Structure, Construction, and Geochemistry of the Highly Elongate, Cretaceous Seven-Fingered Jack Pluton in the Devil's Smokestack Area, North Cascades, Washington
Master of Science (MS)
Construction, Geochemistry, Geology, North Cascades, Pluton, Structure
This thesis provides an analysis of magmatic structures and geochemistry from a portion of the mid-crustal, ~92-90 Ma Seven-Fingered Jack pluton, North Cascades, Washington. The study area was divided into three separate domains. Rocks in the northern domain (~9 km2) are characterized by N-NNW- trending, moderately to steeply plunging magmatic folds that reflect regional shortening. The central (~3 km2) and southern (~3.5 km2) domains are structurally homogeneous and contain a dominant NW-striking magmatic foliation. Schlieren are locally developed, several meters long, thin (cm-scale), and strike NW and dip steeply to the NE. Field data indicate the pluton is constructed of numerous, ≤300 m-wide, ≤1 km-long, sheet-like bodies separated by sharp and gradational contacts that are identified by textural and/or compositional differences. During construction, earlier sheets acted as host rocks to younger increments of melt. Detailed modal analyses (n=39) by point counting, coupled with XRF and ICP-MS geochemical analyses (n=8), indicate that the hornblende-biotite tonalite that comprises the study area is overall chemically and texturally homogeneous. Geochemical data further indicate that parental magmas may have come from a relatively shallow source, compared to the deeper, coeval Tenpeak pluton, and incorporated evolved crustal material.
Elkins, Scott William, "Structure, Construction, and Geochemistry of the Highly Elongate, Cretaceous Seven-Fingered Jack Pluton in the Devil's Smokestack Area, North Cascades, Washington" (2015). Master's Theses. 4537.