minerals Article Allanite in Variscan Post-Collisional Lamprophyre Dykes from Les Guilleries (NE Iberia) as a Part of Rare Earth Elements Recycling in Collisional Orogens Esteban Mellado 1, * , Mercè Corbella 1 and Andrew Kylander-Clark 2 1 Department of Geology, Universitat Autònoma de Barcelona, Edifici Cs, 08193 Bellaterra, Spain; merce.corbella@uab.cat 2 Department of Earth Science, University of California, Santa Barbara, CA 93106, USA; kylander@geol.ucsb.edu * Correspondence: esteban.mellado@uab.cat Abstract: Recent studies of Late Permian calc-alkaline lamprophyre dykes located in the Les Guil- leries Paleozoic massif of the Catalan Coastal Range have revealed that allanite is present as the main REE-bearing accessory phase, which is the object of this study. The lamprophyre dykes are amphibole–plagioclase-dominated spessartites with a wide variety of accessory phases, including titanite, ilmenite, allanite, fluorapatite, spinel, zircon, and sulfides, and show complex alteration textures related to secondary albite, chlorite, epidote, titanite and calcite. The allanite crystal compo- sition, analyzed by SEM-EPMA and LA-ICP-MS, evidences the solid solution between epidote and allanite with a ferriallanite component, similar to what is found in Variscan post-collisional granitoids from western Europe. However, heterogeneity in crystal shapes, sizes, type of zoning, dissolution embayment textures, growth of epidote coronas, mineral paragenesis, and the unique geochemi- Citation: Mellado, E.; Corbella, M.; cal characteristics of allanite crystals suggest multiple crystallization events. At least two types of Kylander-Clark, A. Allanite in allanite–epidote composite grains have been identified: allanite Type I, with regular allanite–epidote Variscan Post-Collisional core-to-rim zoning and a secondary allanite rim; and allanite Type II, with anhedral allanite cores Lamprophyre Dykes from Les surrounded by epidote coronas. Additionally, irregular zoning, complex dissolution textures and REE Guilleries (NE Iberia) as a Part of Rare Earth Elements Recycling in redistribution suggest the occurrence of deuteric and/or post-magmatic processes, which are also Collisional Orogens. Minerals 2022, common in Variscan post-collisional plutons from the Catalan Coastal Range and nearby Paleozoic 12, 954. https://doi.org/10.3390/ massifs. Multivariate statistical analyses of major elements in allanite–epidote composite grains min12080954 show a relationship between major textural and geochemical variations for three out of ten principal components, mainly related to cationic substitutions between ferriallanite-(Ce) and epidote, but also Academic Editors: Sergei Khromykh involving Mn and Ti(REE3+ + Fe2+ + Ti4+ + Mg2+ + Mn2+ = Al3+ + Ca2+ + Fe3+ ). The allanite U-Pb-Th- and Andrei Tsygankov weighted mean age of 265 ± 15 Ma (MSWD = 0.57) is roughly similar to the age of emplacement of Received: 27 June 2022 the lamprophyres in the upper crust in the mid–late Permian, and coincides with the period following Accepted: 26 July 2022 the main tectonometamorphic and magmatic events of the post-collisional evolution in the Catalan Published: 28 July 2022 Coastal Range. Th/U and La/Sm ratios suggest a metamorphic origin for most allanite grains, but a Publisher’s Note: MDPI stays neutral combination of metamorphic processes prior to partial melting, early–late magmatic crystallization, with regard to jurisdictional claims in and/or post-magmatic hydrothermal processes is the most plausible explanation to account for the published maps and institutional affil- diversity of allanite grains in Les Guilleries lamprophyres. iations. Keywords: allanite; geochemistry; EPMA; calc-alkaline lamprophyre; geochemistry; Les Guilleries massif; Variscan orogeny; U-Pb ages Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and 1. Introduction conditions of the Creative Commons Allanite-bearing calc-alkaline lamprophyres are widespread in the Variscan Belt of Attribution (CC BY) license (https:// western Europe [1–4] and generally represent low-volume pulses of mantle-derived mafic creativecommons.org/licenses/by/ magmas variably enriched in LILEs, HFSEs, and REEs, and emplaced in the brittle upper 4.0/). crust as dyke swarms during post-collisional periods of the Variscan orogeny, unlike Minerals 2022, 12, 954. https://doi.org/10.3390/min12080954 https://www.mdpi.com/journal/minerals Minerals 2022, 12, 954 2 of 17 Permian and Cretaceous alkaline lamprophyre dykes that are post-Variscan. While the relative abundance of amphibole–phlogopite vs. plagioclase–K-feldspar is used to classify calc-alkaline lamprophyres and is thus the usual object of studies [5], the diversity of accessory phases present in these rocks is poorly constrained. Many studies of Variscan calc-alkaline lamprophyres have reported the presence of allanite as the main REE-bearing phase [2–4], but little information about their morphology, geochemistry and geochronology has been provided. Recent studies of post-collisional Variscan spessartite dykes in the Les Guilleries massif (Catalan Coastal Range, NE Iberia) have identified allanite as the main REE-carrier phase [6]. Allanite is a member of the epidote group, and its structure can accommodate large quantities of many chemical elements, mainly depending on the system composition rather than on the P-T conditions. This mineral testifies to the diversity of mineral formation environments, as well as to secondary processes such as metamictization and hydrothermal alteration [7,8]. Allanite’s simplified crystal formula is A2 M3 (SiO4 )(Si2 O7 )O(OH), where the A sites are mainly occupied by Ca2+ and REE3+ , and M sites are mainly occupied by Al3+ , Fe3+ , Fe2+ , Mg2+ , Mn2+,3+ , Ti4+ , and Th4+ [8,9]. Solid ferriallanite–allanite–epidote– clinozoisite solid solutions are well known within many igneous, metamorphic and sedi- mentary rocks, and, as they can also be an important repository of Th and U, which makes them a promising object for U-Pb-Th dating [10]. Allanite composition varies in terms of the ratio Fe3+ /(Fe3+ + Al) but is limited by whole-rock composition, so that epidote group minerals in metabasite lithologies are more Fe-rich than those in metasedimen- tary lithologies, which tend to be more Al-rich and typically include zoisite [11]. Slow rates of intra-crystalline Fe3+ -Al exchange, especially at low temperatures, preserve com- plex zonation patterns in individual grains that can serve as a recorders of continuous or discontinuous prograde and retrograde reactions and the P-T-fluid-redox conditions of metamorphism [11]. Allanite can exhibit a large variety of textures depending on the reaction history during metamorphism [12–14]. The transformation of allanite to mon- azite during low-to-medium-grade metamorphism is relatively well known [15]. Allanite commonly forms at the expense of detrital, magmatic, or metamorphic monazite close to the biotite-in reaction, at the transition between the chlorite and biotite zones [13,14,16]; allanite is consumed to form monazite during the staurolite-in reaction, at the transition between the garnet and the staurolite–kyanite zones [14,16]. Thermodynamic modelling in schists shows that the first metamorphic allanite appears at ~425 ◦ C and 4.5 kbar, and transforms to monazite at ~600 ◦ C and 7.5 kbar [16]. The paragenesis allanite+apatite forms during retrograde metamorphism at the expense of monazite via fluid-assisted dissolution-precipitation processes