Synchrotron radiation X-Ray diffraction in situ study of fine-grained minerals in shock veins of Suizhou meteorite

The synchrotron radiation X-ray diffraction technique developed for in situ study at high pressure and temperature has also been used to investigate microscopic mineral inclusions in ultrahigh-pressure metamorphic rocks and deep-mantle samples. Present study added two more examples of successful utilization of synchrotron radiation X-ray diffraction technique for in situ investigations of fine-grained (0.5–30 μm in size) minerals in very thin shock melt veins of the Suizhou meteorite: (i) X-ray diffraction measurement of extremely small-sized vein matrix minerals, and (ii) identification of the micron-sized new mineral tuite embedded in the vein matrix. It has been revealed that the fine-grained vein matrix consists of well crystallized garnet, kamacite and troilite, and the powder diffraction pattern consisting of 17 lines with d-values, intensities (I), relative intensities (I/I ^o) and Miller indices, as well as the cell parameters for the new mineral tuite has also been successfully obtained. The result of present investigations has enriched the content of dynamic high-pressure mineralogy and that of Earth’s mantle geochemistry.     

Mineralogy of phyllosilicate-rich micrometeorites and comparison with Tagish Lake and Sayama meteorites

Four phyllosilicate-rich micrometeorites (MMs) were investigated by a synchrotron radiation X-ray diffraction technique and transmission electron microscopy. Three are saponite-rich MMs and one is a serpentine-rich one. In the saponite-rich MMs, we could not find serpentine, and vice versa in the serpentine-rich MM. In the saponite-rich MMs, major constituent minerals are saponite, Fe- and Ni-bearing sulfides, and magnetite. Two saponite-rich MMs contain fine-grained magnesiowüstite-rich aggregates. The aggregates consist of <50 nm polygonal magnesiowüstite coexisting with minor Fe sulfide grains. Their texture, chemical composition, and the result of heating experiments on matrix fragments of the Tagish Lake carbonaceous chondrite strongly suggest that these aggregates were formed by the breakdown of Mg- and Fe-rich carbonate grains when the MMs entered the Earth’s atmosphere. The estimated major mineral assemblage of the saponite-rich MMs before entering the Earth’s atmosphere is very similar to that of the Tagish Lake carbonate-rich lithology, and we suggest that the MMs and the meteorite were derived from similar asteroids. The major mineral assemblage and texture of the matrix of serpentine-rich MM are similar to the matrix of the Sayama CM2 chondrite that experienced heavy aqueous alteration. Chemical compositions of serpentine in the MM suggest that the degree of aqueous alteration of the MM is weaker than that of Sayama. In the MM, cronstedtite does not coexist with tochilinite, which is different from CM2 chondrites that experienced weak to moderate aqueous alteration. However, the possibility that the serpentine-rich MM was derived from the CM chondrite asteroid cannot be ruled out, because tochilinite can be preferentially decomposed during atmospheric entry heating due to its lower decomposition temperature than that of cronstedtite.     

Mineral classification from quantitative X-ray maps using neural network: Application to volcanic rocks

We developed a mineral classification technique of electron probe microanalyzer (EPMA) maps in order to reveal the mineral textures and compositions of volcanic rocks. In the case of lithologies such as basalt that include several kinds of minerals, X-ray intensities of several elements derived from EPMA must be considered simultaneously to determine the mineral map. In this research, we used a Kohonen self-organizing map (SOM) to classify minerals in the thin-sections from several X-ray intensity maps. The SOM is a type of artificial neural network that is trained using unsupervised training to produce a two-dimensional representation of multi-dimensional input data. The classified mineral maps of in situ oceanic basalts of the Juan de Fuca Plate allowed us to quantify mineralogical and textural differences among the marginal and central parts of the pillow basalts and the massive flow basalt. One advantage of mineral classification using a SOM is that relatively many minerals can be estimated from limited input elements. By applying our method to altered basalt which contains multiple minerals, we successfully classify eight minerals in thin-section.     

