Sediment accretion against a buttress beneath the Peruvian continental margin at 12° S as simulated with sandbox modeling

Reflection seismic data from the Peruvian continental margin at 12° S clearly reveal an accretionary wedge and buttress. Sandbox experiments applying the physical concept of the Coulomb theory allow the systematic investigation of the growth and deformation of such an accretionary structure. The style of deformation of the buttress and the internal structure of the wedge is observed in the sandbox models. The possibility of underplating material beneath the buttress and the amount of tectonic erosion depend on the physical properties of the materials, mainly internal friction, cohesion and basal friction. Boundary conditions such as the height of the subduction gate and the thickness of incoming sand also constrain the style of growth of the model accretionary structure.The configurations of two experiments were closely scaled to reflection seismic depth sections across the Peruvian margin. A deformable buttress constructed of compacted rock powder is introduced to replicate the basement rock which allows deformation similar to that in the seismic data. With the sandbox models it is possible to verify a proposed accretionary history derived from seismic and borehole data. The models also help in understanding the mechanisms which control the amount of accretion, subduction and underplating as a function of physical properties, boundary conditions and the duration of convergence.     

论豫西洛宁—嵩县中生代钙碱性花岗岩类的同源性

本文就华北地台南缘豫西洛宁－嵩县地区中生代钙碱性花岗岩基和小斑岩体的同源性，从成岩时代，成岩环境，岩石学，岩石化学，微量元素尤其是稀土元素以及岩石成因类型等８个方面进行了论证，上述花岗岩基与小斑岩体被认为是太古界太华群重熔产物，属于同一重熔－演化系新认识。     

用多层变密度直接反演法研究下扬子地区的岩石圈构造

本文用多层变密度直接反演方法研究下扬子地区的岩石圈结构,并讨论其大地构造涵义及演化问题。文中给出了三次样条密度-深度函数的重力正演公式,采用非线性最小二乘优化算法,得到岩石圈内G_5、G_6、G_7三个主要密度界面,它们分别相应于中地壳低密度层底面、Moho面和上地幔顶部低密度层上界面。通过岩石圈结构分析,得到以下结果:杭州湾—海盐—嘉兴—长兴—高淳—芜湖隐伏深断裂是一条北西向的一级构造边界,它对下扬子区的大地构造发展和地壳演化有重要影响。     

Crustal structure, fault segmentation, and activity of the Median Tectonic Line in Shikoku, Japan

We conducted a seismic tomographic analysis to estimate the crustal structure beneath the Shikoku and Chugoku regions in Japan. The Philippine Sea slab (PHS slab) subducts continuously in a SE–NW direction beneath this region, and the crustal structure is complex. Furthermore, the Median Tectonic Line (MTL), one of the longest and most active arc-parallel fault systems in Japan (hereafter, the MTL active fault system), is located in this area, and the right-lateral strike–slip movement of this fault system is related to the oblique subduction of the PHS slab. The MTL active fault system has ruptured repeatedly during the last 10 000 years, and has high seismic potential. Our tomographic analysis clarified the heterogeneous crustal structure along the MTL active fault system. This fault system in Shikoku can be divided into two segments, an east segment and a west segment, on the basis of the velocity structure. This segmentation model is consistent with other such models that have been determined from geological and geomorphological data such as fault geometry, slip rate, and faulting history. This consistency suggests that the surface characteristics of the MTL active fault system are related to structural properties of the crust. In particular, a prominent low-velocity (low-V) zone is present in the lower crust beneath the east segment. Our tomographic images show that the lower crust structure beneath the east segment is obviously different from that of the other segment. Furthermore, this low-V zone may indicate the presence of fluid, possibly related to dehydration of the PHS slab. As the presence of fluid in the lower crust affects the activity of the fault, stress accumulation and the fault failure mechanism may differ between the two segments of the MTL active fault system.     

Transverse fault zones of subtle geomorphic signature in northern Evia island (central Greece extensional province): An introduction to the Quaternary Nileas graben

