Water in upper mantle pyroxene megacrysts and xenocrysts – a survey study
2011 (English)In: American Mineralogist, ISSN 0003-004X, Vol. 96, no 0809 Aug-Sept, 1215-1227 p.Article in journal (Refereed) Published
Water content, mineral chemistry and oxidation state of clino- and orthopyroxene xenocrysts and megacrysts was investigated by FTIR (Fourier Transform Infrared) spectroscopy – including FPA (Focal Plane Array) detector mapping, Mößbauer spectroscopy and electron microprobe. A variety of tectonic settings, ages and modes of emplacement are represented by 23 samples from 6 areas (Massif Central, France; Letseng, Lesotho; Colorado, USA; Kakanui, New Zealand; Oahu, Hawaii; New South Wales, Australia). The xenocrysts are from both garnet and spinel peridotites – including lherzolite and harzburgite varieties, and one sample of clinopyroxenite. Water contents vary between ~10 and 600 wt ppm. Samples from Massif Central, Colorado, Kakanui and Hawaii have rather high water contents: 180 – 600 wt ppm. The samples from Lesotho and New South Wales have considerably lower amounts: ~10 – 300 wt ppm. Water contents of xenocrysts and megacrysts from New South Wales vary within a narrow range (clinopyroxene: ~50 wt ppm, orthopyroxene: 15-20 wt ppm), whereas the water content of the Lesothian samples scatter considerably. No significant correlations are observed between water content, mineral chemistry, or oxidation state of the samples. FPA mapping reveals homogenous distribution of water in the pyroxene lattice. The results are compared to available literature and research on hydrogen diffusion in natural mantle pyroxene. Altogether, the data suggest that pyroxene found in fresh peridotite xenoliths partly reflects the water content of the mantle source region. On the other hand, variable mineral chemistry and water contents of megacryst pyroxenes indicate processes such as magmatic equilibration, magma mixing and contamination.
Place, publisher, year, edition, pages
Mineralogical Society of America, 2011. Vol. 96, no 0809 Aug-Sept, 1215-1227 p.
mantle water, pyroxene, mantle xenoliths, megacrysts, FTIR spectroscopy, FPA detector analysis, Mößbauer spectroscopy
Research subject Mineralogy, Petrology and Geochemistry
IdentifiersURN: urn:nbn:se:su:diva-38665DOI: 10.2138/am.2011.3641OAI: oai:DiVA.org:su-38665DiVA: diva2:312460