Geosphere - CONICET Mendoza · Ancient major crustal boundaries among pre-viously amalgamated terranes are inferred to have controlled the development of peripheral rift systems in

Geosphere

doi: 10.1130/GES00572.1 2011;7;219-239Geosphere

Laura Giambiagi, José Mescua, Florencia Bechis, Amancay Martínez and Alicia Folguera AndesPre-Andean deformation of the Precordillera southern sector, southern Central

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ABSTRACT

This paper presents a detailed investiga-tion of the structure and evolution of the Precordillera southern sector (Argentina). We document the development and succes-sive reactivation of regional and discrete structural grain through time, and discuss the existence of a large-scale mechanical anisotropy present in the lithosphere. Our kinematic studies indicate that the Permian orogeny generated a doubly vergent fold-and-thrust belt of transpressive deformation, where strain was partitioned into two differ-ent types of deformation domains. The west-vergent western domain was characterized by partitioned transpression with shorten-ing dominating, and a strike-slip–dominated subdomain. The east-vergent eastern domain was characterized by pure contractional deformation.

Our model for the Late Permian to Early Triassic evolution of the Pre cordillera involves a north-northwest–trending weak-ness zone affected by north-northeast–directed extension, generating an area with transtensional deformation during the Choiyoi volcanism development. Later, dur-ing the Triassic generation of the Cuyana rift basin, the northeast stretching direc-tion was orthogonal to the rift trend, indi-cating pure extensional deformation. We propose a model where the clear parallel-ism between the distribution of an inferred early Paleozoic suture zone, a north-

northwest–trending late Paleozoic belt, and Permian–Triassic rift-related magma-tism indicates the reactivation of a north-northwest–trending long-lived lithospheric weakness zone.

INTRODUCTION

The Andean Mountains compose a linear orogenic belt formed along the contact between the Nazca and South American plates. Although their actual morphology is the result of compres-sional strain at the convergent plate margin dur-ing the Cretaceous–Holocene Andean orogenic cycle, they preserve evidence of previous peri-ods of deformation along the proto-Pacifi c mar-gin of Gondwana. At the studied latitudes, the Argentine Andes include different north-south–trending morphostructural units: from west to east (Fig. 1), these are the Principal Cordillera, the Frontal Cordillera, and the Pre cordillera foreland fold-and-thrust belt. The study area covers the easternmost Frontal Cordillera and the southern sector of the Precordillera, between lat 32°20′S and 33°S (Fig. 1). The Pre cordillera forms a north-south–trending mountain chain, 450 km long and 80 km wide. North of 32°30′S, traditional models for the Precordillera fold-and-thrust belt have involved a thin-skinned tectonic style with complete detachment of a deformed sedimentary cover from a basement dipping gently to the west (Ramos et al., 1986; Allmendinger et al., 1990; von Gosen, 1992). However, in the southern sector, the belt has particular characteristics that refl ect a thick-skinned tectonic style (von Gosen, 1995; Fol-guera et al., 2001; Vergés et al., 2007). In this work we focus our attention on this sector of the Precordillera that appears to have important geological and structural differences from the

northern portion due to the imprint of previous deformational events.

This paper presents a detailed investigation of the Precordillera structure and evolution, focusing on the control of the early Paleozoic structural grain on the subsequent deforma-tional events. We present evidence showing the existence of a Permian doubly verging fold-and-thrust belt, controlled by preexisting early Paleozoic discrete and regional fabrics, and the presence of a preexisting lithospheric weak-ness zone that controlled the location of the Permian–Triassic transtensional system. Our work is based on an integrated study combining fi eld structural analysis, compilation of existing geological maps and data, and extensive fault kinematics analysis provided by fault-slip data from major and mesoscale structures.

TECTONIC SETTING

The prolonged history of convergence against the Gondwana Pacifi c edge resulted in several episodes of contractional, extensional, and strike-slip deformation (Ramos, 1988; Mpodozis and Ramos, 1989). Overprinting relationships between different structures in the Precordillera and the Frontal Cordillera pre-serve evidence of at least four deformational events that took place in early Paleozoic, Early Permian, Late Permian–Middle Triassic, and Miocene–Holocene time.

The early Paleozoic tectonic history of the South American southwestern margin was mainly controlled by this subduction process and the accretion of exotic terranes (Ramos, 1988). At the studied latitudes, this deformation is characterized by two orogenic events; the fi rst occurred during the Middle to Late Ordovician and is referred to as Ocloyic orogeny, and the

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219

Geosphere; February 2011; v. 7; no. 1; p. 219–239; doi: 10.1130/GES00572.1; 16 fi gures.

Pre-Andean deformation of the Precordillera southern sector, southern Central Andes

Laura Giambiagi1,*, José Mescua1,*, Florencia Bechis2,*, Amancay Martínez3,*, and Alicia Folguera4,*1CONICET- CCT (Consejo Nacional de Investigaciones Científi cas y Técnicas–Centro Cientifi co Tecnológico) Mendoza–IANIGLA (Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales), Parque San Martín s/n, 5500 Mendoza, Argentina2IIDyPCA (Instituto de Investigaciones en Diversidad Cultural y Procesos de Cambio), Universidad Nacional de Río Negro, Sarmiento Inferior 3974, CP 8400, San Carlos de Bariloche, Argentina3Departamento de Geología, Facultad de Ciencias Físico-Matemáticas y Naturales, Universidad Nacional de San Luis, Chacabuco 917 (5700), San Luis, Argentina4Servicio Geológico Minero Argentino, Instituto de Geología y Recursos Minerales, Julio A. Roca 651, piso 10, Buenos Aires, Argentina

*E-mails: Giambiagi: [email protected]; Mescua: [email protected]; Bechis: fl [email protected]; Martínez: [email protected]; Folguera: [email protected].



Giambiagi et al.

220 Geosphere, February 2011

second occurred during Devonian time, and is known as Chanic orogeny. The timing of defor-mation of the Chanic orogeny is evidenced by a 385 Ma 40Ar/39Ar date on neocrystalline white mica in a shear zone in the Bonilla area (Davis et al., 2000a).

The late Paleozoic tectonic cycle began with the subduction inception along the present con-tinental margin after the collision of the exotic terranes. In Early Permian time, a widespread contractional event, known as San Rafael orog-eny (Azcuy and Caminos, 1987; Ramos, 1988), generated a wide orogenic belt and crustal thick-ening (Llambías and Sato, 1990; Mpodozis and Kay, 1990). By the end of this compressional phase and before the Permian–Triassic exten-sional one, clockwise block rotations probably took place between 280 and 265 Ma, before the extrusion of the Choiyoi volcanics (Rapalini and Vilas, 1991). These crustal block rotations have been found in the Uspallata-Callingasta Valley and were attributed by Rapalini and Vilas (1991) to dextral strike-slip movements parallel or sub-parallel to the continental margin.

During Late Permian to Early Cretaceous time, rifting was widespread in the South Amer-ican plate. This extensional tectonic regime was a forerunner to the Gondwana fragmen-tation and the South Atlantic Ocean opening (Uliana et al., 1989). During the beginning of this period, between the Late Permian and the Early Triassic, a widespread magmatic event occurred, represented by the Choiyoi Group volcanics and intrusives. The lower part of the

Choiyoi Group represents compositions and geochemical signatures typical of arc magma-tism, whereas the upper acidic magmatics indi-cate the change from a compressive tectonic regime to an extensional one (Llambías et al., 1993). The extensional regime continued during Triassic time and led to the formation of a series of rift systems, with an overall north-northwest trend, formed along the southwestern margin of Gondwana (Charrier, 1979; Uliana et al., 1989). Ancient major crustal boundaries among pre-viously amalgamated terranes are inferred to have controlled the development of peripheral rift systems in southern South America (Ramos et al., 1986; Ramos and Kay, 1991).

When the Mesozoic extensional period was over, by the late Early Cretaceous, a major plate tectonic reorganization took place. By this time, the compressive Andean cycle started (Mpodozis and Ramos, 1989). There is, how-ever, no evidence of this early compression in the studied area, where shortening started dur-ing the Middle to Late Miocene (Irigoyen et al., 2000; Giambiagi et al., 2003). The active thrust front is now located in the eastern border of the Precordillera, near the city of Mendoza, where the Quaternary strata are involved in the Andean deformation.

STRATIGRAPHIC BACKGROUND

Rocks ranging from Cambrian to Pleistocene age crop out in the study area (Figs. 2 and 3). Proterozoic rocks do not crop out in the Precor-

dillera, but U-Pb ages of gneissic xenoliths in Miocene intrusions have shown that the base-ment corresponds to metamorphic rocks of Grenvillian ages (1.1 ± 0.1 Ga; Kay et al., 1996). The Cambrian–Ordovician rocks correspond to metacarbonates and metashales that crop out in the western and eastern sectors, respec-tively. The fi rst are grouped into the Puntilla de Uspallata Formation and the Bonilla Group. They consist of schists, phyllites, quartzites, and greenschists, with lenses and layers of marbles, dolomites, metagabbros, and serpentinites (Keidel, 1939; De Römer, 1964), and the age is assumed to be Cambrian to Ordovician (Varela, 1973; von Gosen, 1995). A greenschist facies metamorphism was deduced by von Gosen (1995), due to incipient to pronounced quartz recrystallization in the Puntilla de Uspallata Formation and the Bonilla Group, respec-tively. Von Gosen assumed that the Puntilla de Uspallata Formation and the Bonilla Group were parts of the same sequences, and proposed that the Bonilla Group may have represented a deeper crustal sequence below the Puntilla de Uspallata Formation and that differences in structural geometries and metamorphism seem to be the effect of different strain and tempera-ture states related to different crustal positions. Mafi c and ultramafi c rock complexes are inter-layered in these metasedimentary rocks north of the study area (Haller and Ramos, 1984; Gerbi et al., 2002). These rocks range in age from Neoproterozoic to Silurian (Davis et al., 2000b). U-Pb zircon ages and Nd isotope data allowed Davis et al. (2000b) to interpret the ultramafi c complex as deep continental crust underplated by ultramafi c and mafi c rocks that underwent granulite facies metamorphism; the mafi c rocks are characterized by shallow-level intrusions and fl ows that underwent lower greenschist facies metamorphism, similar to the Bonilla and Puntilla de Uspallata units. A metasedimentary unit that crops out in the eastern sector of the Cordón del Plata (Heredia et al., 2009) could be tentatively assigned to the Late Ordovi-cian Las Lagunitas Formation that crops out to the south, in the Cordón del Carrizalito range (Tickyj et al., 2009).

