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Editorial Board (IFC) 编辑委员会(国际金融公司)
IF 7.2 1区 地球科学 Q1 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2024-11-05 DOI: 10.1016/S1342-937X(24)00295-8
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引用次数: 0
Enhanced landslide susceptibility mapping in data-scarce regions via unsupervised few-shot learning 在数据稀缺地区,通过无监督的 "少量镜头学习 "增强滑坡易感性绘图
IF 7.2 1区 地球科学 Q1 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2024-11-04 DOI: 10.1016/j.gr.2024.10.011
Linghao Kong , Wenkai Feng , Xiaoyu Yi , Zhenghai Xue , Luyao Bai
Given the critical need to assess landslide hazards, producing landslide susceptibility map (LSM) in regions with scarce historical landslide inventories poses significant challenges. This study introduces a novel landslide susceptibility assessment framework that combines unsupervised learning strategies with few-shot learning methods to increase the accuracy of LSM in these areas. The framework has been practically validated in a representative geological disaster-prone area along the West-East Gas Pipeline in Shaanxi Province, China. We employed three advanced few-shot learning models: a support vector machine, meta-learning, and transfer learning. These models implement feature representation learning for weakly correlated influencing factors through an unsupervised approach, thereby constructing an effective landslide susceptibility assessment model. We compared traditional learning methods and used the receiver operating characteristic (ROC) curve and SHAP values to quantify the effectiveness of the models. The results indicate that the meta-learning algorithm outperforms both the SVM and transfer learning in areas with limited landslide data. The integration of unsupervised strategies significantly improves performance, achieving area under the curve (AUC) values of 0.9385 and 0.9861, respectively. Compared with using meta-learning alone, incorporating unsupervised learning strategies increased the AUC by 4.76%, enhancing both the predictive power of the model and the interpretability of the features. Meta-learning under unsupervised conditions effectively mitigates the evaluation difficulties caused by insufficient landslide records, providing a viable path and empirical evidence for performance improvement in similar data- scarce regions worldwide.
鉴于评估滑坡危害的迫切需要,在缺乏历史滑坡资料的地区绘制滑坡易感性地图(LSM)是一项重大挑战。本研究介绍了一种新型滑坡易发性评估框架,该框架将无监督学习策略与少量学习方法相结合,以提高这些地区滑坡易发性地图的准确性。该框架在中国陕西省西气东输管道沿线具有代表性的地质灾害易发区进行了实际验证。我们采用了三种先进的少拍学习模型:支持向量机、元学习和迁移学习。这些模型通过无监督方法对弱相关影响因素进行特征表示学习,从而构建了有效的滑坡易损性评估模型。我们比较了传统的学习方法,并使用接收者操作特征曲线(ROC)和 SHAP 值来量化模型的有效性。结果表明,在滑坡数据有限的地区,元学习算法优于 SVM 和迁移学习。无监督策略的集成显著提高了性能,曲线下面积(AUC)值分别达到 0.9385 和 0.9861。与单独使用元学习相比,整合非监督学习策略后的 AUC 提高了 4.76%,既增强了模型的预测能力,又提高了特征的可解释性。无监督条件下的元学习有效缓解了滑坡记录不足造成的评估困难,为全球类似数据匮乏地区的性能提升提供了可行路径和实证依据。
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引用次数: 0
How do air pollution and population migration influence income inequality in China
IF 7.2 1区 地球科学 Q1 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2024-11-03 DOI: 10.1016/j.gr.2024.10.010
Baoxi Li , Tiantian Gui , Qinwei Cao
This study aims to investigate the impacts of air quality and population migration on income inequality in China. It introduces a general equilibrium model that air pollution triggers population outflow. The findings reveal that both absolute and relative air pollution cause population outflow and exacerbate income inequality. Using panel data of 292 Chinese cities in 2001–2020, this study finds that deteriorations in air quality—both in absolute and relative terms—widen the income gap but can mitigate income inequality through population outflow. Robustness tests support these findings. This study also uses data from A-share listed companies in China from 2010 to 2020 to explore the nexus between air pollution, human capital, and income inequality. It finds that increased absolute and relative air pollution decrease human capital and increase income inequality. Furthermore, a decrease in employee human capital (non-talents outflow) reduces intra-company income gap. This decrease is caused by a decrease in senior executives’ earnings compared to an increase in general employees’ compensation. However, a reduction in the human capital of senior executives (talents outflow) increases income inequality by boosting the earnings of senior executives.
