An 40Ar/39Ar investigation of the contact effects of a dyke intrusion, Kapuskasing Structural Zone, Ontario

Lee, J. K. W.; Onstott, Tullis C.; Hanes, J. A.

doi:10.1007/bf00320969

Cited by 54 publications

(11 citation statements)

References 25 publications

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“…2) to well above the blocking temperature for Ar in muscovite. Similar degassing effects in contact aureoles of intrusions are documented by Lee, Onstott & Hanes (1990), among others.…”

Section: Discussionsupporting

confidence: 57%

Thermal history of thrust sheets in an orogenic wedge: ⁴⁰Ar/³⁹Ar data from the polymetamorphic Seve Nappe Complex, northern Swedish Caledonides

Svenningsen

2000

Geol. Mag.

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The Seve Nappe Complex in the Scandinavian Caledonides contains the fragmented late Precambrian continent-ocean transition between Baltica and the Iapetus Ocean. This passive margin was fragmented and thrust eastwards over the Baltic Shield during Caledonian orogenesis. The individual thrust sheets in the Seve Nappe Complex went through different P-T-t evolutions, resulting in dramatic metamorphic contrasts: eclogite-bearing nappes are juxtaposed with nappes showing no evidence of Caledonian deformation or metamorphism in their interiors. Strain localization to the marginal parts of the thrust sheets left records of both pre-orogenic (rift) and early orogenic (subduction and subsequent uplift) processes in the thrust sheets of the Seve Nappe Complex. Even though it has been transported several hundred kilometres, only the margins of the eastern part of the Sarektjåkkå Nappe are affected by penetrative Caledonian deformation. This part of the Sarektjåkkå Nappe is dominated by pristine tholeiitic dykes and cross-bedded sandstones. The dykes are 608 ± 1 Ma old and make up 70-80 % of the nappe. Widely spaced thin shear zones of the Ruopsok fault system represent the only Caledonian penetrative deformation in the interior of the nappe. Previously published Ar-Ar dates indicate cooling below the closure temperature of hornblende at c. 470 Ma, but numerous ages have been recorded. Ar dating of biotite and muscovite from a cross-laminated metapsammite in the Sarektjåkkå Nappe gave well-defined ages of 428.5 ± 3.6 and 432.4 ± 3.8 Ma, respectively. Muscovite from a shear zone in the Ruopsok Fault System gave 428.2 ± 4.0 Ma, whereas hornblende from the same locality did not yield interpretable data. The results indicate that these rocks were completely degassed at some unknown time, presumably at the emplacement of the dyke swarm. No subsequent excess argon contamination can be detected. A likely candidate for the degassing event is the emplacement of the dykes at 608 Ma. The interior of the nappe, and thus the entire nappe complex, cooled below ~350°C at around 430 Ma. Cooling from more than 500°C at c. 470 Ma to 350°C at c. 430 Ma suggests an average cooling rate of ≤ 4°C/Ma. A prolonged period of slow cooling (≈exhumation?) following the initial, rapid uplift of the eclogitebearing nappes and Early Ordovician construction of the Seve Nappe Complex is suggested. *

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“…2) to well above the blocking temperature for Ar in muscovite. Similar degassing effects in contact aureoles of intrusions are documented by Lee, Onstott & Hanes (1990), among others.…”

Section: Discussionsupporting

confidence: 57%

Thermal history of thrust sheets in an orogenic wedge: ⁴⁰Ar/³⁹Ar data from the polymetamorphic Seve Nappe Complex, northern Swedish Caledonides

Svenningsen

2000

Geol. Mag.

