Magma mingling in kimberlites: evidence from the groundmass cocrystallization of two spinel-group minerals

Jingyao Xu, Joan Carles Melgarejo, Qiuli Li*, Lisard Torró i Abat, Montgarri Castillo-Oliver

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

We present the results of a detailed petrographic study of fresh coherent samples of the Menominee kimberlite sampled at site 73, located in Menominee County, MI, USA. Our objective is to account for its unusual and complex paragenetic sequence. Several generations of olivine, ilmenite, and spinel-group minerals are described. Early olivine and ilmenite are xenocrystic and were replaced or overgrown by primary minerals. Zoned microcrysts of olivine have a xenocrystic core mantled by a first rim in which rutile, geikielite, and spinel s.s. (spinel sensu stricto) cocrystallized. The in situ U–Pb dating of a microcryst of primary rutile yielded 168.9 ± 4.4 Ma, which was interpreted as the age of emplacement. The groundmass consists of olivine, spinel s.s., a magnesian ulvöspinel–ulvöspinel–magnetite (MUM) spinel, calcite, and dolomite. An extremely low activity of Si is suggested by the crystallization of spinel s.s. instead of phlogopite in the groundmass. The presence of djerfisherite microcrysts indicates high activities of Cl and S during the late stages of melt crystallization. The occurrence of two distinct spinel-group minerals (spinel s.s. and qandilite-rich MUM) in the groundmass is interpreted as clear evidence of the mingling of a magnesiocarbonatitic melt with a dominant kimberlitic melt.

Original languageEnglish
Article number829
Pages (from-to)1-19
Number of pages19
JournalMinerals
Volume10
Issue number9
DOIs
Publication statusPublished - Sep 2020

Bibliographical note

Copyright the Author(s) 2020. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.

Keywords

  • magma mingling
  • kimberlite
  • rutile
  • U–Pb age
  • coexisting spinels
  • qandilite
  • djerfisherite
  • Menominee
  • Michigan
  • USA

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