依兰地区黑龙江增生杂岩碱性玄武质火山碎屑岩中钠质闪石特征及成因探讨

Characteristics and genesis of sodium amphiboles in alkaline basaltic pyroclastic debris of Heilongjiang accretionary complexes in Yilan area

佳木斯地块西侧依兰地区出露一套洋岛型碱性玄武质火山碎屑岩，它由岩屑和细粒火山碎屑物组成。火山碎屑岩在佳木斯地块与松嫩地块之间的古洋盆闭合过程中，发生了低温高压变质作用，在岩石中形成了大量钠质闪石。其中岩屑中的钠质闪石不定向均匀分布，普遍具有环带结构，核部为青铝闪石，边部为蓝闪石；细粒火山碎屑物中的钠质闪石定向分布，均为青铝闪石。这些钠质闪石形成的温压条件相似，形成温度在300～350℃之间，形成压力在0．7GPa左右。根据岩屑和细粒火山碎屑物的矿物成分、钠质闪石的结构构造特征以及火山碎屑岩的变形特征，推测这类岩石在低温高压变质作用过程中钠质闪石形成的首要条件是有足够的钠质来源；在有足够钠质来源的前提下，形成钠质闪石的种类与体系的氧逸度有着直接关系，低氧逸度条件下形成蓝闪石，高氧逸度条件下形成青铝闪石。这些钠质闪石的形成与佳木斯地块、松嫩地块的拼合碰撞以及之后岩石的变形方式有关。

There is a set of oceanic island type alkaline basaltic pyroclastic rocks composed of debris and fine-grained pyroclastic materials in western Jiamusi terrain, Yilan area. These rocks resulted from low temperature and high pressure metamorphism during the closure process of the ancient oceanic basin between Jiamusi terrain and Songnen terrain, and formed a large number of sodium amphiboles in them. The sodium amphiboles in pyroclastic debris are distributed uniformly and non-directionally, and generally show zonal structure. The core is mainly crossite and the edge part is glaucophane. The sodium amphiboles in fine-grained pyroclastic materials are distributed directionally, composed exclusively of crossite. Temperature and pressure conditions for the formation of these sodium amphiboles are quite similar, with temperature between 300 and 350℃ and pressure about 0. 7 GPa. Based on mineral composition of pyroclastic debris and fine-grained pyroclastic debris, structure characteristics of sodium amphiboles and deformation characteristics of pyroelastic debris, it is inferred that the primary conditions for the formation of sodium amphiboles are low temperature and high pressure metamorphism and sufficient sodium source. Under the condition of sufficient sodium source, the kinds of sodium amphiboles have a direct relationship with oxygen fugacity in the system. Glancophane and crossite were formed under low oxygen fugacity and high oxygen fugacity respectively. The formation of these sodium amphiboles is related to the collision between Jiamusi terrain and Songnen terrain and also to the later deformation style of rocks.