Sedimentary Facies,Provenance and Geochronology of the Heshangzhen Group: Implications for the Tectonic Evolution of the Eastern Jiangnan Orogen,South China

The Neoproterozoic Jiangnan orogen plays an important role in the study of the Precambrian tectonic evolution of South China. The tectonic nature of the Neoproterozoic sedimentary basins is still controversial, due to poor understanding of the sedimentary sequences and the lack of geochronological data. Here, we present sedimentological, provenance and geochronological data from the Heshangzhen Group in the eastern Jiangnan orogen. Sedimentological analysis shows that the Luojiamen Formation was deposited in a submarine fan, and the overlying Hongchicun Formation was deposited in front of a fan delta. The youngest detrital zircons constrain the lower Luojiamen and Hongchicun formations with ages of 827.3 ± 8.4 Ma and 825 ± 12 Ma, respectively. The sandstones of the Luojiamen Formation are characterized by a large number of intermediate to felsic volcanic grains, suggesting a volcanic arc source. In contrast, quartz and sedimentary lithic grains increase in the Hongchicun Formation, showing a new input from a collisional orogenic source. Detrital zircon from six sandstone samples in the Luojiamen and Hongchicun formations yield similar age spectra of 930–820 Ma with a peak at ca. 845–860 Ma, with one main cluster at 930–820 Ma. Detrital zircons of 930–845 Ma show a positive value of εHf(t)(+2.4 to +11, mean +7.6), which is similar to the volcanic arc of the nearby Shuangxiwu Group. There are a minor group of zircons with U-Pb ages ranging from 820 Ma to 845 Ma from the middle part of the Luojiamen Formation and Hongchicun Formation, with εHf(t) values between-20 to +2.4, which are consistent with the characteristics of the Shuangqiaoshan Group. within light of the bidirectional paleocurrents in the Luojiamen Formation, it is speculated that the zircons of 820–845 Ma were recycled from the Shuangqiaoshan Group, which is derived from a continental arc to the northwest. Our data suggests that the Luojiamen Formation was formed in an inter-arc basin, while the Hongchicun Formation was formed in an accretionary wedge-top basin. When juxtaposed with the conglomeratic characteristics at the bottom of the Luojiamen Formation, it is believed that the unconformity represented by the ‘Shen Gong Movement' reflects the rapid erosion and accumulation process of island arc volcanic material. The disconformity between the Luojiamen and Hongchicun formations is the imprint of transition from inter-arc basin to accretionary wedge-top basin,which represents the collision between the Shuangxiwu arc and the Yangtze Plate.     

辽东弓长岭—岫岩地区古元古界辽河群变沉积岩的物源及构造背景

辽东弓长岭—岫岩地区位于胶—辽—吉造山带东段,区内发育厚层古元古代变质沉积岩系,本文对这些变质沉积岩进行了岩相学和U-Pb年代学等方面的研究。岩相学特征显示这些岩石变质程度普遍偏低,多为绿片岩相变质条件,未发现高级特征变质矿物。岩石中主要矿物颗粒为石英,其中北辽河群碳酸盐矿物较为发育。根据辽东弓长岭-岫岩地区古元古代变沉积岩碎屑锆石阴极发光（CL）图像,这些锆石普遍具有清晰的振荡环带和较高的Th/U值（>0.3）,表明其原岩来自岩浆岩。结合LA-ICP-MS U-Pb年代学,得到里尔峪组、高家峪组、大石桥组和盖县组碎屑锆石分别呈现出2 159、2 500、2 189/2 530和2 044/2 197 Ma的年龄峰值,表明其沉积物来源于古元古代花岗质岩石和相邻的太古宙杂岩。结合前人资料,本文认为南、北辽河岩群形成于相同的环境并经历了相同的构造演化过程,古元古代弧-陆碰撞模式可能更适用于胶—辽—吉造山带的构造演化。     

