Himalayan Orogenic Belt Research Articles

Neotectonic Activity from Karewa Sediments, Kashmir Himalaya, India

Intermontane basin sedimentation occurred during Pliocene-Pleistocene in the Karewa Basin which formed after the continent-continent collision resulting in the formation of Himalayan orogenic belt around Eocene. These are elongated, narrow, thrust bounded basins which have formed during the late stages of orogeny. Situated at a height of 1700–1800 m above sea level, the Karewa basin received sediments because of ponding of a pre-existing river system and the tectonic movements along the Great Himalayan Ranges in the north and the Pir-Panjal ranges in the south along active faults. About 1300 m thick sediments of largely fluvio-lacustrine, glacio-fluvio-lacustrine and eolian origin are exposed having evidences of neotectonically formed structural features such as folds and faults. Folds are more prominent in the Lower Karewa formation (Hirpur Formation) while faults (mostly normal faults) are abundant in the Upper Karewas (Nagum Formation). Drainage in the area varies from dendritic to anastomosing to parallel. Anastomosing drainage suggests sudden decrease in gradient while presence of linear features such as faults and ridges is evident by parallel drainage. Study of morphometric parameters such as stream length (Lsm) and stream length ratios (RL), bifurcation ratio (Rb), drainage density (D), form factor (Rf), circularity ratio (Rc), and elongation ratio (Re) also indicate intense tectonic activity in the recent past.

Chemo-probe into the mantle origin of the NW Anatolia Eocene to Miocene volcanic rocks: Implications for the role of, crustal accretion, subduction, slab roll-back and slab break-off processes in genesis of post-collisional magmatism

Post-collisional Cenozoic magmatic activity in NW Anatolia produced widespread volcanism across the region. In the Biga Peninsula, in the west, medium-K calc-alkaline to ultra-K rocks with orogenic geochemical signature were emplaced at ~43–15 Ma (Biga orogenic volcanic rocks; BOVR). Volcanic activity in the Central Sakarya region, to the east, is mainly restricted to ~53–38Ma, but also continued during the Early Miocene with small basaltic extrusives (Sakarya orogenic volcanic rocks; SOVR). This study presents a new set of geochemical data (whole rock major and trace elements and Sr–Nd–Pb isotopic compositions), obtained from the Cenozoic calc-alkaline volcanic rocks from these two regions. While there is considerable overlap in the emplacement time of volcanism in the two areas, the post-collisional volcanic rocks of these two regions differ in terms of their geochemical compositions: (1) the BOVR show an age-dependent increase in K and other large-ion lithophile elements (LILE), coupled with an increase in radiogenic Sr and Pb compositions from the Eocene to Miocene; whereas (2) the SOVR are characterized by more sodic compositions with lower K and less radiogenic Sr contents with respect to the BOVR, which were unchanged in Eocene and Miocene. We conclude that these geochemical features were principally related to the distinct modes of subduction-related mantle enrichment processes. We suggest that the Eocene to Miocene progressive enrichment in the BOVR mantle was related to successive subduction of oceanic and crustal materials in the western Aegean, while the SOVR mantle was dominantly enriched during the pre-collisional events. Magma generation in the western region was related to subduction roll-back processes associated with post-collisional extension. In the east, thermal perturbation of the mantle in response to asthenospheric upwelling due to slab break-off process was responsible for the magma generation. The time-dependent increase of K (and other LILE and radiogenic Sr) in the Cenozoic orogenic lavas from the Rhodope to Biga region emphasizes the importance of crustal imbrication and subduction in the genesis of orogenic K-rich lavas of the Alpine–Himalayan orogenic belt.

Investigation of geological, geotechnical and geophysical properties of Kiratli (Bayburt, NE Turkey) travertine

