【作者】 黎敦朋；

【导师】 胡健民； 赵越；

【作者基本信息】 中国地质科学院 ， 构造地质学， 2008， 博士

【摘要】 青藏高原的构造变形及其产生的隆升是当前国际地学界研究的热点与前缘。～65—45Ma以来,印度地体与欧亚大陆的碰撞产生的构造变形是驱动青藏高原崛起的主要动力,高原周缘构造变形带是高原形成演化的重要的构造地貌单元,也是探讨青藏高原隆升的关键区域。青藏高原西北缘地区是高原面最高、地形变化最显著和靠近西构造结的区域,也是新生代构造变形最强烈的地区之一。然而,目前对造成高原隆升的构造变形研究尚待深入,在实际资料上尚需进一步丰富。本论文以青藏高原西北缘西段的西昆仑山及其毗邻盆地的新构造变形为主线,结合沉积响应、岩浆活动、岩石剥露等研究,总结了青藏高原西北缘晚新生代构造变形的演化序列与西域砾岩的成因,分析了动力来源与变形机制,探讨了青藏高原隆升的时代、幅度和方式。研究取得的主要认识如下:青藏高原西北缘的冲断变形带在中新世晚期—早更新世由南南西向北北东方向呈幕式逆冲,高原边缘的逆冲断层具有后展式扩展特征,而盆地边缘的逆冲断层显示为前展式扩展;盆地内部的冲断褶皱变形由造山带向盆地褶皱幅度减弱,多数为与隐伏逆冲断层活动有关的断展褶皱,并形成相关的生长地层。新生代以来最强烈的褶皱冲断变形发生在上新世—早更新世,～1.1—0.7 Ma的昆黄运动最终使中更新世以前地层全面褶皱,并形成区域性的角度不整合。与造山带毗邻的盆地沉积反映了沉积盆地对造山带构造变形的响应。塔西南坳陷新生代沉积可以划分为古新世—早渐新世海相充填序列、晚渐新世—中新世河流—三角洲充填序列、上新世—早更新世山麓堆积3个充填序列,碎屑岩成分统计分析表明青藏高原强烈的剥蚀去顶作用发生于上新世—早更新世,依据沉积相的变化、不整合与楔顶沉积的发育、泥石流堆积、古水流体系的重大转折和生长地层等标定的逆冲断层强烈活动的时代为上新世早期—早更新世。岩浆作用是构造运动的产物,青藏高原西北缘在中新世以前岩浆活动零星,从10—8Ma开始岩浆活动增加,笔者在泉水沟北发现了锆石SHRIMPU-Pb年龄为10.1±0.4 Ma、9.7±0.2 Ma、9.1±0.3 Ma的中新世晚期的3个小型花岗岩岩株,与根据东昆仑断裂走滑速率估算的走滑运动时代一致,地球化学研究表明其为壳幔混合花岗岩,构造就位于走滑拉张区域;此外,在甜水海北新发现了全岩⁴⁰Ar—³⁹Ar年龄为8.3±0.3 Ma的粗面质火山岩。青藏高原西北缘自10—8Ma以来的火山作用逐渐增强,地球化学分析揭示其来源于壳幔过渡带,空间分布受走滑断裂的拉分盆地构造控制,是印亚碰撞壳幔作用的结果。磷灰石裂变径迹（AFT）记录了岩石在地壳最上部约3km的剥露时代,磷灰石裂变径迹的热历史模拟是了解岩石剥露历史的有效手段之一。通过对海拔4700—5600m的高原面上花岗岩的磷灰石裂变径迹分析和热历史模拟,获得了25～17Ma和3～2Ma以来的2阶段快速冷却的热演化历史;对西昆仑山前地形变化最大的陡坡带的逆冲断裂带中的花岗岩的磷灰石裂变径迹分析,主要裂变径迹年龄介于2.9±0.5—0.9±0.3Ma,不同逆冲岩片的磷灰石裂变径迹年龄具有“上新下老”的非正常分布现象,显示后展式的逆冲断层运动控制了陡坡带的岩石冷却剥露,同时也表明高原边缘逆冲断层系约3Ma以来发生了向北的强烈逆冲运动;裂变径迹热历史模拟显示～5Ma以来陡坡带的剥蚀厚度达5—7km,是高原内部剥蚀量的4—8倍,陡坡带快速剥蚀,大量近源粗碎屑在山麓带高速堆积,可能是西域砾岩形成的主要原因,即西域砾岩属构造成因。高原地貌的演化主要受控于构造变形,与西昆仑造山带毗邻的塔西南盆地区域古水流方向在中新世—上新世之交发生偏转,暗示现今青藏高原北缘的构造地貌和水系格局在上新世以前并不存在,是从早上新世阿图什组沉积时才开始逐渐演化形成的:而垂直造山带的山前水系的形成,暗示昆仑山的快速抬升隆起。从在上新世早期古水流方向发生的重大转折,早更新世中晚期山前水系的发育,暗示西构造结从上新世开始不断向北楔入。综合上述资料,结合区域研究成果笔者提出:青藏高原西北缘的隆升是一个与构造变形相适应的多阶段的复杂的抬升过程,经历了～25—17Ma的初期隆升、～10—8Ma的早期小幅隆升、～5.3—3.6Ma的中期快速隆升、～3.6—0.7Ma的晚期强烈隆升以及0.7Ma以来的再次隆升,才最终铸就了青藏高原现今构造地貌格局;而青藏高原主期隆升时代应在上新世—早更新世,主要的隆升形式是通过边界断裂向周缘盆地的逆冲作用完成的,上新世中晚期以来,青藏高原的净隆升量约达2000—3000m。本文的工作以构造地质学多方面的证据支持中国学者长期以来认为青藏高原的隆升是上新世—早更新世的事件。通过构造形迹分析、断层擦痕反演的构造应力场及现代GPS测量结果分析,认为青藏高原西北缘晚新生代构造变形的主要动力来源于印度板块向北北东的挤压作用和塔里木盆地向南南西的阻挡,与帕米尔西构造结向北的楔入作用有关,并显示出上新世早期和早更新世中晚期两次强烈的楔入作用。更多还原

【Abstract】 Tectonic deformation and tectonic uplift of Tibet plateau is the hot topic and research front of present international geoscience community. Since～65—45Ma, neotectonic deformation is the main impetus of uplifting of the plateau, the steep slope zone on the circumference is the important geomorphic unit for studying evolution of Tibetan plateau, it is also one of the key areas for inquiring into the uplifting of the Tibetan plateau. Northwestern margin of Tibet plateau is one of the areas which are the highest, the narrowest and nearer away from west syntaxes, it is also the area where the neotectonic deformation is strongest. However, present-day, tectonic deformation of drived uplift of Tibet plateau are poorly constrained.The thesis summarized the spatial-temporal evolution characteristics, deformation sequence, dynamic source and deformation mechanism of neotectonic movement at northwestern margin of Tibetan plateau, then inquired into the time, amplitude and the model of uplifting of the plateau and discussed the formation and evolution process of steep slope zone and genesis of Xiyu conglomerate through the studying of geometrical and kinematical characteristics of large fault system, sedimentation and tectonic deformation