粤东盆地早侏罗世金鸡组物源分析及其对华南构造背景的约束

华南早中生代构造背景一直存在争议。粤东盆地位于华南东南缘,记录了华南早中生代构造背景的地质信息。文章 以粤东盆地早侏罗世金鸡组碎屑沉积岩为研究对象,采用锆石U-Pb定年方法,结合岩相学、地球化学和古水流数据,探讨 盆地物源及构造背景。测年结果显示早侏罗世金鸡组样品存在八个峰值：196 Ma、247 Ma、320 Ma、432 Ma、770 Ma、 1060 Ma、1820 Ma和2430 Ma。物源分析表明粤东盆地金鸡组物源主要来自盆地的东北侧和北侧两个方向。粤东盆地碎屑 锆石与位于盆地东北侧的永安盆地和北侧的东坑盆地的物源特征相似,反映出早侏罗世中国东南部盆地尽管还是以稳定的 克拉通边缘盆地为特征,但古太平洋板块向华南板块更东侧的俯冲已经开始为中国东南缘盆地提供物源。     

Provenance analysis of the Upper Miocene turbidite sand-bodies in deep-sea basin of northern South China Sea

The International Ocean Discovery Program (IODP) Expedition 367/368 reported massive Upper Miocene deep-sea turbidite in the northern South China Sea basin. The Upper Miocene turbidite sand-bodies at Site U1500 were examined with detrital zircon U-Pb dating to conduct the source-to-sink analysis. This study shows that the U-Pb age spectrums of Site U1500 sample are similar to those detrital zircons from the Miocene Qiongdongnan Basin and the Pearl River Mouth Basin. Multidimensional scaling (MDS) plot also shows that the turbidite sand-bodies at Site U1500 are closely related to the sediments in the Pearl River Mouth Basin and Qiongdongnan Basin. It is likely that the thick deep-sea turbidite succession in the deep-water basin of northern South China Sea was formed by a mixed provenance pattern during the late Miocene. On the one hand, terrigenous sediments from the west of the South China Sea were transported along the Central Canyon to the eastern South China Sea deep-sea basin in the form of turbidity current. On the other hand, terrigenous sediments were also transported from the Pearl River through the slope canyon system to the northern South China Sea in the form of gravity flow . Those mixed sediments from two different source areas have collectively deposited at the deep-sea basin and thus, give rise to turbidite sequence of hundred meters. Provenance analysis of the thick turbidites sand-bodies in the deep-sea basin is of great significance to the profound understanding of the tectonic evolution, filling processes, provenance evolution, and the palaeogeographic characteristics of the Cenozoic basins of the South China Sea.     

南海北部深海盆地上中新统浊积砂体物源分析*

IODP367/368航次在南海北部深海盆地多个站位发现上中新统厚达数百米的大规模深海浊积岩。采用碎屑锆石U-Pb年龄谱系分析方法对U1500站上中新统浊积砂体进行源汇对比分析。研究结果表明U1500站上中新统浊积岩碎屑锆石年龄谱系与其西侧琼东南盆地和北侧珠江口盆地中新世沉积物特征类似。多维排列分析(MDS)结果也显示,该站位样品与珠江口盆地、琼东南盆地沉积物关系密切,表明南海北部深海盆地内厚达数百米的上中新统浊积砂体为南海北部物源和南海西部物源混合堆积形成。南海西部陆源输入物质以浊流搬运的方式,沿中央峡谷从西到东搬运至南海东部深海盆地;南海北部珠江物源以重力流的形式,经南海北部陆坡峡谷搬运至深海盆地中,两种来源的沉积物在深海盆地发生混合沉积,形成U1500站厚达数百米的浊积砂体。南海北部深海盆地厚层浊积砂体物质来源的准确识别,对深刻理解南海新生代盆地的构造演化、沉积物充填过程、物源演变以及古地理特征均具有重要意义。     

中国南方二叠纪层序地层划分与对比

对中国南方二叠纪时期不同沉积盆地类型的沉积层序进行了深入研究,综合各种盆地类型的沉积层序,该期可识别11个层序单元(S₁～S₁₁),其中,栖霞、茅口、吴家坪三阶分别含三个层序,长兴阶两个层序,S₁、S₆、S₇、S₁₁为Ⅰ型,其余为Ⅱ型。层序对比显示,上、中、下扬子的层序数量相近,界面特征各不一致,靠近古陆处在P/C、P₁/P₂界线间缺少层序1～2、3～5个不等;华南太平洋构造域影响区层序体系域具HST>TST结构,特提斯域控制区则具HST     

