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.     

广西来宾蓬莱滩剖面中上二叠统硅质岩的地球化学特征及沉积背景

广西来宾地区中上二叠统广泛发育硅质岩,蓬莱滩剖面和铁桥剖面是本地区中上二叠统出露最好的剖面.本文对蓬莱滩剖面28件硅质岩(分别为中二叠统茅口组3件与上二叠统合山组25件)的主量和稀土元素进行了分析研究,并结合岩石学特征,认为:蓬莱滩剖面合山组硅质岩沉积于受到陆源物质影响的边缘海盆环境,它们的硅质主要来源于硅质生物,为生物成因;而其茅口组硅质岩则沉积于远离陆源物质影响的边缘海盆环境,它们的硅质主要来源于热液,为热液成因.通过与铁桥剖面的热液成因硅质岩的沉积背景对比研究,结果表明:中晚二叠世时期,来宾地区为富硅的边缘海盆环境,而陆源物质输入程度的差异是造成本地区形成不同成因硅质岩的主要因素.     

中亚造山带东段晚古生代伸展构造环境的证据:内蒙古双井地区哲斯组沉积学及年代学研究

本研究从沉积学与年代学角度切入,聚焦于中亚造山带东段晚古生代末期的演化历史。以内蒙古双井地区中二叠统哲斯组陆源粗碎屑沉积岩为研究对象,利用沉积剖面实测、岩相古地理分析及锆石年代学测试等方法,厘定其沉积时限与沉积构造环境,以探讨晚古生代末期中亚造山带东段的构造演化历史。来自哲斯组的2个砂岩样品的最年轻谐和锆石组的谐和年龄分别258. 1±1. 9Ma与261. 6±1. 7Ma,在误差范围内相等,限定了研究区内哲斯组地层的最大沉积年龄约为260Ma,处于中二叠世末的Capitanian期;其主要物质来源包括华北板块太古代至早元古代的结晶基底、华北板块北缘早古生代陆缘弧及中-晚泥盆世西别河组。碎屑锆石年代学与沉积学研究表明,研究区内哲斯组所处沉积盆地类型为伸展构造环境下的裂谷盆地,早期具有短时间内快速充填巨厚层粗碎屑沉积的补偿盆地特征,并伴有活跃的同沉积火山与构造活动,发育近岸水下扇相沉积;晚期逐渐转变为过补偿盆地,发育陆相干旱型冲积扇相沉积;表现出沉积环境由海相变为陆相、碎屑物供应充足且近源低成熟度碎屑增多的盆地充填过程。根据沉积相组合及展布、沉积年龄与碎屑锆石主要结晶年龄间隔等特征,结合研究区存在双峰式火山岩及碱性岩带等证据,哲斯组应代表晚古生代末期的裂谷盆地沉积。上述研究提供了中亚造山带东段二叠纪发生陆内伸展过程的证据。     

安徽省巢湖地区二叠纪栖霞组、孤峰组硅质岩地球化学特征对比及大地构造背景分析

为探讨下扬子地区二叠系硅质岩的硅质来源和形成背景,以巢湖地区二叠纪栖霞组和孤峰组硅质岩为研究对象,收集了前人大量有关栖霞组和孤峰组的研究成果和数据,并对采自栖霞组和孤峰组硅质岩样品进行了主量元素、微量元素、稀土元素测试。栖霞组、孤峰组硅质岩样品测试结果显示,硅质岩的稀土元素经北美页岩标准化后的配分曲线近似平坦型向左倾斜,有弱Ce负异常,且HREE弱富集,反映了热水沉积硅质岩的特征。研究区硅质岩样品的Al Fe Mn三角图中,样品投点分布较广,即Al比值变化范围较大,认为是岩浆在喷发过程中受硅-铝质陆壳混染作用的结果。结合沉积环境判别指标分析认为：栖霞组硅质岩沉积时期其沉积环境主要为大陆边缘环境;孤峰组硅质岩沉积时期其沉积环境为大陆边缘-海盆过渡环境。从栖霞组到孤峰组沉积时期,海侵规模不断变大,水体变深,海盆面积扩大,研究区在不同时期沉积环境存在差异。研究区栖霞组、孤峰组硅质岩的沉积与大陆边缘裂陷活动紧密相关。     

