Miogeocline Extends Into CA on NNE-SSW Trend but Then Vanishes—But Very Similar Rocks Show up in Caborca, Mexico

210 J.H. Stewart

INTRODUCTION one, Neoproterozoic to Triassic rocks wrap around the Lau- rentian (ancestral North American) continental margin with The Mojave-Sonora megashear was proposed by Silver and only minor, if any, lateral structural displacement. In the other, Anderson (1974), Anderson and Silver (1979, 1984), and Ander- the Laurentian margin is truncated by major left-lateral offset son and Schmidt (1983) as a Middle or Late Jurassic left-lateral along the proposed Mojave-Sonora megashear (Stewart et al., fault that displaced Paleoproterozoic and Mesoproterozoic crys- 1984). Debate between proponents of these two ideas has been talline basement rocks from southeastern California to Sonora. lively, and no consensus has been reached concerning which As a part of their original proposal, Silver and Anderson (1974) of the two models is correct. Discussions emphasizing one or noted “intriguing similarities” between Cambrian strata in the the other of the two ideas include Silver and Anderson (1974, Inyo Mountains in eastern California on the northeast side of the 1983), Anderson and Silver (1979, 1984), Dickinson (1981) fault and in the Caborca area in northern Sonora on the southeast Anderson and Schmidt (1983), Stewart et al. (1984), Cohen et side of the fault. They used this similarity to suggest an offset of al. (1986), Ketner (1986), Jacques-Ayala et al. (1991), Anderson 700–800 km along the proposed megashear. Since the original et al. (1991, 1995), Stevens et al. (1992), Sedlock et al. (1993), work of Silver and Anderson, much has been learned about the DeJong and Jacques-Ayala (1993), Bartolini (1993), Stanley Neoproterozoic and Paleozoic stratigraphy in the western United and González-León (1995), Poole et al. (1995a, 1995b, 1991, States and Sonora that bears on the “intriguing similarities” of the 2000a), Marzolf and Anderson (1996, 2000), Anderson (1997), rocks possibly offset by the proposed fault. This paper summa- Marzolf (1997), Caudillo-Sosa et al. (1996), González-León rizes this new information and interprets the data as supporting (1997a, 1997b), Campbell and Anderson (1998), Molina-Garza the original idea of the Mojave-Sonora megashear. and Geissman (1998, 1999), Iriondo et al. (1998), Iriondo Two different models of the Neoproterozoic to Triassic (2001a, 2001b), Stewart et al. (1990, 1997, 1999), Dembosky et continental margin of the western United States and northern al. (1999), Poole and Amaya-Martínez (2000), and Dickinson Mexico have been proposed (Stewart et al., 1984) (Fig. 1). In and Lawton (2001).

118° 114° 110°

NEVADA

COL

UTA 38° ORA

NEW MEXICO ARIZONA

CALIFORNIA

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Peninsular Ran UNITE D STATE MEXICO S

SONORA

PACIFIC OCEAN ges GULF OF CALIFORNIA

BAJA CAL 32° NORTE IFOR 0 200 KM NIA 0 200 KM A B 118° 114° 110° EXPLANATION Cordilleran miogeocline Trend of Cordilleran miogeocline Mojave-Sonora megashear, arrows show relative movement Figure 1. Wraparound and Mojave-Sonora megashear models of Neoproterozoic and Paleozoic rocks in the western United States and northwest Mexico.

Stewart, GSA SP 393, 2005

Miogeocline extends into CA on NNE-SSW trend but then vanishes—but very similar rocks show up in Caborca, Mexico. Which geometry is right? 220 J.H. Stewart

120° 115° 110° 105° 100°

Oregon California Idaho Nevada

40°

Utah Colorado Arizona New Mexico WMD 35°

GM Peninsular Ranges EC United States Figure 12. Distribution of Cordilleran mio- Mexico M Pacific Ocean SM geocline in the western United States and 30° northwest Mexico.

CSF BCN Gulf Texas BCS Sonora Of 0 500 Km. California Explanation Neoproterozoic and Paleozoic Cordilleran miogeocline

Paleozoic continental cover strata

Ouachita orogenic belt

Trend of Cordilleran miogeocline Mojave-Sonora megashear. Position of megashear is not corrected palinspastically for post-Late Jurassic structural dislocations. See text for discussion of location of megashear. Arrows show relative motion. Central Sonora fault (CSF), arrows show relative motion Symbols: BCN, Baja California Norte; BCS, Baja California Sur; EL, El Capitán; GM, Gila Mountains; SB, San Bernardino Mountains; WMD, western Mojave Desert Stewart, GSA SP 393, 2005

commonly considered to have been deposited in deep water against, miogeoclinal strata in the Permian or Early Triassic. As west of the miogeoclinal belt and to have fringed the western described previously, no evidence of the Antler orogeny has been margin of ancestral North America. Transport along thrust faults described in Mexico, and the relation of a continuous succession emplaced these strata over miogeoclinal strata of ancestral North of siliceous strata unbroken by a thrust comparable to the Roberts America. The history of emplacement is complex. In Nevada, Mountains thrust is indicative of the difference in tectonic history the fi rst emplacement took place during the Late Devonian to between Nevada and Mexico. Early Mississippian Antler orogeny, when Ordovician to Devo- Ordovician to Devonian deep-water siliceous rocks of the nian strata were transported along the Roberts Mountains thrust Roberts Mountains allochthon and comparable age strata in the over miogeoclinal strata. Renewed offshelf deep-water deposi- Sonora allochthons (Fig. 13) consist of relatively deep-water tion took place in Nevada in the Pennsylvanian and Permian, marine strata originally deposited along the Laurentian conti- and these rocks were in turn emplaced over miogeoclinal strata nental margin outboard of the Cordilleran miogeocline (Madrid during the Late Permian to Early Triassic Sonoma orogeny. The et al., 1992b). The rocks consist of complexly deformed radio- history of emplacement in Mexico is different. Here Ordovician larian chert, graptolitic shale, quartzite, feldspathic sandstone, to Permian deep-water siliceous strata are in a continuous sedi- siltstone, minor mafi c lava fl ows, bedded tuff, limestone, and mentary succession that was emplaced over, or transpressionally bedded barite (Poole et al. 1991, 1995b; Madrid et al., 1992b; Systematic left-lateral offset of strata and facies 213 Systematic left-lateral offset of strata and facies 213 120° 118° 116° 114° 112° 110° 100° 112° 110°

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CALI0 34° Gulf FOR CALI Sonora NIA Gulf FOR of Sonora NIA BAJ UNITED ST 32° Sahuaripa CALIFO NORTE of Hermosillo shelf Inner A ATE 29° MEXI S California

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H RNIA CO C 0 100 Kilometers UA 30° PACIFIC RNI GUL HI ? C ALIFO H EXPLANATION OCEAN A F SONORA U

20 OF 100 0? A 100 Continental cover strata 0 0 100 200 300 400RNIA KM H 0 100 Kilometers UA 30° Thin miogeoclinal Lower Cambrian strata unconformably above EXPLANATION Neoproterozoic RodinianEXPLANATION strata. No miogeoclinal Outcrop of Lower Cambrian Proveedora Quartzite or Neoproterozoic strata are present 20 Zabriskie Quartzite (includes a few outcrops of100 Lower0? Cambrian 100 Continental cover strata 0 0 100 200 300Harkless 400 KM Formation in Nevada and California that contain quartzite Neoproterozoic and Lower Cambrian miogeoclinal strata of equivalent to Zabriskie Quartzite ArituabaThin miogeoclinal area. Contains Lowerstrata correlative Cambrian with strata Caborca unconformably area, above EXPLANATION but thinnerNeoproterozoic Rodinian strata. No miogeoclinal Outcrop of LowerMojave-Sonora Cambrian megashear. Proveedora Postion Quartzite of megashear or is not corrected palinspastically for post-Late Jurassic structural dislocations. See Thick Neoproterozoic Neoproterozoic and strata Lower are Cambrian present miogeoclinal strata Zabriskie Quartzite (includes a few outcrops of Lower Cambrian of Caborca area consisting dominantly of dolomite, siltstone text for discussion of location of megashear. Arrows show relative Neoproterozoic and Lower Cambrian miogeoclinal strata of Harkless Formationmotion. in Nevada and California that contain quartzite and quartzite equivalent to Zabriskie Quartzite ThickArituaba Neoproterozoic area. Contains and Lower strata Cambrian correlative miogeoclinal with strata Caborca area, 0 10 Isopach line, thickness in meters ofbut Sierra thinner del Viejo. Composed predominantly of dolomite Mojave-Sonora megashear. Postion of megashear is not corrected Control point palinspasticallyFigure 4. Distribution for post-Late and Jurassic thickness structural of Lower dislocations. Cambrian Zabriskie See Thick Neoproterozoic and Lower Cambrian miogeoclinal strata text forQuartzite discussion in California of location and ofNevada megashear. and of theArrows correlative show Proveedorarelative Lineof Caborca separating area lithologic consisting facies dominantly of dolomite, siltstone motion.Quartzite in Sonora. Based on Stewart (1970) and Stewart et al. (1984). and quartzite Mojave-SonoraThick Neoproterozoic megashear, andarrows Lower show Cambrian miogeoclinal strata 0 10 Isopach line, thickness in meters ofrelative Sierra movement del Viejo. Composed predominantly of dolomite Figure 4. Distribution and thickness of Lower Cambrian Zabriskie Figure 5. FaciesControl trends pointof Neoproterozoic and Lower Cambrian strata trending miogeoclinal belt, but not with a wraparound margin in Quartzite in California and Nevada and of the correlative Proveedora in Sonora. Based on data in Stewart et al. (2002). which the inner shelf deposits are on the north and the outer shelf Line separating lithologic facies Quartzite in Sonora. Based on Stewart (1970) and Stewart et al. (1984). Stewart, GSA SP 393, 2005 deposits are on the south. Mojave-Sonora megashear, arrows show relative movement MIDDLE AND UPPER CAMBRIAN MIOGEOCLINAL shale and siltstone, lime mudstone, oolitic limestone, algal-bound Right plot suggests that miogeocline trend in CaborcaSTRATA also cut of. limestone, and oncoid limestone. The Buelna, Cerro Prieto Forma- Figure 5. Facies trends of Neoproterozoic and Lower Cambrian strata trending miogeoclinal belt, but not with a wraparound margin in tion, and Arrojos are lithostratigraphically similar to the Carrara Middle and Upper Cambrian miogeoclinal strata consist inFormation Sonora. andBased contain on dataa trilobite in Stewart fauna etcorrelative al. (2002). to that in the which the innermostly shelf of thick deposits carbonate are successionson the north (Stewart and theand outerSuczek, shelf 1977; Carrara Formation. The Carrara and the Cerro Prieto Formations deposits are onStewart, the south. 1991; Palmer and Hintze, 1992; Stewart et al., 2002). both contain distinctive oncoid limestone. The distinctive stratig- They extend from Idaho, south to eastern California, into the raphy of the Carrara Formation is found only in eastern California MIDDLE ANDSan Bernardino UPPER Mountains,CAMBRIAN and then, MIOGEOCLINAL south of a 600-km gap in shaleand southern and siltstone, Nevada, and lime in themudstone, correlative oolitic Buelna, limestone, Cerro Prieto, algal-bound STRATA outcrops, into northwest Sonora (Fig. 6). Correlation of speciﬁ c limestone,and Arrojos and Formations oncoid inlimestone. Sonora. This The similar Buelna, stratigraphy Cerro Prieto is Forma- units is restricted to the lowermost part of the Middle and Upper suggestive of offset of one to the other. Strata above the Carrara Cambrian succession including the upper part of the Lower Cam- tion,Formation and inArrojos eastern Californiaare lithostratigraphically and southern Nevada similar are assigned to the Carrara Middle brian and succession. Upper Cambrian These rocks miogeoclinalconsist of the Carrara strata Formation consist in Formationto the thick carbonate and contain succession a trilobite of the Bonanza fauna Kingcorrelative Formation. to that in the mostly of thickeastern carbonate California successions and southern (StewartNevada (Palmer and Suczek, and Halley, 1977; 1979) CarraraThe incompletely Formation. exposed The Tren Carrara Formation and in the Sonora Cerro is correlated Prieto Formations Stewart, 1991;and Palmerof the correlative and Hintze, combined 1992; Buelna, Stewart Cerro Prieto, et al., and 2002). Arrojos bothwith thecontain Bonanza distinctive King Formation. oncoid Correlations limestone. of Cambrian The distinctive strata stratig- Formations in northeast Sonora (Cooper et al., 1952; Palmer, 1981; younger than the Tren Formation in Sonora are sketchy and uncer- They extendStewart from et Idaho, al., 1984, south 2002). to Theeastern Carrara California, Formation intoconsists the of raphytain (Stewart of the et Carrara al., 1990, Formation 2002). is found only in eastern California San Bernardino Mountains, and then, south of a 600-km gap in and southern Nevada, and in the correlative Buelna, Cerro Prieto, outcrops, into northwest Sonora (Fig. 6). Correlation of speciﬁ c and Arrojos Formations in Sonora. This similar stratigraphy is units is restricted to the lowermost part of the Middle and Upper suggestive of offset of one to the other. Strata above the Carrara Cambrian succession including the upper part of the Lower Cam- Formation in eastern California and southern Nevada are assigned brian succession. These rocks consist of the Carrara Formation in to the thick carbonate succession of the Bonanza King Formation. eastern California and southern Nevada (Palmer and Halley, 1979) The incompletely exposed Tren Formation in Sonora is correlated and of the correlative combined Buelna, Cerro Prieto, and Arrojos with the Bonanza King Formation. Correlations of Cambrian strata Formations in northeast Sonora (Cooper et al., 1952; Palmer, 1981; younger than the Tren Formation in Sonora are sketchy and uncer- Stewart et al., 1984, 2002). The Carrara Formation consists of tain (Stewart et al., 1990, 2002). 216 J.H. Stewart SystematicSystematic left-lateral left-lateral offset offset of of strata strata and and faciesfacies 215 215 Poole and Sandberg, 1977, 1991; Miller et al., 1992). The Antler 125° 120° 115° 110° 125° 125° 120°120° 115° 110° allochthon115° (Fig. 9)110° is composed of ocean-basin125°125° 120°siliceous 120° strata115°115° 110°110° 45° 45° and was emplaced eastward45° above Devonian and older Paleozoic 45°45° WYOMING IDAHOIDAHO

