caa a22 4500 465791522 CHVBK 20180323112026.0 cr unu---uuuuu 170327e19900801xx s 000 0 eng 10.1007/BF00306543 doi (NATIONALLICENCE)springer-10.1007/BF00306543 Kimball Karen Department of Geology, Rensselaer Polytechnic Institute, 12140, Troy, NY, USA aut Effects of hydrothermal alteration on the compositions of chromian spinels [Elektronische Daten] [Karen Kimball] Chromite spinels in hydrothermally altered rocks from fracture-zone ultramafic rocks and from both ultramafic cumulate pods and sheeted dikes in the Josephine ophiolite, California, display a wide variety of compositions. Alteration of the spinel may not be visible in thin section. The primary composition changes accompanying hydrothermal alteration are increase in Cr/(Cr+Al) and/or Fe2+/(Fe2++Mg). In general, altered spinel grains associated with hornblende and chlorite show an increase in Cr/(Cr+Al) from core to rim. Altered spinel grains associated with serpentine show an increase in Fe2+/(Fe2++Mg) from core to rim but may not show an increase in Cr/(Cr+Al). The compositional zoning in some altered spinel grains appears to result both from reaction of clinopyroxene plus spinel to form hornblende, and from reaction of hornblende to form chlorite. These observations suggest that subsolidus hydrothermal metamorphic effects need to be considered when interpreting spinel compositions and the compositions should not be interpreted solely in terms of igneous processes. Further, the presence of highly altered spinels may be indicative of hydrothermal alteration in rocks where other evidence of such alteration is absent. Springer-Verlag, 1990 Contributions to Mineralogy and Petrology Springer-Verlag 105/3(1990-08-01), 337-346 0010-7999 105:3<337 1990 105 410 https://doi.org/10.1007/BF00306543 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/BF00306543 text/html Onlinezugriff via DOI NATIONALLICENCE 100 1- Kimball Karen Department of Geology, Rensselaer Polytechnic Institute, 12140, Troy, NY, USA aut NATIONALLICENCE 773 0- Contributions to Mineralogy and Petrology Springer-Verlag 105/3(1990-08-01), 337-346 0010-7999 105:3<337 1990 105 410 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer