Stratigraphy and Structure of the Saddlebag Lake Roof Pendant, Sierra Nevada, California

Stratigraphy and structure of the Saddlebag Lake roof pendant, Sierra Nevada, California

CHARLES A. BROOK* Department of Geology, California State University, Fresno, Fresno, California 93740

ABSTRACT more apparent that an understanding of the structural and stratigraphic histories of the Sierran metamorphic rocks is essential to Geologic mapping of the southern part of the Saddlebag Lake understanding the Mesozoic and pre-Mesozoic tectonics of the roof pendant, east-central Sierra Nevada, California, reveals three western margin of North America. Concepts learned here will in rock sequences that have been multiply deformed. The oldest se- turn influence interpretations on the origin of the Sierra Nevada quence consists of the metamorphosed equivalents of marine batholith. With this in mind, I will describe and then attempt to sedimentary rocks of Silurian(?)-Ordovician(?) age. Metamor- correlate rocks and structures in the Saddlebag Lake roof pendant phosed volcanic and volcaniclastic rocks and basal conglomerate with those in other roof pendants of the central Sierra Nevada. As (possibly in part continental) of Permian age unconformably overlie such, this will enlarge upon data and ideas presented in an earlier the older sequence. Another metavolcanic and metasedimentary abstract (Brook, 1974). sequence of unknown age, here designated Permian(?)-Triassic(?), and of uncertain boundary relationships with the two older se- LOCATION quences crops out in the southern part of the pendant. Field observations of minor structures and structural analysis in- The Saddlebag Lake roof pendant is located in the east-central dicate that rocks of the Silurian(?)-Ordovician(?) sequence have Sierra Nevada, California, approximately 10 km west of Mono undergone three episodes of deformation, whereas the Permian and Lake (Fig. 1). The pendant is one of several northwest-trending Permian(?)-Triassic(?) rocks have been affected by only the later roof remnants in a complex of granitic plutons occurring along the two deformations. Axial surfaces of folds formed during the first eastern crest of the Sierra Nevada. The pendant extends from near deformation had an original strike of approximately north but Tioga Pass in Yosemite National Park northwestward 35 km to the have been largely reoriented by later folding. Structures attributed vicinity of Twin Lakes. Although given a separate name by Kistler to the first deformation occur only in the Silurian(?)-Ordovician(?) (1966b), the Saddlebag Lake roof pendant is essentially the north- sequence. Axial surfaces of folds formed during the second defor- ern extension of the larger Ritter Range roof pendant. It has also mation strike N21°W and are the first-formed folds in the Permian been referred to as the "Tioga Pass roof remnant" by Kerrick and Permian(?)-Triassic(?) sequences. All rock sequences were sub- (1970). Granitic plutons bordering the pendant on the west have sequently refolded around axial surfaces striking N61°W. been mapped and described by Broderson (1962) and are Late Cre- Superimposition relationships and trends of fold systems in the taceous in age (Evernden and Kistler, 1970). Granitic plutons on Saddlebag Lake roof pendant are comparable with those in other the east have been studied by Kistler (1966b) and are as old as Late roof pendants of the central Sierra Nevada. This suggests that the Triassic. deformations were episodic and' regional in scale. Ultimate tectonic causes for each deformation may have been different.

INTRODUCTION

Much of the recent literature on the Sierra Nevada of California has dealt primarily with the source and evolution of the volumi- nous granitic magmas that formed the Sierra Nevada batholith (for example, Bateman and Eaton, 1967; Hamilton and Myers, 1967; Kistler and others, 1971; Shaw and others, 1971; Presnall and Bateman, 1973); various hypotheses have been offered and argued. Attention given to metamorphosed remnants of Paleozoic and Mesozoic strata within the batholith has generally been limited to descriptions of their gross geology or to the roles they played relative to intrusion of the plutons. Detailed studies of the metamorphic rocks are few, but those conducted have shown that these pre- batholithic and synbatholithic rocks have undergone a complex history of repeated deformation, metamorphism, uplift, erosion, and deposition (for example, Baird, 1962; Clark and others, 1962; Kistler, 1966b; Kistler and Bateman, 1966; Nokleberg, 1970; Brook, 1974; Brook and others, 1974; Russell and Cebull, 1974; Russell and Nokleberg, 1977). With the development of plate tectonics theory, it is becoming

" Present address: U.S. Geological Survey, 345 Middlefield Road, Menlo Park, Figure 1. Location of Saddlebag Lake roof pendant and its geographic California 94025 relation to the Ritter Range and Mount Morrison roof pendants.

Geological Society of America Bulletin, v. 88, p. 321-334, 14 figs., March 1977, Doc. no. 70301.

321

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Contact, dashed where approximate

Fault, dashed where approximate. Bar and ball on down-thrown block

Shear zone

Antlcli ne

Overturned anticline

"ft" Overturned syncline

Strike and dip of bedding; ball indicates top \\ \ V Inclined Vertical Overturned

Foliations - schistosity and cleavage parallel to axial surfaces; transposed bedding

First generation \ \ Second generation N^

Third generation

Inclined Vertical

\ 2 Lineatlons - axes of minor folds and Intersection of bedding and cleavage. 1 - first generation; 2 - second generation; 3 - third generation

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/88/3/321/3433545/i0016-7606-88-3-321.pdf by guest on 28 September 2021 Figure 2A. Geologic map of southern part of the Saddlebag Lake roof pendant. 1 Ml J

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SQ.aí * Qt : :o m: >- CE Qa, alluvium. < Figure 2A. (Continued). Qt, talus. z Qm, glacial moraine CE ^lü I- < ioti Si; Z> O Glacial till, probably of Tioga Glaciation

;Kcjb,' Ln Cathedral Peak quartz monzonite 3 O LU ;Khd I .Ks(?) >U< • ^ •> - A Half Dome quartz monzonite Sentinenta1(?) granodiorite I- LÜ OL (J 9 t/i Granodiorite of Tioga Lake <8 fgt. yy Undifferentiated tuffs, graywackes , ::jkc¡: LO < and minor ca1c-si1icate hornfels 00 I- Undifferentiated granitic rocks near Ellery Lake < LlI =e>n diorite of < of Mono Dome Saddlebag Lake Ode 11 Lake ( age uncertai n) (age uncertain) Pr cc Rhyodaci te tuff u Metamorphic Rocks CL

