A Laboratory Study of the Beech Granite Plagioclase

Introduction: In northeast Tennessee a complex basement of Pre-Cambrian crystalline rocks either unconformably underlies the oldest Cambrian sediments, or bears a faulted relationship to them. The complexity of these rocks is, indeed, so great that much doubt exists as to the origin and even the nature of their component rock units. Keith (1907, p. 3) subdivided these rocks into two large units: (1) the Cranberry "granite," in this region a highly contorted gneiss of complex lithology, and (2) the Beech granite, a rather porphyritic, generally coarse-grained granite which he considered to have been considerably squeezed and mashed. Of these Keith regarded the Beech to be the younger, since he believed it to have intruded the Cranberry.

The rock samples studied were collected from the White Rocks Mountain Quadrangle, particularly its northern portion, in which Beech granite shows a very typical and rather extensive development (Plate I, in pocket). Beech samples were collected from both sides of the Beech-Cranberry contact as mapped by Keith (1907).