Cenozoicstratigraphyand
structureof theSocorropeak
volcaniccenter,central
NewMexico:a summary
byRichard
M Chamberlin,
Economic
Geologist,
NewMexico
Bureau
of
Mines& Mineral
Resources,
Socorro.
NM
The purposeof this articleis to reviewhigh_
lights of recent work on the Socorro pJak
volcanic centerand to summarizea lengthy
dissertation(Chamberlin,I 980).The geologit
framework of the Socorro geothermalaria,
which includesall of the Socorro peak vol-
progress)hasshownthat the Socorrocauldron
is a segmentof a very large cauldron from
which the Hells MesaTuff was eruptedabout
33 m.y. ago. Thesenew data requiresomerevisions of the stratigraphic sequenceand
cauldron relationships in the Socorro peak
area as previously described(Chapin and
others, 1978;Chamberlin,1980).New stratigraphicunits describedby Chamberlin(19g0)
appearin italics; thesenamesare being for_
malized by Osburn and Chapin (in preparation).
Geologicsetting
In central New Mexico, the Rio Granderift
has broken a northeast-trendingchain of
Oligocenecauldronsand surroundingvolcanic
plateau(part of the Datil-Mogollon volcanic
field) into a seriesof north-trending,tilted,
fault-block ranges and alluvial basins. The
cauldronslie alongthe ancientcrustalflaw of
the Morencilineament,which hasbeenreactivated within the rift as a deep-seated
zone of
lateral shearing(Chapin and others, l97g).
This transverse
shearzoneis a diffusedomain
boundary at the surface, where it separates
fields of tilted fault blocks that are stepped
down and rotated in opposingdirectioni. In
crosssection,the closelyspacedfault blocks
look similar to a train of fallen dominoes
(Chamberlin,1978).
The Socorro Peak volcanic cenrer(fig. l)
lies within the rift at the east end of the
cauldroncomplex,The threemountainranges
and two flanking basinsof the map ruea expose strata that range in age from precam_
brian to Holocene(fig. 2).
dipping sectionon the resurgentdome in the
northern ChupaderaMountains. Previously,
this cauldron-faciestuff was correlatedwith
the 28-m.y.-old Lemitar Tuff (Chapin and
others,1978;Chamberlin,1980).
The greatthicknessof the intracalderaHells
Mesa Tuff and the presenceof welded-tuff
mesobreccias
(rich in fragmentsof Precambrian rocks)are indicativeof subsidence
contemporaneouswith the ash-flow eruptions,
The mesobreccias
were most likelv derived
!o
couldron morgin
Eoto
resurgenl dome
KIil
ol to
oaaao
D
from caving of an oversteepened
wall on the
southeastrim of the caldera (Eggleston,in
progress).Beddedlag-fall brecciasat the top
of the cauldron-faciessection contain fragmentsof semicongealed
magmablown out of
a nearbyignimbritevent.
The northeastern structural-topographic
margin of the Socorrocauldronis exposedin
west-tiltedstrata on the eastface of Socorro
Peak. Here, landslidedepositsderivedfrom
precaldera strata (Madera Limestone and
SpearsFormation)are bankedagainstthe topographicwall of the caldera.During resurgence,a moatlike area betweenthe resurgent
dome and calderawall was filled to overflowing by alternatingeruptions of andesite-torhyodacitelavasand lithic-rich,rhyolitic ashflow tuffs. High-silica rhyolite domes and
tuffs then capped the moat sequence.Assigned to the Luis Lopez Formation, these
moat depositsrange from 800 m, near the
moat axis, to less than 200 m thick at the
buriedcalderawall. During filling, minor subsidenceof the moat areaoccurredalong faults
NEW s[ MEXTCO
$ss++
mop
oreo
foull downside
-rr
* volconic vent
lc
Oligocenecauldrons
I Tower mine
Strongly tilted (35-60 degrees)Oligocene
fle. 1f Grefco mine
volcanicstrata exposedin rangesof the Solmi
lkm
corro Peakvolcaniccenterrepresentremnants
Ti
of the northeastern part of the resurgent
Socorrocauldronthat is now correlatedwith
paleozoicand precameruption of the Hells Mesa Tuff. Approx- FIGURE l-GrNEnel-lzEDcEot-octcMApoF THESoconnoPpnxvoLceNrccENTER;
brian rocks (Pz), Oligocenevolcanic rocks (To), Miocene PopotosaFormation (Tm), late Miocene
imately 0.9 km of denselyweldedcauldronlocgrro Peak Rhyotite (Ts), Oligoceneand Miocene intrusive rocks (Ti), Plioceneto pleistoceneSierra
facies Hells Mesa Tuff is exposedin an eastLadronesFormationand olderpiedmontgravels(erp), andlate
alluvium(e).
euate;naiy
May l98l
NewMexico Geology
blocksthat weretilted 5- l5 degrees'However,
the distribution of the "synrift" (synchronous
with rifting) tuff was not significantly affected
because100-200 m of potential fault-block
Surficial deposits
rpproxlmrlc
topography was filled in by wedge-shaped
rgc In m.y.
