中国大陆地壳“镶嵌与叠覆”的结构特征及其演化

初步探讨了中国大陆地壳“块带镶嵌多层叠覆”的结构特征和多阶段的构造演化过程。中国大陆地壳新元古代中期以来的一级构造单元有中朝、塔里木、扬子、敦煌4个陆块和中央、西北、东北、西南、东南5个造山区(带)。中朝陆块的形成源于古元古代期间发生的古大陆裂解;扬子、塔里木和敦煌陆块的形成源于新元古代早期发生的古大陆裂解。西北造山区的形成源于古生代晚期洋盆关闭、大陆碰撞并叠加新生代陆内再造山;东北造山带的形成过程包括古生代碰撞造山及中生代增生、碰撞造山;中央造山带至三叠纪大陆碰撞才最后形成并叠加有新生代再造山;东南造山带的形成经历了古生代至新生代的多次造山作用;西南造山带主要是中—新生代造山作用的产物。这些单元都具有“块带镶嵌多层叠覆”的结构特征和多阶段构造演化的特点。中国大陆地壳的形成与演化可以划分为太古宙—古元古代、中元古代—新元古代早期、新元古代中期—古新世和始新世以来4个构造阶段,每个阶段都对应不同的超大陆裂解-聚合旋回。其中新元古代中期以来的地壳形成演化与全球洋陆格局中的古亚洲洋、古特提斯洋、古太平洋、特提斯洋和太平洋5个动力学体制有关,相应地可以归结为古亚洲、古特提斯、古太平洋、特提斯和太平洋5个造山域。

我国陆区地壳生热率分布与壳幔热流特征研究

壳幔热流配分代表了一个地区的深部热量来源与最基础的地热背景,为区域地热资源的形成提供了重要的约束条件.本文依托CRUST1.0模型与地质资料,将中国陆区在平面上划分为19个构造区,在垂向上将这些区域从第四系沉积物至上地幔的地层划分为8个圈层,确定了这些圈层的分布范围和厚度.在全国范围内实测放射性生热率数据664组,收集地壳放射性生热率及U、Th、K元素含量数据约1000组,系统地完成了上述区域各圈层的放射性生热率填图,统计得出我国陆区上、中、下地壳生热率的平均值分别为1.31μW·m^(-3)、0.57μW·m^(-3)与0.22μW·m^(-3).在此基础上,结合最新的全国大地热流测量数据(1503组)完成了我国陆区地壳-地幔热流分布的研究.研究结果表明,我国陆区qc/qm>1的面积占80.1%、qc/qm>1.2的面积占65.8%.除我国东部、中部的一些盆地之外,在我国陆区大部分地区,地壳均为大地热流的最主要热源.地壳各圈层中,基底层至中地壳为地壳的主要的产热区域,贡献了平均约50%的大地热流值.本文以面积加权计算得我国陆区地壳热流平均值为39.1 mW·m^(-2),其中青藏高原最高、东南沿海次之,两者分别得益于较大的地壳厚度与较高的基岩地层生热率.我国陆区地幔热流平均值为29.7 mW·m^(-2),与全球地幔热流平均值接近,其中东部沿海地区、环鄂尔多斯地区、藏滇地热带分布区较高.地壳热流、地幔热流的高值区与我国的主要地热资源分布区均具有较好的一致性.

Element Abundances of China's Continental Crust and Its Sedimentary Layer and Upper Continental Crust

China's continental crust (CCC)has an average thickness of 47km,with the uppercontinental crust (CUCC)being 31 km and the sedimentary layer(CSL)5 km in thickness.The CCC,CUCC and CSL measure 12.437×10^17,8.005×10^17 and 1.146×10^17 metric tons in mass,respectively.The mass ratio of the upper continental crust to the lower one is 1.8:1.The element abundances were calculated for the CCC,CUCC and CSL respectively in terms of the chemical compositions of 2246 samples of various types and some complementary trace element data.The total abundance of 13 major elements accounts for 99.6% of the CCC mass while the other minor elements only account for 0.4%.REE characteristics,the abundance ratios of element pairs and the amounts of ore-forming elements are also discussed in the present paper.

Crustal Deformation Derived from GPS in the Chinese Mainland from 1991-2004

Based on GPS data from 1991- 2004 and the least-squares collocation method,we analyze the crustal deformation in the Chinese mainland. The results show that the first-order crustal deformation is unchanged in different periods in the Chinese mainland,which reflects the background of regional tectonic activity. The strain rate is much higher in Western China,especially in the Qinghai-Tibetan Plateau and Sichuan-Yunnan area. The variations in different periods are related with seismicity of strong earthquakes during the same time. The GPS data after 2004 shows the post-seismic deformation of the 2001 Kunlun Mountains M S8. 1 earthquake.