OREGONOREGON miogeoclinal strata producing the Antler orogenic highland. This AND

0 0

WYOMINGWYOMING OREGONOREGON IDAHOIDAHO OREGON H

10 highland fed10 coarse to ﬁ ne clastic material into the Antler trough 200 200 0 0 IG to the east. East of this trough is a basin of largely shale, and to the WYOMINGWYOMING H NEVADANEVADA NEVADA NEVADANEVADA IC 500 500 east of this is limestone along the eastern part of the miogeocline. The Mississipian stratigraphy and structure of miogeoclinal GEN UTAHUTAH UTAHUTAH 40°40° 40° 40° ORO 40° strata in Sonora0 0 is signiﬁ cantly different from that in the western

100 R UTAH 100 CA United States. In Sonora, Mississipian miogeoclinal strata are CA LE L 0 L IFO 0 CALIFORNIA CALIFORNIA NT IFO mostly limestone (Stewart et al., 1997, 1999; Poole et al., 2000b; SIER CALIFORNIA R A R NI N NI A Stewart and Poole, 2002). No Antler orogenic highland, no E RA A ARIZONA V 100 ARIZONA A 100 coarse to fi ne Antler trough strata, and no shale-basin strata are DA 100 ARIZONA 100 0 recognized. The known 35°record of the Antler orogeny is largely ARIZONA EP PK 0SB 35° SB 35° ? ARIZONA 35° SB confi ned to easternmost California, Nevada, and southernSB Idaho. MD SM ? 35° SB UNIOutcrops of Mississippian strata in Sonora are sparse, and BAJA CAL TE UN UNI D STA BAJA CALIF ITED BAJA CAL conceivably,TE TE strata related to the Antler orogeny are covered—orUN STATE D STA S BAJA CALIF ITED TE STATES GULF S if they are present, they have not been discovered. Another possi-GULF OF S UNI IFORNIA NOR TED ST GULF MEX ME BAJA C GULF OF XIC RB ICO OR RB O IFORNIA NOR OF M ATE bility is that170 theMEX strata related30° to the Antler orogeny originally lay EX S RB ICO ORN CCA IC 30° Pacific Ocean OF CALI SL IA RB O 30° Pacific Ocean CAL 170 N NO CCA 30° A G west of CALI known98 outcrops of Mississippian strata in Sonora. In this Pacific Ocean SL IA LIF UL MEX F RP CC Pacific Ocean CALIFORNIA RP SAV TE ORNI NOR ICO 98 132 TE ORNIA N F case, theF MississippianSONORACC carbonate strata of Sonora could be an IFORNIA RP SAV O TE ORNI RP R SONORA A 132 TE 30° Pacific Ocean F offset segmentSONORA of Mississippian strata that lay east of the Antler SONORA C RP A AL OR 0 500 1000 Kilometers IF belt in eastern California. 0 500 1000 Kilometers T O E R SONORA 0 500 1000 Kilometers N EXPLANATION A further possibility, an idea favored0 here, is500 that strata 1000 Kilometers IA EXPLANATION EXPLANATIONrelated to the Antler orogeny died out southward in eastern Cali- Ordovician miogeoclinal strata Zone of unconformableEXPLANATION overlap of Devonian strata over Silurian and Ordovician strata. Dashed where inferred. 100OrdovicianIsopach miogeoclinal of Middle Ordovician stratafornia Eureka and Quartzite never andexisted equivalent in Sonora (Fig.Zone 2) of (Pooleunconformable et al., overlap 2000a). of Devonian strata over0 Silurian and 500 1000 Kilometers strata in western United States, thicknesses in meters. The 100 Isopach of Middle OrdovicianSuch Eureka a Quartzitepossibility and isequivalent supported by the OrdovicianapparentSilurian and strata. absence Devonian Dashed of miogeoclinal whereAntler inferred. strata Eureka and other Ordovician strata are absent in the Paleozoic EXPLANATION stratain in the western Paleozoic United succession States,strata of thicknesses the in San Sonora. Bernardino in meters. A fairly The complete sectionSilurianMojave-Sonora of and Devonian Devonian megashear. and miogeoclinal Mis-Position of strata megashear is not corrected EurekaMountains and other (SBM) Ordovician strata are absent in the Paleozoic palinspastically for post-Late Jurassic structural Mississippiandislocations. See limestone and sandy limestone in the Paleozoic succession ofsissippian the San Bernardino strata close to the presumed westernMojave-Sonoratext for discussion margin megashear. of of location the Mis-Position of megashear. of megashear Arrows isshow not relativecorrected 98MountainsThickness (SBM) in meters of Middle Ordovician Peña Blanca Quartzite palinspasticallymotion. for post-Late Jurassic structuralMississippian dislocations. See fine-grained sandstone, siltstone, and mudstone in Sonora sissippian shelf at Rancho PlaceritosLocalities: intext Sonora for CCA, discussion Cerro (Fig. Carnero; of9) location (Poole RB, Rancho of etmegashear. Bízani; RP, Arrows Rancho show Placeritas; relative 98 Thickness in meters of Middle Ordovician Peña Blanca Quartzite Mojave-Sonora megashear. Position of megashear is not corrected SAV, motion.Sierra Agua Verde; SB, San Bernardino Mountains in Sonora al., 2000b) does not contain coarse clastic strata that could have Mississippian conglomerate, medium- to coarse-grained sandstone, palinspastically for post-Late Jurassic structural dislocations. See Localities: CCA, Cerro Carnero; RB, Rancho Bízani; RP, Rancho Placeritas; SAV, Sierra Agua Verde; SB, San Bernardino Mountainsand siltstone Mojave-Sonoratext for discussion megashear. of location Positionbeen of megashear. ofderived megashear fromArrows is not ashow continuationcorrected relative Figure of the 8. AntlerDistribution highland. of Silurian and Devonian miogeoclinal strata in palinspasticallymotion. for post-Late Jurassic structural dislocations. See Mojave-Sonora megashear. Position of megashear is not corrected The location of the changethe from western areas United containing States and indica-northwestern Mexico. Based on Poole Localities:text for discussionCC, Cerro Cobachi;of location RB, of Rancho megashear. Bízani; Arrows RP, Rancho show Placeritos;relative Figure 8. Distribution of Silurian and Devonian miogeoclinalpalinspastically strata for in post-Late Jurassic structural dislocations. See SB,motion. San Bernardino Mountains;tions SL, Sierra of theLopez Antler orogeny to thoseet al. (1977),that do Poole not is and problematic. Sandberg (1977, 1992a, text 1992b), for discussion Sandberg of location of megashear. Arrows show relative the western United States and northwestern Mexico. Based on Poole Localities: CC, Cerro Cobachi; RB, Rancho Bízani; RP, Rancho Placeritos; and Poole (1992a, 1992b), Sheehan and Boucot (1991),motion. Johnson et al. The southward track of the beltet through al. (1977), Nevada Poole andis well Sandberg defi ned (1977, 1992a, 1992b), Sandberg SB,Figure San 7.Bernardino Distribution Mountains; and thickness SL, Sierra of Ordovician Lopez miogeoclinal strata (1991), Poole et al. (1997, 1998, 2000a, 2000b), Stewart et al. (1997), from structural and sedimentaryandand Poole Stewart data (1992a, (Poole and Poole 1992b), and (2002). Sheehan Sandberg, and Boucot (1991),Localities: Johnson EP, El et Pasoal. Mountains; PK, Pilot Knob Valley; in the western United States and northwestern Mexico. Based on Ross MD, Mojave Desert; RP, Rancho Placeritos; Figure(1977), 7. Distribution Ross et al. and(1991, thickness 1992), Pooleof1991). Ordovician and Where Sandberg miogeoclinal the (1992a), belt Poole entersstrata et California,(1991), Poole its et outcropal. (1997, width 1998, 2000a,less- 2000b), Stewart et al. (1997), and Stewart and Poole (2002). SB, San Bernardino Mountains; SM, Shadow Mountains in theal. western (1995a), United and Stewart States andand Poole northwesternens (2002). and Mexico. recognition Based on of Ross structures related to the belt are less (1977), Ross et al. (1991, 1992), Poole and Sandberg (1992a), Poole et Stewart, GSA SP 393, 2005 certain, although Schweickert and Lahren (1987) and Greene et al. (1995a), and Stewart and Poole (2002). the zone of Devonian truncation. In theFigure San Bernardino 9. Distribution Moun- of Mississippian miogeoclinal and foreland- al. (1997) have described what tains,they noconsider outcrops to of be Ordovician the Roberts or Silurian basin strata strata are known, in the westernand United States and northwestern Mexico. lying rocks and overlap of DevonianMountain strata allochthonis similar to relations emplaced theDevonian during zone of thestrata Devonian Antler rest unconformably truncation. orogeny inIn onthe BasedCambrian San Bernardinoon Poolestrata, (1974),a Moun- rela- Poole and Sandberg (1977, 1991), Miller et in the western United States the where eastern Devonian part strataof the along Sierra the Nevadatains,tion correspondingno in outcrops easternmost of to Ordovician areas California. east ofor theSilurian zoneal. (1992), ofstrata truncation. are and known, Stewart and and Poole (2002). In the western United States, distribution and facies patterns are of Upper Mississippian strata, lyingeastern rocks and margin overlap of the of CordilleranDevonianSouth strata miogeocline of isthese similar outcrops, unconformably to relations the only Devonian possible strata record rest unconformablyof the Antler on Cambrian strata, a rela- modifi ed from Figures 9 and 10 of Poole and Sandberg (1991). in theoverlap western Ordovician United States and Silurian whereorogeny strata Devonian isand in reststrata the on Elalong Cambrian Paso the Mountains, tionMISSISSIPPIAN corresponding the Pilot toMIOGEOCLINAL areas Knob east Valley of the zone STRATA of truncation. AND THE easternstrata margin in areas of to thethe east Cordilleran (Gans,area, 1974; miogeocline and Hills the and Shadow Kottlowski, unconformably Mountains 1983; ANTLER in the Mojave OROGENIC Desert BELTregion of overlapHintze, Ordovician 1988). Outcrops and Silurian in Sonorasouthern strata are and not California restcomplete on Cambrian(Fig. enough 9). to In MISSISSIPPIANthe El Paso Mountains, MIOGEOCLINAL no defi ni- STRATA AND THE expose the presumed depositional relations of Devonian strata The onset of the Late Devonian and Early Mississippian strata in areas to the east (Gans, 1974;tive Hills structural and Kottlowski, record of 1983; the Antler ANTLER orogeny OROGENIC has been recognized, BELT unconformably on Cambrian strata. Outcrops of Paleozoic strata Antler orogeny led to a marked change in the sedimentary and Hintze, 1988). Outcrops in Sonoraand are pre-Mississippian not complete enough and toMississippian and younger Paleozoic syngenetic deposits related to the Antler orogeny. In the Shadow exposein the the San presumed Bernardino depositional Mountains relations provide controlof Devonian on the trendstrata of structuralThe onset setting of ofthe the Late western Devonian United and States Early (Poole, Mississippian 1974; strata contain deformational fabrics similar to each other (Carr et Mountains, Poole (1974) similarly has interpreted clastic strata unconformably on Cambrian strata. Outcrops of Paleozoic strata Antler orogeny led to a marked change in the sedimentary and in the San Bernardino Mountains al.,provide 1997). control However, on the trendPoole of (1974) structural and Carr setting et al. of the(1992, western 1997) United as Antler States (Poole,foreland 1974; basin deposits, although Martin and Walker interpret clastic strata of Early and Late Mississippian age in the (1991) have argued against this interpretation and doubt that Ant- El Paso Mountains as foreland-basin deposits derived from the ler belt rocks exist in the Shadow Mountains. Antler orogenic highland. In the Pilot Knob Valley area, Carr The Antler orogenic belt may die out somewhere south of et al. (1992) interpret metaconglomerate and metaargillite as outcrops in the eastern Sierra Nevada. However, if the inter- Downloaded from specialpapers.gsapubs.org on January 31, 2010

The Pennsylvanian–Early Permian Bird Spring Carbonate Shelf 5

124o 122o 120o 118o 116o 114o 112o 110o 108o

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122o 120o 118o 116o 114o 112o 110o 108o Figure 3. Map showing paleogeographic setting of the Bird Spring Shelf on the late Paleozoic continental margin of southwestern United States. In California, paleogeographic features are offset by the Mesozoic Intrabatholithic BreaksStevens 2 and 3 (IBB2, and IBB3)Stone, and byGSA the Ceno SPzoic 429, San An-2007 dreas, Garlock, and Death Valley–Furnace Creek (DVFCF) Faults. Modiﬁ ed from Stevens (1982), Miller et al. (1992), and Stevens et al. (1992).

1962) have not gained general acceptance. Shelf carbonate strata The seven outcrop areas represented in this study provide a equivalent to parts of the Bird Spring Formation are represented regional transect across the Bird Spring Shelf in California. From by the Callville Limestone (Longwell, 1928) and Pakoon Lime- southeast to northwest, these areas are (1) the Ship Mountains, stone (McNair, 1951) in southeasternmost Nevada, northwestern (2) the Providence Mountains, (3) Old Dad Mountain, (4) Cow- Arizona, and southwestern Utah, and by the Tippipah Limestone hole Mountain, (5) Striped Butte and (6) nearby Warm Spring (Johnson and Hibbard, 1957) in southwestern Nevada. Canyon in the southern Panamint Range, and (7) Panamint Butte In southeastern California, early geologic mapping and strati- in the southern Cottonwood Mountains (Fig. 1). Outcrop areas graphic studies (e.g., Hazzard, 1937, 1954; Hewett, 1956) showed not considered for this study include Marble Canyon in the cen- that the Bird Spring Formation occurs in several widely separated tral Cottonwood Mountains (Stone, 1984) and the Nopah Range ranges in the Mojave Desert region. The formation is now rec- (Hazzard, 1937; Burchﬁ el et al., 1982), where fusulinids are rare ognized as far south as the San Bernardino Mountains (Brown, and the Bird Spring Formation does not extend into the Permian; 1991) and as far north as the Death Valley area (Panamint Range the Clark Mountain Range (Clary, 1967) and the San Bernardino and Cottonwood Mountains) (Stone and Stevens, 1984) (Fig. 1). Mountains (Brown, 1991), where only Pennsylvanian fusulinids Downloaded from specialpapers.gsapubs.org on January 29, 2010

600 C.H. Stevens, P. Stone, and J.S. Miller

Eastern

Figure 2. Index map showing Devonian facies belts, selected Paleozoic sedimentary boundaries on the continental shelf, areas interpreted to be underlain by oceanic crust, and major faults that have displaced facies belts and sedimentary boundaries. Note that in several areas rocks of the outer rise and ocean basin now are underlain by continental crust Stevens et al., because of thrusting of those facies over the continental margin. In addition, outer-rise rocks not now exposed in the Saddlebag Lake area are inferred to underlie the ocean basin facies in that area. CB—Canal Ballenas area; CM—Coy- GSA SP 393, ote Mountains; CV—Cerro El Volcán; CWf—Clemens Well fault; DV-FCfz—Death Valley–Furnace Creek fault zone; EB—El Bisani; Ef—Excelsior fault; Gf—Garlock fault; H—Hermosillo; IBB2—Intrabatholithic break 2; LVVfz—Las 2005 Vegas Valley fault zone; MVf—Mojave Valley fault; RP—Rancho Placeritos; SFf—San Francisquito fault; SGf—San Gabriel fault; SLP—Sierra Las Pinta; SVf—Stewart Valley fault; Tf—Tinemaha fault.

