Shyok Suture Research Articles

The geology of the Shyok suture zone: evidence for Cretaceous extension of the southern Eurasian margin and Eocene India-Eurasia collision

The geology of the Shyok suture zone: evidence for Cretaceous extension of the southern Eurasian margin and Eocene India-Eurasia collision

Geothermal resources and deep tectonic in Leh Ladakh (NW Himalaya), India: Inference from magnetotelluric studies

The geothermal resources and their connectivity with the deep tectonic are meaningful to understand through their structural geometry in the NW Himalayas. Therefore, over the NW-SE profiles, 23 audio Magnetotelluric (AMT) sites and over the SW-NE profile, 15 broadband Magnetotelluric (BBMT) sites were carefully chosen to provide the detailed structure. The electrical models were produced from a 2-D inversion algorithm based on the non-linear conjugate gradient method. The Chumathang-Mahe and Puga-Sumdo regions offer excellent geothermal potential as heat/fluid passes through the Mahe Fault (MF), Zildat Fault (ZF) and Kiagor Tso Fault (KTF). These faults are well revealed in the electrical models beneath the subsurface. The Puga Valley has an excellent geothermal resource at shallow depth. A ∼1000 m thick sulfide mineral body is defined with high conductivity (∼1 Ω-m). The crustal structure shows a highly conductive mid-crust beneath the Ladakh batholiths with no manifestation roots. The signs of the Indus-Tsangpo Suture Zone (ITSZ) and Shyok Suture Zone (SSZ) are well represented in the crustal model and are associated with the steep-dipping faults. The Chumathang-Mahe and Puga-Sumdo geothermal regions are connected with low resistivity body (C1) at shallow depths in the crustal model along the SW-NE profile and offer a path for deep fluid flow. The frictional heat generated in the process of the Indian plate subducting beneath the Tibetan plateau and the collision zone between India and Asia carried to melt. The high heat surface flow indicates the thermal origin of low resistivity. Thus, a ∼10 sq. km low resistivity reservoir is identified beneath the Tso Morari dome in the crustal model that overlies a resistivity feature. The high conductivity at mid-crust determined at active tectonic fabric may be potential geothermal resources yielding high well-productivity.

Paleomagnetic Constraint on the Age of the Shyok Suture Zone

AbstractThe India‐Eurasia collision is a key case study for understanding the influence of plate tectonic processes on Earth's crust, atmosphere, hydrosphere, and biosphere. However, the timing of the final India‐Eurasia continental collision is debated due to significant uncertainty in the age of the collision between the Kohistan‐Ladakh arc (KLA) and Eurasia along the Shyok suture zone. Here we present paleomagnetic results that constrain the Karakoram terrane in northwest India to a paleolatitude of 19.9 ± 8.9°N between 93 and 75 million years ago (Ma). Our results show that the Karakoram terrane was situated on the southern margin of Eurasia in the Late‐Cretaceous. Our results indicate that the KLA and Eurasian continent had a not converged until <61.6 Ma, placing a Paleocene older limit on the age of final closure of the Shyok suture zone. This suggests that the India‐Eurasia collision in northwestern India likely occurred after the closure of the oceanic basin between the KLA and Eurasia. The Paleocene collision event affecting India that has been widely interpreted to represent final India‐Eurasia collision instead records the arc‐continent collision between the KLA and the northern edge of India prior to final India‐Eurasia collision. Final India‐Eurasia collision in northwest India most likely occurred after the closure of the oceanic basin between the KLA and Eurasia.

Distribution of Active Faults and Lithospheric Discontinuities in the Himalayan-Tibetan Orogenic Zone Identified by Multiscale Gravity Analysis

