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1.
Volcanoplutonic complexes in NE Vietnam have recently been interpreted as intraplate products of the Emeishan plume. Alternatively, mafic–ultramafic rocks have been considered as dismembered Palaeotethyan ophiolites juxtaposed along a tectonic mélange zone. New U–Pb zircon geochronological and geochemical datasets presented here suggest a complex geological history that records collision between the Indochina–South China blocks. Mafic–ultramafic rocks exposed within a tectonic mélange (Song Hien Tectonic Zone) include sub-alkaline pillow basalts that define two geochemically distinct ophiolitic suites (SH-1: N-MORB-like, SH-2: transitional E-MORB-like). Both suites have geochemical signatures suggestive of crustal contamination, compatible with a volcanic passive margin/rift setting. We suggest that SH-1 basalts may correlate with the Devonian–Carboniferous Jinshajiang–Ailaoshan–Song Ma branch of the Palaeotethys and form part of the associated Dian–Qiong belt, whereas SH-2 basalts are co-magmatic with Middle–Late Permian mafic–ultramafic intrusive rocks (dolerites, gabbros, peridotites) that developed in a rift basin, most likely on the margin of the down-going South China plate during west-vergent subduction beneath Indochina. During continental orogenesis and thrust stacking, these ophiolitic rocks were juxtaposed with other lithotectonic blocks within the Song Hien Tectonic Zone. Post-collisional relaxation led to the development of a rift basin (Song Hien rift) comprising Late Permian–Triassic volcano-sedimentary strata including < 270–265 Ma terrigenous sandstones, < 252 Ma mudstones, and c. 254–248 Ma felsic effusives. Granites and granodiorites were emplaced across NE Vietnam between c. 252 and 245 Ma in a syn- to post-collisional setting. The Late Permian–Early Triassic felsic magmatic rocks best correlate with coeval rocks in SW Guangxi and the Central and Western Ailaoshan fold belts (China) and the Truong Son fold belt (Vietnam); together they signal the final to post-collisional stages of Indochina–South China collision. We demonstrate that the analysed magmatic rocks in the Lo-Gam–Song Hien domains of NE Vietnam are not genetically linked to the Emeishan Large Igneous Province in the Yangtze block of South China, as has been previously widely proposed. 相似文献
2.
Feifei Zhang Yuejun Wang Xinyue Chen Weiming Fan Yanhua Zhang Guowei Zhang Aimei Zhang 《Gondwana Research》2011,19(4):910-925
A kinematic and geochronological study has been carried out on the Triassic high-strain shear zones in Hainan Island, the southern South China Block. There are WNW- and NE-trending high-strain shear zones with greenschist- to amphibolite-facies metamorphism in this island. Kinematic indicators suggest a dextral top-to-the-NNE thrust shearing for the WNW-trending high-strain shear zones and a sinistral top-to-the-SE thrust shearing for the NE-trending shear zones. The quartz c-axis orientations of mylonitic rocks exhibit the domination of basal slip and some activation of a rhombohedra gliding system. The timing of shearing for these shear zones has been constrained by the 40Ar/39Ar dating analyses of synkinematic minerals. Middle Triassic (242–250 Ma) and late Triassic–early Jurassic (190–230 Ma) have been identified for the WNW- and NE-trending shear zones, respectively. A synthesis of these kinematic and thermogeochronological data points to a two-stage tectonic model for Hainan Island, that is, top-to-the-NNE oblique thrusting at 240–250 Ma followed by top-to-the-SE oblique thrusting at 190–230 Ma. In combination with the available data from the southern South China and Indochina Blocks, it is inferred that South Hainan and North Hainan have affinity to the Indochina and South China Blocks, respectively. The tectonic boundary between South Hainan and North Hainan lies roughly along the WNW-trending Changjiang–Qionghai tectonic zone probably linking to the Song Ma and Ailaoshan zones. The middle Triassic structural pattern of Hainan Island is spatially and temporally compatible with those of the South China and Indochina Blocks, and thus might be a derivation from the amalgamation of the Indochina with South China Blocks in response to the closure of the Paleotethys Ocean and subsequent subduction/collision. 相似文献
3.
