哥伦比亚超大陆在扬子陆块西缘的探秘   总被引：4，自引：0，他引：4       下载免费PDF全文

尹福光  王冬兵  孙志明  任光明  庞维华 《沉积与特提斯地质》2012,(3):31-40

在扬子陆块西缘的拉拉、小关河-东川、大红山等地区出露了3套古元古代Statherian期（1.6～1.8Ga）的浅变质岩系,被分别命名为河口群、通安组-汤丹群-东川群、大红山群。从2.0Ga至1.4Ga期间,其地质历史演化经历：（1）约2.2～1.8Ga的造山运动;（2）约1.7～1.5Ga发生的非造山裂解事件群;（3）约1.7～1.5Ga侵入到古元古代地层的基性岩墙群、层状侵入体事件;（4）因民、落雪地区,约1.5～1.2Ga发生的陆架裂陷事件;（5）上扬子古陆块西缘,约1.0Ga发生的碰撞造山事件。本文重点阐述了扬子陆块西缘1.8～1.6Ga时期大规模裂解事件群的性质、特点和同位素年龄数据,认为上扬子陆块裂解事件群的性质、特点和时代等特征与华北、北美、西伯利亚和西北欧有很大的相似性,并提出了古元古代扬子陆块与其它陆块曾经联合的证据。  相似文献   

Juvenile bottlenecks and salinity shape grey mullet assemblages in Mediterranean estuaries     

Luis Cardona  Bernat Hereu  Xavier Torras 《Estuarine, Coastal and Shelf Science》2008

Previous research has suggested that competitive bottlenecks may exist for the Mediterranean grey mullets (Osteichthyes, Mugilidae) at the fry stage with the exotic Cyprinus carpio (Osteichthyes, Cyprinidae) playing a central role. As a consequence, the structure of grey mullet assemblages at later stages is thought to reflect previous competition as well as differences in osmoregulatory skills. This paper tests that hypothesis by examining four predictions about the relative abundance of five grey mullet species in 42 Western Mediterranean estuary sites from three areas (Aiguamolls de l'Empordà, Ebro Delta and Minorca) differing in the salinity level and occurrence of C. carpio. Field data confirmed the predictions as: (1) Liza aurata and Mugil cephalus were scarce everywhere and never dominated the assemblage; (2) Liza saliens dominated the assemblage where the salinity level was higher than 13; (3) Liza ramado always dominated the assemblage where the salinity level was lower than 13 and C. carpio was present; and (4) Chelon labrosus dominated the assemblage only where the salinity level was lower than 13 and C. carpio was absent. The catch per unit effort of C. labrosus of any size was smaller in the presence of C. carpio than where it had not been introduced, which is in agreement with the juvenile competitive bottleneck hypothesis. Discriminant analysis confirmed that the assemblage structure was linked to the salinity level and the occurrence of C. carpio for both early juveniles and late juveniles as well as adults. The data reported here reveal that the structure of grey mullet assemblages inhabiting Mediterranean estuaries is determined by salinity and competitive interactions at the fry stage.  相似文献   

含不同半径孔洞的颗粒体模型的力学行为数值模拟   总被引：3，自引：0，他引：3  

伍小林  王学滨  潘一山 《中国地质灾害与防治学报》2011,22(1):107-114

本文通过编程建立了非连续介质(颗粒体材料)模型,采用FLAC软件模拟了静水压力条件下不同半径的巷道围岩中的剪切应变增量、最小主应力及最大主应力的分布规律。研究表明,随着孔洞半径的增大,呈圆环形的剪切应变增量与最小主应力的高值区的圈数、呈辐射状的最大主应力的高值区的延伸范围及剪切应变增量的最大值都呈先慢后快的增长趋势。模型中最大的拉应力接近于在模型四周所施加的压应力,而最大的压应力约为所施加的压应力的5～10倍。模型内部的剪切应变增量、最小主应力及最大主应力的分布是高度不均匀的。具有较高的差应力的位置与具有较高的剪切应变增量的位置具有很好的一致性。  相似文献   

Contrasting pressure–temperature–deformation history across a vestigial craton–mobile belt boundary: the western margin of the Eastern Ghats Belt at Deobhog, India     