S(I » r3i u n Conglomerate Porphyritic latite shallow intrusion

-Pbr-

Basal rhyodacite tuff Fels i c tuffs Jnconformi ty- Vpj&.S:

Sands tone SOc SOh fv • z Calc-si1 i cate hornlelses Undifferentiated pelitic, < z quartzofeldspathic, < siliceous, and minor C£ Undifferentiated felsic and mafic tuffs, calc-si1icate hornfels r> minor metasedimentary rocks o 1 Q tr ¡7> -Unconformity- o

STRATIGRAPHY northern Ritter Range pendant. Because of the intrusive nature of part of the Permian(?)-Triassic(?) sequence, the original contact re- Rocks of the Saddlebag Lake roof pendant can be divided into lationship between it and the older two sequences is uncertain. three sequences: (1) a Silurian(?)-Ordovician(?) metasedimentary The base of the Silurian(?)-Ordovician(?) metasedimentary se- sequence, (2) a Permian metavolcanic sequence, and (3) a quence is not exposed in the area studied, nor is it exposed in any of Permian(?)-Triassic(?) metavolcanic and metasandstone sequence the adjacent roof pendants (Kistler, 1966b). The base of the Per- (Fig. 2). The older two sequences are separated from each other by mian metavolcanic sequence is marked by a basal metaconglomer- an angular unconformity and are correlative with units in the ate (and locally a metarhyodacite tuff) that unconformably overlies

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and is in depositional contact with the older metasedimentary sequence. The unconformity is indicated by (1) a distinct and abrupt change in lithologic characteristics of the two sequences, (2) locally truncated units and structures in the underlying metasedimentary sequence, and (3) a change in structural complexity, with the Silurian(?)-Ordovician(?) sequence being more highly deformed than the Permian sequence. All rocks in the pendant have been metamorphosed to the hornblende-hornfels and albite-epidote-hornfels facies of contact metamorphism (Kerrick, 1970).

Silurian(?)-Ordovician(?) Sequence

Rocks of the Silurian(?)-Ordovician(?) metasedimentary sequence consist chiefly of calc-silicate hornfels, quartzofeldspathic hornfels, pelitic hornfels, and siliceous hornfels. These are the metamorphosed equivalents of marl and calcareous quartzite, siltstone(?), shale or mudstone, and chert(?), respectively. Metasandstone and metaconglomerate occur locally north of Saddlebag Lake. The rocks are generally microgranular and thinly Figure 3. Typical thin-bedded nature of Silurian(?)-Ordovician(?) bedded, with individual strata averaging a few centimetres thick. metasedimentary rocks, with bedding transposed into a foliation. Note Few relict sedimentary structures are preserved because of the ex- rootless (first-generation) fold left of pencil. Pencil lies parallel to a crosscut- treme deformation, but graded bedding and cross bedding were ting (third-generation) shear cleavage. locally recognized and were utilized to determine top directions. Isoclinal folding has caused extreme attenuation and shearing of sills (Brook and others, 1974), but closer scrutiny in the field indi- the units (Figs. 3, 6); as a result, most of the bedding has been cates that they are tuff, probably of ash-flow origin.] A whole-rock transposed into a foliation subparallel to the original stratification. Rb-Sr isochron of six metavolcanic rock Samples gives a 250-m.y. Original stratigraphic relationships among the various units are age for this sequence (Fig. 4, Table 1). thus difficult to establish. The basal metaconglomerate is composed mostly of Attempts at dating and correlating the metasedimentary rocks metamorphosed pebbly sandstone and sandy conglomerate, with are formidably hampered by the lack of fossils. The sequence was interbedded sandstone lenses (Fig. 5); pebbly mudstone locally first considered to be Pennsylvanian(P) or early Permian(?) in age predominates. Pebble clasts have been tectonically flattened and (Brook and others, 1974; Kistler, 1966b) on the basis of approxi- impart a crude but distinct foliation to the rocks; mudstone has mate lithologic similarities to Pennsylvanian and Permian(?) rocks been thermally metamorphosed to pelitic hornfels. Conglomeratic described in the Mount Morrison pendant by Rinehart and Ross fractions are generally confined within channels. Pebble clasts con- (1964). The distances involved and likelihood of facies changes sist mostly of siliceous hornfels with lesser amounts of make absolute lithologic correlation almost impossible, but it now quartzofeldspathic, pelitic, and calc-silicate hornfels and rare mar- appears that the metasedimentary sequence has structural and ble. These clast lithologies strongly suggest a provenance in the un- lithologic affinities more characteristic of the Silurian(P) and Or- derlying Paleozoic metasedimentary rocks. The channelized nature, dovician rocks of the Mount Morrison pendant. Russell and Nok- intact framework, pebble imbrication, and general bimodal charac- leberg (1977) showed that the Silurian(P) and Ordovician teristic of the conglomerates suggest deposition by fluviatile pro- metasedimentary rocks of the Mount Morrison pendant contain cesses. Correlative metaconglomerates occur sporadically at the three sets of structures corresponding to three successive deforma- base of the Permian metavolcanic sequence in the northern Ritter tional episodes and that the Pennsylvanian-Permian( ?) Range pendant (Kistler, 1966a, 1966b) and were apparently depos- metasedimentary rocks of that pendant contain only the later two ited between paleotopographic highs in the underlying sets of structures. Similar structural relationships are found in the metasedimentary rocks (Brook and others, 1974). Thus, the basal Saddlebag Lake pendant, where the Silurian(?)-Ordovician(?) se- metaconglomerate is here considered to represent an alluvial type quence contains three sets of structures comparable to the same of deposit. Ferguson and Muller (1949) reported local occurrences three sets of structures in the Silurian(P) and Ordovician rocks of of coarse fanglomerate of Permian age in the Toyabe Range of the Mount Morrison pendant; the Permian metavolcanic sequence west-central Nevada; the fanglomerate is perhaps equivalent in age contains only the later two sets of structures. The correlation is to the basal conglomerate of the Permian sequence. thus based primarily on structural similitude. The metarhyodacite tuffs above and below the metaconglomerate are lithologically very similar — both are crystal lithic tuffs, Permian Sequence probably of ash-flow origin. The tuffs are light gray and contain abundant relict phenocrysts of quartz and feldspar. Dark lenticular Rocks of the Permian sequence, like those of the Silurian(P)- inclusions, probably metamorphosed pumice lapilli, are ubiquitous Ordovician(P) sequence, have been tightly folded but contain one but not plentiful. A well-developed schistosity in the rocks is de- fewer set of structures. Transposition of bedding, a characteristic of fined by the parallel alignment of flattened inclusions and recrystal- the Silurian(?)-Ordovician(?) metasedimentary rocks, is virtually lized micas. The top of the upper metarhyodacite tuff is marked by absent in the Permian strata. The stratigraphic succession of the meta-andesite intrusions along much of its length. Permian sequence could thus be determined with a fair amount of Porphyritic meta-andesite in crude sill-like masses and confidence. The sequence consists of a basal metaconglomerate metamorphosed mafic tuffs make up the andesite complex. The that is locally underlain by a thin metarhyodacite tuff, a thick meta-andesites are characterized by abundant relict phenocrysts of

