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1.
In this paper we discuss the timing of final closure of the Paleo-Asian Ocean based on the field investigations of the Carboniferous–Permian stratigraphic sequences and sedimentary environments in southeastern Inner Mongolia combined with the geology of its neighboring areas. Studies show that during the Carboniferous–Permian in the eastern segment of the Tianshan-Hinggan Orogenic System, there was a giant ENE–NE-trending littoral-neritic to continental sedimentary basin, starting in the west from Ejinqi eastwards through southeastern Inner Mongolia into Jilin and Heilongjiang. The distribution of the Lower Carboniferous in the vast area is sparse. The Late Carboniferous or Permian volcanic-sedimentary rocks always unconformably overlie the Devonian or older units. The Upper Carboniferous–Middle Permian is dominated by littoral-neritic deposits and the Upper Permian, by continental deposits. The Late Carboniferous–Permian has no trace of subduction-collision orogeny, implying the basin gradually disappeared by shrinking and shallowing. In addition, it is of interest to note that the Ondor Sum and Hegenshan ophiolitic mélanges were formed in the pre-Late Silurian and pre-Late Devonian respectively, and the Solonker ophiolitic mélange formed in the pre-Late Carboniferous. All the evidence indicates that the eastern segment of the Paleo-Asian Ocean had closed before the Late Carboniferous, and most likely before the latest Devonian (Famennian). 相似文献
2.
GONG Xuejing YANG Zhusen MENG Xiangjin PAN Xiaofei WANG Qian ZHANG Lejun 《《地质学报》英文版》2017,91(3):898-946
A mosaic of terranes or blocks and associated Late Paleozoic to Mesozoic sutures are characteristics of the north Sanjiang orogenic belt (NSOB). A detailed field study and sampling across the three magmatic belts in north Sanjiang orogenic belt, which are the Jomda–Weixi magmatic belt, the Yidun magmatic belt and the Northeast Lhasa magmatic belt, yield abundant data that demonstrate multiphase magmatism took place during the late Paleozoic to early Mesozoic. 9 new zircon LA–ICP–MS U–Pb ages and 160 published geochronological data have identified five continuous episodes of magma activities in the NSOB from the Late Paleozoic to Mesozoic: the Late Permian to Early Triassic (c. 261–230 Ma); the Middle to Late Triassic (c. 229–210 Ma); the Early to Middle Jurassic (c. 206–165 Ma); the Early Cretaceous (c. 138–110 Ma) and the Late Cretaceous (c. 103–75 Ma). 105 new and 830 published geochemical data reveal that the intrusive rocks in different episodes have distinct geochemical compositions. The Late Permian to Early Triassic intrusive rocks are all distributed in the Jomda–Weixi magmatic belt, showing arc–like characteristics; the Middle to Late Triassic intrusive rocks widely distributed in both Jomda–Weixi and Yidun magmatic belts, also demonstrating volcanic–arc granite features; the Early to Middle Jurassic intrusive rocks are mostly exposed in the easternmost Yidun magmatic belt and scattered in the westernmost Yangtza Block along the Garzê–Litang suture, showing the properties of syn–collisional granite; nearly all the Early Cretaceous intrusive rocks distributed in the NE Lhasa magmatic belt along Bangong suture, exhibiting both arc–like and syn–collision–like characteristics; and the Late Cretaceous intrusive rocks mainly exposed in the westernmost Yidun magmatic belt, with A–type granite features. These suggest that the co–collision related magmatism in Indosinian period developed in the central and eastern parts of NSOB while the Yanshan period co–collision related magmatism mainly occurred in the west area. In detail, the earliest magmatism developed in late Permian to Triassic and formed the Jomda–Wei magmatic belt, then magmatic activity migrated eastwards and westwards, forming the Yidun magmatic bellt, the magmatism weakend at the end of late Triassic, until the explosure of the magmatic activity occurred in early Cretaceous in the west NSOB, forming the NE Lhasa magmatic belt. Then the magmatism migrated eastwards and made an impact on the within–plate magmatism in Yidun magmatic belt in late Cretaceous. 相似文献
3.
