Glossary

Basalt

Fact Sheet:

Chemical Composition: Primarily composed of plagioclase feldspar, pyroxene, and olivine (low in silica, rich in iron and magnesium)
Hardness: 6 on the Mohs scale
Crystal System: Basalt is a fine-grained igneous rock, typically displaying an aphanitic texture
Color Varieties: Dark gray, black, greenish-black, brown
Major Localities: Iceland, Hawaii (USA), India, Russia, and the Pacific Ocean floor
Common Uses: Construction (aggregate, road base), monuments, insulation, and as a component of volcanic activity research

Introduction: Basalt is the most common extrusive igneous rock on Earth, covering more than 70% of the planet’s surface. Formed through the rapid ...

^MMetamorphic Differentiation

Metamorphic differentiation is the process by which compositional banding and mineral segregation occur in a rock during metamorphism. This process is important for understanding the development of gneissic textures, the formation of mineral deposits, and the metamorphic evolution of rocks.

Reference: Ashworth, J. R. (1985). “Migmatites.” Chapman and Hall.

^MMetamorphic Facies

Metamorphic facies are groups of mineral assemblages that form under similar pressures and temperatures during metamorphism. Each facies corresponds to specific tectonic settings and helps geologists interpret the metamorphic conditions and the tectonic history of a region.

Reference: Bucher, K., & Grapes, R. (2011). “Petrogenesis of Metamorphic Rocks.” Springer.

^MMetamorphic Grade

Metamorphic grade refers to the degree of metamorphism that a rock has undergone, typically indicated by the presence of specific mineral assemblages that form under particular temperature and pressure conditions. The concept of metamorphic grade is essential for understanding the thermal history and tectonic setting of metamorphic rocks.

Reference: Bucher, K., & Grapes, R. (2011). “Petrogenesis of Metamorphic Rocks.” Springer.

^MMetamorphism

Metamorphism is the process by which rocks undergo physical and chemical changes due to variations in temperature, pressure, and the presence of chemically active fluids, without melting. This process forms metamorphic rocks and is significant in understanding the Earth’s crust’s evolution and tectonic activity.

Reference: Yardley, B. W. D. (1989). “An Introduction to Metamorphic Petrology.” Longman.

^MMetasomatic Alteration

Metasomatic alteration refers to the process by which a rock’s mineral composition is altered due to the introduction of new chemical components through fluid interactions. This alteration can lead to the formation of economically important mineral deposits and is key to understanding hydrothermal systems.

Reference: Dale, J. (2011). “Fluid-Rock Interactions during Metasomatism.” Elements, 7(5), 315-320.

^MMetasomatism

Metasomatism is the process by which a rock’s chemical composition is altered through the introduction or removal of fluids. This process can lead to significant changes in mineralogy and texture and is important in the formation of ore deposits and the evolution of the Earth’s crust.

Reference: Dale, J. (2011). “Fluid-Rock Interactions during Metasomatism.” Elements, 7(5), 315-320.

^MMid-Ocean Ridge

A mid-ocean ridge is an underwater mountain range formed by plate tectonics where new oceanic crust is created by volcanic activity as tectonic plates diverge. These ridges are key features of the ocean floor and are crucial in understanding seafloor spreading, plate tectonics, and the Earth’s geodynamics.

Reference: Macdonald, K. C. (1982). “Mid-Ocean Ridges: Fine Scale Tectonic, Volcanic and Hydrothermal Processes within the Plate Boundary Zone.” Annual Review of Earth and Planetary Sciences, 10(1), 155-190.

^MMonocline

A monocline is a type of fold in rock layers where the strata are inclined in one direction, creating a step-like structure. Monoclines are often associated with faulting and are important in understanding structural geology, the formation of basins, and the tectonic history of an area.

Reference: Stewart, J. H., Poole, F. G., & Wilson, R. F. (1972). “Stratigraphy and Origin of the Chinle Formation and Related Upper Triassic Strata in the Colorado Plateau Region.” USGS Professional Paper 690.

^MMonogenetic Volcano

A monogenetic volcano is a type of volcano that erupts only once, producing a small volcanic edifice such as a cinder cone, maar, or tuff ring. These volcanoes are important for understanding volcanic processes, the hazards they pose, and the nature of magma sources in various tectonic settings.

Reference: Valentine, G. A., & Gregg, T. K. P. (2008). “Continental Basaltic Volcanoes—Processes and Problems.” Journal of Volcanology and Geothermal Research, 177(4), 857-873.

^MMoraine

A moraine is an accumulation of glacial debris (till) formed by the movement of a glacier. Moraines can be found in various forms, such as lateral, medial, and terminal, depending on their position relative to the glacier. They are important indicators of past glacial activity and are used to reconstruct the history of glaciation.

Reference: Benn, D. I., & Evans, D. J. A. (2010). “Glaciers and Glaciation.” Routledge.

^MMud Breccia

Mud breccia is a sedimentary rock composed of angular fragments of mudstone or shale cemented together. It typically forms in tectonically active regions where mud is fractured and re-cemented due to faulting or other forms of deformation. Mud breccia provides insights into the geological history of deformation and sedimentation in an area.