There are good quality natural stones having different color and texture especially in the Turkey located in Alpine–Himalayan Orogenic Belt. However, there are limited natural stone reserves in NE Turkey. Because Kiratli travertine site is the second largest area with a reserve of 250,000 m3 in the region, this travertine site was chosen as a pilot site for this study. Geological, geophysical and geotechnical investigations were carried out in the study and laboratory tests were conducted. The discontinuity properties of travertine mass were investigated using Ground Penetrating Radar (GPR) method to guide for suitable operating techniques in the natural stone quarry. According to the tests results uniaxial compressive strength values are 25 and 51 MPa, indirect tensile strength values are 3.98–9.18 MPa, P-wave velocities for dry condition are 3717 and 4154 m/s, respectively, for parallel and perpendicular core samples to the deposition direction. The uniaxial compressive strength of the samples was also determined after cycling tests such as wetting–drying and freezing–thawing tests. The travertine samples have less than 10% deterioration after these tests. On the investigated area, the GPR data were acquired with 100 MHz antenna using GPR technique being one of geophysical methods on 7 lines parallel each other in the study. The data were processed utilizing with ReflexW software. It was concluded that the reflection boundaries observed on obtained radargrams originated in discontinuities and weathered parts in dominant rock. It has been suggested that productive raw materials could not be got during the extraction of material travertine in the orientation of quarry when it comes to discontinuities and weathered parts in dominant rock. In these parts, quality travertine material can not be obtained.

Zircon U-Pb geochronology and emplacement history of intrusive rocks in the Ardestan section, central Iran

The Urumieh-Dokhtar Magmatic Arc (UDMA) is part of the Alpine–Himalayan orogenic belt and interpreted to be a subduction-related Andean-type magmatic arc. Along this belt, Eocene volcanics and some gabbroic to granitic bodies crop out. The main rock types of the studied intrusion are granite, granodiorite, and diorite. They have geochemical features typical of magnesian, calc-alkaline, metaluminous to slightly peraluminous granites and I-type intrusive rock that have a strong enrichment in Large-Ion Lithophile (LIL) elements (e.g. Rb, Ba, Sr), and a depletion in High Field Strength (HFS) elements (e.g. Nb, Ti, P), typical of subduction-related magmas. Zircon U-Pb dating was applied to determine the emplacement ages of the different intrusions in the Ardestan area. Among them the Kuh-e Dom diorite is 53.9±0.4Ma old; the Kuh-e Dom granodiorite is 51.10±0.4Ma old; the Mehrabad granodiorite is 36.8±0.5Ma old, the Nasrand granodiorite is 36.5±0.5Ma old, the Zafarghand granodiorite is 24.6±1.0Ma old, and the Feshark granodiorite is 20.5±0.8Ma old. These results delineate more accurately the magmatic evolution related to the Neotethyan subduction from the Lower Eocene to Lower Miocene, and the subsequent Zagros orogeny that resulted from the Arabia-Eurasia collision. The emplacement of these intrusive rocks inside the UDMA, which has a close relationship with the collisional orogeny, is transitional from a subduction-related setting to post-collisional setting in the Ardestan area.

Effects of crustal eclogitization on plate subduction/collision dynamics: Implications for India-Asia collision

2D thermo-mechanical models are constructed to investigate the effects of oceanic and continental crustal eclogitization on plate dynamics at three successive stages of oceanic subduction, slab breakoff, and continental subduction. Crustal eclogitization directly increases the average slab density and accordingly the slab pull force, which makes the slab subduct deeply and steeply. Numerical results demonstrate that the duration time from initial continental collision to slab breakoff largely depends on the slab pull force. Specifically, eclogitization of subducted crust can greatly decrease the duration time, but increase the breakoff depth. The detachment of oceanic slab from the pro-continental lithosphere is accompanied with obvious exhumation of the subducted continental crust and a sharp uplift of the collision zone in response to the disappearance of downward drag force and the induced asthenospheric upwelling, especially under the condition of no or incomplete crustal eclogitization. During continental subduction, the slab dip angle is strongly correlated with eclogitization of subducted continental lower crust, which regulates the slab buoyancy nature. Our model results can provide several important implications for the Himalayan-Tibetan collision zone. For example, it is possible that the lateral variations in the degree of eclogitization of the subducted Indian crust might to some extent contribute to the lateral variations of subduction angle along the Himalayan orogenic belt. Moreover, the accumulation of highly radiogenic sediments and upper continental crustal materials at the active margin in combination with the strong shear heating due to continuous continental subduction together cause rising of isotherms in the accretionary wedge, which facilitate the development of crustal partial melting and metamorphism.

