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1.
《Journal of Asian Earth Sciences》2007,29(2-3):205-214
The complex crustal structure of the Tien Shan has a strong impact on the distribution of strain induced by the India–Eurasia collision, with intracontinental deformation in Eurasia’s interior as a distant effect. The northward propagation of the India–Eurasia deformation front is suggested by the rejuvenation of mountain ranges and intermittent intramontane basins. The Tien Shan basement is formed by the rigid, heterogeneous Precambrian blocks (microcontinents) of Tarim, Issyk-Kul (or Central Tien Shan) and Aktyuz-Boordin, surrounded by a ‘soft’ matrix of Paleozoic accretion–collision belts. The Kyrgyz Tien Shan Mountains are situated between the active structures of the Tarim Plate and the Pamir indenter (south), and the stable Kazakhstan Shield (north). Underplating by the Tarim Plate and thrusting by the Pamirs are responsible for the building of the Cenozoic Tien Shan, the reactivation of its inherited structural fabric and the tectonic layering of the upper lithosphere underlying the area. Large earthquakes (M > 6) delineate the northern and southern margins of the Issyk-Kul microcontinent, indicating that crustal heterogeneity influenced the location of active structures in the northern Kyrgyz Tien Shan. 相似文献
2.
The Taldybulak Levoberezhny gold deposit, located in the eastern part of the Kyrgyz Northern Tien Shan, is hosted in highly deformed Precambrian schist and gneisses that have undergone intense quartz, carbonate, fuchsite and tourmaline alterations. Gold mineralization is ultimately subdivided into two stages based on the observation of alteration assemblages, orebody geometries, and the occurrences of Au-bearing minerals. Negative thermal ionization mass spectrometry Re–Os isotopic analyses of five Au-rich pyrite samples from the early stage yielded an isochron age of 511 ± 18 Ma. Zircon sensitive high-resolution ion microprobe U–Pb dating of a diorite dike sample postdating the late stage mineralization yielded a wide range of ages from 3055 to 291 Ma, while a weighted mean 206Pb/238U age of 414.6 ± 6.8 Ma is believed to represent the age of dike intrusion and the upper limit on the timing of the late stage quartz–tourmaline–gold formation. The pyrite 187Os/188Os(initial) ratio of 0.132 ± 0.011, together with γOs values varying from 0 to + 14, indicate a major mantle component for the source of Os and by inference ore metals, which may be linked to the ophiolite suite of the Kopurelisai Complex in the Taldybulak Levoberezhny area. Considering the geodynamic setting of the Kyrgyz Northern Tien Shan during the early Paleozoic, we suggest that Cambrian mineralization of the Taldybulak Levoberezhny deposit can be attributed to a subduction-related setting, probably associated with the earliest accretion of the Northern Tien Shan. 相似文献
3.
The Cenozoic terrestrial, intermontane Qaidam Basin on the northeastern edge of the Tibetan Plateau contains > 12 km of sedimentary rocks that potentially document the accommodation of India-Asia convergence and the growth of the plateau. The chronology remains incomplete, hindering cross-basin correlation between lithostratigraphic units and their further interpretation. Here we present a high-resolution magnetostratigraphy spanning > 5 km of Paleogene-Neogene sequence at Dahonggou in the Northern Qaidam Basin. Based on correlation with the geomagnetic polarity time scale (GPTS), we have dated the section to being between ~ 52 and ~ 7 Ma. The bottom conglomeratic unit, ranging from > 52 Ma to ~ 44 Ma, was deposited in high-energy environments (e.g., alluvial fan or braided river), reflecting the earliest deformation and uplift of the basin-bounding Qilian Shan fold-thrust belt in response to India-Asia collision. In addition, we identified two major increases in sedimentation rate at 25–16 Ma and after ~ 9.5 Ma and three phases of lesser increases at 52–44 Ma, 38–33 Ma, and 14.6–12.0 Ma. These increases in sedimentation rate are consistent with regional thermochronology and basin analysis studies, which revealed enhanced motion on basin-bounding thrust faults. We argue that these accelerated sedimentation rates indicate pulsed tectonism in the northeastern Tibetan Plateau. The pulse at 25–16 Ma may further relate to phases of strong rainfall linked to an intense monsoon at that time. 相似文献
4.
