Zircons from Collisional Granites, Garhwal Himalaya, NW India: U–Th–Pb Age, Geochemistry and Protolith Constraints

Sumit Mishra,Natalia S Nesterova,Anna V Kervinen,Sergei A Svetov,Alexander I Slabunov

doi:10.3390/min11101071

Sumit Mishra, Natalia S Nesterova + Show 3 more

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https://doi.org/10.3390/min11101071

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Abstract

In the present work, we studied zircons from the less foliated granites of the Chail Group, which form a thrust sheet of the Lesser Himalayan Sequences, Garhwal region. Compositionally, these granites are S–type, formed in a collisional tectonic setting. Zircons possess an internal structure, mineral inclusions, and geochemical characteristics typical of magmatic origin. The U–Th–Pb geochronology and geochemistry were assessed using the laser ablation multi–collector inductively coupled plasma spectrometry (LA–ICP–MS) technique. U–Th–Pb isotope dating of zircons from two different samples revealed their age, estimated from the upper intersection of the discordia, to be 1845 ± 19 Ma. Zircons from one sample contained inherited cores belonging to three age groups: Paleoarchean (3.52 Ga), Neoarchean (2.78 Ga and 2.62 Ga), and Paleoproterozoic (2.1 Ga). Zircons with ages of 3.52, 2.62, and 2.1 Ga were interpreted as magmatic based on their geochemical characteristics. The 2.78 Ga core was interpreted as metamorphic. The observed inheritance is consistent with the melting of sedimentary rocks. The inherited zircons could have originated from Aravalli and Bundelkhand Craton and Paleoproterozoic Aravalli Fold Belt rocks. This confirms that the studied granites are S–type and could have been formed in a collisional environment at 1.85 Ga on the western flank of the Columbia Supercontinent.

Highlights

Zircon (ZrSiO4 ) is an accessory mineral constituent of the majority of igneous and metamorphic rocks, with the zirconium element (Zr) serving as a structural constituent [1].Trace elements (e.g., U, Th, Hf, Y and Lanthanide–rare earth elements (REEs)) are present in zircons in significant amounts [2,3,4]
Zircons from Chail Group granites (Garhwal Lesser Himalayan) display an internal structure typical of magmatic varieties; mineral quartz, apatite, thorite, biotite, allanite, and monazite inclusions; and geochemical characteristics. These zircons can be regarded as minerals formed at a magmatic stage in the evolution of granites
U–Th–Pb isotope dating of magmatic zircons from two different samples was performed to estimate their age from the upper intersection of the discordia at 1851 ± 36 (MSWD = 2.0, n = 15) and 1839 ± 38 (MSWD = 0.94, n = 13) Ma, respectively

Summary

Introduction

Zircon (ZrSiO4 ) is an accessory mineral constituent of the majority of igneous and metamorphic rocks, with the zirconium element (Zr) serving as a structural constituent [1].Trace elements (e.g., U, Th, Hf, Y and Lanthanide–rare earth elements (REEs)) are present in zircons in significant amounts [2,3,4]. Zircon (ZrSiO4 ) is an accessory mineral constituent of the majority of igneous and metamorphic rocks, with the zirconium element (Zr) serving as a structural constituent [1]. Zircon resists alteration in a wide variety of geological settings. The isotopic ratios of the elements within the zircons provide ages and parent magma constraints because of their early formation and refractory nature during subsequent events [1,5,6,7]. The U–Pb ages determined from zircons have traditionally been considered the most accurate method for determining the meaningful crystallization age of granitoids. Zircon geochemistry can provide valuable information to establish the conditions of the environment under which the granitoids were emplaced

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