冀北流纹质淬碎碎屑岩的特征及成因

Discovery and geological characteristics of rhyolitic vitroclastic rocks in Northern Hebei

在北梁火山机构中首次发现瘤状流纹质淬碎碎屑岩，产于晚侏罗世张家口组酸性火山岩地层中。此类岩石呈球度较好的疙瘩状或瘤状。球体含量在８０％以上，大小一般０．５～１０ｃｍ，胶结物为隐晶质、玻质熔岩。岩层下部球体滚动特征明显，层圈构造发育；岩层上部球体未滚动，具有平行流面构造。岩石中球体成因主要是喷发的火山集块—角砾岩，被水冷却时产生淬碎作用，并在滚动中进一步圆化而成。

Tumulose rhyolitic vitroclastic rocks were first found in the Beiliang volcanic edifice. They occur in a layer of acid volcanic rocks of the Late Jurassic Zhangjiakou Formation. The content of spheroids in such kind of rocks is more than 80%. They are generally 0.5～10 cm in diameter, and the cement is cryptocrystalline and glassy lavas. In the lower part of the layer the spheroids show the distinct rolling feature and a well developed layered structure; in the upper part the spheroids do not roll and have a parallel planar flow structure. The spheroids were formed by quenching and clastation of erupted volcanic agglomerates and breccias when wet and rounding of the resulting fragments during rolling.