Himalayan Terrane Research Articles

Carboniferous rifting of the Lhasa Terrane (Tibet, China) and the break-up of East Gondwana based on detrital zircon analyses

The break-up processes of the northern margin of East Gondwana remain uncertain, especially regarding the Lhasa Terrane. In this paper, we conduct a systematic field geological survey, detrital zircon UPb dating, and zircon trace element and Hf isotope analyses in the Carboniferous rift basin in the eastern part of the Lhasa Terrane, including the Nuocuo and Laigu Formations, to reconstruct the break-up history of East Gondwana. The overall Carboniferous depositional environment in the eastern part of the Lhasa Terrane changed from near-shore and shallow marine to slope and moderately deep sea facies, reflecting a transgression. The weighted average age of several of the youngest detrital zircons from the Nuocuo Formation is 346.8 ± 6.4 Ma (4 grains), whereas that of the Laigu Formation is 328.7 ± 6.1 Ma (6 grains). The detrital zircon ages in the Carboniferous strata show similar distributions, dominated by zircons from the Indian continent (∼950 Ma), Australian continent (∼1170 Ma), and Lhasa Terrane (∼340 Ma). The paleogeographic position of the Lhasa Terrane was near the Indian and Australian continents during the Carboniferous. The increase of the ∼340 Ma detrital zircon age peak from the Mississippian to the Pennsylvanian demonstrated that the rift basin recorded a Mississippian magmatic event. The εHf(t) and oxygen fugacity values of partial zircons of ∼340 Ma are similar to those of zircons from intraplate magmatic rocks, further implying the intracontinental rifting in the Lhasa Terrane. Combined with the previous research on magmatic rocks in East Gondwana, including the Lhasa, South Qiangtang, and Himalayan Terranes, our study on sedimentation found that the Lhasa Terrane was in a passive continental margin rifting context during the Mississippian and the rift gradually expanded to become the Sumdo Paleo-Tethys Ocean basin.

Tectono-metamorphic transitions in the higher Himalayan sequence: A clue for Main Central Thrust (MCT) localization in Darjeeling-Sikkim Himalaya

This study recognizes a transition in the modes of ductile deformation across the Himalayan Crystalline Complex (HCC) from field and microstructural evidence. This transition leads to the Main Central Thrust (MCT) zone localization in the Darjeeling-Sikkim Himalaya. In the initial stage of crustal shortening (prior to ∼16 Ma), the HCC experienced temporally varying distributed ductile strains that produced regionally occurring planar fabrics and folds of three generations. Thereafter, the tectonic transition (from distributed to localized deformation) at ∼16 Ma occurred, forming the MCT zone in the HCC. This MCT zone (∼4–6 km thick) marks a diffuse metamorphic/rheological boundary between the hot HCC and the relatively colder Lesser Himalayan terrane to the south. The field data suggests that the base of compressed reverse paleo-isograds at the bottom of the MCT zone coincides with the transition of quartz creep mechanisms, from sub-grain rotation (SGR) to grain boundary migration (GBM). The present study documents the prograde metamorphic imprints to establish the P-T conditions of these multiple deformation episodes. Finally, this study presents a conceptual tectonic model, based on previous laboratory findings, to propose a two-stage tectono-thermal evolution of the Higher Himalaya.

Shear‐Wave Velocity Reveals Heterogeneous Geometry of the Main Himalayan Thrust System and Deep Structure Beneath the Nepal Himalayas

