西藏南拉萨地块西部鸭洼地区侵入岩的锆石年代学和Hf同位素特征

拉萨地块南缘发育了广泛的中、新生代岩浆作用,然而与中、东部地区相比,南拉萨地块西部地区的研究程度还相对偏低,尤其是缺乏中生代以前岩浆活动的发现和研究。本文对南拉萨地块西部鸭洼地区新发现的中、新生代侵入岩开展了详细的锆石U-Pb定年和Hf同位素研究,发现鸭洼地区发育了晚三叠世(210～208Ma)辉长岩和闪长玢岩、晚侏罗世(约155Ma)似斑状二长花岗岩和始新世(约50Ma)花岗斑岩。晚三叠世辉长岩和闪长玢岩具有相对亏损的锆石Hf同位素组成,ε_(Hf)(t)值分别是+1.9～+6.2和-3.0～+7.4。晚侏罗世似斑状二长花岗岩和始新世花岗斑岩则具有明显富集的锆石Hf同位素组成,其ε_(Hf)(t)值分别是-10.0～-5.2和-7.9～-2.7,对应的地壳模式年龄分别是1534～1836Ma和1297～1624Ma,分别反映了古元古代和中元古代古老陆壳物质为主的再循环作用。结合区域文献数据,鸭洼-打加错地区中生代以来由于新特提斯洋的俯冲而发生了明显的地壳增生作用,新生地壳的生长从中生代到新生代早期逐渐进行,并且具有从陆内向海沟逐渐增加的趋势。     

西藏拉萨地块东部尼木—加查地区林子宗群火山岩年代学、地球化学特征及其构造意义

拉萨地块广泛分布中—新生代岩浆活动,研究其对于认识新特提斯洋的演化和理解整个青藏高原的形成过程有着重要意义。对拉萨地块东部尼木—加查地区比马组火山岩进行了年代学与元素地球化学研究,结果显示该比马组火山岩LA-ICP-MS锆石U-Pb年龄为55.2~57.6 Ma,明显晚于已发表的比马组火山岩年龄177~195 Ma,而与林子宗群火山岩年龄(30.4~70.0 Ma)相符。因此,该地区原来认为的比马组火山岩可能需要重新厘定为林子宗群年波组火山岩。研究区火山岩主体为玄武岩、玄武安山岩、安山岩和英安岩,属中、高钾钙碱性系列。地球化学特征显示火山岩整体上富集大离子亲石元素Rb、Th、U等,Nb、Ta、Zr、Ti等高场强元素则表现明显的负异常,具有典型的岛弧火山岩特征。稀土元素配分模式主要表现为轻稀土元素右倾型,Eu表现出无异常到中等的负异常。此外,研究区年波组火山岩年龄晚于拉萨地块中西部年波组形成时代,结合前人的研究成果,可能指示印度与亚洲大陆的碰撞具有西早东晚的特点。     

Microbial Geochemical Characteristics of the Coalbed Methane in the Shizhuangnan Block of Qinshui Basin,North China and their Geological Implications

Methanogens and sulfate reducing bacteria were detected by the 16SrRNA sequencing of coalbed methane(CBM)co-produced water in the south of the Qinshui Basin,which is indicative of the presence of secondary biological gas in the south of this basin,in contradiction to the previous understanding of thermogenic gas.This work systematically collected water samples from the CBM wells in the Shizhuangnan Block and analyzed the microbial geochemical characteristics from the aspects of water ions,hydrogen and oxygen isotopes,dissolved inorganic carbon and microbial diversity.It is shown that the Shizhuangnan Block has a nearly SN-trending monoclinic structure,and the elevation of coal seam decreases gradually from the east to west.Because of the water blocking effect of Sitou fault in the west,the precipitation flowed from the east to west,and gradually transited to stagnant flow area.The concentration variation of some ions such as Na~+,K~+,Ca~(2+),Mg~(2+),Cl~-,HCO~-_3 and total dissolved solids(TDS)suggest the variation of redox condition in the coal reservoir water.The 16SrDNA sequencing analysis of the collected water samples detected the presence of methanogens and sulfate reduction bacteria.The presence of methane production zone and sulfate methane transition zone(SMTZ)was identified.The effect of methanogens in the methane production zone leads to an increase in the methane concentration,resulting in a high gas content in the study area.In the SMTZ,most methane is consumed by anaerobic oxidation due to high sulfate concentrations.     

