Cretaceous to Miocene NW Pacific Plate kinematic constraints:
Paleomagnetism and Ar-Ar geochronology in the Mineoka Ophiolite Melange
(Japan)
Abstract
The Mineoka Ophiolite Melange is located at the intersection of the
Pacific, Philippine Sea, Eurasia and North American plates. The origin
of the Mineoka ophiolite is disputed and it has been ascribed to a fully
subducted plate or part of the Pacific and Philippine Sea plates. In
this paper, we present a kinematic reconstruction of the Mineoka
Ophiolite Melange and its relation with the Pacific Plate, based on new
paleomagnetic data and Ar-Ar geochronology. In addition to standard
analyses for paleolatitudes, we performed a Net Tectonic Rotation
analysis on sheeted dykes to infer the paleospreading direction that
formed the ophiolite. The analysis show that 85–80 Ma MORB pillow lavas
erupted at a paleolatitude of N ~16˚, whereas ca. 50 Ma
pillow lavas formed at N ~34˚. Net Tectonic Rotation
analysis suggests that the spreading direction was NE 60˚. Ar-Ar ages
yielded 53–49 Ma for MOR lavas and 41–35 Ma for island arc volcanism.
The formation of this ophiolite occurred in the back-arc spreading of
the Nemuro-Olyutorsky arcs of the NW Pacific. It infers that the final
consumption of Izanagi below Japan instigated a subduction jump and
flipped its polarity. Subduction initiated parallel to the ridge, and a
piece of the original back-arc crust got trapped near the Japan trench
during the northwards motion of the Philippine Sea Plate. The
contrasting motion between the Pacific and Philippine Sea plates
generated a highly unstable setting followed by a subduction zone that
left a small-sized and short-lived plate, surrounded by subduction
zones.