AbstractThe Himalayas is currently rising due to the collision of the Indian and Asian plates and hosts frequent earthquakes, some of which are devastating, such as the 2015 Mw7.8 Gorkha earthquake. Despite the importance of deep dynamic processes to understand the uplift of the Himalayas and the occurrence of large earthquakes, it remains limitedly constrained due to the lack of a detailed three‐dimensional subsurface image under this region. Here, we construct new models of shear‐wave velocity and radial anisotropy down to the 150 km depth from Rayleigh‐ and Love‐wave tomography in the Nepal Himalayas. We find that the 2015 Gorkha earthquake and its main aftershock occurred in a velocity contrast that is presumably interpreted as Main Himalayan Thrust (MHT). A duplex structure, imaged as relatively high velocities, is inferred to exist above MHT under the Lesser Himalayas. This duplex shows heterogeneous features along the strike of the Himalayas that may control the rupture behavior during the occurrence of a large earthquake. Additionally, a low‐velocity anomaly is observed at depths from Moho to 100 km under the Lhasa Terrane and north of the Himalayan Terrane between 85° and 88°E. We interpret this low‐velocity anomaly to be likely caused by mantle upwelling resulting from either possible Indian slab tearing, or northward subduction of the Indian plate. If this is the case, the north‐south trending rifts that situate within the dispersal of the low‐velocity anomaly are probably associated with the mantle upwelling. This study provides a new independent constraint on the geometry of the MHT system and deep dynamic processes occurring in the Nepal Himalaya.

The impact of a tear in the subducted Indian plate on the Miocene geology of the Himalayan-Tibetan orogen

Abstract The Yadong-Gulu Rift, cutting across the Gangdese belt and Himalayan terranes, is currently associated with a thermal anomaly in the mantle and crustal melting at 15–20 km depth. The rift follows the trace of a tear in the underthrusted Indian continental lithospheric slab recognized by high resolution geophysical methods. The Miocene evolution of a 400-km-wide band following the trace of the tear and the rift, records differences interpreted as indicative of a higher heat flow than its surroundings. In the Gangdese belt, this band is characterized by high-Sr/Y granitic magmatism that lasted 5 m.y. longer than elsewhere and by the highest values of εHf(i) and association with the largest porphyry Cu-Mo deposits in the Gangdese belt. Anomalously young magmatic rocks continue south along the rift in the Tethyan and Higher Himalayas. Here, a 300-km-wide belt includes some of the youngest Miocene Himalayan leucogranites; the only occurrence of mantle-derived mafic enclaves in a leucogranite; young mantle-derived lamprophyre dikes; and the youngest and hottest migmatites in the Higher Himalayas. These migmatites record a history of rapid exhumation contemporaneous with the exhumation of Miocene mafic eclogite blocks, which are unique to this region and which were both heated to >800 °C at ca. 15–13 Ma, followed by isothermal decompression. We suggest that the prominent tear in the Indian lithosphere, sub-parallel to the rift, is the most likely source for these tectono-thermal anomalies since the Miocene.

Fingerprints of the Kerguelen Mantle Plume in Southern Tibet: Evidence from Early Cretaceous Magmatism in the Tethyan Himalaya

AbstractEarly Cretaceous magmatism suggested to be related with the Kerguelen mantle plume has been reported in both the eastern and western Tethyan Himalayan terrane. Coeval magmatism (133–138 Ma) recorded by hypabyssal intrusive rocks have been recently discovered in the central Tethyan Himalaya (TH). The hypabyssal intrusions are dominated by OIB‐like basaltic rocks intruded by later porphyritic/ophitic intermediate rocks and are characterized by strongly light rare earth element enrichment and prominent Na‐Ta depletion and Pb enrichment. The basaltic rocks have low 143Nd/144Nd ratios ranging from 0.512365 to 0.512476 but relatively high 87Sr/86Sr ratios ranging from 0.708185 to 0.708966. The ∊Nd(t) ratios of the basaltic rocks are between −4.33 and −2.20 and initial 87Sr/86Sr ratios are 0.707807 to 0.708557. Geochemical data demonstrate that these rocks have experienced combined crustal assimilation and fractional crystallization processes. Magmatic zircons from the hypabyssal rocks exclusively have negative ∊Hf (t) values ranging from −0.7 to −12.7, suggestive of assimilation of crustal material. Zircons from these hypabyssal rocks have U‐Pb ages ranging from 130 to 147 Ma. Inherited zircons have U‐Pb ages from 397 to 2495 Ma. All the zircons are characterized by negative ∊Hf(t) values. The Jiding ocean island basalt (OIB)‐like magmatism is geochemically and geochronologically comparable with that in the western and eastern Tethyan Himalaya, indicating widespread OIB‐like magmatism in the northern margin of Greater India during the Cretaceous. Collectively, these rocks can be correlated with other early Cretaceous magmatism in western Australia and northern Antarctica. Considering the similarities, we suggest that the Jiding hypabyssal rocks are also genetically related to Kerguelen plume. Within the Yarlung Zangbo Suture Zone (YZSZ), there are also numerous occurrences of OIB‐like rocks derived from mantle sources different from those of N‐MORB‐like magmas. The OIB‐like magmatism in the YZSZ is nearly coeval with that in the TH, and the two are geochemically similar. We suggest that the OIB‐like magmatism in the Neo‐Tethyan ocean and the northern margin of Greater India may represent the dispersed fingerprints of the Kerguelen plume preserved in southern Tibet, China.

