Earth and Planetary Science Letters 289 (2010) 273ndash286

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Earth and Planetary Science Letters

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Paleomagnetic evidence for a pre-early Eocene (sim50 Ma) bending of the Patagonianorocline (Tierra del Fuego Argentina) Paleogeographic and tectonic implications

Marco Maffione ad Fabio Speranza a Claudio Faccenna b Eduardo Rossello c

a Istituto Nazionale di Geofisica e Vulcanologia Rome Italyb Dipartimento di Scienze Geologiche Universitagrave di Roma Tre Rome Italyc CONICET Departamento de Ciencias Geoloacutegicas FCEN Universidad de Buenos Aires Buenos Aires Argentinad Dipartimento di Fisica Universitagrave di Bologna Bologna Italy

Magallanes belt

Corresponding author Istituto Nazionale di GeofisicE-mail address marcomaffioneingvit (M Maffion

0012-821X$ ndash see front matter copy 2009 Elsevier BV Adoi101016jepsl200911015

a b s t r a c t

a r t i c l e i n f o

Article historyReceived 12 February 2009Received in revised form 30 October 2009Accepted 4 November 2009Available online 2 December 2009

Editor ML Delaney

KeywordspaleomagnetismtectonicsPatagonian oroclineFuegian AndesDrake Passage

The southernmost segment of the Andes of southern Patagonia and Tierra del Fuego forms a sim700 km longorogenic re-entrant with an interlimb angle of sim90deg known as Patagonian orocline No reliablepaleomagnetic evidence has been gathered so far to assess whether this great orogenic bend is a primaryarc formed over an articulated paleomargin or is due to bending of a previously less curved (or rectilinear)chain Here we report on an extensive paleomagnetic and anisotropy of magnetic susceptibility (AMS) studycarried out on 22 sites (298 oriented cores) predominantly sampled in Eocene marine clays from theexternal Magallanes belt of Tierra del Fuego Five sites (out of six giving reliable paleomagnetic results)containing magnetite and subordinate iron sulphides yield a positive fold test at the 99 significance leveland document no significant rotation since sim50 Ma Thus the Patagonian orocline is either a primary bendor an orocline formed after Cretaceousndashearliest Tertiary rotations Our data imply that the opening of theDrake Passage between South America and Antarctica (probably causing the onset of Antarctica glaciationand global climate cooling) was definitely not related to the formation of the Patagonian orocline but waslikely the sole consequence of the 32plusmn2 Ma Scotia plate spreading Well-defined magnetic lineationsgathered at 18 sites from the Magallanes belt are sub-parallel to (mostly EndashW) local fold axes while theytrend randomly at two sites from the Magallanes foreland Our and previous AMS data consistently showthat the Fuegian Andes were characterized by a NndashS compression and northward displacing foldndashthrustsheets during Eocenendashearly Miocene times (50ndash20 Ma) an unexpected kinematics considering coeval SouthAmericandashAntarctica relative motion Both paleomagnetic and AMS data suggest no significant influence fromthe EndashW left-lateral MagallanesndashFagnano strikendashslip fault system (MFFS) running a few kilometres south ofour sampling sites We thus speculate that strikendashslip fault offset in the Fuegian Andes may range in thelower bound values (sim20 km) among those proposed so far In any case our data exclude any influence ofstrikendashslip tectonics on the genesis of the great orogenic bend called Patagonian orocline

a e Vulcanologia Rome Italye)

ll rights reserved

copy 2009 Elsevier BV All rights reserved

1 Introduction

The Andean Cordillera is one of the longest mountain belts of theEarth spanning the entire Pacific margin of South America Below 50degSthe trendof the southernmostAndeanbelt decidedly changes fromsimNndashS(Patagonian Andes) to simEndashW (Fuegian Andes) forming a regionalorogenic re-entrant arc commonly referred to as the Patagonian orocline(Carey 1958 Fig 1) This arcuate structure forms at the intersectionbetween the South America Scotia and Antarctica plates (Fig 1) TheScotia plate with its deep-sea pathway (Drake Passage) separating theSouth American and Antarctic continents (Barker 2001 Eagles et al2005 Livermore et al 2005 Lodolo et al 1997 2006) is thought to have

causedfirst-order effects in theglobal paleoclimate In fact the formationof a deep water ldquogatewayrdquo between South America and Antarcticadetermined the onset of the Antarctic Circumpolar Current (ACC)(Lawver and Gahagan 2003 Barker et al 2007a) which is consideredone of themain causes for the development of extensive ice sheets in theAntarctic continent (Barker et al 2007b) and the onset of global climatecooling at the EoceneOligocene boundary (Zachos et al 2001) Theopeningof theDrakepassage is commonly related to the spreadingof theScotia Sea where oceanic anomalies from the West Scotia ridge havebeen dated back to 34ndash28 Ma (Lawver and Gahagan 2003 Livermoreet al 2005 Lodolo et al 2006) but its tectonic relationships with thesymmetrical curvedmarginsof the Patagonian orocline and theAntarcticPeninsula are still unclear

Though a wealth of geological and geophysical data havedocumented ongoing tectonic deformation in the Patagonian andFuegian Andes since sim100 Ma to Present (Dalziel and Palmer 1979

Fig 1 Digital elevation model of the Scotia plate and surrounding regions from the General Bathymetric Chart of the Oceans (GEBCO) Lines with triangles and thicker black linesindicate trench zones and oceanic ridges respectively White arrow indicates the movement of the Antarctic plate with respect to South America according to DeMets et al (1990)SFZ Shackleton Fracture Zone AFFZ Agulhas Falkland Fracture Zone MFFS MagallanesndashFagnano fault system

274 M Maffione et al Earth and Planetary Science Letters 289 (2010) 273ndash286

Winslow 1982 Cunningham 1993 1994 1995 Kohn et al 1995Diraison et al 2000 Lodolo et al 2003 2006 Kraemer 2003 Ghiglioneand Ramos 2005) the kinematics and timing for the formation of thePatagonian orocline are unknown Recently a non-rotational originfor the Patagonian orocline was proposed and its curved shape wasrelated to the tectonic heritage from an original articulated paleo-margin (Ramos and Aleman 2000 Diraison et al 2000 Ghiglione2003 Ghiglione and Ramos 2005 Ghiglione and Cristallini 2007)However paleomagnetic investigations of metamorphic and igneousrocks from the Fuegian Andes (Dalziel et al 1973 Burns et al 1980Cunningham et al 1991 Roperch et al 1997 Beck et al 2000Rapalini et al 2001 2004 2005 Baraldo et al 2002 Iglesia Llanoset al 2003) have systematically revealed so far northwestward-directed paleodeclinations (Fig 2) which conversely seem to indicatethat the orogenic bend formed through rotations of mountain beltsegments with respect to South America The problem with theavailable paleomagnetic data is that both igneous and metamorphicrocks lack paleo-horizontal indicators (implying possible significantbiases on the declination values) and the age of magnetizationacquisition (related to the last metamorphic peak) is questionable(see Rapalini 2007 for an updated review) Therefore both therotational vs non-rotational characters of the Patagonian orocline andthe rotation timing (if existing) are paleomagnetically unconstrainedat present

The most external part of the Patagonian orocline is representedby the thin-skinned Magallanes fold and thrust belt (Fig 2) whereupper Cretaceous to Miocene marine and continental sediments areexposed along folds and thrust sheets sub-parallel to the large-scale

orogenic bend (Winslow 1982 Olivero et al 2001 2003 Ghiglioneet al 2002 Ghiglione 2002 Olivero and Malumiaacuten 2008) The 7 km-thick sedimentary succession exposed in the Magallanes belt of Tierradel Fuego offers in principle the opportunity to paleomagneticallydocument with great accuracy the magnitude and timing of verticalaxis rotations in the southernmost Andes overcoming the problem ofa safe paleo-horizontal evaluation for metamorphic and igneousrocks

In this paper we report the results of an extensive paleomagneticstudy of Eocene to early Miocenemarine and continental sedimentaryrocks from the southeastern Magallanes fold and thrust belt of Tierradel Fuego Our data represent the first reliable paleomagneticconstraint on the formation of the Patagonian orocline and documentthat no vertical axis rotations occurred since early Eocene times(sim50 Ma) A pre-existing Patagonian orocline since at least 50 Maimplies that the significantly younger (sim32 Ma) opening of the DrakePassage was not influenced by Andean tectonics but was rather theexclusive consequence of the Scotia Sea spreading onset

2 Background

21 Geology of the Patagonian and Fuegian Andes and structural settingof the Magallanes belt of Tierra del Fuego

From southwest to northeast five broad morphostructuralprovinces parallel to the arc can be recognized in the southernmostAndes (1) a coastal magmatic arc (Patagonian batholith) (2) amarginal basin assemblage (Rocas Verdes basin) (3) a metamorphic

Fig 2 Digital elevation model of the southernmost Andes redrawn from Ghiglione and Cristallini (2007) showing orogenic structural trends (thin solid white lines) major strikendashslip faults (dashed black lines) basement thrust front (thick solid white line) strikes of shortening axes (black bars) according to Diraison et al (2000) the rift system of theMagellan Straits (black lines with indents) mean magnetic lineation directions according to Diraison (1998) (black double arrow) and previous paleomagnetic directions fromigneous or metamorphic rocks (A = Rapalini et al 2001 B = Rapalini et al 2004 C = Burns et al 1980 D = Dalziel et al 1973 E = Cunningham et al 1991 F = Baraldo et al2002 G = Rapalini et al 2005) MFFS MagallanesndashFagnano fault system Location is in Fig 1

275M Maffione et al Earth and Planetary Science Letters 289 (2010) 273ndash286

core zone (Cordillera Darwin) (4) a fold and thrust belt (Magallanesfold and thrust belt) and (5) an undeformed foreland basin(Magallanes (or Austral) basin) The Magallanes basin is composedof a thick (sim7 km) succession of marine and continental sedimentaryunits ranging from Jurassic to Miocene age (Winslow 1982 Diraisonet al 1997a Olivero and Malumiaacuten 1999 2008 Olivero et al 20012003 Ghiglione et al 2002 Ghiglione and Ramos 2005 Malumiaacutenand Olivero 2006 Rossello et al 2008)

The southern part of the Patagonian orocline is also cut by theMagallanesndashFagnano fault system (MFFS) a roughly EndashW en-echelonleft-lateral strikendashslip fault array running for more than 600 km fromthe Atlantic to the Pacific coast of South America and considered thepresent-day South AmericandashScotia plate boundary (Cunningham 19931995 Barker 2001 Lodolo et al 2003 Eagles et al 2005 Rossello2005) The total displacement of theMFFS (from20 to 55 km) aswell asthe age of its formation (from 100 to 7 Ma) are still a matter of debate(Cunningham 1995 Olivero and Martinioni 2001 Lodolo et al 2003Rossello et al 2004a Eagles et al 2005 Torres-Carbonell et al 2008a)whereas its present-day activity is substantiated by both GPS (Smalleyet al 2003) and seismological (Pelayo and Wiens 1989) evidence

