ALASKA IN 3 ACTS – A POTENTIAL FIELD/TECTONIC STORY

Alaska is a complexly deforming amalgamation of crustal elements at the northern corner of the North American craton. Tectonic understanding of Alaska is hampered by sparse geologic mapping and geophysical data coverage due to poor exposure and difficult logistics. Two major continental strike-slip systems, the Tintina in the north and the Denali to the south, slice up the state into 3 broad sections, North, Central, and South; each region contains elements of accretion and collision. North Alaska, north of the Tintina fault, contains a partially preserved record of subduction/accretion during an arc-continent collision. Intermediate magnetic highs follow the trends of the blueschist/eclogite and ultramafic belts south of the Brooks range. A deep magnetic high underlies the broad North Slope to the north of the Brooks Range and appears to represent a strong crustal element that has resisted tectonic deformation. Central Alaska, south of the Tintina and north of the Denali fault systems, experienced continent-continent collision in the north and arc-plateau collision in the south, but experienced more significant post-collisional deformation than northern Alaska and preserves only middle and lower crust. Magnetically this region is neutral with no high amplitude regional anomalies. South Alaska, south of the Denali fault system, has undergone intermittent subduction since the early Jurassic and has a well-preserved accretionary record. Geophysically, south Alaska is home to world-class magnetic anomalies including the major south Alaska magnetic high following much of the modern arc as well as the Gulf of Alaska magnetic high representing the main collisional body of the Yakutat tectonic block. Regional gravity, geoid, and geothermal data provide information on current crustal strength and geodynamics. The southern Alaska margin is a major geoid high reflecting the dynamics of active subduction combined with the collisional effect of the Yakutat block. Much of central and western Alaska has high heat flow indicative of relatively low overall crustal strength. The North Slope of Alaska has magnetic, gravity and heat flow that indicate a cold and rigid crustal block. The 3-part view of Alaska provides a framework for more detailed investigations of its complex tectonic history and current active deformation.