltepec suites [Vega-Granillo, 2006]. Kinematicindicators as S-C0-type cleavages display a top to the Sshear sense in all localities (references cited). Malone et al.[2002] infer that mylonitic structures represent an EarlyPermian compressive event; alternatively, Weber et al.

[1997] suggest that they indicate an !N–S extensiontentatively assigned to the Early Carboniferous. The defor-mation must occur by the latest Early Permian (from !275to 270 Ma) because it overprints the Early Permian Totol-tepec Stock (!278 Ma) and Tecomate Formation andpredates deposition of the Leonardian Matzitzi Formation.Furthermore, the thrusting of the Cosoltepec and previouslyamalgamated suites over the Chazumba suite requires acompressive deformation. If the Leonardian age of theMatzitzi Formation is correct, the time required to depositthe very thick Chazumba suite and for the subsequentthrusting event must have been brief. In that case, the firstdeformation phase D1CH and regional metamorphism eventM1CH in the Chazumba suite may be ascribed to the latestEarly Permian N–S compressive event (Figure 6). Alterna-tive explanations for the brief time span between theChazumba suite deposition and the Permian compressiveevent are (1) The Matzitzi Formation is not preciselyLeonardian but rather younger in age or (2) the lowercontact of the Matzitzi Formation over the Oaxaca ter-rane–Acatlan Complex boundary is structural rather thandepositional. In the latter case, the Matzitzi Formationwould not constrain the movement between the AcatlanComplex and the Oaxaca terrane and the N–S compressiveevent could have occurred between the Late Permian andMiddle Jurassic. The final amalgamation of Pangea in theSouthern Appalachian concluded about the Wordian stage!265 Ma [Hatcher, 2004] during the late stage of theAlleghanian orogeny. Accordingly, the Permian event inthe Acatlan Complex may be related to that process.

5.8. Mid-Jurassic Event: Plume Rise and Dome-ShapedStructures

[59] The second deformation and lower P/T metamor-phism event D2CH and M2CH in the Chazumba suite, andrelated migmatization, granite intrusion, and regional dom-ing, evidence a mid-Jurassic thermal event. Apparently, theupper structural levels of the Acatlan Complex and its latePaleozoic sedimentary cover are not affected by that event,excepting by the doming deformation. The thermal eventhas been linked to mantle plumes (Figure 13q) [Keppie etal., 2004a]. In this context, the domes may represent themiddle crust response of deep-seated magmas.[60] By Jurassic time, Gulf of Mexico opening displaced

the Maya terrane to the south [Pindell and Dewey, 1982;Pindell, 1985, 1994; Pindell and Kennan, 2001], probablywith the Oaxaca terrane and the Acatlan Complex attached(Figure 14b). Paleomagnetic data indicate !50–60! ofanticlockwise rotation of the Maya block [Molina-Garzaet al., 1992], with a rotation axis near to the south end of theFlorida Peninsula [Handschy et al., 1987; D. E. Bird andK. Burke, Pangea breakup: Mexico, Gulf of Mexico, andCentral Atlantic Ocean, paper presented at 76th AnnualInternational Meeting and Exposition, Society of ExplorationGeophysicists New Orleans, Louisiana, 1 October 2006].That plate reorganization also implies about 1200 kmdisplacement to the south of the SW limit of the Mayablock. By the Late Jurassic, the Acatlan Complex and theOaxaca terrane must have been laterally displaced with

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Figure 14

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respect to the Maya terrane to reach their present position(Figure 14d).

5.9. Late Cretaceous–Paleogene Orogeny: CollisionWith the Guerrero Terrane

[61] The conspicuous large-wavelength folds (Figure 7)deforming both the Acatlan Complex and its overlyingJurassic-Cretaceous platform strata originated during a LateCretaceous-Paleogene orogenic event. That event createdthrust faults like the Papalutla fault (Figure 7) in the westernlimit of the Acatlan Complex exposures, which place rocksof the Cosoltepec suite over Cretaceous sedimentary rocks(section A-A0 in Figure 1). That orogenic event is attributedto the collision of the Acatlan Complex against the Guer-rero terrane [Cerca-Martınez, 2004]. The large Ayu andAhuatempan domes served as buttresses during Late Creta-ceous-Paleogene compression and the axes of major foldsare bent around the domes (Figure 7).

