A Correlation of the Triassic Systems of Nova Scotia

and the Eastern United States with a

Possible Origin of the North Mountain Basalts.

Willi am B. Bur ton.

A thesis submitted to the Dene~tMP~t n~ n~olo~v

Faculty of Art~ ann S~ience in partial fulfillment

of the T'eouirement.~ frrr the ~o-ree of Ratchelor

of Science with Ron ours in Geology.

Approved

Dalhousie University

25th April 1973

Halifax, Nova Scotia.

il

ACKNOWLEDGMENTS

Field work for this project was started in the

summer of 1970 when I worked under Dr. R. P. Sinha

who had just written his Ph. D. thesis on the Petrology

of North Mountain. I would like to thank Dr. Sinha for

his help and direction in UW study of the Triassic

basalts of the Cap d'Or area.

In the summer of 1972 while workinp: for the

Imperial Oil Company I had the chance to study the

Cobequid-Chedabuct·o fault and to observe many of the

nearby diabasic intrusives. For this opportunity I

would like to thank Mr. S. B. ~~cEachern and also

Mr. P. Hannon for his guidance in the field.

Fina1ly, I would like to thank Dr. D. R. Clarke

for his comments and help in the construction of the

paper during the last few months.

iii

TARLE OF CONTENTS

l • Ac kn owledgmen t s . ...................... . il

2. Abs t ra.c t • • • • • • .. • • • • • • • • • • • • • • • • • • • • • • • • iv

J. G e o l o g i c Set t i n g of t h e 11 r j_ Ct.S • __ _ . ..... . A. In t r od u c t i on 0 •••••••••••• • 0 . . . . . I B. Nova Scotia •••• 0 ••••••••• 0 c • . . . . 5 c. Eastern United States " •• 0 ... . . . . 7 D. Petrological r orr.par is on • • . . . . . . . II . E. Conclusion

• • • • • • a • • • • • • . . . . . . . . . 13 .

4. The rTri ass ic of Nova Scotia • • • • • • • • • • • 0 /4 .

A. Sediments . . . . . .. . . . . . . . . . . . . . It. B. Ex tru si ves . . . . . . . . . . • • . . . 17 . c. Intrusives ... . . . . . . . . . . . . . . . . ... ~5.

D. Petrology of the Goshen Pi u !7 s ... 3l. E. Summary and \. on c l u s i on s . .... JS.

s. Structural Geolopy • •••••••••••••••••• If • + 3.

6. Conclusion • ............................. 57.

Cited References • • • • • • • • • • • • • • • • • • • • • • • 6 0.

s. General References . . . . . . . . . . . . . . . . . . . . . 63.

IV

~he petro1o~y and geochemistry of the Nova

S c o t i a Trias s i c v o l c an i c s a re con s i d e r e d in the t e c­

tonic framework of eastern ;\forth America. The pattern

~)r sediment&tion and mBgrnRtism is similar througrjout

the region. Source areas 0f the ex tru si ves range frorr;

l a r ge dykes to p o s s i b l e e en t r a l eruptive a rea s , and a

case is made for c onsiderin F! the- plugs near Goshen,

Guysborough County, as a conduit for the North

Mountain Bas~lts of Nova Scotia.

These plugs (diaba~ic ir;trusions) ar-e approx-

i ma t: e 1 y l 0 0 m i l e s ea s t of t h e c 2 o s e :;t r,; o r t h M our: t a i r.

basalts. This discrepancy can be accounted for if a

dextral strike-slip of llO miles is proposed r·or the

~obequid-Chedabucto fault in the ear·.~y Jurassic. rrhis

type of displacement appears t~ aP-"ree wit-h the tectonic

evolution of Nova Scotia.

GEOLOGIC SETTING OF THE TRIASSIC

A Introduction

rrh ere is a grow in[" body Of evidenCe ~rhi ch St' OW S

that the Atlantic continental margin of North Ame.r·ica

may well have developed in late Triassic times by rift-

in g from A f r i c a ( B i r d and I:€ we y l 97 0 ) • It appears

that initially the continental crust was stretched and

that gr a ben s for me d on e i the r s i d e of a c en t r a l r if t -

now tr:e mid-Atlantic ridp-e, w'here the marp:-in was

thinned and faulted, the continental crust was in­

vaded by dikes which may have resulted in the develop­

ment of volcanoes or sill intrusions.

Mare:inal grabens are usually asynm~etrical, with

the largest faults developing on the side away from

the c en t ra l site, or line, of r i f' t: in g ( B i rd and

Dew e y l 9 7 0 ) • In the c a s e o f n o r· t. h e a s t e r n No r t h A.-·n e r i c a

t hi s is the we s t s i de • Oc e an i c c ru s t is p rod u c e d at

an accreting plate marp-in when the central rift is

torn apart. Flanking grabens, with clastic and vol-

e ani c seq u en c e s which de v e l oped durin g r u pt u re , are

pre s e r v e d on con t i n en t a_l margin s that r: a v e mo v e d away

from the new mid-oceanic ridfle.

- --------~-----------------

FIG I

T rt o. s s 1 c A rea. s of

Ea-st e rY'I f'.__J Or th A('() en ca

( S Powev-s, 1916)

tOO 0 ICO :J.oo NIJ...ES __ _.!_, __ _.[

Scc:de

------------- _______________________ _;

:::; e d :i r:1e n t s we r P de p o s i t e rl in t r_ e s e gr e. ben s .. The C!

~lowed a pericd e c u s e c t, i " i t y .. Today re-rnr + s

( t,l--:ese Triassic ever:t.s car, be seen aloYlc_" tr·e ea;;~er·r'

I I •

Hides p read o asH l t i .: v c; : can j s m and in t r us i ::-: n of

A rr e r i c s EJL d in n or t h we s t Af' r i c: a •

sy ste:.T.o8 tic pat tern. 'J'r'PSA cikes are di.--;c OY'ObC t. to thn

su rr•oun din rr str'ucturaL ,'~'ra:Ln, and appeBr urd'e.: a tefl t0

t'r:e regional struct~re. 'l-ebrendt ard ~'.J'ot.orson ( l97C)

c on s ·1 d e r ~- ~: e cl i k e s to be c 1 o s e 1 :v a.~; s o c i e t e d w i t ~i t t e

.1 ~ 1 · i a l p r1 a s e of c o :-~ t i r1 e n 1. a 1 d r i f' t •

if the f·.tlantic: ':onLinents were restored t'J

their relative r:ositior.~ bef'·:-:r·e ~.!ntiner:·.al drift, a

pat:.ern would eT"ler.Q"e ir. w icr f.ne dikes 1.,JC•!Jiri have the

form of a rao ia 1 swarm. A l 1 t h e rl i k e s w l' ._. l c s e e m t o

convert::e or: a -.:enter .located Lr the vicinity of' the

Bahama platfcr-rn.

It· woul(:J seem proba'cle tbat thi ~; pat tern of

dikes formed in response to tr1e crustal st ~'esses ac-

c om pan y i o g c on t in en t a l b re a k _, 'J p • It wouJd appear

equally probable that the Triassic-tTurassL-~ intrusion

of these dikes also occurred as part of the phenomena~

::) cor:tinenta1 riftinv, and could thus account Co the

j_ntrusion of earJy sea-floor (oceanic) material into

t\1e edges of' tre continental masses.

These intrusive diabases are tholeiitic and

t ~- e i r r, en e r a 1 c o mp o s j t. i on i s we l l w i t h i n the c h e r1i r. a 1

ran~e of oceanic basalts.

