首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
Knowledge of Trans-Himalayan tectono-magmatic evolution is critical to understanding the complex pre-collisional history of southern Eurasia active continental margin. It has been proposed that magmatic rocks of the Trans-Himalayan batholith, extending from southern Tibet to Southeast Asia, are now exposed as the Western Myanmar Arc and Central Granite Belt in Myanmar, yet origin, emplacement, and relationships of the two juxtaposed belts remain poorly constrained. In this study, 2D seismic and drilling data for the Western Myanmar Arc, zircon U-Pb age and Hf isotope and whole-rock geochemical data for magmatic rocks from the arc have been applied. Our seismic profiles, borehole stratigraphic sequences and zircon U-Pb data show that a typical arc-basin system was well developed along the western Myanmar continental margin. The magmatic arc has experienced at least three igneous events in the mid-Cretaceous (110–90 Ma), latest Cretaceous-Early Paleocene (69–64.5 Ma) and Eocene (53–38 Ma), as well as three associated uplift processes in the Late Cretaceous, Eocene and Late Oligocene. Whole-rock geochemical characteristics and zircons showing variable but predominately positive εHf(t) values, suggest a significant juvenile mantle source involving a proportion of ancient subducted sediments and juvenile crustal materials for these typical arc-related magmatic rocks. The identification of mid-Cretaceous to Paleogene magmatic rocks having positive εHf(t) values from the Western Myanmar Arc: 1) indicates that the magmatism can be correlated with the Gangdese arc within the Lhasa terrane of the southern Tibetan Plateau; 2) provides evidence for the proximal-derived model that Paleogene sediments in the Central Myanmar Basin were from the Western Myanmar Arc, but were not delivered by the paleo-Yarlung Tsangpo-Irrawaddy river system from the Gangdese arc; and 3) enables a model of eastward subduction of the Neo-Tethyan/Indian oceanic crust to reflect onset of the magmatism at the mid-Cretaceous and a long-existed back-arc extension in western Myanmar.  相似文献   

2.
The Gangdese magmatic belt, located in the southern margin of the Lhasa terrane and carrying significant copper and polymetallic mineralization, preserves important information relating to the tectonics associated with Indian–Eurasian collision and the crustal growth of southern Tibet. Here we investigate the Quxu batholith in the central domain of the Gangdese magmatic belt and report the occurrence of hornblende gabbros for the first time. We present petrologic, zircon U–Pb–Hf isotopic and bulk-rock chemistry data on these rocks. The hornblende gabbros display sub-alkaline features, and correspond to tholeiite composition. They also show medium K calc-alkaline to low K affinity. The rocks show enrichment in LILEs and LREEs, but are depleted in HFSEs, indicating a subduction-related active continental margin setting for the magma genesis. Our computations show that the gabbroic pluton was emplaced in the middle-lower crustal depth of ca. 18 km. Zircons from the hornblende gabbros yield crystallization age of ca. 210 Ma, revealing a late Triassic magmatic event. Combined with available data from the Gangdese magmatic belt, our study suggests that the northward subduction of the Neo-Tethys oceanic crust beneath the southern margin of the Lhasa terrane might have been initiated not later than the Norian period of Triassic. Zircons from the hornblende gabbro show positive εHf(t) values of 9.56 to 14.75 (mean value 12.44), corresponding to single stage model ages (TDM1) in the range of 256 Ma to 459 Ma, attesting to crustal growth in the southern Lhasa terrane associated with the subduction of the Neo-Tethys oceanic crust.  相似文献   

3.
《Gondwana Research》2014,26(4):1445-1468
The continental crust of the North China Craton (NCC) is a major reservoir of mineral resources with imprints of secular changes in tectonics and metallogeny. The Jiaodong Peninsula, located in the eastern margin of the North China Craton (NCC), is currently one of the largest gold producers over the globe, and preserves the records of multiple magmatic and metamorphic events. Here we characterize the timing and tectonics of the major Mesozoic magmatism and the associated gold metallogeny in this region through a comprehensive U–Pb geochronological and Hf isotope investigation of zircons in a suite of granitoids, mafic magmatic enclaves, melanocratic dikes and melted basement rocks.The Linglong granite, hosting one of the major gold deposits in Jiaodong, shows emplacement ages between 150 and 160 Ma, and the dominantly negative εHf (t) values (− 34.0 to − 23.8) of zircons from this intrusion suggest magma derivation from recycled components in the Archean basement. The Guojialing granodiorite and its mafic magmatic enclaves show similar ages between 123 and 127 Ma, with negative εHf (t) values (− 19.3 to − 16.8), corresponding to crustal magma source. The melanocratic dikes, belonging to pre- and syn-mineralization stages, with U–Pb age range of 126 to 166 Ma display large variation in their zircon εHf (t) values (− 25.7 and 2.3) suggesting the involvement of both recycled crustal and juvenile mantle components. Zircons in the melted basement rocks with ages in the range of ca. 127–132 Ma also display both positive and negative εHf (t) values (− 44.6 and 9.8) indicating a mixture of recycled ancient crust and juvenile magmas. Our study shows that although the peak of gold metallogeny coincided with the tectonics associated with Pacific plate subduction which mobilized and concentrated the ores, the source materials of gold mineralization and magmatism had multiple origins including from the Precambrian basement rocks, Mesozoic granitoids and mantle-derived mafic magmas with extensive mixing of crustal, lithosphere mantle and asthenospheric components. A combination of delamination, mantle upwelling, subduction-related metasomatic enrichment and recycling of ancient components facilitated the gold metallogeny in this region. Our study provides a typical case of juvenile and recycled components in the formation and evolution of continental crust and associated mineral resources.  相似文献   

