洛川黄土-红粘土序列铁氧化物组成及其古气候指示

对洛川黄土、古土壤和红粘土中磁性矿物组成、成因和相关系进行了研究。结果表明:黄土磁性矿物以风尘磁铁矿为主,少量的成土赤铁矿和成土磁赤铁矿;古土壤磁性矿物以成土磁赤铁矿为主,成土赤铁矿次之,少量的风尘磁铁矿和赤铁矿;红粘土磁性矿物以成土赤铁矿为主,风尘磁铁矿和成土磁赤铁矿次之,少量风尘赤铁矿。黄土、古土壤和红粘土磁性矿物组成差异,反映了其形成期不同的古气候特性以及不同气候条件下生物地球化学作用强度的差异。干冷的冰期,黄土弱成土作用形成了以粗颗粒的风尘磁铁矿核 赤铁矿边的磁化率载体。间冰期的温暖湿润的古气候最有利于生物活动,强烈生物活动导致古土壤中大量纳米超细磁赤铁矿/磁铁矿产生,形成以磁赤铁矿为主,风尘磁铁矿核 赤铁矿边为辅的磁化率载体。红粘土成壤期,强降雨强蒸发的长干短湿的高温炎热的古气候使得红粘土化学风化强烈,生物地球化学活动较弱,形成以磁铁矿核 赤铁矿边和磁赤铁矿核 赤铁矿边的磁化率载体。黄土、古土壤和红粘土磁性矿物组成、磁性矿物相关系是其形成期独特的古气候指示。     

陇西第三纪红土磁学性质初步研究

在六盘山以西广泛分布着一套第三纪红色土状沉积,对这套沉积的成因及性质还没 有系统的研究。本文对陇西红土磁学性质的研究发现,该地红土的剩磁载体由主到次依次为磁铁矿、磁赤铁矿和赤铁矿,赤铁矿对剩磁有比较显著的贡献;特征剩磁载体主要是磁铁矿,一些古土壤中的赤铁矿也携带了部分特征剩磁,磁赤铁矿的存在不影响特征剩磁的稳定性。与六盘山以东宝鸡红土最显著的差异是陇西红土中的赤铁矿对磁学性质有明显的影响。与第四纪黄土一古土壤序列的热磁学性质的差异在于陇西红土在高温下仅产生少量或不产生强磁性矿物。这可能暗示着红土中含铁硅酸盐和粘土等矿物(可能在高温下产生磁铁矿)处于与黄土一古土壤的相应矿物不同的演化阶段。     

塔里木盆地西北缘库孜贡苏剖面晚白垩世-早中新世沉积物岩石磁学研究

对塔里木盆地西北缘库孜贡苏剖面晚白垩世-早中新世沉积物进行了热退磁及岩石磁学研究,结果表明岩石热退磁及岩石磁学特征随沉积环境可分为三种类型:潮下、台地边缘浅滩相岩石主要磁性矿物为磁铁矿及少量针铁矿、磁赤铁矿,磁性矿物含量较少、颗粒较小（假单畴）,其天然剩磁强度较小,一般小于1×10-2 A/m,在250℃~500℃能获得稳定特征剩磁方向,特征剩磁由磁铁矿携带;潮间、潮上带岩石主要磁性矿物为磁铁矿,〖JP2〗并含有少量磁赤铁矿、赤铁矿、针铁矿,磁性矿物颗粒为假单畴和多畴,天然剩磁强度一般在1×10-2 ~1 A/m之间,在250℃~580℃能获得稳定特征剩磁方向,特征剩磁由磁铁矿携带;河湖相岩石主要磁性矿物为磁铁矿、赤铁矿,并含有少量磁赤铁矿、针铁矿,磁性矿物含量较多、颗粒较小（假单畴）,天然剩磁强度一般在1×10-1 A/m以上,多数样品特征剩磁由赤铁矿携带,少数由磁铁矿与赤铁矿共同携带。岩石磁学研究对于在沉积环境复杂剖面进行古地磁研究具有重要的意义。     

黄土高原西部红粘土岩石磁学性质及其指示的亚洲内陆中中新世气候变化特征

对黄土高原西部庄浪红粘土进行详细岩石磁学分析表明,沉积物磁性由磁铁矿和赤铁矿主导,并且含有一定量的磁赤铁矿.中中新世大暖期红粘土中磁铁矿、磁赤铁矿含量显著升高;中中新世大暖期前后红粘土中的磁铁矿含量相对较低,赤铁矿相对含量较高,但并未显示较强的磁赤铁矿信息.磁性矿物的整体粒径表现为以SP,SD和PSD颗粒为主,MD颗粒较少.庄浪红粘土磁化率在16.5 ～ 13.8Ma出现峰值,与当时的夏季风强盛、降水丰富、成壤作用较强造成的亚铁磁性矿物相对含量增加密切相关.在全球气候变暖的中中新世大暖期,综合庄浪岩石磁学特征以及陆地和海洋的其他证据可以推测当时东亚冬、夏季风可能同时增强.     

