Genesis of high-magnesian adakitic andesite and the associated calc-alkaline andesite and dacite

2015 Fiscal Year Final Research Report

• Project/Area Number: 25400510
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Petrology/Mineralogy/Economic geology
• Research Institution: Niigata University
• Principal Investigator: Shuto Kenji 新潟大学, 自然科学系, 名誉教授 (50143748)
• Co-Investigator(Kenkyū-buntansha): OSANAI Yasuhito 九州大学, 比較社会文化研究科(研究院), 教授 (80183771)
• Project Period (FY): 2013-04-01 – 2016-03-31
• Keywords: 東北日本弧 / 島弧横断変化 / 島弧玄武岩 / HFSE / 沈み込み成分 / depleted MORB mantle / アセノスフェア / Sr,Nd同位体比

Outline of Final Research Achievements

To investigate the nature and origin of across-arc geochemical variations over time in mantle wedge-derived magmas, we have carried out a geochemical examination of arc basalts spanning an age range of 35 Ma to the present in the NE Japan arc. Back-arc basalts erupted at 24-18 Ma, 10-8 Ma, 6-3 Ma and 2.5-0 Ma have higher contents of both HFSE and REE, and incompatible trace element ratios compared to frontal-arc basalts at any given time. Geochemical modeling using Nb/Yb- Nb shows that the frontal-arc and back-arc compositional differences independent of subduction modification can be explained by different degrees of melting (higher degrees of melting for frontal-arc magmas and lower degrees of melting for back-arc magmas) of a nearly homogeneous DMM-like source. We proposed a depleted asthenospheric mantle upwelling model with interaction between asthenospheric mantle-derived magma and overlying lithospheric mantle to explain geochemical characteristics for 35-0 Ma NEJ basalts.

Free Research Field

岩石学