Abstract

Deformed quartzite breccia of the Onaping Formation, from the northeastern end of the South Range, contains quartz that occurs as elongate ribbons displaying extreme undulatory extinction and small recrystallized grains. The quartz optic axes of the ribbon grains and the recrystallized grains lie on small circle girdles, with the girdle axes approximately normal to the foliation. The angle between the girdles and the girdle axes is approximately 35°. The rocks display a prominent tectonic foliation and this is due to the dimensional preferred orientation of fragments. The quartzite breccia appears to be a natural analog of quartzites experimentally deformed under conditions of intermediate temperature and strain rate.

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