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271.
272.
陕西勉略宁三角区基本地质组成及演化 总被引:5,自引:0,他引:5
陕西勉略宁三角区发育4大套不同构造背景下所形成的岩石组合,表明区内经历了晚太古结晶基底与早中元古浅变质火山岩过渡基底形成、晚元古一早古生代扬子大陆边缘演化、勉略海槽演化及陆内造山4个大的复杂演化阶段,最终形成今日之基本构造格局与地质面貌. 相似文献
273.
274.
Contrasting two types of orogen in Permo-Triassic Japan: Accretionary versus collisional 总被引:1,自引:0,他引:1
Abstract Proto-Japan originated from a continental margin of the Neoproterozoic Yangtze (South China) craton. It represents a unique Permo-Triassic tectonic setting in western Panthalassa, where two distinct types of orogenic belt occurred side by side. There was an accretionary orogen between the Yangtze craton and the Proto-Pacific (Farallon) Plate and a collisional orogen between the Sino-Korean (North China) and Yangtze cratons. This article reviews results of the latest on-land geological studies concerning Permo-Triassic tectonics in Japan and proposes a new plate tectonic interpretation as well as a paleogeographic reconstruction of this particularly unique geotectonic regime. Special emphases are given to (i) the accretion processes and products derived by collision-subduction of the Permian Akiyoshi paleoseamount and Maizuru paleo-oceanic plateau; (ii) the field occurrence of 220-Ma Sangun high-P/T schists and its implication for the exhumation process and 'tectonic sandwich' structure; (iii) the extensive development of a subhorizontal nappe of the pre-Jurassic rocks and their bearing on the orogenic edifice; and (iv) the restricted occurrence of the 250-Ma collision complex in the Hida and Oki belts and the relevant connection to the Precambrian cratons and collision suture in East Asia. The newly proposed paleogeographic reconstruction is also tested by faunal provinciality of Permo-Triassic fossils from shallow-water sediments. 相似文献
275.
Abstract Recent paleomagnetic studies are reviewed in an effort to clarify the relationship between the intra-arc deformation of central Japan and the collision tectonics of the Izu-Bonin Arc. The cusp structure of the pre-Neogene terranes of central Japan, called the Kanto Syntaxis, suggests a collisional origin with the Izu-Bonin Arc. The paleomagnetic results and newly obtained radiometric ages of the Kanto Mountains revealed the Miocene rotational history of the east wing of the Kanto Syntaxis. More than 90° clockwise rotation of the Kanto Mountains took place after deposition of the Miocene Chichibu Basin (planktonic foraminiferal zone of N.8: 16.6–15.2 Ma). After synthesizing the paleomagnetic data of the Japanese Islands and collision tectonics of central Japan, it appears that approximately a half rotation (40–50°) probably occurred at ca 15 Ma in association with the rapid rotation of Southwest Japan. The remainder (50-40°) continued until 6 Ma, resulting in the sharp bent structure of the pre-Neogene accretionary complexes (Kanto Syntaxis). The latter rotation seems to have been caused by the collision of the Izu-Bonin Arc on the northwestward migrating Philippine Sea Plate. 相似文献
276.
中新生代中国及邻区板块碰撞、旋转及离散模式初探 总被引:3,自引:0,他引:3
本文在6000多个资料点的42000余数据的基础上,应用计算机成图技术,以活动论的观点对中国大陆的运动程式进行初探。根据煤和蒸发盐岩沉积范围的变迁以及火山活动的分布特点推断中生代以来,中国大陆在周边各板块的相互作用下,由北向南迁移并作顺时针旋转,从而形成当今的大地构造格局。 相似文献
277.