Ordovician successions in southern-central Xizang (Tibet), China—Refining the stratigraphy of the Himalayan and Lhasa terranes

The Ordovician stratigraphy of southern-central Xizang (Tibet) has been revised based on new conodont data recovered from 43 samples in four stratigraphic units and their integration with existing nautiloid and graptolite data. The Histiodella holodentata and Pygodus serra biozones have been identified respectively in the Alai and Jiaqu formations of the Chiatsun Group exposed near Alai village in Nyalam County within the Himalayan terrane, and the Yangtzeplacognathus foliaceus Subbiozone (lower part of the Pygodus serra Biozone) in the Sangqu Formation exposed at the Guyu section within Zayu County in the Lhasa terrane. Recognition of these biozones has increased the precision of correlation of the middle-upper Darriwilian strata in the region. Regional reassessment of the Ordovician stratigraphy permitted by new biostratigraphic data has allowed revised definitions for the Chiatsun and Keerduo groups and the Sangqu and Xainza formations. The Chiatsun Group is defined herein to include three lithologically distinctive formations in descending order, the Jiaqu, the Alai and the Adang formations. The stratigraphic age for the Jiaqu and Alai formations in the type area ranges from the middle Darriwilian (Histiodella holodentata Biozone) to middle Katian (Hamarodus brevirameus Biozone), but the age of the Adang Formation remains less certain.

Elemental and Sr-Nd isotopic geochemistry of Mesoproterozoic sedimentary successions from NE Lesser Himalaya, northern India: Implications for Proterozoic climate and tectonics

The sedimentation history of northeastern Himalayan Proterozoic basins is poorly known. In the current study, we examine major, trace, rare earth elements (REEs) and Sr-Nd isotope geochemistry of pelites and quartzites from Mesoproterozoic metasedimenatary sequences of Bomdila and Rupa Groups, NE Himalaya in order to understand provenance, tectonic setting and paleoweathering conditions of deposition. The salient geochemical parameters, such as, high SiO2 and Al2O3 concentrations, relatively low MgO values, typical enrichment of immobile incompatible elements (Al2O3/TiO2 = 32.2, Th/Sc = 2.1), fractionated REE patterns (La/Ybn = 28) and a strong negative europium anomaly (Eu/Eu∗ = 0.3–0.7) indicate dominant felsic source for Bomdila sediments. Bomdila sediments show significantly radiogenic εNd0.95Ga values (−10.25 to −17.90, avg. −15.24) compared to Bundelkhand craton (avg. −26) and Singhbhum craton (avg. −30) and yield much younger TDM ages (2.3–2.7 Ga) compared to Archean Bundelkhand (3.2–3.5 Ga) and Singhbhum cratons (3.4–3.9 Ga). These results clearly rule out any significant detritus contribution from old cratonic sources. εNd and TDM data of Mesoprterozoic Bomdila sediments envelop the signature of Lower Proterozoic Inner Lesser Himalayan (ILH) terrane. Prominent U-Pb age peaks at 1702, 1651, ∼1400, 1248 and 1118 Ma in detrital zircons indicate major contribution from Late Paleoroterozoic to Late Mesoproterozic sources. However, initial Nd isotope ratios and TDM do not favour any juvenile inputs. We argue that ILH source terrain may have been extensively reworked during Late Paleoroterozoic to Late Mesoproterozic time and could have been part of a long lived orogenic belt.. Severe depletion of Ca, Na and Sr in Bomdila sediments indicate intense chemical weathering of the source region, and can be attributed to warm and humid climatic conditions, a conclusion which is consistent with the CO2-rich atmosphere during Mesoproterozoic period.

