SEISMIC REFLECTION DATA IMAGES FLUID ESCAPE PIPES BENEATH THE OFFSHORE MANZANILLO VENT FIELD.
A large fluid vent field, herein called the Offshore Manzanillo Vent Field (OMVF), has recently been reported on the continental slope offshore of Manzanillo Mexico. This vent field lies on top of a prominent bathymetric high at water depths of less than 1 Km. The radius of the vent field is roughly 15 km. Several large vents (up to 300m in diameter) are observed within the field.
The source and composition of the vented fluids is presently unknown. BSRs (Bottom simulating reflectors) have been observed in the area indicating the presence of gas hydrates; therefore, the dissolution of gas hydrates may be one source. Alternatively, the seafloor morphology along with total field magnetic anomalies in the area of the OMVF is consistent with the presence of a large seamount located on the subducting Rivera Plate at a depth of 6 to 12 km beneath the OMVF. Worldwide, the process of seamount subduction has previously been shown to fracture the crust overlying the seamount providing a pathway for the water entrained along the megathrust between subducting and overriding plates to rise to the surface where it forms prominent seafloor vents.
In this work, we further analyze a multichannel seismic reflection profile collected during the CORTES-P96 campaign of the RV Hespérides. These data show a prominent fluid escape pipe which extends downward from a vent cone on the seafloor to area of the previously proposed seamount located on the downgoing Rivera plate. Another, less prominent, fluid escape pipe is also observed. Thus, these data indicate that the fluids being vented at the OMVF originate at the underlying megathrust contact between the subducting Rivera and overriding North American plates. Seamount subduction induces crustal fracturing, which increases crustal permeability and allow the fluids to rise to the surface via fluid escape pipes. Further work on the fluid composition is in progress.