漠河盆地中侏罗世沉积源区分析及地质意义

漠河盆地位于额尔古纳地块北缘,其北为蒙古-鄂霍茨克造山带,与紧邻的俄罗斯上阿穆尔盆地在中生代时期同属一个盆地。漠河盆地中侏罗统包括绣峰组、二十二站组、额木尔河组和开库康组。根据盆地碎屑岩中的砾石、岩屑和重矿物的组合特征,确定母岩类型以变质岩和中酸性火成岩为主,少量沉积岩和基性火成岩;结合古水流方向,确定盆地沉积物源主要来自南侧。沉积物源具有多源性:其一为陆块抬升基底,其二为切割的岩浆弧。与区域岩石对比分析表明,陆块抬升基底可能来自古元古界兴华渡口群和寒武系兴隆群,切割的岩浆弧与古生代同碰撞和后碰撞花岗质岩石及早中生代中酸性火成岩有关。根据母岩供给特点,认为中侏罗世沉积时期漠河盆地不是典型的前陆盆地,而应是挤压背景下形成的挤压挠曲盆地或山间盆地。     

大兴安岭中段林西组砂岩LA-ICP-MS碎屑锆石U-Pb年代学及其地质意义

大兴安岭中段扎赉特旗西北部分布大面积的晚二叠世林西组沉积地层,该沉积地层主要为长石砂岩、粉砂岩、长石岩屑砂岩夹不同规模的含砾砂岩及灰岩,中部含有较为丰富的双壳类、植物化石。本次研究针对林西组下部的长石岩屑砂岩进行LA-ICP-MS碎屑锆石U-Pb测年工作,共获得98个有效年龄,年龄分布范围为（2 552.3±22.5）~（227.6±5.4）Ma,大部分年龄位于谐和曲线上,部分结果偏离曲线,根据测试数据按年龄值和频率分布特征大致分为以下几组：上泥盆世—晚二叠世（380.0~246.1 Ma）、志留纪—寒武纪晚期（489.0~413.8 Ma）、中元古代—新元古代（1 239.5～808.1 Ma）、古元古代（2 554.0～1 784.3 Ma）。上述年龄与区域上的岩浆事件基本吻合。综合研究表明研究区内林西组沉积下限为（253.4±1.5） Ma,林西组的物源主体应来自于西拉木伦河—延吉一线,其余锆石来源主要为兴蒙造山带内部、华北板块北缘和东北各地块,1.8和2.5 Ga的碎屑锆石更有可能来自华北板块北缘,华北板块和西伯利亚板块在（253.4±1.5） Ma之前已经完成碰撞、拼合,古亚洲洋已经闭合,兴蒙海槽形成。林西组海相核形石的发现表明晚二叠世大兴安岭中段地区应以海相环境为主,直到三叠纪早期才逐渐转变为陆相沉积环境。     

华北板块北缘东段柳河盆地早白垩世鹰嘴砬子组碎屑锆石U-Pb定年及其地质意义

华北板块北缘在晚中生代受到古太平洋板块西向俯冲作用的影响,发育强烈的构造变形及大规模的岩浆活动.研究区柳河盆地地处华北板块北缘,对其开展研究能够为约束华北板块北缘晚中生代构造演化阶段提供沉积方面的证据.依据对盆地早白垩世鹰嘴砬子组样品碎屑组分、岩性序列、沉积相演化特征的研究,结合碎屑锆石U-Pb年代学判断,盆地样品矿物组成具有石英含量较低,岩屑和长石含量较高的特点,显示沉积物物源主要来自岩浆弧物源区.两组碎屑锆石U-Pb年龄组成相似,以晚中生代为主,古元古代为辅.L1-B178样品（岩心）碎屑锆石存在约127Ma的主峰和约2553Ma的次峰;P303-B3样品（剖面）存在约126Ma的主峰和约2545Ma的次峰,中生代沉积物物源可能来自盆地东北侧丰富的岩浆岩.早白垩世鹰嘴砬子组最年轻碎屑锆石颗粒的U-Pb年龄限定岩层的最大沉积年龄为（125±4）Ma,介于早白垩世巴雷姆阶与阿普特阶,与层内流纹岩样品（124.3±0.7）Ma的锆石加权平均年龄吻合.通过对柳河盆地样品矿物组成特点、沉积相演化和碎屑锆石U-Pb年代学特征综合判断,盆地在（125±4）Ma已接收到古太平板块俯冲作用带来的物源...     

