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Abstract The thermal regime of continental lithosphere plays a fundamental role in controlling the behavior of tectonic plates. In this work, we assess the thermal state of the North American upper mantle by combining shear‐wave velocity models, calculated using data from the EarthScope facility, with empirically derived anelasticity models and basalt thermobarometry. We estimate the depth of the thermal lithosphere‐asthenosphere boundary (LAB), defined as the intersection of a geotherm with the 1300°C adiabat. Results show lithospheric thicknesses across the contiguous US vary between ∼40 km and >200 km. The thinnest thermal lithosphere is observed in the tectonically active western US and the thickest lithosphere in the midcontinent. By combining geotherm estimates with solidus curves for peridotite, we show that a pervasive partial melt zone is common within the western US upper mantle and that partial melt is absent in the eastern and central US without significant metasomatism.
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A Mid‐Lithospheric Discontinuity Detected Beneath 155 Ma Western Pacific Seafloor Using Sp Receiver Functions
Abstract This study probes the lithosphere‐asthenosphere system beneath 155 Ma Pacific seafloor using teleseismic S‐to‐p receiver functions at the Pacific Lithosphere Anisotropy and Thickness Experiment project ocean‐bottom‐seismometers. Within the lithosphere, a significant velocity decrease at 33–50 km depth is observed. This mid‐lithospheric discontinuity is consistent with the velocity contrast between the background mantle and thin, trapped layers of crystallized partial melt, in the form of either dolomite or garnet granulite. These melts possibly originated from deeper asthenospheric melting beneath the flanks of spreading centers, and were transported within the cooling lithosphere. A positive velocity increase of 3%–6% is observed at 130–155 km depth and is consistent with the base of a layer with partial melt in the asthenosphere. A shear velocity decrease associated with the lithosphere‐asthenosphere boundary at 95–115 km depth is permitted by the data, but is not required.
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- PAR ID:
- 10498306
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 51
- Issue:
- 5
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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