Laramidewrench faults, basement-cored uplifts, and complimentarybasins in southernNew Mexico byWilliam R. Seager,Earth Science Department, State University, Las Cruces, NM 88003

Abstract ACKNowLEDGTuENTs-Manyof the ideas 1978;Thompson, 1982).These furassic car- expressedin this paper maturedthrough dis- bonatesprobably thicken southward into the mode Laramide The chief of deformation of E. Chapin, R. Chihuahua trough where evaporites the foreland area of south-central and adjacent cussionswith Glen Brown, C. |urassic parts of southwest New Mexico was uplift of E. Clemons,G. Mack, and S. Thompson III. are diapiric and may be responsible for Lar- relatively simple basement blocks similar in I thank Exxon for permission to use drill hole amide decollement and "thin-skinned" fold- stvle, but smaller in size, to some of those of data from their No. L Prisor well, and C. E. ing in the Chihuahua tectonic belt, including the central Rocky Mountains. Uplifts trend Chapin, S. Cather,G. Mack, and F. E. Kott- the Sierraluarez (Haengii and Gries, 1970). generally west-northwest, and are asymmetric lowski for their reviews of the manuscript. I In Cretaceoustime the Burro uplift-Dem- with steep, southwest-dipping, reverse-faulted especiallv want to thank the New Mexico ing axis (Elston, 1958;Turner, 1.952)extended northeast margins. Broad, less-deformed Bureauof Mines and Mineral Resourcesand northwestward from the West Potrillo southwest flanks plunge into deep Wind River- F. E. Kottlowski, Director, for their contin- Mountains through the basins filled with lower Tertiary type clastic research in into Arizona, separating4.5-km (15,000-f0- rocks 1-2 km (3,000-7,000ft) thick. The general uing support of my geologic style of deformation seems to extend into the southern New Mexico. thick Lower Cretaceousmarine and non- northern margin of southwest New Mexico ter- marine rocks to the south from thin or miss- rane previously regarded as part of the Cor- Paleotectonicsetting and stratigraphy ing sections on the foreland region to the dilleran "overthrust" belt. In this latter region, Precambrian granitic and metamorphic north (Zeller, 1965, 7970;Hayes, 1970).Up- right slip as well as vertical uplift and associ rocks form the basementof all of south-cen- per Cretaceousand lower Tertiary rocks, ated transpressionalthrusting distinguishesat tral and southwestNew Mexicoand adiacent mostlysynorogenic clastic and volcanicrocks, leastsome marginal upthfusts; basinsmay be are nearly 4 km (13,500ft) thick south of the Wind River parts of Arizona. During the Paleozoicthe a mixture of both and Echo Park Burro uplift (Zeller, 1965,197 0 ; Hay es, 7970). types. This interpretation of Laramide tectonic region was buried by a south- and south- North and northeast of the Burro uplift, ma- styles in southern New Mexico has important westward-thickening wedge of marine implications for the searchfor petroleum in the rocks-mostly carbonates. More than 4 km rine and nonmarine Upper Cretaceousrocks Pedregosaand various late Tertiary basinsof (13,500ft) thick in the southwest corner of are as much as 1.9 km (5,500f0 thick where southern New Mexico. New Mexicoand about 2.5km (8,200ft) thick they havebeen preserved in Laramidebasins near El Paso, the Paleozoic section thins (Kelley and Silver, 1952).Syn- to post-oro- Introduction northward to less than L km along a line genic uppermost Cretaceousand lower Ter- Corbitt and Woodward (1973), Drewes between Silver City and Truth or Conse- tiary fanglomerates,red beds, and sandstones (1978, 1982), and Woodward and DuChene quences(Kottlowski, 1963;Greenwood and are of comparablethickness in the sameba- Kelley (1981) have emphasized the importance of others, L977;Thompson, 1982).Epeirogenic sins (Doyle, 1951;Bushnell, 1953; and large-scaleregional overthrust faulting in ex- uplift in Middle , Early , Silver,1952; Seager, 1981). treme southwest New Mexico and southeast and Late Silurian-Middle is rep- Arizona during the Laramide (Cordilleran) resentedby unconformitiesin the sedimen- Age of Laramide deformation orogeny (Drewes, L978), some of which is tary record; these unconformities are partly Clast composition of thick fanglomerate controversial (Davis, 1979). Less well known responsiblefor the overall northward thin- units within the Hell-to-Finish and naoiit is the array of west-northwest to northwest- ning. Thickness variations also reflect late trending basement-cored block uplifts and Paleozoicsubsidence of the PedregosaBasin complimentary basins that have been rec- in the southwestcorner of New Mexico and ognized in the foreland area to the north and adjacentparts of Arizona, as well as subsi- Alsoin thisissue northeast of the overthrust belt (Fig. 1.;Seager, denceof the Orogrande Basin in the south- BacaFormation glyptosaurine 1975, l98l; Brown, 1982; Brown and Cle- centralpart of New Mexico (Greenwoodand lizard P.77 mons, 1983). The purpose of this paper is to others, 1,977;Kottlowski, 1955). Approxi- Cephalopodaptychi lrom Los