Die Deutsche Nationalbibliothek verzeichnet diese Publikation in der Deutschen Nationalbibliograf... more Die Deutsche Nationalbibliothek verzeichnet diese Publikation in der Deutschen Nationalbibliografie; detaillierte bibliografische Daten sind im Internet über http://dnb.d-nb.de abrufbar.
A composite intrusive igneous complex in the central mountain range of Queen Maud Land (Thor Rang... more A composite intrusive igneous complex in the central mountain range of Queen Maud Land (Thor Range), Antarctica, displays charac-teristic features of anorogenic granites. A suite of massive intrusives and various sets of dykes and satellite intrusions are ferroan, alkalic to alkali–calcic, and weakly peraluminous. An early set of plutons consists of charnockitic alkali-granites; a later group of plutons comprises fayalite Qtz-syenites. Coarse mesoperthite is the dominant mineral in all rocks, quartz is abundant and plagioclase is a minor mineral. Olivine (fayalite) is the characteristic mafic mineral, but subcalcic augite and occasionally pigeonite or orthopyroxene are present. In most samples, amphibole is the dominant mafic mineral and its composition is close to end-member hastingsite. It contains high concentrations of F and Cl. Some samples contain igneous fluorite. Thermobarometry suggests a temperature of 900 25C and a pressure of 04 01GPa for the crystallization conditions
The Theodul-Glacier-Unit (TGU) is a 100 m thick and 2 km long slab of pre-Alpine schist, gneiss a... more The Theodul-Glacier-Unit (TGU) is a 100 m thick and 2 km long slab of pre-Alpine schist, gneiss and mafic rocks tectonically emplaced in the eclogite-facies Zermatt-Saas meta-ophiolite nappe (ZSU). The meta-sedimentary rocks occur mostly as garnet-phengite schists with locally cm-sized garnet porphyroblasts. The metavolcanic basic rocks are present as variably retrogressed eclogites showing a continental basalt signature and contain abundant zircon, which is unusual for basalts. The zircons dated with the U–Pb system yield an upper intercept age of 295 ± 16 Ma and a lower intercept age of 145 ± 34 Ma. The early Permian age is interpreted to represent the age of high-grade granulite facies metamorphism, evidence of which is also preserved in the cores of garnet porphyroblasts of the Grt-Ph schists. The lower intercept age corresponds to the time of continental breakup and the initiation of the Tethys in the Mid-Jurassic; these events may have created the TGU as an extensional allocht...
Garnet is a prototypical mineral in metamorphic rocks because it commonly preserves chemical and ... more Garnet is a prototypical mineral in metamorphic rocks because it commonly preserves chemical and textural features that can be used for untangling its metamorphic development. Large garnet porphyroblasts may show extremely complex internal structures as a result of a polycyclic growth history, deformation, and modification of growth structures by intra‐ and intercrystalline diffusion. The complex internal structure of garnet porphyroblasts from garnet–phengite schists (GPS) of the Zermatt area (Western Alps) has been successfully decoded. The centimetre‐sized garnet porphyroblasts are composed of granulite facies garnet fragments overgrown by a younger generation of grossular‐rich eclogite facies garnet. The early granulite facies garnet (G‐Grt) formed from low‐P, high‐T metamorphism during a pre‐Alpine orogenic event. The late garnet (E‐Grt) is typical of high‐pressure, low‐temperature (HPLT) metamorphism and can be related to Alpine subduction of the schists. Thus, the garnet of t...
