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A history of Proterozoic terranes in southern South

America: From Rodinia to Gondwana

C. Casquet ,* w Rapela R.J. Pankhurst c, E.G. Baldo C. Galindo C.M. Fanning J.A. Dahlquist J. Saavedra

aDepartamento de Petrologia Geoquimca, IEO (Unversdad Complutense, CSIC), 28040 Madrd, Spanb Cent de Investgacones Geolgcas (CONICET-UNLP), 1900 L Plata, ArgentnaC 'stng Reseah Assocate, Brtsh Geologcal S, Keyorth Nottngham NG12 S Unted Kngdomd CICTERRA (CONICET-UNC), 5000 Crdoba, ArgentnaeResearch School of Earth Scences, The Australan Natona l Unvers, Canbera, Australa

Insttuto de Agbologa Recursos Natuales CSIC, 37071 Salamanca, Span

KEYORartrz

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W aa ay

The role played by Paleoproterozoic cratons in southe South America from the Mesoproterozoic to the Early Cmbrin is reconsidered here. This peiod nvolved protracted contnental amal

gamaon that led to formaon of the supercontnent odinia, folowed by N eoproterozoic con nental

break-up, with the consequent opening of Clymene and Iapetus oceans, and nally continental

re-assembly as Gondwana through complex oblique collisions in the Late Neoproterozoic to Early

Cambrian. The evidence for this is based mainly on a combination of precise U-Pb SHMP datingand radiogenic isotope data for igneous and metamophic rocks from a large area extending from the

Rio de la Plata craton n the east to the Argentne Precordllera n the west nd as fr north as Arequipa

in Peru. Our intepretaon of the pleogeograpicl and geodynmic evolution nvokes a hypothetical

Paleoproterozoic block (M) embracng basement ulmately older thn 1.7 Ga in the Weste Sieras

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1 Introduction

The role of southe South merican cratons in Rodinia recon

structions, particularly those of mazonia and Rio de la Plata, isa long-debated issue oman, 1991; Dalziel, 1997; Weil et a.,

1998; Omarini et a., 1999; Loewy et a., 2003; Li et a., 2008;Trindade et a., 2006; Cordani et a., 2010; Santosh et a., 2009,among others). The debate was stimulated by the ideas that (1)

Easte Laurentia was juxtaposed to mazonia and the io de laPlata craton in Rodinia at ca. 1 as a result of Grenvillian orogeny,and that (2) Laurentia ried away to its present position in thenorthern hemisphere (present coordinates) in the Late Neo

proterozoic, accompanied by opening of the Iapetus ocean and thenal amalgamation of West Gondwana oman, 1991; Dalziel,

1997 and references therein). However, the models derived fromthese studies took only minor account of the relatively small

outcrops with Paleoproterozoic basement south of mazonia and

west of the io de la Plata craton. The wealth of data now availablefrom detrital zircon ages and crystallization ages of many igneousrocks have transformed this situation. These outcrops are scatteredover a very large region (g. 1), with an extensive cover of

Mesozoic to Cenozoic sedimentary rocks, which hinders correlation between them. The Paleoproterozoic rocks crop out as inliers

within the ndean belt (e.g., the requipa block in Peru; Loewyet a., 2004, and references therein; Casquet et a., 2010), in the

ndean foreland (Sierra de Maz in the Western Sierras Pampeanasof central rgentina; Casquet et a., 2006, 2008a) and in the stable

mainland far om the ndean active margin (e.g., io Apa andParagu in southe Brazil ; Cordani et a., 2010) ig. 1). Otheroccurrences may be hidden farther south in rgentine Patagonia. consequence, the role of these outcrops in Rodinia reconstructionshas been largely underestimated, hindering understanding of the

role played by cratons in the Neoproterozoic-to-Early Paleozoicevolution of southe South merica aer the break-up ofRodinia.

