Thermobarometric studies on the Levack Gneisses: Footwall rocks to the Sudbury Igneous Complex
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Granulite and amphibolite facies gneisses and migmatites of the Levack Gneiss Complex occupy a zone up to 8 km wide around the northern part of the Sudbury Igneous Complex (SIC). Orthopyroxene- and garnet-bearing tonalitic and semipelitic assemblages of granulite facies grade occur within 3 km of the SIC together with lenses of mafic and pyroxenitic rock compositions normally represented by an amphibole +/- cpx-rich assemblage; amphibolite facies assemblages dominate elsewhere in this terrain. These 2.711-Ga gneisses were introduced by (1) the Cartier Granite Batholith during late Archaean to early Proterozoic time and (2) the SIC, at 1.85 Ga, which produced a contact aureole 1-1.5 km wide in which pyroxene hornfelses are common within 200-300 m of the contact. A suite of 12 samples including both the opx-gt and amphibole-rich rock compositions have been studied. Garnets in the semipelitic gneisses are variably replaced by a plg-bio assemblage. Thermobarometric calculations using a variety of barometers and thermometers reported in the literature suggest that the granulite facies assemblages formed at depths in the 21-28 km range (6-8 kbar). Textures and mineral chemistry in the garnet-bearing semipelitic rocks indicate that this terrain underwent a second metamorphic event during uplift to depth in the 5-11 km range (2-3 kbar) and at temperatures as low as 500-550 C. This latter event is distinct from thermal recrystallization caused by the emplacement of the SIC; it probably represents metamorphism attributable to intrusion of the Cartier Granite Batholith. These data allow two interpretations for the crustal uplift of the Levack Gneisses: (1) The gneisses were tectonically uplifted prior to the Sudbury Event (due to intrusion of the Cartier Batholith); or (2) the gneisses were raised to epizonal levels as a result of meteorite impact at 1.85 Ga.Keywords:
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A region of metamorphosed supracrustal rocks (pelite, quartzite, marble, and graywacke) and coeval intrusive igneous rocks crop out in a 250 km long orogenic belt in northern Madagascar. The NW-SE trending belt is situated between a juvenile Neoproterozoic magmatic arc terrane (to the north) and an Archean craton, strongly reworked in early Neoproterozoic times (~800-670 Ma), to the south. Pelitic schist and granulite exposed along a ~70 km long transect from Andapa to Sambava contain assemblages ranging from sillimanite-garnet-biotite-orthoclase-cordierite to sillimanite-garnet- biotite-orthoclase and sillimanite-garnet-biotite-muscovite. These assemblages crop out over much of the area in which migmatites and hornblende + augite ± hypersthene ± biotite + perthite granites are common. Partial melting, biotite dehydration reactions, and granite emplacement are interpreted to have been nearly synchronous on the basis of field, structural, and petrographic observations.
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Research Article| December 01, 1968 Regional Metamorphism, Metasomatism, and Partial Fusion in the Northwestern Part of the Okanogan Range, Washington JAMES W HAWKINS, JR. JAMES W HAWKINS, JR. Geological Research Division, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California Search for other works by this author on: GSW Google Scholar Author and Article Information JAMES W HAWKINS, JR. Geological Research Division, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California Publisher: Geological Society of America Received: 05 Dec 1967 Revision Received: 01 Jul 1968 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1968, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1968) 79 (12): 1785–1820. https://doi.org/10.1130/0016-7606(1968)79[1785:RMMAPF]2.0.CO;2 Article history Received: 05 Dec 1967 Revision Received: 01 Jul 1968 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation JAMES W HAWKINS; Regional Metamorphism, Metasomatism, and Partial Fusion in the Northwestern Part of the Okanogan Range, Washington. GSA Bulletin 1968;; 79 (12): 1785–1820. doi: https://doi.org/10.1130/0016-7606(1968)79[1785:RMMAPF]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The northwestern part of the Okanogan Range, Washington, (in the vicinity of 49°00 ′N., 120°00′W.) comprises regionally metamorphosed rocks, largely of supracrustal origin, plus igneous rocks ranging in composition from quartz diorite to quartz monzonite.Metamorphic rocks include quartz dioritic to trondhjemitic orthogneisses, biotitic and hornblendic schists, gneisses and hornfelses, amphibolites, and calc-silicate gneisses. Mineral assemblages indicate that the region was metamorphosed more or less uniformly under conditions equivalent to the sillimanite-cordierite-orthoclase-almandine subfacies (cordierite amphibolite facies) with possible local transition to granulite facies. The presence of andalusite plus sillimanite indicates metamorphism of the Abukuma type (andalusite-sillimanite facies series) in contrast to the kyanite-sillimanite facies series in the Northern Cascade Range to the west. A single cycle of synkinematic metamorphism followed by a phase or separate cycle of static recrystallization in essentially the same P-T field is shown by rock textures and mineral assemblages. The parent material of the metamorphic rocks included mafic flows, sills and dikes, intermediate composition volcanic rocks and graywackes, minor amounts of carbonate-rich and pelitic sedimentary rocks plus an indeterminate amount of leucocratic igneous rock. Prior to metamorphism the average composition of the parent material was approximately tonalitic.The igneous rocks include intrusive granodioritic and quartz monzonitic rocks (average composition is granodiorite) of the Cathedral batholith (Daly, 1912) with an apparent age of 94.0 ± 2.8 m.y. (K/Ar date on biotite) and older