Multibeam bathymetric survey of the Ipala Submarine Canyon, Jalisco, Mexico (20 degrees N): The southern boundary of the Banderas Forearc Block?

摘要

The Middle America Trench bends sharply northward at 20 degrees N. This, along with the close proximity of the Rivera North America Euler pole to the northern end of this trench, sharply increases the obliquity of subduction at 20 degrees N. By analogy with other subduction zones with similar sharply changing obliquity, significant trench parallel extension is expected to exist in the forearc region near the bend. To evaluate this possibility, multibeam bathymetric, seafloor backscatter and sub-bottom seismic reflection data were collected in this area during the MORTIC08 campaign of the B.O. El Puma. These data image in detail a large submarine canyon (the Ipala Canyon) extending from the coast at 20 degrees 05'N to the Middle America Trench at 19 degrees 50'N. This canyon is 114 km long and is fed by sediments originating from two, possibly three, small rivers: the Ipala, Tecolotlan and Maria Garza. This canyon deeply incises (up to 600 m) the entire continental slope and at least the outer part of the shelf. Within the canyon, we observe meanders and narrow channels produced by turbidity flows indicating that the canyon is active. In the marginal areas of the canyon slumps, rills, and uplifts suggest that mass movements and fluid flow have had a major impact on the seafloor morphology. The seafloor bathymetry, backscatter images and sub-bottom reflection profiles evidence the tectonic processes occurring in this area. Of particular interest, the canyon is deflected by almost 90 degrees at three locations, the deflections all having a similar azimuth of between 125 degrees and 130 degrees. Given the prominence and geometry of this canyon, along with its tectonic setting, we propose that the presence of the canyon is related to extension produced by the sharp change in the plate convergence. If so, the canyon may lie along the southeast boundary of a major forearc block (the Banderas Forearc Block). (C) 2016 Elsevier B.V. All rights reserved.