Today things are hacked up, but in the pieces between can divine the SSW trend possibly turning to SE in Mojave. Note the Permian-Tr plutons—will come back to those. Downloaded from specialpapers.gsapubs.org on January 31, 2010

Tihvipah ABKeel Bird Bird UM MC UM MC er

Slope PB PB PBL PBL CM CM

SRH WSC SRH WSC

Ramp SB DC Basin DC SB Spri Spri

ng ng

ATOKAN BURSUMIAN ~315 Ma ~300 Ma ? ? ? Lower Middle Upper Upper Pennsylvanian CH OD PR Pennsylvanian CH OD PR

N Shelf N Shelf

SH SH ? ? 0 25 KM ? 0 25 KM

Lone Pine Lone Pine LCTCD LCT Bird Bird UM MC UM MC

Darwin Darwin

PB PB PBL PBL CM CM SRH SRH Basin Basin Cgl Mesa Uplift WSC Cgl Mes WSC

SB Sprin SB Sprin DC DC

Basin Basin a Uplift

g g

LATE MIDDLE SAKMARIAN ARTINSKIAN ~291 Ma ~286 Ma ? ? ? ? ? ? Middle Lower CH OD PR Upper Lower OD PR Permian Permian CH N She N She

lf lf

? ? ? ? ? SH ? SH 0 25 KM 0 25 KM

Figure 12. Paleogeographic maps illustrating evolution of the Bird Spring Shelf and adjacent basins during Pennsyl- vanian and Early Permian time. (A) Atokan. (B) Bursumian. (C) Late Sakmarian. (D) Middle Artinskian. Localities Stevens and Stone, shown: CH—Cowhole Mountain; CM—Conglomerate Mesa; DC—Darwin Canyon; MC—Marble Canyon; OD—Old Dad Mountain; PB—Panamint Butte; PBL—Permian Bluff; PR—Providence Mountains; SB—Striped Butte; SH—Ship GSA SP 429, 2007 Mountains; SRH—Santa Rosa Hills; UM—Ubehebe Mine; WSC—Warm Spring Canyon. Palinspastic restorations are modiﬁ ed from Snow and Wernicke (2000). In addition, note that localities CM, PBL, and UM in (A) and (B) are in their inferred positions prior to eastward displacement in the upper plate of the Last Chance thrust (LCT) during Sakmarian time (Stevens and Stone, 2005). Keeler basin (late Penn) inferred to be extensional from truncation event, then shortening in early Permian starved Keeler/Lone Pine basin. Darwin basin interpreted as a foredeep to Conglomerate Mesa uplift. Get very tight age controls indicating LCT moved 3 mm/yr over 10 m.y. Associates extension with left-lateral fault, LCT with Penn. deformation (Pinon orogeny?) in Nevada. C.H. Stevens, P. Stone / Earth-Science Reviews 73 (2005) 103–113 111 Downloaded from specialpapers.gsapubs.org on January 31, 2010

Neoproterozoic to middle Sierra Nevada-Death Valley thrust system Paleozoic facies trends and continental margin Tihvipah ABKeel Bird Bird Late Paleozoic truncated margin UM MC UM MC (Stevens and Greene, 1999) er (Stone and Stevens, 1988) N Slope PB PB Tinemaha fault Last Chance thrust PBL PBL CM CM (Stevens and Greene, 1999) (Stevens and Stone, this volume) SRH WSC SRH WSC East Sierran thrust system Ramp SB DC Basin DC SB Spri Spri (Dunne, 1986)

ng ng Sierra Nevada batholith ATOKAN BURSUMIAN

? ? ?

CH OD PR CH OD PR

N Shelf N Shelf

SH SH ? ? 0 25 KM ? 0 25 KM

Lone Pine Lone Pine LCTCD LCT Bird Bird UM MC UM MC

Darwin Darwin

PB PB PBL PBL Fig. 3. Orientations of major pre-Cenozoic features in east-central California relative to the Neoproterozoic–middle Paleozoic continental CM CM SRH SRH Basin Basin margin and late Paleozoic truncated-margin segments. Cgl Mesa Uplift WSC Cgl Mes WSC

SB Sprin SB Sprin DC DC

Basin Basin a Uplift g ently representg an early episode of subduction and arc of the Sierra Nevada–Death Valley thrust system as LATE MIDDLE magmatism along this southeast-trending continental products of the Morrison orogeny, which is essentially SAKMARIAN ARTINSKIAN margin. These plutons are mostly Triassic in age, but coeval with the Sonoma orogeny recognized in north- ? ? ? ? ? ? Stevens and Stone, CH OD PR some areOD PR Late Permian (Andy Barth, written commu- central Nevada. CH Earth Sci Rev., 2005 N She N nication, 2002).She Thus, deformation associated with the Deformation represented by the Sierra Nevada– lf Sierra Nevada–Deathlf Valley thrust system may have Death Valley thrust system, as well as all subsequent

? ? ? ? ? SH ? SH 0 25 KM 0 25 KM been linked tectonically to the initiation of convergent contractional deformations in the region, are here plate motion and the earliest phase of arc development considered to have been related to compressional Figure 12. Paleogeographic maps illustrating evolution of the Bird Spring Shelf and adjacent basins during Pennsyl- vanian and Early Permian time. (A) Atokan. (B) Bursumian. (C) Late Sakmarian. (D) Middleall Artinskian. along Localities the southeast-trending continental margin tectonics along a southeast-trending segment of the shown: CH—Cowhole Mountain; CM—Conglomerate Mesa; DC—Darwin Canyon; MC—Marble Canyon; OD—Old Dad Mountain; PB—Panamint Butte; PBL—Permian Bluff; PR—Providence Mountains; SB—Stripedduring Butte; SH—Ship the Late Permian as inferred by numerous continental margin. This Late Permian(?) contrac- Mountains; SRH—Santa Rosa Hills; UM—Ubehebe Mine; WSC—Warm Spring Canyon. Palinspastic restorations are modiﬁ ed from Snow and Wernicke (2000). In addition, note that localities CM, PBL, and UM in previous(A) and (B) are in workers.their tional deformation apparently reflects the initiation inferred positions prior to eastward displacement in the upper plate of the Last Chance thrust (LCT) during Sakmarian time (Stevens and Stone, 2005). of plate convergence and subduction that later led to Stevens and Stone, voluminous Sierran arc magmatism. GSA9. SP Summary 429, 2007 and conclusions

The Sierra Nevada–Death Valley thrust system Acknowledgments forms a belt more than 100 km wide, stretching from pendants within the Sierra Nevada eastward to We are grateful to George Dunne and Norm Silber- Death Valley. The thrust faults that form this belt are ling for their careful reviews of the manuscript. Robert characterized by original dips generally of about 25– B. Miller helped greatly, especially in the construction 358W, stratigraphic throws of 2–5 km, and large foot- of the cross-section. wall synclines. The faults are typically spaced on the order of 15–20 km, except for the closer distribution of small faults in the Mount Morrison pendant. References In all areas, age constraints are compatible with a Barth, A.P., Tosdal, R.M., Wooden, J.L., Howard, K.A., 1997. late Early Permian to middle Early Triassic age of Triassic plutonism in southern California: southward younging deformation, with Late Permian being preferred on the of arc initiation along a truncated continental margin. Tectonics basis of regional relationships. We view all the faults 16, 290–304. Downloaded from specialpapers.gsapubs.org on January 31, 2010

The Pennsylvanian–Early Permian Bird Spring Carbonate Shelf 23

as indicated by the transition from the shelf deposits of the Bird and emplacement of the Last Chance allochthon along the west- Spring Formation to the overlying basinal deposits of the Owens ern margin of the shelf in the Early Permian (Stevens and Stone, Valley Group (Fig. 12D) (Stone, 1984; Stone and Stevens, 1984). 2005). Both events can be related to other tectonic events known Drowning of the Bird Spring Shelf in this area coincided with the elsewhere in western North America (Fig. 13). cessation of fossil-bearing sediment-gravity ﬂ ows into the Dar- Development of the Keeler Basin was approximately simul- win Basin, as shown by the lack of such deposits in the relatively taneous with the collision of South America–Africa (Gondwana) ﬁ ne grained, thin-bedded Panamint Springs Member of the Dar- with North America (Laurentia) along the Ouachita-Marathon win Canyon Formation (Stone et al., 1987). orogenic belt and with the origin of cratonal uplifts and basins of Near Conglomerate Mesa at the western margin of the Dar- the ancestral Rocky Mountain region (Kluth and Coney, 1981). win Basin, unit 2 of the sedimentary rocks of Santa Rosa Flat, At the time of this major orogenic episode, a northwest-trend- which may be correlative with the lower part of Fusulinid Zone 4 ing zone of sinistral faulting (late Paleozoic continental trunca- of the Bird Spring Shelf, apparently abuts the antiformal stack at tion fault on Figure 3, more or less equivalent to the California- the front of the Last Chance thrust, and unit 3 overlaps it (Stone Coahuila transform of Dickinson, 2000) is thought to have been et al., 1989). Thus, emplacement of the Last Chance thrust evi- initiated along the western margin of North America (Fig. 13A). dently had been completed when the shelf in the southern Pana- The tectonic relationship of this sinistral fault zone to continen- mint Range subsided. tal collision and development of the Ouachita-Marathon belt is In summary, our data indicate that emplacement of the Last uncertain, although Stevens et al. (1993) and Dickinson (2000) Chance allochthon began early in Bird Spring Shelf Fusulinid have suggested that it accommodated southeastward subduction Zone 3 time and was completed early in Fusulinid Zone 4 time. of oceanic crust beneath Gondwana (Fig. 13A). Whatever the ori- Emplacement of the allochthon, therefore, represents much of gin of the fault zone, the Keeler Basin developed a short distance Sakmarian (middle Wolfcampian) time, which lasted ~10 m.y. to the east as part of the “borderland” shown in Figure 3, probably according to Gradstein et al. (2004). Displacement on the thrust as a result of transtension as originally suggested by Stone and was ~30 km (Stevens and Stone, 2005) indicating a rate of Stevens (1988). 3+ mm/yr. As the allochthon shifted eastward, so did the locus The second event, emplacement of the Last Chance alloch- of subsidence due to loading, as recorded by the sequence of thon, was approximately coeval with continental-margin defor- sedimentological events discussed above. mation in northeastern Nevada (Fig. 13B). There, Trexler et al. (2004) have described a series of contractional deformations TECTONIC CORRELATIONS that affected rocks in the foreland of the remnant Antler Belt from Middle Pennsylvanian to Early Permian time. One event, The two most important tectonic events that occurred dur- the P1 deformation of Trexler et al. (2004), expressed by open, ing evolution of the Bird Spring Shelf in east-central California northeast-trending folds, occurred in the late Asselian, just prior were development of the Keeler Basin west of the shelf begin- to emplacement of the Last Chance thrust. Slightly later, in the ning in the Early to Middle Pennsylvanian (Stevens et al., 2001) same general region, the north-northeast-trending Dry Mountain

A ugh B

Tro tion Belt ah Basin RENTIA HypotheticalIsland Arc TIA LAU subduction? LAUREN Dry Mtn Havallah Basin Havall Deforma ROCKYANCESTRAL MOUNTAINS ? ROCKYANCESTRAL MOUNTAINS SHELF ? SHELF Remnant Last Antler Chance TONAL PLATFORM Thrust Belt Keeler CRA CRATONAL PLATFORM Basin Darwin continental continental t truncati lt Basin truncati l Bird e e B B Spring on fault n Bird on fault n o o Shelf th Spring th ra ra a Shelf Ma ta-M ita- Ouachi Caborca Ouach Block 500 KM on? 500 KM on?

Middle Pennsylvanian GONDWANA GONDWANA Early Permian subducti subducti

Figure 13. Maps showing major paleotectonic features related to the Bird Spring Shelf. (A) Middle Pennsylvanian. (B) Early Permian. Modiﬁ ed from Stevens et al. (1993), Dickinson (2000) and Trexler et al. (2004). Shaded areas are uplifts of the ancestral Rocky Mountains.

