The document provides a detailed description of the lithological units and their structural relationships in an area within the Shulaps ultramafic-ophiolitic complex in southwestern British Columbia. The area studied contains four main lithotectonic units that are in thrust contact with one another: 1) A basal mantle peridotite suite exposed in the north, 2) An overlying Shulaps ophiolitic melange occupying the central and southern parts, 3) An East Liza igneous suite of mafic rocks in the southwest, and 4) Sedimentary rocks of the Cadwallader Group in the west. The melange contains blocks of gabbro, pyroxenite and sedimentary/volcan

1. KEYWORDS: Regional geology, Shulapscomplex, ultra-
mafic, peridotite, ophiolite, serpentinite mtlange, Bridge
River Terrane, Cddwallader Group, East Lira igneous suite,
Yalakom fault.
INTRODUCTION
mountains of the Shulaps Range,within theQaughton Creek
The Shulaps ultramafichafic complex is exposed in the
map area(Schiarizza et al., 1989) approximately SO kilo-
metres northwestofLillooet in the Cordilleraofsouthwestern
British Columbia (Figure 3-4-1). It forms one of the largest
bodies of ultramafic rocksin the orogenic belt, underlyingan
area of approximately 180square kilometres.The complex is
superterranes (Mongeret al., 19821, which is marked in the
situated along the boundary of the Intermontane and Insular
evolution have important bearing on unravelling the tectonic
area by the Yalakom fault system. Its origin and structural
THE ANATOMY OF THE SHULAPSOPHIOLITE
By T.J. Calon, J.G. Malpas and R. McDonald
Memorial University of Newfoundland
collage of suspect terrane:: that form this part of the Cordillera
(Price ef al., 1985; Potter, 1986; Rusmore, 1987).
The Shulapscomplex was first mapped in detailby Leech
(1953). whoconcluded that the peridotites were part ola non-
stratiform plutonic complexthat was later intrudedby maller
lenses of gabbroandpyroxenite.Morerecently, Nagel
origin forthe peridotitecomplex, interpreting it as a residual
(1979) andWright et al. (1982)have suggested an oph olitic
mantle tectonite section. These workers established that the
western basalcontact of thecomplex is a serpentinite
mtlange containingexoticblocks of sedimentaryand vol-
canic rocks.Theserocksare tentativelycorrelated with
which structurally underlies the mtlange. The mtlangc: alsc
supracrustalrocks in the oceanic BridgeRiver ' E wanane,
contains blocksof ultram;ific and mafic plutonicrocks which
mayrepresent fragment!; of Layer 3 of the Bridge Rive1
Oceanic crust. Leech (1953). Nagel (1979) and Wright efal.
(1982) have suggested that stratigraphic relationships exisl

2. Figure 3-4-2. Schematic geological map of the study area, with legend.
between gabbroic andvolcanicrockswithinblocks in the
melange, implyingthatthebasal melange of the Shulaps
complex may represent the highlydismembered remnantsof
Triassic sedimentary apron (Hurley Formation) of the Cad-
a more or less complete ophiolitic suite. A segment of a
wallader volcanic arc assemblage (Rusmore, 1987)lies with
fault contactdirectly to the west of the Shulaps complex.
According to Rusmore(1987) and Potter(1986). the more or
lesscontemporaneousCadwallader arcand Bridge River
ocean basin becamejuxtaposedduring movement on the
Shulaps sole thrust. Since thisthrust has an overall westerly
vergence (Potter, 1986). the arc restorespalinspastically to
the west of the basin. TheBridge River ophiolitic assemblage
may thus have developed in relation to hack-arc spreading
(Potter, 1986).
To date, no modem accountexists of the petrogenesis and
structuralevolution of the mantleperidotite section of the
Shulaps complexandtheunderlyingophiolitic melange.
376
Further, the stratigraphic and structural relationships of the
wallader Terrane and the Shulaps complex remain obscure.
BridgeRiverTerrane,theadjacentfault-boundedCad-
This study was undertaken primarilyto establishthe tectonic
andplutonicevolutionandpetrogenesis of the Shulaps
ophiolite complexandits Mesozoic accretionaryhistory.
Detailed geological mapping on scalesranging from 1:6000
to 1:14 000 was carried out in a two-week period in summer
anarea of approximately 20 squarekilometres centred
1988 anda four-week period in thesummer of 1989,covering
around the upper courses of Jim Creek and East Liza Creek,
along the southwestern edge of the Shulaps complex (Figure
3-4-2).Thisareacomprisesthecriticaltransitionfrom
coherentthrustssheets of residualmantleperidotite of the
Shulaps complex to underlying ophiolitic mClange. It con-
tains the hulk of the exotic blocksof gabbro and pyroxenite in
the melange, together with less abundant smaller blocks of
volcanic and sedimentary rocks. In addition, on the western
British Columbia Geological Survey Branch

3. CADWALLADER GROUP
rnHurley Formation. Sondstones--eholsr: c o l ~ a r e o mshale with
limestone lenma: minor chert. conglamerats ond limeatone brecsio
EAST LIZA IGNEOUS SUITE
~ D I P Y E andpillared mofic metovolcanic rocks
SHULAPS OPHlOLITlC MELANGE. BLOCKS
SHULAPS OPHlOLITlC MELANGE, MAlRIX
La
a
ssrpentinite derivsd from dunite-uahrlite cumulates: with
more coherent ultramafic cumulateblocks
serpentinite derived from Shuloprperidotitesuite:with
mole coherent peridotite tectanite blocks
SHULAPS PERIDOTITE SUITE
Honburgitetectonite: minor dunite and ortbopyroxenits:
*Nth tronsorareive dunite bodies
rocks of theHurley Formation in theCadwalladerGroup.
side it covers a small segmentof the contactwith sedimentary
This reportprovides a detailed descriptionof the lithological
units and their structural relationships in this study area.I
LITHOTECTONIC SUBDIVISION
subdivided into four main lithotectonic units (Figure 3-4-2).
