U-Pb Zircon Geochronology and Nd Isotopic Signatures of the Pre

University of Wollongong Research Online

Faculty of Science - Papers (Archive) Faculty of Science, Medicine and Health

January 2009

U-Pb zircon geochronology and Nd isotopic signatures of the pre-mesozoic metamorphic basement of the Eastern Peruvian andes: growth and provenance of a Late Neoproterozoic to Carboniferous accretionary orogen on the Northwest margin of Gondwana

A Cardona

U G. Cordani

J Ruiz

V A. Valencia

R Armstrong

See next page for additional authors

Follow this and additional works at: https://ro.uow.edu.au/scipapers

Part of the Life Sciences Commons, Physical Sciences and Mathematics Commons, and the Social and Behavioral Sciences Commons

Recommended Citation Cardona, A; Cordani, U G.; Ruiz, J; Valencia, V A.; Armstrong, R; Chew, D; Nutman, A; and Sanchez, A W.: U- Pb zircon geochronology and Nd isotopic signatures of the pre-mesozoic metamorphic basement of the Eastern Peruvian andes: growth and provenance of a Late Neoproterozoic to Carboniferous accretionary orogen on the Northwest margin of Gondwana 2009, 285-305. https://ro.uow.edu.au/scipapers/983

Research Online is the open access institutional repository for the University of Wollongong. For further information contact the UOW Library: [email protected] U-Pb zircon geochronology and Nd isotopic signatures of the pre-mesozoic metamorphic basement of the Eastern Peruvian andes: growth and provenance of a Late Neoproterozoic to Carboniferous accretionary orogen on the Northwest margin of Gondwana

Abstract This study integrates U-Pb zircon geochronology (from LAM-ICP-MS, SHRIMP, and TIMS) with Nd isotopic data from orthogneisses and metasedimentary rocks of the pre-Mesozoic basement of the eastern Peruvian Andes to provide new information on the tectonic evolution and Neoproterozoic-Paleozoic paleogeography of this segment of the proto-Andean margin. A high-grade orthogneiss unit yields U-Pb zircon protolith crystallization ages of ~613 Ma. It was metamorphosed and intruded by an Early Ordovician granitoid. Subsequently, two different volcano-sedimentary sequences were laid down and metamorphosed, probably as a consequence of terrane accretion. The older sequence was deposited and metamorphosed between 450 and 420 Ma, and the younger one was deposited after 320 Ma and metamorphosed at 310 Ma. U-Pb detrital zircon age patterns from the two sequences are within the age intervals 315-480, 480-860, 960-1400, and >1400 Ma. These data strongly suggest geological and spatial links between the different units, implying the existence of active magmatism contemporaneous with the reworking of previously formed orogenic complexes. Mesoproterozoic and older ages suggest that the detrital sources are on the western margin of Gondwana, near the Amazonian Craton and/or other Grenvillian-type domains, such as those found within the Andean belt. Neoproterozoic to Ordovician zircons suggest that this crustal segment was formed on an active margin along the western side of the Amazonian Craton. Whole-rock Nd isotope data from metasedimentary rocks of the two younger units yield εNd(450 Ma, 310 Ma) values between -6.3 and -13.2 and Sm-Nd TDM model ages between 1.6 and 2.1 Ga. The comparison of the Nd isotope record with the U-Pb detrital zircon data suggests that recycling of older crust was an important factor in the growth of the central Peruvian segment of the proto-Andean margin during the Proterozoic and the Early Paleozoic. Different tectonic and paleogeographic models are discussed in light of the new data presented here. © 2009 by The University of Chicago.

Keywords pre, signatures, isotopic, nd, geochronology, zircon, pb, u, mesozoic, basement, metamorphic, eastern, gondwana, peruvian, andes, growth, provenance, late, neoproterozoic, carboniferous, accretionary, orogen, northwest, margin

Disciplines Life Sciences | Physical Sciences and Mathematics | Social and Behavioral Sciences

Publication Details Cardona, A., Cordani, U. G., Ruiz, J., Valencia, V. A., Armstrong, R., Chew, D., Nutman, A. & Sanchez, A. W. (2009). U-Pb zircon geochronology and Nd isotopic signatures of the pre-mesozoic metamorphic basement of the Eastern Peruvian andes: growth and provenance of a Late Neoproterozoic to Carboniferous accretionary orogen on the Northwest margin of Gondwana. The Journal of Geology, 117 (3), 285-305.

Authors A Cardona, U G. Cordani, J Ruiz, V A. Valencia, R Armstrong, D Chew, A Nutman, and A W. Sanchez

This journal article is available at Research Online: https://ro.uow.edu.au/scipapers/983 U-Pb Zircon Geochronology and Nd Isotopic Signatures of the Pre- Mesozoic Metamorphic Basement of the Eastern Peruvian Andes: Growth and Provenance of a Late Neoproterozoic to Carboniferous Accretionary Orogen on the Northwest Margin of Gondwana

A. Cardona, U. G. Cordani,1 J. Ruiz,2 V. A. Valencia,2 R. Armstrong,3 D. Chew,4 A. Nutman,5 and A. W. Sanchez6

Smithsonian Tropical Research Institute, Balboa, Anco´ n, Panama (e-mail: [email protected])

ABSTRACT This study integrates U-Pb zircon geochronology (from LAM-ICP-MS, SHRIMP, and TIMS) with Nd isotopic data from orthogneisses and metasedimentary rocks of the pre-Mesozoic basement of the eastern Peruvian Andes to provide new information on the tectonic evolution and Neoproterozoic-Paleozoic paleogeography of this segment of the proto- Andean margin. A high-grade orthogneiss unit yields U-Pb zircon protolith crystallization ages of ∼613 Ma. It was metamorphosed and intruded by an Early Ordovician granitoid. Subsequently, two different volcano-sedimentary sequences were laid down and metamorphosed, probably as a consequence of terrane accretion. The older sequence was deposited and metamorphosed between 450 and 420 Ma, and the younger one was deposited after 320 Ma and metamorphosed at 310 Ma. U-Pb detrital zircon age patterns from the two sequences are within the age intervals 315–480, 480–860, 960–1400, and 11400 Ma. These data strongly suggest geological and spatial links between the different units, implying the existence of active magmatism contemporaneous with the reworking of previously formed orogenic complexes. Mesoproterozoic and older ages suggest that the detrital sources are on the western margin of Gondwana, near the Amazonian Craton and/or other Grenvillian-type domains, such as those found within the Andean belt. Neoproterozoic to Ordovician zircons suggest that this crustal segment was formed on an active margin along the western side of the Amazonian Craton. Whole-rock Nd isotope data from metasedimentary rocks of the two ␧ Ϫ Ϫ younger units yield Nd (450 Ma, 310 Ma) values between 6.3 and 13.2 and Sm-Nd TDM model ages between 1.6 and 2.1 Ga. The comparison of the Nd isotope record with the U-Pb detrital zircon data suggests that recycling of older crust was an important factor in the growth of the central Peruvian segment of the proto-Andean margin during the Proterozoic and the Early Paleozoic. Different tectonic and paleogeographic models are discussed in light of the new data presented here.

Online enhancements: appendix tables.

Introduction The Neoproterozoic to Late Paleozoic tectonic evo- cluded within the large-scale Terra Australis orogen lution of the proto-Andean margin has been in- (Cawood 2005), a major tectonic belt that extends more than 18,000 km along the Pacific margin of Manuscript received June 25, 2008; accepted January 20, 2009. Gondwana, from South America to Australia. The 1 Instituto de Geocieˆncias, Universidade de Saõ Paulo, Saõ growth of this orogen is related to continuous ocean Paulo, Brazil CEP 05508-080. convergence following breakup of Rodinia and the 2 Department of Geosciences, University of Arizona, Tucson, formation of the paleo-Pacific and Iapetus oceans, Arizona 85721, U.S.A. 3 Research School of Earth Sciences, Australian National Uni- and culminates with the assembly of Pangaea and versity, Building 61, Mills Road, Acton, Australian Capital Ter- the Gondwanide-Alleghenian orogenic event. ritory 0200, Australia. Despite considerable advances in the understand- 4 Department of Geology, Trinity College, Dublin 2, Ireland. ing of several elements of this margin, the timing 5 Institute of Geology, Chinese Academy of Geological Sci- and episodes of arc formation and oceanic plate ences, 26 Baiwanzhuang Road, Beijing 100037, China. 6 Instituto Geolo´ gico Minero y Metalu´ rgico, Avenida Canada convergence versus terrane accretion or dispersion 1470, San Borja, Lima 41, Peru. are issues that are not fully resolved. The tectonic

285 286 A. CARDONA ET AL. evolution of the proto-Andean margin has impli- of the proto-Andean margin has been the focus of cations for paleogeographical reconstructions, re- recent research (Cardona et al. 2006, 2007; Chew gional correlation of orogenic phases, and the evo- et al. 2007b; Ramos 2008a). It has major implica- lution of ancient margins in general (Pankhurst and tions for the Neoproterozoic paleogeography of the Rapela 1998; Keppie and Ramos 1999; Ramos 1999, western Amazonian Craton during Rodinia 2004; Lucassen and Franz 2005). breakup (Chew et al. 2008), the formation and drift Along the eastern Peruvian Andes, between 6ЊS of para-autochthonous Gondwanide terranes, and and 12ЊS a major pre-Mesozoic metamorphic and the Late Paleozoic transition from Laurentia-Gond- magmatic province crops out (ﬁg. 1). This segment wana tectonic interactions in the northern Andes