Fold axes and thrust faults trend sub-parallel to the regionalorogen direction and in Tierra del Fuego they strike from NWndashSE inthe inner sectors to EndashW and ENEndashWSW along the Atlantic coast(Ghiglione et al 2002 Ghiglione 2002 Ghiglione and Ramos 2005Torres-Carbonell et al 2008b) (Figs 2 and 3) These structures are cutby NE-oriented elongate depressions interpreted by Diraison et al

(1997ab) as rift or half-rift systems along which the Magellan Straitdevelops (Fig 2) According to Diraison et al (2000) the shorteningdirections (as inferred by 1600 striated fault planes from theMesozoicndashCenozoic sedimentary cover of the foldndashthrust belt) aremore nearly perpendicular to major folds and thrusts than they are tothe mountains themselves and progressively rotate from N75deg toN43deg from the Patagonian to the Fuegian Andes respectively (Fig 2)Finally some minor NNE-trending right-lateral strikendashslip faults (ieFueguina fault Fig 3b) have been interpreted as Rprime Riedel shear zonesassociated to the major MFFS (Ghiglione et al 2002)

The first orogenic episodes at the southernmargin of South Americawere triggered by themid to late Cretaceous inversion and closing of theback-arc Rocas Verdesmarginal basin (Dalziel et al 1974 Cunningham1994 1995) resulting in shortening ductile deformation and regionalmetamorphism with peak metamorphism occurring between 100 and90Ma (Kohn et al 1995 Cunningham 1995) A first episode of rapiduplift and cooling of the metamorphic core between 90 and 70 Ma(Kohn et al 1995) predated the late Campanian (sim70 Ma) northwardpropagation of compression in the Magallanes basin (Winslow 1982Diraison et al 1997a Ghiglione et al 2002) From that time onward theMagallanes basin developed as a foreland basin (Diraison et al 1997a)At least fourmain compressive events related to an equivalent numberof unconformities recorded by the sedimentary successions occurred intheMagallanes belt in late Paleocene (61ndash55 Ma) earlyndashmiddle Eocene(50ndash43 Ma) early Oligocene (sim30 Ma) and early Miocene (sim20 Ma)times (Olivero and Malumiaacuten 1999 Ghiglione et al 2002 Kraemer

276 M Maffione et al Earth and Planetary Science Letters 289 (2010) 273ndash286

277M Maffione et al Earth and Planetary Science Letters 289 (2010) 273ndash286

2003 Ghiglione and Ramos 2005Malumiaacuten andOlivero 2006 Torres-Carbonell et al 2008b) Virtually undeformed post-early Miocenesedimentary rocks testify the end of tectonic shortening in the southernMagallanes basin (Ghiglione 2002 Ghiglione et al 2002) The tectonichistory of theMagallanes basin has been interpreted as related to eithercompressive (Ghiglione and Ramos 2005) or extensional (Ghiglioneet al 2008) tectonics of Eocene age followed by an OligocenendashearlyMiocene episode in which wrench tectonics dominated

22 Previous paleomagnetic data from the Patagonian orocline and theAntarctic Peninsula

Carey (1958) first proposed that the abrupt curvature of thesouthernmost Andes could be due to oroclinal bending of an initiallystraightorogen thoughpaleomagnetic evidence from the southernmostAndeshas beengatheredonly since the1970s (Dalziel et al 1973 Burnset al 1980 Cunningham et al 1991 Roperch et al 1997 Beck et al2000 Rapalini et al 2001 2004 2005 Baraldo et al 2002 Iglesia Llanoset al 2003) These studies indicate significant post-late Cretaceouscounterclockwise (CCW) rotations (up to 118deg) affecting the internalsouthern Andes below latitude 48degS (Fig 2) It is likely that (at least partof) the largest magnitude rotations arise from local tectonic effectslinked to thrusting (Iglesia Llanos et al 2003) or strikendashslip faulting(Rapalini et al 2001)

However the earliest paleomagnetic studies (Dalziel et al 1973Burns et al 1980) do not pass modern reliability criteria of laboratoryprocedures (eg Beck 1988) while all data from Patagonian andFuegian Andes were invariantly gathered from igneous or metamor-phic rocks thus suffer of significant uncertainties on the paleo-horizontal surface and age of magnetization as well as of possibleincomplete averaging of the paleosecular variation of the geomag-netic field

In detail three localities from the southern Patagonian Andes at a47degS latitude do not show any significant rotation thus defining thenorthern limit of the CCW-rotating domain (Roperch et al 1997 Becket al 2000 Iglesia Llanos et al 2003) To the south a post-lateJurassic CCW rotation of 39deg 57deg and 62deg has been documented fromsedimentary and igneous rocks at Lago San Martin north (49degS722degW) Lago San Martin south (491degS 725degW) and Lago Argentino(502degS 728degW) respectively (Iglesia Llanos et al 2003) Furthersouth Rapalini et al (2001) have evidenced a post-early CretaceousCCW rotation of 118deg from basalts and lavas at the Madre de DiosArchipelago (504degS 754degW Fig 2) while Rapalini et al (2004) havedocumented a 59deg post-late Cretaceous CCW rotation from ophiolitesat the southernmost Patagonian Andes (517degS 736degW) An extensivepaleomagnetic study carried out by Burns et al (1980) on volcanicand metamorphic rocks throughout the Patagonian and FuegianAndes revealed post-late Jurassicndashearly Cretaceous 27ndash40deg CCWrotations Conversely igneous rocks of the Navarino Island andadjacent regions of Chile yielded post-94 and post-77 Ma 150deg and120deg CCW rotations respectively (Dalziel et al 1973) while a 90degpost-late Cretaceous CCW rotation was obtained from volcanic andsedimentary rocks (Cunningham et al 1991) Igneous rocks sampledby Baraldo et al (2002) and Rapalini et al (2005) in the inner part ofthe orogenic belt from Tierra del Fuego documented a 33deg to 66deg post-late Cretaceous CCW rotation

Diraison (1998) gathered 215 cores at 16 sites (six sites fall withinour sampling area) located along the arc of the Magallanes belt belowlatitude 51degS The very weak magnetization of the sampled rocks did

Fig 3 Structural and geological maps of the study areas redrawn from Ghiglione et al(Quaternary) 3 Carmen Silva formation (middle Miocene) 4 Capas de Cabo San Pablo (earlgroup (OligocenendashMiocene) 7 Capas de la Estancia Maria Cristina (earliest Oligocene) 8middle to late Eocene) 10 Leticia formation (upper middle Eocene) 11 Punta Torcida frespective rotation error (grey cone) 13 Direction of the (in situ) site-mean magnetic line

not permit to isolate reliable paleomagnetic directions while well-defined magnetic fabric was recognized at all sites

Finally the arcuate shape of the Antarctic Peninsula mirroring tothe Patagonian orocline could suggest a related tectonic evolutionThe paleomagnetic data from the Antarctic Peninsula (Grunow 1993and references therein) documented two distinct phases of rotationclockwise (CW) with respect to East Antarctica between 175 and155 Ma due to the early opening in the Weddell Sea basin and CCWwith respect to West Antarctica in the 155ndash130 Ma time interval

3 Sampling and methods

In December 2007 we performed an extensive paleomagneticsampling campaign within the southeastern part of the Magallanesbelt of Tierra del Fuego (Figs 2 and 3) Because of the widespreadcover of glacial deposits and the scarce road network most of thesamples (except for sites TF02 and TF03) were collected along thecliffs of the Atlantic coast between Cabo San Pablo and Cerro Colorado(Fig 3) Lower Eocene to lower Miocene marine fine-grainedsediments (siltstones and mudstones) were systematically sampled(only at site TF03 continental clays were gathered)

The oldest sampled marine sediments are those from the PuntaTorcida Fm (early Eocene Olivero and Malumiaacuten 1999 2008) amajor sim400 m thick regressive unit dominated by dark-grey mud-stones with scarce intercalations of light-grey fine sandstones Thisformation is unconformably covered by the upper middle EoceneLeticia Fm consisting of grey and greenish fine bioturbatedglauconitic tuffaceous or lithic sandstones with subordinated fineconglomerates mudstones and tuffaceous sandstones The Leticia Fmis followed by the upper middle to late Eocene Cerro Colorado Fm amajor transgressivendashregressive sequence consisting of a verticalstacking of four coarsening- and thickening-upwards sequenceswith a very high sedimentation rate Each member is composed bydark-grey mudstones at the base intercalation of mudstones andlight-grey sandstones in the middle part and thick grey or yellowishfine to coarse sandstones at the top Finally the younger sampledrocks are those from the Capas de la Estancia Maria Cristina (earliestOligocene Malumiaacuten and Olivero 2006) and the Cabo DomingoGroup in turn including the Desdemona (late OligocenendashearlyMiocene Ghiglione 2002 Malumiaacuten and Olivero 2006) the Capasde Cabo San Pablo (early Miocene Malumiaacuten and Olivero 2006) andthe Carmen Silva (middle Miocene Codignotto and Malumiaacuten 1981)Formations

The continental deposits of the Sloggett Fm (late EocenendashearlyOligocene Rossello et al 2004b Olivero and Malumiaacuten 2008)sampled at site TF03 are conglomerates and sandstones gradinglaterally and vertically to mudstones and coal measures includinglarge trees

In total we collected 298 cylindrical oriented samples at 22 sites(Tables 1 and 2) using a petrol-powered portable drill cooled bywater Site distribution within the sedimentary succession is asfollows (Table 1) eight sites were sampled from the early EocenePunta Torcida Fm ten sites from the upper middlendashlate Eocene CerroColorado Fm one site from the late Eocenendashearly Oligocene SloggettFm one site from the earliest Oligocene Capas de la Estancia MariaCristina one site from the late Oligocenendashearly Miocene DesdemonaFm and one site from the early Miocene Capas de Cabo San Pablo FmAt each site we gathered 9ndash18 cores (14 on average) spaced in at leasttwo outcrops in order to try to average out the secular variation of thegeomagnetic field

(2002) (Fig 3bcd)) Legend 1 Alluvial sediments (Quaternary) 2 Glacial depositsy Miocene) 5 Desdemona formation (late Oligocenendashearly Miocene) 6 Cabo DomingoSloggett formation (late Eocenendashearly Oligocene) 9 Cerro Colorado formation (upperormation (early Eocene) 12 Site-mean rotation with respect to South America withation (Kmax)

277M Maffione et al Earth and Planetary Science Letters 289 (2010) 273ndash286

2003 Ghiglione and Ramos 2005Malumiaacuten andOlivero 2006 Torres-Carbonell et al 2008b) Virtually undeformed post-early Miocenesedimentary rocks testify the end of tectonic shortening in the southernMagallanes basin (Ghiglione 2002 Ghiglione et al 2002) The tectonichistory of theMagallanes basin has been interpreted as related to eithercompressive (Ghiglione and Ramos 2005) or extensional (Ghiglioneet al 2008) tectonics of Eocene age followed by an OligocenendashearlyMiocene episode in which wrench tectonics dominated