In the eastern sector of the Precordillera a passive-margin carbonate succession of Early Cambrian to Middle Ordovician age (Empozada and Cerro Pelado Formations) documents the transition from shallow-marine platform carbon-ate facies to deep-water black shales with olis-toliths of intrabasinal carbonates (Astini et al., 1995; Heredia and Gallardo, 1996). Overlying these rocks, a sequence of clastic sediments has been grouped into the Villavicencio Formation and dated as Silurian to Devonian, although its precise age is uncertain (Cuerda et al., 1993).

100 Km

34°S 34°S

30°S

68°W

30°S

71°WSan Ra fae l

range

FR

ON

TA

LC

OR

DIL

LE

RA

C U Y OBASIN

PR

EC

OR

DIL

LE

RA

AR

EL

LID

RO

CL

API

CNI

RP

Mendoza

Santiago

La Serena

San Juan

CUYANIA

GONDWANA

CHILENIA

Choiyoi Group outcrops

Figure 1. Location map of the study area (modified from Giambiagi and Martínez, 2008), showing the morphostructural units of the Andes between 28°S and 36°S latitude, the inferred boundary between exot ic Chilenia and Cuyania terranes, and the boundary between Cuyania and western Gond-wana (from Ramos, 2004). The box indicates the location of the study area and Figure 3.



Pre-Andean deformation of the Precordillera southern sector

Geosphere, February 2011 221

The early Paleozoic succession is separated from the Carboniferous deposits by an angular unconformity attributed to the Middle to Late Devonian Chañic diastrophism (Furque and Cuerda, 1979; Azcuy and Caminos, 1987). Penn-sylvanian to Early Permian marine clastic depos-its were grouped in the Santa Máxima, Loma de los Morteritos, Jarillal, and El Plata Formations (Rolleri and Criado Roqué, 1969; Caminos, 1965). Carboniferous and Permian granitoids intrude the Carboniferous successions and the Villavicencio Formation (Polanski, 1958).

A thick succession of Permian–Triassic vol-canic rocks and shallow-level batholiths of the Choiyoi Group unconformably overlies the previously deformed rocks. The lower half of the succession is dominated by andesitic lavas and breccias, and the upper half consists of rhyodacitic and lithic pyroclastics and rhyolite fl ows (Martinez, 2005; Giambiagi and Marti-nez, 2008). The lower half comprises typical arc rocks, while upper half consists of sub-alkaline to alkaline rocks that have geochemical characteristics attributed to a magmatic arc of post orogenic character (Martínez, 2005). This

magmatism has been associated with an exten-sional regime, probably related to the fi nal stage of a subduction process (Llambías and Sato, 1995; Llambías, 1999). The injection of basalt into the lower crust, creating a mafi c underplat-ing, contributed to the high volumes of melt and generation of bimodal volcanism (Kay et al., 1989; Llambías et al., 2003).

Early to Late Triassic nonmarine sediments and subordinate volcanic rocks of the Uspallata Group and the Siete Colores Formation were deposited in the Cuyo rift basin. During the

early depositional phase, during the Early to early-Late Triassic (Ávila et al., 2006; Zavattieri and Prámparo, 2006; Spalletti et al., 2008), the sediments were restricted to a series of partially isolated depressions controlled by fault-driven subsidence linked to rifting. This phase was fol-lowed by a period of regional subsidence attrib-uted to thermal decay (Kokogian and Mancilla, 1989; Dellapé and Hegedus, 1995).

After a hiatus of several million years, thrust-ing and uplift of the Principal and Frontal Cordilleras resulted in the development of

ChoiyoiGroup

Bonilla Group-Puntilla de

Uspallata Fm.

Villavicencio Fm.Boca del Ríogranodiorite

Empozada Fm.

Cerro Pelado Fm.

Co. Cacheuta stockCerro Médanos

intrusive

Metarmorphicrocks

Carboniferous-Permianintrusives

El Plata andLoma de los

Morteritos Fms.Jarillal Fm. Santa Máxima Fm.Carboniferous

PROTEROZOIC

Permian

Devonian

Cambrian

Triassic

Neogene

Pleistocene

Precordil leraFrontal Cordil lera

Paleogene

Tectonic events/depositional environmentWestern sector

Divisadero Largoand Papagayos Fms.

UspallataGroup

?

?

Chanic compressive phase/intra-arc basin

Lithospheric extension/rift basin

San Rafael compressivephase

Ocloyic compressive phase

Andean compression/foreland basin

Jurassic-Cretaceous

Passive margin - extensionalphase?

ChoiyoiGroup

ChoiyoiGroup

Back-arc marine basin

*1

*1Middle CambrianOlistolites

Silurian

Ordovician

??

Portezuelo delCenizo Fm.

Siete Colores Fm.

Cerro Redondoandesites

Mogotes Fm.

Quebrada de losSaltitos Fm.

?

Las Lagunitas Fm.

Mariño Fm.

Pájaro Muerto Fm.

?

Mariño Fm.La Pilona Fm.

Metasedimentaryrocks

Metacarbonates

Marine sedimentaryrocks

Intrusives

Intrusives

Marine sedimentaryrocks Volcanics

Continental riftdeposits

Continental deposits

Synorogenic deposits

Quaternary deposits

ylraE

ciozoelaP

Late

c iozoelaP

ylraE

c iozoseM

ci ozo neC

Subvolcanic units

Angular unconformity

Intrusives

Volcanics

Rift basalts

Volcaniclastic deposits

Black shales

Metasedimentaryrocks

High-grademetamorphic rocks

?

Eastern sector

Figure 2. Generalized strati-graphic column of the units that crop out in the Frontal Cordi-llera and western and eastern sectors of the Southern Precor-dillera (from Folguera et al., 2001). Fm.—formation.

Figure 3. Geological-structural map of the southern sector of the Precordillera, southern Central Andes, Argentina. The polyphase deformational history of this sector of the Andes is outlined by the generation time of the structures (different colors represent different defor-mational phases). The area has been divided into two domains, western and eastern, sepa-rated by the Villavicencio fault. C, D, and E are balanced cross sections of the Precordillera (Fig. 4). Faults: 1—Uspallata, 2—Puntilla de Uspallata, 3—Canteras, 4—Bonilla, 5—Burro, 6—Siete Colores, 7—Pampa de Canota, 8—La Polcura, 9—La Manga, 10—Cerro Arenal, 11—Hoyada, 12—Cerro Médanos, 13—Río Blanco, 14—El Salto, 15—Villavicencio, 16—Cerro Pelado, 17—Yaretas, 18—Canota, 19—Del Toro, 20—Guamparito, 21—San Isidro, 22—Melocotón, 23—Divisadero Largo, 24—La Cal, 25—Caracoles, 26—Rincón.



Giambiagi et al.


Cambrian-OrdovicianMetasedimentary rocks

Cambrian-Ordoviciancarbonates

Silurian-Devonian marinesedimentary rocks

Silurian-Devonian intrusives

Permian intrusives

Late Carboniferous -Early Permian marinesedimentary rocks

Permian-Triassic volcanics

Early-Late Tcontinental deposits

riassic

Paleogene continentaldeposits

Neogene-Pleistocenesynorogenic deposits

Quaternary deposits

Reverse fault

Strike-slipfault

Anticline

Syncline

Town site

Normal faultVillage site

Neogene-Quaternarystructures

ylraE

ciozoel aP La

teciozo ela

P

y lraE

cioz os eM

ci ozo neC

Miocene subvolcanic units

Late Permian - MiddleTriassic structures

Early Permian structures

Early Paleozoic shearzones

San Rafael compressionChanic compression

Early Triassic intrusives

Early Permian volcanics

Early-Middle Triassicrift basalts

Early-Middle Triassicvolcaniclastic deposits

Cambrian-Ordovicianblack shales

Early Permian structuresreactivated during

Cenozoic compression

Metasedimentaryunnamed unit

Permian-Triassic structuresreactivated during

Cenozoic compression

MENDOZACITY

C

D

E

USPALLATACITY

POTRERILLOS

10 km

33°00′S

69°20′W

33°00′S

32°30′S

68°50′W69°20′W

32°30′S

Yaretas

1 2

3

4

5

6

7

8

9

10

11

12

1314

15

16

17

18

19

20

21

2223

24

25

26

Fig.

5

Figure 3.





a foreland basin with the accumulation of a 4000-m-thick nonmarine succession during Miocene–Pliocene time (Irigoyen et al., 2000).

METHODOLOGY AND DATA COLLECTION

Field analysis consisted of detailed geo-logical mapping and structural analysis of the southern sector of the Precordillera. Three geo-logical transects are presented to illustrate the major structures of the upper crust (Fig. 4). The cross sections were originally constructed at a scale of 1:25,000, integrating surface geologi-cal and structural data resulting from extensive fi eld surveys. The age of fault activity was bracketed by taking into account the ages of rock units affected and unaffected by fault-ing. In some cases, geometric links between structures allowed the reconstruction of a rela-tive chronology. Palinspastic reconstructions of Andean structures are an important tool for examining and understanding pre-Andean deformation. We systematically back-tilted the Permian–Triassic volcanic rocks and the Trias-sic continental strata to the horizontal position and reconstructed the pre-Andean orientation of structures in order to determine and separate Andean and pre-Andean structures.

