Syme Eric Charles 1975 Sec

8/13/2019 Syme Eric Charles 1975 Sec

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UNIVERSllY OF SASKATCkotoon, Saakatc

Th e outhot hca ogr...: thot the l ibtcwy t l rJlry of SolkCl tchei,..ptiOf\. Mor/e(, the rulhor ogr-o thot pot ,iulon fotP PO'M rr.oy b. ronted by the pro/OUOf IJ( cofauol1 wno Ivpe '-Ir aburv:e, by '''e H.od d IIY- C.rltneflt Of ,.,. Dean of theia unde,. ood 1+>01 d.... recognition will ta g:n to +I. outhot of ,in any . of motorial in thi, thnls. Copyln 0( puDlico, lon 01 anyeNt Clpp


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PETROGENESIS OF THE BOlJNDARY

FLIN FLON AREA, SASKATCHEW

A Thesis

Submitted to the Faculty of Graduatein Partial Fulfilment of the

For th e Degree ofMaster of Science

in the

Department of Geoloical

by

Eric Charles Syme

Saskatoon, Saskatche

1975


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The author has agreed that the LSaskatchewan, may make this thesis frinspection. Moreover, the author has

for extensive copyin of this thesismay be ranted by th e professor or prthp- thesis work recorded herein or, iHead of the Department or th e Dean ofthe thesis work was done. It is undetion will be given to the author of tUniversity of Saskatchewan in any usethesis. Copying or publication or anfor financial gain without approval bSaskatchewan and the author's written

Requests for permission to copyuse of m aterial in this thesis in whoaddressed tOa

Head of th e Department of GeologicalUniversity of SaskatchewanSASKATOON, Canada.


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ABSTRACT

The Precambrian (Aphebian) Boundaof dike-like or lensoid, ultramafic tooccur in a linear zone centred on theManitoba. The intrusions are emplacedrocks and Missi metasedimentary rocks.

Cross-cuttin relationships, petrfeatures of Boundary rocks indicate theof three compositionally distinct, seqroups. The mafic (me la-dioritic) romelanocratic, augite- and biotite-bearinwere intruded and brecciated by succes

containing augite and, eventually, hor

at relatively high fH20 and f02 productiation trend in which successive diffeenriched in M gO relative to FeO. Crysaugite, possibly subordinate olivine,a tholeiitic olivine basalt magma accochemical variation in the ma fic eroup.

Felsic roup rocks (lellco-dioriteand brecciate all mafic group rock typ


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bearin group (wehrlite to olivine gabrence of w eh rlite is in th e core of aintrusion, with which wehrlite is in inCrystal fractionation of subequal amouclinopyroxene, and minor maGnetite, fro

basalt magma accounts for th e observedthe olivine-bearin roup. A reularof intercum ulus hornblende in wehrlitemarins of the body, indicates that thcontent in th e mar;inal zones of th e i

Folding and faul tin of th e Amiskdurin the Hudsonlan Orogeny, and invo

of deformation. S2 axial-plane foliatisecond phase of deformation) are develmembers of th e Boundary ma fic group.contain structures produced during thetion. Emplacement of th e intrusions ointerval late-P2 to late-P3.


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ACKNOWLEDGEMENTS

The writer gratefully acknowledgesconstructive criticism of Dr. R. W. Fosity of Saskatchewan, who supervised th

rrhanks are extended to Dr. M. R. Sand Mr. R. MacQuarrie for their discussThanks are also extended to Mr. E. Hawthin and polished sections, and to Mr.the writer in the operation of th e x-ra

This work was carried out while thResearch Council of Canada postgraduateand University of Saskatchewan graduate1974-75). The research was supported bCouncil of Canada Grant No. A8698 and SCouncil Grant No. 3-385-018 to Dr. R. WResearch Council of Canada Grant No. A


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TABLE OF CONTENT

ACKNOWLED}EMENTS .INTRODUCTION

Objectives of the researchLocation and eneral geology

SHAPE AND CONTACT RELATIONSHIPS

ROCK TYPES

01ivine-bearin rocks Mafic rocks Felsic rocks

METAMORPHISM

Olivine-bearing rocksM afic rocksFelsic rocks Discussion

STRUCTURAL RELATIONSHIPS

Helation to PlRelation to P2Relation to P3

structuresstructuresstructures

A.}E RELATIONSHIPS

:}eneralSequence

of intrusion

PETROCHEMISTRY

Effect of al tera tion Bulk chemical characteristicsHarker diarams


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COMPARISON WITH SIMILAR INTRUSIVES

CONCLUSIONS

REFERENCES

APPENDIX A PETRORAPHIC DESCRIPTIONROCK TYPES

APPENDIX B ESTIMATED MODES OF BOUND

APENDIX C ELECTRON MICROPROBE ANAANALYTICAL TECHNIQUE

TABLES

1. Metamorphic m ineral assemblages

2. Summary of age relationships for3. Chemical analyses and mo lecular

intrusions, and comparative analy4. Olivine partial analyses 5. Clinopyroxene partial analyses 6. lJhase c ompo s i t i o ns i olivine (10

clinopyroxene (Ca, Mp;, and Fe, aplaioclase (mol. percent anorth

7. Linear regression coefficients fodiagrams (olivine-bearin rocks)

8, Linear re ression coefficients fdiagrams (mafic rocks)


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22. Si02 versus FeOT/Mgo, m afic rocks23. F e O T versus FeOT/MgO, mafic rocks24. FeoT/FeOT+MgO versus CaO + M gO fo

clinopyroxenes

25. SME/A120l versus Sio2/A1203 ' molbear ing rocks

27. MgO/A1203 versus Si02/A1203' mol28. CaO/A1203 versus Si02/A1203' mol29. FeO/A1203 versus Si02/A1203' mol30.

31.FeO+;gO/A1203 versus Sio2/A1203'Molar ratio diarams for olivine-(a) Fe203/A12o3 versus SiO? A120versus S102/A120l ' (c) K207A1203(d) Ti02/A1203 vrsus Si02/A1203Molar ratio diagrams for mafic roversus Si02/AI201' (b) NaZO/A120(c) K20/A120, versus Sio2/AI203'versus Si02/AI203' all in moleso

32.

33. Method of calculatine the fractiochemical variation produced by cof a particular phase

34. Compositions of analysed Boundarcompared to pyroxenes from selecassociat ions


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lb. Hornblende wehrlite. Oval olivinehedral clinopyroxene (c) are enclocumuLu s hornblende (h). The clinopslihtly resorbed against hornblenpolarizers. Scale bar represents

2a. Biotite-olivine gabbro. Clinopyroenclosed and embayed by biotite (bSubhedral plagioclase (white) is aby biotite. Plane polarized lightrepresents 0.25 mm

2b. Hornblende-olivine gabbro. Clinopis enclosed, embayed, and replaced(h, dark). Plagioclase (white) isenclosed by hornblende. Plane polScale bar represents 0.35 mm

3a. Biotite-au?;ite mela-diorite. Clinis enclosed and replaced by anhed(b, dark). Plagioclase (white) isPlane polarized liht. Scale baro :3 5 rnm ..........................

3b. Hornblende mela-monzodiorite. Euphenocryst (dark) is colour-zoned.narrow, outermost, light-colouredcrystal is locally resorbed (arrow(p) is anhedral. Crossed polarizerepresents 0.35 mm

4. Igneous layering (alternating lighcoloured bands) developed in a memgroup. The hammer rests on a mafthe layered rock

5. Andesinite. Subhedral plagioclasealbite twinning) is bent and fractdeformation texture was produced bCrossed polarizers. Scale bar rep


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H. FAlsie i n tr-us l ve br-e cc Lv, A larean =u Lar' Lo u nd ar y rna fic (rOUjl rocksvolcanic rocks occur as xenoliths=r-a i.ne d , light pink hornblende ton

9. Small diorite xenolith (light coloblende-rich ultramafic rock (drakmarin of th e Phantom Lake wehrlit

10. Zone of mixin between ultram aficand olivine p;abbro (liht)


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INTRODUCTION

Objectives of th e researchThe Boundary intrusions were de

1960) as a (roup of post-tectonic intultramafic to felsic in composition,Saskatchewan-Manitoba interprovinciaof Flin Flon, Manitoba. They were cet ale (1965, p.38) as a group of re

although the relative ages of th e maestablished. The objectives of thisw hether th e intrusions are indeed relare related. (2) determine th e sequenmine the age of the Boundary intrusiophases of deform ation recognized inand Mukherjee. 1971), and (4) determ

differentiation which may have productional variation.

