Nature and Evolution of Pre-Neoproterozoic Continental Crust in South China: A Review and Tectonic Implications

South China as an amalgamation of the Yangtze and Cathaysia blocks is composed of Archean to Mesoproterozoic basement overlain by Neoproterozoic and younger cover. Both the constituent Yangtze and Cathaysia blocks contain well-preserved Neoproterozoic rocks that have been extensively studied in terms of the age and tectonic nature, but less is known about their earlier crustal history due to the incomplete rock record. Recent efforts in investigating the yet survived crustal nature based on isotopic and elemental signatures preserved in igneous and sedimentary rocks have steadily improved our knowledge about the pre-Neoproterozoic continental crustal evolution in South China. In this paper, we summarize the up-to-date pre-Neoproterozoic records, including petrological, geochronological, geochemical and geophysical data, across South China, and discuss its spatiotemporal patterns of the pre-Neoproterozoic crust and the relevant tectonic events. While the xenocrystic/inherited and detrital zircon records suggest widespread Archean (mainly ca. 2.5 Ga) crustal components within both the Yangtze and Cathaysia blocks, exposed Archean rocks are only limited to isolated crustal provinces in the Yangtze Block. These Archean rocks are dominated by TTGs (tonalite-trondhjemite-granodiorite) with varied ages (3.3–2.5 Ga) and zircon Hf isotopes, indicating a compositionally heterogeneous nature of the Archean Yangtze Block and, by inference, the development of multiple ancient terranes. The early Paleoproterozoic (2.4–2.2 Ga) tectonomagmatic events characterize the western Yangtze Block and are supportive of an east-west subdivision of the Yangtze basement, whereas the late Paleoproterozoic (2.1–1.7 Ga) orogeneses may have affected a larger area covering both the western and eastern parts of the Yangtze Block, and also the Cathaysia Block. The eastern Yangtze Block with generally northeastward-younging late Paleoproterozoic magmatism and metamorphism likely experienced a prolonged 2.05–1.75 Ga orogenic process welding the various Archean proto-continents, consistent with the documentation of a buried late Paleoproterozoic orogenic belt imaged by deep seismic profiling from its central part and of a slightly older ophiolitic mélange in the northern part. The Cathaysia Block was probably involved in a short-lived 1.9–1.8 Ga orogenic event. The two orogeneses overlapped in time and may have contributed to the cratonization of a possible unified South China, and are referred to be linked with the assembly of the Nuna Supercontinent. The subsequent late Paleoproterozoic to early Mesoproterozoic rift successions and intrusions (1.7–1.5 Ga) in the southwestern Yangtze Block, and the ca. 1.43 Ga rifting in Hainan Island of the Cathaysia Block could be responses to the Nuna break-up. Late Mesoproterozoic (1.2–1.0 Ga) magmatism of varied age and nature in different localities of the Yangtze Block is reflective of a complex tectonic process in the context of the assembly of the Rodinia Supercontinent. Similar-aged metamorphism (1.3–1.0 Ga) is recorded in Hainan Island, reflecting the Grenvillian continental collision during the Rodinia assembly, but further studies are necessary to better constrain the late Mesoproterozoic tectonic framework of South China.     

西藏樟木口岸震后滑坡灾害变形InSAR监测分析

位于中国和尼泊尔边境的西藏樟木口岸是国家一类陆路通商口岸,也是西藏最大的边贸中心口岸。2015年尼泊尔大地震之后,西藏樟木口岸因多次发生滑坡灾害,而导致口岸关闭。为了调查樟木口岸区域滑坡灾害的分布和变形情况及更好的服务于区域减灾防灾,利用InSAR技术对覆盖该区域的Sentinel-1A和ALOS-2两种卫星影像数据进行了处理,并通过分析视线向年均形变速率图,圈定了17处疑似滑坡,并对其中的5处典型滑坡进行时间序列形变特征分析,监测识别出的滑坡基本沿318国道所在一侧的波曲河左岸分布。InSAR调查结果表明受地震影响樟木地区的滑坡多分布在沿波曲河左岸的陡峭山体上,中尼公路迪斯岗至友谊桥段的古滑坡出现了局部复活的现象,同时樟木镇居民所在的城区也发育有扎美拉山危岩体崩塌滑坡灾害。      

