The Yukon – Tanana Terrane is a the remnants of a multiply deformed accretionary margin that is bound in AK by the Tintina Fault on the north and Denali Fault to the south. The region has been divided into several important lithotectonic domains that broadly fit into reworked autochthonous crust and structurally overlaying allochthonous units interpreted to have been thrust onto the North American margin. However, the role of extensional deformation on the reactivation of this important boundary has added complexity to the structural history, and obscures the primary relationships between these two important crustal entities. Our recent work involves using petrochronologic techniques (in-situ monazite, zircon, apatite) in attempt to reconcile differing P-T-t paths across this important tectonic boundary. This work integrates mapping with the ADGGS (Alaska Dept of Geologic and Geophysical Surveys) and US Geological Survey.