Pressure-temperature-time path (original) (raw)
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.
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| dbo:abstract | 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 during solid state metamorphism and react to grow into new minerals that are relatively stable. Water is generally involved in the reaction, either from the surroundings or generated by the reaction itself. Usually, a large amount of fluids (e.g. water vapor, gas etc.) escape under increasing P-T conditions e.g. burial. When the rock is later uplifted, due to the escape of fluids at an earlier stage, there is not enough fluids to permit all the new minerals to react back into the original minerals. Hence, the minerals are not fully in equilibrium when discovered on the surface. Therefore, the mineral assemblages in metamorphic rocks implicitly record the past P-T conditions that the rock has experienced, and investigating these minerals can supply information about the past metamorphic and tectonic history. The P-T-t paths are generally classified into two types: clockwise P-T-t paths, which are related to collision origin, and involve high pressures followed by high temperatures; and anticlockwise P-T-t paths, which are usually of intrusion origin, and involve high temperatures before high pressures. (The "clockwise" and "anticlockwise" names refer to the apparent direction of the paths in the Cartesian space, where the x-axis is temperature, and the y-axis is pressure.) (en) PT-тренд метаморфизма (англ. P-T-t path) — запись сопряжённого изменения давления (P) и температуры (T) в ходе геологической истории метаморфических пород. Температуру пород осадочного комплекса до метаморфизма можно принять за ноль, а давление — за одну атмосферу. По мере перекрытия рассматриваемого комплекса другими отложениями и погружения его в более глубокие горизонты температура и давление растут. После достижения ими некоторых критических величин в породе могут произойти минеральные и структурные преобразования. После достижения максимальных значений Р и Т, соответствующих кульминации метаморфизма, начинается обратный процесс выведения пород к поверхности, сопровождающийся снижением температуры и давления. Поскольку породы, которые мы изучаем, теперь находятся на поверхности, то условия финальной стадии процесса будут идентичны первоначальным. Кривая, описывающая изменение РТ-условий от начальной до финальной стадии метаморфических преобразований, является трендом метаморфизма рассматриваемого комплекса. Для первично осадочных пород эта кривая всегда будет замкнутой, коль скоро все начинается и заканчивается на поверхности Земли, в случае же метаморфизованных интрузивных пород начальные, предметаморфические условия могут существенно отличаться в сторону повышения температур и давлений. Тренды в реальных метаморфических комплексах могут иметь сложный вид, обусловленный неоднократными проявлениями импульсов метаморфизма. Нередко выделяются тренды метаморфизма по часовой стрелке или против часовой стрелки. В первом случае вначале проявляется максимум по давлению, а затем — максимум по температуре, во втором случае ситуация обратная. Тренд по часовой стрелке характерен для коллизионного типа метаморфизма и может объясняться увеличением мощности коры в процессе надвигания тектонических пластин. Тренды, направленные против часовой стрелки, часто связывают со стадией зарождения субдукции. Эволюция РТ-параметров процесса по пути компрессионного охлаждения и последующей декомпрессии также может быть характерна, например, для океанических пород, удерживаемых некоторое время без движения в нижней части субдукционного канала. Корректное построение трендов метаморфизма — очень сложная и не всегда решаемая задача. Оно требует количественного определения температур и давлений для разных стадий метаморфизма, для чего обычно используется парагенетический анализ и минеральные геотермобарометры. (ru) |
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| dbp:caption | A typical clockwise P-T-t path representing a collision or subduction setting. Prograde metamorphism occurred upon increasing P-T environment until reaching the peak, followed by near-isothermal decompression , and further exhumation and erosion . (en) During the formation of a fault-bend-fold, the lower segment is heated while the upper thrust sheet is cooled because of thrusting. (en) A common clockwise P-T-t path observed in reality. (en) A typical clockwise P-T-t path . (en) Garnet zones grow from core to rim. Each concentric garnet zone displays different chemical compositions, indicating different P-T conditions. (en) Intrusion of magma results in a great increment in temperature and a slight increase in pressure experienced by the underlying rocks, which gives prograde metamorphism. Cooling of erupted magma causes a near-isobaric temperature drop and leads to retrograde metamorphism of the underlying rocks. (en) Multiple thrusting such as duplexes would result in complex thermal profile of the rocks. (en) Investigating the compositions in each garnet zone can supply information about the different P-T points as well as the trend of the P-T path. (en) A typical anticlockwise P-T-t path representing an intrusion origin. A great temperature increment during prograde metamorphism due to overlying hot magma, followed by near-isobaric cooling in retrograde metamorphism when the magma cools. (en) In continental collision setting, crustal thickening takes place, which brings about prograde metamorphism of underlying rocks. Continuous compression results in the development of thrust belts, which leads to a great drop in pressure experienced by originally underlying rocks and results in near-isothermal decompression . Exhumation and erosion further promote a decrease in P-T condition . (en) |
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| dbp:image | Anticlockwise ptt path1.png (en) Clockwise ptt path.png (en) Continental collision.png (en) Duplex1 ES.svg (en) Faultbendfold.png (en) Formation of Shield Domes.gif (en) PTt garnet zones.gif (en) Ptt path 20b.gif (en) clockwise ptt path.png (en) common clockwise Ptt path.png (en) |
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| rdfs:comment | 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. (en) PT-тренд метаморфизма (англ. P-T-t path) — запись сопряжённого изменения давления (P) и температуры (T) в ходе геологической истории метаморфических пород. Температуру пород осадочного комплекса до метаморфизма можно принять за ноль, а давление — за одну атмосферу. По мере перекрытия рассматриваемого комплекса другими отложениями и погружения его в более глубокие горизонты температура и давление растут. После достижения ими некоторых критических величин в породе могут произойти минеральные и структурные преобразования. После достижения максимальных значений Р и Т, соответствующих кульминации метаморфизма, начинается обратный процесс выведения пород к поверхности, сопровождающийся снижением температуры и давления. Поскольку породы, которые мы изучаем, теперь находятся на поверхности, то усл (ru) |
| rdfs:label | Pressure-temperature-time path (en) PT-тренд метаморфизма (ru) |
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