Plate-tectonics links to the origin of silicic magmatism within a long-lived continental arc in Sikhote-Alin (Russian Far East)

Silicic magmatism in continental arcs could result in hazardous volcanic eruptions. It is also crucial for continental crust formation, particularly for those with a large volume (e.g., large-volume silicic magma systems). Despite their subduction origin, silicic arc magmatism has seldom been linked to the geodynamics of subduction margins.

This study investigates the origin of silicic magmatism in an extensive sampling record of a single, long-lived continental arc at the ~1200 km-long Sikhote-Alin (Russian Far East), and discusses the origin against subduction history from a recent NW Pacific plate tectonic reconstruction (Wu et al., 2022 EPSL). We investigate a large magmatic dataset synthesized from published and unpublished whole-rock geochemistry and zircon U-Pb ages. It reveals two episodes of Cretaceous to Early Cenozoic Sikhote-Alin silicic magmatism that correlates to distinct plate-tectonic settings: (1) a 134-100 Ma episode with high average SiO2= 68.86 wt.% (n= 115) and smaller magmatic flux (~400 km2 per Myr), which was emplaced during oblique subduction / intra-oceanic arc accretion events; and, (2) a more widespread (~1600 km2 per Myr) 95 to 52 Ma large-volume silicic magmatism with mean SiO2= 69.90 wt.% (n= 148) that occurred along an ultrafast convergent margin (12-25 cm/ year). The igneous rock geochemistry shows a more fractionated (e.g., lower Mg#, TiO2) 95 to 52 Ma episode magmatism. Furthermore, the 95 to 52 Ma magmatism yields a higher average zircon Th/U= 0.96 (range from 0.04 to 30.5 in 1980 grains) that may indicate a higher crystallization temperature relative to the 134-100 Ma zircons with lower average Th/U= 0.58 (range from 0.01 to 17.8 in 519 grains). We propose an ultra-fast subduction zone may have extremely high magmatic volatile and magmatic fluxes that feed the large-volume silicic magma systems within the overriding plate. We further discuss the link between subducting plate dynamics and the evolution of silicic magmatism as revealed by zircon trace element geochemistry, apparent Ti-in-zircon crystallization temperature, and zircon saturation temperature of bulk rock composition.