The Shatsky Rise oceanic plateau structure from two-dimensional multichannel seismic refl ection profi les and implications for oceanic plateau formation

The Shatsky Rise is one of the largest oceanic plateaus, a class of volcanic features whose formation is poorly understood. It is also a plateau that was formed near spreading ridges, but the connection between the two features is unclear. The geologic structure of the Shatsky Rise can help us understand its formation. Deeply penetrating two-dimensional (2-D) multichannel seismic (MCS) refl ection profi les were acquired over the southern half of the Shatsky Rise, and these data allow us to image its upper crustal structure with unprecedented detail. Synthetic seismograms constructed from core and log data from scientifi c drilling sites crossed by the MCS lines establish the seismic response to the geology. High-amplitude basement refl ections result from the transition between sediment and underlying igneous rock. Intrabasement refl ections are caused by alternations of lava fl ow packages with differing properties and by thick interfl ow sediment layers. MCS profi les show that two of the volcanic massifs within the Shatsky Rise are immense central volcanoes. The Tamu Massif, the largest (~450 km × 650 km) and oldest (ca. 145 Ma) volcano, is a single central volcano with a rounded shape and shallow fl ank slopes (<0.5°–1.5°), characterized by lava fl ows emanating from the volcano center and extending hundreds of kilometers down smooth, shallow fl anks to the surrounding seafl oor. The Ori Massif is a large volcano that is similar to, but smaller than, the Tamu Massif. *Now at Key Laboratory of Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, 510301, China, and Key Laboratory of Marine Mineral Resources, Ministry of Land and Resources, Guangzhou, 510075, China. Now at Department of Earth and Atmospheric Sciences, University of Houston, Houston, Texas 77204, USA. Zhang, J., Sager, W.W., and Korenaga, J., 2015, The Shatsky Rise oceanic plateau structure from two-dimensional multichannel seismic refl ection profi les and implications for oceanic plateau formation, in Neal, C.R., Sager, W.W., Sano, T., and Erba, E., eds., The Origin, Evolution, and Environmental Impact of Oceanic Large Igneous Provinces: Geological Society of America Special Paper 511, p. 103–126, doi:10.1130/2015.2511(06). For permission to copy, contact editing@ geosociety.org. © 2015 The Geological Society of America. All rights reserved. on June 2, 2015 specialpapers.gsapubs.org Downloaded from