红河断裂带中南段断层岩FT测年及其地质意义

通过对红河断裂带中南段18个糜棱岩、12个角砾岩、10个碎裂岩和8个砂砾岩的显微结构详细观察,部分典型样品的磷灰石裂变径迹测年(简称FT测年,以下同),获得了红河断裂带中南段断层活动转换过程中微观特征的变化:糜棱岩的微结构特征显示红河断裂带早期断层活动为左旋走滑,糜棱岩和未变形的砂砾岩FT年龄均>20Ma,表明这期间红河断裂带曾发生一次构造热事件;碎裂岩和角砾岩的微结构特征显示红河断裂带后期断层活动为右旋走滑,微结构特征不同的碎裂岩和角砾岩的FT年龄可分3个时段(9.9～12.7,6.8～8.4,2～4.6MaBP),表明红河断裂带中新世以来曾发生3次断层位错事件     

龙门山断裂带大地震孕震环境的岩石磁学证据

地震断裂带的孕震环境对于研究地震的发生至关重要.本文以汶川地震断裂带科学钻探2号（WFSD-2）钻孔岩心中的假玄武玻璃、碎裂岩及其围岩为研究对象,通过岩石磁学测试,并结合显微结构观察探讨龙门山断裂带大地震的孕震环境.WFSD-2岩心碎裂岩中的假玄武玻璃是龙门山断裂带曾经发生过大地震活动的岩石学证据,假玄武玻璃具有高磁化率特征,而碎裂岩的磁化率值与围岩相似,假玄武玻璃中的新生磁铁矿是其高磁化率值异常的重要原因之一.假玄武玻璃中较少量的新生磁铁矿暗示了假玄武玻璃的生成环境为含氧量较低的高温还原环境.大地震断裂的摩擦热是改变龙门山断裂带中假玄武玻璃岩石磁学特征的主导因素,流体作用较弱.无高磁化率异常的碎裂岩经历的温度小于300℃,推测假玄武玻璃的生成深度较深.WFSD-2岩心中20余层假玄武玻璃脉体证明映秀—北川断裂带是一条长期活跃的断裂带,龙门山断裂带上曾经发生了多次大地震断裂活动,这些大地震可能发生在深度较大、流体作用较弱的还原性孕震环境中.     

小秦岭拆离断层假熔岩的Raman光谱分析及其成因机制

小秦岭变质核杂岩周缘拆离断层的微角砾岩中发育脉状和角砾状假熔岩 ,Raman光谱分析结果表明假熔岩基质存在 3种结构 :超碎裂细粒结构、隐晶质结构和含微量玻璃质结构 ,3种结构为不同程度超碎裂的结果 ,证明小秦岭拆离断层中假熔岩的成因机制为超碎裂研磨为主的研磨 熔融机制     

太行山北段中新生代断层岩的显微构造研究

太行山北段是大兴安岭 -太行山 -武陵山构造带中段的典型构造区 ,区内 2条主断裂 (紫荆关断裂和乌龙沟断裂 )组成的断裂带发育中、新生代的碎裂岩系列断层岩。通过对断裂带内不同岩性原岩区的断层岩进行详细的显微构造研究 ,分析了 3种主要变形强度类型的断层岩 (碎裂化岩石或构造角砾岩、初碎裂岩、碎裂岩 )的区域分布、显微结构以及微观变形机制 ,鉴定出断层岩中的 3期构造变形叠加 ,结合区域资料探讨了区内中、新生代断层岩反映的 3期主要构造运动及其特征 ,显示出构造强度逐渐减弱的演化趋势     

龙门山断裂带假玄武玻璃特征及断层弱化机制的探讨

与断层相关的假玄武玻璃被认为是地震化石,记录了地震发生过程和断裂机制的重要信息,对认识断层地震活动性具有重要意义.本文综合地表露头及汶川科钻（WFSD-1、WFSD-2）岩心研究,对映秀—北川断裂带南段彭灌杂岩中发育的假玄武玻璃进行详细的结构、构造及矿物成分分析.这些假玄武玻璃以断层脉和单个/网状贯入脉的形式产出,厚度由几毫米到数十厘米不等,与碎裂岩和超碎裂岩相伴生.显微结构观察发现假玄武玻璃中发育大量熔融特征构造,如港湾状熔蚀边、蜂窝状气孔构造、黏滞性流动构造以及针状、球粒状、羽状、纤维状、粒状等多种形态的微晶及微晶集合体,表明其为断层滑动摩擦熔融的产物,指示摩擦熔融润滑是断层滑动过程中最主要的弱化机制.同时热增压和机械润滑机制可能存在于断层滑动的不同阶段.此外,从野外和显微镜下都观察到假玄武玻璃脉具有浅灰、深灰、浅褐、棕褐色及黑色等不同的颜色,可能代表着不同程度的脱玻化作用,并且不同颜色有相互穿插交切关系,可能指示存在多期假玄武玻璃,也就是说,产生假玄武玻璃的大地震事件沿映秀—北川断裂带重复发生.最近的研究认为这些假玄武玻璃形成于晚三叠世时期地下~10—15 km深度.结合须家河组地层中发育的厚层断层泥和角砾岩,~180—280 m宽的映秀—北川断裂岩带是断裂长期活动演化的产物.作为龙门山地区最陡峭的地形边界,映秀—北川断裂带长期地震活动造成的地壳缩短加厚可能是龙门山快速隆升的主要原因.     

