ABSTRACT
.Four problems of tectonic significance were addressed. The first
is a study of the structural emplacement of the Snowcamp ophiolite
over the Rogue-Chetco arc complex during the Nevadan Orogeny in
southwestern Oregon. Similarities in age, pressure and temperature
conditions during thrusting, metamorphic history, and kinematics
indicate that thrusting there was correlative with the nearby
Madstone Cabin thrust. This implies that the overlying ophiolitic
rocks have undergone a similar history as the Josephine ophiolite
and are not exotic to Jurassic North America.
Two projects involve the geochemical and field
relationships of rocks in north-central Maine, which are used to
constrain the tectonic setting of pre-Taconic and early Acadian
magmatic rocks. Early Ordovician basalts and gabbros have MORB
characteristics derived from depleted mantle, but intrude
mélange and continental margin rocks. The most likely
interpretation is that they intruded an active continental margin
as a result of a ridge subduction event. Younger Devonian rocks
are enriched with respect to MORB, but are not to the extent of
other within-plate, plume-related settings. They are associated
with rocks deposited on a continental margin and in the foreland
of a lower plate prior to arrival of the Acadian orogen.
Geochemical analysis indicates a subduction-modified
subcontinental mantle source, and the magmatic rocks are
interpreted to have intruded as a result of lower plate
lithospheric detachment during the early stages of subduction of
the continental margin.
The final project addresses a long-standing
conflict in interpretation of the depositional history and
structural evolution of the Stanbridge Group in southern Quebec,
and the correlative Highgate and Morses Line Formations of
northwestern Vermont. Field relationships in Vermont indicate that
the Highgate and Morses Line Formations were deposited on the
Laurentian shelf and shelf margin, and were later imbricated
during the Taconic Orogeny. The correlative Stanbridge Group in
Quebec likely followed a similar history and is not allochthonous
as previously believed, in the sense that it was not transported
from the Laurentian continental rise.
Schoonmaker, A., 2005. Convergent and collisional tectonics in
parts of Oregon, Maine, and the Vermont/Quebec border. Unpublished
PhD dissertation, State University of New York at Albany. 221 pp.,
+xiii; 7 folded maps.
University at Albany Science Library call number: SCIENCE
MIC Film QE 40 Z899 2005 S36
Copies of this PhD dissertation can be ordered
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