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1.
The Yili Block is one of the Precambrian microcontinents dispersed in the Central Asian Orogenic Belt (CAOB). Detrital zircon U–Pb ages and Hf isotopic data of Neoproterozoic meta-sedimentary rocks (the Wenquan Group) are presented to constrain the tectonic affinity and early history of the Yili Block. The dating of detrital zircons indicates that both the lower and upper Wenquan Groups have two major populations with ages at 950–880 Ma and 1600–1370 Ma. Moreover, the upper Wenquan Group has two minor populations at ~ 1100 Ma and 1850–1720 Ma. According to the youngest age peaks of meta-sedimentary rocks and the ages of related granitoids, the lower Wenquan Group is considered to have been deposited during the early Neoproterozoic (900–845 Ma), whereas the upper Wenquan Group was deposited at 880–857 Ma. The zircon εHf (t) values suggest that the 1.85–1.72 Ga source rocks for the upper Wenquan Group were dominated by juvenile crustal material, whereas those for the lower Wenquan Group involved more ancient crustal material. For the 1.60–1.37 Ga source rocks, however, juvenile material was a significant input into both the upper and lower Wenquan Groups. Therefore, two synchronous crustal growth and reworking events were identified in the northern Yili Block at ca. 1.8–1.7 Ga and 1.6–1.3 Ga, respectively. After the last growth and reworking event, continuous crustal reworking took place in the northern Yili Block until the early Neoproterozoic. Comparing the age patterns and Hf isotopic compositions of detrital zircons from the Yili Block and the surrounding tectonic units indicates that the Yili Block has a close tectonic affinity to the Chinese Central Tianshan Block in the Precambrian. The Precambrian crustal evolution of the Yili Block is distinct from that of the Siberian, North China and Tarim Cratons. Such difference therefore suggests that the Yili Block and the Chinese Central Tianshan Block may have been united in an isolated Precambrian microcontinent within the CAOB rather than representing two different blocks rifted from old cratons on both sides of the Paleo-Asian Ocean.  相似文献   

2.
Owing to the lack of early Neoproterozoic geological and geochronological data, most Rodinia supercontinent reconstruction models do not include the Amuria Block in the Central Asian Orogenic Belt (CAOB), and the Amuria Block was varying attributed to the North China, Siberian or Tarim tectonic affinities. In this study, we identified one early Neoproterozoic granitic pluton (964–947 Ma) and one early Neoproterozoic sedimentary unit (<906 Ma) in the Erguna Terrane. The samples (964–947 Ma) are I-type granitoids, and show high zircon in-situ εHf(t) (−2.1–10.0) and whole-rock εHf(t) (1.4–4.8) and high εNd(t) (−2.3 to −0.8). These granitoids are characterized by high Zr saturation temperature (TZr) (701–835 °C) and no inherited zircons, suggesting high-degree of partial melting of their source rocks. The granites were likely formed by biotite-/muscovite dehydration melting of subalkaline mafic lower crust in a continental arc setting. Detrital zircons of the sandstone sample define an age peak at 923–906 Ma. Early Neoproterozoic age data compilation from the four Amuria microcontinents (i.e., Erguna, Xing'an, Songnen and Jiamusi terranes) in NE China indicate the presence of two major magmatic flare-ups at 964–880 Ma and 850–740 Ma. Considering that early Neoproterozoic magmatic rocks are absent in the Siberian and North China cratons but widespread in the Tarim Craton, we suggested that the Erguna Terrane was part of the Tarim Craton in the Early Neoproterozoic. The Erguna Terrane may have undergone a two-staged Neoproterozoic tectonic evolutionary history: (1) early Neoproterozoic arc accretion in response to the Rodinia assembly, and (2) middle Neoproterozoic break-away from the SW Tarim Craton associated with the Rodinia breakup.  相似文献   