大兴安岭中南段二叠纪砂岩主量元素地球化学特征及物源区构造环境的判别

通过对研究区内广泛发育的二叠系哲斯组和林西组砂岩进行岩相学及主量元素地球化学研究,探讨其物源区及其古构造环境。岩相学研究结果表明:二叠系哲斯组和林西组砂岩成分成熟度较低,表现为源区相对不稳定、快速剥蚀、快速搬运的特征。A-CN-K三角图解显示砂岩母岩中斜长石含量要高于钾长石含量,指示两组砂岩物源区母岩应以具英云闪长岩和花岗闪长岩等岛弧性质的岩浆岩系列为主。主量元素判别图解揭示了物源区主要具活动大陆边缘和大陆岛弧型并含有少量被动大陆边缘物源区特点,且总体呈现出由活动大陆边缘向大陆岛弧型物源区过渡的趋势。结合前人的研究成果,推测二叠纪砂岩的物源区主要为区域内广泛分布的大石寨组火山岩及研究区北侧及北西侧的苏尼特左旗—锡林浩特—西乌旗南岩浆弧物质并含有少量来自华北板块基底的物源供给。     

内蒙古扎鲁特旗上二叠统林西组碎屑锆石LA-ICP-MS U-Pb测年及意义

研究区位于西拉木伦河-长春-延吉断裂以北,区内发育有巨厚的上二叠统林西组,岩性为灰、灰黑、黄绿色的砂板岩组合.研究其年代学特征对确定该区大地构造背景具有重要的指示意义.对采自林西组的砂岩样品进行了锆石LA-ICP-MS U-Pb测年.结果显示,其年龄分布在5个年龄区间：252~300 Ma、305~423 Ma、431~555 Ma、600~999 Ma、1037~2460 Ma.最年轻的年龄为252 Ma,指示林西组沉积时间下限为252 Ma.上述碎屑锆石的年代学研究表明,扎鲁特旗地区晚二叠世林西组物源既有东北地区的变质基底以及其后的构造岩浆事件信息,也包含有南侧华北板块北缘信息,说明在晚二叠世晚期沿西拉木伦河缝合带华北板块北缘与其北侧地块群完成最终碰撞拼贴.     

延边开山屯花岗闪长岩-石英闪长岩体年代学、地球化学特征及对古太平洋板块俯冲作用时限的制约

近年来古太平洋构造域的构造演化备受学者关注。本文报道的延边开山屯地区花岗闪长岩-石英闪长岩体LAICP-MS U-Pb年龄表明其形成时间为早侏罗世早期(198±1Ma),所采样品可根据Zr/Hf值分为高Zr/Hf值组花岗闪长岩和低Zr/Hf值组石英闪长岩。高Zr/Hf值组花岗闪长岩起源深度浅,富集Rb、Th、U、K等大离子亲石元素(LILEs),贫Nb、Ta、Ti等高场强元素(HFSEs),具壳源岩浆的特点。低Zr/Hf值组为壳源岩浆与来自深部的亏损地幔岩浆混合而成,岩石亏损Nb、Ta、Zr、Hf、Ti等高场强元素,具有典型的弧型岩浆地球化学特征。岩体中存在细粒闪长质包体,镜下可见针柱状磷灰石。开山屯岩体属钙碱性系列岩石,结合前人资料,认为其与该地区同时代火成岩组成北-东向分布的早侏罗世活动大陆边缘型火成岩带,而位于该带西侧的小兴安岭-张广才岭地区存在同时代弧后拉张带,两者构成典型的大陆弧与弧后拉张带模型,共同揭示了早侏罗世早期古太平洋板块对东北地区的俯冲作用。     

