[M-IS17] New frontiers in geology

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

*Norikatsu Akizawa¹, Eirini Poulaki², Emily Cunningham³, Alessio Sanfilippo⁴, Tomoaki Morishita⁵, Ashutosh Pandey⁶, Manon Bickert⁷, Paola Vannucchi⁸, Chao Lei⁹, Swanne Gontharet¹⁰, Tetsu Kogiso¹¹, Akihiro Tamura⁵, Noriaki Abe¹², Agata Stefano¹³, Irina Filina¹⁴, Qi Fu¹⁵, Lorna Kearns¹⁶, Ravi Kiran Koorapati¹⁷, Filomena Loreto¹⁸, Luca Magri¹⁹, Walter Menapace²⁰, Victoria Pavlovics³, Philippe Pezard²¹, Milena Rodriguez-Pilco²², Brandon Shuck², Xiangyu Zhao²³, Emily Estes²⁴, Alberto Malinverno²⁵, Nevio Zitellini¹⁸ (1.Earth Planet Sys Sci, Hiroshima Uni, 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.ICP, 21.Montpellier Uni, 22.Texas A&M Uni at Galveston, 23.Shanghai Jiao Tong Uni, 24.Texas A&M Uni, 25.Columbia Uni)

Keywords:IODP Exp.402, Oceanic core complex, Back-arc basin, Mediterranean Sea

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.