Cretaceous albitization and dequartzification of Hercynian peraluminous granite in the Salvezines Massif (French Pyrénées)

The Salvezines Massif in northern French Pyrénées has undergone extensive albitization. The massif consists of gneisses and a leucogranite hosted in Paleozoic sediments (schists and carbonates). The leucogranite was emplaced at the end of the Hercynian orogeny. The granite underwent monazite fractionation during magmatic stages, which induced lowering of REE and Th contents in the most evolved rocks. Hydrothermal alteration during late magmatic stages is also identified through the development of a tetrad effect in the REE patterns of the granite and through the fractionation of ratios like Zr/Hf out of the CHARAC (CHarge RAdius Controlled) range. The granite underwent partial to complete sub-solidus albitization. Progressive metasomatic overprint induced metasomatic replacement of feldspars into albite and dissolution of quartz (episyenitization) together with new albite formation. Hydrothermal muscovite with a sheaf-like structure sometimes crystallised in albitites. Inherited muscovites from magmatic stage and newly formed muscovites from albitites have distinct chemical compositions with the latter being much more phengitic. The initial peraluminous chemistry of the leucogranite was lost during albitization and composition evolved towards a pure albite one (A/CNK = 1). Albitization induced gains in Na and Al, and losses in Si and K. Leaching of REE and U is also identified during albitization, as well as the non-CHARAC behaviour of some elements. δ¹⁸O values of quartz and muscovite in albitized granites are in the magmatic range (about 12 and 9.5‰, respectively). Feldspars acquired high δ¹⁸O values during albitization (up to 15‰). Muscovite grains from albitites have higher δ¹⁸O values than inherited ones and tend towards isotopic equilibrium with albite. The albitizing fluids have interacted with high-δ¹⁸O rocks (probably local carbonates) prior to alter granite. Muscovites inherited from magmatic stages display very characteristic disturbed ³⁹Ar–⁴⁰Ar age spectra with saddle-shapes when a muscovite associated with albitization provided a plateau age at 117.5 Ma for this alteration event. Albitization in the Salvezines Massif just preceded the regional talc/chlorite hydrothermal mineralization. Both events might then represent two outward signs of a huge hydrothermal system at the time of the rotation of the Iberian plate around Europe. The North Pyrenean Metamorphism is identified by ³⁹Ar–⁴⁰Ar analyses at ca. or younger than 100 Ma.     

Multiple crustal sources for post-tectonic I-type granites in the Hercynian Iberian Belt

A post-tectonic plutonic array of felsic I-type granites crops out in the western Hercynian Iberian Belt. Isotope (Sr, Nd, Pb) data favour the absence of an important input of juvenile magmas in late- to post- tectonic Hercynian felsic magmatism in western Iberia, but suggest a reworking of different crustal protoliths, including oceanic metabasic rocks accreted to mid-to-lower crustal levels during the early stages of the collision. I-type granites were derived from different meta-igneous protoliths ranging from metabasic to felsic compositions depending on their geographical position from the external (e.g. Galicia—N Portugal, GNP) to the innermost continental areas (Spanish Central System and Los Pedroches Batholiths). The GNP I-type plutons related to eo-Hercynian accretional terranes have lower initial ⁸⁷Sr/⁸⁶Sr ratios, lower negative εNd values, and higher ²⁰⁶Pb/²⁰⁴Pb ratios than other I-type granites of the Central Iberian zone. These more isotopically primitive Hercynian I-type granites are important in tracking pre-Hercynian accreted oceanic lithosphere terranes.     

Oxygen isotopes composition of sapphires from the French Massif Central: implications for the origin of gem corundum in basaltic fields

