Age of the MGS5 segment of the Milanggouwan stratigraphical section and evolution of the desert environment on a kiloyear scale during the Last Interglacial in China's Salawusu River Valley: Evidence from Rb and Sr contents and ratios     

Shuhuan Du  Baosheng Li  Dongfeng Niu  David Dian Zhang  Xiaohao Wen  Deniu Chen  Yi Yang  Fengnian Wang 《Chemie der Erde / Geochemistry》2011,(1):87-95

The MGS5 segment of the Milanggouwan stratigraphical section in China's Salawusu River Valley records 8.5 sedimentary cycles consisting of dune sands alternating with fluviolacustrine facies or/and paleosols. Based on a comprehensive analysis of the distribution of Rb and Sr within the segment and paleoecological evidence (fossils), it appears that the observed sedimentation cycles mainly resulted from fluctuations between dry-cold and warm-humid climates, which indicates that the MGS5 segment experienced at least eight cold-dry and nine warm-humid climatic fluctuations. Of these, 12 cold–warm climate fluctuations correspond to DO20–DO25 and stadia 21–26 recorded by the NGRIP ice cores. Another five cold–warm climatic fluctuations that occurred during MGS5e correspond to five substages (5e1–5e5) recorded by the GRIP ice cores from Greenland. This kind of high-frequency climatic fluctuation on a kiloyear scale was mainly subject to variations in the strength of the East Asian winter and summer monsoons.  相似文献   

Metamorphic growth and recrystallization of zircons in extremely O-depleted rocks during eclogite-facies metamorphism: Evidence from U-Pb ages, trace elements, and O-Hf isotopes     

Yi-Xiang Chen  Ren-Xu Chen  Qiuli Li  Lu Chen 《Geochimica et cosmochimica acta》2011,75(17):4877-4898

A combined in situ SIMS and LA-(MC)-ICPMS study of U-Pb ages, trace elements, O and Lu-Hf isotopes was conducted for zircon from eclogite-facies metamorphic rocks in the Sulu orogen. The two microbeam techniques sampled various depths of zircon domains, revealing different element and isotope relationships between residual magmatic cores and new metamorphic rims and thus the geochemical architecture of metamorphic zircons which otherwise cannot be recognized by the single microbeam technique. This enables discrimination of metamorphic growth from different subtypes of metamorphic recrystallization. Magmatic cores with U-Pb ages of 769 ± 9 Ma have positive δ¹⁸O values of 0.1-10.1‰, high Th/U and ¹⁷⁶Lu/¹⁷⁷Hf ratios, high REE contents, and steep MREE-HREE patterns with negative Eu anomalies. They are interpreted as crystallizing from positive δ¹⁸O magmas during protolith emplacement. In contrast, newly grown domains have concordant U-Pb ages of 204 ± 4 to 252 ± 7 Ma and show negative δ¹⁸O values of −10.0‰ to −2.2‰, low Th/U and ¹⁷⁶Lu/¹⁷⁷Hf ratios, low REE contents, and flat HREE patterns with weak to no Eu anomalies. They are interpreted as growing from negative δ¹⁸O fluids that were produced by metamorphic dehydration of high-T glacial-hydrothermally altered rocks during continental subduction-zone metamorphism. Differences in δ¹⁸O between different domains within single grains vary from 0.8‰ to 12.5‰, suggesting different degrees of O isotope exchange between the positive δ¹⁸O magmatic core and the negative δ¹⁸O metamorphic fluid during the metamorphism. The magmatic zircons underwent three subtypes of metamorphic recrystallization, depending on their accessibility to negative δ¹⁸O fluids. The zircons recrystallized in solid-state maintained positive δ¹⁸O values, and REE and Lu-Hf isotopes of protolith zircon, but their U-Pb ages are lowered. The zircons recrystallized through dissolution exhibit negative δ¹⁸O values similar to the metamorphic growths, almost completely reset U-Pb ages, and partially reset REE systems. The zircons recrystallized through replacement show variably negative δ¹⁸O values, and partially reset REE, and U-Pb and Lu-Hf isotopic systems. Therefore, this study places robust constraints on the origin of metamorphic zircons in eclogite-facies rocks and provides a methodological framework for linking the different types of metamorphic zircons to petrological processes during continental collision.  相似文献   

