South Tibet Research Articles

The record of the Early Late Paleocene Event (ELPE, 59.5 Ma) in shallow-water Tethys Himalayan carbonates (Zongpu Formation, South Tibet)

ABSTRACT The Early Late Paleocene Event (ELPE, 59.5 Ma) was a short-lived climatic perturbation accompanied by prominent biotic changes. Although the ELPE has been widely recognized from pelagic and continental archives, shallow-marine records remain scarce and poorly documented. To constrain the pattern and magnitude of the ELPE and associated environmental changes, we here present a detailed sedimentologic, biostratigraphic, and stable-carbon-isotope study of upper Paleocene platform carbonates continuously exposed in the Jiajin section of southern Tibet. Two distinct negative carbon-isotope excursions (CIEs) are documented: the first one occurred during shallow benthic zone (SBZ) 3 with a magnitude of ∼ 1.0‰, the second one began near the SBZ3–SBZ4 boundary with a magnitude of ∼ 1.5‰. Carbonate microfacies dominated by packstones with rotaliids and/or dasycladacean algae testify to an open shallow-marine environment. Neither a significant change in paleo–water depth nor evidence of early diagenetic dissolution are documented across the ELPE. The microfacies change observed during the ELPE, characterized by a decrease in the abundance of larger benthic rotaliid foraminifera relative to calcareous green algae, is related to environmental perturbations and increased nutrient supply. The changed trophic level may have resulted from intensified continental weathering promoted in turn by global warming. Compared with biocalcification crises observed in deep-water sedimentary records, shallow-water carbonate production remained relatively unaffected by changes in ocean-water chemistry.

Late Triassic paleogeography of the northern Indian continental margin: Constraints from Nd isotopes of siliciclastic rocks (Tethys Himalaya, South Tibet)

Late Triassic paleogeography of the northern Indian continental margin: Constraints from Nd isotopes of siliciclastic rocks (Tethys Himalaya, South Tibet)

Himalayan Leucogranites: Field Relationships and Tectonics

Himalayan peraluminous leucogranites were derived from in-situ melting of sillimanite + K-feldspar-bearing pelite-migmatite, and were transported via layer-parallel sill complexes and cross-cutting dykes to feed giant sills up to 5 km thick. Partially melted Himalayan middle crust was extruded southwards between two large-scale, north-dipping, synchronous ductile shear zones: the Main Central Thrust (MCT) below and the low-angle normal fault South Tibetan Detachment (STD) above. U-Th/Pb monazite dating constrains granite melting to ~25–18.5 Ma in Manaslu and ~24–13 Ma in Everest-Makalu. The Manaslu sheeted sill complex was emplaced by progressive underplating with the oldest intrusions structurally above younger intrusions. Heat was dominantly derived by internal radioactive heating from crustal thickening with little or no contribution from shear heating along the MCT or from the mantle.

Himalayan Leucogranites: Rare-metal Resources

Himalayan leucogranites were once overlooked for rare-metal resources because they initially were thought to have formed by in-situ partial melting of underlying high-grade metamorphic rocks. However, recent findings have revealed widespread rare-metal mineralizations of Be, Nb/Ta, Li/Rb/Cs, and W/Sn associated with leucogranites in the area, suggesting these mineralizations resulted from extensive fractionation of leucogranitic magmas during long-distance magma transport along the low-angle South Tibetan Detachment System. When combined with coeval Au-Sb-Pb/Zn mineralizations in the Himalayas of the Indian plate, and porphyry Cu-Mo mineralizations in the Gangdese of the Asian plate, a specific Himalayan-type mineralization is proposed to describe the metallogenesis related to the exhumation of the subducted Indian continent, coinciding with the uplift of the Himalayan mountains.

