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931.
微量陨石激光熔样稀有气体测定方法是一种可以在微米尺度上对几毫克陨石样品进行准确稀有气体同位素分析的方法,克服了传统全岩熔融法在测量时存在样品用量大、前处理过程复杂和样品稀有气体分布不均导致不同组分的宇宙射线暴露历史无法进一步区分等问题。但是由于该方法所用样品体积小和样品用量低,要求实验室具有超低本底的稀有气体提取系统,目前国内在微量陨石稀有气体分析技术方面尚处于起步阶段。本文采用金刚石激光样品窗成功研制了超低本底的气体提取系统,通过系统体积标定和天平称量误差、热本底、干扰元素、质量歧视及质谱灵敏度等参数的校正,在中国科学院地质与地球物理研究所建立了微量陨石激光熔样稀有气体测定方法,并对毫克级微量钙长辉长无球粒陨石Millbillillie粉末标样进行了稀有气体同位素含量和比值测定,计算获得准确一致的宇宙暴露年龄。该方法的建立,将为我国迅速发展的比较行星学和深空探测提供重要技术支撑。 相似文献
932.
The Mana district, located in the northern part of the Birimian Houndé greenstone belt in western Burkina Faso, is a world-class Paleoproterozoic orogenic gold district (∼8 Moz) including five gold deposits (Fofina, Nyafé, Siou, Wona-Kona and Yaho). These deposits are located in specific lithostratigraphic domains, and gold is controlled by various structural features. Deposit- and regional-scale mapping, intrusion age and geochemistry, as well as airborne aeromagnetic and electrical resistivity geophysical data, were used to decipher the tectonic evolution of each gold deposit and the district. Five deformational and four gold mineralizing events were recognized.The first deformation event (D1MD: E-W oriented shortening) affected the metamorphosed volcanic and sedimentary rocks of the Lower Birimian group. This early deformation episode was correlated with the formation of gently N-plunging folds (F1MD) and N-S-striking thrusts faults coeval with emplacement of the pre- to synkinematic Wona-Kona and Siou plutons dated at ∼2172 Ma, under greenschist facies metamorphism. The quartz-carbonate veins (V1MD) at Fofina and Siou formed during D1MD at Eoeburnean time, manifesting the first gold event at approximately ∼2172 Ma.The following deformation event (D2MD: E-W oriented extension) is associated with the deposition of the Upper Birimian group (Mana basin) overlying the Lower Birimian group. The geometry of the Mana basin is controlled by the Mana and Maoula shear zones. The Tarkwaian-type rock formation overlying the Upper Birimian group, controlled by the Wona-Kona and Siou shear zones, is constrained at the end of D2MD or at the beginning of the D3MD event with a maximum deposition age at ∼2113 Ma.The third deformation event (D3MD: E-W to WNW-ESE transpression) affected the entire supracrustal rock. Such event is correlated with the formation of map-scale F3MD folds and dextral shear zones during the Eburnean orogeny (∼2113–2090 Ma). A second gold mineralizing event occurred during D3MD and is manifested by quartz-carbonate veins (V3MD) and disseminated sulfides at the Yaho, Fofina and Nyafé and possibly Wona-Kona deposits.The fourth deformation event (D4MD: NNW-SSE transpression) is correlated with sinistral shearing along the major transcurrent faults and the development of asymmetric NNE-striking folds (F4MD) associated with vertical fold axes. Syn-D4MD mineralization is characterized mainly by a strong silicification (Si4MD) with disseminated pyrite and arsenopyrite along the Wona-Kona shear zone and by tiny quartz-carbonate veinlets (V4MD). This event is considered the main gold-bearing event in the western margin of the Mana district.The fifth and last deformation event (D5MD) is brittle in character and was responsible for the formation of E-W subvertical crenulation cleavages and reverse faults under overall N-S shortening. This late deformation event is tentatively associated with a last gold event recorded as free gold associated with muscovite in brittle fractures developed in competent orebodies at the Wona-Kona and Siou deposits. This event could be as young as ∼2022 Ma, the age obtained from Ar-Ar datation of muscovite-schists at the Wona-Kona deposit.Our main contribution is that we decipher multiple gold mineralizing events at the district scale based on deposit- and regional-scale mapping. It is interpreted that gold was introduced as early as ∼2172 Ma and possibly as late as ∼2022 Ma during at least 3 or even 4 shortening tectonic events in a timeframe not yet recognized at the district scale for all the Birimian belts. 相似文献
933.