22 Previous paleomagnetic data from the Patagonian orocline and theAntarctic Peninsula

Carey (1958) first proposed that the abrupt curvature of thesouthernmost Andes could be due to oroclinal bending of an initiallystraightorogen thoughpaleomagnetic evidence from the southernmostAndeshas beengatheredonly since the1970s (Dalziel et al 1973 Burnset al 1980 Cunningham et al 1991 Roperch et al 1997 Beck et al2000 Rapalini et al 2001 2004 2005 Baraldo et al 2002 Iglesia Llanoset al 2003) These studies indicate significant post-late Cretaceouscounterclockwise (CCW) rotations (up to 118deg) affecting the internalsouthern Andes below latitude 48degS (Fig 2) It is likely that (at least partof) the largest magnitude rotations arise from local tectonic effectslinked to thrusting (Iglesia Llanos et al 2003) or strikendashslip faulting(Rapalini et al 2001)

However the earliest paleomagnetic studies (Dalziel et al 1973Burns et al 1980) do not pass modern reliability criteria of laboratoryprocedures (eg Beck 1988) while all data from Patagonian andFuegian Andes were invariantly gathered from igneous or metamor-phic rocks thus suffer of significant uncertainties on the paleo-horizontal surface and age of magnetization as well as of possibleincomplete averaging of the paleosecular variation of the geomag-netic field

In detail three localities from the southern Patagonian Andes at a47degS latitude do not show any significant rotation thus defining thenorthern limit of the CCW-rotating domain (Roperch et al 1997 Becket al 2000 Iglesia Llanos et al 2003) To the south a post-lateJurassic CCW rotation of 39deg 57deg and 62deg has been documented fromsedimentary and igneous rocks at Lago San Martin north (49degS722degW) Lago San Martin south (491degS 725degW) and Lago Argentino(502degS 728degW) respectively (Iglesia Llanos et al 2003) Furthersouth Rapalini et al (2001) have evidenced a post-early CretaceousCCW rotation of 118deg from basalts and lavas at the Madre de DiosArchipelago (504degS 754degW Fig 2) while Rapalini et al (2004) havedocumented a 59deg post-late Cretaceous CCW rotation from ophiolitesat the southernmost Patagonian Andes (517degS 736degW) An extensivepaleomagnetic study carried out by Burns et al (1980) on volcanicand metamorphic rocks throughout the Patagonian and FuegianAndes revealed post-late Jurassicndashearly Cretaceous 27ndash40deg CCWrotations Conversely igneous rocks of the Navarino Island andadjacent regions of Chile yielded post-94 and post-77 Ma 150deg and120deg CCW rotations respectively (Dalziel et al 1973) while a 90degpost-late Cretaceous CCW rotation was obtained from volcanic andsedimentary rocks (Cunningham et al 1991) Igneous rocks sampledby Baraldo et al (2002) and Rapalini et al (2005) in the inner part ofthe orogenic belt from Tierra del Fuego documented a 33deg to 66deg post-late Cretaceous CCW rotation

Diraison (1998) gathered 215 cores at 16 sites (six sites fall withinour sampling area) located along the arc of the Magallanes belt belowlatitude 51degS The very weak magnetization of the sampled rocks did

Fig 3 Structural and geological maps of the study areas redrawn from Ghiglione et al(Quaternary) 3 Carmen Silva formation (middle Miocene) 4 Capas de Cabo San Pablo (earlgroup (OligocenendashMiocene) 7 Capas de la Estancia Maria Cristina (earliest Oligocene) 8middle to late Eocene) 10 Leticia formation (upper middle Eocene) 11 Punta Torcida frespective rotation error (grey cone) 13 Direction of the (in situ) site-mean magnetic line

not permit to isolate reliable paleomagnetic directions while well-defined magnetic fabric was recognized at all sites

Finally the arcuate shape of the Antarctic Peninsula mirroring tothe Patagonian orocline could suggest a related tectonic evolutionThe paleomagnetic data from the Antarctic Peninsula (Grunow 1993and references therein) documented two distinct phases of rotationclockwise (CW) with respect to East Antarctica between 175 and155 Ma due to the early opening in the Weddell Sea basin and CCWwith respect to West Antarctica in the 155ndash130 Ma time interval

3 Sampling and methods

In December 2007 we performed an extensive paleomagneticsampling campaign within the southeastern part of the Magallanesbelt of Tierra del Fuego (Figs 2 and 3) Because of the widespreadcover of glacial deposits and the scarce road network most of thesamples (except for sites TF02 and TF03) were collected along thecliffs of the Atlantic coast between Cabo San Pablo and Cerro Colorado(Fig 3) Lower Eocene to lower Miocene marine fine-grainedsediments (siltstones and mudstones) were systematically sampled(only at site TF03 continental clays were gathered)

The oldest sampled marine sediments are those from the PuntaTorcida Fm (early Eocene Olivero and Malumiaacuten 1999 2008) amajor sim400 m thick regressive unit dominated by dark-grey mud-stones with scarce intercalations of light-grey fine sandstones Thisformation is unconformably covered by the upper middle EoceneLeticia Fm consisting of grey and greenish fine bioturbatedglauconitic tuffaceous or lithic sandstones with subordinated fineconglomerates mudstones and tuffaceous sandstones The Leticia Fmis followed by the upper middle to late Eocene Cerro Colorado Fm amajor transgressivendashregressive sequence consisting of a verticalstacking of four coarsening- and thickening-upwards sequenceswith a very high sedimentation rate Each member is composed bydark-grey mudstones at the base intercalation of mudstones andlight-grey sandstones in the middle part and thick grey or yellowishfine to coarse sandstones at the top Finally the younger sampledrocks are those from the Capas de la Estancia Maria Cristina (earliestOligocene Malumiaacuten and Olivero 2006) and the Cabo DomingoGroup in turn including the Desdemona (late OligocenendashearlyMiocene Ghiglione 2002 Malumiaacuten and Olivero 2006) the Capasde Cabo San Pablo (early Miocene Malumiaacuten and Olivero 2006) andthe Carmen Silva (middle Miocene Codignotto and Malumiaacuten 1981)Formations

The continental deposits of the Sloggett Fm (late EocenendashearlyOligocene Rossello et al 2004b Olivero and Malumiaacuten 2008)sampled at site TF03 are conglomerates and sandstones gradinglaterally and vertically to mudstones and coal measures includinglarge trees

In total we collected 298 cylindrical oriented samples at 22 sites(Tables 1 and 2) using a petrol-powered portable drill cooled bywater Site distribution within the sedimentary succession is asfollows (Table 1) eight sites were sampled from the early EocenePunta Torcida Fm ten sites from the upper middlendashlate Eocene CerroColorado Fm one site from the late Eocenendashearly Oligocene SloggettFm one site from the earliest Oligocene Capas de la Estancia MariaCristina one site from the late Oligocenendashearly Miocene DesdemonaFm and one site from the early Miocene Capas de Cabo San Pablo FmAt each site we gathered 9ndash18 cores (14 on average) spaced in at leasttwo outcrops in order to try to average out the secular variation of thegeomagnetic field

(2002) (Fig 3bcd)) Legend 1 Alluvial sediments (Quaternary) 2 Glacial depositsy Miocene) 5 Desdemona formation (late Oligocenendashearly Miocene) 6 Cabo DomingoSloggett formation (late Eocenendashearly Oligocene) 9 Cerro Colorado formation (upperormation (early Eocene) 12 Site-mean rotation with respect to South America withation (Kmax)

Table 1Anisotropy of magnetic susceptibility results from Tierra del Fuego

Site Formation Latitude degS Longitude degW Age Age(Ma)

nN Km L F T Pprime D(deg)

I(deg)

e12(deg)

TF01 Capas E Maria Cristina 5450819 6630651 Earliest Oligocene 30ndash34 ndash ndash ndash ndash ndash ndash ndash ndash ndash

TF02 Cerro Colorado 5391318 6836002 U MiddlendashLate Eocene 34ndash40 611 264 1023 1056 0376 1084 3114 minus13 18TF03 Sloggett 5455055 6700568 L EocenendashE Oligocene 28ndash37 ndash ndash ndash ndash ndash ndash ndash ndash ndash

TF04 Cerro Colorado 5449756 6637447 U MiddlendashLate Eocene 34ndash40 1011 179 1007 1045 0731 1057 1106 108 19TF05 Cerro Colorado 5449685 6637592 U MiddlendashLate Eocene 34ndash40 1313 202 1010 1040 0564 1057 908 155 13TF06 Cerro Colorado 5449291 6638249 U MiddlendashLate Eocene 34ndash40 1113 243 1020 1026 minus001 1035 946 91 14TF07 Cerro Colorado 5449213 6638316 U MiddlendashLate Eocene 34ndash40 1414 302 1013 1028 0441 1042 281 minus64 4TF08 Punta Torcida 5445557 6649070 Early Eocene 49ndash56 1011 244 1018 1045 0429 1067 586 172 9TF09 Punta Torcida 5446647 6648586 Early Eocene 49ndash56 1012 194 1010 1036 0603 1049 3016 17 5TF10 Punta Torcida 5440377 6655741 Early Eocene 49ndash56 1011 128 1016 1050 0521 1070 948 131 6TF11 Punta Torcida 5443650 6652520 Early Eocene 49ndash56 1111 177 1005 1022 0565 1028 795 243 10TF12 Punta Torcida 5443860 6651984 Early Eocene 49ndash56 89 150 1008 1036 0618 1047 1159 minus113 8TF13 Punta Torcida 5444307 6650858 Early Eocene 49ndash56 1013 170 1014 1027 0293 1041 79 minus149 7TF14 Punta Torcida 5442979 6653755 Early Eocene 49ndash56 1113 187 1008 1023 0662 1030 818 minus174 8TF15 Cerro Colorado 5448060 6645114 U MiddlendashLate Eocene 34ndash40 1313 214 1011 1036 0621 1052 2784 minus24 9TF16 Cerro Colorado 5443369 6654663 U MiddlendashLate Eocene 34ndash40 1213 177 1012 1021 0342 1033 838 minus239 8TF17 Cerro Colorado 5448033 6644112 U MiddlendashLate Eocene 34ndash40 1111 264 1015 1040 0451 1058 84 minus215 18TF18 Cerro Colorado 5448695 6640784 U MiddlendashLate Eocene 34ndash40 79 278 1009 1055 0715 1070 828 minus266 20TF19 Punta Torcida 5439883 6656378 Early Eocene 49ndash56 810 195 1018 1022 0112 1040 3104 11 7TF20 Desdemona 5431318 6669111 L Oligocene ndash E Miocene 20ndash25 1213 212 1004 1055 0774 1065 142 minus84 15TF21 Cerro Colorado 5435286 6664365 U MiddlendashLate Eocene 34ndash40 615 126 1017 1046 0007 1054 2663 minus02 8TF22 Capas Cabo San Pablo 5427540 6673711 Early Miocene 16ndash20 99 185 1007 1048 0759 1060 322 34 24

The geographic coordinates are referred toWGS84 datum Age in Ma is from the geologic timescale of Gradstein et al (2004) nN number of samples giving reliable resultsnumberof studied samples at a site Km mean susceptibility in 10minus6 SI L F T and Pprime are magnetic lineation (KmaxKint) magnetic foliation (KintKmin) shape factor and corrected anisotropydegree respectively according to Jelinek (1981) D and I are in situ site-mean declination and inclination respectively of the maximum susceptibility axis e12 is semi-angle of the95 confidence ellipse around the mean Kmax axis in the KmaxndashKint plane