佳县红粘土磁学性质

黄土/古土壤序列和红粘土均已被证明是风积成因,然而红粘土研究的程度远低于黄土/古土壤序列,比如强发育红粘土获得比较低磁化率值的原因并没有得到清楚解释,红粘土磁化率代用指标问题和红粘土搬运路径等问题还存在较大的争议,红粘土记录古气候意义研究也相对薄弱,因此加强对红粘土的研究,有助于对古气候的理解.佳县位于黄土高原与毛乌素沙漠交接地区,季风区与非季风区过渡地带.对佳县厚60m的红粘土样品进行系统磁学参数测量分析发现,佳县红粘土以软磁性矿物(磁铁矿、磁赤铁矿)为主,同时含有一定量硬磁性矿物(赤铁矿、针铁矿,主要是赤铁矿);强发育古土壤层含有较多软磁性矿物,弱发育古土壤层含有较多硬磁性矿物;磁颗粒粒径基本在0.2μm以下,x＞64×10-8m3/kg时,磁颗粒粒径小于0.1μm.剖面底部磁学参数变化存在异常,原因可能是:赤铁矿含量增加,超顺磁(SP)亚铁磁性颗粒含量急剧减少,单畴(SD)颗粒相对含量增加.该异常原因解释符合前人提出的成壤路径:水铁矿→SP磁赤铁矿→SD磁赤铁矿→SD赤铁矿.     

南方红土的磁性矿物组成及其区域性差异

位于我国热带、亚热带地区的南方红土是我国分布最广的第四纪土状沉积,其经历了较强的化学风化作用,具有典型的磁性矿物组成.磁性矿物是沉积物的重要组成成分.磁性矿物的种类、粒度和含量等信息可以反映沉积物形成时的温度、降水等气候条件.因此,了解红土沉积物磁性矿物组成对于研究南方红土区的环境演化具有重要意义.本文综合分析了安徽室城、浙江长兴、江西九江及广西百色4个剖面不同层位红±样品的x-T曲线、三轴等温剩磁热退磁曲线等岩石磁学结果,发现南方红土的磁性矿物组成主要为磁铁矿、磁赤铁矿、赤铁矿及针铁矿,这些磁性矿物的相对含量不仅具有地带性差异,而且在不同风化阶段也存在差异.其中百色剖面顶部棕色土中磁赤铁矿含量相对其他剖面较高,与百色地区现今较强的风化作用相符.同一剖面内网纹红土中赤铁矿的含量较高,磁赤铁矿的含量相对较低,指示网纹化时期较强的成土作用引起磁赤铁矿向赤铁矿的转化.此外,岩石磁学结果显示百色剖面网纹红土及均质红土中含有一种特殊性质的磁性矿物,即粒度较细、解阻温度较低的成土成因赤铁矿,该矿物为后期强烈风化作用的产物.该次生矿物携带了较强的化学剩磁,引起了百色剖面初始碎屑剩磁的重磁化.该研究表明磁性矿物组成的差异还可以用来解释南方红土剩磁记录的多样性.     

花岗岩上发育的亚热带红土岩石磁学特征

本文对发育于花岗岩上的两个亚热带红土剖面进行了系统的岩石磁学研究,测试了磁化率、频率磁化率、等温剩磁、非磁滞剩磁、磁滞回线等常温磁学参数,选取代表性样品进行了高低温岩石磁学分析,拟探讨亚热带红土磁性矿物的特征及湿热环境下土壤中磁性矿物的转化规律。实验结果表明:亚热带红土的强磁性矿物为磁铁矿、磁赤铁矿;弱磁性矿物为赤铁矿和针铁矿,滞水土层中含有纤铁矿。花岗岩具有较强的磁性,在其上发育的红土也因此具有较强的磁性。花岗岩中的亚铁磁性矿物的磁畴以多畴占主导地位,随着风化强度的增强,逐渐形成较细粒的超顺磁与单畴磁性矿物。亚热带红土中的磁赤铁矿与位于半干旱区黄土高原成土作用形成的磁赤铁矿存在着磁学性质上的差异,表现为具有更高的居里点(约600℃和640℃),可能说明亚热带红土中的磁赤铁矿粒径更粗。两个剖面在磁学性质上存在着明显的差异,泉州剖面磁性矿物以磁铁矿为主,磁化率最高可达1823×10~(-8)m~3/kg,平均值为1033.1×10~(-8)m~3/kg,具有较低的剩磁矫顽力;福州剖面磁性矿物以磁铁矿和部分热稳定磁赤铁矿为主,磁化率最高为385.73×10~(-8)m~3/kg,平均值为91.5×10~(-8)m~3/kg。基于磁学参数分析,认为母质与后期成土作用共同造成了两个剖面的磁学性质差异,但后者起主导作用。磁化率在两个剖面中,均随着深度减小而减小,与温带地区表层土磁化率增强有很大区别。湿热环境条件下,强磁性矿物溶解或转化为弱磁性矿物的程度主导剖面磁化率变化。     

