Sedimentary record of Jurassic northward subduction of the Bangong–Nujiang Ocean: insights from detrital zircons

The subduction polarity and related arc–magmatic evolutional history of the Bangong–Nujiang Ocean, which separated the South Qiangtang terrane to the north from the North Lhasa terrane to the south during the Mesozoic, remain debated. This study tries to reconstruct the subduction and evolution of the Bangong–Nujiang Ocean on the basis of U–Pb and Hf isotopic analyses of detrital zircons in samples from sedimentary rocks of the middle-western section of the Bangong–Nujiang suture zone in Gerze County, central Tibet. The Middle Jurassic Muggargangri Group in the Bangong–Nujiang suture zone was deposited in a deep-sea basin setting on an active continental margin. The Late Jurassic strata, such as the Sewa Formation, are widely distributed in the South Qiangtang terrane and represent deposition on a shelf. The Early Cretaceous Shamuluo Formation in the Bangong–Nujiang suture zone unconformably overlies the Muggargangri Group and was probably deposited in a residual marine basin setting. The detrital zircons of the Muggargangri Group contain seven U–Pb age populations: 2.6–2.4 Ga, 1.95–1.75 Ga, 950–900 Ma, 850–800 Ma, 650–550 Ma, 480–420 Ma, and 350–250 Ma, which is similar to the age populations in sedimentary rocks of the South Qiangtang terrane. In addition, the age spectra of the Shamuluo Formation are similar to those of the Muggargangri Group, indicating that both had a northern terrane provenance, which is conformed by the north-to-south palaeocurrent. This provenance indicates northward subduction of the Bangong–Nujiang oceanic crust. In contrast, two samples from the Sewa Formation yield variable age distributions: the lower sample has age populations similar to those of the South Qiangtang terrane, whereas the upper possesses only one age cluster with a peak at ca. 156 Ma. Moreover, the majority of the late Mesozoic detrital zircons are characterized by weakly positive εHf(t) values that are similar to those of magmatic zircons from arc magmatic rocks in the South Qiangtang terrane. The findings, together with information from the record of magmatism, indicate that the earliest prevalent arc magmatism occurred during the Early Jurassic (ca. 185 Ma) and that the principal arc–magmatic stage occurred during the Middle–Late Jurassic (ca. 170–150 Ma). The magmatic gap and scarcity of detrital zircons at ca. 140–130 Ma likely indicate collision between the Qiangtang and Lhasa terranes. The late Early Cretaceous (ca. 125–100 Ma) magmatism on both sides of the Bangong–Nujiang suture zone was probably related to slab break-off or lithospheric delamination after closure of the Bangong–Nujiang Ocean.     

Towards a more complete record of magmatism and exhumation in continental arcs,using detrital fission-track thermochrometry

The NE Asian margin was the locus of an Andean-style subduction zone during most of the Mesozoic and Cenozoic. The Ukelayat flysch is a 10 to 15 km thick section of marine turbidites that were deposited in a 500 km long forearc basin along the outboard edge of this convergent margin. It was structurally overridden during the early Tertiary by an obducted island arc, the Olytorsky terrane. We present new fission-track (FT) grain ages from unreset detrital zircons. These data provide precise information about depositional age of the Ukelayat and the temporal evolution of the Asian margin continental arc, which provided much of the sediment for the Ukalayat. Because all sandstones contain a large fraction of first-cycle volcanic zircons (euhedral, colorless), we infer that the youngest component of the FT grain age distribution, designated P1, closely approximates the time of deposition. Twenty-seven samples have yielded P1 ages ranging from ~44 to 88 Ma, which indicates continuous magmatic activity in the arc from the Late Cretaceous to Middle Eocene. A second component (P2) records progressive exhumation of the basement to the Okhotsk-Chukotka arc. The difference between P1 and P2 ages indicates steady exhumation at ~200–400 m/Myr from ~90 to 44 Ma. This finding implies the removal of 9 to 18 km of rock in the most deeply exhumed parts of the source region. A change in exhumation rates at ~70 Ma may coincide with an eastward shift in the locus of volcanism from the Okhotsk-Chukotka arc to the younger Western Kamchatka-Koryak arc.     

