Crustal evolution and tectonomagmatic history of the Indian Shield at the periphery of supercontinents

Abstract

River sand detrital zircons from several rivers flowing through the Peninsular Indian cratons were analyzed for U-Pb, Lu-Hf, and O isotopes to characterize the Precambrian crustal evolution of the Indian Shield and to constrain its role in the early supercontinent cycles. Analyzed river sand zircon samples exhibit a prominent age grouping at 2.7–2.4 Ga and additional peaks at 1.8–1.7 Ga, 1.0–0.8 Ga, and 0.6–0.5 Ga. The time-related Hf and O isotope trends of the Indian zircons display a slight offset from the global trends. The age peaks and distinct Hf-O isotopic compositions of the Indian zircons also lack coherence with the global patterns associated with supercontinent cycles, implying a discrete crustal evolutionary history for the Indian Shield. Their contrasting εHf-age trajectories indicate that the Indian Shield was accreted to the Columbia/Nuna supercontinental framework through a collision event that postdated the 2.1–1.8 Ga global-scale orogeny, and was part of a long-lived subduction system along the margin of Rodinia. This implies that the Indian Shield occupied a peripheral paleo-position during the assembly of the two Precambrian supercontinents. The ca. 2.6–2.4 Ga Indian river sand zircons have remarkably low δ18O values that are distinct from the global zircon O isotopic record. This period coincides with the fragmentation of the Archean supercraton and the flaring-up of a subaerial Large Igneous Province that facilitated the generation of 18O-depleted magmas. Depending on whether the 2.6–2.4 Ga zircons with low δ18O values (<4.7 ‰) are considered or not, approximately 2.77 ‰ or 1.78 ‰ rise in the zircon δ18O values occurred between ca. 2.4 Ga and ca. 1.87 Ga (decoupled from zircon Lu-Hf isotopes), further suggesting that the fine-grained sediments were enriched in 18O after the Great Oxidation Event. These high δ18O sediments were subsequently incorporated into the magmatic systems resulting in elevated δ18O in the zircons crystallizing from such melts. Nevertheless, a ca. 0.9 Ga peak of >10 ‰ in δ18O system was followed by a pronounced δ18O drop at ca. 0.759 Ga, suggesting that δ18O of recycled sedimentary reservoirs was not the only controlling factor for zircon δ18O characteristics. Variations in the Hf-O data for Indian and global zircons could be attributed to the initiation of the supercontinent cycle at ca. 2.0 Ga. A significant volume of the juvenile crust was added during the 3.0–2.7 Ga mafic magmatism in the Indian Shield, as underlined by the Hf model ages of all the zircon grains and those with mantle-like δ18O signatures. A gradual addition of continental crust during ca. 3.6 Ga to 3.1 Ga can also be deduced, with the oldest crust being derived from the mantle at ca. 4.4 Ga.