Kang, WenbinLi, WeiDong, YunpengZhang, Le...
16页查看更多>>摘要：The Qinling Complex is the only continental nucleus that outcrops in the North Qinling Orogenic Belt (NQOB) and preserves valuable evolutionary information of NQOB during the early Paleozoic. There are many high-pressure (HP)-ultrahigh-pressure (UHP) metamorphic rocks distributed in the northern and southern parts of the Qinling Complex. Whether the central part (namely the Qihe tectonic slab) underwent a similar HP-UHP metamorphism and what the relationship among different tectonic slabs of Qinling Complex is, are the key to revealing the formation and exhumation process of these HP- UHP rocks. Four episodes of deformation (D1-4) have been recognized in the Qinling Complex. The metamorphic pressure-temperature conditions of syn-D3 amphibolite in the Qihe tectonic slab are limited to 3.3-6.4 Kbar and 479-538 degrees C based on equilibrium modeling, corresponding to an extensional tectonic setting. The U-Pb dating of the amphibolite yielded a protolith age of 714 +/- 46 Ma, an eclogite-facies metamorphic age of 514 +/- 4 Ma, and two stages of retrograde metamorphism at 462 +/- 3 Ma and 418 +/- 5 Ma. The parametamorphic rocks of different tectonic slabs have similar detrital zircon age spectra, which is a very different pattern from adjacent areas of the Qinling Complex. The consistency in the protolith ages, peak metamorphic ages, two stages of retrograde metamorphism, and detrital zircon age from different tectonic slabs in the Qinling Complex indicate that HP-UHP metamorphic rocks from Qinling Complex formed during the same tectonic event. Therefore, the Qinling Complex evolved in deep subduction and underwent eclogite facies metamorphism, followed by superimposed deformation structures and retrograde metamorphism during the two stages of exhumation. (C) 2021 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
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Elsevier
Martins, Pedro L. G.Toledo, Catarina L. B.Silva, Adalene M.Chemale Jr, Farid...
26页查看更多>>摘要：One of the most important occurrences of banded iron formation (BIF) worldwide is situated in the Carajas Mineral Province, southeastern Amazonian Craton. The BIFs are jaspilites and are hosted in the Neoarchean (~2.74 Ga) volcano-sedimentary sequence of the Grao-Para Group. They are mostly composed of cm-thick intercalations of hematite, jasper, and chert. Their primary textures and structures are still preserved, which make them an ideal archive to evaluate the paleomarine environment. Low abundance of Al2O3 (< 1.0 wt%) and HFSE (< 1 ppm) for most BIF samples indicate an essentially detritus-free depositional environment. Overall, the rare earth elements and yttrium (REY) patterns show a weak positive lanthanum (La) anomaly, and a pronounced positive europium (Eu) anomaly (Eu/Eu-PAAS = 1.86 - 5.05), although the presence of true cerium (Ce) anomaly is not evident. Stratigraphic variations in iron isotope compositions, up to 0.80% (delta Fe-56 = +1.10 to +1.90%) over tens to hundreds of meters of stratigraphic section, point to relative changes in the iron isotope composition of Carajas seawater over periods of a few million years. The jaspilites show heterogeneous distribution of Nd isotopic signature throughout the BIF sequence, and rocks from near the basaltic flows/jaspilite contact (type-II) have negative eNd (t) values (-4.97 to -0.90). In contrast, predominantly positive epsilon Nd(t) values (-0.84 to +5.40) are common in the remaining samples (type-I). The strongly positive delta Fe-56 values indicate a low degree of partial oxidation of Fe(II), which, combined with the pronounced positive Eu anomalies and the absence of Ce anomalies, hint towards that the deposition occurred mainly on a deep-sea environment with intense hydrothermal activity under anoxic and suboxic conditions, distal to continental landmasses. Locally, considerable oxygen was probably present in the ancient ocean's water masses, which led to the precipitation of BIFs. (C) 2021 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
原文链接:- NSTL
- Elsevier
Baba, SotaroHorie, KenjiHokada, TomokazuTakehara, Mami...
