Evidence of a modern deep water magmatic hydrothermal system in the Canary Basin (eastern central Atlantic Ocean)

Abstract

New seismic profiles, bathymetric data, and sediment‐rock sampling document for the first time the discovery of hydrothermal vent complexes and volcanic cones at 4800–5200 m depth related to recent volcanic and intrusive activity in an unexplored area of the Canary Basin (Eastern Atlantic Ocean, 500 km west of the Canary Islands). A complex of sill intrusions is imaged on seismic profiles showing saucer‐shaped, parallel, or inclined geometries. Three main types of structures are related to these intrusions. Type I consists of cone‐shaped depressions developed above inclined sills interpreted as hydrothermal vents. Type II is the most abundant and is represented by isolated or clustered hydrothermal domes bounded by faults rooted at the tips of saucer‐shaped sills. Domes are interpreted as seabed expressions of reservoirs of CH4 and CO2‐rich fluids formed by degassing and contact metamorphism of organic‐rich sediments around sill intrusions. Type III are hydrothermal‐volcanic complexes originated above stratified or branched inclined sills connected by a chimney to the seabed volcanic edifice. Parallel sills sourced from the magmatic chimney formed also domes surrounding the volcanic cones. Core and dredges revealed that these volcanoes, which must be among the deepest in the world, are constituted by OIB‐type, basanites with an outer ring of blue‐green hydrothermal Al‐rich smectite muds. Magmatic activity is dated, based on lava samples, at 0.78 ± 0.05 and 1.61 ± 0.09 Ma (K/Ar methods) and on tephra layers within cores at 25–237 ky. The Subvent hydrothermal‐volcanic complex constitutes the first modern system reported in deep water oceanic basins related to intraplate hotspot activity.

Shape and Size Complexity of Deep Seafloor Mounds on the Canary Basin (West to Canary Islands, Eastern Atlantic): A DEM-Based Geomorphometric Analysis of Domes and Volcanoes

“…The classification according to size and slope variables has proved successful in discriminating hydrothermal domes from volcanic edifices, and just a few mismatches in the classification have been identified (i.e., M04, M06, M30, and M33) [42]. M06, M30 and M33 were morphostructurally classified as hydrothermal domes (MT2) despite the fact they have been confirmed as volcanic edifices, whereas M04 was regarded as volcanic mounds (MT4) even though it had been characterized as a peripheral dome of a volcanic/sill complex [41]. All the mounds have been labeled in accordance with the aforementioned classification, but the highlighted mounds are reclassified in regard to their confirmed origin ( Figure 1B).…”

“…This basin has been characterized as having a heterogeneous distribution of various volcanic elevations including seamounts, hills, and seafloor mounds [42,44]. Nevertheless, in the central area of this basin, known as the Subvent Area, these seafloor mounds are hydrothermal domes and scattered volcanoes related to Quaternary intrusive activity that gave rise to a huge magmatic sill complex together with volcanic activity [41]. Indeed, different morphostructural types (MT) of seafloor mounds have been differentiated according to the height, slope and basal area of these seafloor elevations [42] in agreement with various linked sill intrusions and volcanoes, as reported by [41].…”

“…The different genetic processes occurring in the Subvent Area have resulted in a striking seabed landscape including: hydrothermal domes formed above inclined but mainly saucer-shaped intrusions (MT1 and MT2); a huge bulge with a central depression associated with inclined sills at the top of a buried seamount (MT3); volcanic mounds developed at the top of basement highs and hydrothermal volcanic complexes associated with stratified sills (MT4 and MT5) [41,42] (Figure 1B). The classification according to size and slope variables has proved successful in discriminating hydrothermal domes from volcanic edifices, and just a few mismatches in the classification have been identified (i.e., M04, M06, M30, and M33) [42].…”

“…This basin has been characterized as having a heterogeneous distribution of various volcanic elevations including seamounts, hills, and seafloor mounds [42,44]. Nevertheless, in the central area of this basin, known as the Subvent Area, these seafloor mounds are hydrothermal domes and scattered volcanoes related to Quaternary intrusive activity that gave rise to a huge magmatic sill complex together with volcanic activity [41]. Indeed, Figure 1.…”

“…(A) Overview map of the western Canary lower continental slope and location of the study area in the Canary Basin (Central Eastern Atlantic Ocean); (B) Subvent Area bathymetric base map where the forty mounds are morphostructurally classified into five types of edifices [42]. The highlighted mounds are categorized according to their origin following [41].…”