University of Nevada Reno / Polyphase Deformation of Possible Proterozoic to Lower Cambrian Miogeoclinal Rocks of the Dinkey Creek Pendant, Central Sierra Nevada, California

A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Geological Sciences

by Nancy J. m Merritt

Spring 1991 i

MINES UBRAHt lH£S(^

THESIS OF NANCY J. MERRITT

Approved by:

Dr. Richard A. Schweickert - Thesis Advisor

Dr. Ken Hunter - Dean, Graduate Sdhool

University of Nevada Reno May 1991 ii

ACKNOWLEDGEMENTS

The completion of this thesis would not have occurred without the encouragement and support of several very important people. I would like to express my sincere thanks to Dr. Richard Schweickert for originally suggesting the idea of working in the Dinkey Creek pendant, for his guidance both in the field and during the preparation this manuscript, and for his constant belief in the value of this study. To my husband, Charlie, who always knew I would finish, I would like to extend my heartfelt appreciation for his love, support and patience during the final months of preparation. To my parents, Philip E. and Beth N. Merritt, I would like to express my overwhelming gratitude for their emotional and financial support throughout my entire undergraduate and graduate careers. I give credit to them for my profound love for the earth and my insatiable desire to know more.

I would also like to thank my committee members Dr. Malcom J. Hibbard and Dr. Christopher Exline. In addition, I would like to thank Dr. Bruce Wardlaw of the U.S. Geological Survey in Reston, Virginia for examining the carbonates for microfossils, and the U.S. Forest Service at Dinkey Creek for their logistical support. Lastly, I would like to acknowledge the partial funding of grants and scholarships provided by Watson Exploration; The Women's Auxiliary to the American Institute of Mining, Metallurgical and Petroleum Engineers; Chevron Oil; Sigma Xi; and Gulf Oil. iii

ABSTRACT

The structural and stratigraphic re-evaluation of Dinkey Creek pendant (DCP) reveals possible Proterozoic to Lower Cambrian miogeoclinal sediments along the axis of the Sierra Nevada batholith. The rocks consist of quartzite,

feldspathic quartzite, quartz-mica schist, mica schist,

marble and calc-silicate gneiss. Provisional correlations with Johnnie, Stirling, and Wood Canyon Formations are based on correlation with Death Valley facies rocks of Snow Lake pendant (SNLP). Four penetrative deformational events are recorded in DCP. Structural correlations with SNLP indicate D1 deformation occurred prior to the Early Triassic; D2, Early Triassic to Early Cretaceous; and D3 and D4, Early Cretaceous. The metasedimentary rocks are variably mylonitized and are bisected by a major ductile thrust juxtaposing Johnnie over Stirling and Wood Canyon

Formations. A thrust—related megascopic synformal nappe is revealed. Correlation with SNLP is based on similarities in lithology, structure and environments of deposition, and necessitates extensive northward displacement from western Mojave. iv

TABLE OP CONTENTS

Page Signature Page ...... ^

Acknowledgements...... ^ Abstract...... Table of Contents......

List of Illustrations...... List of Plates...... v n List of Tables...... v n

List of Figures...... viii Introduction...... ^

Regional Setting...... 2 Previous Work...... 6

Present Study...... 8 Lithology...... 9

Metasedimentary Rocks...... 10 Quartzite (qtzt)...... 10 Schist (sch)...... 15 Paragneiss (pg)...... 17

Calc-silicate subunit (cs)...... 19 Calc-Silicate Gneiss...... 22 Calc-Silicate Gneiss (csg-b)...... 22 Calc-Silicate Gneiss (csg-g)...... 24 Marble (m)...... 27 Metamorphism...... 27 Protoliths...... 29 Environments of Deposition...... 30 V

Intrusive Rocks...... 32 Metabasaltic Dike and Sill (mb)...... 32

Diorite/Gabbro Intrusion (KJd)...... 37 Dinkey Creek Intrusive Suite...... 37

Dinkey Creek Pluton (Kdc)...... 40 Dinkey Dome Pluton (Kdd)...... 41 Structural Relations...... 42 D1 Structures...... 43 D2 Strucutres...... 46 F2 Folds...... 47 S2 Foliation...... 50

D2 Ductile Deformation...... 52 D2 Faults......

Lithologic Contacts...... 52 D2 Synformal Nappe...... 61

Stratigraphic Continuity...... 63 D3 Structures......

D4 Structures...... 68

Anomalous Structures...... 70

Relation of Metamorphism to Structures...... 74 Summary of Structural History...... 75

Regional Relations and Tectonic Significance.... 77 Shoo Fly Complex and Mount Goddard Pendant... 78 Shoo Fly Complex...... 7g

Mount Goddard Pendant...... 79

Previous Proposed Correlations for Rocks of Dinkey Creek Pendant...... 79

Kings Sequence 79 Boyden Cave Pendant...... 81 Inyo Facies: Mount Morrison Pendant

and Lower Cambrian Poleta Formation.... 82 Mount Morrison Pendant...... 82 Lower Cambrian Poleta Formation___ 83 Inyo Facies vs.

Dinkey Creek Pendant...... 83 Correlation with Death Valley Facies Rocks of Snow Lake Pendant...... 84 Death Valley Facies...... 91

Independence Dike Swarm...... 94 Initial 87Sr/86Sr ratios...... 97 Tectonic Implications...... 97

Summary and Conclusions...... 101 References Cited...... 104 Appendix A ...... 115 vii

ILLUSTRATIONS

PLATES In Pocket

I 1:12,000 scale Geologic Map of Dinkey Creek Pendant II 1:12,000-scale Form Line Map of Dinkey Creek Pendant and Cross-sections

III 1:12,000-scale Interpretive Structural Map IV 1:4,000—scale Geologic Map of Dinkey Lakes Trailhead - Rainbow Mine Area

V 1:4,000-scale Form Line map of Dinkey Lakes Trailhead - Rainbow Mine Area

VI Equal-area Stereographic Projections for Dinkey Creek Pendant

TABLES Page

1 Metamorphic Mineral Assemblages - Dinkey Creek Pendant...... 28

2 Major Element Analyses - Dinkey Creek Pendant... 35 3 Age determinations and initial 87Sr/86Sr values for granitic rocks in the vicinity of Dinkey Creek pendant...... 3 9

4 Summary of structures in Dinkey Creek pendant... 76 5 Similarities between Dinkey Creek and Snow Lake pendants...... 8 6 6 Comparison of structures in Dinkey Creek and Snow Lake pendants...... 88 viii

FIGURES Page

1 Index M a p ...... 3 2 Map of Kings sequence and surrounding rocks. 5 3 Photograph of quartzite unit ...... 11 4a Photograph of cross-bedding in quartzite...... 13 4b Photograph of cross-bedding in quartzite...... 14 5 Photograph of schist unit...... 16 6 Photograph of paragneiss unit ...... 18 7a Photograph of worm burrows in paragneiss...... 20 7b Photograph of deformed worm burrows in

pargneiss...... 21

8 Photograph of orangish-brown calc-silicate

gneiss unit...... 23 9 Photograph of green calc-silicate gneiss unit... 25 10 Photograph of marble unit...... 26

11 Photograph of metabasaltic dike ...... 33 12 Diagram of compositional variations in magma.... 36 13 Map of granitic rocks in the vicinity of Dinkey

Creek pendant...... 38 14 Photograph of Fx fold...... 44 15 Photomicrograph of F-^ fold...... 45 16 Photograph of F2 fold...... 48 17 Photograph of F2 eye fold...... 49 18 Photograph of blastomylonitic fabric...... 52 19 Photograph of sheared isoclines and associated

ductile shear zones...... 54 20 Photograph of intrafolial folds...... 55 ix

21 Shredded and boudinaged layering...... 56 22 Stereoplot of and F2 hingelines, l 2

lineations and possible direction of movement for Dinkey Creek thrust...... 59 23 Photograph of transposed layering...... 64 24 Photograph of F3 fold...... 66 25 Stereoplot of poles to S1-2 with f 3 and f 4 great circles...... 67 26 Photograph of F4 fold...... 69 27 Photograph of anomalous fold...... 71 28 Photograph of anomalous cleavage...... 73 29 Silica variation diagrams comparing whole rock analyses of basaltic rocks of Dinkey Creek pendant and dike rocks of Independence dike swarm...... 96 30 Tectonic map of the Sierra Nevada (after

Schweickert and Lahren, 1990)...... 98 31 Generalized tectonic cross-sections for Dinkey

Creek and Snow Lake pendants...... 100 1

INTRODUCTION

The regional significance of metasedimentary rocks in the Dinkey Creek pendant continues to be the subject of

controversy. in spite of a previous investigation, the age, depositional environments and stratigraphic affinities of these rocks are uncertain. As is true for many of the

pendants in the central and southern Sierra Nevada, the lack of fossils, intense brittle and ductile deformation, polyphase metamorphism, and the discontinuous nature of pre-batholithic wallrocks in the region have complicated regional interpretations.

Debate over the stratigraphic affinities of the rocks in Dinkey Creek pendant has been ongoing since the metasedimentary rocks were originally mapped by Kistler and Bateman (1966). No fossils have been discovered in the remnant rocks, and direct evidence for age is lacking. Utilizing stratigraphic and structural relationships described by Kistler and Bateman (1966), the age of the strata in Dinkey Creek pendant has been proposed as both Mesozoic and Paleozoic based on correlations with Lower Jurassic rocks of Boyden Cave pendant (Moore and Dodge, 1962; Saleeby and other, 1978; Bateman, 1983) and

Ordovician-Devonian strata in the Mt. Morrison pendant (Kistler and Bateman, 1966; Nokleberg and Kistler, 1980; Schweickert, 1981; Nokleberg, 1983), respectively. In addition, Kistler and Peterman (1973) suggested that the rocks of Dinkey Creek pendant are comparable to Lower 2

Cambrian rocks in the White-Inyo mountains of east-central California. More recently, the rocks of Dinkey Creek pendant have been correlated with upper Precambrian and lower Paleozoic rocks of the Death Valley region (Lahren and Schweickert, in press; Lahren and Schweickert, 1989; Lahren, 1989).

The continued uncertainty regarding the age of the rocks of Dinkey Creek pendant, and the likelihood that the rocks may correlate with Proterozoic and lower Paleozoic

miogeoclinal rocks in southeastern California highlight the need for further research. Understanding the nature of the framework rocks within Dinkey Creek pendant is essential for the resolution of stratigraphic affinity. The presence of Paleozoic miogeoclinal rocks in the central Sierra Nevada would have major implications for the regional geology,

deformation, and paleogeography of the Sierra Nevada region. This study presents the results of detailed mapping and structural analysis of Dinkey Creek pendant. It provides a re-evaluation of structural and stratigraphic features, and an examination of stratigraphic correlations for the rocks of Dinkey Creek pendant. In particular, this study reveals evidence for stronger deformation and greater complexity of fold geometry, greater lithologic detail, and possible age constraints.

Regional Setting

Dinkey Creek pendant is situated in the central Sierra 3

SIERRA NEVADA, CALIFORNIA

Figure 1. Location map of the Dinkey Creek pendant, Central Sierra Nevada, California 4

Nevada about 125 km northeast of Fresno, California, in the Sierra National Forest and within the Huntington Lake quadrangle (Figs. 1 and 2). The pendant is triangular- shaped and spans an area of approximately 25 km2.

The metasedimentary rocks of Dinkey Creek pendant are notably nonvolcanic in nature, and are dissimilar in several important respects from Paleozoic wallrocks to the west in the Western Metamorphic belt, and Mesozoic wallrocks to the east in the Ritter Sequence (Fig. 2). The Paleozoic Shoo Fly Complex of the Western Metamorphic belt lies

approximately 25 km northwest of Dinkey Creek pendant. The Shoo Fly Complex is composed of a complexly deformed

sequence of metasedimentary (quartzite, quartzofeldspathic gneiss, garnet schist, calc-silicate, and marble) and minor metavolcanic rocks, and is characteristic of a slope and rise depositional environment (Schweickert, 1981 and Schweickert and Bogen, 1983; Merguerian and Schweickert, 1987) . Pre-Upper Jurassic metavolcanic rocks in the Mount Goddard pendant of the Ritter sequence are located 25 km east of Dinkey Creek pendant (Fig. 2). The Mount Goddard pendant is a remnant exposure of a continental volcanic arc, and consists primarily of volcaniclastic rocks, mafic and felsic lava flows, and rare limestones (Tobisch and Fiske, 1982; Tobisch and others, 1986).

The Dinkey Creek pendant has been included by some authors within the Kings sequence, a tract of metamorphic rocks separating the Western Metamorphic belt and the Ritter sequence (Fig. 2). As defined by Bateman and Clark (1974), and Saleeby and others (1978), the Kings sequence occurs 5

GENERAL GEOLOGIC MAP OF THE SOUTHERN SIERRA NEVADA

Figure 2 . General geologic map of the southern Sierra Nevada. The pendants of the Kings sequence (Bateman and Clark, 1971 and Saleeby, 1976) are included in the pre-Cretaceous metamorphic rocks. (BC=Boyden Cave, DC=Dinkey Creek, G=Goddard, I=Isabella, KC=Kern Canyon, KP-Kaweah Peak, KR=Kaweah River, LKR=Lower Kings River, MK=Mineral King, MM=Mount Morrison, PM=Patterson Mountain, SP-Sequoia Park, T=Tehachapi, TR=Tule River, and YV=Yokol Valley pendants; DV=Death Valley, lN=lnyo Mountains, W=White Mountains, and WMB=Western Metamorphic Belt) 6

within scattered roof pendants between latitudes 37°55'n . and 35°051N. Quartzite, schist, calc-silicate, marble, and minor intermediate to silicic flows, tuff, and epiclastic rocks are exposed in these pendants. Considered to be entirely Late Triassic to Early Jurassic in age, the lithologies of the Kings sequence have been interpreted to represent a complex, continental-margin, magmatic arc depositional environment (Saleeby and others, 1978;

Busby-Spera, 1984). The Triassic-Jurassic age assigned to the Kings sequence is based on fossils recovered from chaotic and epiclastic metasedimentary rocks, and metavolcanic rocks of the Boyden Cave, Mineral King, Yokohl Valley, and Isabella pendants (Moore and Dodge, 1962; Jones and Moore, 1973; Saleeby and others, 1978; Nokleberg, 1983). The Dinkey Creek pendant is markedly similar to pendants in the northern part of the Kings sequence, yet is

lithologically inconsistent with Kings sequence pendants in the south. As shown in this study, rocks at Dinkey Creek pendant are representative of a passive margin sequence.

