Lawsonite-bearing rocks have been commonly reported from the Alps and from many orogenic belts and subduction complexes as main constituents in the oceanic crust (igneous and sedimentary protoliths) and in trench-related metasediments (e.g. Franciscan: Radvanec et al., 1998; Alps: Bousquet et al., 2004; Reinecke, 1998; Greece: Schliestedt, 1986; Okay, 2002 and Ballevre et al., 2003 and references therein). Lawsonite-bearing rocks are seldomly preserved in the subducted continental crust (Pognante, 1989a; Pognante, 1989b; Pognante et al., 1980; Schwartz et al., 2000), particularly if related to the P-T prograde subduction stages.
Moreover, the reconstruction of the tectono-thermal evolution of slices of continental crust that recorded a low to very low thermal gradient during burial and exhumation, may disclose information about tectonic mechanisms of erosion and dragging to depth of slices of the upper plate continent during active subduction of cold oceanic lithosphere.
In this contribution we investigate the tectono-thermal evolution of lawsonite-bearing metabasics of the Ivozio complex in the Sesia-Lanzo Zone (Austroalpine domain of the Western Italian Alps) and describe the metamorphic reactions leading to the production and breakdown of lawsonite; we deduce from them the sequence of thermal regimes characterising the Alpine subduction-collision stages. The protoliths of the metabasic rocks are pre-alpine gabbros accreted to the Austroalpine continental crust during the Variscan orogenic cycle.