FRACTURE-CONTROLLED ASCENT AND EMPLACEMENT OF THE CA. 14.4 MA LAS BURRAS MONZODIORITIC PLUTON DURING SINISTRAL STRIKE-SLIP FAULTING OF THE PUNA AND EASTERN CORDILLERA (SALTA, NW ARGENTINA)

TUBÍA, José María¹, HONGN, Fernando², VEGAS, Néstor³ and ARANGUREN, Aitor¹, (1)Geodinámica, Universidad del País Vasco, Campus de Leioa, Bilbao, 48080, Spain, (2)CONICET. Facultad de Ciencias Naturales, Universidad Nacional de Salta, Buenos Aires,177, Salta, 4400, Argentina, (3)Geodinámica, Universidad del país vasco, Campus de Leioa, Bilbao, 48080, Spain, jm.tubia@ehu.es

New field mapping reveals that part of the Neoproterozoic-Lower Paleozoic Tastil batholith (Salta, NW Argentina) corresponds to a monzodioritic pluton of Miocene age, referred to as the Las Burras pluton. This small (~20 km2) and NE-SW elongated pluton is oblique to the N-trending structures of the Puncoviscana Formation of Neoproterozoic age. U/Pb analyses on zircons yielded an age of 14,4 +/- 0,3 Ma for its emplacement. Anisotropy of magnetic anisotropy, structural and geochemical data of the metaluminous Las Burras pluton are used to analyze its emplacement and tectonic significance. The bulk magnetic susceptibility (K) of the samples varies between 30.74 to 77.23x10-3 SI. The magnetic fabric pattern is well defined. The map of the magnetic foliation outlines an asymmetric dome with steep walls, pointing to a wedge-shaped intrusion with its feeder channel located in the southeastern quadrangle of the intrusion. The ascent and emplacement of the Las Burras monzodiorite point to the infilling of a dilatational site in the brittle crust during transcurrent tectonics. From the kinematic point of view, its emplacement is consistent with the opening of a minor tension fracture related to the sinistral motion of the Calama-Olacapato-El Toro lineament, a zone of crustal weakness corresponding to a strike-slip shear zone of lithospheric scale located at the junction zone of two segments of the subducting Nazca plate with different dipping angle. Several magmatic and volcanic centers, of Tertiary to Quaternary ages, exist along the Calama-Olacapato-El Toro lineament. As the Las Burras monzodiorite is the easternmost Miocene pluton of the Central Andes at this latitude and one of the oldest expression of the magmatism associated with the Calama-Olacapato-El Toro lineament, this new data will significantly contribute to discussions concerning the interplay between lithospheric delamination, magmatism and deformation of the continental crust of the Andes.

Session No. 2--Booth# 33

T2. Plateau and Cordillera Uplift I

Monday, 3 April 2006: 10:35 AM-7:45 PM

Geological Society of America Abstracts with Programs. Speciality Meeting No. 2, p.34

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FRACTURE-CONTROLLED ASCENT AND EMPLACEMENT OF THE CA. 14.4 MA LAS BURRAS MONZODIORITIC PLUTON DURING SINISTRAL STRIKE-SLIP FAULTING OF THE PUNA AND EASTERN CORDILLERA (SALTA, NW ARGENTINA)