The lithospheric structure of the Tibetan Plateau and its adjacent area is a hot topic in geodynamic research. It is important to reveal the mechanism of crustal deformation and tectonic evolution of the study area. In this study, the techniques of wavelet multiscale decomposition and field edge detection were used to study the discontinuities of the lithosphere revealed by multilevel Bouguer gravity anomalies. Specifically, we evaluated the depth characteristics of the major active faults in the study area and identified 15 deep major faults that cut through the lithosphere. They are Chaman fault, Shyok suture zone, Altyn-Tagh fault, Karakash fault, Karakoram fault, Talas-Fergana fault, Kashgarr-Yeshgar transfer system, Rushan-Pshart suture zone, Sangri-Nacuo fault, Main Frontal thrust, Burmese fold belt, Yadong-Gulu fault, Gaoligong fault, Sagaing fault and Nujiang fault. We have also elucidated the tectonic mechanisms of two famous geodynamic phenomena in the Pamir Plateau. The first is the intense intermediate depth seismicity beneath Pamir-Hindukush. It cannot simply be described as the rupture of a subducted residual plate, which could be divided into two distinct tectonic units. One belongs to the Indian plate, the other to the Eurasian plate. Secondly, the mechanism of intense seismicity confined to the western upper crust of the Pamir Plateau could be explained as significant fragmentation of crustal material. Finally, and most importantly, we summarized the coupling mechanism between deep geodynamics and horizontal deformation as observed by modern geodetic techniques. In the upper mantle, the leading edge of the subducting Indian plate reached the SW boundary of Tarim basin and forms a closed structure in western Himalaya. Then, the Tibetan Plateau underwent a tectonic escape towards the east under the continuous compression between the Indian and Eurasian plates. During the process of tectonic escape, the role of the N–S direction normal faults in the Himalayan tectonic zone is limited.

Nature of the Shyok (Northern) Suture Zone between India and Asia: petrology, geochemistry and origin of the Tirit granitoids and associated dykes (Nubra Valley Ladakh Himalaya, NW India)

AbstractThe Shyok Suture Zone is an oceanic remnant of the Neo-Tethyan ocean sandwiched between the Ladakh Batholiths to the south and Karakoram Batholith to the north. The Tirit granitoids in this suture are dark-coloured, relatively rich in ferromagnesian minerals and range from granodiorite–tonalite to gabbro–diorite in composition. Mafic igneous enclaves are quite common and they are intruded by NW–SE parallel doleritic and aplitic dykes. The Tirit granitoids have a wide range of major oxide compositions (SiO2 = 52.1–72.11 wt %, TiO2 = 0.21–1.23 wt %, Al2O3 = 11.42–13.52 wt %, MgO = 1.69–10.69 wt % and CaO = 3.24–9.31 wt %) and show calc-alkaline, metaluminous, I-type characteristics, transitional between primitive and mature arc continental plutons. Rare earth elements (REE) show considerable enrichment in light REE (LREE) as compared to the heavy REE (HREE). Late Cretaceous U/Pb dates (74–68 Ma) show that they formed during the pre-collision northward movement of India. The Tirit dykes are only slightly younger and probably part of the same episode.

Geochemical characteristics and petrogenesis of magmatic rocks of the Shyok suture zone, NW Ladakh Himalaya, India

Geochemical characteristics and petrogenesis of magmatic rocks of the Shyok suture zone, NW Ladakh Himalaya, India

Geochemical analysis of magmatic rocks from Shyok Suture Zone (SSZ) Trans-Himalaya, NW India: Insights for geodynamic evolution of the terrane

The present study discusses the geochemistry of the Early Cretaceous Shyok and Nubra volcanics from the Shyok Suture Zone (SSZ), Trans-Himalaya. Geochemically, the studied volcanic rocks belong to calc-alkaline magma series and vary in composition from basalt-basaltic andesite-andesite-dacite. The SSZ rocks are enriched in light rare earth elements (LREE: La, Ce, Nd) and large ion lithophile elements (LILE: Rb, Ba, U, K, Pb and Sr) while depleted in high field strength elements (HFSE: Nb, P and Ti), analogous to subduction zone magmatism. Their perturbed LILE concentrations coupled with higher 87Sr/86Sr ratios reflect possible influence of post-crystallization processes. Trace element modelling reflects variable degrees of partial melting (~5–30%) of a metasomatised spinel peridotite mantle source followed by fractional crystallization of clinopyroxene and amphibole along with olivine and plagioclase. The Shyok and Nubra volcanics depict positive εNd(t = 110 Ma) values (+2.3 to +5.2), slightly lower than the contemporary Chalt fore-arc boninites (+6.3 to +8.0) and adjoining intra-oceanic island arc rocks along the Indus Tsangpo Suture Zone (ITSZ) such as Nidar ophiolite (+6.8 to +8.7), Shergol gabbros (+5.1 to +8.4) and Dras volcanics (+5.8 to +7.0), therefore reflecting depleted mantle characteristics. In contrast to the ITSZ rocks, the Shyok and Nubra volcanics have enriched LREE-LILE characteristics, indicating their derivation from isotopically depleted and elementally (LREE-LILE) enriched mantle wedge sources. Thus, based on the geochemical and isotopic signatures of the SSZ rocks and their association with continentally derived sediments, we suggest an Andean-type arc system as opposed to ITSZ rocks and associated oceanic sediments, representing intra-oceanic arc system.

