Xenolith data indicate extreme geothermal gradients at shallow depth in eastern Australia contrary to results obtained from models based on thermal conduction. Consequently mechanisms involving partial melting accompanied by underplating must be assumed to supply additional heat unrelated to radiogenic profiles. A mid-crustal heat-source is required to satisfy the xenolith data suggesting a layered structure consisting with episodic underplating at maximum rates approaching 900 m/Myr in eastern Australia. ¿ American Geophysical Union 1990