东阿拉善地块诺尔公群石英岩的碎屑锆石年龄特征——物源区制约及其地质意义

传统上将阿拉善地块东部变质基底"阿拉善岩群"之上的一套以石英岩、浅粒岩、碳酸盐岩及碎屑岩为主的浅变质地层称为诺尔公群,并根据区域地层对比及叠层石化石将其归为"长城纪"。为进一步限定地层时代,对诺尔公群底部3件石英岩进行LA-MC-ICP-MS锆石U-Pb测年,获得的年龄主要集中在2 530~2 500 Ma和1 950~1 850 Ma两个年龄段内,另外还获得少量年龄为~1.69 Ga、~2.0 Ga、~2.15 Ga、~2.35 Ga、~2.7 Ga和~3.4 Ga的锆石。其中,最年轻的碎屑锆石年龄限定了诺尔公群底部石英岩的沉积时代晚于1.69 Ga,结合上覆地层的年龄数据将诺尔公群的沉积时代大致限定为1.69~1.29 Ga,肯定了阿拉善地块存在中元古代地层。石英岩中~2.5 Ga和~1.95 Ga两个显著的碎屑锆石年龄峰符合典型的华北克拉通物源区特征,因此认为,阿拉善地块在太古代-中元古代具有与华北克拉通相似的构造环境,是华北克拉通的一部分。     

Geochemical Constraints of Sediments on the Provenance, Depositional Environment and Tectonic Setting of the Songliao Prototype Basin

The geochemistry of sediments is primarily controlled by their provenances, and different tectonic settings have distinctive provenance characteristics and sedimentary processes. So, it is possible to discriminate provenances, depositional environments and tectonic settings in the development of a sedimentary basin with the geochemistry of the clastic rocks. The analytical results of the present paper demonstrate that sediments in the Songliao prototype basin are enriched in silica (SiO2=66.48-80.51 %), and their ΣREE are 30-130 dmes of that of chondrite with remarkable Eu anomalies. In discriminating diagrams of Eu/Eu vs eeeeeREE and (La/Yb)N vs ΣREE, most samples locate above the line Eu/ Eu=l, on the right of the line Eu/Eu/ΣREE=1 and under the line La/Yb)N/eeeeeREE=1/8, which indicates that the depositional environment of sediments in the basin was oxidizing. In addition, variations of MgO, TiO2, A12O3, FeO+Fe2O3, Na2O and CaO vs SiO2 reflect a tendency of increasing mineral maturity of sediments     

论华财的板溪群及其有关的大地构造问题

研究认为板溪群为雪峰一武陵山区的一个岩石地层单位，由马底驿组和五强溪组组成，是一套正常的沉积地层而不是构造杂岩；华南不存在“华南阿尔卑斯”证据的飞来峰和构造窗；原带状大“板溪群”中含蛇绿岩外来岩块的变质岩系形成于前震旦纪。     

思茅陆块东缘二叠世末期碎屑锆石U-Pb年代学及微量元素组成研究

本文对采自云南哀牢山构造带西侧、思茅陆块东缘二叠纪末的四个砂岩样品中的碎屑锆石进行了LA-ICP-MS U-Pb年龄和微量元素测试,所有样品的年龄谱都显示出250～290 Ma的显著特征峰, XD37、XD40还得到900～1000 Ma的主特征峰和400～600 Ma的次特征峰;另外两个样品XD41和XD50也具有400～600 Ma和900～1000 Ma的特征峰,但是锆石数量较少。绝大部分的碎屑锆石微量元素都指示其源岩来自岩浆弧/造山带构造环境。结合前人研究成果,我们认为这些砂岩沉积于一个靠近思茅陆块边缘的弧后盆地,该弧后盆地可能是哀牢山洋二叠纪自东向西俯冲消减而产生。     

