Geochemical and Petrological Studies on the Early Carboniferous Sidingheishan Mafic–Ultramafic Iintrusion in the Southern Margin of the Central Asian Orogenic Belt, NW China

The Sidingheishan mafic-ultramafic intrusion is located in the eastern part of the Northern Tianshan Mountain, along the southern margin of the Central Asian Orogenic Belt in northern Xinjiang autonomous region of China. The Sidingheishan intrusion is mainly composed of wehrlite, olivine websterite, olivine gabbro, gabbro and hornblende gabbro. At least two pulses of magma were involved in the formation of the intrusion. The first pulse of magma produced an olivine-free unit and the second pulse produced an olivine-bearing unit. The magmas intruded the Devonian granites and granodiorites.An age of 351.4±5.8 Ma(Early Carboniferous) for the Sidingheishan intrusion has been determined by U-Pb SHRIMP analysis of zircon grains separated from the olivine gabbro unit. A U-Pb age of 359.2±6.4 Ma from the gabbro unit has been obtained by LA-ICP-MS. Olivine of the Sidingheishan intrusion reaches 82.52 mole% Fo and 1414 ppm Ni. On the basis of olivine-liquid equilibria, it has been calculated that the MgO and FeO included in the parental magma of a wehrlite sample were approximately10.43 wt% and 13.14 wt%, respectively. The Sidingheishan intrusive rocks are characterized by moderate enrichments in Th and Sm, slight enrichments in light REE, and depletions in Nb, Ta, Zr and Hf. The ε_(Nd)(t) values in the rock units vary from +6.70 to +9.64, and initial ~(87)Sr/~(86)Sr ratios range between 0.7035 and0.7042. Initial ~(206)Pb/~(204)Pb, ~(207)Pb/~(204)Pb and ~(208)Pb/~(204)Pb values fall in the ranges of 17.23-17.91,15.45-15.54 and 37.54-38.09 respectively. These characteristics are collectively similar to the Heishan intrusion and the Early Carboniferous subduction related volcanic rocks in the Santanghu Basin, North Tianshan and Beishan area. The low(La/Gd)_(PM) values between 0.26 and 1.77 indicate that the magma of the Sidingheishan intrusion was most likely derived from a depleted spinel-peridotite mantle.(Th/Nb)_(PM)ratios from 0.59 to 20.25 indicate contamination of the parental magma in the upper crust.Crystallization modeling methods suggest that the parental magma of the Sidingheishan intrusion was generated by flush melting of the asthenosphere and subsequently there was about 10 vol%contamination from a granitic melt. This was followed by about 5 vol% assimilation of upper crustal rocks. Thus, the high-Mg basaltic parental magma of Sidingheishan intrusion is interpreted to have formed from partial melting of the asthenosphere during the break-off of a subducted slab.     

Comparative Study of Hydrogen and Carbon Isotopic Composition of Gases Generated from the Pyrolysis of a Peat under Saltwater and Freshwater Conditions

To understand the influence of the diagenetic water medium on the isotopic compositions of thermogenic coalbed gas, both hydrous and anhydrous closed-system pyrolyses were performed at temperatures of 250°C to 650°C on an herbaceous marsh peat. Compared to the results of anhydrous pyrolysis, the hydrocarbon gases generated from hydrous pyrolyses have very different hydrogen isotopic compositions. However, the carbon isotopic compositions of the hydrocarbon gases became only slightly heavier in hydrous pyrolysis, compared to that from anhydrous pyrolysis. With the progress of thermal evolution from peat to a more advanced thermal maturity of vitrinite reflectance values (Ro) of 5.5% during the pyrolysis, the difference in the average δD value increased from 52‰ to 64‰ between the hydrous pyrolysis with saltwater and anhydrous pyrolysis and increased from 18‰ to 29‰ between the hydrous pyrolysis with freshwater and anhydrous pyrolysis, respectively. The difference in the average δ13C value was only 1‰–2‰ between the hydrous and anhydrous pyrolysis. The relationships between the δD values of the generated hydrocarbon gases and Ro values as well as among δD values of the hydrocarbon gas species are established. The close relationships among these parameters suggest that the water medium had a significant effect on the hydrogen isotopic composition and a minimal effect on the carbon isotopic composition of the hydrocarbon gases. The results of these pyrolyses may provide information for the understanding of the genesis of coalbed gas from herbaceous marsh material with the participation of different diagenetic water media.     