Active faulting within a megacity: the geometry and slip rate of the Pardisan thrust in central Tehran, Iran

Tehran, the capital city of Iran with a population of over 12 million, is one of the largest urban centres within the seismically active Alpine–Himalayan orogenic belt. Although several historic earthquakes have affected Tehran, their relation to individual faults is ambiguous for most. This ambiguity is partly due to a lack of knowledge about the locations, geometries and seismic potential of structures that have been obscured by dramatic urban growth over the past three decades, and which have covered most of the young geomorphic markers and natural exposures. Here we use aerial photographs from 1956, combined with an ∼1 m DEM derived from stereo Pleiades satellite imagery to investigate the geomorphology of a growing anticline above a thrust fault—the Pardisan thrust—within central Tehran. The topography across the ridge is consistent with a steep ramp extending from close to the surface to a depth of ∼2 km, where it presumably connects with a shallow-dipping detachment. No primary fault is visible at the surface, and it is possible that the faulting dissipates in the near surface as distributed shearing. We use optically stimulated luminescence to date remnants of uplifted and warped alluvial deposits that are offset vertically across the Pardisan fault, providing minimum uplift and slip-rates of at least 1 mm yr−1. Our study shows that the faults within the Tehran urban region have relatively rapid rates of slip, are important in the regional tectonics, and have a great impact on earthquake hazard assessment of the city and surrounding region.

Oligocene crustal anatexis in the Tethyan Himalaya, southern Tibet

Recent studies in the Xiaru and Malashan gneiss dome of the Tethyan Himalaya, southern Tibet identify that Xiaru and Paiku tourmaline-bearing leucogranite dike formed at ~28–29Ma. Together with ~28Ma Kuday garnet-bearing leucogranites, it is demonstrated that the Himalayan orogenic belt experienced a major episode of crustal melting in the Mid-Oligocene. Geochemical data indicate that three suites of leucogranite are characterized by large variations in the major and trace element compositions as well as Sr–Nd isotope systematics, which could be explained by combined fractional crystallization and relative contributions of micas and accessory phases dissolved into a crustal melt during decompressional melting of metapelitic rocks. Documentation of Oligocene partial melting of crustal rocks could indicate that the exhumation of deep crustal rocks in the Himalayan orogenic belt could have started as early as Oligocene.

Influence of geology on groundwater–sediment interactions in arsenic enriched tectono-morphic aquifers of the Himalayan Brahmaputra river basin

Summary The present study interprets the groundwater solute chemistry, hydrogeochemical evolution, arsenic (As) enrichment and aquifer characterization in Brahmaputra River Basin (BRB) involving three geologically and tectono-morphically distinct regions located in northeastern India. These study regions consist of the northwestern (NW) and the northern (N) region, both located along the western and eastern parts of Eastern Himalayas and the southern (S) region (near Indo–Burmese Range and Naga hills) of the Brahmaputra basin which show distinct tectonic settings and sediment provenances in the Himalayan orogenic belt. Stable isotopic composition (δ2H and δ18O) in groundwater suggests that some evaporation may have taken place through recharging of ground water in the study areas. The major-ion composition shows that groundwater composition of the NW and N parts are between Ca HCO3 and Ca Na HCO3 while the S-region is dominated by Na Ca HCO3 hydrochemical facies. The major mineralogical composition of aquifer sediments indicates the dominant presence of iron(Fe)-oxide and oxyhydroxides, mica (muscovite and biotite), feldspar, pyroxene, amphibole, abundance of quartz and clay minerals whereas clay is predominantly present in sediments of S-aquifers. These mafic minerals, aluminosilicates and clay minerals might offer available reactive surface for As-adsorption and co-precipitatation with amorphous Fe. These associated adsorbed and co-precipitated As might be released due to reductive dissolution of Fe-oxide and oxyhydroxides in groundwater. These minerals are assumed to be possible sources of As in groundwater. The stability diagrams of groundwater data suggest that solute might have been introduced into groundwater from weathering of K-feldspar, plagioclase, pyroxene of Himalayan rocks, the Siwalik Group and Eastern Syntaxes in NW and N-regions. However, basic cations might be derived from weathering of K-feldspar, plagioclase, pyroxene and olivine those being major constituents in a gabbroic complex (ophiolite) and basalt terrain in S-region. The aquifers of S-region are severely contaminated with dissolved As compared to NW and N regions. Almost more than 92% of groundwater samples in the southern part (maximum 5.53 μM or 415 μg/L) are enriched with As, which draws a distinct difference from the NW and N parts of BRB aquifers. The redox-sensitive solutes (i.e., Fe, Mn, HCO3− and TOC) are positively correlated with As in NW and N-parts; whereas EH shows negative to very weak positive correlation which suggests that a redox-dependent mobilization plays important role in As liberation in NW and N parts of the basin. However, As in southern aquifers is not showing any correlation or weak negative correlation with redox-sensitive solutes; suggesting that multiple reactions and hydrogeochemical processes and their interaction control As mobilization and fate in the S-region of BRB. The occurrence of high concentrations of arsenic in groundwater of Brahmaputra basin is described through a crustal recycling model and tectonic movement between the Indian–Eurasian plates and Burmese micro-continents. As-enriched groundwater in Himalayan foreland basin in the BRB is probably a result of crustal evolution through which As is subsequently mobilized from aquifer matrix to solution in groundwater by water–sediment reaction under favorable biogeochemical conditions. The results of the study indicate geological control (i.e. change in lithofacies, tectonic set-up) on groundwater chemistry and distribution of redox-sensitive solutes such as As.