Themap units in the study area may be conveniently
which are in thrust contact with one another and display the
following stacking order, from structural top to bottom:
(I) The Shulapsperidotite suite, exposed in the northernpart
of the study area (Unit I).
(2) The Shulapsophiolitic mtlangc, which is exposed along
thesouthwesternmargin of the peridotitesuiteand
occupies the central and southern part of the map area
(Units 2 to 7);
(3) The East Lira igneous suite of mafic plutonic and vol-
canic rocks, exposedinthesouthwestern part of the
study area (Units 8 and 9);
Geological Fieldwork 1989, Paper 1990.1
(4) The Cadwallader Group, which comprises sedimentary
rocks of the Hurley Formation and is exposed on the west
flank of the Shulaps complex and East Liza suite (Unit
10).
Together, these four units comprise a complicated.. poly-
phase, southwesterly verging, linkedthrust system, whsch at
transtensional high-angle fault system.
a later stage became overprinted on its western flank by a
The Shulapsperidotite wite occupiesthe upperp"rt cNf the
thrust system. It extends far to thenorth andeast of the study
ShulapsRange. Work by Leech (1953:' and Wright et al.
area (Figure 3-4-1) and underlies the highest peaks within the
tinized, layered harzburgi1.etectonites with locally abundant
(1982) suggests that it consists entirely of variably ssrpen-
dunite bodies. Preliminary field observations suggestthat the
upper thrust unit of mantle peridotite coinsists of a shingled
array of moderately northeast-dipping thrust sheets of more
or lesscoherentperidotite,separated from one another by
shear zones consistingof intensely foliated serpentinite.The
unit has beeninterpreted by Wright e!' al. (1982) a,; an
obducted fragment of depleted oceanic upper mantle.
trending belt. up to 5 kilometres wide,along the s,outh-
TheShulaps ophiolitic mtlange occurs ina northwest
western edge of theShuiaps peridotitesuite. It is spec-
tacularly exposed along the southwesternslopes of the
Shulaps Range. To thenorthwest, it terminatesabruptly
against a high-anglefault system which marks theboumlary
between the Shulaps complex and a fragment of the Cad-
Hog Creek imbricatezone delineated by Potter (1983). The
wallader Terrane. To the southeast, the belt extends in1.o the
peridotitesuite with amoderatelynortheast-dipping s t w -
mklange underlies the imbricatethrust system of the Shulaps
overlies, with gently east-dipping thrust ,contact, metasedi-
tural contact. Potter (1983,1986) hasshown that the belt
directly southeast of the studyarea. Theb'eltthus constitutes
mentary and metavolcanic unitsof the BridgeRiver complex
zone between an upper Flate consisting of atelescoped
a partlyexhumed duplex structure that del7nes the bounc.ary
section of oceanic upper mantle peridotite anda lower plate of
telescoped oceanic supracnlstal sequence!;.
Internally, the mtlangebelt comprisesanumber of smaller
duplexes which form an extension of the Hog Creek imbri-
cate zone.Theseduplexes may be subdivided in terms of both
theprotolithtypes of theserpentinites that make up the
voluminous matrix of the mtlange belt, and the igneous :md
sedimentary lithologiesthat occur as abundant blockswithin
theserpentinitematrix. The matrix of the milange is sJb-
dividedin two northwest-trendingbelts which maintai.~a
consistent structural position in the thrust system, The ser-
pentinitematrix of the upper belt is derivedfrom low-
ingmantle peridotite suite, whereastheprotoliths ofthe
temperature alteration of protoliths found only in the ovmly-
lower belt comprisea suit" of ultramaficcumulate mcks
including dunite, wehrlite and clinopyroxenite. Within each
belt these protoliths arelocallypreserved in more or 18:ss
coherent blocks envelopedby intensely sheared serpentinite.
The ultramafic cumulate prololithsalsooccur at the bases of
two gabbroic blocks within the ultramafic cumulate-derived
serpentinite belt.
377

4. coherent sections of gabbroic to dioritic dikes which locally
Both melange beltscontain abundant boudinsandmore
preservechilledmarginsand contact aureoles of porphy-
Nagel, 1979). However, a clear distinction can be made
roblasticolivine-talc-serpentineschists(Leech,1953;
between the two belts as regards the occurrences of blocks
representing dismembered ultramafic-mafic plutoniccom-
plexes, as well as blocks of sedimentary and volcanic rocks.
The mantle-peridotite-derived serpentinite melange doesnot
appear to contain any such blocks in the area studied. The
most extensive belt of plutonic blocks is situateddirectly
beneaththebasalmantle-peridotite-derivedserpentinite
shear zoneandpreservesthethickestcoherent section of
of plutoniccomplexessituatedstructurallylower in the
ultramafic cumulates observed in the area. Moreover, blocks
ultramafic-cumulate-derived serpentinite melange comprise
generally only higher level gabbroic sectionsof the plutonic
distributedthroughoutthelowerserpentinite belt, but are
complexes. Sedimentary and volcanic blocks are irregularly
particularly prominent in number and size directly beneath
the main belt of plutonic blocks.
