时差对海洋磁力测量地磁日变改正的影响分析

为研究时差对磁测的影响,基于站间同步地磁日变曲线的特征,尝试采用同步比对法和相关分析法计算两站的时差.结论表明:同步比对法和相关分析法能反映站间真实的时差,当测区范围较小时(至少是在本文实例的两个地磁日变站之间),时差对地磁日变改正的影响很小,海洋磁力测量地磁日变改正时可以忽略其影响.     

长江口水下三角洲沉积物记录的古环境演化

长江口水下三角洲60 m的HYZK5钻孔,揭示了末次冰期以来河流相、滨海湖沼相、河口湾-浅海相(前三角洲相)和水下汊道相的沉积环境演化。泥炭层形成于末次冰期的冷湿气候环境;有孔虫丰度的变化反映了12 000 cal.aBP以来海平面迅速上升,但在11 200~10 000 cal.aBP出现短暂的停顿。沉积物的粒度、磁化率、有机碳氮分析结果表明,三者在不同沉积相中存在明显的差异。磁化率在一定程度上可以指示水动力的强弱,间接反映沉积环境的演变,但难以反映气候的变化。河口湾-浅海(前三角洲)相粒度、磁化率和有机碳氮指标的变化均很小,反映了其沉积环境相对稳定。最上层粒径的粗化、磁化率的增大、有机碳氮的减少以及三者波动幅度的加剧,均反映了其处于潮流、波浪、径流等动力相互作用的高能沉积环境,也是长江口北支及其口外水下三角洲衰退的重要证据。虽然粒度、磁化率、有机碳氮和有孔虫丰度指标在较大的沉积环境变化中均有所反映,但由于海陆交互作用的河口地区沉积环境和动力因素的复杂性和多变性,要揭示河口地区冰后期以来的气候演化特征,还需要寻找其他可靠的环境代用指标作更深入的研究。     

磁性矿物还原成岩作用述评

许多海洋－湖泊环境中的沉积物受到还原成岩作用的影响发生磁性颗粒的溶解和自生现象。根据最近二十多年的研究成果,简要介绍了磁性矿物发生还原作用的基本过程、产物和控制因素,成岩作用对沉积物地球化学和磁学特征的改变,成岩自生亚铁磁性铁硫化物的磁学特征以及成岩作用对古地磁和环境磁学记录的影响。     

太阳静日变化的特征分析

根据北京明陵地磁台2010年观测数据,采用磁静日数据,选用其特征值——日变幅度和相位,对太阳静日变化特征进行了初步分析,并用调和分析方法将其分解为3个周期的谐波分量。对地磁数据的分析处理具有一定的参考价值。     

冲绳海槽北段的重磁场特征及地质意义

１９９２年之前,国内对冲绳海槽的调查研究主要集中在海槽的中部和南部,而对其北段的调查研究工作却很少。根据实测的重磁异常,较深入地分析了海槽北段的地球物理场特征,构造活动地壳结构及应力状态,结果表明冲绳海槽北段同样具有强烈的地壳构造活动。     

兴凯湖沉积物磁化率和色度反映的28kaBP以来区域古气候环境演化

对兴凯湖长269 cm的沉积岩心的研究结果显示:沉积物的色度和磁化率特征可以较好地反映区域气候环境变化。沉积物明度分别与红度、磁化率、黏土和有机质含量之间及磁化率与黏土之间有很好的相关性;红度高值与明度低值对应暖湿气候环境,磁化率低值反映沉积物较粗的较低湖面,对应冷干气候。28480~26160 cal.aBP,湖区处于温湿气候时期;22880~18170 cal.aBP,岩心孢粉浓度很低,流域处于末次盛冰期疏桦林草原环境;18170~12650 cal.aBP处于Bφlling/Older Dryas/Allerφd暖期。岩心深度90~78 cm段,对应于新仙女木期;11500~4570 cal.aBP,进入全新世暖期,其中8000~5000 cal.aBP,本区处于全新世大暖期(气候适宜期);4570~1470 cal.aBP气候变为凉干;1470 cal.aBP以来,流域又变为暖湿气候环境,同时,人类活动逐渐增强造成水土流失加剧。     

