An improved chronology for the Arthur’s Seat volcano and Carboniferous magmatism of the Midland Valley of Scotland

The Early Carboniferous Arthur’s Seat volcano in central Edinburgh is of geological significance and landscape value but lacks a precise chronology. New 40Ar/39Ar step-heating plateau analyses date the lowest Lava 1 of the eruptive sequence to 341.2 ± 0.8 Ma (Visean, Holkerian), with Lava 3a at 336.7 ± 4.7 Ma. Intrusive or lava-lake basalts within the Lion’s Haunch Vent are precisely dated at 338 ± 0.6 Ma at Dunsapie and 335.1 ± 0.6 Ma at Crow Hill (Visean, Asbian). Taken together with existing 40Ar/39Ar dates recalculated to recent decay constant and standard values, and U/Pb dates, a revised magmatic chronology consistent with biostratigraphy is presented for the Midland Valley of Scotland. The Garleton Hills Volcanic Formation is older than the Arthur’s Seat Volcanic Formation, whereas the Clyde Plateau and Arthur’s Seat volcanic formations are partly coeval, requiring minor re-adjustments to existing stratigraphy.位于爱丁堡中部的早石炭世亚瑟王座火山（Arthur’s Seat volcano）兼具地质研究价值与景观意义，但目前缺乏精确的年代学数据。新开展的⁴⁰Ar/³⁹Ar步进加热坪年龄分析（40Ar/39Ar step-heating plateau analyses）结果显示，喷发序列最底部的熔岩1（Lava 1）形成于341.2±0.8 Ma（维宪阶霍尔科亚期），熔岩3a（Lava 3a）的形成年代为336.7±4.7 Ma。狮臀喷口（Lion’s Haunch Vent）内部的侵入岩或熔岩湖玄武岩，在邓萨皮（Dunsapie）测点的精确定年结果为338±0.6 Ma，克劳山（Crow Hill）测点则为335.1±0.6 Ma（维宪阶阿斯别阶）。结合重新校准至最新衰变常数与标准值的已有⁴⁰Ar/³⁹Ar定年数据，以及铀-铅（U/Pb）定年结果，本次研究为苏格兰中部谷地（Midland Valley of Scotland）建立了一套与生物地层学（biostratigraphy）相符的修正后岩浆年代学框架。研究表明，加尔顿山火山岩组（Garleton Hills Volcanic Formation）的形成年代早于亚瑟王座火山岩组（Arthur’s Seat Volcanic Formation）；而克莱德高原（Clyde Plateau）火山岩组与亚瑟王座火山岩组存在部分同期性，这要求对现有地层学体系进行小幅调整。