Figure 1. Geochronological provinces of the Amazonian Craton and pre-Mesozoic Andean inliers, including the Mar- an˜ on Complex (modified from Cordani et al. 2000). Published Paleozoic and Precambrian U-Pb crystallization ages from Peru are after Dalmayrac et al. (1988); Wasteneys et al. (1995); Loewy et al. (2004); Chew et al. (2007b). Journal of Geology GROWTH OF A GONDWANAN ACCRETIONARY OROGEN 287 and the major Gondwanide orogenic cycle to the mayrac et al. 1988). However, the results presented south (Bahlburg 1993; Ramos and Aleman 2000; here, combined with recently published geological Cawood 2005; Murphy et al. 2004; Ramos 2008a). constraints from other segments of the Eastern Cor- Detrital U-Pb zircon geochronology and Sm-Nd dillera (Chew et al. 2007b), demonstrate the exis- whole-rock isotopic analyses from sedimentary tence of a more complex Paleozoic tectonic rocks are valuable tools for tectonic, stratigraphic evolution. and provenance studies (see McLennan et al. 1993; Other Proterozoic, Paleozoic, and Triassic plu- Dickinson and Gehrels 2001; Fedo et al. 2003). tonic and metamorphic domains, such as the Illes- When integrated with U-Pb zircon magmatic and cas Massif and the Arequipa-Antofalla terrane, are metamorphic crystallization ages, they provide a exposed in the coastal region of Peru (fig. 2; Was- robust tectonostratigraphic framework to trace the teneys et al. 1995; Loewy et al. 2004; Chew et al. evolving nature of an orogen. 2007a; Cardona et al. 2008). Late Mesoproterozoic In this article, we integrate U-Pb laser ablation– granulite-facies rocks, which are probably part of multicollector–inductively coupled plasma– the Amazonian Craton, have also been reported mass spectrometry (LAM-ICP-MS) and SHRIMP from the Picharı´ river in the Amazon region of Peru measurements on detrital zircons, whole-rock Sm- (fig. 2; Dalmayrac et al. 1988). Nd analyses from metasedimentary rocks, and U- The Maran˜ on Complex. The term “Maranõn Pb SHRIMP and TIMS zircon crystallization ages Complex” has been commonly used in the geolog- from gneisses and granitoids from the pre-Triassic ical literature to include all metamorphic basement metamorphic basement of the eastern Peruvian An- rocks of the Eastern Cordillera (Wilson and Reyes des at ∼10ЊS (fig. 2). These data are used to constrain 1964; Dalmayrac et al. 1988). This composite unit the sedimentary, magmatic, and metamorphic evo- discontinuously extends for more than 500 km be- lution of this segment of the proto-Andean margin. tween 6ЊS and 12ЊS (fig. 2) and includes various low- Geological Setting of the Peruvian Andes. The cen- to middle-grade metamorphic belts of volcano- tral Peruvian Andes between 6ЊS and 14ЊS(fig.2) sedimentary origin. Higher-grade domains are correspond to one of the present-day flat-slab sub- restricted in extent. Stratigraphic relations include duction segments below the Andean chain. Its geo- local unconformities with overlying Ordovician, logical framework includes a prominent Late Me- Carboniferous, or Permian sediments and intrusive sozoic to Cenozoic volcano-sedimentary and contacts with Late Paleozoic granitoids (Wilson and plutonic belt in the Western Cordillera and adja- Reyes 1964; Dalmayrac et al. 1988; Cardona 2006; cent coastal regions (Pitcher and Cobbing 1985; Be- Chew et al. 2007b). navides-Caćeres 1999). Controversy remains about Previous temporal constraints for the geologic the nature of the basement within this region. evolution of this metamorphic basement were Some authors favor the absence of continental base- based on regional extrapolation of local unconfor- ment (Polliand et al. 2005), while others suggest mities with the Early Ordovician fossiliferous sed- that the available geological and geophysical evi- iments, and the previously mentioned Neoprote- dence points to a sialic substrate (Ramos 2008a). rozoic U-Pb zircon lower intercept age from a Sedimentary, plutonic, and metamorphic units migmatitic paragneiss. This loosely constrained ca. attributed to Paleozoic or older pre-Andean cycles 630–610-Ma age was considered as evidence for a are confined to the Eastern Cordillera (fig. 2). The Neoproterozoic orogeny on this segment of the sedimentary units include fossiliferous Ordovician, proto-Andean margin (Dalmayrac et al. 1988). Mississippian, and Late Permian sequences (Dal- However, as discussed here and also presented by mayrac et al. 1988; Zapata et al. 2005), whereas Cardona et al. (2007) and Chew et al. (2007a), this magmatic rocks range in age between the Ordovi- metamorphic basement include several units with cian to Early Triassic (Macfarlane et al. 1999; Mis- a more complicated Neoproterozoic to Late Paleo- kovic et al. 2005; Cardona 2006; Chew et al. 2007b). zoic geological record. An extensive but discontinuous series of meta- Local Geology and Sampling Constraints. The morphic units is also exposed in the core of the Maran˜ on Complex was sampled close to the towns Eastern Cordillera. Commonly referred to as the of Huańuco and La Unioń at ∼10ЊS, (fig. 3). This Maran˜ on Complex (Wilson and Reyes 1964), this region is where the unconformable relationships belt was initially considered pre-Ordovician (prob- with fossiliferous Paleozoic rocks as well as the ably Neoproterozoic) based on local exposures of 610–630-Ma U-Pb zircon age of Dalmayrac et al. undeformed Ordovician rocks and a Neoprotero- (1988) were originally reported. Zircons from 10 zoic U-Pb zircon lower intercept age from a mig- samples of metasedimentary and metaigneous matitic paragneiss (Wilson and Reyes 1964; Dal- rocks were selected for U-Pb analysis by different 288 A. CARDONA ET AL.

Figure 2. Pre-Mesozoic plutonic and metamorphic rocks of the Peruvian Andes. techniques (fig. 3), while 18 metasedimentary (fig. 3). (1) A small inlier of amphibolite-facies whole-rock samples were analyzed for Sm-Nd iso- gneisses yields peak metamorphic temperatures of topes (fig. 3). 590Њ–615ЊC (Cardona et al. 2007) and is intruded Based on lithostratigraphic correlation and local by a mylonitized granitoid. This inlier is enclosed relationships with Paleozoic sedimentary rocks, we within unit (2), a belt of micaceous schists with divide the Maran˜ on Complex into four main units sporadic intercalations of metabasite and calc-sil- Journal of Geology GROWTH OF A GONDWANAN ACCRETIONARY OROGEN 289

Figure 3. Geological map of the Maran˜ on Complex in the Huańuco–La Unio´ n regions (modified from Cobbing and Sanchez 1996a, 1996b; De la Cruz and Valencia 1996; Quispesivana 1996; Martinez et al. 1998). icate rocks, defined here as the Eastern Schist Belt to 7–10 kbar and 540Њ–660ЊC. These peak meta- (ESB). Metamorphic grade varies from lower green- morphic assemblages are in turn affected by a schist to amphibolite facies, with calculated PT lower-grade greenschist-facies crenulation cleavage conditions ranging from 3–5 kbar and 350Њ–450ЊC (Cardona et al. 2007). Mafic and ultramafic rocks 290 A. CARDONA ET AL. crop out as discontinuous lenses along the eastern procedures described by Gehrels et al. (2006). Un- margin of this belt (Grandin and Navarro 1979). knowns and standard zircons were mounted in the Fossiliferous Carboniferous sedimentary rocks un- central portion of the mount area to reduce possible conformably overlie the eastern schists (Dalmaryac fractionation effects. The grains analyzed were se- et al. 1988). (3) A series of isolated migmatite bodies lected randomly from the zircon population on the is spatially linked to some undeformed granitoids sample mount. In detrital samples, grain cores were that outcrop within the ESB. (4) A western belt of analyzed to avoid possible thin metamorphic over- mica schists, referred to here as the Western Schist growths. Zircon crystals were analyzed with a VG Belt (WSB), is characterized by significant interca- isoprobe multicollector ICP–MS equipped with lations of metabasite. Metamorphic grade is mainly nine Faraday collectors, an axial Daly collector, and in the greenschist facies, with peak metamorphic four ion-counting channels. The isoprobe is conditions of 3–4 kbar and 350Њ–400ЊC (Cardona et equipped with an ArF excimer laser ablation sys- al. 2007). This belt is covered by Permian sedi- tem, which has an emission wavelength of 193 nm. mentary rocks. Minor remnants of ultramafic rocks The collector configuration allows measurement of with associated phyllites and slates that crop out 204Pb in the ion-counting channel while 206Pb, 207Pb, on the eastern margin of the western schists are in 208Pb, 232Th, and 238U are simultaneously measured thrust contact with Carboniferous sediments of the with Faraday detectors. All analyses were con- Ambo Group (Grandin and Navarro 1979). ducted in static mode with a laser beam diameter Triassic granitoids clearly intrude both eastern of 35–50 m, operated with an output energy of ∼32 and western schist belts (Cardona 2006). The west- mJ (at 23 kV) and a pulse rate of 8 Hz. Each analysis ern belt is separated from the eastern belt by un- consisted of one 20-s integration on peaks with no deformed Carboniferous sedimentary rocks of the laser firing and 20 1-s integrations on peaks with Ambo Group and remnants of weakly deformed the laser firing. Hg contribution to the 204Pb mass fossiliferous Ordovician rocks (Dalmayrac et al. position was removed by subtracting on-peak back- 1988). Geochemical constraints from the metavol- ground values. Interelement fractionation was canic units combined with Ar-Ar and Rb-Sr geo- monitored by analyzing an in-house zircon stan- chronology suggest that the protoliths of the two dard, which has a concordant TIMS age of -Ma (2j; Gehrels et al. 2008). This stan 3.2 ע belts were deposited in an arc-related setting and 563.5 that they experienced major metamorphic events dard was analyzed once for every five unknowns during the Silurian (eastern schists, ∼420 Ma) and in detrital grains. U and Th concentrations were Late Carboniferous (western schists, 300–310 Ma; monitored by analyzing a standard (NIST 610 Cardona 2006; Cardona et al. 2007). A garnetiferous Glass) with ∼500 ppm Th and U. The Pb isotopic gneiss associated with a banded migmatite body in ratios were corrected for common Pb, using the the ESB sampled at the the same locality where measured 204Pb, assuming an initial Pb composition Dalmayrac et al. (1988) report their Neoproterozoic according to Stacey and Kramers (1975). metamorphic age yielded a Sm-Nd garnet-whole- The uncertainties on the age of the standard, the rock isochron of ca. 295 Ma (Cardona 2006). calibration correction from the standard, the com- Analytical Techniques. Zircon separates and position of the common Pb, and the decay constant whole-rock powders were prepared following stan- uncertainty are grouped together and are known as dard procedures at the laboratories of the Geochro- the systematic error. For the zircon analyses in this nological Research Center of the University of Saõ study, the systematic errors range between ∼1.0% Paulo (CPGeo-USP) and also following Basei et al. and 1.4% for the 206Pb/238U ratio and ∼0.8% and (1995) and Sato et al. (1995). All radiometric data 1.1% for the 207Pb/206Pb ratio. used the decay constants listed in Steiger and Ja¨ger (1977). U-Pb concordia ages and relative probability U-Pb SHRIMP Analyses diagrams were calculated using the program Iso- plot/Ex 3.0 of Ludwig (2003). Tables A1 and A2, U-Pb determinations on single zircon grains were available in the online edition or from the Journal carried out using the SHRIMP I instrument at the of Geology office, show the U-Pb analytical results Australian National University. Cathodolumines- and the Sm-Nd isotopic data, respectively. cence (CL) images were obtained to select zircon domains for each analysis. Because of effects such as the differential yield of metal and oxide species U-Pb LAM-ICP-MS Analyses between elements during sputtering, interelement U-Pb analyses were undertaken at the University ratios were calibrated with a standard whose iso- of Arizona LaserChron laboratory following the topic ratios are known by isotope dilution thermal Journal of Geology GROWTH OF A GONDWANAN ACCRETIONARY OROGEN 291 ionization mass spectrometry (ID-TIMS). Details of ably correlative with the foliation in the adjacent the analytical procedures, including calibration ESB. methods, were presented by Williams (1998) and Zircons from sample CM-80 (9Њ56Ј32ЉS, Stern (1998). 206Pb/238U ratios have an analytical un- 76Њ4Ј19ЉW) of the gneissic unit were analyzed by certainty of typically 1.5%–2.0% from calibration the U-Pb SHRIMP method. This rock contains of the measurements using standard zircons. U muscovite and biotite, with strong banding and a abundance was calibrated with fragments of the mylonitic fabric, and relict magmatic zoned pla- single crystal SL13 zircon standard (238 ppm U). gioclase porphyroclasts. Estimated metamorphic All errors also take into account nonlinear fluc- peak temperatures for the gneissic unit are ∼615ЊC tuations in ion counting rates beyond that expected (Cardona et al. 2007). Crystals are euhedral and from counting statistics (Stern 1998). prismatic. Cathodoluminescence images display U-Pb ID-TIMS. Analyses were undertaken at the variable internal structures of the crystals, includ- CPGeo-USP, following Basei et al. (1995). Zircons ing fully oscillatory and homogenous crystals, or were mechanically abraded with pyrite for 15 min homogenous rims surrounding oscillatory cores. in a steel capsule, leached with hot HNO3, rinsed Some of the zircons are slightly metamict. A total with deionized water, and cleaned in an ultrasonic of 16 analyses were undertaken and yielded con- bath. Isotopic dilution analyses followed standard cordant ages (fig. 4A). Eight homogenous rims, in- procedures and employed a mixed Pb-U spike (after cluding two spots with a single crystal, yield an age Ma ( MSWD p 0.81 ) with Th/U ratios 12 ע Krogh 1973, with minor modification by Basei et of484 al. 1995). The CPGeo uses a VG 354 TIMS with lower than 0.1 and are interpreted as metamorphic five Faraday cup collectors and a Daly detector. zircon “overgrowths” (Vabra et al. 1999). Six pris- Sm-Nd Isotopes. Sm-Nd whole-rock analyses matic crystals with oscillatory cores present a Ma ( MSWD p 35 ע were also undertaken at the CPGeo-USP using a 206Pb/238U mean age of613 Finnegan 262 multicollector mass spectrometer 0.51), which is related to the magmatic protolith, and following the procedures described by Sato et whereas another grain, with a lower Th/U ratio and al. (1995). 143Nd/144Nd ratios have an analytical un- an age of ca. 990 Ma, is interpreted as a premag- certainty of 0.014% (2j). Analytical uncertainty on matic xenocryst. the 147Sm/144Nd ratio is estimated at 0.5%. The La The mylonitized granitoid CM-131A (9Њ58Ј41ЉS, Jolla and BCR-1 standards respectively yielded 76Њ6Ј20ЉW; fig. 4B) exhibits a strong fabric defined -1j) and by small muscovite crystals, with associated re) 0.000025 ע 143Nd/144Nd ratios of0.511849 -1j). Sm-Nd depleted mantle crystallized quartz bands that suggest deforma) 0.000027 ע 0.512662 Њ model ages (TDM) were calculated following De Pao- tional temperatures lower than 400 C (cf. Passchier lo et al. (1991). and Trouw 1996). Five multigrain zircon populations were selected for U-Pb TIMS analysis. Three of the analyzed fractions are strongly concordant, U-Pb Geochronological Results Ma ( MSWD p 5 ע with a 206Pb/238U age of468 Analytical results are listed in table A1 and sample 0.29) that we interpret as the magmatic crystalli- locations are included on fig. 3. Analyses of detrital zation age, whereas the other two fractions are dis- zircons with LAM-ICP-MS followed a quantitative cordant. They present older 206Pb/238U ages of 1478 approach, and zircons were randomly selected Ma, which point to the presence of an older inher- (Gehrels et al. 2006). In order to review metamor- ited component. phic overgrowths, we obtained CL images of the ESB. Detrital zircons from two schist samples zircons before the SHRIMP analysis. For zircons collected near the town of Huańuco (fig. 3) were with ages 11.0 Ga, 207Pb/206Pb ages were preferred, analyzed by the U-Pb LAM-ICP-MS. Sample CM- whereas for the younger grains, 206Pb/238U ages were 116 (9Њ47Ј7ЉS, 76Њ4Ј19ЉW) is a greenschist-facies preferred. Analyses with discordant values 110% calc-silicate schist, and sample CM-228 (9Њ49Ј16ЉS, were discarded. 76Њ1Ј19ЉW) is a garnet-mica schist that has yielded Orthogneiss and Mylonitic Granitoid. This com- PT conditions of 600ЊC and 7 kbar (Cardona et al. posite unit is part of a high-grade metamorphic in- 2007). lier within the ESB. It crops out in the high moun- In general, the zircon crystals are prismatic to tains between the towns of Ambo and Huańuco (fig. rounded, with U/Th ratios !12 that can be related 3). The granitoid intrudes gneissic rocks, whereas to a former magmatic origin (Rubatto 2002). The its relationship with the ESB is probably tectonic. 104 dated zircon grains from sample CM-116 yield Both lithologies were subsequently affected by predominantly concordant ages, with a prominent greenschist-facies mylonitic fabric that is presum- 207Pb/206Pb age population between 960 and 1400 292 A. CARDONA ET AL.

