[S-CG55] Ocean Floor Geoscience

[SCG55-P10] A geological cross-section of the Marie Celeste Transform Fault, Central Indian Ridge: preliminary results from the KH-24-4 cruise of R/V Hakuho-maru

*Kohei Nimura¹, Shiki Machida², Norikatsu Akizawa³, Aoi Harada¹, Naoto Hirano⁴, So Inoue¹, Akira Ishikawa⁵, Kazuki Matsuyama ^1,6, Katsuyoshi Michibayashi^1,7, Tomoaki Morishita⁸, Taiki Nakano⁹, Yuka Niwa⁵, Makoto Sano⁹, Yibing Li¹⁰, Kyoko Okino¹¹ (1.Department of Earth and Planetary Sciences, GSES, Nagoya University, 2.Ocean Resources Research Center for Next Generation, Chiba Institute of Technology, 3.Graduate School of Advanced Science and Engineering, Hiroshima University, 4.Center for Northeast Asian Studies, Tohoku University, 5.Department of Earth and Planetary Science, School of Science, Institute of Science Tokyo, 6.Géosciences Montpellier, CNRS, Université Montpellier 2, 7.Volcanoes and Earth's Interior Research Center, IMG, JAMSTEC, 8.College of Science and Engineering, Kanazawa University, 9.Graduate School of Science, Tohoku University, 10.Institute of Geology, Chinese Academy of Geological Science, 11.Atmosphere and Ocean Research Institute, The University of Tokyo)

Keywords:transform fault, oceanic crust, gabbro, dolerite, basalt, Central Indian Ridge

Scarps along oceanic transform faults expose crust and upper mantle rocks, providing tectonic windows for investigating million-year-scale temporal variations in oceanic crust formation. Pioneering studies of the Vema Transform Fault at the Mid-Atlantic Ridge have shown a 3–4-million-year fluctuation in melt supply to the ridge segment, based on extensive sampling and gravity analysis. However, in-situ rock sampling along transform faults remains limited, and the causes of these fluctuations in melt supply remain unclear.

In this study, we investigated the geological cross-section of the Marie Celeste Transform Fault (MCTF), Central Indian Ridge (CIR). MCTF is a long oceanic transform fault (215 km) that provides access to 11 million years of mid-ocean ridge processes. A prominent transverse ridge is present in the eastern part of MCTF, where the whole oceanic crustal section is likely exposed at the transform valley. During the KH-24-4 cruise of R/V Hakuho-maru in 2024, we dredged 27 sites along the southern wall of MCTF, with a maximum horizontal spacing of ~40 km (~2 million years). This cruise recovered nearly all lithologies composing the oceanic crust, including gabbro, dolerite, and basalt. Basalts were collected from all dredge sites located in the shallow part of MCTF (~2220 m depth) , dolerites from the middle part of the transverse ridge, and gabbroic rocks from its lower part (~5470 m depth).

Our results indicate that the transverse ridge in the eastern part of MCTF provides a well-preserved cross-section of the oceanic crust, from gabbroic layers to dolerite dyke complexes and basaltic lavas. Notably, variations in the depth of the shallowest gabbroic exposures (4480–3728 m) suggest fluctuations in magma supply over time. Our findings reveal a previously unrecognized ~2-million-year cyclicity in oceanic crust formation, significantly shorter than the 3–4-million-year cycle identified at the Vema Transform Fault. This suggests that crustal formation processes may exhibit greater temporal variability than previously thought.