The Experts below are selected from a list of 89529 Experts worldwide ranked by ideXlab platform
Chang Whan Oh - One of the best experts on this subject based on the ideXlab platform.
-
Systematic changes in metamorphic styles along the Dabie–Hongseong and Himalayan collision belts, and their tectonic implications
Journal of Asian Earth Sciences, 2010Co-Authors: Chang Whan OhAbstract:Abstract Different continental collision belts show contrasting metamorphic trend along their length, including the distribution of extreme Metamorphism; i.e., ultrahigh-pressure (>100 km depth) and ultrahigh-temperature (900–1150 °C) Metamorphisms. However, no previous study has succeeded in explaining these trends. The present study investigates the main factors that control the metamorphic trends along collision belts, with reference to the Dabie–Hongseong collision belt between the North and South China blocks and the Himalayan collision belt between the Indian and Asian blocks. In the Dabie–Hongseong collision belt, collision began in the east before 245 Ma and propagated westward until ca. 220 Ma. In the eastern part of the belt, the amount of oceanic slab that subducted before collision was insufficient to pull down the continental crust to the depths of ultrahigh-pressure Metamorphism; however, ultrahigh-pressure Metamorphism occurred in the western part of the belt. Slab break-off also migrated from east to west, with a westward increase in the depth of break-off (from ca. 10 kbar in the west to ca. 35 kbar in the east). These lateral trends along the belt resulted in a westward change from ultrahigh-temperature (915–1160 °C, 9.0–10.6 kbar) to high-pressure (835–860 °C, 17.0–20.9 kbar) and finally ultrahigh-pressure Metamorphism (680–880 °C, 30–40 kbar). In the Himalayan collision belt, collision started from the west at 50 Ma and propagated eastward. The amount of oceanic slab subducted prior to collision was sufficient to pull down the continental crust to the depths of ultrahigh-pressure Metamorphism in the west, but not in the east. Slab break-off started in the west at ca. 46 Ma and propagated eastward, with an eastward decrease in the depth of slab break-off from 27–29 to 17–18 kbar. Consequently, the metamorphic trend along the belt changes eastward from ultrahigh-pressure (690–750 °C, 27–29 kbar) to high-pressure and finally high-pressure granulite facies Metamorphism (890 °C, 17–18 kbar). The differences in metamorphic trend between the Dabie–Hongseong and Himalayan collision belts reflect the amount of oceanic crust subducted prior to collision and the depth and timing of slab break-off along each belt.
-
Phanerozoic high-pressure eclogite and intermediate-pressure granulite facies Metamorphism in the Gyeonggi Massif, South Korea: implications for the eastward extension of the Dabie-Sulu continental collision zone
Lithos, 2006Co-Authors: Chang Whan Oh, V.j. Rajesh, Ian S. Williams, Daniela Rubatto, Mingguo ZhaiAbstract:Abstract Petrological analysis, zircon trace element analysis and SHRIMP zircon U–Pb dating of retrogressed eclogite and garnet granulite from Bibong, Hongseong area, SW Gyeonggi Massif, South Korea provide compelling evidence for Triassic (231.4 ± 3.3 Ma) high-pressure (HP) eclogite facies (M1) Metamorphisms at a peak pressure–temperature ( P – T ) of ca. 16.5–20.0 kb and 775–850 °C. This was followed by isothermal decompression (ITD), with a sharp decrease in pressure from 20 to 10 kb and a slight temperature rise from eclogite facies (M1) to granulite facies (M2), followed by uplift and cooling. Granitic orthogneiss surrounding the Baekdong garnet granulite and the ophiolite-related ultramafic lenticular body near Bibong records evidence for a later Silurian (418 ± 8 Ma) intermediate high-pressure (IHP) granulite facies Metamorphism and a prograde P – T path with peak P – T conditions of ca. 13.5 kb and 800 °C. K–Ar ages of biotite from garnet granulites, amphibolites, and granitic orthogneisses in and around the Bibong metabasite lenticular body are 208–219 Ma, recording cooling to about 310 °C after the Early Triassic metamorphic peak. Neoproterozoic zircon cores in the retrogressed eclogite and granitic orthogneiss provide evidence that the protoliths of these rocks were ∼ 800 and ∼ 900 Ma old, respectively, similar to the ages of tectonic episodes in the Central Orogenic Belt of China. This, and the evidence for Triassic HP/UHP Metamorphism in both China and Korea, is consistent with a regional tectonic link within Northeast Asia from the time of Rodinia amalgamation to Triassic continent–continent collision between the North and South China Blocks, and with an eastward extension of the Dabie–Sulu suture zone into the Hongseong area of South Korea.
Hengcong Lei - One of the best experts on this subject based on the ideXlab platform.
