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1.
The Mongol–Okhotsk Belt, a major structural element of East Asia, is probably the youngest orogenic segment within the Central Asian Orogenic Belt. However, the timing of final closure of the Mongol–Okhotsk Ocean remains unresolved. Here, we present detrital zircon U–Pb–Hf isotopic data and whole-rock geochemical data (major and trace elements and Sm-Nd isotopes) for the metasedimentary rocks from the Un'ya–Bom Terrane, Dzhagdy Terrane, and the eastern part of the Tukuringra Terrane. Our new zircon U-Pb ages suggest that all sedimentary formations along the Dzhagdy Transect are early Mesozoic in age, rather than Paleozoic as previously thought. The detrital zircons from the metasedimentary rocks in the Un'ya–Bom Terrane, the Dzhagdy Terrane, and the eastern part of the Tukuringra Terrane yielded the youngest concordant ages of 194 ± 4, 193 ± 2, and 171 ± 2 Ma, respectively. Moreover, we note that the so-called sedimentary formations of these terranes are not single sedimentary sequences as previously suggested, but a set of an olistostrome or tectonic mélanges composed of rocks of different ages and origins. These sedimentary formations are probably relics of the Mongol–Okhotsk remnant basin that formed in the “gaps” between the southern margin of the North Asian Craton and the Amur Block during their collision. The absence of detrital zircons younger than 171 Ma in the sedimentary rocks of the Mongol–Okhotsk basin implies that the final closure of this basin could have taken place at the boundary of the Early and Middle Jurassic as a result of the collision or the development of the Mongol–Okhotsk orogenic belt in this region. After that, the Mongol–Okhotsk Belt underwent intense deformation related to within-plate strike-slip faulting, which could be attributed to the late Mesozoic rotation of the North Asian Craton relative to the continental massifs of East Asia.  相似文献   

2.
This work presents the results of geological, geochemical, Sm–Nd isotope-geochemical studies of metasedimentary rocks of the Teploklyuchevskaya, Garmakan, and Algaja formations of the Tukuringra Terrane of the eastern part of the Mongol–Okhotsk fold belt, as well as U–Th–Pb geochronological (LA-ICP-MS) studies of detrital zircons from these rocks. It is established that the lower age boundary of formation of the protolith of metasedimentary rocks of the Teploklyuchevskaya Formation is about 243 Ma (Middle Triassic); those of the Garmakan and Algaja formations are ~175 Ma (Lower–Middle Jurassic boundary) and ~192 Ma (Lower Jurassic), respectively. This makes it possible to correlate the Teploklyuchevskaya, Garmakan, and Algaja formations with the youngest sedimentary complexes of the eastern part of the Mongol–Okhotsk fold belt. In terms of geochemistry, the protoliths of metasedimentary rocks of the above-mentioned formations are the most similar to sedimentary rocks of island arcs and active continental margins. The source terrigenous material was transported from the southern frame of the Mongol–Okhotsk fold belt. It is not improbable that Lower Mesozoic deposits of the western part of the Tukuringra Terrane, in particular, and the eastern part of the Mongol–Okhotsk fold belt, as a whole, are relics of residual basins, preserved in “gaps” in the collision zone between the southern margin of plates of the North Asian Craton and the Amur Superterrane.  相似文献   

3.
《Gondwana Research》2014,26(4):1517-1534
Trapped between the Siberian Craton to the north, and the Tarim and North China blocks to the south, the Mongol–Okhotsk Belt represents a young portion of the Central Asian Orogenic Belt. The Andean-type orogeny was caused by the closure of the Mongol–Okhotsk Ocean, whose timing and mode of geodynamic evolution still needs to be clarified in more detail. This paper investigates the lithostratigraphic units of the Gorkhi Formation, which are comprised in the Hangay–Hentey terrane representing the accretionary prism of the northern continental margin of the Mongol–Okhotsk Ocean. In the tectonically disrupted slices of the Gorkhi Formation we identify a typical ocean plate stratigraphy with pelagic to hemipelagic and turbiditic sequences. Locally, shallow marine limestones are found associated with mafic volcanic rocks. XRF and LA–ICPMS measurements of these volcanic rocks clearly indicate an OIB signature. The geochemistry together with lithostratigraphic observations permit us to reconstruct the evolution of a seamount, ranging from its growth in shallow water depths and drowning due to subduction-related subsidence linked with subsequent radiolarian chert, hemipelagic shale and turbiditic sandstone cover sedimentation. Calc-alkaline felsic dikes later intruded the accreted silt and sandstone deposits. Standard sandstone provenance analysis, detrital zircon U–Pb laser ablation ICP-MS dating and Hf isotope ratios in the sandstones document a prevailing continental volcanic arc sourcing during Carboniferous from the northern margin of the Mongol–Okhotsk Ocean.  相似文献   

