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Pegmatitic Trachyandesite Plugs and Associated Volcanic Rocks in the Saline Range-Inyo Mountains Region, California

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Pegmatitic Trachyandesite Plugs and Associated Volcanic Rocks in the Saline Range-Inyo Mountains Region, California Pegmatitic Trachyandesite Plugs and Associated Volcanic Rocks in the Saline Range-Inyo Mountains Region, California GEOLOGICAL SURVEY PROFESSIONAL PAPER 614-D Prepared in cooperation with the California Department of Conservation Division of Mines and Geology Pegmatitic Trachyandesite Plugs and Associated Volcanic Rocks in the Saline Range-Inyo Mountains Region, California By DONALD C. ROSS SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 614-D Prepared in cooperation with the California Department of Conservation Division of Mines and Geology UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1970 UNITED STATES DEPARTMENT OF THE INTERIOR WALTER J. HICKEL, Secretary GEOLOGICAL SURVEY William T. Pecora, Director For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 CONTENTS Page I age Abstract. ___________________-_-_-__-_--------_----_ Dl Trachyandesite caprocks of the Saline Range_________ Dll Introduction. _________________---_-_-------___----- 1 Field description and relations_________________ 11 General name for the Saline Range caprocks___________ 1 Microscopic description________________________ 14 Intrusive trachyandesite-____________________________ 4 Chemical data________________________________ 15 Field description and relations.___________________ 5 Age of the trachyandesite_________________________ 15 Microscopic description ___________--____----_ 5 Felsic to intermediate volcanic rocks _________________ 17 Chemical data. _________--_-__--_-----------_ 9 Owens Valley volcanic rocks_________________________ 18 Comparison of pegmatitic core rocks with similar Chemical characteristics of the Saline Range suite.____. 20 rocks of other areas._______________-----_----_ 10 Regional indications of an alkaline suite._____________. 27 Other occurrences of intrusive trachyandesite ___ 11 References cited.___________________________________ 28 ILLUSTRATIONS PLATE 1. Geologic maps of volcanic rocks in the northern Inyo Mountains region, Inyo County, California._____In pocket FIGURES 1-3. Photograph of 1. Tuff beds capped by cinder and ash beds__________________________________________________ D4 2. Crudely bedded red ash and cinder deposits and sill-like part of north intrusive body of trachyandesite in window in Saline Range__ ___________-___.-_______-_____________-__--_____----_----- 4 3. Contact between intrusive body and cinder beds_ ____________________________________________ 5 4. Photographs showing relations of pegmatitic core rocks to marginal rocks in the southern trachyandesite plug_______________________ ___________________________________________________ ______ 6 5. Photomicrographs of rocks from intrusive trachyandesite plugs__-_________-_________-_____---_-__--_- 7 6. Photographs of selected hand specimens from intrusive trachyandesite plugs________________----___--_- 8 7. X-ray diffraction patterns of selected minerals from specimen 7__-__-__------_------_----__----------- 9 8. Photographs of vesicular and amygdaloidal trachyandesite dike.____-_____-__________-___------------- 12 9-11. Oblique aerial view 9. Across south end of trachyandesite field of Saline Range.__-__--_____-_-____-_____---_------- 13 10. Of locality of specimen 14_____________________________--_________-_-_-__-_____-----_----- 14 11. Northward along east side of the Saline Range trachyandesite field-________________-_-____---- 14 12. Graph showing refractive index of fused samples of volcanic rocks of the Saline Range-Inyo Mountains region.____________________________________________________________________________________ 16 13. Plot of total alkalis and silica for volcanic rocks of the Saline Range area-______-_-___-_____-_--------- 19 14. Variation diagram showing classification of Saline Range-Inyo Mountains suite according to alkali-lime index. _ 20 15. Graph showing relation of refractive index of fused-glass beads to percentage of oxides in chemically ana­ lyzed volcanic rocks._-_______-_____________.___________-__-_____-___-______-_____-_-_-__---- 21 16-18. Graphs showing 16. Selected oxide ratios of volcanic rocks_______-__-_____________-_-___-___-_-----------_----- 22 17. Variation of common oxides and silica in volcanic rocks.___-____-____--_____-_____-_----_---_ 23 18. Relation of oxide percentage to differentiation index of volcanic rocks-________-___-_-_-_-_---__ 24 19. Ternary plots of selected oxides and normative minerals of volcanic rocks.