Kr and Xe isotopic compositions of Fe-Mn crusts from the western and central Pacific Ocean and implications for their genesis

Kr and Xe nuclide abundance and isotopic ratios of the uppermost layer of Fe-Mn Crusts from the western and central Pacific Ocean have been determined. The results indicate that the Kr and Xe isotopic composi-tions, like that of He, Ne and Ar, can be classified into two types： low3He/4He type and high3He/4He type. The low3He/4He type crusts have low84Kr and132Xe abundance, while the high3He/4He type crusts have high84Kr and132Xe abundance. The82Kr/84Kr ratios of the low3He/4He type crusts are lower than that of the air, while the83Kr/84Kr and86Kr/84Kr ratios are higher than those of the air. The Kr isotopic ratios of the high-er3He/4He type crusts are quite similar to those of the air. The128Xe/132Xe,130Xe/132Xe and131Xe/132Xe ratios of the low3He/4He type sample are distinctly lower than those of the air, whereas the129Xe/132Xe,134Xe/132Xe and136Xe/132Xe ratios are higher than those of the air. The low3He/4He type samples have the diagnostic characteristics of the MORB, with excess129, 131, 132, 134, 136Xe relative to130Xe compared with the solar wind. The128Xe/132Xe,130Xe/132Xe and131Xe/132Xe ratios of the high3He/4He type samples are slightly higher than those of the air, and the129Xe/132Xe,134Xe/132Xe and136Xe/132Xe ratios are qiute similar to those of the air. The noble gases in the Fe-Mn crusts are derived from the lower mantle, and they are a mixture of lower mantle primitive component, radiogenic component and subduction recycled component. The helium isotopic ra-tios of the low mantle reservoir are predominantly controlled by primitive He （3He） and U and Th radiogenic decayed He （4He）, but the isotopic ratios of the heavier noble gases, such as Ar, Kr and Xe, are controlled to different extent by recycling of subduction components. The difference of the noble isotopic compositions of the two type crusts is the result of the difference of the noble isotopic composition of the mantle source reservoir underneath the seamounts the crusts occurred, the noble gases of the high3He/4He type crusts are     

现行黄河口水下三角洲海底形貌及不稳定性

高分辨力的声学仪器调查表明,现行黄河口水下三角洲海底的形貌十分复杂,由于高浓度巨量黄河泥沙快速沉积的结果,使河口底坡出现了大量的不稳定性现象,如塌陷冲沟,高密度沉积物重力流,切割—充填结构海底,V形水下河谷、滑塌等。根据海底扰动程度作了分区,划分了地形单元,并对不同的海底形态的成因作了分析。比较了1985和1986年两个航次考查结果的变动,分析了原因。     

侵蚀模型中的遍历理论

引言地貌学家用了20多年的时间先后建立了一些相当复杂的坡面侵蚀模型。例如,杨(Young.1972)总结了四类坡面演化模型:(1)根据直线后退建立的模型;(2)根据蠕动和流动机制建立的模型;(3)涉及形态相互作用的模型;(4)根据过程量测建立的模型。在前两个模型中,明显存在一种可以得出两个基本方程的逼近收敛性:(?)y/(?)t=-b((?)y/(?)x)。(1)式中 y 为高度;t 为时间:x 为位置,以距分水岭的长度来表示;b 为正常数。这个方程显然是描述坡面随时间变化而平行后退的现象,故 b 被称为“后退系数”。     

栾川县自然资源综合开发利用研究

栾川县位于豫西深山区,伊河上游。全县土地面积2477.3平方公里,耕地19.6万亩。1986年总人口26.44万人,农业人口占96％。全县地势东北低西南高,海拔450米到2000米以上,最高峰鸡角尖2212.5米。县内林、牧和土特产资源丰富,矿产资源多样。但如何综合开发利用这些资源,是县城经济振兴中一个急待研究的问题。 一、自然资源的特点 1、以林牧为主的土地利用结构。熊耳山横贯栾川境的中北部,南面是伏牛山。地貌以中低山为主,海拔450米到1000米的中切割低山占总面积的50.6％,     

The Distribution of Different Races in China.

