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1
Guan, Hui Mei, Hai Yan Cheng et Yan Li Kang. « Deformation Analysis and Tectonic Implications of South Tianshan Orogenic Belt, SW China ». Advanced Materials Research 1010-1012 (août 2014) : 1404–7. http://dx.doi.org/10.4028/www.scientific.net/amr.1010-1012.1404.
Texte intégralRésumé :
The Tianshan Orogenic Belt, which is located in the southwestern part of the Central Asian Orogenic Belt (CAOB), is an important component in the reconstruction of the tectonic evolution of the CAOB. In order to examine the evolution of the Tianshan Orogenic Belt, we performed macroscopic, microscopic structure observations analyses with deformed rocks along orogen-perpendicular transects pass Wuwamen in the South Tianshan orogenic belt of south west China, and we propose that the South Tianshan Orogenic belt enterwent a high temperature deformation in Wuwamen area during the plate interactions in Late Paleozoic.
2
Wang, Zeng-Zhen, Xuan-Hua Chen, Zhao-Gang Shao, Bing Li, Hong-Xu Chen, Wei-Cui Ding, Yao-Yao Zhang et Yong-Chao Wang. « Geochronology, geochemistry and tectonic implications of early Carboniferous plutons in the southwestern Alxa Block ». Geological Magazine 159, no 3 (12 novembre 2021) : 372–88. http://dx.doi.org/10.1017/s0016756821000984.
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AbstractThe southeastern Central Asian Orogenic Belt (CAOB) records the assembly process between several micro-continental blocks and the North China Craton (NCC), with the consumption of the Paleo-Asian Ocean (PAO), but whether the S-wards subduction of the PAO beneath the northern NCC was ongoing during Carboniferous–Permian time is still being debated. A key issue to resolve this controversy is whether the Carboniferous magmatism in the northern NCC was continental arc magmatism. The Alxa Block is the western segment of the northern NCC and contiguous to the southeastern CAOB, and their Carboniferous–Permian magmatism could have occurred in similar tectonic settings. In this contribution, new zircon U–Pb ages, elemental geochemistry and Sr–Nd isotopic analyses are presented for three early Carboniferous granitic plutons in the southwestern Alxa Block. Two newly identified aluminous A-type granites, an alkali-feldspar granite (331.6 ± 1.6 Ma) and a monzogranite (331.8 ± 1.7 Ma), exhibit juvenile and radiogenic Sr–Nd isotopic features, respectively. Although a granodiorite (326.2 ± 6.6 Ma) is characterized by high Sr/Y ratios (97.4–139.9), which is generally treated as an adikitic feature, this sample has highly radiogenic Sr–Nd isotopes and displays significantly higher K2O/Na2O ratios than typical adakites. These three granites were probably derived from the partial melting of Precambrian continental crustal sources heated by upwelling asthenosphere in lithospheric extensional setting. Regionally, both the Alxa Block and the southeastern CAOB are characterized by the formation of early Carboniferous extension-related magmatic rocks but lack coeval sedimentary deposits, suggesting a uniform lithospheric extensional setting rather than a simple continental arc.
3
Zhang, Pan, Guocan Wang, Huaguo Liu et Feng Li. « Rodingites in the Darbut Ophiolitic Mélange, West Junggar : New Insights into Rodingitization and Tectonic Evolution ». Minerals 12, no 10 (28 septembre 2022) : 1229. http://dx.doi.org/10.3390/min12101229.
Texte intégralRésumé :
The Darbut ophiolitic mélange is located in the central West Junggar area, southwestern Central Asian Orogenic Belt (CAOB), and rodingites are widespread within serpentinized peridotites in the mélange. Here, we conducted field, structural, mineralogical, and geochemical investigations of the Darbut rodingites for the first time to constrain their metasomatic processes. Rodingites usually occur as strongly sheared blocks surrounded by chloritic blackwall, and their preferred axial surface orientations are subparallel to the serpentinite foliations. Based on the petrology and geochemistry of these metasomatic rocks, two stages of metasomatic processes, namely rodingitization and derodingitization, were recognized: (1) rodingitization of gabbroic protolith was characterized by the input of Ca and the release of Si, K, Na, and LILE; this stage was related to the diapiric emplacement of the Darbut ophiolitic mélange in the Late Carboniferous; and (2) derodingitization of rodingites led to the replacement of Ca-rich minerals by chlorite, accompanied by Mg increase, and depletions of Ca and REE; the derodingitization stage occurred under enhanced CO2/H2O ratio conditions and was likely associated with regional postcollision volcanism in the Early Permian. Hence, the rodingite in the Darbut ophiolitic mélange provides important fingerprints recording the tectonic evolution.
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Chen, Jiafu, Nan Ju et Zhonghai Zhao. « Editorial for Special Issue “Tectonic–Magmatic Evolution and Mineralization Effect in the Southern Central Asian Orogenic Belt” ». Minerals 14, no 10 (30 septembre 2024) : 994. http://dx.doi.org/10.3390/min14100994.
Texte intégralRésumé :
The Central Asian Orogenic Belt (CAOB), one of the world’s largest orogens, extending from the Ural Mountains in the west to the Russian and the Chinese Far East, is the result of long-lived multi-stage tectonic evolution, including Proterozoic to Paleozoic accretion and collision, Mesozoic intracontinental modification, and Cenozoic rapid deformation and uplift [...]
5
Li, Bo, Wen Bo Wei et Le Tian Zhang. « Electrical Structure Revealed by Magnetotelluric Data at the East Part of Central Asian Orogenic Belt, Central Inner Mongolia ». Applied Mechanics and Materials 448-453 (octobre 2013) : 3788–91. http://dx.doi.org/10.4028/www.scientific.net/amm.448-453.3788.
Texte intégralRésumé :
The cental Asian orogenic belt (CAOB) which between the North China Craton and the Siberian Craton is one of the tectono-metallogenic belts in the world. The central Inner Mongolia belongs to the eastern part of the CAOB, recently a series of research and exploration work has been done in this region. However, no breakthrough has been made in the exploration of metal ore. In order to research current mineralization issues in the eastern part of the CAOB, a long magnetotelluric (MT) profile was acquired across the central part of Inner Mongolia. The profile starts within the DongUjimqinqi in the northwest, goes southeastward across the Chagan Obo-Arongqi fault, the Erenhot-Hegenshan fault, the Xilinhot fault and the Linxi fault, and ends around the Xar Moron fault in the northern part of Chifeng city; the strike direction of most faults is southeast; the faults have direct control effect to the magmation and mineralization of this region. The model of electrical structure along the profile can be divided into two regions: widely distributed low resistivity is the key feature north of Nianzigou; high resistance is the key feature south of Nianzigou. The Chagan Obo-Arongqi fault, the Erenhot-Hegenshan fault and the Xilinhot fault all present as a southeastward dipping conductor, which reflects their overthrusting process; there are many high conductivity areas along the faults in the region. The electrical structure to the south of Nianzigou is expressed as a mushroom shape, which reflects the tectonic origin of magmatic rock in this region.
6
Jahn, Bor-ming, Fuyuan Wu et Bin Chen. « Granitoids of the Central Asian Orogenic Belt and continental growth in the Phanerozoic ». Earth and Environmental Science Transactions of the Royal Society of Edinburgh 91, no 1-2 (2000) : 181–93. http://dx.doi.org/10.1017/s0263593300007367.
Texte intégralRésumé :
The Central Asian Orogenic Belt (CAOB), also known as the Altaid Tectonic Collage, is characterised by a vast distribution of Paleozoic and Mesozoic granitic intrusions. The granitoids have a wide range of compositions and roughly show a temporal evolution from calcalkaline to alkaline to peralkaline series. The emplacement times for most granitic plutons fall between 500 Ma and 100 Ma, but only a small proportion of plutons have been precisely dated. The Nd-Sr isotopic compositions of these granitoids suggest their juvenile characteristics, hence implying a massive addition of new continental crust in the Phanerozoic. In this paper we document the available isotopic data to support this conclusion.Most Phanerozoic granitoids of Central Asia are characterised by low initial Sr isotopic ratios, positive εNd(T) values and young Sm—Nd model ages (TDM) of 300-1200 Ma. This is in strong contrast with the coeval granitoids emplaced in the European Caledonides and Hercynides. The isotope data indicate their ‘juvenile’ character and suggest their derivation from source rocks or magmas separated shortly before from the upper mantle. Granitoids with negative εNd(T) values also exist, but they occur in the environs of Precambrian microcontinental blocks and their isotope compositions may reflect contamination by the older crust in the magma generation processes.The evolution of the CAOB is probably related to accretion of young arc complexes and old terranes (microcontinents). However, the emplacement of large volumes of post-tectonic granites requires another mechanism, probably through a series of processes including underplating of massive basaltic magma, intercalation of basaltic magma with lower crustal granulites, partial melting of the mixed lithologic assemblages leading to generation of granitic liquids, followed by extensive fractional crystallisation. The proportions of the juvenile or mantle component for most granitoids of Central Asia are estimated to vary from 70% to 100%.
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Zhao, Yan, Yong Sun, Chunrong Diwu, An-Lin Guo, Wen-Hao Ao et Tao Zhu. « The Dunhuang block is a Paleozoic orogenic belt and part of the Central Asian Orogenic Belt (CAOB), NW China ». Gondwana Research 30 (février 2016) : 207–23. http://dx.doi.org/10.1016/j.gr.2015.08.012.
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Wang, Jian, Yuping Su, Jianping Zheng, E. A. Belousova, W. L. Griffin, Xiang Zhou et Hongkun Dai. « Hidden Eoarchean crust in the southwestern Central Asian Orogenic Belt ». Lithos 360-361 (mai 2020) : 105437. http://dx.doi.org/10.1016/j.lithos.2020.105437.
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Vetrov, E. V., N. I. Vetrova, T. A. Biryukova, A. R. Agatova, O. A. Gavryushkina et D. D. Bulgakova. « Tectonic Evolution of Tuvinian Trough (Northern Part of Central Asian Orogenic Belt) : Synthesis of Geological Data and Results of Feldspar Ar‒Ar Dating ». Geotektonika, no 4 (24 novembre 2024) : 60–79. http://dx.doi.org/10.31857/s0016853x24040045.
