A Geochemical Investigation of the Dynamics of Mantle Melting within the Reunion Plume

Pietruszka/Haurizka-0003359洋中脊和洋岛火山地球化学研究的一个基本目标是推断玄武岩熔体的生成和迁移过程。 年轻熔岩的铀系同位素丰度（例如，226 Ra和230 Th）特别适合于这一目的，因为226 Ra和230 Th的半衰期（分别为1600年和~75 kyr）被认为与岩浆过程的时间尺度相似。 铀系同位素的这一独特特征为研究岩浆成因的性质和时间提供了可能性。 该项目的目标是调查的地幔熔融的动力学内留尼汪羽使用的226 Ra-230 Th-238 U不平衡的一个详细的时间序列的历史熔岩从Piton de la Fournaise火山（1931-1998年）。 这座火山非常适合进行地幔熔融的U系列同位素研究，因为（1）其历史熔岩显示出不相容微量元素比率的系统性时间波动，这被认为是部分熔融程度快速变化的结果，（2）已知它具有均匀的地幔源区。 因此，我们希望能够隔离地幔熔融的U系列同位素签名在Piton de la Fournaise源的异质性，这是困难的，在大多数洋中脊和洋岛火山的复杂影响。 我们将评估一系列融化模型与此数据集。 这些模型的结果将被用来探索地球化学和地球物理参数之间的基本联系的地幔熔融的留尼汪羽，如熔体分数，地幔源区的肥力，地幔熔融和上涌的速度，熔体区的孔隙度，和熔体的产生和运输的机制。 此外，我们将比较我们的新数据和模型结果的Piton de la Fournaise与以前的U系列同位素和其他地球化学工作从基拉韦厄和冒纳罗亚测试的共同假设，夏威夷火山作为其他海洋岛屿火山的模型。

Pietruszka/HauriEAR-0003359A fundamental goal of geochemical research at mid-ocean ridge and ocean-island volcanoes is to infer the process of basaltic melt generation and transport. The U-series isotope abundances of young lavas (e.g., 226Ra and 230Th) are particularly well suited for this purpose because the half-lives of 226Ra and 230Th (1600 yr and ~75 kyr, respectively) are thought to be similar to the time scale of magmatic processes. This unique feature of U-series isotopes offers the potential to study both the nature and timing of magma genesis. The goal of this project is to investigate the dynamics of mantle melting within the Reunion plume using the 226Ra-230Th-238U disequilibria of a detailed time series of historical lavas from Piton de la Fournaise Volcano (1931-1998). This volcano is ideally suited for a U-series isotope study of mantle melting because (1) its historical lavas display systematic temporal fluctuations of incompatible trace element ratios that are thought to result from rapid changes in the degree of partial melting and (2) it is known to tap a homogeneous mantle source region. Thus, we expect to be able to isolate the U-series isotope signatures of mantle melting at Piton de la Fournaise from the complicated effects of source heterogeneity, which is difficult at most mid-ocean ridge and ocean-island volcanoes. We will evaluate a range of melting models with this data set. These model results will be used to explore the basic links between the geochemical and geophysical parameters of mantle melting within the Reunion plume, such as the melt fraction, the fertility of the mantle source region, the rates of mantle melting and upwelling, the melt-zone porosity, and the mechanism of melt generation and transport. Additionally, we will compare our new data and model results for Piton de la Fournaise with previous U-series isotope and other geochemical work from Kilauea and Mauna Loa to test the common assumption that Hawaiian volcanoes serve as models for other ocean-island volcanoes.