JOURNAL
OF GEOPHYSICAL
RESEARCH,
VOL. 95, NO. B1, PAGES 487-500, JANUARY
10, 1990
Late CretaceousDuctile Deformation, Metamorphism
and Plutonism in the Piute Mountains,
Eastern Mojave Desert
JOHN M. FLETCHER
AND KARL E. KARLSTROM
Department
of Geology,
NorthernArizonaUniversity
Flagstaff,Arizona
Late Cretaceousdeformationin the Piute Mountainsinvolvedductilethrustingon a networkof anastomos-
ing northeastand southwest
directedshearzones. The shearzonesoften separateProterozoiclithologies
with strongcompetencycontrasts,suggestingthat Proterozoiccrustal anisotropieswere importantin
controllingthe geometryof the shearzone network. Shearzonesnow divide the crustinto wedge-and
lozenge-shaped
blocks. The Piute Mountainscan be separated
into two kinematicdomains,eachcharacterizedby a dominantsenseof shear. Thrustingin the southwest
directedkinematicdomainendedat 85+7
Ma, the age of the late synkinematicEast Piute pluton. Thrustingin the northeastdirectedkinematic
domain could have lasted until 74+3 Ma, the age of the Lazy Daisy pluton. Postthrustingnorthwestsoutheast
shortening
produceda secondgeneration
of uprightopenfoldswith a northeast
strikingsubvertical
crenulationcleavage. F2 strainincreasestowardthe southand is concentrated
aroundthe marginsof the
Lazy Daisypluton. This deformation
was synchronous
with plutonemplacement.Late Cretaceous
peak
metamorphism
outlastedall ductiledeformation.Peakmetamorphic
gradeincreases
from uppergreenschist
faciesin the northto upperamphibolitefaciesas the Lazy Daisy plutonis approached.Temperatureand
pressure
of approximately
450'(2and2.5-4.0kbarwereachievedduringductilethrusting.Temperatures
of
500ø-54(YCexistedat the onsetof uprightopenfolding, and peak temperatures
as high as 620•C near the
Lazy DaisyplutonoccurredafterF2 uprightfolding. All penetrative
deformation
endedbefore72-71 Ma,
by whichtime the areahad cooledto below 300• (Fosteret al., 1989).
R•-a•os•T•.cr•c S•.a'rma
Parrish,1988;Sevignyet al., 1988];northeastem
GreatBasin,
The
Piute
Mountains
liewithin
abelt
ofsynmetamorphic
andNevada,
Utah,
and
Idaho
[Dallmeyer
etal.,1986;
Snoke
and
synplutonic
lateCretaceous
ductile
deformation
intheeastern
Miller,
1988);
east
central
Great
Basin,
Nevada
and
Utah
[Miller
Mojave
Desert
(Figure
1).Compressional
tectonics
within
thisetal.,1988a,
b;Gans
etal.,1988;
Lee
etal.,1988'
Smith
and
belttypically
involved
thefollowing
characteristics'
(1)thickWright,
1988];
Death
Valley
region,
California
[Lobotka,
1988];
skinned
ductile
thrusting
along
shear
zones;
thrusts
commonly
southeastern
California
asdescribed
previously;
andsouthern
Arizona and northernSonora[Haxel et al., 1984; Reynoldset al.,
place allochthonoussheetsof Proterozoiccrystallinebasement
over
recumbently
folded
Paleozoic
rocks;
inmany
ranges,
thrusts
1988].
This
Cretaceous
tectonism
was
apparently
superimposed
record
variable
directions
oftectonic
transport
[Ring
etal.,1988;
upon
aJurassic
orogenic
event
that
took
place
around
170-150
Reynolds
et al.,1988];
(2)theemplacement
of lateandMainmost
oftheeastem
Cordilleran
metamorphic
belt(see
synkinematic
granitoid
plutons
which
contain
a strong
crustal
previous
references).
signature
interms
ofinherited
zircons
and
S7SrffrSr
ratios
[Miller ThePiute
Mountains
oftheeastem
Mojave
Desert
arean
etal.,1982;
Foster
etal.,1989]'
and
(3)
high-temperature
important
area
for
understanding
deep-seated
Cretaceous
defor'
mation.Theylie alongstrikeandapproximately
100km south
moderate-pressure
regional
metamorphism
atgreenschist
toupperof whatis considered
to bethesouthernmost
extent
of the
amphibolite
facies
[Miller
et al.,1982;
Hoisch
et al., 1988;foreland
foldandthrust
beltin theNewYorkandClark
Reynolds
etal.,1988].
mountains
[Burchfiel
andDavis,
1981]. Thesouthem
As noted by Haxel et al., [1984], compressional
deformation
terminationof thin-skinned
tlwastingoccursapproximately
where
in the easternMojave is similar to the deep-seatedMesozoic
the hingelineof the Paleozoicmiogeoclineintersectsthe
tectonismof the $evier hinterland(e.g., Armstrongand Hansen,
Mesozoicmagmaticarc (Figure1). Farthersouth,Cordilleran
1966;DeWitt, 1980;AllmendingerandJordon,1981]. Exposures
deformation
beginsto reactivatecratonalNorthAmerica. The
of Mesozoicductilefabricsare commonlyfoundin the footwalls
lack of foreland thrustingin the EastemMojave desert area
of mid-Tertiarymetamorphiccore complexesor, as in the case
probably
reflects
a mechanical
response
to theabsence
of a thick
of the easternMojave, showa strongspacialrelationshipto the
Paleozoicmiogeoclinalwedge[Haxel et al., 1984]. Since
core complexes(Figure 1). Althoughdiscontinuously
exposed
hinterland-style
deformation
doescontinuethroughthe eastern
at the surface,Haxel et al. [1984] proposedthat the belt of
Mojave,it is an important
areato studythecharacter
of crustal
Mesozoicductiledeformationis moreor lesscontinuous
at depth
reactivationby compressional
tectonismand evaluate the
and forms one of the primary tectonicelementsof the North
proposed
geometric
and dynamicrelationships
betweendeepAmerican Cordillera. They adoptedthe terminologyof Miller seated Mesozoic deformation and thin-skinnedthrusting [e.g.,
[1980], who referred to the belt as the eastern Cordilleran
PriceandMountjoy,1970;Smith,1981;BoyerandElliott,1982;
metamorphicbelt.
Brown et al., 1986; Miller et al., 1988a]. Late Cretaceous
A periodof ductiledeformation,metamorphism
andplutonism deformational
featuresareparticularlywell displayedin the Piute
that centered around 90-70 Ma is recognizedthroughoutthis Mountains because the rocks exposed in this area have
belt: Ominecacrystallinebelt, BritishColumbia[Journeay,1988;
experienced
relativelylittle mid-Tertiary
extension,
whichis
mainlyfocused
to theeastandwest[Milleret al., 1982;Dokka,
Copyright1990 by the AmericanGeophysicalUnion.
1986; Glazner et al., 1988; Hileman et al., this issue].
Additionally,
theemplacement
of granites
duringdifferent
stages
of deformation
andmetamorphism
allowstheestablishment
of a
Paper number 89JB03296
0148-0227/90/89JB-03296505.00
487
488
FLETCHER
ANDKARLSTROM:
LATECRETACEOUS
DUCTILE
DEFORMATION,
EASTERN
MOJAVE
DESERT
EXPLANATION
•
Mesozoic
thrust
fault
M
.•,
Mylonitized
Tertiary
•'.•/•
detachment
fault
Eastern
limit
of
sedimentarymiogeoclinal
rocks
Paleozoic
••'• Study
area
i
0
t
50 km
Fig.1. Indexmapof theEastem
MojaveDesertshowing
thePiuteMountains
studyareain relation
to otherSouthem
Cordil-
lerantectonic
elements:
theMafiafoldandthrust
belt(MFTB),theSevier
foreland
foldandthrust
belt(FFTB),andthebelt
ofmid-Tertiary
metamorphic
corecomplexes
(lined
pattem),
andtheapproximate
boundary
between
cratonal
andmiogeoclinal
Paleozoic
sedimentation
(M). Mountain
ranges:
Arica(A),BigMafia(BM),Buckskin
(B),Calumet
(C),Chemehuevi
(Ch),
Clark(Cl),Clipper
(Cp),Dome
Rock(DR), rcuvar
0tc),Harquahala
0tq),Iron(I), Kilbeck
Hills(KH),Kingston
(K),Little
Maria(LM),Marble
(M),McCoy(Mc),NewYork(NY),OldWoman
(OW),Palen
(Pln),Plomosa
(Plm),Piute(P),Rawhide
(Rh),Riverside
(Ri),Ship(Sh),Turtle(T),Sacramento
(S),Whipple
(W). Portions
of figure
afterLyle[1982],
Reynolds
et
al. [1986] and Burchfieland Davis [1988].
fairlydetailed
timeframework
between
a number
of orogenicthick-skinned
shortening
characterized
by bothnortheast
and
events.
southwest
directed
ductilethrusting.Thesethrustzonesexhibit
This paper is part of the CollaborativeOld Woman-Piute a complexanastomosing
geometrythat may be a common
Investigative
Effort(COWPIE).Its mainpurpose
is todocumentcharacteristic
of crustalreactivation
wherepreexisting
the geometry
andkinematic
historyof a distinctive
styleof anisotropies
strongly
partition
deformation
around
lozenge-shaped
FLETCHERAND KARLSTROM;LATE CRETACEOUSDUCTILE DEFORMATION,EASTERNMOJAVEDESERT
489
blocks.
Additionally,we will outlinethe relativetiming of graniteto granodiorite
[BenderandMiller, 1987;Woodenet al.,
deformation,
plutonism,and metamorphism
in orderto discuss 1988];a suiteof 1675+16Ma two-micagranites[J.L. Wooden,
theirinteractions
in themiddlecrustduringCretaceous
orogeny.personalcommunication,1989]; the Barrel S•ing pluton which
is a 1419+_7
Ma megacrystic
syeniteandgranite[Gleasonet al.,
1988]; and a seriesof diabasedikes that are believed to correlate
LrrHOSTRATIGRAPHY
with 1100-1200
Ma diabase dikes and sills in central Arizona
Figure2 summarizes
the Proterozoic
lithologicsequence
and [Fitzgibbon,1988].