The South Tian Shan, which is located along the southwestern margin of the Central Asian Orogenic Belt, is widely accepted as a collisional orogen between the Kazakhstan-Yili Block in the north and the Tarim Craton in the south, and the collision is thought to have occurred in either Late Paleozoic or Triassic. Regardless of the timing of the collision, the major magmatic events in the South Tian Shan Orogen should be related to subduction, collision and post-collision. We investigate this problem through U–Pb age of detrital zircons from the eastward-flowing Tekes River and its southern branches flowing through the northern slope of the Chinese South Tian Shan. A total of 500 analyses on 494 zircon grains from five sand samples yield an age range of 2590 to 268 Ma, but they are dominated by Paleozoic magmatic zircon grains, with some Precambrian population, but no Mesozoic and Cenozoic grains were detected. One of the samples from the Tekes River contains zircon grains from the Chinese South Tian Shan and other areas because the river receives its discharge from multiple sources. The other four samples were collected from four branches originating from the Chinese South Tian Shan only. From west to east, the sample from the Kayintemuzhate River shows two peak ages of 475 and 345 Ma, sample from the Muzhaerte (also called Xiate) River has peak ages of 422 and 290 Ma, sample from the Akeyazi River is characterized by a single peak age of 421 Ma, and sample from the Kekesu River shows a more complicated spectra with peak ages of 426, 398, 362, 327, and 285 Ma. When pooled together, the four samples yield four distinct age populations of 500–460, 450–390, 360–320, and 300–270 Ma, indicating the major magmatic events in the Chinese South Tian Shan. These results, combined with regional data, show an absence of Mesozoic magmatic events in the drainage areas of the Tekes River, and thus the South Tian Shan does not seem to be a Triassic orogen because of the lack of syn-collisional and post-collisional magmatism. The 300–270 magmatic event is thought to post-date the closure of the South Tian Shan Ocean, while the 360–320 and 450–390 Ma events were closely related to the northward subduction of the South Tian Shan Ocean. Our results strongly suggest a Late Carboniferous (320–300 Ma) collision between the Kazakhstan-Yili Block and the Tarim Craton. Possibly, the 500–460 Ma magmatism was related to subduction and closure of the Early Paleozoic Terskey Ocean. 相似文献
5.
Neoproterozoic volcanics and granitoids formed at Rodinia margins within a time span of 880 Ma–700 Ma, are well-documented in many terranes of the southern Central Asian Orogenic Belt (CAOB). Ages younger than 550 Ma corresponding to the opening of the Terskey Ocean are also common. However, so far, there were very few published ages in the range 700 Ma–550 Ma from the Kyrgyz Tien Shan. In this paper we present new data for the alkaline Chon-Ashu complex emplaced at the end of the Cryogenian Period of the Neoproterozoic (850–635 Ma, Gradstein et al., 2012). The alkaline complex intrudes the Precambrian metamorphic rocks north of the Nikolaev Line which separates the Northern and Middle Tien Shan terranes in the eastern Kyrgyzstan. The undeformed shallow level alkaline rocks range from olivine gabbro to nepheline and cancrinite syenites and leucosyenites. The differentiated rock assemblage can be explained by fractional crystallization of high-silica mineral phases which drives nepheline-normative melts away from the silica saturation boundary. The alkaline rocks of Chon-Ashu are enriched in LILE and HFSE indicative of their origin from lithospheric mantle. An age of 678 ± 9 Ma (U–Pb, SHRIMP) was obtained for a protolith of country gneiss, and an age of 656 ± 4 Ma was obtained for the crosscutting alkaline rocks of the Chon-Ashu complex. Seven zircon grains recovered from gneiss and alkaline rocks had bright overgrown rims which yielded a cumulative age of 400 ± 8 Ma. A metamorphic event, followed by uplift and emplacement of shallow level alkaline complex, constrains the geodynamic setting. Alkaline rocks usually form in an extensional setting and originate from lithospheric mantle. The 690 Ma xenoliths of mafic granulite from the NW Tarim have been interpreted to originate by mafic underplating. This mafic underplating may have been responsible for metamorphism in the middle crust prior to emplacement of the Chon-Ashu complex. The 670 Ma–630 Ma period of extension and emplacement of enriched alkaline rocks can be also traced on a regional scale through southern Kazakhstan and the northern Tarim. We tentatively interpret these events as a result of mafic underplating and subsequent rifting related to the break-up of Rodinia. During field work at Chon-Ashu, rich chalcopyrite mineralization has been discovered in carbonate veinlets in leucosyenite alkaline dikes and has also been found in the adjacent Cambrian gabbro and granites shown on the map as undivided Devonian–Silurian. Stockwork mineralization predominates though disseminated mineralization is also present. The Cu content reaches 16,184 ppm and is associated with elevated concentrations of Pb, Zn and Ag. The polyphase structural evolution of the area suggests that mineralization could have formed in several genetically unrelated stages. Based on structural and mineralogical evidence we tentatively relate the earliest stage of chalcopyrite mineralization to the late magmatic CO2-rich fluids emanating from the Cryogenian alkaline complex. The Early Devonian thermal event registered by growth of new zircon at 400 Ma has important metallogenic implications on a regional scale. However the origin of two zones of alteration in the undivided Silurian–Devonian granites is ambiguous because their age was not determined geochronologically. The 522 ± 4 Ma Cambrian gabbro of the Tashtambektor Formation is strongly foliated along the splays of the Nikolaev Line, indicating a Hercynian origin of the fabric. Superimposed mineralized stockwork postdates the foliation and suggests a late-Hercynian age of mineralization in gabbro. The new data enable a reassessment of the metallogenic potential of the Eastern Kyrgyz Tien Shan. Presence of not eroded high-level mineralized Neoproterozoic alkaline intrusions points to a previously underestimated metallogenic potential of pre-Hercynian granitoids which may host preserved porphyry systems, skarns and shear-related mineralization. Finally, the Devonian magmato-metamorphic event which caused formation of a number of ore deposits in central Kyrgyzstan and Kazakhstan could also create potential exploration targets in eastern Kyrgyzstan. 相似文献
6.
