The blueschists along the Indus Suture Zone in Ladakh, NW Himalaya

ABSTRACT Blueschists occur along the Indus Suture Zone in Ladakh as tectonic thrust slices, as isolated blocks within mélange units and as pebbles within continental detrital series. In the Shergol-Baltikar section high-pressure rocks within the Mélange unit lie between the Dras-Naktul-Nindam nappes in the north and the Lamayuru units in the south. The blueschists are imbricated with mélange formation of probably upper Cretaceous age. They are overlain discordantly by the Shergol conglomerate of post Eocene (Oligo-Miocene ?) age. Blueschist lithologies are dominated by volcanoclastic rock sequences of basic material with subordinate interbedding of cherts and minor carbonates. Mineral assemblages in metabasic rocks are characterized by lawsonite-glaucophane/crossite-Na-pyroxene-chlorite-phengite-titanite ± albite ± stilpnomelane. In the quartz bearing assemblages garnet is present but omphacite absent. P-T estimates indicate temperatures of 350 to 420°c and pressures around 9–11 kbar. Geochemical investigations show the primary alkaline character of the blueschist, which suggests an oceanic island or a transitional MORB type primary geotectonic setting. K/Ar isotopic investigations yield middle Cretaceous ages for both whole rocks and minerals. Subduction related HP-metamorphism affecting the Mesozoic Tethyan oceanic crust developed contemporaneously with magmatism in the Dras volcanic are and the Ladakh batholith. Subsequent collision of India with Asia obducted relics of subduction zone material which later became involved in nappe emplacement during the Himalayan mountain building.     

Fault systems and Paleo-stress tensors in the Indus Suture Zone (NW Pakistan)

Analysis of fault-striations measured in the Kohistan part of the Indus Suture Zone (NW Himalaya, Pakistan) has been carried out to document dynamic evolution during the brittle stage of the collision of India and Asia. Processing of the data with a direct inversion method identified four stress fields which were chronologically ordered from field evidence as SSE–NNW compression, E–W compression, radial extension and SSW–NNE compression. The last corresponds to the present-day stress field defined from seismic activity. The earlier stress fields are related to times during the Miocene, when convergence-related stresses were disturbed by the formation of the nearby Nanga Parbat and Indus syntaxes.     

Supra-Subduction Zone Environment and Economic Potential of the Nidar Ophiolite of Indus Suture Zone, Eastern Ladakh, the Himalaya

SUPRA-SUBDUCTION ZONE ENVIRONMENT AND ECONOMIC POTENTIAL OF THE NIDAR OPHIOLITE OF INDUS SUTURE ZONE, EASTERN LADAKH,THE HIMALAYA     

Sedimentology, petrography and tectonic significance of the shelf, flysch and molasse clastic deposits across the Indus Suture Zone, Ladakh, NW India

In the Ladakh area of India, a passive Triassic to Lower Cretaceous continental margin is indicated by Indian-shield-derived clastics on the shelf and Atlantic-type turbidites off the continental margin. Mid-Cretaceous initiation of ocean closing is reflected in Pacific-type flysch and associated island are volcanics, which were initially emplaced over the northern Indian continental margin in late Cretaceous times-resulting in the formation of a fore-deep in which flysch and minor continental molasse accumulated briefly during the late Cretaceous. These transient uplifts were, however, rapidly destroyed for by the latest Cretaceous to latest Palaeocene, uniform carbonate sediments were being laid down over the area.

With the early Eocene, the development of a second fore-deep, this time filled with very thick flysch and molasse sediment, indicates a major uplift of the northern Indian margin, which we attribute to the development of an Andean-type magmatic arc on the northern edge of the Indian plate. Uplift and molasse sedimentation in this fore-deep continued through the Oligocene and Miocene, when the collision of India and Asia caused extensive deformation of all the sequences and the shift of molasse sedimentation southwards to the Himalaya foothills and Indo-Gangetic plain.     

