蒙古地区壳幔结构研究

发布时间：2018-01-23 02:21

本文关键词： 蒙古中亚造山带接收函数 Lg波衰减 Pn速度成像　出处：《中国地震局地球物理研究所》2016年博士论文　论文类型：学位论文

【摘要】：中亚造山带是全球显生宙陆壳增生与改造最显著的大陆造山带,受中、新生代构造活动的影响,该区经历了强烈的挤压隆升造山、拉张凹陷成盆及拉张造成的岩浆-火山改造。蒙古位于中亚造山带核心地区,是研究大陆动力学的理想实验室之一。通过该区开展深部结构研究,将有助于了解岩浆底侵、地幔热物质上涌、或地幔柱活动等在该区复杂构造演化过程中的作用。本文基于在蒙古中南部地区布设地震台阵所获得的波形数据,通过接收函数、地震波衰减和Pn速度层析成像等研究手段,获取了该区的壳幔结构,弥补了该区壳幔结构研究的空白,增进了对该区构造演化过程的认识。利用69个流动宽频带地震仪记录的远震波形数据,开展接收函数研究,结果表明,蒙古中南部地区地壳厚度介于38 km～46 km,平均值为43 km。总体上,地壳厚度由西北向东南逐渐减薄。肯特山西部地区地壳厚度较厚,而地壳较薄的地区位于宗巴彦断层与中蒙边境之间的戈壁地区。在蒙古主构造线附近Moho面深度呈现近5 km的变化。布格重力异常与地壳厚度有着很好的相关性。台站下方的地壳平均波速比介于1.68～1.83之间,平均值为1.74,低于全球大陆的平均值1.78。北部山区地壳平均波速比值较低,高的波速比值位于中戈壁的火山区域和南戈壁的中新生代裂谷盆地地区。低的波速比值出现在地壳较厚且富含石英质的肯特山地区,可能是与蒙古-鄂霍茨克海闭合所导致的硅铝质岩浆的侵入有关。进一步的重力模拟研究显示中戈壁地区下地壳的密度较高,约为3000 kg/m3,结合中戈壁地区的高波速比特征以及地质资料,推测中戈壁地区的下地壳应该存在铁镁质麻粒岩,可能与该区新生代火山活动导致地壳部分熔融的残留有关。通过人工挑选了228个近震记录采用反双台法对蒙古中南部地区进行了Lg波Qo值成像研究。反双台法能有效地去除场地效应、仪器响应以及震源函数的影响,从而获得较精确的Q值结果。为了研究该区地壳介质衰减的横向变化,总共挑选了17,015个反双台法射线对,首次获得了该区高精度的Lg波Q0值分布图。Lg波Qo值结果显示以蒙古-鄂霍茨克海缝合线为界,北部地区Q0值较高,南部地区Q0值较低。Lg波Q0值分布与该区的地表构造、壳内横波速度变化以及新生代构造活动性有很好的对应。北部山区地壳活动相对较弱,表现为低衰减,而火山出露集中的中戈壁地区以及新生代断层发育的南戈壁地区则表现为高衰减。该区地壳介质对地震波的高衰减可能与该区的火山活动、新生代断层活动以及壳内的低速有关。利用中国地震台网、国际地震中心(ISC)以及人工挑选的研究区流动台阵所记录的Pn震相走时数据,开展Pn速度层析成像,获得了蒙古及邻区高分辨率的Pn速度成像结果。与前人研究相对比,本研究给出的蒙古中东部地区Pn成像结果具有更高的分辨率。蒙古及邻区的Pn波速度具有显著的横向非均一性,并与地质构造及构造活动性有很好的相关性。该区平均速度约为8.1 km/s,与全球平均值(8.09 km/s)相近,略高于中国地区的平均值(8.05 km/s)。构造活动相对较弱的蒙古东部、准葛尔盆地、塔里木盆地等地区的Pn表现为显著的高速特征,而萨彦山脉、贝加尔裂谷以及杭爱高原等地区则表现为显著的低速结构,可能是火山活动、软流圈物质上涌或地幔柱活动的反映。肯特山地区也存在Pn波低速异常,但其较低的波速比和较高的Lg波Q值,显示其地壳活动性较弱,暗示该地区并没有受到上地幔热物质的影响。
[Abstract]:The Central Asian orogenic belt is the Phanerozoic continental crust growth and transformation of the most significant continental orogenic belt, in effect, the Cenozoic tectonic activities, the region has undergone strong compressional uplifting orogenic extensional basin, depression and tension caused by magma volcano transformation. Mongolia is located in the Central Asian orogenic belt is one of the core areas. The ideal laboratory for continental dynamics study. Through the area to carry out deep structure research, will be helpful to understand the underplating of magma, mantle upwelling, or mantle plume activities in the area of complex structure in the evolution process. In this paper, the waveform data in the central and southern regions of Mongolia seismic array layout based on the obtained. Through receiver function, seismic wave attenuation and Pn velocity tomography and other research methods, to obtain the crust mantle structure in the region, make up the blank of the crust mantle structure in the region, understanding the evolution process of the structure by 69. Mobile broadband seismographs recorded teleseismic waveform data, carry out receiver function research, the results show that the central and southern regions of Mongolia, the crustal thickness ranged from 38 km to 46 km, the average value of 43 km. on the whole, the thickness of the crust from the northwest to the southeast gradually thinning. The thickness of the crust in Shanxi region of Kent is thick, while the crust is the thin area located between the cases of Bayan fault and the Mongolian border region of Gobi. Of nearly 5 km in Mongolia near the main tectonic line Moho depth. The Bouguer gravity anomaly has good correlation with the thickness of the crust. The average crustal velocity beneath the stations than between 1.68 