西澳州Cattle Creek地区铜镍硫化物矿床成矿潜力探讨

西澳州Catlle Creek地区位于金伯利地块西缘霍尔斯克里克(Halls Creek)活动带上,附近发育有深大断裂。研究区内发现多处基性-超基性小岩体及岩脉且存在两处矿化点(带),存在两处1∶5万土壤地球化学甲类综合异常区,二者均主要由Cu、Ni、Au、Mo、Co等元素组成,多个浓集中心,异常套合较好,Cu、Ni的极大值均超过或接近边界品位,甚至工业品位,二者与矿化等信息套合良好。岩体中岩石样品主量元素特征显示其具有辉长岩-苏长岩的成矿专属性特征;在AFM图解上,岩石样品显示原始岩浆为高MgO拉斑玄武岩系列。微量元素原始地幔标准化蛛网图表明岩体岩浆演化过程中发生过明显的陆壳物质同化混染作用。稀土元素配分图反映出成岩过程中有相似的分异演化过程,并表明岩浆在演化过程中存在明显橄榄石分离结晶作用。研究区与萨凡纳矿床具有很高的可对比性,同时符合古大陆内小岩体成矿系统理论。表明研究区具较高的成矿潜力。     

全球二叠系顶部白云岩与沉积相关系统计及其白云石化机制的意义

本文对全球范围内23个典型的研究程度较高的晚长兴期露头进行了研究,逐一检查了晚长兴期白云岩前身沉积的沉积相,结果发现所有白云岩的前身都是浅水相的(除汉中梁山一个剖面外)。相反,目前已经研究的深水相上二叠统碳酸盐沉积物都没有发生白云岩化。这一结果表明,世界范围内上二叠统顶部白云岩的形成机制可能都与海平面下降有关,很可能是蒸发成因的浓缩卤水使沉积物发生白云岩化。据此推断,四川盆地东北部长兴组白云岩也应当是此种成因。     

藏北龙木错—双湖—澜沧江板块缝合带发现晚石炭世—早二叠世洋岛型岩石组合

天泉群岛出露于龙木错—双湖—澜沧江板块缝合带的中西段,也是目前该缝合带上所发现的第一套洋岛型岩石组合。通过野外踏勘、剖面测制等对天泉群岛进行了较为详细的研究,结果显示,天泉群岛由9个孤立、岩石组合不同的洋岛组成,其中独泉沟洋岛、屏风岭洋岛的洋岛组分齐全,见玄武岩、灰岩、砾岩、硅质岩等,其他洋岛的洋岛组分不全。天泉群岛与展金组复理石沉积为整合接触,表明其形成时代为晚石炭世—早二叠世。天泉群岛的厘定,说明龙木错—双湖—澜沧江大洋在晚石炭世—早二叠世仍具有成熟的洋壳。该项研究进一步丰富了龙木错—双湖—澜沧江板块缝合带的演化内容,为反演区域地质演化历史提供了依据。     

藏北羌塘中部日湾茶卡组物源——LA-ICP-MS锆石U-Pb年龄及稀土元素特征

在龙木错—双湖—澜沧江板块缝合带中段的冈玛错—日湾茶卡地区,近东西向展布着一条富含暖水型生物化石的早石炭世地层日湾茶卡组(C1r)。对日湾茶卡组砂岩中的碎屑锆石进行LA-ICP-MS U-Pb定年,分析结果显示存在325~400Ma、400~500Ma、500~600Ma、950~1100Ma、1400~1800Ma和大于1800Ma六个年龄区间;最年轻的碎屑锆石年龄为325 Ma,时代为早石炭世维宪期;碎屑锆石中362 Ma和454Ma的年龄峰值最明显,为龙木错—双湖—澜沧江洋岛弧消减事件和加里东运动的年龄记录,表明碎屑岩的物源区主要来自于扬子大陆周缘。结合古生物化石资料可知,日湾茶卡组属于欧亚大陆扬子型石炭纪沉积地层,为岛弧环境下的一套浅水台型沉积。     

藏北羌塘中部日湾茶卡地区花岗闪长岩LA-ICP-MS锆石U-Pb年龄与地球化学特征

报道了藏北羌塘中部日湾茶卡地区花岗闪长岩体锆石U-Pb年龄和岩石地球化学特征。该花岗闪长岩位于龙木错—双湖—澜沧江板块缝合带西段。岩石样品中的锆石具有较好的晶形,可见典型的岩浆振荡环带结构,具有较高的Th/U值,为典型的岩浆成因锆石。样品锆石LA-ICP-MS技术测得的锆石年龄为211.0Ma±1.8Ma,表明其时代为晚三叠世。全岩地球化学分析表明,该花岗闪长岩具有高Si O2、Al2O3,富碱,低TFe2O3、Ti O2的特征,A/CNK值为0.97~1.04,为准铝质—弱过铝质岩石。稀土元素配分模式显示,配分曲线右倾,伴随较弱的Eu负异常;微量元素蛛网图表现出Nb、Ta、Ti、P亏损和Rb、Th、U、K、Pb富集的特征;样品点在构造环境判别图解上均落入碰撞型花岗岩区。初步分析,其岩浆来源可能为幔源岩浆底侵使古老地壳发生熔融。此碰撞型花岗闪长岩对龙木错—双湖—澜沧江洋碰撞的时限提供了一定的岩石学约束,为龙木错—双湖—澜沧江洋的演化提供了基础地质资料。     