Tectonic Evolution of the Himalayan Fold‐Thrust Belt in the Okhaldhunga Region, Eastern Nepal

AbstractNew regional mapping and two focused geological maps with two crustal‐scale balanced cross‐sections along the Dudh Kosi and Tama Kosi Rivers in the Okhaldhunga region reveal the structural architecture of the eastern Nepal Himalaya. Our detrital zircon U‐Pb ages for 14 samples and igneous zircon U‐Pb ages for four samples show that the Okhaldhunga window primarily exposes the Ramgarh thrust sheet, which is composed of Paleoproterozoic Lesser Himalayan metasedimentary and igneous rocks. Structurally, the Ramgarh thrust sheet lies in the footwall of the Main Central thrust and is underlain by the Lesser Himalayan duplex (LHD), a hinterland dipping bumpy‐roofed duplex, comprising Paleo‐Mesoproterozoic Lesser Himalayan rocks and upper Paleozoic Gondwana Sequence rocks. The frontal part of the LHD is exposed in the southern sector of the Okhaldhunga window, above a major footwall ramp on the Main Himalayan thrust. Neoproterozoic‐Cambrian Greater Himalayan rocks in the hanging‐wall of the Main Central thrust are exposed toward the south in the synformal Mahabharat Range and in the north in the Sagarmatha‐Rolwaling region. Kinematic restorations for our two transects, combined with published chronometric data, indicate that most of the deformation has been accommodated by Lesser Himalayan rocks since Middle‐Late Miocene. The two balanced cross‐sections indicate minimum shortening of ∼561 and 544 km. Comparison of these estimates with published data for rocks structurally below the South Tibetan detachment system in the Himalaya indicates that heterogeneous post‐collisional crustal shortening has determined the current tectonic configuration of the region.

Seawater retreated from the Tethyan Himalaya of south Tibet at ca. 49 Ma, not ca. 34 Ma

Timing of seawater retreat from the Tethyan Himalaya is of great importance, as it provides a minimum age control on the initial India-Asia collision. In south Tibet, however, it is still in dispute, with suggested ages ranging from >50 Ma to ca. 34 Ma. Here we present data of (1) larger benthic foraminifera from the topmost Zongpu Formation; (2) planktonic foraminifera; and (3) detrital zircon U-Pb ages from the Youxia and Shenkeza Formations at Guru, Tingri, and Gamba, with a special emphasis on the poorly studied Guru area. At Guru, existence of the Shallow Benthic Zonation (SBZ) 7 Zone index fossils of Alveolina moussoulensis Hottinger and Al. laxa Hottinger constrains the initial deposition of the Youxia Formation at ca. 54 Ma. Coexistence of the youngest planktonic foraminifera Acarinina boudreauxi Fleisher, Ac. coalingensis (Cushman and Hanna), and Ac. bullbrooki (Bolli) from the Youxia and Shenkeza Formations indicates their final deposition at ca. 49 Ma (E 7 Zone, where E stands for Eocene Planktonic foraminiferal Zone). Zircon U-Pb data are generally similar, with the youngest age peak of ca. 68−50 Ma resulting from input of the Gangdese Arc volcanic detritus. The complete lack of <49 Ma data among >1000 accepted ages implies that marine deposition probably ceased at ca. 49 Ma, consistent with the planktonic foraminiferal result. Integrating with previous results, we conclude that seawater retreated from both south Tibet and Zanskar at ca. 49 Ma. The initial collision happened quasi-simultaneously in the western and eastern Tethyan Himalaya, before ca. 49 Ma. Our findings do not support either a younger collisional age or a diachronous collisional process from the west to the east.

Discovery and genesis of high-temperature geothermal energy adjacent to the South Tibetan Detachment System, central Himalaya

