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Our understanding of oceanic crustal formation is mostly limited to observations of young crust formed in the past several million years, due to the thick sediments on older crust and the remote location of many spreading centers. Here we use 40 m-resolution bathymetric data collected over hundreds of square kilometers during the search for Malaysia Airlines Flight 370 on the flank of the Southeast Indian Ridge, which provides a record of crustal accretion from 11-23 Ma. Spectra calculated from the data show a characteristic timescale of 300-400 kyr and no evidence for periodicity coinciding with glacial cycles. This characteristic timescale could be explained by fluctuations in melt supply and the amount of faulting, leading to variations in crustal thickness. We show that this timescale of variation is consistent with porosity waves observed in a two-phase flow model, which persist over millions of years.

Plain Language Summary A 12-million-year-long record of crustal formation is contained within the seafloor mapping data collected during the search for Malaysia Airlines Flight 370, at a resolution that is 15 times higher than previous maps. These data illuminate the structure of a vast area of crust formed on the Southeast Indian Ridge and show that crustal production, rather than being a constant process, has varied in cycles that last hundreds of thousands of years. This pattern can be explained by the varying amount of molten rock that rises from deep in Earth's mantle, arriving in episodic waves. This behavior could be a general feature of mid-ocean ridges spreading at similar rates, which has not been previously recognized due to a lack of available data.