Zircon U-Pb geochronology of the volcanic rocks from Fanchang-Ningwu volcanic basins in the Lower Yangtze region and its geological implications

The latest eruptions in two important Mesozoic volcanic basins of Fanchang and Ningwu located in the middle-lower reaches of the Yangtze River formed the bimodal volcanic rocks of the Kedoushan Formation and ultrapotassic volcanic rocks of the Niangniangshan Formation, respectively. The representative volcanic rocks of the two Formations were selected for LA-ICPMS zircon U-Pb dating. The results indicate that there exist a large amount of magmatic zircons as indicated by high Th/U ratios in these volcanic rocks. The weighted mean age of 21 analyses is 130.7±1.1 Ma for the Kedoushan Formation, and that of 20 analyses is 130.6±1.1 Ma for the Niangniangshan Formation. These U-Pb ages are interpreted to represent the formation times of the volcanic rocks. In combination with other known geochronological data for Mesozoic volcanic rocks from the Lower Yangtze region, it is proposed that the latest volcanic activations in the Jinniu, Luzong, Fanchang and Ningwu volcanic basins probably came to end prior to ca. 128 Ma. There is no significant time interval between the early and later volcanic activities in the Luzong and Ningwu basins, suggesting a short duration of volcanic activities and thus implying the onset of an extensional tectonic setting at about 130 Ma in the Lower Yangtze region. Integrated studies reveal that the Early Cretaceous magmatic activities and their geochronological framework in the Lower Yangtze region are a response to progressively dynamic deep processes that started with the transformation of tectonic setting from compression to extension, followed by delaminating of the lower part of the thickened lithosphere, lithospheric thinning, asthenosphere upwelling, and crust-mantle interaction.     

大兴安岭北段漠河地区塔木兰沟组火山岩地球化学特征

 大兴安岭北段漠河地区分布有大面积的晚中生代火山岩,塔木兰沟组是其中喷发较早的一期。塔木兰沟组是一套中基性火山岩,包括熔岩和火山碎屑岩,研究其成因对于理解大兴安岭北段的构造演化具有重要意义。对塔木兰沟组火山岩样品进行了系统的主量元素和微量元素地球化学分析。结果表明：样品大部分呈碱性,SiO₂的质量分数为52.7%～57.8%,为中基性岩石,岩石类型为玄武质粗面安山岩和粗面安山岩;相容的过渡族金属元素如Cr、Co、Ni等含量低,微量元素比值如Nb/La、Ba/Nb、Nb/U、Ce/Pb等及稀土元素总量的变化范围大,具有右倾的轻稀土元素富集的稀土元素分布模式。岩石成因分析表明,富集的大陆岩石圈地幔先经历了部分熔融,然后熔浆受到了轻度的地壳物质的混染以及一定程度的分离结晶作用,最终形成了塔木兰沟组火山岩。     

SHRIMP U-Pb zircon dating for the dacite of the Sangxiu Formation in the central segment of Tethyan Himalaya and its implications

The Tethyan Himalaya is located between the In-dus-Yarlung Zangbo suture zone to the north and HigherHimalayan crystallines to the south, paleogeographicallybelonging to the northern margin of “Greater India”. TheSangxiu Formation is used to define a series of specialstrata with rich volcanic interbeds, and is only distributedto the southeast of Yangzuoyong Co within 200 km×50 km along the eastern part of central Tethyan Hima-laya[1]. Based on overlapped relationships of strata andfos…     

内蒙古中部宝力高庙组长英质火山岩U-Pb-Hf同位素特征及其地质意义

锆石SHRIMP U-Pb定年结果显示: 内蒙古中部白音乌拉地区原宝力高庙组的流纹岩形成时代为300.0±2.9 Ma, 属晚石炭世; 青格勒宝拉格地区原宝力高庙组的凝灰岩结晶年龄为159.6±1.4 Ma, 并获得 3颗捕获锆石的年龄分别为291.8±3.4, 304.0±3.3和734.7±9.2 Ma, 应属于晚侏罗世满克头鄂博组。锆石LA-MC-ICP-MS Hf同位素分析显示: 流纹岩锆石ε_Hf(t) 值为+10.5~+12.9, T_DM^C值为493~645 Ma; 凝灰岩岩浆锆石ε_Hf(t)值为+10.1~+13.1, T_DM^C值为369~563 Ma。研究结果表明, 流纹岩源于晚古生代新生地壳的重熔并混入少量老地壳物质, 凝灰岩源于晚古生代地壳的熔融。Hf同位素特征显示晚古生代流纹岩和中生代凝灰岩源于相似的源区, 揭示了晚古生代的一次重要的增生事件, 并且在约160 Ma时期发生过地壳的再造。结合前人的研究成果表明, 兴蒙造山带在约300 Ma时处于古亚洲洋演化过程中岛弧向碰撞后伸展环境的转换时期, 在约160 Ma受到蒙古?鄂霍茨克构造域的影响。     

