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 MAGNANI et al. eld.

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2 Geological Society of America Bulletin, September/October 2004 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. South ~48 km. South of Las Vegas and below 10 km, discussed from oldest to youngest. of CDP 6000 the basement is very shallow; the the section exhibits numerous north-dipping upper 2 km of the image bears a band of bright continuous refl ections (D2) that delineate a OBSERVATIONS but diffuse refl ectivity (B2) fading into a weakly duplex. The duplex occupies the entire middle refl ective upper crust at 8–10 km depth. The crust, having a maximum thickness of 27 km In the northern part of the profi le, at shal- continuity of this transparent region is inter- and a length of >50 km. The structure ends low depth (2 km), a single high-amplitude and rupted by a system of bright, nearly continuous, in the north at a depth of 30–35 km (CDP

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B) South Las Vegas, NM North Manzano Thrust Belt Hermit's PeakPecos Ocate volcanic field Fowler Pass 1.65-1.60 Ga Granite thrust Shear Zone 0 A A B2 A 1.4 Ga granites? 5 B1 E 10 C C 15 C C C D2 C 20 D2 25 D1 D1 D3 30 Depth (km) 35 D3 D2 40 Moho 45 50 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000 13000

Figure 2. (A) Depth-migrated CD-ROM seismic refl ection profi le. Depth conversion computed at 80% of stacking velocities. (B) Interpreted seismic profi le. Refl ectors: A—Great Unconformity; B1 and B2—supracrustal Proterozoic rocks; C—Proterozoic or Cenozoic mafi c sills; D1 and D2—bivergent Paleoproterozoic suture (1.68–1.65 Ga) with opposing dips; E—Manzano thrust belt (1.65–1.60 Ga).

Geological Society of America Bulletin, September/October 2004 3 MAGNANI et al.