南海南部陆缘地质流体类型及其油气成藏意义

南海南部陆缘蕴藏着非常丰富的油气资源。为了解南海南部陆缘流体活动系统以及与油气藏之间的关系,以高精度2D地震资料为基础,对南海南部陆缘流体活动系统的类型、地震反射特征、以及对油气成藏的意义开展了研究。在南海南部陆缘发现了多种流体活动系统,包括:泥底辟/泥火山、气烟囱、管状通道、与构造断层相关的流体活动系统。这些流体活动系统具有不同的地震反射特征,常常出现含气强振幅异常带、弱振幅杂乱反射带以及"下拉"或者"上拱"地震反射形态等流体活动系统的标志特征。流体活动系统受到构造运动和沉积因素的影响,并且与深部高温高压塑性流体密切相关,流体活动系统优先发育在地层薄弱部位。流体活动系统及所伴生的断裂和裂隙常常作为油气富集区的运输通道;并且流体活动系统所运移的强溶蚀性流体和深部热液流体有利于油气储层的形成,特别是对于碳酸盐岩储层的改造尤为明显。因此,流体活动系统不仅能作为油气运移通道,也可以改善储层,对油气成藏具有重要意义。     

基于振动台实验的典型滑坡单元体震动滑移特征发现

针对典型滑坡滑动单元在地震过程中的滑移特征,制作了典型振动台物理模型,通过输入不同频率、峰值和持时的正弦地震波,开展了一系列的实验研究工作,得了一些比较有意义的新成果:（1）在输入地震波强度足够大时会出现瞬时沿滑带向上的滑移行为,存在向上和向下两个滑移屈服加速度;（2）在研究分析中,不可以坡底输入的地震加速度值而应以滑带处局部加速度值作为判别滑移与否和滑移量大小的计算数据;（3）滑体沿滑带产生的永久滑移总量随地震波持时增加呈阶梯波状增长;（4）不同时刻任一周期的振动滑移特征相对独立,且每一地震波周期时间内具有几乎相同的周期性滑移特征,总体滑移量是无数周期内滑移量的累加;（5）在每一地震波周期时间内,滑体向上和向下的滑移特征受控于相应向上和向下屈服加速度,其向上和向下滑移矢量和构成每一周期时间内的永久位移。     

大兴安岭呼中钼多金属矿床成矿流体特征及成矿机制

大兴安岭呼中镇钼多金属矿床产于早白垩世碎裂花岗岩中,矿体形态似层状、脉状或透镜状。成矿阶段分为辉钼矿阶段、铜铅锌阶段、方解石阶段等3个阶段。本矿床中的包裹体主要有气液H_2O包裹体、气相H_2O包裹体、含子矿物H_2O包裹体,CO_2包裹体、CO_2-H_2O包裹体等五大类。辉钼矿阶段均一温度为209.2℃413.4℃,盐度ω(NaCleq)为0.53%16.53%,平均值7.3%,属中低盐度,成矿压力在53.3 68.5 MPa,相应的成矿深度为2 052 2 807 m;铜铅锌阶段为191.5℃351.0℃,盐度ω(NaCleq)为0.88%34.24%,平均值3.96%,属低盐度;方解石阶段207.2℃233.5℃,盐度ω(NaCleq)为3.55%4.18%,平均值3.77%,为低盐度。从辉钼矿阶段到铜铅锌阶段再到方解石阶段,温度及盐度逐渐降低。辉钼矿成矿压力在53.3 72.9 MPa,成矿深度为2 052 2 807 m。成矿过程中发生了CO_2-H_2O不混溶作用,这是导致辉钼矿沉淀的主要机制。矿床类型属中低温浅成热液型矿床。     

从成岩-蚀变特征探讨塔深1井白云岩储层成因

塔深1井钻遇的寒武系地层属于中寒武统阿瓦塔格组和上寒武统丘里塔格下亚群。阿瓦塔格组以灰色-深灰色粉晶-细晶藻白云岩为主,丘里塔格下亚群以灰色-浅灰色晶粒结构白云岩与残余亮晶结构白云岩为主。藻白云岩在阴极发光下以明亮的中等强度砖红色-桔黄色为主要特点,具有相对偏重的δ18O值(-6.3‰~-4.5‰,平均为-5.3‰,VPDB)、相对较高的稀土总量以及与正常海相碳酸盐岩相似的稀土配分样式。晶粒白云岩与残余亮晶结构白云岩在阴极发光下以偏暗的中等强度蓝紫色-砖红色为主要特点,具有相对偏轻的δ18O值(-9.2‰~-5.7‰,平均为-7.5‰,VPDB)、相对偏低的稀土总量、Eu正异常与重稀土明显亏损为特点的稀土配分模式。阿瓦塔格组和丘里塔格下亚群白云岩在上述岩石学特征和地球化学特征上的差异表明储层发育的成岩-蚀变过程存在差异。研究认为,埋藏较深的阿瓦塔格组优质储层的形成受多种因素控制,其中准同生期大气淡水作用下石膏结核的溶解及非稳定碳酸盐矿物的溶解奠定了基础,后期成岩改造及流体作用进行了强化,局部遭充填破坏。     

