How anomalous is the Marion Rise asthenosphere?

大洋中脊火山是从地球内部到地表的最大元素通量，也是大气中碳的重要贡献者。这种通量的大小被认为是由温度控制的，高温导致熔体产量和岩浆作用的增加，以及浅脊。然而，地幔中的成分差异也可能影响熔体的产生，但这一点尚未得到令人信服的证明。马里昂隆起的反常之处在于，尽管隆升深度较浅，但熔体产生量很低。这可能是因为地幔的成分比“正常”的山脊更缺乏熔体成分。这项研究将通过来自海底的玄武岩和地幔岩石的化学成分来研究马里昂隆起地幔是否经历了古老的熔融亏损，从而研究成分对海脊深度和熔体产生的影响。该项目与德国、意大利和芬兰的实验室的研究人员合作，为早期职业科学家提供研究培训和指导机会。研究人员将通过使用最近两次前往马里恩隆起的邮轮收集的样本以及之前邮轮的样本进行调查，以确定西南印度洋海脊东部的印度洋地幔的性质。SWIR的东部包括马里昂隆起，该隆起的轴向深度具有异常薄的地壳，这肯定与其下方地幔的异常地球化学特征有关。这一提议是为了确定这一异常地幔的性质和范围，从而确定马里昂隆起的原因。印度洋洋中脊玄武岩(MORB)与大西洋和太平洋中脊玄武岩(MORB)的同位素组成不同。铅同位素(207Pb/204Pb)的差异表明，这种差异是在地球历史的早期产生的。深海橄榄岩的模式年龄测定将进一步确定不同洋盆的软流圈是否具有不同的年龄。最近两次前往马里昂隆起的邮轮带回了解决上述问题的样本，以及最近在SWIR上更东边的法国探险队获得的样本允许对现有假设进行新的洞察和检验。这项工作集中在深海橄榄岩和相关玄武岩的地球化学分析上，并在地球物理限制的背景下解释这些数据。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Mid-ocean ridge volcanism is the largest element flux from the Earth’s interior to the surface and is an important contributor of carbon to the atmosphere. The magnitude of this flux is assumed to be controlled by temperature, with high temperatures causing increased melt production and magmatism, and shallow ridges. However, compositional differences in the mantle can potentially also influence melt production, but this has not been convincingly shown yet. The Marion Rise is anomalous in that melt production is low although the Rise depth is shallow. This can potentially be explained by a mantle composition that is more depleted in melt components than “normal” ridges. This research will investigate through the chemistry of the basalts and the mantle rocks from the seafloor if the Marion Rise mantle has experienced an ancient melt depletion and thus the effect of composition on ridge depth and melt production. This project is in collaboration with researchers at laboratories in Germany, Italy, and Finland and supports research training and mentoring opportunities for early career scientists.Researchers will investigate, through use of samples collected with two recent cruises to the Marion Rise as well as samples from previous cruises, to determine the nature of the Indian Ocean mantle at the eastern part of the South West Indian Ridge (SWIR). The eastern part of the SWIR includes the Marion Rise, which has anomalously thin crust for its axial depth that must be related to anomalous geochemical characteristics of the mantle beneath. This proposal is to determine the nature and extent of this anomalous mantle and thereby the cause of the Marion Rise. The Indian Ocean mid-ocean ridge basalts (MORB) differ in isotopic composition from Atlantic and Pacific MORB. The differences in Pb-isotopes (207Pb/204Pb) indicates that this difference is created early in Earth’s history. Model age determinations of the abyssal peridotites will further determine if the asthenosphere of the different ocean basins has different ages. Two recent cruises to the Marion Rise, brought back samples that address the above questions, as well as the recent availability of the samples from French expeditions further east on the SWIR allows for new insights and testing of existing hypotheses. The effort is concentrated on geochemical analyses of abyssal peridotites and associated basalts and interpreting these data in the context of geophysical constraints.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.