Application of Persistent Scatterer Interferometry (PSI) in monitoring slope movements in Nainital, Uttarakhand Lesser Himalaya, India

Orogenic movements and sub-tropical climate have rendered the slopes of the Himalayan region intensely deformed and weathered. As a result, the incidences of slope failure are quite common all along the Himalayan region. The Lesser Himalayan terrane is particularly vulnerable to mass-movements owing to geological fragility, and many parts of it are bearing a high-risk of associated disaster owing to the high population density. An important step towards mitigation of such disasters is the monitoring of slope movement. Towards this, the Persistent Scatterer Interferometry (PSI) technique can be applied. In the present study, the PSI technique is employed in Lesser Himalayan town of Nainital in Uttarakhand state of India to decipher and monitor slope movements. A total of 15 multi-date ENVISAT ASAR satellite images, acquired during August 2008 to August 2010 period, were subjected to PSI, which revealed a continuous creep movement along the hillslopes located towards the eastern side of the Nainital lake. The higher reaches of the hill seem to be experiencing accelerated creep of \({\sim }21\) mm/year, which decreases downslope to \({\sim }5\) mm/year. Based on spatial pattern of varying PSI Mean LOS Velocity (MLV) values, high (H), moderate (M), low (L) and very low (S) creeping zones have been delineated in the hillslopes. Given the long history of mass movements and continuously increasing anthropogenic activities in Nainital, these results call for immediate measures to avert any future disaster in the town.

Petrotectonic setting of the provenance of Lower Siwalik sandstones of the Himalayan foreland basin, southeastern Kumaun Himalaya, India

AbstractDetailed petrography and modal analysis of 35 sandstone thin sections was carried out to determine petrotectonic setting of the provenance of the Lower Siwalik molasse of southeastern Kumaun Himalaya. The sandstones are fine‐ to coarse‐grained (0.14–0.63 mm), poorly‐ to moderately‐sorted and comprise lithic arenites, sublithic arenites and lithic greywackes. The sandstones invariably belong to the quartzolithic QtFL (Qt, total quartz; F, feldspar; L, lithic grains) and QmFLt (Qm, monocrystalline quartz; Lt, lithic grains plus polycrystalline quartz) petrofacies, and indicate their derivation from a quartzose‐ and transitional‐recycled orogen provenance under sub‐humid climatic conditions. The framework composition of the sandstones comprises abundant monocrystalline and polycrystalline quartz and low‐ to high‐grade metamorphic rock fragments, along with subordinate feldspar, characterized by low ratios of plagioclase to total feldspar, and accessory minerals. The framework composition and petrofacies characters of these texturally submature sandstones suggest their derivation mainly from the nearby located Great Himalaya terrane and subordinately from the Tethys and Lesser Himalayan terranes. A comparison of the data presented here with the previous similar data from Lower Siwalik of northwestern Pakistan, northwestern India, south‐central Kumaun, western Nepal and southeastern Nepal reveals that like the Lower Siwalik rivers in other sections, the Lower Siwalik rivers of the southeastern Kumaun too drained large parts of the Great Himalayan terrane and some parts of the Tethys and Lesser Himalayan terranes.

Petrogenesis and tectonic association of rift-related basic Panjal dykes from the northern Indian plate, North-Western Pakistan: evidence of high-Ti basalts analogous to dykes from Tibet

