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Processes of crystal-mush remobilization by mafic magma recharges are often related to the outpouring of large volumes of silicic melt during caldera-forming eruptions. This occurred for the Campanian Ignimbrite (CI) eruption (Campi Flegrei, Italy), which produced a voluminous trachy-phonolitic ignimbrite in southern-central Italy about 40 ka ago. We focussed on the proximal-CI deposits at San Martino that are composed of a main sequence of early-erupted, crystal-poor units and a late-erupted (post-caldera collapse) crystal-rich Upper Pumice Flow Unit (UPFU). Detailed micro-analytical geochemical data were performed on glasses and crystals of pyroclasts from these deposits and coupled with Sr-Nd isotopic measurements on glasses. Results show that the CI eruption was fed by two distinct melts for the early-erupted units and the late UPFU, respectively. The glasses of the early-erupted units have negative Eu anomalies and show more evolved compositions and higher Nd isotope ratios than those of the UPFU, which have positive Eu/Eu*. The magmas of the early units formed the main volume of eruptible melt of the CI reservoir, and are interpreted as having been extracted from cumulate crystal-mush without a vertical geochemical gradient within the magma reservoir. The data indicate that the generation of the distinctive UPFU melts involved the injection of a new batch of mafic magma into the base of the CI reservoir. The mafic magma allowed heating and reactivation of the CI crystal-mush by melting of low-Or sanidines (+/− low-An plagioclases), leaving high-An plagioclases and high-Mg# clinopyroxenes as residual phases and a crystal-mush melt, made of 20% of the initial mush interstitial melt (with a composition similar to the early-erupted units) and 80% of sanidine melt. When the mush crystallinity was sufficiently reduced, the mafic magma was able to penetrate into the reactivated crystal-mush, mixing with variable proportions of crystal-mush melt and generating cooler hybrid melts, which underwent further crystallization of high-Or sanidine at variable degrees (10–25%). Finally, possibly a short time before the eruption, the UPFU magmas were able to mix and mingle with the crystal-poor eruptible melts still persisting in the CI reservoir at the time of UPFU emission. We suggest that the complex mechanisms described for the magma evolution feeding the CI eruption may occur whenever a crystal-mush is reactivated by new mafic magma inputs

The Central Atlantic Magmatic Province (CAMP) is a large igneous province (LIP) composed of basic dykes, sills, layered intrusions and lava flows emplaced before Pangea break-up and currently distributed on the four continents surrounding the Atlantic Ocean. One of the oldest, best preserved and most complete sub-provinces of the CAMP is located in Morocco. Geochemical, geochronologic, petrographic and magnetostratigraphic data obtained in previous studies allowed identification of four strato-chemical magmatic units, i.e. the Lower, Intermediate, Upper and Recurrent units. For this study, we completed a detailed sampling of the CAMP in Morocco, from the Anti Atlas in the south to the Meseta in the north. We provide a complete mineralogical, petrologic (major and trace elements on whole-rocks and minerals), geochronologic (40Ar/39Ar and U–Pb ages) and geochemical set of data (including Sr–Nd–Pb–Os isotope systematics) for basaltic and basaltic–andesitic lava flow piles and for their presumed feeder dykes and sills. Combined with field observations, these data suggest a very rapid (

This study reports petrostructural observations in the pargasite and phlogopite-bearing Finero peridotite massif (Italian Western Alps), which suggest that the pervasive foliation in this massif was formed by deformation concomitant with percolation of hydrous Si-rich melts: (1) diffuse contacts, but systematic parallelism between the pyroxenitic layers and the foliation of the peridotite (2) strong shape and crystal preferred orientations (SPO and CPO), but subhedral or interstitial shapes and weak intracrystalline deformation of the hydrous phases, (3) CPO, but interstitial shapes of the pyroxenes, (4) very coarse olivine grain sizes, which are correlated to the olivine abundance, and (5) elongated shapes, but weak intracrystalline deformation, and extremely weak and highly variable CPO of olivine. The pervasive deformation of the Finero peridotite occurred therefore under conditions that allowed coexistence of H2O-CO2-bearing melts, pargasite, and spinel, that is, temperatures of 980-1080 degrees C and pressures

