Journal of Asian Earth Sciences: X最新文献

Assam region is mainly formed by the deposit and erosion process of the Brahmaputra River. The frequency of seismic events results in landform deformation, which highly influences the drainage basin pattern and causes drainage anomalies, having a subsequent effect on the flood distribution pattern. In the present study, morphometric parameters and geomorphic indices for the Assam region are derived from SRTM DEM data of 30 m resolution using GIS to characterize the tectonic activity, which in turn influences the drainage pattern. The indices are classified into three tectonic activity classes, and the average of the classes is combined to generate the indices of relative active tectonics (IRAT). The four classes of IRAT are defined for the study area as (i) very high; Class 1 (1.57–1.80), (ii) high; Class 2 (1.81–2.06), (iii) moderate; Class 3 (2.07–2.26), and (iv) low; Class 4 (2.27–2.30). Class 1 corresponds to basins 1 and 6. Basins 2, 4, and 5 fall under Class 2. Class 3 consists of basins 7, 8, and 9, and Class 4 comprises basins 3 and 10. Results show that most of the study area lies in very high to moderate active tectonic zones and the identified zones are consistent with significant faults and thrusts present in the basins. The combined approach of GIS-based morphometric and geomorphic study allows for identifying deformed landforms resulting from active tectonics. The results can also be employed for the development of watershed management and sustainable land use planning.

This study reports the earliest presumably known collisional magmatism of the NW Iran–eastern Turkey–Caucasus region from the north of Sarab city in East Azarbaijan province, NW Iran. Volcanic rocks of the area comprise alternating lava flows of mainly alkalibasalt, andesite, trachyandesite, dacite and pyroclastics (tuff and ignimbrite) affiliated with high-K calk-alkaline to shoshonitic magmatic series. Ar–Ar geochronology of the glass, matrix and plagioclase laths revealed crystallization time restricted to Late Eocene to Early Oligocene (34.90–30.69 Ma) which is coincident with the onset of the Arabian-Eurasian continental collision. Geochemical data show LREE enrichment compared with HREE and Nb and Ti depletion, indicating that they are subduction related. The Sr-Nd-Pb isotopic data reflect the incorporation of oceanic sediment into the magma source. We suggest that the volcanic rocks were generated from a metasomatised subcontinental lithospheric mantle source through 5 to 10 vol% partial melting in an extensional back arc basin by the Neotethys slab roll-back under the Iranian plateau.

Co-seismic landslides are the most dangerous geological hazards in seismically active mountainous regions. These landslides cause damage to roads, drainage pipelines, buildings, agriculture, and loss of human lives. It is crucial but difficult to precisely map the hazards resulting from earthquake-induced landslides. Newmark's approach is widely used to determine the permanent displacement of a probable sliding mass and simulate the mechanism of seismically-induced slope failure. The present study assesses co-seismic landslide hazards for Uttarakhand state (India), which falls under the highest seismically active zones as per the seismic code of India. It proposes an improved Newmark’s approach aby incorporating rock joint shear strength parameters and the size effect of possible sliding surfaces. Static factor of safety and critical acceleration maps were prepared for the study area by combining various geological, geotechnical, and topographical parameters. The ground motion parameters were determined in terms of surface-level Arias Intensity. Newmark permanent displacement map was prepared by taking critical acceleration and Arias Intensity as input parameters. Finally, the modified Newmark’s model results were compared with the conventional Newmark’s model using the area under curve (AUC) analysis. This assessment approach can be used effectively to forecast the area affected by co-seismic landslide hazards and prepare guidelines for major infrastructure projects and post-disaster damage studies.

The changing nature of detrital signatures in clastic wedges of the Circum-Mediterranean orogenic systems reflect the provenance relations from different source rocks of evolving geo-puzzle terranes, including ophiolite bearing, uplifted continental crust (both shallow to deep crust terranes), volcanic and sedimentary source rocks. We selected here sandstone suites directly occurring over the Mesomediterranean Micropaleoplate during the final stages of closure of the western-southern Tethyan realm. They are unconformably over the internal domains of the Circum-Mediterranean thrust belts, and include Oligocene-to-lower Miocene siliciclastic formations of the Betic Cordillera (As, Bosque, Río Pliego, El Niño, Ciudad Granada, Fuente-Espejos, Alozaina and Viñuela fms), Rif Chain (Fnideq and Sidi Abdeslam fms), and Calabrian terranes (Paludi, Pignolo and Stilo Capo d'Orlando fms). All these sandstone suites range from quartzolitic to quartzofeldspathic detrital modes reflecting close relations with their Paleozoic metasedimentary and plutonic source rocks and their related Mesozoic sedimentary covers. Marked differences have been recognized from western (Betic-Rif) to eastern (Calabria) portions in terms of detritic suites. Detrital suites of the Betic-Rif portions reflect a transition between a craton, transitional and recycled orogenic provenance type. Contrarily, detrital suites of the Calabria portions reflect their transition from transitional continental to basement uplift orogenic provenance reflecting deposition in wedge-top basins during final subduction of the MFB below the MM and the opening of the Mediterranean basin as a backarc.

