U-Pb Dating of Volcanic Rocks and Granites along the Wuyishan Belt: Constraints on Timing of Late Mesozoic Tectonic Events in Southeast China

Five volcanic rock samples and two granite samples taken from the volcanic basins in western Fujian and southern Jiangxi were dated by using the zircon laser albation-inductively coupled plasma mass spectrometry U-Pb method. Together with previously dated ages, the dates obtained provide important constraints on the timing of late Mesozoic tectonic events in SE China. The volcanic rock samples yield ages of 183.1±3.5 Ma, ca. 141 Ma to 135.8±1.1 Ma, 100.4±1.5 to 97.6±1.1 Ma, confirming three episodes of late Mesozoic volcanic activities, which peaked at 180±5 Ma, 140±5 Ma and 100±5 Ma, respectively, along the Wuyishan belt. Moreover, based on field investigations of these volcano-sedimentary basins, we have recognized two compressional tectonic events along this belt. The early one was characterized by Upper Triassic to Middle Jurassic NNE-trending folds that were intruded by late Jurassic granites; and the late one caused the Lower Cretaceous volcano-sedimentary layer to be tilted. The dated age 152.9±1.4 Ma of the granitic samples from the Hetian granitic pluton in the Changting Basin and that from the Baishiding granitic pluton, 100.2±1.8 Ma, in the Jianning Basin, give the upper boundaries of these two tectonic events respectively. Hence, the late Mesozoic tectonic evolution of SE China was alternated between extension and compression.     

0.6～2.0GPa压力下部分熔融角闪辉长岩的纵波波速

利用超声波透射-反射法,测量了0.6～2.0 GPa、最高1 085℃条件下角闪辉长岩的纵波波速(vp),详细统计了部分熔融阶段实验产物组分的体积百分含量,利用矿物含量和弹性参数,计算了角闪辉长岩的纵波波速.实验测量和理论计算显示了较一致的vp-t关系,即高压下角闪辉长岩的vp随温度升高先缓慢降低,在温度约800～900℃后转而大幅下降.实验产物显示,样品在温度达812℃(0.6 GPa)、865℃(1.0 GPa)和919℃(2.0 GPa)后发生矿物脱水和部分熔融,熔体含量随温度升高显著增加.熔体是导致高温阶段岩石vp快速降低的主要原因.在初熔阶段vp随熔体增加而降低尤为显著,可能是初熔时矿物脱水生成的自由水及含水量高的熔体,以微细熔体薄膜浸润矿物边界或裂隙所导致.     

Temporal vP/vS variation characteristics in different zones of China’s Capital Circle area before and after Wen’an earthquake

On July 4, 2006, an earthquake of MS5.1 took place in Wen’an, Hebei Province, just at the south center of China’s Capital Circle area digital seismograph network. It is the strongest event recorded ever since the network went into operation in 2002. We processed the vast amounts of phase data yielded by the 107 digital seismic stations between 2002~2007 using Wadati method. In order to improve the precision and stability of shear and compressional wave velocities (vP/vS) calculation, we impose a number of restrictions on the computation environment and condition, e.g., the earthquakes are densely concentrated, selected stations are limited in range, the number of stations in- volved in the computation is larger than 5 and linear fitting features high precision and small error. Under these restrictions, the study shows that vP/vS in and around Wen’an and Tangshan underwent a normal-low-normal proc- ess one year before Wen’an earthquake, vP/vS became obviously low and the low ratio lasted for about one year, meanwhile, little variation of vP/vS was seen in Xingtai, northwest of Beijing, southwest of Beijing, Beijing-Tianjin and Beijing; after the quake, the vP/vS returned normal in Wen’an and Tangshan. Error and stability analysis of the calculated result for vP/vS shows it is convincible that anomaly appeared in and around Wen’an and Tangshan be- fore Wen’an earthquake.     

塔北西部英买力地区英买2 工区古生界盐构造样式研究

盐构造研究对于油气勘探和理论研究均有着重要的意义。塔北隆起是塔里木盆地的重要勘探区块。根据地震及钻井资料,研究了塔北隆起西部英买力地区英买2 工区古生界盐构造样式、形成机制及其对区域构造的影响。塔北隆起西部古生界发育了与中寒武统膏盐岩有关的盐构造样式,包括盐丘、盐上逆断层、盐上正断层。通过相干图分析可见盐丘从底到顶展示出有规律的变化,盐底变形强的地区在顶部变形弱,而盐底变形弱的地区在顶部变形强;变形强弱的不同在相干图上表现为与周围不协调的椭圆,从盐丘底部到顶部,椭圆的长轴方向逆时针旋转了30°,反映了变形时有走滑运动的分量存在。通过演化剖面恢复,认为古生界盐构造在古生代末基本形成了现在的形态,在三叠纪断裂重新活动,伴随着生长地层发育。膏盐层的分隔作用造成了构造层次之间构造样式的不协调及其分层性特征,盐构造形成的构造裂隙控制了后期火成岩的发育部位。     

