Wollastonite-bearing assemblages from the Dalradian at Fraserburgh, northeast Scotland and their bearing on the emplacement of garnetiferous granitoid sheets
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Abstract Metasediments of the Tayvallich Subgroup of the Dalradian at Kinnairds Head, Fraserburgh are metamorphosed to sillimanite + K-feldspar grade and form part of the classic high- T low- P Buchan metamorphic terrain. Pelitic samples constrain peak-metamorphic conditions to 615±13°C and 2.2±0.2 kbar. At or close to the metamorphic peak, irregular garnetiferous aplites and autopegmatite bodies intruded the metasediments. Thin marble bands within the sequence are dominated by calcite with diopside, and equilibrated with relatively CO 2 -rich, internally buffered fluids. Where these are in close proximity to granitoid pegmatites, wollastonite dominates the matrix, and fractures and veins running through the rock contain concentrations of grossular and vesuvianite. With increasing distance from the pegmatite, vesuvianite and then grossular disappear, and wollastonite is only patchily developed. Such occurrences require a flushing of the marble by metasomatic (siliceous and aluminous) aqueous fluids which were derived from the de-watering of the adjacent pegmatite as it crystallized. The large quantities of dissolved silica led to pervasive wollastonite formation for several metres. The smaller quantities of Al reacted to form Ca-Al-silicates which were confined to the fractures.Keywords:
Dalradian
Pegmatite
Grossular
Wollastonite
Muscovite
Sillimanite
Hornfels
Migmatite
Sillimanite
Geothermobarometry
Staurolite
Migmatite
Muscovite
Isograd
Paragenesis
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Abstract Metasediments of the Tayvallich Subgroup of the Dalradian at Kinnairds Head, Fraserburgh are metamorphosed to sillimanite + K-feldspar grade and form part of the classic high- T low- P Buchan metamorphic terrain. Pelitic samples constrain peak-metamorphic conditions to 615±13°C and 2.2±0.2 kbar. At or close to the metamorphic peak, irregular garnetiferous aplites and autopegmatite bodies intruded the metasediments. Thin marble bands within the sequence are dominated by calcite with diopside, and equilibrated with relatively CO 2 -rich, internally buffered fluids. Where these are in close proximity to granitoid pegmatites, wollastonite dominates the matrix, and fractures and veins running through the rock contain concentrations of grossular and vesuvianite. With increasing distance from the pegmatite, vesuvianite and then grossular disappear, and wollastonite is only patchily developed. Such occurrences require a flushing of the marble by metasomatic (siliceous and aluminous) aqueous fluids which were derived from the de-watering of the adjacent pegmatite as it crystallized. The large quantities of dissolved silica led to pervasive wollastonite formation for several metres. The smaller quantities of Al reacted to form Ca-Al-silicates which were confined to the fractures.
Dalradian
Pegmatite
Grossular
Wollastonite
Muscovite
Sillimanite
Hornfels
Migmatite
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Dalradian
Andalusite
Staurolite
Pelite
Muscovite
Hornfels
Cordierite
Coesite
Isograd
Sillimanite
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The Journal of the Japanese Association of Mineralogists Petrologists and Economic Geologists (1955)
Ina district is located at the northernmost of the Ryoke zone and mainly composed of Ryoke-granites, Ryoke-metamorphics and non-metamorphic sediments. The eastern margin of this district along the median tectonic line is composed of the Kashio Gneiss. These complex grade into non-metamorphic sediments toward west. The Ryoke zone of this area mainly comprises metamorphic rocks, granites and seine migmatites. The Ryoke metamorphic rocks are composed of schistoe hornfels, mica schists, banded gneisses, meta-diabases, quartz schists and crystalline limestones. From mode of occurrence and petrographic feature, migmatites of this area can be divided into the following three rock types. 1 Schistose fine grained biotite granite and granitic gneiss. 2 Gneissose granite. 3 Fine grained two mica migmatite. Schistose coarse and medium grained hornblende-biotite grancdioritee are widely distributed in the southern part. Medium and coarse grained biotite granites occur in the northern part with the form of stock. Kashio Gneiss is composed of porphyritic biotite gneiss and hallefiintaic gneiss. The relation between metamorphism, granitization, and granite intrusion may be explained as follows: 1. The Ryoke metamorphics have been introduced by regional metamorphism and some of them at the eastern part have been passed into the migmatite of the first type. 2. After the metamorphism and granitization, metamorphic rocks were intruded by schistose coarse grained nornblende biotite granite. As a result of tne intrusion, some of invaded rocks have been locally migmatized to the second and third type.
Migmatite
Hornfels
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Migmatite
Protolith
Hornblende
Isograd
Metamorphic core complex
Grossular
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The Acadian of southwestern Connecticut exposes a middle crustal level orogenic zone comprised of multiply-deformed metapelitic and metaplutonic units that have been intruded by a number of generations of crustally-derived leucogranites. U-Pb ages from garnet + muscovite [+-] biotite leucogranites, pegmatites, and pelitic schists constrain the timing of crustal anatexis and amphibolite facies metamorphism. The Ansonia leucogranite (406 [+-] 13 Ma) is a stitching granite that shares the regional foliation with Silurian and Ordovician orthogneisses. A muscovite granite dike (390 [+-] 3 Ma) that cuts a Silurian orthogneiss has been transposed and is foliated. The Shelton muscovite granite (380 [+-] 3 Ma) is deformed by the regional foliation. Undeformed, garnet two-mica granite (376 [+-] 2 Ma) and muscovite pegmatite (375 [+-] 1 Ma) show that kinematic metamorphic recrystallization pre-dated ca. 375 Ma. Volumetrically minor biotite pegmatite is 354 [+-] 3 Ma. Morphologically distinct monazites in pelitic schists give ages ranging from ca. 395 to 376 Ma. Monazite ages in pelitic schists and crystallization ages in leucogranites and pegmatites probably record episodes of heating, fluid influx, and ductile shearing primarily between 420 and 375 Ma, but extending to 354 Ma in southwestern Connecticut.
Leucogranite
Pegmatite
Muscovite
Anatexis
Sillimanite
Dalradian
Pelite
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The Journal of the Japanese Association of Mineralogists Petrologists and Economic Geologists (1957)
In the Iwaizumi district, northern Kitakami-mountainland, various contact-metamorphic rocks are found along the western margin of the Tanohata granodiorite which is subdivided into two main rock types, the Moichi type and the Otomo type. Petrochemically, especially with respect to K2O/Na2O ratio, the two types of granodiorite are remarkably different from each other, as shown in Fig. 6 (solid circles show Moichi type and open circles show Otomo type). In this respect it is interesting to note the metamorphic behavior in the contact aureoles of both Moichi granodiorite and Otomo granodiorite. The former is characterized generally by sillimanite-andalusite hornfels. Sillimanite and andalusite, however, are replaced by muscovite at the immediate contact where muscovite-banded gneiss is developed. On the other hand, at the contact of the Otomo granodiorite there is no banded gneiss and both sillimanite and andalusite remain stable. Sometimes metamorphosed chert with characteristic quartz-porphyroblasts occurs near the contact. Further, in the eastern aureole of the Otomo granodiorite, cordierite-rocks of the Orijärvi type are found in some places on shear zones which contain the Taro bedded cupriferous pyritic deposit.
Andalusite
Sillimanite
Muscovite
Hornfels
Cordierite
Migmatite
Tectonite
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Sillimanite
Muscovite
Cordierite
Migmatite
Pegmatite
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Citations (6)