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1.
苏鲁造山带五莲地区岩浆岩元素和同位素地球化学研究 总被引：6，自引：5，他引：6
对苏鲁造山带五莲地区新元古代和中生代岩浆岩分别进行了主量元素、微量元素、Sr-Nd同位素和氧同位素研究。结果表明,新元古代花岗岩具有显著的LREE富集,高场强元素Nb、Ta、P和Ti负异常。εNd(t)为-12．6--6．9,可能与古元古代老地壳物质再循环有关。锆石δ18O值为-1．02-7．60‰,变化范围较大,近半数样品明显低于典型地幔锆石δ18O 值。新元古代辉长岩具有板内裂谷环境的特征,其εNd(t)在1．6-5．3之间,说明其岩浆起源于亏损地幔,但是经受了一定程度的地壳混染作用。唯一一个辉长岩样品的锆石δ18O值与部分花岗岩锆石δ18O值一样,明显高于典型地幔值,可能是基性岩浆在沿裂谷喷发过程中经历了低温热液蚀变,随后又发生破火山口垮塌,导致蚀变玄武岩在岩浆房重熔而形成高δ18O岩浆。中生代花岗岩和闪长岩表现出明显的高场强元素(Nb、Ta、P和Ti)负异常以及显著的LREE富集。εNd(t)值很低(-19．2 --15．3),同样是由古老地壳物质部分熔融形成。其锆石δ18O变化范围为3．19-6．43‰,大多数样品与典型地幔锆石一样。石英与锆石之间大都达到并保存了氧同位素平衡分馏,而其它矿物(如长石、黑云母和角闪石等)与锆石之间由于受到岩浆期后亚固相热液蚀变而大都表现出明显的氧同位素不平衡分馏。元素和氧同位素特征表明,中生代闪长岩可能是基性下地壳脱水部分熔融并经过结晶分异形成的;花岗岩则可能是由中性下地壳的脱水部分熔融形成的。新元古代花岗岩与中生代花岗岩在微量元素配分模型和Sr-Nd同位素组成上具有十分相似的特征,因此未经历强烈热液蚀变的新元古代花岗质侵入岩可能是中生代花岗岩的原岩。但这些新元古代岩浆岩的锆石δ18O变化范围较大,与中生代岩浆岩相比在流体活动性元素含量上也存在差别,这可能是由于新元古代岩浆岩侵位深度比中生代岩浆岩源区所处深度相对较浅所致。现有的研究结果表明,新元古代岩浆岩的形成与约740-760Ma的Rodinia超大陆裂解有关的裂谷岩浆活动有关,新生地壳物质作为热源启动了热液蚀变,并局部形成了低δ18O岩浆。而中生代岩浆岩则是俯冲陆壳在加厚造山带背景下的部分熔融产物,岩浆源区物质由于所处深度较大没有受到明显的高温大气降水热液蚀变。 相似文献
2.
东秦岭华北地台区岩浆活动的时代及地壳增长和再改造 总被引：3，自引：2，他引：3
同位素年龄资料表明，东秦岭华北地台区，先后在晚太古－早元古代（太华群火山岩）、早中元古代（熊耳群火山岩、张家坪片麻状花岗岩）、中元古晚期－晚元古早期（龙王幢碱性花岗岩）、晚元古代（陶湾群火山岩）、古生代（洛南粗面质火山岩）和中生代等时期，发生过岩浆活动。Ｓｍ－Ｎｄ同位素地质研究揭示，在上述几个时期岩浆活动中，晚太古代和早中元古代的岩浆活动与地壳增长有关，其它时期岩浆活动主要反映地壳自身的再改造。另外，就华北地块大陆地壳整体看，地壳的增长从早太古代至少持续到早元古代。东秦岭华北地台区，在中元古代早期仍然存在有壳－幔分异作用。 相似文献
3.
