华北克拉通南缘中-新元古代沉积地层对比研究及其地质意义

华北克拉通南缘新太古代-古元古代变质结晶基底之上不整合覆盖着巨厚的中-新元古代陆源碎屑岩-碳酸盐岩沉积盖层,根据沉积建造特征,将其划分为三个不同的地层分布小区,分别为嵩箕地层小区、渑池-确山地层小区和熊耳山地层小区.嵩箕小区位于熊耳裂谷盆地东北缘,以硅质碎屑岩(砂岩)为主,渑池-确山地层小区位于熊耳裂谷盆地北缘,以硅质碎屑岩-碳酸盐岩(白云岩)过渡相为主,熊耳山地层小区位于熊耳裂谷盆地南缘,以碳酸盐岩为主.本文通过对三个地层小区的沉积地层剖面和岩石学特征进行研究,认为华北南缘从中元古代开始处于河流相-浅海相的沉积环境,从南向北,海水由深变浅.根据地层的岩性、沉积构造及其组合特征,将其划分为低水位、海侵和高水位沉积体系,最大海侵时期为青白口系早期.通过对熊耳山地区的官道口群的岩相学和地球化学分析,并结合其已有的碎屑锆石年龄和另外两个地层小区的五佛山群和汝阳群的碎屑锆石年龄以及它们的地球化学特征,表明三个地层区的沉积地层在中元古代均处于被动大陆边缘环境,而新元古代则可能处于与大陆岛弧相关的沉积盆地,这一结果表明从中元古代到新元古代华北南缘可能受到秦岭造山带早期微陆块俯冲碰撞的影响,由被动大陆边缘向活动大陆边缘过渡的过程.三套地层最年轻的碎屑锆石207 Pb/206Pb年龄基本上在1600Ma左右,从而限定了其最大沉积时代不早于1600Ma.其锆石年龄大多数都分布于古元古代(1700 ～ 2400Ma),太古代的年龄极少,说明其物源区以古元古代的地质体为主,且碎屑锆石年龄峰值为～ 1.93Ga,反映了华北南缘在～1.93Ga发生过重要的构造-热事件,与华北克拉通古元古代中期发生的变质作用时间(～ 1.91Ga)一致.三套沉积地层的碎屑锆石εHf(t)值变化较大(-20～ +6),表明既有新生地壳物质的加入,也有古老地壳物质的再循环.Hf两阶段模式年龄分布于2.3～3.8Ga之间,明显大于其207pb/206pb年龄,大部分锆石的Hf同位素组成集中于2.6Ga和3.0Ga地壳演化线区域内,峰值为2.75Ga,表明2.75Ga左右是华北克拉通南缘重要的陆壳生长期.     

柴达木盆地北缘全吉群红藻山组凝灰岩锆石U-Pb年龄及其地质意义

全吉群是不整合于柴达木北缘全吉(欧龙布鲁克)地块变质基底之上的第一套盖层型沉积,目前多数研究者认为其时代大体为新元古代晚期。本文在柴北缘全吉山的全吉群红藻山组建组剖面上,对位于该组下部的两层凝灰岩开展了LA-MC-ICPMS锆石U-Pb同位素定年研究,获得其岩浆锆石的U-Pb同位素年龄分别为(1 640±15) Ma和(1 646±20) Ma,标定了红藻山组的形成年龄,为柴北缘中新元古界年代地层的重新厘定与划分,提供了新的、直接的年代学约束,具有重要的科学意义。首先,这一新进展表明,在柴北缘地区,传统的全吉群红藻山组以下各组的时代,并非一直以来的“新元古代晚期南华纪-震旦纪(埃迪卡拉纪)”,而应属于国内的中元古代长城纪、国际上的古元古代固结纪(Statherian,1 800~1 600 Ma)晚期;其次,根据当前定年并结合新近在红藻山组与上覆地层之间发现有古风化壳及区域性不整合、全吉群上部发育有埃迪卡拉纪化石及冰碛砾岩等证据,本文进一步确认,柴北缘全吉群在红藻山组与其上覆黑土山组等地层单位之间其实存在着相当长时间的地层缺失,传统的“全吉群”应予解体。由此并参考已有资料,本文认为,早先代表柴达木地块形成的“全吉运动”并不能与华南的“晋宁运动”对比,而应与华北的“吕梁运动”相当,全吉地块乃至整个柴达木及周边地区的中、新元古代地质演化历史及其大地构造亲缘属性等,都应重新予以考虑。     