4.
New insights on the Paleozoic evolution of the continental crust in the North Patagonian Massif are presented based on the analysis of Sm–Nd systematics. New evidence is presented to constrain tectonic models for the origin of Patagonia and its relations with the South American crustal blocks. Geologic, isotopic and tectonic characterization of the North Patagonian Massif and comparison of the Nd parameters lead us to conclude that: (1) The North Patagonian Massif is a crustal block with bulk crustal average ages between 2.1 and 1.6 Ga TDM (Nd) and (2) At least three metamorphic episodes could be identified in the Paleozoic rocks of the North Patagonian Massif. In the northeastern corner, Famatinian metamorphism is widely identified. However field and petrographic evidence indicate a Middle to Late Cambrian metamorphism pre-dating the emplacement of the ca. 475 Ma granitoids. In the southwestern area, are apparent 425–420 Ma (?) and 380–360 Ma metamorphic peaks. The latter episode might have resulted from the collision of the Antonia terrane; and (3) Early Paleozoic magmatism in the northeastern area is coeval with the Famatinian arc. Nd isotopic compositions reveal that Ordovician magmatism was associated with attenuated crust. On the southwestern border, the first magmatic recycling record is Devonian. Nd data shows a step by step melting of different levels of the continental crust in the Late Palaeozoic. Between 330 and 295 Ma magmatism was likely the product of a crustal source with an average 1.5 Ga TDM (Nd). Widespread magmatism represented by the 295–260 Ma granitoids involved a lower crustal mafic source, and continued with massive shallower-acid plutono volcanic complexes which might have recycled an upper crustal segment of the Proterozoic continental basement, resulting in a more felsic crust until the Triassic. (4) Sm–Nd parameters and detrital zircon age patterns of Early Paleozoic (meta)-sedimentary rocks from the North Patagonian Massif and those from the neighboring blocks, suggest crustal continuity between Eastern Sierras Pampeanas, southern Arequipa-Antofalla and the northeastern sector of the North Patagonian Massif by the Early Paleozoic. This evidence suggests that, at least, this corner of the North Patagonian Massif is not allochthonous to Gondwana. A Late Paleozoic frontal collision with the southwestern margin of Gondwana can be reconcilied in a para-autochthonous model including a rifting event from a similar or neighbouring position to its post-collision location. Possible Proterozoic or Early Paleozoic connections of the NPM with the Kalahari craton or the western Antartic blocks should be investigated.  相似文献   

5.
The Kuh-e Dom Pluton is located along the central northeastern margin of the Urumieh–Dokhtar Magmatic Arc, spanning a wide range of compositions from felsic rocks, including granite, granodiorite, and quartz monzonite, through to intermediate-mafic rocks comprising monzonite, monzodiorite, diorite, monzogabbro, and gabbro. The Urumieh–Dokhtar Magmatic Arc forms a distinct linear magmatic complex that is aligned parallel with the orogenic suture of the Zagros fold-thrust belt. Most samples display characteristics of metaluminous, high-K calc-alkaline, I-type granitoids. The initial isotopic signatures range from εNd (47 Ma) = −4.77 to −5.89 and 87Sr/86Sr(i) = 0.7069 to 0.7074 for felsic rocks and εNd (47 Ma) = −3.04 to −4.06 and 87Sr/86Sr(i) = 0.7063 to 0.7067 for intermediate to mafic rocks. This geochemical and isotopic evidence support a mixed origin for the Kuh-e Dom hybrid granitoid with a range of contributions of both the crust and mantle, most probably by the interaction between lower crust- and mantle-derived magmas. It is seem, the felsic rocks incorporate about 56–74% lower crust-derived magma and about 26–44% of the enriched mantle-derived mafic magma. In contrast, 66–84% of the enriched mantle-derived mafic magma incorporates 16–34% of lower crust-derived magma to generate the intermediate-mafic rocks. According to the differences in chemical composition, the felsic rocks contain a higher proportion of crustal material than the intermediate to mafic ones. Enrichment in LILEs and depletion in HFSEs with marked negative Nb, Ba, and Ti anomalies are consistent with subduction-related magmatism in an active continental margin arc environment. This suggestion is consistent with the interpretation of the Urumieh–Dokhtar Magmatic Arc as an active continental margin during subduction of the Neotethys oceanic crust beneath the Central Iranian microcontinent.  相似文献   