青藏措勤盆地下白垩统则弄群火山岩岩石地球化学特征

青藏高原措勤盆地早白垩世火山活动十分强烈,则弄群火山岩主要分布在措勤盆地中央隆起带的冈底斯构造岩浆岩带中,则弄群以安山岩—英安岩—流纹岩钙碱性系列火山熔岩及火山碎屑岩为主,盆地北部坳陷带中火山活动相对较弱,见有少量玄武安山岩、安山岩。则弄群火山岩岩石化学、地球化学特征分析表明,该火山岩形成于岛弧区构造环境中,这与古特提斯洋壳沿雅鲁藏布江结合带向北俯冲作用有关     

江西南部版石盆地火山岩SHRIMP锆石U-Pb年龄及其地质意义

应用SHRIMP锆石U-Pb定年方法,对江西南部三南-寻乌火山岩带版石盆地原鸡笼嶂组凝灰岩和原版石组流纹岩开展年代学研究.结果表明,凝灰岩SHRIMP锆石U-Pb年龄为(142.5±1.3)Ma,流纹岩SHRIMP锆石U-Pb年龄为(131.4±1.3)Ma.根据新的国际地层表,晚侏罗世与早白垩世的界线划在(145.5...     

长江流域岩体的时空分布与碎屑锆石物源示踪

结合区域大地构造演化,系统总结并讨论了长江流域火成岩的时空分布特征及其对长江中下游沉积物物源的指示意义.结果表明,长江流域岩体的时空分布特征与区域构造演化密切相关;青藏高原新生代酸性侵入岩和火山岩以及云贵川高原晚二叠世峨眉山玄武岩及伴生酸性岩是长江上游地区的特征岩体;汉江和湘江—赣江流域早古生代中酸性侵入岩是长江中游地区的特征岩体;白垩纪中酸性侵入岩和火山岩是长江下游地区的特征岩体.这一成果可直接用于指导长江中下游地区利用碎屑锆石U-Pb年代学和Hf同位素进行物源示踪的工作.在钻孔沉积物中准确识别出这些特征年龄信息,并结合沉积物古地磁年代的标定对研究长江的地质演化历史具有重要指示意义.     

鄂东南大冶地区中生代火山岩时代及意义

文中通过应用SHRIMP锆石微区U-Pb测年技术对马架山组凝灰岩进行了精确测年,判定其形成时代为早白垩世（123.6 Ma）,与长江中下游地区其他火山岩盆地形成时代类似.通过邻区对比,认为白垩纪长江中下游地区处于伸展构造背景.     

高松山金矿床控矿特征、成因及找矿前景

高松山金矿是与火山作用关系较为密切的浅成低温热液型金矿床。矿石类型主要为含金石英脉—构造角砾岩蚀变岩型。矿石硫同位素组成具有深源硫的特点。流体包裹体中H、O同位素反映在成矿的过程中有大气降水加入。矿床产于中生代上白垩统火山岩中,与英安岩、安山岩、安山玢岩、流纹岩关系密切。岩石化学分析反映了活动大陆边缘环境。金矿体与赋矿围岩存在着明显的物性差异,与Au、Ag、As、Sb、Cu有密切的相关关系,并以零磁场、高电阻为特征,从而本区具备了物化探找矿前提。该区为黑龙江东北部的一个重要的找矿远景区。     

Chronological record of the Early Mesozoic underplating in the northern margin of North China─U-Pb chronometry of zircons in the Late Mesozoic andesite from Western Liaoning

Cathodoluminescence spectroscopic analysis of zircons in the uppermost sanukites of the early Cretaceous Yixian Formation in Western Liaoning reveals zoning structures of the zircons in the volcanic rocks. LA-ICP-MS chronometry shows that the central part of the zircons is remnant zircon with a U-Pb dating of 254 Ma, which is consistent with the age of the Early Mesozoic underplating granulites, and that the periphery is zircon crystallizing out of the host magma with a U-Pb dating of 116 Ma, which is highly consistent with the Ar-Ar dating of the host volcanic rocks. Compositions of the clinopyroxenes xenocrystals in the sanukites are similar to those of the clinopyroxenes in the underplating granulites, indicating that the granulites accreted to the lower crust in the Early Mesozoic have been reformed and disrupted by the upwelling diapers of the asthenosphere and taken part in formation of the sanukites in the Late Mesozoic.     

