Diffuse spreading, a newly recognized mode of crustal accretion in the southern Mariana Trough backarc basin

Abstract

South of the latitude of Guam, the Mariana Trough exhibits both trench-parallel and trench-normal extension. In this study, we examined the locus of trench-normal extension separating the Philippine Sea plate from the broadly deforming Mariana platelet. Along this boundary, we identified three distinct modes of extension and described their distinguishing characteristics using deep- and shallow-towed side-scan sonar and ship multibeam data along with regional geophysical, geochemical, and seismicity data. In the west, the Southwest Mariana Rift is an active tectonic rift exhibiting abundant strong earthquakes up to mb 6.7 and limited evidence of volcanism. In the east, the Malaguana-Gadao Ridge is a seafloor spreading center producing few and weak earthquakes less than mb 5. Between these zones, there is an ~20–40-km-wide and ~120-km-long area of high acoustic backscatter characterized by closely spaced volcano- tectonic ridges and small volcanic cones with distributed intermediate-strength seismicity up to mb 5.7. Fresh-looking volcanic rocks with high water contents and strong arc chemical affinities have been recovered from the high-backscatter zone. We interpret this morphologically and geophysically distinct zone as undergoing diffuse spreading, a distributed form of magmatic crustal accretion where new crust forms within a broad zone tens of kilometers across rather than along a narrow spreading axis. Diffuse spreading appears to be a rheological threshold effect enabled by slow opening rates and a high slab-fluid flux that facilitate the formation of a broad zone of weak hydrous lithosphere, within which new crust is accreted. Our findings describe a poorly understood process in plate tectonics, and observations of similar terrains in other backarc basins suggest that this process is not unique to the Mariana Trough.

Ambient Noise Interferometry Using Ocean Bottom Seismometer Data From Active Source Experiments Conducted in the Southernmost Mariana Trench

“…The overall increasing trend of the three models appears similar in the forearc region (Figure 10b), which has not undergone extensive extension (Sleeper et al, 2021). This structure has been interpreted by a lower degree of serpentinization compared to the forearc region of the central Mariana Trench, where mud volcanos and serpentine seamounts exist (Cai et al, 2018;Zhu et al, 2021).…”

“…Additionally, the crustal thickness here is greater than that of the forearc region (Wan et al., 2019). Due to the lack of a mature island arc, this rift zone is amagmatic and different from other arc to back‐arc basin zones with tectonic spreading (Sleeper et al., 2021). The structure and possible mechanism of the formation of the SWMR still need to be better understood.…”

“…Generated by the convergence of the Pacific Plate and the Philippine Sea Plate, the distinct southernmost Mariana subduction zone holds the oldest oceanic crust and the earth's deepest "Challenger Deep" (Figure 1). Unlike Journal of Geophysical Research: Solid Earth 10.1029/2023JB027043 typical subduction zones, this region lacks a mature arc and suffers diffuse deformation, resulting in spatially distributed forearc segments (Martinez et al, 2018;Sleeper et al, 2021). The Southwest Mariana Rift (SWMR) in the backarc region hasn't undergone much opening and is in a stage of tectonic rifting (Martinez et al, 2018).…”

Geographical distribution and driving force of micro-eukaryotes in the seamount sediments along the island arc of the Yap and Mariana trenches

“…As for the Stn. SY196, it was located at the Southwest Mariana Rift, which is an active tectonic rift composed of the remnant arc West Mariana Ridge to the north with scarp heights up to 3,500 m ( 43 ), therefore, possibly sharing similar geological structure and nutrient concentration as the Challenger Deep, likely supporting similar micro-eukaryotic communities. However, this station is on a submarine rise of the rift at a depth of 3,984 m, so micro-eukaryotic community characteristics, e.g., diversity and the composition of metazoan groups, were similar to those in the seamounts.…”

Deep Outer‐Rise Faults in the Southern Mariana Subduction Zone Indicated by a Machine‐Learning‐Based High‐Resolution Earthquake Catalog

“…The Central and Southern Mariana Troughs experienced different opening modes. Magmatic seafloor spreading was relatively focused in the Central Mariana Trough, but the spreading at the southern end of the trough was more diffuse (Sleeper et al., 2021). Subduction behaviors were also different along the trench under the influence of the geometry and the opening modes of the subduction system.…”