Titanium Isotopic Research Articles

Titanium isotopic fractionation during magmatic differentiation

To better investigate the behavior of titanium (Ti) isotopes during magmatic processes, we report high-precision Ti isotope compositions for 60 terrestrial igneous rocks from different geological settings worldwide. Based on their major element compositions and petrographic descriptions, these samples can be subdivided into two groups: Fe-Ti oxide unsaturated and Fe-Ti oxide saturated. The Fe-Ti oxide unsaturated group samples show a narrow δ49/47Ti (δ49/47Ti = [(49Ti/47Ti)sample/(49Ti/47Ti)OL-Ti] × 1000) range (− 0.036 ± 0.043‰ to 0.082 ± 0.021 ‰), and no correlation between δ49/47Ti and the degree of differentiation is observed. By contrast, Fe-Ti oxide saturated group samples show a remarkable δ49/47Ti variation, ranging from 0.005 ± 0.018‰ to 1.914 ± 0.006 ‰, which are positively correlated with SiO2 contents, and negatively correlated with MgO contents. In particular, multiple SiO2 vs. δ49/47Ti trends are observed in Fe-Ti oxide saturated group, which are controlled by crystal fractionation degrees, magma SiO2 compositions, and Fe-Ti oxide compositions during magma differentiation.

Titanium isotopic fractionation in Kilauea Iki lava lake driven by oxide crystallization

Recent work has demonstrated that titanium (Ti) isotopes undergo mass-dependent isotope fractionation during magmatic differentiation, leaving evolved silicic melts preferentially enriched in heavy Ti isotopes. Preferential incorporation of light Ti isotopes in crystallizing Fe-Ti oxides is thought to be the mechanism responsible for this fractionation in magmatic rocks. To test this hypothesis, we present Ti isotope measurements of Fe-Ti oxide mineral separates of Kilauea Iki lava lake samples. We find that the Ti in Fe-Ti oxides is isotopically light while Ti in the residual melt and minerals is isotopically heavy. This result is consistent with the results of density functional theory (DFT) calculations in other studies, which show progressive heavy isotope enrichment for Ti from 6-fold, 5-fold, through 4-fold coordinated minerals. We therefore conclude that Ti isotopes in silicate melts undergo isotope fractionation during the crystallization of Fe-Ti oxides because Ti in oxides is primarily in 6-fold coordination whereas Ti in silicate melts is in 5- or 4-fold coordination (Ti in more evolved magmas tends to be in lower coordination). Based on our mineral separate results, we estimate the fractionation factor at 1000 °C between silicate and oxide Δ49Tisilicate-oxide to be 0.39 ± 0.06‰. This result is consistent with the fractionation factors inferred in previous studies based on Ti isotopic analyses and modeling of bulk rock measurements. We use this fractionation factor and the fractionation factors proposed by previous workers in Rhyolite MELTS to model the δ49Ti evolution of plume lavas. We find the model to generally predict the fractionations observed in Kilauea Iki, as well as the fractionations previously observed in volcanics from Hekla, Iceland and Afar, East Africa.

Titanium isotopic evidence for felsic crust and plate tectonics 3.5 billion years ago.

Earth exhibits a dichotomy in elevation and chemical composition between the continents and ocean floor. Reconstructing when this dichotomy arose is important for understanding when plate tectonics started and how the supply of nutrients to the oceans changed through time. We measured the titanium isotopic composition of shales to constrain the chemical composition of the continental crust exposed to weathering and found that shales of all ages have a uniform isotopic composition. This can only be explained if the emerged crust was predominantly felsic (silica-rich) since 3.5 billion years ago, requiring an early initiation of plate tectonics. We also observed a change in the abundance of biologically important nutrients phosphorus and nickel across the Archean-Proterozoic boundary, which might have helped trigger the rise in atmospheric oxygen.

