Metallogenic Epoch of Nonferrous Metallic and Silver Deposits in the Jiaodong Peninsula, China and its Geological Significance

As China's most important gold-producing district,the Jiaodong Peninsula also contains copper,lead-zinc,molybdenum(tungsten),and other nonferrous metal ore deposits,but the space-time and genetic relationships with gold deposits remain uncertain.To investigate the temporal relationship between these nonferrous metal and gold ore deposits,We collected the samples from a number of nonferrous metallic and silver deposits and metallogenetic rock bodies in the eastern Jiaodong Peninsula for isotopic dating.The results show that the Re-Os isotopic model ages of the Lengjia molybdenum deposit in Rongcheng range from 114.5± 1.8 Ma to 112.6± 1.5 Ma,with an average age of 113.6± 1.6Ma;the LA-ICP-MS ~(206)Pb/~(238)U ages of 33 zircons in the sericitization porphyritic monzogranite that hosts the Tongjiazhuang silver deposit in Rongcheng range between 122 Ma and 109 Ma,with a weighted mean age of 116.04± 0.95 Ma;the LA-ICP-MS ~(206)Pb/~(238)U ages of 31 zircons in the copper metallogenic pyroxene monzodiorite that hosts the Kuangbei copper deposit in Rongcheng range from126 Ma to 106 Ma,with a weighted mean age of 116.6± 1.7 Ma;and the LA-ICP-MS ~(206)Pb/~(238)U ages of19 zircons in the pyroxene monzodiorite surrounding the Dadengge gold and multimetal deposit in Weihai range from 113 Ma to 110 Ma,with a weighted mean age of 111.7± 0.6 Ma.All these results indicate that the metallogenic ages of the silver and nonferrous metallic deposits in the Jiaodong Peninsula are in a limited range from 118 Ma to 111 Ma.Previous studies have demonstrated that the isotopic ages of gold deposits in the Jiaodong Peninsula range from 123 Ma to 110 Ma,while Weideshanian magmatism occurred between 126 Ma to 108 Ma.Both these ranges are grossly consistent with the metallogenic ages of silver and nonferrous metallic deposits in this study,suggesting that the large-scale mineralization occurred in the Early Cretaceous when magmatic activities were strong.This epoch may be linked to the lithosphere thinning and the thermo-upwelling extension in eastern China at that time.In addition,field investigation also shows that gold and nonferrous metallic deposits are distributed nearby the Weideshanian granite,with the nonferrous metallic deposits lying within or surrounding the granite pluton and the gold deposits outside the granite pluton.We propose the following mineralization scenario:In the Early Cretaceous,an intensive lithospheric extension induced partial melting and degassing of the metasomatized lithospheric mantle,which resulted in the formation of mantle-derived fluids enriched in metal elements.During the rapid process of magma ascent and intrusion,crust-derived fluids were activated by the magmatic thermal dome and served to further extract ore-forming materials from the crust.These fluids may have mixed with the mantle-derived fluid to form a crust-mantle mixing-type ore-forming fluid.The high-temperature conditions in the center or in contact with the granitic magmatic thermal dome would have been favorable for the formation of porphyry-type,skarn-type,and hydrothermal-vein-type ores,thus forming a series of Mo(W),Cu,and Pb-Zn deposits in the mid-eastern Jiaodong Peninsula.In contrast,the medium-to low-temperature conditions in the periphery of the magmatic thermal dome would have favored the deposition of gold(silver) ores under the appropriate physiochemical and structural conditions.The metallogenic epoch of the molybdenum,copper,and silver deposits,and their spatio-temporal and genetic relations to the gold deposits,as demonstrated in this study,not only provide important insights to the study of regional metallogeny,our understanding of the metallogenesis of the Jiaodong type gold deposit,and the geodynamic background of the large-scale mineralization in the Jiaodong Peninsula,but also have practical value in guiding the mineral exploration.     