at greenschist facies [17], commonly related to shear zones [13,18]. REE-zoning in igneous allanite has long been recognized as reflecting fractional crys- tallization [19], most commonly from melts of high water content [20]. Experimental data on igneous allanite solubility [21,22] cover a range of melt compositions and pressures. Where allanite forms in magma, it largely controls the LREE content of the melt because it can incorporate them at weight-% level. For Th, U, and Y, as noted above, competition from coexisting phases (zircon, monazite, xenotime, titanite or rutile) may intervene. As sum- marized by Smye et al. [23], REE fractionation in allanite depends on magma composition. Typically, chondrite-normalized REE patterns are steeply negative for early-formed allanite, but depletion of LREEs then leads to nearly flat patterns, and the overall core-to-rim zoning in allanite may end with REE-enriched (or even REE-poor) peripheral epidote [24]. La/Sm vs. Th/U and La/Sm vs. Eu/Eu* (europium anomaly) have been used to discriminate be- tween metamorphic and magmatic allanite, considering that fluid has lower differentiation ability for La (LREE) and Sm (MREE) than magmatic melt, whereas the mobility of U in the fluid is higher than that in the melt [25,26]. This study characterizes allanite crystals from Les Guilleries spessartite dykes (amphibole–plagioclase-dominated lamprophyres) to gain insights about their occurrence, chemical composition, age and petrogenetic implications. The presented data will be useful Minerals 2022, 12, 954 3 of 17 for further comparison and correlation between post-collisional lamprophyre dykes of the European Variscan Belt. 2. Geological Setting The Variscan Belt in NE Iberia is found in the Catalan Coastal Range, the Pyrenees and the Iberian Ranges. Their geology records the syn- to post-collisional magmatic evolution from peak metamorphic conditions in the Late Carboniferous [27] until the end of the orogenic cycle in the Late Permian–Triassic, which is marked by the shift from post- collisional calc-alkaline magmatism to post-orogenic alkaline magmatism [28,29]. Felsic and mafic igneous rocks of Late Carboniferous–Early Permian age and syn- to post-collisional of calc-alkaline affinity outcrop in the area. They appear to have formed from variable degrees of lower crustal assimilation and differentiation and were emplaced in the mid–upper Variscan crust in a local predominantly extensional context. They are linked to a regional dextral strike-slip regime related to late-Variscan shear zones that must have displaced Gondwana to the west with respect to Laurasia during orogenic collapse [30]. The mafic complexes are suggested to have derived from a mantle source enriched in LILEs and LREEs, attributed to metasomatic processes of the lithospheric mantle during previous subduction events [30]. In Les Guilleries Massif, located 80 km NNE of Barcelona, outcrop the oldest Variscan igneous rocks which form the Susqueda complex, the largest basic massif of the Catalan Coastal Range that intruded the Paleozoic basement. The mafic complex is composed of quartz diorites and diorites with calc-alkaline geochemical affinity, together with horn- blende gabbros and hornblendites [31,32]. A syn-collisional diorite sheet has provided a U-Pb age of 323.6 ± 2.8 Ma [33] but most mafic intrusives are younger and post-tectonic [34]. Felsic rocks are younger too; leucogranites have been dated to 305–299 Ma old [33], and porphyritic granites have yielded unpublished U-Pb SHRIMP ages of 284 ± 3 Ma [35], which agrees with the age of similar mafic and felsic plutonic bodies in the nearby Montne- gre Massif (40 Ar/39 Ar ages between ca. 291 and 285 Ma [36]). This massif also contains ultrabasic/basic-to-intermediate rocks associated with late-Variscan calc-alkaline granites, showing mineralogical and geochemical characteristics typical of appinite suites, with cumulate hornblendites and gabbros crystalized from K-rich and fluid-rich magmas, and a complex mingled zone between diorites and biotite granodiorites [37,38]. Les Guilleries lamprophyres appear as a subvertical dyke swarm emplaced in the in- tersection between two perpendicular regional fault systems oriented NE–SW and NW–SE (Figure 1a,b). These dykes crosscut all previous sequences including schist and marbles from the basement and Variscan leucogranites, granodiorites, quartz-monzonites and peg- matites. The lamprophyres are porphyric to panidiomorphic spessartites, with chloritized mafic phenocrysts of different shapes and sizes between 0.5 and 1.5 mm, where amphibole is the only recognizable primary phenocrystal phase [6]. The groundmass contains mainly of chloritized and feldspathic domains (anorthite > k-feldspar), both enclosing variable proportions of amphibole (actinolite to hornblende), titanite, epidote, calcite, ilmenite, allanite, fluoroapatite, spinel, zircon, pyrite, and spinel; and variably replaced by secondary calcite, epidote, chlorite, albite, titanite and quartz. These lamprophyres present a calc- alkaline geochemical signature similar to the other igneous rocks of the area, with hybrid mantle–crust composition typical of these rocks; that is, with enrichments in MgO, Cr and Ni together with LILEs, HFSEs and REEs, and initial Sm-Nd isotopic compositions consistent with an enriched subcontinental lithospheric mantle (SCLM) source [6]. Titanite U-Pb dating yields a MSWD age of 262 ± 7 Ma, which place these dykes as the youngest calc-alkaline mafic intrusion found in the area related to the fragmentation of the Variscan Belt [6]. Minerals Minerals 2022, 2022, 12, 12, x954 4 of4 17 of 18 Figure1.1.(a) Figure (a)Simplified Simplifiedgeological geologicalmap mapofof the the northernmost northernmost Catalan Catalan Coastal Coastal Range Range andand geographic geographic locationof location ofLes LesGuilleries Guilleriesmassif; massif;(b) (b)Photograph Photograph of of LesLes Guilleries Guilleries spessartites spessartites dykes. dykes. 3. 3. Materials Materialsand andMethods Methods Petrographic Petrographicanalyses analysesand andSEMSEMcharacterization characterization of of lamprophyre lamprophyre allanite crystals allanite of of crystals 10 thin sections were performed at the Geology Department and 10 thin sections were performed at the Geology Department and Serveis de Microscòpia Serveis de Microscòpia of the Universitat Autònoma de Barcelona. of the Universitat Autònoma de Barcelona. The chemical composition of allanite was determined using a JEOL JXA-8230 electron The chemical composition of allanite was determined using a JEOL JXA‐8230 electron microprobe at an accelerating voltage of 20 kV and a beam size of 3–5 µm at the Centres microprobe at an accelerating voltage of 20 kV and a beam size of 3–5 μm at the Centres Científics i Tecnològics of the Universitat de Barcelona. Eighteen allanite crystals from two Científics i Tecnològics of the Universitat de Barcelona. Eighteen allanite crystals from two variably altered calc-alkaline lamprophyre dykes were analyzed for three different sets variably of elements altered calc‐alkaline to include lamprophyre Si, Ti, Al, Ca, Fe, Mg,dykes Mn, La, wereCe,analyzed Pr, Nd, Pr, forSm, threeEu,different Dy, Yb, Lu,sets of elements to include Si, Ti, Al, Ca, Fe, Mg, Mn, La, Ba, Zn, Cr, V, K, Na, Th, U and F. Several elements were below detection limits: Eu to Lu Ba, Ce, Pr, Nd, Pr, Sm, Eu, Dy, Yb, Lu, Zn, Cr,ppm), (<1300 V, K,CrNa, < 600Th, U and ppm, F. Several V < 1000 ppm, Th elements and U < 2500wereppm, belowK La > Nd) and Fe concentration, and inversely proportional to Al, Si and Ca concentration (Figure 3). Table 1. Range of chemical compositions obtained by EPMA of defined allanite types. Allanite Type Type I Type I (rim) Type II Type II (EpC) Other Nº of Analyses 24 7 21 6 20 SiO2 30.2–38.1 33.3–36.4 30.8–35.2 37.0–38.4 30.9–37.5 Al2 O3 13.3–24.2 20.7–24.3 12.8–22.0 23.2–24.4 13.4–22.8 CaO 11.1–23.2 15.6–21.1 11.8–19.3 22.2–23.5 11.2–21.3 FeO 10.0–15.1 9.7–10.7 10.3–15.4 11.5–12.8 10.7–16.2 Ce2 O3 0.2–11.4 1.6–6.4 3.8–10.8 0.0–0.6 1.5–11.3 La2 O3 0.1–7.6 0.8–4.2 2.1–5.9 0.0–0.2 0.7–7.3 Nd2 O3 0.0–3.0 0.6–2.0 0.9–3.1 0.0–0.4 0.5–3.4 MgO 0.0–0.6 0.1–0.4 0.2–0.4 0.0–0.2 0.2–0.7 MnO 0.1–0.6 0.5–1.0 0.0–0.4 0.1–0.3 0.1–0.4 TiO2 0.4–2.2 0.2–0.7 0.2–2.8 0.0–0.4 0.1–2.0 UO2