During this study most of the Bmapped at a scale of 1 inchl500 feetand thirty samples were collected. ofor petrographic study and 25 for wh


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northwerlt of Saskatoon, Saskatchewan,Ma nitoba interprovincial boundary. Thlies within the Churchill (structural)Shield, only a few kilom etres north ocontact.

Detailed geological investi


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,-,:

ooON 0 , 2 3 4 5C>

KM

1. Location of the Flin Flo


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in places a zone of pre-Missi subaeat th e contact between the tw o Groupprobably represents alluvial fa n toThe source area was composed primarirocks, but also included a variety ometamorphic rocks.

Four groups of intrusive rocksarea (Stauffer, 1974). Listed in orest, these arel

(1) Small irregular stockswhich intrude th e Amisk volcanic roc

(2) Hypabyssal (mainly diacut both the stocks and the Arnisk Gr

(3) A heterogeneous granitthe hypabyssal rocks and is nonconfoMiss i '}roup.

(4) All post-Missi intrusivare ranodioritic plutons. The Bounwell (1960) and the Phantom Lake postock (Fig. 2) are included in this

Minor faulting, tilting, and po


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phases (Stauffer and Mukherjee, 1971each phase is characterised by a pa

(1) Phase 1 (PI; th e earlito isoclinal, V- to box-shaped foldstrended approximately east-west. Noor metamorphic effects are observed.

(2) Phase 2 (P2) - tightlyv- to box-shaped folds (F2), w ith wschistosity (S2) and lineation (L2).originally approximately north-southwhat due to re-folding. Folding was

metamorphism (M2) largely within th eby intrusion of syntectonic plutons.

(3) Phase 3 (P) - one lafold (F3) that distorts earlier foldwesterly-trending faults was accompmorphism (M), monoclinal drag folation cleavage, and fracture cleavagassociated with P) faulting locally

The first three instrusive grouare pre-P2, and contain S2 foliation


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SHAPE AND CONTACT RELA

The Boundary intrusions crop otrending zone, 10.5 km long by 4 km

town of F1in Flon. Individual intruparallel to this zone (Fig. 2).

Irregular, dike-like shapes anmost common, but th e intrusions dolength to width ratios of normalof th e intrusions are generally 5 twidths. By contrast, porphyritic garea, not related to the Boundary gof 100 times longer than they are w

Tvlost of th e intrusions are smfrom 150 m to 900 m. The largest mcompound intrusion on Phantom Lake,length by 0.9 km in maximum width.

In detail, most of th e largercontacts with the enclosing countryan intrusive mass are generally alall trend of th e intrusion.

The intrusions are generally d


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are sharp, and no obvious mesoscopic ceffects were observed. Chilled marginthere is a slight reduction in th e sizin a narrow zone adjacent to the contabrecciated, th e degree of disruption o

ranging from incorporation of a few xemar6ins to intense veinin and brecciarocks for several metres. The large chantom Lake contains a number of largvolcanic country rock. Some contactsfolds alon the shears were noted in bintrusive bodies.

Intrusive contacts are seldom expdimension. Where th e attitudes of th emeasured, they were found to dip 650 tlocal foliation.


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ROCK TYPES

The Boundary intrusions have beeaccording to th e system of nomenclatulUGS Subcommission on the Systematics

(Streckeisen, 1973). Classificationto correlate mappable rock units withbut th e resulting abundance of rock nmental relationships between rock typ

For the purpose of discussion. tcan be treated in terms of three majmineralogy, texture, alteration. relaoccurrence of th e constituent rock tyare as follows.

(1) Olivine-bearing rocks,and gabbroic varieties.

(2) Mafic rocks; includingminerals. and some ultramafic or monlacking olivine.

() Felsic rocks, includingtypes.

The majority of the ma fic rocks


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li(. 6. 'I'e rnar-y dia,cr:rams d e p ict i.nz ; thth e mafic and felsic ,a;roups of th e BoAreas of low and high point density w(a) m afics - feldspar - quartz. P repof 17 modes in the Phantom Lake area,of >} modes in the Club Lake area. (b)p La=; ioclase


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mafics

FELSICGROUP

MAFICGROUP

o.

feldspar

quart z

b.


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th e ma fic group with respect to mineralcontain 20 percent olivine; rocks interolivine-free mafic group and olivine-ri

Olivine-bearing rocksAll rocks that originally containe

included in this group. Mappable rockare (hornblende) wehrlite. olivine gabultramafic rocks.

W ehrl ite crops out on the shores aLake. It forms a long, narrow body ormasses, for th e most part completely esive rocks comprising th e greater partintrusion centred on Phan tom Lake (Fig.th e belt of wehrlite is conformable witenclosing intrusion. Small bodies of rm afic rock also occur within the largein th e Club Lake area (Fig. 4).

Figure 7 depicts the proportions

occurring in hornblende wehrlite. The


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hornblende

margin

core

olivine+

alteration

Fis. 7. Ternary diagram depicting the

th e wehrlite mass on Phantom Lake. Thma7ic body are much richer in hornblen


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ultramafic body. No sinificant adis observed, while adcumulus additiproduced irres-ular, interlocking adjacent pyroxene crystals (Plate lis unzoned, and is indistinuishablfrom the cumulus phase.

'rhe hornblende is pleochroic (is anhedral in form. Larre hornbletically enclose small olivine or cl(Plate lb). From textural relationbrown hornblende is a late stage prin clinopyroxene and in part the pof intercum ulus liquid. Hornblendevolume percent of the wehrlite - itcore of the ultram afic intrusion, atoward th e marins of th e body (Figis an inverse relation between theand of biotite. Even though biotitrelatively rich in this mineral arevice versa.

The pleochroic, pale brown bi


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there is a slight, gradual decrease inof olivine going from the centre of tholivine) to the margins (40 percent oltion (Wager and Brown, 1967) may be prin abundant olivine and very little hF079 and clinopyroxene Ca46Mg50Fe4. whing much less olivine, and significantclase, has olivine F072 and clinopyroxe

W ehrlite is variably altered, witplaced by serpentine, bowlingite, mag

Clinopyroxene is in part replaced by aThe typically incomplete alteration exultramafic mass on Phantom Lake is inalmost complete serpentinization of smmafic bodies in th e same area.

O livine gabbro forms a discontinu

around th e northern margins of the Phabody (Fig. J). Olivine-bearing gabbroas dikes cutting the ultrama fic mass,Lake area similar dikes cut members o


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Briefly, these rocks are fine sr(Fir,;. R), with hypidiomorphic-granulaturn. 3ubhedral, 1 to 2.5 mm olivinsubhedral, 0.2 to 1.5 mm clinopyroxen

Ca4oM45Fe15) are th e phenocryst phassubhedral plaioclase (An58-49) and cred or brown biotite and pleochroic banhedral, and completely or partially01 ivine, and p Lag i oc Las e , Subhedraland embayed against biotite and hornbreaction relation between pyroxene anfrom which these tw o late magmatic m(Plates z, 2b).

Olivine phenocrysts typically harims of ranulr clinopyroxene. Rarphenocrysts display discontinuous, c

pl8.:ioclase exhibits weak normal zoncores to A 44-55 at crystal m ar in8 .oxides 8.re accessory phases.