of depression basin, late Cenozoic magmatism, the formation and evolution of relief in the steep slope zone and isotopic geochronology in west Kunlun and its north margin at western part of northwestern margin of the Tibetan plateau. There are our main cognitions as follows:Thrusting deformation belt of northwestern in the Tibetan plateau thrusts movement from SSW to NNE for several in late Miocene-eraly Pleistocene. The thrusts of northwestern margin in the Tibetan plateau show backward propagating mode, while the fold-thrust belts of margin in the basin show forward propagating mode. The deformation’s amplitudes of fold-thrust belt in depression basin decrease from orogene to basin, most are fault-propagation fold related to buried thrust and form growth fold or growth strata. The most important deformation has taken place in the sedimentary period in middle Pliocene to early Pleistocene （～3.6-1.1Ma）, regional fold deformation also occur in this period, and forming regional angular unconformity.Filled sequence of the sedimentary basin can reflect tectonic evolution of the basin dominate sedimentation under regional tectonic setting.Kashi group in depression basin of the southwest tarim is sediments of shallow sea to lagoon facies, Wuqia group is sediments of delta to plain fluvial facies, Atushi formation is sediments of fluvial to fan margin facies, while Xiyu conglomerate is upper fan to middle fan alluvial-diluvial deposition. Kashi group is shallow sea facies sediments in stable tectonic setting; Wuqia group is fine grained clastic sediments in relative tectonic quiescent; from Atushi formation fine conglomerate begins to appear, and its component maturity begins to lower, which imply that source area is much nearer and the landform contrast is sharper, Pakabulake formation is parallel unconformable contact with Atushi formation above in the margin of basin, which display that neotectonic movement reinforced and regional uplifting have occurred there; Xiyu conglomerate is almost coarse conglomerate and its component maturity is low, containing massive debris-flow deposit, paleocurrent varies sharply from SE and SEE in the sedimentary period of Wuqia group to NW and NNW in the sedimentary period of Atushi formation, which imply that the landform contrast has further increased, sedimentary rate increase rapidly, fault on the mountain front has activate intensely and the Kunlun mountains fast raised.Magmatic activity is associate matter of tectonic monement. Magmatic activity at northwestern margin of Tibet plateau is rare before Miocene, Magmatic activity begin to increase form10-8Ma. We found three late Miocene small stocks at north Quanshuigou, their zircon SHRIMP U-Pb ages are respectively 10.1±0.4 Ma, 9.7±0.2Ma ,9.1±0.3 Ma, while these ages are agreement of age of east Kunlun strike-slip fault by strike-slip rates estimating.Geochemical character indicates EM II granites, and intruded in pull-apart area of strike-slip fault.Moreover, we found Qitaidaban late Miocene trachyte volcanic at north Tianshuihai, the whole rock ⁴⁰Ar-³⁹Ar age is 8.3±0.3 Ma. Volcanic activity significantly enhanced since 10-8Ma, geochemical analysis is revealed that their origin is admixture of mantle and crust, spatial distribution of magma are contral of pull-apart basin of strike-slip fault, they are result of India-Asia collision