Bathymetry of Mariana trench‐arc system and formation of the Challenger Deep as a consequence of weak plate coupling

Abstract

The Challenger Deep in the southernmost Mariana Trench (western Pacific Ocean) is the deepest point on the Earth's surface (10,920 m below sea level). Its location within a subduction trench, where one plate bends and descends below another, is not surprising. However, why is it located in the southernmost Mariana Trench and not at its central part, where the rate of subduction is higher, where the lithosphere is the oldest (and densest) on the Earth, and where the subducted lithosphere pulling down is the longest in the Earth (∼1000 km or more according to seismic tomography)? We suggest that although subduction rate and slab age generally control trench depth, the width of the plate‐coupling zone is more important. Beneath the central Marianas the subducted slab is attached to the upper plate along a 150‐km‐wide surface that holds the shallow portion of the subducted plate nearly horizontal, in spite of its great load and, thus, counters trench deepening. In contrast, along the south Mariana Trench the subducted length of the lithosphere is much shorter, but its attachment to the upper plate is only along a relatively narrow, 50‐km‐wide, surface. In addition, a tear in the slab beneath this region helps it to sink rapidly through the mantle, and this combination of circumstances allows the slab to steepen and form the deepest trench on the Earth. In a wider perspective, the interrelations shown here between trench deepening, ridge shallowing, slab steepening, and forearc narrowing may shed light on other subduction zones located near edges of rapidly steepening slabs.

A precise bathymetric map of the world’s deepest seafloor, Challenger Deep in the Mariana Trench

“…Previous seismic and bathymetric studies (Fryer et al 2003;Gvirtzman and Stern 2004;Miller et al 2006) show an N-S trending tear in the slab around the southern part of the Mariana Trench. They suggest that the cause of the great depth of the Challenger Deep is partly a result of the subducting lithosphere in the southern part of the Mariana Trench tearing away from the northern part.…”

A Geochemical Study of Crustal Plutonic Rocks from the Southern Mariana Trench Forearc: Relationship to Volcanic Rocks Erupted during Subduction Initiation

“…The narrower the plate-coupling zone is, the weaker the slab will be attached allowing it to hang and exert a "down-pulling" force on the upper plate (also enabling a steep dip) [Gvirtzman and Stern, 2004]. This creates a steeper and deeper trench in the Mariana-type arc, e.g., the deepest ocean floor on earth: the Challengers Deep.…”

“…It seems to follow that the down-pulling force will affect a roll back system, such as is present in the Mariana trench and causing the normal faulting in the forearc [Fryer et al, 2003]. By general definition, the Mariana-type arc is a loosely coupled system, although plate coupling and seismic coupling do vary along the length of the IBM system [Gvirtzman and Stern, 2004;Scholz and Campos, 1995].…”

“…The two end members of the strain classes were strongly extensional (Mariana arc) and strongly compressional (Chilean arc) [Stern, 2002;Uyeda and Kanamori, 1979] shown in Figure 1.3. In addition to the age and absolute motion of the plates, the width of the plate-coupling zone is hypothesized to have an effect on seismic coupling, as well as a large effect on trench depth [Gvirtzman and Stern, 2004]. The terms are differentiated by Gvirtzman and Stern [2004] to mean that plate-coupling is "the resistance of the plates to detach vertically…" while seismic coupling is "…the resistance for two plates to slide past each other."…”

“…In addition to the age and absolute motion of the plates, the width of the plate-coupling zone is hypothesized to have an effect on seismic coupling, as well as a large effect on trench depth [Gvirtzman and Stern, 2004]. The terms are differentiated by Gvirtzman and Stern [2004] to mean that plate-coupling is "the resistance of the plates to detach vertically…" while seismic coupling is "…the resistance for two plates to slide past each other." And they postulate that the two "must be related because both deal with lithosphere-lithosphere contact along the subduction interface.…”