Trace element composition in tuite decomposed from natural apatite in high-pressure and high-temperature experiments

Tuite has been suggested as a potential reservoir for trace elements in the deep mantle,but no evidence confirms this supposition.By using a natural apatite as starting material,the trace-element-bearing tuite large crystals were obtained under highpressure and high-temperature conditions(15 GPa and 1800 K).X-ray diffraction pattern and Micro-Raman spectrum of the run product confirm that tuite was synthesized.The concentrations of trace elements in tuite crystals were analyzed by laser ablation-inductively coupled plasma-mass spectrometry(LA-ICP-MS).The rare earth element patterns of tuite show enrichment of light rare earth elements relative to heavy rare earth elements.Tuite shows high concentrations of Th and Sr,and negative anomalies of Rb,Nb,and Hf.The results show that tuite can accommodate a large amount of trace elements.Tuite might be an important host to accommodate trace elements if there is much apatite subducted into the deep mantle.     

Magnetofossils in the sediment of Lake Baikal, Siberia

A multidisciplinary approach involving rock-magnetics, transmission electron microscopy, and X-ray diffraction was used to identify a biogenic magnetite component in the Lake Baikal, Siberia, sedimentary magnetic record. The distinctive biogenic component to the magnetic record occurs as chains of single-domain, elongate hexagonal and tear-drop cone-shaped magnetite particles. These magnetofossils are inferred to be magnetosomes produced by magnetotactic bacteria living in the surficial sediment throughout Lake Baikal. Postdepositional reduction diagenesis results in the loss of the fine-grained magnetofossils at depth. In addition, this study shows that the fine-grained magnetofossils are removed by the process of storage diagenesis during long periods (21 months) of core storage, which results in a change to a coarser grained, slightly higher coercivity bulk magnetic mineral assemblage. Although the Lake Baikal sedimentary magnetic record has several distinct and complex components, by determining their origin this study has shown that the sediments are well suited for environmental magnetic study.     

Magnetic properties and paleoclimatic implications of loess-paleosol

Detailed rock magnetic investigations and X-ray diffraction (XRD)were carried out on loess-paleosol sequences of the last interglacial-glacial at Znojmo section in Czech Republic. The results indicate that pedogenesis causes susceptibility enhancement in the paleosols, which is similar to that observed in the Chinese Loess Plateau. k-T curves, IRM, and XRD show that magnetite is the dominant magnetic mineral in the loess-paleosol sequences at the Znojmo section, while maghemite, hematite, and pyrite/pyrrhotite are minor minerals. Measurements of anisotropy of magnetic susceptibility (AMS) indicate that the magnetic lineation is smaller than the foliation. The susceptibility ellipsoids are oblate and the directions of the maximum principal axes (Kmax) are distributed randomly, and cannot be used to determine the paleo-wind direction.     

Mineralogy,chemistry and crystallization sequence of clay minerals in altered tholeiitic basalts from the Peru Trench

Petrographic examination of amygdules and veins associated with moderately altered pillow basalts dredged from the Peru Trench has revealed that a consistent pattern of mineral crystallization has occurred. This sequence is: (1) green, weakly pleochroic clay (R.I. > 1.56); (2) dark yellowish brown, non-pleochroic clay (R.I. > 1.56); (3) light yellowish brown to colorless, fibrous, weakly pleochroic clay (R.I. < 1.56); and (4) calcite or celadonite. Chemical and X-ray diffraction analyses suggest that all clay mineral amygdule and vein fillings are dominated by intimate mixtures of an Fe-rich saponite and nontronite with very small admixtures of serpentine and illite. It is argued that sequential mineral fillings of fractures and vesicles may provide significant information about the chemistry of circulating interstitial fluids. For the pillow basalts studied the first-formed clays were enriched in nontronite, thereby suggesting Fe-rich fluids. These in turn were followed by saponite-rich clays and calcite. The change from Fe-and Mg-rich fluids to dominantly Ca-rich fluids is thought to correspond to a change from mafic mineral alteration to plagioclase alteration in the pillow basalts. An increase in the Fe³⁺/Fe²⁺ ratio of clays toward the centers of vesicles may indicate a change toward a more oxidizing environment of alteration.     

Sorption site capacities for Cs on the sedimentary rock in Horonobe area

The sorption behavior of radionuclides depends on the content of minerals in geological media. The sorption of radionuclides on minerals has been interpreted as the uptake on the sorption sites on mineral surfaces. However, conventional investigations such as X-ray diffraction analysis cannot avoid large errors in quantification of minerals. Furthermore, the discrepancies of sorption behavior have been often found even on the same kind of minerals. Therefore, the sorption site capacity cannot be effectively estimated by the quantification of minerals. In this study, the sorption site on sedimentary rock sampled in Horonobe area, where the Horonobe Underground Research Center, JAEA, is located, was estimated from the Cs sorption isotherms obtained by sorption experiments. To deduce the fitting parameters, illite content estimated from the amount of extracted K by alkylammonium treatment and smectite content estimated from the cation exchange capacity measurement were introduced to the fitting procedure. The result shows that the sorption site capacities of smectite and illite in the sedimentary rock in Horonobe area are 1.3–1.7 × 10⁻⁴ and 1.4–4.0 × 10⁻⁵ eq/g, respectively.     

