Detection of the unknown ocean impact event using REY-rich deep-sea mud with low sedimentation rate

2017 Fiscal Year Final Research Report

• Project/Area Number: 16K13895
• Research Category: Grant-in-Aid for Challenging Exploratory Research
• Allocation Type: Multi-year Fund
• Research Field: Geology
• Research Institution: Japan Agency for Marine-Earth Science and Technology
• Principal Investigator: NOZAKI Tatsuo 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, グループリーダー代理 (10553068)
• Co-Investigator(Kenkyū-buntansha): 石川 晃 東京大学, 大学院総合文化研究科, 助教 (20524507) ; 佐藤 峰南 千葉工業大学, 次世代海洋資源研究センター, 上席研究員 (20773394)
• Project Period (FY): 2016-04-01 – 2018-03-31
• Keywords: レニウム-オスミウム同位体 / 白金族元素組成 / レアアース泥 / 隕石衝突 / 北西太平洋 / 南鳥島 / 地球化学 / 全岩化学組成

Outline of Final Research Achievements

We conducted the Re-Os isotope analysis by MC-ICP-MS, whole-rock major, trace and PGE analyses by ICP-QMS on piston core samples collected from the Minami-Torishima Island. Based on these geochemical data, an anomalous layer showing the negative Os-isotope excursion as well as enrichment in PGEs was found. Then, we conducted the petrographic observation using a stereoscopic microscope and SEM, leading the discovery of many spherule grains. These spherules include dendritic spinel grains by microscopic observation of the polished section under the reflected light. Although some parts of petrographical study by using an EPMA was not completed, a sedimentary age of this anomalous layer has the age that no large craters have been reported on land. Consequently, we successfully found the unknown ocean impact event from the Northwestern Pacific Ocean.

Free Research Field

鉱床学・地球化学