FentonHill granodiorite- an80-km (50-mi) right-lateral otlset of the Sandia pluton? byA. WillianLaughlin, Geology/Geochemistry Group,Los Alamos National Laboratory, Los Alamos, New Mexico 87545

Introduction the Jemez , west of the western rim of the Valles cal- The Fenton Hill granodiorite is one of the most distinctive dera. Four deep wells, GT-2, EE-l, EE-2 and EE-3, were drilled Precambrianlithologic units encountered during deep drilling at at Fenton Hill; the deepest of these, EE-2, has a true vertical the Los Alamos National Laboratory Hot Dry (HDR) geo- depth of 4.39km (L4,417ft). Cores,cuttings, and random samples thermal site west of the Valles caldera (Laughlin et al., 1983). from a "junk basket" run behind the drill bit were used by Laugh- Although it differs both mineralogically and chemicallyfrom most Iin et al. (1983)to characterizethe Precambrian basement rocks other Precambrianplutons in central and northern New Mexico, at the site (Fig. 2). petrologic, chemical, and geochronologicaldata suggestthat it is Precambrian basement rocks were encountered at a depth of similar to surface exposures of the Sandia pluton in the Sandia approximately 730m (I,748 ft) in the four Fenton Hill wells. From Mountains east of Albuquerque. If these rocks are pieces of the ftO m (1,748ft) to 2,590 m (8,498ft) the Precambriansection same pluton, a rightJateral offset of approximately 80 km (50 mi) consistsof a metamoryhic complexof various gneissesand schists. along a precursor fault to the Rio Grande rift is suggested.The Between 2,590 m (8,498ft) and 3,000m (9,&13ft) the Fenton Hill senseand amount of this displacementis in agreementwith ear- granodiorite was encountered as a single, continuous intrusive Iier estimatesby Chapin and Cather (1981)and Chapin (1983). 6ody (Fig. 2). Smallerbodies of the granodiorite were encountered at greater depths. The granodiorite is a homogeneo_us.tYPically Fenton Hill granodiorite nonfoliated, sphene-bearing,-rich granitic rock' The major (Anr.), microcline, and The Fenton Hill granodiorite is not exposed at the surface and minerals are , sericitized sphene (l-3V'), has only been encountered in deep geothermal wells at Fenton biotite. Accessoryminerals include the ubiquitous Epidote and cal- Hill, New Mexico and in the Continental Scientific Drilling Pro- zircon, opaque oxides, , and apatite. gram (CSDP) well VC-28 in the Valles caldera. The HDR geo- cite are also present as alteration minerals. 7'762 thermal site at Fenton Hill is in Sandoval County, New Mexico The CSDPwell VC-28 was drilled in 1988to a depth of about 32 km (20 mi) west of Los Alamos (Fig. 1). The site is in Temperature("C)

Abo Formation AbiquiuT

E l< gneissand maficschist 2.0 -c o- o E 2.5 (I) = L F

gneiss,g ranodiorite, minorschist, metavolcanic

4.5 FIGURE l-Index map showing the Fenton Hill hot dry rock (HDR) site, Continental Scientific Drilling Program (CSDP)well VC-2B, and the San- FIGURE 2-Simplified stratigraphic column at the Fenton Hill hot dry dia pluton. rock site.