Previous Work

Generalized geologic mapping of the Dinkey Creek pendant was initially reported by Krauskopf in his 1953 study of tungsten deposits in Madera, Fresno, and Tulare counties, California. Included in his report is a simplified

1:125,000-scale geologic map of a portion of Fresno county including the Dinkey Creek pendant, and summary data and 7

geologic sketch maps of economic skarn rocks for the Garnet Mine (Rainbow Mine) and Mud Lake Claims. Subsequent stratigraphic and structural data for the Dinkey Creek pendant were presented by Kistler and Bateman (1966). m

their study, Kistler and Bateman mapped the entire pendant, excluding the western septum, at a scale of 1:31,680. Major lithologic units, including quartzite, schist, biotite- andalusite and calc-silicate hornfels, and marble, were differentiated and structural features were interpreted to represent three deformational events. The generalized geology of the Dinkey Creek pendant is shown on the

1:250,000-scale Mariposa sheet (Strand, 1967). Bateman and Wones (1972a) compiled mapping by Kistler and Bateman (1966) with additional data to produce the 1:62,500-scale geologic map of the Huntington Lake quadrangle. In addition, Bateman and Wones (1972b) published analytical data for granitic rocks within the Huntington Lake quadrangle. The Dinkey Creek intrusive suite and the peraluminous Dinkey Dome pluton were studied by Guy (1980).

In 1980, existing geologic maps were field checked during an investigation by the U.S. Geological Survey and the U.S. Bureau of Mines to determine the mineral resource potential of the Dinkey Lakes roadless area. A geologic map (Dodge, 1982), a mineral resource potential map (Dodge and others, 1983), both at a scale of 1:62,500, and a mineral resource potential summary report (Dodge and Federspiel, 1983) for the Dinkey Lakes study area were published as a result of this study . In addition, chemical analyses of rocks, stream sediments, and non-magnetic heavy mineral 8

concentrates from the Dinkey Lakes roadless area were published by Adrian and others (1983) and Smith and other (1985) .

Present Study

During the Summer and Fall of 1984, comprehensive structural and stratigraphic analyses of the Dinkey Creek pendant were performed. The western two-thirds of the pendant (17 km2) was remapped at a scale of 1:12,000 on

topographic maps (Plate I). After identifying the intensity and complexity of structure within the pendant, detailed mapping was conducted in the lithologically diverse and structurally complex area between Dinkey Lakes trailhead and Rainbow mine (4.5 km2) at a scale of 1:4,000 on aerial

photographs (Plates II). During the Summers of 1983, 1984, 1985 and 1990, structural and stratigraphic features of possible correlative units in southeastern California were examined. Included in this comparison were exposures of lower Paleozoic rocks in Death Valley and the White-Inyo Mountains, together with the Boyden Cave, Mineral King, Mount Morrison, and Snow Lake roof pendants.

Detailed analysis of the Dinkey Creek pendant involved the study of lithologic units, structural features, and metamorphic fabrics. A total of 64 representative thin sections were prepared and examined. Analysis of mesoscopic structural features consisted of the measurement and classification of folds, cleavages, foliations, lineations, 9

and faults. Carbonate units were sampled and processed for extraction of conodonts and other microfossils. Whole-rock geochemical analyses of samples from a metabasaltic dike and sill were also obtained. Isotopic analysis of detrital zircon from quartzite and igneous zircon from metabasaltic dikes and sills are pending, and are unavailable for inclusion in this manuscript.

LITHOLOGY

The Dinkey Creek pendant exposes an imbricated packet of highly deformed and metamorphosed sedimentary rocks. These include quartzite, feldspathic quartzite, micaceous and

quartz-mica schist, with smaller amounts of calc-silicate gneiss and marble intruded by a metabasaltic dike and sill. These metamorphic rocks have been intruded by a Jurassic or Cretaceous diorite/gabbro body, and Cretaceous granitic rocks of the Dinkey Creek, Dinkey Dome and Eagle Peak plutons.

The metasedimentary rocks were originally subdivided into 5 mappable units by Kistler and Bateman (1966), who proposed a stratigraphic sequence based upon structural and stratigraphic relationships. In this study, the rocks of Dinkey Creek pendant have been subdivided into 6 metasedimentary map units in addition to metabasaltic dikes and sills. Since stratigraphic continuity for the rocks is questionable, based on data to be presented later in the text, lithologic units will be discussed in order of decreasing abundance. The intensity of deformation 10

exhibited by the metamorphic rocks precludes determination of stratigraphic thicknesses, and therefore only structural thicknesses are provided.

The metamorphic rocks are characterized by a strong therma1-metamorphic overprint, a fact emphasized by Kistler and Bateman (1966) through their use of thermal-metamorphic rock names for lithologic units. However, this study

revealed the importance of earlier dynamothermal metamorphic fabrics, and therefore regional metamorphic rock names have been assigned to the lithologic units.

The map units in this study include quartzite, schist, paragneiss, two calc-silicate gneiss units, marble and

metabasaltic dike rocks. The carbonate rocks were analyzed for conodont microfossils in an attempt to produce a direct faunal age date. Samples from the marble, calc-silicate gneiss and paragneiss units were processed for microfossils, but no evidence of conodonts or any other microfossils was discovered in the concentrates.

Metasedimentary Rocks

Quartzite (qtzt) (388 m)

Quartzite, the most extensive unit in the pendant, is exposed in a narrow band in the north central part of the pendant between Dinkey Lakes trailhead and Rainbow mine. This band increases in width to the south, and additional outcrops of quartzite occur north and south of Willow Meadow

(Plates I and II). The quartzite lies in fault contact with Figure 3. Outcrop photograph of medium to thick layers in the quartzite unit. schist along the Dinkey Creek thrust and along the Willow

Meadow thrust. The contact between paragneiss and guartzite is conformable, and the two units are infolded in the southeastern part of the map area. Exposures of quartzite along the periphery of the pendant are truncated by granitic r o c k s .

The resistant quartzite unit is predominantly composed of quartzite, feldspathic quartzite and micaceous, feldspathic quartzite in addition to minor calcareous quartzite. Thin to very thick layers (5mm to 2.5 m) of pink— to buff-weathering, white to gray quartzite are locally interrupted by mm- to cm-scale partings and minor interlayers of mica schist (Fig. 3). Cream to greenish-brown to orange-brown, thinly laminated

ca-^-c—silicate schist, calcareous quartzite and minor marble occur within a layer, 3-4 m thick, adjacent to the Dinkey Creek thrust.

The quartzite is generally strongly foliated to mylonitic, but less deformed rocks are not uncommon. Preserved bedding occurs within less deformed lenses of quartzite and is either massive, parallel laminated or cross-stratified. Cross-beds are tabular to lenticular, and locally sigmoidal, with tangential and angular based foresets (Figs. 4a and 4b). Metamorphic biotite, detrital zircons and/or opaque oxides define the laminae and cross-stratification. Tectonic cross-layering strongly resembles original cross-bedding in some cases and can be difficult to differentiate from true cross-bedding. The quartzite is fine- to coarse-grained, mature, and 13

Figure 4. (a) Outcrop photograph of quartzite unit with well-preserved lenticular to wedge shaped cross—beds showing sharp lower contacts. Beds are overturned with the top direction toward the bottom of the photograph. (b) Outcrop photograph of quartzite unit with well-preserved trough-shaped cross-bedding showing erosional contacts. Beds are upright. moderately well to very well sorted. it is composed of

vitreous quartz, potassium feldspar, plagioclase, muscovite, biotite, chlorite, zircon, tourmaline, apatite and opaque oxides. Sparse very coarse- to granule-sized milky -blue- quartz grains are evident throughout the quartzite. Rare intervals of pebbly quartzite with granules and pebbles of quartz up to 1 cm in length were also noted. Locally,

layers of quartzite contain porphyroblasts of garnet up to .75 cm in diameter. Thin sections of the quartzite exhibit evidence of original quartz grains in addition to quartz

grains at various stages of recrystallization and mylonitic development. Undulose extinction and sutured boundaries are typical of the quartz. Spotted and knotted textures within schist intervals result from concentrations of biotite.

Schist (schl (520 m) Located east and west of the Dinkey Lakes trailhead and in the southwestern portion of the pendant, the unit

primarily consists of brown-weathering, light to dark gray, mica schist, micaceous-feldspathic schist, and quartz-mica schist, subordinate micaceous, feldspathic quartzite, and minor lenses of cream to green calc-silicate and marble (Fig. 5). Resistant exposures of schist occur in fault contact with quartzite along the Dinkey Creek and Willow

Meadow thrusts, and with marble along the Limestone Campsite thrust (Plates I and II). East of Dinkey Lakes trailhead, the schist and calc-silicate gneiss are in conformable contact, and minor infolding occurs in association with F3

17

folds. in Willow Meadow, however, calc-silicate gneiss and schist are in fault contact along the Limestone Campsite thrust. At the periphery of the pendant, exposures of schist are truncated by granitic intrusions.

The schist is strongly foliated to mylonitic. it is relatively homogeneous and is primarily composed of fine- to medium-grained biotite, andalusite, muscovite, plagioclase, potassium feldspar, quartz and garnet. Subtle lamination is produced by slight compositional variations, and mica rich laminae commonly exhibit a silky sheen. Poikiloblasts of andalusite and concentrations of biotite create local

spotted to mottled textures. Small pods and thin layers of calc-silicate schist and minor marble are occasionally

present. The calcareous layers are laterally discontinuous and abruptly pinch out, or are gradational with the mica schist, apparently the result of original facies variations and tectonic thinning.

Paraqneiss (perl (430 m) Outcrops of paragneiss are limited to the eastern edge of the pendant (Plates I and II). The only exposed metasedimentary unit in contact with the paragneiss is the quartzite unit. This contact is conformable and quartzite-paragneiss are locally infolded as mentioned earlier. The paragneiss is truncated by intrusive rocks at its north end and obscured by glacial deposits along its eastern edge. The paragneiss is a heterogeneous unit which includes quartz-mica-schist, micaceous, feldspathic quartzite, feldspathic quartzite and subordinate marble and

19

calc-silicate gneiss (fig. 6). It tends to be resistant/

and forms bold outcrops. The paragneiss is primarily composed of quartz, biotite, potassium feldspar, plagioclase, muscovite, andalusite and garnet.

Strongly foliated to mylonitic, orange-weathering, medium to dark gray quartz-mica schist is thinly

interlayered with white to gray, micaceous, feldspathic quartzite producing a gneissosity that characterizes the unit. Thick interlayers of feldspathic quartzite and

quartzite up to 3 meters thick are finely-laminated, and occasionally exhibit cross-bedding. Layering is strongly disrupted, and broken and boudinaged lenses and interbeds of quartzite are common.

Horizontal, cylindrical-shaped worm burrows occur within both the micaceous, feldspathic quartzite and quartz-mica

schist, although they are more abundant within the competent quartzitic intervals (Fig. 7a). Burrows are filled with a white, coarser quartzite and are commonly flattened and/or sheared making identification difficult (Fig. 7 b ) . The

intensity of the fabric and the preferred orientation of the worm burrows raises the possibility they have undergone passive rotation into parallelism to the Sl-2 layering (discussed later).

Calc~Silicate Subunit (cs): The disrupted carbonate subunit within the paragneiss consists of coarse-grained, highly deformed and recrystallized, buff to light blue-gray marble and thinly-bedded, buff to greenish, calcareous quartzite and calc-silicate schist. Mineral assemblages

(b) Photograph of strongly deformed worm burrows in a foliated, micaceous feldspathic quartzite layer within paragneiss unit. the 22

dominantly reflect thermal metamorphism and lenses and pods of epidote-garnet skarn are locally present. The tungsten

deposit of the Rainbow mine is hosted by this calc-silicate layer.

Calc-Silicate Gneiss (esc)

Two units of calc-silicate gneiss occur primarily in the north central part of the pendant, with minor outcrops in the extreme southwestern part (Plate I). The largest area

of exposure occurs adjacent to Dinkey Creek at the Dinkey Lakes trailhead, and scattered outcrops are present in Meadow (Plates I and II) . The two units are

conformable and are distinguished primarily by color, orange-brown and green, and a metabasaltic sill occurs

approximately along their contact. In both the Dinkey Lakes trailhead and Willow Meadow areas, rocks of the

orange-brown calc-silicate unit appear to be conformable with the marble unit. The contact between the green

calc-silicate gneiss and the schist unit is conformable in the Dinkey Lakes trailhead area, and minor outcrops of green

calc-silicate gneiss in Willow Meadow occur in fault contact with the schist along the Limestone Campsite thrust. Both units thin northward, possibly the result of lateral facies variations and tectonic thinning.

Calc-Silicate Gneiss - orange-brown (csg-b): (132 m) Weathering of Fe-rich minerals gives this calc-silicate unit a distinctive orange-brown color; guartz, calcite, biotite, muscovite, potassium and plagioclase feldspar, and opaque minerals are commonly observed in thin section. Thin 23

inter?avpr<;0ofCrOPK?h0t0g^a^ n °f deformed> thin to medium a u t r ^ t l ^ ?£ marble, calcsilicate gneiss, and calcareous quarzite of the orange-brown calc-silicate gneiss unit 24

to medium layers (1 cm to 25 cm thick) of buff to

bluish gray marble and sandy marble, and buff to medium

gray-brown calcareous quartzite and calc-silicate gneiss are interbedded in approximately equal proportions in this unit (Fig* 8). These interbeds are locally discontinuous, strongly foliated and highly contorted. Marble layers are

fine to coarsely recrystallized, and calc-silicate and

calcareous quartzite layers are fine to medium grained and exhibit pitted textures from the dissolution of calcite.

A zone of probable Tertiary (?) solution breccia is

exposed by Dinkey Creek. In this breccia, angular, foliated clasts up to 30 cm in length are supported by white to buff, coarsely recrystallized calcite.

