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Neoproterozoic magmatism associated with the assembly and configuration of the Rodinia supercontinent is widely distributed in the India-Himalayan terrane. However, its petrogenesis and tectonic settings remain controversial. This study provides new geochronological and geochemical data on the Neoproterozoic bimodal magmatism from the eastern Himalayan orogen. In situ zircon U Pb dating revealed that the protoliths of amphibolites were emplaced at ca. 826 Ma and the granitic gneisses have crystallization ages of 825–820 Ma. The granitic gneisses exhibit geochemical features of A-type granites, with high initial (87Sr/86Sr)i ratio (0.7182–0.7394), low whole-rock eNd(t) (−8.4 to −6.6), and variable zircon eHf(t) (−7.4 to +1.0) values. They were probably generated by partial melting of the ancient lower crust with minor input of mantle components. The amphibolite samples are enriched in light rare earth elements (LREEs) and depleted in heavy rare earth elements (HREEs), suggesting an arc affinity. They have relatively high initial (87Sr/86Sr)i ratios (0.7113–0.7136), low whole-rock eNd(t) (−1.1 to 1.4) and a wide range of zircon eHf(t) (−4.1 to 8.3) values, indicating that the protoliths of amphibolites were likely generated by partial melting of an enriched subduction-modified continental lithospheric mantle. Their geochemical signatures are similar to typical back-arc basin basalts. The presence of coeval A-type granites and arc-related mafic rocks is probably due to the existence of a back-arc system. We argue that the Neoproterozoic bimodal magmatism is a product of back-arc extension initiated at an early stage, resulting from the rollback of the Mozambique Oceanic slab. Combined with previous studies on Neoproterozoic magmas from India and the Himalayas, we suggest that an extensive Neoproterozoic back-arc system may have existed along the northwestern margin of the Rodinia supercontinent. This theory supports a scenario of an Andean-type continental margin for the India-Himalayan terrane during the middle Neoproterozoic.

We present in-situ zircon laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U–Pb ages, whole-rock geochemistry, and Sr–Nd–Pb–Hf isotopes of the Mugagangri monzogranite in the southern margin of the Qiangtang Block, Tibet, western China. The zircons yield a U–Pb age of ca. 123 Ma. The hornblende-bearing monzogranite shows metaluminous to weak peraluminous and high-K calc-alkaline characteristics exemplified by high silica (SiO2 = 67.57–70.57 wt%), high aluminium (Al2O3 = 14.68–15.78 wt%), high potassium (K2O = 4.00–5.14 wt%), high alkali (K2O + Na2O = 7.88–8.62 wt%), and low calcium contents (CaO = 1.72–2.17 wt%), with the aluminium saturation index (A/CNK) ranging from 0.98 to 1.09, suggesting that the Mugagangri monzogranite is a metaluminous to weak peraluminous I-type high-K calc-alkaline granite. Geochemically, similar to the arc magmas, the monzogranite is enriched in large-ion lithophile elements, and relatively depleted in high-field-strength elements. The monzogranite displays relatively high(87Sr/86Sr)i values (0.70972–0.71240), uniform eNd(t) values (−2.24 to −3.40), variable zircon eHf(t) values (−14.1 to +8.0), and high radiogenic Pb isotopic values (206Pb/204Pb = 18.588–18.790, 207Pb/204Pb = 15.616–15.642, and 208Pb/204Pb = 38.838–39.053). These geochemical characteristics indicate that the monzogranite was derived from a mixed source comprising ancient crustal and mantle materials, and experienced frac- tional crystallization during emplacement. We propose that the parental magma of the Mugagangri monzogranite was most likely generated during northward subduction of the Bangong Coujiang Meso-Tethys Ocean.

