Tectonic Overview of Bering Sea-Aleutian Ridge Region: ABSTRACT

Abstract

Known and inferred surficial structural features of the Aleutian Ridge, Terrace, and Trench in the central and western Aleutian arc, Alaska, appear to reflect predominantly tensional strain of diverse orientations. Features on the ridge are inferred to have formed from igneous activity-related tectonism including distension of the surficial skin over rising and spreading epizonal plutons, volcanotectonic subsidence, and rifting; features on the terrace and landward trench wall may have formed from distension of a decoupled surficial skin above a prolongated zone of imbrication and uplift; and those in the trench and on the seaward wall from dynamic loading of the Pacific lithospheric plate by overthrusting and southward migration of the Aleutian tectogene. The plutonism, mbrication, and dynamic loading are interpreted as resulting from a first-order process of crustal foreshortening normal to the arc. This interpretation is consistent with evidence from natural seismicity which indicates predominantly compressional strain across the central and eastern Aleutian arc. Surficial structural features in the eastern Aleutian arc between the continental margin and the volcanic arc appear to reflect directly the first-order compressional strain, whereas the features in the bordering Aleutian Trench are predominantly of tensional origin. Movement vectors for the Pacific plate based on a pole of rotation at lat. 53°N, long. 47°W., indicate normal convergence against the continental margin near Kodiak Island, movement tangential to the arc trend in the vicinity of the Near Islands, and tension oblique to the arc trend in the vicinity of the Commander Islands. If the Aleutian Trench has resulted from crustal foreshortening its presence along the entire arc suggests movement of the Bering Sea plate independent of the Pacific plate. Structural features such as Bowers Ridge in the western Aleutian arc may reflect foreshortening parallel with the arc. Such features may be related to Pacific plate movement, whereas the arc itself there may have resulted from movement of the Bering Sea plate. The eastern Aleutian arc could have resulted from south-to-southeast drift of the Alaskan continental mass hinged to the Canadian mainland along the axis of the Alaska orocline combined with Pacific plate normal convergence. Body forces such as those that might be derived from perturbations of rotational parameters (angular momentum and moments of inertia) of the core-mantle system seem better suited to explain the suggested plate movements than are forces derived from mantle convection. End_of_Article - Last_Page 2467------------