MARIA S. MERIAN MSM69

The oceanic lithosphere is created by sea-floor spreading at mid-ocean ridges and covers approximately 57% of the Earth surface. Crustal thickness and lower crustal velocity are inherently related to the formation of the lithosphere and can be used to infer temporal variations in crustal accretion when moving away from the spreading ridge. After its formation, the shallow lithosphere is affected by hydrothermal circulation in the uppermost permeable crust over tens of millions of years. In turn, heat is removed from the lithosphere by circulating seawater and mineral precipitation modifies and seals open void spaces, affecting the heat loss, seismic velocity, and composition of the crust. In addition, lithosphere cools and thickens with age, resulting in the well-known subsidence of the seafloor, decreasing heat flow, and increasing seismic velocities in the rigid lithospheric mantle. In addition, the depth to the Lithosphere-Astenosphere-Boundary (LAB) increases from approximately Moho depth to several tens of kilometres in Cretaceous crust. While the formation of crust and lithosphere at the spreading ridges is reasonably well studied, little is known about how crustal accretion changed over time and how crust and litho-sphere change when carried away from the underlying heat source. Understanding how lithosphere evolves with age is thus a major challenge in Earth sciences. During MSM69, geophysical surveys on a 580 sm long transect will be acquired in the equatorial Atlantic using seismic refraction and heat flow methods. The goal is to collect a data set which reveals the age-dependent features of the lithospheric structure such as crustal and mantle properties, age-dependent heat flow and major lithospheric boundaries like Moho and the LAB.