《International Geology Review》2012,54(13):1548-1561
The location of the suture zone between the South China and Indochina blocks in northwest Vietnam has been under debate for decades. Generally, the boundary between these blocks has been placed along (1) the Ailaoshan–Red River zone or (2) the Song Ma zone. The Sin Quyen Formation, lying between these zones, was previously regarded as a Palaeo- and Mesoproterozoic sequence. It comprises its provenance and tectonic affinity. We analysed detrital zircons from two paragneisses and one migmatite of the Sin Quyen Formation employing laser ablation inductively coupled plasma mass spectrometry U–Pb dating techniques. U–Pb ages of these zircons show three main periods of zircon formation: ～2.7–3.0, ～2.2–2.5, and ～1.8 Ga, suggesting that Sin Quyen rocks were mainly derived from Palaeoproterozoic and Archaean basement units. Inasmuch as the South China basement comprises rocks of similar ages, we conclude that the Sin Quyen Formation belongs to that block. Our new data strengthen the view that the suture between the South China and Indochina blocks is located within the Song Ma zone. In addition, zircons with U–Pb ages >3.0 thousand million years represent the oldest minerals reported in northwest Vietnam so far, indicating the existence of Mesoarchaean crustal remnants in this region. 相似文献
4.
The Paleotethyan evolution of the Southeast Asia has become better understood in recent years. Questions remain, however, over the role of the Dien Bien Phu Suture Zone in the evolution of the Indochina Block and whether the Song Ma Suture represents the boundary between the Indochina Block and the South China Block. Granitoid geochronological and geochemical data obtained in northern Laos provide new information vis-à-vis these arguments. Zircon U–Pb ages together with whole rock, trace and rare earth element data from 27 granitic rocks from five complexes allow us to conclude that these granites are typical of I-type Indosinian volcanic arc granites. However, the 234–256 Ma I-type granites mismatch the initiation age obtained from the ductile shear zone of the Dien Bien Phu Fault, thus repudiating the existence of the Dien Bien Phu Suture Zone. This then implies that the Qamdo–Simao and Indochina blocks were united. The geochemical and geochronological data further suggest that the main crust in the Indochina Block formed in the Late Paleoproterozoic to Early Mesoproterozoic, much later than the Archean crustal formation age identified east of the Song Ma Suture. Moreover, the 440–404 Ma and 234–256 Ma I-type granites suggest that the boundary between Indochina and South China should be the Jinsha River Suture–Song Ma Suture–Kontum Massif, instead of the Jinsha River Suture–Song Chay Suture. Finally, the Emeishan basalt and granite complexes both form part of the South China tectonic units subducting westward under the Qamdo–Simao and Indochina blocks. 相似文献
5.
海南岛位于印支与华南陆块的交界地带,构造演化复杂,因此海南岛的拼合历史和构造属性一直备受争议.在海南岛三亚荔枝沟地区新识别出的酸性火山岩对于探讨海南岛早中生代的构造属性具有重要指示意义.LA-ICP-MS锆石U-Pb定年结果显示该套酸性火山岩中流纹岩的成岩年龄为241±6 Ma（MSWD=0.9）.地球化学特征表明该套火山岩样品的SiO2含量介于72.34%~77.83%,具较高的Al2O3（10.51%~13.53%）、K2O（2.85%~4.85%）、Na2O（1.75%~3.79%）含量和A/CNK比值（0.99~2.07）,为过铝质钙碱性酸性火山岩.样品稀土元素含量为∑REE=87×10-6~177×10-6,富集轻稀土元素,显示右倾岛弧型稀土元素配分模式,Eu负异常明显.样品富集大离子亲石元素,亏损高场强元素,εNd（t）变化于-12.1~-11.3之间,可被解释为变沉积物部分熔融后经历分离结晶作用的产物.区域对比研究表明该套酸性火山岩可与三江地区的金沙江-哀牢山-松马构造带的中三叠世岩浆岩进行类比,应形成于印支与华南陆块汇聚的构造背景. 相似文献
6.
