The 2405 Ma and 2310 Ma Mafic Dyke Swarms in the Karelian Craton: Age,Chemical and Sr-Nd Isotope Composition,and Tectonic Setting

正Until recently the time period 2400-2200 Ma in the Erath history was characterized by low amount of age data for igneous events,and was even considered as‘magmatic age gap’(Condie et al,2009;Eriksson and Condie,2014).     

南海ODP1148站中中新世(12～18.3 Ma) 天文调谐的年代标尺

ODP1148站深海沉积岩心的磁化率记录显示出较强的周期性变化规律．研究发现,中新世和渐新世的深海地层物性参数具有很强的斜率周期．Shackletoneta1．利用这一规律,以北半球高纬太阳辐射曲线作为天文调谐的目标,以ODP154航次的深海沉积岩心的磁化率记录作为调谐对象,将磁化率的极大值与北半球天文辐射的极小值相对应,建立了14～34Ma的天文调谐的年代标尺．采用相同的方法,利用南海北部ODP1148站深海沉积岩心的磁化率记录和北半球高纬太阳辐射曲线建立了南海中中新世天文调谐的年代标尺．调谐后的磁化率记录显示了很强的斜率周期和较强的岁差周期,并与太阳辐射在这2个记录上高度相关,此外偏心率周期在磁化率记录中也较显著．调谐后1148站的浮游有孔虫事件年龄与ODP154航次采用相同的天文调谐方法获取的事件年龄异常接近,而与传统方法获取的生物地层事件年龄有较大差距,这在一定程度上证明了利用天文调谐的方法建立中新世深海地层年代标尺的可行性．     

Nature of Three Episodes of Magmatism(2181 Ma, 2115 Ma and 1891 Ma) in the Liaohe Rift of North China: Implications for Tectonic Evolution

正To define a tectonic environment switching from rifting to subduction and their respective duration time are usually largely debated.Such case occurs for the Liaohe rift:whether it went through a long subduction from 2100to 1850 Ma or there were two different events in different     

大别山双河硬玉石英岩的超高压变质和退变质事件——SHRIMP测年的证据

应用北京SHRIMPⅡ,精确地测定了大别山双河硬玉石英岩中超高压变质锆石的中心、幔和壳的年龄。大部分锆石中心和幔的年龄集中于239～255Ma之间,加权平均值为243±1Ma(n=23)。壳和含矿物包体的晶域年龄集中在225～234Ma,加权平均值为228±2Ma(n=8)。这些锆石的中心、幔和壳都具有极低的Th/U(0.01～0.09)和REE总量,以及重REE平坦型的配分模式。因此,以锆石内部结构、矿物包体、Th/U值和REE地球化学特征为依据,本文提出了大别山超高压变质作用发生于243±1Ma,退变质作用发生于228±2Ma的新观点。     

Fluvial and tidal sedimentation in the 3000 Ma Mozaan basin,South Africa

The 3000 Ma Mozaan Group comprises three interacting sedimentary environments: (1) braided alluvial plain, (2) offshore shelf, and (3) tidalites. The predominance of planar cross-bedded sandstones in the fluvial sequence indicates that sedimentation was dominated by southerly accreting transverse bars in a distal braided river system. However, the development of lenticular conglomerates suggests the occasional formation of longitudinal gravel bars, probably during periods of high discharge. Argillaceous sediments, some of which are ferrugineous represent an interplay between clastic sedimentation and chemical precipitation on a prograding shelf. The abnormal thickness of these shelf deposits is attributed to facies stacking. The absence of barrier beach deposits suggests that the marginal environment was controlled by macrotidal conditions. Two varieties of tidal sequences are recognized. The first, which forms the classic upward-fining succession, contains ubiquitous ebb-dominated paleocurrents and is interpreted as having been influenced by tidal asymmetry. The other, which lacks the mixed flat unit, was apparently generated by tidal currents flowing parallel to the coastline. The nature of the Mozaan sediments suggests at least incipient cratonization in eastern South Africa 3000 Ma ago.     

Geochemistry and geochronology of the ~620 Ma gold-associated Batouri granitoids,Cameroon

The Batouri gold mining area in southeastern Cameroon is part of the Adamawa–Yadé Domain of the Central African Fold Belt (Pan-African). It is underlain by a variety of granitic rocks, including alkali-feldspar granite, syeno-monzogranite, granodiorite, and tonalite. Geochemical data suggest that these rocks formed by differentiation of I-type tonalitic magma under oxidizing conditions in a continental volcanic arc setting. U–Pb dating of zircons from gold-associated monzogranite-granodiorite at Kambélé gave concordant ages of 619 ± 2 and 624 ± 2 Ma, while Ar–Ar dating of alkali-feldspar granite yielded a non-plateau maximum age of 640–620 Ma. These ages imply that the Batouri granitoids were emplaced during the collision of the West African Craton and the Congo Craton.

