East-west Trending Research Articles

Structural framework of the Wagad uplift and adjoining regions, Kutch rift basin, India, from aeromagnetic data

The Kutch sedimentary basin formed during the Late Triassic breakup of Gondwanaland is characterised by horst and graben structures consisting of several east–west trending uplifts surrounded by low-lying plains. The eastern part of the basin has a diverse landscape comprising the Wagad uplift, Banni plain, Island Belt uplift and the Rann of Kutch. This area is bounded by major faults like the South Wagad Fault (SWF), Gedi fault and the Island Belt Fault. The lineaments/faults present in the region at different depth levels and the propagation of these features through the different sedimentary layers are studied using the semi-detailed aeromagnetic data collected over the basin. The aeromagnetic anomaly map depicts several major E–W, NE–SW and NW–SE oriented lineaments/faults, which probably represent structural trends associated with different stages of evolution of this rift basin. Power spectral analysis of the differential reduced to pole magnetic data indicates the presence of four magnetic interfaces. The slopes identified from the 1D power spectra were used for designing matched bandpass filters for isolating and enhancing the magnetic signatures present within those interfaces. Different edge detection techniques were used to delineate the magnetic contacts/faults/lineaments present in those interfaces. In addition, we have computed the radially averaged power spectrum of 121 subset grids each with a dimension of 20 km × 20 km from which three magnetic interfaces were delineated and compared with the stratigraphic sequence of the Wagad uplift and adjoining regions. A major NE–SW fault is delineated from this analysis and suggests that this fault has depth persistence as it dislocates the different magnetic interfaces. Integration with stratigraphic data suggests that this fault was formed prior to the deposition of Miocene Kharinadi formation. We have interpreted that this fault, forming the eastern limit of the Banni basin, might have formed during the passage of the Indian plate over the Reunion hotspot. Based on the results of the aeromagnetic data analysis and other published data, we propose a generalised evolutionary model for the study region.

Geochemistry and tectonic setting of the supracrustal rocks from the central part of the Bundelkhand craton, India

Supracrustal rocks (mafics and ultramafics) occurs along with banded iron formation, and felsic volcanics around Babina, Dhaura, and Mauranipur linear east-west trends in central part of the Bundelkhand craton represent Archean crust. The mafic and ultramafic rocks geochemically classified into Komatiite and Basaltic Komatiite and have high-Fe Tholeiitic in composition which may relate with the primitive mantle. The major and trace element geochemistry of mafic and ultramafic rocks correspond to hydrated mantle with wedge tectonic sources and ocean ridge geological characteristics.

Deep Structure of Central Menderes Massif: data from deep geothermal wells

The Menderes Massif is a major Alpide metamorphic complex in western Turkey; it is subdivided into southern, central, and northern submassifs by the east-west trending grabens. The basement of the southern Menderes Massif consists of Neoproterozoic micaschists (Selimiye Formation) intruded by Neoproterozoic granites. The basement is overlain by Permo-Carboniferous phyllite, marble, and quartzite (Goktepe Formation), which pass up into a thick sequence of Mesozoic marbles with emery horizons (Milas Marble). The marbles are overlain by latest Cretaceous recrystallized pelagic limestone and Paleocene metaclastics, which are thrusted over by the Lycian nappes. The metamorphism and deformation of the Phanerozoic sequence of the Menderes Massif is Eocene in age. The structure of the central Menderes Massif is controversial with views ranging from an inverted metamorphic sequence to a pile of nappes. Here we report the results from four deep (>3 km) geothermal wells from the central Menderes Massif. Two distinctive lithological units are differentiated in the wells. The top 0.5 to 1 km of the well sections are made up of micaschists, correlated with the Neoproterozoic Selimiye Formation, whereas the lower parts of the wells have cut through graphite-bearing quartzite, phyllite, and marble regarded as being parts of the Goktepe Formation and Milas Marble. The lithological differences are also picked up by a magnetotelluric study, which shows a sharp increase in the conductivity at the contacts of the Selimiye and Goktepe Formations. The question of whether the inversion of the stratigraphic sequence is due to thrusting or recumbent folding is still open.

