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The petrology of lower crustal xenoliths from the Executive Committee Range, Marie Byrd Land Volcanic Province, West Antarctica |
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| Authors: | R J Wysoczanski J A Gamble P R Kyle and M F Thirlwall |
| Institution: | a Geology Dep., RSES, Victoria University of Wellington, P.O. Box 600, Wellington, New Zealand b Dep. of Geosciences, New Mexico Institute of Mining and Technology, Socorro, NM 87801, USA c Geology Dep., Royal Holloway, University of London, Egham, Surrey TW20-OEX, UK |
| Abstract: | Alkaline magmas from the late-Cenozoic Marie Byrd Land Volcanic Province, West Antarctica, have entrained lithospheric xenoliths which vary from spinel lherzolites to supracrustal rocks. Lower crustal xenoliths have been collected from the Executive Committee Range (Mounts Hampton in the north and Mount Sidley in the south) in central Marie Byrd Land, and their petrological characteristics together with preliminary geochemical data are discussed here. Granulite xenoliths include metaigneous gabbros and norites with varying proportions of clinopyroxene, spinel and either olivine or orthopyroxene. Pyroxenites occur together with granulites, which on the basis of their similar mineral assemblage, texture and composition are considered to be related to the granulites. The composition of xenoliths from Mounts Hampton and Sidley differ (e.g. Mount Sidley xenoliths have Mg# 32–80, are relatively LREE enriched and have 87Sr/86Sr of 0.70286–0.70376 and 143Nd/144Nd of 0.512864–0.512870, whereas Mount Hampton xenoliths have Mg# 68–78, are LREE depleted and have 87Sr/86Sr of 0.70420–0.70458 and 143Nd/144Nd of 0.512771–0.512819), defining a major lateral lower crustal discontinuity beneath the Executive Committee Range. Relict igneous textures and low abundances of incompatible elements indicate that the xenoliths initially formed as cumulates rather than as trapped melts. The xenolith suite differs in composition to the host rocks (Mount Sidley VOLCANICS = 87Sr/86Sr of 0.70300–0.70312 and 143Nd/144Nd of 0.512814–0.512907) and cannot be co-genetic with them. They are interpreted here to represent the cumulates of mantle melts that evolved by crystal fractionation at lower crustal depths. |
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