5.10. Tectonic Remarks

[62] Deformational, metamorphic and magmatic historiessuggest a strong correlation between the events in theAcatlan Complex and the Central Mobile Belt of theAppalachian-Caledonian orogen. Tectonically mingled frag-ments with Laurentian and Gondwanan affinity composethese two regions. Pangean reconstructions require post-Jurassic translation of the southern part of Mexico includingthe Acatlan Complex and the Oaxaca and Maya terranes toavoid overlapping by the South America crust (Figure 14)[Handschy et al., 1987]. Thereby, the Acatlan Complex mayhave been located between the Oaxaca-Maya block and theOuachita orogenic belt by Late Permian time, forming asouthern extension of the Appalachian Orogen (Figure 14a).The large-scale tectonic configuration for the Permianconsist of (1) The Laurentian craton; (2) an external zonecorresponding to the Marathon-Ouachita-Appalachian foldand thrust belt; (3) an internal zone composed of thetectonically mingled metamorphic rocks of Laurentian andGondwanan affinities; and (4) Gondwanan-related terranes.Mississippian metamorphic ages are common in the internalzone [Stewart et al., 1999, and references therein]. Theinternal zone may have included the Acatlan Complex[Talavera-Mendoza et al., 2005], the Piedmont zone [Milleret al., 2000], the Dunnage zone [van Staal, 1994], theWiggins terrane [Thomas et al., 1989], the northern partof the Maya terrane (north of the Yucatan Peninsula), wherethere is subsurface information about metamorphic andigneous rocks with Silurian to Pennsylvanian ages [Sedlocket al., 1993; Stewart et al., 1999]; the Coahuila terrane,

mostly a subsurface terrane of pre-Triassic, stronglydeformed, low-grade metamorphic rocks [Handschy et al.,1987; Sedlock et al., 1993, and references therein; Lopez etal., 2001]; and probably the interior metamorphic belt of theOuachita orogenic belt [Flawn et al., 1961; Viele andThomas, 1989]. The Gondwanan and peri-Gondwanan crustis represented by the Carolina terrane [O’Brien et al., 1996],the Suwannee terrane [Rankin et al., 1989], the south andeastern part of the Maya terrane [Sedlock et al., 1993;Stewart et al., 1999; Schaaf et al., 2002], the Oaxaca terrane[Campa-Uranga and Coney, 1983] and part of the SierraMadre terrane [Stewart et al., 1999]. In this model, theproposed Oaxaquia block would have a !NE–SW orien-tation instead of the N–S orientation suggested by Ortega-Gutierrez et al. [1995]. Upper Pennsylvanian, Permian andTriassic granites that may be considered pre-, syn-, andpost-Pangea final amalgamation respectively, intrude theOaxaca terrane [Torres et al., 1993; Sedlock et al., 1993;Stewart et al., 1999; and references therein], the AcatlanComplex [Yanez et al., 1991] and the SW Maya terrane[Damon et al., 1981; Schaaf et al., 2002]. The Permiangranites would make an NE–SW oriented magmatic beltemplaced along the Paleozoic orogen and they are probablyrelated to the late Alleghanian collisional event instead ofthe Farallon plate subduction as proposed by Torres et al.[1993]. Hatcher [2004] reports a suite of Lower-MiddlePermian (300 to 265 Ma) plutons that is largely confined tothe Carolina terrane, which he relates to the Gondwana-Laurentia collision. Similar granites extend to the Hercynianorogen of Europe and Africa [e.g., Giuliani et al., 1989;Faure et al., 2005] where they are interpreted as intruded ina late collisional setting.

6. Conclusions

[63] Seven major thrust sheets compose the AcatlanComplex, each one with its own distinctive stratigraphyand tectonothermal evolution. The Xayacatlan suite is anoceanic volcanosedimentary sequence that was subductedand metamorphosed to eclogite facies. The first two defor-mational metamorphic events in the Xayacatlan suite areattributed to that subduction process. Then, the Xayacatlanrocks were exhumed and subsequently overthrust by the ElRodeo and Tecolapa suites. Lower-Middle Ordoviciangranites and leucogranites intrude the thrust faults. AfterMiddle Ordovician time, the Ixcamilpa suite was depositedin an intra-Iapetian basin near a peri-Gondwanan terrane assuggested by its detrital zircon ages. This suite was sub-ducted under the Xayacatlan–El Rodeo block and meta-morphosed to blueschist facies during an event ascribed to

