Tracing mantle components and the effect of subduction processes beneath the northern Antarctic Peninsula

Understanding subduction processes is critical in assessing the long-term evolution of the upper mantle and continental crust. We present new geochemical data on glassy submarine lavas from the Bransfield Strait, the Phoenix and West Scotia ridges, and previously unpublished data of marine sediments from atop the Phoenix Plate. We combined new and published geochemical data from across the northern sector of the Antarctic Peninsula to unravel both large-scale mantle composition and flow across the region. The geochemistry of Phoenix and West Scotia Ridge basalts supports the hypothesis that both ridges are underlain by Pacific MORB mantle, brought into the region through the eastward expansion of the Scotia Plate. Our modeling suggests the presence of a more depleted Phoenix MORB mantle beneath the South Shetland Islands modified by the addition of 3 % subduction component with a fluid/sediment ratio ranging from 0.18 to 4. The increase in fluid/sediment ratios in the South Shetland Island lavas corresponds to a spatiotemporal progression of volcanism from the southwest (40–140 Ma) to the northeast (30–60 Ma). Finally, we have identified a set of lavas with unique trace element and isotope compositions typical of alkaline volcanism found across other parts of the Antarctic Peninsula. Surprisingly, we find occurrences of these lavas on both sides of the South Shetland Trench, suggesting the presence of a distinct enriched source in the upper mantle throughout the region.

深入理解俯冲过程对于评估上地幔和大陆地壳的长期演化至关重要。本研究呈现了来自布兰斯菲尔德海峡、凤凰山和西斯科特群岛脊的玻璃状海底熔岩的新地球化学数据，以及来自凤凰板块顶部尚未公开发表的海洋沉积物数据。我们将南极半岛北部的新旧地球化学数据相结合，以揭示该区域的大规模地幔成分和流动。凤凰山和西斯科特群岛脊玄武岩的地球化学特征支持了以下假说：两个脊均由太平洋MORB地幔支撑，该地幔通过斯科特板块的向东扩张进入该区域。我们的模型表明，在南设得兰群岛下方存在一个更加贫化的凤凰MORB地幔，并受到3%的俯冲成分的影响，其流体/沉积物比值介于0.18至4之间。南设得兰群岛熔岩中流体/沉积物比值的增加与火山活动的时空演化过程相对应，从西南部（40-140百万年）至东北部（30-60百万年）。最后，我们识别出一系列具有独特的微量元素和同位素组成的熔岩，这些熔岩典型地代表了其他南极半岛地区的碱性火山活动。令人惊讶的是，我们发现这些熔岩出现在南设得兰海沟两侧，这表明整个区域上地幔中存在一个独特的富集源。