The age and nature of Mesozoic-Tertiary magmatism across the Indus Suture Zone in Kashmir and Ladakh (N. W. India and Pakistan)

We report the following new⁴⁰Ar/³⁹Ar ages: 130–150 and 90–100 Ma from monzodiorite and tremolite-actinolite schist of the Kohistan Complex; 44±0.5, 39.7±0.2 Ma from dikes cutting the Ladakh-Deosai Batholith Complex; 130–145 Ma from a diorite in the Shyok melange; and 7.8±0.1 Ma from a late stage monzogranite of the Kärakorum Batholith. A 261±13 Ma age from gneiss of the Karakorum Batholith is of uncertain significance. These dates, previously published ones which we summarize here, and some Sr isotope data suggest the following, (due to subduction switching between the Indian and Asian margins during closing of the Tethys ocean): Late Cretaceous emplacement of the Dras-Kohistan Cretaceous Island arc, followed by rapid cooling between abut 85 and 45 Ma. A quiet phase tectonically on the northern Indian plate during the Palaeocene to early Eocene, when subduction was occurring on the Asian margin. Further southward thrusting of the Indian continental margin associated with the development of an Andean-type arc (the Ladakh-Desosai Batholiths) on the northern Indian margin during the Eocene. An Oligocene Andean arc (the Karakorum Batholiths) on the Asian margin, followed by Miocene collision of the two continents and intrusion of ‘true’ granites derived from partial melting of continental crust.     

Palynological evidence for the Palaeocene evolution of the forearc basin, Indus Suture Zone, Ladakh, India

The discovery of Permian, Mesozoic and Palaeocene palynomorphs from the Nindam forearc basin, exposed along the Indus Suture Zone in Ladakh, is reported. The palynomorphs are from volcanogenic sandstones and are poorly preserved, distorted and show the effects of abrasion (striation marks). The frequent occurrence of Proxapertites indicates the assemblage is at least Palaeocene in age. The Palaeocene palynomorphs and sediments were transported to the Nindam trough from nearby elevated landward regions (islands). These Palaeocene provenance areas were characterized by an estuarine, nearshore, tropical, warm‐humid environment and were situated at equatorial palaeolatitudes. However, the occurrence of Permian and Mesozoic palynomorphs in the assemblage indicates that the Late Palaeozoic and Mesozoic Tethyan sedimentary rocks exposed along the northern margin of the Indian plate were redeposited into the tectonically active Cretaceous–Palaeocene trench–subduction complex that existed between the Indian and the Asian plates until the collision took place at ～50–60 Ma.     

PGE and isotopic characteristics of Shergol and Suru Valley Ophiolites,Western Ladakh: Implications for supra-subduction tectonics along Indus Suture Zone

Present study reports the PGE-geochemistry of mantle peridotites and Nd-isotope geochemistry of arc related mafic rocks from the Indus Suture Zone (ISZ), western Ladakh. The total PGE concentration of the Shergol and Suru Valley peridotites (∑PGE = 96–180 ppb) is much higher than that of the primitive mantle and global ophiolitic mantle peridotites. The studied peridotites show concave upward PGE-distribution patterns with higher palladium-group PGE/Iridium-group PGE ratios (i.e., 0.8–2.9) suggesting that the partial melting is not the sole factor responsible for the evolution of these peridotites. The observed PGE-distribution patterns are distinct from residual/refractory mantle peridotites, which have concave downward or flat PGE-distribution patterns. Relative enrichment of palladium-group PGE as well as other whole-rock incompatible elements (e.g., LILE and LREE) and higher Pd/Ir ratio (1.1–5.9) reflects that these peridotites have experienced fluid/melt interaction in a supra-subduction zone (SSZ) tectonic setting. Also, the Shergol mafic intrusives and Dras mafic volcanics, associated with the studied peridotites, have high ¹⁴³Nd/¹⁴⁴Nd ratios (i.e., 0.512908–0.513078 and 0.512901–0.512977, respectively) and positive ε_Nd(t) (calculated for t = 140 Ma) values (i.e., +5.3 to +8.6 and + 5.1 to +6.6, respectively), indicating derivation from depleted mantle sources within an intra-oceanic arc setting, similar to Spongtang and Nidar ophiolites from other parts of Ladakh Himalaya. The transition from SSZ-type Shergol and Suru Valley peridotites to Early Cretaceous tholeiitic Shergol mafic intrusives followed by tholeiitic to calc-alkaline Dras mafic volcanics within the Neo-Tethys Ocean exhibit characteristics of subduction initiation mechanism analogous to the Izu-Bonin-Mariana arc system within western Pacific.     

