Xenolith Constraints on the Mantle Potential Temperature and Thickness of Cratonic Roots Through Time

Abstract

Abstract The temperature of the convecting mantle and thickness of the lithosphere control many of Earth's processes. However, there is disagreement regarding the evolution of these quantities through time. We use a global data set of mantle xenoliths and xenocrysts to construct paleogeotherms at different eruption ages (16–1,311 Ma) and estimate the temperature and depth of the lithosphere‐asthenosphere boundary (LAB) as a function of mantle potential temperature (Tp). We find that the maximum pressure and temperature (PT) of xenoliths matches the modeled LAB conditions when a Tp of 1,315°C is used. At higher Tp (1,450–1,550) we observe a gap between the maximum PT of xenoliths and the LAB conditions. Because this gap systematically increases with Tp, and the maximum PT of xenoliths has not changed over time, we suggest that there has actually been only minor (<50°C) changes in mantle Tp since the Meso‐Proterozoic. Plain Language Summary The temperature of the convecting mantle and the thickness of the lithosphere control many of Earth's processes. There is disagreement as to whether the temperature of the convecting mantle and thickness of the lithosphere were greater during Earth's early history. In this study we address this issue by using a global data set of mantle xenoliths and xenocrysts. Xenolith pressure and temperature (PT) estimates are used to construct paleogeotherms at different eruption ages and values for mantle potential temperature (Tp) to constrain the conditions of the lithosphere‐asthenosphere boundary (LAB). PT estimates are compared with the LAB conditions at different eruption ages and mantle Tp values. We find that the maximum PT of the samples are similar to the conditions of the LAB when a present day Tp is used (Tp = 1,315°C). Models that use a higher Tp (1,450–1,550°C) result in large gaps between the LAB and the maximum PT of xenoliths and xenocrysts. The size of the gaps increase systematically with higher values for Tp. This, along with the observation that the maximum PT of xenoliths and xenocrysts has not changed over time, suggests that Tp and lithospheric thickness were not significantly greater during the Proterozoic. Key Points Pressure and temperature estimates for 7,303 mantle xenoliths and xenocrysts were used to constrain the thermal structure of the lithosphere Paleogeotherms with higher mantle Tp have artificial gaps between the base of the lithosphere and deepest xenoliths and xenocrysts Modeled and observed pressures and temperatures of the base of the lithosphere are similar when a mantle Tp of 1,315 is used