利用长周期面波研究华北地区地壳与上地幔结构的横向非均匀性

本文以太行山为界将华北地区分为东西两部分,东部为河淮块体,西部为鄂尔多斯块体.利用最小二乘法,从混合路径基阶瑞利面波群速度频散提取两块体的纯路径频散,并反演其地壳、上地幔的层状结构.所得结表果明,两块体的面波频散和地壳、上地幔结构存在明显差异.东部的河淮块体地壳较薄,地壳内平均速度比西部的鄂尔多斯块体壳内平均速度约低0.13km/s,壳内20km深度左右出现低速层;而西部的块体壳内速度成层递增,未见低速层出现.两块体上地幔顶部速度均偏低,地幔低速层的埋藏深度基本相同.但西部块体地幔低速层厚,且比东部块体地幔低速层的速度约低0.3km/s.     

湖北襄樊—福建罗源的大地电磁测量与地壳上地幔电性特征研究

湖北襄樊—福建罗源一千多公里的剖面上作了23个大地电磁测深点。该剖面穿过不同的地质构造单元。 大地电磁测深的结果清楚地反映了剖面内地壳和上地幔的电性结构特征。例如构造单元的形态、边界、断层位置、地壳和上地幔的高导层发育情况等。结果对于了解该区的深部构造背景、探讨深浅构造之间的关系提供了有益信息     

变粘滞度地幔蠕动流的数学模型研究及其应用(二)

本文首先讨论了计算中的有关问题,然后分析了用前篇文章(刘代志,1988)中导出的计算公式,对中国及邻区(东经70°-140°,北纬15°-55°)岩石圈底部切向应力场的计算结果,探讨了其地质应用,特别是在地震危险区划中的应用。     

大陆裂谷区幔源矿物橄榄石在不同应变阶段的位错构造及位错滑移系研究——以法国中央地块及中国汉诺坝新生代玄武岩的二辉橄榄岩包体为例

利用透射电子显微术(TEM)对两个新生代裂谷区的碱性玄武岩(法国中央地块克莱蒙菲朗及中朝板块北部河北万全)中幔源矿物橄榄石的位错亚构造进行研究,通过位错类型、衍射花样、柏格斯矢量及位错滑移系的分析及计算,判断了深源包体从上地幔进入地壳的动力学过程——经历了高温(>1000℃)蠕变、低温(<600℃—800℃)应变及后期局部温度回升阶段,确定了高温滑移系以{OKl}[100]及(001)[100]为主,并存在由(010)[001]及(100)[001)滑移系组成的高温位错网络,计算了低温应变的滑移系为(110)[001]及(010)[001]。     

Analysis and automatic processing in near-field of eight 1992–1994 tsunamigenic earthquakes: Improvements towards real-time tsunami warning

We study eight tsunamigenic earthquakes of 1992–1994 with data from single near-field 3-component long-period stations. The analysis is made from the standpoint of tsunami warning by an automatic process which estimates the epicentral location and the seismic moment through the variable-period mantle magnitudeM _m . Simulations of early warning based on the real-time computation of the seismic moment are also tested with this system, which would give a justified warning in each region of tsunami potentiality. By exploiting the dependence of moment rate release with frequency, the system has the capability of recognizing both tsunami earthquakes such as the 1992 Nicaragua and 1994 Java events, as well as instances of the opposite case of low-frequency deficiency, interpreted as indicating a deeper than normal source (1993 Guam event). We report both the results of delayed-time processing of the near-field stations, and the actual real-time warnings at PPT, which confirm the former.     