藏南错那洞穹隆早渐新世含绿柱石花岗伟晶岩的成因机制及其地质意义

错那洞穹隆位于特提斯喜马拉雅东段,发育钨锡-铍稀有金属成矿作用。错那洞穹隆由上（边部）、中（幔部）、下（核部）3个构造层组成,分别以上、下拆离断层为分界线,其中在幔部强变形带中发育一套同构造变形的含绿柱石花岗伟晶岩。锆石U-Pb年代学表明,该套伟晶岩形成于33.7±0.4Ma（MSWD=1.12）,为早渐新世岩浆活动的产物,明显早于穹隆中目前发现的淡色花岗岩（20~14Ma）。岩石地球化学和Sr-Nd-Hf同位素测试结果显示：（1）错那洞早渐新世花岗伟晶岩为过铝质高钾富钠花岗质岩石,具有较高SiO₂（>69.74%）、高Al₂O₃（>14.58%）及较低的CaO、MgO、MnO、TiO₂的特征;（2）高场强元素及大离子亲石元素均呈现高度变化特征,富集轻稀土元素,亏损重稀土元素;（3）Sr同位素初始值（0.696308～0.751604）与Nd同位素初始值（-11.48～-12.05）总体在角闪岩与泥质片麻岩之间,ε_Hf（t）值介于-5.4～0.1之间（主要集中在-5.4～-1.8）。综合研究表明,错那洞早渐新世含绿柱石伟晶岩是角闪岩与泥质片麻岩混熔的结果,其中泥质片麻岩的部分熔融起主导作用,其形成与藏南拆离系（STDS）的活动密切相关,表明错那洞地区新生代地壳深熔作用主要源岩在早渐新世已完成了从角闪岩向泥质片麻岩的转变。该同构造变形含绿柱石伟晶岩的发现,揭示错那洞穹隆的成穹作用至少在早渐新世便已开始。铍稀有金属可能在早渐新世已有了初始富集,而在中新世大规模岩浆活动中实现了巨量富集。     

Characteristics of shallow geothermal fields in major cities of Tibet Autonomous Region

Based on the project titled “Investigation and evaluation of shallow geothermal energy in major cities of Tibet Autonomous Region”, the distribution characteristics and occurrence conditions of shallow geothermal fields in these cities were introduced in this paper. To this end, relevant data in Lhasa, Shigatse and Nyingchi Cities through vertical thermometry was a focus, so as to analyze groundwater temperature and the distribution law of strata with constant temperature. Then through comprehensive comparisons and analysis of the relationship between groundwater temperature and climate, differences in this aspect of Nagqu City were taken as a typical case to clarify formation of geothermal field and corresponding influence on groundwater temperature, furthermore providing basic data for rational development and utilization of shallow geothermal energy in Tibet Autonomous Region.     

基于地层结构组合的第四纪地质单元划分研究——以皖江经济带沿江丘陵平原区为例

为支撑地质条件复杂地区的水文地质、工程地质和环境地质调查研究,在皖江经济带沿江丘陵平原区通过系统分析第四纪地层的岩性、结构、构造等组合,以地貌以及第四系成因、沉积相和沉积物物源为指标,结合已有区域第四纪研究成果以及年代地层和岩石地层划分标准,进行皖江沿江丘陵平原区“第四纪地质单元”划分,共划分出冲积-湖积平原地质单元、洪积-坡积岗地地质单元和残积-剥蚀丘陵地质单元3个一级地质单元,总结了7种类型第四纪地层结构组合及其特征,为区域水文地质和工程地质调查与研究奠定了基础。     

