A north–south-trending belt of amphibolite facies regional metamorphism parallels the Purcell Trench, transects the Kootenay Arc, and is, in part, fault bounded. Towards the axis of this belt progressively higher pressure metamorphic mineral assemblages are exposed in the contact aureoles of post-kinematic, mid-Cretaceous (~100 Ma) plutons and in metapelites. Contours of K–Ar biotite dates for plutonic rocks (55–95 Ma) are regular, are broadly conformable with metamorphic isograds, appear to cross internal intrusive contacts of post-kinematic plutons, and young towards the highest pressure and temperature regional metamorphic zones. Within the sillimanite zone most micas yield K–Ar dates between 40 and 55 Ma; Rb–Sr muscovite dates for deformed and undeformed pegmatites and for muscovite-bearing monzogranite and granodiorite fall between 53 and 84 Ma. U–Pb zircon dates for the Kaniksu batholith and nearby gneiss of uncertain origin yield a lower concordia intercept of 94 Ma. Micas from mid-Jurassic and mid-Cretaceous plutons yielding conventional K–Ar dates between 55 and 100 Ma also yield plateau-shaped 40 Ar/ 39 Ar age spectra that are indicative of normal closure to Ar diffusion due to cooling during this time interval.Contrasting isotopic cooling curves for plutonic rocks in the Purcell Anticlinorium and in the metamorphic infrastructure imply that these regions had different thermal histories. Combined with metamorphic mineral assemblage data and interpreted in terms of uplift and erosion, these curves support a tectonothermal model for the development of the Kootenay Arc and Purcell Anticlinorium that involves (1) mid-Cretaceous emplacement of post-kinematic plutons into a tectonically dormant supra-structure accompanying renewed heating, deformation, and metamorphism in the deepest levels of an evolving infrastructure; (2) slow cooling from mid- to Late Cretaceous time; (3) uplift and erosion of the continental terrace wedge and post-kinematic plutons and parts of the mid-Cretaceous infrastructure in latest Cretaceous–earliest Tertiary time as these rocks were thrust eastward over a steplike feature in the basement leading to the formation of the Purcell Anticlinorium; and (4) rapid uplift and cooling of the metamorphic infrastructure in Eocene time.
A decade of U–Pb dating of zircon and monazite from high-grade metamorphic rocks in the Kapuskasing uplift has identified a series of magmatic and metamorphic events between 2700 and 2585 Ma, and indicates that the onset of regional granulite metamorphism took place at mid-crustal levels of the southern Superior craton ca. 2660 Ma. New U–Pb ages for zircon and monazite have been used to constrain the age of ductile deformation fabrics at two sites in the Ivanhoe Lake fault zone, the structure along which the granulite-facies Kapuskasing structural zone was uplifted. These results suggest that the fault zone was probably active in the late Archean (as young as 2630 Ma) and again at approximately 2500 Ma.
Research Article| March 01, 1994 1.45 Ga granulites in the southwestern Grenville province: Geologic setting, P-T conditions, and U-Pb geochronology J.W.F. Ketchum; J.W.F. Ketchum 1Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia B3H 3J5, Canada Search for other works by this author on: GSW Google Scholar R. A. Jamieson; R. A. Jamieson 1Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia B3H 3J5, Canada Search for other works by this author on: GSW Google Scholar L. M. Heaman; L. M. Heaman 2Royal Ontario Museum, 100 Queen's Park, Toronto, Ontario M5S 2C6, Canada Search for other works by this author on: GSW Google Scholar N. G. Culshaw; N. G. Culshaw 1Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia B3H 3J5, Canada Search for other works by this author on: GSW Google Scholar T. E. Krogh T. E. Krogh 2Royal Ontario Museum, 100 Queen's Park, Toronto, Ontario M5S 2C6, Canada Search for other works by this author on: GSW Google Scholar Author and Article Information J.W.F. Ketchum 1Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia B3H 3J5, Canada R. A. Jamieson 1Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia B3H 3J5, Canada L. M. Heaman 2Royal Ontario Museum, 100 Queen's Park, Toronto, Ontario M5S 2C6, Canada N. G. Culshaw 1Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia B3H 3J5, Canada T. E. Krogh 2Royal Ontario Museum, 100 Queen's Park, Toronto, Ontario M5S 2C6, Canada Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1994) 22 (3): 215–218. https://doi.org/10.1130/0091-7613(1994)022<0215:GGITSG>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation J.W.F. Ketchum, R. A. Jamieson, L. M. Heaman, N. G. Culshaw, T. E. Krogh; 1.45 Ga granulites in the southwestern Grenville province: Geologic setting, P-T conditions, and U-Pb geochronology. Geology 1994;; 22 (3): 215–218. doi: https://doi.org/10.1130/0091-7613(1994)022<0215:GGITSG>2.3.