Tethyan Himalaya Research Articles

Petrology and geochemistry of Upper Jurassic Weimei Formation sandstones in southern Tibet: implications for provenance and tectonic setting

Located within the centre of the Tethys Himalayas, the Weimei Formation of the Rongbu area in southern Tibet is a littoral- neritic sedimentary association composed of clastic rocks and a few shales. Petrologic characteristics and detrital component statistics indicate that sandstone types include lithic quartz sandstones, with the average content of quartz, feldspar and debris being 77%, 9% and 14%, respectively. The provenance of the Weimei Formation is a recycled orogeny, and the aforementioned sandstones generally have high SiO2 levels, low CaO, K2O and Na2O levels and wide ranges of CIA and CIW values. The primitive mantle-normalised trace element spider diagrams showed unstable content of some elements and losses of Ba, P, Sr, K, Ti and other elements in partial samples. Chondrite-normalised rare-earth element (REE) patterns indicate that the sandstones are characterised by an enrichment of LREE, significant fractionation of LREE and HREE and negative Eu anomalies. Further, ratios of Sm/Nd and Cr/Zr and discriminant diagrams (i.e., La/Yb versus ΣREE, ΣREE versus SiO2/Al2O3, La/Th versus Hf and function discrimination diagrams) reveal that sandstones from the Weimei Formation were derived from ancient quartzose sedimentary rocks and volcanic rocks of continental island arc. Many important parameters (i.e., La, Ce, Pb, Th, Hf, Zr, ΣREE, La/Yb, (La/Yb)N, ΣLREE/ΣHREE, Eu/Eu*, Rb/Sr and Zr/Hf) of samples and tectonic setting discriminant diagrams (i.e., Th versus Co versus Zr/10, La versus Th versus Sc, La versus Th and function discriminant diagrams) indicate that the tectonic setting of the Weimei Formation sandstones from the Tethys Himalayas has both characteristics of a passive margin and continental island arc. By comparing the detrital zircon U-Pb ages and Hf isotopic characteristics of the Weimei Formation with the strata whose provenances have been identified and analysing the weathering, petrography and geochemistry characteristics of Weimei Formation sandstones and the paleogeography conditions of the northern margin of the India craton within the Late Jurassic epoch, we inferred that Weimei Formation sandstones were mainly sourced from the Precambrian metamorphic rocks of the India craton, simultaneously, the sandstones also received minor sedimentary materials from earlier Tethys Himalaya strata whose provenances contained volcanic rocks of the nearby Gangdese volcanic belt. After experiencing weak to moderate weathering, denudation and long-distance transport, the sedimentary materials eventually migrated to the shelf and the top of the continental slope on the northern margin of the Indian continent, where the materials later participated in diagenesis.

A new cryptostome bryozoanPtilotrypafrom the Upper Ordovician Yong Limestone Formation: Tethyan sequence of Kumaun Higher Himalaya, India

AbstractA new species of the Paleozoic bryozoan genusPtilotrypaof the order Cryptostomata is described from the lower part of the Yong Limestone Formation, Katian, Upper Ordovician of the Kumaun Tethys Himalaya:Ptilotrypa bajpaiinew species. The presence of the genusPtilotrypain the Tethyan Himalaya suggests paleogeographic connections to the Upper Ordovician of North America and, consequently, Upper Ordovician age for the lower part of the Yong Limestone Formation. This species displays a reticulate colony shape, which suggests an efficient filtering capacity in an environment with a high primary production. Morphological peculiarities and systematic assignment of the genusPtilotrypaare discussed.UUID:http://zoobank.org/898276c8-2924-4da2-ae96-3392cb2ebbc3

Japan-Nepal Joint Student Himalayan Exercise Program 7 Years

A geotraverse connecting the Kaligandaki and the Tinau rivers via Pokhara in Western Nepal covers all geologic zones of the Himalayan Orogen from the Tethys Himalayan Zone in the north to the Gangetic Plain in the south. The Student Himalayan Exercise Program has aimed to conduct tours of the above geotraverse, provided for Japanese and Nepalese students. The preparation of the program started in 2008, and the practical content of the tour was decided in December 2010 by collecting ideas from several Himalayan geologists in Japan and Nepal and receiving consent of 17 geoscience-related university departments, committing them to give education points for the participation in the exercise, or to examine the possibility of it. After collecting ideas from and sending call-for-participants to geoscience-related departments of over 60 Japanese universities, and after negotiations with several Nepalese trekking agencies, the first Student Himalayan Exercise Tour (SHET) was conducted in March 2012. Since then the exercise tour was conducted every year in March. We are convinced that the SHETs throughout all 7 years (2012-2018) were successful and meaningful, and we therefore suggest that the program should continue further in future.