New Meico Geology August 1991 m (5,781 ft) in the Sulphur Springs area of the western Valles and apatite, whereas the high FerO., FeO, and KrO values are caldera.Sulphur Springsis about 7.5km $.7 m1)northeast of the reflected by the high biotite contents. Fenton Hill site. Precambrianquartz was encountered at a depth of 1,556m (5,105fQ in VC-28, which had been con- tinuously cored. The major minerals in this Precambian quartz monzonite are quartz, plagioclase, microcline, and biotite. The The Sandia granite, actually quattz monzonite to granodiorite, plagioclase is moderately sericitized and the biotite is strongly is exposed in the western escarpment of the Sandia Mountains, chloritized. Accessoryminerals include sphene,opaque oxides, east of Albuquerque. Surface exposures of the granite are com- zircon, and apatite. The subhedral to euhedral sphene is strongly monly weathered. Someof the best exposuresare found in Tijeras altered to leucoxene.Epidote, calcite,chlorite, and sericiteare Canyon where the granodioriteis in contactwith the Cibolagneiss. present as alterationminerals. The northern part of the Sandia granite is in intrusive contact A summary of the whole-rock chemistry of the Fenton Hill with the fuan Tabo series(Brookins and Majumdar, 1989).On the granodiorite from both the Fenton Hill and VC-28 wells is given basis of modal and compositional data from only four samples, in Table1.. Results of neutron activationanalysis of traceelements Condie and Budding (1979) suggested that the Sandia granite are presented in Table 2. The biotite granodiorite is characterized consists of two plutons; the North Sandia pluton and the South by high FerO., FeO, TiOr, KrO, PzO,, and SrO. The high TiO, Sandia pluton (Fig. 3). Rocks of both plutons are typically ho- and PrO, valuesare reflectedby the high modal contentsof sphene mogeneousand medium to coarsegrained. Modal compositions

TABLE 1-Composition of Sandia granite and Fenton Hill granodiorite. All values expressed as percentages.

Columnl2S4S 6 7 8 910 NSP SSP NSP SSP NSP SSP SSP SSP Fenton Hill VC-2B TC-1 AWL-8-81 granodiorite N=4*+ N=5 N=14 N=13 N=5 N=2 N=1 N=1 N=6 N=2 sio, 69.2 6.3 68.0 66.87 69.4 66-6 66.64 63.36 64.27 66.00 Tio, 0.76 I.UJ 0.88 0.95 0.79 1.05 0-94 1.10 0.95 0.76 Alro. 13.7 13.9 14.23 74.24 13.9 74.3 13.52 15.15 74.48 74.59 Fe2O. 4.81* 6.85* 5.35* 5.92* 2.29 2.,) 2.74 3.14 2.96 2.39 FeO nla nla nla nla 3.10 3.1 3.04 3.35 2.92 2.62 Mgo 1.00 1.33 1.77 1.33 0.95 1.24 1.36 1.50 1.39 7.26 MnO n/a nJa 0.11 0.77 nia n/a 0.11 0.r2 0.098 0.083 CaO 2.75 3.73 2.82 2.90 2.29 3.2r J. IJ 3.55 3.11 2.93 NarO 3.29 3.11 3.24 J.JZ 3.34 3.06 3-17 3.28 3.32 J. JA K,O 3.99 3.25 4.U 3.00 3.77 4.02 3.51 3.82 4.23 4.02 Hro* nla nla n/a n/a 0.73 0.81 1.03 0.87 0.98 r.60 HtO n/a nla nla nla 0.06 0.06 0.01 0.04 0.07 0.M PtOt nla nla 0.31 0.31 0.30 0.30 0.34 0.37 0.57 0.35 SrO 0.024 0.023 0.022 0.024 0.025 0.026 0.01 0.02 0.04 0.09 Columns I and 2-Condie and Budding (1979). Columns 3 and 4-Maiumdar (1985). Columns 5 and 6-Enz et al. (1979). Columns 7, 8 and l0-This work. Column 9-Laughlin and Eddy (1977). *Total Fe as FerO. **N:number of samples.All resultsare averaged,except those in columns7 and 8.