内蒙古不同时代花岗岩类Nd、Pb同位素特征及其地质意义 总被引：6，自引：2，他引：4
内蒙古地区连接兴蒙造山带和华北板块两个具不同演化历史、不同性质的大地构造单元。通过分析内蒙古地区华北板块和兴蒙造山带不同位置出露的从太古宙至中生代晚期连续分布的30件花岗岩类样品的Sm Nd同位素及Pb同位素,对比了华北板块与兴蒙造山带不同时代花岗岩类的Nd、Pb同位素性质的差异,揭示了两个构造单元的演化过程。华北板块花岗岩的Nd模式年龄分布于中元古代前,从不同时代花岗岩的Nd同位素特征可见华北板块具有太古宙、晚古生代和早中生代(三叠纪)3期地壳增生历史;兴蒙造山带花岗岩的Nd模式年龄出现于古元古代之后,集中于新元古代和早古生代,其花岗岩的Nd同位素特征表明从新元古代至中生代,该区均具有较显著的地幔物质的注入。兴蒙造山带花岗岩类初始Pb同位素含量总体高于华北板块。晚古生代华北板块花岗岩类可能接受兴蒙造山带物质的直接或间接的贡献。至中生代,华北板块和兴蒙造山带作为一个统一的整体演化。 相似文献
4.
武夷山地区中生代有关火山岩及花岗岩的∈＾ＯＮｄ值为－２．２０～－１１．５０，计算的相对于亏损地幔的Ｎｄ模式年令集中于１６１５－２７７０Ｍａ，Ｓｒ同位素初始比值Ｉｓｒ（０）为０．７０８２～０．７３０８，计算的∈ｓｒ（０）为１０７～４２９，ｆＡ为０．４８～１．０３，这些事实际合反映其物质来源主要由早元古代或晚太古代地壳物质改造而成，并含有少量的地幔物质加入紫金山，铜厂，银山有关岩体主要来自厂上地幔物质 相似文献
5.
北秦岭晚古生代—中生代花岗岩类的Nd.Sr.Pb同位素地球化学特征及Nd.Sr 总被引：1，自引：0，他引：1
北秦岭晚古生代—晚中生代花岗岩类的Ｎｄ，Ｓｒ同位素研究表明：具低放射成因Ｐｂ同位素组成的花岗质岩基主要是南秦岭基底变质岩深熔的产物；而具高放射成因Ｐｂ同位素组成的原地、半原地型花岗岩类是北秦岭丹凤群有关岩石深熔和交代作用形成的产物．它们都可分为Ｉ型和Ｓ型，并可同时共存，岩浆源区中都有基性岩石物质的加入，其区别是基性岩类物质对Ｉ型花岗岩类的贡献分数较大，具有较小的亏损地幔模式年龄；由于岩浆源区中不同物质组成的混合，花岗岩类的亏损地幔模式年龄并不代表真实的壳幔分异事件的年龄．从新元古代到晚中生代，Ｉ型花岗岩类的ｄ（ｔ）和ＴＤＭ具逐渐变小的趋势，反映了地壳中基性岩石物质发生深熔作用的时间逐渐变晚，而Ｓ型花岗岩类的ｄ（ｔ）增大，ＴＤＭ变小，反映了基性岩石物质加入比例的增大，暗示着碰撞作用阶段具更加强烈的岩浆作用 相似文献
6.
扬子克拉通北缘元古宙基底同位素地质年代学和地壳增生历史：Ⅱ．火地垭群 总被引：1，自引：0，他引：1
扬子克拉通地壳的生成始于太古宙，但依据目前的研究成果，其主体形成于元古宙，对位于扬子克拉通北缘，分布在碑坝地区重要的基底岩系之一的火地垭群铁船山组火山岩进行了Ｓｍ－Ｎｄ和Ｒｂ－Ｓｒ同位素地球化学研究．同位素年代学数据表明，铁船山组岩系形成于约（１６６８５）Ｍａ的中元古代，并源于高亏损的地幔岩浆库（ｄ（ｔ）７．５３．１０），且其亏损地幔模式年龄ＴＤＭ（（１．６８±０．１０）Ｇａ）与Ｓｍ－Ｎｄ等时年龄是一致的．Ｒｂ－Ｓｒ同位素年代学揭示出在新元古代早期（约（８６０±１２）Ｍａ的晋宁期）铁船山组岩系受到了构造热事件的改造．该事件与区内大规模的基性－超基性和碱性、中－酸性岩浆活动的同时出现在时间上是一致的．这些晋宁期岩浆作用有着以下共同特征：（１）岩浆源于亏损程度大为降低的岩浆库；（２）模式年龄ＴＤＭ与铁船山组火山岩的形成时代相近．在本区的西乡地区，同为中元古代形成的西乡群底部的白勉峡组火山岩与其周围的晋宁期基性－超基性和碱性、中－酸性岩浆岩在年代学特征、岩浆库性质和亏损地幔模式年龄等多方面与碑坝地区铁船山组火山岩及其周围晋宁期岩浆岩的特征是类似的．这些同位素地球化学特征所揭示的区内地壳增生和晋宁期构造历史进一 相似文献
7.