6.
《Gondwana Research》2013,24(4):1429-1454
Different hypotheses have been proposed for the origin and pre-Cenozoic evolution of the Tibetan Plateau as a result of several collision events between a series of Gondwana-derived terranes (e.g., Qiangtang, Lhasa and India) and Asian continent since the early Paleozoic. This paper reviews and reevaluates these hypotheses in light of new data from Tibet including (1) the distribution of major tectonic boundaries and suture zones, (2) basement rocks and their sedimentary covers, (3) magmatic suites, and (4) detrital zircon constraints from Paleozoic metasedimentary rocks. The Western Qiangtang, Amdo, and Tethyan Himalaya terranes have the Indian Gondwana origin, whereas the Lhasa Terrane shows an Australian Gondwana affinity. The Cambrian magmatic record in the Lhasa Terrane resulted from the subduction of the proto-Tethyan Ocean lithosphere beneath the Australian Gondwana. The newly identified late Devonian granitoids in the southern margin of the Lhasa Terrane may represent an extensional magmatic event associated with its rifting, which ultimately resulted in the opening of the Songdo Tethyan Ocean. The Lhasa−northern Australia collision at ~ 263 Ma was likely responsible for the initiation of a southward-dipping subduction of the Bangong-Nujiang Tethyan Oceanic lithosphere. The Yarlung-Zangbo Tethyan Ocean opened as a back-arc basin in the late Triassic, leading to the separation of the Lhasa Terrane from northern Australia. The subsequent northward subduction of the Yarlung-Zangbo Tethyan Ocean lithosphere beneath the Lhasa Terrane may have been triggered by the Qiangtang–Lhasa collision in the earliest Cretaceous. The mafic dike swarms (ca. 284 Ma) in the Western Qiangtang originated from the Panjal plume activity that resulted in continental rifting and its separation from the northern Indian continent. The subsequent collision of the Western Qiangtang with the Eastern Qiangtang in the middle Triassic was followed by slab breakoff that led to the exhumation of the Qiangtang metamorphic rocks. This collision may have caused the northward subduction initiation of the Bangong-Nujiang Ocean lithosphere beneath the Western Qiangtang. Collision-related coeval igneous rocks occurring on both sides of the suture zone and the within-plate basalt affinity of associated mafic lithologies suggest slab breakoff-induced magmatism in a continent−continent collision zone. This zone may be the site of net continental crust growth, as exemplified by the Tibetan Plateau.  相似文献   

7.
Geophysical data illustrate that the Indian continental lithosphere has northward subducted beneath the Tibet Plateau, reaching the Bangong–Nujiang suture in central Tibet. However, when the Indian continental lithosphere started to subduct, and whether the Indian continental crust has injected into the mantle beneath southern Lhasa block, are not clear. Here we report new results from the Quguosha gabbros of southern Lhasa block, southern Tibet. LA-ICP-MS zircon U–Pb dating of two samples gives a ca. 35 Ma formation age (i.e., the latest Eocene) for the Quguosha gabbros. The Quguosha gabbro samples are geochemically characterized by variable SiO2 and MgO contents, strongly negative Nb–Ta–Ti and slightly negative Eu anomalies, and uniform initial 87Sr/86Sr (0.7056–0.7058) and εNd(t) (− 2.2 to − 3.6). They exhibit Sr–Nd isotopic compositions different from those of the Jurassic–Eocene magmatic rocks with depleted Sr–Nd isotopic characteristics, but somewhat similar to those of Oligocene–Miocene K-rich magmatic rocks with enriched Sr–Nd isotopic characteristics. We therefore propose that an enriched Indian crustal component was added into the lithospheric mantle beneath southern Lhasa by continental subduction at least prior to the latest Eocene (ca. 35 Ma). We interpret the Quguosha mafic magmas to have been generated by partial melting of lithospheric mantle metasomatized by subducted continental sediments, which entered continental subduction channel(s) and then probably accreted or underplated into the overlying mantle during the northward subduction of the Indian continent. Continental subduction likely played a key role in the formation of the Tibetan plateau at an earlier date than previously thought.  相似文献   

8.
大陆弧岩浆幕式作用与地壳加厚:以藏南冈底斯弧为例   总被引：1，自引：0，他引：1  
大陆弧岩浆带位于汇聚板块的前缘,记录了洋陆俯冲过程和大陆地壳生长过程,是研究壳幔相互作用的天然实验室。越来越多的研究发现,大陆弧岩浆的生长与侵位并不是均一的、连续的过程,而是呈现阶段性、峰期性特征,即幕式岩浆作用。弧岩浆峰期与岩浆平静期相比,岩浆增生速率显著增强,易于发生岩浆聚集,继而形成大的岩基,如北美西部科迪勒拉造山带内华达岩基、半岛岩基等。藏南冈底斯岩浆带位于拉萨地体南缘,属于印度-亚洲碰撞带的上盘,其南侧与喜马拉雅地体以雅鲁藏布蛇绿岩带为界。冈底斯弧岩浆形成时代集中在240~50 Ma期间,其形成与演化与新特提斯洋壳岩石圈板片俯冲到拉萨地体之下密切相关。因此,对冈底斯弧型岩浆作用的研究,将很好地揭示大陆型弧岩浆的演化过程,继而反演洋-陆俯冲过程,以及壳幔相互作用过程。通过对冈底斯岩浆带岩浆岩锆石U-Pb及Lu-Hf同位素,以及弧前和前陆盆地碎屑锆石U-Pb和Lu-Hf同位素的收集和整理,结合已经发表的区域地质资料的总结,我们发现冈底斯弧型岩浆演化具有如下特点:1幕式侵位,岩浆峰期为100~80 Ma和65~40 Ma,中间为岩浆平静期;2峰期阶段岩浆聚集,形成巨大岩基;岩石同位素非常亏损,预示着地幔物质的显著参与;3在弧岩浆的峰期阶段,冈底斯地壳厚度有显著增加,说明弧岩浆的峰期侵位对地壳加厚有重大贡献。  相似文献   