The presence of a pre-renvillian continental mass called Pampia has been suggested mos, 1988; Rmos and jovich, 1993),initially as a block embracing most of the present Siras Pampeanas

rean, with a Late Neoproterozoic turbidite basin (the PuncoviscnaFormation) along the weste passive margin that evenally

collided with the requipantofalla block. Ts view was lrgelyretined by Ramos et a (2010) in a recent review of Pampia.

Based largely on our own work since the 1990s in the pre-ndenbasement, we proposed (Casquet et a., 2009) thatbythe end of the

Paleoproterozoic the basement outcrops referred to above, i.e.,requipa, io Apa and Maz, constited a single lrger continental

mass (the MRA craton, Fig. 1). Part of this craton was involved in

Mesoproterozoic orogenies along its northe and weste marginsthat led rst to its accretion to mazonia at ca. 1.3 Ga or erlier,and then amalgamation with Laurena between ca. 1.3 and 1.0 Ga.The latter event involved accretion of juvenile arcs and continental

collision with reworking of older continental crust. Rodinia break-up the lrger continental mass embracing MRA +Laurentia +mazonia (and probably other still unconstrainedcratons) undwent proacted Neoproterozoic riing, as exemplied

by A-type granite and carbonatesyenite intrusions. Opening of anoceanic basin was eventually followed by oblique collision with

some West Gondwna cratons (including Rio de la Plata and Kalahari) to produce the PampeanParaguayraguaia orogeny. This

process was coeval with riingdriing of Laurena and theopening of the Iapetus ocean along the weste margin of the largecontinental mass and represents the nal stage in the formation of

SW Gondwana. We provide here a detailed account of this evoluon.

2 The Paleoproterozoic MARA craton

the Weste Sierras Pampeanas of rgentina, the Maz terrane(comprising the sierras of Maz and Espinal) (g. 1) consists ofa metamorphic ndean-type maatic arc (1.331.26 Ga) and

older metasedimentary rocks. (Casquet et a., 2006; Rapela et a.,2010). The latter contain detrital zircons older than 1.7 Ga and

have Nd model ages of between 1.7 and 2.6 Ga and very radiogenic

Pb, from which we infer that the protoliths were probably cover toa Paleoproterozoic basement older than 1.7 Ga (Casquet et a.,28a). The Maz terrane was rther reworked in the Ordovician

and Silurian by the Famanian orogeny (Casquet et a., 2005).The requipa Massif in southe Peru (Cobbing and tcher,

1972) (g. 1) consists for the most part of Paleoproterozoic

metasedimentary rocks and orthoeisses that record orogenicevents (maatism, sedimentation and metamorphism) between

ca. 1.79 and 2.1 Ga oewy et a., 2004; Casquet et a., 2010).These rocks underwent intense Grenville-age ss ivers, 2008)metamorphism between 1.04 and 0.84 Ga artiole andMartelat, 2003; Loewy et a., 2004; Casquet et a., 2010 andreferences therein). T metamorphism rst recorded in the

requipa Massif by Martiole and Martelat (2003) remains ofdisputed age, either Paleoproterozoic or renvillian artignole

and Martelat, 2003; Casquet et a., 2010). Mixing of Paleoproterozoic and juvenile Grenvillian sources was recognized

farther south in northern Chile and rgentina oewy et a., 2004),lending support to the idea of a continuous basement of Paleo

proterozoic age under this part of the Central ndes, corresponding to the northern part of the requipantofalla craton of

Ramos (1988). A link between the Maz terrane and the northepart of the requipantofalla craton was rst established by

Casquet et al. (2008a) on the basis of detrital zircon evidence andPb and Nd isotope compositions.

Finally the Rio Apa block, south of present-day mazonia

ig. 1), consists of a suite of Paleoproterozoic orthoeissesrecording ieous events at 1.95 Ga, 1.84 Ga, and between 1.72 and

1.77 Ga, as well as medium- to high-grade metamorphism of

ca.1.7 (Cordani et a., 2010). The Rio Apa block was overprinted by a thermal event at ca. 1.3 Ga (Cordani et a., 2010)coincident with the San Ignacio orogeny along the southe margin

of mazonia oger et a., 2005; Cordani and Teixeira, 2007).The three cratonic outcrop areas referred to above, although

separated by hundreds of kilometers, show evidence of common

geological processes evidenced by U-Pb geochronology andsimilar Nd model ages ig. 2). This leads to the idea that all three

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.

