Articles de revues : « Magmatic rocks, Aeolian Islands, petrology, geochemistry »

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Ece, O. I., et Z. E. Nakagawa. « Alteration of volcanic rocks and genesis of kaolin deposits in the Şile Region, northern İstanbul, Turkey. Part II : differential mobility of elements ». Clay Minerals 38, n^o 4 (décembre 2003) : 529–50. http://dx.doi.org/10.1180/0009855033840113.

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AbstractIn the area of S° ile, NW Turkey, Upper Cretaceous calc-alkaline volcanic rocks with compositions ranging from andesite to rhyolite have been recognized. The most widespread rocks of the suite are andesites, which can be grouped into altered and fresh. The oldest altered andesites are the parent rocks for the kaolin deposits of the study area. The Upper Cretaceous volcanic suite consists of spilite, basalt, andesite, trachyandesite, trachyandesitic and hyaloandesitic dacite, rhyolite lavas, tuffs and agglomerates. The highly altered andesites are composed of plagioclase, pyroxene, hornblende, biotite, augite and very fine opaque minerals. During the Turonian, an E –W trending extensional magmatic arc was developed in the Istanbul Tectonic Zone of the oceanic Western Black Sea basin and intermediate volcanic rocks were emplaced, mostly calc-alkaline andesites, suggesting multi-stage magmatism. The significant features of the andesites are: (1) enrichment of LILE (Rb, Ba, K) over HFSE (Zr, Nb, Hf, Ti, Th, U, Y) and LREE (La –Sm), resulting in high Ba/Nb, Th/Nb, Ba/La, K/Ti and Th/La ratios; (2) depletion of LREE over HFSE, MREE and HREE, generating high La/Nb, Ce/Ti, La/Sm and La/Y values; and (3) depletion of Nb, Sr and Ti; all of which are typical of island arc magmatism, with possible back arc signature. The Th-Hf-Ta diagram for tectonomagmatic classification shows that the S° ile calc-alkaline rocks are similar to volcanic rocks from the Mariana Arc, the Aeolian Arc of Salina, Italy, the Skaros island in the Aegean Sea and Sardinia's ignimbrites. Moreover, relatively low La/Th and Ce/Pb ratios suggest that the source region of volcanism was enriched in LILE with respect to REE, indicating crustal contamination during melting.Highly weathered andesitic rocks, rich in smectite, were transported gradually and deposited in a lacustrine basin, a coal-forming dysaerobic environment, in which they were subject to post-depositional alteration, or in situkaolinization, to form a kaolin deposit in the presence of humic and fulvic acids. The mobility of major and trace elements and REEs during the progressive kaolinization of andesitic materials has been investigated to reveal the geochemical characteristics of Upper Cretaceous volcanic parent rocks and to explain mineralogical processes in a kaolin deposit as a daughter rock ‘end-product’ . Alteration is characterized by the loss of Si, Fe, Ca, Na and K, and by the gain of Al, Ti, Zr and LOI. Moreover, Ho, Er and Yb are immobile, and Hf, Zr and Nb are mobile. Th and U are slightly enriched in clay horizons with respect to the andesitic rocks. In addition, Cr, Ga, Nb and Ta enrichments indicate variable sources of terrigenous sediments and differential mobilities of elements in lake waters rich in organic acids. The anatase concentration increases in the <2 mm size fractions as subspherical particles and these precipitate at acidic conditions (pH ≈ 5) during early diagenesis.

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Davì, Marcella, Rosanna De Rosa, Paola Donato, Francesco Vetere, Donatella Barca et Andrea Cavallo. « Magmatic Evolution and plumbing system of ring-fault volcanism : the Vulcanello Peninsula (Aeolian Islands, Italy) ». European Journal of Mineralogy 21, n^o 5 (30 octobre 2009) : 1009–28. http://dx.doi.org/10.1127/0935-1221/2009/0021-1955.