The relatively new theory of plate tectonics

c a ll s for a re- ex ami n a t i on of t h e t ec t on i c de v e 1 o p­

ment of north-eastern ~!orth Ameriea during the Triassic

and J:urassic. Cantin enta-1 drift and t~-"e creation of

the North Atlantic Ocean produced a complex system of

faults and rift valleys still in evidence alon~ the

At.Lantic ccJnt.inental margins or ~;orth Amer>ica and

No;'tL Africa. The r!eolcgical structu1·es, sequences

an d ev en t s in the s e margin a l are as h a v e s u b s tan t i a l

similarities. A great man:: p·eo1ogicaJ studies have

been made in North-eastern t'Jorth America, so that the

similarities in this area can readily be found and doc­

umented. However, the correlation of events between

Nortb America and North Africa require more study on

the African side.

Correlations have been made between Triassic

on tin en ta 1 red beds in various rifts in east ern ort y,

America.. However, no correlation has been attempted

be t ~r: e en the rr r i as s i c v o l c an i c ac t i v it y of Nov a S c o t i a

ar,d that of t-he eastern United States.

In the last ten years considerable controversy

has been generated over the definition of the

Cobequid-Chedabucto fault (Fig. 12. ). Investigations

seem to show that several types and periods of motion

probably took place along this fault. There is evi­

dence for both dip-slip and dextral strike-slip mo­

tion with the possibility of sinistral strike-slip.

B • Nov a Sc o t i a

The c 1 o s in g stages of the Pa 1 e o z oi c era in

North America witnessed the end of the Appalachian

geosyncline. The Appalachian mountains had been folded

up out of the trough during the Perrr:ian by strong

mountain-building forces. As they were reduced by

erosion during the Triassic a new elongated basin of

deposition formed along the eastern flank of the range

extending from South Carolina north-easterly to the

Acadian area in Nova Scotia. The area of deposition,

fed by clastic sediments! carried down by late Triassic

rivers, was actually built on the old rock platform of

the land mass of Appalachia.

-6-

During the time these Appalachian clastic sedi­

ments were being laid down there was considerable in­

termittent volcanic activity. Great flows of basalt

were poured out onto shallow lakes or wet lacustrine

sediments, or were intruded as sheets between the sedi­

mentary layers. This Triassic basin may have lain al­

most adjacent to north-western Africa and may have

been c on t i gu o u s wi t h it .•

J n i; o v a Sc o t i a the T r i a s s i c s y s t em i s c on f 1 n e d

to a northeast-southwest trending belt along the Bay

of F'undy and Minas Basin shores, with a few patches of

sedimentary material on the shores of Chedabucto Bay.

The southern ~oundary of the ~riassic is a non-conformity

on early Paleozoic Meguma strata, later Devonian plutons

and an angu1ar unconformity on \~arboniferous beds

( F i g • I 7 ) • Tho 1 e i i tic basal t s ov e r l i e the Trias sic

s e d i men t s t o a t hi c kn e s s of n ear 1 y 90 0 fee t • The

flows dip from S to 10 degrees under the Bay of Fundy

as the south limb of a gently plunging syncline (Minas

Syncline), which forms such features as Scott's Bay,

Cape Split and Cape Blomidon. In a few places along

the Fundy shore the basalts are in turn overlain unc on­

formably by 16 feet of calcareous limestones and

~reenish sandstones of the Scott's Bav Formation.

other 'rr i as s i c ac t i v i t y in Nov a S c ot i a inc l u d e d

the emplacement of basic intrusives such as the Gre t

5)r~eJburne dike in southern Nova Scotia. In northern

o~a Scotia Triassic intrusives include quartz­

diabase,. diorite and amphibolite dikes in lolchester,

Pictou, Antigonish and Guysborough counties. Recent

p;eolopy in the southern part of Nova. Scotia, es­

pecially on outlying islands, has turned up more die.-

base and diorite dikes. One small olivine-diabase

sill near Shelburne closely resembles the rocks of the ·

T r i as s i c-age North Moun t a in Rasa l t s •

C. Eastern United States

The Triassic system in ea.3tern North America is

collectively called the Newark group. This group is

found in six major elongated basins and several minor

basins which are found from Nova Scotia to North

C a r o l i n a ( s e e Fi g • l ) • In the eastern United States

they consist, typically, of a sandstone sequence, a

shale sequence, diabase of basalt intrusives and basalt

flows in some northern basins. Fossils in the terres-

trial sediments are extremely rare; how er, a few

vertebrate fossils have been found which indicate that

the Newark series is upper Triassic in age. In New

-lj-

s y the Triassic strata dip towards the northwest

d the basal arkose, a red sandstone forma Lion, an

upper red sbale for'rrta~ion and three lava flows have

en matched by an equivalent sequence of Triassic

r oc k s in C on r, e c t i c u L • Th is b as i n con t a i n s rn ore t h a r:

10,000 feet of Triassic sandstones, shales and lava

r J ows. The three lava sheets of the Watchung T'~oun tain s

i n New tT e r s e y c over an are a at pres en t of over f i v e

hundred miles and attain thicknesses of as much as 800

feet (Fig. 2 ). The ring oike of Cushetu~k Mountain

consists of a sheet of diabase n1ore than 100 ~·eet

thick dipping outward at an angle of from SO to 60

de~~ re e s. Basalt dikes al several places may be mea-

s u r e d in ten s of f e e t i n w i d t C:1 and f' r· om hun d r e d s ·J f

feet up to ei~ht miles in length.

Late jn the Triassic, as tbe p.:rea~ basin that

was rentral New Jersey became fil1ed with thousands

of feet of sediment, igneous act:iFity, called the

Palisade disturbance, resulted in the outpouring of

lava from feeder pipes and dikes along the northwest

side of the Triassic basin and intrusions of basalt

and diabase elsewhere. There were three volcanic

episodes ·each separated ~y depositional periods. Each

episode consisted of one or more lava flows which built

up a total thickness of several hundred feet of basalt.

a W'ATCHlJNO 8A5AL. TS

0 PALI':>AOf DIA8A'S(

FIGl

fipes, dikes and other intrusive bodies a n

f ou n d in t h e rr r i as s i c s e d i men t s an d in tr u d in g t h e b or-

dering gneisses. However, there is no proof that t~~ese

dikes and pipes were sources of the several widespread

outpou,rings of lava. Some of these may be sources,

but. most intrusives lie outside the Watchung r~ountain

area of vulcanism. During this late stage of vulcan-

ism the mol~en basalt, finding most of the conduits

bLocked, was intruded between sedimentary beds to form

the Pal i sad e s S i 11 of d i a bas e .. C or re l at i on between

the sill and the Watchunv lavas is indeterminate.

The bulk of the igneous activity in the Triassic basins

is irtrusive or extrusive basalts and both are found

only in New Jersey, Nova Scotia and Connecticut.

Recent evidence seems to show that this Triassic

igneous activity oririnated along a fault line at the

eastern edg~ of the Triassic basin. The basaltic

magma then found it easier to intrude and lift a

great thickness of overlying sediments than to break

through to the surface. rro the west the faults may

still have been active and favourable to form the

series of lava flows. Thus there seems to be a type

of rift valley system with intrusions along both flanks. i •

This type of hypothesis may also be appli~d to the o

gin of the Nova Scotia basalts.

•i

J .. Pet r·o l rison

The geologic environment of the Trias c of t

astern United States closely resembles that of ovA

:)cotia .. 1Ple sequence of sedimentation and the ex-

tens 3_ve magmatic activity is almost ident L~al in both

areas .. 'The extrusive rocks produce normal tholeiitic

flood basalts while the intrusive material forms dia-

base dikes and sills. In both regions the conduits for

the volcanics appear as larf{'e dikes and volcanic plugs.

Petrological comparisons in both areas show very

similar mineral and chemical constituents (~,ig. 10 ) •

F'or example, both show t""Je pyroxeneE~ augite, subc a lcic

augite, and pigeonite in two distinct {lenerations and

a variation in the plagioclase feldspars from An

to An • Also, variation diagrams show that frac-

tiDr;ation of the phases was subject to calcium control.