To unravel the complex history of deforma-tion of the Precordillera during the pre-Andean period, we investigated the structural grain developed in early Paleozoic rocks. Throughout the study area brittle and ductile deformation features were observed and recorded at out-crop (meso) and map (macro) scales. A detailed structural analysis of the early Paleozoic struc-tural grain within the Precordillera was based on 1009 structural measurements of bedding, cleavage, lineations, shear zones, and meso-scopic folds, taken at 38 stations.

For late Paleozoic to Holocene brittle struc-tures, we measured fault orientation, slip direc-tion, and amount and sense of displacement. We selected 33 sites from the study area for fault kinematics analyses; 735 major (displacement >50 m) and mesoscale (displacement <50 m) faults were measured. Slips on individual faults were integrated to determine the orientation of the principal axes of incremental strain within the area. This technique employs the orientation of the shortening and extension axes (P and T axes) to estimate principal directions of brittle strain (Marrett and Allmendinger, 1990), and provides an approximate orientation of the principal strain axes (Twiss and Unruh, 1998). Principal strain axes have been computed using the moment tensor summation method as imple-mented in the FaultKin 4.3 stereonet program of Allmendinger (2001). We calculated the prin-

cipal axes of shortening (λ3) and extension (λ

1)

for the incremental strain tensor associated with each fault using measurements of fault-plane attitude, slip vector, and sense of displacement. An average kinematic solution for each fault population is calculated using linked Bingham distribution statistics to determine the direc-tional maxima of the λ

3 and λ

1 strain axes for the

fault arrays (Marrett and Allmendinger, 1990).In order to avoid errors when assigning a

time for the major structures, a Permian age was assigned for faults affecting the Carboniferous strata but not the Permian–Triassic volcanics. In the same way, a Permian–Triassic age was assigned for faults affecting the Choiyoi and Uspallata Groups but not the Neogene strata. Other criteria used to establish a relative age relationship among structures include crosscut-ting relationships and successive striae observed on fault surfaces.

STRUCTURAL DOMAINS

At the study latitudes, the Precordillera cor-responds to a bivergent fault system that can be structurally divided into western and east-ern structural domains. The Villavicencio fault is considered to represent the major tectonic boundary between the domains (Fig. 3).

Western Domain

The western domain displays a complex structural framework with orientations rang-ing from west-northwest to north-northeast and very complex crosscutting relationships. The regional structure of this zone consists of several main faults, the Uspallata, Puntilla de Uspallata, Canteras, Bonilla, Burro, Siete Colores, Pampa de Canota, La Polcura, La Manga, and La Car-rera fault system (Fig. 3). The predominant vergence of the faults and folds in this area is toward the west, except faults in the eastern sec-tor of the Cordón del Plata range (Fig. 4E).

The Uspallata fault is an inferred structure, the trace of which is interpreted to extend sub-parallel to the Uspallata Valley with a north-northeast trend. It is inferred to be a west-vergent Cenozoic reverse fault uplifting early Paleozoic metasedimentary rocks and Permian–Triassic volcanics. The north-trending east-vergent Pun-tilla de Uspallata fault uplifts the metasedimen-tary rocks on top of the Carboniferous marine sequences. It is a Permian structure unconform-

ably covered by Permian–Triassic volcanics, indicating that it was not reactivated during the Andean compression, except in its northernmost sector where it uplifts Carboniferous strata on top of Permian–Triassic deposits. A splay of this fault, the Canteras fault, extends parallel to it and uplifts Carboniferous sequences on top of the Triassic deposits.

The Bonilla fault is a reverse structure with north-south trend and vergence toward the west. The fact that it juxtaposes Cambrian–Ordovician deeper crustal rocks (Bonilla Group) on top of shallower Cambrian–Ordovician rocks (Puntilla de Uspallata Formation), and that no Silurian–Devonian rocks have been preserved in the west-ern sector of the Precordillera, allows us to con-sider this fault as an early Paleozoic structure. Its late Paleozoic movement was determined by von Gosen (1995), who documented that this structure uplifts the Cambrian–Ordovician rocks on top of the Carboniferous sediments and is unconformably covered by the Permian–Triassic volcanics north of the study area. The north-trending, west-vergent Burro fault sepa-rates contrasting pre-Carboniferous basement units from the Carboniferous marine deposits. The Permian–Triassic volcanics unconformably cover this fault, revealing its Permian age.

Some of these east- and west-vergent faults are cut by northwest- to north-northwest–trending strike-slip faults throughout the west-ern sector of the Precordillera. They were inter-preted by von Gosen (1995) as older structures that were reutilized as strike-slip faults during the Andean deformation. Kinematic analyses of shear planes associated with these faults, and facies and thickness variations across them in the Permian–Triassic volcanics, allow us to infer that some of them were developed dur-ing the Permian–Triassic extensional event and others correspond to reactivated struc-tures, developed during the Permian orogeny (Giambiagi and Martínez, 2008). However, late Paleozoic deposits are crosscut by dextral north-northwest– and sinistral north-northeast–trending strike-slip faults, which cannot be traced into the Permian–Triassic sequences (von Gosen, 1995). Mutual crosscutting relationships between oppositely dipping faults suggest that these faults developed as a conjugate set. Some of these strike-slip faults cut the thrust faults, and some do not, but they predate the Permian–Triassic volcanic rocks. These observations show that the strike-slip faults are most likely

Figure 4. Balanced cross sections of the southern sector of the Precordillera, showing the relation between Andean structures (black lines), Permian–Triassic (blue lines), and late Paleozoic structures (red lines). See Figure 3 for location.



Giambiagi et al.


Co.Médanosfault

Co.Arenalfault

Villavicenciofault

San Isidrofault

Guamparitofault

Yaretasfault

Co. PeladofaultBurro

faultBonillafaultJarillal

faultDel Toro

faultRincón

fault

Villavicenciofault

Puntillade Uspallata

faultUspallatafault

Bonillafault

Pampa de Canotafault Canota

fault

Divisadero Largofault

Cerro de La Gloriafault system

Potrerillostown

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Uspallatacity

BCross-section C Cross-section E

0

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Melocotónfault

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Cordón del Plata

0 5 km

Pre-Carboniferoussedimentary unnamed unit

Late Paleozoic faultReactivated and non-reactivatedCenozoic fault

Permian-Triassicfault

Structures (last movement)

Early Paleozoic ductileshear zone

Cambian-Ordovician metasedimentary rocks

Cambrian-Ordoviciancarbonates

Silurian-Devonian marinesedimentary rocks


Permian intrusives

Late Carboniferous - Early Permian marinesedimentary rocks

Late Permian - EarlyTriassic volcanics

Early to Late Triassiccontinental deposits

Paleogene-Pleistocenecontinental deposits

Quaternary deposits

Ear

lyP

aleo

zoic

Late

Pal

eozo

icE

arly

Mes

ozoi

c

Cen

ozoi

c

Miocene subvolcanic units

Early Triassic intrusives

Ordovicianmetashales

Precambrian metamorphihc rocks

?

??

? ??

?

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to have developed synchronously with the late Paleozoic thrust faults and they are kinemati-cally related to them, while others are geneti-cally related to the Permian–Triassic extension.

The two most prominent Permian–Triassic identifi ed faults correspond to the La Polcura and La Manga faults (Fig. 3). The La Polcura fault extends for >30 km, has a northwest trend, and a vertical displacement of at least 500 m. Slickensides on exposed fault surfaces indicate two sets of striae (Fig. 5). The oldest set shows a sinistral oblique-slip normal movement and the youngest has a sinistral strike slip. The youngest set is inferred to represent the Andean reactiva-tion of the structure. The La Manga fault is sub-parallel to La Polcura fault and merges toward this structure southward. A detailed analysis of its southeastern termination shows that the fault was reactivated during the Andean shortening. Both faults, with a parallel trend but dipping one against the other, delineate a graben structure that probably has controlled the localization of the andesitic breccias and lavas and the lithic ignimbrites of the middle and upper sections, respectively, of the Choiyoi Group (Fig. 5).

The late Paleozoic and Andean deformational events strongly affected the Cordón del Plata range, with the development of north-northeast– to north-south–trending, east-vergent, base-ment-involved reverse faults. Basement blocks are bounded by reverse faults and are crossed by sinistral strike-slip faults with northwest orien-tation (Fig. 3). The La Carrera fault system has been traditionally recognized as responsible for the Andean uplift of the Cordón del Plata range, which reaches an altitude of 6000 m in the Cerro El Plata (Caminos, 1965; Polanski, 1972; Cortés , 1993). The Cerro Arenal fault is the westernmost of these foreland-directed struc-tures (Figs. 3 and 4). It places the Carboniferous to Permian black shales and granitoids on top of the Permian–Triassic volcanics. The Hoyada fault uplifts a thin sheet of the early Paleozoic phyllites over the Carboniferous sequences, but it is unconformably covered by the Permian–Triassic volcanics, indicating a Permian age without subsequent reactivation. Toward the east, a major sheet of Carboniferous marine deposits has been placed over the Neogene syn-orogenic deposits by activity along the Cerro Médanos fault. This fault trends north-northeast north of La Polcura creek, and has a north-south trend south of it. The change in trend is related to the presence of the Cerro Médanos granitoid. The easternmost faults of the La Carrera fault system, the Río Blanco and El Salto faults, affect the Neogene–Quaternary synorogenic deposits (Folguera et al., 2001; Casa, 2005), and show evidence of Quaternary activity (Fauqué et al., 2000; Casa, 2005).