思茅地块西缘龙洞河组放射虫动物群及其地质意义

思茅地块西缘的龙洞河组为一套火山—沉积岩系 ,原定时代为晚石炭世 ,被认为属南澜沧江洋弧后盆地沉积。现在龙洞河组层状硅质岩断片中发现了晚泥盆世放射虫化石 ,在细碧角斑岩之硅质岩夹层中发现了早石炭世放射虫动物群 ,表明龙洞河组不全是晚石炭世地层 ,而是由晚古生代的一些地层断片组成。思茅地块西缘深水沉积盆地的演化始于泥盆纪 ,应为滇西南古特提斯多岛洋的一个分支 ,向南可能与泰国难河带对比。     

拉萨地块西段尼雄地区晚古生代地震事件及其地质意义

拉萨地块晚古生代处于伸展还是挤压背景一直以来存在较大的争议.在拉萨地块西段尼雄地区晚古生代地层中新发现了震积岩.拉嘎组一段震积岩单元位于含砾细砂岩冰水沉积中,可见震裂岩、震褶岩及塑性角砾岩等典型震积岩岩石类型,另见各种与震积岩相关的构造和沉积标志;拉嘎组二段震积岩单元位于潮坪沉积中,见液化卷曲变形及球-枕构造等;下拉组震积岩单元位于下段灰岩中,可见典型的粉（泥）晶灰岩脉和自碎屑角砾岩.下拉组和拉嘎组二段震积岩与燧石结核灰岩紧密共生,由此推测拉萨地块中部分晚古生代燧石结核灰岩可能与地震作用密切相关.结合区域资料,认为拉萨地块西段晚古生代地震事件与冈瓦纳大陆北缘裂陷盆地的发育有关,并为拉萨地块晚古生代演化新增了古地震活动资料.      

Late Permian Sequence Stratigraphic Framework and Controlling Factors in Southern Yangtze Platform and Its Margin

ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｃｏｎｃｅｐｔｓａｎｄｔｅｒｍｉｎｏｌｏｇｙｏｆｍｏｄｅｒｎｓｅｑｕｅｎｃｅｓｔｒａｔｉｇｒａｐｈｙｏｒｉｇｉｎａｔｅｄｆｒｏｍｓｅｉｓｍｉｃｓｔｒａｔｉｇｒａｐｈｙｌｉｎｋｅｄｔｏｐｅｔｒｏｌｅｕｍａｎｄｇａｓｅｘｐｌ...     

佳木斯地块东缘晚古生代大陆边缘构造演化

佳木斯地块位于中国东北微陆块群的最东缘,其东缘地区晚古生代的岩浆和沉积演变进程为欧亚大陆东缘由被动陆缘向活动陆缘构造环境的转化提供了关键证据。年代学和地球化学研究表明,佳木斯地块东缘中泥盆世黑台组砂岩,形成于被动陆缘的构造环境,黑台组上覆的老秃顶子组流纹岩也形成于被动陆缘的构造环境;晚石炭世珍子山组砂岩,形成于活动陆缘的构造环境;早二叠世的二龙山组安山岩以及相邻地区早二叠世的其它火成岩形成于活动陆缘的构造环境。同时,佳木斯地块东缘泥盆-二叠纪的沉积地层也呈现出由浅海相到陆相地层转化的特征。因此,佳木斯地块东缘由被动陆缘向活动陆缘的转化应该发生在中泥盆世到晚石炭世,而该构造环境的转化也为晚古生代时期蒙古-鄂霍茨克洋向欧亚大陆之下俯冲过程的研究提供了关键信息。     

Cratonic reactivation and orogeny: An example from the northern margin of the North China Craton