The geochemical characteristics of the Batouri granitoids as well as their oxidized state (magnetite series) are typical of gold-associated felsic rocks in subduction settings elsewhere. The similarities in age, composition, and geochemical affinities of these granitoids with those reported from other localities in the Adamawa–Yadé Domain reinforce the earlier assumption that the granitic rocks of this domain represent parts of a regional-scale batholith, with commonly small-scale, high-grade auriferous quartz veins in structurally favourable sites. The spatial and temporal association of gold mineralization and the Batouri granitoids may suggest potential for regional-scale, high-tonnage, granite-related gold ore.     

Detrital Zircon of 4100 Ma in Quartzite in Burang, Tibet

A detrital zircon aged 4.1 Ga is discovered by the SHRIMP U-Pb method in a quartzite in Burang County, western Tibet. This is presently the oldest single-grain detrital zircon in China. The Th-U ratios of the two testing points of the 〉4.0 Ga zircon are between 0.76 and 0.86, indicating their magmatic origin. This discovery has offered an important age for investigating the geological evolution of the Qinghai-Tibet Plateau.     

西藏普兰石英岩中发现41亿年碎屑锆石

在西藏普兰县石英岩中,利用SHRIMPU-Pb法测年发现4.1Ga碎屑锆石。该年龄为目前中国最老单颗粒碎屑年龄。>4.0Ga锆石两测点的Th/U值介于0.76~0.86之间,属岩浆锆石。这一发现,为研究青藏高原的地质演化提供了重要的年龄数据。     

准噶尔盆地玛湖坳陷侏罗系储层

通过对玛湖坳陷侏罗系储层特征的研究,表明该区储层主要为辫状河三角洲、河流相砂体。孔隙以溶蚀孔隙、原生粒间孔隙和残余粒间孔隙为主。储集物性变化大,属中-低孔、中-低渗储层。储集性主要受成岩压实和塑性岩屑影响。最后,结合该地区评价标准,将层序D和B划分为较好储层,层序C和A为较差储层。     

Geochemistry and petrogenesis of the 595 Ma shoshonitic Qunai monzogabbro,Jordan

The last stage in the formation of the Arabian Nubian Shield in Jordan was dominated by post-orogenic igneous activity of the ∼610–542 Ma Araba Suite, including a monzogabbroic stock intruding the Saramuj Conglomerate, near the southeastern corner of the Dead Sea. The geological setting, petrography, geochemistry and geothermometry of the monzogabbro and other cogenetic varieties are used to shed light on the petrogenesis of this stock and reveal its magma source. The monzogabbro, megaporphyry dikes, and scattered syenite pockets are co-magmatic and alkaline, potassic and shoshonitic in nature. REE and trace elements patterns indicate that these magmas were produced from a mantle that had been modified by subduction-related metasomatism. The parental mafic magma could have been derived by 10% partial melting of LILE-enriched phlogopite-bearing spinel lherzolite, probably lithospheric mantle, in association with post-collisional extension. Fractional crystallization of this parental magma by olivine and pyroxene gave rise to the monzogabbroic magma.The megaporphyry dikes with their giant labradorite plagioclase megacrysts represent feeders of a voluminous volcanic activity that could have lasted for about 10⁵ years.Thermodynamic modeling applying the MELTS software indicates crystallization of this suite in the temperature range of 1184–760 °C at a pressure of 2 kbars, agreeing with olivine-pyroxene, pyroxene, and two-feldspar thermometry. The modeled mineralogy and sequence of crystallization of constituent minerals using MELTS is in remarkable agreement with the observed modal mineralogy of the monzogabbro. Furthermore, a great degree of congruity exists between the modeled and observed chemistry of the major minerals with only minor discrepancies between modeled composition of biotite and olivine.     