Discovery of an Entrapped Early Permian (ca. 299 Ma) Peri-Gondwanic Sliver in the Cretaceous Shyok Suture of Northern Ladakh, India: Diverse Implications

GSA Logo HomeJoinGSA StoreDonateContact Toggle search Toggle navigation Sign In Toggle Search Advanced Search HomeJoinGSA StoreDonateContact AboutToggle Scientific DivisionsGeographic SectionsLeadershipCommitteesHonors & AwardsWho We AreDiversityEthicsGSA InternationalGSA Foundation MembershipToggle Join / RenewBenefits and DuesGet InvolvedCampus RepsMember RecognitionCode of Ethics PublicationsToggle JournalsGSA TodayBooksGSA StoreInfo & ServicesGeofacetsMeeting Abstracts EventsToggle Annual MeetingFuture Annual MeetingsSection MeetingsPast Meetings & AbstractsPenrose ConferencesThompson Field ForumsField ExperiencesGeoscience CalendarEvents Code of Conduct Education & CareersToggle GeoCareersGeoscience Job BoardGrants & ScholarshipsField ExperiencesNetworking/MentoringK-12 Educator SupportWebinar LibraryGeologic Time Scale Science PolicyToggle News from The HillGSA Policy RolesPosition StatementsCritical IssuesCongressional Science FellowshipScience Policy FellowshipEngage with Policymakers NewsToggle Science Communication FellowshipScience Communication InternshipNews ReleasesNewsroom (for Journalists)GSA In The NewsAnnual Meeting NewsroomSpeaking of Geoscience BlogGSA ConnectionGeoScene Newsletter Keyword Search Home » Publications » GSA Today Abstract View GSA Today Full Text | PDF Discovery of an Entrapped Early Permian (ca. 299 Ma) Peri-Gondwanic Sliver in the Cretaceous Shyok Suture of Northern Ladakh, India: Diverse Implications Rajeev Upadhyay Dept. of Geology (CAS), Kumaun University, Nainital-263001 (Uttarakhand), India, rajeevntl1@gmail.com Saurabh Gautam Birbal Sahni Institute of Palaeosciences, 53 University Road, Lucknow-226007, India Ram Awatar 7/464 A, Vikas Nagar, Lucknow-226022, India Abstract In a significant breakthrough, we report the first discovery of twenty-six genera and thirty-five species of Early Permian (Asselian–Sakmarian and Artinskian; 299 Ma to 276 Ma) Gondwanic palynomorphs from a tectonically emplaced metasedimentary sliver of Shyok Ophiolitic Mélange of the India-Asia Collision zone of Northern Ladakh, India. These palynofloral assemblages are of peri-Gondwanian (Cimmerian) origin and have a strong affinity with the Gondwana assemblage of peninsular India. Similar palynofloral assemblages are also known from Extra-Peninsular India, Salt Range, Karakoram, Antarctica, Australia, South Africa, and South America. The occurrence of Gondwanic sliver within the Shyok Suture is interpreted as a thin flake of active continental margin of peri-Gondwanic microcontinent/Kshiroda plate, which was sliced off during the subduction/collision process, between Ladakh block and Karakoram–Qiangtang-Lhasa terrane and amalgamated with obducted remnants of the accretionary prism of the nascent Shyok Suture. The Shyok Suture closed during the mid- to Late Cretaceous period. Subsequent syn- and post-collision synkinematic episodes tectonically juxtaposed the peri-Gondwanic sliver in the tectonized zone of Shyok Ophiolitic Mélange. The India-Asia collision, which took place ca. 60–50 Ma with the demise of Neo-Tethys Ocean, along the Indus Tsangpo Suture Zone, modified the geometry of accreted ophiolitic stack of the Shyok Suture. Manuscript received 16 Aug. 2020. Revised manuscript received 23 Sept. 2021. Manuscript accepted 27 Oct. 2021. Posted 19 Nov. 2021. © The Geological Society of America, 2021. CC-BY-NC. https://doi.org/10.1130/GSATG481A.1 Search Google Scholar for Rajeev Upadhyay Saurabh Gautam Ram Awatar Search GSA Today Publications Journals Geology GSA Bulletin Geosphere Lithosphere Environmental & Engineering Geoscience GSA Today Full Issue Archive Features Info for Authors Advertising Geoscience Job Board Books Special Papers Field Guides Memoirs Reviews in Engineering Geology DNAG Digital Maps Map & Chart Series Memorials GSA Store Info & Services About Our Publications Editors Author Info Manuscript Submission Data Repository Ethical Guidelines Copyright Subscriptions How to Access Publications Advertising Data Policy Open Access Geofacets Meeting Abstracts Facebook Twitter Instagram YouTube LinkedIn Wordpress HomeAdvertisingFAQsSearchPrivacy PolicyJobs at GSA © 2021 The Geological Society of America, Inc.

