A seismic stratigraphic analysis of Mariana forearc basin evolution

Abstract

[1] New seismic data collected in the 14.5°-18.5°N Mariana segment of the Izu-Bonin-Mariana island arc system image six seismic stratigraphic sequences that can be mapped throughout the inner forearc. These sediments were most likely deposited from 35 Ma to the present. The oldest stratigraphic Units 1, 2, and 3 are syn-rift volcaniclastic deposits. Unit 4 deposits accumulated during a period of mild structural inversion, which resulted in several isolated reverse-faulted anticlines within the forearc sedimentary basin. A late period of extensional deformation began near the end of Unit 5 deposition and continued through Unit 6 sedimentation to the present. Seismic lines show that the basement of the forearc is composed of large rotated fault blocks and half grabens with NE, NW, and NNE trends. Fault offset calculations show that basement faults with dips between 45°and 50°account for only 4% total extension in the forearc. South of 16.3°N, normal growth faults initiated during basement extension offset the frontal arc high from a deep forearc basin. From correlations with the known geologic history, we hypothesize that extension during deposition of Units 1 through 3 corresponds to rifting of the Eo-Oligocene Arc, between 35 Ma and 29 Ma, older deposits being too thin to be seismically resolvable. Localized compression during Unit 4 accumulation occurred some time after Eo-Oligocene rifting in the early Miocene. Late-stage normal faulting near the end of deposition of Unit 5 and throughout Unit 6 accumulation may be associated with the opening of the Mariana Trough backarc basin from 8 Ma years to the present. There is a higher density of these later faults in the inner forearc between 15.5°and 17°N and in the outer forearc between 14°N and 18°N. Recent extension is at least partially accommodated by reactivation of older basement faults with the same NE, NW, and NNE-trends. Stratigraphic relationships indicate that the inner forearc south of 16.3°N has differentially subsided and tilted trenchward, possibly as a result of a recent change in subducting slab geometry or subducted relief under the forearc.

Deformation and faulting of subduction overriding plate caused by a subducted seamount

“…However, our models cannot be directly applied to nonaccretionary wedges due to a different background stress state. For example, background horizontal extension has been inferred from the overwhelming normal faults in seismic profiles of the Mariana subduction zone [ Hussong and Uyeda , ; Chapp et al ., ]. Oakley et al .…”

Sedimentary, volcanic, and tectonic processes of the central Mariana Arc: Mariana Trough back‐arc basin formation and the West Mariana Ridge

“…Beneath basement, an east dipping reflection (∼SP 40) is possibly a thrust fault which resulted in an asymmetric fold in the sediments above. Although it is surprising to see a compressional feature in an extension‐dominated environment, Chapp et al [2008] show other evidence for compression in the central Marianas east of the frontal‐arc high in the inner fore arc. The deformation in the sediments could also be caused by a west dipping, high‐angle normal fault, although this interpretation does not explain the east dipping reflection beneath basement.…”

Geodynamic implications of crustal lithologies from the southeast Mariana forearc

“…Possibilities include: (1) faulting associated with the collision of the Caroline Ridge with the Mariana Trench in the Late Miocene tectonically shuffled rocks in the southern Mariana forearc as has been postulated for interleaved metamorphic rocks and peridotites on Yap Island (see Hawkins and Batiza, 1977;Ohara et al, 2002); (2) rocks with differing histories were chaotically mixed during serpentine diapirism (e.g., Maekawa et al, 1993); (3) epidote amphibolites were mass wasted from crustal outcrops farther upslope onto garnetite-bearing mantle; or (4) normal faulting associated with subduction erosion and exposure of the mantle in the forearc (Reagan et al, 2017) juxtaposed deep crustal amphibolites and garnetites embedded in the upper mantle. Direct evidence for (1) and (2) in the dive area is lacking, whereas evidence for normal faulting and mass wasting in the Mariana forearc is widespread (Martínez et al, 2000;Chapp et al, 2008), suggesting that some combination of (3) and (4) moved rocks from the crust section or uppermost mantle downslope to where they were collected during Shinkai 6500 dive 6K-1232.…”