volcanic texture part-1

7/17/2019 Volcanic Texture Part-1

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Volcanic

extures

A

guide

o the

nterpretation

f textures

n volcanic

ocks

J

McPhie

M.

Doyle

R.

Al len

Centre or Ole Deposit and ExplorationStudies

Un ve

. iq r

f

Tr .ma a



' I-he

publication

f tl .ris ooku-ould

ot har.e een

ossible'ithour

trong upporr

given

bv

the

follolving

rganisirtions:

Golelnme

of

Tasmania

t\ustr:rlian

Rescarch

ouncil

Uniycrsitv f Tasmaniir

Abcrfbr.'le esources

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xplolation

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o be radc

o CODL,SKct

Centle.

Liniversio f lirsmania,

PO Box 252C.,Hobart,

l isrran

ia

7001.

Librarv of Australia

Cataloguing-in-Publication

entry

focelln.

\rolcanic extures:

a guiclc o the interprctarion

of textur es n lolcanic

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Biblioeraphr'.

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Contents

Part1. nterpretingextures:erminologynd echniques

The imprint of

genetic

rocessesn textures

n volcanic eposits.. ....,,.....................---.

E n r p h r . i .r n d r g J r i . J t i o n . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Ar . r pploacho thcgcner ic

nrerpretat ionf texturesn volcanic eposi rs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Two

extural

ategor ies:ohercnt

olcanic

ndvolcanic last ic .

. . . . . . . . . . . . . . . . . . . . . . . . , . . . . . , . . . . . . . .3

Descr ipt ivc

.romenclatureor coherenrolcanic nd

volcanic last ic

eposi ts

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . , . . .

L r a p h i co g g i n ge t h n i q u c

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2

I m p o r r a n re x l u r c \n d

r r u c r u r ( \ . . . . . . . . . . . . . . . . . . . . . . .5

A summ arv f rhc essentialiatures f the seafloor .rassiyeulfide nvironment...................................5

Introduction o the Mount Read

Volcanics .. .. ,.

,,. ... 1

5



Part3. Lavas, yn-volcanicntrusions

nd related olcanrclastic

eposits

ilicic ava lows,

domesand syn-volcanicntrusions

.

r

Subaqueousi l ic icava lows ndextrus ive

omes.. . . . . . . . . . . . . . . . . . . . . . . . .61

Subaqucousart ly x t rus iveryptodomes.. . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .64

Subaqueousyn-volcanici l ls nddykes. . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .64

Volcaniclastic

cposits ssoci:rtedvith silicic ava

domeeruptionsn shirllowvater................................65

CascStudy:Partlyextrusive,ubmarine,

acite rypt odome, ockCreekSouth, vestern

1}smania........66

Part4.

Pyroclast, resedirnentedocaniclastic

nd volcanogenicedimentaryepos

s

f volcaniclasti c

eposits

.................94

E r p l o . i r e

r u p r i . n \

n J

p v r o c l a s r i cc p o . i r . . . . . . . . . . . . . . . .

.

q

<

Explos ive agrrat ic

rup1ons. . . . . . . . . . . . .

.

9

5

P h r c J l o n r J 6 n r l t i c

r u p t i o n s . . . . . . . . . . . . .

. . . . . . . . . . . . q b

I ' h r c a r i .

r

s r c a m

r u p r i o n . . . .

. . . . . . . . . . . . . . . . . . . . . . ( ) t '

Resedimentedvn-erupt iveolcanic last ic

eposi ts . . . . . . . . . . . . . . .

. . . . . . . . . . .96

Volcanogenicedimentary

eposi ts . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .97

nddeposi t ionf volcanic last icart ic les. . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . .97

movement

nd

nass-f low

eposrts . . . . . . . . . . . . . . .

. . . . . . . . . . . .98

Prin.rary yroclasti

Transportnddeposi t ionalrocesses. . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .99

Character is t ics

f

pyroclast iclow

deposi ts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .100

C o r n p o n e n r .

. . . . . . . . . . . . . . . . .u i )

T 1 p c s , , f J e p , ' . i r s .

. . . . , . . . . .0 i ,

' lbxtures

and

nternal

rganisat ionf deposi t ion:r ln i ts . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . .102

C r . r d e . . . . . . . . . . . . . . . . . .

. . . . . . . . . . 1 0 1

Geometryrndaspectauo . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .04

Dimensionsf pyroclast iclorv

eposi ts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .105

Proximal o

distal

extural ariations

.........10i

(

o m p o r i r i o n a lo n a r i o n . . . . . . . . . . . . . .

. . . . . . . . . . . . . .O i

Significar.rcef pyroclasticlorvcleposits

........... 05

Subaqueusly-emplacepyroclast-r ichass-f lorveposi ts. . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .06

Tr2p.grcssiorrf r l rorel i r re.y pyrocl . r . r iclow, . . . . . . . . . . . . . . . . . .

. . . . . . . . .0 t ,

'Welded

ignimbrite nterbeddedvith submarine edimentary

equences ...................10(r

Non-welded,yroc lasr-r ich,ubmarine ass-f lorv

eposi ts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .07

'Water-sr.rpporte

d and gravity-drivenolcaniclastic

ass

lowsand heirdeposits........................................09

Lowdensi ryurbid i ry urrents . . . . . . . . . . . . . . . . . .111

H i g h . d e n , ' i r yu r b i d i r yu r r e n r . ,

. . . . . . . . . . . . . . . . .I I

Volcanic last icurbid i tes. . . . . . . . . . . . .

. . . . . . . . . . . . . . . . I2

r i g n i f i L r n . e . . . . . . . . .

. . . . . . . . . .1 2



Colr.ri. '.

debris lorvs,

olcaniclastic

ebris

lorvs nd

heirdeposits

..............

.......... 2

Vr lcanic lasr ic

ra in- f low

eposi rs . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .114

Volcanic

l ides,olcanic

ebr is

valanchesnd

heirdeposrts

. . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . .114

Massive

ulfide

lasr,bearing

ubmarine olcaniclasric

ass-flow

eposits

............................................

16

Tiact ion

ransportndvolcanic last ic

ract ion urrent

eposi ts . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . .117

Tiacrion:rl edimentary

rructures

..............I 7

Character is t ics

. . . .

. . . . . . , , , ,117

Signi f icancc. . . . . . . . .

. . . . . . . . . .18

Pyroclast ic

urgesnd

heirdeposi ts . . . . . . .