Coexistence of MORB- and OIB-like dolerite intrusions in the Purang ultramafic massif, SW Tibet: A paradigm of plume-influenced MOR-type magmatism prior to subduction initiation in the Neo-Tethyan lithospheric mantle

The Yarlung Zangbo Suture Zone (YZSZ) of South Tibet is divided by the ZhongbaZhada terrane into two subparallel ophiolitic belts in its western end. The peridotite massifs of the southern belt tectonically overlie the Tethyan Himalaya sequence. The Purang peridotite body in this belt is intruded by two groups of dolerite dikes, providing significant compositional, geochronological, and isotopic information about the melting history of the Neo-Tethyan mantle. U-Pb ages of zircons separated from dolerites show that peridotites of West Purang were intruded by an early generation of dikes at 138.5 +/- 2.0 Ma (Valanginian). These dolerites show ocean island basalt (OIB)-type normalized multi-elemental profiles and Sr-Nd isotopic signatures [(La/Yb)(N )= 13-16], high initial Sr-87/Sr-86 ratios (0.70598-0.70765), and low epsilon(Nd)(t) values (-2.6 to -2.3). Zircons separated from this group of dolerites have slightly radiogenic epsilon(Hf)(t) values (+2.6 to +4.6). The next generation of dolerite dikes intruded the East Purang peridotites between 124.5 +/- 2.5 Ma and 124.4 +/- 3.2 Ma (Aptian). These East Purang dolerites show normal mid-ocean ridge basalt (N-MORB)-type normalized multi-element patterns [(La/Yb)(N) = 0.6-0.9] with noticeable negative Nb and Th (+/- Ti) anomalies, and have high Sr-87/Sr-86((i)) (0.70295-0.70618) and high epsilon(Nd)(t) values (+7.7 to +9.2). Zircons separated from the East Purang dolerites show strongly radiogenic epsilon(Hf)(t) values (+3.5 to +17.0).Semiquantitative geochemical modeling demonstrates that the parental magmas of West Purang dolerites were generated from 5 %-10 % polybaric partial melting of a deep-seated juvenile asthenospheric source enriched by plume-type components. In contrast, the parental melts of East Purang dolerites were derived from more than 20% melting of a juvenile spinel-bearing MORB-type mantle source that was modified by subduction-related melts/fluids to a minor extent. A possible tectono-magmatic model for the petrogenesis of the Purang ophiolitic massif could be linked to incipient continental rifting and subsequent oceanic seafloor spreading associated with decompression upwelling of an asthenospheric source contaminated by plume-type components. This plume-proximal seafloor spreading-system was succeeded by the initiation of Neo-Tethyan intra-oceanic subduction close to the active continental margin of Eurasia during the Early Cretaceous.

The Langjiexue Group is an in situ sedimentary sequence rather than an exotic block: Constraints from coeval Upper Triassic strata of the Tethys Himalaya (Qulonggongba Formation)

The Upper Triassic Langjiexue Group in southeastern Tibet has long been an enigmatic geological unit. It belongs tectonically to the northern Tethys Himalayan zone, but provenance signatures of the detritus it contains are significantly different from those of typical Tethys Himalayan sandstones. Because the Langjiexue Group is everywhere in fault contact with Tethys Himalayan strata, its original paleogeographic position has remained controversial for a long time. According to some researchers, the Langjiexue Group was deposited onto the northern edge of the Indian passive continental margin, whereas others interpreted it as an independent block accreted to the northern Indian margin only during final India-Asia convergence and collision in the Paleocene. This study compares the Langjiexue Group and coeval Upper Triassic strata of the southern Tethys Himalayan zone (Qulonggongba Formation). Our new provenance data indicate that Qulonggongba Formation sandstones contain common felsic volcanic rock fragments, minor plagioclase, and euhedral to subhedral zircon grains yielding Late Paleozoic to Triassic ages. These provenance features compare well with those of the Langjiexue Group. Because the Qulonggongba Formation certainly belongs to the Tethys Himalayan zone, the provenance similarity with the Langjiexue Group indicates that the latter is also an in situ Tethys Himalayan sedimentary sequence rather than part of an exotic block. Volcanic detritus including Late Paleozoic to Triassic zircon grains in both Langjiexue Group and Qulonggongba Formation are interpreted to have been derived from the distant Gondwanide orogen generated by Pan-Pacific subduction beneath the southeastern margin of Gondwana. The Qulonggongba Formation, deposited above marlstones of the lower Upper Triassic Tulong Group, is overlain by India-derived coastal quartzose sandstones of the uppermost Triassic Derirong Formation. Deposition of both the Qulonggongba Formation and the Langjiexue Group were most likely controlled by regional tectonism, possibly a rifting event along the northern margin of Gondwana.