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Nicotra, Eugenio, Marisa Giuffrida, Marco Viccaro, Paola Donato, Claudia D'Oriano, Antonio Paonita et Rosanna De Rosa. « Timescales of pre-eruptive magmatic processes at Vulcano (Aeolian Islands, Italy) during the last 1000 years ». Lithos 316-317 (septembre 2018) : 347–65. http://dx.doi.org/10.1016/j.lithos.2018.07.028.

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Key, C. H. « Geochemistry of diorites and associated plutonic rocks of SE Jersey, Channel Islands ». Mineralogical Magazine 51, n^o 360 (juin 1987) : 217–29. http://dx.doi.org/10.1180/minmag.1987.051.360.04.

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AbstractThe plutonic complex in SE Jersey consists of a late Precambrian gabbro-diorite mass which has been intruded by several granites. The status of the diorites which, like the gabbros, often possess a layered structure, is not clear. New geochemical data, including rare earth and trace element analyses, suggest that acid-basic magma mixing was not responsible for the variety of intermediate rocks. Amphibole-controlled fractional crystallization of hydrous basic magma is also unlikely in view of the REE and HFS (high field strength) element distribution. The model which best fits all the available field, petrographic and geochemical evidence is one in which the chemical variation was initially produced by fractional crystallization of anhydrous basic magma and subsequently overprinted by granitic metasomatism. This superimposed calc-alkaline characteristics on the complex and produced hybrid diorites which, because they were above their solidus temperature, recrystallized with textures indicative of a magmatic origin.

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Esperança, S., G. M. Crisci, R. de Rosa et R. Mazzuoli. « The role of the crust in the magmatic evolution of the island of Lipari (Aeolian Islands, Italy) ». Contributions to Mineralogy and Petrology 112, n^o 4 (décembre 1992) : 450–62. http://dx.doi.org/10.1007/bf00310777.

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Cintorrino, Alessia Amelia, Mimmo Palano et Marco Viccaro. « Magmatic and tectonic sources at Vulcano (Aeolian Islands, Southern Italy) : A geodetic model based on two decades of GPS observations ». Journal of Volcanology and Geothermal Research 388 (décembre 2019) : 106689. http://dx.doi.org/10.1016/j.jvolgeores.2019.106689.

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Marzoli, Andrea, Hervé Bertrand, Nasrrddine Youbi, Sara Callegaro, Renaud Merle, Laurie Reisberg, Massimo Chiaradia et al. « The Central Atlantic Magmatic Province (CAMP) in Morocco ». Journal of Petrology 60, n^o 5 (19 avril 2019) : 945–96. http://dx.doi.org/10.1093/petrology/egz021.

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Abstract 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 (<0·3 Ma) emplacement of over 95% of the preserved magmatic rocks. In particular, new and previously published data for the Lower to Upper unit samples yielded indistinguishable 40Ar/39Ar (mean age = 201·2 ± 0·8 Ma) and U–Pb ages (201·57 ± 0·04 Ma), suggesting emplacement coincident with the main phase of the end-Triassic biotic turnover (c.201·5 to 201·3 Ma). Eruptions are suggested to have been pulsed with rates in excess of 10 km3/year during five main volcanic pulses, each pulse possibly lasting only a few centuries. Such high eruption rates reinforce the likelihood that CAMP magmatism triggered the end-Triassic climate change and mass extinction. Only the Recurrent unit may have been younger but by no more than 1 Ma. Whole-rock and mineral geochemistry constrain the petrogenesis of the CAMP basalts. The Moroccan magmas evolved in mid-crustal reservoirs (7–20 km deep) where most of the differentiation occurred. However, a previous stage of crystallization probably occurred at even greater depths. The four units cannot be linked by closed-system fractional crystallization processes, but require distinct parental magmas and/or distinct crustal assimilation processes. EC-AFC modeling shows that limited crustal assimilation (maximum c.5–8% assimilation of e.g. Eburnean or Pan-African granites) could explain some, but not all the observed geochemical variations. Intermediate unit magmas are apparently the most contaminated and may have been derived from parental magmas similar to the Upper basalts (as attested by indistinguishable trace element contents in the augites analysed for these units). Chemical differences between Central High Atlas and Middle Atlas samples in the Intermediate unit could be explained by distinct crustal contaminants (lower crustal rocks or Pan-African granites for the former and Eburnean granites for the latter). The CAMP units in Morocco are likely derived from 5–10% melting of enriched peridotite sources. The differences observed in REE ratios for the four units are attributed to variations in both source mineralogy and melting degree. In particular, the Lower basalts require a garnet peridotite source, while the Upper basalts were probably formed from a shallower melting region straddling the garnet–spinel transition. Recurrent basalts instead are relatively shallow-level melts generated mainly from spinel peridotites. Sr–Nd–Pb–Os isotopic ratios in the CAMP units from Morocco are similar to those of other CAMP sub-provinces and suggest a significant enrichment of the mantle-source regions by subducted crustal components. The enriched signature is attributed to involvement of about 5–10% recycled crustal materials introduced into an ambient depleted or PREMA-type mantle, while involvement of mantle-plume components like those sampled by present-day Central Atlantic Ocean Island Basalts (OIB, e.g. Cape Verde and Canary Islands) is not supported by the observed compositions. Only Recurrent basalts may possibly reflect a Central Atlantic plume-like signature similar to the Common or FOZO components.

