Solid Earth Sciences最新文献

The Banyo Syenitic Pluton (BSP) is located on the south western extension of the Mayo Nolti Shear Zone (MNSZ). It is a NNE-SSW elliptical pluton. On the petrographic view, the BSP displays two rock types namely: hornblende-pyroxene-quartz syenite (HPQS) and hornblende-biotite granite (HBG), intruded in a plutono-metamorphic basement rock consists of biotite granite (BG) and hornblende-biotite gneiss (HBGn). Structural investigations indicate that the study area recorded three deformation phases: D₁, D₂ and D₃. D₁ is a flattening phase characterized by WNW-ESE to NNW-SSE (N110°E to N160°E) trending metamorphic foliation (S₁) with moderate (50°–60°) dips toward NNE to ENE. D₂ trends N–S and is characterized by crenulation cleavages (S₂), N–S sinistral shear and coeval S₂ foliation in hornblende-biotite gneiss. The emplacement of the HPQS and (HBG) took place during this phase considering the N–S global trend of the entire pluton and the NNE-SSW shape of the HPQS in the one hand and sinistral shear deformation microstructures display by plagioclase and K-feldspar crystals in HPQS. D₃ displays NE–SW (N30E to N45E) trend in HBGn and HPQS. Magnetic data indicate an inward-dipping NNE-SSW concentric pattern around station N32. The NNE-SSW elliptic shape and concentric magnetic foliation trajectories displayed by the BSP indicate its synkinematic emplacement during the D₂ N–S sinistral activation of the MNSZ with the feeder zone (station N32) located on the north eastern border. The sinistral activation is related to the Saharan Metacraton convergence over the Cameroon northern margin. This emplacement was disturbed by an overprinting E–W to NNW-SSE dextral syn-D₃ shear phase probably due to the dominant convergence (during its late stage) of the West African Craton over the Cameroon western border. Structural field data and magnetic fabrics infer that the Banyo syenitic pluton was emplaced in a N–S to NNE-SSW oriented fracture initiated during the transcurrent strike-slip MNSZ. The BSP is intruded in HBGn basement rock whose deformation ages are bracketed between 600 Ma (for the early syn-D₁ deformation structures) and 550 (for the late syn-D₃ deformation structures). The location of the BSP on the N–S to NNE-SSW sinistral MNSZ, between the GGSZ to the north and the RLSZ to the south, displaying similar structural features and N–S syn-to late kinematic syenitic plutons respectively dated at 593 Ma and 590 Ma help in dating the BSP pluton at 593 - 590 Ma. This age range dates several synkinematic emplacements of Pan-African younger syenite and granitoids along N–S and NE–SW shear zones during the western Gondwana post-collisional history.

The Kongur-Muztaghata-Maeryang terrane in NE Pamir is considered to be the western extension of the Songpan-Ganze terrane located in the northern Tibetan Plateau. The Kongur-Muztaghata gneiss dome (KMGD) is situated in the north while the Maeryang gneiss dome (MYGD) is in the south. The KMGD comprises Triassic granites and granitic gneiss in the core and Early Paleozoic-Triassic sediments in the mantle that underwent Barrovian-type and Buchan-type metamorphisms. Based on geochemical and geochronological data, the Kongur-Muztaghata magmatic arc was formed around ∼252–204 Ma due to northward subduction of the Paleo-Tethys Jinsha oceanic slab. The collision of the Kongur-Muztaghata magmatic arc and the Qiangtang terrane occurred subsequently. Previous research suggested that the KMGD was formed in the Miocene (21–8 Ma). However, our new in-situ monazite U–Pb data for the mantled metasediment shows that the KMGD was initially formed at ∼198 Ma.

