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.