EAGER: Collaborative Research: Testing the marine carbonate recycling hypothesis

GSTDTAP

项目编号	1747706
	EAGER: Collaborative Research: Testing the marine carbonate recycling hypothesis
	Fangzhen Teng
主持机构	University of Washington
项目开始年	2017
	2017-08-01
项目结束日期	2018-07-31
资助机构	US-NSF
项目类别	Standard Grant
项目经费	49636(USD)
国家	美国
语种	英语
英文摘要	This EArly-concept Grant for Exploratory Research (EAGER) project will test if it is possible to trace geochemically the inclusion of ancient marine carbonates, a common type of sedimentary rock formed in the ocean floor, in volcanic rocks currently erupting in oceanic islands such as Hawaii, Saint Helena and the Cook-Australs. The confirmation of such a crustal recycling process would have a number of significant implications that would advance the field of Earth Sciences. Marine carbonates have a distinctively high content of the radioactive parent U (Uranium), which decays to radiogenic daughter Pb (Lead) isotopes. This project will test this hypothesis using a new combination of geochemical proxies. Recycling of surface sediments via subduction zones into the source of oceanic volcanic rocks has been documented before. The project, however, will try to explore if variations of the stable isotopes of Ca (Calcium) and Mg (Magnesium) could be a good way of tracking this process for subducted carbonates. Finally, it would also help us better constrain the various chemical components in the Earth's mantle and further elucidate the evolution of our planet over time. These results will be accessible and disseminated through presentations in scientific meetings and publications in scientific journals. The unusually radiogenic Pb isotopic ratios of many, if not all, oceanic basalts have generated three major problems, or so-called Pb paradoxes, regarding their mantle sources. These sources must be characterized by 1) long time-integrated high U/Pb, 2) long time-integrated low Th/U and 3) constant Ce/Pb and Nb/U. Although some of the currently proposed solutions to individual Pb paradoxes are highly satisfactory, they are generally independent and at odds with each other. The Pb paradoxes, however, are inter-related and constitute a system of equations that should be solved all together, as the solution to each paradox must also be able explain the other paradoxes. This study hopes to test a hypothesis that recycled marine carbonates, with their high U/Pb and U/Th ratios, can flux-melt the subducted oceanic slab to produce some oceanic basalts. Melts containing mixtures of enriched and depleted mantle components (i.e., between recycled crust and the proposed FOZO and/or DMM mantle components) can generate the radiogenic Pb isotopic ratios and concomitant Pb paradoxes in oceanic basalts. This pilot project will verify the proposed marine carbonate recycling hypothesis through the analysis of a select set of extreme oceanic basalts using coupled Ca and Mg isotopic analysis combined with conventional geochemical methods. The results will have the potential to transform our understanding of mantle geodynamics including the formation of ocean island basalts, recycling of crustal materials, mantle convection, and history and evolution of the composition of the mantle.
文献类型	项目
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/71333
专题	环境与发展全球科技态势
推荐引用方式 GB/T 7714	Fangzhen Teng.EAGER: Collaborative Research: Testing the marine carbonate recycling hypothesis.2017.