Abstract
Research Article| April 01, 1990 Discrimination of ophiolitic from nonophiolitic ultramafic-mafic allochthons in orogenic belts by the Al/Ti ratio in clinopyroxene Robert R. Loucks Robert R. Loucks 1Department of Earth and Atmospheric Sciences, Purdue University, West Lafayette, Indiana 47907 Search for other works by this author on: GSW Google Scholar Geology (1990) 18 (4): 346–349. https://doi.org/10.1130/0091-7613(1990)018<0346:DOOFNU>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Robert R. Loucks; Discrimination of ophiolitic from nonophiolitic ultramafic-mafic allochthons in orogenic belts by the Al/Ti ratio in clinopyroxene. Geology 1990;; 18 (4): 346–349. doi: https://doi.org/10.1130/0091-7613(1990)018<0346:DOOFNU>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 SocietyGeology Search Advanced Search Abstract In mafic igneous suites typical of anorogenic igneous provinces (mid-ocean ridges, back-arc basins, continental rifts, and "hotspots"), clinopyroxenes of tholeiitic and silica-undersaturated rocks incorporate Al in clinopyroxene chiefly via the charge-coupled substitution viMgivSi2 ⇔ viTiivAl2 as the CaTiAl2O6 molecule. This substitution is promoted by high titania activity relative to silica in the melt, and hence is particularly characteristic of silica-undersaturated mafic rocks. Mafic igneous suites of convergent plate margins (i.e., arc tholeiites and calc-alkalic gabbros and basalts) characteristically incorporate Al in clinopyroxene largely as the CaFe3+AlSiO6 molecule. The viMgivSi ⇔ viFe3+ivAl substitution is promoted by relatively high fugacities of H2O and O2, a characteristic feature of arc-axis magmas. Recognition of cumulates that are complementary to compositions of eruptive rocks in arcs is crucial to development of valid petrogenetic models for arc magmas. Plots of tetrahedrally coordinated Al vs. octahedral Ti in augite of gabbroic and ultramafic cumulates show that augite data arrays for arc-related cumulates have a trend of substantially higher Al/Ti in clinopyroxene than do those from rift-related tholeiites. The Al/Ti ratio in clinopyroxene may be utilized to discriminate ophiolitic from nonophiolitic ultramafic-mafic allochthons in orogenic belts. 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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