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1.
荣华锰矿赋存于桂西三叠系百逢组中,为该层位首次发现的中型规模锰矿。笔者通过参与矿区锰矿勘查工作,采用室内外观测、测试、工程揭露和验证等手段,对研究区地层、构造、沉积演化、含矿层位、矿体及矿石矿物特征、矿床成因和找矿标志等方面进行了分析探讨。研究发现荣华锰矿为典型的沉积-锰帽型矿床,严格受地层和构造因素控制;矿石类型主要为氧化锰矿贫锰矿石;氧化锰矿物主要为水羟锰矿、硬锰矿及软锰矿;矿床成因与原始沉积作用、后期风化淋滤等有重要关系;百逢组浊积岩之下、罗楼组碳酸盐岩之上的狭窄范围是荣华锰矿的典型找矿标志,该标志对大量出露三叠系百逢组的桂西地区具有普遍意义,同时指出桂西地区该组地层内具有良好的找矿前景。 相似文献
2.
基于双程波动方程的逆时偏移(RTM)具有原理简单、无倾角限制、具有可以适用于速度任意变化的模型,对各类波正确成像等优点,但采用互相关成像条件会产生严重的低频噪声问题。笔者分析低频噪声的产生机制后提供了一个有效的波场分离去噪方法,将震源和检波点波场分离成不同方向的单成波分量,只对有效路径上的分量进行互相关成像,从而达到去除噪声的目的。并通过模型测试对比了坡印廷矢量滤波、拉普拉斯滤波、波场分离滤波这三种方法的去噪效果,结果表明基于波场分离的去噪方法效果更好。 相似文献
3.
为了扩大资源储量,降低找矿风险,文章运用大地电磁法、地电化学法与吸附相态汞方法组合在高原寒冷地区开展物化信息进行金矿预测研究.通过已知区可行性研究验证方法组合的找矿成效,总结适合高原寒冷景观条件下的物化探找矿模式,即金矿通常位于Au地电化学异常正投影下方、电阻率高低突变带偏低阻体一侧,配套土壤吸附相态汞异常寻找破碎带型金矿较有效.依据上述找矿模式,在忠曲矿区开展金矿预测工作,在矿区西部发现找矿有利地段3处,东部发现找矿可疑地段1处. 相似文献
4.
Hafnium isotopes of zircon represent a well-dated proxy for the evolution of magmatic systems through Earth history. Time series analysis on the hafnium isotopes of zircon reveals a hierarchy of statistically significant periodic signals spanning multiple orders of magnitude (106–109 year cycles). We attribute the hierarchy of cyclicity to organizing mechanisms of mantle and lithospheric convection at various time scales, ranging from short-term cycles in magmatism and subduction to long-term cycles related to oceans, supercontinents, and superoceans. A ∼600-Myr supercontinent cycle is the strongest signal in the global hafnium database and the phase relationship implies elevated mantle-derived magmatism during supercontinent tenure and elevated crustal reworking during plate reorganization, as expected. A half-supercontinent cycle (Wilson cycle) and a double-supercontinent cycle (superocean cycle) are also present, harmonic with the supercontinent cycle, and related to each other by amplitude modulation. Analysis of local magmatic systems of the circum-Pacific subduction girdle surrounding Pangaea reveal similar significant and harmonic cycles of ∼6 and ∼20 Myr attributed to magmatic cycles and ∼60, ∼120, and ∼240 Myr attributed to subduction cycles. All subduction systems reveal a prevalent ∼60 Myr cycle attributed to an upper mantle convective cycle that has two phase relationships, suggesting that advancing and retreating arc systems can be identified with time series analysis. The harmonic hierarchy of geodynamic cycles identified herein controlled by mantle convection on long time scales and lithospheric convection on short time scales arguably completes the picture of cyclicity in the Earth system, complimenting well-known orbital, oceanic, and astronomical cycles. 相似文献
5.
