sign in sign up
<<
Home , Basin and Range Province, Chronometry, Geology of New Mexico, Rio Grande Rift, Southwestern New Mexico

2021 Annual Program Report

VOL. 31, NO. 10 | OCTOBER 2021

The Origin and Tectonic Significance of the Basin and Range– Boundary in Southern New , USA The Origin and Tectonic Significance of the Basin and Range– Boundary in Southern , USA

Jason W. Ricketts, Dept. of Earth, Environmental and Resource , The University of Texas at El Paso, 500 West University Ave., El Paso, Texas 79968, USA, [email protected]; Jeffrey M. Amato, and Michelle M. Gavel, Dept. of Geological Sciences, New Mexico State University, Las Cruces, New Mexico 88003, USA

ABSTRACT separated from the ​thermal boundary and reinforce the idea that extension in the western United by the Plateau, and they exist as the southern Rio Grande rift is a separate States occurred within two iconic domains: distinct structural entities, but in southern structural entity from the adjacent Basin and the Basin and Range and Rio Grande rift. New Mexico, they merge to form an inter- Range Province. These provinces merge in southern New connected zone of extension that continues Mexico to form an interconnected zone of south into Mexico (Fig. 1). The existence of a THE RIO GRANDE RIFT–BASIN AND extension, although the existence, location, discrete boundary between the two domains RANGE BOUNDARY IN SOUTHERN and nature of the boundary between the two and the nature of this transition in southern NEW MEXICO provinces are uncertain. In southern New New Mexico remain unclear, although There are three models for how to assess Mexico, existing thermochronologic, geo- understanding the transition is crucial for the Rio Grande rift–Basin and Range logic, and geophysical data sets, combined assessing how these two extensional prov- Province boundary (Fig. 1): (1) The northern with thermal modeling of zircon (U-Th)/He inces evolved through . The physio- Rio Grande rift is a separate entity from the (ZHe) data, define a subvertical, 30–40-km- graphic expression of extension in southern Basin and Range Province, and is distin- wide boundary that extends through the New Mexico suggests an indistinct or nonex- guished by its narrow width (dark orange in to depths of at least 100 km. istent boundary, favoring models where the Fig. 1); (2) the entire Rio Grande rift exists as Thermal modeling indicates Rio Grande rift is the easternmost segment a separate entity along its entire length (light in the upper of the south- of the Basin and Range Province (Eaton, and dark orange in Fig. 1); and (3) the two eastern Basin and Range exceeded 225 °C 1982). This view is contentious, however, provinces are contiguous and coeval and during magmatism, resetting because thermochronologic (Gavel, 2019) thus the Rio Grande rift is just a localized ZHe dates and creating a thermal boundary and geophysical (e.g., Keller et al., 1990; for the Basin and Range Province on its that coincides with independent geologic Averill and Miller, 2013; Feucht et al., 2019) eastern margin adjacent to the Colorado and geophysical data sets. Although many data sets highlight important differences Plateau (thick dark green line in Fig. 1). We aspects of this boundary are transient, oth- between the two provinces, supporting mod- investigate the nature of a possible boundary ers may become permanent features to els where they exist as two separate, albeit in southern New Mexico, and use “transition define a lithospheric-scale boundary prone contiguous entities. This nontrivial distinc- zone” to refer to a 40-km-wide zone that to reactivation during tectonism. tion has implications for the relative role includes major differences in the crust and This assessment of the boundary supports of plate-boundary versus processes lithosphere. Physiographic maps, which are models in which the southern Rio Grande driving extension in western based on modern topography and drainage rift is a separate structural entity from the (Dickinson, 2002). basins, lump the southern Rio Grande rift adjacent Basin and Range, and this A more complete understanding of the with the Basin and Range Province provides an exceptional case study for boundary requires diverse data sets at dif- (Hammond, 1970). Most workers place the understanding how extensional lithospheric- ferent scales to constrain its current charac- boundary at the eastern edge of the transition scale boundaries evolve to become stable teristics and evolutionary . Here we zone (e.g., Mack, 2004; van Wijk et al., 2018), features of . use thermochronologic data, including apa- which coincides with the western edge of the tite fission-track (AFT), apatite (U-Th)/He rift farther north, but it has not yet been INTRODUCTION (AHe), and zircon (U-Th)/He (ZHe), together clearly documented as to why this is a mean- The Rio Grande rift and Basin and Range with a synthesis of geologic and geophysi- ingful or geologically relevant location in Province are two of the most iconic exten- cal data from to southern New Mexico. sional domains on Earth; the Basin and investigate the nature of the transition at a Range Province is the archetypal example of lithospheric scale. We then document a pro- GEOLOGIC AND GEOPHYSICAL a wide rift, and the neighboring Rio Grande nounced thermal boundary across the tran- MANIFESTATIONS OF A BOUNDARY rift is one of the classic modern examples of sition preserved in ZHe data sets. When In southern New Mexico, independent a narrow continental rift (e.g., Buck, 1991). viewed collectively, these independent data data sets highlight a subvertical boundary For most of its length, the Rio Grande rift is sets reveal a complex and dynamic tectono- 30–40 km wide that extends to depths of at

GSA Today, v. 31, https://doi.org/10.1130/GSATG509A.1. CC-BY-NC.

