Geochemistry and petrology of mafic volcanic rocks from olistostromes in the basal Great Valley Group, northern California Coast Ranges

Abstract

Research Article| November 01, 1988 Geochemistry and petrology of mafic volcanic rocks from olistostromes in the basal Great Valley Group, northern California Coast Ranges GLENN J. MACPHERSON; GLENN J. MACPHERSON 1Department of Mineral Sciences, U.S. National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560 Search for other works by this author on: GSW Google Scholar STEPHEN PAUL PHIPPS STEPHEN PAUL PHIPPS 2Department of Geology, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6316 Search for other works by this author on: GSW Google Scholar Author and Article Information GLENN J. MACPHERSON 1Department of Mineral Sciences, U.S. National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560 STEPHEN PAUL PHIPPS 2Department of Geology, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6316 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1988) 100 (11): 1770–1779. https://doi.org/10.1130/0016-7606(1988)100<1770:GAPOMV>2.3.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation GLENN J. MACPHERSON, STEPHEN PAUL PHIPPS; Geochemistry and petrology of mafic volcanic rocks from olistostromes in the basal Great Valley Group, northern California Coast Ranges. GSA Bulletin 1988;; 100 (11): 1770–1779. doi: https://doi.org/10.1130/0016-7606(1988)100<1770:GAPOMV>2.3.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 The Mysterious Valley formation (MVF) is a 1-km-thick accumulation of chaotic olistostromes, consisting of ophiolitic blocks set in a mudstone and serpentinous mudstone matrix, in the basal Great Valley Group of the northern California Coast Ranges. The MVF overlies serpentinite of the Middle Jurassic Coast Range Ophiolite (CRO).Most igneous blocks from the MVF are mid-ocean-ridge-type tholeiitic basalts (MORB's) with moderate TiO2 contents (1.0%-2.5%) and depletions in light (relative to heavy) rare-earth elements (REE's). Relict clinopyroxenes in these blocks are low-Ti augites. Rare blocks that are light-REE enriched and contain titanaugite probably represent ocean-island-type basalts. Coarse-grained plutonic blocks have not been found; however, abundant blocks of mafic breccia, similar to breccia overlying intact CRO elsewhere in the northern Coast Ranges, contain clasts of ultramafic rock and both cumulus and noncumulus gabbro.Diabase intrusions into the underlying CRO serpentinite are chemically identical to MVF basalts, suggesting a possible relationship between CRO igneous rocks and MVF blocks. Because most MVF basalt blocks are more Ti rich and, in general, more MORB-like than are CRO extrusive basalts, however, the MVF olistostromes are not easily explained as being derived from the uplift and erosion of the ancient CRO. Our chemical data indicate that either (1) MVF basalt blocks were not derived from the CRO; (2) our samples, which are from a geographically limited area, are not representative of the MVF; or (3) the MVF was derived from a more MORB-like part of the CRO that is not well represented in the few analyses presently available from the northern CRO. This content is PDF only. Please click on the PDF icon to access. 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.