Upper mantle anisotropy and crust-mantle deformation pattern beneath the Chinese mainland

Over the past 10 years, the number of broadband seismic stations in China has increased significantly. The broadband seismic records contain information about shear-wave splitting which plays an important role in revealing the upper mantle anisotropy in the Chinese mainland. Based on teleseismic SKS and SKKS phases recorded in the seismic stations, we used the analytical method of minimum transverse energy to determine the fast wave polarization direction and delay time of shear-wave splitting. We also collected results of shear-wave splitting in China and the surrounding regions from previously published papers. From the combined dataset we formed a shear-wave splitting dataset containing 1020 parameter pairs. These splitting parameters re- veal the complexity of the upper mantle anisotropy image. Our statistical analysis indicates stronger upper mantle anisotropy in the Chinese mainland, with an average shear-wave time delay of 0,95 s; the anisotropy in the western region is slightly larger （1.01 s） than in the eastern region （0.92 s）. On a larger scale, the SKS splitting and surface deformation data in the Tibetan Plateau and the Tianshan region jointly support the lithospheric deformation mode, i.e. the crust-lithospheric mantle coherent deformation. In eastern China, the average fast-wave direction is approximately parallel to the direction of the absolute plate motion; thus, the upper mantle anisotropy can be attributed to the asthenospheric flow. The area from the Ordos block to the Sichuan Basin in central China is the transition zone of deformation modes between the east and the west regions, where the anisotropy images are more complicated, exhibiting ＂fossil＂ anisotropy and/or two-layer anis^3trc^py. The c^llisi（3n between the Indian Plate and the Eurasian Plate is the main factor of upper mantle anisotropy in the western region of the Chinese mainland, while the upper mantle anisotropy in the eastern region is related to the subduction of the Pacific Plate and the Philippine Sea Plate beneath the Eurasian Plate.

Modification of the lithospheric mantle by melt derived from recycled continental crust evidenced by wehrlite xenoliths in Early Cretaceous high-Mg diorites from western Shandong, China

This paper reports petrographic, mineral chemical, olivine oxygen isotopic, and whole-rock geochemical data for wehrlite xenoliths from the Early Cretaceous Tietonggou high-Mg diorites in western Shandong Province, in the eastern part of the North China Craton (NCC), and describes the origin of these wehrlites and the processes that affected the deep lithospheric mantle in this area.Wehrlite xenoliths are rounded and vary in size between 3 cm × 4 cm 5 cm and 3 cm 2 cm 1 cm.Olivine within these xenoliths occurs as an isolated residual phase within clinopyroxene, has Fo contents between 89 and 91, and contains between 1414 and 3629 ppm Ni, similar to the values of olivine from peridotite xenoliths in the Cenozoic basalts of eastern China, but lower than the values of olivine from harzburgite xenoliths in the Early Cretaceous high-Mg diorites in western Shandong.In situ oxygen isotope analysis yielded 18 O values of olivine from (6.03±0.33)‰ to (6.82±0.35)‰, averaging (6.5±0.4)‰; this is higher than typical mantle-derived olivine ((5.2±0.3)‰).Compared with clinopyroxenes from peridotite xenoliths in the Late Cretaceous and Cenozoic basalts, clinopyroxenes in the wehrlites contain relatively low concentrations of Na 2 O, TiO 2 , and Al 2 O 3 , high concentrations of CaO, and higher Mg # (91.2-94.1) and Ti/Eu ratios (2082-2845), being similar in composition to clinopyroxenes within harzburgite xenoliths in the Early Cretaceous high-Mg diorites.Clinopyroxenes from wehrlite xenoliths are characterized by low total REE abundance, enrichment in light REEs, and depletion in high field strength elements such as Nb, Ta, Zr, and Hf.Moreover, the 87 Sr/ 86 Sr, 143 Nd/ 144 Nd, and 187 Os/ 188 Os (125 Ma) ratios of these wehrlites vary from 0.70596 to 0.70737, 0.512181 to 0.512416, and 0.12661 to 0.57650, respectively.These data suggest that these wehrlite xenoliths were formed by modification of the lithospheric mantle by melts derived from recycled continental crust.

Horizontal crustal movement in China fitted by adaptive collocation with embedded Euler vector

The crustal movements of the Chinese mainland include an average regional movement trend of the mainland and complex local deformations. Thus, both trends in the crustal movement of the mainland and local distortions should be simultaneously taken into consideration in crustal movement estimations. A combined collocation model based on Euler vector (taken as trend parameters) and local distortions (taken as signals) is proposed in this paper. We assume that prior covariance matrices between signals and observations should be consistent with their uncertainties. Otherwise, the station movement estimates provided by the collocation will be distorted. Thus, an adaptive collocation estimator based on simplified Helmert variance components is applied. This means that the contributions of signals and observations to estimates of crustal movements are balanced and reasonable, and consistent covariance matrices of the signals and observations are achieved through the adjustment of the adaptive factor. The calculation of actual horizontal movements of the Chinese crust shows that the estimates of horizontal crustal movement velocities are made more accurate by the adaptive collocation model.