Petrological study of high-pressure granulites of Shandong : implications for tectonic evolution of the Jiao-Liao-Ji Belt (JLJB) in the eastern block of the North China craton (NCC)

Abstract

High-pressure pelitic granulites and high-pressure mafic granulites discovered from the Jiaobei Massif situated in Jiao Liao-Ji Belt (JLJB), Eastern Block, North China Craton (NCC). The high-pressure granulites were metamorphosed around ~1.90Ga which believed to be the amalgamation of Longgang Block and Nangrim Block took part to form the Eastern Block of the NCC with JLJB as a mobile belt in between. The aim of this study is to examine the mineral assemblages and micro-textures preserved in the high-pressure pelitic and mafic granulites so as to provide petrological evidence for the possible evolution of the JLJB. Both high-pressure pelitic and mafic granulites show mineral assemblages preserved in pre-peak (M1), peak (M2) and post-peak (M3) metamorphism. Minerals before peak metamorphism were preserved as inclusions in garnet (M1). Inclusion-free garnet + matrix index minerals recorded the peak metamorphic mineral assemblages (M2). Presence of “garnet + feldspar + kyanite” in high-pressure pelitic granulite and absence of orthopyroxene in high-pressure mafic granulite imply that the peak metamorphism should have been up to >10kbar, probably caused by subduction-related process / orogenic process. Transformation of sillimanite from kyanite in high-pressure pelitic granulite and “white-eye” structures representing the “hornblende + plagioclase” symplectite on high-pressure mafic granulite indicate decompression and cooling processes during the post-peak metamorphism (M3). Evolution from M1 to M3 reveals a clockwise P-T path. It is suggested that the Paleoproterozoic JLJB should have experienced collisional event with subduction involved in the tectonic evolution.