Study of annual mass balance(2011–2013) of Rikha Samba Glacier,Hidden Valley,Mustang, Nepal

Although Himalayan glaciers are of particular interest in terms of future water supplies, regional climate changes, and sea-level rises, little is known about them due to lack of reliable and consistent data. There is a need for monitoring these glaciers to bridge this knowledge gap and to provide field measurements necessary to calibrate and validate the results from different remote sensing operations. Therefore, glaciological observations have been carried out by the Cryosphere Monitoring Project(CMP) since September 2011 on Rikha Samba Glacier in Hidden valley, Mustang district in western Nepal in order to study its annual mass balance. This paper presents the first results of that study. There are 10 glaciers in Hidden Valley, named G1, G2, G3, up to G10. Of these, G5 is the Rikha Samba Glacier, which has the largest area(5.37 km2) in this valley and the highest and lowest altitudes(6,476 and 5,392 m a.s.l., respectively). The glacier mass balance discussed in this paper was calculated using the glaciological method and the equilibrium line altitude(ELA). The glacier showed a negative annual point mass balance along the longitudinal profile of its lower part from September 10, 2011 to October 3, 2012. Stake measurements from October 4, 2012 to September 30, 2013 indicated a negative areal average of annual mass balance-0.088±0.019 m w.e. for the whole glacier. Based on these observations, the ELA of the Rikha Samba Glacier is estimated at 5,800 m a.s.l. in 2013. This negative balance may be due to rising air temperatures in the region, which have been incrementally rising since 1980 accompanied by little or no significant increase in precipitation in that period. The negative mass balance confirms the general shrinking trend of the glacier.     

Petrology of high-pressure granulites from the eastern Himalayan syntaxis

The eastern Himalayan syntaxis, situated at the eastern terminus of the Himalayas, is the least-known segment of the Himalayas. Recent research in this area has revealed that the syntaxis consists of the Gangdise, the Yarlung Zangbo, and the Himalayan units, each of which is bounded by faults. The Himalayan unit, the northernmost exposed part of the Indian plate, mainly contains amphibolite facies rocks, marked by the assemblages staurolite+kyanite+plagioclase+biotite+muscovite±sillimanite and garnet+amphibole+plagioclase, in the south; to the north, low- to medium-pressure granulite grade pelitic gneisses and marbles are present and are characterized by the assemblages garnet+sillimanite+K-feldspar+plagioclase or antiperthite+biotite+quartz±spinel±cordierite±orthopyroxene in gneisses, and anorthite+diopside±wollastonite and plagioclase+diopside+quartz+phlogopite+calcite in marbles. Within this unit, the Namula thrust system is a series of moderately north-dipping structures that displaced the granulite facies rocks southwards over the amphibolite facies rocks. High-pressure granulites occur as relics within these granulite facies rocks and contain garnet–kyanite granulite and garnet clinopyroxenite. The peak assemblage of the garnet–kyanite granulite includes garnet (core part)+kyanite+ternary feldspar+quartz+rutile. Sillimanite+garnet (rim part)+K-feldspar+ oligoclase+ilmenite+biotite and spinel+albite+biotite or spinel+cordierite±orthopyroxene, which are coronas around sillimanite and garnet, are retrograde products of this peak assemblage. Another peak assemblage includes very-high-Ca garnet (CaO 32–34 wt%, Alm₁₀±Grs_>80) and diopside (CaO 22–24 wt%), scapolite, meionite, quartz, and accessory Al-bearing titanite (Al₂O₃ 4–4.5 wt%). The diopside has kink bands. Partial or complete breakdown of Ca-rich garnet during post-peak metamorphism produced pseudomorphs and coronas consisting of fine-grained symplectic intergrowths of hedenbergite and anorthite. Thermobarometric estimates in combination with reaction textures, mineral compositions, and recent experimental studies indicate that these peak assemblages were formed at P=c. 1.7–1.8 GPa, T =c. 890 °C, and the retrograde assemblages experienced near-isothermal decompression to P=0.5±0.1 GPa, T =850±50 °C. The whole-rock compositions indicate that marble and pelite are plausible candidates for the protoliths. These facts suggest the following (1) sedimentary rocks were transported to upper-mantle depths and equilibrated at those conditions to form these high-pressure granulites, which were then emplaced into the crust quickly. During the rapid exhumation of these rocks, the earlier high-pressure assemblages were overprinted by the later low- to medium-pressure assemblages, that is, the high-pressure granulite belt formed in the syntaxis. (2) The Namula thrust system is an important tectonic boundary in the syntaxis, or even in the Higher Himalaya more generally.     

