Jurassic Dextral and Cretaceous Sinistral Movements Along the Hida Marginal Belt     

Kazuhiro Tsukada 《Gondwana Research》2003,6(4):687-698

The Hida marginal belt (HMB), which consists of various kinds of fault-bound blocks, is located between the continental massif of the Hida belt and the Mesozoic accretionary complex of the Mino belt in Central Japan. Detailed field investigation reveals that the HMB had grown through the two different movements, i.e., Jurassic dextral and Cretaceous sinistral movements. The Jurassic dextral ductile shear zones run in the southern marginal part of the Hida belt and the northern part of the HMB, whereas the Cretaceous sinistral cataclastic shear zones occur in the southern part of the HMB and the northern marginal part of the Mino belt. Geologic map and field evidence seem to suggest that the Jurassic dextral movement form the fault-bound blocks of the HMB to form the basic structure of the Hida marginal belt, i.e., formation of the ‘proto-HMB.’ Following the dextral movement, the sinistral one restructured the ‘proto-HMB’ to complete the present feature of the Hida marginal belt. The Cretaceous sinistral movement might result in the sinistral collision between the proto-HMB and the Mino belt.  相似文献   

A Case Study Of An On-Ice Air Flow Over The Arctic Marginal Sea-Ice Zone     

Timo Vihma  Jörg Hartmann  Christof Lüpkes 《Boundary-Layer Meteorology》2003,107(1):189-217

A case study of warm air advection over the Arctic marginalsea-ice zone is presented, based on aircraft observations with direct flux measurements carriedout in early spring, 1998. A shallow atmospheric boundary layer (ABL) was observed, which wasgradually cooling with distance downwind of the ice edge. This process was mainly connected with astrong stable stratification and downward turbulent heat fluxes of about 10–20 W m^-2, but wasalso due to radiative cooling. Two mesoscale models, one hydrostatic and the other non-hydrostatic,having different turbulence closures, were applied. Despite these fundamental differences betweenthe models, the results of both agreed well with the observed data. Various closure assumptions had amore crucial influence on the results than the differences between the models.Such an assumption was, for example,the parameterization of the surface roughness for momentum (z₀) and heat (z_T). This stronglyaffected the wind and temperature fields not only close to the surface but also within and abovethe temperature inversion layer. The best results were achieved using a formulation for z₀ that took intoaccount the form drag effect of sea-ice ridges together withz_T = 0.1z₀. The stability within theelevated inversion strongly depended on the minimum eddy diffusivity K_min. A simple ad hocparameterization seems applicable, where K_min is calculated as 0.005 timesthe neutral eddy diffusivity. Although the longwave radiative cooling was largest within the ABL, theapplication of a radiation scheme was less important there than above the ABL. This was related to theinteraction of the turbulent and radiative fluxes. To reproduce the strong inversion, it wasnecessary to use vertical and horizontal resolutions higher than those applied in most regional andlarge-scale atmospheric models.  相似文献   

武宁陆相红盆沉积特征与演化浅析     

邹国庆 《江西地质科技》1997,24(2):79-85

本文依据1:5万区调资料,扼要介绍了武宁陆相红盆填图单位的拟定、表示方法及工作原理的应用,重点叙述了红盆内多个冲积扇体特征及其之间的叠覆关系,阐明了盆缘断裂是控制红盆成生、发展演化的主导因素。对红盆成生及演化、时代也作了初步探讨。  相似文献   

泰和盆地构造和演化初探     

王迪文  龙天 《江西地质科技》1997,24(4):165-169

我国大部分地区的小新生代盆地的成生、演化受断裂构造的控制,泰和盆地即是严格受断裂构造控制的走滑拉张型盆地。本文着重从盆地的基底构造、盆缘断裂构造及盆地同生、后期构造阐述了它们与盆地形成和演化的关系。  相似文献   