REVIEW OF THE PORPHYRY ORE DEPOSITS IN THE TETHYAN OROGENIC BELT-A CASE STUDY OF THE BANGPU MO-CU PORPHYRY ORE DEPOSITS, TIBET, CHINA

Ponte Academic JournalSep 2016, Volume 72, Issue 9 REVIEW OF THE PORPHYRY ORE DEPOSITS IN THE TETHYAN OROGENIC BELT-A CASE STUDY OF THE BANGPU MO-CU PORPHYRY ORE DEPOSITS, TIBET, CHINAAuthor(s): H. A. Ahmed ,Chang-Qian Ma, (a,b) Chang-Qian Ma, (a) Lian-Xun Wang, (a) Mukhtar Habib, (c) Kabir Shola Ahmed (c)J. Ponte - Sep 2016 - Volume 72 - Issue 9 doi: 10.21506/j.ponte.2016.9.13 Abstract:Abstract The occurrence of the post-collisional Bangpu Mo-Cu porphyry ore deposits has been reviewed. The Cenozoic deposit is located within the Gangdese Porphyry Copper Belt (GPCB) in Tibet, part of Himalayan (Tethyan) Orogenic Belt, with an estimated resource of over 800,000 and 200,000 tons of Mo and Cu respectively, and an approximate grades of 0.089% Mo and 0.32% Cu. The Mo reserves within the Bangpu deposit accounts for about 60% of the known Molybdenum reserve in Tibet. The mineralization is hosted by Mid- Miocene porphyritic monzogranites, diabase and diorite porphyry and is controlled by extensional structures and are distributed along E-W fault and fracture zones. Isotopic and fluid inclusion analyses suggest that the ore fluids might have been derived from degassed mafic magmas that originate from an upwelling asthenospheric mantle. The Redox state of the magma could be viewed as an important factor in the formation of Mo rich and Cu poor in the study area. Several studies have indicated that the Bangpu porphyry Mo-Cu deposit was generated by post-collisional crustal extension that took place during the Indo-Asian collision that started at 65 Ma. In future, a rigorous fluid-rock interaction studies and determination of Redox state of magma and emplacement mechanisms in the region would give a better understanding of the genetic model that resulted in the formation of Mo-Cu deposits in the area and perhaps a great potential for discovery of additional new deposits in the Tibetan sector of the Tethyan Orogenic Belt. Keywords: Tethyan Orogenic Belt, Bangpu, porphyry Mo-Cu ore deposits, Gangdese, Magmatic degassing. Download full text:Check if you have access through your login credentials or your institution Username Password

Collision and mountain building

The spatial, chronological, and genetic relationships of recent (Late Alpine) collisions to mountain building are considered at three levels of scale: (i) in separate zones of the Arabian–Caucasus segment of the Alpine–Himalayan Orogenic Belt, (ii) throughout the central segment of this belt from the Alps to the Himalalayas, and (iii) in Central Asia and other mountain belts of continents. Three stages of mountain building are distinguished at all three levels. The first stage starts with widespread collision and similar plate interactions from the end of the Eocene to the middle Miocene and is expressed in the formation of uplifts, commonly no higher than the moderately elevated level in regions that concentrate deformations of transverse shortening induced by compression. The second short stage, which embraces the Pliocene–Quaternary and occasionally the end of the Miocene, differs in general, though differentiated in the value and intensification of vertical movements, when the height of mountains increases by 2–3 times. Elevations are spread over certain platform territories and even frameworks of rift zones. This is related not so much to the intensity of compression and shortening as to the compositional transformation of the upper mantle and the lower crust, leading to their decompaction. Comparison with the Hercynian and Caledonian orogenic stages shows that the second phase, predetermined by widespread collision, reflects a more important geodynamic event expressed in a change of the global plate interaction system and its deep-seated sources.

