CALIFORNIA STATE UNIVERSITY, NORTHRIDGE SUPERPOSED MESOZOIC DEFOR~~TIONS~ }) SOUTHEASTERN INYO tt;OUNTAINS, CALIFORNIA A thesis submitted in partial satisfaction of the requirements for the degree of 14aster of Science in Geology by Michael Robert Werner Janu(l.ry 3 i 979 The Thesis of Michael Robert Werner is approved: Or. L. Ehltg}rCSULA) Ca 1i forn i a State Un i vers ·j ty, Northridge ii ACKNOWLEDGEMENTS ~1y respectful thanks to George Dunn£ for suggesting this study and for his helpful comments throughoutthe investigation. I am grateful also to Rick Miller and Perry Eh1ig VJho reviewed the manuscript in various stages of preparation. !'r1y special thanks to my parents for theit~ emotiona1 and 1ogistica·i support, and to Diane Evans who typed the first draft. Calvin Stevens and Duane Cavit, California State University~ San Jose, provided valuable information on stratigraphy; and Jean Ju11iand, geologist of the Desert Plan Staff, BLM, Riverside, made available aerial photographs of the study area.· The Department of Geosciences, California State University. Northridge pi·ovided computer time and financial support. Terry Dunn, CSUN, typed the fina1 manuscript. iii TAaLE OF CONTENTS p~~ ACKNOl~LEDGEHENTS. .. 111 LIST OF ILLUSTRATIONS . vi ABSTRACT ... vii. INTRODUCTION 1 METHOD • 3 ROCK UNITS •. 5 PALEOZOIC STRATIGRAPHY . 5 Perdido Formation 7 Rest Spring Shale . .. 3 Keeler Canyon Formation 10 Owens Vulley Formation 14 MESOZOIC INTRUSIVE ROCKS . 16 • Hunter Mountain batholith 16 Andes 'ite porphyry di kas 17 CENOZOIC UNITS . 18 STRUCTURJl.L GEOLOGY 19 FOLDS • ~ . 19 Introduction 19 Folds in the Nelson Range . 21 F., - The San Lucas Canyon syncline 2"1 j r2 - Northwest-trending folds 31 Folds aajacent to the Hunter Mountain batholith 37 Folds in the Southeastern Inyo r'Jounta·ins 43 Southwest-trending folds 43 Northwest-trending folds . 46 FAULTS ....•. 48 Reverse faults 48 Northwest-trending high angle faults. 53 Northeast-trending high angle faults. 54 DISCUSSION. ; 55 REGIONAL MESOZOIC STRUCTURES . 55 RELATIONSHIP TO REGIONAL STRUCTURES 60 SUMMARY OF MESOZOIC HISTORY. 64 REFERENCES CITED. 66 v LIST OF ILLUSTRATIONS 1 Index map to eastet'n California 2 2 Generalized stratigraphic columns 6. 3 Index map to structural domains 20 4 Structu1al analysis (stereonet diagrams) 22 5 San Lucas Canyon syncline and related minor 27 structures 6 Block diagt~am of the San Luca.s Canyon syncline 33 and Lee Flat anticline ] Minor northwest-trending (F2) folds 35 8 Structures modified by emplacement of the batho1ith 9 Major folds adjacent to the batholith 42 10 Recumbent syncline in domain 12 44 11 Structures related to reverse fault in domain 5 51 12 Index map to major ~lesozoi c structures in 56 eastern California Pi ate 1 Geologic map of the Nelson Range and southern (in Inyo Hountains pocket) 2 Geologic cross sections (in pocket) vi ABSTRACT SUPERPOSED MESOZOIC DEFORMATIONS, SOUTHEASTERN INYO ~lOUNTAINS ~ CALIFORNIA by Michael Robert Werner Master· of Science in Geology Mapping in the Nelson Range and the adjacent southeastern Inyo Mountains shot-Js that this area has experienced at least two episodes of early ~1esozoic d<::formation which produced two sets of folds in Mis- s iss i pp·; ar. through Permian rocks. A 1a ter Mesozoic event may be repre- sented by f!iuHs in this area. The older fold set (F1) consists of generally northeast-trending, upright to southeast-overturned folds. A younger fold set (F~) is t.. superimposed upon and 1ocally refolds F, folds. F2 consists of gen­ erally northwest-trending, upright to northeast-overturned folds with steeply southwest·-dipping axial pl~ne clE-avage. r}~uncation of some F folds the Mm.lt'rt;;.in batholith in the Nelson Range indicates 2 by Hunter The style of r-.) " folds along portions of the intrusive co1tact suggests that emplace- v~ i rnent of the batholith locally appressed and deflected pre.-existing folds. Based on their orientation, sense of vergence and relative age, r 1 folds are believed to be temporally and structurally related to th~ Last Chance thru~t system (Middle (?) Triassic to Early Jurassic). folds are correlated with other northwest-trending fo1ds of pre-Middle Jurassi~ age ~hich occur throughout the ranges immediately east of the Sierra Nevada. Some nm·thwest-striking fauits in this area apparently are intruded by dikes of the Independence swarm and thus may be pre-Late Jurassic in age. If so, these faults may be related to a broad) north1:1est-trending zone of fractures and left-slip faults of Middle to Late Jurassic age which tr2nds obliquely acr-oss this region. viii INTRODUCTION The Nelson Range trends northwest across the southwest corner of the Ubehebe Peak quadrangle in Inyo County, Califon·ria (fig. 1). Paleozoic rocks exposed along the southwest flank of the range and in the eastern foothills of the southern Inyo ~1ountains consist of over 2100 m (6880 ft} of Mississippian thr·ough Permian mat~ine stata. These rocks have been intruded in