materiały: Rock (geology)

Evidence: 83 • authority: 72

Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than 150 to 200 °C (300 to 400 °F) and, often, elevated pressure of 100 megapascals (1,000 bar) or more, causing profound physical or chemical changes. During this process, the rock remains mostly in the solid state, but gradually recrystallizes to a new texture or mineral composition. The protolith may be an igneous, sedimentary, or existing metamorphic rock. Metamorphic rocks make up a large part of the Earth's crust and form 12% of the Earth's land surface. They are classified by their protolith, their c…

Evidence: 66 • authority: 72

Partial melting is the phenomenon that occurs when a rock is subjected to temperatures high enough to cause certain minerals to melt, but not all of them. Partial melting is an important part of the formation of all igneous rocks and some metamorphic rocks (e.g., migmatites), as evidenced by a multitude of geochemical, geophysical and petrological studies. The parameters that influence partial melting include the composition of the source rock, the pressure and temperature of the environment, and the availability of water or other fluids. As for the mechanisms that govern partial melting, the main are decompression melting and flux melting. Decompression melting occurs when rocks are brough…

Evidence: 66 • authority: 72

Gneiss ( NYSE) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. This rock is formed under pressures ranging from 2 to 15 kbar, sometimes even more, and temperatures over 300 °C (572 °F). Gneiss nearly always shows a banded texture characterized by alternating darker and lighter colored bands and without a distinct cleavage. Gneisses are common in the ancient crust of continental shields. Some of the oldest rocks on Earth are gneisses, such as the Acasta Gneiss.

Evidence: 59 • authority: 72

Igneous rock (igneous from Latin igneus 'fiery'), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rocks are formed through the cooling and solidification of magma or lava. The magma can be derived from partial melts of existing rocks in a terrestrial planet's mantle or crust. Typically, the melting is caused by one or more of three processes: an increase in temperature, a decrease in pressure, or a change in composition. Solidification into rock occurs either below the surface as intrusive rocks or on the surface as extrusive rocks. Igneous rock may form with crystallization to form granular, crystalline rocks, or without crystall…

Evidence: 45 • authority: 72

The Pressure-Temperature-time path (P-T-t path) is a record of the pressure and temperature (P-T) conditions that a rock experienced in a metamorphic cycle from burial and heating to uplift and exhumation to the surface. Metamorphism is a dynamic process which involves the changes in minerals and textures of the pre-existing rocks (protoliths) under different P-T conditions in solid state. The changes in pressures and temperatures with time experienced by the metamorphic rocks are often investigated by petrological methods, radiometric dating techniques and thermodynamic modeling. Metamorphic minerals are unstable upon changing P-T conditions. The original minerals are commonly destroyed du…

Evidence: 38 • authority: 88

Supplemental Material: Late orogenic high-temperature overprint in ultra-high pressure or high pressure [(U)HP] metamorphic rocks of the North Qinling Orogen, Central China: Insights into the geodynamics of the exhumation of (U)HP metamorphic rocks. <p>Text S1: Analytical methods of whole-rock major element analyses, mineral chemistry measurements, zircon U-Pb dating and trace element measurements; Figure S1: P/T-H2O/O diagrams for samples QL2105 and QL2106; Figure S2: P–T diagram calculated with an effective bulk-rock composition for sample QL2106; Figure S3: Representative Raman spectra of mineral inclusions in zircons with different ages from samples QL2105 and QL2106; Table S1: Selected…

Evidence: 38 • authority: 92

The Mantle Fe&lt;sup&gt;3+&lt;/sup&gt;/ΣFe Ratio Has Doubled Since the Early Archean.. How mantle redox state developed, particularly the mantle source associated with mid-ocean ridge-like settings, remains a subject of ongoing debate. Here, we employ thermodynamic-thermomechanical numerical simulations to explore the redox properties of melts formed under mid-ocean ridge-like settings in both Archean and modern conditions. By comparing these results with a global database of mid-ocean ridge-like rocks extending back to 3.8 Ga, we reconstruct the mantle's redox evolution since the early Archean. Using the whole-rock Fe³⁺/ΣFe ratio as a robust redox proxy, derived from integrated numerical m…

Evidence: 38 • authority: 92

Modern arc-like water content in the source of 3.1-billion-year-old volcanic rocks.. Whether Archean arc-like volcanism reflects subduction remains debated. We present high-resolution geochemical data from a well-preserved 3.13-3.10 Ga arc-like volcanic succession in Australia's Pilbara Craton, a rare Archean analog of modern arc volcanism retaining fluid-mobile element concentrations consistent with primary magmatic values. The sequence records three primitive lava series typical of modern arcs: tholeiitic, calc-alkaline, and the oldest stratigraphically extensive genuine boninites. Geochemical modelling shows this melt diversity requires at least two mantle sources with distinct depletion…

Evidence: 38 • authority: 92

Coupled anatexis and extreme differentiation are the keys for producing giant lithium-rich pegmatites.. Despite the economic importance of lithium, there is considerable disagreement over the processes that concentrate it and other rare metals in pegmatite-type lithium deposits. Two main processes have been invoked, namely extreme differentiation of a peraluminous granitic magma and direct anatexis of a sedimentary protolith. We use geochemical modeling to quantify lithium enrichment via these two processes from a study of the Jiajika lithium pegmatite field, one of the largest of its type in the world. Based on a lithium-silicon-boron-barium (Li-Si-B-Ba) isotope study involving systematic…

Evidence: 38 • authority: 92

Integrated remote sensing and geochemical data of Shadli mineralized metavolcanics (Egypt): mantle plume-driven magmatism during subduction-rift transition.. The Wadi Ranga-Atshan metavolcanic (WRAM) suite in the Southern Eastern Desert of Egypt is part of the Shadli calc-alkaline metavolcanic belt, which is the main crustal part of the Arabian-Nubian Shield (ANS). Integrated remote sensing, mineral compositions, and whole-rock chemical data are used to elucidate the mantle-plume contribution, petrogenesis, and geodynamic evolution of the ~ 739 Ma Shadli metavolcanics. Remote sensing analysis using Landsat-8 and ASTER band ratios in RGB effectively discriminates between the dominant felsic…

Evidence: — • authority: 72

Metamorphism is the transformation of existing rock (the protolith) to rock with a different mineral composition or texture. Metamorphism usually takes place at temperatures in excess of 150 °C (300 °F), and often also at elevated pressure or in the presence of chemically active fluids, but the rock remains mostly solid during the transformation. Metamorphism is distinct from weathering or diagenesis, which are changes that take place at or just beneath Earth's surface. Various forms of metamorphism exist, including regional, contact, hydrothermal, shock, and dynamic metamorphism. These differ in the characteristic temperatures, pressures, and rate at which they take place and in the extent…

Evidence: — • authority: 72

The rock cycle is a basic concept in geology that describes transitions through geologic time among the three main rock types: sedimentary, metamorphic, and igneous. Each rock type is altered when it is forced out of its equilibrium conditions. For example, an igneous rock such as basalt may break down and dissolve when exposed to the atmosphere, or melt as it is subducted under a continent. Due to the driving forces of the rock cycle, plate tectonics and the water cycle, rocks do not remain in equilibrium and change as they encounter new environments. The rock cycle explains how the three rock types are related to each other, and how processes change from one type to another over time. Thi…