Mesozoic Evolution of the Northern Region of the Jalisco Block, Mexico Based on U-Pb Geochronology

The Jalisco Block is part of the Triassic-Jurassic Guerrero Terrane and is located at the western margin of the Trans-Mexican Volcanic Belt, central Mexico. The basement of this is fault-bounded crustal block has been poorly studied, mainly because of its extensive Miocene-Quaternary volcanic cover and post-Jurassic intrusions.

In this study we selected samples of quartz felsdespatic schists (QFS), marine turbiditic sediments and granitic bodies in order to determine the age and provenance of this basement. Zircons were analyzed using the U-Pb LA-MC-ICPMS geochronological technique at the Laserchron facility, University of Arizona.

Detrital zircon grains were dated from QFS samples from Punta Mita, El Tuito, Atenguillo and Cuale. The results show maximum deposition ages that range from Triassic to Late Creataceous. Subordinate zircon populations from the Carboniferous (297 Ma), Ordovician (446 Ma), Late and Middle Proterozoic (760 Ma, 1041 Ma, 1200 Ma, 1500 Ma) and Archean (~2700 Ma) are also present. Marine turbiditic sediments near San Sebastian have a main age peak at ~131 Ma with minor age peaks at 320 Ma, 480-560 Ma, 743 Ma, 997-1260 Ma and some Archean grains. Granitic intrusions from Atenguillo, Puerto Vallarta, Cuale, and Tomatlan range in age from 59-160 Ma.

The young detrital zircon age peak from QSP and sediments overlap with those determined for other areas of the Guerrero Terrane (139 to 164 Ma) and Alisitos Terrane to the north in Baja California (90-134 Ma). Older population peaks are comparable to those previously determinated for the main Pre-Triassic landmass of Mexico (Mexican “core”), which suggest that the basement of the Guerrero terrane developed in close proximity to this old Mexican core. The provenance of the Archean zircons remains unclear.