MESOZOIC-CENOZOIC MAGMATIC HISTORY OF THE ALASKA RANGE SUTURE ZONE
The Alaska Range Suture Zone has experienced a protracted and complex Mesozoic-Cenozoic magmatic history, with discrete magmatic pulses and lulls. Between ~100-90 Ma a suite of plutons was emplaced in the suture zone during accretion of the Wrangellia composite terrane against North America. This pulse of magmatism was followed by a relative hiatus until ~70 Ma, when a ~15 MY period of wide spread arc magmatism occurred as the proto-Pacific plate underwent oblique subduction along its northeast margin. Additionally, there was a period of magmatism between ~62-50 Ma with intraplate characteristics, atypical of arc processes, possibly a result of post-collisional delamination beneath the suture zone and likely transtentional related magmatism along the Denali Fault during this time period.
From ~55 Ma to ~45 Ma there was another lull in magmatism that is associated with a Paleocene-Eocene ridge subduction event. ~40 Ma to ~30 Ma was a period of high flux magmatism with arc characteristics along the Alaska Range Suture zone as a young-hot Pacific plate underwent flat-slab subduction, possibly in part driven by the hydrostatic affects of the over thickened Alaska Range Suture Zone. Magmatism along the Alaska Range arc waned between ~30 Ma and ~25 Ma, limited primarily to mafic dike-emplacement along the north side of the Denali Fault zone, likely reflecting a transitional period between Pacific plate subduction and flat-slab subduction of the Yakutat microplate. There is sparse arc volcanic activity in the region at ~7 Ma, ~1 Ma, and during the Holocene. Shutting down of the central Alaska Range arc is coincident with the ~26 Ma initiation of the Wrangell arc along the edge of the Yakutat flat-slab. The lack of significant magmatism along the Alaska Range arc during the Neogene is likely reflecting both the affects of the flat-slab subduction of the Yakutat microplate and the resultant transpressive nature of the central Denali Fault system.