内蒙古迪彦钦阿木地区260Ma玄武岩地球化学特征及其地质意义

本文对中亚造山带东段内蒙古迪彦钦阿木地区玄武岩(~260 Ma)开展了岩石学和地球化学的系统研究。元素和Sr-Nd同位素地球化学研究表明,该区玄武岩具有富集LREE和亏损HREE的特征,呈现出明显的Eu正异常,而几乎无Ce异常。微量元素组成表现出富集LILE(如Rb、Th和K)和亏损HFSE(如Nb、Ta、Zr和Hf)的特征。同时,该区玄武岩具有较高的Nb/Ta比值(17),较低的初始87Sr/86Sr比值(0.7026~0.7033),以及正的Nd(t)值(3.6~4.6)。综合分析表明,该区玄武岩具有俯冲带火山岩的地球化学特征,其源区主要为亏损的岩石圈地幔,并局部有软流圈物质的加入,但岩浆演化过程中壳源物质混染程度不高。通过元素判别图解及区域地质资料分析,我们推测该区玄武岩的形成与弧后伸展环境下软流圈物质上涌而导致岩石圈地幔的部分熔融有关。因此,古亚洲洋的闭合时限应该不早于该玄武岩的喷发时间(~260 Ma),并且同期存在古亚洲洋板块向北方的西伯利亚或者南蒙古微陆块的俯冲。     

鄂尔多斯盆地奥陶系马五5亚段沉积微相与古地理演化

碳酸盐岩微相分析有利于认识沉积相展布特征和古地理演化规律,对油气勘探具有指导意义。通过大量薄片、岩心资料在鄂尔多斯盆地奥陶系马五₅亚段划分出MFT1—MFT7七种沉积微相类型及MA1—MA4四种沉积微相序列,沉积微相与生物遗迹化石指示马五₅亚段为潮坪环境。结合沉积前古地形及古海平面变化信息,以单因素图件为基础,采用优势相法编制马五₅²层(Ⅰ)、马五₅¹层(Ⅱ)岩相古地理图,沉积环境受沉积前古地形控制而分异:潮上带、潮间上带、潮间下带及潮下带自西向东依次分布,盆地东部高地形处发育潮间带沉积;随古海平面下降,马五₅¹期沉积相带向东迁移,东部潮间带连片分布。     

Zircon U---Pb and biotite Rb---Sr dating of the wami river granulites, Eastern Granulites, Tanzania: Evidence for approximately 715 Ma old granulite-facies metamorphism and final Pan-African cooling approximately 475 Ma ago

A UPb investigation of suites of zircons from five granulites in the Wami River area, Tanzania, yields a 17-points discordia with upper and lower intercepts at 714_?49⁺³⁶ Ma and 538_?35⁺⁴⁹ Ma, respectively. These systematics are interpreted to indicate an age of approximately 715 Ma (Pan African) for the M1 granulite-facies metamorphism, whereas the lower intercept is related to a stage in the uplift and cooling following the M2 amphibolite-facies retrogradation (elsewhere dated at approximately 650 Ma). Three of the granulites contain minor amounts of an inherited, > 1600 Ma old zircon component, probably derived from the igneous precursors of the granulites. A suite of zircons from the adjacent biotite gneisses may signal a provenance age of approximately 2600 Ma (Tanzania craton?), but the U-Pb systematics do not clearly reflect the amphibolitefacies metamorphism (correlated with the M2 partial retrogradation of the granulites) that transformed the sedimentary sequences into gneisses (any petrographic record of a possible older metamorphic influence being absent). Biotite/whole-rock pairs from the same samples yield Rb-Sr ages between about 470 and 485 Ma for the granulites and about 458 Ma for the gneiss. They are interpreted as ‘cooling ages’ and set an age between about 485 and 460 Ma to the final cooling of the crust through the closure temperature of biotite to Rb-Sr. The subsequent granulite-facies and amphibolite-facies events and their chronology are fitted in the continent—continent collision model for the evolution of the Mozambique belt advocated by the first author.     

鄂尔多斯台地靖边潜台南部中奥陶统马五21岩相古地理

鄂尔多斯盆地中奥陶统马家沟组由于受加里东运动影响而隆起抬升遭受风化,形成良好的岩溶油气储层,对其沉积特征的研究是油气勘探的重点。本文以沉积岩石学为指导,以单因素作图为方法论,结合钻井岩心资料、测井资料的细致分析、统计,选取了地层厚度、白云岩含量、灰岩含量、膏盐含量及泥岩含量等单因素,绘制出马五21的岩相古地理图。研究表明,研究区马五12期处于一个相对的海退期,其主要发育膏云坪、云坪、泥云坪和含泥云坪。根据岩相古地理图,结合马五12地层厚度,推测研究区中部存在一个较浅的洼地,并建立了符合本区马五12的沉积模式。综合以上研究,马五21期岩相古地理特征可概括"陆外为坪,云坪广布,坪中有洼,洼中有膏"。根据本区的岩相古地理条件及区域地质特征,对良好的天然气储层的形成进行了初步的探讨。     