Reactivation of cratonic basement involves a number of processes including extension, compression, and/or lithospheric delamination. The northern margin of the North China Craton (NCC), adjacent to the Inner Mongolian Orogenic Belt, was reactivated in the Late Paleozoic to Early Mesozoic. During this period, the northern margin of the NCC underwent magmatism, N–S compression, regional exhumation, and uplift, including the formation of E–W-trending thick-skinned and thin-skinned south-verging folds and south-verging ductile shear zones. zircon U–Pb SHRIMP ages for mylonite protoliths in shear zones which show ages of 310–290 Ma (mid Carboniferous–Early Permian), constraining the earliest possible age of deformation. Muscovite within carbonate and quartz–feldspar–muscovite mylonites from the Kangbao–Weichang and Fengning–Longhua shear zones defines a stretching lineation and gives ⁴⁰Ar/³⁹Ar ages of 270–250 Ma, 250–230 Ma, 230–210 Ma, and 210–190 Ma. Deformation developed progressively from north to south between the Late Paleozoic and Triassic. Exhumation of lower crustal gneisses, high-pressure granulites, and granites occurred at the cratonic margin during post-ductile shearing (~ 220–210 Ma). An undeformed Early Jurassic (190–180 Ma) conglomerate overlies the deformed rocks and provides an upper age limit for reactivation and orogenesis. Deformation was induced by convergence between the southern Mongolia and North China cratonic blocks, and the location of this convergent belt controlled later deformation in the Yanshan Tectonic Province. This province formed as older E–W-trending Archean–Proterozoic sequences were reactivated along the northern margin of the NCC. This reactivation has features typical of cratonic basement reactivation: compression, crustal thickening, remelting of the mid to lower crust, and subsequent orogenesis adjacent to the orogenic belt.     

河南省太原组沉积时期岩相古地理特征

河南省早二叠世太原组沉积区位于华北盆地南部北秦岭褶皱带栾川—固始深断裂以北地区,当时的沉积盆地受华北地块西隆东倾的构造古地理控制,是晚古生代华北陆表海盆地或碳酸盐岩台地沉积的一部分,发育了一套以碳酸盐岩为主夹碎屑岩和煤为特色的陆表海沉积。太原组岩性以灰—深灰色薄—中厚层状生物屑灰岩为主,夹薄—中厚层状的泥岩、泥灰岩、细...     

河南省晚古生代煤系层序地层格架与沉积演化

通过对露头及钻井资料的研究,河南省晚古生代煤系可划分为1个一级层序(308~252 Ma);以太原组上部灰岩段底界面为区域性沉积间断面,将该一级层序又分为Ms₁和Ms₂两个二级层序;进而依据次级层序界面又细分为20个三级层序。通过对本区沉积演化特征的研究表明:本溪组沉积早期,本区海侵方向为自东向西进行,海侵中心由南向北迁移,而到本溪组沉积晚期,海侵范围扩大,海侵中心部位继续北移,海侵方向由NEE向SWW进行;自太原组沉积开始,区内海侵逐渐达到高潮,海域扩大;到山西组沉积期,区内大面积海退,海域范围向东南退缩,经历了滨海-潮坪-泻湖-下三角洲平原的沉积演化;到下石盒子组至上石盒子组沉积期,海水基本退出华北盆地范围,致使河南境内沉积演化最后经历了从三角洲前缘-下三角洲平原-上三角洲平原沉积的演变过程。研究成果对分析研究区晚古生代成煤、古地理、古环境及聚煤规律具有参考价值。      