Alteration of these rocks is weation features observed are probably


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Fig. 8. Ternary diagrams depicting th e

Boundary olivine gabbro. (a) hornblendeclinopyroxene (b) plagioclase - olivinehornblende + biotite.

hornblende or b


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OLIVINE GABBRO

o.

olivine

plagioclase

b.


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are more common than easily recogtype to another. Nevertheless, thmental petrographic and chemical

likely that most if not all of th ein the Appendix are related to a

The essential features of mashown on a ternary diagram depictand quartz (Fig. 6).

Of all mafic rocks, porphyrdiorite is the most common. Thispseudomorphs after primary clinopyare Ca42Mg44Fe14) 2 to 4 mm in dibeen replaced in a two-stage procto complete replacement by pleoch(2) a metamorphic event which red

pyroxene, and some hornblende, toThe development of hornblende atvery likely due to th e reaction oma0matic fluids (Naldrett et al.,biotite typically has a poikiliticbiotite-olivine gabbros, appears


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melanocratic were used to distinguish b

phases of this rock type. Petrographicthat the rocks have varying proportionsto felsic components.

Mafic-rich dioritic rocks exist wof both hornblende and pseudomorphs aftthese rocks are poor in primary biotitetexturally these rocks are intermediate

augite diorites and a group of hornblenThe hornblende-bearing diorites fo

litic to larger, dominantly pyroxene-beintrusions, or occur as dikes, as th e m

breccias, or as plugs in the pyroxene dcontain appreciable (40 to 60 volume peuhedral hornblende, and have been claquartz and potassium feldspar contentamphibole phenocrysts occasionally dispof zoning and reaction with a liquid phclase is usually subhedral and normallyoptical), but tends more to anhedral foor completely enclose hornblende, with


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\


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afic rocks unusually rich inoccur s po r-ad ically throu


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size is observed between upper aThe monomineralic and very

mafic rock types probably represfractionation on a somewhat larglocal accum ulations of pyroxenederived from liquids which crysritic pyroxene and hornblende doverwhelming majority of m aficrather than hornblende, as theis a very rare rock type).

Felsic rocks

Rocks poor in mafic mineranents comprise the felsic groupFelsic intrusions typically formbodies containing abundant xenointrusions.

Members of th e felsic groucompositions and textures (seedescriptions of the various rocthey are characterized by th e p

and


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These ma fic phases are often altered toand actinolite.

Plagioclase commonly exhibits norin th e andesine range and rims of calcOscillatory zoning is common in the laphenocrysts.

Plagioclase phenocrysts in sampleleuco-diorite, were analysed by x-rayplagioclase crystals are zoned from Aninside the outermost rim. The rim is(Anll)' with fairly abundant blebs ofis probably igneous in origina introducrystals into an alkali-rich liquid win equilibrium could produce mantles ofeldspar on th e plagioclase. Subsequeby exsolution of K-feldspar from the dfeldspar, could produce the observed t

How much of th e patchy replacemem icrocline is due to igneous processesrarely are th e textures as clear-cut aoften the irregular occurrence of mic


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textures.A concentrically zoned felsic

peninsula in Phantom Lake (Fi. 3).of fine 'rained hornblende quartz dpresent onJy locally. It rades ovcoarser, more m afic border facies q7 to 20 m thick, which in turn radthan 1 m ) to a core fac Le s , med ium

(sample CIO) very poor in ma fic mi


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lVlETAMORPH t _;l\ i

Two phases of metamorphism (M2th e Amisk and M issi Groups in the Fland Mukherjee, 1971, Koo, 1973). Th

gionally progressive phase, which octh e development of axial plane schisphase of deformation (P2). Ambrosemetamorphic zones in the Missi Groupprogressive metamorphism. chloritezone in the centre, and garnet zonefirst two zones are the lower and upof Turner's (1968) greenschist faciecorresponds to Turner's (1968) greentional facies. The isograds are ssecond phase of metamorphism (M3) islocallized along faults, equivalentgreenschist facies. It appears to b(Stauffer and Mukherjee, 1971).

The majority of the Boundary inrocks lying within the chlorite zonein the Club Lake area are north of t


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Table 1. Metamorphic mineral assemb

intrusions.

1 ? 1

Serpentine X XmBowlingite X Xm

Magnetite X X X

Iddingsite X

Actinolite X (X)m XBiotite XChlorite (X) (X)m XAlbite XEpidote (X)m (X)mSericiteCarbonate (X)m XSphene (X)mHematite (X)

Quartz

Talc (X)m (X)mTrem olite (X)m

X = present=


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(1968) greenschist facies. Pertinen

morphism in the three Boundary rockbelow.

Olivine-bearing rocks

Metamorphism of the ultram aficthe production of serpentine ratherand carbonate, demonstrating that thduring alteration m ust have had XC02cent (Johannes, 1969). These rocks

percent C 02 (Fig. 12). Sheared ultrother hand, contain appreciable amotalc, establishing that th e fluidshad a significantly greater XC02'

Alteration of th e olivine gabbmost cases is probably deuteric inclinopyroxene, hornblende. biotite,common in th e wehrlites (Appendix Bmetamorphic hydration reactions did

In contrast, th e small ultramafic bBoundary intrusion (Fig. 3) are alm


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th e oldest Boundary rock types, commo

schistosity. Palimpsest textures inthat they were originally pyroxene-ricgabbros).

The biotite-pyroxene diorites haigneous textures and some relict primpyroxene is commonly replaced by actibiotite opaques + epidote, but primbiotite are somewhat more resistant toclase may be replaced by albite + epialthouh primary, weakly zoned plagio(Table 6 lists compositions of some aalbitic plagioclase ranges in composand all have been altered in some degsericite. The more sodic plagioclasethe result of metamorphic degradationcalcic plagioclase.

Hornblende-rich diorites, quartzdisplay the least alteration of all m

Koo (1973) reported the associat

+ calcite + 2Ml phenite in the unshe


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or amphibole. Biotite is not stablefacies according to Turner (1968), so

phase in th e intrusive rocks seems anappearance of biotite would be favourcompositions relatively poor in A 120condit ion prevailing in most mafic ro

The green metamorphic biotite throcks within the chlorite zone is no(1936) biotite isograd. In th e Clubbiotite is a dark, pleochroic brownpresumably has a greater Fe3+/Fe2+ ra(Rimsaite, 1967; primary biotite inis a brown colour as well). The colois essentially the only feature thatBoundary rocks from the chlorite zonbiotite zone (see Appendix B for a cPhantom Lake and Club Lake diorites)

In most m afic rocks, actinolitethe approximate proportion 75125. Scontain chlorite to th e virtual excl(for example, sample CIl, Appendix B


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This is very likely th e reaction whichthe chlorite-rich ma fic rocks. In morich rocks display features indicativestronger than normal hydrothermal actpresence of significant pyrite), and P3roup and Boundary rocks are character

of chlorite and carbonate. Clearly, tciated with PJ fracturing contained massociated with M2.

Felsic rocksFelsic Boundary intrusions are c

preservation of primary igneous texturcitized and saussuritized plagioclaselargely replaced by chlorite, biotite,minor actinolite.

The plagioclase is usually oligoccomplete replacement by albite has ocPatchy blebs of m icrocline in some plar im s may be th e result of late magmatsomatism.


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and occasionally bent and fractured pla(Plate 5 ).

Discussion

The widespread occurrence of palimrelict igneous phases is evidence thatdid not attain equilibrium during metaof th e following factors are probablynon-attainment of equilibriums

(1) Intrusion of the BoundaP2, such that crystallized Boundary roto peak metamorphic temperatures and teSupport for this hypothesis lies in thBoundary rocks display th e greatest de

mineralogical equilibrium within the gsuccessively younger intrusions show iof igneous textures and phases.

(2) The absence. or presencquantities, of a fluid phase in the crrocks would inhibit metamorphic reactioserve primary textures and phases (Spr


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STRUCTURAL RELATIONSH

The Boundary intrusions are emplbeen complexly folded and faulted. Tthe Boundary intrusions relative to thphases proposed by Stauffer and Mukhewere recorded whenever they occurred

and enclosing country rocks. An attem

uish between S2 axial plane foliationand PJ fracture cleavage.

