Collab Study: Tectonomagmatic and Event-Stratigraphic sig- nificant of Lower Paleozoic K-bentonites in the Iapetus Region of North America and Northwestern Europe

PIS将调查巴尔托斯卡迪亚中、上奥陶统地层中蚀变火山灰层(K-膨润土)的构造背景、岩浆成因和地层意义，并将这些数据与北美的类似数据进行比较。初步研究有力地表明，这些位于青金石两侧的钾膨润土层具有共同的物源和共同的构造背景。如果这一迹象被证明是正确的，这些分布最广泛的层位将对奥陶纪具有深远的事件地层学意义，我们对劳伦西亚和波罗的海板块在塔肯造山作用中的位置的理解将得到实质性的改善。同样，整个巴尔托斯卡纳和英国志留纪K-膨润土的丰富表明，从Llandovery到Ludlow时间正在进行板块边缘火山活动。PIS将从爱沙尼亚、瑞典和挪威的岩心和露头收集最广泛的岩层样本。他们将增加关于这些岩层生物地层位置的现有信息，并使用大量样品和选定斑晶的化学指纹来与北美岩层进行准确的对比。这些关系将与传统生物地层学提出的跨大西洋K-膨润土地层关系和利用牙形刺进行的图形对比进行比较。我们还将获得来自黑云母的高分辨率Ar年龄谱和从生物地层良好约束的K-膨润土分离的锆石的U-Pb年龄，这将增加奥陶纪时间尺度的关键年龄。微量元素数据将绘制在判别图上，以解释这些层的构造和岩浆背景。

PIs will investigate the tectonic setting, magmatic origin and stratigraphic significance of altered volcanic ash beds (K- bentonites) in the Middle and Upper Ordovician strata of Baltoscandia and to compare these data with similar data from North America. Preliminary studies strongly suggest these K- bentonite beds on both sides of lapetus had a common source and a common tectonic setting. If this indication proves correct, the most widespread of these beds will have profound event- stratigraphic implications for the Ordovician, and our understanding of Laurentia and Baltica plate positions during the Taconian orogeny will be substantially improved. Similarly, the abundance of Silurian K-bentonites throughout Baltoscandia and the UK indicates ongoing plate-margin volcanism from Llandovery through Ludlow time. PIs will collect samples of the most extensive beds from cores and outcrops in Estonia, Sweden and Norway. They will add to existing information on the biostratigraphic position of these beds and use chemical fingerprinting of both bulk samples and selected phenocrysts to make accurate correlations with North American beds. These will be compared with trans-Atlantic stratigraphic relations of K- bentonites suggested by traditional biostratigraphy and by graphic correlation using conodonts. We will also obtain high- resolution Ar age spectra and U-Pb dates from biotite and zircon separates from biostratigraphically well-constrained K-bentonites that will add key ages to the Ordovician time scale. Trace element data will be plotted on discrimination diagrams to interpret the tectonic and magmatic settings of these beds.