《Comptes Rendus Geoscience》2008,340(2-3):94-111
In Vietnam, the Triassic Indosinian collision affected coevally the Truong Son belt and the Kontum Massif,which were not independent tectonic units, but parts of the same Gondwana-derived Indochina continental block. This thermotectonic event took place synchronously throughout Vietnam, during the Lower Triassic 250–240-Ma time interval, as demonstrated by numerous geochronological data, combining Ar–Ar and U–Pb dating methods. Structural and kinematic investigations, in the Indosinian metamorphic rocks, reveal that the collisional process resulted from a consistent northwest-striking convergence of Indochina with respect to the adjacent blocks. It is suggested that this motion was taken up by a pair of opposite subduction zones: to the north, beneath South China, and to the west, beneath western Indochina, along the Song Ma and Po Ko sutures, respectively. Tectonic markers, calc-alkaline subduction-related volcanism and granitic intrusions and the generation of high-pressure rocks that have been recently discovered support this geodynamic setting, at least along Po Ko. Along the northwest-trending Song Ma zone, the obliquity of the convergence during subduction and subsequent collision resulted in the development, within the Truong Son Belt, of a set of subparallel dextral mylonitic shear zones, under amphibolite-facies metamorphism. The intermediate segments remained weakly metamorphic or even almost devoid of metamorphism. Along Po Ko, the convergence was near-orthogonal, with a left-lateral strike-slip component; the ongoing continental subduction resulted in the reworking of the Kontum granulitic basement and the development of Indosinian HP granulitic conditions; the subsequent extension-related exhumation operated approximately in the same northwestwards direction. This Indosinian evolution, applied on a continental crust that had been probably affected, as in South China, by a Caledonian-related event, as judged by the general unconformity of the Lower Devonian sediments, the widespread occurrence of magmatic crystallisation ages of ca 450 Ma (Ordovician-Silurian), and by the approximately similar age of the primary granulitic episode in the Kontum Massif. The similarities of the Devonian facies over central, northern Vietnam and South China imply a land connection, possibly as a consequence of a Caledonian collision along Song Ma, but this does not preclude a further oceanic opening and a closure during the Indosinian. 相似文献
7.
越南东北部早中生代构造事件的年代学约束 总被引：6，自引：3，他引：3
越南东北部-海南岛-粤西南构造带整体上呈NW-SE走向展布于华南板块的南缘,是理解华南构造演化的关键地区.作为印支运动代表性地区的越南东北部地区Song Chay构造带上,下古生界浅变质沉积岩、上古生界至早-中三叠世未变质的沉积盖层中都发育向北东逆冲推覆,韧性变形域表现为NE-SW向的矿物拉伸线理和上部指NE的剪切变形,而脆性变形域则记录了大量NE极性的褶皱和冲断构造.两广交界的云开地体和海南岛地区存在着相同样式的构造变形.关于这期变形的时间,本文通过对野外地层以及所出露不同时期岩体变形特征的综合研究,并结合高质量的锆石U-Pb年代学数据,在越南的东北部厘定为237 ～ 228Ma.这期广泛分布于华南板块南缘构造事件的动力学机制同Day Nui Con Voi(大象山)微陆块与华南板块在早中生代的构造拼合事件相关.本文认为华南板块在早三叠世开始沿着越南东北部的Song Chay缝合带俯冲拼合于Day Nui Con Voi微陆块之下,因此在早-中三叠世时期,在作为俯冲盘的华南板块南缘发育一系列的褶皱和逆冲推覆构造,晚三叠世印支造山作用结束.因此,华南板块南缘的越南东北部-海南岛-粤西南构造带被一同卷入早-中三叠世同印支板块的碰撞造山体系之中. 相似文献
8.
