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Overlapping A-type and S-type characters in late- to post-tectonic granites – petro-tectonic evolution of late Mesoproterozoic Andhra Konda granite, Nellore Schist Belt, southern India

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Abstract

As the debate continues on whether all A-type granites are anorogenic, we present here new structural and geochemical data and interpretation on a late Mesoproterozoic granitic pluton from the Nellore Schist Belt (NSB), southern India. The Andhra Konda granite, occurring in the central part of the NSB is intrusive into peripheral part of deformed volcano-sedimentary succession of the Vinjamuru Group, near its contact with the Kanigiri Ophiolite. The overall elongation of the granitic stock parallel to the regional strike in the NSB, parallelism of magmatic and mylonitic fabrics and continuum of hypersolidus to subsolidus crystal plastic deformation fabrics are comparable to features of late- to post-tectonic granites. The Andhra Konda granite is peraluminous, alkali-calcic to calc-alkalic and ferroan in composition, and enriched in light rare earth elements (LREE), Cs, Rb and depleted in Eu, Ba, Sr and P. Overlapping geochemical signatures suggest that the granitic magma could have evolved from either ocean island basalt magma or island arc basalt magma, or alternatively originated from partial melting of metasedimentary rocks, with involvement of continental crust in a subduction-related convergent setting. Based on mineral chemistry and geochemical signatures, and relatively higher crystallization temperature, Andhra Konda granite is proposed to be A-type granite, though some overlap in character with S-type exists. Geochemical discrimination also favours late- to post-collisional tectonic setting for the Andhra Konda granite. Andhra Konda granite and geochemically similar 1284 Ma old granitic stocks of Kanigiri in the central NSB possibly represent a phase of granitic magmatism distinct from supposedly rift-related alkaline magmatism in this region, and augment the notion that A-type granites may form and occur in diverse tectonic settings.

Research Highlights

  • New geochemical data and tectonic interpretation from a late-Mesoproterozoic ferroan granite

  • Microstructures show a continuum of hypersolidus to solid-state deformation fabrics as in late-tectonic granites

  • Major and trace element ratios linked to subduction-related partial melting and crustal input

  • Post-tectonic Andhra Konda granite adds to the diversity of A-type granite character

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Acknowledgements

Authors acknowledge Indian Statistical Institute (Kolkata) for funding the research and providing adequate infrastructural facilities and environment for carrying out this research. AS acknowledges the senior research fellowship granted by ISI. We are thankful to the anonymous reviewer for critical but helpful comments and suggestions.

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  1. Geological Studies Unit, Indian Statistical Institute, Kolkata, 700 108, India

    Arnab Sain & Dilip Saha

  2. Department of Geology, Presidency University, Kolkata, 700 073, India

    Arnab Sain

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Lead author Arnab Sain is primarily involved in the field work, data analysis and interpretations. Both the authors (Arnab Sain and Dilip Saha) took responsibility for the article content, including concept, design, analysis and interpretation of data, writing, and revision of the manuscript.

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Sain, A., Saha, D. Overlapping A-type and S-type characters in late- to post-tectonic granites – petro-tectonic evolution of late Mesoproterozoic Andhra Konda granite, Nellore Schist Belt, southern India. J Earth Syst Sci 131, 137 (2022). https://doi.org/10.1007/s12040-022-01889-y

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