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1.
《地学前缘(英文版)》2020,11(4):1123-1131
Collision between the Indian and Eurasian plates formed the ～2500 km long Yarlung Zangbo Suture Zone and produced the Himalaya mountains and Tibetan plateau.Here we offer a new explanation for tectonic events leading to this collision:that the northward flight of India was caused by an Early Cretaceous episode of subduction initiation on the southern margin of Tibet.Compiled data for ophiolites along the Yarlung Zangbo Suture Zone show restricted ages between 120 Ma and 130 Ma,and their supra-subduction zone affinities are best explained by seafloor spreading in what became the forearc of a north-dipping subduction zone on the southern margin of Tibet.The subsequent evolution of this new subduction zone is revealed by integrating data for arcrelated igneous rocks of the Lhasa terrane and Xigaze forearc basin deposits.Strong slab pull from this new subduction zone triggered the rifting of India from East Gondwana in Early Cretaceous time and pulled it northward to collide with Tibet in Early Paleogene time.  相似文献   

2.
冈底斯带晚中生代构造演化模式一直存在争议。此次研究了中冈底斯带扎布耶茶卡北部区域则弄群火山岩的野外特 征和锆石U-Pb年龄。锆石U-Pb定年结果表明,扎布耶茶卡北部则弄群火山岩主要喷发于154.2~142.1 Ma。研究首次获得 晚侏罗世的则弄群火山岩年龄为154 Ma,比前人提出的则弄群火山岩浆活动起始时间（130 Ma） 提前了24 Ma,据此将则 弄群的时代定为晚侏罗世至早白垩世。根据研究获得的最新年代学数据,结合冈底斯带火山岩的前人研究资料,显示冈底 斯带中生代弧火山岩具有从南向北逐渐年轻的趋势。因此,最早期南冈底斯弧中生代火山岩可能与新特提斯洋板片北向俯 冲有关,晚侏罗世至早白垩世的中冈底斯带弧火山岩受到了新特提斯洋板片北向俯冲和班公湖-怒江洋板片南向俯冲的双 重影响,早白垩世中期的北冈底斯带弧火山岩则与班公湖-怒江洋板片的南向俯冲密切相关。研究成果为冈底斯带晚中生 代构造演化模式提供了火山岩方面的新证据。  相似文献   

3.
《International Geology Review》2012,54(16):1957-1979
ABSTRACT

Palaeozoic granitoids and meta-granitoids dominate the metamorphic basement of the Sakar unit of the Sakar-Strandzha Zone (SASTZ) in southeast Bulgaria. In this article, we present new whole-rock geochemical data and U–Pb zircon geochronology for the Sakar unit granitoids. The igneous minerals and textures are preserved, except the meta-granitoids that experienced a weak amphibolite-facies overprint. Geochemistry reveals compositions of peraluminous high-K calc-alkaline I- to S-type granitoids of volcanic arc origin. A major group of LILE-LREE-enriched granitoids and meta-granitoids and a single HFSE-HREE-enriched meta-granitoid are distinguished. U–Pb geochronology has yielded crystallization ages between 305 and 295 Ma for the major group granitoids and a ca. 462 Ma crystallization age of HFSE-HREE-enriched meta-granitoid. Late Palaeozoic granitoids of the Sakar unit show similar compositions and a similar tectonic setting when compared to other granitoids of the SASTZ, confirming a uniform region-wide tectono-magmatic event. As the Late Carboniferous-Permian magmatic arc components extend across the SASTZ, they trace the time-correspondent active continental margin along the Eurasian plate during subduction of the Palaeotethys oceanic lithosphere. The late Palaeozoic Eurasian active continental margin magmatic arc evolution of the SASTZ can be extended into the Serbo-Macedonian-Rhodope zones to the west, where time equivalent meta-granitoids support the same geodynamic context.  相似文献   

