Geological characteristics and tectonic signifcance of unconformities in Mesoproterozoic successions in the northern margin of the North China Block     

Yongqiang Qu  Jianguo Pan  Shouxian Ma  Zhiping Lei  Lin Li  Guoli Wu 《地学前缘(英文版)》2014,(1)

Several stratigraphic breaks and unconformities exist in the Mesoproterozoic successions in the northern margin of the North China Block.Geologic characters and spatial distributions of fve of these unconformities,which have resulted from different geological processes,have been studied.The unconformity beneath the Dahongyu Formation is interpreted as a breakup unconformity,representing the time of transition from continental rift to passive continental margin.The unconformities beneath the Gaoyuzhuang and the Yangzhuang formations are considered to be the consequence of regional eustatic fuctuations,leading to the exposure of highlands in passive margins during low sea-level stands and transgressive deposition on coastal regions during high sea-level stands.The unconformity atop the Tieling Formation might be caused by uplift due to contractional deformation in a back-arc setting,whereas the uplift after the deposition of the Xiamaling Formation might be attributed to a continental collision event.It is assumed that the occurrences of these unconformities in the Mesoproterozoic successions in the northern margin of the North China Block had a close bearing on the assemblage and breakup of the Columbia and Rodinia supercontinents.  相似文献   

Comparison of marine gas hydrates in sediments of an active and passive continental margin     

Keith A. Kvenvolden 《Marine and Petroleum Geology》1985,2(1):65-71

Two sites of the Deep Sea Drilling Project in contrasting geologic settings provide a basis for comparison of the geochemical conditions associated with marine gas hydrates in continental margin sediments. Site 533 is located at 3191 m water depth on a spit-like extension of the continental rise on a passive margin in the Atlantic Ocean. Site 568, at 2031 m water depth, is in upper slope sediment of an active accretionary margin in the Pacific Ocean. Both sites are characterized by high rates of sedimentation, and the organic carbon contents of these sediments generally exceed 0.5%. Anomalous seismic reflections that transgress sedimentary structures and parallel the seafloor, suggested the presence of gas hydrates at both sites, and, during coring, small samples of gas hydrate were recovered at subbottom depths of 238m (Site 533) and 404 m (Site 568). The principal gaseous components of the gas hydrates wer methane, ethane, and CO₂. Residual methane in sediments at both sites usually exceeded 10 mll^?1 of wet sediment. Carbon isotopic compositions of methane, CO₂, and ΣCO₂ followed parallel trends with depth, suggesting that methane formed mainly as a result of biological reduction of oxidized carbon. Salinity of pore waters decreased with depth, a likely result of gas hydrate formation. These geochemical characteristics define some of the conditions associated with the occurrence of gas hydrates formed by in situ processes in continental margin sediments.  相似文献   

Slumping and shallow faulting related to the presence of salt on the Continental Slope and Rise off North Carolina     

K.V. Cashman  P. Popenoe 《Marine and Petroleum Geology》1985,2(3):260-271

Seismic reflection profiles and long- and medium-range sidescan sonar were used to investigate a salt diapir complex and area of slope instability near the base of the Continental Slope off North Carolina. Within the area of investigation three diapirs are bounded on their upslope side by a scarp 60 m high and 50 km long. The slope above the scarp is characterized by a series of shallow rotational normal faults. The bottom below the scarp is furrowed by slide tracks, which were probably carved by large blocks that broke off the scarp face and slid downslope leaving rubble and scree lobes.Extensive slumping in this area appears to be a result of uplift and faulting associated with salt intrusion, which has fractured and oversteepened the slope leading to instability and failure. Sharply defined slide tracks suggest that slope failure above the breached diapir complex is a continuing process, in contrast to much of the surrounding slope area where few instability features were observed.  相似文献   

The Cenozoic Volcanoes in Northeast China     

LIU Jiaqi  Han Jingtai  GUO ZhengFu 《世界地质(英文版)》2002,5(1)

There are more than 600 Cenozoic volcanic cones and craters with abeut 50 000 km2of lava flows in northeast China, which formed many volcanic clusters and shown the features of the continental rift - type volcanoes. Most volcanic activities in this area, especially in the east part of Songliao graben, were usually controlled by rifts and faults with the main direction of NE / NNE in parallel and become younger from the central graben towards its both sides, especially to the east continental margin. It is revealed that the volcanism occurred in northeast China was as strong as that occurred in Japan during the Miocene and the Quaternary. The Quaternary basalt that is usually distributed along river valley is called "valley basalt"while Neogene basalt usually distributed in the top of mounts is called "high position basalt". These volcanoes and volcanic rocks are usually composed of alkaline basalts with ultramafic inclusions, except Changbaishan volcano that is built by trachyte and pantellerite.  相似文献   

新亚欧大陆桥(河南段)经济带地下水资源形势的研究     

温彦 《河南国土资源》1999,(1)

新亚欧大陆桥,是又一条连接亚欧大陆的“黄金通道”。陆桥的开通,给河南城市群的崛起和城乡产业经济的发展带来了契机。作为经济可持续发展限制因素之一的地下水资源,在陆桥（河南段）经济带范围内,能否满足沿线经济对地下水的需求？研究结论是：地下水形势不容乐观,潜力尚有８７×１０８ｍ３／ａ,同时还存在超采量３８８×１０８ｍ３／ａ,城乡开发地下水强度不一,已引发多种环境地质问题,对陆桥（河南段）经济带的发展构成了严重威胁。为缓和陆桥（河南段）沿线用水矛盾,必须遵循“因地制宜,量水为出,适度开发,统一规划”的原则,在开源、节流、管理上做好用水文章,充分发挥地下水资源的整体效益,实现陆桥（河南段）经济带地下水的可持续开发利用。  相似文献   