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引用次数: 0
The lithosphere of South America from seismic tomography: Structure, evolution, and control on tectonics and magmatism 从地震层析成像看南美洲岩石圈:结构、演变以及对构造和岩浆活动的控制
IF 7.2 1区 地球科学 Q1 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2024-11-02 DOI: 10.1016/j.gr.2024.10.012
Bruna Chagas de Melo , Sergei Lebedev , Nicolas Luca Celli , Sally Gibson , Janneke Iza de Laat , Marcelo Assumpção
The thickness, temperature and mechanical strength of the lithosphere vary greatly across South America and have controlled tectonic and magmatic processes during its evolution. Here, we introduce a new tomographic model of South America’s lithosphere and underlying mantle, SACI-24, and analyse this and other state-of-the-art models together with other geological and geophysical data. The new model is obtained by waveform inversion of surface, S and multiple S waveforms globally, but is optimised for South America and the surrounding oceans. SACI-24 is constrained by ∼ 970,000 seismograms from 9259 stations and maps detailed structure of cratonic lithosphere across the continent, highlighting previously unknown complexities and fragmentation. Within the Amazon Craton, the Guiana and Central Brazil blocks show high Vs exceeding 4.8 km/s in the 80–150 km depth range but are separated by lower velocities below the Amazon Basin, matching the locations of ancient rifting and the flood basalts of the Central Atlantic Magmatic Province. In the São Francisco Craton, high velocities extend north and southwest beyond the previously proposed boundaries. Warmer, thinner lithosphere underlies the Paramirim and Pirapora aulacogens, locations of magmatic and rifting cycles. A fragmented cratonic root underlies the Paraná Basin, with thinner lithosphere along its central rift. High velocities south of the Paraná Block indicate the northern Rio de la Plata Craton’s thick root. The Cenozoic intraplate basalts in the Borborema province, along the southern Atlantic coast and in Paraguay occurred in areas of thin lithosphere and near thick-thin lithospheric boundaries. Most flood basalts of the Phanerozoic large igneous provinces also map on low velocity areas. Smaller flood-basalt portions sit atop cratonic lithosphere and offer new evidence on lateral flow of flood-basalt lava and magma within the crust. About 80 % of known diamondiferous kimberlites are on thick lithosphere, with the exceptions indicating cratonic erosion and thinning since their emplacement.
南美洲各地岩石圈的厚度、温度和机械强度差异很大,在其演化过程中控制着构造和岩浆过程。在此,我们介绍了南美洲岩石圈和下伏地幔的新层析成像模型 SACI-24,并结合其他地质和地球物理数据分析了这一模型和其他最先进的模型。新模型是通过对地表波形、S 波形和全球多重 S 波形进行波形反演获得的,但针对南美洲和周边海洋进行了优化。SACI-24 由来自 9259 个台站的 970,000 ∼ 张地震图构成,绘制了整个大陆板块岩石圈的详细结构图,突出显示了以前未知的复杂性和破碎性。在亚马孙克拉通内,圭亚那和巴西中部地块在 80-150 千米深度范围内显示出超过 4.8 千米/秒的高 Vs,但在亚马孙盆地以下则被较低的速度分隔开来,这与古代断裂和中大西洋岩浆省洪积玄武岩的位置相吻合。在圣弗朗西斯科克拉通,高速向北和西南延伸,超出了之前提出的边界。帕拉米林和皮拉波拉丘原的岩石圈较暖、较薄,是岩浆和断裂循环的发生地。巴拉那盆地的地底是一个支离破碎的板块根,其中央裂谷沿线的岩石圈较薄。巴拉那地块以南的高速度表明拉普拉塔河北部克拉通的根部较厚。新生代博博雷马省、大西洋南部沿岸和巴拉圭的板内玄武岩出现在岩石圈较薄的地区和厚-薄岩石圈边界附近。新生代大型火成岩省的大部分洪积玄武岩也分布在低速区域。较小的洪积玄武岩部分位于板块岩石圈之上,为洪积玄武岩熔岩和岩浆在地壳内的横向流动提供了新的证据。已知的含金刚石的金伯利岩约有 80% 位于厚岩石圈上,例外情况表明,这些金伯利岩自形成以来就受到板岩的侵蚀和变薄。
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引用次数: 0
Anatomy of the late Pennsylvanian to early Triassic failed rift system of the Cooper Basin, eastern Australia 澳大利亚东部库珀盆地宾夕法尼亚晚期至三叠纪早期失败裂谷系统剖面图
IF 7.2 1区 地球科学 Q1 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2024-10-24 DOI: 10.1016/j.gr.2024.09.017
Carmine C. Wainman , Peter J. McCabe