Jurassic–Cretaceous arc magmatism along the Shyok–Bangong Suture of NW Himalaya: formation of the peri-Gondwana basement to the Ladakh Arc

The Jurassic–Cretaceous Tsoltak Formation of the eastern borderlands of Ladakh Himalaya consists of conglomerates, sandstones and shales, and is intruded by norite sills. It is the oldest sequence of continent-derived sedimentary rocks within the Shyok Suture. It also represents a rare outcrop of the basement rocks to the voluminous Late Cretaceous–Eocene Ladakh Batholith. The Shyok Formation is a younger sequence of volcaniclastic rocks that overlie the Tsoltak Formation and record the Late Cretaceous closure of the Mesotethys Ocean. The petrogenesis of these formations, ophiolite-related harzburgites and norite sill is investigated through petrography, whole-rock geochemistry and U–Pb zircon geochronology. The youngest detrital zircon grains from the Tsoltak Formation indicate an Early Cretaceous maximum depositional age and a distinctly Gondwanan, Lhasa microcontinent-related provenance with no Eurasian input. The Shyok Formation has a Late Cretaceous maximum depositional age and displays a distinct change in provenance to igneous detritus characteristic of the Jurassic–Cretaceous magmatic arc along the southern margin of Eurasia. This is interpreted as a sign of collision of the Lhasa microcontinent and the Shyok ophiolite with Eurasia along the once continuous Shyok–Bangong Suture. The accreted terranes became the new southernmost margin of Eurasia and the basement to the Trans-Himalayan Batholith associated with the India–Eurasia convergence. Supplementary material: Supplementary figures and Tables S1–S3 are available at https://doi.org/10.6084/m9.figshare.c.5633162

Geochemical modeling, fate distribution, and risk exposure of potentially toxic metals in the surface sediment of the Shyok suture zone, northern Pakistan

The objective of the current study was to assess the contamination of potentially toxic metals (PTMs) in weathered surface sediment, along stream tributaries, and surrounding area of the river Chitral, Shyok suture zone district Chitral, Pakistan. To understand the geochemical features of 113 sediment, samples were collected from the Mirkhani and Drosh area. Then, different statistical tools including the geo-accumulation index (Igeo), cluster analysis (CA), principal component analysis (PCA), and ecological risk assessment (ERA) were used to unravel the origin, intensity, and exposure level of PTMs to control risk and restore the ecosystem within the study area. The results for the PTMs namely nickle (Ni), chromium (Cr), copper (Cu), cadmium (Cd), lead (Pb), zinc (Zn), and cobalt (Co) in Mirkhani and Drosh were in the following ranges: 10–150, 15–210, 15–250, 0.08–1.00, 10–70, 76–240 and 14–51; and 13–240, 17–210, 15–150, 0.08–0.60, 7–140, 47–150 and 13–36 mg/kg, respectively. In consequence, the potential ecological risk caused by Pb, Ni, Cu, Co, Cr, and Zn is reflected by the percentages of samples with an ecological risk index (ERI) greater than one which were 100%, 91%, 100%, 100%, 92%, and 100%, respectively. However, the overall mean decreasing order of ecological risk of PTMs in the district Chitral was Pb > Ni > Cu > Co > Cr > Zn > Cd. Moreover, the PCA yielded 78% variability which indicated that mineral prospects play an important role in the contamination of sediment. Furthermore, the mineral phases of Pb and Zn suggested supersaturation, while that for Cd revealed unsaturation. The results of Igeo, ERI, and CA indicated contamination of PTMs in the study area. The ERI value of Pb, Ni, Cu, Co, Cr, and Zn was higher than 1 suggesting an ecological risk in the study area. Moreover, the current study showed the dominance of geogenic contamination with major contributions from ultramafic rock and known mineral prospects. Therefore, contaminated sediment of the Shyok suture zone is extremely detrimental to the aquatic ecosystem of the study area.

