TITLE:
Carbonatite Occurrence in Ambaji-Sendra Belt of NW Indian Shield: Evidence of Carbonatitic Magmatism in the Subduction Setting
AUTHORS:
Sadaf Siddiqui, Sadaf Fatima, Tavheed Khan, Mohammad Shamim Khan
KEYWORDS:
Aravalli Craton, Ambaji-Sendra Belt Precambrian Carbonatite, Subduction Set-ting
JOURNAL NAME:
International Journal of Geosciences,
Vol.14 No.1,
January
31,
2023
ABSTRACT: The paper represents a new discovery of a late
Mesoproterozoic lenticular and discontinuous, carbonatitic body exposed at Basantgarh, Sendra and
near the Abu-road area of the Ambaji-Sendra belt of the South Delhi Fold Belt. It is medium to coarse-grained and light to dark coloured compact rock. The common
associates of the carbonatitic rock are felsic rocks, rich in alkalies.
Carbonatite contains more than 50% carbonate minerals, the majority of which are calcite,
dolomite, ankerite, augite-aegirine augite and plagioclase. It is classified as calcite carbonatite of the sövite variety due to its coarse-grained character, chemically as calico-carbonatite and magnesio-carbonatite and even as silico-carbonatites for having more than 20% SiO2. The ∑REE contents
of calico-carbonatite samples are nearly 100 times greater than
magnesio-carbonatite. Chondrite normalised REE profiles
of calcio-carbonatites are LREE enriched with nearly flat HREEs whereas the magnesio-carbonatite is characterised by flat REE patterns. The mantle-normalized incompatible trace element spidergram
of Ambaji-Sendra belt carbonatites shows distinct negative anomalies of Ba, Nb, Ta, P, Sm, Eu,
Ti and Y and positive at U and Pb by calcio-carbonatite whereas the magnesio-carbonatite displays negative kinks at K, Zr, Nb, Ta
and Ti and positive at Th, Pb and Sr. The variable and/or contrasting enrichment/depletion in various elements in the two types of Ambaji-Sendra belt carbonatite is attributed
either to significant differences in the type and modal proportion of different
accessory mineral species or selective incorporation of metasomatic fluids during the subduction process. The chemical attributes of Ambaji-Sendra
belt carbonatite suggest its emplacement in subduction settings.