This document discusses the role of water in young oceanic lithosphere and subduction zones, highlighting its impact on density and volcanic activity.
Extract
[...] The document 3 presents a graph of the experimental results of the state of the mantle peridotites as a function of some of their characteristics (temperature, pressure). We note that to obtain a magma (i.e. the appearance of the liquid state), the solidus line must be crossed. Under normal conditions, the solidus is 'dry' and is only crossed for temperatures between approximately 1,100°C at the surface (i.e GPa), 1,300°C at 80 km depth (2.5 GPa) and 1,500°C at 160 km depth (i.e GPa). [...]
[...] We deduce that the density of the oceanic lithosphere increases as it ages. The increase in density occurs due to oceanic hydrothermalism, i.e., the infiltration of seawater through fractures on either side of the ridge. Thanks to document we can say that the infiltrated water will then react with the minerals of the oceanic lithosphere rocks (basalts, gabbros) and will transform these minerals, thus increasing their density. This is a metamorphic transformation. The gabbros (and basalts) will then become green schists (considered near the ridges). [...]
[...] What is the role of water in both young oceanic lithosphere and at the subduction zone level? Water and Subduction Zones The volcanoes of subduction zones emit water-rich gases as well as rocks with hydrated minerals. However, these volcanoes are generally present on the surface of oceanic lithospheres at the edge of subduction zones, sometimes at distant locations from a water source. We can then wonder where the water present in this subduction volcanism comes from. The documentary study below will allow us to show the role of water both in young oceanic lithosphere and at the level of the subduction zone. [...]
