The response of two-phase hydrothermal systems to changing magmatic heat input at mid-ocean ridges

Abstract

Hydrothermal processes at oceanic spreading centers are largely influenced by changing magmatic heat input. I use the NaCl-H 2 O FISHES code to investigate the evolution of surface temperature and salinity as a function of time-varying heat flux at the base of a two-phase, vaporbrine hydrothermal system. I consider a two-dimensional rectangular box that is 1.5 km deep and 4 km long with homogeneous permeability of 10 -13 m 2 . Temperature and pressure at top boundary correspond to seafloor conditions of 10C, 25MPa respectively. Impermeable,

Characterization of Transport-Enhanced Phase Separation in Porous Media Using a Lattice-Boltzmann Method

“…Under some circumstances, this oversaturation eventually leads to volatile exsolution and/or phase separation with the emergence and growth of a second phase. These circumstances have been reported in (1) gas bubble migration in sediments and subsurfaces [2,3], (2) CO 2 sequestration [4][5][6][7][8][9][10] where the dissolved CO 2 exsolves from solution due to depressurization and/or increase in temperature, (3) hydrothermal phase separation [11][12][13] where a denser brine and a lighter lowsalinity vapor coexist at elevated temperatures and pressures, and (4) gas exsolutions in magma reservoirs which can be induced by depressurization episodes and/or crystallization of anhydrous mineral phases driven by cooling [14][15][16]. This conversion from a single-phase to a multiphase system, particularly a mixture of immiscible fluids, is known to alter the system dynamics due the emergence of, such as buoyancy, viscosity contrast, and capillarity.…”

A preliminary 1‐D model investigation of tidal variations of temperature and chlorinity at the Grotto mound, Endeavour Segment, Juan de Fuca Ridge

“…Note that the maximum of S b is within the range of the model predicted chlorinity (30-50 wt % or 5133-8556 mmol/kg) of the end-member brine formed in the basal reaction zone [Choi and Lowell, 2015], which suggests minimal alteration of the end-member brine after it leaves its point of origin. On the other hand, the lower values of S b point to dilution of the end-member brine by less-saline pore fluids during ascent and prior to tidally driven mixing with vapor.…”

“…More importantly, the tidally driven horizontal interstitial flows can drive mixing of pore fluids with contrasting temperature and chlorinity between the discharge zone and its surroundings, which, by itself, can potentially result in the observed tidal variations of venting temperature and chlorinity. To test this hypothesis and better understand subsurface fluid flows and their influences on seafloor venting requires developing a 2-D poroelastic model with both two-phase fluids [Choi and Lowell, 2015] and seafloor tidal loading [Crone and Wilcock, 2005] that accounts for the lateral heterogeneity of crustal and fluid properties, which will be a goal for future research.…”

Seismic evidence that black smoker heat flux is influenced by localized magma replenishment and associated increases in crustal permeability

“…Recent magma injection, on the other hand, induces seismogenic cracking that counteracts the thickening of the TBL by increasing crustal permeability within the reaction zone [Wilcock et al, 2009], a scenario evident beneath Main Endeavour and High Rise, the most robust vent fields on the segment (Figures 2a, 3b, 3c, and 4); magma replenishment may also thin the TBL by limiting crystallization on the roof of the reservoir. The absolute time scales for these interconnected effects are unconstrained, though modeling indicates that magmatic perturbations to the AMC may take from months to years to influence heat flux at the surface [Germanovich et al, 2011]; a decrease in magma resupply would take a similar amount of time to result in a decline in seafloor vent temperatures and heat output [Singh et al, 2013;Choi and Lowell, 2015]. In conjunction with previous microseismicity and hydrothermal studies, we conclude the large variations in heat flux that characterize the Endeavour hydrothermal system are a manifestation of localized magma injection that produces an evolving and strongly heterogeneous crustal permeability structure via induced seismogenic cracking.…”