The Kaymaz gold deposit comprises Damdamca, Karakaya, Küçük Mermerlik, and Kızılağıl ore zones within an area underlain by serpentinite and far-traveled Paleozoic-Mesozoic high-pressure metamorphic rocks. The Kızılağıl ore zone is hosted in silicified quartz schist, whereas the others are hosted in silica altered serpentinite. Pyrite-I, arsenopyrite, marcasite, magnetite, pentlandite, millerite, nickeline, bravoite, and fine-grained native gold and silver comprise the first stage, whereas pyrite-II and chalcopyrite represent the second ore stage. The Kaymaz gold deposit has been defined as a silica-listwaenite hosted gold deposit according to host rock relations and mineralogical properties.

Gold, Ag, and As were found to be highly correlative in whole-rock silica-listwaenite analyses. Higher As content of the pyrite-I, coexisting native gold and silver together with the whole-rock analyses indicate that these metals were derived from the same source, possibly the Kaymaz granite. On the other hand, clathrate formations observed in some of the first stage fluid inclusions confirm that high Ni in the pyrite-I may have been derived from the serpentinites. However, a distinct lack of the separated carbonic phase and clathrate formations in the second stage fluid inclusions as well as their lower T_h and salinities, reveal that higher Co in the pyrite-II possibly dissolved from the metabasites by meteoric solutions.

The Au-Sn-bearing, polymetallic sulfide deposit at Imalia in the western part of Mahakoshal belt, Central India is hosted by recrystallized dolostone and subsidiary phyllitic dolostone. These host rocks are transected by shallow level intrusion of quartz porphyry dykes. There are two major NS trending ore zones (∼1.5 km cumulative length) and a subsidiary-one, confined to fractures and shears in the dolostones or along its contact with the intrusive dykes. Polyphase mineralization include: irregularly disseminated pyrite crystals of diagenetic/metamorphic origin, patchy to stringery Pb-Zn sulfide ores showing pervasive metamorphic fabric, dominant massive vein type pyrite-arsenopyrite ores with significant amounts of invisible gold and tin. Other ore minerals include cassiterite, molybdenite, wolframite and roquesite in a magnetite-rich oxidic halo, and electrum, enargite/luzonite, wittichenite, ourayite, eclarite, aikinite and idaite in the sulfidic veins. Some tentatively identified ore minerals in these veins include calaverite, proustite, famatinite, sakuraiite, and tenorite. Pyrite contains structurally located invisible gold as high as 17.6 ppm whereas arsenopyrite contains a maximum of 20–24 ppm Au. Pyrite also contains unusually high Sn (upto 2673 ppm). The mineralogical assemblage of rare phases and their paragenesis in the Imalia vein type ores reflect the high sulfur (log fS₂ = −9 to −13 bar) and oxygen (logfO₂ = −32 bar) fugacities at a temperature range of 350 °C to 250 °C (according to thermometric calculations) during their emplacement.

Our understanding of climate change impacts on the geomorphology of terrestrial landscapes is often derived from proxy sedimentary records preserved in depositional fluvial and lacustrine basins that integrate landscape responses. At million-year time scales, most mountainous regions are characterized by net erosion and the export of chemically and physically weathered bedrock. For example, in the Khangay Mountains of central Mongolia, late Cenozoic valley-conforming lava flows preserve “snapshots” of hillslope weathering regimes in the headwaters of the Selenga-Baikal depositional system during the consequential climate transition from the late Miocene (ca. 12 Ma) into the Quaternary.

This research aims to characterize the relative importance of chemical and physical weathering to landscape development in this upland intracontinental setting through an investigation of geochemical major and minor trace elemental composition of well-developed paleosols formed in metasediments (middle Orkhon), granite (upper Orkhon), and Miocene fluvial deposits (upper Chuluut) preserved beneath basaltic lavas at 11.9, 7.5 and 3.1 Ma, respectively.

We used the Chemical Index of alteration (CIA), Plagioclase Index of Alteration (PIA), and Chemical Index of Weathering (CIW) to derive an integrated paleoclimate regime from the three lava flow-buried paleosol locations. Results reveal that from the late Miocene into the Pliocene, the climate was warmer and slightly more humid than today in the upland continental interior of west-central Mongolia. This result matches the long-term paleo records from Lake Baikal and late Cenozoic global cooling trends from other proxies.