. . . . . . . . . .11g

Character is t ics

. . . .

. . . . . . . . . .18

Dimcnsions

f pvroclastic

urge

eposits......

.

1

9

Signi f icance. . . . . . . .

. . . . . . . . . .19

Suspension

ransporr nd volcaniclasric

uspension

eposits..............

........ 20

Pyroclast ic

al l

deposi ts . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . .20

Character is t ics

. . . .

. . . . . . . . . .20

l f fater-setr led

pyroclast ical l

deposi ts . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .121

Suspension

edimentation

ssociaredith

subaqueousolcaniclastic

ass lows....,......................,,......121

Part5. Alteration:

n

integral

art

of textural

volution

Alterat ion

venrsn

theMount

Rcad olcanics

. . . . . . . . . . . .

. . . . . . . . . . . . . . .65

Al terat ion

f lavas, hal low

nrrus ions

nd elated

utoclast icreccias

. . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . .166

Mixed

glassyndspherul i t ical ly

ev i t r i f iedones

. . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1( t7

Spherul i t icr microl i t ic

ores

f

lavas

ndshal low

ntrus ions

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .167

Generalrends nd rnpl ica r ions. . . . . . . . . . . . . . . . . . . . . . .68

Orig inal ly lassy

ndpermeable

eposi ts . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . .168

Phyl los i l icate

l terat ion. . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . .163

Two-phasc

ldspar nd

phvllosilicate

lteration

...........................

(r8

General

rends nd mpl icat ions. .

. . . . . . . . . . . . . . . . . . . . .

( r9

References

tnoex

vii



Listof Plates

1 Evenly

porphyriric ndvolcaniclasticextures..............

.................34

4-Micropoikilitic

texturen rhyolite

..........

...........40

-Pumice, scor ia,

ombs nd

uveni le

locks. . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .44

-

Shards.i rh ic ragmcnt.

nd r l l rer ionrrvrpi l l i . . . . . . . . . . . . . . . . .

. . . . . . . . . . . - l t r

-Columnar

. jo ints ,

" t iny

normal

oints"

nd orto isehel l

o ints . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . .50

recciand alus

. . . . . . . . . . . . . . . . . . . . . . . . . . . .72

3-Hyaloc last i te

ar iet ies

nd eedel

ykes. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . .78

14 Peperite

intrusive

5 Pi l lowedava

' lows ndpi l lows. . . . . . . . . .

. . . . . . . . . . . . . .82

6 Rinds nd

crusts n

pi l low

obes. . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .84

8 Products

f s i l ic ici rva omeerupr ionsn

shal low

ater:

unga eds, S\X/ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .88

ava lows nddones. . . . . . . . . . .

. . . . . . . . . . . . .90

n glassy,ubaer ia lhyol i t ic

ava. . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . .92

lorv eposi ts. . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .124

andcomponenrs

f pvroclast iclowdeposi ts . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .126

3 Vapour-phase

rystallisednd slighdywelded gnimbrites

..........128

\Welding

and granophyric rysrall isationexruresn ignimbrite

..............................

30

25-Lithophysae

and spherulitesn welde d gnirnbrire

...........

..........132

n pyroclastic

low deposits nd high-gradegnimbrite...........

........134

\Velded gnimbrite n

the Mount ReadVolcanics.....

..................136

8 Subaqueouslymplaced yroclasticlorvdeposits: orrhern flales,UK..............................................38

0

Syn-eruptive

ubrrarine olcaniclasticegarulbidite.....

............142

1-Volcanic last ic

egaturbid i tes. . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I44

2-Submarine,

i th ic-nch,olcanic last icass-f low

eposi rs. . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . .146

3-Coniponents

in subaqueous,olcaniclasticnass-flolv

eposits...............

................48

4-Deposirs

from subaqueousolcaniclastic

ebris 1ows........ .

........150

5-Deposits

from subaerialahars

nd volcaniclasticebris lows

................................152

6-Subaelial grain-flow nd

volcanic

ebris-avalancheeposits..............

....................154

7

Massivc

ul f ide lastsn submarineolcanic last icass-f low

eposi ts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .i6

38-Traction

current tructuresn volcanogenic

edimentsnd pyroclasticurge

eposits.........................158

9-Subaerialpyroclastic,rl ldeposits ...................160

and structuresn volcaniclasticepositsiom

suspension,lotationand raction .................162

volcaniclastic

eposits

rom

shallow ubmarine xplosivecrivity...................................164

2-Al tercd coherentava nd elated reccia. . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .170

3 Pseudobrecciand

al teredolcanic recc ia. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . .172

4 Al tered

evi t r i fed i l ic icava

. . . . . . . . . . . . . . . . . . . . . . . . .174

5 Al tered umiceous

olcanic last iccposi rs . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . .176

anddelormed

umiceous

olcanic last iceposi ts . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . .178



Acknowledgements

l)roducrior.rofthis bool<

has

dcpcnclecl

n

generous

inltrcial

support flom sponsors f the Kev Centtc fbr Orc Dcpo sit

and Exploration Studies,

in particuJar, he

Ihsmanian

Dcpar tment

of l \ l ines, Abcr fb l . lc Resources,

BHP

F.xploration,CRA. Explorarion. Cicopcko,

):rncontinental,

Pasminco, RGC

f-xp lora t ion and Vestern

Min ing

Corporat ion.

Although the

m:rterialpresentcd ornes

principallv from

ttre collectior.rs

f

.f

Mclt and RLA,

rve made use of some

thin-sections,

and spccinrens

nd photographs ontributcd

bv colleagu es: tcphcn

Abbott,

(luillermo

Alvaraclo,D:rvid

Cooke, Keith Corbctr,

Bruce

(lemmell,

Btucc Houghton,

John Wate s, M:rttherv

Whitc

and Colin Wilson. Wt ale

further ir.rclebted o

Abcrfirl'lc Resoutcesancl Pasrninco br

use of m:rny samples

irrm

drillcore

storcsat Hcllvcr rnd

RoseLrerr'.

Proicssor

oss

-argc niri irtcd hc projcctand

plor-iclecl

mu.ch ppreciatedncoulagefirenthrougihorrtts re:rlis:rtion.

Tl.re first drafi u':rs substantirlh revisedafier rer.iqvsby

Stu:rrtBull and RossLargc

(CODES),

Fcrsus rirzgcralcl

(Pasminco

Explorar ion),Mir lcolm

Horvel ls

Br i t ish

GcologicalSrirvcl-),

Nocl Vhite

(13Hl')

ancl Hiromitsu

Yamagishi

Geolosical

urvev f Hokhrido).

