Potassium-Argon Dates of Biotites from Cordilleran Granites

Baadsgaard, H.; Folinsbee, R. E.; Lipson, Joseph I.

doi:10.1130/0016-7606(1961)72[689:pdobfc]2.0.co;2

Cited by 50 publications

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“…It is conceivable that t z will correlate with the value of 355 M y which Baadsgaard, Folinsbee & Lipson (1961) obtained for the Fitton (Yukon) and Ice Rover (British Columbia) intrusives on the basis of K-Ar dating.…”

Section: Goldfields Region Saskatchewanmentioning

confidence: 89%

Approximate Age of Tectonic Activity Using Anomalous Lead Isotopes

Kanasewich¹

1962

Geophys J Int

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A postulate has been added to the Russell-Farquhar model for anomalous leads which yields a quantitative estimate of the time of their mineralization. Consider tl to t e a time of tectonic activity during which ordinary leads were differentiated from a deep source and either concentrated to form a lead deposit at this time or disseminated throughout the upper crust. Contemporaneously uranium and thorium bearing solutions were incorporated into the same environment. At time t2 tectonic activity recurred in the area. Some of the ordinary leads were remobilized and became contaminated with radiogenic lead to form anomalous lead deposits. Existing lead isotope analyses yield the following results. At Broken Hill, Australia, tl is I 600 million years while t2 is 510 & 80 million years. For Goldfields, Saskatchewan, tl is 2015 My while t2 is 5605 250 My. At Sudbury, Ontario, tl is 1730 My, and t2 is 870 My. For lead deposits around the Ozark Dome area, including Joplin and Bonne Terre, Missouri, tl is 1350 My and tz is about 115 My. For leads in west-central New Mexico, tl is I490 My and t2 is about 69 My. The errors in the estimates are generally quite large but the values quoted are consistent with available geologic data.

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Section: Goldfields Region Saskatchewanmentioning

confidence: 89%

Approximate Age of Tectonic Activity Using Anomalous Lead Isotopes

Kanasewich¹

1962

Geophys J Int

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“…These early studies combined with the K-Ar data of Baadsgaard et al (1961) and a Rb-Sr whole-rock isochron (1 15 Ma) for the White Creek batholith (WCB; Fig. 2) obtained by Wanless et al (19686) suggested that most of the plutons in the Purcell Anticlinorium were emplaced in mid-Cretaceous time.…”

Section: Previous Geochronologymentioning

confidence: 95%

Geochronology and tectonic implications of magmatism and metamorphism, southern Kootenay Arc and neighbouring regions, southeastern British Columbia. Part II: Mid-Cretaceous to Eocene

Archibald¹,

Krogh²,

Armstrong³

et al. 1984

Can. J. Earth Sci.

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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~r/3%r 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 suprastructure 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.Une ceinture de roches de mCtamorphisme rCgional du facies des amphibolites est orientCe nord-sud parallkle au sillon de Purcell, elle coupe transversalement l'arc de Kootenay, et elle est en partie limitCe par des failles. Les roches qui affleurent dans les aurColes de contact des plutons d'ige CrCtacC moyen (-100 Ma) post-tectoniques et les mCtapClites exhibent en direction de l'axe de cette ceinture des assemblages de minCraux mCtamorphiques de pression progressivement croissante. Les courbes des Lges K-Ar sur biotite (55-95 Ma) des roches plutoniques sont regulieres, largement concordantes avec les isogrades metamorphiques, traversent les contacts intrusifs internes des plutons post-tectoniques, et dans les zones mCtamorphiques de pression et tempkrature ClevCes o...

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“…The Brooks Range Geanticline rose in the late Devonian, accompanied by granitic intrusion (Baadsgaard et al 1961 ;Wanless et al 1966), metamorphism, anddeformation (Norrjs et al 1963). Related clastic sediments with maximum thicknesses reported slightly east of the former Richardson Trough, grade from non-marine to marine and from coarser to finer grained eastward and southeastward from the presumed source in Brooks Range Geanticline (Fig.…”

Section: Late Devonian and Mississippian Deposition And Orogenymentioning

confidence: 97%

“…The K-Ar date needs confirmation, however, because an age of 225 m.y. was obtained from another part of the same granitic body (Baadsgaard et al 1961).…”

Section: Greywackementioning

confidence: 99%

Tectonic Evolution of the Northern Canadian Cordillera

Gabrielse¹

1967

Can. J. Earth Sci.

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A tectonic framework that was established in the northern and eastern parts of the northern Canadian Cordillera in the late Proterozoic persisted generally until mid-Devonian time. Late Palaeozoic deposition was strongly influenced by a late Devonian and (or) early Mississippian orogeny, which produced coarse clastic sediments in the northern and western parts of the region, and by a late Pennsylvanian (?) orogeny evident in northern Yukon. The Cassiar and Coast geanticlines were established at least by late Triassic time and controlled the distribution and character of Mesozoic strata southwest of Tintina and Rocky Mountain Trenches.Metamorphism and granitic intrusion were concentrated along Cassiar and Coast Geanticlines. During the Mesozoic and early Tertiary, plutonic activity appears to have occurred at intervals of about 30 million years and was accompanied generally by deformation and development of regional unconformities. Crustal shortening has been much less in Mackenzie Mountains than in southern Rocky Mountains; a marked change in structural style of the eastern Cordillera occurs near Liard River. Many phases of deformation and intrusion have affected rocks in the southwestern part of the region; their differentiation is as yet incomplete.

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Potassium-Argon Dates of Biotites from Cordilleran Granites

Cited by 50 publications

References 0 publications

Approximate Age of Tectonic Activity Using Anomalous Lead Isotopes

Approximate Age of Tectonic Activity Using Anomalous Lead Isotopes

Geochronology and tectonic implications of magmatism and metamorphism, southern Kootenay Arc and neighbouring regions, southeastern British Columbia. Part II: Mid-Cretaceous to Eocene

Tectonic Evolution of the Northern Canadian Cordillera

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