The Tethys Himalaya sedimentary sequence (THS) is characterized by N–S trending extensional rifts (NSTR) and the North Himalayan gneiss domes (NHGD). The Cuonadong dome, as one of the NHGD, is located at the N–S trending Cuona rift in the eastern part of the Tethys Himalaya. The dome had undergone four major deformation events: D1, characterized by top-to-S thrust resulting in N–S shortening and vertical thickening; D2, characterized by vertical thinning and N–S extensional deformation; D3, approximately E–W extensional deformation associated with intrusion of leucogranites; and D4, late collapse structural deformation around the core of the Cuonadong dome. There are numerous granitic dykes at the contact zone between the granite and surrounding rocks in the middle unit of the Cuonadong dome. Field observations show that granite intrusion occurred in part synchronously with D3, E–W extensional deformation. U–Pb–zircon dating shows that the granite crystallization took place at ca. 17.5–15.6 Ma, while muscovite Ar–Ar geochronological data from the deformed pegmatite and mylonitic schist in the Cuonadong dome show that the onset of the E–W extensional deformation is between 16.5 and 14.8 Ma, and suggesting that granite intrusion was synchronous with the E–W ductile extensional deformation in the Cuonadong dome, southern Tibet. Combined with previously published ages of the South Tibetan Detachment System (STDS), our study shows that granite intrusion was at least locally contemporaneous with both the E–W and N–S extensional deformation, especially with the E–W extension.

The Xitieshan deposit (~ 64 Mt at 4.86% Zn, 4.16% Pb, 58 g/t Ag, and 0.68 g/t Au) is hosted by the Middle to Late Ordovician Tanjianshan Group of the North Qaidam tectonic metallogenic belt, NW China. This belt is characterized by island arc volcanic, ultra-high pressure (UHP) metamorphic and ophiolitic rocks. The Tanjianshan Group constitutes a succession of metamorphosed bimodal volcanic and sedimentary rocks, which are interpreted to have formed on the margin of a back-arc ocean basin between the Qaidam block and the Qilian block. Four stratigraphic units are identified within the Ordovician Tanjianshan Group. From northeast to southwest they are: 1) unit a, or the lower volcanic-sedimentary rocks, comprising bimodal volcanic rocks (unit a-1) and sedimentary rocks (unit a-2) ranging from carbonates to black carbonaceous schist; 2) unit b, or intermediate-mafic volcaniclastic rocks, characterized by intermediate to mafic volcaniclastic rocks intercalated with lamellar carbonaceous schist and minor marble lenses; 3) unit c, a purplish red sandy conglomerate that unconformably overlies unit b, representing the product of the foreland basin sedimentation during the Early Silurian; 4) unit d, or mafic volcanic rocks, from base to up, comprising the lower mafic volcaniclastic rocks (unit d-1), middle clastic sedimentary rocks (unit d-2), upper mafic volcaniclastic rocks (unit d-3), and uppermost mafic volcanic rocks (unit d-4). Unit a-2 hosts most of the massive sulfides whereas unit b contains subordinate amounts. The massive stratiform lenses constitute most of the Xitieshan deposit with significant amount of semi-massive and irregularly-shaped sulfides and minor amounts in stringer veins. Pyrite, galena and sphalerite are the dominant sulfide minerals, with subordinate pyrrhotite and chalcopyrite. Quartz is a dominant gangue mineral. Sericite, quartz, chlorite, and carbonate alteration of host rocks accompanies the mineralization. U-Pb zircon geochronology yields three ages of 454 Ma, 452 Ma and 451 Ma for the footwall felsic volcanic rocks in unit a-1, sedimentary host rocks in unit a-2 and hanging-wall unit b, respectively. The Xitieshan deposit is considered to be coeval with the sedimentation of unit a-2 and unit b of the Tanjianshan Group. The Xitieshan deposit has been intensely deformed during two phases (main ductile shear and minor ductile-brittle deformation). The main ductile shear deformation controls the general strike of the ore zones, whereas minor deformation controls the internal geometry of the ore bodies. 40 Ar- 39 Ar age of muscovite from mylonitized granitic gneisses in the ductile shear zone is ~ 399 Ma, which is interpreted to date the Xitieshan ductile shear zone, suggesting that Early Devonian metamorphism and deformation post-dated the Tanjianshan Group. The Xitieshan deposit has many features similar to that of the Bathurst district of Canada, the Iberian Pyrite Belt of Spain, the Wolverine volcanogenic massive sulfide deposit in Canada. Based on its tectonic setting, host-rock types, local geologic setting, metal grades, geochronology, temperatures and salinities of mineralizing fluid and source of sulfur, the Xitieshan deposit has features similar to sedimentary exhalative (SEDEX) and VMS deposits and is similar to volcanic and sediment-hosted massive sulfide (VSHMS) deposits.

