Magma differentiation and nature of the plumbing system at Hualalai Volcano, Hawaii

For his Masters thesis, Pat Shamberger is researching a significant deviation from the usual pattern of Hawaiian volcano development at Hualalai volcano on the Big Island. Approximately four cubic kilometers of trachyte erupted from flank vents of Hualalai between the shield building and post-shield stages. The volcano had erupted only tholeiite for the ~200,000 years prior, and subsequently has produced only alkalic basalt. Trachyte magma is unusual at Hawaiian volcanos, but its magmatic relatives are not. For example, Mauna Kea, West Maui, Kohala, and Waianae Volcanos are dotted with less extreme magmas in the same family. However, in none of these instances did the differentiated magma appear between the shield and post-shield stages of evolution as at Hualalai, and in no other instance is the differentiated magma so different from what came right before and after. Rather, the pattern shown at these other volcanos is for differentiated magmas to appear at the end of the post-shield stage. This is typically interpreted to represent waning magma flux from the mantle caused by plate motion off of a melting region called the mantle plume. One pertinent question we would like to answer is: What caused the differentiated magma to appear early in the sequence?

Another noteworthy feature of the trachyte erupted as a lava flow 100,000 years ago is its very large volume. No other lava flow in the Hawaiian islands is as voluminous as this trachyte flow (called Puu Anahulu) at Hualalai. Pat’s thesis is an investigation to explore questions raised at this location, including: What subsurface conditions led to the production and eruption of this unusual magma? How is Hualalai different from other Hawaiian volcanos? What can we expect to see from Hualalai and its neighboring volcanos in the future? The underlying processes controlling magmatism at Hualalai are important for understanding the growth of ocean island volcanos generally.

To address these questions, Pat is looking at xenolith nodules transported to the summit of Hualalai during an eruption of alkali basalt dated at 2350 years ago. The summit xenoliths are interpreted to be related to formation of the trachyte magma. If so, then they present an opportunity to set limits on the depth, temperature, and chemical environment of the volcanic plumbing system that produced the trachyte. Because they contain a large number of minerals and preserve reaction relationships in the form of mineral textures, the crystalline nodules have the potential to provide more information about trachyte formation conditions than can be extracted from the relatively homogeneous, micro-crystalline trachyte itself.

Shamberger, PJ and Hammer, JE (2003) Extreme Magma Differentiation in a Hawaiian Magma Chamber: An Analysis of Gabbro and Syenite Xenoliths from Hualalai Volcano. Fall AGU.

Image Gallery: Xenoliths