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

团聚地幔柱内地幔熔化动力学的地球化学研究

基本信息

批准号：
0003359
负责人：
Aaron Pietruszka
金额：
$ 5.18万
依托单位：
Carnegie Institution of Washington
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2001
资助国家：
美国
起止时间：
2001-02-15 至 2002-07-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=0003359&HistoricalAwards=false
关键词：
Geochemical Investigation Dynamics Mantle Melting

项目摘要

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.

Pietruszka/HauriEAR-0003359 大洋中脊和洋岛火山地球化学研究的基本目标是推断玄武岩熔体的生成和运输过程。年轻熔岩的 U 系列同位素丰度（例如 226Ra 和 230Th）特别适合此目的，因为 226Ra 和 230Th（分别为 1600 年和 ~75 kyr）的半衰期被认为与时间相似岩浆作用的规模。 U 系列同位素的这一独特特征为研究岩浆生成的性质和时间提供了潜力。该项目的目标是利用 Piton de la Fournaise 火山 (1931-1998) 历史熔岩的详细时间序列的 226Ra-230Th-238U 不平衡来研究留尼旺地幔柱内地幔熔化的动力学。这座火山非常适合对地幔熔化进行 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例的系统时间波动，这被认为是部分熔化程度快速变化造成的；(2)已知可以挖掘均匀的地幔源区。因此，我们期望能够将富尔奈斯峰地幔熔化的U系列同位素特征与源异质性的复杂影响分开，这在大多数洋中脊和洋岛火山中是困难的。我们将使用该数据集评估一系列熔化模型。这些模型结果将用于探索留尼旺地幔柱内地幔熔融的地球化学和地球物理参数之间的基本联系，例如熔融分数、地幔源区的肥力、地幔熔融和上涌的速率、熔融-区域孔隙率以及熔体产生和传输的机制。此外，我们还将比较 Piton de la Fournaise 的新数据和模型结果与之前的 U 系列同位素以及基拉韦厄火山和冒纳罗亚火山的其他地球化学工作，以测试夏威夷火山作为其他海洋岛屿火山模型的普遍假设。