Alluvial and colluvial gem sapphires are common in the basaltic fields of the French Massif Central (FMC) but sapphire-bearing xenoliths are very rare, found only in the Menet trachytic cone in Cantal. The O-isotope composition of the sapphires ranges between 4.4 and 13.9‰. Two distinct groups have been defined: the first with a restricted isotopic range between 4.4 and 6.8‰ (n = 22; mean δ¹⁸O = 5.6 ± 0.7‰), falls within the worldwide range defined for blue-green-yellow sapphires related to basaltic gem fields (3.0 < δ¹⁸O < 8.2‰, n = 150), and overlaps the ranges defined for magmatic sapphires in syenite (4.4 < δ¹⁸O < 8.3‰, n = 29). A second group, with an isotopic range between 7.6 and 13.9‰ (n = 9), suggests a metamorphic sapphire source such as biotite schist in gneisses or skarns. The δ¹⁸O values of 4.4–4.5‰ for the blue sapphire-bearing anorthoclasite xenolith from Menet is lower than the δ¹⁸O values obtained for anorthoclase (7.7–7.9‰), but suggest that these sapphires were derived from an igneous reservoir in the subcontinental spinel lherzolitic mantle of the FMC. The presence of inclusions of columbite-group minerals, pyrochlore, Nb-bearing rutile, and thorite in these sapphires provides an additional argument for a magmatic origin. In the FMC lithospheric mantle, felsic melts crystallized to form anorthoclasites, the most evolved peraluminous variant of the alkaline basaltic melt. The O-isotopic compositions of the first group suggests that these sapphires crystallized from felsic magmas under upper mantle conditions. The second group of isotopic values, typified for example by the Le Bras sapphire with a δ¹⁸O of 13.9‰, indicates that metamorphic sapphires from granulites were transported to the surface by basaltic magma.     

Thermobarometry and granite genesis: the Hercynian low-P, high-T Velay anatectic dome (French Massif Central)

The Velay dome (French Massif Central) offers a quasi-continuous section across an anatectic domain comprising low- to high-grade schists, gneisses and granites. Two main tectonometamorphic events, and their related generation of granitic material, were recognized in addition to a major Barrrovian tangential event (D2) attributed to intracontinental collision tectonics: (i) a medium- to low- P , high- T event (D3) which gave rise to migmatites and syntectonic monzonitic granites and granodiorites, and (ii) a widespread melting event (D4) which led to the generation of migmatities, the Velay granite and post-anatectic granites.
Thermobarometry on samples collected from both the metamorphic envelope and the granitic core distinguishes two distinct geotherms: (i) a first, associated with the D3 event, characterized by P > 5 kbar, T ≤ 750° C and water-present melting (biotite remains stable) which led to large-scale migmatization but minor amount of granites; (ii) a second, associated with the D4 event and characterized by vapour-absent melting ( P = 4–5 kbar, T = 760–850° C) which gave rise to the Velay granites and late-migmatitic granites. The temperature increase during the D4 event is attributed to the intrusion of hot mafic magmas within the crust.
The time-integrated features of the different granitic rocks in the Velay dome can be directly related to a _H2O in the source region and illustrate the progressive dehydration of a middle to lower crustal segment over 60 Ma.     

Lead-isotope evidence for a Hercynian origin of the Salsigne gold deposit (Southern Massif Central,France)

The Salsigne gold deposit contains a complex association of sulphide layers, gold-rich disseminations, quartz-bearing veins and flat reefs, which are hosted by folded and slightly metamorphosed Paleozoic sediments on both sides of a major thrust zone. It is demonstrated that these various Au-As ore types have similar lead-isotope compositions (²⁰⁶Pb/²⁰⁴Pb = 18.22–18.56), which are characteristic of Hercynian ore deposits in the southern Massif Central. The Lower Cambrian to Devonian host rocks and associated Pb-Zn-Ba occurrences display distinctly less radiogenic corrected isotopic signatures (²⁰⁶Pb/²⁰⁴Pb = 17.83–17.98), which are characteristic of Cambrian lead in the Montagne-Noire. Concerning the controversial origin of the Salsigne gold mineralization, these results disagree with the former syngenetic hypothesis and support a new model of Hercynian syntectonic gold concentration.This work was supported by BRGM'S scientific program: Le gisement de Salsigne: caractérisation du modèle et évaluation du potentiel aurifère du district     

Deep crustal source of gneiss dome revealed by eclogite in migmatite (Montagne Noire,French Massif Central)

