摘要
安徽岳西地区与超基性岩伴生的柯石英榴辉岩的共生矿物组合是石榴石+绿辉石+白云石+柯石英+金红石或石榴石+绿辉石+柯石英+斜黝帘石+白色云母+金红石。前一个含白云石组合是本文作者首次发现的。石榴石中铁铝、镁铝和钙铝榴石分子分别为25～63(％)、10～32％和23～44％。绿辉石中硬玉、普通辉石、霓石和钙契尔马克分子分别为35～51％、45～58％、0.2～13％和0～3％。变质作用的温度为600～840℃,压力大于2.7～2.9GPa,形成深度在80km以上。
The coesite-ecolgite in the form of lenses and layers with length from a few cm to several meters occurs in ultrabasic rocks in the area of AnhuiProvince. This is the third occurrence of coesite in metamorphic crustal rocks known in the world.
The mineral assemblages of the coesite-eclogites are garnet+omphacite+dolomite+coesite+rutile, or garnet+omphacite+coesite+muscovite+clinozosite+rutile. Coesite and polycrystalline quartz pseudomorphs after coesite occur as inclusions in garnet and omphacite, and the host crystals show well-developed radial and/or concentric fractures. Electron micropropbe analysis shows that the garnets from the coesite-eclogites are composed of almandine 25～63％, pyrope 10～32％ and grossular 23～44％; Omphacites are composed of jadite 33～51％, aegirine 0～13％, augite 45～58％ and CaTschermark 0～3％.
Garnet-clinopyroxene geothermometry (Powell. 1985) and compatibility between quartz and coesite suggest that temperature for the coesite eclogite metamorphism was higher than 2.7～2.9GPa, and geothermal gradient was about 7℃/km. It indicates that the Dabieshan coesite-eclogites were formed at crustal depths of 80-100km, and produced by the subduction of the North China and Yangtze plates. The continuous underplating and tectonic erosion provided a mechanism for rapid uplift of ultrahigh-pressure metamorphic rocks.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
1992年第1期97-102,共6页
Acta Petrologica Sinica
基金
国家自然科学基金(NSF85040093)
关键词
榴辉岩
白云石
柯石英
变质条件
Coesite-eclogite
Petrology
Metamorphic conditions
Subduction
Underplating
Anhui
