SUBDUCTION VELOCITY CONTROLS ON ARC MAGMATIC FLUX AND GEOCHEMISTRY

Arc magmatism is a direct consequence of subduction plate tectonics. Since the initiation of plate tectonics in 3~2.5 Ga, magmatism has shaped our Earth by promoting continental crust formation, long-term climate change, and the production of mineral resources. Although modern plate convergence velocities in global subduction zones are mostly (96%) slower than 12 cm/yr, recent plate tectonic reconstructions imply faster global plate tectonics since 1 Ga. Thus, ultrafast (>12 cm/yr) subduction-related magmatism was likely more common throughout Earth’s history than Present, with very few modern analogs. In addition, the role of plate convergent velocities in generating arc magmatism is not well-quantified in previous studies, mainly due to poorly constrained down-going plate parameters in ancient subduction zones.

In this study, we utilize linear regression analysis to test the correlation between 1) slow to fast convergence velocities up to 24 cm/yr, and 2) synthesize magmatic arc geochemistry records (e.g., wt.% SiO₂, trace elements, Nd and Pb isotopic compositions) along 100~0 Ma NE Asia continental and the modern Tonga-Kermadec oceanic arcs. We further discuss the regression result against the numerical modeling of magma production in slow to fast subduction zones. We show that faster subduction contributes to a more differentiated (higher average % SiO₂) and isotopically-enriched arc magmatism with higher flux. Ultrafast subduction is associated with continental arcs dominated by >70 % felsic rocks (e.g., 100~52 Ma NE Asia), and oceanic arcs dominated by >60 % intermediate rocks (e.g., modern Tonga). Despite their absence in the modern Earth, continental arcs along ultrafast plate convergence zones may drive faster cyclicity in crustal thickness and magmatic flux, higher continental growth and evolving rates, enhanced porphyritic ore-forming conditions, in contrast to arcs along slower < 12 cm/yr convergent margins.