东亚陆缘扩张带──一条离散式大陆边缘成因的探讨   总被引：19，自引：11，他引：19  

陈国达 《大地构造与成矿学》1997,21(4):285-293

亚洲东部大陆边缘，介于大陆与大洋之间，存在着一条巨型的“沟弧盆”地带。该构造带的出现是亚洲大陆岩石圈演化－运动史上的重大事件之一，它的成因问题流行假说颇多，本文侧重从亚洲东部壳体演化运动历史背景的分析入手，探讨该构造带形成时期的历史动力环境，地壳结构及性质、壳体演化过程的特点，以及壳体增生扩展过程等，阐明了它是由于东亚陆缘扩张所成。并探讨了该陆线扩张带的形成与壳体演化运动的关系及其扩张机因。研究表明：亚洲陆缘扩张带的形成机理，并非“洋壳俯冲、弧后引张”所致。它们主要是陆缘壳体上的大陆类型活动区（华夏地洼型造山带），在其发展的余动期，由于陆缘扩张及陆壳薄化所致。作者认为，从壳体大地构造学这一新思路入手，对该陆缘扩张带成因的深入研究，有助于正确认识该大陆架上广泛分布的有色、稀有金属内生矿床，以及泥炭、褐煤、油气田的构造类型、特点、分布规律及其经济价值。  相似文献   

The Rotational Structure along the Eastern Segment of the Altyn Tagh Fault and Its Implications in Dynamics     

Wang Ping 《中国地震研究》2004,18(4):327-336

As a result of the left-lateral strike-slipping of the Altyn Tagh fault in Neotectonic period, a contra-rotational structure, namely the Zhaobishan vortex structure, has developed at the juncture of the main Altyn Tagh fault and the northern fringe fault of the Qilian Mountains.Preliminary analysis on the deformation and evolution of the Zhaobishan vortex structure. In combination with the previous data, suggests that the tectonic transform between the Altyn Tagh fault and the northern fringe fault of the Qilian Mountains attributes to the deformation of the rotational structure. The existence of a series of rotational structures along the Altyn Tagh fault and on the northeastern edge of the Qinghai-Xizang(Tibet) plateau indicate that as the substance in the northern Qinghal-Xizang (Tibet) plateau moves clockwise around the eastern tectonic knot of the Himalayas, rotational structures become the principal mode on the northern marginal zone of the Plateau of transforming and absorbing tectonic deformation.  相似文献   

Reefs at the edge: coral community structure around Rapa,southernmost French Polynesia          下载免费PDF全文

Mehdi Adjeroud  Carden C. Wallace  Pauline Bosserelle  Claude Payri  Jean‐Louis Menou  Michel Pichon 《Marine Ecology》2016,37(3):565-575

Rapa (27°36′ S, 144°20′ W) is a small (~40 km²) volcanic island isolated in the Southern Austral Archipelago, where direct anthropogenic stressors are extremely limited. Here, we present the results of the first quantitative survey of coral community structure across habitats and depths around the island. Despite its geographical isolation in the depauperate South Central Pacific, its small size and unfavourable environmental conditions (competition with macroalgae, low sea surface temperatures, reduced reef accretion), the diversity of scleractinian corals at Rapa is particularly high (112 species from 32 genera, including 37 species of Acropora) in comparison to other French Polynesian islands and subtropical Pacific locations. Our results indicate that the abundance (>100 colonies per 10 m² recorded at nine of the 17 sampling stations) and cover (>40% at four stations) of corals are relatively high for a marginal reef location. Strong spatial heterogeneity was found, with high variation in diversity, abundance, cover and community composition among stations. Variation in community composition was related to habitat types, with distinct assemblages among fringing reefs within bays, reef formations at bay entrances, and those on the submerged platform surrounding the island. On the platform, a depth gradient was detected, with generic richness, abundance and cover generally greater at deeper stations (18–20 m depth) compared with medium‐depth (10–12 m) and shallow (1–3 m) stations. A gradient was also recorded along bays, with increasing coral diversity and abundance from the bay heads to the bay entrances. The coral community at Rapa was characterized by the presence of several taxa not found in other French Polynesian archipelagos and the rarity of others that are common and abundant in the Society and the Tuamotu islands. Another distinctive feature of reef communities at Rapa is the high cover and dominance of macroalgae, particularly in the shallower parts of the surrounding platform, which probably explains the lower densities of coral colonies recorded there. These characteristics of the diversity and biogeographical composition of coral assemblages at Rapa provide considerable ecological grounds for its conservation.  相似文献   

A Comparative Study of the Coal‐forming Characteristics of Marginal Sea Basins and Epicontinental Sea Basins     

