Pyroxene orientation within the upper mantle

Research Article| April 01, 1982 Pyroxene orientation within the upper mantle NIKOLAS I. CHRISTENSEN; NIKOLAS I. CHRISTENSEN 1Department of Geological Sciences and Graduate Program in Geophysics, University of Washington, Seattle, Washington 98195 Search for other works by this author on: GSW Google Scholar SUSAN M. LUNDQUIST SUSAN M. LUNDQUIST 1Department of Geological Sciences and Graduate Program in Geophysics, University of Washington, Seattle, Washington 98195 Search for other works by this author on: GSW Google Scholar Author and Article Information NIKOLAS I. CHRISTENSEN 1Department of Geological Sciences and Graduate Program in Geophysics, University of Washington, Seattle, Washington 98195 SUSAN M. LUNDQUIST 1Department of Geological Sciences and Graduate Program in Geophysics, University of Washington, Seattle, Washington 98195 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1982) 93 (4): 279–288. https://doi.org/10.1130/0016-7606(1982)93<279:POWTUM>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 NIKOLAS I. CHRISTENSEN, SUSAN M. LUNDQUIST; Pyroxene orientation within the upper mantle. GSA Bulletin 1982;; 93 (4): 279–288. doi: https://doi.org/10.1130/0016-7606(1982)93<279:POWTUM>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 Petrofabric analyses of orthopyroxene and olivine for a suite of rocks from the Bay of Islands ophiolite, Newfoundland, show systematic relationships between the minerals' fabrics, the plane of the Mohorovičić discontinuity determined from the contact of the gabbro and ultramafic sections, and the spreading direction inferred from the attitude of the sheeted dikes. The orthopyroxene c crystallographic axes maxima, which are aligned subparallel to the spreading direction, coincide with olivine a axes maxima. The orthopyroxene b axes and olivine c axes also lie approximately within the plane of the Mohorovičić discontinuity but parallel the ridge, whereas the orthopyroxene a axes maxima and olivine b axes maxima are approximately perpendicular to the Mohorovičić discontinuity. Using olivine and orthopyroxene elastic constants and their pressure derivatives, velocities have been calculated from composite petrofabric data and contoured for varying proportions of olivine and pyroxene. The results of these calculations show that within a vertical direction compressional wave velocities change only slightly with increasing pyroxene content, whereas parallel to the Mohorovičić discontinuity velocities decrease with increasing pyroxene content. Anisotropy decreases from 4% for a rock with 100% olivine to 2.6% for a rock with 50% olivine and 50% orthopyroxene. Also within the plane of Mohorovičić discontinuity, the maximum and minumum velocities occur at approximately the same azimuth for differing percentages of orthopyroxene. A comparison of the calculated anisotropy and the observed seismic anisotropy off the coast of California shows a striking agreement. From this comparison, it is estimated that the percentage of orthopyroxene within the upper mantle of this region varies between 0% and 30%. 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.