Age of Jurassic volcanism and tectonism, southern region, east-central

GEORGE C. DUNNE Department of Geological Sciences, California State University, Northridge, Northridge, California 91330 J. DOUGLAS WALKER Department of Geology, University of Kansas, Lawrence, Kansas 66045

ABSTRACT GEOLOGIC SETTING

Remnants of the eastern fringe of the volcanic and volcanogenic Southern Inyo Mountains sedimentary cover of the Mesozoic batholith are exposed in the southern Inyo Mountains and adjacent Alabama Hills of east- Arc strata in the southern Inyo Mountains are preserved in co- central California. Six new U-Pb dates on volcanic units and crosscutting linear northern and southern belts that are separated by plutons intrusions reveal that the upper parts of both the Inyo Mountains and (Figs. 1, 2). Strata in these two belts are locally folded, but they are Alabama Hills sections accumulated during Middle and Late Jurassic broadly homoclinal and typically face and dip steeply southwest. In time. During this same interval, both sections were steeply tilted and both exposure belts, the volcanic sequence rests on the Union Wash locally folded during one or more episodes of contractile deformation Formation of Triassic age and is limited upward either by a thrust fault occurring in the east Sierran thrust belt. Differences between the largely carrying Paleozoic strata or by alluvial fill of Owens Valley. The Undated lower parts of the Inyo Mountains and Alabama Hills sections Union Wash Formation, of Early and early Middle(?) Triassic age suggest that they were once located farther apart, then later brought into (Stone and others, 1991) is a marine unit, most—and perhaps all—of proximity by thrust faulting or strike-slip faulting. The Inyo Mountains which was deposited prior to the onset of arc volcanism in this region. and Alabama Hills sections are similar to partly coeval strata in the In its northern exposure, the basal contact of the overlying arc se- White Mountains, in that both contain abundant sedimentaiy strata that quence clearly is unconformable, but the amount of stratal omission were in part deposited in or near terrain of moderate topographic relief. decreases southward (Stone and others, 1991). In the southern expo- Together, these areas seem to compose a distinctive arc-marginal dep- sure belt, this basal contact commonly is faulted, and its original nature ositional province different than that represented by partly coeval strata is difficult to interpret. Oborne and others (1983) suggested that the preserved in pendants to the west. contact is gradational and records a continuous transition from shal- low-marine through tidal-flat and distal-stream environments into al- INTRODUCTION luvial-fan environments of the overlying arc sequence. In contrast, Marzolf (1991) proposed that the basal contact of the arc sequence is Mesozoic volcanic and related volcanogenic sedimentaiy strata a major unconformity equivalent to the J0 unconformity of earliest composing the eastern fringe of the Sierran igneous arc are preserved Jurassic age that is widely exposed on the Colorado Plateau. Volcanic in a northwest-trending belt of discontinuous exposures in east-centred rocks in the lower third of the arc sequence are undated; thus these California (Fig. 1). The few published studies of these pendants have contrasting interpretations remain unresolved. provided the broad outlines of the eruptive, deformational, and paleo- The arc sequence of the southern Inyo Mountains can be divided geographic history of this part of the arc (Tobisch and others, 1986; into lower, middle, and upper intervals (Garvey and others, in press). Busby-Spera, 1988; Saleeby and others, 1990). Erosion is evident at each of the contacts between intervals, and the Mesozoic volcanic and volcanogenic sedimentary rocks exposed intervals may be separated by significant unconformities. Each of the in the southern Inyo Mountains and nearby Alabama Hills (Fig. 2) are three intervals can be recognized in both northern and southern ex- little-studied exposures within this belt. A few brief reports and ab- posures, although lateral facies changes result in somewhat different stracts describing these two exposures are available (Oborne and lithosome compositions, thicknesses and vertical succession within others, 1983; Dunne, 1986, 1990; Schneidereit, 1987; Garvey and correlative intervals (Fig. 3). The lower interval, ranging in thickness others, in press), but their age is poorly known because neither ra- from 200 to 480 m, consists of a basal 5- to 25-m-thick, mostly lime- diometric dates nor reliable fossil ages have been obtained for these stone-clast conglomerate (—5% of interval) overlain by volcanogenic rocks. We have determined new U-Pb dates on zircon extracted from conglomerate and breccia (—44%), pebbly volcanogenic sandstone four volcanic units in the southern Inyo Mountains and Alabama Hills and siltstone (—43%), and basaltic lava flow (—8%) units, many of exposures and from two crosscutting intrusions. In this paper, we which are arranged in complexly interfingering, laterally variable len- briefly summarize the geology of the arc volcanic sequence, present soidal arrays that are separated by erosional contacts. Oborne (1983) our new age data, and address implications of these data for the and Oborne and others (1983) concluded that these strata were de- Mesozoic evolution of east-central California. posited on alluvial fans by fluvial and debris-flow processes.

Geological Society of America Bulletin, v. 105, p. 1223-1230, 4 figs., 2 tables, September 1993.

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changes suggest that they accumulated in a terrain of lower relief than did strata of the lower interval. Features such as accretionary lapilli, mudcrack casts, raindrop impact impressions, and festoon cross-bed- ding of probable aeolian origin are evidence of subaerial deposition. The upper interval is >2,600 m thick in the southern exposure belt. If similar fossiliferous units in the southern and northern expo- sure belts are correlative (Fig. 3), then an additional few hundred meters of strata forming the youngest part of this interval may be preserved in the northern exposure. Over most of the southern ex- posure belt, the upper interval consists of volcanogenic conglomer- ate, sandstone, siltstone, and rare calcareous units (—95% of member) and welded tuff and lava-flow units (—5%). Sedimentary units are composed predominantly of sandstone and siltstone featuring parallel and low-angle cross-bedding. Individual lithosomes are laterally ex- tensive, with some traceable for 4 km. Garvey and others (in press) have interpreted these sedimentary features as indicating deposition of most of the upper interval by fluvial processes in terrain of low relief. The upper few hundred meters of this interval consists mostly of massive, matrix- to clast-supported, pebble to boulder volcanic conglomerate and breccia that was probably deposited by debris flows that may reflect an increase in topographic relief. Previously available age limits for arc strata in the southern Inyo Mountains are sparse. These rocks are younger than the Lower and lower Middle (?) Triassic strata of the underlying Union Wash For- mation, and all three stratigraphic intervals are intruded by subver- tical, northwest-trending mafic dikes that Dunne (1986) provisionally correlated with the Late Jurassic (148 Ma) Independence dike swarm (Chen and Moore, 1979). Apparently correlative fluvial strata within the upper interval in both northern and southern exposure belts (Fig. 3) contain poorly preserved fresh-water bivalves and gastropods for which a provisional age of Early to early Late Cretaceous was postulated (J. Hanley, personal commun., in Dunne, 1986).