4.
The Jurassic ophiolites in the South Apuseni Mountains represent remnants of the Neotethys Ocean and belong to the East Vardar ophiolites that contain ophiolite fragments as well as granitoids and volcanics with island-arc affinity. New U–Pb zircon ages, and Sr and Nd isotope ratios give insights into their tectono-magmatic history. The ophiolite lithologies show tholeiitic MOR-type affinities, but are occasionally slightly enriched in Th and U, and depleted in Nb, which indicates that they probably formed in a marginal or back-arc basin. These ophiolites are associated with calc-alkaline granitoids and volcanics, which show trace element signatures characteristic for subduction-enrichment (high LILE, low HFSE). Low 87Sr/86Sr ratios (0.703836–0.704550) and high 143Nd/144Nd ratios (0.512599–0.512616) of the calc-alkaline series overlap with the ratios measured in the ophiolitic rocks (0.703863–0.704303 and 0.512496–0.512673), and hence show no contamination with continental crust. This excludes a collisional to post-collisional origin of the granitoids and is consistent with the previously proposed intra-oceanic island arc setting. The new U–Pb ages of the ophiolite lithologies (158.9–155.9 Ma, Oxfordian to Early Kimmeridgian) and granitoids (158.6–152.9 Ma, latest Oxfordian to Late Kimmeridgian) indicate that the two distinct magmatic series evolved within a narrow time range. It is proposed that the ophiolites and island arc granitoids formed above a long-lived NE-dipping subduction zone. A sudden flip in subduction polarity led to collision between island arc and continental margin, immediately followed by obduction of the ophiolites and granitoids on top of the continental margin of the Dacia Mega-Unit. Since the granitoids lack crustal input, they must have intruded the Apuseni ophiolites before both magmatic sequences were obducted onto the continental margin. The age of the youngest granitoid (~153 Ma, Late Kimmeridgian) yields an estimate for the maximum age of emplacement of the South Apuseni ophiolites and associated granitoids onto the Dacia Mega-Unit.  相似文献   

5.
Turbidites from the Shiquanhe–Namco Ophiolite Mélange Zone(SNMZ) record critical information about the tectonic affinity of the SNMZ and the evolutionary history of the Meso-Tethys Ocean in Tibet.This paper reports sedimentologic,sandstone petrographic,zircon U-Pb geochronologic,and clastic rocks geochemical data of newly identified turbidites(Asa Formation) in the Asa Ophiolite Mélange.The youngest ages of detrital zircon from the turbiditic sandstone samples,together with ～115 Ma U-Pb concordant age from the tuff intercalation within the Asa Formation indicate an Early Cretaceous age.The sandstone mineral modal composition data show that the main component is quartz grains and the minor components are sedimentary and volcanic fragments,suggesting that the turbidites were mainly derived from a recycled orogen provenance with a minor addition of volcanic arc materials.The detrital U-Pb zircon ages of turbiditic sandstones yield main age populations of170–120 Ma,300–220 Ma,600–500 Ma,1000–700 Ma,1900–1500 Ma,and ～2500 Ma,similar to the ages of the Qiangtang Terrane(age peak of 600–500 Ma,1000–900 Ma,～1850 Ma and ～2500 Ma) and the accretionary complex in the Bangong–Nujiang Ophiolite Zone(BNMZ) rather than the age of the Central Lhasa Terrane(age peak of ～300 Ma,～550 Ma and ～1150 Ma).The mineral modal compositions,detrital U-Pb zircon ages,and geochemical data of clastic rocks suggest that the Asa Formation is composed of sediments primarily recycled from the Jurassic accretionary complex within the BNMZ with the secondary addition of intermediate-felsic island arc materials from the South Qiangtang Terrane.Based on our new results and previous studies,we infer that the SNMZ represents a part of the Meso-Tethys Suture Zone,rather than a southward tectonic klippe of the BNMZ or an isolated ophiolitic mélange zone within the Lhasa Terrane.The Meso-Tethys Suture Zone records the continuous evolutionary history of the northward subduction,accretion,arc-Lhasa collision,and Lhasa-Qiangtang collision of the Meso-Tethys Ocean from the Early Jurassic to the Early Cretaceous.  相似文献   

