![]() Petrological investigations show that allanite commonly forms at the expense of detrital or metamorphic monazite (or more rarely detrital allanite Goswami-Banerjee & Robyr, 2015) at 400–450☌ ( Janots et al., 2008,, 2011), close to the biotite-in reaction ( Wing et al., 2003 Goswami-Banerjee & Robyr, 2015), and that it is consumed to form monazite at the staurolite-in reaction (e.g. The metamorphic sequence of REE-bearing minerals in metapelites at low- to medium-grade metamorphism is relatively well known (see Engi, 2017, for a review). Janots et al., 2009 Janots & Rubatto, 2014). ![]() Allanite is stable over a wide range of temperature ( T) and pressure ( P) ( Wing et al., 2003 Janots et al., 2006,, 2008 Tomkins & Pattison, 2007), including relatively low-grade metamorphic conditions, where it may represent the only target mineral for U–Th/Pb dating (e.g. The use of allanite as a geochronometer has progressively increased in recent decades to date metamorphic stages ( Gregory et al., 2007,, 2012 Janots et al., 2009 Kim et al., 2009 Radulescu et al., 2009 Cenki-Tok et al., 2011 Rubatto et al., 2011 Janots & Rubatto, 2014 Loury et al., 2016 Giuntoli et al., 2018). This study also shows that when allanite is the principal phase in a mineral assemblage datable by U–Th/Pb, detailed observations of allanite textures may be highly informative in constraining the timing of its growth relative to other major mineral phases. 180 Ma, and a late greenschist overprint. 200 Ma, a thermal relaxation and exhumation from c. Our results allow different metamorphic stages for the studied transect in the central Longmen Shan to be refined: a prograde path at c. Allanite and its epidote rims, however, are fragmented and partly replaced by a retrograde assemblage of Qz + Pb-depleted (<100 ppm) monazite, providing an age <90–100 Ma. In the two samples collected close to the major Wenchuan Shear Zone-deformed up to mylonitization and retrogressed under greenschist-facies conditions (3–4 ± 1 kbar, 350–400☌)-allanite still preserves the peak metamorphic ages ( c. ![]() The timing of allanite appearance strongly correlates with the biotite-in reaction predicted by the models and observed in microstructures. 200 Ma, whereas syn- to post-garnet allanite has ages of c. This relative chronology is confirmed by in situ U–Th/Pb allanite dating: pre-garnet allanite shows ages of c. In the two samples where allanite is observed as inclusions in garnet, garnet shows no textural zoning and a low Y content ( 520☌). Garnet is, along with allanite, critical to reconstruct the REE budget of these rocks. Allanite is the main rare earth element (REE)-bearing accessory mineral but it exhibits different textures, such as epidote rims with distinct REE contents as well as late inclusion-like dissolution features. All samples experienced similar peak temperatures of 560–600☌. Microstructural observations were combined with whole-rock compositions, detailed mineral characterization, phase equilibria modelling, and in situ U–Th/Pb allanite dating to gain insights into the allanite reactivity relative to other rock-forming minerals. This study focuses on five garnet–biotite metapelites retrogressed to different extents, from the internal domain of the Longmen Shan (eastern Tibet) from which few petrochronological data documenting the metamorphic ages are available. Linking the timing of allanite growth to metamorphic conditions in metapelites is particularly challenging because of the large variety of allanite textures and chemical compositions.
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