Complexly zoned Ti-rich melanite-schorlomite garnets from Ambadungar carbonatite-alkalic complex, Deccan Igneous Province, Gujarat State, Western India

LG Gwalani, NMS Rock, R Ramasamy, Brendan Griffin, BP Mulai

Research output: Contribution to journalArticle

25 Citations (Scopus)

Abstract

Ti-rich garnet phenocrysts from a tephrite ('nephelinite') plug in the Ambadungar complex situated in the Chhota Udaipur alkalic subprovince show concentric zoning. Based on paired orthogonal traverses across three selected crystals (total 81 step-scan point analyses), andradite content ranges from 55 to 86 mol% (the remainder being almost entirely schorlomite), corresponding to the following wt% oxide variations: TiO2 5.5-15.8, CaO 29.6-32.5, MgO 0.3-1.6, Fe2O3 20-26, Al2O3 0.7-3.5%; MnO, V2O3, Na2O and ZrO2 each rarely exceeds 0.5%, Zoning patterns in individual grains from this one rock differ considerably in several ways: (1) there may be 2-5 alternating pale and dark zones, the pale generally being more andradite-rich enriched in Ti, Mg and usually Zr but impoverished in Al; (2) the two orthogonal traverse may or may not be mirror images; (3) monotonic trends (decreasing Ca, Al, increasing Mg, Zr from core to rim) may or may not be present; (4) oscillatory zoning varies in amplitude; and (5) apparent substitutions differ, although all crystals clearly show the Si-Ti substitution inferred for Ti-rich garnets elsewhere. An idealized case is developed from an observed complexly zoned phenocryst population to piece together a history of the alkaline host magma that experienced several events such as polybaric differentiation, magma-mixing, and kinetic effects. (C) 2000 Elsevier Science Ltd. All rights reserved.
Original languageEnglish
Pages (from-to)163-176
JournalJournal of Asian Earth Sciences
Volume18
DOIs
Publication statusPublished - 2000

Fingerprint

Dive into the research topics of 'Complexly zoned Ti-rich melanite-schorlomite garnets from Ambadungar carbonatite-alkalic complex, Deccan Igneous Province, Gujarat State, Western India'. Together they form a unique fingerprint.

Cite this