W i t h the a i d o f a c om p u t e r program, r. T Pii.J nor­

mat i ve values were calculated for· rocks from the North

Mountain basalts, the Palisades diabase and the Great

S h e 1 burn e Dike • The re s u 1 t s s h ow a c 1 o s e s i mi 1 a r i t y

between the mineral constituents of each suite of

rocks. (Computer summary in back pocket). To show

th3 petrological relationships between these three

areas a ternary diagram was used to plot the

'-------·)L_____ ______ v'_;::__

Co.M'j S ·, 2 0 6

(D•ops•de..)

-12.-

I

..... I

Co.Ail S. 2 0 8

( A!"lor--1-h•+e')

---,. \

\

A \

I PLAY.

I

(!.

ll

/ /

I qrz.

FIG 3.

b. Nov-+~ Mo.._.,..,+o..ir- Bo..so-.1+-s

x Po. I•:.:, o.cle.s J) io..l:x..s~ .

o C.-reo.:+ Sl-~\ l>ur(Hc l)J~e. .

S;Oz ( Q"a.rh: .. J

oclase diop8ide and quartz values. Tl'Jese value

ere calculated from the summary of the computer pr

shows how both the North ~'toun tain ba-

sB,_ts and t":-le Great ~~-helburne Dike overlap the fielri

of the Palisades diabase.

E. :onclusion

~here are remarkable petrological similarities

betHeen the eastern United States and the Nova Scotia

igneous Triassic system~. These similarities probably

indicate a much closer relationship both in time and

space between tne two &rroups. It also seems probable

t h a t both i gn e o us s .'T s t ems or i ? in ate d fr om. a c lose l y

related parent magma and that both were affected by

the same magmatic disturbances. is Lrn eous dis-

turbance may well be the result of tf-:e last opening

of tte North Atlantic which probably started in the

La t e Tria 8 8 i c •

THE TI~IASSIC OP NOVA SCOTIA

~)ed i men ts

In the Acadian area of Nova Scotia, t:--1e Tria.ssic

sediments form what is known as the Annapolis FoPrnation.

l t consists of nearly 2, SOO f'eet qf undeformed non-

marine sediments, mainly red conglomerates and fi:1er

detrital rocks. Over these sediments flowed a thi,~k

layer of ~rriassic bas a 1 tie lava forming the North

~ountain basalts. Together, these two formations make

p ~.be b'undy Group. Powers (1916) named the Annapolis

For·<Y,at.ion and subdivided it into two members: the

lower, :PJo: ~vl.1le Formation; the uppAr Plomidon Formation

(Fig .. II \ ) ..

Due to the semi-Arid climate and depositional

coned tions, few f'ossi Ls are fcu::d in tLe scrata. The

few o s ~~- r ac o d s an d s i 1 i c i r i e d a :11 : a r b on i z e d p 1 an t r e-

ma i n s i n d i c a t e La~ e T r i a s s i c a rr e • JV~ ore o v e r , f ish an d

shell remains in the Scott's Bay Formation, w'nict over-

lies the North J~1ountain basalt, tend to confirm Late

Triassic age. In addition, fossils of ~t-:,eria found

by Haycock in the Kentvilile area are compar-able with

E. ovata Lea, which is characteristic of tt-:e Appalachian

:ri. ssis. In t b i s conn e c t i on , Pow e r s { l 9l ;_, ) s t at e s :

'l1t1e paleontolo[!ical and p leobotanical evidence prove

tr~at t£1e Acadian area is part of the ~ewark tern. ,.

Named by Powers in 1916, the Scott's Bay

For rna t i. on i s t b e yo u n p- e s t s eq u en c e of rr r i a s s i c s e d i -

rne o t s ( b' i g • II ) • It is the uppermost formation of the

A c ad i an T r i as s i c a o d l i e s d i s c on f or rna b l y on t h e North

:·~Jountain basalts from which some of u·,e sediments

originated. The formation is composed of up to 16

feet of interbedded arenaceous limestones and cal-

careous sandstones, which are exposed in two small

s t r, u c t ural bas in s on trJ e n or t h shore of Nor t l": Moun t a in •

In 195"/, I. M. Stevenson found several out-

crops of sedimentary rock in the Guysborough area

1- ) • de V. Klein named these outcrops col-

lecti vely as the \,hedabucto Formation. VerteLrate

f o s s i 1 e vi den c e c on f i r ms La t e T r i as s i c age • Voss i l

remains of Archosauria sugpest B correlation with the

Late Triassic of New Jersey and Connecticut.

The Chedabucto Pormation consists of a few

outcrops of continental red beds lithographically com-

parable with the Wolfville Formation an comprising

brownish-red sharpstone conglomerates with minor sand-

stones and siltstones gradational into each other.

___ --~ ._--~ ~--~-~- -~ --L GEOLOGY OF THE GUYS BOROUGH

_____ ::::.-==:::..=..:----­- - --====

CHEDABUCTO BAY

-- ------~ r::~~-- -- j I --~----Jl --~--

AREA

ev

.. " d ud.aeea 11•

~n -~r~!D.V•~r .. ~k• u th4t7 4o Trure area

,. ~ ~~ .. ~~~- - •• .,._..,;- ... '!!i'' ..; - ... 'w! • "" ............ - -· --.

' 1f•t1oel lit•WII~••· ll&b ••\81a et•• "DilGMr&~•• . !1M __ Oen1alll Jta~1N oonsl...,.\e

·it leat •••"'" ~-~ .._ nor~ awe et IUDu

·kala.

aleas

.... u.al atl'ike-alip ., abMit 110 aile•

c•···t~-eto. tul' , ......... , "'• Chedabueto·•••.atl .. aa4 the .O.rr.l8b Paelea have

had a 0~ Ol'iai8e

1117 ot

t::==============~=====================--=-==--=-=-=-=--=·~~===--------~:-·--------------·--------------·-- -----------· ------------- ---··-COI3£QU!D

<S;.l

U TRIASSIC BASi\LTS

Fl 5

ell-twinned usual thout alteration.

r ox ene (pigeon ite and augite) is also quite fresh and

constitutes about 3_5 percent of the rock. It seems

o have crystallized after the plagioclase and tends

to occur in small aggregations.

There seem to be two groups of pyroxene crys­

tals in these basalts, perhaps representing two genera­

tions. The first of large phenocrysts and the second

of quite small phenocrysts. Brown glass appears to

fill in many of the spaces between the three major

constitutents, plagioclase, pyroxene and magnetite.

Specimens with less glass showed ophitic texture with

plagioclase enclosed in au~ite. Sections of pillow

lavas with glassy rinds showed variolitic texture

(Sinha, 1970); however, these are, probably not true

pillows.

Minor constituents in these e.xtrusives include

apatite and hematite. Zeolite-filled amygdules show

an outer brownish rim, followed by a pleochroic green­

yellow zone. Som·e vesicles are filled with clay which

is probably a result of assimilatioo. This type of

assimilation is only shown in the Cape Split flows.

It could be due to either interstratified sediments or

the basal Triassic sediments.

- 20-

Opinions as to the number of flows that con-

stitute the North Mountain basalts vary considerably.

Klein (1960) first noted as many as sixty-six flows,

but later revised the number to sixteen. More re-

c en t 1 y Sinh a ( l 97 0 ) s t a t e s t h at on 1 y f our bas a 1 t i c

flows occur in the North Mountain area. Most of the

authors of the many publications and papers relating

t o the s u b j e c t do n o t c 1 earl y de fin e the t e rm 11 f l ow"

in the context of their study, so that a reconcilia-

tion is difficult.