Texte intégralRésumé :
The Tuvinian rift trough, located in the northern part of the Central Asian orogenic belt (CAOB), was formed in the Early Devonian on late Proterozoic (?)‒Early Paleozoic terranes as a result of the activity of the Altai-Sayan mantle plume. The sedimentary record from the middle Paleozoic to the middle Mesozoic, preserved in the Tuvinian trough, and the middle Paleozoic igneous complexes confined to the structures of the trough, reflect the stages of evolution of the Earth’s crust in the Tuva segment, that necessary for understanding the history of the geological development of the CAOB as a whole. Dating of accessory and rock-forming minerals from igneous rocks using low-temperature geochronology methods allows us to obtain additional information about post-magmatic processes and thereby update the model of tectonic evolution of the region. In this study, we have reconstructed the stages of tectonic development of the Tuvinian trough in the northern part of the CAOB based on the analysis of geological data and new Ar‒Ar dating data on feldspars from mafic intrusions. As a result of this study, the chronology of the previously known stages of post-magmatic processes manifested in the Tuvinian trough was clarified, and new stages were identified according to the tectonic evolution of the CAOB. Ar‒Ar dating of feldspars carried out on eight samples showed four age groups: (i) Late Devonian, (ii) middle Carboniferous, (iii) early Permian and (iv) Early Jurassic. Late Devonian (~377 and 375 Ma) ages record an impulse of mafic magmatism, widely manifested in the northern segments of the CAOB (~380‒365 Ma). Middle Carboniferous (~320 and 319 Ma) dates may be associated with the closure of the Ob-Zaisan branch of the Paleo-Asian ocean as a result of the Kazakhstan-Siberian collision. Early Permian (~290–279 Ma) ages are consistent with the formation of late Carboniferous–Early Permian (~305–275 Ma) large igneous provinces in connection with rifting processes in the northern segments of the CAOB. Finally, a single Early Jurassic (~188 Ma) age marks tectonic reorganization of the CAOB in Late Triassic‒Early Jurassic in response to (i) closure of the Paleotethys ocean with subsequent collision of the Cimmerian blocks and the southern margin of the Eurasian continent and/or (ii) activity of the Mongolian mantle plume.
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Safonova, I. Yu, et А. I. Khanchuk. « SUBDUCTION EROSION AT PACIFIC-TYPE CONVERGENT MARGINS ». Tikhookeanskaya Geologiya 40, no 6 (2021) : 3–19. http://dx.doi.org/10.30911/0207-4028-2021-40-6-3-19.
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The paper presents a review of processes of subduction or tectonic erosion at the Pacific-type convergent margins (PTCM) including definition of “tectonic erosion”, its triggers, driving forces and consequences. We review examples of tectonic erosion at the Circum-Pacific PTCMs and at the fossil PTCMs of the Paleo-Asian Ocean (PAO) currently hosted by the Central-Asian Orogenic Belt (CAOB). Recent geological and stratigraphic studies have shown two types of PTCMs: accreting and eroding. Accreting PTCMs consist of older deposits of accretionary and frontal prisms and grow oceanward, i.e. the trench retreats. Eroding PTCMs are characterized by the destruction of the prism, approaching arc and trench and typically form during shallow-angle and fast subduction of an oceanic slab with oceanic floor topographic highs. The mechanism of tectonic erosion includes destruction of oceanic slab, island arcs, accretionary prism, fore-arc and related prism. Tectonic erosion is a common phenomenon at many Circum-Pacific PTCMs, e.g., in South America, Tonga and Nankai troughs, Alaska. Accretion and subduction of oceanic rises contributes greatly to the processes of formation, transformation and destruction of continental crust at PTCM. The episodes of tectonic erosion can be also reconstructed for an ancient ocean, for example, for the PAO, which evolution and suturing formed the CAOB. Many CAOB foldbelts (Altai, Tienshan, eastern Kazakhstan, Transbaikalia, Mongolia) carry signs of disap-pearance of big volumes of continental crust (arcs). Studying processes responsible not only for the formation of continental crust, but also for the disappearance of big volumes of crustal mate-rial is important for correct evaluation of the nature of intra-continental orogenic belts, e.g., CAOB, and development of reliable tectonic models.
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Sun, Jinlei, Ye Qian, Jinyu Li, Yanjie Shen, Lixiang Zhao et Fegnyue Sun. « Two-Stage Orogenic Cycle of the Eastern Paleo-Asian Ocean from Early Palaeozoic to Early Triassic : Constraints from Magmatic Rocks of the Southeastern Central Asian Orogenic Belt ». Minerals 12, no 8 (19 août 2022) : 1040. http://dx.doi.org/10.3390/min12081040.
Texte intégralRésumé :
The evolution of the eastern Paleo-Asian Ocean (PAO) has controlled the formation of the southeastern Central Asian Orogenic Belt (CAOB). However, the evolution history and final closure time of the eastern PAO still remain controversial, which greatly restricts understanding of the formation process of the CAOB. To address these issues, we provide detailed zircon chronology and Hf isotope and geochemical data of Paleozoic to Triassic magmatic rocks in the southeastern CAOB. We have identified four periods of magmatism as evidenced by: Early Silurian quartz diorites (434.7 Ma), Early Devonian monzogranites (394.2 Ma), Middle Permian granites (260.2–264.5 Ma) and Late Permian-Early Triassic syenogranite (250.8–253.6 Ma). These rocks have features of low MgO and mantle-compatible elements, are enriched in Th, U, K, Pb, Sr, Zr and Hf and depleted in Nb, Ta, La, Ce, P, and Ti. The quartz diorites belong to the medium-K calc-alkaline series with εHf(t) values of −0.76 to 2.21, indicating that they may be derived from partial melting of mafic lower crust with minor contribution of mantle magma. The monzogranites and syenogranite have high Zr + Nb + Ce + Y (260–390; 261–461 ppm, respectively), total alkali contents (9.98–10.80; 8.46–9.29 wt.%, respectively), and high zircon saturation temperature (807–840; 810–885 °C). They can be classified as A-type granites. Monzogranites have εHf(t) values (between −1.20 and +3.34); hence, we believe that they were derived from the crust modified by mantle-derived fluids or melts. Syenogranite have high εHf(t) values (5.49–11.36), and we suggest that they were derived from the juvenile lower crust that originated from the depleted mantle. The granites have high Sr/Y ratios (118–257), low Y (1.42–2.82 ppm), and Yb (0.31–0.41 ppm), consistent with the features of adakite. Considering the εHf(t) isotopic values (2.99–8.50), we suggest that they originated from thickened juvenile lower crust. Combining the results from our own and previous studies, we propose a new evolution model of the eastern PAO from Paleozoic to Triassic. It can be divided into two stages: (1) Late Cambrian to Early Devonian; (2) Early Permian to Triassic. The first stage is the evolution of the Bainaimiao ocean (secondary ocean basin of the PAO), which closed in the Late Silurian and led to the Bainaimiao arc accretion to the North China Cratons. The second stage is the final closure of the eastern PAO during the Late Permian (~254 Ma).
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Cai, Keda, Xiaoping Long, Huayong Chen, Min Sun et Wenjiao Xiao. « Accretionary and collisional orogenesis in the south domain of the western Central Asian Orogenic Belt (CAOB) ». Journal of Asian Earth Sciences 153 (mars 2018) : 1–8. http://dx.doi.org/10.1016/j.jseaes.2017.11.019.
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Cao, Yonghua, Christina Yan Wang et Bo Wei. « Magma oxygen fugacity of mafic-ultramafic intrusions in convergent margin settings : Insights for the role of magma oxidation states on magmatic Ni-Cu sulfide mineralization ». American Mineralogist 105, no 12 (1 décembre 2020) : 1841–56. http://dx.doi.org/10.2138/am-2020-7351.
Texte intégralRésumé :
Abstract Oxygen fugacities (fO2) of mantle-derived mafic magmas have important controls on the sulfur status and solubility of the magmas, which are key factors to the formation of magmatic Ni-Cu sulfide deposits, particularly those in convergent margin settings. To investigate the fO2 of mafic magmas related to Ni-Cu sulfide deposits in convergent margin settings, we obtained the magma fO2 of several Ni-Cu sulfide-bearing mafic-ultramafic intrusions in the Central Asian Orogenic Belt (CAOB), North China, based on the olivine-spinel oxygen barometer and the modeling of V partitioning between olivine and melt. We also calculated the mantle fO2 on the basis of V/Sc ratios of primary magmas of these intrusions. Ni-Cu sulfide-bearing mafic-ultramafic intrusions in the CAOB include arc-related Silurian-Carboniferous ones and post-collisional Permian-Triassic ones. Arc-related intrusions formed before the closure of the paleo-Asian ocean and include the Jinbulake, Heishan, Kuwei, and Erbutu intrusions. Post-collisional intrusions were emplaced in extensional settings after the closure of the paleo-Asian ocean and include the Kalatongke, Baixintan, Huangshandong, Huangshan, Poyi, Poshi, Tulaergen, and Hongqiling No. 7 intrusions. It is clear that the magma fO2 values of all these intrusions in both settings range mostly from FMQ+0.5 (FMQ means fayalite-magnetite-quartz oxygen buffer) to FMQ+3 and are generally elevated with the fractionation of magmas, much higher than that of MORBs (FMQ-1 to FMQ+0.5). However, the mantle fO2 values of these intrusions vary from ~FMQ to ~FMQ+1.0, just slightly higher than that of mid-ocean ridge basalts (MORBs) (≤FMQ). This slight difference is interpreted as the intrusions in the CAOB may have been derived from the metasomatized mantle wedges where only minor slab-derived, oxidized components were involved. Therefore, the high-magma fO2 values of most Ni-Cu sulfide-bearing mafic-ultramafic intrusions in the CAOB were attributed to the fractionation of magmas derived from the slightly oxidized metasomatized mantle. In addition, the intrusions that host economic Ni-Cu sulfide deposits in the CAOB usually have magma fO2 of >FMQ+1.0 and sulfides with mantle-like δ34S values (–1.0 to +1.1‰), indicating that the oxidized mafic magmas may be able to dissolve enough mantle-derived sulfur to form economic Ni-Cu sulfide deposits. Oxidized mafic magmas derived from metasomatized mantle sources may be an important feature of major orogenic belts.
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Starostin, Ivan, Aleksander Chernykh et Mikhail Girfanov. « Paleogeotectonic position of the Kyzyk Chadr porphyry copper ore field, Republic of Tyva ». Ores and metals, no 4 (17 janvier 2024) : 52–73. http://dx.doi.org/10.47765/0869-5997-2023-10019.