多场耦合作用下致密储层地应力场变化规律研究 ——以准噶尔盆地某区为例

地应力是储层改造方案设计、提高油气勘探开发效率的重要指标。致密储层所处环境复杂,需要综合考虑温度-应力-渗流多场耦合作用的影响。为此,以准噶尔盆地中部4区块某三维区致密储层为例,基于COMSOL Multiphyics软件,建立了温度-应力-渗流耦合控制方程,研究了多场耦合作用下研究区致密储层地应力场的变化规律。研究结果表明:研究区最大水平主应力范围在113~134 MPa之间,最小水平主应力范围在106~124 MPa之间,均表现为压应力;在油气开采过程中,最大水平主应力先增大后趋于稳定,随着油气开采的深入,应力变化范围逐渐由井口周围向附近断层延展,并且优先沿着断层的开裂方向发展;在断层的破碎过渡区应力值最小,断层核部应力值介于破碎过渡区与连续地层之间;随着油气开采的深入,致密储层会发生竖向变形,储层最大竖向变形出现在井口附近,位移量超过10 cm,随着距离变远,沉降量不断减小。      

华北地块北缘泥盆纪岩浆活动及其构造背景

晚古生代—早中生代岩浆岩广泛分布在华北地块北缘,构成了沿华北地块北缘呈近东—西向分布的上千公里的岩浆岩带。泥盆纪岩浆岩作为其中的组成部分,虽然分布范围不及石炭—二叠纪岩浆岩广泛,但近十多年来随着研究工作的深入,越来越多的泥盆纪岩浆岩被发现,其构造背景及意义也逐渐引起重视。对华北地块北缘近年来发现的泥盆纪岩浆活动进行总结分析表明,泥盆纪岩浆活动时限在400~360 Ma左右,其中碱性侵入岩和基性—超基性侵入岩时代主要集中在400~380 Ma之间,沿华北地块北缘自东向西均有分布;火山岩则主要集中在400 Ma和360 Ma,主要分布在华北北缘东段的赤峰地区。泥盆纪侵入岩在岩石组合上以碱性杂岩及碱性花岗岩为主,其次为二长闪长岩、基性—超基性杂岩。泥盆纪火山岩则以变质流纹质火山岩—次火山岩—火山碎屑岩及变质玄武安山岩、玄武岩（斜长角闪岩）为主,总体上具有双峰式岩石组合特征。综合研究该地区构造演化历史及泥盆纪岩石组合、弱构造变形特征、岩石地球化学与同位素地球化学组成等,认为泥盆纪岩浆活动的形成与白乃庙岛弧和华北地块在晚志留世发生弧—陆碰撞后的伸展背景有关。华北北缘泥盆纪岩浆岩带的形成对于认识古生代期间地壳增生过程、方式及古亚洲洋最终闭合时间有重要科学意义。      

Attribution of the Langshan Tectonic Belt: Evidence from zircon U-Pb ages and Hf isotope compositions

This study describes a previously unidentified Neoproterozoic mafic dyke emplaced in the northern flank of the Langshan Tectonic Belt. This dyke intruded into the micaquartz schist of the Zhaertaishan Group, and yielded an age of 908 ± 8 Ma. The youngest U-Pb ages of micaquartz schist from the Zhaertaishan Group in the Langshan area were 1118 ± 33 Ma,1187 ± 3 Ma and 1189 ± 39 Ma,suggesting that the depositional age of the protolith of the schist was between 908 ± 8 Ma and 1118 ± 33 Ma. In addition, 436 U-Pb age data and 155 Lu-Hf isotopic data from six samples in the Langshan Tectonic Belt and one Permian greywacke from the Wuhai area show distinct differences between the northern and southern flanks of the Main Langshan area. The U-Pb ages of the northern flank are primarily Meso-Neoproterozoic; similar ages have not been identified in the southern flank to date.Moreover, two-stage Hf model ages of the northern flank feature three age peaks at ～900 Ma,～1700 Ma and ～2600 Ma; this differs from Hf model ages of the southern flank, which feature one strong age peak at ～2700 Ma. These results suggest that the northern and southern flanks of the Main Langshan area have different geochronologic characteristics and should be divided further. Based on the U-Pb ages and Hf model ages, the northern and southern flanks of the Main Langshan area are named the North and South Langshan Tectonic Belts. Comparison of the U-Pb age and two-stage Hf model age distributions from the North Langshan Tectonic Belt, South Langshan Tectonic Belt, Alxa Block and the North China Craton(NCC) reveal that the North Langshan Tectonic Belt is similar to the Alxa Block and that the South Langshan Tectonic Belt is similar to the NCC. In addition, the zircon U-Pb age of 860 ±7 Ma commonly observed in the Alxa Block was detected in the Permian greywacke from the Wuhai area of the NCC, which suggests that the amalgamation of the North and South Langshan Tectonic belts(i.e.,the amalgamation of the Alxa Block and the NCC), occurred between Devonian and late Permian.     

