NEW INSIGHTS ON THE AGE OF THE JALISCO BLOCK (GUERRERO TERRANE OF WEST-CENTRAL MEXICO) FROM U-PB GEOCHRONOLOGY

The Jalisco Block is a fault-bounded crustal fragment, located along the western edge of the Trans-Mexican Volcanic Belt of west-central Mexico, which forms part of the Triassic-Jurassic Guerrero terrane. Because of its extensive Miocene-Quaternary volcanic cover and Cretaceous-Tertiary intrusions, little is known about the basement of the Jalisco block. In order to constrain the evolution and provenance of this basement, we analyzed zircons from several roof pendants, overlying sedimentary units, and granitic bodies. Analyses were conducted by LA-MC-ICPMS. ~100 detrital zircon grains were analyzed from each of five different samples of schist (Punta Mita, El Tuito, Mascota, Atenguillo and Cuale). The main age groups in these samples range from 77 Ma to 240 Ma, and there are subordinate clusters from the Carboniferous (297 Ma), Ordovician (446 Ma), Late and Middle Proterozoic (760, 1041, 1200, 1500 Ma) and Archean (~2700 Ma). Marine turbiditic sediments near San Sebastian yield zircons that are mainly ~131 Ma, with minor age peaks at 320, 480-560, 743, 997-1260, and ~2750 Ma. Granites from different localities (Atenguillo, Puerto Vallarta, Cuale, Mascota and Tomatlan) range from 59 to 90 Ma and overlap with previous constraints on the age of granites and rhyolitic ash flow tuffs from the Jalisco Block. The Mesozoic detrital zircon age peaks from these units overlap with detrital zircon ages determined for other areas of the Guerrero terrane (139 to 164 Ma) and Alisitos terrane (90-134 Ma) in Baja California.