S. Gupta  A. Bhattacharya  M. Raith  & J.K. Nanda 《Journal of Metamorphic Geology》2000,18(6):683-697

At Deobhog, migmatitic gneisses and granulites of the Eastern Ghats Belt are juxtaposed against a cratonic ensemble of banded augen gneiss, amphibolite and calcsilicate gneiss, intruded by late hornblende granite and dolerite. In the migmatitic gneiss unit, early isoclinal folds (syn‐D_1M and D_2M) are reoriented along N–S‐trending and E‐dipping shear planes (S_3M), with (S_1M–S_3M) intersection lineations having steep to moderate plunges. The near‐peak P–T condition was syn‐D_3M (≥900 °C, 9.5 kbar), as inferred from syn‐D_3M Grt+Opx‐bearing leucosomes in mafic granulites, and from thermobarometry on Grt (corona)–Opx/Cpx–Pl–Qtz assemblages. The P–T values are consistent with the occurrence of Opx–Spr–Crd assemblages in spatially associated high‐Mg–Al pelites. A subsequent period of cooling followed by isothermal decompression (800–850 °C, c. 7 kbar) is documented by the formation of coronal garnet and its decomposition to Opx+Pl symplectites in mafic granulites. Hydrous fluid infiltration accompanying the retrograde changes is manifested in biotite replacing Opx in some lithologies. The cratonic banded gneiss–granite unit also documents two phases of isoclinal folding (D_1B & D_2B), with the L_2B lineation girdle different from the lineation spread in the migmatitic gneiss unit. Calcsilicate gneiss (Hbl–Pl–Cpx–Scap–Cal) and amphibolite (Hbl–Pl±Grt±Cpx) within banded gneisses record syn‐D_2B peak metamorphic conditions (c. 700 °C, 6.5 kbar), followed by cooling (to c. 500 °C) manifested in the stabilization of coronal clinozoisite–epidote. The D_3B shear deformation post‐dates granite and dolerite intrusions and is characterized by top‐to‐the‐west movement along N–S‐trending, E‐dipping shear planes. Deformation mechanisms of quartz and feldspar in granites and banded gneisses and amphibole–plagioclase thermometry within shear bands in dolerites document an inverted syn‐D_3B thermal gradient with temperature increasing from 350 to 550 °C in the west to ≥700 °C near the contact with the migmatitic gneiss unit. The thermal gradient is reflected in the stabilization of chlorite after hornblende in S_3B shears to the west, and post‐D_2B neosome segregation along D_3B folds and shears to the east. The contrasting lithologies, early structures and peak metamorphic conditions in the two units indicate unconnected pre‐D₃P–T –deformation histories. The shared D₃ deformation in the two units, the syn‐D₃ inverted thermal gradient preserved in the footwall cratonic rocks and the complementary cooling and hydration of the hanging wall granulites across the contact are attributed to westward thrusting of ‘hot’ Eastern Ghats granulites on ‘cool’ cratonic crust. It is suggested that the Eastern Ghats migmatitic gneiss unit is not a reworked part of the craton, but a para‐autochthonous/allochthonous unit emplaced on and amalgamated to the craton.  相似文献   

高强度绳索取心钻具在巨厚覆盖层煤田勘查中应用     

张跃亭  袁志坚 《中国煤炭地质》2013,(8)

河南省把豫东和豫东南地区巨厚覆盖层下找煤列入“十二五”重点勘查项目。由于巨厚覆盖层大部分厚度在600m以上,钻孔深度均超过1200m,采用常规绳索取心工艺必须下护壁管,施工中对泥浆性能要求苛刻,管材和泥浆成本较高;同时深孔施工常规钻具强度低,断钻、脱扣事故率高,孔内安全得不到保证。而传统的提钻取心工法钻探效率低,职工劳动强度大。鉴于以上问题,研制高强度绳索取心用的钻杆、钻铤、取心器和钻头等钻具,并制定了不同地层和取心条件的冲洗液配方和钻进规程参数。应用表明,高强度绳索取心工艺具有取心率和台月效率高,钻具安全,工人劳动强度低,生产成本相对较低的特点,基本解决了在巨厚覆盖层施工不下护壁套管,普通性能的泥浆就能满足施工要求等技术难题。  相似文献   