19页查看更多>>摘要：In this paper, we report a new metamorphic age for kyanite-bearing garnet-biotite gneiss collected from Akebono Rock, which is located on Prince Olav Coast, in the Lutzow-Holm Complex (LHC), East Antarctica. The metamorphic P-T path estimated from pseudosection modeling, together with garnet compositional zoning and experimentally calibrated geothermobarometry, suggests that the gneiss underwent a clockwise amphibolite-facies P-T history. Two populations of U-Pb zircon ages of 1121-1014 Ma and 972- 904 Ma (n = 65) were identified, with the latter population having a weighted mean age of 937 +/- 6 Ma. The younger population was dated from overgrowth rims and single zircon grains interpreted as metamorphic in origin. Ti-in-zircon thermometry supports crystallization of these zircon domains and grains at a temperature close to the metamorphic peak of 642 degrees C at 937 Ma. Monazite EMP dating from the other four samples show an age between 977 and 917 Ma. These lines of evidence indicate that pro grade metamorphism of the Akebono Rock gneiss occurred during the Tonian, that is, substantially earlier than the LHC regional metamorphic age of late Neoproterozoic to Cambrian. Our results indicate that a fundamental revision of the sequence of metamorphic events in the Prince Olav Coast area of the LHC is required. We also identified three possible relationships between Akebono Rock and other geological units that record Tonian metamorphism, although we cannot determine which relationship is most likely. In particular, linear magnetic anomalies were identified near the boundary between the LHC and the Western Rayner Complex/inland nunataks of western Enderby Land, suggesting the presence of geological discontinuities.(c) 2021 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
原文链接:- NSTL
- Elsevier
Spier, Carlos AlbertoFilho, Cesar Fonseca FerreiraDaczko, Nathan
28页查看更多>>摘要：The age and tectonic history of the chromite-mineralised Bacuri Complex, a layered mafic-ultramafic intrusion emplaced into Archean terranes of the Guyana Shield in the Amazonian Craton, are here investigated. The stratigraphy of the Bacuri Complex consists of an Ultramafic Zone composed of interlayered metaperidotites and chromitites and two mafic zones composed of metamafic rocks (amphibolites). In this study we present whole-rock lithogeochemical data integrated with zircon U-Pb isotopic and trace-element data from amphibolites from the Mafic Zone. The investigated amphibolites consist of hornblende + plagioclase +/- diopside +/- biotite with whole-rock compositions like noritic rocks of Archean layered intrusions. These samples are representative of amphibolites with variable proportions of hornblende and plagioclase, interpreted as resulting from amphibolite facies metamorphism of inter layered norite and leuconorite. We suggest that progressive fractionation of a primitive parental magma led to the formation of plagioclase and orthopyroxene cumulates in the mafic zones. We found that zircons from three metanorite samples comprise euhedral crystals with oscillatory zoning (interpreted to preserve a magmatic crystallisation age), as well as variably recrystallised metamorphic zircons. Their U-Pb Pb-207/Pb-206 ages span over 682 million years, from 3628 Ma to 2942 Ma. Trace element data suggest that magmatic zircons precipitated from late-stage magmatic fluids at ~ 3.34 Ga (3343 +/- 3.5 Ma weighted average age, n = 48, MSWD = 1.3), which defines the Bacuri Complex as one the oldest and best-preserved layered intrusions known. We show that fluid-mediated coupled dissolution-precipitation recrystallisation during metamorphism altered the composition and ages of magmatic zircons. We could not accurately define the number and age of metamorphic events in the 2942-3379 Ma age interval of metamorphic or "disturbed' zircon domains. Our results indicate that continental crust was already established in the Amazonian craton in the Paleoarchean and possibly in the Eoarchean and that it has been reworked since at least the Mesoarchean. (C) 2021 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
原文链接:- NSTL
- Elsevier
Li, ChufanZhang, ZhifeiKershaw, StephenHolmer, Lars E....
9页查看更多>>摘要：The identification of brachiopods requires specialist knowledge held by a limited number of researchers and is very time-consuming. The new technique of deep learning by artificial intelligence offers promising tools to break these shackles to develop computer automatic identification. However, we found that the traditional convolution neural network is not sufficient to automatically identify brachiopod species. Thus, we propose a new tailored Transpose Convolutional Neural Network (TCNN) in order to automatically identify brachiopod fossils with high efficiency. In this network, we add an "upsampling" Transpose Convolutional Layer and synthesize the data of this layer with the data of a Convolutional Layer to fully mix the small and large scales features extracted by the neural network. Compared with the traditional Convolution Neural Network (CNN), the Transpose Convolutional Neural Network (TCNN) can achieve a high identification accuracy using a smaller training data set of images of brachiopods. Results from this study show that the TCNN can achieve 98%, 98% and 97% identification accuracy respectively, with training data sets of 400 images of 3 species, 484 images of 4 species and 630 images of 5 species. In contrast, the traditional CNN can achieve only a low identification accuracy (67%) with 400 images of 3 species and requires 3000 images per 3 species to achieve a 95% identification accuracy. For most of brachiopod species, it is almost an impossible task to collected thousands of samples and as more brachiopod species are fitted into automatic identification, it is significant to have a reliable network which can achieve high accuracy on a small data set. In summary, the TCNN is a more efficient neural network that could be better applied to automatically identify brachiopod fossils. (C) 2021 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
原文链接:- NSTL
- Elsevier
Ahmad, MahmoodAhmed, ZahoorYang, XiyueHussain, Nazim...
