Publication Date:
2019
Description:
〈span〉Arc volcanism and trace-element recycling are controlled by the devolatilization of oceanic
crust during subduction. The type of fluid—either aqueous fluids or hydrous melts—released
during subduction is controlled by the thermal structure of the subduction zone. Recent
thermomechanical models and results from experimental petrology argue that slab melting
occurs in almost all subduction zones, although this is not completely supported by the rock
record. Here we show via phase equilibrium modeling that melting of either fresh or hydrothermally
altered basalt rarely occurs during subduction, even at water-saturated conditions.
Melting occurs only along the hottest slab-top geotherms, with aqueous fluids being released
in the forearc region and anatexis restricted to subarc depths, leading to high-SiO〈sub〉2〈/sub〉 adakitic
magmatism. We posit that aqueous fluids and hydrous melts preferentially enhance chemical
recycling in “hot” subduction zones. Our models show that subducted hydrothermally
altered basalt is more fertile than pristine basaltic crust, enhancing fluid and melt production
during subduction and leading to a greater degree of chemical recycling. In this contribution,
we put forward a petrological model to explain (the lack of) melting during the subduction
of oceanic crust and suggest that many large-scale models of mass transfer between Earth’s
surface and interior may require revision.〈/span〉
Print ISSN:
0091-7613
Electronic ISSN:
1943-2682
Topics:
Geosciences
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