6.
The area of Arghash in northeast Iran, prominent for its gold mineralization, was newly mapped on a scale of 1:20,000 with particular attention to the occurring generations of igneous rocks. In addition, geochronological and geochemical investigations were carried out. The oldest geological unit is a late Precambrian, hornblende-bearing diorite pluton with low-K composition and primitive isotope signatures. This diorite (U–Pb zircon age 554 ± 6 Ma) is most likely a remnant from a Peri-Gondwana island-arc or back-arc basin. About one-third of the map area is interpreted as an Upper Cretaceous magmatic arc consisting of a volcanic and a plutonic part. The plutonic part is represented by a suite of hornblende-bearing medium-K, I-type granitoids (minor diorite, mainly quartz–monzodiorite and granodiorite) dated at 92.8 ± 1.3 Ma (U–Pb zircon age). The volcanic part comprises medium-K andesite, dacite and tuffitic rocks and must be at least slightly older, because it is locally affected by contact metamorphism through the hornblende–granitoids. The Upper Cretaceous arc magmatism in the Arghash Massif is probably related to the northward subduction of the Sabzevar oceanic basin, which holds a back-arc position behind the main Neotethys subduction front. Small occurrences of pillow basalts and sediments (sandstone, conglomerate, limestone) tectonically intercalated in the older volcanic series may be relics of earlier Cretaceous or even pre-Cretaceous rocks. In the early Cenozoic, the Cretaceous magmatic arc was intruded by bodies of felsic, weakly peraluminous granite (U–Pb zircon age 55.4 ± 2.3 Ma). Another strong pulse of magmatism followed slightly later in the Eocene, producing large masses of andesitic to dacitic volcanic rocks. The geochemistry of this prominent Eocene volcanism is very distinct, with a high-K signature and trace element contents similar to shoshonitic series (high P, Zr, Cr, Sr and Ba). High Sr/Y ratios feature affinities to adakite magmas. The Eocene magmatism in the Arghash Massif is interpreted as related to thermal anomalies in crust and mantle that developed when the Sabzevar subduction system collapsed. The youngest magmatic activities in the Arghash Massif are lamprophyres and small intrusions of quartz–monzodiorite porphyries, which cut through all other rocks including an Oligocene–Miocene conglomerate cover series.  相似文献   

7.
在班公湖-怒江结合带西段北侧的拉热拉新岩体东、西两侧,新发现了一些早白垩世岩体、相伴的陆缘火山岩组合和矿(化)点,侵入岩和火山岩的岩石化学特征均显示其成因与中特提斯洋向北俯冲消减密切相关。本文将班- 怒带北侧的火山- 侵入岩带厘定为五峰尖拉热拉新晚侏罗世—早白垩世陆缘火山岩浆弧带,同时讨论了陆缘火山- 岩浆弧带的厘定在分析中特提斯构造演化方面的研究意义。  相似文献   

8.
本文对满洲里地区灵泉盆地、包格德乌拉盆地及额尔古纳地区上护林盆地和恩和盆地及周边的原确定为古生代和中
生代的花岗质岩石进行了岩石学和锆石LA-ICP-MS U-Pb 年代学研究,以便揭示研究区中生代的构造演化历史。研究区内
12 个代表性花岗岩中的锆石均呈自形-半自形晶,显示出典型的岩浆生长环带,结合其较高的Th/U比值（0.31~3.63）,暗
示其为岩浆成因。测年结果表明,该区中生代花岗质岩浆活动可划分成以下三期：（1）中三叠世岩浆活动,可进一步划分
成241 Ma 和229 Ma 两期岩浆事件,241 Ma 黑云母正长花岗岩和229 Ma 正长花岗岩的存在可能与古亚洲洋闭合后的伸展环
境有关;（2）早- 中侏罗世岩浆事件,可进一步划分成（180±5）Ma 和（171±2）Ma 两期岩浆事件,黑云母二长花岗岩-
正长花岗岩组合,结合其斑岩型Mo 矿的存在,反映研究区处于活动陆缘的构造背景,可能与蒙古- 鄂霍茨克洋的俯冲作用
有关;（3）早白垩世早期岩浆活动,可进一步划分成（140~150）Ma 和（134±2）Ma 两期岩浆事件,前者与区域内发育的
吉祥峰组火山岩形成时代相近,后者的火口充填型产状表明它们应是该期岩浆事件演化晚期的产物,该期岩浆事件在松辽
盆地以东地区的缺乏暗示它们形成于伸展环境,并与蒙古-鄂霍茨克缝合带的演化有关。  相似文献   