This paper presents age and geochemical data of a recently identified Late Paleozoic volcanic sequence in central Jilin Province, with aims to discuss the petrogenesis and to constrain the tectonic evolution of the Central Asian Orogenic Belt in this area. Firstly, the volcanic rocks have zircon U-Pb ages of 290–270 Ma. Secondly, they are characterized by(a) ranging in composition from the low-K tholeiite series to high-K calc-alkaline series;(b) enrichment in light rare earth elements and depletion of heavy rare earth elements, with negative Eu anomalies; and(c) negative Nb, Ta, and Ti anomalies. Finally, the volcanic rocks yield εHf(t) values of +7.1 to +17. These data suggest that the central Jilin volcanic rocks were possibly derived from predominant partial melting of a depleted lithospheric mantle that might have been modified by subducted slab–derived fluids. Combined with previous studies, the Late Paleozoic–Early Mesozoic magmatism in Central Jilin can be divided into two stages:(a) a volcanic arc stage(290–270 Ma) represented by low-K to high–K, tholeiite to calc–alkaline plutons and(b) a syn–collisional stage(260–240 Ma) represented by high-K calc–alkaline I-type granites. Furthermore, the timing and the tectonic setting of the above magmatic rocks show that the arc was probably produced by the northward subduction of the Paleo-Asian Ocean and that the final closure of the Paleo-Asian Ocean occurred prior to the Early Triassic. 相似文献
4.
In this paper we present new zircon U–Pb ages, whole-rock major and trace element analyses, and zircon Hf isotopic data for magmatic rocks in the Tuotuohe region of the western segment of the Jinshajiang suture. Our aim is to constrain the Early Permian–Late Triassic tectonic evolution of the region. Zircons from the magmatic rocks of the Tuotuohe region are euhedral–subhedral in shape and display fine-scale oscillatory zoning as well as high Th/U ratios(0.4–4.6), indicating a magmatic origin. The zircon U–Pb ages obtained using LA–ICP–MS are 281 ± 1 Ma, 258 ± 1 Ma, 244 ± 1 Ma, and 216 ± 1 Ma, which indicate magmatism in the Early Permian–Late Triassic. A diorite from Bashihubei(BSHN) has SiO2 = 57.18–59.97 wt%, Al2O3 = 15.70–16.53 wt%, and total alkalis(Na2O + K2O) = 4.46–6.34 wt%, typical of calc-alkaline and metaluminous series. A gabbro from Bashibadaoban(BSBDB) belongs to the alkaline series, and is poor in SiO2(45.46–54.03 wt%) but rich in Al2O3(16.19–17.39 wt%) and total alkalis(Na2O + K2O = 5.48–6.26 wt%). The BSHN diorite and the BSBDB gabbro both display an enrichment of LREEs and LILEs and depletion of HFSEs, and they have no obvious Eu anomaly; they have relatively low MgO contents(2.54–4.93 wt%), Mg# values of 43 to 52, and low Cr and Ni contents(8.07–33.6 ppm and 4.41–14.2 ppm, respectively), indicating they differentiated from primitive mantle magmas. They have low Nb/U, Ta/U, and Ce/Pb ratios(1.3–9.6, 0.2–0.8, and 0.1–18.1, respectively), and their initial Hf isotopic ratios range from +9.6 to +16.9(BSHN diorite) and +6.5 to +12.6(BSBDB gabbro), suggesting their primary magmas were derived mainly from the partial melting of a mantle wedge that had been metasomatized by subduction fluids. Taking all the new data together, we conclude that the western and eastern segment of the Jinshajiang suture regions underwent identical processes of evolution in the Early Permian–Late Triassic: oceanic crust subduction before the Early Permian, continental collision during the Early–Middle Triassic, and post-collisional extension from the Late Triassic. 相似文献
5.
