%0 Journal Article
%A Rapela, Carlos W.
%A Pankhurst, R.J.
%A Casquet Martín, César
%A Baldo, Edgardo G.
%A Galindo Francisco, María Del Carmen
%A Fanning, C.M.
%A Dahlquist, Juan A.
%T The Western Sierras Pampeanas: Protracted Grenville-age history (1330–1030 Ma)of intra-oceanic arcs, subduction–accretion at continental-edge and AMCGintraplate magmatism
%D 2010
%@ 0895-9811
%U https://hdl.handle.net/20.500.14352/41857
%X New U–Pb SHRIMP zircon ages combined with geochemical and isotope investigation in the Sierra deMaz and Sierra de Pie de Palo and a xenolith of the Precordillera basement (Ullún), provides insight intothe identification of major Grenville-age tectonomagmatic events and their timing in the Western SierrasPampeanas. The study reveals two contrasting scenarios that evolved separately during the 300 Ma longhistory: Sierra de Maz, which was always part of a continental crust, and the juvenile oceanic arc andback-arc sector of Sierra de Pie de Palo and Ullún. The oldest rocks are the Andino-type granitic orthogneissesof Sierra de Maz (1330–1260 Ma) and associated subalkaline basic rocks, that were part of anactive continental margin developed in a Paleoproterozoic crust. Amphibolite facies metamorphismaffected the orthogneisses at ca. 1175 Ma, while granulite facies was attained in neighbouring meta-sedimentsand basic granulites. Interruption of continental-edge magmatism and high-grade metamorphismis interpreted as related to an arc–continental collision dated by zircon overgrowths at 1170–1230 Ma.The next event consisted of massif-type anorthosites and related meta-jotunites, meta-mangerites(1092 ± 6 Ma) and meta-granites (1086 ± 10 Ma) that define an AMCG complex in Sierra de Maz. Theemplacement of these mantle-derived magmas during an extensional episode produced a widespreadthermal overprint at ca. 1095 Ma in neighbouring country rocks. In constrast, juvenile oceanic arc andback-arc complexes dominated the Sierra de Pie de Palo–Ullún sector, that was fully developed ca.1200 Ma (1196 ± 8 Ma metagabbro). A new episode of oceanic arc magmatism at 1165 Ma was roughlycoeval with the amphibolite high-grade metamorphism of Sierra de Maz, indicating that these two sectorsunderwent independent geodynamic scenarios at this age. Two more episodes of arc subduction areregistered in the Pie de Palo–Ullún sector: (i) 1110 ± 10 Ma orthogneisses and basic amphibolites withgeochemical fingerprints of emplacement in a more mature crust, and (ii) a 1027 ± 17 Ma TTG juvenilesuite, which is the youngest Grenville-age magmatic event registered in the Western Sierras Pampeanas.The geodynamic history in both study areas reveals a complex orogenic evolution, dominated by convergenttectonics and accretion of juvenile oceanic arcs to the continent.
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