Mass dependent isotope fractionation of stable isotopes between meteorites and planetary materials has been used to assess processes that occurred during formation of Earth and its core. However, thus far little is known about the mass dependent isotope fractionation of Mo in the solar system, and at high temperatures in the Earth, in particular during mantle processes. Molybdenum is a refractory and moderately siderophile element. The processes that might have fractionated Mo in the early solar system include condensation and evaporation of dust grains, metal-silicate segregation, core crystallization, silicate and sulphide melting and aqueous alteration. In order to investigate the processes fractionating Mo isotopes, it is first necessary to assess how much fractionation takes place during mantle melting, estimate the isotopic composition of the bulk silicate Earth, and then make comparisons with primitive and differentiated meteorites. I present double spike Mo isotope data for forty-two mafic and seven ultramafic samples from diverse locations, and nineteen extra-terrestrial samples. The delta^98/95Mo values of all the terrestrial samples (normalized to NIST SRM 3134) exhibit a significant range from +0.53±0.21 to -0.56±0.09‰. The compositions of mid-ocean ridge basalts (MORBs) (+0.03±0.07‰, 2s.d.) and ultramafic rocks (+0.38±0.15‰, 2 s.d.) are relatively uniform and well resolved, providing evidence of fractionation associated with partial melting. In contrast intraplate and ocean island basalts (OIBs) display significant variability within a single locality from MORB-like to strongly negative (-0.56‰). The most extreme values measured are for nephelinites from the Cameroon Line and Trinidade, which also have anomalously high Ce/Pb and low Mo/Ce relative to normal oceanic basalts. The observed relationships between delta^98/95Mo and Ce/Pb, U/Pb and Mo/Ce provide evidence that sulphide plays a critical role in retaining Mo in the mantle and fractionating its isotopic composition in basaltic magmas. If residual sulphides are responsible the Mo isotopic composition, Mo budget of the bulk silicate Earth will be misrepresented by values estimated from basalts. On this basis a revised best estimate of the Mo content in the bulk silicate Earth (BSE) ranging between 251 to 268 ppb is derived, approximately 6 times higher than previously assumed, and similar to the levels of depletion in refractory siderophile elements such as W, Ni and Co. This significantly ameliorates the argument for Mo removal via late stage sulphide extraction to the core. The Mo isotopic composition of the BSE (0.35‰) is distinct from the delta^98/95Mo values found in primitive and iron meteorites. Although Mo isotopic fractionation varies between different phases within a single iron meteorite, and occurs during fractional crystallization in asteroidal cores, most iron meteorites have ddelta^98/95MoSRM3134 (-0.14 to -0.06‰) that are similar to ordinary and CI carbonaceous chondrite (-0.12 to -0.09‰). This range of delta^98/95Moo is not only significantly lighter than the BSE, but also enstatite chondrites, which have delta^98/95Mo values of 0.04 to 0.13‰. Several possible explanations are proposed. (A) Core-mantle differentiation fractionates Mo isotopes. The recently proposed Mo effect of sulphide liquid removal is likely to be minor because this should have generated a light Mo isotope composition for the BSE. However, isotopic fractionation associated with metal-silicate partitioning may be responsible for the heavy Mo in the BSE. (B) A distinct isotopic composition for the late material that contributed Mo to the BSE. Enstatite chondrites (or other putative groups of chondrites with a heavy Mo isotope composition) and sulphur-rich components form the cores of impacting bodies are the most likely candidates that could deliver heavy Mo to Earth. (C) The Mo isotopic composition of the Solar System is heterogeneous in a mass dependent fashion such that heavier Mo isotopes are enriched in the section of the disk from which Earth accreted. There are some difficulties behind each of these models and further work is needed to determine which is correct.