La > Nd. > Nd. Allanites of Type I show ferriallanite-(Ce) cores transitioning towards epidote, fol- lowed by a rim with a higher clinozoisite component and less REE enrichment (Figure 4a). Allanites of Type I show ferriallanite‐(Ce) cores transitioning towards Allanite Type I cores present the highest levels of REEs with a total of REE oxides up to lowed 22.9 wt.%by a rim (Figure with 4b). Typea Ihigher clinozoisite rims have less FeOtot atcomponent the same level and less of Ce REE enrichmen 2 O3 and more Allanite Al 2 O3 at theType I cores same level of CaOpresent theI cores than Type highest levels (Figure 4c,d). of REEs with Additionally, some a cores totalofof REE allanite Type I present the highest MgO and lowest SiO content 22.9 wt.% (Figure 4b). Type I rims have less FeOtot at the same level 2 compared to the rims and of Ce2 to allanite Type II (Figure 4e). Al2Allanite O3 at the Typesame level II cores showof CaOferriallanite–epidote similar than Type I cores solid(Figure solution 4c,d). to TypeAdditionally I cores of with but allanite REEsType I present never below theand 0.2 apfu highest less REEMgO and lowest enrichment SiO in general 2 content when compared compare with Type I cores. Irregularly and to allanite Type II (Figure 4e). zoned domains in Type II present similar geochemical characteristics to parallel-zoned domains of Type I. All allanite types also show an inverse Allanite Type II cores show similar ferriallanite–epidote solid solution to correlation between REE and SiO2 content (Figure 4b). but with REEs never below 0.2 apfu and less REE enrichment in general wh with Type I cores. Irregularly zoned domains in Type II present similar geoch acteristics to parallel‐zoned domains of Type I. All allanite types also sho correlation between REE and SiO2 content (Figure 4b). 9 of 18 Minerals 2022, 12, 954 8 of 17 Figure 4. (a) CationicFigure Al vs.4. REE plot after (a) Cationic Al vs.Petrík et after REE plot al. [46], showing Petrík et al. [46],the position showing of the of the position studied the studied allanites in the ferriallanite‐allanite‐epidote‐clinozoisite system. (b)system. allanites in the ferriallanite-allanite-epidote-clinozoisite SiO2 vs.(b) REE O3REE SiO2 2vs. (sumO 2 3 of (sumrare of rare earth element oxides. earth (c) FeO tot (total element Fe (c) oxides. oxides) FeOtot vs. CeFe2Ooxides) (total 3. (d) Al vs.2O Ce32vs. O3 . CaO. (d) Al2(e) SiOCaO. O3 vs. 2 vs.(e) MgO. AlnMgO. SiO2 vs. Type I: Allanite Type I.Aln AlnType I: Allanite Type Type I.Type II: Allanite Aln Type II: Allanite II. EpC: EpidoteTypecorona. II. EpC: Yellow, Epidote corona. green Yellow, and browngreen and brown areas: allanite areas: allanite from peraluminous from peraluminous and metaluminous and metaluminous Variscan granitoids Variscan granitoids [47]. Purple [47].hydro‐ area: Purple area: hydrothermal allanite [48,49]. thermal allanite [48,49]. 4.3. Principal Component Analyses 4.3. Principal ComponentThe Analyses 10 major oxides (SiO2 , Al2 O3 , CaO, FeO, Ce2 O3 , La2 O3 , Nd2 O3 , MgO, TiO2 , and MnO) of the 78 microprobe point analyses were used for PCA. The first principal compo- The 10 major oxides (SiO2, Al2O3, CaO, FeO, Ce2O3, La2O3, Nd2O3, MgO, TiO2, and nent (PC1) accounts for 75.2% of the sample variance, the second principal component MnO) of the 78 microprobe pointfor (PC2) accounts analyses 11.9%, andweretheused third for PCA.component principal The first principal compo‐ (PC3) accounts for 4.8%. nent (PC1) accountsAccordingly, for 75.2%91.9%of the sample of the variance, variance the second was accounted principal for by the first three component out of ten compo- nents (Figure (PC2) accounts for 11.9%, and the5a).third This means that just principal three principal component (PC3)components accountsdescribe most for 4.8%. of the Ac‐ observed variation which can be visualized in binary plots. As observed in Figure 5, PC1 is cordingly, 91.9% of the variance was accounted for by the first three out of ten components dominated by the anti-correlation between Si-Al-Ca and Fe-LREE-Ti in the allanite–epidote (Figure 5a). This means that of zonation just three both principal allanite Type I components describe and II, while PC2 shows most of the a relation observed with higher MnO variation which canvalues be visualized in the rims in binaryType of allanite plots. As on I. PC3 observed the otherin Figure hand 5, PC1with is associated is domi‐ high TiO2 values in Type nated by the anti‐correlation I, TypeSi‐Al‐Ca between II and other andallanite grains. These Fe‐LREE‐Ti reveal in the the connection between allanite–epidote zo‐ textural and chemical variations, confirming that most of the variance of Les Guilleries nation of both allanite Type I and II, while PC2 shows a relation with higher MnO values lamprophyre allanites is related to the known ferriallanite–epidote solid solution (PC1), in the rims of allanite whileType otherI.subtle PC3 compositional on the otherdifferences hand is associated between coreswith highare and rims TiO 2 values revealed by PC2 in Type I, Type II and andother PC3. allanite grains. These reveal the connection between textural and chemical variations, confirming that most of the variance of Les Guilleries lampro‐ phyre allanites is related to the known ferriallanite–epidote solid solution (PC1), while other subtle compositional differences between cores and rims are revealed by PC2 and PC3. Minerals 2022,12, Minerals2022, 12,954 x 9 ofof1718 10 Figure5.5. Principal Figure Principal component component analysis analysisofof10 10major majoroxides oxidesusing usingmicroprobe microprobe geochemical geochemical data. (a) data. Cumulative (a) Cumulative explained explainedvariance varianceofofthe the10 10principal principal components. components. A total of A total of 91.9% 91.9%ofofthe thevariance varianceisis explained by the first three out of the 10 components. (b–d) correspond to binary plots of the three explained by the first three out of the 10 components. (b–d) correspond to binary plots of the three main principal components. (b) PC1 vs. PC2; (c) PC1 vs. PC3; (d) PC2 vs. PC3. The compositional main principal components. (b) PC1 vs. PC2; (c) PC1 vs. PC3; (d) PC2 vs. PC3. The compositional vector of each major oxide is projected into principal components coordinates for easy visualization vector of each major oxide is projected into principal components coordinates for easy visualization of the main patterns. N = number of point analyses considered. of the main patterns. N = number of point analyses considered. 