Geodynamic controls on the Paleo-Asian oceanic plate evolution: Constraints from Paleozoic intrusive suites along the northern margin of the North China Block

Abstract

Identifying the spatio-temporal variations of arc-relation magmatism is critical for determining the polarity, geometry, localization, and onset of subduction zones on Earth. When and how the Paleo-Asian oceanic plate subducted beneath the northern margin of the North China Block (NCB) have been widely debated. Here we conducted systematic petrological, geochronological, and geochemical investigations on the Paleozoic magmatic rocks in the northern NCB. The Early Paleozoic magmatic rocks (ca. 490–420 Ma) are only distributed in the Bainaimiao arc and show typical continental arc geochemical characteristics, indicating a south dipping subduction zone. The Devonian alkaline rocks (ca. 400–370 Ma) constitute a ∼ 900 km-long magmatic belt in the northern margin of the NCB. Combined with a striking ca. 370–355 Ma magmatic quiescence and the absence of high-pressure rocks during that period, a flat-slab subduction model is proposed to better account for the tectonic evolution of the northern NCB. Subsequently, the Carboniferous to Permian calc-alkaline arc magmatism (ca. 355–250 Ma) began to emerge and showed northward younging and migration, suggesting slab retreat with roll-back of the subducting Paleo-Asian slab and again opening of mantle wedge along the northern NCB. Our findings therefore suggest that the Paleozoic magmatism in the northern NCB records an entire spatio-temporal evolution of the Paleo-Asian oceanic plate from early subduction angle deepening to flat-slab subduction, then slab rollback and finally normal subduction. This is tentatively interpreted as a combined effect from the Paleo-Asian oceanic plate subduction angle change and a migrating keel in the mantle wedge region.