新的区域地质调查在海南岛东北部木栏头地区识别出一套从前未知的中级变质杂岩。木栏头变质杂岩主要沿林新—木栏头—虎威岭—赤坡—七星岭—新埠海—铺前海边沿岸呈基岩或不同尺度的无根岩块断续出露，其主体是钙硅酸盐岩和正、副片麻岩，含有少量斜长角闪岩、石英岩和大理岩，并按分布区域可进一步区分出林新片麻岩- 斜长角闪岩组合、木栏头变质火山岩- 钙硅酸盐岩组合、虎威岭- 七星岭片麻岩- 钙硅酸盐岩- 大理岩组合和新埠海- 铺前片麻岩组合等四套岩石组合。对30件变质基性岩、变质中酸性岩、变质碎屑沉积岩、钙硅酸盐岩以及花岗和伟晶岩脉等不同类型岩石的锆石U- Pb定年结果表明，木栏头变质杂岩的原岩主体是一套二叠纪火山- 沉积岩系，其内含有少量二叠纪花岗质侵入岩以及前寒武纪结晶基底的残留。前寒武纪结晶基底主要包括古元古代晚期（1670 Ma）碎屑沉积岩和中元古代早期（1460~1410 Ma）花岗质片麻岩，晚二叠世碱性花岗岩中还存在大量单一的中元古代晚期（1180 Ma）继承锆石。变质沉积岩中的早期碎屑锆石年龄峰值为2550~2490 Ma、1850~1780 Ma、1600~1560 Ma、1450 Ma和1100 Ma，表明其物源主要来自于海南岛中部的抱板群、石碌群和石灰顶组。二叠纪花岗岩的侵入时代主要为280 Ma和260 Ma，与陆缘弧前盆地环境下形成的火山- 沉积岩系的时代基本一致。这些沉积岩中的碎屑锆石除具有395~345 Ma和280~256 Ma两个年龄峰值外，部分样品还含有960~930 Ma和450~410 Ma两个重要年龄峰值，与前人在海南岛晚古生代地层中获得的年代学结果相似。木栏头变质杂岩经历了晚二叠世—中三叠世（254~235 Ma）高角闪岩相区域变质和深熔作用以及花岗和伟晶岩脉的大规模侵入，独居石U- Pb定年表明中侏罗世（159 Ma）花岗岩脉也侵入其中。结合近年发表的研究资料，我们认为海南岛应属于印支陆块的一部分，由中元古代结晶基底和早古生代盖层构成的琼南地体以及该地体演化而来的琼北构造混杂岩带两个次级构造单元组成，邦溪- 晨星构造带或昌江- 琼海断裂不能被视为华南和印支陆块间的构造边界，真正的古特提斯缝合带（即金沙江- 哀牢山- 马江缝合带的东延）应位于木栏头北部，大致相当于现今琼州海峡断裂的位置。华南和印支陆块间古特提斯洋盆的关闭始于石炭纪（340~300 Ma）洋壳的南向俯冲，形成北部的潮滩鼻榴辉岩和南部的邦溪- 晨星弧后盆地，二叠纪时期（280~255 Ma）洋盆持续俯冲形成海南岛主体大陆岛弧以及木栏头弧前盆地，而后洋盆最终关闭并进入到陆- 陆碰撞和碰撞后伸展阶段，从而形成木栏头变质杂岩以及海南岛内部其他三叠纪变质岩和同期花岗质岩石。 相似文献
9.
南盘江盆地中三叠统碎屑锆石地质年代学:物源及其地质意义 总被引：1，自引：0，他引：1
南盘江盆地的物源及其构造性质至今尚未取得较为一致的认识。目前主要的观点认为其物源主要来自盆地东南面的云开大山地区,盆地的性质为古太平洋板块俯冲所形成的前陆盆地。本文采用碎屑锆石年代学方法,首次报道该盆地中三叠统碎屑锆石年龄组成,分析了该盆地的沉积物源,并基于物源分析探讨了成盆机制和板块间动力学关系。该盆地中三叠统碎屑锆石年龄组成最主要的特征性的年龄分布在320～250Ma之间,此区间内存在280Ma和250Ma两个峰值。通过与相邻各块体锆石年龄谱对比,本研究认为:(1)南盘江盆地的主要物源区应为古特提斯北缘(华南一侧)的石炭-二叠纪岩浆弧,SongMa构造带可能是三叠纪的缝合线,而不是因Sibumasu板块增生到印支板块而导致的板内活化带;(2)该盆地三叠纪时为古特提斯闭合在华南形成的前陆盆地,与古特提斯沿SongMa带向北俯冲闭合有关,前人认为的南盘江盆地形成于古太平洋板块向西北俯冲作用的观点值得商榷。 相似文献
10.