278 M Maffione et al Earth and Planetary Science Letters 289 (2010) 273ndash286

All sampleswereoriented in situusingamagnetic compass correctedto account for the local magnetic field declination value at the samplingarea (sim12deg during the sampling campaign period according to NOAAsNational Geophysical Data Centre (httpwwwngdcnoaagov))

After selecting the most effective temperature steps through theuse of pilot specimens one sample from each core was thermallydemagnetized in eightndashnine steps up to 360 degC All natural remanentmagnetization (NRM) measurements were carried out in the mag-netically shielded room of the paleomagnetic laboratory of the IstitutoNazionale di Geofisica e Vulcanologia (INGV Rome Italy) using a DC-SQUID cryogenic magnetometer (2G Enterprises USA) Demagnetiza-tion datawere plotted on orthogonal diagrams (Zijderveld 1967) andmagnetization components were isolated by principal componentanalysis (Kirschvink 1980) Rotation and flattening values withrespect to stable South America for the individual sites were evaluatedaccording to Demarest (1983) using reference South Americanpaleopoles from Besse and Courtillot (2002)

The low-field anisotropy of magnetic susceptibility (AMS) of allspecimenswas investigated by a KLY-3 bridge (AGICO) while magnetic

Table 2Paleomagnetic results from Tierra del Fuego

Site Formation Geographic coordinates Age Age(Ma)

Bedding(deg)

Latitude degS Longitude degW

TF02 Cerro Colorado 5391318 6836002 U Middle ndash

Late Eocene34ndash40 229ndash26

TF03 Sloggett 5455055 6700568 L Eocene ndash

E Oligocene28ndash37 106ndash50

TF05 Cerro Colorado 5449685 6637592 U Middle ndash

Late Eocene34ndash40 157ndash34

TF08 Punta Torcida 5445557 6649070 Early Eocene 49ndash56 339ndash70TF09 Punta Torcida 5446647 6648586 Early Eocene 49ndash56 213ndash50TF11 Punta Torcida 5443650 6652520 Early Eocene 49ndash56 89ndash25TF13 Punta Torcida 5444307 6650858 Early Eocene 49ndash56 235ndash16TF19 Punta Torcida 5439883 6656378 Early Eocene 49ndash56 223ndash27

Discarded sites (see text) Bedding is expressed in dip azimuth-dip values D and I are sitα95 are the statistical parameters after Fisher (1953) nN is the number of samples giving rel(F) values and relative errors (ΔR and ΔF) (according to Demarest (1983)) are relative to cAmerican paleopoles from Besse and Courtillot (2002)

mineralogy experiments were only performed on selected specimensfrom each siteWe studied the hysteresis properties and the acquisitionof an isothermal remanent magnetization (IRM) up to 500 mT using aMicromagAlternatingGradientMagnetometer (AGMmodel 2900)Wealso investigated the thermal change of the magnetic susceptibilityduring a heatingndashcooling cycle from room temperature to 700 degC usingan AGICO CS-3 apparatus coupled to the KLY-3 bridge and the thermaldemagnetization of a three-component IRM imparted on the specimenaxes according to Lowrie (1990) Fields of 27 06 and 012 T weresuccessively imparted on the z y and x sample axes (respectively) witha Pulse Magnetizer (Model 660 2G Enterprises)

4 Results

41 Magnetic mineralogy

Hysteresis measurements consistently indicate the predominanceof a paramagnetic fraction (likely clayey minerals) in the inducedmagnetization with the hysteresis loops represented by lines passing

Tilt corrected In situ k α95

(deg)nN R

(deg)ΔR(deg)

F(deg)

ΔF(deg)

D(deg)

I(deg)

D(deg)

I(deg)

1762 211 1642 348 197 119 911 63 159 minus542 99

3319 minus359 245 minus540 77 199 914 minus192 207 minus379 157

3336 minus398 3276 minus736 107 140 1217 minus167 192 minus360 114

3286 minus13 3121 664 163 112 1212 minus236 109 minus729 892618 23 2754 320 90 187 913 896 160 minus719 1473466 minus404 86 minus410 588 104 413 minus56 125 minus338 831685 238 1609 292 188 122 913 minus37 123 minus504 972361 324 2443 585 231 97 1111 639 111 minus417 78

e-mean declination and inclination calculated after and before tectonic correction k andiable resultsnumber of studied samples at a site Site-mean Rotation (R) and Flatteningoeval D and I South American values expected at the sampling area considering South

Fig 4 Results of the magnetic mineralogy analyses for representative samples (a) Hysteresis cycle (b) isothermal remanent magnetization (IRM) acquisition curve (c) thermalvariation of the low-field magnetic susceptibility during a heatingndashcooling cycle (black and grey line respectively) and (d) thermal demagnetization of a three-component IRMaccording to the method of Lowrie (1990)

279M Maffione et al Earth and Planetary Science Letters 289 (2010) 273ndash286

very close to the axes origin (Fig 4a) The few ldquoferromagneticrdquo (sensulato) fraction shows saturation remanence (Mrs) values of sim2 nAm2and coercivity of remanence (Bcr) in the range of 28ndash33 mT (Fig 4b)Thermomagnetic curves (Fig 4c) yield a hyperbolic trend up tosim300 degC during heating thus confirming the predominant contribu-tion of the paramagnetic fraction to the low-field susceptibility (ieHrouda 1994) A susceptibility increase between 350 and 520 degC andthe path of the cooling curve (revealing a Curie temperature ofsim580 degC) suggest the formation of new magnetite from theparamagnetic matrix Finally the thermal demagnetization of athree-component IRM (Fig 4d) reveals that the ldquoferromagneticrdquominerals are represented by a largely predominant soft fractiondemagnetized between 550 and 600 degC At sites TF02 and TF19 thesoft and the intermediate coercivity fractions also undergo asignificant drop between 300 and 400 degC

In summary the magnetic mineralogy experiments reveal thatparamagnetic clayey minerals dominate the low-field susceptibilitywhile a small amount of ldquoferromagneticrdquo fraction is generallyrepresented by magnetite and by a mixture of magnetite and ironsulphides at sites TF02 and TF19

42 Anisotropy of magnetic susceptibility

The AMS parameters at both the specimen and the site levels wereevaluated using Jelinek statistics (Jelinek 1977 1978) and arereported in Table 1 The site-mean susceptibility values rangingfrom 126 to 302times10minus6 SI (205times10minus6 SI on average) confirm thepredominant contribution of the paramagnetic clayey matrix on boththe low-field susceptibility and AMS (eg Rochette 1987 Averbuchet al 1995 Sagnotti et al 1998 Speranza et al 1999) The shape of

280 M Maffione et al Earth and Planetary Science Letters 289 (2010) 273ndash286

281M Maffione et al Earth and Planetary Science Letters 289 (2010) 273ndash286

the AMS ellipsoid is predominantly oblate with a mean value of theshape factor (T) of 047 (Table 1) suggesting a prevailing sedimentaryfabric (Hrouda and Janagravek 1976) In addition the low values of thePprime parameter (1030ndash1070) indicate that the sediments underwentonly mild deformation The magnetic foliation (given by the clusteringof the Kmin axes) is well defined at all sites except for sites TF01 andTF03 (Fig 5) and it is always parallel to the local bedding planeconfirming that the sediments host a predominant sedimentary-compactional magnetic fabric

The sites yielding a well-defined magnetic fabric are alsocharacterized by a well-developedmagnetic lineation as documentedby the clustering of Kmax axes from the individual specimens (12 and8 sites display an e12 value lower than 10 deg and 24 deg respectivelyTable 1) Magnetic lineations trend roughly EndashW (on average) in theMagallanes belt (ie sub-parallel to local fold axes and thrust faulttrends Fig 3b and d) while they are simNndashS oriented at two siteslocated in the foreland basin

Our magnetic lineation directions are consistent with thoseobtained at six sites by Diraison (1998) in the same sampling area(Fig 2) The regional-scale Diraisons (1998) work included 16CretaceousndashMiocene sites from both the Patagonian and the FuegianAndes He found a variable magnetic lineation orientation whichmirrored the change of the structural grain of the cordillera along thePatagonian orocline

43 Paleomagnetism

Only eight (out of 22) sites yielded a measurable remanentmagnetization well above the noise level of the magnetometer(sim5 μAm) The characteristic remanent magnetization directions(ChRMs) were isolated at low temperature between 120ndash210 degC and210ndash360 degC (Fig 6) The site-mean values of the maximum angulardispersion (MAD) relative to the calculated ChRMs were always b10 deg(except for site TF03 yielding a 126 deg MAD) Site-mean directions(evaluated according to Fisher 1953) are well defined the α95 valuesbeing comprised between 97deg and 199deg (135deg on average Fig 7 andTable 2) Two out of the eight magnetized sites (TF08 and TF09) werediscarded because of their sub-horizontal paleomagnetic directions(while a minus75deg inclination is expected at the sampling localitiesconsidering the 50 Ma paleopole for South America) The remainingsix reliable paleomagnetic sites are equally distributed into the normaland reverse polarity states and yield except for site TF19 NNW-directed directions (when considered in the normal polarity state)

There are three lines of evidence which support the primarynature of the ChRMs evaluated for the six reliable sites from Tierradel Fuego (1) both the in situ and tilt-corrected directions are farfrom the local geocentric axial dipole (GAD) field direction (D=0degI=minus700deg Fig 7) thus excluding a magnetic overprint (2) dualpaleomagnetic polarities suggest magnetization acquisition duringat least two magnetic polarity chrons (3) the McFaddens (1990)fold test performed on five out of six sites (excluding the scatteredsite TF19 rotated CW by 60ndash90deg with respect to the other sites) ispositive at the 99 significance level (ξin situ=42 ξunfolded=08ξ99 critical value=36) thus supporting a pre-tilting magnetizationacquisition

Since the ages of the rocks (predominantly early to late Eocene) arevery close to age of regional tectonic deformation and strata tilting(earlyndashmiddle Eocene to early Oligocene) a positive fold test is virtuallythe proof for the primary nature of the measured magnetization

Site-mean flattening values with respect to South America arealways negative and range between minus338deg and minus542deg (Table 2)

Fig 5 Schmidt equal-area projections lower hemisphere of the (in situ coordinates) principsites (see Table 1)

Such ldquoshallowingrdquo of the paleomagnetic directions can be explainedconsidering the effects of diagenesis and compaction on clayeysediments (eg Deamer and Kodama 1990) as already observed forsimilar deposits sampled elsewhere (Speranza et al 1997 Maffioneet al 2008) The five clustered sites yield no significant rotation of theMagallanes belt of Tierra del Fuego with respect to South America(minus78degplusmn104deg) since at least the early Eocene times (sim50 Ma)Conversely the scattered TF19 site yields a 639degplusmn111deg CW rotation(Fig 3 and Table 2)