内蒙古隆起晚古生代构造隆升的沉积记录

内蒙古隆起位于华北克拉通与兴蒙造山带的过渡部位,受古亚洲洋俯冲、闭合过程的影响,在晚古生代发生了重要的构造隆升。华北盆地北缘紧靠内蒙古隆起,其晚古生代沉积记录了内蒙古隆起的构造活动历史。本文对盆地冀北—辽西地区的晚石炭—中三叠世地层进行详细的沉积体系分析和物源研究,结果表明:1盆地由远滨—滨岸、扇三角洲、三角洲、河流四种沉积体系充填而成,总体上经历了由海陆交互到陆相的进积充填过程。在晚石炭—早二叠世,盆地边缘发育扇三角洲和河流体系,盆地内部由远滨—滨岸、三角洲与河流体系组成。在中二叠—中三叠世期间盆地整体发育河流体系。盆地的沉积中心位于唐山、宝坻一带;2古水流数据、碎屑锆石U-Pb年龄和Hf同位素表明盆地物源来自内蒙古隆起,源岩由中上元古界碎屑岩和碳酸盐岩、寒武—奥陶系碳酸盐岩、晚古生代岩浆岩以及少量前寒武结晶基底组成。大量沉积岩碎屑颗粒表明内蒙古隆起在晚古生代被沉积盖层所覆盖,在二叠纪末期花岗岩以及片麻岩砾石的出现代表了内蒙古隆起隆升和侵蚀作用的加强;3根据沉积体系和物源变化将盆地划分为三个充填序列,这些序列记录了内蒙古隆起的隆升和侵蚀过程。晚石炭—早二叠世充填序列以沉积岩砾石、泥盆纪碎屑锆石和凝灰岩夹层为特征,物源来自沉积盖层和晚古生代火山岩。该序列记录了内蒙古隆起陆缘弧的初始隆升和同期火山活动。中晚二叠世充填序列以河流环境下的火山碎屑岩和火山岩为主要特征,记录了华北北缘与南蒙地块的碰撞过程,碰撞导致内蒙古隆起的隆升,同时伴随火山喷发。早中三叠世充填序列以辫状河粗碎屑和花岗质砾石为特征,记录了古亚洲洋闭合后的伸展环境。     

内蒙古阿鲁科尔沁旗陶海营子剖面林西组地球化学特征及其对物源-构造背景的制约

大兴安岭中南段上二叠统林西组发育厚层的暗色泥页岩,是区域上重要的上古生界生烃层系之一。阿鲁科尔沁旗陶海营子剖面是林西组的典型剖面之一,本文以该剖面为研究对象,对取自该剖面林西组的10件砂、泥岩样品进行主量元素、微量元素和稀土元素测试分析。剖面样品元素分析和物源判别函数（F₁-F₂）、Ni-TiO₂、La/Th-Hf图解判别结果表明,陶海营子剖面林西组沉积物来源多样,主要来源于上地壳长英质火成物源区和石英岩沉积物源区,还有少量来自中、基性岩火成物源区。剖面样品微量元素PAAS（后太古庙澳大利亚页岩）标准化蛛网图、稀土元素球粒陨石标准化配分模式图、K₂O/Na₂O-SiO₂、Zr/Th、TiO₂-（TFe₂O₃+MgO）图解、物源构造背景判别函数（F₁-F₂）''的分析判别和剖面样品与不同构造环境砂岩地球化学参数对比结果表明,陶海营子剖面林西组物源构造背景具有被动大陆边缘、活动大陆边缘和大陆岛弧特征,构造背景较复杂。综合分析可知,陶海营子剖面林西组物源主要为被动大陆边缘背景下的火成岩、石英质沉积岩,以及活动大陆边缘和大陆岛弧背景下的火成岩。结合前人相关研究成果,推测兴蒙造山带内伸展作用背景下的晚石炭世-二叠纪岩浆型被动陆缘沉积建造和与俯冲背景有关的古生代弧岩浆岩应该是陶海营子剖面林西组的主要物源。     

宁夏北部沙巴台地区太原组沉积层序及其年代地层对比

宁夏北部沙巴台地区的太原组为海陆交互相和三角洲相沉积 ,可划分为 2个三级层序、 4个副层序组和 1 8个副层序。与华南海相沉积层序的对比表明太原组属晚石炭世 Gzhelian晚期至早二叠世 Artinskian中期。下二叠统 Asselian阶的底界 (即 C/P界线 )大体与太原组下部层序的初始海泛面一致 ,可广泛对比。     

Reconstructing Late Paleozoic exhumation history of the Inner Mongolia Highland along the northern edge of the North China Craton

