小江断裂带周边地区三维P波速度结构及其构造意义

作为青藏高原的东南边界,小江断裂带在高原物质的侧向逃逸中发挥着重要的作用.本文利用流动地震台阵及固定台站的走时观测资料,对小江断裂带及周边区域的壳幔三维P波速度结构进行了研究.结果表明,在中上地壳,小江断裂带内部主要为低速异常,其东侧主要为高速异常.在中下地壳,小江断裂带中部为低速异常,北部和南部主要为高速异常,其中北部的高速异常可延伸到地表附近,南部的高速异常可一直延伸到上地幔.我们推测,小江断裂带中部的低速异常与深部热作用有关;北部的高速异常可能是晚古生代地幔柱活动导致大量基性和超基性幔源物质侵入地壳引起的,它的存在对青藏高原物质向南逃逸起到了一定的阻挡作用,可能是导致川滇活动块体北部次级块体快速抬升的重要因素;南部顶界面向北倾斜的高速异常体对川滇活动块体向南滑移起到了进一步的阻挡作用,导致其上覆的中上地壳低速异常区发生较强的变形和强烈的地震活动,同时在上地幔深度范围起到了稳定的作用,使其南部区域的介质受青藏高原物质向南挤出的影响明显减小.     

基于优化滤波法对芦山地震震区重力异常特征的分析

首先对具有代表性的重力异常分离方法进行简单介绍, 在此基础上使用这些方法对同一组理论模型数据进行试验, 优选出异常分离效果较好的优化滤波法对芦山地震震区重力异常特征进行分析, 初步认识此次地震发生的深部构造背景, 得出以下初步结论: 龙门山断裂带在研究区布格重力异常中反映为一条近北东走向的显著重力梯度带. 该梯度带在天全附近分为两支, 芦山地震震区靠近重力梯度带分叉处, 且M_S≥3.0余震同样呈近北东向展布, 与梯度带走向基本一致, 认为此次强地震的发生与重力梯度带下的深部结构及构造活动密切相关; 芦山地震震区浅部结构与深部构造特征存在较大差异, 构造复杂及地壳深浅部耦合关系较差, 说明此次强地震的发生受浅部和深部构造的共同控制.      

陕西汉中盆地水压致裂地应力测量分析研究

汉中盆地位于龙门山断裂带东北段的末端,汶川MS8.0地震发生以后,地震活动存在沿龙门山断裂带向NE向发展的趋势.在汉中盆地西缘进行了两个钻孔的水压致裂地应力测量,来分析震后该区地应力状态,以期为该区的地震危险性研究提供实际资料.这两个钻孔深度均为300m左右,相距33m,取得了较好的地应力测试结果.通过对地应力测试结果的综合分析研究,得到以下认识:①在汉中盆地西缘300m深度地层内,最大水平主应力值为5.69—19.52MPa,最小水平主应力值为3.81—10.90 MPa,垂直主应力值约为1.25—7.03MPa,水平主应力占主导地位,垂直应力为最小应力,该地应力状态有利于逆断层的活动;②汉中盆地西部现今最大水平主应力方向为WNW或近EW向;③汶川地震后,目前汉中盆地及其西部地区仍处于构造应力调整阶段,总体相对稳定.     

龙门山断裂脆塑性转化带内花岗岩的流体特征与裂缝愈合的实验模拟研究

汶川Mw7.9级大地震的发震断层具有高角度逆冲滑动特征.通过对高角度逆断层滑动的力学条件的分析表明,龙门山断裂深部可能存在高孔隙流体压力有利于断层的失稳滑动.利用现有的技术手段无法获得中地壳深度断层内的流体特征.龙门山断裂带是一条逆冲推覆的构造带,这使得地质历史早期的龙门山断裂深部的彭灌杂岩体抬升到地表,并保留了当时的深部流体特征和变形特征.研究地表露头的变形花岗岩能够推断过去的龙门山地区的深部环境,从而了解过去该地区的深部强震孕育机理,这能够帮助理解现今龙门山地区类似汶川地震的强震的发生机理.     

川滇块体东边界主要断裂带运动特性及动力学机制研究

作为青藏高原东南缘的川滇块体,变形剧烈,地震频发.川滇块体的侧向挤出滑移造成了东边界的左旋剪切变形,不同的地震学者利用不同的方法得出了重要的定量结果.大地测量技术特别是GPS技术的快速发展,为断裂带形变场研究提供了高精度的观测数据,也给研究断裂带动态变化特征及其动力学机制提供了动态观测资料约束.因此,有必要综合利用块体运动模型、断裂带本身的构造变形定量分析及数值模拟方法,给出鲜水河—安宁河—则木河—小江断裂带的运动特征及应变积累特性的定量结果.     

青海玉树地区主要活动断裂的遥感影像解译及构造活动性

综合利用IRS-P5、ALOS、Google earth等高分辨率遥感影像及ASTER DEM资料,结合前人研究成果和野外实地考察,总结玉树地区断裂带的遥感影像解译标志,获取其空间展布和分段情况,对断裂的性质和活动性进行了详细的分析。研究中共解译活动断裂18条,总体呈Y字型分布。通过错断水系位错量的量测、三维地貌对比、地形起伏度和历史地震对比等多种分析,断裂活动强度可以分为强烈、中等和弱活动3个等级,其中当江—多彩断裂、玉树断裂和巴塘断裂是玉树断裂带内最主要的活动断裂。     

江山—绍兴断裂带构造格局的新元古代SHRIMP锆石U-Pb年龄证据

报道采自双溪坞群不同岩组岩石样品的锆石年龄,其中,平水组英安质凝灰岩SHRIMP锆石U-Pb年龄为908.2±6.8Ma,双溪坞群北坞组安山岩年龄为901.6±5.5Ma,双溪坞群章村组火山角砾岩安山质角砾岩年龄为899±8Ma,上覆河上镇群骆家门组底砾岩(花岗闪长岩)SHRIMP锆石U-Pb年龄为878.96±4.5Ma。通过年龄数据探讨位于该断裂带的构造背景,依据该年龄数据限定区域地层对比和构造演化序列。锆石U-Pb年龄和地球化学标示了江山—绍兴断裂带北侧双溪坞群的沉积地层,地球化学分析表明该群代表了新元古代早期华南洋的中间岛弧。上述年龄为江山—绍兴断裂带变质地层的对比增添了可靠的年龄依据。     

The dilemma of the Jiaodong gold deposits: Are they unique?