Phanerozoicstratigraphyin the Piute Mountains. Proterozoic
A Paleozoicmetasedimentary
sectionunconformably
overlies
rocks can broadly be divided into an Early Proterozoicsusa- the Proterozoic basement and is considered to be transitional
crustal successionand crosscuttingmetaplutonicrocks. The betweenmiogeoclinaland cratonalfacies [Stoneet al., 1983].
supracrustal
rocks consistof stronglydeformedpelitic and The lowerpart of this sectionconsists
of quartzitecorrelated
quartzo-feldspathic
schists
andgneisses,
withminorarnphibolitewith the CambrianWood CanyonFormationthrougha grey
andquartzite.A groupof graniticorthogneisses,
datedbetween bandedmarblewhich is correlatedwith the lower part of the
1700 and 1726+_9
Ma [Woodenet al., 1988], are often found CambrianBonanzaKing Formation(Figure2). Abovethisis a
complexlyinterleavedwith the supracrustal
sequence. Later thick sectionof carbonatethat includesa massivetan-grey
episodesof Proterozoicmagmatismproduceda numberof in- dolomitic marble and a coarse-grained
white calcitic marble.
tinsionswhich crosscut this gneissicfoliation and appearto The stratigraphicsequenceof these upper units has been
postdate
themainEarlyProterozoic
deformation.Theseinclude controversial.The tan-greydolomiticmarbleis thoughtby all
theFennergneisswhichis a 1683+_5
Ma K-feldsparmegacrysticworkersto be partiallycorrelativewith the upperpart of the
II
SANDSTONE
TERTIARY
PEACH
SPRINGS
TUFF
-113 Mo
SANDSTONE,VOLCANICS,
MESOZOIC
M
½/O
o
2-MICA
72 - 84
GRANITE
Mo
REDWALL
MARBLE
BONANZA
KING
ANGEL
ZABRISKIE
WOOD
FM.
CANYON
DIABASE
BARREL
FENNER
o
K-spor
FM.
QUARTZITE
~1100
1419+_7
Mo
ond gronite
-
Piute
Mountoins
1675_+16
Mo
- 1683__+5 Mr]
megocrystic
GRANITIC
Mo *
PLUTON-
syenite
GNEISS
MARBLE
QUARTZITE
GRANITE
orthogneiss
ORTHOGNEISSES
leucocrotic
o
BANDED
SCHIST
SPRINGS
Northern
o
FM.
DIKES-
megocrystic
2_.-MICA
CONGLOMERATE
GRANODIORITE-
MARBLE
DOLOMITIC
BRIGHT
!•
gronite
ond pegmotite,
gronitic orthogneiss - 172_6+_9Me,
gronitic
ougen orthogneiss
SUPRACRUSTAL
pelitic
ROCKS
schist ond gneiss
metogreywocke
omphibolite
quortzite
Fig. 2. Schematic
lithologiccolumnshowingcross-cutting
relationships
and stratigraphic
sequences
in the PiuteMountains.
490
FLETCHERAND KARLSTROM:LATE CRETACEOUSDUCTILE DEFORMATION,EASTERNMOJAVE DESERT
Middle CambrianBonanzaKing Formation,the Upper Cambrian and 4). Although these rocks are complexly deformed,their
NopahFormation,and/orthe DevonianSultanFormation[Stone distinctive stratigraphyprovides important controls on fold
of the
et al., 1983; Brown, 1984]. Stone et al. [1983] interpretedthe facing-directionsand geometryand allows reconstruction
white marble to be a Cambrian unit lying stratigraphically deformationalhistory. An important aspect of this study,
between the grey-bandedLower Bonanza King and the tan however, is that we were able to trace Mesozoic structures and
dolomitic Upper Bonanza King. In contrast,Brown [1984] fabricsfrom areaswhere they involve Phanerozoicrocksor 1.4
correlated the white marble with the MississippianRedwall Ga plutonsinto the highly deformedEarly Proterozoicbasement
Limestonebased on a similarity in chemistry,lithology, and and thus more completelycharacterizeMesozoiccompressional
deformation.
inferred stratigraphicpositionabove the tan dolomiticmarble.
Thus in areas where his Redwall Limestone lies in contact with
FirstPhaselsoclinalFoldingandDuctileThrusting:
the grey-banded
LowerBonanzaKing, Browninferreda tectonic Northeast-Southwest
Compression
removal of the Cambrian/Devonian dolomite along faults
subparallelto bedding. A definitivesolutionto thisproblemwill
Thrust-relatedF• deformationin the Paleozoicrocks of the
Old Woman and Piute mountainshas been interpretedas a
probablyrequire a study of conodontsin the more weakly
sequenceof stackedbasement-cored
fold nappes[Miller et al.,
metamorphosed
portionsof the range. However, in agreement
1982; Howard et al., 1980; Brown, 1984; Howard et al., 1987].
with Brown [1984], our mapping showsthat the white marble
Our work showsthat complexfolding and transposition
of Paleostratigraphically
overliestheCambrian/Devonian
dolomiticmarble
zoic strataoccurredlargelyin responseto movementalongshem
in less deformedsectionsso that in spite of the abundanceof zones which now form the northeast and southwest boundaries
tectonic contacts, we favor the correlation of the white marble
of the Paleozoicoutcrop (Figure 4). The northeastbounding
shearzone, here namedthe Fennershearzone, dipsmoderately
Both Proterozoicand Paleozoic rocks are intruded by Late to the northeast,while the southwestboundingshearzone, here
Cretaceousstrongly peraluminoustwo-mica granites. These named the Lazy Daisy shearzone, dips to the southwest(Figure
granitesare interpretedto have been derived from midcrustal 4). Theseshearzonesare characterized
by stronglymylonitized
anatexis[Miller et al., 1982] and emplacedduring deep-seatedProterozoicbasementlying structurally above overturnedand
Mesozoiccompressional
tectonismand metamorphism.One of stronglyattenuatedPaleozoicstrata. Isoclinalfoldingandductile
these,the East Piute pluton,yields a U-Pb zirconage of 85+._7thrustingattenuatedthe overturnedsectionsto as little as 1% of
Ma [Fletcher et al., 1988]. Another, the Lazy Daisy pluton, is their original thickness,and althoughstratigraphicsequenceis
petrologicallysimilar to the nearby SweetwaterWash pluton generallymaintained,complete stratigraphicsectionsare rare.
whichhasyieldeda U-Pb ageof 74_+3Ma [Fosteret al., 1989]. The thrustzonestypicallyhavewidthsof 300-600m andextend
A sequenceof Tertiary volcanic and sedimentaryrocks, laterallyfor 5-10 km. Both the scaleandhigh strainssuggest
includingthe 18 Ma PeachSpringsTuff, unconformably
overlie that these shear zones probably represent kilometers of
the Proterozoic, Paleozoic, and Mesozoic crystalline rocks. movementand were importantin burying Paleozoicrocks to
midcrustal levels.
Tertiary strata in the Piute Mountains are commonlyfound in
Shearzoneson the mesoscopic
scalearecharacterized
by an
tilted fault blocks with dominantly westerlydips less than 30ø.
L-$
fabric.
Isoclinal
folds
at
all
scales
transpose
Paleozoic
These Tertiary faults accommodated crustal extension of
sedimentarylayering parallel to the mylonitic fabric in the
approximately20-30%; block rotationcan be restoredso that
Proterozoic
rocks. Elongatequartzpebbles,alignedfeldspars,
Mesozoic and earlier fabrics, while locally brecciated,can be
rods
of
quartz
and sheathfold axeslying in royion:ticfoliation
reconstructed.
with the Redwall
Limestone.
GF_X)MET•Y
AND KINEMATICS
OF LATECRETACEOUS
CO•SIONAL
DEI•ORMATION
definea consistent
northeast
and southwest
plungingstretching
!:neat:on(Figure5a). This lineat:onvery nearlyapproximates
the principleaxis of extensionof the finite strain ellipsoid
[Kelly,1989]andis interpreted
to approximate
thebulktransport
Figure 3 is a geologic map of the south central Piute directions within the shear zones.
Mountainsthat showsthe major structures
and fabricsthat were
MesoscopicF• folds, both within the shearzonesand in atproducedduring two main phasesof MesozoiccompressionaltenuatedPaleozoicsections,are typicallynoncylindrical,
with
deformation: (1) northeast and southwest directed ductile hingelinescurvedwithin fold axial surfaces.Eye-shaped
folds
thrusting that placed Proterozoic rocks structurallyabove and flat elongatesheathsoccur with long axesparallelto the
deformedPaleozoicstrata,and(2) northwest-southeast
shortening stretchinglineat:on. Fold axes der'mea girdle in equal-area
by uprightfolding. Most crustalshortening
andthickeningwas projectionwhich is parallel to the averageorientationof the
accomplishedduring the first deformationalphase (F,) that mylonitic layering and containsa strong point maxima that
involvedisoclinalfoldingin response
to ductilethrustingalong coincideswith the local stretching
lineat:onorientation
(Figures
a network of anastomosingshear zones. These shear zones 5b and 5c). This suggests
that fold hinge lines may have
concentrated
Mesozoicstrainanddividethe crystallinebasement initiated at high angles to, and progressivelyrotated into
into lozenge-shapedblocks. The orientationof shear zones parallelismwith, the movementdirection. Differingdegreesof
throughout the Piute Mountains is variable; however, most hingelinerotationmay represent
variationsin the timingof fold
containa northeastand southwesttrendingstretchinglineafion initiationduringprogressive
simpleshear[Quinquiset al., 1978]
(Figure 5). These lineations are consistentwith northeast- and/or heterogeneous
strain. Cobbold and Quinquis[1979]
southwestsubhorizontalshorteningon a network of variably suggested
thatminimumshearstrainsof 15 arerequiredto form
oriented shear zones.