9.
Lower Cretaceous volcanic lithic arenites, widely distributed in the Tethyan Himalaya, provide insights into the continental breakup of Eastern Gondwana. In southern Tibet they are represented by the Wölong Volcaniclastics. The volcanic rocks that contributed clastic material to the lower parts of this unit were predominantly alkali basalts, whereas rhyolitic/dacitic volcanism becomes the predominant source of the upper strata. Geochemical analyses of basaltic grains and of detrital Cr-spinels from the Wölong Volcaniclastics demonstrate the alkaline character of the volcanism and suggest “within-plate” tectonic setting for the volcanism. Zircon U–Pb ages confirm that this volcanism continued from ～ 140 Ma to ～ 119 Ma. Hf-isotope data on these Early Cretaceous zircons indicate that their parental magmas were mantle-derived, but in the later stage of magmatic activity mantle-derived magmas were mixed with partial melts derived from the continental crust.The Lower Cretaceous volcaniclastics occur along a broad belt paralleling the northern margin of Greater India. The onset of volcaniclastic deposition in the Himalayas appears to become progressively younger toward the west, but it ended synchronously during the Late Albian (～ 102 Ma). The low volume of volcanic rocks and their intra-plate tectonic setting suggest that they are the result of decompressional melting along extensional deep-seated fractures cross-cutting the continental crust, and reflect changes in regional intra-plate tectonic stresses when Greater India began to separate from the Australia–Antarctica supercontinent.  相似文献   

10.
The Central Asian Orogenic Belt (CAOB) formed mainly in the Paleozoic due to the closure of the Paleo-Asian oceanic basins and accompanying prolonged accretion of pelagic sediments, oceanic crust, magmatic arcs, and Precambrian terranes. The timing of subduction–accretion processes and closure of the Paleo-Asian Ocean has long been controversial and is addressed in a geochemical and isotopic investigation of mafic rocks, which can yield important insight into the geodynamics of subduction zone environments. The Xilingol Complex, located on the northern subduction–accretion zone of the CAOB, mainly comprises strongly deformed quartzo-feldspathic gneisses with intercalated lenticular or quasi-lamellar amphibolite bodies. An integrated study of the petrology, geochemistry, and geochronology of a suite of amphibolites from the complex constrains the nature of the mantle source and the tectono-metamorphic events in the belt. The protoliths of these amphibolites are gabbros and gabbroic diorites that intruded at ca. 340–321 Ma with positive εHf(t) values ranging from + 2.89 to + 12.98. Their TDM1 model ages range from 455 to 855 Ma and peak at 617 Ma, suggesting that these mafic rocks are derived from a depleted continental lithospheric mantle. The primitive magma was generated by variable degrees of partial melting of spinel-bearing peridotites. Fractionation of olivine, clinopyroxene and hornblende has played a dominant role during magma differentiation with little or no crustal contamination. The mafic rocks are derived from a Late Neoproterozoic depleted mantle source that was subsequently enriched by melts affected by slab-derived fluids and sediments, or melts with a sedimentary source rock. The Carboniferous mafic rocks in the northern accretionary zone of the CAOB record a regional extensional event after the Early Paleozoic subduction of the Paleo-Asian Ocean. Both addition of mantle-derived magmas and recycling of oceanic crust played key roles in significant Late Carboniferous (ca. 340–309 Ma) vertical crustal growth in the CAOB. Amphibolite–facies metamorphism (P = 0.34–0.52 GPa, T = 675–708 °C) affected these mafic rocks in the Xilingol Complex at ca. 306–296 Ma, which may be related to the crustal thickening by northward subduction of a forearc oceanic crust beneath the southern margin of the South Mongolian microcontinent. The final formation of the Solonker zone may have lasted until ca. 228 Ma.  相似文献   

11.
《Gondwana Research》2014,25(1):309-337
The Trans-Altai Zone in southern Mongolia is characterized by thrusting of greenschist-facies Silurian oceanic rocks over Devonian and Lower Carboniferous volcano-sedimentary sequences, by E–W directed folding affecting the early Carboniferous volcanic rocks, and by the development of N–S trending magmatic fabrics in the Devonian–Carboniferous arc plutons. This structural pattern is interpreted as the result of early Carboniferous thick-skinned E–W directed nappe stacking of oceanic crust associated with syn-compressional emplacement of a magmatic arc. The southernmost South Gobi Zone represents a Proterozoic continental domain affected by shallow crustal greenschist-facies detachments of Ordovician and Devonian cover sequences from the Proterozoic substratum, whereas supracrustal Carboniferous volcanic rocks and Permian sediments were folded into N–S upright folds. This structural pattern implies E–W directed thin-skinned tectonics operating from the late Carboniferous to the Permian, as demonstrated by K–Ar ages ranging from ~ 320 Ma to 257 Ma for clay fractions separated from a variety of rock types. Moreover, the geographical distribution of granitoids combined with their geochemistry and SHRIMP U–Pb zircon ages form distinct groups of Carboniferous and Permian age that record typical processes of magma generation and increase in crustal thickness. The field observations combined with clay ages, the geochemical characteristics of the granitoids and their ages imply that the E–W trending zone affected by tectonism migrated southwards, leaving the Trans Altai Zone inactive during the late Carboniferous and Permian, suggesting that the two units were tectonically amalgamated along a major E–W trending strike slip fault zone. This event was related to late Carboniferous subduction that was responsible for the vast volume of granitoid magma emplaced at 300–305 Ma in the South Gobi and at 307–308 Ma in the Trans-Altai Zones. The formation and growth of the crust was initially due only to subduction and accretion processes. During the post-collisional period from 305 to 290 Ma the addition of heat to the crust led to the generation of (per-) alkaline melts. Once amalgamated, these two different crustal domains were affected by N–S compression during the Triassic and early Jurassic (185–173 Ma), resulting in E–W refolding of early thrusts and folds and major shortening of both tectonic zones.  相似文献   

