Clinopyroxene is a rock-forming mineral that commonly hosts melt inclusions in mafic to intermediate composition volcanic and plutonic rocks. It is highly resistant to alteration compared to other co-existing phenocrysts such as plagioclase. Several recent studies have 40Ar/39Ar dated clinopyroxene in Neoproterozoic to Miocene basalts and dolerites. To assess the viability of the technique at the youngest end of the geologic time scale, we performed 40Ar/39Ar incremental heating experiments on clinopyroxene-hosted melt inclusions from a variety of mafic lithologies and tectonic settings. Most samples produced precise plateau ages including several Quaternary basalts to andesites as young as 0.6 Ma. All data are indistinguishable from new and/or published 40Ar/39Ar ages on groundmass or plagioclase from the same samples. The source of potassium (K) and resulting 40Ar* within clinopyroxene has been debated, but thus far has only been inferred based on 40Ar/39Ar data. Using electron probe microanalysis (EPMA) we show that there is negligible K in the clinopyroxene host, but substantial K (e.g., 1–4 wt%) in trapped melt inclusions and minor amounts in plagioclase inclusions. Thus, melt inclusions, which are common in phenocrysts in basaltic magmas, can be used to obtain accurate and precise 40Ar/39Ar ages for difficult-to-date volcanic and plutonic rocks from the Precambrian to the Pleistocene.

中文翻译：

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单斜辉石熔融包裹体的前寒武纪至更新世 40Ar/39Ar 测年

单斜辉石是一种造岩矿物，通常在镁铁质到中间成分的火山岩和深成岩中含有熔体包裹体。与其他共存的斑晶（例如斜长石）相比，它具有很强的抗蚀性。最近的几项研究已用 40Ar/39Ar 测定了新元古代至中新世玄武岩和辉绿岩中的单斜辉石的年代。为了评估该技术在地质时间尺度最年轻端的可行性，我们对来自各种镁铁质岩性和构造环境的单斜辉石熔融包裹体进行了 40Ar/39Ar 增量加热实验。大多数样本都产生了精确的高原年龄，包括一些第四纪玄武岩和年仅 0.6 Ma 的安山岩。所有数据与来自相同样品的基质或斜长石的新的和/或公布的 40Ar/39Ar 年龄无法区分。单斜辉石中钾 (K) 和由此产生的 40Ar* 的来源一直存在争议，但迄今为止仅根据 40Ar/39Ar 数据推断。使用电子探针微量分析（EPMA），我们发现单斜辉石主体中的钾含量可以忽略不计，但在捕获的熔体包裹体中含有大量的钾（例如，1-4 wt%），斜长石包裹体中含有少量的钾。因此，玄武岩浆中斑晶中常见的熔体包裹体可用于获得前寒武纪至更新世难以测年的火山岩和深成岩的准确且精确的40Ar/39Ar年龄。