Postthrusting,northwest-southeast
sheathfolds from initial perturbations
in layering. Therefore,
compression
produceda secondphase(F2) of uprightopenfolds assumingthat fold hinge line rotation occurred,the high
with a variablydevelopednortheaststrikingsubvertical
crenula- concentration
of fold axesnow parallelto the stretching
lineat:on
tion cleavage. This fabric increasesin intensitytowardthe south is furtherevidencefor high shearstrainswithin the shearzones.
andcrosscuts
the Lazy Daisyplutonof two-micagranite(Figure
Microstructuresassociatedwith F• shearing indicate a
3).
moderatelyhigh- temperature
regime and recorda significant
This paperfocuseson the Paleozoicmetasedimentary
rocks componentof progressivesimple shear. Observedmicrostruclocatedin the centralportionof the PiuteMountains(Figures3 tures includeS-C fabrics,syntheticshearbands,asymmetric
FLETCHER
ANDKARLSTROM:
LATECRETACEOUS
DUCTILE
DEFORMATION,
EASTERN
MOJAVE
DESERT
491
115ø07' 30"
20
S
Foliation and Stretching Lineation
1683 +_5 Ma
•
Traceof SteeplyDippingS2 Cleavage
•
Ductile Shear Zone, Teeth on Upper Plate
••
Tertiary
Fault,
ticks
on
downthrown
side
Ma
ß
-,
'
EAST
PI•UTE
' ' PLUTON
,
. • 85 + 7 Ma
.
%
34ø45'
"'•'•'"•'- •' ' •
r'-'"J
Tertiary
and
Quaternary
I Cretaceous
Aplite
and Pegmatite
•Cretaceous
Granite
;?,,','
• • • ;,•
14
, ½½ I •
CambrianPaleozoic
-Miss.
• Upper
Rocks.
', • • • •
• Lower
Pa
leozoic
Rks,,
.
•-
' •'
Lower
•Barre•
SyenieSprings
and Granite
ß • ,• • • • •
LAZY
DAISY
PLUTON
•
74+3Ma. ,•/
• Fenner
Gneiss
•Leucocrotic
Granite
-
- • • •
• • •.
-
,
• • ••
•
0
•mbrian
•Gronitic Orthogneiss
• Supracrustal
2 km
•!::ii;:'
::•:i:•:•iT::i•.i!;::::..•!!:i!:!!;:i;F:.
:"i•:!iiii:'
.::•i;!½i:i:::;::':":"'":
...........
-....,:•
:,•,'-:
:::::!:::•:
::::::::
:::::•:::
:::::::::
3:. '"-::
:::!::i:i.
:i:i:i:i:i:•:i:•:
::':':-:':-:
....::::i-::•:•:i:•:'
:i:i:i:i.!:•:i:
':i:i:•:•:i::•:
3i3•3i::
i:;i:!:!!
1
_
U.l_
-1•
-2
Fig.3. Schematic
map
andcross
section
ofthesouth
central
Piute
Mountains.
Cross
section
restores
offset
onTertiary
fault
inorder
toshow
Mesozoic
structure.
Numbers
1-5in mapcorrespond
tonumbered
areas
in cross
sections.
1, thebending
of a southwest
directed
shear
zone
intoa northeast
directed
shear
zonealongthenorthern
margin
of the 1417Ma BarrelSprings
pluton;
2, theantiformal
folding
of the
southwestern
overturned
limbof Paleozoic
rocks
intoanupright
limbthatcontinues
tothenorth;
3, overturned
syncline
defined
by Paleozoic
strata
lying
structurally
below
asouthwest
directed
thrust;
4,highly
evolved
granite
phase
oftheEast
Piute
pluton
thatmayhave
been
eraplaced
ina dilatent
opening
inthesouthwest
directed
shear
systems,
5,pegmatite
andaplite
dikes
fromtheEast
Piute
pluton
folded
intheF• shear
zonesand crosscuttingthem.
492
FLETCHER
ANDKARLSTROM'
LATECRETACEOUS
DUCTILEDEFORMATION,
EASTERN
MOJAVEDESERT
115007 ' 30"
.,/224
•
Tu
/
,
-'
.-
EXPLANATION
RockUn•ts:
Pf
Tu
'%'".'..•',
81
rocks,
undivided
." '•.•"•,8
••••
Tu
Tertiary
•
• .... • =•
Lazy
Daisy
PIuton
Dolomitic
3
Tu
•
'
I Bright
Lower
Bonanza
Angel
King Fm. Marble
Pf
/ 88
•
I
Schist
P••
_
Marble
•0•
• 4•-- •:••=
••
61
I0
27
- •
• Wood
Qua
rtzCanyon
ite Fm.
attenuated
sect
44 /.27
of Lower Paleo-
34045 '
Egn
•
•
Egggran
•t•cortho-
5/
gneiss
EIg
/4
•
{60 /•7•
•
•
schist
• gneiss
24
52
•
68
,-..... 59
,• •• 656B
%L ' •
•
•••
57
"
•::'
8•
I
/ • -•
•• •
•
•
•
-
•
19
• / x
x
••
, ",• • /
•
• •
ofshear
across
.
fol•ot•onshown
•'/
/
' •
•
',
,
.
overturned bed-
x '
B,
•2d,ng
ond
stretch
,,
Kg> / SfOliøt'Onøn
0
•gn
x
,,.
•
•
/
•
•
'.
I
I•neot•on.
u ,•/
,
x•
I
I
•
•
Sense
,, ,,
'',I•. ,/ , x _,/• d,p-s,p,
ment
mostly
If•s
movement
'•
-•
,
I /
•
,s mostly str•ke
•
slip.
• -,i- S2
crenulat•
,
',
cleavage
•
•
leucocrotic
gneiss
•
•
1
2 km
•
I
• /
• -
Tertiary
fault
Mesozoicsheor
x
•
•ig. 4. Geologicmapof •e Paleomicmetasedimenta•
r•ks in •e c•tral Pium•o•mins. Oenerali•dfrom 1:3•
ma•g.
sigma-and delta-type
augen,and fractured
feldsparpor- deformation
by cataclastic
flowto theinitiation
of crystal
plastic
phyroclasts
(Figure6). Quartzmicrostructures
recordcrystal deformation.
Mostfeldspar
porphyroclasts
showsomedegree
of
plasticdeformation,
recovery,
andrecrystallization
by high- fracturing
and cataclasis;
however,this is overprinted
by the
temperaturedislocationcreep [Hobbset al., 1976; Tullis and
nucleation
of extremely
finesubgrains
alonginternalmicrocracks
Schmid,
1982]. Theonsetof thermally
activated
recovery
is and rims of porphyroclasts
as well as in tailsof asymmetric
seenin quartzby the occurrence
of rims andnecklaces
of new augen
(Figure
7). Therefore
eventhough
feldspar
wasdeforming
strain-free
grainsalonggrainboundaries,
deformation
bands,or
ductilely,the extentof new graingrowthwaslimitedto small
otherareasof highdislocation
density
in originalhostgrains; subgrains
andnuclei,anddynamic
recrystallization
in comparison
morecompletequartzrecrystallization
texturesare characterized to quartz was much less extensive. The observeddeformation
by mosaics
of subgrains
withbothsutured
andpolygonal
grain mechanisms
in quartzand feldsparare thoughtto operateat
boundaries.Feldsparmicrostructures
recorda transitionfrom
temperaturesabove 450•2 [Simpson,1985]; however, their
FLETCHERAND KARLSTROM:LATE CRETACEOUS
DUCTILE DEFORMATION,EASTERNMOJAVEDESERT
N
493
N
N
e ee•e
AVERAGE Si
A) FI STRETCHING
LINEATIONS
(n = 128)
B) F I FOLD HINGE LINES
NORTHWEST
LIMB
OVERTURNED
C) FI FOLD HINGE LINES
SOUTHWEST
(n =;50)
LIMB
OVERTURNED
(n-
14)
Fig.5. Orientation
data
ofthrust-related
F, fabric
elements.
(a)Northeast
andsouthwest
plunging
F, stretching
lineations
define
thedirections
of tectonic
transport
onoppositely
dipping
ductile
thrusts.
(b)and(c)F, foldhingelines
fromtwoductile
thrusts
show
point
maxima
parallel
tothestretching
lineations
which
suggests
thattheyhavebeen
rotated
toward
thefinite
extension
directionas a consequence
of high shearstrains.
Fig.Oa
Fig.7a
!.'•..
;;.•-:
'-'-;o•:.;!...::
..:'"' '•:•..:..
'.:•*;.--'-,
......
.-•-'"•:.::.'-?:.:-•?
.•:
'L;•;..'~'•..'.
•'•','•,.•"¾•-,..
,,,•,½.•:,, •. %:,*¾,•
'•'.;"'•'
:":'•
......
ß ß.......
::•
...... ',,•.-• '* ß - ' '•'•-. ' -:-;•?:'.•;'!::•½•'.-•
-'•:'*•:-::•--,'"':'..' ':--'•-:',,
-- '•*': • ,,.,,"',3.,,•*:,:•:-:'<'..""
.
-"
%:::
..........
•!:•,;...:..
......
....... t..
.•½.,•.... •.•'
......
•..•.:..-."½-;,,'
--.--•...
..•.' ,' .•$ '"' *
-.?
ß ~.•,,,..:
',K.,•,,,.,
..... ,:'.,
½. %* •
'"..:'..•. ..'
.;½.y•
,.,.s...
½.: •, ß
.................
.,: •, . • . . *,,,,,•½
.
...,:,::*-o'•.ß', ..,;,,.• . •,1'..,,•,•....•.•"•*•.
"':•;•!:::',
*2 ½ ,,,.,•-.:'5
?.
,½'"'",
•,. '.•½,,•
,,• --'•..*.;"
•r,½'"'
5,.•...'.•½.•½;•...,
. ,,,•.•
-. .........
,.t ,..,•
ß .........
'.-'.'.
•'::•;½..-;:.:'-'
:.:
.....
'•,..;.' .
