超级克拉通盆地发育的构造背景及其形成模式探讨

克拉通盆地是所有盆地类型中最稳定、最长寿的盆地,也是地壳和地幔长期垂向变形最重要的地质记录。地史上面积最大的克拉通盆地（超级克拉通盆地）原型面积常超过200×104 km2,对探讨克拉通盆地成因演化具有重要的代表性意义。目前世界各地的研究可以识别出10余个不同时期的超级克拉通盆地。本文根据超级克拉通盆地基底性质、盆地发育的超大陆构造演化背景及其构造特征,将超级克拉通盆地划分为A型盆地和B型盆地两种类型,它们分别以西西伯利亚盆地和刚果盆地为代表。A型盆地形成于超大陆裂解之前至初始裂解的背景下,基底为前期造山带,为短波长盆地。盆地形态不规则性强,内部均一性相对较低,克拉通盆地边缘可能渐变为弧后盆地或前陆盆地。B型盆地形成于超大陆裂解末期（即下一个超大陆汇聚之初）,基底为古克拉通陆块,为长波长盆地,盆地多呈对称的宽缓碟型。A型盆地处于短期活动的热地幔柱之上,伴随早期裂谷作用及其随后的热衰减成盆;B型盆地常处于热点和地貌高地之间的部位,盆地沉降长期受地幔持续缓慢下沉控制。     

新疆铁克里克西段都维吐卫岩体年代学、岩石地球化学特征及地质意义

出露于新疆塔里木南缘铁克里克地区西段的都维吐卫花岗岩体, 侵入赫罗斯坦岩群(Pt1H)黑云二长片麻岩中, 与库浪那古岩群(Pt2K)和大同西岩体呈断层接触, 东部多被博查特塔格组(Jxbc)不整合覆盖。通过地球化学分析, 显示岩体具高Si、高Al、高K, 贫Na、低Ga、低P、低Ti和贫Mg的特征, 铝饱和指数(A/CNK)为1.38~1.43, CIPW标准刚玉分子大于1%, 属高钾钙碱性过铝质花岗岩。在稀土元素方面显示, 轻稀土元素(LREE)富集、重稀土元素(HREE)亏损, 轻重稀土元素分馏明显, Eu出现中等负异常(δEu=0.59~0.82);在微量元素方面, 明显富集大离子亲石元素Rb、Ba、Th和K, 亏损高场强元素Nb、Ta、Ti。岩体LA-ICP-MS锆石U-Pb同位素定年获得年龄为(1 909±47)Ma, 属于古元古代花岗岩。综合分析认为该岩体是造山晚期-同碰撞环境下形成的, 与加厚地壳引起的地壳重熔有关, 推断西昆仑造山带强烈的陆内造山活动应在古元古代已经开始了;结合赫罗斯坦岩群(Pt1H)中角闪斜长片麻岩中锆石年龄记录, 推断2 000~1 800Ma塔里木陆块存在Columbia超大陆聚合事件。     

扬子陆块北缘古-中元古代构造格架：来自马鞍山岩群物源示踪的启示

识别并研究扬子陆块北缘古-中元古代的岩浆-变质-沉积事件,是全面理解该陆块古-中元古代构造演化的基础,也是重建其在Columbia 超大陆向Rodinia 超大陆转变阶段角色和位置的前提。本文对扬子陆块北缘桐柏地区马鞍山岩群的3 件样品进行了碎屑锆石U-Pb 定年和原位Lu-Hf 同位素分析。结果显示,该岩群下部a 岩组片岩中最年轻的单颗粒锆石谐和年龄为1725±30 Ma,上部b 岩组大理岩中最年轻的一批锆石谐和年龄为1626 ~ 1606 Ma,大致分别限定了其最早沉积时代,表明扬子陆块北缘桐柏地区可能存在中元古代早中期沉积地层。马鞍山岩群的碎屑锆石年龄谱范围是2643 ~1606 Ma,呈现出显著的1820 Ma单峰频谱特征,其潜在物源区可能主要来自于扬子陆块北缘外部的桐柏-大别-苏鲁地区（现已卷入中生代高压-超高压变质带）。现有资料指示,扬子陆块北缘在古-中元古代时期可划分为内部和外部两个大地构造单元,二者在古元古代呈现出截然不同的构造演化过程,各单元内中元古代早中期地层的物源区显著不同,可能分别靠近伸展环境的超大陆核部和汇聚环境的超大陆边部。     