龙门山构造带WFSD-2钻孔岩心磁化率特征及其对大地震活动的响应

岩石磁化率特征可以帮助判断岩石的形成环境,对地震过程中滑动摩擦伴随高温的物理-化学变化具有显著反应.本研究以钻穿龙门山中段构造带的汶川地震断裂科学钻探2号孔(WFSD-2)岩心为研究对象,使用Bartington MS2K磁化率仪对500~2283.56 m深度的岩心进行高分辨率无损磁化率测试,并结合岩性特征和显微结构探讨了龙门山构造带主要岩石单元的磁化率特征及其地震断裂活动的磁学响应.磁化率测试结果表明,由花岗岩和火山碎屑岩组成的彭灌杂岩体的磁化率值(数十到数千个10~(-6)SI)普遍高于上三叠统须家河组沉积岩的磁化率值(数个到数十个10~(-6)SI).从WFSD-2岩性分布来看,彭灌杂岩上下出露四段,其磁化率值特征反映它们属于不同的岩石单元,它们与下伏须家河组地层呈断层接触,构成叠瓦状构造,指示了龙门山构造带具有强烈的地壳缩短作用.断裂带中处于滑动带的断层泥和假玄武玻璃具有高磁化率特征,而断层角砾岩和碎裂岩不具有高磁化率值特征,表明断层岩磁化率增高的原因可能主要与地震断裂滑动摩擦过程中高温作用下发生的磁性矿物转换有关,断层岩中高磁化率异常可作为大地震活动的证据.WFSD-2岩心中的映秀—北川断裂带(600~960 m)可识别出约80条高磁化率异常的断层岩带,揭示映秀—北川断裂带是一条长期活动的断裂带,龙门山构造带形成演化过程中伴随着大地震活动.     

北京地区碳酸盐糜棱岩和碳酸盐假熔岩碳氧同位素组成的初步研究

北京地区部分碳酸盐糜棱岩和碳酸盐假熔岩碳氧同位素组成的测试结果表明,碳酸盐岩在发生塑性变形时其δ13C、δ18O值均有不同程度的降低。同位素证据表明,碳酸盐糜棱岩的形成温度较低,并具有缓慢冷却的生成环境;碳酸盐假熔岩具有高温淬冷的同位素地球化学特征,它的形成可能与发震断层的迅速破裂过程有关。研究断层面附近产出的碳酸盐岩的稳定同位素组成对确认古地震事件是有意义的     

干盐池拉分盆地盆内新生断层大地震记录与海原断裂带级联破裂地震事件

沿大型走滑断裂带经常发生导致多个断层段同时破裂的级联破裂地震事件。海原断裂带在1920年海原M 8地震时3个段同时发生破裂,干盐池拉分盆地即为其西段和中段的分段边界。沿该盆地内新生断层的古地震研究揭示了晚更新世末期以来的至少7次古地震事件证据,最新1次事件为1920年海原地震,1920年海原地震之前的1次事件可能与1092年历史地震对应。对比分析表明,这些事件可能均为超过8级的大地震,其复发呈现地震丛集与单个事件相间排列的规律,当前可能处于最近的1个地震丛集期内。该古地震序列与整个海原断裂带的大地震活动历史的对比表明,干盐池拉分盆地内新生断层在级联破裂地震事件发生时并非总是同时破裂,该断层是否参与破裂可能与该次级联破裂事件的震级大小有关。讨论整个走滑断裂带大地震活动历史时应避免仅依据具有一定规模的拉分盆地内部断层的破裂记录。     

