Chapin, C. 8., and Cather, S. M., 1981, Eocene tecronics and sedimentation in the Plateau-Rocky Mountain area, ln Relations of tectonics to ore deposits Palomasvolcanic field, southern in the southern Cordillera, W R. Dickinson and W. D Payne, eds.: Geological Society Digest, v. 14, p. 173-198 NewMexico Dane, C. H., and Bachman, northern G. O., 1965, and Geologic Map of : U.S. Geological Survey, 2 sheets, scale l:500,000 EuBster, H. P., and Hardie, L. A., 1975. Sedimentation in Chihuahuo,Mexico an ancjent playa-lake complex-the Wilkins Peak Mem- ber of the Green River Formation of Wyoming: Geolog- ical Society of America, Bull., v. 86, p. 3 l9-334 0y Eugster, H P., and Surdam, R. C., 1973, Depositional en- ThomasJ. Frantesand Jerry M Hoffer vironment of the Green River Formation of Wyoming-a Depattment ol GeoIog ical Sciences, preliminary report: Geological Society of America, Bull., TheUniversity of (El Paso) v.84,p. l,ll5-1,120 El Paso,Texas Fisher, W L., Brown, L. F., Jr., Scott, A. J., and McGowen, J. H., 1969, Delta systemsin the exploration of oil and gas: University of Texas (Austin), Bureau of Introduction moresides where appears to havebeen ex- Economic Geology, ResearchColloq.,2l2 p The Palomasvolcanic field (late Cenozoic) truded.Fusiform, almond-shaped, cylindrical Fisher,W. L., and Brown, L.F.,1972, Clasticdepositional setsastride the internationalborder in south- ribbon, and cow-dung bombs are locally systems-a genetic approach to facies analysis: Univer- many sity of Texas (Austin), Bureau of Economic Geology, centralLuna County,New Mexico,and north- abundant around the base of of the 2ll p. ern Chihuahua,Mexico, approximately 80 mi cindercones. Fitzsimmons, J. P., 1959, The structure and geomorphol- west of El Paso, Texas (fig. l). The field A number of cinder conesdisplay a basal ogy of west-central New Mexico: New Mexico Geological coversapproximately 380 mi'z and is bounded section of pyroclasticmaterials capped by Society, Guidebook l0th field conference,p. I l2-l l6 ' Galloway, W 8., on the eastand westby longitudes107'35 W. denseflow rock. Thesecones are interpreted . 1977, Catahoula Formation of rhe Texas ' coastal plain-origin, geochemical evolution, and char- and107"55 W., respectively. as the result of lava welling up through a acteristics of uranium deposits: University of Texas Lowman and Tiedemann(1968) named the cinder-spattercone and pondingin the central (Austin), Bureau of Economic Geology, Rept. of In- volcanicrocks the Palomas volcanic field after vent. Subsequenterosion has removed the en- vestigationsNo. 87, 59 p pyroclasticmaterials while removing Gilbert, G. K., 1885, The topographic fearures of lake a brief reconnaissanceof the area.Balk (1962) circling shores: U.S. Geological Survey, Annual Rept., no 5, p. mappedseveral outcrops of the volcanicrocks very little of the more resistantdense flow 69-t23 north of theinternational border. However. to rock (fig. 5). In addition,several cinder cones Grover, N. C., and Howard, C. S., 1938, The passageof published havebeen mapped that containconcentrically turbid water through Lake Mead: American Society of date, no data existon the distribu- Civil Engineers,Transactjons, v . lO3, p.720-732 tion and occurrenceof volcanicfeatures with- orienteddikes at thetop of thecone. Hantzschel, W., 1975, Treatise on invertebrate paleon- in thevolcanic field. Drxss-A numberof basalticdikes are ex- tology, Part W, Trace fossils and problematica: Univer- posedin the Palomasfield. The dikesare of sity of Kansas (Lawrence), 2nd ed., 269 p. Volcanicfeatures olivine and are primarily associated Hjulstrom, F , 1952, The geomorphology of the alluvial The outwash plains (sandurs) of Iceland, and the mechanics with cinder cones. dikes dip nearly ver- Rocksin the Palomasvolcanic field consist tical,are several feet in width, andaverage 400 of braided