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We present integrated in situ zircon U–Pb and Hf isotope data, along with whole‐rock and mineral chemistry data for the Salari granite of western Arunachal Himalaya to constrain its emplacement age, origin, and geodynamic evolution. The investigated Salari granites are high Fe2O3, CaO, and Nb, and low SiO2 and Rb/Sr ratio with fractionated rare earth element patterns ((Ce/Yb)N = 9.90–20.24) and minor negative Eu anomaly (Eu/Eu* = 0.69–0.94). They are metaluminous (molar A/CNK = 0.93–1.07) and have relatively similar FeOt/MgO ratio in biotite (1.58–1.60) to Mg‐biotite, indicating their affinity with I‐type granites. The enrichment of large‐ion lithophile elements with highly depleted negative Nb anomalies is consistent with their origin in a subduction‐related environment. Our zircon U–Pb ages suggest that the magmatic emplacement of the Salari granite took place between 1,791 and 1,768 Ma. The zircon grains have mostly negative εHf(t) values up to −5.5 and yield crustal Hf model ages from 2.4 to 2.8 Ga, suggesting the occurrence of a major crustal growth event in the Neoarchean and re‐melting of the crust during the Palaeoproterozoic. Our new results, that is, zircon U–Pb age and Hf isotope data, in conjunction with the field observations and petro‐mineralogical and geochemical characteristics, suggest that the Salari granite of eastern Himalaya was produced by partial melting of older metabasaltic/metatonalitic rocks in a continental arc setting of the supercontinent Columbia during the Palaeoproterozoic. [ABSTRACT FROM AUTHOR]

This study reports zirconium-in-rutile thermometry data from the Himalayan ultrahigh-pressure eclogites and their retrogressed counterparts. The Zr contents of three textural varieties of rutile i.e. matrix rutile, inclusion phase, and overgrown by ilmenite/titanite from coesite-bearing eclogites, slightly retrogressed eclogites, highly retrogressed eclogites, and amphibolites were analyzed for Zr contents using the electron probe micro-analyser. Majority of the rutile grains exhibited homogeneous chemical compositions in all the aforementioned textural varieties; however, some of grains were relatively heterogeneous. Average temperature values of 729 °C, 727 °C, and 706 °C were obtained for the matrix, inclusion, and overgrown rutiles from UHP eclogites and of 705 °C, 699 °C, and 707 °C for those from HP eclogites, respectively. Slightly retrogressed eclogites yielded similar average T values of 703 °C, 706 °C, and 706 °C, respectively, whereas highly retrogressed eclogites resulted in relatively low average temperatures, ca. 690 °C, 691 °C, and 679 °C, respectively. When compared with these eclogites, lower average T values of 672 °C, 630 °C, and 656 °C were obtained from garnetites, and of 665 °C, 658 °C, and 640 °C from garnet amphibolites, respectively. The relatively homogeneous Zr contents and higher temperature values from the matrix rutile in HP and UHP eclogites suggest peak or near-peak metamorphic crystallization, whereas grains with low Zr contents, yielding low temperature values, were likely to be affected by the late-stage retrogression. • Zirconium-in-rutile thermometry was applied to rutile in the Himalayan UHP eclogites and their retrogressed counterparts. • UHP eclogites preserved peak or near peak metamorphic temperatures that were partially reset in retrogressed rocks • The data are consistent with the conventional thermobarometry • The single mineral thermometry is robust for metamorphic rocks that have insufficient mineral assemblages [ABSTRACT FROM AUTHOR]

Abstract: To better understand Tibetan orogenesis, which involves complex tectonic processes, here we report the first integrated analysis of Hf isotopes of zircon separates and their host rocks from the Transhimalayan batholiths. The rocks studied include 19 granitoids from different parts of the Gangdese batholith, the largest Transhimalayan intrusive complex, and five postcollisional adakites that occurred as plugs or dikes cutting the Gangdese batholith, in the southern Lhasa terrane, southern Tibet. Published zircon Hf isotope data from other Transhimalayan granitoids and the Linzizong volcanic rocks are also synthesized. The magmatic zircons, crystallizing between ca. 200 and 15Ma, show depleted mantle-type Hf isotopic characteristics throughout the Mesozoic but shift markedly in the Paleogene. The Hf isotopic shift is interpreted as tracking the evolving progress of Himalayan sediment subduction driven by the approaching Indian continent, and thus signals the initiation of the India–Asia collision that we infer to have occurred by 55Ma. Our data furthermore indicate that southern Tibet underwent significant crustal thickening during ca. 45 and 30Ma, before emplacement of the postcollisional adakites that exhibit Hf–Nd isotopic systematics suggesting binary mixing of melts from the juvenile Gangdese mafic crust and incorporated Himalayan sediments in the petrogenesis. [Copyright &y& Elsevier]