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A deformed alkaline igneous rock–carbonatite complex from the Western Sierras Pampeanas, Argentina: Evidence for late Neoproterozoic opening of the Clymene Ocean?

Casquet, César and Pankhurst, R.J. and Galindo Francisco, Mª del Carmen and Rapela, Carlos W. and Fanning, C.M. and Baldo, Edgardo G. and Dahlquist, Juan A. and González Casado, José Manuel and Colombo, F. (2008) A deformed alkaline igneous rock–carbonatite complex from the Western Sierras Pampeanas, Argentina: Evidence for late Neoproterozoic opening of the Clymene Ocean? Precambrian research, 165 . pp. 205-220. ISSN 0301-9268

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Abstract

A deformed ca. 570Ma syenite–carbonatite body is reported from a Grenville-age (1.0–1.2 Ga) terrane in
the Sierra de Maz, one of theWestern Sierras Pampeanas of Argentina. This is the first recognition of such a
rock 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. Samples
of 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 between
433 and 612 Ma, with a prominent peak at 560–580Ma defined by homogeneous zircon areas. Textural
interpretation of the zircon data, combined with the constraint of the Rb–Sr data suggest that the carbonatite
complex 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 Western
Sierras Pampeanas basement was joined to Gondwana during both events. Highly unradiogenic 87Sr/86Sr
values in calcites (0.70275–0.70305) provide a close estimate for the initial Sr isotope composition of the
carbonatite magma. Sm–Nd data yield Nd570 values of +3.3 to +4.8. The complex was probably formed
during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic
lower continental crust.


Item Type:Article
Uncontrolled Keywords:DARCs; Syenite; U–Pb SHRIMP zircon dating; Gondwana; Rodinia
Subjects:Sciences > Geology > Petrology
ID Code:12150
Deposited On:02 Feb 2011 13:33
Last Modified:02 Feb 2011 13:33

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