INTRUSIVE IGNEOUS BODIES RELATED TO THE MIDDLE-LATE MIOCENE OBLIQUE RIFT IN SONORA, MEXICO

Miocene hypabyssal outcrops, dates at ca 14 to 10 Ma, are widely distributed in many localities from the coastline of Gulf of California in southern Sonora, and until 60 km in mainland (Guaymas, Graben of Empalme, Sierra El Aguaje).They are thick granophyric bodies (up to 1000m) and thin vitreous to microcrystalline hypovolcanic dykes and sills (down to 100m), both hosted in intermediate to acid volcanic rocks and exposed as isolated hills. Identified flow planes in dykes and found magmatic foliation in granophyric bodies allow to establish good structural relation. Petrographic characteristics of the two types of rocks are dominated by an anhydrous mineralogical association with phenocryst of quartz, sieve feldspar, Fe-Ni oxides and minor pyroxene. The geochemical data of all magmas show an acid (68 to 76% SiO2) and potassic cogenetic suite. Finally, structural and paleomagnetic results permit conclude that orientations of intrusive tabular bodies are first associated with a filling of tensional fractures in a dextral simple shear, and second, in some outcrops, to clockwise rotation related to a posterior development of tension gashes during Late Miocene.