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Eclogites and garnet pyroxenites from Kimberley, Kaapvaal craton, South Africa: their diverse origins and complex metasomatic signatures TEXT SIZE: A A A
We describe the petrography and mineral chemistry of sixteen eclogite and garnet pyroxenite xenoliths from the reworked Boshof road dump (Kimberley) and define three groups that stem from different depths. Group A, the shallowest derived, has low HREE (heavy rare earth element) abundances, flat middle to heavy REE patterns and high Mg# [= 100Mg/(Mg+Fe)]. Their protoliths probably were higher pressure cumulates (similar to 0.7GPa) of mainly clinopyroxene (cpx) and subordinate orthopyroxene (opx) and olivine (ol). Group B1 xenoliths, derived from the graphite/diamond boundary and below show similarities to present-dayN-MORB that were modified by partial melting (higher Mg# and positively inclined MREE (middle REE) and HREE (heavy REE) patterns of calculated bulk rocks). Group B2 samples from greatest depth are unique amongst eclogites reported so far worldwide. The calculated bulk rocks have humped REE patterns with very low La and Lu and prominent maxima at Sm or Eu and anomalously high Na2O (up to 5wt%) which makes protolith identification difficult. The complex trace element signatures of the full spectrum of Kimberley eclogites belie a multi-stage history of melt depletion and metasomatism with the introduction of new phases especially of phlogopite (phlog). Phlogopite appears to be characteristic for Kimberley eclogites and garnet peridotites. Modelling the metasomatic overprint indicates that groups A and B1 were overprinted by volatile- and potassium-rich melts probably by a process of chromatographic fractionation. Using constraints from other metasomatized Kimberley mantle rocks suggest that much of the metasomatic phlogopite in the eclogites formed during an intense episode of metasomatism that affected the mantle beneath this region 1.1 Gyr ago.
 

Publication name

 MINERALOGY AND PETROLOGY, 112 43-56; 1 10.1007/s00710-018-0595-6 1 DEC 2018

Author(s)

 Shu, Qiao; Brey, Gerhard P.; Pearson, D. Graham

Corresponding author(s) 

 SHU Qiao
 shuqiao@mail.gyig.ac.cn  
 Chinese Acad Sci, Inst Geochem, State Key Lab Ore Deposit Geochem, Guiyang 550081, Guizhou, Peoples R China 
 Univ Alberta, Dept Earth & Atmospher Sci, 126 ESB, Edmonton, AB T6G 2E3, Canada

Conference  Conference: 11th International Kimberlite Conference (IKC)
 Location: Gaborone, BOTSWANA
 Date: SEP 18-22, 2017

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