ORCID Profile
0000-0003-1679-1954
Current Organisations
University of Bern
,
University of Adelaide
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Publisher: Elsevier BV
Date: 09-2021
Publisher: Geological Society of London
Date: 17-12-2021
DOI: 10.1144/JGS2021-094
Abstract: The development of in situ laser ablation Lu–Hf geochronology of apatite, xenotime and garnet has opened avenues to quickly and directly date geological processes. We demonstrate the first use of c aign-style in situ Lu–Hf geochronology of garnet across the high- to ultrahigh-pressure Western Gneiss Region in Norway. Mafic eclogites from this region have been the focus of much work, and were clearly formed during continental subduction during the Caledonian Orogeny. However, abundant quartzofeldspathic and pelitic lithologies record a more complex history, with some preserving polymetamorphic age data, and most containing no indication of high-pressure mineral assemblages formed during subduction. Twenty metapelitic and felsic s les spanning 160 lateral kilometres across the Western Gneiss Region have been analysed using garnet Lu–Hf geochronology. The results reveal Caledonian ages for the majority of the garnets, suggesting that some quartzofeldspathic and metapelitic lithologies were reactive and grew garnet during high- to ultrahigh-pressure metamorphism. However, two ultrahigh-pressure eclogite locations, Verpeneset and Fjørtoft, preserve both Caledonian and Neoproterozoic-aged garnets. Despite significant uncertainties on some of the Lu–Hf geochronological ages, laser ablation Lu–Hf efficiently identifies the polymetamorphic history of parts of the Western Gneiss Region, illustrating the effectiveness of this novel analytical method for rapid mapping of metamorphic ages. Supplementary material: All laser ablation Lu–Hf geochronological data for the garnets analysed in this study are available at 0.6084/m9.figshare.c.5715453 Thematic collection: This article is part of the Caledonian Wilson cycle collection available at: c/caledonian-wilson-cycle
Publisher: Copernicus GmbH
Date: 05-04-2023
Abstract: Abstract. The coupling behaviour of H+ and trace elements in rutile has been studied using in situ polarised Fourier transform infrared (FTIR) spectroscopy and laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) analysis. H2O contents in rutile can be precisely and accurately quantified from polarised FTIR measurements on single grains in situ. The benefits of this novel approach compared to traditional quantification methods are the preservation of textural context and heterogeneities of water in rutile. Rutile from six different geological environments shows H2O contents varying between ∼ 50–2200 µg g−1, with large intra-grain variabilities for vein-related s les with H2O contents between ∼ 500 and ∼ 2200 µg g−1. From FTIR peak deconvolutions, six distinct OH absorption bands have been identified at ∼ 3280, ∼ 3295, ∼ 3324, ∼ 3345, ∼ 3370, and ∼ 3390 cm−1 that can be related to coupled substitutions with Ti3+, Fe3+, Al3+, Mg2+, Fe2+, and Cr2+, respectively. Rutile from eclogite s les displays the dominant exchange reactions of Ti4+ → Ti3+, Fe3+ + H+, whereas rutile in a whiteschist shows mainly Ti4+ → Al3+ + H+. Trace-element-dependent H+ contents combined with LA–ICP–MS trace-element data reveal the significant importance of H+ for charge balance and trace-element coupling with trivalent cations. Trivalent cations are the most abundant impurities in rutile, and there is not enough H+ and pentavalent cations like Nb and Ta for a complete charge balance, indicating that additionally oxygen vacancies are needed for charge balancing trivalent cations. Valance states of multivalent trace elements can be inferred from deconvoluted FTIR spectra. Titanium occurs at 0.03 ‰–7.6 ‰ as Ti3+, Fe, and Cr are preferentially incorporated as Fe3+ and Cr3+ over Fe2+ and Cr2+, and V most likely occurs as V4+. This opens the possibility of H+ in rutile as a potential indicator of oxygen fugacity of metamorphic and subduction-zone fluids, with the ratio between Ti3+- and Fe3+-related H+ contents being most promising.