磨子潭-晓天断裂(晓天至佛子岭间)的构造分析

根据断裂带切割变质围岩中各期变形旋回形成的褶皱,断裂带中的断层岩为形成于地表条件下的角砾岩和碎裂岩并切割围岩中各种糜棱岩带,构成上侏罗统火山岩盆地的边界断层等特征,磨子潭-晓天断裂应是晚侏罗世形成于地表条件下的断层;根据断层附近上侏罗统砂岩夹层中的裂隙焊接,磨子潭-晓天断裂在晚侏罗世形成后,还有两次较强烈的活动。据地表、钻探和地震资料,断层面向北倾,倾角向深部变缓     

汶川地震断裂带滑移行为、物理性质及其大地震活动性——来自汶川地震断裂带科学钻探的证据

断裂带物质组成、结构及其物理性质是理解断裂变形机制和地震破裂过程的基础和关键,断裂带地震（黏滑）和非地震（蠕滑）滑移行为不仅对了解地震活动性和山脉隆升过程具有重要意义,而且直接为防震减灾提供科学依据.我们以穿过龙门山映秀—北川和灌县—安县断裂带的汶川地震断裂带科学钻探（WFSD）岩心和地表出露的断裂带为研究对象,通过对断裂岩组成、结构、显微构造和钻孔物性测井数据进行分析研究,确定了龙门山逆冲断裂带滑移行为和物性特征,初步探讨了大地震活动性和有关断裂带的隆升作用：（1）映秀—北川断裂带倾向NW,浅部倾角~65°,发育的断裂岩厚约180~280 m,由碎裂岩、假玄武玻璃（地震化石）、断层泥和断层角砾岩组成.断裂带具有高自然伽马、高磁化率值、低电阻率、低波速等物理性质以及对称型破碎结构.断层泥普遍具有摩擦热效应的高磁化率值和石墨化作用特征,是古地震滑动的岩石记录.表明映秀—北川断裂带为经常发生大地震的断裂带,晚新生代以来类似汶川地震的大地震复发周期小于6000—10000年,具有千年复发周期特征.（2）灌县—安县断裂带倾向NW,浅部倾角~38°,发育的断裂岩厚约40~50 m,仅由断层泥和断层角砾岩组成,具有典型的"压溶"结构,表现出蠕滑性质.除压溶作用外,定向富集的层状黏土矿物和微孔隙的发育使断层强度变弱.断裂带具上盘破碎的非对称型破碎结构,除具低磁化率值特征外,其他物性与映秀—北川断裂带一致.（3）根据断裂岩厚度与断层滑移量相关经验公式关系,以及断层产状,粗略估算映秀—北川断裂带自中生代以来累积垂直位移量大于9 km,灌县—安县断裂带累积垂直位移量小于3 km.映秀—北川断裂带长期大地震产生的累积垂直位移量是龙门山隆升的主要贡献.     

RAYLEIGH WAVE TOMOGRAPHY IN THE CRUST AND UPPER MANTLE OF THE DABIE-TANLU OROGENIC ZONE

Dabie Orogen has a series of special tectonic and geological features which make it important to the study of the tectonic evolution of mainland China and East Asia. The distribution of high pressure/ultra-high pressure metamorphic rocks discovered on the surface, the specific location of a series of deep and shallow sutures in the collisional convergence collage, and the seismogenic environment of shallow earthquakes attract many scientists continuously to study the interesting Dabie Orogen. In this paper, we used waveform records of 200 broadband seismic stations deployed by China Digital Seismograph Network and vertical component records of 21 mobile seismic stations located in the Dabie-Tanlu orogenic zone and its surrounding areas. Based on seismic ambient noise tomography, we have obtained the phase velocity distributions of Rayleigh surface wave with the periods between 8~40s, with the resolution higher than 50km. The high velocity anomalies are observed on the Hong'an-Tongbo region in the images of 8~16s phase velocity, which decreases with increasing periods. These high velocity anomalies are in consistence with the ultra-high pressure(UHP)metamorphic rocks of the region. It leads us an estimation of the extension of UHP metamorphic rocks at various depths. The distribution of these anomalies found in phase velocity maps of 8s to 16s indicates that the estimated depth is up to~20km. The horizontal distribution forms a heart shape, which is narrower on western side and wider on the eastern side. It is very much consistent with the surface observations. The whole shape is similar to a cone that laterally extends its wings on the southwest. It indicates that the high-pressure/ultra-high pressure metamorphic rocks had experienced quick exhumation after they broke and formed a drag at the tail, and the residual area formed by the fast exhumation was likely to be invaded by magma. We agree that it has experienced complex structural history, such as stretching, magmatic emplacement and tectonic extrusion, resulting in the high-pressure/UHP metamorphic rocks finally exhuming on the surface with the structural pattern of narrower on the western margin and wider on the eastern margin in the Hong'an-Tongbo area. The significant phase velocity difference from the period of 8s to 35s on both sides of the southern Tanlu fault zone enables us to infer that the Tanlu fault zone is a deep and huge fault, and the entire crust of the eastern zone of Dabie was cut by the Tanlu fault zone. It demonstrates that the Dabie block is separated from the northern Subei Basin and southern Yangtze blocks, which forms a seismogenic environment suitable for the generation of small-to-intermediate earthquakes in this region. Most of earthquakes in Anhui and adjacent provinces are distributed in those areas where the phase velocities changed dramatically, which are in consistence with the small faults of the upper crust in shallow layers of the Dabie-Tanlu orogenic belt. The shallow-source earthquakes mainly occur in velocity contrast regions, as demonstrated by the short period images. Earthquakes distribution and velocity maps show that the possible distribution of tiny faults of the upper crust can be roughly inferred from the geological structure. It helps to understand the seismogenic environment and seismic hazard in the Dabie areas. We conclude that the shallower faults with different velocity on either side of this region are still seismically active. These results have important significance for understanding the tectonic activity of the research areas.More detail work and further discussion are needed on the velocity structure of the Dabie orogen.     