The Inner Mongolia Highland (IMH), along the northern edge of the North China Craton, was considered to be a long-standing topographic highland, whose exhumation history remains elusive. The aim of this study is to reveal Late Paleozoic exhumation processes of the IMH based on an integrated analysis of stratigraphy, petrography of clastic rocks, and U–Pb ages and Hf isotopes of detrital zircons from Permian–Triassic succession in the middle Yanshan belt. The results of the study show that the Benxi Formation, which was originally regarded as a Late Carboniferous unit, proves to be Early Permian in age because it contains detrital zircons as young as ∼298 Ma. The Lower Shihezi Formation is demonstrated to be a unit whose age spans the boundary of the Middle and Upper Permian, constrained by a U–Pb age of 260 ± 2 Ma from a dacite layer. Clastic compositions of conglomerate and sandstone change markedly, characterised by the predominance of sedimentary components in the Benxi–Shanxi Formations, by large amounts of volcanic clastics in the Lower and Upper Shihezi Formations, and by the presence of both metamorphic and igneous clastics in the Sunjiagou–Ermaying Formations. Sedimentary clastics include chert, carbonate, sandstone and quartzite, which may have been derived from Proterozoic to Lower Paleozoic sedimentary covers. Volcanic clasts were directly related to volcanic eruptions, while granite and gneiss grains were sourced from exhumed Late Paleozoic intrusive rocks and basement rocks. Detrital zircon U–Pb ages can be divided into five populations: 2.6–2.4 Ga, 1.9–1.7 Ga, 400–360 Ma, 325–290 Ma and 270–250 Ma. Precambrian detrital zircons are typically subrounded to rounded in shape, implying a recycling origin. Late Paleozoic zircons show oscillatory zones and their Th/U ratios >0.4, suggesting a magmatic origin. Most Phanerozoic zircons have negative ε_Hf(T) values of −3.2 to −25.5, which are compatible with those of Late Paleozoic plutons in the IMH. The results indicate that the IMH may have been covered with Proterozoic to Lower Paleozoic sedimentary strata, which then underwent subsequent erosion and served as provenances for adjacent Late Paleozoic basins. Vertical changes in both clastic compositions and detrital zircon ages in Permian–Triassic strata imply an unroofing process of the IMH. Three phases of the IMH uplift are distinguished. The first-phase uplift commenced 325–312 Ma and resulted from magmatic intrusion related to southward subduction of the Paleo-Asian Ocean. The second-phase uplift took place in the Middle Permian and may be attributed to crustal contraction related to the collision of the North China Craton and the Southern Mongolia terrane. The third-phase uplift happened at the end of the Permian, and may have been induced by upwelling of calc-alkali magma under an extensional setting.     

Research Status and Advances in Chert and Permian Chert Event

Cherts are concret research objects for petro-tectonic framework and are widespreadly distributed in special sedimentary environments along orogenic belts and depositional basins. Cherts hold abundant origin related information, which plays important role in palogeographic and paleooceanograpic study. This paper reviewed the history and the advancement of research on chert, especially paying more attention to the research progress about both bedded chert and nodular chert in domestic and international research areas. Combined with Permian cherts distribution in China, we discuss research achivements of silica sources, sedimentary environments and original mechanism from cherts deposited in different sedimentary environments such as oceanic rift, oceanic basin and continent shelf. “Permian Chert Event” (PCE) has been used to discribe the widespread biogenic Permian cherts that occurred around the eastern margins of Panthalassa and Paleotethys Ocean. Research results on Permian cherts in eastern Paleotethys Ocean, particularly the Yangtze areas, are examined here, which suggest Permian cherts are not typically biogenic in origin but severely influenced by hydrothermal sedimentation. The seasonal melting of sea ice is assumed engine for PCE in northwest edge of Pangea Supercontinent, but that dose not work in China. Therefore, a hypothesis different form thermohaline circulation and upwelling is proposed here: there would be a periodical hydrothermal fluid system in the eastern Paleotethys Ocean, providing the source of silica for the development of Permian Chert Event on both south and north continent shelves. What is more, some intensively studied Permian outcrops in the Yangtze areas have the potential to be the typical outcrops for PCE research in China.     

