我国东北小古里河-科洛-五大连池-二克山火山带钾质矿物成因及地质意义

摘要

Xiaogulihe-Keluo-Wudalianchi-Erkeshan potassic volcanic rock belt in Northeast China, one of the well preserved volcanic clusters in China, was characterized by the high contents of potassium, alkali and high K20/Na20 ratios ( > 1.2) in the rocks and was attributed to high potassium peralkaline volcanic rocks. Based on the research relating compositions, crystallization conditions of potassic minerals (phlogopites, leucites) in hosted volcanic rocks and mantle peridotite xenoliths with magma component and its source, the authors suggested that lithospheric extension in the studied region was responsible for low-degree decompression melting of phlogopite-bearing peridotites in the mantle and the potassic magma experienced leucites crystallization in shallow crust As magma evolved, the magma tended to be Na-rich and xenomorphic nepheline and sodalite occurred in matrix glass resulting from the crystallization of lots of potassic minerals. The volatile-rich minerals as phlogopite, leucite, aptite, nepheline and sodalite in volcanic rocks and mantle xenoliths also provided the evidence of high abundance of H,O, F, Cl and P in the magma.%东北黑龙江小古里河-科洛-五大连池-二克山火山岩带是我国近代保存最好的火山群之一,此带火山岩的岩石化学特点全都强碱富钾,K2O/Na2O＞1.2,属于一套高钾过碱性火山岩.通过对东北钾质火山岩及金云母橄榄岩地幔捕虏体中钾质矿物金云母、白榴石的成分、结晶环境与岩浆成分及来源关系的研究,认为在岩石圈伸展构造背景下,地幔金云母橄榄岩的低度部分熔融形成钾质岩浆,钾质岩浆上升到地壳浅部经历了白榴石的结晶作用.岩浆演化晚期,因钾质矿物大量晶出导致岩浆相对富钠而出现他形霞石和方钠石等填隙矿物.火山岩及地幔捕虏体中富挥发分矿物金云母、白榴石、磷灰石、霞石和方钠石还提供了钾质岩浆富含H2O、F、Cl、P等挥发分的证据.