宁芜盆地凹山铁矿床辉长闪长玢岩和花岗闪长斑岩的锆石U-Pb年龄及其地质意义   总被引：14，自引：0，他引：14  

段超  毛景文  李延河  侯可军  袁顺达  张成  刘佳林 《地质学报》2011,85(7):1159-1171

宁芜盆地是长江中下游多金属成矿带的重要矿集区之一,是玢岩型铁矿成矿模式建模的基地.玢岩型铁矿床成矿时代的约束对区域成岩成矿作用及成矿动力学背景研究具有重要的意义.凹山铁矿床是宁芜盆地玢岩型铁矿床的典型代表之一,本文选择矿区发育的两种与成矿作用关系密切的岩浆岩为研究对象,进行锆石LA-MC-ICP-MS U-Pb年代学研...  相似文献   

华南燕山晚期构造-岩浆事件与成矿作用——来自广西大瑶山龙头山金矿床的地球化学约束   总被引：2，自引：0，他引：2  

段瑞春  凌文黎  李青  陈子万  刘立芬  杨红梅 《地质学报》2011,85(10):1644-1658

广西贵港大瑶山成矿带位于华南东南沿海成矿带西南端,对矿带内龙头山金矿黄铁矿化斑岩进行定年的结果为96.1±3.0 Ma,与区域内邻近的平天山侵入岩体(96.2±0.4 Ma)相同.龙头山矿床的Sr同位素组成与其锆石的REE特征表明,成矿作用伴随有大量的流体参与;矿化斑岩与区内侵入相岩石相同的形成时代以及矿化斑岩中锆石C...  相似文献   

遥感地质勘查技术与应用研究   总被引：14，自引：0，他引：14  

王润生  陈微  杨苏明  张瑞江  葛大庆  张晓坤  张振华  王品清  郭小方  李丽  熊盛青  聂洪峰  梁树能  齐泽荣  杨金中  闫柏琨  赵福岳  范景辉  童立强  林键  甘甫平 《地质学报》2011,85(11):1699-1743

遥感的发展极大地拓宽了人类的视野和视觉能力,以其宏观性、综合性、多尺度、多层次的特点,已成为地质研究和地质勘查不可缺少的技术手段,在地质调查、矿产勘查、地质环境评价、地质灾害监测和基础地质研究等方面都发挥了越来越大的作用.随着传感器分辨率(空间、光谱、时间、辐射)的不断提高,特别是高光谱和干涉雷达技术的发展,不仅极大地...  相似文献   

Geochemistry of Palaeozoic marine petroleum from the Tarim Basin, NW China: Part 3. Thermal cracking of liquid hydrocarbons and gas washing as the major mechanisms for deep gas condensate accumulations   总被引：2，自引：0，他引：2  

Shuichang Zhang  Jin Su  Xiaomei Wang  Guangyou Zhu  Haijun YangKeyu Liu  Zhenxi Li 《Organic Geochemistry》2011,42(11):1394-1410

The Lunnan Lower Uplift in the Tarim Basin, NW China contains a composite petroleum system with mainly biodegraded heavy oil in the west, normal oil in the center and gas condensate in the east. Twenty-three gas samples and 37 oil samples taken from three major hydrocarbon bearing intervals in the Lunnan lower bulge were analyzed for their stable carbon isotopes and molecular biomarkers. On the basis of their isotopic compositions, biomarkers, especially diamondoids, and integrating the physical properties of the hydrocarbons including densities, GOR and PVT relationships, it has been concluded that the recently discovered deep (6500 m) eastern Lungu giant Ordovician gas condensate pool with an estimated reserve of 723 million bbl oil equivalent is a secondary hydrocarbon accumulation derived from the mixing of an early formed oil and a late formed gas. The extremely dry gases with a gas dryness of >0.98 were derived from thermal cracking of crude oils and charged to an existing oil reservoir causing extensive gas washing and secondary alteration. Compared with most of the hydrocarbons in the Lunnan area, the gas from the eastern Lungu gas condensate pool has a heavier carbon isotopic composition, higher dryness and a higher maturity level. The unique physical, chemical and isotopic compositions of the gas condensate are believed to be a direct result of gas flushing of an early formed eastern Lungu oil pool by a late formed dry gas from oil cracking. The eastern Lungu gas condensate pool is presently characterized by containing “dry gas, heavy oil, abundant aromatics and high wax”.  相似文献   