Titanium isotopes and rare earth patterns in CAIs: Evidence for thermal processing and gas-dust decoupling in the protoplanetary disk

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 49Ti/47Ti, we found that ε50Ti values are somewhat variable among CAIs, and that ε46Ti is highly correlated with ε50Ti, with a best-fit slope of 0.162±0.030 (95% confidence interval). The linear correlation between ε46Ti and ε50Ti 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′49Ti, 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′49Ti 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.

Correlated nanoscale characterization of a unique complex oxygen-rich stardust grain: Implications for circumstellar dust formation

We report the light to intermediate-mass element abundances as well as the oxygen, magnesium, silicon, and titanium isotope compositions of a unique and unusually large (0.8µm×3.75µm) presolar O-rich grain from the Krymka LL3.2 chondrite. The O-, Al-, and Ti-isotopic compositions are largely compatible with an origin from an asymptotic giant branch (AGB) star of 1.5 solar masses with a metallicity that is 15% higher than the solar metallicity. The grain has an elevated 17O/16O ratio (8.40±0.16×10−4) compared to solar, and slightly sub-solar 18O/16O ratio (1.83±0.03×10−3). It shows evidence for the presence of initial 26Al, suggesting formation after the first dredge-up, during one of the early third dredge-up (TDU) episodes. Titanium isotopic data indicate condensation of the grain before significant amounts of material from the He-burning shell were admixed to the stellar surface with progressive TDUs. We observed a small excess in 30Si (δ30Si=41±5‰), which most likely is inherited from the parent star’s initial Si-isotopic composition. For such stars stellar models predict a C/O-ratio<1 even after the onset of TDU, thus allowing the condensation of O-rich dust.The grain is an unusual complex presolar grain, consisting of an Al-Ca-Ti-oxide core, surrounded by an Mg-Ca-silicate mantle, and resembles the condensation sequence for a cooling gas of solar composition at pressures and dust/gas ratios typically observed for circumstellar envelopes around evolved stars. We also report the first observation of phosphorus in a presolar grain, although the origin of the P-bearing phase remains ambiguous.

A link between oxygen, calcium and titanium isotopes in 26Al-poor hibonite-rich CAIs from Murchison and implications for the heterogeneity of dust reservoirs in the solar nebula

PLACs (platy hibonite crystals) and related hibonite-rich calcium-, aluminum-rich inclusions (CAIs; hereafter collectively referred to as PLAC-like CAIs) have the largest nucleosynthetic isotope anomalies of all materials believed to have formed in the solar system. Most PLAC-like CAIs have low inferred initial 26Al/27Al ratios and could have formed prior to injection or widespread distribution of 26Al in the solar nebula. In this study, we report 26Al–26Mg systematics combined with oxygen, calcium, and titanium isotopic compositions for a large number of newly separated PLAC-like CAIs from the Murchison CM2 chondrite (32 CAIs studied for oxygen, 26 of these also for 26Al–26Mg, calcium and titanium). Our results confirm (1) the large range of nucleosynthetic anomalies in 50Ti and 48Ca (our data range from −70‰ to +170‰ and −60‰ to +80‰, respectively), (2) the substantial range of Δ17O values (−28‰ to −17‰, with Δ17O=δ17O−0.52×δ18O), and (3) general 26Al-depletion in PLAC-like CAIs.The multielement approach reveals a relationship between Δ17O and the degree of variability in 50Ti and 48Ca: PLAC-like CAIs with the highest Δ17O (∼−17‰) show large positive and negative 50Ti and 48Ca anomalies, while those with the lowest Δ17O (∼−28‰) have small to no anomalies in 50Ti and 48Ca. These observations could suggest a physical link between anomalous 48Ca and 50Ti carriers and an 16O-poor reservoir. We suggest that the solar nebula was isotopically heterogeneous shortly after collapse of the protosolar molecular cloud, and that the primordial dust reservoir, in which anomalous carrier phases were heterogeneously distributed, was 16O-poor (Δ17O⩾−17‰) relative to the primordial gaseous (CO+H2O) reservoir (Δ17O<−35‰). However, other models such as CO self-shielding in the protoplanetary disk are also considered to explain the link between oxygen and calcium and titanium isotopes in PLAC-like CAIs.