Geology of the Eastern Part of the Volcanic-Kendeng Zone of East Java: Stratigraphy, Structures and Sedimentation Review from Besuki and Situbondo Areas

The Tertiary stratigraphy of Situbondo was constructed by a series of volcanoclastic-carbonate turbidite facies of Menuran Formation with Pacalan limestone Member, and Leprak Formation. These formations formed a regional east-west trending circular anticlinorium. The Tertiary formations were covered by Quaternary volcano-clastic Ringgit Formation and subsequent younger Bagor volcanic products. The oldest Tertiary rock units are the Late Miocene-Pliocene Menuran Formation, with Pacalan Limestone Member. Formation is mainly composed of foram-rich marls and calcareous, sometimes tuffaceous sandstones, with conglomerate intercalations. Sedimentation of this formation is interpreted as to be a mixing, from proximal to distal turbidite, involving volcaniclastic and carbonate sources, in a bathyal open marine environment. The Early Pliocene Leprak Formation overlies conformably the Menuran Formation, which consists of alternating calcareous sandstones and tuff sandstones deposited in a bathyal open marine environment with proximal turbidite mechanism suggesting that basin depocenter was located to the east. Up to Late Pliocene, the region was dominated by developments proximal turbidite volcanoclastic sedimentation of The Leprak Formation, contemporaneous with increasing volcanic activity in the south. Deformation of Plio-Pleistocene in Java is believed to be the last major tectonic period, which forms the west-east trending structures. In Situbondo area, folding structures in this direction involves the Neogene Menuran Formation, Pacalan Member and Leprak Formation. Volcanic activity persists, and increases, with the activity of Ringgit-Beser volcano in Pleistocene. These late events of magmatism, volcanism and uplift were contributed to the last structural configuration of the area.Keyword : Situbondo, structural geology, volcanic-kendeng zone, stratigraphy

Geology of the Eastern Part of the Volcanic-Kendeng Zone of East Java: Stratigraphy, Structures and Sedimentation Review from Besuki and Situbondo Areas

The Tertiary stratigraphy of Situbondo was constructed by a series of volcanoclastic-carbonate turbidite facies of Menuran Formation with Pacalan limestone Member, and Leprak Formation. These formations formed a regional east-west trending circular anticlinorium. The Tertiary formations were covered by Quaternary volcano-clastic Ringgit Formation and subsequent younger Bagor volcanic products. The oldest Tertiary rock units are the Late Miocene-Pliocene Menuran Formation, with Pacalan Limestone Member. Formation is mainly composed of foram-rich marls and calcareous, sometimes tuffaceous sandstones, with conglomerate intercalations. Sedimentation of this formation is interpreted as to be a mixing, from proximal to distal turbidite, involving volcaniclastic and carbonate sources, in a bathyal open marine environment. The Early Pliocene Leprak Formation overlies conformably the Menuran Formation, which consists of alternating calcareous sandstones and tuff sandstones deposited in a bathyal open marine environment with proximal turbidite mechanism suggesting that basin depocenter was located to the east. Up to Late Pliocene, the region was dominated by developments proximal turbidite volcanoclastic sedimentation of The Leprak Formation, contemporaneous with increasing volcanic activity in the south. Deformation of Plio-Pleistocene in Java is believed to be the last major tectonic period, which forms the west-east trending structures. In Situbondo area, folding structures in this direction involves the Neogene Menuran Formation, Pacalan Member and Leprak Formation. Volcanic activity persists, and increases, with the activity of Ringgit-Beser volcano in Pleistocene. These late events of magmatism, volcanism and uplift were contributed to the last structural configuration of the area.Keyword : Situbondo, structural geology, volcanic-kendeng zone, stratigraphy

Divide migration in response to asymmetric uplift: Insights from the Wula Shan horst, North China

Drainage divides play significant roles in shaping landscapes. Nevertheless, they are not static through space and time. Previous numerical models have demonstrated divide motions in response to asymmetric tectonic uplift. However, natural examples that have nicely recorded these processes and hence could verify the results of numerical simulations are still lacking. In this contribution, we integrate the results of digital elevation models (DEMs)-based morphotectonic analysis with the tectonic landforms observed during field surveys to investigate the status of topography and probable drainage evolution history of the Wula Shan (Shan means ‘Mountain(s)’ in Chinese), a roughly west-east trending horst block bounded by normal faults in the Hetao Graben, North China. The results demonstrate that the differences of obtained geomorphic indices are significant between the southern and northern drainage basins; higher hypsometric integral (HI) and normalized channel steepness (ksn) values, and lower ratios of valley floor width to valley height (VF) indicate higher tectonic uplift rate at the southern flank. The main divide of the Wula Shan had migrated northward, which was probably caused by the decrease of asymmetry in vertical uplift associated with the margin faults. We suggest the results of this study may shed new light on divide mobility as well as landscape evolution in actively extending regions.