Detrital zircon geochronology analysis of the Late Mesozoic deposition in the Turpan‐Hami basin: Implications for the uplift history of the Eastern Tian Shan,north‐western China

Analysing the provenance changes of synorogenic sediments in the Turpan‐Hami basin by detrital zircon geochronology is an efficient tool to examine the uplift and erosion history of the easternmost Tian Shan. We present detrital zircon U‐Pb analysis from nine samples that were collected within marginal lacustrine Middle‐Late Jurassic and aeolian‐fluvial Early Cretaceous strata in the basin. Middle‐Early Jurassic (159–172 Ma) zircons deriving from the southern Junggar dominated the Middle Jurassic sample from the western Turpan‐Hami basin, whereas Permian‐Carboniferous (270–330 Ma) zircons from the Bogda mountains were dominant in the Late Jurassic to Early Cretaceous samples. Devonian‐Silurian (400–420 Ma) and Triassic (235–259 Ma) zircons from the Jueluotage and Harlik mountains constituted the subordinate age groups in the Late Jurassic and Early Cretaceous samples from the eastern basin respectively. These provenance transitions provide evidence for uplift of the Bogda mountains in the Late Jurassic and the Harlik mountains since the Early Cretaceous.     

Study and geological implication of detrital zircons in Shuibei Formation of Early Jurassic in Zhangshudun of northeastern Jiangxi Province

The Early Jurassic basin in Zhangshudun of northeastern Jiangxi Province is located in the southeastern part of Jiangnan orogeny, and revealing the basin depositional source is of great importance for understanding and discussing the orogenic events and ancient geography during Early Mesozoic. The research of petrography, detrital zircons U-Pb geochronology, Lu-Hf isotope geochemistry of Early Jurassic clastic rocks was conducted in this paper. The results show that the Early Jurassic Shuibei Formation includes molasse-like deposits and fluviatile-lacustrine facies, and the detrital zircons U-Pb ages are within the wide scope of 2 431~263 Ma, with no existence of synsedimentary or pensynsedimentary detrital zircons. The detrital zircons display a very obvious peak age in Early Paleozoic of 420~380 Ma, with ε_Hf(t) values between -10.7 and -3 and T_DM^C values between 2.08 and 1.58 Ga. The weak peak ages of 370~355 Ma and 858~663 Ma are displayed in Late Paleozoic and Neoproterozoic,respectively, with ε_Hf(t) values of -18.8 to -6.7 and T_DM^C values of 2.08 to 1.58 Ga. The detrital zircons also contain a few Early Mesozoic (263 Ma) and Paleo-Meso proterozoic (2 431~1 224 Ma) ages. The detrital zircons ages and Lu-Hf isotope are similar with geological entities in northwestern Wuyi area of Cathaysia Block, while they are obviously different from the ages of the geological body in southeastern Yangtze region. The detrital materials are mainly from Early Cambrian basement and Paleozoic geological body northwestern Wuyi area. While little detrital rocks may come from northwestern Zhejiang with sedimentary characters of passive continental margin. Combined with the comprehensive regional research results of Early Mesozoic basin, the authors conclude that the southeastern Jingdezhen-Huangshan of eastern Jiangnan orogenic belt was not uplifting with erosion in Early and Middle Jurassic, and the Mesozoic structural-magmatic activities in the inland of South China were the tectonic response to the dive and influx of multiplates. The uplift in the southezstern part of South China caused by the subduction of the paleo-pacific plate to the East Asian continent from the Late Triassic to Early Jurassic can provide provenance for the inland basin, and the tectonic constitution at the turn of the Early-Middle Jurassic has been transformed into the subduction of the paleo-pacific plate.     

赣东北樟树墩早侏罗世水北组碎屑锆石研究及其地质意义

赣东北樟树墩地区早侏罗世盆地处于江南造山带东南缘,揭示盆地沉积物质来源对于认识和探讨周缘早中生代造山事件和古地理格局具有重要意义。对樟树墩早侏罗世盆地开展了岩相学、碎屑锆石U-Pb年代学和Lu-Hf同位素研究。结果表明: 盆地为类磨拉石建造与内陆湖沼含煤建造,碎屑锆石年龄跨度大(2 431~263 Ma),未出现同沉积或准同沉积的碎屑锆石; 碎屑锆石年龄呈现极强的早古生代峰值(420~380 Ma,ε_Hf(t)为-10.7~-3.0, T_DM^C为2.08~1.58 Ga)、弱的新元古代峰值(858~663 Ma,ε_Hf(t)为-18.8~-6.7, T_DM^C为2.79~2.09 Ga)和晚古生代峰值(370~355 Ma),另有少量早中生代((263±5) Ma)、中—古元古代(2 431~1 224 Ma)碎屑锆石记录。碎屑锆石年龄和Hf同位素组成与华夏地块西北武夷山地区所出露地质体组成相似,而与扬子东南缘地质体组成存在显著差异,其碎屑物质主要来自陆内西北武夷山地区前寒武纪基底和古生代地质体,少量碎屑物质可能来源于浙西北地区,具有被动型大陆边缘盆地沉积特征。综合区域上早中生代盆地研究成果,认为江南造山带东段景德镇—黄山东南在早—中侏罗世并未整体隆升剥蚀,华南内陆中生代的构造-岩浆活动是其周缘多板块俯冲汇聚的构造响应,晚三叠世—早侏罗世古太平洋板块向东亚大陆的俯冲造成华南东南部隆升,使其开始为内陆盆地提供物源,至早—中侏罗世之交构造体制转换为古太平洋板块的俯冲消减。     

