Heat Generation in Cratonic Mantle Roots—New Trace Element Constraints From Mantle Xenoliths and Implications for Cratonic Geotherms

Abstract

Abstract Heat generation within the cratonic lithospheric mantle (CLM) is an important but poorly determined parameter for constructing cratonic geotherms. Direct measurement of heat producing element (HPE: K, U, and Th) concentrations in bulk‐rock samples of cratonic mantle roots—provided as xenoliths in volcanic rocks such as kimberlites—is mostly compromised by infiltration of host melt into the xenoliths, resulting in over‐estimates of heat production. Here we use in situ methods (laser ablation inductively coupled plasma mass spectrometry) on minerals from a variety of cratonic mantle peridotites to avoid host‐magma contamination enabling new, more accurate determinations of heat production for a wide spectrum of model mantle lithologies. The most melt‐depleted, least metasomatized peridotites indicate that heat generation in un‐metasomatized depleted cratonic lithospheric mantle is negligible, at ∼0.00004 µW/m3, 102 to 103 times less than models that use more enriched or metasomatized compositions. Refertilized cratonic peridotites, typical of many kimberlite hosted xenoliths, have more elevated, but still low heat generation, of 0.006 µW/m3. We propose that the heat generation of typical cratonic mantle peridotite lies between these two bounds, that is, between 0.00004 and 0.006 µW/m3. Both values produce lower estimates of lithospheric thickness, by ∼10 to up to 80 km, depending on model assumptions, than estimates using higher HPE concentrations measured on bulk‐rock xenolith material.

Keywords

• heat producing elements (K, U, and Th)
• mantle heat generation
• cratonic geotherms
• mantle metasomatism