Full Title: Major tectonic elements and tectonic problems along the line of section from northeastern Oregon to west-central Montana
Author: Donald W. Hyndman
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One 54" x 43" sheet. From text: A west-to-east cross section from northeastern Oregon to west-central Montana crosses the tectonic grain to the northern Rocky Mountains. It begins along the Oregon-Idaho border in rocks of an early Mesozoic volcanic arc developed over oceanic crust, continues through a late Mesozoic batholithic bell that could be interpreted as a deeply eroded volcanic arc over continental crust, onto the upper Mesozoic volcanogenic and nonvolcanic sedimentary rocks of the "back-arc basin," and into the overthrust belt adjacent to the continental platform (Fig. 1 and cross section). The rock groups and their spatial relationships to one another suggest that the section crosses many of the major elements of a continental-margin orogenic belt developed during Mesozoic time. Recent studies suggest that except for the early Mesozoic volcanic-arc complex, the remaining Late Cretaceous to earliest Tertiary tectonic elements may fit this general picture. The early Mesozoic tectonic element does not appear genetically related to the remainder of the orogenic belt, because its volcanic activity apparently occurred much earlier than most activity to the east, and it could be allochthonous for other reasons outlined below…
Published: 9/03/1978
Pages: 11, plus 1 sheet
Product Category: Maps and Charts