5 Discussion

51 Rotational nature of the Patagonian orocline and relations withScotia plate spreading and Drake Passage opening

Our data represent the first paleomagnetic evidence fromsedimentary sequences exposed in the northern foothills of theFuegian Andes and suggest that the curved shape of the orogen wasalready fully acquired at sim50 Ma Some paleomagnetic studies ofcurved orogenic belts have shown that negligible vertical axisrotations affect the outermost orogenic fronts even when strongrotations occur at the innermost belt sectors (eg Kley 1999) Thiswould imply that the rotation magnitude is roughly proportional tothe amount of translation relative to the stable foreland and that ourresults cannot be extrapolated to the whole Fuegian Andes Howeverother studies have documented that large-magnitude rotations canalso occur along the frontal thrusts of a mountain belt and thatrotations gathered from the frontal structures can be extrapolated tothe whole orogen (eg Kissel et al 1995 Speranza et al 2003)Though a rotation variation from the external to the internal units ofTierra del Fuego cannot be excluded (reliable paleomagnetic datafrom the internal zones are lacking) we note that the structuraltrends from the external and internal domains are sub-parallel (seeFig 2) and this supports the extrapolation of our paleomagnetic datato the whole orogen

Therefore the Patagonian oroclinemight be in principle the result ofone of the two following kinematics (1) it is a non-rotational (orprimary) arc (sensu Marshak 1988) resulting from the tectonicdeformation of an original curved paleomargin affected by radialshortening directions (2) it is an orocline formed through rotationsolder than 50 Ma The first scenario has been proposed in several recentpapers (RamosandAleman 2000Diraison et al 2000Ghiglione 2003Ghiglione and Ramos 2005 Ghiglione and Cristallini 2007) thoughnone is based upon proper paleomagnetic evidence Conversely thishypothesis mostly relies upon sand-box analogue model resultsindicating how a suitable change over time in the South AmericandashAntarctica relative plate motion can account for all features observed inthe Patagonian arc (ie shape of the curvature directions and amountsof shortening)

However when the overall paleomagnetic data set from thePatagonian orocline is considered all previous results from the FuegianAndes systematically yield a post-160 to 100 Ma CCW rotation withrespect of South America though the igneous and metamorphic natureof the studied rocksmay implyfirst-orderflawsonboth data quality andmagnetization age We conclude that further paleomagnetic investiga-tions of the pre-lower Eocene sequences from theMagallanes belt of theTierra del Fuego are surely needed to properly understand the rotationalnature of the Patagonian orocline Yet the available paleomagnetic dataset is indeed suggestive of an orogenic bend formed after rotationsoccurring before 50 Ma in late Mesozoicndashearliest Paleogene timesDiraison et al (1997b) speculated that a small CCWrotationof Tierra del

al axes of the AMS ellipsoid and their respective 95 confidence ellipse for all sampled

281M Maffione et al Earth and Planetary Science Letters 289 (2010) 273ndash286

the AMS ellipsoid is predominantly oblate with a mean value of theshape factor (T) of 047 (Table 1) suggesting a prevailing sedimentaryfabric (Hrouda and Janagravek 1976) In addition the low values of thePprime parameter (1030ndash1070) indicate that the sediments underwentonly mild deformation The magnetic foliation (given by the clusteringof the Kmin axes) is well defined at all sites except for sites TF01 andTF03 (Fig 5) and it is always parallel to the local bedding planeconfirming that the sediments host a predominant sedimentary-compactional magnetic fabric

The sites yielding a well-defined magnetic fabric are alsocharacterized by a well-developedmagnetic lineation as documentedby the clustering of Kmax axes from the individual specimens (12 and8 sites display an e12 value lower than 10 deg and 24 deg respectivelyTable 1) Magnetic lineations trend roughly EndashW (on average) in theMagallanes belt (ie sub-parallel to local fold axes and thrust faulttrends Fig 3b and d) while they are simNndashS oriented at two siteslocated in the foreland basin

Our magnetic lineation directions are consistent with thoseobtained at six sites by Diraison (1998) in the same sampling area(Fig 2) The regional-scale Diraisons (1998) work included 16CretaceousndashMiocene sites from both the Patagonian and the FuegianAndes He found a variable magnetic lineation orientation whichmirrored the change of the structural grain of the cordillera along thePatagonian orocline

43 Paleomagnetism

Only eight (out of 22) sites yielded a measurable remanentmagnetization well above the noise level of the magnetometer(sim5 μAm) The characteristic remanent magnetization directions(ChRMs) were isolated at low temperature between 120ndash210 degC and210ndash360 degC (Fig 6) The site-mean values of the maximum angulardispersion (MAD) relative to the calculated ChRMs were always b10 deg(except for site TF03 yielding a 126 deg MAD) Site-mean directions(evaluated according to Fisher 1953) are well defined the α95 valuesbeing comprised between 97deg and 199deg (135deg on average Fig 7 andTable 2) Two out of the eight magnetized sites (TF08 and TF09) werediscarded because of their sub-horizontal paleomagnetic directions(while a minus75deg inclination is expected at the sampling localitiesconsidering the 50 Ma paleopole for South America) The remainingsix reliable paleomagnetic sites are equally distributed into the normaland reverse polarity states and yield except for site TF19 NNW-directed directions (when considered in the normal polarity state)

There are three lines of evidence which support the primarynature of the ChRMs evaluated for the six reliable sites from Tierradel Fuego (1) both the in situ and tilt-corrected directions are farfrom the local geocentric axial dipole (GAD) field direction (D=0degI=minus700deg Fig 7) thus excluding a magnetic overprint (2) dualpaleomagnetic polarities suggest magnetization acquisition duringat least two magnetic polarity chrons (3) the McFaddens (1990)fold test performed on five out of six sites (excluding the scatteredsite TF19 rotated CW by 60ndash90deg with respect to the other sites) ispositive at the 99 significance level (ξin situ=42 ξunfolded=08ξ99 critical value=36) thus supporting a pre-tilting magnetizationacquisition

Since the ages of the rocks (predominantly early to late Eocene) arevery close to age of regional tectonic deformation and strata tilting(earlyndashmiddle Eocene to early Oligocene) a positive fold test is virtuallythe proof for the primary nature of the measured magnetization

Site-mean flattening values with respect to South America arealways negative and range between minus338deg and minus542deg (Table 2)

Fig 5 Schmidt equal-area projections lower hemisphere of the (in situ coordinates) principsites (see Table 1)

Such ldquoshallowingrdquo of the paleomagnetic directions can be explainedconsidering the effects of diagenesis and compaction on clayeysediments (eg Deamer and Kodama 1990) as already observed forsimilar deposits sampled elsewhere (Speranza et al 1997 Maffioneet al 2008) The five clustered sites yield no significant rotation of theMagallanes belt of Tierra del Fuego with respect to South America(minus78degplusmn104deg) since at least the early Eocene times (sim50 Ma)Conversely the scattered TF19 site yields a 639degplusmn111deg CW rotation(Fig 3 and Table 2)

5 Discussion

51 Rotational nature of the Patagonian orocline and relations withScotia plate spreading and Drake Passage opening

Our data represent the first paleomagnetic evidence fromsedimentary sequences exposed in the northern foothills of theFuegian Andes and suggest that the curved shape of the orogen wasalready fully acquired at sim50 Ma Some paleomagnetic studies ofcurved orogenic belts have shown that negligible vertical axisrotations affect the outermost orogenic fronts even when strongrotations occur at the innermost belt sectors (eg Kley 1999) Thiswould imply that the rotation magnitude is roughly proportional tothe amount of translation relative to the stable foreland and that ourresults cannot be extrapolated to the whole Fuegian Andes Howeverother studies have documented that large-magnitude rotations canalso occur along the frontal thrusts of a mountain belt and thatrotations gathered from the frontal structures can be extrapolated tothe whole orogen (eg Kissel et al 1995 Speranza et al 2003)Though a rotation variation from the external to the internal units ofTierra del Fuego cannot be excluded (reliable paleomagnetic datafrom the internal zones are lacking) we note that the structuraltrends from the external and internal domains are sub-parallel (seeFig 2) and this supports the extrapolation of our paleomagnetic datato the whole orogen

Therefore the Patagonian oroclinemight be in principle the result ofone of the two following kinematics (1) it is a non-rotational (orprimary) arc (sensu Marshak 1988) resulting from the tectonicdeformation of an original curved paleomargin affected by radialshortening directions (2) it is an orocline formed through rotationsolder than 50 Ma The first scenario has been proposed in several recentpapers (RamosandAleman 2000Diraison et al 2000Ghiglione 2003Ghiglione and Ramos 2005 Ghiglione and Cristallini 2007) thoughnone is based upon proper paleomagnetic evidence Conversely thishypothesis mostly relies upon sand-box analogue model resultsindicating how a suitable change over time in the South AmericandashAntarctica relative plate motion can account for all features observed inthe Patagonian arc (ie shape of the curvature directions and amountsof shortening)

However when the overall paleomagnetic data set from thePatagonian orocline is considered all previous results from the FuegianAndes systematically yield a post-160 to 100 Ma CCW rotation withrespect of South America though the igneous and metamorphic natureof the studied rocksmay implyfirst-orderflawsonboth data quality andmagnetization age We conclude that further paleomagnetic investiga-tions of the pre-lower Eocene sequences from theMagallanes belt of theTierra del Fuego are surely needed to properly understand the rotationalnature of the Patagonian orocline Yet the available paleomagnetic dataset is indeed suggestive of an orogenic bend formed after rotationsoccurring before 50 Ma in late Mesozoicndashearliest Paleogene timesDiraison et al (1997b) speculated that a small CCWrotationof Tierra del

al axes of the AMS ellipsoid and their respective 95 confidence ellipse for all sampled

Fig 6 Orthogonal vector diagrams of demagnetization data (in situ coordinates) for the 8 sites yielding a measurable remanence Solid and open dots represent projection on thehorizontal and vertical planes respectively Demagnetization step values are in degC

282 M Maffione et al Earth and Planetary Science Letters 289 (2010) 273ndash286

Fuego (related to left-lateral drag exertedby theScotia plate) could haveoccurred in Neogene times as testified by a variable slip (increasingtoward SW) on the extensional structures of the Magellan Straits riftsystem which would have accommodated such a rigid block rotationNevertheless neither the age nor the amount of rotation could beinferred by such field observations

A candidate yielding the possible pre-50 Ma oroclinal bending ofthe Fuegian Andes is the inversion and closure of the Rocas Verdesmarginal basin during midndashlate Cretaceous times Kraemer (2003)demonstrated that the closure of the Rocas Verdes basin could haveproduced a maximum regional CCW rotation of 30deg assuming areasonable basin width of 25 km Therefore we speculate that about

Fig 7 Equal-area projections of the site-mean paleomagnetic directions Open (solid) symbols represent projection onto the upper (lower) hemisphere Open ellipses are theprojections of the α95 cones about the mean directions The star represents the normal polarity geocentric axial dipole (GAD) field direction (D=0deg I=minus700deg) for the study area

283M Maffione et al Earth and Planetary Science Letters 289 (2010) 273ndash286

60deg of the entire 90deg orogenic trend change observed along thePatagonian orocline could be related to a pre-existing articulatedpaleomargin while further 30deg were possibly acquired during themidndashlate Cretaceous closure of the Rocas Verdes basin (Fig 8)