Mesozoic syncollision siliciclastic sediments of the Bols’shoi Lyakhov Island (New Siberian Islands)

Graywackes and shales of the Bols’shoi Lyakhov Island originally attributed to the Mesozoic were subsequently considered based on microfossils as the Late Proterozoic in age. At present, these sediments in the greater part of the island are dated back to the Permian based on palynological assemblages. In the examined area of the island, this siliciclastic complex is intensely deformed and tectonically juxtaposed with blocks of oceanic and island-arc rocks exhumed along the South Anyui suture. The complex is largely composed of turbidites with members displaying hummocky cross-stratification. The studied mineral and geochemical characteristics of the rocks defined three provenances of clastic material: volcanic island arc, sedimentary cover and/or basement of the ancient platform, and exotic blocks of oceanic and island-arc rocks such as serpentinites and amphibolites. All the rock associations represent elements of an orogenic structure that originated by collision of the New Siberian continental block with the Anyui-Svyatoi Nos island arc. Flyschoid sediments accumulated in a foredeep in front of the latter structure in the course of collision. The Late Jurassic volcanics belonging to the Anyui-Svyatoi Nos island arc determine the lower age limit of syncollision siliciclastic rocks. Presence of Late Jurassic zircons in sandstones of the flyschoid sequence in Bols’shoi Lyakhov Island is confirmed by the fission-track dating. The upper age limit is determined by the Aptian-Albian postcollision granites and diorites intruding the siliciclastic complex. Consequently, the flyschoid sequence is within stratigraphic range from the terminal Late Jurassic to Neocomian. It appears that Permian age of sediments suggested earlier is based on redeposited organic remains. The same Late Jurassic-Neocomian age and lithology are characteristic of fossiliferous siliciclastic sequences of the Stolbovoi and Malyi Lyakhov islands, the New Siberian Archipelago, and of graywackes in the South Anyui area in Chukchi Peninsula. All these sediments accumulated in a spacious foredeep that formed in the course the late Cimmerian orogeny along the southern margin of the Arctic continental block.     

班公湖—怒江洋复理石沉积时代:来自改则县亚多村碎屑锆石的制约

木嘎岗日岩群是班公湖?怒江洋的洋盆沉积记录,它的时代归属对约束班公湖?怒江洋的演化具有重要意义.然而自命名以来,木嘎岗日岩群的时代一直争议较大.以班公湖?怒江缝合带中段改则县亚多村一带的木嘎岗日岩群为研究对象,对其进行岩石学和碎屑锆石年代学方面的研究.该区木嘎岗日岩群以薄层砂岩和页岩互层为主,具复理石沉积特征.砂岩碎屑锆石年代学分析结果显示,最小碎屑锆石为149 Ma,最小年龄峰值为156 Ma,指示该地区木嘎岗日岩群的时代为晚侏罗世?早白垩世.在此基础上,对班公湖?怒江缝合带中西段内不同地区木嘎岗日岩群的年龄信息进行搜集和整理,结果显示,木嘎岗日岩群的时代跨度至少为晚三叠世?早白垩世,表明班公湖?怒江洋中西段在晚三叠世?早白垩世内可能是连续演化的.      

Sedimentary response to the paleogeographic and tectonic evolution of the southern North China Craton during the late Paleozoic and Mesozoic

