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

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

The composition of near-solidus partial melts of fertile peridotite at 1 and 1.5 GPa: implications for the petrogenesis of MORB

We have determined the near-solidus melt compositions for peridotite MM-3, a suitable composition for the production of mid-ocean ridge basalt (MORB) by decompression partial melting, at 1 and 1·5 GPa. At 1 GPa the MM-3 composition has a subsolidus plag

Peridotite melting at 1.0 and 1.5 GPa: and experimental evaluation of techniques using diamond aggregates and mineral mixes for determination of near-solidus melts

The experimental determination of liquid compositions in lherzolite as functions of pressure and temperature provides constraints on mantle dynamics and magma genesis. In this paper, we present a detailed evaluation of the use of natural mineral mixes a

Major element and primary sulfur concentrations in Apollo 12 mare basalts: The view from melt inclusions

Major element and sulfur concentrations have been determined in experimentally heated olivine-hosted melt inclusions from a suite of Apollo 12 picritic basalts (samples 12009, 12075, 12020, 12018, 12040, 12035). These lunar basalts are likely to be genetically related by olivine accumulation (Walker et al. 1976a, b). Our results show that major element compositions of melt inclusions from samples 12009, 12075, and 12020 follow model crystallization trends from a parental liquid similar in composition to whole rock sample 12009, thereby partially confirming the olivine accumulation hypothesis. In contrast, the compositions of melt inclusions from samples 12018, 12040, and 12035 fall away from model crystallization trends, suggesting that these samples crystallized from melts compositionally distinct from the 12009 parent liquid and therefore may not be strictly cogenetic with other members of the Apollo 12 picritic basalt suite. Sulfur concentrations in melt inclusions hosted in early crystallized olivine (Fo75) are consistent with a primary magmatic composition of 1050 ppm S, or about a factor of 2 greater than whole rock compositions with 400-600 ppm S. The Apollo 12 picritic basalt parental magma apparently experienced outgassing and loss of S during transport and eruption on the lunar surface. Even with the higher estimates of primary magmatic sulfur concentrations provided by the melt inclusions, the Apollo 12 picritic basalt magmas would have been undersaturated in sulfide in their mantle source regions and capable of transporting chalcophile elements from the lunar mantle to the surface. Therefore, the measured low concentration of chalcophile elements (e.g., Cu, An, PGEs) in these lavas must be a primary feature of the lunar mantle and is not related to residual sulfide remaining in the mantle during melting. We estimate the sulfur concentration of the Apollo 12 mare basalt source regions to be ∼75 ppm, which is significantly lower than that of the terrestrial mantle