4.
Research works carried out for the first time made it possible to determine the age of one of the key geological complexes in the Argun Continental Massif (Central Asian Fold Belt). It has been found that the metarhyolite of the Bondikha Formation is not Middle–Late Riphean, as previously thought, but is of Middle Triassic age (242 ± 6 Ma). Based upon the geochemical characteristics of the volcanics and regional geology of the Bondikha Formation, it can be assumed that they formed during one of the stages of subduction processes in the history of the Mongol–Okhotsk Fold Belt.  相似文献   

5.
U–Pb ID–TIMS zircon analyses of the Dzhigda gabbro–gabbrodiorite Massif (Ilikan block in the southwestern part of the Dzhugdzhur–Stanovoi superterrane) have been carried out. The results demonstrate that the formation of the massif at 244 ± 5 Ma corresponds to one of the stages of formation of the Selenga–Vitim volcano–plutonic belt. The latter stretches along the southeastern margin of the North Asian Craton along its border with the Mongol–Okhotsk fold belt. This indicates that the Selenga–Vitim volcano–plutonic belt along with granitoids and volcanics comprises Permian–Triassic massifs and that this belt is superimposed onto structures of not only the Selenga–Stanovoi terrane but also the Dzhugdzhur–Stanovoi terrane.  相似文献   

6.
《International Geology Review》2012,54(14):1801-1816
We present new geochronological and geochemical data for granites and volcanic rocks of the Erguna massif, NE China. These data are integrated with previous findings to better constrain the nature of the massif basement and to provide new insights into the subduction history of Mongol–Okhotsk oceanic crust and its closure. U–Pb dating of zircons from 12 granites previously mapped as Palaeoproterozoic and from three granites reported as Neoproterozoic yield exclusively Phanerozoic ages. These new ages, together with recently reported isotopic dates for the metamorphic and igneous basement rocks, as well as Nd–Hf crustal-residence ages, suggest that it is unlikely that pre-Mesoproterozoic basement exists in the Erguna massif. The geochronological and geochemical results are consistent with a three-stage subduction history of Mongol–Okhotsk oceanic crust beneath the Erguna massif, as follows. (1) The Erguna massif records a transition from Late Devonian A-type magmatism to Carboniferous adakitic magmatism. This indicates that southward subduction of the Mongol–Okhotsk oceanic crust along the northern margin of the Erguna massif began in the Carboniferous. (2) Late Permian–Middle Triassic granitoids in the Erguna massif are distributed along the Mongol–Okhotsk suture zone and coeval magmatic rocks in the Xing’an terrane are scarce, suggesting that they are unlikely to have formed in association with the collision between the North China Craton and the Jiamusi–Mongolia block along the Solonker–Xra Moron–Changchun–Yanji suture zone. Instead, the apparent subduction-related signature of the granites and their proximity to the Mongol–Okhotsk suture zone suggest that they are related to southward subduction of Mongol–Okhotsk oceanic crust. (3) A conspicuous lack of magmatic activity during the Middle Jurassic marks an abrupt shift in magmatic style from Late Triassic–Early Jurassic normal and adakite-like calc-alkaline magmatism (pre-quiescent episode) to Late Jurassic–Early Cretaceous A-type felsic magmatism (post-quiescent episode). Evidently a significant change in geodynamic processes took place during the Middle Jurassic. Late Triassic–Early Jurassic subduction-related signatures and adakitic affinities confirm the existence of subduction during this time. Late Jurassic–Early Cretaceous post-collision magmatism constrains the timing of the final closure of the Mongol–Okhotsk Ocean involving collision between the Jiamusi–Mongolia block and the Siberian Craton to the Middle Jurassic.  相似文献   

