Japan Geoscience Union Meeting 2018

Presentation information

[EE] Oral

S (Solid Earth Sciences) » S-IT Science of the Earth's Interior & Tectonophysics

[S-IT22] Interaction and Coevolution of the Core and Mantle in the Earth and Planets

Thu. May 24, 2018 9:00 AM - 10:30 AM International Conference Room (IC) (2F International Conference Hall, Makuhari Messe)

convener:Tsuyoshi Iizuka(University of Tokyo), Hidetoshi Shibuya(Department of Earth and Environmental Sciences, Faculty of Advanced Science and Technology, Kumamoto University), Taku Tsuchiya(愛媛大学地球深部ダイナミクス研究センター, 共同), Kenji Ohta(Department of Earth and Planetary Sciences, Tokyo Institute of Technology), Chairperson:Dekura Haruhiko, Yamazaki Daisuke

9:00 AM - 9:15 AM

[SIT22-31] Ediacaran ultra-low geomagnetic field intensity: Evidence for a young inner core

★Invited Papers

*John Anthony Tarduno1, Richard K. Bono1, Rory D. Cottrell1, Francis Nimmo2 (1.University of Rochester, 2.University of California Santa Cruz)

Keywords:inner core, geodynamo, paleomagnetism, paleointensity, Ediacaran, thermal conductivity

The age of Earth’s solid inner core represents a fundamental question in the evolution of the planet. Proposed ages for the onset of inner core nucleation (ICN) span some 2 billion years, from 500 Ma to older than 2500 Ma. Time-averaged paleomagnetic data are required to gain insight into the ancient geodynamo. Previously there have been no time-averaged paleointensity data corresponding to the youngest proposed ages of ICN. Young ICN onset ages imply a relatively high value for core thermal conductivity. Here, we discuss new paleointensity data from single silicate crystals, hosting magnetic inclusions, that fill this data gap. Plagioclase feldspar (Bono et al., 2017) and clinopyroxene data from an Ediacaran-age (ca. 565 Ma) layered mafic intrusion (Quebec, Canada) record extraordinarily low paleofield strengths, lower than any other known time-averaged value and more than 10 times smaller than the strength of the present-day field. This ultra-low field is accompanied by evidence for a hyper-reversal frequency and non-dipolar fields. We interpret these paleomagnetic observations as recording the near collapse of the geodynamo, coincident with ICN, approximately 565 million-years ago.