Geosystems and Geoenvironment最新文献

We investigated the temporal evolution of the andesitic Chimpa volcano of the northern Puna plateau, Central Andes, situated at the geological boundary between the plateau and the Eastern Cordillera domains. The volcanic activity consisted in three constructive volcanic cycles (Basal, Cajon and Chimpa units) showing complex eruptive behaviors (ignimbrites, lava domes. block-and-ash flows, lava flows). We present new U-Pb analyses conducted on the zircon crystals from the Chimpa volcanic rocks. These analyses provide constraints on the magmatic/volcanic tempos and offer insights into the Th and U (and Th/U ratios) systematics of the analyzed zircon crystals. The results suggest a lifespan for volcanism ranging 7.5 to <7.0 Ma, in concomitance with the regional steady-state magmatic phase separating the first two pulses of ignimbritic flare-up in the Altiplano-Puna Volcanic Complex. Moreover, the analyzed zircon crystals exhibit Th/U ratios (0.11–0.34) and Th (33–8860 ppm) and U (52–4258 ppm) that indicate magmatic crystallization from poorly evolved melts at high temperatures. Some discrepancies exist between the calculated zircon concordia age for the third volcanic phase (Chimpa Unit, ca. 7.35 ± 0.071 Ma) and that of the second cycle (Cajon Unit, 6.98 ± 0.057 Ma). We interpret these differences as stemming from the presence of zircon antecrysts in the final eruptive melts. Indeed, a true pre-eruptive event of zircon crystallization (i.e., formation of autocrysts) could not be proven by the existing dataset.

There is a geochronological affinity with some nearby volcanic rocks from the Puna plateau and the Eastern Cordillera domains, particularly considering the rhyolitic products of the Ramadas Volcanic Center and the andesitic to dacitic Almagro volcanic rocks. This highlights the complex behavior of the local magma plumbing system beneath this particular area, resulting in the emission of geochemically variegate volcanic rocks at similar times. This scenario suggests that the composition of the erupting melts are affected by the rheological behavior of the mid-upper-crustal MASH reservoir (the Altiplano-Puna Magmatic Body), which may either facilitate or impede the ascent of poorly evolved magmas derived from the deep crust towards the surface. From this point of view, the relative location of the volcanic centers relatively to the position of the geophysical anomaly may exert an important influence on the petrogenetic paths of magmas.

The disintegration of the Columbia supercontinent during the late Paleoproterozoic generated major rift basins in the constituent continental fragments. The Kaladgi basin, located between the southern part of the Deccan volcanic province (DVP) and the northern part of the Dharwar craton, is a Columbia rift-related basin in southwestern India that preserves a complex history from initial fault-controlled mechanical subsidence during rifting, thermal subsidence along a collision zone, crustal thinning due to stretching and erosion associated with doming. The Paleoproterozoic basins worldwide show higher uranium concentration and many deposits are also established in the Purana basins of India. In the present study, the lithotectonic architecture of this basin using broadband magnetotelluric (∼320 Hz–3000 s) soundings in the western segment of the Kaladgi rift basin along two profiles. Two-dimensional (2-D) inversion of data using a 2-D nonlinear conjugate gradient algorithm along both profiles provides insights into the deeper structure of the basin. Our results reveal a thin sheet of Deccan volcanic, sedimentary successions belonging to the Badami and Bagalkot groups, and Proterozoic sediments from top to bottom beneath this basin. The crustal structure is highly heterogeneous and associated with deep-seated faults, and its thickness increases from the eastern Dharwar craton (∼30 km) to the western Dharwar craton (∼45 km). The crustal conductors are interpreted as mafic intrusions derived from the underplated basalts. The moderate conductive features may correspond to carbonate fluids trapped within the faults/fractures zone during basin initiation. The conductive features in the lower crust and the Moho are interpreted as fluids derived from underplated intrusions through plume impact. The NNW trending Chitradurga Suture Zone (CSZ) signature and the Bababudan-Nallur Shear (BNS) in the crust and upper mantle depth are imaged along both MT profiles. This study provides insights into the lithology and tectonic architecture of a long-lived rift basin involved in multiple tectonic events from the late Paleoproterozoic to the late Cretaceous.