Travel time tomography inversion and the deep structure of the southern Tibet

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试论华北地台中生代超变质作用与地幔热柱作用

本文通过冀西北、胶东等金矿富集区“太古宙”高级变质地体中生代金矿化、变质核杂岩构造、花岗岩、碱性岩等问题的讨论,认为中生代强烈而广泛的混合岩化、花岗岩化、流变“片麻岩”化等超变质作用,是华北地台太古宙高级变质地体变质程度深、同一地质体同位素年龄数据相差悬殊、中生代强烈岩浆活动等异常地质现象的重要原因之一。它既是华北地台活化的重要深部地质作用,亦是深部“去根作用”的具体体现。而中生代地幔热柱作用又是用变质作用、变质核杂岩构造、金矿成矿作用的深部机制,也是华北地台中生代活化的根本原因所在。     

Early Holocene shore displacement and evidence of irregular isostatic uplift northwest of Lake Vänern, western Sweden

In the 1920's the Swedish geologist Lennart von Post found evidence of irregular early Holocene isostatic uplift in the region northwest of Lake Vänern in western Sweden. von Post based his conclusions on levellings of ancient shore lines. These were indirectly dated by pollen stratigraphical investigations in basins situated at approximately the same altitudes as the shore lines. To test von Post's hypothesis, we have adopted a different methodological approach. The sediments in twelve small lake basins, within five minor areas in this region, have been investigated with respect to when they became isolated from ancient Lake Vänern. Initially all the lake thresholds were levelled. Altitudes range between 165 and 96 m above sea level. By combining the results of mineral magnetic and diatom stratigraphical analyses it has been possible to determine the level in the sediment when the basin became isolated. The ¹⁴C age of this isolation level has been inferred from AMS dates based on the NaOH-soluble fraction of bulk sediment, partly with very low organic content. Altogether, 36 radiocarbon datings have been carried out, ranging from 10080 to 8800 ¹⁴C years BP. Pollen analyses, and subsequent correspondence analysis (CA) of all pollen spectra, were carried out around the isolation level in each basin as a complement to the AMS datings.If the region had been subject to irregular isostatic uplift, lakes at the same altitude in the five areas should have been isolated at different times. The AMS determined isolation ages, corrected according to CA of the pollen stratigraphy and compensated for the relatively higher rebound of the northerly situated sites support von Post's conclusion, from the beginning of this century, that the region northwest of Lake Vänern has been subjected to irregular isostatic uplift.     

热液烃的生成与深部油气藏

热液烃不仅分布于洋底,在大陆也有广泛分布,实验表明:热液对碳酸盐岩和沉积有机质的作用均有油气生成;洋底火山岩流体包裹体、原油、有机质Pb、Sr、Nd同位素均表明地幔流体在油气生成中的作用。认识热液烃的存在对开拓深部油气藏的勘探有重要意义。     

大兴安岭北段新林区塔木兰沟组火山岩成因及地幔富集作用

本文报道了大兴安岭北段新林区塔木兰沟组玄武岩样品锆石U-Pb定年结果和岩石地球化学分析,探讨了塔木兰沟组玄武岩的成因及中生代岩石圈地幔的性质。锆石U-Pb定年结果显示,塔木兰沟组玄武岩形成于晚侏罗世(~153Ma),该玄武岩样品的SiO_2含量介于49.96%~59.06%之间,全碱含量介于5.21%~7.44%之间,Mg~#{100×n(Mg~(2+))/[(n(Mg~(2+))+n(Fe~(2+))]}值介于50~94之间。该玄武岩相对富集轻稀土元素(LREEs)、亏损重稀土元素(HREEs),La_N/Yb_N值介于10.7~20.0之间,具有轻微的Eu异常(δEu=0.80~1.09),结合区域研究成果,认为塔木兰沟组玄武岩形成于蒙古—鄂霍茨克洋闭合造山后岩石圈伸展环境,源区岩浆起源于石榴子石相二辉橄榄岩与尖晶石相二辉橄榄岩部分熔融的混合形成,含富含挥发分的金云母和角闪石等,暗示岩石圈地幔经历了交代作用的改造,交代类型以俯冲板片流体/熔体交代为主。结合区域已有研究表明,本区地幔交代富集作用来源于蒙古—鄂霍茨克洋的向南俯冲,塔木兰沟组火山岩形成于蒙古~鄂霍茨克洋闭合造山后岩石圈伸展背景。