Geomorphic evidences of tectonic instability during the Late Quaternary Period along southern Saurashtra,western India

The coastal tract of southern Saurashtra has been studied for spectacular Miliolite Formation—its origin and depositional environment. The region had witnessed two moderate earthquakes of M_w 5.0 and 5.1 during 2007 and 2011. However, there have been limited studies which pronounce the geological and geomorphic evidences of neotectonics in southern Saurashtra. Also, there exists little to no information regarding the presence of faults from the region. The paper presents geological and geomorphic evidences of neotectonics from region between Somnath to Jafrabad, western India. A geospatial dataset was used to highlight the neotectonically active nature of the region, as well as support the claim with field evidences and drainage network anomalies. The morphometric parameters like longitudinal river profile, drainage basin asymmetry, and hypsometric integral suggest neotectonic activeness of the southern Saurashtra region. The southern Saurashtra coastal alluvial plains show presence of knick zone, ravines, coastal marine notches, and offset channels/ridges, which testifies the neotectonically active nature of the region. Presence of these features in Miliolites, Middle to Late Pleistocene age, suggests rejuvenation of the landscape post this period.     

塔里木盆地西北缘沙井子构造带断裂构造分析

沙井子构造带位于塔里木盆地西北缘,是分隔阿瓦提凹陷和温宿凸起的边界断裂。它是塔里木盆地研究最薄弱的大型断裂构造带之一。根据系统、精细的地震资料解释,沙井子构造带存在3套断裂体系:深部楔状冲断构造、狭义沙井子断裂和浅部的伸张构造。深部楔状冲断构造形成于志留纪—泥盆纪,由北西倾向的主冲断层和南东倾向的反冲断层形成构造楔; 构造楔主要由前寒武纪变质岩组成,冲断前锋楔入于寒武系中部,造成上覆地层向温宿凸起方向的急剧抬升。狭义的沙井子断裂,即通常所说的沙井子断裂,为一条高角度基底卷入型挤压走滑断裂,形成于二叠纪末—三叠纪初,错断了早期的深部冲断楔。浅部的伸展构造形成于第四纪早-中期,为一系列较小规模的正断层,沿狭义沙井子断裂呈右步雁列状排列,构成左行剪切张扭性断裂带。深部的楔状冲断构造和浅部的伸展构造是本次研究的新发现。     

Early tertiary deltaic sedimentation around Kalka and Nahan, Punjab Himalaya, India

During the Early Tertiary epoch a basin of deposition covered almost all the present Himalayan foot hill zone. Large quantities of detrital sediments were transported from the northern source area to the depositional basin. The rivers carrying the sediment load formed large delta complexes. In the area studied at least two such delta complexes, one around Kalka and the other around Nahan, were formed; of these the one around Kalka contains the greatest volume of sediments.

The recognition of the deltas is based on: (a) greater abundance of stream deposits than deposits of other environments; (b) lithologic criteria, particularly sedimentary structures, repetitive lithologic associations; (c) the general coarsening-upward nature of the sediments; (d) strong unimodal current direction; (e) the typical lenticular lithogenetic model, common in recent deltas.

The rocks of the Nahan Group are divisible into three formations at Kalka and two formations at Nahan where central formation did not develop. Himalayan tectonism has largely controlled both delta formation and stratigraphy.

The differential rates of sedimentation greatly influenced the rates of subsidence within the Nahan basin. The sediments of the Nahan Group are roughly bounded between two major phases of Himalayan uplift, namely Eocene and middle Miocene tectonic movements. The effects of intermittent tectonic pulses are well depicted in rocks of the Nahan Group. The intensity of the tectonism that controlled both the source-area rise and basin subsidence during deposition of the Nahan Group of sediments was nonuniform, both in vertical and lateral directions. Because of a generally higher rate of deposition compared to the rate of subsidence, the rocks of the Nahan group represent a normal regressive basin-filling sedimentation, forming thick detrital deposits due to progradation of younger deltas beyond the distal end of older deltas.     