Late Jurassic Changmar Complex from the Shyok ophiolite, NW Himalaya: a prelude to the Ladakh Arc

AbstractThe Shyok Suture in western Himalaya preserves a record of the opening and closure of the Mesotethys Ocean between the Shyok ophiolite and Karakoram terrane prior to the India–Eurasia collision. The formation age of the Shyok ophiolite was unknown, which impeded correlation with similar rocks along the Shyok Suture in Pakistan and corresponding sutures in Tibet. We report the first zircon U–Pb ages of a newly documented suite, here named the Changmar Complex. The Changmar Complex gabbronorite and plagiogranite yielded SHRIMP U–Pb zircon Late Jurassic ages of 159.4 ± 0.9 Ma and 151.9 ± 1.5 Ma. Their highly positive initial εHf values (+14.9 to +16.9) indicate a juvenile mantle origin, without continental crust influence on the magma source. The Shyok ophiolite represents either: (1) a separate island arc that preceded formation of the Cretaceous–Eocene Ladakh Arc; or (2) the oldest magmatism and early stage of the Ladakh Arc. Intrusive and extrusive mafic rocks from the Shyok Suture analysed in this study have typical supra-subduction zone enrichment characteristics in their geochemistry and are classified as part of the volcanic-arc ophiolite. The U–Pb age and Hf isotopic signatures for the Shyok ophiolite are similar to the Late Jurassic Matum Das tonalite within the Kohistan Arc; we therefore suggest that they are part of the same intra-oceanic island-arc system that formed in the Mesotethys Ocean prior to Late Jurassic time.

Closure of India–Asia collision margin along the Shyok Suture Zone in the eastern Karakoram: new geochemical and zircon U–Pb geochronological observations

AbstractNew whole-rock geochemical analyses along with laser ablation multi-collector inductively coupled plasma mass spectrometry U–Pb zircon ages of the granite–rhyolite from the Karakoram Batholith, exposed along the Shyok Valley, NW India, have been performed to understand the timing and geochemical evolution of these magmatic bodies and their implications for the geodynamic evolution of the Karakoram Batholith. New geochronological data on granites and rhyolites along with previously published geochronological data indicate that the Karakoram Batholith evolved during Albian time (~110–100 Ma) owing to the subduction of Tethys oceanic lithosphere along the Shyok Suture Zone. This region witnessed a period of no magmatism during ~99–85 Ma. Following this, the Kohistan–Ladakh arc and Karakoram Batholith evolved as a single entity in Late Cretaceous and early Palaeogene times. Late Cretaceous (~85 Ma) rhyolite intrusions within the Karakoram Batholith show calc-alkaline subduction-related signatures with a highly peraluminous nature (molar A/CNK = 1.42–1.81). These intrusions may have resulted fromc. ~13.8 % to ~34.5 % assimilation of pre-existing granites accompanied by fractional crystallization during the ascent of the magma. The contamination of mantle wedge-derived melts with crust of the active continental margin of the Karakoram most likely enhanced the high peraluminous nature of the rhyolite magma, as has been constrained by assimilation fractional crystallization modelling. Two granite samples from the contact of the Shyok Metamorphic Complex and Karakoram Batholith indicate that the post-collisional Miocene magmatism was not only confined along the Karakoram Fault zone but also extends ~30 km beyond the Shyok–Muglib strand.