2

AREQUIMASSIF

Sieras PAMPEANAS

MAZ

Pe de PAL

60

AAONIActon

F

40

aleopoerozoc Archeancratons

20

araucock(>17Ga)_ an Rondoian -Sa Ignacoorogeic bets (156 f .30Ga)

Wesern Sot Amerca ateDMesoroterozoic s (110Ga)

orogeic etSusas orogenic ets s (Sunss,[ Nova Brasaa Agae

10107 Ga) Neoroterozoic o Eary Camrian

orogec es TransBrasiao ieame

Q nferred fau

gure Sketch map of South America showing Pleoproterozoic to Archean cratons nd the Middle-to-Late Mesoproterozoic, andNeoproterozoic to Early Cambrian orogenic belts. The M craton reached its present position after right-laterl oblique accretion to the Rio de

la Plata craton during the Pmpean orogeny and further displacement along the C6rdoba fault. Outcrops in red re Pleoproterozoic and

Mesoproterozoic outcrops referred to in the text. DBF: Desaguadero-Beejo Fault; CF: C6rdoba Fault.

ompaatie eouto o Paeopteooi oks

AREQUIPA RIOAA MAZTERRANE

..7Ga Sedimettion onaleprterc

basee

.7.79Ga Lae felsc magmatis .7.76Ga Graite Gamagatim agmatismU- & reginal (iered m derita

gechrngy -8Ga UHT etami etaor hislT zsSedetai .Ga

n etaedimets)

agatiaite

2Ga ifeed fr detrial 1.41.83Garn magmaismi etasedimets

Nd mde age(T

192.Ga ..Ga ..6Ga

gure The Paleoproterozoic record the three outcrops foing the hypotheticl M craton. Data from Casquet et l. (2008a, 2010) andCordani et l. (2010).

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formed part of a common continental mass before the onset of theMesoproterozoic orogenies. We call this craton MRA (aeraz requipa io pa), consisting of rocks formed between

1.7 and 2.1 and with Nd residence ages (T) between 1.7 and2.6 Ga (Casquet et a., 2009).

3 The Mesoproterozoic evolution of the Maracraton

No evidence has so far been recoized in any of the three

Paleoproterozoic outcrops for signicant igneous or metamorphicactivity between ca. 1.3 and 1.6 Ga, although they experiencedcontrasting ieous and metamorphic events in the second half of

the Mesoproterozoic ig. 3).The Maz terrane records an ndean-type magmatic arc

(1.331.26 Ga) and intermediate amphibolite to granulitefacies metamorphism between 1.23 and 1.17 Ga followed by

emplacement of MCG complexes at 1.071.09 Ga (Casquetet a., 2005, 2006; Rapela et a., 2010). Moreover in the nearby

Sierra de Pie de Palo, and in minor outcrops south of it ig. 1),a Late Mesoproterozoic juvenile arc/ack-arc oceanic complex

has been identied (the Pie de Palo complex) that records protracted subduction between ca. 1. and 1.03 Ga (Kay et a., 1996;

Vujovich et a., 2004; Rapela et a., 2010). The Pie de Palocomplex is the basement of the eniatic, supposedly Laurentiaderived, Precordillera terrane (Thomas and Astini, 1996; for

a review see Ramos, 2004); alteatively the terrane might havebeen para-autochthonous (Aceolaza and Toselli, 2000; Galindo

et a., 2004; Fiey, 2007). any hypothesis, docing of thisterrane to the margin of Gondwana occurred in the mid