B. Heisinger D. Lal A. J. T. Jull P. Kubik S. Ivy-Ochs S. Neumaier K. Knie V. Lazarev E. Nolte 《Earth and Planetary Science Letters》2002,200(3-4):345-355
To investigate muon-induced nuclear reactions leading to the production of radionuclides, targets made of C9H12, SiO2, Al2O3, Al, S, CaCO3, Fe, Ni, Cu, Gd, Yb and Tl were irradiated with 100 and 190 GeV muons in the NA54 experimental setup at CERN. The radionuclide concentrations were measured with accelerator mass spectrometry and γ-spectroscopy. Results are presented for the corresponding partial formation cross-sections. Several of the long-lived and short-lived radionuclides studied are also produced by fast cosmic ray muons in the atmosphere and at depths underground. Because of their importance to earth sciences investigations, calculations of the depth dependence of production rates by fast cosmic ray muons have been made. 相似文献
934.
在占我国最著名的金矿域—胶北金矿域的金矿储量86.3%的招掖金矿带内,广泛分布的燕山期花岗岩类与金矿化作用密切相关。然而,这些花岗岩类的形成时代却是长期困扰地学界的棘手问题,并一直阻碍着有关金矿化问题的探讨。精确的单颗粒锆石U-Pb年代学研究表明,招掖金矿带内花岗岩类玲珑型花岗岩和郭家岭花岗闪长岩均形成于145Ma(分别为145.9±0.5Ma和144.1±0.8Ma)左右的燕山早期(晚侏罗世)。其中存在年龄为2.7Ga左右的继承性锆石,这显示了这些花岗岩类为壳源重熔的产物,而胶东岩群可能为其重要源岩之一。综合已有资料分析,该区与花岗岩类有关的金矿化作用可能发生于100~120Ma区间内。 相似文献
935.
936.
Late Cretaceous chronostratigraphy (Turonian-Maastrichtian): SK1 core Songliao Basin, China 总被引:1,自引:0,他引:1
Non-marine ostracodes,charophytes and palynomorphs are abundant in most Cretaceous lacustrine basins of East Asia.However,their ranges are not directly integrated with marine biota that defines the Cre... 相似文献
937.
938.
Based on results of study of the regional position, chemical composition of ores, fluid inclusions, and age relationships between mineralization and igneous rocks, we propose a geological and genetic model for the formation of gold mineralization of the Zaderzhninskoe deposit. Mineralization is located in the tectonic node of the intersection of two regional structures in the supraintrusive zone of a latent granitoid pluton among the terrigenous rocks of the Verkhoyansk complex, which are regionally metamorphosed to the greenschist facies. The sequential deposition of three types of mineralization—Au-quartz (including early low-gold Au-As and late productive Au-Pb-Zn mineralization), Au-rare-metal, and Au-silver—has been established. The Au-Bi (Te) assemblage contains native bismuth, bismuthinite, hedleyite, Bi sulfotellurides, gustavite group minerals, and secondary minerals—Bi oxides and Bi tellurites with low-grade gold. Hg-containing electrum and kustelite, Ag-Sb and Ag-Pb-Sb sulfosalts, stutzite, Te-Pb-containing canfieldite, freibergite, and Au and Ag sulfides are indicator minerals of the Au-Ag (Sb) assemblage. Ore formation occurred at temperatures from 90 to 340 °C, with the participation of lowly and moderately concentrated solutions with CO2 ± CH4 ± N2 gas phase. A decrease in temperature from Au-quartz mineralization (200-220 °C) to the late epithermal one (160 °C) and a slight increase in the concentration of solutions (up to 10 wt.% NaCl equiv.) have been established. The deposit resulted from the intricate multistage geodynamic evolution of the South Verkhoyansk region. Ore-forming processes are associated with the evolution of magmatic objects. Dating of igneous rocks yields the following ages: diorites—130-137 Ma (Rb-Sr), spessartites—126 ± 3 Ma (Rb-Sr), and kersantites—115 ± 1.7 Ma (Ar/Ar). Early concordant Au-quartz (Au-As) mineralization of the deposit is comparable with metamorphic-related Au-quartz veins of the Yur-Bular type, and its age is taken as > 137 Ma. The time of formation of Au-quartz (Au-Pb-Zn) mineralization is estimated at 123.5 ± 1.6 Ma (Ar/Ar) and is coeval with the time of intrusion of the Early Cretaceous granitoids of the South Verkhoyansk region. The imposed low-temperature mineralization undoubtedly has a younger age. Its formation was followed by the successive deposition of Au-rare-metal mineralization at the final stage of formation of granitoid plutons (~ 120 Ma) and Au-Ag mineralization in the period 100 ± 5 Ma, i.e., the time of formation of late-stage granodiorite-granite intrusions. 相似文献
939.
