We conducted a two-dimensional numerical model to analyze the generation of tectonic over-pressure, which is a positive deviation from lithostatic pressure, for deep slabs which are anchored at the 660 km phase boundary. The formation of the ductile shear zone under a compressional tectonic setting induces tectonic over-pressure. We first propose that an apparent shear zone originated from an elastic heterogeneity in the phase loop, which is the two-phase (i.e., olivine and wadsleyite) coexistence interval around the 410 km boundary within subducting oceanic lithospheres, can cause tectonic over-pressure with a range from 0.3 to 1.5 GPa. This over-pressure significantly impacts the formation of the olivine-wadsleyite phase transition. The flattening of the olivine-wadsleyite interface by over-pressure is well-resolved. Therefore, we argue that the over-pressure should be applied when analyzing the phase boundary within the subducting lithosphere. Our results provide a new insight on the interplay among the phase transition, shear zone formation and tectonic over-pressure.
Bibliographical noteFunding Information:
We thank to two anonymous reviewers for their careful reviews, which significantly improved our manuscript. This research was supported by the National Research Foundation of Korea ( NRF-2014R1A6A3A04055841 ) for B.-D. So and U.S. National Science Foundation grants in the Collaboration of Mathematics and Geosciences (CMG) program and Geochemistry for D.A. Yuen. We also thank discussions with Yuri Podladchikhov.
- Olivine-spinel coexistence zone
- Phase loop
- Phase transition
- Shear heating
- Subducting slab
- Tectonic over-pressure