TABLE 2-Trace-elements in Sandia granite and Fenton Hill granodiorite, analyzed by neutron activation

Sandia granite Fenton Hill granodiorite AWL-8-81 TC-1 9519-1 9520-3 8s38-1b

Ba 800.1 685.5 1109 r652 1829 1374 Dy 11.00 8.131 10.90 15.19 17.55 17.85 U 4.279 3.699 5.582 5.465 2.87 6.224 Sm 11.68 6.386 14.85 16.02 11.53 17.72 w 3359 333.0 457.6 nJa nla n/a Sc 16.59 14.43 16.42 t7.M 3.376 16.74 Cr 27.70 nla 19.41 37.99 72.30 82.07 Co 24.55 25.14 26.43 12.u 9.915 14.51 Zn n/a n/a nla 767.8 88.59 146-5 Rb 155.0 155.0 r25.4 1,r7.9 nla 111.3 Cs 5.582 6.575 5.725 4.406 nia 3.966 Ce 1.49.7 719.2 209.7 237.1 224.2 257.3 Eu 2.M2 1.702 2.772 2.888 7.ffi7 3.27 Tb 7.171 nJa 1.398 1.410 7.248 1.589 Yb 7.029 5.85 8.954 13.35 6.739 14.67 Lu 0.92t9 0.5859 1.089 1.312 0.5499 7.46 Hf 17.82 8.857 13.07 17.33 12.19 18.57 Ta r0.88 3.065 7.799 4.2U nla 3.500 Th 13.02 9.U7 13.57 13.21 13.96 17.75

August 1991 Nao MexicoGeology are shown in a K-feldsparlquartzlplagioclaseternary plot (Fig. 4) To supplement the chemical data presented by Condie and modified from Condie and Budding (1979).The two Sandia plu- Budding (1979)and Brookins and Majumdar (1989),two samples tons plot near the boundary between the granodiorite and quartz of the Sandia pluton were collected in Tijeras Canyon. Analyses monzonite fields, and away from most of the other 29 New Mexico of major and trace elementsin all the samplesare given in Tables Precambrian plutons reported by Condie and Budding (7979). 1 and 2. Chemically, the Sandia pluton, like the Fenton Hill gran- The Fenton Hill granodiorite plots close to the Sandia pluton or odiorite,is characterizedby high FerOr,FeO, K2O, TiOr, and PrOu. plutons within the granodiorite field. Brookinsand Majumdar (7982,1989) and Majumdar (1985)have reexamined the question of whether the Sandia granite is made Geochronolosy granodiorite up of one or two plutons. They presentthe resultsof whole-rock il$J"r{?Hill chemical analysis of 28 samplesof the granite; 13 from the South Extensive geochronologicalwork has been done on the Fenton Sandia pluton and 15 from the North Sandia pluton. Variation Hill granodiorite, the Sandiagranite, and the gneissesinto which diagrams plotted from these data strongly suggest that there is they were intruded. Although a wide variety of isotopic dating only a single pluton. Four of these variation diagrams are repro- meihods have been applied to the Fenton Hill granodiorite and duced here as Fig. 5 with the analyses of the Fenton Hill gran- the Sandiagranite, the emplacementages can be determined most odiorite plotted for comparison.

4.00 (a) s 3.00 NORTH SANDIA 4 *o*rrLARGoH.LLS g SOUTHSANDIA 2.00 ALBUQUERoUE A Jc o MANZANITA o) 1.00

o.4. 0.00 \xY 55.00 60.00 65.00 70.00 75.00 80.00 85.00 PEDERNAL t) 5.00 RATTLESNAKE ^ HILLS 4.00 bS = 3.00

MAGDALENAofi*eorvnoenn (g 2.00 X\ o )A ?:rAJo 1.00 34' 0.00 55.00 60.00 65.00 70.00 75.00 80.00 85.00 FIGURE 3-Sandia and associated Precambrianplutons of central New Mexico. Modified from Condie and Budding (1979). 6.00 (c) s 5.00 Quartz c tr o 4.00 N o*oo o (g A 6 o# ^ z o 3.00 a s-E tr

55.00 60.00 65.00 70.00 75.00 80.00 85.00 6.00

;< 5.00 = 4.00 N Y 3.00

5s.00 60.00 65.00 70.00 75.00 80.00 85.00 Plagioclase ((KrO + NarO)/ (KzO+ Na20 + CaO))x100