New constraints on the relationship between 26Al and oxygen, calcium, and titanium isotopic variation in the early Solar System from a multielement isotopic study of spinel-hibonite inclusions

We report oxygen, calcium, titanium and 26Al–26Mg isotope systematics for spinel-hibonite inclusions (SHIBs), a class of calcium–aluminum-rich inclusions (CAI) common in CM chondrites. In contrast to previous studies, our analyses of 33 SHIBs and four SHIB-related objects obtained with high spatial resolution demonstrate that these CAIs have a uniform Δ17O value of approximately −23‰, similar to many other mineralogically pristine CAIs from unmetamorphosed chondrites (e.g., CR, CV, and Acfer 094). Five SHIBs studied for calcium and titanium isotopes have no resolvable anomalies beyond 3σ uncertainties. This suggests that nucleosynthetic anomalies in the refractory elements had been significantly diluted in the environment where SHIBs with uniform Δ17O formed. We established internal 26Al–26Mg isochrons for eight SHIBs and found that seven of these formed with uniformly high levels of 26Al (a multi-CAI mineral isochron yields an initial 26Al/27Al ratio of ∼4.8×10−5), but one SHIB has a smaller initial 26Al/27Al of∼2.5×10−5, indicating variation in 26Al/27Al ratios when SHIBs formed. The uniform calcium, titanium and oxygen isotopic characteristics found in SHIBs with both high and low initial 26Al/27Al ratios allow for two interpretations. (1) If subcanonical initial 26Al/27Al ratios in SHIBs are due to early formation, as suggested by Liu et al. (2012), our data would indicate that the CAI formation region had achieved a high degree of isotopic homogeneity in oxygen and refractory elements before a homogeneous distribution of 26Al was achieved. (2) Alternatively, if subcanonical ratios were the result of 26Al–26Mg system resetting, the clustering of SHIBs at a Δ17O value of ∼−23‰ would imply that a 16O-rich gaseous reservoir existed in the nebula until at least ∼0.7Ma after the formation of the majority of CAIs.

A new method for MC-ICPMS measurement of titanium isotopic composition: Identification of correlated isotope anomalies in meteorites

A new protocol is presented for precise measurements of titanium isotopes in natural samples. Titanium was separated via ion-exchange and extraction chromatography in two stages. Tests on Ti standard solutions show that isobaric interferences from Ca, V, and Cr can be adequately corrected, as long as these elements are present at atomic ratios of Ca/Ti < 20, V/Ti < 2, and Cr/Ti < 0.1. Furthermore, Zr2+ and Mo2+ have no influences on Ti+ signals when atomic ratios of Zr/Ti < 0.002 and Mo/Ti < 0.04. Compared with these correction limits, the purified solutions have corresponding ratios several orders of magnitude lower, indicating that the chemical separation technique is effective. This newly developed method has been successfully applied to geostandards and a wide variety of bulk meteorites. Our results are in good agreement with the data from Trinquier et al. (Science, 2009, 324, 374–376)1 and reveal a linear correlation between isotope anomalies of two Ti nuclides in bulk meteorites. The correlation reflects incomplete mixing of the carrier phases for Ti isotope anomalies before bulk meteorite formation.

