如何判定俯冲增生杂岩中的高度肢解的洋底高原-海山系统          下载免费PDF全文

肖庆辉  刘勇  程杨  邱瑞照  范玉须  裴斐  杨斌 《沉积与特提斯地质》2021,41(2):152-162

巨型洋底高原或海山系统到达俯冲带发生俯冲以后会在俯冲过程中发生肢解,在增生杂岩带中形成面目全非的小型洋底高原-海山系统的断块或碎片,使得在增生杂岩带中识别古老洋底高原-海山系统变得十分困难。为此,本文提出了基于洋板块地层、岩石学和地球化学联合研究的新方法及其识别标志,重新审定增生杂岩中洋底高原或海山的成因。  相似文献   

Early Cretaceous deformation in the southern Tashkorgan region: Implications for the tectonic evolution of the northeastern Pamir     

《China Geology》2021,4(1):67-76

The Pamir Plateau comprises a series of crustal fragments that successively accreted to the Eurasian margin preceded the India-Asia collision, is an ideal place to study the Mesozoic tectonics. The authors investigate the southern Tashkorgan area, northeastern Pamir Plateau, where Mesozoic metamorphic and igneous rocks are exposed. New structural and biotite ⁴⁰Ar-³⁹Ar age data are presented. Two stages of intense deformation in the metamorphic rocks are identified, which are unconformably covered by the Early Cretaceous sediment. Two high-grade metamorphic rocks yielding 128.4 ± 0.8 Ma and 144.5 ± 0.9 Ma ⁴⁰Ar-³⁹Ar ages indicate that the samples experienced an Early Cretaceous cooling event. Combined with previous studies, it is proposed that the Early Cretaceous tectonic records in the southern Tashkorgan region are associated with Andean-style orogenesis. They are the results of the flat/low-angle subduction of the Neotethyan oceanic lithosphere.©2021 China Geology Editorial Office.  相似文献   

Early Eocene leucocratic sill/dike swarms in the Gangdese belt,southern Tibet: Tectonic implications for Indo-Asian collision     

《China Geology》2021,4(1):56-66

The timing of the initial Indo-Asian collision is a subject of debate for a long time. Besides, the magmatic trace of the collisional process is also unclear. In the present study, the authors report Early Eocene leucocratic sill/dike swarms in the northern edge of the Nymo intrusive complex of the Gangdese belt, southern Tibet. The Nymo intrusive complex was emplaced at ca. 50 –47 Ma and surrounded by the metamorphosed Jurassic-aged Bima Formation volcano-sedimentary sequence along its northern side. At outcrops, the leucocratic sills/dikes intruded along or truncated the deformed foliations of the host Bima Formation, which has been subject to high-temperature amphibolite-facies metamorphism at ca. 50 –47 Ma. Detailed cathodoluminescence image analyses reveal that the zircon grains of the leucocratic sills/dikes have core-mantle textures. The cores yield the Jurassic ages comparable to the protolith ages of the Bima Formation. In contrast, the mantles of zircon grains yield weighted mean ages of ca. 49–47 Ma, representing the crystallization timing of these leucocratic sills/dikes. The coeval ages for the Nymo intrusive complex, the high-temperature metamorphism, and the leucocratic sills/dikes indicate that a close relationship exists among them. The authors tentatively suggest that these leucocratic sills/dikes were generated from partial melting of the Jurassic-aged Bima Formation volcanic rocks, triggered by the high heat from the magma chamber of the Nymo intrusive complex. This Early Eocene tectono-thermal event of coeval magmatism, metamorphism and partial melting was most likely formed during the Indo-Asian collisional setting.©2021 China Geology Editorial Office.  相似文献   

Sensitivity assessment of strontium isotope as indicator of polluted groundwater for hydraulic fracturing flowback fluids produced in the Dameigou Shale of Qaidam Basin          下载免费PDF全文

Zheng Zhao-xian  Cui Xiao-shun  Zhu Pu-cheng  Guo Si-jia 《地下水科学与工程》2021,9(2):93-101