3.
《Gondwana Research》2014,26(4):1627-1643
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 detrital zircon U–Pb dating analyses of sediments from the accretionary mélange from Chinese southwestern Tianshan in this study. A total of 542 analyzed spots on 541 zircon grains from five samples yield Paleoarchean to Devonian ages. The major age groups are 2520–2400 Ma, 1890–1600 Ma, 1168–651 Ma, and 490–390 Ma. Provenance analysis indicates that, the Precambrian detrital zircons were probably mainly derived from the paleo-Kazakhstan continent formed before the Early Silurian by amalgamation of the Kazakhstan–Yili microplate, the Chinese central Tianshan terrane and the Kyrgyz North and Middle Tianshan blocks, while detrital zircons with Paleozoic ages mainly from igneous rocks of the continental arc generated by the northward subduction of the south Tianshan paleocean. The age data correspond to four tectono-thermal events that took place in these small blocks, i.e., the continental nucleus growth during the Late Neoarchean–early Paleoproterozoic (~ 2.5 Ga), the evolution of the supercontinents Columbia (2.1–1.6 Ga) and Rodinia (1.3–0.57 Ga), and the arc magmatism related with the Phanerozoic orogeny. The Precambrian zircons show a similar age pattern as the Tarim and the Cathaysia cratons and the Eastern India–Eastern Antarctica block but differ from those of Siberia distinctly. Therefore, the Tianshan region blocks and the Kazakhstan–Yili microplate have a close affinity to the eastern paleo-Gondwana fragments, but were not derived from the Siberia craton as proposed by some previous researchers. These blocks were likely generated by rifting accompanying Rodinia break-up in late Precambrian times.The youngest ages of the detrital zircons from the subduction mélange show a maximum depositional age of ca. 390 Ma. It is coeval with the end of an earlier arc magmatic pulse (440–390 Ma) but a bit older than a younger one at 360–320 Ma and nearly 70–80 Ma older than the HP–UHP metamorphism in the subduction zone (320–310 Ma).  相似文献   

4.
The continental fragments in Northwest China are key to revealing the tectonic and crustal evolution of the Central Asian Orogenic Belt (CAOB). However, their tectonic correlation, affinity and implications have not been well defined. The early to mid-Paleozoic sediments in the northern Alxa area can help to understand this question. These sediments were deposited in a deep to shallow marine environment during a regression. The southeast paleocurrent attributes their provenance to the northwest. Detrital zircons from the collected sandstones record peak ages of approximately 1726 Ma, 1462 Ma, 915 Ma and 438 Ma. The zircon εHf(t) values are negative to positive at 1726 Ma, 915 Ma and 438 Ma, but only positive at 1462 Ma. The detrital zircon U–Pb ages and Hf isotopes suggest the provenance to be the blocks in Central Tianshan and Southern Beishan or their analogs, rather than the Tarim Craton. The source blocks show no tectonic affinity to the Tarim Craton but might be accreted to it in the Neoproterozoic Rodinia. The provenance analyses show tectonic correlation among the northern Alxa, Tianshan and Beishan orogenic belts. The Late Devonian molasse deposits, geochemical shifting to continental margins and suddenly increased early Paleozoic zircons indicate an arc-continent collision. The discovery of more indicators for continental fragments advocates a multiterrane model and dominant crustal reworking/contamination for the tectonocrustal evolution of the CAOB at least during the early to mid-Paleozoic.  相似文献   

5.
伊犁盆地南缘中-下侏罗统碎屑岩的物源特征,可为南天山造山带的演化提供重要证据。对其碎屑岩锆石U-Pb定年研究结果表明,伊犁盆地南缘坎乡下侏罗统八道湾组砂岩的碎屑锆石年龄集中在290~260 Ma,而下侏罗统三工河组的碎屑锆石年龄集中在350~290 Ma和460~390 Ma,中侏罗统西山窑组的碎屑锆石年龄集中在370~320 Ma和450~390 Ma。所有测试样品中前寒武纪的年龄记录非常少。这些特征表明,伊犁盆地南缘中生代碎屑沉积物主要来自于伊犁-中天山地块南部。测试样品中几乎不存在晚二叠世-中三叠世的碎屑锆石,与南天山造山带的岩浆岩记录一致,暗示在晚二叠世-中三叠世南天山地区并没有发生强烈的与碰撞或后碰撞相关的岩浆活动。该结果不支持塔里木克拉通与伊犁-中天山地块在晚二叠世-中三叠世碰撞的观点。结合高压-超高压变质岩的数据和地层记录,认为塔里木克拉通与伊犁-中天山地块的碰撞发生在晚石炭世。同时,样品中最年轻锆石的年龄数据从早侏罗世到中侏罗世逐渐增大,显示了揭顶沉积的特点。对伊犁盆地南部中生代的锆石年龄数据与同时代南天山地区的锆石年龄数据进行综合对比表明在早-中侏罗世发生构造沉积夷平的特征。  相似文献   

