赣南地区石雷石英闪长岩的成因:岩石化学、副矿物微量元素、锆石U-Pb年代学与Sr-Nd-Hf同位素制约

石雷石英闪长岩是赣南崇-余-犹地区比较特殊的闪长质侵入体。锆石的原位U-Pb定年表明,该岩体侵位于433.5±3.4Ma。全岩主量元素特征上显示出中偏酸性(SiO2=56.92%～64.70%),富Al(Al2O3=14.10%～14.83%),富碱(Alk=6.41%～7.40%)特别是富钾(K2O=3.86%～4.85%),镁、铁含量较高,MgO:3.47%～5.95%,FeOT:5.23%～8.14%以及低磷(P2O5=0.27%～0.4%)的特点;微量元素上主要富集K、Rb、Cs等大离子亲石元素和轻稀土元素,亏损Nb、Ta、Ti、P等高场强元素。磷灰石微量元素特征上显示高度富集稀土元素特别是轻稀土元素的特征;具有Eu的负异常(δEu=0.37～0.45)。ISr位于0.7073～0.7132之间,εNd(t)变化于-8.41～-4.97之间,两阶段钕模式年龄介于1.58～1.86Ga之间,Hf同位素组成相对均一,εHf(t)主要集中变化于-8～-2之间,两阶段Hf模式年龄加权平均为1.77±0.09Ga,这些特征都暗示了该石英闪长质岩体的形成是强烈壳幔相互作用的产物,区内加里东晚期可能发生了局部的岩石圈的减薄。     

敦煌造山带南部红柳峡混杂带基质的沉积学、地球化学和年代学特征及其大地构造意义

敦煌造山带南部红柳峡混杂带基质的研究,为认识敦煌造山带的形成和演化提供了新的依据。本文从沉积学、地球化学和年代学等方面系统讨论了该混杂带基质的特征和形成环境。结果显示,基质的岩石类型主要包括变泥质岩(云母石英片岩)和变质砂岩,普遍发生强烈变形。局部弱变形变质的基质仍保留有原生沉积构造(如T_(ab)、T_(de)、T_(bde)组合的鲍马序列),反映原岩是一套浊积岩复理石。显微岩相学特征显示,基质碎屑组分以长石、石英和岩屑为主,长石和岩屑含量较高,分别为47%和27%,反映大量火成岩物质的加入,且碎屑颗粒的分选性和磨圆度较差,说明搬运距离较近。地球化学方面,低的化学蚀变指数(CIA=49~67),反映复理石基质物源区母岩经历的风化程度较低。高的成分变化指数(ICV0.8)以及Zr/Sc-Th/Sc投图结果显示,沉积物再循环程度低,为近物源区的初次沉积。基质Sc、Cr、Co、Ni含量低,Eu/Eu*、La/Sc、Th/Sc、La/Co、Th/Co和Cr/Th等元素比值类似于来自长英质源区的沉积物,暗示其物源区母岩以中-酸性岩石为主。La/Sc-Ti/Zr和Th-ScZr/10投图结果显示,复理石基质形成于陆缘弧或活动大陆边缘构造背景。弱变形浅变质砂岩的碎屑模式表明,基质的物源来自"切割型弧-过渡型弧"源区。综上,红柳峡混杂带基质在碎屑组成方面,以再循环程度低、近物源堆积的"切割型弧-过渡型弧"源区长英质碎屑组分为主,在沉积构造方面,发育鲍马序列和深水块体搬运沉积(MTD)构造,表明基质形成于陆缘弧或活动大陆边缘的俯冲带海沟环境。碎屑锆石年代学显示三组年龄:2300Ma、1850Ma和423Ma,结合区域地质背景分析,初步认为物源碎屑可能来自混杂带北侧的三危山弧和东巴兔-蘑菇台弧的古生代花岗岩类以及俯冲折返的变质基性岩岩块。复理石基质的变质砂岩中获得的最年轻的岩浆碎屑锆石年龄为389Ma,说明该砂岩形成于中泥盆世之后,暗示敦煌造山带南部红柳峡地区洋盆尚未俯冲完毕,碰撞作用尚未开始。     

大别造山带北缘后碰撞富钾火山岩：地球化学与岩石成因

大别造山带北缘晚中生代富钾火山岩分布在磨子潭-晓天断裂以北的上叠式火山盆地中，主要为一套以钾玄岩-粗安岩-安粗岩-粗面岩为主体的中偏碱性岩石组合，晚期出现少量碱性火山岩。化学成分上具有富碱、富钾、贫钛、氧化系数较高等特点。岩石的Rb、Ba、Th、Pb等大离子亲石元素含量高，富轻稀土，La/Nb、Ba/Nb及LREE/HREE比值高，并且有显著的Nb、Ti负异常和Pb正异常，而铕异常则不明显。富钾火山岩的Isr值较高（=0.70872-0.70895）,εNd(t)值显著偏低（=-14.62--18.51）。根据对岩石产出动力地质背景及地球化学特征的综合分析，结合同位素组成的混合模拟，表明本区富钾火山岩最可能起源于受俯冲陆壳析出流体交代作用所形成的富集地幔（EM I）的部分熔融。     