The Archean Victoria Fjord terrane of northernmost Greenland and geodynamic interpretation of Precambrian crust in and surrounding the Arctic Ocean

In far North Greenland at the head of Victoria Fjord (∼81°30′N), a ∼1000 km2 exposure of Precambrian crystalline basement rocks is a window through the region's extensive latest Neoproterozoic and Paleozoic Arctic Platform sedimentary cover sequence. These basement rocks, named here the Victoria Fjord terrane, are dominated by weakly-foliated granodioritic orthogneisses, with lesser amounts of migmatite. These are intercalated with strips of supracrustal rocks dominated by paragneisses. This poorly-exposed Archean terrane at Greenland's northern tip is succeeded to the south by the extensive east-west trending Paleoproterozoic Inglefield Mobile Belt of juvenile arc rocks.The Victoria Fjord terrane granodiorites have zircon U-Pb ages from 3292 ± 14 Ma to ∼3260 Ma. Reconnaissance U-Pb dating on schlieric migmatite zircons yielded ages of ∼3280, 3400 and 3500 Ma. Paragneiss detrital zircons have ages of mostly ∼2710 Ma, with a minority of 3000–2900 Ma grains. This demonstrates that these sedimentary rocks were not derived from the local basement. Post- Archean magmatic or metamorphic zircon was not detected in any of the samples.Initial εHf of 3290–3260 Ma granodiorite and granite zircons ranges from −4 to +2, and the magmatic protoliths are interpreted as sourced from the melting of somewhat older (3500–3400 Ma) Paleoarchean crust, represented by paleosome in the migmatites. The paragneiss 3000–2900 Ma detrital zircons were derived from juvenile felsic crust of that age. The ∼2710 Ma group show negative correlation of Th/U and initial εHf, such that those with high Th/U up to >2.0 have εHf values of −6 to −10. The ∼2710 zircons were sourced from mafic rocks formed by melting of much older (Paleoarchean?) enriched mantle which was variably contaminated by 3000–2900 Ma crust during its ascent.The Victoria terrane is unique amongst the Archean basement terranes in Greenland because it is dominated by 3500–3260 Ma crust. However, the Arctic basin contains detrital zircons of that age, and rocks of that age also occur in eastern Siberia and northwestern Canada. Implications for high Arctic early Precambrian geodynamics are discussed.

Audio-magnetotelluric investigation of Bakreswar Geothermal Province, Eastern India

Bakreswar Geothermal Province (BGP) lies over the Archaean gneisses and schists formations. The heat flow and geothermal gradient of BGP are \(\sim \)230 mW/m\(^{2}\) and \(95{^{\circ }}\hbox {C}/\hbox {km}\), respectively. The Bakreswar hot spring (BHS) (\(23{^{\circ }}52^\prime 30^{\prime \prime }\hbox {N}\); \(87{^{\circ }} 22^{\prime }30^{\prime \prime }\hbox {E}\)) is located over NNW–SSE trending fault. It lies in the eastern flank of BGP and is connected by Sone–Narmada–Tapti (SONATA) and deep-seated ONGC fault systems. Earlier studies indicated that the geothermal fluid flowed towards the same path as that of deep ONGC fault. In view of this, 24 audio-magnetotelluric soundings in the frequency range 10 kHz–10 Hz were conducted at one end of the deep ONGC fault, which is about 20 km northwest of BHS. The data analysis indicated that the data are internally consistent. Analysis of dimensionality and strike are indicative of complex conductivity structures. The 3D inversion of full impedance was performed to obtain a conductivity model of the study area and resulted in root mean square (RMS) for sites close to unity. The results have been discussed by extracting cross-section along 3 to 7 profiles (four of the profiles are perpendicular to strike, whereas three profiles were oblique to the strike direction and are perpendicular to east–west trending ONGC faults). Several low conducting zones are observed in the profiles drawn parallel and perpendicular to the strike. These common conductors show consistent model features but modified resistivity and dimension. Depth slices from 200 to 1400 m suggest that the conductors in the northern part of the study area are deeper than the conductors in the south. The study area is dominated by several shallow conductors which coincide with several fractures present in the study area. The conductors are surrounded by a resistive feature that can act as an impermeable bed and probably restricts the flow of water within the zone. The four major conductors along the oblique profiles (profiles perpendicular to deep ONGC fault) coincide with deep ONGC fault, through which probably the geothermal fluid flows.

