Zoned Ultrabasic and Basic Gneiss Masses in the Early Lewisian Metamorphic Complex at Scourie, Sutherland
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Journal Article Zoned Ultrabasic and Basic Gneiss Masses in the Early Lewisian Metamorphic Complex at Scourie, Sutherland Get access M. J. O'HARA M. J. O'HARA Grant Institute of Geology, University of EdinburghScotland Search for other works by this author on: Oxford Academic Google Scholar Journal of Petrology, Volume 2, Issue 2, 1961, Pages 248–276, https://doi.org/10.1093/petrology/2.2.248 Published: 01 June 1961Keywords:
Ultramafic rock
Pegmatite
Felsic
Hornblende
Migmatite
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Ultramafic rock
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Greenstone belt
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The Spuhler Peak Metamorphic Suite consists of a thick sequence of Archean metamorphic rocks, dominated by amphibolite, orthoamphibole-garnet gneiss, and hornblende gneiss and containing minor quantities of quartzite, aluminous schist, quartzofeldspathic gneiss, and meta-ultramafic rocks. Although the Spuhler Peak Metamorphic Suite represents less than 3% of Precambrian exposures in the Tobacco Root Mountains, it has been recognized as a unique suite in the region, due in large part to the unusually abundant amphibolite and the spectacular appearance of the orthoamphibole-garnet gneisses.
Hornblende
Ultramafic rock
Migmatite
Isograd
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Journal Article Zoned Ultrabasic and Basic Gneiss Masses in the Early Lewisian Metamorphic Complex at Scourie, Sutherland Get access M. J. O'HARA M. J. O'HARA Grant Institute of Geology, University of EdinburghScotland Search for other works by this author on: Oxford Academic Google Scholar Journal of Petrology, Volume 2, Issue 2, 1961, Pages 248–276, https://doi.org/10.1093/petrology/2.2.248 Published: 01 June 1961
Ultramafic rock
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We performed petrological, geochemical, and geochronological study for the Pyeonghae granite gneiss and the Hada leuco-granite gneiss intruding the Paleoproterozoic meta-sedimentary rocks (pyeonghae formation and Wonnam formation) of the Pyeonghae area located in northeastem part of the Yeongnam (Sobaeksan) massif. The Pyeonghae granite gneiss generally has higher abundance of mafic minerals (biotite etc.), and posesses higher , MgO, CaO, , contents but lower and contents than the Hada leuco-granite gneiss which tends to have slightly high and contents and slightly high larger negative Eu anomalies. However both gneisses reveal very similar REE concentrations and chondrite-normalized patterns and apparently show differentiation trend affected by crystallization of biotite, plagioclase, apatite and sphene. Their peraluminous and calc-alkaline chemistry suggests tectonic environment of volcanic arc. SHRIMP Zircon U-Pb age determinations yield upper intercept ages of () and (), and weighted mean ages of () and () for the Pyeonghae granite gneiss and the Hada leuco-granite gneiss respectively, showing overlapping ages within the error. Our study suggests that the Precambrian granitoids in this area intruded contemporaneously with the Buncheon granite gneissin volcanic arc environment.
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Abstract An unusual zircon SHRIMP dating result of a granitic gneiss from the Qinglongshan eclogite‐gneiss roadcut section is presented in this paper. The very peculiar and complicated internal structures, as well as the very low Th/U ratios (0.01–0.08) of the zircons indicate that they were formed by metamorphic recrystallization. Strongly in contrast with previously published zircon U‐Pb ages of the Dabie‐Sulu UHP metamorphic rocks where protolith ages of 600–800 Ma are commonly recorded, only metamorphic age of 218±5 Ma, defined by 18 analytical spots either in rim or in core of zircons, are recorded in this granitic gneiss. This age represents the time of the complete metamorphic recrystallization overprint on primary magmatic zircons. The recrystallization was derived by the UHP metamorphism, and was strengthened by the early stage of retrograde metamorphic fluid activity.
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Recrystallization (geology)
Metamorphic core complex
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Abstract It has been suggested that the ultrabasic and basic gneiss masses in the Lewisian near Scourie and Drumbeg are layered igneous bodies possibly containing primary igneous mineral assemblages. This hypothesis is reviewed in all its aspects and rejected on the grounds of field relationships, mineralogy, and geochemistry.
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The Korean peninsula is part of the Sino-Korean platform and is composed of Precambrian to Holocene rocks. It can be divided into three cratonic blocks, the Nangrim massif of North Korea, and the Gyeonggi and Ryeongnam massifs of South Korea. The Precambrian rocks in the Ryeongnam massif are dominantly plutonic, while in the Gyeonggi massif the metasedimentary rocks are dominant. This Precambrian basement is overlain by Phanerozoic rocks and intruded by Mesozoic plutonic rocks. This study reports U-Pb zircon ages for Precambrian rocks in the southwestern Ryeongnam and southwestern Gyeonggi massifs. The oldest rocks in both massifs belong to the Gneiss complex which is composed of migmatitic and other gneisses, metasedimentary rocks, and mafic plutonic rocks. In the Ryeongnam massif the Gneiss complex is intruded by granite and porphyroblastic orthogneisses. The Kurye granite gneiss has an age of 2120 and 2113 Ma. The Chailbong granite gneiss is younger, having an age of 1923 Ma. The porphyroblastic gneisses were probably emplaced in at least two episodes. The older ones are dated at 1945, 1935, and 1928 Ma, and a younger porphyroblastic gneiss has an age of 1890 Ma. In the Gyeonggi massif the Gneiss complex is intruded by two granite orthogneisses. The Seosan granite gneiss has an age of 1766 Ma and the Hongseong granite gneiss is 687 Ma old. The age for the Hongseong granite gneiss is a lower concordia intercept age, the upper intercept indicates derivation from a ca. 3 Ga protolith.
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Abstract The Older Metamorphic Group and the Older Metamorphic Tonalite Gneiss are classic examples of Palaeaoarchaean high-grade metamorphic rocks of the Singhbhum Craton of India. The Older Metamorphic Group is a supracrustal assemblage that was probably deposited as a greenstone belt-type succession before c. 3.32 Ga, the low-grade equivalents of which are found in parts of the Iron Ore Group. The Older Metamorphic Tonalite Gneiss represents a suite of granitoids that are tectonically interleaved with the supracrustal gneisses and that formed over an extended period of time, 3.53–3.45 Ga and possibly later, by processes of Archaean crustal growth.
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