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Hetch Hetchy Reservoir Quadrangle, Yo Semite National Park, California- Analytic Data

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Hetch Hetchy Reservoir Quadrangle, Yo Semite National Park, California- Analytic Data Hetch Hetchy Reservoir Quadrangle, Yo semite National Park, California- Analytic Data GEOLOGICAL SURVEY PROFESSIONAL PAPER 774-B Hetch Hetchy Reservoir Quadrangle, YoSemite National Park, California- Analytic Data By RONALD W. KISTLER SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 774-B Chemical, spectro graphic, and modal analyses and potassium-argon age determinations on granitic rocks supplement Geologic Quadrangle Map GQ-1112 UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1974 UNITED STATES DEPARTMENT OF THE INTERIOR ROGERS C. B. MORTON, Secretary GEOLOGICAL SURVEY V. E. McKelvey, Director Library of Congress catalog-card No. 73-600259 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 Price 65 cents (paper cover) Stock Number 2401-02462 CONTENTS Page Abstract .......................................................................................................................................... Bl Introduction .................................................................................................................................. 1 Bedrock units ......................................................................................................... .. .. 1 Analytic data.................................................................................................................................. 1 References .................................................................................................... ................ .. 2 ILLUSTRATIONS Page FIGURE 1. Simplified geologic map of the Hetch Hetchy Reservoir 15-minute quadrangle showing locations of chemically analyzed samples and samples dated by potassium-argon methods ...................................... B4 2-6. Bedrock map showing 2. Volume percent quartz ........................................................................ 6 3. Volume percent potassium feldspar .................................................. 7 4. Volume percent plagioclase ................................................................ 8 5. Volume percent mafic minerals ......................................................... 9 6. Specific gravity ..................................................................................... 10 7. Modes and norms of granitic and volcanic rocks .......................................... 11 TABLES Page TABLE 1. Chemical and spectrographic analyses and norms ....................................... B13 2. Potassium-argon ages.......................................................................................... 14 ill SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY HETCH HETCHY RESERVOIR QUADRANGLE, YOSEMITE NATIONAL PARK, CALIFORNIA-ANALYTIC DATA By RONALD W. KISTLER ABSTRACT than 95 percent of the bedrock in the quadrangle (fig. Modal analyses of 226 samples and chemical analyses of 27 1). Intrusive relations observed in the field and potas­ samples of granitic rocks show that the average compositions of sium-argon and rubidium-strontium dating (Curtis and individual plutons range from quartz diorite to alaskite. Potas­ others, 1958; Evernden and Kistler, 1970; this report) sium-argon analyses of biotite and hornblende separates from made it possible to assign these formations to three age specimens of two granitic rocks yield ages in the range of 82-96 million years. groups. The early Cretaceous group is represented by a single unit of quartz diorite. In each of the Late Juras­ INTRODUCTION sic and Late Cretaceous groups, the oldest formation is The data in this paper are for use with the "Geologic quartz diorite, and the youngest is alaskite or aplite. map of Hetch Hetchy quadrangle, Yosemite National The oldest rocks of the quadrangle are marble, bio- Park, California", U.S. Geological Survey Map GQ- tite-muscovite schist, and quartzite in small roof pend­ 1112 (Kistler, 1973). The Hetch Hetchy quadrangle ants. These rocks, of probable Paleozoic age, are encompasses about 240 square miles in the center of complexly deformed and metamorphosed to horn­ Yosemite National Park. A single road, California State blende hornfels facies. Volcanic mudflows and a trachy- Highway 120, traverses the central part of the area. The andesite flow of Miocene (?) and Pliocene age occur in major topographic feature in the quadrangle is the isolated exposures to the north of the Grand Canyon Grand Canyon of the Tuolumne River, which ranges of the Tuolumne River. A specimen of trachyandesite in elevation from a little less than 4,000 feet along the from Rancheria Mountain has been dated as 9 million river to more than 9,000 feet along the canyon rim. years old (Pliocene) by the potassium-argon