Petrology and Geochemistry

Garnet-(olivine) websterite xenoliths from the lithospheric mantle of the central and northeastern parts of the Siberian Craton contain exsolution microstructures after Si-and Ti-rich precursor garnets. We petrographically, geochemically, and thermobarometrically investigated 13 such xenoliths from the Mir, Obnazhennaya, and Udachnaya kimberlite pipes. All samples contain garnet grains with needle-to lamellae-shaped precipitates (up to 3.0 vol%), including Ti-oxide and/or pyroxene. Orthopyroxene and clinopyroxene grains host oriented lamellae of complementary Ca-rich and Ca-poor pyroxene, respectively, in addition to lamellae of garnet and Ti-and/or Cr-oxides. The common exsolution lamellae assemblages in garnet and pyroxene imply that exsolution occurred during cooling from high-temperature precursors. Exsolution is unlikely to have resulted from variations in pressure, given experimental and thermodynamic constraints. Host mineral partitioning of transition metal and lanthanide elements with different diffusivities record temperatures that range between those of local geotherms and a dry pyroxenite solidus. Inferred magmatic minimum temperatures of 1500-1700 °C satisfy the physical conditions predicted from experimental studies of the solubility of excess Si and Ti in garnet. Gran-ular inclusions of all major minerals within each other imply an overlapping crystallisation history. The reconstructed compositions of the websterite whole-rocks have high MgO contents (15.7-35.7 wt%). A plot of MgO/ SiO 2 versus SiO 2 forms an array, apart from the compositions of natural websterites that formed by interaction of peridotite with basaltic or siliceous melts. The array overlaps the compositional range of komatiite flows from Commondale and Barberton, South Africa, including spinifex, massive, and cumulate subtypes of komatiites. Other major and minor element abundances and ratios of the Siberian websterite suite resemble those of South African Al-enriched komatiites and are distinct from melt-rock reaction websterites. Therefore, the mineral mi-crostructures and geochemistry of the Siberian websterites are suggestive of the former presence of a thermal anomaly. We propose that mantle plume activity or a similar form of lower-mantle ascent played a major role in stabilising cratonic nuclei before amalgamation of the present-day Siberian Craton.

By applying the 40Ar/39Ardating method, age estimates for phlogopites of mantle xenoliths with different parageneses from the Udachnaya and Mir kimberlite pipes (Yakutia, Russia) were obtained. The oldest ages determined are 2.6–2.3 Ga, which far transcends the Paleozoic age of kimberlite entrainment. The phlogopite formation of these ages reflects ancient metasomatic events following rearrangement processes
in the mantle in the Archean–Early Proterozoic, particularly during and after accretion of the Pangea-0 supercontinent. A multistep age spectrum of UV162/09 was obtained from several generations of phlogopite and indicates a later multistage metasomatic process taking place in the mantle under Udachnaya pipe. Several stages of mantle  metasomatism of various ages and scales are detected within the Siberian platform.

Outcrops of the Late Ordovician glacio-marine deposits in Tauride Anatolide Platform contain rare rounded/subrounded glacially transported granitic pebbles. Recently determined crystallization ages of the granitic fragments by LA-ICP-MS U-Pb zircon dating fall in two groups, 575 to 600Ma and 700 to 965 Ma. Crystallization ages are in
the range of juvenile magmatic rocks in the Arabian Nubian Shield except one sample implying pre-0.87 Ga magmatic activity. All dated granitic pebbles geochemically show arc-related compositions and juvenile isotopic systematics (whole rock ƐNd(T), Pb-Pb and zircon ƐHf(T) isotopic data). Marginal arc type sources fit well with the
geochemical and isotopic data of the granitic pebbles of 700 and 800 Ma that have juvenile Hf-TDM and older Nd-TCR modal ages. However, A-type affinity of three samples, ranging from 575 to 600 Ma show that they might have been derived from mixing of juvenile mantle and older crustal sources having older Hf-TDM and Nd-TCR modal ages. A 965Ma granitic fragment has the oldest Hf-TDM andNd-TCRmodel age(s) implying involvement of pre-Neoproterozoic crustal source(s) in its genesis. These results collectively suggest that the glacio-marine successions in the Tauride Anatolide Platform were eroded from Neoproterozoic granitic/meta-granitic/meta-granodioritic rocks in the northern Nubian Shield (Egypt) and were then transported to the Tauride-Anatolide Platform by the glacial sheets during Late Ordovician time.