In orogens worldwide and throughout geologic time, large volumes of deep continental crust have been exhumed in domal structures. Extension-driven ascent of bodies of deep, hot crust is a very efficient mechanism for rapid heat and mass transfer from deep to shallow crustal levels and is therefore an important mechanism in the evolution of continents. The dominant rock type in exhumed domes is quartzofeldspathic gneiss (typically migmatitic) that does not record its former high-pressure (HP) conditions in its equilibrium mineral assemblage; rather, it records the conditions of emplacement and cooling in the mid/shallow crust. Mafic rocks included in gneiss may, however, contain a fragmentary record of a HP history, and are evidence that their host rocks were also deeply sourced. An excellent example of exhumed deep crust that retains a partial HP record is in the Montagne Noire dome, French Massif Central, which contains well-preserved eclogite (garnet+omphacite+rutile+quartz) in migmatite in two locations: one in the dome core and the other at the dome margin. Both eclogites record P ~ 1.5 ± 0.2 GPa at T  ~  700 ± 20°C, but differ from each other in whole-rock and mineral composition, deformation features (shape and crystallographic preferred orientation, CPO), extent of record of prograde metamorphism in garnet and zircon, and degree of preservation of inherited zircon. Rim ages of zircon in both eclogites overlap with the oldest crystallization ages of host gneiss at c. 310 Ma, interpreted based on zircon rare earth element abundance in eclogite zircon as the age of HP metamorphism. Dome-margin eclogite zircon retains a widespread record of protolith age (c. 470–450 Ma, the same as host gneiss protolith age), whereas dome-core eclogite zircon has more scarce preservation of inherited zircon. Possible explanations for differences in the two eclogites relate to differences in the protolith mafic magma composition and history and/or the duration of metamorphic heating and extent of interaction with aqueous fluid, affecting zircon crystallization. Differences in HP deformation fabrics may relate to the position of the eclogite facies rocks relative to zones of transpression and transtension at an early stage of dome development. Regardless of differences, both eclogites experienced HP metamorphism and deformation in the deep crust at c. 310 Ma and were exhumed by lithospheric extension—with their host migmatite—near the end of the Variscan orogeny. The deep crust in this region was rapidly exhumed from ~50 to <10 km, where it equilibrated under low-P/high-T conditions, leaving a sparse but compelling record of the deep origin of most of the crust now exposed in the dome.     

Paleomagnetic results from the Permian Rodez basin implications: the Late Variscan tectonics in the southern French Massif Central

Abstract

A paleomagnetic study has been carried out on three sedimentary formations of the Permian Rodez basin in the southern France. Two of them yield paleomagnetic poles of Saxonian and Thuringian age showing counterclockwise rotation of moderate amplitude, during or after the Thuringian deposition. For the French Massif Central, contrary to its stable southern (Lodève basin) and eastern (Largentière basin) borders, on its southwestern border, in a large area including the Rodez, Saint-Affrique and perhaps Brive basins suffered rotations due to the extensional tectonics during the Late Variscan period. © 2002 Editions scientifiques et médicales Elsevier SAS. All rights reserved.     

Paleomagnetic results from the Permian Rodez basin implications: the Late Variscan tectonics in the southern French Massif Central

A paleomagnetic study has been carried out on three sedimentary formations of the Permian Rodez basin in the southern France. Two of them yield paleomagnetic poles of Saxonian and Thuringian age showing counterclockwise rotation of moderate amplitude, during or after the Thuringian deposition. For the French Massif Central, contrary to its stable southern (Lodève basin) and eastern (Largentière basin) borders, on its southwestern border, in a large area including the Rodez, Saint-Affrique and perhaps Brive basins suffered rotations due to the extensional tectonics during the Late Variscan period.     

Fluid absent melting of a layered crustal protolith: implications for the generation of anatectic granites

We report the result of H₂O-undersaturated melting experiments on charges consisting of a layer of powdered sillimanite-bearing metapelite (HQ36) and a layer of powdered tonalitic gneiss (AGC150). Experiments were conducted at 10 kbar at 900°, 925° and 950°C. When run alone, the pelite yielded 40 vol% strongly peraluminous granitic melt at 900°C while the tonalite produced only 5 vol% weakly peraluminous granitic melt. At 950°C, the pelite and the tonalite yielded 50 vol% and 7 vol% granitic melt, respectively. When run side by side, the abundance of melt in the tonalite was 10 times higher at all temperatures than when it was run alone. In the pelite, the melt abundance increased by 25 vol%. When run alone, biotite dehydration-melting in the tonalite yielded orthopyroxene and garnet in addition to granitic melt. When run side by side only garnet was produced in addition to granitic melt. Experiments of relatively short duration, however, also contained Al-rich orthopyroxene. We suggest that the large increase in melt fraction in the tonalite is mainly a result of increased activity of Al₂O₃ in the melt, which lowers the temperature of the biotite dehydration-melting reaction. In the pelite, the increase in the abundance of melt is caused by transport of plagioclase component in the melt from the tonalite-layer to the pelite-layer. This has the effect of changing the bulk composition of this layer in the direction of minimum-temperature granitic liquids. Our results show that rocks which are poor melt-producers on their own can become very fertile if they occur in contact with rocks that contain components that destabilize the hydrous phase(s) and facilitate dehydration-melting. Because of this effect, the continental crust may have an even greater potential for granitoid melt production than previously thought. Our results also suggest that many anatectic granites most likely contain contributions from two or more different source rocks, which will be reflected in their isotopic and geochemical compositions.     