metarhyodacite tuff, a unit of metamorphosed andesite shallow in- plagioclase (An40±5) set in a partly recrystallized, fine-grained mat- trusions and mafic tuffs (andesite complex), and an upper unit of rix. At the upper end of Saddlebag Lake, andesite forcefully in- metamorphosed volcaniclastic rocks, metatuffs, and minor calc- truded the basal conglomerate and caused extreme attenuation of silicate hornfels. [The metarhyodacite tuffs was first interpreted as both the conglomerate and overlying rhyodacite (Fig. 2). The ande-

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TABLE 1. PARTIAL CHEMICAL ANALYSES AND Rb-Sr ANALYTICAL DATA FOR WHOLE-ROCK ISOCHRON

87 86 Sample no. SiOz K2O Na20 Rb Sr Rb/Sr Sr /Sr (description) (wt %) (wt %) (wt %) (ppm) (ppm)

SL-lv (rhyodacite) 71.60 3.77 0.65 158 129 1.232 0.7173 SL-3va (andesite) 57.84 1.61 2.87 83.2 501 0.166 0.7065 SL-3vd (andesite) 57.48 2.41 4.42 109 638 0.171 0.7067 SL-10v (rhyodacite) 71.82 1.385 1.84 59.7 207 0.288 0.7082 SL-llv (rhyodacite) 72.20 3.13 1.39 120 164 0.732 0.7137 SL-13v (rhyodacite) 72.31 3.73 0.51 144 970 1.482 0.7193 Note: Data courtesy R. W. Kistler (1972, written commun.).

site complex is overlain by a unit of schists and phyllites [the A distinctive, gray metasandstone unit lies stratigraphically metamorphosed equivalents of tuffaceous(?) sandstone and above the mafic and felsic tuff unit. However, the two units are graywacke], with interbedded metatuff and laminated calc-silicate separated by a fault. The metasandstone is relatively homogeneous hornfels. The contact relationship between the two units is unclear with regard to texture and mineral content throughout its thick- but is apparently gradational. ness. The parent rock was most likely a medium-grained quartzite Permian metavolcanic rocks in the Saddlebag Lake pendant are with minor argillaceous matrix; the argillaceous fraction has been directly correlative with Permian metavolcanic rocks in the Ritter recrystallized to mica. Cross-bedding is common throughout the Range and possibly Goddard pendants to the south. Comparable unit, and festoon cross-bedding is locally prominant. However, the volcanic rocks probably of Permian age also occur in the Toyabe metasandstone does not appear stratiform. Range of Nevada (Ferguson and Muller, 1949) and in the northern The "felsic tuff" unit of the Permian(?)-Triassic(?) sequence is White Mountains of California and Nevada (Crowder and Ross, apparently an intrusive complex. It consists of abundant large 1972). blocks of bedded felsic metatuff and fine-grained metasedimentary rocks (schist) enclosed mostly by metamorphosed felsic hypabyssal Permian(?)-Triassic(?) Sequence intrusions. Small metamorphosed mafic intrusions(P) also occur. Bedding attitudes between the isolated blocks of metatuff and Metavolcanic rocks and metasandstone apparently younger than metasedimentary rocks are parallel, and they are congruous with the Permian sequence crop out at the south end of the pendant (Fig. bedding attitudes in the Permian sequence and other rocks of the 2). The rocks are juxtaposed against both Permian and Permian(?)-Triassic(?) sequence. As shown in Figure 2, the "felsic Silurian(?)-Ordovician(?) sequences, but neither the base nor top of tuff' unit is discordant with all older rocks except above the the sequence is exposed. The lowest unit consists of metamor- metasandstone, where it apparently forms a sill. The intrusive phosed mafic and felsic tuffs, mafic hypabyssal intrusions, and complex, as in turn intruded by porphyritic latite. a poorly sorted pebble-conglomerate lens with associated gray- Any explanation for the present position of the Permian(?)- wacke; it is lithologically similar to the andesite complex of the Triassic(P) sequence is as uncertain as its age. Comparable units, especially for the metasandstone, are unknown in either the Saddlebag Lake pendant or the adjacent part of the Ritter Range pendant. The sequence may represent part of a downdropped block of Permian or younger rocks that are nowhere else exposed. In this case, the intrusive complex could have been emplaced along a fault zone bounding the block. Alternatively, the sequence was perhaps deposited in a steep-walled canyon cut into the older sequences. In this case the original contact would have been a buttress unconformity along which the intrusive complex was emplaced. The intrusive complex itself may be some sort of volcanic vent. In any case, interpretation of the Permian(?)-Triassic(?) sequence will remain firmly attached to the horns of a dilemma until someone con- ducts a more thorough study.

STRUCTURE

The distribution of rock units and the investigation of minor structures indicate that the rocks of the Saddlebag Lake pendant have been complexly folded and faulted by three deformations. Folds of each deformation have a characteristic geometry and are distinguished by different styles and orientations. Because major folds in all three rock sequences are indistinct, conclusions about the styles and causes of folding are drawn primarily from a study of minor folds and associated foliations. The superimposition of structural elements of one style and orientation on those of another style and orientation was the basic criteria used to establish the deformational succession. Figure 4. Rb-Sr whole-rock isochron of six metavolcanic rock samples Structural elements related to each of the three deformations are from the Permian sequence. Analytical data are given in Table 1. Rb decay termed first generation, second generation, and third generation. A n constant, k(1 = 1.39 x 10" /yr. (Isochron courtesy R. W. Kistler, 1972, summary of structural elements for each deformation is given in written commun.) Table 2. Structural complexity increases with increased age of the