9.
Zircon U-Pb ages of 163.8–100.4 Ma and 146.6–134.5?Ma are obtained for the granitoids from the Pearl River mouth basin, and from southern Guangdong Province, respectively. These new dating data accord well with the crystallization ages of Yanshanian granitoids broadly in the Nanling. The active continental margin of South China, as revealed by a combination of zircon U-Pb data, underwent a key granitoid-dominated magmatism in 165–100?Ma. Its evolution varied temporally, and spatially, registering under control of the paleo-Pacific slab subduction. The granitoids that occurred in 165–150?Ma broadly from the South China Sea to the Nanling are preferably related to two settings from volcanic-arc to back-arc extension, respectively. The activities of Cretaceous granitoids migrated from the southeastern Guangdong (148–130?Ma) to the Pearl River Mouth basin (127–112?Ma), corresponding to the model of a retreating subduction. The subduction-related granitoid magmatism in South China continued until 108–97?Ma. A tectonic transformation from slab-subduction to extension should occur at ~100?Ma.  相似文献   

10.
Abstract

The granitoid suites encountered by drilling in the northern South China Sea (SCS) remain important for understanding the evolution of the late Mesozoic Southeast Asian continental margin. They comprise a range of rock types including diorite, tonalite, granodiorite, monzogranite and syenogranite with SiO2 spanning 56.4–76.8%. Newly acquired secondary ion mass spectrometry (SIMS) U–Pb ages of samples from 14 boreholes indicate two key magmatic episodes: Late Jurassic (161.6–148.2 Ma) and Early Cretaceous (136.5–101.7 Ma). Jurassic magmatism probably began in late Middle Jurassic time, documented by the dates of inherited zircons. The granitoids are dominated by metaluminous to weakly peraluminous I-type granites, are transitional between magnesian and ferroan, and encompass calc-alkaline, high-K calc-alkaline, and shoshonitic series. The geochemical signatures suggest that these granitoids were mostly generated in a normal continental arc environment. Notable features of the I-type samples are well-defined negative Nb–Ta–Ti anomalies typical of arc-related magmas. Taken together, the late Mesozoic arc granites of the SCS, the accretionary wedge of the Palawan terrane to the southeast, and the zone of lithospheric extension north of the SCS throughout Southeast China, define a southeast-to-northwest trench-arc-backarc architecture for the late Mesozoic Southeast Asian continental margin whose geodynamic setting is related to subduction of the Palaeo-Pacific slab beneath the Asian continent. Two key subduction episodes are recognized, one in Late Jurassic and the other in Early Cretaceous time.  相似文献   

11.
The Gangdese magmatic arc, southeastern Tibet, was built by mantle‐derived magma accretion and juvenile crustal growth during the Mesozoic to Early Cenozoic northward subduction of the Neo‐Tethyan oceanic slab beneath the Eurasian continent. The petrological and geochronological data reveal that the lower crust of the southeastern Gangdese arc experienced Oligocene reworking by metamorphism, anatexis and magmatism after the India and Asia collision. The post‐collisional metamorphic and migmatitic rocks formed at 34–26 Ma and 28–26 Ma respectively. Meta‐granitoids have protolith ages of 65–38 Ma. Inherited detrital zircon from metasedimentary rocks has highly variable ages ranging from 2708 to 37 Ma. These rocks underwent post‐collisional amphibolite facies metamorphism and coeval anatexis under P–T conditions of ~710–760 °C and ~12 kbar with geothermal gradients of 18–20 °C km ? 1, indicating a distinct crustal thickening process. Crustal shortening, thickening and possible subduction erosion due to the continental collision and ongoing convergence resulted in high‐P metamorphic and anatectic reworking of the magmatic and sedimentary rocks of the deep Gangdese arc. This study provides a typical example of the reworking of juvenile and ancient continental crust during active collisional orogeny.  相似文献   

