Abstract

Examination of all available data on Precambrian granulite rocks centered around the Indian portion of Gondwanaland reveals the possible existence of a paired metamorphic belt that can be traced from the Ceylon–south India area west to Madagascar and possibly to Uganda, and east to southwest Australia and east Antarctica. This belt appears to be formed of low-pressure–high-temperature (Abukuma-type) rocks with an adjacent complementary belt with rocks formed by intermediate pressure and intermediate temperature (Barrovian-type). The belt of low pressure and high temperature is characterized by cordierite in pelitic, intermediate, and even mafic rocks, some of which are associated with sapphirine. Andalusite is present locally, coexisting with sillimanite, and wollastonite is found in some calc-silicate assemblages. The belt of intermediate-pressure and intermediate-temperature rocks contains sillimanite-garnet in metapelite, and scapolite-diopside with calcite-quartz in the calc-silicate rocks.

This relation seems common to the granulite rocks of Gondwanaland and serves to illustrate geologic continuity of these segments when brought together in their suggested pre-drift positions. From the scant information available concerning these rocks, a gross metamorphic-structural-chronologic unity may be recognized. Highly deformed granulite rocks of at least Archean age (about 3,000 m.y.) are characteristic; these rocks were metamorphosed and (or) remobilized at about 2,500, 1,300, and 1,000 m.y., ending with a widespread metamorphic event at about 600 m.y.

These paired belts form a pattern on models of reconstructed Gondwanaland, which suggests that plate tectonics processes between Indian, Antarctic-Australian, and African protoplates were in operation in Precambrian time.

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