Alabama Hills

In the Alabama Hills, arc strata form two exposures separated by a pluton (Fig. 2). As in the Inyo Mountains, these strata face and dip moderately to steeply southwest. The more stratigraphically complete Figure 1. Larger outcrops of Mesozoic syn-arc strata, east-central northern exposure consists of a lower and an upper interval separated California. Letter code for localities and related literature source are: by an unconformity (Fig. 3). The lower interval, which has a minimum A, Alabama Hills (this report); Ar, Argus Range (Moore, 1976); B, Butte thickness of —2,000 m, is composed of two groups of rocks present Valley (Cole and others, 1986); G, Goddard (Saleeby and others, 1990); in subequal amounts: (1) rhyolitic crystal lithic ash-flow tuff and vol- nl and si, northern and southern outcrop belts of southern Inyo Moun- canogenic sedimentary strata and (2) two or more generations of tains (this report); M, Mount Morrison (Rinehart and Ross, 1964); O, hypabyssal intrusions that take the form of northwest-trending dikes Oak Creek (Saleeby and others, 1990); RS, Ritter Range/Saddlebag area and sill-like masses. Volcanogenic sedimentary strata consist of vol- (Tobisch and others, 1986; Schweickert and Lahren, 1987); S, Slate canic-lithic to heterolithic conglomerate and breccia and less abun- Range (Smith and others, 1968); W, White Mountains (Hanson and dant, poorly bedded sandstone and siltstone. All exposures of the others, 1987). lower interval display moderate to intense hydrothermal alteration, which together with multiply intruded, abundant hypabyssal rock may indicate proximity to a volcanic feeder. The middle interval, ranging in thickness from 300 to 800 m, The upper stratigraphic interval is composed of two rock units: comprises several silicic crystal lithic welded ash-flow tuff (—65%), (1) discontinuous lenses of sedimentary rocks as much as 10 m thick andesite and rhyolite lava-flow (—25%), and interleaved volcanogenic that rest on the unconformity at the base of this interval, and (2) sedimentary (—10%) units. The sedimentary units consist mostly of rhyolitic crystal lithic ash-flow tuff >450 m thick that rests locally on moderately well bedded sandstone and of pebble to cobble conglom- the sedimentary rocks and elsewhere directly on the lower interval. erate, the clasts of which were predominantly derived from the im- The sedimentary rocks, now intensely recrystallized and variably mediately underlying volcanic unit. Most volcanic.tuff and lava-flow sheared, were originally a mix of aluminum-rich rock such as shale units are less than 150 m thick and can be traced laterally as much as (-80% of unit), quartz arenite (—15%), and heterolithic conglomerate 10 km; their substantial lateral continuity and gradual thickness (-5%).

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Figure 2. Simplified geo- logic map of Mesozoic rock units, southern Inyo Moun- tains and Alabama Hills, showing locations of geo- chronologic samples and of lithostratigraphic columns of Figure 3. Note that lower and middle stratigraphic intervals of the Inyo Mountains section have been combined as one map unit.

The nature of the unconformity separating the upper and lower interpret as a minimum age. Other zircon fractions from this rock do intervals is somewhat obscure because it has been the locus of sub- not lie on a line and our interpretation of a minimum age of 140 ± sequent faulting. We provisionally interpret the unconformity to be 8 Ma relies on the one concordant point. This minimum age is geo- heterolithic in places where rocks of the upper interval seem to rest logically reasonable because felsic dikes of D116 intrude 148 Ma on both sedimentary and hypabyssal units of the lower interval, and Independence dikes. Sample D117 yields a lower intercept age of angular in other places where average bedding in strata of the upper 148.5 ± 1 Ma (Fig. 4, MSWD = 0.92; computed using ISOPLT of interval seems to dip —15° less steeply southwest than average bed- Ludwig, 1983). This age is considered a minimum. We were unable to ding in strata of the lower interval. extract precise ages of the inherited components for either of these Previously available age limits for the Alabama Hills strata were samples because the entire zircon yield was consumed for the analyses provided by crosscutting intrusions. Chen and Moore (1979) obtained presented here. a U-Pb date of—148 Ma for two dikes of the Independence swarm that Samples from the four volcanic units present somewhat ambig- intrudes both lower and upper intervals. Those same authors (1982) uous results. All samples apparently have suffered some Pb loss and obtained a U-Pb date of 85 Ma for the granitoid pluton that intrudes contain a minor inherited component. Pb loss is indicated by (1) the the upper member and truncates Independence dikes. tendency for more magnetic zircon fractions to plot with lower Pb/U ratios but similar Pb/Pb ratios with respect to less magnetic fractions GEOCHRONOLOGY and (2) the tendency of air-abraded fractions to plot with higher Pb/U ratios but similar Pb/Pb ratios with respect to the unabraded fractions. U-Pb zircon dates were obtained for six samples from the Inyo Axenocrystic zircon component is shown by (1) several fractions that Mountains and Alabama Hills in order to more closely define the ages plot with much older Pb/Pb ages and (2) rare fractions where the Pb/Pb of the Mesozoic eruptive, erosional, and deformational events appar- ages are increased but the Pb/U ratios are little changed by air ent in the geology of these areas (Figs. 2, 3). Tables 1 and 2 provide abrasion. the location, lithology, geologic significance, and our isotopic data for Sample D113 (Fig. 4 and Table 2) is illustrative of how we in- these samples. terpret the ages of these rocks. Fractions analyzed from this sample We are most confident about interpreting the ages of the two cluster with the exception of the most magnetic fraction [nm(3)], which intrusive units, samples D116 (felsic dike) and D117 (French Spring clearly shows an inherited component. Pb loss is also evident using the pluton). These units show clear evidence for an inherited, xenociystic criteria given above. Hence it is clear that the zircon behavior for this component in the zircon populations. Sample D116 yielded an inter- sample involves both inheritance and Pb loss. A minimum age for this nally concordant fraction at 140 ± 8 Ma (Fig. 4; Table 2), which we sample is 165 ± 1 Ma using the aj6Pb/23SU age of the oldest, most

