浙西石炭纪层状硅质岩地球化学特征及其意义

在浙西石炭纪地层中存在与地层整合产出的层状硅质岩。硅质岩中ＦｅＯ、ＭｎＯ、ＴｉＯ２、Ａｌ２Ｏ３、ＭｇＯ、ＣａＯ、Ｎａ２Ｏ、Ｋ２Ｏ等含量相对较高，富集Ａｓ、Ｓｂ、Ｂｉ、Ａｕ、Ａｇ、Ｇａ，Ｆｅ２Ｏ３／ＦｅＯ、ＳｉＯ２／Ａｌ２Ｏ３、ＳｉＯ２／（Ｎａ２Ｏ＋Ｋ２Ｏ）、ＳｉＯ２／ＭｇＯ比值较小，稀土元素总量低，Ｃｅ弱负异常，重稀土相对富集，包裹体富含气相组份ＣＨ４、ＣＯ２、Ｎ２、ＣＯ、Ｈ２，具热水沉积硅质岩的地球化学特征。在Ｆｅ—Ｍｎ—（Ｎｉ＋Ｃｏ＋Ｃｕ）三角图及ＳｉＯ２—Ａｌ２Ｏ３、ＳｉＯ２—Ｆｅ２Ｏ３图上均属于热水沉积硅质岩。硅质岩中硅、氧同位素也显示其热水成因之特点。硅质岩的硅同位素和稀土元素Ｃｅ／Ｃｅ※值表明本区层状硅质岩主要是在浅海环境下沉积的。硅质岩的形成温度较高，为９８℃～１５２℃

The geochemical charateristics of the Carboniferous bedded silicolites in West Zhejiang and their sedimentary environment

The bedded silicolites are conformable with the Carboniferous rocks in West Zhejiang.The silicolites can be identified as hydrothermal sediments with a higher content of FeO,MnO,TiO 2,Al 2O 3,MgO,CaO,Na 2O,K 2O and As,Sb,Bi,Au,Ag,Ga,etc.,and a lower ratio of Fe 2O 3/FeO,SiO 2/Al 2O 3,SiO 2/(K 2O+Na 2O) and SiO 2/MgO.There are a small amount of REE,slight negative Ce anomaly and comparatively rich in HREE,and higher content of CH 4,CO 2,N 2,CO,H 2,in inclusions.The silicolites all belong to hydrothermal sediments in Fe—Mn—(Ni+Co+Cu) triangle diagram and SiO 2—Al 2O 3,SiO 2—Fe 2O 3 diagrams.The Silicon and Oxygen isotopes also demonstrate the characteristics of hydrothermal origin.And the Ce/Ce ※ and δ 30 Si in these silicolites show that the silicolites were deposited in shallow water environment.The temperatures for the deposition of silicolites ranged from 98℃ to 152℃.