Subduction zone, along the Geothermal gradient, and at great depth below the volcanoes
The rocks that are formed by high pressure and temperature conditions are generally formed in the environment such as the subduction zone, geothermal gradient and at large depth below the earth's surface. These are considered to be the high grade rocks. These are comprised of minerals that forms at a higher temperature and pressure conditions.
In the subduction zone, the rocks are formed under extremely high temperature and pressure condition, comprising of higher grade minerals.
The geothermal gradient refers to the increasing temperature with increasing depth, where the high grade minerals are formed at high temperature condition and pressure condition.
In the areas below the volcanic region at greater depths, the rocks are comprised of hard and resistant minerals.
when the flood or landslide flows theremnants of plants and animals are taken to the sea and ocean then due to high pressure and temperature they forms fossils in sedimentary rocks and due to the anaerobic condition under the fosdils gets decayed and it forms the layer of mineral. so we can say thatminerals are formed in anaerobic condition under sedimentary rocks.
Explanation: Probably geothermal fields and deep oceans where volcanic eruptions occur.