10 - It’s Geological Mapping – Only different!

Geological mapping of the sea floor using the ROV is an incredible experience. To be able to drive around investigating geological locations, with almost as much freedom as a field geologist on land is pretty special. Indeed, we can begin to construct a geological map just as you would in the field, although because we don't get to hammer or put our hand lens to the rock , the blackened and stained rocks we see through the high resolution cameras sometimes turn out to be not quite as expected when the ROV returns to the surface with samples! But this is the other great thing about using the ROV, which is its capacity to return to the surface with a substantial geological payload. These ‘hand-picked’ samples can be split, hammered and sawn open, and the fresh interiors revealed allowing us to “ground truth” our region of interest.

Following two dives of 24 hour duration the Geoteam has been able to dramatically revise and enhance our understanding of the geology underpinning the Von Damm hydrothermal vent system developed on the flank of the Mt Dent ocean core complex. Oceanic core complexes are the result of tectonic processes that expose the lower crust and even the upper mantle. These rocks are quite different from the volcanic rocks that are usually at spreading ridges; one of the hypotheses we are testing is that these unusual rocks influence the type of hydrothermal mineralisation.

The ROV sea floor operations and sampling has enabled us to gain a clearer understanding of the host rocks and their geographical extent. This has allowed a more detailed picture of the geological processes controlling the location and formation of past and present vent systems in the area. This has revealed a history and extent of past venting across the Von Damm site that has been quite a surprise.

The discovery and study of an active hydrothermal system developed on an oceanic core complex represents something of a first, and we are really looking forward to further advancing our understanding of these unique geological systems.

By Steve Roberts

Steve and Alex examine a rock sample recovered from the ocean floor