143 Microscopic Petrography – Cinder Cones and Associated Flows

The Geology of Crater Lake National Park, Oregon With a reconnaissance of the Cascade Range southward to Mount Shasta by Howell Williams

Microscopic Petrography


Cinder Cones and Associated Flows

In this section, our concern is with the andesitic and basaltic products of the parasitic cones active at about the same time as the Northern Arc of Vents, and with the products of the final activity of Mount Mazama, namely the cinder cone and flow of Wizard Island.

Most geologists, seeing these rocks in the field, would not hesitate to classify them as basalts. The truth is, however, that whereas olivine basalts do occur among them, the majority are more properly to be spoken of as basaltic andesites, “basaltic” on account of their texture and the presence of considerable olivine, but “andesites” on account of their chemical composition. Since they resemble the pre-Mazama lavas within the park and the products of the Union Peak volcano, a brief account will suffice.


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