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The Himalayan–Tibetan orogen is the world's largest active orogen with the thickest continental crust on Earth. However, the timing of crustal thickening of this orogen remains controversial. In recent years, magmatic rocks with adakitic affinities have been widely used to constrain the crustal thickness. Here, we present zircon U–Pb ages, geochemical and Sr–Nd–Pb–Hf isotopic data for the Dala two‐mica granites (eastern Tethyan Himalaya) that may shed light on this issue. Zircon U–Pb dating shows that the Dala two‐mica granites were emplaced at ca. 43 Ma. The granites display adakitic signatures, including high SiO2, Al2O3 and Sr contents, low Y and Yb contents with high Sr/Y (27−67) and La/Yb (35−99) ratios. High K2O and Th contents, low Nb/U, Ce/Pb, Ti/Eu and Nd/Sm ratios and low MgO, Mg#, Cr and Ni contents suggest that the Dala two‐mica granites were derived from partial melting of a thickened lower crust. Low negative zircon εHf(t) values (−10.4 to −0.5) with old two‐stage Hf model ages (1.1–1.8 Ga), high (87Sr/86Sr)i (0.715861–0.717665) with low εNd(t) (−12.5 to −11.3) and high Pb isotopes [(206Pb/204Pb)i=18.783–18.861, (207Pb/204Pb)i=18.783–18.861 and (208Pb/204Pb)i=39.052–39.285], together with previous literature data, indicate that the magma source for the Eocene granites in the Yardoi area was composed of ancient lower crust consisting mainly of garnet‐amphibolite and probably subordinate metapelites of the High Himalayan Crystalline Sequence. The residual mineral assemblage of garnet + rutile + plagioclase ± amphibole in the source region demonstrates that the crust beneath the Himalaya could have been thickened to ﹥50 km in the Eocene. Combining with previous studies, we propose that the Eocene magmatic rocks in the Tethyan Himalaya (e.g. ca. 43 Ma old Dala two‐mica granites) can be best interpreted as the consequence of breakoff of the Neo‐Tethyan oceanic slab. [ABSTRACT FROM AUTHOR]

To better constrain the evolution of the early Palaeozoic orogenesis along the northern margin of Gondwana, we present new petrological, geochronological, and geochemical studies of the Cambrian–Ordovician granitic gneiss in the Dinggye area, central Himalaya. The granitic gneiss is medium‐coarse grained, with porphyritic, augen, banded, or gneissic structure, and has undergone strong deformation. The mineral assemblages are quartz, plagioclase, K‐feldspar, muscovite, and biotite, with minor amounts of accessory minerals. The granitic gneiss samples are characterized by high SiO2, Al2O3, and Rb/Sr contents but low MgO, TiO2, FeOt, and MnO contents, with A/CNK of 1.08–1.38. The REE patterns of the granitic gneiss show high LREE/HREE and negative Eu anomalies. In the trace‐element chondrite‐normalized diagram, the samples show enrichment in LILE (e.g., Rb, Th, U, and K) and depletion in some HFSEs (Nb and Ti). These features indicate that the protolith was a calc‐alkaline and peraluminous S‐type granite. Six analysed samples yielded zircon U–Pb crystallization ages between 480 and 500 Ma, which support the existence of the early Palaeozoic magmatism in the Dinggye area, central Himalaya. High δ18O values (7–10‰, >> a mantle value of 5.3 ± 0.6‰) of magmatic zircon domains and abundant inherited zircons with variable ages (558‐2523 Ma) indicate that the magma was derived from a supracrustal source. Combined with whole‐rock Sr–Nd data (average εNd(t) = −8.1) published previously, we suggest that the granitic gneiss originated from partial melting of old crust, most likely to be the sedimentary rocks of the Himalayan Crystalline Complex. The early Palaeozoic granitic gneiss with a continental arc affinity may have formed in an Andean‐type orogeny involving subduction of the Proto‐Tethyan Oceanic crust beneath the northern margin of the Gondwana supercontinent. [ABSTRACT FROM AUTHOR]

