Present-day stress field and deformation in eastern Austria

 We analysed fault plane solutions and borehole breakouts in the eastern part of the Eastern Alps and found a heterogeneous stress field which we interpret as a transition zone of three different stress provinces: the western European stress province with NW to NNW S_H orientation and mainly strike-slip faulting regime; the Adriatic stress province with a radial stress pattern and thrust faulting to strike-slip faulting regime; and the Dinaric-Pannonian stress province with NE S_H orientation and strike-slip faulting regime. The western Pannonian basin seems to be a part of the transition zone with WNW to NW S_H orientation. A stress regime stimulating strike-slip faulting prevails in the Eastern Alps. The south Bohemian basement spur as a major tectonic structure with a high rheological contrast to surrounding units has a strong influence on the stress field and exhibits the highest seismicity at its tip due to stress concentration. From a constructed vertical stress orientation profile we found stress decoupling of the Northern Calcareous Alps from the underlying European foreland. Both the Molasse and the Flysch-Helvetic zone are considered as candidates for decoupling horizons due to stress orientation observations and due to their rheological behaviour. From seismological and rheological data, we suggest a horizontal stress decoupling across the Eastern Alps caused by a weakened central Alpine lithosphere. Received: 3 July 1998 / Accepted: 4 April 1999     

塔北隆起-库车坳陷区中新生代基底-盖层构造变形机理

利用三维建模软件获取了塔北隆起—库车坳陷区现今及不同时期基底构造格局,为基底构造分析提供了新的技术方法。研究表明,三叠纪—古近纪,塔里木盆地北部块体的基底构造基本处于稳定状态,基底-盖层构造变形不明显;新近纪,克拉苏背斜带以北的塔里木盆地基底明显向天山倾斜,库车基底俯冲变形导致基底转折带逐渐向南迁移,库车前陆盆地形成;第四纪时期,库车-拜城盆地的基底整体向天山下倾斜,基底构造的强转折带迁移到塔北隆起带;新近纪以来库车坳陷的基底转折期与塔北隆起盖层的负反转构造形成期在时间上一致,在空间上,库车坳陷的基底在强烈沉降俯冲的同时,相邻塔北隆起的基底相对隆起,形成库车新生代前陆盆地的前隆;库车前陆冲断带的形成是在库车基底斜坡上伴随天山的推覆而形成的;塔北隆起为库车前陆盆地的前隆,基底俯冲变形及其转折带迁移导致塔北隆起盖层负反转构造的形成。     

合肥地区地热资源潜力评价

地热资源是宝贵的矿产资源,是一种可再生的,优质、环保、清洁能源。合肥是安徽省省会,经济持续快速发展对清洁地热能源的需求不断增长。据有关资料,合肥地区地处莫霍面隆起区,地壳减薄上地幔隆起是合肥地区地温相对高的大的区域地质背景。合肥西,五十里小庙凸起(合肥地区地垒地段)是基底隆起聚热型地热地质成因模式形成地热的有利地段,可作为今后合肥地区地热资源地质勘查的第一靶区。合肥地区的大地构造环境和深部地壳结构对成热条件较为有利,地热资源的潜力较大。     

柴达木周缘印支期花岗岩同位素地球化学特征及其对基底属性的制约

花岗岩同位素地球化学是探讨块体基底属性的重要手段,柴达木和欧龙布鲁克地块中两印支期岩体(香日德岩体和察汉诺岩体)的主量元素、微量元素和Pb-Sr-Nd同位素研究表明,两岩体均属过铝质花岗岩,具相似的微量元素(包括稀土元素)组成模式,Sr-Nd同位素特征显示轻微的不均一性,(87 Sr/86 Sr)t=0.708 46-0.712 89,End(t)=-5.54--7.80,tDM=1.49-1.68 Ga,两个岩体以高放射成因铅为特征,初始铅同位素比值为:(206 Pb/204 Pb)t=18.326-18.644,(207 Pb/204 Pb):=15.560-15.693,(208 Pb/204 Pb)t=38.172-38.549.岩体地球化学特征与基底变质岩显示岩浆派生于中元古代的基底岩石的部分熔融.两岩体与西秦岭花岗岩类Nd-Pb同位素特征对比表明,柴达木和欧龙布鲁克地块基底性质与西秦岭一样,具扬子块体的构造属性.     

岩土体变形破坏机制及井筒破裂模式

以淮北临涣矿区为例,在详细调查分析了破裂井筒的矿井水文地质与工程地质条件及其它背景资料的基础上,根据矿区底含土体及煤系基岩风化带变形破坏的影响因素及形成过程,本文首次论论了岩土体变形破坏的四个发展阶段和井筒破裂的四种模式及其间的关系,并揭示了井筒破裂的,从而为防治井筒破裂和评价井筒稳定性提供了依据。     

银根-额济纳旗盆地航磁反映的构造特征

根据航磁资料,分析和研究银根-额济纳旗盆地的区域构造特征及其演化,同时确定了该区北东向断裂的存在,并探讨该组断裂的发生发展对区域构造的作用.     