《Planetary and Space Science》1999,47(10-11):1371-1376
Implantation of reactive ions into targets of planetary interest is a relevant subject to be studied in the laboratory. It could in fact produce new molecular species that are not native to those surfaces. Presented here are new laboratory results obtained by nitrogen implantation (15–30 keV N+) on frozen mixtures of H2O:CH4 (2:1). These species have been chosen in view of their possible presence on the surface of Jovian and Saturnian satellites and rings. In fact these surfaces are exposed to intense irradiation by magnetospheric and/or solar energetic particles. The laboratory investigation utilizes IR spectroscopy. The main objectives of the present study are to identify newly produced species and to verify if these (or at least if the profile of their IR bands) are different from those produced by unreactive ions impinging on targets in which nitrogen is already present, occurring in the form of frozen NH3 (Strazzulla and Palumbo, 1998) or N2 (Palumbo et al., 1999). I find that CN-bearing group is in fact formed and its IR feature has a profile (peak position and band profile) that differs from that obtained after irradiation or frozen gases containing nitrogen. The relevance the results might have to elucidate the origin of some species observed on Jovian icy moons or predicted to be observed on Saturnian satellites are outlined. 相似文献
6.
Subduction erosion, which occurs at all convergent plate boundaries associated with magmatic arcs formed on crystalline forearc basement, is an important process for chemical recycling, responsible globally for the transport of ~1.7 Armstrong Units (1 AU = 1 km3/yr) of continental crust back into the mantle. Along the central Andean convergent plate margin, where there is very little terrigenous sediment being supplied to the trench as a result of the arid conditions, the occurrence of mantle-derived olivine basalts with distinctive crustal isotopic characteristics (87Sr/86Sr ≥ 0.7050; εNd ≤ −2; εHf ≤ +2) correlates spatially and/or temporally with regions and/or episodes of high rates of subduction erosion, and a strong case can be made for the formation of these basalts to be due to incorporation into the subarc mantle wedge of tectonically eroded and subducted forearc continental crust. In other convergent plate boundary magmatic arcs, such as the South Sandwich and Aleutian Islands intra-oceanic arcs and the Central American and Trans-Mexican continental margin volcanic arcs, similar correlations have been demonstrated between regions and/or episodes of relatively rapid subduction erosion and the genesis of mafic arc magmas containing enhanced proportions of tectonically eroded and subducted crustal components that are chemically distinct from pelagic and/or terrigenous trench sediments. It has also been suggested that larger amounts of melts derived from tectonically eroded and subducted continental crust, rising as diapirs of buoyant low density subduction mélanges, react with mantle peridotite to form pyroxenite metasomatites that than melt to form andesites. The process of subduction erosion and mantle source region contamination with crustal components, which is supported by both isotopic and U-Pb zircon age data implying a fast and efficient connectivity between subduction inputs and magmatic outputs, is a powerful alternative to intra-crustal assimilation in the generation of andesites, and it negates the need for large amounts of mafic cumulates to form within and then be delaminated from the lower crust, as required by the basalt-input model of continental crustal growth. However, overall, some significant amount of subducted crust and sediment is neither underplated below the forearc wedge nor incorporated into convergent plate boundary arc magmas, but instead transported deeper into the mantle where it plays a role in the formation of isotopically enriched mantle reservoirs. To ignore or underestimate the significance of the recycling of tectonically eroded and subducted continental crust in the genesis of convergent plate boundary arc magmas, including andesites, and for the evolution of both the continental crust and mantle, is to be on the wrong side of history in the understanding of these topics. 相似文献
7.