rivers: , D.C., International primarily of Ceographers Union, lTth Congress, Proc., p. 337-342 olivinebasalt and associateddif- ft in length (figs. 6 and 7). Severalof the Johnson, B. D., 1978, Genetic stratigraphy and provenance ferentiatesof andesiteand .The field cindercones are locatedat the intersectionof of the Baca Formation, New Mexico, and the Eagar For- is located on the westernflank of the Rio two or moredike trends. mation, Arizona: M.A. thesis, University of Texas Granderift and displaysa numberof differ- (Austin), I 50 p The dikes display two different orienta- enceswhen compared to olivinebasalt occur- Langbein, W. B., 1961, Salinity and hydrology of closed tions. One group are linear and strike in a rencespreviously lakes: U.S. Geological Survey, Prof. Paper 412, 50 p. investigatedwithin therift in generallynorth direction.These dikes are l-15 Massingill, G L., 1979, Geology of the Riley-Puertecito southern New Mexico. Thesedifferences in- ft wide and extendfor distancesof up to a area, southeastern margin of the Colorado Plateau, clude: l) an older age comparedto the rift Socorro County, New maximumof 2,000ft. Approximately8090 of Mexico: D G.S. thesis, University ,2) the occurrenceof more highly dif- of Texas (El Paso), 301 p.; New Mexico Bureau of Mines themapped dikes are linear. The secondgroup and Mineral ferentiatedmembers, Resources,Open-file Rept l0?,301 p. and 3) the occurrenceof occur as curving ring dikes near the top of McGowen, J. H., 1970, Gum Hollow fan delta, Nueces a numberof interestingvolcanic features, in- severalof the cinder cones;these dikes dip Bay, Texas: University of Texas (Austin), Bureau of cluding "pillow" basalt structures, basalt Economic Geology, Rept. of Investigations No. 69, 9l p. dikes,and lava-capped (fig. Mothersill, J. S., 1975, Lake Chad-geochemistry and sedi- cindercones 2). mentary aspectsof a shallow polymictic lake: Journal of LavRnlows-Olivine-rich basaltflows are Sedimentary Petrology, v. 45,p 295-309 the most dominantfeatures in the field. They Normark, W. R , and Dickson, F. H , 1976, Man-made are moderateto highly weatheredand havea turbidity currents in Lake Superior: Sedimentology, v 23,p.815-831 partialmantle of eoliansand. The flows range Pierce,H A, Damon, P. E., and Shafiqullah,M., 1979, in thicknessfrom I to 40 ft, but averageap- An Oligocene(?)Colorado Plateau edge in Arizona: Tec- proximately l0 ft. They range from highly tonophysics,v.61, p. l-24 vesicularto extremelydense. Potter, S. C 1910, Geology of Baca Canyon, Socorro The County, New Mexico: M.S. thesis, University of olivine basalt displaystypical vertical Arizona, 54 p. joints whereasthe more highly differentiated Smith, N. D., 1975, Sedimentary environments and late membersof andesiteto trachytecomposition Quaternary history of a low-energy mountain delta: are characterizedby well-developedclosely Canadian Journal of Sciences,v. 12, p 2,N4- 2,013 spacedplatyjoints (fig. 3). Snyder, D. O., I 97 | , Stratigraphic analysisof the Baca For- Locally abundantare xenolithsof feldspar, mation, west-central New Mexico: Ph.D. thesis, Univer- quartz, peridotite,and orthopyroxene;these sity of New Mexico, 158 p. rangein sizefrom 2 mm to 4 cm. Surdam, R. C., and Wolfbauer, C. A., 1975, The Green River Formation-a playa-lake complex: Geological CINosncoNES-Over 30 cindercones have Society of America, Bull., v. 86, p. 335-345 been mappedin the volcanic field (Frantes, Theakstone, W. H., 1976, Glacial lake sedimentation, 1981,fig. 4). The cones,ranging from 100to Austerdalsisen, Norway: Sedimentology, v.23, p 671- 350ft in height,show single or multiplevents. 688 The conesare compositeand consistof inter- beddedcinder, ,dense lava, and ro9" toTo lo5o to3o agglutinatedspatter. They have steepslopes FIGURE 1-INoEx MAp sHowrNc pALoMAs vol- and the rim is typicaly breachedon one or CANICFIELD

