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We investigate the structure of the continental lithosphere by combining two approaches: a systematic survey of abrupt changes in seismic properties detected by P‐to‐S converted body waves and an integrated geophysical‐petrological inversion for temperature and density in the upper mantle. We refine the global thermo‐chemical model WINTERC‐G in eastern North America by including detailed regional information on the crust into petrological inversions and combine it with the upper mantle layering beneath eastern North America yielded by anisotropy‐aware receiver‐function analysis. Eastern North America's Archean, Proterozoic and Paleozoic lithospheres show an excellent agreement between the depth to the 1,300°C isotherm that bounds the lithosphere and the depth range where converted waves detect abrupt changes in seismic properties. Boundaries with these abrupt changes reside within the rigid mechanical lithosphere and are uncommon in the convecting mantle beneath it. The boundaries include both impedance increases and decreases with depth, as well as anisotropy changes, and must have developed over the course of the assembly and evolution of the lithosphere. In the asthenosphere below, such heterogeneities appear to have been largely mixed out by convection. The existence of abundant interfaces with diverse origin can account for the commonly observed scattered signals from within the continental lithosphere and presents an alternative to the end‐member concept of the mid‐lithospheric discontinuity as a ubiquitous feature with a uniform origin. Generally, we can define continental lithosphere as a region of conductive heat transport and steep geotherm that is characterized by pervasive internal layering of density, elastic moduli and texture. Plain Language Summary: The outer shell of the Earth called the lithosphere is defined most generally as a layer of rigid colder material overlying a warmer and weaker asthenosphere below. Within the lithosphere heat is conducted from the interior to the outside, resulting in a characteristic increase in temperature with depth. The region below it convects on geological (millions of years) time scale and has a different depth dependence of temperature. In this contribution we use two definitions of the lithosphere to estimate its vertical extent beneath a region of North American continent where lithosphere formed between 3 and 0.3 Ga ago. We detect abrupt changes in physical properties in the upper layers of the Earth using seismic waves from distant earthquakes. We perform a joint inversion of geophysical and petrological constraints to derive temperature profiles with depth. Boundaries scattering seismic waves are detected throughout the depth range where temperature is below 1,300°C. The deepest scattering boundaries are close to this depth in areas where lithosphere formed within the last billion years. In the oldest part of the continent the deepest boundaries are ∼50 km above the temperature of 1,300°C, confirming long‐recognized difference of such ancient lithosphere. Key Points: Beneath eastern North America sharp vertical gradients in seismic properties are pervasive, vary in nature and number, and extend to ∼170 kmDetected gradients reside above the depth to the thermally and mechanically defined lithosphere‐asthenosphere boundaryContinental lithosphere retains pervasive internal layering of density, elastic moduli, and texture, which is mixed out in the asthenosphere [ABSTRACT FROM AUTHOR]

We have calculated the structure and elasticity of low-spin ferromagnetic ε-FeOOH to 140 GPa using density functional theory calculations with a Coulombic self-interaction term ( U). Using these data, the elastic moduli and sound velocities of ε-FeOOH were calculated across the pressure stability of the hydrogen bond symmetrized structure (30 to 140 GPa). The obtained values were compared with previously published values for phase H (MgSiH2O4) and δ-AlOOH, which likely form a solid solution with ε-FeOOH. In contrast to these Mg and Al end-members, ε-FeOOH has smaller diagonal and larger off-diagonal elastic constants, leading to an eventual negative pressure dependence of its shear wave velocity. Because of this behavior, iron-enriched solid solutions from this system have smaller shear wave velocities than surrounding mantle and therefore are a plausible contributor to large low-shear velocity provinces (LLSVPs) which exhibit similar seismic properties. Additionally, ε-FeOOH has substantial shear wave polarization anisotropy. Consequently, if iron-rich solid solutions from the FeOOH-AlOOH-MgSiH2O4 system at the core-mantle boundary exhibit significant lattice-preferred orientation due to the strong shear stresses which occur there, it may help explain the seismically observed S H > S V anisotropy in this region. [ABSTRACT FROM AUTHOR]