The EastLiza igneous suite forms a separate thrust unitof
limited extent in the southwestern part of the map area. It is
pentinite mklange, and overlies intensely folded units of the
structurally overlain by the ultramafic-cumulate-derived ser-
Hurley Formation with markedthrust contact. Inthe south it
comprises gabbroswhich in all field aspects resemble those
of the main gabbro blockswithin the mClange. To the north,
the gabbrosappeartobe in nonconformable stratigraphic
contact with overlyingvolcanic rocks inapoorlyexposed
area dominated by abundant outcropsof dikes with screensof
volcanics. The unit is equivalent to the greenstone-gabbro
complex of Leech (1953).
Sedimentary rocks of the Late Triassic Hurley Formation
of the CadwalladerGroup occupy the western part of the map
area. They comprisean upward-fining sequence of siliciclas-
tic turbidites including some volcaniclastic rocks, associated
limestone brecciaandbedded chert. In the northwest, the
unit is in abrupt, high-anglefault contact withablock of
occurs in anumber of half windows beneath the melangeand
gabbro withintheserpentinite melange. Farther south, it
Hurleylithologies also occur as exoticblockswithin the
the volcanic rocks of the East Liza suite. Rocks resembling
serpentinite mClange.
LITHOLOGY AND STRUCTUREOF
MAP UNITS
SHULAPSPERIDOTITE SUITE(UNIT1)
TheShulaps peridotitesuite comprisesthe bulk of the
ultramafic rocks in the Shulaps complex asdefined by
previousworkers (e.&, Leech, 1953; Wright er al., 1982),
rocks form part of a coherent basal thrust sheet of mantle
and is exposed in the northern part of the study area.The
peridotite that strikes northwest, dips 40" to the northeast,
and is approximately 300metres thick. The sheetis bounded
at its top and bottom by serpentinite shear zones up to 500
metres thick. The boundaries are sharp structural contacts
378
which are parallel to schistosity in the serpentinite matrix of
the shear zones.
Lithologieswithintheperidotitesheet are dominantly
dunite and orthopyroxenite.Compositionallayering is
layeredand massive, foliatedharzburgitewithsubordinate
defined on centimetre to metre scale by modal variations in
the orthopyroxenecontent of the harzburgite, and by parallel
phaseboundariesbetweenharzburgite,duniteand
orthopyroxenite. Numerousirregularly shaped pods of dun-
ranging from less than a metre to several tens of metres in
ite occur withinthe peridotite.Theyare variable in size,
diameter. The dunites cutacross the peridotite tectonitefabric
in an irregular mannerand the margins of the bodies appear
chromite and thin chromite stringers with variable orienta-
undeformed.Most bodiescontain abundant disseminated
and are generally euhedral.
tions. The chromite grains range up to I centimeue in size
A penetrativemineralfoliationandlineation, which in
mostlocalities is parallel to thecompositional layering, is
definedby a weak to moderatepreferredorientation of
observed in the harzburgite. Foliation andlineation are
orthopyroxene and spinel grains varying in size from1 to 15
millimetres. The linearaspect of the fabric is outlined by
chromitepull-aparttextures.The texture of theperidotite
tectonites can he classified as protogranular to mildly por-
phyroclastic. Mesoscopic folds of layering with associated
axial planar foliation have not been observed. Layering and
parallelfoliation have rather constant orientation, dipping
steeply to thenorth-northeast or south-southwest. Mineral
elongationlineations are subverticalinthefoliation plane.
Accordingtodatafrom Leech (1953) and Wright et al.
(1982). the regional attitude of layering and foliation in the
Shulaps complex asa whole is similar tothat observed in the
study area, with steep southwesterly dipspredominating.
The attitude of the planar fabricsis markedly oblique tothe
fabric of the serpentinite shearzones in whichthe main
serpentine foliation has a moderate northeasterly dip.
MANTLE-PERIDOTITE-DERIVED SERPENTINITE
M~LANGE(UNIT2)
The unit forms a zone 300 to 500metres thickthat dips, on
the basal thrustsheet of the mantle peridotitesuite. It
average, at an angle of40" to the north andnortheast, beneath
form the steep cliffs in the western part of the map area.
structurallyoverliesthe belt of large gabbro blocks which
Farther to the east, the unit directly overlies the ultramafic-
cumulate-derived serpentinite belt (Unit 3) on the upper the
upper slope of Shulaps Peak. Where theintervening main
gabbro-block level is missing, the contact between the two
serpentinitebelts may be difficult to identify. However,
suitable outcrops of matrixrockswhich show transitional
stages of alteration of the different protoliths are readily
available on both sides of the contact in most areas.
The main structural grainof the belt is definedby a braided
network of narrow zones containing an intensely schistose
form of fibrous serpentine slickensides, for reverse dip slip
scalyserpentine fabric showing abundant evidence, in the
and oblique slip. Locallytheseserpentinite strands have a
British Columbia Geological SurveyBranch

5. myloniticaspectcontainingwell-developedC-Sfabrics
which invariably indicate southwest-directed thrusting. This
fabric is referred toas the secondgenerationserpentine
constitutes the younger component of a composite serpen-
schistosity (S,) in the legend of the geological map. It
tinite fabric that can be observed in lozenge-shaped serpen-
tinite blocks surrounded by the S, serpentine zones. Within
such blocks an older schistosity (S,) is generally inclinedat a
high angle to the main serpentinite shear zonefabricand
bends gradually or abruptly into the late fabricat the edges of
the blocks. Locally the first generation serpentine schistosity
has itself the appearance of a fine scale C-S fabric.