我国南极科考站附近气旋的特征分析

本文基于欧洲中心的ERA-Interim再分析数据,采用雷丁大学的气旋自动识别与追踪算法,建立了1979-2013年中国南极科学考察站长城站、中山站以及泰山站划定的统计区域内气旋数据集。基于这套数据,分析了3个站区附近气旋的气候特征,包括:气旋数量、空间分布、强度、加深率等,并研究了达到爆发性发展的气旋的时空特征。分析表明,长城站以及中山站气旋数量均有增加趋势,但都未达到显著水平;泰山站气旋数量的减少趋势达到显著性水平。3个站区的气旋统计表明,长城站统计区域内气旋活动最频繁,且爆发性气旋活动相对较多;中山站、长城站气旋的数量和空间分布具有季节变化,气旋数量夏季较其他3个季节偏少、偏弱;泰山站气旋活动最少,并且大部分影响到该站的气旋都处于消亡阶段,气旋的强度较弱,故气旋活动对该站的影响较弱。     

Assessing groundwater vulnerability and its inconsistency with groundwater quality,based on a modified DRASTIC model: a case study in Chaoyang District of Beijing City

Depth to water, net recharge, aquifer media, soil media, topography, impact of the vadose zone media, and hydraulic conductivity of the aquifer (DRASTIC) model based on a geographic information system (GIS) is the most widely adopted model for the evaluation of groundwater vulnerability. However, the model had its own disadvantages in various aspects. In this work, several methods and the technologies have been introduced to improve on the traditional model. The type of the aquifer was replaced by the thickness of the aquifer, and the index of topography was removed. The indexes of the exploitation of the groundwater and the type of land use that reflected the special vulnerability were added to the system. Furthermore, considering the wideness of the study area, the fixed weights in the DRASTIC model were not suitable. An analytic hierarchy process (AHP) method and an entropy weight (Ew) method were introduced to calculate the weights of parameters. Then, the Spearman Rho correlation coefficients between IVI and the Nemerow synthetical pollution index (NI) of the groundwater quality were significantly improved, after the four steps of modification. The level differences with little gaps between Nemerow comprehensive pollution indexes and groundwater vulnerability occupied the proportion of the area from 75.68 to 84.04%, and finally, a single-parameter sensitivity analysis for the two models was used to compute the effective weights of these parameters. By comparison, the DRMSICEL model seems to perform better than the DRASTIC model in the study area. And the results show discrepancies between the vulnerability indices and groundwater quality as indicated by existence of vulnerable areas with bad water quality and vice versa.     

<Emphasis Type="Italic">S</Emphasis>-wave velocity structure and tectonic implications of the northwestern sub-basin and Macclesfield of the South China Sea

Based on the optimum P-wave model, the S-wave velocity structure of a wide angle seismic profile (OBS2006-1), across the northwestern sub-basin (NWSB) and the Macclesfield, is simulated by a 2-D ray-tracing method. The results indicate the S-wave velocities in the upper and lower crust of the NWSB are 3.2–3.6 km/s and 3.6–4.0 km/s, with Vp/Vs ratios of 1.82–1.88 and 1.74–1.82, respectively, which reflect typical oceanic crust characteristics. The S-wave velocity in the upper crust of the NWSB is a little higher in the NNW segment than that in the SSE segment, while the lateral variation of Vp/Vs ratio is in the opposite. We suggest that the NWSB might have experienced asymmetrical magma flows during sea floor spreading, which may have blurred the magnetic anomaly lineation. The comparison of S-wave velocities along the northern margin of the SCS shows that the west section is different from the east section, and the northwestern margin has a non-volcanic crust structure. The S-wave structures and P-wave velocity models along the northern margin, Macclesfield and Reed Bank show that the Macclesfield might have a conjugate relationship with the Reed Bank.     