Numerical investigation of groundwater outbursts near faults in underground coal mines     

Li Lianchong  Yang Tianhong  Liang Zhengzhao  Zhu Wancheng  Tang Chunan 《International Journal of Coal Geology》2011,85(3-4):276-288

Permeable geologic faults in the coal seam can cause intermittent production problems or unexpected amounts of groundwater outburst from the underlying aquifers. With the acknowledgment of the basic mechanism for groundwater outbursts, the groundwater outburst along the fault zones in coal mines are numerically investigated using RFPA, a numerical code based on FEM. The fracture initiation, propagation, and coalescence in the stressed strata and the seepage field evolution in the stress field are represented visually during the whole process of groundwater outburst. The numerically obtained damage evolution shows that the floor strata could be classified as three zones, i.e. mining induced fracture zone, intact zone and fault reactivation zone, in which the intact zone is the key part for resisting groundwater outburst and directly determines the effective thickness of water-resisting rock layer. With understanding of the evolution of stress field and seepage flow in floor strata, the groundwater outburst pathway is calibrated and the transformation of floor rock mass from water-resisting strata to outburst pathway is clearly illuminated. Moreover, it is shown that geometrical configuration, including inclination angle of faults and seam drop along faults, have an important influence on groundwater outburst. Finally, based on geological, hydrogeology survey and numerical results, the mechanism analysis of groundwater outburst in an engineering case is studied, which can provide significantly meaningful guides for the investigation on mechanism and prevention of groundwater outburst induced by faults in practice.  相似文献   

Geological, geochemical characteristics and isotope systematics of the Longqiao iron deposit in the Lu-Zong volcano-sedimentary basin, Middle-Lower Yangtze (Changjiang) River Valley, Eastern China   总被引：8，自引：0，他引：8  

Zhou Taofa  Wu Mingan  Fan Yu  Duan Chao  Yuan Feng  Zhang Lejun  Liu Jun  Qian Bing  Franco Pirajno  David R. Cooke 《Ore Geology Reviews》2011,43(1):154-169

The Middle-Lower Yangtze (Changjiang) River Valley metallogenic belt is located on the northern margin of the Yangtze Craton of eastern China. Most polymetallic deposits in the Changjiang metallogenic belt are clustered in seven districts where magmatism of Mesozoic age (Yanshanian tectono-thermal event) is particularly extensive. From west to east these districts are: E-dong, Jiu-Rui, Anqing-Guichi, Lu-Zong, Tong-Ling, Ning-Wu and Ning-Zhen. World-class iron ore deposits occur in the Lu-Zong and Ning-Wu ore clusters, which are mainly located in continental fault-bound volcanic-sedimentary basins. One of these deposits is the Longqiao iron deposit, discovered in the northern part of the Lu-Zong Basin in 1985. This deposit consists of a single stratabound and stratiform orebody, hosted in sedimentary carbonate rocks of the Triassic Dongma'anshan Formation. A syenite pluton (Longqiao intrusion) is situated below the deposit. The iron ore is massive and disseminated and the ore minerals are mainly magnetite and minor pyrite. Wall rock alteration mostly consists of skarn minerals, such as diopside, garnet, potassic feldspar, quartz, chlorite, phlogopite and anhydrite. Thin sedimentary siderite beds of Triassic age occur as relict laminated ore at the top and the margin of the magnetite orebody. These sideritic laminae are part of Triassic evaporite-bearing carbonate deposits (Dongma'anshan Formation).Sulfur isotopic compositions show that the sulfur in the deposit was derived from a mixture of magmatic hydrothermal fluids and carbonate–evaporite host rocks. Similarly, the C and O isotopic compositions of limestones from the Dongma'anshan Formation indicate that these rocks interacted with magmatic hydrothermal fluids. The O isotopic compositions of the syenitic rocks and minerals from the deposit show that the hydrothermal magnetite and skarn minerals were formed from magmatic fluids. The Pb isotopic compositions of sulfides are similar to those of the Longqiao syenite. Phlogopite coexisting with magnetite in the magnetite ores yielded a plateau age of 130.5 ± 1.1 Ma (2σ), whereas the LA-ICP MS age of the syenite intrusion is 131.1 ± 1.5 Ma, which is slightly older than the age of phlogopite.The Longqiao syenite intrusion may have crystallized from a parental alkaline magma, generated by partial melting of lithospheric mantle, during extensional tectonics. The ore fluids were probably first derived from magma at depth, later emplaced in the sedimentary rocks of the Dongma'anshan Formation, where it interacted with siderite and evaporite-bearing carbonate strata, resulting in the formation of magnetite and skarn minerals. The Longqiao iron deposit is a skarn-type stratabound and stratiform mineral system, genetically and temporally related to the Longqiao syenite intrusion. The Longqiao syenite is part of the widespread Mesozoic intracontinental magmatism (Yanshanian event) in eastern China, which has been linked to lithospheric delamination and asthenospheric upwelling.  相似文献   