-
A Review of Ultrahigh Temperature Metamorphism
Journal of Earth Science, 2018Co-Authors: Hengcong LeiAbstract:Ultrahigh-temperature (UHT) Metamorphism represents extreme crustal Metamorphism with peak metamorphic temperatures exceeding 900 oC and pressures ranging from 7 to 13 kbar with or without partial melting of crusts, which is usually identified in the granulite-facies rocks. UHT rocks are recognized in all major continents related to both extensional and compressive tectonic environments. UHT Metamorphism spans different geological ages from Archean to Phanerozoic, providing information of the nature, petrofabric and thermal evolution of crusts. UHT Metamorphism is traditionally identified by the presence of a diagnostic mineral assemblage with an appropriate bulk composition and oxidation state in Mg-Al-rich metapelite rocks. Unconventional geothermobarometers including Ti-in-zircon (TIZ) and Zr-in-rutile (ZIR) thermometers and phase equilibria modeling are increasingly being used to estimate UHT Metamorphism. Concentrated on the issues about UHT Metamorphism, this review presents the research history about UHT Metamorphism, the global distribution of UHT rocks, the current methods for constraints on the UHT Metamorphism, and the heat sources and tectonic settings of UHT Metamorphism. Some key issues and prospects about the study of UHT Metamorphism are discussed, e.g., identification of UHT Metamorphism for non-supracrustal rocks, robustness of the unconventional geothermometers, tectonic affinity of UHT metamorphic rocks, and methods for the constraints of age and duration of UHT Metamorphism. It is concluded that UHT Metamorphism is of great importance to the understanding of thermal evolution of the lithosphere.
Michael Brown - One of the best experts on this subject based on the ideXlab platform.
-
duality of thermal regimes is the distinctive characteristic of plate tectonics since the neoarchean
Geology, 2006Co-Authors: Michael BrownAbstract:Ultrahigh-temperature (UHT) granulite Metamorphism is documented predominantly in the Neoarchean to Cambrian rock record, but UHT granulite Metamorphism also may be inferred at depth in Cenozoic orogenic systems. The first occurrence of UHT granulite Metamorphism in the record signifies a change in geodynamics that generated transient sites of very high heat flow. Many UHT granulite metamorphic belts may have developed in settings analogous to modern continental backarcs; on a warmer Earth, destruction of oceans floored by thinner lithosphere may have generated hotter backarcs than those associated with the modern Pacific ring of fire. Medium-temperature eclogite–high- pressure (EHP) granulite Metamorphism is documented in the Neoarchean rock record and at intervals throughout the Proterozoic and Paleozoic record. EHP granulite metamorphic belts are complementary to UHT granulite metamorphic belts in that they are generally inferred to record subduction-to-collision orogenesis. Blueschists become evident in the Neoproterozoic rock record, but lawsonite blueschist–eclogite Metamorphism (high pressure [HP]) and ultrahigh-pressure Metamorphism (UHP) characterized by coesite or diamond are predominantly Phanerozoic phenomena. HP-UHP Metamorphism registers the low thermal gradients and deep subduction of continental crust during the early stage of subduction-to-collision orogenesis. A duality of metamorphic belts—reflecting a duality of thermal regimes—appears in the record only since the Neoarchean Era. A duality of thermal regimes is the hallmark of modern plate tectonics, and the duality of metamorphic belts is the characteristic imprint of plate tectonics in the rock record. The occurrence of both UHT and EHP granulite Metamorphism since the Neoarchean marks the onset of a “Proterozoic plate tectonics” regime, which evolved during a Neoproterozoic transition to the modern plate tectonics regime, characterized by colder subduction as chronicled by HP-UHP Metamorphism.
-
p t t evolution of orogenic belts and the causes of regional Metamorphism
Geological Society London Memoirs, 1995Co-Authors: Michael BrownAbstract:Abstract Barrow (1893) introduced three important ideas that furthered understanding of metamorphic processes: (i) the use of critical index minerals in argillaceous rocks to define metamorphic zones and elucidate spatial features of regional Metamorphism; (ii) the concept of progressive Metamorphism; and (iii) the concept of magmatic advection of heat as a possible cause of regional Metamorphism. This article expands upon these themes by reviewing our understanding of the dynamic evolution of orogenic belts as interpreted from the P–T–t paths of metamorphic rocks, and by considering the likely causes of the different kinds of regional Metamorphism that we observe within orogenic belts. Understanding metamorphic rocks allows the distinction of two fundamentally different types of orogenic belt defined by relative timing of maximum T and maximum P . Orogenic belts characterized by clockwise P-T paths achieved maximum P before maximum T , the metamorphic peak normally post-dated early deformation within the belt and additional heating above the ‘normal’ conductive flux has been related to the amount of overthickening. By contrast, orogenic belts characterized by counterclockwise P-T paths achieved maximum T before maximum P , the metamorphic peak normally pre-dated or was synchronous with early deformation within the belt and additional heating above the ‘normal’ conductive flux has been related to the emplacement of plutons. Techniques used to constrain portions of P–T–t paths include: the use of mineral inclusion suites in porphyroblasts and reaction textures; thermobarometry; the use of fluid inclusions; thermodynamic approaches such as the Gibbs method; radiogenic isotope dating; fission track studies; and numerical modelling. We can utilize specific mineral parageneses in suitable rocks to determine individual P–T–t paths, and a set of P–T–t paths from one orogenic belt allows us to interpret the spatial variation in dynamic evolution of the Metamorphism. Recent advances are reviewed with reference to collision Metamorphism, high-temperature-low-pressure Metamorphism, granulite Metamorphism, and subduction zone Metamorphism, and some important directions for future work are indicated.