佳木斯地块北部早古生代沉积建造的时代与物源:来自岩浆和碎屑锆石U-Pb年龄及Hf同位素的制约

本文对出露于佳木斯地块北部金银库组变沉积岩和侵入其中的火成岩脉体中的锆石进行了系统的LA-ICP-MS/SIMS U-Pb定年和Hf同位素研究,旨在限定金银库组的沉积时限,并揭示其物源及沉积环境。3个样品中锆石呈自形-半自形,显示典型的岩浆生长环带或条痕状吸收,暗示其岩浆成因。研究结果显示:采自金银库组绢云母片岩中的碎屑锆石72个分析点给出1 955~457 Ma的年龄区间,主要峰期年龄为814、757、568、491和463 Ma,其ε_Hf（t）值为-13.9~-0.1,Hf同位素一阶段模式年龄T_DM1和二阶段模式年龄T_DM2分别为1 827~1 307 Ma和2 411~1 715 Ma。采自侵入金银库组的花岗细晶岩和辉绿岩分别给出了263和267 Ma的结晶年龄,前者的ε_Hf（t）值为0.9~2.0,Hf同位素二阶段模式年龄T_DM2为1 110~1 047 Ma;后者的ε_Hf（t）值为-7.7~6.4,Hf同位素一阶段模式年龄T_DM1为1 206~662 Ma。结合佳木斯地块及邻区约430 Ma火成岩的存在和金银库组中该期碎屑锆石的缺乏以及碎屑锆石年龄众数及其Hf同位素组成,我们认为金银库组的形成时代应为晚奥陶世至早志留世（463~430 Ma）,形成于被动大陆边缘背景,沉积物源主要来自佳木斯地块及其邻区的古元古代和早古生代早期火成岩。     

哀牢山构造带两侧上志留统-下泥盆统碎屑锆石年代学:物源及其构造意义

哀牢山古特提斯洋的打开时限及其缝合带的具体位置对理解哀牢山古特提斯洋构造演化具有非常重要的意义。本文采用碎屑锆石年代学方法,分析了哀牢山构造带及其两侧不同时期沉积物源的特征及其变化,解译了其物源差别所指示的哀牢山古特提斯洋盆打开时限以及缝合带的构造位置。碎屑锆石年代学显示,哀牢山构造带两侧上志留统碎屑锆石都记录一个~450 Ma的最年轻的峰值和一个格林威尔期造山事件的年龄群(1100~800 Ma),以及一个2600~2400 Ma的次峰;不同于上志留统,构造带东侧下泥盆统碎屑锆石并未出现年轻的~450 Ma峰值年龄信息,西侧U-Pb年龄分布模式与上志留统一致,记录~450 Ma峰值年龄信息,而且构造带两侧下泥盆统碎屑锆石的2600~2400 Ma的峰值明显要强于上志留统。区域上发表的碎屑锆石年代学资料,也揭示相同的年龄峰值。因此,综合区域上的其他地质资料,我们认为哀牢山古特提斯洋盆的打开时限应该在晚志留世-早泥盆世,哀牢山断裂带代表了哀牢山洋盆闭合的位置。     

Zircon U–Pb Ages and Lu–Hf Isotope of the Dongchuan Group in Central Yunnan,China, and their Geological Significance

On the southwestern margin of the Yangtze Block, the Dongchuan Group consists of slightly metamorphosed sedimentary rocks, including silty slate, argillaceous slate, clayey slate, arkose, dolomite, and minor volcanic rocks. To date, it is still a controversy over the depositional age and stratigraphic sequence of the Dongchuan Group. In this study, we analyzed five samples of meta-sedimentary rocks and one sample of meta-tuff from the Yinmin, Luoxue and Etouchang Formations of the Dongchuan Grou...     