Assessment of subsurface status by resistivity technique, being an indirect approach, is pretended to be a strategic factor. Projection of full proof confirmation in this domain is always a challenge and hence outcomes are expressed in possibilities. Intervene of mathematical interpretation on resistivity data generated in the field by different arrays would offer a better choice in building-up the possibility of projecting the actual status. Thus, a study of Wenner-Schlumberger (WS), dipole–dipole (DD) and combined inversion (CI) data of three parallel profiles have been conducted, as a whole, for old and abandoned shallow depth coal mine workings in Jharia coalfield. The study recapitulates influence of sensitivity and uncertainty with depth, apart from resistivity. Statistical significance of the data has been evaluated inclusive of their inter-relationship. PCA presented an encouraging relation of sensitivity with depth. The comprehensible approach of mathematical interpretation helps in cracking a problem of uncertain prediction. Sensitivity and the extent of uncertainty are the parameters to build a strong foundation for evaluating the degree of confidence in prediction accuracy. Artificial Neural Network (ANN) tool has been used to understand the relative importance of sensitivity and uncertainty with depth. The weightage of sensitivity has been observed to be on upper side with respect to uncertainty. The importance of configuration of resistivity survey array has been emphasized based on sensitivity.

The Cuonadong Dome is located at the eastern part of the North Himalayan gneiss domes. Structural and kinematic analysis in the middle unit of the Cuonadong Dome provide significant new insights into the structural deformation of the middle crust in the Northern Himalaya. Field observations, microscopic kinematic and EBSD analyses, and deformation temperature estimates from the mid-crustal rocks of the Cuonadong Dome show high-strain D2 (top-to-N) kinematic fabrics with a downward-to-north progression from dominantly top-to-north shear in the garnet zone, to solely top-to-north shear in the kyanite/sillimanite zone. A combination of mineral assemblages, microstructures, and quartz crystal preferred orientation patterns indicates deformation temperatures associated with D2 kinematic fabrics increase with structural depth from ∼450 °C in garnet zone to > 630 °C in the kyanite/sillimanite zone. These values broadly overlap temperature range deduced from metamorphic petrography (450–630 °C). Microtextural relations indicate that peak metamorphism occurred post-D1 and pre-D2 deformation. Combined with the ∼1000-m-thick ductile deformation zone, the interpreted deformation temperatures yielded an average thermal field gradient of ∼ 180 °C/km over 1.05 km of structural thickness. Based on the geochronologic data, midcrustal D2 extensional deformation in the Cuonadong Dome initiated as early as early Oligocene (32 Ma) and ended during the middle Miocene (∼14 Ma). Comparative studies of D2 ductile deformation in midcrustal rocks from other North Himalayan gneiss domes and the South Tibetan Detachment System indicate that D2 shear zone in the Cuonadong Dome represent the northern part of the South Tibetan Detachment System, and highlight temporal and spatial variation in midcrustal D2 deformation patterns over the southern Tibet during the Himalayan orogeny.

The paper presents petrographic, geochemical, and new U-Pb zircon (LA-ICP-MS) geochronological data on the Upper Lena Fm. sediments which make part of the Cambrian sedimentary cover of the Siberian craton. The composition of lithic fragments in these clastic sediments, including mafic and felsic volcanics and granitoids, along with the correlation of major element ratios and the values of trace-element ratios point to predominant igneous (mainly felsic) rocks in the provenance. The U-Pb ages of detrital zircons from the sampled Upper Lena Fm. sandstones are mostly Early Paleozoic (∼500 Ma), with very few Archean-Paleoproterozoic determinations and quite many Neoproterozoic zircons. Ediacaran and Earliest Cambrian clastic sediments bearing Early Precambrian and Neoproterozoic detrital zircons, as well as Neoproterozoic and Early Paleozoic complexes of the Central Asian Orogenic Belt, could provide material for the Upper Lena clastic deposition. The geochronological evidence shows that the Upper Lena Fm. sandstones were deposited over vast territories of the southern Siberian craton in the Late Cambrian, in a single sedimentary basin, and originated from the same provenance. The Upper Lena deposition event in the Late Cambrian, immediately before the Ordovician period, makes a key milestone in the geological history of Siberia: the end of a large-scale Early Cambrian transgression and the beginning of gradual uplift of the southern craton margin, at least till the Carboniferous, which was associated with the formation of the Central Asian Orogenic Belt, a major tectonic unit of Asia.