Reeside,
J. B., Jr., Applin, P.L., Colbert,E. H.,
Gregory,H. D., Haldey,H. D., Kummel,B.,
Lewis, P. J., Love J. D., Maldonado,M.,
Sanders,J., Silberling,N. J., and Waage,K.,
1957,Correlationof the Triassicformationsof
North Americaexclusiveof Canada:Geological
Society
ofAmerica,Bull.,v. 68,p. l45l-1514
Smith, C. T., 1961,Triassicand Jurassicrocks of
the Albuquerquearea: New Mexico Geological
Society, Guidebook l2th field conference,p.
l2l-128
Stewart,J. H., Poole,F. G., and Wilson,R. F.,
1972,Stratigraphyand origin of the ChinleFormation and relatedUpper Triassicstrata in the
ColoradoPlateauregion:U.S. GeologicalSurvey,
Prof. Paper690,336p.
Till, R., 1974, Statisticalmethods for the earth
scientist(An introduction): New York, John
Wileyand Sons,154p.
Wood, G. H., and Northrop, S. A., 1946,Geology
of the Nacimientoand SanPedroMountainsand
adjacentplateausin parts of Sandovaland Rio
Arriba Counties,New Mexico: U.S. Geological
Survey,Oil and Gas Investigations
Map, OM-57
g
Proterozoic
settin
tectonic
in NewMexico
Socorro,
NM
by KentC. Condie,
Department
of Geoscience,
NewMexicoInstitute
of MiningandTechnology,
Geologicalfeatures
Recentdetailedmappingof Proterozoicterranesin New Mexicohasenhancedour understandingof stratigraphyand tectonicsetting.
Chief areas of investigation (fig. l) are
Precambrian exposuresin the south and
south-centralpart of the state (Condie and
Budding, 1979) and the Sangre de Cristo
Mountains in the northern part of the state
(Robertsonand Moench, 1979; Barrett and
Kirschner,1979;Woodwardand others,1979;
Nielsenand
Scott,1979;Condie,1979).
Diagrammaticcross sectionsfor the Proterozoic rocks in the Manzano and Ladron
Mountainsin centralNew Mexico are shown
in fig. 2. The Manzano successionis charGorrection
acterizedby a lower sequence
of mixedarkose,
In the February 1980 issue of New Mexico
quartzite, and subgraywacke,whose baseis
Geology, the panoramic diagram to accomnot exposed.This sequence
is unconformably
pany the City of Rocks article was omitted.
overlainby a thick succession
of shales(now
That diagram is printed below.
phyllites)with quartziteand arkosebeds.The
youngestrocks are bimodal volcanicswhose
NORTH
felsic componentdominates.The entire suc8/oc
cessionis folded into an overturnedsyncline
k Ronge
and intrudedwith syntectonicto posttectonic
granitic rocks. Unlike the Manzano succes/
,l
sion,the Ladron succession
is characterized
by
P4
a lower bimodalvolcanicsequence
whosebase
slll.o"
is also concealed(Condie, 1976b).Thesevol\ot'\
d'\c'
canicsare gently folded and intruded by the
posttectonic
Capirotegranite.Unconformably
^ dgt'
B u r r oM l s
R o u n dM t n
overlying the granite is a successionof
arkoses,quartzites,and conglomerateswith
minor shaleand bimodal volcanics.This sequenceis gentlyfolded and cut by faults, and
the entire Ladron succession(including the
Capirote granite)is intruded by the posttectonic Ladron quartzmonzonite.
Other supracrustalsuccessions
in New Mexico and southeasternArizona show similar
rock types and relationshipsto granites.All
are characterizedby bimodal volcanicswith
an absenceor sparsityof volcanicor plutonic
.
A
o
\
rocks of intermediatecomposition.Deformaq'$i.
M
t
n
Red
tional featuresreflect chiefly vertical forces.