扬子西缘江浪穹窿核部里伍岩群的形成时代及构造背景

江浪穹窿位于扬子陆块西缘,核部地层里伍岩群为一套变质的火山-沉积岩系。为精确厘定里伍岩群的形成时代并探讨其成岩构造背景,本文进行了LA-ICP-MS锆石U-Pb年代学以及岩石地球化学研究。定年结果表明变沉积岩中碎屑锆石年龄介于2521~262 Ma,其中最年轻一组岩浆成因锆石的~(206)Pb/~(238)U加权平均年龄为552.8±5.7 Ma(MSWD=2.1,n=6)。变沉积岩SiO_2含量变化很大(53.48%~96.08%),显示明显的Eu负异常(Eu/Eu*=0.50~0.67),相对富集大离子亲石元素(Rb、Ba和U等)、亏损高场强元素(Nb、Ta、Zr、Hf和Ti等),其稀土、微量配分模式与大陆上地壳完全一致。变基性火山岩具有很低的SiO_2含量(39.92%~48.27%),其稀土、微量配分模式平坦,类似于E-MORB。结合变基性火山岩的锆石U-Pb定年结果(542±9.0 Ma),本文指出里伍岩群应当形成于新元古代晚期(553~542 Ma),而并非前人所认为的古元古代或中元古代。变沉积岩的物源区主要为扬子西缘新元古代地质体,与变基性火山岩均形成于Gondwana超大陆聚合之后的板片俯冲环境。此外,碎屑锆石的年龄谱反映江浪穹窿可能存在太古宙—古元古代变质基底,并且具有Rodinia超大陆的会聚-裂解事件以及加里东运动的地质年龄记录。     

罗布泊第四纪湖盆物源与盆地构造演化特征：来自LDK01孔碎屑锆石U-Pb年龄证据

为揭示罗布泊盐湖第四系潜在物源区及凹陷阶段性演化过程,本文对罗布泊第一口钾盐科探深钻LDK01孔更新统不同深度样品进行碎屑锆石U-Pb微区定年分析。Th/U比值显示,钻孔碎屑锆石类型主要为岩浆锆石,少量为变质成因锆石。锆石年龄主要集中在209~240Ma、265~304Ma、320~385Ma、406~446Ma、705~880Ma及2376~2405Ma几个区间。综合分析潜在物源区的岩石属性和年龄构成,初步认为罗布泊地区前寒武纪年龄来自北部山前库鲁克塔格地区,加里东期碎屑锆石可能来源于阿尔金造山带和(或)南天山构造带。276Ma的峰值记录了塔里木盆地二叠纪大火成岩省事件,南天山最有可能为主导物源区。印支期和新生代碎屑锆石年龄暗示了北山地块和东天山,甚至较远的帕米尔-西昆仑山等地可能也提供了物源。凹陷周缘富钾岩体广泛出露,经风化、淋滤搬运至罗布泊,为凹陷第四纪成钾提供了有利的物质来源。塔里木盆地内部流域带来的碎屑组分是主要的物质来源,近源地区造山带岩体提供的物源有限。碎屑锆石年龄纵向变化特征显示,罗布泊北部地区在中更新世发生一次明显的构造抬升,可能是导致罗北凹地形成的重要原因。     

Detrital Zircon Geochronology and Provenance of Core Sediments in Zhoulao Town,Jianghan Plain,China

In our study,the U-Pb age spectrum of detrital zircons from terrigenous sediments is used to determine the sources.The Middle and Upper Reaches of the Yangtze River drain the western Yangtze craton and eastern Tibetan plateau,and take lots of sediments to the Jianghan (江汉) plain.Detrital zircons collected from Zhoulao (周老) core provide an ideal sample for the provenance studies.Here we report LA-ICP-MS U-Pb ages of 125 detrital zircons from one sand sample in the core sediments,which is recovered from a dep...     

