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
10șC/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Unpublished MSc.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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