Jinchang Zhang1,2, William W. Sager2,3, Jun Korenaga4
1South China Sea Institute of Oceanology, Chinese Academy of Sciences, China
2Texas A&M University, College Station, Texas, USA
3University of Houston, Houston, Texas, USA
4Yale University, New Haven, Connecticut, USA
IODP drilling data and deep penetrating 2D multichannel seismic (MCS) reflection profiles discover Tamu Massif, the largest (~450 km x 650 km) and the oldest (~145 Ma) edifice within Shatsky Rise oceanic plateau, is the largest underwater single volcano on Earth. Core samples indicate Tamu Massif is characterized by thick massive lava flows, up to ~23 m thick, implying massive and rapid eruptions. MCS profiles show Tamu Massif is a single central volcano with rounded shape and shallow flank slopes (<0.5o-1.5o), constructed by lava flows emanating from the volcano center and extending hundreds of kilometers down smooth, shallow flanks to the surrounding seafloor. Such huge eruptions at one place and in short time (~5 Ma) imply mantle plume origin, but no subaerial erosion shown from MCS profiles implies submerged formation, and lack of dynamic uplift evidence makes the plume hypothesis somewhat unfit. Plate model could also form large igneous provinces, especially for the fact that Shatsky Rise sits at a ridge-ridge-ridge triple junction, so the rise is definitely linked to mid-ocean ridge mechanism. Mid-Ocean Ridge Basalts are recovered from Tamu Massif provide evidence for the plate boundary hypothesis. However, little rifting structure found from MCS profiles supports the idea of spreading ridge related decompression melting of fertile upper mantle material. Neither of the plume or plate hypotheses could explain all the observations obtained from Tamu Massif within Shatsky Rise. It therefore, could have been formed by mantle plume-mid-ocean ridge interaction, and how mantle plume and mid-ocean ridge interact in order to create such a giant volcano remains unknown and requires future work.