南黄海表层沉积物的碎屑矿物、地球化学特征及物源分析

以南黄海中、西部表层沉积物的测试数据为基础,分析了表层沉积物的碎屑矿物组合特征、分布规律和能灵敏指示物源的CaCO₃、TiO₂、Cu、Sr和Ba的含量特征、分布规律,将这些特征分别与黄河和长江沉积物、黄土进行对比,探讨了南黄海中、西部的物质来源。南黄海西北部主要来源于现代黄河物质和山东半岛及邻近海域的侵蚀基岩;苏北黄河三角洲沉积物主要来源于全新世海侵期海水对古黄河沉积物的改造,其次为海水对基岩的侵蚀,现代黄河物质的影响较小;中部表现出多源性,沉积物部分来源于海侵期海水对海底基岩的侵蚀、改造、再沉积,部分来源于长江物质、黑潮物质及古黄河物质,长江物质影响大于古黄河物质;南部主要来源于长江物质。研究结果表明,现代黄河物质影响的范围小于长江物质;古黄河曾于晚更新世在苏北入海。     

南海西南海域表层沉积物中微量元素Ba的地球化学特征

分析南海西南海域表层沉积物中微量元素Ba的地球化学特征,并探讨生物成因Ba的分布及其与表层海水生产力的关系。南海西南海域表层沉积物Ba总量的变化范围为398~1 270 μg/g,平均值为851 μg/g,从上陆坡到下陆坡,沉积物中的Ba含量逐渐增加;微量元素Ba主要赋存于陆源碎屑相和生物成因相中,且明显受到沉积环境水深和陆源物质输入的影响。生物成因Ba含量的变化范围为30.6~938 μg/g,陆坡区和深海区平均值分别为495 μg/g、349 μg/g,占沉积物Ba总量的54％和51％,总体上,与沉积物Ba总量具有相对一致的分布特征。尽管研究区表层沉积物中Al、Ti成分为典型的陆源碎屑组分,但是,利用大陆上地壳Ba/Al比值和陆坡区沉积物回归分析获得的Ba/Al比值进行生物成因Ba的计算,过高地估算了沉积物中陆源Ba的含量;而采用页岩Ba/Ti比值来估算陆坡区表层沉积物中的生物成因Ba含量显得相对可靠。在深海区,利用经验的Ba/Al或Ba/Ti比值均不能获得有效的生物成因Ba值。因此,在获取沉积物中生物成因钡含量时,需结合各海区的特点选取合适的参数来扣除陆源Ba的含量。     

Provenance of the Late Permian Xuanwei Formation in the Upper Yangtze Block: Constraints from the Sedimentary Record and Tectonic Implications

Xuanwei Formation is composed of mudstone, siltstone, and sandstone, with local conglomerate. However, its provenance and tectonic setting have been scarcely studied. In this paper, we use sedimentology, electron probe microanalysis(EPMA), and detrital zircon dating to investigate its source area and depositional tectonic setting. The facies assemblages indicate that it formed in alluvial fan and fluvial river sedimentary environments. The strata thicknesses and facies distribution indicate that the sediment supply was from the west. The results of EPMA show that chromian spinels within the sediments are characterized by high Cr# and varying Mg#. Discrimination plots suggest that these spinels were sourced from large igneous province(LIP) magmatic rocks. The laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS) U–Pb chronology of detrital zircons suggests that the sediments were derived from intermediate–acid igneous rocks dating back to 251–260? Ma. We could, therefore, conclude that the provenance of the Xuanwei Formation is from Emeishan basalt and synchronous felsic igneous rocks, which is consistent with the composition of the detrital framework. The detrital zircon dates also suggest that felsic magmatism occurred during the Late Permian, not after the eruption of the Emeishan basalt. Based on the sedimentary successions and provenance analysis, the tectonic setting for Xuanwei Formation deposition was a volcanic rifted margin.     

Redetermination of the Depositional Age of the Haerdaban Group in the Northern Margin of the Yili Block,Western Tianshan,NW China: Implications for Regional Tectonics and Pb-Zn Mineralization

The Yili Block in the Western Tianshan orogen is a key area for understanding the early crustal formation and evolution of the Central Asian orogenic belt, due to the widely-distributed Precambrian rocks. Also, it hosts a lot of medium– to large-scale sedimentary exhalative(SEDEX) Pb-Zn deposits that mainly occur in Proterozoic metamorphosed clasticcarbonate rocks. In this study, LA-ICP-MS U-Pb analyses were carried out on detrital zircons in siltstones of the Precambrian Haerdaban Group in the ...