Figure 4. U-Pb concordia diagrams from samples CM-80 (A) and CM-131A (B).

Ma (n p 86 ), with 66 of these grains concordant in ratios !1 and yield a well-defined 206Pb/238U age of Ma (fig. 6A). Oscillatory zoned cores yield 8 ע the 1120–1280-Ma age range (fig. 5A). A smaller 325 group of six analyses ranges between 1800 and 1900 ages between 400 and 650 Ma. Ma, whereas two groups of four grains each yield Zircons from migmatite CM-222 (9Њ51Ј50ЉS, ages of 800 and 1480 Ma. 75Њ58Ј32ЉW) exhibiting nebulitic structure were Zircons from sample CM-228 are also concor- also analyzed by SHRIMP. Two main zircon pop- -ulations were observed, a prismatic equidimen ע dant, with the youngest and oldest ages of 465 -Ma (207Pb/206Pb), sional population and a fragmented, ovoid popu 16 ע 6Ma (206Pb/238U) and 2714 respectively (fig. 5B). The dominant zircon population. Internal structures seen in CL images lation ranges between 460 and 860 Ma (n p 71 ), include oscillatory and homogenous domains. with most grains yielding ages younger than 620 Twleve zircons were analyzed and revealed highly Ma. Twenty-one grains with Early Neoproterozoic variable ages (fig. 6B). Oscillatory zoned cores show to Mesoproterozoic ages (960–1240 Ma) were also a concordant age spectrum between 520 and 650 obtained. Two grains have 207Pb/206Pb ages of Ma, with some isolated grains with ages of 890 and Ma, while two additional 1790 Ma. Rims yield early Ordovician ages as well 27 ע 20and 1929 ע 1365 grains are concordant with 207Pb/206Pb ages of as younger ages of 350 and 400 Ma. Although some Ma. Along with some dis- of these analyses are highly discordant due to the 17 ע 26and 2532 ע 2150 cordant old grains, this shows the presence of a small size of the crystals, these data loosely con- Paleoproterozoic and Archean detrital component. strain migmatite development to the Early ESB Migmatites. Two migmatite bodies spatially Carboniferous. associated with the eastern schists were sampled WSB. Four samples from the WSB (fig. 3) were (fig. 3). An apparent metamorphic break is observed analyzed by the U-Pb zircon LAM-ICP-MS (two between the schists and the migmatites, with the samples) and by SHRIMP (two samples). Three of lower-grade greenschist facies changing abruptly to the samples, CM-112 (9Њ32Ј34ЉS, 76Њ38Ј34ЉW), CM- a banded and nebulitic migmatite. Concordant and 116U (9Њ47Ј07ЉS, 76Њ4Ј19ЉW), and CM-133 discordant granite injections crosscut the schists. (9Њ49Ј16ЉS, 76Њ34Ј17ЉW) are muscovite-albite- Eighteen zircons from the banded migmatite quartz schists. The other sample, CM-158 CM-35 (9Њ34Ј17ЉS, 76Њ0Ј54ЉW) that transitionally (9Њ51Ј22ЉS, 76Њ24Ј26ЉW) is a meta-arenite, with por- grade to a micaceous granite and a series of peg- phyroclasts of K-feldspar, muscovite and biotite, matites were dated by SHRIMP. This sample comes and a foliation defined by small white micas. from the same area where Dalmayrac et al. (1988) Zircons from the four samples are mainly pris- reported a Neoproterozoic U-Pb zircon lower in- matic, with some abrasion on the rim tips, probably tercept age from a garnetiferous paragneiss. The due to sedimentary transport. CL imaging on some grains are prismatic to weakly rounded, with CL of the samples show predominantly oscillatory images characterized by cores with oscillatory zon- zoned zircons with lesser homogenous and sector ing and homogenous rims. The rims have Th/U zoned ones. U/Th ratios of most of these zircons Figure 5. U-Pb detrital zircon histograms from metasedimentary rocks of the eastern and western schist belts. A, CM- 116; B, CM-228; C, CM-112; D, CM-158; E, CM-116U; F, CM-133. 294 A. CARDONA ET AL.

Figure 6. U-Pb concordia diagrams from migmatite samples CM-35 (A) and CM-222 (B).

are !12 suggesting a typical magmatic origin (Vabra zircon analyses yield concordant 207Pb/206Pb ages of .Ma 14 ע 19and 1442 ע et al. 1999; Rubatto et al. 2002). 1936 LAM-ICP-MS analysis of 123 zircons from sam- Sample CM-133 was also analyzed by SHRIMP. ple CM-112 exhibits a quasi-continuous age spectra The youngest three zircons from this sample yield between 500 and 2800 Ma (fig. 5C). There is a prom- concordant ages, with two grains defining a mean Ma (2j) and the third 2.3 ע inent 206Pb/238U age population between 500 and 206Pb/238U age of337.2 -Ma. (fig. 5F). The dominant pop 4 ע Ma (n p 63 ) and a lesser one at 1700–2400 Ma yielding385 660 (n p 26 ). Older Archean zircons were also found, ulation includes 22 zircons with ages in the 460– including four grains that yield a weighted mean 720-Ma time interval, with peaks at 468, 530, and 2j). 645 Ma. Eleven zircons yield single ages between) 61 ע average age of2670 Sample CM-158 (n p 93 ), dated by the same 850 and 1300 Ma. Finally, there is a minor sub- method, yields mostly concordant zircon ages (fig. population that yields Paleoproterozoic ages of .Ma 22 ע 28and 2081 ע 5D) in two continuous intervals from between 310 2461 and 800 Ma and between 900 and 1420 Ma (n p Nd Isotopes. Whole-rock samples for Sm-Nd iso- 85). The youngest concordant zircon has a 206Pb/ topic analysis were selected to cover the spectrum -Ma. Although older zircons are of lithologies in the ESB and the WSB. Twelve sam 7 ע 238U age of317 apparently less concordant, they point to the pres- ples from the eastern belt and six from the western ence of Paleoproterozoic and Archean material in belt were analyzed (table A2; fig. 3). All samples the source region. The most abundant subpopula- were thoroughly screened for weathered portions tion (n p 44 ) yields ages between 480 and 640 Ma, and veining. whereas there is another minor population of 13 In order to check for possible postdepositional ␧ grains with ages in the 310–480 Ma range. There alteration, fSm/Nd versus Nd was evaluated for the are also age groups of 640–800 Ma (n p 15 ) and time of deposition of the sedimentary protolith 900–1420 Ma (n p 22 ). (Bock et al. 1994; Cullers et al. 1997). Both belts Zircons from sample CM-116U were analyzed by yield values typical of a sedimentary trend (fig. 7, SHRIMP, and CL images were obtained in order to left), with just one of the samples (CM-83) yielding

select specific spots on the grains. Five of the zir- an fSm/Nd of 0.19, suggesting some fractionation dur- cons show concordant Late Paleozoic 206Pb/238U ing metamorphism. Therefore, the results are con- ages between 324 and 356 Ma (fig. 5E), whereas the sidered to reveal significant information on the other 19 define an age interval between 432 and provenance of the sedimentary protoliths. 591 Ma, (with small peaks at 477, 539, and 582 Ma). Depositional ages for the two metasedimentary Another group of 14 zircons yields Mesoproterozoic belts were estimated based on the youngest detrital ages between 1000 and 1370 Ma, and the last two zircon ages, stratigraphical relationships with ov- Journal of Geology GROWTH OF A GONDWANAN ACCRETIONARY OROGEN 295