西藏拉萨地块过铝质花岗岩中继承锆石的物源区示踪及其古地理意义

富含继承锆石的过铝质花岗岩一般来源于富铝质岩石(如变泥质岩)的部分熔融,因而分析这些继承锆石的U-Pb年龄可以像分析沉积岩碎屑锆石的U-Pb年龄一样,提供过铝质花岗岩源区物质中碎屑沉积物物源区的丰富信息。本文报道了中部拉萨地块早侏罗世过铝质花岗岩的全岩地球化学和锆石U-Pb年代学数据,结合拉萨地块已有二叠纪和晚三叠世过铝质花岗岩的继承锆石年代学数据,总结了目前已有的拉萨地块过铝质花岗岩的继承锆石U-Pb年龄特征(共199个谐和测点)。这些过铝质花岗岩属强过铝质S型花岗岩,其中的继承锆石定义了1250~1100Ma(峰值1181±14Ma)和550~450Ma(峰值494±7Ma)2个最突出的年龄群,分别可比于拉萨地块古生代沉积岩的碎屑锆石年龄峰值(约1170Ma)和寒武纪火山岩的侵位时代,明显不同于西羌塘、安多和特提斯喜马拉雅新元古代-古生代沉积岩中的碎屑锆石年龄频谱。拉萨地块过铝质花岗岩中约1181Ma的继承锆石,可能与拉萨地块古生代沉积岩中的同期碎屑锆石一样,都来自澳大利亚南西部Albany-Fraser造山带和东南极Wilkes等地,而约494的继承锆石,既可能来自澳大利亚西部,也可能来自拉萨地块本地。本文提供了拉萨地块与澳大利亚大陆北缘具有古地理联系的过铝质花岗岩继承锆石U-Pb年龄证据。拉萨地块的研究实践表明,采用过铝质花岗岩继承锆石和古生代沉积岩碎屑锆石相结合的锆石U-Pb年代学方法,可为重建冈瓦纳大陆北缘其它微陆块的古地理和构造岩浆演化提供重要约束。     

Geochemistry and geochronology of meta-igneous rocks from the Tokat Massif, north-central Turkey: implications for Tethyan reconstructions

Located in the eastern Pontides of the Sakarya Zone in north-central Turkey, the Tokat Massif records the closure of both the Paleo-Tethyan (Karakaya Complex) and Neo-Tethyan ocean basins. Meta-igneous samples collected from the region were studied to determine their sources and ages. We find significant geochemical differences between metagabbros of the Karakaya and Neo-Tethyan units in terms of their trace elements: Neo-Tethyan rocks are consistent with generation in an island arc setting, whereas Karakaya assemblages were likely generated in an oceanic spreading-center environment. Karakaya metagabbros also contain glaucophane, consistent with subduction subsequent to formation. Small (2–50 μm) zircon and baddeleyite grains from four Karakaya metagabbros were dated in thin section using an ion microprobe. The results demonstrate the reliability of the method to directly constrain the tectonomagmatic history of these types of assemblages. The rocks yield Late Permian/Early Triassic ²³⁸U/²⁰⁶Pb crystallization ages of 258 ± 14 Ma (±1σ, zircon) and 254 ± 8 Ma (±1σ, baddeleyite) and an Early Cretaceous minimum metamorphic age of 137 ± 8 Ma (±1σ, zircon). Some zircon grains and baddeleyite grains with zircon overgrowths yield Early to Middle Jurassic ages. Here we present a model in which metamorphism and deformation in this region occurred during northward subduction and closure of a Paleo-Tethyan ocean basin and accretion of the Karakaya units to the Laurasian continental margin. This was followed by the onset of closure of the Neo-Tethys during the Campanian-Paleocene and accretion of island arc units to the Tokat region.     