扬子地块南缘晚古生代洋壳存在的Nd同位素证据 总被引：7，自引：0，他引：7
总结我国扬子地块南缘新元古代—早中生代沉积岩目前已发表的Ｎｄ同位素资料发现,这些沉积岩具有随时间变化而其Ｎｄ同位素组成发生漂移的现象。在绝大多数时间里,它们具有２０００Ｍａ左右的Ｎｄ模式年龄,但在１０００～７００Ｍａ的新元古代和＜４００Ｍａ的晚古生代—早中生代时间段中,Ｎｄ同位素模式年龄急剧降低,反映在此时间段内,新生地幔物质已经进入沉积物的物源区。１０００～７００Ｍａ期间的Ｎｄ同位素变化归因于晋宁期的碰撞造山作用而晚古生代－早中生代沉积岩的Ｎｄ同位素变异起因于海盆发育阶段洋壳的出现。即扬子地块南缘在晚古生代—早中生代期间曾经存在过洋壳,且该洋盆可能是古特提斯大洋分支的一部分。 相似文献
8.
苏鲁造山带五莲新元古代花岗岩类成因的Sr-Nd同位素证据 总被引：2，自引：0，他引：2
五莲新元古代花岗岩类分布于五莲断裂以北, 动力变形强, 但变质程度弱, 仅达到绿片岩相.岩性以黑云正长花岗质为主, 少数为石英正长质.岩石中Sr同位素初始值的变化范围很广, 从0.697 306~0.753 765, 除了部分是由于源区的不均一或多源不同比例混合外, 岩浆侵位过程中或固结后的次生扰动可能也起着一定的作用.而它们的εNd (750 Ma) 均为负值且变化范围广(-3.1~-24.3), Nd同位素二阶段模式年龄从1.7~3.4 Ga, 均显示它们的源区以古老的地壳为主, 但具有多源混合的特征.推测五莲新元古代花岗岩类最可能的成因是太古代的TTG片麻岩(主要是其中的英云闪长质组分) 在压力约0.8 Gpa (相当于~25 km的中下地壳) 条件下发生部分熔融, 并混入了不同比例的年轻地幔来源物质.地幔来源物质的加入对于五莲新元古代花岗岩类的成因有重要的影响. 相似文献
9.
孙吴-嘉荫地区早中生代花岗岩的年代学、地球化学与成因 总被引：3，自引：0，他引：3
对小兴安岭北部孙吴-嘉荫地区早中生代花岗岩进行了年代学和地球化学研究,据此探讨其成因及形成的构造背景。锆石U-Pb同位素定年结果表明,研究区早中生代花岗岩分为晚三叠世和早侏罗世两期,形成时代分别为210 Ma和187~181 Ma。晚三叠世碱长花岗岩属铝质A型花岗岩,岩浆源区为新元古代从亏损地幔中增生的基性火成岩地壳。早侏罗世英云闪长岩-花岗闪长岩和二长花岗岩属埃达克岩,是由加厚下地壳物质部分熔融形成的;正长花岗岩-碱长花岗岩与同期埃达克岩具明显不同的地球化学特征,岩浆源区为中元古代从亏损地幔中增生的基性地壳物质。结合区域地质构造演化特征,认为晚三叠世花岗岩是华北板块和西伯利亚板块碰撞造山后伸展构造环境下的产物,早侏罗世花岗岩的形成与古太平洋板块俯冲产生的挤压构造环境有关。 相似文献
10.