4 GSA Today | October 2021 sensitive to temperatures of 30–90 of 30–90 temperatures to sensitive scales. time interseismic at deforming is rift the that indicate also data these but rift, Grande Rio southern the in faults of Quaternary number a greater with sistent con are GPS results Province. Range and Basin eastern adjacent the in 0.31 nstr/yr of 1.45 lower to rates rift Grande Rio the of 8.54 rates strain highest the from transition a sharp Notably, is there rift. Grande Rio southern and Province Range and Basin the in higher magnitude of order an are rates (nstr/yr), strain but of 0.68 rates low strain al., et 2019). has Plains Murray Great The (Fig. 2A; Province Range and Basin the and Plains Great the between rates strain (GPS) show variable system data tioning 2). (Figs. 1and 100 km least Global posi AHe, AFT, and ZHe thermochronology, thermochronology, ZHe AFT, and AHe, plexes in blue and different models for the RGR–Basin and Range Province boundary, as discussed in the text. BR—Basin and Range; Range; and BR—Basin text. the in discussed as boundary, Province CP—Colorado Range Plateau; and GP—; com RM—Rocky RGR–Basin core . the for models metamorphic shows Inset different and (U-Th)/He. blue in ZHe—zircon plexes (U-Th)/He; (mWm AHe—apatite flow heat show lines fission-track; white and AFT—apatite (km), 1990). al., et thickness show (Keller crustal areas show lines Blue Cross-hatched 1979). Morgan, (2004). and Mack of (Seager RGR the boundary of the is basins line deep black recording data dashed Thick 2019). al., et magnetotelluric and (Feucht 2013), Miller, and conductance Averill 2007; crustal bulk (Averill, line system positioning reflection/refraction global 2019), al., 2020), et al., et (Murray Reade data 2019; (GPS) Gavel, 2018; al., thermochronology et Biddle includes 2016; Map al., et Ricketts 1997; transition. Chapin, Province and Range and (Kelley data (RGR)–Basin rift Grande Rio southern the of map 1. Geologic Figure 31°N 32°N33°N

BR BR 30 RGR (AHe, ZHe,and/or Thermochronology sample Proterozoic rocks -Mesozoicrocks Cenozoic volcanicrocks -Quaternarybasinfill Quaternary basaltflow Quaternary Figure 1 CP 109°W ± RM 0.17 nanostrains/ 0.17 ± volcanic field 2.10 nstr/yr in 2.10 in nstr/yr Boot Heel GP Basin and AFT) Range Mogollon Datil volcanic field ° C, C, ± - - 0

Bulk crustalconductance(seimens) 108°W 30 the transition zone (Fig. zone 1; Kelley and transition the al., et 2013), across Guenthner compiled are 2005; al., et 2009; Flowers (Ketcham, 60–120 typically deeper in the southern rift (2–4 km) km) (2–4 rift southern the in deeper typically are al., et 1990;Keller Basins Averill, 2007). (Fig. New Mexico 2C; southwestern in km 35 to rift Grande Rio of the axis the beneath ~28–30 km from increases gradually ness 7312 to Ma. from range dates ZHe transition of the east but dates, AHe and AFT to similar are dates (Fig. 2B). ZHe tances West transition of the dis over short drastically change dates However, of extension. ZHe Cenozoic time the overlap with ages and region, this across variation show little dates AHe and AFT al., 2018; Gavel, 2019; al., et 2020). Reade 1997; al., et 2016;Chapin, Ricketts et Biddle

Across this region, overall crustal thick crustal overall region, this Across 35 500 105 transition rra a

37-23 Macalderas

zoz zone Reflection/refraction line nsn 28 on Magnetotelluric station sis n i tiot ° e confidence ellipse o C, and 50–240 50–240 and C, 1000

n 121 5 1 mm/yr;90% ? 25 5 ? ? 1500 107°W 2000

°

Rio Grande

C, respectively 5 10 10 03 5

Chihuahua

rift 15

06 28

85 85 105 10 5 - - 09 106°W of 900–1000 Moho temperatures higher with associated (Averill, is which 2007), rift Grande Rio southern the within velocities mantle upper and densities decreased highlight models Velocity zone. gravity and transition the in absent becomes and west the to welt thins ~12–21 (Fig. 2C; This km Averill, 2007). of depths at rift Grande Rio southern the of axis the beneath material of high-density (Fig. 1). rift Grande Rio al., et 1990) southern the (Keller in flow al., heat et 1990),Keller higher and 1979; Morgan, (Seager and faulting active volcanism, Quaternary voluminous more include boundary of this expressions shallow (Averill, Additional 1km 2007). of than less depths have which typical Province, Range and Basin the toward shallow abruptly and Gravity models are consistent with awelt with consistent are models Gravity 0 TeT Great Plains New Mexico 120 www.geosociety.org/gsatoday exas

km xas

° 30

C (Hamblock et al., et 2007). C (Hamblock 35

105°W

GPS profil GPS in Fig. 40 2

N e –2 - )

