Tiburon Peninsula

The mineral lawsonite was first described from an occurrence on the Tiburon Peninsula. Lawsonite is a hydrous calcium aluminium sorosilicate mineral. Lawsonite has attracted considerable interest over the last few years because of its importance as a marker of moderate pressure (6-12 kb) and low temperature (300 - 400 °C) conditions in nature. This mainly occurs along continental margins (subduction zones). Lawsonite is a significant metamorphic mineral as it can be used as an index mineral for high pressure conditions. Index minerals are used in geology to determine the degree of metamorphism a rock has experienced. Lawsonite is known to form in high pressure, low temperature conditions, most commonly found in subduction zones where cold oceanic crust subducts down oceanic trenches into the mantle. The initially low temperature of the slab, and fluids taken down with it manage to depress isotherms and keep the slab much colder than the surrounding mantle, allowing for these unusual high pressure, low temperature conditions.

Dromos