INVESTIGATING SERPENTINIZATION WITHIN THE COOK INLET BASIN, ALASKA FROM THE INVERSION OF MAGNETIC DATA

Southcentral Alaska is a tectonically active region with an unusual subduction geometry. Cook Inlet basin (CIB) and surrounding Kenai Lowlands to Kenai mountains located in southcentral Alaska, has a topographic transition from low to high lands. GPS observation indicates the topographic transition is due to uplift of the Kenai mountains and a corresponding subsidence of CIB and the surrounding Kenai Lowlands. Analysis of tectonic processes suggests that the subsidence is related to the formation of an unusually hydrated and serpentinized mantle wedge with lateral variations in heat flow due to a shallow-eastward subducting slab.

This research investigates the thickness and location of the serpentinized body with magnetic data to determine the Curie Point Depth (CPD) using 3D inversion methods. CPD analysis from the 3D inversions shows that the top of serpentinized body is at ~2.5 km and the bottom at ~30 km. Temperature vs depth profiles developed for Cook Inlet basin and surrounding regions estimates a temperature of 580°C at depths ranging from 31.2 to 33.6 km. This depth agrees well with the Curie depth estimate within the CIB (~30 km). The crustal thickness within forearc region is greater than 20 km and this indicates that the magnetic anomaly is within the crustal rock of the North American plate. The models show the magnetic anomaly is not within the mantle wedge. Rayleigh wave tomography and 3D gravity models of the crust beneath the CIB will be generated to further constrain the extent of anomaly from the CPD analysis. Comparing all these geophysical models will give the best interpretation of the zone of serpentinization.