大别山北缘石炭系碎屑岩地球化学及碎屑锆石年代学分析及其对物源区大地构造属性判别的制约

大别山北缘石炭系作为古生代唯一不变质或轻微变质的沉积地层,记录了其物源信息和古生代的构造演化.针对研究区这一地质特征,本文分析了研究区砂岩的碎屑组分、常量元素、微量元素和稀土元素,以及碎屑锆石的同位素年龄,并据此对物源区的大地构造属性进行了研究.研究区碎屑岩主要以中细粒石英砂岩和长石石英砂岩为主,砂岩的QFL平均值为Q 76.2％,F 15.9％,L7.9％,Q/(F+ L) 4.26;主要元素氧化物平均百分含量SiO263.69％,Al2O3 11.25％,MgO 3.66％,CaO 5.15％,Fe2O3T 6.15％,K2O 1.68％,Na2O 0.68％;部分特征微量元素Th,U,Hf,Sc,Zr,Y平均含量分别为10.78×10-6、2.64×10-6、4.39×10-6、15.67×10-6、166×10-6、25.33×10-6.Rb/Sr,Th/U,La/Y,La/Sc,Th/Sc比值分别为1.49、4.10、14.75、31.92和0.89;稀土元素总量ΣREE平均146.2×10-6(54.11×10-6 ～256.0×10-6),Eu异常0.64,轻稀土略有富集,La/Yb为12.58(3.94～15.42),(La/Yb)N为9.02.锆石年龄测定表明,早石炭世地层中碎屑锆石的年龄主要集中在400 ～500Ma,晚石炭世地层中碎屑锆石年龄主要为900～ 1300Ma,其次为2000～ 2800Ma.上述结果表明大别山北缘石炭系沉积物来源于不同的源区,包括早古生代的大陆岛弧、扬子板块中-新元古代基底以及华北板块古-中元古代基底.     

Holocene-emerged notches and tectonic uplift along the Jalisco coast, Southwest Mexico

This paper presents the preliminary results from a study of Holocene-emerged shorelines, marine notches, and their tectonic implications along the Jalisco coast. The Pacific coast of Jalisco, SW Mexico, is an active tectonic margin. This coast has been the site of two of the largest earthquakes to occur in Mexico this century: the 1932 (Mw 8.2) Jalisco earthquake and the 1995 (Mw 8.0) Colima earthquake. Measurement and preliminary radiocarbon dating of emergent paleoshorelines along the Jalisco coast provide the first constraints upon the timing for tectonic uplift. Along this coastline, uplifted Holocene marine notches and wave-cut platforms occur at elevations ranging from ca. 1 to 4.5 m amsl. In situ intertidal organisms dated with radiocarbon, the first ever reported for the Jalisco area, provide preliminary results that record tectonic uplift during at least the past 1300 years BP at an average rate of about 3 mm/year. We propose a model in which coseismic subsidence produced by offshore earthquakes is rapidly recovered during the postseismic and interseismic periods. The long-term period is characterized by slow tectonic uplift of the Jalisco coast. We found no evidence of coastal interseismic and long-term subsidence along the Jalisco coast.     

构造因素与滑坡

本文首先简述了斜坡演化过程与构造运动的关系,然后阐明了滑坡的空间分布、活动周期及活动规模与构造因素的联系。在此基础上指出:构造因素是滑坡产生的基础,对滑坡分布具宏观控制作用,并与滑坡的活动周期和活动规模密切相关,是滑坡研究及其灾害预测、预防研究工作中值得重视的重要因素。     

The Bastar craton,central India: A window to Archean – Paleoproterozoic crustal evolution