Sr-Nd-Pb-Hf isotope mapping combined with U-Pb zircon SHRIMP ages of granitoids from four sampling profiles across terrane boundaries in Uzbekistan reveal distinct reservoir types (cratonic and accretionary), witnessed by the diverse nature and origin of the predominant Paleozoic granitic magmatism that provided hosts for major ore-bodies. The study region comprises four major terranes, including 1) the Sultan-Uvais terrane, 2) the Kyzylkum-Nurata Segment and 3) the Gissar Segment of the South Tien Shan and 4) the Chatkal-Kurama terrane of the Middle Tien Shan. Sr-Nd isotope analyses show a wide range of εNdt (− 5 to + 7) and (87Sr/86Sr)t of 0.704–0.707, indicating involvement of both mantle-derived material and older crustal sources. A wide range of Hf-isotope compositions found in zircons of Chatkal-Kurama granites, Middle Tien Shan (εHf mainly ~ − 5 to + 5), could be due to recycling of older crustal protolith(s); in particular, the earliest (Silurian) granites may be directly derived from 1.5 to 1.7 Ga lower crust. In the Southern Tien Shan, some involvement of subducted oceanic crust is evidenced by strongly juvenile εHft values of up to + 14 and + 16 (Sultan-Uvais, Teskuduk-Kyzylkum). Permo-Carboniferous granitoids, which occur across all terranes also exhibit a wide range of isotope signatures, corresponding to Mesoproterozoic–Neoproterozoic crustal protoliths with a westward increase in juvenile contributions. Pb isotopes (whole-rock) imply the dominance of a crustal component and crust-mantle mixing processes. New age data confirmed: 1) old age of the Turkestan Ocean (505 Ma in Sultan-Uvais), 2) fragments of Silurian island arcs in the accretionary complex of the Chatkal-Kurama terrane (granites of 429–416 Ma) and in the upper allochthon of the South Tien Shan (gabbro 438 Ma in Tamdytau), and 3) a significant volume of granitoid magmatism of subduction or early-collisional stages (around 320–310 Ma) in the Chatkal-Kurama Segment and especially in the Gissar Segment. The westernmost part of the Tien Shan is characterized by multiple subduction processes responsible for 300 million years of geodynamic evolution history (accretionary collage, crustal growth) with the pre-Mesozoic crust formation concluded by Permian post-collisional extensional magmatism. 相似文献
7.
The retreat of the Tethys Sea and the uplift of the Tibetan Plateau play the critical roles in driving Asian climatic changes during the Cenozoic. In the Pamir–Tien Shan convergence zone, over 3000 m of Cenozoic successions, consisting of marine deposits in the lower, continental clay and fine sand in the middle, and molasse in the upper part, record the evolution of the Tethys Sea, the Asian aridification, and the deformation of the Pamir. In this work, the existing biostratigraphic subdivisions and new electronic spinning resonance dating results were used to assign ages to formations within the Ulugqat section. Sedimentary facies analysis and multi-proxy indices were used to reconstruct the paleo-environmental evolution. The results show: (1) the Pamir–Tien Shan convergence zone has undergone progressive environmental changes from shallow marine before ∼34 Ma to arid land at ∼23 Ma and finally to inter-mountain basin by ∼5.3 Ma; (2) the overall increase in mean size of grains, decrease in redness, in magnetic susceptibility, and in proportion of the ultrafine component of the sediments studied revealed a long-term strengthening in potential energy to transporting medium, cooling, and enhanced continental aridity, respectively; (3) the easternmost edge of the Tethys Sea prevailed in the western Tarim Basin from late Cretaceous to early Cenozoic, and finally retreated from this region around the Eocene–Oligocene transition, which in turn strengthened the Asian aridification; (4) accumulation of molasse with an upper age of ∼1 Ma suggests that the deformation front of the Pamir migrated to this area at or before that time. 相似文献
8.