The present study tries to analyze the impact of human activities on the physical and chemical health of the Dwarkeswar River. The river flows through a densely populated area. As a result, nearly 4000 t of sand are being extracted per day from the four segments of the river. Moreover, huge materials are extracted from the river to supply the raw materials of 97 brick kilns developed along the banks of the river. An industrial plant extracts 2,200,000 L d⁻¹ of water from the Dwarkeswar River, besides nearly 80 water lifting pumps. Similarly, a number of bridges are constructed across the river, and embankments are made along the banks. Per day 15.10 million liters of untreated sewage drain into the Dwarkeswar River from Bankura Town. The town also generates 63,111 kg/d of solid waste, some parts of which are disposed on the bank of the river. Intensive field surveys, analysis of multi-dated satellite images, and water quality parameters of the last ten years (2011–2020) were carried out in the present study to assess the impact of these interventions on river morphology, hydrology, and water quality. The comprehensive pollution index (CPI) was used to assess water quality. Results reveal that the Dwarkeswar River is highly affected, including the planform change, reduction of mean discharge and increase in the concentration of pollutants in the river water. The CPI value increased from 0.72 (2011) to 2.81 (2020), which indicates a severe increase in the level of pollution.

>Flash flood in the Himalayan River has made some catastrophic effects on the life people residing in its river banks mainly associated with extreme rainfall events/cloud bursts/the collapse of moraine-dammed lakes which significantly leads to rapid flooding and subsequently disaster in low laying areas. In the present study, we used different equations to determine the flash flood potential index(FFPI) and further, an improved Modified Flash Flood Potential Index (MFFPI) equation has been used to estimate the area with a predisposition to water accumulation. Various thematic layers prepared in the Geographic Information System (GIS) environment and integrated by providing proper weightage to each thematic layer i.e., slope, profile curvature, soil texture, geology and Land Use Land Cover (LULC), flow accumulation, slope, and profile curvature, etc. The MFFPI equation-derived map of Tawi Basin is classified into five zones such as very high hazard (100.40 km²), high hazard (971.60 km²), medium hazard (92.78 km²), low hazard (634.03 km²) and the very low hazard (254.61 km²) areas. Further, the results of the MFFPI were validated with the Analytical Hierarchy Process (AHP) based flood hazard zonation results which shows a very high correlation and similar trends of spatial and areal distribution with the MFFPI. The results of this study are quite useful for the local administration for futuristic planning and management of flood hazards in the Tawi River Basin and many other basins of similar terrain around the world.

Groundwater is a very important resource for socio-economic development. The uncertainty of where potential groundwater resources is located often causes some groundwater development projects to fail. It is common for water resources development projects hitting dry wells after heavy investments of resources. In Mpwapwa District, borehole drilling locations are uncertain, determined by trial-and-error techniques based on geophysical survey methods that involve the study of the behaviour of rock and soil types in specific geological locations. To reduce such uncertainty, this study used remote sensing and GIS-based Fuzzy Analytical Hierarchical Process (F-AHP) to simulate groundwater potential zones (GWPZ) in Mpwapwa District, Dodoma region, Tanzania. The F-AHP model was used to reclassify, weight, and rank various thematic maps, including lithology, soil types, drainage density, lineament, magnetic intensity, slope and elevation. The overall GWPZ map was created by combining the seven (7) ranking thematic map layers in a GIS environment. The resulting GWPZ map that was then validated using two methods: overlaying method and area under the curve (AUC) method. The resulting GWPZ map shows that 19%, 31%, 28% and 22% of the area are classified as very good, good, moderate, poor and very poor zones, respectively. The accuracy of the generated map is 72% using the overlaying method and 93% using the AUC method.