12页查看更多>>摘要：Emerging countries are heading towards economic prosperity; however, the process of development has enhanced their ecological footprint. Therefore, to safeguard the environment, it is essential to identify the factors that affect the ecological footprint (EF). In this perspective, this study explores the effect of financial development, human capital, and institutional quality on the EF in emerging countries. Furthermore, we explore the effect of financial development on EF through the channel of human capital. In addition, we investigate the role of institutional quality in the financial development-EF nexus. Using the panel data from 1984 to 2017, we employed the cross-sectional autoregressive distributed lag (CS-ARDL) technique to conduct the short-run and long-run empirical analysis. The empirical outcomes unveiled that financial development degrades the ecological quality by raising the EF. The findings further unfolded that human capital and institutional quality reduce the EF. Moreover, financial development fosters environmental sustainability through the channel of human capital. Additionally, institution quality reduces the negative ecological impacts of financial development. The causality analysis suggested that any policy related to financial development, human capital, and institutional quality will affect EF but not the other way round. Based on these findings, emerging economies should promote environmental sustainability by promoting human capital and effectively using financial resources. (C) 2021 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
原文链接:- NSTL
- Elsevier
Olu-Owolabi, Bamidele, IDiagboya, Paul N.Mtunzi, Fanyana M.Adebowale, Kayode O....
9页查看更多>>摘要：Soils are highly heterogeneous dynamic mixtures with unique properties. The general properties of each type of soil affect its contaminants sorption; thus, obtaining sorption information about any regional soil may require actual sorption experiments. Hence, two soil types (alfisol-AFL and oxisol-OXL) were sampled and used for ivermectin sorption in order to obtain data on sub-Saharan soils for this new emerging contaminant from agriculture. Environmental parameters such as sorption time, ambient solution pH, ivermectin concentration, temperature and desorption were studied, while data were evaluated using two adsorption isotherm models, four kinetic models and the thermodynamics. The soils were neutral, typical of neutral West African soils and having slightly acidic pHpzc with similar particle size description and medium-to-low CECeff and SOM. Ivermectin sorption equilibrium was fast at 180 min for both soils. The rate constant k for sorption on AFL soil was slightly faster than for the OXL. Solution pH has some degree of influence on the sorption process which exhibited two sorption optimum peaks; one around pH 3 and the other around pH 9.5. Ivermectin sorption was concentration dependent; there was higher sorption as initial concentration increased, while sorption increased significantly with ambient temperature from 19.5 to 29.5 degrees C (approximate to 55%) but there was slight reduction on further temperature increase to 39.5 degrees C compared to sorption at 29.5 degrees C (<= 1%). The magnitude of the estimated energetics signaled a non-spontaneous and increasingly random process, with small size of the Delta H degrees values which were compatible with low energy interactive sorption forces and the overall process was exothermic. The ivermectin sorption process was controlled by external mass transfer (which was concentration dependent), with approximately 81.6% of sorption occurring on the soil surfaces, while 18.4% was within the pores or soil phases. The better fits of the sorption data to both the Freundlich adsorption isotherm model and the homogeneous fractal pseudo-second order model are complementary, and confirms that ivermectin sorption process on both soils involves complex interactions on heterogeneous sorption surfaces which include electrostatic interactions, multi-layer adsorption probably facilitated by it-it interactions between surface sorbed ivermectin molecules and those in solution, possibly trapping of ivermectin molecules within the soil pores, and various van der Waals attractive forces. Though ivermectin was rapidly dissipated on these soils, the hysteresis was high; irrespective of the soil, the amount of ivermectin leached per soil was small, in fact less than 6% of the initial amount sorbed. Our study has vital implications in predicting the fate of specific contaminants in the environment. (C) 2021 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
原文链接:- NSTL
- Elsevier
Stanca, Roxana M.McCarthy, Dave J.Paton, Douglas A.Hodgson, David M....
23页查看更多>>摘要：Commonly, intra-continental wrenching is associated with a high degree of crustal faulting and fragmentation. The resulting continental blocks can undergo vertical-axis rotations, which in turn can lead to the generation of intricate fault networks within and along their boundary regions. Investigations into these structural complexities can support understanding of when and how these continental blocks rotate, and what their position was prior to transform margin formation. In the case of the Falkland Islands Microplate (part of the Falkland Plateau transform margin), its position between South Africa, South America, and East Antarctica prior to the break-up of Gondwana is still debatable. This uncertainty affects the reliability of plate models for this region. Here we integrate gravity and 2D and 3D seismic reflection data from the eastern margin of the microplate (west side of the Falkland Plateau Basin) to provide insights into the tectono-stratigraphic architecture of this area from Jurassic onwards, and into the evolution of the Falkland Islands Microplate. Our findings show that the western part of the Falkland Plateau Basin is an integral part of the microplate, and it underwent deformation in a relatively fast-changing stress regime. Stress field configuration estimates across the Falkland Islands Microplate support an alternation between a NE-SW and NW-SE/WNW-ESE orientation of sigma(3) during the Jurassic and an ENE-WSW oriented sigma(3) during the Lower Cretaceous. Correlations of this local stress configuration with the regional support a Middle to Upper Jurassic rotation of the microplate in a predominantly extensional setting facilitated by the early fragmentation of south-western Gondwana. (C) 2021 The Authors. Published by Elsevier B.V. on behalf of International Association for Gondwana Research.