The MYGD is comprised of an Early Paleozoic-Triassic metasediment mantle and a Cambrian anatexis complex core that underwent Barrovian-Buchan metamorphisms. Our new structural, geochemical, and geochronological data suggest that the protolith of the Maeryang orthogneiss was formed around ∼519-513 Ma, with the surrounding Early Paleozoic metavolcanic rocks erupted at ∼519-508 Ma. Together, they formed the Early Cambrian magmatic complex. In-situ U–Pb dating of monazites and zircon metamorphic rims for the Triassic metamorphic rocks in the mantle indicate that the Barrovian-Buchan metamorphism in the MYGD occurred around ∼206-187 Ma, likely caused by anatexis in the deep crust of the gneiss dome core. Thus, we propose that the KMGD and MYGD underwent a two-stage exhumation: the initial uplift during the Late Triassic-Early Jurassic thermo-tectonic event associated with the Cimmerian orogeny and the late rapid exhumation since the Miocene driven by the collision between the Eurasian and Indian plates.

It is widely recognized that in geothermal fields, meteoric water infiltrates deep into the subsurface of the earth and then travels through cracks and fractures, returning to the surface as it becomes heated. The patterns of fluid flow are primarily determined by the interaction between forces driven by gravity and pressure gradients. The ultimate forms of fluid flow patterns are primarily determined by the anisotropies of permeability associated with fault zones. In this study, a series of numerical simulations utilizing the finite volume approach were conducted to investigate the effects of fault zone architecture on fluid flow patterns and temperature distributions. Four distinct types of fault zone architecture were created in the simulations, including localized barrier, combined conduit-barrier, localized conduit, and distributed conduit. The results revealed that fault zone architecture has only a minor effect on fluid flow velocities and temperature distributions, except in cases along faults with very high permeabilities. The simulations suggest that this type of 2-D numerical modeling can be easily applied and utilized in other faulted geothermal systems.

The provenance of clastic sediments in stream beds, river terraces, rivers, swamps, lakes and beaches from different geological settings was investigated based on their compositional and geochemical variations. The geochemistry data of 622 sediment samples from 22 sites in the Cameroon were compiled to infer the provenance. The results suggest that, their mineralogy is dominated by quartz, low amount of feldspars, clay minerals, heavy minerals, ferric minerals, and rock fragments. The SiO₂/Al₂O₃ ratio indicate that the sediments of Cameroonian region are mostly rich in quartz and clay-minerals. The enrichment of K₂O/Na₂O ratio implies plagioclase disintegration as K-feldspar during weathering and/or K-reintroduction in the system during diagenesis. The sediments are rich in light rare earth elements (LREE) and classified as shale, Fe-shale, Fe-sand, wacke, arkose, litharenite, sublitharenite, and quartzarenite. The sediments are composed of detritus derived from felsic igneous rocks, which correspond to the geology of the source areas. Weathering indices such as chemical index of alteration (CIA), chemical index of weathering (CIW), plagioclase index of alteration (PIA) and, A–CN–K (A=Al₂O₃, CN=CaO∗ + Na₂O, K=K₂O) plot indicated that the source rocks are subjected to low, moderate and intense weathering.

The Bayan Obo REE-Nb-Fe deposit, which reserves the current largest REE resources globally, also hosts 63.4% of China's Nb resources. Previous studies mainly focus on the isotopes and petrographic mineralogy of carbonatite dyke, ore-host dolomite and rare earth ore in Bayan Obo deposit, niobium mineralogy is comparatively insufficient. In order to promote the utilization of niobium resources in the Bayan Obo deposit, we focus on the petrological and mineralogical study on the biotite-type Fe-REE-Nb ore of West Mine, by scanning electron microscope (SEM), X-ray energy spectrum (EDX) imaging and micro-XRF scan. From the analysis, we observe that 1) this type of ore shows relative enrichment in niobium, and the size of niobium-bearing minerals up to 1 mm; 2) the niobium mineral composition are extremely complex, with main niobium minerals including aeschynite, fergusonite and columbite and minor niobium minerals ilmenorutile and baotite; 3) REEs are mainly distributed in monazite, bastnaesite and aeschynite and the particle size of the first two is relatively fine; 4) aeschynite occurring as large aggregates maybe the hydrothermal in origin and fluid–rock interaction leads to the aggregation of biotite and the precipitation of niobium-bearing minerals. This study on biotite type Fe-REE-Nb ore has important insights for mineral processing and directive significance on niobium prospecting in the Bayan Obo deposit.