5 from 240 to 50 °C (Guenthner et al., 2013). 109°W 108°W 107°W 106°W 105°W 1 Compiled ZHe dates (Biddle et al., 2018; A Mogollon Datil volcanic field Rio Grande rift Great Plains Gavel, 2019; Reade et al., 2020) show dra- 0 and Basin and Range matic differences across the transition zone -1 with relation to eU (Fig. 3). In the Basin and 1.45 ± 0.31 nstr/yr 8.54 ± 2.10 nstr/yr 0.68 ± 0.17 nstr/yr rate (mm/yr) zone

Profile parallel -2 Range Province, ZHe dates are consistent for 800 all eU values. In contrast, east of and includ- 700 B Basin and Range Rio Grande rift 600 ing the transition zone, ZHe dates have a wide

) 500 ZHe (n = 118) transition range, where oldest ZHe dates are correlated 400 AHe Date (n = 129) with lowest eU and youngest ZHe dates have 300 200 AFT Date (n = 65) 150 ± 174 Ma highest eU values. This observation suggests 100 that radiation damage in zircon is a primary control on ZHe dates in this region. 80 Forward modeling allows for the calcula- 60 25.4 ± 5.9 Ma tion of ZHe date-eU curves from an input 26.8 ± 5.7 Ma thermal history, and here it provides a means 40 22.2 ± 17.5 Ma Thermochronologic Date (Ma of testing the potential effects of reheating 20 during magmatism (see supplemental mate- 20.5 ± 7.2 Ma 15.2 ± 8.7 Ma rial for complete modeling details1). We use a 0 2 C basin boundary general thermal history of southern New 4 velocity (km/s) 6 Tomographic velocity model Mexico that includes crystallization at 1.6 Ga 8 234567 (Averill and Miller, 2013) and cooling to 350 °C at 1.45 Ga, based on 10 velocity 2740 kg/m3 3 3 40 39 20 2880 kg/m 2700 kg/m moho Ar/ Ar muscovite data (Amato et al., 2011), (km/s) 2880 kg/m3 30 Velocity and gravity 15 °C at 500 Ma based on the of the over- 40 3 3 6 7 8 3280 kg/m 3250 kg/m models (Averill, 2007) lying , and maximum reheat- 50 Anisotropic electrical resistivity ing to 150 °C at 80 Ma from accumulation of Depth (km) model oriented perpendicular to Paleozoic and (Fig. 3A). 100 the rift axis (Feucht et al., 2019) partial melt We include two endmember Proterozoic cool- log (resistivity (Ωm) 150 10 ing : multiple cooling pulses during 0 123 assembly of Rodinia (path 1; Ricketts et al., 200 2021), and multiple pulses of cooling that 109°W 108°W 107°W 106°W 105°W Longitude coincide with assembly and then breakup of Rodinia (path 2; DeLucia et al., 2017). Figure 2. E-W cross section across the transition. (A) Global positioning system velocities across the profile line shown in Figure 1 (Murray et al., 2019). (B) Thermochronologic dates for all samples shown Resulting ZHe date-eU curves are roughly in Figure 1. Average dates are calculated for each data set in the Basin and Range Province and Rio similar to observed ZHe dates for the Grande rift (±1 standard deviation). (C) Stacked geophysical models for the crust and . Note changes in scale with depth. AFT—apatite fission-track; AHe—apatite (U-Th)/He; ZHe—zircon southern Rio Grande rift regardless of the (U-Th)/He; nstr/yr—nanostrain/year. Proterozoic cooling history. Boot Heel volca- nic field magmatism in southwestern New Magnetotelluric data collected along an THE THERMAL IMPRINT OF Mexico occurred from 37 to 26 Ma based on E-W transect through southern New Mexico A BOUNDARY 40Ar/39Ar sanidine (McIntosh show that the upper mantle is moderately ZHe dates from the Basin and Range and Bryan, 2000), and we test the effects of resistive (30–100 Ωm; Feucht et al., 2019). Province (Fig. 2B) largely overlap with ages this on ZHe dates (Fig. 3B). Calculated The one exception is a zone age conductive of volcanic rocks in southwestern New ZHe date-eU curves only match the observed material centered on 107.5°W at the eastern Mexico, suggesting they were likely reset by data for reheating temperatures of >225 °C margin of the transition zone that is excep- magmatism (Gavel, 2019), and we use these and indicate that this thermal event did not tionally pronounced at depths of 50–100 km data to model the heating effects of Oligocene affect ZHe dates in the southern Rio Grande and that may also extend to depths >200 km magmatism in this region. Individual zircon rift. These results suggest that late Oligocene (Fig. 2C). This feature is interpreted to be a grains from a single sample have variable clo- magmatism imprinted a major thermal zone of lithospheric decompression melting sure temperatures due to accumulation of boundary that coincides with independent (Feucht et al., 2019). Interestingly, this region varying amounts of radiation damage that is geologic and geophysical data sets. of decompression melting is slightly asym- proportional to eU (eU = U + 0.235Th), where metric beneath the southern Rio Grande rift low eU, high He retentivity grains typically DISCUSSION and skewed to the west, as opposed to more correspond to oldest ZHe dates and high eU, symmetric lithospheric thinning and mantle low retentivity grains yield youngest ZHe Age and Evolution of the Boundary in (Wilson dates (Guenthner et al., 2013). These proper- The collective data sets suggest that the et al., 2005). ties allow for thermal modeling of ZHe data southern Rio Grande rift is best explained

1Supplemental Material. Full description of zircon (U-Th)/He modeling, inputs, and assumptions. Go to https://doi.org/10.1130/GSAT.S.14794197 to access the supple- mental material; contact [email protected] with any questions.