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。     

GEOLOGICAL STUDIES OF METAMORPHIC ROCKS IN THE VICINITY OF M.C.T./LESSER HIMALAYAN SHEAR ZONE, PARTS OF SIKKIM HIMALAYAS

GEOLOGICAL STUDIES OF METAMORPHIC ROCKS IN THE VICINITY OF M.C.T./LESSER HIMALAYAN SHEAR ZONE, PARTS OF SIKKIM HIMALAYAS     

喜马拉雅造山带核部的变质作用与部分熔融:亚东地区高压泥质麻粒岩的岩石学与年代学研究

喜马拉雅造山带核部的高喜马拉雅结晶岩系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,记录了喜马拉雅造山带的形成与演化历史。本文对喜马拉雅造山带中段亚东地区高喜马拉雅结晶岩系中的泥质麻粒岩进行了岩石学和锆石U-Pb年代学研究,结果表明泥质麻粒岩经历了复杂的变质演化和部分熔融,可识别出三期变质矿物组合。早期进变质矿物组合为石榴石+斜长石+钾长石+黑云母+白云母+石英,峰期变质矿物组合为石榴石+斜长石+钾长石+黑云母+蓝晶石+石英,晚期退变质矿物组合为石榴石+斜长石+钾长石+夕线石+黑云母+白云母+石英。相平衡模拟表明,该泥质麻粒岩经历了高温、高压的峰期变质条件为800~835℃和12.8~14kbar,在进变质和峰期变质过程中经历了白云母和黑云母脱水熔融,所形成的熔体量至少为5%~8%。麻粒岩的晚期退变质条件为720~740℃和7.6~8.3kbar。这表明泥质麻粒岩经历了一条以高压麻粒岩相峰期变质和降温、降压退变质为特征的顺时针P-T轨迹。锆石U-Pb定年结果表明,麻粒岩相变质和深熔作用发生在28.5~17.0Ma。本研究表明高喜马拉雅结晶岩系的上部构造层位经历了高压麻粒岩相变质作用,而不是以前认为的以高温、低压变质作用为特征,并为喜马拉雅造山带构造演化的研究提供了新的见解。     

喜马拉雅造山带加里东期构造作用:以马拉山-吉隆构造带为例

青藏高原是由复合地体和复合造山拼贴体组成,是新元古代以来长期活动、多期造山及新生代最后隆升的基础上形成的高原。最近在马拉山-吉隆构造带中厘定出形成于445~431Ma的碎屑锆石,包括岩浆成因和变质成因,以及447Ma的变质事件,比已有关于安第斯型造山作用的认识晚30~60Myr。主量、微量和同位素特征显示志留纪片麻岩具有和奥陶纪花岗岩一致的地球化学特征,属于同一套岩石。综合已有现象推断出:喜马拉雅地区古生代构造事件持续时间更长,微陆块与冈瓦纳大陆北缘的碰撞作用可能发生在志留纪,引发奥陶纪的岩浆岩发生变质作用,以及志留纪的岩浆活动,这些热事件属于加里东期构造作用。     