北山北部双井子复式岩体年代学、地球化学及其大地构造意义 总被引:4,自引:0,他引:4
北山造山带位于中亚造山带南缘中段地区,连接了东西部构造单元,具有重要的大地构造意义。白山构造带位于北山南北构造单元的结合部位,该构造带广泛出露的侵入岩对于认识北山北部地区晚古生代的构造演化具有重要意义。本次研究针对白山构造带中双井子岩体进行了岩石学、地球化学和锆石U-Pb年代学及Hf同位素研究。双井子花岗闪长岩和钾长花岗岩的LA-ICP-MS锆石U-Pb年龄分别为284.9±1.5 Ma和327.6±1.6 Ma。地球化学研究发现两者都表现出弱过铝质、钙碱性I型花岗岩的特征,并都表现出轻、重稀土元素的分异,且相对富集大离子亲石元素,亏损高场强元素。另外,锆石Hf同位素研究表明两者都具有高的εHf(t)值(5.87~12.24),以及相对年轻的锆石Hf同位素二阶段模式年龄(tDM2=510~961 Ma),表明了双井子岩体应来源于新生下地壳重熔的产物,并且其母岩浆在形成过程过程中可能受到亏损地幔物质的混染,也暗示了北山北部地区在晚石炭世—早二叠世经历了强烈的陆壳生长过程。北山北部地区的红石山蛇绿岩及白山组火山岩的研究成果表明两者都具有俯冲带岩石的特征,表明了白山构造带在石炭纪—中二叠世期间仍处于大洋俯冲阶段。通过本次研究所得数据以及相关的研究成果推测双井子侵入岩应形成于红石山蛇绿岩所代表的古大洋向南俯冲过程。 相似文献
940.
The Puttetti alkali syenite pluton in southern India belongs to the suite of felsic magmatic intrusives emplaced during the Late Neoprotrozoic-Cambrian time during the final phase of amalgamation of the Gondwana supercontinent. In this study, we evaluate the cooling history of this pluton based on various isotopic systems. We present whole-rock Pb-Pb data on the syenite which yields an isochron age of 508±25Ma. Three phlogopite separates from the syenite pluton give K-Ar ages of 454.0±9.0, 448.5±8.9 and 445.6±8.8 Ma indicating cooling age at temperatures of 415°C. U-Pb analyses of zircons from this syenite yielded an age of 572±2 Ma in a previous study. With U-Pb closure temperatures >800 o C, this age probably indicates the timing of emplacement of the Puttetti pluton. Collectively, we estimate from the isotopic age data and respective closure temperatures that the syenite body cooled at about 3.2 o C/Ma from about 800 o C to about 415 o C. The markedly low cooling rate of the syenite pluton, absence of chilled margin effects, and common occurrence of pyroxene, feldspar, phlogopite and zircons megacrysts in the rock indicate that the host granulites were at high temperatures during the emplacement of the syenite magma. The cooling history of Puttetti syenite estimated in this study is closely comparable with the 3–4 o C/Ma cooling rate estimated for a granite pluton in a previous study from Madagascar. Our study suggests protracted cooling rates for the late Pan-African intrusives emplaced within the Gondwana crust, with a long residence history in a hot crust bore they were exhumed to shallower levels. 相似文献