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Exhumation of the Dora Maira ultrahigh‐pressure unit by buoyant uprise within a low‐viscosity mantle oblique‐slip shear zone
Author(s) -
Schmalholz Stefan M.,
Schenker Filippo L.
Publication year - 2016
Publication title -
terra nova
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.353
H-Index - 89
eISSN - 1365-3121
pISSN - 0954-4879
DOI - 10.1111/ter.12227
Subject(s) - geology , buoyancy , subduction , mantle (geology) , slip (aerodynamics) , massif , shear zone , petrology , shear (geology) , geophysics , seismology , geochemistry , mechanics , tectonics , thermodynamics , physics
The Brossasco‐Isasca subunit ( BIU ) of the Dora Maira massif is currently the only known continental crustal ultrahigh‐pressure ( UHP ) unit in the Western Alps. The peak pressure/temperature conditions are 3.5–4.5 GPa/~730 °C; exhumation from ~3.5 GP a to ~1 GPa occurred within 2.2 ± 1.8 Ma, but the exhumation mechanism is incompletely understood. We present a conceptual model for the buoyancy‐driven exhumation of the BIU inside a low‐viscosity, dense mantle shear zone weakened by increased strain rates due to simultaneous strike‐slip and subduction (oblique‐slip) of the European plate. Two‐dimensional thermo‐mechanical models simulate such a buoyant uprise of an ellipse inside an inclined layer. Simulations (i) show the feasibility of the conceptual model, (ii) fit the pressure/temperature/time record and (iii) constrain effective viscosities. The model is compatible with the (i) small volume of continental crustal UHP rock in the Western Alps, (ii) minor erosion during exhumation and (iii) strike‐slip deformation during the exhumation period.