Implication of Mesoproterozoic (∼1.4 Ga) magmatism within microcontinents along the southern Central Asian Orogenic Belt

The southern Central Asian Orogenic Belt contains numerous microcontinents including the Kazakhstan-Yili block, Central Tianshan Arc and Junggar block in the west, the Erguna, Xing'an, Songliao and Jiamusi-Khanka blocks in the east, bridging by the Tuva-Mongolia block, Beishan Orogenic Belt and Alax block in the central region. New geochemical and geochronological data from the microcontinental blocks within the southern Beishan Orogenic Belt provide new insight into the Precambrian crustal evolution of this region. Five granitoids from the Jiujing region yielded igneous zircon 206Pb/238U ages of 1450–1401 Ma, and zircon xenocrysts from late Paleozoic plutons in the Jiujing, Qiaowan, and Shibandun regions have 206Pb/238U ages that also cluster at ∼1.4 Ga. Those data suggest that crust of this age is widespread beneath the southern Beishan Orogenic Belt. The ∼1.4 Ga zircons display depleted Hf isotopic signatures (εHf(t) = 2.0–11.1) and show relatively young two-stage Hf model ages (1.9–1.4 Ga), indicating rapid reworking of juvenile mantle-derived materials. Integrating these results with similar geochronological data from the Kyrgyz North Tianshan, Yili block, Central Tianshan Arc, northern Alxa block and Xilinhot block, we propose that the CAOB incorporates an extensive assemblage of Mesoproterozoic (1450–1360 Ma) magmatism that can be traced over ca. 3000-km long a west-east trending belt. These Mesoproterozoic granitoids display distinct geochemical signatures (e.g., Ga/Al*10,000 ranging from 1.46 to 3.88 and Zr + Nb + Ce + Y varying largely from 101 to 1066 ppm) and show a temporal progression from orogenic to anorogenic over a relatively short period. This suggests a tectonic setting that likely evolved from compressional to extensional environments during 1450–1360 Ma, perhaps resulting from slab roll back. We suggest that the 1450–1360 Ma magmatism along the southern CAOB corresponds with a transition from a compressional to extensional environment on the margin of the Nuna supercontinent.

Impact of Middle Pleistocene (Saalian) glacial lake-outburst floods on the meltwater-drainage pathways in northern central Europe: Insights from 2D numerical flood simulation

The terrestrial margins of the Middle Pleistocene ice sheets in northern central Europe were characterised by the formation of extensive ice-dammed lakes, which were controlled by the blockage of spillways by the ice margin. The largest ice-dammed lake had a volume of ∼224 km³ and formed in a late stage of the first Saalian ice advance (MIS 6) in central Germany. The failure of the ice dam in the bedrock-outlet channel triggered a major glacial lake-outburst flood. Flood-related erosional and depositional features include large-scale scours, trench-like channels, streamlined hills, giant bars and run-up deposits, indicating a wide spreading of the outburst flood in an early stage and the incision of trench-like valleys in a later stage. The incision of large valleys in the proximal flood pathway strongly impacted the regional drainage system by providing an efficient drainage network. The trench-like channels initiated by the lake-outburst flood became a crucial part of the ice-marginal drainage and subsequent fluvial system.The reconstructed outlet hydrographs imply peak discharges of 465,000–673,000 m³s−1. The numerical simulation indicates flow depths of up to 87 m, flow velocities of up to 7 ms−1, peaks of the bed-shear stress of 2500 Nm−2 and the inundation of large parts of northwestern Germany and the northern Netherlands. The numerical simulation of the outburst flood was conducted on both the modern digital elevation model and on palaeotopographic models, representing the palaeotopography prior to the outburst flood and during maximum flood-related incision, respectively.Distally, the outburst flood probably followed an east-west trending route through northwestern Germany and the central Netherlands into the ice-dammed lake in the southern North Sea Basin. The added water volume might have led to the overspill and drainage of the proglacial lakes in the central Netherlands and the North Sea Lake in a chain reaction, eventually opening an east-west trending meltwater-drainage pathway along the southwestern margin of the decaying ice sheet.