12.
The Tarim Craton is one of three large cratons in China. Presently, there is only scant information concerning its crustal evolutionary history because most of the existing geochronological studies have lacked a combined isotopic analysis, especially an in situ Lu–Hf isotope analysis of zircon. In this study, Precambrian basement rocks from the Kuluketage and Dunhuang Blocks in the northeastern portion of the Tarim Craton have been analyzed for combined in situ laser ablation ICP-(MC)-MS zircon U–Pb and Lu–Hf isotopic analyses, as well as whole rock elements, to constrain their protoliths, forming ages and magma sources. Two magmatic events from the Kuluketage Block at ∼2.4 Ga and ∼1.85 Ga are revealed, and three stages of magmatic events are detected in the Dunhuang Block, i.e., ∼2.0 Ga, ∼1.85 Ga and ∼1.75 Ga. The ∼1.85 Ga magmatic rocks from both areas were derived from an isotopically similar crustal source under the same tectonic settings, suggesting that the Kuluketage and Dunhuang Blocks are part of the uniform Precambrian basement of the Tarim Craton. Zircon Hf model ages of the ∼2.4 Ga magmatism indicate that the crust of the Tarim Craton may have been formed as early as the Paleoarchean period. The ∼2.0 Ga mafic rock from the Dunhuang Block was formed in an active continental margin setting, representing an important crustal growth event of the Tarim Craton in the mid-Paleoproterozoic that coincides with the global episode of crust formation during the assembly of the Columbia supercontinent. The ∼1.85 Ga event in the Kuluketage and Dunhuang Blocks primarily involved the reworking of the old crust and most likely related to the collisional event associated with the assembly of the Columbia supercontinent, while the ∼1.75 Ga magmatism in the Dunhuang Block resulted from a mixture of the reworked Archean crust with juvenile magmas and was most likely related to a post-collisional episode.  相似文献   

13.
The Eastern Qinling Orogen (EQO) is a major composite collisional zone located between the North China and the Yangtze cratons. This contribution combines geological and Hf–isotopic data from magmatic rocks associated with mineralization to gain insights into links between the crust architecture and metallogeny, and to focus exploration in the orogen.The new zircon U–Pb dates reported in this study are 434 ± 2 Ma for diorite, 433 ± 2 and 436 ± 2 Ma for monzogranite, and 454 ± 2 Ma for granodiorite in the Nanzhao area; 225 ± 2 Ma for syenite and 160 ± 1 Ma for monzogranite at Songxian; and 108 ± 1 and 102 ± 1 Ma for syenogranite in eastern Fangcheng. Combining our data with those from the entire EQO reveals seven major magmatic events since the Cambrian. These magmatic events took place during the Cambrian–Silurian associated with subduction, Early Devonian magmatism related to a collisional event, Early Permian to Late Triassic magmatism related to subduction, Late Triassic collisional magmatism, Late Triassic to Early Jurassic post–collision magmatism, and Jurassic–Cretaceous magmatism during intra–continental subduction.Lu-Hf isotopic data collected from granitic rocks for this study give εHf(t) values of: − 1.4 to 10.9 for diorite and monzogranite at Nanzhao; − 27.1 to − 15.6 for syenite and − 27.5 to − 25.1 for monzogranite at Songxian; and − 12.9 to − 3.4 for syenogranite in the eastern Fangcheng. Combining Hf isotopic data for the EQO from previous studies, we have evaluated the spatio–temporal distribution of Hf isotopic compositions. The resultant Hf isotopic maps highlight the location of the Kuanping Suture as an important tectonic boundary between the North China and the Yangtze cratons, which separates the EQO into a north part with an old and reworked lower crust and a southern part representing a juvenile lower crust.The Hf isotopic mapping of the EQO also provides information on the distribution of mineral deposits. Porphyry and porphyry–skarn Mo(–W) deposits are associated with magmatic rocks were emplaced in zones with low–εHf and high TDMc values representing old and reworked crustal components. In contrast, porphyry and porphyry–skarn Cu(–Mo) deposits are associated with magmatic rocks emplaced in domains with variable εHf and TDMc values characterized by dominantly reworked old crustal components with minor juvenile material. The magmatic source for the intrusions is characterized by low–εHf and high TDMc values, which are granite–related Mo or Pb–Zn–Ag mineralization.  相似文献   