The Early Triassic Indosinian orogeny in Vietnam (Truong Son Belt and Kontum Massif); implications for the geodynamic evolution of Indochina 总被引：8，自引：0，他引：8
C. Lepvrier H. Maluski Vu Van Tich A. Leyreloup Phan Truong Thi Nguyen Van Vuong 《Tectonophysics》2004,393(1-4):87
New structural field data at various scale and 40Ar–39Ar geochronological results, from the basement rocks in the Truong Son belt and Kontum Massif of Vietnam, confirm that ductile deformation and high-temperature metamorphism were caused by the Early Triassic event of the Indosinian Orogeny in the range of 250–240 Ma. A compilation of isotopic data obtained in other countries along the Sibumasu–Indochina boundary broadly indicates same interval of ages. This tectonothermal event is interpreted as the result of a synchronous oblique collision of Indochina with both Sibumasu and South China, inducing dextral and sinistral shearing along E–W to NW–SE and N–S fault zones, respectively. The collision along Song Ma follows the northwards subduction of Indochina beneath South China and the subsequent development of the Song Da zone which in turn was affected by the Late Triassic Indosinian phase of shortening. Within the Indochina plate, internal collisions occurred coevally in the Early Triassic, as along the Poko suture, at the western border of the Kontum Massif. 相似文献
11.
I. Metcalfe 《Journal of Asian Earth Sciences》2000,18(6)
It is proposed that the Bentong–Raub Suture Zone represents a segment of the main Devonian to Middle Triassic Palaeo-Tethys ocean, and forms the boundary between the Gondwana-derived Sibumasu and Indochina terranes. Palaeo-Tethyan oceanic ribbon-bedded cherts preserved in the suture zone range in age from Middle Devonian to Middle Permian, and mélange includes chert and limestone clasts that range in age from Lower Carboniferous to Lower Permian. This indicates that the Palaeo-Tethys opened in the Devonian, when Indochina and other Chinese blocks separated from Gondwana, and closed in the Late Triassic (Peninsular Malaysia segment). The suture zone is the result of northwards subduction of the Palaeo-Tethys ocean beneath Indochina in the Late Palaeozoic and the Triassic collision of the Sibumasu terrane with, and the underthrusting of, Indochina. Tectonostratigraphic, palaeobiogeographic and palaeomagnetic data indicate that the Sibumasu Terrane separated from Gondwana in the late Sakmarian, and then drifted rapidly northwards during the Permian–Triassic. During the Permian subduction phase, the East Malaya volcano-plutonic arc, with I-Type granitoids and intermediate to acidic volcanism, was developed on the margin of Indochina. The main structural discontinuity in Peninsular Malaysia occurs between Palaeozoic and Triassic rocks, and orogenic deformation appears to have been initiated in the Upper Permian to Lower Triassic, when Sibumasu began to collide with Indochina. During the Early to Middle Triassic, A-Type subduction and crustal thickening generated the Main Range syn- to post-orogenic granites, which were emplaced in the Late Triassic–Early Jurassic. A foredeep basin developed on the depressed margin of Sibumasu in front of the uplifted accretionary complex in which the Semanggol “Formation” rocks accumulated. The suture zone is covered by a latest Triassic, Jurassic and Cretaceous, mainly continental, red bed overlap sequence. 相似文献
12.
海南岛地处印支陆块和华南陆块的交界地带,具有复杂的构造演化史,其拼合机制及精细时代一直备受争议.在海南岛昌江-琼海断裂以北的晨星地区识别出一套具高εNd(t)值的火山岩,对其进行了全岩40Ar-39Ar年代学及主、微量元素和同位素地球化学研究.结果表明,该火山岩的全岩40Ar-39Ar坪年龄为328.1±2.6 Ma,代表了其喷发年龄;该变基性岩SiO2含量为46.92%~52.58%,具有低TiO2、低K2O、高Al2O3的特征;稀土元素丰度为15.1×10-6~28.7×10-6, 呈现N-MORB型微量元素配分曲线, εNd(t)高至9.02~9.85,显示出高度亏损的地球化学特征;其成因被解释为源于受流体交代作用改造的MORB型地幔源区.综合分析表明晨星地区变基性岩的形成可能与古特提斯洋陆俯冲格局下华南与印支陆块间的弧后盆地或有限洋演变有关. 相似文献
13.