Zircon U–Pb ages, geochemical and Sr–Nd–Pb–Hf isotopic constraints on petrogenesis of the Tarom-Olya pluton, Alborz magmatic belt, NW Iran

A petrological, geochemical and Sr–Nd–Pb isotopic study was carried out on the Tarom-Olya pluton, Iran, in the central part of the Alpine–Himalayan orogenic belt. The pluton is composed of diorite, monzonite, quartz-monzonite and monzogranite, which form part of the Western Alborz magmatic belt. LA–ICP–MS analyses of zircons yield ages from 35.7±0.8Ma to 37.7±0.5Ma, interpreted as the ages of crystallization of magmas. Rocks from the pluton have SiO2 contents ranging from 57.0 to 69.9wt.%, high K2O+Na2O (5.5 to 10.3wt.%) and K2O/Na2O ratio of 0.9 to 2.0. Geochemical discrimination criteria show I-type and shoshonitic features for the studied rocks. All investigated rocks are enriched in light rare earth elements (LREEs), large ion lithophile elements (LILEs), depleted in high-field strength elements (HFSEs), and show weak or insignificant Eu anomalies (Eu/Eu*=0.57–1.02) in chondrite-normalized trace element patterns. The Tarom-Olya pluton samples also show depletions in Nb, Ta and Ti typical of subduction-related arc magmatic signatures. The samples have relatively low ISr (0.7047–0.7051) and positive εNd(36Ma) (+0.39 to +2.10) values. The Pb isotopic ratios show a (206Pb/204Pb)i ratio of 18.49–18.67, (207Pb/204Pb)i ratio of 15.58–15.61 and (208Pb/204Pb)i ratio of 38.33–38.77. The εHf(t) values of the Tarom-Olya pluton zircons vary from −5.9 to +8.4, with a peak at +2 to +4. The depleted mantle Hf model ages for the Tarom-Olya samples are close to 600Ma. These isotope evidences indicate contribution of juvenile sources in petrogenesis of the Tarom-Olya pluton. Geochemical and isotopic data suggest that the parental magma of the Tarom-Olya pluton was mainly derived from a sub-continental lithospheric mantle source, which was metasomatized by fluids and melts from the subducted Neotethyan slab with a minor crustal contribution. Subsequent hot asthenospheric upwelling and lithospheric extension caused decompression melting in the final stage of Neotethyan subduction through slab rollback or shortly after the cessation of arc magmatism.

Complex Indian subduction style with slab fragmentation beneath the Eastern Himalayan Syntaxis revealed by teleseismic P-wave tomography

On the eastern margin of the Himalayan orogenic belt, the rapid uplift of the Namche Barwa metamorphic terrane and significant bending of the Yarlung Zangbo suture zone occur. The formation mechanism and dynamics of the Eastern Himalaya Syntaxis (EHS) is still debated. In order to better understand the deep structures beneath the EHS, we deployed 35 broadband seismic stations around the Namche Barwa Mountain. The data were integrated with existing datasets for a 3-D teleseismic P-wave tomography. The results demonstrate complex deep structures and significantly contrasting Indian subduction styles in the eastern Himalaya. In the western region of the EHS, the Indian slab flatly subducts under southern Tibet and might extend to the Bangong-Nujiang Suture. In contrast, a (north)eastward steep subduction occurred in the eastern region of EHS. The contrasting subduction styles result in tearing and fragmentation of the Indian lithosphere between the flat and steep subducting slabs beneath the EHS. Consequently, the hot asthenospheric mantle may rise through the slab window, which might further lead to the rapid uplift of Namche Barwa and the formation of EHS. The lateral variation in subduction/collision mode and slab tearing induced asthenospheric mantle upwelling is similar to that observed in the Hellenide and Anatolide domains of the Tethyan orogen.

