Misra, Kula C.; Anand, Mahesh; Taylor, Lawrence A. and Sobolev, Nikolai V.
Multi-stage metasomatism of diamondiferous eclogite xenoliths from the Udachnaya kimberlite pipe, Yakutia, Siberia.
Contributions to Mineralogy and Petrology, 146(6) pp. 696–714.
The primary garnet (pyrope-almandine)-omphacite
(Cpx 1, 6.5–7 wt% Na2O)-sulfide (Fe-Ni-Co
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 spongy-textured clinopyroxene
(Cpx 2A, 1–3 wt% Na2O), coarser-grained clinopyroxene
(Cpx 2B, 2–5 wt% Na2O), pargasitic amphibole
( 0.8 wt% K2O; 3–3.5 wt% Na2O), kelyphite
(Cpx 3, mostly <1 wt% Na2O; and zoned Mg-Fe-Al
spinel), sodalite, calcite, K-feldspar, djerfisherite
(K5.95Na0.02Fe18.72Ni2.36Co0.01Cu4.08S26Cl ) and a small
amount of K-Ca-Fe-Mg 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 kimberlite.
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