Texte intégralRésumé :
Regional-scale localization conditions of the Kyzyk-Chadr molybdenum-copper porphyry ore field in the southern folded frame of the Siberian Platform are considered. The porphyry mineralization of the field formed at the Salairian (Early Caledonian) phase of development of the Altai-Sayan segment of the
Central Asian Orogenic Belt (CAOB), in connection with small intrusions of the gabbro-diorite-granodioritegranite Kyzykchadr Complex (Є2–3). The formation of the ore-bearing complex was associated with an accretionalcollisional magmatic belt superimposed on a Vendian–Early Cambrian volcanic-sedimentary island-arc substrate. The complex is only known within the local Ozhu uplifted block with a “batholitic” massif of the gabbrotonalite-plagiogranite Tannu-Ola Complex (Є2), but it is suggested that there could existed some analogous accretional-collisional Cambrian intrusions productive for Mo-Cu porphyry mineralization in some other areas, that were later overlapped by Ordovician–Silurian and Early Devonian volcanosedimentary deposits or broken by
intrusive massifs of the Caledonian collisional volcano-plutonic belt. The rocks of the Salairian and Caledonian magmatic belts were deformed during subsequent geotectonic stages, primarily the Late Paleozoic collision, and overlain by younger sedimentary deposits. The position of economic-grade Mo and Mo-Cu porphyry deposits in the southern Altai-Sayan segment of the CAOB is assumed to be confined to areas of spatial superposition
(overlapping) of magmatic belts of the three geotectonic stages: 1) island-arc volcanic belts (V–Є1), 2) “batholithic” intrusions and small intrusions of the magmatic belt of the accretional-collisional stage (Є2–3), 3) the collisional volcano-plutonic belt (O–D1).
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Chen, Wenliang, Minjie Zhang, Guanghuo Tao, Xiaofeng Li, Qian Yu, Xiaojie Fan et Jingwei Zhang. « Ocean–Continent Conversion in Beishan Orogenic Belt : Evidence from Geochemical and Zircon U-Pb-Hf Isotopic Data of Luotuoquan A-Type Granite ». Minerals 13, no 11 (4 novembre 2023) : 1411. http://dx.doi.org/10.3390/min13111411.
Texte intégralRésumé :
Devonian magmatism is one of the most important tectonothermal events in the Central Asian Orogenic Belt (CAOB). However, little is known regarding the petrogenesis and geodynamic setting of the widely distributed Devonian granitoids in the eastern Southern Beishan Orogenic Belt (SBOB). Early-Devonian granitic magmatism has been recognized from the Luotuoquan area, and the granites were emplaced between 404.9 Ma and 399.4 Ma according to LA-ICPMS zircon U–Pb dating. Geochemically, the granites exhibit high SiO2 and Al2O3 contents and are enriched in light rare earth elements as well as Rb, Th, Nd, Zr, and Hf, while being depleted in heavy rare earth elements and Ba, U, Sr, and Ti, with distinct rare earth element fractionation and pronounced negative Eu anomalies. According to the comprehensive analysis, they closely resemble the features typically associated with A-type granites. The zircons εHf(t) values are within the range of +0.90–+5.19 (averaged 3.23) for the monzogranite and syenogranite, whereas their TDM2 values fall between 1.05 and 1.34 Ga, suggesting that the magma source of the monzogranite–syenogranite originated from the partial melting of the Mesoproterozoic crust dominated by metagreywackes. Furthermore, the monzogranite and syenogranite exhibit high temperatures (average 782 °C), thin crustal thickness (average 30 km), and A-type characteristics, suggesting their formation in post-collision extensional settings. We propose the closure of the Beishan Ocean occurred before the early Devonian, followed by a transition in the Southern Beishan Orogenic Belt from a compressional to an extensional setting.
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SHI, GUANZHONG, GUANGZENG SONG, HUA WANG, CHUANYAN HUANG et BEN LI. « Provenance and tectonic setting of the Upper Palaeozoic sandstones in western Inner Mongolia (the Shalazhashan and Solonker belts), China : insights from detrital zircon U–Pb ages and Hf isotopes ». Geological Magazine 156, no 3 (14 décembre 2017) : 547–71. http://dx.doi.org/10.1017/s0016756817000978.
Texte intégralRésumé :
AbstractThe Solonker and Shalazhashan belts are hotly debated tectonic units of the Central Asian Orogenic Belt (CAOB), because they may either represent a Permian or Triassic suture zone of the CAOB, or a rifting zone overprinted on an Early Palaeozoic orogen. Provenance analysis of the Upper Palaeozoic sandstones in these belts may provide useful constraints on this issue. This study collected six sandstone samples from three study areas: the Mandula area of the Solonker Belt, the Quagan Qulu area of the Shalazhashan Belt but close to the Alxa block, and the Enger Us area of the Shalazhashan Belt, for framework petrography, zircon morphology, U–Pb and Lu–Hf isotopic analyses. Framework petrography reveals that the Mandula and Enger Us area samples contain high proportions of volcanic fragments, whereas the samples from the Quagan Qulu area include not only volcanic fragments but also significant amounts of biotite and muscovite. The detrital zircons of the Mandula area and the Enger Us area yield two main age groups: (i) 260–330 Ma, with dominant εHf(t) values of –5 to +12; and (ii) 420–550 Ma, with dominant εHf(t) values of –9 to +9, suggesting that Early Palaeozoic arc-related magmatic rocks and Late Palaeozoic syn-depositional volcanic rocks are the main source rocks. The detrital zircons of the Quagan Qulu area have one main age group of 420–500 Ma and some grains of 0.9–1.1 Ga, 1.4–1.5 Ga, 1.8–1.9 Ga and ~ 2.5 Ga, which derive from the northern margin of the Alxa block. The lithological and fossil assemblages of the Upper Palaeozoic sandstones suggest shallow-marine to deep-water depositional environments and a northward-deepening transition. Based on the zircon spectra, sedimentary environment analysis and previous studies, we argue that the Solonker Belt and the Shalazhashan Belt of the CAOB are in extensional basins of a fore-arc or rifting setting.
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FU, LEBING, JUNHAO WEI, TIMOTHY M. KUSKY, HUAYONG CHEN, JUN TAN, YANJUN LI, LINGJUN KONG et YONGJIAN JIANG. « Triassic shoshonitic dykes from the northern North China craton : petrogenesis and geodynamic significance ». Geological Magazine 149, no 1 (9 mars 2011) : 39–55. http://dx.doi.org/10.1017/s0016756811000173.
Texte intégralRésumé :
AbstractZircon U–Pb ages, major and trace element geochemistry and Sr, Nd and Pb isotope compositions of diorite and diorite porphyry dykes from the Jinchanggouliang (JCGL) gold ore field on the northern margin of the North China craton (NCC) were studied to investigate their sources, petrogenesis and geodynamic significance. LA-ICP-MS zircon U–Pb dating reveals three major age groups of 2500 Ma (n = 2), 253 ± 7 Ma (n = 5) and 227 ± 1 Ma (n = 9). The inherited ages of 2500 Ma, contemporary with the Archaean NCC continental growth, imply that crustal material was involved in the magma source. The igneous zircons with a concordia age of 227 ± 1 Ma may record the emplacement age of the JCGL dykes. Both diorite and diorite porphyry exhibit a wide range of SiO2 and MgO contents and are characterized by high concentrations of Na2O+K2O and Al2O3, and low abundances of P2O5 and TiO2. They are enriched in large ion lithophile elements and light rare earth elements without significant Eu anomalies, and depleted in high-field-strength elements; all are categorized as shoshonitic rocks. All samples show a narrow range of Sr isotope compositions with initial 87Sr/86Sr ratios from 0.70394 to 0.70592, variable εNd(t) values (1.1 to −12.0) and TDM2 ages of 913–1972 Ma. Their Pb isotope compositions form continuous variation trends and plot in the fields between enriched mantle 1 (EM1) and lower continental crust (LCC). The above results suggest that the JCGL dykes studied could have been derived from mixing of lower crust, lithospheric mantle of the NCC and ascending asthenospheric melt in a post-orogenic extensional geodynamic setting. These shoshonitic dykes, together with the geochronological data of regional ENE-trending retrograded eclogites, ophiolites, continental arc magmatic belt, A-type granite, alkaline intrusions and metamorphic core complex from the northern NCC and Central Asian Orogenic Belt (CAOB) suggest that closure of the Palaeo-Asian Ocean (i.e. stage of pre-collision to collision) had completed during latest Permian to earliest Triassic time, and that the CAOB was subsequently tectonically dominated by post-orogenic extensional regimes. The involvement of asthenospheric melt in the magma source implies that the sub-continental lithospheric mantle (SCLM) of the NCC had been modified, and the onset of lithospheric destruction and thinning beneath the northern NCC may have occurred in Middle–Late Triassic time as a result of post-orogenic subducting slab detachment and lithospheric delamination.
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Xue, Jixiang, Yi Shi, Zhenghong Liu et Linfu Xue. « Closure of the Eastern Paleo-Asian Ocean : Evidence from Permian–Triassic Volcanic Rocks in the Northern Margin of the North China Craton ». Minerals 13, no 5 (27 avril 2023) : 606. http://dx.doi.org/10.3390/min13050606.
Texte intégralRésumé :
The Central Asian Orogenic Belt (CAOB) is the world’s largest accretionary orogenic belt, and its formation is related to the closure of the Paleo-Asian Ocean (PAO). However, the closure time and style of the PAO remain controversial. To address these issues, this paper presents zircon U-Pb dating, whole-rock geochemistry and zircon Lu-Hf isotope analyses of the volcanic rocks in the Faku-Kaiyuan area on the northern margin of the North China Craton. The results show that the Bachagou andesites formed in the Early Permian (287 ± 2 Ma), while the Chaijialing andesites and dacites formed in the Late Permian (253.3 ± 3.7 Ma) and Middle Triassic (244.3 ± 1.3 Ma), respectively. The Bachagou andesites and Chaijialing andesites are enriched in LILEs and LREEs and depleted in HFSEs and HREEs, indicating that they formed in the active continental margins. The Chaijialing dacites show similar geochemical signatures to adakite and formed in a syn-collisional setting. Geochemistry and isotopic analysis indicates that the Bachagou andesites were derived from a partial melting of the mantle wedge that was metasomatized by subduction fluids. The Chaijialing andesites were generated from a metasomatized mantle by slab-derived and sediment fluids. The Chaijialing dacites formed by a partial melting of thickened lower crust. Combined with previous research results, we can conclude that the Eastern PAO closed by a scissor-like movement from west to east during the Late Permian–Middle Triassic.
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Zhang, Xue-Bing, Feng-Mei Chai, Chuan Chen, Hong-Yan Quan, Ke-Yong Wang, Shun-Da Li et Shi-Shan Wu. « Using Whole Rock and Zircon Geochemistry to Assess Porphyry Copper Potential of the Tonggou Copper Deposit, Eastern Tianshan ». Minerals 10, no 7 (28 juin 2020) : 584. http://dx.doi.org/10.3390/min10070584.
