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。     

红粘土的磁学性质研究

本文对陕西宝鸡剖面红粘土上部进行了详细的岩石磁学研究，确定了该地区红粘土的主要磁性矿物是磁铁矿。赤铁矿相对含量很少，对剩余磁性贡献较小。磁性质不稳定的磁赤铁矿存在于红粘土中，但不影响剩磁稳定性。特征剩磁载体主要是磁铁矿。磁性矿物的粒度是以准单畴为主。红粘土的短时间弛豫粘滞剩磁很强，因此在零磁空间进行退磁和剩磁测量是非常重要的。     

泥河湾盆地大长梁剖面河湖相沉积序列的细腰磁滞回线性质及其环境意义

对华北泥河湾盆地大长梁剖面更新世河湖相沉积序列进行的多参数岩石磁学研究表明磁铁矿和赤铁矿是大长梁剖面最主要的磁性矿物.磁铁矿的粒度主要为准单畴和多畴,主要来自盆地周围侵蚀的碎屑矿物;赤铁矿主要为风成成因,来源于中国西北部的黄土高原或沙漠地区的化学风化作用产物;某些沉积层中还含有主要由碎屑成因的粗颗粒磁铁矿经低温氧化形成的磁赤铁矿,该过程可能与泥河湾古湖的氧化环境演化密切相关.大长梁剖面的磁滞回线大多具有细腰特征,细腰的明显程度主要由样品中磁铁矿和赤铁矿的相对贡献控制.因此,细腰磁滞回线可以用来衡量泥河湾河湖相沉积物中赤铁矿的相对含量,并进而在一定程度上指示亚洲内陆干旱/半干旱地区化学风化作用的强弱以及相对温湿或冷干的气候环境变化.     

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。     

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.     

还原成岩作用对磁性矿物的影响及古气候意义:以长江口水下三角洲岩芯YD0901沉积物为例

本文对长江口水下三角洲岩YD0901(31°11′N,122°30′E)中0～34.22m的沉积物进行高分辨率岩石磁学研究,结果表明:阶段Ⅰ (0 ～ 8m)中磁性矿物含量高,含有磁铁矿、赤铁矿及少量的硫化物;阶段Ⅱ(8.0～34.2m)中磁性矿物含量低,磁性矿物包括粗颗粒磁铁矿、赤铁矿和铁的硫化物.磁参数结果指示了沉积物垂向上氧化还原环境的改变,由还原环境(阶段Ⅱ)转为氧化环境(阶段Ⅰ).受成岩作用影响,阶段Ⅱ中的细颗粒的磁铁矿颗粒被溶解而生成铁的硫化物,但是粗颗粒磁铁矿和赤铁矿受成岩作用影响较小,可以提取原生的古气候信息.根据磁性矿物含量和矫顽力的变化在1300年至7000年之间识别出4个气候突然变冷事件,沉积物磁性矿物矫顽力反映的气候变化周期为800年和220年.     

中国大陆科学钻探主孔正片麻岩磁性及深部流体活动

通过对中国大陆科学钻探工程主孔花岗质片麻岩进行详细的岩石磁学研究及岩石矿物学分析表明: 花岗质片麻岩磁化率(0.570×10-7~120.450×10-7m3·kg-1, 平均29.996×10-7m3·kg-1)在主孔所有岩石中仅次于蛇纹石化石榴石橄榄岩, 而其天然剩余磁化强度(0.002×10-3~2.109×10-3Am2·kg-1, 平均0.210×10-3Am2·kg-1)则是所有岩性中最低的.磁化率随温度变化曲线、交变退磁曲线及磁滞回线特征表明, 花岗质片麻岩中磁性矿物组合主要成分为磁铁矿, 小部分样品中含有赤铁矿, 其中磁铁矿以多畴为主, 伪单畴磁铁矿仅在少量样品中出现.和同为完全退变质岩的角闪岩(完全退变质榴辉岩)相比, 花岗质片麻岩具有相似的磁性矿物组合, 但其磁铁矿的颗粒明显较大.多畴磁铁矿的形成, 可能和超高压变质岩折返过程中, 花岗质片麻岩较强的流体活动相关.部分分布于花岗质片麻岩主体岩性段外的样品, 具有较高的天然剩余磁化强度, 则可能反映了花岗质片麻岩及周围榴辉岩之间的流体交换.      