Explosive impulse on plates

This paper describes a series of very small scale model tests that were conducted in support of a full scale test program conducted by the Army Research Laboratory at Aberdeen, Maryland for the US Navy to investigate the impulse delivered to a military vehicle by a buried land mine. The full scale tests were conducted in July of 2004 and investigated the effect of various parameters on the impulse delivered. The vehicle was represented by a steel plate and depth of burial, standoff distance, and explosive size (up to 10 pounds of TNT) were changed in the seven tests conducted for the Navy. The full scale tests were conducted in saturated sand. The tests described in this paper used a maximum charge size of 3.3 gm of RDX and PETN. Each of the tests conducted for the Navy were simulated by the small scale tests and a prediction of the impulse that would be measured for each of the tests was made. The small scale tests (as well as the full scale tests results) were also used by the developers of various numerical codes that were also used to predict the impuse that would be measured in the full scale test series.This paper is accompanied by a paper by Taylor et al. (Taylor, L. C., Skaggs, R. R. and Gault, W., 2005, Vertical impulse measurement of mines buried in saturated sand, Fragblast, International Journal for Blasting and Fragmentation, 9, 19-28) in this issue of FRAGBLAST. In the next issue of FRAGBLAST several additional papers will be published. These will be the results of the numerical codes that were used to predict the impulse.     

北京密云环斑花岗岩锆石U-Pb年龄和Hf同位素及其地质意义

密云岩体位于华北克拉通东部,由环斑花岗岩和斑状黑云母花岗岩组成,是典型 A 型环斑花岗岩岩体之一。锆石的 LA-ICPMS U-Pb 年代学研究表明,密云环斑花岗岩形成于1681±10Ma 和1679±10Ma,而围岩片麻岩的原岩形成于2521±14Ma。锆石的 LA-MC-ICPMS Hf 同位素研究表明,太古代片麻岩来源于亏损地幔物质的部分熔融,从而表明2.5 Ca 是华北克拉通地壳重要的生长期;环斑花岗岩中锆石 Hf 同位素组成为δ_(Hf)(t)=～-5,两阶段模式年龄为 T_(DM2)=2.6～2.8Ga,表明它们来源于太古代新生地壳的部分熔融,密云环斑花岗岩侵位于华北克拉通大陆裂解、伸展环境,可能与全球古元古代未期Columbia 超大陆的裂解有关。     

西部华夏地区深部可能存在与华北和扬子大陆相似的太古代基底

华夏地区是否存在古陆是一个长期争论的问题。火山作用的天然超深钻取样,提供了探索大陆基底属性和形成演化过程的重要手段。西部华夏地区地表所出露的最古老岩石不老于中元古代,但对广西省东南部晚中生代—新生代火山岩中锆石捕虏晶的U-Pb年代学和Lu-Hf同位素研究则表明：与华北和扬子大陆相似,西部华夏地区有未暴露的太古代基底。该基底的主体年龄是2.9~2.5 Ga,也有3.85 Ga,3.55 Ga和3.3~3.2 Ga的年龄等。它们的亏损地幔模式年龄（t DM）为2.5 Ga至≥3.9 Ga。说明西部华夏地区的基底经历了复杂的改造过程,包括3.6~3.2 Ga,2.5 Ga,1.0 Ga和0.5 Ga时的地幔物质加入,以及2.0~1.8 Ga和1.6~1.5 Ga时的地壳再熔融事件等。对西部华夏地区强烈改造岩石圈的认识,将有助于从物质组分角度对华南成矿作用背景的思考。     

大别造山带碧溪岭橄榄岩中锆石U-Pb年龄和Hf同位素研究

在详细形态和内部结构研究基础上,对碧溪岭橄榄岩锆石进行了配套的U-Pb年龄和Hf同位素分析。碧溪岭橄榄岩锆石主体是变质成因的,但有少量岩浆锆石残留。这些锆石主体给出了220～210Ma的变质生长/重结晶作用年龄;一颗具较高Th/U比值的锆石给出646Ma的近协和年龄,限定了早期岩浆结晶作用的最小年龄。真正的侵位年龄可以由745Ma的上交点年龄来限定;210～222Ma则记录着深俯冲陆壳折返过程中的锆石生长。除少数颗粒的ε_(Hf)为负值外(-2.9),大部分锆石的ε_(Hf)是正的(高达 8.1)并具新元古代的亏损地幔模式年龄(0.6～1.0Ga,平均0.8Ga)。这些结果说明碧溪岭橄榄岩的初始物质是扬子大陆岩石圈内新元古代岩浆堆积作用产物。这样的岩浆堆积物来源于亏损的软流圈地幔,侵入于扬子的深部地壳之中(如底侵)并部分混染了古老地壳组分。它们随扬子向华北之下深俯冲碰撞和造山带折返过程中经历着复杂的变质改造作用。     

TUNING EFFECTS,LITHOLOGICAL EFFECTS AND DEPOSITIONAL EFFECTS IN THE SEISMIC RESPONSE OF GAS RESERVOIRS*

Synergism of 3-D seismic data, wavelet processing, colour display and interactive interpretation has been exploited in the study of a Gulf of Mexico gas reservoir. Seismic amplitude has been used as a measure of the proportion of a sand/shale reservoir capable of producing gas. This has led to the mapping of net producible thickness of gas sand. The tuning phenomena resulting from geometric effects alone were studied in detail, and tuning curves of various levels of sophistication were used as the basis for amplitude editing. Statistical tuning curves were derived by interactive cross-plotting and deterministic curves by wavelet extraction. Multiple wavelet side lobes cause multiple maxima in the tuning curve. Depositional effects and intrareservoir communication have also been studied by interactive cross-plotting.