The youngest eclogite in central Himalaya: P–T path, U–Pb zircon age and its tectonic implication

Relict omphacite inclusions have been discovered in mafic granulite at Dinggye of China, confirming the existence of eclogite in central Himalayan orogenic belt. Detailed petrological studies show that relict omphacite occur as inclusions in both garnets and zircons, and the peak mineral assemblage of eclogite-facies should be garnet, omphacite, rutile, muscovite and quartz which was strongly overprinted by granulite-facies minerals during the exhumation. Phase equilibria modeling and associated geothermometer predict that the minimum P–T conditions for peak eclogite-facies stage are 720–760°C and 20–21kbar, and those of overprinted granulite-facies are 750°C and 7–9kbar in water-undersaturated condition. Thus, a near isothermal decompression P–T path for central Himalayan eclogite has been obtained. Zircon SHRIMP U–Pb dating of two studied eclogite samples at Dinggye yields the peak metamorphic ages of 13.9±1.2Ma and 14.9±0.7Ma, respectively, which indicates that the Dinggye eclogite should be the youngest eclogite in Himalayan orogenic belt. Geochemical characteristics and zircon analyses show that the protoliths of eclogite in Dinggye are predicted to be continental rift-related basaltic rocks. The eclogite at Dinggye in central Himalaya should be formed by the crustal thickening during the long-lasting continental overthrusting by Indian plate beneath Euro-Asian continent, and its exhumation process may be related with channel flow and orogen-parallel extension. In the middle Miocene (~14Ma), Indian continental crust had reached at least ~65km depth in southern Tibet.

A Review of Groundwater Arsenic in the Bengal Basin, Bangladesh and India: from Source to Sink

The groundwater of the Bengal basin, in Bangladesh and West Bengal state of India, is found to be severely polluted by non-point sourced, geogenic arsenic (As), which has been regarded as the largest public health concern in the human history. The geomorphology and geology of the aquifers play very important role in the three dimensional existence of the As in the groundwater. The provenance of the groundwater As of Bengal basin may be hypothesized to be sourced to the Himalayan orogenic belt, where the contaminant might have originated by deep-seated tectono-magmatism and subsequently introduced to the surficial system by exhumation. Later, sedimentary processes transported the As-laden sediments from the orogenic belt to the peripheral foreland basin of Bengal where, under conducive biogeochemical environment, the As is released from the solid-phase to the circulating groundwater. Ferric hydroxides and pyrite are considered to be the two most important host minerals for As, although clay minerals may also act as important substrates for the sorbed As. The mobilized As then exists in the groundwater until a suitable geochemical sink is available. The mobilization process may be related to reductive-dissolution of metal oxides and hydroxides that exist in the unconsolidated sediments of the Bengal basin. Other mechanisms like pyrite oxidation, redox cycling in surficial soils, and competitive ion exchange are also accepted as potential mechanisms for arsenic mobilization, and multiple processes may simultaneously contribute to the mobilization of As. The processes are significantly complicated by redox disequilibria in the Bengal basin aquifers. These inorganic processes may have been significantly catalyzed and accentuated by microbially mediated activities. The tertiary source of groundwater As is the irrigation return flow from the agricultural fields.

Tectonic setting and general features of coseismic rupture of the 25 April, 2015 <italic>M</italic><sub>w</sub> 7.8 Gorkha, Nepal earthquake

An earthquake of M w 7.8 occurred on 25 April, 2015 in Nepal Himalaya, with a focal mechanism of low-angle thrust, determined unanimously by multiple research agencies. More than 100 aftershocks occurred thus far, including strong ones with magnitude larger than M s7.0, triggered normal-mechanism swarms hundreds of kilometers northeast of the epicenter in Tibet. The mainshock, located in central Himalayan orogenic belt and within the seismic gap between the ruptured zones of the 1934 Bihar M w~8.1 and 1505 Lo Mustang M w~8.2 earthquakes, is the largest one on the Main Himalaya Thrust since 1950 Assam M w~8.4 earthquake. To help a better understanding of the earthquake, we provide in this paper a review on the tectonic setting and geometry of the Himalayan fault system, large historical earthquakes and their rupture areas, pattern of modern microseismicity, general models of seismic cycle in the Nepal Himalaya, and spatial pattern of surface deformation resulted from interseismic loading and coseismic slip. Combining the overall features of coseismic rupture of the mainshock from teleseismic finite fault solutions, we comment on this earthquake regarding to its relationship with the characteristic (typical topography-building) Himalayan events, the comparison with the 2008 Wenchuan M w 7.9 earthquake of similar magnitude, the general condition for low-angle thrust-type rupture reaching surface, and its implication to regional seismic hazard.