During the Late Carboniferous to Early Permian, a rift was formed by post-collisional extension after ocean closure or an island arc-related basin formed by Paleo-Asian Ocean (PAO) subduction in the Xi Ujimqin area. Nevertheless, the closure time of the PAO is still under debate. Thus, to identify the origin of the PAO, the geochemistry and U-Pb age of zircons were analyzed for the extra-large deep marine, polymict clastic boulders and sandstones in the Shoushangou Formation within the basin. The analyses revealed magmatic activity and tectonic evolution. The conglomerates include megaclasts of granite (298.8 ± 9.1?Ma) and granodiorite porphyry (297.1 ± 3.1?Ma), which were deposited by muddy debris flow. Results of this study demonstrated that the boulders of granitoids have the geochemistry of typical I-type granite, characterized by low Zr + Nb + Ce + Y and low Ga/Al values. The granitoid boulders were formed in island arc setting, indicating the presence of arc magmatism in the area that is composed of the Late Carboniferous to Early Permian subduction-related granitoid in southern Xi Ujimqin. Multiple diagrams for determining sedimentary provenance using major and trace elements indicate that Shoushangou sediments originated from continental island arc-related felsic rocks. Detrital zircon U-Pb age cluster of 330–280?Ma was obtained, indicating input from granite, ophiolite, Xilin Gol complex, and Carboniferous sources to the south. The basin was geographically developed behind the arc during the Early Permian period because the outcropped intrusive rocks in the Late Carboniferous to Early Permian form a volcanic arc. The comprehensive analyses of source areas suggest that Shoushangou sediments developed in a backarc basin in response to the northward subduction of the PAO. The backarc basin and intrusive rocks, in addition to previously published Late Carboniferous to Early Permian magmatic rocks of arc unit in Xilin Gol, confirm the presence of an Early Permian trench-arc-basin system in the region, represented by the Baolidao arc and Xi Ujimqin backarc basin. This study highlights the importance and potential of combined geochemical and geochronological studies of conglomerates and sandstone for reconstructing the geodynamic setting of a basin. 相似文献
6.
To the south of Manzhouli, Hulunbuir, Inner Mongolia, experienced a tectonic regime transformation from compression to extension in the mid-Mesozoic. Based on systematic research of the volcanics, petrology, volcanic facies, chronology and geochemistry of rocks in the Buridun area, two stages of volcanics are identified. The first stage named the trachyte series was formed in the late Middle Jurassic (167–163 Ma), its eruption rhythm is pyroxene trachyandesite–trachyandesite–trachyte, and its origin rock is basic volcanics from thickened lower crust, with a tectonic setting in the collision orogeny after the closure of the Mongolia Okhotsk Ocean (MOO). The second stage is a bimodal volcanic rock, formed in the early Late Jurassic (163–160 Ma). The eruption rhythm of basic volcanics in this stage is basaltic andesite–basalt–olivine basalt, which comes from the metasomatized lithospheric mantle, the acidic volcanics of which being characterized by the eruption rhythm of sedimentary-explosive-overflow facies, which came from the partial melting of newly formed lower crust, and this shows the characteristics of A-type granite; the tectonic setting is extension of the lithosphere after collision and closure of the MOO. The changes in the formation age and tectonic setting of the two stages of volcanics demonstrate that the transition time from the compressive system to the extensional system south of Manzhouli is about 163 Ma. 相似文献
7.
The western Kunlun orogen in the northwest Tibet Plateau is related to subduction and collision of Proto-and Paleo-Tethys from early Paleozoic to early Mesozoic. This paper presents new LA-ICPMS zircon U-Pb ages and Lu-Hf isotopes, whole-rock major and trace elements, and Sr–Nd isotopes of two Ordovician granitoid plutons(466–455 Ma) and their Silurian mafic dikes(～436 Ma) in the western Kunlun orogen. These granitoids show peraluminous high-K calcalkaline characteristics, with(87Sr/86Sr)_i value of 0.7129–0.7224, εNd(t) values of -9.3 to -7.0 and zircon εHf(t) values of -17.3 to -0.2, indicating that they were formed by partial melting of ancient lower-crust(metaigneous rocks mixed with metasedimentary rocks) with some mantle materials in response to subduction of the Proto-Tethyan Ocean and following collision. The Silurian mafic dikes were considered to have been derived from a low degree of partial melting of primary mafic magma. These mafic dikes show initial 87Sr/86Sr ratios of 0.7101–0.7152 and εNd(t) values of -3.8 to -3.4 and zircon εHf(t) values of -8.8 to -4.9, indicating that they were derived from enriched mantle in response to post-collisional slab break-off. Combined with regional geology, our new data provide valuable insight into late evolution of the Proto-Tethys. 相似文献
8.
