CIG   05423
CENTRO DE INVESTIGACIONES GEOLOGICAS
Unidad Ejecutora - UE
artículos
Título:
A deformed alkaline igneous rock - carbonatite complex from the Western Sierras Pampeanas, Argentina: evidence for late Neoproterozoic opening of the Clymene Ocean?
Autor/es:
CASQUET, C.; PANKHURST, R.J; GALINDO, C.; RAPELA, C.W.; FANNING, C.M; BALDO, E.G; DAHLQUIST, J.A.; GONZÁLEZ-CASADO, J.M.
Revista:
PRECAMBRIAN RESEARCH
Editorial:
Elsevier
Referencias:
Año: 2008 vol. 165 p. 205 - 220
ISSN:
0301-9268
Resumen:
A deformed ca. 570Ma syenitecarbonatite body is reported from a Grenville-age (1.01.2 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 biotitecalcite carbonatite. Samples
of carbonatite and syenite yield an imprecise whole rock RbSr isochron age of 582±60Ma (MSWD= 1.8;
Sri = 0.7029); SHRIMP UPb spot analysis of syenite zircons shows a total range of 206Pb238Uages between
433 and 612 Ma, with a prominent peak at 560580Ma defined by homogeneous zircon areas. Textural
interpretation of the zircon data, combined with the constraint of the RbSr data suggest that the carbonatite
complex formed at ca. 570 Ma. Further disturbance of the UPb system took place at 525±7Ma
(Pampean orogeny) and at ca. 430440Ma (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 (0.702750.70305) provide a close estimate for the initial Sr isotope composition of the
carbonatite magma. SmNd 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.±60Ma (MSWD= 1.8;
Sri = 0.7029); SHRIMP UPb spot analysis of syenite zircons shows a total range of 206Pb238Uages between
433 and 612 Ma, with a prominent peak at 560580Ma defined by homogeneous zircon areas. Textural
interpretation of the zircon data, combined with the constraint of the RbSr data suggest that the carbonatite
complex formed at ca. 570 Ma. Further disturbance of the UPb system took place at 525±7Ma
(Pampean orogeny) and at ca. 430440Ma (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 (0.702750.70305) provide a close estimate for the initial Sr isotope composition of the
carbonatite magma. SmNd 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.206Pb238Uages between
433 and 612 Ma, with a prominent peak at 560580Ma defined by homogeneous zircon areas. Textural
interpretation of the zircon data, combined with the constraint of the RbSr data suggest that the carbonatite
complex formed at ca. 570 Ma. Further disturbance of the UPb system took place at 525±7Ma
(Pampean orogeny) and at ca. 430440Ma (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 (0.702750.70305) provide a close estimate for the initial Sr isotope composition of the
carbonatite magma. SmNd 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.±7Ma
(Pampean orogeny) and at ca. 430440Ma (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 (0.702750.70305) provide a close estimate for the initial Sr isotope composition of the
carbonatite magma. SmNd 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.87Sr/86Sr
values in calcites (0.702750.70305) provide a close estimate for the initial Sr isotope composition of the
carbonatite magma. SmNd 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.570 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.