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Ping?Li Xinzhuan?GuoEmail author Sibo?Chen Chao?Wang Junlong?Yang Xingfan?Zhou 《Contributions to Mineralogy and Petrology》2018,173(2):16
In order to investigate the origin of the high conductivity anomalies geophysically observed in the mid-lower crust of Tibet Plateau, the electrical conductivity of plagioclase–NaCl–water system was measured at 1.2 GPa and 400–900 K. The relationship between electrical conductivity and temperature follows the Arrhenius law. The bulk conductivity increases with the fluid fraction and salinity, but is almost independent of temperature (activation enthalpy less than 0.1 eV). The conductivity of plagioclase–NaCl–water system is much lower than that of albite–NaCl–water system with similar fluid fraction and salinity, indicating a strong effect of the major mineral phase on the bulk conductivity of the brine-bearing system. The high conductivity anomalies of 10?1 and 100 S/m observed in the mid-lower crust of Tibet Plateau can be explained by the aqueous fluid with a volume fraction of 1 and 9%, respectively, if the fluid salinity is 25%. The anomaly value of 10?1 S/m can be explained by the aqueous fluid with a volume fraction of 6% if the salinity is 10%. In case of Southern Tibet where the heat flow is high, the model of a thin layer of brine-bearing aqueous fluid with a high salinity overlying a thick layer of partial melt is most likely to prevail. 相似文献
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Optical dating is a method of measuring the time since the sample was buried from last thermal event or light exposure. Samples such as quartz and feldspar grains are the most commonly used sediment of measurement. Single-Aliquot Regenerative-dose (SAR) method has become the most acceptable procedure for obtaining the equivalent Dose (De) of a sample. The Standardised Growth Curve (SGC) method provides a possible procedure for measuring a large number of samples; the limitation is that the growth curve fitted by different samples or even different aliquots is divergent. The global Standardised Growth Curve (gSGC) method improves the shortage by normalizing the dose response curves using one regenerative dose OSL signal. The gSGC provides a possible method for obtaining the De value of the sample efficiently and quickly. However, due to the radiation dose rate, operating procedures and instrument error and the selected regenerative-dose normalized dose value, etc., each laboratory should develop their own gSGC which has unique parameters. This study established the gSGC curve and measurement process of our laboratory, and then compared the consistency of the equivalent Dose (De) values from gSGC and SAR methods. In gSGC procedure, the De value of an aliquot can be estimated from the nature signal, one regenerative dose signal and their corresponding test dose signal. It will speed up the optical dating measurement rate of our laboratory and provide reference to establish gSGC in other laboratories. It is found that in the low dose range (0~100 Gy) the obtained De values were well consistent by gSGC and SAR methods. There were obviously differences in the higher dose range (>100 Gy) compared to the SAR results. It may be due to the insufficient number of older samples used to fit gSGC in this study. It is necessary to gradually accumulate more samples to improve the gSGC parameters in the future work. For some aliquots, individual quartz grains do not follow the global standardised growth curve, which leads to some deviations of De from gSGC. However, these two methods could obtain the similar average De value when multiple aliquots measuring. 相似文献
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基于DEM数据的巴丹吉林沙漠沙丘分布规律及其形态参数 总被引：2，自引：2，他引：0
沙丘形态特征是风沙地貌研究的重要内容。数字高程模型（DEM）因卓越的三维地形表达能力被广泛应用于沙丘形态研究中。长期以来,受交通条件和研究方法的制约以及高大沙山分布位置的限定,对巴丹吉林沙漠沙丘形态的研究主要集中在沙漠东南部,缺乏对整个沙漠沙丘分布规律及其形态参数特征的系统认知。而对整个沙漠沙丘形态特征的研究,是区域风沙地貌形成与演化研究的重要组成部分。以巴丹吉林沙漠内所有独立沙丘为研究对象,利用研究区DEM数据和一种新的算法,研究了沙漠内两种主要类型沙丘（横向沙丘、星状沙丘）的分布规律及其形态参数特征。结果表明：沙漠内独立沙丘大约有6 033座,高度9~433 m,高度超过350 m的巨型沙山共有53座,其中星状沙山7座,最大高度383 m;横向沙山46座,最大高度433 m。横向沙丘高度与等效沙丘厚度呈正相关的线性函数关系,星状沙丘高度与等效沙丘厚度呈正相关的对数函数关系,表明在现代气候和环境条件下,横向沙丘高度仍在增加,而星状沙丘高度增长已经趋缓。两类沙丘的主轴向大都垂直于研究区主风向NW-SE。横向沙丘起沙风风向单一,沙丘轴向集中在NE-SW和NNE-SSW方向;星状沙丘起沙风风向略为复杂,沙丘存在多个次级轴向。 相似文献
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标准生长曲线（Standardised Growth Curve,SGC）法的提出为高效快速地测定释光样品的等效剂量（De）值提供了可能。不同实验室的放射源剂量率、操作流程、仪器误差等的不同会导致SGC参数的不同。运用最小二乘法标准化实验剂量校正后的信号Lri/Tri*De得到一条本实验室的标准生长曲线,用来快速得到等效剂量值。通过R软件实现了最小二乘法标准化过程,建立了50、100、150、200、250℃激发温度下的钾长石的标准生长曲线,分析发现250℃下的SGC收敛性最好,由于此温度下的信号衰退率可忽略不计,因此,我们用250℃激发温度下的SGC方程来估计样品的等效剂量。比较250℃ SGC De和250℃ MET-pIRIR De的一致性,发现在0~500 Gy范围内用SGC法估计的De和MET-pIRIR法估计的De非常接近,表明了此范围内SGC法的可靠性,而在>600 Gy范围内出现较大差别。一方面,此范围内用于拟合SGC的数据点较少导致高剂量区域内拟合的方程参数不够准确;另一方面,600 Gy与SGC对应的饱和剂量水平值844.5 Gy已经接近,所以在>600 Gy区域测出的De很可能出现较大偏差。因此需在今后工作中逐步积累更多样品,完善SGC参数,使其也能胜任较老年龄样品。 相似文献
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Wang Xingfan Zhao Hui Sheng Yongwei Geng Jianwei Wang Keqi Yang Hongyu 《中国科学:地球科学(英文版)》2020,63(5):713-725
Science China Earth Sciences - Over a hundred sizable lakes, some even larger than ~1 km2, are distributed across the lowlands between megadunes in the southeastern Badain Jaran Desert (BJD),... 相似文献
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文章通过对涠洲岛珊瑚礁生态系统近20年的环境监测数据的梳理,结合前人研究,分析涠洲岛珊瑚礁生态系统的水质、生态和地貌特征以及极端天气过程(台风和暴雨)对其的影响。结果显示,涠洲岛珊瑚礁生态系统的水质、生态和地貌现状均健康良好,适宜珊瑚礁的生长发育,但总体呈现衰退趋势。极端天气过程的影响会给涠洲岛珊瑚礁生态系统造成短时间内的毁灭性打击。随着人类活动的加剧,涠洲岛珊瑚礁生态环境质量有所降低,应引起足够的重视。对涠洲岛珊瑚礁生态系统长期的监测和研究,不仅可以为保护和开发管理海岛珊瑚礁提供科学支撑,也为验证达尔文的环礁成因学说提供第一手资料。 相似文献
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