Marine dolostones of Carboniferous Huanglong Formation constitute major gas reservoir rocks in eastern Sichuan Basin. However, the investigation with respect to sources of dolomitizing and diagenetic fluids is relatively underexplored. The current study attempts to investigate the REE characteristics of dolomites using seawater normalization standard, and therefore discusses the origins of dolomitizing and diagenetic fluids, on the basis of continuous 47.33-m-long core samples from the second member of Huanglong Formation (C2h2) in eastern Sichuan Basin. Low Th, Sc, and Hf concentrations (0.791 × 10−6, 4.751 × 10−6, and 0.214 × 10−6, respectively), random correlation between total REE concentration (ΣREE) and Fe or Mn abundance, and seawater-like Y/Ho ratios (mean value of 45.612) indicate that the carbonate samples are valid for REE analysis. Based on petrographic characteristics, four dolomite types are identified, including micritic-sized dolomite (type Dol-1), fine-to medium-sized dolomite (type Dol-2), medium-to coarse-sized dolomite (type Dol-3), and coarse-to giant-sized saddle dolomite (type Dol-4). Dol-1 dolomites, characterized by positive Ce anomaly (mean value of 6.398), light REE (LREE) enrichment, and heavy REE (HREE) depletion with mean LREE/HREE ratio of 12.657, show micritic calcite-like REE patterns, indicating seawater origin of their dolomitizing fluids. Dol-1 dolomites were formed in sabkha environment whereas the dolomitizing fluids originated from evaporative brine water due to their micritic crystal sizes and tight lithology. Dol-2 dolomites, particularly subtype Dol-2a barely developing vuggy porosity, also show micritic calcite-like REE patterns, suggesting their dolomitizing fluids were seawater or seawater-derived fluids. This inference is confirmed by low Fe and Mn concentrations, which range from 651 μg/g to 1018 μg/g (mean value of 863 μg/g) and 65 μg/g to 167 μg/g (mean value of 105 μg/g), respectively, whereas homogenization temperatures (Th, mean value of 103 °C) indicate that Dol-2 dolomites were formed under burial environment. Dol-3 dolomites, in form of cements of Dol-2 dolomites, show similar REE patterns to their host minerals (i.e., Dol-2 dolomites), indicating their parent source was possibly derived from Dol-2 dolomites. Dol-3 dolomites have high Fe and Mn concentrations with mean values of 3346 μg/g (ranging from 2897 μg/g to 3856 μg/g) and 236 μg/g (ranging from 178 μg/g to 287 μg/g), respectively, indicating the involvement of meteoric water. Meanwhile, it confirms that the dissolution in Dol-2 dolomites was caused by meteoric water leaching. Positive Eu anomalies (mean value of 1.406) in Dol-4 dolomites, coupled with high homogenization temperatures (mean value of 314 °C), suggest that Dol-4 dolomites precipitated from hydrothermal fluids. High Fe and Mn concentrations (mean values of 2521 μg/g and 193 μg/g, respectively) in Dol-4 dolomites likely results from interactions of hydrothermal fluids with deep burial clastic rocks. 相似文献
8.
We investigate the Mesozoic–Cenozoic thermal history of the Daxi region (central SE South China Block) to evaluate the influence of the subduction of the Paleo-Pacific oceanic plate beneath the SE South China Block along the block's southeast margin on the tectonothermal evolution of the upper plate. We apply a multi-chronological approach that includes U-Pb geochronology on zircon, 40Ar/39Ar dating on muscovite and biotite from granitic rocks as well as fission-track and (U-Th-Sm)/He analyses on zircon and apatite from granitic and sedimentary rocks. The Heping granite, located in the Daxi region, has a magmatic age of ca. 441 Ma. The biotite 40Ar/39Ar ages of ca. 193 Ma for the Early Jurassic Shibei granite and ca. 160 Ma for the Late Jurassic Fogang granite, respectively, reflect magmatic cooling. The Triassic Longyuanba granite yielded a muscovite 40Ar/39Ar age of ca. 167 Ma, recording heating to ≥ 350 °C induced by nearby intrusion of Middle Jurassic granites. Zircon fission-track and (U-Th-Sm)/He ages from Lower Carboniferous–Lower Jurassic sandstones (140–70 Ma) record continuous cooling during the Cretaceous that followed extensive Middle–Late Jurassic magmatism in the Daxi region. Cretaceous cooling is related to exhumation in an extensional tectonic setting, consistent with lithospheric rebound due to foundering and rollback of the subducted Paleo-Pacific oceanic plate. Apatite fission-track (53–42 Ma) and (U-Th-Sm)/He ages (43–36 Ma), and thermal modelling document rapid cooling in the Paleocene–Eocene, which temporally coincides with continental rifting in the SE South China Block in the leadup to the opening of the South China Sea. 相似文献
9.