As the largest siliciclastic sink in the South China block, the Triassic Nanpanjiang basin is generally thought of as a foreland basin related to Indosinian collision between the South China and Indochina blocks. Our basin analysis, spanning an eight years period, provides details of Lopingian to Middle Triassic stratigraphic fill and tectonic subsidence of the basin. Field observation and sedimentological analyses reveal that the basin was not filled by a monotonous turbidite system and suggest instead the development of five primary depositional units constituted by deep-water turbidite systems, mass-transport deposits, condensed drapes, shallow-water isolated carbonate platforms, and volcano-volcaniclastic rocks. The stratigraphic completeness of the basin, the coexistence of widespread but localized carbonate platforms within axially filled deep-water basin, tectonically generated cyclothems of transverse mass-transport deposits along intrabasinal faults and basin fill of extrusive rocks of bimodal composition together apparently call in question the claim that crustal shortening prevailed during the Late Permian to pre-Norian Triassic. Patterns of basin fill, differential tectonic subsidence and very high subsidence rate of the region adjacent to master fault are more closely match the pattern expected for extensional to transtensional basin in a back-arc setting. The crustal extension in the southwestern South China was not consistent with hypothesized Indosinian collision between South China and Indochina blocks, but more likely developed in response to northwestward subduction of the paleo-Pacific plate. Our results, combined with regional considerations, lead to a new model for the Triassic tectonic evolution of South China during Triassic assembly of the southeastern and eastern Asia. 相似文献
14.
《International Geology Review》2012,54(15):1823-1841
ABSTRACTThe Song Ma zone in Northwestern Vietnam is considered as a suture of the South China and Indochina blocks, and plays an important role in understanding the tectonic evolution in Southeast Asia and surrounding areas. Granitic rocks of the Muong Lat complex are distributed in the Song Ma suture, consisting mainly of monzogranite and granodiorite. The rocks are sub-alkaline in affinity with high K contents and characteristics of S-type granite. They have high SiO2, total Na2O + K2O, and Zr contents and high aluminium saturation index values (0.97 to 1.29 with an average of 1.14). All these geochemical signatures, together with high (87Sr/86Sr)i ratios (0.71391 to 0.74568), and low whole rock εNd(t) and zircon εHf(t) values (?13.1 to ?9.4) suggested an origin from partial melting of crustal source rocks. Primitive mantle normalized trace element contents exhibit positive anomalies of Rb, Th, U and Pb, but negative anomalies of Nb, Ta, and Ti, indicating a collision-related environment. The depleted Nd and Hf zircon model ages from investigated samples, in combination with inherited zircon ages, suggest the existence of Precambrian basement in the study region. S-type granites of the late Permian-early Triassic (the Muong Lat, Phia Bioc and Hai Van complexes) in Vietnam were formed by the subduction-collision of the South China and Indochina blocks. 相似文献
15.
福建省古生代至中生代大地构造演化的格架 总被引：10，自引：0，他引：10
松溪—长汀断裂带和福州—永定断裂带是控制福建古生代及以后大地构造演化的两条北东东向的断裂带。地质地球化学资料表明,前者是加里东期的地体碰撞带,沿线分布了构造混杂岩、变质超基性岩体、具有角闪岩相和中压矿物的变质岩以及同碰撞型花岗岩体,以后又发育为A型俯冲带;后者是发育于加里东构造层之上的海西期张裂带,在形成海西期的福州—永定海峡的同时,产生了石炭纪海底双模式火山岩及层控铁矿,印支期的碰撞活动使海峡封闭并发育A型俯冲作用。由此,北东东向的松溪—长汀断裂带和福州—永定断裂带可以将福建划分为三个古生代的构造地层地体:闽北地体、闽中地体和闽东南地体。通过对福建省古生代地体构造分析、古地磁测量及古地理重建,展现在我们眼前是:华南(其中包括福建)在古生代中期从冈瓦纳大陆分离出来后,横渡特提斯海,在古生代末至中生代初到达劳亚大陆,与中朝板块碰撞引起了福建地体间强烈的造山运动。 相似文献
16.
