An experimental study on smectites as nitrogen conveyors in subduction zones

Abiotic passive nitrogen and methane enrichment during exhumation of subducted rocks: Primary multiphase fluid inclusions in high‐pressure rocks from the Cabo Ortegal Complex, NW Spain

“…In the geological cycle of nitrogen, the initial source introduced into the subduction zone is organic material deposited in seafloor sediments (Bebout et al, 2013). During diagenesis and low‐grade metamorphic evolution, nitrogen is released into pore fluids as ammonia (NH 3 ) then transforms into the form of ammonium (NH 4 + ) (Busigny & Bebout, 2013; Cedeño et al, 2019). Having similar charge and ionic radius, the released NH 4 + ion acts as an ideal substitution for K + in such phyllosilicates as clay minerals and micas, and alkali feldspars, confirmed by strong correlation between concentration of nitrogen and LIL elements, such as K, Rb and Cs (Busigny et al, 2003; Halama et al, 2010).…”

“…Having similar charge and ionic radius, the released NH 4 + ion acts as an ideal substitution for K + in such phyllosilicates as clay minerals and micas, and alkali feldspars, confirmed by strong correlation between concentration of nitrogen and LIL elements, such as K, Rb and Cs (Busigny et al, 2003; Halama et al, 2010). The breakdown of micas during prograde metamorphism results in a continuous release of NH 4 + , although high stability of NH 4 + under HP in white micas (phengite) or K‐feldspar (hollandite) allows its retention to great depths (even of the transition zone) depending on redox conditions (Bebout, 2007; Cedeño et al, 2019; Watenphul et al, 2009). Efficiency of nitrogen release, which would equilibrate as N 2 (Li & Keppler, 2014), is mostly controlled by the breakdown of phengite, which is showing a strong correlation with the thermal gradient of subduction zones (Mitchell et al, 2010).…”

“…Efficiency of nitrogen release, which would equilibrate as N 2 (Li & Keppler, 2014), is mostly controlled by the breakdown of phengite, which is showing a strong correlation with the thermal gradient of subduction zones (Mitchell et al, 2010). Consequently, hot subduction paths promote a high degree of N escape, whereas cold geotherms enable the retention of NH 4 + in HP micas or clay minerals resulting in efficient transport of nitrogen into great depths (Cedeño et al, 2019). Previous studies of Ábalos et al (2003) and Puelles et al (2005) highlighted that the studied suites of HP subducted rocks of the COC have been involved in prograde metamorphic evolution following a warm subduction PT path with 13–14°C/km, which would be sufficient for elevated N 2 release (Busigny & Bebout, 2013).…”

An introductory review of the thermal structure of subduction zones: I. Motivation and selected examples

“…Global models provided the suggestion that aqueous fluids and hydrous melts produced enhanced chemical recycling particularly in hot subduction zones (Hernández-Uribe et al, 2019). Applications to specific elemental or isotopic systems include that of Ce and Nd under the Mariana volcanic arc (Bellot et al, 2018) and the determination that nitrogen subduction in clay minerals is only possible in cold subduction zones (Cedeño et al, 2019). Slab surface temperatures strongly correlate with Mg-isotope ratios observed in volcanic arcs confirming a thermal control on processes controlling Mg release from the subducting slab (Hu et al, 2020).…”

An introductory review of the thermal structure of subduction zones: I. Motivation and selected examples

“…Global models provided the suggestion that aqueous fluids and hydrous melts produced enhanced chemical recycling particularly in hot subduction zones (Hernández-Uribe et al, 2019). Applications to specific elemental or isotopic systems include those of Ce and Nd under the Mariana volcanic arc (Bellot et al, 2018) and the determination that nitrogen subduction in clay minerals is only possible in cold subduction zones (Cedeño et al, 2019). Slab surface temperatures strongly correlate with Mg isotope ratios observed in volcanic arcs confirming a thermal control on processes controlling Mg release from the subducting slab (Hu et al, 2020).…”