␧ Figure 7. Left, fSm/Nd versus Nd diagram for evaluation of postdepositional alteration (Bock et al. 1994). Right, Sm-Nd envelopes from the eastern and western schist belts compared with other provinces and tectonic domains.

erlying Paleozoic sedimentary units, intrusive re- and Haeberlin (2002) at close to latitude 8ЊS, within lationships, and constraints on the timing of meta- metamorphic rocks also ascribed to the Maranõn morphism. For the ESB, the youngest detrital zircon Complex. has a 206Pb/238U age of 440 Ma, Ar-Ar muscovite The Nd isotopic evolution trend of the Maranõn metamorphic ages are ca. 420 Ma, and the oldest Complex (fig. 7, right) overlaps with that of the intrusive rock has yielded K-Ar amphibole ages of southwest Amazonian Craton (Cordani et al. 2000). ca. 360 Ma (Cardona et al. 2007). For the WSB, the Sm-Nd model ages of the Maran˜ on Complex are youngest detrital zircon age is ca. 320 Ma, and K- similar to crystallization ages of igneous rocks of Ar muscovite ages are ca. 300 Ma (Cardona 2006). the Rondonian San Ignacio and Sunsas provinces Lower Permian sediments are deposited over the of the Amazonian Craton that were formed be- western schists. Taking all this into account, 430 tween 1.0 and 1.5 Ga (Tassinari et al. 2000). Such Ma and 310 Ma are considered to be close to the an isotopic signature is also similar to the one of probable depositional ages of the eastern and west- the Paleozoic sequences of the Bolivian and Chi- ע ern belts, respectively. Variations up to 30 Ma lean Andes (fig. 7, right), which yield Sm-Nd TDM ␧ ␧ will be practically negligible for the calculated Nd model ages of 1.6–2.2 Ga and Nd values between values. Ϫ6 and Ϫ11 (Lucassen et al. 2000; Egenhoff and The lower- and higher-grade metasediments of Lucassen 2003). ␧ the ESB schists yield negative Nd (430 Ma) values be- Grenvillian-age basement from the coastal Are- tween Ϫ6.3 and Ϫ12.5 (fig. 7, right), whereas sam- quipa massif in southern Peru presents slightly ␧ ples from the WSB also yield similar Nd(320Ma) values older TDM values, between 1.9 and 2.3 Ga (Loewy Ϫ Ϫ in the 7.1 to 13.2 interval. Sm-Nd TDM model et al. 2004), whereas the basement inliers of the ages were calculated after De Paolo et al. (1991) to northern Colombian Andes yield consistent Sm-Nd account for minor Sm/Nd fractionation, and they model ages of 1.6–1.9 Ga (Cordani et al. 2005). yield values between 1.7 and 2.1 Ga for the ESB Tectonostratigraphic Constraints. The geochro- and 1.6–2.0 Ga for the WSB (fig. 4B). nology results reported above provide a new tec- ␧ The negative Nd values from both metasedimen- tonostratigraphic framework for the Maranõn tary belts suggest the presence of old, highly dif- Complex at 10ЊS (fig. 8). U-Pb zircon dating implies ferentiated source areas. Moreover, the variations a ∼613-Ma magmatic event within Grenvillian- ␧ in TDM model ages and Nd values reflect the exis- type basement. This basement was affected by an ע tence of mixed components of different age (cf. amphibolite-facies metamorphic episode at 484 Goldstein et al. 1997; Bock et al. 2000). The great 12 Ma, as indicated by the crystallization of over- similarity of the Nd isotopic signature of the two growths of metamorphic zircon, and was intruded -Ma. Subsequently two vol 2 ע belts together with the detrital zircon data also sug- by granitoids at468 gests that they shared the same sources. Values in cano-sedimentary basins were laid down. The first the same range were obtained by Macfarlane (1999) was metamorphosed in the Middle Paleozoic, and 296 A. CARDONA ET AL.

Figure 8. Schematic tectonic evolution of the Maran˜ on Complex. ESB p Eastern Schist Belt, WSB p Western Schist Belt.

the second one was in the Late Paleozoic. Their age is marginally older than the inferred deposi- depositional history is constrained by their youn- tional age; (3) a subpopulation of the zircon age gest detrital zircons, the timing of metamorphism spectra correlates with the crystallization ages of in both units, and their stratigraphic relationships the orthogneisses and mylonitised plutonic rocks; with the overlying strata. Sedimentation is con- (4) zircons are of predominantly magmatic char- strained to 450–420 and 318–300 Ma for the ESB acter as evidenced by the U/Th ratios and the pre- and WSB, respectively. dominance of oscillatory zoning in CL images; and We attribute the greenschist-facies mylonitic (5) there is a gap in the Paleozoic detrital record event affecting the Ordovician granitoid and ortho- between 440 and 390 Ma. Such data suggest that gneiss to the early Paleozoic deformational event some of these tectonomagmatic events are region- of the ESB. A younger (Late Carboniferous to Early ally widespread and that the growth of both youn- Permian) deformational event is also recorded in ger basins was contemporaneous with magmatic the ESB. It is related to the formation of a crenu- activity. The continuous cannibalism within this lation cleavage and partial resetting of the isotopic orogenic belt, together with the presence of Me- systems (Cardona et al. 2007) as well as the gen- soproterozoic and older detrital zircon ages within eration of migmatites spatially related to granitoid the schists, and inherited zircon ages within plu- intrusions. tons, as well as the similar Nd isotopic signatures ␧ U-Pb detrital zircon results provide additional (negative Nd and Paleoproterozoic Sm-Nd TDM tectonostratigraphic constraints: (1) both eastern model ages) of the two schist belts, indicate that and western belts contain zircon grains that can be they formed on an active continental margin de- temporally related to the immediately preceding posited over old continental crust. geological events; (2) the youngest detrital zircon When the U-Pb detrital zircon data are compared Journal of Geology GROWTH OF A GONDWANAN ACCRETIONARY OROGEN 297 with the Sm-Nd whole-rock results, only 16% of (fig. 9B). This tectonomagmatic event has been re- the analyzed zircons yield crystallization ages older corded along most of the eastern Peruvian Andes, than the Proterozoic whole-rock Sm-Nd model including the northern and southern segments of ages. This trend may reflect a detrital contribution the Maran˜ on Complex (Chew et al. 2007b) and the of siliciclastic particles other than zircon, possibly Arequipa massif in southern Peru, where syn- and including rare earth element–rich phases such as post-tectonic granitoids were emplaced between epidote or monazite (Goldstein et al. 1997; Dickin 472 and 460 Ma (Loewy et al. 2004). Additionally, 2000). However, we consider that it is more feasible in the southern segment of the Eastern Cordillera that the younger Paleozoic and Neoproterozoic of Peru, close to the city of Cuzco, Bahlburg et al. magmatic sources formed in a magmatic arc setting (2006) have demonstrated the existence of an Or- characterized by substantial contamination by dovician back-arc setting. A similar Paleozoic tec- older crust during its formation, as has been shown tonic configuration apparently exists along much to be a common feature within the central Andes of the proto-Andean margin, as seen by the pres- (Lucassen et al. 2004). ence of the Puna and Famatinian magmatic arcs in In the case of the Neoproterozoic to Ordovician the Chilean and Argentinean Andes (Bahlburg and geological record, the existence of well-defined Herve´ 1997; Pankhurst and Rapela 1998; Ramos phases of magmatic activity, together with contin- 2000), and by the presence of Ordovician-Silurian uous zircon detrital input between 660 and 450 Ma, magmatic and deformational events in the north- is compatible with an active margin setting (figs. ern Andes (Burkley 1976; Restrepo-Pace 1995; Ra- 8, 9A). The 480-Ma zircon overgrowths in the mos and Aleman 2000). orthogneiss are probably also linked to phases of The next major tectonomagmatic activity cor- magmatism in such a continental arc environment responds to the Silurian regional metamorphic