中亚地区现代表土磁学特征及其古环境意义*

在中国西北地区主要沙漠、绿洲和戈壁及蒙古国南部戈壁等亚洲中部粉尘源区采集了表土(包括沙漠和土壤)样品,系统分析了样品的磁学性质(包括磁化率、无磁滞磁化率、等温剩磁、磁滞回线和热磁曲线)。结果表明,中亚地区表土样品中主要磁性矿物是铁磁矿,含有赤铁矿和磁赤铁矿,并伴有少量顺磁性矿物;磁性矿物粒度主要是准单畴(PSD)和多畴(MD),超顺磁性颗粒含量较低,接近于中国西部黄土地层含量。中亚地区表土磁性矿物含量总体都较低,磁性矿物含量在空间上与降雨量成正比。研究结果指示西部地区(准噶尔盆地和南部塔里木盆地)表土样品较北部地区(鄂尔多斯高原、阿拉善高原以及蒙古高原)表土样品,其粗颗粒磁性矿物含量高,而细颗粒磁性矿物含量低。本研究结果为黄土地层古土壤磁性增强源自成土过程提供了最直接的证据。     

冀东司家营铁矿床富矿成矿条件研究

根据野外勘查,对冀东司家营铁矿床的普通矿石和富铁矿石进行了岩相学、主量元素、微量元素和稀土元素的研究。富铁矿顺层产于贫矿体中,富铁矿石颗粒与贫铁矿相比稍粗,主要由磁铁矿及铁闪石组成,部分铁闪石蚀变为绿泥石,表明司家营铁矿床的富铁矿矿石的形成与后期热液活动密切相关。司家营铁矿床不同矿石的主量元素分析结果表明,富矿石较普通矿石的石英含量减少,镁铁质矿物含量相对增加,所有矿石中MnO/TFe2O3比值极低,含量变化于0.001～0.01之间,平均值为0.002,指示了矿石的热水沉积成因。普通矿石和富铁矿石的微量元素和稀土元素配分模式有较好的一致性,表明不同类型矿石成矿物质来源可能相同。与磁铁矿普通矿石相比,赤铁矿普通矿石和富铁矿矿石的∑REE+Y含量更高,稀土元素配分曲线相比较更加平缓。造成赤铁矿普通矿石∑REE+Y含量增高和稀土元素配分曲线平缓的原因可能是赤铁矿距离地表较近,遭受后期淋滤作用。关于富铁矿矿石稀土元素∑REE+Y含量最高和稀土元素配分曲线平缓的原因,除了铁质沉积物更易吸收稀土元素外,后期变质热液蚀变也是非常重要的因素。     

宁武天池干海湖泊沉积物的部分非磁滞剩磁研究

应用部分非磁滞剩磁(pARM)谱,对山西宁武天池干海湖泊沉积物携带的磁信息研究表明,粗磁铁矿颗粒(MD)是主要载磁矿物颗粒,其pARM谱在低矫顽力区间(AF20 mT)达到最高值;而细磁铁矿颗粒(PSD-SD)为次要载磁颗粒,其pARM谱在高矫顽力区间(AF20 mT)稍有突起。但是,剖面三个层位具有不同特征,上层(大约7.3~4.0 ka)的粗磁性矿物颗粒含量最高,下层(大约12.0~13.0 ka)次之,而中层(大约12.0~7.3 ka)相对最低;中层的细磁性颗粒含量最高,下层和上层的细磁性颗粒含量次之。pARM谱分析结果与磁滞曲线测量获得的磁畴结果一致。在较高的交变磁场区间获得的pARM可以有效地压抑粗磁颗粒的信息,进而使细磁颗粒的信号增强。应用pARM谱分析,能有效判别样品中磁性矿物的磁畴状态,有助于沉积物的古气候、岩石磁学和古地磁学研究。     