Ophiolites, m6langes, blueschists,$aySOUTH
wackes,and deep-sea
sediments
areabsent.
Primary structuresin the form of crossbedding, varioussolemarkings,and ripple marks
preservedin someof the clasticsedimentsare
papers
Gallfor
being investigated. Festoon crossbedding
The Rocky Mountain Section of the
dominatesin the arkosesand conglomerates;
American Association of Petroleum Geolplanar crossbeddingdominatesin the pure
ogists will meet in Albuquerque April l2-15,
quartzites.Existingdata seemto favor a near1981, at the Hilton Inn. Thomas E. Kelley of
shore,perhapspartly fluvial, environmentof
Geohydrology Associates, Inc., is General . sedimentation
for the coarseclasticsediments,
Chairman of the conference. Papers on Rocky
with the shalesbeing depositedin deeper,
Mountain regions are welcome; contact Lee
quiescentbasins.Provenancestudies(Condie
Woodward, University of New Mexico, or
and Budding,1979)indicatesourceareascomFrank Kottlowski, New Mexico Bureau of
posedchieflyof high-Kgranitesand reworked
Mines and Mineral Resources, Program
supracrustalrocks. No evidenceexistsfor an
Chairman, at your earliest convenience.
n
oldertonaliticsource.
FIGURE l-Drsrnrsurror or PnorErozolc RocKS
in New Mexico, southern Colorado, and southeasternArizona.
Geochemical
and Sr isotopestudies
Geochemical
studiesof mafic and felsicvolcanicsand of graniticrocks havebeenimportant in determiningmagmaorigin and source
composition(Condie,1978a,b; Condieand
Budding, 1979). Mafic volcanic rocks are
tholeiites that range from depleted to
undepletedin light REE (rare-earthelements).
Geochemical
modelstudiesindicatethat these
rocks can be producedby 20-40 percentpartial meltingof a lherzolitesourcein the mantle
followed by up to 30 percentolivine crystallization. REE distributionsdo not allow residual garnet,amphibole,or plagioclasein the
source.Tholeiitesdepletedin REE occuronly
in the Pecosand Tijerasgreenstones
in central
and northernNewMexico.Modelstudiesindicate that theserocks were derivedfrom depletedmantlesourcessimilarto the sourcesof
modern mid-ocean-ridgetholeiites.The absenceof ophiolitesin the supracrustalsuccessionssuggests
that, althoughdepletedmantle
wastapped,oceaniccrustwasnot formed.
Geochemical model studies of felsic
volcanicsand graniticrocksindicatean origin
by partialmeltingof lowercrustalrocks(granulite facies)for granodioritesand rhyodacites
(Condie, 1978b). The high-K granites and
rhyolites seemto have a similar origin folNew Mexico Geology
May 1980
27
lowed by fractional crystallization. Initial
Sr"/Sr" ratios in granitic and felsicvolcanic
rocksvary with age.Low ratios (0.701-0.703)
thegroupdatedfrom 1.75to 1.65
characterize
b.y. and high ratios (0.705 or greater),the
group datedfrom 1.5 to 1.3 b.y. Low initial
ratios in the older group reflect a mantle
source; high ratios in the younger group
reflect either a significant crustal residence
time (approximately300m.y. or more)and/or
contaminationwith radiogenicSr.
Proterozoictectonicsettings
CunneNr THEoRTES-Oneof the major
problemsin geologyis the role of plate tectonics in the evolution of the Precambrian
crust. Although many methods(geometricfit
of continents,history of sea-floorspreading,
and matching stratigraphyand crustal provinces) of identifying plate boundariesand
platemotionscanbe appliedto
reconstructing
eventsof the last 200m.y., few apply to older
geologicterranes.Two theoriesdeal with the
role of plate tectonicsduring Precambrian
time. The strictly uniformitarian theory
(Burke and others, 1977)suggeststhat platetectonic processeshave always operated(at
leastsince2.7 b.y.), while the non-uniformitarian theory maintains that plate tectonics
beganabout I b.y. ago or was manifestin a
different manner before then (Engel and
Kelm, 1972; Wynne-Edwards,1976).Paleomagneticdata suggestthat the presentcontinents were part of one or perhapsa few
prior to I b.y. (Piper, 1976).