Eastern Domain

The eastern domain corresponds to a doubly vergent tectonic range, composed of early Paleozoic–Triassic sedimentary rocks and the Permian–Triassic volcanics. The structures within this zone have north-south to north-northeast trends, and compose the Villa vi-cencio, Cerro Pelado, Yaretas, Canota, Del Toro, Guamparito, San Isidro, Melocotón, Divisadero Largo, and La Cal faults (Fig. 4), and two pre-Andean fault systems, named Caracoles and Rincón. The Villavicencio fault separates two areas with contrasting Cambrian–Ordovician history, suggesting activity of this fault since the early Paleozoic. The early Paleozoic geol-ogy west of this fault is composed of metamor-phic rocks. East of the fault, the early Paleozoic stratigraphy is characterized by carbonates and clastic metasedimentary rocks.

The Cerro Pelado fault uplifts the Cambrian–Ordovician carbonates and mudstones and the Silurian–Devonian metasedimentary rocks of the Villavicencio Formation on top of Carbon-iferous rocks (Fig. 6). This Andean brittle fault is associated with an early Paleozoic ductile shear zone parallel to its actual trace. Because the Carboniferous rocks are not affected by this ductile deformation, we interpreted this shear zone to have developed during the early Paleo-zoic orogeny.

In the Yaretas area, the main style of defor-mation consists of a series of north-northeast–trending thrust faults and fault-propagation folds with a basal detachment in the Silurian–Devonian rocks. Crosscutting relationships indicate three stages of deformation: the fi rst occurred during early Paleozoic time before the deposition of the Carboniferous strata. The second stage occurred during the late Paleozoic by formation of an east-southeast–vergent thrust fault that could not be traced into the Permian–Triassic volcanics. The third stage corresponds to Cenozoic reactivation. The Silurian–Devonian and Pennsylvanian sedimentary rocks are cut by east-vergent low- to medium-angle faults that could not be traced into the Permian–Triassic sequence. These faults belong to the Rincón fault system and are interpreted as representing a Permian thin-skinned fold-and-thrust belt with detachment within the Silurian–Devonian sedi-mentary rocks.

KINEMATIC ANALYSIS

Early Paleozoic Deformation

In order to evaluate subsequent reactivations of the early Paleozoic structures during the Early Permian, Permian–Triassic, and Cenozoic

deformational events, we studied the structural grain of these rocks. Two phases of deformation were recognized in the early Paleozoic rocks of the Precordillera western domain, labeled D1 and D2, which were fi rst studied by De Römer (1964), von Gosen (1995), and Cortés et al. (1997). The fi rst phase, D1, was accompanied by low-grade regional metamorphism (M1) and a pervasive foliation (S1), and produced the dominant structural grain within the Cambrian–Ordovician metasedimentary rocks (Fig. 7). The Puntilla de Uspallata Formation exhibits tight to isoclinal folds (F1) with dimensions from several centimeters (Fig. 8A) to hundreds of meters, and axial planes striking north-south to north-northeast and dips toward the east. The Bonilla Group rocks are affected by penetra-tive cleavage planes oriented subparallel to the bedding, striking north-south and dipping to the east (Fig. 7). F1 folds have, at present, north-south to north-northwest trends and are associ-ated with penetrative axial plane foliation (S1) (Fig. 8B) dipping toward the east. An associ-ated mineral stretching lineation (L1) is marked by aligned sericite and clastic muscovite (von Gosen, 1995). F1 folds are generally asymmet-ric with a vergence of top up to the west. On the stereonet, the cleavage and axial planes are subparallel. Both planes defi ne moderately to steeply east dipping surfaces that are parallel to the mean bedding orientation. The D1 structures in the western domain provide evidence for sig-nifi cant northwest-southeast shortening, with tectonic transport toward the northwest.

The second phase, D2, is much less con-spicuous than D1. It includes a pervasive low-temperature foliation (S2), especially in pelitic layers, as well as reverse faults. This phase was previously recognized by von Gosen (1995) in the Uspallata area affecting the Cambrian–Ordovician metasedimentary rocks. The S2 cleavage is developed in the metashales and metasiltstones as a continuous slaty to phyllitic cleavage, and as a spaced cleavage in metasand-stones. It is represented by northeast-trending folds (F2) on scales of decimeters to tens of meters with vergence toward the northwest and southeast, and axial-plane crenulation cleavage (von Gosen, 1995) (Fig. 8C).

In the eastern sector of the Precordillera, the Silurian–Devonian turbiditic rocks were suit-able for studying the tectonic vergence, because the metamorphic processes produced penetra-tive foliations mainly visible in the metapelitic beds and the stratigraphic polarity was easily recognized. The S1 cleavage is present in pelitic lithotypes, while in metasandstones no visible cleavage is developed (Fig. 8D). These metasedi-mentary rocks have undergone variable degrees and styles of deformation throughout the unit,



Giambiagi et al.


with intensity increasing westward. In the east-ern sector, they present penetrative foliation in the fi ne-grained layers that is commonly oblique to bedding. In the central sector, the unit is mod-erately deformed and well foliated, but there are distinct zones of greater and lesser strain. One of the areas of higher strain corresponds to the westernmost outcrop of the unit, uplifted by the Villavicencio fault, where the rocks have highly planar fabric and isoclinal folds. The foliation within these metasedimentary rocks predomi-nantly strikes northeast and dips to the west.

The timing of D1 and D2 deformations is not precisely defi ned. These deformational events were assumed to be related to the Silurian to Early Devonian thermal event deduced by Buggisch et al. (1994) from radiometric K/Ar dating from fi ne-grained mica fractions of the Cambrian–Ordovician metasedimentary rocks (von Gosen, 1995). D1 and D2 seem to have been continuous and are attributed to a single tectonic event.

Late Paleozoic Deformation

The late Paleozoic rocks are affected by thrust faults and folds with wavelengths and ampli-tudes from several centimeters to kilometers (Fig. 9). This brittle deformational event affects the Pennsylvanian to Early Permian marine deposits, but it does not affect the Late Permian to Early Triassic rocks (Fig. 9C), indicating an Early to Middle Permian age. Within the early Paleozoic rocks this deformation is documented by brittle structures that are diffi cult to distin-guish from Andean structures, except when they are unconformably covered by the Permian–Triassic volcanics. The strike of late Paleozoic faults is north-south to north-northwest in the western domain, and north-northeast to north-east in the eastern domain (Fig. 10). Folds trend from north-northwest to northeast, and their axial planes dip either to the west or the east.

The kinematic analysis permits us to estimate the shortening direction for the Permian com-pressive event (Fig. 10). Fault-slip data along the western sector indicate a contractional regime with a west-northwest–trending λ

3. In the east-

ern sector, kinematic analyses indicate a con-tractional regime with a northwest-trending λ

3.

Although the Permian structure results primar-ily from orogen-normal contraction, the strike-slip fault systems affecting the belt indicate a left-lateral strike-slip regime associated with a north-south–trending λ

3 and an east-west–

trending λ1. In order to reconstruct the Early

Permian contractional regime, these shortening directions should be rotated counterclockwise, up to 80° (Rapalini and Vilas, 1991). By doing this, the Permian contraction should have been southwest directed.

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We reconstructed the geometry of the late Paleozoic structure by a palinspastic restoration of Andean structures (Fig. 11A). The reconstruc-tion of Permian thrust and strike-slip faults sug-gests the development of a doubly vergent fold and thrust belt during the San Rafael orogeny (Fig. 11B). Both western and eastern domain faults were oriented parallel to the early Paleo-zoic tectonic grain. This parallelism between basement grain and late Paleozoic structures as well as the contractional and strike-slip regimes being contemporaneous are evidence of regional strain partitioning. We discuss this in the follow-ing section.

Late Permian–Late Triassic Deformation

The Late Permian–Late Triassic represents two extensional events, one concomitant to an important volume of bimodal volcanism during the Late Permian to Early Triassic, and the other characterized by the development of a continen-tal rift basin during the late-Early to early-Late Triassic. The volcanic and volcaniclastic rocks of

the Choiyoi Group and older rocks are affected by normal- and oblique-slip normal faults with west-northwest to northwest trends (Fig. 12). The great thickness and facies variations of these volcanic rocks near these structures (Figs. 13A–13C), and the relationships between structures and the intrusion of plutonic rocks indicate that they are synmagmatic Permian–Triassic struc-tures (Giambiagi and Martinez, 2008).

The interpretation of the fault-slip data from major and mesoscale faults affecting the Permian–Triassic volcanics indicates a homo-geneous orientation of north-northeast maxi-mum stretching direction (Fig. 12). During this deformational event, two populations of major and mesoscale faults developed. The fi rst population strikes west-northwest to northwest and displays normal offset with a minor or no component of strike-slip. The second popula-tion corresponds to north-northwest–trending oblique-slip normal faults, with sinistral off-sets, such as the La Manga fault (Fig. 12). We interpreted both populations of faults to be newly created faults. Although the major north-

northwest –trending oblique-slip faults could be interpreted as reactivation of late Paleozoic structures, the mesoscale oblique faults cannot be assigned to reactivated structures because they only affect the Permian–Triassic volcanics. This suggests that both major and mesoscale oblique slip faults were developed during the Permian–Triassic extension.

Concomitant to the Triassic synrift conti-nental sedimentation and volcanism, west-northwest to north-northwest extensional faults developed (Figs, 13D, 13E). The faults have a dip-slip offset with a minor strike-slip compo-nent (Fig. 14), indicating that they are newly created Triassic normal faults. Two north-northwest–striking normal faults, the Siete Colores and Pampa de Canota, controlled the deposition of Triassic synrift sedimentary and volcaniclastic rocks. Subordinate north-south–trending dextral strike-slip faults were observed. Fault-slip data for this event indicate a north-east stretching direction. This northeast direc-tion rotates to east-northeast close to the city of Mendoza, where a transfer zone between a northern half-graben with west polarity and a southern one with east polarity was previously interpreted (Legarreta et al., 1992).

