Coupling between different layers of the lithosphere under horizontal drag underneath

Based on a layered rheological model of the lithosphere, the velocity and stress distributions in the lithosphere under horizontal drag underneath were calculated using viscoelastic finite element method of plain strain with finite deformation. In the simulation, different conditions of drag and blocking were assumed to study their influences on the stress distribution and the coupling between different layers. Blocking depth has little influence on the stress level in the whole area and the coupling between different layers, but influences the stress state in the area around the blocking. The area covered by the high stress anomaly becomes larger when the blocking depth becomes deeper, but the magnitude of the value of the maximum shear stress decreases. The greater the viscosity differences between different layers of the lithosphere, the greater the possibility of decoupling between them. Under the drag of normal mantle convection (the convection velocity is about 20 cm·a?1), a lithosphere with a rheological structure similar to that of North China could not have decoupling between different layers, while could have stress distribution with magnitude of several MPa to tens of MPa and could have anomalous areas with stress accumulation if the geological structure is complicated.     

南沙超壳层块边界断裂的运动学与动力学特征

南沙超壳层块被性质不同的超壳断裂所围限,北张南压,东西剪切,共同以南沙软流圈顶面为拆离面而系统运动。其新生代动力学过程可分为四个阶段:K2—E12,北界伸展,古南海向南俯冲,西布增生楔形成;E22—E13,西南海盆扩张,西布增生楔碰撞造山;E23—N11,中央海盆扩张,米里增生楔形成,北巴拉望南缘“A型”俯冲;N21—现在,南部边界大规模逆冲推覆造山,南海扩张停止     

Lava flow internal structure found from AMS and textural data: An example in methodology from the Chaîne des Puys,France

Anisotropy of magnetic susceptibility (AMS) data analysis is a convenient method used to investigate strain and flow during lava flow emplacement. In order to make a sound interpretation, the origin of the AMS signal must be verified. Two questions must be answered: 1) what phase, or phases carry the AMS signal and 2) when was the AMS fabric acquired? The verification steps themselves can provide extra data for interpreting lava flow conditions. Here, we present a methodology to answer the two questions in a 6 km-long Chaîne des Puys trachybasaltic lava flow that descended into the future site of Clermont Ferrand (France) 45,000 years ago. Knowledge of lava flow emplacement will be useful specifically to this site, if a reactivation of the volcanic chain occurs. The results are also of more general interest to understand lava flow emplacement dynamics.     

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3D model of Svecofennian Accretionary Orogen and Karelia Craton based on geology,reflection seismics,magnetotellurics and density modelling: Geodynamic speculations

A 3D model of deep crustal structure of the Archaean Karelia Craton and late Palaeoproterozoic Svecofennian Accretionary Orogen including the boundary zone is presented. The model is based on the combination of data from geological mapping and reflection seismic studies, along profiles 1-EU, 4B, FIRE-1-2a-2 and FIRE-3-3a, and uses results of magnetotelluric soundings in southern Finland and northern Karelia. A seismogeological model of the crust and crust–mantle boundary is compared with a model of subhorizontal velocity-density layering of the crust. The TTG-type crust of the Palaeoarchaean and Mesoarchaean microcontinents within the Karelia Craton and the Belomorian Province are separated by gently dipping greenstone belts, at least some of which are palaeosutures. The structure of the crust was determined mainly by Palaeoproterozoic tectonism in the intra-continental settings modified by a strong collisional compression at the end of the Palaeoproterozoic. New insights into structure, origin and evolution of the Svecofennian Orogen are provided. The accretionary complex is characterized by inclined tectonic layering: the tectonic sheets, ~15 ​km thick, are composed of volcanic-sedimentary rocks, including electro-conductive graphite-bearing sedimentary rocks, and electro-resistive granitoids, which plunge monotonously and consecutively eastward. Upon reaching the level of the lower crust, the tectonic sheets of the accretionary complex lose their distinct outlines. In the seismic reflection pattern they are replaced by a uniform acoustically translucent medium, where separate sheets can only be traced fragmentarily. The crust–mantle boundary bears a diffuse character: the transition from crust to mantle is recorded by the disappearance of the vaguely drawn boundaries of the tectonic sheets and in the gradual transition of acoustically homogeneous and translucent lower crust into transparent mantle. Under the effect of endogenic heat flow, the accretionary complex underwent high-temperature metamorphism and partial melting. Blurring of the rock contacts, which in the initial state created contrasts of acoustic impedance, was caused by partial melting and mixing of melts. The 3D model is used as a starting point for the evolutionary model of the Svecofennian Accretionary Orogen and for determination of its place in the history of the Palaeoproterozoic Lauro-Russian intracontinental orogeny, which encompassed a predominant part of the territory of Lauroscandia, a palaeocontinent combining North American and East European cratons. The model includes three stages in the evolution of the Lauro-Russian Orogen (~2.5, 2.2–2.1 and 1.95–1.87 ​Ga). The main feature of the Palaeoproterozoic evolution of the accretionary Svecofennian Orogen and Lauroscandia as a whole lay in the causal link with evolution of a superplume, which initiated plate-tectonic events. The Svecofennian–Pre-Labradorian palaeo-ocean originated in the superplume axial zone; the accretionary orogens were formed along both continental margins due to closure of the palaeo-ocean.     

