Rare earth element geochemistry of the Woxi W–Sb–Au deposit, Hunan Province, South China

The Woxi W–Sb–Au deposit in Hunan, South China, is hosted by Proterozoic metasedimentary rocks, a turbiditic sequence of slightly metamorphosed (greenschist facies), gray-green and purplish red graywacke, siltstone, sandy slate, and slate. The mineralization occurs predominantly (> 70%) as stratabound/stratiform ore layers and subordinately as stringer stockworks. The former consists of rhythmically interbedded, banded to finely laminated stibnite, scheelite, quartz, pyrite and silty clays, whereas the latter occurs immediately beneath the stratabound ore layers and is characterized by numerous quartz + pyrite + gold + scheelite stringer veins or veinlets that are typically either subparallel or subvertical to the overlying stratabound ore layers. The deposit has been the subject of continued debate in regard to its genesis. Rare earth element geochemistry is used here to support a sedimentary exhalative (sedex) origin for the Woxi deposit. The REE signatures of the metasedimentary rocks and associated ores from the Woxi W–Sb–Au deposit remained unchanged during post-depositional processes and were mainly controlled by their provenance. The original ore-forming hydrothermal fluids, as demonstrated by fluid inclusions in quartz from the banded ores, are characterized by variable total REE concentrations (3.5 to 136 ppm), marked LREE enrichment (La_N/Yb_N = 28–248, ∑LREE/∑HREE = 16 to 34) and no significant Eu-anomalies (Eu/Eu = 0.83 to 1.18). They were most probably derived from evolved seawater that circulated in the clastic sediment pile and subsequently erupted on the seafloor. The bulk banded ores are enriched in HREE (La_N/Yb_N = 4.6–11.4, ∑LREE/∑HREE = 3 to 14) and slightly depleted in Eu (Eu/Eu = 0.63 to 1.14) relative to their parent fluids. This is interpreted as indicating the influence of seawater rather than a crystallographic control on REE content of the ores. Within a single ore layer, the degree of HREE enrichment tends to increase upward while the total REE concentrations decrease, reflecting greater influence and dilution of seawater. There is a broad similarity in chondrite-normalized REE patterns and the amount of REE fractionation of the banded ores in this study and exhalites from other sedex-type polymetallic ore deposits, suggesting a similar genesis for these deposits. This conclusion is in agreement with geologic evidence supporting a syngenetic (sedex) model for the Woxi deposit.     

Clidicostigus gen. nov., the first Mesozoic genus of Mastigini (Coleoptera: Staphylinidae: Scydmaeninae) from Cenomanian Burmese amber

The Mastigitae is a small supertribe of ant-like stone beetles that currently includes nine extant and five extinct genera. Extinct taxa are known within tribes Clidicini and Mastigini; the latter with one genus discovered in Baltic amber. For the first time, a Mesozoic genus of the tribe Mastigini is described, Clidicostigus arachnipes Jałoszyński, Brunke and Bai, gen. et sp. nov., from Cenomanian Burmese amber. The new taxon shares an enlarged and spiny scape and pedicel with its extant relatives but has deep elytral grooves and a strongly elongate and asymmetrical maxillary palpomere IV; the beetle has also enormously elongate maxillary palps and legs. The elongation of appendages in combination with only moderately large eyes is postulated to have evolved as an adaptation to running quickly, with tactile and chemical senses predominating over sight. The mode of life of Clidicostigus might have been similar to that of extant Mastigini, especially of particularly slender South African species that run on the ground and climb bushes and trees in search of prey.     

帕米尔弧形构造带东北缘晚新生代构造活动的沉积与重矿物变化响应

帕米尔弧形构造带东北缘晚新生代沉积特征的研究对于理解帕米尔构造带弧形扩展机制具有重要意义。本文通过对帕米尔弧形构造带东北缘的晚新生代沉积地层的沉积特征对比研究和重矿物采样与组份分析,建立了帕米尔弧形构造带东北缘地区的晚新生代沉积联合柱状对比图和重矿物组份变化曲线。研究结果表明,晚新生代沉积与重矿物变化主要记录了帕米尔弧形构造带东北缘的两期构造活动。第一期构造活动发生在安居安组沉积时期,帕米尔弧形构造带东北缘的和什拉甫剖面、英科1井表现为粗碎屑沉积和对应的不稳定重矿物爆发,而南部的甫沙2井中则并未观察到,这一事件可能反映了喀什-叶城走滑系统在和什拉甫剖面附近的中新世构造启动。第二期构造活动发生在阿图什组沉积期间,帕米尔弧形构造带东北缘全区域出现了一套粗碎屑沉积和对应的不稳定重矿物爆发,反映了帕米尔弧形构造带东北缘在上新世以来大规模向北楔入塔里木盆地内部的构造过程。

     