Focal plane image assembly of subpixel     

Zhong Sidong  Mei Tiancan  Shi Zhongchao 《地球空间信息科学学报》2013,16(4):55-59

This paper describes the scanning assembly principle and construction of scanning assembly sample. The factors that affect assembly accuracy are analyzed. There are tow steps in CCD focal plane scanning assembly. The first is rough assembly, and the second is accurate assembly. In this paper, the moiré fringe is introduced in judging assembly accuracy directly and accurately. The equation for optical transmission characteristics of CCD Moiré fringes is presented. The measurement of Moiré fringes can be completed when some conditions are satisfied. 2D-assembly error can be obtained by using digital correlation filtering technique. Finally, the result of focal plane scanning assembly is presented. The result is in good accordance with theory.  相似文献   

组装式单自由度地震模拟振动台的创新技术研究     

王燕华  程文滚  陈忠范  陆飞 《地震学刊》2010,(4):419-423

首先阐述了东南大学4 m×6 m组装式单自由度地震模拟振动台系统的组成、性能参数以及创新技术的运用;接着深入地论述了如何正确运用台面拼装技术、合理利用现有的基础和导轨,以及现有控制系统的改造和控制方法的选择;最后通过实际的台面背景噪声试验以及波形失真试验,验证了这些创新技术的突出优点。组装系统节约了60%的建设成本;300 kN的最大载重量以及超出93%的信噪比证明,运用创新技术还极大地发挥了组装系统的动态性能。  相似文献   

塔克拉玛干沙漠输电线塔装配式基础试验研究   总被引：2，自引：0，他引：2  

乾增珍  鲁先龙  丁士君 《岩土力学》2011,32(8):2359-2364

为研究新疆塔克拉玛干沙漠地区输电线路工程中的组合装配式杆塔基础承载特性,开展了2种尺寸规格共4个基础在上拔与水平力组合作用下的现场试验,得到了基础顶部和基础底板的荷载-位移曲线、基础底板土压力变化规律。结果表明：上拔与水平力组合作用下,基础顶部上拔荷载-位移曲线为缓变型、水平荷载-位移曲线近似为直线;由混凝土底板和角钢支架所构成的组合装配式基础因自重轻、基础底板上覆沙体结构松散,使得基础的抗倾覆承载能力低。由混凝土底板和角钢支架组成的装配式基础各部件具有良好的协同工作性能,但水平荷载对装配式基础的承载性能影响大。根据基础上拔极限承载力试验值,采用柱式破裂面力学计算模型得到风加沙柱面平均摩擦阻力为2.6 kPa  相似文献   

分块区域三维地质建模方法   总被引：3，自引：0，他引：3  

薛林福  李文庆  张伟  柴社立  刘正宏 《吉林大学学报(地球科学版)》2014,44(6):2051-2058

区域三维地质建模是区域三维地质调查的关键。在大量反复实践的基础上,提出了分块三维地质建模方法,该方法的主要步骤为：以断裂、岩体边界和不整合等为边界,把复杂的三维地质建模区域分解为内部构造相对简单的建模块或建模地质单元;分别对各建模块进行地质地球物理综合研究,编制深部地质剖面,揭示深部地质结构;采用基于剖面的建模方法按照全区统一的坐标系统构建三维地质模型;在完成全区所有建模块三维地质模型构建之后,把各个建模块的三维地质模型集成在统一的三维空间框架下,形成全区的三维地质模型。该方法具有能够简化三维地质建模过程、易于修改完善模型、易于集成模型等优势,能够克服常规的基于剖面的三维地质建模方法中存在的问题,突破了大规模区域三维地质建模的瓶颈。在本溪-临江深部地质调查中的应用表明,采用该方法可以有效构建研究区的三维地质模型,并能充分表达复杂的地下深部地质结构,为开展复杂地区大规模区域三维地质建模提供了一个重要途径。  相似文献   

海草生态系统退化机制及修复对策综述     

毛伟  赵杨赫  何博浩  贾碧莹  李卫东 《中国沙漠》2022,42(1):87-95

人类活动和全球气候变化使得海草生态系统快速退化,形成大面积"海底荒漠",降低了海草生态系统的生态服务功能.近年来,由于各国政府对海洋资源的逐渐重视,海草生态系统的修复进入了一个新的历史阶段.然而,目前成功修复退化海草生态系统的案例很少,急需修复生态学理论对海草修复实践进行指导.基于此,本研究系统论述了海草修复的意义、难...  相似文献