ULTRAMAFIC-CUMULATE-DERIVED
SERPENTINITE MELANGE(UNIT3)
eastem andsouthern parts of the map area. It extends
This component of the mtlange occupiesmost of the
eastwards into the Hog Creek imbricate zone delineated by
Potter (1983).Previous workershave tacitly assumed that the
serpentinitematrix of the mklanpe, as a whole, was derived
however, has revealed that this is only true forthe upper part
from the overlying mantle peridotitesuite. Thepresent study,
entirely of serpentinite derived from ultramafic cumulates.
of the mklange (Unit 2). The matrix of the lower part consists
The main lithologies that acted as protoliths are wehrlite and
dunite, with lesserclinopyroxenite. Theprotolith types of the
cumulates found as coherent sequences at the bases of two
serpentinite matrix are identical,in all aspects, toultramafic
large blocks comprising segments of an ultramafic to gab-
broic plutonic complex (Units4 and 5 , see following section
for description).
derived serpentinite mtlange is that of a huge duplex, sand-
The macroscopic structure of the ultramafic-cumulate-
wiched between the overlying thrust system of themantle
peridotite suite and the underlying thrust system of variably
deformedandmetamorphosedsupracrustal rocks of the
the thrust stack of the East Liza suiteand Hurley Formation in
Bridge River complex in the east (Potter, 1983, 1986). and
the west. The belt reaches a structural thickness of approx-
of smaller, flat-roofed, hinterland-dipping duplex structures
imately I kilometre in the eastern partof the area. A number
have been mappedwithin the belt (Figure 3-4-2). These
blocks of theultramafic-gabbroicplutoniccomplex which
duplexes are focused on shingled stacks of large and smaller
are situated on at least three different structurallevels within
the belt. The roof and floor thrust zones of the duplexes are
outlined by gently to moderately north to northeast-dipping
zones of intensely schistose scaly serpentinite(S,), similar in
styleandorientationpatterns to the second generation ser-
pentinite shearzones observed in the overlyingmantle-
peridotite-derived mtlange belt.Within the duplexes, the
first generationserpentineschistositygenerally dipsmore
boundaries. This schistosity often wraps aroundthe lozenge-
steeply to the north or northeast and curves into the duplex
the appearance that originally much larger coherent sections
shaped plutonic blocks contained in the duplexes, creating
of the plutonic complex were telescoped along shear zones
injected by serpentinite. The Sz serpentinitestrands com-
Geological Fieldwork 1989,Paper 1990.1
monly display C-S mylonite fabrics, particularly in contacit
tors invariably provide e>idence forsouthwesterly thrusting.
zones with larger blocksin the mClange Shear-sense indica-.
The volcanic and sedimentary blocksare all contained within
S, serpentinite strandsanti are consistently aligned with their
longest dimensions parallel to the S, fabric.
flatlying in the southwestern and southeastern parts of the
The overall attitude of the duplex structures is remarkably
belt but steepens to northerly and northeasterlydips o f .10" tcs
50"at the contact with the overlying mantle peridotite thrusl
system (Figure 3-4-2).Most of this change in attitude !,eems
focused on themain beltof plutonic block situated ahngthis
contact,and it appears as if these big blocks acted as a
footwall ramp tothe overlying thrust system.A similar ramp
structure,outlined by flat andsteepS, belts in the floorhrust
zone ofthe melange,iscreated by the underlyingthru!;t stack
of East Liza suite andHuirley Formation, exposed in th,: half
window in the western part of the area (Figure 3-4-2). In the
south, themain S, fabric dips gently to moderately lo the
reaches ofJim Creek.Thi:i structure may mark thelocat on of
south, creatingabroadantiformalzonealong the upper
a blind culmination in the footwall of the mklange, which is
possibly an easterly extension of the EastLiza suite-Hnrley
Formation thrust stack.
BLOCKSOF ULTRAMAFIC-MAFFC
PLUTONIC COMPLEXES
A number of large and small coherent blocks inthe lower
serpentinite belt representdismemberedsections of aplu-
tonic complex (Plate 3-4-Ij. They include a large variety of
lates to high-level, varitextured plagioclase-richgabbros.
intrusive rocks ranging from olivine-rich ultramafic c m u -
They display complex multiple intrusive relationship!<aften
involving a number of igneous phases, and they exhibit, at
Plate 3-4-1. Viewto th,: northwest of the eastem edge OF
the main gabbro blockin the mklange. Lower half of section
in block comprises recessively weathering sicreensof massixe
andlayeredultramaficcumulates belwem moreresistant
dikes. Upper half of section comprises screens ofa variety of
gabbro types betweendikss. The contact between uluama.fic
thephotograph.Thegabbroictodioriticdikeswarmdips
and gabbroic rwks lies alongthe thick dike seen in centre of
moderately to steeply northeast and shows complex internal
geometry (resistant dikes In centre of photograph).
379

6. leastlocally,evidence for heterogeneoushigh-temperature zones. fault-houndedultramaficcumulateenclaves in gab-
plasticdeformationassociated with intrusive events. broic sequences, and lateintrusive dike swarms(Plate 3-4-2).
The scale of these features is generallv small. on averaee 10
ULTRAMAFIC CUMULATES
,,,x,,w "i
c
to 50 metres of outcrop width. They suggest that the gabbro
complexes did not evolvethroughcrystallization in large
-.