12.
High‐pressure (HP) metabasites from the Sancti Spiritus dome (Escambray massif, Central Cuba) have been studied in order to better understand the origin and evolution of the Northern Caribbean boundary plate during the Cretaceous, in a global subduction context. Geochemical and petrological studies of these eclogites reveal two groups with contrasting origins and pre‐subduction metamorphic histories. Eclogites collected from exotic blocks within serpentinite (mélange zone) originated from a N‐MORB type protolith, do not record pre‐eclogitic metamorphic history. Conversely eclogites intercalated in Jurassic metasedimentary rocks (non‐mélange zone) have a calc‐alkaline arc‐like origin and yield evidence for a pre‐subduction metamorphic event in the amphibolite facies. However, all the studied Escambray eclogites underwent the same eclogitic peak (around 600 °C at 16 kbar), and followed a cold thermal gradient during their exhumation (estimated at around 13.5 °C km?1), which can suggest that this exhumation was coeval with subduction. Concordant geochronological data (Rb/Sr and Ar/Ar) support that the main exhumation of HP/LT rocks from the Sancti Spiritus dome occurred at 70 Ma by top to SW thrusting. The retrograde trajectory of these rocks suggests that the north‐east subduction of the Farallon plate continued after 70 Ma. The set‐off to the exhumation can be correlated with the beginning of the collision between the Bahamas platform and the Cretaceous island arc that induced a change of the subduction kinematics. The contrasting origin and ante‐subduction history of the analysed samples imply that the Escambray massif consists of different geological units that evolved in different environments before their amalgamation during exhumation to form the present unit III of the massif.  相似文献   

13.
西藏尼木地区分布一套增生杂岩,其对冈底斯火山岩浆弧的演化具有重要意义。本文对该套增生杂岩中的变质火山岩的地质特征、矿物学、全岩地球化学和锆石U-Pb年代学等方面进行了综合研究。变质火山岩以斜长角闪岩、角闪斜长片麻岩为主,其中,角闪石主要为镁质角闪石,共生的斜长石主要为拉长石;变质火山岩经历了高温-中压变质作用;岩石富Al_2O_3和贫TiO_2,弱富集轻稀土元素(LREE),富集Rb、Sr、Ba等大离子亲石元素(LILE),亏损Nb、Ta、Ti等高场强元素(HFSE),其地球化学特征与火山弧玄武岩的地球化学特征相似,其形成的构造环境为洋内岛弧或活动大陆边缘弧;岩浆锆石U-Pb年龄值为151.4±1.6Ma和150.7±1.4Ma,表明岩石的形成时代为晚侏罗世。综合研究认为,增生杂岩中的变质火山岩是新特提斯洋在晚侏罗世北向俯冲的产物,在陆-陆碰撞之前卷入增生系统,该套变质火山岩不是以往所认为的变质结晶基底。  相似文献   

14.
This paper presents several types of new information including U–Pb radiometric dating of ophiolitic rocks and an intrusive granite, micropalaeontological dating of siliceous and calcareous sedimentary rocks, together with sedimentological, petrographic and structural data. The new information is synthesised with existing results from the study area and adjacent regions (Central Pontides and Lesser Caucasus) to produce a new tectonic model for the Mesozoic–Cenozoic tectonic development of this key Tethyan suture zone.

The Tethyan suture zone in NE Turkey (Ankara–Erzincan–Kars suture zone) exemplifies stages in the subduction, suturing and post-collisional deformation of a Mesozoic ocean basin that existed between the Eurasian (Pontide) and Gondwanan (Tauride) continents. Ophiolitic rocks, both as intact and as dismembered sequences, together with an intrusive granite (tonalite), formed during the Early Jurassic in a supra-subduction zone (SSZ) setting within the ?zmir–Ankara–Erzincan ocean. Basalts also occur as blocks and dismembered thrust sheets within Cretaceous accretionary melange. During the Early Jurassic, these basalts erupted in both a SSZ-type setting and in an intra-plate (seamount-type) setting. The volcanic-sedimentary melange accreted in an open-ocean setting in response to Cretaceous northward subduction beneath a backstop made up of Early Jurassic forearc ophiolitic crust. The Early Jurassic SSZ basalts in the melange were later detached from the overriding Early Jurassic ophiolitic crust.