review the structural characteristics of these mately3 km (10,000ft) of Pennsylvanianand MoyosLimestone P.78 uplifts and basins and to show that some of marine strata accumulated in the ClaytonLake State Park P. 81 the high-angle faults in the overthrust belt, PedregosaBasin and half that amount in the Service/News P. 83 previously considered to be examples of re- Orogrande Basin. Between the two basins, Five-yearcumulative index P.87 gional sled-runner type overthrusts, might Pennsylvanianand Permian rocks thin across also be interpreted as boundary faults of a positive area near the Florida Mountains Gomingsoon basement-block uplifts. Furthermore, some (Kottlowski, 1958,1960). SunsetRidge fluorite deposit of these steep faults display evidence for sig- Triassicand |urassic rocks generally are ab- Stratigraphicnomenclature history of nificant right-lateral strike-slip motion and sent over most of southern New Meico, al- marineUpper rocks in associated transpressional (convergent though marine Jurassicrocks are known from SocorroCounty wrenching) and transtensional (divergent a deep oil test southwest of Las Cruces wrenching) structures (Reading, 1980). (Thompson and Bieberman, 1975; Uphoff, Formations of southwest New Mexico record plete by late (40-43 m.y. B.P.)time. Exposuresin the San Andres and Caballo Early Cretaceousuplift and erosionof Paleo- So far, dating of individual movement phases Mountains reveal the general nature of Lar- zoic and Precambrian rocks from the Burro or recognition of the two-fold evolution of amide uplift margins but offer little insight uplift and/or deformationsouthwest or west Laramidedeformation describedby Chapin into the overall geometry of the uplifts and of New Mexico (ZelIer, L970;Drewes, 1978; and Cather (1981)has not proved possible. basins.In this regard structuresand uncon- G. Mack, personal communication, 1983). formities in the San Diego Mountain-Rob- Laramide deformation commencedin latest Structural style, south-centralNew Mexico ledo Mountains area,together with deep drill- Cretaceoustime with movement phasesre- In south-centralNew Mexico the chief mode hole information in southern Dofla Ana corded by angular unconformitiei between of Laramide deformation was uplift and tilt- County, enhance our interpretation. These the Mojado (Lower Cretaceous) and Ring- ing of large basement fault blocks accom- havepermitted reconstructionof a maior west- bone formation (Upper Cretaceous-lower panied by subsidenceof complimentary northwest-trending Laramide uplift, facing Tertiary), between the Ringbone and the Hi- (Green River-Wind River type) basins. The east-northeast,whose southern flank dips dalgo volcanics, and between the Hidalgo structural style is similar to that of the Lar- southward a few degreesinto a complimen- volcanicsand relatively undeformed middle amide Rocky Mountains of Wyoming and the tary (Wind River-type)basin (Potrillo Basin) Tertiary volcanic rocks (Zeller, 1965, 7970), ColoradoPlateau (e.9., Kelley, 1955; Stearns, filled with lower Tertiarv sedimentarv rocks Loring and Loring (1980)have dated thrusts 1978),although southernNew Mexico struc- more than 2 km (6,500ft; tnict (Fig. a). cutting the Hidalgo volcanicsas Paleocene tures display more structural relief than those In overall geometry the structure resem- in age, about 50 m.y. old. of the Plateau and less than those of the bles the Wind River range of Wyoming and Rejuvenationof at leastthe southeastpart Rockies.Small parts of uplifts are exposed adjoiningparts of the Wind River basin.The of the Burro uplift during the Laramide is in the Caballo, San Andres, Robledo, and northern margin of the uplift, exposedat San suggestedby lower Tertiary fanglomerate , and at San Diego Moun- Diego Mountain, is a west-northwest-strik- (Love Ranch equivalent) outcrops in the tain (Kelley and Silver, 1952; Bachman and ing thrust fault dipping southward 35". Pre- Fluorite Ridge-southern Cooke's Range area Myers, 1969;Seager , 1975, 1981;Seager and granitic rocks form the hanging wall near Deming (Fig. 1). The fanglomerate,a others, in preparation). Large parts of the and a small exposureof folded Paleozoicrocks very coarsegrained, proximal-fan facies,was centraland southernJornada del Muerto and forms the foofwall. Near this marginal thrust, derived largely from Precambrianrocks which MesillaBasins contain remnants of Laramide Love Ranch fanglomerate depositionally must have been exposed south of Fluorite basins. overlies Precambrian rocks indicating uplift Ridge, as Paleozoic and Mesozoic rocks are Laramide uplifts trend west-northwestto and erosion of 2-2.4 km (5,500-8,000ft) of still present to the north. Presumably this northwest, are bordered by steep-faulted Paleozoicand Mesozoicrocks near the thrust uplifted terrane also exposed the Precam- margins that face east-northeastto north- in latest Cretaceousor early Tertiary time. brian rocks of the Florida Mountains which east, and are flanked by broad domains of Farther south, over an area 