Spreading process of the northern Mariana Trough: Rifting‐spreading transition at 22°N

Abstract

[1] We have conducted a geophysical survey of the northern Mariana Trough from 19°N to 24°N. The trough evolves southward from incipient rifting to seafloor spreading within this region. This study aims to clarify the location and time of the rifting-to-spreading transition, which was controversial previously, and processes of seafloor spreading after the transition. The new data set includes swath bathymetry with sidescan images and magnetic vector anomaly. The mantle Bouguer gravity anomaly (MBA) was calculated using the free-air gravity anomaly from satellite altimetry. The rifting-to-spreading transition occurs at about 22°N, which is proved by seafloor-spreading fabric in the bathymetry, clear magnetic lineations, and the bull's-eye pattern in MBA. Four ridge segments separated by three nontransform discontinuities are recognized between 19°N and 22°N. The northernmost segment has relatively abundant magma supply compared with the other segments, which is estimated from a larger segment length, shallower axial depths with no rift valley, and lower MBA. The next segment to the south is, on the other hand, a magma-starved segment with a prominent rift valley. Two anomalously deep grabens (called the Central Grabens) formed by amagmatic extension occur near the segment ends. The succession of magma-rich, magma-starved, and normal segments with increasing distance from the volcanic arc is the same as the observation in the Lau Basin reported by Martinez and Taylor spreading center have been significantly larger than the eastern counterpart in general. The asymmetry may have been caused by an interaction of mantle upwelling systems under the volcanic front and the backarc spreading center and would be a characteristic of backarc spreading.

Examination of Volcanic Activity: AUV and Submersible Observations of Fine-Scale Lava Flow Distributions Along the Southern Mariana Trough Spreading Axis

“…Abyssal hills have not been clearly observed in the eastern off-axis area owing to thick sedimentary coverage and/or overprinting of later arc volcanism (Fryer 1996;Martinez et al 2000). North of 14 N, the spreading center of the Mariana Trough is morphologically similar to slow-spreading mid-ocean ridges, having a deep crustal graben flanked by a zone of abyssal hills (Seama et al 2002;Yamazaki et al 2003), as expected from its slow spreading rate. However, the southern part of the Mariana Trough, where the back-arc spreading axis approaches the volcanic arc (within 10 km at around 13 20 0 N) (Martinez et al 2000), shows a broad and smooth morphological cross section and lacks a deep crustal graben (Fig.…”

“…The spreading axis lies in the eastern part of the basin, indicating asymmetric seafloor accretion (Yamazaki et al 2003;Deschamps and Fujiwara 2003;Deschamps et al 2005;Asada et al 2007). Abyssal hills have not been clearly observed in the eastern off-axis area owing to thick sedimentary coverage and/or overprinting of later arc volcanism (Fryer 1996;Martinez et al 2000).…”

Asymmetric Seafloor Spreading of the Southern Mariana Trough Back-Arc Basin

“…The studies of the geomagnetic anomalies using the Matuyama-Brunhes boundary (0.78 Ma) reported the similarity in the spreading trend; the full spreading rates are 10 km/Myr at 22 N in the northern end (Yamazaki et al 2003) and~64 km/Myr in maximum at 13 N in the southern end (Martinez et al 2000). These two different methods show that the full spreading rate of the Southern Mariana Trough back-arc basin ranges 45-64 km/Myr.…”

The Mantle Dynamics, the Crustal Formation, and the Hydrothermal Activity of the Southern Mariana Trough Back-Arc Basin

“…The spreading rates of the Mariana Trough back-arc basin increase from the north to the south. Studies of the geomagnetic anomalies using the Matuyama-Brunhes boundary (0.78 Ma) reported the full spreading rates of 10 km/Myr at 22 N in the northern end (Yamazaki et al 2003) and of~64 km/Myr in maximum at 13 N in the southern end (Martinez et al 2000). Repeated GPS surveys in the Mariana Islands show similar trend of the full spreading rates; that is 15.9 AE 6.6 km/Myr at 18.7 N and 44.6 AE 2.7 km/Myr at 13.6 N (Kato et al 2003).…”