贵州施秉白云岩溶蚀特性及孔隙特征实验研究

以贵州施秉白云岩为研究对象,从宏观和微观角度分析白云岩的溶蚀特性及孔隙特征,结果显示:(1)在众多影响施秉喀斯特发育的因素中,矿物成分是最基本的内因,水是最关键的外因,孔隙结构起辅助作用。(2)极细晶白云岩的单位表面积溶蚀量一般大于细晶白云岩的,在晶粒相同的情况下,白云岩的溶蚀量与Ca O和Mg O的含量分别成正比,且Mg O的含量影响较Ca O大。(3)施秉白云岩溶蚀速率不仅受岩石矿物颗粒粒径大小的控制,还受岩石内部孔隙结构特征的影响,颗粒粒径越大,孔隙度越高,连通性越好,越有利于水溶液进入,溶蚀量也就越大。(4)施秉白云岩的溶蚀特性是多种因素综合作用的结果,必须把各个因素分离开来,从宏观和微观角度逐个作详细的分析研究,然后综合起来,才能对喀斯特发育规律有更深入的了解。     

四川大陆槽稀土矿床碳酸岩-英碱正长岩锆石U-Pb年代学和Hf同位素性质及其地质意义

川西冕宁-德昌稀土成矿带是中国最重要的稀土成矿带之一,所有稀土矿床均与碳酸岩-正长岩杂岩体有关.前人研究表明,牦牛坪、木落寨和里庄碳酸岩-碱性杂岩体成岩年龄与其相应矿床的成矿年龄基本一致,而大陆槽正长岩年龄与REE矿床的成矿年龄相差甚远.本文对大陆槽碳酸岩、英碱正长岩进行了SHRIMP U-Pb锆石年代学和LA-MC-ICPMS锆石Hf同位素原位测量,它们的形成年龄分别为12.99±0.94Ma、14.53±0.31Ma,表明两者是同时形成的,且与其成矿年龄基本一致.碳酸岩和正长岩的εHf(t)值、Hf模式年龄与它们的εNd(t)值、Nd模式年龄所展现出来的特征一致,说明在其形成过程中有地壳物质的加入.     

古大气CO2浓度重建方法技术研究现状

温室气候引起的全球气候变暖越来越引起人们的关注,大气中不断上升的CO2浓度被认为是导致气候变暖的主要因素.地史时期大气CO2浓度变化与温室气候可能存在类似的关系,可提供参考,因而古大气CO2浓度重建是首要任务.总结近年来古大气CO2浓度重建的进展,重点介绍GEOCARB模型模拟、植物叶片气孔参数和同位素指针的方法和技术.GEOCARB模型是反映全球古大气CO2浓度长期变化的碳相关模型;气孔参数方法是使用气孔比例来估计古大气CO2浓度;同位素指针包括成壤碳酸盐、浮游植物有机质生物标记物、钙质浮游有孔虫、古苔藓植物等,其中成壤碳酸盐碳同位素方法使用最为广泛.国内只是在叶片参数研究方面有一些进展,古大气CO2浓度重建工作任重而道远.     

Metasomatism and sulfide mobility in lithospheric mantle beneath eastern Australia: Implications for mantle Re–Os chronology

Spinel lherzolite xenoliths from Tertiary basaltic host magmas at Allyn River, eastern Australia reveal two distinct petrographic and geochemical types. One group is distinguished by xenoliths with undeformed, equilibrated microstructures and interstitial melt patches; The second group shows deformation and contains abundant fluid inclusions but no melt patches. Trace-element signatures of clinopyroxene in these xenoliths provide evidence for metasomatism by a silicate agent with hydrous component and by a carbonate-rich agent respectively.

Melt patches in the undeformed xenoliths contain secondary minerals including clinopyroxene, olivine, feldspar, Mg- and Ca-rich carbonate, apatite, ilmenite and spinel. They are interpreted to represent volatile-rich melt captured shortly prior to entrainment in the host basalt. Sulfide globules, now recrystallised to discrete sulfide phases but inferred to be molten at lithospheric mantle T and P, are closely associated with the melt patches. The close association between sulfide and highly mobile, volatile-bearing fluid has important implications for the mobility of Re and Os, the use of their isotopes in dating mantle events, and the possible effect of volatile-bearing metasomatic agents on their composition.     