FIGURE4-Ternary diagram of Precambrianplutons in centraland south- FIGURE S-Variation diagrams for Sandiaand Fenton Hill plutons. Mod- central New Mexico. Plutons are: N, North Sandia;S, South Sandia;FH, ified from Maiumdar (1985).(a){d), component vs index. n, Sandia Fenton Hill; Y, YCJB; O, Oj\ta; and ML, Monte Largo. Modified from pluton; A, South Sandia pluton; O, Fenton Hill granodiorite; +, VC-28 Condie and Budding (1979). granodiorite (Fenton Hill).

Nm Mexico Geology Argust 7991 accurately by the Rb/Sr and U/Pb isotopic methods. High tem- Discussion peratures resulting from nearby volcanism (Fenton Hill) and/or Severalworkers have suggestedthat the Colorado Plateauwas (Fenton deep burial Hill and Sandia Mountains) would lead to translated north-northeastward during Laramide deformation loss argon and fission-trackannealing and, thus, lTAr and fission- (Woodward and Callenda+ 1977,Chapin and Cather, 1981,and track ages that are less than the crystallization ages. Such per- Chapin, 1983).To evaluate the magnitude of this translation they turbations for the Fenton Hill samples have been discussed by have examined evidence for offset of various geologic features (7977). Brookins et al. Two ICAr ages of 1.35 and 1.40 Ga hav-e across the zone of decouping, i.e. the Rio Grande rift, focusing been obtained from a sample of the Precambrianrocks from VC- on features that intersect the zone at a high angle. Chapin and 28 by Laughlin and Shafiqullah(unpub. data).This samplewas Cather (1981) found that although the Jemez lineament is well undoubtedly affectedby the present high in situ temperature of defined southwest of the Valles caldera and may continue to the almost 300'C. Taos area, it is poorly defined northeast of Taos. Becausea line Brookins and Laughlin (1983)reported Rb/Sr isochron ages of drawn through the volcanic fields of northeastern New Mexico + + 1.50 0.12 Ga for the Fenton Hill granodioriteand 1.62 0.04 projects southwestward to the Tijeras-Canyoncito fault system Ga for the adjacent gneisses.The large error on the granodiorite nearAlbuquerque, they suggestedthat this fault system is a right- is the result of the small spreadin Rb/Srratios of the homogeneous lateral offset of the femez lineament. If this interpretation is cor- granodiorite. A suite of samples from VC-28 has been collected rect, 90-120 km (56-75 mi) of offset are suggested. for Rb/Sr analysis by D. G. Brookins and work is in progress on Chapin and Cather (1981)also estimated the magnitude of the these samples.Taggert and Brookins (1975)reported Rb/Sriso- displacement from the offset of the Precambrianprovince bound- + chron ages (correctedfor the new decay constant) ofl.47 0.02 ary that trends northeastward acrossNew Mexico. This boundary + Ga for the Sandiagranite and 1.58 0.07Ga for the Cibolagneiss, which separates1.72-1.80 Ga supracrustalrocks in the north from and Brookins and Maiumdar (1982)report a Rb/Srisochron age 1.65-1.72Ga supracrustalrocks in the south, is approximately of 1.44 + 0.04Ga for the Sandiagranite. coincident with the Jemezlineament. The boundary is offset ap- The Rb/Sr isochron age of 1.50 Ga on the Fenton Hill grano- profmately 80 km (50 mi) right laterally acrossthe Rio Grande was confirmed by the Pb/Pbmodel age results of Zartman rift. (1979).His results from sphene and zircon indicate an age of 1.50 (1981) an estimate 55 + Chapin and Cather also obtained of km 0.02Ga. He also calculateda model ageof L.50Ga for microcline (a1 mi) of rightJateral offset of the Capitan lineament as it crosses from the granodiorite. The Sandia granite Rb/Sr isochron is also the Rio Grande rift onto the Colorado Plateau. A correlation of confirmed by lead isotopic data. The Pb2oTlPb2o€dates of Tilton et similar Precambrian and early Paleozoicrocks across the rift in al. (1962'1,Steiger and Wasserburg (7969), and Tilton and Gru- the Caballo Mountains areayielded an estimate of 120km (75mi) + nenfelder(1958) average"l..47 0.02Ga. Steigerand Wasserburg of right-lateral translation. (1969)suggested an original age of formation between 1.49 and Chapin and Cather (1981) state, "The above correlations of l.64Ga. This large range resultedfrom the model used for epi- possible offset features along the eastem Colorado Plateamargin sodic lead loss and from the material analyzed. All lead isotopic are highly speculative but may serve as a starting point in the results were summaized. by Brookins (1974). search for more reliable data." I hope that the data presented in this short note meet the criteria