,L'l.l. -., magmachambers of simple geometrical form, hut rather
The ultramafic cumulates aremainly found in twoblocks, throughspatiallyandtemporallyhighlyvariablemultiple
where they form thepresentstructural base of theplutonicintrusive orocesses.
is in the large block in the centre of the belt. This sequence
sequences-(Figure3-4-2). Their most important occurrence
reaches a total thickness of at least 200 metres and extends
along strike for at least 500 metres. It comprises dominantly
wehrliteandclinopyroxenite, with subordinatechro-
mitiferousdunite,clinopyroxene-bearingdunite,olivine
clinopyroxenite and rare olivine websterite. Plagioclasemay
enites. Thesuite was previously described asthe clinopyrox-
be present, in a highly altered state, in some of the pyrox-
enite unit by Leech (1953) and Nagel (1979). Both authors
clearlyunderestimatedthe total averagemodalamount of
olivine in the suite in favour of clinopyroxene.
clinopyroxeniteandrarewebrterite to two-pyroxene gah-
Compositionally,thegabbroicsuiterangesfrom
bros,clinopyroxene-richgabbrosandanorthosite.
ents, whereas olivine and orthopyroxene are relatively rare.
Clinopyroxeneandplagioclase are the dominant constitu-
Undeformedgabbrosrangetexturallyfrommassiveto
layered, and isotropic to foliated.Medium to coarse-grained
pegmatiticvarieties, especially leucogabbros, are common
in the form of small stocks and irregularly shaped pods and
veins. High-level.varitextured gabbros are thedominant
component in most of the blocks in the mClange belt. They
constitute the top sections of the large plutonic blocks and
The present base of the suite is poorly exposed, but appears form the only constituent of the remaking blocks. Fine scale
to he instructural contactwithunderlyingserpentinite with acompositional layering, occasionally with grain-sizegraded
moderatelynortheast-dipping S2 fabric. In the eastern out-or phase-graded aspect (Plate 3-4-31,is common in a number
crop area of the block, the top of the unit is defined by a 20-
metre-thick, little-deformeddiontedikewith well-developed
layered gabbros. Internally, theultramaficsuite contains a
chilled margins. This dike is immediately overlain by thinly
number of small, fault-bounded enclaves of layered gabbro.
It is also cut by a narrowly spaced diabase dike swarm that
dips on average 55"north-northeast. The ultramafic cumu-
lates thus occuras narrow screens between the late dikes
(Plate 3-4-1).
block is highly variable. The rocks are generallypoorly
The plutonic geometry of the ultramafic suite in the main
layered to massive, and have isotropic texture with anhedral
olivine shapesand randomly orientated stubbydiopside
prisms predominating. Where phase layering is observed, it
is usuallynonplanarand highly discontinuous over short
distances. Layeringattitudesareextremelyvariable from
screen to screenin thedike swarm. Itis not clear whether this
is an original plutonic feature, or an imposed feature due to
defined cyclic sequencesof phase-graded units with a basal
rotation caused by dike intrusion. The suite comprises poorly
clinopyroxene-bearingdunite layer, grading intoathick
wehrlitelayerfollowed by athickolivineclinopyroxenite
bodies within clinopyroxene-rich phases. Poikilitic textures
layer. Olivine-rich phases often occur as irregular, pod-like
of clinopyroxene with olivine andchromite inclusions occur
occasionally in wehrlitic phases. In most rocks clinopyrox-
ene appears to bethe main adcumulus phase.
GABBROIC SEQUENCES(UNIT 5)
The gabbroic sequences constitutethemost voluminous
component of theplutonic blocks inthe melange,as was
blocks complex intrusive relationships between various gah-
alreadynoted by Leech (1953) and Nagel (1979). In all
Plate 3-4-2.Typical appearance of high-level, varitextured
broic phases are indicated by crosscuttingphase domains,
xenolith-charged margins of lateintrusive stocks, S~NC-
gahhro. It comprisessheared and isotropic gabbro, cross-
cutting pegmatitic leucogabbro veins and, behind the ham-
turallycontrolledphaseboundariesincludingfaults and shear mer. a late isotropicdiabase dike.
380 British ColumbiaGeological Survey Branch

7. of localities. The layering displays highly variable attitudes,
even within small areas of a singleblock.Domains of
constant layer attitudeare invariably bounded by crosscutting
varitextured suites, by discrete dlkes of variable width, or by
shear znnesand faults.
Domains of penetrativeplasticdeformationare rare in
contain a well-developed schistosity (subparallelto layering,
most of the blocks. Locally. layered and massivegabbros
where present)and mineral elongation lineation.These rocks
recrystallizedrims of green hornblende, suggesting that
have a porphyroclastic texture of coarse clinopyroxene with
deformationoccurredunderamphibolitefacies conditions.
The deformedgabbros arecon~monly cut by pegmatitic
leucogabbro bodiesanda variety of gabbroic to dioritic
dikes. Narrow,low-temperatureshear Loneb, characterized
blocks and they are generally located alongmacroscopic
by chloritealteration, arecommon throughoutthegabbro
phase contacts. The shear zonesare truncated by younger
intrusive rocks, indicating that they developedduring the
magmatic evolution of the gabbroic complexes
regional strike of the belt Smaller blocks, up to 10mmelres i n
size, have a more rounded shape, and may lie inclined to the
S, serpentinite fabric. Thelargest concentration of blocks is:
in a mylonitic serpentinite zonesituated directly beneath the
large plutonic blocks near the top of the belt, in the c-nual
and western part of the map area.Another conspicuou:;itring
of larger blockslies lowerin the belt inthe easternmost part01
the area, and appears to extend into the Hog Creek imbricate
zone to the east.
