Transport and eruption of mantle xenoliths creates a lagging problem

Mantle-derived xenoliths entrained by low viscosity magmas indicate transport through great thicknesses of orogenic (≤50–80 km) and cratonic (≤20 km) mantle lithosphere. The size and density of xenoliths dictate that, relative to the ascending magma, they continuously settle during transport. This creates a lag time between when the initial sampling magma reaches the Earth’s surface and the arrival of the xenoliths. The magnitude of this lag time depends on xenolith properties, sampling depth and the magma ascent velocity. Here, using settling calculations, we develop this lag time concept and show how eruption durations and volumes can impact the distribution, abundance, and properties (e.g., sample depths, size) of xenoliths. Lag times can account for heterogeneous xenolith distributions within volcanic deposits, the potential biased sampling of the mantle lithosphere, and can constrain minimum eruption volumes required to transport and erupt the deepest sourced xenoliths such as those producing diamondiferous kimberlites.

James K. Russell, Thomas J. Jones