Applications of scanning electron microscopy in earth sciences

This paper expounds upon the basic principle of scanning electron microscopy(SEM),the main features of image types,and different signals,and the applications and prospects in earth sciences research are reviewed.High-resolution field emission SEM allows observation and investigation of a very fine micro area in situ.Using low-vacuum mode SEM,geological insulating samples can be analyzed directly without coating,demonstrating the wide application prospect.Combined with backscatter detector(BSE),energy dispersal X-ray spectroscopy(EDS),cathodoluminescence spectrometry(CL),and electron back-scattering diffraction(EBSD),SEM can yield multiple types of information about geological samples at the same time,such as superficial microstructure,CL analysis,BSE image,component analysis,and crystal structure features.In this paper,we use examples to discuss the geological application of SEM.We stress that we should not only focus on the CL image analysis,but strengthen CL spectrum analyses of minerals.These results will effectively reveal the mineral crystal lattice defects and trace element composition and can help to reconstruct mineral growth conditions precisely.     

Reflectance spectral characterization and mineralogy of acid sulphate soil in subsurface using hypcrspectral data

Acid sulphate soil（ASS） is a kind of soil which is harmful to the environment.ASS is hard to efficiently assess efficiently in the subsurface,although it is detectable on the surface by remote sensing.This paper aims to explore a new way to rapidly assess ASS in the subsurface by introducing a proximal hyperspectral instrument,namely the HyloggerTM system which can rapidly scan soil cores and provide high resolution hyperspectral data.Some minerals in ASS,which usually act as indicators of the severity of ASS,such as iron oxides,hydroxides,and sulphates,as well as some clay minerals,such as kaolinite,have diagnostic spectral absorption features in the reflectance spectral range（400-2500 nm）.Soil cores were collected from a study area and hyperspectral data were acquired by HyloggerTM scanning.The main minerals related to ASS were characterized spectrally,and were subsequently identified and mapped in the soil cores based on their reflectance spectral characteristics.Traditional X-ray diffraction（XRD） and scanning electron microscope（SEM） were also applied to verify the results of the mineral identification.The main results of this study include the spectral characterisation of ASS and its main compositional minerals,as well as the distribution of these relevant minerals in different depth of cores.     

Self-Organizing Maps for identification of zeolitic diagenesis patterns in closed hydrologic systems on the Earth and its implications for Mars

We have conducted a survey of zeolite occurrences in saline-alkaline paleolake deposits on Earth to identify the most prominent zeolite alteration patterns and to characterize the most common authigenic minerals and their paragenetic relationships. We collected the bulk mineral assemblages (from previous and our studies) as identified by X-ray diffraction from zeolitic tuff beds and associated sedimentary beds from thirteen paleolake deposits from the USA, Mexico, Greece, and Tanzania. We applied the Kohonen Self-Organizing Maps (SOM) to look for interesting patterns in the tuff bed mineral assemblages without prescribing any specific interpretation, and for information reduction and classification. Decision Tree (DT) method was applied to characterize these clusters. We were able to define clear class boundaries between fresh glass, non-analcime zeolites, analcime, and K feldspar. The non-analcime zeolites were further grouped into several classes based on mineral type. We also discuss the potential implications for Mars, showing that the mineral assemblages of diagenetic facies identified by SOM and DT can be used to test or validate the orbital, in situ, or modeling results, while the trained SOM provides a robust generalized ability to classify the new mineral assemblage data into the most common diagenetic facies identified in saline-alkaline paleoenvironments that contain zeolites. The study concludes that generalizing the complex geochemical behaviors using unsupervised statistical learning methods can help to identify the most prominent geochemical behaviors.     

Tracing sediment transport history using mineralogical fingerprinting in a river basin with dams utilizing sediment sluicing

Sediment causes a serious problem in relation to dam function. A cooperative sediment sluicing operation has been under way since 2017 to prevent sediment from accumulating in dams in the Mimi River,Miyazaki, Japan. To achieve a smooth and stable operation, it is very important to determine the sediment source and a sediment transport system to maintain the dam’s function. In the current study, the source and transport of sediment from the Mimi River basin have been analyzed with X-ray diffracti...     