Geochemistry, petrography and tectonic significance of the ophiolitic rocks, felsic intrusions and Eocene volcanic rocks of an imbrication zone (Helete area, Southeast Turkey)

The study area is situated in the imbrication zone (northwest of Adıyaman–Gölbaşı, Helete–Savran) of the Southeast Anatolian orogen, part of the Mediterranean–Himalayan orogenic belt. This area is characterized by NEE/SWW-trending, northward-dipping imbricated thrust slices located low in the nappe zone that was finally emplaced onto the Arabian platform during the Mid-Miocene. From top to bottom the main units in the study area are: (1) the Malatya Metamorphics- (2) the Harami Formation- (3) the Göksun Ophiolite–Esence Granitoid- (4) the Helete volcanics and (5) the Savran–Alacık Formation, Hompur–Lice Formation and Midyat Formation. This study contains the Upper Cretaceous–Eocene tectono-magmatic succession (ophiolitic rocks and related felsic intrusions and volcanic rocks), which are located in the Helete area. The unmetamorphosed ophiolitic rocks display an irregular ophiolitic sequence. These rocks are represented by tectonites, cumulated gabbros, isotropic gabbros and sheeted dyke complex and were intruded locally by felsic intrusions (granite, granodiorite, tonalite, dacite, and aplite). These ophiolites locally contain tectonically disrupted thin amphibolitic rocks. The mineral chemistry and geochemical features of these ophiolites indicate that these rocks exhibit sub-alkaline characteristics, and they are similar to those of island arc tholeiites formed in a supra-subduction zone. These ophiolitic rocks, located in the imbrication zone, are interpreted as being the equivalent of the Göksun Ophiolites. The felsic intrusions, which cut these ophiolitic rocks, correspond to the calc-alkaline Esence Granitoids which formed in an arc setting. Based on the 40Ar/39Ar dating method, a plateau age of 80.92±0.29Ma was obtained from a granite sample that cuts the gabbroic rocks. The Helete volcanics, which have a tectonic relationship with the Göksun Ophiolite and the Esence Granitoid, are represented by andesite-basalt (locally pillow lavas), and are overlain by nummulitic carbonate sediments. Geochemical data indicated that, the Helete volcanics evolved from a tholeiitic parental magma and formed in a subduction-related setting.

Sandstone petrology and geochemistry of the Oligocene–Early Miocene Panjgur Formation, Makran accretionary wedge, southwest Pakistan: Implications for provenance, weathering and tectonic setting

The Oligocene–Early Miocene Panjgur Formation is comprised of submarine fan and abyssal plain turbidites deposited within the Makran subduction complex. Sandstones of the formation are litharenite to feldspathic litharenite. Petrographic data indicates a quartzose-recycled provenance dominated by plutonic and metamorphic fragments. Major elements concentrations reveal a moderate level of mineralogical maturity and high values of Chemical Proxy of Alteration (CPA; 88.29) coupled with a high Th/U ratio (9.37), which reveals intense weathering in the source area. The Zr, Nb, Y, and Th concentrations are comparable to upper continental crust (UCC) values and trends in Th/Cr, Th/Co, and Cr/Zr ratios support contribution from a felsic source. However, enrichment in Ni and Cr, reinforced by trends in Ni/Co, Cr/V, V/Ni and Y/Ni ratios, reveals mixing of the felsic source with mafic/ultramafic source terrains. Tectonic discrimination plots suggest continental arc to active continental margin setting. This study supports the Katawaz-delta-Panjgur submarine fan model and upholds the initial southward transport of predominantly felsic detritus from the Himalayan orogenic belt controlled by the Chaman–Ornach Nal transform fault system. This study further adds that the Bela–Muslimbagh ophiolites, associated mélanges and the West Pakistan Fold–Thrust Belt, from the east, and the Chagai–Raskoh volcanic arc, from the west, were also concurrently shedding mafic/ultramafic detritus to the basin, and that the depositional system in the Makran region turned westward, roughly parallel to the present active margin of the Makran accretionary wedge.

New insights into the timing of the India–Asia collision from the Paleogene Quxia and Jialazi formations of the Xigaze forearc basin, South Tibet

