Annual Sheriff Lecture
November 7th, 2016
Hilton Westchase (Google Map Link)
9999 Westheimer Rd, Houston, TX 77042
Speaker: Dr. John Suppe, UH EAS
Lecture Title: The Second Half of Plate Tectonics: Finding the last ~200Ma of subducted lithosphere and incorporating it into plate reconstruction
Click here for registration and more information (HGS website)
About the Speaker
Tomographic imaging is increasingly being used to explore the Earth from the reservoir scale to the global scale. Here we show that petroleum 3D interpretation, data integration, and restoration technologies represent powerful resources for making significant discoveries based on modern tomographic imaging. We illustrated the importance of tomographic data using examples from  global plate tectonics and  the structural geology of mountain belts.
Precise plate-tectonic reconstruction of the Earth has been constrained largely by the seafloor magnetic-anomaly record of the present oceans formed during the dispersal of the last supercontinent since ~200Ma. The corresponding world that was lost to subduction, which accounts for ~100% of the surface area of the Earth, has been only sketchily known. We have developed methodologies, largely within a modified Gocad software environment, to map in 3D these subducted slabs of lithosphere in seismic tomography and to unfold them to the Earth surface, constraining their initial size, shapes and locations (Fig. 1). Slab edges are commonly formed at times of plate reorganization (for example bottom edges typically record initiation of subduction) such that unfolded slabs fit together in picture-puzzle fashion at times of reorganization, as we illustrate for the Nazca slab at ~80Ma and the western Pacific slabs between Kamchatka and New Zealand at ~50Ma (see Fig. 2). Mapping to date suggests that a relatively complete and decipherable record of lithosphere subducted over the last ~200Ma may exist in the mantle today, providing a storehouse for new discoveries.
We illustrate our procedure for obtaining slab-constrained plate-tectonic models from tomography with our recent study of the Philippine Sea plate, whose motions and tectonic history have been the least known of the major plates because it has been isolated from the global plate and hotspot circuit by trenches. We mapped and unfolded 28 subducted slabs in the mantle under East Asia and Australia/Oceania to depths of ~1200km, with a subducted area of ~25% of present-day global oceanic lithosphere. We then incorporated them as constraints into a new globally-consistent plate reconstruction of the Philippine Sea and surrounding East Asia, leading to a number of new and unexpected insights, including:  discovery of a major (8000 km x 2500 km) set of vanished oceans that we call the East Asia Sea that existed between the Pacific and Indian Oceans, now represented by flat slabs in the lower mantle under present-day Philippine Sea, eastern Sundaland and northern Australia,  the Philippine Sea plate collided with the Ryukyu/SW Japan continental margin of Eurasia in arc-arc collision ~20Ma, and  the Philippine Sea nucleated as a small trench back-arc system along the East Asian Sea/Pacific boundary, adjacent to the Manus plume, somewhat analogous to the more recent nucleation of the Bismark Sea at the same Manus plume.
Tomographic images also represent a major driver of new insight into the structure and tectonics at a finer scale, for example at the scale of mountain belts, particularly when coupled with the resource of petroleum 3D interpretation, data integration, and restoration technologies. We illustrate this for the Taiwan mountain belt, which is an active arc-continent collision. Tomographic mapping has led to the discovery of deep rift and continental-margins basins underneath the Taiwan mountain belt (Fig. 3) and has illuminated the unexpected ways in which arc-continent collision and flipping of subduction with reversal of thrust polarity is accomplished in 4D.