With the aim of constraining the influence of the surrounding plates on the Late Paleozoic–Mesozoic paleogeographic and tectonic evolution of the southern North China Craton (NCC), we undertook new U–Pb and Hf isotope data for detrital zircons obtained from ten samples of upper Paleozoic to Mesozoic sediments in the Luoyang Basin and Dengfeng area. Samples of upper Paleozoic to Mesozoic strata were obtained from the Taiyuan, Xiashihezi, Shangshihezi, Shiqianfeng, Ermaying, Shangyoufangzhuang, Upper Jurassic unnamed, and Lower Cretaceous unnamed formations (from oldest to youngest). On the basis of the youngest zircon ages, combined with the age-diagnostic fossils, and volcanic interlayer, we propose that the Taiyuan Formation (youngest zircon age of 439 Ma) formed during the Late Carboniferous and Early Permian, the Xiashihezi Formation (276 Ma) during the Early Permian, the Shangshihezi (376 Ma) and Shiqianfeng (279 Ma) formations during the Middle–Late Permian, the Ermaying Group (232 Ma) and Shangyoufangzhuang Formation (230 and 210 Ma) during the Late Triassic, the Jurassic unnamed formation (154 Ma) during the Late Jurassic, and the Cretaceous unnamed formation (158 Ma) during the Early Cretaceous. These results, together with previously published data, indicate that: (1) Upper Carboniferous–Lower Permian sandstones were sourced from the Northern Qinling Orogen (NQO); (2) Lower Permian sandstones were formed mainly from material derived from the Yinshan–Yanshan Orogenic Belt (YYOB) on the northern margin of the NCC with only minor material from the NQO; (3) Middle–Upper Permian sandstones were derived primarily from the NQO, with only a small contribution from the YYOB; (4) Upper Triassic sandstones were sourced mainly from the YYOB and contain only minor amounts of material from the NQO; (5) Upper Jurassic sandstones were derived from material sourced from the NQO; and (6) Lower Cretaceous conglomerate was formed mainly from recycled earlier detritus.The provenance shift in the Upper Carboniferous–Mesozoic sediments within the study area indicates that the YYOB was strongly uplifted twice, first in relation to subduction of the Paleo-Asian Ocean Plate beneath the northern margin of the NCC during the Early Permian, and subsequently in relation to collision between the southern Mongolian Plate and the northern margin of the NCC during the Late Triassic. The three episodes of tectonic uplift of the NQO were probably related to collision between the North and South Qinling terranes, northward subduction of the Mianlue Ocean Plate, and collision between the Yangtze Craton and the southern margin of the NCC during the Late Carboniferous–Early Permian, Middle–Late Permian, and Late Jurassic, respectively. The southern margin of the central NCC was rapidly uplifted and eroded during the Early Cretaceous.     

First fission-track dating of zircons from Mesozoic complexes of the Crimea

The fission-track dating of detrital zircon from Mesozoic terrigenous complexes of the Crimean mountains has been carried out for the first time. A young zircon population from the Tavria Group of sandstones of the Yaman ravine was dated at 220.1 ± 12.6 Ma, and the zircon population from the same deposits of the Crimea’s southern coast, at 193.6 ± 13.1, 167.1 ± 12.1, and 154.0 ± 10.2 Ma. Sandstones from the lowermost parts of the Demerdzhi Formation on Mount Yuzhnaya Demerdzhi comprise the Middle Jurassic young zircon population (169.9 ± 8.6 Ma). The age of the young zircon population from the Chenka Formation in the region of the Settlement of Observatoriya corresponds to the initial Middle Jurassic (178.9 ± 9.1 Ma). The timing of the cooling of the Mount Kastel massif was established at 149.0 ± 10.9 Ma. In all the considered cases, the age of terrigenous complexes is close to the age of enclosed zircons. Volcanic and/or magmatic rocks that formed synchronously with accumulation of terrigenous complexes in the sedimentary basin are likely to have been sources of zircons. Hence, the data obtained allow the timing of the Triassic-Jurassic magmatism in the Crimean mountains to be refined and three stages of magmatism to be distinguished: Late Triassic (Carnian?), poorly expressed Early Jurassic, and Middle Jurassic (Aalenian-Bathonian).     

Late Palaeozoic and early Mesozoic tectonic and palaeogeographic evolution of central China: evidence from U–Pb and Lu–Hf isotope systematics of detrital zircons from the western Qinling region

The western Qinling region of central China is situated centrally in the Kunlun, Qilian, Qinling, Longmenshan, and Songpan–Ganzi orogens. Late Palaeozoic and Early Mesozoic sediments deposited here may provide keys to understanding the tectonic evolution of the Palaeo-Tethys and collision of the North China and Yangtze Cratons. We conducted in situ U–Pb and Lu–Hf isotope analyses of 568 detrital zircons collected from Upper Palaeozoic to Mesozoic sandstones in the central Qinling block, Taohe depression, and Bailongjiang block in western Qinling to constrain the sources of these sandstones. Our results reveal that the Bailongjiang block has affinities with the Yangtze Craton, from which it may have been rifted. Therefore, the Palaeo-Tethyan Animaqen suture between the two cratons lies north of the Bailongjiang block. We identified the North China Craton as the main source for Triassic flysch in central China. It is possible that the Bailongjiang block could have blocked detritus shed from the North China Craton into the main depositional basins in the Songpan–Ganzi area. The dominance of 300–200 Ma detrital zircons of metamorphic origin in Lower Jurassic sandstones indicates that the Dabie–Qinling orogen was elevated during Early Jurassic time. In addition, our Lu–Hf isotopic results also reveal that Phanerozoic igneous rocks in central China were mostly products of crustal reworking with insignificant formation of juvenile crust.     