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clearly older. If Pb loss occurred during earlier times, then the true age 207 2()6 a approximate is slightly older than the Pb/ Pb age. Hence 165 ± 1 is clearly a o b VI vertical scale minimum age, but the oldest possible minimum age for this rock. Our (N volcanic rock volcanogenic preferred age for sample D113 is 169 ± 4 Ma. This age is derived from a = felsic tuff sedimentary the Pb/Pb ages of the most concordant points [nm(l)>240 and b = lava flow strata O 168 Ma - new U-Pb date nm(l)>240aa fractions] and their analytical error. This is itself a min- H H H H 1 reported here imum age. This preferred interpretation assumes that Pb loss is recent, H H H H > T H H H H M and that these fractions contain a negligible inherited component, but H H H H * 148 Ma - previously that other fractions contain a very minor inherited component. If Pb published hypabyssal dike loss occurred at some time in the past, say at about 100 Ma during the intrusion I = Inde- U-Pb date intrusion of much of the adjacent Sierran batholith, then the true age / / / pendence . \ \ \ F = felsite of this rock could be somewhat older. ./ \/ \/ \. Paleozoic / / / Samples D118 and D120 have similar behavior (Fig. 4 and ,tf \ \t ^ granitoid Table 2). Sample D118 has a minimum age of 164 ± 1 Ma. Our pluton preferred minimum age is 168 ± 4 Ma based on the nm(3) fraction. Sample D120 has a minimum age of 166 ± 1 Ma and a preferred -85 Ma minimum age of 170 ± 4 Ma based on the nm(0) >240 fraction. Sample K \V N / N-tzA N S D115 shows much more scatter and larger analytical errors than do the .170 Ma other samples. This is the result mainly of the lower ^Pb/^Pb ratios (±4) for this rock, which add uncertainty through common-Pb corrections. A minimum age for this rock is 168 ± 3 Ma. This is also our preferred age, although any age between 165 and 195 Ma is reasonable. In the following discussion, we use the symbol with our U-Pb dates to remind readers that these represent approximate min- imum ages.

148 Ma ^ -j DISCUSSION (±D ft Implications for Southern Owens Valley Area

These age data provide several new temporal constraints for the Mesozoic igneous and deformational history of the Sierran arc in the southern Owens Valley area. In discussing these data, we utilize the time scale of Harland and others (1990). -148 Ma (1) These new data demonstrate that the uppermost two-thirds of the previously undated volcanic and volcanogenic section in the southern Inyo Mountains was deposited between —169 Ma and Hi —148 Ma, the younger age being that of a granitoid pluton (sample D117) that intrudes both middle and upper intervals of the Inyo Moun- tains section. This age range indicates that the Cretaceous age pro- ^fHH H H H H H H H H H H H KKJ H HJLr^ I TABLE 1. LOCATION AND GEOLOGIC SETTING OF DATING SAMPLES

Union Union covered Wash Fm Wash Fm Sample Map loc. Lithology Lat. and Geologic relationships no. (Fig. 2) long. Alabama Hills north exposure, south exposure, Inyo Mtns Inyo Mtns SI-D113-1 Welded crystal lithic 36°31'20" Youngest lithosome of middle interval, rhyolite tuff UTSO'M" Inyo Mountains southern exposure Figure 3. Schematic lithostratigraphic columns of Mesozoic syn- belt SI-D115-1 Welded crystal 36°31'0r Second oldest lithosome of middle arc strata of the southern Inyo Mountains and the northern Alabama dacite tuff 117°49'52" interval, Inyo Mountains southern exposure belt Hills. SI-D116-1 Felsite dike 36°31'41" Part of a dike family that intrudes all 117°49'30" three intervals of Inyo Mountains exposure belt as well as maiic dikes correlative with Independence dike swarm; also intrudes previously concordant fraction (shaded point, plotting nearest to concordia). If formed tight folds SI-D117-1 4 Fine-grained 36°40'08" Large pluton that separates and this fraction contains an inherited component, then a chord drawn leucogranite 117°59'36" intrudes all three intervals of both northern and southern exposure through this point to the age of the older component (probably 1400 belts of Inyo Mountains Ma or older for this region) will yield virtually the same age. Any Pb SI-D118-1 5 Welded crystal lithic 36°41'26" Youngest lithosome of middle interval rhyolite tuff 118°01'45' of northern exposure belt of Inyo loss will make the true age of this rock older. If this fraction has Mountains suffered only recent Pb loss and there is no inheritance, then the true SI-D120-1 6 Welded crystal lithic 36°40'05" Youngest lithosome of the northern rhyolite tuff 118°08'10" Alabama Hills section age of the rock is given by the 207Pb/206Pb age (169 Ma), which is

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TABLE 2. ANALYTIC DATA FOR SOUTHERN INYO MOUNTAINS AND ALABAMA HILLS

Fraction Sampie wt, U 206Pb* Measured ratios^ Radiogenic ratios1 Ages (Ma) (mg) (ppm) (ppm) ^Pb/ 207Pb/ 208pb/ ^Pb */ ^Pb'/ z^Pb*/ ^Pb-V 235 238JJ 206p , ^Pb »Pb ^Pb 238u V 206p,,, 235u b

SI-D113-1 nm(0)>240 0.672 419.2 9.231 288.3 (1.9) 0.1005 (5) 0.3578 (4) 0.02563 (12) 0.1750 (15) 0.04952 (34) 163.1 163.7 172.5 (16) nm(0)>240 g 0.478 220.8 4.856 595.7 (3.6) 0.07428 (4) 0.3000 (3) 0.02560 (14) 0.1750 (11) 0.04959 (16) 162.9 163.8 175.9 (8) nm(0)>240 aa 0.156 343.8 7.684 1955 (20) 0.05721 (5) 0.2709 (3) 0.02602 (29) 0.1783 (20) 0.04969 (9) 165.6 166.6 180.3 (5) nm(l)>240 2.675 481.5 10.61 592.4 (6.0) 0.07428 (4) 0.2888 (3) 0.02565 (12) 0.1749 (8) 0.04946 (5) 163.3 163.7 169.9 (2) nm(l)<240 1.040 753.1 16.44 466.5 (3.2) 0.08100 (5) 0.3003 (3) 0.02541 (11) 0.1734 (11) 0.04947 (20) 161.8 162.3 170.4 (10) nm(l)>240 aa 1.700 498.3 11.08 1503 (10) 0.05924 (4) 0.2557 (3) 0.02588 (12) 0.1765 (9) 0.04945 (8) 164.7 165.0 169.2 (4) nm(3)b 1.333 602.0 13.74 262.0 (6.0) 0.1081 (5) 0.3568 (4) 0.02657 (12) 0.1913 (10) 0.05222 (14) 169.0 177.7 295.2 (7)

