Decoding a protracted zircon geochronological record in ultrahigh temperature granulite, and persistence of partial melting in the crust, Rogaland, Norway

Laurent, Antonin; Bingen, Bernard; Duchêne, Stéphanie; Whitehouse, Martin J.; Seydoux‐Guillaume, Anne‐Magali; Bosse, Valérie

doi:10.1007/s00410-018-1455-4

Cited by 36 publications

(28 citation statements)

References 95 publications

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“…In ALR 13‐58, the isomorphic replacement of garnet by cordierite prior to cordierite replacement by osumilite (Figure j) also stands in contrast to previous observations suggesting that cordierite is only a breakdown product of osumilite (Tobi et al., ). Coupling zircon geochronology and microchemistry (Laurent et al., ) with the present monazite data set, suggests melt‐present conditions from 1,040 to 930 Ma in the UHT zone, whereas it is restricted to the 1,040–955 Ma time interval in the orthopyroxene zone. This constrains a minimum temperature of 750°C in the 990–955 Ma time interval for both zones, reflecting very slow cooling rates after M1 metamorphism.…”

Section: Discussionsupporting

confidence: 64%

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Two successive phases of ultrahigh temperature metamorphism in Rogaland, S. Norway: Evidence from Y‐in‐monazite thermometry

Laurent

Duchêne

Bingen

et al. 2018

Journal Metamorphic Geology

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In Rogaland, South Norway, a polycyclic granulite facies metamorphic domain surrounds the late‐Sveconorwegian anorthosite–mangerite–charnockite (AMC) plutonic complex. Integrated petrology, phase equilibria modelling, monazite microchemistry, Y‐in‐monazite thermometry, and monazite U–Th–Pb geochronology in eight samples, distributed across the apparent metamorphic field gradient, imply a sequence of two successive phases of ultrahigh temperature (UHT) metamorphism in the time window between 1,050 and 910 Ma. A first long‐lived metamorphic cycle (M1) between 1,045 ± 8 and 992 ± 11 Ma is recorded by monazite in all samples. This cycle is interpreted to represent prograde clockwise P–T path involving melt production in fertile protoliths and culminating in UHT conditions of ~6 kbar and 920°C. Y‐in‐monazite thermometry, in a residual garnet‐absent sapphirine–orthopyroxene granulite, provides critical evidence for average temperature of 931 and 917°C between 1,029 ± 9 and 1,006 ± 8 Ma. Metamorphism peaked after c. 20 Ma of crustal melting and melt extraction, probably supported by a protracted asthenospheric heat source following lithospheric mantle delamination. Between 990 and 940 Ma, slow conductive cooling to 750–800°C is characterized by monazite reactivity as opposed to silicate metastability. A second incursion (M2) to UHT conditions of ~3.5–5 kbar and 900–950°C, is recorded by Y‐rich monazite at 930 ± 6 Ma in an orthopyroxene–cordierite–hercynite gneiss and by an osumilite gneiss. This M2 metamorphism, typified by osumilite paragenesis, is related to the intrusion of the AMC plutonic complex at 931 ± 2 Ma. Thermal preconditioning of the crust during the first UHT metamorphism may explain the width of the aureole of contact metamorphism c. 75 Ma later, and also the rarity of osumilite‐bearing assemblages in general.

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Section: Discussionsupporting

confidence: 64%

“…(). The tailing of monazite (956 ± 23 Ma; ALR 14‐19; Figure d) and zircon (955 ± 16 Ma; ALR 14‐19; Laurent et al., ) populations down to c . 955 Ma defines a lower bound for melt‐present conditions.…”

Section: Discussionmentioning

confidence: 98%

Two successive phases of ultrahigh temperature metamorphism in Rogaland, S. Norway: Evidence from Y‐in‐monazite thermometry

Laurent

Duchêne

Bingen

et al. 2018

Journal Metamorphic Geology

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“…Furthermore, the step‐age gradient for such a profile would be small enough that a 175 µm radius grain fragment (3.5% of 39 Ar released; Figure a) would yield a plateau age. Nevertheless, the fact that the rocks at Rogaland experienced granulite facies conditions is well established (Blereau et al, ; Drüppel et al, ; Laurent, Bingen et al, ; Tomkins et al, ) and it is generally accepted that the region underwent only limited cooling (temperatures did not drop below the solidus; ≳800ºC) between regional and contact metamorphism (Blereau et al, ; Laurent, Bingen et al, ; Slagstad et al, ). Therefore, the presence of older ages within osumilite is not a function of argon loss through volume diffusion, as diffusive loss under the inferred metamorphic conditions would have removed the older ages entirely.…”