7.
To constrain the tectonic evolution of the eastern segment of the Paleo-Asian Ocean, we conducted zircon U–Pb-Hf dating and whole-rock geochemical analyses for metasedimentary rocks from the Dongnancha Formation in the Huadian area in central Jilin Province, Northeastern (NE) China. Most detrital zircons from the metasedimentary rocks display clear oscillatory zoning and striped absorption in cathodoluminescence (CL) images and have Th/U ratios of 0.1–1.8, thus indicating a magmatic origin. U–Pb isotopic dating using LA-ICP-MS method for zircon samples from the metasedimentary rocks reveals that the depositional age can be constrained to the period between 250 and 222 Ma. Geochemical data reveal low to intermediate degrees of weathering of the source material and compositionally low to intermediate maturity. Detailed analyses of detrital zircon U–Pb-Hf geochronology and geochemistry show that these metasedimentary rocks are derived from a bidirectional provenance. The predominant derivation is from Permian–Early Triassic felsic-intermediate igneous rocks of central Jilin Province and adjacent regions in the northern margin of the North China Craton, although felsic-intermediate igneous rocks and continental material in the eastern segment of the Central Asian Orogenic Belt from the Cambrian–Carboniferous represent additional sources and minor amounts of Paleoproterozoic–Neoproterozoic material have been input from the North China Craton. A number of geochemical indicators and tectonic discrimination diagrams collectively indicate a continental island arc-active continental margin setting for the deposition of the protoliths of the metasedimentary rocks. The results of geochemical and geochronological analyses of the provenance and tectonic setting of the metasedimentary rocks indicate that the Dongnancha Formation was likely deposited in an intermountain basin in a post-orogenic fast uplift setting, suggesting that the final closure of the eastern segment of the Paleo-Asian Ocean in the Huadian area of central Jinlin Province likely occurred between the Early Triassic and Middle Triassic.  相似文献   

8.
Within the northern fringe of the western (Khangai) flank of the Mongol–Okhotsk fold belt, magmatic complexes of intermediate to moderately acidic rocks occur. They comprise widely distributed gabbro–diorites, diorites, tonalites, and granodiorites. Geochronological studies have demonstrated that these rocks were formed in the time span of 437 to 375 Ma. The geochemical affinities of the rocks suggest their formation in subduction tectonic settings; hence, their paleotectonic position corresponds to the continental margin of the Mongol–Okhotsk paleoocean. It has been concluded that this Middle Paleozoic igneous activity occurred in the active continental margin settings, formed by subduction of the paleooceanic plate under the Siberian continent.  相似文献   

9.
The stratigraphic and lithofacies correlability, as well as the predominance of shallow-marine and lagoonal sedimentation settings, have been established for the Riphean-Vendian-Cambrian complexes at the southeastern margin of the North Asian Craton. The fraction of carbonate lithotypes usually increases both upsection (from the Early Riphean to Vendian and Cambrian) and along the lateral direction (from the southern and southwestern platformal zones to the eastern and northeastern folded zones), suggesting that the southern and southwestern areas of the basin represented the marginal and coastal zones, whereas its major part represented a deeper offshore zone. The section is divided into two structural stages: (i) the Riphean riftogenic and riftogenic-depression; (ii) the Vendian-Cambrian depression-plate and plate. We propose to define the Aldan-Maya marginal syneclise (based on the specific features of the sedimentogenesis) and the Aldan-Maya petroliferous zone in the Lena-Tunguska petroliferous province of the Siberian Craton (from the viewpoint of the petroleum geology). The proposed schematic geostructural regionalization of the syneclise includes the Uchur-Maya (Aldan-Maya) plate, the Tompo-Maya (Yudoma-Maya) aulacogen, and the South Verkhoyansk synclinorium. These structures are subdivided into tectonic zones.  相似文献   

10.
The regional lithospheric chemical heterogeneity in-ers that the East Qinling and its adjacent cratonic re-ions,as suggested by some authors,belong to twoeotectonic units,the North China subdomain includinghe North China Craton and its southern continentalhargin(the North Qinling Belt),and the Yangtzeanubdomain comprising the Yangtze Craton and itsorthern continental margin(the South Qinling Belt).In the North Qinling Belt the metamorphosedolcanic rocks and graywackes of the Early Paleozoicanfeng Group south of the Early Proterozoic QinlingGroup show geochemical characteristics resemblinghose of the are volcanies and are graywackes,espectively.The Early Paleozoic granites intruding in hehe Qinling Group also show similar geochemical fea-tures and similar compositional polarities to theare-type granites.The Erlangping Group north ofthe Qinling Group is a volcanic-sedimentary sequenceproduced in an Early Paleozoic back-are basin basedon geochemical evidence.It is therefore believed thatthe North Qinling B  相似文献   