1. The Plains 2. The Hilly Regions     

四颗南天脉冲星在1560 MHz上的偏振观测

本文给出88年6月和7月期间在澳大利亚Parkes进行的一次南天脉冲星偏振观测的部分有意义的结果。频率为1560MHz。采用了Jodrell Bank天文台新研制成的2×16×5MHz滤波系统,使这次观测具有很强的消色散能力和较高的灵敏度。这4颗南天脉冲星具有较强的线偏振,为首次获得的高频偏振资料。     

A Scheme for Objective Analysis of Wind Field Incorporating Multi-Weighting Functions in the Optimum Interpolation Method

A method of objective analysis scheme having three different weighting functions for different conditions of the wind flow has been developed for the Indian region, two of which are anisotropic and third one is isotropic. Basically Gandin’s Optimum Interpolation method is used. The “effective” distance between a grid point and observation point used for the anisotropic functions, has been applied to calculate weighting functions following Benjamin and Seaman (1985) and objective analyses were made at the 700 hPa level for three consecutive days from 6 July to 8 July 1979. The quantitative evaluation of the objectively analysed fields have been made by computing the R.M.S. errors. Ana-lyses obtained using multi-weighting functions (anisotropic) and those obtained using ordinary circular functions (isotropic-Gandin, 1963) have been compared. Also, the centres of the monsoon depressions obtained by this method have been compared with those of subjective analyses.     

He,Ne and Ar isotopic composition of Fe-Mn crusts from the western and central Pacific Ocean and implications for their genesis

The noble gas nuclide abundances and isotopic ratios of the upmost layer of Fe-Mn crusts from the western and central Pacific Ocean have been determined. The results indicate that the He and Ar nu- clide abundances and isotopic ratios can be classified into two types: low 3He/4He type and high 3He/4He type. The low 3He/4He type is characterized by high 4He abundances of 191×10-9 cm3·STP·g-1 on average, with variable 4He, 20Ne and 40Ar abundances in the range (42.8―421)×10-9 cm3·STP·g-1, (5.40―141)×10-9 cm3·STP·g-1, and (773―10976)×10-9 cm3·STP·g-1, respectively. The high 3He/4He samples are characterized by low 4He abundances of 11.7×10-9 cm3·STP·g-1 on average, with 4He, 20Ne and 40Ar abundances in the range of (7.57―17.4)×10-9 cm3·STP·g-1, (10.4―25.5)×10-9 cm3·STP·g-1 and (5354―9050)×10-9 cm3·STP·g-1, respectively. The low 3He/4He samples have 3He/4He ratios (with R/RA ratios of 2.04―2.92) which are lower than those of MORB (R/RA=8±1) and 40Ar/36Ar ratios (447―543) which are higher than those of air (295.5). The high 3He/4He samples have 3He/4He ratios (with R/RA ratios of 10.4―12.0) slightly higher than those of MORB (R/RA=8±1) and 40Ar/36Ar ratios (293―299) very similar to those of air (295.5). The Ne isotopic ratios (20Ne/22Ne and 21Ne/22Ne ratios of 10.3―10.9 and 0.02774―0.03039, respectively) and the 38Ar/36Ar ratios (0.1886―0.1963) have narrow ranges which are very similar to those of air (the 20Ne/22Ne, 21Ne/22Ne, 38Ar/36Ar ratios of 9.80, 0.029 and 0.187, respectively), and cannot be differentiated into different groups. The noble gas nuclide abundances and isotopic ratios, together with their regional variability, suggest that the noble gases in the Fe-Mn crusts originate primarily from the lower mantle. The low 3He/4He type and high 3He/4He type samples have noble gas characteristics similar to those of HIMU (High U/Pb Mantle)- and EM (Enriched Mantle)-type mantle material, respectively. The low 3He/4He type samples with HIMU-type noble gas isotopic ratios occur in the Magellan Seamounts, Marcus-Wake Seamounts, Marshall Island Chain and the Mid-Pacific Sea- mounts whereas the high 3He/4He type samples with EM-type noble gas isotopic ratios occur in the Line Island Chain. This difference in noble gas characteristics of these crust types implies that the MagellanSeamounts, Marcus-Wake Seamounts, Marshall Is- land Chain, and the Mid-Pacific Seamounts originated from HIMU-type lower mantle material whereas the Line Island Chain originated from EM-type lower mantle material. This finding is consistent with varia- tions in the Pb-isotope and trace element signatures in the seamount lavas. Differences in the mantlesource may therefore be responsible for variations in the noble gas abundances and isotopic ratios in the Fe-Mn crusts. Mantle degassing appears to be the principal factor controlling noble gas isotopic abundances in Fe-Mn crusts. Decay of radioactive isotopes has a negligible influence on the nuclide abundances and isotopic ratios of noble gases in these crusts on the timescale of their formation.