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The record of Middle Jurassic volcanism in the Carmel and Temple Cap Formations of southwestern Utah

2001; Geological Society of America; Volume: 113; Issue: 3 Linguagem: Inglês

10.1130/0016-7606(2001)113 2.0.co;2

1943-2674

Bart J. Kowallis, Eric H. Christiansen, Alan L. Deino, Cheng Ning Zhang, Brent H. Everett,

Geological formations and processes

Research Article| March 01, 2001 The record of Middle Jurassic volcanism in the Carmel and Temple Cap Formations of southwestern Utah Bart J. Kowallis; Bart J. Kowallis 1Department of Geology, Brigham Young University, Provo, Utah 84604, USA Search for other works by this author on: GSW Google Scholar Eric H. Christiansen; Eric H. Christiansen 1Department of Geology, Brigham Young University, Provo, Utah 84604, USA Search for other works by this author on: GSW Google Scholar Alan L. Deino; Alan L. Deino 2Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, California 94709, USA Search for other works by this author on: GSW Google Scholar Chengning Zhang; Chengning Zhang 3Department of Geology, Brigham Young University, Provo, Utah 84604, USA Search for other works by this author on: GSW Google Scholar Brent H. Everett Brent H. Everett 3Department of Geology, Brigham Young University, Provo, Utah 84604, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Bart J. Kowallis 1Department of Geology, Brigham Young University, Provo, Utah 84604, USA Eric H. Christiansen 1Department of Geology, Brigham Young University, Provo, Utah 84604, USA Alan L. Deino 2Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, California 94709, USA Chengning Zhang 3Department of Geology, Brigham Young University, Provo, Utah 84604, USA Brent H. Everett 3Department of Geology, Brigham Young University, Provo, Utah 84604, USA Publisher: Geological Society of America Received: 11 Jan 1999 Revision Received: 13 Apr 2000 Accepted: 21 Apr 2000 First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (2001) 113 (3): 373–387. https://doi.org/10.1130/0016-7606(2001)113 2.0.CO;2 Article history Received: 11 Jan 1999 Revision Received: 13 Apr 2000 Accepted: 21 Apr 2000 First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Bart J. Kowallis, Eric H. Christiansen, Alan L. Deino, Chengning Zhang, Brent H. Everett; The record of Middle Jurassic volcanism in the Carmel and Temple Cap Formations of southwestern Utah. GSA Bulletin 2001;; 113 (3): 373–387. doi: https://doi.org/10.1130/0016-7606(2001)113 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 Altered volcanic ash beds in the Middle Jurassic Temple Cap and Carmel Formations in southwestern Utah record a pulse of active arc-related volcanism between 166 and 171 Ma. A second pulse between 148 and 155 Ma has previously been documented in the Upper Jurassic Morrison Formation. Volcanic and volcaniclastic rocks of these same ages have also been identified closer to or within the arc in California in the Inyo Mountains, the Cowhole Mountains, the Palen Mountains, and the central Mojave Desert. The upper part of the volcaniclastic Mount Wrightson Formation and the strata of Cobre Ridge in southern Arizona are ca. 170 Ma in age and appear to be time correlative with the Middle Jurassic formations in southwestern Utah.The altered ash beds found in the Temple Cap and Carmel Formations typically contain phenocrysts of sanidine, quartz, biotite, apatite, zircon, and titanite. Plagioclase was likely present originally in all of the ashes, but was removed by alteration and is now found only in the Temple Cap red beds. Quartz and sanidine are absent in two crystal-poor ash beds that contain two pyroxenes, hornblende, and biotite. Although major and trace element concentrations in the ash beds have been substantially modified, compositions of relict phenocrysts reveal that the magmas were calc-alkaline rhyolites to andesites. Two-pyroxene, two-feldspar, biotite, and biotite-apatite thermometers suggest that crystallization occurred at temperatures ranging from 740 to 910 °C. Hornblende geobarometry yields pressures of 1–2 kilobars for the two ash beds that contain the appropriate buffer assemblage. The mafic silicates all have moderately high Mg/Fe ratios. This fact, combined with the presence of hornblende, biotite, and titanite, suggests that the phenocrysts crystallized at high oxygen fugacities similar to those of the granites of the batholiths of California. The ash probably erupted from a low-lying arc cut by strike-slip faults in what is now southern California and western Nevada.Major Jurassic unconformities occur near or within the ash-bearing formations in southwestern Utah. Laser-fusion single-crystal 40Ar/39Ar measurements have defined the ages of the unconformities and the associated volcanism. The age of the J-1 unconformity, found at the base of the Temple Cap Formation in southwestern Utah, is older than ca. 170.5 Ma. The J-2 unconformity, which lies between the Temple Cap and Carmel Formations, formed between ca. 169 and 168 Ma. The origin of these unconformities is still unclear, but may be related to the Middle Jurassic pulse of magmatism and the oblique plate convergence along the western margin of North America. The age range of ash beds in the Carmel Formation between 166.3 and 168.0 ± ∼0.5 Ma is consistent with a Bajocian-Bathonian boundary of ca. 166 Ma. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.