14.
《Gondwana Research》2014,25(1):170-189
The Lhasa terrane in southern Tibet is composed of Precambrian crystalline basement, Paleozoic to Mesozoic sedimentary strata and Paleozoic to Cenozoic magmatic rocks. This terrane has long been accepted as the last crustal block to be accreted with Eurasia prior to its collision with the northward drifting Indian continent in the Cenozoic. Thus, the Lhasa terrane is the key for revealing the origin and evolutionary history of the Himalayan–Tibetan orogen. Although previous models on the tectonic development of the orogen have much evidence from the Lhasa terrane, the metamorphic history of this terrane was rarely considered. This paper provides an overview of the temporal and spatial characteristics of metamorphism in the Lhasa terrane based mostly on the recent results from our group, and evaluates the geodynamic settings and tectonic significance. The Lhasa terrane experienced multistage metamorphism, including the Neoproterozoic and Late Paleozoic HP metamorphism in the oceanic subduction realm, the Early Paleozoic and Early Mesozoic MP metamorphism in the continent–continent collisional zone, the Late Cretaceous HT/MP metamorphism in the mid-oceanic ridge subduction zone, and two stages of Cenozoic MP metamorphism in the thickened crust above the continental subduction zone. These metamorphic and associated magmatic events reveal that the Lhasa terrane experienced a complex tectonic evolution from the Neoproterozoic to Cenozoic. The main conclusions arising from our synthesis are as follows: (1) The Lhasa block consists of the North and South Lhasa terranes, separated by the Paleo-Tethys Ocean and the subsequent Late Paleozoic suture zone. (2) The crystalline basement of the North Lhasa terrane includes Neoproterozoic oceanic crustal rocks, representing probably the remnants of the Mozambique Ocean derived from the break-up of the Rodinia supercontinent. (3) The oceanic crustal basement of North Lhasa witnessed a Late Cryogenian (~ 650 Ma) HP metamorphism and an Early Paleozoic (~ 485 Ma) MP metamorphism in the subduction realm associated with the closure of the Mozambique Ocean and the final amalgamation of Eastern and Western Gondwana, suggesting that the North Lhasa terrane might have been partly derived from the northern segment of the East African Orogen. (4) The northern margin of Indian continent, including the North and South Lhasa, and Qiangtang terranes, experienced Early Paleozoic magmatism, indicating an Andean-type orogeny that resulted from the subduction of the Proto-Tethys Ocean after the final amalgamation of Gondwana. (5) The Lhasa and Qiangtang terranes witnessed Middle Paleozoic (~ 360 Ma) magmatism, suggesting an Andean-type orogeny derived from the subduction of the Paleo-Tethys Ocean. (6) The closure of Paleo-Tethys Ocean between the North and South Lhasa terranes and subsequent terrane collision resulted in the formation of Late Permian (~ 260 Ma) HP metamorphic belt and Triassic (220 Ma) MP metamorphic belt. (7) The South Lhasa terrane experienced Late Cretaceous (~ 90 Ma) Andean-type orogeny, characterized by the regional HT/MP metamorphism and coeval intrusion of the voluminous Gangdese batholith during the northward subduction of the Neo-Tethyan Ocean. (8) During the Early Cenozoic (55–45 Ma), the continent–continent collisional orogeny has led to the thickened crust of the South Lhasa terrane experiencing MP amphibolite-facies metamorphism and syn-collisional magmatism. (9) Following the continuous continent convergence, the South Lhasa terrane also experienced MP metamorphism during Late Eocene (40–30 Ma). (10) During Mesozoic and Cenozoic, two different stages of paired metamorphic belts were formed in the oceanic or continental subduction zones and the middle and lower crust of the hanging wall of the subduction zone. The tectonic imprints from the Lhasa terrane provide excellent examples for understanding metamorphic processes and geodynamics at convergent plate boundaries.  相似文献   

15.
New geological, geochronological and isotopic data reveal a previously unknown arc system that evolved south of the Kyrgyz Middle Tianshan (MTS) microcontinent during the Middle and Late Ordovician, 467–444 Ma ago. The two fragments of this magmatic arc are located within the Bozbutau Mountains and the northern Atbashi Range, and a marginal part of the arc, with mixed volcanic and sedimentary rocks, extends north to the Semizsai metamorphic unit of the southern Chatkal Range. A continental basement of the arc, indicated by predominantly felsic volcanic rocks in Bozbutau and Atbashi, is supported by whole-rock Nd- and Hf-in-zircon isotopic data. εNd(t) of + 0.9 to − 2.6 and εHf(t) of + 1.8 to − 6.0 imply melting of Neo- to Mesoproterozoic continental sources with Nd model ages of ca. 0.9 to 1.2 Ga and Hf crustal model ages of ca. 1.2 to 1.7 Ga. In the north, the arc was separated from the MTS microcontinent by an oceanic back-arc basin, represented by the Karaterek ophiolite belt. Our inference of a long-lived Early Palaeozoic arc in the southwestern MTS suggests an oceanic domain between the MTS microcontinent and the Tarim craton in the Middle Ordovician.The time of arc-continent collision is constrained as Late Ordovician at ca. 450 Ma, based on cessation of sedimentation on the MTS microcontinent, the age of an angular unconformity within the Karaterek suture zone, and the age of syncollisional metamorphism and magmatism in the Kassan Metamorphic Complex of the southern Chatkal Range. High-grade amphibolite-facies metamorphism and associated crustal melting in the Kassan Metamorphic Complex restricts the main tectonic activity in the collisional belt to ca. 450 Ma. This interpretation is based on the age of a synkinematic amphibolite-facies granite, intruded into paragneiss during peak metamorphism. A second episode of greenschist- to kyanite–staurolite-facies metamorphism is dated between 450 and 420 Ma, based on the ages of granitoid rocks, subsequently affected or not affected by this metamorphism. The latest episode is recorded by greenschist-facies metamorphism in Silurian sandstones and granodiorites and by retrogression of the older, higher-grade rocks. This may have occurred at the Silurian to Devonian transition and reflects reorganization of a Middle Palaeozoic convergent margin.Late Ordovician collision was followed by initiation of a new continental arc in the southern MTS. This arc was active in the Early Silurian, latest Silurian to Middle Devonian, and Late Carboniferous, whereas during the Givetian through Mississippian (ca. 385–325 Ma) this area was a passive continental margin. These arcs, previously well constrained west of the Talas-Ferghana Fault, continued eastwards into the Naryn and Atbashi areas and probably extended into the Chinese Central Tianshan. The disappearance of a major crustal block with transitional facies on the continental margin and too short a distance between the arc and accretionary complex suggest that plate convergence in the Atbashi sector of the MTS was accompanied by subduction erosion in the Devonian or Early Pennsylvanian. This led to a minimum of 50–70 km of crustal loss and removal of the Ordovician arc as well as the Silurian and Devonian forearcs in the areas east of the Talas-Ferghana Fault.  相似文献   