Section: Discussionmentioning

confidence: 99%

“…Although older ( c. 1,070–1,050 Ma) metamorphic monazite and zircon spot ages have been documented (e.g. Drüppel et al, ; Laurent, Bingen et al, ; Laurent et al, ; Slagstad et al, ), these are minor compared to the age populations relating to the two metamorphic peaks. However, as most of the osumilite is inferred to have grown during prograde‐to‐peak regional metamorphism, the older 40 Ar/ 39 Ar osumilite ages indicate that regional metamorphism initiated earlier than as concluded by Bingen, Nordgulen, and Viola () ( c .…”

Section: Discussionmentioning

confidence: 99%

“…1,035 Ma based on U–Pb monazite and zircon geochronology (Blereau et al, ; Degeling, Eggins, & Ellis, ; Drüppel, Elsäßer, Brandt, & Gerdes, ; Laurent, Duchene, Bingen, Bosse, & Seydoux‐Guillaume, ; Laurent et al, ; Möller, O'Brien, Kennedy, & Kröner, ; Slagstad et al, ). Following limited cooling (Blereau et al, ; Laurent, Bingen et al, ; Slagstad et al, ), emplacement of the Rogaland Igneous Complex (RIC) at c . 930 Ma (Schärer, Wilmart, & Duchesne, ) caused contact metamorphism in rocks up to 10 km from the margin of the RIC.…”

Section: Geological Setting and Sample Descriptionmentioning

confidence: 99%

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Closed system behaviour of argon in osumilite records protracted high‐Tmetamorphism within the Rogaland–Vest Agder Sector, Norway

Blereau

Clark

Jourdan

et al. 2019

Journal Metamorphic Geology

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Here, we present results of the first 40Ar/39Ar dating of osumilite, a high‐T mineral that occurs in some volcanic and high‐grade metamorphic rocks. The metamorphic osumilite studied here is from a metapelitic rock within the Rogaland–Vest Agder Sector, Norway, an area that experienced regional granulite facies metamorphism and subsequent contact metamorphism between 1,100 Ma and 850 Ma. The large grain size (~1 cm) of osumilite in the studied rock, which preserves a nominally anhydrous assemblage, increases the potential for large portions of individual grains to have remained essentially unaffected by the effects of diffusive argon loss, potentially preserving prograde ages. Step‐heating diffusion experiments yielded a maximum activation energy of ~461 kJ/mol and a pre‐exponential factor of ~8.34 × 108 cm2/s for Ar diffusion in osumilite. These parameters correspond to a relatively high closure temperature of ~620°C for a cooling rate of 10°C/Ma in an osumilite crystal with a 175 µm radius. Fragments of osumilite separated from the sample preserve a range of ages between c. 1,070 and 860 Ma. The oldest ages are inferred to date the growth of coarse‐grained osumilite during prograde granulite facies regional metamorphism, which pre‐date contact metamorphism that has historically been ascribed to the growth of osumilite in the region. The majority of fragments record ages between c. 920 and 860 Ma, inferred to reflect the growth of osumilite and/or diffusive argon loss during contact metamorphism. The retention of old 40Ar/39Ar dates was facilitated by the low diffusivity of Ar in osumilite (i.e. a closed system), large grain sizes, and anhydrous metamorphic conditions. The ability to date osumilite with the 40Ar/39Ar method provides a valuable new thermochronometer that may constrain the timing and duration of high‐T magmatic and metamorphic events.

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Nanoscale processes of trace element mobility in metamorphosed zircon

Peterman

Reddy

Saxey

et al. 2019

Contrib Mineral Petrol

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Decoding a protracted zircon geochronological record in ultrahigh temperature granulite, and persistence of partial melting in the crust, Rogaland, Norway

Cited by 36 publications

References 95 publications

Two successive phases of ultrahigh temperature metamorphism in Rogaland, S. Norway: Evidence from Y‐in‐monazite thermometry

Two successive phases of ultrahigh temperature metamorphism in Rogaland, S. Norway: Evidence from Y‐in‐monazite thermometry

Closed system behaviour of argon in osumilite records protracted high‐Tmetamorphism within the Rogaland–Vest Agder Sector, Norway

Nanoscale processes of trace element mobility in metamorphosed zircon

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