Mantle Petrology and Tectonics at the Gakkel Ridge

摘要Dickson-0327591首席研究员将研究来自加克尔海岭的北冰洋深海橄榄岩的岩石学和构造背景，加克尔海岭是一个以前无法进入的海底扩张地质端元。它提供了一个了解地球内部的窗口，这对地球化学制图至关重要。 由于超低速的扩张速率，加克尔在构造上与其他海脊不同，沿其1800公里的长度沿着没有转换断层，地壳薄而变化大，地幔暴露丰富。 北极大洋中脊考察（AMORE）是对这一海脊进行取样的第一次尝试，这次考察取得了出乎意料的成功。 有200次成功的疏浚。从3degreesE到87 degreesE，海岭被证明是由由稀疏的岩浆段连接的局部火山中心组成，在36个裂谷壁和底部位置挖掘出橄榄岩。 首席研究员将分析橄榄岩模态矿物学以及约150-200个样品的微量和主要元素。 他还将利用挖掘结果和新的高分辨率Seabeam数据研究构造背景和定位。这一研究将制约橄榄岩和玄武岩之间的关系，地幔熔融在其下限的性质，和北极地幔的组成。这将是一个评估地幔熔融模型和大洋中脊玄武岩成分控制因素的独特机会。因为橄榄岩代表最低的熔融温度洋脊，他们也可以用来直接约束模型的主要成分和变化的MORB source.Broader影响：首席研究员将继续利用各种外联工作，以宣传探险和北极研究的重要性，以广大公众和科学界。 他已经在科学会议上做了一些演讲，并举行了记者组采访。 他向一些著名的国会工作人员和参议员作了介绍。对深海橄榄岩的三项综合研究表明，这些样品的历史比这一提议所暗示的要复杂得多。 在深海橄榄岩中发现了再受精作用、熔体浸渍、高压熔体-岩石相互作用、“过剩橄榄石”等。 这些过程也被广泛认可的捕虏体和P2P型橄榄岩，但PI的建议，希望解释这些GR数据在真空中。 这一领域正在迅速发展，PI需要成为当前的。在这一建议中，PI指出，大约2/3的深海橄榄岩“像简单的熔融残留物”。 这一说法可能与一些研究相矛盾，这些研究表明，大多数深海橄榄岩富含Na和Ti，高于基于分离熔融的预期值（Elthon，JGR，1992; Asimow，EPSL，1999; Baker和Beckett，EPSL，1999）。 这可能是因为大多数深海橄榄岩并不特别像简单的熔融残留物，这一提议并不意味着PI计划考虑这个问题。 此外，在国际矿物学会关于深海橄榄岩矿物成分和模式数据的简编（Dick，1989年;《海洋盆地的岩浆作用》）中，作者在脚注中指出，矿物的镁和铁含量可能不准确。 最后，相对于其他工作者的研究，PI发表的橄榄石数据中的镍似乎系统性地较低（在Dick，1989年，大多数样品中的橄榄石被列为NiO在0.22和0.28重量%之间，这个范围相对于大多数其他工作者发表的深海橄榄岩的结果肯定较低）。 我有点担心PI将样品发送给麻省理工学院的其他人进行分析，而不是亲自监督工作。目标3提出了Gakkel山脊允许人们远离断裂带观察AP的情况，因此我们应该能够测试岩浆段中有更多纯橄榄岩的想法。当然，PI现在已经有了一个关于这个问题的答案的想法，只要看看手工收集的岩石样本。事实上，一个恼人的说法是，有越来越多的数据，大部分未公布，纯橄榄岩是常见的裂谷墙。我不得不怀疑，这些数据中有很多是PI-为什么不披露-为什么这些数据不至少以某种可评估的形式出现，而不是这样的声明。

ABSTRACTDickOPP-0327591The Principal Investigator will study the petrology and tectonic setting of Arctic Ocean abyssal peridotites from the Gakkel Ridge, a previously inaccessible geologic end-member for sea floor spreading. It provides a window into the Earth's interior which critical for geochemical mapping. Due to ultraslow spreading rates, the Gakkel is tectonically distinct from other ridges with no transform faults along its 1800 km length, with thin highly variable crust, and abundant mantle exposures. The Arctic Mid-Ocean Ridge Expedition (AMORE) was the first attempt to sample this ridge and the expedition succeeded beyond all expectations. There were 200 successful dredges. From 3degreesE to 87degreesE, the Ridge proved to consist of local volcanic centers linked by sparsely magmatic segments and peridotites were dredged at 36 rift valley walls and floor locations. The Principal Investigator will analyze peridotite modal mineralogy and trace and major elements of about ~150-200 samples. He will also study the tectonic setting and emplacement using dredge results and the new high-resolution Seabeam data. This research will constrain the relationship between peridotites and basalts, the nature of mantle melting at its lower limit, and the composition of the Arctic mantle. This will be a unique opportunity to assess models for mantle melting and the controls on mid-ocean ridge basalt composition. Because peridotites representing the lowest melting temperatures ocean ridges, they can also be used to direct constrain models for the primary composition and variability of the MORB source.Broader Impacts: The Principal Investigator will continue use various outreach efforts to publicize the expedition and the importance of Arctic research to the general public and scientific community. He has already made a number of presentations at scientific meetings and held press group interviews. He made presentations to a number of prominent congressional staff and senators. There have been three comprehensive studies of abyssal peridotites that show that these samples have much more complicated histories that this proposal implies. Refertilization, melt impregnation, high-pressure melt-rock interactions, "excess olivine" etc. have all been identified in abyssal peridotites. These processes are also widely recognized in xenoliths and massif-type peridotites, but the PI of this proposal wants to interpret these GR data in a vacuum. This field is rapidly advancing and the PI needs to become current.In this proposal the PI states that approximately 2/3 of abyssal peridotites 'are like simple residues of melting'. This statement is perhaps contradicted by studies that show that most abyssal peridotites are enriched in Na and Ti above what is expected based on fractional melting (Elthon, JGR, 1992; Asimow, EPSL 1999; Baker and Beckett, EPSL, 1999). It could be that most abyssal peridotites are not particularly like simple residues of melting, and this proposal doesn't suggest that the PI plans to consider this issue. Moreover, in the PIs compendium of mineral composition and modal data from abyssal peridotites (Dick, 1989; in Magmatism in the Ocean Basins), the Mg and Fe contents of minerals are noted to be potentially inaccurate in a footnote from the author. Finally, it seems that Ni in olivine data published by the PI is perhaps systematically low, relative to studies by other workers (in Dick, 1989, olivine in most samples are listed as having NiO between 0.22 and 0.28 wt% and this range is definitely low relative to results on abyssal peridotites published by most other workers). I am somewhat concerned that the PI sends samples to be analyzed by someone else at MIT, rather than personally overseeing the work.Objective 3 makes the case that the Gakkel ridge allows one to look at AP away from fracture zones-so we should be able to test the idea that there are more dunites within magmatic segments. Surely the PI has an idea about the answer to this right now simply by looking at the rocks collected in hand sample. Indeed, an annoying statement is that there is 'a growing body of data, LARGELY UNPUBLISHED, that dunite is common in rift valley walls.' I have to suspect that much of these data are the PIs-why not published-why aren't the data at least put in some assessable form rather than this statement.