The three deformational phases r

Flon area are defined and summarised

under Location and general geology.

Relation to PI structuresThe east-west trending, tightly-c

have an associated axial-plane foliatiMukherjee, 1971). The zone of Boundaas well as individual intrusive bodiehigh angle (Fig. 2) but nevertheless

any way by the Fl folds. Consequentcertainly post-PI in age.


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in strength to the north of Phsouth of the town of Creightonwell foliated. Amisk and Misin the entire northern part o

W ithin the Boundary intrufound to contain S2 foliationsThe degree of deformation whictype displays is dependent upoage of that rock type, this asunder Age Relationships.

The relationship betweenintrusions and those found inwill be discussed according tohomogeneous sub-areas (Figs. 9

reported are averages.In subarea I, 32 foliatio

in Amisk rocks and Boundary ininterpretation. A possible S2rocks strikes 1440 and dips 58

Amisk volcanic rocks arebut th e Boundary intrusions a


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STRUCTURAL

N

t SU

Flin Flon L.

SUBAREA 2

5 KM

SUBAREA 1


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Fir. 10. Equal-area plots ofoliations, shear foliations

(a) Subarea 1, Ami

foliations, 7 poles to shearcleavaGe. Possible S2 folia

(b) Subarea 1, Bou

reional foliations, 19 polePossible S2 strikes 144, dipfoliation strikes 002, dips

-


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AMISK

S

Poles to region

nEW e

n S2 5

n N5 n

Poles to P3 sh

outcrop, but some exposures wer


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Unfortunately, it was impossiblages of th e foliations when theintrusions in subarea 2 have onfoliation, parallel to the easin the Amisk rocks.

Foliations are well develosome Boundary intrusions in subhave three foliations, althoughstereogram (Fi. 11). The stro

the S2 schistosity for that areJO o southeast. Apart from thistwo sporadically developed. somin some instances are seen to bstrikes OOJo and dips 400 eastand dips JO o south. The exactminor foliations and the majornorth-south trending schistosiorientation and therefore be aor alternatively, it may be athe Flin Flon Lake fault. The


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Fi. 11. Equal-area plots of linfoliations and shear foliations.

(a) Subarea 2, Amisk l

foliations, 17 poles to shear foAverae S2 strikes 023, dips 3strikes 104, dips 29 S. Avera169, dips 68 E.

(b) Subarea 2, Bounda

reional foliations, 6 poles toAverae EW foliation strikes 10shear foliation strikes 166, d

(c) Subarea J. Amisk

foliations, 12 poles to shear foAverage S2 strikes 046, dips )0strikes 088, dips JO o S. Averadips 40 E. Average P3 shear f63 NE. See text for discussio

(d) Subarea 3, Bounda

rerr,ional f'o L iations, 6 poles to 2 strikes 038, dips 34 SEt()()9 d 32') , 1 ps o Average P3 s


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AMISK

SU

SUB


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the poles to foliations may appewith a fairly large degree of sathat cross-cutting relationshipsshow an east-west foliation cuttinstrongly suggests that th e observleast tw o populations. Inasmuchis never observed to be cut by oclassed as th e third, and major.

M issi Group rocks north ofarea 4) are well foliated and l infoliation is th e only foliationand dips 260 southeast. BoundarM issi metasandstones have two fis weak to moderate in strength,foliation in th e M issi. The secalways very weak and occurs onlytain the stronger S2 foliation;0900 and dips 370 south. Whileall th e foliations recorded mayin th e field there appeared to bbetween th e well developed, nort


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Fi. 12. Equal-area plots offoliations, shear foliations,as in Fi,;. 10.

(a) Subarea 4, Miss

lineations. Avera\e S2 strikelineation plunes 28 to 122

(b) Subarea 4, Boun

reional foliations, 7 polestions. Averae S2 strikes 03foliation strikes 090, dips26 to 12Jo azimuth.

(c) Subarea 5, Amis

to S2, 9 poles to shear foliaAverac S2 strikes 162, dipstion strikes 169, dips 62 E

C d) Subarea 5. Bounshear foliations, 4 poles toshear foliation strikes 156,cleavac strikes 110, dips 6


60/186

SUBAREA 4

a.

MISSI

SUBAREA 5--,

'--,\\

\ .c->\ 3

-. C \ (.( \ . : . \ \ \\ :'., t- ; 52 \ ....\ \\np3 .


61/186

intrusions almost always have a less dithan enclosing country rocks, and foliateverywhere within a homogeneous intrusivably is of one age throughout. This sustresses operative during Boundary emplweaker than th e maximum P2 stresses. Arocks may have undergone less penetrativth e enclosin fine grained volcanic rocgreater competence.

The weak east-west trending foliatifactor to the present knowledge of theof th e Flin Flon area. This foliationtion throughout the map-area, strikingand dipping 290 to 370 south. It is foBoundary rocks, but almost always in rowise unfoliated. This, plus th e fact tto cut S2 foliations suggests that th epost-P2 in age. The stress regime whicwas for the most part too weak to imposacross an already existing schistosity,

in the enclosing country rocks, establish


62/186

bers of this group were emplaced prior todeformation.

On a regional scale, inspection of Smap shows that th e majority of the largeemplaced into Amisk Group rocks occur ina large F2 fold - th e Beaver Road Anticliaxial plane of this fold dips 350 east (Munfortunately the attitudes of the intrusarea are unknown. Thus, even though th e

igneous intrusion cuts S2 schistosity treangle (Fig. 2), large P2 folds may havedetermining the locus of intrusion.

Relation to P) structuresAll three major rock groups compris

intrusions display features which can bedeforma tion. The most common structuresfoliations (foliations produced by fault(simple breaks in th e rock), and faults.cleavae (closely spaced parallel surfac

the country rocks end at the co


63/186

others die out shortly after enstill others continue on uninterthrough Boundary rock.

The large, compound Boundahas a well-developed fracture sern part of th e body. The fractapart, striking approximately nto 770 east. The horizontal disin consistantly right-lateral, win the order of 2 to 5 cm . Thisto more pronounced shear zonesrocks.

Serpentine-filled fracturesbearing rocks on Phantom Lake.

fracturing, forming two fracturesect at about 90. One group hand 1100, with the north-southand dominant one, the other grou150. Fracturing in the olivineoriginated during or prior to s

on one fault before movement beg


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and Mukherjee, 1971, p.236). An

tionships between Boundary intrucan help to determine th e relativand faults.

Both Byers et ale (1965) anthat the Phantom Lake fault (Figintrusion on Phantom Lake. Althwas not located during this studm afic rock types indicate that t

portion of the intrusion. Howedike, which cuts th e mafic rocksfault with no apparent offset.at least in part post-dates thethe felsic one.

It is impossible to determia relationship between th e FlinStockwell, 1960) and th e large Bnorth end of Phantom Lake. Alonthe south, a shear zone is inteBoundary intrusions on the west


65/186

block of Amisk volcanic rocks


66/186

moved up and northwest over the

(Stauffer and Mukherjee, 1971)

sugested that since th e direcparallel to the strike of thesion intersected by the fault,pre-fault intrusion may not shofaulting.

An alternative explanationa history of movement which spintrusion emplacement. If ignenearly all fault movement hadsmall displacements could have

th e fault zone without producinA Boundary hornblende ton

western end of Club Lake (Fig.(1960) and Byers et ale (1965)Club Lake fault. This very dion both sides of th e fault witor foliation. It is almost cebut the intrusive magma may ha

cleavages are variable in orientation


67/186

be related to th e dom inant shear direIn summary, the period of Bounda

in part overlapped with th e period offaults locally have an expression intypes, whereas felsic rock types mayby those same structures. Minor PJ ssmall shears, fractures, and fracturein all Boundary rock types. A featureherjee (1971), and confirmed during tany given area th e Boundary intrusion

be aligned parallel to PJ fracture ption, then, probably had a role in deintrusion of rocks in the Boundary grwhich extended past th e end of Bounda

P2 and PJ foliations in Boundarythat most if not all members of the mprior to the end of P2 deformation, atypes were emplaced prior to th e endtotal period of Boundary igneous intruP2 to late P).