Reference: Potter, P. E., Maynard, J. B., & Depetris, P. J. (2005). “Mud and Mudstones: Introduction and Overview.” Springer.

^MMud Crack

Mud cracks are fractures that form in drying mud as it contracts. These features are preserved in sedimentary rocks and provide important evidence of past environmental conditions, such as periodic drying in wetland or shallow marine environments. They are often found in association with evaporite deposits.

Reference: Boggs, S. (2009). “Petrology of Sedimentary Rocks.” Cambridge University Press.

^MMud Volcano

A mud volcano is a geological formation created by the expulsion of mud, water, and gases from the Earth’s subsurface, typically in areas of tectonic activity. Mud volcanoes are important for understanding the release of subsurface fluids, the dynamics of gas migration, and their potential as indicators of hydrocarbon reservoirs.

Reference: Mazzini, A., & Etiope, G. (2017). “Mud Volcanoes as a Source of Energy: From Tectonics to Hydrocarbons.” Geoscience Frontiers, 8(6), 1477-1489.

^MMudstone

Mudstone is a fine-grained sedimentary rock composed primarily of clay and silt-sized particles. It is often formed in low-energy environments such as deep marine basins, lakes, and floodplains. Mudstone is significant in understanding depositional environments, the preservation of fossils, and the geochemical cycles of elements.

Reference: Potter, P. E., Maynard, J. B., & Depetris, P. J. (2005). “Mud and Mudstones: Introduction and Overview.” Springer.

^MMylonite

Mylonite is a fine-grained, foliated rock that forms in fault zones due to intense shearing and deformation. The study of mylonites is important in understanding the mechanics of faulting, the conditions of deformation in the Earth’s crust, and the evolution of tectonic boundaries.

Reference: Passchier, C. W., & Trouw, R. A. J. (2005). “Microtectonics.” Springer.

^NNappe

A nappe is a large sheet-like body of rock that has been thrust over other rocks on a low-angle fault, often over great distances. Nappes are typically found in mountain ranges and are important in understanding the processes of continental collision, mountain building, and the structural geology of orogenic belts.

Reference: Suppe, J. (1985). “Principles of Structural Geology.” Prentice Hall.

^NNappe Fold Structure

Nappe fold structure refers to the large-scale folds associated with the formation of nappes during compressional tectonics. These structures are key features in understanding the deformation processes involved in orogeny and the tectonic evolution of mountain belts.

Reference: Ramsay, J. G., & Huber, M. I. (1987). “The Techniques of Modern Structural Geology, Volume 2: Folds and Fractures.” Academic Press.

^NNeotectonics

Neotectonics refers to the study of recent and ongoing movements and deformations of the Earth’s crust, typically occurring in the late Cenozoic era. This field is important for understanding current tectonic activity, the formation of landforms, and assessing seismic hazards.

Reference: Stewart, I. S., & Hancock, P. L. (1994). “Neotectonics.” In: Hancock, P. L. (Ed.), Continental Deformation. Pergamon, pp. 370-409.

^NNeptunism

Neptunism is an obsolete geological theory that proposed all rocks, including igneous rocks, were formed by the crystallization of minerals in the early Earth’s oceans. Although discredited by modern geology, Neptunism played a role in the development of geological thought and the understanding of rock formation processes.

Reference: Pancaldi, G. (1983). “Neptunism and the Neptunists: A Controversy in Eighteenth-Century German Geology.” History of Science, 21(2), 155-189.

^NNeritic Zone

The neritic zone is the shallow part of the ocean that extends from the low tide mark to the edge of the continental shelf. It is characterized by abundant sunlight, relatively stable temperatures, and high biological productivity. This zone is significant for marine ecology, sedimentation, and the study of coastal processes.

Reference: Thurman, H. V., & Trujillo, A. P. (2010). “Essentials of Oceanography.” Prentice Hall.

^NNonconformity

A nonconformity is a type of unconformity in which sedimentary rocks lie on top of older, eroded igneous or metamorphic rocks. This feature indicates a significant gap in the geological record and is important for understanding the history of erosion, deposition, and tectonic events in a region.

Reference: Press, F., & Siever, R. (2001). “Understanding Earth.” W. H. Freeman.

^NNonconformity

Reference: Press, F., & Siever, R. (2001). “Understanding Earth.” W. H. Freeman.

^NNormal Fault

A normal fault is a type of fault where the hanging wall moves downward relative to the footwall, typically associated with extensional tectonic regimes. Normal faults are significant in understanding the processes of crustal extension, the formation of rift valleys, and the development of sedimentary basins.

Reference: Twiss, R. J., & Moores, E. M. (2007). “Structural Geology.” W. H. Freeman.

^SArchives: Glossary

A subterranean river is an underground watercourse, often formed through the dissolution of soluble rocks, leading to the development of caves and karst landscapes. These rivers are significant in hydrogeology for understanding groundwater flow, aquifer systems, and the evolution of cave systems.

Reference: Ford, D. C., & Williams, P. W. (2007). “Karst Hydrogeology and Geomorphology.” John Wiley & Sons.