THREE-DIMENSIONAL THERMAL INVESTIGATIONS OF ACADIAN TECTONIC MODELS CONSTRAINED BY GEOCRONOLOGY IN CENTRAL MAINE

Reconstruction of tectonic setting in Maine during the Acadian Orogeny is controversial and deficient. A lack of collisional indicators such as ophiolites and blueschists forces researchers to interpret Acadian tectonic setting through more abstract deformational processes. Innovative constraints are obtainable through investigation of the thermal evolution evidenced by suggested tectonic models in Appalachian literature. Two tectonic models with differing subduction geometries have been chosen and the thermal evolution of each is modeled using a three dimensional code to solve the heat flow equation (FLAC3D, ITASCA). The east dipping model suggests lithospheric delamination causing upwelling of asthenospheric material and regional metamorphism. The west dipping model depicts subduction of buoyant continental lithosphere drawn into the system, pinching out hot material caught between the two lithospheres, and resulting in a heating event from mantle wedge material forced westward. Within each geometric framework, the rate, depth and size of the asthenospheric displacement, crustal uplift rates and exhumation are varied and the effect on the thermal evolution of the system observed. Resultant mid-upper crust temperatures are evaluated against geochronology data depicting metamorphic and cooling ages within a northwest trending transect across southern Maine.