One of the main mechanisms participating in theis here who sees a pass under another plate to be recycled within the . Subduction zones are generally associated with intense , often of the explosive type. In addition, most current mountain ranges, or the Himalayas, result from a continental collision which followed the closing of an ocean by the action of a subduction zone. These mountain ranges thus contain many clues that allow us to study, indirectly, the complex mechanism of subduction zones.
The mantle absorbs large amounts of water at subduction zones
Many parameters come into play and their variations make each subduction zone a unique dynamic system.
One of these parameters is water. It is indeed an essential element that will directly impact the fusion capacity of the mantle and thebut also the behavior of the during ascent and .
It has long been known that subduction zones represent highly hydrated environments. As it plunges into the mantle, the subducting plate carries with it an enormous amount ofwaterlogged oceans. This water will significantly hydrate the rocks of the mantle and directly influence the formation of magma. The issued by the on the surface thus bear the signature of this which will also determine the style . More the are hydrated, the more . This explains why .
Finding the initial water content of a magma, a complicated problem
Until now, analysis of volcanic rocks suggested that the mantle, in this context of subduction, contained about 4% water (per unit weight). A new study, however, questions this value, putting forward the idea that the signature present in the volcanic rocks would not be representative of the actual water content of the initial magma. For the authors of the study published init indeed appears likely that certain processes – either at the time of the rapid rise of the magma, or when it arrives at the surface – somehow mask the original water content of the magma. magmatic.
To try to find the exact value of the quantity of water, the team of researchers was interested in a certain type ofthem , which unlike volcanic rocks do not crystallize on the surface but deep within the crust. A new analytical method was also developed to study the composition of plutonic rock samples from and updates according to the tectonic deformation that this immense collision zone undergoes.
A more hydrated coat than we thought
The crystals of these rocks thus show much less signs of alteration than volcanic rocks, exposed to the elements on the surface. Their results show in the end that it is not 4, but more than 8% of water (by weight) that the magma would contain before its crystallization.
These results also provide a better understanding of the formation of deposits ofgold or , which requires a large amount of water. The 4% previously estimated was not enough to explain the formation of of . The problem is now solved. These ore deposits would thus form from magmatic fluids very rich in water (12 to 20%) which would have separated from the initial magma at the time of its crystallization. Understanding the generation of these super-hydric magmatic liquids is therefore of major interest for the search for new deposits.