Collaborative Research: A Uranium-Series and Hafnium Isotope Investigation of the Link Between Partial Melting and Mantle Heterogeneity Beneath the Southeast Indian Ridge

根据该合同，PI将测量东南印度洋脊（SEIR）玄武岩玻璃中的176 Hf/177 Hf和238 U-230 Th-226 Ra-232 Th活动，以测试熔融的深度和速率如何控制洋脊岩浆活动期间下伏地幔中区域异质性的采样。有了这些新的数据，应该有可能找出地幔源的矿物学差异，熔融的深度和程度，以及源成分。选择SEIR进行研究，因为沿着它，在恒定的全扩展速率下发生许多系统变化（70-75毫米/年）和在没有大的转换偏移和附近的海洋岛屿热点的情况下：（a）轴向深度有一个大的向东增加（B）熔体产生速率和地壳厚度沿轴向沿着东减小;（c）来自这一背景的熔岩记录了温度和地幔成分的系统变化。它也是许多玄武岩玻璃的岩石学和同位素分析的主题。PI将搜索并使用230 Th/232 Th、230 Th/238 U、Th/U、226 Ra/230 Th、Ba/Th和176 Hf/177 Hf与这些物理和地球化学变化的相关性来检验两个基本假设：1）在恒定扩张速率下，脊深度的区域性增加主要受熔融深度和速率控制。2)印度洋MORB独特的Pb-Sr-Nd同位素特征是由于浅部软流层中存在石榴辉石岩。

Under this award, the PIs will measure 176Hf/177Hf and 238U-230Th-226Ra-232Th activities in basalt glasses from the Southeast Indian Ridge (SEIR)to test how the depth and rate of melting control the sampling of regional heterogeneity in the underlying mantle during ocean ridge magmatism. With these new data, it should be possible to sort out differences in the mineralogy of the mantle source, the depth and extent of melting, and the source compositions. The SEIR was chosen for the study, because along it a number of systematic variations occur at constant full spreading rate (70-75 mm/y) and in the absence of large transform offsets and nearby ocean island hotspots:(a)there is a large eastward increase in axial depth (2300 to 5000 m) and a morphological transition from axial high to axial valley; (b) there is evidence that melt production rate and crustal thickness decrease eastward along axis; and (c) lavas from this setting record systematic variations in temperature and mantle composition. It has also been the subject of previous petrologic and isotopic analyses of numerous basalt glasses. The PIs will search for and use correlations of 230Th/232Th, 230Th/238U, Th/U, 226Ra/230Th, Ba/Th and 176Hf/177Hf with these physical and geochemical variations to test two fundamental hypotheses:1) A regional increase in ridge depth at constant spreading rate is primarily controlled by the depth and rate of melting. 2) The distinctive Pb-Sr-Nd isotope signature of Indian Ocean MORBs is due to the presence of garnet pyroxenite in the shallow asthenosphere.