The timescale of accretion and core formation of the Earth inferred from Hf-W isotope systematics

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概要

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• The Hf-W chromometer that was developed recently is a very powerful tool because of high time resolution due to short half life and significant partitioning of Hf into the mantle and W into the core. We have developed a mass conservation equation, which includes three important parameters, mass accretion rate, metal separation rate, and redox reaction rate, and searched for the conditions to satisfy the Hf/W and W isotopic compositions of the present Earths mantle. Although previous work has suggested slow accretion (accretion time >50Myr), it could be shorter by an order of magnitude if the metal separation time or redox reaction rate is longer than -100Myr. The slow metal separation rate with rapid accretion is, however, inconsistent with constraints from thermal evolution and fluid dynamics, and slow redox reaction of oxidized materials is the plausible mechanism.

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著者

• OZAWA Kazuhito

  Department of Earth and Planetary Science, The University of Tokyo

• NAGAHARA Hiroko

  Department of Earth and Planetary Science, The University of Tokyo

• Nagahara Hiroko

  Department Of Earth And Planetary Science The University Of Tokyo

• Ozawa Kazuhito

  Department Of Earth And Planetary Science Graduate School Of Science The University Of Tokyo

関連論文

• Formation and deformation mechanisms of pyroxene-spinel symplectite in an ascending mantle, the Horoman peridotite complex, Japan : An EBSD (electron backscatter diffraction) study
• The timescale of accretion and core formation of the Earth inferred from Hf-W isotope systematics
• Cooperation of upper and lower boundary-layer fractionations in a sheet-like intrusion : Composition and microstructure of the Aosawa dolerite sill in Yamagata Prefecture, northeastern Japan
• Geochemical and Os isotopic characteristics of a fresh harzburgite in the Hayachine-Miyamori ophiolite : Evidence for melting under influx of carbonate-rich silicate melt in an infant arc environment

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