16.
The North China Craton (NCC) represents one of only a few cratonic nuclei on the globe with a geological history extending back to the Eoarchean. However, extensive ca. 2.5 Ga crustal reworking has destroyed a considerable portion of the pre-existing crustal record, hindering the investigation of tectonothermal evolution prior to 2.5 Ga. The Huoqiu Complex (HQC), located at the southeastern margin of the NCC, preserves the vestiges of crustal components that survived the ca. 2.5 Ga tectonothermal events, which provide the opportunity to investigate the Meso- to Neoarchean episodic crustal evolution of the NCC. Here we present results from in-situ detrital zircon U–Pb dating and Hf isotope analyses on zircons from three paragneisses in three drill cores that cut through the basement of the HQC. In combination with published data, the concordant age spectra of the detrital zircons in the paragneisses yield 207Pb/206Pb ages of 2343–3997 Ma that cluster into two principal age populations with peaks at 3015 and 2755 Ma. One zircon grain dated at 3997 ± 8 Ma with 98% concordance provides new evidence for 4.0 Ga components in the NCC. The εHf(t) values of all zircons range from − 5.2 to + 6.5, with most of the spots (n = 31 of 47) showing positive values, indicating at least two episodes of juvenile continental crustal growth at 3.01 Ga and 2.75 Ga. The older episode is recorded only in few ancient cratons, suggesting limited crustal accretion occurred globally at a time of subdued mantle-derived magmatism. In contrast, the younger episode is coincident with a global rise in magmatic activity in the early Neoarchean. The geochemical and geochronological data suggest that the 3.01 Ga juvenile crust was likely generated in an island-arc subduction system, whereas the 2.75 Ga crustal rocks were probably formed during magmatic underplating and subsequent partial melting of lower crustal mafic rocks. Consequently, a tectonic transition is suggested from a compressive to an extensional setting along the southeastern margin of the NCC between 3.01 and 2.75 Ga. This sequence of events heralds a shift, from a mixture of net crustal growth and crustal reworking during multiple short-lived magmatic pulses, to fragmentation and dispersal of the early continental nucleus within 260 Ma.  相似文献   

17.
Archean tectonic history of the North China Craton (NCC) involved complex processes of amalgamation of microcontinents along multiple subduction zones prior to the consolidation of the major crustal blocks and their assembly into unified cratonic architecture. Here we report a suite of granitoids, diabase, metabasalts, volcanic tuff, banded iron formations and quartzite from the Yishui Complex along the southern margin of the Jiaoliao microblock within the Eastern Block of the NCC. The geochemical features of the magmatic suite are consistent with calc-alkaline magmatism in a convergent margin setting. In tectonic discrimination diagrams, the mafic suite shows variable IAB, MORB and OIB affinities typical of rocks formed in an arc-related subduction environment. Zircon grains in most of the rocks from Yishui Complex display core–rim texture with the cores showing magmatic crystallization and the narrow structureless rims corresponding to metamorphic overgrowth. The 207Pb/206Pb ages of magmatic zircons show 2504 ± 19 Ma for the volcanic tuff, 2581 ± 21 Ma for the granitoid, 2501 ± 19 Ma for the metavolcanics, 2537 ± 38 Ma for the pyroxenite, and 2506 ± 13 Ma for the diabase. Metamorphism is constrained from the 2451 ± 18 Ma and 2466 ± 23 Ma age groups in the metavolcanics and (meta-) pyroxenites. Zircons from BIF show multiple population with the oldest showing a spot age of 2503 Ma, followed by a number of distinct groups of Paleoproterozoic zircons corresponding to later thermal events. The oldest population of magmatic zircons from the quartzite shows 207Pb/206Pb mean age of 2495 ± 24 Ma. The dominantly positive εHf(t) values of the magmatic zircons from the Yishui suite are broadly consistent with a depleted mantle source with only minor input of crustal components. Their Hf crustal residence ages (TDMC) range from 2586 to 3181 Ma and Hf depleted mantle model ages (TDM) are in the range of 2548–2927 Ma. The data indicate that magma production involved Meso- to Neoarchean juvenile sources within a continental arc setting, suggesting the Jiaoliao microblock as one of the ancient continental nuclei in the NCC. We trace the continuity of a Neoarchean subduction system along the western and southern margins of the Jiaoliao microblock with convergence of the Qianhuai and Xuhuai microblocks towards the Jiaoliao microblock with subduction–accretion–collision during the Archean–Proterozoic transition.  相似文献   