(middleto late Quaternary)
lavas(Chamberlin'
prismsof basaltic-andesite
1978).
SantaFe Croup: (Mioceneto Pleistocene)
In the Socorroarea, nearthe axis of the rift,
Sierra
crustal
extension has been accommodated
Ladrones
4 basaltof SedilloHill
Formation mostly by progressiveslipping and rotation of
closely spaced, originally high-angle normal
upper
faults (referred to here as domino-style norbasaltof BearCanyon
Popotosa
l2-7 SocorroPeakRhyolite
mal faulting). After 20-30 degreesof rotation
Formation the original set of domino faults is abandoned
basaltof Kelly Ranch
and the processcontinueson a second(and
lower PopotosaFormation
third and so on) setof domino blocks (Morton
Black, 1975).Thus, steeplytilted Oligorocksof the Datil-Mogollon volcanicfield (Oli- and
cenestrata are typically repeatedby low-angle
gocene)
normal faults (fig. l, cuspatefault traces)
26 tuff of SouthCanyon
representing rotated early-rift faults. RelaupperLa Jara Peak
tively rapid periodsof domino rotation, peneBasalticAndesite
contemporaneouswith silicic volcanism, are
28 Lemitar Tulf
believedto reflect extremeheat flow and duc*unit of Sixmile
middle La JaraPeak
tile necking of the lithosphere at relatively
BasalticAndesite
Canyon(calderafill)
shallowdepths(Chamberlin,1978).
The Socorro Peak volcanic centerlies along
A-L PeakTuff: pinnaclesmember
the Morenci lineament, a deeply penetrating
lower La Jara PeakBasalticAndesite
crustalflaw with a markedtendencyto "leak"
magmas(Chapin and others, 1978).Within
30 A-L PeakTuff: flow-bandedmember
the rift, crustal extensionin opposing direc33-29 L uis L op ez For mat i on (caldera f ill)
tions has beenaccommodatedat depth by lat33 H^e[sMesarurr
shearingalong the lineament.North of
I :l,T::l*'uT:#'"" eral
31 'sPearsrormatlon J Socorropeak
this transverseshearzone, domino blocks are
#
rotated westerly,and to the south they are
MaderaLimestone(Pennsylvanian)
rotated easterly. Where the transverseshear
SandiaFormation (Pennsylvanian)
zone transects the Socorro Peak volcanic
center(fig. l) it appearsto be a diffuse 8-kmPrecambrianrocks
wide zone of discontinuoustransversehinge
or rnr So- faults and scissorsfaults that have accomFIGURE 2-Rrvrspo srRArrcRApHy
coRRoPEAKvolcANrccErrrn (modifiedafter modated differential rotation of the domino
1980);asteriskindicates
Chamberlin,
unit present
blocks. Narrow horsts and grabensformed by
in subsurface
only.
local overlap of opposing domino sets are
relatively common in the fransverse shear
partly outlining the resurgentdome and along
zone. Dips of strata generallydecreasetoward
ring fractures at the margin; many of these
the axis of the shear zone that is locally
faults actedas feederdikes.
markedby a null line of flat-toppedmesas'
was
About 30 m.y. ago, the A-L Peak Tuff
erupted from the dumbbell-shapedSawmill
Early rift basins
Canyon and Magdalena cauldrons (Chapin
Moderately tilted (10-30 degrees)Miocene
and others, 1978), which overlap the very
large Socorro cauldron as redefined.Near the strata of the PopotosaFormation, which crop
Tower mine (fig. l), the resurgentdome of the out in the rangesand pedimentedbasin-margin
Socorro cauldron is truncated by an arcuate blocks, represent fill of early-rift closed
fault zone that marks the easternedgeof the basins.By the early Miocene,domino-styleextension had produced a broad sag acrossthe
Sawmill Canyoncauldron. The easternhalf of
the Sawmill Canyon cauldron is filled with an rift. The distendedfloor of the lower Popoanomalouslythick section(0.5 km) of Lemitar tosa Basin in the Socorro Peak area was
Tuff that may haveflowed into the preexisting underlain by domino blocks tilted as much as
30 degrees.During the interval 25-20(?)m.y.