History of subduction erosion and accretion recorded in the Yarlung Suture Zone, southern Tibet

Abstract The history of pre-Cretaceous subduction accretion and erosion along the Yarlung Suture Zone remains poorly constrained. We present new geological mapping along c. 200 km of the suture zone, 4881 detrital zircon U–Pb ages, and sandstone petrography for the subduction complex and Tethyan Himalayan strata. We provide the first documentation of the c. 158 Ma marine Xiazha Formation, which contains volcanic clasts of intermediate to felsic volcanic rocks and ooids with both calcareous and volcanic cores. Based on our new data and synthesis of published data, we present a model in which the Zedong arc represents the southwards migration of the Gangdese arc onto a forearc ophiolite that was generated proximal to the southern Asian margin during Neotethyan slab rollback at 160–150 Ma. This contrasts with previous suggestions that the Zedong arc, Yarlung ophiolites and subduction complex rocks developed above an intra-oceanic subduction zone thousands of kilometres south of Asia. Although Gangdese arc magmatism began in the Middle Triassic, the only forearc units preserved are 160 Ma until collision between the Xigaze forearc basin and Tethyan Himalaya at c. 59 Ma. This suggests that almost all pre-Cretaceous forearc assemblages have been removed by subduction erosion at the trench.

Paleomagnetic results of Cretaceous cherts from Zhongba, southern Tibet: New constraints on the India-Asia collision

An oceanic Greater Indian Basin was hypothesized to have formed between ∼120 Ma and ∼65 Ma by regional extension that separated the cratonic India from its northern margin of Tethyan Himalaya (TH). However, the lack of paleomagnetic data from this critical time interval in the TH marks an important gap in our knowledge about the tectonic evolution of the Greater India. We have conducted a paleomagnetic study of a Cretaceous marine succession in Zhongba, southern Tibet that consists of predominantly purple reddish cherts and siliceous limestone. Paleomagnetic samples from 12 sites were subjected to stepwise thermal demagnetization that revealed either two- or three-component magnetizations with the high-temperature component (HTC) typically unblocked at ∼650 °C. The HTCs exhibit dual polarities that yield a positive reversed test at 95% confidence level, suggesting a primary origin of the remanence. With chronologic constraints from the combined analysis of the magnetostratigraphic and radiolarian data, the HTCs yield a mean of Ds = 336.9°, Is = −50.7°, ks = 18.0, α95 = 5.3° for the ∼120.8–93.9 Ma interval of the TH, which corresponds to a paleopole at 25.0°N, 285.7°E (dp/dm = 4.8/7.1°). The apparent polar wander path (APWP) of the TH overall resembles that of cratonic India, suggesting no polarward separation that is sufficiently large to merit an oceanic basin between the TH and cratonic India. Therefore, our new reliable paleomagnetic data from the critical time interval do not support the Greater Indian Basin hypothesis and its implied dual collisional processes between India and Asia. On the other hand, the APWPs exhibit relative shifts for the post-120 Ma segment and the pre-130 Ma segment, indicating relative motions between the TH and cratonic India that most likely resulted from shearing along boundary-parallel faults during the India-Asia collision.

