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Mineral re-equilibration and P-T path of metagabbros, Sierra de San Luis, Argentina; insights into the exhumation of a mafic-ultramafic belt

Gabriele Cruciani, Marcello Franceschelli and Norma Brogioni
Mineral re-equilibration and P-T path of metagabbros, Sierra de San Luis, Argentina; insights into the exhumation of a mafic-ultramafic belt
European Journal of Mineralogy (August 2011) 23 (4): 591-608

Abstract

At La Melada, Sierra de San Luis, Argentina, two lenses of mafic-ultramafic rocks, mainly consisting of metagabbros, are made up of igneous and metamorphic minerals in varying combinations. These rocks are part of a narrow NNE-SSW trending belt along the eastern flank of the Sierra and were affected by Famatinian metamorphism and deformation followed by shear deformation. La Melada metagabbros show a wide variety of microstructures including actinolite+chlorite+quartz pseudomorphs, epidote coronas and epidote+quartz symplectites, actinolite+quartz intergrowths and calcite+chlorite aggregates. These microstructural characteristics witness a complex metamorphic history consisting of a progressive cooling and decompression associated with regional and shear deformation from M0 down to the M1 to M3 greenschist/sub-greenschist stage. Cooling from the M0 stage (T nearly equal 780 degrees C and 6.5<P<8.0 kbar) led to destabilization of pyroxene with talc formation at the M1 stage (T=650-670 degrees C, P<6 kbar). Further cooling resulted in the formation of actinolite+chlorite+ quartz pseudomorphs growing on igneous and metamorphic amphibole (M2 stage, 600<T<625 degrees C and P nearly equal 3.8 kbar). The third re-equilibration stage led to the formation of epidote coronas and epidote+quartz symplectite around igneous plagioclase (M3 stage, 420<T<470 degrees C and 2<P<4 kbar). Calcite+chlorite aggregates partially replacing actinolite are evidence of the last stage of mineral re-equilibration. As compared to P-T path previously reported in the literature, La Melada rocks indicate that mineral re-equilibration reached P-T conditions as low as approximately 420-470 degrees C, with epidote development under (sub-)greenschist-facies P-T conditions. The resulting P-T path is in agreement with the P-T path reconstructed for the country rocks.


ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 23
Serial Issue: 4
Title: Mineral re-equilibration and P-T path of metagabbros, Sierra de San Luis, Argentina; insights into the exhumation of a mafic-ultramafic belt
Affiliation: Universita di Cagliari, Dipartimento di Scienze della Terra, Cagliari, Italy
Pages: 591-608
Published: 201108
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Germany
References: 51
Accession Number: 2011-103487
Categories: Igneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 4 tables, geol. sketch map
S32°58'45" - S32°57'30", W66°01'00" - W66°01'00"
Secondary Affiliation: Universidad Nacional de La Plata, ARG, Argentina
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Schweizerbart'sche Verlagsbuchhandlung. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201152
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