Answer
Two plate tectonic settings in which magma is commonly generated are:
1. Divergent Plate Boundaries: Divergent plate boundaries occur where two lithospheric plates move away from each other. As the plates separate, the underlying asthenosphere rises to fill the gap. The decrease in pressure associated with the divergence causes decompression melting of the mantle rock. Magma is generated and rises to the surface, leading to the formation of new crust. This process occurs prominently at mid-ocean ridges, where the oceanic plates diverge and create underwater volcanic activity. It also occurs in continental rift zones, where the stretching and thinning of the lithosphere can result in volcanic activity.
2. Convergent Plate Boundaries: Convergent plate boundaries occur where two lithospheric plates collide. When an oceanic plate collides with a continental plate or another oceanic plate, the denser oceanic plate typically subducts beneath the less dense plate. The subducting plate descends into the mantle, and as it reaches greater depths, it experiences increasing pressure and temperature. This leads to the release of volatiles (primarily water) from the subducting plate. The addition of these volatiles to the mantle wedge above the subducting plate lowers the melting point of the mantle rocks, resulting in the generation of magma. This magma can rise to the surface and produce volcanic arcs such as the Pacific Ring of Fire.
In both divergent and convergent plate boundaries, the processes associated with plate tectonics create the conditions necessary for magma generation and subsequent volcanic activity.
Work Step by Step
Two plate tectonic settings in which magma is commonly generated are:
1. Divergent Plate Boundaries: Divergent plate boundaries occur where two lithospheric plates move away from each other. As the plates separate, the underlying asthenosphere rises to fill the gap. The decrease in pressure associated with the divergence causes decompression melting of the mantle rock. Magma is generated and rises to the surface, leading to the formation of new crust. This process occurs prominently at mid-ocean ridges, where the oceanic plates diverge and create underwater volcanic activity. It also occurs in continental rift zones, where the stretching and thinning of the lithosphere can result in volcanic activity.
2. Convergent Plate Boundaries: Convergent plate boundaries occur where two lithospheric plates collide. When an oceanic plate collides with a continental plate or another oceanic plate, the denser oceanic plate typically subducts beneath the less dense plate. The subducting plate descends into the mantle, and as it reaches greater depths, it experiences increasing pressure and temperature. This leads to the release of volatiles (primarily water) from the subducting plate. The addition of these volatiles to the mantle wedge above the subducting plate lowers the melting point of the mantle rocks, resulting in the generation of magma. This magma can rise to the surface and produce volcanic arcs such as the Pacific Ring of Fire.
In both divergent and convergent plate boundaries, the processes associated with plate tectonics create the conditions necessary for magma generation and subsequent volcanic activity.