The Xigaze forearc basin provides information on subduction evolution and magmatic growth of the Gangdese arc as well as on the India–Asia continental collision. Recently obtained sedimentological, biostratigraphic, petrographic, geochemical and geochronological data on Cretaceous to Paleogene strata in the Cuojiangding area (Zhongba county, south Tibet) shed new light on the tectonic evolution of the southern margin of the Lhasa Block during closure of Neotethys and initial collision with India. The uppermost Cretaceous Padana and Qubeiya formations, deposited in deltaic to inner shelf environments, and representing the final filling of the Xigaze forearc basin, were unconformably overlain by the Quxia and Jialazi formations, deposited in fan-delta environments during the Paleocene/earliest Eocene. Petrographic data and U–Pb ages of detrital zircons document the progressive unroofing of the Gangdese arc, which remained the dominant source of detritus throughout the Late Cretaceous to Paleogene. Detrital Cr-spinels in the Quxia and Jialazi formations are geochemically similar to those in Cretaceous Xigaze forearc strata but different from those hosted in Yarlung Zangbo ophiolites, suggesting that the latter were not exposed to erosion in the considered time window. Sandstone petrography, Cr-spinel-geochemistry, U–Pb age spectra and Hf isotopic ratios of detrital zircons in the Quxia and Jialazi formations match those in Paleogene sediments deposited on the distal (Sangdanlin and Zheya formations) and proximal Indian margin (Enba and Zhaguo formations), suggesting that the Quxia and Jialazi formations documents syncollisional fan-deltas deposited on top of the nascent Himalayan orogenic belt. In this scenario, the onset of the India–Asia collision predates deposition of the Quxia and Jialazi formations and is thus constrained as younger than 66Ma and older than 58Ma.

Eocene magmatism in the Tethyan Himalaya, southern Tibet

Abstract Recent studies in the Yardoi gneiss dome of the Tethyan Himalaya, southern Tibet demonstrated that the Himalayan orogenic belt experienced a major episode of crustal melting in the Mid-Eocene ( c. 44–40 Ma), represented by the genesis of a suite of high Sr/Y two-mica granites (TMGs) accompanied by leucogranites. Geochemical and U–Pb age data indicate that (1) both the leucogranite and the porphyritic leucogranite formed at c. 44–41 Ma are characterized by similar Sr–Nd–Hf isotope systematics to those in the less evolved TMGs; (2) these three suites of rocks might represent a Mid-Eocene igneous complex derived from partial melting of amphibolite under crustal thickened conditions; and (3) in contrast with the TMGs, leucogranites experienced hydrothermal-magma interactions as well as plagioclase fractional crystallization as revealed from pronounced negative Eu anomalies, much lower Sr concentrations, and elevated common Pb and U concentrations in the latest magmatic zircon overgrowth. Our data suggest that magmatic differentiation of more primitive magmas could have played a critical role in the generation of leucogranites. Documentation of partial melting of deep crustal rocks during the earliest phase of the tectonic evolution of the Himalayan orogen implies that the large-scale collisional orogenic belt could experience intensive partial melting under contraction and thickening conditions, which could profoundly affect the geophysical and geochemical properties as well as rheological properties and facilitate the initiation of movement or flow of deep crustal rocks.

Broadband Seismic Network of Iran and Increasing Quality of Seismic Recordings

In the last decade, the number of seismic stations has increased significantly, and new denser regional networks with advanced technology have been installed worldwide. Moreover, the recent improvements in the quality of seismological instruments have resulted in the application of modern broadband seismometers with high dynamic range digitizers for most seismological studies. Among various seismic data, broadband networks provide valuable data for seismological research. Broadband systems are being widely used in many research areas, such as seismic source studies and frequency‐dependent attenuation in the Earth, particularly from body waves and moment tensor solutions (Marshall et al. , 1972; Douglas, 2001). Tectonically, the Iranian plateau is located in the central part of the Alpine–Himalayan orogenic belt, which is known as one of the most active seismic regions of the world. Many major and strong earthquakes have occurred in Iran during its history (Berberian and Yeats, 1999). The 1962 Boen‐Zahra M s 7.2, 1978 Tabas M w 7.4, 1990 Manjil M w 7.4, and 2003 Bam M w 6.4 earthquakes are among the deadliest earthquakes in the world. Installation of broadband networks greatly helps to monitor the seismicity of the country, obtain accurate crustal velocity models, and study source characteristics. In Iran, major activities related to monitoring of earthquakes are carrying out by the seismography networks of the Geophysical Institute of Tehran University (IGTU) and the broadband seismic network of the International Institute of Earthquake Engineering and Seismology (IIEES). The main purpose of the IGTU network is the determination and announcement of location and magnitude of earthquakes around the country; the IIEES network is mainly used for research purposes. Local networks also have been installed in some provinces and cities, including the seismic network of Khorasan (operated by Mashhad University) and an affiliated network of seismic monitoring of the Tehran Disaster …