Stevens and Stone, GSA SP 429, 2007

Deformation belt in B is Penn deformation in Nevada. There is also deformation like that in A that was left of. Systematic left-lateral offset of strata218 and facies 217J.H. Stewart

pretation of Antler foreland deposits in the El Paso Mountains 125°Nevada, eastern 120° California, and 115° Sonora. Only 110° strata considered to 125° 120° 115 ° 110 ° and Shadow Mountains is correct, then the Antler orogenic belt have been part of ancestral North America are considered here. W 45° BM 45° extends into the central part of the Mojave Desert region, but per- Pennsylvanian-PermianOutboard terranes such as the Taylorsville area in the northernUpper Triassic-Lower Jurassic Sierra Nevada, the Klamath Mountains in northern California, haps not into the westernmost part. The exact distribution of the IDAHO and the Blue MountainsOREGON in southeastern Oregon are excluded. In OREGON Antler orogenic belt is critically important for the interpretation IDAHO BELT central and westernM Nevada,M marine Upper Triassic and Lower W presented here of offset on the Mojave-Sonora megashear. If the M WYOMING KM JurassicKMGF rocks (SilberlingC and Roberts, 1962; Nichols and Sil- WYOMING Antler orogenic belt does extend to the megashear and is offset NI berling, 1977;M Stewart, 1980, 1997) consist of limestone, shale, W NEVADA T left-laterally, it should reappear in Sonora, and so far it has not UTAH sandstone, and conglomerate, largely of LateUTAH Triassic40° age, over- 40° been recognized there. OROGE lain by a thick succession of generally ﬁ ne-grained clastic strata W NEVADA LER LW of Early Jurassic age.NT Interstratiﬁ ed volcanic rocks are locally WSIERRA CALIFORNIA A PENNSYLVANIAN AND PERMIAN MIOGEOCLINAL present in Upper Triassic strata. The exact southward continua- CALIFORNIA

STRATA tion of these rocks isIM uncertain, but they appear to connect with N

M EV ARIZONA UW

strata in the northernM Sierra Nevada (Schweickert, 1978; Stewart, A

M LI DA ARIZONA MD W Pennsylvanian and Permian miogeoclinal strata (Fig. 10) 1997) and then southward to form the Kings sequence35° in the cen- in the western United States (Rich, 1977; Stevens, 1977, 1991; tral and southern SierraSB Nevada. The Kings sequence (Saleeby et 35° Ross, 1991) and Sonora (Pérez-Ramos, 1992; Stewart et al., al., 1978; Saleeby and Busby-Spera, 1992; Saleeby and Busby, UNITED STATES 1993) is a complex assemblageBAJ of quartzite, marble, calc-silicate 1997, 1999; Stewart and Poole, 2002) consist predominantly UN BA ITED STATES rocks, schist, chert-argillite,A and slate, silicic metavolcanic rocks, CALI J of thick successions of shallow-water carbonate strata contain- A CALIFOR G ULF and basalt-andesite metavolcanicFORNIA NOR GF rocks. SeveralMEXICO Late Triassic and ing troughs of deeper-water turbiditic silty to sandy carbonate EA GULF OF CAL W M Early Jurassic fossil localities areOF CALIFORNIA known in the Kings sequence. EX and sandstone and local conglomerate. The strata show the same Pacific Ocean 30° EA ICO The correlation with the Nevada and northern Nevada rocks with NI W 30° Pacific Ocean A SR general distribution pattern as other Neoproterozoic to Jurassic ST NORTE the Kings sequence has beenTE proposedM previously by Stewart SONORA rocks, a pattern that is consistent with an interpretation of offset SONORA IFO (1988) and Saleeby and Busby-Spera (1992). Saleeby and RNI on the Mojave-Sonora megashear. Fusulinids of the McCloud Busby-Spera (1992) show a belt of widespread shallow-water A fauna, or of a McCloud-like fauna, are present in the Inyo Moun- 0Upper Triassic carbonate500 rocks extending1000 Kilometers from western Nevada 0 500 1000 Kilometers tains of eastern California (Magginetti et al., 1988), in the Mojave southward toEXPLANATION form the lower part of the Kings sequence. The Desert (Ross and Ross, 1983), in central Sonora (Nestell, 2000), amountPennsylvanian of igneous and rockPermian in miogeoclinalthis belt is variable,strata and they classify EXPLANATION and at scattered localities elsewhere in the western United States theSedimentary eastern part trough of the belt in Nevada as a backarc basin and the Outcrop of marine and some nonmarine Upper Triassic and (Fig. 10). This fauna is generally considered to have formed in western part of the belt in westernmost Nevada and the entire Lower Jurassic strata a continental borderland outboard of the Cordilleran miogeo- M KingsFusulinids sequence of McCloud in California fauna or as McCloud-like a magmatic faunas arc containing abun- W Strata containing the Early Jurassic bivalve Weyla cline, or perhaps at the edge of the miogeocline. The presence GF dantGiant sedimentary fusulinids rocks. Mojave-Sonora megashear. Position of megashear is not corrected Mojave-SonoraSouth of the megashear. southern PositionSierra Nevada,of megashear marine is not Uppercorrected Trias- palinspastically for post-Late Jurassic structural dislocations. See of the McCloud-like fauna indicates a similarity of the eastern palinspastically for post-Late Jurassic structural dislocations. See text for discussion of location of megashear. Arrows show relative California and Sonora strata, suggestive that one was offset from sic textand for Lower discussion Jurassic of location strata of aremegashear. not exposed Arrows for show a relativedistance of motion. motion. the other. However, the widespread distribution of this fauna ~700 km. Exposures of Upper Triassic and Lower Jurassic strata Localities: EA, El Antimonio area; BM, Blue Mountains; Localities:reappear KM, Klamath in Sonora Mountains; on the EA, southwest El Antimonio; side of the megashear. KM, Klamath Mountains; LI, Lake Isabella; L, Luning Formation; precludes the precise matching of one area to another. Arguing MD, Mojave Desert; SB, San Bernardino Mountains; These strata vary from marine limestone, mudstone, sandstone, SR, Sierra Santa Rosa; T, Taylorsville area; UW, Union Wash against possible offset are Mississippian to Permian strata at ST, Sierra Santa Teresa; MI, Inyo Mountains and lenticular conglomerate in northwest Sonora (Stanley and Sierra Santa Teresa in Sonora that have a different stratigraphy González-León, 1995; González-León et al., 1996; Lucas and Figure 11. Distribution of Upper Triassic and Lower Jurassic marine and and history than comparable age strata in eastern California Figure 10. Distribution of Pennsylvanian and Permian miogeoclinal rocks in the westernEstep, United1999) Statesto interstratiﬁ and northwestern ed marine Mexico. to nonmarine Based onsuccessions Rich nonmarine continental margin strata. Based on Stewart (1980, 1997), Nokleberg (1983), Saleeby et al. (1978), and Stewart et al. (1997). Dis- (Stewart et al., 1997). (1977), Rossof siltstone, (1991), Stevenscarbonaceous (1991), shale, Stewart coal et (graphite),al. (1997), andsandstone, Stewart peb- But are youngerThe Upper units Permian truncated Monos Formation and in theo f El set??Antimo- Can we look at latest Paleozoic to unravel?tribution of the Early Jurassic bivalve Weyla after Saleeby and Busby and Pooleble (2002). to boulder Distribution conglomerate, of McCloud and or sparse McCloud-like tuff (Cojan fauna and after Potter, (1993), Lucas and Estep (1997, 1999), Damborenea and González-León nio area of northwest Sonora (Cooper et al., 1953; Stewart et Ross and 1991;Ross (1983), Stewart Magginetti and Roldán-Quintana, et al. (1988), and 1991; Nestell Stewart (2000). et al., 1997) (1997), and N.J. Silberling (2002, personal commun.). al., 1990, 1997) may lie near or outboard of the Cordilleran in east-central Sonora. margin (Fig. 10). The Monos Formation consists of two differ- Stanley and González-León (1995) have suggested that ent lithologic units, a lower turbiditic succession of siltstone, strata that contain a distinctive Late Triassic sponge and coral limy siltstone, and detrital fossiliferous limestone and an upper 1983). Theassemblage evidence in from the Luning the Monos Formation Formation in western suggests Nevada that and it the Middle Norian (Silberling, 1984; Lucas and Estep, 1999; N.J. unit of resistant fossiliferous limestone locally containing giant may be anAntimonio accreted Formationterrane or (equivalentin an unusual to setting the combined near the Antimonio, edge Silberling, personal commun., 2002). Marzolf (1997), Anderson fusulinids (Dunbar, 1953). The lower turbiditic unit has been of the miogeocline.Rio Asunción, In either and Sierra case, dethe Santa edge Rosaof the FormationsUpper Permian of Lucas (1997), and Marzolf and Anderson (2000) also have suggested interpreted as a relatively deep-water deposit (Stewart et al., miogeoclineand Estep, appears 1999) to in lie the in El a Antimonio westward position,area in Sonora compatible were offset offset of lower Mesozoic strata from western Nevada and eastern- 1990, 1997) near or outboard of the miogeocline, and the upper with thefrom megashear western model Nevada and to Sonoranot with (Fig. the 11).wraparound However, model. the evidence most California to Sonora on the basis of facies distribution, hia- unit could be either shallow-water deposits or slide blocks into of apparent offset is questionable because the coralline part of tal geometry, and cross-cutting relations. On the basis of Lower a deep-water environment. The gigantic fusulinids are unusual. MARINEthe UPPERLuning Formation TRIASSIC is lowest AND Norian LOWER and JURASSICthe presumably cor- Triassic marine sedimentary strata, Lucas et al. (1997; Lucas Similar fusulinids are not known in strata of the Cordilleran ROCKSrelative coralline part of the Antimonio Formation is uppermost and Estep, 1999) suggest a correlation of Lower and Middle(?) miogeocline and are only known in the western United States in accreted terranes of the eastern Klamath Mountains in north- Marine and locally nonmarine rocks of Upper Triassic and ern California and in northeastern Washington (Ross and Ross, Early Jurassic age (Fig. 11) are widespread in central and western Downloaded from specialpapers.gsapubs.org on January 29, 2010

548 F.G. Poole et al. ° ° ° 30 25 35

500 BWb

90 F O

+ SB +

AOT Ou

KILOMETERS

M E X I C C I X E M G U L F O O F L U G

Tp Sau +

Akb Ouachita

+ ? Yp °

95 ? Wu ribed in Table 1, and location of Figure 4. 1, and location of Figure Table ribed in Poole et al., GSA SP 393, 2005 393, GSASP al., et Poole + + + + +

+ FWb + + + + + 72

Lu IZ 85 +

° + Kb +

Ab Es 84 100 83 + ° 81 + T T 100 78 71

+ Ma 82 77

+ DRu

+ ? + ? 80

AWAu

PDb Mb 79 + 70 +

++ LB

VVb CBp + 58 + SM

+ CB + 62 63

+ Dt 76 +

Su ? Au +

+ Db + + +

NWs SGu + 60 + + +

+ Mfb

61 Dp + °

Marathon ? 8 °

105 Tt IZ 69 + 105

39 Pu +

+ + + + + + + 38 +

+ 68 +

+ Uu )

+ 7 Pz 75

37 OGb

? 67

e ?

a +

( + Pb ?

+ Pxb

+ + 59 h + 36

66 ++ c 74 r +

FMu SNu

A + FB 6 65

. ZDu . 27

64 25

11 + +

l . .

a 40 t ? . .

. .

110

28 n .

e 46 24 45

n 43

Hb . 9 i . 23 t 5

+ 44

. 25 10 . .

n 110 CAs

49 +

o CST

Sa . .

+ .

c .

s 57 + 41

? .

Eu 16 . + 29 ? n . .

. .

47 48

+ a

. . r MMb 42

. + . T . .

56 30 .

? 18 ? 55 54

TATES 50 4

53 GCs

12 Sonora 17 35 13 51 ? ?

? BCT ° UNITEDMEXICO S 34 2 33 115 32

1 ? 3 52 31 14

? Fig. 4 15

Area of

O C E A N A E C O

P A C I F I C I F I C A P NV 20 21 Figure 3. Regional map of southern Laurentia showing late Paleozoic geologic features and localities mentioned in text and desc geologic features and localities mentioned in text late Paleozoic map of southern Laurentia showing Figure 3. Regional 19 ° 22 35 Collision of Gondwana and Laurentia Collision of Gondwana Is Is Caborca set olatef Paleozoic? Downloaded from specialpapers.gsapubs.org on January 29, 2010

564 F.G. Poole et al.

CENTRAL SONORA2 OUACHITA MTS, AR Age SYSTEM/ MARATHON MINAS DE BARITA and BLACK KNOB 1 REGION, TX3 (Ma) SERIES AREA RIDGE, OK4 FACIES SEQ FACIES

U No Data Skinner Ranch – Hess M and younger fms PERMIAN ? No Data L Lenox Hills Fm 0 - 85 Neal Ranch Fm 0 - 100 ? Rancho Gaptank Fm 0 - 815 300 U Nuevo Fm >1000 Haymond Fm <1400 PENNSYLVANIANM Atoka Fm 2700 - 8500 Dimple Ls 75 - 280 Johns Valley Fm 125 - 300

L Synorogenic strata Jackfork Gp 350 - 2100 Los Chinos Cgl 0 - 15 Tesnus Fm 100 - 2000 U Stanley Gp 1100 - 3350 El Paso Mtns (close to MISSISSIPPIAN ? proposed truncation) has 350 L Cerro Tasajo Ls 0 - 75

Los Pozos Fm 50 - 150 lower Mississippian U Arkansas Novaculite 70 - 290 ? conglomerate DEVONIAN Caballos M Novaculite 30 - 210 400 L U Missouri Mtn Sh 0 - 100 SILURIAN L El Torote Ls 0 - 8 Blaylock Ss Persimmon Gap Sh 0 - 12 0 - 250 U Polk Ck Sh 0 - 60 450 El Yaqui Chert 5 - 150 Maravillas Fm 30 - 150 Bigfork Chert 200 - 240 Preorogenic strata Preorogenic Womble Sh 100 - 1000 M Woods Hollow Sh 55 - 150 ORDOVICIAN El Mezquite Shale 100 - 150 Fort Peña Fm 40 - 200 Blakely Ss 100 - 180 Mazarn Sh 300 - 1000 L Alsate Shale 8 - 30 El Quemado Shale >300 Marathon Fm 260 - 330 Crystal Mtn Ss 200 ? Dagger Flat Ss 100 - 300 Collier Sh 20 - 300 500 U ? No Data ? CAMBRIAN M No Data No Data

1System/Series boundaries: Claoué-Long et al. (1992), Cooper (1999), Harland et al. (1990), Jin et al. (1997), Landing et al. (2000), Menning et al. (2000), Sandberg and Ziegler (1996), Sando (1985), Stone et al. (2000), Tucker et al. (1998). 2Sonora: Poole et al. (in progress). 3Marathon: Barrick and Noble (1995), Ellison and Powell (1989), Ethington et al. (1989), Finney (1986), McBride (1989), Noble (1990, 1994), Ross (1978, 1979, 1986), Ross and Ross (1995). 4Ouachita: Barrick and Haywa-Branch (1994), Ethington et al. (1989), Finney (1986), Hass (1951), Lowe (1989), Morris (1989).

