【作者】 陈立春；

【导师】 冉勇康；

【作者基本信息】 中国地震局地质研究所 ， 构造地质学， 2011， 博士

【摘要】 乌鲁木齐一带是北天山山前构造系东西向发生转换的地区。区内构造地表活动变形特征复杂,既有正向又有反向、既有逆断又有正断和走滑。论文工作试图尽量降低研究中的不确定性,以求对这些构造的晚第四纪活动性、构造之间的关系及其变形机制有所新的认知。开展的主要研究工作和采用的研究方法是:(1)研究区地貌时间标尺的建立针对测年问题,考虑到研究区第四纪地貌面非常发育,论文工作对这些地貌面展开了野外调查和3S技术数字地貌分析,在此基础上进行了区域性地貌面的划分与定年及其所蕴含的构造-气候-地表过程耦合关系分析,建立了研究区的地貌时间标尺。(2)几个主要地点的活动构造与古地震研究为了尽可能降低研究中的不确定性,针对研究区地貌和构造活动特点,论文工作开展了研究区1/5万活动断裂地貌单元填图技术和逆冲推覆型陡坎古地震识别技术的研究,之后,运用这些技术以及所建立的地貌时间标尺,对研究区几个代表性地点的活动构造与古地震进行了剖析。(3)研究区主要活动构造之间的关系分析本着构造系统、构造过程的思想,对研究区主要活动构造之间的空间与时序关系进行了尝试性的分析,并对北天山山前逆冲推覆构造系在乌鲁木齐一带的构造样式转换关系及其转换机制进行了初步探讨。(4)转换区主要构造晚第四纪活动性分析基于各研究点的活动构造与古地震研究结果以及研究区主要活动构造之间的时空关系分析结果,从构造系统与构造过程的角度,对转换区构造系的晚第四纪活动性进行了分析,在此基础上,对转换区的地震构造单元划分与未来地震危险性进行了初步探讨。取得的主要认识和结论如下:(1)研究区厘定的5级区域性地貌面为研究区的地貌时间标尺。区域性地貌面Ⅴ堆积时代约730～550kaB.P.,550kaB.P.进入间冰期后至约200kaB.P.之间,地貌体间歇性抬升,并演化为多级高基座阶地。区域性地貌面Ⅳ堆积时代约200～130kaB.P.,130kaB.P.进入末次间冰期后抬升成面,表层较广泛发育一稳定的古土壤层,直至74kaB.P.左右;区域性地貌面Ⅲ为研究区特有的“黄土帽子”面,第一次黄土过程约74～59kaB.P.;进入约59～55kaB.P.,黄土表层局部不完全钙壤化;第二次黄土过程约55～42kaB.P.。区域性地貌面Ⅱ约42～23kaB.P.,早期区域性地貌面Ⅳ和Ⅲ开始较大面积侵蚀下切,王家沟等二级河流形成,这些二级河流的侵蚀河道以及出山口的冲洪积扇形堆积即形成区域性地貌面Ⅱ的雏形;23～15ka间,区域性地貌面Ⅱ可能局部侧蚀加积;15～12ka,区域性地貌面Ⅱ下切成广泛的阶地面或戈壁平原,表层开始发育不完全钙壤,表层黄土也土壤化。区域性地貌面Ⅰ区域性地貌面Ⅱ大面积暴露成面后,经新仙女木事件,进入全新世,12～8.5ka间,河流以侧蚀堆积为主,8.5～4ka是全新世气候最适宜期,河流下切,形成现代戈壁以下的最广泛一级河流阶地。(2)北天山山前逆冲推覆构造系东西向转换是通过乌鲁木齐转换区构造系来实现的,转换区构造系以北倾的单斜构造为基本特征,第四纪活动表现为既有正向又有反向、既有逆断又有正断和走滑变形,并且,晚更新世以来部分反向断裂可能已发生负反转。其变形机制可解释为近南北向挤压沿先存构造面产生的变形分解以及由此产生的“斜交双向挤压挟持”模式。(3)转换区构造系地表活动构造可归为柴窝堡盆地南缘断裂与雅玛里克断裂、西山断裂组(含西山、四道岔NW向、王家沟、九家湾断裂组)-碗窑沟断裂、八钢-石化断裂、甘泉堡断裂几个序次以及板房沟断裂。其中,西山断裂组-碗窑沟断裂和甘泉堡断裂是构造系中最主要的全新世活动断裂,前者晚更新世晚期以来共发生过4次事件,依次为:事件Ⅰ,约(59.7～45.5)kaB.P.,沿九家湾断裂组地表正断变形;事件Ⅱ,约(38.8～37.9)kaB.P.,沿王家沟断裂组北侧3条断裂逆冲-褶皱变形;事件Ⅲ,约(27.5～23.2)kaB.P.,沿碗窑沟断裂逆冲-褶皱变形;事件Ⅳ,约(12～10.5)kaB.P,沿王家沟断裂组北侧3条断裂逆冲-褶皱变形、九家湾断裂组正断变形。大震的平均重复间隔约13ka,未来存在发生地表破裂的危险。甘泉堡断裂最新两次事件时间限定为:事件Ⅰ,约(51.1～50.3)kaB.P.以后、26.9kaB.P.之前,但更接近下限年龄,这次事件可能就是碗窑沟断裂的事件Ⅲ;事件Ⅱ,(14～11)kaB.P.,可能为来自其东侧阜康-吉木萨尔断裂地表事件的扰动。此外,论文也给出了各研究点翔实的断裂晚第四纪活动性活动参数以及关于地震构造单元划分与未来地震危险性的两点启示。更多还原

