NEW TITANIUM ISOTOPE DATA FOR ALLENDE AND EFREMOVKA CAIs

• Published in: The Astrophysical journal 2009-09, Vol.702 (2)
• Main Authors: Leya, Ingo, Schoenbaechler, Maria, Kraehenbuehl, Urs, Halliday, Alex N.
• Format: Article
• Language: English
• Subjects: ABUNDANCE; ALUMINIUM; ALUMINIUM 26; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BERYLLIUM 10; CALCIUM; CALCIUM 41; CHONDRITES; MARS PLANET; MASS BALANCE; METEOROIDS; MOON; NEUTRONS; NICKEL 62; NUCLEAR REACTIONS; NUCLEOSYNTHESIS; SOLAR SYSTEM; TITANIUM; TITANIUM 46; TITANIUM 47; TITANIUM 48; TITANIUM 50; ZIRCONIUM 96
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1088/0004-637X/702/2/1118;COUNTRYOFINPUT:INTERNATIONALATOMICENERGYAGENCY(IAEA)

We measured the titanium (Ti) isotope composition, i.e., {sup 50}Ti/{sup 47}Ti, {sup 48}Ti/{sup 47}Ti, and {sup 46}Ti/{sup 47}Ti, in five calcium-rich-aluminum-rich refractory inclusions (CAIs) from the oxidized CV3 chondrite Allende and in two CAIs from the reduced CV3 chondrite Efremovka. Our data indicate that CAIs are enriched in {sup 50}Ti/{sup 47}Ti and {sup 46}Ti/{sup 47}Ti and are slightly depleted in {sup 48}Ti/{sup 47}Ti compared to normal Ti defined by ordinary chondrites, eucrites, ureilites, mesosiderites, Earth, Moon, and Mars. Some CAIs have an additional {sup 50}Ti excess of {approx}8{epsilon} relative to bulk carbonaceous chondrites, which are enriched in {sup 50}Ti by {approx}2{epsilon} relative to terrestrial values, leading to a total excess of {approx}10{epsilon}. This additional {sup 50}Ti excess is correlated with nucleosynthetic anomalies found in {sup 62}Ni and {sup 96}Zr, all indicating an origin from a neutron-rich stellar source. Bulk carbonaceous chondrites show a similar trend, however, the extent of the anomalies is either less than or similar to the smallest anomalies seen in CAIs. Mass balance calculations suggest that bulk Allende Ti possibly consists of a mixture of at least two Ti components, anomalous Ti located in CAIs and a normal component possibly for matrix and chondrules. This argues for a heterogeneous distribution of Ti isotopes in the solar system. The finding that anomalous Ti is concentrated in CAIs suggests that CAIs formed in a specific region of the solar system and were, after their formation, not homogeneously redistributed within the solar system. Combining the CAI data with improved model predictions for early solar system irradiation effects indicates that a local production scenario for the relatively short lived radionuclides can be excluded, because the production of, e.g., {sup 10}Be, {sup 26}Al, and {sup 41}Ca, would result in a significant collateral shift in Ti isotopes, which is not seen in the measured data.