The timing and size of the last great earthquake in the central Himalaya continues to excite scientific controversy, despite a decade of palaeoseismological investigations. The studies along the frontal thrust in the Indian part of the central Himalaya disclose a faulting event between 14th and 15th century, and a dominant view presupposes the 1505 CE earthquake as the likely source. Here we evaluate the database along with independent inputs to determine the timing of the last faulting event on the frontal thrust of the central Himalaya. From the historical perspective, the Nepalese archives make a direct reference to a significant earthquake in 1344 CE, and the Indian sources hint at a restoration phase for the mid‐14th century monuments in the northern plains and coeval destruction to the ancient temples in the central Himalaya. Aside from the constraints generated from the earthquake proxies including liquefaction features and deformed stalagmites, the previous and currently acquired geological data from multiple trenches across the frontal thrust show that the last faulting event occurred between 13th and 14th centuries—the time interval coinciding with the 1344 CE earthquake. The episodic valley fills debris flow depositions identified in the Pokhara Valley in the east‐central Nepal provide additional constraints for the 1344 CE earthquake along with two previous ones in 1255 and 1100 CE. The consilience of multiple pieces of evidence from India and Nepal in combination with the new data inputs from two trench locales implicates the 1344 CE as the last of the medieval sequence of earthquakes. With a rupture length of ~600 km of the central Indian Himalaya and an average slip of 15 m, this earthquake is consistent with moment magnitude of Mw ≥8.5. An earthquake of similar size is overdue in this part of the Himalaya, considering the long elapsed time of ≤700 years. [ABSTRACT FROM AUTHOR]

Abstract: The India–Asia collision resulted in the construction of the vast Himalayan orogen. The northern Himalayan domain began to experience extensional tectonics since Eocene–Oligocene transition (EOT) when the Himalayan orogeny was still in progress. Major structures generated by the extension in the northern Himalaya include the south Tibet detachment system (STDS), the north Himalayan gneiss domes (NHGD), and the north–south trending rifts (NSTR). The earliest emplacement of syn-deformational leucogranite at ~36–32Ma along the STDS marks the initial transformation from thickening to thinning in the northern Himalayan domain at EOT. The thickening before EOT caused crustal partial melting, which formed the weak root of the thickened orogen or the so-called “channel flow”. This “channel flow” triggered the collapse of the orogen, extrusion of the greater Himalayan crystalline complex (GHC), and the onset of extensional tectonics of the STDS. The similarities in tectono-thermal history and geochemistry of rocks between the STDS and NHGD suggest that the formation of the NHGD has a direct relationship to the activity of the STDS. The extension of STDS and the resultant thinning caused further partial melting of the crust, leading to the larger-scale emplacement of leucogranite during Miocene (27–13Ma). Diapirism of these plutons shaped the domes in NHGD, exposing the GHC and the shear zones of the STDS in the northern Himalaya. In Gyirong, another tectonic transform from extension to shortening occurred after ~18.7Ma. In Dinggye region, the STDS was offset by the NSTR, culminating the deformation at ~13Ma when the NSTR began to be active. This indicates another tectonic transform in the northern Himalaya at ~13Ma, when the N–S extension of the STDS ceased and gave way to E–W extension of the NSTR, marking the end of the peak granitic magmatism in northern Himalaya. Multiple episodes of deformation in the major structures, such as the STDS, MCT and NSTR, and superposition of different structures indicate a multiphase orogenic process in the Himalayas, in which mountain building and collapse occurred alternately, with the formation of NSTR and conjugate shear zones in Tibet. This tectonic scenario was possibly controlled by the India–Asia convergent rate. We propose that the extension was an integral part of the orogenic process rather than a simple marker of the culmination of the orogeny. [Copyright &y& Elsevier]

