鄂尔多斯盆地延长组坡折带演化及其对砂体的控制作用——以延长组长6油层为例

本文在研究鄂尔多斯盆地构造与沉积背景基础上,通过古水深恢复、地层厚度统计、沉积相组合分析、地震剖面解释等方法,识别出盆地内部有四条沉积坡折带。坡折带的发育受湖盆地形控制。东北部发育三条多级缓坡坡折带,西南发育一条陡坡坡折带,分别控制着研究区三角洲前缘砂体和西南浊积砂体的展布形态。随着沉积中心的迁移和沉积相演化,坡折带和砂体规模在长6不同时期都有所变化。     

华北克拉通与全球构造

华北克拉通是中国境内独具特色的大地构造单元,它既不同于新建立的华泰克拉通,又明显有别于扬子地台和塔里木地台。为追溯其形成和演化历史,将全球视为一个整体,在世界范围内寻找与其有宗谱关系的地体。经过认真的对比和鉴别,发现西伯利亚地台、加拿大地盾与中国的华北地台具有特殊的渊源关系。三者合计由14个太古宙原生陆壳块体,于古元古代末(1.79~2.2Ga)通过造山运动碰撞聚合在一起,形成了笔者所称的古劳亚大陆。后者最重要的地质标志就是统一的中元古代盖层,此即中国的长城系、蓟县系,俄罗斯西伯利亚的里菲系和北美洲的层群A、层群B。早寒武世,西伯利亚地台脱离了古劳亚大陆。中寒武世之初即536Ma,古劳亚大陆与形成于1000~1300Ma的Rodinia发生构造拼接,缔造了具有全球规模但命运短暂的超级大陆——Pannotia。这次构造拼接的意义不可低估,在时间上它恰好与骨骼化后生动物的快速发展(“生物大爆炸”)相吻合。过去长时间人们无法理解的,为什么远隔重洋的北美洲-澳大利亚-中国,寒武系中—上统的沉积类型和生物群具有高度一致性的问题,也随之迎刃而解。寒武纪末期510Ma,Pannotia解体并一分为二,在古劳亚大陆与古冈瓦纳大陆之间的地域形成了南太平洋。直到奥陶纪晚期即440Ma前后,古劳亚大陆才分裂,形成了北太平洋,中国北方包括华北和华泰2个克拉通在内,与北美洲的劳伦古陆和内陆地台,才各奔西东。回溯华北地台的渊源,作为一个整体它曾与西伯利亚地台共存了1.3Ga,而与北美的加拿大地盾至少共同度过1.4Ga之久。     

贺根山缝合带阿萨格图钾玄质火山岩锆石LA-ICP-MS U-Pb年龄、地球化学特征及构造意义

内蒙古西乌珠穆沁旗阿萨格图火山岩出露于贺根山缝合带迪彦庙蛇绿混杂岩南侧,岩石类型为粗安岩、粗面岩和粗面英安岩。粗安岩锆石LA-ICP-MS U-Pb同位素测年获得火山岩形成年龄为132.1±0.7 Ma。岩石地球化学显示火山岩属于钾玄岩系列,岩石高Na_2O+K_2O(7.61%～10.35%)、高K_2O(3.94%～6.04%)、高Al_2O_3(16.32%～17.99%)、低TiO_2(0.45%～0.95%),富集Rb、Ba、U等大离子亲石元素(LILE)和轻稀土元素(LREE),亏损Nb、Ta和Ti等高场强元素(HFSE)。稀土元素含量为109.62×10~(-6)～174.68×10~(-6),稀土元素配分曲线为右倾式分布。岩石学和岩石地球化学特征表明,阿萨格图地区白垩纪火山岩与洋壳俯冲作用有关,形成于俯冲板片断离—后造山伸展构造背景。古亚洲洋俯冲洋壳析出流体交代上覆地幔形成贺根山缝合带富集地幔,随后的俯冲板片断离—后造山伸展作用触发富集地幔部分熔融产生该钾玄质岩浆。结合贺根山缝合带的壳幔电性结构和晚古生代蛇绿岩—岛弧岩浆岩、中生代后造山A型花岗岩的时空分布与演化,初步建立了该区钾玄质火山岩的板片断离—后造山伸展地球动力学模式。     