for more reliable data and con- Equivalence of the Fenton Hill granodiorite tribute to our understanding of early displacementalong the PIa- and the Sandia granite teau margin. AcxNowr-ppcunNrs-This work was performed under the aus- Although it is difficult to prove that two plutonic rocks are pices of the U. S. Department of Enetgy. R. W. Charles assisted comagmatic without continuity in outcrop, a number of miner- in sample collection of the Sandia granite and Gardner alogical, chemical, and geochronologicallines of famie evidencecan be provided samplesof Precambrianrocks from VC-28. C. E. Chapin brought to bear to suggestthat the correlation is probable. Clearly, encouraged the author to publish these results. Scott Baldridge, thesetwo units are similarand probablycrystallized at about 1.50 Schon Levy, Doug Brookins, Paul Bauer, and Chris Mawer re- Ga. They are chemicallyand mineralogically very similar and have viewed the manuscript and provided helpful comments. undergone related magmatic histories. The probability of corre- lation is increasedbecause the two units are compositionallydis- tinct from other plutons in the region. References Both plutonic rocks are chemically similar in both major and trace elements. They are distinctive in having high TiO, and I(rO Bauer, P W., and Lozinsky, R. P, 1986, Proterozoic geology of supracrustal and granitic rocks in the Caballo Mountains, southem New Mexico: New Mexico relative to SiOr. On a temary diagram of quartzJk-feldspar/pla- GeologicalSociety, Guidebook to 37th Field Conference,pp.743-1.49. gioclase modal mineralogy, the Fenton Hill granodiorile plots Brookins, D. G., 7974, Radiometric age determinations from the Sandia granite, close to the Sandia pluton. Plutons with similar modal mineral- New Mexico: summary and interpretation: Isochron/West,no. 10, pp. 11-14. ogy, reported by Condie and Budding (1979),include the Monte Brookins, D. G., Forbes,R. B., Tumer, D. L., Laughlin, A. W., and Naeser,C. W., 7977, Rb-Sr, K-Ar, and fission-track geochronologicalstudies of samples from Largo and Ojita plutons. The Sandia, Monte Largo, and Ojita LASL drill holes GT-1, GT-2, and EE-l: lns Alamos National Laboratory Rept. plu_tonscrop out within a relatively small areaeast of Albuquerque LA-629-MS,27 pp. and could be connectedat depth. The Sandia,Fenton Hill; Monte Brookins, D. G., and Laughlin, A. W., l9fl3, Rb-Sr geochronologicalinvestigatjon Largo, and Ojita plutons are the most plagioclase-richof the 32 of Precambriansmples from deep geothermaldrill holes, Fenton Hill, New Mex- ico: Joumal Volcanologyand Gmthermal Research,v. 15, pp. 43-58. plutons shown in Fig. 4. Brookins, D. G., and Majumdar, A., 79f12,The Sandia granite: single or multiple Anothgr point of similarity befween the Sandiagranite and the plutons?: New Mexico GeologicalSociety, Guidebook to 33rd Field Conference, Fenton Hill granodiorite is presented in table 5 of Condie and pp.227-223. Budding (1979).These authors show that the North and South Brookins, D. G., and Maiumdar, A., 1989,Geochronologic study of Precambrian rocks of the SandiaMountains, New Mexico: GeologicalSociety of America, Spe- Sandia plutons, in contrast to 28 other plutons in central and cial Paper 235, pp.147-754. south-central New Mexico, are characterizedby high (1-1.5%) Chapin, C. 8.,7983, An overyiew of Lararnide wench faulting in the southem sphene contents. Only one other pluton, the White Sands, con- Rocky Mountains with emphasis on petroleum exploration: Rocky As- tained more than a trace of sphene. Bauer and Lozinsky (1986), sociation of Geology, Guidebook to 1983Field Conference,pp. 759-179. Chapin, C. 8., and Cather, S. M., 1981,Eocene tectonics and sedimentation in the however, have reported high sphene contents in a Proterozoic Colorado Plateau-RockyMountain area; in Dckinson, W R., and Payne, W. D. pluton in the Caballo Mountains. As discussedabove, the Fenton (eds.), Relations of tectonics to ore deposits in the southern Cordillera: Arizona Hill granodiorite is also characterizedby high sphene contents. Geological Society,Dgest, v. 14, pp. 173-198. No available chemical, mineralogic, or geochronological evi- Condie, K. C., and Budding, A. t.,1979, Geology and geochemistryof Precambrian rocks, central and south-centralNew Mexico: New Mexico Bureau of Mines and dence refutes the suggestion that the Fenton Hill granodiorite Mineral Resources,Memoir 35, 58 pp. and the Sandia pluton are equivalent. Enz, R. D., Kudo, A. M., and Brookins, D. G., 1979,Igneous origin of the orbicular