4.4.LA-ICP-MS 4.4. LA‐ICP‐MSIn InSitu SituU-Th-Pb U‐Th‐PbAges Ages Radiometric dates Radiometric dates obtained obtainedfrom from29‐point 29-point analyses analyses(Supplementary (Supplementary Material Table Materials S2) in different growth domains of five allanite crystals range between Table S2) in different growth domains of five allanite crystals range between ~234–362 Ma ~234–362 Ma ( 207Pb‐ (corrected Pb/ UPb/ date),Uand form a single form aisochron with anwith age anof 265 age ±of15265 Ma±(MSWD 207 206 238 206 238 Pb-corrected date), and single isochron 15 Ma = 0.57, Figure (MSWD = 0.57,6); this age Figure is equivalent 6); this to the 262 age is equivalent ± 7 262 to the Ma ± U‐Pb 7 Ma age obtained U-Pb from titanites age obtained from of the same lamprophyres, interpreted as the age of lamprophyre emplacement titanites of the same lamprophyres, interpreted as the age of lamprophyre emplacement [6]. [6]. It is important to note that the compositional changes in Type I, Type It is important to note that the compositional changes in Type I, Type II and other allan-II and other allanite grains ite grainsoccur occurin in a range a range of of a few a few micrometers, micrometers, smaller smaller than than thetheLA‐ICP LA-ICP spotspotsize sizeofof15 micrometers, 15 micrometers, andandtherefore thereforethe theages ages obtained obtained could averages of could represent averages ofdifferent different growthdomains, growth domains,and andnotnot necessarily necessarily an exact an exact period period of crystal of crystal growth. growth. Additionally, Additionally, given given the highthe high uncertainty uncertainty of individual of individual allaniteallanite dates, dates, the the of scatter scatter datesofisdates is probably probably the result the of analytical result scatter scatter of analytical rather than rathergeologic scatter.scatter. than geologic Nevertheless, younger Nevertheless, dates in younger allanite dates in al‐ Type laniteI Type and older I anddates olderin allanite dates Type IIType in allanite are consistent with textural II are consistent relationships. with textural The relationships. rims of allanite The rims Type Type of allanite I also Ishow the youngest also show ages, but the youngest ages,asbut theyasare always they thinnerthinner are always than 5than micrometers, the dates 5 micrometers, are averaged the dates are averagedwithwith the the internal partpart internal of the grain. of the grain.On Onthe theother other hand, the timespan covered by the isochron age between ~280–250 Ma is roughly the same Minerals 2022, 12, x. https://doi.org/10.3390/xxxxx www.mdpi.com/journal/minerals Minerals 2022, 12, x 11 o Minerals 2022, 12, 954 10 of 17 as the timespan covered by the late evolution of southern branch of the Variscan Belt; t hand, the timespan covered by the isochron age between ~280–250 Ma is roughly the same is, as athe late Carboniferous–Permian timespan covered by the late collisional evolution ofevent, southern with localized branch of themagmatic recycling, Variscan Belt; tensional and that is, a late transcurrent tectonic Carboniferous–Permian settings, collisional exhumation event, of magmatic with localized metamorphic terranes, recycling, development extensional andof localizedtectonic transcurrent volcano‐sedimentary settings, exhumation basins [50]. The terranes, of metamorphic time spanand also co development sponds to theofperiod localizedfollowing volcano-sedimentary basinsto[50]. the main syn‐ The time span also post‐collisional corresponds tectonometamorphic to the period following the main syn- to post-collisional tectonometamorphic and magmatic magmatic evolution of the Catalan Coastal Range under the peak metamorphic conditi evolution of the Catalan Coastal Range under the peak metamorphic conditions in Late in Late Carboniferous described above in the Geological Setting section, with specific Carboniferous described above in the Geological Setting Section, with specific periods of riods 305–299 ofMa305–299 Ma for leucogranites, for leucogranites, 288 Ma forpluton, 288 Ma for the Aiguablava the Aiguablava pluton, and 285 Ma for and 285 Ma porphyritic porphyritic granites [33,36]. granites [33,36]. Figure 6. (a)Allanite 6. (a) AllaniteTera–Wasserburg Tera–Wasserburg concordia diagram using measured 207 Pb/ 206 Pb and Figure concordia diagram using measured 207Pb/ 206Pb and 238U/2 238 U/206 Pb ratios corrected for common Pb and Th content, with the data conversion performed by ratios corrected for common Pb and Th content, with the data conversion performed by Isoplot Isoplot 3.7. Allanite Allanite data fromdata thefrom twothe two samples samples are plotted are plotted at 2σ at 2σ andanduncertainties uncertainties on onlower lower intercept intercept ages ages are 95% confidence, with overall weighted average of 262 ± 95% confidence, with overall weighted average of 262 ± 7 Ma. (b) Histogram showingthe 7 Ma. (b) Histogram showing the freque frequency distribution distribution of defined of defined allanite allanite typestypes ranging ranging from from 234and 234 and 362 362 Ma. Ma.Dated Dated allanite crystals allanite crystals incl include the onesthe inones in Figure Figure 2a,b,e,g. 2a,b,e,g. Titanite Titanite U‐PbU-Pb datesfrom dates from[6] [6] are are shown shownfor comparison. for comparison. Complementary geochemical data reveal that U and Th concentrations are in the rangeComplementary of 4–45 ppm and geochemical data reveal 4–368 ppm, respectively that U and Th (Supplementary concentrations Materials Table S2). are in range AllaniteofType 4–45I presents ppm and 4‐368ppm, variable respectively REE patterns (Supplementary with a tendency Material Table S2). All towards slightly-negative-to- ite Type I presents variable REE patterns with a tendency towards positive Eu anomalies, decreasing Ce content, and variable trace element ratiosslightly‐negative (Figure 7). The mostEu positive REE-rich cores decreasing anomalies, of allanite Type I present and Ce content, flat HREE variablepatterns trace and the highest element ratios (Figure HREE content. Allanite Type II, on the other hand, presents exclusively negative Eu The most REE‐rich cores of allanite Type I present flat HREE patterns and the high anomalies, with similar HREE content in irregularly zoned cores but slightly variable LREE HREE content. Allanite Type II, on the other hand, presents exclusively negative Eu ano content, and epidote coronas with similar patterns but with total REE content lower by one alies, with similar Th/U order of magnitude. HREEratioscontent in irregularly are relatively low for zoned cores all allanite butand types, slightly variable allanites of LR content, and epidote Type I present coronas higher La/Sm with ratios. similar Other patterns allanite butroughly grains are with total similarREE content lower to allanite Type I, although unique features of some grains could also be present. one order of magnitude. Th/U ratios are relatively low for all allanite types, Trace element ratios and allan of Type of all allanite–epidote grainsLa/Sm I present higher (low Th/U andOther ratios. La/Sm, variable allanite Eu/Eu*) grains areplot in the similar roughly field of to alla metamorphic origin or closer to it in the diagram plots of La/Sm vs. Th/U and La/Sm vs. Type I, although unique features of some grains could also be present. Trace element Eu/Eu* [25,26]. tios of all allanite–epidote grains (low Th/U and La/Sm, variable Eu/Eu*) plot in the f of metamorphic origin or closer to it in the diagram plots of La/Sm vs. Th/U and La/ vs. Eu/Eu* [25,26]. Minerals 2022, 12, x Minerals 2022, 12, 954 12 of 18 11 of 17 Figure 7.7.Trace Figure Traceelements elements of allanite fromfrom of allanite Les Guilleries lamprophyre Les Guilleries dykes obtained lamprophyre by LA-ICP-MS. dykes obtained by LA‐ICP‐ (a) Chondrite-normalized REE patterns of defined allanite types. Normalizing MS. (a) Chondrite‐normalized REE patterns of defined allanite types. Normalizing values are from Sun values are from and McDonough Sun and McDonough [51]. (b) Ce(b) [51]. vs. Ce Eu/Eu* [Eu/Eu* vs. Eu/Eu* = (Eu)cn/[(Sm)cn [Eu/Eu* × (Gd)cn]0.5]. = (Eu)cn/[(Sm)cn (c) Th/U × (Gd)cn]0.5]. (c)vs. Th/U vs. La/Sm. (d) La/Sm. (d) Eu/Eu* Eu/Eu* vs. vs. La/Sm. La/Sm. Magmatic Magmaticand andmetamorphic metamorphic allanite fields allanite fromfrom fields [25,26]. [25,26]. 