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191.
192.
Group velocities of Rayleigh and Love waves along the paths across the Black Sea and partly Asia Minor and the Balkan Peninsula are used to estimate lateral variations of the crustal structure in the region. As a first step, lateral variations of group velocities for periods in the range 10–20 s are determined using a 2D tomography method. Since the paths are oriented predominantly in NE–SW or N–S direction, the resolution is estimated as a function of azimuth. The local dispersion curves are actually averaged over the extended areas stretched in the predominant direction of the paths. The size of the averaging area in the direction of the best resolution is approximately 200 km. As a second step, the local averaged dispersion curves are inverted to vertical sections of S-wave velocities. Since the dispersion curves in the 10–20 s period range are mostly affected by the upper crustal structure, the velocities are estimated to a depth of approximately 25 km. Velocity sections along 43° N latitude are determined separately from Rayleigh and Love wave data. It is shown that the crust under the sea contains a low-velocity sedimentary layer of 2–3 km thickness, localized in the eastern and western deeps, as found earlier from DSS data. Beneath the sedimentary layer, two layers are present with velocity values lying between those of granite and consolidated sediments. Velocities in these layers are slightly lower in the deeps, and the boundaries of the layers are lowered. S-wave velocities obtained from Love wave data are found to be larger than those from Rayleigh wave data, the difference being most pronounced in the basaltic layer. If this difference is attributed to anisotropy, the anisotropy coefficient = (SH - SV)/Smean is reasonable (2–3%) in the upper layers, and exceeds 9% in the basaltic layer. 相似文献
193.
德国大陆科学钻探的地壳流体研究 总被引:3,自引:0,他引:3
简要地介绍了德国大陆科学钻探过程中壳流体的开发成果,以及与流体研究相关的某些问题。德国两个大陆科学钻孔提供了可达9191m深结晶基底中古流体和现代流体样品,以及它们留在矿物和岩石化学、同位素成分上的指纹。据此,再以再造地壳流体的时空分布、化学成分、迁移途径、源区和演化过程。 相似文献
194.
Dynamic pattern characteristics of fault deformation and gravity field in the development process of Yongdeng M S =5.8 earth quake 总被引:3,自引:0,他引:3
DynamicpaterncharacteristicsoffaultdeformationandgravityfieldinthedevelopmentprocesofYongdengMS=5.8earthquakeZAISENJIANG... 相似文献
195.
Preliminary results of measuring the crustal deformation in Qinghai-Xizang area using GPS technique 总被引:5,自引:0,他引:5
GPS repetition measurement tbta in Qinghai-Xizatlg (Tibetan) area in 1992 and 1994 have been used to determine the change
rates of seven bascline vectors of Lhasa-Wenquan, etc. It is the first time to obtain the direct observation results of the
large-scale crustal horizontal motions in this area. Thesc preliminary results also for the first time provide the direct
observation evidence for some important geophysical and geological viewpoints, such as the northward gradual reduce of the
effect of the northward push-pressing to Eurasian continent by Indian Plate in the Qinghai-Xizang area, having a southward
strike slip movement of the Chuan-Dian diamond block, etc. 相似文献
196.
Constraints on the age of basement and crustal growth in Tianshan Orogen by Nd isotopic composition 总被引:3,自引:0,他引:3
Based on study of Nd isotopic composition for 101 rocks of various types from Tianshan Orogen, the age and character of basement
and continental crustal evolution of the Tianshan Orogen were proposed. It is deduced that the continental crustal basement
of the Tianshan Orogen was formed 1. 8 Ga ago. The protolith of its metamorphic rocks was derived from long-term depleted
mantle source in the ancient are tectonic setting probably. The Tianshan Orogen is obviously different from the North Tarim
Block in age of basement and post-evolution history. It was also shown that Paleozoic continental crustal growth happened
extensively in the Tianshan Orogen, which is distinguished from Yangtse Block and Cathaysia Block in eastern China.
Project supported by the National Natural Science Foundation of China (Grant No. 49633250). It belongs to the National “305”
Project in Xinjiang, which is one of the National Key Projects in the Ninth Five-Year Plan (96-915-07-05A). 相似文献
197.
A reprocessing program to enhance the correlation between the surface geology and the seismic data has been completed for seismic line 9 (eastern 100 km) and line 10 in the central region of the Trans-Hudson Orogen of Saskatchewan, Canada. The new seismic images through lateral continuity of reflectivity provide sufficient detail to resolve the discrepancy between the low-dipping, layer-parallel and dextral-reverse nature of the Sturgeon-Weir shear zone (line 9) observed in the field and its steeply dipping (apparent) normal displacement character interpreted on the basis of the initial processing. Furthermore, the new interpretation provides a strong confirmation of the role of Pelican Thrust as a major detachment zone — the main `sole thrust' — along which juvenile allochthons have been carried across the Archaean microcontinental block. The images are also refined enough to suggest: (a) a boundary within the Pelican Thrust between its internal and external suites; (b) a possible boundary separating a lower (older?) Archaean basement from its upper (younger?) counterpart; and (c) sub-Moho events (M2) which reveal possible involvement of the upper mantle in the collisional tectonic process in addition to the well defined Moho (M1) which probably represents the youngest of the post-collisional detachments. 相似文献
198.