Texte intégralRésumé :
Eastern Tianshan hosts a number of porphyry Cu deposits. However, these mainly formed in the Jueluotage Belt, in the middle part of Eastern Tianshan. The Tonggou porphyry Cu mineralization is an exception to this, since it is located in the Bogda Orogenic Belt, north of Eastern Tianshan. We obtained new zircon U-Pb ages, whole-rock geochemical data, zircon Hf isotope data, and zircon trace element compositions. LA-ICP-MS zircon U-Pb dating indicates a crystallization age of 302.2–303.0 Ma for the Tonggou mineralized granodiorite (TMG), which suggests that the Tonggou porphyry Cu mineralization formed in the Late Carboniferous period. εHf (t) data (1.8–14.1) for TMG suggests it was sourced from juvenile crustal melts, mixed with some mantle materials. TMG displays low ΣREE, compatible elements (Ba, Sr, Zr, and Hf), Zr/Hf and Nb/Ta ratios, as well as clearly negative Eu anomalies in whole rocks analyses. In addition, TMG is enriched in P, Hf and Th/U ratios in zircon, and has lower crystallization temperatures (734 to 735 °C) than the Daheyan barren granodiorite (DBG) (753 to 802 °C). Whole rock and zircon geochemical analyses show that the TMG was formed by fractional crystallization to a greater extent than the DBG in the Bogda Orogenic Belt. Moreover, zircon grains of the TMG show high Ce4+/Ce3+ ratios (159–286), which are consistent with related values from large porphyry deposits of the Central Asian Orogenic Belt (CAOB). High Ce4+/Ce3+ ratios reflect oxidizing magmas as a result of fractional crystallization, which indicates that the Tonggou deposit has potential to host a large porphyry Cu deposit.
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Likhanov, I. I. « Evidence of Grenville and Valhalla Tectonic Events at the Western Margin of the Siberian Craton from Rocks of the Garevka Complex (North Yenisei Ridge) ». Петрология 31, no 1 (1 janvier 2023) : 49–80. http://dx.doi.org/10.31857/s0869590323010053.
Texte intégralRésumé :
The tectonic evolution of the Siberian cratonic margins offers important clues for global paleogeographic reconstructions, particularly with regard to the complex geological history of Central Asia. The Yenisey Ridge fold-and-thrust belt at the western margin of the Siberian Craton forms part of the Central Asian Orogenic Belt (CAOB) and is a key to understand the Precambrian tectonic evolution of the Siberian Craton and crustal growth in the CAOB. Understanding the tectonic evolution of the Yenisei Ridge is crucial for solving the debate related to the role of the Siberian Craton within the Rodinia supercontinent assemblies and breakup with the opening of the Paleoasian ocean. Here we report new data on the petrogenesis, tectonic settings, thermodynamic conditions, metamorphism and protolith ages for compositionally contrasting rocks of the Garevka metamorphic complex, obtained from the results of mineralogical-petrological, geochemical, and isotope-geochronological studies. Possible models and geodynamic settings for their formation are discussed. Based on the results of U-Pb dating of zircons, two new pulses of Neoproterozoic endogenous activity at the western margin of the Siberian craton were established, associated with Grenville (930–900 Ma) and (880–845 Ma) post-Grenville Valhalla (880–845 Ma) accretion-and-collision processes. These episodes of regional crustal evolution are correlated with the synchronous successions and similar style of rocks along the Arctic margin of Rodinia and supports the spatial proximity of Siberia and North Atlantic cratons (Laurentia and Baltica), which is consistent with the proposed Neoproterozoic paleogeographic reconstructions of the Rodinia configuration.
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ZHOU, JIAN-BO, SIMON A. WILDE, GUO-CHUN ZHAO, XING-ZHOU ZHANG, CHANG-QING ZHENG, HU WANG et WEI-SHUN ZENG. « Pan-African metamorphic and magmatic rocks of the Khanka Massif, NE China : further evidence regarding their affinity ». Geological Magazine 147, no 5 (10 février 2010) : 737–49. http://dx.doi.org/10.1017/s0016756810000063.
Texte intégralRésumé :
AbstractThe Khanka Massif is a crustal block located along the eastern margin of the Central Asian Orogenic Belt (CAOB) and bordered to the east by Late Jurassic–Early Cretaceous circum-Pacific accretionary complexes of the Eastern Asian continental margin. It consists of graphite-, sillimanite- and cordierite-bearing gneisses, carbonates and felsic paragneisses, in association with various orthogneisses. Metamorphic zircons from a sillimanite gneiss from the Hutou complex yield a weighted mean206Pb/238U age of 490 ± 4 Ma, whereas detrital zircons from the same sample give ages from 934–610 Ma. Magmatic zircon cores in two garnet-bearing granite gneiss samples, also collected from the Hutou complex, yield weighted mean206Pb/238U ages of 522 ± 5 Ma and 515 ± 8 Ma, whereas their metamorphic rims record206Pb/238U ages of 510–500 Ma. These data indicate that the Hutou complex in the Khanka Massif records early Palaeozoic magmatic and metamorphic events, identical in age to those in the Mashan Complex of the Jiamusi Massif to the west. The older zircon populations in the sillimanite gneiss indicate derivation from Neoproterozoic sources, as do similar rocks in the Jiamusi Massif. These data confirm that the Khanka Massif has a close affinity with other major components of the CAOB to the west of the Dun-Mi Fault. Based on these results and previously published data, the Khanka Massif is therefore confirmed as having formed a single crustal entity with the Jiamusi (and possibly the Bureya) massif since Neoproterozoic time.
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Liu, Zhenjiang, Jianping Wang, Shaobo Cheng et Jiajun Liu. « Tempo-Spatial Tungsten Metallogeny in the Xing’an–Mongolia Orogenic Belt : Insights from the Early Cretaceous Shamai Tungsten Deposit Case Study in Northeastern China ». Minerals 15, no 1 (16 janvier 2025) : 80. https://doi.org/10.3390/min15010080.
Texte intégralRésumé :
The Xing’an–Mongolia Orogenic Belt (XMOB) is located in the eastern part of the Central Asian Orogenic Belt (CAOB). The region’s notable tectonic complexity and extensive tungsten mineralization offer a unique opportunity to explore metallogeny mechanisms in orogenic areas. This study focuses on the Shamai tungsten deposit as a case study, presenting results from LA–ICP–MS U–Pb dating of fine-grained, medium-grained, and porphyritic biotite monzogranite samples from the deposit, along with in situ zircon Hf isotopic and plagioclase Pb isotopic analyses. The fine-grained, medium-grained, and porphyritic biotite monzogranite were emplaced at 142.5, 141.9, and 140.2 Ma, respectively. These samples contain zircons with εHf(t) values ranging from 3.2 to 7.9 and 4.2 to 7.6, respectively, yielding TDM2 model ages from 996 to 692 Ma and 923 to 708 Ma. These findings suggest that the magmas in the Shamai deposit were produced by partial melting of juvenile crustal material mixed with mantle-derived components. The tungsten mineralization periods in the Eastern XMOB region can be divided into three stages: Early Paleozoic (ca. 520–475 Ma), Triassic (ca. 250–200 Ma), and Jurassic to Early Cretaceous (ca. 190–130 Ma). The highest concentration of tungsten mineralization in the XMOB occurs within the Xing’an Block during the Jurassic to Early Cretaceous period. Yanshanian magmatism and the most significant tungsten metallogenic events are likely influenced by an extensional setting and oceanic slab rollback, shaped by the tectonic evolution of the Mongol-Okhotsk Ocean and the Paleo-Pacific Ocean.
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Fan, Yuxu, Qinghui Xiao, Tingdong Li, Yang Cheng, Yan Li, Lingjun Guo et Pengyue Luo. « Geochronology, geochemistry, Sr–Nd–Hf isotope composition of the late Permian adakite in West Ujimqin, Inner Mongolia : petrogenesis and tectonic implications ». Canadian Journal of Earth Sciences 59, no 1 (janvier 2022) : 46–58. http://dx.doi.org/10.1139/cjes-2019-0002.
Texte intégralRésumé :
We report herein on new zircon U–Pb ages, the major and trace elements of whole-rock, and the Sr–Nd–Hf isotope composition for adakitic intrusives collected from the West Ujimqin district in the Southeast region of the Central Asian Orogenic Belt (CAOB). These data provide important constraints on the petrogenetic evolution and geodynamic setting of late Permian magmatism in the Southeast CAOB. The U–Pb dating of zircon shows that the ages of Seerbeng pluton and Nuhetingshala pluton in West Ujimqin are 255.3 ± 0.71 and 254.4 ± 1.2 Ma, respectively, which signifies that these are products of magmatic activity in the late Permian. The adakitic intrusives are characterized by high levels of Sr (Sr ≥ 741 ppm), low Y, low Yb, high Sr:Y ratios, and strongly fractionated rare earth elements (10.3 < LaN/YbN < 22.5), which is similar to the features of the adakite. The magmatic zircons exhibit positive Hf values (+8.1 to +13.3), and young two-stage model ages vary from 430 to 760 Ma. The high εNd(t) and low (87Sr:86Sr)i indicate that the adakitic granite derived from the partial melting of subducted oceanic slab. The high level of Mg# [100 × Mg/(Mg + Fe) in atomic number] and abundant Cr–Ni indicate that magmatic melts interacted with olivine rocks in the mantle. Considering these results and the regional rock assemblies, we conclude that the Paleo-Asian Ocean had not yet completely closed in the late Permian, and northward subduction continued, with the subducted slab possibly breaking off.
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Powerman, Vladislav, Andrey Shatsillo, Nikolai Chumakov, Igor Kapitonov et Jeremy Hourigan. « Interaction between the Central Asian Orogenic Belt (CAOB) and the Siberian craton as recorded by detrital zircon suites from Transbaikalia ». Precambrian Research 267 (septembre 2015) : 39–71. http://dx.doi.org/10.1016/j.precamres.2015.05.015.
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Zhao, Yan, Wenhao Ao, Jianghao Yan, Mingguo Zhai, Hong Zhang, Qian Wang et Yong Sun. « Paleozoic tectonothermal event in Mt. Dongbatu, Dunhuang terrane, southernmost Central Asian Orogenic Belt (CAOB) : Implications for petrogenesis and geological evolution ». Lithos 326-327 (février 2019) : 491–512. http://dx.doi.org/10.1016/j.lithos.2018.12.037.
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Gao, Feng, Yuanfeng Cheng, Ruiqing Guo, Xiaoqiang Liu et Zengxin Liu. « The Late Carboniferous Mafic–Ultramafic Complex Induced by Slab Breakoff in Eastern North Tianshan, Central Asian Orogenic Belt ». Minerals 13, no 10 (4 octobre 2023) : 1293. http://dx.doi.org/10.3390/min13101293.
