Structural and stratigraphic analysis of a metasedimentary inlier within the Coast Plutonic Complex, British Columbia, Canada

Structural and stratigraphic analysis of a metasedimentary inlier within the Coast Plutonic Complex, British Columbia, Canada
Douglas, B. J.
Princeton University, New Jersey
x, 298 p., Illus., Maps.
The Khutzeymateen Group within the Coast Plutonic Complex is dominated by graywackes and volcaniclastics that may be divided into lower, middle, and upper parts. The lower and upper parts have a wide range in lithofacies which include leucogneiss, quartzo-feldspathic gneiss, garnet-biotite schist, calc-silicate gneiss, and amphibolite. The middle part fines upwards and contains graywackes, siltstones, fibrolite schists, and calc-silicate lithologies. Based on the lithologic sequences, whole-rock compositions, and the tectonic setting, the Khutzeymateen Group is believed to have been deposited in an inter-arc basin within an intermittently active island arc system. The Khutzeymateen Group is correlated with rocks of the Gravina-Nutzotin belt of southeastern Alaska on the basis of lithologies, bulk compositions, depositional environment, and the presence of a zoned ultramafic complex similar to the Alaskan-type ultramfic complexes. This correlation implies a Late Jurassic to Early Cretaceous age for the deposition of the Khutzeymateen Group. The Khutzeymateen Group is in fault contact with the Central Gneiss Complex. The Central Gneiss Complex also could have been deposited within this island arc. The Khutzeymateen Group and the Central Gneiss Complex were synchronously metamorphosed and deformed. Metamorphism reached peak conditions of 450 (+OR-) 100 MPa and 650(DEGREES) (+OR-) 50(DEGREES)C, and was synchronous with an isoclinal folding event (F(,1); 340(DEGREES),15(DEGREES)) that has a penetrative foliation (S(,1)) and strong mineral lineation (L(,1)). F(,1) folding was followed by a chevron folding (F(,2); 335(DEGREES),15(DEGREES)). F(,1) minor folds predominate within pelitic lithologies, and F(,2) minor folds predominate within regularly layered quartzo-feldspathic lithologies. Open F(,3) folds (065(DEGREES),35(DEGREES)) cause F(,1), L(,1), and F(,2) to dip north and south. Subsequent deformation is related to differential uplift on the Larch Creek Fault. Post-D(,3) faults and minor shear zones have a 230(DEGREES),90(DEGREES) orientation. Transmission electron microscopy of samples from the Khutzyemateen area along with shock samples from near Sudbury, Ontario show that the density of dislocations in quartz and feldspar may be correlated. The dislocation density within both quartz and feldspar was found to increase at about the same rate with increased stress. Differential stress calculated from dislocation density is 100 MPa for the Khutzeymateen Group samples.
Ph. D. dissertation
Minerals Data and Information Rescue in Alaska (MDIRA)