藏北羌塘中部日湾茶卡组物源——LA-ICP-MS锆石U-Pb年龄及稀土元素特征

在龙木错—双湖—澜沧江板块缝合带中段的冈玛错—日湾茶卡地区,近东西向展布着一条富含暖水型生物化石的早石炭世地层日湾茶卡组(C1r)。对日湾茶卡组砂岩中的碎屑锆石进行LA-ICP-MS U-Pb定年,分析结果显示存在325~400Ma、400~500Ma、500~600Ma、950~1100Ma、1400~1800Ma和大于1800Ma六个年龄区间;最年轻的碎屑锆石年龄为325 Ma,时代为早石炭世维宪期;碎屑锆石中362 Ma和454Ma的年龄峰值最明显,为龙木错—双湖—澜沧江洋岛弧消减事件和加里东运动的年龄记录,表明碎屑岩的物源区主要来自于扬子大陆周缘。结合古生物化石资料可知,日湾茶卡组属于欧亚大陆扬子型石炭纪沉积地层,为岛弧环境下的一套浅水台型沉积。     

塔中北斜坡鹰山组岩溶储层发育规律

塔中北斜坡奥陶系鹰山组的岩溶储层具有巨大的油气潜力。随着勘探和开发工作的细化,需要明确鹰山组内岩溶储层在空间上的展布形态。依据三维地震资料的反射特征,认为鹰山组顶部发育了四期次岩溶作用,经历了地层剥蚀—剥蚀与岩溶作用共存—岩溶发育—充填的成岩过程。各期次岩溶作用发生时潜水面逐渐上升,伴随有高构造部位的削蚀。提出了岩溶储层的多期次发育模式。     

How many sutures in the southern Central Asian Orogenic Belt：Insights from East Xinjiang-West Gansu（NW China）？

How ophiolitic mèlanges can be defined as sutures is controversial with regard to accretionary orogenesis and continental growth.The Chinese Altay,East junggar,Tianshan,and Beishan belts of the southern Central Asian Orogenic Belt（CAOB） in Northwest China,offer a special natural laboratory to resolve this puzzle.In the Chinese Altay,the Erqis unit consists of ophiolitic melanges and coherent assemblages,forming a Paleozoic accretionary complex.At least two ophiolitic melanges（Armantai,and Kelameili） in East Junggar,characterized by imbricated ophiolitic melanges,Nb-enriched basalts,adakitic rocks and volcanic rocks,belong to a Devonian-Carboniferous intra-oceanic island arc with some Paleozoic ophiolites,superimposed by Permian arc volcanism.In the Tianshan,ophiolitic melanges like Kanggurtag,North Tianshan,and South Tianshan occur as part of some Paleozoic accretionary complexes related to amalgamation of arc terranes.In the Beishan there are also several ophiolitic melanges,including the Hongshishan,Xingxingxia-Shibangjing,Hongliuhe-Xichangjing,and Liuyuan ophiolitic units.Most ophiolitic melanges in the study area are characterized by ultramafic,mafic and other components,which are juxtaposed,or even emplaced as lenses and knockers in a matrix of some coherent units.The tectonic settings of various components are different,and some adjacent units in the same melange show contrasting different tectonic settings.The formation ages of these various components are in a wide spectrum,varying from Neoproterozoic to Permian.Therefore we cannot assume that these ophiolitic melanges always form in linear sutures as a result of the closure of specific oceans.Often the ophiolitic components formed either as the substrate of intra-oceanic arcs,or were accreted as lenses or knockers in subduction-accretion complexes.Using published age and paleogeographic constraints,we propose the presence of （1） a major early Paleozoic tectonic boundary that separates the Chinese Altay-East Junggar multiple subduction system     