《Gondwana Research》2014,25(1):170-189
The Lhasa terrane in southern Tibet is composed of Precambrian crystalline basement, Paleozoic to Mesozoic sedimentary strata and Paleozoic to Cenozoic magmatic rocks. This terrane has long been accepted as the last crustal block to be accreted with Eurasia prior to its collision with the northward drifting Indian continent in the Cenozoic. Thus, the Lhasa terrane is the key for revealing the origin and evolutionary history of the Himalayan–Tibetan orogen. Although previous models on the tectonic development of the orogen have much evidence from the Lhasa terrane, the metamorphic history of this terrane was rarely considered. This paper provides an overview of the temporal and spatial characteristics of metamorphism in the Lhasa terrane based mostly on the recent results from our group, and evaluates the geodynamic settings and tectonic significance. The Lhasa terrane experienced multistage metamorphism, including the Neoproterozoic and Late Paleozoic HP metamorphism in the oceanic subduction realm, the Early Paleozoic and Early Mesozoic MP metamorphism in the continent–continent collisional zone, the Late Cretaceous HT/MP metamorphism in the mid-oceanic ridge subduction zone, and two stages of Cenozoic MP metamorphism in the thickened crust above the continental subduction zone. These metamorphic and associated magmatic events reveal that the Lhasa terrane experienced a complex tectonic evolution from the Neoproterozoic to Cenozoic. The main conclusions arising from our synthesis are as follows: (1) The Lhasa block consists of the North and South Lhasa terranes, separated by the Paleo-Tethys Ocean and the subsequent Late Paleozoic suture zone. (2) The crystalline basement of the North Lhasa terrane includes Neoproterozoic oceanic crustal rocks, representing probably the remnants of the Mozambique Ocean derived from the break-up of the Rodinia supercontinent. (3) The oceanic crustal basement of North Lhasa witnessed a Late Cryogenian (~ 650 Ma) HP metamorphism and an Early Paleozoic (~ 485 Ma) MP metamorphism in the subduction realm associated with the closure of the Mozambique Ocean and the final amalgamation of Eastern and Western Gondwana, suggesting that the North Lhasa terrane might have been partly derived from the northern segment of the East African Orogen. (4) The northern margin of Indian continent, including the North and South Lhasa, and Qiangtang terranes, experienced Early Paleozoic magmatism, indicating an Andean-type orogeny that resulted from the subduction of the Proto-Tethys Ocean after the final amalgamation of Gondwana. (5) The Lhasa and Qiangtang terranes witnessed Middle Paleozoic (~ 360 Ma) magmatism, suggesting an Andean-type orogeny derived from the subduction of the Paleo-Tethys Ocean. (6) The closure of Paleo-Tethys Ocean between the North and South Lhasa terranes and subsequent terrane collision resulted in the formation of Late Permian (~ 260 Ma) HP metamorphic belt and Triassic (220 Ma) MP metamorphic belt. (7) The South Lhasa terrane experienced Late Cretaceous (~ 90 Ma) Andean-type orogeny, characterized by the regional HT/MP metamorphism and coeval intrusion of the voluminous Gangdese batholith during the northward subduction of the Neo-Tethyan Ocean. (8) During the Early Cenozoic (55–45 Ma), the continent–continent collisional orogeny has led to the thickened crust of the South Lhasa terrane experiencing MP amphibolite-facies metamorphism and syn-collisional magmatism. (9) Following the continuous continent convergence, the South Lhasa terrane also experienced MP metamorphism during Late Eocene (40–30 Ma). (10) During Mesozoic and Cenozoic, two different stages of paired metamorphic belts were formed in the oceanic or continental subduction zones and the middle and lower crust of the hanging wall of the subduction zone. The tectonic imprints from the Lhasa terrane provide excellent examples for understanding metamorphic processes and geodynamics at convergent plate boundaries. 相似文献
9.
A 2000 km long dextral Talas-Fergana strike–slip fault separates eastern terranes in the Kyrgyz Tien Shan from western terranes. The aim of this study was to constrain an age of dextral shearing in the central part of the fault utilizing Ar–Ar dating of micas. We also carried out a U–Pb–Hf zircon study of two different deformed granitoid complexes in the fault zone from which the micas for Ar dating were separated. Two samples of the oldest deformed Neoproterozoic granitoids in the area of study yielded U–Pb zircon SHRIMP ages 728 ± 11 Ma and 778 ± 11 Ma, characteristic for the Cryogenian Bolshoi Naryn Formation, and zircon grains analyzed for their Lu–Hf isotopic compositions yielded εHf(t) values from −11.43 to −16.73, and their calculated tHfc ages varied from 2.42 to 2.71 Ga. Thus varying Cryogenian ages and noticeable heterogeneity of Meso- to Paleoproterozoic crustal sources was established for mylonitic granites of the Bolshoi Naryn Formation. Two samples of mylonitized pegmatoidal granites of the Kyrgysh Complex yielded identical 206Pb/238U ages of 279 ± 5 Ma corresponding to the main peak of Late-Paleozoic post-collisional magmatism in the Tien Shan (Seltmann et al., 2011), and zircon grains analyzed for their Lu–Hf isotopic compositions yielded εHf(t) values from −11.43 to −16.73, and calculated tHfc ages from 2.42 to 2.71 Ga indicating derivation from a Paleoproterozoic crustal source. Microstructural studies showed that ductile/brittle deformation of pegmatoidal granites of the Kyrgysh Complex occurred at temperatures of 300–400 °C and caused resetting of the K–Ar isotope system of primary muscovite. Deformation of mylonitized granites of the Bolshoi Naryn Formation occurred under high temperature conditions and resulted in protracted growth and recrystallization of micas. The oldest Ar–Ar muscovite age of 241 Ma with a well defined plateau from a pegmatoidal granite of the Kyrgysh Complex is considered as a “minimum” age of dextral motions along this section of the fault in the Triassic while younger ages varying from 227 Ma to 199 Ma with typical staircase patterns indicate protracted growth and recrystallization of micas during ductile deformations which continued until the end of the Triassic. 相似文献
10.