华南中生代大地构造研究新进展

华南地区中生代构造动力体制经历了从特提斯构造域向滨太平洋构造域的转换,由此产生了强烈的陆内造山作用和岩浆活动,形成了复杂构造组合的晚中生代陆内造山带和火成岩省。本项研究在下列几个方面取得了新的进展:(1)通过对雪峰山地区沅麻盆地的野外调查和构造测量,确定了该盆地晚中生代-早新生代5期构造应力场及其演替序列:中晚侏罗世近W—E向挤压、早白垩世NW—SE向伸展、早白垩世中晚期NW—SE向挤压、晚白垩世近N—S向伸展、古近纪晚期NE—SW向挤压。构造应力场方向的变化记录了不同板缘的动力作用对该区的影响。(2)识别了湖南地区晚古生代-早中生代海相地层中发育的横跨叠加褶皱构造,并基于地层接触关系和已有火成岩同位素年代学数据分析,认为该地区横跨叠加褶皱构造记录了中生代两期构造挤压和地壳增厚事件:早期近东西向褶皱构造是对三叠纪华南地块南北边缘大陆碰撞和增生作用的远程响应,晚期NE—NNE向褶皱构造则是对中晚侏罗世古太平洋板块向华南大陆之下低角度俯冲作用的变形响应。(3)对湖南衡山西缘拆离断裂带的变形结构和运动学特征进行了详细的调查和构造测量,确定了衡山变质核杂岩构造,并对拆离带中韧性剪切变形的钠长岩脉的锆石进行了SHRIMP U-Pb测年,从而确定了华南地区伸展构造的起始时代约137 Ma,即早白垩世早中期。(4)通过锆石U-Pb年代学测试分析,揭示了东南沿海长乐—南澳构造带早白垩世2期构造-岩浆事件:早期(147~135 Ma)表现为强烈的混合岩化作用和深熔作用形成的片麻状花岗岩、花岗片麻岩等;晚期(135~117 Ma)岩浆岩以含石榴子石花岗岩为主。这个结果表明东南沿海构造带是晚中生代陆缘造山带,造山作用可能起始于晚侏罗世,于早白垩世早中期(135 Ma)以来发生伸展垮塌。在上述研究结果的基础上,探讨了华南地区三叠纪"印支运动"和中、晚侏罗世"燕山运动"的表现及其产生的板块构造动力体制及其转换时代、早白垩世从挤压构造应力体制向伸展构造应力体制转变的时间节点。     

Detrital zircon U–Pb ages along the Yarlung-Tsangpo suture zone, Tibet: Implications for oblique convergence and collision between India and Asia

Age-dating of detrital zircons from 22 samples collected along, and adjacent to, the Yarlung-Tsangpo suture zone, southern Tibet provides distinctive age-spectra that characterize important tectonostratigraphic units. Comparisons with data from Nepal, northern India and the Lhasa and Qiangtang terranes of central Tibet constrain possible sources of sediment, and the history of tectonic interactions.Sedimentary rocks in the Cretaceous–Paleogene Xigaze terrane exhibit strong Mesozoic detrital zircon peaks (120 and 170 Ma) together with considerable older inheritance in conglomeratic units. This forearc basin succession developed in association with a continental volcanic arc hinterland in response to Neotethyan subduction under the southern edge of the Eurasia. Conspicuous sediment/source hinterland mismatches suggest that plate convergence along this continental margin was oblique during the Late Cretaceous. The forearc region may have been translated > 500 km dextrally from an original location nearer to Myanmar.Tethyan Himalayan sediments on the other side of the Yarlung-Tsangpo suture zone reveal similar older inheritance and although Cretaceous sediments formed 1000s of km and across at least one plate boundary from those in the Xigaze terrane they too contain an appreciable mid-Early Cretaceous (123 Ma) component. In this case it is attributed to volcanism associated with Gondwana breakup.Sedimentary overlap assemblages reveal interactions between colliding terranes. Paleocene Liuqu conglomerates contain a cryptic record of Late Jurassic and Cretaceous rock units that appear to have foundered during a Paleocene collision event prior the main India–Asia collision. Detrital zircons as young as 37 Ma from the upper Oligocene post-collisional Gangrinboche conglomerates indicate that subduction-related convergent margin magmatism continued through until at least Middle and probably Late Eocene along the southern margin of Eurasia (Lhasa terrane).Although the ages of detrital zircons in some units appear compatible with more than one potential source with care other geological relationships can be used to further constrain some linkages and eliminate others. The results document various ocean closure and collision events and when combined with other geological information this new dataset permits a more refined understanding of the time–space evolution of the Cenozoic India–Asia collision system.     

