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LA-MC-ICP-MS dating of zircon from chromitite of the Archean Bangur Gabbro Complex, Orissa, India – Ambiguities and constraints.

By P.V. Sunder-Raju, E. Hanski and Y. Lahaye

Abstract

The Mesoarchean chromitites in the Singhbhum craton provide the main source of chromium in India. We report here results of in-situ dating of zircon grains that were found in chromitite of the ultramafic rocks belonging to the southern part of the Archean Baula Complex. The chromite-bearing ultramafic rocks are cut by a gabbronorite intrusion, which has earlier been dated by SHRIMP at 3122 ± 5 Ma (Augé et al., 2003, Precambrian Research 121, 85–101). We performed in situ isotopic analysis of zircon grains by LA-MC-ICP-MS (Laser Ablation Multicollector Inductively Coupled Plasma Mass Spectrometry) and obtained a precise age of 2835.7 ± 8.2 Ma (2d), which is inconsistent with the age of the gabbronorite. We also determined the Pb-Pb isotopic composition of galena found in chromitite and found it to be highly radiogenic given the Archean age of its host rock. We discuss the potential reasons for these ambiguities, such as later Neoarchean or even Proterozoic tectono-magmatic events, and stress the importance of future detailed petrographic, mineralogical and isotopic studies to solve the dilemmas

Topics: LA-MC-ICPMS; Bangur Gabbro; Chromitite; India
Publisher: Institut Cartogràfic i Geològic de Catalunya
Year: 2015
OAI identifier: oai:raco.cat:article/302722
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