Rift related magmatism during Permian time in the northern margin of Indian plate is represented by basic dykes in several Himalayan terranes including north western Pakistan. The field relations, mineralogy and whole rock geochemistry of these basic dykes reveal significant textural, mineralogical and chemical variation between two major types (a) dolerite and (b) amphibolite. Intra-plate tectonic settings for both rock types have been interpreted on the basis of low Zr/Nb ratios (< 10), K/Ba ratios (20–40) and Hf-Ta-Th and FeO-MgO-Al2O3 discrimination diagrams. The compositional zoning in plagioclase and clinopyroxene, variation in olivine compositions and major elements oxide trends indicate a vital role of fractional crystallization in the evolution of dolerites, which also show depletion in rare earth elements (REEs) and other incompatible elements compared to the amphibolites. The equilibrium partial melting models from primitive mantle using Dy/Yb, La/Yb, Sm/Yb and La/Sm ratios show that amphibolite formed by smaller degrees (< 5%) of partial melting than the dolerites (< 10%). The trace elements ratios suggest the origination of dolerites from the subcontinental lithospheric mantle with some crustal contamination. This is consistent with a petrogenetic relationship with Panjal trap magmatism, reported from Kashmir and other parts of north western India. The amphibolites, in contrast, show affinity towards Ocean Island basalts (OIB) with a relatively deep asthenospheric mantle source and minimal crustal contribution and are geochemically similar to the High-Ti mafic dykes of southern Qiangtang, Tibet. These similarities combined with Permian tectonic restoration of Gondwana indicate the coeval origin for both dykes from distinct mantle source during continental rifting related to formation of the Neotethys Ocean.

Zircon U–Pb dating and phase equilibria modelling of gneisses from Dinggye area, Ama Drime Massif, central Himalaya

The tectonic affinity of the Ama Drime Massif in central Himalaya remains a subject of debate. We provide evidences of the metamorphic conditions and new geochronological data for orthogneiss and paragneiss in the Riwu area, eastern side of Ama Drime Massif. The peak P–T conditions for garnet gneiss is 13–14 kbar and 750–765 °C using phase equilibria modelling. The zircon U–Pb dating results reveal that the orthogneiss has a crystallization age of 1,848 ± 12 Ma and zircon rims age of 1,767 ± 18 Ma. Three major age peaks characterize all detrital zircons from the paragneisses: 975, 1,161, and 1,749 Ma. These new data integrated with previous literature data indicate that (a) the Ama Drime Massif might be ascribed to the Greater Himalayan Series; and (b) the Himalayan terrane may have been located closer to both the India and Lhasa terranes during the amalgamation of the supercontinent Columbia.

Upper Triassic reef coral fauna in the Renacuo area, northern Tibet, and its implications for palaeobiogeography

Upper Triassic reef corals from the Riganpeicuo Formation in northern Tibet represent important scleractinian coral fauna that help explain the palaeobiogeography of the eastern Tethys region during the Late Triassic period. The corals were discovered in bedded limestone in patch reefs or biostromes of the Renacuo area. In this paper, 15 genera and 25 species are identified and categorized, the systematic composition of these corals and their relationships with other Triassic coral faunas are also discussed. The results show that these corals are composed of the typical elements of the western Tethys, with the following genera and species that are endemic to China: Radiophyllia cf. astylatus, Margarosmilia zogangensis and Conophyllopsis qamdoensis, and the genera Retiophyllia, Margarosmilia, Hydrasmilia, Procyclolites, Pamiroseris, Araiophyllum, Stylophyllopsis, Stylophyllum and Guembelastraea provide important links to the Tethys province. The coral fauna also highlights the connection between the Qiangtang terrane and the Songpan-Ganzi fold belt, but shows that the areas are distinct from the Himalayan terrane. It has been interpreted that the Qiangtang terrane and the Songpan-Ganzi fold belt were in the vicinity of the gradually-closed Paleo-Tethys Ocean, which resulted in the free transmigration of the benthonic organisms of these areas. On the other hand, the Himalayan terrane was separated from the Qiangtang terrane by a wide ocean–meso Tethys during the Late Triassic period, which made it impossible for the benthonic organisms on both flanks to freely migrate toward the opposite continental margins.