The rapid increase in population and infrastructural development has triggered unplanned groundwater development leading to severe stress on groundwater couple with several unsuccessful boreholes or failure of existing in the University of Calabar, Calabar (Nigeria). Hence, an integrated hydrogeological study was undertaken in the university using vertical electrical sounding (VES), to delineate and characterise aquifers and assess the groundwater quality for drinking and irrigation uses, in addition to evolution and human health risk assessment. The results reveal two water bearing units. The first is composed of medium-coarse-gravelly sand with thickness and resistivity in the range 3.6–118.8 m and 540–3500 Ω m, while the second underlying the first aquifer is composed of clayey, fine-medium sand with resistivity and thickness values in the range 44–2200 Ω m and 50 - α. Aquifer parameters from VES and pumping tests showed average hydraulic conductivity (K) and transmissivity (T) of 180 m/day and 25,740 m²/day for the first aquifer and 180 m/day and 21,384 m²/day for the second aquifer. Regionally, the groundwater flow in the university occurs toward the south. Hydrochemical data show that all the physical parameters, major and minor ions, trace and rare earth elements are within the maximum acceptable limits for drinking and agricultural uses. The dominant hydrochemical facies are Na⁺-Ca²⁺-Cl^--SO₄^2-, Mg²⁺-Ca²⁺-HCO₃^--Cl^- and Ca²⁺-Mg²⁺-HCO₃^--Cl^- with silicate weathering, ion exchange and reverse ion exchange as the major processess controlling the groundwater chemistry. Health risk of water through oral (drinking) and dermal (bathing) pathways showed that values of hazard quotients (HQs) and hazard index (HI) of all the trace elements (Al, As, Cd, Co, cr, Cu, Fe, Mn, Ni, Pb, Zn) were less than one. This suggests that these elements does not pose any adverse risks to the local people through drinking and bathing, but children are more sensitive than adults. This study will serve as a guide for future sustainable development and management of groundwater resource in the university and its environs.

The high light rare earth elements contents (up to 412 ppm) in the weathering crust over the REE industrial grade were observed in the Huangmeijian alkaline pluton of the Luzong Volcanic Basin, firstly revealing the mineralization potential of ion-adsorption rare earth elements deposit in central Anhui Province.

Based on results of geological survey and mineral resources research over the past decades, the authors have systematically summarized the metallogenic geologic settings of Laos, Cambodia, Vietnam, Thailand, Myanmar, Malaysia, Indonesia, and the Philippines in Southeast Asia. Mineral geological database has been established, regional geological maps, geotectonic units with division maps, magmatic rock distribution maps and metallogenic regularities of some important metallogenic belts in Southeast Asia have been compiled. The distribution characteristics of major minerals such as copper, gold, aluminum, potassium, nickel, chromium, tungsten and tin, lead and zinc, iron, manganese and antimony, and the genetic types of these minerals are summarized. Meanwhile, twenty metallogenic belts are divided and nine main metallogenic epochs are summarized. We also analyze the influence of the tectonic evolution of the East Tethys, as well as the subduction and collision between the Indian-Australian plate, the Pacific plate, the Philippine sub-plate and the Eurasian plate on the mineralization in Southeast Asia. This study provides a number of valuable data and geological information for understanding the spatial distribution and temporal evolution of minerals, and the prospecting targets in Southeast Asia.