Structural analysis of tin-bearing mineralization in Bou El Jaj district (Hercynian Central Massif,Morocco)

The aim of this paper is to characterize the geological setting of tin-bearing mineralization at the Bou El Jaj (BLJ) sector, located in the NE termination of the Moroccan Central Massif, South of Meknes city, along the NE-SW-striking shear zone. The main tin mineralization corresponds to a NNE-SSW altered corridor of tourmaline, about 10 to 12 km long, from BLJ to Achmmach mount. The geological structures are affected by three ductile deformation phases D1, (E-W shortening), D2 (NW-SE shortening), and D3 (N-S shortening), overprinting folds, and one brittle deformation event D4 (NW-SE shortening), which was synchronous with alteration and mineralization. The tourmaline-altered sediments occur in two parallel veins, about 2.5 km long and 200 m wide for each one, and are controlled by structures such as bedding, main cleavage, thrusts, and joints. Tin mineralization as cassiterite is always associated with tourmaline alteration and is controlled by the different structures.     

A-type granites of crustal origin ultimately result from open-system fenitization-type reactions in an extensional environment

The origin of A-type granites and rhyolites are ultimately relatable to mantle-derived melts and fluids in a zone undergoing extension. The basaltic magmas are accompanied by an alkaline fluid phase, dominantly H₂O + CO₂, which will induce alkali metasomatism of the granulitic crust above. The distinctive mineralogy and geochemistry are thus a direct result of the tectonic environment of formation. Metaluminous and peralkaline granites are magmatic compositions that typically contain evidence of crust and mantle in their genetic baggage, but peraluminous A-type granites may well be caused by efficient loss of alkalis during epizonal degassing. A-type granites and rhyolites are members of a vast family of rift-related magmas that include those of syenitic, nepheline syenitic and carbonatitic character. The fluid phase at work is alkaline. It can carry a host of trace elements in solution, in particular the high-field-strength elements and the rare earths. It can fenitize and fertilize a refractory lower crust, and prepare the precursor for near-complete melting. Some examples of A-type granitic magma do arise by efficient fractional crystallization of a mantle-derived basaltic magma, with or without accompanying assimilation, but many arise by partial or complete melting of an alkali-metasomatized crust.     

Metasomatism and melting history of a Variscan lithospheric mantle domain: evidence from the Puy Beaunit xenoliths (French Massif Central)

Mantle xenoliths from Puy Beaunit (French Massif Central) are compositionally varied, ranging from relatively fertile spinel lherzolites to refractory spinel dunites. Fertile peridotites have registered a modal (amphibole-bearing lherzolites) and cryptic metasomatic event that took place before the last Permian (257 Ma) melting episode. Depletion processes have been constrained by chemical modelling: the depletion is related to different degrees of partial melting, but two major melt extraction episodes are needed to explain the range of major element composition. The second event was responsible for the local large-scale dunitification of former residues. The first melting event (F25%) and metasomatic enrichment are attributed to an ancient fluid and/or liquid infiltration that could be related to a pre-Variscan regional subduction (located to the north of the Beaunit area). Texture acquisition and major deformation of the mantle xenoliths were sub-contemporaneous of the subduction and would result from lithospheric delamination. The second melting event (F17%) produced high-Mg basalts with calc-alkaline trace element signature that gave rise to the Permian underplating episode recognised in western Europe.     

New Early Permian paleomagnetic results from the Brive basin (French Massif Central) and their implications for Late Variscan tectonics

In order to assess the structural evolution of the Brive basin and the Paleozoic activity of surrounding major faults in the French Massif Central, we carried out a paleomagnetic study on Early Permian rocks from this basin. Positive-fold tests and solely reversed polarities indicate that the characteristic remanent magnetization is likely to be primary. Early Permian tilt-corrected site mean declinations vary from 207°–167° indicating that the Brive basin experienced internal vertical-axis rotations. On the contrary, Late Permian paleomagnetic site means exhibit a circular Fisherian distribution showing no relative rotations. Detailed analyses of Permian paleomagnetic data from five contemporaneous basins of the French Massif Central reveal that these basins share the same equatorial paleolatitude with stable Europe throughout the Permian. However, in Early Permian, three of the five basins experienced differential rotations. The Saint-Affrique basin not only suffered internal deformation during the Early Permian, but the basin as a whole underwent a full-scale counterclockwise vertical-axis block rotation with respect to stable Europe. As a consequence, paleomagnetic data from similar late orogenic basins have to be thus carefully considered for establishment of Apparent Polar Wander paths.     