Wang-Chun Xu Hong-Fei Zhang Nigel Harris Liang Guo Fa-Bing Pan 《Gondwana Research》2013,23(2):715-725
The lower Bomi Group of the eastern Himalayan syntaxis comprises a lithological package of sedimentary and igneous rocks that have been metamorphosed to upper amphibolite-facies conditions. The lower Bomi Group is bounded to the south by the Indus–Yarlung Suture and to the north by unmetamorphosed Paleozoic sediments of the Lhasa terrane. We report U–Pb zircon dating, geochemistry and petrography of gneiss, migmatite, mica schist and marble from the lower Bomi Group and explore their geological implications for the tectonic evolution of the eastern Himalaya. Zircons from the lower Bomi Group are composite. The inherited magmatic zircon cores display 206Pb/238U ages from ~ 74 Ma to ~ 41.5 Ma, indicating a probable source from the Gangdese magmatic arc. The metamorphic overgrowth zircons yielded 206Pb/238U ages ranging from ~ 38 Ma to ~ 23 Ma, that overlap the anatexis time (~ 37 Ma) recorded in the leucosome of the migmatites. Our data indicate that the lower Bomi Group do not represent Precambrian basement of the Lhasa terrane. Instead, the lower Bomi Group may represent sedimentary and igneous rocks of the residual forearc basin, similar to the Tsojiangding Group in the Xigaze area, derived from denudation of the hanging wall rocks during the India–Asia continental collision. We propose that following the Indian–Asian collision, the forearc basin was subducted, together with Himalayan lithologies from the Indian continental slab. The minimum age of detrital magmatic zircons from the supracrustal rocks is ~ 41.5 Ma and their metamorphism had happened at ~ 37 Ma. The short time interval (< 5 Ma) suggests that the tectonic processes associated with the eastern Himalayan syntaxis, encompassing uplift and erosion of the Gangdese terrane, followed by deposition, imbrication and subduction of the forearc basin, were extremely rapid during the Late Eocene. 相似文献
11.
Simon Nachtergaele Elien De Pelsmaeker Stijn Glorie Fedor Zhimulev Marc Jolivet Martin Dani?ík Mikhail M.Buslov Johan De Grave 《地学前缘(英文版)》2018,9(5):1495-1514
This study provides new low-temperature thermochronometric data, mainly apatite fission track data on the basement rocks in and adjacent to the Talas-Fergana Fault, in the Kyrgyz Tien Shan in the first place.In the second place, we also present new detrital apatite fission track data on the Meso-Cenozoic sediments from fault related basins and surrounding intramontane basins. Our results confirm multistaged Meso-Cenozoic tectonic activity, possibly induced by the accretion of the so-called Cimmerian blocks to the Eurasian margin. New evidence for this multi-staged thermo-tectonic activity is found in the data of both basement and Meso-Cenozoic sediment samples in or close to the Talas-Fergana Fault.Zircon(U-Th)/He and apatite fission track data constrain rapid Late TriassiceE arly Jurassic and Late JurassiceE arly Cretaceous basement cooling in the Kyrgyz Tien Shan around 200 Ma and 130 -100 Ma respectively. Detrital apatite fission track results indicate a different burial history on both sides of the Talas-Fergana Fault. The apatite fission track system of the Jurassic sediments in the Middle Tien Shan unit east of the Talas-Fergana Fault is not reset, while the Jurassic sediments in the Fergana Basin and Yarkand-Fergana Basin, west of the fault zone, are partially and in some cases even totally reset. The totally reset samples exhibit Oligocene and Miocene ages and evidence the Cenozoic reactivation of the western Kyrgyz Tien Shan as a consequence of the India-Eurasia convergence. 相似文献
12.
The Tibetan Plateau (TP) is the highest plateau in the world, which has been the focus of Cenozoic geological studies. The Northeast Tibetan Plateau (NETP) is a key location to decipher the Cenozoic evolution history of the TP. Understanding the building of the Qimen Tagh Mountains located in NETP will help to constrain the development of the northern boundary of the main TP, test the existence of a Paleo-Qaidam Basin and test the eastward growth model of the TP. In this study, granite samples from the Qimen Tagh Mountains were dated by LA-ICPMS and apatite fission track (AFT). The LA-ICPMS zircon U–Pb ages give two magmatic events around ~ 405 and ~ 255 Ma from two different sites. AFT modeling shows that the initial uplift took place at ~ 40–30 Ma in these mountains, which should be controlled by the Altyn Tagh Fault. Compiling previously low-temperature thermochronometry results, it reveals that the initial Cenozoic uplift of the northern boundary of the TP (Qimen Tagh and East Kunlun mountains), soon after the India–Eurasia collision in the southern TP, has divided the Paleo-Qaidam Basin into several sub-basins. The approximate NE–E growth process occurred along the lithospheric Altyn Tagh and Kunlun faults. The current basin and range morphology of the NETP took place around ~ 8 Ma. 相似文献
13.
Sedimentological and geochronological analyses were performed on Carboniferous strata from central Inner Mongolia (China) to determine the tectonic setting of the southeastern Central Asian Orogenic Belt (CAOB). Sedimentological analyses indicate that the widespread Late Carboniferous strata in central Inner Mongolia were dominated by shallow marine clastic-carbonate deposition with basal conglomerate above the Precambrian basement and Early Paleozoic orogenic belts. Based on lithological comparison and fossil similarity, five sedimentary stages were used to represent the Carboniferous deposition. The depositional stages include, from bottom to top, 1) basal molassic, 2) first carbonate platform, 3) terrigenous with coeval intraplate volcanism, 4) second carbonate platform, and 5) post-carbonate terrigenous. These five stages provide evidence for an extensive transgression in central Inner Mongolia during the Late Carboniferous. Detrital zircon geochronological studies from five samples yielded five main age populations: ~ 310 Ma, ~ 350 Ma, 400–450 Ma, 800–1200 Ma and some Meso-Proterozoic to Neoarchean grains. The detrital zircon geochronological studies indicate that the provenances for these Late Carboniferous strata were mainly local magmatic rocks (Early Paleozoic arc magmatic rocks and Carboniferous intrusions) with subordinate input of Precambrian basement. Combining our sedimentological and provenance analyses with previous fossil comparison and paleomagnetic reconstruction, an inland sea was perceived to be the main paleogeographic feature for central Inner Mongolia during the Late Carboniferous. The inland sea developed on a welded continent after the collision between North China Craton and its northern blocks. 相似文献
14.