Texte intégralRésumé :
The Late Carboniferous to Early Permian is a critical period of the Chinese Tianshan, witnessing the tectonic transition from subduction to post-collisional extension during the final amalgamation of the Central Asian Orogenic Belt (CAOB). The late Carboniferous Mozbaysay mafic–ultramafic complex in the Qijiaojing–Balikun area, eastern North Tianshan, provides important clues for revealing the nature and timing of this tectonic transition. The Mozbaysay complex comprises mainly hornblende gabbros and lherzolites. LA-ICP-MS U-Pb zircon ages of hornblende gabbro yielded a weighted mean age of 306 ± 1.9 Ma for this complex. These mafic–ultramafic rocks have high contents of MgO (up to 30 wt.%), Cr (up to 2493 ppm), and Ni (up to 1041 ppm), but low contents of SiO2 (40.34–47.70 wt.%). They are enriched in LREE and show characteristics of enriched mid-ocean ridge basalts (E-MORB). The relatively high Th/Yb and Ba/Nb ratios imply the mantle sources could have been metasomatized by slab–mantle interaction with aqueous fluids from dehydration of the subducted slab. Thus, these mafic–ultramafic rocks were most likely produced by partial melting of the asthenospheric and lithospheric mantle with a slight influence of slab-derived fluids. Therefore, we suggest that the formation of these Late Carboniferous mafic–ultramafic rocks was triggered by the decompression-induced influx of asthenospheric heat and melting through a slab window during post-collisional slab breakoff. Combined with geological data, the petrogenetic links of the Late Carboniferous mafic–ultramafic rocks in eastern North Tianshan to slab breakoff suggest that the tectonic transition from convergence to post-collision most likely initiated in situ at ca. 306 Ma and lasted to ca. 300 Ma.
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WANG, YU, ZHAOHUA LUO, M. SANTOSH, SHUZHI WANG et NA WANG. « The Liuyuan Volcanic Belt in NW China revisited : evidence for Permian rifting associated with the assembly of continental blocks in the Central Asian Orogenic Belt ». Geological Magazine 154, no 2 (3 février 2016) : 265–85. http://dx.doi.org/10.1017/s0016756815001077.
Texte intégralRésumé :
AbstractThe basaltic pillow lavas in the Liuyuan region of NW China, considered to be part of an ophiolitic suite, have been central to the models on tectonic setting, evolution and timing of the final closure of the Palaeo-Asian Ocean. New field evidence on the sedimentary units associated with the basalts reveals comparable sequences in the northern and southern flanks of the Liuyuan Volcanic Belt with coarse to fine sediments from periphery to the centre. The dacites and rhyolites formed coevally with the pillow basalts. The pillow basalts are interlayered with lacustrine sandstone, claystone and clayey lake deposits. Detrital zircons from these sediments yield zircon U–Pb ages of 291–285 Ma. Andesites, dacites and rhyolites from the basaltic sequence yield U–Pb ages of 280–277 Ma, similar to the 282–280 Ma ages of gabbros that intrude the pillow lavas. All these rocks cover the 460–440 Ma granite and greenschist basement and have been intruded by gabbros of c. 272 Ma age, with subsequent (230–227 Ma) north–south contractional thrusting and folding. The data from our study are incompatible with the existing models that consider the basalts as part of an ophiolitic suite. Along the northern continental margin of China from west to east, the Tarim, Dunhuang-Alxa and North China cratonic areas all show evidence for regional extension through rifting during early–middle Permian time. These rift features and basaltic eruptions occurred coevally with the assembly of various microcontinental blocks against the Siberian craton at c. 300–250 Ma, synchronous with amalgamation of the Central Asian Orogenic Belt (CAOB) on the northern side of the Liuyuan Rift. These events were also broadly synchronous with formation of the global supercontinent Pangea.
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Li, Ai, Jian Wang et Yue Song. « Petrology, mineral chemistry, and geochemistry of Late Triassic Ni–Cu ore-bearing mafic–ultramafic intrusions, Hongqiling, northeastern China : petrogenesis and tectonic implications ». Canadian Journal of Earth Sciences 56, no 2 (février 2019) : 111–28. http://dx.doi.org/10.1139/cjes-2018-0014.
Texte intégralRésumé :
The Hongqiling magmatic Ni–Cu sulfide deposit, situated on the southern margin of the eastern Central Asian Orogenic Belt (CAOB), is composed of over 30 mafic–ultramafic intrusions. These ore-bearing intrusions are composed mainly of harzburgite, lherzolite, websterite, orthopyroxenite, and norite (gabbro). The constituent minerals are olivine, diopside, bronzite, calcic-hornblende, plagioclase, and spinel with orthopyroxene as a dominant mineral in these intrusions. These ore-bearing intrusions are not Alaskan-type complexes. Spinel and clinopyroxene both exhibit different chemical compositions from those in the Alaskan-type complexes. The rocks that make up the intrusions have high contents of MgO (average value = 25.20 wt.%) and low TiO2 (average value = 0.58 wt.%). The high MgO contents of the minerals and the high Mg# (71) of the calculated melt in equilibrium with olivine demonstrate that the parental magma of the Hongqiling mafic–ultramafic intrusions was a high-Mg tholeiitic magma. The Hongqiling ore-bearing mafic–ultramafic intrusions and the calculated “trapped liquids” for the olivine-orthopyroxene cumulate rocks are all enriched in large-ion lithophile elements and depleted in high field strength elements. The Ce/Pb, Ta/La, Th/Yb, and (La/Sm)PM values and the depletion of Nb and Ta suggest that the magma experienced crustal contamination. The Hongqiling ore-bearing intrusions display many similarities with mafic–ultramafic intrusions that formed in a post-collisional extensional environment in the western CAOB (e.g., Huangshanxi). Common features include their whole-rock compositions and mineral chemistry. Combined with the evolutionary history of the eastern segment of the CAOB, we believe that the Late Triassic Hongqiling mafic–ultramafic intrusions formed in a post-collisional extensional environment.
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Chen, Jingsheng, Dexin Tian, Bin Li, Yi Shi, Zhonghui Gao, Yi Tian, Weiwei Li, Chao Zhang et Yan Wang. « Permian Granitic Plutons from the Northern Margin of the North China Craton : Implications for the Tectonic Evolution of the Central Asian Orogenic Belt ». Minerals 13, no 12 (17 décembre 2023) : 1554. http://dx.doi.org/10.3390/min13121554.
Texte intégralRésumé :
As the world’s largest accretionary orogen, the Central Asian Orogenic Belt (CAOB) underwent continuous juvenile crustal growth in the Phanerozoic. The northern margin of the North China Craton (NCC) and its adjacent area form the eastern segment of the CAOB, which is a key area for learning about the geological evolution of the Paleo-Asian Ocean (PAO). In the Permian, the west of the northern margin of the NCC was a post-collision extensional environment, while the east was in a subduction stage. As a connecting area, the Permian evolution of the PAO in the middle of the northern margin of the NCC has not been systematically studied. In order to fill the gap and understand the continuous temporal and spatial evolutionary process of the PAO, this paper focuses on the Permian granitic rocks in the Chifeng area. Zircon U-Pb dating and the geochemical analysis of whole-rock major and trace elements were conducted to build a granite chronological framework, and to discuss the genesis and tectonic background of the granitic rocks, along with tectono-magmatic evolutionary history in the Chifeng area. The respective LA-ICP-MS zircon U-Pb dating results from eight samples are 269 ± 1, 268 ± 3, 260 ± 4, 260 ± 1, 260 ± 1, 255 ± 2, 254 ± 2 and 256 ± 1 Ma, respectively. These results, combined with previous data, revealed that the Permian granitic rocks had undergone three events of magmatism: (1) monzogranitic-syenitic phase (294–284 Ma; Cisuralian); (2) monzogranitic phase (269–260 Ma; Guadalupian) and (3) late monzogranitic-syenitic phase (256–254 Ma; Lopingian). From the Early Permian (294–284 Ma) to the Middle Permian (269–260 Ma), granites with fine-medium-grained locally porphyritic texture and massive structure showed a high-potassium calc-alkaline series formed in a compressional setting, indicating a continuous collision between the Xing’an-Mongolian Orogenic Belt (XMOB) and the NCC. During the Late Permian-Early Triassic (256–248 Ma), granites with massive structure and medium-grained texture in the Chifeng area were magmatism dominated by A- and I-type granites of high-potassium calc-alkaline series, combined with the coeval basic rocks, which constituted a typical “bimodal” rock assemblage. This suggests that the Chifeng area was located in an extensional setting where the subducting slab broke off during the collision between the XMOB and NCC. These granitic plutons from the Permian are believed to have been generated by the subduction-collision of the Paleo-Asian oceanic crust beneath the NCC, according to emplacement time and occurrence location. Our findings provide strong evidence for Permian continuous temporal and spatial tectonic evolution and the characterization of the eventual closure of the PAO in Chifeng area at the northern margin of the NCC.
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Wang, Xin-Shui, Jun Gao, Reiner Klemd, Tuo Jiang, Ji-Lei Li, Xi Zhang et Sheng-Chao Xue. « The Central Tianshan Block : A microcontinent with a Neoarchean-Paleoproterozoic basement in the southwestern Central Asian Orogenic Belt ». Precambrian Research 295 (juillet 2017) : 130–50. http://dx.doi.org/10.1016/j.precamres.2017.03.030.
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КУЗНЕЦОВА, Л. Г., С. И. ДРИЛЬ et С. И. ШКОЛЬНИК. « THE AGE, COMPOSITION, AND PROVENANCES OF TERRIGENOUS ROCKS IN THE SOUTH OF THE SANGILEN BLOCK OF THE CENTRAL ASIAN OROGENIC BELT ». Геология и геофизика 65, no 3 (3 juin 2024) : 353–75. http://dx.doi.org/10.15372/gig2023185.