35 km (22 ml) in many placesare nonconformably overlain gently folded or tilted rocks. (Farthernorth, broad, including the modern RobledoMoun- by Iower Tertiaryfan debris(Brown and Cle- in the northern Caballo and Fra Cristobal tains, thin post-orogenic Love Ranch fan- mons, 1983;G. Mack, personal communi- ranges,Laramide sfuctures swing into a more glomerate overlies successivelyyounger cation, 1983) and are cut by high-angle northerly trend, becoming parallel with the Paleozoicstrata up to Lower Permian Hueco Laramidefaults discussedlater in this paper. centraland northern New Mexico Rockies). Limestone. This erosional truncation sug- Farther east and northeast in south-central Uplift margins are distinguished by narrow gests that the soufhern flank of the uplift New Mexico, precise dating of Laramide zonesof steepto moderatelydipping reverse movementphases has so far not proved pos- and thrust faults, which dip southwest and sible, although availableevidence also indi- modify monoclinalflexures. Uptft along these catesa culminationof Laramidedeformation marginsranges from 1 to 5 km (3,500-17,000 New A4exfic@ in latestCretaceous-early Tertiary time (e.g., ft), and the monoclinal folds seemingly are Kelley and McCleery, 1960;Seager, 1981). drapes acrossthe edges of basement fault GEOLOGY The orogenicdeposit associatedwith Lar- blocks.The Bear Peak fold and thrust zone . Scisnceand Ssrvice amide deformation in the San Andres-Ca- in the southern is a Volume 5, No. 4, November 1983 ballo-Las Cruces areas is the Love Ranch good example, and this zone also illustrates published quarterly by Formation (Kottlowski and others, L956) some of the subsidiary thrusts that can de- New Mexico Bureau ofMines and Mineral Resources consisting mostly of fanglomerateand, in velop in the compressedbeds on the down- adivision ofNew Mexico Institute ofMining& Technology Laramide basins, finer grained red beds, thrown side of the fault zone (Fig. 3a). BOARD OF REGENTS brown sandstones,and coal (Fig. 2). Upper An uplift Ex Officio margin exposed in the central Toney Anaya, Covernor of Ne|| Mexico parts of the Love Ranch are relatively un- and southern Caballoschanges along strike Leonard DeLayo, Srperintendenl oJ Public Instruclion deformed, overlap the margins of deeply from simple, like the BearPeak fold and thrust Appointed Judy Floyd, Pres., 19'7'7-198'7,Las Cruces eroded uplifts, and interfinger with upper zone, to more complex (Fig. 3b,c). In this William G. Abbott, Secty/Trcas., 196l-1985, Hobbs Eocene volcanic rocks; they are therefore example, the level of erosion of the footwall, Donald W Mods, 1983-1989, Los Alamos largelypost-orogenic Robert Lee Sanchez, 1983-1989, Albuqwrque and of late Eoceneage. from high in the Paleozoicsection to the Pre- Steve Tones, 196'7-1985, Socorro Lower parts of the formation are strongly cambrian, revealsthat the uplift-margin fault deformed adjacent to Laramide faults and dips more (- New Mexico lnstitute ofMining& Technology steeply 50) where it trans- President . Laurence H. Lattman interfinger with strata of McRae lithology, a gressesPrecambrian rocks, flattening to 30- New Mexico Bureau of Mines & Mineral Resources unit whose lowest beds are Late Cretaceous 40" at higher levels. The marginal fault also Director . .. FrankE.Kottlowski Deputf Dircctor in age(Bushnell, 1953). Consequently, lower bifurcateslocally into two strands, each as- George S. Austin Subscriptions: Issued quarterly, February, May, August, parts of the Love Ranch are synorogenic and sociated with a monoclinal flexure or large November; subscription price $6.00/yr. may be as old as latest Cretaceous.Near ba- overturned fold (Fig. 3c). The hanging wall Editoriol motter: Contributions of possible marerial for sin centers(South and Potrillo Ba- rocks of this consideration in future issues of NMG are welcome. Jornada uplift, also exposedin the south- Articles submitted for Dublication should be in the ed- sins), complete sections of Love Ranch em Caballos,were broadly folded and eroded itor's hands a minimum of five (5) months before date Formation are I-2 km thick and probably locally to the Precambrianby late Eocenetime of publication (February, May, August, or November). in Address inquiries to Marla D. Adkins-Heljeson, editor of range age from Late Cretaceous to late (involving erosionof 2.5 km [8,200ft] of Pa- New Mexico Ceology, New Mexico Bureau of Mines & Eocene, although the bulk of the formation leozoicand Mesozoicrocks), as indicatedboth Mineral Resources.Socorro. NM 87801 probably is Tertiary. These relationships by clastsof Precambrianrock in Love Ranch Published as public domain, thereJore rcproducible without pem support a latest Cretaceousto early Tertiary fanglomerate and by local nonconformities ision. So urce credit requ ested. Circulotion: age for T,dramidedeformation in 1,4{n south-cen- betweenPrecambrian granite and Love Ranch Prirter. University of New Mexico Printing Plant tral New Mefco, deformation that was com- Formation.