Neotectonics is a major factor for controlling landform development in tectonically active Chittagong Tripura Fold Belt (CTFB) region, along the western flank of the Indo-Burma ranges. Morphotectonic parameters are excellent indicators for landscape morphology evaluation to highlight past and ongoing tectonic processes in a region. To investigate the matter, different morphometric indices such as linear, areal, and relief parameters were quantified using the Digital Elevation Model (DEM) data and its attributes of Chengi River Basin (CRB) and Myinee River Basin (MRB) in CTBF. All the computations for morphometric characteristics and visualization were performed in the Geographical Information System (GIS) and statistical platforms. The CRB and MRB are identified as fifth and fourth-order basins with a total area of 503.53 km² and 267.28 km², respectively which have low drainage frequency. The Bifurcation ratio (Rb) value of both these basins is indicative of structural control. TSI controls the upper course of the rivers and the variations have been observed in year-wise Topographic Sinuosity Index (TSI) distribution. The Asymmetry Factor (AF) in both these basins indicates that CRB is tilting towards the western side, whereas the MRB is tilting towards the eastern side. Moreover, these two rivers are elongated in nature indicates tectonic activity along with Google earth (GE) seamless mosaic image-based longitudinal profiles indicates significant deformation along their courses. In addition, the moderate Hypsometric Integral (HI) value shows a convex shape in the lower portion, which might be related to the upliftment along a fault or perhaps an upliftment associated with recent folding. The overall results in both these basins indicate the presence of tectonic activity. Therefore, morphotectonic analyses using DEM, Landsat satellite data, and GE seamless data are found useful in this study and could be considered an ideal tool for any complex basin morphotectonic study.

The Upper Assam Basin is an intermontane foreland basin surrounded by gigantic mountain belts in NE India. The structural geometry of the basin is controlled by the tectonic interactions of the Himalayan orogenic belt in the north, Mishmi thrusts in the east, and the Assam-Arakan fold-and-thrust belts in the south. The basin has received significant attention not only because of its complex geological set-up but also due to its petroliferous nature for hosting significant hydrocarbon resources. The present study attempts to explore the tectonic subsidence history of the Cenozoic succession using subsurface stratigraphic details of ten (10) boreholes drilled within the upper shelf of the basin. Subsidence analysis is carried out using the backstripping technique. It is observed that the tectonic subsidence in the basin developed through four different stages. During the Paleocene-Eocene epoch, the basin witnessed slow subsidence. It increased gradually through Oligocene and attained rapid speed in the Miocene. Further, during the deposition of post-Miocene sediments (Plio-Pleistocene epoch), the tectonic subsidence in the basin remained accelerated. Subsidence curves obtained from the studied borehole depict a convex-upward profile, indicating that the basin attained a foreland configuration over time and is presently a SE dipping shelf bounded by opposite verging fold-and-thrust belts. Overall, the basin experienced tectonic subsidence of ∼2 km throughout its lifespan with an average subsidence rate of ∼30 m/Ma. This case study prominently elucidates the tectonic history of the basin, which underwent during the Cenozoic time. Our findings stress the importance of subsidence analysis through the backstripping technique as a potential approach for untangling the geohistory of sedimentary basins worldwide.