Publisher: Geological Society of America
Date: 14-04-2022
DOI: 10.1130/G49784.1
Abstract: Garnet is a fundamental expression of metamorphism and one of the most important minerals used to constrain the thermal conditions of the crust. We used innovative in situ laser-ablation ICP-MS/MS Lu-Hf geochronology to demonstrate that garnet in metapelitic rocks enclosing Cambrian eclogite in southern Australia formed during Laurentian Mesoproterozoic metamorphism. Garnet porphyroblasts in hibolite-facies metapelitic rocks yielded Lu-Hf ages between 1286 ± 58 Ma and 1241 ± 16 Ma, revealing a record of older metamorphism that was partially obscured by metamorphic overprinting during ca. 510 Ma Cambrian subduction along the East Gondwana margin. Existing detrital zircon age data indicate the protoliths to the southern Australian metapelitic rocks were sourced from western Laurentia. We propose that the metapelitic rocks of southern Australia represent a fragment of western Laurentian crust, which was separated from Laurentia in the Neoproterozoic and incorporated into the East Gondwana subduction system during the Cambrian. The ability to obtain Lu-Hf isotopic data from garnet at acquisition rates comparable to those for U-Pb analysis of detrital zircon means, for the first time, the metamorphic parentage of rocks as expressed by garnet can be efficiently accessed to assist paleogeographic reconstructions.
Publisher: Elsevier BV
Date: 02-2023
Publisher: Elsevier BV
Date: 08-2019
Publisher: Wiley
Date: 11-12-2020
DOI: 10.1111/JMG.12516
Publisher: Geological Society of America
Date: 20-09-2022
DOI: 10.1130/G49288.1
Abstract: Igneous and metamorphic rocks contain the mineralogical and geochemical record of thermally driven processes on Earth. The generally accepted thermal budget of the mantle indicates a steady cooling trend since the Archean. The geological record, however, indicates this simple cooling model may not hold true. Subduction-related eclogites substantially emerge in the rock record from 2.1 Ga to 1.8 Ga, indicating that average mantle thermal conditions cooled below a critical threshold for widespread eclogite preservation. Following this period, eclogite disappeared again until ca. 1.1 Ga. Coincident with the transient emergence of eclogite, global granite chemistry recorded a decrease in Sr and Eu and increases in yttrium and heavy rare earth element (HREE) concentrations. These changes are most simply explained by warming of the thermal regime associated with granite genesis. We suggest that warming was caused by increased continental insulation of the mantle at this time. Ultimately, secular cooling of the mantle overcame insulation, allowing the second emergence and preservation of eclogite from ca. 1.1 Ga until present.
Publisher: Elsevier BV
Date: 2021
Publisher: Institution of Engineering and Technology (IET)
Date: 16-02-2021
DOI: 10.1049/ELP2.12037
Publisher: Springer Science and Business Media LLC
Date: 17-07-2020
Publisher: Wiley
Date: 21-09-2017
DOI: 10.1111/JMG.12277
Publisher: Elsevier BV
Date: 09-2020
Publisher: Wiley
Date: 17-03-2022
DOI: 10.1111/JMG.12660
Abstract: In this study, data from garnet‐kyanite metapelites in ultrahigh‐pressure (UHP) domains of the Western Gneiss Region (WGR), Norway, are presented. U–Pb geochronology and trace element compositions in zircon, monazite, apatite, rutile and garnet were acquired, and pressure–temperature ( P–T ) conditions were calculated using mineral equilibria forward modelling and Zr‐in‐rutile thermometry. Garnet‐kyanite gneiss from Ulsteinvik record a prograde evolution passing through ~690–710°C and ~9–11 kbar. Zircon and rutile age and thermometry data indicate these prograde conditions significantly pre‐date Silurian UHP subduction in the WGR and are interpreted to record early Caledonian subduction of continental‐derived allochthons. Minimum peak conditions in the Ulsteinvik metapelite occur at ~28 kbar, constrained by an inferred garnet+kyanite+omphacite+muscovite+rutile+coesite+H 2 O assemblage. The retrograde evolution passed through ~740°C and ~7 kbar, first recorded by the destruction of omphacite and followed by the partial replacement of kyanite and garnet by cordierite and spinel. Garnet‐kyanite metapelite from the diamond‐bearing Fjørtoft outcrop documents a polymetamorphic history, with garnet forming during the late Mesoproterozoic and limited preservation of high‐pressure Caledonian assemblages. Similar to the Ulsteinvik metapelite, zircon and rutile age data from the Fjørtoft metapelite also record pre‐Scandian Caledonian ages. Two potential tectonic scenarios are possible: (1) The s les were exhumed at different times during pre‐Scandian subduction of the Blåhø nappe, or (2) the s les do not share a history in the same nappe complex, instead the Ulsteinvik metapelite is a constituent of the Seve‐Blåhø Nappe, whilst the Fjørtoft metapelite shares its history within a separate nappe complex.
No related grants have been discovered for Renée Tamblyn.