Instrumental recording of slow deformation waves in the South Baikal geodynamic study site

Instrumental monitoring of rock deformation in the South Baikal geodynamic study site showed that they are realized in the form of long-term variations in different directions superimposed with short-time anomalous spikes. Analysis of the measured spatiotemporal monitoring series showed that anomalous deformations are caused by the propagation of deformation waves through the mountainous rocks. We estimated their lengths, periods, directions, and velocity of spatial migration. We found that propagation of deformation waves is accompanied by an increase in the temperature of rocks at each point of monitoring.

     

蒙古国Oyu Tolgoi外围碱长花岗岩LA-ICP-MS锆石U-Pb定年及其地质意义

位于蒙古国Oyu Tolgoi超大型斑岩型铜-金矿床南20km的碱长花岗岩区,构造上处于西伯利亚板块南缘近东西向和北东向深大断裂所挟持的戈壁-天山古生代岛弧带内。利用LA-ICP-MS U-Pb同位素测年法对研究区碱长花岗岩中的锆石进行高精度的年代学测试,获得~(206)Pb/~(238)U年龄加权平均值为286.00±0.91Ma,为早二叠世。研究区具有多期次成岩、成矿特征,本次定年不仅为该区多期次岩浆活动提供了直接的年龄证据,也为该区找矿指明了方向。     

蒙古中南部地区地壳各向异性及其动力学意义

利用蒙古中南部地区布设的69套宽频带数字地震仪2011年8月—2013年7月记录的远震事件,使用时间域反褶积方法提取接收函数,并挑选高质量Pms震相,通过改进的剪切波分裂方法对研究区地壳各向异性参数进行了研究,最终获取了1473对各向异性参数.经过统计分析,有48个台站可以归纳出两个方向的各向异性,11台站得到单个方向的各向异性,而剩余10个台站各向异性方向比较发散.结果显示,各向异性在蒙古中南部地壳中呈不均匀分布,有54个台站得到了NE-SW向各向异性,快波偏振方向平均值为N58°E±16°,与最大水平主应力σHmax方向和区域内主要断层走向一致,说明这部分地壳各向异性的主要成因存在于上地壳,可能与流体填充的微裂隙有关.而NW-SE向各向异性在53个台站被观测到,各向异性方向变化范围平均N132°E±16°,与研究区大部分SKS分裂快波方向具有较好的一致性,说明下地壳成岩矿物晶体定向排列是各向异性的主要成因.研究区地壳各向异性的分层特征总体上支持岩石圈受到NE-SW向挤压的动力学模型.     

中蒙边界中西段地层划分与对比

中国与蒙古交界地区,早前寒武系—新生界分布广泛,地层划分系统差别较大。以区域岩石地层组合及构造演化特征为背景研究认为,从新疆阿尔泰段至蒙古戈壁-天山段,地层具有连续性,可统一划分对比;并以额尔齐斯-布尔根断裂、喀拉麦里断裂、Borzon断裂及东蒙古-迭布斯格断裂为界,由西向东将中蒙边界中西段地层划分为阿尔泰地层分区、准噶尔-戈壁阿尔泰地层分区和北山-戈壁天山地层分区,并对区内地层单元进行了统一划分与对比。     

First results of GPS measurements on the Ulaanbaatar geodynamic testing area

First results of the analysis of GPS measurement data obtained from 18 sites of two local networks in the vicinity of Ulaanbaatar (Mongolia) for the period 2010–2015 have been presented. Horizontal velocity vectors are consistent with each other in the ITRF2014 system and with the velocities of the IGS permanent station ULAB. The sites move in the E–SE direction at a rate of 25–30 mm/yr, with the displacement azimuth averaging 105°. With respect to Eurasia, the vectors for most of the sites are slighly turned to the south, but they are still of SE orientation with the azimuth range of 130°–150° and magnitude values of 2–4 mm/yr. Relative horizontal velocities tend to decrease towards southeast that determines a zonal distribution of different type of relative strain patterns. The western part of the Ulaanbaatar network is characterized by the W–E oriented extension with the elongation rate ε₁ = 12–16 × 10^–8 yr^–1. The shortening NW–SE trending strain with calculated value ε₂ = 22.4 × 10^–8 yr^–1 characterizes the network’s eastern part. The highest values of the maximum shear strains (ε_max = 10–14 × 10^–8 yr^–1) form an extended area in the center of the testing ground, which is elongated in the northeastern direction, conformably with the strike of the major geologic structures. The strain distribution pattern of the Emeelt network located within the eponymous seismogenic structures is characterized by the crustal elongation (5 × 10^–6 yr^–1) trending SE–NW and less pronounced shortening in the SW–SE directions.The axial part of the fault crossing the network in the NW direction exhibits maximum deformations.     

蒙古中南部地区噪声层析成像

依托中蒙国际合作项目"远东地区地磁场、重力场及深部构造观测与模型研究",我们首次获取了蒙古中南部地区密集的地震台阵观测资料.本研究收集了69套宽频带台站2011年8月至2013年7月间的垂直向连续记录,利用噪声互相关方法计算了台站间的经验格林函数,并采用基于连续小波变换的频时分析方法,提取了1478条周期6~30s的瑞雷波的相速度频散曲线.利用DitmarYanovskaya方法,我们构建了研究区6~30s瑞雷波的高分辨率(0.5°×0.5°)相速度分布图.结果表明,蒙古中南部地区的地壳上地幔速度结构存在横向非均匀性,但并不显著(相对变化~±2%).短周期(如6s)的相速度分布与地表地质构造具有明显的相关性,具体来说,北部山盆显示为高速,南部盆地、戈壁滩均显示为低速;随着周期的增大(如15s,20s),地形的控制作用相对减弱.较长周期(30s)的相速度分布图上,南部的高速区进一步扩大,与南部地壳厚度较薄有关.蒙古主构造线南北两侧相速度分布有明显差异,暗示它不仅是地表地形和构造的分界线,而且还是地壳结构的分界线.从6~30s中戈壁一直显示为低速,可能与该区新生代火山活动有关;研究区北部杭爱山—肯特盆地一直显示为相对的高速,与该区具有较老、稳定的地层有关.