68/186

fragments of volcanic oriin. The m at


69/186

mafic, or ultramafic in composition. Tbodies rane in size from only a few mmetres, and contacts w ith unbrecciated

poorly defined.

Intrusive breccias attain their mment in th e larger, dominantly mafic BThe mafic intrusions are heterogeneous

multiple intrusion and much brecciationby later ma fic magmas. The fragmentsbreccias are in almost every case morematrix (Plate 6). Felsic and olivine-types never occur in the xenolith popugranodiorite xenoliths do occur, but threlated to syntectonic plutons underlythe Amisk rocks. Xenoliths of volcanitively common. In general, most of theintrusive breccias are in th e 5 to 30are subangular to rounded.

Intrusive breccias with a felsictive in outcrop (Plates 7 & 8). The b


70/186


71/186


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more than 20 percent of the breccia bo


73/186

breccias occur as isolated, irregularwithin a larger ma fic intrusion, or asalong th e margins of larger felsic dike

Intrusive breccias with an ultramstricted to th e marginal zone of the wLake (Fig. J). The breccia zone is nois probably nowhere more than about 10olivine gabbro border zone of the wehabsent, hornblende-rich rocks of ultrambe seen to vein, dike, and brecciate thdiorite wall rocks. In addition, diorliths are fairly common in the massiveof th e marginal zone. The xenoliths a

(less than )0 em ) and subrounded to su(Plate 9). In places where th e olivinis present, th e contact between hornbland hornblende w eh rlite is a complex zsuggestive of mixing of semi-consolidamafic crystal mushes (Plate 10). Defiolivine gabbro are observed in ultram a


74/186


75/186

The marginal portions, at least


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sufficiently mobile to vein andwall rocks, and to mix w ith th egabbro border zone.

The small, completely serpwhich are located in the largeon Phantom Lake are brecciated

These dun-weathering serpentinbrecciated throughout their egreen, medium grained pyroxen

pyroxenite is smal l comparednite, so rotation or completecommon. The highly altered nthe absence of mafic xenolithveining by pyroxenite - featurwehrlite body - suggest thatdifferent age or origin than tPhantom Lake. In fact, evidenshows that the serpentinites mgroup rocks and not to the we

Intrusive breccia also oc

Boundary intrusion rock types were obs

The 'cross-cutting relations obser


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summarized in Table 2. The relative atypes can be correlated with th e degrealteration and penetrative deformationrocks. W ehrlite and olivine gabbro armembers of th e ma fic or felsic groups,bearing rocks are completely unfoliatealtered. Unfoliated to weakly foliateare cut by unfoliated felsic and olivinand felsic types contain relict primarmetamorphic mineral assemblages. A gr

altered, moderately to well foliated mmafic, felsic, and olivine-bearing int

In summary, cross-cutting relatioof alteration and deformation indicaterock types are melanocratic and ultram

mafic group. In successively youngerreplaces pyroxene and biotite as the dplagioclase increases in modal abundanquartz appears, and, ultimately, rnicr

Table 2. Summary of Boundary intrusioships. Rock units (numbered 1 to 11)


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hand vertical column. Xenoliths of thdesignated X under th e appropriate co

rocks (numbers 1 to 6). Dikes of unirock units, and are designated D in ththe country rock they cut.

Xenoliths

Unfoliated,

incompletelyaltered.

Unfoliated

(4 - 6) to

weakly foliat-ed (6 - 8),

incompletelyaltered.

1. W ehrlite

2. Olivine Xgabbro

3. Felsic

4. Hornblendemela-monzodiorite

5. Hornblendediorites6. Biotite- X

augite diorite7. Hornblendite

8. Hornblendepyroxenite

The relative ages of the Boundarythe of intrusion to be (1)


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sequence em

magma during late P2, differentiationof th e magma produced the ma fic groupof th e felsic dikes. and (3) intrusionmagma into the already crystallized mcrystallization of this second mafic molivine-bearing rocks. Emplacement an

all Boundary intrusions was completed

PETROCHEM

The twenty-five samples se


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element analysis represent esstional variation exhibited by t3). Only a few rare or severerepresented.

Effect of alterationThe Boundary intrusions ha

alteration, so the possibilitymetamorphism or deuteric alteraMajor redistribution of elemenabsence of complete recrystallianalysed samples. The effectsof volatiles can be assessed qtion of alkalis, the only othelikely to have occurred, is moand Baragar (1971) recommend thratio and recalculation of the

H 20 or C02 should be considereddata for severely altered rocks

The ratio can

Table 3. Chemical compositions (oxidesmolecular norms of Boundary intrusions,


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with CIPW norms.Table )a .

Si02A120)Fe20)PeOMOCaONa20K 20H20CO2Ti02P20SMnOS

CIO68.4016.04

1.131. 34o.RR1.124.803.681.210.890.080.130.000.184

0.09

99.79

Less O=S

Total

Felsic

C468.5014.86

1.650.941.552.435.273.000.640.350.240.210.040.007

0.00

99.69

C18fS6.1S15.892.131.261.503.264.563.530.720.170.510.270.040.006

0.00

99.99

Analyst. Mr. K. Ramla1, University of Man

QorabanIene

di{:shY{

20.8522.1343.93

4.84

2.481.78

18.4317.9247.85

8.1)

1.070.940.133.380.46

15.8920.9941.2112.55

0.790.540.253.621.70

Table 3b.

Fel


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166 C19SiO 60.90 58.35A123 14.19 16.34Fe503 2.81 2.87Fe 3. 57 2.66M,c;O 5.30 3.25CaO 3.96 3.41Na50 5.06 4.84K2 0.84 J.77H 0 1.85 2.77C 2 0.38 0.16Ti02 0.45 0.74P205 0.28 0.57MnO 0.09 0.08S 0.068 0.004Less o=s 0.03 0.00

Total 99.71 99.81

Q 10.62 3.58or 5.03 22.73ab 46.11 44.40an 13.72 11.97Iene

ro 1.71 0.62di en 1.32 0.46fs 0.39 0.35h {en 13.51 8.69Y fs 3.94 1.77oltoamt ).27 2.02il 1.22 1.05ap 0.97 1.20ce 0.03

Table 3c.

Mafic

168 170 51SiO 55.05


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53.15 52.45A12O) 11.)6 9.24 12.46Feo) 2.80 3.2) 2.)9Fe 5.44 6.25 6.06MgO 9.90 1).90 10.90CaO 6.54 6.72 6 .. 93N a20 4.58 2.)6 3.)7K 20 0.48 0.63 o e 51

HbO1.99 3.14 3.11

C 2 0.72 0.21 0.60Ti02 0.81 0.62 0.49P20S 0.20 0.28 0.)7MnO 0.14 0.18 0.14s 0.066 0.016 0.003Less 0-' ' 0.0) 0.01 0.00.::>

Total 100.04 99.92 99.78

Q 0.24 2.90 0.06or 2.84 3.78 3.07ab 41.3) 21.58 30.94an 9.11 1).04 17.74Iene

r 8.71 7.59 5.95di en 7.2) 6.44 4.79fs 1.47 1.15 1.16h en 20.27 32.70 25.97Y fs 4.13 5.84 6.27Olnmt 2.95 3.44 2.56il 1.1) 0.88 0.70ap 0.43 0.60 0.80cc 0.17 0.05

Table 3d.Mafic

c16 2S C20SiO


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50.90 48.25 46.65A12b3 12.89 11.74 12.61Feto) ).68 ).88 ).76Fe 5.42 6.66 7.)8MO 9.95 11.97 11.71CaO 7.4) 9.25 9.28Na20 ).12 2.24 2.29K20 1.96 1.4) 1.45J-i 0 2.)8 2.)1 2.64Cb 0.52 0.47 0.35Tib2 0.81 0.73 0.93P205 0.45 0.45 0.51MnO 0.19 0.21 0.21s 0.005 0.012 0.015Less O=S 0.00 0.01 0.01

Total 99.70 99.80 99.77

Qor 11.77 8.60 8.78ab 28.52 20.54 21.08an 15.71 18.13 20.27Iene

r 7.56 10.28 9.37di en 5.95 8.50 7.54fs 1.61 1.78 1.83hy{en 9.45 10.41 2.82fs 2.57 2.18 0.6901 { 9.45 11.12 17.052.57 2.33 4.14mt 2.73 4.14 4.02il 1.15 1.03 1.32ap 0.95 0.95 1.10ee

Table 3e.