6 GSA Today | October 2021 0 1000 Rio Grande rift ZHe (n = 98) young alluvium (Mack, 2004). In the south- path 1 100 A Basin and Range ZHe (n =20) ern Rio Grande rift, the timing of initial Figure 3B 800 200 path 2 Proterozoic (73%) extension was inferred by Amato et al. 300 600 Paleozoic (22%) 40 39 (2019) to have begun by ca. 27 Ma when Ar/ Ar muscovite cooling Cenozoic (5%) 400 age southern New Mexico the voluminous Uvas were erupted 400 lighter shades are (Amato et al., 2011) (Clemons, 1979), which was coeval with mperature (ºC) 500 sedimentary (19%) ZHe Date (Ma ) Te 600 Crystallization 200 deposition of the Thurman Formation 50 μm grain size 700 12345 (Boryta, 1994). Extension was active through 0 the late Quaternary as evidenced by long fault 1800 1400 1000 600 200 0 0 400 800 1200 1600 2000 Time (Ma) eU (ppm) scarps that bound major rift flank uplifts. 0 1000 Thermochronologic data from the study B Earlier thermal area offer an opportunity to further con- 50 history uses path 2 800 strain the of extension and compare to 100 600 the sedimentary record and regional tectonic 150 °C 150 Boot Heel history. Inverse thermal history modeling of 175 °C 400 200 Volcanism AHe, AFT, and ZHe data in southern New

mperature (ºC) 200 °C

(McIntosh and ZHe Date (Ma ) Te 225 °C Mexico suggests that main cooling in the 250 Bryan, 2000) 200 250 °C southeastern Basin and Range Province was 300 0 from 35 to 14 Ma (Gavel, 2019). In contrast, 100 80 60 40 20 0 0 400 800 1200 1600 2000 Time (Ma) eU (ppm) thermal modeling documents distinctly

Figure 3. (A) Forward modeling and calculated zircon (U-Th)/He (ZHe) date-eU curves compared to a younger cooling from 25 to 5 Ma in the compilation of ZHe dates from the southern Rio Grande rift and Basin and Range Province (Biddle et southern Rio Grande rift east of the transi- al., 2018; Gavel, 2019; Reade et al., 2020), where Basin and Range Province data are west of 108°W tion (Fig. 1) to create a complex and highly longitude and Rio Grande rift data are east. ZHe date-eU curves are calculated from a thermal history using the helium diffusion model of Guenthner et al. (2013). 1—assembly of Rodinia; 2—breakup of dynamic lithospheric boundary that formed Rodinia; 3—Ancestral ; 4—Laramide ; 5—Neogene exhumation. (B) Testing during diachronous pulses of extension. the effects of magmatic reheating in the Boot Heel volcanic field. Grain size used on modeling is the average of all zircon grains. Initial Cenozoic development of the bound- ary occurred from 35 to 25 Ma when the as an active extensional province that devel- become more pronounced in independent southeastern Basin and Range Province oped adjacent to the generally inactive data sets, suggesting that many of the dif- experienced voluminous magmatism in the southeastern Basin and Range Province ferences across this boundary are controlled Boot Heel volcanic field and coeval exten- (Fig. 1). The data do not support models by differences in the timing of extension sion (Fig. 4; McIntosh and Bryan, 2000; where the northern Rio Grande rift is sepa- from the Basin and Range Province to the Gavel, 2019), and extension had not yet initi- rate from the Basin and Range of southern Rio Grande rift. ated in the Rio Grande rift. Evolution of the New Mexico (dark orange in Fig. 1) or that Constraining the timing of extension boundary dramatically slowed from 25 to the entire Rio Grande rift is the easternmost across the transition zone provides context 14 Ma when extension in both provinces arm of the larger Basin and Range Province for how and when the boundary evolved. occurred. Thermochronologic data indicate (dark green line in Fig. 1). Many of the Regionally, the easternmost metamorphic that the main phase of rapid extension ended observed manifestations of a boundary in core complexes in southern Arizona are the at 14 Ma in the Basin and Range Province, southern New Mexico can be understood in Pinaleño, active from 29 to 19 Ma (Long et although slower extension likely continued the context of active extension in the south- al., 1995), and the Catalina-Rincon, active until 6 Ma. During this time, formation of ern Rio Grande rift and a relative lack from 27 to 20 Ma (e.g., Davy et al., 1989). the boundary may have continued again as thereof in the Basin and Range Province. Post-detachment extension in the region Rio Grande rift extension outpaced Basin Active lithospheric extension produces persisted until the onset of seafloor spread- and Range Province extension. However, a higher mantle conductance through partial ing in the Gulf of at 6 Ma (e.g., crucial difference at this stage is that contin- melting, higher strain rates, active faulting, Lizarralde et al., 2007). The sedimentary ued formation of the boundary was due to young volcanism, thinner crust, decreased record of extension in southwestern New active extension to the east of the boundary upper mantle velocities and densities, and Mexico is relatively unexplored compared (Rio Grande rift) rather than extension to the possibly deeper basins within the southern to the central and northern segments of the west (Basin and Range Province). Formation Rio Grande rift, where the westernmost Rio Grande rift because there are few out- of the boundary accelerated again at 6 Ma expression of each of these features defines crops of Miocene and older basin strata. when Basin and Range Province extension a 30–40-km-wide subvertical boundary Available data suggest that initial Basin and dramatically decreased and continued to the that extends through the lithosphere (Fig. Range Province extension in this region . Thermochronology is thus consis- 2). At the surface, we place the boundary at was under way during the Oligocene based tent with the available sedimentary record the eastern edge of the transition zone, on thickness of fill and and, when viewed within the context of the because this coincides with changes in basin sparse age control from interbedded volca- regional tectonic framework, reveals impor- depth, Quaternary faulting, volcanism, active nic rocks (Mack, 2004). Although main tant differences in the timing of extension strain rates, and bulk crustal conductance extension is thought to have ceased by across the transition zone, where boundary (Fig. 1). As active extension continues in the 6 Ma, minor Quaternary extension is evi- evolution occurred in two discrete pulses southern Rio Grande rift, the boundary will dent by short fault segments that offset and continues today.