Transpression and Exhumation of Granitoid Plutons along the Northern Part of the Nehbandan Fault System in the Sistan Suture Zone,Eastern Iran

Geotectonics - Geometry and kinematics of deformation across the Nehbandan Fault System (NFS) have been studied in the Bibimaryam and Damdameh areas in the Sistan Suture zone (SSZ). Nearly vertical...     

Geophysical exploration of the Kalahari Suture Zone

Fancamp Resources Limited of Montreal, Canada, commenced exploration of the Kalahari Suture Zone in southwest Botswana in 1996, following the interpretation of airborne magnetic surveys covering 400 km of strike along the Kalahari Suture Zone. Initial focus was on mafic/ultramafic intrusions associated with the Tshane Complex as potential targets for CuNiPGM mineralization, but these targets are now considered to be too deeply buried (> 700 m) to be of economic significance at this time. The exploration focus has been redirected to several prospective large coincident magnetic/gravity anomalies. These are considered prospective targets for Olympic Dam-type CuCo mineralisation associated with alkaline intrusive complexes, and/or NiCuCoPGM mineralisation associated with basic intrusive complexes. The two most important and prospective targets are the so-called 'Great Red Spot' and Tsetseng Complex. Additional ground geophysical surveys and deep drilling are planned for the next phase of exploration. These large targets are of high priority and represent tremendous potential for mineral development in the sparsely populated area of western Botswana.     

Host rock characteristics and source of chromium and beryllium for emerald mineralization in the ophiolitic rocks of the Indus Suture Zone in Swat,NW Pakistan

Bodies of magnesite-rich rocks (magnesite ± talc ± quartz ± dolomite), locally containing emerald deposits, occur within the Swat Valley. These rocks, part of the Indus suture mélange group, are distributed mostly along contacts of serpentinized ultramafic rocks with carbonate ± graphite-bearing metasedimentary rocks. Their field association, petrographic details, mineralogical composition and geochemical characteristics show that they likely formed due to carbonate alteration of previously serpentinized ultramafic rocks by CO₂-bearing fluids released as a result of metamorphism of spatially associated, originally sedimentary rocks of the Indo-Pakistan plate.Locally, late-stage hydrothermal activity affected these highly fissile magnesite-rich rocks to produce veins and stockworks of quartz as well as emerald, Cr-rich tourmaline and Cr, Ni-rich muscovite. Detailed petrographic and mineral chemical investigations suggest that all three Cr-bearing silicates are genetically related and their Cr, as well as Ni and Mg found in Cr-rich muscovite and Cr-rich tourmaline, was derived from the original ultramafic protoliths.Detailed geochemical comparison reveals that relative to non-mineralized sections, magnesite-rich rocks in mineralized zones show significant enrichment in B and Be as well as As, Pb, Zr, Rb, Ba, W, Sn, Sr and Y. Boron and Be enrichment in these rocks appears to be structurally controlled. More extreme B and Be enrichment is evident in small granitic dikes cutting granite gneisses and in Miocene leucogranitic stocks at Malakand 45 km southwest. These geochemical features argue strongly for a leucogranite-associated source for Be-transporting fluids to the emerald's host rocks.     

西藏班公湖-怒江缝合带白垩系沉积特征及其构造意义

班公湖—怒江位于西藏中部 ,西起班公湖日土 (33.5°N ,79°E) ,向东经由措勤、尼玛、那曲至东部怒江带 ,走向近东西、其中部大致平行于北纬 32°线 ,延长大于 15 0 0km。该带蛇绿岩发育 ,是中生代板块缝合线 ,是南部拉萨地块与北部羌塘地块的分界线。其中段班戈地区白垩系地层发育 ,包括下白垩统底部川巴组 (K1c)、多巴组 (K1d)、郎山组 (K1l)和上白垩统江巴组 (K2 j)。川巴组为浅海相黑色页岩、泥岩、粉砂岩、砂岩、煤层和火山岩 ;多巴组为含有海侵夹层的陆相碎屑岩建造 ,海侵层为含园笠虫 (Orbitolinasp .)钙质砂岩 ;郎山组为浅海相—泻湖相台地型碳酸盐岩沉积 ;江巴组以陆相、厚层块状的砂砾岩红层为特征。本区白垩系层序的总体特征 ,是以海相火山岩—细碎屑岩为先导、经海陆过渡相碎屑岩和海相碳酸盐岩到陆相红层 ,形成于与B型俯冲作用有关的活动大陆边缘构造背景.     