应用矿物磁测技术和X射线衍射研究氧化土中的磁性矿物

应用矿物磁测、Ｘ射线衍射和化学分析对氧化土的磁性矿物进行了研究。结果表明矿物磁测及磁分离技术与Ｘ射线衍射结合是鉴别土壤中磁性矿物的类型及其晶粒特征的有效方法,证明氧化土中的主要氧化铁矿物是赤铁矿和磁赤铁矿,针铁矿次之,磁铁矿偶见,其磁赤铁矿的含量可达１．６２％￣１．９２％。土壤中磁性矿物的晶粒特征多以超顺磁性和稳定单畴态存在,认为磁性矿物的成因是通过缓慢的成土化学作用产生的。     

碎屑储集岩热磁特征与磁性矿物识别

对采自渤海湾盆地济阳坳陷孤南洼陷4口探井的22块古近系沙河街组碎屑储集岩标本进行了细致的磁化率-温度曲线、三轴饱和等温剩磁热退磁测试,研究不同含油级别的储集岩的热磁特征与磁性载体,结果表明:孤南洼陷沙河街组储集岩磁性矿物及其组合可以划分为3种类型:磁铁矿、针铁矿+磁黄铁矿+磁铁矿、赤铁矿+磁铁矿,岩石的磁性载体及其组合与岩石的颜色、岩性等沉积学特征密切相关,而与含油性关系不明显;在氩气环境中加热,含油标本中的磁铁矿Hopkinson峰低而宽,甚至不明显,居里温度附近曲线多呈锯齿状,冷却过程中,磁铁矿重现作用不明显,烃类有机质对碎屑储集岩中沉积成因磁铁矿的热磁行为具有一定的控制作用;烃类流体侵位,储集岩中的磁性矿物及其组合未发生明显变化,亦不存在某种演化序列或规律性,烃类流体化学重磁化不具普遍性。     

等温剩磁获得曲线的累积对数高斯模型在泥河湾盆地磁组分识别中的运用

基于饱和等温剩磁(SIRM)获得曲线遵循累积对数高斯模型(CLG)的假设，利用改进的CLG模型分析，成功地对采自泥河湾河—湖相层上部的许家窑剖面样品所含的主要载磁组分进行了分离；结合先前的岩石磁学结果，进一步验证了高矫顽力的赤铁矿和低矫顽力的磁铁矿／磁赤铁矿为许家窑样品的主要载磁矿物，并对各磁组分对SIRM的贡献进行了定量估算；对CLG模型的优缺点和实用性进行了探讨；结合剩磁矫顽力曲线特征，尝试提出了X参数的概念。     

NEW MAGNETOSTRATIGRAPHIC AND SEDIMENTOLOGIC RESULTS FROM TERTIARY SEDIMENTS OF THE HOH XIL BASIN, NORTHERN QINGHAI-TIBET PLATEAU: IMPLICATIONS FOR THE CENOZOIC TECTONIC HISTORY OF THE TIBET PLATEAU

NEW MAGNETOSTRATIGRAPHIC AND SEDIMENTOLOGIC RESULTS FROM TERTIARY SEDIMENTS OF THE HOH XIL BASIN, NORTHERN QINGHAI-TIBET PLATEAU: IMPLICATIONS FOR THE CENOZOIC TECTONIC HISTORY OF THE TIBET PLATEAU     

Depositional magnetization of Carboniferous Limestones from the Craven Basin of northern England

