Journal Article

Receiver Function Analysis Reveals Lateral Variations in Temperature and Water Content in the Mantle Transition Zone Beneath Eastern North America

Liu, Shangxin, Long, Maureen D., Aragon, John C., Benoit, Margaret H., King, Scott D.

2023

Overview

Using recently collected high‐resolution seismic data along a dense linear transect across Ohio, West Virginia, and Virginia (called Mid‐Atlantic Geophysical Integrative Collaboration (MAGIC) profile), we analyze P‐to‐S receiver functions to investigate the undulations of the mantle transition zone (MTZ) discontinuities (410‐ and 660‐km) beneath the central Appalachian region. Our results incorporating the effects of local crustal and mantle structures suggest shallowing of both the 410‐ and the 660‐km discontinuities from the northwest (inland) to the southeast (coast) along MAGIC profile. Hydro‐thermal upwelling beneath the eastern U.S. coastal plain due to a hydrated MTZ and hot upwelling return flow associated with the descending lower mantle Farallon slab is consistent with our observations of MTZ structure considering 3D velocity heterogeneity. The inferred hydrous hot upwelling rising into the upper mantle may trigger dehydration melting atop the 410‐km discontinuity, which may help to explain the presence of a low velocity upper mantle anomaly beneath the region today. Plain Language Summary The dynamic and tectonic processes of passive continental margins that do not lie on plate boundaries are poorly understood compared with active continental margins. The mantle flow patterns beneath the eastern North America, a long‐lived passive continental margin, are debated, due to limited local high‐resolution seismic studies. Using a dense seismic array through Ohio, West Virginia, and Virginia (called MAGIC profile) with unprecedented resolution, we investigate the undulations of 410‐ and 660‐km discontinuities (boundaries of the mantle transition zone) beneath the eastern U.S. by analyzing seismic waves that have been converted at these discontinuities. After correcting for local crustal and mantle structures, we identify positively correlated shallowing of the 410‐ and 660‐km discontinuities from the inland to the coast, which are hard to explain by thermal heterogeneity alone. Our findings suggest the existence of hot upwelling return flow associated with the neighboring descending Farallon slab in the lower mantle beneath the eastern U.S. When this passive hot return flow rises through the hydrated transition zone into the upper mantle, dehydration melting atop 410‐km discontinuity may be triggered. The buoyant melt may further rise through the upper mantle, providing a potential explanation for upper mantle velocity anomalies beneath the region. Key Points Seismic receiver functions image mantle transition zone discontinuities from a regional high‐resolution transect across the eastern U.S The results are difficult to reconcile with either thermal or hydration variations alone in the transition zone Local hydro‐thermal upwelling due to hydrated transition zone and hot return flow associated with the descending Farallon slab may exist

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Anomalies / Boundaries / Coastal plains / Continental margins / Dehydration / dehydration melting / Discontinuity / eastern North America / Farallon slab / Flow distribution / Function analysis / Heterogeneity / Lower mantle / mantle transition zone / Melting / Moisture content / Ocean circulation / P-waves / Plate boundaries / receiver functions / Return flow / Seismic activity / Seismic arrays / Seismic data / Seismic studies / Seismic waves / Seismological data / Seismology / Tectonic processes / Tectonics / Temperature variations / Transition zone / Upper mantle / Upwelling / Velocity / Water content