摘要
Eclogitic garnet-amphibole rocks are scattered around me Songshugou ultramafic bodies in Qinling Mountains . Three metamorphic stages are recognized in terms of petrography, mineral chemistry and geothermobarometry . The first alhite-amphibole stage was of greenschist facies metamorphism with typical mineral assemblage of actinolite+epidote+chlorite+albite ; the pressure and temperature conditions were equal to or lower than 500MPa and about 400 ℃ .The second prograde eclogitic garnet-amphibole stage was of amphibole-eclogite fades metamorphism with typical mineral assemblage of garnet+hornblende± clinopyroxene+ruffle without ptagioclase ,the pressure condition was at least 1000- 1200MPa and the temperature about 600 ℃ .The third retrograde epidote-amphibole stage was of epidote-amphibolite fecies with assemblage of plagioclase+hornblende+epidote+ilmenite/titanite , the temperature was 500-600 ℃ and the pressure from 800MPa down to 500MPa .All three stages took place in one single tectonothermal event called Jinningian movement at about 1000Ma .The p-T path shows a hairpin shape and thus indicates a metamorphism in the sobduction environment. The metamorphk processes of the garnet- amphibole rocks thus provides a significant evidence for the pbte tectonic movement prevailing in the late Middle Proterozoic period.
Eclogitic garnet-amphibole rocks are scattered around me Songshugou ultramafic bodies in Qinling Mountains . Three metamorphic stages are recognized in terms of petrography, mineral chemistry and geothermobarometry . The first alhite-amphibole stage was of greenschist facies metamorphism with typical mineral assemblage of actinolite+epidote+chlorite+albite ; the pressure and temperature conditions were equal to or lower than 500MPa and about 400 ℃ .The second prograde eclogitic garnet-amphibole stage was of amphibole-eclogite fades metamorphism with typical mineral assemblage of garnet+hornblende± clinopyroxene+ruffle without ptagioclase ,the pressure condition was at least 1000- 1200MPa and the temperature about 600 ℃ .The third retrograde epidote-amphibole stage was of epidote-amphibolite fecies with assemblage of plagioclase+hornblende+epidote+ilmenite/titanite , the temperature was 500-600 ℃ and the pressure from 800MPa down to 500MPa .All three stages took place in one single tectonothermal event called Jinningian movement at about 1000Ma .The p-T path shows a hairpin shape and thus indicates a metamorphism in the sobduction environment. The metamorphk processes of the garnet- amphibole rocks thus provides a significant evidence for the pbte tectonic movement prevailing in the late Middle Proterozoic period.
基金
The project is supported by National Nature Science Fountation of China No.48900015