Detrital zircon provenance investigation from the Neoproterozoic successions of the South China Block: Paleogeographic implications

We report U-Pb isotopic data for detrital zircons from the Late Neoproterozoic Dengying Formation on the northern margin of the Yangtze Block and the other published Neoproterozoic U-Pb isotopic data in the South China Block (SCB), which provide critical constraints on the provenance of these sediments and further shed light on the Neoproterozoic paleogeographic evolution of the SCB in the context of the Rodinia and the succeeding Gondwana supercontinents. The SCB-northern India provenance linkage has started from the Cryogenian. Single Neoproterozoic zircon population from the Upper Cryogenian suggests local detritus supply and the western margin of the Yangtze Block was possibly on an arc setting. Therefore, we speculate that the SCB was independent or located along the margin of Rodinia supercontinent during the Cryogenian. Detrital zircon age spectrum of this study shows similarity with the Cryogenian samples in the eastern Yangtze Block, but with the addition of ‘Pan-African’ age population, which implies that the SCB-India assemblage had been linked with the Gondwana supercontinent during the Ediacaran. Except for a small amount of recycled materials, the Late Neoproterozoic detritus in part of the western Yangtze Block were predominantly derived from the Panxi-Hannan Belt. Early Paleozoic detrital zircon age spectrum of the Tethyan Himalaya is similar with the Late Neoproterozoic age spectra of the Cathaysia Block, whereas appears to be different from the Late Neoproterozoic age spectra of the western Yangtze Block, which implies that the northern India was probably linked with the southern margin of the SCB during the Ediacaran time interval. Finally, the SCB assembled with the western Australia during the Early Paleozoic.

Coda Q estimation for Kinnaur region and surrounding part of NW Himalaya

Spatial variation of coda wave attenuation is obtained for the Kinnaur Himalaya using the single backscattering model based on the data of 376 local earthquakes ranging in magnitude from 1.5 to 4.5. A frequency-dependent S-coda wave quality factor, Qc = 69f1.0 (Qc = Q0fn), is obtained at eight central frequencies between 1.5 and 24 Hz for epicenter distance ≤ 30 km. The “n” values are found to vary highly, maximum in the tectonically and seismically active High Himalaya, intermediate in the seismically active Kaurik-Chango region, and least in the Spiti valley. Q0 (Qc at 1 Hz) is high in the High Himalaya, with values ranging from 87 to 109 which matches with already published works. It decreases towards NNE, the value is lowest in the Tethys Himalaya which varies between 49 and 55. To investigate attenuation with increasing depth, the Qc is estimated at eight coda wave window lengths between 20 and 90 s. With increasing window length, equivalent to increasing lapse times, the Q0 increases from 46 ± 3 to 493 ± 34 and n value decreases from 1.07 to 0.58. Further by dividing the entire coda wave data into four groups of epicenter distances, i.e., 0–25, 26–50, 51–75, and 76–100 km, Qc relations are estimated to vary as 111f0.93, 183f0.80, 264f0.73, and 296f0.71, respectively, for four groups. The increase of Qc with increasing lapse time is interpreted as a decrease of heterogeneity with depth. The data is reasonably fit in the power-law decay of turbidity.

The Himalayan Foreland Basin from collision onset to the present: a sedimentary–petrology perspective

Abstract This chapter summarizes the available stratigraphic, petrographical and mineralogical evidence from sediments and sedimentary rocks on the evolution of the Himalayan belt and its associated foreland basin. The use of compositional signatures of modern sediments to unravel provenance changes and palaeodrainage evolution through time is hampered by a poor match with detrital modes of ancient strata markedly affected by selective chemical dissolution of unstable minerals during diagenesis. Only semi-quantitative diagnoses can thus be attempted. Volcanic detritus derived from Transhimalayan arcs since India–Asia collision onset at c. 60 Ma was deposited onto the Indian lower plate throughout the Protohimalayan stage, with the exception of the Tansen region of Nepal that is characterized by quartz-arenites yielding orogen-derived zircon grains. During the Eohimalayan stage, begun in the late Eocene when most sedimentation ceased in the Tethys Himalayan domain, low-rank metasedimentary detritus was overwhelming in the central foreland basin, where a widespread unconformity developed spanning locally as much as 20 myr. Volcanic detritus from Transhimalayan arcs remained significant in northern Pakistan. Arrival of higher-rank metamorphic detritus since the earliest Miocene, and the successive occurrence of garnet, staurolite, kyanite and finally sillimanite, characterized the Neohimalayan stage, when repeated compositional changes in the foreland-basin succession document the stepwise propagation of crustal deformation across the Indian Plate margin and widening of the thrust belt with exhumation of progressively more external tectonic units. The correspondence in time between the activity of major thrusts and petrofacies changes indicates a promising approach to accurately reconstruct the geological evolution of the coupled orogen–basin system. Conversely, a poor conceptual framework and the general reliance on ad hoc mechanisms to explain phenomena unpredicted by simplified models represent major factors limiting the robustness of palaeotectonic interpretations. Improved knowledge requires taking into full account the dynamic role played by still poorly understood subduction processes – rather than exclusively the effect of passive loading – as well as the role played by the presence of inherited structures on the downgoing Indian Plate, which control both lateral variability of orogenic deformation and the location of depocentres in the foreland basin.

