Japan Geoscience Union Meeting 2018

Presentation information

[JJ] Oral

B (Biogeosciences) » B-CG Complex & General

[B-CG09] Decoding the history of Earth: From Hadean to the present

Mon. May 21, 2018 3:30 PM - 5:00 PM Convention Hall B (CH-B) (2F International Conference Hall, Makuhari Messe)

convener:Tsuyoshi Komiya(Department of Earth Science & Astronomy Graduate School of Arts and Sciences The University of Tokyo), Yasuhiro Kato(Department of Systems Innovation, Graduate School of Engineering, University of Tokyo), Katsuhiko Suzuki(国立研究開発法人海洋研究開発機構・海底資源研究開発センター), Chairperson:Komiya Tsuyoshi

4:00 PM - 4:15 PM

[BCG09-03] How to make continents from oceanic arcs

★Invited Papers

*Yoshihiko Tamura1 (1.R & D Center for Ocean Drilling Science, Japan Agency for Maine-Earth Science and Technology)

Keywords:oceanic arc, andesite, plate tectonics

Where the crust is thin, melting occurs at relatively low pressures in the mantle wedge producing andesitic magmas. Where the crust is thick, melting pressures are higher and only basaltic magmas tend to be produced (Tamura et al., 2016, Scientific Reports). Many different models of continental growth rate have been proposed. The implication of this hypothesis is that the rate of continental crust accumulation, which is andesitic in composition, would have been greatest soon after subduction initiated on Earth, when most crust was thin.
In a hotter early Earth, however, the extents of melting were higher in mantle plumes, beneath spreading ridges, and in arcs. If so, the crust in such settings was generally thicker, rather than thinner, compared to the present day. Another implication of this hypothesis is that the production of continental crust might have been impossible in the early Earth if the oceanic crust had been thick. Why are the oldest rocks 4 Ga? Where had the rocks of Hadean gone? We haven’t had continental crust before 4 billion years because of the thick crust, thus the older rocks had returned to mantle by plate tectonics.