Abstract The Australasian tektite (AAT) strewn field is the largest strewn field on the Earth with about ∼10–30% coverage, both land and ocean, but a clearly identified source impact crater is absent despite the young age of AAT of ca. 790 ka. A genetic link between the Australasian tektites and their unequivocal parental materials is therefore largely impossible to establish. Nevertheless, the nature of the parental materials and the extent of volatilization can be constrained using the splash form tektites, carrying the chemical signatures of high-temperature processes, and the layered (so-called Muong Nong-type) tektites, which are less chemically homogenized and exceptionally abundant in the AAT field. New high-precision Sr, Nd and Pb isotopic measurements were obtained for a chemically and petrographically well-characterized suite of AAT, which included the Muong Nong-type (MN-AAT) with precisely known field locations in Laos and splash forms (SF-AAT) from different parts of the strewn field. In addition, optically dark and light zones of the MN-AAT were also separately analyzed. Homogeneous eNd values from −11.8 to −11.2, combined with a narrow range of two-stage Nd model ages from 1.67 to 1.72 Ga for the entire AAT suite, point to a well-mixed source, in terms of REE, of the crustal segment from which the sedimentary material for tektites was ultimately derived. The Sr isotopic data largely overlap for SF-AAT and MN-AAT (87Sr/86Sr = 0.71636–0.72021) and indicate Paleozoic to Mesozoic sedimentary parentage. However, late Neogene to early Quaternary re-deposition and formation of a thick silt-sized sedimentary section with vertical stratification is required to comply with 10Be data. Lead isotope systematics documents at least three different components which can perhaps be represented by different mineral phases, such as feldspar, zircon, organic matter adsorbed on young sediments etc., sorted during fluvial transport and final deposition. In addition, the SF-AAT have systematically lower Pb contents than the MN-AAT, and generally show isotopically heavier Pb isotopic ratios. This is theoretically consistent with a preferential volatilization of lighter Pb isotopes during evaporation and considerably larger Pb loss from SF-AAT when compared to MN-AAT. Nevertheless, further experimental work would be necessary to unambiguously distinguish kinetic fractionation from source mixing.

中文翻译：

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澳大利亚陨石的 Sr-Nd-Pb 同位素系统学：对目标材料的性质和组成以及 Pb 可能的挥发损失的影响

摘要 澳大拉西亚 tektite (AAT) 散布场是地球上最大的散布场，陆地和海洋的覆盖率约为 10-30%，但尽管 AAT 的年龄很小，但没有明确识别的源撞击坑。790 卡。因此，澳大拉西亚的 tektites 与其明确的亲本材料之间的遗传联系在很大程度上是不可能建立的。然而，母体材料的性质和挥发程度可以通过使用带有高温过程化学特征的飞溅形式的 tektite 和层状（所谓的 Muong Nong 型）tektite 来限制，它们的化学性质较低在 AAT 领域均质化且异常丰富。获得了新的高精度 Sr、Nd 和 Pb 同位素测量结果，用于化学和岩相学充分表征的 AAT 套件，其中包括在老挝具有精确已知场地位置的 Muong Nong 型 (MN-AAT) 和来自散布场地不同部分的飞溅形式 (SF-AAT)。此外，还分别分析了 MN-AAT 的光学暗区和亮区。从 -11.8 到 -11.2 的均匀 eNd 值，结合整个 AAT 套件的两阶段 Nd 模型年龄从 1.67 到 1.72 Ga 的狭窄范围，表明地壳段的 REE 来源混合良好玻璃陨石的沉积材料最终来源于此。SF-AAT 和 MN-AAT 的 Sr 同位素数据在很大程度上重叠（87Sr/86Sr = 0.71636–0.72021），表明古生代至中生代沉积亲缘关系。然而，新近纪晚期至第四纪早期的再沉积和垂直分层的厚粉砂大小沉积剖面的形成需要符合 10Be 数据。铅同位素系统学记录了至少三种不同的成分，它们可能由不同的矿物相代表，例如长石、锆石、吸附在年轻沉积物上的有机物等，在河流运输和最终沉积过程中分选。此外，SF-AAT 的 Pb 含量系统性地低于 MN-AAT，并且通常显示出更高的同位素比值。这在理论上与蒸发过程中较轻的 Pb 同位素优先挥发以及与 MN-AAT 相比 SF-AAT 的 Pb 损失要大得多。尽管如此，