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911.
912.
Using aeromagnetic data acquired in the area from the Cerro Prieto geothermal field, we estimated the depth to the Curie point isotherm, interpreted as the base of the magnetic sources, following statistical spectral-based techniques. According to our results the Curie point isotherm is located at a depths ranging from 14 to 17 km. Our result is somewhat deeper than that obtained previously based only in 2-D and 3-D forward modeling of previous low-quality data. However, our results are supported by independent information comprising geothermal gradients, seismicity distribution in the crust, and gravity determined crustal thickness. Our results imply a high thermal gradient (ranging between 33 and 38 °C/km) and high heat flow (of about 100 mW/m2) for the study area. The thermal regime for the area is inferred to be similar to that from the Salton trough. 相似文献
913.
绘制了重力测值的时变曲线和空间等值线,从动态的角度分析了1998年1月张北6.2级地震前的流动重力异常的演化及特征。结果显示,地震前的重力场呈下降变化,震中位于异常中心附近的重力变化高梯度区。 相似文献
914.
T2cutoff是核磁共振测井中的一个重要参数,它决定了核磁共振测井测量的有效孔隙度、渗透率、自由流体饱和度、束缚水饱和度等参数的精确程度.目前国内外普遍选取的T2cutoff为:砂泥岩储层取33ms,碳酸盐岩储层取92ms.实际研究发现T2cutoff应是变化的量而并非单一值.简单的运用单一的T2cutoff来计算各种地层参数势必会产生误差甚至得出错误的解释结论.叙述了33ms作为T2cutoff的由来及其不合理性,同时分析了目前国内外确定T2cutoff的各种方法及其适用性. 相似文献
915.
石英尾砂对旱地表土磁性的影响及其环境意义 总被引:1,自引:0,他引:1
对安徽省凤阳县石英尾砂、受尾砂影响的表土、旱地表土和城镇表土进行了磁学测量,结果表明这4类样品的磁性特征明显不同。尽管这4类样品的磁化率均由磁铁矿主导,但旱地表土中可能含少量磁赤铁矿,石英尾砂、受尾砂影响的表土和城镇表土中可能含少量铁的氢氧化物(如纤铁矿),受尾砂影响的表土中还含少量赤铁矿。城镇表土中磁铁矿的含量明显高于其他3类样品,受尾砂影响的表土中的磁铁矿含量介于石英尾砂和旱地表土之间。城镇表土中磁铁矿的粒径范围较宽,小于1 μm,石英尾砂中磁铁矿的粒径大于0.1 μm,旱地表土中磁铁矿的粒径小于0.1 μm,受尾砂影响的表土中磁铁矿的粒径介于旱地表土与石英尾砂的粒径之间。城镇表土的磁化率与频率磁化率呈负相关,旱地表土的磁化率与频率磁化率呈正相关,而受石英尾砂影响的表土的磁化率与频率磁化率没有明显的相关关系。在城市工业和交通等人类活动的影响下,城镇表土的磁性较旱地表土增强。而在石英砂生产这一人类活动的影响下,受尾砂影响的表土的磁性较旱地表土减弱,这是由石英尾砂中磁性矿物的含量较旱地表土4的少所致。 相似文献
916.
A.F. Lanza 《Astronomische Nachrichten》2007,328(10):1066-1069
Sequences of Doppler images of the young, rapidly rotating late-type stars AB Dor and LQ Hya show that their equatorial angular velocity and the amplitude of their surface differential rotation vary versus time. Such variations can be modelled to obtain information on the intensity of the azimuthal magnetic stresses within stellar convection zones. We introduce a simple model in the framework of the mean-field theory and discuss briefly the results of its application to those solar-like stars. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
917.
长白山区泥炭沼泽磁化率特征及其环境意义 总被引:1,自引:0,他引:1
以长白山区泥炭沼泽为研究对象,沿不同海拔选择赤池、锦北、大牛沟、金川和哈尔巴岭5个代表性采样点。通过对沼泽垂直剖面的精细采样,利用210Pb和137Cs方法对5个剖面进行高精度定年,综合研究和分析泥炭沉积物质量磁化率沿深度垂直分布特征,进而揭示其环境意义。结果表明,长白山区泥炭沼泽磁化率在表层具有明显的富集规律,富集时间始于20世纪初,并在20世纪后期达到峰值,且其富集含量可达以下层位富集平均值的5~10倍;长白山区泥炭磁化率的表聚性特征反映了在盛行西风等自然因素作用下,大气降尘和城市扩张等多种人类活动对区域环境的影响,很好地指示了区域磁性颗粒物污染扩大和加剧趋势。 相似文献
918.
919.
QiaoQin Xie TianHu Chen XiaoChun Xu ChengSong Qing HuiFang Xu YuBing Sun JunFeng Ji 《中国科学D辑(英文版)》2009,52(3):313-322
The dominant magnetic minerals and carriers of magnetic signals within the Chinese Loess Plateau are magnetite, maghemite,
hematite, and goethite. In this study, we investigated the provenance and evolution of magnetic minerals during loess pedogenesis,
using X-ray diffraction (XRD) and optical and electron microscopy, including field emission scanning electron microscopy (FESEM)
and high-resolution transmission electron microscopy (HRTEM). Our results reveal that single- and multiphase mineral assemblages
among magnetic minerals in the loess-paleosol sequence have been formed. Partial oxidation of coarse eolian magnetite has
occurred in the desert source area and the oxidation degree is enhanced after deposition of the dust upon the Chinese Loess
Plateau. This mode of origin resulted in a microtexture consisting of an inner magnetite core surrounded by a hematite rim,
and strongly affected the magnetic characteristics of the loess. Goethite coexists with hematite in the loess and paleosol,
and nanometer-scale hematite is formed upon goethite rims via dehydration. Our study provides direct mineralogical evidence
of the magnetic record and paleoclimatic implications of the loess-paleosol sequence of the Chinese Loess Plateau.
Supported by National Natural Science Foundation of China (Grant Nos. 40772032 and 40573054) and National Basic Research Program
(Grant No. 2007CB815603) 相似文献
920.
Deep crustal structures of eastern China and adjacent seas revealed by magnetic data 总被引:5,自引:0,他引:5
Through reduction to the North Pole and upward continuation of the total field magnetic anomalies, we analyze magnetic patterns
and spatial distributions of different tectonic blocks and crustal faults in eastern China and adjacent seas. Depths to the
Curie isotherms are further estimated from radially averaged amplitude spectra of magnetic data reduced to the pole. Data
reductions effectively enhance boundaries of regional tectonic belts, such as the Dabie ultra-high metamorphic belt, the Tanlu
Fault, and the Diaoyudao Uplift. Curie depths are estimated at between 19.6 and 48.9 km, with a mean of 31.7 km. The Subei
Basin and the south Yellow Sea Basin in the lower Yangtze block show relatively deep Curie isotherms, up to about 35 km in
depth, whereas in the surrounding areas Curie depths are averaged at about 25 km. This implies that the lower Yangtze Block
has experienced a unique tectonic evolution and/or has unique basement lithology and structures. From a regional perspective,
sedimentary basins, such as the Subei Basin, the south Yellow Sea Basin, and the East China Sea Basin, normally show deeper
Curie isotherms than surrounding uplifts such as the Diaoyudao Uplift and the Zhemin Uplifts. Curie isotherms also upwell
significantly in volcanically active areas such as the Ryukyu Arc and the Cheju Island, confirming strong magmatic and geothermal
activities at depth.
Supported by National Natural Science Foundation of China (Grant Nos. 40776026 and 40876022) and National Basic Research Program
of China (Grant No. 2007CB411702) 相似文献