Portal de Periódicos da CAPES

Textural and chemical variations of olivine and chrome spinel in the East Dover ultramafic bodies, south-central Vermont

1978; Geological Society of America; Volume: 89; Issue: 5 Linguagem: Inglês

10.1130/0016-7606(1978)89 2.0.co;2

1943-2674

Mark A. Hoffman, David Walker,

Paleontology and Stratigraphy of Fossils

Research Article| May 01, 1978 Textural and chemical variations of olivine and chrome spinel in the East Dover ultramafic bodies, south-central Vermont MARK A. HOFFMAN; MARK A. HOFFMAN 1New York State Museum and Science Service, Geological Survey, State Education Building, Albany, New York 122233Present address: Phelps Dodge Exploration East, Inc., 11484 Washington Plaza West, Reston, Virginia 22090 Search for other works by this author on: GSW Google Scholar DAVID WALKER DAVID WALKER 2Hoffman Laboratory, Harvard University, Cambridge, Massachusetts 02138 Search for other works by this author on: GSW Google Scholar Author and Article Information MARK A. HOFFMAN 1New York State Museum and Science Service, Geological Survey, State Education Building, Albany, New York 122233Present address: Phelps Dodge Exploration East, Inc., 11484 Washington Plaza West, Reston, Virginia 22090 DAVID WALKER 2Hoffman Laboratory, Harvard University, Cambridge, Massachusetts 02138 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1978) 89 (5): 699–710. https://doi.org/10.1130/0016-7606(1978)89 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 MARK A. HOFFMAN, DAVID WALKER; Textural and chemical variations of olivine and chrome spinel in the East Dover ultramafic bodies, south-central Vermont. GSA Bulletin 1978;; 89 (5): 699–710. doi: https://doi.org/10.1130/0016-7606(1978)89 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 Regional metamorphism of upper-greenschist to epidote-amphibolite facies produced variations of olivine and chrome spinel textures and compositions within the East Dover ultramafic bodies that can be attributed to differing intensities of recrystallization of the ultramafic rocks. Olivine shows a progressive change from highly strained grains in the least recrystallized rocks to relatively strain-free grains in the most recrystallized rocks. Fo content of olivine bears a direct relationship to texture: with increase in degree of recrystallization, olivine changes composition from Fo90 to Fo97. Chrome spinel grains are ubiquitously rimmed by opaque spinels. Variations in thickness of these rims and shape of the translucent chrome spinel cores occur in a regular manner. Thickest rims occur around the most anhedral cores, and these are found in the most strongly recrystallized rocks. Euhedral chrome spinels with thin opaque spinel rims are found in the least recrystallized rocks. With increasing recrystallization, Mg/(Mg + Fe) and A1/(A1 + Cr) ratios increase in the spinel cores.Zones of intensity of recrystallization indicated by both olivine and spinel textures and compositions are geographically concentric with the map outlines of the ultramafic bodies. Observed textural and compositional variations suggest a reaction involving simultaneous serpentinization and recrystallization of olivine in the presence of an oxidizing fluid. Partial buffering of this fluid (which originated in the country rocks) and subsequent development of a substantial fo2 gradient between the margins and cores of the larger ultramafic bodies resulted in a more nearly complete reaction at the margins than in the cores of the bodies. This reaction need not have occurred as a single event, and equilibrium was only maintained on the scale of hand specimens (fo2, olivine composition) to fractions of mineral grains (spinel composition). 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.