汉诺坝玄武岩中麻粒岩类捕掳体的岩石学特征

Petrological Investigations on the Granulite Xenoliths from Hannuoba Basalts, Northern Sino Korean Craton

根据矿物组合特征，汉诺坝玄武岩中的麻粒岩捕掳体可划分为四种类型：长英质麻粒岩、苏长质麻粒岩、二辉二长麻粒岩和二辉麻粒岩，其中以二辉麻粒岩最为常见。麻粒岩捕掳体均具变质重结晶结构以及块状或条带状构造。不同种类的麻粒岩捕掳体在矿物组成和矿物成分上存在明显差别，但各主要矿物之间存在一定的成分相关性。应用Ｗｏｏｄ和Ｂａｎｎｏ二辉石温度计的计算结果表明，含二辉石麻粒岩捕掳体的平衡温度分布于８００°～９５０℃之间，主要集中于９００°±５０℃范围内，具Ｏｐｘ＋Ｃｐｘ＋Ｐｌ矿物组合的二辉麻粒岩捕掳体的形成压力范围约为０．６～１．１ＧＰａ。二辉二长麻粒岩落在相似的温压范围内。麻粒岩捕掳体在９５０℃处的突然消失指示了第三纪时汉诺坝地区岩石学壳幔边界的温度。

According to their mineral assemblages, the granulite xenoliths entrained by Cenozoic Hannuoba basalts are divided into four groups: felsic granulites, noritic granulites, two pyroxene two feldspar granulites and two pyroxene granulites, with the two pyroxene granulites most common. The xenoliths are all in recrystallized structure and homogeneous or layered texture. The modes of the xenoliths and the composition of the major phases are different from group to group, but some potential compositional connection exists between clinopyroxene, orthopyroxene and plagioclase. As the major component of the lower crust, the two pyroxene granulites are concentrated in the P T range of 800°～950℃ and 0 6￣1 1 GPa, with the two pyroxene two feldspar granulites in the similar P T range. The extinction of the two pyroxene bearing granulites within the temperature range higher than 950℃ indicates the position of petrological crust mantle boundary beneath Hannuoba area.