5. Discussion 5. Discussion The textural and chemical heterogeneities of allanite–epidote composite grains found in LesThe textural Guilleries and chemical spessartite dykes heterogeneities suggest a complex ofgeological allanite–epidote story with composite grains found multiple crystal- in Les Guilleries lization periods thatspessartite could be dykes relatedsuggest a complex to metamorphic, geological magmatic, storyhydrothermal and/or with multiple crys‐ tallization processes. periods However, that could most be related grains are withinto metamorphic, magmatic, and/orsolid the ferriallanite–allanite–epidote hydrothermal so- lution and generally present the same cationic substitutions, as indicated processes. However, most grains are within the ferriallanite–allanite–epidote solid solu‐ by PC1 of the principal tion component and generally analysis, present thewhich same accounts for 75% of theas cationic substitutions, compositional indicated byvariability PC1 of the prin‐ (Figures 5b,c and 8a). Allanite crystals are also affected by secondary cipal component analysis, which accounts for 75% of the compositional variability replacement, and (Fig‐ therefore some primary features may have been modified by later processes. Nevertheless, ures 5b,c and 8a). Allanite crystals are also affected by secondary replacement, and there‐ petrographic, geochemical and statistical results show at least two distinct types of allanite– fore some primary features may have been modified by later processes. Nevertheless, pet‐ epidote composite grains. Allanite Type I, encountered in the feldspathic part of the matrix, rographic, correspondsgeochemical and statisticalcrystals, to subhedral parallel-zoned resultsfrom show at least twoallanite REE-enriched distinct types cores of allanite– grading epidote composite grains. Allanite Type I, encountered in the feldspathic towards epidote with a secondary rim of less REE-enriched allanite, the latter with a higher part of the ma‐ trix, corresponds clinozoisite componentto subhedral parallel‐zoned and characteristic slight Mncrystals, from REE‐enriched enrichment, as revealed by allanite PC2 of cores grading towards epidote with a secondary rim of less REE‐enriched the principal component analysis (Figures 5b,d and 8b). Allanite Type I is apparently allanite, the latter with youngera higher clinozoisite than allanite Type IIcomponent and shows aand characteristic variable slight Eu anomaly, beingMnnegative enrichment, in the as mostrevealed REE-enriched by PC2 of thecores, and positive principal component towards the less analysis REE-enriched (Figures 5b,d and rim8b). (Figure 7). Allanite Allanite Type I is ap‐ Type II, encountered parently younger than in the chloritized allanite Type part of the II and matrix, shows corresponds a variable to REE-rich Eu anomaly, cores being negative surrounded by epidote coronas, presents a negative Eu anomaly, in the most REE‐enriched cores, and positive towards the less REE‐enriched rim and is, apparently, the(Figure oldest (Figures 6 and 7). 7). Allanite Type II, encountered in the chloritized part of the matrix, corresponds to REE‐ rich cores surrounded by epidote coronas, presents a negative Eu anomaly, and is, appar‐ ently, the oldest (Figures 6 and 7). Minerals 2022, Minerals 12,12, 2022, 954x 13 of 12 18 of 17 Figure8.8. Cationic Figure Cationicplots plotsofofdefined defined allanite types allanite relating types the groups relating of elements the groups resulting of elements from thefrom resulting principal component analyses. (a) REE3+ + Fe2+ + Ti4+ +2+Mg2+ +4+Mn2+ vs. Al3+ + Ca 2+ + Fe3+ showing the the principal component analyses. (a) REE + Fe + Ti + Mg + Mn vs. Al + Ca2+ + Fe3+ 3+ 2+ 2+ 3+ cationic substitutions in allanite structure. (b) Ce vs. Mn. (c) Ce vs. Ti. (d) Fe vs. Ti. [apfu] = atoms showing the unit. per formula cationic substitutions See explanation in in theallanite text. structure. (b) Ce vs. Mn. (c) Ce vs. Ti. (d) Fe vs. Ti. [apfu] = atoms per formula unit. See explanation in the text. Les Guilleries lamprophyres represent, to date, the last magmatic pulse with a calc‐ Les Guilleries alkaline geochemical lamprophyres signature of the represent, to date,Range Catalan Coastal the last magmatic and pulse with Eastern Pyrenees. a calc- It oc‐ alkaline curred in a post‐collisional tectonic setting related to lithospheric‐scale dextral mega shear It geochemical signature of the Catalan Coastal Range and Eastern Pyrenees. occurred zones whichin adeveloped post-collisional duringtectonic orogenicsetting collapserelated before tothelithospheric-scale onset of generalized dextral mega Triassic shear zones which developed during orogenic collapse before extension [30]. These mafic dykes were emplaced in the upper Variscan crust after thethe onset of generalized Triassic main syn‐extension [30]. These mafic to post‐collisional dykes were magmatism whichemplaced evolved in the upper Variscan batholitic‐sized crust after calc‐alkaline the main syn- granitoids, to post-collisional minor mafic intrusions magmatism with local which evolved ultramafic batholitic-sized cumulates, calc-alkaline and peraluminous granitoids, leucogranite minor bodies. mafic intrusions An enriched SCLMwithorigin localhas ultramafic cumulates, been inferred andfor indirectly peraluminous the most leucogranite bodies.ofAn mafic components theenriched SCLM magmatic post‐collisional origin hassystem, been inferred and Lesindirectly Guilleries for the most lampro‐ mafic phyres components must representof thethepost-collisional least differentiated magmatic sample system, from thisand Les Guilleries lampro- subduction‐related en‐ richedmust phyres SCLMrepresent source [6]. theAccording to the obtained least differentiated sampleages, fromthethis emplacement of the lampro‐ subduction-related enriched phyressource SCLM was also [6].cogenetic According withtovolcanism the obtainedin pull‐apart ages, the basins evolving from emplacement calc‐alkaline‐ of the lamprophyres to‐alkaline geochemistry during Permian times [28] and later was was also cogenetic with volcanism in pull-apart basins evolving from calc-alkaline-to- affected by regional scale syn‐ to post‐magmatic hydrothermal alteration. alkaline geochemistry during Permian times [28] and later was affected by regional scale syn- toConsidering post-magmatic this interpretation, hydrothermaland the coincidence of allanite U‐Th‐Pb dates with alteration. the late Variscan evolution of the area, Considering this interpretation, and the it is suggested coincidence thatofallanite allanitecrystallization U-Th-Pb dateswas witha the multi‐stage process related to (i) the metamorphic evolution of the SCLM source, late