SI-D115-1 nm(-l)<240 aa 0.098 180.9 4.169 1399 (14) 0.06053 (12) 0.2711 (4) 0.02683 (21) 0.1850 (16) 0.05001 (17) 170.7 172.4 195.6 (8) nm(0)aa 0.146 160.7 3.649 207.0 (1.7) 0.1205 (4) 0.4004 (6) 0.02642 (36) 0.1804 (36) 0.04951 (69) 168.1 168.4 172.2 (33) nm(2)>240 eu 1.445 173.6 3.880 240.7 (1.7) 0.1111 (5) 0.4127 (5) 0.02602 (12) 0.1794 (18) 0.05000 (40) 165.6 167.6 195.2 (19) nm(2)>240b 0.254 247.1 5.473 255.8 (2.4) 0.1075 (5) 0.3972 (4) 0.02578 (16) 0.1781 (22) 0.05009 (50) 164.1 166.4 199.2 (24) nm(2)>240 rd 0.402 172.4 3.817 149.7 (1.0) 0.1475 (7) 0.5169 (5) 0.02577 (19) 0.1748 (28) 0.04920 (64) 164.0 163.6 157.5 (31)

SI-D116-1 f, eu 0.080 164.5 3.408 576.7 (4.1) 0.07716 (16) 0.2500 (3) 0.02412 (40) 0.1719 (30) 0.05168 (28) 153.6 161.0 271.4 (12) c, eu 0.062 91.20 1.713 184.2 (1.8) 0.1284 (11) 0.3668 (5) 0.02187 (86) 0.1477 (66) 0.04898 (96) 139.4 139.8 146.9 (46) rd 0.115 159.0 3.133 355.8 (2.4) 0.09420 (12) 0.3947 (6) 0.02294 (41) 0.1688 (33) 0.05335 (35) 146.2 158.4 343.8 (15)

SI-D117-1 nm(0) eu 0.824 233.1 4.732 1568 (16) 0.05919 (7) 0.3637 (4) 0.02362 (13) 0.1622 (10) 0.04981 (12) 150.5 152.7 186.1 (6) nm(2)<240 eu 0.089 98.69 2.005 239.0 (2.4) 0.1105 (4) 0.4928 (9) 0.02365 (84) 0.1591 (64) 0.04879 (87) 150.7 149.9 137.6 (42) nm(2) eu 0.111 208.0 6.408 292.0 (2.9) 0.1179 (21) 0.3333 (14) 0.03587 (37) 0.3397 (47) 0.06869 (58) 227.2 296.9 889.4 (17)

SI-D118-1 nm(-l) aa 0.152 315.0 6.977 2487 (25) 0.05544 (5) 0.2641 (3) 0.02578 (13) 0.1760 (10) 0.04952 (8) 164.1 164.6 172.4 (4) nm(0)>240 4.071 465.0 10.06 2178 (14) 0.05639 (5) 0.2537 (3) 0.02519 (12) 0.1724 (8) 0.04964 (5) 160.4 161.5 178.3 (2) nm(l)<240 aa 0.127 303.7 6.701 927.8 (7.4) 0.06539 (8) 0.2849 (4) 0.02568 (22) 0.1759 (16) 0.04968 (14) 163.5 164.6 180.2 (7) nm(l)>240 1.048 436.4 9.440 1364 (9.5) 0.06044 (5) 0.27% (3) 0.02518 (12) 0.1724 (9) 0.04966 (7) 160.3 161.5 179.2 (4) nm(2)<240 0.459 507.9 10.84 1264 (1.8) 0.06124 (3) 0.2382 (3) 0.02485 (12) 0.1700 (8) 0.04962 (4) 158.2 159.4 177.1 (2) nm(3)<240 b 0.764 610.7 13.13 1392 (4.5) 0.06000 (3) 0.2452 (3) 0.02503 (12) 0.1706 (8) 0.04944 (5) 159.4 160.0 168.6 (3) m(3)<240 b 1.594 709.4 14.80 505.1 (1.4) 0.07890 (4) 0.3032 (3) 0.02429 (ID 0.1668 (8) 0.04980 (9) 154.7 156.6 185.5 (5)

SI-D120-1 nm(0)<240 0.321 601.8 13.06 2725 (25) 0.05495 (3) 0.2298 (3) 0.02527 (12) 0.1727 (8) 0.04955 (6) 160.9 161.7 174.1 (3) nm(0)>240 2.360 329.5 7.294 3538 (25) 0.05363 (3) 0.2178 (3) 0.02576 (12) 0.1757 (8) 0.04947 (4) 164.0 164.4 170.1 (2) nm(0)>240 aa 0.515 481.6 10.73 4274 (43) 0.05295 (3) 0.2357 (3) 0.02594 (13) 0.1771 (9) 0.04951 (4) 165.1 165.5 171.9 (2) nm(0)>240 aa 0.903 420.5 9.393 8360(84) 0.05127 (3) 0.2240 (3) 0.02600 (14) 0.1775 (10) 0.04951 (4) 165.5 165.9 172.1 (2) nm(l)<240 0.480 706.0 15.40 3124 (22) 0.05426 (3) 0.2203 (3) 0.02540 (13) 0.1735 (9) 0.04955 (4) 161.7 162.5 174.1 (2) nm(3)<240 b 0.457 617.4 13.69 7048 (SO) 0.05229 (3) 0.1867 (3) 0.02582 (12) 0.1787 (8) 0.05020 (3) 164.3 166.9 204.5 (2)