February1982 New Mexico Geologt almost vertically and partially encirclethe vent basalt grading inward to fine-grained dense tially sank while squeezingsoft sedimentbe- area. basalt. tween and around what are now seen as CoNcsNrnlc BASALT sTRUCTURES-In a The above structures, seen only in two sphericalpillowlike structures. l6 mi south of Palo- dimensions, represent pillow basalts or large roadcut approximately Compositionof basalts mas along Mexico Highway 25 are exposed lava toes. The presenceof interbedded hydro- oval to circular structures of densebasalt with clastic materials. which are stratified with The mineralogy and chemistry of the interbedded hydroclastic materials. The struc- graded bedding present locally, indicates ex- Palomas volcanic rocks are summarizedin tures range from 5 to over 25 ft in diameter trusion of basalt into a hydrous environment table l. Basedupon their composition,three and display concentric jointing patterns (fig. (fig. 9). The basalt flows may have flowed into major rock types are represented:olivine 8). They display an outer rim of very glassy a shallow lake where they broke up and par- basalt,, andtrachYte. F

rE Alluviuh-. Ool-_ !r/rr,dt de@sits o( tond,.ilt,a4d grdv€lrcoter. the ftol lz lg -T----l blson ptoin ut.c.n hilt and nountain g.oup. Qol Coal.tced olu,io/ loorloorllansJ c6lotn. sffie yountrr st.oh al/utiun; ldlgo d.cds cdt..ed bv aind b/Nn tahd

Bosoll-fb...Aosott llor3,tco.io,c/nde. aod tPdilc.i l.$ thaa 50fl lnick j tlot roct it hnso to fflabl., t.oy lo b/ack, o/iv/n.-.ich basdtt F;T*;l and int tn.dldta dilla..ntioles, cohtolns phanocrfsrs ol otivine,cJinoqv' ll\l roren,ond p/ogioclas.; an.frt/n d olitin. b idinqtit is cohnoh. Ihd- aosn dik6. T-- l Gif o (? ) Conqlomerote- tu.|/ e.t.d and bcdded, wk/t cenanted 's ceglom.ole, @ngloma.otic sondtlonc, nudsloia, and sillslona, lolo/ | I

UNCON FORMITY

Rhyoliie ond lolile Flots,bl.ccios,ond tulls ol /i|hl-qrdt to raddish I Trl I brcsn lntol/la ood lotit€; tlicro.ts P.oOdblv erc$ds 5OOll io south.m ptl of o..d; Plrelatllct doh/noDl /n no.lheotl

UN CONFORMITY

luonzonile,rhyolile,ond lolile drkes ctosalv related/n age onden- lr.b-l I posilon to quortz honron/te inlrut/on; hasl dhes o.e gorphy//lic; only | orlncioat di*es o.e 5hovn.

Xenol;lhs Hlshtt s)licillod ond silcolad ,eno//ths of Poteazolc ond EttudlCrelaceoB sedimantoly rocht tilhln q,or12 nonzontlt. Quorf r monzonife-Auil cotolad,nediun to l/ne groined, aeuiqlorubr t:--l lo sl/ghl/t porphyr/ltc quortz nonzonile; conqted esenlid//! of o/i40' t'l c/dte, polosh lc/dsPor, ond tome ho.nbtende- ---r-----l Andesite-To-F/o?r, ,tacciot, o9s/onardtes, dnd tufft of g/avish Nrp/c r ondctite; tfrcrftst hol etceed LOOO0; on&sine dnd ho/tbt.Ddedle lrolroil najol conttilueDtsj pu.ptlsh colo. is duc lo finary di3seninol& henohte Ioi lntrusirc oidesitc of etsanllo/ty tha somc conpa6/th, d. erl.ue/vc aDdesllc i lfpico//! Po.phytilrc contoinhq ho.nb/ende Phenocrv.tt

Oldet lol i e' A.ecc/os, ta lded lulls, dDd 5 u bol dina I e Prp rv.' tic f /ott E ol g.ot lo fe/tovith ldn lollle;rachs ore c1nstdeldb/y oUeled; chtorile