Structure of crust and upper mantle beneath NW Himalayas, Pamir and Hindukush by multi-scale double-difference seismic tomography

The India-Asia collision and subsequent subduction initiated the evolution of major tectonic features in the Western Syntaxis. The complex tectonic structure and shallow to deep seismicity have attracted geoscientists over the past two decades. The present research is based on a 3D tomographic inversion of P-wave arrival time data to constrain the crustal and upper mantle structure beneath the NW Himalayas and Pamir-Hindukush region using the Double-difference tomography. We utilized a very large multi-scale dataset comprising 19,080 earthquakes recorded at 397 local and regional seismic stations from 1950 to 2017. The northward dipping seismic zone coinciding with the low velocity anomaly suggests the subduction of the Indian lower crust beneath the Hindukush. The extent of the northward advancing Indian slab increases from east to west in this region. We observed no signs of northward subduction of the Indian plate under the Hindukush beyond 71°E longitude. The Indian plate overturns due south after interacting with the Asian plate beneath the southern Pamir, which correlates with the counter-clockwise rotation of the Indian plate. The Asian plate is also imaged as a southward subducting seismic zone beneath the southern Pamir. In the NW Himalayas, the northward subducting Indian plate appears as a gently dipping low velocity anomaly beneath the Karakoram Block. The stresses caused by the collision and subduction along the Shyok Suture and Indus Suture are translated to the south. The crustal scale seismicity and high velocity anomalies indicate an intense deformation in the crust, which is manifested by syntaxial bends and thrust faults to the south of the Main Mantle Thrust.

Electrical resistivity structures and tectonic implications of Main Karakorum Thrust (MKT) in the western Himalayas: NNE Pakistan

We discovered a conductive zone along Main Karakoram Thrust which could be an indication of flat subduction of Kohistan island arc beneath the Eurasian plate. Kohistan island arc collided with the Karakoram Block of the Eurasian Plate in the Early Cretaceous. However, according to findings of many researchers, the subduction ceased about 75 Ma ago. The presence of the conductive zone is an indication of current magmatism or hydrothermal fluids. Maximum low-frequency band data from Fourteen sites with recording periods of 10−2–103 s was acquired along a profile crossing MKT. Our results reveal the existence of multiple low resistivity zones beneath the region extending from shallow to the depths of more than 100 km. These low-resistivity zones might be a signature of the ongoing magmatic activities or hydrothermal fluids along the Shyok Suture Zone. In addition, we discovered another large conductive body towards the south of the study area which could be a result of uprising magmatic plumes generated by the subducting Indian plate along the Indian suture zone and their entrapment in the overlying Kohistan block.

Pamir Plateau formation and crustal thickening before the India-Asia collision inferred from dating and petrology of the 110–92 Ma Southern Pamir volcanic sequence

The formation of the Pamir is a key component of the India-Asia collision with major implications for lithospheric processes, plateau formation, land-sea configurations and associated climate changes. Although the formation of the Pamir is traditionally linked to Cenozoic processes associated with the India-Asia collision, the contribution of the Mesozoic tectonic evolution remains poorly understood. The Pamir was formed by the suturing of Gondwanan terranes to the south margin of Eurasia, however, the timing and tectonic mechanisms associated with this Mesozoic accretion remain poorly constrained. These processes are recorded by several igneous belts within these terranes, which are not well studied. Within the Southern Pamir, the Albian-Turonian volcanic rocks and comagmatic plutons of the Kyzylrabat Igneous Complex (KIC) provide an important and still unconstrained record of the Pamir evolution. Here we provide the age, origin and the geodynamic setting of the KIC volcanics by studying their petrology, zircon U-Pb geochronology, geochemistry and isotope composition. 17 samples from the KIC volcanics yield U-Pb ages spanning from 92 to 110Ma. The volcanics are intermediate to acidic in composition (SiO2=56–69wt%) and exhibit high-K calc-alkaline and shoshonitic affinity (K2O/Na2O=1–2.2wt%). They show enrichment in LILE and LREE and depletion in HFSE and HREE with negative Ta, Ti and Nb anomalies, suggesting an arc-related tectonic setting for their formation. Low εNd(t) values (from −9.1 to −4.7), relatively high 87Sr/86Sr(i) ratios (0.7069–0.7096) and broad range of zircon εHf values (from −22.6 to −1.5) suggest a mixture of different magma sources. These features suggest that volcanics were derived by crustal under- or intraplating of an enriched subduction-related mantle shoshonitic magmas, by heating and partial melting of the lower crust, and by mixing of both magma components. Our results further imply that the KIC volcanics represent a shoshonitic suite typical of an evolution from active continental arc to post-collisional setting with a steepening of the Benioff zone and thickening of the crust toward the back-arc. This setting is best explained by the subduction - collision transition along the Shyok suture due to accretion of the Kohistan island arc to the Karakoram. This suggests that a significant part of the crustal shortening and thickening accommodated in the Pamir occurred in the Mesozoic before the India-Asia collision with implications for regional tectonic models. This further suggests the Pamir was already a major topographic feature with potentially important paleoclimate forcing such as the monsoonal circulation.