Specific features of the mineral composition and petromagnetic properties of rocks from the Minami-Khiosi submarine volcano (Mariana island arc)

Complex studies of the mineral composition and petromagnetic properties of the rocks which compose an edifice of the Minami–Khiosi submarine volcano located in the Mariana island arc are carried out for the first time. The Minami–Khiosi Volcano is a part of the Khiosi volcanic complex within the alkaline province of the Idzu–Bonin and Mariana island arcs. All of the rocks analyzed are enriched in K₂O (1.34–3.30%), Ba (370–806 ppm), and Sr (204–748 ppm). The basalt has a porhyric texture and contains mosTy olivine phenocrysts as individual crystals and growths with a size up to 2 cm; the groundmass is finecrystalline. The samples studied contain at least three Fe-bearing oxide minerals. These are predominant magnetite and less abundant ilmenite and Fe hydroxides. It is established that the samples studied are magnetically isotropic and have high values of natural remanent magnetization and Königsberger ratio. Similarly to the other island-arc Late Cenozoic submarine volcanoes in the western part of the Pacific Ocean, the samples studied are strongly differentiated by the value of natural remanent magnetization and magnetic susceptibility. The low-coercivity magnetic minerals (titanomagnetite and magnetite) of the pseudo-single-domain structure, as well as high-coercivity minerals (hematite) are the main carriers of magnetization. The high values of natural remanent magnetization are explained by the pseudo-single-domain structure of the titanomagnetite grains, whereas the high values of magnetic susceptibility result from the high concentration of ferromagnetic grains.     

Petromagnetic parameters of bottom sediments as indicators of the climatic and environmental changes in the central zone of the Sea of Okhotsk during the last 350 kyr

Bottom sediments from the central zone of the Sea of Okhotsk were preliminarily dated. The petromagnetic parameters of two groups of samples formed at cold and warm climatic stages were studied. Warm oxygen isotopic stages and substages were characterized by the coexistence of pseudo-single-domain allogenic magnetite and predominant magnetite and greigite (pyrrhotite) grains subject to biologic control. At cold stages, sediments containing a mixture of pseudo-single-domain and multidomain terrigenous magnetite particles accumulated. The petromagnetic curves agree with the normalized standard oxygen isotopic curve over the last 350 kyr of the column section.     

Investigating the potential of using environmental magnetism techniques as pollution proxy in urban road deposited sediment

The use of mineral magnetic techniques as pollution proxy for road deposited sediment was explored using various statistical approaches. Standard techniques were adopted for measurement of mineral magnetic and geochemical parameters. The analyses of magnetic parameters revealed that the samples were dominated by ferrimagnetic minerals and multidomain grains. This implied that the magnetic fractions in the samples might be of anthropogenic origin. Results also indicate that the samples were dominated by low coercive, magnetically soft minerals. Thermomagnetic curves confirmed magnetite as the remanence bearing magnetic mineral having a Curie point temperature of ~580 °C. The strong association observed between magnetic susceptibility, susceptibility of anhysteric remanent magnetization and saturation isothermal remanent magnetization and aluminum, titanium, manganese, iron, chromium and lead demonstrated that these metals occurred as ferrimagnetic particles of technogenic origin resulting from vehicular sources. Assessment of pollution status of the road deposited sediment identified silicon and lead as the priority pollutants of concern. Generally, pollution load index was <1 (mean, 0.66 ± 0.14), indicating that the samples were not polluted in the overall, but the metals were in the buildup stage requiring constant monitoring. The sources of pollutants from principal component and cluster analyses identified the sources of pollution to be mainly from vehicular emissions such as brake linings, exhaust materials, tire wear, corroded metal parts, abrasion of lubricating oil and road construction materials. This study found that mineral magnetic techniques offer great potential as pollution proxy for soil pollution studies.     