supercontinents
platetectonicswereoperIf Phanerozoic-type
ating, the maximumsizeof new oceanbasins
allowed within a supercontinentwould be
I,000 km or lessand individualcratonswould
be allowed to rotate independentlyof each
other only 10-20 degrees.Geological and
geochronologicalevidencefrom Africa does
FIGURE 2-Dre.cnluulrrc cRosssEcrroNsor Pnorenozolc RocKS(m, mixed clasticsediments;q,
A,
not support a convergent-plate-boundary quartziteand arkose;p, peliticsediments;
f, felsicvolcanics;a, mafic volcanics;c, conglomerates).
origin for Precambrianmobile belts(Kroner,
ManzanoMountains;B, LadronMountains(afterCondie' 1976b).
1977).Evidencefavors an ensialicorigin for
is the KaapvaalBasin
succession
by little if any contemporary stable-craton
African mobile beltsprior to I b.y. although edgeassociations
someinvestigatorsstill interpretthesemobile deformation.Continentalcollisionboundaries in SouthAfrica. Oneof the oldestknown con(about I b.y.)
belts as continent-continent
collision bound- such as suturesare generallythought to be tinentalrifts is the Keweenawan
Proterozoic
area.
Some
(Burke
Lake
Superior
in
the
zones
and
m6lange
that
characterized
by
shear
aries
and others,1977).
Modern plate regimesare characterized
by containsexoticblocksof ophiolite,arc succes- supracrustalsuccessions,however, do not
specific rock associationsand structural sions, blueschists,and deep-seasediments. readily fit into a plate-tectonicmodel. The
and theCapeSmith fold
historieswhich,when found in older terranes, Ancientsuturezones,however,aredifficult to Labradorgeosyncline
help interpretation of tectonic setting. In
recognizebecauseof complexplate histories belt in Canadahavebeeninterpretedin plateterms of rock associations,divergent-plate or deeper level of exposurein the crust. tectonicand otherstructuralframeworks.
Early to middleProterozoic(2.5-1.0b.y.)
boundariesare commonly characterizedby Recently,diversegeologicalevidencehasbeen
seemto occur in disophiolites (ultramafic rocks successively used to identify Precambriansutures, and supracrustalsuccessions
overlain by layeredgabbro, sheeteddiabase many geologistsare not surethat suturescan tinct geographicprovinces.Many greenstone
dikes,and pillowedbasalts);convergent-plate be accuratelyidentifiedwhenthey do not fall beltsin the Churchill Provincein Canadaare
boundariesby arc associations(calc-alkaline within the framework of the original defini- Proterozoic(Moore, 1977).Proterozoicsucprimary textures
cessionswith well-preserved
volcanics and batholiths, graywackes,and tion.
others); continental rifts by bimodal volDistinctiveophiolite, arc, continental-rift, and structuresalso occur in peninsularIndia
canics,arkoses,and conglomerates;
and stable and stable-cratonsuccessions
havebeeniden- (Pichamuthu,1975),in the Birrimian in West
cratons and trailing continental edges by tified in someProterozoicterranes.The oldest Africa (Burke and Dewey, 1972),and in the
(shale, car- well-described
mature sedimentarysuccessions
ophiolitesoccurin Pan-African southwestUnitedStates.
