Publication Date

Spring 2015

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Geology

Advisor

Robert Miller

Keywords

Construction, Geochemistry, Geology, North Cascades, Pluton, Structure

Subject Areas

Geology

Abstract

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.

Download

Share

COinS