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

About 30 square miles of the area of this report is underlain by metamorphic rocks. The three largest masses, completely surrounded by igneous rocks, are roof pendants. They have a general orientation that parallels the attitude of known roof rocks to the north and west.

Regular, persistent layers of differing mineralogical composition in the schistose rocks of the largest metamorphic body, as well as the interlayering of the schists with marble and quartzite suggests that metamorphic layering is a reflection of sedimentary bedding. Schistosity is essentially parallel to the metamorphic layering.

The metamorphic body of Redwood Mountain is a sequence of metasedimentary rocks similar to the larger mass to the south. The most easterly pendant body probably contains a large amount of silicic metavolcanic rocks and is notably lacking in quartzite and marble. The remaining small metamorphic bodies are either root portions of roof pendants or large xenoliths.

No fossils were found in the area covered by this report, but fossiliferous rocks are known to be about 15 miles to the southeast, at Mineral King, where Durrell (1940) collected fossils that were dated as Upper Triassic. The metamorphic rocks are definitely older than the plutonic intrusives, as the intrusive rocks truncate the metamorphic ones and have caused contact metamorphism within them.

In the following descriptions, modifying mineral names are applied to metamorphic rock names. The modifiers are listed in order of increasing abundance of the minerals.

Mica-Feldspar-Quartz Schist. Schist is the most common of the metasedimentary rocks and is most abundant in the western part of the largest metamorphic mass, the Redwood Mountain body, and in some of the large xenoliths. The rocks are dark gray to black on fresh surfaces, but have a distinctive reddish-brown weathered surface. The reddish-brown color is commonly reflected in the soil adjacent to schist outcrops.

An approximate average composition of the schists is 25 percent potash feldspar and intermediate plagioclase, 25 percent biotite, and 35 percent quartz. The remaining 15 percent is muscovite, epidote in the more calcarcous schists, magnetite, zircon, apatite, garnet and rarely andalusite. The parent rocks were probably shales, argillaceous siltstones, and fine-grained sandstones in an intermixed sequence. An alternation of micaceous-feldspathic and quartzose layers is common and the layers range in thickness from a fraction of a millimeter up to 5 mm.

Quartzite. Fine-grained, massive quartzite, ranging from cloudy white to dark gray in color, is second to the schist in abundance and is most common in the southeastern portion of the largest pendant. Resistant quartzite beds form prominent narrow ridges on both sides of the Middle Fork of the Kaweah River near Hospital Rock; the local name Devil's Rockpile is applied to an area of blocky quartzite rubble from the ridge just north of the Hospital Rock Camp. The most common type of quartzite is predominantly quartz with subordinant amounts of feldspar and mica. Small amounts of diopside are also present, as are the common accessory minerals apatite, magnetite, and zircon. The parent rock of the quartzite was sandstone or chert with some argillaceous and calcarcous impurities.

Calcarcous Metamorphic Rocks. Calcareous rocks—in particular, marble—are abundant in a band trending northwest through the largest pendant. The most prominent outcrops of the band are in the canyon of the Marble Fork of the Kaweah River, along Paradise Ridge, and near Crystal Cave. Smaller isolated marble and calc hornfels masses are found along Generals Highway east of the Ash Mountain Park Headquarters. The fine- to coarse-grained marble is snow white to dark gray in color, much of it is banded, and the alternating gray and white layers probably reflect original bedding. A great variety of calc-silicate minerals has been developed where impurities were present in the marble, or where material has been added from the plutonic rocks. The calc-silicate materials are commonly pod-like and discontinuous, but in some localities well-layered plagioclase pyroxene hornfels probably reflects original composition and bedding. The calc-silicate minerals are best developed in the isolated calcareous bodies east of the Ash Mountain Park Headquarters and around the Barrington tungsten mine on the North Fork of the Kaweah River. The most common minerals are calcite, pyroxene of the diopside-hedenbergite series, garnet of the grossularite-andradite series, wollastonite, idocrase, quartz, plagioclase, epidote, hornblende, and biotite. Scheelite is also found locally in the calcareous rocks.