to 1.83, the average value is 1.74 lower than that. The average value of the global continental crust 1.78. in northern area of average velocity ratio is low, the high velocity ratio is located in the Gobi volcano area and southern Gobi in the Cenozoic rift basin. The low velocity ratio in the crust is thick and Rich in quartz Kent mountain area, may be related to invasion of the Mongolia Okhotsk Sea closure caused by Salic magma. Further gravity simulation study showed higher density in the Gobi area of the lower crust is about 3000 kg/m3, with high speed bit Gobi area sign and geological data, the lower crust that in Gobi area there should be mafic granulites, may be related to the Cenozoic volcano activity in the residues of partial melting of the crust. The artificial selected 228 earthquake records by the two station method of South Central Mongolia area for imaging of Lg wave Qo value. The anti taiwan method can effectively remove the double site effect and effect of source instrument response function, so as to obtain more accurate results of Q value. In order to study the lateral variation of crustal attenuation, a total of 17015 selected anti rays on the two station method, for the first time by the A high precision Lg the value distribution of the.Lg wave Q0 wave Qo results show that taking the Mongolia Okhotsk suture line as the boundary, North South high Q0 value, low Q0 value of.Lg wave Q0 value distribution and surface structure of the region, the shell shear wave velocity change and the CENOZOIC TECTONICS the activities of a good correspondence. In northern area of crustal activity is relatively weak, low attenuation, and the volcano exposed in concentrated region of Gobi and the Cenozoic faults in the southern Gobi area shows high attenuation. The crust medium on seismic wave attenuation and the area of high volcano activity, Cenozoic the fault activity and the shell of the low speed. The use of China seismic network, the International Seismological Centre (ISC) and time phase flow research area artificial selection Pn seismic array in the recorded data, carry out Pn velocity tomography, obtained in Mongolia and adjacent areas of high resolution Pn speed Imaging results. Compared with previous studies, the Mongolia Middle East Pn imaging results of this study are given with higher resolution. The Pn wave velocity in Mongolia and its adjacent areas with significant lateral heterogeneity, and the geological structure and tectonic activity have good correlation. The average speed of about 8.1 km/s, and the global average (8.09 km/s) similar, slightly higher than the average value of China area (8.05 km/s). The tectonic activity is relatively weak in eastern Mongolia, Junggar basin, Pn area of the Tarim basin for the high speed characteristic, and the Sayan mountains, Baikal rift and hangay plateau region for low velocity structure may be significant, volcano activities reflect the upwelling of the asthenosphere or mantle plume. Kent mountain area also has the Pn wave velocity anomalies, but Lg wave Q of the low velocity ratio and high value, show the crustal activity is It is weak, suggesting that the area is not affected by the hot matter in the upper mantle.

【学位授予单位】：中国地震局地球物理研究所
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P315.2

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