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Mandarano, Michela, Antonio Paonita, Mauro Martelli, Marco Viccaro, Eugenio Nicotra et Ian L. Millar. « Revealing magma degassing below closed-conduit active volcanoes : Geochemical features of volcanic rocks versus fumarolic fluids at Vulcano (Aeolian Islands, Italy) ». Lithos 248-251 (avril 2016) : 272–87. http://dx.doi.org/10.1016/j.lithos.2016.01.026.

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Stroncik, Nicole A., Andreas Klügel et Thor H. Hansteen. « The magmatic plumbing system beneath El Hierro (Canary Islands) : constraints from phenocrysts and naturally quenched basaltic glasses in submarine rocks ». Contributions to Mineralogy and Petrology 157, n^o 5 (8 novembre 2008) : 593–607. http://dx.doi.org/10.1007/s00410-008-0354-5.

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Luchetti, A. C. F., A. J. R. Nardy, F. B. Machado, J. E. O. Madeira et J. M. Arnosio. « New insights on the occurrence of peperites and sedimentary deposits within the silicic volcanic sequences of the Paraná Magmatic Province, Brazil ». Solid Earth 5, n^o 1 (10 mars 2014) : 121–30. http://dx.doi.org/10.5194/se-5-121-2014.

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Abstract. The PMP (Paraná Magmatic Province) is characterized by lava flows of the Early Cretaceous Serra Geral Formation which covers about 75% of the Paraná Basin (southern and southeastern Brazil), composed of a thick (up to 1600 m) volcanic sequence formed by a succession of petrographically and geochemically distinct units of basic and silicic composition. The whole package must have been emplaced during approximately 3 million years of nearly uninterrupted activity. A few aeolian sandstone layers, indicating arid environmental conditions (the Botucatu Formation), are interlayered in the lower basalts. Above the basalts, the Palmas and Chapecó Members are composed of silicic volcanic rocks (quartz latites, dacites, rhyodacites and rhyolites) and basalts. This paper presents new evidence of sedimentation episodes separating silicic volcanic events, expressed by the occurrence of sedimentary deposits. Interaction between the volcanic bodies and the coeval unconsolidated sediments formed peperites. The sediments were observed between basaltic lava flows and silicic rocks or interlayered in the Palmas-type rocks, between the Chapecó-type rocks and overlying basaltic flows, between silicic bodies of the Palmas and Chapecó types, and interlayered within Palmas-type units. The observed structures indicate that the sediments were still wet and unconsolidated, or weakly consolidated, at the time of volcanism, which, coupled with the sediment features, reflect environmental conditions that are different from those characterizing the Botucatu arid conditions.