Thus the final configuration of the Patagonian orocline wascompleted well before than the onset of the Scotia plate spreading atsim32 Ma (Barker 2001 Lawver and Gahagan 2003 Eagles et al 2005Livermore et al 2005 Lodolo et al 2006) This implies that the openingof the Drake Passage deep-sea pathway at the EocenendashOligoceneboundary (Barker 2001 Eagles et al 2005 Livermore et al 2005Lodolo et al 1997 2006) likely determining first-order effects in theglobal paleoclimate (Lawver and Gahagan 2003 Barker et al 2007ab)was decidedly unrelated to the evolutionary history of the Patagonianorocline and most likely the sole consequence of the Scotia platespreading

Resting apart from the five non-rotated sites site TF19 yields asim60deg CW rotation (Figs 3 and 7) This site is located in proximity ofthe Fueguina fault (Fig 3) a right-lateral strikendashslip fault interpretedas an Rprime Riedel shear fracture associated to the major left-lateral MFFS(Ghiglione et al 2002) Thus we interpret this large-magnitude CWrotation as a local effect related to right-lateral displacement along theFueguina fault similar to paleomagnetic evidence gathered fromother strikendashslip faults exposed elsewhere (eg Sonder et al 1994Maffione et al 2009)

52 Tertiary tectonics of the Magallanes belt of Tierra del Fuegoevidence from magnetic fabric

The well-definedmagnetic lineations gathered at 20 out of 22 sitesfrom Tierra del Fuego offer the opportunity to unravel with greataccuracy the finite deformation pattern of the Magallanes belt of theFuegian Andes In fact there is wide evidence from other orogens thatAMS of fine-grained sediments represents a valuable strain proxyeven in absence of other visible strain markers (eg Sagnotti et al1998 Maffione et al 2008) The magnetic lineation gathered from a

fold belt normally trends sub-parallel to the local fold axis or anywayparallel to the maximum elongation axis (ε1) of the strain ellipsoid

Along the Atlantic coast between Cabo San Pablo and CerroColorado the magnetic lineations from Tierra del Fuego consistentlydefine the extent the external orogen where they trend roughly EndashWsub-parallel to local fold axes while they are NndashS (on average) at twonorthernmost sites located in the undeformed foreland (Fig 3 andFig 5) At site TF19 the magnetic lineation trends NWndashSE thusconfirming the significant CW rotation with respect to otherneighbour sites evidenced by paleomagnetic data likely due to theFueguina fault activity Apart from the sites located along the Atlanticcoast magnetic lineation is oriented NWndashSE at site TF02 again sub-parallel to local fold axes (Fig 3)

The general EndashW trending of the magnetic lineations between CaboSan Pablo and Cerro Colorado coupled with the lack of paleomagneticrotations proves that a roughly NndashS directed compressive tectonicregime was active in the southern Magallanes basin synchronous withsedimentation In fact it has been shown that the magnetic fabric ismostly sensitive to the pristine tectonic regime acting duringsedimentation or shortly after prior to complete sediment lithification(eg Sagnotti et al 1998 Faccenna et al 2002) Therefore our AMSdata from the Atlantic coast coupled with those from Diraison (1998)support a NndashS oriented shortening acting during sediment deposition(ie during early Eocenendashearly Miocene times 50ndash20 Ma)

The origin of this tectonic regime is not completely clear A NndashScompression in the Magallanes basin (see also Lagabrielle et al 2009)of Tierra del Fuego is in apparent contrast with the relative motionbetween Antarctica and South America whichwas characterized from46 Ma by a WNWndashESE oriented sinistral component changing to aclear EndashW direction since sim20 Ma (Livermore et al 2005) Conse-quently the Livermore et al (2005) plate kinematic model gatheredby numerical inversion techniques applied on a (not conjugated)marinemagnetic anomaly set from theWeddell Sea should be revisedon the light of our reconstruction Alternatively Eocene NndashSshortening might also be related to the vanishing activity of thesoutheastern tip of the Andean subduction zone which may have

Fig 8 Tectonic reconstruction of the South AmericandashAntarctica plate boundary since120 to 50 Ma 120 Ma extensional episode related to the opening of the Rocas Verdesmarginal basin (RVMB) 100 Ma inversion and closure of the RVMB probablyaccompanied by a CCW rotation of the Fuegian Andes 50 Ma northward thrust-sheet emplacement in the Fuegian Andes SSA southernmost South America AFFZAgulhas Falkland Fracture Zone TF Tierra del Fuego FI Falkland (Malvinas) IslandsAP Antarctic Peninsula RVS suture of the Rocas Verdes marginal basin

284 M Maffione et al Earth and Planetary Science Letters 289 (2010) 273ndash286

been retreating northward Within this frame the Magallanes basincould be directly interpreted as a flexural-related basin developingduring the formation of the orogenic belt However further data onthe deep belt structure are needed to fully understand the tectonicsetting and validate tectonic hypotheses

AMS data may also serve to evaluate the relative relevance ofthrust vs strikendashslip tectonics in the Fuegian Andes where both the

displacement and onset age of the MagallanesndashFagnano strikendashslipfault system are a matter of debate Variable displacement amounts ofsome tens of kilometres have been postulated so far (20ndash30 kmOlivero and Martinioni (2001) 40km Lodolo et al (2003) 48kmTorres-Carbonell et al (2008a) 55 km Rossello et al (2004a)) whileages of the onset of the MFFS activity vary between 100 and 7 Ma(Cunningham 1995 Torres-Carbonell et al 2008a) At sites along theAtlantic coast the magnetic fabric of the sampled rocks reveals a NndashScompression acting during EocenendashMiocene times (50ndash20 Ma) whichis compatible with both pure northward-directed thrust-sheetemplacement and strain partitioning related to left-lateral shearalong the EndashW segment of the MFFS located sim10 km south of thesampling area

Sites from Cerro Colorado and site TF03 are located sim5 km andsim200 m (respectively) from the MFFS thus their paleomagneticdirections and magnetic lineation trends can be used to assesswhether left-lateral strikendashslip activity has caused local CCW rotations(eg Sonder et al 1994 Maffione et al 2009) We note that rotationvalues from sites TF03ndashTF05 are not significantly different from thoseat sites TF11ndashTF13 located several kilometres more distant from theMFFS and magnetic lineations from Cerro Colorado are not CCWrotated with respect to sites located further north along the externalorogen sector (Fig 3) Therefore we conclude that strikendashslip shearalong the MFFS has not caused large-magnitude rotations in theFuegian Andes and displacement along the fault is likely in the lowerbound among those put forward in the past (sim20 km according toOlivero and Martinioni (2001)) In any case there is surely noinfluence of strikendashslip tectonics for the formation of the Patagonianorocline (see ldquostrikendashslip orogenrdquo model by Cunningham (1993))

6 Conclusions

Five lower Eocenendashlower Oligocene paleomagnetic sites from theMagallanes belt of Tierra del Fuego consistently yielding a positivefold test indicate a lack of paleomagnetic rotations in the FuegianAndes since sim50 Ma Further data from older sediments are needed toassess whether the Patagonian orocline is a primary arc developedabove an articulated paleomargin or it formed after rotations olderthan 50 Ma However previous paleomagnetic evidence from meta-morphic and igneous rocks (even if not fully reliable) from theinternal part of the orogenic bend may suggest that the arc is mostlyprimary (ie developed above an articulated paleomargin) and that afurther 30deg CCW rotation occurred in midndashlate Cretaceous timesduring the closure of the Rocas Verdes marginal basin A pre-existingPatagonian orocline at 50 Ma implies that opening of the DrakePassage at sim32 Ma was the exclusive consequence of the Scotia platespreading where 32plusmn2 Ma oceanic anomalies are documented

A well-developed magnetic fabric from 20 sites (consistent withpast AMS results from Diraison (1998)) coupled with paleomagneticevidence documents an early Eocenendashearly Miocene (50ndash20 Ma) NndashSshortening in the Magallanes belt of Tierra del Fuego associated tonorthward fold and thrust belt propagation Both paleomagnetic andAMS data do not reveal any significant influence from the postulatedleft-lateral shear along the EndashW MagallanesndashFagnano fault

Therefore we speculate that the horizontal displacement along theMFFS may range in the lower bound values (sim20 km) among theestimates put forward so far In any case our data indicate that strikendashslip tectonics has not contributed at all to the genesis of the greatorogenic re-entrant known as Patagonian orocline

Acknowledgements

MM gratefully acknowledges H Soloaga L Waltter and F Oliva(Inspector and Sergeants of the Police Department in Tolhuin) fortheir logistic support given for the sampling campaign at Cabo SanPablo G Gonzaacutelez Bonorino and Emilio Saez helped us for lodgement

285M Maffione et al Earth and Planetary Science Letters 289 (2010) 273ndash286

in CADIC (Ushuaia) and in the Panaderia La Union (Tolhuin)respectively We are grateful to R Somoza for the fruitful discussionson the Andean tectonics and to J Kley and EPSL Editor P Delaney forproviding careful and constructive reviews of this manuscript MMand FS were funded by INGV while CF and ER were supported by theUniversitagrave di Roma Tre The Italian authors wish to dedicate this paperto the memory of Renato Funiciello an incomparable ldquomaestrordquo ofboth geology and humanity

References

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Baraldo A Rapalini A Tassone A Lippai H Menichetti M Lodolo E 2002 Estudiopaleomagneacutetico del intrusivodel cerroHewhoepen Tierra del Fuego y sus implicanciastectoacutenicas 15deg Congreso Geoloacutegico Argentino El Calafate Actas 1 285ndash290

Barker PF 2001 Scotia Sea regional tectonic evolution implications for mantle flowand palaeocirculation Earth-Sci Rev 55 1ndash39

Barker PF Filippelli GM Florindo F Martin EE Scher HD 2007a Onset and role ofthe Antarctic Circumpolar Current Deep-Sea Res II 54 2388ndash2398

Barker PF Diekmann B Escutia C 2007b Onset of Cenozoic Antarctic glaciationDeep-Sea Res II 54 2293ndash2307

Beck Jr ME 1988 Block rotations in continental crust examples fromWestern NorthAmerica In Kissel C Laj C (Eds) Paleomagnetic Rotations and ContinentalDeformation Kluwer Academic Dordrecht

Beck Jr ME Burmester R Cembrano J Drake R Garciacutea A Herveacute F Munizaga F2000 Paleomagnetism of the North Patagonian Batholith southern Chile Anexercise in shape analysis Tectonophysics 326 (1ndash2) 185ndash202

Besse J Courtillot V 2002 Apparent and true polar wander and the geometry of thegeomagnetic field over the last 200 Myr J Geophys Res 107 (B11) 2300doi1010292000jb000050

Burns KL Rickard MJ Belbin L Chamalaun F 1980 Further paleomagneticconfirmation of the Magallanes orocline Tectonophysics 63 75ndash90

Carey SW 1958 The tectonic approach to continental drift in continental drift asymposium Geology Department Univ Tasmania Hobart Tasmania 177ndash355

