Carbon and nitrogen input fluxes and recycling efficiencies in the Manila Subduction Zone in the South China Sea

Controlled by the subduction-collision system of the Neo-Tethyan tectonic domain, a large number of small marginal basins and their associated subduction zones have developed along ancient suture zones, e.g., the South China Sea (SCS) and Manila subduction zone. These marginal basins provide an example to study the carbon(C) and nitrogen(N) cycling mechanisms coupled between surface reservoirs and the deep mantle during the late evolution of the Neo-Tethyan tectonic domain. As fluid-active and volatile elements, C and Nn play important roles in the transport and climate between the atmosphere, hydrosphere, and lithosphere, as well as in crust-mantle material cycling. International Ocean Discovery Program (IODP) Sites U1431, U143, and U1503 recovered near-complete sequences of oceanic crust from initial spreading to relict ridges. These samples provide a suitable opportunity to quantify C and N input fluxes and recycling efficiencies in the Manila subduction zone. Here, we measure the C and N concentrations as well as isotope values of sediments and basalts from the SCS using a Thermo Scientific FLASH 2000 Elemental Analyzer and a Delta V Isotope Ratio Mass Spectrometer. The C and N input fluxes to the Manila subduction zone were further calculated by combining different computational models. Using the C and N concentrations of the SCS oceanic crust as a reference, we estimated unit C and N input fluxes to these marginal sea subduction zones associated with the Neo-Tethyan tectonic domain. In addition, we collected ³He, Ne, Ar, N₂, and CO₂ concentrations in the emissions from the high-temperature geothermal systems associated with the Luzon arc, which were used in the final calculations of arc-volcanic output fluxes from the Luzon arc as well as C and N cycling efficiencies in the Manila subduction zone. The above data provide new insights into the cycling of volatiles during global-scale tectonic events.
Supplemental Table S1. Carbon and Nitrogen concentrations and isotopic compositions of the SCS samples.
Supplemental Table S2. The cut-off depth of the 100 ºC isotherm.
Supplemental Table S3. The concentrations of ³He, Ne, Ar, N₂, and CO₂ (mmol/mol of dry gas) in emissions from high-temperature geothermal systems ssociated with Luzon arc.
Supplementary Methods.