www.geosociety.org/gsatoday 7 WEOur analysis in southern New Mexico is 35-25 Ma: Initial extension/magmatism in the Basin and Range essentially a 2D cross-sectional view of the Magmatism resets boundary, and further data sets to the south ZHe dates in are needed to test whether the transition zone upper crust crust has an overall NS or NW trend and coincides with major Proterozoic boundaries. Based on available data, we therefore suggest that ini- lithospheric mantle tial development of the boundary occurred Region of during the late with Basin and Range decompression Boundary emerges at the eastern Province extension and resulted from sepa- melting edge of extension and volcanism. rate driving mechanisms from the Basin and 25-6 Ma: Active extension in Rio Grande rift and Basin and Range Range Province to the Rio Grande rift.

Preservation Potential in the Initial Rio Grande rift extension at 25 Ma Geologic Record

Mid-crustal If active extension is the underlying cause Crustal thinning beneath the intrusion for most of the observed differences across axis of the Rio Grande rift the transition, then some boundary features No growth of the boundary due to lack of magmatism coupled are transient, such as differences in heat with active extension on either side of the boundary. Basin flow, conductance, and upper mantle veloci- and Range extension slows after 14 Ma. ties and densities on either side of the bound- ary. These features will likely vanish when Present: Active extension in the Rio Grande rift high heat flow extension ceases. In contrast, permanent Quaternary faulting and boundary features include changes in basin volcanism depth, changes in the style of extension mid crustal (presence or absence of metamorphic core welt complexes), different patterns in volcanism, Boundary is Region of warm Moho differences in the timing of faulting, and the well-established decompression (900-1000 °C) and composed of melting thermal imprint on thermochronologic data both transient and warm upper sets (Fig. 4). These permanent features will permanent features transition zone mantle become more pronounced as Rio Grande rift extension continues. Permanent and tran- Future: No extension in the Rio Grande rift or Basin and Range sient boundary features are similar to the Rio deeper Grande rift boundary in central New Mexico. basins In this well-defined segment of the rift, the boundary is demarcated by differences in thinned crust mantle velocities (West et al., 2004), crustal younger older thickness (Wilson et al., 2005), surface heat ZHe dates ZHe dates at surface at surface flow (Reiter et al., 2010), and extensional Boundary is defined by basins bounded by normal faults. The transi- permanent crustal features tion from thinned lithosphere with these characteristics to adjacent unaffected litho- Figure 4. Schematic W-E cross sections showing the evolution of the Basin and Range Province–Rio Grande rift boundary. ZHe—zircon (U-Th)/He. sphere over short distances is a classic and definitive description of a continental rift boundary, and this has been documented in These independent data sets document the and Range Province was more influenced other worldwide (e.g., Achauer and timing of formation of a near-vertical, litho- by plate boundary effects (Bird, 2002). Masson, 2002; Corti, 2009). spheric-scale boundary in southern New Cenozoic development of the boundary may Lithospheric-scale boundaries are long- Mexico, but do not address the origins of also have been superimposed upon N-S– lived features of continents that can form this feature. It may have emerged during trending or NW-trending extensional Neo- through a multitude of major tectonomag- Oligocene magmatism in the Boot Heel vol- proterozoic structures that likely formed matic events. Once established, these fea- canic field, which modified the chemical within an overall convergent tectonic setting tures are prone to reactivation (e.g., New structure of the lithosphere and created a during Grenville orogenesis (e.g., Karlstrom Madrid fault zone; Hurd and Zoback, 2012) sharp thermal gradient that influenced and Humphreys, 1998; Timmons et al., and are therefore influential in guiding the extensional tectonism on either side. This 2001). However, evidence for their existence style and geometry of future deformation model may indicate separate driving mecha- or history is cryptic in southwestern New (Karlstrom and Humphreys, 1998). Across nisms, where mantle processes are responsi- Mexico, and such structures have been more the , Rocky Mountains, and ble for Rio Grande rift extension and mag- thoroughly documented in central and north- Midcontinent , there are numerous matism (Ricketts et al., 2016) and the Basin ern New Mexico (Karlstrom et al., 2004). examples of Ancestral Rocky and