Note: nm(#) = nonmagnetic on Frantz separator at angle of tilt # degrees. m(#) = magnetic on Frantz separator at angle of tilt # degrees. >240 = size in standard mesh, aa = air abraded fraction, g = hand-picked clear fraction, c - coarse-grained fraction, f = line-grained fraction, eu = euhedral fraction, rd = rounded grain fraction, b = bulk fraction (no hand picking to distinguish populations). Zircon dissolution followed the methods of Krogh (1973) and Parrish (1987). Elemental separation was done with a HBr anion column chemistry for lead and HQ column chemistry for uranium. Air abrasion followed the methods of Krogh (1982). Decay constants used were ™U = 0.15513 X 10"® yr-1 and 235U = 0.98485 x 10~® yr"1 (Steiger and Jager, 1977). Isotopic analyses were determined on a VG Sector multicollector thermal ionization mass spectrometer. A mass fractionation correction of 0.10% ± 0.05%/amu, as determined by standard runs on NBS 981 (common lead) and NBS 982 (equal atom lead), was applied to the lead data. Samples were spiked with either a mixed 205Pb/,2:i5U spike or a mixed 2,ftI1b/235U spike. Errors on Pb/^Pb were minimized by use of a Daly multiplier and are typically on the order of 1% or less. Errors for 2n6Pb/2twPb were reduced further on samples spiked with 205Pb by using a dynamic Daly calibration after the technique of Roddick and others (1987, p. 115). Common lead corrections were made using values determined from Stacey and Kramers (1975) for the interpreted crystallization age. •Radiogenic component. 5Ratios corrected for spike and mass fractionation only. lumbers in parentheses are analytical errors. For measured and radiogenic ratios this is the 2-sigma value for the ratio; for example, 0.1750 (15) means 0.1750 ± 0.0015. For the 207Pb/206Pb age, the value is in m.y. Errors were computed using data reduction program PBDAT of Ludwig (1983).

visionally assigned to the upper interval of the Inyo Mountains section another (Fig. 3). Some of these differences, such as abundance of on the basis of poorly preserved fresh-water fossils is in error unless hypabyssal rocks and intensity of hydrothermal alteration, may sim- an unrecognized fault or unconformity exists between the fossil lo- ply reflect proximity of the Alabama Hills exposure to a local volcanic calities and the pluton. The lower third of the Inyo Mountains section, feeder. There is no unit in the Inyo section, however, that corresponds which remains undated, may be as old as Middle to Late Triassic if to the several-hundred-meter-thick rhyolite ash-flow tuff unit forming Oborne and others (1983) are correct, or Early Jurassic if Marzolf the lowest exposures of the Alabama Hills section (Fig. 3). Prior to (1991) is correct. —25% right-oblique, late Cenozoic extension across Owens Valley (2) The proposed correlation of the three stratigraphic intervals (Wernicke and others, 1988), the distance between Mesozoic strata in in the northern and southern exposure belts of the Inyo Mountains is the Alabama Hills and Inyo Mountains would have been —3.75 km. consistent with the nearly identical preferred ages (168 Ma and Figure 2 reveals that this gap probably was filled by the northward 169 Ma, respectively) of the youngest lithosome of the middle interval continuation of the large thrust plate of Paleozoic strata that rests on in each area. arc strata in the Inyo Mountains. Arc strata in the Alabama Hills could (3) Our data establish a chronologic tie between some of the arc be the youngest strata of this same thrust plate or could form a struc- strata in the Alabama Hills and those in the southern Inyo Mountains turally higher thrust plate. In either case, retrodeformation of a sche- in that both areas received deposits of rhyolite ash-flow tuff at matic cross section across this belt (for example, Dunne, 1986, Fig. 4) —169 Ma. Those parts of the two sections lying below these approx- suggests that prior to thrusting these Mesozoic rocks probably would imately coeval tuff units, however, are substantially different from one have lain farther to the west than at present, and this greater original

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0.0266 1 1 1 1 i . i i 1 l'I

I68y/ 0.048 - 280/ - 0.0262 - \<*>yy/ 3 0.040 -

- 164 y/• / / 0.0258 - 200 F3 0.032 - y/

- 162 C^ 160 ^ "" Sample Sl-D 117-1 - 0.0254 Age = 148.5 ± 1 Ma Sample SI-D113-1 0.024 MSWD = 0.92 / i i i i >'7 1 i i i 0.172 0.174 0.176 0.178 0.180 0.18 0.22 0.26 0.30 0.34

207Pb/235u 207Pb/235u

0.0274 i i 1 1 y i i 1 I 1 1 1 0.0264 172 166

164 0.0266 - / 0.0256 - 162

- /l66 . -

0.0258 158 - 0.0248 v 156 ^^

Sample SI-D 115-1 Sample SI-D 118-1 0.0250 1 1 i i 0.0240 I 1 i i i i i 0.174 0.178 0.182 0.186 0.168 0.172 0.176

207Pb/235u 207Pb/235u

0.026 1 1 1 / 1 1 1 1 0.0264 - 160>

0.024 - 0.0260 •V^7 - - - a. /// ^ S 0.0256 162 0.022

Sample SI-D 116-1 _ Age = 140 Ma 0.0252 Sample SI-D 120-1 " i i i 0.020 1 i i i 0.14 0.15 0.16 0.17 0.172 0.174 0.176 0.178

207Pb/235u 207Pb/235u Figure 4. Concordia plots for the Inyo Mountains and Alabama Hills data. Sample name is given on each plot. Ellipses show the 2-o- analytical error for the points, except for D117 where the errors are too small to show at the scale of the diagram. Point with shaded error ellipse represents most concordant fraction of Sample D113 (see text for discussion). Errors were computed using PBDAT of Ludwig (1983). The nm(3) fraction for sample D113 is not shown.

distance between the Alabama Hills and Inyo Mountains may explain is difficult given the complex slip history that this zone of faulting may the differences between these two sections. have undergone (Saleeby and Busby-Spera, 1992). Northwest-trending, late Mesozoic strike-slip faults inferred to lie (4) Previous speculations (Dunne, 1986; Griffis, 1986) that many beneath the floor of Owens Valley (Silver and Anderson, 1974; Oldow, of the mafic dikes exposed in the southern Inyo Mountains are part of 1984; Kistler, in press) may also have played a role in juxtaposing these the Independence dike swarm are consistent with our new data. These two unlike sections. Assessing the net impact of these faults, however, dikes cut volcanic rocks as young as ~ 169 Ma, but in turn are intruded