The sedimentary blocks (Unit 7) comprise mainly bedded
andmassive chert, and thin to medium-beddedturbiditic
siltstone and sandstone. In one block, bedded chert iis inter-
layered with a unit of stronglysilicifiedand minerdired
volcanicrocks I O mBtresthick.Smallblocks of
recrystallizedlimestone,limestonebreccia,and o e r t y
matrix-supported pebble cconglomerate with abundant :elsic
igneous clasts arerare. One small block of coarse pyroclastic
rock was found in JimCreek near a Mock containirg an
upward-facing 20-metre r,equence of pyritiferous Iminated
shale-siltstone, white bedded chert with shale partings, and
massivegreywackewithsiltstonerip-upclasts.This
sequence appears correlative with a more extensive unit of
siliciclasticrocks withinterbedded chert and rarevol-
caniclastic rockswhich is exposed on the lower slopes vest of
Plate 3-4-3. Fine-scale, phase-graded layeringin gabbro-
anorthositesequencewhichform!.anisolatedplutonic unit
within theeaslernpar1of the main gabbrohlock. This gabbro
xenolith of ultramafic ~ ~ n ~ u l a t r sshown on the right-hand
sequence is in fault-controlled. intmsive contactwith a large
side of the photograph. The resistant dark-weatheringunit
above the layered gabbro is a crosscutting diorite dike with
chilled marsins against gabbro.
BLOCKSOF SEDIMENTARYAND VOLCANIC
ROCKS(UNIT 6 AND 7)
tains a numberof blocks (approximately 30)of sedimentary,
The ultramafic-cumulate-derivedserpentinite belt con-
volcanicandvolcaniclasticrocks in thestudy area. Such
blocks have also been reported by Potter (19x3)from the Hog
Creek imbricate zone.Whereas theplutonic blocks in the
thebelt, the blocks of supracrustalrocksrepresent a truly
serpentinite can reasonably be considered as indigenous to
exotic element, justifyingthe use of the term milange.
dimension rarely exceeding 200 metres. Larger blocks tend
Most blocks are rather small in !size, their longest outcrop
Plate 3-4-4. Detail of highly schistose, thinly layeral
to be tabular in shape with tapered edges. Theyaregenerally quartz phyllite, cut by brecciatedquart2dioritedike in
aligned parallel to the S2 fabric in thesurroundingserpen-
tinites. with their longest dimensiontrending parallel to the
sedimentary knocker within the serpentinite melange in thc
easternmost partof the study area.
Geological Fiddwork 1989, Riper 1990.1 ,381

8. Jim Creek (Schiarizza et al., 1989). The large block in the
southeastern part of themapareacontains an intensely
foliated sequence of thinlylayeredpelites cut by small
yry (Plate 3-4-4) that do not extend into the adjacent serpen-
brecciated pods and dikes of hornblende plagioclaseporph-
tinite matrix (see also Archibald et al., 1989). Most blocks
show effectsof lowergreenschist facies metamorphismasso-
ciated with deformation in theform of cleavage development
and, locally, mesoscopic cleavage folding.
Volcanic blocks (Unit6 )are less abundant than sedimen-
tary blocks. They comprise massive and pillowed lava and
pillow breccia. In some localities, the lavas show variolitic
and/or vesicular texture; some contain feldspar phenocrysts
and chlorite pseudomorphs presumably after primary pyrox-
ene or amphibole. Pillow breccias locally contain lenses of
chert and limestone brecciaup to several metres in size. The
volcanic rocksappeartorangefrom basaltic to daciticin
composition. They are generallystronglyaltered dueto
silicification and low greenschist facies metamorphism, and
pillowsandcleavagedevelopmentinthe matrix of pillow
show heterogeneous deformation in theform of flattening of
breccias.
DIKESIN SERPENTINITE MELANGE
Numerous disrupted fragments of dikes occurwithin both
types of serpentinite belts. They rangein composition from
an abundant componentof the dike suite. Somelarge dikes in
gabbroic to dioritic;hornblende-porphyritic quartz dioriteis
the eastern partof the area aremultiple intrusive, ranging in
compositionfrom pyroxenite to gabbro and flow-banded,
feldspar-porphyritic diorite (Plate 3-4-5).Manygabbroic
dikes are strongly altered to either rodingite. greenschist or
talc schist. Ontheotherhand,manydioriticdikes are
remarkablyfreshandpreservewell-developedchilled
margins.
The dike fragmentsdisplay a variety of shapes reflecting
the degree of their deformation andrelated alteration. They
rangefromsmalltolarge,rounded or lozenge-shaped
boudinsto ratherstraightand continuousdikesegments,
some of which extend upto 100metres along strike.Boudins
are completely surrounded by foliated serpentinite and are
aligned parallelto eitherS, or S, as the main externalfabric.
They often occur in clusters with conspicuous parallel or en
echelonalignmentintheserpentinitefabric,reflecting
boudinagedsingledikesoriginallyorientedparallel or
oblique to the external fabric, respectively. Some clusters,
however, are so dense that they must have resulted from
boudinage of parallel dike swarms. Straight dike fragments
ofthedioriticsuitegenerallypreservechilledmarginsagainst
either the S, or S, fabric of theserpentinite matrix. Their
grained chill zonesoften show foliation development related
contactsare, however, invariably sheared, andthefine-
to postintrusion deformation of the serpentinite matrix. The
field relationships indicate that bothpre-SI and post-S, dike
define both early andlate dike suites, whereasdioritic dikes
suites arepresent in themelange (seebelow). Gabbroic dikes
almost all post-SI.Dikes in the mantle-peridotite-derived
(particularlythose with preservedchilledmargins)are
Occurrences in the ultramafic-cumulate-derived serpentinite
serpentinite beltare relatively rarecompared to the abundant
382
part of the serpentinite melange. Flow-bandedquartz diorite
Plate 3-4-5.Detail of composite dike fragmentin eastern
dike, withfeldsparphenocrystalignment, is intrusive into
sheared and altered isotropic gabbro.
belt. They are dominantly part of thelate dioriticsuite
contacts of the belt.
