T - Structure and . Metamorphism in the ' Mono Craters Quadrangle * Sierra Nevada, California ( By RONALD W. KISTLER : CONTRIBUTIONS TO GENERAL GEOLOGY GEOLOGICAL SURVEY BULLETIN 1221-E UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1966 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY William T. Pecora, Director For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price 50 cents (paper cover) CONTENTS Page Abstract __ -_.---------___---___---___-_-___-.-_______---.-_.____ El Introduction._____________________________________________________ 2 Previous geologic investigations._________-___-_--__-_-___-___-._ 3 Scope of report and acknowledgments._.-_____.____.__-_--_--__-_ 4 Metamorphic rocks._______________________________________________ 4 _l Stratigraphy and structure_-__-__________-____._-___------__-_ 4 Petrography...__'--______-_________________-_______--_-_______ 22 Metamorphic assemblages..-.__._--.__-.-_-._-__-_--_--_.-_ 22 Textures...._---__....___...__.._.._...._..-__.-__.__.._ 23 ' Mineralogy._---__----------.-----.__--_---_-__-------_-.- 24 Deformation.__._._-____.____.__.__.____.._...._.._._..____.__ 29 '"** Generations of folding..____________________________________ 29 , Extent and cause of deformation in the pendant rocks._________ 34 Ages of the deformational episodes_--_--_--_--__------------- 38 Temporal relation of deformational episodes to granitic intrusions. 39 Conditions of metamorphism___--_________--____--________-_--_-_--_ 41 Faulting....-__---_-_--__-----__----___---__----_-_--------------- 42 Range-front faults.__..__--______-.____.__-_________----__-_--- 42 Range-front embayment._---__-_--___--__________-__-__-------- 43 Range-front embayment and the Mono Craters.___________________ 47 * Summary. ________________________________________________________ 49 References cited.--___---____-____---__----___-_-_________-----_--_ 50 ILLUSTRATIONS Page PLATE 1. Sketch map and structural diagrams for roof pendants in the Mono Craters quadrangle, California_________---___ In pocket 2. Location map and mineral paragenesis of sectioned specimens of metamorphic rocks, Mono Craters quadrangle, California..In pocket FIGURE 1. Index map showing location of Mono Craters quadrangle. E2 2. Map showing location of roof pendants in the quadrangle. _____ 5 3. Photograph of congolmerate at base of the Koip sequence... 6 4. Map showing outcrop area of the Lewis sequence.----------- 5. Photograph of tight folding in thin-bedded metamorphosed siltstone in the Lewis sequence, Log Cabin Mine roof pendant ____________________________________________ 6. Photograph of minor folds in a calc-silicate hornfels in the Lewis sequence, Gull Lake roof pendant..______________________ in IV CONTENTS Page FIGURE 7. Photograph of folds in the Lewis sequence, Gull Lake roof pendant-______---_--_______-__._______-_._______ E10 8. Sketch map of Log Cabin Mine roof pendant showing location of lithologic sections A-A1 and B-B' ________ 13 9. Map showing outcrop area of Koip sequence.__________ 14 10-15. Photographs of parts of the Koip sequence: 10. Steeply dipping graywackes and volcanic rocks. _ 15 11. Complex folding in metamorphosed graywackes and volcanic rocks._______________________ 15 12. Fold in volcanic phyllite.-__--------_-----_-_ 16 13. Folds in foliated volcanic rock________________ 16 14. Lineations caused by intersecting cleavage and bedding_ _______________________________ 17 15. Technically elongated pebbles in volcanic wacke. 18 16. Analytical data and rubidium-strontium isochron age- determination graph.__-__-__-___-_-_-___-_-._____ 19 17. Map showing outcrop area of Dana seq uence.. ------ 20 18. Photograph of scour and fill in sandstone unit of the Dana sequence.__________________________________ 21 19. Photograph of bedding in the Dana sequence at top of Mount Dana___--_----_______________________ 21 20. Photograph of bedding in the Dana sequence on south­ west flank of Mount Dana___________--___-________ 22 21-26. Photomicrographs of metamorphic rocks in the quad­ rangle: 21. Wollastonite skarn__________________________ 24 22. Crystalline lithic tuff ____________________ 25 23. Crystalline lithic wacke-.-------------------- 26 24. Muscovite-biotite schist_______-_____--____- 27 25. Subfeldspathic lithic wacke___-____.__-_____ 28 26. Metamorphosed basalt_____________________ 29 27. Structural geometry of domains in the Koip sequence and synoptic geometry of /3 axes and axial planes in the Koip and Dana sequences___-_-----____________ 31 28. Snyoptic diagram of principal fold axes in the Lewis sequence._______________________________________ 34 29. Sketch map showing strike of axial surfaces of folds in deformed wallrocks and roof rocks in the Sierra Nevada.