帕米尔弧形构造带的构造过程与地貌特征

帕米尔弧形构造带是印度-欧亚板块碰撞变形最强烈的地区之一,是研究构造过程、地貌演化以及气候变化及其相互作用的理想场所。本文基于前人的研究成果,对帕米尔弧形构造带新生代构造单元、地貌特征和动力学演化模型进行了总结归纳,包括:主要构造单元的活动起止时间、活动量及活动速率;帕米尔弧形构造带现今的地貌特征(水系和冰川的分布);帕米尔弧形构造带6种主要的地球动力学演化模型的主要样式、优点及限制。论文提出了帕米尔弧形构造带晚新生代构造研究的三个重要的科学问题:精细厘定构造带内部的不同断裂带运动学特征和相互关系;深部地质过程与浅部响应相结合,探讨构造带形成的深部地质过程控制;将构造过程、气候特征与地貌演化作为一个耦合系统开展研究。     

Influence of structural position on fracture networks in the Torridon Group,Achnashellach fold and thrust belt,NW Scotland

In fold-and-thrust belts rocks undergo deformation as fold geometries evolve. Deformation may be accommodated by brittle fracturing, which can vary depending on structural position. We use 2D forward modelling and 3D restorations to determine strain distributions throughout folds of the Achnashellach Culmination, Moine Thrust Belt, NW Scotland. Fracture data is taken from the Torridon Group; a thick, coarse grained fluviatile sandstone deposited during the Proterozoic. Modelling infers a correlation between strain and simple curvature; we use simple curvature to infer how structural position and strain control fracture attribute variations in a fold and thrust belt.In high curvature regions, such as forelimbs, fracture intensities are high and fractures are short and oriented parallel to fold hinges. In low curvature regions fractures have variable intensities and are longer. Fracture orientations in these regions are scattered and vary over short distances. These variations do not relate to strain; data suggests lithology may influence fracturing. The strain history of fold structures also influences fracturing; structures with longer deformation histories exhibit consistent fracture attributes due to moderate-high strain during folding, despite present day low curvature. This is in contrast to younger folds with similar curvatures but shorter deformation histories. We suggest in high strain regions fracturing is influenced by structural controls, whereas in low strain regions lithology becomes more important in influencing fracturing.     

Microstructural evidences for thermal runaway and deep palaeoseismic activity (Cabo Ortegal,NW Spain)

Abstract The occurrence of high‐pressure granulite facies tectonites with features at the outcrop and thin section scale, characteristic of both pseudotachylytes and ultramylonites, is reported in the Cabo Ortegal complex (NW Spain). We interpret that these rocks formed due to a seismic event at great depth (1.4 GPa) under high‐temperature conditions (740 °C). Shear heating and thermal runaway mechanism would have been responsible for the failure of the still hot and mechanically rigid granulites and provoked melt formation and the accumulation at dilatational jogs. Ambient high P and T conditions would have led to subsequent recrystallization of the previously formed melt accounting for the present weak planar fabric.     

Geomorphic investigation of the Late-Quaternary landforms in the southern Zanskar Valley,NW Himalaya

The Suru, Doda and Zanskar river valleys in the semi-arid region of Southern Zanskar Ranges (SZR) preserve a rich repository of the glacial and fluvial landforms, alluvial fans, and lacustrine deposits. Based on detailed field observations, geomorphic mapping and limited optical ages, we suggest four glaciations of decreasing magnitude in the SZR. The oldest Southern Zanskar Glaciation Stage (SZS-4) is inferred from glacially polished bedrock and tillite pinnacles. The SZS-4 is ascribed to the Marine Isotopic Stage (MIS)-4/3. The subsequent SZS-3 is represented by obliterated and dissected moraines, and is assigned to MIS-2/Last Glacial Maximum. The multiple recessional moraines of SZS-2 glaciation are assigned the early to mid Holocene age whereas, the youngest SZS-1 moraines were deposited during the Little Ice Age. We suggest that during the SZS-2 glaciation, the Drang-Drung glacier shifted its course from Suru Valley (west) to the Doda Valley (east). The study area has preserved three generations of outwash gravel terraces, which broadly correlate with the phases of deglaciation associated with SZS-3, 2, and 1. The alluvial fan aggradation, lacustrine sedimentation, and loess deposition occurred during the mid-to-late Holocene. We suggest that glaciation was driven by a combination of the mid-latitude westerlies and the Indian Summer Monsoon during periods of cooler temperature, while phases of deglaciation occurred during enhanced temperature.     