Lava flows erupted at Axial Seamount in 1998, 2011, and 2015 are chemically heterogeneous and display decreases in MgO content in their glass rinds with increasing distance from the summit. The trends are consistent with eruption temperature decreases down the rift zones of ~0.5 °C/km within 20 km of the caldera and ~0.9 °C/km at greater distance (only observed in the 2011 eruption). Cooling during magma transport in dikes is the likely cause of the temperature trends observed, related to the effects of cooler wall rocks in areas with less frequent dike intrusions. Flows also cooled as they advanced on the seafloor at rates 3-5 times greater than observed at Kilauea volcano in Hawaii for subaerial tube-fed pahoehoe flows. Lavas erupted in and near the caldera in 1998 and 2011 are slightly enriched transitional mid-ocean ridge basalt that are aphyric and have glass MgO content of 7.1-7.6 wt %. The 2015 lavas have similarly enriched incompatible element compositions typical of transitional mid-ocean ridge basalt, but those erupted inside and on the northeast rim of the caldera contain higher glass MgO of 7.8-8.3 wt % and more abundant plagioclase phenocrysts typical of the normal mid-ocean ridge basaltic lavas erupted between 1290 and 1370 CE. The brief recharge period between the 2011 and 2015 eruptions did not allow magma stored in the shallow reservoir to cool and degas as much as between prior eruptions since 1650 CE, suggesting that the most recent recharge period was shorter than the multicentennial average. Plain Language Summary Axial Seamount on the Juan de Fuca mid-ocean ridge erupted multiple lava flows of basaltic lava in 1998, 2011, and 2015. The composition of the flows was determined by analysis of 290 lava samples as well as a single sample of volcanic sand produced during mildly explosive eruptive activity in 2015. The lava flows are all hot spot influenced mid-ocean ridge basalt containing few crystals. Basalts cooled at rates of 0.5-1 °C/km and crystallized 15-20% crystals as they were transported away from the summit in dikes. They cooled at rates of ~3 °C/km as they flowed away from the eruptive fissures. Melt composition from the summit region varies in MgO content and temperature. The hottest lavas, at 1201 °C, were those erupted at the summit in 2015 after a 4-year repose period, whereas cooler basalts, at ~1186 °C, erupted at the summit in 2011 after a 13-year repose period. The 1998 lavas had a similar maximum MgO content and temperature to those erupted in 2011 and so may have had a similar repose period, consistent with the average repose period during the last 350 years of eruptive activity. The 2015 summit lavas were the hottest to erupt at Axial Seamount in the last 350 years.

ABSTRACT
Processes of sedimentation, between the Cenozoic Era, and the Miocene Epoch, have resulted in the Niger Delta; an overall regressive, 1,200 meters-thick, succession of sediments, composed of distinct siliciclastic units, which are major-ly three(3) in number; The Akata, Agbada, and Benin, Formations, through several transgressive and regressive cycles, dependent upon periods of eustatic sea level changes, occurring during their origination.
Formative processes also have resulted in structural features within the Niger Delta, which include the occurrence of growth-fault systems and roll-over anticlines,which serve as hydrocarbon-trapping mechanisms.

