Formation and exposure history of non-magmatic iron meteorites and winonaites: Clues from Sm and W isotopes
Formation and exposure history of non-magmatic iron meteorites and winonaites: Clues from Sm and W isotopes
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非岩浆铁陨石和winonaites的形成和暴露历史：来自Sm和W同位素的线索
DOI：
10.1016/j.gca.2012.02.012
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发表时间：
2012
影响因子：
5
通讯作者：
C. Mezger
中科院分区：
文献类型：
--
作者：
Schulz;Upadhyay;Münker;C. Mezger
本文介绍了非岩浆铁陨石群和威诺岩的金属和硅酸盐的新的W和Sm同位素测量结果，并与文献资料进行了汇编，以评估它们的暴露历史和母体形成。我们报告了八种IAB金属的高精度182 W数据，并辅以文献数据，介绍了一种计算其零暴露值的方法。我们的估计揭示了IAB铁陨石复合体的常见放射性182 W签名为−2.83±0.03 ε-单位。这意味着金属在太阳系形成后的5.06+0.42/−0.41Ma分离。对地核形成的精确年龄估计与之前对硅酸盐熔融的182 Hf-182 W年龄（4.6+0.7/-0.6Ma; Schulz等人，2009）和winonaites的形成（4.8+3.1/-2.6Ma; Schulz et al.，2010年），它们被认为是来自同一个母体。如果解释为有利于小行星范围内（因此最有可能是内部）的热源，这些年龄对应于IAB/winonaite母体在太阳系形成后的102 Ma的吸积年龄。然而，金属从未分组IAB标本分离在显着不同的时间。在太阳系形成后13 Ma时Mundrabilla金属的分离可以通过撞击触发的熔池形成来最好地解释，这一过程也可能导致11 Ma和14 Ma之间IAB硅酸盐和winonaites的变质作用（Schulz等人，149 Sm和150 Sm的组成，表明宇宙射线的影响，为五个IAB硅酸盐揭示了相关的暴露年龄从金属相，以及数据对三个winonaite，提供没有令人信服的证据暴露硅酸盐在近表面区域的IAB/winonaite母小行星。本文测量了6块IIE铁陨石的钨同位素组成，并在文献中报道了它们的组成，揭示了太阳系形成后的3次连续的金属分凝事件，分别发生在103 Ma、1013 Ma和1028 Ma。虽然最古老的事件可能由内部热源解释，但撞击为后者提供了唯一可行的解释。从IIE金属推断的热事件的延长的时间跨度得到来自沃森的两个硅酸盐夹杂物的182 Hf-182 W数据的支持（Snyder等人，2001）和迈尔斯（这项研究）。来自迈尔斯陨石的硅酸盐包裹体的钐同位素数据没有提供2π暴露的证据。
New W and Sm isotope measurements for metals and silicates of non-magmatic iron meteorite groups and winonaites are presented and compiled with literature data to assess their exposure history and parent body formation. We report high-precision182W data for eight IAB metals supplemented by literature data and introduce a method to calculate their zero-exposure values. Our estimate reveals a common radiogenic182W signature of −2.83±0.03 ε-units for the IAB iron meteorite complex. This suggests metal separation at 5.06+0.42/−0.41Ma after solar system formation. The refined age estimate for core formation agrees remarkably well with previously published182Hf–182W ages for silicate melting (4.6+0.7/−0.6Ma; Schulz et al., 2009) and the formation of winonaites (4.8+3.1/−2.6Ma; Schulz et al., 2010), which are assumed to be derived from the same parent body. If interpreted in favour of an asteroid-wide (and therefore most likely internal) heat source, these ages correspond to an accretion age for the IAB/winonaite parent body of ∼2Ma after solar system formation. However, metals from ungrouped IAB specimen segregated at significantly different times. Separation of Mundrabilla metals at ∼13Ma after solar system formation can best be explained via impact triggered melt pool formation, a process that could also be responsible for metamorphism of IAB silicates and winonaites between ∼11 and ∼14Ma (Schulz et al., 2009, 2010).149Sm and150Sm compositions, indicative of cosmic ray effects, for five IAB silicates reveal a correlation with exposure ages obtained from metal phases and, together with data on three winonaites, provide no compelling evidence for exposure of silicates within near surface regions of the IAB/winonaite parent asteroid. Tungsten isotope compositions of metals from six IIE iron meteorites, measured in this study and reported in the literature, reveal three consecutive metal segregation events at ∼3, ∼13 and ∼28Ma after formation of the solar system. Whereas the oldest event could potentially be explained by internal heat sources, impacts provide the only viable explanation for the latter. A prolonged time-span for thermal events, as deduced from IIE metals, is supported by182Hf–182W data for two silicate inclusions from Watson (Snyder et al., 2001) and Miles (this study). Samarium isotope data for a silicate inclusion from the Miles meteorite provides no evidence for 2π-exposure.