http://www.sciencedirect.com/science/article/pii/S1674987113001606

The paper reviews previous and recently obtained geological, stratigraphic and geochronological data on the Russian-Kazakh Altai orogen, which is located in the western Central Asian Orogenic Belt （CAOB）, between the Kazakhstan and Siberian continental blocks. The Russian-Kazakh Altai is a typical Pacific-type orogen, which represents a collage of oceanic, accretionary, fore-arc, island-arc and continental margin terranes of different ages separated by strike-slip faults and thrusts. Evidence for this comes from key indicative rock associations, such as boninite- and turbidite （graywacke）-bearing volcanogenic-sedimentary units, accreted pelagic chert, oceanic islands and plateaus, MORB-OIB-protolith blueschists. The three major tectonic domains of the Russian-Kazakh Altai are： （1） Altai-Mongolian terrane （AMT）; （2） subduction-accretionary （Rudny Altai, Gorny Altai） and collisional （Kalba-Narym） terranes; （3） Kurai, Charysh-Terekta, North-East, Irtysh and Char suture-shear zones （SSZ）. The evolution of this orogen proceeded in five major stages： （i） late Neoproterozoic-early Paleozoic subduction-accretion in the Paleo-Asian Ocean; （ii） Ordovician-Silurian passive margin; （iii） Devonian-Carboniferous active margin and collision of AMT with the Siberian conti- nent; （iv） late Paleozoic closure of the PAO and coeval collisional magmatism; （v） Mesozoic post-collisional deformation and anarogenic magmatism, which created the modern structural collage of the Russian- Kazakh Altai orogen. The major still unsolved problem of Altai geology is origin of the Altai-Mongolian terrane （continental versus active margin）, age of Altai basement, proportion of juvenile and recycled crust and origin of the middle Paleozoic units of the Gorny Altai and Rudny Altai terranes.     

北祁连下古城花岗岩体LA ICP MS锆石U Pb年代学及岩石化学特征

下古城花岗岩体分布于北祁连造山带南缘,岩性主要为石英闪长岩—花岗闪长岩,SiO2质量分数在58.78%~69.53%之间,Al2O3含量为14.30%~15.30%之间,A/CNK为0.86~1.08,属准铝质—弱过铝质,钙碱性—高钾钙碱性系列的I型花岗岩。整体上,具有低SiO2,高CaO、FeOT和MgO的岩石地球化学特征。稀土总量(ΣREE)为87.22×10-6~150.54×10-6,ΣLREE/ΣHREE为6.24~11.11,表明轻重稀土弱分异。富集大离子亲石元素Rb、Th、U、Pb、La等,亏损高场强元素Nb、Ta、P、Ti等,说明下古城花岗岩主要由壳源物质部分熔融形成。锆石原位Lu-Hf同位素分析结果表明,石英闪长岩的εHf(t)=-5.7~-0.7,二阶段模式年龄(tDM2)为1.51~1.83Ga,暗示源岩可能主要为中元古代增生的地壳物质。LA-ICP-MS锆石U-Pb年代学结果表明,下古城石英闪长岩的侵位年龄为505.4±4.1Ma(MSWD=0.78,n=21),与北祁连造山带南缘的柯柯里花岗岩(512Ma~501Ma)、野马咀花岗岩(~508Ma)形成的地球动力学背景相似,均属于北祁连洋向南俯冲活动大陆边缘的岛弧环境。     

西藏申扎地区二叠系下拉组中吴家坪期化石的发现及其意义

重新研究了西藏申扎木纠错地区下拉组剖面,发现该地区下拉组从空谷晚期到吴家坪期连续,露头出露较好,下与昂杰组泥页岩整合接触,上与木纠错组白云质灰岩整合接触。该剖面根据不同的岩性及生物组合可分为三段,其中前二段亦在申扎县北的下拉地区较为发育,时代为空谷晚期至卡匹敦期;但下拉地区由于受断层和褶皱影响强烈,未完全保存第三段,而该段在木纠错剖面中出露较好,并在其含燧石结核灰岩中发现了牙形类Clarkina liangshanensis(Wang)和类Codonofusiella schubertelloides Sheng,确认其时代为乐平世吴家坪期,首次确认下拉组的上部可以延伸至吴家坪期。     

藏北商旭造山型金矿床的发现及意义

西藏双湖县商旭金矿床位于班公湖-怒江缝合带中段。矿体赋存于中-下侏罗统木嘎岗日群浅变质复理石中,受北西西向断裂构造控制,呈透镜体状、脉状,或者似层状产出;矿石矿物以自然金为主,矿石类型为石英脉型和蚀变岩型,围岩蚀变特征明显。该矿床主要受地层及构造因素控制,矿区的构造、围岩蚀变、矿物、地球化学异常等可作为找矿标志。野外地质调查和矿床对比研究显示,商旭金矿床在矿物共生组合、蚀变类型、构造类型等方面,与典型的造山型金矿床相似,其成因类型属于造山型金矿床。商旭金矿床的发现为班公湖-怒江成矿带金等贵金属矿产的地质找矿工作开辟了新的方向。     