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Caracausi, A., M. Ditta, F. Italiano, M. Longo, P. M. Nuccio, A. Paonita et A. Rizzo. « Changes in fluid geochemistry and physico-chemical conditions of geothermal systems caused by magmatic input : The recent abrupt outgassing off the island of Panarea (Aeolian Islands, Italy) ». Geochimica et Cosmochimica Acta 69, n^o 12 (juin 2005) : 3045–59. http://dx.doi.org/10.1016/j.gca.2005.02.011.

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Mattioli, M., G. Serri, E. Salvioli-Mariani, A. Renzulli, P. M. Holm, P. Santi et G. Venturelli. « Sub-volcanic infiltration and syn-eruptive quenching of liquids in cumulate wall-rocks : the example of the gabbroic nodules of Stromboli (Aeolian Islands, Italy) ». Mineralogy and Petrology 78, n^o 3-4 (1 juillet 2003) : 201–30. http://dx.doi.org/10.1007/s00710-002-0232-1.

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McNab, Fergus, et Patrick Ball. « meltPT : A Python package for basaltic whole-rock thermobarometric analysis with application to Hawaiʻi ». Volcanica 6, n^o 1 (21 février 2023) : 63–76. http://dx.doi.org/10.30909/vol.06.01.6376.

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Quantifying the depths and temperatures from which igneous rocks are derived is an important step in understanding volcanic, magmatic and mantle processes. We present meltPT, a Python package that allows users to apply twelve published whole-rock thermobarometers within a consistent framework, as well as combine thermobarometric results and geothermal models to estimate mantle potential temperatures. We apply meltPT to basaltic rocks from mid-ocean ridges and the Hawaiian Islands. We find mid-ocean ridge basalts equilibrate between 1–2 GPa and 1275–1475 ℃, corresponding to an ambient mantle potential temperature of ~1400 ℃. We estimate that the Hawaiian plume has an excess temperature of ~150 ℃. Hawaiian melt-equilibration depths increase from 1–3 GPa to 2.5–5 GPa through each island's life cycle. Our results indicate that multiple lithologies are present within the plume, and that transient plume reconfiguration in response to changing plate velocity is a viable mechanism for generating Hawaiʻi's two geochemically distinct plume tracks.

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Salvioli-Mariani, E., M. Mattioli, A. Renzulli et G. Serri. « Silicate melt inclusions in the cumulate minerals of gabbroic nodules from Stromboli Volcano (Aeolian Islands, Italy) : main components of the fluid phase and crystallization temperatures ». Mineralogical Magazine 66, n^o 6 (décembre 2002) : 969–84. http://dx.doi.org/10.1180/0026461026660071.

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Abstract The studied gabbroic nodules occurring in the Petrazza pyroclastic rocks consist mainly of plagioclase (An95–87), olivine (Fo83-73) and clinopyroxene (Mg# 90–77), with subordinate opaques (Ti-magnetite) and amphibole (Mg-hastingsite), which constitute the cumulate minerals. Interstitial material has a relatively high, but variable, degree of vesicularity and consists of variable amounts of glass and quenched crystals of plagioclase (An71–55), amphibole, clinopyroxene and rare biotite, olivine and opaques. Silicate melt inclusions are abundant in the cumulate minerals, but complete homogenization to melt has been observed only in the inclusions occurring in clinopyroxene, where the temperatures of homogenization vary from 1134 to 1190°C. Microthermometric investigations of fluid inclusions and of the shrinkage bubble of the melt inclusions suggest that the magma contained CO2. The apparent scarcity of H2O indicates that this component was strongly partitioned into the magma at the time of crystallization of the investigated minerals; this is further supported by the occurrence of (1) daughter biotite- and amphibole-bearing inclusions which show that the H2O activity in the magma was sufficiently high to allow their crystallization, and (2) calcic plagioclase (An95–87) which can be crystallized from a high-alumina basaltic magma at pressure ≤2 kbar, temperatures in the range 1050–1100°C and in the presence of 3–4 wt.% of water (MELTS software simulations). The composition of the melt inclusions suggests that the hosting plagioclase, olivine and clinopyroxene crystallized from slightly different batches of magma. The S content in the melt inclusions of clinopyroxene and olivine is high (up to 0.41 wt.%). The presence of Fe-Cu(-Ni)-rich blebs of sulphide in plagioclase, olivine, amphibole, and locally in the melt inclusions too, further supports the important role of sulphur in the primitive magmas of the investigated gabbros. Small differences in redox conditions or in the Fe content of the melts favoured S mobilization as sulphide.