November 1983 New Mexico Geology ."s-.* 3'..i-\ F /\ - \d "=fu i,= #1 i\"'dr ." 1.$::_ \7 [. fro CristobolMts. fli"'r;""'too {.\co$\cuo'"o ft{ ntH'4 -oor.' # u-t'ili or.oe-{'oqo\\or' \r/-;4""'"'i'' ,r,I \N1,.;) Tro ff.ffi t t\,h^ndresMs 'tq+s '\*ry1e $}=,,$* \ac(f>"''n*s l;,-?t,ip-oa,, ''^'2,.*r;ntf,, ;rk'nk"'r'*( ** l!ii \\ ='r-#;::,j=M?r"N; r *".'u*i,.,gnDea.Mrn L''k*'"'o .'1F qfr-'ni:A f $"".-*^T"':::::"" \,["'i$,3,, .W Hs*Sryfit,ffi:* o'*;is ;lB;:i *i. €t=H*MT$;;r.,,i*:lk Y&;W.,,v)). r;ffi;;-"1*i*\,"-k {i*l;s'*t'ffly+;inn*** ;- i'ui'"( ""h. 13" :s t. =="-;0,""''"Q\$til;.;-*;- --k::-vdi{.o'o-"," I:iY=S)-Gronite lS : i H roedrjKr:"::_Di\it=;!$-il;.;-*: .HTHUAHUA l-.i =S ? i Pr !'G 5*" s;!$uo"J .-,."$**oqu*\ ..,tJ t--\""i."'l6tt Approximofenorrhern ou,,.$*-.--*" *, 1S ":ti cop Corditteron ;lj :.- .-o' hfiqf tim'itsof overfhrrri- .s "1,.n.,",.. belt of (1970) iri"€' s Anrmos-Mts'-: -' preorosenicond synorogenic COrbitf ond WoOdword ', 0f.'rrttz rocxs'@t o-o-o-o-o ltr.t ! ""=i I i A":"Nii,.l*\s ondDrewes(tg78) .. E, .f t1:::l_.1.1""-..,i^,?,i,:?^-,Ihrusl or reverse loults/ ondOnd DrewesDf eWeS (t982)(1982) .-.-.-.-,.-.-.-.-. 4".i ! i-l5 (orrows show strike-slip molion ) =fuli; --i.-l -rli_*,d O 5Okm FIGURE l-Location map, southwest New Mexico; note location of Figs. 3, 4, 6,7, and 9 structure sections.

dipped south a few degrees. Thirty km (18 mi) still farther south, in the Grimm and others American Arctic Limited No. 1 Mobil 32 oil test, Cretaceous and rocks overlie the Hueco, and basinal clastic rocks Love Ronch Formofion SW Love Ronch Formoiion (sandstone,coal, fine-grained red beds) cor- relative with the Love Ranch are more than bosrn bosinfocies focies 2 km (6,500ft) thick (Thompson and Bieber- Poleo,z o ic man, 1975;Uphoff, 1978;Thompson, 1982). r OCKS/ Mesozo ic Thus the uplift is strikingly asymmetric, with Mesozoic Precombrionrocks a broad southern flank that dips perhaps 10- rocks - Poleozoicrocks lkm 12' southward into a deep, complimentary basin. The slope is interrupted in at least one kmlO 5 O placeby a steep, south-dipping reversefault, with displacement of approximately 300 m IIGUS! 2-Diagrammatic section showing features of Laramide uplifts and basins in south-central New lvlexico; note syn- and post-orogenic relationships in Love Ranch Formation adjacent to uplift (1,000 f0, that is exposed in the northern marSrns. RobledoMountains. Whereasthe north-south

Neu;Mexico Geology November 1983 cross-sectionalgeometry of this uplift is fairly gional overthrust (Corbitt and Woodward, movement along the fault. However, com- well constrained,its eastemand westem limits 1973;Woodward and DuChene, L981), has pelling evidence for substantial right{ateral areunknown becauseof cover of young rocks. recently been reinterpreted as the upthrust slip also is indicated primarily by large-scale margin of a basement block (Brown, 7982; drag of Paleozoicfootwall rocks in the foot- Florida-Big Hatchet-Little Hatchet Brown and Clemons, 1983). The fault dips wall adjacentto the southeastexposures of Mountains approximately 85osouthwest (after removal the upthrust (Fig. 5). Adjacent to the fault, A major northwest-trending reverse fault of IateTertiary tilt). Brown (L982),Brown and the southern limb of the drag fold seemingly in the southern Florida Mountains, previ- Clemons(1983), and Clemonsand Brown (in has been segmentedinto complex thin slices ously interpreted as the front edge of a re- press) argued for predominantly vertical bordered by low-angle faults, which are stackedand shearedout in the footwall along the length of the fault to the northwest (Fig. NE 6). Most of the faulting resulted in younger rocks displaced over older (normal faults), but some produced typical thrust rela- ) ouo,n,onn. of younger. Both styles ofexposures tionships older over of faulting "root" downward into the major I reversefault and are considered to be a pro- duct of transpression in the fault zone. Numerous high-angle normal faults also in- 2km dicate local extension in the zone. Another indication of strike slip along the major re- tI verse fault is the dissimilar Precambrian rockson either side of the fault (Fig. 5), which .t o also yield different K-Ar ages (Clemons, in 321 press).However, a component of northeast motion is also indicated by thrust-faulted, northeast-vergent folds, located in footwall rocks. Collectively, the structures indicate oblique right slip on the major steep fault, z rm witha smallcomponentofmovementtoward the northeast, and strong transpression of , bedded footwall rocks. If the length of the sheared-outlimb of the drag fold is a reliable index, the amount of strike slip could be 5-6 o km (3-3.5 mi), which is probably at least as much, if not more, than the vertical compo- nent of movement. The uplifted basement block in the south- ern Florida Mountains appears to be only one component of a much broader, faulted basement uplift, as shown inFig. 7. The ba- sin adjacent to the northem flank of the uplift is identified by the full section of Paleozoic and Cretaceousrocks exposedin the Fluorite Ridge-GoatRidge-Cooke's Rangearea a few kilometers north of Deming. Very coarse grained proximal-fan deposits of early Ter- p€ tiary age (Starvation Draw member of Rubio PeakFormation; Clemons, 1982)overlie Cre- km2 I taceousrocks in this area and were derived Paleo- FIGURE 3-a.) Composite cross section through Bear Peak fold and thrust belt, southern San Andres largely from Precambrian and lower Mountains. b,c.) Cross sections through Laramide uplift in southern . Effectsof late zoic rocks. The uplift margin exposing these Tertiary block faulting have been removed from all three sections.Th-Tertiary Love Ranch Formation, Precambrian-Paleozoicrocks presumably was K-Cretaceousrocks, Pu-upper Paleozoicrocks, Pl-lower Paleozoicrocks, and p€-Precambrian rocks. located not far south of the Fluorite Ridge areain an area now covered by bolson grav- +-LoromidePotri|loBosin_<-LoromideRob|edo-SonDiegoup|ift+N q loteTertiory Mesillo Eosin loteTerf iory Robledo horst loteTertiory foult blocks Grimmond olhers no.l Son Diego Mln. Mobil32 , T.0.2r.759ft t2 -5.OOOft Ts - s.l. 2 --5.OOO iet-'\ --ro.ooo KJ --r5,ooo Pu I PI . 8km I \\ | / 20.ooo FIGURE 4-Cross section through Laramide Potrillo Basin and Robledo-San Diego uplift. Note overlap and thinning of Tl unit onto uuplift and truncation of Pu and PI units beneath the Tl unconformity. Ts-Santa Fe Group (Tertiary), Tv-middle Tertiary volcanic rocks, Tl-lower Tertiary fanglomerate,sandstone, and coal (Love Ranch and correlative units), Kf-Cretaceous-furassic rocks, Pu-upper Paleozoicrocks, Pl-lower Paleozoic rocks, p€-Precambrian rocks, and Ti-Tertiary intrusive rocks.