Annual report of IGCP Project No.440 in 2003 Rodinia assembly and breakup

With the latest information on geology, isotop chronology, geochemistry and aerial geophysics, the structural enviroment, geological event characterists and evolution history of component units of Rodinia Supercontinent on a global scale are discussed. And some neo views and genetic pattern are provided. The East Eurppean Craton had a complex evolution history between 1.7 and 0.9 Ga. The arthors propose a new reconstruction of Laurentia acient land and Siberia at ca. 1 050-1 000 Ma. The largest litho-structural record of the Meso-Neoproterozoic orogenic collage in South America made up the western border of the South American Platform African Cratons are the result of convergence of Paleoproterozoic/Archaem Cratonic blocks. A part of Eastern Antarctica attached to southern Africa in Mesoproterozoic.Neoproterozoic felsic magmatic events in New India made the western border of Rodinia Pre-Grevoillian Laurentia was established as a major continental block by the end of the Paleoproterozoic. South China is geologically plausible to be between southern Laurentia and eastern Australia. Yangzi-Tarim connection or neighborhood is proposed. According to the abovementionded, the assembly and breakup paattem of Rodinia proposed by Pisarevsky is tested. It telles that primary break up is along the western border of Laurentia ancient land, which is similar to northern Atlantic. Another characteristic is that some continents are not considered as component parts of Rodinia, eg. India, Congo and San-Francisco.     

Topographically‐independent ice flow in northwestern British Columbia: implications for Cordilleran Ice Sheet reconstruction

Studies in southern British Columbia have shown that Cordilleran Ice Sheet flow was controlled by topograph, even in full glacial time. New ice‐flow evidence from the Nass River region, northern British Columbia, however, indicates that ice was thicker there and that the continental ice‐sheet phase of glaciation was reached. Inspection of high elevation sites has revealed a suite of ice‐flow indicators (mainly striae) undetected by earlier work. These suggest that at the Last Glacial Maximum (Fraser Glaciation), ice flowed southwestward across the Nass River region from an ice divide that probably was located in the Skeena Mountain area. Comparisons with adjacent work allow this divide to be mapped over a wide area. The results suggest that maximum ice thicknesses in the northern part of the Cordilleran Ice Sheet were larger than reported previously. The location of storm tracks in full glacial time may have played an important role in the production of an ice sheet that was thicker in northern British Columbia than it was in the southern half of the province. During deglaciation, ice thinned and gradually became confined to fiords and valleys, resulting in numerous and variable ice‐flow directions at that time. Topographic control was thus exerted on ice flow only after the glacial maximum was reached, despite the significant amount of relief in this region. Copyright © 2002 John Wiley & Sons, Ltd.     

The Paleoproterozoic North Hebei Orogen: North China craton's collisional suture with the Columbia supercontinent

