California Division of Mines Speial Report 53 Igneous and Metamorphic Rocks of Parts of Sequoia and Kings Canyon National Parks, California

The area described in this report includes about 150 square miles on the west slope of the Sierra Nevada in Tulare County, California. Approximately 30 square miles of this area is underlain by elongated roof pendants of metamorphic rocks that dip steeply and strike northwest. Two of the major metamorphic bodies are predominantly metasedimentary; the third probably contains some leucocratic metavolcanic rocks. The remainder of the area is underlain by 13 mappable plutonic types ranging in composition from gabbro to alaskite.

Inter-pluton contacts are generally sharp. Contacts between plutonic rocks and metamorphic rocks are either sharp or show injection zones with varying amounts of assimilation. The abundance of lit-par-lit zones at lower altitudes may reflect the nearness of the pendant roots.

The magma was emplaced in part by assimilation and stoping, but no evidence was found in support of forcible injection. The small amount of wall rock, however, precludes conclusions as to the dominant intrusion mechanism.

The relative age of the various plutons is commonly difficult if not impossible to determine, but one well established sequence involves four of the most important units. The four bodies show an increase in silicity with a decrease in age, and also a concentric pattern with each succeeding younger body intruding the core of the older pluton.

The age of the metamorphic rocks was not determined; the plutonic rocks are assumed to be Jurassic Cretaceous on the basis of dating elsewhere in the Sierra Nevada and in associated plutonic areas.

Xenoliths are rare in the plutonic rocks in general, but are locally abundant. Some rhythmic hornblende layering is probably due to alternate settling of hornblende crystals and sweeping by convection currents. The origin of most of the inclusions is unknown, but some have formed by the recrystallization of metamorphic rocks and gabbro.

FIGURE 1. Index map of Sequoia area. (click on image for an enlargement in a new window)