Laser step–heating &lt;sup&gt;40&lt;/sup&gt;Ar/&lt;sup&gt;39&lt;/sup&gt;Ar analyses of biotites from meta–granites in the UHP Brossasco–Isasca Unit of Dora–Maira Massif, Italy

Itaya, Tetsumaru; Hyodo, Hironobu; Imayama, Takeshi; Groppo, Chiara

doi:10.2465/jmps.171201

Cited by 5 publications

(4 citation statements)

References 34 publications

(56 reference statements)

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“…Itaya et al [57] reported excess argon-bearing K-feldspar from metagranite in the UHP Brossasco-Isasca Unit of Dora Maira Massif, Italy, and pointed out the possibility that K-feldspar has trapped the EAW generated by the argon release from micas during the exhumation and cooling of the host lithologies. Itaya et al [58] carried out laser step-heating 40 Ar/ 39 Ar analyses of biotite from the same metagranite and found the biotite crystals which have old age fractions (800 to Another example is represented by some kyanite grains from the river sand in NE Japan, which gave extremely old 40 Ar/ 39 Ar ages (8-6 Ga: [54]). These very old ages have been interpreted as due to the fact that kyanite recrystallized in the host rocks under ultra-high argon pressure derived from radiogenic argon in potassium-rich phases such as phengites during the Barrovian-type retrogression of UHP rocks.…”

Section: Figure A2mentioning

confidence: 99%

Section: Figure A2mentioning

confidence: 99%

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Regional-Scale Paleoproterozoic Heating Event on Archean Acasta Gneisses in Slave Province, Canada: Insights from K–Ar and 40Ar/39Ar Chronology

Sato,

Hyodo,

Sugiura

et al. 2024

Minerals

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Slave Province in Canada is an Archean granite–supracrustal terrane at the northwestern corner of the Canadian Shield. It is bordered by the Thelon–Taltson orogen (2.0 to 1.9 Ga) to the southeast and the Wopmay orogen (1.9 to 1.8 Ga) to the west. Acasta gneisses, exposed in the westernmost Slave Province, and the Wopmay rocks, located close to the gneisses, were systematically collected for K–Ar and laser step-heating 40Ar/39Ar single-crystal analyses of the biotite and amphibole. The K–Ar biotite ages of the four Wopmay samples range from 1816 ± 18 Ma to 1854 ± 26 Ma. The 40Ar/39Ar biotite analyses of the three Wopmay samples yield plateau ages of 1826 ± 21 Ma, 1886 ± 13 Ma, and 1870 ± 18 Ma. These ages fall within the reported U–Pb zircon age range of the Wopmay orogen. The K–Ar biotite ages of the fifteen Acasta gneisses range from 1779 ± 25 Ma to 1877 ± 26 Ma, except for one younger sample (1711 ± 25 Ma). The 40Ar/39Ar analyses of the biotite crystals from three samples give the plateau ages of 1877 ± 8 Ma, 1935 ± 14 Ma, and 1951 ± 11 Ma. The K–Ar amphibole ages from twelve samples range from 1949 ± 19 Ma to 1685 ± 25 Ma. Two samples of them give ages older than the zircon U-Pb age of Hepburn plutons. The 40Ar/39Ar analyses of the amphibole crystals show varied age relations. The two samples give plateau ages of 1814 ± 22 Ma and 1964 ± 12 Ma. Some samples exhibit apparent old ages of ~2000 Ma in the middle temperature fractions. These old fractions result from the amphibole crystals, originally formed in the Archean, being affected by the thermal events during the Wopmay orogeny but not fully resetting. These observations suggest that the K–Ar system ages of the biotite and amphibole in the Archean Acasta gneiss were rejuvenated during the Paleoproterozoic ages. The Discussion explores the possibility that the heat source rejuvenating the K–Ar system ages may have arisen due to asthenospheric extrusion into the wedge mantle, a process likely triggered by subduction rollback.

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Section: Figure A2mentioning

confidence: 99%

Section: Figure A2mentioning

confidence: 99%

Regional-Scale Paleoproterozoic Heating Event on Archean Acasta Gneisses in Slave Province, Canada: Insights from K–Ar and 40Ar/39Ar Chronology

Sato,

Hyodo,

Sugiura

et al. 2024

Minerals

Self Cite

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“…This crystal appears to be significantly older than 2000 Ma in the middle temperature fractions, suggesting that excess argon is trapped in the biotite crystal. Biotite may happen to trap the excess argon waves that occurred in the contact aureoles [27] and in the regional metamorphic belts such as the Barrovian-type metamorphic belt, the eastern Tibetan Plateau [28] and the Dora Maira Massif of Western Alps, Italy [29]. This suggests that the Acasta gneiss originally contained biotite.…”

Section: Laser Step-heatingmentioning

confidence: 99%

Regional-Scale Paleo–Proterozoic Heating Event on Archean Acasta Gneisses in Slave Province, Canada: Insights from K–Ar and 40Ar/39Ar Chronology