UNCONFORMITY

Upper limeslone-Sparca/y lotsilifa.ou., liqht lo dork glov' thi,-to thh, Kul I bed&d tnettoE; Nt. lhon 3frtt thick;upPer 24oll contoins ndulol che.l lhal lncle.e. in omount uped.d

Limeslone conglomerole- L/heslona ond /inetlone - cherl conglonerde; oboul 45O/l thtct; Pcbb/es, cobtl.s, ond lhe fel bouldeft ore sutungu- lat to tcll /ouDd.d aDd consitt of varidut /incslo,e tth tone ttognenk I Kc I ol che.t,dalomitc,aodsdndttone] motrix is //nv' terl line lacod..e' g.oined quartt ond chc.t sdadstoae; botat 35-4Oft is /igll qrdv' ten- tlcrlot, ctEstoninoted sondstffir leDs6 ol re&ish o.koeE sondstone and 3/llslone in uPPe/ Porl. J

[ro$ive limeslone-6rd/, cod rse /v c.vt to / / i na / i ne sloo e o ba u I J95 tl I X-r I thid;sona chc.ty and sllicoaB beds; nea. loP orc scottc.ed lanses of /imcslonc' Pe bble c oao/oncrolc

f''--]]l Bosol closlic tocks- about 37511 ol chert cong/omc.dta'artoticto no I I qua.tzo.c .ondstone, Dola red siltttone, drd g/at ti/iceous liDectona

,"**",ail g Hueco Formolion Morc thor s25rt at chert @stomerote, siliceous n/ta [J : | | crtttotrac L@cato4e, oDd nots'ta tina.tone ] u,u**" r"

Pennsylvonion tacls-about 560lt th/ck oad Probabtl of Drddle Pann i I fP sllvonian AEe / a/nost conpt.te/y kstititarcu. rac.ystd/rzd linestonc ercepl lat portioq ond /antet ol sha/8,ondo @-l/ thict .andstunc, l Escobroso LLmeslone- L/ghl-?/oy, mo.si@,uino/do/' ond cherly litu- I Me I tloDe;mole thon J6Oft thich but onty the uPpe.mo.t Polt is erpotedlD = th6 rdDae, ]

ttncrtohet f;l Fusse'mon Dolom, e- ilorDtetnd dolodtes dnd ' rcretol - rvpLot | l hund.cd teetthcr, td?vuggy host:'e dotontt. it oltheunit. l * Crnder sPoiler con€

---'-conlacl

Doshed where opprorimolely locoted. dotted where conceoled

*'-- " rou"

Doshed where opproximolely locoted.dolt€d where conceoled A tt . l't7". o | 2 3 4mi El /^e FE----l 9l t: -l /c' I o | 2 3 4kh EEE ,r€ E Approximot6 M.oh O.clinolion Robinson FIGURE 2-Cpo1ocrc uap on Peloves volcANrc FTELD;Tres Hermanas Mountains mapped by Balk (1962) and Sierra Boca Grande mapped by and Clark (1981).