8 GSA Today | October 2021 Laramide basement uplifts that reactivated Witcher, J.C., and Ulmer-Scholle, D.S., eds., Las ny, E.Y., 2007, A composite geologic and seismic inherited structures (Soreghan et al., 2012; Cruces Country III: New Mexico Geological profile beneath the southern Rio Grande rift, New Bader, 2019), including Proterozoic exten- Society Guidebook, v. 69, p. 127–135. Mexico, based on xenolith mineralogy, tempera- Bird, P., 2002, Stress direction history of the western ture, and pressure: Tectonophysics, v. 442, p. 14– sional fault systems (Marshak et al., 2000; and Mexico since 85 Ma: , 48, https://doi.org/10.1016/j.tecto.2007.04.006. Timmons et al., 2001). These events attest to v. 21, https://doi.org/10.1029/2001TC001319. Hammond, E.H., 1970, Classes of land surface the longevity of extensional structures in Boryta, J.D., 1994, Single-crystal 40Ar/39Ar prove- form (map), in The National Atlas of the United continental lithosphere and their susceptibil- nance ages and polarity of rhyolitic States of America: U.S. Geological Survey, scale ity for reactivation. We propose that after tuffaceous of the Thurman Formation 1:7,500,000, p. 62–63. (late Oligocene), Rio Grande rift, New Mexico Hurd, O., and Zoback, M.D., 2012, Regional stress extension in the Basin and Range Province [M.S. thesis]: Socorro, New Mexico, New Mexico orientations and slip compatibility of and Rio Grande rift ceases, this boundary Institute of Mining and Technology, 82 p. focal planes in the : will persist as a stable feature of North Buck, W.R., 1991, Modes of continental lithospher- Seismological Research Letters, v. 83, p. 672– American lithosphere, possibly guiding ic extension: Journal of Geophysical Research. 679, https://doi.org/10.1785/0220110122. future tectonic structures through reactiva- Solid Earth, v. 96, p. 20,161–20,178, https://doi​ Karlstrom, K.E., and Humphreys, E.D., 1998, Per- .org/10.1029/91JB01485. sistent influence of Proterozoic accretionary tion of normal faults. Clemons, R.E., 1979, Geology of Good Sight boundaries in the tectonic evolution of south- Mountains and Uvas Valley, southwest New western North America: Interaction of cratonic ACKNOWLEDGMENTS Mexico: New Mexico Bureau of Mines and Min- grain and mantle modification events: Rocky We thank John Singleton, an anonymous review- eral Resources Circular, v. 169, 32 p. Mountain Geology, v. 33, p. 161–179, https://doi​ er, and editor Mihai Ducea for comments that Corti, G., 2009, Continental rift evolution: From .org/10.2113/33.2.161. helped strengthen the arguments made in this paper. initiation to incipient break-up in the Main Karlstrom, K.E., Amato, J.M., Williams, M.L., Becky Flowers and Jim Metcalf at the University of Ethiopian Rift, East : Earth-Science Heizler, M., Shaw, C.A., Read, A.S., and Bauer, Colorado TRaIL lab in Boulder, Colorado, USA, Reviews, v. 96, p. 1–53, https://doi.org/10.1016/​ P., 2004, Proterozoic tectonic evolution of the helped acquire (U-Th)/He data. This work is sup- j.earscirev.2009.06.005. New Mexico region: A synthesis, in Mack, G.H., ported by NSF grants EAR-1624538 to Ricketts and Davy, P., Guérin, G., and Brun, J.-P., 1989, Thermal and Giles, K.A., eds., The Geology of New Mex- EAR-1624575 to Amato. constraints on the tectonic evolution of a meta- ico: A Geologic History: New Mexico Geologic morphic core complex (Santa Catalina Moun- Society, Special Publication 11, p. 1–34. tains, Arizona): Earth and Planetary Science Keller, G.R., Morgan, P., and Seager, W.R., 1990, REFERENCES CITED Letters, v. 94, p. 425–440, https://doi.org/​ Crustal structure, gravity anomalies and heat Achauer, U., and Masson, F., 2002, Seismic 10.1016/0012-821X(89)90159-3. flow in the southern Rio Grande rift and their re- tomography of continental rifts revisited: From DeLucia, M.S., Guenthner, W.R., Marshak, S., lationship to : Tectonophys- relative to absolute heterogeneities: Tectono- Thompson, S.N., and Ault, A.K., 2017, Thermo- ics, v. 174, p. 21–37, https://doi.org/10.1016/0040​ physics, v. 358, p. 17–37, https://doi.org/10.1016/ links denudation of the Great Un- -1951(90)90382-I. S0040-1951​(02)00415​-8. conformity surface to the supercontinent cycle Kelley, S.A., and Chapin, C.E., 1997, Cooling histo- Amato, J.M., Heizler, M.T., Boullion, A.O., Sanders, and snowball Earth: Geology, v. 46, p. 167–170, ries of mountain ranges in the southern Rio A.E., Toro, J., McLemore, V.T., and Andronicos, https://doi.org/10.1130/G39525.1. Grande rift based on apatite fission-track analy- C.L., 