Research on water-rock interaction quantitatively models geochemical reactions and transport of s... more Research on water-rock interaction quantitatively models geochemical reactions and transport of solutes as coupled phenomena. We studied the chemical evolution of surface waters in Zermatt-Matterhorn area, Switzerland. The chemical characteristics of the surface water have been used to infer the mechanisms of solute acquisition in open system in geologically diverse Alpine catchments. The surface water in study area is predominantly controlled by the interaction of meteoric water with the exposed rocks. Dissolving primary minerals of the predominantly metamorphic rocks contribute to the observed total dissolved solids with leaving behind a residue of newly formed insoluble minerals. A total of 102 water samples were collected mainly from small water bodies located in Zermatt-Matterhorn area representing the geographical and lithological diversity. Altitudes of sampling locations range from 1600m to 3200m. Since water samples were from water bodies at high elevation, water-rock interaction was little affected by anthropogenic or biologic contributions. Temperature, pH, and electric conductivity were measured on site. Total dissolved solids was relatively low and varies from 6 to 244 mg/l. Dominant solutes are Ca, Mg, HCO3, SO4 and minor components are Na, K, NO3, Cl and Si, while F and B occur in traces only. The calculation of saturation states with PHREEQC shows that all surface waters are undersaturated with respect to all relevant minerals. Statistical analysis of the composition data shows that Ca-HCO3-SO4 and Na-K-SiO2 are strongly correlated. Three chemical types of water can be distinguished: Ca-HCO3, Mg-HCO3 and Ca-SO4. A hydro-geochemical inverse model has been set up for interpreting the water-rock interaction that estimated the contributions of the various rock-forming minerals to the composition of the waters. It shows that: 1) Ca-HCO3 water result from interaction of precipitation with mafic schist or calcareous micaschist, the reaction can be summarized as: 1) Meteoric water + CO2 + O2 + pyrite + epidote + chlorite + albite + phengite + "halite" = "quartz" + goethite + kaolinite + Ca-HCO3 water and 2) Meteoric water + CO2 + O2 + calcite + pyrite + albite + phengite + chlorite ± "halite" = ±"quartz" + goethite + kaolinite + Ca-HCO3 water. Magnesium-rich Mg-HCO3 water is produced from reaction of precipitation with serpentinite: 3) Meteoric water + CO2 + O2 + antigorite + diopside + phengite + pyrite = magnesite + talc + goethite + Mg-HCO3 water. Sulphate-rich Ca-SO4 water occur mainly in gneiss and granite catchments, where the precipitation interacted with pyrite-baring rocks according to the reaction: 4) Initial water ± CO2 + O2 + pyrite + plagioclase + K-feldspar + chlorite ± halite = goethite + kaolinite + albite ± quartz + Ca-SO4 water.
Granitoid rocks comprise granites, alkali-feldspar granites, granodiorites and tonalites, and con... more Granitoid rocks comprise granites, alkali-feldspar granites, granodiorites and tonalites, and constitute a large portion of the continental crust. Because the main constituents — alkali-feldspar, plagioclase, quartz, biotite, muscovite, hornblende — are found over a wide range of P-T conditions, this rock group is not a very useful indicator of metamorphic grade and is therefore largely neglected in textbooks on metamorphic petrology. Unlike wet sedimentary rocks, granitoid rocks will enter the metamorphic realm in a predominantly dry state. In order to start metamorphic reactions, some hydration is necessary. The access of a water-rich fluid will be facilitated by tectonic activity. Also, in the absence of penetrative deformation, granitoid rocks retain remarkably well their original igneous structures.
Library of Congress Cataloging-in-Publication Data Bucher, Kurt, 1946-Petrogenesis of metamorphic... more Library of Congress Cataloging-in-Publication Data Bucher, Kurt, 1946-Petrogenesis of metamorphic rocks / Kurt Bucher, Martin Frey.-7th, completely revised and updated ed. p. cm. Includes bibliographical references and index.
The Penninic nappe stack in the Central and Western Alps was formed in a collision zone environme... more The Penninic nappe stack in the Central and Western Alps was formed in a collision zone environment after the closure of the Penninic oceans in the Paleogene. This study reports Lu-Hf garnet-whole rock ages of 56.5 ± 2.7 and 58.2 ± 1.4 Ma for two eclogite samples from the Theodul Glacier Unit, which is inserted within the structurally uppermost parts of the ophiolitic Zermatt-Saas Zone. The distribution of major elements, Mn, Y, and Lu in garnet, and specifically an enrichment of Lu in the cores, indicate that the ages record prograde growth of garnet during pressure increase. They provide direct evidence for the continuation of subduction during the ''Paleocene restoration phase'', often regarded as a tectonically quiescent period due to a reduction in clastic sediment deposition, lack of folds and thrusts of this age, and a cessation of Africa-Europe convergence as derived from the magnetic anomaly pattern in the Atlantic Ocean. The evidence for ongoing subduction in the absence of Africa-Europe convergence suggests that the subduction system was driven by gravity acting on the downgoing slab in a rollback setting, and that subduction was balanced by extension of the upper plate. The overlap of the Lu-Hf ages of both samples from the Theodul Glacier Unit show that this tectonic element represents a coherent body. The difference with respect to the 48 Ma Lu-Hf age of the Lago di Cignana Unit, another element of the Zermatt-Saas Zone, shows that the Zermatt-Saas Zone consists of tectonic subunits, which reached their respective pressure peaks over a prolonged period of approximately 10 Ma.
