中太平洋海盆富稀土沉积层及其声学特征

REE-rich sediments in the Central Pacific Basin and their acoustic characteristics

为了解中太平洋深海富稀土沉积物的地层特征及稀土富集机制,2013年中国地质调查局广州海洋地质调查局在中太平洋海盆西部以地球物理探测与地质取样相结合的调查方式,对该区域开展了浅地层剖面测量、单道地震测量、重力活塞沉积物柱状取样。通过浅剖、单道地震声学探测,揭示了研究区域地层单元:(1) 0~12 m,第四纪—晚渐新世远洋粘土沉积;(2) 12~58 m,中渐新世—始新世(晚白垩世?)沸石层、灰岩;(3) 58~127 m,晚白垩世钙质超微化石软泥、白垩;(4) 127~144 m,灰岩、燧石;(5)玄武岩基岩。沉积物岩性及元素地球化学分析结果表明,深海沉积物中稀土元素的富集主要为生物磷灰石、火山热液组分的贡献,而陆源组分并不利于稀土元素的富集。研究区富稀土沉积层主要为顶部透明的远洋粘土层,而下部渐新世以来的高阻抗燧石层,可认为是富稀土沉积物的底界。在大洋稀土沉积物调查中,以浅地层剖面特征为指导,快速锁定目标沉积层,为潜在的深海稀土资源勘探提供技术支撑。

To understand the enrichment mechanism of rare earth elements(REE)in the deep-sea sediment,and the regional stratigraphy of the Central Pacific Basin,Guangzhou Marine Geological Survey carried out shallow stratigraphic profile survey,single channel seismic profile survey and piston core sediment sampling in 2013,based on the method of geophysical exploration in combination with geological sampling.The following five stratigraphic units were identified by means of shallow stratigraphic profile survey and single channel seismic profile survey:①0~12 m,Quaternary-Upper Oligocene pelagic clay;②12~58 m,Middle Oligocene-Eocene(Late Cretaceous?)chert layer and limestone;③58~127 m,Late Cretaceous nannofossil ooze,chalk;④127~144 m,limestone with chert;e,and basalt.The results of lithology and element geochemical analysis indicate that the enrichment of REE in deep-sea sediments is mainly due to the contribution of biogenic apatite and volcanic hydrothermal components,while terrigenous components are not conducive to the enrichment of REE.The REE-rich deposits in the study area are mainly in pelagic transparent clay layers on the top,while the high impedance chert layers in the lower part since Oligocene can be considered as the bottom boundary of the REE-rich deposits.The results show that the targeted sedimentary layer can be quickly identified in the REE-rich sediment survey,under the guidance of shallow stratigraphic profile survey,which can provide technical support for the exploration of deep-sea potential REE resources.