内蒙古锡林浩特地区中元古代锡林浩特岩群的厘定及其意义

通过大比例尺填图和剖面研究, 将内蒙古锡林浩特地区的"锡林郭勒杂岩"解体分为3大部分: 一套表壳岩、晚元古代基性-超基性侵入岩和早古生代酸性侵入岩.在此基础上根据变质岩的岩性组合和变形变质特点, 可将其中的表壳岩化分为4个岩性段: 黑云(石榴石)斜长片麻岩, 间夹多层条纹状斜长角闪岩, 在其顶部多见薄层含磁铁石英岩; 中粗粒黑云斜长片麻岩和细粒长英质片麻岩; 混合岩化条带状黑云(角闪)斜长片麻岩, 含石榴石黑云二长片麻岩夹条纹状斜长角闪岩组合; 夕线石黑云斜长片麻岩, 条纹状黑云斜长片麻岩, 间夹含石榴石黑云母石英片岩.通过对比区域内宝音图群、艾勒格庙组、白乃庙群等古老地块的岩石组合, 发现在原岩建造、变质级别、沉积环境等特征上均有区别, 应将这套表壳岩单独厘定为锡林浩特岩群, 它们组成了锡林郭勒微陆块前寒武变质基底岩系, 其地质特征的研究对锡林郭勒微陆块基底的形成和演化及华北板块与西伯利亚板块的构造关系演化有重要意义.      

陆地沉积物对大洋缺氧事件的响应：六盘山群黑色页岩地球化学特征及其意义

通过对六盘山群中上部湖相沉积中一层黑色页岩年代（113.45~112.98 Ma）及其下部泥灰岩的元素地球化学特征研究发现,黑色页岩形成于干热而相对湿润气候背景下的缺氧还原环境中,与典型缺氧事件黑色页岩的地球化学特征基本一致,说明该黑色页岩记录了六盘山地区对全球白垩纪大洋缺氧事件OAE1b (约113～111 Ma)的响应,可能指示该期大洋缺氧事件是一次全球性的气候变化事件。     

The collision between the Milky Way and Andromeda

We use an N -body/hydrodynamic simulation to forecast the future encounter between the Milky Way and the Andromeda galaxies, given present observational constraints on their relative distance, relative velocity, and masses. Allowing for a comparable amount of diffuse mass to fill the volume of the Local Group, we find that the two galaxies are likely to collide in a few billion years – within the Sun's lifetime. During the interaction, there is a chance that the Sun will be pulled away from its present orbital radius and reside in an extended tidal tail. The likelihood for this outcome increases as the merger progresses, and there is a remote possibility that our Sun will be more tightly bound to Andromeda than to the Milky Way before the final merger. Eventually, after the merger has completed, the Sun is most likely to be scattered to the outer halo and reside at much larger radii (>30 kpc). The density profiles of the stars, gas and dark matter in the merger product resemble those of elliptical galaxies. Our Local Group model therefore provides a prototype progenitor of late-forming elliptical galaxies.     

1999年轮台5.1级地震近场地倾斜资料异常分析

利用小波分析独特的时—频分析特性,对轮台5,1级地震前近场多台地倾斜连续观测资料进行了多尺度分解,分析结果发现在地震前震中附近的地倾斜台站几乎都接收到了相同频段的异常信号,周期为几天到十几天,异常信号出现在各个台站的时间也大致相同,主要集中在震前3-4个月：震前异常具有从外围向震中发展且幅度明显增强的时空演化特征。分析认为：这些异常可能与1999年轮台5,1级地震的孕育过程有关。     

Protolith ages and deformation mechanism of metamorphic rocks in the Zhangbaling uplift segment of the Tan-Lu Fault Zone

Protolith ages and Indosinian deformation mechanism of metamorphic rocks in the Zhangbaling uplift segment of the Tan-Lu Fault Zone are important, unsolved problems. Our LA-ICP-MS zircon dating work indicates that protolith ages of the greenschist-facies Zhangbaling Group are 754–753 Ma, and those of the amphibolite-facies Feidong Complex are 800–745 Ma. These rocks belong to the earliest cover of the Yangtze Plate. Their ages and metamorphic features suggest that the rocks did not come from the Dabie Orogen. The Indosinian structures in the Zhangbaling Group and lower Sinian strata formed in a flatlying ductile detachment zone with a shear sense of top-to-the-SSW whereas those in the underlying Feidong Complex are characterized by ENE-WSW inclined folds developed under a ductile regime. It is suggested therefore that the sinistral Tan-Lu Fault Zone of the Indosinian period is buried under the Hefei Basin west of the Zhangbaling uplift segment and the uplift segment is a displaced block neighboring the fault zone. Detachment deformation between the upper rigid and lower ductile crust during displacement of the Zhangbaling uplift segment resulted in the formation of the flat-lying ductile detachment zone and its underlying drag fold zone of a ductile regime. The protolith ages and deformation mechanism in the Zhangbaling uplift segment further prove sinistral origination of the Tan-Lu Fault Zone during the continent-continent collision of the North China and Yangtze plates and support the indentation model for the two-plate collision that considers the Tan-Lu Fault Zone as an oblique convergence boundary.     