Geochronological framework and Pb, Sr isotope geochemistry of the Qingchengzi Pb–Zn–Ag–Au orefield, Northeastern China

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.     

镭同位素示踪隆教湾的海底地下水排泄

福建省漳州市降教湾海水中镭同位素的研究,目的是评价海底地下水排泄量.在2007年6月的航次中,垂直于岸线的9 km剖面上布置15个站位,每个站位用潜水泵采集表层海水样60L于塑料桶中.水样运回实验室后,立即用装有锰纤维的PVC管以虹吸的方式富集水样中的镭同位素,水通过PVC管的流速小于300 ml/min.224Ra活度用连续射气法测定,测完224Ra后密封7d以上,然后用汽接射气法测定226Ra活度.224Ra和226Ra活度都呈现自岸向海逐渐降低的规律,表明扩散控制镭同位素的分布,由224Ra获得68.83 km2d-1的扩散系数,同时226Ra形成-0.963dpm1001-1km-1的活度梯度.用扩敞系数和活度梯度建立的226Ra的离岸通最为6.62×1011dpmkm-2d-1,这个通量一定是得到SGD输入的镭支持,从而获得隆教湾的海底地下水排泄量是3.03×109m3km-2d-1.该排泄量包括陆源地下淡水排泄量和再循环海水排泄量,绝大部分可能足再循环海水,有待进一步研究.     

Magma Origin and Evolution of Tengchong Cenozoic Volcanic Rocks from West Yunnan,China: Evidence from Whole Rock Geochemistry and Nd‐Sr‐Pb Isotopes

Tengchong Cenozoic volcanics that have record key information on the tectonic evolution and mantle features of the southeast margin of the Tibetan Plateau are of great importance because of its unique eruption history spanning the entire Quaternary period. Magma origin and evolution of Tengchong Cenozoic volcanic rocks were studied on the basis of Nd-Sr-Pb isotope and major and trace element data from different eruptions in the Ma’anshan area. Different samples within one eruption show relative identical lithologies, chemical and isotopic compositions. However, the geochemical features for the five eruptions are distinct from each other. These volcanic rocks show low Mg# values (<45), moderate to high fractionation of LREEs and HREEs, and enrichment of Pb and Ba and depletion of Nb. Tengchong Cenozoic volcanic rocks were derived from an enriched mantle based on Nd-Sr-Pb isotopic studies. And lines of evidence show that crustal contamination should be involved before the eruption of different periods of Tengchong Cenozoic volcanic rocks. Older subducted components may be responsible for adakite recycling at various stages of evolution, which results in the origin of the enriched mantle source magma accounting for the isotopic features of Tengchong Cenozoic volcanic rocks. Segregated primitive magma pulsating injected into magma chamber, fractional crystallized and contaminated with crust component. Finally, magmas with distinct chemical and isotopic compositions for each eruption formed. The extension of the northeast segment of the Yingjiang tectonic belt triggered the pulsating eruption of the Cenozoic volcanics in the Tengchong area.     

Identifying low-temperature hydrothermal karst and palaeowaters using stable isotopes: a case study from an alpine cave,Entrische Kirche,Austria

