HR: 0800h
AN: T11B-0379    [Abstracts]
TI: Southeast Directed Thrusting Associated With the Leading Edge of the Wrangellia Composite Terrane: The Chulitna Block South Central Alaska.
AU: * Gilman, T L
EM: tgilman@geosc.psu.edu
AF: The Pennsylvania State University, 338 Deike Building, University Park, PA 16802 United States
AU: Fisher, D
EM: fisher@geosc.psu.edu
AF: The Pennsylvania State University, 338 Deike Building, University Park, PA 16802 United States
AB: Structural mapping of the Chulitna block in south central Alaska reveals a regional scale southeast-vergent, anticline-syncline pair and a series of related southeast-directed thrusts that record the imbrication of the leading edge of the Wrangellia Composite Terrane (WCT). The Chulitna block has been recognized as an unusual Paleozoic through Mesozoic collage of oceanic and clastic rocks that are not found anywhere else in Alaska or the North American Cordilleran. The distribution of these rocks varies across strike from southeast to northwest. In the southeast portion of the field area the oceanic rocks are a Late Devonian (Famennian) ophiolitic sequence including highly sheared serpentinite that is typically altered to magnesite and quartz, basalt (occasionally pillowed), gabbro (with possible cumulate texture), and red radiolarian chert. In the northwest of the map area, the marine rocks are composed of pillow basalts, basalts, and weakly metamorphosed limestones with Norian age fossils. Trace element chemistry of the basalts has been likened to the Late Triassic Nikolai greenstone of the WCT (Clautice et al., 2001). Conformably overlying the oceanic rocks in the northwest of the map area are Triassic red colored conglomerates, sandstones, and siltstones. In the southeast of the field area, these Triassic red rocks unconformably overlie the ophiolitic sequence. The clasts of the Triassic red beds are primarily composed of the underlying red radiolarian chert, basalt, and serpentinite. The main structure in the map area is an anticline-syncline pair that folds all the strata within the Chulitna block. The structure has a steep overturned limb, with a wavelength of ~2 km and an amplitude of ~1 km. To the southeast, there are a pair of out-of-syncline thrusts that juxtapose the serpentinites with overlying units. Large asymmetric folds in the area show a reversal in vergence across the hinge of the larger scale anticline and syncline pair, suggesting they are parasitic folds in an area dominated by regional southeast-directed thrusting. Southeast vergence along the leading edge of the WCT contrasts with the northwest-directed thrusting that typifies the northwest margin of the Talkeetna mountains to the east
DE: 8108 Continental tectonics: compressional
SC: Tectonophysics [T]
MN: Fall Meeting 2005