Magma dynamics at mid-ocean ridges by noble gas kinetic fractionation: Assessment of magmatic ascent rates     

《Earth and Planetary Science Letters》2006,241(1-2):138-158

Despite its impact in understanding oceanic crust formation and eruptive styles of related volcanism, magma dynamics at mid-ocean ridges are poorly known. Here, we propose a new method to assess ascent rates of mid-ocean ridge basalt (MORB) magmas, as well as their pre- and sin-eruptive dynamics. It is based on the idea that a rising magma can reach a variable degree of both CO₂ supersaturation in melt and kinetic fractionation among noble gases in vesicles in relation to its ascent rate through the crust. To quantify the relationship, we have used a model of multicomponent bubble growth in MORB melts, developed by extending the single-component model of Proussevitch and Sahagian [A.A. Proussevitch, D.L. Sahagian, Dynamics and energetics of bubble growth in magmas: analytical formulation and numerical modeling, J. Geophys. Res. 103 (1998), 18223–18251.] to CO₂–He–Ar gas mixtures. After proper parameterization, we have applied it to published suites of data having the required features (glasses from Pito Seamount and mid-Atlantic ridges). Our results highlight that the investigated MORB magmas display very different ranges of ascent rates: slow rises of popping rock forming-magmas that cross the crust (0.01–0.5 m/s), slightly faster rates of energetic effusions (0.1–1 m/s), up to rates of 1–10 m/s which fall on the edge between lava effusion and Hawaiian activity. Inside a single plumbing system, very dissimilar magma dynamics highlight the large differences in compressive stress of the oceanic crust on a small scale. Constraints on how the systems of ridges work, as well as the characteristics of the magmatic source, can also be obtained. Our model shows how measurements of both the dissolved gas concentration in melt and the volatile composition of vesicles in the same sample are crucial in recognizing the kinetic effects and definitively assessing magma dynamics. An effort should be made to correctly set the studied samples in the sequence of volcanic submarine deposits where they are collected. Enhanced knowledge of a number of physical properties of gas-bearing MOR magmas is also required, mainly noble gas diffusivities, to describe multicomponent bubble growth at a higher confidence level.  相似文献   

大洋热盐环流研究的一个焦点：北太平洋是否有深水形成     

刘宇  管玉平  林一骅 《地球科学进展》2006,21(11):1185-1192

现代大洋热盐环流的特点之一是北大西洋有深水形成而北太平洋没有，这种不对称性对周边气候产生了重要影响。尽管理论上认为大洋热盐环流可能存在对应不同气候的多平衡态，但北太平洋是否曾有过深水形成已成为目前学术争论的一个热点。简要介绍了最新的热盐环流研究成果，重点分析现代北太平洋无深水形成的原因，其中亚洲季风的水汽输送和低蒸发是两个重要的影响因子。  相似文献   

气象电视会商会议系统的使用和维护          下载免费PDF全文

贺耀武  张红雨  王文春  余明祥 《山西气象》2006,(2):28-30

本文介绍省台———国家气象中心的电视会议系统的构成原理,总结省台与国家气象中心电视会商系统使用维护过程中的经验,对系统的使用和正在进行安装调试的“省—市—县”电视会商系统的使用提供借鉴。  相似文献   

Assimilated Tidal Results of Tide Gauge and TOPEX/POSEIDON Data over the China Seas Using a Variational Adjoint Approach with a Nonlinear Numerical Model   总被引：3，自引：0，他引：3  

韩桂军  李威  何忠杰  刘克修  马继瑞 《大气科学进展》2006,23(3):449-460

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井间断层的计算机分析方法     

周小军  薛林福  戴立明  李三忠 《应用地球物理》2006,3(3):133-140

井间断层分析的研究,是油气储层地质研究的一项重要基础性工作,对油气的运移和聚集其中重要的控制作用。它是利用测井资料,以地层分层为基础,采用计算机技术实现井间断层分析的一种井间断层自动分析方法。动态波形匹配算法是本次研究采用的主要算法,它能够很好地建立井间地层之间的对比关系,通过曲线拟合、特征提取、匹配代价计算等步骤,自动绘制井间地层对比的路径图解。本文在对各种构造的路径图分析的基础上,总结出正断层、逆断层、不整合、同沉积断层、犁式断层和地层尖灭等30种情况下的路径图模式,提出路径图模式及相关概念。在大港油田的实例分析中取得了很好的效果。  相似文献   

中国西北地区云的分布及其变化趋势   总被引：8，自引：1，他引：8  

陈勇航  陈艳  黄建平  郑志海  苏婧  黄鹤 《高原气象》2007,26(4):741-748

利用1983年7月—2001年9月ISCCP D2云的月平均资料,针对西北地区15种不同类型云的分布特征进行了分析,给出了中、低云量之和以及高云量在3个气候子区的多年变化趋势,初步探讨了其形成机制。结果表明:水层云、冰层云、水雨层云、冰雨层云和深对流云的光学厚度和云水路径值最大;水层云主要出现在天山山区、北疆地区和陕西南部,冰层云主要出现在北疆地区,水雨层云、冰雨层云和深对流云以及水高层云、冰高层云、卷层云的云量高值区在天山—昆仑山—祁连山一带以及陕南和/或陇南地区,因此上述地区也是有利于人工增水作业的地区。近20年中,高云量在3个气候区都呈明显下降趋势,中、低云量之和则呈上升趋势。西北地区云与地气系统之间可能存在这样一个过程:地面气温的升高,促使地面蒸发加剧,从而导致中、低云量增多而使降水增多,同时高云云量减少。  相似文献   

