Abstract

Three cogenetic minerals, namely, muscovites, biotites, and apatites from the Bhilwara (Rajasthan) mica belt of India have been dated by the fission track method. The muscovite ages are ~800 m.y. and the biotite and apatite ages are ~600 m.y. The geological annealing suffered by these minerals has been assessed. The observed discordancies of the ages in the three minerals, each having different annealing characteristics, are interpreted in terms of the thermal history of the region. A cooling rate of ~ 1/4° m.y.−1, after the occurrence of the last major metamorphic activity (i.e. the Delhi orogenic cycle) in the region, has been inferred.

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