The Yavapai-Mazatzal boundary: A long-lived tectonic element in the lithosphere of southwestern North America M.B. Magnani† Department of Earth Science, Rice University, Houston, Texas, USA K.C. Miller Department of Geological Sciences, University of Texas, El Paso, Texas, USA A. Levander Department of Earth Science, Rice University, Houston, Texas, USA K. Karlstrom Department of Earth and Planetary Sciences, New Mexico University, Albuquerque, New Mexico, USA ABSTRACT bivergent orogen that we also suggest is a the nature of the Yavapai-Mazatzal boundary Paleoproterozoic zone of weakness that has and no explanation for its transitional character. A seismic refl ection profi le crossing the subsequently acted as a conduit for magmas Likewise the signifi cance of major tectonic linea- Jemez lineament in north-central New and a locus of tectonism. ments in today’s lithosphere has been controver- Mexico images oppositely dipping zones of sial. The Jemez lineament, originally defi ned as refl ections that converge in the deep crust. Keywords: inherited features, low angle an alignment of Tertiary–Quaternary volcanic We interpret these data as a Paleoprotero- boundary, transition zone, deep seismic pro- centers (Mayo, 1958), is a northeast-trending, zoic bivergent orogen, centered on the Jemez fi le, bivergent orogen. ~100-km-wide zone characterized by active uplift lineament, that formed during original (Wisniewski and Pazzaglia, 2002), low seismic Proterozoic crustal assembly by collision of INTRODUCTION velocity in the mantle (Dueker et al., 2001), and Mazatzal island arcs with Yavapai proto– repeated reactivation (Aldrich, 1986). Its south- orth American continent at ca. 1.68 1.65 Ga. A widely accepted model for growth of the ern edge also coincides approximately with the The two major sets of refl ections within the southwestern United States emphasizes Protero- southern edge of a 300-km-wide transition zone Yavapai-Mazatzal transition boundary dip zoic southward accretion of juvenile lithosphere between the Yavapai (1.8–1.7 Ga) and Mazatzal at 15° 20°, and we interpret them as part of a to the North American continent between 1.8 (1.7–1.6 Ga) Proterozoic provinces (Karlstrom south-dipping thrust system and as a north- and 1.6 Ga (Hamilton, 1981; Bowring and Karl- and Humphreys, 1998). This paper presents new dipping crustal-scale duplex that formed syn- strom, 1990). This model has subsequently been deep-crustal seismic refl ection results across the chronously with the thrust system. The upper challenged by evidence for pre 1.8 Ga crust Jemez lineament of New Mexico. On the basis crust shows structures recording a succession south of the Wyoming craton (Hawkins et al., of seismic and geologic data, we argue that the of tectonic and magmatic events from the 1996; Hill and Bickford, 2001), suggesting that Jemez lineament represents both a Paleoprotero- Paleoproterozoic to the Holocene. Notable recycling of previously accreted crust could have zoic suture zone and a long-lived intracontinental among these structures is a system of nappes been a prominent process in the early stages of tectonic and magmatic boundary. that formed during development of the biver- the tectonic history of the southwestern United The 170-km-long seismic refl ection line gent orogen. Elements of the nappe system States. Whereas locations with evidence for pre (Fig. 1) was acquired in 1999 as part of the are exposed in Rocky Mountain uplifts and 1.8 Ga inheritance are found either proximal to National Science Foundation Continental have been dated as having formed at 1.68 Ga, Archean terranes (Hill and Bickford, 2001) or Dynamics Program within the Rocky Moun- at depths of 10 km and at temperatures in the Mojave province (Hawkins et al., 1996), tains Project (CD-ROM; CD-ROM Working of >500 °C. We also see continuous bright no evidence for an inherited component is found Group, 2002). The profi le, recorded with a refl ections in the upper part of the middle in either the Mazatzal province or most of the 1001-channel system and Vibroseis sources crust that we associate with basaltic sills that Yavapai province. This circumstance suggests (CDP [common depth point] interval = 12.5 m; postdate accretion. The data show that the that, at least in these provinces, the accretionary source interval = 100 m; 8–60 Hz sweep), Yavapai-Mazatzal suture is low angle (~20°), model remains the most plausible option. extends north-south just east of the Rocky an observation that