新疆独山子山前活断层和活褶皱及古地震研究

本文初步研究了新疆独山子山前活断层、活褶皱构造。这些表层构造有着不同性质的地表变形,是多次古地震活动的反映。文中将这些古地震遗迹分为四期,并计算了该断层带的地震复发周期和平均位移速率。     

宁夏沙坡头地区黄河弯曲的成因

在宁夏沙坡头地区,黄河出黑山峡进入中卫盆地处形成一个异常的“Ω”型的弯曲。这不是一般的蛇曲,而是一个穿过两组不同方向与不同性质的活动走滑断裂的河流位错现象。它的出现与此处近东西向的中卫－同心断裂系的左旋走滑和北北西向的常乐－兴仁断裂系的右旋走滑活动的双重作用有关     

The role of gravitational collapse in controlling the evolution of crestal fault systems (Espírito Santo Basin,SE Brazil)

A high-quality 3D seismic volume from offshore Espírito Santo Basin (SE Brazil) is used to assess the importance of gravitational collapse to the formation of crestal faults above salt structures. A crestal fault system is imaged in detail using seismic attributes such as curvature and variance, which are later complemented by analyses of throw vs. distance (T-D) and throw vs. depth (T-Z). In the study area, crestal faults comprise closely spaced arrays and are bounded by large listric faults, herein called border faults. Two episodes of growth are identified in two opposite-dipping fault families separated by a transverse accommodation zone. Statistical analyses for eighty-four (84) faults show that fault spacing is < 250 m, with border faults showing the larger throw values. Fault throw varies between 8 ms and 80 ms two-way time for crestal faults, and 60–80 ms two-way time for border faults. Fault length varies between ∼410 m and 1750 m, with border faults ranging from 1250 m to 1750 m. This work shows that border faults accommodated most of the strain associated with salt growth and collapse. The growth history of crestal faults favours an isolated fault propagation model with fault segment linkage being associated with the lateral propagation of discrete fault segments. Importantly, two episodes of fault growth are identified as synchronous to two phases of seafloor erosion, rendering local unconformities as competent markers of fault reactivation at a local scale. This paper has crucial implications for the understanding of fault growth as a means to assess drilling risk and oil and gas migration on continental margins. As a corollary, this work demonstrates that: 1) a certain degree of spatial organisation occurs in crestal fault systems; 2) transverse accommodation zones can form regions in which fault propagation is enhanced and regional dips of faults change in 4D.     

Distinguishing tectonically-and gravity-driven synsedimentary deformation structures along the Apulian platform margin (Gargano Promontory,southern Italy)

The assessment of deformation types within the slope of a carbonate platform can be complicated by the possible interaction of rooted (tectonically-induced) and superficial (gravity-driven) structures. An ideal case study to document and distinguish tectonically- and gravity-driven structures is provided by the Cretaceous slope-to-basin carbonates exposed in the Gargano Promontory, southern Italy. These carbonates formed adjacent to the Apulian platform margin, which was oriented approximately NE–SW to NW–SE along the southern and northern edges of the promontory, respectively. Slump-related folds are characterised by axial planes typically oriented either sub-parallel or at small angles to the strike of the inferred paleoslope. In fact, the strike of folds is roughly NE–SW in the southern portion of the study area, whereas it is NW–SE in the northern part. Correspondingly, gravity-driven normal and reverse faults strike sub-parallel and at acute angles to the adjacent Apulian paleoslope. Cretaceous tectonic faults in the slope-to-basin carbonates form two principal sets striking NW–SE and WNW-ESE. The former set is made up of normal faults and the latter one includes mainly oblique-slip normal faults. Neither normal nor oblique-slip normal faults show any relationship with the geometry of the paleoslope. The results obtained from this study may help the interpretation of subsurface data in those geological contexts in which the interplay of gravitational and tectonic processes is responsible for deformation.     