'fhe

procluctionearnncluded

unc

Pongrarz

dcsiqn

nd

desktop ublishing),

cirnctrc

:rnkin and

Kirsn Whalev

(rvping),

Dcbbic

Harding

(drauehtins),

irron Stephens

:rndN:romiL)cards

thin-section

ndslab

lepalation), recl

Koolhof

tcchnical

dr-ice ncl

ome

photographv)

ncl,{lisot.r

Jones finalediting).

I X



Part . nterpreting

extures:erminology

nd

techniques

The important caskof exploring for bxe metal ore deposia

in ancient submarine

volcanic sequences egins with

geological mapping, which in turn depends on correct

identification foutcrops

and hand

specimens.The

ext nd

illusrarions that follow are designed to help

meet

this

significant

challenge, by providing a guide to the inter-

pretation of common textures and structures

in volcanic

d,eposlts.

Volmnit

depositsinclude onsolidaredvolcaniclastic

and coherenr volcanic rocks, and unconsol idated

volcaniclastic aggregates. he examplesusedare principally

ftom the Mount Read Volcanics in western Tasmania, a

deformed, Cambrian, largely submarine volcanic sequeoce

that hosts major

massive sulfide

deposia

(Large

1992).

\qe havealso ncluded, for comparison, eramples rom other

well-exposed

and

younget

submarine volcarric

sequences,

and fiom subaerial volcanic sequences.

The

mpintoi

genetic rocesses

n extures

n

volcanic

eposits

The development of rexrures n volcanic deposits can be

considered

n termsofthree main stages,

(1)

creation of

original textures by eruption

and emplace-

menr

Processes;

(2)

modiiication

of original textures by syn-volcanic

processes

oxidation,

degassing, ydration, vapour-phase

alteration,

high-temperature devitrificarion, hydro-

thermal

alteration);

(3)

modification

by post-volcanic

processes

hydrarion,

devitrification,

hydrothermal alteration, diagenesis,mea-

morphism,

deformation,weathering).

Ofoveriding importance in the crearionoforiginal taxtures

in primary

volcaric

deposis is the eruption style, n particular

whether

explosive

r effixive

(Fig.

1). Explosive ruptions

ptoduce

a wide

varieq,

of

procla:tic deposis. Effusive

eruptiorc

prodttce

laaa

float

ard

kra domes \,at comprise

coherent

and

autoclasdc

6cies.

A drird categoryof' volcanic"

' , . .

deposits

is

created

by the

syn-volonic

emplacemenr of

oypndona,

@kes

and.sill:, and also ncludes coherenr and

auoclastic acies. n activevolcanic eranes,

whe*rer

subaerial

or subaqueous,diversevolcaniclastic deposirsare generated

by

non-volcanic processes,

pecifically by

resedimentation

coeval irh or ndependent feruptionsand by weachering,

erosion and

reworking

of

pre-existing volcanic deposits.

These are sometimes referred co as xcondary

volcaniclxric

deposirs, whereas undisturbed

plrodastic and autodxdc

deposts are

pimary

Mechanisms of particle transporc and

deposition areofgreat importance in the creation oforiginal

t€xrures and structures

in

pltoclastic, resedimented

ald

volcanogenic edimenrarydeposirs.Lavas, syn-volcanic

intrusions and many

rypes

of primary pyroclasdc

deposis

are hot at the time of emplacement or deposirion. Then

original textures are almost invariably modified

by

processeselated o cooJing.AII gpes ofvolcanic and volcad-

clasticdeposis, pdticularly thos€ hat initially

contained

volcanic

glass,

carr be subject to post-volcanic exrural

modification.

Emphasisndorganisation

Thisguide mphxr,esheprinciprl enericroce\e.

responsible

or

the

creation

f original ertures,

nd he

most common syn-volcanicmodifications. The organisarion

olthe pLates nd cext ellectsa process-orienrcd lassiicarion

(Fig.

1) that atso ncludes olonidastic deposits enerated

by resedimentarion and by purely sedimencaryprocexes.

The clasi0cation shows he main

trarsport

and deposition

mechanisms nvolved in the formation of pyroclastic,

resedirnentedvolcaniclastic and volcanogenic sedimentary

deposits. It is very important

to appreciate

that

similar

mechanisms

perate

n eachofthese

categories

rrd,hence,

similar textures ard structures may result.

Componena, texturesand srrucures

(Part

2) are

nherenr

properties f volcanicdeposirs

nd

provide

rhe basis or

1



VOLCANIC

RUPTION

EFFUSIVE

EXPLOSIVE

suspension

RES

EDII\4ENTATION

suspension

(syn

vol

can

c int u

sion

s)

cohercnt

ava

(or

ntrusion)

lava

flows

lastic

pyroclastic

flow

deposits

fall

deposits

Encircled

umbers:

elevantart

f

guide

Boxes: rocesses

Italics:

eposjts

resedimented

(syn-eruptive)

volcan

clastic

deposits

vo

can o

ge

n c

sed m

entary

de

pos

ts

REWORKING

WEATHERING,

ROSION,

AND

POST-ERUPTIVE)

ESEDIIVENTATION

mass-llow

suspension

Fig

1

Gefetic

classfcaton

oj vocafic

deposits

o n - e r c l a r u r e .

o m e

i ' e r i g h r . o . r s , " i n r .

1

nrerorerarion.

ur

mmy

nerely

ugge.r

" nunber

l e9uaJJ1al id lrerna., 'e.. -e setecriont , omponenr.

nd structures

n Part

2 is

nor comprehensive

ut

conceruares

on features

chat help

distinguish

lrom

coherent

olcanic

deposits,

hat

survive

an\,enr

equen.es

nd.rr

be re(ogni..d

n our. rop

or

specimen

ith a hand ens.

Pa_rt

ofthe guide

describes

strucrures

nd icies

associarions

n the

products

ofefftrsive

erupdons

tara

nows

and

tava

domes)and

syn-volcanic,

high level ntrusions sills,dyhes, ryptodomes). heseare

qpically

associated

ifi

aurodasric

deposits

hat

are

generated

by non

explosive

ragmenration (quenching,

auto,

brecciarion).