【Abstract】 The North Tienshan piedmont tectonics has obvious E-W variations near Urumqi.The characteristics of the tectonic deformation on the surface are complicated here.Normal faults, reverse faults, and strike-slip faults are co-existing. This researchattempts to minimize the uncertainties in understanding of the late Quaternaryactivities of the tectonics, the relationship among the structures, and deformationmechanism of this area.The main work and approaches are follows:(1) Construction of the time scale of the geomorphic evolution in the study areaThe Quaternary geomorphic surfaces developed well in the study area.Topographic analysis by 3S techniques and field surveys were performed toinvestigate the geomorphic surface. Based on that, regional geomorphic surfaces weredivided and dated. Coupling among the tectonics, climate, and earth surface processwas analyzed. Then the time scales of the geomorphic evolution in the study areawere established.(2) Research on active faults and paleoearthquakes at several typical sitesIn order to minimize the uncertainties of the study, a landform-oriented mappingtechnique at 1:50,000 scale for investigating the activity of faults and a fewapproaches for identifying paleo-events recorded by the pressure ridge scarps weredeveloped. These approaches and time scale of the geomorphic evolution were usedto study the active faults and paleoearthquakes at several typical sites.(3) Analysis of relationship among the major active structuresIn the view of the tectonic system and tectonic process, spatial and temporalrelationships of the main active tectonics are analyzed. Then the mechanism oftransform of the tectonic styles of the north Tienshan piedmont thrus system arediscussed.(4) study of the late Quaternary behavior of the main structures in the Urmuqitransform regionBased on the fault activities and paleoearthquake research results at eachsurveyed sites and the temporal-spatial relationship among main active structures inthe study area, late Quaternary behaviors of the active tectonic system in the Urmuqi transform region were analyzed. Besides, two suggestions were given to the divisionof the seismic tectonic units and to prediction of the future seismic risk.The main results are as follows:(1) Five regional geomorphic surfaces are determined to define time scales of thegeomorphic evolution.Regional geomorphic surface V was deposited at about 730~550ka B.P.Intermittent uplifts occurred between 550ka B.P. when an interglacial period started,and 200ka B.P. during which multiple high pedestal-terraces were developed.Regional geomorphic surface IV was deposited at about 200~130ka B.P. It’suplifted during the last interglacial period, which is from 130ka B.P. to 74ka B.P. Anancient soil layer is widespread on the surface IV.Regional geomorphic surface III is covered with loess. The first period of theloess deposition is about 74~59ka B.P.. Part of the loess was calcified on the surfaceduring 59 ~ 55ka B.P. The second period of the loess deposition is 55~ 42ka B.P.Regional geomorphic surface II started to form at about 42~23ka B.P., when theearly regional geomorphic surfaces III and IV were cut and eroded. Tributaries, suchas Wangjiagou, formed. The eroded channels and alluvial fans of the tributaries builtthe embryonic form of regional geomorphic surfaces II. During 23~15ka, the regionalgeomorphic surfaces II may aggraded partly by lateral erosion. At 15~12ka B.P.,regional geomorphic surfaces II became widespread terraces or the Gobi plain. Itssurface began to develop incomplete calcium soil. The surface loess turned into soil.Regional geomorphic surfaces I was formed after the regional geomorphicsurfaces II was exposed in a large range. After the young Dryas event, it went into theHolocene. During 12~8.5 ka B.P., the accumulation of the main rivers was dominatedby lateral erosion. From 8.5~4ka B.P., it was the most suitable climate in Holocene forriver incision. A widespread river terrace formed under the present Gobi plain.(2) The E-W transform of the North Tienshan piedmont thrust system isaccommodated by the Urumqi transform zone, where thrusts are domainant with backthrusts, sinistral strike-slip faults, and normal faults coexisting. A few back faults havepossibly exprienced inversion since the late Pleisstocene. The deformation mechanismof the tectonic system in the Urumqi transform region can be explained using themodel of two-direction oblique compression.(3) The surface active tectonics in the Urmuqi transform region can be classifiedinto several tectonic series as: the first, the southern marginal fault of the Chaiwopu basin and the Yamalike fault; the second, the Xishan fault group (including the Xishan,Sidaocha NW, Wangjiagou, Jiujiawang fault groups) and the Wanyaogou fault; thethird, Bagang-Shihua fault; and the fourth, the Ganquanpu fault. Among them, theXishan fault group-Wanyaogou fault and Ganquanpu fault are the main active faultsin the Holocene. The former have had occurred 4 paleo- events since late Pleistocene:Event I (ca.59.7~45.5 ka B.P.), normal faulting along the Jiujiawang fault group;Event II (ca.38.8~37.9 ka B.P.), thrusting and folding along three faults north of theWangjiagou fault group; Event III (ca.27.5~23.2 ka B.P.), thrusting and folding alongthe Wangyaogou fault; and Event IV (ca.12 ~ 10.5 ka B.P.), thrusting and foldingalong three faults north of the Wangjiagou fault group, normal faulting along theJiujiawang fault group. The average earthquake recurrence interval is about 13ka.Surface ruptures may occur in the future. The latest two events along the Ganquanpufault are as follows: Event I (after ca. 51.1 ~ 50.3ka B.P., before 26.9ka B.P., morelikely close to the later one), this event may correspond to the event III of theWanyaogou fault; Event II (ca. 14 ~ 11 ka B.P.), probably a surface disturbance eventcaused by the Bukang-Jimusaer fault in the east.In addition, this dissertation reports detailed parameters of late Quaternaryactivities at all of the surveyed sites along the faults, and gives two suggestions ondivision of the seismic tectonic units and prediction of the future seismic risk.更多还原