6.
本文对巴仑台地区中天山南北边缘的变形花岗岩体进行了详细的锆石LA-ICP-MS-U-Pb年代学研究。中天山北缘花岗质片麻岩中岩浆锆石结晶年龄为630.0±5.0 Ma,代表了中天山微陆基底的新元古代岩浆事件年龄;其变质增生锆石边的年龄为440.9±3.3 Ma,精确限定了中天山北缘洋盆闭合与碰撞造山作用的时代为早志留世。中天山南缘糜棱岩化花岗闪长岩中岩浆锆石结晶年龄为389.5±3.2 Ma,指示出中天山南缘洋壳在中泥盆世向北俯冲形成陆缘岩浆弧;其变质增生锆石边的年龄为362.1±4.3 Ma,精确限定了中天山南缘洋盆闭合与碰撞造山作用的时代为晚泥盆世末期。研究结果还表明中天山微陆块具有年龄为2.5Ga和1.8Ga的古老结晶基底。  相似文献   

7.
Located between the Turpan-Hami, Junggar and Tarim blocks, the Central Tianshan zone is an important component of the Central Asian Orogenic Belt (CAOB) and crucial linkage between the Siberian, Kazakhstan, Junggar, Turpan-Hami and Tarim blocks. The Hongliujing granite associated with Nb–Ta mineralization in the Central Tianshan zone, dated at ca. 740 Ma using zircon LA-ICP-MS dating, is the first reported Neoproterozoic intrusion with a reliable and precise age in the Chinese Central Tianshan. The Hongliujing granite shares all the characteristics of A-type granites. It contains predominant alkali feldspar, and is characterized by high contents of SiO2, Na2O + K2O, K2O and high field strength elements (such as Nb, Ta, Zr, Ga and Y), and low contents of CaO, MgO, Ba and Sr, with high FeOt/(FeOt + MgO) and Ga/Al ratios typical of A-type granites. Based on the geochemistry and zircon Hf isotope data, we propose that the Hongliujing granite was most likely produced by partial melting of basic rocks in the lower crust which may have been derived from mantle magmas. The Hongliujing granite belongs to A1-type granites, which indicate a rifting formation environment, suggesting that like the Tarim Block, the Central Tianshan zone recorded Neoproterozoic rift-related igneous events related to the breakup of the Rodinia supercontinent. Our study verifies that not only the Tarim Block is related to the breakup of the Rodinia supercontinent, but also it is true for some key blocks in CAOB such as the Central Tianshan. Our new geochemical and geochronologic data also support and strengthen the notion that the Central Tianshan zone may be a part of the Tarim Block.  相似文献   

8.
The Eastern Kunlun Range, as a high-elevation and granitoid-rich tectonic element in northern Tibet, records Paleozoic–Mesozoic amalgamation process of the East Asia continent and Cenozoic uplift of the Tibetan Plateau. However, Precambrian evolution of the Eastern Kunlun remains poorly understood and relations between Eastern Kunlun and adjacent terranes (e.g., Qaidam and Qilian) during the Phanerozoic accretion process are still highly controversial. We use detrital zircon U-Pb geochronological and Hf isotopic data of Proterozoic and Paleozoic metasedimentary rocks from the Eastern Kunlun Range, to reconstruct its origin and subsequent evolutionary history. Detrital zircons of the Proterozoic rocks are dominated by early–middle Neoproterozoic ages (700–1000 Ma), with two age peaks at ca. 800 Ma and ca. 920 Ma and εHf(t) values ranging from −10 to 5. The youngest detrital zircon ages (648–788 Ma) demonstrate that these investigated Proterozoic strata, which were previously mapped as Paleoproterozoic to Mesoproterozoic, were most likely deposited in the middle–late Neoproterozoic. Abundant 0.9–1.0 Ga detrital zircon crystals are consistent with those crystalline rocks of similar ages across the Kunlun-Qaidam and Qilian terranes, which are generally interpreted as the product of Grenvillian orogenesis. These findings support the hypothesis that these terranes were probably within a single continental landmass (named as KQQ block) during the Neoproterozoic. The high similarity of detrital zircon ages, Hf isotopes and Neoproterozoic lithostratigraphy between western Yangtze and KQQ blocks, supports a temporary connection of the KQQ block to western Yangtze in Rodinia supercontinent. Detrital zircons of the analyzed Paleozoic rocks are characterized by 390–490 Ma age populations. These results, in combination with published granitoids data of the northern Tibet, favor a scenario in which the Kunlun-Qaidam and Qilian terranes underwent separated subduction and accretion processes during the late Cambrian–Devonian, but together formed an upper plate to northward subduction of the Paleo-Tethys during the Permian–Triassic.  相似文献   

