Patterns of thermal maturity as diagnostic criteria for interpretation of melanges

Abstract

Melanges are common constituents of ancient subduction complexes. Interpretations of melange genesis fall into five general categories: (1) gravitationally induced lateral spreading of the slope apron; (2) large-scale mass wasting (olistostromes); (3) subduction-driven viscous flow within “channels” at the base of the accretionary wedge; (4) diapiric injection; and (5) tectonic deformation within shear zones. interpretations are more viable when thermal-maturity data are considered along with structural and stratigraphic aspects. To document each distinct type of thermal-maturity signature, paleotemperature data must be extracted from both the matrix lithologies and the blocks of sedimentary rock within a melange, as well as from surrounding formations or structural domains.