Understanding the geologic history and position of the North China craton in the Paleoproterozoic Columbia supercontinent has proven elusive. Paleoproterozoic orogenic episodes (2.00–1.85 Ga) are temporally associated with ultimate stabilization of the North China craton (NCC), followed by the development of extensive craton-wide rift systems at 1.85–1.80 Ga. The age difference between the sedimentary cover and the metamorphic basement is up to 500–700 Ma, suggesting that uplift and doming of cratonic basement occurred in the latest Paleoproterozoic. Mafic dike swarms (1.80–1.77 Ga) and anorogenic magmatism (1.80–1.70 Ga) record the extensional breakup and dispersal of the North China craton during this stage. The late Paleoproterozoic tectonic framework and geological events documented provide important constraints for reconstruction of the NCC within the Late Paleoproterozoic supercontinent of Columbia.An east-west striking thousand kilometer long belt of khondalites (granulite facies metapelites) stretches along the northern margin of the North China craton, on the cratonward side of the Northern Hebei orogenic belt. This granulite belt includes Mg–Al (sapphirine bearing) granulites that reached ultrahigh-temperature “peak” metamorphic conditions of  1000 °C at 10 kbars at 1927 ± 11 Ma. Following peak ultrahigh-temperature conditions, the rocks underwent initial isobaric cooling and subsequent isothermal decompression, and these trajectories are interpreted to be part of an overall anti-clockwise P-T evolution indicating that the northern margin of the craton experienced continental collision at 1.93–1.92 Ga. The position of the khondalite belt south of the Northern Hebei orogenic belt makes it analogous to Tibet, a continental collision-related plateau characterized by double crustal thicknesses and granulite facies metamorphism at depth. We suggest that the tectonic evolution of the NCC during this period was closely related to the assembly and break-up of the Columbia supercontinent, and that the NCC was adjacent to the Baltic and Amazonian cratons in the period 2.00–1.70 Ga. Craton-wide extension occurred within 100–150 Ma of collision along the northern margin of the craton at 1.93–1.92 Ga. It is concluded that mantle upwellings are chiefly responsible for the breakup of the NCC from the Paleoproterozoic supercontinent.     

Voyage of the Indian subcontinent since Pangea breakup and driving force of supercontinent cycles: Insights on dynamics from numerical modeling

Recent advances in three-dimensional numerical simulations of mantle convection have aided in approximately reproducing continental movement since the Pangea breakup at 200 Ma. These have also led to a better understanding of the thermal and mechanical coupling between mantle convection and surface plate motion and predictions of the configuration of the next supercontinent. The simulations of mantle convection from 200 Ma to the present reveals that the development of large-scale cold mantle downwellings in the North Tethys Ocean at the earlier stage of the Pangea breakup triggered the northward movement of the Indian subcontinent. The model of high temperature anomaly region beneath Pangea resulting from the thermal insulation effect support the breakup of Pangea in the real Earth time scale, as also suggested in previous geological and geodynamic models. However, considering the low radioactive heat generation rate of the depleted upper mantle, the high temperature anomaly region might have been generated by upwelling plumes with contribution of deep subducted TTG(tonalite-trondhjemite-granite) materials enriched in radiogenic elements. Integrating the numerical results of mantle convection from 200 Ma to the present, and from the present to the future, it is considered that the mantle drag force acting on the base of continents may be comparable to the slab pull force, which implies that convection in the shallower part of the mantle is strongly coupled with surface plate motion.     

Terminal Pleistocene change in mammal communities in southeastern Washington State,USA

Small mammal communities in western North America experienced declines in taxonomic richness across the late Pleistocene to Holocene transition (PHT), a recent natural global warming event. One community also experienced a decline in evenness and others replaced one species with a congener. Variability in response of small mammal communities to PHT warming is apparent. At the presently arid and xeric Marmes site in the Columbia Basin of southeastern Washington State, megafauna were absent by about 13,000 cal yr BP, evenness of small mammals declined about 11,700 cal yr BP and again about 11,400 cal yr BP whereas richness declined about 11,400 cal BP. Regional faunal turnover was, however, minimal among small-bodied taxa. Local mammal communities are depauperate as a result of megafaunal extinctions and subsequent decreases in small-mammal richness and evenness. The latter chronologically corresponds with a decrease in primary productivity driven by increasing warmth and aridity. More faunas must be studied in order to fully document the range of variability in the responses of mammalian communities to PHT warming. Documentation of patterns in those responses will facilitate understanding and enhance predictive accuracy with respect to responses of mammalian communities to modern global warming.     

Bacteriological investigation of the neuston and plankton in the Fraser River estuary,British Columbia

Microbiological parameters were examined in the surface microlayer (150 μm) and the subsurface waters (1 m) of the Fraser River estuary (British Columbia) at salinities of 0, 15 and 25‰. Little difference was observed in the neustonic variables between these three stations. A comparison of the neuston with the plankton over the estuary as a whole revealed elevated detritus, particulate organic carbon and nitrogen but reduced ATP, heterotrophic activity and percentage respiration in the neuston. Enrichment of bacterial numbers or dissolved organic carbon was not observed in the surface microlayer.