This paper re-assesses the tectono-thermal evolution of the frontal Infratatricum part of the Inner Western Carpathians orogen based on new geological-petrological and zircon fission track (ZFT) data and published 40Ar–39Ar and K–Ar data. The study area is in the Považský Inovec Mts. in Western Slovakia, where the Infratatric Inovec Nappe comprises a
micaschist-gneiss basement and Upper Carboniferous–Lower Cretaceous cover with the Jurassic–Lower Cretaceous Humienec Succession; this latter is reconstructed from olistoliths in the Horné Belice Succession Upper Cretaceous flysch. The Infratatric Inovec Nappe posterior part is thrust over its frontal Humienec tectonic Slice with infolded Upper Cretaceous sediments. This nappe exhibits very low-temperature tectono-thermal overprinting, and this is documented by electron probe microanalysis of metamorphic phases and P–T estimates. The late Early Cre ta ceous age of this D1 stage event at approximately 115–95 Ma is recorded by 114 ±2 and 106 ±4 Ma phengitic white mica 40Ar–39Ar ages from a Lower Cretaceous cherty slate, and by 101±3 Ma 40Ar–39Ar age and 102±4 Ma ZFT age from Permian meta-sandstone. The Inovec Nappe was thus derived from an Albian–Early Cenomanian accretionary wedge. The hemipelagic Upper Turonian to Lower Santonian red marls and upward syn-orogenic Upper Santonian to Maastrichtian flysch were deposited on the frontal attenuated part of the Inovec Nappe-type basement in the inferred Pieninic–Váhic (~South-Penninic) zone. This flysch contains olistolithic to clastogeneous metamorphosed material, including the Lower Cretaceous slates, supplied from the posterior part of the Inovec Nappe. The 40Ar–39Ar age of 86±2 Ma from this nappes’ Permian meta-sandstone is consistent with D2 thrusting at approximately 95–85 Ma and Horné Belice foreland flysch basin supply in the D3 stage at ~85–65 Ma. The Inovec Nappe frontal Humienec tectonic Slice with infolded Upper Cretaceous sediments suggests formation of a Paleocene–Eocene
accretionary wedge at approximately 65–40 Ma in the D4 stage. This event is con strained by 40Ar–39Ar age of 48 ±2 Ma from the Tatricum hanging wall blastomylonites and whole-rock K–Ar age of 46 ±3 Ma from a Permian basalt olistolith in the footwall Infratatricum Horné Belice flysch. The Infratatricum finally became part of an Eocene accretionary wedge north of
the Hrádok–Zlatníky thrust-fault, and reheating and exhumation cooling is documented by 57–37 Ma ZFT ages. Although the Infratatricum exhibits Late Cretaceous and Eocene tectono-thermal imprints, it is a remnant of the Early Cretaceous structure at the In ner West ern Carpathian front. This imposes the Infratatricum as a dis tal continental margin of the Penninicum.

The Southeast Anatolian ophiolites outcropping in the Southeast Anatolian Orogenic Belt (Southeast of Turkey) mark the closure of the southern branch of the Neotethys Ocean associated with the collision between the Arabian Plate and Anatolian microplate. We present new geochemical, zircon U-Pb age, zircon Lu-Hf, and Sr-Nd isotopic data on the Southeast Anatolian Ophiolites to understand their formation ages, magma genesis, and geotectonic implications. The ophiolites, which are related to island arc igneous rocks, consist of mantle peridotites and crustal rocks (less dunite, gabbros, sheeted dykes, massive, and pillow basalts). The flat rare-earth element (REE) patterns, depletion in Nb and Ta, and enrichment in LILEs (Ba, Rb, Th, Sr, Pb) of gabbros suggest close similarities with very low Ti (boninitic) lavas found in the forearc regions. Using laser ablation inductively coupled plasma-mass spectrometry, zircon separated from leucogabbros, diabase dykes, and plagiogranites yield U-Pb ages of 92 and 83 Ma, which are interpreted to represent the formation ages of the ophiolites. The zircons in the gabbros and plagiogranites are dominated by positive εHf(t) values (between +3.1 and + 17.45) with a few negative εHf(t) values. High εHf(t) features are consistent with derivation from Mid-oceanic Ridge Basalt (MORB)-source mantle. The negative εHf(t) values of the zircons suggest the involvement of subducted sedimentary rocks. The southeast Anatolian ophiolites represent an SSZ-type ophiolite and are part of the Late Cretaceous oceanic lithosphere of the southern branch of the Neotethys Ocean that opened during the Late Triassic and closed during the Late Cretaceous.