Calc-Silicate Gneiss - green (csg-g): (93 m) Medium to coarsely recrystallized, cream marble and sandy marble constitute nearly 70 percent of the unit. Marble layers ranging from 1 cm to 1 m in thickness are interlayered with calcareous quartzite and calc-silicate gneiss ranging from 1 cm to 10 cm in thickness (Fig. 9). A predominance of green calc-silicate minerals impart a characteristic greenish-hue to the marble and sandy marble, and a green to yellowish-green color to the calcareous quartzite and calc-silicate gneiss. The mineral assemblage in most rocks includes calcite, quartz, epidote, garnet, and diopside. Interbeds and lenses of calc-silicate and calcareous quartzite are locally broken and boudinaged, and are commonly pitted due to the dissolution of calcite. The entire unit is intensely deformed and exhibits a strong 25

Figure 9. Outcrop photograph of thin to medium layered, marble-rich, green calc-silicate gneiss unit. 26

Figure 10. Outcrop photograph of the blue—gray marble unit showing a strong, penetrative foliation distinguished by color and grain size variations. 27

foliation.

Mart>le (M) (8 8 m)

Medium blue-gray marble is exposed in the vicinity of the Dinkey Lakes trailhead and in scattered outcrops within Willow Meadow (Plates I and IX). The unit consists of massive, fine— to coarse-grained, highly deformed and

recrystallized marble (Fig. 10). a strong, penetrative

foliation to mylonitic fabric is defined by faint color and grain size variations. Bleached zones and small veins of

white, coarsely recrystallized calcite are locally present.

The veins typically define en-echelon arrays. The marble is slightly impure and primarily contains eguidimensional to elongated, recrystallized calcite with minor quartz,

muscovite, tremolite, wollastonite and garnet. Possible

cross-bedding similar to tectonic cross-layering was rarely observed.

Metamorphism

Polyphase metamorphism of the Dinkey Creek pendant complicates the interpretation of metamorphic conditions for the pendant. Metamorphic mineral assemblages associated with dynamothermal metamorphism have been overprinted and locally completely recrystallized during later thermal metamorphism, although the dynamothermal fabrics commonly have retained their integrity. Mineral assemblages associated with dynamothermal metamorphism are commonly difficult to distinguish from mineral assemblages associated 28

METAMORPHIC MINERAL ASSEMBLAGES

Rock Unit Mineral Assemblage

guartzite qz + ksp + plag + mus + bt + chi + zr + tour ± ap + sph + op

schist bt + and + mus + ksp + plag + qtz + chi + gar + tour + zr + sph + op

paragneiss qz + bt + plag + mus + ksp + and + gar + tour + chi + sph + zr + op

calc-silicate gneiss (b) qz + clc + bt + mus + plag + wol + diop + and + tour + ksp + sea + chi ± ep + op

calc-silicate gneiss (g) clc + qz + ep + gar + diop + wol + plag + micro + chi + sea + ves + act ± ap + zr + sph + op

marble clc + trem + mus + wol + gar + qz + plag + diop + sea ± ap + op

Table 1. Metamorphic mineral assemblages for metasedimentary rocks of the Dinkey Creek pendant. Act=actinolite, and=andalusite, ap=apatite, bt=biotite, clc=calcite, chl=chlorite, diop=diopside, ep=epidote, gar=garnet, ksp=potassium feldspar, micro=microcline, mus=muscovite, op= opague, plag=plagioclase, sca= scapolite, sph=sphene, trem=tremolite, tour=tourmaline, ves=vesuvianite, wol=wollastonite, zr=zircon. 29

with thermal metamorphism due to compositionally controlled growth of the thermal metamorphic minerals parallel to

regional fabrics. Relict mineral assemblages associated with regional tectonic fabrics (Table 1) suggest upper greenschist facies. A thermal metamorphic overprint of hornblende hornfels facies has been superimposed on the dynamotherma1 metamorphic fabric. Table 1 presents a

summary of mineral assemblages for the individual lithologic units.

Protoliths

In spite of tectonic and metamorphic overprints, the metasedimentary rocks of Dinkey Creek pendant are

distinctive, and protoliths can easily be deduced. The

quartzites and feldspathic quartzites are predominantly composed of quartz and/or feldspar, and, where original

textures are preserved, are well-sorted and well-rounded. These characteristics indicate that the quartzites and

feldspathic quartzites were derived from quartz arenites and feldspathic arenites. The calcareous quartzites most likely developed from quartz arenites with varying amounts of calcareous cement. The variable amounts of alumino- S‘’-^--*-cat-es , micas and quartz in the schist and paragneiss suggest that protoliths for the mica schists and quartz-mica schists were clay-rich and ranged from mudstones to silty mudstones and feldspathic siltstones. Marbles were originally pure to impure limestones. Textures of some of 30

the marbles together with the presence of diopside and scapolite and increased proportions of Mg and Ca in metabasaltic dikes and sills contaminated by marble (discussed later) suggest that the marbles may have been

dolomitic. The occurrence of calc-silicate minerals, micas, quartz and rare andalusite together with calcite in the calc-silicate schists indicate that these rocks originally

were marls ranging from argillaceous limestones (dolomitic?) to calcareous siltstones.

Environments of Deposition

Although intense deformation and polyphase metamorphism have significantly altered the metasedimentary rocks of

Dinkey Creek pendant, preserved sedimentary structures and inferred protoliths provided important evidence concerning the environments of deposition. Kistler and Bateman (1966) concluded the metamorphic rocks originally were shallow

marine deposits. However, deposition within submarine-fan to basin-plain settings in a complex, continental margin, magmatic arc (Saleeby and others, 1978; Busby-Spera, 1984) has been more commonly accepted for rocks of Dinkey Creek pendant by virtue of inclusion in the Kings sequence. Data presented in this study supports a shallow marine environment as suggested by Kistler and Bateman (1966), and I propose that the sediments accumulated on a continental shelf in a passive margin setting.

The occurrence of extensive and compositionally mature quartzite and feldspathic quartzite is characteristic of 31

high-energy environments with abundant sand availability such as shoreline and subtidal zones. Tabular, lenticular and sigmoidal cross bedding observed within the quartzite were probably generated by strong, shallow-water, tidal or storm-enhanced currents indicative of nearshore or inner continental shelf environments (Harms and others, 1982; Walker, 1984; Johnson and Baldwin, 1986). Coarse sands

locally containing pebbles are consistent with nearshore or inner shelf environments where current velocities are

sufficient for transporting grains of these sizes. The lack of channels, scours, and lateral variability preclude deposition in a sandy, fluvial system.

In the schist unit, the thick sequence of aluminum-rich mudstone, silty mudstone, siltstone, and feldspathic siltstone with minor micaceous quartzite and carbonate

layers suggest deposition in a terrigenous subtidal zone on a continental shelf along a passive margin. The laminated and locally cross-bedded sands and carbonates interbedded with silty mudstones and siltstones of the paragneiss unit

suggest a shallower, more energetic terrigenous subtidal zone than the schist unit. The inner continental shelf region is an area of extensive bioturbation, and abundant horizontal worm burrows are locally preserved within feldspathic arenites, silty mudstones and siltstones of the paragneiss. Both the schist and paragneiss units were probably deposited in an environment slightly deeper and less energetic than that required for the quartzite unit.

The limestones, argillaceous limestones and calcareous 32

siltstones characteristic of the calc-silicate gneiss

suggest deposition in a terrigenous to carbonate transition zone along the inner continental shelf. Possible

cross-bedding within the marble unit suggests deposition in

a shoal environment associated with a carbonate bank (Halley and others, 1983; James, 1984).

Inferred lithologic and preserved sedimentologic evidence within the rocks of Dinkey Creek pendant strongly suggest the rocks were deposited in a shallow marine

continental shelf environment along a passive continental margin. The absence of interlayered volcanic or

volcaniclastic rocks and the lack of sedimentary features consistent with submarine-fan and basin-plain facies

apparently preclude the interpretation of a magmatic arc depositional environment.

Intrusive Rocks

Metabasaltic Dike and Sill (md)

Dark gray to black, aphanitic to microporphyritic metabasaltic rock intrudes the carbonate units near the Dinkey Lakes trailhead (Plate II). A sill, 0.5 to 2 meters thick, separates the two calc-silicate gneiss units (Fig. 11)/ and a dike of similar width cross-cuts the northern end of the marble unit. The metabasaltic unit is gray brown to orange-brown on weathered surfaces and exhibits a blocky appearance. It is weakly foliated in association with late-stage folds within the pendant.

The metabasaltic dike and sill are aphanitic to very Figure 11. Outcrop photograph of the basaltic sill (center of photograph) intruded along the contact between the orange-brown calc-silicate gneiss unit (background) and the green calc-silicate gneiss unit (foreground). 34

fine-grained, and in thin section exhibit intergranular to glomeroporphyritic textures. The dike and sill contain hornblende, biotite, apatite (typically fractured), wollastonite, pyroxene, and epidote, together with

interstitial intermediate and sodic plagioclase, and trace amounts of guartz and orthoclase. Accessory minerals include zircon, sphene, tourmaline (?) and magnetite. The mineralogy of the dike and sill does not reflect primary

composition, but rather is indicative of contamination by the carbonate host rock during emplacement, and alteration

during subseguent greenschist metamorphism. The presence of carbonate xenoliths and weak foliation are consistent with this interpretation. The original mineralogy is inferred to have been primarily pyroxene, hornblende, biotite, intermediate to calcic plagioclase feldspar.

Whole rock chemical analyses of the metabasaltic dike and sill are listed in Table 2. The 5 analyzed samples include three samples from the sill intruding the

calc-silicate units and two samples from the dike intruding the marble unit (Plate II). The low Si02 and high Ca and Mg values in DCP-D1 reflects contamination of the dike by the

host carbonate rock. The reason for the higher Si02 value in DCP-S3 is unknown. The Na20 + K20 content in

relationship to Si02 indicates the dike and sill are basalt

to trachyandesite in composition (Fig. 12). Due to the possible mobility of alkalies during metamorphism, the relationship between Na20 + K20 to Si02 may not be representative of the original composition. In the chemical 35

MAJOR ELEMENT ANALYSES - DINKEY CREEK PENDANT

DCP-D1 DCP-D2 DCP-S1 DCP-S2 DCP-S3

Si02 43.3 48.5 48.4 48.8 55.2 A1203 14.5 13.6 13.4 12.7 13.2 CaO 12.1 8.52 8.5 6.76 5.11 FeO 9.7 11.35 11.2 12.6 9.7 Fe203 2.92 2.19 2.45 2.2 2.42 K20 0.57 0.88 0.86 1.5 0.97 MgO 7.12 4.8 4.82 4.96 2.83 MnO 0.21 0.23 0.23 0.25 0.26 Na20 2.95 3.67 3.63 3.75 5.23 P205 0.23 0.55 0.4 0.23 0.71 Ti02 4.34 3.65 3.65 3.82 2.25 Volatiles 1.57 1.44 1.82 1.58 1.22

Total 99.51 99.38 99.33 99.15 99.10

Table 2. Chemical analyses of dikes and sills in the Dinkey Creek pendant. Titrametric analysis for FeO, Gravimetric analysis for Loss-On-Ignition, and Direct Current Plasma - Emission Spectrometer analysis for all other elements (Bondar-Clegg, Reno, NV, analyst). Volatiles are reported as a modification of the Loss-On-Ignition determination as described by Lechler and Desilets (1987). 36

COMPOSITIONAL VARIATIONS IN THE DIKE AND SILL OF DINKEY CREEK PENDANT

Figure 12. Diagram of compositional variations in magmas (after Cox^ and others, 1979) with plots of geochemical data from the dike and sill in Dinkey Creek pendant. 37

classification scheme of Irvine and Baragar (1971), which

distinguishes subalkaline, alkaline and peralkaline volcanic rocks, the metabasaltic rocks are transitional between alkalic and subalkalic, and tholeiitic.

Diorite/Gabbro Intrusion (KJd)

Small masses of diorite to hornblende gabbro with

variable textures and compositions intrude the metamorphic rocks at the northeastern edge of the pendant near Rainbow mine (Plate I). The intrusion is medium to very dark gray, fine grained to porphyritic, and is chiefly composed of

biotite, hornblende and plagioclase in variable proportions. The relation of the diorite/gabbro intrusion to the

metabasaltic dike and sill is uncertain. The age of this intrusion is not well constrained and is considered either Jurassic or Cretaceous. Cross-cutting relationships indicate the diorite is intruded by the Dinkey Dome and Dinkey Creek plutons and is, therefore, older than 104.1 Ma (Stern and others, 1981).

Dinkey Creek Intrusive Suite

The Dinkey Creek intrusive suite contains, from oldest to youngest, the Dinkey Creek, McKinley Grove, Snow Corral Meadow and Dinkey Dome plutons (Fig. 13). These plutons range in composition from tonalite and quartz diorite to granodiorite, quartz monzonite and garnetiferous quartz monzonite. Petrography of the Dinkey Creek intrusive suite was presented by Guy (1980), and the following lithologic descriptions of the Dinkey Creek and Dinkey Dome plutons are 38

GRANITIC ROCKS IN THE VICINITY OF DINKEY CREEK PENDANT

119° 10' 119° 05 '

Figure 13._ Map showing the distribution of granitic rocks in the vicinity of Dinkey Creek pendant. (Kbl=Blue Canyon Quartz Diorite, Kbm=Bald Mtn. Quartz Monzonite, Kep=Eagle Peak Granodiorite, Kmc=McKinley Grove Granodiorite, Kmg=Mount Givens granodiorite, Krl=Red Lake granodiorite, Ksm=Snow Corral Meadow Quartz Monzonite, KJd=diorite/gabbro complex) 39

GRANITIC ROCKS IN THE VICINITY OP DINKEY CREEK PENDANT

Granitic Rocks Age (87Sr/86Sr)i

Red Lake Granodiorite 90.1 Ma

Big Creek Granodiorite 88.5 Ma

Eagle Peak Granodiorite 88.9 Ma

Bald Mountain Quartz Monzonite 91.1 Ma

Mount Givens Granodiorite 84-89 Ma* . 7082 92.8 Ma* .7092 .7095

Dinkey Dome Quartz Monzonite 89.8 Ma .7080

Lower Bear Creek Quartz Monzonite 92.6 Ma

Snow Corral Meadow Quartz Monzonite 88.8 Ma

Dinkey Creek Granodiorite 90 Ma .7094 104.1 Ma* .7106 107 Ma** 110 ± 11 Ma# 118 Ma***

Tabie 3. Age determinations and initial 87Sr/86Sr values for granitie rocks in the vicinity of Dinkey Creek pendant. are listed in order of increasing relative age (top to bottom) based on field relations established by a? ! Won?s (1972a)• (K/Ar ages from Bateman and Wones } ' ,!!L?at? an and Wones (1972a), (**) Evernden and K^S^ ler (1989)/' (***) Kistler and others, 1965; (#) Rb/Sr isochron age from Bateman and Wones (1972a); (*) 87o /^635U age froin stern and others (1981); initial , Sr/ Sr values from Hurley and others (1965). K/Ar ages ve been converted for the new age and abundance constants as per Dalrymple (1979). 40

taken from his work. Age determinations and initial 87Sr/86Sr values are listed in Table 3 .