After extensive study of the North Mountain

area and the extent of flows and flow units, it a.p-

pears to me that following the huge basal unit only

about three or four major volcanic eruptions occur red.

Some areas do show a sli~htly larger number of flows,

but most of these appear to be local flow units due in

to topographic irregularities and irregularity~erup-

tions.

The lowest flow, the Cape Spencer or Blomidon

flow (Sinha, 1970), is by far the most extensive flow • I

with a thickness of about 600 feet. It is character-

istically dark and massive with columnar jointing and

very little or no amygdaloidal top. This flow fol-

lowed by the lower Cape Split flow which shows no

j o in t in g , a l a amygdaloidal top and character-

s t i c a 11 y br own i sh-red • Th e upper Cape S p li t ow is

~ milar except that it has a more dark-purple tinge to

t~Je basalt. Both flows contain a large percentage of

z e o l i t e s bu t to ge the r are no more than 8 0 fee t t h i c k.

Just before the last flow interstratified sedi­

ments occur indicatin~ two major extrusive events.

The Goshen plugs include two large extrusive vents and

further studies may show a relationship between the

basalt flows and the vent through which they were

erupted.

The t op unit i s the Sc ott ' s Ea. y f 1 ow • It is

compact, grey and has rinds of iron oxide or some­

times chert along the joints. It is about 80 feet

thick but the vesicular top is n~ver complete due to

erosion.

Throughout the whole North Mountain there is,

to date, no evidence of volcanoes, fissures or other

feeders. In 1960 A B:udg:ins suggested topographic

ring structures on Long Island in Digby County as a

chain of ex t ru s i v e vent s , but p e t r o l og i c a l e v ide n c e is

lacking. The only other 1 oc at ion in the North

Mountain area which has lbeen suggested as the source of

the North Mountain basalts is on the north shore of

Minas Basin (Marster, 1890; Powers 19 : MacNeil and

Take 1966). The following evidence points to a vol­

canic source in this area in the vicinity of the

'w a s s on 1 s B l u f f - F i v e Is 1 an d s ar e a •

Peperites

In 195 3 Michel said '' Peperi tes ( peperi tic

breccias) re~ult from intrusion, fragmentation and

mixture of basaltic magma with shalJ.ow water and wet

l a c us t ri n e c a 1 c are o u s , ar g i 11 a c e o u s or d i at o mac e o u s

sedjrnents." The majority of the peperites occurring

in Nova Scotia are found on the north shore of Minas

Basin. Here basaltic lava was extruded onto shallow

water sediments from a nearby source. As the lava

cooled rapidly, the gaseous basal material rose

through the above flow causing extensive fragmentation

associated with escaping gases and solutions. The

restricted occurrence of these peperites to the north

shore of the Minas Basin suggests a local extrusive

vent.

Volcanic Bombs

In the whole Tri~ssic sequence v ol can ic bombs

embedded in sediments underlying lava flows have been

-lund only in the Wasson's Bluff - Five Islands area ..

,, ey have a thin rim of baked sediment indicating tLat

tL bombs were hot when emplaced in the sediments.

5::,ha (19'/0) notes that the downwarping of the under­

lyine: strata indicates that they were dropped into

t h e s e d i men t s , probably from a n ear by v en t. A l s o ,

pyroclastic material at McKay Head near Wasson 1 s

Bluff and other nearby areas shows occasional beds of

thin to thick tuffs. No other pyroclastic materials

have been found in the North Mountain area.

Flow Directions

The basal unit shows no tubular vesicles so

that flow directions can only be deduced from the

trend of the c o 1 u mn a r join t in g • As the la v a c oo led an d

formed columnar jointing, there could still have been

a very slow creep of the viscous portion. This might

tend to send the columnar basalt in the direction of

flow. If this is in fact the case then the lava

flowed southwest down the Bay of Fundy in an average

azimuth direction of 250°.

Due to the absence of int erf low sediments it

would seem that only a re1atively short time elapsed

before the next volca.nic event. This second unit, the

: OvJer Cape Split flow (Sinha 1970) dif s cons der-

biy fr·om the basal unit. It shows good tubular

v~sicles especially along its bottom contact. T~e

,1irection of these ves-:.cles shows a general trend of

the lava fr·om the northeast (the Minas Basin area! to

the southwest.

TVTi n era liz at ion

The mineralization of the basalts in the \.Jasson 's

Bluff- Five Islands area is especially diverse and

abundant. As one progresses from this ares to the

southwest there is a marked decrease in minera1izatioc.

Certain zeolites are particula:r·ly abundant in

the extreme northeastern outcrops and some, such as

chabazite and gmelinite, are almost completely re­

stricted to this area.

Siliceous sinters are also fairly abundant here

but are very rare or absent further southwest.

MacNeil and Take (1966) found evidence of

native silver and base metal sulphide mineralization

which they say is closely associated with the source

of the basalts.

lntrusives

The northernmost confirmed r of the group

o Triassic-Jurassic dikes is in southern Nova Scotia

and is kr;own as the Great Shelburne Dike. The

Canaciian Geological Survey (1969) indicates that there

may a1 so be another dike off-shore, having the same

cen eral strike.

In Triassic times, prior to continental drift,

the Nova Scotia dikes are seen to be paral .1 e1 to the

late Triassic dikes in the Anti-Atlas Mountains of

Morocco. Both sets of dikes are parallel to the

proto-Atlantic rift. In f''!oroc co the dikes are as-

sociated with sills and basalt flows in Triassic red

heds similar to the Newark series of the Appalachian

region.

The Great Shelburne Dike is a quar·tz-diabase in­

trusive extending along the soutL shore of No' a Scotia

from the LaHave Islands to Pubnico, a distance of

about 70 miles. rrhe dike intrudes the Ordovician

Meguma Group and the Devonian granites. Like the

Palisade sill it is a typical tho iite. There are

only a few outcrops of this dike and it s best re­

vealed by aeromagnetic maps which show an anomaly along

the length of the dike. The dike is best exposed at

1 s wh ere it has a wid t h of o v e r 0 feet.

th the contacts are not exposed a decrease in

€! c E! in s i z e is e v i den t on bot h s i d e s s u sting a

r_ ar·by contact.

~.r h i s diabase is a me d i u m- t o- c oars e 8'r a in e d

ro~k with light grey plagioclase laths enclosing

vrAenish-black pyroxene. These pyroxenes weather to a

red-brown and 'the plagioclase to a yellowish grey.

This makes outcrops and boulders easily recognizable.

The rock shows good oph it ic texture, under the

microscope, with plagioclase (mainly labradorite) and,

rarely, andesine in the outer zone of a few zoned

laths. There is only minor serictic alteration of the

pl agi oc lase. Augite is locally altered to urali te

which in turn seems to be altered to chlorite.

Hic1·ographic intergrowths of quartz and sodic platio-

c lase are abundant. Other minerals include a few crys-

tals of apatite and skeletal ma~netite crystals.

Another possible Trias sic intrusive exists on

the south shore of Minas· Basin, 10 miles north of

Windsor. On the north shore- of Johnson Cove diabase

sills cut Horton Bluff shales. In 1905 H. Fletcher

described these as "fhree small areas of trap'' re-I

lated to the North Mountain basalts. Petrolopica.lly

/

HANTS C.o ·

/

N or-thurnberland

_,/"'

/' /

Stra.l.t

\ \

~

./"' _./

HAL..I~AX c..o

_./

-::;

PIC.TOU C.O.

\ ---/\-· -------/

\ '\

\ \

-- --~~··

_...---

GVY5130f\OIJC.H Co.

\

9

Ocean

(

~ /

INDEX

}(

MAP-

CENTRAL NOVA SCOT!

