Titanium offers a burgeoning isotope system that has shown significant promise as a tracer of magmatic processes. Recent studies have shown that Ti displays significant massdependent variations linked to the crystallisation of Fe-Ti oxides during magma differentiation.We present a comprehensive set of Ti isotope data for a range of differentiation suites from alkaline (Ascension Island, Afar and Heard Island), calc-alkaline (Santorini) and tholeiitic (Monowai seamount and Alarcon Rise) magma series to further explore the mechanics of Ti isotope fractionation in magmas. Whilst all suites display an increase in 49/47 Ti (deviation in 49 Ti/ 47 Ti of a sample relative to the OL-Ti reference material) during magma differentiation relative to indices such as increasing SiO 2 and decreasing Mg#, our data reveal that each of the three magma series have contrasting 49/47 Ti fractionation patterns over comparable ranges of SiO 2 and Mg#. Alkaline differentiation suites from intraplate settings display the most substantial range of variation ( 49/47 Ti = +0.01 to +2.32 ), followed by tholeiites (-0.01 to +1.06 ) and calc-alkaline magmas (+0.06 to +0.64 ). Alkaline magmas possess high initial melt TiO 2 contents which enables early saturation of ilmenite + titanomagnetite and a substantial degree of oxide crystallisation, whereas tholeiitic and calc-alkaline suites crystallise less oxide and have titanomagnetite as the dominant oxide phase. Positive slopes of FeO*/TiO 2 vs. SiO 2 during magma differentiation are related to high degrees of crystallisation of Ti-rich oxides (i.e. ilmenite). Bulk solid-melt Ti isotope fractionation factors co-vary with the magnitude of the slope of FeO*/TiO 2 vs. SiO 2 during magma differentiation, this indicates that the modal abundance and composition of the Fe-Ti oxide phase assemblage, itself is controlled by melt composition, governs Ti isotope fractionation during magma evolution. In addition to this overall control, hydrous, oxidised calc-alkaline suites display a resolvable increase in 49/47 Ti at higher Mg# relative to drier and more reduced tholeiitic arc suites. These subparallel Ti isotope fractionation patterns are best explained by the earlier onset of oxide segregation in arc magmas with a higher oxidation state and H 2 O content. This indicates the potential of Ti isotopes to be utilised as proxies for geodynamic settings of magma generation.

We report novel techniques allowing the measurement of Nd-isotope ratios with unprecedented accuracy and precision by multi-collector inductively coupled plasma mass spectrometry. Using the new protocol, we have measured the Nd-isotopic composition of rock and synthetic Nd standards as well as that of the Allende carbonaceous chondrite.

Tracking the secular evolution of 142 Nd/ 144 Nd anomalies is important towards understanding the crust-mantle dynamics in the early Earth. Excessive scatter in the published data, however, precludes identifying the fine structure of 142 Nd/ 144 Nd evolution as the expected variability is on the order of few parts per million. We report ultra-high precision 142 Nd/ 144 Nd data for Eoarchean and Palaeoarchean rocks from the Isua Supracrustal Belt (SW Greenland) that show a well-resolved 142 Nd/ 144 Nd temporal variability suggesting progressive convective homogenisation of the Hadean Isua depleted mantle. This temporally decreasing 142 Nd/ 144 Nd signal provides a direct measure of early mantle dynamics, defining a stirring timescale of <250 Myr consistent with vigorous convective stirring in the early mantle. The 142 Nd/ 144 Nd evolution suggests protracted crustal residence times of ~1000-2000 Myr, inconsistent with modern-style plate tectonics in the Archean. In contrast, a stagnant-lid regime punctuated by episodes of mantle overturns accounts for the long life-time estimated here for the Hadean proto-crust.

No abstract

The terrestrial planets endured a phase of bombardment following their accretion, but the nature of this late accreted material is debated, preventing a full understanding of the origin of inner solar system volatiles. We report the discovery of nucleosynthetic chromium isotope variability (μ 54 Cr) in Martian meteorites that represent mantle-derived magmas intruded in the Martian crust. The μ 54 Cr variability, ranging from −33.1 ± 5.4 to +6.8 ± 1.5 parts per million, correlates with magma chemistry such that samples having assimilated crustal material define a positive μ 54 Cr endmember. This compositional endmember represents the primordial crust modified by impacting outer solar system bodies of carbonaceous composition. Late delivery of this volatile-rich material to Mars provided an exotic water inventory corresponding to a global water layer >300 meters deep, in addition to the primordial water reservoir from mantle outgassing. This carbonaceous material may also have delivered a source of biologically relevant molecules to early Mars.

No abstract

No abstract

We use high-precision neodymium isotope data for sequentially acid-leached components of the primitive carbonaceous chondrite Tagish Lake to identify a non-classical 150Nd-rich presolar carrier phase that has not been identified as of yet in meteorites. The distinct isotopic signature of this carrier can be attributed to the intermediate neutron capture process (i-process) occurring in asymptotic giant branch (AGB), super-AGB, or post-AGB stars or, alternatively, the slow capture process (s-process) occurring in rotating massive stars. The 150Nd-rich carrier appears to be heterogeneously distributed in the solar protoplanetary disk resulting in systematic isotope variations between carbonaceous and non-carbonaceous solar system materials. Carbonaceous chondrites that accreted in the outer disk are depleted in this carrier relative to non-carbonaceous materials that accreted in the terrestrial planet-forming region. Calcium-aluminum-rich inclusions that represent the earliest formed disk solids record the largest depletion of this carrier. This distribution pattern is contrary to that seen for the carriers of other neutron-rich isotope anomalies (48Ca, 54Cr, 95,97Mo, etc.) that have defined carbonaceous/non-carbonaceous isotope dichotomy so far. Irrespective of the exact astrophysical origin of these carriers, divergent distribution of presolar dust as a function of physicochemical processing in the solar protoplanetary disk best explains the solar system isotope dichotomy as opposed to changes in the composition of the infall.