Codignotto JO Malumiaacuten N 1981 Geologiacutea de la regioacuten al Norte del paralelo 54 S dela Isla Grande de Tierra del Fuego Rev Asoc Geol Argent 36 44ndash88

Cunningham WD 1993 Strikendashslip faults in the southernmost Andes and developmentof the Patagonian orocline Tectonics 12 (1) 169ndash186

Cunningham WD 1994 Uplifted ophiolitic rocks on Isla Gordon southernmost Chileimplications for the closure history of the rocasVerdesmarginal basin and the tectonicevolution of the Beagle Channel region J South Am Earth Sci 7 (2) 135ndash147

Cunningham WD 1995 Orogenesis at the southern tip of the Americas the structuralevolution of the Cordillera Darwin metamorphic complex southernmost ChileTectonophysics 244 197ndash229

Cunningham WD Klepeis KA Gose WA Dalziel IWD 1991 The Patagonianorocline new paleomagnetic data from the Andean magmatic arc in Tierra delFuego Chile J Geophys Res 96 (B10) 16061ndash16067

Dalziel IWD Palmer KF 1979 Progressive deformation and orogenic uplift at thesouthernmost extremity of the Andes Geol Soc Amer Bull 90 259ndash280

Dalziel IWD Kligfield T LowrieW Opdyke ND 1973 Paleomagnetic data from thesouthernmost Andes and the Antarctandes In Tarling DH Runcorn SK (Eds)Implication of Continental Drift to the Earth Sciences vol 1 Academic PressLondon pp 37ndash101

Dalziel IWD De Wit MF Palmer KF 1974 Fossil marginal basin in the southernAndes Nature 250 291ndash294

Deamer GA Kodama KP 1990 Compaction induced inclination shallowing insynthetic and natural clay-rich sediments J Geophys Res 95 (B4) 4511ndash4529

Demarest HH 1983 Error analysis of the determination of tectonic rotation frompaleomagnetic data J Geophys Res 88 4321ndash4328

DeMets C Gordon RG Argus DF Stein S 1990 Current plate motions Geophys JInt 101 425ndash478

Diraison M 1998 Evolution ceacutenozoiumlque du Bassin de Magellan et tectonique des AndesAustralesMem docGeosci Rennes 85 1ndash332 ISBN2-905532-84-X ISSSN 1240-1498

Diraison M Cobbold PR Gapais D Rossello EA Gutieacuterrez PA 1997a Neogenetectonics within the Magellan basin (Patagonia) VI Simposio BolivarianoExploracioacuten petrolera en las cuencas subandinas Cartagena Memorias AsociacioacutenColombiana de Geoacutelogos y Geofiacutesicos del Petroacuteleo Bogotaacute Tomo I pp 1ndash14

Diraison M Cobbold PR Gapais D Rossello EA 1997b Magellan Strait Part of aNeogene rift system Geology 25 703ndash706

Diraison M Cobbold PR Gapais D Rossello EA 2000 Cenozoic crustal thickeningwrenching and rifting in the foothills of the southernmost Andes Tectonophysics316 91ndash119

Eagles G Livermore RA Fairhead JD Morris P 2005 Tectonic evolution of the westScotia Sea J Geophys Res 110 B02401 doi1010292004JB003154

Faccenna C Speranza F DAjello Caracciolo F Mattei M Oggiano G 2002Extensional tectonics on Sardinia (Italy) insights into the arc-back-arc transitionalregime Tectonophysics 356 213ndash232

Fisher RA 1953 Dispersion on a sphere Proc R Soc Lond 217 295ndash305Ghiglione MC 2002 Diques claacutesticos asociados a deformacioacuten transcurrente en

depoacutesitos sinorogeacutenicos del Mioceno inferior de la Cuenca Austral Rev Asoc GeolArgent 57 103ndash118

Ghiglione MC 2003 Estructura y evolucioacuten tectoacutenica del Cretaacutecico-Terciario de lacosta Atlaacutentica de Tierra del Fuego [PhD thesis] Buenos Aires Universidad deBuenos Aires pp 150

Ghiglione MC Cristallini EO 2007 Have the southernmost Andes been curved since LateCretaceous time An analog test for the Patagonian Orocline Geology 35 (1) 13ndash16

Ghiglione MC Ramos VA 2005 Progression of deformation in the southernmostAndes Tectonophysics 405 25ndash46

Ghiglione MC Ramos VA Cristallini EO 2002 Estructura y estratos de crecimientoen la faja plegada y corrida de los Andes fueguinos Rev Geol Chile 29 (1) 17ndash41

Ghiglione MC Yagupsky D Ghidella M Ramos VA 2008 Continental stretchingpreceding the opening of the Drake Passage evidence from Tierra del FuegoGeology 36 (8) 643ndash646

Gradstein FM Ogg JG Smith AG 2004 A Geologic Time Scale 2004 CambridgeUniversity Press pp 589

Grunow AM 1993 New paleomagnetic data from the Antarctic Peninsula and theirtectonic implications J Geophys Res 98 (13) 815ndash13833

Hrouda F 1994 A technique for the measurement of thermal changes of magneticsusceptibility of weakly magnetic rocks by the CS-2 apparatus and KLY-2Kappabridge Geophys J Int 118 604ndash612

Hrouda F Janagravek F 1976 The changes in shape of the magnetic susceptibilityellipsoid during progressive metamorphism and deformation Tectonophysics34 135ndash148

Iglesia Llanos MP Lanza R Riccardi AC Geuna S Laurenzi MA Ruffini R 2003Palaeomagnetic study of the El Quemado complex and Marifil formationPatagonian Jurassic igneous province Argentina Geophys J Int 154 599ndash617

Jelinek V 1977 The statistical theory of measuring anisotropy of magneticsusceptibility of rocks and its application Geofyzika Brno pp 88

Jelinek V 1978 Statistical processing of magnetic susceptibility on groups ofspecimens Stud Geophys Geod 22 50ndash62

Jelinek V 1981 Characterization of the magnetic fabrics of rocks Tectonophysics 7963ndash67

Kirschvink JL 1980 The least-squares line and plane and the analysis ofpaleomagnetic data Geophys J R Astron Soc 62 699ndash718

Kissel C Speranza F Milicevic V 1995 Paleomagnetism of external southern andcentral Dinarides and northern Albanides implications for the Cenozoic activity ofthe Scutari-Pec transverse zone J Geophys Res 100 14999ndash5007 doi101016S0040-1951(02)00638-8

Kley J 1999 Geologic and geometric constraints on a kinematic model of the Bolivianorocline J S Am Earth Sci 12 221ndash235

Kohn MJ Spear FS Harrison TM Dalziel IDW 1995 40Ar39Ar geochronology andP-T-t paths from the Cordillera Darwin metamorphic complex Tierra del FuegoChile J Metam Geol 13 251ndash270

Kraemer PE 2003 Orogenic shortening and the origin of the Patagonian orocline (56degrees S Lat) J South Am Earth Sci 15 731ndash748

Lagabrielle Y Goddeacuteris Y Donnadieu Y Malavieille J Suarez M 2009 The tectonichistory of Drake Passage and its possible impacts on global climate Earth PlanetSci Lett 279 (3ndash4) 197ndash211

Lawver LA Gahagan LM 2003 Evolution of Cenozoic seaways in the circum-Antarctic region Palaeogeogr Palaeoclimatol Palaeoecol 198 11ndash38

Livermore R Nankivell A Eagles G Morris P 2005 Paleogene opening of DrakePassage Earth Planet Sci Lett 236 459ndash470

Lodolo E Coren F Schreider AA Ceccone G 1997 Geophysical evidence of a relictoceanic crust in the southwestern Scotia Sea Mar Geophys Res 19 439ndash450

Lodolo E Menichetti M Bartole R Ben-Avraham Z Tassone A Lippai H 2003MagallanesndashFagnano continental transform fault (Tierra del Fuego southernmostSouth America) Tectonics 22 (6) 1076 doi1010292003TC001500

Lodolo E Donda F Tassone A 2006 Western Scotia Sea margins improvedconstraints on the opening of the Drake Passage J Gephys Res 111 B06101doi1010292006JB004361

Lowrie W 1990 Identification of ferromagnetic minerals in a rock by coercivity andunblocking temperature properties Geophys Res Lett 17 (2) 159ndash162

Maffione M Speranza F Faccenna C Cascella A Vignaroli G Sagnotti L 2008 Asynchronous Alpine and CorsicandashSardinia rotation J Geophys Res 113 B03104doi1010292007JB005214

Maffione M Speranza F Faccenna C 2009 Bending of the Bolivian orocline andgrowth of the Central Andean plateau paleomagnetic and structural constraintsfrom the Eastern Cordillera (22ndash24degS NW Argentina) Tectonics 28 TC4006doi1010292008TC002402

Malumiaacuten N Olivero EB 2006 El Grupo Cabo Domingo Tierra del Fuegobioestratigrafiacutea paleoambientes y acontecimientos del EocenondashMioceno marinoRev Asoc Geol Argent 61 (2) 139ndash160

Marshak S 1988 Kinematics of orocline and arc formation in thin-skinned orogensTectonics 7 (1) 73ndash86

McFaddenPL 1990Anewfold test forpaleomagnetic studiesGeophys J Int 103 163ndash169Olivero EB Malumiaacuten N 1999 Eocene stratigraphy of southeastern Tierra del Fuego

island Argentina AAPG Bull 83 (2) 295ndash313Olivero EB Malumiaacuten N 2008 MesozoicndashCenozoic stratigraphy of the Fuegian

Andes Argentina Geologica Acta 6 (1) 5ndash18Olivero EB Martinioni DR 2001 A review of the geology of the Argentinian Fuegian

Andes J South Am Earth Sci 14 175ndash188Olivero EB Malumiaacuten N Palamarczuk S Scasso RA 2001 El Cretaacutecico superior-

Paleogeno del aacuterea del Riacuteo Bueno costa atlaacutentica de la Isla Grande de Tierra delFuego Rev Asoc Geol Argen 57 (3) 199ndash218

Olivero EB Malumiaacuten N Palamarczuk S 2003 Estratigrafiacutea del Cretaacutecico superior-Paleoceno del aacuterea de bahiacutea Thetis Andes Fueguinos Argentina acontecimientostectoacutenicos y paleobioloacutegicos Rev Geol Chile 30 245ndash263

286 M Maffione et al Earth and Planetary Science Letters 289 (2010) 273ndash286

Pelayo AM Wiens DA 1989 Seismotectonics and relative plate motion in the ScotiaSea region J Geophys Res 94 7293ndash7320

Ramos VA Aleman A 2000 Tectonic evolution of the Andes In Cordani U et al(Ed) Tectonic evolution of South America Rio de Janeiro Brazil Proceedings ofthe 31 deg International Geological Congress Rio de Janeiro Brazil In-folio ProducaoEditorial pp 635ndash685

Rapalini AE 2007 A paleomagnetic analysis of the Patagonian orocline Geol Acta 5(4) 287ndash294

Rapalini AE Herveacute F Ramos VA Singer S 2001 Paleomagnetic evidence of a verylarge counterclockwise rotation of the Madre de Dios archipelago southern ChileEarth Planet Sci Lett 184 (2) 471ndash487