辽北地区早-中二叠世变质火山-碎屑岩年代学和地球化学特征:对华北板块北缘东段构造演化的启示SCIEI北大核心CSCD

新识别的“下二台”构造杂岩作为华北板块北缘东段分布的构造混杂岩带重要组成部分,其物质组成、形成时代和构造属性仍需进一步研究,这将为探讨华北板块北缘东段晚古生代构造演化提供重要依据。作者在“下二台”构造杂岩中识别出一套早-中二叠世变质火山-碎屑岩,其以变质碎屑岩为主,并夹变质火山岩,二者在野外产出上混杂在一起。变质火山岩原岩类型包括流纹岩、英安岩、安山岩、玄武安山岩,为一套钙碱性火山岩,属于准铝质-弱过铝质岩石。根据岩相学和地球化学特征,将其分为变质酸性火山岩和变质中-基性火山岩;二者均相对富集轻稀土元素,亏损重稀土元素,轻重稀土元素分馏明显,Eu负异常不明显,但变质酸性火山岩明显亏损P、Ti元素,结合高场强元素相关性特征,认为二者不是同一基性岩浆分异的产物。变质火山岩锆石LA-ICP-MS U-Pb同位素年龄为272~288Ma,代表其原岩结晶年龄,时代为早二叠世;变质酸性火山岩原始岩浆来源于地壳物质的部分熔融,变质中-基性火山岩原始岩浆来源于岩石圈地幔(俯冲带附近),并遭受了地壳物质的混染,二者均形成于活动大陆边缘火山弧环境。变质碎屑岩原岩恢复为泥砂质沉积岩和砂泥质沉积岩,相对亏损轻稀土元素,富集重稀土元素,轻重稀土元素分馏较明显,Eu异常不明显。两件碎屑岩样品锆石LA-ICP-MS U-Pb同位素年龄主要介于267~347Ma,推断其沉积下限为267Ma和269Ma,均为中二叠世;泥砂质沉积岩可能来源于再旋回的以长英质岩石为母岩的沉积岩,砂泥质沉积岩可能来源于再旋回的以长英质和镁铁质岩石为母岩的沉积岩,二者分别形成于活动大陆边缘大陆岛弧和大洋岛弧环境。下二台地区早-中二叠世变质火山-碎屑岩为“下二台”构造杂岩重要组成部分,它表明二叠纪时期华北板块北缘东段经历了三个构造演化阶段:早二叠世古亚洲洋加速俯冲,形成新的大陆弧阶段;中二叠世古亚洲洋持续俯冲,大陆弧和大洋弧碰撞阶段;晚二叠世陆-陆碰撞前阶段。     

大兴安岭中段上二叠统-下三叠统接触关系研究——来自碎屑锆石年代学的证据

华北板块北缘与其北部地块之间古亚洲洋闭合的时限,涉及到大陆形成过程中的古洋陆格局及演化过程的重建。晚二叠世-早三叠世大兴安岭地区的构造演化过程是承上启下的转折时期,即是古亚洲洋向古太平洋构造体系转变的关键时期。本文通过对大兴安岭中段龙江地区上二叠统林西组和下三叠统老龙头组砂岩样品进行系统的碎屑锆石U-Pb同位素年代学研究,证实林西组和老龙头组存在280 Ma、370 Ma和500 Ma的三组峰值年龄,分别代表物源区存在早二叠世大石寨组火山岩、晚泥盆世-早石炭世岩浆弧以及北侧地块的统一基底,林西组和老龙头组碎屑锆石最小年龄分别为254Ma和247 Ma,结合野外实测剖面研究结果,认为上二叠统林西组和下三叠统老龙头组连续沉积,整合接触。1∶20万地质图显示内蒙古东部大兴安岭大部分地区缺失三叠系,笔者发现研究区晚侏罗世满克头鄂博组、白音高老组与下伏晚二叠世林西组呈角度不整合接触,结合大兴安岭中部零星出露的早三叠世地层、二连盆地参1井中也存在早三叠世地层,综合分析认为研究区应存在早三叠世地层,上二叠统与下三叠统应为连续沉积,现今多数地区早三叠世地层的缺失是由于后期构造抬升剥蚀造成的。根据上二叠统林西组和下三叠统老龙头组中碎屑锆石存在1800 Ma左右的典型华北板块基底年龄和两者的整合接触关系,结合内蒙古贺根山缝合带中花岗闪长岩244 Ma的年龄以及双井子岩体、哈拉图岩体、吉林中部大玉山岩体均为后碰撞的地球化学特征,认为华北板块北缘与其北侧地块群最终闭合时间应为P3-T1。     