TABLE 2. CHARACTERISTICS OF FIRST-, SECOND-, AND THIRD-GENERATION STRUCTURES IN THE SADDLEBAG LAKE ROOF PENDANT

Sequence Folds Foliations Lineations (F) (S) (L)

F,, isoclinal S„ transposed bedding (subparallel to L„ axes of minor F, folds, intersection of bedding bedding on F, fold limbs), axial-plane and S, cleavage at F, fold hinges, mineral Silurian(?)-Ordovician(?) cleavage, local schistosity streaks

.Fa, open 52, shear cleavage, axial-plane cleavage L2, axes of minor F2 folds 53, shear cleavage

F2, isoclinal 52, axial-plane cleavage, schistosity, tec- L2, axes of minor F2 folds, intersection of bedding Permian and Permian(?)- tonically flattened pebbles; parallel to and S2 cleavage at F2 fold hinges, mineral Triassic(?) bedding on F2 fold limbs streaks

,F3, open 53, axial-plane cleavage L3, axes of minor F3 folds

rocks; structures indicative of all three generations are found in the north-plunging syncline as seen in Figure 6. The axial surface of the Silurian(?)-Ordovician(?) sequence, but only second- and third- fold is approximately vertical. generation structures occur in the Permian and Permian(?)- Minor first folds reflect their major counterparts in style and Triassic(P) sequences. orientation, a phenomenon not unexpected for spatially related Preferred orientations for folds of each deformation were deter- folds in metamorphic tectonites. They generally appear as isoclinal mined by plotting measurements of structural elements in lower similar folds with simple hinges and attenuated limbs (Fig. 7); some hemisphere projections on an equal-area net (see Weiss, 1959). are rootless (Fig. 3). Thus, they have characteristics of the flexural- Each fold system has a cognate set of minor structures (foliations) slip folds of Turner and Weiss (1963) and the flexural-flow folds of that parallel axial surfaces. In fact, these "axial-planar"-related Donath and Parker (1964). Minor first folds are best developed in elements are the most abundant minor structures in the pendant. In thinly bedded rocks of alternating lithologies: most cases a direct relationship exists between foliation and bed- The result of extreme compression and progressive flexural-slip ding. That is, foliation is generally parallel to bedding (except at folding during the first deformation are readily illustrated by the hinges of contemporaneously formed folds) and is therefore af- discontinuity of "bedding" contacts in the Silurian(?)- fected in the same manner as bedding by later deformation. There- Ordovician(P) rocks. The attenuation of fold limbs and differential fore, measurements of bedding were combined with the more shear along bedding surfaces coincident with slip directions have abundant measurements of foliations parallel to bedding to ensure transposed much of the bedding into a foliation (see Whitten, an adequate number of readings in determining fold orientations. 1966, p. 181; Fig. 3). Contacts between lithologic units on fold Collective diagrams thus show the preferred (statistical mean) limbs are generally tectonic on both major and minor scales. orientations for axial planes of folds as indirectly determined from Transposed bedding, prevalent throughout the Silurian(?)- the maxima of poles to bedding and foliations. Few measurements Ordovician(P) rocks, was not observed in Permian and younger of bedding around fold noses were collected because of the rocks. Transposed bedding is consequently one of the basic criteria difficulty in obtaining accurate measurements. Consequently, the used to define the first deformation. data do not permit determinations of girdles to poles nor, in turn, Original orientations of first folds are difficult to determine be- fold axes (fi). cause of the structural complexity of the Silurian(?)-Ordovician(?) sequence. In order to evaluate first-fold orientations, an east-west First-Generation Structures section across the metasedimentary sequence was mapped in detail (Fig. 6). This area was then divided into three areas of approximate Structures considered to be the result of the first deformation occur only in rocks of the Silurian(?)-Ordovician(?) sequence. Sub- stantial refolding and reorientation of first-generation structures during later deformational events have obscured much of the evidence for the first deformation. Minor structures, particularly the transposed bedding, give the only real hints about the first deformation. First folds are isoclinal with simple hinges and appressed limbs. Only two major first folds were recognized with certainty, a syncline and an anticline east of the shear zone shown in Figures 2 and 6. First folds west of the shear zone are indistinguishable from second folds; the anticline north of Saddlebag Lake (Fig. 2) is perhaps a second fold. The large, north-plunging syncline north of Tioga Lake is delineated by the outcrop pattern of a thick calc- silicate hornfels unit. The fold is overturned to the east as beds on both limps dip steeply to the west. The western limb is sheared out a few hundred metres north of the fold nose. The flexures in the fold limbs, as indicated by both the outcrop pattern and the changes in strike of first-general foliations, clearly show the superimposition of later (perhaps second-generation) folds. The anticline near Ellery Lake is indicated by the outcrop pattern of a Figure 5. Metaconglomerate with interbedded metasandstone lenses at siliceous hornfels unit (Fig. 6). The core of the anticline is exposed base of Permian sequence. Pebbles have been tectonically flattened and on the face of a very steep slope; thus, it has the map pattern of a define a foliation that is parallel to bedding.

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Siliceous hornfels Undifferentiated pelitic, Ca1c-si1icate hornfels quartzofeldspathic, and siliceous hornfels Figure 6. Detail map of distribution of lithologic units in the Silurian(?)-Ordovician(?) sequence across southern part of the Saddlebag Lake roof pendant. Structure symbols are the same as for Figure 2. Structure diagrams show preferred orientations of first-fold axial planes in each subarea. A, 61 poles to transposed bedding and bedding contoured at 3,10,18, and 25 percent per 1 percent area. B, 200 poles to transposed bedding and bedding contoured at 3, 7, and 12 percent per 1 percent area. C, 62 poles to bedding contoured at 2.7, 14.5, and 32 percent per 1 percent area. Dots indicate orientations of first-generation lineations. Tick marks indicate true north.