Kewal K. Sharma 《Journal of Earth System Science》1998,107(4):265-282
The geology and tectonics of the Himalaya has been reviewed in the light of new data and recent studies by the author. The data suggest that the Lesser Himalayan Gneissic Basement (LHGB) represents the northern extension of the Bundelkhand craton, Northern Indian shield and the large scale granite magmatism in the LHGB towards the end of the Palæoproterozoic Wangtu Orogeny, stabilized the early crust in this region between 2-1.9 Ga. The region witnessed rapid uplift and development of the Lesser Himalayan rift basin, wherein the cyclic sedimentation continued during the Palæoproterozoic and Mesoproterozoic. The Tethys basin with the Vaikrita rocks at its base is suggested to have developed as a younger rift basin (~ 900 Ma ago) to the north of the Lesser Himalayan basin, floored by the LHGB. The southward shifting of the Lesser Himalayan basin marked by the deposition of Jaunsar-Simla and Blaini-Krol-Tal cycles in a confined basin, the changes in the sedimentation pattern in the Tethys basin during late Precambrian-Cambrian, deformation and the large scale granite activity (~ 500 ± 50 Ma), suggests a strong possibility of late Precambrian-Cambrian Kinnar Kailas Orogeny in the Himalaya. From the records of the oceanic crust of the Neo-Tethys basin, subduction, arc growth and collision, well documented from the Indus-Tsangpo suture zone north of the Tethys basin, it is evident that the Himalayan region has been growing gradually since Proterozoic, with a northward shift of the depocentre induced by N-S directed alternating compression and extension. During the Himalayan collision scenario, the 10–12km thick unconsolidated sedimentary pile of the Tethys basin (TSS), trapped between the subducting continental crust of the Indian plate and the southward thrusting of the oceanic crust of the Neo-Tethys and the arc components of the Indus-Tangpo collision zone, got considerably thickened through large scale folding and intra-formational thrusting, and moved southward as the Kashmir Thrust Sheet along the Panjal Thrust. This brought about early phase (M1) Barrovian type metamorphism of underlying Vaikrita rocks. With the continued northward push of the Indian Plate, the Vaikrita rocks suffered maximum compression, deformation and remobilization, and exhumed rapidly as the Higher Himalayan Crystallines (HHC) during Oligo-Miocene, inducing gravity gliding of its Tethyan sedimentary cover. Further, it is the continental crust of the LHGB that is suggested to have underthrust the Himalaya and southern Tibet, its cover rocks stacked as thrust slices formed the Himalayan mountain and its decollement surface reflected as the Main Himalayan Thrust (MHT), in the INDEPTH profile. 相似文献
199.
LIU Dequan TANG Yanling ZHOU RuhongXinjiang Bureau of Geology Mineral Exploration Development No. W. Karamay Rd. Urumqi Xinjiang 《《地质学报》英文版》1998,72(4):339-349
The great majority of the Palaeozoic orogenjc belts of Central Asia are of the intercontinental type, whose evolution always follows a five-stage model, i.e. the basal continental crust-extensional transitional crust-oceanic crust-convergent transitional crust-new continental crust model. The stage for the extensional transitional crust is a pretty long, independent and inevitable phase. The dismembering mechanism of the basal continental crust becoming an extensional continental crust is delineated by the simple shear model put forward by Wernike (1981). The continental margins on the sides of a gently dipping detachment zone and moving along it are asymmetric: one side is of the nonmagmatic type and the other of the magmatic type with a typical bimodal volcanic formation. In the latter case, however, they were often confused with island arcs. This paper discusses the five-stage process of the crustal evolution of some typical orogenic belts in Xinjiang. 相似文献
200.
本文在Agterberg和Divi(1978)的地壳丰度地质统计模型(CrustalAbundanceGeostastics,简称CAG)的基础上,提出了一种成矿省成矿元素区域背景值下限的简易计算方法。在区域背景值未知的情况下,根据成矿省某成矿元素的截切品位和金属量,可由此法计算出其地壳平均丰度最小值,以此作为成矿省中该元素区域背景值。将这一方法运用于华南Sb成矿省所得Sb元素区域背景值与通过区域地球化学方法得到的华南地区Sb的地壳平均丰度值相近,这充分说明这种地壳平均丰度最小值法的可靠性。 相似文献