POST-12 Million Year Clockwise Rotation in the Central Columbia Plateau, Washington

The Pomona flow (12 m.y. B.P,) of the Columbia River Basalt Group was sampled for paleomagnetic analysis at 32 sites in the Yakima Fold Belt of the central Columbia Plateau to assess the pattern of deformation. Field directions from anticlinal ridges are found to be rotated clockwise relative to sites from synclinal areas. Two geographic patterns of rotation are present. The primary pattern is one in which the greatest amount of rotation occurs in the crest-hinge area of the anticlines and decreases into synclines. A secondary pattern, in which the amount of rotation is consistent within a geometric segment but varies among them, is superimposed on the primary pattern. The pattern of clockwise rotation is interpreted to be the result of local tectonic rotation occurring along a closely spaced north-northwest trending primary shear system and northeast trending secondary shear system. The shear system and concurrent rotation are interpreted to have developed during the growth of the Yakima folds. The relationship between the paleomagnetic data and the geologic structures can be used to constrain tectonic models for the Columbia Plateau. The data reported in this study indicate that clockwise rotation can not be attributed to rigid block or microplate rotation, but support models that predict localized dextral shear. Furthermore, it is postulated that this mechanism may contribute to clockwise rotation observed in other parts of the western United States.

[1]  M. Beck,et al.  Paleomagnetism of intrusive rocks in the Coast Range of Oregon: Microplate rotations in middle Tertiary time , 1980 .

[2]  M. Beck.  Paleomagnetic record of plate‐margin tectonic processes along the western edge of North America , 1980 .

[3]  Terry L. Tolan,et al.  Intracanyon flows of the Columbia River Basalt Group in the lower Columbia River Gorge and their relationship to the Troutdale Formation , 1984 .

[4]  D. Swanson,et al.  Magnetostratigraphy and correlation of Miocene basalts of the northern Oregon coast and Columbia Plateau, Southeast Washington , 1979 .

[5]  S. M. Price,et al.  Geologic studies of the Columbia Plateau: a status report , 1979 .

[6]  P. Coney,et al.  The Growth of Western North America , 1982 .

[7]  M. Beck.  Discordant paleomagnetic pole positions as evidence of regional shear in the western Cordillera of North America , 1976 .

[8]  R. Coe,et al.  "Paleomagnetism and geology of Eocene volcanic rocks of southwest Washington, Implications for mechanisms of tectonic rotation"" , 1985 .

[9]  R. Bates,et al.  Tectonic rotations in the Cascade Range of southern Washington , 1981 .

[10]  A. Cox,et al.  Post-Oligocene tectonic rotation of the Oregon Western Cascade Range and the Klamath Mountains , 1981 .

[11]  N. J. Silberling,et al.  Mesozoic stratigraphy: the key to tectonic analysis of southern and central Alaska , 1979 .

[12]  Brian R. Globerman,et al.  Paleomagnetism and tectonic significance of Eocene basalts from the Black Hills, Washington Coast Range , 1982 .

[13]  M. Beck,et al.  Paleomagnetism and tectonic significance of the Goble Volcanic Series, southwestern Washington , 1979 .

[14]  R. Duncan,et al.  Tillamook Volcanic Series: Further evidence for tectonic rotation of the Oregon Coast Range , 1981 .

[15]  A. C. Waters,et al.  Stratigraphic and lithologic variations in the Columbia River basalt , 1961 .

[16]  S. Gillett,et al.  Magnetostratigraphy of the Columbia River basalt, Pasco Basin and vicinity, Washington , 1981 .

[17]  R. Simpson,et al.  Paleomagnetic evidence for tectonic rotation of the Oregon Coast Range , 1977 .

[18]  R. Simpson,et al.  Post 12 m.y. rotation of southwest Washington , 1982 .

[19]  V. Camp.  Geologic studies of the Columbia Plateau: Part II. Upper Miocene basalt distribution, reflecting source locations, tectonism, and drainage history in the Clearwater embayment, Idaho , 1981 .

[20]  R. Wells.  Geologic map of the eastern Willapa Hills, Cowlitz, Lewis, Pacific, and Wahkiakum counties, Washington , 1981 .

[21]  N. Watkins,et al.  Magnetostratigraphy and oroclinal folding of the Columbia River, Steens, and Owyhee basalts in Oregon, Washington, and Idaho , 1974 .

[22]  A. Cox.  Remanent Magnetization of Lower to Middle Eocene Basalt Flows from Oregon , 1957, Nature.

[23]  P. Coney,et al.  Cordilleran suspect terranes , 1980, Nature.

[24]  W. Macdonald,et al.  Net tectonic rotation, apparent tectonic rotation, and the structural tilt correction in paleomagnetic studies , 1980 .

[25]  R. Freund.  Kinematics of transform and transcurrent faults , 1974 .