Arc Magmatism Controlled by Switches in Tectonic Style: Insights From the NE Asian Margin in the Cretaceous.

A relation between tectonics and arc magmatism has been proposed in the west Pacific‐type accretionary orogens, but the specific mechanism remains unclear. This study examines the Cretaceous records in NE Asia in order to unravel this link. Two tectono‐magmatic episodes, namely the Early and Late Cretaceous, are recognized. The first episode was under (trans‐)extension, consisting of both mafic and felsic, depleted and enriched, and deep‐ and shallow‐derived arc magmas. The second episode experienced several compressive events with highly evolved and shallow‐derived (mid‐crustal level) arc magmas. We propose that (trans‐)extension thinned the arc crust, facilitating deep mafic magmas to ascend and cool rapidly, maintaining their geochemical diversity. Compression led to magmatic emplacement around the middle crust; and the warm crust allowed highly‐evolved granitoids to form. Therefore, tectonic setting controls arc magmatism in NE Asia, and is likely representative of other west Pacific‐type orogens. Plain Language Summary: Arc magmas are produced where oceanic plates subduct into the mantle. Their chemical composition varies in different tectonic settings, but the specific mechanism is unclear. We explore this question using the NE Asian setting during the Cretaceous. Here, the Early Cretaceous arc magmas reveal diverse compositions when in a setting undergoing extension. However, the Late Cretaceous magmas uniformly contain high silica contents when the continental crust was under compression. This implies that thin arc crust under extension facilitated the ascent of deeply‐derived magmas and these cooled rapidly and kept their chemical diversity. In contrast, crust under compression prohibited the ascent of deep magmas, instead inducing crustal melting and slower cooling in the middle crust, thus increasing the silica content. Therefore, tectonics strongly affected the nature of arc magmatism in NE Asia, and possibly other west Pacific‐type orogens. Key Points: Cretaceous magmatism in the NE Asian arcs was diverse during extension, but highly evolved under compressionExtension induced deep magmas to ascend and cool rapidly; Compression restrained deep magmas and extended coolingArc magmas were controlled by alternating extensional and compressional regimes during subduction retreat in west Pacific‐type orogens [ABSTRACT FROM AUTHOR]