Tungsten isotopes in eucrites revisited and the initial ~(182)Hf/~(180)Hf of the solar system based on iron meteorite data

摘要

We present a revised chronology for the formation and differentiation of the eucrite parent body based on ~(182)Hf–~(182)W chronometry. A very short (<600 kyr) time interval between metal segregation and silicate differentiation can be demonstrated. The non-cumulate eucrites formed 9.1±2.6 Myr after the start of the solar system. This is significantly later than recently proposed in the literature but in good agreement with Sr, Pb and Cr isotopic data. The comparison with Mg isotopes is complex and more data are required to discuss the consistency of the Al–Mg and the Hf–W chronometers. The Hf–W timescale is calibrated with a new estimate of the ~(182)Hf/~(180)Hf initial ratio of the solar system of (1.60±0.25)×10~(-4). This estimate, deduced from iron meteorite W isotope data, is about 50% higher than recently suggested.