西藏普兰地区拉昂错蛇绿岩中辉绿岩的锆石SHRIMP U—Pb年龄及其地质意义

蛇绿岩中的辉绿岩岩墙是洋脊扩张的产物．其形成年龄代表了扩张事件的时间,也代表了蛇绿岩的形成时代？对雅鲁藏布江缝合带西段拉昂错蛇绿岩中的辉绿岩岩墙进行锆石SHRIMPU—Pb定年,得出加权平均年龄为120．2Ma±2．3Ma,代表辉绿岩的结晶年龄。结合已有的关于雅鲁藏布江蛇绿岩的形成年龄（西段休古嘎布122．3Ma±2．4Ma,中段大竹卡126．0Ma±1．5Ma、吉定123．0Ma＋_1．8Ma,东段罗布莎162．9Ma±2．8Ma）的报道,表明拉昂错地区特提斯洋海底扩张的时代与体古嘎布地区一致．雅鲁藏布江西段与中段地区洋盆的形成时代一致,但晚于东段的发育时代。这意味着整个东提斯洋盆的发育时代存在东早西晚的特点。     

阿尔金南缘构造带西段辉绿岩墙群的地球化学特征及构造环境

对阿尔金南缘构造带西段辉绿岩墙群的岩石学和地球化学的详细研究表明,该区辉绿岩墙群为拉斑系列岩石,其主量元素以中等TiO2(1.19%～1.59%)、高MgO(5.51%～7.88%)、贫K2O(0.04%～0.84%)和P2O5(0.10%～0.20%)、Na2OK2O为特征;高场强元素(HFSE)丰度特征显示其为E-MORB型或过渡型玄武岩质岩石;稀土元素总量相对较高,轻重稀土元素分馏不显著[(La/Yb)N=1.93～3.61,LREE/HREE=3.01～4.10],在球粒陨石标准化配分模式图上呈略富集型.结合玄武岩构造环境判别图解综合分析推测,它们可能形成于一种裂谷向MORB环境过渡的构造环境,即初始小洋盆构造环境.     

Dike rock generation and magma interactions in the Bir Safsaf igneous complex,south-west Egypt: Implications for the Pan-African evolution in north-east Africa

The geological setting, ages, petrography and geochemistry of late Pan-African ( 580 Ma) calc-alkaline and tholeiitic dike rocks in the Bir Safsaf igneous complex of south-west Egypt are discussed. These basaltic to rhyolitic dikes intruded contemporaneously and shortly after the intrusion of granitoids. The major and trace element data, Sr and Nd isotope relations, in combination with textural observations, confirm complex interactions between most of the intermediate calcalkaline dike melts and plutonic melts, with different degrees of mixing, assimilation, replenishment and tapping of magma chambers. Trachytic and rhyolitic dikes are strongly differentiated melts from the granitic pluton. The tholeiitic dikes evolved dominantly by fractional crystallization processes. It is inferred that open system and closed system processes operated in calc-alkaline magma chambers, and that the calc-alkaline melts came from a garnet-and amphibole-bearing mantle, modified by a subduction component. Tholeiitic rocks were formed later by fractional crystallization and assimilation processes. Magma ascent of both dike types took place in an extensional environment and the presumed subduction zone has to be seen in connection with the Atmur-Delgo suture zone.     

新疆库鲁克塔格地区二叠纪脉岩群岩石地球化学特征，Nd、Sr、Pb同位素组成与岩石成因

库鲁克塔格地区二叠纪脉岩群非常发育,主要岩石类型是辉绿岩,并有少量的斜闪煌斑岩、斜长玢岩和花岗斑岩。花岗斑岩属高钾钙碱性系列,具有A型花岗岩的稀土元素和微量元素地球化学特征;斜长玢岩的地球化学特征与花岗斑岩相似,二者都亏损U、Nb、Ta。斜闪煌斑岩的岩石化学组成属过碱性系列,显著富集轻稀土元素和大离子亲石元素。辉绿岩的岩石化学组成以钙碱性系列为主,稀土元素总量变化较大,Cs、Rb、Ba、Th元素丰度变化大,普遍亏损U、Nb、Ta。研究证明,辉绿岩脉的这些地球化学特征都与同化混染作用有关,大离子亲石元素丰度的变化还与热液蚀变有关。辉绿岩具有富集型Nd、Sr同位素组成,且变化范围大,是岩浆源区同化混染作用的结果。它们的铅同位素组成属低U(Th)/Pb值的正常铅,主要受混染物控制,并不代表源区特征。库鲁克塔格地区岩石圈地幔Nd、Sr、Pb同位素比塔里木板块西缘岩石圈地幔的富集程度更高,且变化范围大,反映了这两个地区岩石圈地幔的演化历史存在明显差异。     