Structural Architecturing of the Western Khisor Range, North of Saiyiduwali: Implications for Hydrocarbon Prospects, KPK, Pakistan

Western Khisor Range segment of the Trans-Indus ranges is a south-vergent, east-west trending foldthrustbelt that protrudes southward into Himalayan foreland deep. The frontal flanks of range are characterizedby east-west trending parallel to enechelon, plunging local anticlines and synclines structures. General structuralstyle of folds was observed asymmetric to overturn and dominantly south vergent. The frontal outskirts of thestudy area is demarcated by a youngest partly emergent thrust fault named as Khisor Thrust. Outcrops projectionto subsurface of the structural features suggests a thin-skinned tectonic mechanism for growth of the westernKhisor Range where gliding surface for the frontal thrust sheet being located within the Cambrian rocks ofJhelum Group at a maximum depth of 4km. The structural evolution of the western Khisor Range is generallyascribed to southward directed thrust transferral system along the basal decollement being observed at base ofthe Cambrian Khewra Sandstone. Along this detachment horizon the Khewra Sandstone emplaced over theRecent alluvium and boulder bed deposits. The Khisor Thrust fault bulldozed the fore limb of the SaiyiduwaliAnticline and demarcates the north-western proximity of the Punjab Foredeep. The Khisor Thrust sheet ispredominantly comprised of the shallow marine rocks of Paleozoic to Mesozoic, laterally extended along therange. The stratigraphic framework of the western Khisor Range is considerably related and correlative to theeastern Trans-Indus and Salt ranges. Cambrian strata of the western Khisor Range comprise of Jhelum Groupwhere its apex is underlain by the Permian Nilawahan and Zaluch groups rocks, consists of the Sardhai andAmb formations. The Sardhai Formation was observed 50m thick and consists of dark gray to blackish gray andblack carbonaceous shale while the lower constituents of the Amb Formation contains dark gray carbonaceousand calcareous shale up to 30m thick, which is favorable setting for hydrocarbon potential of the area. Blendingof structural style and stratigraphic framework of the western Khisor Range urges that the south-westernforedeep in proximity of Saiyiduwali is significantly associated for the hydrocarbon research, as thickcarbonaceous lithofacies of both formations are viable potential source rocks.

Characteristics of tectonic deformation of the melange zone in the Lachlan Orogen along eastern coast of Australia

ABSTRACT The Narooma-Batemans Bay (NBB) area along the southeast coast of Australia is a part of the eastern zone of the Early Paleozoic Lachlan Orogen. In the NBB, a set of rock association consisting of turbidites, siliceous rock, basic lava, and argillaceous melange zone is mainly developed. According to systematic field geological survey, the deformation of 3 stages (D1, D2, and D3) was identified in the NBB. At stage D1, with the original bedding S0 in a nearly east-west trending as the deformation plane, tight folds, isoclinal folds, and other structures formed in the NBB accompanied by structural transposition. As a result, crenulation cleavage developed along the axial plane of the folds and schistosity S1 formed. At stage D2, with north-south-trending schistosity S1 as the deformation plane, a large number of asymmetrical folds and rotated porphyroclasts formed owing to thrusting and shear. At stage D3, left-lateral strike-slip occurred along the main north-south-trending schistosity. Based on the analysis of the characteristics of tectonic deformation in the NBB and summary of previous research results, it is determined that the early-stage (D1) deformation is related to Ordovician Macquarie arc-continent collision and the deformation at stages D2 and D3 is the result of the westward subduction of Paleo-Pacific Plate. That is, it is not the continuous westward subduction of the Paleo-Pacific Plate that constitutes the evolution model of the NBB as previously considered.

