Asymmetric textural and structural patterns of a granitic body emplaced at shallow levels: The La Chinchilla pluton, northwestern Argentina

MACCHIOLI GRANDE, M.; ALASINO P.H.; ROCHER, S.; LARROVERE M.A.; ALASINO, P.H., DAHLQUIST, J.A., GALINDO, C. Y CASQUET, C.

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2015 p. 58 - 68

0895-9811

New mapping and a detailed structural study of the La Chinchilla stock, Sierra de Velasco, NW Argentina, suggest an asymmetrical shape of the pluton and provide strong evidence for its shallow emplacement depth. The pluton is a Lower Carboniferous monzogranite composed of K-feldspar, quartz, plagioclaseand biotite. It exhibits an internal asymmetric textural zoning, defined by porphyritic granite in the southeastern region to equigranular granite in the northwestern region. The presence of subhorizontal dikes in the northwestern area, where the contacts dip shallowly, and subvertical dikes intruding thehost rock nearby steep-dipping intrusive contacts in the southeastern region are compatible with an overall asymmetrical shape and internal structure of this pluton. Considering published crystallization ages, a dominant strain field occurring at around 12 Ma is inferred based on magmatic fabrics in thepluton and its host rock (the Huaco pluton), with a principal shortening direction oriented SW-NE, consistent with the general NWeSE strike of the body. Field evidence supports brittle fracturing and block displacement as the dominant emplacement mechanism, suggesting that magmatic stopingdominated during the late stage of the evolution of the magma chamber.