Part

4 deals

with

volcaniclasric

depos;rs

qrodlced

y

explo, ive

erupr

on,

'pr ; rar ,

oyro. :

Li .

deDorrr\r.

heir.rr

errprire

e.edimenred

quivalenr..

nd



volcaniclasric

eposits esulring

rom surfaceproccsses

operating

on pre-existing olcanic

sequences

volcanogcnic

sedimentarvdcposits).

lorrect

nterpretation

fthese

eposits

lelies

on recognitionof

(1)

structures ncl ithofacics

characreristics

hat inclicate

ranspon and clepositional

processes;

2)

texrurcsand structures

har ndic:rtewhether

or not the particles

verchot when deposited;

3)

rextures f

constituentparticles

har indicate clast-forrning

rocesses.

Finalll', n Part

5,

the alterirtion exrulesn

volcanic equences

rhathostn.r:r-ssive

ulfidcdeposits re evierved,

singexamples

lion.r he Mount

RcadVolcanics. n irnporrant

aim of

this

part

is to shorv hat

unravell ing he

conrplexweb of

interrelatcd

processesnvolvcd

in alteration

of

volcanic

deposits

s

critically

dependent n hrowledge

ofthe original

textures

and horv thel' ftrrm.

Tl rr

e. 'enr ia l r r r r r . .

of rhe orrr n. r in

B(rer ic

dregol ie\

considered ere lavas

nd syn-volcanicnrrusions,

yro-

clastic

dcposits, eseclimentcd

olcaniclastic

epositsand

volcanogcnic

edimentary

eposits are sumrrariscdn

Figures

,3,4,

5.

Explanations

fall the erms

sed n rhese

figures br

tcxturesi omponents

and processesre

givcn n

the corrcsponding art

of rhe tcxr.

An

approacho

the

genetic

nterpretation

f

texturesn vocanrc

deposits

Identification

nd nrerpretation

fvolcanic exturesnvolvcs

a bler.rd

f

proccss-oriented

olcanologv

nd sedimentologl',

and prinarily dependson careful obsenationsm:rdeat a

rangc

of sc:rles. roficiencv

mproves

dramaticallyu'ith an

awarencssf geneticplocesses

nd b1. dopting

a sr,stemaric

approach o

description. (c rherefore mphasisc:

(1)

the useofappropriate

erminology or

the accurateield

dcscriptionof volcanic

deposits;

(2)

recordingoutcrop

and drillcore sections

by

means

of

graphic ogs;

(3)

dentification

oforiginal volcanic exrlrres,

nd discrin.r-

ination of these rom

tcxtures aftributable

ro alteration,

defbrmation

and/or mctirmorphism;

(4) recognition of rexturcs and structules diagnosticof

emplacement rocesses,n

particul:u, oherent acies

lavas,

intrusions)

ersusvolcaniclastic

cics

auroclastic,

yroclastic,

resedimented,

olcanogenic

edimenrary)

(5)

recognitionof

outcrop fcarures iagnostic

of panicular

depositionalsettir.rgs,n

particular, subaerial

versussub-

aqueous nvironments, nd relatively

eepversus clativelv

shallow ubaqueous ettings.

Two

extural ategories:

oherent olcan

and

volcaniclastic

The

diverse cneticprocessesnvolvcd

n the formation

of

volcanic

deposits csulr in original

rexrures har can

bc

classifiednto

cither of nvo categorics:

uolcartit'lastic

r

coberent.l''he

crnt volcaniclastic"s

descriptive nd

applics

to

deposits omposedprcdominantly

of

volcanic

panicles

(Fisher

961).

he particlcs

av beany

shape ndsize. o

specifi

clasr-forming rocesscs,

nnsporr

and dcposirional

processes,

r settings re mplied.

Texruresn volcaniclastic

deposits ncompass norrlous

variation

but, in general, re

ch:rracterised

y the presence

f separate articles

or fiag-

ments, of mixrures

of a ferv

or

manv

different particle

shapes, izes

and wpes, or, in many

cases, f bedding

or

othersedinentary

tructuresndicating

p:rrticulate

ransport

and deposition.

The fcrur rnain

genetic categorics

f

volcaniclastic

cposirs

autoclastic,

vroclastic,esedimenred

and

volcanogenic

cdimentary)

achhavesetsof

disting,

uishing eaturesndnumerous

urther

ubdivisions

Parrs

and 4J.

Coherent olcanic

exruresorm from

coolingancl

olidifi-

cation of molten

lava or magma.

The most

ubiquitous

hallmark is porphyritic

texture,

espcci:rllv he presence

f

evenJy

istributed,

euhcdr:rlcrl.stals

har have narrow

size

ranges. phyric, aphaniticand rotallyglassycxtures realso

coherenr. esicles,lorv

oliarions, pherulitcs

nd ithophysac

ale

common n deposits

wirh coherent

extures, hough not

indepcndently

cliagnostic,

nd also

occur in volcaniclasric

deposirs.Coherer.rt

exturcsoccul plincipally

in lava lorvs

and n intrusions.

There

arc rwo additional

texturalcategorics

har can

be

useftrl,

parricularly n

ancienrsequencesn

thc earlv

stages

ofnapping

or ogging

and n stronglyaltered

ocks. pparent

uolcanichstic

exttres

areverv common in

alrered oherent

lavas

and intrusions,

as a result

of

patchy

or

domainal

alteration r fiacture-and oint-controlled lteration PartJ).

The apparent

cxrures n man)r

cases uperficiallv

esemble

rvclded gnimbrirc

or co:rrseithic

breccia.

Sonreunaltered

microspheruliric

r micropoikiliric

avas nd ntrusions

also

displavapparcnt

volcaniclastic

extures, nd rcscrr-rble

ell-

sorted, massive

andstor.re.ppnrent

coherent

exturesare

best developed n

sornevery

densclywelded primary

pyroclasric

deposits,

espcciallv heomorphic

and lavalike

igninbrircs

(Part

4). Li

these, he

glassypyroclasts

havc

completelvcoalesced

nd are no longcr

separately

istin-

guishable,and

crystal piuticles

are dominantly

complete

euhedra. inc-grained,nassiver planar aminated olcani-

clastic

eposits,uchasshard-rich

mudsrone,

may display

app:rrent

coberent extures

as a result of recrystallisation

t lur ing iagcnc. i .

rnd l rerar iorr .