Sawmill Canyon depressionfrom a sourceto
ago, as much as 3fi) m of heterolithic mudthewest.
flows and conglomerates,which are now
Developmentof rift structures
anomalous in their extreme induration and
In the southern Lemitar Mountains, brick-red color, were shed northward off
rhyolite to high-silicarhyolite ash-flow sheets cauldron-relatedhighlands.The unusualcharacter of the red mudflow faciesmay be due to
of the A-L Peak Tuff, Lemitar Tuff, andtuff
of South Canyonare separatedby threenorth- contemporaneoushot-spring activity in the
ward-thickeningtonguesof the La Jara Peak source area or to alteration during a subseBasaltic Andesite (redefined). This bimodal quent geothermal event. Widespread potassium metasomatismof the Oligocenevolcanic
magmatic associationmarks the onset of rifting about 30 m.y. ago (Chapin, 1979).The rocks in the Socorro-Magdalenaarea(Chapin
compositionally zoned (64-77 percent SiOr) and others, 1978)may be related to either an
early Miocenehydrothermal event (ChamberLemitar outflow sheet covered early rift
Stratigraphic units
=-l--
lin, 1980) or a late Miocene hydrothermal
event,or to both. At SocorroPeak, the red
mudflow facies intertongueswith more normal-looking gray fanglomeratesshed from a
persistent eastern margin of the Popotosa
Basin. Oligocene rhyolite domes near the
cauldron margin initially formed a topographic barrier separatingthe red and gray
facies.
By middle Miocenetime, about 20-12m.y.
ago, the heat-flow regimeof the Datil volcanic
period had dissipated.This causeda changein
the style of rifting to that of wide tilted-block
uplifts and basins (wide dominoes?).At this
time, a largetilted block formed in the MagdaIena area, approximately 15 km to the west,
which changedthe axis of the PopotosaBasin
to a north-southtrend.During this period' the
Socorro Peak areawas coveredby as rnuch as
800 m of playa deposits.Thesegypsum-bearing, calcareous,playa claystonesintertongu€
wilh pale-redand buff-colored distal alluvialfan deposits(conglomeraticsandstones)at the
eastand west fringes of the map area. At the
Grefco perlitemine (fie. l) uppermostPopotosa fanglomerates,which were derived from
highlandseastof the modern Rio Grandevalley (Socorro Basin), bury the north flank of
this 7-m.y.-oldrhyolitedome'
From 12 m.y. to 7 m.y. ago, numeroussilicic domesand tuffs of the SocorroPeok Rhyotite, which range from early rhyodacitesto
late-stagehigh-silica rhyolites, were periodically erupted onto the playa floor contemporaneouswith ongoing sedimentation. The
Socorro Peak volcanic center is essentially
defined by this cluster of late Miocene silicic
domesthat now form the highlandsof the Socorro Mountains. The vents for these domes
delineatea north-northwest-tr€ndingintrusive
belt, about I I km long, which is widestwhere
it crossesthe buried ring-fracture zone of the
Socorro cauldron. Thin flows of xenocrystic
basaltic andesite(basalt of Kelly Ranch) and
alkalic basalt (basalt of Bear Canyon) are interbeddedin upper Popotosaplaya muds, respectively below and above lavas of the
Socorro Peak Rhyolite.
The modern ranges of the Socorro Peak
volcanic center gen€rally existed as shallow,
suballuvial blocks prior to eruption of the
Socorro Peak Rhyolite. This is indicated by
prisms of the playa facies that wedge out
under these lavas toward the crests of the
modernuplifts. The playa faciesalsogenerally
thins toward the south end of the map area.
Here, blocks of Oligocenebedrock were unconformably overlappedby late Miocene lavas near the south (mostly structural) margin
of the playa. During, or shortly after, the late
Miocene silicic volcanism,a secondperiod of
domino-style normal faulting rotated upper
Popotosa strata (and older faults and strata)
as much as 15 degreesprior to deposition of
the SierraLadronesFormation.
