Sm-Nd ISOTOPIC AGE OF LAMPROPHYRES IN THE GEZHEN GOLD-BEARING SHEAR ZONE ON HAINAN ISLAND AND ITS GEOLOGICAL IMPLICATIONS

Sm-Nd isotopic compositions of eight lamprophyre samples, which come from the Gezhen gold-bearing shear zone on western Hainan Island, are measured. The Sm-Nd isochron age is 495.98±13.14 Ma, (143Nd/144Nd) 0=0.512094, εNd(t) ranges from +1.80 to +2.00 and TDM from 982 Ma to 1196 Ma (average: 1060 Ma). The authors point out that the whole-rock Sm-Nd isochron age (495.98 ± 13.14 Ma) really represents the petrogenetic age of lamprophyre and the time of magmatism during subsequent subduction.     

Cretaceous and Tertiary terrane accretion in the Cordillera Occidental of the Andes of Ecuador

New field, geochronological, geochemical and biostratigraphical data indicate that the central and northern parts of the Cordillera Occidental of the Andes of Ecuador comprise two terranes. The older (Pallatanga) terrane consists of an early to late (?) Cretaceous oceanic plateau suite, late Cretaceous marine turbidites derived from an unknown basaltic to andesitic volcanic source, and a tectonic mélange of probable late Cretaceous age. The younger (Macuchi) terrane consists of a volcanosedimentary island arc sequence, derived from a basaltic to andesitic source. A previously unidentified, regionally important dextral shear zone named the Chimbo-Toachi shear zone separates the two terranes. Regional evidence suggests that the Pallatanga terrane was accreted to the continental margin (the already accreted Cordillera Real) in Campanian times, producing a tectonic mélange in the suture zone. The Macuchi terrane was accreted to the Pallatanga terrane along the Chimbo-Toachi shear zone during the late Eocene, probably in a dextral shear regime. The correlation of Cretaceous rocks and accretionary events in the Cordillera Occidental of Ecuador and Colombia remains problematical, but the late Eocene event is recognised along the northern Andean margin.     

2-D viscoelastic FEM simulation on stress state in the deep part of a subducted slab

Introduction It is found that there are some relationships between the thermal structures of subduction zones and the deep seismicity, while the mechanism relates the thermal structure and the deep seismicity is still unsure (Helffrich, Brodholt, 1991; Furukawa, 1994; Kirby, et al, 1996). From 1980s, geoscientists have constituted a series of numerical simulations on the stress states of subduction slabs. Based on the kinetic computation of Sung and Burns (1976a, b), Goto, et al (1983, 1987…     

含预制软弱带的岩石破裂过程的数值模拟

考虑到岩石脆性破坏过程中介质的不均匀性之特点，对岩石样品中含预制弱介质条带的岩石样品破坏过程进行二维有限元数值模拟，并对弱介质带的破坏贯通过程、新的断层的产生和有关的地震活动进行了研究．数值模型展示了岩石从变形、微观破坏到整体破坏的全过程以及微震活动的时空分布特征．应力、应变和微震活动的时空分布形象地描绘了岩石变形的局部化和时空迁移等现象，这与实际地壳中所观测到的现象是一致的．此外，模拟结果与实验观测结果也是一致或相似的．      

Shallow seismicity, stress distribution and crustal deformation pattern in the Andaman-West Sunda arc and Andaman Sea, northeastern Indian Ocean

Shallow seismicity and available source mechanisms in the Andaman–westSunda arc and Andaman sea region suggest distinct variation in stressdistribution pattern both along and across the arc in the overriding plate.Seismotectonic regionalisation indicates that the region could be dividedinto eight broad seismogenic sources of relatively homogeneousdeformation. Crustal deformation rates have been determined for each oneof these sources based on the summation of moment tensors. The analysisshowed that the entire fore arc region is dominated by compressive stresseswith compression in a mean direction of N23^°, and the rates ofseismic deformation velocities in this belt decrease northward from 5.2± 0.65 mm/yr near Nias island off Sumatra and 1.12 ±0.13 mm/yr near Great Nicobar islands to as much as 0.4 ±0.04 mm/yr north of 8^°N along Andaman–Nicobar islandsregion. The deformation velocities indicate, extension of 0.83 ±0.05 mm/yr along N343^° and compression of 0.19 ±0.01 mm/yr along N73^° in the Andaman back arc spreadingregion, extension of 0.18 ± 0.01 mm/yr along N125^° andcompression of 0.16 ± 0.01 mm/yr along N35^° in NicobarDeep and west Andaman fault zone, compression of 0.84 ±0.12 mm/yr N341^° and extension of 0.77 ± 0.11 mm/yralong N72^° within the transverse tectonic zone in the Andamantrench, N-S compression of 3.19 ± 0.29 mm/yr and an E-Wextension of 1.24 ± 0.11 mm/yr in the Semangko fault zone ofnorth Sumatra. The vertical deformation suggests crustal thinning in theAndaman sea and crustal thickening in the fore arc and Semangko faultzones. The apparent stresses calculated for all major events range between0.1–10 bars and the values increase with increasing seismic moment.However, the apparent stress estimates neither indicate any significantvariation with faulting type nor display any variation across the arc, incontrast to the general observation that the fore arc thrust events showhigher stress levels in the shallow subduction zones. It is inferred that theoblique plate convergence, partial subduction of 90^°E Ridge innorth below the Andaman trench and the active back arc spreading are themain contributing factors for the observed stress field within the overridingplate in this region.     

新疆且末县吐孜敦古地震形变带及其年代问题

新疆且末县拟在吐拉乡阿尔金活动断裂带上修建水库。水库近场区内沿阿尔金活动断裂存在一条古地震破裂形变带。为了对水库进行安全性评价 ,采用地貌风化剥蚀法确定了古地震形变带的形成年代。该次古地震事件的发生时间大约距今 4 0 0年前     

河南经济技术开发区发展前景与对策

文章阐述了经济技术开发区在区域经济发展过程中的作用。根据河南省经济技术开发区的发展现状和存在的问题，分析了加入WTO后开发区所面临的机遇和挑战，并在此基础上从开发区环境营造，运行机制，筹资方式，产业发展，城市建设等方面提出了加快河南省经济技术开发区发展的对策。     

北江大堤植草护坡效应研究

北江大堤在航运的浪涛侵蚀以及洪水和雨水的冲蚀下，部分河段边坡已变得支离破碎，对广州和珠江三角洲地区的防洪安全构成了严重威胁。香根草和百喜草都能耐较长时间的水淹，并都有较强的抗逆性。结合土石方工程，并辅以三维网覆盖，将香根草和百喜种在北江两岸的边坡上。结果，这一护坡措施不仅有较地防止了洪流冲蚀和雨水侵蚀，较好地起到了固土护坡作用，而且绿化美化了河岸边坡，成功解决了河湖水库的河岸带难以植被覆盖的难题。