Structuralhistory of Paiarito fault zone in the EspanolaBasin, , NewMexico

byMatthew p. Gotombek,Department ofGeology and Geography, University ofMassachusetts, Amherst, MA, and Lunar and Planetary Institute, Houston, TX

Introduction fill (Santa Fe ) with the down faults that cut the SantaFe Group at The central section of the Rio Grande rift rocks of the Sangrede Cristo uplift. The west- least20 km to the westof the easternmargin consists of three distinct, north-trending en ern margin of the Espaflola Basin is marked of the EspafiolaBasin. The westernedge of echelon basins that step to the right. These by a seriesof northeast-trending, down-to-the- the Velardegraben is definedby the Pajarito predominantly three basins are from south to north: the east faults. However, part of this fault zone is fault zone which exhibits Albuquerque-Belen, Espafiola, and San Luis covered by young volcanics, indicating inac- down-to-the-eastdisplacements. In the Jemez Basins. Individual basins are approximately tivity in the past few m.y. Mountains,this fault zonecuts a l.l-m.y.-old pro- 60 km wide, fault bounded, and asymmetric, Manley (1979) defined the central intrarift ash-flow tuff (Doell and others, 1968), with valley-fill sediments tilted oppositely in Velarde graben within the Espaflola Basin. ducing a prominent fault scarp (Golombek' each successive basin (Kelley, 1979). Sedi- Stratigraphic relations indicate that the 1981).The objectivesof this study are to de- ments within the Espafiola Basin are tilted to Velarde graben began forming in early Plio- fine the kinematics,timing, and tectonicsof the west. cenetime; detectableseismicity (Jiracek, 1974) the Pajarito fault zone by meansof detailed The border faults of the Espafiola Basin are and crustal subsidence (Reilinger and York, mappingand structuralanalysis, thereby pro- poorly exposed.Moreover, the easternedge of 1979) indicate that it is still active. Manley viding new insight into the evolutionof this the Espaflola Basin is not marked by a single (1979) mapped the eastern border of the portion of the Rio Granderift. Completedis- major fault (fig. l) but is defined by the both Velarde graben as a zone of prominent yet par- cussionof theseresults is reportedin Golom- depositional and faulted contact of the basin tially obscured north-trending, west-side- bek(1982). StratigraPhY Volcanic rocks of the havebeen combined into threegroups (Bailey and others, 1969; Smith and others, 1970; Griggs, 1964):the oldest (age datesof 9.1-8.5m.y.; Dalrympleand others, 1967) found as highlands in the southern JemezMountains, the intermediate-age Polva- deraGroup (agedates of 7.4'3.7 m.y.; Dal- rymple and others, 1967)found as highlands in the northern JemezMountains, and the youngestTewa Group (age datesof 1.4-0.4 m.y.; Doell and others, 1968)erupted from centralcalderas in the JemezMountains and found within and flanking them as broad, gently dipping plateaus(fig. 2). Beneaththe volcanicrocks are the formationsof the (Galushaand Blick, l97l), a pre- dominantly ,fossiliferous, sedimen- tary sequencethat accumulatedduring rifting. The SantaFe Group restsunconformably on the GalisteoFormation, which was deposited in prerift Eocenebasins (Stearns, 1943).

General characteristics The Pajarito fault zoneextends in a north- northeastdirection along the eastflank of the JemezMountains (fig. l). Markedchanges oc- cur in both the stratigraphicsections of vol- canicrocks and the characterof the fault zone EXPLANATION along strike. These structural and strati- graphic changespermit subdivisionof the Quoternory lo Miocene T--l Lower Tertlory, Mesozoic, fault zone into segments(fig. 2). Theseseg- volconic rocks of I I ond Poleozoicrocks are,from north to south: Jemez Mounloins U ments 1) SeNra Clann sncvnNr-single large r:'i] Precombrion rocks fault scarp100-200 m high; fault cuts f-'r'l ouolernory to Pliocene intermediate-agePolvadera Group tholeiitic ond olkoli Ll rocks and derivedvolcaniclastic sedi- bosolts -a.- ments; Conlocl 2) Gul,:E MoUNTAIN srclranNr-complex Pliocene lo Eocene zone of small faults with displace- .v Foult ( bor ond boll on downlhrown side) | | sedimentory rocks within eastand west; L-J the Espofrolo Bosin mentsdown both to the \._ intermediate-age River fault zone disrupts PolvaderaGrouP rocks and derived FIGURE l-GexeneuzED cEoI-ocrcrvrlp or EspeNoleBnsrx, Rro GnnNoERtFr, NEw MExtco(from Man- volcaniclasticsediments; ley, 1979,with modifications).