A-type granites form in anorogenic settings and typically have high REE concentrations, K2O, Na2O, SiO2, FeOtotal, but low contents of Al2O3, MgO, CaO compared to other granite types. They have been divided in two groups according to their geochemical characteristics: differentiates of mantle-derived magmas (A1), and granites that are the result of melting depleted, lower crust (A2). The two largest A-type granites of the Mesozoic White Mountain Batholith of New Hampshire are the Mount Osceola and Conway granites. Electron microprobe analyses of biotite and amphibole in both granites are similar to those in other A-type granites: Fe-rich, but low MgO, and Al2O3. Whole-rock major and trace elements compositions of the Mount Osceola and the Conway granites are similar; both have high contents of REE, Zr, Nb, high Nb/Y ratios, and low CaO, Eu, and Sr and other compatible elements. Based on their high Nb/Y ratios, both granites are classified as mantle-derived magmas (A1). Microanalyses of ẟ18O and ƐHf of zircon show significant crustal contamination in both granites. The ẟ18O values for zircons from the Mount Osceola are between 7.4-8.9‰, and for the Conway Granite are 7.0-8.1‰. These values are distinct from mantle zircon (ẟ18O 5.3±0.3‰), which indicates large degrees of crustal contamination in both granites. Additionally, ƐHf (188Ma) for the Mount Osceola zircon ranges from -1.1 to +3.4, and those from the Conway Granite range from -2.1 to +4.6, indicating magma derivation in depleted mantle (ƐHf > 0) along with a crustal component. Although both granites have A1 compositions suggesting a mantle-derivation, this simple process is not recorded by the zircons. These zircons crystallized after considerable crustal contamination of mantle-derived A1 magmas and missed capturing the signature of that mantle component.

The Saglek-Hebron Gneiss Complex (SHC) is located in Northern Labrador within the Nain Province. It has recorded multiple magmatic events over more than 1 billion years, making it ideal to study the evolution of mantle-derived rocks through time. Here we present a 147Sm-143Nd isotopic study focussing on the different generations of mantle-derived rocks in the SHC. A total of 83 samples have been analysed, including: 1) mafic metavolcanic rocks; 2) ultramafic rocks divided into two distinct groups (a Fe-rich group enriched in incompatible elements and more depleted ultramafic rocks with lower Fe contents); 3) mafic metamorphosed dikes called the Saglek dikes; and 4) undeformed mafic dikes. Some samples exhibit evidence of post-magmatic geochemical and isotopic disturbance but only the least disturbed samples have been considered to constrain the timing of formation of the different lithologies and the isotopic composition of their mantle source. The mafic metavolcanic rocks combined with the co-genetic low-Fe ultramafic rocks yield an isochron age of 3819 ± 190 Ma (MSWD=34, n=25) with an initial εNd value of +2.3 ± 0.6. The high-Fe enriched ultramafic rocks yield a younger age of 3433 ± 220 Ma (MSWD=10.4, n=10) with an initial εNd= +1.8 ± 0.5. The two generations of mafic dikes appear to have been emplaced in the Mesoarchean and the Neoarchean. The Saglek dikes yield an isochron age of 3565 ±120 Ma (MSWD=1.17, n=10) with an initial εNd value of +1.7 ± 0.1, while the Sm-Nd isochron age for the undeformed mafic dikes is 2694 ±79 Ma (MSWD=3.2, n=21) with an initial εNd value of +1.7 ± 0.1. All generations of mantle-derived rocks yield positive initial εNd values, where only the Eoarchean rocks display an initial Nd isotopic composition similar to the depleted mantle. The Mesoarchean ultramafic rocks, Saglek dikes and Neoarchean mafic dikes display almost identical initial εNd values, despite an age difference of ~800 Ma. This could suggest the contribution of distinct mantle sources or, if all generations of mantle-derived rocks in the SHC were produced from the same mantle source, it implies that this source evolved with a nearly chondritic Sm/Nd ratio for almost the whole Archean Eon. The fact that the initial isotopic compositions of the mantle-derived rocks appear to deviate from the depleted mantle with time, could also suggest an increasing interaction with older evolved crust.