In

order for rhe field

gcologist o procced

further

to

appropriate

cscriprive

erminology nd,

hereafter,o genetic

interpretation,t

isnecessary'first

o makea

decision egarding

the textural

categorl', hat is, rvhether

volcaniclastic

or

cohcrent. As more

information

becornes

availablc rom

rnapping

r thin-scction

tudies,

ndundent:urding

ncreases,

rhat nitial

decisionshould

be revierved nd

evaluated.



LAVAS

ND

SYN-VOLCANIC

NTRUSIONS

coherent

acies

.

porphyritic

exture

evenly

istributed

uhedral

crystals)

r aphanitic

'

high

T

devilrification

extures

ommonn

groundmassspherulites,ithophysae,icropoikilitic

texture)

.

internally

assive

r low oliated

t

PUmiceous

.

non-vesicular

vesicular

I

'sconaceous

ffi

coherenlacies

autoclasticacies:

@

jigsawJit

exture

autoclastic

acies

monomict

clasts

with

porphyrit ic

exture

r

aphaniticexture

abundant

igsawJit

exture

autobreccia

slabby,low

oliated

lastswith

agged

nds; agged

or blocky,

massive

lasts

clast

margins ot

quenched

pumiceous

r scoriaceous

lasts

ommon

low

proportion

f clasts iner

han

2 mm

separate

rystal agments

ncommon

hyaloclastite

breccia

blocky lastswithcurviplanarurfaces

clastmargins

ave

or

had)

glassy

roundmass;

clast nterio rs lassy

r crystall ised

'tiny

normal

oints

along last

margins

very

coarse

and o

granule

ize

1-4

mm)

matrix

maybe

abundant

separate

rystalragments

an

be abundant

pumiceous

r scoriaceous

lasts

maybe

present

@ jissawjit extJre. edirnent atrix

S

resedimented

silicic:

subaerial

r subaqueousava

basaltic

utobreccia

@

pil low

av a

pillow

ragment

reccia

enclosrng

equences

ffiffi

E

4

silicic

or basaltic:

subaqueous

eeder

yke

subaqueous

avas

F

g

2 characterist

s of cohereft

nd autoc

stc lacies

f avas

andsyn-vorcanic

ntrus

fs

(part

3)



PYROCLASTIC

EPOSITS

deposits from

explosive magmatic

and

p

h e

atomagmatic eru

ptio

n

s

.

composed f crystals.

umice

r scoria

lasts,

other essvesicular

uvenile

lasts,ithic

ragments

. pumice r scoria ndotheruvenile lasts how

porphyrit jc

exture,

r areaphanitic

.

abundant

rystalragmentsn matrix

.

lithic lasts

parse o abundant

explosive magmatic

.

abundant

ubble-wall

lass

hardsn matrix

.

pumice

r scoria lasts

sually avewispy

or

ragged

margins, nd enticular,

laty

r blocky hapes

.

accretionaryapilli

ccur

'

welded

r non-welded

phreatomagmatic

.

abundant locky

ndsplintery

lass

hards

.

pumice

r scoria nd

other

uvenile

lasts

re

typically

locky; urviplanar

urfaces ommon

.

accretlonaryapilli

ommon

.

usually on-welded

.

dominantly

sh and ine apilli

deposits

from

phreatic

eruptions:

composed

f

lithic

yroclasts;

ydrothermally-altered

clasts ommon

accretionaryapil l i ommon

small olumes

<<

1 km

3),

limited

xtent

<2

km

rom

source)

mainlyall

andsurge

eposits

non-welded

pyroclastic

flow

deposits:

block nd

sh low eposit,

r

scoria ndash low

eposit

lapii:

pumice

r

scoria

FEl

poorly

esicutar

uveniie

lE-l

rithic

Fll

ffi

r

enclosrng

equences

pumice

or scoria fall

deposits:

non-welded

al l

non-welded

gnimbrite

pyroclasti

su

ge

deposits

welded gnimbrite

phreatic

or

phreatomagmatic

all:

welded all lava-likegnimbrite

ffi

F

g

3

Charactertcs of deposltsrom

explos e

erupt ns

pr

mary

pyroclast

depos

s)

part

4) .



RESEDMENTE,D

S\N-ERUPTIVE,

VOLCANI

CLASTIC DEPOST

dominated y exturally

nmodified

uvenile

lasts

narrow

ange

f clast ypesandcomposition

sedimentationnits

andsuccessions

f unitsarecompositionally

niform

r show

systematichanges

bedformsndicateapid

eposition

massJlow

eposits ommon)

resed mented

autocl stic

de

pos

ts

shallow

subaqueous:

.

mixture

f autoclasticnd

pyroclastic

articles

.

combination

f massjlowand raction

urrent

bedforms

.

dominated y clasts oarser

han

2

mm

oeep

suoaqueous:

.

poorly

esicular,

uenched

avaclasts ominant.

mainlymass-flow

edforms

.

mayhave

primary

ipsup o

-25"

.

granule

cobble izeclasts

ominant

.

associated ith

n situhyaloclastite

ndcoherent

lava

resed

mented

autoclasic deposits

shallowubaqueous

clast ypes:

resedmented

pyrocl

stic de

posits

.

composed f

pyroclasts

subaerial

and shallowsubaqueous:

.

combination

f mass-flow,yperconcentrated

low

and raction

urrent edforms

.

depletedn ineash

deep subaqueous:

. very hickmass-flowedimentationnits hatconsist f a

massive,

rystal-

nd

ithic

last-rich

aseanda

normally raded

r stratified,

umice-

ndshard-rich

top

.

intraclasts

resent

ear

baseof mass-flow

nits

.

laminated,

hard-rich

nits

settled

rom

suspension)

resedimented

pyroclastic

deposils

subaerialnd hailow

ubaqueous

L 9 l

l;lt

E

pumrce

lithic

poorly

esicular,

uencheduvenile

ffi

oeep

uoaqueous

E

sandand iner,

uvenile

enclosingeguences

ff

oeep

suoaqueous

F

g

4 Charactertcs of resedimented

yn-erupte volcaniclast ic

eposits

part

)



VOLCANOGEN

C

SEDIMENTARY

EPOSITS

.

mixture

f volcanic ndnon-volcanic

lasts

.

volcanic

lasts omprise

ifferentompositions

nd ypes

.

volcanic

lasts ounded

'

moderateo

good

sorting

according

o clast ensity)

subaerial nd

shallowsubaqueous

eposits:

'

dominated

y raction urrent

edforms

deep

subaqueous

eposits:

.

dominated y mass-flow

edforms

.

medium-very

hick abular

eds

non-volcantc

iasts:

l==

l:-_--l

E

E1;>"-'-

IZ-]

pebb

s

-

boulders

volcanrc

lasts:

El

non-

o

poorly-vesicular,

2mm

@]

pumice

r scoria, 2 mm

shard-r h mud

mixed olcanic

ndnon-vo anic

sand

Fig.