....'.•5'?.•.
r.,",•...'•,,•.
......
..,,,,
-,,•.½'..
•,.½•,;•
•..'".,;•.,,,•;,.':-'•,.,•,.,.,.:..:
•,,
.,,,.,..,,½
..........,.,½,-.,,r,
.:.,,.•
...........
...........
.* .,...::
•.:.;½':':
,-•.'.,',•
•,* ,•*
....
--
'• '4 •,,...½* .... .,....•.0,,,•.-...;•:.•.;;.•2•.½;...•'::;•::,.... ..•
.•.-
•- ..-.' .. :
•. ..... ..
"'""*'i?•i'•
"---:;
.;'%
..... ' -:.,,'
• •..'>.•"':%-•":
..•.,-:...:::.:.
::•;•;•
................
':.....-.•.½..-.,•:;:',,.,:
' ...:'-•,.•.'.,.'•.,,.,',•'='.
c,' ,,,,
-• :.-.-.--:':-•.
"'
....................
":.'-'.:..<
•.'-:
'.;.'•_%-:•".,:'•.
,.%%v%""':'
,¾v:
%'-.,
../.y'-:':'*-•;,
.................
...
';;"::%½,•--'
.•,."v;;,:-,:"
T"• •,• "'"
*- , :;...
..:.• ....
•.:.:..................,:.f•* •.•,z-• .
........
.•-,..--;::..--:
..- :,,.,j•;',,,•,a....
,,.......
.••,,-::
..........,.,.,.,•-•.,,•.,%•,•.
,•.: ...•
.•...,•..'
--...•
•- . -.•-..•
. .........
..
.•
ßß-;'
%'"'?¾-.L;.'•,:'.?
.'.."-..•.•'•...'.;."•,
•'½'•.",;.(4•,,•:•;;?'•'
""• •'• .:''.>'--'"•.•
:...'•'ø• •"• *..•%.,I,•
•'e -:-.':?•-**'.-'
.....:-o.•-½.
•'•-:.-:*-....½.-•/.•
,. •..:..•"'"•
•"•'•,•J.;.•:•::."•l•
' ;,,
..'-.•-a•
• ;".4--'*.•'
ß...:
"'tt':::"
:-" ', •, •?•-.,'-..
•.• •.•.•.• ,,•....L•>.... .•.½--.:--. - :.,•....•1• ß ---•...::
...-•-:.•:...
...... ....-•
• .:-"•
3-%
'*;
•.•-•
ß • ,,ß"•'•2<-,
' •'-'...•
...,•....... -..
:.:..•,,,
',•j..
, ,.>.•
•>,•• ,:',:*
.:
:-:,•! .
::--
,,•'*
'ø.• ß,,.*•..;.,'*.'•.,.,;'•
*..;:,/?...½',.,..,' ß"*
-,*,*,,:':,,•,"'•
•*.-• -,•'•,,. ;•-•*
,;":"
:.';i"t,;........•%:,.
';:" .;:•--',•"
.'::'...'-..':"*'"•--'-•'•:.:.•
.,,.,
**'..-'"•";:c.•
•.'..'•';;
...'.•
ß--?';'"
'..:""*":
.i ß-•.'*'., ,j,:. ..j•'*..:..
o,,,,,..•
.-.-.'*'..... ,•.•-.
- * ;r .. -.:..*"
'.'" '
' ........
ß
....... '*- ..:
'•:•llmi•..•-1
Fig.6b
Fig.7b
Fig. 7. Ductilelydeformedfeldsparporphyroclast
showsthe nucleation
Fig. 6. Kinematicindicators
from F, shearzones. (a) Sinistralaugen and growth of subgrainsalong microcracksand in dynamically
tails. (a) planelight; (b) crossed
nichols.
andsynthetic
shearbands.(b) Quartzribbonwith sinistralasymmetry. recrystallized
494
FLETCHER
ANDKARLSTROM:
LATECRETACEOUS
DUCTILE
DEFORMATION,
EASTERN
MOJAVE
DESERT
activation
is strongly
dependera
onPmo,P•,,•, strainrate,and strata, or that crosscutlate Cretaceousgranites are obviously
magnitude
of f'mitestrain[TullisandYund,1980].
Mesozoicin age (Figure 3). Theseshearzonescharacteristically
Kinematicanalysisprovedcriticalin correlating
the discon- show a well-developedmylonitic fabric with stronggrain size
tinuously
exposed
shearzonesandworkingoutthegeometry
and reduction and thus can be distinctively traced through the
styleof thrust-related
deformation.
The two oppositely
dipping generallycoatsetgrainedProterozoicgneisses.Shearzonesin
shearzonesthatboundthePaleozoic
rockshaveopposing
sensesthe westernmostpart of Figure 3 comain a similar mylonitic
of shearalongmostof theirlengthandnow forma conjugatefabric, and althoughentirelyrestrictedto Proterozoicrocks,they
pair of ductile thrusts. The Fenner shearzone showssouthwest are interpretedto be Mesozoicin age becausethey crosscutthe
directedtectonictransport,
whilethe Lazy Daisyshearzoneis 1419 Ma Barrel Springs pluton. This pluton postdatesthe
predominately
northeast-directed
(Figure4). However,as the regionalProterozoichigh-grademetamorphismand deformation
latter thrustis followedto the north,it showsan apparentthat is bracketed between 1710 and 1683 Ma in the Piute
reversalin tectonictransport
(location2 of Figure3) thatis most Mountains[Ring et al., 1988; Woodenet al., 1988].
easilyinterpreted
asa laterreactivation
of thethrust.Depending As shown in Figure 3, Mesozoic shear zones form an
on its originalsenseof movemere(northeast
or southwest),
two anastomosing
networkthat dividesthe Proterozoicbasementinto
large-scale
geometric
interpretations
canbe hypothesized
for the lozenge-shaped
blocks. Coarse-grained
gneissiclayeringwithin
complexlyfoldedPaleozoicstrata(Figure8).
the blocks is often oriented parallel to the boundary-forming
If the Lazy Daisy shear zone was originally southwest-shear zones, suggestingthat this initial Proterozoicfabric was
directed, it can be correlated with the Fenner shear zone and the
variably modified and reorientedduringMesozoiccompression.
large-scale
fold geometrywouldbe an overturnedsynclinethat Field relationshipsshow that the gneissiclayeringis crosscutby
is antiformally refolded with its overtumed limb cut or middle Proterozoic dikes which are themselves intemally
reactivated by later northeastmovementsas shown in the deformedand displaya tectonicfabricparallelto their walls. A
schematic
composite
crosssectionin Figure8a. Alternatively, likely scenariowhich explainstheserelationshipsinvolves(1)
if the Lazy Daisy shearzonewas originallynortheast
directed, formationof the gneissicfabric during the 1710-1683 Ma high
the large-scale
structure
in the Paleozoicmetasedimentary
rocks grademetamorphicand deformationalevent, (2) later intrusion
would be a refoldednappe with the southwestdirectedthrust of the cross-cutting
(e.g., 1419 Ma) Proterozoicdikes,locally at
overprinting
thenortheast
directedthrustasshownin Figures8b high anglesto the layering,and (3) rotationand deformationof
and3. Presentdatapermiteithergeometricinterpretation,
with the tabulardikes as the gneissiclayeringwithin the blockswas
differentimplied kinematichistoriesas discussed
below.
reorientedduring Mesozoic shearing[cfi Lister and Williams,
Mesozoicshearzonescan be mappedbeyondthe Paleozoic 1982, Figure 5]. Therefore,althoughMesozoicdeformationis
outcropthroughvariablymylonitizedProterozoic
basement.The interpretedto have affectedthe entire middle to upper crest,it
mainproblem
whichconfronted
thisphaseof thestudyinvolved was heterogeneouslypartitioned and concentratedinto shear
differentiatingMesozoicfabricsfrom Proterozoicfabricsin the zones.
highly deformedgneissicpackages. Shearzonesthat bound
Mesozoicshearzonestendto be localizedalonglithologic
Paleozoicoutcrops,thatcontainsliversof dismembered
Paleozoic contacts
that separate
rockswith strongcompetency
contrasts,
1400
1200
- 1400
_
.o.o.
IOO0
½ ,
12OO
_
800
-
IOOO
600
-
800
400
-
600
200
-
_
- 400
-
0
Egg
O•
A,
••
I
I
O 5
I
Y=.84
2OO
B.
•m
h
Fig.
8. Alternate
geometric
interpretations
ofF,folds
inthePaleozoic
metasedimentary
rocks.
Tertiary
fault
restored
toshow
Mesozoic
geometry.
Circled
letters
correspond
tolocations
inFigrtheast-directed
thmsting
overprinting
southwest
directed
thrust
mbols
forrock
units
same
asFigure
4.(a)antiformally
refolded
overturned
syncline
with
northeast
directed
thrusting
overprinting
southwest
directed
thrusting.
(b)Refolded
nappe
with
southwest
directed
thrusting
overprinting
northeast
directed
thrusting.
Symbols
forrock
units
same
asFigure
4.
