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The densities of fluid inclusions in quartz from high-pressure, low-temperature metamorphic rocks are generally inconsistent with the P-T conditions derived from solid-phase equilibria. Therefore, some process of change must regularly have occurred during exhumation. However, evidence of decrepitation is frequently lacking. Consideration of the rates of change of P and T in metamorphic rocks shows...
The breakdown reactions of antigorite: (1) forming talc + forsterite + water at low pressures and (2) forming forsterite + clinoenstatite + water at high pressures were determined in reversed equilibrium experiments. Results on reaction (1) were found to be in good agreement with former experimental determinations by both Johannes [Johannes, W., 1975. Zur Synthese und thermischen Stabilitat von Antigorit...
Recent research on ultrahigh-pressure rocks in Val Gilba and the Brossasco area has revealed the complete textural preservation of large volumes of a premetamorphic granite, together with its former contact aureole, that was subducted to depths of > 100 km, as indicated by coesite pseudomorphs. Petrographic studies indicate that, although most minerals have been affected by metamorphism, biotite...
Metagabbros in the core series of the Menderes Massif, for some time considered as post orogenic Miocene intrusives, revealed a strong poly-metamorphic history. The metagabbro bodies exhibit a pronounced zonation. Within their cores, igneous minerals are still preserved. Coronitic textures are interpreted as results of a high temperature, possibly granulitic overprint. The outer parts of the metagabbro...
Metagabbros in the core series of the Menderes Massif, for some time considered as post orogenic Miocene intrusives, revealed a strong poly-metamorphic history. The metagabbro bodies exhibit a pronounced zonation. Within their cores, igneous minerals are still preserved. Coronitic textures are interpreted as results of a high temperature, possibly granulitic overprint. The outer parts of the metagabbro...
Experimental results in the simplest possible systems up to generally 20-50 kbar, in a few cases 100 kbar, bearing on the PT-stability limits of 17 end member borosilicates and borates are summarized. Except for the sillimanite-structure-type minerals grandidierite and werdingite, which break down near 10 kbar, the following phases are stable up to much higher pressures and no influence of boron coordination...
The breakdown reactions of antigorite: (1) forming talc + forsterite + water at low pressures and (2) forming forsterite + clinoenstatite + water at high pressures were determined in reversed equilibrium experiments. Results on reaction (1) were found to be in good agreement with former experimental determinations by both Johannes [Johannes, W., 1975. Zur Synthese und thermischen Stabilitat von Antigorit...
In the ultrahigh-pressure metamorphic terrane of the Dora-Maira massif, western Alps, magnesiochloritoid (up to 97 mol% end-member) occurs along with ellenbergerite, talc, chlorite or kyanite as prograde inclusions in a few pyrope megablasts. Whereas most pyrope megablasts in this terrane are relatively homogeneous (Prp90-Prp98), the magnesiochloritoid-bearing megablasts commonly preserve a clear...
Eclogites from different parts of the Variscan basement of the Bohemian Massif show a variation in temperatures recorded at peak pressures as well as during subsequent exhumation. These differences are reflected in the extent of modification of pre-, syn- and post-eclogite facies garnet compositions and by the types of reactions taking place at garnet rims. Munchberg Massif eclogites formed at conditions...
Experiments in the piston-cylinder apparatus were undertaken to synthesize the assemblage of phengite, garnet, kyanite and quartz or coesite. In the system K 2 O MgO Al 2 O 3 SiO 2 H 2 O (KMASH), compositional data of phengite were obtained for 13 experimental runs in the range of 30 to 45 kbar and 850 o C to 1100 o C. The same was achieved...
Constraints on the state of stress at deep levels of convergent plate boundaries can be obtained from the microstructural record of high-pressure metamorphic rocks, provided that this record has remained unchanged during exhumation. The inclusion patterns in poikiloblastic garnet of a metapelite from the Eclogite Zone of the Tauern Window, Eastern Alps, reveal a foam microstructure of quartz controlled...
In the Dabie ultrahigh-pressure terrane of east-central China, coesite-bearing jadeite quartzites occur locally as intercalated layers with marble and mafic eclogite. This rock assemblage is, in turn, enclosed within quartzofeldspathic gneisses. Metamorphic parageneses and kelyphitic textures reveal a multistage metamorphic evolution and complex exhumation history. The primary peak metamorphic assemblage...
The metamorphic and deformational history of coesite-bearing, ultrahigh-pressure metamorphic oceanic crust from Lago di Cignana, Valtournanche, western Alps, as recorded along the decompression and cooling path, has been resolved to derive constraints on the physical state of the crust during exhumation. The following history is proposed: Eclogites derived from pillow basalts were deformed by dislocation...
The metamorphic and deformational history of coesite-bearing, ultrahigh-pressure metamorphic oceanic crust from Lago di Cignana, Valtoumanche, western Alps, as recorded along the decompression and cooling path, has been resolved to derive constraints on the physical state of the crust during exhumation. The following history is proposed: Eclogites derived from pillow basalts were deformed by dislocation...
The preservation of coesite-bearing ultrahigh-pressure metamorphic rocks in orogenic belts indicates that continental crust can be buried to a depth exceeding its present thickness. The exhumation of these rocks requires large scale flow patterns not yet understood. By analogy to the use of flow laws for quartz for the higher crustal levels, rheological data and a flow law for coesite are required...
The preservation of coesite-bearing ultrahigh-pressure metamorphic rocks in orogenic belts indicates that continental crust can be buried to a depth exceeding its present thickness. The exhumation of these rocks requires large scale flow patterns not yet understood. By analogy to the use of flow laws for quartz for the higher crustal levels, rheological data and a flow law for coesite are required...
In the Dabie ultrahigh-pressure terrane of east-central China, coesite-bearing jadeite quartzites occur locally as intercalated layers with marble and mafic eclogite. This rock assemblage is, in turn, enclosed within quartzofeldspathic gneisses. Metamorphic parageneses and kelyphitic textures reveal a multistage metamorphic evolution and complex exhumation history. The primary peak metamorphic...
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