原文链接:- NSTL
- Elsevier
Wojtulek, Piotr MarianSchulz, BernhardKlemd, ReinerGil, Grzegorz...
23页查看更多>>摘要：The Variscan Central-Sudetic Ophiolites (CSO) are located in the Sudetes, the NE segment of the Bohemian Massif. The Devonian CSO display highly depleted, harzburgite mantle sections containing gabbroic dykes and local occurrences of mostly isotropic, large gabbroic bodies as well as volcanic rocks. The ultramafic rocks locally show melt percolation-derived clinopyroxene-olivine aggregates and chromitites. The low REE composition and depletion in LREE relative to HREE of the clinopyroxene as well as the chromite Cr# and Mg# values are typical for phases formed from refractory melts occurring in the supra-subduction zone environment. The gabbroic bodies consist of differently evolved, mostly cumulate rocks, while the volcanic rocks form a relatively monotonous basalt sequence. The trace element compositions of both the plutonic and volcanic rocks display depleted N-MORB affinities, their derivation from a refractory mantle source is further reflected by previously published depleted mantle-like Sr-Nd isotopic compositions. The ultramafic and mafic members of the CSO show greenschist- to lower amphibolite-facies metamorphic overprints. The occurrence of depleted harzburgites and isotropic gabbros forming the mantle and the crustal sections of the CSO, respectively, indicate intermediate- to slow-spreading conditions and a heterogeneous structure of the oceanic lithosphere, untypical for layered ophiolites. The geochemical characteristics of the melt-percolation phases of the ultramafic rocks, the bulk-rock compositions of the mafic rocks and the homogeneous volcanic sequences suggest a formation of the CSO in a mature back-arc basin setting, lacking subduction-derived contamination. Spreading rate conditions and geochemical affinities of the CSO are similar to those of other Devonian ophiolites localized along the Variscan Belt, for instance the Upper Ophiolitic Units in the NW Iberian Massif (Spain), thereby confirming the general absence of N-MORB type lithosphere in the European Variscan Orogen. (C) 2021 The Author(s). Published by Elsevier B.V. on behalf of International Association for Gondwana Research.
原文链接:- NSTL
- Elsevier
Ramachandran, S.Rupakheti, Maheswar
22页查看更多>>摘要：Recent satellite observations of atmospheric aerosol loading over Asia indicate a dipole pattern in the aerosol optical depth (AOD) with a substantial decrease in AOD over East Asia and persistent increase in AOD over South Asia, the two global hotspots of aerosol emissions. Aerosol emissions over Asia are also changing rapidly. However, the evolution of physical, optical and chemical columnar aerosol characteristics, and their radiative effects over time, and the resultant impacts of such evolving trends on climate and other associated risks are not yet properly quantified, and used in climate impact assessments. In order to do so, we closely examine, in addition to satellite observations, for the first time, high-quality, ca. two-decade long ground-based observations since 2001 of aerosols and their radiative effects from several locations in the Indo-Gangetic Plain (IGP) in South Asia and the North China Plain (NCP) in East Asia. A clear divergence in the trends in AODs is evident between the IGP and the NCP. The single scattering albedo (SSA) is increasing, and the absorption AOD due to carbonaceous aerosols (AAOD(CA)) is decreasing over both regions, confirming that aerosols are becoming more scattering in nature. The trends in observed aerosol content (AOD) and composition (SSA) are statistically significant over Kanpur in the IGP and Beijing in the NCP, two locations with longest ground-based records. The aerosol radiative forcing of atmosphere (ARF(ATM)) and resultant atmospheric heating rate (HR) are decreasing over both regions. However, current regionally coherent and high annual HR of 0.5-1.0 K day(-1) has severe implications to climate, hydrological cycle, and cryosphere over Asia and beyond. These results based on high-quality observations over a large spatial domain are of great significance and are crucial for modelling and quantifying aerosol-climate interactions. (C) 2021 The Author(s). Published by Elsevier B.V. on behalf of International Association for Gondwana Research.
原文链接:- NSTL
- Elsevier