5800–6000). South of CDP 2000, yet another set The refl ectors labeled E in Figure 2 are the translation of one island arc onto another. Local of north-dipping diffuse refl ectivity (D3) enters southernmost identifi ed on the profi le, and their surface outcrops show that the precollision the profi le at a depth of 25 km and fades out at interpretation relies on the structures observed Yavapai crustal rocks extend southward to about depth of 43 km. At the northernmost end of the in outcrops of Proterozoic rocks in the Pedernal CDP 6500. South of this point, 1.67–1.65 Ga line, the refl ectivity is generally absent below Hills and the Manzano Mountains (60 km and rocks exposed in the Sandia Mountains and the ~30 km. In the center and the south, refl ections 120 km to the southwest, respectively). Here Pedernal Hills belong to the Mazatzal province. are present to depths as great at 40–43 km, but 1.65 Ga south-dipping imbricate thrust faults We suggest therefore that the rocks that consti- do not defi ne continuous refl ecting surfaces. are documented as part of the Manzano thrust tute the duplex imaged at middle-crust depth are belt (Thompson et al., 1991). part of the Mazatzal arc terrane and that they INTERPRETATION OF SEISMIC DATA Interpretation of the deeper refl ection pack- were backthrust southward during the collision ages (D1 and D2 in Fig. 2) is based on compari- at 1.67–1.65 Ga between the Yavapai continent From borehole data, surface outcrops, and son of the seismic image to models for orogenic and the Mazatzal island arc. The amalgamation geologic maps, we interpret with certainty refl ec- development (e.g., Willet et al., 1993) that are of the island arc to the continent produced the tor A as the Great Unconformity, above which is consistent with the island-arc collision model bivergent suture that we observe in the crust an almost undeformed section of Phanerozoic for development of the Southwest (see Karl- today. Continued convergence led to north- sedimentary sequences (Powell, 1875; Baltz, strom and Humphreys, 1998). We interpret the ward movement along the Manzano thrust belt 1999). The lack of topography and deformation southward-dipping refl ection package (D1) and (refl ector E) at 1.65–1.60 Ga onto previously of the unconformity and the overlying sedi- the crustal duplex structure (D2) as a 1.65 Ga deformed Mazatzal terrane rocks. mentary rocks suggests that little deformation Paleoproterozoic bivergent orogenic belt cre- We interpret the bright arched refl ections (C in occurred east of the Front Range faults in the ated by collision of Mazatzal island arcs with Fig. 2) that crosscut the seismic profi le as mafi c sedimentary section as far south as CDP 6000. the Yavapai margin that was already accreted intrusions, on the basis of their high amplitude, The Great Unconformity is not well imaged to the proto–North American continent. The geometry, and depth range. Refl ectors with to the south because the sedimentary cover is 45-km-thick suture zone represents the crustal these characteristics have been interpreted as much thinner (~450–1200 m) and is cut by late expression of the lithospheric boundary between mafi c intrusions on many other seismic profi les Paleozoic high-angle faults that extend into the the Yavapai and the Mazatzal provinces. Teleseis- around the world, often corroborated by surface underlying Precambrian rocks (Broadhead and mic results across the Jemez lineament in New extrusive rocks or documented well data (e.g., King, 1988). We interpret the base of refl ectivity Mexico (Dueker et al., 2001) show a south-dip- Goodwin et al., 1989; Ross and Eaton, 1997; (B2, Fig. 2) as the contact between Precambrian ping low-velocity body extending into the mantle Papasikas and Juhlin, 1997). Furthermore, pre- rocks and inferred granitic crust (see below). to a depth of 120 km, consistent with southward liminary calculation of the polarity of the bright We interpret the undulating horizon and over- subduction of the Yavapai lithosphere under the refl ections (C) indicate that they have the same turned fold (B1 in Fig. 2) imaged just below the Mazatzal arc. The geometry of the D1 refl ectivity polarity as that of the Great Unconformity (A), Great Unconformity at a depth of 3–5 km (CDP suggests top-to-the-north thrusting, imbricating which is known from well data to have a posi- 9000–13500) as the subsurface expression of Mazatzal supracrustal rocks onto Yavapai base- tive impedance contrast. This observation likely Proterozoic nappes that crop out in the Laramide ment. Such an interpretation is supported by the rules out molten magma as a possible origin for uplifts to the west (Fig. 1). Exposed in these observation that the projection to the surface of the refl ectors. ranges are the lower limb and part of the hinge the D1 refl ectivity occurs in the Cimarron Moun- Crosscutting relationships in the seismic data of a north-facing nappe, imbricated by several tains where the Proterozoic Fowler Pass shear demonstrate only that the sills postdate accre- south-dipping, top-to-the-north ductile thrusts zone crops out. This shear zone is considered tion. However, regional geology suggests that and cored by the 1.68 Ga Guadalupita granitic a fundamental Proterozoic crustal boundary as they are likely to be Mesoproterozoic or late gneiss (Riese, 1969; Read et al., 1999). Remark- it juxtaposes profoundly different rock types Tertiary in age. In southeastern New Mexico, ably, the seismic data image the entire nappe, the characterized by diverse deformation histories a major mafi c magmatic episode led to the seismic signature of which probably originates (Grambling and Dallmeyer, 1993). Although intrusion of the 1.1 Ga Pecos Mafi c Intrusive from a 1200-m-thick quartzite layer (Ortega no constraints on activity before 1.4 Ga exist, Complex (Keller et al., 1989; Adams and Formation), a regional stratigraphic marker the oldest fabric on both sides of the fault is ca. Miller, 1995). Additional evidence for mafi c in the 1.69 Ga Hondo Group. South of CDP 1.7 Ga (Carrick, 2002). We therefore suggest that magmatism of this age comes from well data, 9000 (Pecos thrust), where the refl ectivity loses the D1 refl ectivity is the continuation at depth of 50 km southeast of our profi le, where an age of coherence, lies the ca. 1.4 Ga Hermit’s Peak a proto–Fowler Pass shear zone that juxtaposed 1090 Ma has been obtained for a gabbro intrud- granite (Read et al., 1999). Although the extent the supracrustal Mazatzal rocks with Yavapai ing metasedimentary and metavolcanic rocks of of this magmatic body to the south is unknown, packages during the early stages of the suturing. the Debaca sequence (Amarante et al., 2000). we speculate that the lack of refl ectivity at this In this interpretation the north-dipping crustal Refl ectors similar to those seen in the CD-ROM depth across most of the southern sector of the duplex system (D2 in Fig. 2) would have been data tie gabbro in the well to industry refl ection profi le is due to the presence of upper-crustal emplaced during island-arc–continental colli- data (Amarante et al., 2000). Another possibil- granitoids that intruded the crust during dif- sion. According to surface geology, rocks above ity is that the intrusions are ca. 1.3 Ga in age ferent Proterozoic tectonic events. Exposures the D1 thrust are tectonically and magmatically and are associated with bimodal magmatism of 1.4 Ga granites in the Manzano and Sandia mixed elements of both the Yavapai and Mazat- in the Southern Granite-Rhyolite province as uplifts (Priest and Sandia plutons) suggest that zal provinces (e.g., Shaw and Karlstrom, 1999). observed in the Texas Panhandle (Van Schmus the subsurface bodies were most likely emplaced In the subsurface, the suture zone itself likely et al., 1993; Barnes et al., 2002). during the 1.4 Ga “anorogenic” magmatic event consists of highly deformed, structurally mixed Alternatively, nearby surface exposure of (Karlstrom and Humphreys, 1998), although an metasedimentary, metavolcanic, and meta- basalt and basaltic andesites of Tertiary to age of 1.65 Ga cannot be ruled out. plutonic rocks, tectonized during large-scale Quaternary age (Baltz, 1999; Green and Jones,

