北大巴山碱质基性—超基性潜火山杂岩的辉石矿物研究

北大巴山碱质基性-超基性潜火山杂岩中有7种岩石含有新鲜的单斜辉石,它们分属于透辉石、普通辉石及霓辉石。单斜辉石可划分为5种成因类型:(1)斑晶、微斑晶及微晶;(2)深源捕虏晶;(3)半同源捕虏晶;(4)异源捕虏晶;(5)地幔型捕虏晶,本文涉及前4类辉石。单斜辉石的研究表明:(1)7种含辉石的岩石为同源岩浆结晶分异作用的产物,源岩浆为碱性-过碱性幔源岩浆。(2)初始岩浆形成于77km以下深度,上升过程中岩浆曾在3个不同深度储积。(3)岩浆上升至近地表处,在冷凝固结前曾有多次潜火山隐爆活动发生。(4)霓辉石捕虏晶的出现代表区内存在另一种碱基性岩浆活动。(5)辉石成分指示碱质基性-超基性次火山杂岩形成于陆边板内裂陷带。

THE STUDY OF PYROXENE MINERALS OF ALKALI-BASIC-ULTRABASIC SUBVOLCANIC COMPLEX FROM NORTHERN DABA MTS.

In alkali-basic-ultrabasic subvolcanic complex of northern Daba Mts. there are seven rock types which contain fresh clinopyroxenes; those are diopside, augite and aegirine-augite. Clinopyroxenes can be divided into five genetic types; 1.phenocryst, microphenocryst and microcryst; 2.deep-seated xenocryst; 3.semi-cognate xenocryst; 4.accidental xenocryst; and 5.mantle-derived xenocryst. The first four types of clinopyroxene are only discussed in this paper. The results of study on clinopyroxene indicate, 1.Seven clinopyroxene-bearing rocks are products of crystallization differentiation of cognate magma. Its source magma is alkali-peralkalic mantle-derived magma; 2.Initial magma formed at depth lower than 77 kin. During ascending the magma reservoired at three levels; 3.When the magma ascended near the surface there occurred subvolcanic cryptoexplosion of magma many times; 4.Aegirine-augite xenocrysts represent another alkali-basic magma activities, 5.Chemical compositions of clinopyroxene indicate that alkali-basic-ultrabasic subvolcanic complex of this area was generated in a geological setting of interplate rift zone on the continental margin.