Textural and chemical evolution of a fractionated granitic system: the Podlesí stock, Czech Republic

The Podlesí granite stock (Czech Republic) is a fractionated, peraluminous, F-, Li- and P-rich, and Sn, W, Nb, Ta-bearing rare-metal granite system. Its magmatic evolution involved processes typical of intrusions related to porphyry type deposits (explosive breccia, comb layers), rare-metal granites (stockscheider), and rare metal pegmatites (extreme F–P–Li enrichment, Nb–Ta–Sn minerals, layering). Geological, textural and mineralogical data suggest that the Podlesí granites evolved from fractionated granitic melt progressively enriched in H₂O, F, P, Li, etc. Quartz, K-feldspar, Fe–Li mica and topaz bear evidence of multistage crystallization that alternated with episodes of resorption. Changes in chemical composition between individual crystal zones and/or populations provide evidence of chemical evolution of the melt. Variations in rock textures mirror changes in the pressure and temperature conditions of crystallization. Equilibrium crystallization was interrupted several times by opening of the system and the consequent adiabatic decrease of pressure and temperature resulted in episodes of nonequilibrium crystallization. The Podlesí granites demonstrate that adiabatic fluctuation of pressure (“swinging eutectic”) and boundary-layer crystallization of undercooled melt can explain magmatic layering and unidirectional solidification textures (USTs) in highly fractionated granites.     

石渠－甘孜－雅江重力正异常带的特征及其地质意义

综合区域地质、岩石物性和航磁资料的分析，认为石渠－甘孜－雅江剩余布格重力正异常带可能是被“挤入”西康群之下、埋藏于深部的前古生代离散陆块与二叠纪玄武岩及“义敦群”存在的综合反映。该异常带的连续延伸，说明甘孜－理塘构造带南段的主体部分已由北西转至南西走向。该重力异常带位置是重要而明显的构造分区界线。     

攀西地区基性-超基性岩地球化学及嵌套韵律层的分形动力学研究

攀西地区层状基性 -超基性岩体从下到上具有套叠式韵律结构的特征 ,这种韵律由岩石的颜色、矿物的成分、结构等表征。在长期的地球重力作用下 ,物质的液态分异或固相结晶分异为层状岩体韵律成因的关键。提出用类似于 Cantor分形集合法构筑重力分异时空分形集合 ,结果以色谱条带图和直方图表达 ,并与攀枝花层状岩体的野外岩石观察的颜色韵律以及岩体实测的矿物成分、长石的 An号码进行了对比 ,表明岩体实测数据与构筑的重力分异时空分形理论图式很相似 ,揭示了攀西层状基性 -超基性岩体的套叠式韵律结构在成因上具有时空分形的特征     

基于地壳分层的唐山地震断层震后变形分析

本文利用球体粘弹性地球模型研究唐山地震断层基于地壳分层的震后变形影响，计算四种不同类型的地球分层模型（均匀模型和三种地壳分层模型）产生的震后变形场，分析不同模型对地表变形的影响异同，定量研究了实际地壳分层模型与均匀地壳模型计算的地表变形差异.计算结果显示，相对均匀粘弹性地球模型，利用分层的地壳结构模型，计算的唐山地震断层附近区域震后28年积累的变形，两者最大差值水平方向可达20mm，垂直变形相差10mm左右.计算的结果显示地壳结构的差异对震后地表变形的影响很大，超过现有高精度测量技术的精度.如果利用该区的实测资料进行反演研究，必须根据实际地壳构造情况考虑地壳分层的影响.