Andean Deformation

Andean deformation and uplift are the causes of the present elevation of the Precordillera and the Frontal Cordillera. At the latitudes of the study area, this Andean orogenic phase started in Early Miocene time in the Principal Cor-dillera, reaching the study area during the Late Miocene to Early Pliocene (Irigoyen et al., 2000; Giambiagi et al., 2003). Early and late Paleo-zoic faults with a favorable orientation with respect to Andean compressional stresses were reactivated as reverse faults, whereas reactivated Permian–Triassic faults show sinistral displace-ments (Cortés et al., 2006; Terrizzano et al., 2009). In the Precordillera, many of the faults for which we have documented pre-Andean activity affect at present the Permian–Triassic rocks, proving that the Neogene compression reactivated these preexisting structures. These data suggest that the doubly vergent character of the Andean Precordillera fold-and-thrust belt is mainly the result of the reactivation of Paleozoic structures.

DISCUSSION

Late Paleozoic Partitioned Transpression

Deformation in transpressional zones is often compartmentalized into domains where the dif-ferent components of bulk strain are segregated

Early Paleozoiccarbonates

Late Paleozoicmarine deposits

Cerro Pelado

A N S

B N S

Permian-TriassicChoiyoi Group


Early Paleozoicmetamorphic rocks

Cerro Pelado fault

Burro fault

1 km

1 km



Figure 6. Two major late Paleozoic faults reactivated during the Andean compression. (A) Cerro Pelado fault. (B) Burro fault.



Giambiagi et al.


(Molnar, 1992; Tikoff and Teyssier, 1994). Structural and geophysical studies of active con-vergent margins suggest that strain partitioning is so ubiquitous that it must be considered as the normal way for noncoaxial nonplane strain to be accommodated (Fossen et al., 1994; Jones and Tanner, 1995; Holdsworth et al., 1998). During oblique transpressional shortening, a noncoaxial strain component is usually partitioned into dis-crete narrow zones dominated by simple-shear wrenching that delineate broader zones of dis-tributed, largely coaxial, pure-shear deforma-tion (Molnar, 1992; Jones and Tanner, 1995).

Based on structural geometry and overprinting links, two main domains of structures related to the Late Permian orogeny have been recognized (Figs. 15A, 15B). Crosscutting of late Paleozoic structures in the western domain indicates that contractional and strike-slip events occurred syn-chronously and that their different kinematics are

probably joined. This domain is characterized by partitioned transpression with a shortening-dominated subdomain, plus one strike slip-dominated, in the western and eastern regions, respectively. Close to the Villavicencio fault, the mesoscale faults display a strike-slip regime with a north-south principal shortening direction that tends to be parallel to the fault. In contrast, western and eastern sectors show a west to west-northwest principal shortening direction, generally oriented orthogonally to the late Paleozoic faults.

Our kinematic analysis indicates that strain was partitioned into two different types of deformation domains. The western domain was deformed by heterogeneous simple shear. In this sector, the bulk strain compartmentaliza-tion into predominantly strike-slip and dip-slip deformation zones is not complete. Instead, this domain is characterized by strain heterogeneity, with mutually crosscutting strike-slip and dip-

slip faults indicating synchronous shortening and wrenching. The eastern domain, however, was deformed by homogeneous pure shear. The strain compartmentalization model requires the preexistence of one zone of weakness, along which a component of simple shear can be accommodated (Jones and Tanner, 1995). Such weakness might include the Villavicencio shear zone, interpreted to represent a rheological anisotropy (Fig. 11).

Reactivation of Regional and Discrete Structural Grain

Fault reactivation processes play an impor-tant role in upper crustal dynamics. Structural reactivation of discrete structures occurs when displacements are repeatedly focused along well-defined, preexisting features such as faults or shear zones (Holdsworth et al., 1997).

69°00’W

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Figure 7. (A) Structural grain map of early Paleozoic deformation showing Cambrian to Devonian outcrops. (B) Kinematic data of ductile early Paleozoic structures from the western domain. (C) Kinematic data of ductile early Paleozoic structures from the eastern domain.





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Figure 8. Early Paleozoic defor-mation. (A–C) Folding and foliations affecting the Cam-brian–Ordovician Puntilla de Uspallata Formation (A and B), and Bonilla Group (C). (D) S1 foliation in the Silurian–Devo-nian Villavicencio Formation.

Figure 9. Early Permian defor-mation in Pennsylvanian to Early Permian marine sedi-mentary rocks. (A) Folding and incipient development of folia-tion in the Jarillal black shales. (B) Flexural folding in the Jarillal Formation. (C) Angu-lar unconformity between the Permian–Triassic Choiyoi vol-canics and the late Paleozoic Santa Máxima sedimentary rocks folded in an open syncline.



Giambiagi et al.


69°00’W

LATE PALEOZOIC DEFORMATION

Shortening axes(meso-scale fault)

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Giambiagi et al.


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POTRERILLOS

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Theoretical, experimental, and microstructural studies have shown that there are numerous fault and shear zone processes that may lead to weakening of preexisting structures (Handy, 1989; Rutter et al., 2001). Fault zones in the brittle regime are likely to have lower cohe-sive strength and sliding friction than host rock (Donath and Cranwell, 1981).

In previous sections we documented the late Paleozoic partitioned transpression. To account for this transpression, we proposed a model with important reactivation of preexisting planes of weakness in the upper and lower crust. The model of an obliquely convergent margin, where convergence is decoupled into a component of convergence normal to the margin and a shear component taken up by strike-slip movement parallel to it, cannot account for our structural data and kinematic analysis. Del Castello et al. (2005) showed that variable unbalanced topog-raphy and overburden are responsible for highly variable stress orientation. They suggested that temporal evolution of the topography might be key in controlling the transition from gener-ally favored strike slip to relatively more effi -cient pure slip. However, this is not consistent with the observed crosscutting relation between thrusts and strike-slip faults. Instead, we favor a model where thrusts and strike-slip faults develop simultaneously in response to the prin-cipal shortening direction that was not normal to the preexisting fabric, and we argue that the existence of an obliquely convergent margin is not necessary to explain the observed strain par-titioning, though we do not discard it.

The strike and dip of the early Paleozoic foliation in the western domain (azimuth, Az, 1°–11°, dipping steeply toward the east) and in the eastern domain (Az 31°–46°, dipping steeply toward the west), coincides with the trend and dip of the late Paleozoic brittle structures (Figs. 7 and 10). This indicates that the preexisting planes of foliation represent weakness planes that had a strong infl uence on the strike of sub-sequent brittle structures, and also on the dip of these fracture planes. In this way, the double vergence of the late Paleozoic belt is inferred to be primarily controlled by the regional struc-tural grain (Fig. 15). Moreover, fi eld evidence and kinematic data show that some ductile shear zones are bounded by brittle contractional faults of late Paleozoic and Cenozoic time, suggest-ing that early Paleozoic ductile shear zones were reactivated many times during the succes-sive brittle deformational events. Examples of repeatedly reactivated structures are the Bonilla and Villavicencio faults; fi eld evidence indicates that a previous early Paleozoic shear zone was reactivated during the Permian brittle contrac-tional event, and reutilized during the Andean

contractional event. However, not all ductile shear zones reactivated subsequently, and some late Paleozoic contractional faults were con-trolled by the regional fabric and not by discrete structures. This is explained by the fact that reactivation of these shear zones depends pri-marily on the relative strengths of the shear zone and their host rock, and their orientation in the prevailing stress fi eld (Angelier, 1984; White et al., 1986, and references therein).

Lithospheric Reworking

In continental lithosphere, much of the defor-mation is controlled by preexisting anisotropies in the underlying rocks (Dunbar and Sawyer, 1989; Butler et al., 1997; Holdsworth et al., 1997; Tommasi and Vauchez, 2001). This con-trol can be related to regional or discrete fabric reactivations (Coward, 1995; Holdsworth et al., 1997) or reworking of the lithospheric-scale vol-ume of rocks, which corresponds to the repeated focusing of metamorphism, deformation, and magmatism at an orogenic scale (Vauchez et al., 1998; Tommasi and Vauchez, 2001; Holds-worth et al., 2001). Mantle anisotropies, such as rheological heterogeneities and mechanical anisotropies, that developed during orogenic events and were subsequently frozen in the litho-spheric mantle, can survive for a long period of time and play a role in preferential inception of rifting several hundred million years after the orogenesis (Vauchez et al., 1998). These large-scale mechanical anisotropies of the lithospheric mantle are due to the formation of pervasive crystallographic and/or tectonic fabrics pro-duced by the alignment of olivine crystals during major tectonic episodes (Tommasi and Vauchez, 2001). The tectonic inheritance permits the sys-tematic reactivation of ancient tectonic zones by strain localization even if the extension direction is not normal to the structural trend of the belt (Vauchez et al., 1998).

In the previous sections we documented the development and successive reactivation of regional and discrete structural grain through time. Here we discuss the existence of a large-scale mechanical anisotropy present in the lithosphere. The Permian–Triassic evolution

of southwestern South America, between lat 31°S and 34°S, was characterized by the devel-opment of a great amount of volcanism under oblique extensional conditions. This trans-tensional event resulted in the generation of a new complex fault system that concentrated the oblique-slip normal displacement related to a north-northeast–south-southwest stretch-ing (Fig. 15C). On the surface, this fault system corresponds to a fault array of north-northwest–trending sinistral oblique-slip normal faults and north-northwest– to northwest-trending dip-slip normal faults. Pure normal faults are inferred here to represent newly created Permian–Triassic structures, without infl uence of the Paleozoic structural grain. Even though oblique-normal faults are usually related to reactivation of preexistence weakness planes (Bott, 1959), our structural study of the western domain indi-cates that only few north-northwest–trending faults could be related to reactivation of late Paleozoic strike-slip faults. This suggests that the oblique-normal Permian–Triassic faults are newly created structures, not related to the Paleozoic grain. However, a clear parallelism between the north-northwest–trending early Paleozoic deformational zone (related to the inferred suture zone between the Chilenia and Cuyania terranes), and the Permian–Triassic volcanic outcrops has been previously out-lined (Ramos et al., 1986; Kay et al., 1989). In the tectonic model presented here we propose that the inferred early Paleozoic suture zone acted as a lithospheric weakness zone, which induced strain localization and guided litho-spheric reworking during the extensional event. This explains the transtensional deformation along a north-northwest weakness zone during Permian–Triassic time with a north-northeast–oriented extensional direction, and the develop-ment of newly created oblique-normal faults.