The onshore intracratonic Cooper Basin of eastern Australia developed during the Late Pennsylvanian to Middle Triassic periods at paleolatitudes of approximately 50°S within the Gondwanan sector of Pangea. Despite the wealth of data available, including the drilling of over 4,800 boreholes, there is limited knowledge about the Cooper Basin’s origins and evolution. To better understand the basin’s geological history, legacy data sets, including composite 2D seismic sections, well logs, measured sections, and 1D burial history models from the west of the basin, are integrated to reinterpret the basin’s tectonic and sedimentary evolution. Interpretation of the seismic sections and calculated subsidence rates indicates an earlier active rift phase with grabens and half-grabens that transitioned, in the latest Permian, into a regional sag phase. The evolution of tectonic styles heavily influenced the paleogeographic evolution of the basin fill and resulting depositional architecture. The basin sediments are entirely terrestrial in nature and facies reflect a transition from glacial environments in the late Pennsylvanian to warmer and drier conditions in the early Triassic. During much of the Permian the basin was underfilled and the relative low influx of fluvial sediment did not keep pace with creation of accommodation, allowing the development of extensive mire and lake systems. Coal beds are up to 30 m thick. By contrast, the basin appears to have been overfilled during the latest Permian to Triassic with rivers flowing along the central axis of the basin. The synchroneity of commencement of rifting, termination of rifting, and commencement of a sag phase within the failed rift systems of the Cooper Basin, the East Gondwana Interior Rift, and the East Australian Rift strongly suggests a continent-wide period of extension related to significant changes in plate motions during the Late Pennsylvanian to Middle Triassic.
澳大利亚东部的陆上地壳内库珀盆地发育于宾夕法尼亚晚期至三叠纪中期,位于泛大陆冈瓦纳地区约 50°S 的古纬度上。尽管有丰富的数据,包括钻探了 4,800 多个钻孔,但人们对库珀盆地的起源和演化仍知之甚少。为了更好地了解该盆地的地质历史,我们整合了遗留数据集,包括复合二维地震剖面图、测井记录、实测剖面图以及盆地西部的一维埋藏史模型,以重新解释该盆地的构造和沉积演化。对地震剖面的解释和计算的沉降速率表明,早期为活跃的裂谷阶段,有地堑和半地堑,在二叠纪晚期过渡到区域下陷阶段。构造样式的演变在很大程度上影响了盆地填充物的古地理演变以及由此产生的沉积结构。盆地的沉积物完全是陆相沉积,其面貌反映了从宾夕法尼亚晚期的冰川环境向三叠纪早期的温暖干燥环境的过渡。在二叠纪的大部分时间里,盆地填埋不足,相对较少的河道沉积物涌入跟不上容纳性的形成,从而形成了广泛的沼泽和湖泊系统。煤层厚达 30 米。相比之下,盆地在二叠纪晚期至三叠纪期间似乎被过度填充,河流沿着盆地的中轴线流淌。库珀盆地、东冈瓦纳内部裂谷和东澳大利亚裂谷等断裂系统的断裂开始、断裂结束和下陷阶段开始的同步性,有力地说明了在晚彭西凡尼世至中三叠世期间,整个大陆的延伸与板块运动的重大变化有关。
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引用次数: 0
Hydrothermal overprinting of the Li-rich strata deposited in the Mesoproterozoic Wumishan Formation, Hebei Province, North China 华北地区河北省中新生代五米山地层富锂辉石地层的热液叠加作用
IF 7.2 1区 地球科学 Q1 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2024-10-24 DOI: 10.1016/j.gr.2024.10.009
Fei Xu , Baoqiang Zhao , Hanjie Wen , Hefan Liu , Xiaofeng Li , Yu Chen , Yi Cui , Chengyu Mi , Jian Yang , Chuan Wang
Lithium (Li), as a strategic critical metal, plays a pivotal role in the emerging energy landscape, particularly in the context of Li-ion batteries driving the new energy economy. Recently, Li-rich strata (with Li2O > 0.3 wt%) have been discovered in the Mesoproterozoic Wumishan Formation in Hebei Province, North China, suggesting a prospective Li reservoir. This study investigates these Li-rich strata using geochemical and in-situ micro-analytical techniques to explore the occurrence of Li and the formation mechanism of Li-host minerals, aiming for a comprehensive understanding of the supernormal enrichment of Li. The Li-rich samples are predominantly composed of dolomite and quartz, followed by clay minerals such as illite, interstratified illite–smectite (I/S), and