鄂尔多斯盆地延川南区块目的煤层含气性分析

为计算鄂尔多斯盆地延川南区块煤层气资源量、甄选有利区带及确定先导性试验井组的部署,对全区探井的煤层含气性进行综合分析。结果显示:区块内煤层气含量为5.54~19.56m3/t;兰氏体积为13.59~33.78m3/t,兰氏压力为2.06~3.72MPa,含气饱和度为41.48%~92.19%;临储压力比为19.18%~84.28%。区块整体含气性显示较好,开发较为有利,其中以包括Y3、Y6等井在内的万宝山构造带为煤层气开发的最有利区带。     

黔西地区构造变形特征及其煤层气地质意义

黔西地区处于特提斯与滨太平洋两个构造域的交接地带,多期性质不同的构造作用形成了现今错综复杂的构造变形特征。根据构造变形的差异,可划分为织金-纳雍NE向构造变形区、水城-紫云NW向构造变形区和黔西南复杂构造变形区。在野外地质的基础上,结合微观变形特征和矿物流体包裹体测试分析,认为黔西地区构造变形属于上地壳低温-中低温环境下的脆性-脆韧性变形;由于黔西地区基底构造相对稳定,成煤期后断块内部变形较弱,煤储层形成了一定程度的构造裂隙,有助于渗透率的提高,煤层气勘探开发前景良好。     

Experimental study of poromechanical behavior of saturated claystone under triaxial compression

This paper presents experimental results of drained and undrained triaxial compression tests of saturated Meuse–Haute/Marne claystone. The emphasis is to study the evolution of pore pressure with growth of microcracks and the effect of pore pressure on mechanical behavior. Basic mechanical responses are first investigated through drained triaxial compression tests, showing nonlinear stress strain relations, volumetric dilatancy and pressure sensitivity. In undrained triaxial compression tests, the pore pressure exhibits a transition from increase to decrease due to the transition from volumetric compressibility to dilatancy caused by the growth of microcracks. The failure surfaces, determined by total stress and Terzaghi’s effective stress under undrained condition, are compared with the one under drained condition.     

Spatial heterogeneity of cyanobacteria-inoculated sand dunes significantly influences artificial biological soil crusts in the Hopq Desert (China)

Artificial biological soil crusts (ABSCs), formed by inoculating Microcoleus vaginatus Gom. and Scytonema javanicum Born. et Flah. onto the topsoil of desert dunes, proved to be effective tools for the stabilization of moving dunes and promotion of soil fertility. As dominant driving forces in arid habitats, the abiotic environmental conditions of undulating dunes produce a gradient of abiotic stresses on cyanobacteria. Cyanobacteria are considered pioneering phototrophs in early soil crust communities in deserts. In this study, the development of ABSCs under various environmental site conditions was investigated using 16S rRNA-based polymerase chain reaction, denaturing gradient gel electrophoresis (DGGE), and soil property measurements. After inoculation in 2002 and long-term development, patchy moss crusts were observed on the dunes. All of the available sequenced bands in the DGGE gels belonged to Oscillatoriales and Nostocales. The dominant Nostocales genus in the ABSCs was still Scytonema; however, more Oscillatoriales genera were identified, which belonged to Microcoleus and Phormidium. The cyanobacterial compositions of different slope types were significantly distinct (p < 0.05), particularly those from windward slopes. The crusts of the top-dune slopes were more heterogeneous. In addition, the soil physicochemical properties and richness indices of the windward slopes were significantly lower than those of the leeward and interdune slopes (p < 0.05). Compared with uninoculated control dunes, all of the inoculated dunes had far higher biodiversities.     

Variation of albedo to soil moisture for sand dunes and biological soil crusts in arid desert ecosystems

Surface albedo plays a crucial role in the energy balance of soils. The surface albedo and surface soil moisture of bare sand and biological soil crusts (BSCs) were concurrently observed on field plots of shifting sand dune and in revegetated desert ecosystems at Shapotou, northwestern China, to study relationships between surface albedo, solar elevation angle, and surface soil moisture. Results indicated that rainfall exerted a remarkable lowering effect on the variation of surface albedo by increasing surface soil moisture. Surface albedo was an exponential function of solar elevation angle, and the normalized surface albedo (solar elevation angle effect was removed) decreased exponentially with the increase of surface soil moisture. Sand surface had a higher albedo (0.266) than BSCs (0.226) when the surfaces were very dry. However, sand surface albedo became increasingly lower than that of BSCs when the surfaces were in wet conditions and when the soil moisture exceeded a critical value. The changes in soil surface albedo from sand dune to BSCs after revegetation in shallow soil profiles associated with the variation of the surface soil moisture can be seen as an indicator of the degree of sand dune stabilization when compared with the original shifting sand dune soil.