November 1983 New Mexico Geology els. Farther south, near Deming, the Seville 1o7"37'30"W Trident No. 1 McSherrywell penetratedPre- cambrianrocks at II,590 ft beneathQuater- + 1 + J ++ i f + + nary-Tertiary basin fill and Tertiary volcanic + J + + ++ r+ ].+ rocks (S. Thompson III, written communi- + + + f f + ++++ + T + + + | ++ l- + cation,1983). Significantly, no lower Tertiary + + + + +++ t+ fan deposits (Starvation Draw Member and + -t + + I + + + + + +++ + + + + + ++++++++ LoboFormation of Lemley,1982) were found + + + t ++tres++++ above the Precambrian.Still farther south, + f l- + ++t++f++ \ + + + + f ++++++ outcropsin the Florida Mountains reveal thin + I t- +++f++++ Lobo fan deposits nonconformably above + + ++ + + + + + + + + + t f + sfrikelines Precambrianor lower Paleozoicrocks, and + + +++++++++++ F + t ++ + ++i +f +++r; fwo steep faults, both downthrown to the t + + + + + + + + ++ north, have been mapped. One of thesefaults + + + t + + + + *#fiil was describedin the previous paragraph.The + + + I nearly full section of Paleozoicrocks exposed 32.O5-N in the TresHermanas Mountains, southwest ?pt strike of the Florida Mountains, seemingly repre- p€q lines sents the southern flank of the broad uplift. t-/t Thus, the broad uplift spans the region from I/ / \ - t just south of Fluorite Ridge to the southern - / l- t_ tt t- / / ? Florida Mountains, an area where Precam- \' . \ \'r.l brian and lower Paleozoic N,\)--'r'-- rocks were deeply )-.,'r\$-' ' erodedand widely exposedin early Tertiary ,0"),). , rike lines showingdip time. Individual fault blocks stairstepdown d irection to the north or northeastas a result oi move- ment on steep faults with major strike-slip q!'rrr components of motion. The uplift is pre- sumed to have had the same northwesterly a trend as the faults. Its location along strike --r-.''-it- \/ \ /\ / \t with the earlier Mesozoic Burro uplift sug- 4-'- t \ I geststhat the Laramide block uplift may have - r / /l 'I [-l ,t.- l- ,\|/ been reactivated along Burro uplift struc- fures. l-1\ 1 ./1. \-/)rn^ l\ \ \ Somewhat similar structural relationships ",/-L.l exist at Granite Pass and Hatchet Gap be- tl tween the Big Hatchet and (Fig. 1). Zeller (1970,1975)mapped drag and second-orderfolds south of Hatchet Gap which suggestan important right-lateral FIGURE S-Geologic map of southern part of Florida Mountui.,r; g"olotgyafter Brown component l'rt#r), at"-o.r, of movement on a major west- and Brown (in press), and Clemons (in press). Lines with tick marks are strike lines showing dip northwest-trendingsteep fault (Fig. 8). This direction. Note large drag in Paleozoicstrata at southeastend of range and different Precambrianrocks fault, and the southwest-dippingreverse fault on either side of Florida Mountains "upthrust," both of which are taken as evidence of significant right which juxtaposes Precambrian granite and slip on "upthrust." The blue-shadedarea is complexly broken by closely spacednormal and thrust faults; Lower Cretaceoussedimentary rocks at it is bounded by low-angle faults which steepen downward to merge with Florida Mountains up- GranitePass (just north of HatchetGap), may thrust.Tv-middle Tertiary volcanic rocks, Tlr-Love Ranch fanglomerate, Pz-Paleozoic sedimentary be interpretedas oblique-slipupthrusts mai- rocks, p€s-Precambrian syenite, and p€g-Precambrian granite ginal to an uplifted basement block. (A Lar- amide age for these faults is interpreted becauseof their reverse-faultgeometry, their FloridoMts. uPthrusl northwest trend which is truncated by late Tertiary, north-trending, range-boundary faults, and the intrusion of the Granite Pass p€s fault by a stockof mid-Tertiary granite.)The uplifted block includes all of the modern (Fig. 9). Generally, Pa- leozoic strata in the Big Hatchet range dip no verlicol €roggerolion southwestward, although broad folds are present. Fold axes and northeastward-dip- NW ping thrusts indicate tectonic transport to- /Florido Mts uPihrusl ward the southwest over large parts of the Tpoott range, a relationship that seems more con- sistentwith horstlike block uplift of the range qooo and/or transpression of hanging wall rocks 5,ooo (Fig.9), rather than regionalnortheast over- thrusting (S. Thompson, III, written com- 4poo munication, 1983).North of Granite Pass, FIGURE 6-Cross sections acrossFlorida Mountains "upthrust" (oblique-slip reverse fault) taken from thick Cretaceous and Tertiarv sedimentarv Brown (1982)and Brown and Clemons (in press). Thrusting in footwall rocks seems to be rdsult of rocks and Hidalgo volcanic roiks of the Littl-e transpression. See Fig. 1 for location. Tlr-Love Ranch fanglomerate, Pu-upper Paleozoic rocks, Pl- Hatchet Mountains were preserved in the lower Paleozoicrocks, p€s-Precambrian syenite, p€g-Precambrian granite, A-strike-slip movement basin footwall of the faults of Granite Pass away from viewer, and T-strike-slip movement toward viewer. F