11.
In this article we present geochemical and isotope characteristics of rocks of the Unerikan, Selitkan and Aezop–Yamalin volcano–plutonic zones of the eastern termination of the Mongol–Okhotsk Orogenic Belt. The obtained data demonstrate that the Mesozoic igneous rocks of the Mongol–Okhotsk sector of the Pacific Folded Belt were formed due to the melting of the continental crust in a tectonic setting corresponding to a suprasubduction one.  相似文献   

12.
《Gondwana Research》2014,25(1):48-102
The Asian continent formed during the past 800 m.y. during late Neoproterozoic through Jurassic closure of the Tethyan ocean basins, followed by late Mesozoic circum-Pacific and Cenozoic Himalayan orogenies. The oldest gold deposits in Asia reflect accretionary events along the margins of the Siberia, Kazakhstan, North China, Tarim–Karakum, South China, and Indochina Precambrian blocks while they were isolated within the Paleotethys and surrounding Panthalassa Oceans. Orogenic gold deposits are associated with large-scale, terrane-bounding fault systems and broad areas of deformation that existed along many of the active margins of the Precambrian blocks. Deposits typically formed during regional transpressional to transtensional events immediately after to as much as 100 m.y. subsequent to the onset of accretion or collision. Major orogenic gold provinces associated with this growth of the Asian continental mass include: (1) the ca. 750 Ma Yenisei Ridge, ca. 500 Ma East Sayan, and ca. 450–350 Ma Patom provinces along the southern margins of the Siberia craton; (2) the 450 Ma Charsk belt of north-central Kazakhstan; (3) the 310–280 Ma Kalba belt of NE Kazakhstan, extending into adjacent NW Xinjiang, along the Siberia–Kazakhstan suture; (4) the ca. 300–280 Ma deposits within the Central Asian southern and middle Tien Shan (e.g., Kumtor, Zarmitan, Muruntau), marking the closure of the Turkestan Ocean between Kazakhstan and the Tarim–Karakum block; (5) the ca. 190–125 Ma Transbaikal deposits along the site of Permian to Late Jurassic diachronous closure of the Mongol–Okhotsk Ocean between Siberia and Mongolia/North China; (6) the probable Late Silurian–Early Devonian Jiagnan belt formed along the margin of Gondwana at the site of collision between the Yangtze and Cathaysia blocks; (7) Triassic deposits of the Paleozoic Qilian Shan and West Qinling orogens along the SW margin of the North China block developed during collision of South China; and (8) Jurassic(?) ores on the margins of the Subumusu block in Myanmar and Malaysia. Circum-Pacific tectonism led to major orogenic gold province formation along the length of the eastern side of Asia between ca. 135 and 120 Ma, although such deposits are slightly older in South Korea and slightly younger in the Amur region of the Russian Southeast. Deformation related to collision of the Kolyma–Omolon microcontinent with the Pacific margin of the Siberia craton led to formation of 136–125 Ma ores of the Yana–Kolyma belt (Natalka, Sarylakh) and 125–119 Ma ores of the South Verkhoyansk synclinorium (Nezhdaninskoe). Giant ca. 125 Ma gold provinces developed in the Late Archean uplifted basement of the decratonized North China block, within its NE edge and into adjacent North Korea, in the Jiaodong Peninsula, and in the Qinling Mountains. The oldest gold-bearing magmatic–hydrothermal deposits of Asia include the ca. 485 Ma Duobaoshan porphyry within a part of the Tuva–Mongol arc, ca. 355 Ma low-sulfidation epithermal deposits (Kubaka) of the Omolon terrane accreted to eastern Russia, and porphyries (Bozshakol, Taldy Bulak) within Ordovican to Early Devonian oceanic arcs formed off the Kazakhstan microcontinent. The Late Devonian to Carboniferous was marked by widespread gold-rich porphyry development along the margins of the closing Ob–Zaisan, Junggar–Balkhash, and Turkestan basins (Amalyk, Oyu Tolgoi); most were formed in continental arcs, although the giant Oyu Tolgoi porphyry was part of a near-shore oceanic arc. Permian subduction-related deformation along the east side of the Indochina block led to ca. 300 Ma gold-bearing skarn and disseminated gold ore formation in the Truong Son fold belt of Laos, and along the west side to ca. 250 Ma gold-bearing skarns and epithermal deposits in the Loei fold belt of Laos and Thailand. In the Mesozoic Transbaikal region, extension along the basin margins subsequent to Mongol–Okhotsk closure was associated with ca. 150–125 Ma formation of important auriferous epithermal (Balei), skarn (Bystray), and porphyry (Kultuminskoe) deposits. In northeastern Russia, Early Cretaceous Pacific margin subduction and Late Cretaceous extension were associated with epithermal gold-deposit formation in the Uda–Murgal (Julietta) and Okhotsk–Chukotka (Dukat, Kupol) volcanic belts, respectively. In southeastern Russia, latest Cretaceous to Oligocene extension correlates with other low-sulfidation epithermal ores that formed in the East Sikhote–Alin volcanic belt. Other extensional events, likely related to changing plate dynamics along the Pacific margin of Asia, relate to epithermal–skarn–porphyry districts that formed at ca. 125–85 Ma in northeastmost China and ca. 105–90 Ma in the Coast Volcanic belt of SE China. The onset of strike slip along a part of the southeastern Pacific margin appears to correlate with the giant 148–135 Ma gold-rich porphyry–skarn province of the lower and middle Yangtze River. It is still controversial as to whether true Carlin-like gold deposits exist in Asia. Those deposits that most closely resemble the Nevada (USA) ores are those in the Permo-Triassic Youjiang basin of SW China and NE Vietnam, and are probably Late Triassic in age, although this is not certain. Other Carlin-like deposits have been suggested to exist in the Sepon basin of Laos and in the Mongol–Okhotsk region (Kuranakh) of Transbaikal.  相似文献   

