[M-IS17] 地質学のいま

[MIS17-10] Geochemical characteristics of felsic granitoids hosted by mantle peridotites at a continent-ocean transition zone in the Tyrrhenian Sea

*秋澤 紀克¹、Poulaki Eirini ²、Cunningham Emily ³、Sanfilippo Alessio ⁴、森下 知晃⁵、Pandey Ashutosh ⁶、Bickert Manon ⁷、Vannucchi Paola ⁸、Lei Chao ⁹、Gontharet Swanne ¹⁰、小木曽 哲¹¹、田村 明弘⁵、安邊 啓明¹²、Stefano Agata ¹³、Filina Irina¹⁴、Fu Qi ¹⁵、Kearns Lorna¹⁶、Kiran Koorapati Ravi ¹⁷、Loreto Filomena¹⁸、Magri Luca ¹⁹、Menapace Walter ²⁰、Pavlovics Victoria³、Pezard Philippe²¹、Rodriguez-Pilco Milena²²、Shuck Brandon ²、Zhao Xiangyu ²³、Estes Emily²⁴、Malinverno Alberto²⁵、Zitellini Nevio ¹⁸ (1.広島大学 地球惑星システム学プログラム、2.Louisiana State Uni、3.Uni Utah、4.Uni Pavia、5.Kanazawa Uni、6.IISER TVM、7.Uni Brest、8.Uni Florence、9.China Uni、10.Sorbonne Uni、11.Kyoto Uni、12.JAEA、13.Uni Catania、14.Uni Nebraska、15.Uni Houston、16.Uni Leeds、17.Binghamton Uni、18.CNR-ISMAR、19.Uni Tasmania、20.ICM、21.Montpellier Uni、22.Texas A&M Uni at Galveston、23.Shanghai Jiao Tong Uni、24.Texas A&M Uni、25.Columbia Uni)

キーワード： IODP Exp.402、海洋コアコンプレックス、背弧海盆、地中海

The Continent-Ocean Transition (COT) zone is a fundamental place where we can understand the Earth’s unique process of continental lithosphere break-up and formation of new oceanic crust. The Tyrrhenian Sea is an ideal study area to investigate the COT process because deep-mantle materials with different COT magmatic records have been exhumed to the seafloor by detachment faults. IODP Exp 402 took place from 9 February to 8 April 2024 in the Tyrrhenian Sea and recovered mantle peridotites from two drill sites. The peridotites are intercalated with felsic granitoids with various deformation intensities. Calculated normative anorthite-albite-orthoclase compositions of the granitoids show that these samples are classified in the trondhjemite to granite series. The granitoids are abundant in Na₂O content up to 7.6 wt% and are subaluminous in terms of Aluminous Saturation Index (ASI < 0.9). Because these granitoids are similar in chemical characteristics to those of igneous-type granitoids, we hypothesize that the granitoid magmas were generated during the COT in the Tyrrhenian Sea. Considering their zircon-apatite U-Pb geochronology data and microstructures (Poulaki et al., 2025; Abstract of EGU annual conference), the granitoid magmas intruded into the peridotites at Pliocene ages and the granitoids accommodated strain during exhumation along the detachment fault. The “unusual” granitoid magmas probably facilitated the formation of the oceanic core complex in this magma-poor continental margin.