The recently discovered Zhuxi W–Cu ore deposit is located within the Taqian–Fuchun Ore Belt in the southeastern edge of the Yangtze Block, South China. Its inferred tungsten resources, based on new exploration data, are more than 280 Mt by 2016. At least three paragenetic stages of skarn formation and ore deposition have been recognized: prograde skarn stage; retrograde stage; and hydrothermal sulfide stage. Secondly, greisenization, marmorization and hornfels formation are also observed. Scheelite and chalcopyrite are the dominant metal minerals in the Zhuxi deposit and their formation was associated with the emplacement of granite stocks and porphyry dykes intruded into the surrounding Carboniferous carbonate sediments (Huanglong and Chuanshan formations) and the Neoproterozoic slate and phyllites. The scheelite was mostly precipitated during the retrograde stage, whereas the chalcopyrite was widely precipitated during the hydrothermal sulfide stage. A muscovite 40Ar/39Ar plateau age of about 150 Ma is interpreted as the time of tungsten mineralization and molybdenite Re–Os model ages ranging from 145.9 ± 2.0 Ma to 148.7 ± 2.2 Ma (for the subsequent hydrothermal sulfide stage of activity) as the time of the copper mineralization. Our new molybdenite Re–Os and muscovite 40Ar/39Ar dating results, along with previous zircon U–Pb age data, indicate that the hydrothermal activity from the retrograde stage to the last hydrothermal sulfide stage lasted up to 5 Myr, from 150.6 ± 1.5 to 145.9 ± 1 Ma, and is approximately coeval or slightly later than the emplacement of the associated granite porphyry and biotite granite. The new ages reported here confirm that the Zhuxi tungsten deposit represents one of the Mesozoic magmatic–hydrothermal mineralization events that took place in South China in a setting of lithospheric extension during the Late Jurassic (160–150 Ma). It is suggested that mantle material played a role in producing the Zhuxi W–Cu mineralization and associated magmatism. 相似文献
10.
The Hetai goldfield, located in the southern segment of the Qinzhou Bay-Hangzhou Bay Juncture Orogenic Belt (QHJB), is the largest concentration of gold deposits in Guangdong Province, South China. The gold mineralization is hosted within the late Neoproterozoic to early Paleozoic Yunkai Group and strictly confined to mylonite (ductile shear) zones. The nature of the structural control of mineralization, in particular the role of ductile versus brittle deformation and their ages, which remain unclear despite numerous previous studies, are examined in this paper through an integrated study of geochronology and mineralogy.Lamellar and filament structures shown by pyrite and pyrrhotite in the ores suggest that sulfidation took place during ductile deformation and syntectonic metamorphism, but the majority of the ores are associated with brittle deformation features. In combination with macroscopic and microscopy observations on shear fabrics, LA-ICP-MS U-Pb dating on zircons of hydrothermal origin from mylonites suggests that the Hetai goldfield was subjected to two shearing events: an early sinistral ductile shearing at ca. 240 Ma, and a late dextral ductile-brittle shearing at ca. 204 Ma (Indosinian). These ages are ca. 90–30 Ma older than the previously published gold mineralizing ages of ca. 175–152 Ma (Yanshanian), suggesting that the main gold mineralization and related brittle deformation significantly postdate the ductile deformation. This inference is supported by the mineralization temperatures estimated from geothermometers of arsenopyrite (ca. 350–290 °C), chlorite (ca. 260–230 °C), and sphalerite (ca. 230–170 °C) intergrown with native gold, which are considerably lower than that for the ductile deformation (500–300 °C or higher). Based on these data, we propose that the gold mineralization in the Hetai goldfield predominantly occurred during the Yanshanian event, and only minor gold mineralization and associated sulfidation took place during the earlier Indosinian ductile deformation. 相似文献