Stop 4. Pine Valley Monzogranite

Return to the intersection of Sunrise Highway and Old Highway 80. Turn right (west) and drive approximately 150 yards to the fresh outcrops on either side of the road.

This unit is a leucocratic biotite-bearing monzogranite with trace amounts of hornblende. It is unique in that it contains 1 to 2 cm. megacrysts of alkali feldspar and, despite its location in the magnetite zone of the PRB, has essentially no magnetic susceptibility. Although the parts of this pluton studied thus far do not show significant deformation, apophyses of this unit mapped within the CLMSZ have a superimposed penetrative solid-state deformation(Todd and Shaw, 1979; Leeson, 1988). Zircons from this outcrop yielded a concordant age of 118 Ma that is consistent with a similar unit 10 miles to the north for which an age of 119 Ma has be-en reported (L.T. Silver as cited in Todd and Shaw, 1979). This constrains the movement picture on the CLMSZ to post 118 but pre 94 Ma.

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