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Kay, Suzanne Mahlburg, Brian R. Jicha, Gary L. Citron, Robert W. Kay, Ashley K. Tibbetts et Tiffany A. Rivera. « The Calc-Alkaline Hidden Bay and Kagalaska Plutons and the Construction of the Central Aleutian Oceanic Arc Crust ». Journal of Petrology 60, n^o 2 (24 décembre 2018) : 393–439. http://dx.doi.org/10.1093/petrology/egy119.

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Abstract Calc-alkaline plutons are the major crustal building blocks of continental margins, but are rarely exposed in oceanic island arcs. Two of the best examples are the ∼10 km wide Hidden Bay and Kagalaska plutons that intrude Eocene mafic volcanic–sedimentary rocks on Adak and Kagalaska islands in the central Aleutian arc. Twenty new Ar/Ar and U/Pb ages, coupled with published ages, show that the Hidden Bay pluton was intruded in multiple stages from ∼34·6 to 30·9 Ma, whereas the Kagalaska pluton was intruded at ∼14 Ma. The plutons largely consist of medium- to high-K2O hornblende-bearing cumulate diorite (53–55 wt % SiO2) and hornblende–biotite granodiorite (57–64 wt %), with lesser amounts of gabbro (50–52 wt % SiO2), leucogranodiorite (67–69 wt % SiO2) and aplite (76–77 wt % SiO2) that can generally be linked to each other by crystal fractionation. The compositions of these plutons are generally similar to those of continental plutons, except for more oceanic-like large ion lithophile element and isotopic signatures (87Sr/86Sr = 0·703–0·7033; ɛNd = 9·4–7·7) that reflect oceanic- rather than continental-type crustal contaminants. Chemical similarities between the Hidden Bay homogeneous gabbros and high-Al basalts in Adak Pleistocene-Holocene volcanoes indicate little temporal evolution in the general character of the mantle-derived basalts. Rather than a unique arc setting and distinctive magmas, formation of the Aleutian calc-alkaline plutons seems to require a sufficient crustal thickness (∼37 km) and a high enough water content to stabilize pargasitic hornblende amphibole in a relatively closed magma system that favors increasing K, Ti and H2O at the end of a magmatic cycle. This termination of magmatism coincides with a northward migration of the magmatic front that is inferred to be associated with fore-arc subduction erosion. In accord with Adak region crustal architecture based on seismic data, crystallization models for the plutons suggest that mantle-generated hydrous arc basalts fractionated olivine and clinopyroxene in the lower crust to form high-Al basaltic composition magmas that rose into the mid-crust, where gabbro and diorite crystallized to form the magmas that buoyantly rose into the upper crust and crystallized to form the volumetrically dominant granodiorite (58–63 wt % SiO2). The most important temporal changes in chemistry can be explained by fore-arc crust incorporated into the mantle wedge by fore-arc subduction erosion creating ‘adakitic’ signatures at times of northward arc migration and a change to a more continental subducted sediment component at the time of Plio-Pleistocene glaciation.

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Troll, V. R., A. Klügel, M. A. Longpré, S. Burchardt, F. M. Deegan, J. C. Carracedo, S. Wiesmaier et al. « Floating stones off El Hierro, Canary Islands : xenoliths of pre-island sedimentary origin in the early products of the October 2011 eruption ». Solid Earth 3, n^o 1 (13 mars 2012) : 97–110. http://dx.doi.org/10.5194/se-3-97-2012.