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.     

Relationship between magnetic properties and heavy metals of urban soils with different soil types and environmental settings: implications for magnetic mapping

Two types of soil (fluvisols and anthrosols) were collected from different environmental settings (suburb and industrial area) in Wuhan, central China, aiming to examine the applicability of magnetic mapping for heavy metal pollution of urban soil in a large region. Magnetic measurements and chemical analysis indicated elevated magnetization and heavy metal concentrations of topsoils in the industrial area. Magnetic susceptibility (χ), anhysteretic remanent magnetization (ARM) and saturation isothermal remanent magnetization (SIRM) of fluvisols are much higher than those of anthrosols, but contrary for frequency-dependent susceptibility, indicating that soil magnetism strongly depends on the soil type/condition. Predominant magnetic carrier in topsoils in industrial area is pseudo-single-domain/multi-domain magnetite. Environmental scanning electron microscope/energy dispersive X-ray examination of the magnetic extracts from these topsoils revealed abundant spherical particles with diameters of 10–50 μm that are rich in iron-oxides, and could be attributed to the nearby industrial activities (e.g., steel work and power generation). Significant correlations were observed between magnetic concentration-related parameters (e.g., χ, ARM and SIRM) and concentrations of Cu, Pb, Zn, Hg and Tomlinson pollution load index. These results proposed that magnetic proxy mapping of soil pollution is an effective, fast and inexpensive tool for delineation of heavy metal pollution. However, interpretation of magnetic properties for such a purpose must be done on a site-specific basis, taking into account the possibilities of pedogenic enhancement/depletion under the specific soil conditions.     

Physicochemical formation conditions of banded iron formations and high-grade iron ores in the region of the Kursk Magnetic Anomaly: Evidence from isotopic data

The oxygen and carbon isotopic compositions of minerals from banded iron formations (BIFs) and high-grade ore in the region of the Kursk Magnetic Anomaly (KMA) were determined in order to estimate the temperature of regional metamorphism and the nature of rock-and ore-forming solutions. Magnetite and hematite of primary sedimentary or diagenetic origin have δ¹⁸O within the range from +2 to 6‰. During metamorphism, primary iron oxides, silicates, and carbonates were involved in thermal dissociation and other reactions to form magnetite with δ¹⁸O = +6 to +11‰. As follows from a low δ¹⁸O_av = ?3.5‰ of mushketovite (magnetite pseudomorphs after hematite) in high-grade ore, this mineral was formed as a product of hematite reduction by organic matter. The comparison of δ¹⁸O of iron oxides, siderite, and quartz from BIFs formed at different stages of the evolution of the Kursk protogeosyncline revealed specific sedimentation (diagenesis) conditions and metamorphism of the BIFs belonging to the Kursk and Oskol groups. BIF of the Oskol Group is distinguished by a high δ¹⁸O of magnetite compared to other Proterozoic BIFs. Martite ore differs from host BIF by a low δ¹⁸O = ?0.2 to ?5.9‰. This implies that oxygen from infiltration water was incorporated into the magnetite lattice during the martite formation. Surface water penetrated to a significant depth through tectonic faults and fractures.     