trondhjemitic to leucogranodioritic rocks. The older igneous series comprises partly gneissose syntectonic intrusive rocks, and directionless late to post-tectonic rocks which lack intrusive contacts. The latter are interpreted as anatectites formed by (partial) fusion of rocks of quartz dioritic to trondhjemitic composition during regional metamorphism. Field and petrographic data indicate that the anatectites have not been deformed. The average chemical composition of the older igneous series is trondhjemitic. A small layered gabbroic pluton, characterized by iron-rich olivine and pyroxene, has intruded the metamorphic series. Its age relative to the Cathedral batholith is not known.The metamorphism was pre-late Cretaceous and, by analogy with surrounding areas, probably was pre-mid Jurassic but post-Paleozoic. The age of the eugeosynclinal rocks, which were parent materials for the metamorphic rocks, is unknown, but a mid- to late-Paleozoic age is suggested by comparison with rocks of known age in adjacent areas. These eugeosynclinal rocks were definitely sialic, their average composition being tonalitic. A comparison between the average chemical composition of the metamorphic rocks and syn-metamorphic plutons and the average composition of eugeosynclinal rocks of the Pacific rim, such as graywackes, suggests that the rocks of the Okanogan Range may have been formed by nearly isochemical metamorphism of eugeosynclinal sedimentary and volcanic rocks. This content is PDF only. Please click on the PDF icon to access. 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The Southern Jilin complex represents the northeasternmost exposure of the basement rocks in the Eastern block of the North China craton and consists of intensely foliated tonalitictrondhjemitic-granodioritic (TTG) gneisses, weakly foliated syn-tectonic potassium granites, posttectonic hypersthene-quartz diorite and clinopyroxene granodiorite and a minor amount of supracrustal rocks. The supracrustal rocks include ultramafic to felsic volcanic rocks, BIF, felsic paragneisses, pelitic gneisses, calc-silicates, and marbles metamorphosed from amphibolite to granulite facies. The petrological evidence from the mafic granulites and pelitic gneisses indicates three metamorphic mineral assemblages (M1 to M3). The early prograde assemblage (M1) is preserved as mineral inclusions within minerals of the peak assemblages, represented by hornblende + plagioclase + quartz ± biotite in the mafic granulites and biotite + plagioclase + quartz in the pelitic gneisses, with P-T conditions estimated at ~0.6 GPa and ~750°C. The peak assemblage is represented by orthopyroxene + clinopyroxene + garnet + plagioclase + quartz in the mafic granulites and garnet + sillimanite + plagioclase + quartz + biotite in pelitic gneisses, with P-T conditions estimated at 0.84-0.87 GPa and 800-850°C. The post-peak assemblage is characterized by garnet + quartz symplectic coronas in mafic granulites and kyanite replacing sillimanite in the pelitic gneisses, which probably occurred at ~0.85 GPa and 760°C. These mineral assemblages and their P-T estimates define an anticlockwise P-T path involving nearly isobaric cooling, reflecting an origin related to the intrusion and underplating of large amounts of mantle-derived magmas, which are considered to have been related to the interaction of upwelling mantle plumes with the lithosphere in the Eastern block of the North China craton in the Late Archean.
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Research Article| November 01, 1985 A Proterozoic granulite-facies terrane on Roan Mountain, western Blue Ridge belt, North Carolina–Tennessee GERALD L. GULLEY, JR. GERALD L. GULLEY, JR. 1Shell Western E & Pine., P.O. Box 60775, New Orleans, Louisiana 70160 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1985) 96 (11): 1428–1439. https://doi.org/10.1130/0016-7606(1985)96<1428:APGTOR>2.0.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation GERALD L. GULLEY; A Proterozoic granulite-facies terrane on Roan Mountain, western Blue Ridge belt, North Carolina–Tennessee. GSA Bulletin 1985;; 96 (11): 1428–1439. doi: https://doi.org/10.1130/0016-7606(1985)96<1428:APGTOR>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Polymetamorphosed gneisses of Proterozoic age crop out on Roan Mountain, North Carolina–Tennessee, near the western edge of the Blue Ridge belt. These gneisses display Grenville-age, granulite-facies assemblages, including two-pyroxene metabasites and gar-net-sillimanite-orthoclase metapelites. All gneisses were intruded by diabase dikes of the late Precambrian Bakersville Gabbro. Paleozoic amphibolite-facies metamorphism locally formed garnet and amphibole in mafic rocks and kyanite in metapelitic rocks.Two pyroxene geothermometry and mineral stability curves define temperature-pressure ranges of 750–847 °C and 6.5–8.0 kbar for the granulite-facies metamorphism. This metamorphism probably occurred within the lower crust at depths of 23–28 km. Pressure-temperature conditions for the major Paleozoic metamorphism are not well constrained but are estimated to be 700–740 °C and 7.5–9.0 kbar. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
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A review of the rocks of supracrustal origin in the amphibolite and granulite facies terrane in southern Karnataka was presented. In addition to introducing the metasediments in the field area of the workshop, a review was presented of the common occurrence of metasediments in amphibolite and granulite facies rocks worldwide. Models of granulite metamorphism must include a mechanism for the burial of these sediments to the depths recorded by the geobarometers in granulite metamorphism in addition to their reexposure at the surface. Unfortunately, the common occurrence of supracrustals in granulite facies rocks, sometimes with remarkably little deformation was deemed significant.
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