ZHAO Honggang  LI Ying  CHANG Xiangchun  LI Zengxue  LIU Haiyan  ZHAO Cunliang 《《地质学报》英文版》2021,95(1):121-130

The coal-forming characteristics,as well as the similarities and differences between epicontinental sea basins and continental marginal sea basins developed during different time periods,were analyzed in this study by adopting comparative analysis thoughts and methods.The results obtained in this study revealed that epicontinental basins and marginal sea basins are both characterized by the main development of thin coal seams or extremely thin coal seams.In addition,changes in sea levels were determined to be the main controlling factors for coal formation,and there were similarities in the continent-sea interactions and coal-forming sedimentary systems of the different basins.However,there were also significant differences observed in the sea level change events,basin basement structural characteristics,coal seam stability levels,accumulation and aggregation characteristics,and the migration patterns of coal-forming materials.For example,the marginal sea basins in the South China Sea were found to be characterized by strong tectonic activities,diversity and complexity.The basin structures showed complex patterns of depressions,uplifts and concave or sag uplifts,which tended to lead to greater complexity in the paleogeographic patterns of the coal formations.This had subsequently resulted in complex coal-forming processes and paleogeographic characteristics,in which the coal-forming zones displayed bead-like distributions,and the enrichment areas and centers were scattered.The practical significance of studying the similarities and differences of the coal-forming characteristics between epicontinental basins and marginal sea basins is that the results can potentially be used to guide the predictions of coal-measure coal seam distributions in South China Sea,as well as provide valuable guidance for future explorations of natural gas reservoirs related to coal measures in the South China Sea area.  相似文献   

唐古拉山侏罗系盖覆区空喀拉-温泉-澜沧江结合带鉴别标志     

张森琦 《地球科学与环境学报》2000,22(1)

结合带局部地段被与结合带演化密切伴生的各类盆地盖覆是各造山带中的一种普遍现象 ,因而初步将盖覆结合带的盆地划分为二类 :一是以边缘前陆盆地为代表的盖覆结合带而不破坏结合带的纵向盖覆性盆地 ;二是以横推断层盆地为代表的盖覆且破坏结合带的横向破坏性盆地。区内海相侏罗纪盆地实为与空喀拉温泉澜沧江结合带演化密切相关的盖覆结合带的陆内俯冲型边缘前陆盆地。深部地球物理探测资料证实了结合带在盖覆层之下仍存在 ,更说明结合带两侧板块构造建造对比明显有异 ,分属两类不同性质的大陆边缘 ,进而得出了结合带在研究区内潜伏于盖覆层之下的结论 ,从而建立了结合带存在的三方面的鉴别标志  相似文献   

北极薄冰-煎饼冰区域中不同重力波驱动形成海流的敏感性分析     

张雪妍  戴海瑨  赵军  殷何卿 《海洋学报(英文版)》2020,39(3):123-129

A coupled ocean-ice-wave model is used to study ice-edge jet and eddy genesis during surface gravity wave dissipation in a frazil-pancake ice zone. With observational data from the Beaufort Sea, possible wave dissipation processes are evaluated using sensitivity experiments. As wave energy dissipated, energy was transferred into ice floe through radiation stress. Later, energy was in turn transferred into current through ocean-ice interfacial stress. Since most of the wave energy is dissipated at the ice edge, ice-edge jets, which contained strong horizontal shear, appeared both in the ice zone and the ocean. Meanwhile, the wave propagation direction determines the velocity partition in the along-ice-edge and cross-ice-edge directions, which in turn determines the strength of the along-ice-edge jet and cross-ice-edge velocity. The momentum applied in the along-ice-edge(cross-ice-edge)direction increased(decreased) with larger incident angle, which is favorable condition for producing stronger mesoscale eddies, vice versa. The dissipation rate increases(decreases) with larger(smaller) wavenumber, which enhances(reduces) the jet strength and the strength of the mesoscale eddy. The strong along-ice-edge jet may extend to a deep layer(> 200 m). If the water depth is too shallow(e.g., 80 m), the jet may be largely dampened by bottom drag, and no visible mesoscale eddies are found. The results suggest that the bathymetry and incident wavenumber(magnitude and propagation direction) are important for wave-driven current and mesoscale eddy genesis.  相似文献