Late Permian core-surface-magnetosphere conditions revealed by single crystal paleointensities from the Emeishan large igneous province.

The Late Permian encompasses the end-Guadalupian and end-Permian extinctions, commonly linked to emplacement of the ca. 260 million-year-old Emeishan and ca. 252 million-year-old Siberian large igneous provinces, respectively. During this interval, geomagnetic intensity declined from the strong Permo-Carboniferous Reversed Polarity Superchron (PCRS) state, yet the magnitude and potential biological consequences of this weakening remain unclear. Here we present integrated geochronological, paleomagnetic, and single crystal paleointensity results from Emeishan gabbro. Plagioclase crystals, bearing single domain magnetic inclusions, yield a time-averaged dipole moment of 4.1 ± 0.7 ×1022 A m2, ~51% of the present-day value, indicating an abrupt decline. However, the field and magnetosphere were far from being sufficiently depressed to cause ozone depletion and enhanced surface ultraviolet B radiation capable of driving extinctions. The abrupt drop likely reflects changes in core-mantle boundary heat flux associated with deep-slab penetration into the lower mantle and mantle plume activity, ultimately reducing dynamo efficiency.