Olivine-bearing


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102 C8 C8dSi02 46.05 46.95 46.95 43A1203 12.23 10.62 10.72 6Pe203 2.89 1.8, 1.86 4FeO 8.78 8.) 8.22 8M O 12.93 16.15 15.4) 18CaO 11.16 9.56 10.56 12Ha20 2.16 1.97 1.89 0K20 0.36 0.99 1.02 0H2O 1.28 1.67 1.21 3CO2 0.33 0.30 0.38 0Ti02 0.71 0.72 0.82 0P205 0.53 0.42 0.40 0MnO 0.25 0.22 0.21 0s 0.023 0.023 0.016 0

Less O:S 0.01 0.01 0.01 0

Total 99.67 99.76 99.70 99

Qor 2.16 5.82 6.01 0ab 19.54 17.60 16.05 5an 22.82 17.19 17.69 15Iene

r 11.82 10.95 12.76 18di en 9.04 8.79 10.22 15fs 2.78 2.16 2.54 3h {en 0.71 1.18 5Y fs 0.22 0.29 101{fO

19.69 25.86 24.24 22fa 6.06 6.37 6.03 4mt 3.05 1.91 1.94- 5il 0.99 1.01 1.14 0ap 1.12 0.88 0.84 0ee 0

Table 3f.

A


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Si02 47.01A1203 15.57Fe203 2.32FeO 11.57M gO 5.25CaO 9.77Na20 3.00K 20 0.31

5 1.64Ti52 3.20P205 0.32

nO 0.20S

Less O=S

Total 100.16*ineludes Cr203 = 0.0810,

V203 = 0.0410Qor 1.87ab 25.39an 28.10Iene

roi en 15.17. fs{en 11.92hy fs{fO 5.9301 famt 3.36il 6.08

ap 0.76

Table 3g.

Explanation of column headings


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CIO Quartz m onzod ioriteC4 Hornblende granodioriteC18 Phantom Lake porphyritic granodiorCIS Hornblende quartz monzodioriteC14 Hornblende quartz diorite166 Hornblende tonaliteC19 Porphyritic 1euco-diorite112 Porphyritic leuco-dioriteC12 Hornblende quartz diorite (chill)Cll Hornblende quartz diorite (border)168 Hornblende mela-quartz diorite170 Hornblende mela-quartz dioriteS 1 Hornblende mela-quartz dioriteC7 Hornblende mela-diorite

I Bioti te-augi te m ela-diori te

C20 JC6 Hornblende pyroxeniteCl7 Hornblendite102 Hornblende-olivine mela-gabbroC8 Biotite-olivine mela-gabbroC8d Duplicate analysis of C824 Hornblende wehrlitelS7 Plagioclase biotite olivine clinop124 W ehrliteA Olivine tholeiite, Albemarle Islan

and Williams, 1969, p. 121, no. 63B Fine-grained hornblende gabbro, no

body II, Ontario (Watkinson and Irno. 160 - 114).

assemblages have oxidation ratios rangiwith ilmenite-magnetite-hematite assem


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tion ratio of 40. and those with magnehave oxidation ratios of 43 or reaterMost m afic and olivine-bearin Boundaryratios of less than 37 (Fig. 13), and

adjustment of the Fe203/Feo ratio (thaoxidation has occurred). The Fe203/Feooxidation ratios eater than 37 weretotal iron basis) to (1) the Fe20)/Feorock types listed by Nockolds (1954),ratio in unoxidized Boundary intrusionscomposition. The resulting adjusted Fsame regardless of whether method (1)

Norms for oxidized samples were cwith the original proportions of FeO athe corrected proportions. The effectsrectin for oxidation are (1) in felsicquartz and magnetite, and increase hyp

(2) in m afic rocks. to decrease magnethene. diopside, forsterite. and faya

Fi. 13. Total iron (expressed as FeOratio (mol. 2 Fe20J x 100/2 Fe20J+Feo)


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sions. Rocks plotting to th e left ofessentially unoxidized; rocks plottingdashed line have suffered more extremefor discussion.


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16 - II

-e I0 12 - 0 01

0 I 068 Q ) 0 I xr- 0Q) IXu, I x

4 11.1- I

0 I I II

0 20 4OXIOA TION R

olivine - bearing rocko mafic rocks

h = hornblende cu> cum

rock types are pink to brick red in copotash feldspar is not common. Petrogfelsic rocks has shown that plaioclase


91/186

cores) often have a very fine red dusthem atite undoubtedly imparts th e re d cand contributes to the high Fe2o)/FeOin a review of the literature on the sfeldspar, suggests that more than oneponsible for the re d c010uration. One1969) involves reaction between plagioand primary ferromagnesian minerals to

albite, sericite, and chloritized mafias felsic Boundary rock types are charplagioclase and chloritized biotite anmechanism appears to explain the wideshem atite in the felsic rocks. The calfrom plagioclase during the reaction iubiquitous fine grained epidote or sa

Nearly all rock types display somrelative to an assumed datum (Fig. 14significantly hydrated rock is a part

6 o.

-


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-e0 4 .. 00 00 pO 0


93/186

Watkinson and Irvine (1964).The C 02 content in Boundary rocks

stant at about 0.4 percent (see Fig. 1Recalculation of th e analyses on

basis allows all comparisons to be onis required because a volatile conten) percent affects the other constituen(Irvine and Baragar, 1971). In all dianalyses, the Boundary analyses have b

volatile-free, unless otherwise noted.The volatile contents of the Bou

uncommonly high for partially metamorpratios can be realistically adjusted,values approaching primary values. Th

likely to have been changed are the aand comparison with similar rock typesth e K20/Na20 ratio has been reduced in166, and 168.

to normal basalts, gabbros, and diorAlmost every Boundary rock type p

field on an alkali-silica plot (Fig. 1


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Boundary norms contain appreciable hypThe one mafic sample which plots in th15) is a hornblendite, containing normleucite. The two felsic ro cks w hich palkaline field are rich in oligoclasequently Na20). both have hypersthene itherefore more properly classified asgabbro contains only minor hy, indicatbulk composition for these biotite- anrocks.

The felsic rocks have low normati(Fig. 16), in agreement with the low mfor the group, while ma fic and olivinerich in normative pyroxene and olivine

On an AFM diagram (Fig. 17) analyintrusions plot in th e calc-alkaline festablished by several post-Missi felsin the Flin Flon - Amisk Lake area. A


95/186

10

-e 80._.:

60N 0

+ 40 0N ho 0 z

2

.. opo 35 40 45 50

FiG' 15. Na20 + K 20 versus Si02 for tDividing line is after Irvine and Baraas in Fig. 13.

100


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x opw 80 r-0 z0:: 60 :::> h 0 _J 00 0(.)