intruded along S , shearzones neartheupperandlower
Late dikes have locallyimprinted contactmetamorphic
effects on the surrounding serpentinite. The most common
tine? talc, andolivine +talc tmagnesite. The rockshave a
contactmetamorphicassemblagesareolivine +serpen-
porphyroblastic textureof elongate olivine crystalsin a white
felted matrix. The porphyrohlasts are often pseudomorphed
by fine-grained, brown-weathering magnesite +talc aggre-
gates. These rocks were first recognizedby Leech (1953) and
later studied in some detail by Nagel (1979), who correctly
suggested that the olivine schists formed by prograde meta-
concludedthattheolivine was generated at temperatures
morphism of originallylow-temperatureserpentinite. He
around 400°C. but ignored the effectsof Xco,. This is prob-
ably erroneous in view of the common occurrenceof magne-
temperature range for the stability of olivine in the contact
site in the assemblage; high Xco, would slightly lower the
aureoles. Nagelinferred a magmatic source for the heat that
causedthestatic metamorphism, hut did not link theheat
The present study has shown that some contact aureoles are
source directly to the abundant dike suites in the mklange.
British Columbia Geological Survey Branch

9. still attached to the dike walls. whereasothers have been
detached from the dikes by later shearing that led to the
development of the Sz serpentine schistosity. The latest
thus interpreted to he syn-S,.
widespread dike intrusion event recorded in the melange is
EASTLIZAIGNEOUS SUITE (UNITS 8 AND 9)
The suite is treated as aseparatelithotectonic unit, in
contrast to the interpretation of Nagel (1979) who considered
thrust contact by ultramafic-cumulate-derivedserpentinites
it to be a block in the serpentinite. It is overlain with clear
along its eastern and southernmargins(Plate 3-4-6). It
structurally overlies sedimentary rocks of the Cadwallader
Group, and nowhere in the study area can it he shown to he
underlain by serpentinite. The floor thrust of the serpentinite
broad easterly plunging antiform that extends eastward into
melange is thus drawn at the top of the unit and defines a
the Hog Creek imbricate zone.
extrusiverocksdisplayingcomplicatedigneousrelation-
The unit comprises mafic to intermediateintrusiveand
ships. Leech (1953) and Nagel (1979)have suggested that a
transitional contact exists between gabbrosandvolcanic
rocks.Gabbroicrocks underlie the southem part of the
outcrop area andappear to be overlain with nonconformable
stratigraphiccontact by pillowed lavas in the northThe
contact zone is poorly exposed, but local field relationships
suggest that it dips gently north-northeast.
The intrusive sequence (Unit 8) consists mainly of fine-
scale layered two-pyroxene gabbroswith minor interlayered
These rocks show a well-developed tectonic foliation sub-
websterite,clinopyroxeniteandanorthosite(Plate 3-4-61,
parallel to layering, as well as discreteplastic shear zones
overprinting the foliation. Layering attitudes arehighly vari-
able, as was also noted by Nagel (1979). The rocks have a
porphyroclastictexture,outlined by flattenedpyroxene
grains with tailed recrystallized margins of brown and green
pleochroic hornblende indicating deformation under amphi-
bolite facies conditions. The deformed gabbros arecut by
small, irregularly shaped stocks of isotropic, fine-grained to
pegmatitic gabbros; by variably textured gabbroic veins; and
by abundant fine-grainedgabbroic to dioriticdikes which
have highlyvariableorientation. This intrusive sequence
resemblesthe high-level gabbros of the plutonicblocks in
many respects.
by an increase in theoccurrence of dikes, by frequent
The contact zone with the volcanic rocks is characterized
microgabbroicstocks,andnarrowscreens of intensely
phases. Locally, dike swarms appear to have coalesced into
sheared pillowed andmassivelavasbetweenintrusive
certainly not well developed along the contact zone. Small
small sheeteddike sections, but asheeteddikecomplex is
plugsandsills of microgabbro are found locally, higher
within the volcanic succession.
The volcanic rocks (Unit 9) comprise mainly pillow lava
cut by fine-grained diabase dikes. In mildly deformed parts
with subordinate massive flows and pillow breccia; they are
of the sequence, the pillows are small in size, ranging up to
0.5 metre in diameter,androunded in shape(Plate3-4-7).
Geological Fieldwork 1989,Paper 1990-1
They arefined grained tcm aphanitic and locally vesicular and
porphyritic; the original ferromagnesian phenocry,< t '.,now
occur as chloritic pseudomorphs.Massive flows are up to 2
metres thick and locally show banding outlinedby concentra-
greenschistfaciesassemblages with abundantquartz,epi-
tions of amygdules. The rocks are stronglyaltered to low
doteandchlorite;silicification is intenseand widespread.
Compositionallythe lavas appear torangefrom bar.alt to
dacite.
in&sedimentary rocksof ItheHurly Formationis well exposed
The thrust contactbetween the volcanic rocksand unjerly-
along the upper easternslopesof East Lixa Creek. In thc lava!;
it is a zone of silicic banded mylonite and phyllonitr with
well-developed C-S fabricsup to 1 rnetre thick. At one
locality, the thrust is clearly cut by a diorite dike that can be
traced over some distance into the underlying sedinmtary
rocks. Various shear-sen:;e criteria in the mylonites consis..
tently indicate southwest..directed thrusting, identical to the
movement pattern of tht: S, serpentinitemylonites which.
directly overlie thevolcanicrocksinthenorthern part of
outcrop area of the East Liza suite. Delormation associated
with thisthrustinghas not been recognized with cerzainty
t . .