Earlier studies on Palaeoproterozoic (∼1800 Ma) alkaline (shoshonitic) rocks comprised of limited petrochemical data on the Bari syenite and other contiguous felsic rocks emplaced in anorogenic rift setting along the Son-Narmada North Fault (SNNF). Using new major and trace element data-sets, this study offers means of study of origin, source of magma, tectonic settings and geodynamic implications. The major oxide chemistry grouped Bari rocks into high alkali, but low CaO bearing peraluminous alkaline rocks. These rocks represent high abundance of HREE, Zr, Nb, Ga, Y, Eu, Ba and Sr. Primitive mantle normalized REE and trace elemental patterns correspond to A-type suite, suggesting origin of the magma mainly from the mantle. Significantly, anomalous Th/U and Rb/Cs values revealed crustal contamination of the melt, derived from partial melting of the mantle. Moreover, binary data plots between La vs. La/Sm and La vs. La/Yb are pointing towards crustal assimilation which was concomitant with the fractional crystallization of the mantle derived melt. Thus, crustal contamination coupled with the fractional crystallization of the melt mainly contributed to the formation of syenite melt. But, a high degree of partial melting of the lower crust was primarily responsible for the formation of Bari granite. The enrichment of incompatible elements in the syenite rocks suggests involvement of mantle metasomatism in their genesis. The magmatic processes related to the formation of syenite, lamprophyre, ultramafics, mafic and granite bodies were operative in the diverse magmatic realm and initiated earlier at the waning stage of the Mahakoshal orogeny and continental rifting, but magma emplaced later during Post-Mahakoshal orogeny and Pre-Vindhyan sedimentation that also in a rifted basement of the Bundelkhand craton at ∼1800 Ma during the amalgamation of the Columbian Supercontinent.

Microseism noise, which occurs in the period range of 2–20 s, is the most energetic band in the earth's background spectra. In the present study, we examined the amplitude spectra and directional characteristics of microseism in the Indian Ocean. We use the data from ten openly accessible land stations located all around the Indian Ocean. The probability power spectral density was used to characterize the microseism. To characterize the microseism, we employ the frequency dependent polarization approach, which is governed by the Eigen value decomposition of the 3 × 3 spectral covariance matrix. The spatial and temporal variation of microseism was investigated in order to better understand its distribution in the Indian Ocean region, which is regarded as a global source of microseism. For some stations, we observe the splitting of double frequency microseism into short period (2–5 s) and long period (6–10 s) microseism. The polarization analysis reveals the dominant sources of the microseism are located in the Southern Ocean. We also correlated the spatio-temporal variation of significant wave heights (swh) with the power spectral densities at each station. We observe a remarkable correlation between power spectral density with the significant wave height (swh) in both spatially and temporally in secondary microseism band. We also characterize the dominant surface wave types in the microseism band. In long period band Rayleigh waves are dominant and Love waves are prominent in the short period band.

The Bundelkhand craton in India preserves important records of archean geological evolution, where several ultramafic rocks belonging to the Babina Greenstone Belt (BGB) occur as isolated and oval shaped bodies. These rocks are composed of olivine, orthopyroxene, amphiboles, and serpentine along with accessory mineral phases like chromian spinel and ilmenite. Here we present the major and trace element geochemistry of these ultramafic rocks that are characterised by low SiO₂ (45.16–49.00 wt%), high MgO (24.41–29.15 wt%) and moderate Fe₂O₃ (5.82–9.95 wt%) with high Ni (1164–1674 ppm), Cr (1532–3477 ppm) and Cu (14.7–39.5 ppm) suggesting primary magmatic nature. The rocks show low rare earth element (REE) content (ΣREE 2.1–3.5 ppm) with depleted LREE pattern and flat to slightly fractionated HREE pattern similar to abyssal peridotite signature. The Nb/Yb ratio ranges between 0.01 to 0.20 (average = 0.03), similar to that of N-MORB, suggesting magma derivation from a depleted mantle source, further substantiated by the Th/Yb vs. Ta/Yb plot. Trace elements like Ta and Pb show positive spikes, whereas La, Nb, Pr and Ce show depleted nature. The rocks generally have low platinum group elements (PGE) content (<150 ppb) except one sample where it goes up to 388 ppb. The ΣPPGE concentration is higher than ΣIPGE for all the samples and the high Pd/Ir ratio (7.55–20.98) indicating the derivation of these ultramafic rocks from low degree of partial melting. Our data suggest that the ultramafic rocks were derived from a depleted mantle source at a shallow depth with affinity towards abyssal peridotite. These rocks might represent residue after extraction of low degree melt (∼2–10%) in a mid-oceanic ridge (MOR) setting, which were captured and brought to shallow levels and subsequently exposed on the surface.