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 SocietyGeology Search Advanced Search Abstract In the southwestern Grenville province, the parautochthonous Britt domain includes a variety of pre-Grenvillian metamorphic and plutonic rocks that were reworked at upper amphibolite facies during the Grenvillian orogeny. Near Pointe-au-Baril, Ontario, a crustal block containing pre-Grenvillian granulite facies mineral assemblages and pre-Grenvillian to early Grenvillian tectonic fabrics has been identified. The block is bounded on the northwest and southeast by extensional shear zones that may have isolated it from regional late Gren- villian deformation. Multiequilibria pressure-temperature (P-T) calculations for orthopyroxene-bearing mafic rocks suggest conditions of 625-700 °C and 7.2-8.4 kbar for the pre-Grenvillian metamorphism. The granulite facies assemblages were locally overprinted during higher pressure Grenvillian metamorphism, which peaked at 720-775 °C and 10.8-11.5 kbar. U-Pb zircon data from migmatitic, mafic supracrustal gneiss indicate metamorphism and leucosome development at ca. 1450-1430 Ma, in agreement with other pre-Grenvillian metamorphic ages for the Central gneiss belt and Grenville Front tectonic zone. An expanding data base on pre-Grenvillian events in the southwestern Grenville province indicates that high-grade metamorphism at ca. 1450-1430 Ma affected a large region of crust and was coeval with widespread felsic to intermediate plutonism. 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.
The region is divided into two domains, which are defined by their contrasting petrology, structure, and aeromagnetic anomaly pattern. The northern domain is underlain by east-trending, steeply south-dipping, migmatized garnet–biotite paragneiss. The southern domain is underlain by gneissic tonalite and trondhjemite, intruded by granite plutons, and with abundant amphibolite inclusions.Twelve U–Pb isotopic age determinations of zircons from two gneisses and four granite bodies from the eastern Lac Seul region of the English River Gneiss Belt indicate the following sequence of events. The tonalite gneiss of the southern domain was emplaced definitely more than 3008 m.y. ago and probably more than 3040 ± 40 m.y. ago. Local anatexis or injection associated with regional metamorphism produced a local pegmatite leucosome in the paragneiss 2681 ± 20 m.y. ago. Late- or post-orogenic granites, which invade both the paragneiss and the tonalite, were emplaced 2660 ± 20 m.y. ago, after the major metamorphism in the region. The youngest rock in the area, a cross-cutting pegmatitic granite, was emplaced 2560 ± 40 m.y. ago.
U-Pb zircon and monazite dates for granulite-facies basement xenoliths from the Popes Harbour dyke on the eastern shore of Nova Scotia provide strong evidence that the Meguma terrane overlies Avalonian basement. Slightly discordant (1.6%), "facetted" zircons from a mafic granulite indicate a minimum crystallization age of ~629 Ma, with near-concordant (0.7%) rounded zircons suggesting a maximum age for the last metamorphic event affecting the zircons at ~575 Ma. Two near-concordant (-0.9 to 0.4%) monazite fractions from a pelitic granulite indicate a major metamorphic disturbance at 378 ± 1 Ma, ~10 Ma prior to dyke entrainment and coincident with Meguma regional metamorphism. Projections from 378 Ma through four highly discordant (15-42%) metapelite zircon fractions give provenance ages between 880 and 1050 Ma and two others project to maximum ages of ~1530 Ma. Unlike Meguma sediments which lack Grenvillian-age (~1 Ga) detrital zircons and are dominated by ~2000 Ma detrital zircons, these dates indicate a dominantly Grenvillian-age provenance for the pelitic xenoliths. The "Avalonian" igneous, metamorphic, and provenance ages from the xenoliths suggest the Meguma rests on Avalonian basement. Because Avalonian sediments need a Grenvillian provenance and Meguma sediments lack such a source but require a 2.0 Ga component missing in the xenoliths, it seems unlikely the Meguma was deposited on Avalonian crust. Thus the dating places on firmer footing the suggestion from earlier structural, seismic, and geochemical work that the Meguma structurally overlies Avalonian terrane. Thrusting occurred between the time of earliest Meguma deformation (~400 Ma) and intrusion of the xenolith-bearing dyke (~370 Ma).