Depositional Age,Provenance Characteristics and Tectonic Setting of the Ailaoshan Group in the Southwestern South China Block 总被引：1，自引：0，他引：1
The depositional and metamorphic ages and provenances of the Ailaoshan(ALS) Group in the Ailaoshan-Red River(ALS-RR) shear zone, southwestern South China Block(SCB), were investigated to constrain the tectonic history of the southwestern SCB. In this study, we use petrology, geochemical analysis, zircon cathodoluminescence imaging and UPb geochronology to analyse samples of quartzite, garnet-bearing two-mica schist and metapelite. The age spectra of detrital zircon grains from these metasediments show two dominant age peaks at 550–424 Ma and 876–730 Ma and two subordinate peaks at 970–955 Ma and ～2450 Ma. The youngest peak, corresponding to the early Palaeozoic, accounts for more than 20% of the total dates and constrains the deposition of the ALS Group to the Palaeozoic rather than the Palaeoproterozoic as traditionally thought. Moreover, two peaks of metamorphic ages corresponding to the Permo-Triassic and Cenozoic were also identified, and these ages document the tectonothermal events associated with the Indosinian collision between the Indochina Block and the SCB and the Himalayan collision between the Indian and Asian plates. Geochemical data suggest that the provenances of the ALS Group were dominated by continental arc and recycled metasedimentary rocks. The comparison of probability density distribution plots of the detrital zircon U-Pb age data indicates that the Neoproterozoic detritus in the ALS Group was probably derived from the arc-related Neoproterozoic intrusive bodies in the northwestern and southwestern SCB. Furthermore, the early Palaeozoic detritus might have been sourced from eroded early Palaeozoic strata and magmatic plutons in Cathaysia and volcanic rocks in the western Indochina Block. 相似文献
17.
《International Geology Review》2012,54(14):1769-1782
The early Palaeozoic tectonic evolution of South Mongolia is not well constrained due to the limited exposure of early Palaeozoic rocks in the area and the scarcity of both geochemical and geochronological data. In order to help rectify this situation, we have conducted detailed studies on the Biluutiin ovoo ophiolite in South Mongolia to provide constraints on the tectonic evolution of the region during this period. The Biluutiin ovoo ophiolite consists of ultramafic rocks, mylonitic gabbro, basalt, tuff sandstone, plagiogranite, calcite, and chert. Gabbro and plagiogranite samples from the ophiolitic complex yielded SHRIMP zircon ages of 525 ± 5 Ma and 503 ± 6 Ma, respectively. Biluutiin ovoo ophiolitic basalts display LREE and LILE enrichment and strong HFSE depletion, indicating that the ophiolite is supra-subduction zone (SSZ) type. Plagiogranite with adakite-like geochemical compositions suggests that palaeo-ocean subduction occurred in South Mongolia during Cambrian time. Intruding granite yielded a SHRIMP zircon age of 353 ± 2 Ma, indicating that the ophiolite was emplaced before early Carboniferous time. Identification of the Cambrian ophiolitic complex and the occurrence of Cambrian adakites indicate that southern Mongolia underwent a period of active volcanism during the Cambrian. The Cambrian formations are likely correlated to the early Palaeozoic subduction-accretion belt of Western Mongolia. 相似文献
18.
The convergence process between South China and the Indochina Block is still controversial. A large number of igneous rocks scattered along the current China‐Vietnam border provide a good opportunity to investigate the tectonic evolution. Babu ophiolites, cropping out in the southeastern Yunnan province (SW China), consist primarily of metaperidotite, serpentinite, pillow basalt (metabasalt), gabbro, metadiabase. Most of them are fault contacted and strongly sheared, especially between metaperidotite/serpentinite and metabasalt. U‐Pb zircon analyses yield an Early Permian formation age of ～278 Ma. Basalts and metagabbros show light rare earth elements (LREEs)‐depleted and heavy rare earth elements (HREEs)‐flat REE patterns, and large ion lithophile elements (LILEs)‐depleted primitive‐normalized spider diagrams without Nb‐Ta anomalies, which is similar to N‐MORB. Metaperidotites have low initial 187Os/188Os (0.122‐0.126) and γOs values, and indicate that they were derived from a depleted mantle source. Relative low (87Sr/86Sr)i and high εNd(t) values of basalts and metagabbros also support their DMM origin. The petrological, geochemical and isotope characteristics suggest that Babu ophiolites were N‐MORB‐type and represent remnants of an Early Permian oceanic crust. Mafic‐ultramafic rocks exposed in Cao Bang area (NE Vietnam) have recently been considered as dismembered Paleotethyan ophiolites instead of were genetically linked to the Emeishan Large Igneous Province. U‐Pb zircon analyses suggest an Early‐Middle Permian age (274 ±18 Ma) for the formation of ultramafic rocks. Both whole rock geochemistry and Cr‐spinel mineral chemistry show MORB‐like characteristics. Field observations suggest that Babu and Cao Bang ophiolite complex structurally overlie Middle‐Triassic deposits, and form a tectonic mélange zone. It developed from the subduction of a Paleotethyan subsidiary ocean basin between the South China and Indochina blocks until their collision.. 相似文献
19.