Abstract: The Namche Barwa Complex (NBC) in the eastern Himalayan syntaxis, south Tibet, is generally interpreted as the north-eastern extremity of the exposed Greater Himalayan Sequence, comprising Neoproterozoic to early Paleozoic sedimentary strata along the northern margin of the Indian continent. Field and petrological investigations indicate that the NBC consists mainly of orthogneiss, paragneiss, amphibolites and calc-silicate rocks. U–Pb zircon data demonstrate that the protoliths of the orthogneiss formed during late Paleoproterozoic at ca. 1610Ma and also in early Paleozoic at ca. 490–500Ma. The amphibolites were derived from mafic magmatic rocks formed during 1645 to 1590Ma. Zircons in the paragneisses have highly variable inherited zircon ages ranging from the Neoarchean to early Paleozoic, with four major age populations of 2490Ma, 1640Ma, 990Ma and 480Ma. The calc-silicate rock has zircons with early Paleozoic metamorphic age of 538Ma. Almost all the rocks of the NBC have been metamorphosed during Cenozoic with the metamorphic zircon U–Pb ages ranging from 8 to 30Ma and a peak at 23Ma. These, together with previous results suggest that the NBC was originally derived from an Andean-type orogeny following the Columbia supercontinent assembly, and experienced multiple reworking during the Grenvillian, Pan-African and Himalayan orogenies. We conclude that the NBC in the eastern Himalayan syntaxis was derived from different provenance and tectonic setting as compared to those of the Greater Himalayan Sequence which constitutes the high-grade metamorphic core of the western and central Himalayan orogenic belt. We thus infer that the NBC was originally part of the eastern segment of the Central Indian Tectonic Zone. [Copyright &y& Elsevier]

Plagioclase ultraphyric basalts (PUBs) are an important unit of the Abor magmatic complex (AMC) of the eastern Himalaya, containing ≥35 vol% plagioclase phenocrysts. Apart from the eastern region, PUBs have not been reported in any other part of the Himalayas. However, very little information is available about their origin and significance in the evolution of the eastern margin of the Indian plate and the Himalayan orogeny. In this contribution, we present the first zircon U Pb age data of the PUBs along with whole-rock geochemistry, Sr Nd isotopic ratios, mineral chemistry, and quantitative textural analysis, to understand the evolutionary history of the AMC and subsurface magma chamber activities. The PUBs formed from highly evolved magma (<6 MgO wt%), having high Fe 2 O 3 (9.06–12.29 wt%) and Ti/Y ratios (>500). Their εNd (t) values (−0.02 to +2.66) suggest plume magma source. A small difference in anorthite contents (<5 mol%) is observed from the thick core (An 47–58) with lower anorthite contents towards the rim (An 34–47) of the plagioclase phenocrysts, which is an indication of weakly zoned characteristics. Crystal size distribution shows a non-linear and concave upward trend with a relatively gentler slope towards the coarser plagioclase populations, which can be attributed to the hybrid crystallization of plagioclase-bearing magma and its subsequent differentiation with cumulates of plagioclase inside the magma chamber. The zircon U Pb age of these PUBs records two magmatic events - Early Paleozoic (505–473 Ma) at the core and Early Cretaceous (134–126 Ma) at the rim that are consistent with the previously proposed magmatic events of AMC with Gondwana assembly and break-up. Encounter of such dual ages in zircons does not support the usual condition of PUBs formation through crystal floatation in a slow cooling process of a single magma chamber. Therefore, considering the evidences observed in crystal size distribution, core-rim anorthite variation, geochemistry, and age data, we propose that the PUBs of AMC, eastern Himalaya were formed due to injection of a hot and young magma during the Early Cretaceous into an old and cold mush zone containing pre-existing plagioclase phenocrysts formed during the Early Paleozoic. The results further support that the newly injected magma formed the rim of the plagioclase phenocrysts and the groundmass of the PUBs. • First successful attempt to date the PUBs of Eastern Himalaya by zircon U Pb method. • Zircon U Pb yield two magmatic events - 505-473 Ma and 134–126 Ma for PUBs. • Whole-rock geochemistry point towards an enriched mantle source. • Plagioclase textural indicates a complex magmatic history. • PUBs formed by injection of new magma to an older magma chamber. [ABSTRACT FROM AUTHOR]

