藏南嘉黎断裂古乡—通麦段多期活动特征及其构造意义

嘉黎断裂是青藏高原南部呈北西西—南东东向喀喇昆仑—嘉黎断裂系的重要组成部分,被认为代表了北拉萨地块和中拉萨地块之间的构造界线。关于嘉黎断裂的构造性质和演化过程等仍存在争议,其不同期次构造过程仍需要进一步研究。在详细的区域地质填图基础上,以嘉黎断裂古乡—通麦段为研究对象,重点调查了该断裂带不同期次变形的几何学与运动学特征,基于新获得的不同方位断层面与擦痕特征等资料,恢复和计算该区的不同期次应力场及方向,并据此解析该区的多期构造叠加关系,探讨嘉黎断裂在不同应力场下的多期活动特征以及相关的区域构造演化过程和大地构造背景,在此基础上讨论了嘉黎断裂对拟建铁路工程的影响。研究结果显示,嘉黎断裂晚新生代以来仍有活动迹象,并具有多期构造叠加特征,从早到晚依次为左旋走滑(D₁)、正倾滑(D₂)和右旋走滑(D₃)。嘉黎断裂作为东喜马拉雅构造结地区重要的变形调节构造,其多期活动性质反映了地块间的相对运动特征及区域应力场的转换过程,这对认识青藏高原南缘的新生代构造演化过程具有重要意义。     

盐源县西范坪－模范村喜马拉雅期斑岩群地质特征及找矿前景探讨

盐源喜马拉雅期石英二长斑岩群和斑岩铜矿的发现和肯定，结束了康滇地轴中段攀西地区无喜马拉雅期斑岩和斑岩铜矿的历史。对认识该区大陆板内岩浆成矿作用及找矿工作具有特殊意义。本文就其地质特征及找矿前景作扼要介绍。     

高喜马拉雅混合岩特征及其成因

混合岩是深熔作用的存在标志,对研究中下地壳深熔作用机制、地壳流变以及造山带演化和花岗岩的成因具有重要意义.文中对西藏林芝地区和聂拉木地区的混合岩进行了详细的岩相学、岩石学和地球化学特征的研究.岩相学特征显示,研究区的混合岩可划分为浅色体、中色体和暗色体3个基本组成部分.对三者切割分离,分别进行了主量元素和稀土元素的分析.结果表明:浅色体由迁移的熔体结晶形成;中色体可以是未发生熔融的原岩,也可以经由未发生迁移的熔体与熔融残留体反应形成;暗色体是由迁移汇集后的熔体与中色体反应形成.由于聚集的熔体可以为暗色矿物的结晶提供良好的结晶空间和物质来源,因此暗色体多数以窄条带产出于浅色体边缘.浅色体和暗色体通常具有岩浆岩的结构,矿物粒径粗大且分布不具有定向性,这是其区别于中色体的重要特征.浅色体显示出明显Eu正异常,暗示长石大量参与了部分熔融过程,并且初始熔体在近源区的冷凝过程中长石优先结晶.浅色花岗岩的Eu负异常可能与熔体在源区的长石结晶有关.退变质反应有可能使部分熔融反应形成的矿物完全消失,因此不宜将反应矿物存在与否作为发生过脱水熔融的判别标准.     

Pressure-temperature Evolution of the Metapelites in the Motuo Area,the Eastern Himalayan Syntaxis

The Motuo area is located in the east of the Eastern Himalayan Syntaxis. There outcrops a sequence of high-grade metamorphic rocks, such as metapelites. Petrology and mineralogy data suggest that these rocks have experienced three stages of metamorphism. The prograde metamorphic mineral assemblages(M1) are mineral inclusions(biotite + plagioclase + quartz ± sillimanite ± Fe-Ti oxides) preserved in garnet porphyroblasts, and the peak metamorphic assemblages(M2) are represented by garnet with the lowest XSps values and the lowest XFe# ratios and the matrix minerals(plagioclase + quartz ± Kfeldspar + biotite + muscovite + kyanite ± sillimanite), whereas the retrograde assemblages(M3) are composed of biotite + plagioclase + quartz symplectites rimming the garnet porphyroblasts. Thermobarometric computation shows that the metamorphic conditions are 562–714°C at 7.3–7.4 kbar for the M1 stage, 661–800°C at 9.4–11.6 kbar for the M2 stage, and 579–713°C at 5.5–6.6 kbar for the M3 stage. These rocks are deciphered to have undergone metamorphism characterized by clockwise P-T paths involving nearly isothermal decompression(ITD) segments, which is inferred to be related to the collision of the India and Eurasia plates.     

