【作者】 陈波；

【导师】 陈超；

【作者基本信息】 中国地质大学 ， 地球探测与信息技术， 2013， 博士

【摘要】 地球岩石圈在地表和地下荷载作用下会进行均衡沉降或隆起,均衡响应的状态(局部均衡或区域均衡)和快慢,取决于岩石圈自身的热力学性质。利用这种均衡响应信息可以计算岩石圈有效弹性厚度(Te),其主要反映了岩石圈在长期(>105年)构造载荷作用下抵抗变形的能力,是研究大陆岩石圈大规模构造和岩石圈动力学的有力工具。研究岩石圈有效弹性厚度的空间变化,对于了解具有复杂地质构造和地壳形变的中国大陆岩石圈的力学特征和演化,进而对其动力学机制进行分析至关重要。中国大陆并非一个巨型前寒武纪克拉通为主体的单一大陆,而是由大量小型克拉通和夹持其间的造山带所组成的拼合大陆。大陆西南缘受到印度一澳大利亚板块快速向北运移的碰撞挤压,东部遭遇太平洋和菲律宾板块向欧亚大陆的俯冲,北部则受到西伯利亚板块的阻挡。考虑到如此复杂的结构和地球动力作用,必然造成中国大陆各主要陆块存在明显的相互作用。因此,非常有必要详细地研究整个中国大陆及邻区的岩石圈有效弹性厚度分布,有助于了解中国各陆块的岩石圈强度的变化,对研究华北克拉通破坏、青藏高原隆升以及整个中国大陆复杂的构造变形及其岩石圈动力学机制等具有非常重要的意义。本文采用基于地形和布格重力异常数据的多窗谱相关法和Fan小波谱相关法获得了完整且高分辨率的中国及邻区的岩石圈有效弹性厚度,并根据Te分布对中国大陆的大地构造和岩石圈动力学提出了新的认识。首先,通过模型实验,系统分析了多窗谱和Fan小波谱相关法的主要参数对反演结果的影响,并对比验证了两种谱方法反演Te的有效性。其次,基于实测地形和卫星重力场模型数据,获得了完整且高分辨率的中国及邻区岩石圈有效弹性厚度分布。反演结果表明：两种谱相关法获得的Te横向分布基本一致,都呈现出中国及邻区Te具有剧烈的空间横向变化；几个明显的高T。值主要分布在稳定的克拉通盆地；而低T。值主要分布于年轻的造山带地区,并且各构造单元内部的T。存在明显的不均一性。最后,利用获得的Te分布,结合地质、大地测量和地球物理等资料,得到了以下新认识：(1)对比中国大陆的Te横向变化和地震震中分布表明,岩石圈有效弹性厚度的大小和空间变化与地震分布存在密切的联系。Te高的地区一般对应构造相对稳定区,地震较少发生,说明了高强度的岩石圈具有抵抗变形和地震的能力。中国大陆板内地震主要集中在T。约为10-40km的区域或Te陡变带,表明了岩石圈强度弱的地区或岩石圈强度发生显著变化的陡变带,是岩石圈应力和能量最容易累积和释放的地区,往往是地震孕育的有利地带。(2)通过分析中国大陆及邻区的Te横向变化和构造单元热年龄、地表热流以及地幔横波速度分布表明,岩石圈热年龄和热结构的变化对中国大陆岩石圈有效弹性厚度的影响较大；高Te地区一般具有低的地表热流,而低Te的区域一般对应高的热流值：同时Te和地幔100km深度的横波速度呈正相关。但是,由于中国地区特殊的地质构造,加之岩石圈复杂的演化过程及其结构的各向异性,导致这些反映岩石圈性质和结构的参量与Te的关系也存在一定的离散性和不确定性。(3)对华北陆块Te空间变化分析表明,西陆块的鄂尔多斯盆地远远高出地壳平均厚度(约42km)的高Te值,说明了古老克拉通岩石圈的高强度主要反映了其具有强的上地幔岩石圈；相比稳定且高Te的西陆块,东陆块Te变化剧烈且明显偏小,表明华北东陆块高强度的太古宙岩石圈已经变弱,但是局部高Te值可能暗示了局部地区仍保留有较厚的克拉通岩石圈。(4)结合华南陆块Te分布和地幔成像结果表明,四川盆地可能不是一个均一的刚性克拉通,其盆地内部岩石圈存在明显的各向异性：扬子陆块的古老克拉通陆核可能存在于四川盆地中东部以及贵州北部、重庆武陵山和湖南雪峰山以西地区。华南陆块中东部大部分区域呈低Te值,结合地表构造特征和地幔热结构推断,俯冲到华南陆块之下的古大洋岩石圈引起的热地幔动力作用可能是显著降低华南陆块(特别是中东部)岩石圈的综合力学强度的主要原因。在受到四周多个板块汇聚的应力下,低强度的华南岩石圈更容易产生变形,从而在壳内形成现今宽广的褶皱带和广泛的岩浆活动。(5)青藏高原下地壳广泛分布的塑性地壳流、热上地幔和高热状态,可能是青藏高原中部、东部和东南部Te普遍低的主要影响因素。结合Te的分布表明,青藏高原的变形可能不仅局限在地体缝合线和走滑断裂带,低岩石圈综合强度的高原地体内部(尤其是中部和东南部)也具有连续形变的条件。(6)结合地质、大地测量和地球物理资料,对中国东部华北陆块、华南陆块、西部青藏高原和塔里木盆地的岩石圈有效弹性厚度分析表明,中国大陆岩石圈综合强度主要受深部地幔结构的影响；特别是中新生代以来西南印度—欧亚大陆碰撞俯冲,东部太平洋板块的俯冲和三叠纪华南陆块和华北陆块的陆陆碰撞俯冲,引起的地幔热动力过程对中国岩石圈强度结构进行了强烈的改造,也正是这种复杂的岩石圈强度结构影响着中国大陆中生代以来复杂的岩石圈构造演化和变形。更多还原