松辽盆地沉积层结构的短周期地震背景噪声成像研究

使用位于松辽盆地内部的NECESSArray台阵连续两年背景噪声数据,通过波形互相关和多重滤波方法提取到2~14 s较短周期的Rayleigh波群速度和相速度频散曲线,基于快速行进（FMM）面波成像方法得到群速度和相速度成像结果,并采用最小二乘迭代线性方法反演获得了松辽盆地深至12 km的三维S波速度结构.本文成像结果显示：松辽盆地内部S波速度分布的横向不均匀性与该区域的构造单元呈现出良好的空间对应关系.从地表至下方的6 km深度,盆地北部比南部表现出更加强烈的低速异常,这一特征可能与盆地南北的沉积构造差异有关.中央坳陷区低速异常的边界与嫩江断裂走向相互平行,表明盆地基底断裂对盆地形成演化具有一定的控制作用.在垂直速度结构剖面中,2.9 km·s^-1的S波速度等值线与地震反射剖面显示的盆地基底深度大致对应.基于S波速度模型和盆地基底速度（2.9 km·s^-1）,我们获得精细的松辽盆地沉积层厚度模型,结果表明松辽盆地的沉积层厚度分布呈现出中间厚、四周薄的特征,中央坳陷区的沉积层厚度范围大约在3~6 km.

     

中国大陆及其周边板内地震活动的整体演化模式（一）

以活断层网络为结构框架的中国大陆及其周边地区可视为一个“断层运动与蕴震”系统。用自耦合方法初步研究发现，该蕴震系统是一个时间结构有序的耗散系统，这种时间结构的有序是在远离平衡态的条件下，通过系统与环境物质，能量的变换而建立和维持的。它在演化过程中遵循着非平衡相变的若干特点，这就是临界慢化，分岔与减熵等，以能量积累的负反馈方式开始，以能量大释放的正反馈方式结束的螺旋式地震活动周期是中国大陆及其周边板     

综合地球物理方法在华南桂中海相残留盆地沉积相预测中的应用

沉积相研究是盆地隐蔽油气藏勘探中重要的研究内容之一,综合利用地球物理方法有效识别构造、岩性或沉积相差异是盆地隐蔽油气藏勘探的前提.本文基于重力、航磁、地震等综合地球物理资料,通过重磁异常正演剥离和剖面正反演拟合技术研究了华南桂中地区海相地层的密度分布特征,预测了岩相、沉积相的变化规律.研究发现,本区中、下泥盆统海相地层存在横向的岩性、岩相变化,研究区西北、东南部的台地相区重力异常高、岩石拟合密度值高;中部“X”型台地边缘相区重力异常杂乱、岩石拟合密度变化范围大;东部台沟相区重力异常低、岩石拟合密度值低.利用综合地球物理方法预测沉积相为盆地岩性圈闭油气藏和生物礁油气藏勘探提供了新的研究思路,研究成果已得到初步检验,但还有待进一步完善与实践.     

皂市水库诱震地质条件及危险性初评

对湖南皂市水库库区及区域地壳运动、沉积建造以及浅部岩溶、古岩溶及深部岩溶作用作了较深入的研究与探讨,对与库区关系较密切的断裂及其活动性进行了考察,否定了沿主要库段南缘分布的袁公渡断裂.在上述工作基础上,认为水库区不存在诱发较大地震的地质条件,即使诱发较小有感地震,对大坝亦无影响。     

基于浅层地震勘探与钻孔联合地质剖面探测的苏北盆地倪湖庄-七里墩断裂研究

浅层地震勘探与钻孔联合地质剖面探测是隐伏断层定位与活动性鉴定的基本手段,需在实际工作中不断总结完善。通过采用浅层地震勘探技术,查明了淮安市区附近隐伏断裂的基本格局,并结合钻孔联合地质剖面探测与第四纪年代学测定,确定了新发现的倪湖庄-七里墩断裂的最新活动时代及活动特征。倪湖庄-七里墩断裂为近南北走向、倾向西的高角度正断层,断层倾角72°～82°,探测断裂长度为43 km。浅层地震勘探揭示其断面具有近直立或呈S形的上下反倾特点,指示具有走滑性质。该断裂错断了北东走向淮阴-响水断裂与北西走向无锡-宿迁断裂,最新活动时代为中更新世中晚期。本次探测工作对技术方法进行了探索,并提出以下建议：针对新发现的隐伏断裂,宜采用从已知点向外逐次探测的方式,即完成上一条测线的设计、施工与解译工作后,根据探测结果布设下一条测线;基于地震时间剖面进行钻探设计时,既要考虑断层两盘反射波组延伸与变形特征,又要考虑物探解译上断点与实际上断点的埋深差异;在河流下游开展钻孔联合地质剖面探测与地层对比时,需充分考虑局部地貌条件差异与第四纪海平面对陆域地表过程的影响。     

利用DE算法反演地壳速度模型和地震定位

利用差异演化（Differential Evolution）非线性全局优化算法,设计了一种反演地壳速度模型和进行地震定位的方法,并给出了反演结果的具体分析.利用有限差分算法计算速度模型的走时场,可以节省大量的计算量,加快计算过程.反演得到的地壳速度模型和地震的震源参数可以直接用于地震层析成像研究,还可以利用地震层析成像得到的三维速度结构对地震重新定位,从而得到较为精确的震源参数.地壳速度模型的反演方法也可以用于三维速度结构的反演.     

景泰5．9级地震前后的重力变化研究

通过对河西地区重力复测资料进行系统分析,从动态的观点研究了2000年6月6日景泰5．9级地震孕育过程中的重力场演化特征。重力动态图像较清晰地反映了本区重力场的准均匀态→地震孕育的非均匀态→发震的演化过程,还分析研究了特征重力变化与强震活动原关系。