Hydrogeochemical processes that would occur in polluted groundwater and aquifer system, may reduce the sensitivity of Sr isotope being the indicator of hydraulic fracturing flowback fluids(HFFF) in groundwater. In this paper, the Dameigou shale gas field in the northern Qaidam Basin was taken as the study area, where the hydrogeochemical processes affecting Sr isotope was analysed. Then, the model for Sr isotope in HFFF-polluted groundwater was constructed to assess the sensitivity of Sr isotope as HFFF indicator. The results show that the dissolution can release little Sr to polluted groundwater and cannot affect the εSr(the deviation of the 87 Sr/86 Sr ratio) of polluted groundwater. In the meantime, cation exchange can considerably affect Sr composition in the polluted groundwater. The Sr with low εSr is constantly released to groundwater from the solid phase of aquifer media by cation exchange with pollution of Quaternary groundwater by the HFFF and it accounts for 4.6% and 11.0% of Sr in polluted groundwater when the HFFF flux reaches 10% and 30% of the polluted groundwater, respectively. However, the Sr from cation exchange has limited impact on Sr isotope in polluted groundwater. Addition of Sr from cation exchange would only cause a 0.2% and 1.2% decrease in εSr of the polluted groundwater when the HFFF flux reaches 10% and 30% of the polluted groundwater, respectively. These results demonstrate that hydrogeochemical processes have little effect on the sensitivity of Sr isotope being the HFFF indicator in groundwater of the study area. For the scenario of groundwater pollution by HFFF, when the HFFF accounts for 5%(in volume percentage) of the polluted groundwater, the HFFF can result in detectable shifts of εSr(ΔεSr=0.86) in natural groundwater. Therefore, after consideration of hydrogeochemical processes occurred in aquifer with input of the HFFF, Sr isotope is still a sensitive indicator of the Quaternary groundwater pollution by the HFFF produced in the Dameigou shale of Qaidam Basin.  相似文献   

Fluid source and physicochemical conditions of the polymetallic mineralization in Gawuch Formation,Kohistan Island Arc,NW Pakistan     

《Chemie der Erde / Geochemistry》2023,83(1):125949

The Cu-Sb-Pb polymetallic vein deposit is hosted by metavolcanics rocks of the Gawuch Formation at the Kaldom Gol area of the northwest Kohistan arc terrain in northern Pakistan. The mineralization is closely associated with the dioritic to granodioritic rocks of the Lowari pluton, which was intruded into the Gawuch metavolcanics. Details of ore characterization and processes of ore genesis of this evidently hydrothermal mineralization are not well documented. Integrating petrographic, mineral-chemical and isotopic investigations, this study aims to comprehend the source of hydrothermal fluids, geochemical evolution, mineral inclusions and physicochemical conditions of the Cu-Sb-Pb polymetallic vein deposit in Gawuch metavolcanics in the Kohistan arc terrain in northern Pakistan. The mineralization is distinguished into three types of ore-gangue associations: Type Ia, Type Ib, and Type II. The textural study revealed two pyrite generations: (i) Py1 displaying euhedral to subhedral habits and containing scarce inclusions, and (ii) Py2 occurring as anhedral grains hosting abundant inclusions. Type Ia is characterized by Py1 associated with abundant quartz (Qz) showing comb texture, sericite (Ser), and minor chlorite (Chl). Type Ib comprises Qz + Ser + Chl and Py2, chalcopyrite (Ccp), and magnetite (Mag). Type II is represented by mosaic quartz, rhombic adularia, and bladed calcite, and the ore minerals fahlore and galena. Alteration zones composed of Qz-Ser ± Chl and Qz-Ser-Chl, surround Type I (a, b) and Type II veins, respectively. Fahlore and galena mostly replace pyrite of Type Ia and chalcopyrite of Type Ib. In addition, malachite, azurite, hematite and covellite occur as secondary (supergene) minerals. The Co/Ni ratios (>1) of Kaldom Gol pyrites suggest that the ore-forming fluids were hydrothermal in origin and Py1 and Py2 solidified at 221–304 °C and 225–261 °C, respectively. The LA-ICP-MS time-resolved depth profiles confirm the existence of sphalerite, and chalcopyrite inclusions in pyrite (Py1 and Py2) and millerite, bravoite, vaesite, Au-tellurides, native Au and galena inclusions in chalcopyrite and fahlore. Sulfur isotope compositions of pyrites (δ³⁴S = Py1, −0.58 to +2 ‰; δ³⁴S = Py2, −0.24 to +2.04 ‰) indicate that the ore-forming fluids were derived from magmatic source (s). The mineral assemblage, hydrothermal alterations, textures, temperature and δ³⁴S of pyrites suggest that the Cu-Sb-Pb polymetallic mineralization at Kaldom Gol represents an intermediate-sulfidation type of epithermal deposit.  相似文献   

