Final answer:
Subduction derived magma beneath a thick continental crust leads to partial melting, contributing to the creation of magmas that ascend and cause volcanism. This process forms volcanic arcs and can lead to the uplift and creation of mountain ranges, with the potential exposure of ophiolites. The continental crust, being thick and less dense, undergoes deformation, thickening, and uplift rather than subduction.
Step-by-step explanation:
When subduction derived magma encounters thick continental crust, several geological processes take place. First, the oceanic plate, being denser, subducts beneath the continental plate at a subduction zone, where it is subjected to high pressures and temperatures. This leads to the melting of the subducted plate several hundred kilometers below the surface.
Subsequently, as the subducted oceanic crust partially melts, it can contribute to the creation of magmas that are less mafic than the original basaltic composition. If this magma ascends into the thick continental crust, it may cause volcanism and the formation of volcanic arcs parallel to the subduction zone. These arcs are often comprised of volcanoes that feature a range of eruptive styles and compositions, from mafic to felsic.
Continental crust primarily composed of granite is less dense and thicker compared to oceanic crust, which is predominantly basaltic. As such, rather than being subducted, continental crust deforms, thickens, and often results in the uplift and creation of mountain ranges. The collision of continental crust also leads to the exposure of ophiolites, sequences of oceanic crust that are thrust onto the continental margins during subduction.
Continent-continent collisions and the resulting mountain building processes can also expose deep-seated rocks through uplift and erosion, creating complex geologic structures that include a combination of igneous, metamorphic, and sedimentary rocks.