Géochimie et signification géotectonique des volcanites du Cryogénien inférieur du Saghro (Anti-Atlas oriental,Maroc) / Geochemistry and geotectonic significance of Early Cryogenian volcanics of Saghro (Eastern Anti-Atlas,Morocco)

Abstract

The Early Cryogenian groups of Sidi Flah, Kelaat Mgouna and Boumalne (Saghro, Anti-Atlas, Morocco) are constituted by turbiditic deposits and interbedded lavas, accumulated in tectonic basins. At Sidi Flah, volcanics are transitional showing initial rift tholeiites (IRT) fingerprint and alkali basalts of oceanic island basalt (OIB) compositions. At Kelaat Mgouna, volcanics consist of low-Nb continental tholeiites. At Boumalne, basalts are of IRT composition. The volcanic and sedimentary formations belong to a nascent rift caused by thermal doming along a SW-NE axis, the Saghro rift. The continental break-up occurred in the early Neopro- terozoic and during the Rodinia supercontinent dislocation, within a continent called “Ibero-saharian Craton” which was in front of the West-African Craton located near the South Pole. The Saghro rift is contemporaneous to the opening of an oceanic domain represented by Central Anti-Atlas ophiolites and related to the extension of the Brazialiano Ocean. © 2001 Éditions scientifiques et médicales Elsevier SAS     

扬子地块西北缘刘家坪地区大滩花岗岩体年代学、地球化学及其构造环境

对扬子地块西北缘后龙门山地区大滩花岗岩体进行了锆石U-Pb年代学和岩石地球化学研究,以便对其形成时代和岩石成因进行约束.研究结果表明,大滩花岗岩体中锆石均发育岩浆韵律环带结构,具有较高的Th/U比值(0.22 ～ 1.57),为岩浆成因锆石.LA-ICP-MS锆石U-Pb测年结果表明其形成于806±19Ma(MSWD=0.56),为新元古代晚期.大滩花岗岩体具有高SiO2(74.12％～77.10％)和较高的Al2O3(11.86％ ～ 12.56％)含量,A/CNK在0.95～1.05之间(平均为1.01),属过铝质花岗岩,具有I型花岗岩特征;稀土元素总量(∑REE)为(97.69～ 189.60)×10-6(平均为140.85×10-6),稀土元素配分曲线显示具Eu弱—中等亏损的轻稀土富集型;高场强元素(Th、Nb、Ta、P等)具有明显的负异常,大离子亲石元素(Rb、Sr、Ti等)具有明显的负异常.岩体是以火成岩部分熔融形成的花岗质岩浆上升侵位过程中形成的,是一种典型的壳源成因类型.大滩花岗岩体岩浆起源于下地壳,是新元古代扬子地块西北缘活动大陆边缘俯冲以及弧陆碰撞造山作用导致的地壳增厚下地壳部分熔融的产物,形成于同碰撞(挤压环境)向碰撞后(伸展环境)转化阶段,即后造山期,是Rodinia超大陆初始裂解阶段产物.     

具有守恒特性的二维溃坝洪水演进数值模型

基于结构网格,采用有限体积法建立了二维水动力学模型,模拟溃坝洪水在复杂实际地形条件下的流动过程。该模型采用中心迎风格式求解界面通量,并结合对界面变量的线性重构,使其具有空间上的二阶精度。分别采用中心差分方法和半隐式方法对底床坡度项和摩擦阻力项进行离散,保证了模型的和谐性和稳定性。对于复杂地形条件下溃坝洪水的模拟,负水深的产生是影响模型稳定的关键因素。当库朗特数小于0.25时,模型能够保证任何时刻的计算水深都是非负的,而无需对负水深单元进行特殊处理。因此,相比于现有的大部分溃坝洪水模型,该模型具有更强的鲁棒性和稳定性。     

The Neoproterozoic Hongliujing A-type granite in Central Tianshan (NW China): LA-ICP-MS zircon U–Pb geochronology,geochemistry, Nd–Hf isotope and tectonic significance

