Multistage metasomatism of diamondiferous eclogit

Authors: Kula C Misra Mahesh Anand Lawrence A Taylor Nikolai V Sobolev

Publish Date: 2003/12/20

Volume: 146, Issue: 6, Pages: 696-714

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Abstract

The primary garnet pyropealmandineomphacite Cpx 1 65–7 wt Na2Osulfide FeNiCo mss assemblage of the two diamondiferous eclogite xenoliths studied U33/1 and UX/1 experienced two mantle metasomatic events The metasomatic event I is recorded by the formation of platy phlogopite ~ 10 wt K2O prior to incorporation of the xenoliths in the kimberlite The bulk of the metasomatic alteration consisting of spongytextured clinopyroxene Cpx 2A 1–3 wt Na2O coarsergrained clinopyroxene Cpx 2B 2–5 wt Na2O pargasitic amphibole ~ 08 wt K2O 3–35 wt Na2O kelyphite Cpx 3 mostly 1 wt Na2O and zoned MgFeAl spinel sodalite calcite Kfeldspar djerfisherite K595Na002Fe1872Ni236Co001Cu408S26Cl and a small amount of KCaFeMg glass is ascribed to the metasomatic event II that occurred also in the upper mantle but after the xenoliths were incorporated in the kimberlite A pervasive chloritic alteration mainly clinochlore + magnetite that overprints earlier assemblages probably took place in the upper crustal environment The diamonds are invariably associated with secondary clinopyroxene and chlorite but the diamonds formed before the entrainment of the xenoliths in the Udachnaya kimberliteFinancial support for this study was provided by NSF grant EAR 99–09430 LAT We are thankful to Allan Patchen at the University of Tennessee Knoxville for assistance with the electron microprobe analyses and to William D Carlson Richard Ketchum and Cambria Denison at the University of Texas Austin for their assistance with the HRXCT data We also thank Timothy Grove and Mark Schmitz for constructive reviews that resulted in significant improvement of the manuscript

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