Figure 5. Generalized stratigraphic sections characteristic of the Sonora, Marathon, and Ouachita segments of the Ouachita-Marathon-Sonora orogenic system. Thickness ranges in meters. Similar patterns represent correlative strata. Poole et al., GSA SP 393, 2005

El Paso Mtns also have a pretty thick sequence of Ordovician-Cambrian deep water clastic seds and quite a bit of Devonian (including, apparently, a Devonian ash fall tuf—El Paso Mtn Geol Map) Downloaded from specialpapers.gsapubs.org on January 29, 2010

New reconstruction of the Paleozoic continental margin of southwestern North America 609

Downloaded from specialpapers.gsapubs.org on January 29, 2010

600 C.H. Stevens, P. Stone, and J.S. Miller

Eastern

Figure 2. Index map showing Devonian facies belts, selected Paleozoic sedimentary boundaries on the continental shelf, areas interpreted to be underlain by oceanic crust, and major faults that have displaced facies belts and sedimentary boundaries. Note that in several areas rocks of the outer rise and ocean basin now are underlain by continental crust because of thrusting of those facies over the continental margin. In addition, outer-rise rocks not now exposed in the Saddlebag Lake area are inferred to underlie the ocean basin facies in that area. CB—Canal Ballenas area; CM—Coy- ote Mountains; CV—Cerro El Volcán; CWf—Clemens Well fault; DV-FCfz—Death Valley–Furnace Creek fault zone; EB—El Bisani; Ef—Excelsior fault; Gf—Garlock fault; H—Hermosillo; IBB2—Intrabatholithic break 2; LVVfz—Las Vegas Valley fault zone; MVf—Mojave Valley fault; RP—Rancho Placeritos; SFf—San Francisquito fault; SGf—San Gabriel fault; SLP—Sierra Las Pinta; SVf—Stewart Valley fault; Tf—Tinemaha fault.

Stevens et al., GSA SP 393, 2005

Figure 4. Paleogeographic reconstruction, step 2. Restoration of Cretaceous sinistral displacement of the Peninsular Ranges on the Nacimiento fault. See discussion in text. Abbreviations and symbols as in Figure 2.

Recall the elements of the Permian here. If we restore for Cz and likely K faults, we get picture on right. Note in particular the distribution of Permian- Triassic plutons and how they cross the Devonian facies belts in NW. Downloaded from specialpapers.gsapubs.org on January 29, 2010

Downloaded from specialpapers.gsapubs.org on January 29, 2010

600 C.H. Stevens, P. Stone, and J.S. Miller 614 C.H. Stevens, P. Stone, and J.S. Miller

Eastern

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New reconstruction of the Paleozoic continental margin of southwestern North America 609

Figure 2. Index map showing Devonian facies belts, selected Paleozoic sedimentary boundaries on the continental shelf, areas interpreted to be underlain by oceanic crust, and major faults that have displaced facies belts and sedimentary boundaries. Note that in several areas rocks of the outer rise and ocean basin now are underlain by continental crust because of thrusting of those facies over the continental margin. In addition, outer-rise rocks not now exposed in the Saddlebag Lake area are inferred to underlie the ocean basin facies in that area. CB—Canal Ballenas area; CM—Coy- ote Mountains; CV—Cerro El Volcán; CWf—Clemens Well fault; DV-FCfz—Death Valley–Furnace Creek fault zone; EB—El Bisani; Ef—Excelsior fault; Gf—Garlock fault; H—Hermosillo; IBB2—Intrabatholithic break 2; LVVfz—Las Vegas Valley fault zone; MVf—Mojave Valley fault; RP—Rancho Placeritos; SFf—San Francisquito fault; SGf—San Gabriel fault; SLP—Sierra Las Pinta; SVf—Stewart Valley fault; Tf—Tinemaha fault.

Figure 7. Paleogeographic reconstruction, step 4B. Restoration of sinistral displacement on a proposed Penn- sylvanian continental truncation fault predating the Mojave-Sonora megashear. See discussion in text. Abbre- viations and symbols as in Figure 2. Figure 4. Paleogeographic reconstruction, step 2. Restoration of Cretaceous sinistral displacement of the Peninsular Stevens et al., GSA SP 393, 2005 Ranges on the Nacimiento fault. See discussion in text. Abbreviations and symbols as in Figure 2.

The paleogeographic reconstruction presented here is cannot be completely ruled out; in fact, it would result in a more Recovering the SW end of the miogeocline… similar in some respects to that of Stevens et al. (1992), who also linear belt of Permian and Triassic plutons than in the present interpreted the continental margin to have been truncated by late reconstruction after restoration of the inferred Late Triassic thrust Paleozoic sinistral faulting that caused large southward displace- faulting (compare Figs. 4 and 5). On the other hand, the previous ment of both the Caborca block and rocks of the El Paso Moun- reconstruction does not account for the presence of Precambrian tains. This previous reconstruction, however, placed the trunca- continental crust west of the El Paso Mountains, as interpreted in tional fault east of the present position of the El Paso Mountains this paper, or for the probable role of the Foothills Suture in a late rather than along the Foothills Suture to the west and did not Paleozoic continental truncation event (Saleeby, 1992). Thus, the require the El Paso terrane to have been thrust eastward to its previous reconstruction would require substantial modiﬁ cation to present position in the Late Triassic. This previous reconstruction remain a viable alternative to the one presented here. RAINS ET AL.

in the El Paso Mountains, the interval between the uplift of deep-marine rocks and the incursion of volcaniclastic sediments was also ~10 m.y. Limited Permian subduction initiation in the southern California region contrasts with more extensive Triassic subduction development along the trace of the subsequent Mesozoic arc. Saleeby (2011) suggested that Triassic subduction followed latest Permian compressive tectonics along the oceanic transform-continental margin interface. His detailed Central Southern study of remnants of the transform within the Kings-Kaweah ophiolite California California belt (KKO, Fig. 1) gives an age of ≥200 Ma; this transform would have

Walker Pass pluton (3) Walker El Paso Mountains (2), (4), (5), (6) San Bernardino Mountains (1) Mountains Bernardino San San Gabriel Mountains (1) NW Black Mountain (1) Granite Mountains (1) SE resulted in a large density contrast between outer continental and nega- tively buoyant transform oceanic lithosphere, i.e., conditions favoring 200 Ma subduction initiation in the Triassic along the length of the transform. However, in the Early Permian, as mentioned herein, a record of contrac- Tr tion occurring at the same time as uplift in the El Paso Mountains is found from the western El Paso terrane in the Kern Plateau (Dunne and Suczek, 250 Ma 1991) through the southern Inyo Mountains and vicinity (Stevens and Pm Stone, 2007; Stone et al., 2009), supporting an earlier occurrence of perhaps “induced” subduction. We speculate that the localization of Permian subduction in the El Paso Mountain region and its apparent southward 300 Ma propagation were associated with a preexisting condition either associ- IP 100 km ated with the lithospheric structure of the soon-to-be subducting oceanic plate (e.g., change in age/structure/thickness across a transform or fossil spreading or other aseismic ridge at that paleolatitude) or the presubduc- Key to magmatic record tion geometry of the overriding plate (e.g., older indentation or jog asso- Pluton ciated with a prior tectonic regime). (Dating uncertainty Andesitic included in rectangle volcanism length) Regional Ramiﬁ cations of Subduction Initiation

Apparent trend of magmatism Whereas we interpret the Permian sedimentary record of the El Paso Mountains to show a proximal sequence consistent with subduction initia- Pennsylvanian continental truncation event. tion, it is also worth considering potential far-fi eld effects, such as those Age is very generalized. discussed by Holford et al. (2009), and implied by geodynamic models Rains et(Gurnis al., Lithosphere et al., 2004) ,(Fig. 2012 1), which may include shoreline migration on Figure 14. Magmatic activity from ca. 300 Ma to ca. 200 Ma between the craton and uplift of the Last Chance allochthon (e.g., Snow, 1992). southernmost central California and southern California, given geo- The numerical models imply that several-hundred kilometers inboard graphic locations based on Permian paleogeographic reconstruction of of the trench, on the overriding plate, the rock record would show subtle Rather surprising apparent growth of the arc to the SE fromStevens El et al.Pasos. (2005). Reconstructed locations are projected to proposed Pennsylvanian–Permian truncation fault line. Plotting of magmatic activ- vertical changes at subduction inception, followed by more substantial sub- ity based on various studies suggests a trend from Permian initiation in sidence as subduction resistance lessened (Fig. 13). Taking into account or near the El Paso Mountains, with magmatism spreading in Triassic the removal of Basin and Range extension and shortening the distance, time. Later tectonic events south of the El Paso Mountains have removed shoreline regression on the western edge of the Colorado Plateau between volcanic cover, leaving only plutons to mark magmatic activity (Barth and ca. 285 and ca. 278 Ma, as determined by sedimentary isopachs (Zahler, Wooden, 2006). Bar in Pennsylvanian time is a generalized schematic of 2006, and sources cited within), may be refl ecting the lithospheric fl ex- the truncation fault that cut across the continental margin (Stevens et ure predicted by modeling (Fig. 1). Between ca. 275 Ma and ca. 270 Ma, al., 2005). References for magmatic activity: (1) Barth and Wooden (2006), (2) Carr et al. (1997), (3) Dunne and Saleeby (1993), (4) Martin and Walker both the El Paso Mountains and the Colorado Plateau show evidence of (1995), (5) Miller et al. (1995), (6) interpretation from this study. transgression/subsidence in opposition to global eustatic trends (Fig. 8) but consistent with vertical motions suggested by the geodynamic model of Gurnis et al. (2004). deepening marine sequence that suggests subsidence below the CCD. Deep-marine strata occur throughout member B, where renewed carbon- SUMMARY AND CONCLUSIONS ate infl ux suggests progressive shallowing/uplift. Coarsening of sediment and increased carbonate at the base of member C are consistent with fur- Petrologic investigation of Permian metasedimentary rocks in the El ther shallowing. This shallowing trend was overprinted by input from the Paso Mountains reveals a rock record indicating uplift (member A) and evolving magmatic arc, as fi rst indicated by disseminated volcaniclastic subsidence (member A, middle and top, and member B) before infl ux of debris near the base of member C, which then becomes more volcanicla- volcaniclastic sediments and renewed shallowing (member C). stic-dominated upward, consistent with deposition on a prograding vol- At the base of member A, upward-coarsening conglomeratic strata caniclastic apron. Very coarse-grained bioclastic limestone near the top indicate uplift. A high-energy environment with variable fl ow energy is of the measured section indicates a very shallow-marine setting prior to suggested by fairly large chert and argillite clasts and variable amounts proximal magmatism (andesite intrusions and fl ows). of matrix. Sharp contacts, upward fi ning, and lack of sedimentary struc- The time span of subduction initiation to magmatism in the Gurnis et tures are consistent with gravity-fl ow deposits. Clast composition sug- al. (2004) model is less than 10 m.y. (Fig. 13). For the Permian section gests derivation from deep-marine sedimentary rocks. However, the lack

550 www.gsapubs.org | Volume 4 | Number 6 | LITHOSPHERE Research Paper

32000 62000 32000 62000 UTM zone 11 UTM zone 12 4200 S I E R R A N E

Bishop St. George Paria UTAH COLORADO Scheelite suite 232–219 Ma V A D Muddy Mtns ARIZONA NEW NE MEXICO CALIFORNIA Las C O L O R A D O A VA DA Vegas P L A T E A U Cameron Mojave suite Figure 1. Map of Chinle Formation exposures (black) and Early Mesozoic magmatic 260–240 Ma Cedar Ranch 3900 Kingman P- North Park arc (gray); arrows are paleocurrent direc- not Tr exposed tions (after Stewart et al., 1972b; Basdekas, rocks Flagstaff Holbrook Joseph 1993). Labels in boxes indicate Chinle Granite Mtn suite Hunt sample sites. Inset map shows Protero- Victorville M O J A V E City 235–230 Ma zoic crustal provinces of southwestern Lau rentia (after Wooden et al., 2012; Whit- Twentynine Palms San Bernardino suite, Parker meyer and Karlstrom, 2007). Coordinates D E S E R T 120o W Grenville province are in Universal Transverse Mercator (UTM; 25 0–240 Ma San Bernardino 1.1–0.9 Ga NAD83 datum). P-Tr—Permo-Triassic; Ptz— “A-type” granites Proterozoic. San Gabriel suite 1.5–1.3 Ga Blythe Yavapai and Mazatzal 220–207 Ma C h provinces, 1.8–1.6 Ga i n le Older Ptz and Archaean

tr P un provinces, < 3.0 Ga Yuma e k 3 CALIFORNIA r st 600 m ream BAJA CALIFORNIA o ARIZ - SONORA, Tr o ON ia 32 N A s MEXI s ic CO Sonoita a Ouachita rc orogenic Sonoita Suite belt ~270–260 Ma113 o TERRANES OF NogalesEASTERN MEXICO

We report here on a detailed detrital- and volcanic-zircon study of these basal ment flux, Riggshowever, et remained al., Geosphere from the higher-elevation, 2016 landmass to the east. fluvial sandstones and the volcanic clasts within them. Although paleocurrent Our purpose, therefore, is to document the diversity within the basal Chinle directions (Stewart et al., 1972a) in general indicate that the Shinarump river Formation and to propose how arc magmatism along the margin is reflected systems flowed from southeast to northwest, a distinct Triassic detrital zir- in these retro-arc sedimentary rocks. Note summary of ages of Permian into early Triassiccon signature togetheron left. with theOldest presence continentalof Triassic volcanic clasts rocks and local receiving detritus from this arc is Chinle. Interestingly, these might not be quite as old as start of arc… northeast flow directions record a significant contribution from the Cordilleran magmatic arc. We propose that the initial ~35–40 m.y. of arc magmatism oc- TECTONIC SETTING curred in an offshore arc, broadly analogous to the evolving Ryukyu arc-trench system, where the Philippine Sea is subducting under the Eurasian continental The Cordilleran magmatic arc developed across a truncated Paleozoic mio- plate. As subduction became established and arc crust evolved and thickened geoclinal margin along western Laurentia (Fig. 1) recorded by carbonate and by intra-arc contractional deformation and magmatism, the arc and retro-arc siliciclastic passive-margin platform strata deposited on Precambrian base- rose above sea level, providing a fluvial pathway for the deposition of arc-de- ment. The early to mid-Paleozoic margin trended northeast-southwest, and rived detritus into the Chinle basin. The dominant direction of flow and sedi- Pennsylvanian–Permian sinistral strike-slip faulting created a northwest-south-