The 193 °C geothermal fluids have been newly discovered in Lolo at the depth of 350 m through drilling in May 2024, identifying the occurrence of high-temperature geothermal energy adjacent to the South Tibetan Detachment System. Studies on such geothermal field will provide new insights into the distribution of high-temperature geothermal systems in Xizang. Here, we present element geochemistry (major and trace elements) and multi-isotope (H, O, and Sr) compositions of thermal spring, geothermal well, river, and snow waters to reveal the formation of the Lolo high-temperature geothermal system. The major elemental results of water samples show that the Lolo geothermal waters belong to Na-HCO3 type, mainly affected by carbonate dissolution, silicate weathering, and cation exchange through water-rock interaction. The positive correlations of trace alkali metals (Li, Rb, and Cs) and metalloid (B) with Cl indicate that these elements were derived from the same source, mainly released from Himalayan leucogranites with minor slate and limestone via water-rock reaction. The interpretation is further supported by varied Sr isotopic values recorded in geothermal waters. Combination of major and trace elements, and H-O isotopic results reveals that the geothermal waters were sourced from meteoric precipitation from the eastern parts of the region at an elevation of ∼4733 m, which were conducted along the WE-trending fault (F5). The temperature of deep geothermal reservoir was calculated to be 204–205 °C by using quartz geothermometers, and the temperature of shallow reservoir has been calculated to be 100–130 °C based on chalcedony geothermometers and computed mineral saturation index by PHREEQC. The shallow thermal fluids were suggested to be formed by mixing of deep thermal fluids with cold groundwater near to the surface, evidenced by positive linear correlations between B and Cl. The deep-circulated meteoric waters have been heated by partial melting and the circulation depth is up to ∼5 km. These new findings help us understand the formation of Lolo geothermal field and also provide guides in high-temperature geothermal resources exploration adjacent to the South Tibetan Detachment System.

The making of Mt Everest: channel flow and low-angle normal faults in the compressional Himalayan orogen

Mt Everest (8849 m) spans the Greater Himalayan Sequence metamorphic rocks and the base of the unmetamorphosed Tethyan sedimentary rocks in the Nepal–South Tibet Himalaya. Two north-dipping, low-angle normal faults cut the massif: the upper Qomolangma Detachment placing Ordovician sedimentary rocks above Everest Series greenschist–amphibolite facies rocks; and the lower Lhotse Detachment placing Everest Series schists above sillimanite gneisses, migmatites and leucogranites. The two faults merge northwards into one large ductile shear zone (the South Tibetan Detachment). Pressure–temperature constraints and structural restoration show that the South Tibetan Detachment acted as a passive roof fault during extrusion of the footwall. At least 120 km of southward flow of the footwall rocks occurred during the Miocene, resulting in the exhumation of rocks that were buried to 5.5 kbar ( c. 18–22 km depth) below the detachment, juxtaposing them against hanging wall rocks that are essentially unmetamorphosed. The low-angle normal faults were operative during north–south convergence and reflect the exhumation of a locked passive roof fault, unrelated to any crustal extensional processes. U–(Th)–Pb dating of peraluminous leucogranites exposed on Mt Everest (21–20 Ma), Nuptse ( c. 19–18 Ma) and along the Rongbuk valley (15.6–15.4 Ma) show that ductile extrusion occurred during the Early Miocene, with brittle faulting at <15.4 Ma during exhumation.

Top-to-south shear at the base of the eastern Tethyan Himalayan Sequence during the Eocene-Oligocene Himalayan orogeny

The early mountain building processes in the Himalayan orogen are still not clear because of extensive deformation and metamorphism since the Miocene. A large gently dipping ductile shear zone, referred as the Tethyan Himalayan Décollement (THD), is defined here as the sole décollement of the south-verging Tethyan fold-and-thrust belt in the Lhozag-Cuona area of the eastern Himalayan orogen. The ∼4 km-thick THD is characterized by a top-to-south shear sense, moderate T/P Barrovian to high T/P Buchan type metamorphism and Eocene-Miocene partial melting. Zircon U-Pb dating of metasedimentary rocks and granitic gneisses from the THD yields protolith ages of the Late Cambrian to Early Ordovician. Based on structural analysis, zircon U-Pb ages, monazite U-Pb ages and mica 40Ar/39Ar thermochronology, the THD was the boundary shear zone at the top of the Greater Himalayan Crystalline Complex (GHC) and accommodated the persistent north-south shortening in the Tethyan Himalayan Sequence (THS) from ∼50 Ma to 20–17 Ma. From ∼20–17 Ma, the top-to-north South Tibetan Detachment System (STDS) was predominantly activated to juxtapose the unmetamorphosed or low-grade THS over the GHC. This tectonic transition can be attributed to the roof collapse in the eastern Himalaya (younger than that of the central-western Himalaya), which triggered rapid exhumation of the GHC and the northern Tethyan Himalayan gneiss domes. Hence, the THD was the predecessor of the STDS and a prolonged pathway for leucogranitic melts from the Eocene to early Miocene. The transition from the THD-controlled crustal thickening in the Eocene and Oligocene to the STDS-controlled extrusion in the Miocene shed insights on a new synthesis of the tectonic wedging model for the Himalayan evolution.

