新疆北天山巴音沟蛇绿岩的地质特征   总被引：3，自引：1，他引：3  

邬继易  刘成德 《岩石学报》1989,5(2):76-87

巴音沟蛇绿岩虽受强热构造作用肢解,但仍保存有较完整的蛇纹石化超基性岩、状层辉长岩、基性熔岩(下部块状、上部枕状)和放射虫硅质岩的层序组合。岩石化学、地球化学、放射虫等古生物资料表明,它代表一个中石炭世陆缘海盆迅速扩张形成的洋壳和上地幔的残片。其侵位发生在中石炭世未海盆的封闭期间。  相似文献   

闽北前寒武纪变质岩的P—T—t轨迹和其形成的动力学过程   总被引：2，自引：0，他引：2  

梅华林  庄建民 《福建地质》1993,12(3):182-194

闻北前寒武纪变质岩是华夏古陆基底的重要组成部分。本文通过对闽北麻源群和马面山群变质岩详细的变质变形关系的研究和石榴子石环带测定P-T-t轨迹的应用,结合构造地质和同位素年代学的资料,证实了麻源群变质岩形成于早元古代或更老年代,在早元古代末期遭受过中压、中高温变质,但在晚元古代晋宁期与中元古代形成的马面山群岩石一起经历了强烈的变质变形作用,表现为早元古代麻源群岩石遭受强烈改造,具有早期地壳再活化特点。麻源群岩石完整的晋宁期变质P-T-t轨迹不支持正常大陆碰撞的假说,它的形成与异常的地幔热流有关,很可能为一种地壳增厚和地幔减薄的动力学模式。  相似文献   

Sedimentary Features of Shallow Ancient River Channels on the Northern Shelf of the South China Sea1     

Kou Yangqi  Du Deli 《《地质学报》英文版》1995,8(1):85-98

Abstract Quaternary buried ancient river channels are widespread in the shallow-level sediments of the northern shelf of the South China Sea. The sedimentary sequence mainly of fluvial deposits comprise an important component part of the low-stand system tract and transgressive system tract in the study region. The plannar variation and spatial association of the sedimentary features such as incised valley fillings, deltaic foreset wedges and block slides of shelf-marginal fans reflect the palaeogeographic environment during the fall of the regional sea level in the northern part of the South China Sea. Based on the high-resolution seismic reflection data and gelogical data from boreholes, the present paper makes an integrated interpretation of the Quaternary ancient river channels in the shallow sediments of the study area, studies the sedimentary features of the ancient channels such as their spatial distribution, seismic facies reflection indicators, sedimentary facies and sand-body types, and discusses their formational setting and evolutionary model, with the main purpose to render a service to the hydrocarbon resources exploration and development and marine engineering in the northern shelf of the South China Sea.  相似文献   

A sedimentary facies model for perennial and meromictic saline lakes: Holocene Medicine Lake Basin, South Dakota, USA     

Blas L. Valero-Garcés  Kerry R. Kelts 《Journal of Paleolimnology》1995,14(2):123-149

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Changes in post world war ii distribution and status of monsoon rainforests in the Darwin area     

William J. Panton 《The Australian geographer》1993,24(2):50-59

Monsoon rainforests in the Darwin area occur as isolated patches ranging in size from 2 to 112 ha. Aerial photographic records over a 45 year period indicate a 60 per cent reduction in the cover of pre‐1945 rainforest. Urban development, cyclone damage, weed invasion and wildfire were identified as the major causes of this contraction. Urban development contributed 40 per cent of the total rainforest loss during this period. Rainforests occurring on dry substrates have been most affected by urban development. Cyclonic storm damage and indirect human affects such as weed invasion and anthropogenic fires continue to disturb the remaining rainforest patches. Although the largest expanses of rainforest presently occur within parks and reserves, providing adequate protection from further urban encroachment, smaller remnants occurring on vacant crown land are vulnerable to changes in land use. As well as the introduction of appropriate legislation, the control of fire and weeds should be given the highest priority by land managers to ensure the stability and long‐term maintenance of this remnant vegetation.  相似文献   

Interpretation of210Pb profiles and verification of the CRS dating model in PIRLA project lake sediment cores     

Michael W. Binford  Jeffrey S. Kahl  Stephen A. Norton 《Journal of Paleolimnology》1993,9(3):275-296