Mineralogical characteristics of airborne particles collected in Beijing during a severe Asian dust storm period in spring 2002

Asian dust storm (ADS) samples were collected on March 20,2002 in Beijing,China. High-resolution field emission scanning electron microscopy with energy dispersive X-ray detector (FESEM-EDX) and X-ray diffraction (XRD) were used to study the morphology,chemical compositions,number-size dis-tributions and mineralogical compositions of ADS particles. The mineral particles were major compo-nents in the ADS samples,accounting for 94% by number. The XRD analysis indicated that the dust particles were dominated by clay (40.3%),and quartz (19.5%),followed by plagioclase (8.4%),calcite (7.5%),K-feldspar (1.5%),hematite (0.9%),pyrite (0.9%),hornblende (0.4%) and gypsum (0.3%),with a certain amount of noncrystalline materials (20.3%). Clay minerals were mainly illite/smectite mixed lay-ers (78%),followed by illite (9%),kaolinite (6%),and chlorite (7%). In addition to these main minerals,FESEM-EDX also detected some trace minerals,such as dolomite,pyrite,thenardite,as well as heavy minerals represented by rutile,ilmenite and apatite. The mineralogical compositions of the 2002-03-20 Asian dust storm and the Saharan dust plumes were similar but the clay mineralogy showed a great distinction,with the illite/smectite mixed layers being common in the Asian dust storm but illite being common in the Saharan dust plumes.     

Mineralogy and temporal relations of coexisting authigenic minerals in altered silicic tuffs and their utility as potential low-temperature dateable minerals

Coexisting fine-grained (0.1–20 μm) authigenic silicate minerals separated from altered tuffs in Miocene and Plio-Pleistocene lacustrine deposits were characterized petrographically and using X-ray powder diffraction. The authigenic minerals are dominated by clinoptilolite, erionite, phillipsite, K-feldspar, silica, calcite, smectite, and randomly interstratified illite/smectite. Minor accessories of opal-CT, cristobalite, and barite are present with the major alteration minerals. Authigenic minerals from altered tuffs were dated using the K/Ar method to evaluate the utility of these minerals for determining the time of alteration in low-temperature diagenetic environments. The eruption ages of some of these zeolite-rich tuffs were determined using the ⁴⁰Ar/³⁹Ar method on single sanidine and plagioclase minerals. The K/Ar isotopic ages of the fine-grained K-feldspar show minimal variation compared with results from the clinoptilolite separates. The isotopic ages from the authigenic K-feldspar (15-13.8 Ma) and some of the zeolites (16.-6.7 Ma) are similar to the eruption ages of the tuffs and indicate early alteration. Despite their open-framework structure, zeolites apparently can retain part or all of their radiogenic argon under favorable conditions (e.g., saturated environment). How much of the radiogenic argon is retained is estimated from the isotopic ages of other coexisting secondary minerals that are commonly dated by the K/Ar method. Although zeolite isotopic ages should be interpreted with caution, they may be useful to constrain temporal relations of low-temperature diagenetic processes when used in conjunction with other dateable minerals.     

地下水补给型湖泊表层沉积物矿物组成及其形成机制——以巴丹吉林沙漠湖泊群为例

盐湖中的矿物沉积记录着丰富的环境气候变化信息,是古环境研究的重要对象.在无地表径流补给的盐湖中,其矿物组成及沉积特征与有地表径流补给的湖泊相比是否有一定的特殊性,是值得探讨的问题.采集巴丹吉林沙漠33个不同矿化度地下水补给型湖泊的表层沉积物和10个地表风积砂样品,通过X衍射的方法,分析样品的矿物组成.结果显示:湖泊表层沉积物主要为石英、长石、辉石、云母等碎屑矿物,部分湖泊含有少量的碳酸盐和氯化物盐类矿物.湖泊沉积物的矿物组成与湖水矿化度的关系较为密切,淡水湖仅分布碎屑矿物,微咸水湖含有碎屑矿物和碳酸盐类矿物,盐湖含有碎屑矿物、碳酸盐类矿物和氯化物.风积砂样品中主要为碎屑矿物,占总矿物含量的90%,对湖泊沉积物的矿物组成影响较大,但对湖泊沉积物中的盐类矿物没有贡献,表明湖泊表层沉积物中盐类矿物主要是自生作用形成的.虽然本地区湖泊边缘的沉积物中盐类矿物种类相对较少并且含量较低,但其盐类矿物组成与分布能够响应湖水矿化度的变化,其环境指示意义与有径流补给的盐湖相同,可以指示其湖水的盐度.因此,可以从巴丹吉林沙漠地下水补给型湖泊沉积的盐类矿物中提取相应的古环境信息,用于恢复古气候和古环境的研究.     