西南天山前陆盆地侏罗纪-白垩纪盆山格局——来自碎屑锆石年代学的证据

目前对天山地区,特别是天山南缘中生代盆山格局认识尚存分歧。本文着眼于侏罗纪-白垩纪这一盆山演化关键阶段,利用碎屑锆石LA-ICP-MS U-Pb定年法对西南天山前陆盆地康苏剖面中侏罗统杨叶组、下白垩统克孜勒苏群沉积开展物源分析。发现中侏罗统杨叶组碎屑锆石U-Pb年龄分布于369~2687 Ma间,基本分布在369~404 Ma(约占4%)、418~501 Ma(约占19%)和544~2687 Ma(约占77%)3个范围;下白垩统克孜勒苏群碎屑锆石U-Pb年龄分布于243~2820 Ma间,集中于253~414 Ma(约占35%)、423~489 Ma(约占27%)和668~2820 Ma(约占37%)3个范围。中侏罗统碎屑锆石年龄分布范围广,各年龄组分均较突显,反映中侏罗世西南天山前缘流域体系宽广,天山内各主要源区均得到沟通,物源范围广阔。下白垩统克孜勒苏群锆石年龄分布明显集中,反映早白垩世西南天山前缘源区范围有所缩小。西南天山前缘与库车前陆盆地的物源构成在中侏罗世存在一定差异,而在早白垩世呈现相似特征。包括西南天山前陆盆地在内的天山南缘或于早白垩世经历一期小规模构造反转,导致山-盆构造分异与抬升-剥蚀增强。     

Early Mesozoic unroofing pattern of the Dabie Mountains (China): Constraints from the U-Pb detrital zircon geochronology and Si-in-white mica analysis of synorogenic sediments in the Jianghan Basin

This paper presents the results of an integrated U-Pb detrital zircon geochronology and Si-in-white mica analysis for synorogenic sediments in the Jianghan Basin to the south of the Dabie Orogen. The results provide an improved understanding of the provenance of these sediments and the unroofing pattern of the early Mesozoic Dabie Mountain. Si contents of detrital white micas range from 3.09 to 3.34 atoms pfu for the upper Triassic sandstones whereas 3.06 to 3.59 atoms pfu for the lower and middle Jurassic sandstones. The majority of detrital white micas in the lower Jurassic sandstones is phengitic and originated exclusively from the Dabie high- to ultrahigh- pressure rocks. The U-Pb dating results of the detrital zircons for seven samples suggest that these synorogenic sediments have a significant change of provenance from late Triassic to early and middle Jurassic. For the upper Triassic sandstone, the U-Pb age clusters of these zircons are characterized by ~ 420-450 Ma, ~ 750-820 Ma, ~ 1050-1200 Ma and ~ 2500 Ma with minor Luliangian (~ 1700–2000 Ma) components. In contrast, the zircon ages of the Jurassic sandstones are dominated by the Luliangian (~ 1700–2000 Ma) ages with only minor Caledonian (~ 420-450 Ma) and Greenville (~ 1050-1200 Ma) ages. In combination with other available geological data, it can be concluded that the Dabie HP-UHP rocks might initially be exposed to the surface at the beginning of early Jurassic (~ 190 Ma). The Jiangnan terrain (also named “Jiangnan old continental in Chinese) to the south of the Jianghan basin provided the predominant supply of upper Triassic sediments, whereas the Paleoproterozoic Yangtze crustal materials (overlying the present Dabie Complex at the time) were the important provenance of the Jurassic sediments in the Jianghan basin.     

Sedimentary provenance of the Hengyang and Mayang basins,SE China,and implications for the Mesozoic topographic change in South China Craton: Evidence from detrital zircon geochronology

Detrital zircon U–Pb data from sedimentary rocks in the Hengyang and Mayang basins, SE China reveal a change in basin provenance during or after Early Cretaceous. The results imply a provenance of the sediment from the North China Craton and Dabie Orogen for the Upper Triassic to Middle Jurassic sandstones and from the Indosinian granitic plutons in the South China Craton for the Lower Cretaceous sandstones. The 90–120 Ma age group in the Upper Cretaceous sandstones in the Hengyang Basin is correlated with Cretaceous volcanism along the southeastern margin of South China, suggesting a coastal mountain belt have existed during the Late Cretaceous. The sediment provenance of the basins and topographic evolution revealed by the geochronological data in this study are consistent with a Mesozoic tectonic setting from Early Mesozoic intra-continental compression through late Mesozoic Pacific Plate subduction in SE China.     

