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941.
贵州新元古代大塘坡期巨量锰矿成矿物质来源分析 总被引:1,自引:0,他引:1
新元古代大塘坡期,贵州松桃等地形成锰矿集聚区,并发育4个世界级锰矿床,累计探明锰资源量达7亿t。但是什么地质条件下,能导致如此巨量的锰质富集成矿,其成矿物质来源问题一直没有得到满意的解释。本文通过对含锰岩系大塘坡组基底板溪群及海底火山岩中锰含量特征、江南造山带演化以及Rodinia超大陆解体与锰矿成矿关系分析,认为基底板溪群中锰含量高,MnO含量达到0. 16%,板溪群风化壳中锰含量更高,MnO达0. 88%。板溪群中的同期岛弧玄武岩含MnO更高,达到0. 25%,它们可能是锰矿成矿的物源层,是形成巨量锰矿的基础;江南造山带造山挤压变质作用,引起板溪群和岛弧玄武岩中锰质活化、迁移富集;Rodinia超大陆解体,在650 Ma发生拉张裂谷作用,使活化富锰变质流体沿着断裂喷流出海底,形成大量锰矿。 相似文献
942.
利用地下水水化学和同位素测试分析成果,结合区域地质、水文地质条件研究了平谷北山山区侧向补给情况和中桥水源地地区第四系松散孔隙水和下伏岩溶水关系。结果表明:研究区第四系松散孔隙水和基岩岩溶地下水均来源于大气降水,地下水化学类型均为HCO-3-Ca2+?Mg2+ 型;平谷北山山前基岩岩溶水侧向补给平原区第四系松散孔隙水和下伏岩溶地下水;通过D值估算得到中桥水源地第四系浅层地下水的山区岩溶水侧向补给和垂向降水入渗补给比例为57:43;中桥水源地基岩岩溶水接受山区岩溶水侧向补给和第四系孔隙水垂向越流补给比例为87:13。研究成果为平谷地区地下水资源量评价和地下水动力场数值模型的建设提供了关键参数,为区域地下水的合理开采和有序回补涵养提供了科学依据。 相似文献
943.
Overpressure is a hot topic in the study of sedimentary basins. It is important in generation,maturation migration,and accumulation of hydrocarbon,but the effects of overpressure on rock frame have not been investigated. In this study,experiments were carried out to study the effects of overpressure on rock frame structures using five core samples from the Junggar basin,Northwest China. The deformations and velocities for the samples were measured at different effective pressures related to non-equilibrium compaction and fluid expansion overpressure mechanisms. The results show that the effect of overpressure on rock frames gradually increases when the effective pressure drops down to a certain value (called critical pressure). Moreover,non-equilibrium compaction mechanism has more effects on rock frames than fluid expansion mechanism under the same effective pressure. Furthermore to study rock frame structural changes,we use Kuster and Toks?z's expressions to simulate the effective aspect ratios of inclusions α (penny shapes) for different effective pressures. The results show that the α decreases dramatically when the effective pressure decreases from the critical pressure. Changes of α can be interpreted as responses to the rock frame changes when grains conform one another by rotating and self-adjusting. However,different mechanisms of overpressure have different effects on rock frames. The rock frame can be affected more easily by overpressure in shallow regions generated by non-equilibrium compaction mechanism. Once this kind of rock frames are preserved after overpressure releases to a normal hydrostatic pressure,they can be identified by their specific rock frame characters. This method provides a new way to study overpressure release and fluid migration and accumulation. 相似文献
944.
945.
Kristine L. Delong Suyapa Gonzalez Jeffrey B. Obelcz Jonathan T. Truong Samuel J. Bentley Sr Kehui Xu Carl A. Reese Grant L. Harley Alicia Caporaso Zhixiong Shen Beth A. Middleton 《Boreas: An International Journal of Quaternary Research》2021,50(3):871-892
Approximately 13 km south of Gulf Shores, Alabama (United States), divers found in situ baldcypress (Taxodium distichum) stumps 18 m below the ocean surface. These trees could have only lived when sea level fell during the Pleistocene subaerially exposing the tectonically stable continental shelf. Here we investigate the geophysical properties along with microfossil and stratigraphical analyses of sediment cores to understand the factors that lead to this wood’s preservation. The stumps are exposed in an elongated depression (~100 m long, ~1 m deep) nested in a trough of the northwest–southeast trending Holocene sand ridges and troughs with 2–5 m vertical relief and ~0.5 km wavelength. Radiocarbon ages of the wood were infinite thus optically stimulated luminescence (OSL) dating was used to constrain the site’s age. Below the Holocene sands (~0.1–4 m thick), separated by a regional erosional unconformity, are Late Pleistocene mud-peat (72±8 ka OSL), mud-sand (63±5, 73±6 ka OSL), and palaeosol (56±5 ka OSL) facies that grade laterally from west to east, respectively. Foraminiferal analysis reveals the location of the terrestrial-marine transitional layer above the Pleistocene facies in an interbedded sand and mud facies (3940±30 (1σ) 14C a BP), which is part of a lower shoreface or marine-dominated estuarine environment. The occurrence of palaeosol and swamp facies of broadly similar ages and elevation suggests the glacial landscape possessed topographic relief that allowed wood, mud and peats to be preserved for ~50 ka of subaerial exposure before transitioning to the modern marine environment. We hypothesize that rapid sea-level rise occurring ~60 or ~40 ka ago provided opportunities for local flood-plain aggradation to bury the swamp thus preserving the stumps and that other sites may exist in the northern Gulf of Mexico shelf. 相似文献
946.
947.