, "-. - . " -,. ,,. 7''
Plate 3-4-6. Detail of thrust conta8:t betweenbasal
mylonite of serpentinite mklange and underlyinggablrro,
with steep fine-scale laysrinp, of East Lira igneous suite.
dipping schistosity (S,) ;and a later, mylonitic serpentinite
Composite fabric in serpmtinite consists 'of an early steeply
fabric (S2) which is subpxrallel to the thrust contact.
Plate 3-4-7. Mildly defc~rmed pillow lavasof East Lira
igneous suite in western part of study area.
383

10. :entral Window
jouthwest Domain
...............
, ,
,
_" ,
i
Figure 3-4-3. Orientation patternsof cleavage fold systems in three domainsofHurley Formation:(A-C)northwestern domain, (D-F)
northern half-window, (G-I) southwestern domain. A. D. G are plots for poles to bedding: B, E, H are plots for poles to axial planar
hemisphere projection.
cleavage; C, F, I are plots of beddinglcleavage intersection lineations and axesof small-scale folds; all plots are in equal area, lower
384 Brirish Columbia GeologicalSurvey Branch

11. within the volcanic sequence. The presumed thrust contact
between gabbros and Hurley Formation is nowhere exposed
in thestudy area. The contact is deformed in macroscopic
cleavage folds with associated thrusts. The folding is spec-
tacularlydeveloped in the Hurley footwall (see below). it
caused widespread cleavage formation with associated flat-
tening of pillows in the volcanic sequence. Thiscleavage dips
steeply to the southwest and obscures many of the original
features of the volcanicsequence; it is only locally developed
complex extensional fault system that controls much of the
in thegabbros to the south. All structures arecut by a
present outcroppattern of the eastern contactof the East Liza
suite with the serpentinite melange (see also below).
CADWALLADERGROUP,HURLEYFORMATION
(UNIT10)
This unit comprisesa variety of siliciclastic and calcareous
tion,are assigned to theLate 'Triassic Hurley Formation
sedimentary rockswhich, onthe basis of lithological correla-
(Rusmore, 1987).To date, howeyer, no biostratigraphic data
are availableforthe unit in the maparea. Themost prominent
sandstones and laminated greyto black siltstones, which are
sequence in the unit consists of thin to medium-bedded grey
and crosslamination.It contains interbeddedlimestone, chert
turbiditic in nature displaying grading as well as convolute
andpebble conglomerate, whichbecome more abundant
towards the stratigraphic base of the unit. Massive, locally
fossiliferous limestone and limestone breccia occur as dis-
continuouslensesup to 5 metresthick.White to grey,
range from 0.5 to 3 metres in thickness. Matrix-supported
massive chert beds intercalated with the siliciclasticrocks
pebble conglomeratescontain subroundedclasts of felsic and
mafic (sub-)volcanic rocks. Theturbidite sequence becomes
consisting of medium to thick-bedded (up toI metre), graded
more calcareous towards its stratigraphic top (Plate 3-4-8).
calcarenites, calcareous shales and rare, thin discontinuous
limestone beds. Theunit is cut by rare, thin dikes ranging in
composition from basalt to quartz diorite.
associated with intense axial planarcleavagedevelopment
All rocks of theunit are affected by regionalfolding
(Plate 3-44),The foldsystem comprises several orders of
folds,rangingfromsmallcrenulationstomacroscopic
antiform-synform pairs. Orientationpatterns of thefold
system are presented in Figure 3-4-3for three domainsin the
study area. Folds in the northwestern domain, directly west
of thenorthernmostgabbroblocks in the serpentinite
m6Iange(Figure 3-4-2) define a plane,subcylindrical,
folds are close to tight,asymmetric with easterly vergence.
steeply inclined system that plunges gently to the north; the
The folds in the northern half-window of Hurley Formation
(Figure 3-4-2)define a plane, noncylindrical, close to tight
system for which foldasymmetry is not well established. The
folds are steeply northeasterly inclinedand markedly doubly
plunging(Figure 3-4-3).Dueto severe late extensional
faulting, it is not clear whether or not this folding affects the
thrust contacts with the overlying serpentinites and volcanic
rocks. A penetrativecleavage with identicalorientation is
observed in the volcanic rocks, but doesnot appear to affect
Geological Fieldwork 1989,Paper 1990-1
the S, serpentinite mylonites. Thefold system in the south-
western domain, along the eastern slopeof East Lira Creek,
is nonplanarnoncylindrical, closeto tight; it is :steeply
inclined to the southwest;andplunges mainly to the sodheast
(Figure 3-4-3).It is markedlyasymmetricwitheast-
northeasterlyvergenceexpressed by steeply westdigping
overturned shortlimbsand associatedmoderately west-
dipping thrusts. the fold and thrust system clearly ic.volves
not only the Hurley Fornlation, but also the overlying East
Lizavolcanicrocks and S2 serpentinitemylonites (tf the
melange. in one small areain the northern partof the dcmain
(Figure 3-4-Z),the volcanic rocks and serpentinitesdefinean
overturned antiform-synform pair that is cut on its vcstern
side by an easterlyvergingthrust syst,:m comprising: thin
sheets of volcanicandsedimentaryrocks. The thruslsare
outlined by thin phyllitic C-S mylonitezonesconsistently
showingnorth-northeast-directed movement. The fold and
thrustsystemeffectivelyterminates ag.ainst a late, normal
fault in the east and is cut by numeroussmall exterlsional
faults which are not shown on the map.
thin-beddedcalcareousshales of Hurley Formation, C,xl-
Plate 3-4-8. Limb domainof mesoscopic cleavage folc.in
wallader Group. This foldis aparasitic smcture in thecon:of
a southeast-plungingantiform. Noteangular relationship
between bedding and axial planar cleavagf:.
385

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