Age, distribution, tectonics, and eustatic controls of the Paranense and Caribbean marine transgressions in southern Bolivia and Argentina     

R.M. Hernndez  T.E. Jordan  A. Dalenz Farjat  L. Echavarría  B.D. Idleman  J.H. Reynolds 《Journal of South American Earth Sciences》2005,19(4):495-512

Marine transgression onto the South American continent took place at least twice in the Miocene along distinct paleogeographic corridors. The first event occurred between 15 and 13 Ma and the second between 10 and 5? Ma. Each event has particular dominant variables (tectonism, eustacy, sediment accumulation rate) that permitted the preservation of the record and development of the sea on the continent. The 15–13 Ma transgression was tectonically and eustatically controlled, flooding older sedimentary accommodation zones on the South American plate during a global high sea level, whereas the 105? Ma event was predominantly tectonically controlled, generated by tectonic loading created in the Cordillera Oriental fold-and-thrust belt. A new 7.72±0.31 Ma ⁴⁰Ar/³⁹Ar date from the Río Parapetí in Bolivia suggests that the 15–13 Ma transgression registered in Argentina produced no continental connection to the Caribbean transgression, registered in Bolivia, because of temporal constraints.  相似文献   

Metamorphic evolution of the Maud Belt: P–T–t path for high-grade gneisses in Gjelsvikfjella, Dronning Maud Land, East Antarctica     

Avinash Bisnath  Hartwig E. Frimmel 《Journal of African Earth Sciences》2005,43(5):505-524

A metamorphic petrological study, in conjunction with recent precise geochronometric data, revealed a complex P–T–t path for high-grade gneisses in a hitherto poorly understood sector of the Mesoproterozoic Maud Belt in East Antarctica. The Maud Belt is an extensive high-grade, polydeformed, metamorphic belt, which records two significant tectono-thermal episodes, once towards the end of the Mesoproterozoic and again towards the late Neoproterozoic/Cambrian. In contrast to previous models, most of the metamorphic mineral assemblages are related to a Pan-African tectono-thermal overprint, with only very few relics of late Mesoproterozoic granulite-facies mineral assemblages (M₁) left in strain-protected domains. Petrological and mineral chemical evidence indicates a clockwise P–T–t path for the Pan-African orogeny. Peak metamorphic (M_2b) conditions recorded by most rocks in the area (T = 709–785 °C and P = 7.0–9.5 kbar) during the Pan-African orogeny were attained subsequent to decompression from probably eclogite-facies metamorphic conditions (M_2a).The new data acquired in this study, together with recent geochronological and geochemical data, permit the development of a geodynamic model for the Maud Belt that involves volcanic arc formation during the late Mesoproterozoic followed by extension at 1100 Ma and subsequent high-grade tectono-thermal reworking once during continent–continent collision at the end of the Mesoproterozoic (M₁; 1090–1030 Ma) and again during the Pan-African orogeny (M_2a, M_2b) between 565 and 530 Ma. Post-peak metamorphic K-metasomatism under amphibolite-facies conditions (M_2c) followed and is ascribed to post-orogenic bimodal magmatism between 500 and 480 Ma.  相似文献   

Kinematic analysis of sinistral cataclastic shear zones along the northern margin of the Mino Belt, central Japan   总被引：1，自引：0，他引：1  

Masakazu Niwa  Kazuhiro Tsukada  Shiro Tanaka 《Journal of Asian Earth Sciences》2005,24(6):787