喜马拉雅东构造结岩石圈板片深俯冲的地球物理证据

2009～2010年在南迦巴瓦地区进行了宽频带地震和大地电磁探测,分别处理获得东构造结及其邻区的地下300km以上的P波速度图像和两条大地电磁电阻率剖面。通过资料的对比和综合解释,发现电阻率分布与地震波速有较好的对应关系。研究结果表明:南迦巴瓦变质体的上地壳部分呈现明显高速高阻特征,为两侧的雅鲁藏布江缝合带所夹持;中下地壳具有不均匀性,且普遍呈低速低阻特征;印度板块在藏东南向欧亚板块的俯冲前缘越过嘉黎断裂,抵达班公湖-怒江缝合带;在拉萨地体的高速俯冲板片以下100km至200km深度范围内存在大规模的低速异常带,其上盘中下地壳也广泛发育低速高导体,指示青藏高原东南缘可能存在韧性易流动的物质向东、东南逃逸的通道,为印度板块在南迦巴瓦的深俯冲动力学模式提供了地球物理证据。     

Tectonic settings of porphyry Cu–Mo–Au deposits in the Himalayan–Tibetan orogen,East Tethys

Porphyry Cu (Mo–Au) deposits in the Himalayan–Tibetan orogen formed during the Late Triassic, Early Cretaceous, Eocene, Oligocene, and Miocene and can be classified into different metallogenic belts according to their petrologic features, mineralization ages, and tectonic settings. A close spatial relationship to regional strike–slip faults is evident in all five belts. Porphyry Cu (Mo–Au) deposits exist in a wide range of tectonic environments, including island arc, syn-collision, post-collisional convergence, and continental-transform plate boundaries.

Porphyry Cu deposits cluster in the southernmost part of the Yidun–Zhongdian Belt, along the N–S-trending Gaze River dextral strike–slip fault. Porphyry Cu deposits in the Lijiang–Jinping Belt lie along the Ailaoshan–Red River continental–transform shear zone and the associated strike–slip faults. The Yulong–Malasongduo porphyry belt is controlled by the Cesuo Fault, a NNW-trending regional dextral transcurrent fault that is associated with Palaeogene westward continental oblique subduction along the Jinsha suture. In the Gangdis Belt, Miocene porphyry Cu deposits are localized along N–S-trending normal faults, which were produced by transpression within the regional NW–SE-trending Karakoram–Jiali fault zone (KJFZ). A close spatial relationship between porphyry Cu deposits and strike–slip faults also exists for the Bangong–Nujiang Belt.     

西藏米林县片麻状黑云花岗闪长岩地球化学特征、锆石U-Pb定年及Pb-Sr-Nd同位素组成

喜马拉雅是印度与欧亚板块俯冲碰撞作用形成的全球最年轻、规模最大和正在活跃的造山带。利用LA-ICP-MS锆石U-Pb测年技术对位于东喜马拉雅构造结侵入南迦巴瓦岩群的片麻状黑云花岗闪长岩进行了测年,获得岩浆结晶年龄为515.5±2.3 Ma(早寒武世),提供了泛非构造-岩浆事件在东喜马拉雅构造结的记录。岩石地球化学分析表明,SiO2含量为66.47%~72.42%,A/CNK指数为0.98~1.08,平均1.03,在A/NK-A/CNK指数图解中样品大部分落入过铝质区,里特曼指数σ为1.53~3.08,为钙碱性系列,在SiO2-K2O图解上大部分样品投入高钾钙碱性系列区,在Harker图解中所有样品中的TiO2、MgO、FeOT、MnO、K2O随着SiO2含量的变化增加而减少,Na2O随着SiO2含量的增加而增加,均呈较好的线性关系。稀土元素配分模式为轻稀土元素富集的右倾曲线,(La/Yb)N为19.1~63.8,出现弱Eu负异常(δEu=0.24~0.88);微量元素表现出Ba、Nb、Ta、Sr、Zr亏损,而大离子亲石元素Rb、Th和U相对富集的特征。Sr、Nd同位素组成表明,丹娘乡片麻状黑云花岗闪长岩具有负εNd(t)值(-8.67~-10.57)和较老的Nd模式年龄(tDM=1.84~3.42),说明其来源可能是上地壳物质,结合87Sr/86Sr初始比值特征,推断丹娘乡片麻状黑云花岗闪长岩是在高温环境下经部分熔融形成的。通过构造环境判别图及岩石地球化学研究认为丹娘乡准铝质-弱过铝质片麻状黑云花岗闪长岩形成于后碰撞造山环境,结合新得到的513 Ma同位素年龄,认为泛非碰撞造山事件早寒武世在东喜马拉雅构造结一带可能结束,进入后碰撞造山的构造演化阶段。     