东北地区显生宙花岗岩的成因与地壳增生 总被引：141，自引：54，他引：87
东北地区显生宙花岗岩极为发育,特别是中生代印支—燕山期岩体分布面积巨大,可称之为巨型花岗岩省。其主要的成因类型是Ｉ－分异型和Ａ－型,而Ｓ－型花岗岩极为少见。区域地质分析表明,这些花岗岩的主体是在古亚洲域洋壳消失后形成的,其成因与由大量板块俯冲而导致的区域深部热异常或地幔柱有关。从地球化学特点上看,这些花岗岩主要表现为低的初始锶（ＩＳｒ≈０．７０５）和高初始钕（εＮｄ（ｔ）＞０,显示其形成与地幔关系密切。对其年轻的钕模式年龄（ｔＤＭ＜１０００Ｍａ）的分析表明,地质历史上的新元古代－显生宙也是地壳增生的重要时期;同时,垂向增生也是地壳生长的重要机制。 相似文献
11.
12.
内蒙古中—东部地区基底岩石、花岗岩和玄武岩的Nd同位素组成及其对该区地壳演化的指示 总被引：8，自引：6，他引：2
对出露于内蒙古地区的华北地台北缘中段及兴蒙造山带内共21件不同岩性的样品进行Nd同位素研究。这些样品的Nd模式年龄值表明:兴蒙造山带与华北地台具完全不同的特征,兴蒙造山带以年轻的亏损地幔模式年龄为特征(tDM=0.4~1.1 Ga),普遍低于华北地台西段的tDM值(1.8~3.4 Ga)。锡林浩特地块作为独立块体具与兴蒙造山带不同的特征,锡林浩特地块的亏损地幔模式年龄介于兴蒙造山带年龄与华北地台年龄之间。Nd模式年龄计算结果表明内蒙古地区华北地台北缘的地壳增生事件主要集中于中元古代之前,而兴蒙造山带地壳增生事件自新元古代开始。通过对内蒙古地区华北地台北缘εNd(t)值随时间的变化分析可知,在中元古代及海西期均存在古老地壳的再循环及新地壳的增生事件。内蒙古兴蒙造山带地壳增生速率表明该区地壳主要增生事件发生于1 000~700 M a,其后形成的岩浆岩所反映的增生过程表明有古老地壳组分的参与。 相似文献
13.
《Russian Geology and Geophysics》2007,48(1):61-70
We studied geology and main rock assemblages of the Precambrian Kan, Arzybei, and Derba terranes of the Central Asian Fold Belt which border the Siberian craton in the southwest. The Precambrian terranes include three isotopic provinces (Paleoproterozoic, Mesoproterozoic, and Neoproterozoic) distinguished from the Sm-Nd isotope compositions of granitoids, felsic metavolcanics, and metasediments. The terranes formed in three stages of crustal evolution: 2.3–2.5, 0.9–1.1, and 0.8–0.9 Ga. Proterozoic juvenile crust was produced by subduction-related magmatism; it was originally of transitional composition and transformed into continental crust by potassic plutonism as late as the Late Vendian-Cambrian. Terrigenous sediments in the Arzybei and Derba terranes vary in T(DM) Nd model ages from 1.0 to 2.0 Ga. The Nd ages of the underlying metavolcanics and lowest T(DM) of metasediments indicate that terrigenous sedimentation started in the Neoproterozoic. It was maintained by erosion of Mesoproterozoic-Neoproterozoic crust and, to a lesser extent, of Early Precambrian rocks on the craton margin or in Paleoproterozoic terranes. Ar-Ar dating of amphiboles and biotites from metamorphic rocks and U-Pb dating of zircons from granitoids yielded 600–555 and 500–440 Ma, respectively, corresponding to the Vendian and Early Paleozoic stages of nearly synchronous metamorphism and plutonism. Accretion and collision events caused amalgamation of the Paleoproterozoic, Mesoproterozoic, and Neoproterozoic terranes in the Vendian and their collision with the Siberian craton. The lateral growth of the paleocontinent completed in the Late Ordovician. 相似文献
14.
