华北克拉通中部大陆地壳断面磁性结构研究及意义

为探讨华北克拉通中部地壳的磁性结构与深部地质过程之间的相互关系,测量了五台-集宁地壳剖面４４件岩石样品的磁性参量及磁滞回线．结合岩石学、地球化学及磁卫星资料的综合研究结果表明,整个断面具有明显的磁性分带结构特征．上地壳、中地壳与下地壳上部岩石饱和磁化强度（Ｊｓ）的平均值分别为５８．７Ａ／ｍ、６８１．２Ａ／ｍ与１０６８．０Ａ／ｍ,而饱和等温剩磁ＪＳＩＲＭ为４．１Ａ／ｍ、７７．９Ａ／ｍ和１３８.４Ａ／ｍ.磁性与变质相及成分对应分析显示,断面内的磁性结构主要受变质作用控制（尤其是变酸性岩与变基性岩）．Ｊｓ值的变异系数Ｖｃ,上地壳为６２．２％、中地壳为６２．５％、下地壳为１４３．７％,而ＪＳＩＲＭ值的变异系数则分别为７０７％、８６．１％、１６５.４％．中一下地壳之间Ｖｃ值的差异远大于上一中地壳,显示了地壳深部磁性强度的非均一分布特征．本区中一下地壳岩石的磁化强度明显高于秦岭造山带北缘的登封群与太华群,这一差异可能与两区地壳深部热结构的明显差异相关．结合磁卫星长波长磁异常分析推测,地壳断面中基性麻粒岩的磁性代表了区域下地壳的磁化强度,如果地壳深部的剩余磁性以热粘滞剩磁（ＴＶＲＴ）为主,则可估算出...     

Subsurface Temperature Changes Due to the Crustal Magmatic Activity – Numerical Simulation

Geothermal aspects of the hypothesis, relating the earthquake swarms in the West Bohemia/Vogtland seismoactive region to magmatic activity, are addressed. A simple 1-D geothermal model of the crust was used to assess the upper limit of the subsurface heating caused by magma intrusion at the assumed focal depth of 9 km. We simulated the process by solving the transient heat conduction equation numerically, considering the heat of magma crystallization to be gradually released in the temperature interval 1100°C to 900°C. The temperature field prior to the intrusion was in steady-state with a surface temperature of 10°C and heat flow of 80 mWm ^–2 , the temperature at the 9 km depth was 270°C. The results suggest that the temperature and heat flow in the uppermost 1 km of the crust begin to grow 100 ka after the intrusion emplacement only, and that the amplitudes of the changes for the realistic lateral extent (a few kilometres) of the intrusion are very small. It was also found that the rate of magma solidification depends strongly on the thickness of the intrusion. It takes about 100 years for a 50 m thick sill to cool down from 1100°C to 600°C, which value represents the lower limit of the solidus temperature. The same cooling takes only 60 days if the sill is 2 m thick. If the nature of the strongly reflected boundaries, interpreted from the January 1997 Nový Kostel seismograms, is connected with the fresh emplacement of magma, the calculated cooling rates have a predictive potential for the temporal changes of the waveforms.     

Simulation of liquefaction beneath an impermeable surface layer

A joint element is proposed, which can simulate the three phases of behaviour of an impermeable layer over a liquefied sand layer. The analysis tracks the post-liquefaction reconsolidation of the sand, the simultaneous development of a water film between the layers and the settlements resulting from the subsequent drainage of the water film. The element is incorporated in a finite element program, which can be used to simulate the behaviour of layered systems. The effectiveness of the program is demonstrated by simulation of the performance of a model soil deposit of two layers in a centrifuge test.     

Flow behaviour of the submarine glacigenic debris flows on the Bear Island Trough Mouth Fan, western Barents Sea

Using 3·5 kHz high-resolution seismic data, gravity cores and side-scan sonar imagery, the flow behaviour of submarine, glacigenic debris flows on the Bear Island Trough Mouth Fan, western Barents Sea was studied. During their downslope movement, the sediments within the uppermost part of the debris flows (<3 m) are inferred to have been deformed as a result of the shear stress at the debris–water interface. Thus, the uppermost part of the flow did not move downslope as a rigid plug. If present, a rigid part of the flow was located at least some metres below the surface. At c . 1000 to at least 1600 m water depth, the debris flows eroded and probably incorporated substrate debris. Further downslope, the debris flows moved passively over substrate sediments. The hypothesis of hydroplaning of the debris flow front may explain why the debris flows moved across the lower fan without affecting the underlying sediments. Detailed morphological information from the surface of one of the debris flow deposits reveals arcuate ridges. These features were probably formed by flow surge. Hydroplaning of the debris flow front may also explain the formation of flow surge. The long runout distance of some of the large debris flows could be due to accretion of material to the base of the debris flow, thereby increasing in volume during flow, and/or to hydroplaning suppressing deceleration of the flow.