Mantle plume-triggered rifting closely following Neoarchean cratonization revealed by 2.50–2.20 Ga magmatism across North China Craton

Abstract

The Earth experienced fundamental tectonic transformation and paleoclimatic upheavals during the early Paleoproterozoic (2.50–2.20 Ga). However, the tectonic framework of this crucial period is challenging to define precisely because of the tectono-magmatic “slowdown”. Here we carry on a comprehensive compilation of published 2.50–2.20 Ga magmatism in the North China Craton (NCC), in order to provide key constraints on the Archean-Proterozoic transition. All the rocks can be divided into two stages including three subgroups: stage 1 (2.50–2.42 Ga), stage 2–1 (2.42–2.25 Ga), and stage 2–2 (2.25–2.20 Ga). Rocks of stage 1 are mainly gabbros, sanukitoid-like rocks, diorites, tonalite-trondhjemite-granodiorite (TTG), and potassic granites. The TTGs are medium to high pressure (MP-HP) series and likely derived from subducted slabs. The gabbros and sanukitoid-like rocks were from enriched mantle sources. The diorites and K-rich granites were from partial melting of different levels of crust. The rock associations are representative of the continuation of the Neoarchean cratonization and record a tectonic shift from subduction-collision to post-collision. The youngest high-K granites (ca. 2.42 Ga) may mark the real termination of the “Neoarchean” cratonization in the NCC. Rocks of stage 2–1 are mainly komatiitic rocks, gabbros, low-pressure (LP) TTGs, diorites, and A-type granites. Rocks of stage 2–2 comprise basalt-dacite-rhyolite and granitic anatectic melt. The komatiitic rocks likely derived from the asthenospheric mantle possibly related to a plume setting. The mafic rocks were sourced from an ancient and enriched subcontinental lithospheric mantle. The upwelling mantle-derived melts further induced partial melting of the cratonic lower to upper crust to form the LP TTGs, diorites, and A-type granites. The stage 2 rock associations were emplaced as typical intraplate magmatism, recording initiation and development of a plume-triggered rift setting. These observations are further supported by our new data on 2.32–2.27 Ga rocks in the southern NCC, including, but not limited to, LP-TTGs, gabbros, and A-type granites. Subsequently, rifting continually developed (2.20–2.10 Ga) and a tectonic transition ensued from passive to active continental margin (2.20–2.05/2.00 Ga, e.g., Peng et al., 2012) until subduction-collision-post-collision occurred (1.95–1.80 Ga; e.g., Zhao et al., 2002a, 2002b). From a global perspective, the early Paleoproterozoic tectono-magmatic events in the NCC tend to be synchronized to those of the world including rifting magmatism, and large igneous provinces (LIPs), etc. During the early Paleoproterozoic rifting processes, sulphur dioxide (e.g., SO2) was likely to be released into the atmosphere by magmatic events (e.g., LIPs), and continental uplift would have induced weathering, erosion, and delivery of bioessential nutrients to the ocean, all these were vital to the paleoenvironmental changes, lowering pCO2 and introducing glacial conditions.