Dinkey Creek Pluton (Kdc): The Dinkey Creek pluton occurs along the western edge of the Dinkey Creek pendant.

Considered a granodiorite, the Dinkey Creek pluton typically ranges in composition from tonalite to quartz diorite. The pluton contains quartz, plagioclase, hornblende, biotite, minor potassium feldspar and accessory minerals such as

titanite, zircon, apatite, monazite, magnetite and ilmenite. Two generations of albite are distinguished by albite twinning versus oscillatory zonation. Biotite and

hornblende commonly occur as clots. Mafic inclusions in the Dinkey Creek pluton have a similar mineralogy, but different modal distribution and textures than the encompassing rock.

A weak to strong igneous foliation occurs within the pluton and orientations are highly variable.

The Dinkey Creek pluton is the oldest unit of the Dinkey Creek intrusive suite and provides the only direct age constraint for the metasedimentary rocks. The 92.8 Ma Mount Givens granodiorite intrudes Dinkey Creek pluton, thus provides a minimum age for the Dinkey Creek intrusion.

Bateman and Wones (1972b) reported potassium-argon ages of 85 and 89.8 Ma from biotite and hornblende, respectively. Previously reported ages include a 107 Ma K/Ar age (Evernden and Kistler, 1970), a 118 Ma K/Ar age (Kistler and others, 1965), and a Rb/Sr whole rock isochron age of 110 + li Ma

(Bateman and Wones, 1972a). More recently, Stern and others

(1981) reported 207Pb/235U, 208Pb/232Th and 206Pb/238U ages 41

of 91.0 Ma, 93.9 Ma, and 104.1 Ma, respectively, for the

granodionte of Dinkey Creek. Younger potassium-argon ages are considered reset ages resulting from the intrusion of

the Mount Givens pluton (Evernden and Kistler, 1969; Bateman and Wones, 1972a,b). Evernden and Kistler (1969), and Bateman and Wones (1972a) considered the Dinkey Creek intrusion to be part of the 121-104 my Huntington Lake intrusive epoch.

Dinkey Dome Pluton (Kdd)s The Dinkey Dome pluton occurs along the southern and eastern edges of the pendant. The

Dinkey dome is a garnetiferous quartz monzonite consisting of quartz, plagioclase, orthoclase, biotite, garnet,

muscovite and minor aluminosilicate minerals. The quartz grains range up to 7 mm in size. Myrmekitic textures occasionally occur along boundaries between

quartz-plagioclase and potassium feldspar-plagioclase. The plagioclase cores exhibit twinning but are commonly altered to sericite. Biotite and garnet are usually associated in clusters up to 2 mm in size, and muscovite generally occurs as broken laths in association with andalusite or

sillimanite. Garnets are fractured, but rarely contain

inclusions. Aluminosilicate polymorphs rimmed by muscovite with corundum represent remnants of included metasedimentary rock (Guy, 1980).

The 85 - 89.8 Ma potassium-argon age determinations for the Dinkey Dome pluton (Bateman and Wones, 1979b) are also considered suspect, probably reset by the younger Mount Givens pluton (Guy 1980). Dinkey Dome is intruded by the

88.9 Ma Eagle Peak pluton (Bateman and Wones, 1972a,b) and 42

the 92.8 Ma Mount Givens Pluton, and is considered to be

contemporaneous with the Dinkey Creek intrusion (Guy, 1980)

STRUCTURAL RELATIONS

The metamorphic rocks of Dinkey Creek have experienced a greater degree of deformation and exhibit fold geometries

that are more complex than previously portrayed by Kistler

and Bateman (1966), who reported three generations of folds and interpreted layering as bedding. in this study,

additional fold generations have been identified together with structural features indicative of penetrative ductile deformation. Four phases of deformation have been

established from style and orientation of minor folds and

cognate structures, and from overprinting relationships. Complex interference patterns that have resulted from the

interaction of four fold generations are most pronounced in zones of greatest ductility contrast. A fifth fold style with a unique orientation was tentatively identified, but its position with respect to the deformational succession was not completely established due to insufficient data on superposition. A summary of the structural history for the Dinkey Creek pendant is presented in Table 4 .

Penetrative structures resulted from the D ± through D4 deformational events, and a fifth fold generation represents a non-penetrative deformation. D2 and D 3 structures are dominant throughout the pendant and exert the strongest control on the overall map pattern. The most prominent 43

map-scale structure exposed in the pendant is an east-vergent D 2 imbricate structure (Plate I). This

imbricate structure is characterized by a minimum of four imbricated thrust (?) sheets that dismember megascopic,

east-vergent, recumbent F2 folds. The superposition of f 3 folds on the F2 folds and thrusts resulted in a complex, double zig-zag interference pattern. D4 structures are responsible for flexures in F2 and F 3 fold hingelines, and structures are not evident at map-scale.

The dominant layering in the pendant is a strongly developed composite S-^ foliation (Plate I and II). This

layering defines the megascopic F2 and F 3 folds, generally strikes north to northwest, and is predominantly west-dipping. The S1-2 layering developed in association with isoclinal folding during d x and D2, and is considered to represent transposed layering throughout the pendant. The intensity of deformation disclosed in this study precludes Kistler and Bateman's (1966) interpretation of a simple stratigraphic sequence.

D-l Structures

D1 structures are not readily discernible, possibly as a result of having been obscured by later deformation.

Map-scale F-l folds have not been observed and minor F-l folds are only locally preserved.

F-l folds are N-trending, plunging inclined to recumbent isoclines with simple hinge zones (Fig. 14). Hinge surfaces dip moderately to gently west and hingelines plunge gently 44

Figure 14. Outcrop photograph of a Fx isoclinal fold coaxially refolded by a F2 fold in spotted micaceous- feldspathic schist within the schist unit (spotted texture results from concentrations of biotite) 45

Figure 15. Photomicrograph of relic Fx folds defined by quartz-mica layers within an S2 microlithon (S2 foliation is subhorizontal). Limbs of these folds have been dismembered and/or sheared off. (Width of photograph is 7 mm) 46

northward (Plate VI). Fl folds show no evidence of

deforming an earlier tectonic fabric, and therefore are considered to deform original bedding.

An S ± foliation defined by the parallel alignment of mica is folded in the hinge zones of F2 folds and is the

primary reasoning for D1# Rare exposures of F-l folds are limited to areas where subsequent deformations are least

pronounced or to lithologies where ductility contrasts

enhanced the recording of folds. Microstructures associated with this earliest phase of deformation are occasionally

evident in thin section. The photomicrograph in Figure 15 shows rare F^ microfolds, almost completely obliterated by

D2 deformation, within a S2 microlithon. Limbs of these F-l microfolds are truncated, or are displaced and rotated, by the S2 schistosity.

The D-l structures predated D2 deformation and intrusion of the metabasaltic dike and sill. The 104.1 Ma Early

Cretaceous age of the Dinkey Creek granodiorite provides the only direct age constraint for deformation.

D2 Structures

Structural features that resulted from penetrative D 2 deformation are extremely important with respect to the map pattern and the overall structural grain of the pendant.

East-vergent imbricate thrusting (?) in conjunction with east- to northeast-vergent folding occurred during the D 2 deformational event. The imbricate structure developed 47

contemporaneously with major east-vergent F2 folds within the lowest structural plate. In addition, the Sl_2 fabric which characterizes the pendant developed during D2

deformation. The D2 deformation postdates D ± and predates intrusion of the metabasaltic rocks. As with Dlf the

mid-Cretaceous granodiorite of Dinkey Creek provides the only direct age constraint for D 2 deformation.

Fo Folds

F2 folds are N-NW trending, plunging inclined to

recumbent, long limbed isoclines with simple to complex, and occasionally thickened hinge zones (Fig. 16). Hinge

surfaces of F2 folds dip gently to moderately west-southwest and hingelines plunge gently to moderately north-northwest (Plate VI).

Minor F2 folds are prominent within all lithologic units m the pendant and are distinguished from the coaxial F ± folds in that they deform an earlier tectonic fabric (S-^ .

Interference patterns resulting from F ± and F2 isoclines are not common, but vague arrowhead patterns within calc-silicate gneiss, schist and paragneiss appear to be the result of their superposition. Rare eye folds resulted from the refolding of F ± or F2 folds during D 2 deformation (Fig. IV).

The Fx and F2 isoclinal folds are coaxial suggesting that the two phases of deformation were related and may represent a single progressive event, D-^. Progressive deformation during D2 is also indicated by the refolding of

|S gi,.5S«s-3SM ;.aa,-&ss v The eye fold resulted from refoldina of an 1 2 f°ld during D2 shear zone deformation. 50

F2 isoclines by geometrically similar coaxial folds.

This refolding of f 2 isoclines is interpreted to represent late phase F2 folding during the waning phases of D 2

deformation. The similarity in style between early- and late-phase F2 folds complicates differentiation and

therefore they have not been distinguished. Both the early

and late phases of F2 folds exhibit variable orientations of

hingelmes and hinge surfaces resulting from rotation during later deformational events.

S? Foliation

A hinge surface-parallel S2 foliation, compositional layering and collateral cleavage developed coevally with F 2 isoclines. This fabric is dominant throughout the pendant and commonly delineates a composite S 1_2 layering. The S ±

foliation has been isoclinally folded and rotated into parallelism with S2 hinge surfaces.

The penetrative S1_2 cleavage is typically a discrete, planar, spaced cleavage, and is locally an anastomosing

differentiated cleavage, and rarely slaty to schistose. The

sl-2 fabric is the dominant microstructure evident in thin section and is distinguished by mineral segregation, and preferred shape and crystallographic orientations. The parallel alignment of micas (biotite and/or muscovite) typically defines the foliation. Other minerals such as garnet and andalusite occur in layers parallel to S1_2, although this may reflect S-^ compositional control during 51

later thermal metamorphism.

Mineral stretching lineations (L2) occur in some outcrops primarily in the hinge zones of F 3 folds developed in schist and calc-silicate gneiss.

Major F2 folds in the southeastern part of the pendant along Dinkey Creek are defined by the quartzite/paragneiss contact, S1_2 foliation orientations in the quartzite and paragneiss, and calc-silicate layers within the paragneiss

(Plate I). These folds were regarded as F ± folds by Kistler and Bateman (1966). These major F2 folds are overturned to the east with paragneiss and quartzite occurring in the

cores of synforms and antiforms, respectively. Hinge

surfaces dip moderately west and trend north and northwest. Minor parasitic folds are abundant within the hinge zones of these major folds.

P9_Puctile DeforniaHnn

Several additional D2 structural features within the Dinkey Creek pendant indicate the importance of intense ductile deformation. Such features include 1) an intense

astomylonitic fabric, 2) shredded and boudinaged layering, 3) mtrafolial folds, 4) sheared isoclines and 5) outcrop- scale ductile shear zones.

All metasedimentary units within the pendant are

characterized by a blastomylonitic fabric (Fig. 18). This fabric is most pronounced within the quartzite and paragneiss units within the lowest structural plate (Plate

VI)• In these rocks, blastomylonite occurs zonally and is 52

Figure 18. Outcrop photograph of strong foliation and deveI^eda!r?hfquartzitehunii?St0I"yl0nitl° fabri° 53

coeval with the Sl_2 foliation and cleavage. The

blastomylonitic fabric strikes north-northwest and is vertical or dips steeply to moderately west. Zones of

blastomyIonite range in width from 2cm-10m with boundaries that are sharp or gradational with the s1_2 fabric.

Laterally, the zones of blastomylonite are discontinuous. They create a rough anastomosing pattern in the quartzite

and paragneiss. Curiously, stretching lineations associated

with the blastomylonite are not commonly observed within the

pendant. This may be the result of recrystallization during subsequent regional and thermal metamorphic events. Weakly mylonitized rocks are sharply bounded by

blastomylonite or grade into blastomylonite through increasing degrees of mylonitic development. Sheared

isoclines and corresponding minor ductile shear zones are

associated with the intermediate to late stages of mylonite development in the eastern part of the pendant (fig. 19).

Intrafolial folds and shredded and boudinaged layering are also associated with mylonitic fabrics, and are more

commonly exposed throughout the entire pendant (fig. 20 and 21). The marble and calc-silicate gneiss units north of Dinkey Lake trailhead and the disrupted calc-silicate

interbed within the paragneiss show map-scale boudinage and tectonic thinning.

Mesoscopic ductile shear zones range from less than 1 cm to 0.5 m in width. These shear zones occur predominantly within the quartzite unit and are developed primarily along pelitic intervals. The shear zones commonly truncate the

57

limbs of F2 isoclinal folds. Megascopic ductile shear zones (ie: Dinkey Creek Thrust) also occur in association with sheared limbs of megascopic F2 isoclinal folds (discussed below).

Do Faults

The metasedimentary rocks are complexly shuffled by west dipping, low angle faults (Plates I and II). Due to the

approximate parallelism of the D2 faults with S1_2 layering, and the association of shearing with the recumbent F2 folds, these faults are considered to be D2 thrust faults. The

structurally lowest thrust juxtaposes schist over quartzite that is infolded with paragneiss; the central thrust places schist over marble; and the structurally highest thrust places quartzite over schist. The three thrusts are

approximately parallel and are longitudinal to the major structures within the pendant.

The structurally lowest thrust, herein referred to as the Dinkey Creek thrust, is prominent and well exposed, and

bisects the pendant. Along the central schist-quartzite contact, it locally both truncates and parallels the S1_2 foliation/cleavage. Pods of cream-green marble and

calc-silicate gneiss, paragneiss and crush breccia occur locally along the thrust. Evidence for ductile shearing along the thrust is dominant, although minor post-mylonite brecciation also occurred. Mylonitic layering associated with the thrust is parallel to, and gradational with, the

^1~2 fabric. The association of mylonitic fabric with s^_2 58

layering suggests that the Dinkey Creek thrust formed during D2 deformation. Post-mylonite brecciation may reflect a

transition from ductile to brittle conditions during late d 2 deformation or may have resulted from post-D2 brittle reactivation of the Dinkey Creek thrust.

