Initiation of modern-style subduction in the Neoarchean: From plume to subduction with frequent slab break-off

Abstract

Abstract Fundamental geodynamic changes from vertical tectonics to lateral subduction occurred during the Neoarchean, yet detailed processes related to this transition and initiation of modern-style subduction remain enigmatic. Successive Neoarchean magmatic rocks including both plume-derived komatiites and subduction-related supracrustal and intrusive rocks appeared and preserved key information on the late Archean geodynamic changes in the Western Shandong Province granite-greenstone belt (WSP), North China Craton. In this study, whole-rock geochemical and Sm-Nd isotopic data and zircon U-Pb and Lu-Hf isotopes are reported for early Neoarchean supracrustal and intrusive rocks for the WSP. Temporally, the early Neoarchean magmatic movements in the WSP can be subdivided into two stages, including the early stage (2.77–2.69 Ga) and the late stage (2.69–2.60 Ga). Spatially, from southwest to northeast, intrusive rocks with similar ages define three belts (A, B, and C). Early stage tholeiitic and enriched meta-basalts were plume-related, representing oceanic crust opening from a pre-early Neoarchean continent. Slab subduction at least initiated at ca. 2.74 Ga and generated various Neoarchean tonalite-trondhjemite-granodiorites, quartz diorites, and arc-related volcanic rocks and mafic intrusions. Episodic emergence of meta-basaltic rocks and/or mafic intrusions with depleted εHf(t) values and low (La/Yb)N ratios indicates frequent slab break-offs during ca. 2.70–2.68 Ga, 2.66–2.64 Ga, and 2.62–2.60 Ga due to a relatively hotter mantle and regional heating by mantle plume. Secular geochemical changes of mafic and felsic rocks in this study outline roles of slab subduction in contributions of cooling the mantle, secular mantle refertilization, and crustal growth.