Late rift basinsand ranges
Betweenabout 7 m.y. and 4 m.Y. ago,
renewedhigh-anglenormal faulting (horst and
graben style), combined with epeirogenic
G
New Mexico Geologlt
May l9El
uplift (Chapin, 1979),exhumedthe Socorro
and Lemitar blocks and elevatedthem sufficiently to topographicallydisrupt the popotosaBasin.During this period,a major southflowing river (the ancestral Rio Grande) entered and beganto fill the developingSocorro
Basin. Gently tilted (G-10 degrees)early
Plioceneto middle Pleistocenestrata of the
Sierra LadronesFormation form westwardthickeningwedgesin the Socorroand La Jencia Basins to the east and west of Socorro
Peak (fig. l). Just east of the high-angle
(65-75 degrees)range-boundingfault zoneat
the foot ofSocorro Peak,the SierraLadrones
Formation is at least350 m thick and may be
significantly thicker. About 4 m.y. ago,
olivine basalt lavas that were erupted from
ventsnear SedilloHill (basaltof SedilloHill)
flowed eastwarddown a broad valley cut on
the upper Popotosa playa facies and onto
channel sands of the ancestral Rio Grande
(SierraLadronesfluvial facies).Since4 m.y.
ago, the modernrangeshavecontinuedto rise
and shed piedmont gravelsthat intertongue
with the fluvial sands.
In late Quaternarytime continueduplift,
faulting, and entrenchmentof tributariesto
the Rio Grandehave all enhancedthe modern
topography.UpperPopotosaplayaclaystones
on the flanks of the Socorro Mountainsare
largely masked by landslide blocks derived
from the Socorro Peak Rhyotite. patterns of
elevation variation in late Miocene and pliocenelavas,when coupledwith moderndrainage patterns,suggestthe possibility of late
Quaternary magmatic doming along an axis
trendingwest-southwest
from Socorropeak.
1980,Cenozoic stratigraphy and structure
of the Socorro Peak volcaniccenter,central New
Mexico: New Mexico Bureauof Mines and Mineral Resources,
Open-fileRept. l18, 2 vols.,495
p.
Chapin, C. 8., 1979,Evolution of the Rio Crande
rift-a summary, /z Rio Grande rift-tectonics
and magmatism,R. E. Riecker,ed.: Washington,
D.C., AmericanGeophysical
Union, p. l-5
Chapin,C. E., Chamberlin,R. M., Osburn,G. R.,
White, D. L., and Sanford,A. R., 1978,Exploration framework of the Socorro geothermalarea,
New Mexico, ln Field guide to selectedcauldrons
and mining districts of the Datil-Mogollon volcanicfield: New Mexico GeologicalSociety,Spec.
Pub. No. 7, p. ll4-129
ChacoEnergydonates$6,500
to Bureauof Mines
Chaco Energy Co. has given $6,500 to the New Mexico Bureauof Mines and Mineral Resources,a division of New Mexico Institute of Mining and Technology,as second-yearfunding
to study fossil plant remainsnearHospahin northwestNew Mexico.
The nature of the plants is significant in the formation of the coal depositsleasedby Chaco
EnergyCo.Theseplant remainsincludeancienttreestumps,leaves,and roots fossilizedin place
in the Cretaceousswamps,as well as driftwood bar and beachdeposits.Standingfossii tree
trunksin growthpositionare known from scattered
areasof the SanJuanBasin.
A. T. Cross,professorof geologyat MichiganStateUniversity,and co-workerA. Jameossanaieareinterpretingthe plant collections.John Taylor of the ChacoEnergystaff hasmapped
the geologyof the fossillocalitiesand providedcoresof fossil-bearing
rocksfrom Chaco'sdiilling program.Studiesof nearbyvertebratefossilsin coal-bearingCretaceous
rock bedsarebeing
conductedby D. L. Wolbergand studiesof marinefossilsby S. C. Hook, both paleontologisti
with the New MexicoBureauof Minesand Mineral Resources.
prcducttcn
Adobe
rc",fi,r"d f.
M8p no.
County
Sanh Fe
Silta F€
Conclusion
The primary control of recurrentmagmaintrusion, hydrothermal activity, and silicic
volcanism at Socorro Peak has been the
"leaky" Morenci lineament,expressedas a
transverseshearzone of the Rio Grande rift.
Eruptive periodsin the Socorro peak volcanic
centerhave beendated at 33-29, l2-9,7, and,
4 m.y. In light of this pasthistory,it is not surprising that geophysically defined magma
bodies,which provide a heat sourcefor the
presentgeothermalanomaly, are again rising
under the SocorroPeakvolcaniccenter.