Morphotectonics, slope stability and paleostress studies from the Bhagirathi river section, western Himalaya (Uttarakhand, India)

We study parts of Tethyan, Higher and Lesser Himalayan rocks along the Bhagirathi river valley for morphotectonic analysis. The spatial and linear properties of the 21 watersheds (WSs) and the Bhagirathi main watershed provide strong evidence of active tectonics mainly in the WS 3 (through which the South Tibetan Detachment passes), WS 9 (no fault runs), WS 12 (Vaikrita and Munsiari Thrusts cross) and WS 17 (Basul and Tons Thrusts occur). The Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) has been used to rank the sub-watersheds as per the intensity of their recent tectonic activity. Seven morphometric parameters are used for the TOPSIS analysis. From the Lesser Himalayan section additionally, we perform landslide and paleostress studies. Eleven slopes cuts and 24 landslides were investigated to determine the mode of failure in a portion of the Rishikesh-Gangotri Highway. Landslides in soil strata is caused mainly by the low cohesion and due to the presence of coarse-grained loose materials. In the present study, most landslides (and earthquakes) have occurred in the vicinity of major thrusts. Where there is a high frequency of slickenside related to brittle normal faulting (K2 zone, near Dunda, Singuni and Dharasu Thrusts), a higher earthquake frequency of 4.0 - 6.6 magnitude is observed from the data set of around last 60 years. Paleostress analysis on data-sets of normal, reverse and strike-slip movements using the WinTensor software (ver. 5.8.8) yields NNE-SSW direction of extension for normal slip, NE-SW compression for reverse movement, and a pure strike-slip tensor with NNE-SSW shortening and WWN-SSE direction of maximum extension. The K2 zone where these deformations were most documented, is also the place of slope instability and a much higher present-day tectonic activity. (Words: 283)

Calcareous nannoplankton fluctuation within the Albian-Cenomanian Boundary Event of the Tethyan Himalaya

A hemipelagic succession 29m thick, situated in South Tibet within the Tethyan Himalaya tectonic unit, has been investigated for its calcareous nannofossil content. A total of 17 samples were subject to qualitative and semi-quantitative analysis. The studied interval belongs to the upper Albian-lowermost Cenomanian and extends into the UC0 nannofossil zone; based on the last occurrence of Hayesites albiensis, the UC0a and UC0b-c subzones were recognized. The most abundant nannofossil of the Youxia section is Watznaueria barnesiae. Other common taxa are Eiffellithus turriseiffelii, Eprolithus floralis, Rhagodiscus spp., and Zeugrhabdotus spp. In the lowermost part of the studied section, below the beginning of the Albian-Cenomanian Boundary Event (ACBE), i.e., prior to the δ13C positive excursion related to OAE1d, the nannofossils confined to high paleolatitudes, namely Repagulum parvidentatum, Seribiscutum primitivum, and Sollasites horticus, are present with a low abundance. This occurrence is believed to be evidence of a short episode of cooler surface waters linked to a transgressive event. The nannofossil abundance and diversity, along with the fluctuation patterns of the nutrient and temperature indices throughout the section, reflects a primary signal of mesotrophic to eutrophic conditions from the base of the succession up to the two oldest δ13C peaks of ACBE, both late Albian in age and within the OAE1d. By contrast, the dominance of Watznaueria barnesiae, representing more than 80% of the total assemblages, along with the significant drop in abundance and diversity shown by nannofossils within late phases of ACBE, are interpreted as a diagenetic signal. Mesotrophic to eutrophic conditions returned towards the top of the studied succession, where Biscutum constans and Zeugrhabdotus erectus again show a higher abundance.