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Abstract. A submarine eruption started off the south coast of El Hierro, Canary Islands, on 10 October 2011 and continues at the time of this writing (February 2012). In the first days of the event, peculiar eruption products were found floating on the sea surface, drifting for long distances from the eruption site. These specimens, which have in the meantime been termed "restingolites" (after the close-by village of La Restinga), appeared as black volcanic "bombs" that exhibit cores of white and porous pumice-like material. Since their brief appearance, the nature and origin of these "floating stones" has been vigorously debated among researchers, with important implications for the interpretation of the hazard potential of the ongoing eruption. The "restingolites" have been proposed to be either (i) juvenile high-silica magma (e.g. rhyolite), (ii) remelted magmatic material (trachyte), (iii) altered volcanic rock, or (iv) reheated hyaloclastites or zeolite from the submarine slopes of El Hierro. Here, we provide evidence that supports yet a different conclusion. We have analysed the textures and compositions of representative "restingolites" and compared the results to previous work on similar rocks found in the Canary Islands. Based on their high-silica content, the lack of igneous trace element signatures, the presence of remnant quartz crystals, jasper fragments and carbonate as well as wollastonite (derived from thermal overprint of carbonate) and their relatively high oxygen isotope values, we conclude that "restingolites" are in fact xenoliths from pre-island sedimentary layers that were picked up and heated by the ascending magma, causing them to partially melt and vesiculate. As they are closely resembling pumice in appearance, but are xenolithic in origin, we refer to these rocks as "xeno-pumice". The El Hierro xeno-pumices hence represent messengers from depth that help us to understand the interaction between ascending magma and crustal lithologies beneath the Canary Islands as well as in similar Atlantic islands that rest on sediment-covered ocean crust (e.g. Cape Verdes, Azores). The occurrence of "restingolites" indicates that crustal recycling is a relevant process in ocean islands, too, but does not herald the arrival of potentially explosive high-silica magma in the active plumbing system beneath El Hierro.

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Denlinger, Roger P., et Ashton Flinders. « Density structure of the island of Hawai'i and the implications for gravity-driven motion of the south flank of Kīlauea Volcano ». Geophysical Journal International 228, n^o 3 (4 octobre 2021) : 1793–807. http://dx.doi.org/10.1093/gji/ggab398.

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SUMMARY The discovery that large landslides dissected the Hawaiian Islands, scattering debris over thousands of square kilometres of seafloor, changed our ideas of island growth and evolution. The evidence is consistent with catastrophic flank collapse during volcano growth, and draws our focus to the currently active island of Hawai'i, the volcanoes Mauna Loa and Kīlauea, and particularly to the actively mobile south flank of Kīlauea. Both the weight distribution and pressure within an extensive magmatic system are perceived to affect stability, but the role of gravitational body forces and island density distribution has not been quantitatively assessed. We use seismic velocities derived from tomography to model the density distribution of the island of Hawai'i and find that olivine-rich melts and rocks in Hawaiian volcanoes result in a close association of seismic velocity and density. The resultant density model reproduces more than 95 per cent of the observed gravity disturbance signal wherever tomographic control exists and provides a basis for evaluating the body forces from gravity. We also find that if the decollement is weak, then gravitational body forces can produce slip that explains most seismo-tectonic and volcano-tectonic structural features of Kīlauea. Where the decollement is in a state of incipient slip from this weight distribution, fluctuations in magma pressure can trigger accelerated slip on the decollement. Yet this is only true of the south flank of Kīlauea. Though weight and magma distributions produce significant forces driving the west flank of Mauna Loa seaward, this flank is relatively stable. Stability over most of the last decade indicates a strong foundation beneath the west flank of Mauna Loa, perhaps as a result of past landslides that scraped clay-rich sediments from the decollement.

