Major discoveries in metamorphic petrology, as well as other geological disciplines, have been made in the Alps. The regional distribution of Late Cretaceous–Tertiary metamorphic conditions, documented in post-Hercynian metasediments across the entire Alpine belt from Corsica–Tuscany in the west to Vienna in the east, is presented in this paper. In view of the uneven distribution of information, we concentrate on type and grade of metamorphism; and we elected to distinguish between metamorphic paths where either pressure and temperature peaked simultaneously, or where the maximum temperature was reached at lower pressures, after a significant temperature increase on the decompression path.The results show which types of process caused the main metamorphic imprint: a subduction process in the western Alps, a collision process in the central Alps, and complex metamorphic structures in the eastern Alps, owing to a complex geodynamic and metamorphic history involving the succession of the two types of process. The western Alps clearly show a relatively simple picture, with an internal (high-pressure dominated) part thrust over an external greenschist to low-grade domain, although both metamorphic domains are structurally very complex. Such a metamorphic pattern is generally produced by subduction followed by exhumation along a cool decompression path. In contrast, the central Alps document conditions typical of subduction (and partial accretion), followed by an intensely evolved collision process, often resulting in a heating event during the decompression path of the early-subducted units. Subduction-related relics and (collisional/decompressional) heating phenomena in different tectonic edifices characterize the Tertiary evolution of the Eastern Alps. The Tuscan and Corsica terrains show two different kinds of evolution, with Corsica resembling the western Alps, whereas the metamorphic history in the Tuscan domain is complex owing to the late evolution of the Apennines. This study confirms that careful analysis of the metamorphic evolution of metasediments at the scale of an entire orogen may change the geodynamic interpretation of mountain belts.

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Andalusite occurs as an accessory mineral in many types of per aluminous felsic igneous rocks, including rhyolites, aplites, granites, pegmatites, and anatectic migmatites. Some published stability cunes for And = Sil and the water-saturated granite solidus permit a small stability field for andalusite in equilibrium with, felsic melts. We examine 108 samples of andalusite-bearing felsic rocks from more than 40 localities worldwide. Our purpose is to determine the origin of andalusite, including the T-P-X controls on andalusite formation, using eight textural and chemical criteria: sizecompa tibility with grain sizes of igneous m inera ls in the same rock; shape-ranging from euhedral to anhedral, with, no simple correla tion with, origin; state of aggregation-single grains or clusters of grains; association with, muscovite-with, or without, rims of mono crystalline or polycrystalline muscovite; inclusions-rare mineral inclusions and melt inclusions; chemical composition-andalusite with, little significant chemical variation, except in iron content (0-08-1-71 wt. °/o FeO); compositional zoning-concentric, sec tor, patchy, oscillatory zoning cryptically reflect growth, conditions; compositions of coexisting phases-biotites with. high, siderophy llite-eastonite contents (AT ~2-68 ± 0-07 atoms per formula unit), muscovites with 0-57-4-01 wt % P'eO and 0-02-2-85 wt % TiOg, and apatites with. 3-53 ± 0-18 wt % F. Coexisting muscovite-biotite pairs have a wide range of F contents, and FSt = 1-612FAIs + 0-015. Most coexisting minerals have compositions consistent with, equilibration at. magmatic conditions. The three principal genetic types of andalusite in felsic igneous rocks are: Type 1 Metamorphic-(a) prograde metamorphic (in ther mally metamorphosed peraluminous granites), (b) retrograde metamorphic (inversion from sillimanite of unspecified origin), (c) xenocrystic (derivation from local country rocks), and (d) restitic (derivation from source regions); Type 2 Magmatic-(a.) peritectic (water-undersaturated, TJ) associated with, leucosomes in migma tites, (b) peritectic (water-undersaturated, T^J, as reaction rims on garnet, or cordierite, (c) cotectic (water-undersaturated, T j direct, crystallization from a silicate melt, and (d) pegmatitic (watersaturated, T^J, associated with, aplite-pegmatite contacts or peg matitic portion alone; Type 3 Metasomatic-(water-saturated, magma-absent), spatially related to structural discontinuities in host, replacement, of feldspar and/or biotite, intergrowths with, quartz. Tie great, majority of our andalusite samples show one or more textural or chemical criteria suggesting a magmatic origin. Of the many possible controls on the formation of andalusite (excess AfOy,, water concentration and fluid evolution, high. Be-B-LiP , high. F, high. Fe-Mn-Ti, and kinetic considerations), the two most, important, factors appear to be excess Af03 and the effect, of releasing water (either to strip alkalis from the melt, or to reduce alumina solubility in the melt). Of particular importance is...