Sco..le of M:ies

1ey seern identical with the other Triass c jn usiv s

d lithoJogically they are at least post-

s iss L ppian.

The only other possible Trjassic dikes sou of

the obequid-CYedabuc to fault are found in the Truro

area. On the Salmon River, J/4 mile upstream from the

j u rJ c L i on o f' B 1 a c k H i v e r , a d i a b a s e dike c u t s r or~ k s of

t L e C an s o group an d shows min or a l t e r a t i on of ad­

jacent Riversdale shales. The diabase consists

mainly of augite, which has altered locally to uralite,

with manor plagioclase (An 60 ) pyrite and calcite.

F1r om the aeromagnetic profiles (Map No. 787G) the dike

a pr.lears to strike eastwest and dip steeply to the

north. It seems likely that this dike was intruded

along the adjacent Riversdale fault which is part of

the Cobequid-Chedabucto fault system.

On Penny Mountain, also in the 'rruro area, just

east of the old Truro-Pictou Hight-1ay, H. Pletcher

(1889) describes a hill of black diorite", but no

positive outcrops are evident today. However, dia­

base and altered rocks of the ranso and Riversdale

group are found as float in the area. "Using the

aeromagnetic maps this intrusive was located more

precisely and shows an eas.t-west trend across the hill.

Th mineralogy of the diabase float is alm t den-

ti a to that of the dikes described earlier.

~here are a preat many diabasic intrusives

just nort'r, of t11e Cobequid-Chedabucto fault line. ;\

feH of those e:xarrir,ed are summarized in the fo~ l,,w­

in g paragraphs.

In Pictou County basic intrusives rocks cut

batt Windsor and Canso strata. At Centredale, dark­

green, fine-grained diabase has metamorphosed Winds or

3ha e to an argillite. The diabase is predomj nantly

augite and plagioclase (labradorite) with smaller

arr:ounts of hornblende, muscovite, chl:;ri t e, epidote

and magnetite. There ls only minor sericitization of

t b e p l a 9 i o c lase , and mod e rate a 1 t e r a t i on of au p: i t e an d

hornb] en de to chlorite. Simi1ar diabase dikes out­

crop on Black Brook and on Cameron 3rook south of

Hopewell. These intrusives all sr:ow good ophi tic

texture and, often, reactioYJ rims of epidote around

horn b 1 end e.

The dikes in Pictou County do not strike east­

west as in the Truro area but seem to parallel fault

planes that strike northwest-southeast. Stresses pro­

ducing this type of fault system could have resulted

from dextral strike-slip along the Cobequid-Chedabucto

fault.

The most important group of ic tru ves

occurs near Goshen, Guysborough County at the

waters of the Salmon River (Fig. 8 ). In this area

numerous diabasic and gabbroic dikes, sills and small

plutons all cut Paleozoic rocks. Aeromag netic maps

are helpful in delineating these intrusives. These

Goshen intrusives include diabase, gabbro and amyg­

daloidal diabase. They intrude rocks of the Horton

group producing a coo tact metamorphic halo. Meta­

morphism has produced argillites, quartzites and slates

from Horton sediments as well as a gneissosity which

seems to parallel the boundary of the intrusives.

(Fig. 8 ).

D. Petrology of the Goshen Plu~

The plugs are easily recognised in the field as

small. hills or knobs up t 50 feet in height. Their

texture is seriate to microporphyritic, but much of the

groundmass has been replaced by chlorite and epidote.

There is no apparent flow alignment of phenocrysts but

vesicles d elop flow bands near the contacts.

The essential minerals of the plugs are plagio­

clase (An 60 ) and augite. The anhedral to sub­

hedral augite grains are sometimes twinned oo ( 100).

N

HA

----· --- ~·

,.-' I l

" - / ).-Ia_

1

I

HA

\

I (

I I

~

\

HA

-

(

~ /

M etite occurs as subhedral to euhed crystals

which are often s"keletal. There are, throughout the

plup;s, small amounts of orthopyroxene.

Secondary alteration of the plugs can be seen

by extensive albitization of plagioclase phenocrys-

tals which now contain larr,e patches of chlorite and

epidote. Of the few vesicles found most are filled with

radiating bundles of chlorite.

The following is e. short description of a few

thin sections of rocks from the Goshen plup.;s :-

A -1 Di a bas e • (South R i v e r Lake Quarry )

Somewhat irregular, altered laths of labrador­

ite are partially enclosed in rims of alkali

f e l d spar ( alb i t e ) • Ferro ma gn e s ian min era 1 s in­

elude ortho-pyroxene, augite, biotite. The

biotite is altered to magnetite and chlorite.

Accessories include subhedral magnetite, and

epidote.

B-ll Diabase prophyry. (Erin v i ll e Qu a r r y ) •

This rock contains large altered phenocrysts of

labradorite containing chlorite and epidote. The

fine-grained matrix in yludes pl i oc lase horn­

blende, biotite and magnetite. There is also

min or carbon at e f i ll in g s an d a few e u he d ra l

crystals.

8 Diabase. ( H oppen de ) . Mainly composed of a1bitized labradorite and

anhedral augite with ophitic texture. The

aug i te is s 1 i p: h t 1 y a 1 t e r e d to u r ali t e and b i o­

t i t e • Thi s r oc k rna y a 1 so c on t a in a r e w grains

of pigeonite indicative of near surface intru­

sives. Other minerals include up to 5% apatite

and 10% ma.gn et it e.

When comparing the petrology of the Goshen plugs

with well-known diabases there is found to be close

similarity; especially with the Palisades sill and the

Great Sb e l b u rn e Dike • ( 111 i g • I 0 ) •

In Connecticut, within the Newark system,

several. volcanic plugs have been the source of basal­

tic lava flows. The following comparison of these

pluvs with those near Goshen indicates that they are

very similar:-

(1) Both volcanic plugs have chemical analyses that

correspond to average tholeiitic diabases.

( 2) The essent 1 nerals of the plugs are plagio-

clase and augite, with minor magnetite and

orthopyroxene.

( 3 ) The two main constituents, pl oc

a.ugi t e, show good oph ic texture.

e and

(4) Both diabases coot n vesic s filled with

chlorite and show secondary alteration.

()) The plugs in both areas intrude sedimentary

rocks prod u c in g con t a c t au r eo l e s that are

substantially larger than the surface area of

the plugs.

(6) Volcanic bombs and tuffs seem to have originated

from these vents, as well as basal tic flows.

These similarities su g~es t that the Goshen

plup-s, like those in Connecticut, acted as conduits to

lava flows. In Connecticut the flows are adjacent

to the parental volcanic pluers whereas in Nova Scotia

the flows have been offset from the plugs by a major

dextral fault.

Partial chemical analyses of a few of the in­

trusive rocks from the Goshen area (below) have been

compared with similar tholeiites from the North

Mountain, the Great Shelburne Dike, and the Palisades

( fi' i g • I 0 ) •

r r~~~4 Al 2 03 Fe.T /'13 0 Ca..O K;(O \-, Oz. P2 Os

I A-1 ~50·80 1'1-10 12 64 j$-JO ! rl·tf-6 o-m _.2 Ob- 0·4.3

---------·------

B-It I 4-~JO 14 50 13·93 5·60 '1·58 0-84 3 -It- 2 01 - -----·---------

13- 4-0 I 5" 5"6 6·70 'l-06 0· 8"5" J-oa o ·¢S

-----------

14·50 l ~ 36 ~-~0 Y·84- 0 7~ ~ ·71 0 67 ----- -----

Mineralogical similarities also exist with the

North JVlounain basalts and the Great Sr1elburne Dike.

The mineral ranges of these two grours are compared

below with the Goshen intrusive.

Labradorite

1Au gi te

Pigeonite

L' A tN Lund (1930) Hudgins (1960)

3 8-50~~ av.