New Mexico Ceology February1982 TABLE l-Cnnrrcel coMposrrroN AND MINERAL- The olivine basaltsare fine-grained to glassy ocy oF volcANrc RocKS, Palovns FrELD (l = and contain abundant olivine and pyroxene. * : number of analyzed samples, total Fe Chemically, they have low SiO', Na,O, and reported as FerOr). KrO concentrations and high MgO concentra- Chemical Olivin€ tions. In the field, the basalts are typically Oxides Basalt (37') Andesite (7') Trachyte (8t) dark gray to black and dense. sio, 45.26 52.63 57.95 The andesitesand are more coarse Tio, 2.38 1.66 I -40 grained and contain more plagioclasethan the Al,or 14.57 15.25 15.37 basalts. Chemically, they contain more SiOz, '7.03 FerO'+ 1t.83 9.93 Na'O, and KrO and less MgO, FezO:, and MnO 0.l6 0.l5 0.r2 CaO than the basalts. The and Mgo 10.59 3.96 1.45 't.15 trachytes are generally light to brown in color CaO 9.09 5.03 and display platy jointing. Na:O 2.93 4.58 5.12 KrO l.l6 1 1') 3.00 Basalt agesand origin P,O' 0.54 0.63 0.63 FIGURE 6-Bnsnlr DrKEourcRop. sourHwESToF Field relationships show that the olivine 98.5I 9o 99.66V0 97.l0Vo PALOMAS basalts are younger than the andesitesand tra- (Frantes, 1981). Three occurrences of Mineralogy Olivine basalt Andesile-Trachyte chytes olivine basalt have been dated (K-Ar) from Plagioclase JJ 60 (An'o) (Anor) southern Luna County, New Mexico, giving Clinopyroxene 20 ll datesof2.96 + 0.07,3.91 + 0.18,and 5.17 + Olivine + 0.ll m.y. (Hawley, 1981).The Palomas vol- Iddingsite 18 4 canic rocks are therefore at least Pliocene in Biotite 0 8 age. Magnetite 9 9 The rocks of the Palomas field are clearly Glass 20 8 differentiated, and it is suggestedthat the dif- 10090 10090 ferentiation is becauseof fractionation in the magma closeto the earth's surface. Solidification indexes (SI) of the Palomas volcanic rocks were calculated (after Kuno and others, 1957) and found to range from 57.1 in an olivine basalt sample to 4.9 in a FIGURE 7-Clospup oF BASALTDrKE sHowN rN Flc trachyte. Many of the olivine basaltsand all of 6; note dense nature of basalt and vertical joint- the intermediate rocks in the Palomas volcanic lng. field have SI values less than 35. Renault (1970) reports that SI values less than 35 are thought to result from differentiation of basaltic magma within the crust. Several olivine basalt samples have values of SI greater than 35 which implies little or no dif- ferentiation. The lack of differentiation in some of the olivine basalts suggeststhat they pI-Ary FIGURE 3-Cr-osnr-y spAcED JOINTING IN were transported from the mantle in a rela- BASALT FLow located approximately 16 mi south tively short period of time, whereas the other of Palomas on Mexico Highway 25. olivine basalts and intermediate rocks previ- ously mentioned probably resided in a magma chamber in the crust long enough for signif- icant differentiation to occur. The presenceof high-pressure phase xeno- oRIENTED FIGURE 8-DrNsr. coNcENTRICALLY crysts such as enstatite and feldspar are fur- JOINTINGIN BASALTTOE OR PILLOW STRUCTURE, EX. ther evidence that some of the basalts were posed in roadcut approximately l5 mi south of surface from the mantle in Palomas, Mexico. Lighter colored materials are brought to the a primarily clay and silt. short period of time. The plagioclase-rich rocks (andesites and trachytes) are older than the olivine basalts and therefore were emplaced first. Theserocks FIGURE 4-CrNnrn-sperrER coNES, lN BACK represent successive tapping of a differen- GROUND,AT NORTH END OF VOLCANIC FIELD tiated magma reservoir. This type of activity has been suggestedfor the basalts in the near- by West Potrillo Mountains by Hoffer (1976). The intermediate rocks represent eruptions from the top of the magma chamber, where plagioclase and biotite, being less dense than the magma, concentrated. Later eruptions were from the lower part of the reservoir where clinopyroxene, olivine, and densemafic xenoliths concentrated. This explains the occurrence of the more differentiated flows underlying the olivine and clinopyroxene FIGURE 5-CrNnEn-sperrER coNE (LowER sl-opEs FICURE 9-Pennllrl-nEDDED HyDRocLASTlc phenocrysts, lack of peridotite xenoliths, OF CINDER) CAPPED BY DENSE LAVA FLOWS (CLIFFS): MATERIALSOVERI AIN BY DENSEBASALT; TOAdCut TresHermanas Mountains in backeround. approximately 15 mi south of Palomas, Mexico. (continued on p. lQ

