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61.
The discovery of the Early Mesozoic basic granulite xenoliths in the Harqin area of the Inner Mongolia Autonomous Region (for short Inner Mongolia) is reported for the first time in this paper. According to the mineral assemblage the xenoliths include two-pyroxene granulite, clinopyroxene granulite, and hypersthene granulite. Their protolytes are mainly gabbroite rocks. The zircon U?Pb age of the granulite xenoliths is 251 Ma, and K?Ar age of the hypersthene is 229 Ma. They represent the times of metamorphism and cooling of the granulite facies respectively. The host rock of the xenoliths is Early Mesozoic biotite-quartz diorites, whose whole-rock K?Ar age is 219 Ma. This discovery confirms existence of an Early Mesozoic underplating in the North China Craton, which is of much importance in research on the Early Mesozoic mantle-crust interaction in the concerned area. 相似文献
62.
63.
长城系团山子组火山岩颗粒锆石U-Pb年龄及其地质意义 总被引:46,自引:1,他引:46
蓟县中-上元古界典型剖面之邻区平谷县境内,长城系团山子组连续发育两层厚度各为1m左右的富钾粗面安山岩,发育气孔构造和绳状构造。其中存在三种不同成因类型锆石,应用颗粒锆石U-Pb测定年龄技术,得到:(1)自生锆石,其U-Pb不一致上交点年龄为1683±67Ma,代表该火山岩形成年龄;(2)捕获锆石,多为原碎屑锆石,较年轻的一种捕获锆石的207Pb/206Pb表面年龄为1823±68Ma,这限定了长城系底界年龄应新于1823Ma;(3)后生热液锆石,其U-Pb年龄为460Ma左右,反映后期热液事件发生的时代。 相似文献
64.
Presented in this paper are the newly obtained grain zircon U-Pb ages of volcanic rocks of the Lueliang Goup and associated Kuanping granitic migmatitic gneiss in Shanxi Province.The zircon U-Pb ages of bimodal volcanic rocks(basalt and rhyolite)of the Upper Lueliang Group indicate that the rocks erupted at about 2100 Ma.So the Lueliang Group was formed during the Early Proterozoic.In the area studied the second-stage metamorphism experienced by the Lueliang Group is the dominant one which took place at about 1806 Ma.i.e.,during the late Early Proterozoic. 相似文献
65.
GEOCHEMICAL CHARACTERISTICS OF GRANITES AND ITS STRUCTURAL GENETIC ENVIRONMENT IN THE NANDAN-HECHI METALLOGENETIC BELT, NORTHWEST GUANGXI 总被引:3,自引:0,他引:3
The Nandan-Hechi metallogenetic belt is the most important tin-polymetallic producing district in China, and is the location of the Dachang super-large tin deposit. Based on the detailed field investigation and isotopic data, the stages of magmatic activity in the Nandan-Hechi metallogenetic belt have been lined out in this paper. Through the study about the geochemical characteristics of different granites, and by using ω(Al2O3)-ω(SiO2), ω(TFeO)/[ω(TFeO) ω(MgO)]-ω(SiO2), AFM, ACF and Rb-Yb Ta, Rb-Y Nb,Ta-Yb, Nb-Y discrimination diagrams in combination with regional geological setting analysis, the authors carried out analyses about the structural environment for the formation of the granites, and discussed the structural environment and dynamic setting for the large scale mineralization in this area. Our study indicates that the majority of the granites in Nandan-Hechi metallogenetic belt belong to the POG type,while the later stage alaskite belongs to the RRG CEUG type. The granites were formed at the stage of structural transformation from postorogenic phase to intraplate setting. But the major structural environment is characterized by steady regional extension. The formation age for the granites coincides with the time for this transformation, and this translation environment is favored for large-scale metallogenesis. 相似文献
66.
The CO2 migrated from deeper to shallower layers may change its phase state from supercritical state to gaseous state (called phase transition). This phase transition makes both viscosity and density of CO2 experience a sharp variation, which may induce the CO2 further penetration into shallow layers. This is a critical and dangerous situation for the security of CO2 geological storage. However, the assessment of caprock sealing efficiency with a fully coupled multi-physical model is still missing on this phase transition effect. This study extends our previous fully coupled multi-physical model to include this phase transition effect. The dramatic changes of CO2 viscosity and density are incorporated into the model. The impacts of temperature and pressure on caprock sealing efficiency (expressed by CO2 penetration depth) are then numerically investigated for a caprock layer at the depth of 800 m. The changes of CO2 physical properties with gas partial pressure and formation temperature in the phase transition zone are explored. It is observed that phase transition revises the linear relationship of CO2 penetration depth and time square root as well as penetration depth. The real physical properties of CO2 in the phase transition zone are critical to the safety of CO2 sequestration. Pressure and temperature have different impact mechanisms on the security of CO2 geological storage. 相似文献
67.