Sedimentary melange (debris-flow deposits) locally includes ophiolitic extrusive rocks of boninitic composition that were metamorphosed under high-pressure low-temperature conditions. Slices of mainly Cretaceous clastic sedimentary rocks within the suture zone are interpreted as a deformed forearc basin that bordered the Eurasian active margin. The basin received a copious supply of sediments derived from Late Cretaceous arc volcanism together with input of ophiolitic detritus from accreted oceanic crust.

Accretionary melange was emplaced southwards onto the leading edge of the Tauride continent (Munzur Massif) during latest Cretaceous time. Accretionary melange was also emplaced northwards over the collapsed southern edge of the Eurasian continental margin (continental backstop) during the latest Cretaceous. Sedimentation persisted into the Early Eocene in more northerly areas of the Eurasian margin.

Collision of the Tauride and Eurasian continents took place progressively during latest Late Palaeocene–Early Eocene. The Jurassic SSZ ophiolites and the Cretaceous accretionary melange finally docked with the Eurasian margin. Coarse clastic sediments were shed from the uplifted Eurasian margin and infilled a narrow peripheral basin. Gravity flows accumulated in thrust-top piggyback basins above accretionary melange and dismembered ophiolites and also in a post-collisional peripheral basin above Eurasian crust. Thickening of the accretionary wedge triggered large-scale out-of-sequence thrusting and re-thrusting of continental margin and ophiolitic units. Collision culminated in detachment and northward thrusting on a regional scale.

Collisional deformation of the suture zone ended prior to the Mid-Eocene (~45?Ma) when the Eurasian margin was transgressed by non-marine and/or shallow-marine sediments. The foreland became volcanically active and subsided strongly during Mid-Eocene, possibly related to post-collisional slab rollback and/or delamination. The present structure and morphology of the suture zone was strongly influenced by several phases of mostly S-directed suture zone tightening (Late Eocene; pre-Pliocene), possible slab break-off and right-lateral strike-slip along the North Anatolian Transform Fault.

In the wider regional context, a double subduction zone model is preferred, in which northward subduction was active during the Jurassic and Cretaceous, both within the Tethyan ocean and bordering the Eurasian continental margin.  相似文献   

15.
The Haji‐Abad ophiolite in SW Iran (Outer Zagros Ophiolite Belt) is a remnant of the Late Cretaceous supra‐subduction zone ophiolites along the Bitlis–Zagros suture zone of southern Tethys. These ophiolites are coeval in age with the Late Cretaceous peri‐Arabian ophiolite belt including the Troodos (Cyprus), Kizildag (Turkey), Baer‐Bassit (Syria) and Semail (Oman) in the eastern Mediterranean region, as well as other Late Cretaceous Zagros ophiolites. Mantle tectonites constitute the main lithology of the Haji‐Abad ophiolite and are mostly lherzolites, depleted harzburgite with widespread residual and foliated/discordant dunite lenses. Podiform chromitites are common and are typically enveloped by thin dunitic haloes. Harzburgitic spinels are geochemically characterized by low and/or high Cr number, showing tendency to plot both in depleted abyssal and fore‐arc peridotites fields. Lherzolites are less refractory with slightly higher bulk REE contents and characterized by 7–12% partial melting of a spinel lherzolitic source whereas depleted harzburgites have very low abundances of REE and represented by more than 17% partial melting. The Haji‐Abad ophiolite crustal sequences are characterized by ultramafic cumulates and volcanic rocks. The volcanic rocks comprise pillow lavas and massive lava flows with basaltic to more‐evolved dacitic composition. The geochemistry and petrology of the Haji‐Abad volcanic rocks show a magmatic progression from early‐erupted E‐MORB‐type pillow lavas to late‐stages boninitic lavas. The E‐MORB‐type lavas have LREE‐enriched patterns without (or with slight) depletion in Nb–Ta. Boninitic lavas are highly depleted in bulk REEs and are represented by strong LREE‐depleted patterns and Nb–Ta negative anomalies. Tonalitic and plagiogranitic intrusions of small size, with calc‐alkaline signature, are common in the ophiolite complex. The Late Cretaceous Tethyan ophiolites like those at the Troodos, eastern Mediterranean, Oman and Zagros show similar ages and geochemical signatures, suggesting widespread supra‐subduction zone magmatism in all Neotethyan ophiolites during the Late Cretaceous. The geochemical patterns of the Haji‐Abad ophiolites as well as those of other Late Cretaceous Tethyan ophiolites, reflect a fore‐arc tectonic setting for the generation of the magmatic rocks in the southern branch of Neotethys during the Late Cretaceous. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