The Bastar craton in central India, surrounded by cratonic blocks and Paleoproterozoic to Neoproterozoic orogenic belts, is a window to investigate the Archean-Paleoproterozoic crustal evolution and tectonic processes. Here we propose a new tectonic classification of the craton into the Western Bastar Craton (WBC), Eastern Bastar Craton (EBC), and the intervening Central Bastar Orogen (CBO). We present petrologic, geochemical and zircon U-Pb, REE and Lu-Hf data from a suite of rocks from the CBO and along the eastern margin of the WBC Including: (1) volcanic successions comprising meta-andesite and fine-grained amphibolite, representing arc-related volcanics along a convergent margin; (2) ferruginous sandstone, in association with rhyolite, representing a volcano-sedimentary succession, deposited in an active trench; and (3) metamorphosed mafic-ultramafic suite including gabbro, pyroxenite and dunite invaded by trondhjemite representing the section of sub-arc mantle and arc root adjacent to a long-lasting subduction system. Petrologic studies indicate that the mafic-ultramafic suite crystallized from an island arc tholeiitic parental magma in a suprasubduction zone environment. The chondrite-normalized and primitive mantle normalized diagrams of the mafic and ultramafic rocks suggest derivation from MORB magma. The mixed characters from N-MORB to E-MORB of the studied samples are consistent with subduction modification of a MORB related magma, involving partial melting of the metasomatized mantle wedge. Our zircon U-Pb age data suggest that the cratonic nuclei was constructed as early as Paleoarchean. We present evidence for active subduction and arc magmatism through Mesoarchean to Neoarchean and early Paleoproterozoic, with the trench remaining open until at least 2.3 Ga. Two major crust building events are recognized in the Bastar craton: during Mesoarchean (recycled Paleoarchean subduction-related as well as juvenile/depleted mantle components) and Neoarchean (accretion of juvenile oceanic crust, arc magmatism including granite batholiths and related porphyry mineralization). The final cratonization occurred during latest Paleoproterozoic, followed by collisional assembly of the craton and its incorporation within the Peninsular Indian mosaic during Mesoproterozoic. In the global supercontinent context, the craton preserves the history of Ur, the earliest supercontinent, followed by the Paleo-Mesoproterozoic Columbia, as well as minor thermal imprints of the Neoproterozoic Rodinia and associated Grenvillian orogeny.     

从西南天山超高压变质带多期构造变形看天山古生代构造演化

通过对西南天山阿克雅孜和木扎尔特地区高压-超高压变质带构造几何学和岩石变形相关运动学的详细剖析,厘定出高压-超高压变质岩石及其相关围岩的构造单元。详细研究表明,研究区可划分为三个构造单元:北部单元、中部单元和南部单元。确定了每个构造单元的构造几何学特征及各个构造单元之间的相互关系。通过分析岩石变形特征和叠加关系,确定了岩石所记录多期变形的运动学特征。根据研究区的多期构造变形特点,建立了阿克雅孜和木扎尔特河地区构造演化序列。共划分出四期构造可识别的事件(E1-E4),分别代表了E1:高压-超高压岩石折返过程;E2:高压-超高压岩石造山带的早期改造过程;E3:北部构造事件对高压-超高压造山带影响;E4:走滑构造对高压-超高压造山带的叠加。沿造山带系列构造分析表明,西南天山高压-超高压带中发育的四期构造事件沿中天山北缘具有很好的一致性,各期构造事件也有一定的横向可对比性。在此基础上通过对多期变形事件的构造背景的探讨,建立了整个天山在古生代的构造拼合过程,揭示我国西部洋壳相关的深俯冲造山带形成过程和参与深俯冲作用(超)高压变质岩的变形变质历史。     

面向分类的高光谱影像局部线性嵌入算法研究

局部线性嵌入算法(LLE)能很好保存数据点的局部性质,因此有很好的数据可视化效果,但它不是一种很好的面向分类的特征提取方法。因为它存在样本外点学习能力差和忽略了样本类别信息的缺点。对此,本文提出一种分类型局部线性嵌入算法。所提方法通过计算重构误差来判定样本类别,并引进平移向量和缩放因子对距离修正,显著提高类别可分性。在对高光谱影像进行分类的试验中验证了该方法的有效性。     