Trace element abundances and magnesium, calcium, and titanium isotopic compositions of grossite-containing inclusions from the carbonaceous chondrite Acfer 182

The carbonaceous chondrite Acfer 182 contains Ca,Al-rich inclusions (CAIs) that differ from most CAIs in other meteorites. Many of them contain grossite (CaAl 4O 7), whose modal abundance exceeds 30 vol % in most of these CAIs (“grossite-rich inclusions”). Similar inclusions have been found only in the CH chondrite ALH85085 and the CR chondrite Acfer 059-El Djouf 001. Ion microprobe analyses of trace elements were made on nineteen CAIs from Acfer 182 and two CAIs from Acfer 059-El Djouf 001, of AlMg isotopes on eighteen Acfer 182 and the two Acfer 059-El Djouf 001 inclusions, and of calcium isotopes on ten Acfer 182 inclusions (on six of them also of titanium isotopes) and one Acfer 059-El Djouf 001 inclusion. Trace element and isotopic signatures of grossite-containing inclusions from Acfer 182 resemble those of some inclusions from ALH85085. Volatility-fractionated trace element abundance patterns, ranging from ultrarefractory-depleted (similar to Group II pattern) to volatile-enhanced, are predominant (17 CAIs, including both inclusions from Acfer 059-El Djouf 001). Two inclusions have ultrarefractory patterns, one has a Group III pattern, and one inclusion has a Group III-related pattern similar to patterns found in HAL-type inclusions. Only one CAI from Acfer 182, but both inclusions from Acfer 059-El Djouf 001, have nonlinear excesses of 26Mg corresponding to the initial 26Al 27Al ratio of ∼ 5 × 10 −5. None of the twenty inclusions has a significant intrinsic isotopic mass fractionation of Mg. Titanium is normal in all analyzed CAIs and only small 48Ca excesses (4.3 and 3.8‰) are present in two inclusions. Isotopes of both Ca and Ti show no significant intrinsic mass fractionations. Grossite-containing inclusions from Acfer 182 occur in different petrographic contexts. In many cases petrographic characteristics are correlated with trace element abundances. Almost all inclusions studied in this work have a condensation history but no evidence for extensive evaporation processes is present. Many of the CAIs must have formed by direct gas-solid condensation, while some inclusions with clearly identifiable igneous textures formed from a refractory melt. Grossite, whose formation was the subject of controversy in the past, probably condensed from a reservoir with a higher-than-chondritic Ca/Al-ratio and depleted in the highly refractory trace elements, or crystallized from a Ca,Al-rich melt. The two ultrarefractory inclusions from Acfer 182 have extremely high refractory trace element abundances (sometimes exceeding 10 5 × CI). The lack of isotopic fractionation indicates a formation at very high temperatures by condensation rather than evaporation. The lack of 26Mg excesses in almost all inclusions from Acfer 182 is best explained by heterogeneous distribution of 26Al in the primitive solar nebula. Grossite-rich inclusions having volatility-fractionated ultrarefractory-depleted trace element abundance patterns and lacking 26Mg excesses could be the complement of platy hibonites (PLACs) from Murchison with Group III or ultrarefractory patterns and likewise no 26Mg excesses.

Carbon, nitrogen, magnesium, silicon, and titanium isotopic compositions of single interstellar silicon carbide grains from the Murchison carbonaceous chondrite