新疆卡拉麦里上-中泥盆统间角度不整合和346.8 Ma后碰撞火山岩的意义

在东准噶尔卡拉麦里地区的五彩湾一带出露一套具磨拉石特征的火山沉积建造, 下部为具磨拉石特征的砾岩、砂岩, 上部为一套中基性的火山熔岩夹中酸性的火山凝灰岩.1:20万卡拉麦里山幅将其归入下石炭统松喀尔苏组.通过1:5万地质调查研究发现, 该火山沉积建造底部以一套粗砾岩高角度不整合于下-中泥盆统卡拉麦里组之上, 含晚泥盆世植物化石Prelepidodendron sp.(先鳞木), 中上部火山岩LA-ICP-MS锆石U-Pb年龄为346.8±3.3 Ma, 且被年龄为341.1±4.0 Ma~340.9±5.1 Ma后碰撞花岗岩侵入, 表明其形成时代为晚泥盆世-早石炭世, 时代上对应于北准噶尔地层分区的上泥盆统克安库都克组.该套地层中上部的火山岩的岩石组合为玄武岩、玄武安山岩、夹少量的流纹质凝灰岩, 岩石化学特征上属钙碱性-高钾钙碱性系列, (La/Yb)_N=2.97~6.66, Nb、Ta亏损, 部分样品Zr、Ti弱显亏损, Nb/U、Ce/Pb比值分别为7.43~20.88、3.17~12.45.地球化学特征表明其兼具板内火山岩和弧火山岩的某些特点, 形成于后碰撞伸展环境, 是卡拉麦里洋盆于晚泥盆世之前闭合后后碰撞岩浆活动的产物.这一研究成果对广为关注的卡拉麦里洋盆的闭合时间进行了很好的限定.      

Discovery of ~338 Ma Shibanjing Plagiogranite in the Beishan Area,NW China,and its Geological Significance

The Beishan area,located on the southern margin of the Central Asian orogenic belt,includes four main ophiolitebearing belts.From north to south,these are the Hongshishan ophiolitic belt,the Jijitaizi-Xiaohuangshan ophiolitic belt,the Hongliuhe-Xichangjing ophiolitic belt,and the Fluitongshan ophiolitic belt(Fig.la).To date,only two ophiolites have been identified in the Jijitaizi-Xiaohuangshan ophiolitic belt.     

宁夏固原寺口子剖面色度记录的29 Ma以来气候演化

宁夏自治区南部固原寺口子剖面位于青藏高原东北缘,记录了青藏高原隆升、扩展与区域气候变化之间的相互作用过程,重建该地区气候演化历史对于揭示高原隆升与全球气候变冷对亚洲大陆腹地干旱化的影响具有重要意义。通过对寺口子剖面晚渐新世—第四纪地层沉积物色度(a~*、b~*、L~*)的系统测量,建立了29～0.5 Ma颜色指标变化序列,结合研究区内已发表的磁化率、孢粉和总无机碳数据,揭示出该区域气候经历了四个阶段:29～24.8 Ma为最湿热阶段、23.8～18 Ma为较湿热阶段、18～5 Ma为逐渐变冷阶段、5～0.5 Ma为快速变冷阶段。剖面记录了25～24 Ma、18 Ma、5 Ma两次显著的气候变冷事件和3 Ma气候变暖事件。结合青藏高原东北缘新生代盆地气候代用指标,发现这些气候变冷事件和3 Ma气候变暖事件具有区域性。通过对比深海氧同位素记录、北太平洋粉尘通量记录、青藏高原构造隆升事件和研究区气候演化特征,我们认为青藏高原隆升和全球气候变化共同控制了区域气候演化,但在不同时期所起作用有所差异。     

