ABSTRACT
Rocks that were at
mid-crustal depths during early Proterozoic time are found in the
White Tank Mountains, a mid-Tertiary metamorphic core complex
located 65 kilometers west of Phoenix. These rocks allow us
to infer how the Proterozoic mid-crust behaved in relation to the
upper crust, which is well exposed in the Transition Zone of
central Arizona. Proterozoic metamorphics, a foliated
Proterozoic tonalite pluton, several Cretaceous-Tertiary granitic
plutons, and numerous Tertiary dikes are all present. The
metamorphics are interpreted to be mainly sedimentary and
volcanic in origin, possibly correlating to the Union Hills and
Alder groups. The tonalite pluton was intruded as tabular
sheets of varying composition during the formation of the older
foliation (S1).
Structures documenting the
Proterozoic deformational events can be divided into early
foliation development, a gentle folding of this foliation, and
the development of a younger foliation along discrete shear
zones. The older foliation (S1) strikes northeast and is
correlated to the dominant northeast-striking fabric in the
Transition Zone. Folding of the S1 foliation and the
presence of a younger foliation (S2) in the White Tank Mountains
but not in the Transition Zone suggest a difference in behavior
between the mid-crust and the upper crust in the Proterozoic.
Several types of
remote sensing imagery were used to aid in the geologic mapping
of the White Tank Mountains. Imagery from the Thermal
Infrared Multispectral Scanner (TIMS) and the NS001 instrument
allow a geologist to view the field area in the thermal infrared
and in the visible to near-infrared, respectively. Though
accurate geologic mapping is not possible with this imagery
alone, the imagery is a useful tool when combined with field
observations. The TIMS imagery is an effective tool for
mapping lithologic units defined by their silicate
mineralogy. The NS001 instrument is not as effective for
bedrock mapping, but is a very useful tool for mapping Quaternary
deposits and surfaces.
Bedrock Geology Project
Abstract
Overview
Proterozoic rock units
Proterozoic Structures
Remote Sensing techniques
References and
Acknowledgments
Geology and Web pages by Steven Wood and Stephen J. Reynolds, Dept. of Geology, Arizona State University, Tempe, AZ -- July 1998