Magmatic additions to the middle and lower crust during rifting govern basin response to tectonic inversion in a magma-rich back-arc (NE Japan)
Abstract
Magmatic additions to the middle and lower crust during rifting introduce rheological heterogeneities into the deeper rift architecture which may directly influence the mode of basin reactivation under tectonic inversion. Rifting of the magma-rich Sea of Japan back-arc (NE Japan) in the Middle Miocene left a series of failed-rift basins strung along the western side of the Japan island arc. In at least two of these basins, the northern Fossa Magna and Niigata basins, the inversion behavior appears to be controlled by reverse-fault reactivation of the rheological boundary between the original arc crust and a magma body that was intruded under the rift axis during back-arc opening. After inversion, the basins continued to subside - accumulating as much as 3500 m of Quaternary sedimentary deposition in the case of the Niigata Basin - while at the same time, folding and thrusting deformed the basin fill. We attribute this unusual response to reverse faulting on a wedge thrust comprised of an upper, moderately steep, inward-dipping fault and a lower, moderately steep, outward-dipping fault that developed along the rheological boundary between the intrusive body and the arc crust. Movement on the outward-dipping rheological boundary is thrusting arc crust over sedimentary fill and causing the basin floor to continue to subside. The accompanying insertion of the crustal wedge into the side of the basin is driving thin-skinned deformation in the basin fill via a detachment that originates low in the sedimentary section. Basin subsidence may be enhanced by densification at the base of the intrusive body as it enters the stability field of garnet granulite at depth. At least one destructive crustal earthquake in the back arc region, the 2007 Chuetsu-oki earthquake, is associated with such an outward-dipping rheological boundary fault. Thus, mobilization of the rheological boundary between the deep intrusive body under the rift basin and the adjacent arc crust is producing both thin-skinned deformation at the surface and basement-involved faulting that reaches into the middle to lower crust.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.T31D0349V
- Keywords:
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- 8104 Continental margins: convergent;
- TECTONOPHYSICSDE: 8105 Continental margins: divergent;
- TECTONOPHYSICSDE: 8157 Plate motions: past;
- TECTONOPHYSICSDE: 8178 Tectonics and magmatism;
- TECTONOPHYSICS