---_------------------_-------------_--- 37 30. Graph and analytical data for rubidium-strontium whole-rock age determinations and potassium-argon age determinations______________-----_-_-_----- 40 31. Sketch map showing range-front faults bordering the Sierra Nevada in the Mono Craters quadrangle _. 42 22. Geologic map of Mono Craters vicinity_.___-._____-_ 44 33. Photograph of mylonite near contact between hornblende- bearing quartz monzonite and porphyritic quartz monzonite at Grant Lake-__--_-____----__-----_--_ 46 34. Sketch map showing relation of Mono Craters ring- fracture zone to the geophysically determined subsi­ dence beneath Mono Lake.________________________ 48 CONTENTS TABLES Page TABLE 1. Lithologic units in the sequences in roof pendants, Mono Craters quadrangle._______-.-____-___.-_-_--_____ E7 2. Lithologic sections in the Lewis sequence, Log Cabin Mine roof pendant, showing altitudes along lines ^-A'andB-B'of figures.--..-------------------- 12 3. Summary of mineralogy of the metamorphic rocks in the Mono Craters quadrangle._________________________ 23 4. Schematic diagram showing number of deformations determined in several roof pendants and areas of wall- rock in the Sierra Nevada. ___-______--______--_-___ 36 CONTRIBUTIONS TO GENERAL GEOLOGY STRUCTURE AND METAMORPHISM IN THE MONO GRATERS QUADRANGLE, SIERRA NEVADA, CALIFORNIA By KONALD W. KlSTLER ABSTRACT The Mono Craters quadrangle, California, was an area of marine sedimenta­ tion during most of the Paleozoic. Rocks of Devonian and Mississippian ages have not been identified and may be absent; such a hiatus would suggest that the area was structurally high during the Antler orogeny, which affected rocks to the northeast in Nevada. Marine miogeosynclinal sedimentary rocks of Ordovician(?), Silurian(?), Pennsylvania!! (?), and Permian (?) age, called the Lewis sequence, were tightly folded along north-striking axial surfaces during a Permian (?) deformation tentatively correlated with the Sonoma orogeny of the same age in Nevada. Volcanic and clastic sedimentary rocks, called the Koip sequence, were de­ posited in the Late Permian (?) unconformably on the folded Lewis' sequence immediately after the Sonoman deformation. Both the Lewis and the Koip sequences were subsequently folded during a deformation that occurred in the Early or Middle Triassic. Axial surfaces of folds formed in this deformation strike northwest and are vertical or steeply dipping. A sequence of granodiorite and quartz monzonite plutons was intruded into the Permian (?) and older lay­ ered rocks in the Late Triassic and Early Jurassic, perhaps during the waning stages of this orogeny. Coarse clastic sedimentary rocks and volcanic rocks, called the Dana sequence, were deposited in the Early Jurassic unconformably on the Koip sequence. The Lower Jurassic and older rocks were all folded during the Nevadan orogeny of Late Jurassic age. A pluton of granodiorite, one of a sequence of plutons in the central Sierra Nevada, was intruded into the area of the quadrangle during the Late Cretaceous. The effects of all three deformations are of regional extent and have been observed in the wallrocks and other roof pendants of the Sierra Nevada. The large-scale structures in the intruded pendant rocks could not be related to con­ tacts with plutons. With the exception of the hornblende-bearing quartz mon­ zonite in the east-central part of the quadrangle, the plutons were evidently emplaced passively. Mineral assemblages in the roof pendants are the result of a complex metamor- phic history and are compatible with the hornblende hornfels facies of contact metamorphism and the almandine amphibolite facies of regional metamorphism. El E2 CONTRIBUTIONS TO GENERAL GEOLOGY The Cenozoic history of the quadrangle is one of uplift and erosion. It is not well defined until the glacial advances and the volcanism in the pleistocene. Most of the faulting along the front of the Sierra Nevada in the quadrangle took place during the Pleistocene in the interval between the Sherwin Glaciation and the eruption of the Bishop Tuff. Since eruption of the Bishop Tuff, a maximum of 2,800 feet of displacement has occurred under Mono Lake along faults to the east of those along the range front. INTRODUCTION The Mono Craters 15-minute quadrangle in east-central California includes parts of the Basin and Range and Sierra Nevada physio­ graphic provinces (fig. 1). Several thousand feet of the more than 6,500 feet of topographic relief in the area is due to displacement along faults that separate the two provinces. The crest of the Sierra Ne­ vada is a sinuous line near the west boundary of the mapped area. Stream drainage is eastward from this crest into Mono Lake Basin