The influence of Cretaceous paleolatitude variation of the Tethyan Himalaya on the India-Asia collision pattern

Identifying when, where, and how India and Asia collided is a prerequisite to better understand the evolution of the Himalayan-Tibetan Plateau. Whereas with essentially the same published paleomagnetic data, a large range of different India-Asia collision models have been proposed in the literature. Based upon the premise of a northwards-moving Indian plate during the Cretaceous times, we analyze the significant variations in relative paleolatitude produced by a nearly 90° counterclockwise (CCW) rotation of the plate itself during the Cretaceous. Interestingly, recent studies proposed a dual-collision process with a Greater India basin or post-Neo-Tethyan ocean for the India-Asia collision, mainly in the light of divergent Cretaceous paleolatitude differences of the Tethyan Himalaya between the observed values and expected ones computed from the apparent polar wander path of the Indian plate. However, we find that these varied paleolatitude differences are mainly resulted from a nearly 90° CCW rotation of a rigid/quasi-rigid Greater Indian plate during the Cretaceous. On the other hand, when the Indian craton and Tethyan Himalaya moved as two individual blocks rather than a united rigid/quasi-rigid Greater Indian plate before the India-Asia collision, current available Cretaceous paleomagnetic data permit only multiple paleogeographic solutions for the tectonic relationship between the Indian plate and the Tethyan Himalayan terrane. We therefore argue that the tectonic relationship between the Indian plate and the Tethyan Himalayan terrane cannot be uniquely constrained by current paleomagnetic data in the absence of sufficient geological evidence, and the so-called Greater India basin model is just one of the ideal scenarios.

Neoproterozoic magmatism in eastern Himalayan terrane

Geochronological investigation on gneisses of granitic to leucogranitic compositions in Cuona, south Tibet, reveal that their protoliths formed at 808.8±7.9–816.4±3.4Ma and 855.8±7.0Ma, respectively. Zircon rims from the granitic gneiss record a metamorphic age of 739.4±4.3Ma. Lu-Hf isotopic analyses on zircon grains with Neoproterozoic ages yield negative εHf(t) values from −9.0 to −4.2, and the corresponding two-stage Hf model ages are 1965–2228Ma. Whole-rock geochemical data indicate that all granitic gneisses are K-riched calc-alkali series. These new data together with literature data show that (1) the Himalayan terrane experienced an episode of Neoproterozoic magmatism at 850–800Ma; (2) the Neoproterozoic magma of granitic compositions were derived from partial melting of ancient crusts, possibly due to the thermal perturbation related with the breakup of the Rodinia supercontinent.

The crustal density structures and deformation scratches in the Qinghai-Tibet Plateau

After introducing the principals of the multi-scale scratch analysis method of regional gravity data, this paper presents the results of its application to the Qinghai-Tibet Plateau, producing three sets of density disturbance, ridge coefficient, and edge coefficient images. The density disturbance images can be used to delineate the hardness and rheological properties of continental tectonic units. The ridge coefficient images can be used to delineate deformation belts, and the edge coefficient images can be used to determine positioning boundaries of the structural division of the units. These images provide crustal geological and tectonic information from different aspects with depth information, which are able to give quantitative constrains to any possible tectonic models. To the upper crust, these results are basically coincident with surface geological and tectonic mapping. They can also provide more structural information of the middle and lower crust, which conventionally is hard to be accurately inferred. For instance, the density disturbance images show the source-zones and squeezed flows of channel flows in the lower crust, as well as the position of the subduction front of the Indian plate beneath the Himalayan mountain range. The ridge coefficient images provide the positions of suture zones, deformation and subduction volcanic belts, ancient collision belts and strike-slip zones. By combining with these edge coefficient images, one can draw out tectonic maps with different structural units in the middle and lower crust. For example, very high density terranes such as the Kashmir and Chayuhe, are divided from the Himalayan terrane, giving physical reasons for the formation of the western and eastern structural knots in the India–Eurasia collisional belt. The multi-scale scratch analysis not only provides the plane geometry of structures and deformation belts, but also their depth extension and stereoscopic patterns. For instance, a decrease of the low-density volume from the lower crust to the upper implies possible diapiric intrusions of the low-density channel flows.

