Reconciling late Neogene Pacific absolute and relative plate motion changes

Abstract

New models of Pacific absolute plate motion relative to hot spots and models of relative plate motion involving the Pacific plate all agree there was a significant change in the late Neogene (Chron 3A, ∼5.89 Ma), reflecting a more northerly absolute motion than previously determined. As Pacific absolute plate motion became slightly more northerly, left‐stepping transform segments came under compression. Some left‐stepping segments became microplates with clockwise rotation; others show clear evidence of compressional deformation. Conversely, right‐stepping transforms came under tension, and many developed intratransform spreading centers or show similar evidence for transform magmatism. Several large left‐stepping transform offsets represent portions of the Nazca plate protruding into the Pacific and as such act as obstacles to the more northerly Pacific absolute plate motion. We suggest these obstructions act to enhance the generally tensile equatorial Pacific stress regime caused by distant slab pull. As a consequence, the greater French Polynesia region has experienced diffuse volcanism that increased considerably following the Chron 3A plate motion change. We propose that since the Hawaii‐Emperor Bend time, the distant Pacific slab pull and the friction between the large, buoyant Ontong Java plateau and the northern margin of the Australia plate have produced episodes of increased tensile stresses in the equatorial Pacific. We believe these stress excursions are responsible for much of the intraplate volcanism observed in a wide triangular region from Samoa to the East Pacific and Pacific‐Antarctic Rises.