Field report:Research along the Yarlung Suture Zone in Southern Tibet,a persistent geological frontier

The Yarlung Suture Zone in Southern Tibet marks the boundary between India and Asia-formerly separated by an ocean basin-and is a critical record of the tectonic processes that created the Tibetan Plateau. The Yarlung Suture Zone is also a frontier research area, as difficulty of access has limited research activity, providing ample opportunities for new discoveries. This paper documents field research conducted by the authors along the Yarlung suture zone in eastern Xigaze(Shigatse, Rikaze)County, ~250 km west of the city of Lhasa, in July 2017. The goal of this research was to map the Suture Zone structure in detail, and more specifically to understand the branching relationships between two major fault systems-the Great Counter Thrust and Gangdese Thrust. A summary of early geological exploration is included to provide context for this research.     

Petrology of chloritoid–ilmenite-rich rocks in the Indus Suture mélange of Pakistan: Implications for the Cretaceous paleolatitude of Kohistan

The Indian Plate and Kohistan Island Arc are juxtaposed to the north of Peshawar along the Indus Suture, which is characterized by a tectonic mélange consisting of ultramafic, mafic, and a variety of sedimentary rocks. Within metavolcanic greenstones, there are small, lensoid bodies comprising quartz, white mica (up to 4.5 wt% FeO), chlorite (pseudothuringite to ripidolite), pyrite, and abundant chloritoid (up to 60%) and ilmenite. These lenses consist essentially of SiO₂, TiO₂, Al₂O₃ and iron oxide. There is a clear petrographic and geochemical (major, trace and RE element) transition from these rocks to their host greenstones, suggesting a common parentage. The greenstones contain high TiO₂, Fe₂O₃ and P₂O₅. Their chondrite-normalized patterns show enrichment in light REE, depletion in heavy REE, negative Eu and positive Yb anomalies. Because the greenstones have probably been altered, the present set of data is not capable of deciphering the tectonic setting of these rocks, but previous geochemical studies have suggested an island arc setting for volcanic rocks in the mélange. By chemical analogy with lateritized basalts, the chloritoid-rich rocks are considered to be the product of weathering of basalts in tropical, probably equatorial, conditions before the northward drift of Kohistan. Mélange formation and greenschist facies metamorphism occurred during the collision of the Indian Plate and the Kohistan Magmatic Arc, to its north, in the Late Cretaceous-Early Tertiary.     

Geological Features of the Eastern Sector of the Bangong Co-Nujiang River Suture Zone: Tethyan Evolution

According to an analysis of the geological features in the eastern sector of the Bangong Co-Nujiang River suture zone, the Tethyan evolution can be divided into three stages. (1) The Embryo-Tethyan stage (Pz1): An immature volcanic arc developed in Taniantaweng (Tanen Taunggyi) Range, indicating the existence of an Embryo-Tethyan ocean. (2) The Palaeo-Tethyan stage (C-T2): During the Carboniferous the northern side of the Taniantaweng Range was the main domain of the Pa-laeo-Tethyan ocean, in which developed flysch sediments intercalated with bimodal volcanic rocks and oceanic tholeiite, and Pemian-Early Triassic arc granites were superimposed on the Taniantaweng magmatic arc; on the southern side the Dengqen-Nujiang zone started secondary extension during the Carboniferous, in which the Nujiang ophiolite developed, and the Palaeo-Tethyan ocean closed before the Middle Triassic. (3) The Neo-Tethyan stage (T3-E): During the Late Triassic the Dengqen zone developed into a relatively matural ocean basin, i     

甘孜-理塘结合带中部花岗岩的地质特征

对处于甘孜-理塘结合带中心部位的花岗岩，前人依据其产出的构造背景认为它是结合带的一部分，为多期构造-岩浆活动的产物。本次区调通过岩石学、岩石化学、地球化学和锆石U-Pb内位素年龄测定测定值的研究，确定该花岗岩形成于燕山期，隶属于义敦岛弧花岗岩浆带，后构造推覆定位。