Petrology of Late Jurassic-Early Cretaceous Tusaquillas and Abra Laite-Aguilar plutonic complexes (Central Andes, 23°05’S - 66°05’W): A comparison with Rift related magmatism of NW Argentina and e Bolivia

Abstract

The Late Jurassic-Early Cretaceous Tusaquillas and the Abra Laite-Aguilar Plutonic Complexes represent the most extensive intrusive bodies belonging to the rift-related magmatism developed in NW Argentina from Upper Jurassic to Lower Eocene. Both complexes are characterized by rocks of a wide compositional spectrum, ranging from gabbro and diorite to syenogranite and monzogranite. Geochemical and isotopic data obtained on from samples of the two complexes allowed to distinguish rocks with: 1) basic composition (SiO2=45-52 wt%), low HFSE and REE contents, low initial 87Sr/86Sr ratio (R0=0.703198-0.705868) and high ε t Nd (3.82 to 1.51); 2) felsic compositions (SiO2=70-77 wt%, low HFSE and REE, high R0 (0.708677-0.722668) and low ε t Nd (-3.85 to -1.77); 3) intermediate features, i.e. SiO2=53-69 wt%, R0=0.703303-0.713121, ε t Nd 2.10 to -4.97. On the whole, the data suggest that the basic rocks could have been derived from a mantle source with OIB-like signature, whereas the granitic rocks could have been generated by partial melting of a radiogenic crust. Geochemical and isotopic characteristics of intermediate rocks suggest complex interactions (FC, AFC and mixing processes) between mantle derived magmas and crustal materials. In order to have a more complete scenario of the magmatic events which affected the south-central part of South America in the Jurassic-Cretaceous times, the Tusaquillas and the Abra Laite-Aguilar Plutonic Complexes have been compared with coeval NW Argentina (Rangel and Hornillos) and E Bolivia (Velasco) magmatic provinces. In view of the comparative data, we tentatively propose that the E Bolivia and NW Argentina magmatic provinces could be related to the same regional petrogenetic event, probably linked with the extensional tectonics that affected the western Gondwana at pre-drift times.