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This study presents new secondary ion mass spectrometry (SIMS) reference materials (RMs) for measuring water contents in nominally anhydrous orthopyroxenes from upper mantle peridotites. The enstatitic reference orthopyroxenes from spinel peridotite xenoliths have Mg#s between 0.83 and 0.86, Al2O3 ranges between 4.02 and 5.56 wt%, and Cr2O3 ranges between 0.21 and 0.69 wt%. Based on Fourier-transform infrared spectroscopy (FTIR) characterizations, the water contents of the eleven reference orthopyroxenes vary from dry to 249 ± 6 µg/g H2O. Using these reference grains, a set of orthopyroxene samples obtained from variably altered abyssal spinel peridotites from the Atlantic and Arctic Ridges as well as from the Izu-Bonin-Mariana forearc region was analyzed by SIMS and FTIR regarding their incorporation of water. The major element composition of the sample orthopyroxenes is typical of spinel peridotites from the upper mantle, characterized by Mg#s between 0.90 and 0.92, Al2O3 between 1.66 and 5.34 wt%, and Cr2O3 between 0.62 and 0.96 wt%. Water contents as measured by SIMS range from 68 ± 7 to 261 ± 11 µg/g H2O and correlate well with Al2O3 contents (r = 0.80) and Cr#s (r. = -0.89). We also describe in detail an optimized strategy, employing both SIMS and FTIR, for quantifying structural water in highly altered samples such as abyssal peridotite. This approach first analyzes individual oriented grains by polarized FTIR, which provides an overview of alteration. Subsequently, the same grain along with others of the same sample is measured using SIMS, thereby gaining information about homogeneity at the hand sample scale, which is key for understanding the geological history of these rocks., Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659, Bavarian Equal Opportunities Sponsorship - Realization Equal Opportunities for Women in Research and Teaching, Friedrich-Alexander-Universität Erlangen-Nürnberg (1041)

Van Gölü’nün doğusundaki çarpışma ile ilişkili Otlakbaşı volkanizması farklı açılma çatlaklarından püskürerek meydana gelmiştir. Bu çalışmada, Otlakbaşı bazaltik volkanizmasının yeni yaş verisi ve ana oksit, iz ve nadir toprak element jeokimyasal karakteristikleri incelenmiştir. Ar-Ar yaş verisi bu bazaltik volkanizmanın bilinen Kuvaterner yaşının aksine Erken Pliyosende püskürdüğüne işaret eder. Volkanik ürünleri alkali-subalkali ayrım çizgisine yakın ve bazaltik bileşimdedirler. Fraksiyonel kristallenme ile birleşik kıtasal kirlenme (AFC) modellerinin sonuçları, magma odası evrim süreçlerinde fraksiyonel kristallenmenin kıtasal kirlenmeye göre ihmal edilebilir olduğuna ve kıtasal kirlenmenin fraksiyonel krsitallemeye oranının (r değeri) 0.1 ile 0.35 arasında değiştiğine işaret eder. Büyük iyon yarıçaplı litofil elementlerin ve (BİYL) hafif nadir toprak elementlerin (HNTE) yüksek alan şiddetli elementlere (YAŞE) göre zenginleşmesi ve hareketli iz elementlerin (Ba, Th) davranışı, Otlakbaşı bazaltik volkanizmasının manto kaynak bölgesinin dalmış sedimentlerden türeyen ergiyikler ile zenginleştiğini ortaya koymuştur. Fraksiyonlanma doğrulaması yapılan örneklerin Rb ve K elementlerindeki tüketilme, manto kaynak alanında flogopit ve/veya amfibolün var olabileceğine işaret eder. Kısmi ergime modelleme çalışmalarının sonuçları, bu bazaltik volkanizmanın baskın olarak spinel peridotit kaynağının ergimesi ile üretilebileceğini göstermiştir. Metasomatize olmuş spinelce zengin litosferik mantonun ergimesi, Otlakbaşı bazaltik volkanizmasının püskürmesinden sorumlu olabilir.

alkaline) since Jurassic times (Guiraud et al. 2005). Moreover, paleomagnetic data, suggest that the drifting of the African plate during the last 100 Ma has been very limited, thus allowing for the keeping the contact with the deeper mantle. Starting from these premises, the peridotite xenoliths, hosted in nephelinitic basalts from the Waw En-Namus volcano and investigated in comparison with those from Gharyan area (Beccaluva et al., 2007), could shed a light on the evolution of the Libyan sub-continental lithospheric mantle and on the geodynamic events that affected it over time. The mineral phases of such xenoliths, as well as few glassy veins, were studied in order to determine major and trace elements compositions. Three types of olivines, orthopyroxenes, clinopyroxenes, and spinels were recognized (magmatic, peridotitic and related to melt-peridotite reactions), as well as the presence of Na, K and ultra-potassic (UK) glasses. The investigated glasses, selected among those which apparently have been not (or scarcely) modified in their composition by peridotite-melt reactions, show higher La/Yb and Zr/Hf ratios with respect to Waw En-Namus lavas implying the involvements of slightly different mantle sources. Moreover, the presence of UK glasses (characterized by a strong Pb positive anomaly) suggest the involvement, as source, of a lithospheric or sub-lithospheric component. The mantle phases indicate a moment of basaltic extraction starting from a depleted (DMM-like) condition followed by a recent metasomatism. In the apparently not metasomatized ones, Th/Yb and Ta/Yb ratios suggest that ancient metasomatic events, which probably occurred during the Pan-African cycle, played a role in their history. In comparison, the metasomatized mineral phases, according with the recent geophysical data (Begg et al., 2009), mainly suggest relationships with the continuous asthenospheric upwelling. Beccaluva, L., Bianchini G., Ellam, R.M., Marzola, M., Oun, K.M., Siena, F., Stuart, F.M. (2008). 253– 277 in: Coltorti, M., & Grégoire, M., (eds.). Geol. Soc. Lond. Spec. Publ. 293. Begg, G.C., Griffin,W.L., Natapov, L.M., O’Reilly S.Y., Grand, S.P., Hronsky, J.M.A., Djomani, Y.P., Swain, C.J., Deen, T., Bowden, P. (2009). Geosphere, 5, 23-50. Guiraud, R., Bosworth, W., Thierry, J., Delplanque, A. (2005). Journal of African Earth Sciences, 43, 83-143

The Nemby mantle xenoliths are represented by spinel peridotites variably affected by “metasomatic processes” in Proterozoic times (1.2–0.5 Ga). Clinopyroxene compositional variations mainly reflect variably degrees of basalt extraction and mantle “metasomatic processes”. Clinopyroxene crystal chemistry allows to estimate the equilibration pressure by V(Cell) and V(M1) relationship. The investigated clinopyroxenes yielded a pressure range of 12–18 kb. Therefore, the Nemby xenoliths are representative of about 20 km thickness of subcontinental lithospheric mantle of the South America platform at Tertiary times (ca. 46 Ma).

X-ray crystal structure refinements and microprobe analyses of clinopyroxenes from two suites of spinel-peridotite nodules are compared for an understanding of the structural response to a decrease in Ca content. The kinking of the tetrahedral chain (O3-O3-O3 angle) of the C2/c structure associated with decreased Ca content shows behavior similar to that observed for the A-tetrahedral chain of the P21/c structure. Contemporaneously the occupancy of the M2′ split site increases. In addition, as a consequence of the low Ca content, the M2 polyhedron dominates the structural rearrangement of the clinopyroxenes considered here.