QUANTIFYING ISOTOPIC FLUX FROM CHEMICAL WEATHERING OF SUBDUCTION AND COLLISION MAGMATISM BY INTEGRATING GLOBAL ZIRCON ISOTOPIC DATABASE, PLATE RECONSTRUCTION MODEL, AND PALEO-CLIMATE SIMULATIONS

The global distribution of igneous rocks generated by subduction and collision magmatism holds information about the relationship between magma composition and plate tectonics. These rocks located in high-elevation orogenic belts also influence the isotopic composition of seawater through erosion and chemical weathering.

In this study, we first used a global database of zircons, along with the plate reconstruction models, to map the original locations of samples on tectonic plates using the GPlates software. Results show that from 550 Ma to ~400-350, during the assembly of the Gondwana supercontinent, the global zircon Hf isotopic composition (εHf(t)) show overall evolved isotopic signatures as the subduction and collision mostly involving old continents. From ~250 Ma to ~35 Ma, during the assembly and the dispersal of the Pangea supercontinent, global zircon εHf(t) show overall juvenile isotopic signatures suggesting the subduction and collision during this period involved accreted, young oceanic terranes that served as the juvenile basements for arc and collisional magmatism. Such change of global zircon εHf(t) from evolved to juvenile signatures is consistent with the trend of the normalized seawater Strontium isotopic ratio suggesting the influence of tectonics of supercontinent on seawater isotopic composition via chemical weathering.

To further evaluate the isotopic flux due to chemical weathering, we combine the spatial distribution of zircon samples with the global distribution of annual precipitation and average surface temperature derived from paleo-climate simulations. We semi-quantify the isotopic flux to elucidate the potential linkage between supercontinent cycles and the chemical weathering signatures from continental magmatism.