A fault‐driven circulation model for the Lost City Hydrothermal Field

Abstract

The Lost City Hydrothermal Field on the Atlantis Massif is an off‐axis hydrothermal system, hosted in serpentinized ultramafic and metagabbroic rocks, that discharges through high‐permeability faults and fractures. High‐pH fluids vent through carbonate chimneys with temperatures ranging between 24°C and 91°C, and vent fluid geochemistry indicates quantitative removal of magnesium and water‐rock reactions consistent with heating to between 250°C and 300°C, conductive cooling, and mixing with seawater. This paper develops a relatively simple, steady state, fault‐controlled fluid circulation and crustal heat transfer model that is consistent with these observations. The model results predict that the (1) heat output at Lost City is ~4 × 104 W, (2) circulation depth is approximately 2.7 km, and (3) permeability of the fault zone is ~10−14 m2. The model assumes that the hydrothermal system mines heat from the adjacent country rock, and it does not appear that heat from serpentinization reactions or cooling intrusions is needed to drive the system. Because it takes ~105a for the current model to reach steady state, earlier episodes of hydrothermal activity at LCHF may have operated differently and vent temperatures may have been higher.

Magmatic-tectonic conditions for hydrothermal venting on an ultraslow-spread oceanic core complex

“…We propose two alternate models to explain the seismic velocity structure and the presence of the VDVF. In the first model (Fig 3B) thermomechanical conditions is a central premise of many structurally controlled hydrothermal systems (e.g., Sibson, 1990) and recent analytical modeling finds that deep crustal faulting can drive moderate-temperature venting without magmatic input (Lowell et al, 2017). If true, the heat of exhumation, along with heat from serpentinization Publisher: GSA Journal: GEOL: Geology DOI:10.1130/G39045.1…”

“…Previous models have proposed that the death of an OCC is marked by an episode of magmatism and generation of OCC-cutting high-angle faults (MacLeod et al, 2009). This "life-cycle" of OCCs in turn affects the type of hydrothermal activity (McCaig et al, 2007), though it is unclear if such venting is driven by deep magmatism (Allen and Seyfried, 2004), serpentinization (Früh-Green et al, 2003) and/or lithospheric heat that is channeled by deeply penetrating faults (Lowell et al, 2017). Moreover, if magmatism is Publisher: GSA Journal: GEOL: Geology DOI:10.1130/G39045.1 Page 4 of 38 fluctuating around a lower average at ultraslow-spreading centers than at slow-spreading centers (Rubin and Sinton, 2007), then the life cycle of OCCs at more magma-poor ultraslow-spreading centers may differ from this model, where an increase in magmatism causes an OCC-mode of seafloor spreading, and a decrease in magmatism marks the death of the detachment fault.…”

Volcanic‐Tectonic Structure of the Mount Dent Oceanic Core Complex in the Ultraslow Mid‐Cayman Spreading Center Determined From Detailed Seafloor Investigation

“…Magmatic diking could have formed the southern horst, but we observe no neovolcanic zone associated with this feature on its trace along the seafloor. Lastly, lithospheric heat (Lowell, 2017) and/or heat from serpentinization (Früh-Green et al,…”

Low Enthalpy Geothermal Systems in Structural Controlled Areas: A Sustainability Analysis of Geothermal Resource for Heating Plant (The Mondragone Case in Southern Appennines, Italy)

“…Combining all data, a geothermal model that controls the mineralization of groundwater at the base of Mt. Petrino can be proposed [1,10,22,26,60,61]. According to this model, the geothermal reservoir corresponds to the carbonate bedrock of the Mondragone plain.…”

“…In fact, fault-controlled geothermal sites are accompanied by hydrothermal activity, hot fluid circulation, and mineralization processes [22,23]. Fracturing and chemical dissolution of carbonates increase the permeability of rocks, enhancing the advection of hot fluids and generating heat and mass transport [24][25][26][27][28]. The setting of carbonate bedrock in Mondragone plain corresponds to this hydrogeological model.…”