Shear wave splitting across the Mid-Atlantic region of North America; a fossil anisotropy interpretation

• Published in: Geology (Boulder) 2017-06, Vol.45 (6), p.555-558
• Main Authors: White-Gaynor, Austin L, Nyblade, Andrew A
• Format: Article
• Language: English
• Subjects: Anisotropy; Appalachian Phase; Appalachians; body waves; continental margin; Continental margins; Earth; Eastern U.S; elastic waves; Fossils; Geophysics; Laurentia; Lithosphere; mantle; Mountains; New England; North America; Orientation; Orogeny; paleogeography; Paleozoic; Pangaea; Pangea; Pennsylvania; Permian; Precambrian; Rhyolite; Rhyolites; Rotation; S-waves; seismic networks; seismic waves; Shear; SKS-waves; solid Earth (tectonophysics); Splitting; United States; wave splitting
• ISSN: 0091-7613; 1943-2682
• DOI: 10.1130/G38794.1

New shear wave splitting measurements (n = 76) from the Mid-Atlantic section of North America, when combined with previously reported measurements, provide improved clarity to patterns of seismic anisotropy across the region, including a rotation of fast polarization directions (Φ) from east-west to northeast-southwest in Pennsylvania (USA). We attribute the patterns in Φ to frozen-in (i.e., fossil) anisotropy in the lithospheric mantle. Most Φ directions parallel the strike of the Appalachian orogen, except in parts of New England, where Φ directions are oriented perpendicular to both the strike of the orogen and continental margin. The Φ directions parallel to the strike of the Appalachian orogen, including those that rotate from east-west to northeast-southwest in Pennsylvania, are consistent with the expected orientation for fossil anisotropy developed during the Appalachian orogenic cycle. The Φ directions in New England, perpendicular to the continental margin, are consistent with the expected orientation for fossil anisotropy developed during the breakup of Pangea, and Φ directions at locations west of the Appalachian Mountains in areas not affected by the Appalachian orogeny can be explained by fossil anisotropy developed during the Proterozoic suturing of the Granite-Rhyolite Province and Elzevir block to the eastern margin of Laurentia.