4 Geological Society of America Bulletin, September/October 2004 THE YAVAPAI-MAZATZAL BOUNDARY

South North intrusions have ponded at several crustal levels 0 A before reaching the surface, perhaps exploiting MAZATZAL 10 preexisting faults or zones of weakness of Pre- YAVAPAI cambrian or/and Laramide age. The observation 20 1.68– 1.65 Ga that the bright refl ections do not seem to be 30 affected by the Mississippian–Pennsylvanian Depth (km) uplift that shaped the Great Unconformity sup- 40 ports a young age for the intrusions. 50 The lower crust and the Moho are not well defi ned by individual refl ections or strongly refl ective zones: rather refl ectivity just dies off 0 B at Moho levels, and at Moho depth only scat- 10 tered refl ectivity is observed. Amplitude-decay B1 calculations suggest that the lack of Moho 20 E 1.65–1.60 Ga refl ectivity is not attributable to poor signal pen-

30 D1 etration but rather to a nonrefl ective lower crust. Depth (km) D2 Nearly spatially coincident CD-ROM seismic 40 refraction data detect the Moho at 43–45 km, 50 the depth at which refl ective packages terminate on the profi le we describe (Snelson, 2001). The refraction data show intermittently strong wide- angle refl ections. Despite careful processing and analysis, no strong refl ectors appear in the 0 C higher-frequency (8–60 Hz) vertical-incidence 10 1.4 Ga granites B1 data as Moho depths are reached. 20 E 1.45 –1.35 Ga DISCUSSION 30 D1 Depth (km) D2 40 Interpretations of refl ector A, the Great Unconformity, and refl ector B1, a Precambrian 50 nappe structure, are well correlated with local and regional geology. Such is not the case with the interpretations of refl ection package D1 and Manzano Thrust Belt Pecos D2, the Precambrian suture, which is model 1.65-1.60 Ga thrust 0 based, or refl ection C, a Tertiary–Quaternary or B1 D Proterozoic magmatic feature, which are based 10 E C on refl ection character, borehole data, and sur- 20 D1 1.35 Ga– face evidences. D2 Present The duplex refl ectors (D2) and the north-dip- 30 Depth (km) ping refl ectivity (D1) imaged at middle- and 40 lower-crust depths could have a variety of

50 origins. We propose that (1) they represent, respectively, a crustal duplex system and a 0 50 Km crustal-scale thrust zone that accommodated Figure 3. Tectonic model. (A) Subduction of the Yavapai margin generates the Mazatzal vol- the underthrusting of the Yavapai crust beneath canic arc. Mazatzal sediments are deposited over Yavapai basement (1.70 Ga). (B) Mazatzal the Mazatzal crust during the Mazatzal orogeny arc collides with the Yavapai margin, and as deformation progresses, bivergent structures (Conway and Silver, 1989) and (2) they record nucleate (1.68–1.65 Ga). (C) At 1.4 Ga a regional anorogenic magmatic event affects the sta- the impressive shortening associated with the ble lithosphere, producing 10 km of uplift and subsequent denudation and the emplacement orogenic collage. The Alpine orogeny is a of granitic and basaltic magma. (D) Mafi c sills intrude the cratonic lithosphere, possibly modern analogue whose scale is similar to the exploiting the presence of the preexistent Proterozoic suture (1.1 Ga to Holocene). tectonic model for the Mazatzal-Yavapai col- lision (Fig. 3) The geometry of the refl ectivity (oppositely dipping refl ections on both sides 1997), indicate that the bright refl ections could a suite of basaltic and intermediate-composi- of the suture) and the scale of the observed represent the intrusive counterpart of the extru- tion lavas (ranging from alkali olivine basalts suture (the structures are imaged along a 170- sive rocks observed along the Jemez lineament. to dacites) 8.3–0.8 Ma in age. The petrology km-long profi le and appear to continue beyond The northern part of the line crosses into the of these volcanic rocks is indicative of crustal the northern end) show a close similarity with Ocate fi eld, a Quaternary volcanic center that is contamination by mixing of a basaltic melt the structures observed in the Alps both by one of several basaltic complexes that defi ne the with a crustal granodiorite (Nielsen and Dun- seismic images and surface geology (Schmid Jemez lineament. The eruptive center exposes gan, 1985). This fi nding suggests that these et al., 1996). In the Alpine system, further

Geological Society of America Bulletin, September/October 2004 5 MAGNANI et al.