GEOSPHERE | Volume 12 | Number 2 Riggs et al. | Chinle Formation and Early Mesozoic arc 440 Research Paper

The range of Permo-Triassic ages also bears examination, as dispersal 113°W 111°W paths must accommodate disparate areas that would have been sources. The 38°N oldest common Permian grains in our samples are ca. 280–285 Ma. These, together with ages to ca. 260 Ma, make up <5% of the total grains and are rare in all samples except North Park, and are inferred to derive from the Sonoran Muddy St. George segment of the arc (Fig. 1). Mountains UTAH The San Bernardino intrusive suite and plutons in the northern Mojave Desert (Fig. 1; Miller et al., 1995; Barth and Wooden, 2006) likely sourced ca. Paria ARIZONA 260 and ca. 240 Ma grains in many of the samples. The correlation with the Las CCameron O L O R A D O San Bernardino suite is suggested both by age and by similar Th/U ratios Vegas North Holbrook (Fig. 6). Data presented by Miller et al. (1995) do not include Th/U values; our Cedar Park preliminary results from these rocks show a reasonable overlap in Th/U val- P L A T ECameronCCa mA roUon Ranch ues between 260–250 Ma grains in these plutons and in the detrital zircons CALIFORNIANE V in the Shinarump Member. Age and Th/U also support the derivation of ca. ADA < 260 Ma 260–280 Ma 235–230 Ma grains from the Granite Mountain suite (Fig. 1). older Phanerozoic Many grains younger than ca. 230 Ma have less-certain sources. The in- 35°N Flagstaff Grenville (~1000– Hunt trusive suites documented by Barth and Wooden (2006) have only rare 230– 1100 Ma) 220 Ma ages. Additionally, many detrital grains in this range have Th/U ratios ~ 1400 Ma Joseph higher than both older components of the sandstones and rocks of the intru- 1600–1800 Ma City Archaean sive suites (Fig. 6). Riggs et al. (2012) speculated that an as-yet-undocumented source for zircons in middle Chinle Formation sandstones is buried or has been eroded, but lay approximately in the Colorado River basin. Figure 3. Pie plots demonstrating major detrital-zircon age similarities and differences between Chinle Formation sample sites. Chinle exposures are shown in black; arrows indicate paleo- The breakdown of ages and potential source areas allows distinctions to current directions. Little correlation exists between percentages of different-age zircons and be drawn between the sample sites, leading, in turn, to enhanced understand- position with respect to the Cordilleran arc. ing of dispersal pathways; sites are discussed here from west to east. The Muddy Mountains (Fig. 1) site contains a group of zircons between ca. 240 Chinle Detrital Zircons and 243 Ma which match the San Bernardino suite in age and Th/U, grains 10 between 230 and 236 Ma likely derived from the Granite Mountains suite, and grains between ca. 225 and 230 Ma that do not have an obvious source. Thus we infer that this area, which was close to the arc, either was fed by a stream x system that tapped a relatively confined area within the arc or received de- xxx + tritus from Plinian ash columns. Proterozoic grains are well represented and 1 x + x+ x xx were derived either from uplifted arc basement or from easterly sources. The xx x xx x xx xxx x + + lack of igneous clasts, however, is surprising considering the likely proxim- xxxx+ xxx x x+ x ++xx+ x+x+x+x x ity to the arc. It should be reemphasized, however, that overall the percent- Th/U + + + x+ +xx+xx++++ + x ++ ++++ age of volcanic clasts in any Shinarump conglomerate bed is generally very + ++ Cameron + low (i.e., ≤5%), such that the clasts are more anomalous by their presence 0.1 +x x Paria than absence. North Park The Cedar Ranch sample site contains two distinct groups of Permo-Trias- ++ + Hunt sic zircons. A diffuse cluster between ca. 237 and 240 Ma is consistent in age x Cedar Ranch and Th/U ratios with derivation from the San Bernardino and/or Granite Moun- x290 300 Holbrook tain suites in the Mojave Desert. Zircon grains between ca. 230 and 225 Ma 0.01 Joseph City dominate the Permo-Triassic signature of this site. These grains overlap Mo- 200 210 220 230 240 250 260 270 280 Muddy Mountains + jave Desert plutons in age and Th/U to a lesser extent than the older grains, Ma and are in part distinctive from similar-age grains in the Muddy Mountains Figure 4. Th/U versus age plot for detrital grains.Riggs et al., Geosphere, 2016 sample. Thus we infer that some recycling of older grains may have occurred, but that the 230–225 Ma group reflects derivation from a specific part of the arc Subset of Permian-Triassic zircons. Suggests presence of arc even back to 280 Ma.

GEOSPHERE | Volume 12 | Number 2 Riggs et al. | Chinle Formation and Early Mesozoic arc 457 Research Paper

10 Chinle Detrital Zircons Hunt sandstone 10 Sonoran plutonic Hunt clast Mojave plutonic Paria North Park Hunt 1 1 Cedar Ranch Th/U Holbrook

U Joseph City

Th / Muddy Mountains Cameron 0.1 Clasts 0.1 10 Holbrook sandstone

Holbrook clast 0.01 200 210 220 230 240 250260 270280 290 Ma

1 Figure 6. Comparison of age and Th/U for detrital zircons, clast zircons,Riggs and et Triassic al., Geosphere plutonic, 2016

Th/U suites of southern and southeastern California. Pluton data from the Mojave Desert suites are from Barth and Wooden (2006). Dashed line for Paria is due to the very few Triassic Lag in timing reﬂects, authors argue, presencezircons of inmarine that sample arc (nuntil = 6). Lighter-colorc 230 Ma. band within Mojave plutonic ﬁeld is area of few zircon ages.

and that these grains were genetically related to volcanic clasts found in other 0.1 samples (cf. Riggs et al., 2013). 10 The North Park sample is unique in its comparatively high percentage (13%) of Permian grains. Six of these grain lie in a discrete cluster from 288 to Joseph City sandstone 282 Ma, and their source is uncertain. Zircons of this age are inferred by Dickin- Joseph City clast son and Gehrels (2008) to derive from the East Mexico arc; we question this interpretation for reasons provided above. On the western margin of Laurentia, however, transcurrent faulting was likely active at ca. 280 Ma, and subduction was established by ca. 270 Ma. Thus these grains are not considered likely to 1 be derived from the Cordilleran margin. The majority of grain ages are in a Th/U comparatively narrow range, from ca. 270 to 247 Ma (n = 13); ages and Th/U are compatible with derivation from the Mojave Desert plutons and the Sonora portion of the arc (Fig. 6). The youngest grains from the Holbrook, Hunt, and Joseph City samples are very similar in their age and chemistry; Hunt and Joseph City samples additionally have an older group of grains in the ca. 240–260 range Ma that 0.1 220 225 230 235 240 245 250 were likely derived from the San Bernardino suite and/or older plutons in the northern Mojave Desert (Miller et al., 1995); Th/U ratios support correlation Ma with both suites of plutons (Fig. 6). Grains as young as 218 Ma may have been

Figure 5. Th/U versus age plot for zircons in volcanic clasts from Hunt, Holbrook, and Joseph subject to lead loss; on probability density plots the maxima are between 226 City compared with detrital zircons in sandstone from the same sample site. Cameron site and 223 Ma (Fig. 4), and these older ages may be more suitable estimates is not shown because clasts and sandstone were not collected from the same location.

GEOSPHERE | Volume 12 | Number 2 Riggs et al. | Chinle Formation and Early Mesozoic arc 458 Permian subduction initiation in the El Paso Mountains, California | RESEARCH

Member System Permian section, El PasoSeries Mts Lithology: percent composition Meters Global sea level above with interpreted water depth KEY base 100 m 0 m –100 m Pgg 1000 ca. 260 Ma 250 Andesite

900 Argillite, siltstone

g Leonardian latest in Quartz arenite w 800 o ll C a Arkose, non- h volcaniclastic S 260 700 ca. 270 Ma Regression Volcaniclastic sandstone after ca. 268 Ma

Other sandstones 600 late Wolfcampian to early Leonardian

B Permian Time (Ma) Conglomerate

500 270 Carbonate, silicified limestone, recrystallized chert 400

Hydrothermal "alterite" 300-m-thick covered interval. Igneous intrusion Laterally, argillite beds A OC 300 Ordovician– Cambrian 280 Shallower 200 Dee Deeper pen Relative water ing depth as inferred 100 from sedimentary After ca.

facies OC 280 Ma OCca 0 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Rains et al., Lithosphere, 2012 Figure 8. Vertical column on left shows relative percentages of lithologies (0%–100%) in 20 m slices from the base to the top of measured section, normalized to 100% for each 20 m. Member A (Pha), is dominated by sandy meta-conglomerate, meta- carbonate, and meta-siltstone. The sandy conglomerate in Pha lacks marine bioclasts and may have been deposited subaeri- Facies changes in El Paso Mtns not global—whatally. isMember this B (Phb) telling contains meta-carbonateus about and SW meta-siltstone. margin The base c. of 280 member Ma? C (Phc) is(WOrth deﬁ ned by the noting occurrence that this same deepening was inferred by of plagioclase-rich arkosic rocks and is dominated by volcaniclastic rocks throughout, with an interval of rare supermature Snow long ago as a fore deep in front of the Lastmeta-quartz Chance sandstone, thrust and local interbeds system). of meta-carbonate. Top of measured section is meta-andesite. Age constraints are: lower member A, ca. 280 Ma; lower member C, ca. 270 Ma (Carr et al., 1997); capping andesite, 262 ± 2 Ma (Martin and Walker, 1995); and 260 ± 5 Ma for the intruding Permian pluton (Miller et al., 1995). The interpreted water depth of deposition of El Paso Mountains strata is compared to the Permian global sea-level curve from Haq and Schutter (2008). The global sea-level curve shows a rise relative to the baseline (dotted line at 0 m) for positive (left) and a fall for negative (right) values. Superposed on vertical column is an El Paso Mountains (EPM) relative sea-level curve (thick line) based on distribution of shallow versus deep-water facies. The El Paso Mountains water depth changes, based on strata interpretation, are one to two orders of mag- nitude greater than global sea-level variation and out-of-phase with global sea-level changes for the early deepening trend at ca. 280 Ma, so the depositional environments are a consequence of vertical tectonics (see text).

in a recrystallized mud matrix. Iron-stained grayish-orange, laminated to Member B (Phb) is more calcareous than member A (Pha) and consists thinly bedded argillite to sandy siltstone beds form a continuously exposed of thinly to thickly bedded, medium- to dark-gray argillite and medium- section near the top of the member. In thin section, one sample contains gray to yellowish-brown calcareous argillite interbedded with dark-yel- very angular to well-rounded, fi ne- to very fi ne-grained chert lithic frag- lowish-orange calc-siltstone. Covered intervals between outcrops are ments (~20%), quartz grains (~7%), angular to subangular opaque grains more extensive than in member A (Pha). In thin section, all samples from (~7%), and trace sponge spicules, set in a cherty-silty clay matrix (~60%) member B (Phb) consist of clay or silt with local sponge spicules, and with patchy calcite cement. The opaque minerals defi ne lamination. opaque, (organic?) material.

Member System PermianSeries section, El Paso Mts Lithology: percent composition Meters Global sea level above with interpreted water depth KEY base 100 mSubduction0 m –100 initiation m model (Gurnis et al., 2004) compared with Pgg 1000 sedimentary record of El Paso Mountains ca. 260 Ma 250 El Paso Mountains Changes at margin of Colorado Plateau? Andesite sedimentary record 0.0 m.y. position of seafloor 1 (based on isopachs) A 0 900 A ca. 285 Ma Argillite, siltstone Denser slab (subducting plate) - 1

g Leonardian latest n i 1 Quartz arenite w Change by 0.2 m.y. B ca. 280 Ma 800 o Uplift and erosion in 0 Conglomerate derived Local sea- l C B l nascent forearc level rise? Denser slab (subducting plate) - 1 from uplift and erosion of Arkose, non- a deep-marine sedimentary volcaniclastic h 260 S Change by 3.0 m.y. 1 rocks (base of member A) 700 0 C ca. 270 Ma RegressionC Subsidence results in fine- Volcaniclastic Subducting plate -1 sandstone after grained calcareous facies ca. 268 Ma Subsidence begins - 2 of member A. in forearc Trench - 3

Other sandstones 600 late Wolfcampian to early Leonardian

B Permian Time (Ma) Change by 5.4 m.y. 1 D ca. 278 Ma Conglomerate D 0 Subsidence and deepening Local sea- Subducting p continues in forearc, late - 1 level fall 500 270 producing fine-grained Carbonate, silicified Subsidence continues - 2 noncalcareous facies limestone, recrystal- Trench in forearc. Forearc extension of member A. lized chert - 3 400

