Sulfide breccias from the Semenov-3 hydrothermal field, Mid-Atlantic Ridge: authigenic mineral formation and trace element pattern

The aim of this paper is the investigation of the role of diagenesis in the transformation of clastic sulfide sediments such as sulfide breccias from the Semenov-3 hydrothermal field (Mid-Atlantic Ridge). The breccias are composed of marcasite\u2013pyrite clasts enclosed in a barite\u2013sulfide\u2013quartz matrix. Primary hydrothermal sulfides occur as colloform, fine-crystalline, porous and radial marcasite\u2013pyrite clasts with inclusions or individual clasts of chalcopyrite, sphalerite, pyrrhotite, bornite, barite and rock-forming minerals. Diagenetic processes are responsible for the formation of more diverse authigenic mineralization including framboidal, ovoidal and nodular pyrite, coarse-crystalline pyrite and marcasite, anhedral and reniform chalcopyrite, inclusions of HgS phase and pyrrhotite\u2013sphalerite\u2013chalcopyrite aggregates in coarse-crystalline pyrite, zoned bornite\u2013chalcopyrite grains, specular and globular hematite, tabular barite and quartz. The early diagenetic ovoid pyrite is enriched in most trace elements in contrast to late diagenetic varieties. Authigenic lower-temperature chalcopyrite is depleted in trace elements relative to high-temperature hydrothermal ones. Trace elements have different modes of occurrence: Se is hosted in pyrite and chalcopyrite; Tl is related to sphalerite and galena nanoinclusions; Au is associated with galena; As in pyrite is lattice-bound, whereas in chalcopyrite it is related to tetrahedrite\u2013tennantite nanoinclusions; Cd in pyrite is hosted in sphalerite inclusions; Cd in chalcopyrite forms its own mineral; Co and Ni are hosted in chalcopyrite

New Olivine Reference Material for In Situ Microanalysis

A new olivine reference material – MongOL Sh11‐2 – for in situ analysis has been prepared from a central portion of a large (20 cm × 20 cm × 10 cm) mantle peridotite xenolith from a ~ 0.5 Ma old basaltic breccia at Shavaryn‐Tsaram, Tariat region, central Mongolia. The xenolith is a fertile mantle lherzolite with minimal signs of alteration. Approximately 10 g of 0.5 to 2 mm gem quality olivine fragments were separated under binocular microscope and analysed by EPMA, LA‐ICP‐MS, SIMS and bulk analytical methods (ID ICP‐MS for Mg and Fe, XRF, ICP‐MS) for major, minor and trace elements at six institutions worldwide. The results show that the olivine fragments are sufficiently homogeneous with respect to major (Mg, Fe, Si) and minor and trace elements. Significant inhomogeneity was revealed only for phosphorus (homogeneity index of 12.4), whereas Li, Na, Al, Sc, Ti and Cr show minor inhomogeneity (homogeneity index of 1–2). The presence of some mineral and fluid‐melt micro‐inclusions may be responsible for the inconsistency in mass fractions obtained by in situ and bulk analytical methods for Al, Cu, Sr, Zr, Ga, Dy and Ho. Here we report reference and information values for twenty‐seven major, minor and trace elements

MPI-Ding reference glasses for in situ microanalysis: New reference values for element concentrations and isotope ratios

We present new analytical data of major and trace elements for the geological MPI-DING glasses KL2-G, ML3B-G, StHs6/80-G, GOR128-G, GOR132-G, BM90/21-G, T1-G, and ATHO-G. Different analytical methods were used to obtain a large spectrum of major and trace element data, in particular, EPMA, SIMS, LA-ICPMS, and isotope dilution by TIMS and ICPMS. Altogether, more than 60 qualified geochemical laboratories worldwide contributed to the analyses, allowing us to present new reference and information values and their uncertainties (at 95% confidence level) for up to 74 elements. We complied with the recommendations for the certification of geological reference materials by the International Association of Geoanalysts (IAG). The reference values were derived from the results of 16 independent techniques, including definitive (isotope dilution) and comparative bulk (e.g., INAA, ICPMS, SSMS) and microanalytical (e.g., LA-ICPMS, SIMS, EPMA) methods. Agreement between two or more independent methods and the use of definitive methods provided traceability to the fullest extent possible. We also present new and recently published data for the isotopic compositions of H, B, Li, O, Ca, Sr, Nd, Hf, and Pb. The results were mainly obtained by high-precision bulk techniques, such as TIMS and MC-ICPMS. In addition, LA-ICPMS and SIMS isotope data of B, Li, and Pb are presented

Peridotite Melting at 1 GPa: Reversal Experiments on Partial Melt Compositions Produced by Peridotite-Basalt Sandwich Experiments

One of the goals of igneous petrology is to use the subtle and more obvious differences in the geochemistry of primitive basalts to place constraints on mantle composition, melting conditions and dynamics of mantle upwelling and melt extraction. For thi

Crystallization temperatures of tholeiite parental liquids: Implications for the existence of thermally driven mantle plumes

To compare magmatic crystallization temperatures between ocean island basalt (OIB) proposed to be plume-related and normal mid-ocean ridge basalt (MORB) parental liquids, we have examined and compared in detail three representative magmatic suites from both ocean island (Hawaii, Iceland, and Réunion) and mid-ocean ridge settings (Cocos-Nazca, East Pacific Rise, and Mid-Atlantic Ridge). For each suite we have good data on both glass and olivine phenocryst compositions, including volatile (H2O) contents. For each suite we have calculated parental liquid compositions at 0.2 GPa by incrementally adding olivine back into the glass compositions until a liquid in equilibrium with the most-magnesian olivine phenocryst composition is obtained. The results of these calculations demonstrate that there is very little difference (a maximum of ∼20 °C) between the crystallization temperatures of the parental liquids (MORB 1243-1351 °C versus OIB 1286-1372 °C) when volatile contents are taken into account. To constrain the depths of origin in the mantle for the parental liquid compositions, we have performed experimental peridotite-reaction experiments at 1.8 and 2.0 GPa, using the most magnesian of the calculated parental MORB liquids (Cocos-Nazca), and compared the others with relevant experimental data utilizing projections within the normative basalt tetrahedron. The mantle depths of origin determined for both the MORB and OIB suites are similar (MORB 1-2 GPa; OIB 1-2.5 GPa) using this approach. Calculations of mantle potential temperatures (TP) are sensitive to assumed source compositions and the consequent degree of partial melting. For fertile lherzolite sources, TP for MORB sources ranges from 1318 to 1488 °C, whereas TP for ocean island tholeiite sources (Hawaii, Iceland, and Réunion) ranges from 1502 °C (Réunion) to 1565 °C (Hawaii). The differences in TP values between the hottest MORB and ocean island tholeiite sources are ∼80 °C, significantly less than predicted by the thermally driven mantle plume hypothesis. These differences disappear if the hotspot magmas are derived by smaller degrees of partial melting of a refertilized refractory source. Consequently the results of this study do not support the existence of thermally driven mantle plumes originating from the core-mantle boundary as the cause of ocean island magmatism

Crustal origin for coupled ultra-depleted and plagioclase signatures in MORB olivine-josted melt inclusions: evidence from the Siqueiros Transform Fault, East Pacific Rise

Geochemical data from melt inclusions in olivine phenocrysts in a picritic basalt from the Siqueiros Transform Fault on the northern East Pacific Rise provide insights into the petrogenesis of mid-ocean ridge basalts (MORB). The fresh lava contains ∼ 1