北祁连大岔大坂两类辉长岩的地质地球化学特征及其构造环境

Geological and Geochemical Characteristics of Two Types of Gabbro in Dachadaban, North Qilian and Its Tectonic Environment

在北祁连大岔大坂蛇绿岩中出露的两类辉长岩具有不同的地球化学特征 :辉长岩Ⅱ以富Si、Mg和贫Ti、P为特征 ,与辉长岩Ⅱ有关的辉绿岩Ⅱ以及枕状熔岩具玻安岩的特征 ,说明产于岛弧的弧前环境 ;辉长岩Ⅰ和辉绿岩Ⅰ具N -MORB的特征 ,推测产于弧后盆地环境。两类辉长岩的地质地球化学特征表明它们可能形成于慢速扩张的洋脊环境。

Two types of gabbro are exposed in Dachanaban ophiolite in North Qilian Mountains. One is in the lower part of the ophiolite, called gabbro Ⅰ, whereas the other intruded as dikes into pillow lava with boninite character in the upper part of the ophiolite, called gabbro Ⅱ. These two types of gabbro show different geochemical characteristics. Gabbro Ⅱ is characterized by rich Si, Mg and poor Ti, P, and diabase Ⅱand poillow lava associated with gabbro Ⅱ have features of boninite, suggesting a fore_arc environment. By contrast, gabbro Ⅰ and diabase Ⅰ is of N_MORB, assuming a back_arc basin setting. Geochemical characteristics of two types of gabbro suggest that their formation environment is an oceanic ridge of low spreading rate.