technique A dense forest, mainly on thick till and moraines (Dalrymple, 1963). deposited by ancient glaciers, covers about one-half of the quadrangle. ANALYTIC DATA F. C. Calkins (1930) published a geologic map of The specific gravity and modal composition of 226 part of the Yosemite Valley region that includes the samples of granitic rock were determined. Modal analy­ southeast corner of the quadrangle. Calkins assigned sis permits the volume percentage of the major minerals relative ages to the granitic formations and described of a granitic rock (quartz, potassium feldspar, plagio- their petrology. F. E. Matthes (1930) discussed the clase, and mafic minerals) to be calculated by determin­ glaciology of the Yosemite region and described in ing the mineral constituent present at each of 1,000- detail the tills and moraines along Yosemite Creek in 2,000 regularly spaced points on a sawed stained slab the south-central part of the Hetch Hetchy quadrangle. of the sample. The volume percentage of each mineral The present mapping and geologic study extend the species is shown for each sample locality on the simpli­ pioneering work of these men and is part of a continu­ fied bedrock map of the quadrangle in figures 2-5. The ing series of geologic investigations of bedrock geology percentages were contoured by visual inspection to of the central Sierra Nevada batholith (Bateman and show the compositional patterns for each mineral. Spe­ others, 1963). cific gravities are shown in figure 6. Chemical analyses by the rapid method of Shapiro BEDROCK UNITS and Brannock (1962) were made of 27 representative Twelve major granitic formations ranging in compo­ samples from 11 of the granitic units and of a single sition from quartz diorite to alaskite constitute more trachyandesite sample. Potassium-argon ages of biotite Bl B2 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY and hornblende separated from samples of two of the Calkins, F. C., 1930, The granitic rocks of the Yosemite region, granitic rocks were determined. The locations of the in Matthes, F. E., ed., Geologic history of the Yosemite chemically analyzed and the dated samples are shown Valley: U.S. Geol. Survey Prof. Paper 160, p. 120-129. Curtis, G. H., Evernden, J. F., and Lipson, J. I., 1958, Age in figure 1. The chemical data, together with semiquan- determination of some granitic rocks in California by the titative spectrographic analyses and CIPW norms, are potassium-argon method: California Div. Mines Spec. given on table 1. The analytical data used in the age Rept. 54,16 p. determinations are given on table 2. Dalrymple, G. B., 1963, Potassium-argon dates of some Ceno- Modes of the granitic rocks, recalculated to 100 per­ zoic volcanic rocks of the Sierra Nevada, California: Geol. cent, are plotted on triangular diagrams whose corners Soc. America Bull., v. 74, p. 379-390. are quartz, plagioclase, and potassium feldspar in figure Evernden, J. F., and Kistler, R. W., 1970, Chronology of emplacement of Mesozoic batholithic complexes in Cali­ 7. In the same figure, norms of the chemically analyzed fornia and western Nevada: U.S. Geol. Survey Prof. Paper samples are plotted on triangular diagrams whose 623, 42 p. corners are normative quartz, plagioclase (albite plus Kistler, R. W., 1973, Geologic map of the Hetch Hetchy quad­ anorthite), and orthoclase. rangle, Yosemite National Park, California: U.S. Geol. Survey Geol. Quad. Map GQ-1112. REFERENCES CITED Matthes, F. E., 1930, Geologic history of the Yosemite Valley: Bateman, P. C., Clark, L. D., Huber, N. K., Moore, J. G., and U.S. Geol. Survey Prof. Paper 160,137 p. Rinehart, C. D., 1963, The Sierra Nevada batholith a Shapiro, Leonard, and Brannock, W. W., 1962, Rapid analyses synthesis of recent work across the central part: U.S. Geol. of silicate, carbonate, and phosphate rocks: U.S. Geol. Survey Prof. Paper 414-D, 46 p. Survey Bull. 1144-A, 56 p. FIGURES AND TABLES B4 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 38°00' + + + + + + + + + + ) + + + + + + + + + +/ -t- + -t- + + + -t--t--i-+/; ;v.--.y:-.: : J37°45' 119°45 119°30' 8 KILOMETERS FIGURE 1. Simplified bedrock geology of the Hetch Hetchy 15-minute quadrangle and locations of chemically analyzed samples and samples dated by potassium-argon methods. HETCH HETCHY RESERVOIR QUADRANGLE, CALIFORNIA B5 EXPLANATION VJ!PVj j j _i _i j _i j j j j Volcanic mudflows and trachyandesite :/:-.Kh;::.V.'- Aplite Hal " Dome Quartz Monzonite CretaceousPlioceneUpperCretaceousLower ~^^ ^J^i\7\~ Sentinel ( jranodiorite ill! ^ ffi Y Dsemite Creek Quartz diorite of Granodiorite Mount Gibson of Rose Qu artz diorite of Ta marack Creek Granodiorite of Granodiorite of Quartz diorite of South Fork of Tuolumne River 80 UJ o 28 Diorite ms mv Metamorphic rocks ms, sedimentary rocks mv, volcanic rocks H-40-64 Chemically analyzed sample H-27 Sample dated by
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