structural homogeneity on the basis of map patterns. Axial planes subarea B, two sets of shear cleavages are found crosscutting the in subarea A have a preferred strike of N22°W and dip of 84°SW, transposed bedding. Although seldom together at the same out- in subarea B they strike N8°W and dip 83°W, and in subarea C crop, one set is subparallel to second-fold axial surfaces, and the they are vertical and strike N30°W (Fig. 6, A, B, and C, respective- other set is subparallel to third-fold axial surfaces. (2) The syncline ly). The orientation of the large syncline in subarea B is considered has been refolded and apparently not reoriented by second- to be near the original orientation of first-generation folds for the generation folding. Otherwise, the syncline would be expected to following reasons: (1) Where transposed bedding strikes north in have a more northwesterly orientation should it be a refolded

second-generation fold. (3) The orientation of the axial plane as defined in Figure 6, B closely coincides with the orientations of axial planes determined for first-generation folds in corresponding rock sequences in nearby roof pendants (see Kistler, 1966b). The orientation of folds in subarea A closely coincides with the preferred orientation of second folds in the adjacent Permian sequence (compare Fig. 6, A and Fig. 10, B), Wavelengths of folds in subarea A are also smaller than in other areas of the roof pendant. This suggests that first-generation folds in subarea A have been tightened and reoriented into positions subparallel to second- generation axial surfaces (see Brook and others, 1974). The preferred strike of first-generation structures determined in subarea C can also reasonably be explained as a result of reorientation during later deformation. The above lines of reasoning therefore suggest that first-fold axial surfaces in the Saddlebag Lake roof pendant had original strikes of near north and dips of near vertical. The present northwest orientation of most first-generation structures as shown in Figure 2 is believed to be due primarily to reorientation by the sec- Figure 7. Minor first fold in thinly bedded alternating siliceous (light) ond deformation. The angular unconformity between the and peli tic (dark) hornfels units, Siluriani ?)-Ordovician(?) sequence. Hinge Silurian(?)-Ordovician(?) metasedimentary sequence and the Per- of fold shows incipient shearing along axial-plane cleavages. mian metavolcanic sequence gives further credence to the first deformation. Not all first-generation lineations are systematically related to first-fold axes (that is, they are not all B lineations), as shown by the wide scatter of points in subareas A and B. Several of the steeper lineations in these subareas are mineral streaks in the plane of the transposed bedding and are probably the result of slippage along bedding surfaces during folding (see Billings, 1972, p. 416). How- ever, axes of several minor first folds in these two subareas are also steep, undoubtedly the result of late-stage shearing and later refolding. Most of the lineations measured in subarea C are fold axes which plot around a maximum that plunges about 30°NW. Be- cause of refolding and shearing, this value is probably somewhat greater than the original plunge of first folds.

Second-Generation Structures

Second-generation structural elements occur in all three rock sequences of the Saddlebag Lake pendant. Second folds are the first- formed folds in the Permian rocks and either reorient and (or) re- Figure 8. Minor second fold in metavolcanic rocks of the Permian se- fold all first-generation structures in the Silurian(?)-Ordovician(?) quence. Irregularity of fold limbs is due to superimposition of minor third- rocks. generation folds. Axial trend of second folds is approximately N20°W; Parallel bedding contacts on opposite fold limbs in the Permian axial trend of third folds is approximately N60°W. sequence indicate that the major second fold — a syncline — is isoclinal. The few minor second folds observed in the sequence reflect this fold style; they are tight, similar folds with simple hinges (Fig. 8). However, major and minor second folds in the Silurian(?)-Ordovician(?) sequence are open and asymmetric (Fig. 9). This inconsistency between fold styles should not be unexpected in rocks of differing ages affected by multiple deformations. Superimposed folds of a later deformation normally have smaller amplitudes, are more open, and plunge steeply (Turner and Weiss, 1963, p. 140-142). Such is the case for second folds in the Silurian(?)-Ordovician(?) sequence. However, this difference in fold styles (or fold intensities) for second folds is probably due more to dissimilar competancies of the two rock sequences involved rather than to unexplained differences in the severity of the second deformation. This hypothesis is compatible with the con- cept of disharmonic folding discussed by Badgley (1965, p. 55). Second folds, like the first folds, have characteristics of folds formed by flexural slip. Second-generation foliations are summarized in Table 2.

Because field observations indicate that second-generation (first- Figure 9. Minor first-generation fold with superimposed minor second- formed) folds in the Permian sequence are isoclinal, poles to bed- generation fold and associated shear cleavage, Silurian(?)-Ordovician(?) se- ding and poles to foliations parallel to bedding were utilized to de- quence. Axial trend of first fold is about N0°; axial trend of second fold is termine the preferred orientations of second-fold axial planes. about N30°W.

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Figure 10. Structure diagrams showing preferred orientations of second-fold axial planes as determined from poles to bedding and foliations parallel to bedding in the Permian sequence (A, B) and the Permian(?)-Triassic(?) sequence (C). A, 96 poles contoured at 2, 10, 21, and 36 percent per 1 percent area. B, 184 poles contoured at 3,10,16, and 22 percent per 1 percent area. C, 85 poles contoured at 5,10, and 14 percent per 1 percent area. Dots indicate orientations of second-generation lineations. Tick marks indicate true north.

Thus, lower hemisphere plots (Fig. 10, A and B, respectively) show more westwardly in this area. The Permian(?)-Triassic(?) rocks a second-fold axial plane striking N18°W and dipping 85°NE in the have a preferred strike of N53°W and dip 75°SW (Fig. 10, C). northern half of the Permian sequence and striking N25°W and Minor third folds are incipiently developed in the sequence where dipping 87°SW in the southern half of the sequence. An average bedding is not parallel to the trend of third-fold axial surfaces. This strike of N21°W and nearly vertical dip is easily assumed. This av- indicates that the Permian(?)-Triassic(?) sequence was folded for eraged value is most likely near the original orientation for second- the first time by second-generation deformation and then largely fold axial planes, because they are apparently refolded rather than reoriented by third-generation folds. reoriented by third folds. Measured plunges of second-fold axes in the Permian sequence range from 20° to 80°. Third-Generation Structures Bedding and foliation surfaces in the Permian(?)-Triassic(?) sequence are continuous with those in the Permian sequence but have Third-generation folds were observed mostly in the Permian se- been reoriented into trends parallel to third folds (Fig. 2). Strikes of quence. Here, superimposition of major third folds is indicated by planar structures in the two older sequences also begin trending the broadly undulant contact pattern on the limbs of the major

folding. Such is the case for first folds. Abundant transposed bedding and axial-plane cleavage indicate that simple flexural slip was not the only folding mechanism. The fact that first lineations are not evenly distributed along great circles in Figure 6, B and C, indicates that pure slip was not the only folding mechanism either (see Weiss, 1959). Hinges of some minor first folds are offset along cleavages parallel to their axial surfaces (Fig. 7). This evidence suggests that first folds were initially located by flexural mechanisms, after which slip along axial surfaces became the dom- inant deformational process. Late-stage slip or shear during the first deformation can readily explain the occurrance of several rootless folds as well as the ubiquitous transposed bedding and tectonic contacts on fold limbs.