explains why the bound- The assembly boundaries, i.e., the sutures Mountain Front Range faults, following the ary between the provinces has previously between accreted island arcs and oceanic frag- eastern edge of the outcrops of Proterozoic been so hard to defi ne in the surface geology. ments within these provinces, have always been rocks in the Sangre de Cristo Mountains, and The Jemez lineament overlies the root of this diffi cult to identify. In spite of the large number extends south of Las Vegas onto the Great Plains of studies carried out in the southwestern United east of the Pedernal Hills (Fig. 1). The poststack †E-mail: [email protected]. States, there is no agreement on the location and depth-migrated seismic image (Fig. 2), although GSA Bulletin; September/October 2004; v. 116; no. 7/8; p. 000–000; doi: 10.1130/B25414.1; 3 fi gures. For permission to copy, contact [email protected] © 2004 Geological Society of America 2 America Bulletin, Geological Societyof 108˚0’0"W 107˚0’0"W 106˚0’0"W 105˚0’0"W 104˚0’0"W 37˚0’0"N Volcanic rocks (Quaternary, I I Miocene and Oligocene) I INCE I ROV Denver I I I Rio Grande rift sediment APAI P I YAV I Mts TZAL I I I I APAI-MAZAION I Phanerozoic rocks undivided I YAV I I TRANSIT I I I I I 1.4 Ga plutons nde I I I I Arch I 1.7 - 1.65 Ga plutons I I Sierra Gra I Albuquerque I VINCE 13000 1.67 - 1.65 Ga Mazatzal crust TZAL PRO MAZA 1.69 Ga 36˚0’0"N 12000 I Hondo + Vadito Groups km I 10000 I 0 100 200 I Sangre de Cristo I I pre ~ 1.7 Ga Yavapai crust I 9000 I I Santa T I etal. MAGNANI Z I Fe 8000 I JEME I LINEAMEN I I I Las Vegas I I I I Volcanic vents I I I 6000 I LINEAMENT I I I I JEMEZ I I I I I I 10000 I 5000 I I September/October I Seismic reflection profile I I 11000 I I I I I 4000 with CDP points I 12000 I I I 3000 I II Sandia Mts I I Miocene normal fault I I I I 35˚0’0"N Albuquerque I I 2000 I I I I I I I I Paleoproterozoic thrust I 1000 I 2004 I Pennsylvanian strata ManzanoI Mts zero isopach I Pedernal I I Hills Jemez Lineament I MORENCI I I 050100 Km Laramide reverse fault LINEAMENT I and monoclines 107˚0’0"W 106˚0’0"W 105˚0’0"W 104˚0’0"W Figure 1. Simplifi ed geologic map of the northern New Mexico showing basement rocks, Tertiary–Quaternary volcanic centers and Rio Grande rift sediments. CD-ROM seis- mic line is shown with CDP numbers (thick solid line). OVF—Ocate volcanic fi eld; JMVF—Jemez Mountains volcanic fi eld, MTVF—Mount Taylor volcanic fi eld. THE YAVAPAI-MAZATZAL BOUNDARY complicated, can be interpreted on the basis of laterally continuous event (identifi ed as A in refl ectors at 10–12 km depth (C) that form an present knowledge of the evolution of south- Fig. 2) separates almost undeformed sedimen- arch in the section over a length of >100 km. western North America developed from surface tary rocks from folded and faulted basement The apex of the arch is beneath Las Vegas, New mapping, geochemistry, and geochronology. structure. Depth to basement in the north is 2 km Mexico. To the south, between CDP 1250 and The striking features of the profi le are (1) (1.2 s). This refl ection shallows over the Sierra CDP 2250 are three south-dipping refl ections the prominent undeformed refl ection at the Grande uplift near Las Vegas, New Mexico, and (E) traceable at depths of 2 to 10 km. base of the Paleozoic sedimentary rocks north in the south appears only intermittently at the At depths of >8 km, the differences between of the Jemez lineament and the absence of this shallowest resolvable depths (~300 m). the northern and the southern part of the pro- refl ection to the south, (2) simple, bright, sub- Immediately beneath the sedimentary cover fi le are even more remarkable. In the northern horizontal refl ections in the upper and middle in the north is a group of undulating coherent section the bright refl ectors (C in Fig. 2) at crust, (3) the change in the dip of refl ectivity refl ections (B1 in Fig. 2) extending to ~8 km 12–15 km overprint a southward-dipping 8-km- north and south of the Jemez lineament in the depth that, upon close examination, are seen to thick band of refl ectors (D1) that extends from middle crust, and (4) the absence of signifi cant be made up of a number of short refl ection seg- 9 km depth at the northern edge of the profi le, Moho refl ectivity. These features are described ments. The undulating refl ectors disappear into to ~33 km depth near CDP 11000, a distance of below from shallowest to deepest and are then a featureless region south of CMP 10500.