9.
UPb dating of detrital zircons from metamorphic and unmetamorphosed siliciclastic units in northern, central, and southern parts of the late Paleozoic South Tianshan (STS) orogen allows us to elucidate depositional ages and provenances of studied deposits and provide important insights into Paleozoic tectonics and evolution of the southwest Central Asian Orogenic Belt (CAOB). In the northern flank of the orogen, the depositional age of metasandstones of the Kembel Complex has been constrained to 446–417 Ma. Greenschist-facies metasandstones of the Kan Complex, associated with the Turkestan suture and previously related to Proterozoic, yielded maximum depositional ages of 438–428 Ma based on the youngest clusters of detrital zircons, although the occurrence of a few younger grains implies, that these rocks may be late Silurian to Devonian in age. Greenschists of the Kan Complex were likely metamorphosed during the Mississippian (>330 Ma), based on the early Serpukhovian age of overlying strata. A similar depositional age has been proven for sandstones of the Balykty Formation, east of the Talas-Ferghana Fault. Detrital zircons ages for these metasediments suggest clastic provenances within Northern and Middle Tianshan. In the axial parts of the STS, coarse-grained turbidite sandstones yielded Silurian to Early Devonian maximum ages. The axial part of the STS was separated from continental domains in the north and south by deep-marine basins; therefore, these turbidite sandstones must have been derived from a local provenance in the STS. This local provenance is comprised of Precambrian crustal fragments, as indicated by high concentration of Precambrian magmatic zircons in detrital populations, along with Silurian and Devonian arc magmatic rocks. Precambrian crust can be inferred in the basement of the Alai microcontinent and Baubashata carbonate platform, which represented the likely provenance areas. Detrital zircons with Ediacaran 650–550 Ma ages in turbidites suggest that during the Neoproterozoic, these crustal fragments may have comprised a single continental domain with the Karakum-Tajik (Garm massif) and Tarim microcontinents, where magmatic rocks and detrital zircons with such ages have been also previously dated. Devonian slope turbidite facies of the Tarim Craton in the south Ferghana Range contain Precambrian detrital zircons with ages matching those of the Tarim, and numerous Paleozoic zircons clustering at 446 and 441 Ma. Paleozoic zircon ages indicate the occurrence of unidentified Ordovician and early Silurian magmatic rocks in northern and western Tarim. New data provide further evidence that Paleozoic evolution of CAOB was controlled by northward motion of the Precambrian terranes rifted off the Gondwana and colliding with the continental masses of Kazakhstan and Siberia in the north.  相似文献   

10.
华北克拉通是否同华南克拉通一样保存有与Rodinia超大陆聚合和裂解有关的年龄记录是理解华北克拉通元古宙构造演化的重要科学问题.本文对位于华北克拉通燕辽裂陷槽的北京西山地区的寒武系和侏罗系碎屑岩进行锆石LA-ICP-MS U-Pb年代学研究,目的是通过碎屑锆石年龄揭示华北克拉通前寒武纪尤其是古元古代末-新元古代重要地质事件.定年结果显示,北京西山寒武系徐庄组的钙质细砂岩中碎屑锆石年龄峰值主要集中在～1.38Ga和～1.14Ga.此外,还有～ 1.56Ga、～912Ma、～814Ma、～740Ma、～630Ma和～507Ma的年龄组.侏罗系窑坡组长石质岩屑细砂岩和粉砂质泥岩中碎屑锆石年龄峰值主要集中在～2.5Ga、1.88～1.8Ga、～1.74Ga、～1.6Ga和186Ma.此外,还有～2.77Ga、～2.0Ga、～1.2Ga、～488Ma、～256Ma和～233 Ma的年龄组.这三个岩石具有较低的成分和结构成熟度,指示较近的物源区,其碎屑物质可能大部分来自华北克拉通内部和北缘,因此其碎屑锆石的年龄组可记录华北克拉通前寒武纪重要地质事件.～2.77Ga、～2.5Ga、2.1～ 2.0Ga和1.88～1.8Ga的年龄组分别对应华北克拉通早前寒武纪发生地壳生长、克拉通化、裂谷和造山等重要地质事件;～ 1.74Ga、～ 1.6Ga、～ 1.56Ga、～1.38Ga、～912Ma和～814Ma的年龄组记录了华北克拉通最终克拉通化后开始的古元古代末-新元古代的多期裂谷事件.与1.3～ 1.0Ga、～740Ma和～630Ma的年龄组相对应的岩石在华北克拉通出现甚少,而该时期的岩浆岩和变质岩在华南克拉通广泛发育,且可能与Rodinia超大陆汇聚和裂解的不同阶段相对应.华北克拉通显生宙碎屑岩中碎屑锆石保存的古元古代末-新元古代地质事件的记录对探讨华北克拉通在元古宙的地质演化及华北克拉通与华南克拉通的关系可提供重要的依据.  相似文献   

