北京十三陵地区长城系大红峪组中层凝灰岩的发现

北京十三陵地区长城系大红峪组前人认为没有火山岩。作者在该地区工作时发现在大红峪组有一层层凝灰岩存在。此层凝灰岩根据颜色可分为三亚层,其主要粘土矿物为蒙脱石;碎屑物中含厚板状透长石和自形晶双锥短柱状锆石;具强熔结凝灰结构、假流纹构造;岩石中K_2O含量较高。由此证明,此层的确为凝灰岩。又因其野外产状与大红峪组沉积岩层一致,故认为此层凝灰岩是长城系大红峪组时喷发的。

The Discovery of Tuffite from Dahongyu Formation, Changcheng System of Ming Tombs, Beijing

There are no reports before about volcanic rocks in Dahongyu Formation, Changchong System of Ming Tombs area. One layer of tuffite was discovered by tile authors. The tuffite was composed of three different colour beds.The clay mineral is mainly montmorillonite. The pyroclastic minerals include sanidine in thick-plate shape and euhedra zircon with short cone-shaped twin.Obvious welded tuff texture and pseu-flowage structure have been found in tile tuffite, tuffite contains higher K_2O contentTherefore, the authors consider that this layer could be tuffite. Its attitude is consistent with the sedimentary formations of Dahongyu Formation,Hence, the tuffite should be ejected in the time of forming Dahongyu Formation.