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Menéndez, Inmaculada, Marc Campeny, Luis Quevedo-González, José Mangas, Xavier Llovet, Esperança Tauler, Vidal Barrón, José Torrent et Jorge Méndez-Ramos. « Distribution of REE-bearing minerals in felsic magmatic rocks and paleosols from Gran Canaria, Spain : Intraplate oceanic islands as a new example of potential, non-conventional sources of rare-earth elements ». Journal of Geochemical Exploration 204 (septembre 2019) : 270–88. http://dx.doi.org/10.1016/j.gexplo.2019.06.007.

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Chiodini, Giovanni, Stefano Caliro, Giorgio Caramanna, Domenico Granieri, Carmine Minopoli, Roberto Moretti, Lavinia Perotta et Guido Ventura. « Geochemistry of the Submarine Gaseous Emissions of Panarea (Aeolian Islands, Southern Italy) : Magmatic vs. Hydrothermal Origin and Implications for Volcanic Surveillance ». Pure and Applied Geophysics, 28 mars 2006. http://dx.doi.org/10.1007/s0024-006-0037-y.

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Sotiriou, Paul, Karsten M. Haase, Kathrin P. Schneider, Anna Grosche, Kristina Noebel et Allan R. Chivas. « Growth of the upper crust in intra-oceanic island arcs by intrusion of basaltic magmas : the case of the Koloula Igneous Complex, Guadalcanal, Solomon Islands (SW Pacific) ». Contributions to Mineralogy and Petrology 177, n^o 11 (novembre 2022). http://dx.doi.org/10.1007/s00410-022-01972-z.

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AbstractThe Pleistocene (2.2–1.5 Ma) Koloula Igneous Complex (KIC) on Guadalcanal in the Solomon island arc consists of a low-K calc-alkaline sequence of ultramafic to felsic plutonic rocks. We present whole-rock major and trace element and Sr–Nd-Pb isotope data, as well as mineral compositions that record the magmatic evolution of the complex. The intrusive sequence is grouped into two cycles, Cycle 1 and 2, comprising gabbroic or dioritic to granodioritic rocks. The major and trace element data of each cycle forms a single calc-alkaline fractional crystallisation trend. The distinct radiogenic isotope and incompatible element compositions of the Cycle 1 and 2 intrusions imply slightly different mantle sources. The KIC formed by shallow (0.1 GPa) fractional crystallisation of mantle-derived Al-rich basaltic parental magmas (6–8 wt.% MgO) that were formed by deeper-level (0.7 GPa) fractionation of olivine and pyroxene from Mg-rich (~ 11 wt.% MgO) primary magmas in the Solomon intra-oceanic island arc. Olivine, clinopyroxene, plagioclase, amphibole, biotite, apatite, and Fe–Ti oxides fractionated from the KIC’s high-Al basaltic parental magmas to form calc-alkaline magmas. Liquid line of descent trends calculated using mass balance calculations closely match major element trends observed in the KIC data. The KIC crystallised at shallow, upper crustal depths of ~ 2.0–3.0 km in ~ 20 km-thick island arc crust. This complex is typical of other Cenozoic calc-alkaline ultramafic to felsic plutons in Pacific intra-oceanic island arcs in terms of field relationships, petrology, mineral chemistry and whole-rock geochemistry. Hornblende fractionation played a significant role in the formation of the calc-alkaline felsic plutonic rocks in these Cenozoic arc plutons, causing an enrichment of SiO2 and light rare earth elements. These plutons represent the fossil magma systems of arc volcanoes; thus, the upper arc crust is probably generated by migration of magmatic centres.

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Altunkaynak, Şafak, Ercan Aldanmaz et Daniel Nývlt. « Effects of mantle hybridization by interaction with slab derived melts in the genesis of alkaline lavas across the back-arc region of South Shetland subduction system ». Journal of Petrology, 19 octobre 2022. http://dx.doi.org/10.1093/petrology/egac111.