Geological Evaluation of EIGEN-6C4 and GOCE Derived Gravity Models in and around Karakoram Shear Zone, Leh, India

ABSTRACT New generation high resolution gravity models derived from space-borne gravity data, integrated with land based surveys, have enabled understanding of regional gravity field over regions, which are till date considered to be inaccessible for land surveys, especially in mountainous terrains. In this study, we evaluate two high resolution gravity models EIGEN-6C4 and GO_CONS_GCF_2_TIM_R5 in order to understand its usability in identification of meso-scale regional geological features and lithological boundaries around the Karakoram shear zone, in Leh, India. The EIGEN-6C4 is a “hybrid” model integrating data from space-borne sensors and terrestrial data, whereas GO_CONS_GCF_2_TIM_R5 is a model derived from the latest space-borne GOCE sensor. Bouguer gravity anomaly has been derived for both the models and compared. It is seen that, the GOCE derived model pertains to the regional gravity field of the region and compares well with the regional derivative of the EIGEN-6C4 model. Further, the EIGEN-6C4 has been analyzed using horizontal derivatives (dx, dy), analytical signal (ANS) and tilt derivative (TDR) techniques. These, derived maps are then overlain on published geological map of the area to understand the correlation between sub-surface geology vis a vis gravitational signal. The major and distinct geological signatures as derived from the various derivative maps correlate well with the existing geological map. The source boundaries derived from the TDR map agrees reasonably well with the lithological boundaries. Further, the anomaly and derivative maps from EIGEN-6C4 indicates towards a possible continuation of the Shyok suture zone in the region. Therefore, for the given spatial extent of the area under consideration, the GOCE derived model represents the regional field, whereas the EIGEN-6C4 data and derivatives are of sufficient resolution for understanding the geological variability in and around the Karakoram shear zone.

Early Cretaceous subvolcanic calc-alkaline granitoid magmatism in the Nubra-Shyok valley of the Shyok Suture Zone, Ladakh Himalaya, India: Evidence from geochemistry and U–Pb SHRIMP zircon geochronology

The lithounits constituting the Ladakh Himalaya are exposed along the Indus and Shyok Sutures Zones of northwest Himalaya. The Shyok Suture Zone (SSZ) in northern Ladakh represents a highly tectonized zone of a back-arc basin, which is mainly composed of volcano-sedimentary formations (Shyok and Khardung Formations) intimately, associated with intrusive granitoids. In the Nubra-Shyok valley of the SSZ calc-alkaline granitoids of batholithic dimension are exposed in the Tirit region, referred herein as the Tirit granitoids, which are intrusive evidently into the Shyok volcanic (rhyolite) rocks belonging to the Shyok Formation. In this valley the northern margins of granitoids of the Ladakh batholith can also be found intrusive into the metasediments (shale/slate) and metavolcanics of the Shyok Formation. The compositions and crystallization pressures (~66 to 91MPa) of amphiboles in the intrusive Tirit granitoid corroborate a calc-alkaline nature and solidification of Tirit granitoid melt at subvolcanic level equivalent to a minimum of 2.5km to a maximum of 3.5km thick overburden of Shyok volcanics. U–Pb SHRIMP zircons from the Tirit granitoids have yielded mean crystallization ages of 109.4±1.1Ma and 105.30±0.80Ma, which strengthen the idea of Early Cretaceous subduction beneath the Karakoram terrain. Inherited older zircon cores (278–393Ma, 476–519–713–952Ma and 1933Ma) suggest a contribution from heterogeneous Palaeozoic and Proterozoic sources in the generation of the Tirit granitoids similar to those observed elsewhere in the Karakoram-Kohistan region. A mean crystallization age (105.30±0.80) of zircons in the Tirit granitoid hosting xenoliths of porphyritic volcanics places a minimum eruption age of ca. 105Ma for the Shyok volcanics. The Ladakh granitoid, Tirit granitoids and porphyritic volcanic xenolith belong to a calc-alkaline series. A mean crystallization age (67.32±0.66Ma) for zircon in the Ladakh granitoid implies that the Shyok metasediments (shale/slate) were deposited and metamorphosed prior to ca. 68Ma. Present and earlier determined ages on Tirit granitoids revealed that the subduction-related calc-alkaline magmatism in the Nubra-Shyok valley of the SSZ prevailed between 110 and 68Ma, and hence a minimum age of Early Cretaceous can be suggested for development of the SSZ.