Rock metamorphism is always associated with processes and changes. Metamorphism reworks rocks in ... more Rock metamorphism is always associated with processes and changes. Metamorphism reworks rocks in the Earth’s crust and mantle. Typical effects of rock metamorphism include: • Minerals and mineral assemblages originally not present in a rock may form, the new mineral assemblages grow at the expense of old ones. Consequently older minerals may disappear (e.g. metapelitic gneiss may originally contain Sil
The Allalin gabbro is a 2 km  0Á5 km block of layered olivinegabbro and troctolite included in t... more The Allalin gabbro is a 2 km  0Á5 km block of layered olivinegabbro and troctolite included in the Zermatt^Saas ophiolite nappe of the Western Alps. Comprehensive texture, mineral and rock composition data together with a thermodynamic analysis of the complex phase associations permit a detailed reconstruction of the igneous and metamorphic reaction history recorded by the gabbroic rocks. Based on rock and mineral composition data, the Allalin gabbro represents part of a Middle Jurassic underplate of mafic magma at the base of the continental crust of the Apulian plate (Dent Blanche^Sesia Lanzo system). Granulite-facies recrystallization during cooling at $8258C and 1Á0 GPa, involving the formation of Opx^Grt coronas between Ol^Pl, can be related to crustal thickening. Eocene subduction of the Tethys oceanic lithosphere under the Apulian plate detached the gabbro from the base of the continental crust and incorporated it into the ophiolite. Increasing pressure in the descending slab had little effect on parts of the gabbro, which still locally contain unaltered igneous Ol, Aug and Pl and wellpreserved magmatic textures. With increasing subduction depth an increasing amount of aqueous fluid accessed the gabbro and transformed Pl to Zo^Jd^Ky^Qtz. At about 2Á5 GPa (93 km) at c. 6108C, a dramatic hydration process converted most of the rocks (490 vol. %) into a fully hydrated eclogite-facies assemblage of Omp þ Zo þTlc þ Cld AE Grt AE Ky þ Rt. The full hydration under water-present conditions occurred at the greatest depth reached by the gabbro. After detachment from the downgoing slab (i.e. along the ascent path), Gln, Pg and Mrg formed as additional hydrates. This last phase of hydration desiccated the metagabbro at a depth of c. 78 km and from then on the rocks were essentially devoid of a free fluid phase. The Allalin gabbro provides strong evidence that the fundamental high-pressure transformation of mafic rocks involves the hydration of gabbro to form eclogite.
The Luliangshan garnet peridotite massif is an ultramafic complex in the North Qaidam UHPM belt, ... more The Luliangshan garnet peridotite massif is an ultramafic complex in the North Qaidam UHPM belt, NW China. The strongly layered complex comprising garnet-bearing dunite, garnet-harzburgite, garnet-lherzolite and garnet-pyroxenite and garnet-free dunite, occurs together with eclogite embedded in various continental gneisses. The geological setting, the internal structure, bulk-composition, rare earth elements, isotopic and mineral composition data show that the garnet peridotite derives from a middle Ordovician Alaskan-type layered sub-arc cumulate intrusion of ascending mantle wedge melts. An abyssal peridotite protolith can be excluded. During the Ordovician-Silurian continental collision, thickening and foundering, the Luliangshan peridotite complex was exposed to ultrahigh pressures (UHP) reaching 5.5 GPa possibly >6 GPa at temperatures of 900°C (perhaps up to 1000°C) corresponding to a depth of 200 km. The extreme pressure conditions have been derived from thermobarometry using mineral compositions of the garnet peridotite assemblages, but they are supported by a wealth of decompression-induced mineral exsolutions in UHP minerals and by diamond inclusion in zircon. The Luliangshan garnet peridotite has experienced four stages of retrograde overprint during exhumation that lasted into the Devonian: (i) decompression-induced unmixing of the UHP minerals; (ii) garnet kelyphitisation; (iii) amphibole overprinting and (iv) serpentinization. Hydrous minerals occurring within peak metamorphic assemblage represent pseudo-inclusions, that is reaction products of reactions related to various stages of decompression and cooling rather than prograde inclusions during porphyroblast growth.
