One of the most fundamental processes in geology is the formation of new crust at mid-ocean ridges. This phenomenon, driven by plate tectonics, has been extensively studied over the years, but there are still many aspects that remain poorly understood.
Recently, a team of scientists from France was able to remotely monitor a significant event on the border between the Australian and Antarctic plates using a newly installed monitoring system.
The site where the events took place is located in the Amsterdam–Saint Paul Plateau, a seafloor feature that rises above the deep ocean plane. The rift between the two plates runs right through the middle of this plateau, which is interpreted as being driven by the presence of a deep ocean hotspot. Despite the indications of tectonic activity, only two volcanic islands are present in the area: Amsterdam and St. Paul.
The team took advantage of a French research vessel to deploy a series of underwater monitoring stations along the spreading zone. These included hydrophones that could provide rough locations of seismic events and transmitters that allowed them to track any changes in the distance between monitoring sites. Later visits from the French supply ships performed three-dimensional mapping of the seafloor in the area.
The data collected by the team shows that most of the spreading occurred in a relatively short time window, with some key events happening without any obvious seismic activity. The researchers say that this sort of activity is typical of the formation of dykes, thin but long and tall structures formed by the intrusion of molten rock.
The monitoring system also detected a drop in sensors located in the valley at the center of the spreading region, which accelerated until the sensors were sinking at a rate of about 5 centimeters a minute before slowing. However, subsidence continued well after the initial events, with a total of 4.2 meters over a six-day period.
The researchers interpret this as a magma reservoir beneath the ridge draining. Consistent with that, the temperature of the water at the nearby instruments started rising at the same time, suggesting that magma was interacting with the seawater. The team also observed that instruments on opposite sides of the central valley started moving farther apart, in some cases by well over a meter.
After the site had returned to background levels of activity, a new imaging of the site took place. The resolution is quite poor, but even so, there are some sites that were over 90 meters higher than they had been during the previous mapping. The researchers estimate the total amount of new material at about 150 million cubic meters.
To understand how all these events might be connected, the team performed modeling of the events using different configurations of magma source, dyke extent, and fault geometries. Only a small number of models could produce the sorts of changes the instruments picked up.
The findings provide new insights into the process of plate tectonics and the formation of new crust at mid-ocean ridges. The study highlights the importance of continued monitoring and research in this field, which can help us better understand the processes that shape our planet.
Source: Original article