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

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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 H DO NEW MEXICO ARIZONA CALIFORNIA 34° 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° SB 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° NEVADA CO Agua Prieta 120° 118° 116°UTAH 114° 112° 110° 100° 112° United States110° LOR CO Mexico NEVADA UTAH United StatesNogales Agua Prieta ? LOR 38° Mexico A Nogales ? DO 38° A 31° DO 31° Caborca Caborca NEWNEW 0 0 ARIZONA 70 70 ARIZONA MEXICOMEXICO 600 600 Santa AnaSanta Ana 500 0 36° 500 0 400 36° 400 shelf Outer 30 shelf Outer 30 0 0 0 2 0 2 0 10 0 10 30° 30° 0 34° 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 CO C BAJ Sahuaripa RNI UNITEDGUL ST HI 32° PACIFICCALIFO ? C shelf Inner NORTE ALIFO H Hermosillo OCEAN A F A SONORA U OF ATE 29° MEXI S A California 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
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