High pressure metamorphic rocks and their tectonic environment in northeastern China

Abstract

This paper deals with the high-pressure metamorphic rocks mainly of the Ondor Sum Group in Inner Mongolia and the Heilongjiang Group in the Jiamusi massif. A high pressure/low temperature metamorphic mineral assemblage of glaucophane schist facies and greenschist facies characterized by lawsonite, jadeitic pyroxene, glaucophane and pumpellyite has been recognized in the Ondor Sum Group. In northeastern China the high pressure metamorphic rocks are mainly distributed in the ancient intercontinental area, north of the Sino-Korean platform. A part of them is distributed on the outer margin of the Caledonian fold belt along the north edge of the Sino-Korean platform and it was dated at 445.6 ± 15 Ma by 39Ar/ 40Ar isochron method on glaucophane schist and at 509 ± 40 Ma by RbSr isochron method on whole rock of meta-basalt. These isotopic data indicate an early Paleozoic age of the subduction on the north edge of the Sino-Korean platform. The other part is the Heilongjiang Group of Jiamusi massif on the outer margin of the Xingkaiian fold belt. The Heilongjiang Group was intruded by a granite of 460 Ma (KAr). The lithological feature of the high pressure metamorphic rocks of the Heilongjiang Group is possibly correlated to that in the Altay-Sayan district (540–900 Ma). These facts suggest a probable Sinian-early Cambrian subduction.