Rrsulrs FRoM THE Souruwnsr-Major
bonate,quartzite)and minor mafic volcanics mobilebelts(LeBlanc,1976).Examplesof arc
(Condie, 1976a).
successions
are the 1.8-b.y.Coronationgeo- Proterozoicsupracrustalbeltsin New Mexico
In terms of structural history, divergent- syncline(Hoffman, 1973)and the lower part and adjacentareasof Colorado and south(Condie easternArizona are shownin fig. l; Precamplate-boundaryand continental-rift associa- of the 1.3-b.y.GrenvilleSupergroup
tions are characterized
by normal faultingand and Moore, 1977),both in Canada.A conver- brian rocks in this region rangein age from
gravityslumpfeatures;convergentboundaries gent-plate-boundary
modelhasalso beenpro- about 1.8 to 1.0 b.y. (Condieand Budding,
1979).DetailedU-Pb zirconstudies(Anderson
and collision boundariesby strong compres- posed for the Svecofennian(1.8 b.y.) in
sional features; and stable-craton-trailing- Finland (Hietanen,1975).The oldestknown and Silver, 1976)suggesttwo cyclesof Pro28
May 1980
New Mexico Geology
terozoic volcanism-sedimentation
in Arizona,
each followed by deformation, metamorphism, and plutonism. The earliest cycle
( I .82- I .72 b.y . , in central Arizona) probably
extends into Colorado and northern New
Mexico (Barker and others, 1976).The second
cycle(1.72-1.66b.y., in southeasternArizona)
probably extends into central and northern
New Mexico. Isotopic evidencefor Archean
basementhas not been found in the Southwest. Existing Sr-isotopedata suggestthat if
the supracrustal volcanics were erupted and
depositedon sialic basement, such basement
must be less than 200 m.y. older than the
volcanism(Condie and Budding, 1979).
Existing data on lithologies in the Proterozoic supracrustal belts in the Southwest indicate a diversity of rock types. Successions
(fig. l) are characterizedby quartzite, shale,
arkose, and bimodal (mafic and felsic) volcanic components;most successions
in central
Arizona are characterized by calc-alkaline
volcanic and graywacke suites. The surrounding plutonic rocks in all areasare dominantly
granodiorite and quartz monzonite intruded
into supracrustal successions. Basement for
the supracrustals has not yet been found.
Metamorphic grade ranges from lower greenschistfaciesto upper amphibolite facies.
Towenrs A TECToNTcMoDEl-Opinions
vary regarding the tectonic setting of this
region during the Proterozoic. Based on fragmentary geochemical evidence from several
trondhjemites, Barker and others (1976) have
suggestedthat a northerly dipping subduction
zone may have existed beneath Colorado and
northern New Mexico at approximately 1.8
b.y. On the other hand, Hills and others
(1975)have suggested
a southerlydipping subduction zone beneath Colorado, based on
lithologic assemblages.Hills and others further suggest the closing of a marginal-sea
basin and suturing of Proterozoic crust
against Archean crust along the Nash ForkMullen Creek shearzone exposedin southeast
Wyoming. Silver and others (1977)propose a
"magmatic arc" model for the Proterozoic of
the Southwest; Anderson and Silver (1976)
have likened the Jerome-Prescottsupracrustal
belt to an Archean greenstone belt. The absence of evidence for oceanic crust (ophiolites), volcanic arcs (andesites, graywackes,
and blueschists), or sutures (shear zones and
m6lange) in the Proterozoic of New Mexico
and adjacent regions in Colorado and southeastern Arizona does not favor the existence
of a convergent-plate-boundary in this region
during this time. Existing data are, however,
consistentwith a continentalrift systemin this
area from 1.75 to 1.65 b.y. (Condie and Budding, 1979). The number and orientation of
rifts and the nature and age of the continental
crust upon which such a rift system may have
developed are problems being addressed by
current research.
Mexico: Geological Society of America, Bull., v.
8 7 , p . 1 8 9 -1 9 8
B a r r e t t , M . E . , a n d K i r s c h n e r ,C . E . , 1 9 7 9 , D e p o s i tional systemsin the Rinconada Formation, Taos
County, New Mexico: New Mexico Geological
Society, Guidebook 30th field conference, p.
