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Titanium isotopes are a promising tracer for planetary differentiation processes. The application of this tracer is, however, currently hampered by the lack of a robust estimate for the chondritic reservoir. Here, we conducted an inter-comparison Ti isotope study of three laboratories with the aim of providing an accurate and precise estimate for the chondritic reservoir. While previous estimates may suffer from heterogeneities on the sampling scale, we chose ordinary chondrites to minimise uncertainties associated with the necessary corrections for nucleosynthetic isotope variations in chondrites, and to allow the analysis of sufficiently large sample sizes representative for bulk meteorites. Titanium isotope data reported by the different laboratories are in good agreement with each other. Ordinary chondrites of different subgroups (H, L, LL) and petrologic types (3–6) display identical Ti isotope compositions within uncertainties (average δ49Ti = +0.023 ± 0.009 ‰, 2SE, n = 20; permille deviation of 49Ti/47Ti from the OL-Ti standard). The average Ti isotope composition of ordinary chondrites is within 2SE identical to that of OIBs (+0.029 ± 0.005 ‰, 2SE, n = 52) and all pre 2.7 Ga mafic and komatiitic rocks (+0.019 ± 0.006 ‰, 2SE, n = 58), indicating that the δ49Ti values of the bulk silicate Earth and ordinary chondrites are indistinguishable. Furthermore, our average Ti isotope composition of ordinary chondrites overlaps with those of the Moon, Mars and Vesta, suggesting a homogeneous inner Solar System in terms of mass-dependent Ti isotopes. [ABSTRACT FROM AUTHOR]

• AOAs and CAIs formed from isotopically comparable materials. • AOAs and CAIs formed in a common region of the protoplanetary disk. • AOAs may be one of many chondrule precursor components. • The protoplanetary disk experienced a large-scale change in isotopic composition. Amoeboid olivine aggregates (AOAs) are the most abundant type of refractory inclusions found in most carbonaceous chondrite groups. AOAs are thought to be genetically related to calcium-aluminum-rich inclusions (CAIs) and potential chondrule precursor components, although the precise physical and temporal details of AOA formation and their relationship to other chondritic components remain unclear. In this study, we measured the chromium and titanium isotopic compositions of eight AOAs from four different CV chondrites with the goal of evaluating potential genetic links between AOAs, CAIs, and chondrules. These are the first Cr and Ti isotopic data reported beyond a single AOA previously measured for Cr and a different single AOA previously measured for Ti. The results presented here show that the ε54Cr and ε50Ti isotopic compositions of AOAs are indistinguishable from those of CAIs, suggesting that AOAs and CAIs formed from a common region of the disk. We also demonstrate, based on the comparison of the Cr and Ti isotopic composition of AOAs to previously measured chondrules, that mixing between AOAs and an NC compositional endmember alone cannot fully explain the range of measured chondrule compositions. Although AOAs may have been important chondrule precursor components along with AOA olivine, CAIs, fragments of earlier generation chondrules, and fine-grained matrix material, this observation requires another currently unknown component to be involved in chondrule formation. [ABSTRACT FROM AUTHOR]

Abstract Titanium and calcium are both refractory lithophile elements. Significant stable isotopic variations on Ti and Ca have been documented within calcium, aluminum-rich inclusions (CAIs) in carbonaceous chondrites. To trace the condensation history of Ti in the solar nebula, we conducted a high-precision double-spike Ti stable isotopic study on a large set of chondrites. The studied chondrites have a homogeneous bulk Ti stable isotopic composition (δ 49/47Ti IPGP-Ti = −0.069 ± 0.018‰, 2se, n = 22, i.e., the per mil deviation of the 49Ti/47Ti ratios relative to the IPGP-Ti reference material). The homogeneity across eleven chondrite groups implies that chondrites have acquired, through the condensation sequence at equilibrium, the average stable isotopic composition of Ti in the refractory solids that condensed early in the solar nebula. In contrast, the light Ca stable isotopic compositions of bulk chondrites can be attributed to either the presence of CAIs (CV-, CM- and CO-type) or parent-body aqueous alteration (CR- and CI-type). [ABSTRACT FROM AUTHOR]

Understanding the relationships between and among chondritic components of various chondrite groups is of prime importance for deciphering the dynamics of material transport and planetary accretion in the early Solar System. Here we obtain insights into these processes and the reservoirs present by investigating the nucleosynthetic Ti isotopic signatures of individual Ca,Al-rich inclusions (CAIs) and Na–Al-rich chondrules from ordinary and CO chondrites. This specific type of chondrule is of interest as it is thought to have incorporated refractory, CAI-like material as precursors. Our data show that CAIs from ordinary and CO chondrites exhibit 50 Ti excesses that are indistinguishable from CV CAIs, and thus indicate a common source reservoir for refractory inclusions in ordinary, CO, and CV chondrites. Na–Al-rich chondrules from CO chondrites also show 50 Ti excesses, indicating the presence of CAIs from this reservoir in the precursor materials of CO chondrules. In contrast, Na–Al-rich chondrules from ordinary chondrites show no 50 Ti excesses and are indistinguishable from the bulk values for ordinary chondrites. Thus, known CAIs cannot have been the refractory precursor of the Na–Al-rich chondrules in ordinary chondrites. Consequently, within the accretion region of the ordinary chondrites, two different types of refractory components must have existed: (1) a 50 Ti-enriched refractory component that is present as CAIs and either arrived at the accretion region of the ordinary chondrites after chondrule formation, or was only present in insignificant amounts, and (2) another type of refractory material without a 50 Ti excess, which was involved as precursor in the chondrule formation process. Our data thus imply that refractory components with condensation signatures must have formed in at least two isotopically distinct nebular regions. These may be related to non-carbonaceous and carbonaceous source regions, that is, the inner and outer Solar System, divided by the early formation of Jupiter. [ABSTRACT FROM AUTHOR]