乌拉溪铝质A型花岗岩：松潘—甘孜造山带 早燕山期热隆伸展的岩石记录

乌拉溪岩体位于松潘—甘孜造山带南段,江浪穹隆北部。LA-ICP-MS锆石U-Pb定年获得岩体年龄为159.31±0.9Ma。岩石中出现含钙钠长石和铁叶云母等A型花岗岩典型矿物;岩体具有高SiO2、Na2O和K2O含量,高FeOt/MgO、Ga/Al比值,以及低TiO2、CaO和MgO含量特征;稀土元素配分模式呈右倾海鸥型,Eu负异常明显;微量元素富含Rb、Nb和Ga等高场强元素,原始地幔标准化蛛网图显示出Ba、Sr、P和Ti亏损;岩体中锆石的古核稀少,锆石饱和温度计算显示岩体成岩温度很高(变化在967~984℃之间);岩体还相对富铝,A/CNK=0.97~1.27,分布比较集中,都大于0.95,过碱指数(NK/A=0.74~0.91)较低,均在1之下。以上特征表明乌拉溪二云母花岗岩为铝质A型花岗岩。锆石n(176Hf)/n(177Hf)比值变化于0.282228~0.282749,平均值为0.282586,fLu/Hf为-0.99~-0.10,平均值为-0.90,εHf(t)绝大多数为负值,变化于-15.88~1.77之间,平均值为-3.14,说明岩石形成是壳源物质占主导地位,可能为江浪穹隆核部元古宙变质核杂岩的部分熔融。结合区域构造演化,本文认为乌拉溪二云母花岗岩形成于陆—陆碰撞之后的伸展环境,是甘孜—松潘造山带在燕山早期增厚的地壳因伸展松弛而发生减压熔融的产物。     

湘东南—赣西地区加里东期沉积演化特征

通过对研究区加里东期沉积物的野外地质调查、剖面横向对比和岩相古地理编图,发现研究区加里东期主要发育五种沉积相类型,分别为碳酸盐岩陆棚相、碎屑岩—碳酸盐岩混积陆棚相、冰海相、欠补偿型硅质岩—页岩盆地相和补偿型浊积岩盆地相。剖面横向对比显示,研究区加里东期沉积物由西向东为连续相变沉积,横向上各种沉积相指状交叉、相互过渡;岩相古地理研究表明,加里东期湘东南—赣西地区主要发育硅质岩—页岩盆地相和浊积岩盆地相两大相带,从南华纪—奥陶纪时期两大相带的发育规模略有差异,在两大相带的结合部往往发育两种沉积相的交叉过渡带。笔者认为该区沉积相的过渡性质对探讨华南洋加里东期属性的问题有重要意义。     

中生代济源盆地沉积充填特征及其对秦岭、 太行山隆升作用的响应

中生代是济源盆地形成并发展的重要时期。秦岭造山带在晚三叠世造山以及太行山在中侏罗世隆升对济源盆地的沉积格局产生了显著影响,这段时间,盆地始终处在一个盆山相互作用的阶段,将盆地与造山带的构造演化联系起来,有利于更好的认识这一构造沉积响应过程。本文通过对济源盆地中生代地层、沉积及其充填特征的研究,将盆地中生界划分为4个构造层序:TS1、TS2、TS3、TS4,其中TS1充填了下三叠统刘家沟组、和尚沟组和中三叠统二马营组、油房庄组,它是在扬子、秦岭及华北板块汇聚的背景下形成的内陆克拉通型层序。TS2、TS3分别充填了上三叠统椿树腰组、谭庄组和下侏罗统鞍腰组(义马组)、中侏罗统杨树庄组,它们都具有前陆盆地型充填特征,分别响应的是秦岭造山带造山作用沿洛南—栾川断裂以及三门峡—鲁山—舞阳断裂发生的逆冲推覆作用。TS4充填的是中侏罗统马凹组,受太行山隆升作用的影响,形成了厚层的磨拉石堆积。在此基础上,可将济源盆地盆山系统演化归为3个阶段:早—中三叠世大陆基底隆升与内陆克拉通型盆地,晚三叠世—中侏罗世早期秦岭造山与前陆盆地,中侏罗世晚期太行山隆升与山间盆地。显然,济源盆地响应了秦岭造山及太行山隆升,秦岭造山带晚三叠世造山表现为两次逆冲推覆作用,而太行山主体隆升应在中侏罗世晚期,标志着华北克拉通破坏进入高峰期。