鲜水河断裂带南北构造差异性的地球物理分析

对鲜水河断裂带重磁异常进行向上延拓,通过计算观测面高度异常与延拓后异常之间的相关系数得出最佳向上延拓高度,该延拓高度所对应的延拓结果即为研究区构造背景产生的异常值。向上延拓结果显示布格重力异常值沿鲜水河断裂带自北西向南东逐渐增大,反映出下地壳底边界沿该方向呈升高趋势,可能由青藏高原地壳软弱物质 “东向逃逸” 所致。化极后ΔT磁异常延拓结果表明鲜水河断裂带南东段的康定—石棉以东为强磁性刚性基底。以鲜水河断裂带为分界的不同地块之间基底岩石及地层物性的不同是断裂带南北磁性差异的主导原因。对鲜水河断裂带两侧各约50 km范围内地震的震源深度进行统计,经投影至剖面及线性拟合求出鲜水河断裂带的三维几何形状。结果表明鲜水河断裂带总体倾向南西,倾角近乎直立,范围约为57°—88°。      

根据变形岩石的显微构造特征探讨断层的活动性

本文是通过一条断层及其围岩物质的显微构造的对比研究来探讨断层活动性的尝试。配合热释光年代学方法的测定结果,表明该断层自更新世以来曾发生过多次新的活动,主断裂形成时的古应力大约为700巴左右     

逆断层对致密岩石构造裂缝发育的约束控制

致密岩石(如火山岩和碳酸盐岩)可广泛发育构造裂缝,这类致密岩石的构造裂缝数值建模是构造裂缝地震解释、地震反演和油藏数值模拟的基础.我国西北各盆地普遍发育逆断层,通过在新疆巴楚地区微波塔逆断层和一间房逆断层分别布置实测剖面对野外测量的构造裂缝面密度进行定量分析,发现受逆断层控制的裂缝面密度与逆断层面的曲率呈线性关系;裂缝...     

用裂变径迹法研究断层活动年龄的初步探讨

裂变径迹年代测定是研究断层活动年龄的新方法,它基于磷灰石中裂变径迹的退火效应。本文报导了取自郯庐断裂带等地区12个磷灰石和一个榍石的裂变径迹年龄,结果表明,在断裂带中磷灰石裂变径迹的退火效应非常明显,效应随离断层带的距离增加而减弱。结合断层带的活动特点和原岩的年龄,对断层带中磷灰石裂变径迹年龄的解释及今后的研究方向作了探讨     

Isotopic characteristics of shoshonitic rocks in eastern Qinghai-Tibet Plateau: Petrogenesis and its tectonic implication Isotopic characteristics of shoshonitic rocks in eastern Qinghai-Tibet Plateau: Petrogenesis and its tectonic implication

The Cenozoic magmatic rocks of shoshonitic series in the easternQinghai-Tibet Plateau include potassic alkaline plutonic rocks, volcanic rocks, lamprophyres and acidic porphyries. Analytical results show that these different lithological rocks are extremely similar in Sr, Nd and Pb isotopic compositions with the range of 0.705 187-0.707 254 for 87Sr/86Sr, 0.512 305-0.512 630 for 143Nd/144Nd, 18.53-18.97 for 206Pb/204Pb, 15.51-15.72 for 207Pb/204Pb and 38.38-39.24 for 208Pb/204Pb. They are isotopically similar to the EMII end-member. This indicates that mantle metasomatism must have taken place in their source region. The formation of these particular rocks is related to crustal thinning and mantle upwelling in a large-scale strike-slip and pull-apart fault zone at about 40 Ma in northern and eastern Qinghai-Tibet Plateau.     