【Abstract】 Under surface and subsurface loading, the lithosphere should respond isostatically by subsidence or uplift. The nature and degree of these responses or compensation-local or regional, fast or slow, are determined by the thermal and mechanical properties of the lithosphere. These responses can be used to estimate the effective elastic thickness (Te), which shows the deformation-resistant capacity of the lithosphere subjected to the long-term (>105yr) tectonic loading, and is also an effective tool to study the large-scale tectonics of continent and dynamics of lithosphere. The spatial variations of Te are of great importance to address lithospheric mechanical behavior, evolution and dynamics of China Mainland with complex geological structure and deformation.The Chinese Mainland is not a single giant craton; it comprises a number of the stable blocks and several active orogens. Several major processes control its tectonics:the rapid collision of the India-Australia plates with Eurasia in the southwest, the subduction of the Pacific and Philippine Sea plates in the east, and the continental extension in the Baikal rift in the north. Due to such complex structure and dynamics, there must be interactions amongs different blocks. Thus, it is necessary to investigate in detail Te distribution for the whole Chinese mainland, in order to study the destruction of the North China Craton and the uplift of Tibetan Plateau, and to better understand the whole continental tectonic deformation and lithopheric dynamics.Based on the topography and Bouguer gravity anomaly data, this thesis has obtained the spatial variations of Te in China and surroundings with high resolution using multitaper and wavelet coherence methods. Some new understandings of the geotectonics and dynmanics are presented on the basis of the new Te map. Firstly, to evaluate the performance of the multitaper and wavelet coherence methods, the synthetic model tests with the given Te are carried out. The model tests clearly indicate that both methods are capable of resolving Te efficiently. Secondly, based on the topography and gravity data from the new combined satellite-terrestrial model, Te variations over China and surroundings are estimated using these two methods. The results show that the Te values estimated by the multitaper are agreement with those of the Fan wavelet; and the variations of Te are significant over Chinese Mainland. Generally, Te is high in the cold stable cratonic blocks and low Te generally correspond to the young Phanerozoic orogens, however significant lateral changes also exist within these structures. Finally, combined with the information from geology, GPS, and seismic tomography, the new understandings of the geotectonics and dynmanics in China and surroundings are as follows:(1) Comparison of the Te spatial variations and distribution of earthquakes indicates that there are close link between elastic thickness and seismicity over Chinese Mainland. The stable areas with high Te are characterized by a lack of seismicity, which suggests that the stable tectonic provinces with high Te effectively resist deformation. Most of the earthquakes are situated in the low Te areas (10-40km) or steep Te gradient zones, which indicates that the weak lithosphere and areas with steep change of Te are prone to accumulate and then release tectonic stresses causing earthquakes.(2) The quantitative analysis by comparing the lateral variations of Te over China and surroundings with the thermal age of tectonic provinces, heat flow and shear-velocity for the mantle indicates that the thermal structure of lithosphere has great influence on Te variations over China Mainland, and Te positively correlates with the mantle S-velocity at100km. Area of high Te exhibit low heat flow and high mantle seismic velocities at～100km, and vice versa. However, due to the special geological structure, complex lithospheric evolution and anisotropy over China Mainland, the correlations between Te and other lithospheric proxies may be scattered, resulting in some degree of uncertainty.(3) The spatial variations of Te in the NCB show that Te values of the Ordos craton are much higher than the average crustal thickness (-42km). This suggests that the high Te in the old stable craton largely relates to a strong and thick lithospheric mantle. Compared with the stable West Block with remarkably higher Te, the Te values within the East Block are lower and vary dramatically. This suggests that the originally strong Archean lithosphere of the eastern NCB has been weakened, but the localized high Te zones indicate that the Archaean mantle relics are likely preserved in some parts.(4) Combining with the tomography models, The Te variations of South China Block show that the Sichuan basin is not a uniform rigid craton, but is obviously anisotropic; the old cratonic nucleus of the Yangtze Block may exist in the eastern Sichuan Basin, northern Guizhou, Chongqing and northwestern Hunan. Low Te (<20km) prevail over most areas of the middle and eastern parts of the SCB. Combining with the surface tectonic features and mantle themal structure, we propose that the lithospheric strength of the SCB (especially in the eastern part) has been reduced by the processes related to the subduction of the old oceanic lithosphere. In turn, the weakened lithosphere tends to deform under the surrounding strong convergence stresses, leading to the broad fold belts and a wide range of magmatic activity observed today. (5) Within the Tibetan Plateau, the prevailing low Te values in the middle, eastern and southeastern parts might be associated with the ductile crustal flow, hot upper mantle and high thermal regime. The prevailing low Te values of the Tibetan plateau indicate that the deformation of the Tibetan lithosphere might be not only sistributed in the suture or fault zone, but also coherently distributed within the Plateau, particularly in the middle, eastern and southeastern parts.(6) The variations of Te over the NCB, SCB, and Tibet Plateau together with the geological, GPS, and seismic tomography data indicate that the lithospheric strength of China Mainland is a result of various interacting tectonic processes, which continuously modified and reworked the lithosphere structure. In particularly, hydration and thermal dynamic processes associated with the subduction of the ancient Pacific plate under Eurasia, and the rapid convergence of India and Eurasia in the southwest during Mesozoic-Cenozoic are the dominant processes, which modified (mainly weaken) the lithosphere of the China Mainland.更多还原