Coexisting diverse P–T–t paths during Neoarchean Sagduction: Insights from numerical modeling and applications to the eastern North China Craton

Abstract

The Eastern Block of the North China Craton preserves a Neoarchean greenstone-granite rock association with typical dome-and-keel structures. Metamorphic data for these rock assemblages record both anticlockwise P–T paths involving near-isobaric cooling (IBC) and clockwise paths with nearly isothermal decompression (ITD) from nearby locations leading to controversial and contradictory interpretations. To resolve the presence of coexisting diverse P–T paths, and to place them within a viable geodynamic regime, we conducted 2D thermomechanical numerical models with the initial and boundary conditions similar to that of the Neoarchean eastern North China Craton. Our model results reveal that heat transferred from the high-temperature lower boundary and crustal density inversion leads to crustal-scale sagduction that generates the observed dome-and-keel architecture and results in four major types of P–T–t paths: (1) an anticlockwise IBC-type P–T–t path in which the supracrustal rocks progressively sink to a deep crustal level through sagduction, and experience a long-lived residence followed by ambient mantle cooling without significant exhumation; (2) an clockwise ITD-type P–T–t path where the supracrustal rocks sink to the deep crust and are partly captured by upwelling felsic magmas, resulting in rapid exhumation to a middle crustal level; (3) a newly identified crescent-type P–T–t path that reveals an integrated burial-exhumation cycle characterized by an initial high dT/dP burial stage, followed by the rapid exhumation to the upper crust and extensive low dT/dP cooling; (4) a hairpin-type P–T–t path in which deeply buried supracrustal rocks experience a slow exhumation rate. The dome-and-keel architecture and P–T–t paths produced by the numerical model conform to the structural, metamorphic and geochronological data of the Eastern Block. We propose that the geological complexity of eastern China and temporally coexisting diverse P–T–t paths most likely developed under a mantle plume related crustal-scale sagduction geodynamic regime in Neoarchean.