Abstract New apatite fission track (AFT) ages have been obtained from a synformal nappe of the Higher Himalayan Crystallines emplaced over the Lesser Himalayan metasedimentary zone of the Arunachal Himalaya, India. The AFT cooling ages within the nappe range between 5.0 ± 0.8 and 14.4 ± 1.3 Ma. Modelled exhumation rates calculated from these cooling ages vary from 0.25 ± 0.12 to 0.69 ± 0.25 mm a −1 , which indicates slow exhumation since the Middle to Late Miocene. The AFT cooling ages are younging on both the northern and southern flanks of the synform and the oldest ages are confined to the core. The close mimicking of a shallow crustal exhumation pattern with the synformal structure suggests a strong control of the development of the synform on the exhumation path of the rocks and hence a tectonics–exhumation linkage in the central Arunachal Himalaya. Comparison of these AFT ages with the regional thermochronological record of the Eastern Himalaya reflects a variation in exhumation rates with strike. The AFT age pattern in the central Arunachal Himalaya does not match the pattern of precipitation, which suggests an absence of climate-driven tectonic deformation via focused erosion.

Abstract 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 SiO 2 , Na 2 O + K 2 O, Rb, Zr and low Fe 2 O 3 , 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.

Abstract Felsic magmatic bodies are exposed widely in the Bomdila region of the western Arunachal Himalaya, NE India. The litho-units of this region are primarily composed of two-mica (muscovite–biotite (ms–bt)) granite gneiss, referred to herein as the Bomdila granite gneiss (BGGn), and the metasediments of the Bomdila Group forming an integral part of the NE Lesser Himalayan thrust sheet. Phase petrology, whole-rock elemental geochemistry and zircon U–Pb–Lu–Hf isotopes of the BGGn have been investigated in order to decipher the origin and timing of felsic magmatism and its implications for understanding the pre-Himalayan tectonic environment. Modally, the BGGn can be classified into monzogranite, syenogranite and quartz-rich granitoids. The composition of muscovite (Ti = 0.03–0.07, average Na = 0.07 and Al IV = 2.50–2.90 apfu), biotite (FeO t /MgO = 3.1–4.6, 2Al⇌3Fe and Mg⇌Fe substitutions, and the presence of siderophyllite) and tourmaline (Fe/Fe + Mg = 0.56–0.96, Ca < 0.17 apfu) implies their primary magmatic nature crystallized typically in a peraluminous (S-type) felsic parental melt. This is further supported by the presence of ms–bt, whole-rock molar Al 2 O 3 /CaO + Na 2 O + K 2 O (A/CNK = 1.03–1.64) and normative corundum. Whole-rock multi-cationic parameters indicate a syn-collisional tectonic environment. However, the content of Rb (average 300 ppm) and high-field strength elements (HFSEs) in the BGGn indicates syn- to post-collisional tectonic settings. The BGGn parental melt was most likely to have been generated by dehydration melting of metasedimentary sources at middle–upper crustal depths. Geochemical modelling constrains the evolution of the parental melt of the BGGn by a moderate degree of fractional differentiation ( F = 0.45) involving a biotite–plagioclase–K-feldspar–muscovite–titanite–apatite (bt–pl–Kfs–ms–ttn–ap) assemblage. Laser ablation-multicollector-inductively coupled plasma-mass spectrometry (LA-MC-ICP-MS)-analysed zircons from the BGGn yield a weighted mean 207 Pb/ 206 Pb age of 1752 ± 23 Ma as the crystallization age for the zircons in the BGGn melt, which falls well within the period of magmatism formed during the Columbia supercontinent accretionary orogen. The observed negative ε Hf (t) values (−1.67 to −7.99) and three-stage Hf-model ages (2818, 2586–2424 and 2393–2250 Ma) of zircons, strongly point to the involvement of ancient continental crust and source heterogeneity (Neoarchean–Paleoproterozoic continental crust) in the generation of the BGGn melt. The reworked ancient crustal components would have once been part of the northern Indian lithosphere, as indicated by the observed 207 Pb/ 206 Pb concordant ages (2436, 2136, 2013 Ma) of the inherited zircons.

Abstract Snow albedo is an important climate parameter as it governs the amount of solar energy absorbed by the snow and can be considered a major contributor to the surface radiation budget. The present study deals with the estimation of temporal variation of snow albedo at the upper elevation zone of glaciated Mago Basin of Arunachal Pradesh in eastern Himalaya. Moderate Resolution Imaging Spectroradiometer (MODIS) Daily Snow Products (MOD10A1 and MYD10A1) at 500 m spatial resolution were used. Both the MODIS data for ten years (2003–13) and the Advanced Spaceborne Thermal Emission and Reflection (ASTER) digital elevation model (DEM) of the study area were downloaded from NASA DAAC of NSIDC. The percentage area under different snow types (dry snow, wet snow, firn and ice) was determined by masking the upper elevation zone of the DEM into the albedo images. The average monthly slopes show a decreasing trend in area (%) of dry snow and wet snow and an increasing trend for firn and ice. Dry snow and wet snow cover percentages were observed to be decreasing, whereas firn and ice cover showed an increasing trend for most of the months. Firn dominated the type of snow, followed by ice then wet snow; the smallest area (%) was that of dry snow for the study period.