11.
Neoproterozoic sedimentary sequences in the South China Block provide great opportunity to examine the tectonic evolution and crustal accretion during this period. This study presents U–Pb ages and Hf isotope composition of detrital zircons and Nd isotope composition of whole rocks of the Neoproterozoic sequences from the Yangtze Block, part of the South China Block. Age patterns of detrital zircons imply that the source area experienced three major periods of magmatic activity at 2,300–2,560, 1,900–2,100 and 770–1,000?Ma and two major episodes of juvenile crust accretion at 2,600–3,400 and 770–1,000?Ma. The maximum age of the Gucheng glaciation can be restricted at?~768?Ma from the youngest detrital zircon ages, probably corresponding to the Kaigas glaciation rather than to the Sturtian glaciation. High La/Sc ratio and low Cr/Th, Sc/Th and Co/Th ratios of the sedimentary rocks point to a derivation from dominantly felsic upper continental crustal sources, whereas large variation of εNd(t) and εHf(t) values indicates that mantle-derived magmatic rocks also provided material to the sedimentary sequences in different degrees. The shift in εNd(t) values of whole rocks and U–Pb age spectra of detrital zircons records the evolution from a back-arc to retro-arc foreland to a rift basin. Age distribution of detrital zircons from the Neoproterozoic sequences, compared with those of the major crustal blocks of Rodinia, implies that the position of the Yangtze Block was probably adjacent to northern India rather than between Australia and Laurentia before the breakup of the Rodinia supercontinent.  相似文献   

12.
《Gondwana Research》2014,25(1):383-400
U–Pb geochronologic and Hf isotopic results of seven sandstones collected from Late Carboniferous through Early Triassic strata of the south-central part of the North China Craton record a dramatic provenance shift near the end of the Late Carboniferous. Detrital zircons from the Late Carboniferous sandstones are dominated by the Early Paleozoic components with positive εHf(t) values, implying the existence of a significant volume of juvenile crust at this age in the source regions. Moreover, there are also three minor peaks at ca. 2.5 Ga, 1.87 Ga and 1.1–0.9 Ga. Based on our new data, in conjunction with existing zircon ages and Hf isotopic data in the North China Craton (NCC), Central China Orogenic Belt (CCOB) and Central Asian Orogenic Belt (CAOB), it can be concluded that Early Paleozoic and Neoproterozoic detritus in the south-central NCC were derived from the CCOB. Zircons with ages of 1.9–1.7 Ga were derived from the NCC. However, the oldest components can't be distinguished, possibly from either the NCC or the CCOB, or both. In contrast, detrital zircons from the Permian and Triassic sandstones are characterized by three major groups of U–Pb ages (2.6–2.4 Ga, 1.9–1.7 Ga and Late Paleozoic ages). Specially, most of the Late Paleozoic zircons show negative εHf(t) values, similar to the igneous zircons from intrusive rocks of the Inner Mongolia Paleo-Uplift (IMPU), indicating that the Late Paleozoic detritus were derived from the northern part of the NCC. This provenance shift could be approximately constrained at the end of the Late Carboniferous and probably hints that tectonic uplift firstly occurred between the CCOB and the NCC as a result of the collision between the South and North Qinling microcontinental terranes, and then switched to the domain between the CAOB and the NCC. Additionally, on the basis of Lu–Hf isotopic data, we reveal the pre-Triassic crustal growth history for the NCC. In comparison among the three crustal growth curves obtained from modern river sands, our samples, and the Proterozoic sedimentary rocks, we realize that old components are apparently underestimated by zircons from the younger sedimentary rocks and modern river sands. Hence, cautions should be taken when using this method to investigate growth history of continental crust.  相似文献   