Effect of superstrong magnetic field on electron screening at the crusts of neutron stars

The influences of electron screening (ES) and electron energy correction (EEC) are investigated by superstrong magnetic field (SMF). We also discuss in detail the discrepant factor between our results and those of Fushiki, Gudmundsson and Pethick (FGP) in SMF. The results show that SMF has only a slight effect on ES when B < 10⁹ T on the surfaces of most neutron stars. Whereas for some magnetars, SMF influence ES greatly when B > 10⁹ T . For instance, due to SMF the ES potential may be increased about 23.6% and the EEC may be increased about 4 orders of magnitude at ρ/μ_e = 1.0×10⁶ mol/cm³ and T₉ = 1. On the other hand, the discrepant factor shows that our results are in good agreement with FGP's when B < 10⁹ T . But the difference will be increased with increasing SMF.     

Effect of strong magnetic field on chemical potential and electron capture in magnetar

The chemical potential of electrons in a strong magnetic field is investigated. It is shown that the magnetic field has only a slight effect on electron chemical potential when B<10¹¹ T, but electron chemical potential will decrease greatly when B>10¹¹ T. The effects of a strong magnetic field on electron capture rates for ⁶⁰Fe are discussed, and the result shows that the electron capture sharply decreases because of the strong magnetic field.     

水成沉积与风成沉积及古土壤的磁组构特征

晚第四纪水成沉积、风成沉积、古土壤等的磁组构研究表明,不同成因的沉积物具有明显不同的磁组构特征。一般地,水成沉积的体积磁化率Ｋ受物源和水动力因素控制,Ｐ和Ｆ均＞１．０２,ｑ＜０．５;风成沉积的Ｋ受物源控制,内陆黄土的Ｋ明显高于沿海黄土及海岸风沙Ｋ,Ｐ和Ｆ均＜１．０２,ｑ的平均值＞０．５５;古土壤的Ｋ受母质沉积类型和成土环境的氧化还原条件控制,内陆古土壤的Ｋ偏高,沿海古土壤的Ｋ偏低,内陆古土壤的Ｋ远高于沿海古土壤的Ｋ,Ｐ和Ｆ均＜１．０２,ｑ的平均值在０．５左右。运用典型沉积的磁组构特征对比分析未知沉积物,可以得到未知沉积物的物源、沉积过程和环境信息。     

Three-dimensional inversion of marine magnetic anomalies: Implications for crustal accretion along the Mid-Atlantic Ridge (28°–31°30′ N)

We present magnetic field data collected over the Mid-Atlantic Ridge in the vicinity of the Atlantis Fracture Zone and extending out to 10 Ma-old lithosphere. We calculated a magnetization distribution which accounts for the observed magnetic field by performing a three-dimensional inversion in the presence of bathymetry. Our results show the well-developed pattern of magnetic reversals over our study area. We observe a sharp decay in magnetization from the axis out to older lithosphere and we attribute this decay to progressive low temperature oxidation of basalt. In crust which is 10 Ma, we observe an abrupt increase in magnetic field intensity which could be due to an increase in the intensity of magnetization or thickness of the magnetic source layer. We demonstrate that because the reversal epoch was of unusually long duration, a two-layer model comprised of a shallow extrusive layer and a deeper intrusive layer with sloping polarity boundaries can account for the increase in the amplitude of anomaly 5. South of the Atlantis Fracture Zone, high magnetization is correlated with bathymethic troughts at segment end points and lower magnetization is associated with bathymetric highs at segment midpoints. This pattern can be explained by a relative thinning of the magnetic source layer toward the midpoint of the segment. Thickening of the source layer at segment endpoints due to alteration of lower oceanic crust could also cause this pattern. Because we do not observe this pattern north of the fracture zone, we suggest it is a result of the nature of crustal formation process where mantle upwelling is focused. South of the fracture zone, reversals along discontinuity traces only continue to crust 2 Ma old. In crust >2 Ma, we observe bands of high, positive magnetization along discontinuity traces. We suggest that within the discontinuity traces, a high, induced component of magnetization is produced by serpentinized lower crust/upper mantle and this masks the contribution of basalts to the magnetic anomaly signal.