13.
We report zircon U-Pb geochronology,geochemistry and Sr-Nd-Pb isotope data from mafic granulites and garnet amphibolites of the Wuhe Complex in the southeastern margin of the North China Craton (NCC).In combination with previous data,our results demonstrate that these rocks represent fragments of the ancient lower crust,and have features similar to those of the granulite basement in the northern margin of the NCC.A detailed evaluation of the Pb isotope data shows that Pb isotopes cannot effectively distinguish the role of the Yangtze Craton basement from that of the NCC basement with regard to the source and generation of magmas,at least for southeastern NCC.The age data suggest that the protoliths of the granulites or amphibolites in the Wuhe Complex were most likely generated in Neoarchean and that these rocks were subjected to Paleoproterozoic(1.8-1.9 Ga) high-pressure granulite facies metamorphism. This study also shows that the Precambrian metamorphic basement in the southeastern margin of the NCC might have formed in a tectonic setting characterized by a late Neoarchean active continental margin.  相似文献   

14.
Zircon U-Pb ages and geochemical analytical results are presented for the volcanic rocks of the Naozhigou, Ergulazi, and Sidaogou Formations in the Linjiang area, southeastern Jilin Province to constrain the nature of magma source and their tectonic settings. The Naozhigou Formation is composed mainly of andesite and rhyolite and its weighted mean 206Pb/238U age for 13 zircon grains is 222±1 Ma. The Ergulazi Formation consists of basaltic andesite, basaltic trachyandesite, and andesite, and six grains give a weighted mean 206Pb/238U age of 131±4 Ma. The Sidaogou Formation consists mainly of trachyandesite and rhyolite, and six zircon grains yield a weighted mean 206Pb/238U age of 113±4 Ma. The volcanic rocks have SiO2=60.24%–77.46%, MgO=0.36%–1.29% (Mg#=0.32–0.40) for the Naozhigou Formation, SiO2=51.60%–59.32%, MgO=3.70%–5.54% (Mg#=0.50–0.60) for the Ergulazi Formation, and SiO2=58.28%–76.32%, MgO=0.07%–1.20% (Mg#=0.14–0.46) for the Sidaogou Formation. The trace element analytical results indicate that these volcanic rocks are characterized by enrichment in light rare earth elements (LREEs) and large ion lithophile elements (LILEs), relative depletion in heavy rare earth elements (HREEs) and high field strength elements (HFSEs, Nb, Ta, and Ti), and negative Eu anomalies. Compared with the primitive mantle, the Mesozoic volcanic rocks in the Linjiang area have relatively high initial 87Sr/86Sr ratios (0.7053-0.7083) and low εNd(t) values (?8.38 to ?2.43), and display an EMII trend. The late Triassic magma for the Naozhigou Formation could be derived from partial melting of a newly accretional crust with the minor involvement of the North China Craton basement and formed under an extensional environment after the collision of the Yangtze Craton and the North China Craton. The Early Cretaceous volcanic rocks for the Ergulazi and Sidaogou Formations could be formed under the tectonic setting of an active continental margin related to the westward subduction of the Izanagi plate.  相似文献   