Impact of geohydrology and neotectonic activity on radon concentration in groundwater of intermontane Doon Valley, Outer Himalaya, India

 Radon concentration was measured in 133 water samples from tubewells, handpumps, dug wells and springs of the Doon Valley, Outer Himalaya, India. The observed radon values were found to vary from 10 to 154 Bq/l whereas radium in selected water samples varied from 0.11 to 0.75 Bq/l. Three different clusters of high radon values were observed in the north-western, central and south-eastern parts of the Doon Valley. These clusters were found to be associated with tectonics (thrust/fault) and associated uranium mineralization in the area. In general, radon concentration in groundwater was found to be positively correlated with the depth of the wells, whereas no significant correlation was observed between radon concentration in groundwater and the water temperature, pH value, conductivity and altitude of the water samples. An attempt has also been made to determine the nature and extent of aquifers in the Doon Valley on radon concentration in groundwater. The variation in radon concentration within the groundwater of the study area was found to be controlled by the neotectonic activity and geohydrological processes that occur in the area. The impact of these activities on radon concentration in groundwater are discussed. Received: 17 September 1999 · Accepted: 11 April 2000     

Paleomagnetic constraints on neotectonic deformation in the Kashi depression of the western Tarim Basin,NW China

A paleomagnetic study is reported of Eocene to Pliocene formations from the Kashi depression, which aims to constrain the pattern of neotectonic deformation within the western sector of the Tarim Basin in northwest China. With the exception of Pliocene specimens from one locality (East Kulukeqiati) which show large within site-mean variations in declination, most sites from five sampled formations yield well-grouped characteristic remanent magnetizations and positive fold tests and are of probable post-depositional detrital origin. First-order consistency of paleomagnetic results from a range of rock ages and localities demonstrates that only small inter-locational vertical-axis rotation has occurred here and indicates that the Kashi depression is decoupled from the remainder of Tarim to the east and has behaved as a quasi-rigid block which has rotated by 20–30° counterclockwise relative to Eurasia and North China since the late Pliocene. The crustal-scale Talas-Ferghana Fault cuts the Tian Shan and meets the Kashi depression in the region immediately to the northwest of the study region and we find no paleomagnetic evidence for differential rotations to suggest that this fault zone extends southwards across the Kashi depression to link with the North Pamir Thrust Fault (NPTF). Instead, we argue that the southern extension of this zone is a transform-orogen junction with southward motion of the eastern wall accommodated by southward thrusting at the margins of the south Tian Shan and the Tarim Basin. We propose that dextral transpression around the margins of the crustal block incorporating the Kashi depression was responsible for the contrasting amounts of thrusting on the NPTF in the southwest and the South Tian Shan Thrust Fault in the north. Extensive evidence for neotectonism in the bordering zones of this block, as well as some paleomagnetic evidence from low unblocking temperature components, indicates that the deformation produced by block rotation is ongoing.     

Patchy charnockites from Jenapore, Eastern Ghats granulite belt, India: Structural and petrochemical evidences attesting to their relict nature

The charnockite patches that occur within leptynite host, in and around Jenapore, northern sector of the Eastern Ghats granulite belt, are disposed in a linear fashion and generally have sharp lithological contact with the host leptynite. Sometimes the patches and foliations of the host are cofolded. Also, the patches sometimes have the internalS ₁ foliation, while the host leptynite records onlyS2 foliation. Mineralogically and chemically patchy charnockites and host leptynites are distinct entities, and cannot be related by any prograde and retrograde reactions. Particularly important is the peraluminous granitic composition and high Rb/Sr ratios of the leptynites, presumably resulting from biotite-dehydration melting; as against metaluminous granodioritic to tonalitic composition and low Rb/Sr ratios of the patchy charnockites, presumably resulting from hornblende-dehydration melting. The charnockite patches here can be interpreted as caught up patches or xenolith within granitic melt (leptynite). Mg-rich rims of garnet in the charnockite patch were probably caused by heat from the crystallising melt or decompression during ascent of melt.     

