Dallas H. Abbott and Mitchell Lyle
Age of oceanic plates at subduction and volatile recycling
Geophysical Research Letters(October 1984), 11(10):951-954
Index Terms/Descriptors: crust; decarbonation; degassing; dehydration; gases; geochemical cycle; geochemistry; mantle; mathematical models; oceanic crust; plate tectonics; plates; reactions; subduction; theoretical studies; thermal effects; trenches; volatiles
The age of the subducting plate as it enters the trench controls the maximum depth of volatile transport by the downgoing plate. As the slab descends and heats up, decarbonation and dehydration reactions cause alteration minerals and sediments to release volatiles. Our calculations show that subducting oceanic plates <11 m.y. old in oceanic arcs and <34 m.y. old in continental arcs heat up so rapidly that no H 2 O or CO 2 can return to the asthenosphere. Instead, these volatiles rise into the over-riding lithospheric plate. CO 2 and H 2 O are released differently during subduction. A thickly-sedimented plate subducting beneath an oceanic arc will return H 2 O to the asthenosphere only if the subducting plate is older than 11 m.y. and CO 2 only if it is older than 25 m.y. If Archaean oceanic lithosphere had a maximum age of 30-50 m.y. and an average age of 10-18 m.y., then the amount of volatile recycling to the asthenosphere could have been much lower than at present, despite a greater total consumption rate.