Hydrothermal "alterite" 300-m-thick covered interval. 1 E ca. 275 Ma Igneous intrusion Uplift begins. Shallower Laterally, argillite beds A E Change by 0 Local sea- Subducting depths lead to carbonate level rise OC 300 p 6.6 m.y. - 1 production and fine-grained late Ordovician– Uplift in forearc - 2 calcareous facies of member B. Cambrian Trench Trench rollback 280 - 3 Shallower 200 D 1 F ca. 270 Ma ee F 0 Plagioclase-rich sands Deeper pe Subducting Arc magmatism after ~10 m.y. (local uplift?), followed by ni pla - 1 Relative water ng te as subducting plate reaches subsequent volcaniclastics 100 depth as inferred magmatic depths - 2 as magmatic arc develops Trench (member C). from sedimentary After ca. - 3 +200 +100 0 –100 km

facies OC 280 Ma OCca 0 Figure 13. Evolution of subduction initiation based on dynamic modeling (Gurnis et al., 2004; Hall et al., 2003) using example 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% of an oceanic fracture zone with crustal density differencesRains across aet zone al., of Lithosphereweakness. Figure, 2012 is adapted from Gurnis et al. (2004) and Hall et al. (2003); position of plates is reversed for this adaptation. Compression is given as 2 cm/yr, and plate ages Figure 8. Vertical column on left shows relative percentages of lithologies (0%–100%) in 20 m slices from the base to the top in the model are 10 m.y. (right, younger) and 40 m.y. (left, older). Time spans (0.0, 0.2, 3.0, 5.4, 6.6 m.y.) are based on modeling. of measured section, normalized to 100% for each 20 m. Member A (Pha), is dominated by sandy meta-conglomerate, meta- carbonate, and meta-siltstone. The sandy conglomerate in Pha lacks marine bioclasts(A) and Juxtaposition may have been deposited of oceanic subaeri- lithosphere with age/density differences across fracture zone/zone of weakness, as described in Interpreted as early phase ofally. subduction Member B (Phb) contains initiation.meta-carbonate and meta-siltstone. We’ll The come base of member backtext. C (Phc)(B) Initialisto defi ned thecompression by the arc occurrence deformsmuch overriding later, slab. but (C–D) Forearcthis subsidencewould occurs seem as the toplates help decouple clinch (Gurnis et truncational., by Permian. of plagioclase-rich arkosic rocks and is dominated by volcaniclastic rocks throughout,2004). with an(E) interval Overriding of rare slab supermature moves trenchward. Vertical motion is relative to ocean fl oor; models are consistent with data from meta-quartz sandstone, and local interbeds of meta-carbonate. Top of measured sectionCenozoic is meta-andesite. ocean Agearcs constraints (Gurnis et are: al., 2004). In adapting model to the El Paso Mountains (EPM) on right, the “younger” plate of lower member A, ca. 280 Ma; lower member C, ca. 270 Ma (Carr et al., 1997); capping andesite,model is 262 equated ± 2 Ma (Martin with andunderlying, Walker, less dense, transitional continental-margin lithosphere of the El Paso Mountains terrane. 1995); and 260 ± 5 Ma for the intruding Permian pluton (Miller et al., 1995). The interpretedSubducting water depth plate of deposition is assumed of El P toaso be denser oceanic lithosphere. Note that vertical motions of forearc region in model follow the Mountains strata is compared to the Permian global sea-level curve from Haq and Schuttersame (2008).pattern The as global that sea-level interpreted curve from the Permian sedimentary record in the El Paso Mountains. Furthermore, far-fi eld effects shows a rise relative to the baseline (dotted line at 0 m) for positive (left) and a fall atfor right negative edge (right) of model values. maySuperpos be comparableed to patterns of transgression and regression as recorded in sedimentary isopachs of on vertical column is an El Paso Mountains (EPM) relative sea-level curve (thick line) thebased western on distribution Colorado of shallow Plateau versus (based on isopach compilations by Zahler, 2006; see Fig. 1). deep-water facies. The El Paso Mountains water depth changes, based on strata interpretation, are one to two orders of mag- nitude greater than global sea-level variation and out-of-phase with global sea-level changes for the early deepening trend at ca. 280 Ma, so the depositional environments are a consequence of vertical tectonics (see text). more buoyant than subducting oceanic crust and lithosphere. As described Looking only at southern California, the observed pattern of south- already, some authors have suggested the El Paso terrane was translated western Cordilleran Permian–Triassic plutons, based on palinspastic from northern California and left behind on a sliver of the postulated late reconstruction of Stevens et al. (2005), suggests that magmatism began in a recrystallized mud matrix. Iron-stained grayish-orange, laminated to MemberPaleozoic B (Phb) transform/truncation is more calcareous than memberfault (e.g., A (Pha) Stevens and consists et al., 2005; Dickinson, in a small area (El Paso Mountains) before spreading south (Barth and thinly bedded argillite to sandy siltstone beds form a continuously exposed of thinly2000). to thickly Alternatively, bedded, medium- as mentioned to dark-gray already, argillite andif the medium- Antler belt extended to Wooden, 2006) (Fig. 14). This pattern may be analogous to the Ceno- section near the top of the member. In thin section, one sample contains gray towhat yellowish-brown is now central calcareous California, argillite interbeddedlittle or no with latitudinal dark-yel- translation of the zoic initiation and propagation of subduction along the Puysegur Ridge, very angular to well-rounded, fi ne- to very fi ne-grained chert lithic frag- lowish-orangeEl Paso calc-siltstone. Mountains Coveredterrane intervalsmay have between occurred outcrops in the are Pennsylvanian or New Zealand, and consistent with the record of restricted nucleation and ments (~20%), quartz grains (~7%), angular to subangular opaque grains more extensivePermian than (Dickinson, in member A 1981; (Pha). InStone, thin section, 1984; all Carr samples et al.,from 1984; Snow, 1992; progression of volcanism along that margin (Sutherland et al., 2006). (~7%), and trace sponge spicules, set in a cherty-silty clay matrix (~60%) memberDunne B (Phb) and consist Saleeby, of clay 1993; or silt Stevens with local et al.,sponge 2005). spicules, In any and case, it is proposed The overall Permian sedimentary pattern of the El Paso Mountains with patchy calcite cement. The opaque minerals defi ne lamination. opaque,that (organic?) left-lateral material. transform faulting brought oceanic lithosphere into juxta- appears consistent with models for “induced” or “forced” subduction ini- position with the El Paso Mountains terrane, enabling the necessary den- tiation, rather than “spontaneous” subduction (Gurnis et al., 2004; Stern, sity contrast and creating an opportunity for subduction initiation along a 2004; Sutherland et al., 2006) (Fig. 13). Specifi cally, initial uplift is evi- LITHOSPHERE | Volume 4 | Number 6 | www.gsapubs.org through-going zone of weakness. 543 denced at the base of member A by sandy conglomerate, followed by a

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Geotectonic features of the Antler orogen (Late Devonian–Early Mississippian), the Ancestral Rocky Mountains province Figure Figure 6 (Pennsylvanian–Early Permian), and the Sonoma orogen (Late Permian–Early of Triassic) the American North Cordillera (allochthons of Antler and Sonoma age are combined, but note the uncertain continuity of tectonic trends along the trans-Idaho discontinuity of Figure 5). See text for discussion of Kootenay structural arc (KA) and remnants of Paleozoic arc assemblages in Quesnellia (Qu) and Stikinia (St). Key active faults: RMT, Devonian-Mississippian Roberts Mountains thrust; California-Coahuila Triassic transform. Gondwanan Mexico restored (after Dickinson GCT, & Lawton 2001a) to position before Permian-Triassic mid-Mesozoic Golconda thrust; CCT, Permian- opening of the Gulf of fault and Mexico. Tintina systems De-CS-FW-QC are Cenozoic structures. See Figure 5 for geographic legend. Standing back,Standing doeshow all in? ﬁt this ARM uplift SLaB strike-slip basin Beginning southern California (e.g., Snow, 1992; Stevens KS r ARM basin SLaB flexural basin HB Elko ca. 355 Ma and Stone, 2005) and Sonora (Poole et al., 2005). Carbonate shelf Basin of uncertain affinity Equato Ely Late Paleozoic structures in Nevada commonly Oceanic basin with schematic spreading centers RM have northeast-southwest fold axes, recording Thrusted basinal rocks with N Laurentian provenance b e Thrusted basinal rocks with Gondwanan provenance northwest-southeast shortening notably oblique arch Afb/As to the margin (e.g., Miller et al., 1984; Trexler 120° 110° 100° FC Figs. 1B-D Miogeoclin et al., 2004) and inconsistent with margin-per- HB pendicular shortening. Superposed folds record KS RM Afb/ 40° arch repeated shortening events (Trexler et al., 2004; Asb 1 Future Cashman et al., 2011, 2016). ) anscontinental 2 BS continental Tr Initiation of sedimentary basins likewise 3 Region of intracratonic truncation KB deformation (ARM propagated from northwest to southeast (Fig. 2). The Bird Spring shelf in southern California anscontinental SLaB Tr Former foundered in mid-Pennsylvanian time to form Region Neoproterozoic Caborca 30° paleotransform the Keeler basin (Stone and Stevens, 1988). block 4 In central Sonora, thick Upper Mississippian O-M suture margin MM to Pennsylvanian carbonate strata represent a Sonora EF similar local outer-shelf basin (Stewart et al., A allochthon 0 km 1000 B 0 km 1000 1997). The early middle Permian Mina México ARM uplift SLaB strike-slip basin Beginning southern California (e.g., Snow,Beginning 1992; Stevens Former Beginning KS r foreland basin, the youngest and southernmost ARM basin SLaB flexural basin Elko ca. 355 Ma ca. 310 Ma Havallah ca. 290 Ma HB and Stone,HB 2005) and Sonora (Poole et al., 2005). extensional SLaB basin, records emplacement of the Sonora Carbonate shelf Basin of uncertain affinity Equato KS ES RM Ely Late Paleozoic structures in Nevada commonly basin allochthon over Caborca (Poole et al., 2005) as Oceanic basin with schematic spreading centers Future Thrusted basinal rocks with N Laurentian provenance b have northeast-southwest fold axes, recording e arch DB Golconda arch the block was stopped at the westward-propagat- Thrusted basinal rocks with Gondwanan provenance northwest-southeast shortening notably oblique arch BS thrust ing Ouachita-Marathon suture (Fig. 1D). Afb/As to the margin (e.g., Miller et al., 1984; Trexler 120° 110° 100° FC Last Pennsylvanian–Permian continental-margin Figs. 1B-D Miogeoclin et al., 2004) and inconsistent with margin-per- Chance basins record ongoing deformation along the HB pendicular shortening. Superposed folds record 40° KB thrust Laurentian margin. The early Permian Darwin KS RM Afb/ arch Asb repeated shortening events (Trexler et al., 2004; basin formed when the Keeler basin was thrust 1 Caborca ) Future Cashman et al., 2011, 2016). anscontinental block in anscontinentalnnsylvanian Equator anscontinental over the shelf in the upper plate of the Last 2 BS continental Tr transiInitiationt of sedimentaryTr basins likewise Tr Permian Equator Chance thrust (Figs. 1C, 1D, and 2; Stevens and 3 Region of intracratonic truncation RNB Middle Pe rly KB deformation (ARM propagated from northwest to southeast (Fig. 2). Ea Stone, 2005). Sediment gravity fow deposits The Bird Spring shelf in southern California drego sa Pe n anscontinental MM basi of the Rancho Nuevo Formation, now in the SLaB Tr Former foundered in mid-Pennsylvanian time to form Region Neoproterozoic Sonora allochthon (Fig. 1D; Poole et al., 2005), Caborca 30° paleotransform the Keeler basin (Stone and Stevens, 1988). accumulated adjacent to the Caborca block and block 4 In central Sonora, thick Upper Mississippian O-M suture margin Sonora provide evidence for a long-lived deep-water MM to Pennsylvanian carbonate strata represent a allochthon EF basin from Early Pennsylvanian through early Sonora EF similar local outer-shelf basin (Stewart et al., A allochthon 0 km 1000 B C D Permian time (Figs. 1C and 2). 0 km 1000 1997). The early middle Permian Mina México Beginning Former Detrital zircon (DZ) provenance data are con- Beginning Figureforeland 1. A: Location basin, the map youngest of southwestern and southernmost Laurentia indicating key Southwestern Laurentian ca. 310 Ma Havallah ca. 290 Ma sistent with sinistral translation along the SLaB. HB extensional BorderlandSLaB strike-slip (SLaB) basintectonic elements in relation to uplifts and basins of Ancestral Rocky Moun- KS ES ARM uplift SLaB basin, records emplacement of the Sonora Beginning Middlesouthern Ordovician California quartzose (e.g., turbidites Snow, in the 1992; Stevens basin tainsSLaBallochthon (ARM) flexural orogen. over basi Caborca nOrange (Poole dashedKS et al., line 2005) and diagonalas Elko rule rindicate SLaB region as defined ARMFuture basin herein. Bold numerals indicate column locations of Figure 2. B: Early ca.Mississippian–Early 355 Ma allochthonsand Stone, of 2005)Nevada andand Sonora Sonora contain (Poole a ca. et al., 2005). DB the block was stopped at the westward-propagatHB - arch CarbonateGolconda shelf arch PennsylvanianBasin of uncertain (Tournaisian–Bashkirian) affinity paleogeography. Equato Intracratonic ARM deformation, 1.8 Ga DZ age peak and subordinate Archean BS ing Ouachita-Marathon suture (Fig. 1D). Ely Late Paleozoic structures in Nevada commonly Oceanicthrust basin with schematicrelated spreading to Gondwana-Laurentia centers collision (KluthRM and Coney, 1981) rather than SLaB deformation, grains from a source in cratonal Laurentia north Last has notPennsylvanian–Permian yet begun to affect region continental-margin of Transcontinental arch. C: Middle Pennsylvanian–early have northeast-southwest fold axes, recording Thrusted basinal rocks with N Laurentian provenance b of the Transcontinental arch (Fig. 1; Gehrels and Chance Permianbasins (Moscovian–Sakmarian) record ongoing deformation paleogeography. alongLawton the et D: al., Early Geology Permian–middlee , 2017 Permian (Artin- skian–Wordian?) paleogeography. Abbreviations: Afb/Asb—Antler foreland and successor Dickinson, 1995; Gehrels and Pecha, 2014; Linde KB thrust Thrusted basinal rocks with GondwananLaurentian provenancmargin. Thee early Permian Darwin northwest-southeast shortening notably oblique basins; BS—Bird Spring shelf; DB—Darwin basin;Afb/As EF—El Fuerte block; ES—Elyarch shelf; HB— et al., 2016). Cambrian deep-water arenites of the basin formed when the Keeler basin was thrust to the margin (e.g., Miller et al., 1984; Trexler Caborca 120° 110° Havallah basin;100 KB—Keeler° basin; KS—PermianFC Klamath-Sierra arc terrane; MM—Mina México Harmony Formation in central Nevada likewise block in forelandover thebasin; shelf O-M—Ouachita-Marathon in the upper plate of the suture; Last RM—Roberts Mountain allochthon; RNB— anscontinentalnnsylvanian Equator anscontinental Miogeoclin haveet al., a northern 2004) Laurentian and inconsistent source; their immawith- margin-per- transit Tr Tr RanchoChance NuevoFigs. thrust basin. (Figs.1B- LocationsD1C, 1D, and of 2; equator Stevens inand B–D are from Blakey (2016). HB y Permian Equator ture textural characteristics suggest that they RNB Middle Pe Earl pendicular shortening. Superposed folds record Stone, 2005). Sediment40° gravity fow deposits KS RM sa were transported along the Laurentian margin Afb/ Pedrego arch MM basin of the Rancho Nuevo Formation, now in the repeated shortening events (Trexler et al., 2004; Standing back, how does all this ﬁt in? And does this Asbmake sensea singlewith back-arc the basinAncestral that narrowed Rockies? southward met[Wonder at a triple junction how south this of themight basin (Figs. look as on a tectonic a proper entity (Linde, palinspastic 2016), rather than bybase] 1 (SilberlingSonora andallochthon Roberts, (Fig. 1962; 1D; Colpron Poole etand al., Nel 2005),- 1B and 1C). After SLaB deformation, the Haval- longshore transport and/or spilling of shelf sand ) Future Cashman et al., 2011, 2016). son,accumulated 2009). Opening adjacent of the toSlide the MountainCaborca block basin andlah basin was thrustanscontinental over the Laurentian margin into adjacent basins (e.g., Ketner, 1968; Gehrels 2 BS continental Tr Initiation of sedimentary basins likewise Sonora alongprovide a transform-dominated evidence for a long-lived spreading deep-water system, during the Sonoma orogeny to form the Gol- and Dickinson, 1995). In contrast, allochthonous 3 EF Region of intracratonic truncation allochthonKB recordeddeformationbasin byfrom geochemical Early(ARM Pennsylvanian and isotopic through variation early conda allochthon (Fig. 1D; Burchfel and Davis, Ordovicianpropagated quartzites from of northwest the El Fuerte toterrane southeast in (Fig. 2). C D of UpperPermian Devonian–lower time (Figs. 1C Permian and 2). mafc rocks 1975; Colpron and Nelson, 2009). Sinaloa,The Bird directly Spring south ofshelf the SLaB in southern (Figs. 1A California Detrital zircon (DZ) provenance data are con- SLaB anscontinental of the Slide Mountain terrane in Canada (Piercey and 1D), have Gondwanan DZ sources and were Figure 1. A: Location map of southwestern Laurentia indicating key SouthwesternTr Laurentian sistent with sinistral translation along theForme SLaB. r foundered in mid-Pennsylvanian time to form Borderland (SLaB) tectonic elements in relation to uplifts andRegion basins of Ancestral Rocky Moun-et al., 2012), likely propagated southward from EVOLUTION OF THE SLaB REGION deformed in late Permian time (Vega-Granillo et Middle Ordovician quartzose turbiditesNeoproterozoic in the tains (ARM) orogen. Orange dashed line and diagonal rule indicateCaborca SLaB region as definednorthern Canada beginning30° in Late paleotransformDevonian Initiation of SLaB deformation was dia- al.,the 2008). Keeler The deformationbasin (Stone there records and Stevens,fnal 1988). herein. Bold numerals indicate column locations of Figure 2. B:bloc Earlyk Mississippian–Earlytime allochthons (e.g., Colpron of Nevada and Nelson, and Sonora 2009). Wecontain infer a ca.chronous and propagated southward (Link et closure of the Ouachita-Marathon suture between Pennsylvanian (Tournaisian–Bashkirian) paleogeography. Intracratonic ARM deformation,4 margin In central Sonora, thick Upper Mississippian that1.8 a south-propagating Ga DZO-M age suture peak ridge-transform and subordinate system Archean al., 1996; Cashman et al., 2016). Deformation Gondwana and Laurentia. related to Gondwana-Laurentia collision (Kluth and Coney, 1981) rather thanMM SLaB deformation, in thegrains Havallah from basin,a source a trench in cratonal west ofLaurentia the Klam north- ranged from Mississippian in central Nevada to IndependentPennsylvanian evidence forcarbonate late Paleozoic strata abso- represent a has not yet begun to affect region of Transcontinental arch. C: Middle Pennsylvanian–early of the Transcontinental arch (Fig. 1; Gehrels and Permian (Moscovian–Sakmarian) paleogeography. D: Early Permian–middleSonora Permian (ArtinEF -ath arc, and the Caborcan continental transform (e.g., Trexler et al., 2003) to middle Permian in lutesimilar northward local translation outer-shelf of Laurentia basin provides (Stewart et al., A allochthon 0 Dickinson,km 1995; Gehrels1000 and Pecha,B 2014; Linde skian–Wordian?) paleogeography. Abbreviations: Afb/Asb—Antler foreland and successor 0 km 1000 1997). The early middle Permian Mina México basins; BS—Bird Spring shelf; DB—Darwin basin; EF—El Fuerte block; ES—Ely shelf; HB— et al., 2016).Beginning Cambrian deep-water arenites of the Former Havallah basin; KB—Keeler basin; KS—Permian Klamath-Sierra arc terrane; MM—Mina México Harmony Formation in central Nevada likewise Beginning 676 Havallah www.gsapubs.orgforeland | basin,Volume 45the | Number youngest 8 | GEOLOGY and southernmost foreland basin; O-M—Ouachita-Marathon suture; RM—Roberts Mountain allochthon; RNB— have aca. northern 310 Laurentian Ma source; their imma- ca. 290 Ma Rancho Nuevo basin. Locations of equator in B–D are from BlakeyKS (2016).HB ES extensional SLaB basin, records emplacement of the Sonora Downloaded fromture http://pubs.geoscienceworld.org/gsa/geology/article-pdf/45/8/675/2315559/675.pdf textural characteristics suggest that they basin by University of Colorado Boulder user allochthon over Caborca (Poole et al., 2005) as on 05 February 2021were transported along the Laurentian margin Future a single back-arc basin that narrowed southward met at a triple junction south of the basin (Figs. as a tectonic entity (Linde, 2016), rather than by arch DB Golconda arch the block was stopped at the westward-propagat- (Silberling and Roberts, 1962; Colpron and Nel- 1B and 1C). After SLaB deformation,BS the Haval- longshore transport and/or spilling of shelf sand ing Ouachita-Marathon suture (Fig. 1D). son, 2009). Opening of the Slide Mountain basin lah basin was thrust over the Laurentian margin into adjacent basins (e.g., Ketner, 1968; Gehrels thrust along a transform-dominated spreading system, during the Sonoma orogeny to form the Gol- and Dickinson, 1995). In contrast, allochthonousLast Pennsylvanian–Permian continental-margin recorded by geochemical and isotopic variation conda allochthon (Fig. 1D; Burchfel and Davis, Ordovician quartzites of the El ChancFuerte terranee in basins record ongoing deformation along the of Upper Devonian–lower Permian mafc rocks 1975; Colpron and Nelson, 2009).KB Sinaloa, directly south of the SLaBthrust (Figs. 1A of the Slide Mountain terrane in Canada (Piercey and 1D), have Gondwanan DZ sources and were Laurentian margin. The early Permian Darwin et al., 2012), likely propagated southward from EVOLUTIONCaborca OF THE SLaB REGION deformed in late Permian time (Vega-Granillo et basin formed when the Keeler basin was thrust northern Canada beginning in Late Devonian Initiation of SLaB deformation was dia- al., 2008). The deformation there records fnal block in anscontinentalnnsylvanian Equator anscontinental over the shelf in the upper plate of the Last time (e.g., Colpron and Nelson, 2009). We infer chronous andtransi propagatedt southward (LinkTr et closure of the Ouachita-Marathon suture between Tr that a south-propagating ridge-transform system al., 1996; Cashman et al., 2016). Deformation Gondwana and Laurentia. Permian Equator Chance thrust (Figs. 1C, 1D, and 2; Stevens and RNB Middle Pe arly in the Havallah basin, a trench west of the Klam- ranged from Mississippian in central Nevada Independent evidence for late Paleozoic abso- E Stone, 2005). Sediment gravity fow deposits sa ath arc, and the Caborcan continental transform (e.g., Trexler et al., 2003) to middle Permian in lute northward translation of Laurentia provides Pedrego MM basin of the Rancho Nuevo Formation, now in the Sonora allochthon (Fig. 1D; Poole et al., 2005), 676 www.gsapubs.org | Volume 45 | Number 8 | GEOLOGY accumulated adjacent to the Caborca block and