桂西北与辉绿岩类岩石有关的金矿地质特征--以百色龙川金矿为例

龙川金矿位于桂西北地区，是一个与辉绿岩类岩石有一定时空联系的典型蚀变岩型金矿。该矿产于辉绿岩体与地层的接触带，严格受接触带和挤压破碎带的共同控制。辉绿岩起着沟通深部与浅部构造，并使深部的含矿流体沿挤压破碎带上升、沉淀而成矿的作用。在桂西北有多处与龙川金矿地质环境类似的地区，在此类地区寻找该类型金矿床有较好的前景。     

Flow and fracture maps for basaltic rock deformation at high temperatures

Understanding how the strength of basaltic rock varies with the extrinsic conditions of stress state, pressure and temperature, and the intrinsic rock physical properties is fundamental to understanding the dynamics of volcanic systems. In particular it is essential to understand how rock strength at high temperatures is limited by fracture. We have collated and analysed laboratory data for basaltic rocks from over 500 rock deformation experiments and plotted these on principal stress failure maps. We have fitted an empirical flow law (Norton’s law) and a theoretical fracture criterion to these data. The principal stress failure map is a graphical representation of ductile and brittle experimental data together with flow and fracture envelopes under varying strain rate, temperature and pressure. We have used these maps to re-interpret the ductile–brittle transition in basaltic rocks at high temperatures and show, conceptually, how these failure maps can be applied to volcanic systems, using lava flows as an example.     

砂岩岩脉(岩墙、岩床)的一种可能成因——冲蚀沟槽的充填

黄河三角洲的边滩、心滩上发育了大量冲蚀沟槽（冲槽）．这些冲蚀沟槽深数厘米至1m～2m，宽数厘米至数米，长数十厘米至十几、二十余米，但以深数十厘米，宽数厘米至十余厘米，长数米者多见。形态多样，有直立板片状、直立楔状、“⊥”状、梯形状、“U”形状及树枝状等，其内有时被风成砂充填。经成岩作用后，它们便会转变成砂岩岩脉（岩墙、岩床）。因此，冲蚀沟槽的（砂）充填可能是一种砂岩岩脉（岩墙、岩床）的形成方式．     

Origin of composite dikes in the Gouldsboro granite, coastal Maine

Composite dikes, consisting of aphyric basaltic margins and phenocryst-rich rhyolitic interiors, cut the Gouldsboro granite of coastal Maine at many localities. Limited hybridization (exchange of crystals, commingling, and mixing) occurs in most of the dikes and indicates that the two magmas were contemporaneous with emplacement of rhyolitic magma following closely in time the initial emplacement of the basaltic dike. Petrographic characteristics and geochemistry indicate that the source of the rhyolite was resident magma in the Gouldsboro granite magma chamber. The composite dikes formed when basaltic dikes ruptured the Gouldsboro magma chamber, permitting partly crystallized magma from the margin of the chamber to flow outward into the center of the basaltic dikes. Field relations of similar composite dikes in other areas (e.g., Iceland, Scotland) are consistent with this model. A second type of composite dike (silicic margins with chilled basaltic pillows) commonly cuts mafic intrusions along the Maine coast and probably formed when a granitic dike ruptured an established chamber of mafic magma, permitting resident mafic magma to collapse downward into the still Liquid granitic dike. Most composite dikes have probably formed when a magma chamber was disrupted by a dike of contrasting magma rather than by tapping a stratified magma chamber.     

肥东花岗质岩脉的变形及年代学特征对郯庐断裂带早白垩世构造活动的指示

郯庐断裂带肥东段位于大别造山带与苏鲁造山带之间。在肥东段西韦采石场内发育了大规模的北北东向左行走滑韧性剪切带和一条低角度的韧性滑脱正断层。走滑韧性剪切带为郯庐断裂带走滑活动的产物,低角度滑脱正断层则代表了伸展背景下的构造活动。低角度滑脱正断层上、下盘发育未变形和变形的岩脉,走滑韧性剪切带内外也发育有受剪切带活动而变形的岩脉。对采石场内岩脉的构造和同位素年代学研究表明,低角度韧性滑脱正断层在129~126Ma之间发生过剪切活动,走滑韧性剪切带的活动时间在125Ma之后。综合研究认为,郯庐断裂带的伸展活动可能开始于早白垩世早期(130Ma),但在早白垩世并非一直处于伸展活动之中,125Ma之后的左行走滑活动很可能发生在早白垩世的晚期。