| 1. |
- Bedini, Enton, et al.
(författare)
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Use of airborne hyperspectral and gamma-ray spectroscopy data for mineral exploration at the Sarfartoq carbonatite complex, southern West Greenland
- 2018
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Ingår i: Geosciences Journal. - : Springer. - 1226-4806 .- 1598-7477. ; 22:4, s. 641-651
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Tidskriftsartikel (refereegranskat)abstract
- The Sarfartoq carbonatite complex occurs in the transition zone between Archaean and Paleoproterozoic gneisses in southern West Greenland. The Sarfartoq carbonatite complex hosts ore deposits and occurrences of rare earth elements and niobium. In this study, airborne HyMap hyperspectral imagery and coincident airborne gamma-ray spectroscopy data were analysed for mineral exploration of Sarfartoq carbonatite complex. The study area included the carbonatite core zone and a hydrothermally altered shear zone prospective for rare earth elements mineralization in the southern margin of the carbonatite complex. The analysis of the hyperspectral imagery was focused on the mapping of the spatial distribution of carbonatite, fenite and limonite. Significant anomalies of uranium, thorium and potassium were outlined from the gamma-ray spectroscopy data. Decision trees were used to combine the results from the hyperspectral image analysis and airborne gamma-ray spectroscopy. Significant anomalies of thorium at the hydrothermally altered shear zone coinciding with the presence of carbonatite rocks are generally indicative of outcropping rare earth element mineralization. The study indicates the benefits of coincident airborne hyperspectral and gamma-ray spectroscopy surveys for the mineral exploration of carbonatite complexes.
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| 2. |
- Gido, Nureldin A. A., et al.
(författare)
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A gravimetric method to determine horizontal stress field due to flow in the mantle in Fennoscandia
- 2019
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Ingår i: Geosciences Journal. - : Springer. - 1226-4806 .- 1598-7477. ; 23:3, s. 377-389
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Tidskriftsartikel (refereegranskat)abstract
- Mass changes and flow in the Earth's mantle causes the Earth's crust not only to movevertically, but also horizontally and to tilt, and produce a major stress in the lithosphere.Here we use a gravimetric approach to model sub-lithosphere horizontal stress in theEarth's mantle and its temporal changes caused by geodynamical movements likemantle convection in Fennoscandia. The flow in the mantle is inferred from tectonicsand convection currents carrying heat from the interior of the Earth to the crust. Theresult is useful in studying how changes of the stress influence the stability of crust.The outcome of this study is an alternative approach to studying the stress and itschange using forward modelling and the Earth's viscoelastic models. We show that thedetermined horizontal stress using a gravimetric method is consistent with tectonicsand seismic activities. In addition, the secular rate of change of the horizontal stress,which is within 95 kPa/year, is larger outside the uplift dome than inside.
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| 3. |
- Giongo, Adriana, et al.
(författare)
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Distinct deep subsurface microbial communities in two sandstone units separated by a mudstone layer
- 2020
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Ingår i: Geosciences Journal. - : Springer. - 1226-4806 .- 1598-7477. ; 24, s. 267-274
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Tidskriftsartikel (refereegranskat)abstract
- Deep subsurface microbial communities are more abundant in coarse-grained sedimentary rocks such as sandstones than in fine-grained mudstones. The low porosity and low permeability of mudstones are believed to restrict microbial life. Then, it is expected that distinct, isolated microbial communities may form in sandstones separated by mudstones. In this context, the connectivity between microbial communities in different sandstone units can be investigated to infer evolutionary patterns of diversification in space-time, which may potentially contribute with relevant data for analyses of hydraulic connectivity and stratigraphic correlation. In this work, we used high throughput DNA sequencing of a ribosomal 16S gene fragment to characterize the prokaryotic communities found in Permian sandstone samples of the same core that are separated by one mudstone interval, in the Charqueadas coal field, Parana Basin (Southern Brazil). Our samples were collected at ∌300 m deep, in porous sandstones separated by a thick mudstone package. Differences in the bacterial community structure between samples were observed for the classified OTUs, from phylum to genus. Molecular biology might be further applied as a possible tool to help to understand the spatial and temporal distribution of depositional facies, and the efficiency of low permeability rocks to compartmentalize reservoirs. Ongoing studies aim to extend the present investigation into further analyses regarding lateral changes in microbial communities present in the same sandstone units.
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| 4. |
- Meng, Qingpeng, et al.
(författare)
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Heavy mineral analysis to identify sediment provenance in the Dan River drainage, China
- 2016
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Ingår i: geosciences journal. - : Springer Science and Business Media LLC. - 1226-4806 .- 1598-7477. ; 20:4, s. 449-462
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Tidskriftsartikel (refereegranskat)abstract
- Identifying the provenance of sediments carried by modern rivers can provide information on earth surface processes and help us to interpret geological history more clearly. The types and distribution patterns of surface sediments deposited in river systems are determined mainly by the fluvial flux and weathering of the proximal source rocks. In this paper, analysis of the heavy mineral content of 99 surface sediment samples was used to identify the source of the sediments carried by the Dan River in China. The objectives of this study are to: (1) determine the characteristics and distribution of the sediments, and (2) identify and classify the various depositional areas according to their differing source areas. The Dan River is divided into the lower, middle, and upper reaches to investigate the spatial distribution of heavy minerals. The main minerals detected were amphiboles, pyroxene, epidote, garnet, tourmaline, zircon, apatite, rutile, sphene, anatase, pyrite, and ilmenite. Generally, ilmenite (0.7% to 69.1%), amphibole (0% to 93.6%), epidote (0% to 53.3%), garnet (0% to 36.7%) and pyroxene (0% to 42.0%) were the most frequent detrital heavy minerals in the studied river sections. The Dan River and its tributaries are characterized with respect to their heavy mineral assemblages and heavy mineral indexes. Six depositional areas are distinguished and classified as Depositional area A (the Laoguan, Qi, and Xian rivers), Depositional area B (the Qingyou and Wuguan rivers), Depositional area C (the Laojun River), Depositional area D (the upper reaches of the Dan River), Depositional area E (the Yinhua River), and Depositional area F (the Tao River). The provenance study indicated that the sediments were derived mainly from the proximal exposed rocks. Sediments in the middle reaches of the Dan River were derived from Depositional areas B, C, and E, whereas sediments in the lower reaches were derived mainly from the local rocks along the river. Similar heavy mineral assemblages were obtained from Danjiangkou Reservoir and Depositional area A, especially for the Laoguan River, indicating the significant influence of Depositional area A on the reservoir.