Sato,

Hyodo,

Sugiura

et al. 2023

Preprint

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Slave Province in Canada is an Archean granite-supracrustal terrane at the northwestern corner of the Canadian Shield. It is bordered by the Thelon–Taltson orogen (2.0 to 1.9 Ga) to the south-east and the Wopmay orogen (1.9 to 1.8 Ga) to the west. Acasta gneisses exposed in the western-most Slave province and the Wopmay rocks close to the gneisses were collected systematically for K-Ar and laser step-heating 40Ar /39Ar analyses of the biotite and amphibole. The K-Ar biotite ag-es of the four Wopmay samples range from 1816 ± 18 Ma to 1854 ± 26 Ma, which is within the reported U-Pb zircon age range of the Wopmay orogen. The K-Ar biotite ages of the fifteen Acasta gneisses range from 1779 ± 25 Ma to 1877 ± 26 Ma, except for a younger sample (1711 ± 25 Ma). The 40Ar/39Ar biotite analyses of the three samples from the Wopmay orogen give the plateau ages of 1826 ± 21 Ma, 1886 ± 13 Ma, and 1870 ± 18 Ma. On the other hand, the 40Ar/39Ar analyses of the biotite crystals from the Acasta gneiss show a variety of ages. Three samples show the plateau ages of 1877 ± 8 Ma, 1935 ± 14 Ma, and 1951 ± 11 Ma. These plateau ages are a little older than the total gas ages. The 40Ar/39Ar analyses of the amphibole crystals show more varied age rela-tions. The two samples show consistent age relations between the plateau ages (1814 ± 22 Ma and 1964 ± 12 Ma) and the total gas ages (1789 ± 23 Ma and 1967 ± 11 Ma), respectively. Some sam-ples have the apparent old age of 2000 Ma in the middle temperature fractions. These old frac-tions are due to that the originally existed amphibole crystals formed in Archean were affected by the thermal events during the Wopmay orogeny. but did not fully reset. The results suggest that the K-Ar system ages of the biotite and amphibole of the Archean Acasta gneiss that is aged from 4200 to 2600 Ma of zircon U-Pb ages were rejuvenated in the Paleo–Proterozoic ages. The heat source that rejuvenated the K-Ar system ages may have arisen due to the asthenospheric intrusion into the wedge mantle, which took place because of the subduction rollback.

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“…In situ 40 Ar/ 39 Ar ultraviolet (UV) laser-ablation spot analyses is one of the most used methods for giving absolute time constraints and, in particular, data obtained from minerals oriented along metamorphic foliations provide ages of deformation (see e.g. Itaya et al, 2018;Wiederkehr et al, 2009;Villa et al, 2014 and reference therein).…”

Section: Introductionmentioning

confidence: 99%

Timing of exhumation of meta-ophiolite units in the Western Alps: New tectonic implications from 40Ar/39Ar white mica ages from Piedmont Zone (Susa Valley)

Ghignone

Sudo

Balestro

et al. 2021

Lithos

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A multidisciplinary approach to the study of collisional orogenic belts can improve our knowledge of their geodynamic evolution and may suggest new tectonic models, especially for (U)HP rocks inside the accretionary wedge. In the Western Alps, wherein nappes of different origin are stacked, having recorded different metamorphic peaks at different stages of the orogenic evolution. This study focuses on the External (EPZ) and Internal (IPZ) ophiolitic units of the Piedmont Zone (Susa Valley, Western Alps), which were deformed throughout four tectonometamorphic phases (D1 to D4), developing different foliations and cleavages (S1 to S4) at different metamorphic conditions. The IPZ and EPZ are separated by a shear zone (i.e. the Susa Shear Zone) during which a related mylonitic foliation (SM) developed. S1 developed at high pressure conditions (Epidote-eclogite vs. Lawsonite-blueschist facies conditions for IPZ and EPZ, respectively), as suggested by the composition of white mica (i.e. phengite), whereas S2 developed at low pressure conditions (Epidote-greenschist facies conditions in both IPZ and EPZ) and is defined by muscovite. White mica defining the SM mylonitic foliation (T1) is mostly defined by phengite, while the T2-related disjunctive cleavage is defined by fine-grained muscovite. The relative chronology inferred from meso-and micro-structural observations suggests that T1 was nearcoeval respect to the D2, while T2 developed during D4. A new set of radiometric ages of the main metamorphic foliations were obtained by in situ Ar/Ar dating on white mica. Different generations of white mica defining S1 and S2 foliations in both the IPZ and EPZ and SM in the SSZ, were dated and two main groups of ages were obtained. In both IPZ and EPZ, S1 foliation developed at ~46-41 Ma, while S2 foliation developed at ~40-36 Ma and was nearly coeval with the SM mylonitic foliation (~39-36 Ma). Comparison between structural, petrological and geochronological data allows to define time of coupling of the different units and consequently to infer new tectonic implications for the exhumation of meta-ophiolites of the Piedmont Zone within axial sector of the Western Alps.

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Laser step–heating <sup>40</sup>Ar/<sup>39</sup>Ar analyses of biotites from meta–granites in the UHP Brossasco–Isasca Unit of Dora–Maira Massif, Italy

Cited by 5 publications

References 34 publications

Regional-Scale Paleoproterozoic Heating Event on Archean Acasta Gneisses in Slave Province, Canada: Insights from K–Ar and 40Ar/39Ar Chronology

Regional-Scale Paleoproterozoic Heating Event on Archean Acasta Gneisses in Slave Province, Canada: Insights from K–Ar and 40Ar/39Ar Chronology

Regional-Scale Paleo–Proterozoic Heating Event on Archean Acasta Gneisses in Slave Province, Canada: Insights from K–Ar and 40Ar/39Ar Chronology

Timing of exhumation of meta-ophiolite units in the Western Alps: New tectonic implications from 40Ar/39Ar white mica ages from Piedmont Zone (Susa Valley)

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