Variscan evolution of the area, it is suggested that allanite crystallization was a multi- (ii) mag‐ maticprocess stage evolution after to related partial (i) themelting until emplacement, metamorphic evolution of(iii) thedeuteric/autometasomatic SCLM source, (ii) magmatic processes common in lamprophyres due to their high volatile evolution after partial melting until emplacement, (iii) deuteric/autometasomatic content, and/or (iv) processes post‐ magmatic hydrothermal alteration. Older allanite relicts encountered in this study (allan‐ common in lamprophyres due to their high volatile content, and/or (iv) post-magmatic ite Type II, Figure 6) could represent unique windows to this enriched SCLM source and hydrothermal alteration. Older allanite relicts encountered in this study (allanite Type be a recorder of its metamorphic evolution in an environment evolving from peak com‐ II, Figure 6) could represent unique windows to this enriched SCLM source and be a pression to strike‐slip motions, and of its later extension during orogenic collapse, related recorder of its metamorphic evolution in an environment evolving from peak compression to mantle delamination, asthenospheric upwelling, rapid exhumation and low degree of to strike-slip motions, and of its later extension during orogenic collapse, related to mantle delamination, asthenospheric upwelling, rapid exhumation and low degree of partial melting favored by shear zones. This is supported by the similar ferriallanite–epidote composition of most allanite grains which are consistent with the nearly isochemical Minerals 2022, 12, x. https://doi.org/10.3390/xxxxx www.mdpi.com/journal/minerals Minerals 2022, 12, 954 13 of 17 evolution of a metabasic source in a nearly closed system, except for allanite Type I rims which are apparently the youngest and represent an abrupt change in thermodynamic conditions. Measured Th/La and Sm/La ratios (Figure 7c,d) are also indicative of the metamorphic origin of older grains, but we do not discount the possibility that these ratios could also be related to post-emplacement metamorphic retrogression in some of the grains, considering a rapid exhumation environment. The change from Type II to Type I allanite may also be related to a change in metamorphic conditions in the SCLM source during exhumation, or alternatively, to a change in stress conditions from dominant compression to dominant extension in the lamprophyre SCLM source. The later could explain why older allanite Type II crystals are generally rounded and anhedral while younger allanite Type I presents subhedral crystals with seemingly simple shear characteristics (Figure 2a,b). On the other hand, the unique Mn enrichment in allanite Type I rims and the higher clinozoisite component suggest a later event with a change in thermodynamic conditions that could be related to late magmatic and/or post-magmatic processes (the replacement of Mn-ilmenite by titanite as observed could be a viable mechanism to provide Mn to the system). Some unique Ti-enriched cores, revealed by PC3 of the principal component analysis, could also be associated with the latest hydrothermal processes as these are encountered in all allanite types and only in those allanite–epidote grains in which the alteration affected the internal parts of the grains (for example Figure 2f presents a high Ti core, while Figure 2d,e do not). The increase in Ti is related to increases in REEs, which suggest REEs are locally remobilized and recrystallized in hydrothermally affected cores (Figure 8c). Abundant secondary titanite suggests Ti was available during post-magmatic processes and the replacement of ilmenite by titanite—or the dissolution of Ti-rich amphiboles as observed—could be viable mechanisms to provide Ti to the system. Ti-enriched cores also present an increase in the ferriallanite component (Figure 8d), which is characteristic of hydrothermal ferriallanite [48,49]. Different concentrations of REEs, the slope and curvature in the REE patterns and the presence or absence of Eu anomalies (Figure 7) could also reflect competition between allanite and other minerals as the allanite crystals grew [15]. Therefore, the observed variations of REEs within grains and between samples may in part reflect local time-dependent changes of fluid or solid interactions of the lamprophyre magma or dykes, either in the lamprophyre’s source prior to—or during—partial melting, or after consolidation in the crust. A question remains whether the enrichment of the lamprophyre‘s SCLM source with rare earth elements was an ancient event that occurred before Variscan times, or whether it was the tectonic activity of the Variscan orogeny that generated lithospheric scale shear sys- tems that allowed REE-rich fluids to penetrate the upper mantle/lower crust and crystallize as allanite in several steps during the syn- to post-collisional evolution of the mantle source. The first proposition implies the occurrence of ancient subduction-collision events, which indeed have been recorded in the area, dating from Ordovician times [52]. There is also a regional correlation in Sr and Nd isotopic compositions among the Variscan calc-alkaline lamprophyres of Western Europe that could be related to enriched mantle domains at the northern edge of Gondwana during Variscan times [6,53]. The second possibility—of a Variscan lithospheric-scale shear—implies that the oldest allanite relics could represent the beginning of the tectonic activity in the SCLM source of Les Guilleries lamprophyres during the Variscan post-collisional evolution of NE Iberia. Additionally, considering the known allanite–monazite transformations, the lack of monazite relics could also suggest a metamor- phic re-equilibration of the lamprophyre’s source under greenschist facies conditions after peak metamorphic conditions, consuming all monazite into allanite+apatite. Abundant apatite crystals around allanite Type I could be the result of monazite re-equilibration and dissolution. The epidote coronas around older allanite crystals (allanite Type II) may have prevented recrystallization at higher metamorphic conditions retaining previous features; therefore, it cannot be ruled out that higher metamorphic conditions were reached in the source of the lamprophyres. Minerals 2022, 12, 954 14 of 17 Finally, it is also possible that both possibilities occurred. In this case, there would have been a recurrent recycling of rare earth elements during successive Wilson cycles, with subduction of REE-rich crustal material, REE transfer to the mantle via fluids, melts and mechanical mixing, and back up to the crust via tectonic exhumation and volcanic- magmatic systems originated from partial melting of REE-enriched mantle domains. From this discussion, it can be seen that the study of allanite crystals is a useful tool to unravel the history of deeper parts of orogenic systems. 