| Abstract: | Paleomagnetic studies of rocks from the Bonin and Mariana Island arcs indicate that these island arcs have undergone substantial rotation and northward translation since their formation 40 to 45 Ma. These rotations are inconsistent with existing models of marginal basin and island arc formation. The data presently available suggest to us that the Mariana and Bonin island arcs rotated as one tectonic element at the margin of the Philippine Sea and Pacific plate. These observations demonstrate that large vertical axis rotations are present in the island arc environment, prior to any interaction with a continental landmass. Since many circum-Pacific marginal terranes have been assigned island arc origins, these pre-accretion rotations should be considered when interpreting paleomagnetic results for possible microplate reconstructions. Knowledge of the structural and rotational styles of oceanic pre-accretionary deformations may prove useful for separating these pre-accretion effects from those imposed by the accretionary process in future studies aimed at deciphering the geologic history of island arc marginal terranes. |
