Garnet

17 Mar 2018

The assumption is that Plate Tectonics is a fact at https://phys.org/print440354779.html ... which must also pertain to the origin of garnet. This mineral or rock is said to help us understand how subduction takes place. As one plate moves under another one water is squeezed out of minerals to lubricate earthquakes and fuel volcanoes (or so we are told). A spectroscopic investigation of garnet containing fragments of quartz is said to have explained the puzzle. The main point to take onboard is that powerful earthquakes at plate boundaries as well as volcanoes require water - but where does the water come from? No mention is made of the discovery of reserves of water in the lower crust and upper mantle -as much water as exists in the world's oceans. Instead, a more complicated source is proposed - water squeezed out of rocks (which produces other rocks such as the garnets).

As one plate is pushed under another sediments and minerals are carried deep into the Earth, it is believed, and the pressure and temperatures increase with depth. Liquid water is squeezed from the pores or fault lines in rocks but minerals such as the micas, serpentine, and  chlorites contain water as part of their mineral structure. When such minerals succomb to increased temperature and pressure they release water. This fact is used to run the modellng or simulation. In the process new minerals are formed - such as the garnets. It is produced by the breakdown of water bearing chlorites. Garnet forms under pressure we are told and it can harbour other minerals in a vice like grip (as as the quartz). The researchers used garnets found in the Aegean region . and samples were taken to a laboratory where they were subject to Raman spectroscopy which uses laser light to shine on the sample. The energy of photons is shifted up or down based on the interaction between the light and the sample - the difference between the frequency of the outgoing and the returning light provides a signature. Quartz has a well known signature but the quartz attached to the garnet had a higher value - indicating pressure on the grain. The researchers were able to use the higher signature  to indicate the depth at which the garnet crystalised around the quartz. This is said to prove the garnet was formed at a low depth in the region where volcanoes and earthquakes are said to originate. Does this prove subduction takes place?