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“…Each of these ages corresponds to a northern Australian basin or a magmatic event that in many cases is also recorded by uraninite in the 207 Pb/ 206 Pb system. Figure 10 compares ages obtained from illite and sericite by the 40 Ar/ 39 Ar method of Lee et al (1990) and 207 Pb/ 206 Pb ages from uraninite by the LA-ICP-MS method of Kyser et al (2003). A small narrow peak at 1788+10 Ma is only recorded by illite in diagenetic aquitards belonging to the Kombolgie Subgroup.…”

Section: Age Determinations and Implicationsmentioning

confidence: 98%

“…Crystalline illite and sericite samples extracted from the alteration assemblage within the deposits and sandstone from the Kombolgie Subgroup were analysed using the 40 Ar/ 39 Ar method of Lee et al (1990). These samples often give disturbed age spectra that are bellshaped or indicate strong superficial 40 Ar* loss or 39 Ar recoil.…”

Section: Age Determinations and Implicationsmentioning

confidence: 99%

Advances in understanding the Kombolgie Subgroup and unconformity-related uranium deposits in the Alligator Rivers Uranium Field and how to explore for them using lithogeochemical principles

Polito

Kyser

Alexandre

et al. 2011

Australian Journal of Earth Sciences

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The Alligator Rivers Uranium Field (ARUF) includes the mined and unmined Jabiluka, Ranger, Koongarra and Nabarlek unconformity-related uranium deposits and several small prospects including the newly discovered King River prospect. Uranium mineralisation is hosted by a variety of metamorphosed Nimbuwah Domain lithologies that are unconformably overlain by the Kombolgie Subgroup, a basin package of unmetamorphosed arenites and mafic volcanics. All of the uranium deposits and prospects preserve an identical alteration assemblage that is subdivided into a distal and proximal alteration zone. The distal alteration zone comprises an assemblage of sericite and chlorite that replace albite and amphibole. In some cases, this alteration can be traced 41000 m from the proximal alteration zone that is dominated by uraninite, hematite, chlorite and sericite. Uranium precipitated in the basement as uraninite at 1680 Ma at around 2008C from a fluid having d 18 O fluid values of 3.0+2.8% and dD fluid values of 728+13% VSMOW reflecting an evolved marine source. These geochemical properties are indistinguishable from those recorded by diagenetic illite and chlorite that were collected from the Kombolgie Subgroup sandstones across the ARUF. The illite and chlorite formed in diagenetic aquifers, and where these aquifers intersected favourable basement rocks, such as those containing graphite or other reductants, U was precipitated as uraninite. Therefore, it is proposed that the Kombolgie Subgroup is the source for fluids that formed the deposits. A post-ore alteration assemblage dominated by chlorite, but also comprising quartz+dolomite+sulfide veins cut the uranium mineralisation at all deposits and has historically been recorded as part of the syn-ore mineralisation event. However, these minerals formed anywhere between 1500 to 630 Ma from fluids that have distinctly lower d 18 O fluid values around 1.5% and lower dD fluid values around 745% reflecting a meteoric water origin. Despite unconformity-related uranium deposits having a large alteration halo, they remain difficult to find. The subtle alteration of albite to sericite several hundred metres from mineralisation occurs in isolation of any increase in trace elements such as U and radiogenic Pb and can be difficult or impossible to identify in hand specimen. Whole rock geochemical data indicate that Pearce Element Ratio (PER) analysis and General Element Ratio (GER) analysis may vector into this subtle alteration because it does not rely on an increase in trace elements to identify proximity to ore. PER and GER plots, Al/Ti vs (2Ca þ Na þ K)/Ti, Na/Al vs (Na þ K)/Al, K/Al vs (Na þ K)/Al and (Fe þ Mg)/Al vs (Na þ K)/Al provide a visual guide that readily distinguish unaltered from altered samples. A plot of (Na þ K)/Al and (Fe þ Mg)/Al on the x-axis against the concentration of trace elements on the y-axis reveals that U, Pb, Mo, Cu, B, Br, Ce, Y, Li, Ni, V and Nd are associated with the most intensely altered samples. The lithogeochemical vectors should aid explorers search...