The 1.1 Ga Natal Metamorphic Province (NMP) lies at the heart of a world-wide system of Grenville age mobile belts which welded early continental fragments into the Mesoproterozoic supercontinent of Rodinia. Structural analysis of the three tectonostratigraphic terranes in Natal reveals a kinematic history characterized by prolonged NE-SW plate convergence, manifested as early thrust tectonics and later pervasive sinistral transcurrent shearing. Consequently, superimposed on the Natal tectonostratigraphic terranes is a kinematic subdivision into tectonic domains which are characterized by shallow, south-west dipping foliations, south-west plunging stretching lineations and north-east verging recumbent folds, and by younger domains with subvertical shear fabrics, subhorizontal to oblique lineations and folding about near-vertical axes. Microtextural and petrographic analyses suggest that the later shearing took place under high temperature conditions of at least 500°C. The recorded kinematic indicators suggest that early subhorizontal compressional tectonics gave rise to tectonic thickening of the crust, progressively followed by oblique transcurrent shearing within a transpressional regime. The shearing event in the southern arc-related terranes was associated with the widespread emplacement of late kinematic rapakivi granite -charnockite plutons, with A-type granite geochemical characteristics. This orogenic event took place around 1100 Ma during prolonged NE-SW collisional convergence along the southern margin of the stable Archean foreland, which lay to the north. 相似文献
278.
Rajneesh Bhutani Kanchan Pande T. R. Venkatesan 《Journal of Earth System Science》2004,113(4):737-754
New40Ar-39Ar thermochronological results from the Ladakh region in the India-Asia collision zone provide a tectono-thermal evolutionary
scenario. The characteristic granodiorite of the Ladakh batholith near Leh yielded a plateau age of 46.3 ± 0.6 Ma (2σ). Biotite from the same rock yielded a plateau age of 44.6 ± 0.3 Ma (2σ). The youngest phase of the Ladakh batholith, the leucogranite near Himya, yielded a cooling pattern with a plateau-like age
of ∼ 36 Ma. The plateau age of muscovite from the same rock is 29.8 ±0.2 Ma (2σ). These ages indicate post-collision tectono-thermal activity, which may have been responsible for partial melting within the
Ladakh batholith. Two basalt samples from Sumdo Nala have also recorded the post-collision tectono-thermal event, which lasted
at least for 8 MY in the suture zone since the collision, whereas in the western part of the Indus Suture, pillow lava of
Chiktan showed no effect of this event and yielded an age of emplacement of 128.2 ±2.6 Ma (2σ). The available data indicate that post-collision deformation led to the crustal thickening causing an increase in temperature,
which may have caused partial melting at the base of the thickened crust. The high thermal regime propagated away from the
suture with time. 相似文献
279.
F. Nilforoushan F. Masson P. Vernant C. Vigny J. Martinod M. Abbassi H. Nankali D. Hatzfeld R. Bayer F. Tavakoli A. Ashtiani E. Doerflinger M. Daignières P. Collard J. Chéry 《Journal of Geodesy》2003,77(7-8):411-422
The rate of crustal deformation in Iran due to the Arabia–Eurasia collision is estimated. The results are based on new global positioning system (GPS) data. In order to address the problem of the distribution of the deformation in Iran, Iranian and French research organizations have carried out the first large-scale GPS survey of Iran. A GPS network of 28 sites (25 in Iran, two in Oman and one in Uzbekistan) has been installed and surveyed twice, in September 1999 and October 2001. Each site has been surveyed for a minimum observation of 4 days. GPS data processing has been done using the GAMIT-GLOBK software package. The solution displays horizontal repeatabilities of about 1.2 mm in 1999 and 2001. The resulting velocities allow us to constrain the kinematics of the Iranian tectonic blocks. These velocities are given in ITRF2000 and also relative to Eurasia. This last kinematic model demonstrates that (1) the north–south shortening from Arabia to Eurasia is 2–2.5 cm/year, less than previously estimated, and (2) the transition from subduction (Makran) to collision (Zagros) is very sharp and governs the different styles of deformation observed in Iran. In the eastern part of Iran, most of the shortening is accommodated in the Gulf of Oman, while in the western part the shortening is more distributed from south to north. The large faults surrounding the Lut block accommodate most of the subduction–collision transition. 相似文献
280.
钢筋混凝土结构倒塌分析的前沿研究 总被引:13,自引:1,他引:13
结构倒塌分析主要涉及三个难点,即不连续位移场的描述、接触碰撞分析以及结构倒塌过程中大位移、大转动的描述。本文就国内外研究现状针对结构倒竭的评定标准以及上述三个难点做出评述,同时介绍了作者近期工作,并对今后研究工作做了展望,以供参考。 相似文献