The western margin of the Triassic Cuyo basin extends for >700 km and is located above the presumed early Paleozoic bound-ary between the Cuyania and Chilenia ter-ranes (Ramos and Kay, 1991). The results of our kinematic analysis along the Pre cordillera southern sector have implications for the tectonic development of Triassic basins along

Figure 15. Kinematic structural evolution model of the southern sector of the Precordillera. (A) Regional and discrete structural grain in early Paleozoic rocks. (B) Early Permian transpressive deformation. Newly created brittle faults were controlled by the early Paleo-zoic regional and discrete fabric. Our model proposes a northwest contraction direction and the generation of a partitioned transpressional domain west of the Villavicencio fault, and a pure shear compressional domain east of this fault. (C) Proposed model for the Late Permian–Early Triassic transtensional deformation, with newly created dip-slip and oblique-slip extensional faults. (D) Late-Early to early-Late Triassic pure normal faults.



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the southwestern margin of Gondwana. Our geological and kinematic analyses of the Trias-sic normal faults indicate that these structures were not reactivations of preexisting structures. Instead, they were newly created dip-slip nor-mal faults perpendicular to the stretching direc-tion, thus supporting the view that these basins were generated under a pure extensional event (Fig. 16B). Results show that a Late Permian to Early Triassic north-northeast transtensional event was followed by a late-Early to early-Late Triassic northeast pure extensional event (Fig. 16). This change in the extensional direc-tion occurred at the time when an eastward shifting of the locus of deformation took place. In this way, the western border of the Cuyo rift basin represents the easternmost extension of the Permian–Triassic volcanic outcrops. This indicates that the lithospheric strength in the reworking zone increased during the develop-ment of the Permian–Triassic magmatic event, and subsequent extension along the Permian–Triassic volcanic outcrops was not favorable.

Among the principal controls that can increase the lithospheric strength are thinning of the crust, changing of the lower crust compo-

sition, and cooling of the lithosphere (England , 1983; Kusznir and Park, 1984; Sonder and England, 1989; Ranalli, 2000). For our study case, strengthening of the lithosphere could be related to different factors, such as change of the crust composition and thinning of the crust. The Permian–Triassic rhyolite province is on the outer margins of the Gondwana superconti-nent and represents remelting and reworking of crust that was accreted several hundred million years earlier (Kay et al., 1989). This province appears to be related to a relatively hot mantle that yielded basalts that underplated and melted the preexisting crust (Mpodozis and Kay, 1992). Basalt formed in the mantle rises and becomes trapped in the lower crust, resulting in substan-tial crustal melting. This pre–Middle Triassic mafi c crustal underplating could have had a signifi cant effect during the subsequent Middle to Late Triassic extensional event in changing the lower crust composition, and thus increas-ing the lithospheric strength. The geochemical analysis of Permian–Triassic volcanism sug-gests progressive crustal thinning (Kay et al., 1989; Llambías et al., 2003; Martínez, 2005; Kleiman and Japas, 2009), consistent with the

transtensional setting (Giambiagi and Martínez, 2008), which could have increased the litho-spheric strength.

CONCLUSIONS

In this paper we described ductile discrete and regional structural fabrics and brittle faults that were repeatedly reactivated with differ-ent kinematic characteristics during successive deformation episodes affecting the southern sector of the Precordillera in the southern Cen-tral Andes. Based on structural geometry, over-printing relationships, and kinematic analysis, we recognize four main groups of structures related to the different stages of the tectonic evolution of this portion of the Andes. The Cambrian–Quaternary units of the Pre cordillera contain complex patterns of both super-imposed and reactivated structures that allow us to unravel the deformational histories of the Andes at lat 32°S–33°S. Considerable varia-tions in structural styles in the southern sector of the Precordillera are the results of a series of superimposed deformational events from the early Paleozoic to the Holocene. The tectonic

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Giambiagi et al.


inheritance of these older structures accounts for contrasting structural styles along strikes and between the Cordillera Frontal and eastern and western domains of the Precordillera.

The first deformation episode is related to west-east to northwest-southeast crustal shortening that controlled the development of regional and discrete structural fabric during the early Paleozoic. The regional fabric corresponds to north to north-northeast foliation dipping east in the western domain of the Precordillera, and north-northeast to northeast foliation dipping west in the eastern domain. The north-south–trending, west-dipping shear zones present in the western domain represent the discrete fab-ric, while the regional foliation represents the regional fabric. These early Paleozoic basement anisotropies have played a signifi cant role in subsequent structural development of the area.

The Early Permian San Rafael orogeny was responsible for the west-northwest to north-west noncoaxial contractional deformation and the generation of a doubly vergent fold-and-thrust belt. The reactivation of early Paleozoic regional and discrete fabrics during the late Paleozoic orogeny generated a partitioned transpressional system. Our study shows that both the regional and discrete early Paleozoic ductile fabrics localized subsequent brittle deformation. The fabric with steep north-trending foliation in the western domain and steep northeast-trending foliation in the east-ern domain controlled the trend and dip of late Paleozoic faults; some of the early Paleozoic shear zones were reactivated during this brittle deformational event.

The Permian–Triassic evolution in this sector of the Andes was characterized by the devel-opment of a great amount of volcanism under oblique extensional conditions. Kinematic analy-ses of faults developed during the extrusion of this volcanism suggest that the oblique-rifting setting was primarily controlled by the presence of a preexisting anisotropy within the litho-sphere. A clear parallelism between the distribu-tion of an inferred suture zone between two ter-ranes accreted against South America during the early Paleozoic, a north-northwest–trending late Paleozoic belt developed during the San Rafael orogenic phase, and Permian–Triassic rifting, suggests that tectonic inheritance permitted the reactivation of a north-northwest–trending long-lived lithospheric weakness zone.

ACKNOWLEDGMENTS

This research was supported by grants from the Agencia Nacional de Promoción Científi ca y Tec-nológica (PICT 07-10942) and CONICET (Consejo Nacional de Investigaciones Científi cas y Técnicas; PIP 5843 and PIP 638) to Giambiagi. We thank M. Etcheverría, M. Tunik, S. Barredo, V. Ramos,

N. Heredia, J.L. Alonso, G. Gallastegui, J. García Sansegundo, P. Farías, R. Rodríguez, and A. Zavat-tieri for helpful discussions and comments, and two anonymous reviewers for their critical and helpful suggestions.

REFERENCES CITED

Allmendinger, R.W., 2001, FaultKinWinFull version 1.2.2. A program for analyzing fault slip data for WindowsTM computers: http://www.geo.cornell.edu/geology/faculty/RWA/programs.html.

Allmendinger, R.W., Figueroa, D., Snyder, D., Beer, J., Mpodozis, C., and Isacks, B.L., 1990, Foreland short-ening and crustal balancing in the Andes at 30°S latitude: Tectonics, v. 9, p. 789–809, doi: 10.1029/TC009i004p00789.

Angelier, J., 1984, Tectonic analysis of fault slip data sets: Journal of Geophysical Research, v. 89, p. 5835–5848, doi: 10.1029/JB089iB07p05835.

Astini, R.A., Benedetto, J.L., and Vaccari, N.E., 1995, The early Paleozoic evolution of the Argentina Pre-cor dillera as a Laurentian rifted, drifted and collided terrane: A geodynamic model: Geological Society of America Bulletin, v. 107, p. 253–273, doi: 10.1130/0016-7606(1995)107<0253:TEPEOT>2.3.CO;2.

Ávila, J.N., Chemale, F., Jr., Cingolani, C.A., Armstrong, R., and Kawashita, K., 2006, Combined stratigraphic and isotopic studies of Triassic strata, Cuyo Basin, Argen-tine Precordillera: Geological Society of America Bul-letin, v. 118, p. 1088–1098, doi: 10.1130/B25893.1.

Azcuy, C.L., and Caminos, R., 1987, Diastrofi smo, in Archangelsky, S., ed., El sistema carbonífero en la República Argentina: Córdoba, Argentina, Academia Nacional de Ciencias, p. 239–252.

Bott, M., 1959, The mechanisms of oblique slip faulting: Geological Magazine, v. 96, p. 109–117, doi: 10.1017/S0016756800059987.

Buggisch, W., von Gosen, W., Henjes-Kunst, F., and Krumm, S., 1994, The age of early Paleozoic deformation and metamorphism in the Argentine Precordillera—Evi-dence from K-Ar data: Zentralblatt für Geologie und Paläontologie, Teil, v. 1, p. 275–286.

Butler, R.W.H., Holdsworth, R.E., and Lloyd, G.E., 1997, The role of basement reactivation in continental defor-mation: Geological Society of London Journal, v. 154, p. 69–71, doi: 10.1144/gsjgs.154.1.0069.

Caminos, R., 1965, Geología de la vertiente oriental del Cordón del Plata, Cordillera Frontal de Mendoza: Asociación Geológica Argentina, Revista, no. 20, p. 351–392.

Casa, A.L., 2005, Geología y neotectónica del piedemonte oriental del cordón del Plata en los alrededores de El Salto [Trabajo Final de Licenciatura]: Buenos Aires, Argentina, Universidad de Buenos Aires, 157 p.

