摘要
大别山北部镁铁-超镁铁质岩带中的榴辉岩主要有两种产状,一是产于变形较强(面理化)的橄榄岩中,另一种是产于片麻岩中。其中,绿辉石中硬玉端元组分大多为Jd=20mol％～52mol％。产于橄榄岩和片麻岩中榴辉岩的石榴子石成分分别相当于Coleman的B型和C型榴辉岩。石榴子石成分特征及钠质单斜辉石中石英针状出溶体的出现表明,本区榴辉岩早期可能经历过超高压变质作用,且至少经历了3个变质阶段,即:①榴辉岩相峰期变质阶段,主要矿物共生组合为石榴子石+绿辉石+金红石±蓝晶石+石英(或柯石英假象?),p≥2.5GPa、t=595～874℃;②高压麻粒岩相变质阶段,主要矿物共生组合为石榴子石+透辉石+紫苏辉石+钛铁矿+尖晶石+斜长石等,p=1.1～1.37GPa、t=817～909℃;③角闪岩相变质阶段,主要矿物共生组合为角闪石+斜长石+磁铁矿等,p=0.5～0.6GPa、t=500～600℃。该区榴辉岩独特的麻粒岩相退变质阶段,表明榴辉岩在折返初期并未能上升到中上地壳,而处于下地壳,它与南部超高压变质岩有不同的p-t演化史,即在榴辉岩相峰期变质之后经历了近等温减压(或稍升温减压)和降温减压变质过程。
The eclogites from the mafic-ultramafic belt in the Northern part of the Dabie Mountains are distributed as lenses in the foliated peridotites and the ortho-gneisses. Generally, the end members of ompacites are Jd = 20 mol%- 52 mol% The garnet composition, mineral assemblage of eclogite facies and oriented quartz exsoluiton in Na-clinopyroxene indicate the eclogites here underwent a Triassic ultrahigh-pressure metamorphism. At least the three metamorphic stages of eclogites here can be distinguished; (1)the peak metamorphic stage with om-phacite +garnet+ rutile ± kyanite + quartz (after coesite ?) mineral assemblage of ecogite facies, p≥2. 5GPa and t=595- 874℃ ;(2)the high-pressure granulite facies stage with garnet + diopside + hypersthene-Klmenite +spinel+plagioclase ±corundum ± olivine, p=1. 1-1. 37GPa and t = 817-909℃ ;(3)the amphibolite facies one with amphibole+ plagioclase+magnetite, p = 0. 5-0. 6GPa and t=500-600℃ ,After the peak metamorphism of eclogite facies they underwent an approximate isotherm-decrease pressure and then decrease temperature-decrease pressure process with a clockwise metamorphic p-t veolution. The metamorphic p-t path of the e-clogites from the northern Dabie Mountains is different fron one in the southern Dabie Mountains.
出处
《地质学报》
EI
CAS
CSCD
北大核心
2001年第3期385-395,T005,共12页
Acta Geologica Sinica
基金
国家自然科学基金(编号49794041)
安徽省地质矿产局资助项目的成果
关键词
榴辉岩
变质温压条件
超高压变质作用
镁铁-超镁质岩带
大别山
角闪岩
石榴子石
eclogite
metamorphic p-t condition
ultrahigh-pressure metamorphism
mafic-ultramafic belt
Northern part of the Dabie Mountains