Figure 14. Hypothetical plate tectonic evolution from the Late Permian to Late Cretaceous. (a) Sketch of the Pangeareconstruction with location of main belts of the Appalachian-Caledonian orogen (Appalachian region modified fromNeugeabauer [1989]). (b) Late Permian reconstruction with proposed location of the Acatlan Complex and the Oaxacaterrane in the northern Gulf of Mexico (adapted from Pindell [1985]). (c) During initial Gulf of Mexico opening, theAcatlan Complex moved adjacent to the Yucatan Peninsula. (d) By Middle-Late Jurassic the Acatlan Complex moved to thewest against the southern part of the Sierra Madre terrane. (e) Late Cretaceous collision of the Acatlan Complex andthe Guerrero terrane. CM, Chiapas Massif. Terranes are Coa, Coahuila; J, Juarez; M, Mixteco; Ma, Maya; O, Oaxaca; SiMa,Sierra Madre; C, Carolina; Ch, Chortis.

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the latest Ordovician-Silurian. The Lower Silurian conti-nental magmatic arc of the Esperanza suite was also sub-ducted and metamorphosed to medium-T eclogite facies bythe latest Early Late Silurian [Vega-Granillo et al., 2007].This event is provisionally attributed to the collision be-tween two continental peri-Gondwanan blocks. Isostatic andcompressive forces could have triggered the uplift of theEsperanza suite during the Early Late Devonian, causing thetransition from eclogite to amphibolite facies, local migma-tization and emplacement of Upper Devonian leucogranites.During the early Late Devonian, the Esperanza suite wasthrust over the block formed by the El Rodeo, Xayacatlanand Ixcamilpa suites, resulting in a generalized deforma-tional metamorphic event. The resulting composite blockwas subsequently thrust over the Cosoltepec suite depositedalong the northwestern Gondwanan margin [Talavera-Mendoza et al., 2005]. That thrust is the final stage in theclosing of the Rheic Ocean. The early Late Devonianthrusting may create a piggyback basin where the relativelydeep-water sedimentary sequence of El Otate Formationwith Famennian fossils was deposited. At the Devonian-Mississippian boundary, the impingement of the Acatlanterrane against the Gondwanan Oaxaca terrane producedanother deformational metamorphic event that overprintedthe whole Acatlan Complex and the Famennian El OtateFormation. Subsequently, the Acatlan Complex wasuplifted, cooled and partially eroded prior to deposition ofthe Lower Mississippian (Kinderhookian) to Leonardianplatform sequence of the Patlanoaya Formation. Duringthe Leonardian, the Acatlan Complex was displaced withrespect to the Oaxaca terrane along a dextral strike-slipfault. The motion along that fault created a pull-apart basinwhere the Chazumba suite was deposited !275 Ma ago. A

major thrusting with !N–S movement direction and top tothe S shear sense occurred about the same time involving allthe suites of the Acatlan Complex, as well as the UpperDevonian and Lower Permian granites and parts of theplatform sequence (Tecomate Formation). During the Mid-dle Jurassic, a plume rise produced regional doming and anoverprinting metamorphism-deformational event in theChazumba and Cosoltepec suites, which do not reach thelate Paleozoic platform sequence. Finally, by Late Creta-ceous, collision of the Acatlan Complex and the Guerreroterrane caused regional folding and local thrust faults inboth terranes [Salinas-Prieto et al., 2000; Cerca-Martınez,2004].[64] Lithological suites, metamorphic-magmatic events,

deformational phases and geochemical signatures of theAcatlan Complex have correlatives in the Appalachianchain of eastern North America. Considering that palins-pastic reconstructions of the Pangea indicate an overlap ofsouthern Mexico and northern South America, we proposethat the Acatlan Complex may have been located in thenorth part of the Gulf of Mexico as a southern extension ofthe Appalachian chain. The Acatlan Complex may havebeen displaced to its present location through an anticlock-wise movement of the Yucatan Peninsula. That displace-ment occurred during the Jurassic and accompanied theGulf of Mexico opening. On that basis, the tectonometa-morphic events in the Acatlan Complex may be useful for amore comprehensive understanding of the geological evo-lution of the Appalachian-Caledonian orogen.

[65] Acknowledgments. This work was supported by a CONACYT-Mexico grant (J32549-T) to Diana Meza-Figueroa. We gratefully acknowl-edge Timothy Lawton and Tim Wawrzyniec, whose valuable suggestionsimprove the manuscript.

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"""""""""T. Calmus, Estacion Regional del Noroeste,

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J. Ruiz, Department of Geosciences, University ofArizona, Tucson, AZ 85721, USA.

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