Ages,Sources and Tectonic Settings of the Triassic Igneous Rocks in the Easternmost Segment of the East Kunlun Orogen,Central China 总被引：5，自引：0，他引：5
REN Haidong WANG Tao ZHANG Lei WANG Xiaoxi HUANG He FENG Chengyou TESCHNER Claudia SONG Peng 《《地质学报》英文版》2016,90(2):641-668
U–Pb analysis of zircons from igneous rocks in the Elashan Mountain, easternmost segment of the East Kunlun Orogen yielded 252–232 Ma. Geochemically, these rocks are mainly high in SiO_2, K_2O and K_2O+Na_2O contents, low in P_2O_5 and TiO_2 contents, depleted in Ba, Sr, P, Ti and enriched in U, Hf, Zr, showing features of I–type granite. The zircon εHf(t) values of the Early Triassic Jiamuge'er rhyolite porphyry(252±3 Ma) are positive(+1.6 to +12.1), suggesting a juvenile crustal source mixing with little old crustal component, and the zircon εHf(t) values of the Middle Triassic Manzhang'gang granodiorite(244±3 Ma) and Dehailong diorite(237±3 Ma) are predominately negative(-8.4 to +1.0), indicating an older crustal source. In comparison, the zircon εHf(t) values of the Late Triassic syenogranites from Suigen'ergang(234±2Ma), Ge'ermugang(233±2 Ma) and Yue'ergen(232±3 Ma) plutons vary from-3.8 to +5.0, suggesting a crust-mantle mixing source. From Early–Middle Triassic(252–237 Ma) to Late Triassic(234–232 Ma), the geochemical characteristics of these rocks show the change from a subduction–collision setting to a post-collision or within-plate setting. By comparing of these new age data with 77 zircon U–Pb ages of igneous rocks of the eastern part of East Kunlun orogen from published literatures, we conclude that the igneous rocks of Elashan Mountain and these of the eastern part of East Kunlun Orogen belong to one magmatic belt. All these data indicate that the Triassic magmatic events of the eastern part of East Kunlun Orogen can be divided into three stages: 252–238 Ma, 238–226 Ma and 226–212 Ma. Statistically, the average εHf(t) values of the threestage igneous rocks show a tendency, from the old to young, from-0.75±0.25 to lower-2.65±0.52 and then to-1.22±0.25, respectively, which reveal the change of their sources. These characteristics can be explained as a crust-mantle mixing source generated in a subductional stage, mainly crust source in a syn–collisional stage and a crust-mantle mixing source(lower crust with mantle-derived underplating magma) in a post-collisional stage. The identification of these three magmatic events in the Elashan Mountain, including all the eastern part of East Kunlun Orogen, provides new evidence for better understanding of the tectonic evolution of the northward subduction and closure of the Paleo-Tethyan(252–238 Ma), the collision of the Songpan–Ganzi block with the southern margin of Qaidam block(238–226 Ma), and the post–collisional setting(226–212 Ma) during the Early Mesozoic period. 相似文献
9.
LI Zuochen PEI Xianzhi LI Ruibao PEI Lei LIU Chengjun CHEN Youxin XU Tong YANG Jie WEI Bo 《地质学报》2015,89(4):1213-1225
Investigation of the petrogenesis and the origin of zircons from the volcanic rocks of the Liujiaping Group of the back-Longmenshan tectonic belt in the northwest margin of the Yangtze Block is conducted by analysis of U–Pb geochronology and geochemistry. Results show that selected zircons are characterized by internal oscillatory zonings and high Th/U ratios (0.43–1.18), indicating an igneous origin. Geochronological results of LA–ICP–MS U–Pb dating of the Liujiaping Group zircons yield an age of 809 ± 11 Ma (MSWD = 2.2), implying that the volcanic rocks were formed in the Late Neoproterozoic. Geochemical analysis shows that the rocks are calc-alkaline, supersaturated in Al, and metaluminous to weakly peraluminous. Rare-earth elements are present at high concentrations (96.04–265.48 ppm) and show a rightward incline and a moderately negative Eu anomaly, similar to that of continental rift rhyolite. Trace element geochemistry is characterized by evident negative anomalies of Nb, Ta, P, Th, Ti, inter alia, and strong negative anomalies of K, Rb, Sr, et al. We conclude that the Liujiaping Group volcanic rocks resulted from typical continental crust source petrogenesis and were formed in a continental margin setting, which had no relation to subduction, and thus, were the products of partial melting of the lower crust due to crustal thickening caused by active continental margin subduction and arc–continent collision orogeny in the northwestern Yangtze Block and were triggered by the breakup of the Rodinia supercontinent during the Neoproterozoic. 相似文献
10.