扬子板块北缘镇巴地区吴家坪组富Li-REE-Nb-V黏土岩地球化学特征及其地质找矿意义

沉积型锂矿主要产于黏土岩中,黏土岩的主微量元素可有效识别沉积物源及沉积环境。本文首次报道扬子板块北缘镇巴地区二叠系吴家坪组黏土岩锂、稀土、铌、钒等元素超异常富集的特征,基于详细的地球化学研究和区域地质资料,分析吴家坪组黏土岩的形成环境及沉积物源,并探讨扬子板块北缘锂、稀土找矿方向。研究表明,镇巴地区吴家坪组黏土岩产于晚二叠世,发育于吴家坪组与阳新组的平行不整合界面之上,代表了古风化壳沉积,黏土岩的Li2O最高品位0.39%,ΣREO（稀土氧化物总量）最高品位0.142%,V2O5最高品位0.26%,Nb2O5最高品位0.022%。主、微量元素地球化学特征指示黏土岩形成于咸化-半咸化海水相,氧化-还原过渡、碱性的沉积环境,对应于黏土岩化阶段。综合矿物学、地球化学、区域地质资料,认为研究区吴家坪组黏土岩来源于峨眉山大火成岩省的玄武岩,锂元素的富集与火山岩受流体交代-淋滤有关。扬子板块北缘广泛发育吴家坪组黏土岩,规模较大,锂、稀土、铌、钒综合成矿效果较好,找矿潜力巨大,应重点关注与沉积间断面有关的关键金属矿产,助力新一轮找矿突破。     

黔西南下三叠统飞仙关组沉积物源分析对峨眉山大火成岩省火山剥蚀序列的重建约束

峨眉山大火成岩省在形成后遭受了强烈的风化剥蚀，与右江盆地构成了独特的源- 汇沉积体系，相关的碎屑沉积记录是重建峨眉山大火成岩省晚期火山序列、揭示大火成岩省岩浆演化的关键。本文对黔西南地区右江盆地北缘下三叠统下部飞仙关组开展了详细的沉积物源研究。飞仙关组泥岩由长石、石英和黏矿物等组成，具有低SiO2、高TiO2含量和低Al2O3/TiO2值的特征，具Eu的弱负异常，微弱的Nb、Ta负异常。基于Al2O3/TiO2和La/Sm物源图解分析，研究样品的主要物源由峨眉山大火成岩省的高- Ti玄武岩和少量酸性火山岩构成，这与右江盆地晚二叠世的碎屑沉积物源组成一致。碎屑锆石具有～260 Ma 的年龄峰值，对应锆石具有较低的Th/Nb和较高的Nb/Hf值，均支持峨眉山大火成岩省作为主要的沉积物源区，而同时存在的>400 Ma的碎屑锆石则对应于峨眉山玄武质岩浆上升时所捕获的华南地壳物质。与上二叠统的碎屑锆石U- Pb年龄组成和锆石化学组成对比分析表明，峨眉山大火成岩省在晚二叠世到早三叠世早期剥蚀的火山岩构成了一定的火山序列，反映了该大火成岩省晚期从强烈地壳混染到分异结晶为主的岩浆演化过程。     