Volcanogenic Cu–Pb–Zn bodies in granulites of the central Arunta Block, central Australia

Abstract Small unexploited copper-lead-zinc deposits, characterized by a distinctive wall-rock association of cordierite quartzite, silica-undersaturated rocks, calc-silicate rocks and impure marbles, occur in quartzofeldspathic gneisses and mafic granulites of the Strangways Metamorphic Complex, central Arunta Block, central Australia. Available data support the hypothesis that these are metamorphosed volcanogenic ore bodies. The chemical compositions of the quartzofeldspathic gneisses are comparable with those of less metamorphosed felsic igneous rocks, particularly the felsic igneous rocks emplaced in the North Australian Orogenic Province in the interval 1880–1800 Ma; and the mafic granulites are chemically similar to basalts (olivine-normative tholeiites). The wall-rock suite can be correlated from chemistry and lithological association with the suites of wall rocks found in unmetamorphosed volcanogenic ore deposits. That the protolith of the cordierite quartzites may well have been leached tuff, similar to the illite-chlorite-quartz tuff found in volcanogenic ore deposits, is also shown by retrogression of the granulitefacies assemblage: cordierite-garnet-ortho-pyroxene-biotite-quartz in the cordierite quartzites to cordierite-anthophyllite-bearing assemblages and thence to chlorite-muscovite-quartz assemblages. Lenses of silica-undersaturated rocks with spinel and, less commonly, sapphirine are interpreted as the metamorphosed equivalents of chlorite-rich pods found within leached tuffs in volcanogenic ore deposits. The wall rocks form sheet-like bodies; this suggests that they were deposited in relatively shallow water, thus precluding the formation of massive sulphides.     

与花岗岩有关的绿岩带再生型金矿床特征——以华北陆块北缘中段为例

华北陆块北缘中段广泛分布太古宙绿岩带 ,同时也是我国中生代岩浆活动最发育的地区。中生代强烈的陆内造山运动 ,对区内早期的绿岩带和其中的金及金矿床进行强烈的活化改造 ,形成壳源深熔花岗岩和有关的再生型金矿床。文中详细论述了区内与壳源深熔花岗岩有关的绿岩带再生型金矿床的地质特征 ,花岗岩和金矿床与太古宙绿岩带密切的空间分布和成因关系 ,并讨论了金矿的成矿模式。与成矿有关的花岗岩是造山带的产物 ,岩石富碱质、属钙碱性系列 ,形成深度较浅 ,塑性流变弱 ,常具似斑状结构 ,岩体常为多期次侵入 ,岩性多样 ,分异好 ,岩脉发育。硫、铅同位素组成显示花岗岩、金矿床和绿岩带具有亲缘关系。成矿流体富氯和富硫 ,盐度变化较大。金矿床形成在燕山早、中期。     

华北克拉通对前寒武纪超大陆旋回的基本制约

全球大陆克拉通在前寒武纪至少记录了3次超大陆聚合－裂解的构造旋回。不同大陆前寒武纪地质的研究证明，板块的构造模式可以前推至新太古代。超大陆的聚合表现为大规模造山带的穿时性发育，而裂解则表现为大陆裂谷系、非造山花岗岩及巨型基性岩浆岩省的同期快速发育。广泛的区域地质研究揭示华北克拉通前寒武纪地质构造演化具有明显的阶段性差异特征，克拉通主体形成于新太古代陆壳增生与碰撞造山过程。华北克拉通在太古宙末期首次经历强烈的裂解作用，在古元古代晚期涉及强烈的陆缘再造作用。在古元古代末期发生第二次大规模的裂解活动，随后以中元古代末期的造山带拼合为Rodinia超大陆的组成部分。详细的区域构造对比证明，华北克拉通长期以来与波罗的地质、东南极克拉通、印度南部克拉通、巴西克拉通等具有构造亲缘关系。     

Precursors Revealed by the Multifractal Dimension Around Ordos Block,North China

Seismicity around the Ordos Block in the northern part of China has been studied by the multifractal dimensions with the help of complete data set of earthquakes with M≥2.5 since 1977.Seven regions around this block have been examined whiere the eight large earthquakes with M≥6.0 for the complete data occurred.In oirder to display the temporal distribution of the correlation dimension D2,a moving window of fixed number of events is used in every of the seven regions.Except for two regions with less seismic activity,all other five regions have obviously been found to display sudden changes of the correlation dimension for the events with M≥4.5.