Styles of alteration of ti oxides of the kimberlite groundmass

implications on the petrogenesis and classification of kimberlites and similar rocks

Jingyao Xu*, Joan Carles Melgarejo, Montgarri Castillo-Oliver

*Corresponding author for this work

Research output: Contribution to journalArticle

2 Citations (Scopus)
2 Downloads (Pure)

Abstract

The sequence of replacement in groundmass perovskite and spinel from SK-1 and SK-2 kimberlites (Eastern Dharwar craton, India) has been established. Two types of perovskite occur in the studied Indian kimberlites. Type 1 perovskite is found in the groundmass, crystallized directly from the kimberlite magma, it is light rare-earth elements (LREE)-rich and Fe-poor and its ΔNNO calculated value is from -3.82 to -0.73. The second generation of perovskite (type 2 perovskite) is found replacing groundmass atoll spinel, it was formed from hydrothermal fluids, it is LREE-free and Fe-rich and has very high ΔNNO value (from 1.03 to 10.52). Type 1 groundmass perovskite may be either replaced by anatase or kassite along with aeschynite-(Ce). These differences in the alteration are related to different f(CO2) and f(H2O) conditions. Furthermore, primary perovskite may be strongly altered to secondary minerals, resulting in redistribution of rare-earth elements (REE) and, potentially, U, Pb and Th. Therefore, accurate petrographic and chemical analyses are necessary in order to demonstrate that perovskite is magmatic before proceeding to sort geochronological data by using perovskite. Ti-rich hydrogarnets (12.9 wt %-26.3 wt % TiO2) were produced during spinel replacement by late hydrothermal processes. Therefore, attention must be paid to the position of Ca-Ti-garnets in the mineral sequence and their water content before using them to classify the rock based on their occurrence.

Original languageEnglish
Article number51
Pages (from-to)1-15
Number of pages15
JournalMinerals
Volume8
Issue number2
DOIs
Publication statusPublished - 6 Feb 2018

Bibliographical note

Copyright the Author(s) 2018. 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

  • perovskite alteration
  • Ti-rich garnet
  • aeschynite-(Ce)
  • kassite
  • anatase
  • hydrothermal perovskite

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