Reconnaissance level geomorphological observations in the northern part of Evia (Euboea) Island, suggest that a major topographic feature, the 17 km long and 15 km wide Nileas depression (NDpr), corresponds to a previously undetected graben structure, bounded by fault zones of ENE–WSW to NE–SW general strike. These fault zones have been active in the Quaternary, since they affect the Neogene deposits of the Limni–Histiaia basin. They strike transverse to the NW–SE active fault zones that bound northern Evia in the specific area and are characterised along most of their length by subtle geomorphic signatures in areas of extensive forest cover and poor exposure.The NDpr was formed during the Early–Middle Quaternary, after the deposition of the Neogene basin fill. During the Middle–Late Quaternary, the NW–SE fault zones that bound northern Evia have been the main active structures, truncating and uplifting the NDpr to a perched position in relation to the northern Gulf of Evia graben and the submarine basin on the Aegean side of the island. The present-day morphology of the NDpr, with an interior (floor) comprised of Middle Pleistocene erosional surfaces extensively dissected by drainages, was shaped by erosion during this uplift. Judging from their geomorphic signatures, the fault zones that bound the NDpr must have been characterised by low or very low rates of activity during the Late Quaternary. Yet, that they may still be accommodating strain today is suggested by moderate earthquakes that have been recorded within the NDpr.The fault zone at the SE flank of the NDpr (Prokopi–Pelion fault zone) may be very important in terms of earthquake segmentation of the active NW–SE Dirfys fault zone that controls the Aegean coast of northern Evia, given that the intersection between the two presents striking morpho-structural similarities with the intersection of two fault zones with the same directions on the mainland (the Atalanti and Hyampolis fault zones), which is known to have acted as a barrier to the propagation of the Atalanti earthquake ruptures in 1894.     

福建街面水库地震活动背景

福建街面水库2006年10月下闸蓄水,分析了街面水库库区历史地震和现今地震震中分布、震源深度、震源机制解等地震活动特点,并结合水库诱发地震的特点认为街面水库存在诱发地震的可能。     

华北克拉通古元古代构造事件

本文讨论了华北克拉通的古元古代表壳岩系、高压麻粒岩和孔兹岩系的若干问题,提出了(1)华北克拉通在约2500Ma太古宙结束时已基本形成.在2300Ma之前处于相对稳定的构造环境;(2)2300～1950Ma期间,华北克拉通经历了一次基底陆块的拉伸-破裂事件,在克拉通内部发育了晋豫、胶辽裂陷盆地和丰镇陆内凹陷盆地;(3)约1900Ma期间,有地幔上涌并伴随辉长岩浆的底侵作用,引起大青山-丰镇地区的超高温变质作用.底侵的辉长岩浆作为岩体和岩墙在下地壳就位,并发生高压麻粒岩相变质作用;(4)约1850Ma期间,华北克拉通经历了一次挤压构造事件,导致了裂陷盆地的闭合和焊接,形成晋豫和胶辽两个类似于现代陆.陆碰撞型的造山带;(5)在华北克拉通的北缘,华北克拉通可能与其北部的另一古老陆块或岛弧拼合,其拼合带应位于白云鄂博以北.现在已残缺不全.孔兹岩系可能代表了平行于北缘造山带的一条构造带.与北部造山带的俯冲碰撞相关的陆内深部逆掩造成了麻粒岩相岩石的形成和抬升;(6)白云鄂博群、化德群和渣尔泰(-狼山)群是与长城系相同时期发育的被动大陆边缘裂谷盆地;(7)1850～1700Ma期间,华北克拉通进入伸展构造体制,导致基底抬升,产生裂陷槽、基性岩墙群和非造山岩浆活动.     

Geodynamic hazard and risk assessments for sites close or in tectonic zones with shear movements

No region is excluded from actions of recent geodynamic short- or long-term effects which can be observed even on the Earth’s surface. The article delivers a geodynamic hazard assessment for the anthropogenic objects threatened by permanent shear movements occurring along tectonic faults and a way how to mitigate and/or eliminate the object risk. The proposed approach is applied to a case example of a motorway tunnel leading through rock masses where dynamically active zones with shear movements along their faults are expected. To detect the shear movements among rock masses, the contemporary satellite geodetic GPS methodology was used.     

兰州地区现代应力场的构造解析

在对兰州地区兴隆山北缘断裂、白杨树沟断裂和西湾-雷庄断裂等的活动性研究的基础上,根据断裂擦痕斜角资料,结合区域其他构造应力场资料,应用构造应力解析方法计算了兰州的构造应力场。研究结果表明:①兰州地区区域构造应力场主压应力方向总体在NE到近EW向的范围内;②现今构造应力场继承了更新世以来的构造应力场;③深部和表层构造应力场基本一致;④区域构造运动是以水平构造应力为主导的。     

Use of laser ablation ICP-MS to determine trace element distributions in coals, with special reference to V, Ge and Al

Laser ablation ICP-MS has been used to produce element profiles from polished coal samples. The elements analysed (V, Ge, Ni, Cu, Zn, Sr and Ba) were those known to have an organic association, with the addition of Al and Fe as controls on the clay and pyrite abundances. The element profiles were compared with the petrography and a statistical analysis was also carried out. Sporinite was found to have low trace element concentrations, inertinite higher concentrations of detrital elements and vitrinite higher concentrations of V, Ge and Al. The relationships between these elements are explored and all are thought to be present in the organic matter and not as minerals. It is thought that these elements became concentrated during diagenesis, with the possibility that some of the Al could be residual. The Cu/Ni ratio in the pyrite is relatively constant, suggesting constant ionic proportions during diagenesis, and possibly a seawater source.