FLETCHER AND KARLSTROM:LATE CRETACEOUSDUCTILE DEFORMATION, EASTERNMOJAVE DESERT
495
suggestingthat anisotropiesin the crystallinebasementmay have sensesof movementintersectis along the northernmarginof the
been a factor in partitioningMesozoicdeformation. As shown 1417 Ma Barrel Springspluton. Here a southwest-directed
shear
in Figure3, shearzonesoften follow contactsbetweenthe supra- zone bends in a dextral sense as it merges with a northeastcrustalgneissesand more competentplutonssuchas the Fenner directed(dextral) shearzone (location 1 of Figure 3). Prelimigneiss,locatednortheastof the large Paleozoicoutcrop;a leuco- nary nøAxfl9Ax
ages from hornblendein the shearzonesalso
cratic granite/pegmafite
intrusion,lying southwestof the Paleo- suggeststhat northeastthrustingmay have outlastedsouthwest
zoic outcrop;and the Barrel Springspluton in the southwestern thrusting (D.A. Foster, personal communication, 1989).
most portion of the Piute Mountains. Perhaps due to the Hornblendefrom a southwestdirectedshearzone yields an 85irregular nature of these contacts,shear zones throughoutthe 90 Ma age, while a samplefrom a shearzone in the northeastrange are variably orientedand show both strike-slipand dip- directedkinematicdomainyields a 74 Ma age. Mesozoicpeak
slip movement parallel to the northeast-southwest
trending metamorphictemperaturesin the area with the 85-90 Ma age
stretchinglineation. In severalplacesit was noticedthat when were unlikely to have exceeded the homblende blocking
the shear zones diverge from the contact of a pluton, they temperature (about 500øC) and reseuing therefore probably
becomemore diffuse and poorly defined. Although this pattern occurred by dynamic recrystallization and crystal plastic
applies to many shear zones in the Piute Mountains, well- deformationduring thrustingor by heating associatedwith the
developed mylonite zones are found in theologically preferentialmigrationof hydrothermalfluids throughactiveshear
zone
homogeneous
rock types, and somecontactsbetweenProterozoic zones. The 74 Ma hornblendeis from a higher-temperature
rock types are unsheared, suggesting that nucleation and and thusreflectscoolingthroughabout500øC. These two ages
propagationof shear zones was controlledonly in part by suggestthat southwestdirectedthrustingendedat about85 Ma
preexistinganisotropies.
and that northeastdirected thrustingmay have lasted until 74
Some shear zones are folded into large-scaleF• folds with Ma. The kinematic model of two temporallydistinct eventsis
low amplitude to wavelength ratios and hingelines oriented compatiblewith the first geometricinterpretationof the folded
nearly perpendicularto the stretchinglineafion(see crosssection Paleozoic strata (Figure 8a). This geometrysuggeststhat a
of Figure 3). The folds are kinematicallycompatiblewith F• southwestdirectedthrustwas antiformallyfolded and portionsof
shortening,and while the orientationof the stretchinglineation one limb were later reactivatedby northeastdirectedthrusting.
on oppositelydipping limbs varies in plunge, it maintainsa
An alternativeinterpretationfor the kinematichistory is that
consistentnortheast-southwest
trend. Although bulk northeast- both sensesof ductile thrustingoverlappedin time and occurred
southwestshorteningfollowing thrustingcould have produced by conjugatemovementsand deep-seatedtectonicwedging[Ring
folds of this orientation,the absenceof an axial planar cleavage et al., 1988; cf. Price, 1986; Hamilton, 1988]. Conjugateshear
associatedwith thesefolds and their irregulardistributionsuggest bands were observed in outcrop and may be a mesoscopic
that they formed during thrusting. We considerthe openly analog to the large-scalestructure. Shear zones from the two
folded shear zones to have resultedmainly from movementon kinematicdomainsqualitativelyrecordsimilar strainsand seem
structurallylower or adjacentnonplanarductile thrustsby drag to have developed under comparable pressure/temperature
goldingand/orby mechanismsbroadlyanalogousto fault bend conditions.They are essentiallyindistinguishable
in termsof (1)
foldingin shallowerlevel thrustbelts [cf. Suppe,1983].
•2,• the dominant
the mesoscopicstyle of the mylonitic foliation, c
As shownin Figure3, the networkof shearzonesin the Piute quartz and feldspardeformationmechanisms,(3) the degreeof
Mountains can be divided into two main kinematic domains that
attenuationof overturnedPaleozoicmetasedimentary
rocks, (4)
are characterizedby stackedductile thrustswith a prevailing the orientationof the horizontalcomponentof slip in the two
sense of tectonic transport. Ductile thrustsnortheastof the shearsystems,and (5) the characteristic
overallplanestrainsthat
largestPaleozoicoutcropshow top to the southwestmovement, are recorded by pebbles in shearedWood Canyon Quartzite
while those to the southwest of the Paleozoic rocks record
[Kdly, 1989].
mostly top to the northeasttransport. The schematiccross
In the conjugateshearzone model, the Barrel Springspluton
sectionin Figure 3 showsthe complexlyfolded Paleozoicstrata can be considereda large-scaletectonic wedge with a relative
lying in the footwallsof the two ductile thrustdomains. These resolvedmovementvector down to the southwestalong the two
domains must converge with each other above the range; shearzonesat its margins(Figure 3). Opposingand possibly
however, the overprinting relationships between them are contemporaneous
movement on these shear zones would cause
presentlyuncertain.
their intersectionto migratewith the wedgingpluton. However,
It is possiblethat the opposingsensesof thrustingdeveloped completelycontemporaneous
movementon all shearzonesin the
in two temporally and kinematicallydistinct eventswith top to Piute Mountains network would creme significantstrain comthe northeastoverprintingtop to the southwest. The timing of patibility problems at their intersectionsand throughoutthe
southwestdirectedthrustingis constrainedby the emplacement deforming crust. Therefore the conjugate shearing model
andcrystallization
of the 85+_7Ma EastPiutepluton. The main suggests
that even thoughthe shearzonesmusthave overprinted
phaseof this two-micagraniteis stronglydeformedby F• thrusts each other as the network evolved through time, these
and shows well-developedzones of S-C mylonites. However, crosscutting
relationshipswere resolveddifferently at different
highly evolved phasesof the pluton occur both as isoclinally intersections. This kinematic model is consistent with the second
folded layers in the shear zones and as dikes that crosscutthe geometricinterpretationfor the folded Paleozoicstrata(Figure
mylonitic foliafion. Some of thesedikes have orientationsthat 8b). This geometrysuggeststhat southwestdirectedthrusting
are compatiblewith tension gashesin the southwestdirected overprintednortheastdirectedthrustingin centralportionof the
shearsystem(locations4 and 5 of Figure3). K.E. Karlstrom range, with the reverseoverprintingrelationshipseen at the
et al. (manuscript
in preparation,
1989)usetheserelationships
to Barrel Springspluton.
showthat the last stagesof thrustingin this areacoincidedwith
In summary,our datapermiteither(1) two temporallydistinct
the f'malstagesof crystallization
of the 85_+7Ma East Piute thrustingeventsor (2) shorteningby conjugateshearing. These
modelsare testableby additionalstudyof overprimingrelationpluton.
The timing of northeastdirected thrustingis not well shipsbetweenshearzoneswith opposingsensesof movement
constrained. At the presentlevel of mapping in the Piute and a more completecharacterization
of thermochronology
in the
Mountains,the only placewheretwo shearzoneswith opposing two kinematic domains. In either case, however, the strong
496
FLETCHERAND KARLSTROM'LATE CRETACEOUS
DUCTILE DEFORMATION,EASTERNMOJAVEDESERT
parallelismof the F, stretchinglineationand thus the direction
of tectonictransporton the ductilethrustssuggeststhat they all
formedduring a Late Cretaceousorogenicevent that ultimately
produceda bulk northeast-southwest
crustalshorteningduringa
time spanof about 10-15 Ma.
SecondPhase Upright Open Folding:
Northwest-Southeast
Compression
F• shear zones, isoclinal folds and other structuresrelated to
ductilethrustingare overprintedby a later phase(F:) of upright
open folds with a northeast-striking
crenulationcleavage(S2).
Figure9 showsthe spatialdistribution
of theS: cleavageandthe
styleof F• overprintingin the PiuteMountains.The S• cleavage
forms a broad fan and increases
in intensitytowardthe Lazy
Daisy pluton in the southadjacentto which it locally becomes
the dominantdeformationalfabric. Similarly, mesoscopicand
macroscopic
foldsbecome
morenumerous
andhigheramplitudeFig.10. S•defined
by aligned
biotitethatapparently
grewin thesyntoward the south. An equal-areaprojectionof poles to S• S• differential
strees
field. Noterelatively
uncrenulated
S•compositional
(Figure9) showsthatthe S• axialplanarcleavageis statisticallylayering
(horizontal).
subparallelto the northeastandsouthwest
plungingF• stretching
lineation. Thus folding about S: did not reorient the stretching
lineation but did produce a shorteningstrain which is nearly
cleovoge
orthogonalto that accomplished
by F• thrusting.
The microstructuralevolution of the S• cleavage can be
SE
A
inferred from the variation in style that is seen in a northwestsoutheasttransectfrom areas of weak F• folding to areas of
strongerF• folding. In its leastdevelopedform, the S: cleavage
is defined by a preferred orientation of syntectonicbiotite
porphyroblasts
that overgrowa relativelyundeformedS• foliation
(Figure 10). Microfolding and buckling of the S• foliation
producedan axial planar crenulationcleavage that commonly
contains aligned biotite porphyroblasts. Quartz aggregates,
deformedmainly by dislocationcreep,recordthis shorteningby
the developmentof subgrainsthat are elongateparallel to the S•
crenulation cleavage. Asymmetric crenulations show the
incipient developmentof a differentiatedcrenulationcleavage
resultingmainly from pressuresolutionand diffusion of quartz
away from the shorterlimbs. These limbs define thin cleavage
domainsparallel to S• and are characteristically
composedof less
solublephyllosilicatesand opaques(Figure 11a). Once formed
by pressuresolution, the cleavagedomainsbegan accommodating simple shear as documentedby apparentlytruncatedand
offset compositionallayering and the occurrenceof asymmetric
biotitefish (Figure l lb). The biotitefish showopposingsenses
of shearon opposinglimbs of F• microfolds. Therefore,in this
setting, deformation at the grain scale seems to have been
stronglypartitionedinto simpleshearanddissolution
in cleavage
(or mica-M) domains, and flattening by buckling of S• in
microlithon (or quartz-Q) domains as outlined by Bell et al.
[1986] and Bell [1986].
Increased F• deformation toward the south resulted in a
stronglydifferentiatedcrenulationcleavage(Figure 12a). In its
km
most advancedstage,near the margin of the Lazy Daisy Pluton,
i
i
S:
locally forms a continuouscoarselycrystallineschistositythat
0
.5
almost completely transposescompositionallayering. Here,
deformationat the grain scaleis apparentlydominatedby simple
shearas recordedby asymmetricpressureshadowsaroundearly
Fig. 9.