The tectonic complexity in the Maluku region is caused by the interaction of the three main plates in this area, namely: the Philippine, the Australian, and the Eurasian. The origin of volcanic rock-forming material from Jailolo Mount., Sahu Mount., Gamkonora Mount., and Ibu Mount. in West Halmahera Regency is the aim of this study. Petrographic, trace elements, rare earth elements analysis are also used to study rock formation processes and correlations between sample groups. Bipolar microscope was used for petrographic interpretation whereas ICP-MS was applied to measure the trace and rare earth elements content. Almost all samples are classified as andesite based on the comparison of the quartz, K-feldspar, and plagioclase compositions. There is a possibility of mixing between oceanic crust and continental crust of the studied Holocene volcanic which is indicated by La/Yb versus Nb/La diagrams. Fractional crystallization is considered more influential in rock formation compared to partial melting. The effect of plagioclase fractionation on the four volcanic rock groups are shown by the Y versus Sr/Y diagram and rare earth spider diagram patterns. Increased levels of rare earths in samples from Gamkonora Mount.and Sahu Mount. are strongly influenced by crystallization of plagioclase during rock formation.

Thallium (Tl) isotope compositions of ocean island basalts (OIBs) have been proposed as a novel tracer of subducted ocea-nic crust and sediments in ocean island basalt sources, which could act as direct confirmation that deep mantle recycling eventually resurfaces through mantle upwelling to form ocean island basalt magmatism. However, it is unknown if oceanic crust that went through an active subduction zone would retain the Tl isotope compositions recorded in hydrothermally altered oceanic crust and authigenic marine sediments. In this study we present Tl isotope and concentration data for samples of sub-ducted oceanic crust from five different locations: Zambezi Belt, Zambia; Cabo Ortegal complex, Iberian Massif, Spain; Ras-pas Complex, southwest Ecuador; Syros island, Cyclades, Greece; Tian Shan, northwest China. Thallium concentrations in most samples follow strong linear relationships with K, Rb, Cs and Ba, which strongly suggest that the mineral phengite is the primary control of Tl abundances in subducted oceanic crust. This conclusion is consistent with recent Tl data sets for arc lavas that imply residual phengite in the arc lava source regions as a strong control of Tl recycling. We find that Tl isotope compositions vary widely and systematically in each location depending on the protolith, metamorphic and metasomatic history of the samples. Samples from Cabo Ortegal and Raspas Complex reveal Tl isotope compositions similar to their pro-toliths, which were comprised of low-temperature altered oceanic crust. Tian Shan metamorphic rocks and Zambian eclogites reveal invariant Tl isotope values indistinguishable from average mantle, which is best explained by overprinting by metamorphic fluids that contained high concentrations of Tl and other alkali metals. Samples from Syros reveal a range of Tl isotope compositions from normal mantle towards values for pelagic clay sediments. The sediment-like values in Syros likely arose from fluids released from the surrounding mélange matrix that consists of serpentinite, metagabbros and metased-iments. Each of the three Tl isotope ranges observed for subducted oceanic crust samples here are mirrored by individual OIB locations. Cabo Ortegal and Raspas Complex display Tl isotope compositions identical to St. Helena, suggesting that the HIMU component likely comprises subduction modified low-temperature altered oceanic crust. Thallium isotope ratios in Zambia and Tian Shan eclogites and blueschists are identical to lavas from Iceland, whereas Syros metamorphic rocks overlap almost exactly with lavas from Hawaii. Our data, therefore, show that Tl isotope compositions of oceanic crust and sediments can be traced through the subduction process and eventually is expressed largely unmodified in ocean island basalts.

