The crustal structure of the Wrangellia Terrane along the East Glenn Highway, eastern‐southern Alaska

Journal of Geophysical Research B: Solid Earth
By: , and 

Links

Abstract

Recently acquired seismic refraction data from eastern‐southern Alaska provide new information on the structure and composition of the Wrangellia and adjacent terranes. The data comprise a 160‐km‐long refraction profile along the East Glenn (Tok‐Cutoff) Highway that was collected as part of the U.S. Geological Survey's multidisciplinary Trans‐Alaska Crustal Transect program. The upper 3 km of the Wrangellia terrane and associated rocks is characterized by low compressional wave velocities (Vp = 1.9, 3.3, 4.6, 5.6 km s−1) and high‐velocity gradients common to most onshore seismic refraction profiles. There is also clear seismic expression of the West Fork fault system as a steep, down‐to‐the‐southwest fault that separates the Peninsular terrane to the southwest and the metamorphic complex of Gulkana River to the northeast. In contrast, no seismic expression occurs for the Paxson Lake fault, which separates the Wrangellia terrane from the metamorphic complex of Gulkana River. Adjacent to the Denali fault, within the Wrangellia terrane, two high‐velocity bodies (Vp = 6.6 km s−1) occur in the upper crust. One of these extends to ∼10‐km depth and correlates with a late Paleozoic dioritic complex, suggesting that the Wrangellia terrane is at least 10 km thick in this part of Alaska. From 5 to 23 km depth, the crust appears seismically homogeneous, with velocity increasing from Vp = 6.2 to Vp = 6.6 km s−1. Beneath this level, the crust is less well resolved, although evidence exists for a low‐velocity zone between 23 and 26 km and a possible southwest dipping interface at 35 km. No identifiable mantle refraction or reflection is observed, possibly indicating a crust as thick as 55 km. The relatively low seismic velocities in the upper 23 km of the crust compare favorably with laboratory‐measured velocities on pelitic schists and intermediate‐composition plutonic rocks (granites and granodiorites), both of which are recognized in Wrangellia. We interpret the seismic velocities to indicate that silicic‐to‐intermediate‐composition rocks are important constituents of the basement of this part of Wrangellia. Geologic evidence indicates that the Alaskan part of the Wrangellia terrane is a Paleozoic and Mesozoic island arc: our seismic evidence indicates it may have been built mostly on continental crust as opposed to the fragment of Wrangellia from Vancouver Island which was probably built on oceanic crust.

Study Area

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title The crustal structure of the Wrangellia Terrane along the East Glenn Highway, eastern‐southern Alaska
Series title Journal of Geophysical Research B: Solid Earth
DOI 10.1029/JB094iB11p16037
Volume 94
Issue B11
Year Published 1989
Language English
Publisher Wiley
Contributing office(s) Geology, Minerals, Energy, and Geophysics Science Center
Description 21 p.
First page 16037
Last page 16057
Country United States
State Alaska
Other Geospatial Eastern- Southern Alaska
Google Analytic Metrics Metrics page
Additional metadata about this publication, not found in other parts of the page is in this table