EXAMINING TRANSIENT THERMAL-RHEOLOGICAL INTERACTION DURING COLLISIONAL OROGENESIS USING NUMERICAL MODELING: IMPLICATIONS FOR CHANNEL FLOW AND CRITICAL WEDGE MODELS

Two quantitatively-supported models, critical wedge and channel flow, have been applied to the Himalaya and proposed for other large collisional systems as mechanisms for shortening accommodation during orogen evolution. These two models are fundamentally distinct and until recently have been viewed as mutually exclusive. While there remains support for these mechanisms being incompatible end-members, in more recent studies it has been proposed that either: (1) both geodynamic mechanisms may operate simultaneously yet in spatially distinct parts of the larger composite orogenic system or (2) both mechanisms are present yet they operate at temporally distinct intervals, wherein the orogen progressively develops through stages dominated by mid-crustal channel flow followed by shallow thrust stacking and duplex development. In both scenarios, the mechanism active at each stage in orogen evolution is presumably dependent upon local to regional scale rheological conditions (as a function of orogen dynamic and thermal evolution) that are likely to be transient in both space and time. Here, we present results from numerical experiments of a 2-D large collisional orogen that focus on the how thermal structure affects rheological conditions – which vary both spatially and temporally – and attempt to explain the mechanical and thermal-kinematic linkages between the two aforementioned mechanisms.