University of Iowa
2017-2018 Ocean Discovery Lecturer
The Early History of the Azu-Bonin-Mariana Subduction System as Revealed by Diving and Drilling
The non-accretionary Izu-Bonin-Mariana (IBM) fore-arc has an ophiolitic crust with depleted peridotites overlain by gabbroic rocks, dolerites, basalts and boninites. This sequence is interpreted to have formed in the immediate aftermath of subduction initiation in the western Pacific at about 52 Ma. This event was part of a major plate reorganization that had significant impact on global tectonics, and perhaps on global climate. Because subaerial exposure in the IBM fore-arc is limited, much of what we know is based on underwater field work conducted using the Shinkai 6500 deep diving submersible and, more recently, the JOIDES Resolution during IODP Expedition 352. I will briefly discuss the remarkable operations of these vessels, and then present the results of the collective research of the scientific teams from these expeditions. The main focus will be on results from Expedition 352, which drilled an intact reference section through boninites and basalts in Bonin fore-arc. I will discuss the geology, geochronology, petrology, and geochemistry of the drilled volcanic rocks, and the implications of our research for why subduction started in the IBM system, how this oceanic island arc developed, and its relationship to global tectonics.
Dr. Reagan has studied volcanism associated with the initiation and early evolution of subduction in the western Pacific for more than 35 years, most recently as a co-chief scientist on IODP Expedition 352.