The Cuonadong super-large Be-W-Sn rare metals deposits are hosted by skarns and marbles in the middle unit of the Cuonadong Dome. Rocks in the Cuonadong Dome record four major deformational events: D1, top-to-S thrust; D2, top-to-N extension; D3, approximately E–W extensional deformation; and D4, late collapse structural deformation. Skarns and/or marbles featured by the directional alignment of skarn minerals are exposed in garnet-staurolite-bearing mica schist, and are closely related to the deformed leucogranites and pegmatites. The boundary between leucogranites and skarns is locally gradual or sharp, which suggests that skarns and the deformed leucogranites resulted from the synkinematic magmatism and the strong activity of the STDS. Ar-Ar dating of muscovite from the deformed granites in the middle unit and biotite from granitic gneiss in the core yielded Ar-Ar plateau ages of 15.0 ± 0.2 Ma and 13.9 ± 0.4 Ma, respectively, which reflects the age of syntectonic magmatism, and the activity time of the STDS at the Cuonadong Dome, respectively. Ar-Ar dating of biotite from marble in the middle unit yielded Ar-Ar plateau age of 16.1 ± 0.2 Ma, which was interpreted as the formation age of the synkinematic skarns. Skarns in the Cuonadong Dome were related to the detachments and formed in association with the emplacement of leucogranites. Therefore, we suggest that the formation of the Cuonadong Be-W-Sn skarn deposit was contemporaneous with the intrusion of leucogranitic magma and the top-to-north extensional deformation along the STDS.

The Cuonadong dome exposes in east-southern margin of the North Himalayan gneiss domes (NHGD), which is reported first time in this study. The Cuonadong dome is located at the southern part of the Zhaxikang ore concentration area, which is divided into three tectono-lithostratigraphic units by two curved faults around the dome geometry from upper to lower (or from outer to inner): the upper unit, middle unit and lower unit, and the outer fault is Nading fault, while the inner fault is Jisong fault. The Cuonadong dome is a magmatic orthogneiss and leucogranite mantled by orthogneiss and metasedimentary rocks, which in turn are overlain by Jurassic metasedimentary and sedimentary rocks. The grades of metamorphism and structural deformation increase towards the core, which is correspondence with the Ridang Formation low-metamorphic schist, tourmaline granitic–biotite gneiss, garnet–mica gneiss and mylonitic quartz–mica gneiss. The Cuonadong dome preserves evidences for four major deformational events: firstly top-to-S thrust (D1), early approximately N–S extensional deformation (D2), main approximately E–W extensional deformation (D3), and late collapse structural deformation (D4) around the core of the Cuonadong dome, which are consistent to three groups lineation: approximately N–S-trending lineation including L1 and L2, E–W trending L3, and L4 with plunging towards outside of the dome, respectively. The formation of the Cuonadong dome was probably resulted from the main E–W extensional deformation which is a result of eastward flow of middle or lower crust from beneath Tibet accommodated by northward oblique underthrusting of Indian crust beneath Tibet. The establishment of the Cuonadong dome enhanced the E–W extension of the NHGD, which is further divided into two structural dome zones according to the different extensional directions: approximately N–S extensional North Himalayan gneiss domes (NS-NHGD) and E–W extensional North Himalayan gneiss domes (EW-NHGD). The NS-NHGD developed by a dominantly N–S contraction and locally extensional regime and keep a close relationship to the South Tibetan Detachment System, whereas the EW-NHGD formed by an E–W extensional deformation along the north–south-trending rifts.

In situ U–Pb geochronology, Lu–Hf isotopes and REE geochemical analyses of detrital zircons from Cambrian–Devonian sandstones in the Truong Son Belt, central Vietnam, are used to provide the information of provenance and tectonic evolution of the Indochina Block. The combined detrital zircon age spectra of all of the samples ranges from 3699 Ma to 443 Ma and shows with dominant age peaks at ca. 445 Ma and 964 Ma, along with a number of age populations at 618–532 Ma, 1160–1076 Ma, 1454 Ma, 1728 Ma and 2516 Ma. The zircon age populations are similar to those from time equivalent sedimentary sequences in continental blocks disintegrated from the East Gondwana during the Phanerozoic. The younger zircon grains with age peaks at ca. 445 Ma were apparently derived from middle Ordovician–Silurian igneous and metamorphic rocks in Indochina. Zircons with ages older than about 600 Ma were derived from other Gondwana terrains or recycled from the Precambrian basement of the Indochina Block. Similarities in the detrital zircon U–Pb ages suggest that Paleozoic strata in the Indochina, Yangtze, Cathaysia and Tethyan Himalayas has similar provenance. This is consistent with other geological constrains indicating that the Indochina Block was located close to Tethyan Himalaya, northern margin of the India, and northwestern Australia in Gondwana.

