Jurassic magmatism and sedimentation in the Palen Mountains, southeastern California: Implications for regional tectonic controls on the Mesozoic continental arc Benjamin N. Fackler-Adams* Department of Geological Sciences, University of California at Santa Barbara, Cathy J. Busby Santa Barbara, California 93106 James M. Mattinson } ABSTRACT Our stratigraphic data also document a INTRODUCTION locally interfingering contact between the Stratigraphic and geochronologic data from Dome Rock sequence and the overlying Jurassic strata in the Palen Mountains, south- three regionally extensive Mesozoic strati- McCoy Mountains Formation, the chrono- eastern California (Fig. 1A), record the local ini- graphic units exposed in the Palen Mountains, stratigraphic extent and tectonic significance tiation, development, and demise of continental California, provide constraints on (1) the dura- of which are controversial. We have dated arc magmatism. These volcanic rocks have previ- tion of supermature craton-derived sedimen- three units along and below this contact: (1) a ously been loosely determined by regional litho- tation within the Jurassic magmatic arc, green ignimbrite concordantly overlain by (2) stratigraphic correlations as Middle to Late Juras- (2) the timing of cessation of Jurassic magma- a pink ignimbrite capped by a pink nonwelded sic in age (Reynolds et al., 1987; 1989; Tosdal et tism in southeastern California, and (3) plate- tuff, and (3) a pink plug-dome complex that in- al., 1989). The volcanic rocks are underlain by margin scale correlation of siliciclastic units trudes the pink ignimbrite and the dome talus eolian quartz arenite, and overlain by the thick that record the initiation of Gulf of Mexico rift- of which interfingers with the pink tuff. The siliciclastic McCoy Mountains Formation (Figs. related sedimentation. These three regionally dome talus also interfingers with maroon silt- 1 and 2). The ages, and therefore tectonic signif- extensive units occur as a 7.5-km-thick con- stone, a unit that is regionally typical of the icance, of these regionally extensive units have formable succession in the Palen Mountains, basal McCoy Mountains Formation. The U-Pb been controversial. We document contact rela- consisting dominantly of (1) eolian quartzose zircon dates of the green ignimbrite and the tions among these units through detailed facies sandstone (upper member of the Palen forma- pink ignimbrite overlap within error (155 ± 8 analysis of volcanic, volcaniclastic, and sedimen- tion), (2) silicic volcaniclastic rocks and asso- Ma and 162 ± 3 Ma, respectively). U-Pb data tary rocks. This analysis, together with U-Pb ciated plugs and domes (Dome Rock se- for zircon fractions from the plug-dome zircon dating of key volcanic units, constrains quence), and (3) terrigenous sedimentary complex do not further constrain the age of the both the nature and duration of volcanism in this rocks (McCoy Mountains Formation). upper Dome Rock sequence, due to complex segment of the Jurassic arc and the ages of the Our data constrain the age of the eolian inheritance and lead loss, but are consistent underlying and overlying sedimentary strata. The quartz arenite (upper Palen formation) to with the other dates. Taken together, these data results of this work permit tectonic reconstruc- Middle to latest Early Jurassic time (Toarcian demonstrate that the lowermost McCoy tions of interactions between the subduction to Bathonian) because its upper part is locally Mountains Formation is late Middle to early margin of western North America and the rift interbedded with the basal Dome Rock Late Jurassic (Bathonian to Oxfordian) in age. margin of the Gulf of Mexico–Atlantic realm. sequence, which we have dated as 174 ± 8 Ma A late Middle to early Late Jurassic age for Eolian quartz arenite at the lower part of the (U-Pb zircon). This age for the eolian quartz the lower unit of the McCoy Mountains Palen Mountains section has been previously cor- arenite suggests that potentially correlative Formation supports the previous interpreta- related with the Lower Jurassic Navajo Sand- Middle Jurassic cratonal rocks on the present- tion that development of the extensional- stone on the basis of composition and strati- day Colorado Plateau include the Page Sand- transtensional McCoy basin (southeastern graphic position (Marzolf, 1980; LeVeque, 1982; stone, eolian parts of the Carmel Formation, California and western Arizona) and the Bisbee Hamilton, 1987; Tosdal et al., 1989). The unusual and the Temple Cap Sandstone, all of south- basin (southeastern Arizona) was broadly association of supermature craton-derived quartz western Utah and northern Arizona. Correla- coeval, within the limits of sparse isotopic data arenites with volcanic