Texte intégralRésumé :
Впервые получены петрогеохимические, изотопные (Sm-Nd) и геохронологические U-Th-Pb (LA-ICP-MS по детритовым цирконам) характеристики терригенных пород из мощной толщи в южной части Сангиленского блока, входящего в состав Центрально-Азиатского складчатого пояса (ЦАСП). Установлено, что они фациально неоднородны: в субширотном направлении с запада на восток наблюдается переход от граувакковых песчаников с примесью пирокластики к существенно более кремнекислым литоидным аренитам. Геохронологические данные по детритовым цирконам из преобладающих граувакковых песчаников позволяют выделить следующие интервалы конкордантных оценок их возраста (млн лет): 787—907, 1873—2236, 2613—2725 и 2902—2977. С учетом максимального из установленного на сегодняшний день раннекембрийского (520 млн лет) возраста прорывающих их магматических пород возможный период накопления терригенных толщ южной части Сангиленского блока оценивается значительным интервалом 520—790 млн лет. На основании анализа полученных геохимических, изотопных (Sm-Nd) и геохронологических (U-Th-Pb) данных вероятными источниками сноса для терригенных отложений южной полосы (ЮП) являлись неопротерозойские и раннедокембрийские островодужные и окраинно-континентальные комплексы. Их относительные пропорции в составе осадков, по-видимому, изменялись с удалением от бассейна седиментации (в современных координатах с запада на восток): снижалась доля ранненеопротерозойских ювенильных пород и возрастала доля раннедокембрийских метаморфических комплексов. Обнаружение в терригенных породах Сангиленского блока детритовых цирконов палеопротерозойского и мезоархейского возраста, поставщиками которых не могли быть известные комплексы композитного докембрийского фундамента Тувино-Монгольского микроконтинента, позволяет рассматривать в качестве их источников другие кратонные блоки ЦАСП We have first determined the petrogeochemical, Sm–Nd isotope, and U–Th–Pb geochronological (detrital-zircon LA-ICP-MS) characteristics of terrigenous rocks from a thick sequence in the south of the Sangilen block, which is part of the Central Asian Orogenic Belt (CAOB). The rocks are heterogeneous in facies composition: From west to east, there is a transition from graywacke sandstones with an admixture of pyroclastics to much more silicic lithoid arenites. Geochronological data on detrital zircons from the predominant graywacke sandstones mark the following intervals of concordant ages (Ma): 787–907, 1870–2236, 2613–2725, and 2900–2980. With regard to the oldest determined age (early Cambrian, 520 Ma) of the igneous rocks intruding these sandstones, the possible period of accumulation of terrigenous sequences in the south of the Sangilen block is estimated at 790–520 Ma. The obtained geochemical, Sm–Nd isotope, and U–Th–Pb geochronological data point to Neoproterozoic and early Precambrian island arc and continent-marginal complexes as probable provenances for the terrigenous deposits of the “southern band”. The relative proportions of rocks of these complexes in the deposits changed with distance from the sedimentary basin (from west to east, in modern coordinates): The portion of early Neoproterozoic juvenile rocks decreased, and the portion of early Precambrian metamorphic complexes increased. The Paleoproterozoic and Mezoarchean detrital zircons found in the terrigenous rocks of the Sangilen block could not originate from any known Precambrian complexes of the Tuva–Mongolian microcontinent. This gives grounds to regard other craton blocks of the CAOB as their sources
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Kruk, N. N., M. L. Kuibida, E. N. Sokolova, P. D. Kotler et V. A. Yakovlev. « Late devonian calc-alkaline high-k fractionated “Ferroan” I-type leucogranites (Rudny Altai) ». Doklady Rossijskoj akademii nauk. Nauki o Zemle 515, no 2 (15 octobre 2024) : 229–36. http://dx.doi.org/10.31857/s2686739724040078.
Texte intégralRésumé :
The paper presents the geological, geochemical and isotope-geochronological studies of the Rudny Altai granitoids in the west of Central Asian Orogenic Belt (CAOB) – the front part of the Altai convergent margin of the Siberian continent. Isotopic U–Pb dating of zircons showed an age range from 367 to 363 Ma. Geochemical characteristics indicate the relevance of leucogranites to calc-alkaline high-K series (SiO2 73 wt.%, Na2O+K2O = 6.9–9 wt.%, Na2O/K2O = 0.7–1.2), with calc-alkaline and alkaline-calcic affinities (MALI = 6.32–8.41). They bear meta- to weakly-peraluminous values (A/CNK = 0.9–1.2), high Fe* index (0.84–0.97) and high fluorine (0.04–0.17 wt.%) content. Variations of HFSEs, LILEs contents, Ga/Al ratios and strong negative A/CNK-P2O5 correlation indicate their affinity with fractionated I-type granitoids. Rare metal (beryllium) mineralization is spatially and genetically related to leucogranites. It is assumed that the formation of granitoids was associated with shearing setting at the convergent margin of the Siberian continent, as a result of oblique subduction of the Irtysh-Zaisan ocean plate.
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Wang, Erteng, Xinwei Zhai, Wanfeng Chen, Lei Wu, Gaorui Song, Yun Wang, Zhiang Guo, Jiaolong Zhao et Jinrong Wang. « Late Devonian A-Type Granites from the Beishan, Southern Central Asia Orogenic Belt : Implications for Closure of the Paleo-Asia Ocean ». Minerals 13, no 4 (18 avril 2023) : 565. http://dx.doi.org/10.3390/min13040565.
Texte intégralRésumé :
The closing time of the Paleo-Asian Ocean (PAO) has long been in the focus of research as well as of controversial debates. The Paleozoic A-type granites distributed in the Beishan Orogenic Belt (BOB) at the southern margin of the Central Asian Orogenic Belt (CAOB) provide pivotal clues to constrain the closure of the PAO. In this paper, the newly recognized Duhongshan A-type granites from the middle Huaniushan arc in the BOB (zircon LA-ICP-MS U-Pb ages of ca. 376–374 Ma) are thoroughly studied. The rocks have high SiO2, K2O contents with peralkaline character, and display high Zr + Nb + Ce + Y contents (354–543 ppm), 10,000 × Ga/Al (4.1–4.9), Y/Nb (3.2–5.3), Rb/Nb ratios (8.5–14.1), and a zircon saturation temperature in the range of 877–950 °C, indicative of A2-type granites affinities. The Duhongshan granites display enriched in Th and U; depleted in Ba, Sr, and Ti; with slightly positive whole-rock εNd(t) values (+1.86 to +2.21), indicating an origin related to partial melting of lower crustal material in post-collision extension settings. Combined with previous reported results, we conclude that the granitoids in the middle Huaniushan arc were mostly formed around 424–367 Ma and can be divided into two types based on petrochemistry: (a) A-type granites, which generally have high SiO2 and K2O, derived from the relatively shallow crustal source in post-collision tectonic settings; and (b) adakite and I-type granites, which display high Sr/Y ratios as well as Nb, Ta, and Ti depletion, likely generated from the melting of juvenile crust in active continental margin arcs. Integrating the previous regional investigations, we propose that the Hongliuhe–Niujuanzi–Xichangjing Ocean (HNXO) of the PAO was closed and transformed in the post-collision extensional tectonic stage during the Late Devonian and formed as post-collision magmatism, while the arc magmatism may be related to the subduction of the Liuyuan Ocean, which is located in the Southern HNXO.
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Khromykh, S. V., P. D. Kotler, A. E. Izokh et N. N. Kruk. « A REVIEW OF EARLY PERMIAN (300–270 MA) MAGMATISM IN EASTERN KAZAKHSTAN AND IMPLICATIONS FOR PLATE TECTONICS AND PLUME INTERPLAY ». Geodynamics & ; Tectonophysics 10, no 1 (23 mars 2019) : 79–99. http://dx.doi.org/10.5800/gt-2019-10-1-0405.
Texte intégralRésumé :
The history of the Central Asian Orogenic Belt (CAOB) was marked by several major events of magmatism which produced large volumes of volcanic and intrusive (mafic-ultramafic and granitic) rocks within a relatively short time span (30–40 Ma) over a vast area. The magmatic activity postdated the orogenic stages of accretionary-collisional belts in Central Asia and likely resulted from the impact of mantle plumes that formed Large Igneous Provinces (LIPs). The formation of the Tarim–South Mongolia LIP at 300–270 Ma is the best known among the major Permian events of basaltic and granitic magmatism. Early Permian igneous rocks (volcanic, subvolcanic and intrusive suites that vary from ultramafic to felsic compositions) of the same age range (300 to 270 Ma) have been recently found also in Eastern Kazakhstan, within the late Paleozoic Altai collisional system. The compositions and ages of the rocks suggest that the Eastern Kazakhstan magmatism was the northward expansion of the Tarim LIP. The spread of the Tarim LIP was apparently facilitated by lithospheric extension after the Siberia-Kazakhstan collision. The extension led to rheological weakening of the lithosphere whereby deep mantle melts could penetrate to shallower depths. The early Permian history of Eastern Kazakhstan was controlled by the interplay of plate tectonic and plume processes: plate-tectonic accretion and collision formed the structural framework, and the Tarim mantle plume was a heat source maintaining voluminous magma generation.
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Wu, Lei, Xinwei Zhai, Erteng Wang, Wanfeng Chen, Gaorui Song, Feifei Zheng, Jiaolong Zhao, Jinrong Wang et Haidong Wang. « Early Permian Post-Collision Extensional Setting in the Southern Beishan Orogenic Belt : Evidence from the Zhangfangshan Granodiorite and the Baishantang Bimodal Volcanic Rocks ». Minerals 13, no 12 (22 novembre 2023) : 1468. http://dx.doi.org/10.3390/min13121468.
Texte intégralRésumé :
Outcrops of late Paleozoic magmatic rocks are common in the Southern Beishan Orogenic Belt (SBOB), Southern Central Asian Orogenic Belt (CAOB), which is a key object for the understanding of regional tectonism and defining the final closure time of the Paleo-Asian Ocean (PAO). We present zircon U-Pb chronology and whole-rock geochemistry data for late Paleozoic granodiorites and bimodal volcanic rocks from the Shuangyingshan-Huaniushan unit in the north Huitongshan-Zhangfangshan ophiolitic belt in the SBOB. The Zhangfangshan granodiorites (LA-ICP-MS, Ca. 288 Ma) are A2-type granite enriched in Rb, Th, Pb and LREEs and depleted in Nb, Ta, Ti, Sr, Ba and HREEs. They have varying MgO and TFe2O3 contents with high Mg# (38.56~48.97) values; the Lu/Yb ratios (0.14~0.15) of these granodiorites are similar to mantle-derived magma. A clear plagioclase zoning structure and acicular apatite occur in mineral assemblages derived from magma mixing between mafic and felsic magmas. The Baishantang bimodal volcanic rocks (272 Ma) consist of rhyolite and basaltic andesite. Baishantang rhyolites are A2-type felsic rock enriched in Rb, Th, Pb and LREEs and depleted in Nb, Ta, Ti, Sr, Ba and HREEs, with negative εNd(t) and εHf(t) (−5.2~−4.8 and −2.2~−1.9, respectively). Rhyolites originated from the partial melting of the crust, influenced by mantle material. Basaltic andesites belong to calc-alkaline series and have an enrichment of Rb, Ba, Th, U, Pb and LREEs, are weakly enriched in Zr-Hf, and are depleted in Nb, Ta, Ti and HREEs. The Nd-Hf isotopes of these basaltic andesites are not coupled with negative εNd(t) (−2.8~−0.4) and positive εHf(t) (1.8~5.5) values. These characteristics indicate that they originated from the partial melting of the mantle mixed with sediment-derived melts. In combination with previous studies, our findings show that the early Permian Zhangfangshan granodiorites and Baishantang bimodal volcanic rocks formed in a post-collision extensional setting, and the Huitongshan-Zhangfangshan ocean had been closed before early Permian.
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Wang, Jian, Keiko Hattori, Yanchen Yang et Haiqi Yuan. « Zircon Chemistry and Oxidation State of Magmas for the Duobaoshan-Tongshan Ore-Bearing Intrusions in the Northeastern Central Asian Orogenic Belt, NE China ». Minerals 11, no 5 (10 mai 2021) : 503. http://dx.doi.org/10.3390/min11050503.