The meta-basic volcanic rocks in the Tengtiaohe Zone yield zircon U–Pb ages of 258.8±2.5 Ma and 259.2±1.8 Ma, respectively which agree with the ages of flood basalts of ELIP and are similar to the basaltic rocks and komatiites from the Song Da Zone in northern Vietnam. The results suggest that the age of meta-basic volcanic rocks is Late Permian, rather than the Early Permian or Early Carboniferous ages as previously inferred. Most meta-basic volcanic rocks are strongly enriched in LREEs relative to HREEs and display trace element patterns similar to the ELIP high-Ti basalts, and are enriched in LILEs with negative Sr anomalies. Their initial ~(87)Sr/~(86) Sr ratios range from 0.705974 to 0.706188 and εNd(t) from-0.82 to-2.11. Their magmas were derived from an enriched and deep mantle source without significant crustal contamination. These meta-basic volcanic rocks formed in ELIP. Therefore, the Tengtiaohe Zone is not an ophiolite zone and can link to the Song Da Zone in northern Vietnam. 相似文献
11.
CHEN Hongjie WANG Nan WU Cailai LEI Min ZHENG Kun ZHANG Xin GAO Dong 《《地质学报》英文版》2018,92(4):1366-1383
The South Altyn continental block is an important geological unit of the Altyn Tagh orogenic belt, in which numerous Neoproterozoic granitoids crop out. Granitoids are mainly located in the Paxialayidang–Yaganbuyang area and can provide indispensable information on the dynamics of Rodinia supercontinent aggregation during the Neoproterozoic. Therefore, the study of granitoids can help us understand the formation and evolutionary history of the Altyn Tagh orogenic belt. In this work, we investigated the Yaganbuyang granitic pluton through petrography, geochemistry, zircon U–Pb chronology, and Hf isotope approaches. We obtained the following conclusions:(1) Yaganbuyang granitoids mainly consist of two-mica granite and granodiorite. Geochemical data suggested that these granitoids are peraluminous calc–alkaline or high-K calc–alkaline granite types. Zircon U–Pb data yielded ages of 939±7.1 Ma for granodiorite and ~954 Ma for granitoids, respectively.(2) The εHf(t) values of two–mica granite and granodiorite are in the range of-3.93 to +5.30 and-8.64 to +5.19, respectively. The Hf model ages(TDM2) of two-mica granite and granodiorite range from 1.59–.05 Ga and 1.62–2.35 Ga, respectively, indicating that the parental magma of these materials is derived from ancient crust with a portion of juvenile crust.(3) Granitoids formed in a collisional orogen setting, which may be a response to Rodinia supercontinent convergence during the Neoproterozoic. 相似文献
12.
13.
The paper reviews geological, geochronological and geochemical data from the Late Paleozoic – Mesozoic magmatic complexes of the Siberian continent north of the Mongol-Okhotsk suture. These data imply that these complexes are related to the subduction of the Mongol-Okhotsk Ocean under the Siberian continent. We suggest that this subduction started in the Devonian, prior to the peak of magmatic activity. Studied magmatic complexes are of variable compositions possibly controlled by changes of the subduction regime and by possible input from enriched mantle sources (hot spots).The oceanic lithosphere of the Mongol-Okhotsk Ocean had shallowly subducted under the Siberian continent in the Devonian. Steeper subduction in the Early – Late Carboniferous led to switching from an extensional to compressional tectonic regime resulting in fold-thrust deformation, to the development of duplex structures and finally to the thickening of the continental crust. This stage was marked by emplacement of voluminous autochthonous biotite granites of the Angara-Vitim batholith into the thickened crust. The igneous activity in the Late Carboniferous – Early Permian was controlled by the destruction of the subducted slab. The allochthonous granitoids of the Angara-Vitim batholith, and the alkaline granitoids and volcanics of the Western Transbaikalian belt were formed at this stage. All these complexes are indicative of extension of the thickened continental crust. A normal-angle subduction in the Late Permian – Late Triassic caused emplacement of various types of intrusions and volcanism. The calc-alkaline granitoids of the Late Permian – Middle Triassic Khangay batholith and Late Triassic Khentey batholith were intruded near the Mongol-Okhotsk suture, whereas alkaline granitoids and bimodal lavas were formed in the hinterland above the broken slab. The Jurassic is characterized by a significant decrease of magmatic activity, probably related to the end of Mongol-Okhotsk subduction beneath the studied area.The spatial relationship of the Late Permian – Middle Triassic granitoids, and the Late Triassic granitoids is typical for an active continental margin developing above a subduction zone. All the Late Carboniferous to Late Jurassic mafic rocks are geochemically similar to subduction-related basalts. They are depleted in Nb, Ta, Ti and enriched in Sr, Ba, Pb. However, the basaltoids located farther from the Mongol-Okhotsk suture are geochemically similar to a transition type between island-arc basalts and within-plate basalts. Such chemical characteristics might be caused by input of hot spot related enriched mantle to the lithospheric mantle modified by subduction. The Early Permian and Late Triassic alkaline granitoids of southern Siberia are of the A2-type geochemical affinities, which is also typical of active continental margins. Only the basaltoids generated at the end of Early Cretaceous are geochemically similar to typical within-plate basalts, reflecting the final closure of the Mongol-Okhotsk Ocean. 相似文献
14.