6. Conclusions Allanite crystals of 10–100 µm length have been identified in the matrix of late Variscan calc-alkaline lamprophyre dykes of Les Guilleries Massif (NE Variscan chain of the Iberian peninsula). Based on the complex zoning and alteration textures of the allanite crystals, two predominant types have been distinguished: Allanite Type I is found in feldspathic zones and consists of subhedral cores with regular parallel zoning that transitions smoothly into epidote; Allanite Type II corresponds to anhedral cores with irregular zoning that are in sharp contact with epidote coronas and are observed in chloritized zones. Both types show gradations from ferriallanite-(Ce) to epidote. A principal component analysis of allanites reveals an anti-correlation between Si-Al- Ca and Fe-LREE-Ti-Mg in all grain types (PC1), which accounts for 75% of variations. PC2 relates to high concentrations of Mn in the rims of Type I, whereas PC3 is related to high Ti contents. These three principal components account for 92% of compositional differences, which can be summarized as REE3+ + Fe2+ + Ti4+ + Mg2+ + Mn2+ = Al3+ + Ca2+ + Fe3+ . In situ U-Th-Pb dates of 29 analytical points in allanite crystals yield a weighted mean age of 265 ± 15 Ma. The coincidence of allanite dates in Les Guilleries lamprophyres with the period following the main syn- to post-collisional Variscan magmatism in the Catalan Coastal Range (280–250 Ma), in conjunction with the differences in allanite tex- tures, suggest the allanite crystals from this study represent multi-stage metamorphic, magmatic and/or hydrothermal processes that occurred both before partial melting of the lamprophyre’s source and later, during the early, late and post-magmatic evolution of the post-collisional system. The low ratios of Th/U and La/Sm and variable Eu/Eu* of all analyzed allanites plot within or near the metamorphic domain. This could be due to previous ancient subduction-collision events recycling allanite, possibly in Ordovician times, or to a Variscan lithospheric-scale shear, with the oldest allanite relicts representing the beginning of the tectonic activity in the SCLM source of Les Guilleries lamprophyres (and maybe the entire Variscan collisional system of NE Iberia). In any case, recurrent recycling of rare earth elements with subduction of REE-rich crustal material into the mantle seems plausible. Petrological, geochemical and geochronological results from this study are consistent with the interpretation that Les Guilleries lamprophyre dykes represent mantle-derived magmas that were emplaced into the brittle upper crust during late Permian times at the final stages of the Variscan orogenic collapse. This occurred in relation to shear zones, lithospheric thinning, asthenospheric upwelling, and partial melting of subduction-related enriched SCLM domains. The Variscan basement of the Catalan Coastal Range and Eastern Pyrenees record the transition from a contractional or transpressional tectonic regime, characterized by crustal thickening, to a strike-slip regional setting that occurred during lithospheric delamination during late Variscan times, prior to the extensional collapse of the orogen and the breakup of Pangea. The results from this study suggest allanite could be a useful tool to indirectly elucidate the history of deeper parts of this system that are apparently not manifested at the surface. Minerals 2022, 12, 954 15 of 17 Supplementary Materials: The following supporting information can be downloaded at: https: //www.mdpi.com/article/10.3390/min12080954/s1, Table S1: Allanite chemical data from EPMA. Table S2: Allanite chemical data from ICP-MS. Author Contributions: Conceptualization and investigation: E.M. and M.C.; formal analysis: E.M. and A.K.-C.; writing and visualization: E.M.; writing—review and editing: M.C. and A.K.-C.; supervision: M.C.; funding acquisition: M.C. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by the Spanish Ministerio de Economía, Industria y Competi- tividad [PID2019-109018RB-I00] and [2015-66335-C2-2-R] and by a CONICYT-BECAS CHILE/2017- [72180523] grant to the first author. Data Availability Statement: All data used in this article is contained in Supplementary Materials. Conflicts of Interest: The authors declare no conflict of interest. References 1. Owen, J.P. Geochemistry of lamprophyres from the Western Alps, Italy: Implications for the origin of an enriched isotopic component in the Italian mantle. Contrib. Mineral. Petrol. 2008, 155, 341–362. [CrossRef] 2. Seifert, T. Metallogeny and Petrogenesis of Lamprophyres in the Mid-European Variscides; IOS Press: Amsterdam, The Netherlands, 2008. 3. Soder, C. Geochemistry and Petrology of Lamprophyres from the Hellenides and the European Variscides. Ph.D. Thesis, University of Heidelberg, Heidelberg, Germany, 2017. 4. Errandonea-Martin, J.; Sarrionandia, F.; Carracedo-Sánchez, M.; Gil Ibarguchi, J.I.; Eguíluz, L. Petrography and geochemistry of late- to post-Variscan vaugnerite series rocks and calc-alkaline lamprophyres within a cordierite-bearing monzogranite (the Sierra Bermeja Pluton, southern Iberian Massif). Geol. Acta 2018, 16, 237–255. 5. Le Maitre, R.; Streckeisen, A.; Zanettin, B.; Le Bas, M.; Bonin, B.; Bateman, P. (Eds.) Igneous Rocks: A Classification and Glossary of Terms: Recommendations of the International Union of Geological Sciences Subcommission on the Systematics of Igneous Rocks, 2nd ed.; Cambridge University Press: Cambridge, UK, 2002. 6. Mellado, E.; Corbella, M.; Navarro-Ciurana, D.; Kylander-Clark, A. The enriched Variscan lithosphere of NE Iberia: Data from post-collisional Permian calc-alkaline lamprophyre dykes of Les Guilleries. Geol. Acta 2021, 19, 1–23. [CrossRef] 7. Deer, W.A.; Howie, R.A.; Zussman, J. Rock-Forming Minerals, Vol. 1B: Disilicates and Ringsilicates, 2nd ed.; Longman: Harlow, UK, 1986. 8. Gieré, R.; Sorensen, S.S. Allanite and other REE-rich epidote group minerals. Rev. Mineral. Geochem. 2004, 56, 431–493. [CrossRef] 9. Armbruster, T.; Bonazzi, P.; Akasaka, M.; Bermanec, V.; Chopin, C.; Giere, R.; Heuss-Assbichler, S.; Liebscher, A.; Menchetti, S.; Pan, Y. Recommended nomenclature of epidote-group minerals. Eur. J. Mineral. 2006, 18, 551–567. [CrossRef] 10. Catlos, E.J.; Sorensen, S.S.; Harrison, T.M. Th–Pb ion-microprobe dating of allanite. Am. Mineral. 2000, 85, 633–648. [CrossRef] 11. Grapes, R.H.; Hoskin, W.O. Epidote group minerals in low-medium pressure metamorphic terranes. Rev. Mineral. Geochem. 2004, 56, 301–345. [CrossRef] 12. Finger, F.; Broska, I.; Roberts, M.P.; Schermaier, A. Replacement of primary monazite by apatite-allanite-epidote coronas in amphibolite facies granite gneiss from the eastern Alps. Am. Mineral. 1998, 83, 248–258. [CrossRef] 13. Janots, E.; Engi, M.; Berger, A.; Allaz, J.; Schwarz, J.O.; Spandler, C. Prograde metamorphic sequence of REE minerals in pelitic rocks of the Central Alps: Implications for allanite–monazite–xenotime phase relations from 250 to 610 ◦ C. J. Metamorph. Geol. 2008, 26, 509–526. [CrossRef] 14. Janots, E.; Berger, A.; Engi, M. Physico-chemical control on the REE-mineralogy in chloritoid-grade metasediments from a single outcrop (Central Alps, Switzerland). Lithos 2011, 121, 1–11. [CrossRef] 15. Engi, M. Petrochronology based on REE-minerals: Monazite, allanite, xenotime, apatite. Rev. Mineral. Geochem. 2017, 83, 365–418. [CrossRef] 16. Goswami-Banerjee, S.; Robyr, M. Pressure and temperature conditions for crystallization of metamorphic allanite and monazite in metapelites: A case study from the Miyar Valley (high Himalayan Crystalline of Zanskar, NW India). J. Metamorph. Geol. 2015, 33, 535–556. [CrossRef] 17. Budzyń, B.; Harlov, D.; Williams, M.; Jercinovic, M. Experimental determination of stability relations between monazite, fluorapatite, allanite, and REE-epidote as a function of pressure, temperature, and fluid composition. Am. Mineral. 2011, 96, 1547–1567. [CrossRef] 18. Cenki-Tok, B.; Darling, J.; Rolland, Y.; Rossi, M.; Engi, M. Allanite Behavior in Upper-Mid Crustal Shear Zones: Can we Date Deformation Directly? Example from the Mont Blanc Massif and Implications on Its Alpine Evolution. Terra Nova 2011, 0, 1–9. 