Abyssal Serpentinites: Transporting Halogens from Earth’s Surface to the Deep Mantle

• Main Authors: Lilianne Pagé, Keiko Hattori
• Format: Article
• Language: English
• Published: MDPI AG 2019-01-01
• Series: Minerals
• Subjects: serpentinite; halogens; subduction; deep mantle
• Online Access: https://www.mdpi.com/2075-163X/9/1/61

Serpentinized oceanic mantle lithosphere is considered an important carrier of water and fluid-mobile elements, including halogens, into subduction zones. Seafloor serpentinite compositions indicate Cl, Br and I are sourced from seawater and sedimentary pore fluids, while F may be derived from hydrothermal fluids. Overall, the heavy halogens are expelled from serpentinites during the lizardite⁻antigorite transition. Fluorine, on the other hand, appears to be retained or may be introduced from dehydrating sediments and/or igneous rocks during early subduction. Mass balance calculations indicate nearly all subducted F is kept in the subducting slab to ultrahigh-pressure conditions. Despite a loss of Cl, Br and I from serpentinites (and other lithologies) during early subduction, up to 15% of these elements are also retained in the deep slab. Based on a conservative estimate for serpentinite thickness of the metamorphosed slab (500 m), antigorite serpentinites comprise 37% of this residual Cl, 56% of Br and 50% of I, therefore making an important contribution to the transport of these elements to the deep mantle.