20-40% av.

0-15%

GO~HEN1NTHtJSIVES

40-60% av.

25-40% av.

GREAT DIKE Lawrence ( 1966)

45-60/S av.

18-4.5% av.

I

I 0-10% Orthopyroxene

Glass and Magnetite 5-10~~ 10-200~ av. 15% ~~------------+-----~-----------------

0-.5%

10-JO% av. lA% I

A RfSO F E L L

I. 3 4 s-. b 7. 5' 9

s1o.2. 50· ao 49 · 3n 4q 41 51 ·80 47. tJ6 48 ·30 s-1 '70 j-o r 7 4q to

Al,zq /-4. I /Lt 50 /5 'jq j 3 '13 14-~q 13-+o 15Ao /4- 65" 11 8'0

F~o I Fa..! o1j ll ) c_,~ 13 q 3 13 31- 12 OS L I · 34- 1 ~-- s-6 I o ·So ( 0 6{ i.2. ·b'f-

1'"'150 b J I 5 bO 61.7 6-50 '-{' 1'8 6 ·co 6·70 b 'f'S" IO Jo

(a_O I 0 ''TO q.s 8 q -65" g. 6'5" 7 8b. Lf·Ob q So 9' 3 3 7 86

K2 0 o·z?l 0· 81- 0-5"'0 0·75" 0·77 0 '65" 0·98' Q. 7"i t)·5'7

02. 2 05' 3' 14- l-6t I· 6 'J 1 ·s-o 3 .oo 1- I I l l 3 ( /0

Pz05 0·23 2 0( 0·16 O·l.O 0·32 Q. 6S" o-14 0 ·IS 0 43

F'IG 10.

f. Ave.ro.c1

.c. +-ho\e .. .'r ii-i c. ba..soJt O.'f'd._ d..io..bo.se.. , Noc..ko\c:L<>;, (tqS'1- f 101.1)

z. Goshen Inh·u'bi\1€.. - cUo..bo...se.. - f3-ll Wes+- Erir.v;lle..

3 N'orth. Noun-\-()..in Ba.'5o...lt 1

Si.,-..ho.__ (1q70 #31(\).

4. Ave:f'CL~e... C-ompos c' i-io n. 0 ~ -the. 'PCL\; so...d.e 'S t' ..,-f.'("'v$'1 Oh ( t< W'o..\lr..e..r lqGq)

5. N o.;-t-h. Houn+o...i""' 6o.so..lt- ( McKo..j Hd. J SiAho.. !<l. 70.

6. L::O..sf Mou"+a..in - clio.. ba.se.. i"'-f-r.usion -EM-I

7. GrecL:f- .D~ke... , SI·H!.Jiou'('l"\e., ( ..(QcvV"enc..e.. !Cf66J

5. PcdisCLde~ cLo.bo...se, 5pr;f'\'Jf;e1cl New Je'("'se~ (wo...tke_.-- F· lGl.<to)

q, Goshen Irt+rusivc. - dia..loa..s~ -Sout-h.. ~iver ~RE.. Quo.rrj · A-1

E (' .._) an d C on c l us i on s

It seems very likely that the intrusives of

t. e Gost:en area were once basal tic plup-s and that tb

necks served as the conduit for basal tic flows. ·~e

v o 1 c an i c con e s which mu s t h a v e ex i s t e d on t h e s u r r a c e

could have been removed by e.ciation. However, there

is no evidence in the area of any extrusive post-

Carboniferous or Triassic flows. It is therefore sug-

gested that these volcanic necks might have been the

conduits for the North l"'lountain basalts, the outflows

being in a south-westerly direction crossing the im-

mediately adjacent fault line.

In summary, the following factors support this

proposition:-

( l) The plugs are composed of diabases which

closely resemble the North Mountain basalts

both petrologically and veochemically.

(2) The diabases vary from the contact to their

centre. For ample, one of the inner rings s

considerably richer in apatite than one fur-

ther out.

(3) 'rhe contact metamorphic aureole is larger than

the surface area of the plugs which suggests

that there may well have been a conside 1.

amount of magma passing through thes con uit

(4) 'The plugs are very similar to volcanic plus in

Connecticut that have been identified as con­

duits for local basalt flows.

The origin of the North Mountain basal L s seems

to lie near the intensely block-faulted north limb of

the Minas syncline, just south of the Cobequid­

Chedabucto Fault. MacNeil and Take (1966) stated 9

"rr he r e i s c on c l u s i v e ev i d en c e that a chain of T ri as s i c

volcanoes existed in the block-faulted zone near the

Cobequid Border Fault ••• " Along the north shore

of Minas Basi~, near b,ive Islands, sill, agglomerates,

volcanic tuff's, bombs, pipes, base metal sulphide

mineralization and a unique zeolite assemblage all

seem to testify to the above statement.

The volcanoes reported by MacNeil and Take and

the Goshen volcanic plugs in Guysborough County lie on

opposite sides of the Cobequid-Chedabucto fault and

are approximately 110 miles apart. The discrepancy

in distance between the Goshen plugs and the extru­

sive material can be resolved by postulating a dextral

strike-slip along the Cobequid-Chedabucto fault. This

p~acement would have occurred after ext s o

--)r t:,[l North Mountain basalts, sometime durin

ea ly ,Turass}c.

Jf' a source f'or the North fv1ountain basalts rloes

lie tTear the nortr: shore of Minas Basi~ one important

question arises. Is it

would extrude lava that

likely that a single source

travelled along a basin for a

dis ance of 125 miles or more? The g;ently dippinp,

linear character of the North Mountain flow sup-p:ests

that the basalts might have been extruded from fissures

an d n o t from v o 1 c an i c c en t r e s • Howe'' e r, the C o 1 u m bi a

f?:iver district shows vast plateaus of basalts that have

been extruded from a local source and nave travelled

almost 100 miles in several directions. ( H o l me s , l 96 S ) •

It seems almost certain that there once was,

in the area around Five Islands, at least one extru­

sive vent which was the source of these volcanic

materials. It also seems lik8ly that the vent or

v en t s in fa c t ext ru d e d l a v a • ri'h ere has a l ways been a

marked difference between the North Mountain basalts

and the basalts on the north shore of l1in as Basin.

Klein, (1960) described the two as different basaltic

areas lying strati graphiq ally apart: he named those of

the north shore of Minas Basin the McKay Head basalts.

te novJP pr>, Sinha (1970) demonstrated . t t y

e e tratt ica lly identical and he, therefore

1' •(p-·n('np pr t~em into t!--)e North Mountain ba alt~

ever· heless. t\-J(' "'l"f"l"'ir. i"roups may well exist;

Nortr·1 ~loun tain basalts and Klein's old Me r'J3.y Head

basalts (Fig. II). rrhe two groups would be strati­

gra.pLically similar but could derive from dif fe~ent

sources.

In conclusion it is suggested that in the Late

Triassic the Goshen plugs were positioned just to the

north of Hasson's Bluff and Five Islands. From this

p :) s i t i on i' t i s p o s s i b 1 e t h at the s e v e n t s c c u l d ha v e

ex t ru d e d all the bas a l t s of the North Moun t a in , and

t"here is an even stronger probabi 1ity that they served

as a chain of extrusive vents producing the volcanic

tuffs, bombs, agglomerates, associated mineraliza­

tion and flows of the I~cKay Head basalts.

K 1 e i n (tqGo)

An n o..p o I is - Co~ (\ w 0- I t Yo...\ I Q_Y , Kinqs , Co.