16.
李奋其  刘伟  耿全如 《地球学报》2010,31(6):781-790
大规模的早白垩世火山岩呈孤岛状广泛展布于冈底斯北部地区。1: 25万区域地质调查在那曲地区圈定出晚白垩世、中-晚侏罗世火山岩。在充分研究前人资料的基础上, 对出露状况较好的那曲县城晚白垩世火山岩、哈尔麦中-晚侏罗世火山岩进行了野外调研, 它们均为安山质火山岩系, 均与一套黑色砂板岩呈角度不整合接触, 同时对其进行了LA-ICP-MS锆石U-Pb定年, 便于进行区域对比。那曲地区的中生代火山岩多数锆石具有生长环带, 部分锆石显示核边结构。采自那曲东县城、哈尔麦的2件安山岩样品的年龄分别为116.3±1.4 Ma、111.37±0.73 Ma, 它们的形成时代基本一致, 应该为同一地质事件的产物。区域对比表明, 早白垩世火山作用是北冈底斯带最为强烈的一次火山活动, 其活动时间大致在110 Ma左右, 之后是早白垩世岛弧型深成中酸性侵入活动。冈底斯北带早白垩世火山作用究竟与狮泉河-嘉黎大洋俯冲有关, 还是与班公湖-怒江洋壳俯冲有关, 目前尚难定论。  相似文献   

17.
The Ust-Belaya ophiolite terrane in the West Koryak Orogen, which is the largest in northeastern Asia, consists of three nappe complexes. The upper Ust-Belaya Nappe is composed of a thick (>5 km) sheet of fertile peridotites and mafic rocks (remnants of the proto-Pacific lithosphere); its upper age boundary is marked by Late Neoproterozoic plagiogranites. In the middle Tolovka-Otrozhny Nappe, the Late Precambrian lherzolite-type ophiolites are supplemented by fragments of tectonically delaminated harzburgite-type ophiolites, which make up the Tolovka rock association. The isotopic age of metadacite (K-Ar method, whole-rock sample) and zircons from plagiogranite porphyry (U-Pb method, SHRIMP) determines the upper chronological limit of the Tolovka ophiolites as 262–265 Ma ago. It is suggested that igneous rocks of these ophiolites were generated in a backarc basin during the Early Carboniferous and then incorporated into the fold-nappe structure in the Mid-Permian. This was the future basement of the Koni-Taigonos arc, where the Early Carboniferous ophiolites together with Late Neoproterozoic precursors were subject to low-temperature metamorphism and intruded by plagiogranite porphyry dikes in Permian-Triassic. The polymicte serpentinite mélange, which was formed in the accretionary complex of the Koni-Taigonos arc comprises rock blocks of the upper units of Late Precambrian ophiolites (in particular, plagiogranite), the overlying Middle to Upper Devonian and Early Carboniferous deposits, as well as Early Carboniferous (?) Tolovka ophiolites and meta-ophiolites. Mélange of this type with inclusions of Late Precambrian “oceanic” granitoids also developed in the lower Utyosiki Nappe composed of Middle Jurassic-Lower Cretaceous sedimentary and volcanic sequences, the formation of which was related to the next Uda-Murgal island-arc systems.  相似文献   