U–Pb dating of single detrital zircon grains from Mesozoic sandstone in the Beipiao Basin in the eastern Yan-Liao Orogenic Belt, China: provenance and correlation of tectonic evolution

Single grain U–Pb ages of sediments from the Beipiao Basin, Northeast China were conducted to determine the evolution of basin provenance. Zircons from a sandstone in the Upper Triassic Laohugou Formation yield a wide range of ages and, according to their U–Pb ages, fall into four groups: 209.3±4.0–304.2±4.9, 1565.5±71–2154±50, 2400±35–2499±9, 2512±11–2557±74 Ma. These ages indicate that the zircons were principally derived from Late Archean, Proterozoic and Late Paleozoic plutonic rocks. Intrusions in the Mongolian Accretion Belt and the northern margin of the North China Block (NCB) were probably the main source of the sediments in the basin, but the easterly Liaodong Block also provided minor detrital material, with lower U–Pb ages, during the Late Triassic. Most of the U–Pb ages from zircons collected from a sandstone in the Lower Jurassic Beipiao Formation range from 194.3±2.9 to 233.8±4.2 Ma, reflecting the major sediment source during the Early Jurassic. Zircons derived from Late Indosinian plutonic rocks increased, which suggests that the detritus was supplied mainly from the interior of the Yan-Liao Orogenic Belt, especially from the Liaodong Block. Late Indosinian zircons (200–230 Ma) were eroded and deposited in the Lower Jurassic Beipiao Formation, and this implies that intensive tectonic activation and uplift of the Yan-Liao Orogenic Belt in the Mesozoic commenced in the Late Indosinian.     

Jurassic-Cretaceous Basin-range Pattern in the Southwestern Tian Shan Foreland Basin: Evidence from Detrital U-Pb Zircon GeochronologyEI北大核心CSCD

The Mesozoic basin-range pattern in the Tian Shan area is actively debated, especially on the southern flank of the Tian Shan. This important and contrasting hypothesis involves an intracontinental foreland basin, and a passive subsiding basin characterized by a wide source area, a weak basin-range differentiation, as well as a positive physiographic feature. This study focuses on the critical stage of basin-range relationship and reports detrital zircon U-Pb ages from the sandstones of Middle Jurassic Yangye Formation and Lower Cretaceous Group collected from the Kangsu section, aiming to constrain the Mesozoic provenance of the southwestern Tian Shan foreland basin. The U-Pb isotopic ages of zircons from these two units of clastic rocks were obtained by using in situ LA-ICP-MS. The U-Pb ages of detrital zircons from the Middle Jurassic series range from 369 Ma to 2687 Ma and can be divided into three main groups: (1) 369-404 Ma (accounting for 4%), (2) 418-501 Ma (accounting for 19%), (3) 544-2687 Ma (accounting for 77%), and the zircon ages from the Lower Cretaceous series range from 243 Ma to 2820 Ma and can be divided into three groups: (1) 253-414 Ma (accounting for 35%), (2) 423-489 Ma (accounting for 27%), (3) 668-2820 Ma (accounting for 37%). All age groups are prominent in the Middle Jurassic sample, suggesting a large-scale drainage system and wide source area characterized by established connection between the basin and main sources. The distribution of U-Pb ages of detrital zircons from the Lower Cretaceous sample has more groups and reflects a shrink age in coeval source area. The southern flank of southwestern Tian Shan and the Kuqa rejuvenated foreland basin have difference sediment provenance during the Middle Jurassic, whereas in the Early Cretaceous they have similar sedimentary provenance. The southwestern Tian Shan foreland basin, as well as the other areas of the south margin of the Tian Shan underwent a minor tectonic inversion and adjustment throughout the Early Cretaceous, which led to an intension in basin-range differentiation and corresponding uplift-exhumation, and a deconstruction of the link between sedimentary piedmont and older basements distributed in interior of the mountain. © 2017, Science Press. All right reserved.     