EAR-0208020 to Rice University and EAR-9614269, Canyon, Arizona: Geological Society of America Bul- compression after the collisional stage led to the EAR-0003578, and EAR-0207794 to the University letin, v. 108, p. 1167–1181. formation of a bivergent orogen with a southern of Texas at El Paso. Hill, B.M., and Bickford, M.E., 2001, Paleoproterozoic and a northern foreland and the propagation of rocks of central Colorado: Accreted arc or extended older crust?: Geology, v. 29, p. 1015–1018. thrusting in both directions. We propose a simi- REFERENCES CITED Karlstrom, K.E., and Humphreys, E.D., 1998, Persistent lar scenario, in which the Mazatzal arc—created infl uence of Proterozoic accretionary boundaries in Adams, D.C., and Miller, K.C., 1995, Evidence for late the tectonic evolution of southwestern North America: by the 1.68–1.65 Ga subduction of the passive middle Proterozoic extension in the Precambrian Interaction of cratonic grain and mantle modifi cation margin of the Yavapai block—eventually col- basement beneath the Permian basin: Tectonics, v. 14, events: Rocky Mountain Geology, v. 33, p. 161–180. lided against the Yavapai margin and imbri- p. 1263–1272. 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Rocky Mountains paleotectonics: Socorro, New Powell, J.W., 1876, Exploration of the Colorado River of the nitic bodies in the crust (Fig. 3C). The thermal Mexico Institute of Mining and Technology, v. 38, West and its tributaries: Washington, D.C., Smithson- event produced a 10 km surface uplift and the scale 1:125,000. ian Institution, 291 p. Barnes, M.A., Anthony, E.Y., Williams, I., and Asquith, G.B., Read, A.S., Karlstrom, K.E., Grambling, J.A., Bowring, eventual subsequent erosional denudation. 2002, Architecture of 1.38–1.34 Ga granite-rhyolite S.A., Heizler, M., and Daniel, C., 1999, A middle- complex as revealed by geochronology and isotopic crustal cross section from the Rincon Range, northern CONCLUSIONS and elemental geochemistry of subsurface samples New Mexico: Evidence for 1.68 Ga, pluton-infl uenced from west Texas, U.S.A.: Precambrian Research, tectonism and 1.4 Ga regional metamorphism: Rocky v. 119, no. 1-4, p. 9–43. Mountain Geology, v. 34, p. 67–91. The seismic data show two Paleoproterozoic Bowring, S.A., and Karlstrom, K.E., 1990, Growth, sta- Riese, R.W., 1969, Precambrian geology of the southern crustal structures that we interpret as a bivergent bilization and reactivation of Proterozoic lithosphere part of the Rincon Range [M.S. thesis]: Socorro, New in the southwestern United States: Geology, v. 18, Mexico Institute of Mining and Technology, p. 103. orogen formed at an accretionary suture. The p. 1203–1206. Ross, G.M., and Eaton, D.W., 1997, Winagami refl ection features have survived subsequent Proterozoic Broadhead, R.F., and King, W.E., 1988, Petroleum geology sequence: Seismic evidence for postcollisional mag- and substantial Phanerozoic tectonism. This of Pennsylvanian and Lower Permian strata, Tucumcari matism in the Proterozoic of Western Canada: Geol- Basin, east-central New Mexico: New Mexico Bureau ogy, v. 25, p. 199–202. new image of a Proterozoic bivergent suture of Mines and Mineral Resources Bulletin 119, p. 76. Schmid, S.M., Pfi ffner, O.A., Froitzheim, N., Schoenborn, G., also sheds light on the long-standing puzzle of Carrick, T.L., 2002, Proterozoic tectonic evolution of the and Kissling, E., 1996, Geophysical-geological transect Cimarron Mountains, northern New Mexico [M.S. and tectonic evolution of the Swiss-Italian Alps: Tecton- why the boundary between Yavapai crust to the thesis]: El Paso, University of Texas, 76 p. ics, v. 15, p. 1036–1064. north and the Mazatzal crust to the south is so CD-ROM Working Group, 2002, Structure and evolution of Shaw, C.A., and