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“…The 40Ar/ 39Ar mineral ages for polymetamorphic rocks are commonly intermediate to the timing of superimposed metamorphisms, recording a relict isotopic component from earlier events, even in cases where the superimposed metamorphism or metamorphisms exceeded the nominal closure temperature of the minerals for a substantial length of time (for muscovite, [1][2][3][4][5][6]. Recent laser studies (4)(5)(6)(7)(8)(9) indicate that gradients in 40Ar concentration form at a scale controlled by the crystal size (up to -1000 pm), with a form that is characteristic of the thermal evolution. The occurrence of relict isotopic compositions in thermally complex samples and the scales of isotopic gradients determined by laser studies suggest that grain size, microstructural characteristics, and ionic substitutions have substantial effects on argon retention and closure age.…”

mentioning

confidence: 99%

Laser ⁴⁰ Ar/ ³⁹ Ar Evaluation of Slow Cooling and Episodic Loss of ⁴⁰ Ar from a Sample of Polymetamorphic Muscovite

Hames

Hodges

1993

Science

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Volume diffusion models predict that crystals with large diffusion dimensions can record a wide range of thermal conditions in the Earth's crust. Direct measurements of the zoning of radiogenic argon-40 in single muscovite porphyroblasts, from a complex terrain in the Vermont Appalachians, record multiple crustal events that span 150 million years. The crystal radius was the effective dimension for argon diffusion (approximately 1000 micrometers). Late deformation features inside the crystals locally decreased the diffusion dimension and promoted loss of argon-40. Zoning patterns of radiogenic isotopes, as observed in this study, are an increasingly important diagnostic tool for studying the thermal record of tectonic processes.

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An 40Ar/39Ar investigation of the contact effects of a dyke intrusion, Kapuskasing Structural Zone, Ontario

Cited by 54 publications

References 25 publications

Thermal history of thrust sheets in an orogenic wedge: ⁴⁰Ar/³⁹Ar data from the polymetamorphic Seve Nappe Complex, northern Swedish Caledonides

Thermal history of thrust sheets in an orogenic wedge: ⁴⁰Ar/³⁹Ar data from the polymetamorphic Seve Nappe Complex, northern Swedish Caledonides

Advances in understanding the Kombolgie Subgroup and unconformity-related uranium deposits in the Alligator Rivers Uranium Field and how to explore for them using lithogeochemical principles

Laser ⁴⁰ Ar/ ³⁹ Ar Evaluation of Slow Cooling and Episodic Loss of ⁴⁰ Ar from a Sample of Polymetamorphic Muscovite

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An 40Ar/39Ar investigation of the contact effects of a dyke intrusion, Kapuskasing Structural Zone, Ontario

Cited by 54 publications

References 25 publications

Thermal history of thrust sheets in an orogenic wedge: 40Ar/39Ar data from the polymetamorphic Seve Nappe Complex, northern Swedish Caledonides

Thermal history of thrust sheets in an orogenic wedge: 40Ar/39Ar data from the polymetamorphic Seve Nappe Complex, northern Swedish Caledonides

Advances in understanding the Kombolgie Subgroup and unconformity-related uranium deposits in the Alligator Rivers Uranium Field and how to explore for them using lithogeochemical principles

Laser 40 Ar/ 39 Ar Evaluation of Slow Cooling and Episodic Loss of 40 Ar from a Sample of Polymetamorphic Muscovite

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Thermal history of thrust sheets in an orogenic wedge: ⁴⁰Ar/³⁹Ar data from the polymetamorphic Seve Nappe Complex, northern Swedish Caledonides

Thermal history of thrust sheets in an orogenic wedge: ⁴⁰Ar/³⁹Ar data from the polymetamorphic Seve Nappe Complex, northern Swedish Caledonides

Laser ⁴⁰ Ar/ ³⁹ Ar Evaluation of Slow Cooling and Episodic Loss of ⁴⁰ Ar from a Sample of Polymetamorphic Muscovite