Multiproxy Isotopic and Geochemical Analysis of the Siwalik Sediments in NW India: Implication for the Late Cenozoic Tectonic Evolution of the Himalaya

AbstractProvenance analysis of the Sub‐Himalayan Late Miocene‐Pleistocene foreland basin deposits (Siwaliks) from the Dehradun reentrant area provides a 10‐Myr long record of the denudation history and tectonic evolution of the northwestern Indian Himalaya. We studied Siwalik sediments exposed along the Mohand‐Rao and Haripur‐Khol sections, using detrital zircon U‐Pb geochronology, major and trace elements, and Sr‐Nd isotope geochemistry. Results suggest that the erosion pattern has been relatively stable since the Late Miocene with sediments derived from the Tethyan Himalayan (THS), Greater Himalayan (GHS), and outer‐ (oLHS) and inner‐Lesser Himalayan (iLHS) sequences. Provenance data indicate that erosional unroofing of the Lesser Himalayan Crystalline sequences (LHCS) initiated around 6 Ma, possibly related to out‐of‐sequence movement of the Ramgarh‐Munsiari Thrust. Our data also suggest erosional recycling of older foreland basin deposits into younger Siwaliks since ~5.5 Ma, which may indicate the time of thrust propagation from the Lesser Himalaya into the foreland basin. While the iLHS has been exposed to erosion since at least ~10 Ma, the Siwaliks were dominated by materials derived from the GHS and THS sources. We interpret these results as an indication that tectonic uplift and erosion of the orogenic wedge occurred in response to duplexing of the iLHS and concomitant high topography and rock uplift rate in the Greater and Tethyan Himalaya. Comparing the provenance of the Siwalik sediments with that of the modern Ganga and Yamuna river sediments further indicates that deposition during the Late Cenozoic was most likely accomplished by southward flowing transverse Himalayan rivers, analogous to the modern ones.

Paleomagnetic and Geochronological Results From the Zhela and Weimei Formations Lava Flows of the Eastern Tethyan Himalaya: New Insights Into the Breakup of Eastern Gondwana

AbstractThe breakup of eastern Gondwana is among the hottest topics in the Earth sciences because of its effect on global climate during the Jurassic‐Cretaceous, its influence on the evolution of life, and its importance to paleogeographic reconstruction. To better constrain the Jurassic and Cretaceous paleogeographic position of the Tethyan Himalaya and the breakup of eastern Gondwana, a combined paleomagnetic and geochronological study was performed on the Zhela and Weimei Formations lava flows, dated at ~138–135 Ma, in the Luozha area of the eastern Tethyan Himalaya. Both positive fold and reversal tests together with a maximum grouping at 100% unfolding indicate that the characteristic remanent magnetization directions are primary magnetizations acquired before folding. The tilt‐corrected directions yielded a paleopole at 0.9°N, 293.4°E with A95 = 7.0° and a corresponding paleolatitude of 53.5°S ± 7.0°S for the Luozha sampling area (28.9°N, 91.3°E), validating that the original erupted position of the Zhela and Weimei Formations lava flows was located in the center of the Kerguelen mantle plume. Our new results, together with the published paleomagnetic, geochronological, and geochemical results, demonstrate that the Comei‐Bunbury large igneous province originated from the Kerguelen mantle plume. The temporal and spatial relationships between the Comei‐Bunbury large igneous province and the Kerguelen mantle plume indicate that eastern Gondwana initially rifted at ~147 Ma and that the Indian Plate fully separated from the Australian‐Antarctic Plate before ~124 Ma.

