%0 Journal Article
%A Casquet Martín, César
%A Pankhurst, R.J.
%A Galindo Francisco, María Del Carmen
%A Rapela, Carlos W.
%A Fanning, C.M.
%A Baldo, Edgardo G.
%A Dahlquist, Juan A.
%A González Casado, José Manuel
%A Colombo, F.
%T A deformed alkaline igneous rock–carbonatite complex from the WesternSierras Pampeanas, Argentina: Evidence for late Neoproterozoic openingof the Clymene Ocean?
%D 2008
%@ 0301-9268
%U https://hdl.handle.net/20.500.14352/49541
%X A deformed ca. 570Ma syenite–carbonatite body is reported from a Grenville-age (1.0–1.2 Ga) terrane inthe Sierra de Maz, one of theWestern Sierras Pampeanas of Argentina. This is the first recognition of such arock assemblage in the basement of the Central Andes. The two main lithologies are coarse-grained syenite(often nepheline-bearing) and enclave-rich fine-grained foliated biotite–calcite carbonatite. Samplesof carbonatite and syenite yield an imprecise whole rock Rb–Sr isochron age of 582±60Ma (MSWD= 1.8;Sri = 0.7029); SHRIMP U–Pb spot analysis of syenite zircons shows a total range of 206Pb–238Uages between433 and 612 Ma, with a prominent peak at 560–580Ma defined by homogeneous zircon areas. Texturalinterpretation of the zircon data, combined with the constraint of the Rb–Sr data suggest that the carbonatitecomplex formed at ca. 570 Ma. Further disturbance of the U–Pb system took place at 525±7Ma(Pampean orogeny) and at ca. 430–440Ma (Famatinian orogeny) and it is concluded that the WesternSierras Pampeanas basement was joined to Gondwana during both events. Highly unradiogenic 87Sr/86Srvalues in calcites (0.70275–0.70305) provide a close estimate for the initial Sr isotope composition of thecarbonatite magma. Sm–Nd data yield Nd570 values of +3.3 to +4.8. The complex was probably formedduring early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoiclower continental crust.
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