2011, Syntectonic 1.46 Ga magmatism and Dickinson, W.R., 2002, The Basin and Range sis—A reconnaissance survey: New Mexico rapid cooling of a gneiss dome in the southern Province as a composite extensional domain: Geology, v. 9, p. 1–14. Mazatzal Province: Burro Mountains, New Mex- International Geology Review, v. 44, p. 1–38, Ketcham, R.A., 2005, Forward and inverse modeling ico: Geological Society of America Bulletin, https://doi.org/10.2747/0020-6814.44.1.1. of low-temperature thermochronometry data, in v. 123, p. 1720–1744, https://doi.org/10.1130/ Eaton, G.P., 1982, The Basin and Range Province: Reiners, P.W., and Ehlers, T.A., eds., Low-Tem- B30337.1. Origin and tectonic significance: Annual Review perature Thermochronology: Techniques, Inter- Amato, J.M., Richard, N., and Johnson, E.R., 2019, of Earth and Planetary Sciences, v. 10, p. 409– pretations, and Applications: Reviews in Mineral- Late Miocene basalts of the , 440, https://doi.org/10.1146/annurev.ea.10​.050182​ ogy and Geochemistry, v. 58, p. 275–314, https:// New Mexico, in context of the history of mafic .002205. doi.org/10.1515/9781501509575-013. magmatism in the Rio Grande rift: Geological So- Feucht, D.W., Bedrosian, P.A., and Sheehan, A.F., Lizarralde, D., Axen, G.J., Brown, H.E., Fletcher, ciety of America Abstracts with Programs, v. 51, 2019, Lithospheric signature of late Cenozoic ex- J.M., Gonzalez-Fernandez, A., Harding, A.J., no. 5, https://doi.org/10.1130/abs/2019AM-336785. tension in electrical resistivity structure of the Rio Holbrook, W.S., Kent, G.M., Paramo, P., Suther- Averill, M.G., 2007, A Lithospheric Investigation Grande rift, New Mexico, USA: Journal of Geo- land, F., and Umhoefer, P.J., 2007, Variation in of the Southern Rio Grande Rift [Ph.D. thesis]: physical Research. Solid Earth, v. 124, p. 2331– styles of rifting in the : Nature, El Paso, Texas, The University of Texas at El 2351, https://doi.org/10.1029/2018JB016242. v. 448, p. 466–469, https://doi.org/10.1038/​ Paso, 213 p. Flowers, R.M., Ketcham, R.A., Shuster, D.L., and nature06035. Averill, M.G., and Miller, K.C., 2013, Upper crustal Farley, K.A., 2009, Apatite (U-Th)/He thermo- Long, K.B., Baldwin, S.L., and Gehrels, G.E., 1995, structure of the southern Rio Grande rift: A chronometry using a radiation damage accumu- Tectonothermal evolution of the Pinaleño–Jack- composite record of rift and pre-rift tectonics, in lation and annealing model: Geochimica et Cos- son Mountain core complex, southeast Arizona: Hudson, M.R., and Grauch, V.J.S., eds., New mochimica Acta, v. 73, p. 2347–2365, https://doi​ Geological Society of America Bulletin, v. 107, Perspectives on Rio Grande Rift Basins: From .org/10.1016/j.gca.2009.01.015. p. 1231–1240, https://doi.org/10.1130/0016-7606​ Tectonics to Groundwater: Geological Society of Gavel, M.M., 2019, Low-temperature thermochro- (1995)107<1231:TEOTPO>2.3.CO;2. America Special Paper 494, p. 463–474, https:// nological constraints on Neogene extension in the Mack, G.H., 2004, Middle and late Cenozoic crust- doi.org/10.1130/2013.2494(17). Rio Grande rift and Basin and Range of southern al extension, sedimentation, and volcanism in Bader, J.W., 2019, Structural inheritance and the role New Mexico [M.S. thesis]: Las Cruces, New the southern Rio Grande rift, Basin and Range, of basement anisotropies in the Laramide structur- Mexico, New Mexico State University, 144 p. and southern Transition Zone of southwestern al and tectonic evolution of the North American Guenthner, W.R., Reiners, P.W., Ketcham, R.A., Nas- New Mexico, in Mack, G.H., and Giles, K.A., Cordilleran foreland, Wyoming: Lithosphere, v. 11, dala, L., and Giester, G., 2013, Helium diffusion in eds., The : A Geologic p. 129–148, https://doi.org/​10.1130/​L1022.1. natural zircon: Radiation damage, anisotropy, and History: New Mexico Geologic Society, Special Biddle, J., Ricketts, J.W., and Amato, J.M., 2018, the interpretation of zircon (U-Th)/He thermochro- Publication 11, p. 389–406. Constraining timing of extension in the southern nology: American Journal of Science, v. 313, Marshak, S., Karlstrom, K.E., and Timmons, J.M., Rio Grande rift and Basin and Range using apa- p. 145–198, https://doi.org/10.2475/03.2013.01. 2000, Inversion of Proterozoic extensional faults: tite and zircon (U-Th)/He thermochronology, in Hamblock, J.H., Andronicos, C.L., Miller, K.C., An explanation for the pattern of Laramide and Mack, G.H., Hampton, B.A., Ramos, F.C., Barnes, C.G., Ren, M., Averill, M.G., and Antho- Ancestral Rockies intracratonic deformation,