黑龙江省东部早古生代晨明组物源区特征及其构造背景

为揭示黑龙江省东部早古生代晨明组沉积物源区特征及其沉积构造背景,对晨明组进行了地球化学特征研究。结果表明：晨明组岩石样品化学蚀变指数（I_CA）值和斜长石蚀变指数（I_PA）值较低、成分变异指数（I_CV）值中等偏高,指示晨明组沉积物来源于不成熟的物质源区,并经历了较弱的化学风化作用和活动构造背景下的初次循环;LREE富集、HREE稳定和明显的负Eu异常,指示沉积物源区物质具有明显的上地壳特征且沉积物源岩为长英质火成岩;主量、微量和稀土元素特征共同指示晨明组形成于活动大陆边缘环境或大陆岛弧环境。结合前人研究成果,判定晨明组沉积物来源于经历了弱-中等程度化学风化作用的早古生代花岗质岩,沉积构造背景可能为靠近大陆岛弧的活动大陆边缘环境。     

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。     

Detrital Zircon U‐Pb Ages and Geochemistry of the Silurian to Permian Sedimentary Rocks in Central Inner Mongolia,China: Implications for Closure of the Paleo‐Asian Ocean

The Solonker suture zone has long been considered to mark the location of the final disappearance of the PaleoAsian Ocean in the eastern Central Asian Orogenic Belt(CAOB). However, the time of final suturing is still controversial with two main different proposals of late Permian to early Triassic, and late Devonian. This study reports integrated wholerock geochemistry and LA-ICP-MS zircon U-Pb ages of sedimentary rocks from the Silurian Xuniwusu Formation, the Devonian Xilingol Complex and the Permian Zhesi Formation in the Hegenshan-Xilinhot-Linxi area in central Inner Mongolia, China. The depositional environment, provenance and tectonic setting of the Silurian-Devonian and the Permian sediments are compared to constrain the tectonic evolution of the Solonker suture zone and its neighboring zones. The protoliths of the silty slates from the Xuniwusu Formation in the Baolidao zone belong to wacke and were derived from felsic igneous rocks with steady-state weathering, poor sorting and compositional immaturity. The protoliths of metasedimentary rocks from the Xilingol Complex were wackes and litharenites and were sourced from predominantly felsic igneous rocks with variable weathering conditions and moderate sorting. The Xuniwusu Formation and Xilingol Complex samples both have two groups of detrital zircon that peak at ca. 0.9–1.0 Ga and ca. 420–440 Ma, with maximum deposition ages of late Silurian and middle Devonian age, respectively. Considering the ca. 484–383 Ma volcanic arc in the Baolidao zone, the Xuxiniwu Formation represents an oceanic trench sediment and is covered by the sedimentary rocks in the Xilingol Complex that represents a continental slope sediment in front of the arc. The middle Permian Zhesi Formation metasandstones were derived from predominantly felsic igneous rocks and are texturally immature with very low degrees of rounding and sorting, indicating short transport and rapid burial. The Zhesi Formation in the Hegenshan zone has a main zircon age peak of 302 Ma and a subordinate peak of 423 Ma and was deposited in a back-arc basin with an early marine transgression during extension and a late marine regression during contraction. The formation also crops out locally in the Baolidao zone with a main zircon age peak of 467 Ma and a minor peak of 359 Ma, and suggests it formed as a marine transgression sedimentary sequence in a restricted extensional basin and followed by a marine regressive event. Two obvious zircon age peaks of 444 Ma and 280 Ma in the Solonker zone and 435 Ma and 274 Ma in Ondor Sum are retrieved from the Zhesi Formation. This suggests as a result of the gradual closure of the Paleo-Asian Ocean a narrow ocean sedimentary environment with marine regressive sedimentary sequences occupied the Solonker and Ondor Sum zones during the middle Permian. A restricted ocean is suggested by the Permian strata in the Bainaimiao zone. Early Paleozoic subduction until ca. 381 Ma and renewed subduction during ca. 310–254 Ma accompanied by the opening and closure of a back-arc basin during ca. 298–269 Ma occurred in the northern accretionary zone. In contrast, the southern accretionary zone documented early Paleozoic subduction until ca. 400 Ma and a renewed subduction during ca. 298–246 Ma. The final closure of the Paleo-Asian ocean therefore lasted at least until the early Triassic and ended with the formation of the Solonker suture zone.     