ATLAS III in situ heating test in boom clay: Field data,observation and interpretation   总被引：1，自引：0，他引：1  

G.J. Chen  X. Sillen  J. Verstricht  X.L. Li 《Computers and Geotechnics》2011

The ATLAS III small scale in situ heating test aimed at assessing the thermo-hydro-mechanical (THM) effects on the Boom clay of the significant temperature gradients generated in this host rock as a consequence of the geological disposal of radioactive, heat-emitting wastes. This paper presents data on temperature, pore water pressure and total stress measured during the experiment and highlights several interesting observations regarding the thermal anisotropy and THM coupling in the Boom clay. The test has a simple geometry and well defined boundary conditions, which facilitates the comparison between measurement and numerical modeling studies. These studies included three dimensional coupled THM modeling of the test. The good agreement between measurement and numerical modeling of temperature and pore water pressure yields a set of THM parameters and confirms the thermo-mechanical anisotropy of the Boom clay.  相似文献   

Holocene monsoon climate documented by oxygen and carbon isotopes from lake sediments and peat bogs in China: a review and synthesis   总被引：1，自引：0，他引：1  

Jiawu Zhang  Fahu Chen  Jonathan A. Holmes  Hui Li  Xiaoyan Guo  Junlan Wang  Shuang Li  Yanbin Lü  Yan Zhao  Mingrui Qiang 《Quaternary Science Reviews》2011,30(15-16):1973-1987

There has been much recent debate about Holocene climate variation in the monsoon region of China, especially the temporal pattern of variations in precipitation, the time-transgressive nature of the Holocene precipitation maximum, and the extent to which variations in regions influenced by the Indian Summer Monsoon (ISM) and the East Asian Summer Monsoon (EASM) have been synchronous. We summarize and compare carbonate oxygen-isotope records (δ¹⁸O_carb) from ten lakes within the present-day ISM region. We discuss their paleoclimate significance considering the present-day moisture source, isotopic composition of precipitation and the hydrological setting. The δ¹⁸O_carb records are controlled mainly by the isotopic composition of lake water, which in turn is a function of regional Precipitation/Evaporation (P/E) balance and the proportion of precipitation that is monsoon-derived. We normalized the δ¹⁸O_carb data and used these records to generate an integrated moisture index. This index, along with oxygen-isotope records from speleothems and carbon-isotope records (δ¹³C_org) from peats within the monsoon region, suggests that Holocene climate was broadly synchronous across the monsoon region and, within the limits of accuracy of the existing age models, provides no strong evidence for previously-proposed anti-phasing of the ISM and the EASM. Stable-isotope records from lake sediments and peat bogs have excellent potential for providing high-quality paleoclimate data for monsoon Asia, and complement high-resolution speleothem sequences, which are only found in certain localities.  相似文献