Fieldtrip guide to the metamorphic framework rocks of the Lake Isabella area, southern Sierra Nevada, California

Abstract

Metamorphic framework rocks of the southern Sierra Nevada occur primarily as N to NW striking, steeply dipping septa, within or separating granitoid plutons. The Lake Isabella area offers an excellent opportunity to study some of the interesting structural and stratigraphic problems posed by the southern Sierra framework rocks. Figure 1 is a generalized geologic map of the Lake Isabella region which focuses mainly on the metamorphic framework rocks. The map is derived primarily from our detailed mapping which was based on several earlier field studies. The general distribution of the major igneous and metamorphic units of the region was originally mapped by Miller and Webb (1940) with contributions by Jenkins (1961) and Alvarez (1962). Miller and Webb (1940) termed the distinctive quartz-rich metasedimentary rocks and marble of the region the Kernville series. Detailed mapping immediately adjacent to Lake Isabella by L.E. Weiss (unpublished data) revealed some of the complex deformation patterns in rocks of the Kernville Series, and also led to the discovery of the only fossil 1oca1ity of the region. In later regional studies Saleeby and others (1978) noted that the Kernville Series and newly discovered silicic metavolcanic rocks of the area were similar to the Kings sequence of the central Sierra as defined by Bateman and Clark (1974), Metamorphic framework rocks referred to as the Kings sequence by these workers consist of quartz-rich metasedimentary strata, marble, local pelite and scattered intervals of silicic metavolcanic rocks forming numerous steeply dipping septa in the central part of the range. Recognizing that regional workers are more familiar with Kings sequence rocks of the central Sierra, Saleeby and others (1978) suggested that Kernv111e Series rocks be termed Kings sequence, and that such rocks also extend southward from the Lake Isabella area to the southern terminus of the range, Thus the Kings sequence extends for ~300 km along the axis of the Sierra Nevada, and constitutes one of the major framework elements of the range.

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