Early Cretaceous bimodal magmatism in the eastern Tethyan Himalayas, Tibet: Indicative of records on precursory continental rifting and initial breakup of eastern Gondwana

In this study, we report a bimodal magmatic suite of gabbroic-granitic rocks in the Cuona area of the eastern Tethyan Himalayas, which is related to the rifting event between Greater India and western Australia in eastern Gondwana. Whole-rock major and trace elements, SHRIMP zircon U-Pb geochronology and Hf isotopic analysis were conducted to reveal the petrogenesis of the bimodal suite and through this to explore the tectonic implications. Our main findings include the following. First, the gabbros and granites were emplaced synchronously at 140–137 Ma, considering the field relationships they comprise a bimodal suite. Second, the gabbros are enriched in light rare-earth-elements (LREE), depleted in heavy rare-earth-elements (HREE) with slight Eu anomalies, and have εHf(t) values of +0.04 − +8.30, which as a whole, suggests that they were derived from an ocean island basalt (OIB)-like mantle source. Third, the granites display low MgO, CaO, and Al2O3, marked enrichment in LREE, highly refracted HREE with strongly negative Eu anomalies and εHf(t) values of −2.01 to +1.71, all of which ultimately gives the characteristics of A1-type granites. Based on these observations, we propose that the bimodal suite is formed in a continental rift. Specifically, the gabbros originated from the mantle plume, whereas the granites derived from the upper crust with garnet-bearing metapelite. This rifting event initiated at 140 Ma, which places bounds on the initial breakup of eastern Gondwana, specifically the separation of Greater India from western Australia.

Calcareous algae from the Ordovician succession (Thango Formation) of the Spiti Basin, Tethys Himalaya, India

AbstractThe calcareous algae Dasyporella silurica, Moniliporella multipora and Vermiporella fragilis are reported for the first time from the Middle Ordovician (Dapingian to Darriwilian) Thango Formation of the Spiti Basin of northern India (Pin Valley, Tethys Himalaya). Moniliporella multipora is reported for the first time from the entire Spiti Basin. This algal assemblage is broadly comparable to that of the directly overlying Takche (=Pin) Formation in the Spiti Basin, as well as that reported from the Ordovician succession of the Tarim Basin and from Kazakhstan. The presence of these calcareous algae is of biogeographical and biostratigraphical significance as it indicates a shallow marine depositional environment for the Thango Formation of the Spiti Basin.

Discussion on “Calcareous algae from the Ordovician succession (Thango Formation) of the Spiti Basin, Tethys Himalaya, India”

Discussion on “Calcareous algae from the Ordovician succession (Thango Formation) of the Spiti Basin, Tethys Himalaya, India”

Garnetiferous Metamorphic Rocks in Jaspa Granite, Himachal Pradesh, India:Implication of Tethyan Himalayan Metamorphism and Tectonics

Garnetiferous Metamorphic Rocks in Jaspa Granite, Himachal Pradesh, India:Implication of Tethyan Himalayan Metamorphism and Tectonics

Metamorphic P-T path and SIMS zircon U-Pb dating of amphibolite of the Namche Barwa Complex, southeast Tibet, China

Amphibolite from the core and the outer part of the Namche Barwa Complex (NBC), southeast Tibet, experienced upper amphibolite facies metamorphism and records clockwise metamorphic P-T paths. Prograde (M1), peak (M2) and retrograde (M3) metamorphic mineral assemblages were identified in both amphibolite types. The M2 P-T conditions in the core and outer part of the NBC are similar: Zhibai amphibolite (ZBA, from the core), ~750 °C/10 kbar; Paixiang amphibolite (PXA, from the outer part), 670–750 °C/ 8.5–10.5 kbar. SIMS zircon U-Pb dating suggests that the protolith of PXA (the outer part of the NBC) formed at ~90–80 Ma, similar to the mafic dykes within the Tethyan Himalaya. This magmatism is probably related to tectonic events on the northern Indian passive margin before its collision with the Eurasian Plate. Furthermore, zircon records metamorphism from Oligocene to late Miocene (~30 Ma to ~10 Ma) in the ZBA, while PXA only documents a Miocene metamorphic event (~9 Ma). It is inferred that from Oligocene to late Miocene, semi-continuous advection of relatively hot material from the depth might have operated only in NBC core, thus exhuming the ZBA to a shallower level, while this material did not efficiently reach/affect the PXA. At late Miocene (~10 Ma) rapid exhumation started to propagate to the outer part of NBC and both units were amalgamated as a coherent block.

