K-Ar Apparent Ages, Peninsular Ranges Batholith, Southern California and Baja California

Abstract

Research Article| June 01, 1975 K-Ar Apparent Ages, Peninsular Ranges Batholith, Southern California and Baja California DANIEL KRUMMENACHER; DANIEL KRUMMENACHER 1Department of Geology, San Diego State University, San Diego, California 92182 Search for other works by this author on: GSW Google Scholar R. GORDON GASTIL; R. GORDON GASTIL 1Department of Geology, San Diego State University, San Diego, California 92182 Search for other works by this author on: GSW Google Scholar JONATHAN BUSHEE; JONATHAN BUSHEE 1Department of Geology, San Diego State University, San Diego, California 92182 Search for other works by this author on: GSW Google Scholar JOAN DOUPONT JOAN DOUPONT 1Department of Geology, San Diego State University, San Diego, California 92182 Search for other works by this author on: GSW Google Scholar Author and Article Information DANIEL KRUMMENACHER 1Department of Geology, San Diego State University, San Diego, California 92182 R. GORDON GASTIL 1Department of Geology, San Diego State University, San Diego, California 92182 JONATHAN BUSHEE 1Department of Geology, San Diego State University, San Diego, California 92182 JOAN DOUPONT 1Department of Geology, San Diego State University, San Diego, California 92182 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1975) 86 (6): 760–768. https://doi.org/10.1130/0016-7606(1975)86<760:KAAPRB>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation DANIEL KRUMMENACHER, R. GORDON GASTIL, JONATHAN BUSHEE, JOAN DOUPONT; K-Ar Apparent Ages, Peninsular Ranges Batholith, Southern California and Baja California. GSA Bulletin 1975;; 86 (6): 760–768. doi: https://doi.org/10.1130/0016-7606(1975)86<760:KAAPRB>2.0.CO;2 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 More than 200 K-Ar apparent ages have been determined from minerals from the Peninsular Ranges batholith of southern California and northern Baja California. In general, the apparent ages show a progressive decrease from about 120 m.y. in the southwestern (coastal) pan of the batholith to less than 70 m.y. in the northeastern (desert) part. The gradients for biotite and hornblende ages can be represented by contours of equal ages. Both concordant and discordant hornblende-biotite pairs and minerals, from a variety of plutonic and metamorphic rock types, share in the apparent-age gradient. Ages for hornblende average 5 m.y. older than the ages for coexistent biotite. Isotopic U-Pb and Pb-α measurements on zircon indicate ages greater than those calculated from K-Ar ratios of hornblende or biotite. It is believed that in the Peninsular Ranges province, the U-Pb ages for zircon approximate the ages of emplacement, whereas concordant K-Ar ages may or may not approximate the ages of emplacement, depending on the depth of emplacement and the rate of uplift and denudation. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.