What processes can change sedimentary rock into metamorphic rock?
A. Subduction and high pressure
B. Erosion and lithification
C. Heating and cooling
D. Uplift and erosion
The correct answer and explanation is:
The correct answer is A. Subduction and high pressure.
Sedimentary rock can be transformed into metamorphic rock through a process known as metamorphism. This occurs primarily under conditions of high pressure, temperature, and chemically active fluids, typically at significant depths within the Earth’s crust. The process begins when sedimentary rocks are subjected to tectonic forces, such as those found at convergent plate boundaries, particularly in subduction zones.
At subduction zones, one tectonic plate is forced beneath another, pushing the sedimentary rock deeper into the Earth’s crust. As the rock descends, it is exposed to increasing pressure and temperature. The heat comes from the surrounding hot mantle, while the pressure increases due to the overlying rocks. These extreme conditions cause the minerals in the sedimentary rock to become unstable and re-crystallize, forming new minerals and textures. This process can lead to the formation of foliated metamorphic rocks like slate, schist, and gneiss, or non-foliated metamorphic rocks like marble and quartzite, depending on the conditions and the original sedimentary rock.
The key element here is pressure and temperature. Pressure causes the minerals to compress and align in a particular orientation, while heat accelerates the chemical reactions that alter the minerals. This combination of factors, driven by tectonic forces at subduction zones, is what drives the transformation from sedimentary to metamorphic rock.
In contrast, erosion and lithification (B), heating and cooling (C), and uplift and erosion (D) are part of different geological processes. Erosion and lithification are involved in the formation of sedimentary rock, while heating and cooling typically relate to igneous processes. Uplift and erosion may expose metamorphic rocks but do not directly contribute to their formation.