Crustal structure and mantle transition zone thickness beneath a hydrothermal vent at the ultra-slow spreading Southwest Indian Ridge (49°39′E): a supplementary study based on passive seismic receiver functions

As a supplementary study, we used passive seismic data recorded by one ocean bottom seismometer (OBS) station (49°41.8′E) close to a hydrothermal vent (49°39′E) at the Southwest Indian Ridge to invert the crustal structure and mantle transition zone (MTZ) thickness by P-to-S receiver functions to investigate previous active seismic tomographic crustal models and determine the influence of the deep mantle thermal anomaly on seafloor hydrothermal venting at an ultra-slow spreading ridge. The new passive seismic S-wave model shows that the crust has a low velocity layer (2.6 km/s) from 4.0 to 6.0 km below the sea floor, which is interpreted as partial melting. We suggest that the Moho discontinuity at ~9.0 km is the bottom of a layer (2–3 km thick); the Moho (at depth of ~6–7 km), defined by active seismic P-wave models, is interpreted as a serpentinized front. The velocity spectrum stacking plot made from passive seismic data shows that the 410 discontinuity is depressed by ~15 km, the 660 discontinuity is elevated by ~18 km, and a positive thermal anomaly between 182 and 237 K is inferred.     

柴北缘二郎洞地区L 构造岩变形特征及其地质意义

柴北缘二郎洞地区出露包含早古生代岩石组合的达肯大坂岩群,其构造变形期次和变形时代研究接近空白, 本文首次在其中发现了面理微弱, 而拉伸线理十分发育的L 构造岩,对其详细的构造解析对认识柴北缘构造演化具有重要意义。二郎洞达肯大坂岩群存在两期构造变形作用（D₁、D₂）,D₁ 期变形表现为兼具逆冲分量的左旋走滑剪切,D₂ 期变形表现为兼具正断性质的右旋走滑剪切。D₁ 期变形产生LS 构造岩和L 构造岩。其中L 构造岩中矿物拉伸线理的倾伏向约为142°,与柴北缘造山带延伸方向一致,倾伏角一般在2°～54°。对L 构造岩以及侵入其中的未变形次安山岩进行LA-ICP-MS 锆石U-Pb定年,获得它们的结晶时间分别为457 Ma 和406 Ma,L 构造的变形时代可能介于457～406 Ma 之间。根据长石、石英等矿物的变形形式,估计L 构造岩的变形温度在380 ℃～420 ℃之间, 应形成于地下13～14 km 深处。在构造特征分析和岩相学研究的基础上,结合柴北缘早古生代岩浆活动时代构架,我们认为二郎洞地区L 和LS 构造岩的原岩可能是原特提斯洋向北俯冲增生过程中形成的早古生代弧花岗岩,由于柴达木-东昆仑板块和祁连陆块之间的斜向碰撞,导致局部地区出现挤压并沿造山带延伸方向走滑活动。在走滑剪切作用下使地壳流变层中的弧岩浆岩体向地表挤出,局部成分相对均匀的花岗质岩石,因具有较强的岩石力学性能而形成了L构造岩。     

Seismic behaviors of soil slope in permafrost regions using a large-scale shaking table

Large-scale shaking table model tests were carried out to study the dynamic behaviors of slopes and failure mechanism of landslide in permafrost regions. The model slope was constituted of silty clay layer stacked on an ice layer with 8° surface slope. Acceleration, displacement, and pore pressure were measured subjected to vertical and horizontal seismic loadings. The horizontal wave has a stronger influence on the failure of the model than the vertical wave motion, and the natural frequency of vibration in the horizontal direction decreased obviously at the failure state. The model slope has three components of different nonlinear mechanical properties, which are the soil layer, soil-ice interface, and ice layer. The amplification factor of peak ground acceleration is obviously smaller at the soil-ice interface than that at the soil and ice layer. The acceleration responses are nonlinear because of the nonlinear soil properties and degradation of modulus with increasing horizontal acceleration. Especially, excess pore pressure generation was observed near the soil-ice interface of the slope subjected to higher input acceleration, which resulted in the decrease of the effective stress. Failure surface appeared to be the soil-ice interface, which was consistent with the field observations of landslides in permafrost regions. Slope failure could be defined based on the massive movement of the slope, characterized by integral sliding pattern along the soil-ice interface without the distinct deformation inside the sliding body. The results show that the sliding of the slope with soil layer at gentle gradient is mainly triggered by the combined action of horizontal seismic wave, existence of soil-ice interface, and pore pressure generation in permafrost regions.     