Traverses across amphibole-chlorite schist metamorphic reaction zones at contacts between meta-igneous and ultramafic rocks in high-pressure mélange zones were analyzed for highly siderophile element (HSE) concentrations and 187 Os/ 188 Os in two mélange zones (Catalina Schist, Santa Catalina Island, CA, and Attic-Cycladic Complex, Syros, Greece) in order to investigate the relative effects of mechanical mixing and diffusive and advective transport by fluids in subduction-related reaction zones. Results from Catalina Schist traverses show co-varying elevated concentrations of Os, Ir, Ru, Cr, and MgO and inversely correlated initial 187 Os/ 188 Os that display irregular patterns across the chlorite-actinolite schist reaction zones. These elements are strongly enriched in peridotite relative to mafic crust, and are relatively fluid immobile. The observations suggest that these components were added via mechanical mixing of mantle peridotitic material with material derived from mafic blocks. In a traverse across a Syros mafic eclogite block with a narrow chlorite schist reaction zone and broader glaucophane-rich reaction zone, the Os, Ir, Ru, and Cr concentrations in the chlorite schist are just barely higher than those in the eclogite block, while the initial 187 Os/ 188 Os ratio falls between the eclogite core and adjacent serpentinite. These compositions show a relatively minor metasomatic exchange between eclogite block and serpentinite. A second sample set from Syros was chosen across a contact zone between a meta-tuffite and a serpentinite because previous studies suggest it was not affected by mechanical mixing. This traverse contains a ~1 m wide complex metasomatic reaction zone that is used to study the relative contributions of diffusive and advective transport. The traverse reveals strong mobilization of Os, Ir, Ru and Pt beyond the scale of the outcrop, and minor advective enrichment of Re and Pd. This indicates that all HSE may be mobilized by fluid advection beyond the local scale in some subduction zone mélange zones.

Websterite and garnet orthopyroxenite and clinopyroxenite dykes crosscutting harzburgite occur in the hanging wall of a Cretaceous eclogitized continental fragment of the Upper Austroalpine Unit in the Eastern Alps. The dyke textures reflect pressure-temperature changes from the mantle, subduction channel and an accretionary wedge. A clinopyroxenite dyke, dated at 252 ± 2 Ma on zircon by U\ \Pb SIMS, provided ε Hf (t) zircon values of 16-8 (av. 11 from 18 spots) suggesting a depleted mantle source. The rock modal mineral composition and the mineral and whole-rock chemistry revealed that the pyroxenite dykes' petrogenesis is most likely related to sub-crustal cumulate-type melt derivates, less evolved for websterites and highly evolved for clino-and orthopyroxenites. The porphyroclastic clinopyroxene1 (10-13 mol% CaTs), orthopyroxene1, spinel1 and amphibole1 are inferred remnants after magmatic phases. They contain Ti-spinel and ilmenite exsolutions which indicate cooling of the dykes in harzburgite in a Spl stability field (D0-1 stage). Garnet exsolutions in Cpx1, Opx1 and Amp1, and Cpx exsolutions in Amp1 document continuous cooling and/or pressure increase (D0-2 stage). The Grt coronas around Spl1, Opx1, Cpx1 and Amp1, and the granoblastic matrix of Prp-Grs-rich Grt (or Cr-Spl in websterites), low-Al Cpx, low-Al Opx, Fe-enriched olivine, zoisite, kyanite, rutile and pargasite record a subduction channel compression (D1 stage). While the formation of Cpx-Grt or Amp-Grt symplectites replacing the Cpx1 and Amp1 rims suggests the HP-HT decompression (D2-1 exhumation stage). The Grt (or Cr-Spl) replacement by Spl, and Opx1, Cpx1 and Prg replacement by Ol-Spl, Opx-Spl or Prg-Spl symplectites document continuous HT decompression (D2-2 exhumation stage). The MP/MT-LT conditions were estimated from tremolite, Grs-rich Grt, Sr-epidote, clinozoisite, Cl-apatite, titanite, Ce-allanite, chlorite, serpentine and talc assemblage (D3 stage). Anticlockwise P-T path was reconstructed for the D0 to D1 stages followed by almost isothermal exhumation (D2) and emplacement in the Cretaceous accretionary wedge (D3). The pseudosection P-T calculation from a clinopyroxenite dyke yielded 850-825 °C and 25-28 kbar (D1). The whole-rock and mineral trace element data of relic Cpx1 and Amp1, Grt(1-3), Ep-Zo, and younger zircon ages due to Pb-loss, reflect the impact of metamorphic fluids during the D1 to D3 evolutionary stages.