Petrographic and mineral chemistry investigation of the high-grade chrysotile asbestos-bearing Zvishavane Ultramafic Complex,south central Zimbabwe     

《Chemie der Erde / Geochemistry》2023,83(2):125950

The Zvishavane Ultramafic Complex (ZUC) in the south central part of the Zimbabwe craton is comprised of coarse-grained serpentinites, metadunites and metagabbros and hosts Africa's largest reserves, and largest mine, of high-grade chrysotile asbestos. Magnesiohornblende, actinolite, plagioclase (An_0.6–41.9), augite, diopside and clinozoisite constitute the mineralogy of the ZUC. Forsteritic olivine (>Fo₉₀) was altered to form chrysotile and antigorite minerals, although some primary olivines are preserved. Contents of Al₂O₃ range from <1 to >2.5 wt% at TiO₂ values of <0.7 wt% consistent with an island arc setting for the ZUC that originated from tholeiitic magmas. The Zvishavane Ultramafic Complex was metamorphosed at relatively high temperatures (542-779 °C) and low pressures (1.2-2kbars), consistent with contact metamorphism. Intrusion of several granitic batholiths relatively close to the ZUC likely triggered hydrothermal fluid migration which metamorphosed the ZUC. The associated asbestos deposits likely formed during hydrothermal circulation events. Zoned amphiboles, the occurrence of magnesiohornblende and actinolite, as well as cross-cutting serpentine veins are consistent with at least two stages of alteration and/or metamorphism of the ZUC. The lack of a thrust contact between the ZUC and its country rocks is consistent with the ZUC having intruded into the host Zvishavane Gneiss Complex and possibly acted as a feeder to the nearby Mberengwa greenstone belt (MGB). However, the occurrence of near end-member forsteritic olivine, the presence of zoned amphiboles, and faulting within the ZUC are all suggestive of an ophiolitic origin although forsteritic olivines also occur in intrusive layered complexes. Metamorphism of the ZUC, ascribed to intrusion of multiple batholiths and possibly the MGB, likely led to the formation of ZUC chrysotile asbestos deposits.  相似文献   

Micrometallogeny and hydrothermal fluid evolution of the Iju porphyry Cu deposit,NW Kerman,Iran: Evidence from fluid inclusions,Laser Raman spectroscopy,and SO isotope systematics     

《Chemie der Erde / Geochemistry》2023,83(2):125956

The Iju Cu porphyry is located in the NW part of the Kerman Magmatic Copper Belt (KMCB). It is related to a ~ 9 Ma granodiorite porphyry intrusion, with three main stages of hydrothermal activity. The homogenization temperatures for the fluid inclusions are in the ranges of 200–494 °C, and their salinities vary from 4.0 to 42.8 wt% NaCl equiv., which are typical magmatic-hydrothermal fluids. The δ³⁴S values of sulfides range from −0.4 to +3.2 ‰ (V-CDT), and the δ³⁴S values of anhydrite samples range from +11.6 to +16.8 ‰. The δ³⁴S values of sulfides show a narrow range, implying a homogeneous sulfur source. The oxygen isotopic composition of hydrothermal water in equilibrium with quartz samples ranges from +3.4 to +6.0 ‰ (V-SMOW) consistent with the hydrothermal fluids having a magmatic signature, but diluted with meteoric waters in the main mineralizing stage. The most important factors responsible for metal precipitation in the Iju porphyry deposit are fluid boiling, oxygen fugacity decrease and cooling followed by dilution with meteoric water. The primary fluids of the Iju Cu deposit are characterized by relatively high temperature and moderate salinity, and are CO₂-rich, indicating a typical post-collisional porphyry system.  相似文献   

