Craton Destruction 2: Evolution of Cratonic Lithosphere After a Rapid Keel Delamination Event

Abstract Cratonic lithosphere beneath the eastern North China Craton has undergone extensive destruction since early Jurassic times (approximately 190 Ma). This is recorded in its episodic tectonic and magmatic history. In this time, its lithosphere changed thickness from approximately 200 km to <60 km. This change was associated with a peak time (approximately 120 Ma) of lithospheric thinning and magmatism that was linked with high surface heat flow recorded in rift basins. We believe that these records are best explained by a two‐stage evolutionary process. First, approximately 100 km of cratonic “keel” underlying a weak midlithospheric discontinuity layer (approximately 80–100 km) was rapidly removed in <10–20 Ma. This keel delamination stage was followed by a protracted (approximately 50–100 Ma) period of convective erosion and/or lithospheric extension that thinned the remaining lithosphere and continuously reworked the former cratonic lithospheric mantle. This study focuses on numerical exploration of the well‐recorded second stage of the eastern North China Craton's lithospheric evolution. We find that (1) lithospheric mantle capped by thick crust can be locally replaced by deeper mantle material in 100 Ma due to small‐scale convective erosion; (2) asthenospheric upwelling and related extension can replace lithospheric mantle over horizontal length scales of ~50–150 km, and account for observed “mushroom‐shaped” low‐velocity structures; (3) modeling shows conditions that could lead to the multiple eastern North China Craton magmatic pulses between 190 and 115 Ma that are associated with temporal and spatial changes in magma source petrology and a magmatic hiatus; and (4) a “wet” midlithospheric discontinuity layer provides a potential source material for on‐craton magmatism.