Geophysical characteristics of the southern Mariana Trough, 11°50′N–13°40′N

Abstract

Abstract. Despite slow opening rates generally inferred for the Mariana Trough, the southernmost part of the basin has "fast spreading" geophysical and morphologic characteristics that are unlike the features of the basin to the north. A side-scan sonar and geophysical survey maps the eastern part of the basin and the seafloor spreading center between 11 ø50'N and 13ø40'N and identifies the following characteristics: the ridge across-axis profile forms a triangular to rounded high with relief of 100 to 500 m and cross-sectional area variations of 1 to 7 km2; the along-axis mantle Bouguer gravity gradient is 0.2 mGal/km; axial segmentation occurs as overlapping axes and small deviation in trend; no transform fault offsets exist despite significant changes in the trend of the spreading center. Characteristics of the surrounding basin include shallower overall depth than in the north; no well-developed frontal arc high in the southernmost trough; the close proximity of submarine arc-type volcanoes to the spreading center; and tectonic fabric that is at a high angle to the trend of the spreading center on the eastern flank but is concordant on the western flank. These characteristics imply different tectonic and magmatic conditions in the southern trough from the rest of the basin. We propose that these effects are related to (1) the geometry of trench rollback in the southern trough leading to trench-parallel extension generating inward radiating extensional faults; (2) decoupling of the trench-parallel extensional strain by the spreading center so that it primarily affects the eastern flank of the basin; and (3) augmentation of the spreading center's magmatic budget by arc magmatic sources contributing to its fast spreading character. Although these effects may be accentuated in the southern Mariana Trough by the geometry of trench rollback and position of the slab, which here underlies the spreading center, they reflect distinct volcanic and tectonic processes which are varyingly expressed in back arc systems but are not normally found at mid-ocean ridges.

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

“…They also argue that the lack of sediments covering the deformed ocean floor further indicates that the accelerated extension and southward migration of the Mariana Trench in this region has occurred recently. One may argue that extensional faulting of forearcs alone is not enough to prove slab rollback, because normal faulting may also be caused by basal subduction erosion, but we still favor the rollback interpretation based on two additional lines of evidence: the shallow asthenosphere penetration between the two plates (this study) and the opening rate of the Mariana Trough back arc basin that increases southward Kato et al, 2003;Martinez et al, 2000]. These three processes are all explained by rapid rollback of the subducting slab.…”

“…At that point, the forearc narrows to only $50 km, and the distance from the actively spreading Mariana Trough back arc basin, which must be underlain by shallow asthenosphere, to the trench narrows to $100 km. In between, a dispersed group of seamounts (at about 142.5°E 11.8°N, Figure 1a) appear to be the southward continuation of the magmatic arc [Fryer, 1996;Fryer et al, 1998;Martinez et al, 2000]. The crust of this newly developing magmatic arc may not have thickened a lot, but even if the crust is 10-km thick, the depth of about 2.0 km below sea level indicates that here too, only 50 km away from the trench, the asthenosphere is very shallow.…”

“…Location of a proposed slab tear is marked by a thick white line. Location of the Mariana Trough spreading axis from Martinez et al [2000]. (b) Cartoon illustrating the geometry of the subducting Pacific plate under the entire Mariana-Japan-Kurile arc system (drawn after Gudmundsson and Sambridge [1998]).…”

Mineralogical and Geochemical Characteristics of Hydrothermal Minerals Collected from Hydrothermal Vent Fields in the Southern Mariana Spreading Center

“…The proximity, as well as the radial faulting pattern of the eastern backarc basin south of 13 10 0 N, may facilitate channeling of arc magma to the spreading center (Fryer 1995;Fryer et al 1998). Martinez et al (2000) proposed that the welldeveloped spreading system, in contrast to the rifting-stage system of the Northern Mariana Trough, channels arc magma efficiently along the backarc-spreading axis. They also suggested that the small arc seamounts in the Southern Mariana Trough may also support the derivation of the arc magmatic budget to the spreading center.…”

The Fina Nagu volcanic complex: Unusual submarine arc volcanism in the rapidly deforming southern Mariana margin

“…It is located between the southern terminus of the Mariana Trough back-arc spreading center, called the Malaguana-Gadao Ridge (referred to as the Southern Mariana Trough by Brounce et al [2014]), and the Southeastern Mariana Forearc Rift, an unusual region of forearc extension and related volcanism [Fryer, 1995;Ribeiro et al, 2013b]. The southernmost Marianas, between the Malaguana-Gadao Ridge in the west, the Mariana trench in the east and the south, and the Alphabet seamount volcanic province in the north, is a tectonically complex and rapidly deforming region [Fryer, 1995;Kato, 2003;Martınez et al, 2000]. The upper plate is extending southeast-northwest, accommodated by spreading along the Malaguana-Gadao Ridge.…”