Blown sand environment characteristics and bridge sand hazard mechanisms of expressways in the South Tibet Valley.

South Tibet expressways are built in the Yalu Tsangpo valley along the route to high-altitude and cold-temperature valleys, which are the main environmental characteristics of the region. Given that the blown sand environment and its potential harm are unclear, targeted prevention and control are not conducive, but its absence would result in severe wind-sand hazards on these expressways. In this research, the blown sand environment of the South Tibet Valley and the mechanism of sand damage to expressway bridges were studied via field observations, wind tunnel experiments and numerical simulations. The sand-moving wind is mainly west wind. The sand-moving wind frequency, sand drift potential, and maximum possible sand transport quantity are high in winter and spring (November-April) and low in summer and autumn (May-October). The sand drift direction is in the east direction. Expressway bridges have a considerable impact on the near-surface blown sand environment, forming a zone for increasing the wind speed between the top of the slope shoulder of the windward side of the bridge to the center of the bridge abutment, forming a zone for weakening the wind speed between the - 3H distances of the upwind direction to the bottom of the slope middle of the windward side of the bridge, further forming a zone for weakening the wind speed centered in the slope shoulder of the leeward side of the bridge. The wind speed within a distance of 40H downwind direction of the bridge generally did not recover. The wind-sand flow is partially blocked when it passes through the bridge and accumulates near the bridge, which cause harm. The impact of the bridge on the blown sand environment in the downwind is greater than that in the upwind. The results of this study can provide a reference for preventing and controlling wind-sand hazards on South Tibet expressways.

The fate of the Xigaze forearc basin after Late Cretaceous filling (South Tibet)

The fate of the Xigaze forearc basin after Late Cretaceous filling (South Tibet)

South Tibetan Detachment System (STDS), NW Himalaya: A possible Cambro–Ordovician tectonic terrane boundary, and its Cenozoic remobilization

The South Tibetan Detachment System is an important extensional fault zone, separating the Greater Himalayan Sequence from the overlying Tethyan Himalayan Sequence, and is well exposed in the upper reaches of the Dhauliganga valley, NW Himalaya. This fault system is characterized by the occurrence of an extensive Cambro–Ordovician granite belt between Sutlej and Dhauliganga valleys, although only a few small granitoids intrude the high-grade mylonite gneiss of the Greater Himalayan Sequence in its immediate footwall. These bodies yielded U-Pb zircon crystallization ages between 498.92 ± 5.5 Ma and 486.54 ± 2.3 Ma. This work postulates that the South Tibetan Detachment System evolved as a major proto-tectonic marginal extensional terrane boundary during the Cambro–Ordovician Kurgiakh/Bhimphedian Orogeny, when it was the conduit for emplacement of the Cambro–Ordovician granite belt. Denudation of the Neoproterozoic Greater Himalayan Sequence and the Paleozoic granites on its footwall provided approximately ∼ 10 km thick sediments into the Tethyan Basin due to this fault system as a master growth fault. Reactivation of this fault system controlled further melting and emplacement of the Higher Himalayan Leucogranite belt during the Cenozoic. Zircon growth is observed in two distinct modes: pulsative from the Late Eocene to Early Oligocene, with peaks at 33.99 ± 1.07 Ma, 30.53 ± 0.32 Ma and 25.03 ± 0.54 Ma; and in the continuous mode from 23.68 ± 0.94 Ma to 13.30 ± 0.30 Ma, in the Miocene, for nearly 10.0 myr. These datasets reveal some of the oldest pulsative movements in the Late Eocene–Early Oligocene during crustal thickening, thrusting and associated metamorphism, followed by continuous extension during the Miocene. Data from the South Tibetan Detachment System are distinct in character, and do not support either its eastwards younging or diachronous movements along the Dhauliganga valley.