This paper reports results and analysis of²¹⁰Pb-activity measurements in 51 lake-sediment cores from 32 lakes in the four PIRLA (Paleoecological Investigations of Recent Lake Acidification) project regions (Adirondack Mountains [New York], Northern New England, Northern Florida, and the Northern Great Lakes States). General application of the Constant Rate of Supply (Constant Flux) model for²¹⁰Pb dating is valid for lakes in the PIRLA study, although application of the model is equivocal in a few lakes.²¹⁰Pb inventories and profiles are replicable among closely spaced cores within a lake. Specific²¹⁰Pb activity in surface sediments is negatively correlated with bulk sediment accumulation rate in seepage lakes, but not in drainage lakes. Drainage lakes with lower pH have lower unsupported²¹⁰Pb inventories in sediments, but the relationship does not occur in seepage lakes.²¹⁰Pb profiles in only seven of the cores, all from either the Adirondacks or the northern Great Lakes states, exhibit exponential decay curves. Deviations from an exponential profile include a flattening of the profile in the top few cm or excursions of one or a few measurements away from an exponential curve.²¹⁰Pb dates typically agree with other chronostratigraphic markers, most of which are subject to greater uncertainty. Several hypotheses, including sediment mixing, hydrologic regime, sediment focusing, and acidification, are proposed to explain variation of²¹⁰Pb distribution among lakes and regions. Hydrologic factors exert control on unsupported²¹⁰Pb inventories in PIRLA lakes, and there is a strong focusing effect in drainage lakes but a weak focusing effect in seepage lakes.This is the third of a series of papers to be published by this journal following the 20^th anniversary of the first application of²¹⁰Pb dating of lake sediments. Dr P. G. Appleby is guest editing this series.  相似文献   

北疆阿巴宫-库尔提断裂带显微组构的运动学和动力学分析   总被引：3，自引：0，他引：3  

杨新岳 《大地构造与成矿学》1990,14(1):29-42

研究了阿尔泰地区NW走向高角度冲断构造中主干的阿巴宫—库尔提断裂带。详细研究了断裂构造岩的变形构造和组构及其所显示的运动学和动力学特征。结果表明:存在早、晚更替且性质不同的变形显微构造。早期以糜棱岩中的韧性变形构造为主,发育有递进变形的不对称构造(压力影、旋转变斑晶、S—C构造等),是断裂中剪切变形运动指向的主要判据。晚期为脆性破裂构造,与早期变形组构具继承、叠加关系。研究了石英光轴的组构形式,证实存在:早期共轴纯剪变形的小圆环带组构和非共轴简单剪切变形中,呈递变关系的点极密—大圆环带—交叉大圆环带组构型式。对变形构造和组构所作的运动学和动力学分析结果表明:阿—库断裂带的形成和变形历史为:①地壳早期NE挤压收缩环境,形成劈理化带;②在持续NE向挤压作用下,大规模剪切、逆冲叠置,和地壳加厚,产生重熔岩浆和流体再分配效应,促使糜棱岩带形成和发展;③晚期地壳NE向挤压下,以垂直差异抬升和大量碎裂岩化高角度逆冲断裂的继承、叠加为特征。在区域大地构造的关系上:①、②对应于地槽褶皱、封闭的地槽体制(海西期),③对应于地洼体制(后海西期)。  相似文献   

长江中下游地震同青藏高原北部地震的相关性     

李蓉川 《地震研究》1990,13(3):246-255

本文对比了1910—1987年发生的长江中下游地震和青藏高原北部地震,发现两者有比较好的对应关系。一般是,青藏高原北部先发生M≥6级地震,而后长江中下游地区发生M≥19/4级地震。对1910年以来的21次地震进行了统计分析,得到复相关系数R=0.74,能够在很高的显著性水平上通过F检验。地震活动在时间、空间、强度上的相关,现代构造运动及应力场等事实表明,长江中下游地震活动可能主要受青藏高原向东的横向推移运动的影响。  相似文献   

鄂北地区碱性岩的时代及成因   总被引：7，自引：2，他引：7  

李石 《岩石学报》1991,7(3):27-36

产于鄂北的花山寨、观子山、杀熊洞和庙垭四个碱性岩体,其K-Ar、U-Pb和Rb-Sr同位素年龄值为215～306Ma,成岩时代属海西—印支期。根据~(87)Sr/~(86)Sr初始值,杀熊洞岩体(0.7032)和庙垭岩体(0.7029)的成岩物资来源于上地幔,观子山岩体(0.7041)的成岩物质属幔壳混源型,但仍以幔源为主,花山寨岩体(0.7092)的成岩物质则主要来源于下地壳。  相似文献   

北半球增暖对我国气侯的影响     

屠其璞 《南京气象学院学报》1991,(3)

本文在分析100多年来北半球平均气温长期变化基本特征的基础上,讨论了北半球气温变化对我国气候变化的影响。结果表明,我国大范围气温距平与北半球平均气温有显著的正相关,长江中下游和华北平原的温度距平值平均为北半球平均气温距平的1.4-1.6倍。还表明,我国降水距平分布与北半球气温变化也有一定的联系。在北半球平均气温偏高和偏低年份,欧亚地区500hPa环流特征的差异是显著的。这表明,我国大范围气候距平与北半球平均气温距平的统计相关是有一定的物理基础的。  相似文献