Evaluating the Complex 40Ar/39Ar Age Progressions Along the Cook-Austral Ocean Islands Representing Archetype Secondary Hotspot Volcanism

Oregon State University, Corvallis OR

Investigators

Abstract

Seamounts are among the most abundant volcanic features on Earth. There are more than 20,000 seamounts on the seafloor that are taller than 1 kilometer, and there are hundreds of thousands of smaller seamounts. On the other end of the size spectrum, ocean islands represent a limited number of extremely large seamounts that have emerged above the sea surface. Linear arrangements of seamounts and ocean islands in the Pacific are common and these are prominently represented by the Hawaiian-Emperor and Louisville hotspot trails, both of which are called primary hotspot trails, each of which is believed to have formed above its own long-lived mantle plume that is sourced deep in the mantle. However, more than 80% of the known seamount trails in the Pacific are of quite a different nature and can be classified as secondary and tertiary hotspots. We know surprisingly little about these and other similar linear volcanic trails, although they are more common than primary trails. This research improves our understanding of secondary and tertiary hotspots in order to obtain fundamental knowledge of ocean basin volcanism. The work targets volcanic rocks in the Cook-Austral region. This region is home to one of the most enigmatic hotspot systems, harboring up to four hotspot trails that are younger than 30 million years and that, together, exhibit a complex age and geographic pattern. Research involves 40Ar/39Ar age dating of new samples from eight Cook-Austral oceanic islands and reanalysis of other samples from Cook-Austral seamounts and ocean islands whose ages were determined by a less precise dating method (K/Ar). The new dates will allow us to determine the validity of the current volcanic age patterns in the western Pacific Ocean and improve our knowledge of the mantle plume geometry in the Cook-Austral region. Broader impacts of the work include student training and engagement of groups under-represented in science and engineering in the research program. Relatively large amounts of geochronological data are available for the youngest volcanic islands and seamounts in Pacific hotspot trails, but most are inaccurate K/Ar ages. This impedes our ability to answer the major outstanding question as to why young 0-30 million year old secondary hotspot trails exhibit such a large variability in their age progressions. As a result, the Cook-Austral hotspots are often ignored in plate motion modeling, yet the nature of these secondary hotspots lies at the heart of the mantle plume debate. This research uses modern 40Ar/39Ar age dating and sample processing and leaching methods that will allow: (1) more accurate determinations of the current age progressions for the Rurutu and Macdonald Cook-Austral hotspot trails, (2) determination of the causes of the present bi-modal age distributions on certain volcanoes, and (3) what are the implications are for Pacific tectonic plate motions. All samples will be analyzed by employing the latest 40Ar/39Ar incremental heating methods using ARGUS-VI multi-collector mass spectrometers in the Oregon State University Argon Geochronology Lab.