Figure 9. Paleogeography of the western margin of the Amazonian Craton (including the Maran˜ on Complex) between 600 and 300 Ma (modified from Cawood et al. 2001; Murphy et al. 2004a; Cordani et al. 2005.) 298 A. CARDONA ET AL. event recorded by the ESB and by the reworked sion of the arc-related basins (Herve´ et al. 1995; Ordovician magmatic basement. It also coincides Collins 2002; Stern 2002; Cawood and Buchan with a major gap in the magmatic record between 2007). The actual position of the Carboniferous 440 and 390 Ma, a feature that has been docu- continental magmatic arc more than 350 km from mented in other segments of the Eastern Cordillera the paleotrench (V. A. Ramos, pers. comm., 2007) of Peru (Chew et al. 2007b) as well as in northern can be explained with the accretion of a terrane Chile (Bahlburg and Herve´ 1997; Bahlburg and that causes the widening of the continental margin. Vervoort 2007). Recently Ramos (2008a) reviewed The late Paleozoic “Gondwanide” orogeny has the available evidence for possible terrane accre- been also documented in the Chilean Andes, where tion along the Peruvian margin. He considered that Late Carboniferous turbiditic sequences are de- the Paracas terrane was accreted to the Peruvian formed and are associated with the evolution of a margin during the Ordovician. Alternatively, we subduction complex (Bahlburg and Herve´ 1997; suggest that this event may be slightly younger Willner et al. 2005). In the Eastern Cordillera of the and may be represented by the Silurian medium- Bolivian Andes, a major deformational event be- pressure, Barrovian-type regional metamorphism tween 290 and 320 Ma has been recognized (Jacobs- within the ESB (fig. 9C). hagen et al. 2002), while in the Argentinean Andes, The restricted Silurian and the Devonian mag- a similar deformational event has been envisaged matic activity that followed the mentioned accre- for the Early Permian, as a consequence of a flat- tionary event may be related to a change in plate slab subduction process (Ramos 2008b). Within the vectors, or to an oblique convergent margin with northern Andes (Ecuador, Colombia, Venezuela) a restricted magmatic activity (fig. 9C). In contrast, few suites of syntectonic granitoids and some meta- several terrane-related accretionary events have morphic belts have been linked to the accretion of been documented in other segments of the Andean continental terranes associated with the formation belt in Argentina, Chile, and Colombia in Silurian of Pangaea and with the evolution of subduction of and Devonian time (Thomas and Astini 1996; Ra- the proto-Pacific lithosphere (Ramos and Aleman mos 2000, 2004; Ordoń˜ ez-Carmona et al. 2006). 2000; Vinasco et al. 2006; Cardona et al. 2008). Moreover, in the Chilean Andes there is evidence Following the orogenic phases, a period of major of a passive margin environment during this time extension with basin formation and bimodal mag- interval (Bahlburg and Herve´ 1997; Bahlburg and matism was installed along most of the Andes Vervoort 2007). (Kontak et al. 1985, 1990; Ramos 2000; Franzese Magmatic arc activity was reestablished in the and Spalletti 2001; Sempere et al. 2002; Miskovic Carboniferous, as evidenced by the U-Pb detrital et al. 2005). This latter extensional process has been record, the volcanic protoliths of the western related to a change in the convergence velocity be- schists, andesite flows associated with the Missis- tween the Pacific and South American plates dur- sipian Ambo Group (Dalmayrac et al. 1988), the U- ing the final assembly of Pangea, with the conse- Pb migmatite ages reported in this study, and K-Ar quent orogenic collapse of the Late Paleozoic amphibole and biotite ages of between 356 and 291 orogen (Gurnis 1988; Ramos and Aleman 2000). Ma (Cardona 2006). This activity is widespread Provenance of the Maran˜ on Complex. The U-Pb along the central and northern segments of the detrital zircon ages of the metamorphic rocks of Eastern Cordillera of Peru (Chew et al. 2007b; Mis- the Maran˜ on Complex indicate contributions from kovic et al. 2005, Miskovic and Schaltegger 2008). at least four main sources: Carboniferous-Ordovi- The end of the Late Paleozoic tectonic cycle is cian (n p 48 U-Pb detrital zircon analyses), Cam- marked by a major regional metamorphic event of brian–Middle Neoproterozoic (n p 207 ), Late Neo- Late Carboniferous–Early Permian age that affects proterozoic–Mesoproterozoic (n p 190 ), and an the western belt and produces the development of older discontinuous record that extends until 2.95 a crenulation cleavage within the eastern belt (Car- Ga (n p 66 ). As discussed above, the Neoprotero- dona et al. 2007). This metamorphic episode may zoic and Paleozoic sources must be related to the be connected with an apparent shutoff in magmatic continuous reworking of the continental margin, activity (fig. 9D). It is also expressed farther south while contemporaneous arc magmatism was in ac- in central Peru by the development of syntectonic tion. Taking into account the great similarities in migmatites at ca. 310 Ma (Chew et al. 2007b) and detrital zircon populations observed in the different in northern Peru by deformation of Carboniferous units of the Maran˜ on Complex, we used the entire granitoids along major shear zones (Haeberlin detrital record of the Maran˜ on Complex to con- 2002). Terrane accretion, or changes in the sub- strain further the provenance regions of the Cam- duction configuration may have caused the inver- brian to Proterozoic detritus (fig. 8). Journal of Geology GROWTH OF A GONDWANAN ACCRETIONARY OROGEN 299

Zircons older than Mesoproterozoic (including constrain the source of this detrital population in- some Archean) can be attributed to several geolog- clude the following: (1) the age-equivalent Brasili- ical provinces in the Amazonian Craton (Tassinari ano orogens at the eastern margin of Amazonia are et al. 2000). Moreover, the Sm-Nd TDM model ages far removed from the proto-Andean margin; (2) between 1.6 and 2.1 Ga are also comparable with within the western Amazon Craton, tectonomag- those of the granitoids of the Rondonian San Ig- matic events within this time period have not been nacio and Rio Negro–Juruena belts of the Amazo- found (Tassinari et al. 2000); (3) although Neopro- nian Craton and those of the Proterozoic inliers in terozoic rift-related magmatism is relatively com- the northern Andes (Cordani et al. 2000, 2005; mon on the Laurentia and Baltica margins during Loewy et al. 2004; Cordani and Teixeira 2007). Rodinia breakup (e.g., Tollo et al. 2004), it is pre- A significant zircon population is encountered dominantly mafic in character, and hence, its in- between 1.3 and 0.90 Ga (n p 156 ) with major volvement as a major detrital zircon source to peaks at 1030, 1230, and 1320 Ma. These ages re- proto-Andean sedimentary sequences is likely to be flect tectonomagmatic episodes related to Grenvil- limited (Cawood et al. 2001; Bream et al. 2004; lian-type orogens that culminated with the juxta- Thomas et al. 2004; Carter et al. 2006). position of Laurentia and Baltica with the Amazon It is commonly assumed that separation between Craton, in the process of agglutination of Rodinia Laurentia and Amazonia took place at about 570 (Hoffman 1991). Proximal sources for these might Ma, whereas between Laurentia and Baltica it was be the Rondonian San Ignacio and Sunsas provinces around 600 Ma (Bingen et al. 1998; Cawood et al. of the Amazonian Craton (Litherland et al. 1989; 2001; Kinny et al. 2003). We consider that the ex- Tassinari et al. 2000; Cordani and Teixeira 2007). tensive Neoproterozoic detrital record at the west- Alternative sources are a few Proterozoic basement ern margin of Gondwana must be related to a major inliers found along the northern Andean belt, in felsic-intermediate magmatic source that is more Colombia and Venezuela (Cordani et al. 2005). In likely to have an arc affinity, and therefore, an al- Peru, two Grenvillian domains have been recog- ternative tectonic scenario could be an earlier sep- nized. First, the Arequipa Massif, characterized as aration between Amazonia and Baltica-Laurentia major terrane including magmatic and high-grade followed by the installation of an active margin metamorphic rocks with 0.97–1.2 Ga (Wasteneys operated by subduction since at least 640 Ma. This et al. 1995; Loewy et al. 2004; Chew et al. 2007a). continental arc is considered to be the major feeder Second, in the southeastern part of the Peruvian of the extensive Neoproterozoic to Cambrian zir- Amazon basin, there is an isolated massif of gran- con found in the Maran˜ on schist belts. This in- Ma ferred Neoproterozoic subduction phase started 23 ע ulite that has yielded a U-Pb age of1140 (Dalmayrac et al. 1988). earlier than those already envisaged for Laurentia, The above evidence seems to imply that a major Baltica, and other segments of the proto-Andean Grenvillian-related domain extends along this seg- margin, considered respectively at 500, 550–560, ment of the western margin of Gondwana, includ- and 600 Ma (Rapela et al. 1998; Van Staal et al. ing the central Peruvian and Colombian Andes. 1998; Cocks and Torsvik 2005; Escayola et al. Moreover, if we consider the position of the Ron- 2007). However, the 640 Ma subduction process donian San Ignacio orogenic belts at the south- would be contemporaneous with the initiation of western edge of the Amazonian Craton, we envis- subduction-related magmatism on several peri- age that this Grenvillian domain may continue also Gondwana terranes, including the southernmost under the Acre and Solimo˜ es sedimentary basins. Pampean terrane of the proto-Andean margin (Mur- The Neoproterozoic crystallization age of the phy et al. 2004; Escayola et al. 2007) CM-80 orthogneiss protolith falls within the age Another consequence of this tectonic configu- interval of the Cambrian to Neoproterozoic detrital ration is the potential connection with several peri- zircon ages (n p 207 ) whose major peaks are at 545, Gondwanan terranes such as Avalonia, Ganderia, 595, and 645 Ma. This population is the most abun- Carolinia, and Iberia. These terranes formed as in- dant in the detrital record in other segments of the traoceanic and continental arcs and yield U-Pb and eastern Peruvian Andes, south of Lima (Chew et Sm-Nd isotopic signatures that might place them al. 2007a, 2008). It is of special interest, as the role in the vicinity of the Amazonian Craton at the of the proto-Andean margin in relation with the northwest margin of Gondwana from 650 Ma until processes of Rodinian fragmentation and subse- the Cambro-Ordovician when they departed (Kep- quent Gondwana assembly is poorly understood pie et al. 1998; Murphy et al. 2000, 2004a; Gutier- (Pankhurst and Rapela 1998; Chew et al. 2008). rez-Alonso et al. 2003; Ingle et al. 2003; Collins and Critical issues that must be considered in order to Buchan 2004; Carter et al. 2006; Reusch et al. 2006; 300 A. CARDONA ET AL.

Rogers et al. 2006). Concrete evidence of the ac- Complex at 10ЊS in the Eastern Cordillera of the cretion of these terranes to the continental margin Peruvian Andes provide a tectonostratigraphic is still scarce. However, examples may be found in framework for the proto-Andean margin from the the Venezuelan Andes, where syntectonic Neopro- Neoproterozoic until the Late Carboniferous. terozoic granitoids associated with a low- to me- These include development of an arc since 620 Ma dium-grade metamorphic event are reported from or earlier that lasted until the Silurian, while a ma- the Bella Vista Group (Burkley 1976; Ramos and jor metamorphic event occurred at about 480 Ma. Aleman 2000). If these terranes were accreted dur- 2. Two separate volcano-sedimentary basins ing the Neoproterozoic, they might provide a mech- formed within an arc-related setting. The older ba- anism for the structural inversion of the passive sin was deformed and metamorphosed during the margin of the Amazonian Craton that must have Middle Silurian under regional (Barrovian) meta- formed after the Rodinia breakup. The detrital zir- morphic conditions that may have been related to con populations of the Peruvian segment of the ocean closure and a terrane accretionary event. The proto-Andean margin are also comparable with the younger basin was formed during the Carbonifer- detrital zircon record of these peri-Gondwanan ter- ous, and its inversion at around 300–310 Ma may ranes (Keppie et al. 1998; Murphy et al. 2000, be related to either a terrane accretionary event or 2004b; Gutierrez-Alonso et al. 2003; Ingle et al. to a change in subduction dynamics. In between 2003; Collins and Buchan 2004; Carter et al. 2006; the deposition of these two basins there is a Silurian Reusch et al. 2006; Rogers et al. 2006), which also to Devonian gap in the magmatic record. This tec- indicates a possible connection. tonic evolution is part of the long-lived peri-Gond- Paleogeographic studies from central Peru have wanan Terra Australis orogen that commenced af- suggested that a terrane with continental basement ter the separation between Laurentia and Godwana. was located against the western margin of the East- It evolved by subduction of the proto-Pacific ocean ern Cordillera, bounded to the east by the Maranõn and lasted until the Gondwanide-Alleghenian oro- Complex (see reviews by Ramos and Aleman 2000; genic events that culminated in the assembly of Ramos 2008a). This inferred terrane, termed “Para- Pangaea (Cawood 2005). cas,” has been considered a conjugate margin to the 3. Provenance constraints based on U-Pb detrital Oaxaquia terrane (Ramos and Aleman 2000; Ramos zircon data have shown that this margin grew on 2008a), a major Gondwanan Mesoproterozoic do- the edge of the Amazonian Craton, and was prox- main with an Ordovician sedimentary cover imal to major orogenic belts of Grenvillian and that forms the southern portion of Mexico (Ortega- Brasiliano age. The presence of a Neoproterozoic Gutierrez et al. 1995; Keppie and Ortega-Gutie´rrez orogenic belt at the proto-Andean margin suggests 1999). However, the Nd isotope record from Oaxa- an earlier fragmentation of the margins of Gond- quia and the U-Pb detrital record from its younger wana with Baltica and Laurentia (Chew et al. 2008) Paleozoic cover sequences (Weber and Ko¨ hler 1999; and a possible connection with several Peri-Gond- Gillis et al. 2005) do not exhibit the strong Neo- wanan arc-related terranes. proterozoic to Cambrian signature found within 4. The Paleoproterozoic Sm-Nd TDM model ages the Maran˜ on segment of the Proto-Andean margin. contrast with the younger U-Pb zircon detrital ages Recent reviews of Rodinian paleogeography have and indicate that recycling of older crust was an questioned the Peruvian connection with the Oaxa- important element in the Mesoproterozoic, Neo- quia microcontinent (Keppie and Dostal 2007). Al- proterozoic, and Early Paleozoic evolution of the though the position of the conjugate terrane re- Peruvian segment of the proto-Andean margin. mains uncertain, we think that a major terrane 5. The growth of this active convergent margin dispersion event took place during the Neoprote- results from several stages of subduction as well as rozoic, either associated with Rodinia breakup or terrane accretion and dispersion. Whereas some with the departure of Avalonia-Cadomia-type ter- events may be of local character, the synchronicity ranes. Young south to north Meosozic dispersion with similar events along the Andean chain may events are also possible, as suggested by recent pa- reflect a more regional-scale plate tectonic control leomagnetic data from the Colombian Andes (Bay- (Cawood and Buchan 2007; Ramos 2008a). ona et al. 2006).

