大别地区榴辉岩中几种超高压变质矿物研究

根据镜下观察,在大别地区东南部榴辉岩中陆续发现柯石英、金刚石和文石等三种超高压变质矿物,拉曼分子探针检测进一步证实了这些发现。柯石英和文石均被包裹于石榴石或绿辉石晶体之内,而基质中则分别以低压多型变体石英和方解石的形式存在,说明其保存除快速构造抬升的外部条件外,还与寄主矿物机械阻力及晶内低压缩性有关。作为榴辉岩相的早期共生矿物,它们的出现证明该区榴辉岩经历了超高压变质作用。     

Carbon and Oxygen Isotopic Composition of Surface-Sediment Carbonate in Bosten Lake (Xinjiang, China) and its Controlling Factors

Bosten Lake is a mid-latitude lake with water mainly supplied by melting ice and snow in the Tianshan Mountains. The depositional environment of the lake is spatially not uniform due to the proximity of the major inlet and the single outlet in the western part of the lake. The analytical results show that the carbon and oxygen isotopic composition of recent lake sediments is related to this specific lacustrine depositional environment and to the resulting carbonate mineralogy. In the southwestern lake region between the Kaidu River inlet and the Kongqi River outlet, carbon isotope composition (δ13C) values of the carbonate sediment (-1‰ to -2‰) have no relation to the oxygen isotope composition of the carbonate (δ18O) values (-7‰ to -8‰), with both isotopes showing a low variability. The carbonate content is low (<20%). Carbonate minerals analyzed by X-ray diffraction are mainly composed of calcite, while aragonite was not recorded. The salinity of the lake water is low in the estuary region as a result of the Kaidu River inflow. In comparison, the carbon and oxygen isotope values are higher in the middle and eastern parts of the lake, with δ13C values between approximately +0.5‰ and +3‰, and δ18O values between -1‰ and -5‰. There is a moderate correlation between the stable oxygen and carbon isotopes, with a coefficient of correlation r of approximately 0.63. This implies that the lake water has a relatively short residence time. Carbonate minerals constitute calcite and aragonite in the middle and eastern region of the lake. Aragonite and Mg-calcite are formed at higher lake water salinity and temperatures, and larger evaporation effects. More saline lake water in the middle and eastern region of the lake and the enhanced isotopic equilibrium between water and atmospheric CO2 cause the correlating carbon and oxygen isotope values determined for aragonite and Mg-calcite. Evaporation and biological processes are the main reasons for the salinity and carbonate mineralogy influence of the surface-sediment carbonate in Bosten Lake. The lake water residence time and the CO2 exchange between the atmosphere and the water body control the carbon and oxygen isotope composition of the carbonate sediment. In addition, organic matter pollution and decomposition result in the abnormally low carbon isotope values of the lake surface-sediment carbonate.     

富锶文石的发现及其研究

富锶文石是文石的变种,其化学式为(Ca,Sr)CO3。二轴晶,负光性,2▽=9,折光率Ng=1.6620,Nm=1.6561,Np=1.5168,D=3.34,H=3.75,比磁化系数为0.32×10-6CGSMcm3/g。矿物为白色,透明,呈细小晶粒状或砂糖状集合体。易溶于稀盐酸。斜方晶系,晶胞参数a=4.61,b=7.89,c=5.78。矿物产于内蒙古白云鄂博铁、铌、稀土矿床的脉状含铌、稀土白云石碳酸盐岩中,在自然界中产出含锶如此之高的变种是罕见的。该矿物的发现对研究碳酸盐矿物中钙、锶元素类质同象置换机理和晶体光学均具有一定的学术意义。     

珍珠层中文石晶体择优取向的XRD极图分析

本文采用XRD极图方法对海水大珠母贝、企鹅珍珠贝及淡水三角帆蚌贝壳珍珠层中文石晶体的结晶学定向进行了研究。根据文石的 ( 0 0 2 )和 ( 0 12 )极图可以推断 ,三种贝壳珍珠层文石的a轴平行珍珠层面 ,c轴垂直珍珠层面。在珍珠层面上 ,二种海水壳珍珠层中文石的a轴亦存在强烈的择优取向现象 ,大珠母珍珠层中文石a轴沿与壳生长纹方向呈 2 0 0°左右的夹角分布 ,企鹅珍珠贝沿近平行壳生长纹的方向分布 ;淡水三角帆蚌珍珠层文石a轴亦平行珍珠层面分布 ,但其择优取向不如海水壳明显 ,在珍珠层面上沿各个角度上均有分布。     