Strat,grophic Successton of Triassic Rocks -Neva~ ot1~

Go.s 1 n Noy-+h Shoy-e

i

Ann o.po I' s -(o,.-nv.r~\ I 1 s Vo..\\e'j, K1n~s Co

--------------------+--------------··-----·------·---+-+--------------- -------- -

C5lomtd..of\ Fov-rno..t lC>r"\ B \om ; d...o v"'~ F o r'r'l"0- t 1 o r>

_j_ _________________ -----1 i :I i'

T--

M 1 n (.1.. S G s 1 Vl

t'fo( +h Sno"e

-----------------r------1 He-~=~ ---~~~-~J---~-~s~ l t -----l~---·------------------------------+-----'---------------------~ !

Wolf Vt I I e. ~ oy10o.t i oY~ Wo ( f v 1 \ <2. F OY"rYvJ.J-; ov'

------------------L-------------- ---------Fl G II

.wor f \/1 I )e FOYY'YlQ...t ion Wa \ fv 1 \I e F o" (Y\.(lt- , ~: (1

The C o be q u i d- Ch e d a b u c t o fa u l t i s par t of a l on

2ystem of faults extending northeasterly along the

Atlant.ic seaboard, across Acadia and through Newfound d.

The whole system seems to have been active since the

1ate Devonian with most of the structural movements

tak ng place throughout the Carboniferous. However,

the robequid-Chedabucto fault appears to have been

active in the rate Triassic or early Jurassic as well.

Along the entire fault system the latest phase

of slippage was dextral with the exception of the Harvey­

Hopewell fault in s out bern New Brunswick, w~~ ere a

sinistral movement followed larger dextral slips .. A

arboniferous dextral displacement of 12S miles has

been estimated in southern New Brunswick by Webb

(1969) who has also suggested a similar displacement

on the Cobequid-Hollow fault and perhaps 65-100 miles

in Newfoundland. There is no evidence of dextral slip

along the Cobequid-Chedabucto fault in the Carboniferous

but during the late Triassic there appears to be a

strong probability of a dextral strike-slip of 110

miles for the following reasons.

\

\

(

\ ) l ~/

PALl NSPASTIC

MARITIME

MAP OF

PROVINCES

THE

/

( l ) 1 f th e G o s h e n p 1 up s are t h e o u r c e are

fur the basa1 ts of the

been displaced 110 miles.

of FUn they have sine

(~-}) The Triassic sediments exposed near

Guy sborough seem to be d i sp laced from their counter­

parts in the Minas Basin area.

(J) There is a general mismatch of rock types

and ages across the fau 1 t. A repositioning of the

southern po~rti..on of Nova Scotia 110 miles to the

east aligns many identical rock groups.

(4) rr,he Mississippian rocks of the Windsor­

S h u ben ac ad i e re g i on co u 1 d h a v e l a i n j u s t s o u t h of

their counterparts in tre Antivonish-Canso Strait

area~

(5) Dextral stri e-slip motion is indicated

by secondary sinistral dra.g faults on the northern

side (Fig. /6 ).

(6) The epic enter of the d Banks earth-

quake of 1929 lies almost due east along the strike

of the fault and this may indicate recent motion

a l on g t hi s fa u 1 t z on e. ( Fig • 13 ) •

0 50 IO<J 1~0

q 100

NII\ITIC.AI- MIL£-' I

6o•

GRAND BANKS ~·

£p,cenfe_r F~r -;-;, 12 Grand. f3a.n ks

Eo.....--f-1-...Xvo.Ae- ( JC(;.q)

J:IG. 13.

1\ e en t 1 y p u b l i shed data in d i c at e s th a t t h e

·umberland Basin just north of the Cobequid complex

-~ , ~ a 1 s o p a r t of a r i f' t s y s t em ha v in g i t s ow n d n

a ion and structural envit>cmments. Subsidence prot~ o-

1y began in the late Cevonian perhaps resulting t·rom a

~T"aben or rift after the Appalachian orogeny. t also

seems likely that this period marked the first ap-

pe ranee of the Cobequid fault as block faultinr

oc8urred on both sides of the Cobequid arch, witL t~le

central Nova Scotia rift beinp formed on the soutr,

side. nere Horton group rocks were deposited in a

r i f t v a l 1 e y with t he C o be q u i d on it s n or t 1-L e r n b our;­

dar y an d the We s t Hi v er-St • Mary ' s fa u l t t o the

south. Later Carboniferous north-south thrust fault-

in g prod u c e d the R i v e r s d a l e I:<' au l t an d o t he r s in the

Truro area. A section through the East l"1ountain area

shows the relationship of Carboniferous and [Triassic

strata to these thrust faults (Fig. 14 ). There is

e v i den c e that s t i 11 1 at e r, pe r haps d u r in g- t_:, he r !l ria s s i c ,

extensive dextral movement occurred on the Gobequid­

Cherlabucto fault offsetting the once-related Cobequid­

Hollow fault line. The other segment of the Hollow

fault, therefore, should reappear south of the

Cobequid fa.u 1 t in the Bey of Fundy (Fig. 12 ) •

·---

4

/ /

/ /

/ /

/

4

\

3

3

2

F I 14-

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

/ /

0

L__

/ /

/ /

/

s-oo §00

/

1/ T J s-/

/

I ~~ I I

+ 5 \5)

Althou~h there was probably substantial pr

r .ssic strike-s p faulting on the Cabot-Hollow

raul t, the Belleisle fault, and the Harvey-Hopew

f'aul t, no strike-slip 'nad yet occurred on the

Cobequid-C'_-Iedabucto fault. Luring the late rrriassic

tensional movements reopened many of the Carboniferous

rift basins along eastern North America. Similarly

str ctural activities also occurred on the eastern

portion of the North African craton. In "0Jova Scotia

this produced major dip-slip displacement along the

Cobequid-Chedabucto fault with the Cobequid Arch on

t r. e west moving up re 1 at i v e to the Triassic rift v a 11 e y

t o the s ou t h •

After the Triassic period the Cobequid-Chedabucto

fa u l t was re-a c t i v at e d pro b a b 1 y as a t ran s form fa u 1 t •

~ovement of the crust away from tte accretin~ plate

mar·~Tin of the mid-Atlantic caused the Nova Scotia

platform south of the Cobequ1d-~hedabucto fault to move

we s t r e 1 a t i v e t o the northern c rat on • 0 i s d ex t r a l

strike-slip motion displaced once related geological

features and left the crustal blocks in their present

position. As the North Atlantic continued to open

the older oceanic basement slowly subsided. This

subsidence probably caused dip-slip motion of the

mrrmm

r ~t

Rnh

r '"'"'---. ____...1 pre -W. HIGHLANDS

X P L A N A T I 0 N RP -- Normal

R ha --===-- Inferred ._,.

~eb ( Intrusives

lv v l pre-~ E. HIGHLANDS

/"' FIG IS

fa u It s t ri k -slip omitted)

/

fa u \ t

Plate 1. Geologic map of C3illard Graben and \"icinity, Branford, r\ew H.JVI'n \\ .diJII._!f,,rd, c.id!,,rd .t!ld I ),,rl..ttll 7 1:: llllllllk <JII,!dr\IH.:l·'

John E. Samkr'i, ha'>~-d on ddailt:d mappi!l:..; i11 Hr:111ford, '1\f"w ILn!·n, and .dl11:.:f<>I:i ljti.idr.tr•gln ( lrn1t1 \!,l..ttlil , 111.] j),,I!'Jll.W I' minor omitted Bl.Kl areas are water ( bkn ;.ll,d Long bLwd So••r1d J

qu d--l'hedabuc Lo fault. Exarninat on

o;· tie fault in the hiversdale and J,ake r:den ar s

'·,ows that -::,he latest motions were of tLis e

.1. E. ::a~!der~i ( l ~) has identified de.x tra l

s t r ike- s l i p f au l L s in T r i as s i c r o c k s in e w tr e r s e

matching once conti~uous anticlines. On the north-

western boundary fault of the j\Jew .Jersey rift ~'e es­

ti tes a strike-slip of about 12 miles and this, he

says, ·~post-dates up-on-the-west dip-slip motions of

~; ~J t c) 1 0 , 0 0 0 f e e t • ''

'l1 he geological map of the Gaillard graben and

vicinity of Connecticut (Fig. IS ) shows another

ex amp 1 e of l at e T r i as s i c r i f t in g in n or t h e as tern Nor t h

America. The graben is bordered by a strike-slip

fault to the north-west with a normal border fault to

the south. This southern fault may be similar in

or i p: in t o the We s t R i v e r- S t • : l a r· y ' s fa u l t of c en t r a 1

Nova Scotia. The Triassic sequence of sediments and

volcanics in the graben has been deformed i}lt o a large

shallow syncline analogous to the Bay of >.'undy.

