Zircon U–Pb ages and Lu–Hf isotopes of metagranitoids from the Subansiri region, Eastern Himalaya: implications for crustal evolution along the northern Indian passive margin in the early Paleozoic

We studied the zircon U–Pb ages, Hf isotopes, and whole-rock and mineral chemistry of metagranitoids from the Subansiri region of the Eastern Himalaya to constrain their emplacement age, origin and geodynamic evolution. The investigated metagranitoids have high SiO₂, Na₂O+K₂O, Rb, Zr and low Fe₂O₃, Nb, Ga/Al ratios with fractionated rare earth element patterns [(Ce/Yb)_N=6.46–42.15] and strong negative Eu anomalies (Eu/Eu*=0.16–0.44). They are peraluminous (molar A/CNK=1.04–1.27) and calc-alkaline in nature, with normative corundum (1.04–3.61) and relatively high FeO^t/MgO ratios in biotite (c. 3.38), indicating their affinity with S-type granites. The time of emplacement of the Subansiri metagranitoids is constrained by zircon U–Pb ages between 516 and 486 Ma. The zircon grains have negative ε_Hf(t) values ranging from –1.4 to –12.7 and yield crustal Hf model ages from 1.5 to 2.2 Ga, suggesting the occurrence of a major crustal growth event in the Proterozoic and re-melting of the crust during the early Paleozoic. The geochemical data in conjunction with the U–Pb ages and Hf isotope data suggest that the Subansiri metagranitoids were produced by partial melting of older metasedimentary rocks in the Indian passive margin.