Lower mantle minerals in Oman ophiolitic chromitite trace its deep origin

<title>Abstract</title> <bold>Ophiolites, fragments of oceanic lithosphere thrust onto continents, provide key insights into crust and mantle processes. For many years, geologists believed oceanic crust forms through partial melting of the decompressing upper mantle, partly based on studies of Oman and Cyprus ophiolites. However, we report here a lower-mantle mineral assemblage preserved in the Oman ophiolite, challenging this long-standing view. The assemblage includes calcium ferrite- structured magnesiochromite (CF-chromite), magnesiowüstite, amorphous SiO</bold>_{<bold>2</bold>}<bold> (formerly stishovite), amorphous MgSiO</bold>_{<bold>3</bold>}<bold> (formerly bridgmanite), and high-pressure clinoenstatite, indicating formation at pressures exceeding 26 GPa, or depths around 720 km. This discovery reveals interaction between lower and upper mantle systems during oceanic crust formation, reshaping our understanding of this process.</bold>