12l-126
Burke, K., and Dewey, J. F., 1972, Orogeny in
Africa, in African geology, T. F. J. Dessauvagie
and A. J. Whiteman, eds.: Ibadan University
Press,p. 583-608
Burke, K., Dewey, J. F., and Kidd, W. S. F., 1977,
World distribution of sutures-the sites of former
oceans:Tectonophysics,v. 4O,p. 69-99
Condie, K. C., 1976a, Plate tectonics and crustal
e v o l u t i o n :N e w Y o r k , P e r g a m o nP r e s s ,3 8 0 p .
1976b, Geologic map of Precambrian
rocks of the Ladron Mountains, SocorroCounty,
New Mexico: New Mexico Bureau of Mines and
M i n e r a l R e s o u r c e sG
, e o l . M a p 3 8 , s c a l e1 : 2 4 , 0 0 0
1 9 7 8 a , C e o c h e m i c a le v i d e n c ef o r u n d e pleted upper mantle beneath New Mexico during
the Proterozoic (abs.): Geological Society of
A m e r i c a , A b s t r a c t sw i t h P r o g r a m s ,v . 1 0 , p . 1 0 0
1 9 7 8 b ,G e o c h e m i s t r yo f P r o t e r o z o i cg r a nitic plutons from New Mexico: Chemical Geolo g y , v . 2 l , p .l 3 l - 1 4 9
1979, Precambrian rocks of the Taos
Range and vicinity, northern New Mexico: New
Mexico Geological Society, Guidebook 30th field
c o n f e r e n c ep, . 1 0 7 - l I I
C o n d i e K . C . , a n d B u d d i n g , A . J . , 1 9 7 9 ,P r e c a m brian rocks of central and south-central New Mexico: New Mexico Bureau of Mines and Mineral
R e s o u r c e sM
, em. 35, 58p.
Condie K. C., and Moore, J. M., 19'77G
, eochemistry of Proterozoic volcanic rocks from the Grenville Province, eastern Ontario: Ceological
Association of Canada, Spec. Paper 16, p.
149-168
Engel, A. E. J., and Kelm, D. L., 1972, PrePermian global tectonics: a tectonic test:
Ceological Society of America, Bull., v. 83, p.
2325-2340
Hietanen, A., 1975, Generation of K-poor magmas
in the northern Sierra Nevada and the Svecofennian of Finland: U S. Geological Survey, Journal
o f R e s e a r c hv, . 3 , p . 6 3 1 - 6 4 5
H i l l s , F . A . , H o u s t o n , R . S . , a n d S u b b a r a y u d u ,C . ,
1975, Possible Proterozoic plate boundary in
southern Wyoming (abs.): Geological Society of
A m e r i c a , A b s t r a c t sw i t h P r o g r a m s ,v . 7 , p . 6 1 4
H o f f m a n , P ' , 1 9 ' 7 3 ,E v o l u t i o n o f a n e a r l y P r o terozoic continental margin: the Coronation
geosyncline, northwestern Canadian Shield:
Royal Society of London, Philosophical TransactionsA, v.273,P.547-581
Kroner, A., 197'I' The Precambrian geotectonic
evolution of Africa plate accretion versus plate
destruction: Precambrian Research, v. 4, p.
163-213
LeBlanc, M., 1976, Proterozoic oceanic crust at Bon
Azzar: Nature, v. 261, p. 34-35
Moore, J. M., 1977,Orogenic volcanism in the Proterozoic of Canada: Geological Association of
C a n a d a ,S p e c .P a p e r 1 6 , p . 1 2 7 - 1 4 8
Nielsen, K. C., and Scott, T. 8., Jr., 1979, Precambrian deformational history of the Picuris
Mountains, New Mexico: New Mexico Geological
Society, Guidebook 30th field conference, p.
