Detectable Continental Crust in the Earth's Deep Interior Inferred From Thermodynamic Modeling

Compelling evidence indicates that continental crust can subduct to > 300 km and even enter the mantle transition zone (MTZ). However, detecting continental materials within the deep Earth is challenging due to our incomplete knowledge about their physical properties at mantle conditions. We use a newly compiled mineral-physical database coupled with thermodynamic modeling to calculate seismic velocities of the subducted continental crust (SCC) beyond 150 km. Results show that the SCC has one seismically detectable window depth (300-390 km) with 4% V P anomaly. Besides, the upper crust has another two window depths (<250 < 250 km and 610-660 km) with anomalies of- 6.4%--1.6% and- 7.6%-- 2.2%, and 3.6%-7.9% and 3.9%- 8.6% for V P and V S compared to those of the ambient mantle, respectively. These predicted SCC characteristics match seismic anomalies at mantle depths and suggest subducted upper crust potentially contributing to the high-velocity anomalies in the MTZ.