Texte intégralRésumé :
The Duobaoshan (DBS)-Tongshan (TS) porphyry Cu–(Mo) deposit (4.4 Mt Cu, 0.15 Mt Mo) is located in the northeastern part of the central Asian orogenic belt (CAOB) in northeastern China. It is hosted by early Ordovician dioritic to granodioritic intrusions which are characterized by the subduction-related geochemical signatures including high concentrations of large ion lithophile elements (LILEs) and light rare earth elements (LREEs), and low concentrations of heavy REEs (HREEs) and high-field -strength elements (HFSEs), such as Nb, Ta, Zr and Ti in bulk rock compositions. Furthermore, they show adakitic geochemical signatures of high Sr/Y ratios (29~55) due to high Sr (290~750 ppm) and low Y (<18 ppm). Zircon trace element abundances and published Sr-Nd-Hf isotope data of these rocks suggest that the parental magmas for these ore-bearing intrusions were rich in H2O and formed by partial melting of a juvenile lower crust/lithospheric mantle or metasomatized mantle wedge during the northwestward subduction of the Paleo-Asian Ocean before the collision of the Songnen block with the Erguna-Xing’an amalgamated block in the early Carboniferous. Values of Ce4+/Ce3+ and Ce/Nd in zircons are 307~461 and 14.1~20.3 for mineralized granodiorites, and 231~350 and 12.4~18.2 for variably altered diorite and granodiorites in DBS, whereas those for DBS-TS microgabbros are 174~357 and 7.4~22, and 45.9~62.6 and 5.0~5.8 for the early Mosozoic Qz-monzonites, respectively. Zircon Eu/Eu* values are high and similar among mineralized granodiorites (~0.6), altered diorite and granodiorites (~0.6) and the Mesozoic Qz-monzonites (~0.8), whereas the values are low and variable for the DBS-TS microgabbros (0.3~0.6). The magma oxidation state calculated from zircon chemistry and whole rock compositions are FMQ +1.0 to +1.5 in mineralized samples, and FMQ +2.4 to +4.2 in altered samples. The values are comparable to those for the fertile intrusions hosting porphyry Cu-Mo-(Au) deposits in the central and western CAOB and elsewhere in the world. Elevated oxidation state is also observed in the TS microgabbros, FMQ +1.4 to +1.9, and the early Mesozoic Qz-monzonites, FMQ +2.4 to +2.5. Comparison of zircon geochemistry data from porphyry deposists elsewhere suggests that positive Ce anomalies are generally associated with fertile intrusions, but not all igneous rocks with high Ce anomalies are Cu fertile. The findings in this study are useful in exploration work and evaluating oxidation state of magmas for porphyry Cu-(Mo) deposits in the region and elsewhere.
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Wu, Datian, Zhumin Li, Junchao Lv, Jia Xu et Guanglong Shu. « Redetermination of the Zalantun Group in the ARong Qi Area of Da Hinggan Mountains (Northeastern China) : Evidence from Petrology, Geochronology and Geochemistry ». Minerals 12, no 2 (3 février 2022) : 197. http://dx.doi.org/10.3390/min12020197.
Texte intégralRésumé :
The Da Hinggan Mountains are an important area in the tectonic evolution of the Central Asian Orogenic Belt (CAOB), and there are disputes over the closure time of the Paleo-Asian Ocean and the amalgamation spatiotemporal relationship between the Ergun-Hinggan Massif and the Songnun Massif. The geochronology and geochemistry of the Late Cambrian-Late Silurian volcanic rock assemblages in the ARong Qi area at the eastern margin of the Da Hinggan Mountains are studied in this paper. The results suggest that the U-Pb zircon ages of the Late Cambrian, Late Ordovician and Late Silurian volcanic rock assemblages are 507.5 ± 1.0 Ma, 456.2 ± 1.0 Ma, 446.1 ± 0.95 Ma and 423.3 ± 1.4 Ma, respectively. The Late Cambrian-Late Silurian volcanic rocks are quasi-aluminous-peraluminous, belonging to calc-alkaline-shoshonite series, which is rich in HREE but has insignificant europium anomalies. There are abundant large ion lithophile elements (LILE) in the rock, and remarkable Nb, Ta and Ti negative anomalies. The previous data and the current study indicate that a continental margin arc tectonic setting existed in the ARong Qi-Zalantun region during the Early Paleozoic, which is inferred to be the product of the subduction-accretion-amalgamation of the plates along the eastern margin of the Ergun Massif during the Early Paleozoic.
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KANG, Lei, Wenhua JI, Tao WANG, Wenming LI et Jiming SUN. « Late Carboniferous‐Early Permian Mafic‐Ultramafic Complexes in Beishan, Southwestern Central Asian Orogenic Belt and Their Significance ». Acta Geologica Sinica - English Edition 93, S3 (mai 2019) : 113–15. http://dx.doi.org/10.1111/1755-6724.14261.
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Zhang, Yan-Long, Chuan-Zhou Liu, Wen-Chun Ge, Fu-Yuan Wu et Zhu-Yin Chu. « Ancient sub-continental lithospheric mantle (SCLM) beneath the eastern part of the Central Asian Orogenic Belt (CAOB) : Implications for crust–mantle decoupling ». Lithos 126, no 3-4 (octobre 2011) : 233–47. http://dx.doi.org/10.1016/j.lithos.2011.07.022.
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Cai, Keda, Min Sun, M. M. Buslov, Bor-ming Jahn, Wenjiao Xiao, Xiaoping Long, Huayong Chen et al. « Crustal nature and origin of the Russian Altai : Implications for the continental evolution and growth of the Central Asian Orogenic Belt (CAOB) ». Tectonophysics 674 (avril 2016) : 182–94. http://dx.doi.org/10.1016/j.tecto.2016.02.026.
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Sun, Yong-gang, Bi-le Li, Feng-yue Sun, Qing-feng Ding, Ye Qian, Liang Li, Qing-lin Xu et Yu-jin Li. « Geochronology, geochemistry, and Hf isotopic compositions of early Permian syenogranite and diabase from the northern Great Xing’an Range, northeastern China : petrogenesis and tectonic implications ». Canadian Journal of Earth Sciences 57, no 12 (décembre 2020) : 1478–91. http://dx.doi.org/10.1139/cjes-2019-0200.
Texte intégralRésumé :
Geodynamic evolution in the late Paleozoic is significant for understanding the final amalgamation of the Central Asian Orogenic Belt (CAOB). No consensus has yet been reached regarding the late Paleozoic geodynamic evolution of the northern Great Xing’an Range (GXR) in northeastern China, the eastern CAOB. Furthermore, late Paleozoic syenogranite–diabase dyke association is present in the Xiaokele area in northern GXR. It provides an important opportunity to understand the nature of magmatism and the geodynamic evolution during this period. This paper presents new zircon U–Pb ages, zircon Hf isotopic compositions, and geochemical data of whole rocks for Xiaokele syenogranite and diabase. Zircon U–Pb dating suggests that the Xiaokele syenogranite (292.5 ± 0.9 Ma) and diabase (298.3 ± 1.5 Ma) were emplaced during the early Permian. The Xiaokele syenogranites have high SiO2 contents, low MgO contents, and enriched zircon εHf(t) values, suggesting that their primary magma was generated by the partial melting of the juvenile crustal material. The Xiaokele diabases have low SiO2 contents, high MgO contents, are enriched in large-ion lithophile elements, depleted in high-field-strength elements, and exhibit enriched zircon εHf(t) values. They derived from a lithospheric mantle source that had previously been metasomatized by slab-derived fluids. Combined with previous research results, we believe that the continent–continent collision between the Xing’an and Songliao blocks occurred during the late early Carboniferous – early late Carboniferous (330–310 Ma), and the two blocks were transformed into a post-collisional extensional setting during the latest Carboniferous – early Permian.
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Han, Yigui, et Guochun Zhao. « Final amalgamation of the Tianshan and Junggar orogenic collage in the southwestern Central Asian Orogenic Belt : Constraints on the closure of the Paleo-Asian Ocean ». Earth-Science Reviews 186 (novembre 2018) : 129–52. http://dx.doi.org/10.1016/j.earscirev.2017.09.012.
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Liu, Bo, et Bao-Fu Han. « Identification of lateral inhomogeneity of arc basement by reconstructing the Late Devonian arc belt in the southwestern Central Asian Orogenic Belt ». Journal of Geodynamics 132 (décembre 2019) : 101668. http://dx.doi.org/10.1016/j.jog.2019.101668.
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Li, Yalong, Wei Yue, Xun Yu, Xiangtong Huang, Zongquan Yao, Jiaze Song, Xin Shan, Xinghe Yu et Shouye Yang. « Tectonic Evolution of the West Bogeda : Evidences from Zircon U-Pb Geochronology and Geochemistry Proxies, NW China ». Minerals 10, no 4 (10 avril 2020) : 341. http://dx.doi.org/10.3390/min10040341.
Texte intégralRésumé :
The Bogeda Shan (Mountain) is in southern part of the Central Asian Orogenic Belt (CAOB) and well preserved Paleozoic stratigraphy, making it an ideal region to study the tectonic evolution of the CAOB. However, there is a long-standing debate on the tectonic setting and onset uplift of the Bogeda Shan. In this study, we report detrital zircon U-Pb geochronology and whole-rock geochemistry of the Permian sandstone samples, to decipher the provenance and tectonic evolution of the West Bogeda Shan. The Lower-Middle Permian sandstone is characterized by a dominant zircon peak age at 300–400 Ma, similar to the Carboniferous samples, suggesting their provenance inheritance and from North Tian Shan (NTS) and Yili-Central Tian Shan (YCTS). While the zircon record of the Upper Permian sandstone is characterized by two major age peaks at ca. 335 Ma and ca. 455 Ma, indicating the change of provenance after the Middle Permian and indicating the uplift of Bogeda Shan. The initial uplift of Bogeda Shan was also demonstrated by structural deformations and unconformity occurring at the end of Middle Permian. The bulk elemental geochemistry of sedimentary rocks in the West Bogeda Shan suggests the Lower-Middle Permian is mostly greywacke with mafic source dominance, and tectonic setting changed from the continental rift in the Early Permian to post rift in the Middle Permian. The Upper Permian mainly consists of litharenite and sublitharenite with mafic-intermediate provenances formed in continental island arcs. The combined evidences suggest the initial uplift of the Bogeda Shan occurred in the Late Permian, and three stages of mountain building include the continental rift, post-rift extensional depression, and continental arc from the Early, Middle, to Late Permian, respectively.
