کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
6427947 | 1634726 | 2015 | 10 صفحه PDF | دانلود رایگان |
![عکس صفحه اول مقاله: Planetesimal differentiation revealed by the Hf-W systematics of ureilites Planetesimal differentiation revealed by the Hf-W systematics of ureilites](/preview/png/6427947.png)
- Ureilites have smaller 182W deficits than most magmatic iron meteorites.
- Hf-W model age dates silicate melt extraction at 3.3±0.7 Ma after CAI formation.
- This is â¼2-3 Ma later than core formation in most iron meteorite parent bodies.
- Ureilite parent body accreted at â¼1.6 Ma after CAI formation.
- Ureilite parent body contained too little 26Al to induce complete melting.
Determining the timescales of the accretion and chemical differentiation of meteorite parent bodies provides some of the most direct constraints on the formation of planetesimals and the earliest stages of planet formation. We present high-precision Hf-W isotope data for a comprehensive set of ureilites, ultramafic mantle restites derived from a partially melted and incompletely differentiated asteroid. All samples are characterized by strong 182W deficits, indicating that silicate melt extraction on the ureilite parent body at 3.3±0.7 Ma after CAI formation postdated core formation in iron meteorite parent bodies by â¼2-3 Ma. Thermal modeling of planetesimal heating by 26Al-decay combined with the new Hf-W data indicates that the ureilite parent body accreted at â¼1.6 Ma after CAI formation and, therefore, more than â¼1 Ma later than iron meteorite parent bodies, but more than â¼0.5 Ma earlier that most chondrite parent bodies. Due to its relatively 'late' accretion, the ureilite parent body contained too little 26Al to cause complete melting and, therefore, would have probably remained incompletely differentiated even without exhaustion of 26Al by silicate melt segregation. Our results show that both in terms of degree of differentiation and accretion timescale the ureilite parent body is intermediate between fully differentiated and undifferentiated bodies, implying that there is an inverse correlation between extent of melting and metal-silicate separation versus time of accretion and differentiation.
Journal: Earth and Planetary Science Letters - Volume 430, 15 November 2015, Pages 316-325