Ordovician during the Famatinian orogeny amos et a., 1998;Casquet et a., 2001; Galindo et a., 2004; Ramos, 2004). Over

lying the Pie de Palo complex is an imbricate thrust system thatreworked basement consisting of Late Mesoproterozoic orthogneisses and metasedimentary rocks overlain b y a N eoproterozoic

sedimentary cover (Casquet et a., 2001; Mucahy et a., 2011).Ts basement underwent pre-Famatinian metamorphism underconditions close to those of the Maz terrane, to which it is prob

ably equivalent (Casquet et a., 2001). Orogenic activity betweenca. 1.3 and 1.0 in the Maz terrane and the e de Palo complexcan be interpreted as resulting from the approach and eventualcollision of the MRA craton (and the juxtaposed mazonia)

with Laurentia to produce the middle to Late Mesoproterozoicorogenic belt that nges mazonia on the west, with outcrops as

far north as Colombia (Cardona et a., 2010, and referencestherein) ig. 1).Paleomagnetic data for ca. 1.2 Ga are compatible

with this interpretation (Tohver et a., 2004). The relative positionsof the oceanic Pie de Palo Complex and the continental Maz

terrane in the Mesoproterozoic orogen are difcult to retrievebecause of Famatinian oblique thrusting in Sierra de Pie de Paoand protracted post-Paleozoic activity along the Berme

joDesaguadero fault that separates the block containing theSierra de Pie de Palo and the rgentine ecordillera om that

containing the sierras of Maz and Espinal (g. 1).The io Apa block underwent a strong thermal episode at ca.

1.3 Ga with temperatures above 300C, which affected the entireregion (Cordani et a., 2010). This corresponds to the San Ignacio

orogeny (1.341.32 Ga; Boger et a., 2005), the main belt ofwhich developed farther north, along southern mazonia ig. 1),

and is one of several 1.561.3 Ga orogenic belts constituting theRondonia-San Iacio province of southern mazoniaettencourt et a., 2010, and references therein). The lack of

evidence in the io Apa block for the Late MesoproterozoicSunss orogeny s.l. (1.201.07 Ga; Boger et a., 2005; Cordani

and Teixeira, 2007) suggests that it, and consequently theMRA craton, was accreted to the southern mazonia margin

during the San Iacio orogeny, and was a mainly stable region inLate Mesoproterozoic times. Deformation associated with the

Sunss orogeny, long considered the main representative of therenville orogeny in southern South merica, occurred farthernorth along branched transcurrent belts and pull-apart basins

Gv v R e M terre e e terre equp l R lkM tel e tet e

900

I- 04-0 85 G

Dlw- g-T

regl

1000erm

-1 .9-7 G -1.3

GClx terc leet TG e

Iexte, emceme

f CG mexe. -11 G ,21 G100 xmt ggre New uctrelte Semet

erre c gmm tc B

1.31.17 G-11 G

rcctet ll

Ircele mg

100 lterc tceg 1.Gaggre metm rc/rc cec plex

te tel ege NRB cec rc lv

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GRNVI CIV GIN FNG URI?GRVlN STLE

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Fire M-t-Lat Mrtrz ut t rat r aa t aut t a rt

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ig. 1) involving local metamorphism and granitic magmatism(for a review see Teixiera et a., 2010). The Paragu block ofEaste Bolivia ig. 1) also has Paleoproterozoic basement older

than ca. 1.7 Ga (Boger et a., 2005) that was accreted to SWmazonia during the San Ignacio orogeny ettencourt et a.,

2010) and could thus also have been part of The history of the requipa massif differs in that it shows

evidence for true Grenville-age (ss Rivers, 2008) low- high-Tregional metamorphism between ca. 1.04 and 0.85 Ga, younger

than in the Maz terrane and io Apa block (Loewy et a., 2004;Casquet et a., 2010). The massif was probably an inlier in the