南冲绳海槽及其邻域的磁性基底与地壳结构

研究区域的基底断裂构造十分发育。EW、NEE和NE向基底大断裂宏观上构成和控制区域地质构造的基本格架;NS、NNW和NW向断裂多为张扭性平移断层,它们对基本格架起强烈的分割破坏和错断作用,形成和控制次一级区域差异性的构造运动和岩浆活动特征。东海陆架边缘隆起带磁性基底埋深一般为3～4km.基底由前中新世变质岩系及不同时期形成的火成岩类组成。地壳厚度为24-28km,为大陆地壳。南冲绳海槽盆地磁性基底埋深一般为5～7km,可划分出4个次一级盆地。基底极可能由前中新世以来海槽张裂运动所形成的玄武岩层或部分变质岩系组成,靠近陆坡坡脚处可能包括前第三纪的老地层。地壳厚度为15～20km,地壳为亚大洋型。     

东海西湖凹陷北部基底构造特征

根据最新的重磁资料,反演了西湖凹陷北部的基底深度,推断解释了火成岩和断裂构造,结合相关地质和构造方面资料,对西湖凹陷北部基底性质和基底构造特征进行了分析,深化了对西湖凹陷北部基底构造特征的认识。研究认为,区内的断裂构造主要由NE向和NW向两组断裂构成。NE向的断裂主要为年代较老的大断裂,它们在构造上被NW向的断裂错断,并被NW向断层复杂化;西湖凹陷的火成岩比较发育,火成岩主要沿着大的断裂带以及断裂带的两侧分布,形成许多串珠状的火成岩带。岩浆岩的分布受断裂控制明显,尤其是在NE向断裂与NW向断裂交汇处,更是岩浆活动的主要地区;西湖凹陷北部的古新近系基底构造主体走向为NE向,但明显受NW向断裂的改造,形成东西分带、南北分块的构造特征。西湖凹陷基底构造起伏较大,绝大部分的基底深度都在5000m以下,总体上呈南高北低、凸凹相间分布,由东到西分别为保俶斜坡、三潭深凹、浙东中央背斜带、白堤深凹和天屏冲断带5个次级构造单元。     

Reinterpretation of the northern South China Sea pre-Cenozoic basement and geodynamic implications of the South China continent: constraints from combined geological and geophysical records

The pre-Cenozoic northern South China Sea(SCS) Basin basement was supposed to exist as a complex of heterogeneous segments, divided by dozens of N-S faulting. Unfortunately, only the Hainan Island and the northeastern SCS region were modestly dated while the extensive basement remains roughly postulated by limited geophysical data. This study presents a systematic analysis including U-Pb geochronology, elemental geochemistry and petrographic identification on granite and meta-clastic borehole samples from several key areas. Constrained from gravity-magnetic joint inversion, this interpretation will be of great significance revealing the tectono-magmatic evolution along the southeastern margin of the Eurasian Plate. Beneath the thick Cenozoic sediments, the northern SCS is composed of a uniform Mesozoic basement while the Precambrian rocks are only constricted along the Red River Fault Zone. Further eastern part of the northern SCS below the Cenozoic succession was widely intruded by granites with Jurassic-to-early Cretaceous ages. Further western part, on the other hand, is represented by meta-sedimentary rocks with relatively sporadic granite complexes. To be noted,the western areas derived higher-degree and wider metamorphic zones, which is in contrast with the lowerdegree and narrower metamorphic belt developed in the eastern region. Drastic collisions between the Indochina Block and South China continent took place since at least late Triassic, resulting in large-scale suturing and deformation zones. At the westernmost part of the northern SCS, the intracontinental amalgamation with closure of the Meso-Tethys has caused fairly stronger and broader metamorphism. One metamorphic biotite granite is located on the suturing belt and yields a Precambrian U-Pb age. It likely represents the relict from the ancient Gondwana supercontinent or its fringes. Arc-continental collision between the Paleo-Pacific and the southeast China Block, on the other hand, results in a relatively narrow NE–SW trending metamorphic belt during the late Mesozoic. Within the overall geological setting, the Cenozoic SCS oceanic basin was subsequently generated from a series of rifting and faulting processes along the collisional-accretionary continental margin.     

Zircon U-Pb geochronology,Hf isotopes,and geochemistry constraints on the age and tectonic affinity of the basement granitoids from the Qiongdongnan Basin,northern South China Sea

Studies in the northern South China Sea(SCS) basement remain important for understanding the evolution of the Southeast Asian continental margin. Due to a thick cover of sediments and scarce borehole penetration, little is known about the age and tectonic affinity of this basement. In this study, an integrated study of zircon U-Pb geochronology, Hf isotopes, and whole-rock major and trace elements on seven basement granitoids from seven boreholes of Qiongdongnan Basin has been carried out. New z...