Quartz and calcite veins are omnipresent in the Indus basin sedimentary rocks (IBSRs) of the Indus Tsangpo suture zone (ITSZ) which were formed by the accumulation of sediments derived from both sides of the tectonic plate. These veins appear to have formed just after the sediment diagenesis and were deformed together with the IBSR. The veins were studied for their rare earth elemental and isotopic geochemistry (C–O–Sr–Pb). The light rare earth element/mid rare earth element with an Eu/Eu* ratio of the veins (quartz and calcite) is >1 for the northern side (Tibetan side) and <1 for the southern side, indicating a mantle/magmatic and marine-related fluid source, respectively. The carbon, oxygen and strontium isotopes range from - 14 ‱ to - 1 ‱ VPDB, + 5.7 ‱ to + 24.9 ‱ Vienna standard mean ocean water and 0.7056 to 0.7099, respectively. The Sr–O mixing model points towards the mantle-enriched fluid on the northern side of the IBSR, whereas on the southern side, the fluid was nearly marine. The intermixing of the fluid took place in the middle part of the Indus basin sediments comprising a mixed litho-unit succession. Similar characteristics of vein fluids with the host rocks indicate the derivation of fluids from the associated host IBSR, further substantiated by the lead isotopic systematics. [ABSTRACT FROM AUTHOR]

As prototypes of crust-derived remelted S-type granite, Himalayan leucogranites have considerable relevance in crustal evolution and associated metallogeny. However, given their highly differentiated character, the petrogenesis of these rocks has remained controversial. This study reviews the geochemical and isotopic data from >2000 samples of Himalayan Cenozoic granitoids to evaluate their genesis. The Himalayan leucogranites include two major belts: the northern zone occurs in the Tethyan Himalayas and gneiss domes, and the southern zone is exposed mainly at the top of the Higher Himalayas. The ages of these rocks show a southward younging trend from 49 Ma to 1 Ma. The main rock types are two-mica granites and garnet-tourmaline-bearing muscovite granites, whereas Eocene and Miocene intermediate-mafic and adakitic rocks are developed mainly in the northern belt. The leucogranites originated from incongruent disequilibrium partial melting of the Greater Himalayan Crystalline Complex and underwent a high degree of differentiation and fractional crystallization. The rocks are strongly peraluminous and characterized by high Si, K, and Na; low Ca, Fe, Mg, Ti, and Mn; and low rare earth elements with obvious tetrad effects and negative Eu anomalies. A more striking feature of these granites is their high Rb/Sr and Y/Ho values and low Th/U, Nb/Ta, Zr/Hf, and K/Rb values. The Sr–Nd–Pb–Hf isotopes indicate that the proportion of older crustal material in the magmatic source area gradually increased from the Eocene to the Pliocene. The Cenozoic magmatic activity can be divided into five stages—49-40 Ma, 39–29 Ma, 28–15 Ma, 14–7 Ma, and 6–0.7 Ma—and their geotectonic settings are related to the break-off of the Neo-Tethyan oceanic plate, low-angle underthrusting of the Indian continental lithosphere, break-off or rollback of the Indian plate, tearing of the Indian lithospheric slab or delamination of the lithospheric mantle, and rapid extrusion and uplift of the Eastern and Western Himalayan Syntaxis resulting from flat subduction of the Indian continent, respectively. Stream sediment geochemical data from previous work show high positive anomalies for some rare metals in the Himalayas. The average contents of Li, Be, Sn, Ta and Cs in pegmatite are 2466 ppm, 93 ppm, 29 ppm, 14 ppm and 61 ppm, respectively. All these elements have enrichment coefficients higher than 10 compared to the upper continental crust. Recent progress in ore prospecting shows that the Himalayan Cenozoic leucogranite is emerging as a new world-class rare metal metallogenic belt. [Display omitted] • First comprehensive review of the world-famous Himalayan leucogranites. • The leucogranites originated from partial melting of GHC. • They underwent a high degree of differentiation and fractional crystallization. • They cover five stages: 49–40 Ma, 39–29 Ma, 28–15 Ma, 14–7 Ma, and 6–0.7 Ma. • The Himalayas are emerging as a new world-class rare metal metallogenic belt. [ABSTRACT FROM AUTHOR]