The origin of Gangjiang adakite-like intrusions and associated porphyry Cu–Mo mineralization in the central Gangdese porphyry Cu belt, southern Tibet

The Gangjiang Cu–Mo deposit is located in the central Gangdese porphyry Cu belt (GPCB), south Tibet. Geological investigation reveals that the Gangjiang deposit is characterized by early potassic alteration, followed by late phyllic and argillic alteration. Late alteration has different degrees of overprinting over the potassic alteration zone. Copper-Mo orebodies are predominantly hosted in the potassic and phyllic alteration zones of the Miocene monzogranite porphyry (MGP) and granodiorite porphyry (GDP). In this study, we present the chemistry and Sr–Nd–Pb–Hf–O isotope compositions of fertile MGP and GDP, barren tonalite porphyrite (TP), and microgranular mafic enclaves (MMEs). Chemical compositions indicate that these intrusions are I-type granites that show high–K calc-alkaline signatures. The negative correlation between Dy/Yb and SiO2 indicates that the intrusions experienced fractionation of amphibole. They have high Sr/Y (>70) and La/Yb (>38) ratios, strong negative Nb–Ta–Ti anomalies, and positive Pb anomalies are typical for arc magma. The high Mg# of various porphyry intrusions (43–65) and MMEs (47–58) indicate the input of mafic components. Various intrusions have whole-rock 87Sr/86Sr(t=13Ma) ratios of 0.70529 to 0.70674, negative εNd(t=13Ma) (−5.0 to −1.2), positive zircon εHf(t) (1.2–9.8), and homogeneous δ18O (5.8–7.1 ‰, mean 6.6 ‰). The MMEs have similar Sr–Nd–Pb–Hf–O isotopic compositions with their host rocks. The features reveal that the Gangjiang adakite-like intrusions and MME samples were derived from the partial melting of the Lhasa Paleoproterozoic crust, with contributions from the juvenile mantle that has been metasomatized by subducted sediments-derived melts. Note, the MGP, GDP, and two types of MMEs have slightly lower δ18O values (down to 4.76 ‰) but higher εNd(t) (up to −1.2) than barren TP, indicating their formation involves more mantle components. Furthermore, the MMEs in the TP and MGP have high Cu contents (up to 1485 ppm), similar to the phenomenon occurs in the Qulong deposit. The Cu-rich MME is probably formed by Cu-refertilization by the underplate arc magma in the juvenile crust. The εHf(t) and εNd(t) values of fertile porphyries increased from the Jiru, Gangjiang, to Qulong deposit indicating increased mantle material additions from the west to the east section of the GPCB. These variations in mantle components have led to an increase in the size of the porphyry Cu deposits from Jiru to Gangjiang, and then to Qulong.

The Role of Lower Crustal Rheology on Surface Deformation During Oblique Extension: Insights From Sandbox Modeling

AbstractExtensive researches have been conducted on the relationship between surface deformation and the properties of upper crust. However, the link between surface deformation and lower crustal rheology, especially in a three‐dimensional context, remains unclear. In this study, we utilize sandbox modeling to investigate the impact of lower crustal rheology on surface deformation during oblique extension. Under the same conditions, six models with different lower crustal viscosities, both with and without syn‐kinematic deposits, are conducted. The results indicate that a decrease in lower crustal viscosity may contribute to an increase in: (a) graben width, (b) graben length, (c) graben spacing, (d) the number of isolated rifts and (e) topographic relief of oblique extensional systems, while also leading to a reduction in the total number of grabens. Notably, there exists a negative linear correlation between graben spacing and lower crustal viscosity. In map view, the angle between fault strike and the direction of pre‐existing discontinuities increases as the viscosity of the lower crust decreases. Furthermore, the frequency of large rakes (>50°) decreases with decreasing lower crustal viscosity. These findings align with natural examples such as the East African Rift System, Weihe Graben and the South Tibetan Rift in terms of geomorphology, tectonics, and crustal rheology. Through a comprehensive comparison of the graben width, spacing, and the angle between fault strike and the direction of pre‐existing discontinuities, our study provides valuable insights into the rheology of the lower crust in natural settings.