chlorite, with minor amounts of K-feldspar, albite, biotite, calcite, baryte, fluorite and fluorapatite. In-situ analysis and 7Li NMR spectroscopy reveal that Li predominantly occupies the octahedral sites within the structures of authigenic illite and I/S, while its absence in clastic illite, clastic chlorite, unaltered K-feldspar, and dolomite. The presence of veined minerals (e.g., fluorite, baryte, and calcite) and a strong positive correlation between Li and F imply that post-depositional hydrothermal fluids have significantly contributed to the formation of Li-host minerals. The paragenesis of these minerals suggests that Li-bearing illite has formed through the hydrothermal alteration of K-feldspar. These Li-bearing illites subsequently transformed into Li-bearing I/S, consisting of illite-rich I/S and smectite-rich I/S, under continuous hydrothermal alteration. Lithium could have been leached from the surrounding carbonate rock and tuff through water–rock interaction and subsequently enriched by post-depositional hydrothermal fluids in specific regions, leading to mineralization. These findings provide valuable insights for targeting exploration of this promising Li resource.
锂(Li)作为一种战略性关键金属,在新兴能源领域发挥着举足轻重的作用,尤其是在锂离子电池推动新能源经济发展的背景下。最近,在中国北方河北省的中新生代五米山地层中发现了富锂地层(含 Li2O > 0.3 wt%),这表明该地层具有潜在的锂储层。本研究利用地球化学和原位显微分析技术对这些富锂地层进行了研究,探讨了锂的存在和锂寄主矿物的形成机制,旨在全面了解锂的超常富集。富锂样品主要由白云石和石英组成,其次是伊利石、互层伊利石-直闪石(I/S)和绿泥石等粘土矿物,以及少量的钾长石、白云石、生物橄榄石、方解石、重晶石、萤石和氟磷灰石。原位分析和 7Li NMR 光谱显示,在自生伊利石和 I/S 结构中,锂主要占据八面体位,而在碎屑伊利石、碎屑绿泥石、未改变的 K 长石和白云石中则没有锂。脉石矿物(如萤石、重晶石和方解石)的存在以及锂和F之间的强正相关性意味着沉积后热液在很大程度上促成了锂宿主矿物的形成。这些矿物的副成因表明,含锂伊利石是通过热液蚀变 K 长石形成的。这些含锂伊利石随后在持续的热液蚀变作用下转化为含锂I/S,包括富含伊利石的I/S和富含闪长岩的I/S。锂可能是通过水与岩石的相互作用从周围的碳酸盐岩和凝灰岩中沥滤出来的,随后在特定区域被沉积后热液富集,导致成矿。这些发现为有针对性地勘探这一前景广阔的锂资源提供了宝贵的见解。
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引用次数: 0
The impact of Pangean subducted oceans on mantle dynamics: Passive piles and the positioning of deep mantle plumes 泛大陆俯冲洋对地幔动力学的影响:被动堆积和深地幔羽流的定位
IF 7.2 1区 地球科学 Q1 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2024-10-23 DOI: 10.1016/j.gr.2024.10.007
Philip J. Heron , Juliane Dannberg , Rene Gassmöller , Grace E. Shephard , Jeroen van Hunen , Russell N. Pysklywec
Seismic imaging of the Earth’s interior reveals plumes originating from relatively hot regions of the lowermost mantle, surrounded by cooler material thought to be remnants of ancient subducted oceans. Currently, there is no clear consensus on the internal composition of the hot regions, with end-member conditions being that they are thermo-chemical in nature or purely thermal plume clusters. Previous modelling studies have shown a range of scenarios where deep chemical heterogenities or purely thermal anomalies are essential in developing appropriate present-day mantle dynamics. Here, we add to this discussion by quantifying the location of rising mantle plumes using numerical 3-D global mantle convection models constrained by 410 million years of palaeo-ocean evolution (encompassing the formation and breakup of supercontinent Pangea). Our study compares numerical simulations with purely thermal convection to those where a deep thermo-chemical anomaly is laterally mobile. The results show that models both with and without large-scale chemical heterogeneities can generate appropriate present-day plume dynamics, which illustrate the power of sinking ocean plates to stir mantle ow and control the thermal evolution of the mantle. Our models add to the discussion on bottom-up and top-down mantle dynamics, indicating the difficulty in unravelling the processes using numerical models alone.
