Domal structures and high-grade metamorphism in the Higher Himalayan Crystalline, Zanskar Region, north-west Himalaya, India     

R. KUNDIG 《Journal of Metamorphic Geology》1989,7(1):43-55

ABSTRACT In the main Himalayan range in the Ladakh-Zanskar area, domal structures have been observed at structurally deeper levels in the tectonic unit of the Higher Himalayan Crystalline. Their formation occurred during a second, temperature-dominated phase (M₂) of high-grade regional metamorphism, characterized by the semipelitic paragenesis of sillimanite-K-feldspar and incipient anatexis. The doming event reveals a local system of synmetamorphic uplift superimposed on a regional system of northeast-southwest trending compression. In the main Himalayan range the development of the dominant S₂ foliation is related to deformation during the doming phase, which started early in the M₂ event. The deformation propagated continuously north-east and south-west with time. In the north-east, on the northern slopes of the main Himalayan range, this deformation is expressed by extensional shear movements of the upper tectonic levels finally leading to the late- to postmetamorphic normal fault system of the Zanskar shear zone. Towards the south-west, deformation is expressed by compressional movements, e.g. at the Main Central Thrust (MCT) in the Kishtwar window area. The observed compression and extension is inferred to relate to an increased uplift of the domal bulges of the tectonic Kishtwar window and of the whole main Himalayan range.  相似文献   

中阿尔金南缘志留纪高压泥质片麻岩的发现及其构造地质意义     

马拓  刘良  盖永升  杨文强  王超  康磊  廖小莹  PAK SangWan 《岩石学报》2019,35(6):1800-1818

在中阿尔金南缘西段尤努斯萨依北部原划长城系巴什库尔干岩群中首次发现一套高压泥质片麻岩。根据岩相学观察和矿物化学成分可识别出其四期矿物共生组合:早期为石榴子石+多硅白云母+单斜辉石(?)+斜长石+黑云母+石英+金红石+钛铁矿;第二期为石榴子石+蓝晶石+钾长石+斜长石+黑云母+石英+金红石+钛铁矿;第三期为石榴子石+夕线石+钾长石+斜长石+黑云母+石英+金红石+钛铁矿;晚期为石榴子石+夕线石+斜长石+黑云母+石英+钛铁矿。依据矿物内部一致性热力学数据,基于THERMOCALC 3. 40程序平台,计算出P-T视剖面图,并结合矿物等值线、矿物对温压计等计算,依次确定四期变质温压条件为15. 8～18. 3kbar/646～729℃、10. 30～12. 30kbar/781～821℃、8. 50～9. 60kbar/812～838℃和4. 65～5. 70kbar/698～725℃。上述四期变质阶段共同构成一个早期降压升温后降压降温的顺时针型演化的P-T轨迹,指示出与陆壳俯冲-折返相关的变质地质事件。利用LA-ICP-MS进行的锆石原位微区U-Pb定年和微量元素分析结果表明,该岩石记录了432. 0±2. 7Ma、401. 4±2. 5Ma和381. 1±2. 4Ma三期变质年龄,可能分别代表了该岩石早期高压、中期高压麻粒岩相-麻粒岩相和后期角闪岩相变质阶段的时代。该高压岩石出露于中阿尔金地块西段南缘长城系巴什库尔干岩群之中,与南侧以断裂带分隔的赋存于阿尔金岩群之中的南阿尔金高压-超高压岩石出露的构造位置明显不同,其峰期变质时代(～432Ma)亦明显不同于南阿尔金高压-超高压岩石的峰期变质时代(～500Ma)。因此,该高压岩石与南阿尔金高压-超高压岩石显然不能构成同一条变质岩带。结合区域地质背景和前人关于柴北缘陆壳属性高压-超高压岩石峰期变质时代(～430Ma)的研究成果综合分析,本文初步认为该高压岩石可能是柴北缘高压-超高压变质岩带的西延或是被中新生代以来阿尔金复杂多期次走滑断裂系迁移而就位于中阿尔金南缘的部分柴北缘高压-超高压变质岩片/岩块。  相似文献   