The magnetic properties of Quaternary and Tertiary sediments in the southern North Sea

Cores from boreholes penetrating late Quaternary, glacial, interglacial and postglacial sediments and the underlying late Cenozoic delta complex of the southern North Sea have been examined for their magnetic properties. A magnetic polarity stratigraphy has been established as an aid to biostratigraphic dating of the sediments; the Kaena-Gauss and Gauss—Matuyama transitions and the base and top of the Olduvai subchron have been identified. The strength and stability of laboratory-induced isothermal remanent magnetisation display clear magneto-petrological variations, which match lithostratigraphic changes in the cores. Principal component analysis has picked out a basin-wide and palaeoenvironmental consistency in the magnetic data. Large, multi-domain magnetite grains predominate in the post-deltaic and fluvio-deltaic sediments, whereas smaller greigite or titanomagnetite grains are concentrated in the intertidal and marine deltaic facies. Since heavy mineral analysis indicates that most of the deltaic detritus derived from common source areas, the differences in magnetic mineralogy have probably been caused by the sediment transport processes operating within the delta complex.     

山西吕梁袁家村条带状铁建造沉积相与沉积环境分析

山西吕梁作为华北克拉通上条带状铁建造(BIF)的重要产区之一,位于华北中央构造带中。袁家村BIF分布于吕梁岚县袁家村一带,极有可能是华北克拉通内最为典型的Superior型BIF。与华北克拉通其他大多数BIF相比,袁家村BIF具有明显的差异性,其中包括它的形成时代(2.3~2.1Ga)、铁建造类型和低级变质程度(低绿片岩相)等。因此,研究袁家村BIF具有特殊的研究意义,可为探讨大氧化事件之后古海洋氧化还原状态以及国内Superior型BIF的成因提供研究基础。袁家村BIF产于吕梁群袁家村组变沉积岩系的下部,前人根据上覆和下伏含火山岩地层的时代,推测袁家村组的形成时代为2.3~2.1Ga。BIF整体产状陡倾,沿北北东-北东东向呈L形带状分布。依据原生矿物的共生组合及产出特征,可将BIF沉积相划分为氧化物相(60%)、硅酸盐相(30%)和碳酸盐相(10%)。氧化物相是本区BIF最主要的沉积相,主要矿物为赤铁矿、磁铁矿和石英,从而可进一步划分为赤铁矿(24%)和磁铁矿(36%)亚相;硅酸盐相BIF以大量硅酸盐矿物出现为特征,散布于研究区,主要矿物组成除了石英和磁铁矿之外,还有铁黑硬绿泥石、绿泥石、铁滑石、镁铁闪石和阳起石等。在与碳酸盐相BIF构成过渡相的BIF中,还可发现大量的铁白云石。而碳酸盐相主要矿物为菱铁矿、铁白云石和石英等,主要发育于研究区的南部。依据含铁岩系构造格局特点复原获得了原始沉积相分布略图,沉积相主要呈南北向延展,自东向西显示出相变规律,西边为碳酸盐相,东边为氧化物相,其间是过渡的硅酸盐相。通过袁家村BIF的岩相学和含铁矿物化学成分的研究,可大致推测原始沉积的矿物组成为无定形硅胶、水铁矿、与铁蛇纹石和黑硬绿泥石组成类似的铁硅酸盐凝胶、富Al的粘土碎屑和含铁、镁、钙的碳酸盐软泥。这些沉积物在随后的成岩期和绿片岩相的区域变质作用下发生矿物之间的相互转变。BIF中主要含铁矿物的PO-P-Eh 2CO2和pH相关图解说明除了赤铁矿之外,其他矿物均是在较低氧逸度环境中形成的,且所有矿物共存的水体系为中性到弱碱性。袁家村BIF氧化物相中发育豆粒、内碎屑结构和板状交错层理等原始沉积构造,指示氧化相部分是在相对高能的浅水环境下沉积的。但BIF大部分应该形成于浪基面以下(200m)较为深水的环境中,沉淀可能同时发生于上部氧化和下部还原的水体之中,由于还原弱酸性的深部富铁海水在海侵的过程中上升到浅部相对氧化和弱碱性的浅水环境中,因为Eh、pH及氧逸度等物化条件的骤然变化,最终导致铁质的沉淀和沉积相自上而下的变化。