Multibeam Bathymetric Survey of the Ipala Submarine Canyon, Jalisco. Mexico (20°N): The Southern Boundary of the Banderas Forearc Block?

Abstract:

The Middle America Trench bends sharply northward at 20°N. This, along with the close proximity of the Rivera-North America Euler pole (e.g., Suárez et al., 2103) to the northern end of the Middle American trench (the Jalisco Subduction Zone), produces a sharp increase in the obliquity of subduction at 20°N. By analogy with other subduction zones where this situation occurs,a significant trench parallel extensional stress field is expected to exist in the forearc region near the bend. Given the poor bathymetric coverage previously existing in this area, to verify that such stresses are present in the forearc area of the Jalisco Subduction Zone, multibeam bathymetric, seafloor backscatter and sub-bottom seismic reflection data were collected during the MORTIC08 campaign of the B.O. EL PUMA using the Kongsberg EM300 multibeam system and TOPAS sub-bottom profiler. Consistent with the analogy, these data image in detail a large submarine canyon extending from the coast at 20°05'N to the Middle America Trench at 19°50'N. This canyon, which we call the Ipala canyon (the canyon head lies offshore of the town of Ipala, Jalisco) is approximately 120km in length and is most likely fed by two, possibly three, small rivers, namely: the Ipala, Tecolotlán and Maria Garza rivers. . The seafloor and subbottom seismic reflection images also expose the tectonic processes that are actively influencing the present day geomorphology of the canyon region. Specifically, the new information indicates that much of the physical geography of seafloor is the result of active tectonic deformation of the plate margin, including uplift, erosion along structural lineaments and faulting. Of particular interest, the canyon is deflected by almost 90° at three locations, the deflections all having a similar azimuth of between 125° and 130°. Given the prominence and geometry of this canyon, along with its tectonic setting, we propose that this canyon is the result of extensional stresses produced by the sharp change in the plate convergence direction in this area and that the canyon delineates the southeast boundary of a major forearc block, which we call the Banderas Forearc Block.