V. M. Savatenkov V. V. Yarmolyuk A. M. Kozlovsky Z. B. Smirnova O. E. Sviridova 《Petrology》2018,26(4):351-367
The Khangai batholith is one of the largest groups of granitoid plutons produced in Central Asia in the Late Permian–Early Triassic, at 270–240 Ma. The batholith occurs in the Khangai collage of Precambrian terranes, which include Early Precambrian crustal blocks (Dzabkhan and Tarbagatai) and Early to Late Neoproterozoic structures of the Songino block in their surroundings. The axial zone of this collage is overprinted by a basin filled with Devonian volcanic–siliceous rocks and Early to Middle Carboniferous terrigenous rocks. The isotopic parameters (Nd and Pb) of granitoids in the Khangai batholith indicate that the melts were derived from compositionally contrasting crustal sources and a single mantle one. The massifs hosted in the Precambrian blocks were produced with the involvement of lower crustal material, with various ages of the origin of the crust and its differentiation into upper and lower ones. The crust of the Tarbagatai and Dzabkhan blocks was produced in the Early Archean and was differentiated at the Archean–Proterozoic boundary. The crust of the Songino block was formed in the Paleoproterozoic and differentiated in the Early Neoproterozoic. According to the Pb and Nd isotopic parameters of granitoids in the Khangai Basin, the regional continental crust was close to the juvenile one, i.e., the continental crust of the Khangai Basin had still not been differentiated by the time when the Khangai batholith was produced. A single mantle source was involved in the origin of the melts of granitoids of the Khangai batholith in various tectonic blocks. The evolution of the Pb isotopic composition of this sources is consistent with the Stacey–Kramers model at µ = 9.5. This source can be identified with the enriched mantle, which has a higher U/Pb ratio than the depleted mantle and lower εNd(T) of 0 to +2. 相似文献
15.
天山0．9Ga新元古代花岗岩SHRIMP锆石U-Pb年龄及其构造意义 总被引：8，自引：0，他引：8
天山造山带的中天山隆起带中广泛出露着新元古代花岗岩类岩石。获得了东天山星星峡和西天山温泉地区片麻状花岗岩中锆石的SHRIMP U-Pb年龄,分别为（942±7）Ma（2σ）和（919±6）Ma（2σ）。这些花岗岩以特有的粗粒、巨大的眼球状片麻结构为特征。主元素数据表明它们属于过铝质的二长花岗岩,具有高SiO2（≥170％）、高K2O＋Na2O（7％～≥8％）,且K2O〉Na2O。这些新元古代花岗岩类岩石具不同的REE含量,但它们有近于平行的REE分布曲线和明显的Eu负异常,同时代的星星峡混合岩具有较高的REE含量,明显富集LREE。它们的微量元素蛛网图几乎完全相同,均有明显的Nb、Sr、Ti、P负异常。基于Nd同位素组成研究,其εNd（t）在-4至-0之间,Nd模式年龄tDM为2．0～1．6Ga。由于放射成因Sr同位素组成非常高,不可能得到精确有意义的Sr同位素初始值。上述特征均表明这些新元古代花岗岩形成于大陆边缘构造环境,由古元古代地壳重熔并经历了高度的结晶分异作用而形成。综合近年来发表的关于天山各地段,诸如温泉、赛里木湖以东、拉尔敦达坂、巴仑台和星星峡等地区较为可靠的锆石U—Pb年龄数据,我们认为天山新元古代花岗岩类岩石主要形成于960-910Ma。结合塔里木盆地周边古老地块年龄的研究结果,可以推断在早新元古代时期塔里木周边和天山的古老地块可能曾组成Rodinia超大陆的一部分。 相似文献
16.