19. Levinson, A.A. A system of nomenclature for rare-earth minerals. Am. Mineral. 1966, 51, 152–158. 20. Beard, J.; Sorensen, S.; Gieré, R. REE zoning in allanite related to changing partition coefficients during crystallization: Implications for REE behaviour in an epidote-bearing tonalite. Miner. Mag. 2006, 70, 419–436. [CrossRef] Minerals 2022, 12, 954 16 of 17 21. Klimm, K.; Blundy, J.D.; Green, T.H. Trace Element Partitioning and Accessory Phase Saturation during H2 O-Saturated Melting of Basalt with Implications for Subduction Zone Chemical Fluxes. J. Petrol. 2008, 49, 523–553. [CrossRef] 22. Hermann, J. Allanite: Thorium and light rare earth element carrier in subducted crust. Chem. Geol. 2002, 192, 289–306. [CrossRef] 23. Smye, A.; Roberts, N.; Condon, D.; Horstwood, M.; Parrish, R. Characterising the U-Th-Pb systematics of allanite by ID and LA-ICPMS: Implications for geochronology. Geochim. Cosmochim. Acta 2014, 135, 1–28. [CrossRef] 24. Oberli, F.; Meier, M.; Berger, A.; Rosenberg, C.; Gieré, R. U-Th-Pb and 230 Th/238 U disequilibrium isotope systematics: Precise accessory mineral chronology and melt evolution tracing in the Alpine Bergell intrusion. Geochim. Cosmochim. Acta 2004, 68, 2543–2560. [CrossRef] 25. Gregory, C.J.; Rubatto, D.; Hermann, J.; Berger, A.; Engi, M. Allanite behaviour during incipient melting in the southern Central Alps. Geochim. Cosmochim. Acta 2012, 84, 433–458. [CrossRef] 26. Janots, E.; Rubatto, D. U–Th–Pb dating of collision in the external Alpine domains (Urseren zone, Switzerland) using low temperature allanite and monazite. Lithos 2014, 184–187, 155–166. [CrossRef] 27. Reche, J.; Martínez, F.J. Evolution of bulk composition, mineralogy, strain style and fluid flow during an HT-LP metamorphic event: Sillimanite zone of the Catalan Coastal Ranges, Variscan basement, NE Iberia. Tectonophysics 2002, 348, 111–134. [CrossRef] 28. Arche, A.; López-Gómez, J. Origin of the Permian-Triassic Iberian Basin, central-eastern Spain. Tectonophysics 1996, 266, 443–464. [CrossRef] 29. Perini, G.; Cebria, J.M.; Lopez-Ruiz, J.; Doblas, M. Carboniferous-Permian mafic magmatism in the Variscan belt of Spain and France: Implications for mantle sources. Geol. Soc. Spec. Publ. 2004, 223, 415–438. [CrossRef] 30. Liesa, M.; Aguilar, C.; Castro, A.; Gisbert, G.; Reche, J.; Muñoz, J.A.; Vilà, M. The role of mantle and crust in the generation of calc-alkaline Variscan magmatism and its tectonic setting in the Eastern Pyrenees. Lithos 2021, 406–407, 106541. [CrossRef] 31. Enrique, P. The Hercynian intrusive rocks of the Catalonian Coastal Ranges (NE Spain). Acta Geol. Hisp. 1990, 25, 39–64. 32. Esteve, S.; Sunyer, J.; Culí, L.; Cirés, J.; Alías, G. El complejo intrusivo diorítico-gabroico de Susqueda (Macizo del Montseny- Guilleries, Cataluña): Unidades litológicas y características petrográficas. Geogaceta 2016, 60, 99–102. 33. Martínez, F.J.; Reche, J.; Iriondo, A. U-Pb SHRIMP-RG zircon ages of Variscan igneous rocks from the Guilleries massif (NE Iberia pre-Mesozoic basement): Geological implications. C. R. Geosci. 2008, 340, 223–232. [CrossRef] 34. Esteve, S.; Enrique, P.; Alías, G. Relaciones intrusivas y cronología relativa del plutón básico de Susqueda con las rocas metamórficas encajantes (Cordillera Prelitoral Catalana). Geogaceta 2018, 63, 107–110. 35. Martínez, F.J.; Universitat Autònoma de Barcelona, Barcelona, Spain. Personal communication, 2022. 36. Solé, J.; Cosca, M.; Sharp, Z.; Enrique, P. 40Ar/39Ar Geochronology and stable isotope geochemistry of Late-Hercynian intrusions from north-eastern Iberia with implications for argon loss in K-feldspar. Int. J. Earth. Sci. 2002, 91, 865–881. 37. Butjosa, L.; Enrique, P.; Galán, G. Las hornblenditas, gabros y dioritas del Macizo del Montnegre (Barcelona, Cordilleras Costero Catalanas). Geogaceta 2013, 54, 35–38. 38. Galán, G.; Enrique, P.; Butjosa, L.; Fernández-Roig, M. Spinels of Variscan olivine hornblendites related to the Montnegre granitoids revisited (NE Spain): Petrogenetic evidence of mafic magma mixing. Geol. Acta 2017, 15, 323–336. 39. Saxena, S.K.; Walter, L.S. A statistical-chemical and thermodynamic approach to the study of lunar mineralogy. Geochim. Cosmochim. Acta 1974, 38, 79–95. [CrossRef] 40. Ubide, T.; Gale, C.; Larrea, P.; Arranz Yagüe, E.; Lago San José, M.; Tierz, P. The Relevance of Crystal Transfer to Magma Mixing: A Case Study in Composite Dykes from the Central Pyrenees. J. Petrol. 2014, 55, 1535–1559. [CrossRef] 41. Iwamori, H.; Albarède, F. Decoupled isotopic record of ridge and subduction zone processes in oceanic basalts by independent component analysis. Geochem. Geophys. Geosyst. 2008, 9, 1525–2027. [CrossRef] 42. Spencer, K.; Hacker, B.; Kylander-Clark, A.; Andersen, T.; Cottle, J.; Stearns, M.; Poletti, J.; Seward, G. Campaign-style titanite U-Pb dating by laser-ablation ICP: Implications for crustal flow, phase transformations and titanite closure. Chem. Geol. 2013, 341, 84–101. [CrossRef] 43. Kylander-Clark, A.; Hacker, B.; Cottle, J. Laser-ablation split-stream ICP petrochronology. Chem. Geol. 2013, 345, 99–112. [CrossRef] 44. Kylander-Clark, A. Expanding Limits of Laser-Ablation U-Pb Calcite Geochronology. Geochronology 2020, 2, 343–354. [CrossRef] 45. von Blackenburg, F. Combined high-precision chronometry and geochemical tracing using accessory minerals: Applied to the Central-Alpine Bergell intrusion (central Europe). Chem. Geol. 1992, 100, 19–40. [CrossRef] 46. Petrík, I.; Broska, I.; Lipka, J.; Siman, P. Granitoid Allanite-(Ce) sub-stitution relations, redox conditions and REE distributions (on an Example of I-Type Granitoids, Western Carpathians, Slovakia). Geol. Carpath. 1995, 46, 79–94. 47. Broska, I.; Petrík, I. Accessory Phases in the Genesis of Igneous Rocks. In Modelling of Magmatic and Allied Processes; Kumar, S., Singh, R., Eds.; Society of Earth Scientists Series; Springer: Cham, Switzerland, 2014. 48. Vlach, S.R.F.; Gualda, G.A.R. Allanite and chevkinite in A-type granites and syenites of the Graciosa Province, southern Brazil. Lithos 2007, 97, 98–121. [CrossRef] 49. Hirtopanu, P.; Andersen, J.; Fairhurst, R.J.; Jakab, G. Allanite-(ce) and its associations, from the Ditrau alkaline intrusive massif, East Carpathians, Romania. Proc. Rom. Acad. Series B 2013, 15, 59–74. 50. Schulmann, K.; Catalán, J.R.; Lardeaux, J.; Janousek, V.; Oggiano, G. The Variscan orogeny: Extent, timescale and the formation of the European crust. In book: The Variscan Orogeny: Extent, Timescale and the Formation of the European Crust. Geol. Soc. Spec. Publ. 2014, 405, 1–6. [CrossRef] Minerals 2022, 12, 954 17 of 17 51. Sun, S.S.; McDonough, W.F. Chemical and isotopic systematics of oceanic basalts implications for mantle composition and processes. In Magmatism in the Ocean Basins; Saunders, A.D., Norry, M.J., Eds.; Geological Society of London: London, UK, 1989; pp. 313–345. 52. Navidad, M.; Castiñeiras, P.; Casas, J.M.; Liesa, M.; Fernández-Suárez, J.; Barnolas, A.; Carreras, J.; Gil-Peña, I. Geochemical characterization and isotopic age of Caradocian magmatism in the northeastern Iberian Peninsula: Insights into the Late Ordovician evolution of the northern Gondwana margin. Gondwana Res. 2010, 17, 325–337. [CrossRef] 53. Dijkstra, A.H.; Hatch, C. Mapping a hidden terrane boundary in the mantle lithosphere with lamprophyres. Nat. Commun. 2018, 9, 3770. [CrossRef]