Tectonic evolution of the Explorer‐Northern Juan de Fuca Region from 8 Ma to the present

Abstract

New magnetic anomaly data, in conjunction with Sea Beam and SeaMARC II data, has been used to schematically model the tectonic development of the Explorer‐Northern Juan de Fuca Region with a series of five ridge‐offset propagators during the last 8 m.y. The Sovanco Fracture Zone played a major role in the evolution of this area since its origin as a spreading center offset between the Explorer and Juan de Fuca Ridges approximately 7.4 Ma. Between this time and 2.5 Ma, the transform migrated southwards due to southward propagation of Explorer Ridge, and lengthened by the addition of three propagating ridge offsets as well as by asymmetric spreading to the east on Explorer Ridge. Since the independence of Explorer Plate at 4 Ma, there has been clockwise rotation of the Explorer Spreading Center relative to the Juan de Fuca Ridge. In response to forces acting at the convergent margin, the Sovanco Fracture Zone also underwent clockwise reorientation, and in the process developed into a broad zone of shear. The tectonic deformation associated with this rotation distorted the previously existing N‐S magnetic anomaly pattern. Explorer Seamount, a major geological feature in the region, is modeled as a presently extinct southern spreading segment of the Explorer Ridge system which was isolated by the northward migration of the west end of the Sovanco Fracture Zone. The recent (<1 Ma) tectonic evolution of Explorer Ridge involved both northward and southward propagation of Southern Explorer Ridge, as well as an eastward ridge jump during the Brunhes. Ih the northern portion of the study area, the axis of spreading jumped 40 km to the NW around 0.3 Ma, from the eastern Explorer Deep to the western Explorer Rift.