The direction of movement along the Dinkey Creek thrust is unknown since stretching lineations are rare. As

indicated by the stereoplot in Figure 22, F-l and F2

hingelines approximately parallel L2 stretching lineations from localities throughout the pendant. The parallelism of these structural features suggests that the isoclinal F ± and F2 folds were passively rotated, and thus may indicate the

transport direction for the ductile thrust. Figure 22 also

shows the mean S1-2 foliation/cleavage/compositional layering overlaid on F^, F2 and L2. The orientation of the

f 1-f 2"L2 cluster relative to the mean S-^ layering suggests possible oblique dip-slip movement for the Dinkey Creek thrust.

Outcrops of the remaining two faults are scarce, and glacial deposits obscure their locations. The faults have been inferred on the basis of missing lithologies and orientations of S ± _ 2 layering. The central thrust, herein referred to as the Limestone Campsite thrust, is suggested by the absence of calc-silicate gneiss along the schist- marble contact. The clearest evidence for the Limestone

Campsite thrust is provided by a small exposure along Dinkey

Creek north of Dinkey Lakes trailhead (located on Plate II). At this exposure, marble is juxtaposed against schist with FI AND F2 FOLD HINGELINES AND L2 MINERAL STRETCHING LINEATIONS

OBLIQUE DIP-SLIP

Q L2 mineral stretching lineations N=ll F2 hinge lines N=72 FI hinge lines N=2 0 c mean Sl-2 (Dinkey Creek thrust)

iofJFSin™ l?neS1; S e?,S^ re°gfap!?lc Projection of FI and F2 comparison to the mean Sl-2SfnJ f f e t c h i n g lineations in Possible obliouS f thS entlre Pendant, thrust (parallel toPSi ?? ?°v;ment £°5 the Dinkey Creek W, F2 and 12 to the meai Sl-f b? ^he orientation of tional layering. S1 2 follation/cleavage/composi- 60

small pods (approximately l m in length by ,5m in width) of calc-silicate gneiss caught up along the contact. The

thrust plane parallels the Sl_2 foliation/cleavage and is moderate to shallowly dipping.

The structurally highest thrust, herein referred to as the Willow Meadow thrust, is completely concealed by Quaternary deposits. it has been inferred entirely from

structural relations. Orientations of S-^ layering in the westernmost exposures of schist and quartzite north and south of Willow Meadow (Plate I) are locally discordant to

the schist-quartzite contact. Although infolding of these two units along their contact occurs locally, it does not appear to be significant enough to explain the marked discordance in S^_2 orientations.

Both the Limestone Campsite and Willow Meadow thrusts approximately parallel the Dinkey Creek thrust, and are refolded, together with the Dinkey Creek thrust, by a disharmonic, megascopic D3 synform between Willow Meadow and Limestone Campsite (Plate I). Consequently, these thrusts are interpreted to have developed during D2 deformation. The exact relationships of these westernmost faults to the Dinkey Creek thrust, and whether the faults are ductile in nature are unknown.

Kistler and Bateman (1966) defined the contact between the quartzite and paragneiss as a faulted lithologic boundary based on down-dip truncation of the calc-silicate layers. However, field evidence does not necessitate faulting along the exposed contact, and down dip truncation is not required by the discontinuous character of the 61

calc-silicate interbeds. In this study, the calc-silicate interbeds are interpreted to be folded and not truncated down dip. The contact is apparently conformable and no relative offsets or truncation are evident.

Lithologic Contacts: Although many of the major lithologic contacts are obscured by cover, where exposed

they are characteristically planar in nature. Given the

degree of internal deformation exhibited by all lithologic units, the lack of significant infolding along lithologic

contacts appears rather incongruous. Although infolding associated with D3 deformation was observed along various

contacts, infolding associated with d 2 or D2 is limited to

the quartzite-paragneiss contact along Dinkey Creek in southeastern part of the pendant (Plate I). Whether

lithologic boundaries in the northern and western parts of the pendant are indeed conformable contacts is therefore unclear. Some may actually represent zones of limited displacement.

D2 Synformal Nappe

°2 structural patterns within the paragneiss and quartzite define a complex synform in the southern part of the pendant. Kistler and Bateman (1966) recognized this synform, but extended it northwest across the Dinkey Creek thrust. Detailed mapping for this study, however, revealed a northward continuation of the synform defined by the calc-silicate subunit within the paragneiss (Plate I) 62

Outcrops of the calcareous subunit are relatively

continuous in the Rainbow Mine area, but are discontinuous southward near Miningtown Meadow although compositional variations remain relatively consistent. Isolated segments of the layer display lateral thinning and boudinage or

exhibit abrupt, discordant contacts with the paragneiss. Locally, lenses are in fact rootless isoclinal fold closures

Considering the preponderance of shredded and boudinaged layering throughout the pendant, and predominantly in the lowermost plate, the structural features associated with the calcareous marker unit suggest the isolated lenses represent boudins of a formerly continuous, but complexly folded

interbed. Connection of these boudins based upon mesoscopic and megascopic structures within the paragneiss and

quartzite, and structures within the boudins themselves,

reveals a megascopic synformal nappe in the lower plate of the ductile fault (Plate VI). The nappe is characterized by 1) a complex hinge zone represented by major F2 isoclines along Dinkey Creek in the southeastern part of the pendant and 2) truncation and shearing of the western limb along the ductile Dinkey Creek thrust. These features are consistent with minor F2 structures observed throughout the pendant. The F2 synformal nappe was refolded by a megascopic F3 fold near Rainbow mine, as indicated by structural orientations within the boudins of the marker and within the paragneiss.

This relation is also inferred from superposition of folds at outcrop scale. 63

Stratigraphic Continuity

The metasedimentary rocks of Dinkey Creek pendant are easily misconstrued as a simple stratigraphic sequence suggested by the apparent simplicity of the map pattern, if the intensity and complexity of deformation are not

recognized. A simple stratigraphic succession was proposed by Kistler and Bateman (1966) based on their interpretations that 1) layering throughout the pendant represents original

bedding and 2) relict top indicators exist and are useful in providing an upward younging direction. However, evidence summarized here invalidates their interpretation.

As noted earlier, layering throughout the pendant is a composite S - ^ hinge surface foliation resulting from the

transposition of S-^ during and D2. Transposition of S-^ is thought to be complete due to the extreme rarity of

fold closures and the partial transposition of S- ^ during D2. Consequently, the primary layering throughout the

pendant does not represent original bedding (Fig. 23). The

intense isoclinal folding that occurred during D i _2 ,

together with complete transposition of layering, invalidate the use of relict top indicators within the pendant. These

features, the uncertain nature of the lithologic contacts, and the intensity of D2 ductile deformation indicate that stratigraphic continuity is unlikely to exist in Dinkey

Creek pendant, and suggest that the rocks represent a series of imbricate tectonic slices.

65

D3 Structures

D3 structures have a pronounced effect on the structural pattern of the Dinkey Creek pendant. Major D3 structures in the northern half of the pendant include 1) an antiform in

the northeast near Rainbow Mine, defined by the calcareous subunit within the paragneiss and by orientations of s 1 _ 2 foliation, and 2) a synform defined by the marble,

calc-silicate gneisses, schist and quartzite in the northwest near Willow Meadow (Plate I). Minor F3 folds

occur throughout the pendant and are NW-trending, plunging upright to inclined, disharmonic, tight to close,

asymmetric, similar folds (Fig. 24). S3 hinge surfaces are vertical or dip steeply westward, hingelines plunge steeply northwest (Plate VI), and hinge zones are sharp to rounded.

A spaced cleavage (S3) associated with F3 folds is parallel to F3 hinge surfaces and transverse to the S- ^ layering.

S3 fabrics typically range from simple cracks, locally lined with insoluble residues, to crenulation cleavage with gradational or discrete boundaries. Other accessory D3 structures include kink bands, crenulation folds and,

occasionally, corresponding crenulation lineations (l 3 ) , in addition to en echelon extension fractures.

Microscopic F3 folds and associated S3 cleavage are visible in thin section. Epidote and opaque minerals define the s3 cleavage. Biotite-phlogopite micas parallel to S1_2 are buckled by F3 crenulation folds and are cut by associated S3 crenulation cleavage. Brittle deformation during D3 is evident from microscopic and mesoscopic S3 66

folds orange-brown S s s s ^ jy r^ h .Note *&*'%-* interference J ^ j f g J ^ r o i > T l <«/c ^ ^ /ceM>0.ITI0||M. LRYERTMn

W DCP

N=2 75 N=2 66

poles to SI 2 foliation/cleavage/compositional layering mean hinge line for F3 folds mean hinge line for F4 folds ci?SLShno?LiEtSCg a£d F?.“ e 68

fractures ranging up to 15 cm in width. Locally,

displacement from less than 1cm to 2m occurs along these S3 surfaces.

Deformation during D3 is primarily responsible for the refolding and reorientation of D2 structures. Double

zig-zag interference patterns resulted from refolding of F ± and F2 isoclines by F3 folds (Fig. 24). On the stereoplot of poles to S!_2 layering (Fig. 25), a girdle is defined whose maximum lies near the intersection of the great

circles normal to F3 and F4 hingelines. This suggests that

the S-l_2 girdle is a function of refolding by F3 and F4

folds. Furthermore, the better fit of the F3 great circle

indicates the D3 deformational event was largely responsible for the S3_2 girdle pattern.

Map-scale F3 folds near the Dinkey Creek trailhead (Plate II) folded the metabasaltic sill together with the orange-brown and green calc-silicate gneiss units.

Therefore, the timing of D3 deformation is bracketed between the intrusion of the metabasaltic dike and sill, and the intrusion of the Early Cretaceous granodiorite of Dinkey Creek.

D4 Structures

The D4 structures consist predominantly of minor folds and related cleavage parallel to F4 hinge surfaces. Major f4 folds are not obvious in the map pattern, although, flexures in major fold traces are attributed, in part, to 69

aigF?ei ^ ‘ -,?uJcr°P Photograph c an open F4 fold refolding limbed lsloclinal fo] calc-silicate gneiss unit. m the orangish—brown 70

the D4 deformation (Plates I and II). f 4 Folds are

E-W-trending, upright to plunging upright, open to close and asymmetric (Fig. 26). In addition, the F4 folds are parallel folds and exhibit simple hinge zones. Hinge

surfaces are approximately vertical and strike E-W (Plate VI). F4 folds are present throughout the pendant, but are most common in the north part of the pendant west of Dinkey Creek. They occur locally in the northeast and southern parts of the pendant. A planar, spaced cleavage (S4)

associated with F4 folds is typically transverse to Sl_2 layering. Where F3 folds have been refolded by F4 folds

within the calc-silicate gneiss units, possible dome and

basin interference patterns have been noted. d 4 postdates D3, but otherwise it has the same timing relative to the

metabasaltic sill and the Dinkey Creek granodiorite.

Anomalous Structures

A non-penetrative fifth fold style with a unique orientation was occasionally observed within Dinkey Creek pendant. These folds are similar in style to F3 folds,

though they differ markedly in orientation. The anomalous

folds are asymmetrical, disharmonic, northeast-trending, tight to close with sharp to rounded, simple hinge zones (fig 27). Hinge surfaces strike northeasterly and

hingelines plunge steeply northeast; the folds are upright to plunging inclined. Located primarily in the north central part of the pendant within the schist, and in the south within the quartzite and paragneiss, these folds 71

tight to^lose^fold lrTth^aSrrti t" ano”alous NE-trending, looking approximately north? ® Unit

characteristically deform the Sl_2 foliation, and therefore are considered to postdate D2 folds. Incomplete data on superposition makes the relative timing of these

northeast-trending folds difficult to establish. Due to their similarity in style to F3, the anomalous folds may possibly be related to D3 deformation, although their NE trends are inconsistent with F3. Alternatively, these

anomalous folds may be related to late stage D2 deformation. Anomalous cleavage fabrics occur locally within the orange-brown calc-silicate gneiss unit west of Dinkey Creek near the Dinkey Creek trailhead (fig. 28) . The cleavage is associated with stubby, northwest-trending, tight to

isoclinal, plunging upright, disharmonic folds that occur within thinly layered marble interlayered with

calc-silicate. The cleavage is roughly parallel to the

northwest-trending, hinge surfaces of these "sausage" folds. Relatively abrupt changes occur in cleavage orientations at lithologic boundaries; this resembles cleavage refraction resulting from competence contrasts. However, a feature inconsistent with cleavage refraction is that cleavage

planes within the more competent calc-silicate layers are at a lower angle to lithologic layering than cleavage in the less competent marble. On close examination, extensions of some of these "sausage" folds can be traced into the calc-silicate layers, where it appears that the hinge surfaces of these folds have been refolded. Lithologic layering, on the other hand, was not significantly impacted by this later deformation. associated w ? ^ C£°P,.ph°tograph of anomalous cleavage orangish-brown^cafc-silicatZ f°ldS developed in S I in the less competent marble lavprS,Unit: ^he S2 cleavage vertical and changes oriJntStio£ approximately competent calc-siP sharply within the more during D3 silicate layer as a result of refolding 74

Although some degree of cleavage refraction may have contributed to the development of the anomalous cleavage fabric, the pre-existing orientations of lithologic

layering, folds and cleavage probably were responsible in part for the buckling of cleavage surfaces independent of

lithologic layering. The "sausage" folds are inferred to be related to F2 folds, with deformation of hinge surfaces and associated cleavage occurring during d 3 .

Relation of Metamorphism to Structure

Multiple dynamotherma1 metamorphic events overprinted by strong thermal metamorphism makes the relation between

metamorphism and structure unclear. Mineral assemblages preserved in the rocks of Dinkey Creek pendant (Table 1) are

dominantly influenced by thermal metamorphic overprinting.

Preserved dynamothermal metamorphic fabrics corresponding to

D2 and d 2 have been strongly overprinted by thermal metamorphic minerals that grew parallel to the Sl_2

compositional layering, thereby obscuring d 2 mineral

assemblages and complicating metamorphic interpretations. Metamorphic minerals associated with regional metamorphic fabrics related to D3 and D2 indicate greenschist facies

during dynamothermal metamorphic conditions, although a higher grade of metamorphism cannot be ruled out.

Mesoscopic and microscopic dynamothermal metamorphic fabrics formed during D3 and D4 clearly indicate greenschist facies conditions. 75

Summary of Structural History

In summary, the polyphase deformation of the Dinkey

Creek pendant included one non-penetrative folding event and

four penetrative deformational events distinguished by style and orientation of mesoscopic folds and corresponding structures, in addition to overprinting of structures and cross-cutting relationships of igneous intrusives.