New Mexico Ceology August1982 3) Palenrro PLATEAUsEclreNr-promi- (Manley, 1979),suggesting the entireVelarde mainedin about the sameplace during its ac- nent 100-m fault scarp in youngest grabenfloor rampsup. tive life, then the stratigraphicrecord at the which underliesthe Becausetotal displacementacross the Paja- peripherywould showan abrupt changefrom gentlyeastward-sloping Pajarito Pla- rito fault zone has been from 200 to 600 m mostly igneousrocks to mostly volcaniclastic teau:and during its entirehistory (5 m.y. ago-present; sedimentsin a direction radially away from 4) Sr. PernR's DoME secvnNr-wedge- Manley, 1979),central depressions (indicated the volcaniccenter. This rapid facieschange shaped zone of two faults; Keres by gravity minima; Cordell, 1979)filled with betweenKeres and PolvaderaGroup volcanics Group rocks on upfaultedside adja- 2-2.5 km of low-densitysediments were prob- and volcaniclasticsediments appears to have centto 30-100-mfault scarp. ably formedby old faultsthat becameinactive controlledthe positionand trend of the Paja- by middleMiocene and are not presentlyvisi- rito fault zone. The fault zone bows and/or Displacements bleon thesurface. The relativecontribution of stepseastward where two largevolcanic com- Wherethe fault zonecuts the l.l-m.y.-old prerift and synrift sedimentsto this gravity plexesare presentin the St. Peter'sdome and BandelierTuff it has produceda prominent minima is unknown.However, in at leastone Guaje Mountain segments,but the zone is 50-100-m-highfault scarp(Golombek, l98l). placealong the Pajarito fault zone(St. Peter's found further west in betweenand at either Correlationof ash-flowbeds across the fault dome), prerift sedimentaryrocks probably end of the volcaniccomplexes. One complex indicatethat in most placesthe scarpheight is contributesignificantly to the anomaly(Gol- in the Guaje Mountain segmentwas suffi- equal to the stratigraphicdisplacement. Dis- ombek,1982). cientlymassive to interferewith the develop- placementsof rock units older than the Ban- ment of the Velarde graben, causing the delier Tuff were estimatedusing standard Controlson thelocation and trend of the grabento ramp up. techniquesthat utilizeknowledge of the strati- Pajaritofault zone Extensional Tectonics graphy.These estimates of the total displace- Abrupt facies changes between older vol- mentacross the fault during its 5-m.y.history canics and volcaniclastic sediments of the Mesoscopicfracture data were collectedat arebetween 200-600 m. Ratesof displacement Jemez Mountains appear to have controlled 30 stations,most of which are in the Tshirege for the time periods0-5, 0-1.1, and l.l-5 the local position, trend, and character of the Member of the BandelierTuff. Slickensides m.y. ago rangefrom .020to .136mm/. Pajarito fault zone. Erosion during the active on mesoscopicfaults in the TshiregeMember The lack of significant east-side-downdis- life of a volcanic dome would result in the dep- are typicallywell developedwith very smooth placementsin the Guaje Mountain segment osition of volcaniclastic sedimentsin an apron and polishedsurfaces. Displacements were in- (fig. 2) implies that the west side of the around the dome. Thus, the periphery of a variably pure dip-slip and normal, indicating Velardegraben locally ramps up. An east-side- volcanic dome would be characterized by in- extensionapproximately perpendicular to the down fault is present(fig. l) along the east terfingering of volcanics and volcaniclastic strikeof the fault. Fig. 3 illustratesthe trace of side of the Velarde graben at this latitude sediments. If the periphery of a dome re- the Pajarito fault zone, the extensiondirec- tions for eachstation in the BandelierTuff, and compositeplots for each domain (area with similarly striking mesoscopicfaults and derivedextension directions). Every domain has an extensiondirection orientedapprox- tln BondelierTuf f ( 1.4-l.tm.y.) Sonlo Cloro imatelyperpendicular to the local trend of the segment fault zone. Theseextension directions could (7.4-37m.y.) N PolvoderoGroup resultfrom reorientationof the regionaleast- westextension by the Pajarito fault zoneto a Volconiclosticsediments n (7.4-2.8n.y.1 direction perpendicularto the fault zone in eachsegment. In addition. most domainshave extension KeresGroup(9. t-8.5 m.y.) Guoje m directionsoriented approximately parallel to Mounloin I'F subparallelto the localtrend of the fault zone. Sonlo Fe Group segmenl E-JJ Theseextension directions could be becauseof stressrelease parallel to the intermediatestress (-/ Con?oct directionwhich will be locally parallelto the fault if the direction of maximum extension hasbeen reoriented so as to be approximately perpendicularto the fault zone. This implies Foult (bor ond boll that both theintermediate and minimumstress on downlhrownside) directionswere tensional. Tectonic and geologic history of Espafiola Basin Pojorifo in Pajarito fault zone area N Plofeou In the area of the Pajarito fault zone, the se9ment earlydevelopment of the Rio Granderift was markedby the depositionof SantaFe Group sediments(early Miocene) directly on flat- lying, prerift GalisteoFormation and did not involvepervasive faulting or tilting. Localized O 6km faulting createdcentral depressions, indicated by gravity minima, in the EspaflolaBasin. Sedimentation concomitant with faulting allowedaccumulation of thick deposits(2-2.5 km) of SantaFe Group within the centralde- St. Peler's dome pressions(fie. 4a). Faulting endedby middle segment Miocene,when filling of the EspafiolaBasin was completedin the study area (approxi- mately l0 m.y. ago); these faults are not FICURE 2-SecvnHrs or PnleRrro FAULTzoNE. presentlyvisible on thesurface.