ACKNOWLEDGMENTS Conclusions We wish to acknowledge the support received from 1. Lithostratigraphic evidence, U-Pb zircon geo- the Saõ Paulo State Research Agency (FAPESP), chronology and Nd isotopic data from the Maranõn grant 02/072488-3. We thank the colleagues and the Journal of Geology GROWTH OF A GONDWANAN ACCRETIONARY OROGEN 301 staff of the Geochronological Research Center of edged for discussions and help during field work. the University of Saõ Paulo for technical help and Thorough and clear reviews and suggestions by V. fruitful discussions. J. Machare´ and O. Palacios of A. Ramos, J. Aleinikoff, and A. Anderson are ac- the Peruvian Geological Survey (INGEMMET) are knowledged. The assistance of M. Marulanda dur- acknowledged for their logistical support and help ing field work and other stages of this research is provided during several stages of this research. A. deeply appreciated. These results are part of A. Car- Zapata and J. Galdos of INGEMMET are acknowl- dona’s PhD thesis at the University of Saõ Paulo.

REFERENCES CITED

Bahlburg, H. 1993. Hypothetical southeast Pacific con- new provenance constraints for part of the Laurentian tinent revisited: new evidence from the middle Pa- Margin. Geol. Soc. Am. Mem. 197:459–474. leozoic basins of northern Chile. Geology 21:909–912. Burkley, L. A. 1976. Geochronology of the central Ven- Bahlburg, H.; Carlotto, V.; and Ca´rdena, J. 2006. Evidence ezuelan Andes. PhD dissertation, Case Western Re- of Early to Middle Ordovician arc volcanism in the serve University, Cleveland, 150 p. Cordillera Oriental and Altiplano of southern Peru, Cardona, A. 2006. Reconhecimento da evoluçaõ tectoˆn- Ollantaytambo Formation and Umachiri beds. J. S. ica da proto-margem Andina do centro-norte Peruano, Am. Earth Sci. 22:52–65. baseada em dados geoquı´micos e isoto´ picos do em- Bahlburg, H., and Herve´, F. 1997. Geodynamic evolution basamento da Cordilheira Oriental na regiaõ de Hua´- and tectonostratigraphic terranes of northwestern Ar- nuco-La Unio´ n. PhD thesis, Universidade de Saõ gentina and northern Chile. Geol. Soc. Am. Bull. 109: Paulo. 247 p. 869–884. Cardona, A.; Cordani, U.; and Nutman, A. 2008. U-Pb 40 39 Bahlburg, H., and Vervoort, J. D. 2007. LA-ICP-MS geo- SHRIMP zircon, Ar/ Ar geochronology and Nd iso- chronology of detrital zircons in Late Paleozoic tur- topes from gneissic and granitoid rocks of the Illescas bidite units of northern Chile: implications for terrane massif, Peru´ : a southern extension of a fragmented processes. Goldschmidt Conf. Abstr. 71 15S:A51. Late Paleozoic orogen? In VI South American Sym- Basei, M. A. S.; Siga, O., Jr.; Sato, K.; and Sproeser, W. posium on Isotope Geology, San Carlos de Bariloche, M. 1995. A instalaçaõ da metodologia U-Pb na univer- Argentina. Extended abstracts. sidade de Saõ Paulo. An. Acad. Bras. Cienc. 67:221– Cardona, A.; Cordani, U.; Ruiz, J.; Valencia, V.; Nutman, 237. A.; and Sanchez, A. 2006. U-Pb detrital zircon geochronology and Nd isotopes from Paleozoic meta-sed- Bayona, G.; Rapalini, V.; and Costanzo-Alvarez, V. 2006. imentary rocks of the Maran˜ on Complex: insights on Paleomagnetism in Mesozoic rocks of the northern the proto-Andean tectonic evolution of the eastern Andes and its implications in Mesozoic tectonics of Peruvian Andes. In Proceedings, V South American northwestern South America. Earth Planets Space 58: Symposium on Isotope Geology, Punta del Este, Uru- 1–18. guay, p. 208–211. Benavides-Caćeres, V. 1999. Orogenic evolution of the Cardona, A.; Cordani, U.; and Sanchez, A. 2007. Meta- Peruvian Andes: the Andean cycle. In Skinner, J., ed. morphic, geochronological and geochemical con- Geology and ore deposits of the central Andes. Soc. straints from the pre-Permian basement of the eastern Econ. Geol. Spec. Publ. Ser. 7, p. 61–107. Peruvian Andes (10ЊS): a Paleozoic extensional-accre- Bingen, B.; Demaiffe, D.; and van Breemen, O. 1998. The tionary orogen? 20th Colloquium on Latin American 616 Ma old Egersund basaltic dyke swarm, SW Nor- Earth Sciences, April 11–13, Kiel, Germany. Abstracts, way, and Late Neoproterozoic opening of the Iapetus p. 29–30. Ocean. J. Geol. 106:565–574. Carter, B. T.; Hibbard, J. P.; Tubrett, M.; and Sylvester, Bock, B.; Bahlburg, H.; Wo¨ rner, G.; and Zimmermann, P. 2006. Detrital zircon geochronology of the Smith U. 2000. Tracing crustal evolution in the southern River Allochthon and Lynchburg Group, southern Ap- central Andes from Late Precambrian to Permian with palachians: implications for Neoproterozoic-Early geochemical and Nd and Pb isotope data. J. Geol. 108: Cambrian paleogeography. Precambrian Res. 147:279– 515–535. 304. Bock, B.; McLennan, S. M.; and Hanson, G. N. 1994. Rare Cawood, P. A. 2005. Terra Australis Orogen: Rodinia element redistribution and its effects on the neodym- breakup and development of the Pacific and Iapetus ium isotope system in the Austin Glen Member of the margins of Gondwana during the Neoproterozoic and Normanskill Formation, New York, USA. Geochim. Paleozoic. Earth Sci. Rev. 69:249–279. Cosmochem. Acta 58:5245–5253. Cawood, P. A., and Buchan, C. 2007. Linking accretionary Bream, B. R.; Hartcher, R. D.; Miller, C. F.; and Fullagar, orogenesis with supercontinent assembly. Earth Sci. P. D. 2004. Detrital zircon ages and Nd isotopic data Rev. 82:217–256. form the southern Appalachian crystalline core, Geor- Cawood, P. A.; McCausland, P. J. A.; and Dunning, G. R. gia, South Carolina, North Carolina and Tennessee: 2001. Opening Iapetus: constraints from the Lauren- 302 A. CARDONA ET AL.