安徽庐枞盆地泥河铁矿床成矿流体性质:来自He-Ar-H-O同位素的证据

安徽庐江泥河铁矿床位于长江中下游成矿带庐枞中生代火山岩盆地,受控于切穿至Moho面的罗河-缺口断裂,矿床具有典型玢岩型铁矿的特征。泥河铁矿床硬石膏-透辉石-磁铁矿阶段流体3He/4He=0.14~0.76Ra(平均0.3548Ra),40Ar/36Ar=262.2~364.9(平均299.3),δ18OSMOW=-2.16‰~5.04‰,δDSMOW=-40.7‰~-34.8‰;硬石膏-黄铁矿-磁铁矿阶段流体3He/4He=0.0108~0.1301Ra(平均0.0697Ra),40Ar/36Ar=221.4~401.4(平均315.1),δDSMOW=-31.8‰~-15.4‰,δ18OSMOW=-2.72‰~1.88‰;高岭石-硬石膏-石英-黄铁矿阶段流体3He/4He=0.0162~0.0223Ra(平均0.0193Ra),40Ar/36Ar=312.5~367.6(平均340.05),δDSMOW=-25‰~-8‰,δ18OSMOW=-6.59‰~-4.89‰。成矿流体的同位素特征显示,幔源流体可能参与了泥河铁矿床早期的成矿作用,后期改造型饱和大气降水逐步加入并占据成矿作用的主导地位。研究结果表明,长江中下游地区中生代强烈的壳幔相互作用,是形成区域巨量金属矿床的重要机制,区域的深大断裂构成了幔源岩浆、幔源物质参与浅部成矿的通道。     

苏鲁地体折返与郯庐断裂活动:莱阳盆地中生界碎屑锆石年代学的制约

胶莱盆地位于苏鲁造山带的北缘,其莱阳群沉积对反演郯庐断裂和苏鲁造山带中生代的折返过程具有重要的制约作用。本文利用LA-ICP-MS方法对莱阳盆地的莱阳群碎屑岩和青山群火山岩进行锆石U-Pb年龄测定,分析其年龄谱特征,探讨其沉积物源区,进而为苏鲁造山带的折返机制提供依据。(1)莱阳盆地发育莱阳群和青山群为代表的中生代沉积岩,锆石年龄测试得到莱阳群形成时代为125±0.6Ma;青山群形成时代为119±1Ma,表明两者都是早白垩世中-晚期的沉积产物;(2)超高压带北缘莱阳盆地与合肥盆地的碎屑锆石年龄谱对比表明,莱阳盆地的沉积物无论沉积时代还是物源区均明显不同与郯庐断裂西侧的合肥盆地,表明郯庐断裂应该形成于两个盆地形成之前,可能为三叠纪-早侏罗世之间;(3)莱阳盆地内发育大量的华北型碎屑物质,进一步表明在扬子大陆板块俯冲过程中华北板块曾经仰冲到扬子板块之上;(4)莱阳盆地发育少量的新元古代岩浆和印支期变质锆石的年龄,表明早白垩世苏鲁超高压变质岩已经折返到地表;(5)超高压变质岩与中生代岩浆岩同时作为莱阳盆地的物源,结合五莲拆离断层的同期活动和莱阳盆地的同时代沉积,说明苏鲁超高压带中生代的折返具有与变质核杂岩类似的大型伸展构造背景。     

浅议不同规范对活动断裂定义的差异——以昆明市为例

现行的勘察设计行业《岩土工程勘察规范》(GB50021-2001/2009年版)、《建筑抗震设计规范》(GB50011-2010)、《工程场地地震安全性评价》(GB17741-2005),对于活动断裂的定义有一定差异,使得不同的勘察设计单位对同一条断裂的评价结果不一致,甚至相互矛盾。本文以昆明市为例,通过分析不同规范对于活动断裂的定义,指出其中的问题与差异,结合典型断层地质剖面与震害实例,简要阐述地质上判定活动断裂的主要依据,即不应以《岩土工程勘察规范》(GB50021-2001/2009年版)规定的全新地质时期(一万年)内有无地震活动来判定断裂是否为全新活动断裂,应以《工程场地地震安全性评价》(GB17741-2005)规定的断裂是否错动地表或近地表相应时代的地层,来判定其活动时代。     

