Emplacement history of volcaniclastic turbidites around the central Azores volcanic islands: Frequencies of slope landslides and eruptions
Emplacement history of volcaniclastic turbidites around the central Azores volcanic islands: Frequencies of slope landslides and eruptions
复制标题
DOI：
10.1130/ges02570.1
复制
发表时间：
2023-03
期刊：
影响因子：
2.5
通讯作者：
Yu-Chun Chang;N. Mitchell;J. Schindlbeck‐Belo;T. Hansteen;A. Freundt;Christian Hübscher;R. Quartau
中科院分区：
文献类型：
--
作者：
Yu-Chun Chang;N. Mitchell;J. Schindlbeck‐Belo;T. Hansteen;A. Freundt;Christian Hübscher;R. Quartau
火山岛通过爆炸性喷发、熔岩排放、大陆架上的生物生产和斜坡的破坏等过程向周围的海洋输出碎屑物质。这就提出了一个问题，即是否可以在近海发现地质事件（特别是火山爆发和山崩）并确定其日期，以及是否可以利用沉积物岩心揭示任何关系（例如与气候变化的关系）。火山活跃的亚速尔群岛中部岛屿（法亚尔、皮科、圣若热和特塞拉）及其邻近的海底盆地是进行此类分析的潜在良好候选者。在这里，四个重力岩心收集的岛屿之间的年代地层构造的基础上，12个放射性碳日期和两个日期来自地球化学相关的主要volcanicerebridites浊积岩与熔结凝灰岩的Faial和Terceira群岛。从半远洋层段建立水深模型，以估计个别浊流日期。浊积岩的沉积是通过将盆地面积乘以层厚来模拟的，考虑到各种浊积岩变薄速率和方向。滑坡产生的浊积岩的体积仅与其相邻的上斜坡海底滑坡谷的最大体积相当;因此，岩芯中的此类浊积岩可能来自这些最大的滑坡。人们发现，来自山体滑坡和火山碎屑密度流的浊积岩之间的就位间隔大多为几千年。滑坡产生的浊流和半远洋沉积速率的频率都是最高的，在过去的8千年。与前一时期相比，据解释，高的半远洋沉积速率与海平面上升有关，从而使更多的大陆架生物产生和海岸侵蚀释放出更多的颗粒。海底滑坡的频率同时增加，也可能与来自岛屿的沉积物供应增加有关，导致不稳定沉积物在海底斜坡上更快地堆积。值得注意的是，火山碎屑密度流起源的浊积岩的就位频率并不意味着在其他地方发现的全新世喷发频率降低。
Volcanic islands export clastic material to their surrounding oceans by explosive eruptions, lava emissions, biogenic production on their shelves, and failure of their slopes, amongst other processes. This raises the question of whether geological events (in particular, eruptions and landslides) can be detected offshore and dated, and whether any relationships (for example, with climate changes) can be revealed using sediment cores. The volcanically active central Azorean islands (Faial, Pico, São Jorge, and Terceira), with their neighboring submarine basins, are potentially good candidates for such an analysis. Here, chronostratigraphies of four gravity cores collected amongst the islands are constructed based on twelve radiocarbon dates and two dates derived by geochemically correlating primary volcaniclastic turbidites with ignimbrites on Faial and Terceira Islands. Age-depth models are built from the hemipelagic intervals to estimate individual turbidite dates. Volumes of turbidites are modeled by multiplying basin areas with bed thickness, allowing for various turbidite thinning rates and directions. The volumes of landslide-generated turbidites are only comparable with the largest volumes of their adjacent upper-slope submarine landslide valleys; therefore, such turbidites in the cores likely derive from these largest landslides. Emplacement intervals between turbidites originating from both landslides and pyroclastic density currents are found to be mostly a few thousand years. Frequencies of landslide-generated turbidites and hemipelagic sedimentation rates were both highest in the past 8 k.y. compared to preceding periods up to 50 k.y. High hemipelagic sedimentation rates are interpreted to be related to sea-level rise, allowing more shelf bioproduction and release of particles by coastal erosion. The coincident increased frequencies of submarine landslides may also be associated with the increased sediment supply from the islands, resulting in a more rapid build-up of unstable sediments on submarine slopes. Notably, the emplacement frequencies of turbidites of pyroclastic density current origins do not suggest the decreased eruption frequency toward the Holocene that has been found elsewhere.