地球内部的地震成像显示,羽流源自最下层地幔中相对较热的区域,周围是较冷的物质,被认为是古代俯冲洋的残余物。目前,关于热区的内部组成还没有明确的共识,最终的成员条件是热化学性质或纯粹的热羽流集群。以往的建模研究表明,在一系列情况下,深层化学异质性或纯粹的热异常对发展适当的当今地幔动力学至关重要。在此,我们利用受 4.1 亿年古海洋演化(包括超大陆潘加大陆的形成和解体)制约的三维全球地幔对流数值模型,对上升地幔羽流的位置进行量化,从而为这一讨论添砖加瓦。我们的研究将纯热对流的数值模拟与深层热化学异常横向移动的数值模拟进行了比较。结果表明,有大规模化学异质性和无大规模化学异质性的模型都能产生适当的现今羽流动力学,这说明了下沉大洋板块搅动地幔欠层和控制地幔热演化的能力。我们的模型为有关自下而上和自上而下地幔动力学的讨论增添了新的内容,表明仅使用数值模型难以揭示这些过程。
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引用次数: 0
Responding to green finance with emission reduction and value-added: The role of enterprise environmental investment 以减排和增值应对绿色金融:企业环境投资的作用
IF 7.2 1区 地球科学 Q1 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2024-10-21 DOI: 10.1016/j.gr.2024.10.008
Yao Wang , Shengling Zhang , Zihao Wu , Yu Hao , Ruijie Li
Responding to China’s green finance policy with enterprise environmental investment (EEI) constitutes a crucial link in achieving environmental governance objectives, exerting crucial influence on the nation’s green transformation and high-quality development. Taking the pilot policy of China’s Green Finance Reform and Innovation Experimental Zone (GFRP) in 2017 as a quasi-natural experiment, this study systematically evaluates the effect of GFRP policy on the decisions of EEI and further explore whether the investments are used for passive end-of-pipe treatment (EOP) or positive source prevention (SP) by using firm-level data. The results indicate that GFRP policy can significantly promote EEI, and mainly reflected in SP, rather than EOP. Through potential mechanism analysis, it can be concluded that GFRP policy facilitates EEI by alleviating financial constraint, reducing agency cost, and enhancing environmental information disclosure. Heterogeneity analysis suggests that there exists asymmetry in policy effects, with greater impacts in high green finance development areas, low concentration industries and large-scale enterprises. Furthermore, micro-level performance consequences examination reveals that the enterprises’ decision to increase EEI under GFRP policy not only effectively realizes energy conservation and emission reduction but also contribute to facilitating enterprise value, to achieve green transformation. This study holds significant policy implications, providing empirical evidence to policymakers for the refinement and dissemination of green finance policy, and offering valuable insights for enterprise investment and management decisions.