Summary

Field observations aided by preferred orientation diagrams and comparison with nearby roof pendants thus show that rocks of the Figure 11. Profile view of minor third-generation fold, Permian se- Saddlebag Lake pendant contain three fold systems. Original quence. strikes of axial surfaces for folds of each system are summarized in Figure 13. First-fold axial surfaces originally had a northward second-generation syncline (Fig. 2). Minor third folds superim- orientation, second-fold axial surfaces strike about N21°W, and posed on minor second folds as shown in Figure 8 are few. Third third-fold axial surfaces strike about N61°W. Structural complex- folds are open, asymmetrical, and have nearly vertical axial planes ity increases with increased age of the rocks: first-generation struc- (Fig. 11). Third-generation structures in the Silurian(?)- tures occur only in the Silurian(?)-Ordovician(?) sequence, whereas Ordovician(P) sequence consist primarily of shear cleavages that second- and third-generation structures occur in all three rock se- are oblique to the transposed bedding and subparallel to third-fold quences. axial surfaces. It is these third-generation shear cleavages that sup- Fold styles and interpreted fold mechanisms imply that each fold port the contention that the Silurian(?)-Ordovician(?) sequence has system was largely the result of compressive tectonic forces. The been affected by the third deformation, because third-generation possibility that folds were caused by forceful emplacement of the folds are not recognized with certainty in this oldest sequence. bordering plutons is negated by the fact that granitic contacts trun- Figure 12, the collective diagram of poles to third-generation cate first-, and second-, and third-generation structures. Bordering axial surfaces and cleavages, shows that third-fold axial planes are plutons were passively emplaced. Local accordance between grani- vertical and strike N61°W. Fold axes are generally steep and are tic contacts and metamorphic structures and the general north- scattered along the preferred strike, indicating superimposition on westward trend of the western contact between the roof pendant steeply dipping, earlier rotated surfaces (in this case, folded bed- and the Cretaceous plutons (Fig. 2) suggest that intrusion was con- ding). trolled, at least in part, by pre-existing wall-rock structures, especially those developed during the second deformation. Fold Mechanics Faults Visual inspection of minor fold styles, axial-plane cleavage, and lineations parallel to fold axes indicates that second and third folds The northwest-trending faults in the Permian and Permian(?)- were formed by flexural slip. Tectonically elongated pebbles in the Triassic(?) sequences in the Saddlebag Lake pendant are continu- basal conglomerate of the Permian sequence lends further evidence ous with the northwest-trending faults mapped by Kistler (1966a) in support of flexural-slip folding during the second deformation in the northern Ritter Ridge pendant. Fault surfaces are nearly ver- (see Turner and Weiss, 1963, p. 489). However, deformational tical, with eastern sides down. The faults generally truncate both mechanisms that produced the first-generation folds and related bedding and second-generation folds and foliations at small angles. structures were evidently more complicated. However, where faults parallel the bedding (as shown for the Many folds in metamorphic tectonites have characteristics that southern part of the pendant in Fig. 2), they have apparently been are not strictly compatible with either flexural-slip or slip models of folded around third-fold axes. This evidence suggests that the faults

Figure 12. Synoptic structure Figure 13. Original strikes of diagram showing preferred orien- axial planes of folds in Saddlebag tation of third-fold axial planes as Lake roof pendant. Contem- determined from poles to third- poraneous folds have same trend in generation axial surfaces and both Silurian (?)-Ordovician(?) and cleavages. Contours are at 8, 24, Permian sequences. F„ F2, and F3 and 32 percent per 1 percent area are first-, second-, and third- for 25 poles. Dots indicate orienta- formed folds, respectively, in each tions of third-generation linea- sequence and should not be con- tions. Tick mark indicates true fused with first-, second-, and north. third -generation folds.

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Mono Lake ~|— Strikes of fold axes and 118° probable times of deformations

Devoniani?) - Mississippian(? )

Early Triassic - Middle Cretaceous

Middle Cretaceous - Late Cretaceous

Mesozoic metamorphic rocks

Paleozoic metamorphic rocks

Ultramafic rocks Figure 14. Strikes of axial planes of folds in roof pendants and wall rocks of central Sierra Nevada. Axial planes of folds that have similar trends are considered to have formed during same general time span and therefore are given the same symbol. Mesozoic folds that have similar trends are not neces- sarily contemporaneous but were probably produced by several deformational events, during which time stress orientations remained relatively uniform. References to lettered localities are given in Table 3. [Updated and modified after Kistler (1966b, Fig. 29). Times of deformation after Russell and No- kleberg (1977).]

