Volcanic "pipe system" creates black smoker

Geologists discover keys to mantle-crust interaction on oceanic ridges

Tube worms of the species Riftia pachyptila © University of Oregon
Read out

Black smokers, the geysers of the deep sea, are found mainly in the volcanically active regions of the seabed. For years the common doctrine assumes that only the magma production as "drive" for these hydrothermal vents is crucial. Now, researchers in Nature report that a special volcanic "pipe system" explains why one volcano produces black smokers, while another does not.

Hydrothermal vents occur most often where the plates of the earth's crust move apart, such as the mid-ocean ridge and where magma swells to the surface at the same time. That this coincidence is crucial has now been discovered by Douglas R. Toomey of the University of Oregon and colleagues from four other research organizations. For years they have been studying the geology of the seabed in the Eastern Pacific.

Secret of the chimneys in the Eastern Pacific

Their study area extended along the geologically very fast moving East Pacific Rim, a region that includes two major transform perturbations, large short-lived spreading zones, and numerous axis shifts and rock dislocations. To analyze the processes in the upper coat, they let a kind of portable tomograph down to the seabed. These carried out seismic measurements, from which later, as in a tomographic image, sectional images of Magmabewegungen were created by the mantle into the earth's crust.

The data show that segmentation of the oceanic ridge is closely related to asymmetry of the cladding current. "The mantle moves differently than the plates, so it has a strong impact on the reorganization of the plate boundary, " Toomey explains. "If people have looked at these systems in the past, they saw an area that is volcanically and hydrothermally active. They therefore assumed that the magma supply is particularly large here and a lot of it comes to the surface. "

Alignment of magma upstream and plate boundary crucial

{2r} display

"Our study, on the other hand, shows that it is the piping system rather than the amount of magma available to control the eruptions. In other words, how the magma develops as it flows through the pipe system determines whether or not it exits to the surface. Only where the magma outflow and the plate boundary meet does it penetrate regularly ig magma through the crust upwards. If the "conduction system" between the mantle and the crust does not match, the magma will cool down and move more sideways. The largest part then remains under the seabed.

"The mantle is moving in one direction, the plate boundary is trying to keep up, " Toomey explains. We have been talking for years about passive flow models for these oceanic plate boundaries that the magma effluents from the mantle passively follow the plate motion. But now we see that the sheath current is not completely passive and is not controlled only by the overlapping plates. Instead, the mantle provides the driving force for the plate movement. This realization is remarkable and surprising

(University of Oregon, 22.03.2007 - NPO)