15.
LA-ICP-MS zircon U–Pb ages and geochemical data are presented for the Mesozoic volcanic rocks in northeast China, with the aim of determining the tectonic settings of the volcanism and constraining the timing of the overprinting and transformations between the Paleo-Asian Ocean, Mongol–Okhotsk, and circum-Pacific tectonic regimes. The new ages, together with other available age data from the literature, indicate that Mesozoic volcanism in NE China can be subdivided into six episodes: Late Triassic (228–201 Ma), Early–Middle Jurassic (190–173 Ma), Middle–Late Jurassic (166–155 Ma), early Early Cretaceous (145–138 Ma), late Early Cretaceous (133–106 Ma), and Late Cretaceous (97–88 Ma). The Late Triassic volcanic rocks occur in the Lesser Xing’an–Zhangguangcai Ranges, where the volcanic rocks are bimodal, and in the eastern Heilongjiang–Jilin provinces where the volcanics are A-type rhyolites, implying that they formed in an extensional environment after the final closure of the Paleo-Asian Ocean. The Early–Middle Jurassic (190–173 Ma) volcanic rocks, both in the Erguna Massif and the eastern Heilongjiang–Jilin provinces, belong chemically to the calc-alkaline series, implying an active continental margin setting. The volcanics in the Erguna Massif are related to the subduction of the Mongol–Okhotsk oceanic plate beneath the Massif, and those in the eastern Jilin–Heilongjiang provinces are related to the subduction of the Paleo-Pacific Plate beneath the Eurasian continent. The coeval bimodal volcanic rocks in the Lesser Xing’an–Zhangguangcai Ranges were probably formed under an extensional environment similar to a backarc setting of double-direction subduction. Volcanic rocks of Middle–Late Jurassic (155–166 Ma) and early Early Cretaceous (145–138 Ma) age only occur in the Great Xing’an Range and the northern Hebei and western Liaoning provinces (limited to the west of the Songliao Basin), and they belong chemically to high-K calc-alkaline series and A-type rhyolites, respectively. Combined with the regional unconformity and thrust structures in the northern Hebei and western Liaoning provinces, we conclude that these volcanics formed during a collapse or delamination of a thickened continental crust related to the evolution of the Mongol–Okhotsk suture belt. The late Early Cretaceous volcanic rocks, widely distributed in NE China, belong chemically to a low- to medium-K calc-alkaline series in the eastern Heilongjiang–Jilin provinces (i.e., the Eurasian continental margin), and to a bimodal volcanic rock association within both the Songliao Basin and the Great Xing’an Range. The volcanics in the eastern Heilongjiang–Jilin provinces formed in an active continental margin setting related to the subduction of the Paleo-Pacific Plate beneath the Eurasian continent, and the bimodal volcanics formed under an extensional environment related either to a backarc setting or to delamination of a thickened crust, or both. Late Cretaceous volcanics, limited to the eastern Heilongjiang–Jilin provinces and the eastern North China Craton (NCC), consist of calc-alkaline rocks in the eastern Heilongjiang–Jilin provinces and alkaline basalts in the eastern NCC, suggesting that the former originated during subduction of the Paleo-Pacific Plate beneath the Eurasian continent, whereas the latter formed in an extensional environment similar to a backarc setting. Taking all this into account, we conclude that (1) the transformation from the Paleo-Asian Ocean regime to the circum-Pacific tectonic regime happened during the Late Triassic to Early Jurassic; (2) the effect of the Mongol–Okhotsk suture belt on NE China was mainly in the Early Jurassic, Middle–Late Jurassic, and early Early Cretaceous; and (3) the late Early Cretaceous and Late Cretaceous volcanics can be attributed to the subduction of the Paleo-Pacific Plate beneath the Eurasian continent.  相似文献   

16.
The Paleoarchean age (3.34 Ga) of subalkali granite magmatism first established for the Kukhtui uplift of the Okhotsk Massif suggests a formation time of the mature continental K-rich crust in this region as early as the Paleoarchean. According to the geological structural, mineralogical–geochemical, geochronological, and isotopic–geochemical data, the Kukhtui uplift can be considered as the most ancient Paleoarchean province in Russia: the ancient consolidation core of the sialic protocrust of the Okhotsk–Omolon Craton.  相似文献   