developed before third folding and after second folding. Vertical As data is collected, it becomes increasingly apparent that folds displacement along the fault at the base of the Permian sequence in in the metamorphic rocks conform to a regional pattern earlier es- the southern part of the pendant is only about 185 m and does not tablished by Kistler (1966b). Not only do fold systems maintain negate the probability that the western limb of the anticline shown their axial orientations throughout the central Sierra Nevada as in Figure 6 was truncated by the angular unconformity prior to shown in Figure 14, but styles of folding also remain remarkably faulting. An unconformity can logically create a surface of weak- constant. This evidence suggests that the roof pendants have been ness along which faulting should be expected. little rotated or otherwise affected by intrusion of contiguous plutons (see also Brook and others, 1974). STRUCTURAL COMPARISON WITH OTHER ROOF Kistler (1966b) and Kistler and Bateman (1966) proposed that PENDANTS AND REGIONAL TECTONICS each fold system represents a separate and distinct period of regional deformation and that the folding was caused by regional It is generally recognized that axial planes of contemporaneously tectonic forces and not by forceful emplacement of plutons. Evi- formed folds in tectonic environments maintain statistically uni- dence of passive intrusion of plutons bordering the Saddlebag Lake form orientations over considerable distances (Ramsay, 1958). and other pendants and the correlation of fold systems between Thus, fold systems in the Saddlebag Lake pendant can be compared pendants certainly support their conclusions. Angular uncon- with those in other roof pendants. Strikes of axial planes for fold formities separating both lithologic and structural domains in the systems occurring in roof pendants and wall rocks across the cen- Saddlebag Lake and Ritter Range pendants and the superimposi- tral part of the Sierra Nevada are shown in Figure 14 and Table 3. tion of folds give further evidence for episodic deformations. First-, second-, and third-generation folds and structures in the Timing of the deformational episodes was discussed by Russell Silurian(?)-Ordovician(?) sequence of the Saddlebag Lake pendant and Nokleberg (1977). They concluded that folds with axes strik- have almost identical counterparts in the lower Paleozoic rocks of ing generally north (first-generation folds) were formed during De- the Ritter Range pendant (Kistler, 1966b), the Mount Morrison vonian or Mississippian time, possibly during some phase of the pendant (Russell and Nokleberg, 1977), the Strawberry Mine pen- Antler orogeny. Folds with axes trending N20°-30°W (second- dant (Nokleberg, 1970), and the Dinkey Creek pendant (Kistler generation folds) were probably formed during one of several and Bateman, 1966). The first-formed (second-generation) folds in pulses of deformation with similar stress fields between Early the Permian sequence apparently correspond to first-formed folds Triassic and middle Cretaceous time. Folds with axes trending in the Permian rocks of the Ritter Range pendant (Kistler, 1966b), N50°-60°W (third-generation folds) were probably formed be- the Pennsylvanian and younger rocks of the Mount Morrison pen- tween middle and Late Cretaceous time. dant (Russell and Nokleberg, 1977), and the Goddard pendant The deformation producing the second-generation folds in the (Kistler and Bateman, 1966). Third folds in the Saddlebag Lake Saddlebag Lake roof pendant probably occurred between Early pendant most likely correspond to the first-formed folds in the and Middle Triassic time. The second deformation is bracketed in Dana sequence of the northern Ritter Range pendant (Kistler, age by the whole-rock Rb-Sr isochron on the Permian metavolcanic 1966b) and the second-formed folds in the Goddard pendant (Kis- rocks and by the truncation of second-generation structures by tler and Bateman, 1966). Late Triassic plutons in the southern Ritter Range pendant (Kistler,

TABLE 3. ORIENTATIONS AND RELATIVE CHRONOLOGIC ORDER OF FOLD SYSTEMS IN ROOF PENDANTS AND WALL ROCKS OF THE CENTRAL SIERRA NEVADA

Location Age of rocks Strikes of axial planes of fold systems 1 st-formed 2nd-formed 3rd-formed

A Saddlebag Lake roof pendant Silurian( ?)-Ordovician( ?) N8°W N21°W N61°W (this report) Permian, Permian(?)-Triassic(?) N21°W N61°W

B Log Cabin Mine roof pendant Siluriani ?)-Ordovician( ?) N0° (Kistler, 1966b)

C Ritter Range roof pendant Paleozoic NO" N30°W N50°W (Kistler, 1966b) Permian N30°W N50°W N50°W Jurassic( ?)-Cretaceous( ?) D Strawberry Mine roof pendant NO0 N30°W N60°W (Nokleberg, 1970) Paleozoic

E Mount Morrison roof pendant Silurian( ?)-Ordovician N0° N25°W N60°W (Russell and Nokleberg, 1^74) Pennsylvanian-Permian(?) N25°W N60°W

F Dinkey Creek roof pendant Paleozoic N20°W N60°W N5°E (Kistler and Bateman, 1966)

G Goddard roof pendant Permian-Mesozoic N75°W N25°W (Kistler and Bateman, 1966)

H Bishop Creek roof pendant Paleozoic N0° (Bateman, 1965)

I Western metamorphic belt Jurassic N30°W (Clark and others, 1963)

J Western metamorphic belt Jurassic N25°W (Best, 1963) N40°W

K Kaweah River Mesozoic N35°W (Durrell, 1940) (approx.)

L Mineral King roof pendant Triassic N25°W (Christensen, 1963)

1966a). [The granodiorite of Mono Dome (Fig. 2) and the quartz Permian(?)-Triassic(?) sequence occurred later than the deforma- monzonite of Lee Vining Canyon (Kistler, 1966a) were considered tion first affecting the Permian sequence but before the "third" de- by Evernden and Kistler (1970) to have maximum ages of 210 formation as referred to here. Structural continuity between the se- m.y.] Because second-generation folds are the first-formed folds in quences implies that the two deformations would have had similar the Permian metavolcanic sequence, the second deformation thus stress fields. As a consequence, distinguishing between structures occurred sometime between 240 m.y. and 210 m.y. ago. Silberling formed by the respective deformational events would indeed be (1973) established that eastward thrust faulting took place in the difficult, if not impossible. "Second-generation" structures in the Cordillera during latest Permian and Early Triassic time, an event Saddlebag Lake roof pendant, all of which appear to have been commonly referred to as the Sonoma orogeny. Second folds in the produced by a single deformation, may actually have been pro- Saddlebag Lake roof pendant are most likely related to this event. duced by several events. This idea is compatible with the hypothesis Although the Sonoma orogeny probably culminated with of Russell and Nokleberg (1977) in which they suggested the oc- emplacement of the Golconda thrust fault in earliest Triassic time currence of multiple deformations with similar stress fields between (Speed, 1971), the disturbance as a whole is considered by Johnson Early Triassic and middle Cretaceous time. (1971) to have been relatively continuous since Pennsylvanian The ultimate cause of each deformation raises another point to time. Evidence for at least incipient deformation and (or) uplift question. Within the confines of plate tectonics theory it is gener- prior to formation of second folds is suggested by the unconformity ally agreed that deformation occurs when two plates interact and separating Permian metavolcanic rocks and Paleozoic that deformation is localized along linear belts at or near plate metasedimentary rocks in the Saddlebag Lake, Ritter Range, and boundaries (for example, Dewey and Bird, 1970). A reasonable as- Mount Morrison pendants (Brook and others, 1974). The con- sumption is that the present location of the Sierra Nevada marks glomerates at the base of the Permian sequence in the Saddlebag the approximate western margin of the North American plate dur- Lake and Ritter Range pendants perhaps represent debris shed ing late Paleozoic and much of Mesozoic time. Therefore, it is also from highlands created in Paleozoic rocks during earlier Permian reasonable to make the assumption that each deformation repre- time. sents a time of active plate convergence. Episodic orogenesis is not The question arises as to whether the Permian(?)-Triassic(?) se- an improbability (Helwig and Hall, 1974) and, combined with ro- quence was folded along with the Permian sequence for the first tation of one plate relative to the other, can easily account for the time during the second deformation. Although bedding and folia- reorientation of compressive forces required to form superimposed tions between the two sequences are congruent, the contact be- folds. tween the sequences is apparently occupied by an intrusion (the Kistler and others (1971) approached the problem from a dif- "felsic-tuff" unit) as previously discussed. A possibility that must ferent viewpoint and suggested that deformations producing the be considered is that the deformation first affecting the folds were related to successive intrusive epochs of the Sierra