Huining Wang Fulai Liu Jing Li Zaibo Sun Lei Ji Zhonghua Tian Lishuang Liu M. Santosh 《Journal of Metamorphic Geology》2019,37(4):439-478
The Changning–Menglian orogenic belt (CMOB) in the southeastern Tibetan Plateau, is considered as the main suture zone marking the closure of the Palaeo‐Tethys Ocean between the Indochina and Sibumasu blocks. Here, we investigate the recently discovered retrograded eclogites from this suture zone in terms of their petrological, geochemical and geochronological features, with the aim of constraining the metamorphic evolution and protolith signature. Two types of metabasites are identified: retrograded eclogites and mafic schists. The igneous precursors of the retrograded eclogites exhibit rare earth element distribution patterns and trace element abundance similar to those of ocean island basalts, and are inferred to have been derived from a basaltic seamount in an intra‐oceanic tectonic setting. In contrast, the mafic schists show geochemical affinity to arc‐related volcanics with the enrichment of Rb, Th and U, and depletion of Nb, Ta, Zr, Hf and Ti, and their protoliths possibly formed at an active continental margin tectonic setting. Retrograded eclogites are characterized by peak metamorphic mineral assemblages of garnet, omphacite, white mica, lawsonite and rutile, and underwent five‐stage metamorphic evolution, including pre‐peak prograde stage (M1) at 18–19 kbar and 400–420°C, peak lawsonite‐eclogite facies (M2) at 24–26 kbar and 520–530°C, post‐peak epidote–eclogite facies decompression stage (M3) at 13–18 kbar and 530–560°C, subsequent amphibolite facies retrogressive stage (M4) at 8–10 kbar and 530–600°C, and late greenschist facies cooling stage (M5) at 5–8 kbar and 480–490°C. Laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) U–Pb spot analyses of zircon show two distinct age groups. The magmatic zircon from both the retrograded eclogite and mafic schist yielded protolith ages of 451 ± 3 Ma, which is consistent with the ages of Early Palaeozoic ophiolitic complexes and ocean island sequences in the CMOB reported in previous studies. In contrast, metamorphic zircon from the retrograded eclogite samples yielded consistent Triassic metamorphic ages of 246 ± 2 and 245 ± 2 Ma, which can be interpreted as the timing of closure of the Palaeo‐Tethys Ocean. The compatible peak metamorphic mineral assemblages, P–T–t paths and metamorphic ages, as well as the similar protolith signatures for the eclogites in the CMOB and Longmu Co–Shuanghu suture (LCSS) suggest that the two belts formed part of a cold oceanic subduction system in the Triassic. The main suture zone of the Palaeo‐Tethyan domain extends at least 1,500 km in length from the CMOB to the LCSS in the Tibetan Plateau. The identification of lawsonite‐bearing retrograded eclogites in the CMOB provides important insights into the tectonic framework and complex geological evolution of the Palaeo‐Tethys. 相似文献
15.