Schematic map of the Paleozoic metasedimentaryrocks syn-S•garnetswhich preservethe only relics of S• as inclusion
highlightingthe distributionof large-scaleF: folds and the mesoscopic trails (Figure 12b).
S: cleavage. Stereonetplot of polesto S: and mesoscopic
F: hingelines
The timing of F• folding is constrainedby the crystallization
Trend
of
S
2l
' F2 synform
/ F2ont,form
••;2
showa steeplydippingnortheasttrendingaverageS: orientation. (a) and
(b) - Insetsare sketchesfrom photographs
of F•/F: overprintingrelation- of the 7423 Ma Lazy Daisyplutonwhichis crosscut by theS•
ships. (a) An eye-shapedF• fold that is refoldedby openF: folds. (b) cleavage. Althoughthis fabric can be tracedcontinuouslyinto
Isodinal F• folds with curvilinearhingelines that are transectedby the the country rocks, it is much less well developed within the
pluton. These relationshipscan be explainedby two possible
S: cleavage.
FLETCHERAND KARLSTROM: LATE CRETACEOUSDUCTILE DEFORMATION, EASTERNMOJAVE DESERT
Fig. 1la
--:•i:•i•:•&!"'. •.;•¾:.•.;-•:;:
. ':•7•....
•'•:•::•.....
:•,•
'•:•
..•.•...::?
..•
.•:•---..•.•-•:•<•
.•,•?-.•:;•::.
•..½
::••:•.•..
.•.5"
•::
•..-'-;•'
•'.......
fi•:
•' :.
:•;.•-'•'•
....
:..::
.- ::.
:•:..•,•:.
....-•::.?:...--•:
..,•:..
.::...'.,..'
.....
•?:•-:'.--•:j
.....................
•:,...':•-:"•::.:..
497
Fig. 12a. S•asa strongly
differentiated
crenulation
cleavage.Crenulated
S• now only preserved
in microlithon(quartz-rich)
domainandcannot
be tracedacrossS• cleavage(mica-rich)domains(vertical).
"::•:'•?:•
•.::-•?
::?.::;'::•::
.......
...:...
.........
.:. "•....•,•,•'
• .... •'•½-•.
::•.:.•::::,- • -•i•"':i..
. ::•.........:•-•...:;
'../•:.-.•,
•.
7:.
-
'?•"••'-'--.4'
--...--..•:.:,
•..
.•:•.
•-
-•,•..
:..•.•
:.. ,::•:..
...-."
??.::•.?
•.......
::.::•..::.
--.•:-'.
. •.•:.--•..:.-.•
': .::•?.•:•.
:•:.'•--
•.-',:-'••
......
produced orders of magnitude less shorteningthan the earlier
transpositionand ductile thrusting. Since F• shorteningwas
nearly orthogonalto that of F• ductile thrusting,it is difficult to
relate kinematicallythe two in a singleprogressivedeformation.
The spatialdistributionof S• suggeststhat it may recordstresses
generatedby pluton emplacement. However, a similar northeast
trendingfabric,overprintinglate Cretaceous
ductilethrusting,is
presentin many mountainrangesthat make up the belt of late
Cretaceousductile deformationin the easternMojave Desert:
FennerHills [Kelly, 1989], PiuteMountains,Old Woman Mountains,Kilbeck Hills [Horinga, 1988], Arica Mountains[Jackson
and Burks, 1987], HarquahalaMountains[Reynoldset al., 1987].
Thus it is possiblethat this last deformationalfabric recordsa
changein regional stresses.
:'"•7517:
•:•-
'•'•.,.•%-":::
'•"•
.?•''4
•?•'-:,¾
....
.
.
•' '.•:
.
.
Fig. 11b
Fig. 11. (a) $: as a pressuresolutioncleavageor incipientdifferentiated
crenulationcleavage. Pressuresolutionwas localizedon shortlimbs of
asymmetriccrenulationswhich are mainly composedof phyllosilicates
and opaques. (b) Simple shearmicrostructures:
right-side-upbiotite fish
in S:.
timing schemes.The granitecouldhave crystallizedlate during
F: folding and only partially recordedthe fabric. Heat and
fluids emitted before and during crystallization may have
enhancedductility and allowed more advancedstagesof F•
deformationto have occurredaroundthe pluton. Alternatively,
it may havecrystallizedearly and actedas a competent
block or
buttressthat concentrated
F: strainalong its margins. The first
interpretation
is supported
by a strong
increase
in metamorphic
grade towardsthe Lazy Daisy Pluton [Hoischet al., 1988]
recordedby syn-F• porphyroblasts
[Fletcher, 1989]. In either
case,however,F: openfoldingoufiastedthe f'malcrystallization
of the74+3Ma LazyDaisyPlutonandwascompleted
before72
ß
:"'•---.!•:"•"
Ma, the •øAr/•Arageon biotite,muscovite,
andK-sparfrom the
pluton,andthetimeby whichtheplutonhadcooledto below Fig.12b. S•asa continuous
schistosity.
S•is nolonger
seenin the
300ø(2[Fostereta/., 1989].
matrix and is preserved
only as inclusiontrails in early syn-S•
The regionaltectonicsignificance
of this latestdeformafionalporphyroblasts.
Asymmetric
pressure
shadows
around
garnet
suggest
that
phaseremainsto be fully established.
F• uprightopenfolding deformation
at thisstage
involved
simple
shear.
498
FLETCHERAND KARLSTROM:LATE CRETACEOUS
DUCTILE DEFORMATION,EASTERNMOJAVEDESERT
RE•TrVETrentoOr Ducrl• DEFORMATION.
M•-T•Oam•SMAm) PtzrrosISM
tion of F2 deformation,while peak temperatures
of 580ø-620øC
from garnetrims [Hoischet al., 1988] occurredjust afterthe end
Figure
13summarizes
therelative
timing
oflateCretaceous
ofF2folding.
deep-seated
orogenic
events
inthePiute
Mountains.
Southwest
These
timing
relationships
allow
ustodiscuss
some
ofthe
directed
thrusting
andpossibly
allF• ductile
thrusting
ended
processes
ofdeep-level
orogenesis
and
theinteractions
between
synchronously
with
thecrystallization
ofthe85+7
MaEast
Piuteplutonism,
metamorphism,
andductile
deformation.
Although
pluton.
Northeast
directed
ductile
thrusting
c•uld
have
lasted
regional
metamorphism
toupper
greenschist
facies
was
mainly
a productof tectonicburial, local high-temperature
moderateuntil 74 Ma. The 7423 Ma Lazy Daisy plutonis crosscutby
pressureconditionsseemsto have been primarily a result of
the S• cleavageand probably crystallizedduring the second
thermal effects related to the emplacementof the Lazy Daisy
deformationalphaseof upright open folding. Peak metamorpluton. High-gradealuminosilicates
in the Bright Angel Schist
phisminvolvingtemperatures
of 580ø-620ø(2
andpressures
of 2.5-
are only observedwithin 5 km of the pluton'smargin, and they
grew synchronously
with its emplacementduring F2 folding.
T. Hoisch, personalcommunication,1989] occurredafter the
Field relationshipsin the Piute Mountainssuggestmutually
terminationof F• deformationbut obviouslybeforerapidregional
facilitating interactionsbetweenMesozoic ductile deformation
uplift and coolingthroughabout300•C at 72 Ma [Fosteret al.,
and the emplacementof granites. F• deformation becomes
in press].
markedlymore intensetoward the Lazy Daisy pluton perhapsas
The timing of porphyroblast growth relative to the
development of deformational fabrics suggests increasing a result of thermal softeningof the crust aroundthe syntectonic
pluton and/or emplacement-related
stresses. The East Piute
metamorphictemperaturesduring deformation. The pressurepluton was emplacedalong activeFl shearzoneswhich created
temperature conditions of F1 ductile thrusting are poorly
dilatantopeningsin the crust (K.E. Karlstromet al., manuscript
constrainedby a trivariant syn-SaAFM assemblageof biotite,
4.0 kbar [Miller et al., 1982; Hoisch et al., 1988; D.A. Foster,
muscovite,
andquartz.However,
it seems
reasonable
thatinpreparation,
1989)
and
may
have
also
acted
asconduits
that
temperatures
ofapproximately
450øC
were
achieved
based
on aided
magmatic
ascent
and
emplacement
[Hutton,
1988].
feldspar
ductility
[Simpson,
1985],
and
that
most
tectonic
burial
D•sctlssioN
AND
CONCLUSIONS
and thus a large amountof the 2.5-4.0 kbar peak pressurewas
accomplished
duringFa ductilethrusting.The onsetof rapidly
The dominant
mechanism
of lateCretaceous
crustalshortening
increasing
temperature
to upperamphibolite
faciesconditions
and in thePiuteMountainsinvolvednortheast
andsouthwest
directed
the growthof garnet,staurolite,andalusite,
andbiotiteoccurred ductilethrusting.Althoughtheshearzonesarebroadlyarranged
synchronous
with F2 folding [Fletcher,1989]. Temperature
es- into kinematic domainswith a prevailing sense of tectonic
timatesof 500•-530øCfrom garnetcorescorrespond
to theinitia- transport,
crustalshortening
on the scaleof the entirerangewas
RELATIVE
85
Ma
TIMING
74 Ma
72
Ma
I
I
I
,
I
FI ductilethrusting
F2 upright
I•egionalcooling
open
folding
and uplift
=........•.
•.....•.
:..::........=•...•.-..,..-.-......-..-...•..•.-:••...
• .:.•::..::::.`.::•:•:•:....=:•:•.....=:.::•....=•:•:•.
.•....:::...[.:.__......,
.._..•.
•
Deformation
i
I
i
EAST PIUTE
PLUTON
LAZY
DAISY
PLUTON
I
I
i
Plutonism
i
I
570
600
Thermal
History
and
Metamorphism
-
STAUROLITE
OUT.
-620
(GARNET
C
RIMS)
REACTION
500-530ø
C /?