Die Deutsche Nationalbibliothek verzeichnet diese Publikation in der Deutschen Nationalbibliograf... more Die Deutsche Nationalbibliothek verzeichnet diese Publikation in der Deutschen Nationalbibliografie; detaillierte bibliografische Daten sind im Internet über http://dnb.d-nb.de abrufbar.
A composite intrusive igneous complex in the central mountain range of Queen Maud Land (Thor Rang... more A composite intrusive igneous complex in the central mountain range of Queen Maud Land (Thor Range), Antarctica, displays charac-teristic features of anorogenic granites. A suite of massive intrusives and various sets of dykes and satellite intrusions are ferroan, alkalic to alkali–calcic, and weakly peraluminous. An early set of plutons consists of charnockitic alkali-granites; a later group of plutons comprises fayalite Qtz-syenites. Coarse mesoperthite is the dominant mineral in all rocks, quartz is abundant and plagioclase is a minor mineral. Olivine (fayalite) is the characteristic mafic mineral, but subcalcic augite and occasionally pigeonite or orthopyroxene are present. In most samples, amphibole is the dominant mafic mineral and its composition is close to end-member hastingsite. It contains high concentrations of F and Cl. Some samples contain igneous fluorite. Thermobarometry suggests a temperature of 900 25C and a pressure of 04 01GPa for the crystallization conditions
The Theodul-Glacier-Unit (TGU) is a 100 m thick and 2 km long slab of pre-Alpine schist, gneiss a... more The Theodul-Glacier-Unit (TGU) is a 100 m thick and 2 km long slab of pre-Alpine schist, gneiss and mafic rocks tectonically emplaced in the eclogite-facies Zermatt-Saas meta-ophiolite nappe (ZSU). The meta-sedimentary rocks occur mostly as garnet-phengite schists with locally cm-sized garnet porphyroblasts. The metavolcanic basic rocks are present as variably retrogressed eclogites showing a continental basalt signature and contain abundant zircon, which is unusual for basalts. The zircons dated with the U–Pb system yield an upper intercept age of 295 ± 16 Ma and a lower intercept age of 145 ± 34 Ma. The early Permian age is interpreted to represent the age of high-grade granulite facies metamorphism, evidence of which is also preserved in the cores of garnet porphyroblasts of the Grt-Ph schists. The lower intercept age corresponds to the time of continental breakup and the initiation of the Tethys in the Mid-Jurassic; these events may have created the TGU as an extensional allocht...
Garnet is a prototypical mineral in metamorphic rocks because it commonly preserves chemical and ... more Garnet is a prototypical mineral in metamorphic rocks because it commonly preserves chemical and textural features that can be used for untangling its metamorphic development. Large garnet porphyroblasts may show extremely complex internal structures as a result of a polycyclic growth history, deformation, and modification of growth structures by intra‐ and intercrystalline diffusion. The complex internal structure of garnet porphyroblasts from garnet–phengite schists (GPS) of the Zermatt area (Western Alps) has been successfully decoded. The centimetre‐sized garnet porphyroblasts are composed of granulite facies garnet fragments overgrown by a younger generation of grossular‐rich eclogite facies garnet. The early granulite facies garnet (G‐Grt) formed from low‐P, high‐T metamorphism during a pre‐Alpine orogenic event. The late garnet (E‐Grt) is typical of high‐pressure, low‐temperature (HPLT) metamorphism and can be related to Alpine subduction of the schists. Thus, the garnet of t...