Drainage morphometry of Himalayan Glacio-fluvial basin,India: hydrologic and neotectonic implications

Morphometric analysis, being widely used to assess the drainage characteristics of the river basins, has been found to be a useful tool to delineate the glacial till covered overburden material as well as to identify areas prone to flash floods in present studies. A number of parameters including the stream frequency, drainage density and drainage texture suggest that the unconsolidated, unstratified and highly permeable glacially deposited overburden till material facilitates the infiltration of snowmelt and rainwater in the Pindari glacio-fluvial basin, Eastern Kumaun Himalaya, India. Likewise, other till overburden covered glacial and proglacial areas of Higher Himalayan regions have been contributing to the groundwater budget. The shape parameters further suggest that the sub-basins with higher form factor are more prone to flash floods. Besides this, the anomalies in the morphometric parameters have been found to be a useful tool to delineate zones of active tectonics in such areas.     

Sulfur and carbon isotope compositions in the stratiform Zn-Pb-Cu sulfide deposits of the Rajpura-Dariba belt,Rajasthan, NW India: A model of ore genesis

The sulfur isotope composition of 86 sulfide minerals from the Middle Proterozoic, metamorphosed, stratiform, sediment-hosted Zn-Pb-CU sulfide deposits of Dariba and Sindeswar Kalan located within the Rajpura-Dariba belt in Rajasthan, NW India, have been determined. In addition, 16 carbonaceous and 2 carbonate rock samples from the ore zone have been analyzed for their C_tot and C_org contents and carbon isotope compositions. The sulfur isotope compositions range from 9.1 to –6.7 (mean value of 1.9). Increasing ³⁴S values stratigraphically upward are observed, particularly for pyrite and pyrrhotite suggesting a syngenetic origin for the sulfur. No marked lateral isotopic variations or isotopic variation in minerals from successive laminae in banded ore samples occur. Fractionation of sulfur isotopes between coexisting sulfides suggests that the original isotopic pattern was basically preserved during the amphibolite-facies metamorphism suffered by the deposits. C_org in carbonaceous rocks ranges 0.5–9.3 wt%, with ¹³C values between –21 and –31 (mean of –25.4) in keeping with the biogenic derivation of the carbon. Recrystallized dolostones have ¹³C values close to –14.4Geological evidence and isotopic features are consistant with the following genetic scheme: (a) base-metal ores along the belt formed from geothermal emanations carrying H₂S, produced by the chemical reduction of seawater sulfates and leaching of mafic volcanics, in a semiclosed (with respect to SO₄), shallow-water, rift-related basin with high biological activity; (b) pyrite and pyrrhotite formed diagenetically by bacterial reduction of sulfate in pore seawater in a system open to H₂S, thus bringing about the gradual enrichment of ³⁴S in these minerals stratigraphically upward; and (c) northward in the belt, at Sindeswar Kalan, the basin of ore deposition was relatively more open.     

Neotectonic activity of the Bomdila Fault in northeastern India from geomorphological evidences using remote sensing and GIS

One of the major geological structures across the Brahmaputra valley, which stretches from the Eastern Himalayas up to the Naga Hills, is the Bomdila Fault. Parts of the courses of the rivers – the Brahmaputra, Dhansiri (south-S), Bargang and many others – are aligned along this structure. The influence of this structure on the courses of these rivers has been studied in detail using topographic maps, satellite data and field evidences. The signatures obtained such as: (a) an unusually linear course of the lower part of the Dhansiri (S) river from Golaghat up to Dhansirimukh, (b) the abandonment of the westerly course of the earlier Dhansiri (S) river (flowing through Kaziranga) towards the present NW direction by avulsion, (c) knick bends in the MBT–MCT and Naga Thrust of Belt of Schuppen, (d) a linear 15 m high topographic scarp on the left bank of the Dhansiri (S) near Numaligarh and (e) an anomalous SE–NW trending course of the Brahmaputra from Dhansirimukh up to Hartamuli along with the parts of the rivers Buroi and Bargang on the north in the same trend infers the influence of a fault-type structure. Since all these linear segments of the rivers align along the NW–SE trending Bomdila Fault, it infers the influence of the later on the courses of these rivers. The neotectonic activity along this fault might have caused the linear high scarp and abandonment of earlier river courses.     