Charrier, R., 1979, El Triásico de Chile y regiones adya-centes de Argentina: una reconstrucción paleogeográ-fi ca y paleoclimática: Comunicaciones, v. 26, p. 1–37.

Cortés, J.M., 1993, El frente de corrimiento de la Cor-dillera Frontal y el extremo sur del valle de Uspallata, Mendoza, in Congreso Geológico Argentino and Congreso de Exploración de Hidrocarburos, 12th, Volume 3: Mendoza, Asociación Geológica Argen-tina, p. 168–178.

Cortés, J.M., Casa, A., Pasini, M.M., Yamin, M.G., and Ter-rizzano, C.M., 2006, Fajas oblicuas de deformación geotectónica en Precordillera y Cordillera Fron-tal (31°30′–33°30′LS). Controles paleotectónicos: Revista de la Asociación Geológica Argentina, v. 61, p. 639–646.

Cortés, J.M., González Bonorino, G., Koukharsky, M., Pereyra, F., and Brodtkorb, A., 1997, Hoja geológica 3369–09, Uspallata, Mendoza: Buenos Aires, Servicio Geológico Minero Argentino, 142 p.

Coward, M.P., 1995, Inversion tectonics, in Hancock, P.R., ed., Continental deformation: New York, Pergamon, p. 289–304.

Cuerda, A., Cingolani, C., and Bordonaro, O., 1993, Las secuencias sedimentarias eopaleozoicas, in Ramos, V.A., ed., Geología y Recursos Naturales de Men-doza, Congreso Geológico Argentino and Congreso de

Exploración de Hidrocarburos, Relatorio, Volume 1, Mendoza: Buenos Aires, Asociación Geológica Argen-tina, p. 21–30.

Davis, J.S., Roeske, S.M., McClelland, W., and Kay, S.M., 2000a, Mafi c and ultramafi c crustal fragments of the southwestern Precordillera terrane and their bearing on tectonic models of the early Paleozoic in western Argentina: Geology, v. 28, p. 171–174, doi: 10.1130/0091-7613(2000)28<171:MAUCFO>2.0.CO;2.

Davis, J.S., Roeske, S.M., McClelland, W., and Snee, L.W., 2000b, Closing the ocean between the Pre cordillera terrane and Chilenia: Early Devonian ophiolite emplacement and deformation in the southwest Pre-cordillera, in Ramos, V.A., and Keppie, J.D., eds., Laurentia-Gondwana connections before Pangea: Geo-logical Society of America Special Paper 336, p. 115–138, doi: 10.1130/0-8137-2336-1.115.

Del Castello, M., McClay, K.R., and Pini, G.A., 2005, Role of preexisting topography and overburden on strain partitioning of oblique doubly vergent conver-gent wedges: Tectonics, v. 24, TC6004, doi: 10.1029/2005TC001816.

Dellapé, D., and Hegedus, A., 1995, Structural inversion and oil occurrence in the Cuyo basin of Argentina, in Tankard, A.J., et al., eds., Petroleum basins of South American: American Association of Petroleum Geolo-gists Memoir 62, p. 359–367.

De Römer, H.S., 1964, Sobre la geología de la zona de El Choique, entre el cordón de los Farallones y el cordón de Bonilla, quebrada de Santa Elena, Uspallata (pro-vincia de Mendoza): Asociación Geológica Argentina Revista, v. 19, p. 9–18.

Donath, F.A., and Cranwell, J., 1981, Probabilistic treatment of faulting in geological media, in Carter, N.L., et al., eds., Mechanical behaviour of crust rocks: The Handin Volume: American Geophysical Union Geophysical Monograph 24, p. 231–241.

Dunbar, J.A., and Sawyer, D.S., 1989, How preexisting weaknesses control the style of continental breakup: Journal of Geophysical Research, v. 94, p. 7278–7292, doi: 10.1029/JB094iB06p07278.

England, P., 1983, Constraints on the extension of continen-tal lithosphere: Journal of Geophysical Research, v. 88, p. 1145–1152, doi: 10.1029/JB088iB02p01145.

Fauqué, L., Cortés, J.M., Folguera, A., and Etcheverría, M., 2000, Avalanchas de rocas asociadas a neotec-tónica en el valle del río Mendoza, al sur de Uspallata: Asociación Geológica Argentina Revista, v. 55, p. 419–423.

Folguera, A., Etcheverria, M., Pazos, P., Giambiagi, L., Cortés , J.M., Fauqué, L., Fusari, C., and Rodriguez, M.F., 2001, Descripción de la Hoja Geológica Potrerillos (1:100.000): Subsecretaría de Minería de la Nación, Dirección Nacional del Servicio Geológico, 262 p.

Fossen, H., Tikoff, B., and Teyssier, C., 1994, Strain model-ling of transpressional and transtensional deformation: Norsk Geologisk Tidsskrift, v. 74, p. 134–145.

Furque, G., and Cuerda, A.J., 1979, Precordillera de La Rioja, San Juan y Mendoza, in Turner, J.C., ed., Geología Regional Argentina: Academia Nacional de Ciencias Córdoba, p. 455–522.

Gerbi, C., Roeske, S.M., and Davis, J.S., 2002, Geology and structural history of the southwest Precordillera mar-gin, northern Mendoza Province, Argentina: Journal of South American Earth Sciences, v. 14, p. 821–835, doi: 10.1016/S0895-9811(01)00080-3.

Giambiagi, L., Ramos, V.A., Godoy, E., Alvarez, P.P., and Orts, S., 2003, Cenozoic deformation and tectonic style of the Andes, between 33° and 34° south latitude: Tec-tonics, v. 22, 1041, doi: 10.1029/2001TC001354.

Giambiagi, L., and Martinez, A.N., 2008, Permo-Triassic oblique extension in the Uspallata-Potrerillos area, western Argentina: Journal of South American Earth Sciences, v. 26, p. 252–260, doi: 10.1016/j.jsames.2008.08.008.

Haller, M.J., and Ramos, V.A., 1984, Las ofi olitas fama-tinianas (Eopaleozoico) de las Provincias de San Juan y Mendoza, in Proceedings, Congreso Geológico Argentino, 9th, Volume 2: Buenos Aires, Asociación Geológica Argentina, p. 66–83.

Handy, M.R., 1989, Deformation regimes and the rheo-logical evolution of fault zones in the lithosphere:





The effects of pressure, temperature, grain size and time: Tectonophysics, v. 163, p. 119–152, doi: 10.1016/0040-1951(89)90122-4.

Heredia, N., Faria, P., García Sansegundo, J., and Giambiagi, L., 2009, El basamento paleozoco de la Cordillera Frontal de los Andes en el Cordón del Plata (Provin-cia de Mendoza, Argentina), in Proceedings, Congreso Geológico Chileno, 12th, Santiago, p. S9–S035.

Heredia, S., and Gallardo, G., 1996, Las megaturbiditas de la Formación Empozada: un modelo interpretativo para el Ordovícico turbidítico de la Precordillera Argentina: Revista Geológica de Chile, v. 23, p. 17–34.

Holdsworth, R.E., Butler, C.A., and Roberts, A.M., 1997, The recognition of reactivation during continental deformation: Geological Society of London Journal, v. 154, p. 73–78, doi: 10.1144/gsjgs.154.1.0073.

Holdsworth, R.E., Strachan, R.A., and Dewey, J.F., eds., 1998, Continental transpressional and transtensional tectonics: Geological Society of London Special Pub-lication 135, 408 p.

Holdsworth, R.E., Hand, M., Miller, J.A., and Buick, I.S., 2001, Continental reactivation and reworking: an intro-duction, in Miller, J.A., et al., eds., Continental reacti-vation and reworking. Geological Society of London Special Publication 184, p. 1–12.

Irigoyen, M.V., Buchan, K.L., and Brown, R.L., 2000, Mag-netostratigraphy of Neogene Andean foreland-basin strata, lat 33°S, Mendoza Province, Argentina: Geologi-cal Society of America Bulletin, v. 112, p. 803–816, doi: 10.1130/0016-7606(2000)112<803:MONAFS>2.0.CO;2.

Jones, R.R., and Tanner, P.W.G., 1995, Strain partitioning in transpression zones: Journal of Structural Geology, v. 17, p. 793–802, doi: 10.1016/0191-8141(94)00102-6.

Kay, S.M., Ramos, V.A., Mpodozis, C., and Sruoga, P., 1989, Late Paleozoic to Jurassic silicic magmatism at the Gond-wana margin: Analogy to middle Proterozoic in North America?: Geology, v. 17, p. 324–328, doi: 10.1130/0091-7613(1989)017<0324:LPTJSM>2.3.CO;2.

Kay, S.M., Orell, S., and Abruzzi, J.M., 1996, Zircon and whole rock Nd-Pb isotopic evidence for a Grenville age and a Laurentian origin for the basement of the Precordilleran terrane in Argentina: Journal of Geol-ogy, v. 104, p. 637–648, doi: 10.1086/629859.

Keidel, J., 1939, Las estructuras de corrimientos paleozoicos de la sierra de Uspallata. (provincia de Mendoza): Physis, v. 14, p. 3–96.

Kleiman, L.E., and Japas, M.S., 2009, The Choiyoi vol-canic province at 34°S–36°S (San Rafael, Mendoza, Argentina): Implications for the late Palaeozoic evo-lution of the southwestern margin of Gondwana: Tectonophysics, v. 473, p. 283–299, doi: 10.1016/j.tecto.2009.02.046.

Kokogian, D., and Mancilla, O., 1989, Análisis estratigrá-fi co secuencial de la Cuenca Cuyana, in Chebli, G., and Spalleti, L., eds., Cuencas Sedimentarias Argentinas: Universidad Nacional de Tucumán serie Correlación Geológica, v. 6, p. 169–210.

Kusznir, N.J., and Park, R.G., 1984, Intraplate lithosphere deformation and the strength of the lithosphere: Royal Astronomical Society Geophysical Journal, v. 79, p. 513–538.