Middle to Late Mesoproterozoic orogenic belt that only underwentlate-orogenic metamorphism. However its pre-orogenic location

and the geodynamic setting of metamorphism remain uncertain.With respect to location Dalziel (1992, 1994) and Sadowsi andBettencourt (1996, and references therein) proposed that the

requipa massif was the tip of a promontory of Laurentia.Subsequently Loewy et al. (2004) suggested that the requipa

massif and its southward extension may have been part of a largercraton in collision with mazonia. With respect to metamorphism

an extensional setting in the Grenvillian hinterland has beenhypothesized on the grounds that extension was widespread over

southe mazonia at this time (equivalent to the Rigolet event ofthe renville orogeny; Casquet et a., 2010). Siicantly,

accretion of MRA to mazonia during the San Iacio orogenywould explain the input of detrital zircons with ages between1.2 and 1.6 Ga to the Late Mesoproterozoic Atico basin in re

quipa, for which no local sources have been recoized (Casquetet a., 2010). malgamation of Laurentia and the MRA craton

(with mazonia) in the Mesoproterozoic at ca. 1.2 Ga (Tohveret a., 2002) was an important contribution to the formation of

Rodinia.

4 Neoproterozoic to Early Paleozoic evolution

The Neoproterozoic to Early Paleozoic history is summarizedfocusing on evidence om the Sierras Pampeanas of rgentina.

Riing events and the Clymene ocean

Protracted rifting of Rodinia took place throughout the Neoproterozoic. Two early aborted riing events, at ca. 840 and760 Ma, are represented by A-type granitoids in Sierra de Maz

and Sierra de Pie de Palo, bearing zircons with juvenile Hf and isotopic signatures aldo et a., 2006; Colombo et a., 2009;

Rapela et a., 2011). Further rifting occurred at ca. 570 Ma

(Ediacaran), represented by a carbonatite-nepheline syenitecomplex in the Sierra de Maz (Casquet et a., 2008b). Wesuggest that this latter event probably initiated opening of the

Clymene ocean (Fig. 4). This ocean was named by Trindadeet al. (2006), who argued on the basis of paleomaetism

for such a Late Neoproterozoic ocean between mazonia +Laurentia on the one hand and West Gondwana cratons, such asRio de la Plata and Kalahari, on the other. As an alteative to

the Pampia model of Ramos (1988) and Ramos et al. (2010), we

envisage that MRA was attached to the former continentalmass and that the closure of this ocean led to the Pampeanorogeny (Casquet et al., 2009). 570 Ma is just within error of the

Sm-Nd age of 647 77 Ma for alleged Pampean ophiolite relics(whole-rock errorchron with MSWD = 7.6), obtained by

Escayola et al. (2007).

Te Dfunta Correa sedimenta sequence

Further evidence for the Clymene ocean comes from the Srisotope composition of platform carbonates of the Dinta Correa

sequence, which was deposited on the Paleoproterozoic andMesoproterozoic basement of the Weste Sierras Pampeanas in

the Late Neoproterozoic arela et a., 2001; Galindo et a., 2004;Rapela et a., 2005; Murra et a., 2011). From comparison with the

Sr-isotope composition of seawater through time, Galindo et al.(2004) deduced a maximum age of 580 Ma (Ediacaran) for the

sequence in Sierra de e de Palo. This accords with the similarndings of Varela et al. (2001) for equivalent carbonate cover in

Sierra de Umango (Weste Sierras Pmpeanas) and of Murraet al. (2011) for marbles om Sierra de ncasti (Easte SierrasPampeanas). Similar Ediacaran shallow-marine carbonates that

were post-glacial with respect to the Marinoan (ca. 635 Ma) andGasiers (ca. 580 Ma) events are recorded elsewhere in southe

South merica isi et a., 2007). Ts evidence for extensive

carbonate platforms at ca. 580 Ma is compatible with the existenceof the Clymene ocean during Ediacaran time (g. 4).

