Petrologic Study of the Sierra Ancha Sill Complex, Arizona
1970; Geological Society of America; Volume: 81; Issue: 6 Linguagem: Inglês
10.1130/0016-7606(1970)81[1733
ISSN1943-2674
Autores Tópico(s)Mineralogy and Gemology Studies
ResumoResearch Article| June 01, 1970 Petrologic Study of the Sierra Ancha Sill Complex, Arizona C. E NEHRU; C. E NEHRU Department of Geology, Brooklyn College of the City University of New York, Brooklyn, New York, 11210 Search for other works by this author on: GSW Google Scholar MARTIN PRINZ MARTIN PRINZ Department of Geology and Institute of Meteoritics, University of New Mexico, Albuquerque, New Mexico 87106 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1970) 81 (6): 1733–1766. https://doi.org/10.1130/0016-7606(1970)81[1733:PSOTSA]2.0.CO;2 Article history received: 11 Aug 1969 rev-recd: 15 Dec 1969 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation C. E NEHRU, MARTIN PRINZ; Petrologic Study of the Sierra Ancha Sill Complex, Arizona. GSA Bulletin 1970;; 81 (6): 1733–1766. doi: https://doi.org/10.1130/0016-7606(1970)81[1733:PSOTSA]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 The Sierra Ancha sill complex is a major high-alumina basaltic intrusive of late Precambrian age in the central Arizona dolerite province. It consists of three zones: lower dolerite, 200 ft; microtroctolite (fine-grained plagioclase-olivine rock with minor coarse-grained poikilitic augite), 235 ft; upper dolerite, 275 ft. Dolerite zones crystallized from high-alumina basaltic magma and are taken to represent parent magma; chilled contacts have been deuterically altered, especially for potassium. The parent magma is similar to late Precambrian high-alumina basaltic magmas that crystallized anorthositic rocks and differs from high-alumina basalts from orogenic regions or major layered intrusions. Sierra Ancha rocks probably correlate with late Precambrian dolerite-sill areas in Grand Canyon, Arizona, Panamint Range, California, and other areas in the southwestern United States, and indicate a large high-alumina basaltic petrologic province. The three zones constitute separate and concordant sills. Microtroctolite is hypothesized to have formed at depth in the magma reservoir by undercooling, rapid nucleation, secondary enlargement, and diffusional interaction of interstitial and overlying magma; this material was intruded as a crystal mush. An alternative hypothesis is that liquid of troctolitic composition developed in the lower portion of the reservoir by liquid fractionation; it was then emplaced and crystallized after under-cooling. The upper dolerite sill differentiated upward from high-alumina basalt to lower alumina basalt by a process of crystallization and diffusion with overlying magma as in the process outlined by Hess (1960). Andesine anorthosite with excellent flow texture, locally found in the lower dolerite, probably formed as a crystal cumulate in the upper part of the reservoir by flotation. Dolerite pegmatite contains deuteric albite as its plagioclase; the deuteric process is analogous to spilitization. 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.
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