依兰-伊通断裂新构造活动规律分析

作为郯庐断裂带北段主干的依兰-伊通断裂, 其新构造活动性与活动规律仍然存在不同的认识.本次工作通过详细的野外调查, 发现该断裂内活断层广泛存在, 由东、西两支北东走向的主干活断层构成, 沿着古近纪地堑边界断层发育.这些活断层主要呈破碎型结构, 多为逆右行平移活动.通过对这些活断层一系列实测擦痕反演应力场, 显示它们多是在东西向挤压中活动的, 而现今应力场转变为北东东-南西西向区域性挤压.依据本次野外观察与¹⁴ C定年, 并结合前人定年结果与近代地震分布, 表明依兰-伊通西支活断层的最新活动时代为全新世与晚更新世相间, 而东支活断层的最新活动时代主要为早-中更新世.依兰-伊通断裂内活断层显示了明显的差异性活动, 表现为西支的活动强度明显大于东支, 西支的最新活动时代皆晚于东支, 沿走向上活动性强、弱相间与最新活动时代不断变化, 以及近代地震活动不均一分布.它们沿走向上的分段性、差异性活动主要是因为被一系列北西向断层切断所致.     

Luminescence dating of neotectonic activity on the southwestern coastal plain,Taiwan

The southwestern coastal plain of Taiwan is heavily urbanised, with a population of more than 6 million. The area is known to be subsiding, and the resulting basin is filled with thick fluvial deposits, of at least 200 m thickness. In the past century, three large earthquakes have occurred in the area; two caused surface ruptures, and resulted in large property loss and more than 2000 casualties. There is an urgent need for an understanding of the dynamics and recurrence intervals of this neotectonic activity, but little is known of the chronology of the late Pleistocene deposits. Recently more than 20 cores longer than 250 m were taken from the coastal plain as part of a large hydrogeological investigation, and basic data on lithology, hydrogeology and palaeobiology were collected. The base of these cores is beyond the ¹⁴C age limit, and so the application of luminescence dating to these sediments has been investigated.Optically stimulated luminescence methods have been applied to quartz sand-sized grains extracted from 29 samples. Dosimetry based on gamma spectrometry is also compared with ICP-MS and XRF analyses. In the age range up to ∼40 ka, radiocarbon ages are compared with the luminescence results, to give confidence that the initial bleaching of these sediments was sufficient. The luminescence ages are then discussed and differential rates of basin subsidence are deduced. It is clear from these data that the study area is tectonically active, and it may be that regions of similar subsidence rate correlate with identifiable geological structures.     

In-situ LA-ICP-MS trace elemental analyses of magnetite: Cu-(Au,Fe) deposits in the Khetri copper belt in Rajasthan Province,NW India