The Xiaohongshilazi deposit located in central Jilin Province, Northeast China, is a newly discovered and medium‐scale Pb–Zn–(Ag) deposit with ore reserves of 34,968 t Pb, 100,150 t Zn, and 158 t Ag. Two‐stage mineralization has been identified in this deposit. Stratiform volcanic‐associated massive sulfide (VMS) Pb–Zn mineralization interbedding with the marine volcanic rocks of the Late Carboniferous–Early Permian Daheshen Formation was controlled by the premineralization E–W‐trending faults. Vein‐type Pb–Zn–(Ag) mineralization occurs within or parallel to the granodiorite and diorite porphyries controlled by the major‐mineralization N–S‐trending faults that cut the stratiform mineralization and volcanic rocks. To constrain the age of vein‐type Pb–Zn–(Ag) mineralization and determine the relationship between mineralization and magmatism, we conducted LA–ICP–MS U–Pb dating on zircon from the ore‐bearing granodiorite and diorite porphyries and Rb–Sr dating on metal sulfide. Granodiorite and diorite porphyries yield zircon U–Pb weighted‐mean 206Pb/238U ages of 203.6 ± 1.8 Ma (Mean Standard Weighted Deviation [MSWD] = 1.8) and 225.6 ± 5.1 Ma (MSWD = 2.3), respectively. Sulfides from four vein‐type ore samples yield a Rb–Sr isochron age of 195 ± 17 Ma (MSWD = 4.0). These results indicate a temporal relationship between the granodiorite porphyry and vein‐type Pb–Zn–(Ag) mineralization. The granodiorite associated with vein‐type mineralization has high SiO2 (68.99–70.49 wt.%) and Na2O (3.9–4.2 wt.%; Na2O/K2O = 1.07–1.10) concentrations, and A/CNK values of 0.95–1.04; consequently, the intrusion is classified as a high‐K, calc‐alkaline, metaluminous I‐type granite. The granodiorite porphyry is enriched in large‐ion lithophile elements (e.g. Rb, Th, U, and K) and light REE and is depleted in high‐field‐strength elements (e.g. Nb, Ta, P, and Ti) and heavy REE, indicating that it represents a subduction‐related rock that formed at an active continental margin. Furthermore, the granodiorite porphyry has Mg# values of 31–34, indicating a lower crustal source. Based on petrological and geochemical features, we infer that the ore‐bearing granodiorite porphyry was derived from the partial melting of the lower crust. In summary, mineralization characteristics, cross‐cutting relationships, geochronological data, and regional tectonic evolution indicate that the region was the site of VMS Pb–Zn mineralization that produced stratiform orebodies within the Late Carboniferous–Early Permian marine volcanic rocks of the Daheshen Formation, followed by mesothermal magmatic hydrothermal vein‐type Pb–Zn–(Ag) mineralization associated with granodiorite porphyry induced by the initial subduction of the Paleo‐Pacific Plate beneath the Eurasia Plate during the Late Triassic–Early Jurassic. 相似文献
16.
SONG Peng WANG Tao TONG Ying ZHANG Jianjun HUANG He ZHANG Lei QIN Qie SHEN Huan 《《地质学报》英文版》2019,93(5):1169-1187
Carboniferous magmatism is one of the most important tectonothermal events in the Central Asian Orogenic Belt(CAOB). However, the final closure time of the Kalamaili Ocean between East Junggar and Harlik Mountain is still debated. Early Carboniferous(332 Ma) and late Carboniferous(307–298 Ma) granitic magmatism from Kalamaili fault zone have been recognized by LA-ICP-MS zircon U-Pb dating. They are both metaluminous highly fractionated I-type and belong to the high-K calc-alkaline. The granitoids for early Carboniferous have zircon ε_(Hf)(t) values of-5.1 to +8.5 with Hf model ages(T_(DM2)) of 1.78–0.83 Ga, suggesting a mixed magma source of juvenile material with old continental crust. Furthermore, those for late Carboniferous have much younger heterogeneous zircon ε_(Hf)(t) values(+5.1 to +13.6) with Hf model ages(T_(DM2)=1.03–0.45 Ga) that are also indicative of juvenile components with a small involvement of old continental crust. Based on whole-rock geochemical and zircon isotopic features, these high-K granitoids were derived from melting of heterogeneous crustal sources or through mixing of old continental crust with juvenile components and minor AFC(assimilation and fractional crystallization). The juvenile components probably originated from underplated basaltic magmas in response to asthenospheric upwelling. These Carboniferous highly fractionated granites in the Kalamaili fault zone were probably emplaced in a post-collisional extensional setting and suggested vertical continental crustal growth in the southern CAOB, which is the same or like most granitoids in CAOB. This study provides new evidence for determining the post-accretionary evolution of the southern CAOB. In combination with data from other granitoids in these two terranes, the Early Carboniferous Heiguniangshan pluton represents the initial record of post-collisional environment, suggesting that the final collision between the East Junggar and Harlik Mountain might have occurred before 332 Ma. 相似文献
17.