The two earliest deformational events, D ± and D2, are

considered to have developed during progressive deformation resulting in the sequential development of coaxial east- northeast-vergent isoclinal folds, and a pervasive Sl_2 transposed layering delineated by parallel foliation, cleavage and compositional layering. The megascopic

east-vergent imbricate thrust structure and associated synformal nappe resulted during D2 deformation. Features

indicative of d 2 ductile deformation occur throughout the

pendant. Intense deformation and complete transposition of layering during D2 disrupted lithologic units within the

pendant, and thus stratigraphic continuity is not preserved.

Di structures predated the D2 event, and both deformations occurred prior to the intrusion of the metabasaltic dike and sill, and intrusion of the 104.1 Ma Dinkey Creek pluton.

D3 deformation is represented by northwest-trending F3 folds and S3 cleavage, and was primarily responsible for the reorientation of F ± and F2 isoclines and d 2 thrusts. Double zig-zag interference patterns resulted from the superposition of F3 on Fx and F2 folds. D3 postdated the 76

SUMMARY OP STRUCTURAL HISTORY - DINKEY CREEK PENDANT

d 4 WSW-WNW-trending, open Post D3 and folds; hinge surface intrusion of parallel cleavage basaltic dike rocks; Pre 104.1 Ma Dinkey Creek pluton

D 3 NW-trending, tight to Post D2 and close folds; hinge intrusion of surface parallel cleavage basaltic dike rocks; Pre D4 and 104.1 Ma Dinkey Creek pluton

D3? or NE-trending, tight to Post S3_2 D2.5• close folds

D2 N-trending, long-limbed F? Post Di; Pre isoclines; S-^ foliation/ D3, intrusion cleavage/compositional of basaltic layering, transposed rocks and layering, blastomylonite; 104.1 Ma Ij2 stretching lineations; Dinkey Creek imbricate thrust structure Pluton

Di N-trending, F3 isoclines; Pre }2 . and foliation intrusion of basaltic dike rocks and 104.1 Ma Dinkey Creek pluton

Creek p4ndantmarY °f structures identified in the Dinkey 77

metabasaltic intrusion and predated intrusion of the Early Cretaceous granodiorite of Dinkey Creek.

Deformation resulting from D4 is not obvious at

map-scale, but is expressed by mesoscopic east-west trending

folds and associated cleavage. d 4 was partly responsible

for the refolding of D, and D2 structures, and exerted only local influence on D3 structural orientations. Although D4 postdated D3, D4 deformation is constrained by the same relative timing of intrusions.

Anomalous, non-penetrative northeast-vergent folds have not been assigned to the relative deformational sequence because insufficient data on superposition exists. These anomalous folds are similar in style to F3 folds, though not

m orientation, and may possibly have been related to D2 or D3 deformations.

REGIONAL RELATIONS AND TECTONIC SIGNIFICANCE

A variety of correlations have been proposed for the rock units of Dinkey Creek pendant, but none of these correlations has proven completely acceptable,

inconsistencies in lithology, structural history, and/or

environments of deposition have contributed to the continued debate over the stratigraphic affinity of the Dinkey Creek Pendant. Lower Paleozoic rocks in the Shoo Fly Complex to the northwest and in the Mount Goddard pendant to the east contrast markedly with the rocks of Dinkey Creek pendant.

Significant differences also exist between the Dinkey Creek Pendant and parts of the Kings sequence to the south, with 78

which it is commonly grouped. Consequently, I infer that the Dinkey Creek pendant originated in a depositional environment dissimilar to those inferred for surrounding rocks, and was tectonically transported to its current location in the Sierra Nevada.

Shoo Fly Complex and Mount Goddard Pendant

Shoo Flv Complex

Lower Paleozoic rocks of the Shoo Fly Complex, 25 km northwest of Dinkey Creek pendant (Fig. 2), compose a

complexly deformed structural assemblage of quartzite,

quartzofeldspathic gneiss, garnet schist, calcsilicate,

marble, chert, gabbroic to granitic orthogneisses, syenite,

and amphibolite (Schweickert, 1981; Schweickert and Bogen, 1983; Merguerian and Schweickert, 1987). Structures

recorded in the Shoo Fly are exceedingly complex and define seven phases of superimposed deformation, including overprinting of mylonitic fabrics and extensive transposition (Schweickert, 1981; Schweickert and Bogen, 1983; Merguerian and Schweickert, 1987). The greater structural complexity reported for the Shoo Fly Complex together with the occurrence of orthogneiss and amphibolite contrast sharply with rocks of the Dinkey Creek pendant.

Extensive quartz arenites representative of deposition on a shallow continental shelf are lacking within the Shoo Fly

Complex. Instead, turbidites in the Shoo Fly indicate Probable deposition in a continental slope and rise 79

environment.

Mount Goddard Pendant

Pre-Upper Jurassic metavolcanic rocks of the Mount Goddard pendant, 25 km east of Dinkey Creek pendant (Fig. 2), comprise a thick section of tuffs, breccias, lava

flows, sills, and ash-flow tuffs, along with rare limestone, deposited m a subaerial to subaqueous environment

associated with a continental volcanic arc (Tobisch and Fiske, 1982; Tobisch and others, 1986). Two phases of

Cretaceous tectonic structures have been considered to be genetically related to the dynamic evolution of the magmatic arc (Tobisch and others, 1986; Patterson, 1989). The Dinkey Creek pendant is notably non-volcanic and bears no

resemblance to the metavolcanic rocks of the Mount Goddard pendant. The structural complexity of the Dinkey Creek

pendant also contrasts sharply with the structural style of the metavolcanics rocks of Mount Goddard pendant.

Previously Proposed Correlations for Rocks of Dinkey Creek Pendant

Kings Sequence

Bateman and Clark (1974) originally distinguished the metasedimentary and metavolcanic rocks between Yosemite Valley and the Mineral King pendant as the Kings sequence

(Fig- 2). Later, Saleeby and others (1978) extended the Kings sequence southward to the Garlock fault to include metasedimentary and metavolcanic rocks of the Tule River, 80

Kern Canyon, Isabella, and Tehachapi pendants, a

Triassic-Jurassic age was initially assigned to the Kings sequence based on fossils recovered from a unit in the

Boyden Cave pendant, and was later upheld by faunal age

determinations for the Mineral King, Yokohl Valley, and Isabella pendants (Moore and Dodge, 1962; Jones and Moore, 1973, Saleeby and others, 1978, Nokleberg, 1983).

Regardless of the fossil localities, many authors have

argued that the Kings sequence is in part Paleozoic in age (Kistler and Bateman, 1966; Kistler and Peterman, 1973,

Moore and Others, 1979; Schweickert, 1981; Nokleberg, 1983). The quartzite, schist, calc-silicate, marble, and minor intermediate to silicic flows, tuff, and epiclastic rocks exposed in pendants of the Kings Sequence have been considered to have been deposited in a complex,

continental-margin, magmatic arc depositional environment (Saleeby and others, 1978; Busby-Spera, 1984). The

mterstratified metasedimentary and metavolcanic rocks typical of the southern pendants of the Kings Sequence represent deposition along axial and frontal regions of a

continental margin magmatic arc (Saleeby and others, 1978;

Busby-Spera, 1984). in contrast, metasedimentary rocks of northern pendants in the Kings sequence are devoid of

mterstratified metavolcanic rocks, and contain thick, cross-bedded quartzites suggestive of deposition on a passive continental margin (Kistler and Bateman, 1966; Girty 1985). The Mesozoic age and inclusion in the Kings sequence, argued previously for the Dinkey Creek pendant, 81

have largely been based on lithologic correlations with the Boyden Cave pendant.

Boyden Cave pendant: Rocks of the Boyden Cave pendant, 40 km south-southeast of Dinkey Creek, have been subdivided into three distinct lithologic sequences: An eastern

sequence comprised of calc-silicate hornfels, slate, and dacitic to andesitic metavolcanic rocks; a central chaotic unit; and a western sequence of cross-bedded quartzite,

marble, calc-silicate schist and andalusite-biotite schist (Moore and others, 1979; Girty 1977b). The Dinkey Creek

pendant is distinctly dissimilar to both the eastern and central units, but is markedly similar to the western

sequence at Boyden Cave. Early Jurassic ammonites (Moore and Dodge, 1962; Jones and Moore, 1973; Saleeby and others, 1976) discovered in the Boyden Cave pendant were recovered from a silty interval in the central chaotic unit, which

ctonically overlies older metasedimentary rocks to the west (Girty 1985).

Two generations of structures in the older rocks of

Boyden Cave pendant bear similarities to structures in the Dinkey Creek pendant described here (Girty, 1977a). m

addition, the nature of the quartzite, and environments of

deposition for the western sequence are closely comparable to rocks in Dinkey Creek pendant. The quartzite units in both the Boyden Cave and Dinkey Creek pendants consist of metamorphosed quartz arenites and feldspathic arenites of similar maturity and composition. Furthermore, styles of cross-bedding in the quartzites of Dinkey Creek and Boyden

Cave pendants suggest deposition in shallow-water, tide- or 82

wave-influenced environments (Girty, i 985; this report).

The marble, calc-silicates and andalusite-biotite schists at Boyden Cave pendant also resemble metasedimentary rocks at Dinkey Creek, and are indicative of deposition on a shallow continental shelf environment.

Inyo Facies; Mount Morrison Pendant and Lover Cambrian Poieta Formation

The Inyo facies, as defined by Stewart (1970), is a

thick section of uppermost Precambrian and Cambrian strata consisting of siltstone, limestone, dolomite, very fine to fine-grained quartzite, and rare amounts of fine- to

medium-grained quartzite. Strata of the Inyo facies are finer grained and more carbonate-rich than correlative strata to the east (Stewart, 1970). The Lower Cambrian

Poieta Formation occurs within the Inyo facies (Stewart,

1970) and the Mount Morrison pendant has been correlated

with Inyo facies strata to the east (Foster, 1987; Moore and Foster, 1980; Nokleberg, 1983)

Mount Morrison pendant: A thick sequence of

fossiliferous Ordovician to Silurian strata exposed in the Mount Morrison pendant, 50 km northeast of Dinkey Creek pendant (Fig. 2), is composed of pelitic and calc-silicate hornfels, calcareous quartzite, marble, slate and metachert (Rinehart and Ross, 1964). The structural history of the

Mount Morrison pendant includes three deformational events (Russell and Nokleberg, 1974, 1977). Structural 83

similarities together with similarities in depositional environments have been cited for metasedimentary rocks in the Dinkey Creek and Mount Morrison pendants (Kistler and Bateman, 1966). However, the Dinkey Creek pendant differs lithologically in many important aspects: metachert is

distinctly lacking, thick, pure quartz arenite predominates, and calc-silicates and marble are proportionately less abundant than in Mount Morrison pendant.

Lower Cambrian Poleta Formation: The Poleta Formation in the White-Inyo Mountains, 85 km east of Dinkey Creek pendant, has been suggested as a correlative to the

metasedimentary rocks of Dinkey Creek pendant (Fig. 2)

(Kistler and Peterman, 1973). The carbonate-rich, Lower Cambrian rocks of the Poleta contain abundant oolitic,

bioclastic and pelletal limestones interstratified with

sandstone, shale and mudstone deposited in shallow-water continental shelf environments (Moore, 1976). Structures within the Poleta Formation represent two phases of

deformation including folding, high-angle faulting and thrust faulting (Sylvester and Babcock, 1975). Although

environments of deposition for Dinkey Creek are somewhat

similar to that of Poleta, the structural history for Dinkey Creek is far more complex. Additionally, the Poleta

Formation does not contain thick sections of pure quartz arenite and has a greater proportion of carbonate when compared to the metasedimentary rocks of Dinkey Creek pendant.

Inyo facies vs. Dinkey Creek pendant: Disparities between the rocks of Dinkey Creek pendant and lithologies of 84

the Poleta Formation and Mount Morrison pendant are generally true for other units of the Inyo facies in the

western Cordillera. In particular, quartzites of the Inyo facies are finer grained and more carbonate-rich than the quartzite of Dinkey Creek pendant, and are typically less than 60 meters thick. (Stewart, 1970). Consequently, an

alternate source area must be sought for the metasedimentary rocks of Dinkey Creek.

CORRELATION WITH ROCKS OF DEATH VALLEY FACIES IN SNOW LAKE PENDANT

Metamorphic rocks of the Death Valley facies have

recently been identified in the Snow Lake pendant (Lahren, 1989; Lahren and Schweickert, 1988a, 1989), about 120 km

north-northwest of Dinkey Creek pendant, along the northern boundary of Yosemite National Park within Emigrant

Wilderness (Fig. 2). The uppermost Precambrian to Lower

Cambrian metasedimentary rocks comprise a thick sequence of quartzite and feldspathic quartzite, quartz-mica schist, marble, and calc-silicate schist completely lacking in interlayered metavolcanic rocks (Lahren, 1989). These units have been correlated with the Stirling Quartzite, Wood

Canyon Formation, Zabriskie Quartzite, and Carrara Formation (Lahren, 1989; Lahren and Schweickert 1988a, 1989). m addition, rocks possibly correlative with the Lower Triassic Fairview Valley Formation unconformably overlie the older 85

metasedimentary rocks (Lahren, 1989; Lahren and Schweickert, 1989) .

Although age diagnostic fossils are absent in both the Snow Lake and Dinkey Creek pendants, remarkable similarities in lithology, structure, and environments of deposition

strongly support a correlation (Table 5). The absence of volcanic rocks within an assemblage of quartz arenite, feldspathic arenite, siltstone, mudstone, marl, and

limestone or dolomite is identical to the lithologic nature of rocks of the Dinkey Creek pendant. The presence at Snow Lake pendant of thick, cross-bedded, pure quartz arenites

similar in maturity and composition to the Dinkey Creek quartzite further supports the lithologic comparison.

Furthermore, environments of deposition represented by the Snow Lake and Dinkey Creek quartzites are identical, as are

environments of deposition in a shallow continental shelf inferred for the remaining lithologies (Lahren 1989; this study) .

The Snow Lake pendant is characterized by abundant trace fossils including S k o l i t h o s within quartz-mica schist and micaceous, feldspathic quartzite layers of the Wood Canyon and Carrara Formations (Lahren 1989). Despite the apparent lack of the trace fossil S k o l i t h o s at Dinkey Creek pendant, abundant horizontal worm burrows are locally preserved in

the quartz-mica schist and micaceous, feldspathic quartzite layers in the eastern part of Dinkey Creek pendant.