August 1991 Nan Mexico Geology rocks of the Sandia Mountains, New Mexico: GeologicalSociety of America, Bul- Taggert, J. E., and Brookins, D. G.,7975, Rb-Sr whole rock age determinations for letin, v. 90, Part I, p. 138-140,Part II, p. 349-380. Sandia granite and Cibola Bneiss,New Mexico: Isochron/West,no. 12, PP. 5-8. Laughlin, A. W., and Eddy, A. C.,9n, Perrographyand geochemistryof Precam- Tilton, G. R., Wetherill,G. W., and Davis,G.L.,l962,Mineral agesfrom the Wichita brian core samplesfrom GT-2 and EE-1: Los Alamos Scientificlaboratory Rept. and Arbuckle Mountains, Oklahoma and the St. Francis Mountains, Missouri: LA-5930-MS, s0 pp. Journal of GeophysicalResearch, v. 65, pp. 4011-4020. taughlin, A. W., Eddy, A. C., Laney,R., and Aldrich, M. J., Jr., 1983,Geology of Tilton, G. R., and Grunenfeldet, M. H., 1958,Sphene: uranium-lead ages:Science, the Fenton Hill, New Mexico, hot dry rock site: Joumal of Volcanologyand Geo- v. 759, pp.1458-1451.. thermal Research,v. 15, pp. 27-41. Woodward, L. A., and Callender, J F., 9n, Tectonicframework of the San Juan Majumdar, A., 1985,Geochronology, geochemistry, and pehology of the Precam- Basin: New Mexico GeologicalSociety, Guidebook to 28th Field Conference,pp. brian Sandiagranite, Albuquerque, New Me{co: Unpublished Ph.D. dissertation, 2W)72. Louisiana State Univ., 212 pp. Zaftman, R. E., 1979,Uranium, thorium, and lead concentrationsand lead isotopic Steiger, R. H., and Wasserbuig,G J., 1969,Comparative U-Th-Pb systematicsin composition of biotite granodiodte (sample 9527Jb) from LASL drill hole GT-2: 2.7 x 10" yr plutons of different geologic histories: Geochimicaet Cosmochimica Los Alamos Scientific Laboratory, Rept. LA-7923-MS, 18 pp. Acta, v. 33, pp.7273-7232. fl