AcKNowLEDGMENTS-C.
E. Chapin and G.
R. Osburn,both of the New MexicoBureauof
Mines and Mineral Resources,critically reviewedthis manuscript.Many of the keyinterpretationspresentedherewereinitiated by C.
E. Chapin or developedjointly with him during the author'smappingof the Socorropeak
area. Financial support for the dissertation
was providedby the New Mexico Bureauof
Mines and Mineral Resourcesand by a grant
(76-201) from the New Mexico Energy ResourcesBoardthroughthe EnergyInstituteat
New MexicoStateUniversity.
SantaFe
SantaFc
SantaFe
Taos
Taos
4l
Taos
Taos
Taos
Tonance
Valencia
valencia
References
Chamberlin,
R. M,, 1978,Structural
development
of theLemitarMountains,
anintrarifttiltedfaultblockuplift, centralNewMexico(abs.):LosAlamos ScientificLaboratory,Conferenceproc.,
LA-7487-C,
p.22-24
May l98l
Net, Mexico Geolog!
Eggleston,T. L., in progress,Geologyof the central
and southern Chupadera Mountains, Socorro
County, New Mexico: M.S. thesis,New Mexico
Institute of Mining and Technology
Morton, W. H., and Black,R., 1975,Crustalattenuationin Afar, rn Afar depression
of Ethiopia,A.
Pilger and A. Rosler,eds.: Stuttgart,Schweizerbart, p. 55-65
Osburn,G. R., and Chapin,C. 8., in preparation,
Stratigraphicnomenclaturefor Cenozoicrocks of
the northeasternDatil-Mogollon volcanic field,
New Mexico: New Mexico Bureauof Mines and
Mineral Resources,StratigraphicChart I
Osburn, G. R., and Petty, D. L., in preparation,
Ceologyof the Molino Peakquadrangle,Socorro
County,New Mexico
D
Nrmc rnd locrtlon
Al Montano
Rt 2,B,ox224
SantaFe, NM
Albcn E. Baca
Rr. I, Box99
SantaF€, NM
RodriguezBroth€rs
Rt. 6, Box 22
Sarta Fe, NM
Tod Brown
c/oGeneral Deliveri
Cerrillos,NM
Montoya Adobes
4m Arroyo Tcnorio
Sann Fe, NM
Emilio Abeyra
P.O. Box I ?7
Ranchode Taos,NM
TaosPueblo
Nativeproducts
P.O Box 18,16
Taos,NM
Marion Threehawks,
Mgr.
JoeTrujillo
P.O. Box 633
Ranchode Taos,NM
RalphMondragon
P.O. Box 199
Ranchode Taos,NM
JoePachco
P.O Boxl74
Taos,NM
HumbertoCamacho
P.O. Box63l
Mountainair,NM
RioAbajoAdobes
105W. Aragon
Bclcn,NM
Jeny Sanchez,Mgr.
OreroBrothers
Rt. 2, Box 774
Los Lunas,NM
AlfonsCariuo
Les Palomas,Mexico
Stateof
Chihuahua,
Mcxico
Stateof
LconardoDuran
Chihuahua, lrsPalomas,Mexico
Mexico
Telcphonc
Approximrle
anrud
preducdon
TyD€producalonrqulpmenl
4714227
2,000
Hoe, shovels, front-end loader, and wooden
foms
455-1542
3,000
Hoe, shovels, and wooden forms
47t-1510
100,000
No phone
3,000
Hoe, shovcl, and wooden forms
988-3504
10,000
Ho€, shovcl, and wooden forms
Hoe, shovcls, front-end loader, w@den
foms, and delivery rrucks
758-3022
12,0@
Ho€, shovels, wheclbarrow, and wooden
foms
?58-8761
47,000
Backhoe, h@, shovels, wheelbarrow, and
wooden forms
7 58-9768
60,000
Front.end loader, ready-mix mounted on
ground, wooden forms, and dclivery truck
758-3U4
15,000
Pugmill, mud vehiclc, and wooden forms
75t-9848
Lffi
Hoe, shovel, wheelbarrow, and wooden forms
No phonc
5,0@
Hoe, shovels, whelbarrow,
foms
t64-6191
and wooden
150,000
Fronr-end loader, wooden forms, and delivery
rucx
864{054
40,0@
Front-end loader, wood€n forms, and delivery
trucks
No phone
30,000
H@, shovels, and wooden forms
No phone
5,000
Hoc, shovcl, and woodcn forms