海南岛抱伦金矿床双峰式侵入杂岩地球化学特征及对金成矿作用的启示     

林弟  宛胜  胡在龙  吕常艳  单强  梁晓  魏昌欣  袁勤敏  高鹏 《矿床地质》2023,42(6):1229-1246

位于海南岛西南部的抱伦金矿产于尖峰岩体外接触带,与辉绿岩脉密切伴生,这些侵入岩蕴含了金矿成矿作用与岩浆活动-构造演化-成矿体系关系的重要信息。文章报道了对抱伦尖峰花岗岩和辉绿岩开展岩石学、锆石U-Pb年代学、元素和Sm-Nd同位素地球化学研究的成果。本次工作获得了尖峰花岗岩的LA-ICP-MS方法锆石U-Pb年龄为(234.9±2.8)Ma,与辉绿岩构成双峰式侵入杂岩组合。辉绿岩属亚碱性玄武岩系列,相对富集Th、Nb、Ta等强不相容元素,无Nb、Ta、Ti亏损,显示与富集洋中脊玄武岩(E-MORB)相似的地球化学特征,其ε_Nd(t)值为4.11,指示了亏损的源区性质;尖峰花岗岩属高钾钙碱性岩系的铝质A型花岗岩,相对富集K、Rb、Th、Ce等元素,相对亏损Sr、Ba、Nb、Ta、P、Ti等元素,其ε_Nd(t)值为-7.61～-7.80,指示了再循环地壳源区。抱伦辉绿岩为交代型地幔降压熔融的产物,而尖峰花岗岩起源于中元古界泥质和杂砂岩地壳源岩于低压、高温环境下的部分熔融,该双峰式侵入杂岩与金成矿作用形成于造山后伸展-减薄构造背景。双峰式侵入杂岩的...  相似文献   

基于A- CGAN的深反射地震数据随机噪声压制方法研究     

韩建光  王卿  许媛  刘志伟 《地质论评》2023,69(4):2023040015-2023040015

基于深度学习的地震数据噪声压制方法是当前地震数据去噪处理的重要方向。深度学习方法突破了传统滤波处理的局限,在对常规地震数据的噪声压制中表现出效率高、信噪分离效果好的特点。但针对深部弱有效反射数据,当前的深度学习方法特征提取能力有限,难以取得较好的去噪效果。笔者等结合深反射地震数据特点,针对当前深度学习噪声压制方法在特征提取及对数据集依赖上的局限,提出了基于注意力循环生成对抗网络(Attention Cycle- Consistent Generative Adversarial Networks,A- CGAN)的深反射地震数据随机噪声压制方法。借助循环一致生成对抗网络(Cycle- Consistent Generative Adversarial Networks,Cycle- GAN)的域映射思想,降低对数据集的要求。为了构建适用于深反射地震数据的去噪网络,从3个方面对Cycle- GAN进行改进：在Cycle- GAN的生成器（去噪器）中加入残差结构和注意力机制,用于加深网络深度和提高其特征提取能力;在Cycle- GAN的鉴别器中使用块判决,提高鉴别精度和准确度;在损失函数部分加入感知一致性损失函数,提升网络模型恢复纹理细节信息的能力。通过合成地震数据和实际深反射地震数据测试,验证了优化算法的有效性,体现了良好的应用价值。  相似文献   

A Comparison Study on the δD Value of Polycyclic Aromatic Hydrocarbons in Hydrous Pyrolysate of Herbaceous Peat with Different Water Medium     

DUAN Yi  WU Yingzhong  XING Lantian  WU Yingqin  ZHAO Yang  LI Zhongping  MA Lanhu  DUAN Mingchen 《《地质学报》英文版》2023,97(6):1734-1743

To investigate the influence of diagenetic water media on the hydrogen isotopes of individual sedimentary aromatic compounds, a series of hydrous pyrolyses were conducted on herbaceous peat. Polycyclic aromatic hydrocarbons (PAHs) in hydrous pyrolysed samples and their hydrogen isotopic composition characteristics were studied. The aqueous medium demonstrated a significant influence on the hydrogen isotopic composition of the individual PAHs generated during pyrolysis. The results showed that the PAHs formed after pyrolysis in the presence of a saltwater medium with high δD value from a salt lake had a heavy hydrogen isotopic composition. The PAHs formed after pyrolysis in the presence of a fresh water medium with low δD value from a swamp had a light hydrogen isotopic composition. The difference in the average PAH δD value between the two hydrous experiments varied from –174‰ to –109‰, suggesting that the hydrogen isotopic composition of individual sedimentary PAHs can reflect the source of the diagenetic water medium. In addition, a comparative study found that the hydrogen isotopes of PAHs were superior to those of n-alkanes in the same sample for diagenetic water indications. The results indicated that the exchange of water-derived inorganic hydrogen and organic hydrogen was more intensive in freshwater experiments than in saltwater experiments. With an increase in the simulation temperature, the average δD value of PAHs generated in the hydrous simulation experiments showed an increasing trend, reflecting that the δD value of sedimentary PAHs formed with the participation of diagenetic water media was still closely related to the thermal maturity of organic matter. Comparative studies showed that the δD values of different types of organic compounds produced by hydrous pyrolysis of peat were in the order, PAHs > n-alkanes > methane.  相似文献