40 w>l- 20 0::0z

0 I I

100 80 60

NORMATIVE PLAGCOMPOSITIO

Fig. 16. Normative colour index versu

Fi. 17. AFM diagram for various rockAmisk Lake area. Boundary intrusion so denotes post-Missi felsic plutonic


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Lake porphyritic granodiorite; 2, Phan

granodiorite dike (R. MacQuarrie, persLake hornblende Granodiorite C R . MacQ

l, Snake Rapids pluton (Eastwood, 194

Gabbro ( ) and diorite (D) compositionAmisk }roup differentiation trend is aanalyses from Koo (1973), Mukherjee (1

(pers. comm.).


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MU0 I-N Q) IJ..W;.....J 00:r:+ I-0

O JIJ..

calc-alkali differentiation (Carmichathe Boundary intrusions, the virtual arock types strongly suggests that the


99/186

are . 12. related.

Analyses of Amisk volcanic rocksdifferentiation trend on the AFM diagrdering the difference in age between tthe Boundary intrusions, and the diffetion trends (the Boundary ma fic trendin a later section). there is no compthat the Boundary intrusions represenmagma reservoir.

Two major points are made from a

bulk chemical compositions of the Bou(1) almost all rock types a(2) felsic Boundary intrusio

similar to post-Missi felsic plutons,in any way other than physical settingrock types.

Harker diagrams

20a. A l2 03

8

oh 0


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20

o ---------------e 20

I--Z 10wI- -ZoU o30xo

10

oh

op

oh

10 ::::--- 0o 0-'(J


101/186

0.8 oh

o

------ I 0..


102/186

a ----------wt-Z 80.4 /.:/-oow opI9 a I------JL.--____Lxo

0 .4

-eo O . 4

op

oh

oh

40 45 50Si02

Pi, . 20. Variation diagrams for th eJymbo1s as in Fi. 1).

eneral variation in chemistry of aof limited use in determining th e ex

produced th e variation.


103/186

The major limitations inherentas follows {Pearce, 1968)1

(1) A Harker diagram of onanother purports to show a relationsvariables. In fact, all variables aexample, a rock containing (by weigh45 percent Si02 necessarily contains

A Harker diagram of A120) versus Si0ternary diagram A1203-Si02-all otherother than Al20J or Si02 is added toth e system, the weight percents of A'rhus on the Harker diagram, there wship between A1203 and Si02 even thoof these oxides in the system is unc

(2) The slope of th e relativariables on a Harker diagram is usuas deduced from th e variation in absvariables. Not only the magnitude b

sition of the starting material. Aupon th e mechanism of fractionationmechanism is to be independently dete


104/186

With these limitations in mind,diagrams of Boundary analyses can bethe bulk chemical characteristics of

rocks do not represent l iquids (fortextured ultram afic rocks and the higrocks), so the curves do not correspolines of descent.

Linear relationships are obtainethree major rock groups (see Figs. 1be taken as evidence that th e memberrelated (Pearce, 1968). Between groor discontinuities occur on severalthe M gO versus Si02 diaram (Fig. lR

slope occurs between the olivine-beaand a significant gap separates theThese relationships are also evide nt

Si02 plot (Fig. 18a). Less pronouncbetween groups on the CaO, K20 . Ti02

the felsic rocks are the products of eof a Boundary mafic magma (because maj

The analysis of th e Phantom Lakewithin the trend establ ished


105/186

plots byintrusions on all the Harker diagrams.evidence linking felsic Boundary intrusgranodioritic plutonism.

Considering the petrography of themafic rocks, and th e trends exhibited

Harker diagrams, a plausible working htionation of olivine is responsible foexhibited by th e olivine-bearing rocks

pyroxene may be responsible for the mapossible to define the role, if any, oin th e production of th e olivine-bearininterpretation of differentiation proclight of the deficiencies inherent in

Differentiation trendsFigure 21 contrasts th e tw o major

tiation trends. Analyses of olivine-baround an iron-enrichment

FiG' 21. FeOT/FeOT+MgO versus Si02 T

(FeOT). Trends of Skaeraard liquids arocks are after Carmichael (1964). B


106/186

andesite, A = andesite, D = dacite; R

solid line represents the trend definedintrusions, dashed line represents th e

olivine-bearing rocks. Note that the mtrend of decreasing FeoT/FeoT+MgO withSymbols as in Fig. 13.

-----------------------------


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(/) x' 0 x:J0- \S O)

_J -oo X-0 - o0 V0 x-

) sec0

) X

m


108/186

70

:


109/186

* /.60 c//j/a v/ 0

-eI0 /0 0\.,_: 0

\ / 50 \

/o /\

(f) po S/ \ ---/

40 oh

o 2 3

FeOT IMgFi. 22. Si02 versus FeOT/MeO for ma

16

14 0 p


110/186

12I0

0 I

100

01 ?'


111/186

for the Ben Nevis igneous complex, andWones (1973) for an intrusion at Finnmacases Fe/Fe+Mg ratios decrease in biotipyroxenes from progressively more felsiauthors attribute the Mg-enrichment trerapidly increasing f02 during crystallizf0 2 increased rapidly, from approximatea crystallization temperature of 7000 C

Clinopyroxenes from successive Boudifferentiates are enriched in FeO relarate of iron enrichment decreases goingolivine gabbro (Fig. 24). Notably, clinrocks have a constant FeOT/FeOT+MgO rat

No hornblendes were analysed durininasmuch as the FeOT/FeoT+MgO ratio fordecreases in successive differentiates,successive hornblendes do become sligh


112/186

o 0.6

oen2: 0.4

-0+

o 0.2

0 LL 40 35 30 5

CaO+ MgOFig. 24. FeOT/FeoT+MgO versus CaO + Msion whole rocks and clinopyroxenes.from which clinopyroxenes have been an

Clinopyroxenes from ma fic group rocks

FeOT+MO ratio. 0 represents whole ras in Fig. 13. Note that the Fe/Mg ra

increasing Si02 content unaccompanied bth e absence of iron-enrichm ent in augitof Mg-enrichment in hornblendes from suall stronly suggest that relatively hi


113/186

creasing values of f0 2 characterized thdifferentiation. For th e olivine-beariin clinopyroxenes and whole rocks implidecreasing values of f02

Presnall (1966) and Osborn (1962)

constant f0 2 spinel has a large primarysystem Mg2Si04-Feo-CaSiOJ-Si02.

The pr

volume prevents a liquid from moving tocontents during crystallization. The Bof Si02 enrichment without iron enrichmdue to (1) lack of iron enrichment inphenocryst phases, particularly augite,of magnetite. Both processes are due tconstant (or increasing) f0 2 in th e difmagma.

Effect of fH20

at 2 to 10 Kb (PH20 = PTotal)' Intercuin the marginal zones of the Boundaryto dem onstrate this reaction. The horand has in part replaced clinopyroxene


114/186

regular increase in modal hornblende frmargins of the wehr1ite body (Fig. 7)water content in th e intercumulus liquKennedy (1955) suggested that water, ina uniform partial pressure throughoutto portions of the magma which are coolowest confining pressure, that is . theparts of a magma chamber. Intrusion owet country rocks also results in th eat intrusion margins. Clearly both thcontributed to the inferred high watercumulus liquid of th e wehrlite margina

Best (1963) and Best and Mercy (1

of fH20 on the differentiation of thecomplex in California. a complex whichways to th e Boundary intrusions. Rockrange from troctolite to granophyre, th

tiates. Pyroxene, hornblende, and biodifferentiates show enrichment of Fe r

fH20 is indicated by the abundance ofwhile the f0 2 (estimated on th e basis


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tions) was low - 10-10 to 10-15 bars atemperatures of 11000 to 9000 C - and

during crystallization. The Guadalupetypical calc-alkaline differentiationlow f0 2 determined for the magma, theOsborn's (1959, 1962) hypothesis thatconstant

f0 2is required to produce th

Rather, the trend is produced by a higthe crystallization of hornblende in pfor much of the differentiation sequenrich in Fe and poor in Si relative totionation of hornblende would depleteenrich it in Si02 relative to fractionEarly crystallization of biotite wouldblende effect . High values of fH20,lead to Si02-rich, FeO-poor differentiprohibits the crystallization of hornb

