Fate of Hydrocarbons in Iron-Bearing Mineral Environments during Subduction

Aleksandr Serovaiskii,Vladimir Kutcherov,Georgios Aprilis,Catherine Mccammon,Ilya Kupenko,Aleksey Chernoutsan,Leonid Dubrovinsky,Elena Mukhina,Michael Hanfland,Daniil Kudryavtsev,Aleksandr Chumakov

doi:10.3390/min9110651

Abstract

Subducted sediments play a key role in the evolution of the continental crust and upper mantle. As part of the deep carbon cycle, hydrocarbons are accumulated in sediments of subduction zones and could eventually be transported with the slab below the crust, thus affecting processes in the deep Earth’s interior. However, the behavior of hydrocarbons during subduction is poorly understood. We experimentally investigated the chemical interaction of model hydrocarbon mixtures or natural oil with ferrous iron-bearing silicates and oxides (representing possible rock-forming materials) at pressure-temperature conditions of the Earth’s lower crust and upper mantle (up to 2000(±100) K and 10(±0.2) GPa), and characterized the run products using Raman and Mössbauer spectroscopies and X-ray diffraction. Our results demonstrate that complex hydrocarbons are stable on their own at thermobaric conditions corresponding to depths exceeding 50 km. We also found that chemical reactions between hydrocarbons and ferrous iron-bearing rocks during slab subduction lead to the formation of iron hydride and iron carbide. Iron hydride with relatively low melting temperature may form a liquid with negative buoyancy that could transport reduced iron and hydrogen to greater depths.

Highlights

Subduction processes are involved in the deep carbon cycle through the transport of carbon between the Earth’s surface and its interior
Minerals 2019, 9, 651 located close to subduction zones [8] and there are no compelling reasons to exclude the involvement of hydrocarbons in subduction
Mössbauer spectra show that there were no chemical reactions between paraffin oil and Fe2+ -bearing materials at conditions corresponding to slabs subducting to depths of ~200 km (Table 1)

Summary

Introduction

Subduction processes are involved in the deep carbon cycle through the transport of carbon between the Earth’s surface and its interior. Known carbon species in the Earth’s interior are CO2 and CH4 fluid or gas [4,5], diamond [1,6], carbonates [2,3], carbides [7], and carbonated silicate melts [4]. Petroleum hydrocarbons may be released from the reservoir rock individually and in connection with reservoir minerals and could chemically interact (faster or slower depending on their aggregate state and pressure-temperature conditions) with surrounding minerals at the corresponding thermodynamic conditions. It is expected that petroleum-containing rocks will experience increasing pressures and temperatures, starting from ambient (at the surface) to 2000(±100) K and 10(±0.2) GPa (at 300 km depth), representing the slab and surrounding mantle conditions [9]

Methods

Results

Discussion

Conclusion