Abstract

The Cretaceous Deep Creek stock, a quartz diorite intrusion in the southern Seven Devils Mountains of west-central Idaho, consists of a funnel-shaped western portion and a lobe-shaped eastern prong. The western portion is concentrically zoned with an inward increase in potassium feldspar, quartz, and non-opaque accessories and decrease in biotite, hornblende, and opaque accessories.

The orientation of primary platy flow structure and marble xenoliths, as well as the mineral distribution, suggest that the western portion of the stock may extend to depth, but that the eastern prong is a shallow lobe. The platy flow structure is thought to have originated (1) by shear flow alignment of platy minerals parallel to contacts early in the emplacement history of the stock, and (2) by orientation of platy minerals normal to the direction of greatest magmatic pressure during the later stages of intrusion.

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