13.
《International Geology Review》2012,54(16):2036-2056
ABSTRACT

The Chinese Southwest Tianshan Orogenic Belt is located along the boundary between the Central Asian Orogenic Belt (CAOB) and the Tarim Block (TB), NW China. It records the convergence of the Tarim Block and the Middle Tianshan, and is, therefore, a crucial region for understanding the Eurasia continental growth and evolution. The Wulagen (geographical name) metasedimentary rocks of the Wuqia area (mainly metamorphic sandstones and mica schists) form one of the metamorphic terranes in the Southwestern Tianshan Orogenic Belt. The geochronology of these rocks is poorly known, which hampers our understanding of the tectonic evolution of the belt. We analyzed 517 zircon grains for detrital zircon U–Pb dating and 93 zircon grains for in situ Lu–Hf isotopic compositions from the Wulagen metasedimentary rocks. The analyzed zircon grains yield Neoarchean to late Paleozoic U–Pb ages with major age peaks at ~2543 Ma, 1814 Ma, 830 Ma, 460 Ma, and the youngest cluster of zircon (magmatogene) ages is 395 Ma. The zircon U–Pb data show that the late Paleozoic (Early Devonian) is the maximum depositional age of the Wulagen metasedimentary rocks, rather than the previously considered Precambrian period. The zircons with Paleozoic ages yield εHf(t) values of ?22.0 to +11.3 and two-stage model ages (TDM2) of 3.95 to 1.30 Ga, suggesting that the parental magmas were formed from partial melting of pre-existing crustal rocks. Our zircon U–Pb geochronology and Hf isotopic data indicate the major source regions for the Wulagen metasedimentary rocks was the Kyrgyzstan North Tianshan. The zircon age population of 600–400 Ma (peak at ~460 Ma) has negative εHf(t) values (?15.0 to ?0.6) and Mesoproterozoic two-stage model ages, suggesting that the early Paleozoic magmatism resulted mainly from the melting of ancient crust, which played an important role in crustal evolution in the southern CAOB.  相似文献   

14.
The Great Xing’an Range in Northeast China is located in the eastern part of the Central Asian Orogenic Belt. From north to south, the Great Xing’an Range is divided into the Erguna, Xing’an, and Songliao blocks. Previous U–Pb zircon geochronology results have revealed that some ‘Precambrian metamorphic rocks’ in the Xing’an block have Phanerozoic protolith ages, questioning whether Precambrian basement exists in the Xing’an block. We present laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) U–Pb dating results for zircons from suspected Precambrian metamorphic rocks in the Xing’an block. Meta-rhyolites of the Xinkailing Group in Nenjiang yield magmatic ages of 355.8 Ma. Detrital zircons from phyllites of the Xinkailing Group in Duobaoshan yield populations of ca. 1505, ca. 810, and ca. 485 Ma, with the youngest peak constraining its depositional age to be <485 Ma. Zircons from amphibolitic gneisses of the Xinkailing Group in Nenjiang have magmatic ages of 308.6 Ma. Mylonitic granites of the Xinkailing Group in Nenjiang have zircon magmatic ages of 164 Ma. Detrital zircons from two-mica quartz schists of the Luomahu Group in the Galashan Forest yield ca. 2419, ca. 1789, ca. 801, ca. 536, ca. 480, and ca. 420 Ma, with the youngest peak indicating its depositional age as <420 Ma. Detrital zircons from mylonitized sericite–chlorite schist of the Ergunhe Formation in Taerqi yield populations of 982–948, ca. 519, and ca. 410 Ma, with the youngest peak demonstrating that its depositional age is <410 Ma. These zircon ages for a range of lithologies show that the Great Xing’an Range metamorphic rocks formed during the Phanerozoic (164–485 Ma) and that this crust is mostly Palaeozoic. Based on these results and published data, we conclude that there is no evidence of Precambrian metamorphic basement in the Xing’an block. In summary, the age data indicate that Precambrian metamorphic basement may not exist in the Xing’an region.  相似文献   