^40Ar-^39Ar geochronology of Cenozoic Linzizong volcanic rocks from Linzhou Basin, Tibet, China, and their geological implications

Whole-rock and mineral separate Ar-Ar dating was carried out for the Linzizong volcanic rocks at Linzhou Basin in Tibet to constrain the time span of volcanism and the corresponding stratigraphic sequence. Sampling was based on detailed geologic mapping and stratigraphic sequence of Dianzhong, Nianbo, Pana Formations, systematically from the bottom to near the top. The results indicate that the Linzizong volcanic rocks erupted from Paleocene to middle of Eocene (64.43--43.93 Ma). Among them, the Pana Formation formed from ca. 48.73 to 43.9 Ma, the Nianbo Formation around 54 Ma and the Dianzhong Formation from 64.4 to 60.6 Ma. In combination with evidence from the geochemical characteristics of the volcanic rocks, and from stratigraphy in southern Tibet, it is postulated that the age of the lowest member in the Dianzhong Formation of the Linzizong volcanic rock, which overlies unconformably the Late Cretaceous Shexing Formation, likely corresponds to the inception of the collision between Indian and Asian continents in southern Tibet.     

长江下游火山岩的二个变异趋势及其形成机制

长江下游地区若干盆地不同旋回火山岩的化学成分存在２个不同的变异趋势，即富硅趋势和富钾趋势。富硅趋势主要由分离结晶作用形成的。富钾趋势的成因较为复杂。庐枞富钾趋势的形成与分离结晶作用有关，溧水富钾趋势涉及分离结晶与混染作用。而宁芜富钾岩石是由独立的母岩浆形成的。     

浙西北钟吕群流纹岩锆石U-Pb年龄及其年代地层学意义

 钟吕群出露于浙西北地区,为一套强变形、浅变质的碎屑岩-火山岩系,其下未见底,上被南华纪休宁组不整合覆盖。传统上将其对比于赣东北双桥山群。本文主要研究钟吕群流纹岩的锆石U-Pb 年龄。样品A120408-4 采自苏庄断层以北,层位上属钟吕群的中上部,岩性为灰白色致密块状流纹岩,强烈片理化。样品A120408-4 中获得大量锆石,完成LA-ICP-MS 锆石UPb定年测点38 个,获得年龄加权平均值为(777.1±3.6)Ma,结合地层特点及变质变形特征,得出钟吕群主体相当于河上镇群上墅组,应属扬子古陆新元古代晚期大陆裂谷的地质记录。     

内蒙古四子王旗地区中二叠世火山岩年代学、地球化学特征及构造意义

对华北克拉通与兴蒙造山带结合部位的内蒙古四子王旗地区出露的一套原定为中?下侏罗统的流纹岩进行岩石学、岩石地球化学、锆石U-Pb同位素年代学和Hf同位素组成研究, 确定其岩石成因及地球动力学意义。新获得的流纹岩和流纹斑岩LA-ICP-MS锆石U-Pb 年龄分别为262±2和261±2 Ma, 表明流纹岩的时代应为中二叠世晚期。四子王旗地区流纹岩多属高钾钙碱性系列和钾玄岩系列岩石, 具有高硅、高碱、富铝以及贫钙、贫镁的特征。稀土元素总量较大, 配分曲线明显右倾, 具有中度到重度Eu负异常, 富集大离子亲石元素Rb, Th和轻稀土元素, 亏损Nb, Ta, Sr和Ba等元素。火山岩的ε_Hf(t)为负值(-25.97~-11.94), 可能主要来源于古老地壳熔融岩浆。该套火山岩具有高硅流纹岩的地球化学特征, 表明岩浆经历过结晶分异过程, 岩浆喷出与深部幔源岩浆的加热有关。结合相关构造判别图解, 判断该套火山岩可能形成于后碰撞伸展阶段。     

Chronological record of the Early Mesozoic underplating in the northern margin of North China─U-Pb chronometry of zircons in the Late Mesozoic andesite from Western Liaoning

Cathodoluminescence spectroscopic analysis of zircons in the uppermost sanukites of the early Cretaceous Yixian Formation in Western Liaoning reveals zoning structures of the zircons in the volcanic rocks. LA-ICP-MS chronometry shows that the central part of the zircons is remnant zircon with a U-Pb dating of 254 Ma, which is consistent with the age of the Early Mesozoic underplating granulites, and that the periphery is zircon crystallizing out of the host magma with a U-Pb dating of 116 Ma, which is highly consistent with the Ar-Ar dating of the host volcanic rocks. Compositions of the clinopyroxenes xenocrystals in the sanukites are similar to those of the clinopyroxenes in the underplating granulites, indicating that the granulites accreted to the lower crust in the Early Mesozoic have been reformed and disrupted by the upwelling diapers of the asthenosphere and taken part in formation of the sanukites in the Late Mesozoic.     