Age and structure of the Shyok suture in the Ladakh region of northwestern India: Implications for slip on the Karakoram fault system

A precise age for the collision of the Kohistan-Ladakh block with Eurasia along the Shyok suture zone (SSZ) is one key to understanding the accretionary history of Tibet and the tectonics of Eurasia during the India-Eurasia collision. Knowing the age of the SSZ also allows the suture to be used as a piercing line for calculating total offset along the Karakoram Fault, which effectively represents the SE border of the Tibetan Plateau and has played a major role in plateau evolution. We present a combined structural, geochemical, and geochronologic study of the SSZ as it is exposed in the Nubra region of India to test two competing hypotheses: that the SSZ is of Late Cretaceous or, alternatively, of Eocene age. Coarse-continental strata of the Saltoro Molasse, mapped in this area, contain detrital zircon populations suggestive of derivation from Eurasia despite the fact that the molasse itself is deposited unconformably onto Kohistan-Ladakh rocks, indicating that the molasse is postcollisional. The youngest population of detrital zircons in these rocks (approximately 92 Ma) and a U/Pb zircon date for a dike that cuts basal molasse outcrops (approximately 85 Ma) imply that deposition of the succession began in the Late Cretaceous. This establishes a minimum age for the SSZ and rules out the possibility of an Eocene collision between Kohistan-Ladakh and Eurasia. Our results support correlation of the SSZ with the Bangong suture zone in Tibet, which implies a total offset across the Karakoram Fault of approximately 130–190 km.

A GIS-based stream sediment geochemical model for gold and base metal exploration in remote areas of northern Pakistan

This study investigates the strength of a GIS-based and statistical approach for the analysis of stream sediment geochemical data in the development of predictive models for Au and base metal mineralisation in remote and glaciated areas of northern Pakistan. The study is based on a large (~2,000 samples) geochemical dataset generated as a result of extensive sampling campaigns by the Australian Aid Program, Pakistan Mineral Development Corporation (PMDC) and Sarhad Development Authority (SDA). The data were analysed using factor analysis to identify elemental associations and subsequently imported into ArcGIS 9.2 for spatial analysis. The model successfully detected the occurrence of known stibnite veins and disseminations in Chitral, porphyry Cu (skarns) in Domal Nissar and Skardu, and Ni-PGE occurrences in the mafic-ultramafic rocks of Chilas. Spatial catchment anomaly maps (based on 90th, 95th and 99th percentiles) were compared with the GIS-based model to delineate prospective areas, which included Asheriat, Teru, Pakora, Gilgit, Shishi, Imit and Chalt, mainly along the Shyok suture zone, while geochemical anomalies in Kafiristan, upper Mastuj and Lshkarwaz are associated with the Reshun fault. A strong geochemical anomaly in Astore River reflecting mineralization possibly associated with the Indus suture zone. The model was also used to interpret deposit type for gold and base metal anomalies. The majority of Au anomalies were fault related, associated with suture zones, which suggests a dominantly structural rather than lithological control on mineralisation in northern Pakistan.

Distribution of gold in different size fractions of stream sediments as a guide to bedrock gold mineralisation along the Shyok Suture Zone and adjacent areas of the Kohistan Island Arc, Pakistan

This paper describes a new exploration methodology using stream sediments in remote and glaciated regions of northern Pakistan. Gold concentrations in 268 samples from grain size fractions collected in 10 catchments were studied to detect possible mineralisation in the area. The 10 catchments were identified as anomalous from the spatial analysis of gold data in a regional stream sediment dataset. The multi-size fraction approach successfully identified known gold prospects as well as new areas of gold mineralisation. The previously unknown catchments were ranked in terms of their prospectivity for gold, with the most prospective catchments (decreasing in rank) being: Teru, Asheriat and Pakora. The studied catchments, the coarse (<1.68 mm–400 μm) and fine size (<75 μm) fractions of the stream sediments were found to give the most reliable indication of gold prospectivity. It is therefore advised that exploration programs carried out in high-altitude terrains, similar to those in northern Pakistan, utilise the approach of multiple-sediment size fractions to locate prospective areas for mineralisation.