Lithospheric discontinuity structure in Alaska, thickness variations determined by Sp receiver functions

Abstract

We present the first broad-scale image of lithospheric thickness across the major tectonic domains of Alaska based on S wave receiver functions and joint interpretation with the potential field, seismic velocity, and heat flow measurements. Thus, we provide context for the distribution of strain throughout the Alaskan orocline. In the north, below the Brooks Range, a 130 km thick lithosphere is resolved, consistent with the presence of strong lithosphere that deflects strain to the south into central and southern Alaska. In southern Alaska beneath the Chugach and St. Elias Mountains, multiple interfaces are present, and we interpret a thinner (80-90 km) North American lithosphere above a deeper interface that represents the base of the Yakutat microplate, thereby extending it to the area below the Wrangell Volcanic Field and St. Elias Mountains. Immediately north of the E-W striking Denali Fault, shallow negative conversions (80 km) denote thin lithosphere in the greater back-arc region where heat flow is observed to be high. Thin lithosphere in eastern Alaska and adjacent Yukon Territory coincides with the occurrence of inboard crustal seismicity and may be indicative of transmitted compression caused by the collision of the Yakutat microplate. Relatively thin lithosphere (<90 km) south of the Arctic Alaska domain that is deforming throughout the Alaskan orocline may result from lithospheric thinning associated with guided deformation. Expansion of this model using the upcoming Transportable Array will be critical to establish lateral continuity (or lack thereof) of lithospheric structure and directly discriminate between existing regional deformation models.