500
(GARNET
CO
ES••.•
_•'R
: And
300'• C +-25 ø C
.300
.•_ (K-SPAR BLOCKING
V
TEMPERATURE)
Fig. 13. Relative timing of late Cretaceousorogeniceventsin the Piute Mountains. Note that the time scalebetween72 and 74 Ma has been
expanded
to showa four-eventsuccession
duringthisperiod:crystallization
of the Lazy Daisypluton,termination
of F• uprightopenfolding,peak
metamorphism,
and regionalcoolingand uplift (datafor figure in part after Foster et al., [1989].
FLETCHER AND KARLSTROM: LATE CRETACEOUSDUCTILE DEFORMATION, EASTERN MOJAVE DESERT
499
more homogeneousand contrastswith the stronglyanisotropic Boyer,S.E.,andD. Elliott,Thrustsystems,
Am.Assoc.of Pet. Geol.66,
shortening
seenin unidirectional
thrustbelts. The kinematics (9), 1196-1230.,
1982.
andstyleof compressional
deformation
werestrongly
influencedBrown,
H.,Discussion:
Correlation
ofmetamorphosed
Paleozoic
strata
of
by heterogeneities
in theProterozoic
basement
andby the thesoutheastern
Mojave
Desert
Region,
Califomia
and
Arizona,
Geol.
relatively
high-temperature
moderate-pressure
conditions
(about
Soc.
Am.
Bull.
95,p.1482-1485,
1984.
Brown, R.L., J.M. Journeay,L.S. Lanes,D.C. Murphy, and C.J. Rees,
450X2
and2.5-4.0
kbar)during
thrusting.
Themainfactor Obduction,
backfolding
and
piggyback
thrusting
inthemetamorphic
controlling
theductile
thrust
geometry,
besides
theexternal
stress hinterland
of thesoutheastern
Canadian
Cordillera.
J. Struct.
Geol.,
regime,wasthe variableinitialorientation
of contacts
between 17,(3/4),255-268,
1986.
Proterozoicplutons and less competentschistsand gneisses.Burchfiel,B.C., and G.A. Davis, Mojave and environs,in The
Development
of California,RubeyVolume1, editedby
This again contrastswith the primary control of a layered Geotectonic
EnglewoodCliffs, N.J., 1981.
stratigraphicsequenceon the geometryof thin-skinnedthrust W.G. Ernst,pp. 217-252,Prentice-HaH,
Burchfiel, B.C., and G.A. Davis, Mesozoic thrust faults and Cenozoic
belts.
As mentioned earlier, late Cretaceous ductile deformation,
metamorphism, and plutonism are found in the eastern
Cordilleran metamorphicbelt which extends throughoutthe
Sevier hinterland and into California, Arizona, and Sonora
low-anglenormalfaults,easternSpringMountains,Nevada,and Clark
Mountains Thrust Complex, California, in This Extended Land-
GeologicExcursions
in theSouthern
BasinandRange,editedby D.L.
Weide, and M.L. Faber, pp. 87-109, Spec. Pub. 2, Universityof
Nevada-LasVegas, 1988.
Mexico. This regionalcorrelation
of hinterland-style
tectonismCobbold,
P.R.,andH. Quinquis,
Development
of sheath
foldsin shear
may provide some importantinsightsinto the role of ductile
regimes,
J. Struct.Geol.2, 119-126,1979.
compression
on themechanics
andgenesis
of otherCordilleranDallmeyer,
R.D.,A.W.Snoke,
andE.H.McCee,
TheMesozoic-Cenozoic
tectonic
elements.
Thin-skinned
thrusting
in theforeland
fold tectonothermal
evolution
oftheRuby
Mountains,
East
Humbolt
Range,
Nevada:A Cordilleranmetamorphiccore complex,Tectonics,5, (6),
and thrustbelt is primarily restrictedto the late Proterozoicto
931-954, 1986.
Paleozoic miogeoclinal wedge and thus shortens only the DeWitt, E., Commenton "Geologicdevelopmentof Cordilleranmetamor-
uppermost
partof thecrust.Several
authors
havesuggested
that phiccore
complexes",
Geology,
8,6-17,1980.
deep-seated
thrusting
in the hinterland
is integrally
relatedto Dokka,
R.K.,Patterns
andmodes
of earlyMiocene
crustal
extension,
forelandthrusting.Many tectonicmodelsproposethe existence
CentralMojaveDesert,California,
Extensional
Tectonics
of theSouth-
of a basement
duplexor mastersolethrustthatrootsto thebase
western
UnitedStates,
edited
byMayer,L., Spec.Pap.Geol.Soc.Am.
of thecrustandcarries
thrusts
fromboththeexposed
hinterland 208,75-96,1986.
andforeland
in itshanging
wall[Brown
etal.,1986;
Milleret Fitzgibbon,
T.T.,Tectonic
significance
andcharacterisctics
ofmiddle
Proterozoicdiabasesheets,easternMojave DesertRegion,California
al., 1988a; 1988b]. In contrast,Mesozoiccrustalshorteningin
andArizona(abstract);
Geol.Soc.Am.Abstr.Programs,20, 160, 1988.
theeastern
Mojave
andsouthern
Arizona
occurs
ina single
belt Fletcher,
J.M.,
Late
Cretaceous
ductile
deformation,
metamorphism,
and
thatis apparently
unrelated
to thin-skinned
foreland
thrust
belt plutonism
in thePiuteMountains,
eastern
Mojave
Desert,
Master's
deformation.A geneticrelationshipbetweenforelandthrusting thesis,89 pp.,North.Ariz.Univ.,1989.
and hinterlandcrustal shorteningmay be commonbut is not Fletcher,
J.M.,K.E. Karlstrom,
T.E.Ring,J.E.Wooden,
andD.A. Foster,
ubiquitous.One cautionsuggested
by thisstudyis thatramp-
Tectonic
styleandtimingof deep-seated
Mesozoic
crustal
shortening:
fiat and duplexgeometries
for hinterland
deformation
(e.g., PiuteMountains,
eastern
Mojave
Desert
(abstract),
Geol.Soc.Am.
Boyer
andElliot,
1982;
Brown
etal.,1986;
Milleretal.,1988a, Abstr.
Programs,
20,A272-A273,
1988.
1988b)
areoversimplified
in areas
where
strong
preexisting
Foster,
D.A.,
M.T.
Harrison,
and
C.F.
Miller,
Age,
inheritance,
and
uplift
historyof the Old Woman-Piute
batholith,Californiaand implications
crustal
anisotropies
arepresent.
In these
areas,
asin thePiute forK-feldspar
agespectra,
J.Geol.
97,232-243,
1989.
Mountains,
tectonicblockswith wedgeand lozenge-shaped
Gans,
P.B.,J.Lee,E.L.Miller,M. Kunk,
andJ.F.Sutter,
Uplifthistory
geometriesmay predominate.
of mid-crustal
rocksin theeastern
GreatBasin(abstract),
Geol.Soc.
Am. Abstr.Programs,20, A17, 1988.
Glazner,A.F., J.M. Bartley,and J.D. Walker, Geologyof the Waterman
Acknowledgements.
The authors are grateful for fruitful
Hills detatchmentfault, Central Mojave Desert, California, in This
discussionswith other COWPIE investigators: Calvin Miller,
Extended Land - Geologic Excursions in the Southern Basin and
Tom Hoisch, David Foster, Mark Harrison, Tom Ring, Mike
Range,editedby D.L. WeideandM.L. Faber,Spec.Pub.2, University
of Nevada-LasVegas, 225-237, 1988.
Kelly, Jim Kingsbury,and Eric Bender. The manuscriptwas
improvedfollowinghelpfulreviewsfrom Keith Howardand Gleason,
J.D.,C.F. Miller,andJ.L. Wooden,
BarrelSpringalkalic
ClarkBurchfiel.Research
wasfacilitated
by a grantformthe complex:
1.4Gaanorogenic
plutonism
intheOldWoman-Piute
Range,
National ScienceFoundation(EAR-8609153) and fundingfrom
the NorthernArizona University OrganizedResearchFund.
easternMojave Desert, California (abstrac0, Geol. Soc. Am. Abstr.
Programs, 20, 164, 1988.
Hamilton,W., Tectonicseuingand somevariationswith depthof some
Cretaceousand Cenozoic structuraland magmaticsystemsof the
westernUnitedStates,in Metamorphism
and CrustalEvolutionof the
WesternUnitedStates,RubeyVolumeVII, editedby W.G. Earnst,pp
Allmendinger,R.W., and T.E. Jordon,Mesozoicevolution,hinterlandof
2-40, Prentice-liaR,EnglewoodCliffs, N.J., 1988.
the Sevierorogenicbelt, Geology, 9, 308-313, 1981..
Haxel, G.B., R.M. Tosdal,D.J. May, andJ.E. Wright, LatestCretaceous
Armstrong,R.L., and E.C. Hansen,Cordilleraninfrastructure
in the Great
andearlyTertiaryorogenesis
in south-central
Arizona:Thrustfaulting,
Basin, Am. J. Sci., 264, 112-127, 1966.
regionalmetamorphism,
and graniticplutonism,Geol. Soc.Am. Bull.,
Bell, T.H., Foliation developmentand refractionin metamorphicrocks:
95, 631-653, 1874.
Reactivationof earlier foliations and decrenulationdue to shifting Hileman, G.E., C.F Miller, and M.A. Knoll, Mid-Tertiary structural
patternsof deformationpartitioning,J. of Metamorph.Geol., 4, 421evolutionof the Old WomanMountainsArea: Implicationsfor crustal
R•CES
444,1986.
extension
across
southeastern
California,
J. Geophys.
Res.,thisissue
Bell,T.H.,MJ. Rubenach,
andP.D.Fleming,
Porphyroblast
nucleation,
Hobbs,
B.E.,W.D.Means,
andP.F.Willimas,
AnOutline
ofStructural
growthanddissolution
in regional
metamorphic
rocksas a function Geology,
571pp.,JohnWiley,NewYork,1976.
of deformation
partitioning
during
foliation
development,
J. Metamor-Hoisch,T.D., C.F. Miller, M.T. Hiezler,T.M. Harrison,and E.F.
ph.Geol.,
4, 37-67,1986.