A Stable Southern Margin of Asia During the Cretaceous: Paleomagnetic Constraints on the Lhasa‐Qiangtang Collision and the Maximum Width of the Neo‐Tethys

AbstractThe timing of the north‐south collision between two terranes can be determined by the overlap of their paleolatitudes or the change of their convergence rate. For example, the overlapping paleolatitudes of the Lhasa terrane and Tethyan Himalaya and the dramatic decrease in the velocity of the Indian plate are usually ascribed to the India‐Asia collision at ~55 Ma. However, little is known about the paleolatitudinal evolution and velocity change of the Lhasa terrane resulting from the Lhasa‐Qiangtang collision during the Jurassic‐Cretaceous period. To better constrain the velocity change of the Lhasa terrane during this period, to constrain when and where the Lhasa‐Qiangtang collision occurred, and to assess the distribution of land and sea in the Tethyan realm, we provide a high‐quality Cretaceous paleomagnetic pole obtained from the limestone from the western part of the Lhasa terrane, which yields a paleolatitude of ~16.8° ± 1.9°N for the sampling area (32.2°N, 80.8°E) during the time interval of ~113–72 Ma. We compile existing paleomagnetic results from the Lhasa terrane, Qiangtang terrane, Tethyan Himalaya, and India and reveal that the Lhasa‐Qiangtang collision most likely occurred at or near the J/K boundary at ~19°N for the reference point at (32°N, 88°E) and that the Neo‐Tethys reached its maximum width (≥~7450 km) during this period.

A Preliminary Evaluation on the Prospects of Hydrocarbon Potential in the Carbonaceous Shales of Spiti and Chikkim Formations, Tethys Himalaya, India

In the present investigation, an attempt has been made to explore the possibility of hydrocarbon prospects in the carbonaceous shale deposits of Spiti and Chikkim formations exposed in the Spiti valley of the Tethys Himalaya. Twenty samples, collected from successive levels of these litho-units, have been subjected to maceral analysis, Rock-Eval Pyrolysis and six samples to Fourier Transform Infra-red Spectroscopy (FTIR) and nuclear magnetic resonance (NMR) analyses. The study reveals the presence of mainly kerogen-III type of organic matter but some of the shale samples have shown a good amount of total organic carbon (TOC) to the tune of 3.19% which is sufficient to produce hydrocarbon. The results indicate the presence of methane occurring as free and fixed hydrocarbon in the shale samples. Few levels are especially rich in hydrocarbon. They have shown encouraging results with potential for generating liquid as well as lighter hydrocarbon. The data is also supported by the FTIR and NMR studies.

Protolith lithostratigraphy of the Greater Himalayan Series in Langtang, Nepal: implications for the architecture of the northern Indian margin

Abstract Reconstruction of the protolith lithostratigraphy of amphibolite-facies metasedimentary rocks of the Greater Himalayan Series (GHS) in Nepal documents a single, long-lived passive-margin succession that was deposited along the northern margin of the Indian Craton. In the Langtang area, Paleoproterozoic gneisses are unconformably overlain by a succession of upper Neoproterozoic–Ordovician fluvio-deltaic quartzite, basinal pelite and psammitic beds that grade upsection into micaceous semipelite and pelite. U–Pb zircon geochronology yields maximum depositional ages between c. 815 and 460 Ma for the GHS in Langtang. Regional variations in the composition and thickness of the GHS along the length of the Himalaya are attributed to siliciclastic depocentres centred on Zanskar in northern India, Langtang and Everest in central to western Nepal, which contrast with coeval marine carbonate shelf deposition in the Annapurna region. The protolith lithostratigraphy documented for Langtang provides a coherent framework for interpreting subsequent Cenozoic Himalayan deformation, specifically the homogeneously distributed layer-normal shortening (i.e. flattening) and layer-parallel stretching (i.e. transport-parallel stretching) that characterizes the GHS. Within the context of a single protracted northern Indian marginal sedimentary succession, the distinction between the Lesser, Greater and Tethyan Himalaya is structural rather than lithostratigraphic in origin.