The pure marble was undoubtedly derived from limestone, and argillaceous, siliceous, and dolomitic impurities probably account for the well-layered calc-hornfels. The variance of composition of many adjacent, thin layers and the parallelism of these layers to the schistosity of the associated rocks suggests that the calc-silicate minerals represent the reconstitution of impure calcareous rocks. The irregular pod-like occurrences of calc-silicate minerals as well as occurrences at contacts between marble and igneous rocks can best be explained by the addition of magmatic material. The unaltered condition of the marble at some contacts, even where it is engulfed in plutonic rocks, demonstrates that magmatic material was not added in all places.

Amphibolite and Amphibole Schist. Amphibolite and amphibole schist are locally abundant north of Amphitheater Point, and less common as lenses in the schist and quartzite elsewhere in the roof pendants. The amphibolitic rocks are dark green, fine to medium grained, and generally somewhat schistose. Hornblende and intermediate plagioclase are the principal constituents, but some specimens are as much as 40 percent diopside. Biotite, quartz, and clinozoisite are less abundant; magnetite, titanite, apatite, zircon, pyrite, and rutile (?) are present as accessory minerals.

The parentage of the amphibolitic rocks is in doubt. One specimen from a layer of schist associated with the belt of amphibolite north of Amphitheater Point has a relict pyroclastic texture, and another specimen has relict quartz and feldspar phenocrysts in a recrystallized groundmass (photos 23, 24). These two specimens suggest the amphibolite is an altered volcanic rock. Directly west of the amphibolite, however, is a belt of marble. The proximity of calcareous rocks and the presence of diopside in some of the amphibolites also suggests a possible calcareous parentage for the amphibolites. It is well established that amphibolites can originate either by the metasomatism of carbonate sediments or by the reconstitution of basic igneous rocks (Adams, 1909; Engel and Engel, 1951; Poldervaart, 1953). The present study did not reveal sufficient evidence to choose between the two possible modes of origin of the amphibolitic rocks.

Metavolcanic Rocks. Rocks with relict volcanic or tuffaceous textures are rare in the roof pendants. Some of the hornfels and schist of the easternmost large roof pendant have affinities with volcanic rocks and will be considered as possible metavolcanic rock.

North of Amphitheater Point a small amount of metadacite is present. The rock has a blastoporphyritic texture, with plagioclase, quartz, and hornblende phenocrysts. The square cross-section of the quartz phenocrysts is suggestive of a volcanic origin. Associated specimens with elastic quartz grains suggest a tuff or tuffaceous sediment.

Cream-colored, fine-grained, massive metarhyolite (or metarhyolite tuff) is recognizable locally in the easternmost roof pendant. Associated with it is some light-colored hornfels with only hints of relict phenocrysts, or possibly relict elastic grains. Mineral proportions vary, but an average is 30 percent each of oligoclase-andesine, potash feldspar, and quartz, and 10 percent biotite. The chemical composition of the average compares favorably with common rhyolite, but could also represent an arkosic sediment. If the leucocratic hornfels is a metasediment, it is markedly dissimilar to the metasedimentary rocks of the other pendants. The scarcity of calcareous rocks, quartzite, and thinly banded mica schist in the eastern pendant suggests that the body may be chiefly a sequence of metavolcanic rocks.

Interpretation of Metamorphism. Well-developed schistosity in most of the metamorphic rocks, as well as the development of augen structure locally, indicates shearing. Almandine garnet was found at only one locality; the remainder of the metamorphic rocks are representatives of the biotite zone of Harker (1950).

Some of the schist and marble shows features characteristic of thermal or contact metamorphism. The development of andalusite, diopside, wollastonite, grossularite, and idocrase is characteristic of contact deposits. The growth of poikiloblastic muscovite crystals in a random orientation in some of the schists (photo 21) is suggestive of a second period of metamorphism superimposed on the regional metamorphism that formed the schists. The formation of the large, randomly oriented muscovite crystals could be related to the thermal metamorphism or to some later hydrothermal conditions.