the Nelson Range by the Hunter Mountain batholith of late Early Jurassic age. Initial regional mapping of the Ubehebe Peak quadrangle and vicinity by McAllister (1952~ 1956) demcn:itrated the predominance of north-and northwest-trending folds of Mesozoic age in the Paleozoic rocks of the Nelson Range and southern Inyo Mountains. Locally developed east­ trending folds, as we11 as northwest-trending folds roughly parallel to the intrusive contact in the Nelson Range, were believed to be the result of forceful batholithic emplacement (McAllister, 1956). North­ west-trending folds were also reported in the Darwin quadrangle to the south (Hal1 and MacKevett, 1962) and in the Cerro Gordo district to the west (l~erriam~ 1963), ·and these also were believed to have ·formed dudng emp1acement of nearby plutons. Recent geological investigations in areas adjoining the Nelson Range indicate that many folds pre·-date plutonism and that the ranges immediately c-ast of the Siert~a Nevada contain one of the most complete records of Mesozoic deformation in eastern California (Dunne and Gulliver> 19'16; Dunne and others. 1978). In the Talc City Hills, Gulliver (~971. l976a, l976b) reports three phases of Mesozoic folding, at least two of which are genetically related to faults of tegiona1 1 2 I 168 " . ~ "-r"- . ~..... ~ CD \!\ .,.. ~ ""' "? Q -vo <, -t-S' <. <;I'V 4-~ 0 ~-~- ,.;o (') '1- , -CD ~ .J.. 1'~ ...... 0 (,n a "~ DM Lone II -:1-l ~ DH 'Y 0 }?' ~ 0'\ ::0 ~ @ 0 0 N G'> "!) ~ c. 0 {,/) ~ ! 'P l "!) I ~p ':D Q "P - ;2!. ~· ·'- I G'> tP '( 0 t1'\ I 0 5 . miiss 25 ?'""' - j ~=- \ -<» "P(<\ 0 km 25 ~ \ ~ I! L___________ ,___ _I ~\'\ J Figure 1. Index map to eastern California. Ubehebe Peak quadrangle ano study area shmm ·in gray. /~bbreviatior.s are as follmvs: CG, Cerro Gor-do; GH~ Darv;in H'!l1s; Di-i, Dry iVlountain; K) Keeler; fY1C~ t•lazourka Canyon; QS. Quartz Spring; SR, Santa Rosa H1lls; TC, Talc City Hills; UP, Ubehebe ?eak; rlM, Hunter Mountain. 3 extent. In the Darwin Hills, Dunne and Gulliver (1976) recognized four deformational phases which span the Mesozoic aild are characterized by folds and faults of distinctive style and geometry. Elayer (1974) reports four phases of folding near Cerro Gordo in the southern Inyo i'<lountains, although, subsequent work by Nora (1978) in this same area suggests a somewhat simpler stru~tura1 history. The purpose of the present investigation was to determine whether the Nelsen Range and nearby eastern slopes of the southern Inyo Mount­ ains share a similar history of multiple superposed Mesozoic deformation as reported in adjoining areas. Preliminary work shov.Jed that this area bears the imprint of at least two phases of early Mesozoic deformation (Werner, 1978). These deformational phases are believed to be gene­ tically and temporally correlated with major structural features which define a portion of an early Mesozoic orogenic belt in eastern Califor­ nia (Burchfiel and others, 1970). ~1ETHOD The study area (fig. l) which consists of approximately 100 sq km, was mapped during 70 days of field work between June, 1976 and Septembe~ 1977. Field data were plotted directly on portions of the Ubehebe Peak, Darwin> and New York Butte 15' tcpographic quadrang1es which had been enlarged to a scale of 1:15,625 (approx. 4 inches to 1 mile). Field investigation was augmented by the use of color aeri31 photographs (scale 1:20,000) taken in December, 1975 for the Bureau of Land Manage- ment. Preoaration and contoudng of stel~eor.et diagrams \vas a~ded by the use of the Ca'lifornia State University~ Northridge (CSUN) CDC 3170 4 computer using the FORTRAN program PETROFAB (Werner, 1977}. ROCK UNITS PALEOZOlC STRATIGRAPHY Paleozoic sedimentary rocks which crop out w·ithin the study area consist of over 2100 m (6880 ft) of marine limestone, shale, siltstone, sandstone, and conglomerate which range in age from f~ississippian to Permian. Mississippian units are primarily fine-grained, siliceous clastics and include the Perdido Formation and Rest Spring Shale. Penn­ sylvanian and Permian strata, originally mapped as Bird Spring Formation by ~tcA11ister (1956), are assigned to the Keeler Canyon and Owens 'Ialley Formations and comprise a monotonous sequence of interbedded limestone and shale. This investigation indicates that rapid lateral variations in lithology character·ize several portions of the late Paleozoic section. Field evidence suggests that these variations can be attributed to ·iocal unconformities, possibly due to submadne erosion, as weii as facies changes associated with the transition from shelf carbonates to foreland bastn deposition which characterized this region during the late Paleozoic (Stevens and others, in preparation). Figure 2 shows composite stratigraphi: columns for both the north­ ern and southern ha"lves of the study area. These stratigraphic columns were compiled from field notes and cross sections. Lithologies are much generalized and thicknesses are approximate.