This Early Grant for Exploratory Research (EaGER) is to support an exploratory project to investigate the compositional evolution of an active, but yet understudied volcano, Savai'i, located on the western fringe of the Samoan Islands. A 20th century Savai'i eruption displaced an entire village, and understanding the timing and evolution of this volcanism is of social importance for the local islanders.
Savai'i was essentially repaved with large volumes of rejuvenated volcanism, in contrast to other ocean islands (e.g., Hawaii, the Canary Islands and Mauritius). Eruption of Samoan rejuvenated volcanism is limited to the western three islands, and their close proximity (~150 km) to the northern terminus of the Tonga trench suggest that Samoan rejuvenated volcanism may have a different origin than in other hotspots. In the last 5 million year (Ma), the distance between Savai'i and the trench has decreased due to plate motion and slab roll-back. Thus, trench-related stresses and materials may be responsible for the volume, duration and unusual enriched compositions of Samoan rejuvenated lavas. The rejuvenated stage may be completely exposed in a 500m deep gorge on the south side of Savai'i that covers a 2 Ma history. This gorge offers an unprecedented opportunity to sample a long-lived sequence of Samoan rejuvenated lavas. Key samples from this canyon are needed to determine whether material from the Tonga trench is represented in Samoan rejuvenated lavas, and whether such a trench signature increases with time. In comparison to Hawaiian volcanic stages, the rejuvenated stage at Savai'i seems volumetrically larger, longer-lived, and geochemically more enriched. Currently, the extent and volume of the rejuvenated volcanism is constrained by one 2Ma trachyte cobble from Savai'i, isotopically indistinguishable from rejuvenated lavas, and found in a stream that drains the gorge. In order to better constrain if the compositional change could indicate a shift in source composition while the volcano was still in its shield stage, a more detailed sampling of the site needs to be performed. This EaGER will enable two early-career PIs (Jasper Konter from UT-El Paso and Matthew Jackson from Boston University) to travel to Savai'i for a more complete sampling of the area to ascertain if a long term geochemical and petrologic study of the island is indeed justified.