片麻岩穹窿与伟晶岩型锂矿的成矿规律探讨          下载免费PDF全文

许志琴  付小方  赵中宝  李广伟  郑艺龙  马泽良 《地球科学》2019,44(5):1452-1463

"片麻岩穹窿"是指中下地壳热动力过程产生的与岩浆作用(或混合岩化作用)密切相关的穹状构造,是折返造山的产物.片麻岩穹窿的形成经历了从垂直上升的地壳流导致的岩浆上涌的挤压收缩到岩体侵位的顶部伸展机制的转化过程,这一过程有利于富含锂-铯-钽型(LCT)型伟晶岩的生成和锂族元素的富集.研究表明,位于青藏高原北部的中国松潘-甘孜-甜水海印支造山带是中国大型"伟晶岩型"锂矿资源赋存的基地,松潘-甘孜东南部的超大型甲基卡型伟晶岩型锂矿带,产于具有巴罗式"低/中压-高温"变质组合的三叠纪复理石围岩中,早中生代花岗岩以及衍生的大量含锂稀土矿物的伟晶岩脉侵位有成因关系.研究认为,探究片麻岩穹窿的形成过程和构造成因机制;识别花岗岩-含矿伟晶岩的地球化学属性,揭示花岗岩浆分异作用与含矿伟晶岩相演变的成因联系,以及锂元素迁移、富集熔浆的过程;圈定三叠纪地层中巴罗式变质相带的展布,探明富锂伟晶岩矿带赋存的有利变质相带及形成的P-T条件;揭示"变形-变质-岩浆深熔-成矿"的时空耦合、制约与相互作用,再造造山过程中锂资源富集和保存的规律,以及建立成矿动力学模式;是揭示片麻岩穹窿与伟晶岩型锂矿的成矿规律的重要科学途径.  相似文献   

内蒙古乌拉特中旗色尔腾山岩群东五分子岩组锆石SHRIMP定年及其地质意义     

王挽琼  刘正宏  徐仲元  白新会 《吉林大学学报(地球科学版)》2019,49(4):1053-1062

色尔腾山岩群是华北克拉通中西部早前寒武纪变质结晶基底的主要组成部分,对研究华北克拉通基底演化具有十分重要的意义。色尔腾山岩群的形成时代是目前研究的热点之一,本文通过岩石学和锆石SHRIMP U-Pb定年研究,查明了内蒙古乌拉特中旗乌兰乡查干哈达地区色尔腾山岩群东五分子岩组的岩石组成和年代学特征。东五分子岩组遭受了后期岩浆和构造作用的强烈破坏,未见顶底,主要由中细粒斜长角闪岩、细粒黑云斜长片麻岩、眼球状细粒黑云斜长片麻岩、条带状细粒黑云斜长片麻岩和细粒黑云角闪片岩组成,矿物组合特征指示岩石经历了低绿片岩相-低角闪岩相变质。其中,眼球状细粒黑云斜长片麻岩出露相对较厚,与细粒黑云斜长片麻岩多呈互层状产出,局部偶夹细粒黑云斜长片麻岩。本次研究选取其中新鲜的细粒黑云斜长片麻岩进行了锆石SHRIMP U-Pb测年分析,其锆石多呈自形-半自形,发育震荡环带,主体为岩浆成因,锆石SHRIMP U-Pb定年结果为（1 930.7±9.6）Ma,代表原岩（中酸性火山岩）冷凝结晶年龄,表明东五分子岩组经历变质作用的时代应晚于1 930 Ma。  相似文献   

High to ultrahigh temperature contact metamorphism and dry partial melting of the Tasiuyak paragneiss,Northern Labrador     

R. K. Mitchell  A. Indares  B. Ryan 《Journal of Metamorphic Geology》2014,32(6):535-555

Contact aureoles of the anorthositic to granitic plutons of the Mesoproterozoic Nain Plutonic Suite (NPS), Labrador, are particularly well developed in the Palaeoproterozoic granulite facies, metasedimentary, Tasiuyak gneiss. Granulite facies regional metamorphism (M_R), c. 1860 Ma, led to biotite dehydration melting of the paragneiss and melt migration, leaving behind biotite‐poor, garnet–sillimanite‐bearing quartzofeldspathic rocks. Subsequently, Tasiuyak gneiss within a c. 1320 Ma contact aureole of the NPS was statically subjected to lower pressure, but higher temperature conditions (M_C), leading to a second partial melting event, and the generation of complex mineral assemblages and microstructures, which were controlled to a large extent by the textures of the M_R assemblage. This control is clearly seen in scanning electron microscopic images of thin sections and is further supported by phase equilibria modelling. Samples collected within the contact aureole near Anaktalik Brook, west of Nain, Labrador, mainly consist of spinel–cordierite and orthopyroxene–cordierite (or plagioclase) pseudomorphs after M_R sillimanite and garnet, respectively, within a quartzofeldspathic matrix. In addition, some samples contain fine‐grained intergrowths of K‐feldspar–quartz–cordierite–orthopyroxene inferred to be pseudomorphs after osumulite. Microstructural evidence of the former melt includes (i) coarse‐grained K‐feldspar–quartz–cordierite–orthopyroxene domains that locally cut the rock fabric and are inferred to represent neosome; (ii) very fine‐ to medium‐grained cordierite–quartz intergrowths interpreted to have formed by a reaction involving dissolution of biotite and feldspar in melt; and (iii) fine‐scale interstitial pools or micro‐cracks filled by feldspar interpreted to have crystallized from melt. Ultrahigh temperature (UHT) conditions during contact metamorphism are supported by (i) solidus temperatures >900 °C estimated for all samples, coupled with extensive textural evidence for contact‐related partial melting; (ii) the inferred (former) presence of osumilite; and (iii) titanium‐in‐quartz thermometry indicating temperatures within error of 900 °C. The UHT environment in which these unusual textures and minerals were developed was likely a consequence of the superposition of more than one contact metamorphic event upon the already relatively anhydrous Tasiuyak gneiss.  相似文献   