大陆下地壳的研究进展综述   总被引：3，自引：0，他引：3  

孔华  谢窦克 《地球物理学进展》1998,13(4):9-22

大陆下地壳对认识整个地壳的组成演化具有重要意义,对大陆下地壳的研究正在世界范围蓬勃开展,大陆下地壳的研究基于两个方面：一是太古代地壳剖面的研究,二是麻粒岩包体的研究,相比较而言后者的研究程度要难得多,下地壳包体出露少,成分多为麻粒岩,且无一例外地都含有基性麻粒岩,对其成因现基本趋于一致认识,即由幔源岩浆底侵至地壳再受变质而成,然后被火山作用带至地表,因此,基性麻粒岩包体更可能反映了现今大陆下地壳的  相似文献   

德国大陆科学钻探的地壳流体研究   总被引：3，自引：0，他引：3  

张泽明 《地质科技情报》1998,17(2):7-12

简要地介绍了德国大陆科学钻探过程中壳流体的开发成果,以及与流体研究相关的某些问题。德国两个大陆科学钻孔提供了可达９１９１ｍ深结晶基底中古流体和现代流体样品,以及它们留在矿物和岩石化学、同位素成分上的指纹。据此,再以再造地壳流体的时空分布、化学成分、迁移途径、源区和演化过程。  相似文献   

大陆造山带基底岩块中的基性岩墙群研究——以南秦岭武当地块为例   总被引：12，自引：0，他引：12  

周鼎武  张成立  刘颖宇 《地球科学进展》1998,13(2):151-156

基性岩墙群是大陆和大陆造山带内发育的特殊地质体,包含丰富的地球动力学信息。造山带内基底岩块是造山作用过程卷入造山带的外来或原地地块（陆块）,基底岩块中基性岩墙群的发育及其变形、变质特征,既为造山带内存在古老陆块和古陆块的裂离提供了证据,也为造山过程的构造动力学研究提供了重要信息。加强造山带基底岩块中基性岩墙群的多学科综合研究,对于探讨大陆造山带的形成、演化及其动力学过程具重要意义。  相似文献   

Composition and pre-metamorphic geodynamic setting of the ultrahigh-pressure metabasic rocks from Dabie Shan,E-China     

U. Altenberger  R. Schmid  R. Oberhänsli 《International Journal of Earth Sciences》2008,97(6):1301-1314

As part of the Yangtze plate, segments of the Dabie Shan terrane of Central China underwent ultra-high pressure metamorphism during Triassic subduction. We studied the geochemistry of the abundant eclogites to evaluate the nature of the protoliths and their geodynamic setting. Although some previous geochemical work exists, the analyses and interpretation herein are based on a new subdivision of the ultra-high pressure sequence into basement and cover units (Changpu and Ganghe Unit), revealing new and important results. In addition, eclogites of the so-called HP Unit south of the UHP units were studied. Whereas the large ion lithophile elements indicate postmagmatic, metasomatic changes of some samples, the high-field strength elements and the rare earth elements display original magmatic trends. The geochemical characteristics of the eclogites of the ultra-high pressure areas display a strong dependence on their “structural” and geographic position. The eclogites of the basement and the Changpu Unit indicate melt intrusion and extrusion in a continental rift system, i.e. during extensional tectonics. In contrast, the Ganghe Unit is characterized by a pronounced chemical homogeneity. The composition of the eclogites indicates generation from a mantle source highly influenced by slab-derived fluids. Those of the HP Unit show similar characteristics. Magmatism of the Ganghe and HP Unit probably occurred in a continental arc setting. A similar age for both units, geographically and/or tectonically separated, is possible. The geodynamic interpretation based on the geochemistry of the four units points to a Neoproterozoic scenario in which the protoliths of the HP and the cover units could have been of similar age and deposited in one evolving geological system. A rift-related larger-scale basin might have formed, e.g. a continental back-arc basin behind a magmatic arc after or simultaneous to sedimentation and magmatism in the magmatic arc. Alternatively, magmatism occurred in independent geodynamic settings, distinct in time and space. The units were juxtaposed during exhumation, after subduction to varying depths.  相似文献   

滇西点苍山—哀牢山变质岩系锆石SHRIMP定年及其地质意义   总被引：21，自引：14，他引：7  

李宝龙  季建清  付孝悦  龚俊峰  宋彪  庆建春  张臣 《岩石学报》2008,24(10):2322-2330

滇西点苍山和哀牢山主体分别由下元古界苍山群和哀牢山群深变质岩系组成,被认为是前寒武纪结晶基底。选取点苍山的花岗闪长质糜棱岩(DCS-1)和哀牢山元江段黑云母花岗闪长质片麻岩(SM07-1)之中的锆石进行U-Pb SHRIMP定年。样品DCS-1和SM07-1测年结果分别为233±2.6Ma和239.8±2.8Ma。结合前人对滇西地区花岗质岩类所做的研究,揭示滇西地区在三叠纪经历一期在空间上广泛分布的岩浆事件,点苍山花岗质糜棱岩和哀牢山花岗质片麻岩的原岩为三叠纪侵位的花岗岩,其构造环境属于大陆裂谷,反映了滇西地区在三叠纪地壳物质的重新调整,而该变质岩系不是前寒武纪的结晶基底,其变质作用与山体出露地表过程和新生代构造作用有关。  相似文献