Charactert cs of vo

canogef sed nentary

epos s

(,-p

ast

c

vo

canc depos

s)

paft

1).

Descr

tive

omenclature

orcoherentolcanic

and olcaniclastdeposits

Isolated

utcrops nd hand

spccimens

f ancient olcanic

rocks

arely xhibitcleal

and unanbiguous

e'videnceftheir'

origins. ecause

ncertainrvsp:ut ofthe practical

ealiq'of

working

on volc:rnic equences,

r is aclvisable

o bcginwith

Iithological

nd

ithofacies

erninoloqy,

Lrntil here s

adequate

justification

or

applving elms hat havc

geneticmplications.

L i tbological

erminologl ' prov ides

nformat ion

on

composition,

om;ronents nd

glain sizc.LithoJ)ries

erron,

ologyprovidesnformarion

on facics

haracteristics

vident

at outcrop cale n thc fleld, such as stmctures,nternal

organisarion nd geornetrv.

Ceriear erminolow

provides

information

on eruption

and emplacernent

rocessesor'

primarv

olcanic nd volcaniclasri c

eposits,

nd on sub-

sequentcdeposition,losion,

ransporr

nd deposirional

processes

or reseclimented

od r''olcanogcnic

cdimenrarv

deposits.t

also rakes nto

account facies

geomcrry and

facies ssociarions

r a range fscales,

ron single

ruprive

or sedimentation

nits to entire volcanic

cenrres.

Existing

dcscriptiveithological

l:rssifications

ctually.

involve nplicir

disrinctions

cnvcen epositsvith

coherent

and volcaniclasticexturesand, in rhis respect, rre also

genetic.Having

decidcd ,hether

the rcxrule s cohercnr

or

volcaniclastic

r, in

diflicult cases,

pparenrcoherenr

or

apparent

olcaniclastic,

t is

rhenpossible

o build descriptivc

names

using conbinations

of lithological

and lithof-acics

terms

Tabies

, 2).The naming

chernc

houldbe

adapted

to suit the

aims rnd scale

f the rextural

analvsis,he range

ofcompositionaJ ariationprescnt, rnd the stateofpresen.

ation of the volcanic

scquence.

ln naming

cohercnr volcanic

dcposirs, he

emphasis r.r

ar'ailable classifications

s orr

cheurical cor.nposition

rvhich.

ofcourse,

can onlv be roughlv

gucsseclr.r he ficld.

In most

cascs,r is possible

o distinguish nappable

nits, so ong as

the

te

minologT-

s used

consistentlr', eqardless

f rhe absolute

accurac).

of the

tcrms. If necessarr',

he composition

subdivisions

hol n in

' lhbie

1 can

be

nadc

more plccisc

bv

:rdding

pcrcentage imirs

lbr the phenocrr-st

bundanccs.

Adjusrnrents

can

be

made

ro horv

tcrms are used, f

and

rvhen rccuratcmoclalor chcmicalanallses ccomeavailablc.

For

deposits virh

coherent

and apparent

cohcrcnt errurcs,

gcnetic interprctation

rvi l l

scck to cliscrirninirre

etrvcen

lavas,

1'n-volcanic

ntrusior.rs,

osr-l.olcanicntrusions

an d

vcry denselv vclded

pyroclastic

deposits,

and

rvill

clepend

on atlditior.ral

erailed nlblrration

on texturcs

in thirr,

section,contact relationship s

nd

qconetrr:

T l r c

p r o h l c m

, i

i l - b r r i l r

c n . r i . n r c r ; r c r , i L i o n

\ n r , , r . '

selious

tor nanring

tleposits vith volcmiclastic

retllres.

l-hcrc

is no telrrr inology

hat

applicsgeneralli

ro all volcani-

cJasriceposirs

irho Lrt

enetic

mplicarions.

Relativellnon-

gcnctic telns havc been borror,ved fronr

scdimentologv

(Fisher

1961)(

lablc

2) and, ftrl

rhat reason,

are

fir

fiom

satisfactory..

n other

contexts, thcsc

terms are

used for

epiciastic

dcposits,

arrd n volcanic

terrirnes, r.riv

ome of

the volcanicl:rst ic

epositshave h:rt

origin. Further.rrore,

f

these

terms :rle

used

in

a general

descriprile sense,

hcv ar.e

7



no longer efGctiveas terms specifically

or

volcanogenic

sedimentary eposits.

Nevertheless,

he borrowed ermsare

the best currently availableand will remain so, unril the

nomenclature roblem

is

solvedby agreement mong

volcanologists nd sedimcntologists. ut of

nccessiry

he

borrowed erms are used

in

the scheme

or

building

descriptive

ames or volcaniclastic

eposits

Table

2). For

these

deposits,

enetic nterpretationseeks o

discriminate

between

our main

categorieshat arebased n

fragmentation

and transport

processes autoclastic, pyroclastic,

resedimented

yn-eruptive

olcaniclastic,

nd

volcanogetric

sedimentary

epiclastic

olcanic). n each case, here are

finer scale enetic nterpretationshat imply eruptionsryles,

transport and

deposition

mech:rnisms, nd depositional

envilonments

Parts

J

and 4). Lithological erms used or

primary pyroclastic

deposits

(Fig.

6; Table

3)

are well

established, ut their use

presupposes

hat

interpretation.

Note, in particular, hat

"tuff"

is resen'edor primarv pylo-

clastic deposits.

Tuffaceous"

implies the presence f

pyroclastsand is commonly applied to reworked and

resedimented yroclast-rich eposits.There is, at present,

no

adequate

erminology for autocl:rstic eposits,nor for'

resedimented yn-eruptivepyroclasticand autoclastic

deposits.

he terms given n Table

3

arc mcrcly thosc hat

are requentlyused, vith somcmodifications ddedhere or

consistenrywith established rain size classifications f

pvroclastic nd volcanogenic edimentary cposits.

