长江口—东海内陆架悬浮重矿物组成与颗粒特征

Composition and particle characteristics of suspended heavy minerals in Yangtze River estuary and East China Sea inner continental shelf

沉积物重矿物矿物组成和颗粒大小对揭示沉积物源和水动力分选过程具有重要指示意义。然而,受研究手段的制约,对于长江细粒沉积的重矿物组成和物源、水动力分选之间关系的探究还尚属空白。本研究利用自动定量矿物分析系统(TIMA)对长江口—东海内陆架不同水层悬浮物的重矿物组成和颗粒大小进行了研究,同时,结合电子探针分析对细粒级重矿物自动识别结果进行了验证。研究表明,长江口悬浮物中特征重矿物组合为角闪石—绿帘石—铁质金属矿物,与长江下游沉积物特征重矿物组合一致。长江口悬浮物与长江下游沉积物的重矿物组成具有极好的相关性,指示其来源与长江有关。而长江口外悬浮物中赤/磁铁矿相对富集,可能是强潮作用导致的中等密度重矿物再搬运和扩散的结果。值得关注的是,在舟山群岛附近站位悬浮物样品中发现了铬铁矿的异常富集,推测与海区人类生产活动有关。长江口悬浮重矿物颗粒绝大部分为粗粉砂—极细砂,富集在悬浮物中的较粗粒级(Φ<D_(0.5))中,主要由径流携带搬运。不同水层悬浮物中不同类型重矿物的粒径无明显差异,受沉降差异的影响小。

The mineral composition and particle size of heavy minerals in sediment are important indicator for revealing sediment sources and hydrodynamic sorting processes.However,due to the limitations of research methods,there is still no research on the relationship between the heavy mineral composition,provenance and hydrodynamic sorting of fine-grained sediments in the Yangtze River.In this study,the TESCAN Integrated Mineral Analyzer(TIMA) was used to study the composition and particle size of heavy minerals in different water layers of the Yangtze River Estuary and East China Sea inner continental shelf.In parallel,the automatic identification results of fine-grained heavy minerals were verified by electronic probe analysis.The study shows that the characteristic heavy mineral assemblages in the suspended solids in the Yangtze River Estuary is hornblende,epidote and ferruginous metal minerals,which is consistent with the characteristic heavy mineral assemblages in the sediments of the lower reaches of the Yangtze River.There is an excellent correlation between the heavy mineral composition of suspended matter in the Yangtze River estuary and sediment in the lower reaches of the Yangtze River,indicating that its source is related to the Yangtze River.However,hematite/magnetite is relatively enriched in the suspended matter outside the Yangtze River estuary,which may be the result of the reworking and diffusion of medium density heavy minerals caused by strong tide.It is worth noting that abnormal enrichment of chromite appears in suspended matter samples at stations near Zhoushan Islands,which may be related to human production activities in the sea area.The vast majority of suspended heavy mineral particles in the Yangtze River Estuary are coarse silt to extremely fine sand,enriched in the coarser fractions(Φ<D_(0.5))of suspended solids,which are mainly carried and transported by runoff.There is no significant difference in the particle size between different types of heavy minerals in suspended solids in different water layers,indicating that they are less affected by sedimentation differences.