《Gondwana Research》2014,26(4):1644-1659
The formation of a series of intermountain basins is likely to indicate a geodynamic transition, especially in the case of such basins within the central South China Block (CSCB). Determining whether or not these numerous intermountain basins represent a division of the Cretaceous Pan-Yangtze Basin by exhumation of Xuefeng Mountains, is key to understanding the late Mesozoic to early Cenozoic tectonics of the South China Block (SCB). Here we present apatite fission track (AFT) data and time–temperature modeling in order to reconstruct the evolution history of the Pan-Yangtze Basin. Fourteen rock samples were taken from a NE–SW-trending mountain–basin system within the CSCB, including, from west to east, the Wuling Mountains (Wuling Shan), the south and north Mayang basins, the Xuefeng Mountains (Xuefeng Shan) and the Hengyang Basin. Cretaceous lacustrine sequences are well preserved in the south and north Mayang and Hengyang basins, and sporadically crop out in the Xuefeng Mountains, whereas Paleogene piedmont proluvial–lacustrine sequences are only found in the south Mayang and Hengyang basins. AFT results indicate that the Wuling and Xuefeng mountains underwent rapid denudation post-84 Ma, whereas the south and north Mayang basins were more slowly uplifted from 67 and 84 Ma, respectively. Following a quiescent period from 32 to 19 Ma, both the mountains and basins have been rapidly denuded since 19 Ma. Both the AFT data and sedimentary facies changes suggest that the Cretaceous deposits that cover the south–north Mayang and Hengyang basins through to the Xuefeng Mountains define the Cretaceous Pan-Yangtze Basin. Integrating our results with tectonic background for the SCB, we propose that rollback subduction of the paleo-Pacific Plate produced the Pan-Yangtze Basin, which was divided into the south–north Mayang and Hengyang basins by the abrupt uplift and exhumation of the Xuefeng Mountains from 84 Ma to present, apart from a period of tectonic inactivity from 32 to 19 Ma. This late Late Cretaceous to Paleogene denudation resulted from movement on the Ziluo strike–slip fault, which formed due to intra-continental compression most likely associated with the Eurasia–Indian plate subduction and collision. Sinistral transpression along the Ailao Shan–Red River Fault at 34–17 Ma probably transformed this compression to the extrusion of the Indochina Block, and produced the quiescent window period from 32 to 19 Ma for the mountain–basin system in the CSCB. Therefore, the initiation of exhumation of the Xuefeng Mountains at 84 Ma indicates a switch in tectonic regime from Cretaceous extension to late Late Cretaceous and Cenozoic compression. 相似文献
15.
The Palaeozoic to Mesozoic igneous and metamorphic basement rocks exposed in the Mérida Andes of Venezuela and the Santander Massif of Colombia are generally considered to define allochthonous terranes that accreted to the margin of Gondwana during the Ordovician and the Carboniferous. However, terrane sutures have not been identified and there are no published isotopic data that support the existence of separate crustal domains. A general paucity of geochronological data led to published tectonic reconstructions for the evolution of the northwestern corner of Gondwana that do not account for the magmatic and metamorphic histories of the basement rocks of the Mérida Andes and the Santander Massif. We present new zircon U–Pb (ICP-MS) data from 52 igneous and metamorphic rocks, which we combine with whole rock geochemical and Pb isotopic data to constrain the tectonic history of the Precambrian to Mesozoic basement of the Mérida Andes and the Santander Massif. These data show that the basement rocks of these massifs are autochthonous to Gondwana and share a similar tectono-magmatic history with the Gondwanan margin of Peru, Chile and Argentina, which evolved during the subduction of oceanic lithosphere of the Iapetus Ocean. The oldest Palaeozoic arc magmatism is recorded at ~ 500 Ma, and was followed shortly by Barrovian metamorphism. Peak metamorphic conditions at upper amphibolite facies are recorded by anatexis at ~ 477 Ma and the intrusion of synkinematic granitoids until ~ 472 Ma. Subsequent retrogression resulted from localised back-arc or intra-arc extension at ~ 453 Ma, when volcanic tuffs and interfingered sedimentary rocks were deposited over the amphibolite facies basement. Continental arc magmatism dwindled after ~ 430 Ma and terminated at ~ 415 Ma, coevally with most of the western margin of Gondwana. After Pangaea amalgamation in the Late Carboniferous to Early Permian, a magmatic arc developed on its western margin at ~ 294 Ma as a result of subduction of oceanic crust of the palaeo-Pacific ocean. Intermittent arc magmatism recorded between ~ 294 and ~ 225 Ma was followed by the onset of the Andean subduction cycle at ~ 213 Ma, in an extensional regime. Extension was accompanied by slab roll-back which led to the migration of the arc axis into the Central Cordillera of Colombia in the Early Jurassic. 相似文献
16.