Neu Mexico Geology November 1983 -Reiuven oled Burro uPlift (Loromide)+ picfure in southwest New Mexico, and ba- s N RingboneBosin >

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Fronklin i\4ts, Mis b Hotche\ o R i cd Mexico FIGURE 8-Geologic map of Granite PasFHatchet l'>l{.Erosion Gap area between Little and Big Hatchet Moun- '-''Lordmide io Precombrion in D/irt km tains (after Zeller, 1970,1975).Tg-Tertiary granite, o 5O lime :::,:Loromide K{retaceous rocks, Pu-upper Paleozoicrocks, Pl- uiuir bosins lower Paleozoicrock, and pCg-Precambrian gra- nite. FIGURE 10-Interpretive paleotectonic map of southwest New Mexico in Laramide time showing inferred pattern of west-northwest-trending Wind River, as well as mixed Wind River-Echo Park(?)- type basins, and southwest-dipping, northeast-facing,basement-cored block uplifts (uplifts locally have southwest-facingthrust margins, as in the Big Hatchet Mountains). Uplifts in southwest New Mexico exhibit important oblique right slip and associatedtranspressional structures on boundary faults. Con- trol for uplifts and basins is from cross sections and wells indicated on map, as well as from nature of outcropping pre-rniddle Tertiary rocks in mountain ranges beyond these sections (Fig. 1). Laramide uplifts were inferred in modern mountain rangeswhere pre-late Eoceneerosion cut deeplyinto Paleozoic rocks, or locally into the Precambrian rocks; Laramide basins were inferred where nearly complete sectionsol Paleozoicand Mesozoic rocks are still present today, andlor where thick Upper Cretaceous- lower Tertiary basin-filling rocks are known. Nevertheless, diagram is highly speculative in that data points are few and widely separated (see Fig. 1). General northwest trend of structures is based on trend of exposeduplift boundary faults. Inset in upper left suggestsPecos "buckles" are tears separating compressedand shortened crust of southwest New Mexico from uncompressedand unshortened crust of southeastNew Mexico.

BiS Hotchet Mts. Little Hotchet Mts. N of fset Gronite offsei sectionHotchet Po9s / offset.. elev.(ft) secli on -jejrgl Bor ridge Gop | ry/ 5poo K \Pu /\ \-- Pu :59OO n\Jmerous intrutiult -lopoo Jp€ l- r r5.ooo

JIGURE 9-Diagrammatic section through the Little Hatchet-Big Hatchet Mountains (seeFig. L for location and note offsets of section). Big Hatchet Mountains,are interpreted as basement-coredblock uplift, the Little Hatchets as compressedblock (transpression?)in front of marginal oblique-slip reversefaults. Tg-Tertiary granite, K-Cretaceous rocks, Pu-upper Paleozoicrocks, Pl-lower Paleozoicrocks, and p€-Precambrian rolts, A-strike-slip movement away from viewer, T-strike-slip movement toward viewer I:>

New Mexico Geolo3y November 1983 References of Economic Paleontologists and Mineralogists, Per- Mountains area, New Mexico: New Mexico Bureau of rnian Basin Section, PublicationT0-12, pp. 55-69. Mines and Mineral Resources,Memoir 16, 128 pp. Bachman,G. O., and Myers, D. A.,1969, Geologyof the Hayes, P T.,1970, Cretaceouspaleogeography of south- -, 1970,Geology of the Little Hatchet Mountains, Bear Peak area, Dofla Ana County, New Mexico: U.S. eastern Arizona and adiacent areas: U.S. Geological Hidalgo and Grant Counties, New Mexico: New Mex- GeologicalSurvey, Bulletin 1,277-C,46 pp. Suwey, ProfessionalPaper 658-8, 42pp. ico Bureau of Mines and Mineral Resources,Bulletin Brown, C. 4.,1982, Geology of the Mahoney mine-Gym Kelley, V C., 1955,Monoclines of the Colorado Plateau: 96,22pp. Peakarea, Florida Mountains, Luna County, New Mex- GeologicalSociety of America, Bulletin, v. 65, pp.789- -, 1975, Structural geology of ico: M.S. thesis, New Mexico State University, 82 pp. 804. quadrangle, Hidalgo County, New Mexico: New Mex- Brown, G. A., and Clemons, R. E., 1983,Florida Moun- -, 7971,Geology of the Pecoscountry, southeastern ico Bureau of Mines and Mineral Resources,Circular tairo section of southwest New Mexico overthrust belt- New Mexico: New Mexico Bureauof Mines and Mineral L46,23pp n a reevaluation: New Mexico