排序方式： 共有71条查询结果，搜索用时 562 毫秒
1.
Mantle-derived carbonatites provide a unique window in the understanding of mantle characteristics and dynamics, as well as insight into the assembly and breakup of supercontinents. As a petrological indicator of extensional tectonic regimes, Archean/Proterozoic carbonatites provide important constraints on the timing of the breakup of ancient supercontinents. The majority of the carbonatites reported worldwide are Phanerozoic, in part because of the difficulty in recognizing Archean/Proterozoic carbonatites, which are characterized by strong foliation and recrystallization, and share broad petrologic similarities with metamorphosed sedimentary lithologies. Here, we report the recognition of a ~1.85 Ga carbonatite in Chaihulanzi area of Chifeng in north China based on systematic geological, petrological, geochemical, and baddeleyite U-Pb geochronological results. The carbonatite occurs as dikes or sills emplaced in Archean metasedimentary rocks and underwent intense deformation. Petrological and SEM/EDS results show that calcite and dolomite are the dominant carbonate minerals along with minor and varied amounts of Mg-rich mafic minerals, including forsterite (with Fo > 98), phlogopite, diopside, and an accessory amount of apatite, baddeleyite, spinel, monazite, and ilmenite. The relatively high silica content together with the non-arc and OIB-like trace element signatures of the carbonatite indicates a hot mantle plume as the likely magma source. The depleted Nd isotopic signatures suggest that plume upwelling might be triggered by the accumulation of recycled crust in the deep mantle. As a part of the global-scale Columbia supercontinent, the Proterozoic tectonic evolution of the North China Craton (NCC) provides important insights into the geodynamics governing amalgamation and fragmentation of the supercontinent. The Paleo-Mesoproterozoic boundary is the key point of tectonic transition from compressional to extensional settings in the NCC. The newly identified ~1.85 Ga carbonatite provides a direct link between the long-lasting supercontinental breakup and plume activity, which might be sourced from the “slab graveyard,” continental crustal slabs subducted into asthenosphere, beneath the supercontinent. The carbonatite provides a precise constraint of the initiation of the continental breakup at ~1.85 Ga. 相似文献
2.
3.
INTRODUCTIONThe distribution of remaining oil is often de-scribed qualitatively .The remaining oil distributedinthe whole reservoir is calculated according to thecharacteristics of the space distribution of the satura-tion of remaining oil . Logging data are required toaccomplish this . However , many such projects can-not be completed.This method of studyingremainingoil distribution cannot be quantified efficiently and isunable to provide an effective quantitative forecast ofthe distribu… 相似文献
4.
闽北地区中侏罗世火山岩的发现及其地质意义 总被引：3，自引：2，他引：1
中侏罗世火山岩在东南沿海分布极少,但对区域中生代构造-岩浆活动过程及大地构造演化的研究具有重要意义。在闽北地区大面积白垩纪火山岩区调查中,在政和铁山地区发现中侏罗世火山岩,用LA-ICP-MS同位素测试技术测得的锆石U-Pb年龄为173.63±0.80Ma。火山岩属钙碱性系列流纹质熔结凝灰岩,显示过铝质、富钾、富集大离子亲石元素,亏损高场强元素等地球化学特征,推断其形成于陆缘弧环境,与古太平洋板块早期俯冲作用有关。 相似文献
5.
6.