Transformation relationship among different magnetic minerals within loess-paleosol sediments of the Chinese Loess Plateau

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)     

Catalytic decarboxylations of fatty acids in immature oil source rocks

More attention has been paid to the formation conditions of petroleum and gas[1,2]. It is gen-erally accepted that various types of organic materials have served as the most important source of petroleum and gas in sediments. The formation of hydrocarbons…     

Opaque minerals in geothermal well no. 7, Krafla, Northern Iceland

Study of the opaque minerals from well No. 7, Krafla, indicates two mineral assemblages: (1) hydrothermally altered igneous minerals and (2) secondary minerals that have precipitated from the geothermal fluid at depths down to 2140 m, and at temperatures up to more than 340°C. Chief amongst the chemically precipitated minerals are pyrite, pyrrhotite and goethite, which is described here for the first time in an Icelandic geothermal drill hole.The geothermal system at Krafla has been periodically disturbed by the influx of volcanic emanations; this article attempts to interpret, by use of thermochemical calculations, the processes affecting the precipitated mineral assemblage.     

3D Mapping of calcite and a demonstration of its relevance to permeability evolution in reactive fractures

There is a need to better understand reaction-induced changes in fluid transport in fractured shales, caprocks and reservoirs, especially in the context of emerging energy technologies, including geologic carbon sequestration, unconventional natural gas, and enhanced geothermal systems. We developed a method for 3D calcite mapping in rock specimens. Such information is critical in reactive transport modeling, which relies on information about the locations and accessible surface area of reactive minerals. We focused on calcite because it is a mineral whose dissolution could lead to substantial pathway alteration because of its high solubility, fast reactivity, and abundance in sedimentary rocks. Our approach combines X-ray computed tomography (XCT) and scanning electron microscopy. The method was developed and demonstrated for a fractured limestone core containing about 50% calcite, which was 2.5 cm in diameter and 3.5 cm in length and had been scanned using XCT. The core was subsequently sectioned and energy dispersive X-ray spectroscopy was used to determine elemental signatures for mineral identification and mapping. Back-scattered electron microscopy was used to identify features for co-location. Finally, image analysis resulted in characteristic grayscale intensities of X-ray attenuation that identify calcite. This attenuation mapping ultimately produced a binary segmented 3D image of the spatial distribution of calcite in the entire core. To demonstrate the value of this information, permeability changes were investigated for hypothetical fractures created by eroding calcite from 2D rock surfaces. Fluid flow was simulated using a 2D steady state model. The resulting increases in permeability were profoundly influenced by the degree to which calcite is contiguous along the flow path. If there are bands of less reactive minerals perpendicular to the direction of flow, fracture permeability may be an order of magnitude smaller than when calcite is contiguous. These results emphasize the importance of characterizing spatial distribution of calcite in heterogeneous rocks that also contain a similar abundance of less reactive minerals.     

Catalysis of aluminosilicate clay minerals to the formation of the transitional zone gas

It has been shown that the major clay minerals of the biothermocatalytic transitional zone source rock are montmorillonite, illite/montmorillonite (I/M) interlayer mineral, illite, kaolinite and chlorite. Within the depth of the transitional zone, montmorillonite could convert to the I/M ordered interlayer mineral via the I/M disordered one, i.e. in the intercrystalline layer of montmorillonite, A1³⁺replaces Si⁴⁺abundantly, resulting in a surface charge imbalance and the occurrenec of a surface acidity. By means of the pyridine analytic method, the surface acidity of these aluminosilicate clay minerals is measured. The catalysis of aluminosilicate clay minerals, such as montmorillonite, illite and kaolinite to the thermo-degraded gas formation of the transitional zone is simulated in the differential thermal analysis-gas chromatography system and the alcohol dehydration catalyzed by clay minerals is employed to discuss this catalytic mechanism. Experiments have shown that montmorillonite is the major catalyst in the formation of the transitional zone gas and it lowers the thermo-degraded temperature of organic matter by 50°C.