内蒙古东北部上二叠统林西组沉积环境

在前人研究的基础上,应用地球化学方法,对内蒙古东北地区上二叠统林西组的沉积环境进行了研究。林西组的岩性为灰黑色泥岩、粉砂质泥岩、页岩,灰色泥质粉砂岩、细砂岩。通过常量元素、微量元素和稀土元素的分析,发现林西组砂泥岩样品整体具有高SiO2、Al2O3、V、Zr、Ba,低P2O5、Mn、CaO、Cd的特点;通过沉积环境判别指标的分析,确定林西组为开阔的淡水环境,主要为陆相沉积体系,在其沉积初期为海陆交互环境。同时根据沉积构造和岩性组合,将林西组进一步划分为滨浅湖、半深湖—深湖的湖泊沉积体系和三角洲前缘、前三角洲的三角洲沉积体系。     

郯庐断裂带张八岭隆起南段肥东群石榴角闪岩变质P-T演化史对其构造属性的制约

通过对张八岭隆起南端肥东群中磁铁石榴铁闪石岩的岩相学、矿物成分分析和热力学评价,并结合野外地质填图和共生围岩分析表明,该岩石经历了5期变质作用,展现了顺时针的P-T演化特征,早期阶段表现为近等压升温,晚期阶段为降温降压的过程,其峰期变质平均P-T条件为:524℃和0.49GPa.结合地质背景和郯庐断裂带的演化特征分析,早期过程可能反映的扬子基底所经历的区域变质过程,晚期过程可能是由于郯庐断裂的后期抬升分量所致,不具有造山带的P-T演化特征.对比前人对宿松群的变质演化历史的研究,肥东群和宿松群峰期变质压力差可达0.8GPa,表明两者属于不同变质级别的块体.因而,肥东群和宿松群不能作为被郯庐断裂左行错开的标志层.由此表明,张八岭隆起南段所出露的肥东群变质杂岩,属于扬子板块上的变质基底,郯庐断裂带活动中将其剥露地表,并没有经历过大别造山带的变质作用.     

Precambrian mafic magmatism in the Western Dharwar Craton,southern India

Mafic rocks of Western Dharwar Craton (WDC) belong to two greenstone cycles of Sargur Group (3.1–3.3 Ga) and Dharwar Supergroup (2.6–2.8 Ga), belonging to different depositional environments. Proterozoic mafic dyke swarms (2.4, 2.0–2.2 and 1.6 Ga) constitute the third important cycle. Mafic rocks of Sargur Group mainly constitute a komatiitic-tholeiite suite, closely associated with layered basic-ultrabasic complexes. They form linear ultramaficmafic belts, and scattered enclaves associated with orthoquartzite-carbonate-pelite-BIF suite. Since the country rocks of Peninsular Gneiss intrude these rocks and dismember them, stratigraphy of Sargur Group is largely conceptual and its tectonic environment speculative. It is believed that the Sargur tholeiites are not fractionated from komatiites, but might have been generated and evolved from a similar mantle source at shallower depths. The layered basic-ultrabasic complexes are believed to be products of fractionation from tholeiitic parent magma. The Dharwar mafic rocks are essentially a bimodal basalt-rhyolite association that is dominated by Fe-rich and normal tholeiites. Calc-alkaline basalts and andesites are nearly absent, but reference to their presence in literature pertains mainly to carbonated, spilitized and altered tholeiitic suites. Geochemical discrimination diagrams of Dharwar lavas favour island arc settings that include fore-, intra- and back-arcs. The Dharwar mafic rocks are possibly derived by partial melting of a lherzolite mantle source and involved in fractionation of olivine and pyroxene followed by plagioclase. Distinctive differences in the petrography and geochemistry of mafic rocks across regional unconformities between Sargur Group and Dharwar Supergroup provide clinching evidences in favour of distinguishing two greenstone cycles in the craton. This has also negated the earlier preliminary attempts to lump together all mafic volcanics into a single contemporaneous suite, leading to erroneous interpretations. After giving allowances for differences in depositional and tectonic settings, the chemical distinction between Sargur and Dharwar mafic suites throws light on secular variations and crustal evolution. Proterozoic mafic dyke swarms of three major periods (2.4, 2.0–2.2 and 1.6 Ga) occur around Tiptur and Hunsur. The dykes also conform to the regional metamorphic gradient, with greenschist facies in the north and granulite facies in the south, resulting from the tilt of the craton towards north, exposing progressively deeper crustal levels towards the south. The low-grade terrain in the north does not have recognizable swarms, but the Tiptur swarm consists essentially of amphibolites and Hunsur swarm mainly of basic granulites, all of them preserving cross-cutting relations with host rocks, chilled margins and relict igneous textures. There are also younger dolerite dykes scattered throughout the craton that are unaffected by this metamorphic zonation. Large-scale geochemical, geochronological and palaeomagnetic data acquisition through state-of-the-art instrumentation is urgently needed in the Dharwar craton to catch up with contemporary advancements in the classical greenstone terrains of the world.