Multi-collector 40Ar/39Ar dating of microtektites from Transantarctic Mountains (Antarctica): A definitive link with the Australasian tektite/microtektite strewn field
Multi-collector 40Ar/39Ar dating of microtektites from Transantarctic Mountains (Antarctica): A definitive link with the Australasian tektite/microtektite strewn field
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DOI：
10.1016/j.gca.2021.01.046
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发表时间：
2021-02-23
影响因子：
5
通讯作者：
Harvey, Ralph P.
中科院分区：
文献类型：
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作者：
Di Vincenzo, Gianfranco;Folco, Luigi;Harvey, Ralph P.
微陨石代表高速/远端陨石撞击喷射物。证明在整个东南极洲多个地点发现的微玻璃陨石由属于澳大利亚玻璃陨石/微玻璃陨石散布场的同质地质物体组成，对于确定地球上最大和最年轻的已知玻璃陨石场的实际范围至关重要，该区域是由类似于 0.8 Ma 前的小行星撞击产生的。这项研究提出了新的 40Ar/39Ar 分析，通过多接收器稀有气体质谱仪对来自横贯南极山脉两个关键地点的单个微玻璃陨石进行了分析：维多利亚地北部的米勒山和格罗夫纳山脉以南 1,000 多公里的雷蒙德山。结果表明，颗粒被至少一种外来 Ar 成分严重污染，这与尺寸或本体化学成分无关，并且妨碍了对 40Ar/39Ar 数据的直接解释。对三同位素相关图中的逐步加热和总聚变分析的数据进行分析，得出了两个位置无法区分的等时线年龄，综合等时线平均值为 800 +/- 89 ka（95% 置信水平）。这些年龄结果比之前发表的 40Ar/39Ar 年龄测定结果提高了一个数量级以上，比之前的裂变径迹日期提高了 4 倍，从而提供了确凿的证据，表明在南极洲横贯山脉发现的微玻璃陨石属于单一来源——澳大利亚区域。这项研究加强了澳大利亚区域的向南延伸（与在低纬度深海沉积物中发现的澳大利亚微玻璃陨石类似，向南延伸了 4,000 公里），因此意味着发射距离距印度支那的假定撞击位置近 12,000 公里。从广泛的角度来看，结果还揭示了来自横贯南极山脉的微小玻璃陨石（受到外来氩的高度污染）和澳大利亚宏观玻璃陨石（受到轻微或可忽略不计的污染）之间的对比行为。尽管未来专门的实验工作，旨在定义亚微尺度微玻璃陨石的物理均匀性以及了解Ar同位素的真实颗粒内空间分布是必要的，但我们推测性地假设玻璃陨石和微玻璃陨石之间的对比行为可能反映了不同环境中的位移。 (C) 2021 Elsevier Ltd. 保留所有权利。
Microtektites represent high-velocity/distal meteorite impact ejecta. Demonstrating that microtektites found at several locations throughout East-Antarctica consist of a homogeneous class of geological objects belonging to the Australasian tektite/microtektite strewn field is fundamental to define the actual extent of the largest and youngest known tektite field on Earth produced by an asteroidal impact similar to 0.8 Ma ago. This study presents new 40Ar/39Ar analyses performed by multicollector noble gas mass spectrometry on individual microtektites from two key locations in the Transantarctic Mountains: Miller Butte, in northern Victoria Land, and Mount Raymond, over 1,000 km further south, in the Grosvenor Mountains. Results indicate that particles are heavily contaminated by at least one extraneous Ar component, which is not correlated with size nor with bulk chemical composition, and precludes a straightforward interpretation of 40Ar/39Ar data. Analysis of data from step-heating and total fusion analyses in three-isotope correlation diagrams yielded indistinguishable isochron ages from the two locations, with a combined isochron average of 800 +/- 89 ka (95% confidence level). These age results improve by more than one order of magnitude previously published 40Ar/39Ar age determinations and improve by 4 times a previous fission track date, thus providing conclusive evidence that microtektites found throughout the Transantarctic Mountains of Antarctica belong to a single source - the Australasian field. This study strengthens the southward extension of the Australasian field (similar to 4,000 km southward with respect to Australasian microtektites recovered at lower latitudes from deep sea sediments), thus implying a launch distance of nearly 12,000 km from the putative impact location in Indochina. From a broad perspective, results also reveal a contrasting behavior between microtektites from the Transantarctic Mountains, highly contaminated by extraneous Ar, and Australasian macroscopic tektites, weakly or negligibly contaminated. Although future dedicated experimental work, aimed at the definition of physical homogeneity of microtektites at the submicroscale and at the understanding of the true intra-particle spatial distribution of Ar isotopes are necessary, we speculatively hypothesize that the contrasting behavior between tektites and microtektites may reflect displacement in different environments. (C) 2021 Elsevier Ltd. All rights reserved.