Carboniferous Limestones in the Craven Basin of northern England carry a stable natural remanent magnetization (NRM) the intensity of which is facies dependent. Dark argillaceous limestones are most strongly magnetized and pure, pale coloured limestones most weakly magnetized. Partial thermal and alternating field demagnetization suggest that magnetite is the principal carrier of the remanence although some haematite is present in the limestone. The presence of magnetite is confirmed by the low temperature transition, isothermal remanent magnetization (IRM build-up curves) and microprobe analysis. Partial demagnetization of IRM and ARM suggest that the magnetite is relatively coarse grained and in the multidomain state. There are no indications of pseudo-single domain behaviour but magnetite of this type cannot be excluded as a possible remanence carrier. A grain size estimate of 10–20 μm based on coercive force and remanent coercive force is compatible with the theoretical consideration of grain size. The limestones show a weak but marked magnetic susceptibility anisotropy. This anisotropy defines a depositional fabric which indicates that the magnetization is a depositional remanent magnetization (DRM). A DRM was acquired by each specimen before compaction and cementation and was preserved because of the reducing conditions which prevailed in the early diagenetic environments of the limestones.     

Palaeomagnetic study of the Ronda peridotites (Betic Cordillera, southern Spain)

A palaeomagnetic study of the Ronda peridotites (southern Spain) has been carried out on 301 samples from 20 sites, spread along the three main outcrops of the ultrabasic complex: Ronda, Ojén and Carratraca massifs. Different lithologies and outcrops with different degrees of serpentinization have been sampled and analysed. Rock magnetic experiments have been carried out on a representative set of samples. These measurements include: Curie curves, hysteresis cycles, isothermal remanent magnetization (IRM) acquisition curves, thermal demagnetization of IRM imparted along three orthogonal axes and magnetic bulk susceptibility. Results indicate that magnetite is the main magnetic mineral present in the samples. Stepwise thermal and alternating field (AF) demagnetization of the natural remanent magnetization (NRM) reveals the presence of a characteristic remanent magnetization (ChRM) carried by magnetite, and in some sepentinized samples, a northward component with variable unblocking temperatures up to 250–575 °C. The appearance and the relative intensity of this northward component are strongly related to serpentinization degree. Taking into account the geological history of the peridotites, the ChRM has been considered as a thermo-chemical remanent magnetization acquired during the first serpentinization phase associated to the post-metamorphic cooling of this unit. On the basis of radiometric and fission track analysis, the ChRM is proposed to have been acquired between 20 and 17–18 Ma. The inclination of the mean direction of the ChRM statistically coincides with the expected inclination for stable Iberia during the Oligocene–Miocene. The declination of the ChRM differs from the expected declination, indicating clockwise block rotations of 41±12° about vertical axes since the cooling of the peridotites. When applying a compositional layering correction, the ChRM directions fail to pass this kind of fold test, thus, the compositional layering was not a palaeohorizontal during ChRM acquisition time. Normal and reversed polarities of the ChRM are reported, showing that at least one reversal of the Earth's magnetic field took place during ChRM acquisition process. A tentative polarity zonation within the peridotitic outcrops is also suggested. No evidence is found from these data for the previously proposed simultaneity between post-metamorphic cooling and rotation of the peridotites.     

武昌地区街道尘埃磁学特征及其对环境污染的指示意义

对在武昌地区4个功能区域(青山、洪山、东湖风景区、东湖开发区)主要交通街道收集的尘埃样品进行详细的环境磁学测量,包括质量磁化率、频率磁化率、等温剩磁退磁系数以及典型样品的磁滞回线参数等。研究结果表明:尘埃样品中剩磁载体均以亚铁磁性矿物为主,样品中的磁性颗粒呈现低矫顽力的磁铁矿特征,软磁性的磁性矿物是样品剩余磁性的主要载体。尘埃样品χ、SIRM的区域分布特征受区域周围工业、车流量及道路状况等多种环境因素的影响,在4个功能区域中存在明显的磁性差异:青山工业区污染较重,东湖开发区、洪山、东湖风景区次之;硬剩磁(HIRM)的分布可能指示了道路交通来源的磁颗粒特征,东湖开发区和青山工业区由于行驶的货车和重型车辆较多,表现出硬剩磁量值较高。与其他城市(兰州、西安、南京、徐州等)相比,整个武昌地区街道尘埃样品的磁性含量仍较高,说明在城市环境方面还有待于进一步改善和保护。     

TERTIARY BLOCK ROTATIONS AND PYRRHOTITE/ MAGNETITE GEOTHERMOMETRY IN THE TETHYAN HIMALAYA(SHIAR KHOLA,CENTRAL NEPAL)

