Next Article in Journal
Aqueous Fe(II)-Induced Phase Transformation of Ferrihydrite Coupled Adsorption/Immobilization of Rare Earth Elements
Previous Article in Journal
A Review of Flotation Separation of Mg Carbonates (Dolomite and Magnesite)
Article Menu
Issue 8 (August) cover image

Export Article

Open AccessArticle
Minerals 2018, 8(8), 355; https://doi.org/10.3390/min8080355

On the Chemical Composition and Possible Origin of Na–Cr-Rich Clinopyroxene in Silicocarbonatites from Samalpatti, Tamil Nadu, South India

1
Czech Geological Survey, Klárov 3, CZ-118 21 Prague 1, Czech Republic
2
Faculty of Science, Charles University in Prague, Albertov 6, CZ-128 43 Prague 2, Czech Republic
3
Faculty of Science, Masaryk University, Kotlářská 2, CZ-602 00 Brno, Czech Republic
*
Author to whom correspondence should be addressed.
Received: 26 June 2018 / Revised: 10 August 2018 / Accepted: 11 August 2018 / Published: 17 August 2018
Full-Text   |   PDF [3047 KB, uploaded 18 August 2018]   |  

Abstract

Mineralogical and chemical data are presented for a suite of Na–Cr-rich clinopyroxenes associated with chromite, winchite (sodium-calcium amphibole), titanite and calcite in Mg-Cr-rich silicocarbonatites from the Samalpatti carbonatite complex, Tamil Nadu, South India. The Mg-Cr-rich silicocarbonatites occur as 10–30 cm large enclaves in pyroxenites. The chemical composition of the pyroxenes differs among individual enclaves, with variable proportions of diopside, kosmochlor and jadeite-aegirine end-members. These compositions fill a previously unoccupied space in the kosmochlor-diopside-jadeite+aegirine ternary plot, indicating a distinct origin of kosmochlor-rich pyroxene compared with previous findings from diverse settings. The Na–Cr-rich clinopyroxene has low ΣREE = 9.2 ppm, with slight enrichment in LREE (LaN = 7), coupled with low HREE (YbN = 0.6), and flat HREE, paralleled by a significant fractionation of Nb/Ta (2408) and Th/U (26.5). Sodic metasomatism (fenitization) associated with either carbonatite emplacement at shallow levels or during carbonatite ascent through the upper mantle most likely was the major process operating in the area. We suggest two scenarios of the formation of Na–Cr-rich pyroxene: (1) from mantle-derived chromian mineral phases (spinel and/or garnet) through fenitization, with subsequent corrosion by growing winchite due to volatile influx; (2) via metasomatic reaction of Cr-rich garnet in mantle peridotite due to reaction with Na-rich carbonatite melt. Collectively, the appearance of kosmochlor may play an important role in deconvolving metasomatic processes, and fenitization in particular. If combined with petrologic experiments, it could improve our understanding of the origin and subsequent history of chemical signatures of carbonate-rich materials in the mantle. View Full-Text
Keywords: Na–Cr-rich pyroxene; kosmochlor; chromite; sodic metasomatism; silicocarbonatite; mineral chemistry; Samalpatti carbonatite complex Na–Cr-rich pyroxene; kosmochlor; chromite; sodic metasomatism; silicocarbonatite; mineral chemistry; Samalpatti carbonatite complex
Figures

Figure 1

This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

Supplementary material

SciFeed

Share & Cite This Article

MDPI and ACS Style

Krátký, O.; Rapprich, V.; Racek, M.; Míková, J.; Magna, T. On the Chemical Composition and Possible Origin of Na–Cr-Rich Clinopyroxene in Silicocarbonatites from Samalpatti, Tamil Nadu, South India. Minerals 2018, 8, 355.

Show more citation formats Show less citations formats

Note that from the first issue of 2016, MDPI journals use article numbers instead of page numbers. See further details here.

Related Articles

Article Metrics

Article Access Statistics

1

Comments

[Return to top]
Minerals EISSN 2075-163X Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert
Back to Top