Located between the Turpan-Hami, Junggar and Tarim blocks, the Central Tianshan zone is an important component of the Central Asian Orogenic Belt (CAOB) and crucial linkage between the Siberian, Kazakhstan, Junggar, Turpan-Hami and Tarim blocks. The Hongliujing granite associated with Nb–Ta mineralization in the Central Tianshan zone, dated at ca. 740 Ma using zircon LA-ICP-MS dating, is the first reported Neoproterozoic intrusion with a reliable and precise age in the Chinese Central Tianshan. The Hongliujing granite shares all the characteristics of A-type granites. It contains predominant alkali feldspar, and is characterized by high contents of SiO₂, Na₂O + K₂O, K₂O and high field strength elements (such as Nb, Ta, Zr, Ga and Y), and low contents of CaO, MgO, Ba and Sr, with high FeO^t/(FeO^t + MgO) and Ga/Al ratios typical of A-type granites. Based on the geochemistry and zircon Hf isotope data, we propose that the Hongliujing granite was most likely produced by partial melting of basic rocks in the lower crust which may have been derived from mantle magmas. The Hongliujing granite belongs to A1-type granites, which indicate a rifting formation environment, suggesting that like the Tarim Block, the Central Tianshan zone recorded Neoproterozoic rift-related igneous events related to the breakup of the Rodinia supercontinent. Our study verifies that not only the Tarim Block is related to the breakup of the Rodinia supercontinent, but also it is true for some key blocks in CAOB such as the Central Tianshan. Our new geochemical and geochronologic data also support and strengthen the notion that the Central Tianshan zone may be a part of the Tarim Block.     

http://www.sciencedirect.com/science/article/pii/S167498711200103X

The supercontinent cycle has had a profound effect on the Earth's evolution since the Late Archean but our understanding of the forces responsible for its operation remains elusive. Supercontinents appear to form by two end-member processes: extroversion, in which the oceanic lithosphere surrounding the supercontinent (exterior ocean) is preferentially subducted (e.g. Pannotia), and introversion in which the oceanic lithosphere formed between dispersing fragments of the previous supercontinent (interior ocean) is preferentially subducted (e.g. Pangea). Extroversion can be explained by “top–down” geodynamics, in which a supercontinent breaks up over a geoid high and amalgamates above a geoid low. Introversion, on the other hand, requires that the combined forces of slab-pull and ridge push (which operate in concert after supercontinent break-up) must be overcome in order to enable the previously dispersing continents to turn inward. Introversion may begin when subduction zones are initiated along boundaries between the interior and exterior oceans and become trapped within the interior ocean. We speculate that the reversal in continental motion required for introversion may be induced by slab avalanche events that trigger the rise of superplumes from the core-mantle boundary.     

琼东南盆地二号断裂带坡折区速度研究进展

琼东南盆地二号断裂带是构造分区的标志性断层之一,该断裂带下降盘为中央凹陷带.区域研究表明中央凹陷带具有良好的生烃潜力,所以该区带一直被认为是有利的油气勘探区带.但是由于该区带水深剧烈变化,多期坡折带快速推进沉积形成大套泥岩,使得该区带的速度很难确定,所以速度问题成为制约着琼东南盆地坡折带勘探的难点问题.笔者首先分析现有速度谱的质量,了解速度整体变化趋势;其次考虑已钻井的速度分析结果;结合地震剖面地层的变化信息进行速度解释,采用解释能量团中心的标准进行速度解释;最后在精细速度解释的基础上,对二维剖面正演模型速度进行分析,建立速度体,证实构造目标的存在.     

Simulation of dam-break waves on movable beds using a multi-stage centered scheme

This paper presents the application of the multi-stage first-order centered scheme GMUSTA to solve a two-phase flow model with four equations for simulating dam-break floods without and with sediment transport.Computation of generalized Riemann invariants can be particularly complex and costly in simulating dam-break floods with sediment transport.GMUSTA numerical scheme,which does not require complete knowledge of the eigenstructure of the hyperbolic mathematical model,offers a suitable and attractive option.The quality of the dam-break flood simulations with GMUSTA scheme is verified by comparing the results against laboratory tests and some experimental data available in the literature,on fixed and mobile bed conditions,with different bed materials and flush or stepped bottoms.The numerical results reproduce quite well the experimental evidence,proving that the model is capable of predicting the temporal evolution of the free-surface and the bed.The GMUSTA scheme,which is not only simple to implement but also both accurate and computationally efficient,is proposed as an appropriate tool for integrating non-equilibrium sediment-transport models.