Andesite and lava
Category£º Andesite and lava |
Andesite is an extrusive igneous rock consisting primarily of plagioclase plus pyroxene and/or hornblende. Biotite, magnetite, quartz and sphene are common constituents.
Andesite has the equivalent composition to the plutonic igneous rock, diorite.
Andesite is named after the Andes mountain range. These rocks are found near the subduction zones of ocean tectonic plates, along continental margins.
Andesite forms at convergent plate margins and is thought to be the product of partial melts of the water-rich subducting oceanic crustal basalts or of the intervening wedge of lower crustal rocks above the subducting plate. While andesite is common in younger arc systems such as the Cascades, it is nearly absent in the older Sierra Nevadas, possibly a consequence of erosion.