Ces études servent de simulation des caractéristiques du terrain dans le sens où la
confirmation et l’amélioration des résultats seront faites en passant par d’autres études
approfondies notamment par investigation mécanique in situ pour connaitre avec exactitude
l’épaisseur et la qualité du sol de recouvrement et leurs conditions locales avant l’implantation
d’un ouvrage de génie-civil.
Cependant une manipulation rigoureuse de ces résultats permettra d’avoir des bons
rendements dans l’application aux travaux publics et de génie-civil. Notons que l’entité
administrative Quartier Luano n’a été couverte que sur environ 2km2 pour un périmètre dont la
forme rapprochée est un triangle équilatéral.
En effet plus de 50% de la surface du secteur est couvert de sols limoneux moyennement
plastique et pouvant absorber au moins 40% d’eau sans se comporter comme un liquide et les sols
A6 et A7-5 sont représentés systématiquement le long de la rivière Luano étant plus plastiques.
Les sols limoneux A4 peuvent contenir au plus 40% d’eau sans avoir un comportement liquide
pour une plasticité similaire à celle de sols A5.Les sols A2-4 et A3 sont faiblement représentés ici
et sont peu plastiques et se comportent comme liquide pour des teneurs faibles. Notons cependant
que le comportement général du secteur peut être dit moyen à faible du faite de la surface couverte
par les sols de types A4, A5 et A6.
Dans tous les cas et pour toutes les méthodes, une semelle filante présente une portance
faible et sa contrainte admissible correspondante. En guise de travailler en sécurité, les plus faibles
valeurs sont considérés.
 Le sol A2-4 à une portance la plus faible de 422,4419 kPa et dont la contrainte admissible
plus faible est 140,814;
 Le sol A4 est caractérisé par une capacité portante de 201.57592 kPa et une contrainte
admissible de 67.19198 kPa;
 Le sol A5 est caractérisé par une capacité portante de 221.5722 kPa et une contrainte
admissible de 73.8574 kPa;
 Le sol A6 est caractérisé par une capacité portante de 224.2126 kPa et une contrainte
admissible de 74.73754 kPa.
Le sol A2-4 présente donc une bonne portance comparativement à celles de trois autres qui sont
presque voisines mais pour tous les types de sols, le désordre dû à une faible capacité portante peut
être évité en augmentant la surface de contact fondation-charge.
Les résultats d’estimation du tassement à l’aide du logiciel SETTLE 3D 2.0 et leur
comparaison avec la portance et la contrainte admissible, en prenant les valeurs les plus faibles,
montrent que:
 Le tassement admissible pour le sol A2-4 est inférieur à 1,2m et à craindre 2,15m afin de
ne pas arriver à la rupture du sol. Ce sol se caractérise comme dit haut par un comportement
généralement lié à sa constitution ;
 Pour le sol A4, on peut admettre un tassement de 0,7m et à ne pas dépasser 1,1m ;
 Le sol A5 peut supporter jusqu’à un tassement de 0,27 m sans dommage aux ouvrages mais
pour un tassement de 0,8m, le sol va se rompre ;
 Le sol A6 a un tassement admissible de 0,3m tandis qu’il est à craindre de dépasser 0,83m.
Nous constatons ainsi que le sol peut sensiblement se tasser sans induire un désordre sur la
suprastructure tandis que les autres types sont susceptibles d’atteindre la rupture à partir d’un
tassement de 30cm.
Notons aussi que les sols A7 et A6 de ce terrain sont susceptibles de subir la thixotropie du fait
de leur nature et leur relation avec la rivière Luano.
En général, nous dirons que les sols identifiés au Quartier Luano, ont de comportements
différents face à la contrainte pouvant leur être appliquée mais le tassement peut être réduit en
élargissant la surface de contact ouvrage-sol.
Les comportements mécaniques de ces sols peuvent être améliorés en augmentant la portance par
compactage ou préchargement du terrain surtout pour les sols A5et A6 ou en procédant par le
drainage lorsqu’il s’agit du sol A6.