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Nevada batholith. They interpreted (p. 864) the folds as being America Bull., v. 75, p. 45-62. "second order drag folds associated with right-lateral wrench Durrell, C. D., 1940, Metamorphism in the southern Sierra Nevada, north- movement in the crust above the developing loci of intrusion." east of Visalia, California: California Univ. Dept. Geol. Sci. Bull., Such a mechanism may well indeed be responsible for folds formed v. 25, p. 1-118. during the Mesozoic, the time of emplacement of the Sierra Nevada Evernden, J. F., and Kistler, R. W., 1970, Chronology of emplacement of Mesozoic batholithic complexes in California and western Nevada: batholith, but cannot be called upon to explain folds that formed U.S. Geol. Survey Prof. Paper 623, 42 p. during the early Paleozoic Antler orogeny, because plutonism of Ferguson, H. G., and Muller, S. W., 1949, Structural geology of the batholithic proportions in the Cordillera did not begin until Late Hawthorne and Tonopah quadrangles, Nevada: U.S. Geol. Survey Triassic time (Gilluly, 1965). I suggest that second-generation folds Prof. Paper 216, 53 p. in the Permian sequence of the Saddlebag Lake pendant may have Gilluly, J., 1965, Volcanism, tectonism, and plutonism in the western been the direct result of thrust faulting during the emplacement of United States: Geol. Soc. America Spec. Paper 80, 63 p. the Golconda thrust fault. Folds in roof pendants of the Sierra Hamilton, W., and Myers, W. B., 1967, The nature of batholiths: U.S. Nevada may therefore have been caused by more than one process. Geol. Survey Prof. Paper 554-C, 30 p. Thus, the question remains open to investigation — or speculation. Helwig, J., and Hall, G. A., 1974, Steady-state trenches?: Geology, v. 2, p. 309-316. Johnson, J. G., 1971, Timing and coordination of orogenic, epeirogenic, ACKNOWLEDGMENTS and eustatic events: Geol. Soc. America Bull., v. 82, p. 3263-3298. Kerrick, D. M., 1970, Contact metamorphism in some areas of the Sierra Work on the Saddlebag Lake roof pendant was begun as a Mas- Nevada, California: Geol. Soc. America Bull., v. 81, p. 2913-2938. ters thesis at California State University, Fresno, under the supervi- Kistler, R. W., 1966a, Geologic map of the Mono Craters quadrangle, sion of W. J. Nokleberg. The work was continued while I was a Mono and Tuolumne Counties, California: U.S. Geol. Survey Geol. student at the University of California, Santa Barbara. I thank Quad. Map GQ-462. R. W. Kistler for providing base maps and the isotopic age deter- 1966b, Structure and metamorphism in the Mono Craters quadrangle, Sierra Nevada, California: U.S. Geol. Survey Bull. 1221-E, p. El- minations of six metavolcanic rock samples and for his expressed E53. interest throughout the course of this study. Critical review of the Kistler, R. W., and Bateman, P. C., 1966, Stratigraphy and structure of the manuscript and comments on means of improving it by P. C. Dinkey Creek roof pendant in the central Sierra Nevada, California: Bateman, M. G. Best, and E. A. Johnson are gratefully acknowl- U.S. Geol. Survey Prof. Paper 524-B, 14 p. edged. Kistler, R. W., Evernden, J. R., and Shaw, H. R., 1971, Sierra Nevada plutonic cycle: Pt. 1, Origin of composite granitic batholiths: Geol. Soc. America Bull., v. 82, p. 853-868. REFERENCES CITED Nokleberg, W. J., 1970, Geology of the Strawberry Tungsten Mine roof pendant [Ph.D. thesis]: Santa Barbara, Univ. California, Santa Bar- Badgley, P. C., 1965, Structural and tectonic principles: New York, Harper bara, 156 p. and Row, 521 p. Presnall, D. C., and Bateman, P. C., 1973, Fusion relations in the system Baird, A. K., 1962, Superposed deformations in the central Sierra Nevada NaAlSi308- CaAl2Si2Og- KAlSi308-Si02-H20 and the generation of foothills east of the Mother Lode: California Univ. Dept. Geol. Sci. granitic magmas in the Sierra Nevada batholith: Geol. Soc. America Bull., v. 42, p. 1-70. Bull., v. 84, p. 3181-3202. Bateman, P. C., 1965, Geology and tungsten mineralization of the Bishop Ramsay, J. G., 1958, Superimposed folding at Loch Monar, Inverness-shire district, California: U.S. Geol. Survey Prof. Paper 470, 208 p. and Ross-shire: Geol. Soc. London Quart. Jour., v. 113, p. 271-307. Bateman, P. C., and Eaton, J. P., 1967, Sierra Nevada batholith: Science, Rinehart, C. D., and Ross, D. C., 1964, Geology and mineral deposits of v. 158, p. 1407-1417. the Mount Morrison quadrangle, Sierra Nevada, California: U.S. Best, M. G., 1963, Petrology and structural analysis of metamorphic rocks Geol. 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Quad. Map GQ-222. Bull., v. 70, p. 91-106. Crowder, D. F., and Ross, D. C., 1972, Permian(?) to Jurassic(?) metavol- Whitten, E.H.T., 1966, Structural geology of folded rocks: Chicago, Rand canic and related rocks that mark a major structural break in the McNally, 663 p. northern White Mountains, California-Nevada: U.S. Geol. Survey Prof. Paper 800-B, p. B195-B203. Dewey, J. F., and Bird, J. M., 1970, Mountain belts and the new global MANUSCRIPT RECEIVED BY THE SOCIETY NOVEMBER 7, 1974 tectonics: Jour. Geophys. Research, v. 75, p. 2625-2647. REVISED MANUSCRIPT RECEIVED JULY 15, 1975 Donath, F. A., and Parker, R. B., 1964, Folds and folding: Geol. Soc. MANUSCRIPT ACCEPTED JULY 18, 1975 Printed in U.S.A.

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