GROWTH AND EVOLUTION OF THE ISLAND OF HAWAII: PERSPECTIVES FROM HSDP DEEP DRILLING

The Hawaiian island chain, and the Big Island in particular, present a fascinating example of the interplay of mantle and crustal dynamics, magma production and transport, volcano growth and petrological evolution, lava transport, submarine volcanic sedimentation and diagenesis, and landscape evolution in a region with large contrasts in precipitation and erosion. The volcanoes themselves are not typical, being extremely large as a consequence of the exceptionally high magma production rate in a hot mantle plume with a large buoyancy flux. The longevity of the Hawaiian hot spot and the systematic movement of the Pacific plate allow for the system to be viewed as a steady state feature of reasonable simplicity and promote the application of geodynamic models, but there are also along-chain variations in volcano growth rates and geochemistry, across-chain asymmetries, variations in the trend of the chain, and complications with the subsidence models. The Hawaii Scientific Drilling Program (1993 to 2007) added a new dimension to the study of Hawaiian volcanoes through the recovery of 4600 meters of core from Mauna Kea and Mauna Loa. The core has been intensively characterized, including geochronology, petrology and geochemistry. The ages from the cores extend to 700,000 years; 2/3 of the lifetime of the Mauna Kea volcano. The petrology and geochemistry confirm structure in the plume, and both expected and unexpected petrological changes with lava age. The timescale of volcano construction is longer than previously thought, and hence the deduced models for the island’s growth and evolution are considerably different. We have developed models to link the volcanic growth to the structure and melting in the mantle plume, and to account for the overlapping nature of the volcanoes as well as subsidence. Such models allow us to deduce the internal structure of the island, better estimate the volume of the volcanoes, understand how magma production relates to volcano growth, map geochemical and petrological variations to structure in the mantle plume and structure near the base of the mantle. To first-order, we can account for the formation and evolution of the island of Hawaii “from the bottom up,” starting with geodynamical models for mantle flow and melting rates, and using HSDP geochronology as a guide.