Evidence of back-folding in the Beas Valley puts Himalayan tectonic models on trial

Field structural observations from the Himachal Himalaya, in the northwest of the mountain belt, challenge existing tectonic models and raise questions as to their validity. Microstructures and geochronological data reveal two discrete episodes of Barrovian metamorphism, the earliest during the Eocene-Oligocene transition, before an early period of recumbent folding. This metamorphic event occurred in association with a km-scale extensional ductile shear zone that is itself now recumbently folded on the km-scale, with an axial plane pressure solution cleavage. The Eocene-Oligocene gneiss complex is thus exposed in its core. The second episode of Barrovian metamorphism occurred in association with another regional-scale extensional shear zone during the Oligo-Miocene transition, thus synchronous to the South Tibetan Detachment System. This transects the recumbent fold stack. Microstructures show that the Main Central Thrust was initiated after the second phase of extension, and the associated second episode of Barrovian metamorphism had ceased operating. Further, the previously unrecognized km-scale Phojal Back-fold affects all of the above structures. Confusion caused by the misidentification of this structure led to the tectonic-wedge model, but this hypothesis can be invalidated by the structural evidence presented here. Our data support an alternative hypothesis that requires tectonic mode-switches in association with a succession of accretion events as India indents into Eurasia.

Unveiling the geoheritage, cultural geomorphology and geotourism potential of Zanskar region, NW Himalaya, India

The Zanskar region, nestled in the heart of the Tethyan Himalaya, represents a significant geological and cultural repository that has remained relatively unexplored by the global tourism industry. This study investigates Zanskar's geoheritage and cultural geomorphology, highlighting its importance for geotourism and advocating for the implementation of sustainable development to preserve its fragile ecosystem. Flowing northward from the Higher Himalayas, the Zanskar River, one of the largest northeast-flowing tributary of the Upper Indus River Basin (UIRB), traverses the complex, strongly folded, and thrusted Zanskar Range via a steep, narrow 60-kilometer-long gorge. Zanskar has consistently garnered attention from geoscientists and tourists owing to its unique geographic location and remoteness. Many areas and routes in Zanskar are challenging to reach, but it stands out as a prime location where glaciers can be accessed by road, making it an ideal destination for studying geoscience. Geologically, the study area is part of the Zanskar Range, with its boundaries defined by the Ladakh Range to the northeast and the Great Himalayan Range to the southwest. The Indus Tsangpo Suture Zone, the Tethyan Sedimentary Sequence, and the Higher Himalayan Crystalline Sequence are exposed from north to south. Zanskar serves as a pristine field museum for studying young Himalayan orogenic tectonics, featuring prominent exposures such as the Zanskar Shear Zone (ZSZ)/South Tibetan Detachment System (STDS) and the structural outcrop of Zangla, showcasing a variety of folding types. These folds signify different phases of deformation resulting from the Indo-Eurasian collision. Moreover, it serves as a prime sequence of Quaternary Glacial Periods (QGP), providing an ideal natural laboratory and an open, practical classroom for geoscientists and Earth science students. We propose ten geoheritage sites in Zanskar, which encompass cultural, geomorphological, and geological attractions with potential for geotourism in this region.