藏东雅鲁藏布江大拐弯蛇绿岩变基性岩类岩石地球化学再研究

在1:25万区域地质填图和专题研究的基础上,再次对喜马拉雅东构造结地区雅鲁藏布江蛇绿混杂带中变基性岩的常量元素、微量元素和Sr-Nd-Pb同位素地球化学特征进行了深入研究,进一步阐明了SSZ型蛇绿岩的成因。变基性岩类可分为具有玻安岩类、IAT和OIB特征的3类。玻安岩类为LREE呈略亏损—平坦型,稀土元素总量低,∑REE为7.56×10-6～20.89×10-6,富相容元素Cr、Ni和常量成分MgO、Al2O3,形成于弧前环境。IAT类为本带的主要类型,在蜘蛛图上有一定的Nb、Ta亏损,REE为大致平坦型,稀土元素总量低,∑REE为37.84×10-6～55.75×10-6。OIB类为LREE较富集型,稀土元素总量高,∑REE为102.09×10-6～240.95×10-6,与IAT和MORB相比,具较高的La、Nb、P、Ti含量,而相容元素Cr、Ni等含量较低。Sr、Nd、Pb同位素组成反映PREMA(或BSE)和EMI提供了源区,暗示未分异的原始地幔和下地壳参与形成了原始岩浆。推测新特提斯洋盆演化经历了较早的地幔柱、洋岛阶段,形成了MORB-OIB组合;较晚期为洋内弧阶段,形成了SSZ型蛇绿岩和IAT组合。     

江南隆起带北缘新生代构造演化的石英ESR年代学研究

运用α石英热活化ESR定年法对江南隆起带北缘35件样品进行了研究。结果显示,江南隆起带北缘的石英脉ESR年龄范围在195.8~3.4 Ma之间,主要集中在喜山期(75~3.4 Ma)。结合其他地质证据,江南隆起带北缘新生代构造演化可以划分为伸展断陷期(75~61.5 Ma)和挤压隆升期(43.2~3.4 Ma)两个阶段。前者以发育正断层和断陷盆地为特征,后者以重力滑脱构造为特征。喜山期的构造作用对先存构造进行了强烈的改造,包括南华北、中下扬子和江南隆起带北缘的整个中国东部地区在喜山期都经历了显著的构造活动。ESR测年结果与江南隆起带已有地质事实相吻合,检验了ESR测年的可靠性。     

喜马拉雅造山带地震活动及其相关地质灾害

喜马拉雅造山带是地球上海拔最高、规模最大的陆陆板块俯冲碰撞带在这条长达2 500 km的板块边界上,近年来多次发生破坏性地震,造成大规模的滑坡、房屋倒塌等次生灾害,给人民生命和财产安全造成严重的威胁。分别选取尼泊尔喜马拉雅、喜马拉雅东构造结和喜马拉雅西构造结地区近期发生的3个地震震群作为研究实例,基于中国科学院青藏高原研究所在研究区架设的区域流动地震台站记录的波形资料,对地震的震源位置和震源机制解进行计算。结果表明,在尼泊尔喜马拉雅地区,主喜马拉雅逆冲断裂是大地震的主要发震构造;东构造结地区的地震以逆冲和走滑型为主,表明印度板块向北东方向的逆冲推覆和青藏高原向东南逃逸的侧向挤出是该地区的主要构造背景;西构造结地区中深源地震多发,揭示了高角度大陆深俯冲的几何形态。     

喜马拉雅山脉新生代差异隆升的裂变径迹热年代学证据

裂变径迹年龄资料记录的雅鲁藏布江以南的喜马拉雅山脉的冷却年龄具有明显的时空差异性。在南北方向上,特提斯喜马拉雅的冷却年龄主要在8 Ma以前,局部为5.0~2.6 Ma,而高喜马拉雅的冷却年龄集中在5 Ma以后,大多数在3 Ma以来;在东西方向上体现在喜马拉雅东西构造结之间的高喜马拉雅带上,东喜马拉雅的不丹东部区域的裂变径迹热年代学数据揭示了8.0~3.0 Ma的冷却剥露的历史;东喜马拉雅的不丹西部区域为7.0~1.4 Ma;中喜马拉雅的尼泊尔地区为5.0~0.2 Ma;西喜马拉雅的印度西北部地区为3.0~1.0 Ma。最年轻的裂变径迹年龄显示出由中间向两侧增大,反映了地质晚近时期东西构造结间的高喜马拉雅山脉的剥露幅度由中间向两边减弱的趋势,揭示了以中喜马拉雅为隆升中心向两边拓展的趋势。综合有关裂变径迹年代学资料表明,喜马拉雅山脉的隆升主要发生在中新世以来,其表现为18~11 Ma、9 Ma以来的两个快速隆升期。喜马拉雅山脉隆升的动力体制可能由早期的挤压隆升—中新世的伸展隆升—上新世以来构造隆升为主,局部气候作用和构造作用耦合的山脉隆升机制。