武夷山成矿带燕山期岩浆-成矿活动的深部动力学机制一直是学者们研究的热点。已有的研究结果表明,武夷山成矿带及邻区的上地幔存在着显著的低速异常,可能与地表的岩浆-成矿活动存在着密切的联系。本研究利用分布在华夏地块98个固定地震台站以及59个流动地震台站所记录到的278个远震事件,采用远震层析成像方法构建了武夷山成矿带及邻区上地幔三维P波速度结构模型。成像结果表明,武夷山成矿带及其东侧的上地幔存在着显著的低速异常,代表了热物质富集的地幔楔,且上地幔的热物质在这些地幔楔间进行着横向流动。东南沿海的地幔过渡带存在着一个显著的低速异常,推测为新生代欧亚板块与菲律宾海板块碰撞俯冲的产物。南岭成矿带下方的低速异常从上地幔一直向上延伸到上地壳,可能指示了一个热物质上涌的通道。结合已有的研究结果,本研究认为武夷山成矿带燕山期岩浆-成矿活动可能与古太平洋板块的俯冲和后撤所引起的热物质上涌有关。
相似文献948.
Xiba Granitic Pluton in the Qinling Orogenic Belt,Central China: Its Petrogenesis and Tectonic Implications 总被引:4,自引:0,他引:4
ZHANG Fan LIU Shuwen CHEN Xu LI Qiugen DAI Junzhi YANG Kai WU Fenghui CHEN Youzhang 《《地质学报》英文版》2012,86(5):1128-1142
Xiba granitic pluton is located in South Qinling tectonic domain of the Qinling orogenic belt and consists mainly of granodiorite and monzogranite with significant number of microgranular quartz dioritic enclaves. SHRIMP zircon U–Pb isotopic dating reveals that the quartz dioritic enclaves formed at 214±3 Ma, which is similar to the age of their host monzogranite (218±1 Ma). The granitoids belong to high-K calc-alkaline series, and are characterized by enriched LILEs relative to HFSEs with negative Nb, Ta and Ti anomalies, and right-declined REE patterns with (La/Yb)N ratios ranging from 15.83 to 26.47 and δEu values from 0.78 to 1.22 (mean= 0.97). Most of these samples from Xiba granitic pluton exhibit εNd(t) values of ?8.79 to ?5.38, depleted mantle Nd model ages (TDM) between 1.1 Ga and 1.7 Ga, and initial Sr isotopic ratios (87Sr/86Sr)i from 0.7061 to 0.7082, indicating a possible Meso- to Paleoproterozoic lower crust source region, with exception of samples XB01-2-1 and XB10-1 displaying higher (87Sr/86Sr)i values of 0.779 and 0.735, respectively, which suggests a contamination of the upper crustal materials. Quartz dioritic enclaves are interpreted as the result of rapid crystallization fractionation during the parent magmatic emplacement, as evidenced by similar age, texture, geochemical, and Sr-Nd isotopic features with their host rocks. Characteristics of the petrological and geochemical data reveal that the parent magma of Xiba granitoids was produced by a magma mingling process. The upwelling asthenosphere caused a high heat flow and the mafic magma was underplated into the bottom of the lower continent crust, which caused the partial melting of the lower continent crustal materials. This geodynamic process generated the mixing parent magma between mafic magma from depleted mantle and felsic magma derived from the lower continent crust. Integrated petrogenesis and tectonic discrimination with regional tectonic evolution of the Qinling orogen, it is suggested that the granitoids are most likely products in a post-collision tectonic setting. 相似文献
949.
在岩心储层研究及测井解释的基础上,动静结合确定了八区下乌尔禾组油藏的有效储层划分标准,在此基础上,运用综合评价方法将储层划分为4类,其中I类最好,IV类最差。对比四次加密试验井,储层评价效果好,储层厚度的预测误差率在5%以内,储层类型符合率为80%。统计岩心及成像测井资料显示,下乌尔禾组天然裂缝以构造高角度缝为主,人工裂缝以压裂羽状缝为主,各类裂缝多为闭合缝。结合开发动态资料分析认为:储层发育优势区控制了油井高产区,油层储层条件越好,初期产能越高;裂缝的存在导致注入水优先沿裂缝突进,使油井出现裂缝水窜、见水不见效等开发特征;综合分析发现油水井的驱替通道、储层及裂缝发育情况导致油井不同见效情况。在静动态研究基础上实施的四次加密试验井,90%以上的井可达到预期设计产能。 相似文献
950.
Dan Yin Longcang Shu Chundong Xu Zhenlong Wang Emmanuel Kwame Appiah-Adjei 《Environmental Earth Sciences》2012,66(2):399-407
This study presents an approach for transferring the qualitative analysis of groundwater sustainability for development to
quantitative evaluation by an analogy of two similar regions. A concept of groundwater exploitation sustainability (GES),
which is an evaluation index based on water supply capability, eco-geo-environment maintaining capability and the harmony
between water and society, is put forward. The fuzzy analytic hierarchy process method is applied to calculate the GES for
the Xiangshan and Dianchang karst groundwater sources in the Huaibei city, Anhui Province, China. The GES of the Xiangshan
karst system was calculated to be 0.53 and represents medium exploitation sustainability, while that for the Dianchang is
relatively high with a value of 0.70. These two karst systems are separate units but have similar hydrogeological conditions.
The Dianchang area had limited groundwater observation data, while the Xiangshan area had long series of observation data,
which enabled the computation of the sustainable yield. The sustainable yield of the Xiangshan karst area was used to calibrate
the GES, and develop a linear equation between the GES and sustainable yield, which was used to calculate the sustainable
yield of the Diangchang karst area as 40.4 million m3. 相似文献