17.
孙林华  桂和荣 《地球学报》2011,32(5):523-532
在对安徽省北部宿州新元古代史家组砂岩地球化学特征分析的基础上,结合前人发表的淮南和凤阳新元古代刘老碑组页岩的地球化学数据,对它们的物源和构造背景进行了对比讨论.结果表明:刘老碑组页岩的地球化学特征表明其来自于中-酸性火成岩高程度的首次风化,而史家组砂岩则来自于经历了再循环的古老地壳物质较低程度的风化.刘老碑组页岩相对史...  相似文献   

18.
We present a review of major gold mineralization events in China and a summary of metallogenic provinces, deposit types, metallogenic epochs and tectonic settings. Over 200 investigated gold deposits are grouped into 16 Au-metallogenic provinces within five tectonic units such as the Central Asian orogenic belt comprising provinces of Northeast China and Tianshan-Altay; North China Craton comprising the northern margin, Jiaodong, and Xiaoqinling; the Qinling-Qilian-Kunlun orogenic belt consisting of the West Qingling, North Qilian, and East Kunlun; the Tibet and Sanjiang orogenic belts consisting of Lhasa, Garzê-Litang, Ailaoshan, and Daduhe-Jinpingshan; and the South China block comprising Youjiang basin, Jiangnan orogenic belt, Middle and Lower Yangtze River, and SE coast. The gold deposits are classified as orogenic, Jiaodong-, porphyry–skarn, Carlin-like, and epithermal-types, among which the first three types are dominant.The orogenic gold deposits formed in various tectonic settings related to oceanic subduction and subsequent crustal extension in the Qinling-Qilian-Kunlun, Tianshan-Altay, northern margin of North China Craton, and Xiaoqinling, and related to the Eocene–Miocene continental collision in the Tibet and Sanjiang orogenic belts. The tectonic periods such as from slab subduction to block amalgamation, from continental soft to hard collision, from intracontinental compression to shearing or extension, are important for the formation of the orogenic gold deposits. The orogenic gold deposits are the products of metamorphic fluids released during regional metamorphism associated with oceanic subduction or continental collision, or related to magma emplacement and associated hydrothermal activity during lithospheric extension after ocean closure. The Jiaodong-type, clustered around Jiaodong, Xiaoqinling, and the northern margin of the North China Craton, is characterized by the involvement of mantle-derived fluids and a temporal link to the remote subduction of the Pacific oceanic plate concomitant with the episodic destruction of North China Craton. The Carlin-like gold metallogenesis is related to the activity of connate fluid, metamorphic fluid, and meteoric water in different degrees in the Youjiang basin and West Qinling; the former Au province is temporally related to the remote subduction of the Tethyan oceanic plate and the later formed in a syn-collision setting. Porphyry–skarn Au deposits are distributed in the Tianshan-Altay, the Middle and Lower Yangtze River region, and Tibet and Sanjiang orogenic belts in both subduction and continental collision settings. The magma for the porphyry–skarn Au deposits commonly formed by melting of a thickened juvenile crust. The epithermal Au deposits, dominated by the low-sulfidation type, plus a few high-sulfidation ones, were produced during the Carboniferous oceaic plate subduction in Tianshan-Altay, during Early Cretaceous and Quaternary oceanic plate subduction in SEt coast of South China Block, and during the Pliocene continental collision in Tibet. The available data of different isotopic systems, especially fluid D–O isotopes and carbonate C–O systems, reveal that the isotopic compositions are largely overlapping for different genetic types and different for the same genetic type in different Au belts. The isotopic compositions are thus not good indicators of various genetic types of gold deposit, perhaps due to overprinting of post-ore alteration or the complex evolution of the fluids.Although gold metallogeny in China was initiated in Cambrian and lasted until Cenozoic, it is mainly concentrated in four main periods. The first is Carboniferous when the Central Asian orogenic belt formed by welding of micro-continental blocks and arcs in Tianshan-Altay, generating a series of porphyry–epithermal–orogenic deposits. The second period is from Triassic to Early Jurassic when the current tectonic mainframe of China started to take shape. In central and southern China, the North China Craton, South China Block and Simao block were amalgamated after the closure of Paleo-Tethys Ocean in Triassic, forming orogenic and Carlin-like gold deposits. The third period is Early Cretaceous when the subduction of the Pacific oceanic plate to the east and that of Neo-Tethyan oceanic plate to the west were taking place. The subduction in eastern China produced the Jiaodong-type deposits in the North China Craton, the skarn-type deposits in the northern margin (Middle to lower reaches of Yangtze River) and the epithermal-type deposits in the southeastern margin in the South China Block. The subduction in western China produced the Carlin-like gold deposits in the Youjiang basin and orogenic ones in the Garzê-Litang orogenic belt. The Cenozoic is the last major phase, during which southwestern China experienced continental collision, generating orogenic and porphyry–skarn gold deposits in the Tibetan and Sanjiang orogenic belts. Due to the spatial overlap of the second and third periods in a single gold province, the Xiaoqinling, West Qinling, and northern margin of the North China Craton have two or more episodes of gold metallogeny.  相似文献   