鄂尔多斯盆地白垩系洛河组风成砂岩地球化学与物源区特征:以靖边县龙洲乡露头为例

通过镜下观察,岩石常量元素、稀土微量元素含量测定等手段对鄂尔多斯盆地白垩系洛河组风成砂岩进行实验分析,研究其地球化学和物源区特征。确定洛河组风成砂岩地球化学岩石类型为长石砂岩和亚长石砂岩,沉积物的成熟度较高;物源区为被动大陆边缘构造背景占主导地位的再旋回造山带,并含有大陆岛弧的特性;沉积物母岩为变质岩、沉积岩,并含少量的酸性、中基性岩浆岩;物源区气候寒冷干旱,为氧化环境,化学风化程度低。     

大兴安岭中段索伦地区林西组岩石地球化学特征与沉积构造环境

大兴安岭中段林西组是重要的含烃源岩层位,烃源岩的形成与生烃母质生物活动和埋藏时的古气候、古构造、古环境息息相关。通过岩石地球化学分析可以恢复林西组沉积时期的气候与构造环境,利用Sr、Li、Ga 含量、Sr/Ba 值、U/Th 值、δU及Sr/Cu 值,从古盐度、氧化还原环境、古气候等方面分析了索伦地区林西组的沉积环境,认为林西组沉积时可能经历了中等—较强风化后的再沉积作用,总体为淡水—微咸水的氧化环境,气候温湿; Al₂O₃/(Al₂O₃+Fe₂O₃)值、K₂O/Na₂O- SiO₂关系以及稀土元素特征表明: 林西组形成于靠近大陆岛弧的活动大陆边缘,由早期弧后盆地的海陆过渡相半咸水环境向陆相的淡水环境演变,有利于有机质的富集和保存,是寻找烃源岩的有利层位。研究成果可为该区烃源岩勘查提供指导。     

Geochemical characteristics and depositional environment of the Middle Permian mudstones from central Qiangtang Basin,northern Tibet

Geochemical characteristics of the Middle Permian mudstones from the Longge Formation in the Jiaomuri area, central uplift zone of Qiangtang Basin have been analysed to constrain their provenance, tectonic setting, depositional redox condition and palaeoclimate. Based on the geochemical parameters like CIA, PIA, ICV values and Th/U, K/Rb ratios indicate that the source rocks were affected by low degree weathering conditions. The U/Th, V/Cr, Ni/Co, V/Sc ratios and U_au, C‐values of samples suggest that the mudstones were formed in an oxic environment, with arid palaeoclimate. Bulk‐rock geochemistry analysis indicates that they are mainly arkose and subarkose, derived from dominantly andesitic rocks, probably a mixing of felsic and mafic provenance. The CIA, PIA and ICV values of these samples suggest that the Longge mudstones are compositionally immature and related to moderate weathering. The tectonic discrimination diagrams, as well as critical trace and REE characteristic parameters imply an oceanic arc or continental arc setting for the depositional basin of mudstones from the Longge Formation, probably back‐arc basin. This study supports an occurrence of archipelagic oceanic basins in the Jiaomuri area in the Middle Permian, which provides evidence for the research of the Longmu Co–Shuanghu–Lancangjiang Suture. Copyright © 2015 John Wiley & Sons, Ltd.     