August1982 New Mexico Geology n=lo3 a) Eenlv MrocENn rrve. Fault depicted allowed ac- cumulation of 2-2.5 km of low-density sedimentary fill (Santa Fe Group) in central subbasin within Espafrola Basin.

n=43

b) 8-9 u.v. aco. Faults of central subbasin have be- + o^" come inactive. west tilting, due to movement on faults defining western margin of Espaflola Basin, oo has occurred after eruption of Keres Group vol- canicsin St. Peter's dome area. - n=39 .J: .-)_ )A' /\

n=40 FIGURE 3-KINeulrlcs or Prunntro reulT zoNE.Dotted line is trace of major faults of Pajarito fault zone; solid lines indicate extensiondirections for all stations in Bandelier Tuff. Composite fracture-domain plots c) Jusr nnron ro 5 v.y. lco. Volcanism has on lower hemisphere equal area projection; n : number of faults for indicated stations. Because faults at shifted to north depositing Polvadera many stations cluster into two distinct setsindicating two extensiondirections, faults have been coded into Group. QTvc are eroded volcaniclastic sediments from Keres and Polvadera two sets:solid dots are poles to faults that cluster into setsthat strike north to east, open circlesare poles to Grouos. faults that cluster into setsthat strike north to west. Domains are, from north to south: Santa Clara seg- ment and northern Guaje Mountain segment, southern Guaje Mountain segment, seg- ment, and St. Peter's dome segment. Extension directions perpendicular to local trend of fault zone aie due to reorientation of regional east-westextension by Pajarito fault zone. Extension directions parallel (northern Guaje Mountain segment) and parallel to subparallel (Pajarito Plateau and St. Peter's dome segments)to local trend of fault zone are thus parallel to intermediate stressdirection if reorientation oc- curs as suggestedabove, thus implying that both minimum and intermediate stress directions are tensional. North-northeast-extensiondirections in southern Guaje Mountain segmentdo not fit proposed pattern.