Paleoenvironmental changes and depositional history of the Korea (Tsushima) Strait since the LGM     

《Journal of Asian Earth Sciences》2007,29(1):84-104

Two deep cores (SSDP 102 and SSDP 105) from the southeastern inner shelves of Korea were examined in order to reconstruct the paleoenvironmental history of the Korea Strait during postglacial sea-level fluctuations. The results of the lithofaces, organic geochemical components, foraminiferal assemblages, and stable isotopes show that the Korea Strait was influenced in different ways by river discharges and open-ocean currents, according to their temporal and spatial variability.The results of core SSDP 105 indicate that the southeastern coast of Korea was probably a shallow coastal environment, such as a shoreface or beach, by about 17.5 cal ka. The area remained a coastal environment that was affected by high energy conditions and partly by freshwater input during the transgressive period of 17.5–8.1 cal ka. The area has changed to a modern-type shelf environment influenced by the inflow of the Tsushima Current and by the high supply of fine-grained sediments derived from the Nakdong River since 8.1 cal ka.Meanwhile, the results of core SSDP 102 taken from the Nakdong River mouth reveal that the river mouth area was most likely a terrestrial or fluvial environment at least before 13.9 cal ka. It then changed to the estuarine (deltaic) environment that was directly affected by the Nakdong River between 13.9 and 7.0 cal ka, and established a modern-type shelf (prodeltaic) environment, which is similar in many respects to the southeastern coast of Korea after temporarily undergoing erosion between 7.0 and 6.1 cal ka.  相似文献   

An 8.1Ma calcite record of Asian summer monsoon evolution on the Chinese central Loess Plateau   总被引：5，自引：0，他引：5  

Chen XiuLing  Fang XiaoMin  An ZhiSheng  Han WenXia  Wang Xin  Bai Yan  Hong Ye 《中国科学D辑(英文版)》2007,50(3):392-403

Carbonates in loess-red clay sequences consist mainly of calcite and dolomite. The EDTA analysis of carbonates in different size fractions and magnetic susceptibility reveal that calcite is a sensitive index of summer monsoon. The chemical analysis of carbonates and calcite from an 8.1 Ma loess-red clay sequence at Chaona on the Chinese central Loess Plateau shows that the evolution of the Asian summer monsoon experienced four stages, namely 8.1―5.5 Ma, 5.5―2.8 Ma, 2.8―1.5 Ma and 1.5―0 Ma, with increasing intensification and fluctuation, suggesting a possible combining impacts of uplift of the Tibetan Plateau and global changes on the Asian summer monsoon.  相似文献   

Theorem of turbulent intensity and macroscopic mechanism of the turbulence development     

Hu YinQiao  Chen JinBei  Zuo HongChao 《中国科学D辑(英文版)》2007,50(5):789-800

Turbulence is one of the most common nature phenomena in everyday experience, but that is not adequately understood yet. This article reviews the history and present state of development of the turbulence theory and indicates the necessity to probe into the turbulent features and mechanism with the different methods at different levels. Therefore this article proves a theorem of turbulent transpor- tation and a theorem of turbulent intensity by using the theory of the nonequilibrium thermodynamics, and that the Reynolds turbulence and the Rayleigh-Bénard turbulence are united in the theorems of the turbulent intensity and the turbulent transportation. The macroscopic cause of the development of fluid turbulence is a result from shearing effect of the velocity together with the temperature, which is also the macroscopic cause of the stretch and fold of trajectory in the phase space of turbulent field. And it is proved by the observed data of atmosphere that the phenomenological coefficient of turbulent in- tensity is not only a function of the velocity shear but also a function of temperature shear, viz the sta- bility of temperature stratification, in the atmosphere. Accordingly, authenticity of the theorem, which is proved by the theory of nonequilibrium thermodynamics, of turbulent intensity is testified by the facts of observational experiment.  相似文献   

A filtering approach for estimating lake water quality from remote sensing data     

《International Journal of Applied Earth Observation and Geoinformation》2007,9(1):50-64

In this paper we consider the estimation of lake water quality constituent distributions from hyperspectral remote sensing data. We present a computational approach that can be used to assimilate information from mathematical evolution models into data processing. The method is based on a reduced order iterated extended Kalman filter, and a convection–diffusion model is used to describe the movement of the water quality constituents. The performance of the technique is evaluated in a simulation study. The results show that the filter approach with an appropriate evolution model yields estimates that have better spatial and temporal resolutions than those obtained with conventional methods. Furthermore, the use of a feasible evolution model may make it possible to obtain information also on the concentrations in the lower parts of the lake.  相似文献