ACTIVE DISPLACEMENT PARTITIONING AND ARC-PARALLEL EXTENSION OF THE ALEUTIAN VOLCANIC ARC BASED ON GLOBAL POSITIONING SYSTEM GEODESY AND KINEMATIC ANALYSIS

Abstract

Global Positioning System geodesy and structural analysis of parts of the Aleutian island chain support the interpretation of forearc migration westward along right-lateral transcurrent faults. Measured displacements are essentially arc parallel in the eastern (Unalaska Island) and western (Attu Island) parts of the arc and vary from 3.1 mm/yr to 31.4 mm/yr, respectively. At the center of the arc (Adak) subduction of the Amlia fracture zone disrupts the pattern of arc-parallel displacement and records an upper plate velocity of 9.6 mm/yr parallel to plate motion. Where active, displacement partitioning accommodates 30% 50% of the strike-slip component of plate convergence. In the area of impeded subduction partitioning ceases, suggesting that the process is sensitive to the degree of coupling across the plate-boundary megathrust. The differential arc-parallel displacements observed at the ends of the arc together with structural relations indicate substantial arc-parallel extension, which may play an important role in exhumation of high-pressure low-temperature metamorphic rocks in ancient arc systems.