TERTIARY BLOCK ROTATIONS AND PYRRHOTITE/ MAGNETITE GEOTHERMOMETRY IN THE TETHYAN HIMALAYA(SHIAR KHOLA,CENTRAL NEPAL)1　AppelE ,M櫣ｌｌｅｒＲ ,WidderRW .PalaeomagneticresultsfromtheTibetanSedimentarySeriesoftheManangarea (northcentralnepal) [J].GeophysJInt ,1991,10 4:2 5 5～ 2 6 6 . 2　AppelE ,PatzeltA ,ChoukerC .SecondarypalaeoremanenceofTethyansedimentsfromtheZanskarRange (NWHimalaya)[J].GeophysJInt,1995 ,12 2 :2 2 7～ 2 42 . 3　B…     

黄土高原西部白草塬剖面L1和S1记录的古地磁场特征

文章详细介绍了黄土高原西部白草塬剖面L₁和S₁的高精度岩石磁学和古地磁学结果,讨论了白草塬剖面记录古地磁场的特征,从古地磁学角度探讨白草塬剖面黄土沉积的连续性。白草塬剖面黄土沉积物中,磁铁矿和磁赤铁矿是主要的亚铁磁性矿物,粗粒的碎屑磁铁矿是其天然剩磁和特征剩磁的主要载体。白草塬剖面L₁和S₁没有记录任何地磁漂移。其中,L₁没有记录MonoLake或Laschamp地磁漂移的原因可归结于黄土沉积物堆积过程的不连续性和/或粗颗粒载磁矿物的重磁化,但前者是主要原因,而堆积过程的不连续性是导致S₁没有记录Blake地磁漂移的主要原因。因此,白草塬剖面的L₁和S₁分别存在约2000年和4000～6000年的沉积不连续。     

Magnetic record associated with tree ring density: Possible climate proxy

A magnetic signature of tree rings was tested as a potential paleo-climatic indicator. We examined wood from sequoia tree, located in Mountain Home State Forest, California, whose tree ring record spans over the period 600 – 1700 A.D. We measured low and high-field magnetic susceptibility, the natural remanent magnetization (NRM), saturation isothermal remanent magnetization (SIRM), and stability against thermal and alternating field (AF) demagnetization. Magnetic investigation of the 200 mm long sequoia material suggests that magnetic efficiency of natural remanence may be a sensitive paleoclimate indicator because it is substantially higher (in average >1%) during the Medieval Warm Epoch (700–1300 A.D.) than during the Little Ice Age (1300–1850 A.D.) where it is <1%. Diamagnetic behavior has been noted to be prevalent in regions with higher tree ring density. The mineralogical nature of the remanence carrier was not directly detected but maghemite is suggested due to low coercivity and absence of Verwey transition. Tree ring density, along with the wood's magnetic remanence efficiency, records the Little Ice Age (LIA) well documented in Europe. Such a record suggests that the European LIA was a global phenomenon. Magnetic analysis of the thermal stability reveals the blocking temperatures near 200 degree C. This phenomenon suggests that the remanent component in this tree may be thermal in origin and was controlled by local thermal condition.     

Magnetic properties of the Chelyabinsk meteorite: Preliminary results

This paper presents the distribution of magnetic susceptibility, χ₀, in fragments of the Chelyabinsk ordinary chondrite (LL5, S4, W0, fall of February 15, 2013) from the collection of the Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, and results obtained by standard magnetic techniques for the meteorite material, including thermomagnetic analysis, measurements of natural remanent magnetization (NRM) and saturation isothermal remanent magnetization (SIRM), as well as the spectra of their alternating field demagnetization at amplitudes up to 170 mT, measurements of hysteresis loops and back-field remanence demagnetization curves at temperatures from 10 K to 700°C etc. The mean logχ₀ values for the light-colored (main) lithology of the meteorite material and impact-melt breccia from our collection are 4.54 ± 0.10 (n = 66) and 4.65 ± 0.09 (n = 38) (×10^?9 m³/kg), respectively. According to international magnetic classification of meteorites, Chelyabinsk falls within the range of LL5 chondrites. The mean metal content was estimated from the saturation magnetization, M _s, of the light- and dark-colored lithologies as 3.7 and 4.1 wt %, respectively. Hence, the dark lithology is richer in metal. The metal grains are multidomain at room temperature and show low coercive force, B _c (<2 mT) and remanent coercive force, B _cr (15–23 mT). The thermomagnetic analyses of the samples showed that the magnetic properties of the Chelyabinsk meteorite are controlled mainly by taenite and kamacite at temperatures >75 K. In the temperature range below 75 K, magnetic properties are controlled by chromite; the magnetic hardness of the samples is maximal at 10 K and equals to 606 and 157 mT for the light- and dark-colored lithologies, respectively.