The ca. 126e120 Ma Au deposits of the Jiaodong Peninsula, eastern China, define the country＇s largest gold province with an overall endowment estimated as＆gt;3000 t Au. The vein and disseminated ores are hosted by NE-to NNE-trending brittle normal faults that parallel the margins of ca. 165e150 Ma, deeply emplaced, lower crustal melt granites. The deposits are sited along the faults for many tens of kilometers and the larger orebodies are associated with dilatational jogs. Country rocks to the granites are Pre-cambrian high-grade metamorphic rocks located on both sides of a Triassic suture between the North and South China blocks. During early Mesozoic convergent deformation, the ore-hosting structures developed as ductile thrust faults that were subsequently reactivated during Early Cretaceous ＂Yan-shanian＂intracontinental extensional deformation and associated gold formation. 〈br〉 Classification of the gold deposits remains problematic. Many features resemble those typical of orogenic Au including the linear structural distribution of the deposits, mineralization style, ore and alteration assemblages, and ore fluid chemistry. However, Phanerozoic orogenic Au deposits are formed by prograde metamorphism of accreted oceanic rocks in Cordilleran-style orogens. The Jiaodong de-posits, in contrast, formed within two Precambrian blocks approximately 2 billion years after devolati-lization of the country rocks, and thus require a model that involves alternative fluid and metal sources for the ores. A widespread suite of ca. 130e123 Ma granodiorites overlaps temporally with the ores, but shows a poor spatial association with the deposits. Furthermore, the deposit distribution and mineral-ization style is atypical of ores formed from nearby magmas. The ore concentration requires fluid focusing during some type of sub-crustal thermal event, which could be broadly related to a combination of coeval lithospheric thinning, asthenospheric upwelling, paleo-Pacific plate subduction, and seismicity along the continental-scale Tan-Lu fault. Possible ore genesis scenarios include those where ore fluids were produced directly by the metamorphism of oceanic lithosphere and overlying sediment on the subducting paleo-Pacific slab, or by devolatilization of an enriched mantle wedge above the slab. Both the sulfur and gold could be sourced from either the oceanic sediments or the serpentinized mantle. A better understanding of the architecture of the paleo-Pacific slab during Early Cretaceous below the eastern margin of China is essential to determination of the validity of possible models.     

Latest active age and model of the faults in Longquanshan fault belt

Longquanshan fault belt belongs to Longmenshan foreland uplift, which is closely related to the uplift evolution of Longmenshan in Qinghai-Tibet Plateau. In order to explore the fault activity model, period and era characteristics of Longquanshan fault belt, some gouge samples were collected at different fault locations of Longquanshan fault belt. SEM was adopted for trace and dissolution micromorphology observation, and ESR was used to test the latest active age. Combined with the regional seismic data, further research on the seismic potential of Longquanshan fault belt was conducted. The results show that the main model of activity in Longquanshan fault belt is stick slip, with creep characteristics. The faults are characterized by multiple periods of activity. The strong acitivity era is the Early Pleistocene-Middle Pleistocene, there were obvious activities in the Late Pleistocene, and there weren’t any obvious activities in the Pliocene. The latest active ages measured by SEM, ESR, TL range from (1210±121) to (110±10.0) ka. The latest active age and activity is characterized with segmen tation, featured with weak activity in the middle segments and strong activity in the north and south segments. Longquanshan fault belt is an active fault belt with certain seismic potential. The earthquakes are distributed zonally along Longquanshan fault belt. However, its activity has been greatly reduced, compared with Longmenshan fault belt in the western part.     

Piezomagnetic In-situ Stress Monitoring and its Application in the Longmenshan Fault Zone

The relative change of in-situ stress is an inevitable outcome of differential movement among the crust plates. Conversely, changes of in-situ stress can also lead to deformation and instability of crustal rock mass, trigger activity of faults, and induce earthquakes. Hence, monitoring real-time change of in-situ stress is of great significance. Piezomagnetic in-situ stress monitoring has good and longtime applications in large engineering constructions and geoscience study fields in China. In this paper, the new piezomagnetic in-situ stress monitoring system is introduced and it not only has overall improvements in measuring cell＇s structure and property, stressing and orienting way, but also enhances integration and intelligence of control and data transmission system, in general, which greatly promotes installing efficiency of measuring probe and quality of monitoring data. This paper also discusses the responses of new piezomagnetic system in large earthquake events of in-situ stress monitoring station at Qiaoqi of Baoxing and Wenxian of Gansu. The monitoring data reflect adjustments and changes of tectonic stress field at the southwestern segment of and the northern area near the Longmenshan fault zone, which shows that the new system has a good performance and application prospect in the geoscience field. Data of the Qiaoqi stress-monitoring station manifest that the Lushan Earthquake did not release stress of the southwestern segment of the Longmenshan fault zone adequately and there still probably exists seismic risk in this region in the future. Combined with absolute in-situ stress measurement, carrying out long-term in-situ stress monitoring in typical tectonic position of important regions is of great importance for researchers to assess and study regional crust stability.