Aragonite depositional facies in a Late Ordovician calcite sea,Eastern Laurentia

The Black River (Upper Ordovician – Sandbian) and Trenton (Upper Ordovician – Katian) groups are traditionally interpreted as a deepening-upward succession deposited in a progressively subsiding Appalachian Basin margin that contained warm-water, marine, photozoan deposits that pass upward into cool-water, marine, heterozoan carbonates. This succession is customarily interpreted to reflect an incursion of cold, high-latitude ocean waters into the area. This view is herein confirmed for coeval carbonates in the northern part of the basin, particularly the St. Lawrence Platform. They are now well explained in this study on the basis of recent studies of cool-water carbonates and calcite–aragonite seas. Overall the succession is one of Sandbian photozoan ramp deposits succeeded by Katian heterozoan ramp carbonates that changed back to photozoan ramp deposits prior to the Hirnantian glaciation. The current interpretation, that deposition took place throughout a calcite sea time, seems at odds with this series of strata. Instead it is herein proposed that deposition took place during an aragonite sea time wherein calcite sea-like sediments accumulated under cold ocean-water temperatures. Such an interpretation is supported by recent experimental data that supports the importance of seawater temperature on CaCO₃ polymorph precipitation. If correct, this means that some of the evidence for calcite sea deposition through time brought about by global tectonics, should be re-evaluated to make sure it was not simply cool-water carbonate production.     

室温条件下青海湖水中镁离子浓度对沉淀碳酸钙同质多像类型的调控

青海湖是我国唯一报道过的现代湖底沉积物中白云石、方解石和文石等多种碳酸盐矿物共存的高原内陆咸水湖泊.以青海湖水和除菌青海湖水作为载体,以CaCl2和MgCl2·6 H2O作为反应原料,在实验室常温条件下采取控制变量法制备出不同浓度Mg2+参与下的钙质沉淀物,探讨Mg2+浓度对沉淀物类型的影响.仅添加CaCl2时,青海湖...     

青蛤贝壳韧带的结构色及微结构

采用XRD、热失重分析、反射光谱及高分辨FE-SEM对青蛤贝壳韧带的矿物组成,结构色及微结构进行系统研究,结果表明:1)青蛤韧带由78%文石矿物,18%的蛋白质及少量的水组成,文石矿物呈纤维状,纤维的直径约138 nm,相邻纤维中心的间距约164 nm;2)韧带可呈现蓝,黄色结构色;3)韧带具有明显的层状结构特征,生长层的厚20μm~40μm,同一生长层中文石纤维长轴定向排列,而相邻层纤维长轴的定向不一致,并呈现一种新的结构类型“-交叉棱柱层”结构。再者,青蛤韧带中的文石纤维构成了一类特殊的2D准周期光子晶体。     

Whiting events and the formation of aragonite in Mediterranean Karstic Marine Lakes: new evidence on its biologically induced inorganic origin

This paper discusses the formation of whiting events, drifting milky clouds of water, and their role in the formation of recent aragonite sediments in a semi-enclosed, karstic, marine lake on the island of Mljet (Adriatic Sea). This study is based on detailed structural, morphological and sedimentological characterization of, and strontium distribution in, particles originating from suspended matter and sediments. The particles were examined by X-ray diffraction and electron diffraction analyses, scanning and transmission electron microscopy, as well as electron microprobe energy dispersive X-ray analyses and atomic absorption spectroscopy. Morphological features, granulometric characteristics, strontium enrichment and characteristic details of the aragonite structure in the needle-like particles were identical in both the suspended matter collected during whiting events and in the bottom sediments. The whiting events, which occasionally occurred in surface waters, were found to be sites of short-term active authigenic aragonite precipitation and the main source of fine-grained aragonite mud. This study exemplifies the role of biologically induced inorganic precipitation processes in the formation of recent aragonite mud in a restricted Mediterranean environment.     

南海西沙海槽的碳酸盐结壳及其对甲烷冷泉活动的指示意义

冷泉碳酸盐岩是指示南海北部可能发育天然气水合物的重要证据之一。对在西沙海槽采集到的冷泉碳酸盐结壳颗粒进行了形貌、稳定同位素等的研究,讨论和揭示了冷泉碳酸盐结壳的形成机理及其与甲烷冷泉活动的关系。结果表明,碳酸盐结壳具有多孔结构,冷泉矿物为文石和重晶石,文石呈针状,含量为39.5%—46.6%,重晶石呈矮柱状,含量为15.6%—21.2%,它们均是从流体中沉淀出来的。重晶石的δ34S值为23.47‰—26.32‰,表明硫同位素发生正漂移,属于与冷泉流体有关的成岩成因重晶石。文石的碳同位素轻度亏损,δ13C值为-13.30‰—-29.59‰,主要来源于热解成因气,但结合了少量正常海水的溶解碳,δ18O值为2.32‰—3.74‰,指示碳酸盐结壳形成时的温度为3.5—9.7℃。研究表明,碳酸盐结壳形成于流体活动缓慢的环境,是深部富含Ba2 的甲烷冷泉流体向上排放和喷溢,在近海底遇到向下渗漏的富含SO42-海水,发生缺氧甲烷氧化反应沉淀出文石,流体中剩余的重34S的SO42-与Ba2 形成重晶石,因此,碳酸盐结壳是西沙海槽存在甲烷冷泉活动的证据。研究结果为进一步开展该海域潜在天然气水合物的调查和研究提供了新证据。