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   

Volcanism in the Vitim Volcanic Field, Siberia: Geochemical Evidence for a Mantle Plume Beneath the Baikal Rift Zone   总被引：6，自引：1，他引：5  

JOHNSON  J. S.; GIBSON  S. A.; THOMPSON  R. N.; NOWELL  G. M. 《Journal of Petrology》2005,46(7):1309-1344

The Baikal Rift is a zone of active lithospheric extension adjacentto the Siberian Craton. The 6–16 Myr old Vitim VolcanicField (VVF) lies approximately 200 km east of the rift axisand consists of 5000 km³ of melanephelinites, basanites, alkaliand tholeiitic basalts, and minor nephelinites. In the volcanicpile, 142 drill core samples were used to study temporal andspatial variations. Variations in major element abundances (e.g.MgO = 3·3–14·6 wt %) reflect polybaric fractionalcrystallization of olivine, clinopyroxene and plagioclase. ⁸⁷Sr/⁸⁶Sr_i(0·7039–0·7049), ¹⁴³Nd/¹⁴⁴Nd_i (0·5127–0·5129)and ¹⁷⁶Hf/¹⁷⁷Hf_i (0·2829–0·2830) ratiosare similar to those for ocean island basalts and suggest thatthe magmas have not assimilated significant amounts of continentalcrust. Variable degrees of partial melting appear to be responsiblefor differences in Na₂O, P₂O₅, K₂O and incompatible trace elementabundances in the most primitive (high-MgO) magmas. Fractionatedheavy rare earth element (HREE) ratios (e.g. [Gd/Lu]_n > 2·5)indicate that the parental magmas of the Vitim lavas were predominantlygenerated within the garnet stability field. Forward major elementand REE inversion models suggest that the tholeiitic and alkalibasalts were generated by decompression melting of a fertileperidotite source within the convecting mantle beneath Vitim.Ba/Sr ratios and negative K anomalies in normalized multi-elementplots suggest that phlogopite was a residual mantle phase duringthe genesis of the nephelinites and basanites. Relatively highlight REE (LREE) abundances in the silica-undersaturated meltsrequire a metasomatically enriched lithospheric mantle source.Results of forward major element modelling suggest that meltingof phlogopite-bearing pyroxenite veins could explain the majorelement composition of these melts. In support of this, pyroxenitexenoliths have been found in the VVF. High Cenozoic mantle potentialtemperatures (1450°C) predicted from geochemical modellingsuggest the presence of a mantle plume beneath the Baikal RiftZone. KEY WORDS: Baikal Rift; mafic magmatism; mantle plume; metasomatism; partial melting  相似文献   

Magnetic anomalies across Bastar craton and Pranhita-Godavari basin in south of central India     

I. V. Radhakrishna Murthy  S. Bangaru Babu 《Journal of Earth System Science》2009,118(1):81-87

Aeromagnetic anomalies over Bastar craton and Pranhita-Godavari (P-G) basin in the south of central India could be attributed to NW-SE striking mafic intrusives in both the areas at variable depths. Such intrusions can be explained considering the collision of the Bastar and Dharwar cratons by the end of the Archaean and the development of tensile regimes that followed in the Paleoproterozoic, facilitating intrusions of mafic dykes into the continental crust. The P-G basin area, being a zone of crustal weakness along the contact of the Bastar and Dharwar cratons, also experienced extensional tectonics. The inferred remanent magnetization of these dykes dips upwards and it is such that the dykes are oriented towards the east of the magnetic north at the time of their formation compared to their present NW-SE strike. Assuming that there was no imprint of magnetization of a later date, it is concluded that the Indian plate was located in the southern hemisphere, either independently or as part of a supercontinent, for some span of time during Paleoproterozoic and was involved in complex path of movement and rotation subsequently. The paper presents a case study of the utility of aeromagnetic anomalies in qualitatively deducing the palaeopositions of the landmasses from the interpreted remanent magnetism of buried intrusive bodies.  相似文献   