Yeso Formation Schneider, I. F., 7975, Recent tidal deposits, Abu Dhabi, UAE, Arabian Gulf; in Ginsburg, R. N. (ed.), Tidal deposits: New York, Springer-Verlag, pp.249214. (Continuedfrom p. 49) Seager,W. R., and Mack, G. H., in press, Geology of Mcleod Tank quadrangle, Siena County, New Mexico: New Mexico Bureauof Mines and Mineral Resources, Kottlowski, F. E., 1965, Sedimentary basins of south-cenkal and southwestern New Geologic Map. Mexico: American Association of Petroleum Ceologists, Bulletin, v. 49, pp.21,20- Shinn, E. A.,1968, Practical significanceof birdseye structures in carbonaterocks: 21.39. Journal of Sedimentary Petrology, v. 38, pp. 215-223. Kottlowski, F. E., Flower, R. H., Thompson, M. L., andFoster, R. W., 1955, Strati- Shinn, E. A., 7983,Tidal flat environment; in Scholle, P A., Bebout, D. G., and graphic studies of the San Andres Mountains, New Mexico: New Mexico Bureau Moore, C. H. (eds.), Carbonatedepositional environments:American Association of Mines and Mineral Resources, Memoir 1, 132 pp. of PehroleumGeologists, Memoir 33, pp. 1.72)1.0. Langbein, W. 8., and Schumm, S. A., 1958, Yeld of sediment in relation to mean Thode, H. G., Monster, J., and Dunford, H.8., 7961,,Sulfur isotope gmchemistry: annual precipitation: American Geophysical Union, Transactions, v.39, pp.7076 Geochimicaet Cosmochimica Acta, v.25, pp. 159-1.74. 1084. Wilkinson, B. R., 1982, Cyclic cratonic carbonatesand Phanerozoic calcite seas: Nelson, E. P., 79ffi, Geology of the Fra Cristobal Range, south-central New Mexico: Journal of Geological Education, v. 30, pp. 789-203. New Mexico Geological Society, Cuidebook to 37th Field Conference, pp. 83-91. Wilpolt, R. H., and Wanek, A. A.,1951, Geology of the region from Socono and Sarg, J. F., 1981, Petrology of the carbonatrevaporite facies transition of the Seven San Antonio east to Chupadera Mesa, Socorro County, New Mexico: U.S. Geo- Rivers Formation (Guadalupian, Permian), southeast New Mexico: Joumal of Sed- logical Survey, Oil and Gas Investigations, Preliminary Map OM 121. imentary Petrology, v.51, pp.73 96.

Grassy Lookout quadrangle Ferguson, C. A., 1988, Geology of the Tenmile Hill 7llz-min quadrangle, Socorro County, New Mexico: New MexicoBureau of Mines and Mineral Resources,Open- (Continuedfrom p. 54) file Report283,21 pp.,2 plates. Ferguson, C. A., 1990,Geology of the GrassyLookout 7rl:-min quadrangle,Socono County, New Mexico:New Mexico Bureauof Mines and Mineral Resources,Open- References file Report3{t6, 4l pp.,3 plates. Aldrich,M. J.,Jr., Chapin, C. E., and Laughlin,A. W., 1985,Stress history and Gile, L. H., Hawley, f. W, and Grossman, R. 8., 1981,Soils and geomorphology tectonic development of the Rio Grande rift, New Mexico: fournal of Geophysical in the Basin and Range area of southern New Mexico-guidebook to the Desert Research, v.91, pp. 6799-6271,. Proiect: New Mexico Bureau of Mines and Mineral Resources,Memoit 39,222 Chamberlin, R. M., 1983, Cenozoic domino-style crustal extension in the Lemitar PP. Mountains, New Mexico-a summary: New Mexico Geological Smiety, Guide- Lipman, P- W., 1976,Caldeta

Nm MexicoGeology August 191