Abstract

ARVIZU, Harim E. et al. Permiam granitic rocks in the Sierra Pinta, NW Sonora, Mexico: Subduction magmatism associated to the onset of the active continental margin of southwestern North America. Rev. mex. cienc. geol [online]. 2009, vol.26, n.3, pp.709-728. ISSN 2007-2902.

Multidisciplinary studies in the Sierra Pinta area in NW Sonora, including U-Pb zircon geochronology, mayor and trace element geochemistry as well as Sm-Nd isotopic studies have allowed a precise characterization of Permian granitic rocks. The results suggest the existence of a suite of Permian granitoids with U-Pb zircon ages between ~275 y ~258 Ma. Initial epsilon Nd values between -19.2 and -10.4 and corresponding Nd model ages (T_DM) between 2.5 and 1.6 Ga, as well as some geochemical characteristics, indicate melting of Proterozoic crustal basement associated to the early stages of subduction forming the continental magmatic arc of SW North America. It is likely that this Permian magmatic pulse in NW Sonora was part of a larger event in the American Cordillera extending from western-southwestern USA, passing through northern Mexico and up to central and southern Mexico and, perhaps, to northern South America (i.e., Colombia). We suggest that the occurrence of the Permian granitoids in Sierra Pinta is associated with a Paleoproterozoic crustal weakness zone formed by a narrow stretch of the Yavapai crustal province. This weakness zone could have acted as a channel-way that facilitated the ascent towards higher crustal levels of the first magmas generated by subduction.

Keywords : granitic rocks; U-Pb geochronology; zircon; geochemistry; Sm-Nd isotopic studies; Permian; Sierra Pinta; Sonora; Mexico.