Abstract
Field, structural, and isotopic studies in the southeastern Eagle
Quadrangle
reveal a complex Mesozoic history involving major metamorphism,
fold development,
thrusting, and igneous intrusion. These events may be related to
the accretion
of a terrane, possibly Stikine, to the North American continental
margin.
40Ar/39Ar incremental heating experiments on metamorphic minerals
from
amphibolite facies rocks reveal Late Triassic to Middle Jurassic
plateau
ages interpreted as the age of major metamorphism. Large scale
northeast
trending folds within these rocks formed after the major
metamorphism and
before the intrusion of an undeformed, unmetamorphosed
cross-cutting dike
in Middle Jurassic. These folds probably developed in response to
northwest-southeast
compression related to terrane accretion.
A major thrust system which separates the amphibolite facies
metamorphic
rocks on the south from lower grade rocks to the north is
characterized
by complex thrust melanges, distinct faults, and shear zones
between and
within the two groups of rocks. There are distinct differences in
the structural
character of rocks on either side of this fault zone as indicated
by differences
in fold style and orientation of major fold generations. Thrusting
involved
ophiolitic material as suggested by the presence of serpentinized
ultramafic
rocks and silica-carbonate rocks within the thrust zone. Ar/Ar
data from
a sample within the fault zone indicates that thrusting occurred
after
major metamorphism and before 187 ± 2 Ma.
40Ar/39Ar data also show that a major batholith (Taylor Mountain)
within
the southern terrane was intruded just after the peak of
metamorphism at
about 207 ± 2 Ma and cooled at an average rate of
10ºC/Ma with
the metamorphic rocks.
The Taylor Mountain batholith may be related to the Klotassin
suite
of northwestern Canada and the metamorphic terrane may be the
extension
of the Stikine block into east-central Alaska.
Cushing, G.W., 1984. The tectonic evolution of the eastern Yukon
Tanana
Upland, Alaska.
Unpublished MSc. thesis, State University of New York at Albany.
255
pp., +vi
University at Albany Science Library call number: SCIENCE
Oversize
(*) QE 40 Z899 1985 C88
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