Magnetite is common in many ore deposits and their host rocks, and is useful for petrogenetic studies. In the Khetri copper belt in Rajasthan Province, NW India, there are several Cu-(Au, Fe) deposits associated with extensive Cu ± Fe ± Au ± Ag ± Co ± REE ± U mineralization hosted in phyllites, schists and quartzites of the Paleoproterozoic Delhi Supergroup. Ore bodies of these deposits comprise dominantly disseminated and vein-type Cu-sulfide ores composed of chalcopyrite, pyrite, and pyrrhotite intergrown with minor magnetite. There are also Fe-oxide ores with minor or no Cu-sulfides, which are locally overprinted by the mineral assemblage of the Cu-sulfide ores. In addition to the Fe-oxide and Cu-sulfide ores, the protolith of the Delhi Supergroup includes banded iron formations (BIFs) with original magnetite preserved (i.e. magnetite-quartzites) and their sheared counterparts. In the sheared magnetite-quartzites, their magnetite and quartz are mobilized and redistributed to magnetite and quartz bands. Trace elemental compositions of magnetite from these types of ores/rocks were obtained by LA-ICP-MS. The dataset indicates that different types of magnetite have distinct concentrations of Ti, Al, Mg, Mn, V, Cr, Co, Ni, Zn, Cu, P, Ge and Ga, which are correlated to their forming environments. Magnetite grains in magnetite-quartzites have relatively high Al (800–8000 ppm), Ti (150–900 ppm) and V (300–600 ppm) contents compared to those of BIFs in other regions such as the Yilgarn Craton, Western Australia and Labrador, Canada. The high Al, Ti and V contents can be explained by precipitation of the magnetite from relatively reduced, Al–Ti-rich water possibly involving hotter, seafloor hydrothermal fluids derived from submarine mafic volcanic rocks. Magnetite in sheared magnetite-quartzites is generally irregular and re-crystallized, and has Ni, Mn, Al, Cu and P contents lower than the magnetite from the unsheared counterparts, suggesting that the shearing-related mobilization is able to extract these elements from original magnetite. However, elevated contents of Ti, V, Co, Cr, Ge and Mg of the magnetite in the sheared magnetite-quartzites can be ascribed to involvement of external hydrothermal fluids during the shearing, consistent with occurrence of some hydrothermal minerals in the samples.Compositions of magnetite from the Fe-oxide and Cu-sulfide ores are interpreted to be controlled mainly by fluid compositions and/or oxygen fugacity (fO₂). Other potential controlling factors such as temperature, fluid–rock interaction and co-precipitating minerals have very limited impacts. Magnetite in the Cu-sulfide ores has higher V but lower Ni contents than that of the Fe-oxide ores, likely indicating its precipitation from relatively reduced, evolved fluids. However, it is also indicated that the two types of magnetite do not show large distinctions in terms of concentrations of most elements, suggesting that they may have precipitated from a common, evolving fluid. We propose a combination of Ge versus Ti/Al and Cr versus Co/Ni co-variation plots to discriminate different types of magnetite from the Khetri copper belt. Our work agrees well with previous studies that compositions of magnetite can be potentially useful for provenance studies, but also highlights that discrimination schemes would be more meaningful for deposits in a certain region if fluid/water chemistry and specific formation conditions reflected in compositions of magnetite are clearly understood.     

Generation of leucogranites in the Kerala Khondalite belt,Southern India

Psammitic and pelitic gneisses of the Kerala Khondalite belt in southern India were subjected to granulite-facies metamorphism and migmatisation through fluid-absent biotite dehydration-melting which led to the generation of garnet-bearing leucogranites. Geochemical investigations provide support that the leucogranites were generated from gneisses compositionally similar to those into which they were emplaced.The intrusion of apatite-rich granites subsequent to the garnet-bearing leucogranites is recognized predominantly in leptynitic gneisses. A comparison of the chemical composition of both garnet- and apatite-bearing varieties displays a systematic shift to intermediate compositions (increase in CaO, FeO, LREE, Zr, Y; decrease in SiO₂ and δ¹⁸O) which coincides with higher modal abundances of apatite, garnet and biotite and decreasing contents of quartz and alkalifeldspar. The observation that apatite occurs in aggregates together with biotite and/or garnet as well as the extreme concentrations of FeO, LREE and Zr in some of the apatite-beraing granites which clearly exceed the maximum solubility values for these elements in granitic melts indicates that dehydration-melting alone, as it has been proposed for the generation of garnet-bearing leucogranites, cannot have been responsable for generation of apatite-rich leucogranites but that additional processes like crystal entrainment and accumulation or liquid removal must also have played a role.     

Orientations of palaeotectonic features as a key to understanding the neotectonic block rotation of the Kocaeli peninsula,NW Turkey

Due to northward subduction of Neotethys, the ?stanbul zone collided with the Sakarya zone in northwest Turkey during the early Eocene. Subsequently, this region was subjected to compressional forces during the late Eocene–early Miocene period. Folds, thrusts and reverse faults developed approximately parallel to long axes of the ?stanbul zone. NNW–SSE oriented conjugate strike‐slip faults developed with continued contraction. In addition to the orientations of palaeotectonic features, the morphotectonic, stratigraphic and seismic characteristics expose differences between the northeastern Marmara peneplain and the southern Black Sea highland. This study reports causes of this diversity reflecting the neotectonic evolution of the ?stanbul zone. The diversity is related to the clockwise rotation of the Kocaeli peninsula between two dextral zone‐bounding faults and two sinistral block‐bounding faults. The principle factors of this process were the development of the North Anatolian fault zone (NAFZ) and the related evolution of the Adapazar?–Karasu fault zone (AKFZ), the Bosphorus fault zone (BFZ) and the Northern Boundary fault (NBF).