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| 5. |
- Tenzer, Robert, et al.
(författare)
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Global model of the upper mantle lateral density structure based on combining seismic and isostatic models
- 2013
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Ingår i: Geosciences Journal. - : Springer Science and Business Media LLC. - 1226-4806 .- 1598-7477. ; 17:1, s. 65-73
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Tidskriftsartikel (refereegranskat)abstract
- We compile the global model of the upper mantle lateral density structure with a 2x2 arc-deg spatial resolution using the values of the crust-mantle density contrast estimated relative to the adopted crust density model. The combined least-squares approach based on solving Moritz's generalization of the Vening-Meinesz inverse problem of isostasy is facilitated to estimate the crust-mantle density contrast. The global geopotential model (EGM08), the global topographic/bathymetric model (DTM2006.0) including ice-thickness data, and the global crustal model (CRUST2.0) are used to compute the isostatic gravity anomalies. The estimated upper mantle densities globally vary between 2751 and 3635 kg/m(3). The minima correspond with locations of the divergent oceanic tectonic plate boundaries (along the mid-oceanic ridges). The maxima are found along the convergent tectonic plate boundaries in the Andes and Himalayas (extending under the Tibetan Plateau). A comparison of the estimated upper mantle densities with the CRUST2.0 data shows a relatively good agreement between these two models within the continental lithosphere with the differences typically within +/- 100 kg/m(3). Much larger discrepancies found within the oceanic lithosphere are explained by the overestimated values of the CRUST2.0 upper mantle densities. Our result shows a prevailing pattern of increasing densities with the age of oceanic lithosphere which is associated with the global mantle convection process.
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| 6. |
- Tenzer, Robert, et al.
(författare)
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The sub-crustal stress estimation in central Eurasia from gravity, terrain and crustal structure models
- 2017
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Ingår i: Geosciences Journal. - Seoul, Korea : Geological Society of Korea. - 1226-4806 .- 1598-7477. ; 21:1, s. 47-54
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the horizontal stress field beneath crustal structures of central Eurasia. The numerical procedure applied for a simultaneous determination of the sub-crustal stress and the crustal thickness from the global gravity, terrain and crustal structure models is based on solving Navier-Stokes' problem which incorporates the inverse solution to the Vening Meinesz- Moritz's problem of isostasy. The numerical results reveal that a spatial distribution of the sub-crustal stress in this study area closely resembles the regional tectonic configuration comprising parts of the Eurasian, Indian and Arabian lithospheric plates. The maximum shear stress intensity is generated by a subduction of the Indian plate beneath the Tibetan block. The intra-plate tectonic configuration is marked by the stress anomalies distributed along major active strike-slip fault systems and sections of subduction which separate the Tibetan and Iranian blocks from the rest of the Eurasian plate. The most pronounced intra-plate stress anomalies are related with a subduction of the Eurasian plate beneath the Tibetan block. We also demonstrate that a prevailing convergent orientation of stress vectors agree with the compressional tectonism of orogenic formations (Himalaya and Tibet Plateau, Than Shan, Zargos and Iranian Plateau), while the extensional tectonism of continental basins (Tarim, Ganges-Brahmaputra, Sichuan) is manifested by a divergence of stress vectors.
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| 7. |
- Zhang, Wen, et al.
(författare)
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Age and petrogenesis of Mingshui-Shuangjingzi granites from the northern Beishan area, northwest China, and their implications for tectonic evolution
- 2017
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Ingår i: Geosciences Journal. - : Springer Science and Business Media LLC. - 1226-4806 .- 1598-7477. ; 21:5, s. 667-682
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Tidskriftsartikel (refereegranskat)abstract
- The Mingshui and Shuangjingzi granitic plutons are exposed in the northern Beishan area, in the southern Central Asia Orogenic Belt. U-Pb zircon dating indicates that Mingshui secondary intrusive lithosfacies and Shuangjingzi quartz monzodiorite formed at 328 ± 2 Ma and 272 ± 2 Ma, respectively. The former is composed of grey white monzogranites and potassic altered flesh red monzogranites. Geochemistry indicates they are calc-alkaline I-type granites. Shuangjingzi granites are mainly composed of unfractionated calc-alkaline I-type quartz monzodiorite, granodiorite and monzogranite. The Mingshui grey white monzogranites with negative initial εNd (–2.0 to–1.7) and moderate initial 87Sr/86Sr values (0.706740 to 0.710092) were probably derived from mixing of the depleted mantle (juvenile) component and the Palaeoproterozoic–Archean crust (or sedimentary) component and represent volcanic arc granites. The Shuangjingzi quartz monzodiorites are most likely derived from mafic to intermediate igneous protolith and represent post-collisional granites. This work, combined with the regional geology, suggests the Palaeo-Asian Ocean closed between 328 Ma and 272 Ma in the northern Beishan area.
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