New Crustal Framework in the Amazon Craton Based on Geophysical Data: Evidences of Deep East-West Trending Suture Zones

The Tapajos mineral province (TMP), in the Brazilian Amazon Craton, comprises NW-SE Paleoproterozoic insular magmatic arcs accreted to the Carajas Archean Province (CAP). We present new geological and geophysical data pointing toward a different evolutionary model for the TMP. Results obtained from magnetic data indicate that NNW-SSE trending structures occur at shallow crustal levels. Furthermore, an E-W structural framework shows up at 15.4 km depth, in disagreement with the accreted island arc orientation. These E-W structures are associated with north-dipping blocks, reflecting ductile compressive tectonics, similar to the tectonic setting found in the CAP. We interpret these E-W structures of the TMP as the continuity westwards of similar structures from the CAP, under the Paleoproterozoic volcanic rocks of the Uatuma Supergroup. Based on this evidence, we propose that Paleoproterozoic arcs have been formed in an Archean active continental margin, instead of in island arcs. This novel tectonic setting for the TMP has significant implications for the tectonic evolution and the metallogenic potential of the southern portion of the Amazon craton, particularly for Paleoproterozoic magmatic-hydrothermal (epithermal and porphyry) precious and base metal systems.

Gravity Structure around Mt. Pandan, Madiun, East Java, Indonesia and Its Relationship to 2016 Seismic Activity

Abstract Java Island is part of the island arc influenced by subducting Indo-Australian beneath Eurasian tectonic plates, therefore there is high seismic activity and an active volcanic chain trending East-West. One of the volcanoes in Java Island is Mt. Pandan, northern part of Madiun, East Java region, which is known as one of the dormant volcano in the region. According to the list of volcanoes in Indonesia Mt. Pandan is not classified as an active volcano. The previous studies mentioned that Mt. Pandan is a modern volcano which is located in the Kendeng zone. On June 25, 2015, there was felt earthquake (M 4.2) causing several houses damaged around Mt. Pandan as reported by Agency for Meteorology, Climatology, Geophysics (BMKG), Indonesia and then in February 2016, more than twenty small earthquakes (M < 4) occurred again in the area. In order to understand the structure beneath Mt. Pandan, we have conducted gravity measurement and seismicity analysis through hypocenter relocation. Our results show prominent low gravity and density anomalies by forward modeling derived from residual anomaly around Mt. Pandan area. The clusters of small earthquakes appear at depths of less than 30 km beneath Mt. Pandan. The selected focal mechanism of the event in the area is left-lateral faulting in the north and oblique dominant thrust in the south of Mt. Pandan. Some indications related to submagmatic activities such as hot springs and warm ground is found. Our interpretation is this phenomenon may be related to tectonic and magmatic activities. On the other hand, it confirms also that Mt. Pandan is probably a modern volcanic center.

Re-examination and reinterpretation of the stratigraphy of the Matjies River Formation, Cango Caves Group, Neoproterozoic to early Palaeozoic Saldania Belt, South Africa

Abstract The carbonate-siliciclastic rocks of the late Neoproterozoic Matjies River Formation, Cango Caves Group (CCG) in South Africa, form part of the Neoproterozoic to early Palaeozoic Saldania Belt. Re-examination of the Matjies River Formation, consisting of the Nooitgedagt and overlying Kombuis members, led to a revision of the stratigraphy and interpretation of the geology of this formation. The discovery of unconformities, locally associated with palaeovalleys and/or ferruginous sedimentary rocks, makes it possible to subdivide the Matjies River Formation into a number of unconformity-bounded sequences which comprise coarsening upward and to a lesser extent fining upward sedimentary cycles. The unconformities and palaeovalleys are of tectonic and/or possibly glaciogenic origin. The clastic sediments of the Nooitgedagt Member were thought to be supplied from an eastern source area. However, the occurrence of thick very coarse, locally poorly-sorted conglomerates, which occur in a restricted north to south trending zone, also indicates a northern and/or southern provenance for the Nooitgedagt Member. The Nooitgedagt Member has been deformed in north-northeast - south-southwest trending synclines and anticlines during the Neoproterozoic to early Palaeozoic Pan-African Orogeny. East-west trending synclines and anticlines, which formed during the Palaeozoic and early Mesozoic orogenic events, are quite common in the overlying Kansa Group and Cape Supergroup but were not found in the Matjies River Formation. Soft-bodied Ediacaran-type and skeletal fossils were found in the Nooitgedagt and Kombuis members and indicate an Ediacaran age for the Matjies River Formation.