tian Margin in Newfoundland. Geol. Soc. Am. Bull. del cuadrańgulo de Panao, 20L. Lima, Peru, Instituto 113:443–453. Geolo´ gico Minero y Metalu´ rgico. Chew, D. M.; Kirkland, C. L.; Schaltegger, U.; and Good- De Paolo, D. J.; A. M. Linn; and Schubert, G. 1991. The hue, R. 2007a. Neoproterozoic glaciation in the Proto- continental crustal age distribution: methods of de- Andes: tectonic implications and global correlation. termining mantle separation ages from Sm-Nd iso- Geology 35:1095–1099. topic data and application to the southwestern U.S. J. Chew, D. M.; Magna, T.; Kirkland, C. L.; Miskovic, A.; Geophys. Res. 96:2071–2088. Cardona, A.; Spikings, A.; and Schaltegger, U. 2008. Dickin, A. P. 2000. Crustal formation in the Grenville Detrital zircon fingerprint of the Proto-Andes: evi- Province: Nd isotope evidence. Can. J. Earth Sci. 37: dence for a Neoproterozoic active margin? Precam- 165–181. brian Res. 167:186–200. Dickinson, W. R., and Gehrels, G. E. 2003. U-Pb ages of Chew, D. M.; Schaltegger, U.; Kosler, J.; Whitehouse, M. detrital zircons from Permian and Jurassic eolianite J.; Gutjahr, M.; Spikings, R. A.; and Miskovic, A. sandstones of the Colorado Plateau, USA: paleogeo- 2007b. U-Pb geochronologic evidence for the evolu- graphic implications. Sediment. Geol. 163:29–66. tion of the Gondwanan margin of the north-central Egenhoff, S. O., and Lucassen, F. 2003. Chemical and Andes. Geol. Soc. Am. Bull. 119:697–711. isotopical composition of Lower to Upper Ordovician Cobbing, E. J., and Sanchez, A. W. 1996a. Mapa geolo´ gico sedimentary rocks (central Andes/South Bolivia): im- del cuadrańgulo de La Unio´ n, 20J. Lima, Peru, Insti- plications for their source. J. Geol. 111:487–497. tuto Geolo´ gico Minero y Metalu´ rgico. Escayola, M. P.; Pimental, M.; and Armstrong, R. 2007. ———. 1996b. Mapa geolo´ gico del cuadrańgulo de Yan- Neoproterozoic backarc basin: sensitive high-resolu- ahuanca, 21J. Lima, Peru, Instituto Geolo´ gico Minero tion ion microprobe U-Pb and Sm-Nd isotopic evi- y Metalu´ rgico. dence from the eastern Pampean ranges, Argentina. Cocks, R. L., and Torsvik, T. H. 2005. Baltica from the Geology 35:495–498. late Precambrian to mid-Palaeozoic times: the gain Fedo, C. M.; Sircombe, K. N.; and Rainbird, R. H. 2003. and loss of a terrane’s identity. Earth Sci. Rev. 72:39– Detrital zircon analysis of the sedimentary record. In 66. Hanchar, J. M., and Hoskin, P. W. O., eds. Zircon: re- Collins, A., and Buchan, C. 2004. Provenance and age views in mineralogy and geochemistry. 53:277–303. constraint of the South Stack Group, Anglesey, UK: Franzese, J. R., and Spalletti, L. A. 2001. Late Triassic– U-Pb SIMS detrital zircon data. J. Geol. Soc. Lond. 161: early Jurassic continental extension in southwestern 743–746. Gondwana: tectonic segmentation and pre-break-up Collins, W. J. 2002. Hot orogens, tectonic switching, and rifting. J. S. Am. Earth Sci. 14:257–270. creation of continental crust. Geology 30:535–538. Gehrels, G. E.; Valencia, V.; and Pullen, A. 2006. Detrital Cordani, U. G.; Cardona, A.; Jimenez, D.; Liu, D.; and zircon geochronology by laser-ablation multicollector Nutman, A. P. 2005. Geochronology of Proterozoic ICPMS at the Arizona LaserChron Center. In Ol- basement inliers from the Colombian Andes: tectonic szewski, T.D., ed. Geochronology: emerging oppor- history of remmants from a fragmented Grenville belt. tunities. Paleontol. Soc. Pap. 12:67–76. In Vaughan, A. P. M.; Leat P. T.; Pankhurst, R. J., eds. Gehrels, G. E.; Valencia, V.; and Ruiz, J. 2008. Enhanced Terrane processes at the margins of Gondwana. Geol. precision, accuracy, efficiency, and spatial resolution of Soc. Lond. Spec. Publ. 246:329–346. U-Pb ages by laser ablation–multicollector–inductively Cordani, U. G.; Sato, K.; Teixeira, W.; Tassinari, C. C. G.; coupled plasma–mass spectrometry. Geochem. Geo- and Basei, M. A. S. 2000. Crustal evolution of the phys. Geosyst., doi: 10.1029/2007GC001805. South American Platform. In Cordani, U. G.; Milani, Gillis, R. J.; Gehrels, G. E.; Ruiz, J.; and Flores de Dios, E. J.; Thomaz, A., and Campos, D. A., eds. Tectonic L. 2005. Detrital zircon provenance of Cambrian- evolution of South America. 31st International Geo- Ordovician and Carboniferous strata of the Oaxaca logical Congress, Rio de Janeiro, p. 19–40. terrane, southern Mexico. Sediment. Geol. 182:87– Cordani, U. G., and Teixeira, W. 2007. Proterozoic ac- 100. cretionary belts in the Amazonian Craton. In Hatcher, Goldstein, S. L.; Arndt, N. T.; and Stallard, R. F. 1997. R. D., Jr.; Carlson, M. P.; McBride, J. H.; and Martıńez- The history of a continent from U-Pb ages of zircons Catalań, J. R., eds. 4-D framework of continental from Orinoco River sand and Sm-Nd isotopes in Ori- crust. Geol. Soc. Am. Mem. 200:297–320. noco basin river sediments. Chem. Geol. 139:269–284. Cullers, R. L.; Bock, B.; and Guidotti, C. 1997. Elemental Grandin, G., and Navarro, J. 1979. Las rocas ultrabasicas distributions and neodymium isotopic compositions en el Peru, las intrusiones lenticulares y los sills de of Silurian metasediments, western Maine, USA: re- la regio´ n de Huanuco-Monzon. Bol. Soc. Geol. Peru distribution of the rare earth elements. Geochim. Cos- 63:99–115. mochim. Acta 61:1847–1861. Gurnis, M. 1988. Large-scale mantle convection and the Dalmayrac, B.; Laubacher, B.; and Marocco, R. 1988. Car- aggregation and dispersal of supercontinents. Nature acteres generales de la evolucio´ n geolo´ gica de los An- 332:695–699. des Peruanos. Instituto Geolo´ gico Minero y Metal- Gutierrez-Alonso, G.; Fernańdez-Sua´rez, J.; Jeffries, T. E.; u´ rgico, Bol. 12, 313 p. Jenner, G. A.; Tubrett, M. N.; Cox, R.; and Jackson, De la Cruz, J., and Valencia, M. 1996. Mapa geolo´ gico S. E. 2003. Terrane accretion and dispersal in the Journal of Geology GROWTH OF A GONDWANAN ACCRETIONARY OROGEN 303

northern Gondwana margin: an Early Paleozoic ana- Krogh, T. E. 1973. A low contamination method for de- logue of a long-lived active margin. Tectonophysics composition of zircon and extraction of U and Pb for 365:221–232. isotopic age determination. Geochim. Cosmochim. Haeberlin, Y. 2002. Geological and structural setting, age, Acta 37:485–494. and geochemistry of the orogenic gold deposits at the Litherland, M.; Annells, R. N.; Darbyshire, D. P. F.; Pataz Province, Eastern Andean Cordillera, Peru. PhD Fletcher, C. J. N.; Hawkins, M. P.; Klinck, B. A.; Mitch- thesis, University of Geneva. ell, W. I.; et al. 1989. The Proterozoic of eastern Bolivia Herve´, F.; Pankhurst, R. J.; Drake, R.; and Beck, M. E. and its relationship to the Andean mobile belt. Pre- 1995. Pillow metabasalts in a mid-Tertiary exten- cambrian Res. 43:157–174. sional basin adjacent to the Liquin˜ e-Ofqui fault zone: Loewy, S. L.; Connelly, J. N.; and Dalziel, I. W. D. 2004. the Isla Magdalena area, Ayseń, Chile. J. S. Am. Earth An orphaned basement block: the Arequipa-Antofalla Sci. 8:33–46. basement of the central Andean margin of South Hoffman, P. A. 1991. Did the birth of North America America. Geol. Soc. Am. Bull. 116:171–187. turn Gondwana inside out? Science 252:1409–1411. Lucassen, F.; Becchio, R.; Wilke, H. G.; Franz, G.; Thirl- Ingle, S.; Mueller, P. A.; Heatherington, A. L.; and Ko- wall, M. F.; Viramonte, J.; and Wemmer, K. 2000. Pro- zuch, M. 2003. Isotope evidence for the magmatic and terozoic-Paleozoic development of the basement of tectonic histories of the Carolina terrane: implications the central Andes (18–26ЊS)—a mobile belt of the for stratigraphy and terrane affiliation. Tectonophy- South American craton. J. S. Am. Earth Sci. 13:697– sics 371:187–211. 715. Jacobshagen, V.; Mu¨ ller, J.; Wemmer, K.; Ahrendt, A.; and Lucassen, F., and Franz, G. 2005. The early Palaeozoic Emmanuil, M. 2002. Hercynian deformation and Orogen in the central Andes: a non-collisional orogen metamorphism in the Cordillera Oriental of southern comparable to the Cenozoic high plateau? In Vaughan, Bolivia, central Andes. Tectonophysics 345:119–130. A. R. M.; Leat, P. T.; and Pankhurst, R. J., eds. Terrane Keppie, J. D.; Davis, D. W.; and Krogh, T. E. 1998. U-Pb processes at the margins of Gondwana. Geol. Soc. geochronological constraints on the Precambrian Lond. Spec. Publ. 246:257–273. stratified units in the Avalon Composite terrane of Lucassen, F.; Trumbull, R.; Franz, G.; Creixell, C.; Nova Scotia, Canada: tectonic implications. Can. J. Va´sques, P.; Romer, R. L.; and Figueroa, O. 2004. Dis- Earth Sci. 35:222–236. tinguishing crustal recycling and juvenile additions at Keppie, J. D., and Dostal, J. 2007. Rift-related basalt in active continental margins: the Paleozoic to recent the 1.2–1.3-Ga granulites of the northern Oaxacan compositional evolution of the Chilean Pacific margin Complex, southern Mexico: evidence for a rifted arc (36–41ЊS). J. S. Am. Earth Sci. 17:103–119. on the northwestern margin of Amazonia. Proc. Geol. Ludwig, K. J. 2003. Isoplot 3.00. Spec. Publ. 4, Berkeley, Assoc. 118:63–74. CA, Berkeley Geochronology Center, 70 p. Keppie, J. D., and Ortega-Gutie´rrez, F. 1999. Middle Macfarlane, A. W. 1999. Isotopic studies of northern An- America Precambrian basement: a missing piece of dean crustal evolution and ore metal source. In Skin- the reconstructed 1-Ga orogen. Geol. Soc. Am. Spec. ner, B. J., ed. Geology and ore deposits in the central Pap. 336:199–210. Andes. Econ. Geol. Spec. Publ. Ser. 7, p. 195–217. Keppie, J. D., and Ramos, V. 1999. Odyssey of terranes Macfarlane, A. W.; Tosdal, R. M.; Vidal, C.; and Paredes, in the Iapetus and Rheic oceans during the Paleozoic. J. 1999. Geologic and isotopic constraints on the age In Ramos, V. A., and Keppie, J. D., eds. Laurentia and and origin of auriferous quartz veins in the Parcoy Gondwana connections before Pangea. Geol. Soc. Am. mining district, Pataz, Peru´. In Skinner, B., ed., Ge- Spec. Pap. 336:267–276. ology and ore deposits in the central Andes. Econ. Kinny, P. D.; Strachan, R. A.; Kocks, H.; and Friend, C. Geol. Spec. Publ. Ser. 7, p. 267–279. R. L. 2003. U-Pb geochronology of late Neoproterozoic Martinez, W.; Valdivia, E.; and Cuyubamba, V. 1998. Geo- augen granites in the Moine Supergroup, NW Scot- logıá de los cuadrańgulos de Aucayacu, Rio Santa Ana land: dating rift-related, felsic magmatism during su- y Tingo Marıá (hojas 18-k, 18-l, 19-k). Boletıń Ser. A, percontinent break-up? J. Geol. Soc. Lond. 160:925– Carta Geolo´ gica Nacional, vol. 112, Lima, Instituto 934. Geolo´ gico Minero y Metalu´ rgico, 204 p. Kontak, D. J.; Clark, A. H.; Farrar, E.; Archibald, D. A.; McLennan, S. M.; Hemming, S.; McDaniel, D. K.; and and Baadsgaard, H. 1990. Late Paleozoic–early Meso- Hanson, G. N. 1993. Geochemical approaches to sed- zoic magmatism in the Cordillera de Carabaya, Puno, imentation, provenance and tectonics. Geol. Soc. Am. southeastern Peru: geochronology and petrochemis- Spec. Pap. 284, p.21–40. try. J. S. Am. Earth Sci. 3:213–230. Miskovic, A., and Schaltegger, U. 2008. Tectono-mag- Kontak, D. J.; Clark, A. H.; Farrar, E.; and Strong, D. F. matic evolution and crustal growth along west-central 1985. The rift-associated Permo-Triassic magmatism Amazonia since the late Mesoproterozoic: evidence of the Eastern Cordillera: a precursor of the Andean from the Eastern Cordillera of Peru. 7th International orogeny. In Pitcher, W. S.; Atherton, M. P.; Cobbing, Symposium on Andean Geodynamics (Nice, 2008). E. J.; and Beckinsale, R. D., eds. Magmatism at a plate Extended abstracts p. 337–338. edge: the Peruvian Andes. London, Blackie & Son, p. Miskovic, A.; Schaltegger, U.; and Chew, D. M. 2005. 36–44. The Paleozoic-Mesozoic geodynamic transition along 304 A. CARDONA ET AL.