1228 Geological Society of America Bulletin, September 1993

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by ~ 140 Ma felsite dikes. The granite of French Spring (sample D117) tectonism—perhaps irregularly arrayed in both time and space, and has a minimum age that is, considering analytical error limits, the same we provisionally ascribe Middle Jurassic deformation in the east age as the Independence dike swarm (Chen and Moore, 1979). Chro- Sierran thrust belt to such an episode. nologic studies in the Mojave Desert and Sierra Nevada (Dunne and others, 1991; Walker and others, 1990b: Lahren and others, 1990; Miller and others, 1991) have revealed that previously unrecognized Implications for Regional Jurassic Volcanism and Paleogeography plutonism accompanied emplacement of the Independence swarm, and the Inyo Mountains pluton seems to be another such example. Our results allow an expanded view of Jurassic volcanism and (5) Our chronologic data demonstrate that some of the contractile paleogeography of the eastern fringe of the Sierran arc when compared structures composing the East Sierran thrust belt in this region de- with the four other exposures of dated Jurassic strata in east-central veloped between —168 Ma and —148 Ma. During this interval, Jurassic California. These are in the Goddard, Oak Creek, and Ritter Range volcanic strata in the Inyo Mountains were tilted steeply southwest pendants and the White Mountains (Fig. 1). Saleeby and others (1990), and locally folded during one or more episodes of deformation (Dunne, noting that the Ritter, Goddard, and Oak Creek pendants share most 1986, p. 13). The timing of tilting and folding is determined by two or all of several key features, proposed that these pendants are rem- observations: (1) nonfolded Independence dikes as well as the felsite nants of a distinctive, east Sierran wallrock province. Common fea- dikes that cut them intrude folded strata at least as young as ~ 169 Ma; tures of these pendants include (1) episodic accumulation of domi- (2) Independence dikes presently dip within 10° of vertical—their nantly silicic volcanic and minor sedimentary units between —230 and assumed initial dip—where they intrude Middle Jurassic strata that —100 Ma, (2) broadly west-facing sections, (3) presence of angular commonly dip 60° to 70° SW. One or more additional, less intense unconformities of various ages, and (4) development of northwest- episodes of similarly oriented deformation occurred after emplace- trending faults followed by intrusion of the sections and these faults ment of the Independence dikes, which commonly are foliated and cut by Middle and Late Jurassic hypabyssal and plutonic rocks. by contractile faults (Dunne, 1986). The northwest-trending reverse The composite Inyo Mountains/Alabama Hills volcanic section fault in the northern exposure belt of the Inyo Mountains (Figs. 2,3) contains features two through four, but differs in two important as- is probably another expression of the east Sierran thrust belt. It jux- pects of feature one. First, the composite Inyo Mountains/Alabama taposed middle and upper stratigraphic intervals sometime after Hills section is composed of —60% sedimentary strata rather than —168 Ma, but it was then intruded by a granite pluton at —148 Ma consisting largely of volcanic rock. Second, the Inyo Mountains/ (Fig. 3). Alabama Hills Mesozoic section seems to have accumulated in dep- We interpret these folds, the fault, and presumably the south- ositional environments different from those in the Ritter Range and westward tilt of the Mesozoic section to be integral components of the Goddard pendants. In the Inyo Mountains section, much of the lower east Sierran thrust belt, which coincides with the east margin of the interval accumulated on alluvial fans draining terrains of at least mod- Sierran arc and which can be tracked southward into the Mojave erate topographic relief (Oborne, 1983). The middle and most of the Desert (Dunne and others, 1983). There, Walker and others (1990a) upper interval accumulated in fluvial and lacustrine environments of demonstrated that a ductile reverse-sense shear zone formed in the low topographic relief, but the locally very coarse, debris-flow con- Cronese Hills between 155 Ma and 166 Ma. Walker and Martin (1991) glomerate that is abundant in the upper part of the upper interval may described contractile structures at several other localities within the reflect renewed uplift. In contrast, strata of the Ritter Range pendant Mojave part of the east Sierran thrust belt for which their limited accumulated in alternating subaqueous and subaerial settings of very chronologic data are permissive of Middle to Late Jurassic ages of low topographic relief that were shallow marine during the Early deformation. We presently believe that the contractile structures in Jurassic (Fiske and Tobisch, 1978). In the Goddard pendant, Middle the Inyo Mountains and Mojave parts of the east Sierran thrust belt Jurassic strata accumulated in low-relief settings that were alternately are broadly correlative and that they developed during one or more subaerial and indeterminate marine or lacustrine subaqueous, episodes of contractile deformation throughout a >225-km-long reach whereas strata of possible latest Jurassic age were deposited in sub- of this thrust belt during Middle or Late Jurassic time. Many of the aerial environments (Tobisch and others, 1986). thrust faults that override Mesozoic volcanic units throughout the east Jurassic arc-related strata in the White Mountains (Fates, 1985; Sierran thrust belt may have been emplaced at this time. If this is true, Hanson, 1986; Hanson and others, 1987) more closely resemble those future radiometric dating work should reveal that volcanic units of the Inyo Mountains/Alabama Hills than those of the Ritter Range, younger than Late Jurassic age are absent from the immediate foot- Goddard, and Oak Creek pendants. The White Mountains section walls of these thrust faults. consists of >30% sedimentary strata that is in part of Late Jurassic The tectonic significance of this contractile deformation remains age, and these strata were deposited by an energetic fluvial system that in dispute. Busby-Spera (1988) and Busby-Spera and others (1990) drained an uplifted region exposing Paleozoic strata (Fates, 1985). speculated that the Sierran arc was broadly transtensional to exten- In summary, available data suggest to us that the Inyo Mountains/ sional until late Middle Jurassic time. Saleeby and Busby-Spera (1992) Alabama Hills and White Mountains sections represent a distinctive proposed that the east Sierran thrust belt might be an expression of arc-marginal depositional province that differs from that represented wallrock "return flow" beneath rising magma in the axial part of the by rocks of the Ritter Range, Goddard, and Oak Creek pendants in broadly extensional or transtensional arc. Burchfiel and others (1992), containing a much larger proportion of sedimentary strata and in Saleeby and Busby-Spera (1992), and Smith and others (in press), having accumulated at least in part near areas of greater topographic however, presented evidence of episodic Middle Jurassic contractile relief than apparently was common to the west. The differences be- events at many localities in the Sierran arc and back-arc regions. In tween these two adjacent depositional provinces probably largely accord with the transform-influenced tectonic setting of the Sierran arc reflect natural transverse variations across the arc, with a decreasing espoused by Saleeby and Busby-Spera (1992), we believe that these volcanic rock/sedimentary rock ratio to be expected toward the fringe events reflect local and perhaps regional episodes of transpressive of the arc. We speculate that uplifted source areas, some of which

