云南马关含橄榄岩捕虏体的玄武岩和煌斑岩

岩体地质简述马关县南部已发现的4个玄武岩火山颈和12条煌斑岩岩脉都分布在木厂一老厂一带。区内主要发育泥盆纪地层,大地构造位置在华南台块滇桂台向斜的西南角。褶皱平缓,主要是一些成北东走向长度不过几公里的短轴背斜和短轴向斜。沿褶皱走向常有一些断裂,顺着这些断裂有许多辉长辉绿岩小侵入体。蒿子坝火山颈位于老厂篙子坝村北约二百米处,是群峦丛中一个低低的小峰,呈椭圆锥状,高出地面不过二、三十米,其根部水平截面长径为近东西方向,长85米,短径60米(图1)。火山颈由两个岩相组成:中央相是由玄武岩胶结的火山角砾岩;边缘相是含橄榄岩捕虏体的玄武岩,岩相宽度不过几米。煌斑岩岩脉多牛夹在沉积岩岩层间,其产状好象岩床。猫耳岩"岩床"位于木厂节节坡村南一里许,岩体出露在猫耳岩峭壁的根部,厚2—3米,长128米(图2)。

OLIVINE BASALT AND CAMPTONITE WITH PERIDOTITE XENOLITHS FROM MAKWAN,YUNNAN

Both olivine basalt and camptonite from Makwan are characterized by containing peridotite xenoliths.On the basis of their common characters in mineral constituents and chemical composition,the author reaches the conclusion that both olivine basalt and camp- tonite were the common magma reservoir.The constituents of the peridotite xenoliths are magnesian olivine,enstatite-bronzite,chromferous diopside and brown spinel.Because of the poikiloblastic texture and the"laddar extinction"of the olivine crystals,it is suggested that these peridotite xenoliths may be fragments of upper mantle which had been carried to the earth surface by the alkali basaltic magma.