Abstract: The granitic gneisses in the cores of north Himalayan gneiss domes (NHGD) and at the crest of the high Himalayas form part of the greater Himalayan crystalline complex (GHC). These rocks are characterized by the assemblage of quartz, plagioclase, K-feldspar, biotite, muscovite and minor garnet. Here we present results from LA-ICPMS zircon U–Pb dating of six granitic gneiss samples, which reveal formation ages of ca. 500–473Ma and suggest a long-lived magmatism during early Paleozoic in the GHC. Geochemical data show that these rocks are characterized by high SiO2 (70.93–74.59wt.%), K2O (4.22–5.91wt.%), A/CNK values (>1.1) and low Na2O/K2O (0.42–0.83), and enrichment in Rb, Th, U, depletion in Ba, Nb, Ta, Sr, Zr, and strong negative Eu anomalies. These features suggest that the protoliths of the gneisses are high potassium calc-alkaline and peraluminous S-type granites derived from partial melting of crustal materials. The high initial 87Sr/86Sr (>0.706) and negative ε Nd(t) (−6.2 to −10.6) of the granitic gneisses compare with those of the metasedimentary rocks in the GHC, indicating that the granites were generated from partial melting of the sedimentary protoliths. Based on the geochronological, whole-rock geochemical and Sr–Nd isotopic data presented in this study, we suggest that the granites formed in a back-arc setting with a continental arc-affinity related to the subduction of the Proto-Tethyan Oceanic lithosphere. The mafic magmatic underplating, triggered by the subduction, rollback and the break off of Proto-Tethyan Ocean slab, resulted in partial melting of the crust in the GHC. Integrating results from previous studies, we propose an Andean-type orogeny along the margin of the Gondwana. [Copyright &y& Elsevier]

Abstract: Charnockites, occurring in the well-studied Gangdese batholith in the southern Lhasa terrane, eastern Himalayan orogen, consist of orthopyroxene, clinopyroxene, plagioclase, and minor quartz and K-feldspar, and show adakitic affinity. Here we present a systematic study on the fluid inclusions in Gangdese charnockites which reveals that the primary fluid inclusions occur isolated or randomly distributed and as trails along intragranular fractures in quartz, and that the secondary ones occur along healed mircofractures and coexist commonly with mineral inclusions of calcite, magnetite and hematite within the host plagioclase and quartz. The fluid inclusions contain dominantly near-pure CO2 with traces of N2. Most of the primary fluid inclusions have low CO2 homogenization temperatures and with densities of 1.138–1.013g/cm3 suggesting trapping pressures of 0.7–1.0GPa at temperatures of 850–950°C. We propose a model in which the southward subduction of Neo-Tethyan mid-oceanic ridge beneath the Lhasa terrane resulted in the release of heat and CO2 from the upwelling asthenosphere through a slab window, providing high-temperatures (HT) and dry CO2-rich fluids for the formation and stabilization of the adakitic charnockite as well as the associated HT granulite-facies metamorphic rocks in the Late Cretaceous, prior to the final collision of the Indian plate with the Asian continent. Our study provides new insights into the geodynamics of Andean-type orogeny in the southern Tibetan Plateau during the Late Mesozoic. [Copyright &y& Elsevier]

• Porphyry and epithermal type of gold deposits in the hinterlands of the Bagrote valley. • Proximal source and high content of gold in pyrite suggest probable mineralization beneath the current level of erosion. • Gold occurs in pyrite in the form of micro to nano inclusions as Au0 instead of Au+1. • Ore forming fluids were derived from orogenic belts with minor contribution of lower crust. The Bagrote valley in North Pakistan, belonging to the Kohistan island arc, is well-known for regional placer gold mining. However, no economically feasible in situ hydrothermal gold deposits have been discovered in this region due to rugged terrain and remote nature of its location in the western Himalaya. The streams draining the Main Karakoram Thrust (MKT)/Shyoke suture zone carry placer gold in sediments as well as old river terraces, although the primary source remains unknown. In this paper, we employ a multiparametric approach including, X-ray Diffraction (XRD) analysis, thermoelectricity, major and trace element geochemistry and isotopic characteristics