The Cuonadong deposit is located in the Cuonadong gneiss dome of the eastern Tethyan Himalaya and is characterized as a large- to superlarge-scale Sn polymetallic deposit in the Himalaya orogen. The mineralization pattern includes skarn W-Sn mineralization in the strong shear zone of the dome mantle, hydrothermal Sn-W veins controlled by north-south-trending rifts (NSTRs), and Be-Rb mineralization in pegmatitic leucogranite. The results of this study show that the zircon U-Pb age of undeformed (postkinematic) leucogranites is 15.5 ± 0.1 Ma (n = 28, MSWD = 1.4), the cassiterite U-Pb age of the vein-type Sn-W orebody is 14.3 ± 0.5 Ma (n = 40, MSWD = 3.2), and the muscovite Ar-Ar age of beryl-bearing pegmatitic leucogranite is 15.2 ± 0.2 Ma (MSWD = 1.5). The isotopic dating results demonstrate that the Cuonadong Sn-W-Be-Rb mineralization has a close genetic relationship with the Miocene (ca. 16–14 Ma) leucogranite magmatic hydrothermal activity in the Cuonadong dome. The deformed (synkinematic) two-mica granite (18 Ma) was cut by the Sn-W ore veins (14 Ma) faulted by NSTRs, indicating that the E-W-trending extension of the NSTRs initiated at ca. 18–14 Ma. The Himalaya leucogranite belongs to a highly fractionated granite with high Sn content (>15 ppm). In conclusion, the Himalaya leucogranite is considered to be tin granite in this study, and therefore, the Himalaya presents high potential for Sn polymetallic mineralization prospecting.

The Xitian tungsten–tin (W–Sn) polymetallic deposit, located in eastern Hunan Province, South China, is a recently explored region containing one of the largest W–Sn deposits in the Nanling W–Sn metallogenic province. The mineral zones in this deposit comprise skarn, greisen, structurally altered rock and quartz-vein types. The deposit is mainly hosted by Devonian dolomitic limestone at the contact with the Xitian granite complex. The Xitian granite complex consists of Indosinian (Late Triassic, 230–215 Ma) and Yanshanian (Late Jurassic–Early Cretaceous, 165–141 Ma) granites. Zircons from two samples of the Xitian granite dated using laser ablation-inductively coupled mass spectrometer (LA-ICPMS) U–Pb analysis yielded two ages of 225.6 ± 1.3 Ma and 151.8 ± 1.4 Ma, representing the emplacement ages of two episodic intrusions of the Xitian granite complex. Molybdenites separated from ore-bearing quartz-veins yielded a Re–Os isochron age of 149.7 ± 0.9 Ma, in excellent agreement with a weighted mean age of 150.3 ± 0.5 Ma. Two samples of muscovites from ore-bearing greisens yielded 40Ar/39Ar plateau ages of 149.5 ± 1.5 Ma and 149.4 ± 1.5 Ma, respectively. These isotopic ages obtained from hydrothermal minerals are slightly younger than the zircon U–Pb age of 151.8 ± 1.4 Ma of the Yanshanian granite in the Xitian area, indicating that the W–Sn mineralization is genetically related to the Late Jurassic magmatism. The Xitian deposit is a good example of the Early Yanshanian regional W–Sn ore-forming event (160–150 Ma) in the Nanling region. The relatively high Re contents (8.7 to 44.0 ppm, average of 30.5 ppm) in molybdenites suggest a mixture of mantle and crustal sources in the genesis of the ore-forming fluids and melts. Based upon previous geochemical studies of Early Yanshanian granite and regional geology, we argue that the Xitian W–Sn polymetallic deposit can be attributed to back-arc lithosphere extension in the region, which was probably triggered by the break-off of the flat-slab of the Palae-Pacific plate beneath the lithosphere.