Structural and metamorphic architecture of the Zanskar Himalaya, Suru Valley region, NW India: Implications for the evolution of the Himalayan metamorphic core

New 1:50,000-scale geological mapping in the Zanskar Himalaya of NW India, covering 2,400 km2, is integrated with structural and petrographic analysis to document the evolution and key tectonometamorphic relationships within the Himalayan metamorphic core. The integrated dataset constrains the regional three-dimensional geology and relationships between lithostratigraphy, folds, faults, deformation fabrics, metamorphic isograds, and growth of porphyroblasts within the context of five main deformation phases. Following the initial collision of India and Asia, NW−SE-oriented deformation is recorded by D1 (greenschist-facies) fabrics and D2 (greenschist- to amphibolite-facies) fabrics. D2 represents the main tectonometamorphic deformation phase associated with crustal thickening and produced the dominant regional penetrative fabric through crenulation and transposition of D1 fabrics. Thrust-sense D2 fabrics were reactivated during D3 as the Greater Himalayan Sequence was exhumed along the normal-sense Zanskar Shear Zone, which is part of the South Tibetan Detachment System. D3 fabrics, associated with movement on the Zanskar Shear Zone, were temporally continuous with crenulation and mesoscale folding, recording progressive kilometer-scale backfolding and backthrusting toward the NE between the Greater Himalayan Sequence−Tethyan Himalayan Sequence and the adjacent Indus Suture Zone. Finally, D4 and D5 are recorded as kilometer-scale open folding of older planar and linear structures. The orientation of mineral isograd surfaces ranges from subparallel to oblique with respect to D2 planar structural elements. The growth of pelitic and metabasic peak metamorphic phases from greenschist to upper-amphibolite facies is synchronous with or postdates D2 fabrics. D3 fabrics wrap thermal peak porphyroblasts and realign linear mineral phases. Tectonic thinning adjacent to D3 normal faults is documented by reduced structural spacing of isograds and alignment of isograd surfaces parallel to the faults. D4 and D5 structures modify the trace of all regional metamorphic isograds. Collectively, these observations imply that the thermal peak of metamorphism was reached after the main phase of deformation (D2), and predated movement on the Zanskar Shear Zone (D3). The results document numerous classical elements of collisional orogenesis, including implied clockwise P-T paths, polyphase deformation, and a complete Barrovian metamorphic isograd sequence supplemented by complementary metabasic isograds. The Zanskar Himalaya, unlike other areas of the Himalayan metamorphic core, records metamorphic conditions primarily attained following substantial crustal thickening rather than during subsequent decompression and exhumation. The reduced expression and/or discontinuous nature of exhuming fault systems, which produces variable levels of crustal exposure, may account for this lateral heterogeneity across the mountain belt. Deciphering the complex kinematics of continental tectonics requires the integration of observations and data over large length scales and a range of structural levels.

Multi-stage leucogranite emplacement in the Yalashangbo dome in northern Himalaya: Trigger and consequence of faulting along the South Tibet Detachment System

Leucogranitic dikes emplaced at the lower-middle crust are particularly widespread in the Himalayas. How the magmatic activities evolved in relation to faulting along the Southern Tibetan Detachment system (STDS) remains debated. In this study, we investigate the multi-stage leucogranitic emplacement in relation to the structural evolution of the detachment fault in the Yalashangbo dome through detailed macro- and microscopic structural observations, LA-ICP-MS monazite U-Th-Pb dating, and whole-rock geochemical analysis of the leucogranitic dikes. We identified late syn- and post-kinematic granitic dikes from the dome. Timing of dominant STDS faulting is constrained from 27 to 17 Ma. Based on synthesis of geochronological and geochemical results of the present and previous studies, we suggest that two dominant stages of granitic emplacement occurred from Eocene to Miocene along the High Himalayas. An early stage of leucogranitic activity was probably ascribed to partial melting of mafic juvenile lower crust due to heating related to asthenosphere upwelling as the result of slab tearing or break-off during the Indian subduction. Emplacement of the leucogranitic melts subsequently softened the middle and lower crust and triggered the initiation of detachment faulting along the STDS as early as ca. 35 Ma. The large-scale detachment faulting likely led to intensive localized decompression melting of the lower crust. Contemporaneous detachment faulting in the lithospheric mantle allowed heat transfer from the asthenosphere to the lower crust, enhancing lower crustal melting and leading to generally higher crystallization temperatures in the late syn-kinematic granites than the post-kinematic ones.