Later ma fic differentiates contain incrhornblende and decreasing amounts of auuntil finally hornblende is the only mathe rocks. The abundance of hydrous ma


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mafic group rocks and in olivine gabbrofH20 values for th e magma(s) which prodThe m afic differentiation trend, in whientiates are enriched in Si02 and depleand 23), is due in part to th e hornblelization of hornblende during the lattecrystallization history of th e mafic maof biotite (with augite) for th e major

In summary, th e combined effects orelatively high or increasing f02 in thlized the mafic group rocks produced thof slight MgO-enrichment in successivehih fH20 allowed th e crystallization oblende early in th e differentiation seqhigh or increasing f0 2 prohibited Fe-enpossibly produced weak Mg-enrichment inprobably resulted in th e precipitation

FRACTIONAL CRYSTALLIZATION

IntroductionPearce (1968) devised a method of

analyses which provides much more inform


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of fractional crystallization than condiagrams. The method was used to subsolivine and clinopyroxene fractionationand Mason (1968) for the Dundonald sillwell as to dem onstrate that the chemicaPalisade sill is consistent with fractiand pyroxene from a single, relativelymagma (Pearce, 1970). Murray (1972) us

to support th e theory that the sequencein th e Tulameen zoned ultram afic compleoriginated by fractionation of olivinebasaltic liquid.

It can be shown mathematically thavariables by a constant does not changerelationship between th e variables. Anof elements (oxides, sulphides. etc.)context, if it has been neither added t

For example, fractionation of oliliquid removes MgO, FeO, and Si02 from

components in the system remain consta(moles, grams, litres of Al203' N a20 ,


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their concentrat ions by weight may chation process. A molar ratio plot of Mproduces th e same relationship as betwof M gO and Si02. If olivine is th e onth e slope of the relationship betweenand Si02/A1203 will be the same as th ethe fractionating olivine.

Molar ratio diagrams can be usedmechanism(s) which produced th e observ

in a rock suite. Unlike Harker diagraof the relationship between variableslent amounts of variants are compared.lationship between variables is dependcompositions of fractionating phases, aof the composition of the parent m atercumulus phases are known or assumed, th

total chemical variation produced by th

pattern is obtained in the diagrams, tthe pattern is taken to substantiate tvariants are not related, a coherent ptained.


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(2) The process must not hav(that is , intermediate rock types mussampling).

(3) There must be no signifirocks. Any chemical variation presenth e process to be investigated.

(4) There must be at least t(5) At least one component m

in absolute amounts during fractionatinot known, but is inferred from othera coherent pattern in the m olar ratioassumption.

The necessary conditions are met

and mafic groups of the Boundary intru(1) Petrography, field relat

tionships, and major element variationindicate that some process of differen

iron in some samples, and possibly reOxidation ratios were adjusted to reafor tw o samples (c6 and 124), and allare compared on a volatile-free basis


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of alkalis would not significantly af(3) No component is known to

in absolute amounts during differentiaconstant can be inferred from petrograThe olivine-bearing rocks and most ofolivine and/or clinopyroxene, so a reais that fractionation of one or bothponsible for the variation. FractionClinopyroxene removes MgO, FeO, CaO,while other components remain constanOn this basis the choice of A1203 asjustified, because N a 2 0 and K 20 may hand Ti02' P 2 0 5 ' and MnO are only minoBoundary rock types.

Molar ratio diagramsFigures 25 to 32 are A1203 molar

Linear trends are

fractionation of the indicated phases,which were determined by x-ray microproin Tables 4, 5, and 6.

The lines on Figs. 25 to 32 were


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points by linear regression (the lineacients are listed in Tables 7 and 8).blende cumulate, was not included in thmafic linear regression l ines, inasmucrock type clearly was not produced byconsideration. Hornblende cumulates w

only in the very latest stages of mafi(1) Fis. 25 and 26. SME/A1

Pearce (1972) devised th e silicafunction (SME = It CaO + M gO + t FeOcritical test for th e common case of opyroxene fractionation. The plot, whiclinopyroxene and olivine formulae, pronly if olivine and/or clinopyroxene avariation. The observed slopes, for band mafic rocks, are approximately 0.9fractionating clinopyroxenes from idea

Table 4. O livine partial analyses, weightSample

124 157 24 C8

FeO 20.73 19.99 26.86 25.35

42.33 41.67 39.60 36.83


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CaO 0.04 0.11 0.06 0.07

MnO 0.08 0.49 0.37 0.29

124 wehrl i te157 plagioclase-biotite olivine clinopyro24 hornblende wehrliteC8 biotite-olivine mela-gabbro102 hornblende-olivine mela-gabbro

Table 5. Clinopyroxene partial analyses,

Sampie

124 157 24 C8 102

' 'eO 2.78 5.78 7.39 7.46 8.91

MO 17.40 16.35 15.92 15.16 15.23CaO 22.37 19.16 19.60 18.98 18.87

A1203 nd nd nd 2.78 nd

Ti02 nd nd nd 0.92 nd

MnO 0.20 0.05 0.20 0.20 0.12

Table 6. Phase compositionsl olivineatomic percent), clinopyroxene (atomic

Fe), and plagioclase (molecular percen


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Sample Olivine ClinopyroxeneCa M g F

124 78.6 45.9 49.7 4157 78.8 41.3 49.0 9

24 72.4 41.3 46.6 12C8 72.1 41.3 46.6 12

102 67.7 40.1 45.1 14

25 42.2 44.1 13

123 41.0 45.0 14C16 41.9 44.0 14

112 40.7 45.5 13

opt. = optical determ ination

Sample numbers as for Tables 4 and 5.


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Table 8. Linear regression coefficien

diarams (mafic rocks).

VB.


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Si02/A1203 SME/A1203.. VB. MgO/A1203It vs. CaO/A1203If vs. FeO/A12oJ (0)It vs. FeO/A120J (c)II vs. Fe20J/A120J (0)I. vs. Fe20J/A120J (c)II vs. FeO + MgO/A1203 (0)tt vs. FeO + MgO/A1203 (c).. vs. Na20/A1203II vs. K2O/A1203 vs. Ti02 A1203

b = Y-interceptm = slope of th e relationshipr2 E goodness of fit , r2 = 1 repres

o

25---------------


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20oE

- 15Mo 10


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(2) Fig. 271 MgO/Al20J versu}ood linear trends are established

rocks on this plot. The observed slopebetween those expected by fractionationor clinopyroxene alone, so clearly som


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has produced the variation. The slope

by olivine-bearing rocks is steeper th

indicating a greater proportion of fradurins crystallization of wehrlite andduring crystallization of the mela-dio

(J) Fig. 28. CaO/Al203 versOn this diagram, olivine cumulate

liquids must plot on a line with slopeare not zero, which establishes that fCa-bearing phase must have occurred.

slopes are interme diate between trends

tion of either olivine or clinopyroxen(4) Fi. 29& Feo/Al203 vers

This plot is extremely sensitivethe fractionating Fe-bearing phases (iThe Fe203/FeO ratio also has a direct

30-----------25 0


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010

C /lQ)_..;

20 Si02EM

150 ,0N _..;


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E 0(.)

(V)04N-..J


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E 10M0N

__, 5


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slope at +2. This diagram is especiaminin proportions of fractionating pof variable olivine composition duringlization is removed.

Analyses of felsic Boundary intruth e trends established by the olivine-

demonstrating conclusively that th e ferepresent final, Si02-rich liquids proof olivine and pyroxene.

(6) Fis. 3la and 32as Fe2The slopes for th e olivine-bearin

rocks are identical (0.04). Neithercan be expected to incorporate enoughobserved variation. The most likelyzero trends is fractionation of small

(7) Figs. JIb and 32bl Na2

35

300(/)(l)o 25E

oz+oQ)

LL


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Mo 20N

Syme Eric Charles 1975 Sec

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Transcript of Syme Eric Charles 1975 Sec