孙吴-嘉荫盆地晚白垩世地层物源及构造背景

为揭示孙吴-嘉荫盆地晚白垩世富饶组和太平林场组的物源特征及其构造背景,对两组样品进行了碎屑锆石LA-ICP-MS U-Pb定年和地球化学特征研究.富饶组碎屑锆石55个测点产生以下年龄峰值:65 Ma、280 Ma和496 Ma,太平林场组碎屑锆石78个测点产生以下年龄峰值:98 Ma,189 Ma,240 Ma和488 Ma,表明富饶组和太平林场组具有混合物源的特征.Al₂O₃/TiO₂平均值分别为41.42和29.31,结合主量、微量及稀土元素特征和碎屑锆石峰值年龄,确定富饶组和太平林场组物源主要为晚中生代长英质火成岩和沉积岩.地球化学和区域构造演化特征共同揭示富饶组和太平林场组物源区构造背景为活动大陆边缘,区域内晚中生代岩浆事件、佳木斯地块北部麻山群及广泛分布的古生代花岗岩为盆地晚白垩世地层提供了沉积物源.      

Late Jurassic-Cretaceous fluvial evolution of central Africa: Insights from the Kasai-Congo Basin,Democratic Republic Congo

The Congo Basin in central Africa is one of the largest intracratonic sedimentary basins in the world. The geological knowledge of Congo Basin is mainly based on studies from the central part of the basin (“Cuvette Centrale”). We present the results of sedimentary provenance investigations of the Jurassic–Cretaceous strata from the southwestern part of the basin, called the Kasai region. This study combines sandstone petrography with U-Pb and Lu-Hf analyses of detrital zircons to assess the stratigraphy, sedimentary provenance and drainage history of the Upper Jurassic-Cretaceous strata in the Kasai region. The stratigraphy is subdivided into a single Upper Jurassic unit (J1) and four Cretaceous units (C1–C4). Petrographically, sandstones from all units except the conglomeratic C3 are texturally and compositionally mature, dominated by quartzarenite and subarkosic compositions. These characteristics can be attributed to considerable recycling of older sedimentary strata and crustal sources, along with long distance fluvial and aeolian processes. The analyses of fifteen detrital zircon samples from the Upper Jurassic–Cretaceous strata yielded mainly Archean and Proterozoic zircons. This result suggests that sandstones are likely sourced from the underlying Archean-Paleoproterozoic Congo–Kasai Craton and from nearby Proterozoic mobile belts, particularly the Irumide and Lufilian Belts to the south of the basin. The dominance of Archean and Proterozoic detrital zircons in Upper Jurassic–Cretaceous strata suggests that the Kasai portion of the Congo Basin experienced exhumation and erosion, which is possibly associated with far-field reactivation of Archean and Proterozoic structures during and following Gondwana rifting in the late Mesozoic. A large fluvial drainage network sourced from the south of the basin, is interpreted to have developed across central Africa during the Late Jurassic–Cretaceous. This fluvial system is believed to have flowed northward across the Congo Basin and ultimately drained into a wrench fault system called the Central African Shear Zone, which extends in an ENE direction from the Gulf of Guinea through Cameroon into Sudan and Kenya.     

鲁西隆起侏罗系碎屑主物源来自华北北缘:锆石U-Pb和Hf同位素年代学证据

鲁西隆起保存并出露比较完整的晚中生代沉积记录,是研究华北东部晚中生代构造演化的重要窗口。本文采用碎屑锆石LA-MC-ICP-MS测年方法分析鲁西隆起北缘淄川地区坊子组和三台组中的两个砂岩样品,以此探讨华北东部侏罗纪的沉积物源并约束构造古地理格架。两个砂岩样品具有近似的U-Pb年龄谱。古元古代和新太古代两组U-Pb年龄及其Hf同位素组成与广泛出露于北部的华北克拉通基底一致,根据缺乏新元古代中期(850～700 Ma)岩浆年龄和三叠纪变质年龄的事实,以此可以排除扬子板块以及现今临近于鲁西隆起东南部的苏鲁造山带物源。坊子组和三台组碎屑锆石显生宙年龄(393～256 Ma)记录的晚古生代岩浆活动均未发现于鲁西隆起及其邻近地区,而可以与大量出露于华北北缘及其北部的兴-蒙造山带的岩浆活动进行对比。此外,相当部分的显生宙碎屑锆石(183 Ma、462 Ma和324～154 Ma)具有正的ε_Hf(t)值(0.9～12.7)同位素特征,也与兴-蒙造山带特征相似,且三台组砂岩中显生宙碎屑锆石及其中ε_Hf(t)值为正值的比例较坊子组均增多。研究认为,华北北缘及其北部的兴-蒙造山带在侏罗纪时从早到晚不断抬升、剥蚀,形成相对华北克拉通内部的高地势特点,由此大量的剥蚀产物向南输运而成为鲁西隆起侏罗系的主要碎屑物源。