In this paper, cataclastic shear zones along the northern margin of the Mino Belt, central Japan are described, and the significance of the shearing in the tectonic evolution of SW Japan is examined. The Mino Belt in SW Japan is composed of accretionary complexes of Jurassic to Early Cretaceous age. Field investigation revealed that remarkable cataclastic shear zones trending east to northeast run along the northern margin of the Mino Belt. Closely spaced cleavage is developed in these shear zones. Lineation on the cleavage plunges at shallow to moderate angles. Deformation structures (e.g. composite planar fabric and asymmetric structure of clasts) in the sheared rocks clearly indicate a sinistral sense of shear. The shearing ceased by latest Cretaceous time, because the sheared rocks are overlain by unsheared Upper Cretaceous volcanic rocks. The sinistral shearing may be closely related to Cretaceous sinistral movement along the eastern margin of Asia. Sinistral shearing along the northern margin of the Mino Belt can be considered as a key for re-examining the tectonic development of SW Japan.  相似文献   

CGD-1型大口径全套管冲击抓斗的设计和应用          下载免费PDF全文

冯起赠  宋志彬  王年友 《探矿工程》2005,32(6):38-40

CGD－1型大口径全套管冲击抓斗主要是配套全套管钻机施工而研制的。该抓斗主要适用于复杂地层的施工。介绍了该抓斗的技术参数、性能特点、主要结构及试验情况。  相似文献   

岩土钻掘设备的液压步履机构          下载免费PDF全文

王世玉  薛军 《探矿工程》2005,32(6):41-43

因液压步履移位最方便，辅助时间短，换向灵活，移位对孔准确，大型岩土钻掘设备施工的群孔现场实现近距离的自行迁移多采用液压步履机构。详细叙述了双向移动和单向移动加转向步履机构的结构和特点。  相似文献   

浅埋暗挖技术在南平市天台隧道工程施工中的应用          下载免费PDF全文

李耀卿 《探矿工程》2005,32(12):56-58

主要介绍了在Ⅱ、Ⅲ类围岩中施工城市浅埋隧道的施工技术，以“短开挖、快封闭、强支护、勤量测”为指导，将隧道分成上、下两个台阶进行开挖，及时进行初期支护，保证施工始终处于安全状态。  相似文献   

厦门市海沧区北市花岗岩矿滑坡形成机制及治理设计     

王广和张海生  王慧珍 《中国地质灾害与防治学报》2005,16(B12):41-45

厦门市海沧区北市花岗岩矿滑坡发生于2004年10月30日14时。滑坡位于呆场的西端帮顶部的第四系填土和淤泥质土层中，滑体将该区域原设的抗滑桩剪断、拔出、推移，土石迅速越过矿区运输公路，塌落到采场工作面，将正在作业的2名工人和生产设备掩埋。滑坡宽度约60m，最大垂直厚度约14m，总体积约13000m^3。由于滑坡对原有防护体系的破坏，根据滑体调查和极限平衡计算结果，滑坡处于不稳定状态，直接威胁着整个采场设备和未来生产的安全。必须对北市花岗岩矿滑坡进行专项治理。滑坡宜采用治水、削坡减载和支挡相结合的综合治理措施。  相似文献   

Pan-African Tectonism in the Western Maud Belt: P-T-t Path for High-grade Gneisses in the H.U. Sverdrupfjella, East Antarctica     

BOARD  W. S.; FRIMMEL  H. E.; ARMSTRONG  R. A. 《Journal of Petrology》2005,46(4):671-699