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Nomuulin, Amarbayar, Noriyoshi Tsuchiya, Otgonbayar Dandar, Atsushi Okamoto, Masaoki Uno, Undarmaa Batsaikhan et Jiajie Wang. « Multi-stage serpentinization of ultramafic rocks in the Manlay Ophiolite, southern Mongolia ». Mongolian Geoscientist 26, no 53 (30 décembre 2021) : 1–17. http://dx.doi.org/10.5564/mgs.v26i53.1787.
Texte intégralRésumé :
Serpentinization of ultramafic rocks in ophiolites is key to understanding the global cycle of elements and changes in the physical properties of lithospheric mantle. Mongolia, a central part of the Central Asian Orogenic Belt (CAOB), contains numerous ophiolite complexes, but the metamorphism of ultramafic rocks in these ophiolites has been little studied. Here we present the results of our study of the serpentinization of an ultramafic body in the Manlay Ophiolite, southern Mongolia. The ultramafic rocks were completely serpentinized, and no relics of olivine or orthopyroxene were found. The composition of Cr-spinels [Mg# = Mg/(Mg + Fe2+) = 0.54 and Cr# = Cr/(Cr + Al) = 0.56] and the bulk rock chemistry (Mg/Si = 1.21–1.24 and Al/Si < 0.018) of the serpentinites indicate their origin from a fore-arc setting. Lizardite occurs in the cores and rims of mesh texture (Mg# = 0.97) and chrysotile is found in various occurrences, including in bastite (Mg# = 0.95), mesh cores (Mg# = 0.92), mesh rims (Mg# = 0.96), and later-stage large veins (Mg# = 0.94). The presence of lizardite and chrysotile and the absence of antigorite suggests low-temperature serpentinization (<300 °C). The lack of brucite in the serpentinites implies infiltration of the ultramafic rocks of the Manlay Ophiolite by Si-rich fluids. Based on microtextures and mineral chemistry, the serpentinization of the ultramafic rocks in the Manlay Ophiolite took place in three stages: (1) replacement of olivine by lizardite, (2) chrysotile formation (bastite) after orthopyroxene and as a replacement of relics of olivine, and (3) the development of veins of chrysotile that cut across all previous textures. The complex texture of the serpentinites in the Manlay Ophiolite indicates multiple stages of fluid infiltration into the ultramafic parts of these ophiolites in southern Mongolia and the CAOB.
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Long, Xiaoping, Jin Luo, Min Sun, Xuan-ce Wang, Yujing Wang, Chao Yuan et Yingde Jiang. « Detrital zircon U-Pb ages and whole-rock geochemistry of early Paleozoic metasedimentary rocks in the Mongolian Altai : Insights into the tectonic affinity of the whole Altai-Mongolian terrane ». GSA Bulletin 132, no 3-4 (8 juillet 2019) : 477–94. http://dx.doi.org/10.1130/b35257.1.
Texte intégralRésumé :
Abstract The tectonic affinity of the terranes and microcontinents within the Central Asian Orogenic Belt (CAOB) remains controversial. The Altai-Mongolian terrane (AMT), as a representative tectonic unit in the Mongolian collage, plays a vital role in reconstructing evolution history of the CAOB. The well-preserved early Paleozoic sedimentary sequence covering in this terrane could be considered as a fingerprint to track its provenance and tectonic affinity. Here, we present new whole-rock geochemistry, detrital zircon U-Pb dating, and Hf isotopic analysis for the metasedimentary rocks from the Mongolian Altai in order to shed new light on the tectonic affinity of the AMT. The youngest detrital zircon ages and the regional intrusions constrain the depositional time of the Mongolian Altai sequence to between Late Silurian and Early Devonian, which is consistent with the Habahe group in the western Chinese Altai. The features of whole-rock geochemistry and the cumulative distribution curves of the detrital zircon age spectra indicate that the Mongolian Altai sequence was probably deposited in an active continental setting during early Paleozoic. The zircon age spectra of our samples are all characterized by a main age group in the early Cambrian (peak at 541 Ma, 522 Ma, 506 Ma and 496 Ma, respectively), subdominant age populations during the Tonian, as well as rare older zircons. The nearby Lake Zone of Ikh-Mongol Arc most likely provided plenty of early Paleozoic materials, the subdominant Neoproterozoic detrital zircons could be supplied by the felsic intrusions along the western margin of the Tuva-Mongol microcontinent, and the sparse older zircons may be derived from its basement material. The Precambrian age distribution of the AMT is quite similar to both the Tarim and Siberia cratons, but the Siberia Craton displays a closer resemblance in Hf isotopic composition with the AMT. Thus, we believe that the Siberia Craton contains a closer tectonic affinity with the AMT, and that the Tuva-Mongol microcontinent possibly rifted from the western margin of this craton after the Tonian. To the south of the AMT, recent studies indicated the Yili and Central Tianshan blocks in the Kazakhstan collage of the western CAOB likely have a closer affinity with Gondwana. Therefore, the microcontinents in the CAOB most likely derived bilaterally from both the Siberia Craton and the Gondwana supercontinent. Moreover, our Hf isotopic compositions indicate two significant continental growth events in the Tonian and early Paleozoic, respectively.
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Zhang, Chuan-Lin, et Hai-Bo Zou. « Permian A-type granites in Tarim and western part of Central Asian Orogenic Belt (CAOB) : Genetically related to a common Permian mantle plume ? » Lithos 172-173 (juillet 2013) : 47–60. http://dx.doi.org/10.1016/j.lithos.2013.04.001.
Texte intégral
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LUO, QUN, CHEN ZHANG, SHU JIANG, LUOFU LIU, DONGDONG LIU, XIANGYE KONG, XIAOYU LIU et XINPENG WANG. « Partial melting of oceanic sediments in subduction zones and its contribution to the petrogenesis of peraluminous granites in the Chinese Altai ». Geological Magazine 156, no 4 (25 janvier 2018) : 585–604. http://dx.doi.org/10.1017/s0016756817001029.
Texte intégralRésumé :
AbstractLate Carboniferous magmatism in the Chinese Altai provides an important view of geodynamic processes active during crustal growth in the Central Asian Orogenic Belt (CAOB). In this study, five representative peraluminous granite plutons from the Chinese Altai were selected for systematic geochronological, geochemical and Sr–Nd–Hf isotopic analyses (Table 1). These granites were emplaced between 449 and 327 Ma in an active subduction zone, and have moderate to high SiO2 (66.54–76.13 wt%), moderate Na2O+K2O (6.27–7.66 wt%), and high Al2O3 contents (12.43–16.18 wt%). All granite samples in this study showed significant decoupling of the Nd and Hf isotope systems. Results show negative εNd(t) values (−3.3 to −0.9), and predominantly positive εHf(t) values (+0.24 to +8.01, n=57) except for a few negative εHf(t) values (−7.44 to −0.03, n=9), high Mg# values (28.69–53.33), high Nd/Hf ratios (4.26–43.57), and enrichment of large-ion lithophile elements (LILEs; e.g. Pb, Th, and U), suggesting that the granites were derived from the partial melting of oceanic sediments and the associated mantle wedge, with fractionation of plagioclase, K-feldspar and biotite. In situ zircon Hf isotopic analyses yield negative εHf(t) values from −30.6 to −13.7 for the zircon xenocrysts. The U–Pb ages and Hf isotopic ratios of these zircon xenocrysts were probably inherited from oceanic sediments. Zircon saturation temperatures suggest that these peraluminous granites were emplaced at 537–765°C. We propose that: (1) the Nd isotopic system more faithfully reflects the source of peraluminous magmas in the Chinese Altai than the Hf isotopic system, and (2) the oceanic sediment recycling was an important process during continental growth in the CAOB.
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Vladimirov, V. G., V. A. Yakovlev et I. V. Karmysheva. « MECHANISMS OF MAGMATIC MINGLING IN COMPOSITE DYKES : MODELS OF DISPERSION AND SHEAR DILATATION ». Geodynamics & ; Tectonophysics 10, no 2 (24 juin 2019) : 325–45. http://dx.doi.org/10.5800/gt-2019-10-2-0417.
Texte intégralRésumé :
This article is focused on the intrusion and formation of combined dykes. Two main groups of conventionally magmatic mingling are distinguished: (1) plutonic bodies, and (2) combined dykes. The first group is represented by small basite inclusions that are uniformly scattered in granitoid bodies, and includes elongated swarms and tails of small bodies. The second group includes composite dykes with the indicators of mechanical mingling of basic and acid melts. Despite the similarities in the structural and textural features and the indicators of mechanical mingling of melts, these two groups are characterized by clearly different proportions of the volumes of contrasting melts and differ in the duration of formation, place of melt mingling, and tectonic setting. None of the available models was able to explain the occurrence of magmatic mingling structures in individual dykes. In our study, the mingling mechanisms of contrasting melts are discussed using the data on the geological objects located in West Sangilen, an area of the Central Asian Orogenic Belt (CAOB). The general and specific parameters of combined dikes of the Saizyral and Tavyt‐ Dag sites are considered. The models of shear dilatation and dispersion are proposed for explaining the mechanisms of magmatic mingling in combined dykes.
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Zheng, Shuo, Yarong Zhou, Yanfei An, Xiangyu Cui et Pilong Shi. « Granitoid Mapping with Convolutional Neural Network from ASTER and Landsat 8 OLI Data : A Case Study in the Western Junggar Orogen ». Remote Sensing 17, no 3 (23 janvier 2025) : 384. https://doi.org/10.3390/rs17030384.
Texte intégralRésumé :
The Western Junggar Orogen (Xinjiang) is featured by widespread granite intrusions and substantial Au-Cu-Mo resources, making it an ideal site to study granitoids and their metallogenic link. Here, we first conducted geological surveys and analyses with ASD spectrometry, polarized light microscopy (PLM), and X-Ray diffraction (XRD) to determine the granitoid lithology. Then, we used spectral and remote sensing data statistics and rock textural features to select band combinations from ASTER and Landsat 8 OLI VNIR-SWIR data. Three band combinations, i.e., spectral absorption bands + T1, SWIR + T1, and VNIR-SWIR + T1, serve as the input layers for convolutional neural networks (AlexNet, VGG16, and GoogLeNet). They are used for remote sensing identification of granitoid lithology and the assessment of its accuracy. The results highlight the AlexNet model’s superior performance, as evidenced by the highest weighted F1 score (91.98%) and kappa coefficient (0.84) with ASTER VNIR-SWIR + T1 as the input layers. We suggest that the AlexNet model can best identify the granitoid subtypes (with ASTER images) in the Western Junggar. In contrast, Landsat 8 OLI images performed poorly, possibly because they have only two SWIR bands. We offer detailed spatial distribution characteristics of granite subtypes and provide remote sensing exploration methods for studying polymetallic ore belts in the Central Asian Orogenic Belt (CAOB).