西南印度洋中脊地质构造对地幔部分熔融的影响:深海橄榄岩尖晶石成分证据

慢速-超慢速扩张西南印度洋中脊普遍发育转换断层,洋脊分段性明显,是研究地质构造与地幔部分熔融关系的理想场所。对西南印度洋中脊(52°20′53°30′E)Gallieni转换断层与Gazelle转换断层之间洋脊段6个站位的深海橄榄岩研究发现:尖晶石Cr#的变化范围为0.194～0.329,对应的地幔部分熔融程度为7.6%～13.0%,反映全球洋中脊系统中低程度的地幔部分熔融,并且离转换断层近的地幔部分熔融程度低于洋脊分段中心,这种差异除了受转换断层的冷却作用影响外,还可能与洋脊分段中心更强的岩浆抽提作用有关。将研究区与全球其他洋脊对比发现,尖晶石Cr#及对应的地幔部分熔融程度随洋脊扩张速率的降低而降低,在探讨地幔部分熔融程度与洋脊扩张速率的相关性时,通过对转换断层效应的校正,能够更准确地反映地幔部分熔融程度随洋脊扩张速率的变化趋势。     

南海东北部陆坡结核成因及对冷泉活动的指示

本文对2018年利用“海龙Ⅲ”ROV在南海东北部陆坡采集到的多金属结核样品进行了矿物学和地球化学分析。结果表明研究区结核以棒状为主,具有2层结构。结核外层的矿物学和元素组成特征与水成型多金属结核较为相似。结核内层多发育孔洞,以针铁矿为主,有黄铁矿残余,Fe、As元素含量高,Mn、REE等元素含量低。NH-2结核样品内部的碳酸盐组分的全岩δ¹³C为-30.91‰。所研究结核样品的早期形成过程与冷泉活动密切相关,结核生长后期冷泉活动停止或是减弱,在等深流作用下结核黄铁矿被氧化成针铁矿,之后锰铁氧化物继续在结核外部生长。     

单颗粒电子探针能谱定量分析方法研究进展

对单颗粒电子探针能谱定量分析涉及的样品制备方法、定量分析校正方法、测试条件以及数据处理方法等进行了简要介绍,并对该技术的最新研究成果、发展趋势及其应用前景进行了评述,最后指出了国内在该研究领域存在的问题并提出了相应的解决方案。     

Chemical composition and petrogenesis of plagioclases in plagioclase-phyric basalts from the Southwest Indian Ridge(51°E)

Electron microprobe analysis was conducted on plagioclase from the plagioclase ultraphyric basalts(PUBs)erupted on the Southwest Indian Ridge(SWIR)(51°E) to investigate the geochemical changes in order to better understand the magmatic processes occurring under ultraslow spreading ridges and to provide insights into the thermal and dynamic regimes of the magmatic reservoirs and conduit systems. The phenocryst cores are generally calcic(An_(74–82)) and are depleted in FeO and MgO. Whereas the phenocryst rims(An_(67–71)) and the plagioclase in the groundmass(An_(58–63)) are more sodic and have higher FeO and MgO contents than the phenocryst cores. The crystallization temperatures of the phenocryst cores and the calculation of the equilibrium between the phenocrysts and the matrix suggest that the plagioclase cores are unlikely to have crystallized from the host basaltic melt, but are likely to have crystallized from a more calcic melt. The enrichment in incompatible elements(FeO and MgO), as well as the higher FeO/MgO ratios of the outermost phenocryst rims and the groundmass, are the result of plagioclase-melt disequilibrium diffusion during the short residence time in which the plagioclase crystallized. Our results indicate that an evolved melt replenishing under the SWIR(51°E) drives the eruption over a short period of time.