February1982 New Mexico Geology Whereto buyUSGS topographic maps Palomasvolcanic field The following dealerscarry a selectedinventorv of (continued from p. 8) USGS 7% min and l5 min topographicquadrangle maps of their respectiveareas: significantly lower MgO concentration, total Fe content, and higher SiO, and alkali content Mountainsand Rivers The Trailmaster Vic Topmiller, Jr. of the andesitesand trachytes relative to the 2320 Central Ave. SE White Rock ShoppingCenter 1609N. Gold olivine basalts. Albuquerque, NM 87106 Los Alamos, NM 87544 PO Box 201 The Trailmaster II Maxae'sBooks SilverCity, NM 88061 References 5401 Central Ave. East Bent Street RoswellMap & BlueprintCo., Inc. Balk, R , 1962, Geologic map of Tres Hermanas Moun- Albuquerque,NM 87108 PO Box 1836 410N. Main tains: New Mexico Bureau of Mines and Mineral Backwoods Taos, NM 87571 Roswell, NM 88201 Resources,Geologic Map 16, scale l:48,000 6307 Menaul Frantes, T. J., 1981, The geology palomas Blvd. NE Tex Sporting& Pawn of the volcanic Albuquerque,NM SierraSports, Inc. field, Luna County, New Mexico, and Chihuahua, Mex- 871l0 307 West Mermod Street 307S. Pueblo Rd. ico: University of Texas (El Paso), M.S. thesis, p. 70 The WildernessCentre Carlsbad, NM 88220 Hawley, J. W., 1981, Pleistocene and Pliocene history of 2421 San Pedro NE Taos, NM 87571 Pat's Sporting Goods the international boundary area, southern New Mexico, Taos Mountain Albuquerque,NM 871l0 Outfitters Box I 633 rn Geology of the border, southern New Mexico-north- Box 1862 SandiaMountain Outfit ters Ruidoso, NM 88345 ern Chihuahua: El Paso Geological Society, Field Trip For WildernessPeople Taos, NM 87571 Cuidebook, p. 26-32 Hoffer, porrillo 961I Menaul Blvd. NE The Paint & Print Shop J. M., 1976, Geology of the Basalt field, south-central New Mexico: New Mexico Bureau Albuquerque, NM 87I I 2 120N. 2nd St. of Mines and Mineral Resources,Circ. 149, p. 30 Raton, NM 87740 Holman's Kuno, H., Yamasaki, K., Iida, C., and Nagashima, K., 401 Wyoming Blvd. NE Bill's Pack Rat 1957, Differentiation of Hawaiian magmas: Japanese Albuquerque,NM 87123 200Austin St. Journal of Geology and Geography, v.29, p. 179-218 Lowman, P. S., and Tiedemann, Trico International Truth or Consequences,NM 87901 H. A., 1968. Terrain photography from Gemini spacecraft-Final geologic PO Box l5l9l Montgomery Ward report: Goddard Space Flight Center, X-644-71-15. D. Rio Rancho Plaza 522Broadway t4-23 Rio Rancho,NM 87174 Truth or Consequences,NM 87901 Renault, J., l9?0, Major-element variations in the potrillo, Gallup Blueprint OCS Sporting Goods, Unlimited Carrizozo, and McCarthy's basalt fields, New Mexico: New 303S. 2nd 406 Broadway Mexico Bureau of Mines and Mineral Resources, Circ. | 13,22p. Callup, NM 87301 Truth or Consequences,NM 87901 Robinson, B. R., and Clark, K. F., t981, Reconnaissance San Juan Reproduction Co. Blueprints & Maps geology of the Sierra Alta-Boca Grande area, Chihua- 135N. Airport Drive 120S. Water hua, Mexico: El Paso Geological Society, Field Trip Farmington, NM 87401 Las Cruces,NM 8800t Guidebook,p.62-63 n Alpine Sports, Inc. Donald H. Wiese& Co. l2l Sandoval 525 S. Melendres Santa Fe, NM 87501 Las Cruces, NM 88001 Culak Surveying, Inc. BaseCamp 121West Hemlock l2l W. San FranciscoSt. Deming, NM 88030 Santa Fe, NM 87501 The WildernessSociety Healy-Mathews Staioners,Inc. Catwalk Road 515Cerrillos Road Glenwood, NM 88039 SantaFe, NM 87501 Herb WarkinsSurv. & Mapping Wilderness Bookstore 515Market Sr. PO Box 321,El Prado PO Box 472 Taos, NM 87529 Silver City, NM 88061 Los Alamos Stationers Silver Sports 1907Central St. I l6 N. Bullard Los Alamos, NM 87544 Silver City, NM 88061

NDnPrcl I 0TrtuEr oo US POSTAGI PAID SOCORRONEW [4IXICO PERI\4ITNO9