Fragments of the mantle and crust from beneath the Sierra Nevada batholith: Xenoliths in a volcanic pipe near Big Creek, California

Research Article| June 01, 1988 Fragments of the mantle and crust from beneath the Sierra Nevada batholith: Xenoliths in a volcanic pipe near Big Creek, California F.C.W. DODGE; F.C.W. DODGE 1U.S. Geological Survey, 345 Middlefield Road Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar J. P. LOCKWOOD; J. P. LOCKWOOD 2U.S. Geological Survey, Hawaii National Park, Hawaii 96718 Search for other works by this author on: GSW Google Scholar L. C. CALK L. C. CALK 1U.S. Geological Survey, 345 Middlefield Road Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar Author and Article Information F.C.W. DODGE 1U.S. Geological Survey, 345 Middlefield Road Menlo Park, California 94025 J. P. LOCKWOOD 2U.S. Geological Survey, Hawaii National Park, Hawaii 96718 L. C. CALK 1U.S. Geological Survey, 345 Middlefield Road Menlo Park, California 94025 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 (6): 938–947. https://doi.org/10.1130/0016-7606(1988)100<0938:FOTMAC>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 Email Permissions Search Site Citation F.C.W. DODGE, J. P. LOCKWOOD, L. C. CALK; Fragments of the mantle and crust from beneath the Sierra Nevada batholith: Xenoliths in a volcanic pipe near Big Creek, California. GSA Bulletin 1988;; 100 (6): 938–947. doi: https://doi.org/10.1130/0016-7606(1988)100<0938:FOTMAC>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 A Miocene volcanic pipe that cuts Cretaceous granodiorite is exposed in the central Sierra Nevada near the town of Big Creek, California. The volcanic magma began its ascent from a mantle source as an alkalic basalt but was extensively contaminated by incorporation and assimilation of silicic plutonic rocks during ascent, resulting in a "pseudo-andesitic" composition. The conduit cut through the entire thickness of the Sierra Nevada batholith, as well as the underlying lower crust and upper mantle, and the magma entrained a diverse, polygenetic assemblage of igneous and metamorphic xenoliths, including peridotites, eclogites and granulites, schists and hornfels, and gabbroids and granitoids. Some xenoliths of the high-grade metamorphic xenolith group are of particular interest in elucidating the nature of the uppermost mantle and crust beneath the Sierra Nevada.Garnet granulites, the most abundant rock type of the mafic high-grade metamorphic assemblage, and eclogites are restricted to the central area of the pipe. These xenoliths are essentially bimineralic, consisting of colorless to pale green clinopyroxene and garnet; eclogites contain brilliant emerald green clinopyroxene. The clinopyroxenes, which have a broad range of compostions [Mg/ (Mg + Fe) = 0.45-0.90], have a >20% jadeite component in eclogites. Garnets also have a range of compositions [Mg/(Mg + Fe) = 0.30-0.70], with those from eclogites being the most Fe rich. One of the xenoliths contains Ca-rich garnet (grs + adr > 90%). Feldspathic granulites contain plagioclase of An45-70, and some lack garnet. Hornblende occurs in some granulites, and a few amphibolites are present.Likely protoliths are ocean-floor basalts for the eclogites and Precambrian limestone for the grossular-clinopyroxene rock. The Big Creek xenoliths attest to the former presence of subducted oceanic lithosphere beneath the western Sierra Nevada. 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.