Extensive high-grade polydeformed metamorphic provinces surroundingArchaean cratonic nuclei in the East Antarctic Shield recordtwo tectono-thermal episodes in late Mesoproterozoic and lateNeoproterozoic–Cambrian times. In Western Dronning MaudLand, the high-grade Mesoproterozoic Maud Belt is juxtaposedagainst the Archaean Grunehogna Province and has traditionallybeen interpreted as a Grenvillian mobile belt that was thermallyoverprinted during the Early Palaeozoic. Integration of newU–Pb sensitive high-resolution ion microprobe and conventionalsingle zircon and monazite age data, and Ar–Ar data onhornblende and biotite, with thermobarometric calculations onrocks from the H.U. Sverdrupfjella, northern Maud Belt, resultedin a more complex P–T–t evolution than previouslyassumed. A c. 540 Ma monazite, hosted by an upper ampibolite-faciesmineral assemblage defining a regionally dominant top-to-NWshear fabric, provides strong evidence for the penetrative deformationin the area being of Pan-African age and not of Grenvillianage as previously reported. Relics of an eclogite-facies garnet–omphaciteassemblage within strain-protected mafic boudins indicate thatthe peak metamorphic conditions recorded by most rocks in thearea (T = 687–758°C, P = 9·4–11·3kbar) were attained subsequent to decompression from P >12·9 kbar. By analogy with limited U–Pb singlezircon age data and on circumstantial textural grounds, thisearlier eclogite-facies metamorphism is ascribed to subductionand accretion around 565 Ma. Post-peak metamorphic K-metasomatismunder amphibolite-facies conditions is ascribed to the intrusionof post-orogenic granite at c. 480 Ma. The recognition of extensivePan-African tectonism in the Maud Belt casts doubts on previousRodinia reconstructions, in which this belt takes a pivotalposition between East Antarctica, the Kalahari Craton and Laurentia.Evidence of late Mesoproterozoic high-grade metamorphism duringthe formation of the Maud Belt exists in the form of c. 1035Ma zircon overgrowths that are probably related to relics ofgranulite-facies metamorphism recorded from other parts of theMaud Belt. The polymetamorphic rocks are largely derived froma c. 1140 Ma volcanic arc and 1072 ± 10 Ma granite. KEY WORDS: Maud Belt; Pan-African orogeny; geochronology; P–T–t path, East Antarctica  相似文献   

The 17 March 2005 Kuzulu landslide (Sivas, Turkey) and landslide-susceptibility map of its near vicinity   总被引：3，自引：0，他引：3  

Candan Gokceoglu  Hakan A. Nefeslioglu  Tolga Can 《Engineering Geology》2005,81(1):65-83

Landslides are common natural hazards in the seismically active North Anatolian Fault Zone of Turkey. Although seismic activity, heavy rainfall, channel incisions, and anthropogenic effects are commonly the main triggers of landslides, on March 17, 2005, a catastrophic large landslide in Sivas, northeastern of Turkey, the Kuzulu landslide, was triggered by snowmelt without any other precursor. The initial failure of the Kuzulu landslide was rotational. Following the rotational failure, the earth material in the zone of accumulation exhibited an extremely rapid flow caused by steep gradient and high water content. The Agnus Creek valley, where Kuzulu village is located, was filled by the earth-flow material and a landslide dam was formed on the upper part of Agnus Creek. The distance from the toe of the rotational failure down to the toe of the earth flow measured more than 1800 m, with about 12.5 million m³ of displaced earth material. The velocity of the Kuzulu landslide was extremely fast, approximately 6 m/s. The main purposes of this study are to describe the mechanism and the factors conditioning the Kuzulu landslide, to present its environmental impacts, and to produce landslide-susceptibility maps of the Kuzulu landslide area and its near vicinity. For this purpose, a detailed landslide inventory map was prepared and geology, slope, aspect, elevation, topographic-wetness index and stream-power index were considered as conditioning factors. During the susceptibility analyses, the conditional probability approach was used and a landslide-susceptibility map was produced. The landslide-susceptibility map will help decision makers in site selection and the site-planning process. The map may also be accepted as a basis for landslide risk-management studies to be applied in the study area.  相似文献   

人口生态生产:人地作用机制下"三江并流"世界遗产保护的新视角     

熊理然  骆华松 《云南地理环境研究》2005,17(6):69-73

基于不同人口需要而进行的人类活动对“三江并流”区的地理环境产生了巨大影响,形成了独具特色的人地作用机制。这一作用机制一方面对“三江并流”世界遗产的保护构成了威胁,但另一方面,通过人口生态生产,实现人口数量、质量、结构和分布的生态化,改进人类活动,也可优化“三江并流”区的地理环境,保护“三江并流”世界遗产,实现该地区的可持续发展。  相似文献