FOREST BIOME - ScholarsArchive at Oregon State University

8.120
TITLE: Geological and Geochemical Profiles and the Dynamics of Rock Alteration.:
Western and High Cascade Range
OBJECTIVES:
Although primarily a geologic investigation, the study will provide basic
information relative to an understanding of landscape evolution and soil development
in the H. J. Andrews Experimental Forest. This study also complements
earlier work and work in progress by the principal investigators in an area
of similar geologic and geomorphic setting in the South Umpqua National Forest.
The study consists of two parts, the objectives of which are to provide:
1. a detailed geologic map of all rock units, and basic mineralogical and
chemical information of the major rock units and their vertical and
lateral variations;
2. information concerning the mineralogical and chemical makeup of regolith
and soils developing on these major rock units.
As a natural consequence of the two main objectives, the study may also
provide a mineralogical-chemical profile demonstrating bulk mobility and
stability of major rock forming constituents in the weathering cycle.
The area is one of complex volcanic parentagez a detailed geologic map is
therefore basic to an understanding of the sequence of events and processes
responsible for development of the rock sequence. At least one full field
season is required for basic field mapping and sampling of rock and soil units.
The rocks of this region may be divided into two groups. One group consists
of older Tertiary rocks of the western Cascade Range modified by surficial
alteration-erosion at an earlier date, subsequently buried and subjected to
chemical-mineralogical alteration related to this burial, and later eroded and
chemically altered exposing the present rock sequence. The older Tertiary
rocks are overlain to the east by Pliocene to recent volcanic rocks of the
High Cascade Range. From a purely geologic viewpoint, the vertical variation
of chemical and mineralogical constituents can tell us much concerning processes
operative in the lower levels of the crust and in the upper mantle at the
time of deposition of this sequence. In like manner, the same information is
of vital significance in piecing together knowledge relating to aggradation
of the predominantly volcanic western margin of the continental United States
in Oregon. It may also provide clues regarding processes responsible for
formation of recent volcanoes of the High Cascade Range.
APPROACH:
it is important for comparison with areas of similar geologic and geomorphic
setting, especially along strikes of the Cascade trend, that a complete vertic=;1
sequence of samples be obtained in the study area. Rock samples will also be
obtained in order to detect significant lateral variations in mineralogychemistry
of given lithologic units. Variations in the vertical sequence may
provide basic data necessary for recognition of significant trends in evolution
of volcanic products. As an example, a study of a sequence of rocks of similar
age to rocks of the proposed study area, but in an area some 100 miles to the
south, reveals a predominant trend of increasingly basic character from bottom
to top. In addition to regional geologic implications regarding comparison cf
trends in the two areas, this variation might be of significance to regio=nal