CIG   05423
CENTRO DE INVESTIGACIONES GEOLOGICAS
Unidad Ejecutora - UE
artículos
Título:
Petrology and geochemistry of the banded iron formation in the Eastern Sierras Pampeanas of San Luis Argentina: implications for the evolution of the Nogolí Metamorphic Complex
Autor/es:
GONZÁLEZ, P.D.; SATO, A.M.; LLAMBIAS, E.J.; PETRONILHO, L.
Revista:
JOURNAL OF SOUTH AMERICAN EARTH SCIENCES
Referencias:
Año: 2008
ISSN:
0895-9811
Resumen:
Abstract
The metamorphosed banded iron formation from the Nogolí Metamorphic Complex of western Sierra
de San Luis, Eastern Sierras Pampeanas of Argentina (Nogolí area, 32°55S 66°15W) is classified
as an oxide facies iron formation of Algoma Type, with a tectonic setting possibly associated with an
island arc or back arc, on the basis of field mapping, mineral and textural arrangements and whole
rock geochemical features. The banded iron formation origin is mainly related to chemical
precipitation of hydrogenous sediments from seawater in oceanic environments. The primary chemical
precipitate is a result of solutions that represent mixtures of seawater and hydrothermal fluids, with
significant dilution by mafic-ultramafic volcanic and siliciclastic materials. Multi-stage TDM model
ages of 1670, 1854 and 1939 Ma and positive, mantle-like xNd(1502) values of +3.8, +1.5 and +0.5 from
the banded iron formation are around the range of those mafic to ultramafic meta-volcanic rocks of
Nogolí Metamorphic Complex, which are between 1679 - 1765 Ma and +2.64 to +3.68 respectively.
This Sm and Nd isotopic connection suggests a close genetic relationship between ferruginous and
mafic-ultramafic meta-volcanic rocks, as part of the same island arc or back arc setting. A previous
Sm - Nd whole rock isochron of ~1.5 Ga performed on mafic-ultramafic meta-volcanic rocks led to
the interpretation that chemical sedimentation as old as Mesoproterozoic is possible for the banded
iron formation. A clockwise P-T path can be inferred for the regional metamorphic evolution of theAlgoma Type, with a tectonic setting possibly associated with an
island arc or back arc, on the basis of field mapping, mineral and textural arrangements and whole
rock geochemical features. The banded iron formation origin is mainly related to chemical
precipitation of hydrogenous sediments from seawater in oceanic environments. The primary chemical
precipitate is a result of solutions that represent mixtures of seawater and hydrothermal fluids, with
significant dilution by mafic-ultramafic volcanic and siliciclastic materials. Multi-stage TDM model
ages of 1670, 1854 and 1939 Ma and positive, mantle-like xNd(1502) values of +3.8, +1.5 and +0.5 from
the banded iron formation are around the range of those mafic to ultramafic meta-volcanic rocks of
Nogolí Metamorphic Complex, which are between 1679 - 1765 Ma and +2.64 to +3.68 respectively.
This Sm and Nd isotopic connection suggests a close genetic relationship between ferruginous and
mafic-ultramafic meta-volcanic rocks, as part of the same island arc or back arc setting. A previous
Sm - Nd whole rock isochron of ~1.5 Ga performed on mafic-ultramafic meta-volcanic rocks led to
the interpretation that chemical sedimentation as old as Mesoproterozoic is possible for the banded
iron formation. A clockwise P-T path can be inferred for the regional metamorphic evolution of theTDM model
ages of 1670, 1854 and 1939 Ma and positive, mantle-like xNd(1502) values of +3.8, +1.5 and +0.5 from
the banded iron formation are around the range of those mafic to ultramafic meta-volcanic rocks of
Nogolí Metamorphic Complex, which are between 1679 - 1765 Ma and +2.64 to +3.68 respectively.
This Sm and Nd isotopic connection suggests a close genetic relationship between ferruginous and
mafic-ultramafic meta-volcanic rocks, as part of the same island arc or back arc setting. A previous
Sm - Nd whole rock isochron of ~1.5 Ga performed on mafic-ultramafic meta-volcanic rocks led to
the interpretation that chemical sedimentation as old as Mesoproterozoic is possible for the banded
iron formation. A clockwise P-T path can be inferred for the regional metamorphic evolution of thexNd(1502) values of +3.8, +1.5 and +0.5 from
the banded iron formation are around the range of those mafic to ultramafic meta-volcanic rocks of
Nogolí Metamorphic Complex, which are between 1679 - 1765 Ma and +2.64 to +3.68 respectively.
This Sm and Nd isotopic connection suggests a close genetic relationship between ferruginous and
mafic-ultramafic meta-volcanic rocks, as part of the same island arc or back arc setting. A previous
Sm - Nd whole rock isochron of ~1.5 Ga performed on mafic-ultramafic meta-volcanic rocks led to
the interpretation that chemical sedimentation as old as Mesoproterozoic is possible for the banded
iron formation. A clockwise P-T path can be inferred for the regional metamorphic evolution of theP-T path can be inferred for the regional metamorphic evolution of the
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banded iron formation, with three distinctive trajectories: (1) Relict prograde M1-M3 segment with
gradual P and T increase from greenschist facies at M1 to amphibolite facies at M3. (2) Peak P-T1-M3 segment with
gradual P and T increase from greenschist facies at M1 to amphibolite facies at M3. (2) Peak P-TP and T increase from greenschist facies at M1 to amphibolite facies at M3. (2) Peak P-T
conditions at high amphibolite-low granulite facies during M4. (3) Retrograde counterpart of M4, that
returns from amphibolite facies and stabilizes at greenschist facies during M5. Each trajectory may be
regarded as produced by different tectonic events related to the Pampean? (1) and the Famatinian (2
and 3) orogenies, during the Early to Middle Paleozoic. The Nogolí Metamorphic Complex is
interpreted as part of a greenstone belt within the large Meso- to Neoproterozoic Pampean Terrane of
the Eastern Sierras Pampeanas of Argentina.4. (3) Retrograde counterpart of M4, that
returns from amphibolite facies and stabilizes at greenschist facies during M5. Each trajectory may be
regarded as produced by different tectonic events related to the Pampean? (1) and the Famatinian (2
and 3) orogenies, during the Early to Middle Paleozoic. The Nogolí Metamorphic Complex is
interpreted as part of a greenstone belt within the large Meso- to Neoproterozoic Pampean Terrane of
the Eastern Sierras Pampeanas of Argentina.5. Each trajectory may be
regarded as produced by different tectonic events related to the Pampean? (1) and the Famatinian (2
and 3) orogenies, during the Early to Middle Paleozoic. The Nogolí Metamorphic Complex is
interpreted as part of a greenstone belt within the large Meso- to Neoproterozoic Pampean Terrane of
the Eastern Sierras Pampeanas of Argentina.
Keywords: banded iron formation, oxide facies, Algoma Type, Sierra de San Luis, Eastern Sierras
Pampeanas of Argentina.banded iron formation, oxide facies, Algoma Type, Sierra de San Luis, Eastern Sierras
Pampeanas of Argentina.