19.
North-eastern China and surrounding regions host some of the best examples of Phanerozoic juvenile crust on the globe. However, the Mesozoic tectonic setting and geodynamic processes in this region remain debated. Here we attempt a systematic analysis of the spatio-temporal distribution patterns of ore deposits in NE China and surrounding regions to constrain the geodynamic milieu. From an evaluation of the available geochronological data, we identify five distinct stages of ore formation: 240–205 Ma, 190–165 Ma, 155–145 Ma, 140–120 Ma, and 115–100 Ma. The Triassic (240–205 Ma) magmatism and associated mineralisation occurred during in a post-collisional tectonic setting involving the closure of the Paleo-Asian Ocean. The Early-Mid Jurassic (190–165 Ma) events are related to the subduction of the Paleo-Pacific Ocean in the eastern Asian continental margin, whereas in the Erguna block, these are associated with the subduction of the Mongol–Okhotsk Ocean. From 155 to 120 Ma, large-scale continental extension occurred in NE China and surrounding regions. However, the Late Jurassic magmatism and mineralisation events in these areas evolved in a post-orogenic extensional environment of the Mongol–Okhotsk Ocean subduction system. The early stage of the Early Cretaceous events occurred under the combined effects of the closure of the Mongol–Okhotsk Ocean and the subduction of the Paleo-Pacific Ocean. The widespread extension ceased during the late phase of Early Cretaceous (115–100 Ma), following the rapid tectonic changes resulting from the Paleo-Pacific Oceanic plate reconfiguration.  相似文献   

20.
Zircon U-Pb ages and geochemical analytical results are presented for the volcanic rocks of the Naozhigou, Ergulazi, and Sidaogou Formations in the Linjiang area, southeastern Jilin Province to constrain the nature of magma source and their tectonic settings. The Naozhigou Formation is composed mainly of andesite and rhyolite and its weighted mean 206Pb/238U age for 13 zircon grains is 2224±1 Ma. The Ergulazi Formation consists of basaltic andesite, basaltic trachyandesite, and andesite, and six grains give a weighted mean 206Pb/238U age of 131±4 Ma. The Sidaogou Formation consists mainly of trachyandesite and rhyolite, and six zircon grains yield a weighted mean 206Pb/238U age of113±4 Ma. The volcanic rocks have SiO2=60.24%-77.46%, MgO=0.36%-1.29% (Mg#=0.32-0.40) for the Naozhigou Formation, SiO2=51.60%-59.32 %, MgO=3.70 %-5.54% (Mg#=0.50-0.60) for the Ergulazi Formation, and SiO2=58.28%-76.32%, MgO=0.07%-1.20% (Mg#=0.14-0.46) for the Sidaogou Formation. The trace element analytical results indicate that these volcanic rocks are characterized by enrichment in light rare earth elements (LREEs) and large ion lithophile elements (LILEs), relative depletion in heavy rare earth elements (HREEs) and high field strength elements (HFSEs, Nb, Ta, and Ti), and negative Eu anomalies. Compared with the primitive mantle, the Mesozoic volcanic rocks in the Linjiang area have relatively high initial 87Sr/86Sr ratios (0.7053-0.7083) and low eNd(t) values (-8.38 to -2.43), and display an EMII trend. The late Triassic magma for the Naozhigou Formation could be derived from partial melting of a newly accretional crust with the minor involvement of the North China Craton basement and formed under an extensional environment after the collision of the Yangtze Craton and the North China Craton. The Early Cretaceous volcanic rocks for the Ergulazi and Sidaogou Formations could be formed under the tectonic setting of an active continental margin related to the westward snbduction of the Izanagi plate.  相似文献   

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