Abstract

The accompanying tectonic map of the Sierra Nevada of California has been compiled from both published and unpublished sources. It represents trends of plates (cleavage-, bedding-, flow-, and shear-layers), in both the metamorphic and the granitic rocks. The exposed edges of these plates combine into lanes, such as the San Andreas Rift, and curves, such as the westward hook of the southern part of the Sierra. These forms appear in all sizes down to that of the hand specimen.

On this map the Sierra becomes a shift zone with principal motion horizontal shear along the lanes, and with displacement northwestward on the Pacific side. Subsidiary motion starts at inequalities in strength and creates curves in which the inner parts are thrust upward and outward toward their convex sides. The resultant motion is clockwise in horizontal section.

Heat concentrated inside the curves promotes crystallization through grades of metamorphism that end with granite. The granite is found in funnel-shaped units enlarging upward to maximum surface diameters of 12 miles. As such units become frozen together, the resulting pluton grows so strong that continuing motion is forced out into the weaker material. For example, present motion is confined to the San Andreas, Walker and other lanes outside the main granite body.

The heat escaping from such structures toward or to the surface is represented by ore deposits, volcanoes, and hot springs.

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