Detrital zircon geochronology and Nd isotope geochemistry of the basal succession of the Taebaeksan Basin, South Korea: Implications for the Gondwana linkage of the Sino-Korean (North China) block during the Neoproterozoic–early Cambrian

The paleogeographic configuration of continental blocks around East Gondwana during the Neoproterozoic–early Cambrian is controversial. This study reports the U–Pb ages of detrital zircons and Nd isotopic composition of the Neoproterozoic–early Cambrian succession developed on the Precambrian basement in South Korea, which formed the southeastern portion of the Sino-Korean block (SKB) in its present configuration. Three stratigraphic units are addressed in this study: the Neoproterozoic Jangsan, early Cambrian Myeonsan, and early–middle Cambrian Myobong Formations. Both the Jangsan (white to pink quartz sandstone) and Myeonsan (dark gray ilmenite-rich sandstone/shale) formations are barren and are unconformably and conformably overlain, respectively, by the dark gray, fossiliferous fine-grained Myobong Formations. The Jangsan and Myeonsan Formations contain zircons with Archean–Paleoproterozoic ages, indicative of detritus derived from the local Precambrian basement. In contrast, the Myobong Formation is dominated by Mesoproterozoic to Neoproterozoic zircons, which are not represented in the local Precambrian basement. The Sm–Nd model ages of the Myobong Formation are younger than those of the underlying strata, indicative of significant changes in provenance during the deposition of this formation. Comparison with coeval sediment having Gondwana signatures in the southern margin of the SKB and the Tethyan Himalayan terrane strongly suggests that the Myobong Formation was derived from orogens in East Gondwana. The results of this study reveal that the timing of the Myobong Formation deposition marks the onset of a sedimentation episode on the southeastern margin of the SKB, which was related to the emergence of a vast source province in East Gondwana, possibly aided by the Cambrian transgression onto the SKB. In comparison with the published literature, we argue for the paleogeographic continuity of the SKB with the northern margin of East Gondwana, possibly between northwestern Australia and northeastern India during the Neoproterozoic–early Cambrian.

Depositional environment and provenance of the upper Permian–Lower Triassic Tianquanshan Formation, northern Tibet: implications for the Palaeozoic evolution of the Southern Qiangtang, Lhasa, and Himalayan terranes in the Tibetan Plateau

This article reports the depositional environment and provenance for the Tianquanshan Formation in the Longmuco–Shuanghu–Lancangjiang suture zone, and uses these to better understand the tectonic evolution of this region. Zircons in the andesite of the Tianquanshan Formation yielded concordia ages of 246, 247, and 254 Ma, indicating that the Tianquanshan Formation formed during the late Permian–Early Triassic. The Tianquanshan Formation consists of flysch and ocean island rock assemblages, indicating that the Longmuco–Shuanghu–Lancangjiang Palaeo-Tethys Ocean continued to exist as a mature ocean in the late Permian–Early Triassic. The detrital zircons in the greywackes of the Tianquanshan Formation yielded peak ages of 470–620, 710–830, 910–1080, 1450–1660, and 2400–2650 Ma, indicating the provenance of the Tianquanshan Formation was either Indian Gondwana or terranes that have an affinity with Indian Gondwana in the Tibetan Plateau (i.e. the Southern Qiangtang, Lhasa, and Himalayan terranes). The Ordovician quartzites, Carboniferous sandstones, Carboniferous–Permian diamictites, and the Upper Permian–Lower Triassic greywackes in the Southern Qiangtang, Lhasa, and Himalayan terranes all contain detrital zircons with youngest ages of ca. 470 Ma, indicating their source areas have been in a stable tectonic environment since the Ordovician, and this inference is supported by the continuous deposition in a littoral–neritic passive margin in these regions from the Ordovician to the lower Permian. Combining the present results with regional geological data, we infer that the Southern Qiangtang, Lhasa, and Himalayan terranes were all in a stable passive continental margin along the northern part of Indian Gondwana during the long period from the Ordovician to the early Permian. At early Permian, because of the opening of the Neo-Tethys Ocean, the tectonic framework of this region underwent a marked change to a rifting and active environment.

