Isotopic systematics of zircon indicate an African affinity for the rocks of southernmost India

Chris Clark,Richard J M Taylor,Alan S Collins,Martin Hand

doi:10.1038/s41598-020-62075-y

Chris Clark, Richard J M Taylor + Show 2 more

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https://doi.org/10.1038/s41598-020-62075-y

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Journal: Scientific Reports	Publication Date: Mar 25, 2020
Citations: 18	License type: open-access

Affiliation: Curtin University, University of Adelaide

Abstract

Southern India lies in an area of Gondwana where multiple blocks are juxtaposed along Moho-penetrating structures, the significance of which are not well understood. Adequate geochronological data that can be used to differentiate the various blocks are also lacking. We present a newly acquired SIMS U–Pb, Lu–Hf, O isotopic and trace element geochemical dataset from zircon and garnet from the protoliths of the Nagercoil Block at the very tip of southern India. The data indicate that the magmatic protoliths of the rocks in this block formed at c. 2040 Ma with Lu–Hf, O-isotope and trace element data consistent with formation in a magmatic arc environment. The zircon data from Nagercoil Block are isotopically and temporally distinct from those in all the other blocks in southern India, but remarkably correspond to rocks in East Africa that are exposed on the southern margin of the Tanzania–Bangweulu Block. The new data suggest that the tip of southern India has an African affinity and a major suture zone must lie along its northern margin. All of these blocks were finally brought together during the Ediacaran-Cambrian amalgamation of Gondwana where they underwent high to ultrahigh temperature metamorphism.

Highlights

Southern India lies in an area of Gondwana where multiple blocks are juxtaposed along Mohopenetrating structures, the significance of which are not well understood
This argument was supported by the adakitic geochemical signatures of the Nagercoil charnockites and which are similar to the Neoproterozoic arc-related igneous rocks that have been identified to the north in the southern Madurai Block[21] (Fig. 2)
The formation of the characteristic charnockite assemblages present in the exposed Nagercoil Block gneisses is a result of the high-grade metamorphism during the Neoproterozoic–Cambrian orogenic event, this idea will be further tested in this study through the collection of rare earth elements in zircon rims and garnet[23,24]

Summary

Introduction

Southern India lies in an area of Gondwana where multiple blocks are juxtaposed along Mohopenetrating structures, the significance of which are not well understood. The new data suggest that the tip of southern India has an African affinity and a major suture zone must lie along its northern margin All of these blocks were brought together during the Ediacaran-Cambrian amalgamation of Gondwana where they underwent high to ultrahigh temperature metamorphism. Santosh et al suggest that the magmas were generated immediately prior to the amalgamation of Gondwana along a Pacific-type subduction margin This argument was supported by the adakitic geochemical signatures of the Nagercoil charnockites and which are similar to the Neoproterozoic arc-related igneous rocks that have been identified to the north in the southern Madurai Block[21] (Fig. 2). Johnson et al.[25] have constrained the pressure–tempetrature–time (P–T–t) history of the Nagercoil Block rocks to be comparable to those recorded within the adjoining Madurai and Trivandrum Blocks[10,26,27]

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