Summary: Initiation of crustalscale thrusts triggered by metamorphic
reactions at depth: Insights from a comparison
between the Himalayas and Scandinavian Caledonides
and Torgeir B. Andersen4
Received 31 August 2009; revised 25 December 2009; accepted 1 February 2010; published 2 September 2010.
 Active eclogitization has recently been inferred at
depth beneath the Himalaya from geophysical observa-
tions, and the mechanical consequences of eclogitiza-
tion can be observed in the field in the eroded and
extended nappe stack of the Scandinavian Caledonides.
There, Proterozoic metastable granulites and igneous
protoliths underwent partial eclogitization during the
collision of Baltica with Laurentia. The reaction began
in pseudotachylites and veins and eventually formed a
connected network of eclogitefacies shear zones that
localized deformation and weakened the lower crust