Collaborative Research: Hf-Isotopes as Tracers of Highly Depleted Oceanic Mantle

大洋中脊火山活动是地球上规模最大、最重要的化学分异过程之一。 岩浆是由地幔的选择性熔化产生的，它将一些元素和元素比例带到地球表面，而将其他元素作为残留物留在地幔中。 在迄今为止研究的所有潜在的地球化学示踪剂中，铪（Hf）和钕（Nd）似乎是最强大的，不仅有助于我们了解地幔的化学演化，而且有助于我们了解熔融分离和洋中脊火山作用的年龄和过程。 这项研究将使用来自各大洋中脊的深海橄榄岩样本，重点是最近发现的北极超慢速扩张加克尔脊的样本，那里的地幔岩露出海底。 它将侧重于确定地幔源的比例，这些地幔源融化形成了海底喷发的绝大多数火山岩。 为了做出这一确定，将测量微量元素以及Hf和Nd同位素，其中Hf同位素阐明熔融过程，而Nd提供年龄限制。 这项工作补充，但不重叠，Gakkel深海橄榄岩的地球化学研究。 这项工作的更广泛影响包括对学生进行最先进的地球化学分析技术培训，并让高中学生及其教师参与研究。 它还将涉及实验室及其活动的高中参与者。

Volcanic activity on mid-ocean ridges constitutes one of the largest scale and most important chemical differentiation processes on earth. Magmas, created from the selective melting of Earth's mantle, bring some elements and elemental ratios to Earth's surface and leave others behind as residues in Earth's mantle. Of all the potential geochemical tracers examined to date, Hafnium (Hf) and Neodymium (Nd) appear to be the most powerful in helping us understand not only the chemical evolution of the mantle but also the ages and process of melt segregation and mid-ocean ridge volcanism. This research will use samples of abyssal peridotite from various mid-ocean ridges, emphasizing samples from the recently discovered ultra-slow spreading Gakkel Ridge in the Arctic, where mantle rocks outcrop on the seafloor. It will focus on determining the fraction of the mantle source that melts to form the vast majority of volcanic rocks erupted on the seafloor. To make this determination, trace elements and Hf and Nd isotopes will be measured, with the Hf isotopes illuminating the melting process and Nd providing age constraints. This work complements, but does not overlap with, a geochemical study of Gakkel abyssal peridotites. Broader impacts of the work include student training in state-of-the art geochemical analytical techniques and engaging high school students and their teachers in the research. It will also involve the high school participants in the laboratory and its activities.