|MadSci Network: Earth Sciences|
Dear Ashley, The plates whose collision is uplifting the Andes Mountains are the South American plate and the Nazca plate. The Nazca plate extends eastwards from the East Pacific Rise, a constructive plate boundary at which new ocean floor is being formed. The Nazca plate is moving eastwards from the East Pacific Rise. The South American plate is moving westward from the Mid Atlantic Ridge. Where these two plates meet the Nazca plate is being subducted beneath the South American plate. The Andes Mountains lie above the subduction zone. The subducting slab is heated by friction and by the hot mantle into which it is descending. This heating causes partial melting of the slab and the overlying mantle, generating magma that rises into the crust. Most of the magma cools and solidifies in the lower crust, adding to its volume – a process known as underplating. Some of it rises into the upper part of the crust and may erupt to form the volcanoes of the Andes range. The high heat flow above the subducting slab also reduces the density of the crust, causing the crust to become isostatically buoyant. Both underplating and the isostatic uplift of the region contribute to the formation of the Andes. I hope this answers your question. Best wishes, David Scarboro
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