The area south of the prominent east–west trending Salzach Valley at the northern rim of the Central Alps of Austria has long been known to host anomalously warm springs emerging from a highly deformed calcite marble (Klammkalk). This unit also hosts cavities whose shapes suggest a hydrothermal karst origin and which are lined by calcite spar. We report here petrographic and isotopic evidence suggesting that dissolution by ascending low-temperature thermal waters also played an important role in the origin of a large cave in this region, Entrische Kirche. A paleo cave wall, preserved behind a thick flowstone in the interior of this cave, revealed a brownish bleaching zone which contrasts to the medium grey colour of the unaltered marble beneath. Across this zone the C and O isotope values gradually decrease by 3 and 11‰, respectively. These compositions are very different from those of the speleothem above but are similar to phreatic calcite spar from hydrothermal karst cavities in other outcrops in the area, where the absence of two-phase fluid inclusions suggests a low-temperature (less than ca. 50°C) hydrothermal origin. U/Th dating of the flowstone capping the alteration zone yielded a minimum age of the thermal water invasion in Entrische Kirche of ca. 240 kyr. There is no evidence in Entrische Kirche that these palaeowaters reached the point of calcite precipitation, but it is physically conceivable that higher and as yet unexplored parts of this deep (ca. 900 m) cave contain cavities lined by phreatic cave spar.     

上海黏土压缩回弹变形的微观机理

黏土变形微观机理的研究过去多针对土体加载压缩开展,随着研究的深入,黏土卸载回弹变形的微观机理也逐步得到重视,但目前对此研究还很少。本文采用单向压缩及回弹试验、扫描电镜及压汞试验对上海黏土压缩及回弹变形过程中土体的微观特性及其变化进行了研究。研究结果表明,微观结构参数的变化能反映黏土的宏观变形特征。在加载过程中,随固结压力增加,土体孔隙体积减小,孔隙数量先增加再减小,孔隙平均形状系数的增加先急后缓,孔隙形态分维数先急剧减小后缓慢减小。在卸载过程中,随固结压力减小,孔隙数量增加,平均形状系数略有减小,孔隙形状分维数略有增加。加载压缩过程中,固结压力较小时中、小孔隙体积所占比例变化不大,而当固结压力较大时小孔隙所占比例显著增加、中孔隙所占比例明显减小。在卸载回弹过程中,各级固结压力下小孔隙都占绝对优势,但固结压力较大时中孔隙所占比例较大,而固结压力较小时中孔隙所占比例较小,黏土卸载回弹变形主要是小孔隙体积的少量增加。     

准噶尔盆地吉木萨尔凹陷二叠系芦草沟组储层介—宏孔孔隙结构特征及控制因素

吉木萨尔芦草沟组页岩油资源潜力巨大,为探究其储层介—宏孔孔隙结构特征及控制因素,以研究区芦草沟组钻井岩心为对象,利用X射线衍射、铸体薄片、扫描电镜、孔渗测试、高压压汞、氮气吸附、分形理论、相关性分析等方法,对其储层特征、孔隙结构及控制因素进行了讨论。研究发现：1）研究区芦草沟组储层是一套以长英质碳酸盐岩（A岩）、长英质黏土岩（B岩）、灰/云质细粒长英沉积岩（C岩）、混积岩（D岩）为主的低孔—特低孔、特低渗储层,主要孔隙类型为溶孔,此外还发育有剩余粒间孔、晶间孔、微裂缝;2）研究区芦草沟组储层孔隙分布复杂,孔径分布曲线呈现多峰形,介孔提供了大部分孔容和比表面积;高压压汞计算的宏孔分形维数均值和氮气吸附计算的介孔分形维数均值分别为：2.864 7、2.507 5,介孔孔隙结构复杂程度相对较低;3）有机质丰度有利于A岩、B岩和C岩宏孔孔隙结构的发育,会导致C岩介孔和D岩孔容、比表面积减小;有机质演化程度对A岩介孔、B岩和C岩介孔起到建设作用,对C岩宏孔、D岩介—宏孔有破坏做用;4）脆性矿物含量越高C岩介孔和D岩孔容比表面积越大,而A岩、B岩宏孔、C岩宏孔孔容、比表面积减小;黏土矿物对A岩介孔、C岩介孔及D岩的孔隙系统发育起到建设作用,对B岩宏孔和C岩宏孔有破坏作用。孔隙结构的发育主要受有机质（有机质丰度、有机质演化程度）和矿物组份（脆性矿物含量、黏土矿物含量）的影响,不同岩性、不同尺度的孔隙发育影响因素各有差异。