Normal faulting and viscous buckling in the Tibetan Plateau induced by a weak lower crust

Flow of weak lower crust has been invoked to reconcile observed topographic gradients, uniform elevations, slow seismic velocity, and high conductivity measured in the Tibetan Plateau, with viscosity estimates of 1016–1021 Pa·s. Here we investigate the dynamic response resulting from a range of lower crust viscosities in a 3-D lithospheric-scale geodynamic simulation of the India–Eurasia collision zone to determine bounds of physically viable lower crustal strengths. We show that thickening of the plateau is accommodated through viscous buckling of the upper crust in response to lower crustal flow for a lower crustal viscosity on the order of 1020 Pa·s. This generates two east–west trending bands of surface subsidence and dilatation consistent with observed normal faulting and estimates of vertical velocity. These results suggest viscous buckling of the upper crust, induced by lower crustal flow from gravitational pressure gradients due to high topography, is responsible for the observed extension in Tibet.

Hydrothermal Alteration in Porphyry Cu-Mo-Au Mineralizations of the Chagai Arc, Balochistan, Pakistan

Subduction-related east-west trending Chagai Arc located in the western part of Pakistan. This arc is the western extension of Tethyan Magmatic Belt which is about 5000 km long and extends from central Europe, Turkey, Iran, and Pakistan. During the last four decades, several porphyry copper settings were reported from the Chagai Arc. Seven more famous occurrences are selected for the present study owing to more detailed work carried out on them. From west to east these deposits include Saindak, Reko Diq (formerly known as Koh-e-Dalil), Humai, Missi, Durbanchah, Dasht-e-Kain and Ziarat Pir Sultan. Hydrothermal alterations in the porphyry copper setting of Chagai Arc are mostly associated with tonalite porphyry stocks, except Durbanchah and Humai prospects which are hosted in dacite porphyry stocks, whereas Missi Prospect occurs in a granodiorite batholith. The alteration is normally developed in a concentric zonal pattern as observed in the majority of the world deposits, except that absence of a regular argillic and peripheral zone. In most of the occurrences the potassium silicate alteration zone (K-alteration zone) occurs usually within the intrusive porphyry stock, but in Saindak and Reko Diq deposit, some of the adjacent wall-rock sediments, and in Durbanchah setting the microdioritic country rock, has also undergone the K-alteration. Quartz sericitic or phyllic alterations zones are developed in all the occurrences as continuous or discontinuous haloes around the K-alteration zone except in Durbanchah prospect. In Humai prospect an advanced argillic alteration zone is developed around the K-alteration zone. Propylitic alteration has also developed in almost all settings and generally encircles the quartz sericitic alteration. The oxide mineralization is generally represented by goethitic jarositic, hematitic limonites and malachite, with minor pitch limonite, chrysochola, neotocite, brochanthite and molybdite. Hypogene mineralization is represented by pyrite, chalcopyrite and minor bornite. A regular supergene sulfide enrichment is only reported from the Reko Dik deposit and represented by chalcosite and covellite in other deposits restricted incipient type supergene sulfide enrichment is encountered. In terms of ore reserves the Riko Dik deposit is on the top with 2,200 million tons of copper followed by Saindak with 412 million tons and Dasht-e-Kain 350 million tons. Grade wise Reko Diq Deposit is again on the top with 0.53% Cu, 0.01% Mo and 0.3g/t Au, followed by Saindak with 0.4% Cu, 0.015% Mo and 0.35 g/t Au. Dasht-e-Kain deposit contains 0.35% Cu and 0.015% Mo. Gold has not been reported from the Dasht-e-Kain deposit. From other deposits of the Chagai Arc ore reserves and grade are not reported so far.