以企业环保投资(EEI)响应中国绿色金融政策,是实现环境治理目标的关键环节,对国家绿色转型和高质量发展具有重要影响。本研究以2017年中国绿色金融改革创新试验区(GFRP)试点政策为准自然实验,系统评估了GFRP政策对企业环保投资决策的影响,并通过企业层面的数据进一步探讨投资是用于被动的末端治理(EOP)还是积极的源头防治(SP)。结果表明,GFRP 政策能显著促进 EEI,且主要体现在 SP 上,而非 EOP。通过潜在机制分析,可以得出结论:GFRP 政策通过缓解财务约束、降低代理成本和加强环境信息披露来促进 EEI。异质性分析表明,政策效应存在不对称性,在绿色金融高发展地区、低集中度行业和大型企业中影响更大。此外,微观层面的绩效后果分析表明,企业在 GFRP 政策下增加 EEI 的决策不仅有效实现了节能减排,还有助于提升企业价值,实现绿色转型。本研究具有重要的政策意义,为政策制定者完善和推广绿色金融政策提供了经验证据,并为企业投资和管理决策提供了有价值的启示。
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引用次数: 0
Tectono-magmatic evolution of the Indian crust in western Himalayas during Paleoproterozoic: Insights from Nanga Parbat and Indus syntaxis in northern Pakistan 古近古生代喜马拉雅山西部印度地壳的构造-岩浆演化:从巴基斯坦北部的南迦帕尔巴特山和印度河综脉获得的启示
IF 7.2 1区 地球科学 Q1 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2024-10-19 DOI: 10.1016/j.gr.2024.10.006
Muhammad Sajid , Michael Wiedenbeck , Muhammad Arif , Johannes Glodny , Nowrad Ali , Humaad Ghani , Jessica A. Stammeier
The Paleoproterozoic tectono-magmatic history of the Indian plate has been modelled mostly based on investigations of the Indian parts with limited studies considering the Pakistani domains of the mountain range. In this study we investigate basement rocks and younger intrusions of the Indian crust from within the core of the Indus Syntaxis and the Nanga Parbat Syntaxis in northern Pakistan, with the goal of establishing a chronology for the entire tectono-magmatic progression of northwestern Indian plate margin, including the source rocks that were ultimately involved in the formation of younger magmatic pulses. We present in-situ zircon U-Pb geochronology and O-isotopes complemented by whole rock geochemistry of granitoids and paragneisses that yielded evidence for two distinct, large-scale Paleoproterozoic magmatic events that took place in ∼ 1860 Ma and ∼ 2200 Ma in the Indian crust. Later, leucogranites (6.4 ± 0.1 Ma) intruded into the Nanga Parbat basement that were the result of melting of the basement induced by rapid uplift. The δ18OSMOW compositions of zircons from our basement samples range between 7.5 to 9.1 ‰, indicating the derivation of parental magma from the crustal source while the younger leucogranite is somewhat lighter with δ18O ranging between 7.06 to 8.23 ‰. Geochemical data show extensional tectonic settings for the basement rocks that have an A-type affinity, again pointing to a crustal precursor. We propose little to no δ18O exchange took place between the young anatectic melt and basement rocks during crustal evolution. Moreover, geochemical signatures record the crystallization of basement rocks dominated the northwestern margin of Indian plate in a post-orogenic setting in an overall extensional tectonic realm. Based on these observations, we infer that the northwestern Indian margin has experienced a large-scale magmatism during Paleoproterozoic associated with the amalgamation of the Columbia supercontinent.
印度板块的古新生代构造-岩浆史模型主要是基于对印度部分的研究,而对巴基斯坦境内山脉的研究有限。在这项研究中,我们调查了印度地壳的基底岩石和较年轻的侵入体,这些岩石来自巴基斯坦北部的印度河综合地轴和南加帕尔巴特综合地轴的核心区域,目的是为印度西北板块边缘的整个构造-岩浆演化过程建立年表,包括最终参与形成较年轻岩浆脉冲的源岩。我们展示了原位锆石U-Pb地质年代学和O-同位素,并辅以花岗岩和片麻岩的全岩地球化学,这些证据表明印度地壳在1860Ma∼和2200Ma∼发生了两次不同的、大规模的古新生代岩浆事件。后来,白云岩(6.4 ± 0.1 Ma)侵入南迦帕尔巴特基底,这是快速隆升引起基底熔化的结果。基底样本的锆石成分δ18OSMOW介于7.5至9.1‰之间,表明母岩浆来自地壳源,而较年轻的白榴石成分较轻,δ18O介于7.06至8.23‰之间。地球化学数据显示,基底岩石具有A型亲和力的延伸构造背景,这再次表明了地壳的前身。我们认为,在地壳演化过程中,年轻的无极性熔体与基底岩石之间几乎没有发生δ18O交换。此外,地球化学特征记录了印度板块西北边缘基底岩石的结晶过程,该过程是在整体伸展构造背景下的后成因环境中进行的。根据这些观察结果,我们推断印度西北边缘在古近古生代经历了与哥伦比亚超大陆汞齐化有关的大规模岩浆活动。
