Details

Autor(en) / Beteiligte

• He, Yuhui
• Lü, Yan

Titel

Anisotropic Pn Tomography of Alaska and Adjacent Regions

Ist Teil von

• Journal of geophysical research. Solid earth, 2021-11, Vol.126 (11), p.n/a

Ort / Verlag

Washington: Blackwell Publishing Ltd

Erscheinungsjahr

2021

Link zum Volltext

Quelle

Wiley Online Library Journals Frontfile Complete

Beschreibungen/Notizen

• We use Pn tomography with coordinate rotation to image in Alaska and adjacent areas and obtain a new Pn velocity and anisotropy model. The observed Pn velocities correlate well with the local geological structures. Low Pn velocities are observed beneath the Aleutian volcanic arc, which may reveal partial melting related to plate dehydration. However, it is separated by a distinct high‐velocity anomaly, suggesting a slab tear. The slightly low Pn velocities beneath the Denali volcanic gap suggest that a small amount of magma is produced but is insufficient to form surface volcanoes. We observe sharp bending of the fast directions on the two sides of the northeast edge of the Yakutat Plate, which reveals the plate’s bending. Large‐scale low velocities are observed beneath the northwestern Cordillera, which may be due to the upwelling of hot material from the deep mantle. The Pn fast directions are parallel to the Queen Charlotte‐Fairweather fault system, consistent with the shear strain direction of the faults, reflecting that the influence of the plate boundary is far‐reaching and that the deformation of the crust and the upper mantle is coupled. Our study provides new constraints on the complex deformation beneath Alaska and adjacent areas. Plain Language Summary The Pacific Plate and Yakutat microplate are subducted beneath the North American plate, resulting in complex geological structures and ongoing volcanic activities in Alaska. We used an improved seismic imaging method to invert the velocity and anisotropy of the uppermost mantle in Alaska. In our new model, the low velocities may show the distribution of magma sources of surface volcanoes in the uppermost mantle. The discontinuity of low velocities beneath the Aleutian volcanic arc may indicate that the plate was torn during subduction. A slightly low‐velocity anomaly was observed beneath the Denali volcanic gap, indicating the production of molten material, but not enough to form surface volcanoes. The anisotropy parallel to the trench and transition faults reflects the olivine crystal arrangement direction in the uppermost mantle. This study provides more information on the plate collision and subduction processes. Key Points We use improved Pn tomography method with coordinate rotation to image uppermost mantle structure of Alaska Low Pn velocities beneath the Aleutian volcanic arc are separated by distinct high velocity beneath Cook Inlet Basin suggesting a slab tear The anisotropic structure beneath Queen Charlotte‐Fairweather fault system reveals the coupling of the crust and upper mantle deformation