Research on water-rock interaction quantitatively models geochemical reactions and transport of s... more Research on water-rock interaction quantitatively models geochemical reactions and transport of solutes as coupled phenomena. We studied the chemical evolution of surface waters in Zermatt-Matterhorn area, Switzerland. The chemical characteristics of the surface water have been used to infer the mechanisms of solute acquisition in open system in geologically diverse Alpine catchments. The surface water in study area is predominantly controlled by the interaction of meteoric water with the exposed rocks. Dissolving primary minerals of the predominantly metamorphic rocks contribute to the observed total dissolved solids with leaving behind a residue of newly formed insoluble minerals. A total of 102 water samples were collected mainly from small water bodies located in Zermatt-Matterhorn area representing the geographical and lithological diversity. Altitudes of sampling locations range from 1600m to 3200m. Since water samples were from water bodies at high elevation, water-rock interaction was little affected by anthropogenic or biologic contributions. Temperature, pH, and electric conductivity were measured on site. Total dissolved solids was relatively low and varies from 6 to 244 mg/l. Dominant solutes are Ca, Mg, HCO3, SO4 and minor components are Na, K, NO3, Cl and Si, while F and B occur in traces only. The calculation of saturation states with PHREEQC shows that all surface waters are undersaturated with respect to all relevant minerals. Statistical analysis of the composition data shows that Ca-HCO3-SO4 and Na-K-SiO2 are strongly correlated. Three chemical types of water can be distinguished: Ca-HCO3, Mg-HCO3 and Ca-SO4. A hydro-geochemical inverse model has been set up for interpreting the water-rock interaction that estimated the contributions of the various rock-forming minerals to the composition of the waters. It shows that: 1) Ca-HCO3 water result from interaction of precipitation with mafic schist or calcareous micaschist, the reaction can be summarized as: 1) Meteoric water + CO2 + O2 + pyrite + epidote + chlorite + albite + phengite + "halite" = "quartz" + goethite + kaolinite + Ca-HCO3 water and 2) Meteoric water + CO2 + O2 + calcite + pyrite + albite + phengite + chlorite ± "halite" = ±"quartz" + goethite + kaolinite + Ca-HCO3 water. Magnesium-rich Mg-HCO3 water is produced from reaction of precipitation with serpentinite: 3) Meteoric water + CO2 + O2 + antigorite + diopside + phengite + pyrite = magnesite + talc + goethite + Mg-HCO3 water. Sulphate-rich Ca-SO4 water occur mainly in gneiss and granite catchments, where the precipitation interacted with pyrite-baring rocks according to the reaction: 4) Initial water ± CO2 + O2 + pyrite + plagioclase + K-feldspar + chlorite ± halite = goethite + kaolinite + albite ± quartz + Ca-SO4 water.
Granitoid rocks comprise granites, alkali-feldspar granites, granodiorites and tonalites, and con... more Granitoid rocks comprise granites, alkali-feldspar granites, granodiorites and tonalites, and constitute a large portion of the continental crust. Because the main constituents — alkali-feldspar, plagioclase, quartz, biotite, muscovite, hornblende — are found over a wide range of P-T conditions, this rock group is not a very useful indicator of metamorphic grade and is therefore largely neglected in textbooks on metamorphic petrology. Unlike wet sedimentary rocks, granitoid rocks will enter the metamorphic realm in a predominantly dry state. In order to start metamorphic reactions, some hydration is necessary. The access of a water-rich fluid will be facilitated by tectonic activity. Also, in the absence of penetrative deformation, granitoid rocks retain remarkably well their original igneous structures.
Library of Congress Cataloging-in-Publication Data Bucher, Kurt, 1946-Petrogenesis of metamorphic... more Library of Congress Cataloging-in-Publication Data Bucher, Kurt, 1946-Petrogenesis of metamorphic rocks / Kurt Bucher, Martin Frey.-7th, completely revised and updated ed. p. cm. Includes bibliographical references and index.
The Penninic nappe stack in the Central and Western Alps was formed in a collision zone environme... more The Penninic nappe stack in the Central and Western Alps was formed in a collision zone environment after the closure of the Penninic oceans in the Paleogene. This study reports Lu-Hf garnet-whole rock ages of 56.5 ± 2.7 and 58.2 ± 1.4 Ma for two eclogite samples from the Theodul Glacier Unit, which is inserted within the structurally uppermost parts of the ophiolitic Zermatt-Saas Zone. The distribution of major elements, Mn, Y, and Lu in garnet, and specifically an enrichment of Lu in the cores, indicate that the ages record prograde growth of garnet during pressure increase. They provide direct evidence for the continuation of subduction during the ''Paleocene restoration phase'', often regarded as a tectonically quiescent period due to a reduction in clastic sediment deposition, lack of folds and thrusts of this age, and a cessation of Africa-Europe convergence as derived from the magnetic anomaly pattern in the Atlantic Ocean. The evidence for ongoing subduction in the absence of Africa-Europe convergence suggests that the subduction system was driven by gravity acting on the downgoing slab in a rollback setting, and that subduction was balanced by extension of the upper plate. The overlap of the Lu-Hf ages of both samples from the Theodul Glacier Unit show that this tectonic element represents a coherent body. The difference with respect to the 48 Ma Lu-Hf age of the Lago di Cignana Unit, another element of the Zermatt-Saas Zone, shows that the Zermatt-Saas Zone consists of tectonic subunits, which reached their respective pressure peaks over a prolonged period of approximately 10 Ma.
