Thermal and compositional anomalies in a detailed xenolith-based lithospheric mantle profile of the Siberian craton and the origin of seismic midlithosphere discontinuities

Abstract The fine structure and thermal state of >200-km-thick cratonic lithosphere remain poorly explored because insufficient sampling uncertainties in pressure (P) temperature (T) estimates. We report exceptionally detailed compositional profiles the continental lithospheric mantle (CLM) Siberian craton based on petrographic, situ chemical, P-T data for 92 new garnet peridotite xenoliths from Udachnaya kimberlite, as well literature data. profile is complex, with samples indicating model conductive geotherms between 40 35 mW/m2 at ~55–130 km, colder (35 geotherm) 140 to 190 hotter layers CLM base (190–230 km) ~135 km. latter, previously unidentified, anomalous midlithospheric horizon has rocks up 150 °C than geotherm, that are rich clinopyroxene, have low Mg#, melt-equilibrated rare earth element patterns. posit this formed a depth range where ascending melts stall (e.g., via loss volatiles redox change), heat wall-rock harzburgites, transform them lherzolites or wehrlites. This may explain some seismic midlithosphere discontinuities (MLDs) cratons. By contrast, we found no metasomatic volatile-rich amphibole, phlogopite, carbonate matching MLD, nor composed peridotites distinct melt-extraction degrees. below km contains both coarse variably deformed heated reworked (Mg#Ol down 0.86) by localized lithosphere-asthenosphere interaction.