Rapalini AE Calderoacuten M Herveacute F Cordani U Singer S 2004 First PaleomagneticResults on the Sarmiento Ophiolite Southern Chile implications for the PatagonianOrocline Geosur 2004 Internat Symp on the Geology and Geophysics of theSouthernmost Andes the Scotia Arc and the Antarctic Peninsula Buenos AiresBolletino de Geofisica Teoacuterica ed Applicata vol 45 pp 246ndash249

Rapalini AE Lippai H Tassone A Cerredo ME 2005 An AMS and paleomagneticstudy across the Andes in Tierra del Fuego 6th International Symposium onAndean Geodynamics (ISAG 2005 Barcelona) Extended Abstracts pp 596ndash599

Rochette P 1987 Magnetic susceptibility of the rock matrix related to magnetic fabricstudies J Struct Geol 9 1015ndash1020

Roperch P Chauvin A Calza F Palacios C Parraguez G Pinto L Goguitchaivilli A1997 Paleomagnetismo de las rocas volcaacutenicas del Juraacutesico tardiacuteo al Terciariotemprano de la regioacuten de Ayseacuten (Coyhaique-Cochrane) 8 deg Congreso GeoloacutegicoChileno vol 1 Universidad Catoacutelica del Norte Actas Antofagasta pp 236ndash240

Rossello EA 2005 Kinematics of the Andean sinistral wrenching along the FagnanondashMagallanes Fault Zone (ArgentinandashChile Fueguian Foothills) 6th InternationalSymposium on Andean Geodynamics Barcelona Actas pp 623ndash626

Rossello EA Haring CE Nevistic AV Cobbold PR 2004a Wrenching along theFagnanondashMagallanes fault zone northern foothills of the Fueguian Cordillera(ArgentinandashChile) preliminary evaluation of displacements 32 deg InternationalGeological Congress Firenze CD-Room

Rossello EA Ottone EG Haring CE Nevistic VA 2004b Significado tectoacutenico ypaleoambiental de los niveles carbonosos paleoacutegenos de Estancia La CorrentinaAndes Fueguinos Argentina Asoc Geol Argentina Revista Geologiacutea de laPatagonia (Buenos Aires) vol 59 (4) pp 778ndash784

Rossello EA Haring CE Cardinali G Suaacuterez F Laffitte GA Nevistic AV 2008Hydrocarbons and petroleum geology of Tierra del Fuego Argentina In

Menichetti M Tassone A (Eds) Tierra del Fuego Geology and Geophysics Newadvances and perspective (Geosur 2004) vol 6 (1) Geologica Acta BarcelonaEspantildea pp 69ndash83

Sagnotti L Speranza F Winkler A Mattei M Funiciello R 1998 Magnetic fabric ofclay sediments from the external northern Apennines (Italy) Phys Earth PlanetInter 105 73ndash93

Smalley Jr R Kendrick E Bevis MG Dalziel IWD Taylor F Lauria E Barriga RCasassa G Olivero EB Piana E 2003 Geodetic determination of relative platemotion and crustal deformation across the ScotiandashSouth America plate boundary ineastern Tierra del Fuego Geochem Geophys Geosystems 4 1ndash19

Sonder LJ Jones CH Salyards SL Murphy KM 1994 Vertical-axis rotations in theLas Vegas Valley Shear Zone southern Nevada Paleomagnetic constraints onkinematics and dynamics of block rotations Tectonics 13 (4) 769ndash788

Speranza F Mattei L Sagnotti M 1997 Tectonics of the Umbria-Marche-Romagna Arc(central northern Apennines Italy) new paleomagnetic constraints J Geophys Res102 (B2) 3153ndash3166

Speranza F Maniscalco R Mattei M Di Stefano A Butler RWH Funiciello R 1999Timing and magnitude of rotations in the frontal thrust systems of southwesternSicily Tectonics 18 (6) 1178ndash1197

Speranza F Maniscalco R Grasso M 2003 Pattern of orogenic rotations in central-eastern Sicily implications for the timing of spreading in the Tyrrhenian Sea J GeolSoc Lond 160 183ndash195

Torres-Carbonell PJ Olivero EB Dimieri LV 2008a Control en la magnitud dedesplazamiento de rumbo del Sistema Transformante Fagnano Tierra del FuegoArgentina Rev Geol Chile 35 63ndash79

Torres-Carbonell PJ Olivero EB Dimieri LV 2008b Structure and evolution of theFuegian Andes foreland thrustndashfold belt Tierra del Fuego Argentina Paleogeo-graphic implications J South Am Earth Sci 25 417ndash439

Winslow MA 1982 The structural evolution of theMagallanes Basin and Neotectonicsin the Southernmost Andes In Cradock C (Ed) Antarctic Geoscience Universityof Wisconsin Madison pp 143ndash154

Zachos J Pagani M Sloan L Thomas E Billups K 2001 Trends rhythms andaberrations in global climate 65 Ma to present Science 292 686ndash693

Zijderveld JDA 1967 AC demagnetization of rocks analysis of results In CollinsonDW Creer KM Runcorn SK (Eds) Methods in Paleomagnetism Elsevier NewYork pp 254ndash286

286 M Maffione et al Earth and Planetary Science Letters 289 (2010) 273ndash286

Pelayo AM Wiens DA 1989 Seismotectonics and relative plate motion in the ScotiaSea region J Geophys Res 94 7293ndash7320

Ramos VA Aleman A 2000 Tectonic evolution of the Andes In Cordani U et al(Ed) Tectonic evolution of South America Rio de Janeiro Brazil Proceedings ofthe 31 deg International Geological Congress Rio de Janeiro Brazil In-folio ProducaoEditorial pp 635ndash685

Rapalini AE 2007 A paleomagnetic analysis of the Patagonian orocline Geol Acta 5(4) 287ndash294

Rapalini AE Herveacute F Ramos VA Singer S 2001 Paleomagnetic evidence of a verylarge counterclockwise rotation of the Madre de Dios archipelago southern ChileEarth Planet Sci Lett 184 (2) 471ndash487

Rapalini AE Calderoacuten M Herveacute F Cordani U Singer S 2004 First PaleomagneticResults on the Sarmiento Ophiolite Southern Chile implications for the PatagonianOrocline Geosur 2004 Internat Symp on the Geology and Geophysics of theSouthernmost Andes the Scotia Arc and the Antarctic Peninsula Buenos AiresBolletino de Geofisica Teoacuterica ed Applicata vol 45 pp 246ndash249

Rapalini AE Lippai H Tassone A Cerredo ME 2005 An AMS and paleomagneticstudy across the Andes in Tierra del Fuego 6th International Symposium onAndean Geodynamics (ISAG 2005 Barcelona) Extended Abstracts pp 596ndash599

Rochette P 1987 Magnetic susceptibility of the rock matrix related to magnetic fabricstudies J Struct Geol 9 1015ndash1020

Roperch P Chauvin A Calza F Palacios C Parraguez G Pinto L Goguitchaivilli A1997 Paleomagnetismo de las rocas volcaacutenicas del Juraacutesico tardiacuteo al Terciariotemprano de la regioacuten de Ayseacuten (Coyhaique-Cochrane) 8 deg Congreso GeoloacutegicoChileno vol 1 Universidad Catoacutelica del Norte Actas Antofagasta pp 236ndash240

Rossello EA 2005 Kinematics of the Andean sinistral wrenching along the FagnanondashMagallanes Fault Zone (ArgentinandashChile Fueguian Foothills) 6th InternationalSymposium on Andean Geodynamics Barcelona Actas pp 623ndash626

Rossello EA Haring CE Nevistic AV Cobbold PR 2004a Wrenching along theFagnanondashMagallanes fault zone northern foothills of the Fueguian Cordillera(ArgentinandashChile) preliminary evaluation of displacements 32 deg InternationalGeological Congress Firenze CD-Room

Rossello EA Ottone EG Haring CE Nevistic VA 2004b Significado tectoacutenico ypaleoambiental de los niveles carbonosos paleoacutegenos de Estancia La CorrentinaAndes Fueguinos Argentina Asoc Geol Argentina Revista Geologiacutea de laPatagonia (Buenos Aires) vol 59 (4) pp 778ndash784

Rossello EA Haring CE Cardinali G Suaacuterez F Laffitte GA Nevistic AV 2008Hydrocarbons and petroleum geology of Tierra del Fuego Argentina In

Menichetti M Tassone A (Eds) Tierra del Fuego Geology and Geophysics Newadvances and perspective (Geosur 2004) vol 6 (1) Geologica Acta BarcelonaEspantildea pp 69ndash83

Sagnotti L Speranza F Winkler A Mattei M Funiciello R 1998 Magnetic fabric ofclay sediments from the external northern Apennines (Italy) Phys Earth PlanetInter 105 73ndash93

Smalley Jr R Kendrick E Bevis MG Dalziel IWD Taylor F Lauria E Barriga RCasassa G Olivero EB Piana E 2003 Geodetic determination of relative platemotion and crustal deformation across the ScotiandashSouth America plate boundary ineastern Tierra del Fuego Geochem Geophys Geosystems 4 1ndash19

Sonder LJ Jones CH Salyards SL Murphy KM 1994 Vertical-axis rotations in theLas Vegas Valley Shear Zone southern Nevada Paleomagnetic constraints onkinematics and dynamics of block rotations Tectonics 13 (4) 769ndash788

Speranza F Mattei L Sagnotti M 1997 Tectonics of the Umbria-Marche-Romagna Arc(central northern Apennines Italy) new paleomagnetic constraints J Geophys Res102 (B2) 3153ndash3166

Speranza F Maniscalco R Mattei M Di Stefano A Butler RWH Funiciello R 1999Timing and magnitude of rotations in the frontal thrust systems of southwesternSicily Tectonics 18 (6) 1178ndash1197

Speranza F Maniscalco R Grasso M 2003 Pattern of orogenic rotations in central-eastern Sicily implications for the timing of spreading in the Tyrrhenian Sea J GeolSoc Lond 160 183ndash195

Torres-Carbonell PJ Olivero EB Dimieri LV 2008a Control en la magnitud dedesplazamiento de rumbo del Sistema Transformante Fagnano Tierra del FuegoArgentina Rev Geol Chile 35 63ndash79

Torres-Carbonell PJ Olivero EB Dimieri LV 2008b Structure and evolution of theFuegian Andes foreland thrustndashfold belt Tierra del Fuego Argentina Paleogeo-graphic implications J South Am Earth Sci 25 417ndash439

Winslow MA 1982 The structural evolution of theMagallanes Basin and Neotectonicsin the Southernmost Andes In Cradock C (Ed) Antarctic Geoscience Universityof Wisconsin Madison pp 143ndash154

Zachos J Pagani M Sloan L Thomas E Billups K 2001 Trends rhythms andaberrations in global climate 65 Ma to present Science 292 686ndash693

Zijderveld JDA 1967 AC demagnetization of rocks analysis of results In CollinsonDW Creer KM Runcorn SK (Eds) Methods in Paleomagnetism Elsevier NewYork pp 254ndash286