Numerical model of the effect of serpentinites on the exhumation of eclogitic rocks: insights from the Monviso ophiolitic massif (Western Alps)

The intimate association of serpentinite melange with eclogites worldwide suggests that serpentinites may have played an important role in the exhumation of eclogites. Serpentinites may have formed by fluid percolation in the mantle wedge or by underplating of oceanic serpentinites, We have tested numerically the role of serpentinites in the exhumation of eclogites using physical parameters obtained in the Monviso massif of the Western Alps. Our calculation shows that the buoyancy of serpentinized peridotites in dense anhydrous peridotites may contribute to the exhumation of eclogitic blocks. Small eclogitic blocks (< km(3)) may be exhumed in completely hydrated mantle wedge, but it is not common considering the absence of totally serpentinized peridotites in mantle wedges. The exhumation of large eclogitic blocks (> 50 km(3)) requires a viscosity of the serpentinite wedge to be between 10(20)and 10(21) Pa and a density difference between the serpentinite wedge and the surrounding mantle on the order of 100-400 kg m(- 3) This condition is satisfied by only partially hydrated peridotites containing 10-50% serpentinites, Such serpentinized peridotites are expected to form at a depth ranging from 20 to 60 km in subduction zones by dehydration of subducting plates. Our conclusion is supported by the common occurrences of partially hydrated peridotites in close association with high-pressure to ultra-high-pressure metamorphic rocks. (C) 2001 Elsevier Science B.V. All rights reserved.