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Abstract Late Miocene to Late Pleistocene alkaline lavas in the northernmost part of the Antarctic Peninsula and its off-lying islands are the latest stage of magmatic activity that took place in response to lithospheric extension in the back-arc region of the South Shetland subduction system. The alkaline magmatism occurred much later than the main pulse of Cretaceous arc magmatism and generated basaltic extrusive rocks during several sub-aqueous/sub-glacial and sub-aerial eruption periods. The suite consists primarily of alkali olivine basalts with oceanic island basalt (OIB)-like trace element signatures, characterized by elevated highly to less incompatible element ratios compared to MORB. The samples have higher 87Sr/86Sr (0.70301–70365), and lower 143Nd/144Nd (0.51283–0.51294) and 176Hf/177Hf (0.28291–0.28298) than depleted MORB mantle. Their lead isotope ratios vary within a limited range with 206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb ratios of 18.797–18.953, 15.577–15.634, and 38.414–38.701, respectively. Sr, Nd, Hf and Pb isotope systematics suggest involvement of diverse source materials in the genesis of the alkaline magmas. Evaluation of radiogenic isotope and trace element data indicates that the source of the alkaline melts had a complex petrogenetic history, reflecting the effects of mantle hybridization along the slab mantle interface through interaction of mantle wedge peridotites with volatile-bearing, siliceous melts produced by melting of subducted sediments and basaltic oceanic crust. Hf-Nd isotope and trace element projections further demonstrate that the metasomatizing melt was likely generated by eclogite partial melting at sub-arc to post-arc depths, in equilibrium with a garnet-bearing residue and involved breakdown of high field strength elements (HFSE) retaining phases. Consumption of metasomatic amphibole during partial melting of hybridized peridotite at the wet solidus appears to have had a significant effect on the final melt compositions with high HFSE, Na and H2O contents.

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Follmann, Jörg, Froukje M. van der Zwan, Jonas Preine, Christian Hübscher, Romain Bousquet et Nico Augustin. « Gabbro Discovery in Discovery Deep : First Plutonic Rock Samples From the Red Sea Rift Axis ». Frontiers in Earth Science 9 (23 novembre 2021). http://dx.doi.org/10.3389/feart.2021.742815.

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Plutonic rocks such as gabbros provide information on magmatic and tectonic processes which occur beneath a mid-ocean rift axis as well as on the formation of the oceanic crust. Igneous rocks, reported from the Red Sea Rift valley, have been limited to extrusive basalts so far. The only deeper crustal rocks found in the Red Sea area are from the rift flanks and are interpreted as late-stage continental rift magmatism. Here, we present the geochemistry of the first recovered gabbro fragments from the axis of the Red Sea Rift, sampled from a crater structure within the brine-filled Discovery Deep at the axis of the Red Sea Rift. Petrology and geochemistry show characteristics of a typical mid-ocean ridge gabbro formed at shallow crystallization depth. Clinopyroxene core mineral data fall within two groups, thus pointing to a multiphased magmatic history, including different magma batches and a joint late-stage fractional crystallization. Geobarometry, based on clinopyroxene cores, suggests lower crystallization pressures than similar geobarometric data reported for gabbroic samples from Zabargad (8–9 kbar) and Brother’s Islands (2.5–3.5 kbar) at the rift flanks. However, based on the evolved whole rock composition, its multiphase history, the thickness of the crust, the current location of the samples, and the uncertainties in the barometer, geobarometric estimates for the samples are likely overestimated. Instead, we propose that these rock fragments originate from the upper part of a fully developed oceanic crust in the central Red Sea Rift. High-resolution bathymetry and sparker seismic data reveal that the Discovery Deep is characterized by a significant normal fault and a strong reflector near the rift axis, which we interpret as a potential sill intrusion in an approximate depth of 400 m. Based on the lack of progressive alteration and the sampling location within a sediment-free crater structure, we interpret that the emplacement of the gabbros has to be geologically recent. We interpret the gabbro either as a xenolith transported by the eruptive volcanism that formed the crater, potentially related to the sill intrusion visible at depth, or as intrusive gabbro, which was uplifted and deposited in a talus fan by the adjacent normal fault, exposed by the formation of the volcanic crater.

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Articles de revues sur le sujet « Magmatic rocks, Aeolian Islands, petrology, geochemistry »

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