www.geosociety.org/gsatoday 9 United States: Geology, v. 28, p. 735–738, https:// 2016, Synchronous opening of the Rio Grande establishment of northwest- and north-trending doi​.org/10.1130/0091-7613(2000)28​<735​:IOPEFA>​ rift along its entire length at 25–10 Ma supported tectonic grains in the southwestern United 2.0.CO;2. by apatite (U-Th)/He and fission-track thermo- States: Geological Society of America Bulletin, McIntosh, W.C., and Bryan, C., 2000, Chronology chronology, and evaluation of possible driving v. 113, p. 163–181, https://doi.org/10.1130/0016​ and geochemistry of the Boot Heel volcanic mechanisms: Geological Society of America -7606(2001)113<0163:PMCAGE>2.0.CO;2​ . field, New Mexico, in Lawton, T.F., McMillan, Bulletin, v. 128, p. 397–424, https://doi.org/​ van Wijk, J., Koning, D., Axen, G., Coblenz, D., N.J., and McLemore, V.T., eds., Southwest Pas- 10.1130/B31223.1​ . Gragg, E., and Sion, B., 2018, Tectonic subsi- sage—A Trip through the Phanerozoic: New Ricketts, J.W., Roiz, J., Karlstrom, K.E., Heizler, dence, geoid analysis, and the Miocene- Mexico Geological Society Field Conference M.T., Guenthner, W.R., and Timmons, M.J., unconformity in the Rio Grande rift, southwest- Guidebook, v. 51, p. 157–174. 2021, Tectonic controls on basement exhumation ern United States: Implications for mantle up- Murray, K.D., Murray, M.H., and Sheehan, A.F., in the : The power of welling as a driving force for rift opening: Geo- 2019, Active deformation near the Rio Grande combined zircon (U-Th)/He and K-feldspar sphere, v. 14, p. 684–709, https://doi.org/10.1130/ 40 39 rift and Colorado Plateau as inferred from con- Ar/ Ar thermochronology: Geology, https:// GES01522.1. tinuous global positioning system measure- doi.org/10.1130/G49141.1. West, M., Ni, J., Baldridge, W.S., Wilson, D., Aster, ments: Journal of Geophysical Research. Solid Seager, W.R., and Morgan, P., 1979, Rio Grande rift R., Gao, W., and Grand, S., 2004, Crust and upper Earth, v. 124, p. 2166–2183, https://doi.org/​ in southern New Mexico, west Texas, and north- mantle wave structure of the southwest 10.1029/​​​2018JB016626. ern , in Rieker, R.E., ed., Rio Grande United States: Implications for rifting and sup- Reade, N.Z., Biddle, J.M., Ricketts, J.W., and Amato, Rift: Tectonics and Magmatism: Washington, port for high elevation: Journal of Geophysical J.M., 2020, Zircon (U-Th)/He thermochronologic D.C., American Geophysical Union, p. 87–106, constraints on the long-term thermal evolution https://doi.org/10.1029/SP014p0087. Research, v. 109, B03309, https://doi.org/10.1029/​ of southern New Mexico and western Texas: Soreghan, G.S., Keller, G.R., Gilbert, M.C., Chase, 2003JB002575. Lithosphere, v. 2020, 8881315, https://doi.org/​ C.G., and Sweet, D.E., 2012, Load-induced sub- Wilson, D., Aster, R., West, M., Ni, J., Grand, S., 10.2113/2020/8881315. sidence of the Ancestral Rocky Mountains re- Gao, W., Baldridge, W.S., Semken, S., and Patel, Reiter, M.R., Chamberlain, R.M., and Love, D.L., corded by preservation of landscapes: P., 2005, Lithospheric structure of the Rio 2010, New data reflect on the thermal antiquity Geosphere, v. 8, p. 654–668, https://doi.org/​ Grande rift: Nature, v. 433, p. 851–855, https:// of the Socorro body locale, Rio Grande 10.1130/GES00681.1​ . doi.org/10.1038/nature03297. rift, New Mexico: Lithosphere, v. 2, no. 6, Timmons, J.M., Karlstrom, K.E., Dehler, C.M., p. 447–453, https://doi.org/10.1130/L115.1. Geissman, J.W., and Heizler, M.T., 2001, Pro- Manuscript received 20 Mar. 2021 Ricketts, J.W., Kelley, S.A., Karlstrom, K.E., terozoic multistage (ca. 1.1 and 0.8 Ga) extension Revised manuscript received 1 June 2021 Schmandt, B., Donahue, M.S., and van Wijk, J., recorded in the Grand Canyon Supergroup and Manuscript accepted 11 June 2021

10 GSA Today | October 2021