Legarreta, L., Kokogian, D.A., and Dellapé, D.A., 1992, Estructuración terciaria de la Cuenca Cuyana: ¿cuánto de inversión tectónica?: Asociación Geológica Argen-tina Revista, v. 47, p. 83–86.

Llambías, E., 1999, El magmatismo gondwánico durante el Paleozoico superior—Triásico, in Caminos, R., and Panza, J., eds., Geología Argentina: Servicio Geológico Minero Argentino, Buenos Aires, Anales, v. 29, p. 373–376.

Llambías, E., and Sato, A., 1990, El batolito de Colangüil (29–31°S) Cordillera Frontal de Argentina: estructura y marco tectónico: Revista de la Asociación Geológica Argentina, v. 17, p. 99–108.

Llambías, E., and Sato, A., 1995, El batolito de Colangüil: transición entre orogénesis y anorogénesis: Asociación Geológica Argentina Revista, v. 50, p. 111–131.

Llambías, E.J., Kleiman, L.E., and Salvarredi, J.A., 1993, El magmatismo gondwánico, in Ramos, V.A., ed., Geología y Recursos Naturales de Mendoza, Congreso Geológico Argentino and Congreso de Exploración de Hidrocarburos, 12th, Mendoza: Asociación Geológica Argentina, Relatorio I, p. 53–64.

Llambías, E., Quenardelle, S., and Montenegro, T., 2003, The Choiyoi Group from central Argentina: A sub-alkaline transitional to alkaline association in the craton adjacent to the active margin of the Gondwana conti-nent: Journal of South American Earth Sciences, v. 16, p. 243–257, doi: 10.1016/S0895-9811(03)00070-1.

Martinez, A.N., 2005, Secuencias volcánicas Permo-Triásicas de los cordones del Portillo y del Plata, Cor-dillera Frontal, Mendoza: su interpretación tectónica [Ph.D. thesis]: Buenos Aires, Universidad de Buenos Aires, 275 p.

Marrett, R., and Allmendinger, R.W., 1990, Kinematic análi-sis of fault-slip data: Journal of Structural Geology, v. 12, p. 973–986, doi: 10.1016/0191-8141(90)90093-E.

Molnar, P., 1992, Brace-Goetze strength profi les, the par-titioning of strike-slip and thrust faulting at zones of oblique convergences, and the stress-heat fl ow paradox of the San Andreas fault, in Evans, B., and Wong, T.-F., eds., Fault mechanics and transport properties of rocks: London, Academic Press, p. 435–459.

Mpodozis, C., and Kay, S.M., 1990, Provincias magmáti-cas ácidas y evolución tectónica de Gondwana: andes Chilenos (28°-31°S): Revista Geológica de Chile, v. 17, p. 153–180.

Mpodozis, C., and Kay, S.M., 1992, Late Paleozoic to Tri-assic evolution of the Gondwana margin: Evidence from Chilean Frontal Cordillera batholiths (28°S to 31°S): Geological Society of America Bulletin, v. 104, p. 999–1014, doi: 10.1130/0016-7606(1992)104<0999:LPTTEO>2.3.CO;2.

Mpodozis, C., and Ramos, V.A., 1989, The Andes of Chile and Argentina, in Ericksen, G.E., et al., eds., Geology of the Andes and its relation to hydrocarbon and mineral resources: Circum-Pacifi c Council for Energy and Min-eral Resources Earth Science Series, v. 11, p. 59–90.

Polanski, J., 1958, El bloque varíscico de la Cordillera Frontal de Mendoza: Asociación Geológica Argentina Revista, v. 12, p. 165–196.

Polanski, J., 1972, Descripción geológica de la Hoja 24 a-b—Cerro Tupungato, provincia de Mendoza: Buenos Aires, Argentina, Dirección Nacional de Geología y Minería Boletin 128, p. 1–110.

Ramos, V.A., 1988, The tectonics of the Central Andes: 30° to 33° S latitude, in Clark, S.P., et al., eds., Processes in continental lithospheric deformation: Geological Soci-ety of America Special Paper 218, p. 31–54.

Ramos, V.A., 2004, Cuyania, an exotic block to Gondwana: Review of a historical success and the present prob-lems: Gondwana Research, v. 7, p. 1009–1026, doi: 10.1016/S1342-937X(05)71081-9.

Ramos, V.A., and Kay, S., 1991, Triassic rifting and asso-ciated basalts in the Cuyo basin, central Argentina, in Harmon, R., and Rapela, C., eds., Andean magmatism and its tectonic setting: Geological Society of America Special Paper 265, p. 79–91.

Ramos, V., Jordan, T., Allmendinger, R., Mpodozis, C., Kay, S.M., Cortés, J.M., and Palma, M.A., 1986, Paleozoic terranes of the Central Argentine–Chilean Andes: Tectonics, v. 5, p. 855–880, doi: 10.1029/TC005i006p00855.

Ranalli, G., 2000, Rheology of the crust and its role in tectonic reactivation: Journal of Geodynamics, v. 30, p. 3–15, doi: 10.1016/S0264-3707(99)00024-1.

Rapalini, A.E., and Vilas, J.F., 1991, Tectonic rotations in the late Palaeozoic continental margin of southern South America determined and dated by palaeomagnetism: Geophysical Journal International, v. 107, p. 333–351, doi: 10.1111/j.1365-246X.1991.tb00829.x.

Rolleri, E.O., and Criado Roque, P., 1969, Geología de la provincia de Mendoza: Jornadas Geológicas Argen-tinas, 4th, Actas, v. 2, p. 1–60.

Rutter, E.H., Holdsworth, R.E., and Knipe, R.J., 2001, The nature and tectonic signifi cance of fault-zone weaken-ing: An introduction, in Holdsworth, R.E., et al., eds., The nature and tectonic signifi cance of fault zone weakening: Geological Society of London Special Publication 186, p. 1–11.

Sonder, L.J., and England, P.C., 1989, Effects of a temper-ature-dependent rheology on large-scale continental extension: Journal of Geophysical Research, v. 94, p. 7603–7619, doi: 10.1029/JB094iB06p07603.

Spalletti, L.A., Fanning, C.M., and Rapela, C.W., 2008, Dat-ing the Triassic continental rift in the southern Andes: The Potrerillos Formation, Cuyo Basin, Argentina: Geologica Acta, v. 6, p. 267–283.

Terrizzano, C.M., Cortés, J.M., Fazzito, S.Y., and Rapalini, A.E., 2009, Neotectonic transpressive zones in Precor-dillera Sur, Central Andes of Argentina: A structural and geophysical investigation: Neues Jahrbuch für Geologie und Paläontologie, v. 253, p. 103–114, doi: 10.1127/0077-7749/2009/0253-0103.

Tickyj, H., Rodríguez Raising, M., Cingolani, C.A., Alfaro, M., and Uriz, N., 2009, Graptolitos Ordovícicos en el sur de la Cordillera Frontal de Mendoza: Asociación Geológica Argentina Revista, v. 64, p. 295–302.

Tikoff, B., and Teyssier, C., 1994, Strain modeling of dis-placement-fi eld partitioning in transpression orogens: Journal of Structural Geology, v. 16, p. 1575–1588, doi: 10.1016/0191-8141(94)90034-5.

Tommasi, A., and Vauchez, A., 2001, Continental rifting parallel to ancient collisional belts: An effect of the mechanical anisotropy of the lithospheric mantle: Earth and Planetary Science Letters, v. 185, p. 199–210, doi: 10.1016/S0012-821X(00)00350-2.

Twiss, R.J., and Unruh, J.R., 1998, Analysis of fault slip inversions: Do they constrain stress or strain rate?: Journal of Geophysical Research, v. 103, p. 12,205–12,222, doi: 10.1029/98JB00612.

Uliana, M.A., Biddle, K., and Cerdán, J., 1989, Mesozoic extension and the formation of Argentine sedimentary basins, in Tankard, A., and Balkwill, H.R., eds., Exten-sional tectonics and stratigraphy of the North Atlantic margins: American Association of Petroleum Geolo-gists Memoir 46, p. 599–614.

Varela, R., 1973, Estudio geotectónico del extremo sudoeste de la Precordillera de Mendoza, República Argen-tina: Asociación Geológica Argentina Revista, v. 28, p. 241–267.

Vauchez, A., Tommasi, A., and Barruol, G., 1998, Rheologi-cal heterogeneity, mechanical anisotropy and deforma-tion of the continental lithosphere: Tectonophysics, v. 296, p. 61–86, doi: 10.1016/S0040-1951(98)00137-1.

Vergés, J., Ramos, V.A., Meigs, A., Cristallini, E., Bettini, F.H., and Cortés, J.M., 2007, Crustal wedging triggering recent deformation in the Andean thrust front between 31°S and 33°S: Sierras Pampeanas-Precordillera interaction: Journal of Geophysical Research, v. 112, B03S15, doi: 10.1029/2006JB004287.

von Gosen, W., 1992, Structural evolution of the Argen-tine Precordillera: Río San Juan section: Journal of Structural Geology, v. 14, p. 643–667, doi: 10.1016/0191-8141(92)90124-F.

von Gosen, W., 1995, Polyphase structural evolution of the southwestern Argentine Precordillera: Journal of South American Earth Sciences, v. 8, p. 377–404, doi: 10.1016/0895-9811(95)00021-7.

White, S.H., Bretan, P.G., and Rutter, E.H., 1986, Fault-zone reactivation: Kinematics and mechanics: Royal Society of London Philosophical Transactions, v. 317, p. 81–97.

Zavattieri, A.M., and Prámparo, M.B., 2006, Fresh-water algae from the Upper Triassic Cuyana basin of Argentina: Palaeoenvironmental implications: Palaeon tology, v. 49, p. 1185–1209, doi: 10.1111/j.1475-4983.2006.00596.x.

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