18.
In southeast Anatolia, there are number of tectonomagmatic units in the Kahramanmaraş–Malatya–Elazığ region that are important in understanding the geological evolution of the southeast Anatolian orogenic belt during the Late Cretaceous. These are (a) metamorphic massifs, (b) ophiolites, (c) ophiolite-related metamorphics and (d) granitoids. The granitoids (i.e. Göksun–Afşin in Kahramanmaraş, Doğanşehir in Malatya and Baskil in Elazığ) intrude all the former units in a NE–SW trending direction. The granitoid in Göksun–Afşin (Kahramanmaraş) region is mainly composed of granodioritic and granitic in composition. The granodiorite contains a number of amphibole-bearing mafic microgranular enclaves of different sizes, whereas the granite is intruded by numerous aplitic dikes. The granitoid rocks have typical calcalkaline geochemical features. The REE- and Ocean ridge granite-normalized multi-element patterns and tectonomagmatic discrimination diagrams, as well as biotite geochemistry suggest that the granitoids were formed in a volcanic arc setting. The K–Ar geochronology of the granitoid rocks yielded ages ranging from 85.76±3.17 to 77.49±1.91 Ma. The field, geochemical and geochronological data suggest the following Late Cretaceous tectonomagmatic scenario for southeast Anatolia. The ophiolites were formed in a suprasubduction zone tectonic setting whereas the ophiolite-related metamorphic rocks formed either during the initiation of intraoceanic subduction or late-thrusting (∼90 Ma). These units were then overthrust by the Malatya–Keban platform during the progressive elimination of the southern Neotethys. Thrusting of the Malatya–Keban platform over the ophiolites and related metamorphic rocks was followed by the intrusion of the granitoids (88–85 Ma) along the Tauride active continental margin in the southern Neotethys.  相似文献   

19.
Abstract: Age of magmatism and tin mineralization in the Khingan‐Okhotsk volcano–plutonic belt, including the Khingan, Badzhal and Komsomolsk tin fields, were reviewed in terms of tectonic history of the continental margin of East Asia. This belt consists mainly of felsic volcanic rocks and granitoids of the reduced type, being free of remarkable geomagnetic anomaly, in contrast with the northern Sikhote‐Alin volcano–plutonic belt dominated by oxidized‐type rocks and gold mineralization. The northern end of the Khingan‐Okhotsk belt near the Sea of Okhotsk, accompanied by positive geomagnetic anomalies, may have been overprinted by magmatism of the Sikhote‐Alin belt. Tin–associated magmatism in the Khingan‐Okhotsk belt extending over 400 km occurred episodically in a short period (9510 Ma) in the middle Cretaceous time, which is coeval with the accretion of the Kiselevka‐Manoma complex, the youngest accretionary wedge in the eastern margin of the Khingan‐Okhotsk accretionary terranes. The episodic magmatism is in contrast with the Cretaceous‐Paleogene long–lasted magmatism in Sikhote–Alin, indicating the two belts are essentially different arcs, rather than juxtaposed arcs derived from a single arc. The tin‐associated magmatism may have been caused by the subduction of a young and hot back‐arc basin, which is inferred from oceanic plate stratigraphy of the coeval accre‐tionary complex and its heavy mineral assemblage of immature volcanic arc provenance. The subduction of the young basin may have resulted in dominance of the reduced‐type felsic magmas due to incorporation of carbonaceous sediments within the accretionary complex near the trench. Subsequently, the back‐arc basin may have been closed by the oblique collision of the accretionary terranes in Sikhote–Alin, which was subjected to the Late Cretaceous to Paleogene magmatism related to another younger subduction system. These processes could have proceeded under transpressional tectonic regime due to oblique subduction of the paleo‐Pacific plates under Eurasian continent.  相似文献   

20.
在青藏高原中部中拉萨地块之上新识别了一套晚侏罗世-早白垩世早期岩浆岩,本次对其中麻米地区出露的火山岩进行了锆石U-Pb定年与全岩主微量元素分析研究工作.测年结果显示麻米火山岩形成于晚侏罗世（152~150 Ma）,岩石地球化学具有高SiO2、高全碱含量（Na2O+K2O）、低MgO、低P2O5的特征,并显示明显的Eu、Sr、Ba等元素的亏损,具有高分异I型花岗质岩石的特征.结合区域上报道的同期中酸性侵入岩资料,麻米酸性火山岩起源于古老地壳物质重熔并经历了广泛的结晶分异作用.本文研究表明中拉萨地块上晚侏罗世-早白垩世早期岩浆作用形成于洋壳俯冲背景,应该是新特提斯洋北向俯冲过程中引发的弧型岩浆事件.   相似文献   

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