华北克拉通南部古元古界熊耳群中海绿石的发现及其地质意义

The Discovery and Geological Significance of Glauconites from the Palaeoproterozoic Xiong'er Group in the Southern Part of the North China Craton

海绿石是一种富钾、富铁的含水层状铝硅酸盐矿物,一般形成于慢速、弱还原、较深水的环境中,在沉积学领域常被作为指示海相的矿物。华北克拉通南部熊耳—中条拗拉谷中广泛发育的古元古界熊耳群,是华北克拉通结晶基底形成后规模最大、涉及范围最广的火山活动产物。该群以火山熔岩占绝对优势,沉积岩和火山碎屑岩主要分布在大古石组及马家河组,仅占地层总厚度的4.3%。晋南垣曲地区的马家河组砂岩中发现原生的海绿石,为探讨熊耳群火山岩的形成环境提供依据。分析显示,熊耳群中的海绿石大部分K2O含量大于8%,具有高成熟度海绿石的特点。发育海绿石砂岩的元古宙地层和岩相学特征,反映其形成于高能的浅海环境,明显不同于现代海绿石的形成环境。华北克拉通南部在熊耳群早期就开始有海侵事件,随着熊耳—中条拗拉谷的发育,海侵作用增强。马家河组中原生海绿石的存在直接地指示了晋南地区在熊耳群晚期为海相环境。

Glauconite is a kind of hydrous layered aluminium silicate mineral,which is commonly refered to as a marine facies indicative mineral.Numerous studies have demonstrated that glauconites minerals usually form in modern oceans with high depths and slowly sedimentary rates.The Paleoproterozoic Xiong＇er Group,widely occurring in the Xiong＇er-Zhongtiao aulacogen in the southern margin of the North China craton,represents the most intensive magmatism after the formation of the crystalline basement of the North China craton.The Xiong＇er Group is occupied by volcanic lavas as well as minor sedimentary rocks and volcanic clastic rocks（4.3% in thickness）.The sedimentary rocks occur as interbeds in the Dagushi and Majiahe Formations of the Xiong＇er Group.Glauconites were discovered in the sandstone from the Majiahe Formation,which gives us a opportunity to elucidate the formation environment of the Xiong＇er Group.Sedimentological and petrographic studies indicate that the glauconites have high content of K2O（ 〉8%）,showing that these glauconites belong to the high-evolved glauconites.The characteristics of glauconites from the Majiahe Formation reflect that they formed in a high-energy shallow sedimentary environment,not in a environment with a slowly sedimentary rate.Shortly afiter the extension of the Xiong＇er-Zhongtiao aulacogen,transgression was northward in the Palaeoproterozoic era.At the early stage of the Xiong＇er Group,the southern part of Henan province was in a marine environment,whereas the northern part is still in a continental environment.At the later stage,the southern area of Shanxi province was in the marine environment,as indicated by the discoveries of glauconites in the Majiahe Formation.