西藏当雄南部约54Ma辉长岩-花岗岩杂岩的岩石成因及意义

近年来在拉萨地块南部识别的多处基性岩浆活动对揭示地幔源区成分和相关动力学问题提供了重要线索.本文对拉萨-当雄一带原认为是早白垩世茶苍卡辉长岩-浦迁花岗岩杂岩中获得了始新世幔源岩浆活动记录.研究区出露的3种岩石类型及其U-Pb锆石年龄分别是正长闪长岩、碱性角闪二长花岗岩(54.0±0.3Ma)和钾玄质碱性辉长岩(53.8±0.4Ma).其中辉长岩锆石εHf(t)值为-6.6～ -4.2、Hf模式年龄t(O)M为0.88 ～0.97Ga;二长花岗岩εHf(t)为-10.2～ -6.5,Hf地壳模式年龄tDMC为1.5 ～ 1.7Ga.三类岩石都具有富碱、富钾特征,它们具相似的稀土和微量元素含量,均显示大离子亲石元素和Pb富集、高场强元素Nb、Ta、Ti和P亏损等特征.闪长岩和花岗岩的Sr和Nd同位素特征相似,87Sr/86 Sr比值为0.711 ～0.712,εNd(t)为-9.1 ～ -7.1;而辉长岩分别是0.708和-4.8～ -4.9.本文与拉萨地块南部和中部已有结果共同表明,新生代岩浆岩的分布与成分显示了与俯冲带极性吻合的规律性变化特征,即从雅鲁藏布缝合带向北,岩石的富集组分逐渐增加,越过洛巴堆-米拉山断裂带进入具有地壳基底的中部拉萨地块后,岩石则明显增加了地壳富集组分,很好显示了基底成分对岩浆作用的控制.拉萨地块南部大约47Ma开始出现的富集组分,很可能是中部拉萨地块富集的古老地壳基底物质参与和控制的结果,而与印度大陆地壳物质的俯冲无关.茶苍卡辉长岩可能来源于受到早期俯冲来源流体交代的富集岩石圈地幔物质的部分熔融,而茶苍卡角闪二长花岗岩主要来源于古老地壳物质的重熔,但是有幔源物质参与.茶苍卡辉长岩不同于典型岛弧玄武岩,而与板内玄武岩或伸展背景下形成的玄武质岩石类似,其成因很可能与大约52Ma的特提斯洋壳板片断离和岩浆大爆发有关.     

Study of melt and a clast of 546 Ma magmatic arc rocks in the 65 Ma Chicxulub bolide breccia,northern Maya block,Mexico: western limit of Ediacaran arc peripheral to northern Gondwana

The basement of the Maya block of eastern Mexico is generally covered by Mesozoic and Cenozoic platformal carbonate rocks. However, the 65.5 Ma Chicxulub meteorite impact in the northern Yucatan Peninsula excavated deep into the crust and brought crystalline basement fragments into the impact breccias. Common Pb isotopic data from impact melt and a granitic clast from drill core (Y6) are highly radiogenic, consistent with the Archaean derivation. A granodiorite clast in this breccia from drill core (Yaxcopoil-1) yielded a continuous range of concordant ²⁰⁶Pb/²³⁸U laser ablation inductively coupled plasma mass spectrometry zircon ages between 546 ± 5 Ma and 465 Ma, with three discordant zircons having ²⁰⁶Pb/²³⁸U ages between 130 Ma and 345 Ma. The ca. 546 Ma age is interpreted as the age of granodiorite intrusion, with younger ages representing variable Pb loss during melting associated with the meteorite impact. This is consistent with previous U–Pb zircon data that gave an upper intercept age of 550 ± 15 Ma at Chicxulub, which becomes 545 ± 5 Ma when combined with the zircon data from distal ejecta. Such arc rocks are absent in the southern Maya block, and in the neighbouring Oaxaquia terrane (s.s.) they are replaced by a 546 ± 5 Ma plume-related dike swarm. On the other hand, Ediacaran arc rocks continue through the peri-Gondwanan terranes of the Appalachians and Europe (Florida, Carolinia, Avalonia, Iberia, Armorica, Massif Central, Bohemia, and NW Africa). Arc magmatism in these areas ended between 570 Ma (Newfoundland) and 540 Ma (Carolinia/UK) as the subduction zone was replaced by a transform fault along the northern Gondwanan margin. This age range is synchronous with the two-stage birth of Iapetus, suggesting that both are related to major plate reorganization. The source of plume-related dikes may have been located at the rift–rift–transform triple junction between Laurentia, Baltica, and Gondwana.     

安徽马鞍山高村采场矿坑地下水疏干预测

根据马鞍山高村铁矿露天采场矿区地质及水文地质特征,对矿区的基岩裂隙地下水系统进行概化。结合高村采矿场历史疏干资料和观测孔的地下水动态观测资料,建立了矿区地下水水流模型。然后按照露天采场的开采计划,论证矿坑地下水疏干对策,分别对2个开采规划期进行地下水疏干预测,为安全开采和经济有效地防治地下水提供设计依据。