Gejiu is geographically located near Gejiu city, SW China. It is one of the largest tin-polymetallic districts in the world and contains approximately 3 million tons (Mt) of Sn and smaller quantities of Cu, Pb, and Zn. The deposit primarily yields three different types of ore: skarn-hosted ore, basalt-hosted stratiform ore, and carbonate-hosted stratiform ore. Kafang is one of the primary ore deposits in the Gejiu district and is an unusual occurrence hosted in basaltic rocks. Genetic models of the Kafang deposit suggest that it is related either to Anisian (Lower stage of Middle Triassic) Gejiu basalts or to Cretaceous Gejiu granite. In this study, we performed zircon SIMS U–Pb dating, major and trace element analyses, and Sr–Nd–Pb isotopic analyses for the Gejiu basalts and S isotopic analyses for stratiform Cu ore. Our results and previous studies are used to interpret the petrogenesis of the Gejiu basalts and the origin of the basalt-hosted stratiform Cu deposit. The SIMS zircon U–Pb analyses of the Gejiu basalts yield an age of 244.4 Ma. The trace element ratios of the Gejiu basalts are similar to those of ocean island basalt and have positive εNd(t) values (ranging from 0.6 to 2.5) and uniform (87Sr/86Sr)i values (ranging from 0.70424 to 0.70488). These ratios are close to those of the Permian Emeishan flood basalt. Thus, the Gejiu basalts may represent coeval volcanisms within the plate involving remelting of the Emeishan plume head through a stress relaxation process after the main plume event. The Pb and S isotopic compositions of the Gejiu basalts and the stratiform Cu ores indicate that the source of Cu and S is primarily derived from the Gejiu basalts. However, the age of sulfide mineralization (84.2–79.6 Ma) and the age of hydrothermal alteration (85.5–81.9 Ma) are temporally consistent with the age of the Cretaceous granite emplacement (85.5–83.3 Ma). From a petrological and geochemical study, we determine that the Gejiu basalts may have been subjected to pervasive granite-related hydrothermal alteration during the emplacement of granite. These processes increase the K and Mg contents of basalt and probably caused the formation of the Cu ores. Thus, the Kafang stratiform Cu deposit can be considered as a granite-related hydrothermal deposit. 相似文献
7.
Gang Yu Jiangfeng Chen Chunji Xue Yuchuan Chen Fukun Chen Xiaoyue Du 《Ore Geology Reviews》2009,35(3-4):367-382
The Qingchengzi orefield in northeastern China, is a concentration of several Pb–Zn, Ag, and Au ore deposits. A combination of geochronological and Pb, Sr isotopic investigations was conducted. Zircon SHRIMP U–Pb ages of 225.3 ± 1.8 Ma and 184.5 ± 1.6 Ma were obtained for the Xinling and Yaojiagou granites, respectively. By step-dissolution Rb–Sr dating, ages of 221 ± 12 Ma and 138.7 ± 4.1 Ma were obtained for the sphalerite of the Zhenzigou Zn–Pb deposit and pyrargyrite of the Ag ore in the Gaojiabaozi Ag deposit, respectively. Pb isotopic ratios of the Ag ore at Gaojiabaozi (206Pb/204Pb = 18.38 to 18.53) are higher than those of the Pb–Zn ores (206Pb/204Pb = 17.66 to 17.96; Chen et al. [Chen, J.F., Yu, G., Xue, C.J., Qian, H., He, J.F., Xing, Z., Zhang, X., 2005. Pb isotope geochemistry of lead, zinc, gold and silver deposit clustered region, Liaodong rift zone, northeastern China. Science in China Series D 48, 467–476.]). Triassic granites show low Pb isotopic ratios (206Pb/204Pb = 17.12 to 17.41, 207Pb/204Pb = 15.47 to 15.54, 208Pb/204Pb = 37.51 to 37.89) and metamorphic rocks of the Liaohe Group have high ratios (206Pb/204Pb = 18.20 to 24.28 and 18.32 to 20.06, 207Pb/204Pb = 15.69 to 16.44 and 15.66 to 15.98, 208Pb/204Pb = 37.29 to 38.61 and 38.69 to 40.00 for the marble of the Dashiqiao Formation and schist of the Gaixian Formation, respectively).Magmatic activities at Qingchengzi and in adjacent regions took place in three stages, and each contained several magmatic pulses: ca. 220 to 225 Ma and 211 to 216 Ma in the Triassic; 179 to 185 Ma, 163 to 168 Ma, 155 Ma and 149 Ma in the Jurassic, as well as ca. 140 to 130 Ma in the Early Cretaceous. The Triassic magmatism was part of the Triassic magmatic belt along the northern margin of the North China Craton produced in a post-collisional extensional setting, and granites in it formed by crustal melting induced by mantle magma. The Jurassic and Early Cretaceous magmatism was related to the lithospheric delamination in eastern China. The Triassic is the most important metallogenic stage at Qingchengzi. The Pb–Zn deposits, the Pb–Zn–Ag ore at Gaojiabaozi, and the gold deposits were all formed in this stage. They