Karlstrom, K.E., 1999, The Yavapai- Mazatzal broad and transitional. Clearly, the entire crust is the lithosphere beneath the Rocky Mountains: Initial crust boundary in the Southern Rocky Mountains: results from the CD-ROM experiment: GSA Today, Rocky Mountain Geology, v. 34, no. 1, p. 37–52. composed of Yavapai and Mazatzal material that v. 12, no. 3, p. 4–10. Snelson, C.M., 2001, Investigating seismic hazards in west- has been tectonically mixed within the orogen. Conway, C.M., and Silver, L.T., 1989, Early Proterozoic ern Washington and in the Rocky Mountains: Implica- This suture has persisted in the crust as a zone rocks (1710–1610 Ma) in central to southwestern tions for seismic hazards and crustal growth [Ph.D. Arizona, in Jennings, J.P., and Reynolds, S., eds., Geo- thesis]: El Paso, University of Texas, 248 p. of weakness, allowing magma penetration until logic evolution of Arizona: Tucson, Arizona Geologi- Thompson, A.G., Grambling, J.A., and Dallmeyer, R.D., the present as evidenced by modern local extru- cal Society Digest 17, p. 165–186. 1991, Proterozoic tectonic history of the Manzano Dueker, K., Yuan, H., and Zurek, B., 2001, Thick-structured Mountains, central New Mexico: New Mexico Bureau sive rocks. The boundary zone appears spatially Proterozoic lithosphere of the Rocky Mountain region: of Mines and Mineral Resources Bulletin, v. 137, correlated with bright crosscutting refl ections GSA Today, v. 11, no. 12, p. 4–9. p. 71–77. that we interpret as Middle Proterozoic or Ter- Goodwin, E.B., Thompson, G., and Okaya, D.A., 1989, Van Schmus, W.R., Bickford, M.E., and Condie, K.C., 1993, Seismic identifi cation of basement refl ectors: The Early Proterozoic crustal evolution, in Reed, J.C., Jr., tiary–Quaternary basaltic intrusions. Teleseismic Bagdad refl ection sequence in the Basin and Range et al., eds., Precambrian: Conterminous U.S.: Boulder, results (Dueker et al., 2001) show that the crustal Province–Colorado Plateau transition zone, Arizona: Colorado, Geological Society of America, Geology of suture zone is underlain by a region of mantle Tectonics, v. 8, p. 821–831. the North America, v. C-2, p. 270–281. Grambling, J.A., and Dallmeyer, R.D., 1993, Tectonic evo- Willett, S., Beaumont, C., and Fullsack, P., 1993, Mechani- having low compressional and shear velocities. lution of Proterozoic rocks in the Cimarron Mountains, cal model for the tectonics of doubly vergent compres- This mantle anomaly is a likely source of pres- northern New Mexico, USA: Journal of Metamorphic sional orogens: Geology, v. 21, p. 371–374. Geology, v. 11, p. 739–755. Wisniewski, P.A., and Pazzaglia, F., 2002, Epeirogenic ent-day basaltic magma generation. Green, G.N., and Jones, G.E., 1997, The digital geologic controls on Canadian River incision and landscape map of New Mexico in ARC/INFO format: U.S. Geo- evolution, Great Plains of northeastern New Mexico: ACKNOWLEDGMENTS logical Survey Open-File Report OF-97-52, 9 p. Journal of Geology, v. 110, p. 437–456. Hamilton, W.B., 1981, Evolution of continental crust by We thank our colleagues in the CD-ROM work- arc magmatism: U.S. Geological Survey Professional Report P1275, 162 p. MANUSCRIPT RECEIVED BY THE SOCIETY 3 JUNE 2003 ing group and Chris Andronicos for the stimulating Hawkins, D.P., Bowring, S.A., Bradley, R.I., REVISED MANUSCRIPT RECEIVED 24 OCTOBER 2003 MANUSCRIPT ACCEPTED 17 NOVEMBER 2003 discussions at every stage of this work. Funding Karlstrom, K.E., and Williams, M.L., 1996, U-Pb for this research was provided by National Science geochronologic constraints on the Paleoproterozoic Foundation grants EAR-9614777, EAR-003539, and crustal evolution of the Upper Granite Gorge, Grand Printed in the USA

6 Geological Society of America Bulletin, September/October 2004