桂西北晚古生代乐业孤立碳酸盐岩台地沉积特征与演化阶段

桂西北乐业台地是右江盆地北部典型的晚古生代孤立碳酸盐岩台地。从中泥盆统唐家湾组至上二叠统合山组均由碳酸盐岩构成,与北侧陆棚区多样的沉积类型及台地周边泥质-硅质岩深水沉积形成鲜明对比。台地内上古生界主要由台缘生物礁组合和礁后澙湖组合两种浅水碳酸盐沉积类型构成。地层发育与沉积特征主要受基底沉降、海平面波动、气候变化和盆地内生碳酸盐沉积速率控制。研究表明,乐业台地是在右江盆地强烈扩张、沉降过程中由扬子地台南缘破裂的微地块向盆地滑移而形成的孤立台地。它的演化经历了边缘台地（D1-D2）、孤立台地（D3-P2）和淹没台地（P3-T1）3个发展阶段。孤立台地是其最重要的主体特征,反映了右江盆地在晚古生代强烈扩张、沉降,扬子地台边缘拉伸、破裂,微地块向盆地滑移的构造背景。乐业孤立台地的形成及演化模式可能具有普遍性,也适用于右江盆地西北部其他晚古生代孤立碳酸盐岩台地。     

Late Paleozoic provenance shift in the south-central North China Craton: Implications for tectonic evolution and crustal growth

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 ε_Hf(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 ε_Hf(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.     

Permian marine sedimentation in northern Chile: new paleontological evidence from the Juan de Morales Formation,and regional paleogeographic implications

Permian marine sedimentary rocks that crop out in northern Chile are closely related to the development of a Late Paleozoic magmatic arc. A study of Upper Paleozoic units east of Iquique (20°S) identified three members within the Juan de Morales Formation, each of which were deposited in a different sedimentary environment. A coarse-grained terrigenous basal member represents alluvial sedimentation from a local volcanic source. A mixed carbonate-terrigenous middle member represents coastal and proximal shallow marine sedimentation during a relative sea-level rise related with a global transgression. Preliminary foraminifer biostratigraphy of this middle member identified a late Early Permian (late Artinskian–Kungurian) highly impoverished nodosarid–geinitzinid assemblage lacking fusulines and algae, which is characteristic of temperate cold waters and/or disphotic zone. The upper fine-grained terrigenous member represents shallow marine siliciclastic sedimentation under storm influence. The Juan de Morales Formation consists of continental, coastal and shallow marine sediments deposited at the active western margin of Gondwana at mid to low latitudes. A revised late Early Permian age and similar paleogeography and sedimentary environments are also proposed for the Huentelauquén Formation and related units of northern and central Chile, Arizaro Formation of northwestern Argentina, and equivalent units of southernmost Peru.     

西秦岭地区晚二叠世—早三叠世沉积相分析和沉积古环境再造

青海省同仁地区处于祁连和秦岭造山带的接合部，构造演化历史悠久。本次工作在该地区隆务河一带发现较好的二叠—三叠系剖面。将该剖面从下而上划分为上二叠统石关组、下三叠统果木沟组和江里沟组，其中江里沟组又进一步划分为下部的浊积岩段和上部的风暴岩段，初步确定了二叠—三叠纪的界线。沉积序列、沉积相和沉积物表明上二叠统石关组和下三叠统果木沟组为一套陆源碎屑浊积岩，下三叠统江里沟组下部为一套不纯的内碎屑浊积岩，而下三叠统江里沟组上部为风暴岩沉积。根据沉积相和火山岩夹层的地球化学特征认为该地区上二叠统石关组和下三叠统果木沟组处于半深海的活动大陆边缘，下三叠统江里沟组早期的浊积岩段处于较稳定的半深海大陆边缘。根据沉积相和遗迹化石，恢复了晚二叠世—早三叠世的海平面变化特征。