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 þ chlorite þ quartz pseudomorphs, epidote coronas and epidote þ quartz symplectites, actinolite þ quartz intergrowths and calcite þ 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 (T780C and 6.5 , P , 8.0 kbar) led to destabilization of pyroxene with talc formation at the M1 stage (T ¼ 650–670 C, P , 6 kbar). Further cooling resulted in the formation of actinolite þ chlorite þ quartz pseudomorphs growing on igneous and metamorphic amphibole (M2 stage, 600 , T , 625 C and P 3.8 kbar). The third re-equilibration stage led to the formation of epidote coronas and epidote þ quartz symplectite around igneous plagioclase (M3 stage, 420 , T , 470 C and 2 , P , 4 kbar). Calcite þ 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 420–470 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.
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|Titolo:||Mineral re-equilibration and P-T path of metagabbros, Sierra de San Luis, Argentina: insights into the exhumation of mafic-ultramafic belt|
|Data di pubblicazione:||2011|
|Tipologia:||1.1 Articolo in rivista|