Research Article| May 01, 2015 Timing of rifting in the southern Gulf of California and its conjugate margins: Insights from the plutonic record Jose Duque-Trujillo; Jose Duque-Trujillo 1Centro de Geociencias, Universidad Nacional Autónoma de México, Campus Juriquilla, Querétaro, 76230 Querétaro, México Search for other works by this author on: GSW Google Scholar Luca Ferrari; Luca Ferrari † 1Centro de Geociencias, Universidad Nacional Autónoma de México, Campus Juriquilla, Querétaro, 76230 Querétaro, México †luca@unam.mx. Search for other works by this author on: GSW Google Scholar Teresa Orozco-Esquivel; Teresa Orozco-Esquivel 1Centro de Geociencias, Universidad Nacional Autónoma de México, Campus Juriquilla, Querétaro, 76230 Querétaro, México Search for other works by this author on: GSW Google Scholar Margarita López-Martínez; Margarita López-Martínez 2Departamento de Geología, Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE), Carretera Ensenada-Tijuana No. 3918, 22860 Ensenada, Baja California, México Search for other works by this author on: GSW Google Scholar Peter Lonsdale; Peter Lonsdale 3Scripps Institution of Oceanography, University of California at San Diego, La Jolla, California 92093, USA Search for other works by this author on: GSW Google Scholar Scott E. Bryan; Scott E. Bryan 4School of Earth, Environmental and Biological Sciences, Queensland University of Technology, Brisbane, Queensland 4001, Australia Search for other works by this author on: GSW Google Scholar Jared Kluesner; Jared Kluesner 3Scripps Institution of Oceanography, University of California at San Diego, La Jolla, California 92093, USA §Present address: Department of Earth and Planetary Sciences, University of California, Santa Cruz, California 95064, USA. Search for other works by this author on: GSW Google Scholar Doris Piñero-Lajas; Doris Piñero-Lajas 2Departamento de Geología, Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE), Carretera Ensenada-Tijuana No. 3918, 22860 Ensenada, Baja California, México #Present address: Departamento de Oceanografía Física, Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE), Carretera Ensenada-Tijuana No. 3918, 22860 Ensenada, Baja California, México. Search for other works by this author on: GSW Google Scholar Luigi Solari Luigi Solari 1Centro de Geociencias, Universidad Nacional Autónoma de México, Campus Juriquilla, Querétaro, 76230 Querétaro, México Search for other works by this author on: GSW Google Scholar GSA Bulletin (2015) 127 (5-6): 702–736. https://doi.org/10.1130/B31008.1 Article history received: 08 Oct 2013 rev-recd: 02 Sep 2014 accepted: 29 Oct 2014 first online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Jose Duque-Trujillo, Luca Ferrari, Teresa Orozco-Esquivel, Margarita López-Martínez, Peter Lonsdale, Scott E. Bryan, Jared Kluesner, Doris Piñero-Lajas, Luigi Solari; Timing of rifting in the southern Gulf of California and its conjugate margins: Insights from the plutonic record. GSA Bulletin 2015;; 127 (5-6): 702–736. doi: https://doi.org/10.1130/B31008.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The Gulf of California is a young example of crustal stretching and transtensional shearing leading to the birth of a new oceanic basin at a formerly convergent margin. Previous studies focused along the southwestern rifted margin in Baja California indicated rifting was initiated after subduction and related magmatism ceased at ca. 14–12.5 Ma. However, the geologic record on the Mexico mainland (Sinaloa and Nayarit States) indicates crustal stretching in the region began as early as late Oligocene. The timing of cooling and exhumation of pre- and synrift plutonic rocks can provide constraints on the timing and rate of rifting. Here, we present results of a regional study on intrusive rocks in the southern Gulf of California sampled along the conjugate Baja California and Nayarit-Sinaloa rift margins, as well as plutonic rocks now exposed on submerged rifted blocks inside the gulf. Forty-one samples were dated via U/Pb zircon and 40Ar/39Ar mineral ages, providing emplacement age and thermochronological constraints on timing and rate of cooling. We found an extensive suite of early and middle Miocene plutons emplaced at shallow depths within the basement Cretaceous–Paleocene Peninsular Range and Sinaloa-Jalisco Batholiths. Early Miocene granitoids occur in an elongated WNW-ESE belt crossing the entire southern gulf from southern Baja California to Nayarit and Sinaloa. Most have an intermediate composition (<67 SiO2 wt%), but a distinctive group of high-silica granites (>75 SiO2 wt%) was emplaced 20.1–18.3 Ma, near the end of the early Miocene. Age span and chemical composition of the early Miocene silicic plutons essentially overlap ignimbrites and domes exposed in the southern Sierra Madre Occidental and in southern Baja California, suggesting that eruptive sources for the early Miocene ignimbrite flare-up may also have been located within the southern Gulf of California. Early Miocene plutons cooled below the 40Ar-39Ar biotite closure temperature (350–400 °C) in less than 2.5 m.y., which we interpret as evidence of a regional extensional event leading to the opening of the Gulf of California. A less widely distributed suite of intermediate-composition, middle Miocene granitoids (15–13 Ma) was sampled from the central-western part of the gulf, west of the Pescadero Basin, and these correspond to an episode of scarce volcanism recorded by the middle and upper members of the onshore Comondú Group in Baja California. Our widely spaced sampling of the generally sediment-covered igneous crust suggests that middle Miocene primary volcanic rocks are much less abundant than implied by previous models in which the gulf was the site of a robust Comondú arc. Thermobarometry data also indicate a very shallow depth (<5 km) of emplacement for the middle Miocene plutonic rocks. Some of these rocks also show a distinctive inequigranular texture indicative of at least two crystallization stages at different pressure. Early and middle Miocene granitoids away from the gulf axis yielded 40Ar-39Ar cooling ages very close to U-Pb zircon ages, demonstrating rapid cooling to <350 °C, which we attribute to their shallow emplacement and, possibly, to exhumation soon after intrusion. Since Comondú-age and middle Miocene magmatism in the gulf region coincided with rapid cooling of young plutons that predate the end of subduction, we suggest that intense crustal stretching controlled the pattern and timing of Comondú-age magmatism, rather than the middle Miocene magmatism controlling the locus of <12 Ma extension. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