海南岛古元宙变质基底性质和地壳增生的Nd、Pb同位素制约 总被引：15，自引：0，他引：15
基于海南地壳各类型岩石的63个样品Nd和Pb同位素分析数据,研究了海南地块元古宙地壳变质基底的时代、特征和演化。研究结果表明,海南岛元古宙变质基底成熟度低,基底变质岩系的母岩物质来源于长期亏损的地幔源区,主要形成时代为古元古宙晚期－新元古宙;不同时代花岗岩具有较高的εNd(t)值和较低的Nd模式年龄,主要形成于幔源物质参与下的或含地幔成分较多的初生地壳再循环。地壳增生具幕式增生的特点,并在2．0Ga、1.7Ga、1.2Ga出现高峰;Pb同位素组成既不同于扬子地块又不同于华夏地块,介于两地块之间,和Nd同位素特征具有一致或耦合关系。结合海南岛地质特征,初步认为不能单纯地将海南岛基底理解为华南地块统一南延部分或是华夏古陆的部分,可能为不同的构造块体。 相似文献
17.
Impact cratering and their resultant geological phenomena are recognised as significant factors in the lithological and biologic evolution of the earth. Age-dating of impact events is critical in correlating cause and effects for these catastrophic processes. The Falconbridge and Drury Township (Twp) intrusions were emplaced at the contact between Neoarchaean basement and Palaeoproterozoic volcanosedimentary rocks, and also lie at the southeast and southwest edges of the Sudbury Igneous Complex (SIC), within its thermal contact aureole. The Falconbridge Twp intrusion is dated at 2441 ± 3 Ma by U-Pb zircon, with evidence of Archaean inheritance from its host granitoids. Granitoids from the southernmost Abitibi Subprovince are dated here between 2670 ± 11 Ma for an undeformed Algoman granite, and 2696 ± 18 Ma for a foliated granitoid, consistent with existing data from the Abitibi Greenstone Belt and from the Wawa Subprovince. Major and trace element geochemical evidence, common-Pb isotopic compositions, and εNd2440 values between 0 and −1 are all consistent with a Palaeoproterozoic origin for the Falconbridge Twp intrusion, and support inclusion in the East Bull Lake-type suite of leucogabbroic plutons and sills.In contrast, the Drury Twp intrusion gives a U-Pb zircon age of 1859 ± 13 Ma, coincident with the date of SIC-emplacement. While the major and trace element compositions are comparable to the Falconbridge data, the Drury displays significant heterogeneity in εNd2440, with values ranging from +3.7 to −0.1, and contains more radiogenic Pb isotopic compositions. Field, geochemical and isotopic evidence clearly distinguishes this intrusion from constituents of the SIC itself, and indicates that the Drury too is a Palaeoproterozoic intrusion. This requires that apparently unshocked, undeformed magmatic-looking zircon has been grown or reset in a postmagmatic setting. This has significant implications for the identification of mantle-derived magmas and crustal remelts associated with large impact craters. A resetting mechanism involving aggressive hydrothermal alteration of zircon facilitated by halogen-complexing is proposed, inducing rapid, postshock lead loss and subsequent annealing. 相似文献
18.
厘定大别-苏鲁超高压造山带南缘变质岩带的形成时代和地球化学特征有助于区域地层对比研究和对这一造山带演化过程的深入理解。采用单颗粒锆石U—Pb同位素稀释法和蒸发法定年,获得来自苏鲁地体南部海州群上部云台组的3个云母石英片岩样品的碎屑锆石年龄,且集中于800～740Ma之间。全岩初始εNd（800Ma）值变化在-12．8～-8．8之间,两阶段亏损地幔Nd模式年龄为2．1～2．4Ga。这些特征类似于大别山南部宿松地区副片麻岩,指示较单一的沉积物源。结合区域地层对比资料,碎屑锆石年龄限定了海州群云台组的沉积时代可能为新元古代,晚于740Ma左右。其主要沉积物质源自新元古代岩浆岩,归属于扬子陆块 相似文献
19.
