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，PIs将测量来自东南印度海岭（SEIR）玄武岩玻璃中的176Hf/177Hf和238u -230 - 226ra - 232th活动，以测试在洋脊岩浆活动期间，熔融深度和速率如何控制下地幔区域非均质性采样。有了这些新数据，应该有可能整理出地幔源矿物学上的差异，熔融的深度和程度，以及源成分。之所以选择SEIR进行研究，是因为在没有大的变换偏移量和附近的海洋岛屿热点的情况下，SEIR在恒定的完全扩散速率（70-75 mm/y）下发生了许多系统变化：(a)轴向深度向东增加（2300至5000 m），并且从轴向高到轴向谷的形态转变；(b)有证据表明，熔体产生速率和地壳厚度沿轴向东减小；(c)这一背景下的熔岩记录了温度和地幔成分的系统变化。它也是以前许多玄武岩玻璃岩石学和同位素分析的主题。PIs将寻找并利用230Th/232Th， 230Th/238U, Th/U, 226Ra/230Th， Ba/Th和176Hf/177Hf与这些物理和地球化学变化的相关性来验证两个基本假设：1)脊深以恒定扩展速率的区域增加主要由深度和熔化速率控制。2)印度洋浅层软流圈中存在石榴石辉石岩，形成了独特的Pb-Sr-Nd同位素特征。

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.