鄂西黄陵背斜地区虽已发现众多矿点,但是矿床规模较小,找矿潜力不明。由于区内植被茂盛、覆盖严重,致使地质异常信息被削弱或掩盖,对进一步找矿工作造成了严重干扰。本次研究使用成分数据分析和能谱-面积(S-A)分形模型识别与金矿化相关的异常,结果表明:(1)等距对数比(ILR)变换后的主成分分析结果相比对数(Log)变换更能够反应元素的共生组合规律,第一主成分(PC1)元素组合为Au-Cu-Ag,且Au元素占有最大的载荷,与金矿密切相关,PC1元素组合异常的分布模式与矿点的分布更加吻合;(2) S-A方法抑制了黄陵背斜区域水系沉积物的背景模式,增强了异常模式;(3)根据地质特征和以往勘查工作情况,圈定了三处找矿远景区,为该地区金矿下一步勘查工作提供了重要依据。 相似文献
69.
滩坝砂是一种发育在滨浅湖高能环境的薄互层沉积,是以往未被重视的、认识程度较低的碎屑岩储集体。围绕滩坝砂成因与成藏的难点,研究了东营凹陷沙四上亚段滩坝砂沉积特征和分布规律,明确了滩坝砂成藏要素与富集规律。提出了滩坝砂沉积受古地貌、古水动力(波浪、湖流)和古基准面控制的"三古控砂"机制和油气成藏受断裂裂隙、有效储层、烃源岩超压控制的"三元控藏"认识,指出断陷盆地中长期基准面持续上升,短期基准面频繁震荡形成了大面积分布的滨浅湖滩坝砂沉积,烃源岩生烃增压与成岩过程中耗水降压共同作用下的"压-吸充注"是滩坝砂岩大面积含油的主要原因。 相似文献
70.
Jianping?Zheng W.?L.?GriffinEmail author Suzanne?Y.?O’Reilly Fengxiang?Lu Chunmei?Yu Ming?Zhang Huimin?Li 《Contributions to Mineralogy and Petrology》2004,148(1):79-103
Mafic xenoliths from the Paleozoic Fuxian kimberlites in the North China craton include garnet granulite, and minor pyroxene amphibolite, metagabbro, anorthosite and pyroxenite. The formation conditions of the amphibolites are estimated at 745–820 °C and 7.6–8.8 Kb (25–30 km); the granulites probably are derived from greater depths in the lower crust. LAM-ICPMS U–Pb dating of zircons from four granulites reveals multiple age populations, recording episodes of magmatic intrusion and metamorphic recrystallisation. Concordant ages and upper intercept ages, interpreted as minimum estimates for the time of magmatic crystallisation, range from 2,620 to 2,430 Ma in three granulites, two amphibolites and two metagabbros. Lower intercept ages, represented by near-concordant zircons, are interpreted as reflecting metamorphic recrystallisation, and range from 1,927 to 1,852 Ma. One granulite contains two metamorphic zircon populations, dated at 1,927±55 Ma and 600–700 Ma. Separated minerals from one granulite and one amphibolite yield Sm–Nd isochron ages of 1,619±48 Ma (143Nd/144Nd)i=0.51078), and 1,716±120 Ma (143Nd/144Nd)i=0.51006), respectively. These ages are interpreted as recording cooling following metamorphic resetting; model ages for both samples are in the range 2.40–2.66 Ga. LAM-MC-ICPMS analyses of zircon show a range in 176Hf/177Hf from 0.28116 to 0.28214, corresponding to a range of Hf from –34 to +12. The relationships between 207Pb/206Pb age and Hf show that: (1) the granulites, amphibolites and metagabbro were derived from a depleted mantle source at 2.6–2.75 Ga; (2) zircons in most samples underwent recrystallisation and Pb loss for 100–200 Ma after magmatic crystallisation, consistent with a residence in the lower crust; (3) metamorphic zircons in several samples represent new zircon growth, incorporating Hf liberated from breakdown of silicates with high Lu/Hf; (4) in other samples metamorphic and magmatic zircons have identical 176Hf/177Hf, and the younger ages reflect complete resetting of U–Pb systems in older zircons. The Fuxian mafic xenoliths are interpreted as the products of basaltic underplating, derived from a depleted mantle source in Neoarchean time, an important period of continental growth in the North China craton. Paleoproterozoic metamorphic ages indicate an important tectonic thermal event in the lower crust at 1.8–1.9 Ga, corresponding to the timing of collision between the Eastern and Western Blocks that led to the final assembly of the North China craton. The growth of metamorphic zircon at 600–700 Ma may record an asthenospheric upwelling in Neoproterozoic time, related to uplift and a regional disconformity in the North China craton. 相似文献