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引用次数: 0
Heterogeneous water distribution in between peridotite xenoliths from Kaapvaal Craton kimberlites: Constraints on diamond barren nature of kimberlites 卡普瓦尔克拉通金伯利岩橄榄石间的异质水分布:金伯利岩金刚石贫瘠性质的制约因素
IF 7.2 1区 地球科学 Q1 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2024-10-16 DOI: 10.1016/j.gr.2024.10.004
Sahroz Khan , Nóra Liptai , István J. Kovács , Yana Fedortchouk , Tivadar M. Tóth
Nominally anhydrous mantle minerals (olivine, pyroxenes, garnets, etc.) in 11 peridotite xenoliths from four different uneconomic and economic Kaapvaal Craton kimberlite pipes (Matsoku, Thaba Putsoa, Pipe 200 and Bultfontein) have been investigated using Fourier transform infrared spectroscopy (FTIR). All xenoliths contain accessories of garnet, diopside, chromite, and phlogopite. High orthopyroxene content (>30 mol vol.%) in most xenoliths from all kimberlites and its interconnected channel-like nature hint towards hydrous siliceous fluid metasomatism. Peridotite xenoliths from uneconomic kimberlites show development of phlogopite and clinopyroxene (± chromite) forming veins and in garnet rims suggesting metasomatism by alkaline silico-carbonatite (possibly kimberlite-related) melt. The xenoliths contain significant H2O in olivine (17–62 ppm), orthopyroxene (21–230 ppm), and clinopyroxene (87–833 ppm), whereas garnets are dry and only show IR absorbance bands at > 3,670 cm−1 for contamination of hydrous minerals. Compared to the economic kimberlites in the Kaapvaal Craton, the uneconomic kimberlite xenoliths from this study have lower orthopyroxene and olivine H2O content. In the xenoliths affected by garnet breakdown metasomatism, the H2O content of orthopyroxene and olivine is higher and lower, respectively. The structural hydroxyl distribution profile across olivine and higher inter-mineral water partition coefficient, suggest diffusion of hydrogen and possible re-equilibration. Statistical analysis of the olivine spectra suggests that hydrogen bands at 3540, 3624, 3638, and 3672 cm−1 are a good discriminant of economic and uneconomic kimberlites and in literature, they are associated with metasomatism, weathering-associated processes, high water activity, and oxygen fugacity. The lower water concentration in xenoliths from uneconomic kimberlite from the margin of the craton than the economic kimberlites from the interior of the Kaapvaal Craton and identified metasomatism hints towards dehydration of xenoliths by water-poor and CO2-rich melts in tectonized cross-lithospheric zones causing diamond resorption and may be responsible for the diamond-poor nature of uneconomic kimberlites in northern Lesotho.
采用傅立叶变换红外光谱法(FTIR)对来自四个不同的非经济和经济卡普瓦尔克拉顿金伯利岩管道(Matsoku、Thaba Putsoa、Pipe 200 和 Bultfontein)的 11 块橄榄岩异长岩中的标称无水地幔矿物(橄榄石、辉石、石榴石等)进行了研究。所有独居石都含有石榴石、透辉石、铬铁矿和辉绿岩。来自所有金伯利岩的大多数闪长岩中的正长石含量较高(30 mol vol.%),其相互连接的通道状性质暗示了水硅质流体变质作用。来自非经济金伯利岩的橄榄石闪长岩显示出辉绿岩和霞石(±铬铁矿)形成的矿脉以及石榴石边缘的发育,这表明是碱性硅碳酸盐岩(可能与金伯利岩有关)熔体的变质作用。橄榄石(17-62 ppm)、正长石(21-230 ppm)和菱镁矿(87-833 ppm)中的析出物含有大量的 H2O,而石榴石是干燥的,仅在 > 3,670 cm-1 处显示出红外吸光度带,表明受到含水矿物的污染。与卡普瓦尔克拉通的经济金伯利岩相比,本研究中的非经济金伯利岩的正长石和橄榄石 H2O 含量较低。在受石榴石击穿变质作用影响的闪长岩中,正长石和橄榄石的 H2O 含量分别较高和较低。橄榄石的羟基结构分布图和较高的矿物间水分配系数表明氢的扩散和可能的再平衡。橄榄石光谱的统计分析表明,3540、3624、3638 和 3672 cm-1 处的氢带可以很好地区分经济金伯利岩和非经济金伯利岩。与来自卡普瓦尔克拉通内部的经济金伯利岩相比,来自克拉通边缘的非经济金伯利岩的析出物中的水浓度较低,而且已查明存在变质作用,这表明在构造化的跨岩石圈地带,贫水和富含二氧化碳的熔体使析出物脱水,导致金刚石重吸收,这可能是莱索托北部非经济金伯利岩贫乏金刚石的原因。
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