Both pendants have been intruded by mafic dikes, and

both are associated with a dioritic/gabbroic intrusion older than nearby Cretaceous granitic rocks. The 150 Ma mafic and 86

SIMILARITIES b e t w e e n d i n k e y c r e e k a n d s n o w l a k e p e n d a n t s

Metasedimentary Rocks

quartzite, feldspathic quartzite, micaceous and quartzite, feldspathic quartz-mica schist, calc- quartzite, quartz-mica silicate gneiss, marble schist, marble, calc- silicate schist (devoid of interstratified metavolcanic rocks) (devoid of interstratified metavolcanic rocks)

Nature of Inferred Protoliths for Peliti,, ttt^ + o Aluminum-rich sediments Aluminum-rich sediments

Characteristics of quartz arenites Thick, cross—bedded, pure quartz arenites and feld- Thick, cross—bedded, pure spathic quartz arenites quartz arenites and feld- spathic quartz arenites

Inferred Depositional Environments Shallow marine continental shelf environment Shallow marine continental shelf environment

Associated Intrusive Rooicg Basaltic dikes and sills 150 Ma Independence dike Gabbro/diorite complex swarm and 150 Ma gabbro/ diorite complex

Structure

d 1-d4 penetrative events Dl~D4 penetrative events and one non-penetrative event (D2>5? or d 3?) and two non-penetrative events (D2>5 and d 5 )

5A Comparison of characteristics of rocks in thP Dinkey Creek and Snow Lake pendants. the 87

felsic dikes at Snow Lake pendant have been correlated with the -148 Ma independence dike swarm of western Mojave and eastern California (Schweickert and Lahren, 1990). Mafic dikes at Dinkey Creek are undated, but the cross-cutting Dinkey Creek pluton provides a minimum age constraint of

104.1 Ma (stern and others, 1981). The relative age of the

metabasaltic dikes and sills of Dinkey Creek with respect to

structural events is identical to that of dikes of Snow Lake pendant (Table 6). At Snow Lake pendant, the 150 Ma

gabbro/diorite complex is thought to be related to the mafic and felsic dikes (Lahren and others, 1990). However, at Dinkey Creek pendant, the relationship between the

diorite/gabbro intrusion and the mafic dikes is uncertain. The age of the diorite/gabbro complex at Dinkey Creek is unknown, although a minimum age of 104.1 Ma (stern and

others, 1981) results from the cross-cutting relationship of the Dinkey Creek pluton.

Four penetrative deformational events together with

non-penetrative northeast-trending structures are recorded m the rocks of both the Dinkey Creek and Snow Lake pendants (Lahren and Schweickert, 1988a; Lahren 1989; this study).

Decisive correlation of the structures is hindered by the absence at Dinkey Creek pendant of the Fairview Valley overlap sequence and granitic rocks equivalent to Bigelow Lake, and the lack of radiometric age data for the mafic dikes. Notwithstanding, strong similarities in overall structural sequences are noted for the Dinkey Creek and Snow Lake pendants (Table 6) . 88

STRUCTURAL COMPARISON OF DINKEY CREEK AMD SHOW LAKE PENDANTS Snow Lake Pendant (Stirling-Carrara) Dinkey CreeK Pendant (Johnnie-Wood Canyon) Oblique Slip Fault Hornblende Andesite Dike Oblique Slip Fault

Granodiorite of Fremont Lake Alaskite of Grace Meadows Granite of Upper Twin Lake

D5 Forsyth Peak Shear Zone Granite of Bond Pass Granodiorite of Eagle Peak Granodiorite of Lake Harriet Qtz. Monzonite of Dinkey Dome Granodiorite of Dinkey Creek D4: WNW-WSW-trending, open folds F D4 : WNW-WSW-trending, open to close folds D3: NW-trending, open-close folds D3: NW-trending, tight to close folds Independence Dike Swarm Basaltic dikes and sills D2.5: NE-trending, open to close folds D2.5? (D3?)* NE-trending, tight to close folds Granite of Bigelow Lake Gabbro/Diorite Complex Diorite/Gabbro complex ** D2 : Folds D2 : Thrusts and tight to D2: Late stage isoclines close isoclinal folds D2 : Thrusts and isoclinal folds, ductile deform- ation, si-2 foliation, compositional layering and cleavage Deposition of Fairview Valley Formation.

01: Long limbed isoclines Isoclinal folds and S0-S1 compositional Dl: layering SI foliation i r ^

pre-104 dlorite/gabbro complex='

Stosse ay. ha Ma, r EagleS HBF Peak granodiorite=88.9 s.-sssES^ssj^ssi' Ma. 89

initially during the D, deformation, isoclinal folding distorted original bedding resulting in the characteristic S„ x Sl fabric of snow Labe pendant (Lahren, 1989), and the initiation of the Sl_2 fabric of Dinkey Creek pendant. D, deformation affected all metasedimentary rocks in both

pendants and produced synchronous and progressive megascopic folding and thrusting, characteristic of the overall-map patterns (Lahren, 1989; this study). m addition, the Sl_2

fabric of Dinkey Creek pendant became well defined. The D2 deformational episode in both pendants was followed by the intrusion of microgranite and microdiorite dikes in Snow Lake pendant (Lahren, 1989), and a metabasaltic dike and sill in Dinkey Creek pendant.

in Snow Lake and Dinkey Creek pendants, two penetrative events, D3 and D„, occurred after the emplacement of the

igneous dikes and sills. In both pendants, the D3 event was responsible for the folding of the dikes and sills, along

with reorientation of pre-existing folds (Lahren, 1989; this study). Deformation during D4 also contributed to reorientation of previous folds, and doming of

-egastructures in the Snow Lake pendant (Lahren, 1989).

Effects of the d 4 deformation are less pronounced in the Dinkey Creek pendant.

Northeast-trending folds which post-date development of the Sl_2 foliation in the Dinkey Creek pendant could possibly correlate with the non-penetrative northeast-trending D2.5 folding event documented in Snow Lake pendant (Lahren, 1989), or may be related to later deformation. The non-penetrative D5 deformation and Tertiary faulting in snow Late pendant (Lahren, 1939, have not been recognized in the Dinkey Creek pendant.

Similarities in general fold orientations also exist, although some inconsistencies in fold styles are noted, isoclinal folds associated with Dl deformation in Snow Lake pendant are variable in orientation (Lahren, 1989, compared

with dominantly north-trending isoclinal folds of Dinkey Creek. The Dinkey Creek episode of D2 deformation was

significantly more intense than D2 deformation in Snow Lake pendant, and, as suggested by the coaxial nature of Fl and F2 folds in Dinkey Creek pendant, may have dominantly

influenced the orientation of F2 folds. The greater degree

of deformation during D2 in Dinkey Creek pendant may also account for differences in F2 fold styles. Long-limbed

isoclinal folds characterize d 2 deformation in Dinkey Creek

pendant in comparison to shorter limbed, asymmetrical, tight to isoclinal F2 folds defining D2 in Snow Lake pendant

(Lahren, 1989; this study,. F3 and F4 folds in Dinkey Creek are similar in orientation and somewhat similar in style to

F3 and F4 folds in Snow Lake pendants. However, both the F3 and F4 folds in Dinkey Creek generally have tighter intenimb angles than the corresponding F3 and F4 folds in Snow Lake pendant.

If structural events are correlated based on fold styles alone, discrepancies in structural orientations and relative timing of deformational events are apparent. However, the differences in fold styles noted during the correlation of overall structural sequences may actually reflect variations 91 - Reno ■0044

in the intensity of deformation. stronger deformation is indicated by structures within the Dinkey Creek pendant, and suggests that the rocks are representative of a deeper crustal slice.

Death Valley Facies

Rocks of the Death Valley facies consist of uppermost Proterozoic to Cambrian sandstone, quartzite, conglomerate,

shale, siltstone, and limestone representative of a shelf environment (Stewart, 1970,. m contrast with rocks of the Inyo facies, the Death Valley facies is significantly thinner and is quartzite-rich.

Correlation of the rocks of Snow Lake pendant rocks with the western Mojave-San Bernardino Mountains Death Valley facies rocks was based on lithologic, stratigraphic and

trace fossil similarities; inferred depositional I environments; nature of quartz arenites; associated granitic rocks; and presence of Independence dike swarm and common overlap sequence (Lahren, 1989; Lahren and Schweickert, 1989; Lahren and others, 1990).

Similarly, I propose that the Dinkey Creek pendant also represents rocks of the Death Valley facies based upon lithologic and structural similarities, inferred depositional environments, inferred protoliths for pelitic units, and the nature of quartz arenites compared with the heath valley facies rocks of Snow Lake pendant. On account of Stratigraphic uncertainties and the absence of age Jiitnuwh

92 - Reno >"'0044

diagnostic fossils and S k o lit h o s in the Dinkey Creek

pendant, the proposed lithologic correlations with the Death valley facies discussed below are very tentative.

The quartzite of Dinkey Creek is the most extensive unit within the pendant, and provides the best evidence for

correlation with rocks of the Death Valley facies. The

Zabriskie and Stirling Quartzites of the Death Valley facies are the only thick cross-bedded quartz arenites exposed in the central Cordillera of comparable composition and

thickness to the Dinkey Creek quartzite (Stewart, 1970; Hunt and Mabey, 1966). The Stirling Quartzite contains up to 15% feldspar in contrast to the Zabriskie Quartzite, which is

composed almost entirely of quartz (Hunt and Mabey, 1966; Stewart, 1970). Subordinant horizons of pebbly quartzite

containing granules and pebbles of quartz are also uniquely characteristic of the Stirling. m addition, the Stirling Quartzite is a significantly thicker unit, ranging up to 1500 m, versus the Zabriskie Quartzite which is

approximately 300 m thick (Hunt and Mabey, 1966; Stewart,

1970) . The greater thickness and percentage of feldspar of

the Stirling Quartzite support a tentative correlation with the thick quartzite to feldspathic quartzite unit at Dinkey

creek. The presence of pebbly intervals containing granules and pebbles of quartz within the quartzite unit at Dinkey Creek further supports this correlation.

A likely correlation for the schist unit is more troublesome. Rocks of the Death Valley facies that are Possibly correlative with the schist unit include the 93

Johnnie, Wood Canyon, and Carrara Formations. The Carrara is the least likely correlation since relatively homogeneous sections o£ shale and siltstone, comparable in thickness to the schist unit, are not typical of the heterogeneous Carrara Formation (Hunt and Mabey, 1966; Stewart, 1970). The Wood canyon and Johnnie Formations contain sections of shale and siltstone more comparable in thickness to the schist unit of Dinkey creek, m contrast to the schist unit, the Wood Canyon Formation is relatively heterogeneous and contains abundant interstratified quartzites (Hunt and Mabey, 1966; Stewart, 1970). Sections of the Johnnie Formation contain aluminum-rich phyllitic siltstone and silty claystone together with minor amounts of carbonate and sandstone (Hunt and Mabey, 1966; Stewart, 1970) that are more similar to the schist unit in Dinkey Creek pendant. Trace fossils are prevalent in the Wood Canyon Formation whereas they are lacking in the Johnnie Formation (Hunt and Mabey, 1966; Stewart, 1970). The lack of trace fossils in the schist unit, and the occurrence of thick sections of relatively homogeneous, aluminum-rich siltstone and Claystone in the Johnnie Formation favor a correlation. The lithologic heterogeneity of the paragneiss unit is Consistent with the lithologic variability of the Carrara Formation and the upper and lower members of the Wood Canyon Formation (Hunt and Mabey, 1970; Stewart, 1970). Correlation of the paragneiss unit with the Carrara Formation poses stratigraphic problems in the Dinkey creek Pendant by placing Carrara conformably over Stirling Quartzite. Assuming the quartzite of Dinkey Creek is indeed 94

Stirling Quartzite, the paragneiss unit cannot represent the Carrara Formation. It follows that the paragneiss unit in Dinkey Creek is possibly equivalent to the Wood Canyon Formation. The occurrence of calc-silicate rocks and the clay-rich nature of politic horizons in the paragneiss are consistent with lithologies found in the Wood Canyon Formation and further support this correlation. The marble and calc-silioate units at Dinkey Creek pendant could represent carbonate intervals in any of the Johnnie, Wood Canyon or Carrara Formations. Alternatively, the marble could represent a slice of the Bonanza King Formation. A compelling correlation is impossible given the present data. However, correlation of the carbonate units with part of the Johnnie Formation is preferred here solely on the basis of correlation of the schist unit with the Johnnie, and the assumption that the contact between the schist and orange-brown calc-silicate gneiss is conformable. The presence of the younger Wood Canyon Formation in the eastern part of Dinkey Creek pendant and progressively older units to the west (Stirling and Johnnie) is consistent with the relative ages proposed by Kistler and Bateman (1966) despite the intense deformation and thrusts documented Within the pendant. These correlations are preliminary and •ore complex stratigraphic relationships may in fact exist. independence dike swarm: Firm conclusions regarding the correlation of mafic dikes and sills in Dinkey Creek pendant with the Independence dike swarm are impossible based on the current data. Preliminary comparisons of lithologic and petrographic data and whole rock analyses suggest similarities as well as differences. Rocks of the

independence dike swarm in the western Mojave, southeastern California and in snow Lake pendant exhibit both mafic and felsic members (Chen and Moore, L979; Lahren, & ^

Dinkey Creek pendant, only mafic dikes and sills occur. The metabasalt at Dinkey Creek is similar in texture and

mineralogic composition to dikes of the Independence dike swarm in Snow Lake pendant (Lahren, 1989), but relative proportions of minerals vary.

comparisons of whole rock analyses for the Independence dike swarm of western Mojave, eastern California (Chen and Moore, 1979) and Snow Lake pendant (Lahren, 1989) with mafic dikes and sills from Dinkey Creek pendant are presented on silica variation diagrams in Figure 29. Except for the differences in Al2o3, Feo (total iron), oxides within the

metabasaltic rocks of Dinkey Creek are relatively consistent with oxides in the mafic members of the Independence dike swarm. Due to the limited number of samples from the dike and sill Of Dinkey creek, the best fit curves can appear significantly different when, in fact, variations are only slight.