are temporally and spatially associated with the Triassic magmatic activity. Mineralization is very weak in the Jurassic. Ag ore at Gaojiabaozi was formed in the Early Cretaceous, which is suggested by the young Rb–Sr isochron age, field relations, and significantly different Pb isotopic ratios between the Pb–Zn–Ag and Ag ores. Pb isotopic compositions of the Pb–Zn ores suggest binary mixing for the source of the deposits. The magmatic end-member is the Triassic granites and the other metamorphic rocks of the Liaohe Group. Slightly different proportions of the two end-members, or an involvement of materials from hidden Cretaceous granites with slightly different Pb isotopic ratios, is postulated to interpret the difference of Pb isotopic compositions between the Pb–Zn–(Ag) and Ag ores. Sr isotopic ratios support this conclusion. At the western part of the Qingchengzi orefield, hydrothermal fluid driven by the heat provided by the now exposed Triassic granites deposited ore-forming materials in the low and middle horizons of the marbles of the Dashiqiao Formation near the intrusions to form mesothermal Zn–Pb deposits. In the eastern part, hydrothermal fluids associated with deep, hidden Triassic intrusions moved upward along a regional fault over a long distance and then deposited the ore-forming materials to form epithermal Au and Pb–Zn–Ag ores. Young magmatic activities are all represented by dykes across the entire orefield, suggesting that the corresponding main intrusion bodies are situated in the deep part of the crust. Among these, only intrusions with age of ca. 140 Ma might have released sufficient amounts of fluid to be responsible for the formation of the Ag ore at Gaojiabaozi.Our age results support previous conclusions that sphalerite can provide a reliable Rb–Sr age as long as the fluid inclusion phase is effectively separated from the “sulfide” phase. Our work suggests that the separation can be achieved by a step-resolution technique. Moreover, we suggest that pyrargyrite is a promising mineral for Rb–Sr isochron dating. 相似文献
8.
In recent decades,a few Godunov-type,finite volume two-dimensional(2D)unstructured grid,coupled flow,and sediment models(GF2DUCM)have been developed for flows over erodible beds.These kinds of models are generally analyzed as a Vertex Model(VM)that define topography at the cell vertex,which can lead to the non-conservation of mass regarding flow,sediment,and bed evolution.Here,a full cellcantered variable storage method(Central Model or CM)is applied as the solution of the GF2DUCM.In this method,terrain elevation is defined at the cell centroids;this accurately describes the physical relations between the water depth and topography deformation.This approach can fully eliminate calculation errors in topography deformation at local cells caused by the interpolation of topography deformation at the cell vertex,and reduced uncertainty in the computation of the GF2DUCM.The model performance is systematically tested using a series of laboratory experiments,which demonstrate the mass conservation feature and high accuracy in reproducing hydrodynamic and morphological processes. 相似文献
9.
10.
《Applied Geochemistry》1993,8(6):529-549
Changes in the distribution of inorganic solutes in a shallow ground water contaminated by crude oil document a series of geochemical reactions initiated by biodegradation of the oil. Upgradient of an oil body floating on the water table, oxidation of oil to carbonic acid dissolves carbonate minerals in the aquifer matrix. In this oxidized zone pH is depressed ∼1 pH unit, and the concentrations of Ca, Mg and HCO3− increase to more than twice that of the native ground water. In the anoxic zone beneath the oil body concentrations of dissolved SiO2, Sr, K, Fe and Mn increase significantly. Here, Fe is mobilized by microbial reduction, pH is buffered by the carbonate system, and silicates weather via hydrolysis and organic-acid-enhanced dissolution. Farther down-gradient the ground water is reoxygenated and Fe precipitates from solution, possibly as iron hydroxide or iron carbonates, while SiO2 precipitates as amorphous silica. Other solutes, such as Mg, are transported more conservatively down-gradient where contaminated and native ground water mix.The observed changes in inorganic aqueous chemistry document changes in water-mineral interactions caused by the presence of an organic contaminant. These organic-initiated interactions are likely present in many contaminated aquifers and may be analogous to interactions occurring in other organic-rich natural waters. 相似文献