Te Puncoviscana Formation

The Puncoviscana Formation (Turner, 1960) is a thick, mainly

siliciclastic partly turbiditic, succession (Jezk, 1990; Omariniet a., 1999; Zimmermann, 2005 and references therein) that

crops out in northe rgentina and allegedly throughout most of

the easte Sierras Pampeanas (e.g., Schwartz and Gromet, 2004;

Rapela et a., 2007). has been the subject of much controversyin terms of its age and tectonic setting of sedimentation. The

Formation is important that it shows the main evidence for theEarly Cambrian Pampean orogeny, in the form of penetrative

deformation and metamorphism, the grade of the latter increasingfrom the Puna and Sierras Orientales in the north (very low- to

low-grade) to the Sierras de Crdoba in the south (high-grade).The Formation was also host to the Pampean plutonic arc in the

south, formed between ca. 550 and 530 Ma apela et a., 1998;Schwartz et a., 2008; Iaizzotto et a., 2011). The term Puncoviscana Formation in the literature embraces sedimentary

rocks probably older, coeval and younger than the Pampeanmagmatic arc with the only constraint that they are older than the

unconformably overlying Middle to Late Cambrian MesonGroup (e.g., Omarini et a., 1999; Adams et a., 2008, 2011;

Escayola et a., 2011, and references therein). We restrict ourtreatment here to that part of the siliciclastic succession that hosts

the maatic arc in the south, which is of relevance to the early

history of the Puncoviscana sedimentary basin. This southetract is mainly pelitic and contains characteristic detrital zirconspopulations with major peaks at 1100960 Ma and 680570 Maand lacks grains derived om the nearby Rio de la Plata craton

(2.022.26 Ga) (Schwartz and Gromet, 2004; Escayola et a.,2007; Rapela et a., 2007). Sedimentation here took place on

the easte margin of the Clymene ocean between ca. 570 Ma(the approximate age of the youngest detrital zircons) and ca.

530 Ma (g. 4); the older age being coincident with that of the

anorogenic carbonatitesyenite event referred to above. Thepaleogeographical position was probably distant om the Rio de

la Plata craton, to which the Puncoviscana Formation basementbecame juxtaposed through right-lateral displacement during

Pampean subduction and collision (Schwartz and Gromet, 2004;Rapela et a., 2007; Verdecchia et a., 2011). However, the

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a 57-54 M f h ym

Laurenlia + MARA Cymee Oea

wsp Grevia beEdacaa

patformswth carbate

Lw, Pu ,ovicanaf.b 43 M

apetus Ocea

Cea atfrm?

C 32 M

h dm b

Brasiia-ariepPa Afrca Oge

ay ambra magmati ar

m q Crdba fat

Pamea Orgey

Patfrm

Eater Serra Pampeaa

Fire 4 3-D iagrams showing geotectonic evoluon during the Neoproterozoic nd the Eary Cmbrin that led the Pmpen orogeny ndnal mlgamation of MRA to Gondwana. See text for explnaon. The gure highlights the role played by the opening of the Clymene ocenin the Late Neoproterozoic nd its subsequent closure the Ery Cambrin coevl with drifng of Laurentia in the west en rute to the norhehemisphere.

sedimentary setting of this tract of the Puncoviscana Formation

remains uncertain; a fore-arc basin was suggested Rapela et al.(2007) but a passive margin setting for the older part of the

tract cannot be discounted.

5 The Pampean orogeny and the amalgamationof SW Gondwana

Subduction started in the Late Neoproterozoic or Early Cambrianalong the eastern margin of the Clymene ocean, giving rise to the

Pampean orogeny. n I-type ndean-type magmatic arc devel

oped between ca. 550 and 530 Ma (Rapela et a., 1998; Schwartzet a., 2008; Iannizzotto et a., 2011) (Fig. 4). At the same time

Laurentia ried away om RA + mazonia in the west(present coordinates), resulting in opening of the Iapetus ocean(Dalziel, 1997) and with development of passive margin sedi

mentary sequences well preserved along the Appalachian margin

of Laurentia and in the Precordillera terrane of weste rgentina(e.g., Astini et a., 1995; Thomas and Astini, 1996). nal closureof the Clymene ocean occurred between 530 and 520 Ma as

implied by the ages of intermediate Barrovian-type collisionalmetamorphism and coeval S-type plutonism apela et a., 1998;

Rapela et a, 2002; Otamendi et a, 2009) ig. 4).