Provenance and tectonic setting of the Lower Cambrian Niutitang formation shales in the Yangtze platform,South China: Implications for depositional setting of shales

Geochemical compositions of the Lower Cambrian Niutitang Formation shales in the southeastern Yangtze Platform margin were investigated for provenance, tectonic setting, and depositional environment. The shale samples are characterized by higher abundances of large ion lithophile elements (Cs, Ba, and Pb), lower abundances of high field strength elements (Cr, Sc, and Co) and transition elements (Th, Zr, Hf, Nb, and Ta) relative to average shale. North American shale composition (NASC) -normalized rare earth element (REE) patterns are observed, with negative Ce anomalies, negative Eu anomalies, and positive Y anomalies. The chemical index of alteration (CIA) varies from 68.67–74.93. Alkali and alkaline element contents and CIA values suggest that the source rocks have undergone moderate weathering. The index of compositional variability (ICV), Zr/Sc and Th/Sc ratios vary from 0.53 to 1.07, 5.31 to 8.18 and 0.52–1.02, respectively. ICV values and relationships between Zr/Sc and Th/Sc ratios indicate negligible sedimentary recycling. The Al₂O₃/TiO₂ (14–26) and TiO₂/Zr (56–77) ratios imply that the source rocks of the investigated shales had intermediate igneous compositions. However, Cr/V ratios and a La/Th–Hf discrimination diagram suggest that the intermediate compositional signal of the source rocks was derived from a mixture of 75% mafic and 25% felsic igneous rocks rather than intermediate igneous rocks. The major source was the Jiangnan continental island arc with bimodal igneous rocks, lying to the south of the study area, together with a contribution from granites and gneisses uplifted and eroded in the Yangtze Block. Discrimination of tectonic setting using major and trace elements indicates that the source rocks originated in a transitional setting from active continental to passive margin, consistent with the failed intracontinental rift model for the evolution of the South China plate. The Niutitang Formation shales were deposited in a rift basin setting under conditions of anoxic bottom water in a redox-stratified water column, with organic-rich shales prospective for shale-gas production being found in deep-water downslope and basin environments rather than the shallow-water shelf.     

Geochemistry of Carboniferous Sandstones (Sardar Formation), East‐Central Iran: Implication for Provenance and Tectonic Setting

Geochemical analysis of sandstones from the Sardar Formation (from two stratigraphic successions) in east-central Iran were used for identification of geochemical characterization of sandstones, provenance and tectonic setting. Sandstones in the two lithostratigraphic successions have similar chemical compositions suggesting a common provenance. Bulk-rock geochemistry analysis of Carboniferous sandstones from Sardar Formation indicates that they are mainly quartz dominated and are classified as quartzarenites, sublitharenites and subarkoses, derived from acid igneous to intermediate igneous rocks. Discrimination function analysis indicates that the sandstones of Sardar Formation were derived from quartzose sedimentary provenance in a recycled orogenic setting. Also, major and trace elements in sandstones of Sardar Formation (e.g., K2O/Na2O vs. SiO2) indicate deposition in a stable passive continental margin (PM). Chemical index of alteration (CIA) for these rocks (> 65%) suggests a moderate to relatively high degree of weathering in the source area.     

大兴安岭中南段下二叠统寿山沟组典型泥岩地球化学特征及其地质意义

西乌珠穆沁旗地区下二叠统寿山沟组泥岩为大兴安岭中南段发育的较好烃源岩.通过对寿山沟组泥岩中的主量、微量、稀土元素特征的分析,深入剖析了寿山沟组的物源、构造背景及其风化作用.岩石样品ICV值分布于1.15～1.57,平均值为1.33,认为样品基本未受到二次成岩作用影响.通过A－CN－K三角图判断寿山沟组泥岩受到一定的钾交代作用,经过校正得到CIA_corr值为54.28～70.06,平均值为65.33,表明物源区经历了初等—中等的化学风化作用.通过主量－微量元素多变量物源区环境分析,认为寿山沟组泥质沉积物主要来源于长英质物源区,且混有少量铁镁质火山岩源区物质,其构造背景为大陆岛弧.综合分析认为,大兴安岭中南段下二叠统寿山沟组泥岩的沉积特征归因于古亚洲洋二叠纪初期洋壳的俯冲作用.