Dating of detrital zircons from the Dabure clastic rocks: the discovery of Neoproterozoic strata in southern Qiangtang, Tibet

ABSTRACTThis article reports the results of field mapping and the petrology of clastic rocks in the Dabure area, southern Qiangtang, Tibet, together with the results of U–Pb dating of detrital zircons from these rocks. The Dabure clastic rocks are characterized by low compositional and textural maturity, and they have been affected by lower greenschist facies metamorphism. The deposits exhibit the typical features of turbidites. Altogether, 279 detrital zircons were selected for U–Pb dating, and the ages fall into five groups: 550–650, ~800, 900–1100, 1600–1800, and 2300–2500 Ma. In general, the ages of the detrital zircons that are older than ~550 Ma are similar to those found elsewhere in the southern Qiangtang and Himalayan terranes. The most reliable youngest age of a detrital zircon from the Dabure clastic rocks is ~550 Ma. In the southern part of the Tibet Plateau, strata with the same ages and lithologies as the Dabure clastic rocks are widespread, especially in the Himalayan terrane. Combining our data with previous work on the basalts in the Dabure area (the Dabure basalts), we tentatively suggest that the Dabure clastic rocks represent the late Ediacaran (~550 Ma) sedimentary record for the Qiangtang terrane, and that before the late Neoproterozoic the southern Qiangtang terrane was possibly connected to the Himalayan terrane.

New insights into the India–Asia collision process from Cretaceous paleomagnetic and geochronologic results in the Lhasa terrane

To further constrain the India–Asia collisional process, a combined paleomagnetic and geochronologic study has been carried out on the Upper Cretaceous Jingzhushan Formation redbeds and the Lower Cretaceous Dianzhong Formation volcanic rocks dated at ~121–117Ma from the Cuoqin area in the central Lhasa terrane. Stepwise thermal demagnetization successfully isolated reliable characteristic remanent magnetization (ChRM) directions that include dual polarity and pass positive fold tests at 95% and 99% confidence levels, indicating prefolding primary magnetizations. The tilt-corrected site-mean direction for 33 redbed sites is D=316.8°, I=30.2° with α95=5.4°, corresponding to a paleopole at 49.0°N, 344.3°E with A95=5.3°, and the other for 12 volcanic sites is D=350.5°, I=25.5° with α95=7.7°, corresponding to a paleopole at 70.5°N, 292.9°E with A95=7.4°. Our new paleomagnetic results, together with reliable Cretaceous paleomagnetic data obtained from the Lhasa terrane, demonstrate that the southern margin of Asia was located at ~15.1°N during the Cretaceous. Comparison with the apparent polar wander paths (APWP) of India and the Cretaceous–Paleocene paleopoles of the Himalayan terrane suggests that the India–Asia collision was likely a complex process, which consists of the collision of the Lhasa and Himalayan terranes at 54.0±2.1Ma, the longtime subduction of an intra-oceanic basin between the Himalayan terrane and the Indian craton from ~54.0 to ~40.4Ma, and the collision of the Himalayan terrane and the Indian craton at 40.4±4.1Ma. Comparing with the Late Cretaceous average pole of the East Asia APWP reveals that a latitudinal convergence of 780±240km has taken place between the Lhasa terrane and East Asia (the Hexi corridor) since the India–Asia collision; the amount of latitudinal shortening deduced from paleomagnetic data is very consistent with the 600–1000km accommodated by the Cenozoic fold and thrust belts between the Lhasa terrane and Hexi corridor.

Where does India end and Eurasia begin?

The Indus Suture Zone is defined as the plate boundary between India and Eurasia. Here we document geochronological data that suggest that Indian rocks outcrop to the north of this suture zone. The inherited age spectrum of zircons from mylonitic gneiss collected in the southern part of the Karakorum Batholith is similar to those obtained from the Himalayan Terrane, the Pamir and is apparently Gondwanan in its affinity. These data are taken to indicate that the Karakorum Terrane was once a component of Gondwana, or at least derived from the erosion of Gondwanan material. Several continental ribbons (including the Karakorum Terrane) were rifted from the northern margin of Gondwana and accreted to Eurasia prior to India-Eurasia collision. Many therefore consider the Karakorum Terrane is the southern margin of Eurasia. However, we do not know if rifting led to the creation of a new microplate(s) or simply attenuated crust between Gondwana and these continental ribbons. Thus there is a problem using inherited and detrital age data to distinguish what is “Indian” and what is “Eurasian” crust. These findings have implications for other detrital/inherited zircon studies where these data are used to draw inferences about the tectonic history of various terranes around the world.