At the start of the Pampean orogeny (ca. 550 Ma) the Paleo

proterozoic and Mesoproterozoic basement of the Weste SierrasPampeanas was part of a large but ephemeral continental mass

ried om Laurentia apela et a., 2007; Casquet et a., 2009),consisting of together with mazonia ig. 4). TheWestern Sierras Pampeanas probably formed the southern tail ofthis landmass apela et a., 2007).Participation of the Pie de Paocomplex in this new continental assemblage cannot be ruled out in

the hypothesis of a para-autochthonous ecordillera terrane

(Galindo et a, 2004; Fiey, 2007).The Pampean orogeny involved oblique closure of the

Clymene ocean between RA +mazonia and other Westondwana cratons (io de la Plata, Kalahari, ), ultimate collision of these continental masses bringing to an end the formation

of Gondwana (Trindade et a., 2006; Rapela et a., 2007). Wesuggest that these collisions were responsible for the formation ofa continuous mobile belt embracing the Pampean orogen in the

south and the Paraguay and raguaia belts further north ig. 1),

all of which have igneous, metamorphic and structural features incommon apela et a., 2007; Moura et a., 2008; Bandeira et a.,2011; McGee et a., 2011). Moreover, no evidence of Cambrian

orogeny has yet been convincingly demonstrated for the westemargin of mazonia (e.g., Chew et a., 2007). Consequently, this

orogenic belt was probably part of the Terra Australis orogen of

C d (2005) l h h h S h i h i i d d i N

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Cawood (2005), although the South merican tract that wedescribe here follows a different trend along easte mazoniaig. 3). The Trans-Brasiliano lineament of Cordani et al. (2003)

ig. 1) is interpreted as a late Pampean mega-fault equivalent tothe Crdoba Fault (e.g., Rapela et a., 2007) ig. 4) responsible

for the na assembly of easte South merica continentalmasses before Pngea. On the other hand the weste margin of

MRA +mazonia (now part of Gondwana) facing the Iapetusocean remained passive until the Early Ordovician when it

evolved into an ndean-type orogeny that persisted throughout thePaleozoic and the Mesozoic, evolving into the present ndean

margin of South merica.

6. Conclusions

Southern South merica contains an outstanding record of

Rodinia formation, rther supercontinent break-up in the Neoproterozoic and nal re-assembly of continental blocks in SW

Gondwana in the Early Cambrian. We suggest here that severalminor Paleoproterozoic blocks, such as the Maz terrane in the

Weste Sierras Pampeanas, the requipa block including itssouthe extension, and the Rio Apa block, at least, formeda major continental mass, i.e., the MRA craton, which collided

with mazonia at ca. 1.3 Ga. The resulting continent furtheramalgamated to Laurentia during Middle and Late Mesoproter

ozoic orogenies as part of Rodinia formation. Protracted break-upof Rodinia took place in the Neoproterozoic as recorded by

episodic anorogenic maatism and eventual opening of theClymene ocean in Ediacaran times. Post-glacial platform

carbonates formed in this ocean followed by deposition of thelargely turbiditic Puncoviscana Formation along the easte

margin in Late Ediacaran to Early Cambrian times. Eastwardright-lateral subduction led to closure of the Clymene oceancoeval with Laurentia driing away to the west to open the Iapetus

ocean. The proto-ndean margin formed at this time andremained passive till the start of the ndean-type Famatinian

orogeny in the Early Ordovician. Final closure of the Clymene

ocean led to oblique collision of the large continental mass formedby +mazonia with other West Gondwana cratons(Kalahari, Rio de la Plata . ) to produce the transpressional

PampeanParaguayraguai orogenic belt in the EarlyCambrian, and brought to an end the assembly of SW Gondwana.

Acknowledents

We acknowledge Dr. M. Santosh for his ind invitation to publishthis review of our scholarly work and we acknowledge comments

by three anonymous reviewers that have contributed to improvethe manuscript. nancial support over the last years was through

Spanish C and CIN grants CGL2005-02065BE andCGL2009-07984, UCM-Santander grant GR58/08 and rgenti

nian grant 1728 PICT 1009.

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