High salinity fluid inclusions formed from recycled seawater in deeply subducted alpine serpentinite

摘要: Abstract The origin of high-pressure brines has been investigated in the Erro-Tobbio peridotite (Western Alps), a mantle slice that was exposed to seafloor Mesozoic Ligurian-Piedmontese Tethys and later involved Alpine subduction. Hydrothermal alteration by seawater-derived fluids led replacement assemblage Cl-bearing serpentine (0.35 wt% Cl), brucite (0.2 wt%), Cl- alkali-bearing phyllosilicates Cl; 0.2–0.55 Na2O; 1–5 K2O). Relics these hydrous phases occur olivine + titanian clinohumite antigorite assemblages formed at 2.5 GPa 550–600°C during partial devolatilization veining hydrothermally altered peridotite. lack chlorine alkalis are coeval with fluid inclusions trapped syn-eclogitic veins. salt-saturated contain up 50 Cl, Na, K, Mg Fe. High chlorinity probably achieved rehydration relict minerals deposition data presented suggest hydrothermal signature inherited eclogitic due partitioning into phase. presence salty eclogitized peridotites can indicate deep recycling fluids. Hydrous ultramafic systems therefore act as large-scale carriers seawater mantle.