Research Article| June 01, 1990 Are the alteration halos of massive sulfide deposits syngenetic? Evidence from U-Pb dating of hydrothermal rutile at the Kidd volcanic center, Abitibi subprovince, Canada E. S. Schandl; E. S. Schandl 1Department of Geology, Royal Ontario Museum, 100 Queen's Park, Toronto, Ontario M5S 2C6, Canada Search for other works by this author on: GSW Google Scholar D. W. Davis; D. W. Davis 1Department of Geology, Royal Ontario Museum, 100 Queen's Park, Toronto, Ontario M5S 2C6, Canada Search for other works by this author on: GSW Google Scholar T. E. Krogh T. E. Krogh 1Department of Geology, Royal Ontario Museum, 100 Queen's Park, Toronto, Ontario M5S 2C6, Canada Search for other works by this author on: GSW Google Scholar Author and Article Information E. S. Schandl 1Department of Geology, Royal Ontario Museum, 100 Queen's Park, Toronto, Ontario M5S 2C6, Canada D. W. Davis 1Department of Geology, Royal Ontario Museum, 100 Queen's Park, Toronto, Ontario M5S 2C6, Canada T. E. Krogh 1Department of Geology, Royal Ontario Museum, 100 Queen's Park, Toronto, Ontario M5S 2C6, Canada Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1990) 18 (6): 505–508. https://doi.org/10.1130/0091-7613(1990)018<0505:ATAHOM>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation E. S. Schandl, D. W. Davis, T. E. Krogh; Are the alteration halos of massive sulfide deposits syngenetic? Evidence from U-Pb dating of hydrothermal rutile at the Kidd volcanic center, Abitibi subprovince, Canada. Geology 1990;; 18 (6): 505–508. doi: https://doi.org/10.1130/0091-7613(1990)018<0505:ATAHOM>2.3.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 SocietyGeology Search Advanced Search Abstract The Kidd volcanic complex is composed of felsic volcanic and subvolcanic rocks of Archean age. The felsic rocks are intercalated with sedimentary rocks, and are in contact with komatiitic ultramafic rocks. Large diorite plutons were emplaced into the rhyolite, and the complex is overlain by younger basalts. Metasomatic events affecting the lithology of the Kidd volcanic complex include silicification, extensive CO2 metasomatism (carbonate), K-metasomatism (sericite-fuchsite), and chlorite and minor carbonate alterations. Petrographic evidence, supported by stable isotope and fluid inclusion studies, suggests that silicification and early carbonate alteration were synvolcanic, and therefore related to ore deposition. During subsequent extensive K-metasomatism, sericite precipitated in the rhyolite, and fuchsite precipitated in the ultramafic rocks. Although chlorite post-dates K-metasomatism, the micas and chlorite are both found in anastomosing microfissures, commonly occupying the same set of fractures.Hydrothermal rutile formed by the breakdown of magnetiteilmenite during K-metasomatism and chlorite alteration gives an age of 2624 ±62 Ma (95% confidence level) by Pb-Pb isotopic measurements. It is therefore approximately 100 m.y. younger than syngenetic massive sulfide mineralization (2717 ±2 Ma). Sulfide stringers within sericite and chlorite veins suggest some remobilization of the ores during these later events. This alteration assemblage, generally thought to be intimately associated with mineralization, is identical to that found associated with many lode-gold deposits in the Superior province. Recent dating of micas and rutile associated with gold deposits in the Abitibi subprovince gives comparable ages to the rutile in the Kidd volcanic complex, which must therefore record a widespread, late hydrothermal event affecting mineralized rocks. 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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