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Krogh, T. E., 1973, A low contamination method for hydrothermal decomposition of zircon and ex- exposed Paleozoic rocks, may have originated partly in response to traction of U and Pb for isotopic age determinations: Geochimica et Cosmochimica Acta, v. 37, episodes of contractile deformation in the East Sierran thrust belt. p. 485-494. Krogh, T. E., 1982, Improved accuracy of U-Pb zircon ages by the creation of more concordant systems using air abrasion techniques: Geochimica et Cosmochimica Acta, v.) 46, p. 637-649. Lahren, M. M., Schweickert, R. A., Mattinson, J. M., and Walker, J, D., 1990, Evidence of uppermost ACKNOWLEDGMENTS Proterozoic to Lower Cambrian miogeoclinal rocks and the Mojave-Snow Lake fault: Snow Lake pendant, central Sierra Nevada, California: Tectonics, v. 9, p. 1585-1608. Longiaru, S., 1987, Tectonic evolution of Oak Creek volcanic roof pendant, eastern Sierra Nevada, Financial support for this work was provided partly by National California (Ph.D. thesis]: Santa Cruz, California, University of California, 242 p. Ludwig, K. R., 1983, Plotting and regression programs for isotopic geochemists, for use with the HP Science Foundation Grants EAR89-16802 and EAR92-05096 to 86/87 microcomputers: U.S. Geological Survey Open-File Report 83-849, 102 p. Walker. Acknowledgment is made also to the donors of The Petro- Marzolf, J., 1991, Lower Jurassic unconformity (J-0) from the Colorado Plateau to the eastern Mojave Desert; evidence of a major tectonic event at the close of the Triassic: Geology, v. 19, p. 320-323. leum Research Fund, administered by the American Chemical Soci- Miller, J., Glazner, A., Martin, M., and Walker, J. D., 1991, Age relations, chemical and isotopic signature, and tectonic implications of Middle and Late Jurassic plutonism in the central and ety, for additional partial support of this research. We thank Mark Mojave Desert: Geological Society of America Abstracts with Programs, v. 23, p. 249. Martin and Jon Linn of the Isotope Geochemistry Laboratoiy for help Moore, S., 1976, Geology and thrust fault tectonics of parts of the Argus and Slate Ranges, Inyo County, California [Ph.D. thesis]: Seattle, Washington, University of Washington, 128 p. in sample preparation. Helpful review comments by Cathy Busby, Obome, M.S., 1983, Stratigraphy of Early to Middle (?) Triassic marine-to-continental rocks, southern Inyo Mountains, California [M.S. thesis]: Northridge, California, California State University, Eugene Fritsche, Rachel Gulliver, Mark Martin, and an anonymous 101 p. reviewer are also gratefully acknowledged. Oborne, M. S., Fritsche, A. E., and Dunne, G. C., 1983, Stratigraphic analysis of Middle (?) Triassic marine-to-continental rocks, Southern Inyo Mountains, east-central California, in Gurgell, K- D., ed., Geologic excursions in stratigraphy and tectonics: From southeastern Idaho to the southern Inyo Mountains, California, via Canyonlands and Arches National Parks, Utah: Utah Geological REFERENCES CITED and Mineral Survey Special Studies 60, p. 54-59. Oldow, J., 1984, Evolution of a late Mesozoic back-arc fold and thrust belt, northwestern Great Basin, Busby-Spera, C., 1988, Speculative tectonic model for the early Mesozoic arc of the southwest Cor- USA: Tectonophysics, v. 102, p. 245-274. dilleran : Geology, v. 16, p. 1121-1125. Parrish, R. R., 1987, An improved micro-capsule for zircon dissolution in U-Pb geochronology: Chemi- Busby-Spera, C., Mattinson, J., Riggs, N., and Schermer, E., 1990, The Triassic-Jurassic magmatic arc cal Geology, v. 66, p. 99-102. in the Mojave-Sonoran Deserts and in the Sierran-Klamath region: Similarities and differences in Roddick, J. C., Loveridge, W. D., and Parrish, R. R., 1987, Precise U/Pb dating of zircon at the sub- paleogeographic evolution, in Harwood, D., and Miller, M., eds., Paleozoic and early Mesozoic nanogram Pb level: Chemical Geology (Isotope Geoscience Section), v. 66, p. 111-121. paleogeographic relations; Sierra Nevada, Klamath Mountains and related terranes: Geological Rinehart, C. D., and Ross, D. C., 1964, Geology and mineral deposits of the Mount Morrison quadrangle, Society of America Special Paper 255, p. 325-338. Sierra Nevada, California: U.S. Geological Survey Professional Paper 385, 106 p. Chen, James, and Moore, James, 1979, Late Jurassic Independence dike swarm in eastern California: Saleeby, J. B., and Busby-Spera, C., 1992, Early Mesozoic tectonic evolution of the western U.S. Geology, v. 7, p. 129-133. Cordillera, in Burchfiel, B. C., Lipman, P. W., and Zoback, M. L., eds., The Cordilleran orogen, Chen, James, and Moore, James, 1982, Uranium-lead isotopic ages from the Sierra Nevada batholith, conterminous U.S.: Boulder, Colorado, Geological Society of America, The Geology of North California: Journal of Geophysical Research, v. 87, p. 4761-4784. America, Volume G-3, p. 107-168. Cole, R. C., Marzolf, J. E., and Avent, J., 1986, The transition from shallow marine sedimentation to Saleeby, J. B., Tobisch, O., Kistler, R. W., and Longiaru, S., 1990, Middle Cretaceous silicic meta- orogenic arc volcanism: The Triassic Butte Valley and Warm Springs Formations, southern volcanic rocks in the Kings Canyon area, central Sierra Nevada, California, in Anderson, J. L., Panamint Range—Another piece of the puzzle: Geological Society of America Abstracts with ed., The nature and origin of Cordilleran magmatism: Geological Society of America Memoir 174, Programs, v. 18, p. 96. p. 251-270. Dunne, G. C., 1986, Geologic evolution of the southern Inyo Range, Darwin Plateau, and the Argus and Schneidereit, D. C, 1987, Stratigraphy of Mesozoic volcanic and sedimentary rocks, Inyo Mountains, Slate Ranges, east-central California—An overview, in Dunne, G. C., compiler, Mesozoic and California: Geological Society of America Abstracts with Programs, v. 19, p. 448. Cenozoic structural evolution of selected areas, east-central California (Geological Society of Schweickert, R. A., and Lahren, M., 1987, Continuation of the Antler and Sonoma