LARGE SCALE CRUSTAL-BLOCK VERTICAL EXTRUSION BETWEEN THE HINES CREEK AND DENALI FAULTS COEVAL WITH SLIP LOCALIZATION ON THE DENALI FAULT SINCE CA. 45 MA: HAYES RANGE, ALASKA

Strike-slip faults by their nature undergo primarily horizontal motion. Yet across the globe we find regions of high topography and deep exhumation along these wrench structures with no apparent correlation with geometric complexities or fault dip. The high peak region of the Hayes Range, central Alaska, is bound by two Mesozoic suture zone faults: the Denali Fault to the south and Hines Creek Fault to the north. The high topography area has peaks over 4000 m and locally has experienced over 14 kms of Neogene exhumation, yet the mountain range is located on the convex side of the Denali Fault Mount Hayes Restraining Bend where slip partitioning alone cannot account for this zone of extreme exhumation. Through the application of U-Pb zircon, ⁴⁰Ar/³⁹Ar (hornblende, muscovite, biotite, K-feldspar), apatite fission-track, and (U-Th)/He geo-thermochronology, we test if these two parallel suture zone structures are working in tandem to vertically extrude the BeHinD block (Between the Hines Creek and Denali Faults) on the convex side of the Mount Hayes Restraining Bend. We document that since at least 45 Ma the Denali Fault has been bent and localized in a narrow fault zone (<160 m), the Mount Hayes Restraining Bend is fixed to the north side of the Denali Fault, and that the BeHinD block has been undergoing vertical extrusion and tilting as a relatively coherent block along the free faces of two lithospheric scale suture zone faults. A bent Denali Fault by ca. 45 Ma supports the long stranding Alaska orocline hypothesis that has Alaska bent by ca. 44 Ma. The Yakutat flat slab is coupled with southern Alaska and pushing southern Alaska to the north against the Denali Fault at ~ 4 mm/yr based on geodetic modeling. This convergence is currently driving vertical extrusion of the BeHinD block.