《Gondwana Research》2014,25(3):1202-1215
The South China Block, consisting of the Yangtze and the Cathaysia blocks, is one of the largest Precambrian blocks in eastern Asia. However, the early history of the Cathaysia Block is poorly understood due largely to intensive and extensive reworking by Phanerozoic polyphase orogenesis and magmatism which strongly overprinted and obscured much of the Precambrian geological record. In this paper, we use the detrital zircon U–Pb age and Hf isotope datasets as an alternative approach to delineate the early history of the Cathaysia Block. Compilation of published 4041 Precambrian detrital zircon ages from a number of (meta)sedimentary samples and river sands exhibits a broad age spectrum, with three major peaks at ~ 2485 Ma, ~ 1853 Ma and ~ 970 Ma (counting for ~ 10%, ~ 16% and ~ 24% of all analyses, respectively), and four subordinate peaks at ~ 1426 Ma, ~ 1074 Ma, ~ 780 Ma and ~ 588 Ma. Five of seven detrital zircon age peaks are broadly coincident with the crystallisation ages of ~ 1.89–1.83 Ga, ~ 1.43 Ga, ~ 1.0–0.98 Ga and ~ 0.82–0.72 Ga for known igneous rocks exposed in Cathaysia, whereas, igneous rocks with ages of ~ 2.49 Ga and ~ 0.59 Ga have not yet been found. The Hf isotopic data from 1085 detrital zircons yield Hf model ages (TDMC) between ~ 4.19 Ga and ~ 0.81 Ga, and the calculated εHf(t) values between − 40.2 and 14.4. The Archean detrital zircons are exclusively oval in shape with complicated internal textures, indicating that they were sourced by long distance transportations and strong abrasion from an exotic Archean continent. In contrast, the majority of detrital zircons in age between ~ 1.9 and ~ 0.8 Ga are euhedral to subhedral crystals, indicative of local derivation by short distance transportations from their sources. The oldest crustal basement rocks in Cathaysia were most likely formed by generation of juvenile crust and reworking of recycled Archean components in Late Paleoproterozoic at ~ 1.9–1.8 Ga, rather than in the Archean as previously speculated. Reworking and recycling of the continental crust are likely the dominant processes for the crustal evolution of Cathaysia during the Mesoproterozoic to Neoproterozoic time, with an intervenient period of significant generation of juvenile crust at ~ 1.0 Ga.Precambrian crustal evolutions of the Cathaysia Block are genetically related to the supercontinent cycles. By comparing detrital zircon data from Cathaysia with those for other continents, and integrating multiple lines of geological evidence, we interpret the Cathaysia Block as an orogenic belt located between East Antarctica, Laurentia and Australia during the assembly of supercontinent Columbia/Nuna at ~ 1.9–1.8 Ga. The Cathaysia Block amalgamated with the Yangtze Block to form the united South China Block during the Sibao Orogeny at ~ 1.0–0.89 Ga. The Laurentia–Cathaysia–Yangtze–Australia–East Antarctica connection gives the best solution to the paleo-position of Cathaysia in supercontinent Rodinia. The significant amount of ~ 0.6–0.55 Ga detrital zircons in Cathaysia and West Yangtze have exclusively high crustal incubation time of > 300 Ma, indicating crystallisation from magmas generated dominantly by crustal reworking. This detrital zircon population compares well with the similar-aged zircon populations from a number of Gondwana-derived terranes including Tethyan Himalaya, High Himalaya, Qiangtang and Indochina. The united South China–Indochina continent was likely once an integral part of Gondwanaland, connected to northern India by a “Pan-African” collisional orogen. 相似文献
17.
In the Menderes Massif (western Taurides) a Neoproterozoic basement comprising metasediments and intrusive granites is imbricated between Paleozoic platform sediments. U–Pb–Hf zircon analyses of Menderes rock units were performed by us using LA-ICP-MS. The U–Pb detrital zircon signal of the Neoproterozoic metasediments is largely consistent with a NE African (Gondwana) provenance. The oldest unit, a paragneiss, contains significant amounts (~ 30%) of Archean-aged zircons and εHf (t) values of about a half of its Neoproterozoic zircons are negative suggesting contribution from Pan-African terranes dominated by reworking of an old crust. In the overlying, mineralogically-immature Core schist (which is still Neoproterozoic), the majority of the detrital zircons are Neoproterozoic, portraying positive εHf (t) values indicating derivation from a proximal juvenile source, resembling the Arabian–Nubian Shield.The period of sedimentation of the analyzed metasediments, is constrained between 570 and 550 Ma (Late Ediacaran). The Core schist sediments, ~ 9 km thick, accumulated in less than 20 My implying a tectonic-controlled sedimentary basin evolved adjacent to the eroded juvenile terrane. Granites, now orthogneisses, intruded the basin fill at 550 Ma, they exhibit ± 0 εHf (t = 550 Ma) and TDM ages of 1.4 Ga consistent with anatexis of various admixtures of juvenile Neoproterozoic and Late Archean detrital components. Granites in the northern Arabian–Nubian Shield are no younger than 580 Ma and their εHf (t) are usually more positive. This implies that the Menderes does not represent a straightforward continuation of the Arabian–Nubian Shield.The lower part of the pre-Carboniferous silisiclastic cover of the Menderes basement, comprises a yellowish quartzite whose U–Pb–Hf detrital zircon signal resembles that of far-traveled Ordovician sandstones in Jordan (including 0.9–1.1 Ga detrital zircons), supporting pre-Triassic paleorestorations placing the Tauride with Afro-Arabia. The detrital signal of the overlying carbonate-bearing quartzitic sequence indicates contribution from a different source: the majority of its detrital zircons yielded 550 Ma and ± 0 εHf (t = 550 Ma) values identical to that of the underlying granitic gneiss implying exposure of Menderes-like granites in the provenance.260–250 Ma lead-loss and partial resetting of the U–Pb system of certain zircons in both basement and cover units was detected. It is interpreted as a consequence of a Permian–Early Triassic thermal event preceding known Triassic granitoid intrusions. 相似文献
18.