orogenic belts to the America Cordilleran Section meeting guidebook, field trips 2 and 14): Los Angeles, California, eastern Sierra Nevada, California, and Late Triassic thrusting in a compressional arc: Geology, California State University, p. 3-21. v. 15, p. 270-273. Dunne, G. C., 1990, Mesozoic stratigraphy and structure of the eastern fringe of the Sierra Nevada Silver, L., and Anderson, T., 1974, Possible left-lateral early to middle Mesozoic disruption of the igneous arc, east-central California: Geological Society of America Abstracts with Programs, southwestern North American craton margin: Geological Society of America Abstracts with Pro- v. 22, p. 20. grams, v. 6, p. 955. Dunne, G. C., and Walker, J. D., 1991, New age constraints on Jurassic volcanism and tectonism, Smith, D. L., Wyld, S. J., Miller, E. L., and Wright, J. E., in press, Progression and timing of Mesozoic southern Owens Valley area, east-central California: Geological Society of America Abstracts crustal shortening in the northern Great Basin, western U.S.A., in Dunne, G., and McDougall, K., with Programs, v. 23, p. A248-A249. eds., Mesozoic paleogeography of the western United States: Pacific Section SEPM (Society for Dunne, G. C., Moore, S. C., Gulliver, R. M., and Fowler, J., 1983, East Sierran thrust system, eastern Sedimentary Geology), Pacific Coast Paleogeography Symposium 2. California: Geological Society of America Abstracts with Programs, v. 15, p. 322. Smith, G., Troxel, B., Gray, C., Jr., and Von Huene, R., 1968, Geologic reconnaissance of the Slate Dunne, G. C., Saleeby, J., and Farber, D., 1991, Early synbatholithic ductile faulting in the southern Range, San Bernardino and Inyo Counties, California: California Division of Mines and Geology Sierra Nevada: New U/Pb age and geobarometric constraints for the Kern Plateau fault zone: Special Report 96,33 p. Geological Society of America Abstracts with Programs, v. 23, p. 20. Stacey, J. S., and Kramers, J. D., 1975, Approximation of terrestrial lead isotope evolution by a two- Fates, D. G., 1985, Mesozoic(?) metavolcanic rocks, northern White Mountains, California: Structural stage model: Earth and Planetary Science Letters, v. 26, p. 207-221. style, lithology, petrology, depositional setting and paleogeographic significance {M.S. thesis]: Steiger, R. H., and Jäger, E., 1977, Subcommission on geochronology: Convention on the use of decay Los Angeles, California, University of California at Los Angeles, 224 p. constants in geo- and cosmochronology: Earth and Planetary Science Letters, v. 1, p. 369-371. Fiske, R. S., andTobisch, O. T., 1978, Paleogeographic significance of volcanic rocks of the Ritter Range Stone, P., Stevens, C., and Orchard, M., 1991, Stratigraphy of the Lower and Middle(?) Triassic Union pendant, central Sierra Nevada, California, in Howell, D. G., and McDougall, K. A., eds., Mes- Wash Formation, east-central California: U.S. Geological Survey Bulletin 1928, 26 p. ozoic paleogeography of the western United States: Society of Economic Paleontologists and Tobisch, O., Saleeby, J., and Fiske, R., 1986, Structural history of continental volcanic arc rocks along Mineralogists, Pacific Section, Pacific Coast Paleogeography Symposium 2, p. 209-221. part of the eastern Sierra Nevada, California: A case for extensional tectonics: Tectonics, v. 5, Garvey, T., Dunne, G., and Fritsche, E., in press, Depositional environments and paleogeographic p. 65-94. significance of Mesozoic volcanic and volcaniclastic strata in the southern Inyo Mountains, east- Walker, J. D., and Martin, M. W., 1991, Style and timing of Middle to Late Jurassic deformation in the central California [abs.]: American Association of Petroleum Geologists Bulletin, v. 77. Mojave Desert and eastern California: Geological Society of America Abstracts with Programs, Glazner, A., 1991, Plutonism, oblique subduction, and continental growth: An example from the Mes- v. 23, p. A249. ozoic of California: Geology, v. 19, p. 784-786. Walker, J. D., Martin, M. W., Bartley, J. M., and Coleman, D. S., 1990a, Timing and kinematics of Griffis, R., 1986, Mesozoic intrusions of the Long John Canyon area, southern Inyo Mountains, in deformation in the Cronese Hills, California, and implications for Mesozoic structure of the south- Dunne, G. C., compiler, Mesozoic and Cenozoic structural evolution of selected areas, east- ern Cordillera: Geology, v. 18, p. 554-557. central California (Geological Society of America Cordilleran Section meeting guidebook, field trips 2 and 14): Los Angeles, California, California State University, p. 57-66. Walker, J. D., Martin, M. W., Bartley, J. M., and Glazner, A. F., 1990b, Middle to Late Jurassic Hanson, R. B., 1986, Geology of Mesozoic metavolcanic and metasedimentary rocks, northern White deformation belt through the Mojave Desert, California: Geological Society of America Abstracts Mountains, California [Ph.D. dissert.]: Los Angeles, California, University of California at with Programs, v. 22, p. 91. Los Angeles, 231 p. Wernicke, Brian, Axen, G. J., and Snow, J. K., 1988, Basin and Range extensional tectonics at the latitude of Las Vegas, Nevada: Geological Society of America Bulletin, v. 100, p. 1738-1757. Hanson, R. B., Saleeby, J. B., and Fates, D. G., 1987, Age and tectonic setting of Mesozoic metavol- canic and metasedimentary rocks, northern White Mountains, California: Geology, v. 15, p. 1074-1078. Harland, W. B., Armstrong, R. L., Cox, A. V., Craig, L. E., Smith, A. G., and Smith, D. G., 1990, A geologic time scale 1989: Cambridge, England, Cambridge University Press, 263 p. Kistler, R. W., in press, Jurassic intrabatholithic faulting, Sierra Nevada, California, in Dunne, G., and MANUSCRIPT RECEIVED BY THE SOCIETY MAY 12,1992 McDougall, K., eds., Mesozoic paleogeography of the western United States: Pacific Section REVISED MANUSCRIPT RECEIVED JANUARY 12,1993 SEPM (Society for Sedimentary Geology), Pacific Coast Paleogeography Symposium 2. MANUSCRIPT ACCEPTED JANUARY 19,1993

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