15.
A typical feature of the Precambrian complexes of the Kokshetau, Ishkeolmess, Erementau-Niyaz, and Aktau-Dzhungaria massifs of Northern and Central Kazakhstan is the presence of the end Mesoproterozoic-beginning of the Neoproterozoic quartzite-schist sequences in these sections. The lower and upper parts of these sequences are mostly composed of schists with interlayers of quartzites and marbles and of quartzitic sandstones, respectively. It is suggested that the quartzite-schist sequences represent the sub-platform cover of a large continental block and were formed in the regressive basin with widely abundant facies of submarine deltas and a littoral shoal. The presence of horizons and the lenses enriched in zircon-rutile heavy concentrate with the amount of accessory minerals of 10-70% characterizes the quartzite-schist sections of the Kokshetau and Erementau-Niyaz massifs. The U-Pb age of zircons from one such locality in the central part of the Erementau-Niyaz massif was analyzed by LA-ICP-MS. The Concordia ages of zircons are in the intervals 1041 ± 13-1519 ± 14, 1623 ± 14-1931 ± 14, and 2691 ± 14-2746 ± 14 Ma. One age was 2850 ± 14 Ma. The age distribution is characterized by clear peaks of 1.08, 1.20. 1.34, 1.46, 1.65, 1.89, and 2.70 Ga and weak peaks of 1.13 and 1.68 Ga. The age of the majority of zircons ranges from 1309 ± 14 to 1519 ± 14 Ma. Our data indicate that mostly Neoproterozoic rocks with a subordinate role of Paleoproterozoic and Neoarchean complexes served the feeding sources for the quartzite-schist sequence of the Erementau-Niyaz massif. The Mesoproterozoic and Paleoproterozoic events identified for the detrital zircons of the Erementau-Niyaz massif are completely manifested only in Laurentia. In the first approximation, these events coincide with the assembly and breakup of the Columbia/Nuna supercontinent (～1650–1580 and 1450–1380 Ma) and assembly of the Rodinia supercontinent (1300–900 Ma).  相似文献   

16.
The paleoposition of North China Craton in Rodinia has long been in controversial. This paper mainly focuses on the U–Pb geochronological studies of detrital zircons obtained from Bayan Obo Group exposed in the Shangdu area, Inner Mongolia, aiming to provide more information for interprating this problem. Based on the acquired data, this paper comes to the following conclusions. Firstly, the depositional age of Bayan Obo Group might be from Meso– to Neoproterozoic according to the zircons U–Pb dating results. The lower succession of this group, namely Dulahala and Jianshan formations deposited between 1800 and 1650 Ma. The Halahuogete and Bilute formations deposited between 1500 and 1350 Ma. For Baiyinbaolage and Hujiertu formations, their depositional age was 1250–900 Ma. Secondly, for the provenance of Bayan Obo Group, this paper believes detrital zircons with age of 2.51–2.71 Ga and 2.00–2.48 Ga were from Guyang, Xi Ulanbulang and Zhuozi area; the Khondalite Belt provided detrital zircons with age of 1.95–1.80 Ga; zircons with age of 1.60–1.75 Ga might come from granitic rocks in Miyun Area. The magmatism after 1.60 Ga was rarely recorded in the NCC, therefore those zircons with ages younger than 1.60 Ga might come from outside of NCC. The magmatism with the same age existed in Baltic, Amazonia and Laurentia. Based on previous paleomagnetic researches, this paper proposes that NCC might receive detritus from Baltic during 1560–1350 Ma and had affinity with Laurentia and Amazonia at ～0.9 Ga in Rodinia. Baltic, Amazonia and Laurentia might be potential provenances for non–NCC detritus in Bayan Obo Group.  相似文献   

17.
传统认为志留系巴龙贡噶尔组广泛分布于南祁连地区,近年来在其中解体出了新元古代拐杖山岩群,对其开展锆石年龄研究对了解该地层的沉积时代、物源性质以及与邻近板块的亲缘性具有重要意义。本文选取党河南山地区拐杖山组岩群中的黑云斜长石英片岩和石英片岩,进行LA-ICP-MS锆石U-Pb定年并讨论其地质意义。实验结果表明:由下及上碎屑锆石样品的U-Pb测年的最大沉积年龄分别为-794Ma、-746Ma和-713Ma,表明该变质地层至少沉积于-794Ma之后,在-740Ma时期伴有火山活动,并且部分地层可能沉积于-713Ma以后,时代应划归为新元古代。样品碎屑锆石以867-700Ma年龄区间最为集中,表明全吉地块与中祁连地块的基底岩系可能作为源区为拐杖山岩群提供了碎屑物质,同时响应了Rodinia超大陆裂解事件。通过与全吉地块、中祁连地块、柴达木地块、华北板块、澳大利亚板块以及扬子板块的碎屑锆石频谱对比,南祁连地区与其周缘地块以及扬子板块在元古宙时期显示了较好的亲缘关系,但其物源主要来自全吉地块与中祁连地块,而与扬子地块关联较小。  相似文献   