The geology of Northern Vietnam offers critical clues on the convergence history between the South China and Indochina blocks. We constrain the tectonic evolution of the South China and Indochina blocks using geochemical, mineral chemical and geochronological data collected from mafic–ultramafic rocks exposed in the Cao Bang area, Northeastern Vietnam. These rocks show significant enrichment in large ionic lithophile elements (LILEs) such as Cs, Rb, Ba, Th, U, and Pb and depletion in high field strength elements (HFSEs) such as Nb, Ta, Zr, and Ti showing [Nb/La]N between 0.28–0.41, [La/Yb]N = 3.94–10.00 and Zr/Y = 2.0–4.4. These geochemical features as well as the petrology and mineral chemistry of the Cao Bang mafic–ultramafic magmas are comparable to those of magmatic complexes formed in a back-arc environment. The basalts yield Rb–Sr whole rock ages of 263 ± 15 Ma, that are consistent with the zircon U–Pb and K–Ar ages reported in previous studies from the same area. The spatial and temporal distribution of the arc magmas within the Indochina block and along the southern margin of the South China block suggest that the Permo-Triassic mafic–ultramafic magmas formed during a tectonic event that is different from the subduction and collision event between the Indochina and South China blocks. 相似文献
20.
华南西南缘凭祥地区位于特提斯构造域东端,华南与印支陆块碰撞缝合带的北部,该区出露的三叠纪中酸性火山岩是古特提斯洋俯冲过程中在华南陆块边缘形成的大陆弧产物,这些火山岩同时携带的大量来自华南陆块基底的捕获锆石为华南陆块的构造热事件研究将提供重要的信息。对凭祥地区三叠系北泗组英安岩进行了同位素年代学、地球化学及锆石Hf同位素研究,获得了一个英安岩样品的加权平均年龄为（227.8±1）Ma,这些英安岩具有高SiO2、K2O含量,极低的MgO、MnO和CaO含量,富集大离子亲石元素（Rb、Ba、Th和U）和亏损高场强元素（Nb、Ta）的特点,显示了典型的岛弧岩浆作用特征,代表古特提斯洋向北俯冲至华南陆块之下形成的大陆弧产物。其余两个英安岩样品中的70粒锆石主要为来自华南陆块基底的捕获锆石,其年龄数据变化区间较大,为1010~231 Ma,这些捕获锆石U-Pb年龄频谱分布主要集中在四个区间:11010~800 Ma（峰值900 Ma）,其锆石的εHf（t）值为4.5~15.1,响应扬子和华夏陆块之间聚合-裂解-再聚合的构造演化事件,反应了其幔源岩浆的广泛参与;2720~620 Ma（峰值680 Ma）响应南华纪已拼合的扬子-华夏陆块的再次发生裂解;3490~400 Ma（峰值450 Ma）,其锆石的εHf（t）值为2.2~-7.8,响应华南早古生代加里东运动有关的壳-幔相互作用岩浆事件;4280~230 Ma（峰值250 Ma）,其锆石εHf（t）值为-13.6~-16.5,地壳模式年龄为2.3~2.1 Ga,代表了印支与华南陆块之间古特提斯洋俯冲闭合的岩浆事件。文章的研究结果揭示了凭祥北泗组英安岩与华南陆块的亲缘性,其结晶年龄限定了华南与印支陆块之间的古特提斯洋俯冲结束、陆-陆开始碰撞的最晚时限为中-晚三叠纪。 相似文献