Active fault survey on the Tanlu fault zone in Laizhou Bay

Introduction The Tanlu fault zone, the largest active structure in the eastern region of China, is character-ized by right lateral strike-slip movement with dip-slip component in the Quaternary; it shows great significance for the modern seismicity (FANG et al, 1976; Institute of Geophysics, China Earthquake Administration, 1987; GAO et al, 1980; MA, 1987; LI, 1989; CHAO et al, 1995). The Tanlu fault zone is the boundary between the Jiaoliao block and the North China Plain block of …     

Reconstructing the evolution of fault zone architecture: Field‐based study of the core region of the Atera Fault,Central Japan

In order to reconstruct the architectural evolution of a fault zone with heterogeneous structures, we studied the Atera Fault in Central Japan, and described the detailed mesoscopic and microscopic features of the zone. The fault zone studied consists of a 1.2‐m wide fault core of fault breccia mixed with fragments derived from welded tuff, granite, and mafic volcanic rocks. The 1.2‐m wide fault core is bordered by a western damage zone characterized by a welded tuff fault breccia and an eastern damage zone characterized by a granite cataclasite. A secondary fault core, a 30‐cm wide granite‐derived fault gouge, cross‐cuts the granite cataclasite. Although welded tuff fault breccia and granite cataclasite are also pervasively fractured and fragmented, the fault cores are significantly affected by fragment size reduction due to intense abrasive wear and comminution. The 1.2‐m wide fault core includes fragments and a sharp dark layer composed of mafic volcanic rocks, which can be correlated with neighboring 1.6 Ma volcanic rocks. This observation places a younger constraint on the age of the fault core formation. Carbonate coating on basalt fragments in the 1.2‐m wide fault core has also been fractured indicating the repetition of intense fragmentation. Bifurcated, black and gray veins near the 1.2‐m wide fault core are likely injection veins, formed by the rapid injection of fine material within fault zones during seismic events. The granite‐derived fault gouge, characterized by hard granite fragments without intense brecciation and microfracturing, in a kaolinite‐rich clay matrix, is interpreted as the most recent slip zone within the exposed fault zone. A preview of published geological and hydrological studies of several fault zones shows that clay‐rich fault cores can exhibit much lower permeability than the adjacent damage zones represented in this present case by the welded tuff fault breccia and granite cataclasite.     

汶川地震破裂带断层岩纵波速度与孔隙度关系的实验研究

分布于地震破裂带上的断层岩具有高孔隙度的特征.该特点造成了其弹性波速度与结晶岩石和沉积岩存在明显的差异.确定断层岩的弹性波速度与孔隙度和矿物组成的关系对于利用地震资料探测深部断层和测井资料的解释至关重要.在10~600 MPa条件下,本文对地震断层岩的纵波波速（V_p）和总孔隙度（φ_t）进行了测量,并深入分析了V_p与孔隙度的关系.结果表明在10~600 MPa的压力范围内,V_p（p）随着压力的增高呈现对数增加,其增长率随着压力的上升而逐渐减小,遵从∂V_p（p）/∂p=a_v/p的变化规律.断层岩中的孔隙度随着压力的增高呈对数减小.与传统的认识不同,实验发现在压力高达600 MPa以上,大多数断层岩中仍然可以残留可观的孔隙量.分析显示V_p与总孔隙度及总粘土含量呈负线性相关.该发现有助于认识深部流体的活动通道特征,有助于理解断层带中存在大量粘土矿物、断层带内的物质可被大量带出、围陷波的形成等地质和地球物理现象.     

Results of the study of anisotropy of elastic properties of rocks from the Luchlompolo fault zone (Pechenga region,Kola Peninsula)

Elastic characteristics of rock samples from the Luchlompolo fault zone taken from outcrop surfaces are compared with elastic characteristics of core samples of the Kola ultradeep borehole taken in an analogous interval. An inversion consisting of a discrepancy between the schistosity levels of rocks in the borehole (below the Luchlompolo fault) and their analogues at the surface (above the fault) is explained by a considerable difference in the force actions that caused the schistosity and layering of rocks in the borehole and at the surface. A kinematic scheme of the fault is constructed, and a hypothesis about the existence of an inversion point (region) in the fault zone and its probable collecting properties is put forward.An inverse dependence of variations in density characteristics of rocks on acoustic dichroism and their elastic anisotropy coefficient for transverse waves is established for the first time.