18.
In situ U–Pb dating and Hf isotopic of detrital zircons from beach sediments of Yalong Bay were analyzed to trace sedimentary provenance and reveal the crustal evolution of Hainan Island in South China. The grain size distribution of the sediments displays a clear single-peak feature, indicating the sediments were formed under the same condition of hydrodynamic force. The detrital zircons had Th/U ratios of greater than 0.1, and REE pattern displayed a positive Ce anomaly and a negative Eu anomaly, indicating that these zircons are predominantly of magmatic origin. The U–Pb spectrum of detrital zircons mainly peaked at the Yanshanian (96–185 Ma), Hercynian–Indosinian (222–345 Ma) and Caledonian (421–477 Ma). A portion of the detrital zircons were of Neoproterozoic origin (728–1,003 Ma), which revealed that the basement in the eastern region of Hainan Island was mainly of Neoproterozoic, with rare Archean materials. The positive ε Hf(t) values (0 to +10.1) of the Neoproterozoic detrital zircons indicated that the juvenile crust grew in the southeastern Hainan Island mainly during the Neoproterozoic period. The Neoproterozoic orogeny in the southeastern part of the island (0.7–1.0 Ga) occurred later than in the northwestern region of the island (1.0–1.4 Ga). Importantly, the Grenvillian orogeny in the southeastern area of Hainan Island shared the same timing with that of the western Cathaysia Block; i.e., both areas concurrently underwent this orogenic event, thereby forming a part of the Rodinia supercontinent. Afterwards, the crust experienced remelting and reworking during the Caledonian Hercynian–Indosinianand Yanshanian accompanied by the growth of a small amount of juvenile crust.  相似文献   

19.
运用LA-ICP-MS锆石U-Pb年代学方法,分析探讨了鄂尔多斯盆地南缘南曹德组和庄河沟组的沉积时代、物源特征及其所处的华北(鄂尔多斯地块)与北秦岭地体之间的构造演化关系。结果表明:两件砂岩样品的碎屑锆石年龄谱基本一致,测年数据集中分布在820~995 Ma(n=13)、1041~1203 Ma(n=23)、1223~1451 Ma(n=36)、1458~1650 Ma(n=24)、1659~1935 Ma(n=39)、2017~2445 Ma(n=7)6个区间,对应的峰值年龄分别接近832Ma、1120 Ma、1330 Ma、1590 Ma、1856 Ma和2090 Ma。这与邻区经典的震旦系正目观组和罗圈组具有相似的碎屑锆石年龄谱特征,年轻主峰年龄832Ma,包含有4个820~834Ma的年轻单颗粒锆石年龄,显著有别于以往认为与之可比的研究区近邻剖面锆石U-Pb高频主峰年龄主要集中在454Ma的奥陶系平凉组,由此认为南曹德组和庄河沟组应属于新元古代晚期832Ma之后或震旦纪的沉积岩石单元。锆石U-Pb年龄谱的区域对比进一步揭示,南曹德组和庄河沟组的滨浅海沉积碎屑物源明显具有来自华北(鄂尔多斯)陆块与北秦岭(杂岩)地体的双向混合物源特征,表明华北陆块与北秦岭地体至少在832Ma之前的格林威尔晚期已经碰撞拼合为一体,随后在新元古代晚期拼合大陆边缘接受了大致与Rodinia超大陆裂解事件相当的陆缘海相碎屑岩沉积。  相似文献   

20.
《Gondwana Research》2015,28(4):1392-1406
The Ider Complex of the Tarbagatai Block in northwestern Mongolia is part of a Precambrian microcontinental terrane in the Central Asian Orogen Belt and has experienced a polymetamorphic tectono-metamorphic evolution. We have investigated an enderbitic gneiss, derived from a quartz diorite and a charnockite, derived from a leucogranite, and zircon SHRIMP data reveal late Archaean protolith ages of 2520–2546 Ma for these rocks. Metamorphic overgrowth on these zircons as well as newly-formed metamorphic zircons document a high-temperature metamorphic event (T = 930–950 °C) at about 1855–1860 Ma. Nd whole-rock isotopic systematics show these and other gneisses of the Ider Complex straddling the CHUR-line in a Nd isotope evolution diagram, suggesting both crustal reworking and input of some juvenile material, with Nd model ages ranging between ca. 2.5 and 3.1 Ga. Hf-in-zircon isotopic data provide a similar pattern and also yielded Archaean Hf crustal model ages. The metamorphic zircons seem to have inherited their Hf isotopic composition from the igneous grains, suggesting a complex process of dissolution, transportation, and re-precipitation involving a fluid phase during high-grade metamorphism. The zircon age patterns do not make it possible to unambiguously assign the Tarbagatai Block to any of the cratons bordering the Central Asian Orogenic Belt, since age peaks at ca. 2520–2550 and ca. 1860 Ma are common in the Siberian, North China and Tarim cratons.  相似文献   

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