内蒙古1∶5万乌音呼日勒庙等四幅区域地质矿产调查新进展

内蒙古1∶5万乌音呼日勒庙等四幅区域地质矿产调查项目取得的新进展及主要成果为: 根据岩石组合、动植物化石及同位素年龄等,重新厘定、划分了16个岩石地层填图单位,在多个组段沉积岩层位中首次发现丰富的动、植物化石,建立了各地层年代学格架; 将侵入岩重新解体划分为4个填图单元,并建立了侵入岩年代学格架; 新发现1处规模较大的韧性变形带,主要为逆—左行走滑韧性断层,时代归属于中三叠世末期,为额尔古纳河—阿龙山NE向韧性变形域的南部延伸; 新发现矿(化)点20处,其中金属矿点3处,金属矿化点6处,非金属矿点9处,非金属矿化点2处; 总结了该区成矿规律,圈定了成矿远景区及找矿靶区。     

大兴安岭北段扎兰屯地区晚古生代早期花岗质岩浆作用——对额尔古纳 兴安地块和松嫩地块拼合时限的制约

扎兰屯地区位于二连 贺根山 黑河构造带中段,区内发育韧性变形叠加的晚古生代早期花岗岩类。本文在详尽的野外地质调查基础上,对该套花岗岩类的锆石U- Pb年代学和地球化学进行系统分析,研究其成岩年代序列,探讨岩石成因及构造背景,厘定韧性构造叠加的时限,进一步揭示扎兰屯地区额尔古纳 兴安地块和松嫩地块的拼合过程,为兴蒙造山带的区域构造演化研究提供新材料。大量年代学研究显示,扎兰屯地区晚古生代早期花岗质岩浆作用发生于405~325Ma之间,该作用可进一步细化为早中泥盆世(Ⅰ期、405~380Ma)、晚泥盆世—早石炭世初(Ⅱ期、365~350Ma)和早石炭世晚期(Ⅲ期335~325Ma)等3期。其中Ⅰ期和Ⅱ期花岗岩类属高钾—钾玄质钙碱性、准铝质—弱过铝质花岗岩类,可能为俯冲背景下岛弧岩浆活动形成的I型 分异I型花岗岩;Ⅲ期花岗岩类属中—高钾钙碱性、准铝质—弱过铝质花岗岩类,可能为后碰撞背景下岩浆活动形成的分异I型- A型花岗岩。该套花岗岩类普遍叠加韧性变形,可能为碰撞后侧向逃逸作用的产物,变形时限为晚石炭世末—早二叠世(308~290Ma)。大兴安岭北段晚古生代早期花岗质岩浆作用与额尔古纳 兴安地块和松嫩地块的碰撞拼合作用有关,扎兰屯地区二者的碰撞拼合时限可能为早石炭世中期。     

黔东松桃地区燕山期构造特征研究——以高地超大型锰矿床为例

黔东松桃地区构造格局主要是受到燕山运动影响形成。燕山早期,区内处于SEE—NWW向区域挤压收缩,形成了NNE—SSW向褶皱和断裂。下寒武统杷榔组—变马冲组地层和南华系下统大塘坡组地层作为两套滑脱层,在构造变形过程中起到滑脱作用,滑脱层内褶皱变形强烈,以大量紧闭、顶厚不协调褶皱为主要构造样式,而其上、下岩层则以断块或宽缓褶皱变形为主,以软弱层为界面,其上、下岩层发生逆冲滑脱作用,形成了区内隔槽式褶皱的构造样式。燕山晚期,区内处于NNE—SSW挤压为主,形成了区内NWW向小型褶皱和断裂,同时燕山晚期构造横跨叠加在早期变形之上,导致早期NNE向褶皱枢纽呈波状起伏,轴迹弯曲,部分地区形成了构造穹窿和构造盆地,部分早期断层呈左行走滑性质。在燕山早、晚两期构造作用下,高地矿区含锰岩系作为软弱滑脱层,向猴子坳向斜的核部进行滑脱聚集,使其在向斜的核部富集,翼部相对减薄。同时,由于犁式正断层的存在,也影响了锰矿层的保存与破坏。     

Water system characteristics of Karst river basins in South China and their driving mechanisms of hydrological drought

Natural Hazards - It is common knowledge that drought is considered one of the most damaging natural disasters in terms of economic costs, societal problems, and ecological impacts. In this study,...