the western Gondwanan margin: geochemical and Ramos, V. A., and Aleman, A. 2000. Tectonic evolution chronometric constraints from the Eastern Peruvian of the Andes. In Cordani, U. G.; Milani, E. J.; Thomaz- Cordillera. In Abstracts, 3rd Swiss Geoscience Meet- Filho, A.; and Campos, D. A., eds.Tectonic evolution ing, Zurich. of South America. 31st International Geological Con- Murphy, J. B.; Fernandez-Suarez, J.; Jeffries, T.; and Stra- gress, Rio de Janeiro, p. 635–685. chan, R. A. 2004a. U-Pb (LA-ICP-MS) dating of detrital Rapela, C. W.; Pankhurst, R. J.; Casquet, C.; Baldo, E.; zircons from Cambrian clastic rocks in Avalonia: ero- Saavedra, J.; Galindo, C.; and Fanning, M. 1998. The sion of a Neoproterozoic arc along the northern Gond- Pampean orogeny of the southern proto-Andes: Cam- wanan margin. J. Geol. Soc. 161:243–254. brian continental collision in the Sierras de Cordoba. Murphy, J. B.; Pisarevsky, S. A.; Nance, R. D.; and Keppie, In Pankhurst, R., and Rapela, C. W., eds. The Proto- D. 2004b. Neoproterozoic-Early Paleozoic evolution Andean margin of Gondwana. Geol. Soc. Lond. Spec. of peri-Gondwanan terranes: implications for Lauren- Publ. 142:181–218. tia-Gondwana connections. Int. J. Earth Sci. 93:659– Restrepo-Pace, P. 1995. Late Precambrian to Early Me- 682. sozoic tectonic evolution of the Colombian Andes, Murphy, J. B.; Strachan, R.; Nance, R.; Parker, K.; and based on new geochronological, geochemical and iso- Fowler, M. 2000. Proto-Avalonia: a 1.2–1.0 Ga tec- topic data. PhD dissertation, University of Arizona, tonothermal event and constraints for the evolution Tucson. 195 p. of Rodinia. Geology 28:1071–1074. Reusch, D. N.; Van Staal, C. S.; and McNicoll, V. J. 2006. Ordoń˜ ez-Carmona, O.; Restrepo, J. J.; and Pimentel, M. Detrital zircons and Ganderia’s southern margin, M. 2006. Geochronological and isotopical review of coastal Maine. Geological Society of America North- pre-Devonian crustal basement of the Colombian An- eastern Section (39th annual) and Southeastern Sec- des. J. S. Am. Earth Sci. 21:372–382. tion (53rd annual) Joint Meeting, Washington, DC. Ortega-Gutierrez, F.; Ruiz, F.; and Centeno-Garcia, E. Session 51, paper 4. 1995. Oaxaquia, a Proterozoic microcontinent ac- Rogers, N.; Van Staal, C.; McNicoll, V. J.; Pollock, J.; creted to North America during the late Paleozoic. Zagorevski, A.; and Whalen, J. 2006. Neoproterozoic Geology 23:1127–1130. and Cambrian arc magmatism along the eastern mar- Pankhurst, R., and Rapela, C. W. 1998. The Proto-Andean gin of the Victoria Lake Supergroup: a remnant of Gan- margin of Gondwana. Geol. Soc. Lond. Spec. Publ. derian basement in central Newfoundland? Precam- 142, 383 p. brian Res. 14:320–341. Passchier, C. W., and Trouw, R. A. 1996. Microtectonics. Rubatto, D. 2002. Zircon trace element geochemistry: Berlin, Springer, 288 p. partitioning with garnet and the link between U-Pb Pitcher, W. S., and Cobbing, E. J. 1985. Phanerozoic plu- ages and metamorphism. Chem. Geol. 184:123–138. tonism in the Peruvian Andes. In Pitcher, W. S.; Ath- Sato, K.; Tassinari, C.C.G.; Kawashita, K.; and Petro- erton, M. P.; Cobbing, E. J.; and Beckinsale, R. D., eds. nilho, L. 1995. O me´todo geocronolo´ gico Sm-Nd no Magmatism at a plate edge: the Peruvian Andes. Lon- IG/USP e suas aplicaço˜ es. An. Acad. Bras. Cienc. 67: don, Blackie & Son, p. 19–25 313–336. Polliand, M.; Schaltegger, U.; Frank, M.; and Fontbote´, Sempere, T.; Carlier, G.; Soler, P.; Fornari, M.; Carlotto, L. 2005. Formation of intra-arc volcanosedimentary V.; Jacay, J.; Arispe, O.; et al. 2002. Late Permian– basins in the western flank of the central Peruvian Middle Jurassic lithospheric thinning in Peru and Bo- Andes during Late Cretaceous oblique subduction: livia, and its bearing on Andean-age tectonics. Tec- field evidence and constraints from U-Pb ages and Hf tonophysics 345:153–181. isotopes. Int. J. Earth Sci. 94:231–242. Stacey, J. S., and Kramers, J. D. 1975. Approximation of Quispesivana, L. 1996. Mapa geolo´ gico del cuadrańgulo the terrestrial lead isotope evolution by a two-stage de Huanuco, 20K. Lima, Peru, Instituto Geolo´ gico Mi- model. Earth Planet. Sci. Lett. 26:207–221. nero y Metalu´ rgico. Steiger, R. H., and Ja¨ger, E. 1977. Subcommission on geo- Ramos V. A. 1999. Plate tectonic setting of the Andean chronology: convention on the use of decay constants Cordillera. Episodes. 22:183–190. in geo- and cosmochronology. Earth Planet. Sci. Lett. ———. 2000. The southern central Andes. In Cordani, 36:359–362. U. G.; Milani, E. J.; Thomaz-Filho, A.; and Campos, Stern, R. A. 1998. High-resolution SIMS determination D. A., Tectonic evolution of South America. 31st In- of radiogenic trace-isotope ratios in minerals. In Cabri, ternational Geological Congress, Rio de Janeiro, p. L. J., and Vaughan, D. J., eds. Modern approaches to 561–604. ore and environmental mineralogy. Mineralogical As- ———. 2004. Cuyania, an exotic block to Gondwana: sociation of Canada Short Courses, ser. 27, p. 241– review of a historical success and the present prob- 268. lems. Gondwana Res. 7:1009–1026. Stern, R. J. 2002. Subduction zones. Rev. Geophys., doi: ———. 2008a. The basement of the central Andes: the 10.1029/2001RG000108. Arequipa and related terranes. Ann. Rev. Earth Planet. Tassinari, C. G.; Bettencourt, J. S.; Geraldes, M. C.; Ma- Sci. 36:289–324. cambira, M.; and Lafon, J. M. 2000. The Amazonian ———. 2008b. Patagonia: a Paleozoic continent adrift? J. Craton. In Cordani, U. G.; Milani, E. J.; Thomaz, A.; S. Am. Earth Sci. 26:235–251. and Campos, D. A. eds. Tectonic evolution of South Journal of Geology GROWTH OF A GONDWANAN ACCRETIONARY OROGEN 305

America. 31st International Geological Congress, Rio gneisses and granitoids of the Colombian central An- de Janeiro, p. 41–96. des. J. S. Am. Earth Sci. 21:355–371. Thomas, W. A., and Astini, R. A. 1996. The Argentine Wasteneys, H. A.; Clark, A. H.; Ferrar, E.; and Langridge, Precordillera: a traveler from the Ouachita embay- R. J. 1995. Grenvillian granulite-facies metamorphism ment of North American Laurentia. Science 273:752– in the Arequipa Massif, Peru: a Laurentia-Gondwana 757. link. Earth Planet. Sci. Lett. 132:63–73. Thomas, W. A.; Astini, R. A.; Mueller, P. A.; Gehrels, G. Weber, B., and Ko¨ hler, H. 1999. Sm-Nd, Rb-S and U-Pb E.; and Wooden, J. L. 2004. Transfer of the Argentine geochronology of a Grenville Terrane in Southern Precordillera terrane from Laurentia: constraints from Mexico: origin and geologic history of the Guichicovi detrital-zircon geochronology. Geology 32:965–968. Complex. Precambrian Res. 96:245–262. Tollo, R. P.; Aleinikoff, J. N.; Bartholomew, M. J.; and Williams, I. S. 1998. U-Th-Pb geochronology by ion mi- Rankin, D. W. 2004. Neoproterozoic A-type granitoids croprobe. In McKibben, M. A.; Shanks, W. C. P., III; of the central and southern Appalachians: intraplate and Ridley, W. I., eds. Applications of microanalytical magmatism associated with episodic rifting of the Ro- techniques to understanding mineralizing processes. dinian supercontinent. Precambrian Res. 128:3–38. Rev. Econ. Geol. 7:1–35. Vabra, G.; Schmid, R.; and Gebauer, D. 1999. Internal Willner, A. P.; Thomson, S. N.; Kro¨ ner, A.; Wartho, J.-A.; morphology, habit and U-Th-Pb microanalysis of am- Wijbrans, J. R.; and Herve, F. 2005. Time markers for phibolite-to-granulite facies zircons: geochronology of the evolution and exhumation history of a Late Pa- the Ivrea Zone (Southern Alps). Contrib. Mineral. Pet- rol. 134:380–404. laeozoic paired metamorphic belt in north-central Њ Њ Ј Van Staal, C. R.; Dewey, J. F.; Mac Niocaill, C.; and Chile (34 –35 30 S). J. Petrol. 46:1805–1833. Mckerrow, W. S. 1998. The Cambrian-Silurian tec- Wilson, J. J., and Reyes, L. 1964. Geologia del cuadrańgulo tonic evolution of the northern Appalachians and Brit- de Pataz. Lima, Carta Geolo´ gica Nacional, 91 p. ish Caledonide: history of a complex, west and south- Zapata, A.; Sańchez, A.; Carrasco, S.; Cardona, A.; Gal- west Pacific-type segment of Iapetus. In Blundell, D. dos, J. H.; Cerro´ n F.; and Sempere, T. 2005. The Lower J., and Scott, A. C., eds. Lyell: the past is the key to Carboniferous of the western edge of Gondwana in the present. Geol. Soc. Lond. Spec. Publ. 143:199–242. Peru and Bolivia: distribution of sedimentary basins Vinasco, C. J.; Cordani, U. G.; Gonza´lez, H.; Weber, M.; and associated magmatism. 6th International Sym- and Pelaez, C. 2006. Geochronological, isotopic, and posium on Andean Geodynamics (Barcelona, 2005). geochemical data from Permo-Triassic granitic Extended abstracts, p. 817–820.