Oxygen isotope heterogeneities in the earliest protosolar gas recorded in a meteoritic calcium aluminum-rich inclusion
Oxygen isotope heterogeneities in the earliest protosolar gas recorded in a meteoritic calcium aluminum-rich inclusion
复制标题
陨石富含钙铝包裹体中记录的最早原太阳气体中的氧同位素异质性
DOI：
10.1016/j.epsl.2007.09.003
复制
发表时间：
2007
影响因子：
5.3
通讯作者：
E. Zinner
中科院分区：
文献类型：
--
作者：
J. Aléon;A. Goresy;E. Zinner
结合岩石学，氧和镁同位素和微量元素分析的化合物钙，铝丰富的夹杂物（CAI）从Efremovka减少CV 3碳质球粒陨石显示，它包括一个富镁，16 O丰富的捕虏体CAI，以前改变的星云，影响广泛熔融，16 O耗尽，A型主机CAI结束前不久的主机的结晶。捕虏体中的褶曲区域可能是由撞击过程中产生的部分熔体快速结晶而形成的。在主机CAI的氧同位素比值与黄长石化学和位置的包裹体。紧挨CAI的沃克-洛弗林边缘内部的区域由富含16 O的钙黄长石组成，Δ 17 O的范围低至−20‰，但黄长石逐渐变得贫16 O（Δ 17 O ≤ 0‰），并向内部富含Mg。在镁同位素分馏的情况下，这种变化最好归因于O同位素之间的星云气体和部分熔融的包裹体在其结晶过程中的交换。这一事件持续了不到200小时，这意味着主机CAI之间的两个星云水库与不同的O同位素组成在这段时间内进行了运输。对可能的传输机制的研究表明，传输发生在小于1个天文单位的距离上。两个包裹体的26 Al/27 Al比值都接近标准值4.1×10− 5，这意味着在太阳系诞生后最多67万年，富含16 O的储存空间有限，而具有典型行星同位素组成的贫16 O储存空间可用于行星形成。
Combined petrologic, oxygen and magnesium isotopic and trace element analyses of a compound calcium–aluminum-rich inclusion (CAI) from the Efremovka reduced CV3 carbonaceous chondrite reveal that it consists of a Mg-rich,16O-rich xenolithic CAI, previously altered in the nebula, that impacted an extensively molten,16O-depleted, type A host CAI shortly before the end of the host's crystallization. Convoluted regions in the xenolith were probably formed by rapid crystallization of the partial melt produced during impact. Oxygen isotopic ratios in the host CAI are correlated both with melilite chemistry and location in the inclusion. The region immediately inside the Wark–Lovering rim of the CAI consists of16O-rich gehlenite with Δ17O ranging down to −20‰ but melilite becomes progressively16O-poor (Δ17O∼0‰) and Mg-rich towards the interior. In the absence of Mg isotopic fractionation, this variation is best attributed to O isotopic exchange between the nebular gas and the partially molten inclusion during its crystallization. This event lasted less than 200 h, which implies that the host CAI was transported between two nebular reservoirs with distinct O isotopic compositions during this time. Examination of possible transport mechanisms suggests that the transport occurred over a distance of less than 1 astronomical unit. The close-to-canonical26Al/27Al ratio of 4.1×10−5determined from both inclusions implies that at most 670,000 yr after the birth of the Solar System, the16O-rich reservoir was spatially limited and an16O-poor reservoir with typical planetary isotopic composition was available for planet formation.