Metamorphism

• The changes in the Earth's crust are driven by solid-state reactions and deformation processes.
• Magma is a mixture of molten and semi-molten rock found beneath the surface of the Earth, usually made up of a hot liquid base, minerals crystallized by the melt, solid rocks incorporated into the melt from the surrounding confines, and dissolved gases.
• The least-dense magma rises to the top, while the densest magma sinks near the bottom of the magma chamber.
• If the magma reaches the surface of the Earth, it is ejected by a volcano or other vent and is then called lava.
• Over time, the magma may cool and solidify to form a pluton or large igneous intrusion.
• If the magma is ejected onto the Earth’s surface as lava, it cools and solidifies to form igneous rock.
• The igneous rock undergoes weathering or breakdown to form sediment.
• The deposited sediment undergoes lithification, the processes that turn it into a rock.
• If the sedimentary rock is buried beneath more sediment, the heat and pressure of burial can cause metamorphism, transforming the sedimentary rock into a metamorphic rock.
• Magma can also bring heat from the mantle as it rises up into the crust, raising the temperature of the surrounding crustal rock.
• Magma can affect the Earth’s crust in several ways: it can force overlying rock apart and enter the newly formed fissures, cause blocks of rock to break off and sink into the magma chamber, or melt the rock into which it intrudes.
• On the other hand, high pressures, particularly when applied unequally from different directions (differential stress), can lead to the deformation and reorientation of minerals, contributing to changes in texture.
• These fluids, often rich in water and carbon dioxide, can facilitate the transport of ions between minerals, enabling chemical reactions and the growth of new minerals.
• The presence of hot, chemically reactive fluids can also play a crucial role in metamorphism.
• During metamorphism, the original minerals in the rock, known as the protolith, can become unstable and start to react with each other in response to changes in temperature, pressure, and the presence of hot fluids.
• These reactions can lead to the growth of new minerals that are stable under the new metamorphic conditions.
• Metamorphism can also lead to significant changes in the texture of rocks.
• The new minerals can have different chemical compositions compared to the original minerals, reflecting the changes in the environmental conditions.
• For instance, the rock may undergo recrystallization, where small mineral grains combine to form larger ones, resulting in a more coarse-grained texture.
• The rock may develop a foliated texture, characterized by a layered or banded appearance, due to the alignment of platy or elongated minerals under directional pressure.
• Metamorphism is a geological process that involves the transformation of one rock type into another due to changes in pressure and temperature, and the presence of chemically reactive fluids.
• The changes in mineral components and texture are largely driven by variations in pressure and temperature.
• High temperatures can facilitate the growth of new minerals by providing the energy needed for chemical reactions.
• These changes occur in the solid state, meaning that the rock does not melt during metamorphism.
• Magma can also form through decompression melting, which involves the upward movement of Earth’s mostly solid mantle to an area of lower pressure.
• Magma can be created when hot, liquid rock intrudes into Earth’s cold crust.
• Intrusion: In some cases, rising magma can cool and solidify without reaching the surface.
• Intrusive Magmatic Activity: The theory proposes that igneous rocks such as gabbro, diorite, granite, and pegmatite originated from intrusive magmatic activity.
• Driving Forces: Plutonism is driven by heat concealed within Earth’s interior and occurs over the course of thousands if not millions of years.
• Instead, the cooled and solidified igneous mass crystallizes within the crust to form an igneous intrusion.
• Formation of Sedimentary Rock: The eroded rocks are re-formed into layers of sedimentary rock by heat and pressure, and raised again.
• Magma Formation: Magma from the mantle or lower crust rises through the crust towards the surface.
• Weathering and Erosion: There is a continuing gradual process of weathering and erosion wearing away rocks, which were then deposited on the sea bed.
• Intrusion of Molten Masses: This process is usually accompanied by the intrusion of molten masses that harden to form igneous rock (granites).
• Solidification: Magmas that reach the surface and solidify form extrusive landforms.
• Viscous (thick) magma produces volcanoes characterized by explosive eruptions, while non-viscous (runny) magma produces volcanoes characterized by effusive eruptions pouring large amounts of lava onto the surface.
• Eruption: If magma reaches the surface, its behavior depends on the viscosity of the molten constituent rock.
• Driving Forces: Movement of molten rock in the mantle, caused by thermal convection currents, coupled with gravitational effects of changes on the earth’s surface (erosion, deposition, even asteroid impact and patterns of post-glacial rebound) drive plate tectonic motion and ultimately volcanism.
• Plutonism is the geologic theory that the igneous rocks forming the Earth originated from intrusive magmatic activity.
• As the liquid rock solidifies, it loses its heat to the surrounding crust, melting the surrounding rock into magma.