Garnet Lu-Hf speed dating: A novel method to rapidly resolve polymetamorphic histories

Simpson, Alexander; Glorie, Stijn; Hand, Martin; Spandler, Carl; Gilbert, Sarah

doi:10.1016/j.gr.2023.04.011

Cited by 21 publications

(4 citation statements)

References 74 publications

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“…Resulting Lu‐Hf dates were calculated as 2‐point (inverse) isochron ages in IsoplotR (Vermeesch, 2018), where the second point comprised an initial 177 Hf/ 176 Hf anchor of 3.55 ± 0.05, which spans the entire range of initial 177 Hf/ 176 Hf ratios of the terrestrial reservoir (e.g., Glorie, Hand, et al., 2023; Spencer et al., 2020). The obtained inverse isochron age for secondary reference material BP‐1 garnet was 1,752 ± 21 Ma (2σ uncertainty including propagated uncertainty from Hogsbo), which is in good agreement with previously published Lu‐Hf dates (1,745 ± 14 Ma and 1,744 ± 13 Ma; Glorie, Mulder, et al., 2023; Simpson et al., 2023, respectively). The same uncertainty filter applied to the U‐Pb ages was employed.…”

Section: Methodssupporting

confidence: 90%

“…Finally, polyphase growth recording multiple orogenic events is likely to be less important in garnet than in more refractory geochronometers (e.g., the U‐Pb system in zircon) because relict or detrital garnet is thought to seldom survive diagenesis and the early stages of prograde metamorphism (Cave et al., 2015; Garzanti et al., 2018; Manzotti & Ballèvre, 2013). However, inherited garnet, which is retained in polycyclic crystalline bedrock without being released to the sedimentary system, may record multiple metamorphic events (e.g., Argles et al., 1999; Simpson et al., 2023; Walker et al., 2021). Polyphase garnet is thus a possible mechanism for the differing U‐Pb and Lu‐Hf ages, although it is not clear why this would preferentially cause one radioisotope system to record older ages unless U was preferentially incorporated during core growth.…”

Section: Discussionmentioning

confidence: 99%

“…Recycling of detrital garnet into younger orogens is thus expected to be rare, although it has been reported (Manzotti & Ballèvre, 2013). Garnet is also commonly eliminated from metasediment during the early stages of metamorphism (Cave et al., 2015), but the preservation of inherited garnet retained in polycyclic crystalline bedrock has also been reported (Argles et al., 1999; Simpson et al., 2023; Walker et al., 2021). Significantly, a compositional control on garnet diagenetic stability has been documented, with a decrease in the Ca content of bulk garnet separates with burial depth and an increase in Fe content (Morton & Hallsworth, 2007).…”

Section: Introductionmentioning

confidence: 99%

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Detrital Garnet Geochronology by In Situ U‐Pb and Lu‐Hf Analysis: A Case Study From the European Alps

Mark,

O’Sullivan,

Glorie

et al. 2023

JGR Earth Surface

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Detrital geochronology employing the widely‐used zircon U‐Pb proxy is biased towards igneous events and metamorphic anataxis; additionally, zircon is highly refractory and frequently polycyclic. Garnet, a rock‐forming and thus commonly‐occuring mineral, is predominantly metamorphic and much less refractory. Here, we report in‐situ U‐Pb and Lu‐Hf ages from detrital garnet hosted in ancient and modern sediments of the European Alps. Both geochronometers are biased towards the most recent garnet‐crystallising metamorphic event in the source area, with fewer inherited ages. This likely reflects efficient removal of inherited garnet during diagenesis and metamorphism, and is in contrast to detrital zircon, apatite, and rutile U‐Pb data which largely record pre‐Alpine ages. Neither the U‐Pb nor Lu‐Hf system in garnet exhibits a relationship between age recovery and composition. However, the Lu‐Hf system in garnet yields significantly better age recovery than the U‐Pb system. Estimated initial 238U/206Pbc values at the time of crystallization are near unity for the garnet analysed in this study, suggesting that garnet does not significantly partition U from Pb during crystallization, at least for the generally almandine‐rich garnets analysed in this study. Hence, Lu‐Hf geochronology of detrital garnet offers an effective method to detect and date the most recent phase of mid‐grade metamorphism in sub‐anatectic source areas, in which detrital zircon U‐Pb analysis may be of less utility.

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Section: Methodssupporting

confidence: 90%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Detrital Garnet Geochronology by In Situ U‐Pb and Lu‐Hf Analysis: A Case Study From the European Alps

Mark,

O’Sullivan,

Glorie

et al. 2023

JGR Earth Surface

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“…The 177 Hf was subsequently calculated from 178 Hf, assuming natural abundances. The 175 Lu was measured on mass as a proxy for 176 Lu (see details in Simpson et al, 2021Simpson et al, , 2023. In addition to Lu and Hf isotopes, other trace elements, including a selection of other rare-earth elements (REEs) (details in File S1 in the Supplement), were measured simultaneously to monitor for inclusions.…”

Section: Methodsmentioning

confidence: 99%

First in situ Lu–Hf garnet date for a lithium–caesium–tantalum (LCT) pegmatite from the Kietyönmäki Li deposit, Somero–Tammela pegmatite region, SW Finland

Szentpéteri,

Cutts,

Glorie

et al. 2024

Eur. J. Mineral.

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Abstract. The in situ Lu–Hf geochronology of garnet, apatite, fluorite, and carbonate minerals is a fast-developing novel analytical method. It provides an alternative technique for age dating of accessory minerals in lithium–caesium–tantalum (LCT) rare-element (RE) pegmatites where zircon is often metamict due to alteration or radiation damage. Currently most dates from Finnish LCT pegmatites are based on columbite-group minerals (CGMs), but their occurrence is restricted to mineralised zones within the pegmatites. Accessory minerals such as garnet and apatite are widespread in both mineralised and unmineralised LCT pegmatites. Lu–Hf dating of garnet and apatite provides an exceptional opportunity to better understand the geological history of these highly sought-after sources for battery and rare elements (Li, Nb, Ta, Be) that are critical for the green transition and its technology. In this paper we present the first successful in situ Lu–Hf garnet date of 1801 ± 53 Ma for an LCT pegmatite from the Kietyönmäki deposit in the Somero–Tammela pegmatite region, SW Finland. This age is consistent with previous zircon dates obtained for the region, ranging from 1815 to 1740 Ma with a weighted mean 207Pb / 206Pb age of 1786 ± 7 Ma.

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Continental evolution from detrital mineral petrochronology

Mulder,

Cawood

2025

Treatise on Geochemistry

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Garnet Lu-Hf speed dating: A novel method to rapidly resolve polymetamorphic histories

Cited by 21 publications

References 74 publications

Detrital Garnet Geochronology by In Situ U‐Pb and Lu‐Hf Analysis: A Case Study From the European Alps

Detrital Garnet Geochronology by In Situ U‐Pb and Lu‐Hf Analysis: A Case Study From the European Alps

First in situ Lu–Hf garnet date for a lithium–caesium–tantalum (LCT) pegmatite from the Kietyönmäki Li deposit, Somero–Tammela pegmatite region, SW Finland

Continental evolution from detrital mineral petrochronology

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