川滇地块西部差异性旋转的构造意义:青藏高原东南缘白垩纪红层古地磁学新证据

印度-欧亚板块碰撞以来青藏高原内部及其周缘地区经历了复杂的构造演化,复杂构造变形区的复合构造使得古地磁的数据解释究竟代表区域的构造旋转还是只能反映局部的构造变形一直是备受关注的问题.本文通过采集川滇地块西缘渔泡江断裂东侧三岔河地区白垩纪红层古地磁样品,揭示采样区差异性旋转并探讨川滇地块西部自中新世以来的构造演化规律.前人的地质调查表明川滇地块渔泡江断裂东侧上白垩统赵家店组地层发育倾伏褶皱.三岔河剖面以三岔河镇为界分为南北两段,三岔河南段剖面高温剩磁分量平均方向在倾斜校正后D_s=29.3°,I_s=45.7°,k_s=54.3,α₉₅=6.6°,倾伏地层产状校正后D_s=30.6°,I_s=46.6°,k_s=69.3,α₉₅=5.8°;而三岔河北侧剖面高温剩磁分量平均方向在倾斜校正后D_s=350.4°,I_s=42.1°,k_s=69.4,α₉₅=9.2°,倾伏地层产状校正后D_s=347.4°,I_s=41.9°,k_s=96.6,α₉₅=7.8°;两组高温剩磁分量均通过了褶皱检验,表明其获得于褶皱形成之前.相对于东亚稳定区80 Ma古地磁极,三岔河南侧剖面发生了20.5°±4.8°的顺时针构造旋转量,与楚雄盆地核部之间不存在差异性旋转;但三岔河镇以北剖面却发生了22.7°±6.6°的逆时针旋转.综合分析川滇地块内部的古地磁数据表明自中新世以来川滇地块南部楚雄盆地经历了约20°的顺时针构造旋转,而三岔河镇北侧经历了约20°逆时针旋转.进一步分析表明三岔河北侧剖面相对于南侧剖面经历了约40°的逆时针旋转,可能由于研究区的滑脱构造导致岩石薄弱层拆离滑脱所引起.

     

Fracture development in Paleozoic shale of Chongqing area (South China). Part two: Numerical simulation of tectonic stress field and prediction of fractures distribution

A tectonics sedimentation evolution has been researched in Southeast Chongqing, and the reasonable Longmaxi shale highstand system tract (HST) and transgressive system tract (TST) geological model were built respectively based on the rock mechanical test and acoustic emission experiment which the samples are from field outcrop and the Yuye-1 well. The Longmaxi shale two-dimension tectonic stress field during the Cenozoic was simulated by the finite element method, and the distribution of fractures was predicted. The research results show that the tectonic stress field and the distribution of fractures were controlled by lithology and structure. As a result of Cretaceous movement, there are trough-like folds (wide spaced synclines), battlement-like folds (similar spaces between synclines and anticlines) and ejective folds (wide spaced anticlines), which are regularly distributed from southeast to northwest in the study area. Since the strain rate and other physical factors such as the viscosity are not taken into account, and the stress intensity is the main factor that determines the tectonic strength. Therefore, the stronger tectonic strength leads the higher stress intensity in the eastern and southeastern study area than in the northwest. The fracture zones are mainly concentrated in the fold axis, transition locations of faults and folds, the regions where are adjacent to faults. The fragile mineral contents (such as siliceous rock, carbonate rock and feldspar) in the shelf facies shale from south of the study area are higher than in the bathyal facies and abyssal facies shale from center of the study area. The shales characterized by low Poisson’s ratio and high elastic modulus from south of the study area are easily broken during Cenozoic orogenic movement.     

论新疆深大断裂特征与地震的关系(1)

新疆地区大地构造演化及地质构造运动非常强烈、复杂,由此而发育形成了许多规模巨大的深大断裂.这些断裂对于区域构造环境、构造运动方式以及变形特征都起着重要的作用.通过对深大断裂的研究,对于进一步认识区域应力场的变化和大地震孕育发生的过程有着十分重要的意义.     

青藏高原腹地班戈—双湖一带晚新生代伸展构造 及动力学机制

在青藏高原腹地,晚新生代以来除发育南北向的伸展构造以外,还发现有一系列时代较新的近东西向正断层控制的伸展构造,空间上呈现出平行排列的宽缓凹槽及其间相对狭窄的山梁相互间隔的活动地貌结构特点,称这种地貌结构为"槽梁地貌"。数字高程模型(DEM)的研究表明,研究区近东西向的伸展构造在地貌上切割了近南北向的双湖盆地。结合断层运动学、年代学及盆地沉积作用的研究,认为近东西向的伸展构造的发育最早可能始于中新世,与近南北向的伸展构造交织发育,断裂的活动性在第四纪随着高原腹地海拔抬升得到了显著的增强。青藏高原隆升后重力作用导致了不同方向断陷盆地的发育。