桐柏山南坡的韧性走滑剪切构造   总被引：2，自引：0，他引：2  

韦必则 《现代地质》1993,7(3):285-292

桐柏山南坡的韧性走滑剪切构造是大陆内部造山带在剪切体制下的典型构造之一,以多期韧性再造的叠置为特征。文中详述了它们的几何学特征、走滑剪切应变带内岩石的变形特点,并依据地质标志分析了它们的运动学方向,对它们的流变学意义及其在桐柏造山带构造演化中的作用作了初步探讨。  相似文献   

大山片麻岩地质特征及侵位机制研究     

吕鹏  曲永贵 《吉林地质》1999,18(1):32-38

大山片麻岩的原财为奥长化岗石,呈不规则状侵入柳树河子片麻岩中,年龄２７亿年左右,太古代阜平运动晚期侵位的。侵位与当时区域上大规模的韧性剪切作用密切相关。由于剪切带各相关位置的位移量的差异,形成空间,给岩浆被动就位了有利场所,形成大山片麻岩古深成岩体。  相似文献   

恒山地区部分熔融地质体填图方法的尝试     

徐朝雷  宋春玲  赵祯祥  米广尧  魏荣珠 《地质通报》1999,18(3)

五台群地层呈东西向分布在恒山东段中部,其北为高角闪岩相的恒山片麻杂岩,两者岩性呈渐变过渡关系,由此萌发出片麻杂岩是五台群地层部分熔融而来的思路。经过填图实践,总结出地层与片麻岩体之间存在着仍属地层范畴的片麻岩层这一无序岩石地层单位,并建立起它的填图标志。与地层呈渐变关系的片麻岩体外貌复杂、边界不清,不同于具有一定侵入关系、边界明显、成分均一的片麻岩体,据此划分了原地片麻岩体与异地片麻岩体两个系列。  相似文献   

文昌鱼精子发生的核孔复合体冷冻蚀刻电镜观察     

林加涵  林海宁  方永强 《海洋与湖沼》1999,30(3):245-249

1994-1996年每年3月、7月在厦门同安琼头海域采集雄性文昌鱼,采用冷冻蚀刻的常规技术,研究文昌鱼精子发生核孔复合体的变化规律。结果表明,在核孔复合体结构中很可能存在着作为运输物质的中央颗粒。各种生殖细胞中的核孔复合体的大小和密度不同,平均值约为:精原细胞（60±1.20）nm,（2.9±0.04）孔／μm2;初级精母细胞（76±1.80）nm,（4.8±0.05）孔／μm2;次级精母细胞（72±1.30）nm,（4.6±0.03）孔／μm2;精细胞（97±1.40）nm,（5.4±0.06）孔／μm2。这与细胞的生理功能有关。核孔复合体的分布具有明显的极性特点,主要集中在靠初级精母细胞的高尔基区一侧和靠精细胞的前项体一侧的核膜上,表明了细胞核局部的功能差异。  相似文献   

湖泊和水库营养灰色聚类分析     

关则良  周元建 《广东海洋大学学报》1993,(2)

选取浮游植物初级产量、浮游植物现存量、有机物耗氧量、总氮、无机氮、总磷、活性磷等七项指标,由德尔菲法确定各指标的类别界限值和权重,用灰色系统理论的定权灰色聚类方法,借用计算机对23个湖泊和水库营养类型主要参数作灰色聚类分析,以建立一种划分我国湖泊和水库营养类型的有效方法,作为渔业生产的依据。  相似文献