Geophysical Log-based Coal Characterization of Middle Permian Barakar Formation from North Karanpura Coal Field, India

Abstract North Karanpura coal field is the western most marginal coal bearing segment of east-west trending Damodar valley basin. It consists of middle Permian Barakar Formation with sandstone, siltstone, coal and shale being the dominant lithofacies, deposited in a fluvial meandering environment, giving rise to repetitive fining upwards cycles. Study of geophysical logs, the drilled core holes were used to identify lithofacies, correlate coal seams with split-merge behavior; which has been used to understand lateral and vertical facies disposition. Geophysical logs have been employed to compute various coal assay parameters – ash, fixed carbon, moisture, volatile content, cleat porosity, vitrinite reflectance seam wise. Study of log based coal assay parameters, calibrated with lab based values depicts lateral coal quality variation, i.e. decreasing ash content, higher fixed carbon from east to west, which can be a great proxy for future development of field or mine planning.

Alteration Heterogeneities in Peridotites Exhumed on the Southern Wall of the Atlantis Massif (IODP Expedition 357)

Serpentinized and metasomatized peridotites intruded by gabbros and dolerites have been drilled on the southern wall of the Atlantis Massif (Mid-Atlantic Ridge, 30°N) during International Ocean Discovery Program (IODP) Expedition 357. They occur in seven holes from five sites making up an east-west trending, spreading-parallel profile that crosscuts this exhumed detachment footwall. Here we have taken advantage of this sampling to study heterogeneities of alteration at scales less than a kilometer. We combine textural and mineralogical observations made on 77 samples with in situ major and trace element analyses in primary and serpentine minerals to provide a conceptual model for the development of alteration heterogeneities at the Atlantis Massif. Textural sequences and mineralogical assemblages reveal a transition between an initial pervasive phase of serpentinization and subsequent serpentinization and metasomatism focused along localized pathways preferentially used by hydrothermal fluids. We propose that these localized pathways are interconnected and form 100 m- to 1 km-sized cells in the detachment footwall. This change in fluid pathway distribution is accompanied by variable trace element enrichments in the serpentine textures: deep, syn-serpentinization fluid-peridotite interactions are considered the source of Cu, Zn, As, and Sb enrichments, whereas U and Sr enrichments are interpreted as markers of later, shallower fluid-serpentinized peridotite interaction. Alteration of gabbros and dolerites emplaced in the peridotite at different lithospheric levels leads to the development of amphibole, chlorite and, or, talc-bearing textures as well as enrichments in LREE, Nb, Y, Th, Ta in the serpentine textures of the surrounding peridotites. Combining these observations, we propose a model that places the drill holes in a conceptual frame involving mafic intrusions in the peridotites and heterogeneities during progressive alteration and emplacement on the seafloor.

Evaluation of Rockfall-hazard Potential For Rockville, Utah, Following a 2013 Fatal Rockfall

Abstract In December 2013, a rockfall in the town of Rockville, Utah, released an estimated 2,700 tons (2,450 tonnes) of rock from a 400-ft (122-m) high slope; the rock struck a house at the base of the slope, resulting in two fatalities. We performed detailed field and laboratory investigations to (1) identify the modes of failure and factors contributing to rockfalls along the east-west trending, south-facing slope where it passes through the town; (2) identify sections of the slope that pose the highest hazard for future property damage or injury; and (3) suggest potential remedial measures. Field investigations included mapping discontinuities, establishing stratigraphy, measuring slope geometry, and evaluating potential failure modes at four selected sites. Laboratory investigations included determining dry density, friction angle, and slake durability index of rock samples. Using the Dips software, we determined the principal joint sets and performed a kinematic analysis. The maximum rollout distances for rock blocks of various sizes were determined for each of the study sites using the RocFall software. Results of the kinematic analysis and field observations indicate that wedge, plane, and toppling failures are possible within the Shinarump Conglomerate Member of the Chinle Formation and the Upper Red Member of the Moenkopi Formation along the entire slope. Based on the results of the study, we developed a rockfall-hazard map that indicates that the western portion of the town faces the highest hazard from potential rockfalls. The most feasible future remedial measure is not to build close to the hazardous slopes. Other possible remedial measures include removing loose rock blocks, installing rock anchors, and using drapery mesh.