海拉尔盆地乌尔逊-贝尔凹陷挤压构造的发现及其地质意义

海拉尔盆地是叠置于内蒙古-大兴安岭古生代碰撞造山带之上的中-新生代盆地,总体上呈北东向展布,由三坳、两隆五个一级构造单元组成,自西向东依次为扎贲诺尔坳陷、嵯岗隆起、贝尔湖坳陷、巴彦山隆起和呼和湖坳陷, 其中乌尔逊凹陷、贝尔凹陷是位于贝尔湖坳陷凹陷南部的两个二级构造单元。研究表明,乌尔逊-贝尔凹陷在早白垩世大磨拐河期-伊敏期早期、伊敏期末期分别经历了北西 南东向、近东西向两次较长时间的挤压作用,使伸展断陷中的部分控陷正断层发生反转作用,在研究区形成了新的断层传播褶皱、断层转折褶皱以及叠瓦构造和双重构造、突发构造、构造三角带等。由于挤压构造的几何学、运动学特征的不同及隆升速率与同构造生长地层沉积速率的比值在空间上的差异,同挤压地层层序在不同构造部位也表现出不同的沉积特点,其构造特征与造山带十分相似。乌尔逊-贝尔凹陷中两次挤压构造的发现,说明中国东北地区的地壳厚度在早白垩世并非一直处于伸展减薄状态,而是在上述两次挤压时期地壳处于叠置增厚的特点,在空间上形成挤压坳陷型盆地和陆内(板内)造山带相间分布的构造格局。     

辽西地区晚侏罗世张家口组及其地质意义

辽宁省西部地区张家口组是在近几年来1:5万、1:25万区域地质调查的基础上发现和建立的,主要分布于金岭寺-羊山盆地的东缘、北票盆地西缘、四家子-铁营子盆地及凌源三十家子盆地东缘,呈北东向沿断裂带分布.岩性为一套偏酸、偏碱性的火山岩,以爆发相的火山角砾岩、集块岩及凝灰岩为主,呈角度不整合覆于晚侏罗世土城子组之上,其上被早白垩世义县组角度不整合覆盖.形成于挤压造山与伸展构造的过渡环境,是古亚洲构造域压性体制与滨太平洋活动带张性体制构造转换阶段的产物.地层时代为晚侏罗世.     

走滑断裂、"挤压性盆-山构造"与油气资源关系的探讨

了解含油气盆地的形成及其演化的影响因素对于含油气盆地的勘探和开发是至关重要的．以美国西部的圣安德烈斯断裂带及伴生的南加州油气盆地作为参考,对中国青藏高原北部与阿尔金走滑断裂系相关的盆-山构造进行了剖析．探讨阿尔金走滑断裂系在其演化过程中,怎样控制区域应力场、变形构造及盆地的形成,进而制约油气的迁移和圈闭．分析结果表明与圣安德烈斯断裂带在美国南加州的盆-山构造体系所起的作用相比较,阿尔金走滑断裂系在青藏高原北部的盆-山构造体系的形成和演化中起相似的作用．青藏高原相对于塔里木盆地的斜向运动导致在阿尔金走滑断裂的东南形成走滑-挤压构造域．形成一系列的走滑和推覆构造,在地形上表现为包括柴达木盆地在内的有序的盆-山相间的构造体系,与南加州富含油气的盆地相似,阿尔金走滑断裂及相配套的走滑-逆冲推覆构造促使在这些盆地中形成富集油气的构造。     

挤压地区物理模拟研究进展

构造物理模拟是目前研究构造变形过程与成因机制最为有效的手段。在系统展示并归纳国内外研究成果的基础上, 总结了物理模拟实验的理论、材料及技术进展。在挤压地区, 构造物理模拟已经被证明是一种模拟逆冲褶皱系统演化过程的强有力工具; 在推覆体或双冲构造、冲断带的反转与基底卷入、挤压造山作用与表面过程、挤压地区构造转换带及地幔对流与板块碰撞俯冲等方面取得了很大进展。     

地震地电方法在天祝—景泰6.2级地震前的预测预报

本文通过对天祝—景泰6.2级地震监测预报工作全过程的研究,展示了地电方法监测预报地震的新进展。另外,对如何运用地电场的分布变化规律及地电阻率异常时间、幅度的特征进行监测预报作了探讨。     

Neogene Through Quaternary Tectonic Reactivation of SW Iberian Passive Margin

Southwest Portugal, the Gulf of Cadiz and Morocco are under the potential threat of natural hazards linked to seismicity and tsunami generation. We report the results of two multi-channel seismic (MCS) surveys carried out in 1992 and 1998 along the continental margin and oceanic crust of SW Iberia. This MCS data set shows the evidence of the compressional deformation which involves both the continental and the oceanic crust of the study area. The area of deformation extends from the southern border of the Tagus Abyssal Plain to the Seine Abyssal Plain, encompassing the continental margin of SW Portugal. Most of the structures observed are probably related to a Mid-Miocene phase of Africa-Europe plate convergence. In this paper we discuss the recent advances on the identification of the tectonic structures that are still active and that may generate great earthquakes and tsunamis. The tectonic structures identified are located respectively at the Guadalquivir Bank, along the eastern border of the Horseshoe Abyssal Plain and along the southern continental slope of SW Portugal.BIGSETS Team: L. Mendes Victor, C. Corela, A. Ribeiro, D. Cordoba, J. J. Danobeitia, E. Grácia, R. Bartolomé, R. Nicolich, G. Pellis, B. DellaVedova, R. Sartori, L. Torelli, A. Correggiari, L. Vigliotti.