These examples of Triassic rifting and later

dextral Strike-Slip fau 1 tin g SrcOW the mB. j Or fa.u 1 t on

the west or northwest side of' the rift away from the

accreting plate margin. The faults also seem to have

li f"l.ed as rlier block-faul s with h bl l

st moving up ..

A ce c en t e am r l e of t hi s t y p e of r u l t i n

~~e initial riftlng of two plates is given by :J

and Berr" r lc;r:;;C). They ex arnined the firs· moti uf

e rthquakes in thA V\'e~d.ern rift valley of' East J, rica

and alth'JUt·~b the data was not extensive enough to cle-

t e r min e tr. e pre d omi n an c e of fa u 1 t in f, the fir s t m o­

tions were dip-slip faulting on steeply dipping

planes of known faults or on faults parallel to them.

This was followed by strike-slip faulting on the near­

vertical faults as horizontal motions bepan. Also,

es pointed out by D3wey and Bird (1970), trle major

fa u l t s o c c u r on trJ. e s i d e away fr orn t r. e ac c r e t in g mar­

gi~ with block faults on the opposite side of the

rif't. Both of these situations seem to fit the posi­

tion of the Cobequid-Chedabucto fault.

I suggest that these rift structures and tte sub­

sequent wrench faulting were caused by the separ·ation

of Afr·ic a from North Amer·ic a during the ear 1.y s ta9es of

sea-floor spread in g. The complexity of' faults and

rifts along the zone of separ•ation between the two con­

tinents is prcbably a result of cr·ustaJ fragmentation.

Differential motion caused transposition of fragments

Oif1 00 on t in en ~ t o an o t r • The s o u the r n c t -nj of

eva Scctia, which includes the Plat for·m, was

'JLably one of these crustal fragments. It could e

e ined its posi t:on against North America by sub-

stantial dextraJ strike-slip along the C::obequid-

Chedabucto transform fault durung the Jurassic. fr1e

c or r· el_ at i on s J h a v e rna d e a c ro s s the Cob e q u i d- C h ed a b u c t o

f'aul do not include muct evidence for pre-Triassic

rna t c L i r: ~~. It is possible, therefore, that the rift

and fGult structures described could be due to the

s o u the r n U o v a & o t i a p l a t f orm mo v i r: g ba c k in t o

original position. This sequence of events would

start with the crustal fragments in approximately

their r r e s en t p o s i t i on • First , the s t ret c hi n g of the

crust between Africa and North America, during the

late Triassic, pulled t1-le southern portion of tJova

Scotia eastward along the Cobequid-Chedabucto fault.

Then, after several at tempts at a centra1 rift per-

haps along the Bay of ~undy and through the Anti-

Atlas WDuntains the present mid-Atlantic rift opened

east of the Nov a Scotian fragmen Finally, as the

ocean floor began to move away from this accreting

plate margin the Cobequid-Chedabucto fault became a

transform fault. Differential movement of oceanic

st then caused the southern Nova Scotia a

west in relation to the northern platfo o

ume its present position.

If a large dextral displacement is postulate

for the Cobequid-Chedabucto fault several second ry

faults can be explained. In the Eden Lake area of

Pi c t o u c o u n t y sever a l s e c on dar y fa u l t s ar e p r od J c e d

sinistral drag on the north side of the fault.

Sinistral displacements of nearly one mile can be

0

seen from the offset of Brown's Mountain rocks, (Fig. /6 ) •

The L'Ardoise thrust block of southeastern Cape Breton

is bordered on the west side by a long northeasterly

fault which extends from St. Peter's to En on Lake

along the Salmon River, then curves eastward into ra

Bay. L. tT. \>.leeks (1954) observed zones of dra;:.:r-

folding and faultin~ with dextral movement and struc­

tures in pre-Horton ian rocks to the north ttat suggest

dextral; in relation to the geology would seem not

unlikely that this is a wrench fault related to, and

conceivably resulting from. dextral movement along the

Cobequid-Chad cto fault.

The structural forces that folded the Triassic

rocks in the Bay of Fundy area are probably due to an

east-west compression. The rocks have been very

) --

GEOLOGY Of IHE EDEN LAK£ APEA

/

/

I l I

/

/ /'

// 2, / ·.

/

~ -------~-

/

3.

' -------...._ I

"\ / /'

~

/ ( 1 / '-...

6'.

QJ HOf\TON" (, P..OU P ,.f; "TfJ..II'\'S5tC.. i' IN"TAU~.VAfS

I 3 I AASAl~ G~ov~ GJ DEVONIAN C. A. A-N rT I.H MIL.!(!>

m BP.OWN'5 MT- C.P.OUP P~OPOS!;i:O STAI~t -51-.IP I'VVV!..

m 6A:><.Tt:::fl..:!t ~P...OOI'<- FM. Fl"'v<..TS, Fl

i ly folded into the Minas Syncline where

stratum dips from 5 to 10 degrees. This folding

p obably took place in the early Jurassic as the mo­

tion of the southern platform of Nova Scotia pushed 0he

'Triassic· basin against the New Brunswick platform

(Fig. 12.. ).

CONCLUSION

During the Late Triassic there was considerable

tectonic and magmatic tivity along the Atlantic rnar-

gin of North America and North Africa. In North

America sequences of rifting, sedimentation and mag­

matism seem to correlate very well between Nova Scotia

and the eastern Un.i ted States. These events are

probably coincident with or perhaps even resultant

from the last opening of the North Atlantic ..

The Triassic tholeiites of both Nova Scotia and

the eastern United States inculde extensive basaltic

flows, large die. basic dikes and many smaller intru-

sives. Petrologically and geochemically the tholei-

ites in the two areas appear closely related.. These

rocks may all have originated from the injection of

pare n tal oc e an i c rna gma in t o the c on t in en t a 1 rna r gin s

during the initial stages of North Atlantic rifting.

Near Goshen, Nova Scotia, there is a group of

diabasic intrusives which are almost identical to the

other Triassic· intrusives of eastern North America. The

Goshen intrusives appear to be volcanic plugs and their

conduits could have fed volcanoes or have extruded

lava flows. These plugs are so!Tle 100 mi s to the east

of the HcKay Head~North Mountain basalts; but it will

be noted that they are located just to the north of

the Cobea uid-Chedabucto fault whereas the McKa_y Head- 11 J'-'·

basalts lie just to the south of the fault.

There is evidence of a dextral strike-slip

fault of approximately 100 miles along the Cobequid­

Chedabucto fault in the early Jurassic. This would

mean that the Goshen plugs would then have been ad­

jacent to the Wasson's Bluff-Five Islands area of the

Me Kay Head basalts on the north shore of Minas Basin.

There is also evidence that the conduits of the

Goshen plugs extruded a considerable volume of lava.

It is concluded therefore that the conduits could well

have been the source of the Triassic flows both for

the McKay Head area and perhaps also for the entire

North Mountain formation.

- 0-

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