宾川小龙潭斑岩铜钼矿找矿新思路的讨论及前景分析

本文结合矿区最新勘查成果, 从成矿背景、物质来源、矿化特征等方面揭示了矿区具有较好的成矿地质条件和矿化信息。笔者通过疏理决定矿区找矿方向的关键环节, 提出矿区斑岩体的侵入方向与区域NE向构造-岩浆带一致, 主导矿区富碱斑岩带总体呈NE向展布并由NW向SE侵入的认识, 进一步调整了找矿思路。并分析展现了矿区具有寻找大型-超大型斑岩铜钼矿床的前景, 对区域喜山期富碱斑岩带的地质找矿工作具有一定的启示作用。     

Quantitative Biostratigraphic Analysis upon the Upper Cretaceous in Tethyan Himalaya

Biostratigraphic analysis is an essential element for understanding global tectonics and the evolution of life on Earth. Quantitative analysis of sedimentary sequences provides the precise age constraints on timing of significant events in Earth’s history. This paper presents results from quantitative stratigraphic analysis of Upper Cretaceous Tethyan Himalayan sequences. This analysis resulted in a new composite stratigraphic section for the Cretaceous strata of Tibet (TIBETKCS). The eight Upper Cretaceous sections were analyzed in this study and 12 planktonic foraminifera zones were recognized based on available data. Quantitative measurements were made using a Graphic Correlation with Graphcor 3.0 software and correlated to the world standard Cretaceous Composite Section (MIDKCS). The sections were also examined using Constrained Optimization software by CONOP9. Level Penalty was applied as the rule to measure misfit among automatically correlated sections. The new TIBETKCS correlates well with planktonic foraminifera ages from previous work in southern Tibet. A fitting equation of y=?0.19x+305 with a correlation coefficient of 0.94 was obtained from this work. The ages of the first and last appearances of 64 planktonic foraminifera can be calculated with this equation with ± 0.3 Ma precision. This level of precision is approximately 10 times higher than age determinations with traditional methods. Two extinction events were resolved within this analysis at ~93.5 Ma and ~85.5 Ma corresponding to the Ocean Anoxic Events at Cenomanian–Turonian and Coniacian–Santonian boundaries respectively.     

印度大陆俯冲过程中的高压变质与深熔作用：东喜马拉雅构造结南迦巴瓦杂岩的相平衡模拟研究

位于东喜马拉雅构造结的南迦巴瓦杂岩是高喜马拉雅结晶岩系的一部分,是印度大陆深俯冲到欧亚板块之下经历了高压变质作用的产物。基于岩相学和矿物化学研究,本文对南迦巴瓦杂岩中的泥质变质岩进行了相平衡模拟研究。结果表明,泥质岩石经历了高压麻粒岩相变质作用,峰期矿物组成是石榴石+蓝晶石+黑云母+斜长石+钾长石+石英+金红石,峰期变质条件是~820℃,13.0~13.5kb,表明印度大陆至少俯冲到了约45km深度,构成了青藏高原的加厚下地壳。高压泥质变质岩在进变质和峰期变质过程中经历了白云母和黑云母脱水反应引起的部分深熔,熔融程度可达27vol%,形成了花岗质成分的熔体,构成了喜马拉雅造山带淡色花岗岩的源区。因此,青藏高原具有一个深熔融的中下地壳,为其侧向流动提供了有利的流变学环境。