PATTERNS OF THERMAL MATURITY AS DIAGNOSTIC-CRITERIA FOR INTERPRETATION OF MELANGES

Melanges are common constituents of ancient subduction complexes. Inte rpretations of melange genesis fall into five general categories: (1) gravitationally induced lateral spreading of the slope apron; (2) larg e-scale mass wasting (olistostromes); (3) subduction-driven viscous fl ow within ''channels'' at the base of the accretionary wedge; (4) diap iric injection; and (5) tectonic deformation within shear zones. Inter pretations are more viable when thermal-maturity data are considered a long,vith structural and stratigraphic aspects. To document each disti nct type of thermal-maturity signature, paleotemperature data must be extracted from both the matrix lithologies and the blocks of sedimenta ry rock within a melange, as well as from surrounding formations or st ructural domains.