Rock metamorphism is always associated with processes and changes. Metamorphism reworks rocks in ... more Rock metamorphism is always associated with processes and changes. Metamorphism reworks rocks in the Earth’s crust and mantle. Typical effects of rock metamorphism include: • Minerals and mineral assemblages originally not present in a rock may form, the new mineral assemblages grow at the expense of old ones. Consequently older minerals may disappear (e.g. metapelitic gneiss may originally contain Sil
The Allalin gabbro is a 2 km  0Á5 km block of layered olivinegabbro and troctolite included in t... more The Allalin gabbro is a 2 km  0Á5 km block of layered olivinegabbro and troctolite included in the Zermatt^Saas ophiolite nappe of the Western Alps. Comprehensive texture, mineral and rock composition data together with a thermodynamic analysis of the complex phase associations permit a detailed reconstruction of the igneous and metamorphic reaction history recorded by the gabbroic rocks. Based on rock and mineral composition data, the Allalin gabbro represents part of a Middle Jurassic underplate of mafic magma at the base of the continental crust of the Apulian plate (Dent Blanche^Sesia Lanzo system). Granulite-facies recrystallization during cooling at $8258C and 1Á0 GPa, involving the formation of Opx^Grt coronas between Ol^Pl, can be related to crustal thickening. Eocene subduction of the Tethys oceanic lithosphere under the Apulian plate detached the gabbro from the base of the continental crust and incorporated it into the ophiolite. Increasing pressure in the descending slab had little effect on parts of the gabbro, which still locally contain unaltered igneous Ol, Aug and Pl and wellpreserved magmatic textures. With increasing subduction depth an increasing amount of aqueous fluid accessed the gabbro and transformed Pl to Zo^Jd^Ky^Qtz. At about 2Á5 GPa (93 km) at c. 6108C, a dramatic hydration process converted most of the rocks (490 vol. %) into a fully hydrated eclogite-facies assemblage of Omp þ Zo þTlc þ Cld AE Grt AE Ky þ Rt. The full hydration under water-present conditions occurred at the greatest depth reached by the gabbro. After detachment from the downgoing slab (i.e. along the ascent path), Gln, Pg and Mrg formed as additional hydrates. This last phase of hydration desiccated the metagabbro at a depth of c. 78 km and from then on the rocks were essentially devoid of a free fluid phase. The Allalin gabbro provides strong evidence that the fundamental high-pressure transformation of mafic rocks involves the hydration of gabbro to form eclogite.
The Luliangshan garnet peridotite massif is an ultramafic complex in the North Qaidam UHPM belt, ... more The Luliangshan garnet peridotite massif is an ultramafic complex in the North Qaidam UHPM belt, NW China. The strongly layered complex comprising garnet-bearing dunite, garnet-harzburgite, garnet-lherzolite and garnet-pyroxenite and garnet-free dunite, occurs together with eclogite embedded in various continental gneisses. The geological setting, the internal structure, bulk-composition, rare earth elements, isotopic and mineral composition data show that the garnet peridotite derives from a middle Ordovician Alaskan-type layered sub-arc cumulate intrusion of ascending mantle wedge melts. An abyssal peridotite protolith can be excluded. During the Ordovician-Silurian continental collision, thickening and foundering, the Luliangshan peridotite complex was exposed to ultrahigh pressures (UHP) reaching 5.5 GPa possibly >6 GPa at temperatures of 900°C (perhaps up to 1000°C) corresponding to a depth of 200 km. The extreme pressure conditions have been derived from thermobarometry using mineral compositions of the garnet peridotite assemblages, but they are supported by a wealth of decompression-induced mineral exsolutions in UHP minerals and by diamond inclusion in zircon. The Luliangshan garnet peridotite has experienced four stages of retrograde overprint during exhumation that lasted into the Devonian: (i) decompression-induced unmixing of the UHP minerals; (ii) garnet kelyphitisation; (iii) amphibole overprinting and (iv) serpentinization. Hydrous minerals occurring within peak metamorphic assemblage represent pseudo-inclusions, that is reaction products of reactions related to various stages of decompression and cooling rather than prograde inclusions during porphyroblast growth.
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