Downloaded from http://pubs.geoscienceworld.org/gsa/geology/article-pdf/45/8/675/2315559/675.pdf Sonora provide evidence for a long-lived deep-water by University of Colorado Boulder user on 05 February 2021 allochthon EF basin from Early Pennsylvanian through early C D Permian time (Figs. 1C and 2). Detrital zircon (DZ) provenance data are con- Figure 1. A: Location map of southwestern Laurentia indicating key Southwestern Laurentian sistent with sinistral translation along the SLaB. Borderland (SLaB) tectonic elements in relation to uplifts and basins of Ancestral Rocky Moun- tains (ARM) orogen. Orange dashed line and diagonal rule indicate SLaB region as defined Middle Ordovician quartzose turbidites in the herein. Bold numerals indicate column locations of Figure 2. B: Early Mississippian–Early allochthons of Nevada and Sonora contain a ca. Pennsylvanian (Tournaisian–Bashkirian) paleogeography. Intracratonic ARM deformation, 1.8 Ga DZ age peak and subordinate Archean related to Gondwana-Laurentia collision (Kluth and Coney, 1981) rather than SLaB deformation, grains from a source in cratonal Laurentia north has not yet begun to affect region of Transcontinental arch. C: Middle Pennsylvanian–early of the Transcontinental arch (Fig. 1; Gehrels and Permian (Moscovian–Sakmarian) paleogeography. D: Early Permian–middle Permian (Artin- skian–Wordian?) paleogeography. Abbreviations: Afb/Asb—Antler foreland and successor Dickinson, 1995; Gehrels and Pecha, 2014; Linde basins; BS—Bird Spring shelf; DB—Darwin basin; EF—El Fuerte block; ES—Ely shelf; HB— et al., 2016). Cambrian deep-water arenites of the Havallah basin; KB—Keeler basin; KS—Permian Klamath-Sierra arc terrane; MM—Mina México Harmony Formation in central Nevada likewise foreland basin; O-M—Ouachita-Marathon suture; RM—Roberts Mountain allochthon; RNB— have a northern Laurentian source; their imma- Rancho Nuevo basin. Locations of equator in B–D are from Blakey (2016). ture textural characteristics suggest that they were transported along the Laurentian margin a single back-arc basin that narrowed southward met at a triple junction south of the basin (Figs. as a tectonic entity (Linde, 2016), rather than by (Silberling and Roberts, 1962; Colpron and Nel- 1B and 1C). After SLaB deformation, the Haval- longshore transport and/or spilling of shelf sand son, 2009). Opening of the Slide Mountain basin lah basin was thrust over the Laurentian margin into adjacent basins (e.g., Ketner, 1968; Gehrels along a transform-dominated spreading system, during the Sonoma orogeny to form the Gol- and Dickinson, 1995). In contrast, allochthonous recorded by geochemical and isotopic variation conda allochthon (Fig. 1D; Burchfel and Davis, Ordovician quartzites of the El Fuerte terrane in of Upper Devonian–lower Permian mafc rocks 1975; Colpron and Nelson, 2009). Sinaloa, directly south of the SLaB (Figs. 1A of the Slide Mountain terrane in Canada (Piercey and 1D), have Gondwanan DZ sources and were et al., 2012), likely propagated southward from EVOLUTION OF THE SLaB REGION deformed in late Permian time (Vega-Granillo et northern Canada beginning in Late Devonian Initiation of SLaB deformation was dia- al., 2008). The deformation there records fnal time (e.g., Colpron and Nelson, 2009). We infer chronous and propagated southward (Link et closure of the Ouachita-Marathon suture between that a south-propagating ridge-transform system al., 1996; Cashman et al., 2016). Deformation Gondwana and Laurentia. in the Havallah basin, a trench west of the Klam- ranged from Mississippian in central Nevada Independent evidence for late Paleozoic abso- ath arc, and the Caborcan continental transform (e.g., Trexler et al., 2003) to middle Permian in lute northward translation of Laurentia provides

676 www.gsapubs.org | Volume 45 | Number 8 | GEOLOGY

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Tectonic synthesis of the Ouachita-Marathon-Sonora orogenic margin of southern Laurentia 575 28°55' 109°52.5' on Figure 10 on Figure ′ ynorogenic rocks, au- ´ C-C Thrust fault Location of Figure 12 Location of Figure structural data Anticline Line of cross section Overturned anticline Strike-slip fault Strike-slip Contact Syncline Overturned syncline Normal fault UNMAPPED A–E Cerro Los Novillos Sierra Martinez

Poole et al., GSA SP 393, 2005 393, GSASP al., et Poole

Thrust

Thrust EXPLANATION Syncline

109° 55'

Mezquite

Chinos

Gato A

A Mezquite

ysch, major faults and folds, and location of fold-orientation studies of Figure 12. of studies fold-orientation of location and folds, and faults major ysch,

El El A

Quaternary-Tertiary gravels Quaternary-Tertiary (Laramide) plutons Early Tertiary Synorogenic foredeep flysch (Permian) Synorogenic turbidites and deep- water flysch (Mississippian-Permian) deep-water black shale, Preorogenic turbidite, and chert (Ordovician-Mississippian) Carbonate-shelf rocks (Cambrian-Permian) Los de A D A

˜ Una E D E E UNMAPPED Cerro Las Rastras 109°57.5' UNMAPPED 109°57.5' 3 KILOMETERS

′ 2 C SONORA 1 ed geologic map of the Minas de Barita area, central Sonora, showing distribution of allochthonous Paleozoic preorogenic and s BC C UNMAPPED E 0 N 28°55' 28°57.5' 28°52.5' Figure 11. Simpliﬁ ﬂ Permian foredeep and rocks Paleozoic carbonate-shelf parautochthonous to tochthonous Localities A–E on map denote areas of structural measurements for stereo plots A-E on Figure 12. Outline of map shown on Figure shown A-E on Figure 12. Outline of map A–E on map denote areas of structural measurements for stereo plots Localities Note that bothwe have the deep water facies and rocksthe shallow shelf in close quarters, like the situation in eastern NV