Stoddard,
LateCretaceous
regional
metamorphism
in southeastern
Bender,
E.E.,andC.F.Miller,Petrology
of theFenner
gneiss,
a major Califomia,
in Metamorphism
andCrustal
Evolution
of theWestern
Proterozoic
metaplutonic
unitintheeastern
Mojave
Desert,
California United
States,
Rubey
Volume
VII,edited
byW.G.Ernst,
pp.538-571.
(abstract),
Geol.Soc.Am.Abstr.
Programs,
19,358,1987.
Prentice-Hall,
Englewood
Cliffs,N.J.,1988.
500
FLETCHER AND KARLSTROM: LATE CRETACEOUSDUCTILE DEFORMATION, EASTERN MOJAVE DESERT
Horinga,E.D., Ductile deformationassociated
with the Scanlonthrust Quinquis, H., C.L. Audren, J.P. Bmn, and P.R. Cobbold, Intense
in the Kilbeck Hills, southeastern
California (abstract),Geol. Soc.Am.
progressiveshearin 11ede Groix blueschistsand compatibilitywith
Abstr. Programs,19, 170, 1988.
subductionor obduction,Nature, 273, 43-45, 1978.
Howard, K.A., Miller, C.F., and P. Stone, Mesozoic thrustingin the Reynolds,S.J., J.E. Spencer,S.M. Richard,and S.E. Laubach,Mesozoic
easternMojaveDesert,Californai:Geol.Soc.Am.Abstr.Programs,12, stmcturesin west-centralArizona, in Geology and Ore Depositsof
112, 1980.
Arizona and the Southwest,editedby B. Beaty and P.A.K. Wilkinson,
Howard, K.A., B.E. John,and C.F. Miller, Metamorphiccorecomplexes, Ariz. Geol. Soc. Dig. 16, 35-51, 1986.
Mesozoic ductile thrusts, and Cenozoic detachments:Old Woman Reynolds,S.J., J.E. Spencer,Mesozoicstructuralevolutionof the Mafia
Mountains-Chemehuevi Mountains transect, California and Arizona,
fold and thrust belt, west-central Arizona and southeastCalifomia,
Ariz. Bur. Geol. and Min. Tech.,SpecialPaper 5, 365-382, 1987.
Geol. Soc.Am. Abstr.Programs,19, 818, 1987.
Huuon,D.H.W., 1988,Igneousemplacement
in a shearzonetermination:Reynolds,S.J., G.B. Haxel,•S.M. Richard,R.M. Tosdal, and S.E.
The biotite granite at Strontian,Scotland,Geol. Soc. Am. Bull, 100
1479-1492, 1988.
Laubach,Geologicseuing of Mesozoicand Cenozoicmetamorphism
in Arizona, in Metamorphismand Crustal Evolution of the Western
UnitedStates,RubeyVolumeVII, editedby W.G. Ernst,pp. 466-501,
Prentice-Hall,EnglewoodCliffs, N.J., 1988.
Jackson,J.L. and R.J. Burks,Significanceof crenulationcleavagein the
Area Mountains, southeastern
Califomia (abstract),Geol. Soc. Am.
Abstr. Programs 19, 391, 1987.
Richard,S.M., and J.R. Sutter,Structural
and•øArfnArchronology
of
Joumeay,J.M., Relic P-T regimesof the Monasheecomplex: A record Mesozoic deformation,HarquahalaMountains, west-centralArizona
of repeated imbrication and heat transfer, southeastOmineca belt
(abstract),Geol. Soc.Am. Abstr. Programs,19, 818, 1987.
(abstract),Geol. Soc. Am. Abstr. Programs20, A 19, 1988.
Ring, T.E., J.M. Fletcher,M.M. Kelly, and K.E. Karlstrom,Mesozoic
Kelly, M.M., Structuralstudiesin the Fenner Hills, Ship and Marble
cmstal shorteningby deep-seatedtectonicwedgingalong Proterozoic
mountains,eastemMojave Desert,Califomia, M.S. thesis,North. Ariz.
anisotropies,
Geol. Soc. Am. Abstr. Programs,20, 224, 1988.
Univ., Flagstaff, 1989.
Sevigny, J.H., E.D. Ghent, and P.S. Simony, PTt evolution of the
Lee, J., C. Huggins, E.L. Miller, P.B. Gans, and J.E. Wright,
northernMonasheeMountains,southernOminecacrystalinebelt, British
Polymetamorphismin the nonhem Snake Range, Nevada (abstract), Columbia(abstract),Geol. Soc.Am. Abstr.Programs,20, A19, 1988.
Geol. Soc. Am. Abstr. Programs,20, A17, 1988.
Simpson,C., Deformation of granitic rocks acrossthe brittle-ductile
Lister, G.S., and P.F. Williams, The partitioning of deformationin
transition,J. Struct. Geol., 7, 503-511, 1985.
flowing rock masses,Tectonophysics,
92, 1-33, 1982..
Smith,A.G., Subductionand coevalthrustbelts,with particularreference
Lobotka, T.C., Mesozoic thermal history of the Panamint Mountains, to North America, in Thrust and Nappe Tectonics,edited by K.R.
Death Valley area, California (abstract),Geol. Soc. Am. Abstr. McClay, and N.J. Price, Spec.Publ. 9, Geol. Soc. of London, 111Programs,20, A17, 1988.
124, 1981.
Lyle, J.H., Interrelationship
of Mesozoicthrustfaultingandmid-Tertiary Smith,D.L., and J.F. Wright, Late Cretaceous
plutonismand associated
detachmentfaultingin the RiversideMountainssoutheastem
Califomia,
deformationand metamorphismin central Nevada (abstract),Geol.
in Mesozoic-Cenozoic
TectonicEvolutionof theColoradoRiverRegion, Soc.Am. Abstr. Programs,20, A17-A18, 1988.
California-Arizona-Nevada,
editedby E.G. Frost,and D.L. Martin, pp. Snoke,A.W., and D.M. Miller, Metamorphicand tectonichistoryof the
470-491, CordilleranPub., San Diego, 1982.
northeastemGreat Basin, in Metamorphismand Crustal Evolution of
Miller, C.F., K.A. Howard, and T.D. Hoisch, Mesozoic thrusting, the WesternUnited States,Rubey VolumeVII, editedby W.G. Ernst,
metamorphism,and plutonism,Old Woman-PiuteRange,southeastem pp. 606-647, Prentice-Hall,EnglewoodCliffs, N.J., 1988.
California, in Mesozoic-Cenozoic
TectonicEvolutionof the Colorado Spencer,J.E., and S.J. Reynolds, InteractionbetweenMesozoic and
River Region, California-Arizona-Nevada,
edited by E.G. Frost and
Cenozoic tectonic features in the BuckskinMountainsand adjacent
D.L. Martin, pp. 561-581, CordilleranPub., San Diego, 1982
areas,west-centralArizona and southeastem
Califomia (abstract),Geol.
Miller, D.M., Structural geology of the northem Albion Mountains, Soc.Am. Abstr. Programs19, 852, 1987.
south-centralIdaho: in Cordilleran Metamorphic Core Complexes, Stone,P., K.A. Howard, and W. Hamilton, Correlationof Paleozoicstrata
edited by M.D. Criuenden,Jr., P.J. Coney, and G.H. Davis, Mem.
of southeastem
Mojave Desert region,Califomia and Arizona: Geol.
Geo. Soc. Am., 153, 399-423, 1980.
Soc. Am. Bull. 94, 1135-1147, 1983.
Miller,E.L~,P.B.Gans,J.E.Wright,andJ.F.Sutter,
Metamorphic
historySuppe,J., Geometry
andkinematics
of fault-bend
folding,Am.J. Sci.,
of the east-centralBasin and Range province:Tectonic settingand
283, 648-721, 1983.
relationshipto magmatism,in Metamorphismand Crustal Evolution Tullis, J., and S. Schmid, Short course on ductile deformation
mechanisms and microstinctures, Struct. Geol. Div., Geol. Soc. Am.,
of the WesternUnited States,Rubey VolumeVII, edited by W. G.
Ernst,pp. 649-682, Prentice-Hall,EnglewoodCliffs, N.J., 1988a.
Boulder, Colo., 1982.
Miller, E.L., P.B. Gans,andJ.F. Wright, Cretaceous
crustalstructureand Tullis, J., and R.A. Yund, Hydrolyric weakeningof the Westerlygranite
metamorphisrn,
hinterlandof the Sevier thrustbelt, Nevada (abstract), and Hale albite rock, J. of Struct.Geol. 4, 439-451, 1980.
Geol. Soc. Am. Abstr. Programs,20, A18, 1988b.
Wooden, J.L., D.M. Miller, and K.A. Howard, Early Proterozoic
Parrish,R.R., Compressionaland extensionalthermal evolutionof the
chronologyof the easternMojave Desert (abstract),Geol. Soc. Am.
Valhalla complex, Omineca belt, hinterlandof the Rockies, British
Abstr.Programs,20, 243, 1988.
Columbia (abstract),Geol. Soc.Am. Abstr. Programs20, A 19, 1988.
Price, R.A., The southeasternCanadian Cordillera: Thrust faulting,
J.M. FletcherandK.E. Karlstrom,Department
of Geology,Box 6030,
tectonicwedging,and delaminationof the lithosphere,
J. Struct.Geol.,
NorthernArizonaUniversity,Flagstaff,AZ 86011.
8, 239.254, 1986.
Price R.A., and E.W. Mountjoy, Geologicstructureof the Canadian
Rocky Mountains between Bow and AbathaskaRivers-A progress
report, Structureof the CanadianCordillera, edited by J.O. Wheeler,
Spec.Pap. Geol. Soc. Can., 6, 7-25, 1970.
(Received March 8, 1989;
revised October 9, 1989;
acceptedOctober9, 1989.)