大平掌铜多金属矿床火山岩构造环境的地球化学证据

大平掌铜多金属矿床是滇西目前发现的最重要海相火山岩块状硫化物矿床,其主要含矿建造为大凹子组火山岩系。大凹子组火山岩系主要岩性为中酸性火山熔岩及其火山碎屑岩夹细碧岩,其次还含多层硅质岩、凝灰质粉砂岩、沉凝灰岩、碳质或钙质页岩及碳酸盐岩等。通过结合已有的地球化学数据和最新的地球化学数据,对该区域的火山岩构造环境进行比较系统的研究。矿区细碧岩、英安岩等明显地Na2O>K2O;而凝灰岩和蚀变流纹岩则相反。矿区主要火山岩均以相对富集U、Th、La、Nd、Hf、Sm和相对亏损Rb、Ba、Nb、Sr、Ti、P为特征。火山岩的稀土元素总体上具有LREE>HREE的特点,LREE略微富集。综合大平掌火山岩主量、痕量元素岩石地球化学特征,表明大凹子组火山岩系形成于消减作用环境下的火山岛弧与弧后裂陷盆地的过渡带,并具有裂陷带双峰系列火山岩组合的特点。     

内蒙古西乌旗地区二叠纪双峰式火山岩的年代学、地球化学特征和地质意义

为了加深对中亚造山带东段晚古生代构造背景的认识, 选取内蒙古西乌旗地区二叠纪火山岩进行年代学和地球化学研究。分别利用X光荧光光谱(XRF)、SHRIMP锆石U-Pb测年、ICP-MS和ISOPROBE-T方法测定研究区火山岩的主量元素含量、年龄、微量元素和稀土元素含量及Sr-Nd同位素。结果表明, 这套火山岩的SiO₂含量集中分布在53.54%~54.71%和72.61%~80.81%两个区间, 分别属于玄武安山岩和流纹岩, 构成双峰式火山岩组合。流纹岩SHRIMP锆石U-Pb年龄为279 ± 4.3 Ma, 说明它喷发于早二叠世。玄武安山岩轻稀土略富集而重稀土略亏损, (La/Yb)_N为2.06~2.34, 有轻微的Eu负异常, 富集大离子亲石元素和高场强元素, Nb, Ta和Sr有明显的负异常, 推断其来源于深部非原始地幔, 很大程度上受地壳成分的混染。流纹岩亦略富集轻稀土, 略亏损重稀土, (La/Yb)_N为1.70~3.81, 有很强的Eu负异常, Sr, P和Ti相对强烈亏损, Nb和Ta轻度亏损, K, Zr和Hf相对富集, 具有较高的正ε_Nd(t)值(+3.98~+5.62)和年轻的模式年龄T_DM(490~690 Ma), 具有A型花岗岩的特征, 推断其为新生陆壳来源。综合地球化学特征、区域地质特征和前人研究资料, 这套双峰式火山岩具有板内成因特征, 形成于碰撞后的伸展环境。     

下扬子地区盆地的"四层楼"结构及其动力学机制

下扬子地区震旦纪以来经历了不同的大地构造与地球动力学背景 ,盆地演化相应地经历了震旦纪—中三叠世海盆→晚三叠世—中侏罗世沿江前陆盆地→晚侏罗世—早白垩世火山岩盆地→晚白垩世—早第三纪陆相伸展盆地。下扬子地区震旦纪—中三叠世海盆发育于伸展性被动大陆边缘。沿江前陆盆地形成于扬子与华北板块碰撞活动中的前陆变形带上。火山岩盆地出现于区域性走滑剪切和环太平洋岩浆弧背景下。库拉—太平洋板块高角度、高速正面向东亚大陆下的俯冲 ,造成了岩石圈上拱拉张 ,从而产生了晚白垩世—早第三纪的陆相伸展盆地。随着西太平洋边缘弧后盆地的出现及印度与欧亚板块的碰撞 ,中国东部遭受近东西向挤压 ,从而结束了下扬子地区的盆地演化历史。     

一种求解服务选取问题的混合蚁群算法

摘 要：为解决大规模服务选取问题,本文提出了一种混合蚁群算法（HACO）。该算法先采用动态skyline服务查询过程过滤抽象服务类相关的冗余候选服务,以大力缩减空间提高查找效率,然后利用聚类设计动态构造图来引导蚂蚁的搜索方向,从而确定局部服务选取的搜索区域;基于已经确定的局部服务选取的搜索区域,利用启发式策略选取具体的组合服务。我们采用标准的真实数据集和综合产生的数据集对我们的方法进行试验评估,以及和最近提出的相关组合服务算法进行对比。实验结果在解的质量和处理时间方面效果显著     

银根盆地苏红图组火山岩特征及其与油气的关系

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