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

• Published in: Geophysical research letters Vol. 51; no. 17
• Main Authors: Li, Yibing, Chen, Yi, Palin, Richard M., Tian, Xiaobo, Liang, Xiaofeng, Liu, Lijun
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16.09.2024; Wiley
• Subjects: Anomalies; Continental crust; Depth; Earth crust; Earth mantle; Geological mapping; high‐velocity anomalies; mantle transition zone; mineral‐physical database; Modelling; Physical properties; Seismic activity; Seismic data; Seismic velocities; seismic velocity; Seismological data; Seismology; subducted continent crust; Subduction (geology); thermodynamic modeling; Thermodynamic models; Thermodynamics; Transition zone
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2024GL111556

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% VP anomaly. Besides, the upper crust has another two window depths (<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 VP and VS 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. Plain Language Summary In this study, we explore how pieces of Earth's outer layer, known as the continental crust, can dive deep into the layer beneath it, called the mantle, reaching depths of up to 660 km. Seismologists struggle to observe this because using current seismological methods is hard to detect crustal signals beyond 150–180 km. To address this challenge, we performed detailed calculations using a newly compiled mineral‐physical database to understand how subducted continental crust (SCC), behave under high pressures and temperatures. Our research reveals a specific depth range, from 300 to 390 km, where the SCC produces a unique seismic signal that stands out by about 4%. Additionally, the upper parts of the continental crust show distinct signals below 250 km and between 610 and 660 km due to variations in seismic velocities and their ratios. Our findings help to map out where these hidden pieces of crust can be found in the Earth's mantle, corroborating with seismic data from regions such as the Hindu Kush and Myanmar, as well as in the mantle transition zone beneath ancient continental areas. This work opens new pathways for understanding the Earth's inner dynamics and the fate of its crustal components over geological timescales. Key Points We compiled a new mineral‐physical database for subducted lithosphere derived from experimental results and first‐principle calculations Thermodynamic modeling indicates a seismically detectable window depth for bulk continental crust and two additional depths for upper crust High VP anomalies in the mantle transition zone may represent subducted upper continental crust