functionary of matle and crust.The AFT ages record the cooling and denudation history of rock in the uppermost crust about 3km, and AFT modeling is a effective means what understand rocks erosion’s history.We acquired the AFT age of 24.8～14.0Ma by analyzing the AFT of granite on the surface of plateau in north Quanshuigou, which show that this granite undergo two rapid cooling periods which are 25～17Ma and 5～2Ma through thermal history simulation. The age concentrated in 5～2 Ma by analyzing the AFT of granite in Xinjiang-Tibetan highway from Kudi to Mazha, reflecting rapid cooling since Pliocene. By analyzing the AFT of granite of Yuetangnengdailiya in steep slope zone of west Kunlun Mountains, show that the age is very new and their main interval is 2.9±0.5～0.9±0.3Ma, different rocks have the characteristic of the upper the younger, the lower the older, presenting backward propagation thrust nappe structure; also reflecting rapid cooling since middle Pliocene.Geomorphic of Tibetan Plateau is controlled of tectonic deformation.The development of drainage system is obviously controlled and affected by neotectonics. Drainage system in west Kunlun mountains and its margin can fall into two classes: longitudinal drainage to the south of main peak of West Kunlun mountains, and transverse drainage to the north according to the relationship between drainage and tectonic. Longitudinal drainage generally extend in EW direction approximately, the rivers are long, the valley is wide and the gradient is small, is a ancient geomorphic unity and the age is not later than 3.82Ma. Transverse drainage generally extend in SN direction approximately, the rivers are short and the gradient is large, upper part of the valley is wide while the lower is narrow, it generally develops 4-6 terraces, indicating it’s a young geomorphic unity which formed after 1.1±0.1 Ma, showing intense neotectonic movement.Synthesize the research of tectonic deformation , such as a series of fold systems and regional large fault zone, integrating with sedimentation, regional magmatic activity, the AFT age, and evolution of drainage landform, we bring forth that: tectonic upliftt at northwestern margin of Tibet plateau is a multistage,complex uplifting process that is a agreement of tectonic deformation, underwent initial uplift at 25-17Ma, eraly little uplift of at 10-8Ma, middle speed uplift at～5.3—3.6Ma, late aggravated uplift at～3.6—0.7Ma, and slower uplift since0.7Ma, then the plateau uplift intensely, reaching its highest altitude and was brought into the cryosphere.The most important uplift took place at middle Pliocene-middle early Pleistocene （～3.6-0.7Ma）, main uplift form is thrust movement by from boundary thrust for peripheral basin, ground uplift amount is about 2000～3000m in northwestern margin of Tibetan plateau since middle Pliocene-middle early PleistoceneAuthor think that neotectonic dynamic source at northwestern margin of Tibetan plateau comes from the NNE direction compression of Indian plate and the SSE direction hold up of Tarim basin and is associated with the northward wedging effect of west Pamir syntaxis through the analysis of tectonic trace ,modern tectonic stress field and present-day GPS data, imply that it is related of west structural knot. Besides, it indicated stronger wedge in early Pliocene and middle-late Pleistocene.更多还原