and volcaniclastic rocks tion with the Navajo Sandstone can not be in southeastern Arizona, and was the result of has long been recognized in the Mesozoic arc of precluded, although this seems unlikely rifting during opening of the Gulf of Mexico. southwestern North America (Miller and Carr, because one must assume the maximum error We suggest that the much more abrupt vol- 1978; Bilodeau and Keith, 1979, 1984, 1986; on both the U-Pb zircon age and the uncer- canic to sedimentary transition in southeastern Marzolf, 1980). Wright et al. (1981) reported a tainties on the stage boundaries to obtain an California, relative to that recorded in south- U-Pb zircon date of 190–195 Ma from arc vol- overlap of only 1 m.y. ern Arizona, may reflect a greater component canic rocks intercalated with eolian quartz aren- of strike-slip faulting relative to extension in a ite in the Baboquivari Mountains of southeastern regionally transtensional regime. We speculate Arizona. On the basis of this date, Bilodeau and *e-mail: [email protected] that this resulted from along-strike variation in Keith (1986) correlated eolian quartz arenites in plate-margin orientation. several southern Arizona ranges with the Lower GSA Bulletin; November 1997; v. 109; no. 11; p. 1464–1484; 13 figures; 3 tables. 1464 MAGMATISM AND SEDIMENTATION IN THE PALEN MOUNTAINS ° A ° BS 115 114 CALIFORNIA CX ARIZONA GR LM Fig.1B BM GW HQ PA PM Figure 1. (A) Shaded areas show uplifted NV MC Q LHQ Tertiary and older basement. B—Blythe, Q— Las B I-10 Quartzsite. Localities referred to in the text in- Vegas DR I-10 clude: DR—Dome Rock Mountains, LH— CA AZ BRH 33°30' Livingston Hills, MC—McCoy Mountains, Fig.1A PA—Palen Mountains. Other ranges that N TP LH K Phoenix contain relevant rocks (Palen formation, PV TM 0 10 20 30 km Dome Rock sequence, McCoy Mountains For- mation) include: BM—Big Maria Mountains, BRH—Black Rock Hills, BS—Buckskin B EXPLANATION 50 Mountains, CX—Coxcomb Mountains, GR— 00' Figure 3 ° Jmms- Lower McCoy Granite Mountains, GW—Granite wash 1 kilometer 115 Mountains Fm, dominantly Mountains, HQ—Harquahala Mountains, 70 Cretac. Jurassic- sandstone PA-17 K—Kofa Mountains, LM—Little Maria Mountains, PM—Plumosa Mountains, PV— Jdr3-Rhyolite ignimbrite, lava, Palo Verde and Mule Mountains, TM—Trigo & hypabyssal Mountains, TP—Trigo Peak. Location of map rocks in B is shown by box. The inset shows the loca- Jdr1 & Jdr2- Rhyo- tion of A and the regional distribution of dacite tuffs w/ lesser intrusions Jurassic supracrustal arc rocks in south- & tuffaceous Jurassic western North America (hachured; after Dome Rock Sequence sedimentary rocks Busby-Spera, 1988). (B) Generalized geologic Jp - map of the Palen Mountains (after Stone and 65 q Upper Palen Fm., dominantly quartz Pelka, 1989). The map shows the distribution arenite of major rock types and the locations of U-Pb Palen Fm. zircon samples (PA-17, PA-19, PA-12, and Undifferentiated PA-8). The locations of lithofacies maps in Fig- sedimentary rocks PA-19 ures 3 and 7 are shown by boxes. Jurassic Triassic or 40 50 PA-17 U-Pb zircon sample PA-12 PA-8 35 Contact 60 Fault 45 ° 20 Strike & dip of 33 49' bedding or pumice 20 foliation & of over- 50 40 Figure 7 turned bedding 33°48' Jurassic Navajo Sandstone of the Colorado volcanic rocks and eolian quartz arenite and dominantly fluvial siliciclastic unit, as thick as Plateau and its western continuation, the Aztec dated the volcanic rocks as late Middle Jurassic 8 km, exposed in southeastern California and Sandstone. Because this lithologic association is using the U-Pb zircon method. These new data western Arizona (Harding and Coney, 1985; so unusual, workers have subsequently correlated further strengthen the hypothesis that the Jurassic Dickinson et al., 1986, 1987). Until recently, the all supermature quartz arenites interstratified arc acted as a depocenter for supermature craton- age and therefore the tectonic setting of the with Jurassic arc volcanic rocks in California and derived sands throughout much of Jurassic time McCoy Mountains Formation have been poorly Arizona with the Navajo Sandstone (see refer- (Busby-Spera, 1988). constrained. Paleomagnetic data were interpreted ences in Busby-Spera et al., 1990a). Recent U-Pb The McCoy Mountains Formation is another by Harding et al. (1983) to indicate a pre-Late zircon dating of volcanic rocks with interstrati- poorly understood component in the Mesozoic Jurassic age for the McCoy Mountains Forma- fied sandstones, however, indicates that deposi- regional stratigraphic framework of the south- tion. This interpretation was considered invalid tion of supermature sandstones within the Juras- western Cordillera. It is important because it for reasons elaborated by Stone et al. (1987) and sic arc spanned