Geology, v. 5, no. 2, pp. Resources,Memoir 24,75 pp. 2529. Kelley,V. C., and McCleary, J. T., 1960,Laramide orogeny Bushnell, H. P., 1953,Geology of the McRaeCanyon area, in south-cenhal New Mexico: American Association oI Sierra County, New Mexico: M.S. thesis, University of Petroleum Geologists, Bulletin, v. M, pp. 1,419-1.,420. New Mexico, 105 pp. Kelley, V. C., and Silver, C., 1952,Geology of the Caballo Chapin, C. E., and Cather, S. M., 1981,Eocene tectonics Mountains: University of New Mexico, Publicationsin and sedimentation in the Colorado Plateau-Rocky GeologySeries, no. 4,286 pp. Mountain area; in, Dickinson, W. R. and Payne, W. D. Kottlowski, F.8., 1958,Pennsylvanian and Permian rmks (eds.), Relations of tectonics to ore deposits in the near the late Paleozoic Florida islands: Roswell Geo- southernCordillera: Arizona Geological Society Digest, logical Society,11th field conference, pp.79-87. v. 74, pp. 773-798. -, 1960, Summary of Pennsylvanian sections in Clemons, R. E., 1982, Geology of MassacrePeak quad- southwest New Mexico and southeast Arizona: New rangle, Luna County, New Mexico:New Mexico Bureau Meico Bureau Mnes and Mineral Resources,Bulletin of Mines and Mineral Resources,Geologic Map 51, scale 66,787pp. l:24,000. -,7963, Paleozoicand Mesozoic strata of southwest -, Geology of the South Peak quadrangle, Luna and south-central New Mexico: New Mexico Bureau County, New Mexico: New Mexico Bureau of Mines Mines and Mineral Resources,Bulletin 79,l0O pp. and Mineral Resources,Geologic Map 59, scale1:24,0N, -, 1965, Sedimentary basins of south-central and ln Dress. southwestem New Mexico: American Association of Clembns,R. E., and Brown, G. A., Geology o{ Gym Peak Petroleum Geologists, Bulletin, v. 49, pp.2,1202,1,39. quadrangle, Luna County, New Mexico: New Mexico Kottlowski, F. E., Flower, R. H., Thompson, M. L., and Bureauof Mines and Mineral Resources,Geologic Map Foster, R. W., 1956, Stratigraphic studies of the San 58, scale1,:24,000, in press. Andres Mountains, New Mexico: New Mexico Bureau Coney, P J.,1975, Plate tectonicsand the Laramide oro- of Mines and Mineral Resources,Memoir 1, 132 pp. geny; in Woodward, L. A. and Northrop, S. A. (eds.), Lemley, I. S., 1982,The Lobo Formation and lithologically Tectonicsand mineral resourcesof southwestern North similar units in Luna and southwestern Dofia Ana America: New Mexico GeologicalSociety, Special Pub- Counties, New Mexico: M.S. thesis, New Medco State lication 6, pp. 5-10. University, 95 pp. -, 7978,The plate tectonic setting of southeastern Loring, A. K., and Loring, R. 8., 1980, Age of thrust Arizona: New Mexico Geological Society, Guidebook faulting, Little Hatchet Mountains, southwestern New to 29th field conference, pp.285290. Mexico: Isochron/West, no. 27, pp. 29-30. Corbitt, L. L., andWoodward, L. A., 1973,Tectonicframe- Reading, H. G., 1980,Characteristics and recognition of work of Cordilleran foldbelt in southwesternNew Mex- shike-slip fault systems;in Ballance,P. R. and Reading, ico: American Association of Petroleum Geologists, H. G. (eds.), S€dimentation in oblique-slip mobile zones: Bulletin, v. 57, pp. 2,207J,2'1,6. Intemational Association of Sedimentologists,Special Shortcourse in Davis, G. H., 7979, Laramide folding and faulting in Publication 4, pp. 7-26. southeasternArizona: American Journal of Science,v. Seager,W. R., 7975, Cenozoic tectonic evolution of the water-welldesign 279, pp.543-569 Las Cruces area: Society, New Mexico Geological "Optirnizing the yields of water wells," Dckinson, W R., and Snyder, W. 5.,1978, Platetectonics Guidebook to 26th annual field conference, pp.297- an inten- of the Laramide orogeny; in Matthews, V., III (ed.), 327. sive two-dav short course, will be offered bv the Laramidefolding associatedwith basementblock fault- -/ 1981/Geology of the Organ Mountains and south- Continuing bducation Department of New M'exico ing in the western United States:Geological Society of ern SanAndres Mountains, New Medco: New Mexico Institute of Mining and Technology in Socorro, America, Memoir 151, pp. 355-365. Bureau of Mines and Mineral Resources,Memoir 36. New Mexico. Doyle, G. H., 7951, Geology of the northern Caballo 97 pp. The coursewill be held November 10-11, 1983, Mountains, Sierra County, New Mexico: M.S. thesis, Seager,W. R., Hawley, J.W., andKottlowski, L E., Geol- at Macey ConferenceCenter on the New Mexico New Mexico Institute of Mining and Technology, 51 ogy of area, Dofla Ana County, Techcampus. This