《Quaternary Research》2014,81(3):400-423
The way in which the NE Tibetan Plateau uplifted and its impact on climatic change are crucial to understanding the evolution of the Tibetan Plateau and the development of the present geomorphology and climate of Central and East Asia. This paper is not a comprehensive review of current thinking but instead synthesises our past decades of work together with a number of new findings. The dating of Late Cenozoic basin sediments and the tectonic geomorphology of the NE Tibetan Plateau demonstrates that the rapid persistent rise of this plateau began ~ 8 ± 1 Ma followed by stepwise accelerated rise at ~ 3.6 Ma, 2.6 Ma, 1.8–1.7 Ma, 1.2–0.6 Ma and 0.15 Ma. The Yellow River basin developed at ~ 1.7 Ma and evolved to its present pattern through stepwise backward-expansion toward its source area in response to the stepwise uplift of the plateau. High-resolution multi-climatic proxy records from the basins and terrace sediments indicate a persistent stepwise accelerated enhancement of the East Asian winter monsoon and drying of the Asian interior coupled with the episodic tectonic uplift since ~ 8 Ma and later also with the global cooling since ~ 3.2 Ma, suggesting a major role for tectonic forcing of the cooling. 相似文献
19.
Western Tibet, between the Karakorum fault and the Gozha–Longmu Co fault system, is mostly internally drained and has a 1.5–2 km amplitude relief with km-large valleys. We investigate the origin of this peculiar morphology by combining a topography analysis and a study of the Cenozoic sedimentation in this area. Cenozoic continental strata correspond to a proximal, detrital fan deposition, and uncomformably rest on a palaeorelief similar to the modern one. Zircon U–Pb dating from trachytic flows interbedded within the Cenozoic continental sediments indicates that detrital sedimentation occurred at least between ca 24 and 20 Ma in the Shiquanhe basin, while K/Ar ages suggest it may have started since ~ 37 Ma in the Zapug basin. The distribution of continental deposits shows that present-day morphology features, including km-large, 1500 m-deep valleys, were already formed by Early Miocene times. We suggest that today's internally drained western Tibet was externally drained, at least during late Miocene, contemporaneously with early motion along the Karakorum Fault. Detailed study of the present day river network is compatible with a dextral offset on the Karakorum Fault of 250 km at a rate of ~ 10 ± 1 mm/yr. Displacement along the Karakorum fault possibly induced the shift from external to an internal drainage system, by damming of the Bangong Co ~ 4 Ma ago, leading to the isolation and preservation of the western Tibet relief. 相似文献
20.
Magnetostratigraphy of deep drilling core SG-1 in the western Qaidam Basin (NE Tibetan Plateau) and its tectonic implications 总被引：1，自引：0，他引：1
Weilin Zhang Erwin Appel Xiaomin Fang Chunhui Song Olaf Cirpka 《Quaternary Research》2012,78(1):139-148
The Qaidam Basin is the largest intermontane basin of the northeastern Tibetan Plateau and contains a continuous Cenozoic sequence of lacustrine sediments. A ~ 1000-m-deep drilling (SG-1) with an average core recovery of ~ 95% was carried out in the depocenter of the Chahansilatu playa (sub-depression) in the western Qaidam Basin, aimed to obtain a high-resolution record of the paleoenvironmental evolution and the erosion history. Stepwise alternating field and thermal demagnetization, together with rock magnetic results, revealed a stable remanent magnetization for most samples, carried by magnetite. The polarity sequence consisted of 16 normal and 15 reverse zones which can be correlated with chrons 1n to 2An of the global geomagnetic polarity time scale. Magnetostratigraphic results date the entire core SG-1 at ~ 2.77 Ma to ~ 0.1 Ma and yielded sediment accumulation rate (SAR) ranging from 26.1 cm/ka to 51.5 cm/ka. Maximum SARs occurred within the intervals of ~ 2.6–2.2 Ma and after ~ 0.8 Ma, indicating two episodes of erosion, which we relate to pulse tectonic uplift of the NE Tibetan Plateau with subsequent global cooling. 相似文献