of pyrite associated with placer gold with a view to identify the nature of the unknown deposits and ore forming fluids on the catchment of the Bagrote valley. Pyrite in the Bagrote valley placers is euhedral to subhedral indicating the proximal gold sources. The high rate of occurrence of N-type thermoelectric coefficients (89%) with low P-type (11%) and crystallization temperature (290 °C−380 °C) combined with chemical features indicate that the pyrite was derived from porphyry or epithermal type of magmatic hydrothermal gold deposits from the hinterlands of the Bagrote valley. The X-Ray elemental maps show that Fe, As, Mo and Ni are homogenously distributed from core to rim suggesting stable crystallization condition without any alteration by later fluids. The calculated chemical formula of pyrite of our samples is [Au0.0006Fe] S2.004], plots of Au-As and Au-Fe shows that gold occurs in pyrite as micro to nano inclusion as Au0. The δ 34 S V - CDT values of pyrite range from – 0.6‰ to 0.9‰ with an average of −0.02‰, indicating the derivation of sulfur from a homogeneous magmatic source. The Pb isotope data indicates that the Pb was sourced from orogenic-type source, with minor contribution of lower crust. The narrow variations in 206Pb/204Pb and 208Pb/204Pb values suggest a single lead source. The low, medium and high Mo/Ni ratios reflect a mixed provenance for the auriferous pyrite. The average value of γ (71.8%), of pyrite computed from thermoelectric parameters (XnP), suggests that the dominant part of the primary source that contributes to the placers might have already been eroded. However, the proximal source and with high content of gold in the pyrite grains (up to 1160 ppm) suggest the possibility of significant economic mineralisation below the present erosion level of the deposits in the hinterlands of Bagrote Valley. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two fundamental types of collisional orogens have been proposed. • Cold orogens are characterized by brittle fault systems and limited magmatism. • Hot orogens are characterized by ductile flow and widespread partial melting. • MVT Pb–Zn and orogenic gold deposits can occur in both cold and hot orogens. • Porphyry Cu deposits are only associated with hot orogens. It is commonly believed that the thermal regime of collisional orogens evolves from cold to hot with time. Here, we compare the Alpine and Himalayan-Tibetan orogens in terms of their thermal regimes recorded in metamorphic rocks, volcanic suites and related xenoliths, and main mineralization types. The results highlight the fact that the Alpine orogen mostly remained in a relatively cold regime from oceanic subduction to post collision stages. In contrast, most of the Himalayan-Tibetan Plateau rapidly reached and was maintained in a relatively hot regime during the whole course of the collision, except for narrow plate boundary domains. We therefore propose that the thermal regime of collision is inherent to a given geodynamic setting, and that the Alpine and Himalayan-Tibetan orogens represent two fundamental types of collisional orogens, cold and hot, respectively. The main mineral deposit types within collisional orogen include Mississippi Valley type Pb–Zn, orogenic gold, and porphyry Cu deposits. The Mississippi Valley type Pb–Zn and orogenic gold deposits can occur in both cold and hot orogens but porphyry Cu deposits are only associated with hot orogens. Major factors that influence the thermal regime of collisional systems include the rate of continental subduction, the rheology of the underlying lithospheric mantle, the thickness of the overlying lithosphere and radiogenic heat production. Here we propose the removal of suborogenic mantle lithosphere and upwelling of asthenosphere also plays an important role on the thermal structure of collision zones. These processes disturbe the thermal balance of the orogens and cause widespread partial melting of the crust, resulting in the formation of magma-related deposits (i.e., granite-related W-Sn deposits and porphyry Cu deposits). We further give a brief overview of other examples around the globe, such as Pyrenees and Caledonides that reperesent cold orogens versus Variscan and Zagros-Iranian Plateau exemplifying hot orogens. [ABSTRACT FROM AUTHOR]