查干凹陷中央构造带不同断阶带原油成熟度特征差异及其成因分析

查干凹陷中央构造带被巴润断裂系分隔成多个断阶,东侧第一断阶和第二断阶含油范围小而西侧第三断阶和第四断阶含油范围大。东部断阶原油成熟度高而西侧断阶原油成熟度低,表现为:第一断阶和第二断阶CPI大多数大于1.20,OEP多数大于1.30,Pr/Ph多数在0.60以下,Ph/nC_(18)普遍高于1.00;第三断阶和第四断阶CPI和OEP小于1.20,Pr/Ph多数在0.60以上,Ph/nC_(18)普遍小于1.00。通过规则甾烷分布特征和原油成熟度特征的分析,确定靠近洼陷的第三和第四断阶的原油更多来自于洼陷中心的烃源岩供烃,而第一断阶和第二断阶则主要是构造带本地烃源岩供烃。钻井、测井资料表明,断层发育诱导裂缝带和滑动破碎带,其中滑动破碎带物性较差,具有良好的封堵性能。非线性随机反演结果表明,巴润3号断层南段致密滑动破碎带稳定发育。断层生长指数研究表明,断层主要在苏二晚期活动,并且巴润3号断层活动性较弱。研究区断层SGR普遍在25%以上,在断层静止期具有良好的封闭性。烃源岩生排烃史模拟和流体包裹体均一温度分析表明,中央构造带主要成藏时间为苏二末期—银根早期,成藏期巴润3号断层由于活动强度较弱,同时沿着断层致密滑动破碎带发育,导致洼陷中形成的原油不易穿过3号断层继续向构造带东侧运移;因此第一断阶和第二断阶主要依赖本地烃源岩供烃,而第三第四断阶为洼陷中心供烃,烃源岩的差异最终导致了不同断阶带原油成熟度的差异。     

不规则载荷影响地表近场垂向位移和倾斜观测的定量计算

基于均匀的、各向同性的半无限弹性体的点状载荷模型引起周边垂向位移场变化的解析解,本文推导了水平倾斜场的解析解计算方法,给出了二维、三维不规则形状载荷对地面或地下某点的垂直位移和水平倾斜的解析解计算方法。并对比分析了质点简化模型和不规则模型的差异性。最后给出了据不规则形状载荷模型得到的近场垂直位移以及水平倾斜场的展布特征。研究结果表明,相对质点简化模型,不规则载荷模型对近场的刻画具有一定优势;二维不规则形状载荷模型的建立,使得将载荷散点化后再将矢量叠加进行计算成为可能;三维不规则形状载荷模型在载荷散点化后,通过赋予散点的不同权重进行载荷重新分配,然后用矢量计算法获取位移场的变化;在二维和三维不规则载荷散点化后的矢量叠加过程中都存在着较明显的收敛过程,表明该计算方法的正确性和可行性。     

敦煌鸣沙山-月牙泉近地表风沙输移路径及强度

利用鸣沙山-月牙泉景区多点同步风况和输沙通量资料,探讨了近地表流场特征、风沙活动强度及输移路径;基于1985和2009年两期遥感影像,揭示高大沙山动态变化及其对月牙泉的影响。月牙泉主要受南北沙山夹击,尤其是北沙山南移更为突出,直接威胁月牙泉存在。近年来,受地形、周边建筑物和外围树木的影响,月牙泉景区近地表流场改变,导致区域输沙动态平衡破坏。因此,月牙泉风沙防治应从恢复近地表风沙流场角度考虑,遵循风沙动态平衡原则,打通月牙泉景区东风通道,恢复均衡环流结构,这是维系高大沙山与月牙泉共存的关键。