Takeshi Imayama - One of the best experts on this subject based on the ideXlab platform.
-
regional middle paleozoic Metamorphism in the southwestern gyeonggi massif south korea its implications for tectonics in northeast asia
Journal of Asian Earth Sciences, 2017Co-Authors: Takeshi Imayama, Jimin JeonAbstract:Abstract The Hongseong area in the southwestern Gyeonggi Massif in South Korea is considered to represent the eastward extension of the Qinling–Dabie–Sulu collision belt in China. We have carried out zircon U–Pb SHRIMP dating and P–T estimations of the gneisses and amphibolites in the eastern Wolhyeonri complex within the Hongseong area in order to constrain their metamorphic and tectonic evolutions. The protoliths of the migmatitic biotite gneisses formed during the Neoproterozoic and underwent granulite-facies Metamorphism (750–880 °C, 12–15 kbar) at 442–413 Ma. These rocks subsequently experienced amphibolite-facies retrograde Metamorphism at 585–660 °C and 7.5–10.3 kbar. Mylonitic biotite gneiss, hornblende gneiss, and folded amphibolite in the study area yield metamorphic ages that range from 429 to 420 Ma. The protoliths of some garnet amphibolites that formed at 470–456 Ma are arc magmatic rocks; they experienced Metamorphism at the boundary between amphibolite- and eclogite-facies (ca. 625–700 °C and 13–15.5 kbar) before 418 Ma and underwent retrograde amphibolite-facies Metamorphism (ca. 625–700 °C and 8–9 kbar) at 418–405 Ma. These data suggest that a regional intermediate-P/T metamorphic event occurred during the Middle Paleozoic. In contrast, Paleoproterozoic augen gneiss blocks enclosed in the Deokjeongri gneiss complex preserve evidence of high-pressure (HP) Metamorphism (840–960 °C, 17–21.8 kbar) at 234–230 Ma, which are similar to the previously reported results from eclogite blocks in this area. The occurrence of Middle Paleozoic regional Metamorphism before the Permo-Triassic HP Metamorphism in the Hongseong area may be correlated with the Middle Paleozoic Metamorphism in the Qinling belt in China; such regional metamorphic events were caused by the collision of microcontinents with the North or South China Cratons prior to the collision between the North and South China Cratons in the Permo-Triassic.
David E. Kelsey - One of the best experts on this subject based on the ideXlab platform.
-
On ultrahigh-temperature crustal Metamorphism
Gondwana Research, 2008Co-Authors: David E. KelseyAbstract:Abstract Ultrahigh-temperature (UHT) Metamorphism is the most thermally extreme type of crustal Metamorphism, with the crust capable of withstanding temperatures ≥ 900 °C. Mineral assemblages diagnostic of UHT Metamorphism commonly occur in Mg–Al-rich rock compositions that are unfortunately relatively rare in nature. These include sapphirine + quartz, orthopyroxene + sillimanite ± quartz and osumilite. However, UHT Metamorphism has been diagnosed using more common garnet + aluminous orthopyroxene assemblages, as well as ternary feldspars and metamorphic pyroxenes. The worldwide number of UHT localities exceeds 40, and may continue to increase as petrologists apply new retrieval methods for extracting information from mineral assemblages in conjunction with mineral chemistry, e.g. the aluminium content of orthopyroxene, and calculated phase equilibria, based on thermodynamic datasets that continue to be refined and improved. This contribution presents a review of UHT Metamorphism, including: 1) the history of experiments that have ultimately lead to the precise P–T constraints we can now place on the generation and evolution of UHT mineral assemblages; 2) the diagnostic assemblages; 3) the age distribution of UHT Metamorphism; 4) the use of calculated phase equilibria to constrain the evolution of UHT rocks; 5) the duration of UHT metamorphic episodes, which is a very active field of research at present; and, 6) the tectonic scenarios that have been proposed for the generation of UHT conditions in the deep crust. The two fundamental types of orogenic systems, namely accretionary and collisional, have been proposed to be potential sites for UHT Metamorphism. In contrast to current geodynamic models that are typically unable to account for UHT metamorphic conditions in the deep crust, it may be possible that UHT Metamorphism can occur during ‘normal’ tectonic events. If UHT Metamorphism can occur on a regional scale during ‘normal’ tectonism, it is important to understand all aspects of UHT Metamorphism and the implications it has for lithospheric rheology, crust–mantle interactions and the geodynamics of granulite facies Metamorphism.