Volcanism was underway by l0 m.y. ago, shed off the volcanic constructs in the north about when the western margin border faults and south (fig. 4c). became active. West tilting of sediments and The Pajarito fault zone and Velarde graben old volcanics (Keres Group) occurred from 8.5 subbasin formed about 5 m.y. ago. Volcanism d) PnnsnNr. Paj".ito fuult ron" formed about 5 m.y. to 7.5 m.y. ago. BecauseSanta Fe Group sedi- in the north slowed by 3 m.y. ago and shifted ago with movement continuing to present displacing Bandelier ments on the upthrown side of the Pajarito to the center of the Jemez Mountains. culmi- Tuff. Canyons eroded through Pajarito Plateau. fault zone are tilted to the west at the same (or nating with the eruptions of the Bandelier larger) angle than Santa Fe Group sediments Tuff 1.4 and l.l m.y. ago. The last volcanic FICURE 4-Evor-urroNlRy on the downthrown (east) side, faults respon- activity occurred about 0.4 m.y. ago, but BLocK DTAGRAMoF Plllnlto FAULTzoNE annl. Symbols for geologic sible for the west tilting must be located to the faulting along the Pajarito fault zone has con- units: Tuff, west, probably along the western border of the tinued present, Qb-Bandelier QTvc-volcaniclastic to the offsetting the Bandelier sediments, Tp-, Tk-Keres Espaflola Basin (fig. 4b). With eruption of the Tuff as much as 100 m in the past l.l m.y. Group, Tsf-Santa Fe Group (synrift deposits), Polvadera volcanic Group, activity shifted (fig. ad). Tg-Galisteo Formation (prerift deposits), northward. Volcaniclastic sediments were (continued on p. 48) pattern-pre-Galisteo rocks.

