Neoarchean crustal evolution of the eastern block in the North China Craton : lithological, structural and metamorphic constraints

Abstract

North China Craton (NCC) is one of the oldest cratonic block in the world which has records as early as Hadean eon. The Precambrian tectonic evolution of NCC has raised strong debate about the numbers of micro-continental blocks, time of amalgamation of small blocks and the causal relationship of tectonic processes, etc. especially for the two most significant metamorphic events at 2.5 and 1.8 billion years ago. In this study, the Neoarchean tectonic evolution of eastern block of NCC will be focused since the advancement of metamorphic Pressure-Temperature path reconstruction, the 2.50 Ga regional metamorphism of the eastern block has been found to follow an anticlockwise path with isobaric cooling, which indicates the tectonic model of the event would be rift environment, mantle plume models (hotspots) or continental magmatic arc setting. However, by investigating the lithological, structural and metamorphic constraints, mantle plume model is believed to be favored and supported by following evidence. (1) No systematic age and lithological progression across the around 800 km wide in Eastern Block. (2) The time between the emplacement of high grade tonalitic-trondhjemitic-granodiorite (TTG) and subsequent regional metamorphism was very short. (3)εHf values and Hf model ages show major depleted mantle events but with increased involvement of crustal recycling across the Eastern Block from 2.9 Ga to 2.5 Ga. (4) Bimodal volcanism. (5) The common occurrence of komatiites in greenstone belts indicate the extremely high temperature was experienced. (6) Widespread domiform structures. (7) Absence of characteristics of active margins and (8) Anticlockwise P-T paths with isobaric cooling, but depleted mantle events but with increased involvement of crustal recycling across the Eastern Block from 2.9 Ga to 2.5 Ga. (4) Bimodal volcanism. (5) The common occurrence of komatiites in greenstone belts indicate the extremely high temperature was experienced. (6) Widespread domiform structures. (7) Absence of characteristics of active margins and (8) Anticlockwise P-T paths with isobaric cooling, but without paired metamorphic belt.