AncierrLolcanic

e9uence.

r1 conrain on-pr imary

mineral assemblages,

sa result of hydlothermal alteration

or metamorphism. he distinction berween hese rigins s

critically mportant n mineralcxploratiotr. orboth coherent

6 4 2 m m

l a p i l l i

volcanicandvolcaniclastic eposits, escriptiveerminologl'

can includc alteration mineralogy and

distribution

(

lables 1, 2). Omissionof the alter:rtion erm implies hat

the deposit is essentiallyunaltered. Alteration minerals

frequently ncounteredn volcanic ostsequenceso rnassive

sulfidedeposits re istcd bclow:

Ch/orite a particularlycommon metamorphicphase n

andesiric nd basaltic olcanics, ut also an important

hydrothermal

lterationphasc n silicic

(rhyolitic

or dacitic)

volcanicsn the foonvallof volcanic-hosted assive ulfide

(VHMS)

deposits;

Sericita rcsults rom met:rmorphism f silicic volcanics,

especially

olcaniclastic

cposits;t is alsoa major, egionally

extensive ydrothermalaltcrirtionphase n the foorwall of

\rFlMS deposits nd relatedchcmicalsediments;

Silicd generallyvpical of hydrothern.ral lteration

of all

compositions ut not a common trretan-torphichase;

Plrite an important hydrothermalalterationphase

hat

is cxtensively eveloped n the footwall of many VHMS

deposrtsi

(iarbonate

fi'equentlv ssociated ith metan.rorphism

f

dacitic,

andesiticand

basaltic

volcanics,

and also

results

fiom hydrothermal ltelarionofvolcanics n

close

roximity

to VLIMS deposits;

Epidox uncommon asa hydrothermalalterationphase,

but typicalofmetamorphosedndesitic ndbasahic olcanics.

Othel, ess ommon

alteration

hases

hat

may

be associated

with VHMS

deposits realbite,

K-feldspar, ematite

and a

variety

of clay

minerals.

blocks lhd bombs

> 6 4 m m

< 2 m m

a s n

pyroclastic

breccla

Fig

6 Grain ize ermsused

or

primary yroolastic

ocks

Fsher

1966b).



Descriptiveamesor

coherentavas

nd

ntrusions

ldealcombination:

@ +

@ +

@ +

alteration texture lithofacies

erm

composition

e.g. sericitic,

ighly

uartz-phyric,

oarse,low-bandedhyolite

moderatelyesicular,

oorly

livine-phyric,ine, olumnar

ointed

asalt

lvlinimum:

@

+

O

e.g. blocky

ointed

hyolite; assive

asalt

@

+

O

e.g.

hornblende-phyric

ndesite;phanitic

acite(?)

@

+

O

e.g. ser ic i te-s i l icarhyol i te(?) ;chlor i te-epidoteandesi te(?)

@ coueosrrron

a. estimate ased

n

phenocryst

ssemblage:

.

thyolitet Kjeldspar r

quartz r

Ca-poor

lagioclase

ferromagnesian

hase;

biotite,

amphibole,

yroxene,

ayalite)

'dacite:

plagioclase

ferromagnesian

hase:

biotite. mphibole.

yroxene quartz

r

KJe.dspar)

.

andesitet

plagioclase

ferromagnesian

hase:

biotite, mphibole,

yroxene

r

olivine)

.

basalt:

pyroxene

Ca-rich

plagioclase

olivine

b. oraphaniticamples,

stimate ased n colour:

.

rhyolite(?),

acite(?) :

palegrey,pink,

cream,

pale

green

,

andesite(?),

asalt(?) dark

rey,

arkblue, ark

reen,

ark

purple

@

rrHorRcres

.

massive

r flow-foliated,low-banded,lowlaminated

.

ointing:

olumnar, adial olumnar, oncentric,ortoise

hell,blocky,

rismatic, laty

.

pillows

r

pseudo-pillows

@

rexrune

.

porphyritic:

a.

phenocrysts

Iype

(quarlz-phyric

..,

pyroxene-phyric

.., etc.)

--.

abundance

poorly

.., moderately.., highly

.. )

-

size

(fine

<1

mm, medium 1

5

mm,

coarse

>5

mm)

b.

groundmass

-

glassy,

ryptocrystalline.icrocrystall ine,ery ine

grained

.aphanitic:

uniformlymicrocrystalline

. aphyric: no phenocrysts resent

.

glassy:

composed f volcanic

lass

.

non-vesicular

r

vesicular

or

amygdaloidal):

parsely

. , moderately

.., highly ..,

pumiceous

..,

sccnaceous

. .

.

spherulitic, icrospherulitic,ithophysae-bearing

@

nlrrnnrroru

.

mineralogy:

hlorite, ericite, ilica,

yrite,

arbonate,eldspar, ematite

..

.

d str ibution:issemnated, odular,

potted,

ervasive, atchy

..

Tab

e

1 Descript

e names orcoherent vasand ntrusions



ldealcombination:

/ i \ ^ - ^ , ^ , ^ , - -

\ .r / \.:hAI\ DtZtr mudhudstone

sand/sandstone

Descriptive

ames

or

volcaniclastic

eposits

+ @ + @ +

lithofacies

erm

components grain

size

e.g. chloritic-pyritic,

ery

hickly

bedded, olcanic

ithic

breccia

thinly nterbedded,

hard-richmudstone

nd crystal-rich

andstone

@

alteration

l\.4inimum:

@

+

O

e.g. crystal-rich

andstone;

umice

ranute

reccia

@

+

O

e.g. laminated

udstone;poorly

orted,

assive

reccia

@

+

O

e.g.

pyritic

andstone;

htorit icreccia

< 1 / 1 6m m

t h6-2

mm

gravel/conglomerate

r breccia:

granule

2

4 mm

pebbte

4-64

mm

cobbte

64-256

mm

boulder

>256 mm

@

coveoruerurs

@

urHorncrrs

.

massive

non-bedded)

r stratified

bedded)

.

bedding: aminated

< 1

cm

.

equalor unequal

hickness

very

hinlybedded

1-3

cm

.

laterally

ven

or uneven

hickness

thinlybedded

3-10 cm

.

laterally

ontinuous

r discontinuous

medium

bedded

10-30

cm

.

cross-bedded,

ross-laminated

thickly

bedded

30-100

cm

very hickly

bedded >

100

cm

.

massive non-graded)

r

graded:

normal

1,

reverse 1,

normal-reversei, reverse-normal

.

fabric:

clast-supportedormatrix-supported

poorly

orted,moderately

orted,well

soded

.

jo_inting:

locky,

rismatic,

olumnar,

laty

@

nrrcnnrror

.

mineralogy:

hlorite,

ericite, ilica,

yrite,

arbonate,

eldspar,

ematite

..