华北地区NNW向断裂的现代活动性特征

本文根据华北地区NNW向断裂对海岸线方向，地貌现象，温泉地热异常和微震震中的控制作用，特别是根据NNW向断裂在华北地区地震活动中的表现，阐述了华北地区NNW向断裂的现代活动性特征，并且认为地震监测中NNW向断裂是一组应予以重视的现代活动性断裂。     

南海西南部珊瑚礁区活动断裂分析

利用SEABAT8111多波束系统在南海西南部珊瑚礁区海域进行地形地貌探测,同时还进行了单道和多道地球物理调查。探测表明该区珊瑚礁礁体的活动断裂主要有NE、NW、SN向3组。NE向断裂主要分布在岛礁区内,是晚燕山期南海第一次海底扩张时形成的断裂系,强烈活动于晚白垩世—始新世,晚第三纪以来继承性活动,以张剪性断裂为主,现今活动性中等至弱。NW向断裂主要分布在曾母盆地,以张剪性断裂为主,切割至基底,强烈活动于渐新世至上新世,构成了曾母盆地的主要张裂期,第四纪仍有活动,均为弱活动断裂。SN向断裂主要有南海西部的滨海断裂带,它是南海SN向扩张时期的转换断层,具张剪性,为中活动断裂,是南海西南部珊瑚礁区活动性较强的断裂,该断裂带历史上曾有火山活动和地震活动的记录。     

Kane Fracture Zone

The Kane Fracture Zone probably is better covered by geophysical survey data, acquired both by design and incidentally, than any other fracture zone in the North Atlantic Ocean. We have used this data to map the basement morphology of the fracture zone and the adjacent crust for nearly 5700 km, from near Cape Hatteras to the middle of the Mesozoic magnetic anomalies west of Cap Blanc, northwest Africa. We use the trends of the Kane transform valley and its inactive fracture valley to determine the record of plate-motion changes, and we interpret the basement structural data to examine how the Kane transform evolved in response to changes in plate motion. Prior to about 133 Ma the Kane was a small-offset transform and its fracture valley is structurally expressed only as a shallow ( < 0.5 km) trough. In younger crust, the offset may have increased to as much as 190 km (present offset 150 km) and the fracture valley typically is up to 1.2 km deep. This part of the fracture valley records significant changes in direction of relative plate motion (5°–30°) near 102 Ma, 92 Ma, 59 Ma, 22 Ma, and 17 Ma. Each change corresponds to a major reorganization of plate boundaries in areas around the Atlantic, and the fracture-zone orientation appears to be a sensitive recorder of these events. The Kane transform has exhibited characteristic responses to changes in relative plate motion. Counterclockwise plate-motion changes put the left-lateral transform offset into extension, and the response was for ridge tips at the ridge-transform intersections to propagate across the transform valley and against the truncating lithosphere. Heating of this lithosphere appears to have produced uplift and formation of a well developed transverse ridge that bounds the inactive fracture valley on its older side. The propagating ridge tips also rotated toward the transform fault in response to the local stress field, forming prominent hooked ridges that now extend into or across the inactive fracture valley. Clockwise (compressional) changes in relative plate motion produced none of these features, and the resulting fracture valleys typically have a wide-V shape. The Kane transform experienced severe adaptions to the changes in relative plate motion at about 102 Ma (compressional shift) and 92 Ma (extensional shift), and new transform faults were formed in crust outside the contemporary transform valley. Subsequently, the transform offset has been smaller and the rates of change in plate motion have been more gradual, so transform-fault adjustment has been contained within the transform valley. The fracture-valley structure formed during extensional and compressional changes in relative plate motion can be decidedly asymmetrical in conjugate limbs of the fracture zone. This asymmetry appears to be related to the ‘absolute’ motion of the plate boundary with respect to the asthenosphere.