International audience; Mantle xenoliths enclosed in the Plio-Quaternary alkaline basalts from Bou Ibalrhatene, Middle Atlas, Morocco, are characterized by a wide range of lithological and chemical heterogeneity, consistent with metasomatism of their lithospheric mantle source. Subordinate porphyroclastic to protogranular spinel-lherzolites associated with websterites exhibit major and trace element signatures, along with a depleted mantle isotopic affinity, that testify to ancient melt extraction processes, possibly during Neo- to Paleoproterozoic times. These samples show large ion lithophile element (LILE) enrichments that have been imparted a long time after the accretion of their protoliths to the lithosphere, induced by alkaline melts rising from upwelling HIMU-like asthenosphere since the late Cretaceous or Eocene. Extensive sectors of the percolated lherzolite and harzburgite mantle progressively approached chemical equilibrium with the migrating melts, forming porphyroblastic amphibole-rich ultramafic rocks with strong LILE enrichment, highly variable (enriched to strongly depleted) high field strength element (HFSE) abundances and HIMU-like isotopic signatures. As a result, the older depleted lithosphere was progressively refertilized. The presence among the Bou Ibalrhatene ultramafic xenoliths of both Fe- and Mg-rich wehrlites is a rare occurrence in xenolith suites. The Fe-rich wehrlites formed by the migration through dunitic channels, which opened during earlier reactive porous flow, of larger and larger volumes of rising alkaline melts, becoming progressively less evolved in composition and more similar to the erupted lavas. In contrast, subordinate Mg-rich wehrlites characterized by the presence of apatite, extreme LILE enrichment and HFSE depletion testify to the localized chemical effects of either carbonatite melts related to the oldest (i.e. Eocene) volcanic activity in the area or, more probably, to highly evolved SiO2-saturated silicate melts that vanished through interaction with the lithosphere. As a whole, the textural, petrographic and chemical characteristics of the Bou Ibalrhatene xenoliths suggest prolonged thermo-chemical erosion of an originally heterogeneous lithosphere with a dominant depleted mantle isotopic signature by melts rising from a HIMU-like asthenospheric mantle source in response to intraplate tectonic reactivation and rifting of the Pan-African basement. The overall scenario envisaged for lithosphere-asthenosphere interaction beneath the Middle Atlas is similar to that inferred for other Cenozoic Central-Northern African volcanic centres, such as Hoggar (Algeria) and Gharyan (Libya). The majority of the mantle sectors beneath the NE-SW volcanic alignment associated with the Trans-Moroccan fault system consist of rejuvenated lithosphere formed by small-scale, shallow-mantle upwelling and accretion of asthenospheric material since late Cretaceous or Eocene times.

Sm–Nd, Lu–Hf, Rb–Sr and SIMS U–Pb data are presented for meta-gabbroic eclogites from the eclogite type-locality (Hauy, 1822) Kupplerbrunn–Prickler Halt and other areas of the Saualpe (SE Austria) and Pohorje Mountains (Slovenia). Mg-rich eclogites derived from early gabbroic cumulates are kyanite- and zoisite rich, whereas eclogites with lower Mg contents contain clinozoisite ± kyanite. Calculated P–T conditions at the final stages of high-pressure metamorphism are 2.2 ± 0.2 GPa at 630–740 °C. Kyanite-rich eclogites did not yield geologically meaningful Sm–Nd ages due to incomplete Nd isotope equilibration, whereas Sm–Nd multifraction garnet–omphacite regression for a low-Mg eclogite from Kupplerbrunn yields an age of 91.1 ± 1.3 Ma. The Sm–Nd age of 94.1 ± 0.8 Ma obtained from the Fe-rich core fraction of this garnet dates the initial stages of garnet growth. Zircon that also crystallized at eclogite facies conditions gives a weighted mean U–Pb SIMS age of 88.4 ± 8.1 Ma. Lu–Hf isotope analysis of a kyanite–eclogite from Kupplerbrunn yields 88.4 ± 4.7 Ma for the garnet–omphacite pair. Two low-Mg eclogites from the Gertrusk locality of the Saualpe yield a multimineral Sm–Nd age of 90.6 ± 1.0 Ma. A low-Mg eclogite from the Pohorje Mountains (70 km to the SE) gives a garnet–whole-rock Lu–Hf age of 93.3 ± 2.8 Ma. These new age data and published Sm–Nd ages of metasedimentary host rocks constrain the final stages of the eo-Alpine high-pressure event in the Saualpe–Pohorje part of the south-easternmost Austroalpine nappe system suggesting that garnet growth in the high-pressure assemblages started at c. 95–94 Ma and ceased at c. 90–88 Ma, probably at the final pressure peak. Zircon and amphibole crystallization was still possible during incipient isothermal decompression. Rapid exhumation of the high-pressure rocks was induced by collision of the northern Apulian plate with parts of the Austroalpine microplate, following Jurassic closure of the Permo-Triassic Meliata back-arc basin.