18.
In northeastern Vietnam, Late Paleozoic and Permo-Triassic granitic plutons are widespread, but their tectonic significance is controversial. In order to understand the regional magmatism and crustal evolution processes of the South China block (SCB), this study reports integrated in situ U–Pb, Hf–O and Sr–Nd isotope analyses of granitic rocks from five plutons in northeastern Vietnam. Zircon SIMS U–Pb ages of six granitic samples cluster around in two groups 255–228 Ma and 90 Ma. Bulk-rock εNd (t) ranges from −11 to −9.7, suggesting that continental crust materials were involved in their granitic genesis. In situ zircon Hf–O isotopic measurements for the granitic samples yield a mixing trend between the mantle- and supracrustal-derived melts. It is suggested that the granitic rocks were formed by re-melting of the continental crust. These new data are compared with the Paleozoic and Mesozoic granitic rocks of South China. We argue that northeastern Vietnam belongs to the South China block. Though still speculated, an ophiolitic suture between NE Vietnam and South China, so-called Babu ophiolite, appears unlikely. The Late Paleozoic to Mesozoic magmatism in the research area provides new insights for the magmatic evolution of the South China block.  相似文献   

19.
《Gondwana Research》2013,24(4):1378-1401
The Qilian Orogen at the northern margin of the Tibetan Plateau is a type suture zone that recorded a complete history from continental breakup to ocean basin evolution, and to the ultimate continental collision in the time period from the Neoproterozoic to the Paleozoic. The Qilian Ocean, often interpreted as representing the “Proto-Tethyan Ocean”, may actually be an eastern branch of the worldwide “Iapetus Ocean” between the two continents of Baltica and Laurentia, opened at ≥ 710 Ma as a consequence of breakup of supercontinent Rodinia.Initiation of the subduction in the Qilian Ocean probably occurred at ~ 520 Ma with the development of an Andean-type active continental margin represented by infant arc magmatism of ~ 517–490 Ma. In the beginning of Ordovician (~ 490 Ma), part of the active margin was split from the continental Alashan block and the Andean-type active margin had thus evolved to western Pacific-type trench–arc–back-arc system represented by the MORB-like crust (i.e., SSZ-type ophiolite belt) formed in a back-arc basin setting in the time period of ~ 490–445 Ma. During this time, the subducting oceanic lithosphere underwent LT-HP metamorphism along a cold geotherm of ~ 6–7 °C/km.The Qilian Ocean was closed at the end of the Ordovician (~ 445 Ma). Continental blocks started to collide and the northern edge of the Qilian–Qaidam block was underthrust/dragged beneath the Alashan block by the downgoing oceanic lithosphere to depths of ~ 100–200 km at about 435–420 Ma. Intensive orogenic activities occurred in the late Silurian and early Devonian in response to the exhumation of the subducted crustal materials.Briefly, the Qilian Orogen is conceptually a type example of the workings of plate tectonics from continental breakup to the development and evolution of an ocean basin, to the initiation of oceanic subduction and formation of arc and back-arc system, and to the final continental collision/subduction and exhumation.  相似文献   

20.
The Palaeozoic to Mesozoic igneous and metamorphic basement rocks exposed in the Mérida Andes of Venezuela and the Santander Massif of Colombia are generally considered to define allochthonous terranes that accreted to the margin of Gondwana during the Ordovician and the Carboniferous. However, terrane sutures have not been identified and there are no published isotopic data that support the existence of separate crustal domains. A general paucity of geochronological data led to published tectonic reconstructions for the evolution of the northwestern corner of Gondwana that do not account for the magmatic and metamorphic histories of the basement rocks of the Mérida Andes and the Santander Massif. We present new zircon U–Pb (ICP-MS) data from 52 igneous and metamorphic rocks, which we combine with whole rock geochemical and Pb isotopic data to constrain the tectonic history of the Precambrian to Mesozoic basement of the Mérida Andes and the Santander Massif. These data show that the basement rocks of these massifs are autochthonous to Gondwana and share a similar tectono-magmatic history with the Gondwanan margin of Peru, Chile and Argentina, which evolved during the subduction of oceanic lithosphere of the Iapetus Ocean. The oldest Palaeozoic arc magmatism is recorded at ~ 500 Ma, and was followed shortly by Barrovian metamorphism. Peak metamorphic conditions at upper amphibolite facies are recorded by anatexis at ~ 477 Ma and the intrusion of synkinematic granitoids until ~ 472 Ma. Subsequent retrogression resulted from localised back-arc or intra-arc extension at ~ 453 Ma, when volcanic tuffs and interfingered sedimentary rocks were deposited over the amphibolite facies basement. Continental arc magmatism dwindled after ~ 430 Ma and terminated at ~ 415 Ma, coevally with most of the western margin of Gondwana. After Pangaea amalgamation in the Late Carboniferous to Early Permian, a magmatic arc developed on its western margin at ~ 294 Ma as a result of subduction of oceanic crust of the palaeo-Pacific ocean. Intermittent arc magmatism recorded between ~ 294 and ~ 225 Ma was followed by the onset of the Andean subduction cycle at ~ 213 Ma, in an extensional regime. Extension was accompanied by slab roll-back which led to the migration of the arc axis into the Central Cordillera of Colombia in the Early Jurassic.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号