The Origin and Survival of Chemical Heterogeneities in the Earth&#39;s Mantle

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项目编号	1754186
	The Origin and Survival of Chemical Heterogeneities in the Earth's Mantle
	Igor Puchtel
主持机构	University of Maryland College Park
项目开始年	2018
	2018-06-01
项目结束日期	2021-05-31
资助机构	US-NSF
项目类别	Continuing grant
项目经费	103371(USD)
国家	美国
语种	英语
英文摘要	Accurately determining the Earth's chemical composition has been and remains one of the most fundamental challenges in Earth sciences. It has important implications not only for the long-debated question of how terrestrial planets form and evolve, but also for our understanding of the consequences of the ongoing processes on our planet. The Earth's mantle is the largest of all terrestrial reservoirs; it constitutes 83% of the Earth's volume and extends to 2900 km below its surface. The chemically and isotopically heterogeneous nature of this vast reservoir has long been established as a result of previous pioneering studies of the terrestrial rock record. Some of the heterogeneities have been argued to be primordial, reflecting initial planetary accretion/differentiation and magma ocean crystallization processes. Others were likely created as a result of a protracted, violent terrestrial accretion history, or to have resulted from later processes associated with the dynamic regime of the planet, especially crustal recycling. Despite the long-term, concerted research effort, the nature, origin, scale, and longevity of early mantle chemical and isotope heterogeneities are still not well understood. This project is aimed at filling the existing gaps in our understanding of these fundamental issues by applying a carefully chosen, comprehensive set of state-of-the-art modern analytical tools to a collection of unique 3.5 to 2.7 billion year old komatiite samples from western Australia. These samples are especially advantageous to study processes that occurred within the first 2 billion years of Earth history, before the crust formation and recycling processes, similar to those occurring today, took over as the main driver of chemical differentiation of the Earth's interior and erased all the evidence of Earth's youthful exuberance. This research effort is aimed at constraining the origin and temporal evolution of chemical and isotopic heterogeneities in the early Earth's mantle. The primary goals are to: (1) assess the magnitude of chemical/isotopic heterogeneities recorded in the mantle sources of 3.52 to 2.69 Ga komatiites from Western Australia, (2) establish which of such fundamental early Earth processes, as late accretion, magma ocean crystallization, primordial crust extraction, and crustal recycling, were responsible for creating these heterogeneities, and (3) integrate the new short- and long-lived isotopic and trace element abundance data for these rocks with the existing data for Archean komatiite systems into models for the origin and temporal evolution of global chemical/isotope heterogeneities in the Earth's mantle. In order to achieve these goals, the team will study isotope systematics, and lithophile trace element and highly siderophile element abundances in diamond drill core samples of the 3.5 to 2.7 Ga komatiite systems using the thermal ionization mass-spectrometry and inductively-coupled plasma mass-spectrometry techniques. These komatiitic systems are from the ancient Pilbara and Yilgarn Cratons of Western Australia, and their formation spans a time interval of ca. 800 Ma of Earth history. These localities were selected in order to cover the greatest possible extent of temporal variations within spatially related Archean cratons, because the selected samples are well preserved by Archean standards and are expected to provide a window into the early terrestrial mantle, and because limited existing data indicate that these komatiite systems record very early mantle differentiation processes. The results are expected to allow us to assess the possible effects of differentiation of a primordial magma ocean, late accretion, and crustal recycling, as well as permit new constraints to be placed on the mixing times of the mantle during the first half of Earth's history. 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.
文献类型	项目
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/72658
专题	环境与发展全球科技态势
推荐引用方式 GB/T 7714	Igor Puchtel.The Origin and Survival of Chemical Heterogeneities in the Earth's Mantle.2018.