I l3-120
P i c h a m u t h u , C . S . , 1 9 7 5 , S o m e a s p e c t so f t h e P r e cambrian geology of India: Ceology, Mining, and
Metallurgy Society of India, Quarterly Journal, v.
4 7, p . 2 5 - 4 3
Piper, J. D. A., 1976, Paleomagnetic evidence for a
Proterozoic supercontinent: Royal Society of
London, Philosophical Transactions A, v. 280, p.
469-490
R o b e r t s o n , J . M . , a n d M o e n c h , R . H . , 1 9 7 9 ,T h e
Pecos greenstone belt: a Proterozoic volcanosedimentary sequencein the southern Sangre de
Cristo Mountains, New Mexico: New Mexico
Geological Society, Guidebook 30th field conf e r e n c e ,p . 1 6 5 - 1 7 3
S i l v e r , L . T . , a n d o t h e r s , 1 9 7 7 ,C h r o n o s t r a t i g r a p h i c
elements of the Precambrian rocks of the southwestern and far western United States: Geological
Society of America, Abstracts with Programs, v.
9,p.1176
Woodward, L. A., Parchman, M. A., Edwards,
D . L . , a n d H u s l e r , J . W . , 1 9 7 9 ,S t r a t i g r a p h ya n d
mineralization of Hell Canyon greenstone belt,
New Mexico: New Mexico Geological Society,
Guidebook 30th field conference,p. 189-195
Wynne-Edwards, H. R., 1976, Proterozoic ensialic
orogenesis: the millipede model of ductile plate
t e c t o n i c sA: m e r i c a nJ o u r n a lo f S c i e n c e v, . 2 7 6 , p .
n
927-953
Pleistocene
h0rse
skulldiscovered
On July 20, 1979, while checking roadcut exposures along Sapillo Creek north of Lake
Roberts in southwestern New Mexico, Jon Sandor, research assistant, and John Hawley, environmental geologist, New Mexico Bureau of Mines and Mineral Resources,discovered bone
fragments and teeth in Pleistocenesteam-terracedeposits. The exposure was located in a position of active erosion along a major road in the Gila National Forest. Recovery of specimens
was approvedby the Mimbres District of the U.S. ForestService.
On July 26, Sandor, Hawley, and New Mexico Bureau of Mines and Mineral Resources
vertebrate paleontologist Donald Wolberg returned to the site and excavated the skull of a
Pleistocene horse. The specimen (NMBM&MR VP 10001), the partial skull of a mature but
relatively young horse, consistsof a full palate with cheek teeth and partial braincase with right
maxilla-lacrimal, frontal, and squamosal. The left side of the skull was severelyeroded prior to
recovery; only the left cheek tooth row and associatedareasof the left maxilla remain. All upper
per incisors were recovered in association with the skull, except for a single upper incisor that
was found isolated, approximately I m from the skull. The premaxilla is representedby a mere
fragment of bone associatedwith four of the incisors. The lower jaw and postcranial elements
are absent.
References
This specimenrepresentsa small horse, Equus conversidens,extant in the Yarmouthian to late
Anderson,C. A., and Silver,L. T., 19'16,
Yavapai
series-a greenstonebelt: Arizona Geological Wisconsinan (Pleistocene)of Kansas, Oklahoma, Texas, New Mexico, Arizona, Florida, and
the Valley of Mexico. Wisconsinan specimensare sometimes assignedto subspeciesE. conyerSociety,
Digest,v. 10,p. l3-26
Barker,F., Arth, J. C., Peterman,
Z. 8., andFried- sidens littoralrs Hay. Preliminary analysis of VP 10001 indicates tooth morphology,
man,I., 1976,The 1.7-1.8b.y. old trondhjemites measurements,and skull morphology well within the limits of E. conversidens.A detailed study
of southwesternColorado and northern New of the materialis in progress.
n
New Mexico CeologJ
May 1980
29