Late Triassic Granites From the Quxu Batholith Shedding a New Light on the Evolution of the Gangdese Belt in Southern Tibet 总被引：2，自引：0，他引：2
The Gangdese magmatic belt formed during Late Triassic to Neogene in the southernmost Lhasa terrane of the Tibetan plateau. It is interpreted as a major component of a continental margin related to the northward subduction of the Neo-Tethys oceanic slab beneath Eurasia and it is the key in understanding the tectonic framework of southern Tibet prior to the India-Eurasia collision. It is widely accepted that northward subduction of the Neo-Tethys oceanic crust formed the Gangdese magmatic belt, but the occurrence of Late Triassic magmatism and the detailed tectonic evolution of southern Tibet are still debated. This work presents new zircon U-Pb-Hf isotope data and whole-rock geochemical compositions of a mylonitic granite pluton in the central Gangdese belt, southern Tibet. Zircon U-Pb dating from two representative samples yields consistent ages of 225.3±1.8 Ma and 229.9±1.5 Ma, respectively, indicating that the granite pluton was formed during the early phase of Late Triassic instead of Early Eocene(47–52 Ma) as previously suggested. Geochemically, the mylonitic granite pluton has a sub-alkaline composition and low-medium K calc-alkaline affinities and it can be defined as an I-type granite with metaluminous features(A/CNK1.1). The analyzed samples are characterized by strong enrichments of LREE and pronounced depletions of Nb, Ta and Ti, suggesting that the granite was generated in an island-arc setting. However, the use of tectonic discrimination diagrams indicates a continental arc setting. Zircon Lu-Hf isotopes indicate that the granite has highly positive εHf(t) values ranging from +13.91 to +15.54(mean value +14.79), reflecting the input of depleted mantle material during its magmatic evolution, consistent with Mg~# numbers. Additionally, the studied samples also reveal relatively young Hf two-stage model ages ranging from 238 Ma to 342 Ma(mean value 292 Ma), suggesting that the pluton was derived from partial melting of juvenile crust. Geochemical discrimination diagrams also suggest that the granite was derived from partial melting of the mafic lower crust. Taking into account both the spatial and temporal distribution of the mylonitic granite, its geochemical fingerprints as well as previous studies, we propose that the northward subduction of the Neo-Tethys oceanic slab beneath the Lhasa terrane had already commenced in Late Triassic(~230 Ma), and that the Late Triassic magmatic events were formed in an active continental margin that subsequently evolved into the numerous subterranes, paleo-island-arcs and multiple collision phases that form the present southern Tibet. 相似文献
18.
The Late Triassic igneous rocks in the Yidun terrane can provide vital insights into the evolution of Plaeo-Tethys in western China. We present new zircon U-Pb, whole-rock geochemistry, and Sr-Nd-Pb-Hf isotopic data for the Litang biotite monzogranites, Yidun terrane. The biotite monzogranites have a zircon U-Pb age of 206.1±1.0 Ma(MSWD=1.9,n=30), which indicates Late Triassic magmatism. The biotite monzogranites display I-type affinity, high Na_2O(3.38-3.60 wt%) contente,medii SiO_2(67.12-69.13 wt%), and low P_2 O_5 contents(0.10～0.12 wt%). They enriched in Rb,and Ba and depleted in Nb and Ta, with negative Eu anomalies(Eu/Eu*=0.74—0.81). They have evolved Sr-Nd-Pb-Hf isotopic composition, i.e.,(~(87) Sr/~(86 )Sr)i=0.714225 to 0.714763, negative ?_(Nd(t)) values of -2.0 to-2.6 with two-stage Nd model ages ranging from 1.01 to 1.05 Ga, negative ?_(Ht)(t)) values o f-3.4 to-4.1 with two-stage Hf model ages of 1.85 to1.88 Ga, suggesting a matured crustal sources. Their low Al_2O_3/TiO_2 ratios and medium Cao/Na_2O ratios, medium Mg~# and SiO_2 contents, low [molar Al_2O_3/(MgO+FeO~T)] values, and high [molar Cao/(MgO+FeO~T)] values indicate that the Litang biotite monzogranite was formed by partial melting of metabasaltic rocks. Based on the previous studies, we propose that the Litang biotite monzogranite derived from the westward subduction and closure of the Ganzi-Litang ocean during the Late Triassic-The mantle wedge-derived mafic melts provided sufficient heat for partial melting of ancient metabasalt protolith within the middle-lower crust. 相似文献