short coursehas been designed New and PP Mexico: New Mexico Bureauof Mines Mineral water-resourcemanagers, Drewes, Harald, 7978,The Cordilleran orogenic belt be- Resources,Geologic Map, scale 1,:24,000,in prepara- for architects, en- tween Nevada and Chihuahua: Geological Society of tion. gineers, geologists, and land developers. The America, Bulletin, v.89, pp. 647-657. Stearns,D. W., 7978,Faulting and forced folding in the courseoffers an opportunity to update and famil- -, 1982a,Some general features of the El Paso-Wick- Rocky Mountains foreland: in Matthews, V., III (ed.), iarize topJevel management and key personnel enburg transectof the Cordilletan orogenic belt, Texas Laramidefolding associatedwith basementblock fault- with methods and materials for optimum produc- to Arizona: ln Drewes, H. (ed.), Cordilleran overthrust ing in the western United States:Geological Society of tion from new or existing water wells. belt, Texasto Arizona field conierence:Rocky Mountain America, Memoir 151, pp. 1J5. Instructors for the course include W. K. Sum- Association of Geologists, pp. 87-96. Thornpson, Sam, III, 1,982,Orl and gas exploration wells mers, president and senior geologist, W. K. Sum- -, 1982b,Geologic map of the Cochise Head quad- in southwesternNew Mexico; in Drewes, H. (ed.), Cor- Associates,Inc. of Socorro.Mr. rangle and adjacent areas, southeasternArizona: U.S. dilleran overthrust belt, Texasto Arizona, field confer- mers & Summers' Geological Survey, Miscellaneous Geologic Investiga- ence: Rocky Mountain Association of Geologists, pp. firm is active in design of wells and ground-water tions Map I-1312. lJo- I f-1. resourcemanagement ProSrams.Michael D. Drewes, Harald, and Thorman, C. H., 1980a,Geologic Thompson, Sam, III, and Bieberman,R. A., 1975,Oil and Campbell,author of "Water Well Technology" and map of the Steinsquadrangle and the adjacentpart-of gas exploration wells in Dofra Ana County, New Mex- B. G. Hammock, authority in preparation of plans, the Vanar quadrangle, Hidalgo County, New Mexico: ico: New Mexico GeologicalSociety, Guidebook to 26th specifications,and contract management/will add U.S. GeologicalSuruey, Miscellaneous Geologic Inves- annual field conference, pp. 771,-174. their areas of exDertiseto the course. One con- tigations Map I-1220. Tumer, G. L.,1952, The Deming axis, southeasternAri- tinuing education unit is offered for completion of -, 1980b,Geologic map of the Cotton City quadran- zona, New Mexico, and trans-PecosTexas: New Mexico gle and the adjacentpart of the Vanar quadrangle, Hi- GeologicalSociety, Guidebook to 13th annual field con- the course. dalgo County, New Mexico: U.S. Geological Suruey, ference, pp. 59-71. Luncheons, a cocktail party, and Southwestern Mscellaneous Geologic Investigations Map l-1221. Uphoflphofl T. L., 1978,Subsurface shatigraphy and structure barbecueare planned in conjunction with the short Elston, W. 8., 1958, Buno uplift, northeastem limit of of the Mesilla and Hueco Bolsons,El Pasoregion, Texas course,offering participants a chanceto meet and sedimentary basins of southwestern New Mexico and and New Mexico: M.S. thesis, University of Texasat El mingle with each other. The costs of the social southeasternArizona: American Association of Petro- r"aso,raso, r)t) PP. functions are in addition to the course fee. leum Geologists, Bulletin, v. 42, pp.2,513-2,577. Wilcox,ilcox, R. E.,IE., Harding, T. P., and Seely,D. R., 1973,Basic The course fee is $175.00for those registering Greenwood, 8., Kottlowski, F. E., and Thompson, Sam, wrench tectonics:American Association of Petroleum after October 1. Complete information, including III, Dn, Petroleum potential and stratigraphy of Ped- Geologists,Bulletin, v. 57, pp. 74-95. regosa Basin-Comparison with Permian and Oro- Woodward, L. A., and DuChene, H. R., 1981,Overthrust courseoutline/ may be obtained by contacting the grande Basins: American Association of Petroleum belt of southwestern New Mexicecomoarison with Continuing Education Department, NMIMT, Geologists, Bulletin, v. 51, no. 9, pp.7,448-7,469. Wyorning-Utah overthrust belt: American Association Campus Station, Socorro,NM 87801,or by calling Haenggi, W. T., and Gries, J. C., 1970, Structural evo- of Petroleum Geologists, Bulletin, v. 65, pp.722-729. W. K. Summers, Socorro (505) 835-2095. lution of northeastem Chihuahua tectonic belt: Sociew Zeller, R. A., Jr., 1965, Shatigraphy of the Big Hatchet

76 November 1983 Nat Mexico Geology