Stratigraphic, structural, petrochemical and geochronological studies were carried out to define the nature and genesis of magmas of the Las Burras-Almagro-El Toro magmatic complex. This is located in the Eastern cordillera of Central Andes (24° S), at about 300 km back of the volcanic arc, in the easternmost sector of the Calama-Olocapato-El Toro lineament. The Las Burras-Almagro-El Toro complex consists of a monzogabbro to monzogranite laccolith-like intrusion and of basaltic andesitic to dacitic volcanic rocks. Seven lithostratigraphic members have been identified in the tertiary sedimentary sequence of the study area. New radiometric K-Ar determinations have given ages of 14 Ma age for intrusive rocks and of 12.78 to 6.39 Ma for volcanic rocks. Two magmatic phases were recognized. Intrusive and volcanic rocks of the older magmatic phase (14-12 Ma) are characterized by Ba/Nb, La/Ta and isotopic ratios (87Sr/86Sr: 0.704339-0.705281, 143Nd/144Nd: 0.512713-0.512598) approaching intraplate characteristics and could have been generated in an isotopically depleted lithospheric mantle rich in K, Rb and Th, with a scarce crustal contamination. The products of the younger magmatic phase (11-6 Ma), have higher Ba/La and La/Ta and 87Sr/86Sr (0.706738-0.708729) and lower 143Nd/144Nd (0.512433-0.512360). These products could have been originated from mixing of mantle-derived magmas and continental crust melts. The increased role of the crust in magma genesis after 12 Ma may correlate with the crustal thickening associated with the Eastern Cordillera compressional evolution and the Brazilian shield underthrusting at the back of the Andes. The Calama-Olocapato-El Toro fault system had a limited control on the emplacement of the intrusion, which was linked to N-S trending strike-slip structures in a context of convergence, while it seems to have closely controlled the rise and emplacement of the younger volcanic rocks, erupted along WNW-ESE and N-S structures, probably reactivated as extensional systems.
Mazzuoli, R., Vezzoli, L., Omarini, R., Acocella, V., Gioncada, A., Matteini, M., et al. (2008). Miocene magmatic and tectonic evolution of the easternmost sector of a transverse structure in Central Andes at 24°S. GEOLOGICAL SOCIETY OF AMERICA BULLETIN, 120, 1493-1517.
Miocene magmatic and tectonic evolution of the easternmost sector of a transverse structure in Central Andes at 24°S
ACOCELLA, Valerio;
2008-01-01
Abstract
Stratigraphic, structural, petrochemical and geochronological studies were carried out to define the nature and genesis of magmas of the Las Burras-Almagro-El Toro magmatic complex. This is located in the Eastern cordillera of Central Andes (24° S), at about 300 km back of the volcanic arc, in the easternmost sector of the Calama-Olocapato-El Toro lineament. The Las Burras-Almagro-El Toro complex consists of a monzogabbro to monzogranite laccolith-like intrusion and of basaltic andesitic to dacitic volcanic rocks. Seven lithostratigraphic members have been identified in the tertiary sedimentary sequence of the study area. New radiometric K-Ar determinations have given ages of 14 Ma age for intrusive rocks and of 12.78 to 6.39 Ma for volcanic rocks. Two magmatic phases were recognized. Intrusive and volcanic rocks of the older magmatic phase (14-12 Ma) are characterized by Ba/Nb, La/Ta and isotopic ratios (87Sr/86Sr: 0.704339-0.705281, 143Nd/144Nd: 0.512713-0.512598) approaching intraplate characteristics and could have been generated in an isotopically depleted lithospheric mantle rich in K, Rb and Th, with a scarce crustal contamination. The products of the younger magmatic phase (11-6 Ma), have higher Ba/La and La/Ta and 87Sr/86Sr (0.706738-0.708729) and lower 143Nd/144Nd (0.512433-0.512360). These products could have been originated from mixing of mantle-derived magmas and continental crust melts. The increased role of the crust in magma genesis after 12 Ma may correlate with the crustal thickening associated with the Eastern Cordillera compressional evolution and the Brazilian shield underthrusting at the back of the Andes. The Calama-Olocapato-El Toro fault system had a limited control on the emplacement of the intrusion, which was linked to N-S trending strike-slip structures in a context of convergence, while it seems to have closely controlled the rise and emplacement of the younger volcanic rocks, erupted along WNW-ESE and N-S structures, probably reactivated as extensional systems.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
