High resolution volcanology and geochemistry of mid ocean ridge segments flanking the 9°40'S melt anomaly and the Ascension hot spot

洋中脊火山作用在全球范围内研究熔体生成和地幔过程中起着关键作用。SPP MARSouth地区特别适合研究不同地幔源的高分辨率影响，因为这里既有肥沃的地幔（9°40'S熔融异常），也有疑似热点火山活动（阿森松岛），同时还有典型的枯竭MORB。在项目第一阶段进行的同位素和高精度HFSE分析结果表明，需要对以前的地球动力学模型进行修订，特别是根据新的Hf-Nd同位素数据。此外，我们关于阿森松岛海底和陆上火山活动的新数据表明，我们发现了与上升的地幔柱无关的独特地幔源。基于这些有希望的结果，我们将在项目的第二阶段重点研究喷发离子尺度的火山学和地球化学调查。主要目的是表征地幔非均质性对喷发规模的影响，并揭示阿森松岛的起源。第二个重点将是在MORB熔化过程中HFSE（包括W）的行为。第一个结果表明，W-Nb-Ta丰度几乎没有分馏，这与实验预测有明显的对比。基于扩展的数据集，我们将通过痕量元素建模来解决这个难题。

Mid-ocean ridge volcanism plays a key role in the investigation of melt generation and mantle processes on a global scale. The SPP MARSouth area is particularly suited to investigate the influences of different mantle sources at high resolution, as fertile mantle (9°40'S melt anomaly) and alleged hot spot volcanism (Ascension Island) are both present together with typical depleted MORB. Results from isotope and high-precision HFSE analyses, performed during the first phase of the project, show that previous geodynamic models need to be revised, in particular in the light of new Hf-Nd isotope data. Moreover, our new data for submarine and subaerial volcanism on Ascension demonstrate that distinctive mantle source were tapped that are not related to a rising mantle plume. Based on these promising results we will focus our research during the second phase of the project on erupt ion-scale volcanological and geochemical investigations. The principal aims are to characterize eruption-scale effects of mantle heterogeneities and to unravel the origin of Ascension Island. A second focus will be on the behavior of HFSE (including W) during MORB melting. First result indicate that W-Nb-Ta abundances are little fractionated, which is in marked contrast to experimental predictions. Based on an expanded dataset, we will address this conundrum by trace element modeling.