Compare And Contrast How Magmas Are Generated At Mid-Ocean

1450 WordsMar 28, 20176 Pages
COMPARE AND CONTRAST HOW MAGMAS ARE GENERATED AT MID-OCEAN RIDGES AND SUBDUCTION ZONES. According to Middlemost (1988)’s basic definition, magma is a heated rock-forming substance that is created within a planet and exists only below Earth. When magma escapes to the Earth’s surface and is extruded, they are known as lavas. Grotzinger and Jordan (2010) suggests that magma mainly comes from the asthenosphere- the upper part of the mantle. Magmas are usually generated when rocks are under the right temperature and pressure conditions to undergo partial melting (Grotzinger and Jordan, 2010). At high temperatures and low enough pressures, rocks would reach its melting point easily. It is known for a fact that temperature increases with depth…show more content…
Subduction zone magmas are formed by convergent plate boundaries between oceanic-continental plates or oceanic-oceanic plates (at least one tectonic plate has to be oceanic) (see Fig.1). According to Grotzinger and Jordan (2010), when the oceanic lithosphere gets subducted, there is fluid induced melting occurring to the mantle wedge. Therefore, this generates magmas of varying composition. From Prichard et al.’s findings, mid-ocean ridge magmas are usually basaltic in composition whereas subduction zone magmas are andesitic and more silicic. Subduction zone magma compositions also depend on the materials being subducted. Hence, in terms of chemical composition, the subduction zone magmas and are definitely more varied compared to the mid-ocean ridge magmas. Subduction zone magmas range from basaltic to rhyolitic- with andesitic magmas being the most common (Grotzinger and Jordan, 2010). Fig.2 Geothermal gradient varying in different geological settings: also showing the solidus for MOR and subduction zone mantle rock MAGMA GENESIS Middlemost (1988) states that in the mantle at depths between 60-250 km (i.e. the low-velocity zone), magma can be generated through either of the 3 ways; when you add

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