Late Cenozoic Alkalic Basaltic Magmas in the Western Colorado Plateaus and the Basin and Range Transition Zone, U.S.A., and Their Bearing on Mantle Dynamics

Abstract

Research Article| November 01, 1974 Late Cenozoic Alkalic Basaltic Magmas in the Western Colorado Plateaus and the Basin and Range Transition Zone, U.S.A., and Their Bearing on Mantle Dynamics M. G. BEST; M. G. BEST 1Department of Geology, Brigham Young University, Provo, Utah 84601 Search for other works by this author on: GSW Google Scholar W. H. BRIMHALL W. H. BRIMHALL 1Department of Geology, Brigham Young University, Provo, Utah 84601 Search for other works by this author on: GSW Google Scholar Author and Article Information M. G. BEST 1Department of Geology, Brigham Young University, Provo, Utah 84601 W. H. BRIMHALL 1Department of Geology, Brigham Young University, Provo, Utah 84601 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1974) 85 (11): 1677–1690. https://doi.org/10.1130/0016-7606(1974)85<1677:LCABMI>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 M. G. BEST, W. H. BRIMHALL; Late Cenozoic Alkalic Basaltic Magmas in the Western Colorado Plateaus and the Basin and Range Transition Zone, U.S.A., and Their Bearing on Mantle Dynamics. GSA Bulletin 1974;; 85 (11): 1677–1690. doi: https://doi.org/10.1130/0016-7606(1974)85<1677:LCABMI>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 Late Cenozoic volcanism along the eastern margin of the Basin and Range province in northern Arizona and Utah has created a suite of essentially alkalic basaltic lavas similar to those occurring in other regions of recent uplift, extensional tectonism, and high heat flow. The lavas were derived from a series of partial melts of the mantle, modified to varying degrees by polybaric fractionation of olivine and possibly plagioclase and clinopyroxene during ascent to the surface. Basanite and alkali olivine basalt melts originated at depths of at least 65 km and possibly as much as 95 km (20 to 30 kb) by variable but generally small degrees of partial melting. More voluminous hawaiite magmas originated at shallower depths by a somewhat greater degree of partial melting and were more substantially modified by crystal fractionation prior to extrusion.Magmas parental to the lava extrusions became increasingly divergent in composition with time, reflecting a broadening depth interval of partial melting in the mantle. Concurrent eruptive activity and block faulting generally shifted eastward with time at a rate of approximately 1 cm/yr. These time-space-composition variations, in combination with the observed essentially marginal localization of basaltic volcanism for the whole Basin and Range province, are explained in terms of upper mantle dynamics. We envisage upwelling mantle or plume activity beginning sometime in the middle to late Cenozoic in the core area of the Basin and Range province and causing progressive thinning or "erosion" of the lithosphere. Erosion ultimately produced a steep, keellike asthenosphere-lithosphere boundary beneath the Colorado Plateaus and the Basin and Range transition zone. Eastward-flowing mantle peridotite from the core of the plume was throttled against this keel, causing localized shear heating. This heat enhanced partial melting so that sufficient liquid was created to separate from the refractory residuum and to rise to the surface. Diapiric uprise of magma, or partially melted mantle in the uppermost mantle, or injection of a swarm of dikes into the lower crust, might have weakened and attenuated the overlying brittle crust, causing concurrent faulting. Eastward erosion of the keel and site of partial melting as time progressed allowed eruptive and fault activity to also migrate. 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.