New Mexico Geology August1982 Palarito fault zone LateCretaceous leaflocality Unia Thickness (continuedfrom p. 41) (continuedfromp.45) No. I)escripaion (cm, inches) APPENDIX A (continued) References Siltstone, gray-green; scattered Bailey,R. A., Smith,R. L., and Ross,C. S., 1969,Strati- subrounded plant fragments; well- Totsl ahickness-16.t4m (55.9ft) graphic nomenclatureof volcanic rocks in the Jemez sorted,averaging 5 mm (.2 inches)in Unil Thickness Mountains, New Mexico: diameter l5.2 6.1 U.S. GeologicalSurvey, Bull. No. Description (ctn, inches\ 1274-P,p.l-19 C Mudstone, gray-green; a few Cordell, L., 1979,Gravimetric expressionof graben fault- 010 White sandstone,medium-grained; scattered stem fragments; poorly ing in Santa Fe country and the EspafrolaBasin, New with larg€ plant fragments up to 5 sortedup to 3 x 5 cm (1.2x 2 inches) 3.8 t.5 Mexico: New Mexico Geological Society, Guidebook cm'1;well indurated and forms char- D Mudstone, gray-gre€n; occasional 30th field conference,p. 59-64 acteristic popcorn surface texture horizons with leaves 3 cm (1,2 Dalrymple,G. B., Cox, A., Doell,R. R., and Gromme,C. upon weathering;some hoodoo (col- inches)in length and also horizons geornagneticpolarity S., 1967, Pliocene epochs:Earth umnsor pinnacles)development 89 of poorly sortedstems up to 1,3 x 2 and PlanetaryScience Letters, v.2, p. 163-173 009 White sandstone, fine-grained; cm (.5x .8inches) 22.8 9.1 Doell, R. R., Dalrymple,G. 8., Smith,R. L., and Bailey, about 5q0 plant debris concentrated gray-green; R. A., 1968, Paleomagnetism,potassium-argon ages, Mudstone, many in laminae. Undulating bedding jumbled and geology of and associatedrocks of the leaves,many of which over- finely developed; well indurated 2-5 cm (.8-2 Valles , New Mexico: Geological Society of lap; leavessubcomplete with frne laminationsand mud oart- America, Mem. | 16,p. 2l | -248 inches)in length,small fragmentsup rngs 60 (.2 inches)in length; poorly Galusha,T., and Blick, J. C., 1971,Stratigraphy of the to 5 mm (.4-2 SantaFe Group, New Mexico: AmericanMuseum of Na- 008 Dark gray-greenmudstone with 15- sorted stem fragments l-5 cm (.3 tural History,Bull., v. lrM, art. l, 128p. 20olo plant debris up to 3.5 cm'1; inches)in lengthand up to .75cm Golombek,M. P., 1981,Geometry and rate of extension coarsensupward 30 inches) wide; slickensidesup to 39 (16 across the Pajarito fault zone, Espaiola Basin, Rio oo7 Gray-green mudstone with about cm inches)in length, leaveson (.12 Crande rift, northern New Mexico: Geology, v. 9, p. 590 plant fragments and stems; laminaeaveraging .3 cm inches) a, 2t-24 gradesupward into 008 28 t1 apart 17.8 -, gray-green; 1982,Geology, structure, and tectonicsof the Paja- 006 Sandstone,white, medium-grained; Mudstone, scattered (a), a) 7.6 3.0 rito fault zone in the EspafiolaBasin of the Rio Grande with large fragmentsof plants up to leavesfew in number: lens of grades rift, New Mexico: GeologicalSociety of America, Bull., 5 cm'; about loqo plant content z5 IO few scatteredcomplete leaves ln revlew laterally into stems and poorly 005 Mudstone, gray-green; with Griggs, R. L., 1964,Geology and ground water resources sortedsmall plant fragments,but no approximately l09o carbonaceous of the Los Alamos area, New Mexico: U.S. Geological leaves;stems 5-10 cm (2-4 inches) debris;coarsens upwards into 006 6l 24 Survey,Water-supply Paper 1753,107p. long and up to I cm (.4 inches)wide, Jiracek,G. R., 1974,Geophysical studies in the Jemez 0(X Carbonaceousmudstone, dark-gray; fragmentsare subrounded2-.25 mm Mountains region, New Mexico: New Mexico Geological up to 40qoplant debrisis up to 2 cm' (.08-.01 inches) in diameteri O) b) 5.0 2.0 Society,Guidebook 25th field conference,p. 137-144 poorly sorted;coarsens upwards; be- sameas lateral, stem-richportion of Kelley, V. C., 1979, Tectonics, middle Rio Grande rift, comesmuch lesscarbonaceous later- (a), sharp contact with plant-rich New Mexico, tr Rio Granderift-tectonics and - ally (about l09o) 28 lI portion of (a) tism, R. E. Riecker,ed.: Washington,D.C., American 003 Olive sandstone, medium-grained; G Lateral from (a) and (b) siltstone, GeophysicalUnion, p. 57-70 with some iron staining along bed- yellow-green;few broken plant frag- Manley, K., l9?9, Stratigraphyand structureof the Espa- ding planes;5-1090 plant debris tt7 47 ments(no leaves);lens-shaped cross flola Basin, Rio Granderift, New Mexico, in Rio Grande 002 Gray siltstone;590 plant debris;iron section7 x 60 x 15 cm (2,8 x 24 x 6 rift-tectonics and magmatism, R. E. Riecker, ed.: stainingin fractures l8 inches) 7.0 2.8 Washington, D.C., American p. Geophysical Union, Mudstone, gray-green; full of 7l-85 001 White sandstone;fine-grained lenses of sand rich in carbonizedplant de- overlapping complete leaves that Reilinger,R. 8., and York, J. 8., 1979,Relative crustal bris and silt lacking plant debris; cover 10090of surface on laminae subsidencefrom levelingdata in a seismicallyactive part lensessubparallel to bedding; fines about every .5 cm (.2 inches);inter- of the Rio Grande rift, New Mexico: Geology, v. 7, p. varia- vening layers produce complete t39-143 upward into 002; much lateral tion in plant debriscontent (5-20q0) 30 T2 leavesnot overlapping 7,7 3,1 Smith, R. L., Bailey,R. A., and Ross,C. S., 1970,Geo- gray-green; logic map of the JemezMountains, New Mexico:U.S. Mudstone, large stems GeologicalSurvey, Misc. Inv. Map I-571 APPENDIX B-MsesunEp secrroN 5-10 cm (2-4 inches)long and I cm (.4 Stearns,C. 8., 1943, The Galisteo Formation of north- inchcs) wide, also rnany small Unil Thickness pieces, centralNew Mexico:Journal of Ceology,v. 51, p. 301- stem subroundedfrom 3 to 8 No. Descriplion (cm, tnches\ (.12 319 E mm to .32inches) in diameter 15.2 3.1 Concretion, dark-brown; siderite J Grades down with less stem to with veins of barite; rare, poorly subrounded fragments less than 2 preserved leaf impressions extend mrn (.08 inches)in diameter to un- laterallyl.8m(5.9ft) 35.6 14.2 fossiliferousgray-green mudstone 45.9 IE.4 o

il0. Bol[ 0rBanilrnon U.SPOSTAGI PAIII SOCORRO,NEW PERMIINO 9