Geology Reference
In-Depth Information
Oregon Klamath Mountain
terranes and major faults
(after Pessagno and Blome,
1990; Harper and Wright,
1984; Blake, et al., 1985)
continent and when the same terrane was rotated into
its present orientation. The timing determines whether
the plate rotation occurred when the terrane was still
an independent part of an oceanic plate or whether it Snow Camp, Pickett Peak, Yolla Bolly, Gold Beach,
was moved after it had become welded to the main and Sixes River terranes. The overall grain of the
continent. Present evidence suggests that all Klamath Klamath terranes curves northeast by southwest with
terranes had completed their swinging clockwise the convex side to the northwest.
motion by the early Cretaceous. This established the Among the Klamath Mountain terranes, the
early Cretaceous as the time by which the multiple, Western Paleozoic and Triassic terrane, which is
composite Klamath terranes became joined to the significantly older than subterranes of the Western
stable North American continent. Klamath belt, was accreted in middle late Jurassic then
rotated to its current northwest facing configuration in
Individual Terranes
Mesozoic and Tertiary time. Also known as the Apple-
After delineating and mapping these terranes, gate, this terrane has been subdivided into three
the process of grouping the many isolated pieces subterranes. The Rattlesnake Creek subterrane origi-
together is the next step in reconstructing their origins nated as an ocean crust or "ophiolite". The Hayfork
and history. In the Oregon Klamath province there are subterrane, which represents a volcanic island archipel-
seven recognized terranes which are further subdivided ago, is laminated between the Rattlesnake and May
into multiple subterranes. Two terranes in the Klama- Creek subterranes. The May Creek, which is also
ths of northern California, the Eastern Klamath terrane ophiolitic, has been heavily distorted and altered by
and the Central Metamorphic terrane, do not extend heat and pressure to high grade metamorphic rocks.
into Oregon. From east to west, or from the oldest to The Western Paleozoic and Triassic terrane has tropi-
youngest, Oregon Klamath terranes include the West- cal fossil faunas similar to those found in the Cache
ern Paleozoic and Triassic belt, the Western Klamath Creek terrane in British Columbia and the Baker
terrane, also known as the Western Jurassic belt, the
terrane in the Blue Mountains.