湖南瑶岗仙复式花岗岩岩石成因及与钨成矿关系

瑶岗仙复式花岗岩体位于南岭复杂构造带北端,赋存着大型瑶岗仙钨矿床。瑶岗仙花岗岩高硅、富碱,属于高钾钙碱性系列,为分异的S型花岗岩。系统的单颗粒锆石LA-ICP-MS U-Pb同位素年龄测定表明,瑶岗仙复式花岗岩体有多期成岩事件,分别为:170Ma形成的粗粒二云母花岗岩,162Ma形成的中细粒二云母花岗岩,157Ma形成的细粒白云母花岗岩,表明花岗质岩浆经历了多期脉动侵位。元素地球化学及Sr-Nd同位素特征表明,瑶岗仙花岗岩成岩物质来源于古元古代的泥质岩。瑶岗仙花岗岩成岩年龄为170~157Ma,处于燕山期陆内伸展-减薄的构造环境。瑶岗仙花岗岩的成岩事件与钨矿床成矿事件在时空上高度吻合,花岗岩岩浆经历了高度分离结晶并产生富挥发分的流体,表明花岗岩可能为岩浆期后热液阶段成矿作用提供了原始流体和物质来源。     

Phase equilibria and melt productivity in the pelitic system: implications for the origin of peraluminous granitoids and aluminous granulites

Peraluminous granitoid magmas are a characteristic product of ultrametamorphism leading to anatexis of aluminous metasedimentary rocks in the continental crust. The mechanisms and characteristic length-scales over which these magmas can be mobilized depend strongly on their melt fraction, because of their high viscosities. Thus, it is of fundamental importance to understand the controls exerted by pressure, temperature and bulk composition of the source material on melt productivity. We have studied experimentally the vapour-absent melting behaviour of a natural metapelitic rock and our results differ greatly from those of previous experimental and theoretical investigations of melt productivity from metamorphic rocks. Under H₂O-undersaturated conditions, bulk composition of the source material is the overriding factor controlling melt fraction at temperatures on the order of 850–900° C. Granitoid melts formed in this temperature interval by the peritectic dehydration-melting reaction: $$\begin{gathered} Biotite + plagioclase + aluminosilicate + quartz \hfill \\ = melt + garnet \hfill \\ \end{gathered} $$ have a restricted compositional range. As a consequence, melt fractions will be maximized from protoliths whose modes coincide with the stoichiometry of the melting reaction. This “optimum mode” (approximately 38% biotite, 32% quartz, 22% plagioclase and 8% aluminosilicate) reflects the fact that generation of low-temperature granitoid liquids requires both fusible quartzo-feldspathic components and H₂O (from hydrous minerals). Metapelitic rocks rich in mica and aluminosilicate and poor in plagioclase contain an excess of refractory material (Al₂O₃, FeO, MgO) with low solubility in low-temperature silicic melts, and will therefore be poor magma sources. Melt fraction varies inversely with pressure in the range 7–13 kbar, but the effect is not strong: the decrease (at constant temperature) over this pressure range is of at most 15 vol% (absolute). The liquids produced in our experiments are silicarich (68–73 wt% SiO₂), strongly peraluminous (2–5 wt% normative corundum) and very felsic (MgO+FeO^* +TiO₂ less than 3 wt%, even at temperatures above 1000° C). The last observation suggests that peraluminous granitoids with more than 10% mafic minerals (biotite, cordierite, garnet) contain some entrained restite. Furthermore, because liquids are also remarkably constant in composition, we believe that restite separation is more important than fractional crystallization in controlling the variability within and among peraluminous granitoids. We present liquidus phase diagrams that allow us to follow the phase relationships of melting of silica-and alumina-saturated rocks at pressures corresponding to the mid- to deep-continental crust. Garnet, aluminosilicate, quartz and ilmenite are the predominant restitic phases at temperatures of about 900° C, but Ti-rich biotite or calcic plagioclase can also be present, depending on the bulk composition of the protolith. At temperatures above 950–1050° C (depending on the pressure) the restitic assemblage is: hercynitic spinel+ilmenite+quartz±aluminosilicate. Our results therefore support the concept that aluminous granulites (garnet-spinel-plagioclase-aluminosilicate-quartz) can be the refractory residuum of anatectic events.