Evolution of the late Ordovician–Silurian Caledonian orogeny (ca. 460–420 Ma) in the South China Block (SCB) remains controversial due to the overprinting Triassic (Indosinian) and Jurassic-Cretaceous (Yanshanian) orogenic tectonics and the absence of enough petrologic records. This work reported a systematic study of whole-rock geochemistry, zircon U–Pb geochronology and Hf isotopes of the first Caledonian A-type granitoids (Dishui) in Jinxiu county, Guangxi (SW China). The Dishui granitoids are tectonically located in the southwestern Qin-Hang suture belt, which is the largest ancient orogenic belt formed by the collision of the Yangtze and Cathaysia blocks in South China. The Dishui granitoids consist primarily of a syenogranite pluton with a small-scale granodiorite porphyry dike. The Dishui syenogranite and granodiorite porphyry have LA-ICP-MS zircon U–Pb ages of 437.9 ± 1.0 Ma (MSWD = 0.77) and 436.6 ± 0.8 Ma (MSWD = 1.7), respectively. The syenogranite has high contents of SiO₂ (73.20–77.35 wt.%), total alkalis (Na₂O + K₂O = 7.42–8.99 wt.%), total REE (198–445 ppm), high field strength elements (HFSEs: Zr + Nb + Ce + Y = 253–520 ppm), and 10,000∗Ga/Al (2.93–3.11) and FeO_t/(FeO_t + MgO) (0.77–0.96) ratios and high F concentration, resembling highly-fractionated A-type granite. The granodiorite porphyry displays similar A-type granite affinities, including high (Zr + Nb + Ce + Y) (410–485 ppm), 10,000∗Ga/Al (2.47–4.59), and zircon saturation temperature (T_Zr = 908–927 °C), medium to high SiO₂ (64.56–64.95 wt.%), Fe₂O₃ (7.70–8.11 wt.%), and MgO (3.69–4.09 wt.%), and low FeO_t/(FeO_t + MgO) (0.61–0.64), resembling magnesian unfractionated A-type granitoid. The Dishui syenogranite and granodiorite porphyry dike have zircon ε_Hf(t) value and two-stage model age (T_DM2) of −3.9 to +1.5 and 1.32–1.66 Ga, and −1.7 to +11.8 and 0.94–1.53 Ga, respectively, both much more depleted than many Caledonian gneissic/massive granites and the Devonian A-type granites (ε_Hf(t) = −14.9 to −3.5) in South China. All these data suggest that the Dishui syenogranite was derived from partial melting of the Proterozoic metamorphic basement with mantle-derived melt input, and the magma subsequently underwent extensive fractionation. Meanwhile, the Dishui granodiorite porphyry was likely derived from the same crustal melt with more mantle-derived input. New ages of the Dishui A-type granitoids (ca. 436–437 Ma) in the Qin-Hang belt indicate a tectonic transition from syn-collisional crustal thickening to post-collisional extension at ∼437 Ma in South China.

Earth and planetary sciences require extensive microanalyses to quantify most common major and minor elements O, Na, Mg, Al, Si, K, Ca, Ti, Cr, Mn, Fe and Ni in minerals/rocks. With O usually calculated, this is frequently done with expensive electron probe X-ray microanalyzer using a wavelength dispersive method (WDS), and much less so with expensive ground-based scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectrometer (EDS). Both instruments are not readily accessible to many scientists though. Here we selected eight natural minerals, containing those elements to various amounts, to test the performance of an economical desktop SEM attached with an EDS consisting of just one 10 mm² silicon drift detector (SDD). The compositions of the minerals were established by extensive electron probe X-ray microanalyses (EPMA)-WDS conducted under routine analytical conditions. They were used to evaluate the performance of the desktop SEM/SDD-EDS system. The examination shows that under modest analytical conditions it can generate accurate results for those elements, with detection limits (∼0.1 wt%) much comparable to routine WDS analyses. Therefore, economical desktop SEM/SDD-EDS system can be an affordable and widely-accessible instrument for extensive and accurate quantification of those most common major and minor elements in minerals/rocks.