Previous studies have shown that CV and CM chondrites incorporated Ca, Al-rich inclusions (CAIs) with different isotopic characteristics, which may represent different snapshots in the isotopic evolution of the early Solar System. To better understand how the isotopic characteristics of CAIs vary between different chondrite groups, we have studied calcium and titanium isotopes in CAIs from CM, CO, and CR chondrites. We show that all three chondrite groups contain CAIs with large anomalies in 48 Ca and/or 50 Ti (10s of ‰ or 100s of ε -units) as well as CAIs with no anomalies resolved beyond measurement uncertainties. Isotopically, the anomalous CO and CR chondrite CAIs resemble the platy hibonite crystals (PLACs) from CM chondrites, but they are more mineralogically complex. The new data are consistent with the well-established mutual exclusivity relationship between incorporation of 26 Al and the presence of large anomalies in 48 Ca and 50 Ti. The two highly anomalous CO chondrite CAIs have correlated anomalies in 46 Ti and 50 Ti, while most other highly anomalous CAIs do not. This result could indicate that the reservoir with coupled 46 Ti and 50 Ti that was sampled by bulk meteorites and CV chondrite CAIs already existed before arrival and/or homogeneous distribution of 26 Al in the protoplanetary disk. Among the studied CM chondrite CAIs are ten spinel-hibonite inclusions (SHIBs) with known oxygen isotopic compositions. Our results show that these objects sampled a reservoir that was well-mixed in oxygen, calcium, and titanium isotopes. We further show that SHIBs tend to be slightly enriched in the heavy calcium isotopes, suggesting that their formation history was different from CV chondrite CAIs. [ABSTRACT FROM AUTHOR]

Titanium isotopic compositions (mass-dependent fractionation and isotopic anomalies) were measured in 46 calcium-, aluminum-rich inclusions (CAIs) from the Allende CV chondrite. After internal normalization to 49 Ti/ 47 Ti, we found that ε 50 Ti values are somewhat variable among CAIs, and that ε 46 Ti is highly correlated with ε 50 Ti, with a best-fit slope of 0.162 ± 0.030 (95% confidence interval). The linear correlation between ε 46 Ti and ε 50 Ti extends the same correlation seen among bulk solar objects (slope 0.184 ± 0.007). This observation provides constraints on dynamic mixing of the solar disk and has implications for the nucleosynthetic origin of titanium isotopes, specifically on the possible contributions from various types of supernovae to the solar system. Titanium isotopic mass fractionation, expressed as δ′ 49 Ti, was measured by both sample-standard bracketing and double-spiking. Most CAIs are isotopically unfractionated, within a 95% confidence interval of normal, but a few are significantly fractionated and the range δ′ 49 Ti is from ∼−4 to ∼+4. Rare earth element patterns were measured in 37 of the CAIs. All CAIs with significant titanium mass fractionation effects have group II and related REE patterns, implying kinetically controlled volatility fractionation during the formation of these CAIs. [ABSTRACT FROM AUTHOR]

Titanium isotopes are potential tracers of processes of evaporation/condensation in the solar nebula and magmatic differentiation in planetary bodies. To gain new insights into the processes that control Ti isotopic variations in planetary materials, 25 komatiites, 15 chondrites, 11 HED-clan meteorites, 5 angrites, 6 aubrites, a martian shergottite, and a KREEP-rich impact melt breccia have been analyzed for their mass-dependent Ti isotopic compositions, presented using the δ 49 Ti notation (deviation in permil of the 49 Ti/ 47 Ti ratio relative to the OL-Ti standard). No significant variation in δ 49 Ti is found among ordinary, enstatite, and carbonaceous chondrites, and the average chondritic δ 49 Ti value of +0.004 ± 0.010‰ is in excellent agreement with the published estimate for the bulk silicate Earth, the Moon, Mars, and the HED and angrite parent-bodies. The average δ 49 Ti value of komatiites of −0.001 ± 0.019‰ is also identical to that of the bulk silicate Earth and chondrites. OL-Ti has a Ti isotopic composition that is indistinguishable from chondrites and is therefore a suitable material for reporting δ 49 Ti values. Previously published isotope data on another highly refractory element, Ca, show measurable variations among chondrites. The decoupling between Ca and Ti isotope systematics most likely occurred during condensation in the solar nebula. Aubrites exhibit significant variations in δ 49 Ti, from −0.07 to +0.24‰. This is likely due to the uniquely reducing conditions under which the aubrite parent-body differentiated, allowing chalcophile Ti 3+ and lithophile Ti 4+ to co-exist. Consequently, the observed negative correlation between δ 49 Ti values and MgO concentrations among aubrites is interpreted to be the result of isotope fractionation driven by the different oxidation states of Ti in this environment, such that isotopically heavy Ti 4+ was concentrated in the residual liquid during magmatic differentiation. Finally, KREEPy impact melt breccia SaU 169 exhibits a heavy δ 49 Ti value of +0.330 ± 0.034‰ which is interpreted to result from Ti isotopic fractionation during ilmenite precipitation in the late stages of lunar magma ocean crystallization. A Rayleigh distillation calculation predicts that a δ 49 Ti value of +0.330‰ is achieved after removal of 94% of Ti in ilmenite. [ABSTRACT FROM AUTHOR]