新疆霍什布拉克铅锌矿床微量元素地球化学

霍什布拉克铅锌矿床是新疆西南天山地区晚古生代碳酸盐岩容矿的重要矿床。本文采用高精度电感耦合等离子质谱(ICP-MS)对主要矿石矿物(黄铁矿、方铅矿、闪锌矿)和热液脉石矿物方解石进行了微量元素地球化学研究。研究表明,黄铁矿、方铅矿、闪锌矿、方解石具有较为相似的稀土元素特征,Eu正异常明显,弱负或弱正Ce异常指示成矿流体最初由相对氧化的条件演化为还原条件。与霍什布拉克岩体、容矿围岩的稀土元素组成进行对比后发现,硫化物及热液方解石稀土元素配分曲线部分与重结晶泥晶灰岩重合,结合前人同位素地球化学研究,认为容矿坦盖塔尔组碳酸盐岩为成矿提供了必要的成矿物质及成矿流体组分。Ga/In值显示闪锌矿为低温成矿;硫化物明显富集LREE,Hf/Sm、Nb/La和Th/La值小于1,显示铅锌成矿过程中成矿流体主体以富Cl为特征;Y/Ho、Zr/Hf和Nb/Ta值变化范围相对较小,表明成矿期流体性质相对较为稳定,基本未混入外来流体。     

http://www.sciencedirect.com/science/article/pii/S1674987111000752

A series of environmentalegeological problems have been caused by over-exploitation of deep groundwater (i.e., confined aquifer water) in the North China Plain. In order to better understand the status of deep groundwater over-exploitation and the resultant environmentalegeological problems on a regional scale, the over-exploitation of groundwater has been assessed by way of the groundwater exploitation potential coefficient (i.e., the ratio of exploitable amount of deep groundwater to current exploitation), cumulative land subsidence, and long-term average lowering rate of the groundwater table. There is a good correlation among the results calculated by the different methods. On a regional scale, deep groundwater has been over-exploited and there is no further exploitation potential under the current conditions. The groundwater exploitation degree index takes the exploitation in 2003 as the reference for the calculations, so the results mainly reflect the degree of current groundwater exploitation. The results of over-exploitation of deep groundwater obtained by land subsidence data and long-term average rate of depression of the water table mainly reflect environmentalegeological problems caused by exploitation of deep groundwater.     

内蒙古阿力奔铅多金属矿床地质特征及矿床成因

阿力奔铅多金属矿床为一产于乌拉山群片麻岩之中的石英脉--蚀变岩型矿床,其矿化以铅为主,同时伴生有铜、锌、金和银等。矿化分为两个阶段,即早期的浸染--细脉浸染铜--铅--锌矿化及晚期的方铅矿--闪锌矿--石英脉型矿化。流体包裹体研究表明,早期阶段矿化石英中主要发育气液两相及富气相包裹体,均一温度分别为281. 6 ℃ ～ 357. 6 ℃及343. 5 ℃ ～ 351. 4 ℃,盐度分别为4. 18% ～ 9. 60% NaCl 及1. 05% ～ 1. 90%NaCl; 晚期阶段石英中主要发育气液两相流体包裹体,其均一温度为152. 6 ℃ ～ 335. 8 ℃,盐度为2. 74 % ～ 8. 55%NaCl。综合分析认为,成矿流体早期以岩浆热液为主,晚期有大量大气降水加入,矿床属中温岩浆热液成因类型。     

超压真空密实技术在尾矿库治理中的应用研究

超压真空密实技术是近几年发展起来的软土处理技术,采用独特防淤堵排水板、结合增压技术,用于矿山尾矿库的加固治理,提高尾矿库安全,避免事故的发生。     

CO_2-H_2O流体不混溶对Au溶解度的影响——以贵州省贞丰县水银洞金矿床为例

运用热力学原理和方法,研究了CO2-H2O流体不混溶作用对Au的溶解度的影响。结果表明,贵州水银洞金矿床的成矿流体是一种富含挥发分（fCO2=70.79MPa）、酸性（pH=3.71）、还原性（fO2=0.50×10-36MPa）、中温（267℃）、具有超压（180MPa）性质的含Au（a∑Au=3.744×10-8mol/L）流体。当超压流体的封闭层——炭质页岩因断裂作用而被破坏时,热液体系的压力发生骤降（28.50～35.30MPa）,CO2-H2O流体发生不混溶作用,并有大量CO2溢出。CO2的流失可使成矿溶液的CO2逸度和O2逸度降低（fCO2=0.80MPa、fO2=2.512×10-42MPa）,酸碱度升高（pH=4.32）,同时伴随温度的下降（224℃）,成矿热液中Au溶解度的降低（a∑Au=3.790×10-9mol/L）,从而快速沉淀下来成矿。