view Abstract Citations (249) References (151) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Carbon, Nitrogen, Magnesium, Silicon, and Titanium Isotopic Compositions of Single Interstellar Silicon Carbide Grains from the Murchison Carbonaceous Chondrite Hoppe, Peter ; Amari, Sachiko ; Zinner, Ernst ; Ireland, Trevor ; Lewis, Roy S. Abstract Seven hundred and twenty SiC grains from the Murchison CM2 chondrite, ranging in size from 1 to 10 micrometers, were analyzed by ion microprobe mass spectrometry for their C-isotopic compositions. Subsets of the grains were also analyzed for N (450 grains), Si (183 grains), Mg (179 grains), and Ti (28 grains) isotopes. These results are compared with previous measurements on 41 larger SiC grains (up to 15 x 26 micrometers) from a different sample of Murchison analyzed by Virag et al. (1992) and Ireland, Zinner, & Amari (1991a). All grains of the present study are isotopically anomalous with C-12/C-13 ratios ranging from 0.022 to 28.4 x solar, N-14/N-15 ratios from 0.046 to 30 x solar, Si-29/Si-28 from 0.54 to 1.20 x solar, Si-30/Si-28 from 0.42 to 1.14 x solar, Ti-49/Ti-48 from 0.96 to 1.95 x solar, and Ti-50/Ti-48 from 0.94 to 1.39 x solar. Many grains have large Mg-26 excesses from the decay of Al-26 with inferred Al-26/Al-27 ratios ranging up to 0.61, or 12,200 x the ratio of 5 x 10-5 inferred for the early solar system. Several groups can be distinguished among the SiC grains. Most of the grains have C-13 and N-14 excesses, and their Si isotopic compositions (mostly excesses in Si-29 and Si-30) plot close to a slope 1.34 line on a Delta Si-29/Si-28 versus Delta Si-30/Si-28 three-isotope plot. Grains with small C-12/C-13 ratios (less than 10) tend to have smaller or no N-14 excesses and high Al-26/Al-27 ratios (up to 0.01). Grains with C-12/C-13 greater than 150 fall into two groups: grains X have N-15 excesses and Si-29 and Si-30 deficits and the highest (0.1 to 0.6) Al-26/Al-27 ratios; grains Y have N-14 excesses and plot on a slope 0.35 line on a Si three-isotope plot. In addition, large SiC grains of the Virag et al. (1992) study fall into three-distinct clusters according to their C-, Si-, and Ti-isotopic compositions. The isotopic diversity of the grains and the clustering of their isotopic compositions imply distinct and multiple stellar sources. The C- and N-isotopic compositions of most grains are consistent with H-burning in the CNO cycle. These and s-process Kr, Xe, Ba, and Nd suggest asymptotic giant branch (AGB) or Wolf-Rayet stars as likely sources for the grains, but existing models of nucleosynthesis in these stellar sites fail to account in detail for all the observed isotopic compositions. Special problems are posed by grains with C-12/C-13 less than 10 and almost normal and heavy N-isotopic compositions. Also the Si- and Ti-isotopic compositions, with excesses in Si-29 and Si-30 relative to Si-28 and excesses in all Ti isotopes relative to Ti-48, do not precisely conform with the compositions predicted for slow neutron capture. Additional theoretical efforts are needed to achieve an understanding of the isotopic composition of the SiC grains and their stellar sources. Publication: The Astrophysical Journal Pub Date: August 1994 DOI: 10.1086/174458 Bibcode: 1994ApJ...430..870H Keywords: Carbon Isotopes; Magnesium Isotopes; Meteoritic Composition; Murchison Meteorite; Nitrogen Isotopes; Silicon Carbides; Silicon Isotopes; Stellar Composition; Titanium Isotopes; Abundance; Astrophysics; Cosmic Dust; Interstellar Chemistry; Mass Spectroscopy; Nuclear Fusion; Astrophysics; METEOROIDS; NUCLEAR REACTIONS; NUCLEOSYNTHESIS; ABUNDANCES full text sources ADS |

Isotopes of titanium in Aldebaran

view Abstract Citations (11) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Isotopes of titanium in Aldebaran. Lambert, D. L. ; Luck, R. E. Abstract The titanium isotopic abundance ratios in the K5 giant Aldebaran (Alpha Tau) are estimated from photoelectric high-resolution (40 mA) scans of portions of the TiO gamma-system (0, 0) band between 7070 and 7082 A. An application of spectrum synthesis techniques shows that the overall Ti isotopic abundance ratio is terrestrial to within 50%, with individual ratios terrestrial to within 25%. The (1, 0) and (0, 1) gamma-system band heads are reviewed as potential isotopic abundance indicators in late M stars. Publication: The Astrophysical Journal Pub Date: January 1977 DOI: 10.1086/154950 Bibcode: 1977ApJ...211..443L Keywords: Abundance; Late Stars; M Stars; Titanium Isotopes; Giant Stars; High Resolution; Stellar Atmospheres; Stellar Spectra; Astrophysics full text sources ADS |