The aim of this work is to describe the relationships between tectonic structures, volcanism, petrochemical features and hydrothermal alteration along the Plio-Quaternary Olacapato-San Antonio de los Cobres fault zone, that transversally crosses the Andean chain and the Puna Plateau at about 24° S. This fault zone belongs to the larger Calama-Olacapato-El Toro (COT) structure, where extensive Miocene–Quaternary magmatic activity developed in arc and backarc settings and formed transverse volcanic chains, comprising stratovolcanoes and large calderas with widespread ignimbrite sheets and intrusions. The magmatic products are variable in age and in geochemical characteristics from the active volcanic arc to the Eastern Cordillera. The Pliocene–Quaternary monogenetic and mainly basaltic-andesite centers may relate to lithospheric delamination in an extensional regime, active since ca. 3–4 Ma. The investigated area is characterised by calcalkaline volcanic products of different ages resting on a basement of mainly Palaeozoic metamorphic and igneous rocks. We collected structural data and sampled Plio-Quaternary volcanic deposits (e.g. Negro de Chorrillos and San Jerónimo), basement rocks and hydrothermal alteration zones that occur along this fault zone. We performed first preliminary minero-petrographic studies by means of OM and XRD. The petrographic data of volcanics indicate the calc-alkaline affinity: andesitic, dacitic and minor basaltic rocks are porphyritic with phenocrysts of plagioclase, orthopyroxene, amphibole and minor clinopyroxene and biotite, in a glassy groundmass. Low-T hydrothermal alteration (usually argillic), probably related to the Plio-Quaternary volcanism, occurs along discrete segments of the fault zone, involving both volcanic deposits and basement rocks. The preliminary geochemical analyses (ICP-MS and ICP-AES) fall in the sub-alkaline field and show a range from basaltic andesite to dacites, with considerable variation in the K2O content. The aim of our further investigations is to improve the knowledge of the tectonic and magmatic evolution of this area, reflecting different magma sources and crustal thicknesses.
Cavallo, A., Nardin, A., Tibaldi, A., Corazzato, C., Lanza, F., Bonali, F. (2010). Relationship between structures, petrochemical features and hydrothermal alteration along the Plio-Quaternary Olacapato-San Antonio fault zone (NW Argentina). Intervento presentato a: ILP's Second Potsdam Conference, Potsdam, Germany.
Relationship between structures, petrochemical features and hydrothermal alteration along the Plio-Quaternary Olacapato-San Antonio fault zone (NW Argentina)
CAVALLO, ALESSANDRO;TIBALDI, ALESSANDRO;CORAZZATO, CLAUDIA;Bonali, F.
2010
Abstract
The aim of this work is to describe the relationships between tectonic structures, volcanism, petrochemical features and hydrothermal alteration along the Plio-Quaternary Olacapato-San Antonio de los Cobres fault zone, that transversally crosses the Andean chain and the Puna Plateau at about 24° S. This fault zone belongs to the larger Calama-Olacapato-El Toro (COT) structure, where extensive Miocene–Quaternary magmatic activity developed in arc and backarc settings and formed transverse volcanic chains, comprising stratovolcanoes and large calderas with widespread ignimbrite sheets and intrusions. The magmatic products are variable in age and in geochemical characteristics from the active volcanic arc to the Eastern Cordillera. The Pliocene–Quaternary monogenetic and mainly basaltic-andesite centers may relate to lithospheric delamination in an extensional regime, active since ca. 3–4 Ma. The investigated area is characterised by calcalkaline volcanic products of different ages resting on a basement of mainly Palaeozoic metamorphic and igneous rocks. We collected structural data and sampled Plio-Quaternary volcanic deposits (e.g. Negro de Chorrillos and San Jerónimo), basement rocks and hydrothermal alteration zones that occur along this fault zone. We performed first preliminary minero-petrographic studies by means of OM and XRD. The petrographic data of volcanics indicate the calc-alkaline affinity: andesitic, dacitic and minor basaltic rocks are porphyritic with phenocrysts of plagioclase, orthopyroxene, amphibole and minor clinopyroxene and biotite, in a glassy groundmass. Low-T hydrothermal alteration (usually argillic), probably related to the Plio-Quaternary volcanism, occurs along discrete segments of the fault zone, involving both volcanic deposits and basement rocks. The preliminary geochemical analyses (ICP-MS and ICP-AES) fall in the sub-alkaline field and show a range from basaltic andesite to dacites, with considerable variation in the K2O content. The aim of our further investigations is to improve the knowledge of the tectonic and magmatic evolution of this area, reflecting different magma sources and crustal thicknesses.
I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