Detrital zircons (DZ) and Nd isotopic characteristics constraint maximum depositional ages of two distinct Paleoproterozoic and Neoproterozoic terranes across the Main Central Thrust zone (Munsiari Group) in the Himalaya. New DZ ages and Nd isotopic characters are reported from the Inner Lesser Himalaya (iLH) sedimentary belt (Berinag Group quartzite) and the Munsiari Group through the Great Himalayan Sequence (GHS–Vaikrita Group) across the MCT to the lower parts of the Tethyan Himalayan Sequence (THS) along the Alaknanda–Dhauli Ganga valleys, Uttarakhand Himalaya. The iLH Berinag Group quartzite yielded nearly unimodal DZ U-Pb ages between 2.05 and 1.80 Ga with εNd(0) values of −17 and −23, while the overthrust Munsiari Group, bounded by the Munsiari Thrust at the base and the Vaikrita Thrust (MCT) at the top, represents the Proterozoic magmatic arc with ∼1.95 and 1.89 Ga U-Pb zircon age population with an average of −25 εNd(0) value; the arc developed during the Columbia Supercontinent assembly. In contrast, overthrust Great Himalayan Sequence (GHS–Vaikrita Group) above the MCT is characterized by entirely new Neoproterozoic 1.05–0.85 Ga zircon population, which appears for the first time in this sequence, and has higher εNd(0) values (average −16). Tectonically overlying the GHS, the Tethyan Himalayan Sequence (THS) has first appearance of the Early Paleozoic detrital zircons, with its εNd(0) values like the GHS. Broadly, these characters persist throughout the Himalayan belt from Himachal to NE Himalaya. The iLH sediments were possibly derived from northernly ∼1.9 Ga magmatic arc, and southern the Archean–Proterozoic Aravalli–Bundelkhand nuclei of the Indian craton. Potential sources for the GHS sediments may be a northerly ‘destroyed’ Neoproterozoic magmatic arc whose remnants exists within the Himalaya as the Neoproterozoic granitoids, and possibly be the iLH sedimentary belt, an ‘In-board’ Aravalli–Delhi Fold Belt (ADFB)–Central Indian Tectonic Zone (CITZ) in the south. 相似文献
20.
Ding Tiping Open Research Laboratory of Isotope Geology Chinese Academy of Geological Scieoces Beijing China 《中国地质大学学报(英文版)》2004,15(2):216-219
The formation depth of metamorphic rocks in the Dabie ultrahigh pressure metamorphic (UHPM) zone influences not only our understanding of formation mechanism and evolution processes of collision orogenic belt, but also the studies on earth's interior and geodynamic processes. In this study, the isotopic data of metamorphic rocks in the Dabie UHPM zone are discussed to give constraints on the formation depth in the Dabie UHPM zone. The εSr of eclogite in the Dabie UHPM zone varies from 18 to 42, and the εNd varies from -6.1 to -17, both of them show the characters of isotopic disequilibrium. The oxygen isotope studies indicate that the protoliths of these UHPM rocks have experienced oxygen isotope exchange with meteoric water (or sea water) before metamorphism and no significant changes in the processes of metamorphism on their oxygen isotope composition have been recorded in these rocks. Except for one sample from Bixiling, all samples of eclogite from Dabie UHPM zone show the 3He/4He ratios from 0.79×10-7 to 9.35×10-7, indicating the important contribution of He from continental crust. All Sr, Nd, O and He isotopic studies indicate that the UHPM rocks retain the isotopic characteristics of their protoliths of crust origin. No significant influence of mantle materials has been found in these metamorphic rocks. Trying to explain above isotopic characteristics, some researchers assume that the speeds of dipping thrust and uplifting of rocks were both very high. In this condition, there will not be enough time for isotopic exchange between crust protolith and mantle materials. Therefore, we can not see the tracer of mantle materials in these UHPM rocks. However, this assumption can not be justified with available knowledge. Firstly, it was estimated that the whole process of UHPM took at least 15 Ma. During such a long period, and at the metamorphic temperature of ≥700 ℃, the protolith of crust origin can not escape from isotopic exchange with mantle materials if the UHPM have happened in the mantle depth of ≥100 km. In contrast, all problems will be dismissed if we assume that the UHPM have happened at the depth still in crust. 相似文献