新疆喀拉通克铜镍硫化物矿床成矿岩浆作用过程   总被引：5，自引：2，他引：3  

贾志永  张铭杰  汤中立  李文渊  任立业  胡沛青 《矿床地质》2009,28(5):673-686

喀拉通克铜镍硫化物矿床3个主要含矿镁铁质岩体的主量元素、微量元素和铂族元素组成分析及母岩浆组成估算结果表明:3个岩体中不同类型岩石的主要氧化物含量的变化具玄武质岩浆结晶分异的特征;在MgO含量为10%～15%区间,SiO2含量迅速增高;微量元素和稀土元素原始地幔标准化配分模式相似,具Nb和Ta亏损,K、Sr富集的特征.与1号和2号岩体相比,3号岩体中大离子亲石元素及轻稀土元素相对富集,(La/Yb)N介于6.8～9.2之间,δEu显示轻微负异常,在460 m深度表现出Cu-Ni等成矿元素与SiO2含量同时剧变的特征,铂族元素配分模式与2号岩体相似.上述结果显示,3个岩体可能是同源岩浆不同期次的产物,原始岩浆为高镁玄武岩浆.成矿岩浆演化过程中经历的岩浆分离结晶作用和富硅地壳组分混染可能是成矿岩浆硫饱和及硫化物熔离的主要诱因.  相似文献   

内蒙古解放营子花岗闪长岩岩浆混合机制——来自斜长石和角闪石的矿物化学证据     

吕前露  刘建峰  赵硕  郭春丽  车亚文 《岩石矿物学杂志》2022,41(2):322-338

为揭示华北克拉通北缘中晚三叠世解放营子花岗闪长岩的岩浆混合机制,对寄主岩石和镁铁质包体中斜长石和角闪石开展了电子探针分析.分析结果显示,多斑和少斑包体边部的斜长石斑晶发育An值增加的突变环带,环带的An值为32～46,明显高于核部和边部斜长石的An值(18～31),而核部的An值与寄主岩石中斜长石的An值一致,该特征指...  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   

Ordovician Granitoids and Silurian Mafic Dikes in the Western Kunlun Orogen, Northwest China: Implications for Evolution of the Proto-Tethys     

ZHANG Qichao  WU Zhenhan  LI Shan  LI Kan  LIU Zhiwei  ZHOU Qing 《《地质学报》英文版》2019,93(1):30-49

The western Kunlun orogen in the northwest Tibet Plateau is related to subduction and collision of Proto-and Paleo-Tethys from early Paleozoic to early Mesozoic. This paper presents new LA-ICPMS zircon U-Pb ages and Lu-Hf isotopes, whole-rock major and trace elements, and Sr–Nd isotopes of two Ordovician granitoid plutons(466–455 Ma) and their Silurian mafic dikes(～436 Ma) in the western Kunlun orogen. These granitoids show peraluminous high-K calcalkaline characteristics, with(⁸⁷Sr/⁸⁶Sr)_i value of 0.7129–0.7224, ε_Nd(t) values of -9.3 to -7.0 and zircon ε_Hf(t) values of -17.3 to -0.2, indicating that they were formed by partial melting of ancient lower-crust(metaigneous rocks mixed with metasedimentary rocks) with some mantle materials in response to subduction of the Proto-Tethyan Ocean and following collision. The Silurian mafic dikes were considered to have been derived from a low degree of partial melting of primary mafic magma. These mafic dikes show initial ⁸⁷Sr/⁸⁶Sr ratios of 0.7101–0.7152 and ε_Nd(t) values of -3.8 to -3.4 and zircon ε_Hf(t) values of -8.8 to -4.9, indicating that they were derived from enriched mantle in response to post-collisional slab break-off. Combined with regional geology, our new data provide valuable insight into late evolution of the Proto-Tethys.  相似文献   

西南天山柯坪地区萨尔干基性岩脉U-Pb年代学及地球化学特征     

霍海龙  陈正乐  陈贵民  张青  韩凤彬  张文高 《地质力学学报》2019,25(S1):60-65

柯坪地区发育一套沿走滑断层侵位的萨尔干基性岩脉,其产出于西南天山造山带与塔里木克拉通的接触部位,具有重要的意义。文章通过对萨尔干基性岩脉样品进行锆石LA-ICP-MS U-Pb年代学、岩石地球化学分析,探讨西南天山中新生代陆内造山作用过程。结果表明,萨尔干基性岩脉的LA-ICP-MS锆石U-Pb年龄为（49.14±0.8） Ma,表明该套岩石形成于始新世。地球化学表明该套岩石形成于与青藏高原碰撞远程效应相关的构造背景。  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