Reconnaissance study of Precambrian metamorphic rocks, northeastern Sino-Korean shield, People's Republic of China

Abstract

In eastern Liaoning and southern Jilin Provinces, People9s Republic of China, rocks of late Archean, early and middle Proterozoic ages consist of interlayered recrystallized banded iron-formations, pelitic schists, maric and ultramafic amphibolites, and quartzofeldspathic gneisses. The latter two lithologies are volumetrically dominant and include both supracrustals and orthogneisses/orthoamphibolites. New analytical data document the chemically primitive nature of maficultramafic amphibolite and tonalitic granulites of Archean age, which are overlain and invaded by more evolved Proterozoic supracrustal and plutonic units, now metamorphosed. Late Archean (2.8-2.9 b.y.) rock types include metakomatiitic/metatholeiitic pyroxene-bearing amphibolites, and granulitic tonalite gneisses. Early and middle Proterozoic Fuping/Wutai (2.4-2.5 b.y./1.9-2.0 b.y.) and Zhongtiao (1.6-1.8 b.y.) orogenies produced amphibolite/epidote amphibolite and anchimetamorphic to greenschist-facies overprints, respectively. Mineral assemblages suggest intermediate crustal levels of recrystallization for the late Archean low-rank granulite facies metamorphism (and/olig + pargasitic hbl + Ti-rich bio ± opx ± cpx ± garn: 700 ± 100 °C, 6-7 kbar), progressively shallower depths for early and middle Proterozoic amphibolite (olig + blue-green hbl + brown bio: 500 ± 100 °C, 5 ± 1 kbar) and greenschist- (alb + chi + ep + act + phengite: 400 ± 50 °C, 2-3 kbar) facies events. Late Archean and early Proterozoic recrystallizations took place under P-T conditions characteristic of moderately thick sialic crust and inferred Island-arc-like heat fluxes. Crustal growth locally terminated, and the Sino-Korean craton was stabilized about 1.7 b.y. ago. Much later, the complex was affected by a thermal event accompanying Mesozoic calc-alkaline plutonism/volcanism, apparently during the terrane assembly of east Asia.