____________-_____------_---_ 25 20. Graphs showing trace-element trends in volcanic rocks___--_________________________-___-_----___-_-_ 26 TABLES TABLE 1. Analyses of volcanic rocks in the northern Inyo Mountains-Saline Range region._______________________ D2 2. Thin-section modes, Saline Range volcanic rocks_______________-__-___________--------_-__---------- 15 3. Potassium-argon ages of trachyandesites________________-_____-__-___------_-----_-_--------------- 16 4. Normative mineral comparison of Owens Valley flows._________________________.___-___-_--------_-- 19 in SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY PEGMATITIC TRACHYANDESITE PLUGS AND ASSOCIATED VOLCANIC ROCKS IN THE SALINE RANGE-INYO MOUNTAINS REGION, CALIFORNIA By DONALD C. Ross ABSTRACT as field examination and even thin-section determina­ Two small late Tertiary volcanic plugs (made up of interme­ tion is insufficient to ascertain the chemical character­ diate plagioclase, sanidine, clinopyroxene, olivine, and metallic istics of these largely aphanitic rocks. As the chemical opaque minerals) on the west flank of the Saline Range grade from fine-grained pilotaxitic trachyandesite at their margins to data slowly accumulate, it is becoming apparent that coarse-grained, miarolitic, pegmatitic rocks at their cores. The there is a large alkalic province of Cenozoic volcanic plugs intrude layers of cinder, ash, and tuff that lie immediately rocks in this region that might go undetected without beneath a vast volcanic cap which covers about 125 square miles such data. and whose black olivine-bearing rocks are dominantly trachy- The great bulk of the volcanic rocks cover most of andesites that contain about 2 percent K2O. that part of the Saline Range that is within the Chemical analyses and semiquantitative spectrographic anal­ yses were determined for 16 volcanic specimens from the area. Waucoba Wash quadrangle and adjoining parts of the These chemical data are supplemented by determinations of the lower east slopes of the Inyo Mountains. These volcrnic index of refraction of fused-glass beads from 54 volcanic spec­ rocks are dominantly a great caprock flood of trachy­ imens. Potassium-argon determinations from K-feldspar and andesite flows and agglomerate. A window on the vest clinopyroxene of one of the plugs and from three whole-rock flank of the Saline Range exposes the unusual fine to samples of the capping flows give uppermost Pliocene ages. These new chemical data extend the large area in the Sierra coarse-grained intrusive rocks of the plugs as well as Nevada and western Great Basin where late Cenozoic mafic cinder beds, tuff, and tuffaceous sedimentary rocks that volcanic rocks seem to be typically alkaline and particularly underlie the volcanic caprock. Beneath the capp;ng rich in KjO. trachyandesite elsewhere in the Saline Range are a few INTRODUCTION exposures of more felsic volcanic rocks and alluvial deposits with ash and pumice-rich layers. Volcr.nic On the west flank of the Saline Range, a window in rocks are absent at higher altitudes in this part of the a vast field of upper Cenozoic trachyandesitic volcanic Inyo Mountains, but low on the western slopes tHre rocks exposes two small plugs that have coarse-grained are several patches of dark basaltic ash and cinders, in pegmatitic cores that grade marginally into a fine­ part mixed with alluvial material that originated from grained pilotaxitic rock. The purpose of this report is a small volcanic center just north of the area of p^te to describe these rather unusual rocks and their volcanic lA at the west base of the Inyo Mountains or that associates and to present the chemical and petrogra- originated from volcanic centers at the east base of the phic data that have been accumulated on these vol­ Sierra Nevada to the west. The volcanic rocks shown canic rocks during the geologic mapping of a cross in Owens Valley are the ends of basaltic flows that section of the Inyo Mountains (Independence and originate along faults (marked by alined cinder cones) Waucoba Wash 15-minute quadrangles). Location of along the east front of the Sierra Nevada (Moore, 19*3). the volcanic rocks of this region is shown on plate 1. Geologic maps of and reports about the two quad­ GENERAL NAME FOR THE SALINE RANGE CAPROCKS rangles already published (Ross, 1965, 1967a, b) show their distribution in more detail and also contain brief The flood of black volcanic rocks capping the Saline descriptions of these units. Range, which commonly contain visible phenocrysts of Published chemical data on volcanic rocks of this olivine and (or) pyroxene are, by field classification, region are scarce. It therefore seems particularly desir­ basalt. As can be seen from table 1, however, tHse able to get chemical data on the volcanic rocks of the rocks do not have the chemical composition of typical Inyo Mountain-Saline Valley region into the literature, basalts (see, for example, table 2 in Yoder and Tilley Dl tod TABLE 1. Analyses, in percent, of volcanic rocks in the northern Inyo Mountains-Saline Range region [Chemical
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