Interpretation of variations in whole rock geochemistry are complicated by the intensity of deformation, the prevalence of dynamothermal and thermal metamorphism, and ■etasomatic alteration. Open-system behavior during dynamothermal and thermal metamorphism may account for variations in the more mobile elements such as Na2o. The reason for the slightly higher FeO (total iron, content in I L ! . : 96 - Reno K~-7.no 4/) 7 - ','4

o a DCP K \ _____SNLP \ ♦ o • SNLP D DCP - o IDS L V s \ * ♦ 3 id s r v \ X ° ♦ SNLP h \ N X . o 0 IDS ;— \ □ \ 0 sfvjLp DS r'; :'S d c p — ♦ v :

12 " ' l------!—^ ------40 L \ 50 60 70 80

S102 (Wt.%)

□ CC P □ DCP ♦ DCP ♦ SNLP I 15 - ♦ SNLP • • 0 ID S 0 IDS a A - 10 o N ^ 3 ♦ cNsg - ♦ ° X > » , D S o 5 - r 14 . O ____ .___.__ -yf------SNLP anct iDS c* J r O •'■sL (nearly identical) T X ♦ i------CCP 0 50 60 70 80 40 50 60 70 80 SI02 (Wt.%) ' Si02 (Wt.%) 'M 20 " n DCP * SNLP * o IDS 0 s A ~ 10 N s ^ IDS 3 0 s o * ^ 0 ' ^ SNLP 5 =

0 —«------1------'—— — 40 50 60 70 80

SI02 (Wt.%) Si02 (Wt.%)

6 • 5 • DCP 9 ---- * . / IDS • __^ A 4 < ♦

• \ o Figure 29. Silica variation diagrams 3 Xoo X o X • ot major elements comparing analyses 3 y ♦ irom the independence dike swarm (IDS) ^>SNLP Uhen and Moore, 1979), Independence dike swarm at Snow Lake pendant (SNLP) ♦ a XX DCP ILahren, 1989), and dikes and sills at • 1 SNLP Dinkey Creek pendant (DCP). FeO* = • 0 IDS total iron reported as Fe203 + FeO. 0 I ' l l —r- 4C 50 60 70 80

SI02 (Wt.%) 97

the metabasaltic rocks of Dinkey Creek is uncertain, but may reflect contamination from Fe-rich carbonate wall rocks. Reasons for the discrepancy in A1203 are unciear. Although a high degree of scatter is noted for the A1203 content in the independence dike rocks from Snow Lake pendant and southeastern California, this does not appear to explain the variations in A1203 in the metabasaltic rocks of Dinkey Creek.

Initial 87Sr/86Sr ratios: Initial 87Sr/86Sr ratios greater than 0.706 are believed to be representative of granitic rocks that have intruded Precambrian to Paleozoic miogeoclinal continental crust, and the sri = 0.706 line is considered to represent the approximate limit of Paleozoic marine shelf-type sedimentation (Kistler and Peterman, 1973) .

The correlation of rocks of Dinkey creek pendant with rocks of the Precambrian to Paleozoic miogeoclinal Death Valley facies is supported by initial ^ S r / ^ ^ S r ratios reported for granitic intrusions in the vicinity of the Jinkey Creek pendant: Dinkey Creek, 0.7094 and 0.7106;

>mkey Dome, 0.7080 and 0.7228; and Mount Givens, 0.7082 1-7092, and 0.7095 (Hurley and other, 1965) (Table 3).

TECTONIC IMPLICATIONS

Assuming the correlation with snow Lake pendant is rcurate, the Dinkey Creek pendant represents part of a »rge, displaced crustal slice along the axis of the sierra •WTtrrrwTraiMaa

emphasizing the inferred^r^e of the'Earl'^Cr^taceou^M ^ Sierra NeVada batholith omit* BC Bcyden Cave pendant; CC, Carson Ci y CF Coaidale F a u f r " ^ ! ^ ^ f3Ult' Abbr^iations a, Hi Us; DC, Dinkey Creek pendant- DV Deaih Valiev- pf It ;.CG' Clfco Grova; CH. Candelaria FR> Fr/ Mountains; FX, Fox Range- GH Glen Aulin^nH ,ce'slor Fault'- EPM, El Paso Mountains; Mountain; KP, Kern P U t e a u ; L? Lake Isatelfa- LM ! ?e"dantS; GS< Goldstone; IM, iroA King pendant; MM, Miller Mountain- MMP Mnnn/»n ' . Lane Mountain; LPR, La Panza Range; MIC, Miner Pilot Knob v4lle;; PM, Piu^e Mouniain^eSant■ Z '^ HT' M°Unt TaUac P ^ a n t ; V RD> Rodman Mountains; RRP Ritter Range^pendant■ SBM San r * Ran“?; PT Pattenson Mountain pendan Pendant; SWLP, Snow Lake pendant; SR^Sweetwater TMt"h'SLP, Saddlebag L OF, Waterman detachment fault; WL, Walker Lake; WR, Wassuk R^nge;"an^T^erin^t^.' ViCt°rViUe 99

Nevada batholith. As proposed by Lahren (1989), Lahren and

Schweickert (1988a, 1989) and Schweickert and Lahren (1990, 1991) the slice originated in a region far to the south, possibly m the western Mojave. The Dinkey Creek and Snow Lake pendants, together with the correlative Glen Aulin, May Lake, Patterson Mountain and Boyden Cave pendants, were reportedly transported northward as part of the Snow Lake block (Lahren, 1989; Lahren and Schweickert, 1988b, 1989; Schweickert and Lahren, 1990, 1991). The northward

translation of the Snow Lake block occurred along the dextral Mojave-Snow Lake fault postulated by Lahren and Schweickert (1988b, 1989) (Fig. 30). The structures

associated with D3 and D4 deformations in Dinkey Creek

pendant may have resulted from translation of the Snow Lake

block along the Mojave-Snow Lake fault (Lahren 1989; Lahren

and Schweickert, 1988a, 1989; Schweickert and Lahren, 1990). The NW and WNW orientations of F3 and F4 in relation to the NNW orientation of the proposed Mojave-Snow Lake Fault are consistent with this interpretation. Timing of movement on the Mojave-Snow Lake fault is not well constrained, but

probably occurred post-148 Ma and pre-lio Ma (Lahren and Schweickert, 1989; Lahren, 1989).

Structural correlations between Dinkey Creek and Snow Lake pendant also suggest that the D± and D2 deformational events of Dinkey Creek pendant are equivalent to the pre-150 Ma D1 and D2 events in Snow Lake pendant (Lahren and others, 1990). if these correlations are correct, then the Dx deformation in Dinkey Creek pendant possibly resulted from GENERALIZED TECTONIC SECTIONS won DINKEY CREEK AND SNOW LAKE PENDANTS

Dinkey Creek Pendant Snow Lake Pendant

(Llhrln^igsIrSn^DiSkey^rSa^pSSdlnts? f°r Sn°W Lake 101

the accretion of Sonomia along the southern extension of the Golconda thrust (Lahren, 1989; Lahren and Schweickert, 1989; schweickert and Lahren, 1990, in press), similarly, the o ' thrusts in Dinkey Creek pendant (Dinkey Creek, Limestone Campsite and Willow Meadow thrusts) may be genetically

related to the Bigelow Peak, Buckskin, and Quartzite Peak thrusts of Snow Lake pendant, and may have resulted from

Triassic to mid-Jurassic intraarc thrusting (Lahren, 1989; Schweickert and Lahren, 1990, in press).

SUMMARY AND CONCLUSIONS

The recent detailed investigation of stratigraphy and structure of the Dinkey Creek pendant, central sierra

Nevada, reveals the presence of metasedimentary rocks of miogeoclinal affinity. Furthermore, correlation of rocks at Dinkey Creek pendant with Death Valley facies rocks of Snow hake pendant suggests Proterozoic to Lower Cambrian strata occurs in the Dinkey creek pendant, and supports the

inclusion of the Dinkey creek pendant in the Snow Lake block

Of Lahren and Schweickert (1989). Preliminary correlation of the lithologic units at Dinkey creek pendant with rocks of the Death Valley facies suggests that the Johnnie Formation, the Stirling Quartzite and the Wood Canyon

Formation occur in the Snow Lake block 120 km south of Snow Lake pendant.

The variably mylonitized rocks of Dinkey Creek pendant represent a zone of concentrated deformation which possibly 102

resulted from Triassic to mid-Jurassic intraarc thrusting. Compared with Snow Lake pendant, the similarities in

structural sequences and fold orientations, and variations in fold styles suggest the concentrated deformation

developed as a direct consequence of a deeper crustal setting for the Dinkey Creek pendant.

Provisional correlations suggest that the Dinkey Creek thrust juxtaposes Precambrian Johnnie Formation over the

younger Precambrian Stirling Quartzite. Furthermore, the Stirling Quartzite and Wood Canyon Formation form a

synformal nappe in the lower plate of the Dinkey Creek

thrust. Lithologic correlations also suggest that repeated sections of Johnnie Formation are exposed as a result of imbrication on the Limestone Campsite thrust, while the

Willow Meadow thrust places Stirling Quartzite on Johnnie Formation. The resulting tectonic package is similar in nature to the imbricate packet exposed in the Snow Lake pendant (Fig. 32).

Previous correlations proposed for the Dinkey Creek pendant are inconsistent with lithologic, structural, and

depositional features. The alternate correlation with rocks of the Death Valley facies in Snow Lake pendant is based on 1) similar lithologic assemblages, 2) the absence of

volcanic rocks, 3) similar composition and maturity of

cross-bedded quartzites, 4) overall similarities in structural sequences, 5) inferred environments of deposition, 6) consistent initial 87Sr/86Sr ratlos for associated granitic rocks, 7) association of metamorphic 103

rooks with dioritic to gabbroic intrusions of similar nature and relative timing, and 8) the presence of metabasaltic dike rocks potentially related to Independence dike swarm.

The presence of Precambrian to Cambrian miogeoclinal rocks in Dinkey Creek pendant sharply contrasts with the

Triassic-Jurassic continental-margin magmatic arc rocks in the southern parts of the Kings sequence, suggesting that tectonic complexity of the Kings sequence is far greater than previously believed and that the Kings sequence requires redefinition. 104

r e f e r e n c e s c i t e d

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desert and their implications for timing and mechanisms of continental truncation: Tectonics, v. 7, n. 3, p. APPENDIX A MAJOR ELEMENT ANLAYSES - INDEPENDENCE DIKE SWARM (CHEN AND MOORE, 1979)

1DS-1 IDS-3 IDS-5 IDS-6 IDS-7a IDS-7b

Si02 52.72 51.03 56.32 52.71 71.72 49.64 Ti02 1.10 1.06 0.68 1.48 0.27 0.77 ai2o 3 17.75 16.91 18.40 16.01 13.95 14.68 Fe203 2.13 4.70 3.36 5.17 0.86 4.36 FeO 6.99 3.38 4.23 4.58 1.02 5.42 MnO 0.162 0.140 0.150 0.208 0.073 0.231 MgO 4.36 5.24 3.46 4.25 0.47 7.21 CaO 7.49 10.24 7.01 8.14 1.73 10.92 Na20 3.28 2.86 3.60 3.49 4.15 2.63 K20 2.17 1.69 1.54 1.46 4.17 1.58 p 2o 5 0.29 0.39 0.18 0.78 0.08 0.23 Volatiies 1.21 2.57 1.19 1.33 1.09 2.09

Total 99.64 100.21 100.12 99.61 99.58 99.76

IDS-9 IDS-10 1DS-15 IDS-16

Si02 49.50 60.02 66.95 46.13 Ti02 0.89 0.63 0.41 0.77 Al203 15.17 16.57 15.08 13.80 Fe203 3.68 3.16 1.61 3.68 FeO 5.18 2.52 1.94 6.65 MnO 0.166 0.109 0.081 0.185 MgO 7.07 2.59 1.75 13.04 CaO 8.61 4.74 4.11 9.50 Na20 3.27 3.66 3.71 1.35 K20 1.72 3.26 2.78 1.02 p2o 5 0.30 0.23 0.10 0.20 Volatiles 4.67 3.06 .82 4.26

Total 100.23 100.^6 99.34 100,54

REFERENCE: Chen, J.H. and Moore, J.G., 1979, Late Jurassic Independence dike swarm in eastern California: Geology, v. 7, p. 129-133. 117

MAJOR ELEMENT ANALYSES - INDEPENDENCE DIKE SWARM SNOW LAKE PENDANT (LAHREN, 1989)

SL-467 SL-543 SL-543A SL-911 SL-9SS SL-998A

SiOs 72.4 69.1 47.6 69.3 47.8 49.2 TiCb 0.34 0.56 1.64 0.58 3.32 1.56 2 3 15.6 17.9 15.0 15.7 17.4 AI O 13.9 6.21 Fe203 1.98 1.59 3.36 1.31 3.28 FeO 1.18 1.70 5.70 2.35 6.83 5.67 0 .12 0.12 0.22 MnO 0.10 0.18 0.18 0.13 0.22 6.90 0.72 5.35 7.35 MgO 11.0 10 .2 CaO 0.53 0.97 1.33 9.23 3.89 2.84 3.67 2.35 1.79 NasO 4.04 1.00 K20 5.15 5.48 1.15 4.96 1.81 0.15 0.31 0.13 0.51 0.31 PpO s 0.081 2.21 Volatiles 0.51 0.76 1.93 0.99 1.78 CO O O 100.62 Total 100.14 100.51 100.46 100.62

SL-1000 SL-1001 SL-1012 SL-1014 SL-1015 SL-1015A

2 69.5 47.2 51.5 76.3 73.3 49.9 Si0 0.11 Ti02 0.53 3.03 1.67 0.38 1 19 A!203 15.8 16.1 16.8 13.2 14.3 17.6 2 4.28 3.16 0.56 0.73 2.35 Fe C>3 1.51 0.88 1 FeO 0.88 9.02 4.28 0.75 b. U 0.20 0.14 MnO 0.093 0.54 0.018 0.050 0.45 5.55 5.49 0.15 0.98 7.02 MgO 11.6 12.0 CaO 1.36 8.69 0.77 2.85 Na20 5.76 0.56 3.69 3.66 4.92 2.44 K20 3.69 2.95 0.37 4.14 1.57 0.87 0.34 0.076 0.10 0.26 PpO c, 0.14 0.49 1.66 Volatiles 0.46 1.64 1.28 0.42 0.48

Total 100.17 100.05 100.38 100.15 100.54 100.53

REFERENCE? , , ^ _ cior*r*^ Lahren, M.M., 1989, Techtonic studies of the Sierra Nevada: Structure and Stratigraphy of Miogeoclinal rocks in Snow Lake pendant, Yosemite-Emigrant wilderness; and TIMS analysis of.the Northern Sierra terrane [Ph.D. thesis]: Reno, University of Nevada Reno, 260 p.