Premium
On the Stability of Talc in Subduction Zones: A Possible Control on the Maximum Depth of Decoupling Between the Subducting Plate and Mantle Wedge
Author(s) -
Peacock Simon M.,
Wang Kelin
Publication year - 2021
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2021gl094889
Subject(s) - geology , mantle wedge , mantle (geology) , transition zone , forearc , subduction , petrology , slab , geophysics , forsterite , enstatite , geochemistry , seismology , tectonics , physics , meteorite , astronomy , chondrite
Geophysical observations including surface heat flow data indicate the subducting slab becomes fully coupled to the overlying mantle wedge at ∼70–80 km depth. This maximum depth of decoupling (MDD) separates cool, stagnant forearc mantle from warmer, convecting mantle capable of generating arc magmas. Thermodynamic calculations demonstrate that talc is stable in H 2 O‐undersaturated parts of the mantle wedge where its stability is controlled by the pressure‐dependent, fluid‐absent reaction: talc + forsterite = antigorite + enstatite, which occurs at pressures ∼2–2.5 GPa (∼70–80 km depth) and temperatures <650°C. At shallower depths, H 2 O‐undersaturated portions of the basal mantle wedge contain talc, which experimental studies show dramatically weakens rocks. At greater depths, talc is restricted to silica‐rich portions of the mantle wedge. The common MDD in subduction zones may reflect the downdip transition from a talc‐present decoupled shear zone to a talc‐absent fully coupled interface along the base of the mantle wedge.