UePb LA-ICP-MS geochronology of detrital zircon grains from low- grade metasedimentary rocks...
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UePb LA-ICP-MS geochronology of detrital zircon grains from low- grade metasedimentary rocks (Neoproterozoic e Cambrian) of the Mojotoro Range, northwest Argentina Pamela A. Aparicio González a, * , Márcio M. Pimentel b , Natalia Hauser b , M. Cristina Moya a a Universidad Nacional de Salta, Facultad de Ciencias Naturales, Geología, Buenos Aires 177, 4400 Salta, Argentina b Instituto de Geociências, Universidade de Brasilia (UnB), Brazil a r t i c l e i n f o Article history: Received 22 May 2013 Accepted 5 October 2013 Keywords: UePb Zircon grains Low grade metasedimentary rocks Mojotoro Range a b s t r a c t The rst results of UePb detrital zircons were obtained in three lithostratigraphic units of the Punco- viscana Complex in NW Argentina: Chachapoyas, Alto de la Sierra and Guachos Formations. The Cha- chapoyas Formation has a maximum sedimentation age of 569 Ma and a minimum age of 533 Ma, based on the UePb age of an int rus ive porph yry granitic . The Alto de la Sierra Formation, compos ed by sandstones and volcaniclastic rocks, has a maximum age of 543 Ma. A maximum age of 517 Ma is here report ed for the depositio n of the Guachos Formatio n, the young est unit. The conta ct between the Chachap oyas and Guachos formatio ns is by a tecto nic relation, and it s probably coincident with a stratigraphic unconformity between them (unconformity Tilcara I). The Lizoite Formation is overlying by an unconformity (Tilcara II unconformity) the Puncoviscana Complex, and represents the basal unit ofthe Mesón Group. The provenance zircon data for that formation indicate a maximum depositional age of513 Ma. 2013 Elsevier Ltd. All rights reserved. 1. Introduction The Eastern Cordillera basement of the NW of Argentine is a heter ogen eous succ essi on of sili cicl astic and chemi cal roc ks, intruded by volcanic, subvolcanic and plutonic/subvolcanic rocks, of NeoproterozoiceEarly Cambrian age, identied as the Precam- brian basement ( Keidel, 191 0) underlying with angular unconfor- mi ty the Cambri an and Ord ovici an dep osi ts of the Mes ón and Santa Victoria Groups. The unit was de ned as the Puncoviscana For- mation (Turner, 1960) in the Santa Victoria range (Fig. 1), and was assigned to the NeoproterozoiceCambr ian (Mirré and Aceñolaza, 1972) due to the presence ofOldhamia, a fossil trace of the Lower Cambrian. Aceñolaza et al. (1988) and Aceñolaza and Aceñolaza (2005) iden tif y all the bas ement of the Eas ter n Cordi ll era as a het er ogeneous gro up of roc ks affected by low- gra de meta- morphism, the Puncoviscana Formation s.l. Zimmermann (2005), correlates this stratigraphic core that outcrops in the Argentinean northwest with the rocks of medium and high metamorphic grade of the eastern Pampean Ranges . This last author iden ti es the Puncoviscana Formations.l. with the name ofPuncoviscana Com- plex, a term according with the nomenclatu re for metamorphic and sedimentary rocks of the British Geological Survey ( Hallworth and Knox, 1999). In this paper the Puncoviscana Complex term sensu article 32 of the Cód igo Arg entinode Est rat igr afí a is use d to identi fy all the stratigraphic core of the Eastern Cordillera. The lithological heterogeneity of the stratigraphic core of the regi on was highl ight ed thro ugh diffe rent sedi mento logi cal and stratigraphical studies, where diverse carbonatic and clastic facies are recognized ( Jezek, 1990). These were totally or partially iden- tied in the Sancha, Las Tienditas, Puncoviscana sensu stricto, Cor- ra lit o and Gua cho s Formations (Salty et al. , 1975; Bal dis y Omarini, 1984; Moya, 1998)(Fig. 1). In the last decade, several studies were carried out in different parts of the Puncoviscana Complex to determine the age of deposi- tion and tectonic setting. Whole rock geochemistry ( Omarini et al., 1999; Do Campo and Guevara, 2005; Zimmermann, 2005) and Ue Pb studies for different parts of the Eastern Cordi llera ( Adams et al., 2008; Haus er et al., 2010; Ada ms, 2011; Esc ayo la et al. , 2011 ) sh ows a complex populatio n distribution patterns and a heterogeneity in the maximum depositional ages of the Puncoviscana Complex. Many contributions related with the content of ichnofossils of the base- ment, indica tes an Ediac aran-e arly Cambria n age, current ly accep ted for the stratigraphic core of the region ( Mángano and Buatois, 2004; *Corresponding author. Tel.: þ55 21 34969077. E-mail addresses: pamelaaparicio@gmai l.com(P.A. Aparicio González), marcio@ unb.br (M.M. Pimen tel), [email protected](N. Hauser ), moyacris@ arnet.com.ar(M.C. Moya). Contents lists available at ScienceDirect Journal of South American Earth Sciences journal homepage: www.elsevier.com/locate/jsames 0895-9811/$ esee front matter 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jsames.2013.10.002 Journal o f South American Earth Sciences 49 (201 4) 39 e50
UePb LA-ICP-MS geochronology of detrital zircon grains from low- grade metasedimentary rocks (Neoproterozoic e Cambrian) of the Mojotoro Range, northwest Argentina
UePb LA-ICP-MS geochronology of detrital zircon grains from low-grade metasedimentary rocks (Neoproterozoic e Cambrian) of theMojotoro Range, northwest Argentina
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