.

distribution:

isseminated,

odular,

potted,

ervasive,

atchy

..

Tab

e 2 Descrlptlve

ames or volcaniclast lc

eposits.



GRAIN

SIZE

VOLCANICLASTIC

DEPOSITS

N

GENERALnd

VOLCANOGENIC

SEDIIVENTARY

DEPOSITS

AUTOCLASTIC

EPOSITS

RESEDII\IENTED

AUTOCLASTIC

DEPOSITS

Hyaloclast

e Autobreccia

[,4ixture

r

uncertainrigin

<

1/16

mrn voican

mu0stone

f ne

hyaloclastite

,)

autoclastic

mudstone

resedlmented

ne

hyaloclastite,

resedimented

uloclastic

nudstone

1116-2

m volcanic

andstone

hyaloclastite

sandstone

autoclastrc

sandstone

resedimented

yaloclastlte

andstone,

resedlmented

utoclast

sandstone

24nm

v0lcanrc

c0nglomerate.

volcanic

reccia

g

an

rar

hya

clastiie

granu

f

aul0Drecc

granular

autoclastic

reccia

resedimented

ranular

yaloclastite.

resedimentedranular

utobrecc

,

resedimentedranular

utoclasticreccia

ffi4 mm

hyaloclastite

recc

autobrecc

auloclastic

reccia

resedimented

yaloclastite

reccla,

resedimented

utobreccia,

resed ented

utoclast

breccia

> 6 4 m m

coarseya

claslite

breccra

c0arse

aul00recc

coarse uloclastic

Dreccta

resedrmented

oarseyaloclaslite

reccla,

resedimented

oarseutobreccla,

resedimented

oarse

utoclast

breccia

GBAIN

SIZE

PYROCLASTIC

EPOSITS

PYROCLAST-RICH

EPOSITS

Unconsolidated

tephra

Consolidated

pyroc

stc ock

RESEDIIVENTED

YN.ERUPTIVE

Posf

ruptlve

esedimented

r

reworked,

runceriain

rigin

<

1/16mm

fine sh

fine uff

resedimented

sh-richudstone

tuffaceous

udstone

1/16-2 m

coarse

sh

coarse

ufi

resedimenled

sh-rich

andslone

tuffaceous

andstone

2-64 n

lap l i lephra

lapillistone

or

apilli

tulf

or ulf-breccia)

resedimented

yroclast-rich

lapillistone,

resedlmenledumice

apillistone,

resedimenledumice

nd i ihic

apillstone

tuff ceousonglomerate,

tulfaceous

reccia

> 6 4 m m

bomb

fluidal

shape)tephra,

block

angula4

repnra

agg merate

bombs

presenu,

pyr0clastic

reccta

resedimented

yroclaslrich

reccia,

resedimeniedumice

reccia.

resedimentedumice

nd thic

Drecc

Tabe3

Gran

s

ze

based

genetic

nomenc

atureJor

common

ypes

of vo caniclast

depos s

N4od ed

rom F

shef

(igtjt)and

Schridt

(1981.

1 1



ogging echnique

pictorial

epresentation

fsectionshrough

nd/or olcanic equences.'l

e

aim

s

o

record

ariations n tcxturcs,structuresJ edforrns,grain

size

contact

elationships

y aschenatic,

implif ied, ictorial

Graphic ogging s an especially fTective ay of

his information for dlillcore sections. he log

emind he observer, r a glance, fthe acrualdeposir

nd,

herefore, equires isciplined bservations,

n

internal

variatior.rs,

he natureud position of

ancl elationships etrveen uccessivearts of thc

his swleoflogging s ror onJva thoroughsystem

sedimentary nd

volcanic

secluences,ut

observationsoward those

eatules

hat aid

of emplacement rocesscs nd depositional

Most standardexplorirtiondrill log lorms

shects rc designed

or

cornputerapplications

nd

or textural analysisand volcanological

he format fbr graphic ogs

is

sirrple: the

vertical

a,<is

depth or thicknessand the horizontal aris

Adjacent

space

s

used

for

l.ounging

direction

indicators,measurementsf

maximum particle size, sampling nformation

succinct

ithological

description.

Ordinary field

nd standard

ogging orms

can

both be adapted

this format

(Figs

7,

8). Syrnbols

Fig.

9) are used

on

ogs o convcynvo sortsof

informarion:

omposition

texture. Composition symbolsrepresent nterpreted

henocryst izeand abundance, nd

or

both

coherent aciesand

juvenile,

essentiallv

clastic

acies. exrure ymbolsepresentheappear-

of the volcanicunits,

including

different

sortsof

and approximate elative

Massivecoherent avasand inrrusionscan be

ust

by compositionsvmbols.

uvenile

clast-rich

depositsand lava- or intrusion-related

situ

breccia an be shorvnby combinationsof composi-

and texture

svmbols.Many texturesymbolsalso mply

size, s hey do in sedimcntologicalogs.1'hesymbols

and

for non-volcanic ediment-

comnronly used

r.r

sedimentology.

of a section s the

most

obvious

but not

he easiestlace o begin ogging.

A lar

betterapproach

o

reviewquickly the entirc section,

n

order to

find the

complicatedparts, and to start there.

Having logged

parts, t is usually possible o

progress o adjacent,

difficult intervalsuntil the

log is

complete.

Complex

r rel:rtionships an be deciphered

v constructing

ogs at largcr scales.

The

accompanving

onsists 1'lithological nd ithofacieserms hat

iarures and

complement he graphic

additional information;

for example,percentage

f important components

uchasphenocrvsts,

wpes

of lithic clasts

resent. n general, achdepositional

emplacement nir is logged hen described

more or lcss

in turn, so t is mperative o devote ine to

locating

ontacts.

For altcrcd ocks, hc descriptionalso

ncludes

a summary

of alterationmineralogyand textures.Graphic

logging is

very vcrsatilcand can be adapted o cater

or

any special

features nd relationships.Horvcvet ir is

important

to be

conststent.

rhqo{ifLc x - monomict,".lgsaw

-6f

,

'spt

+qtz

volconicloshc

s1

mudsl

rYlxed op-docil€

muds{

'

FPe'ile'

mos6ive

'shGbhyric

ooclTe

_

tnTTUston

grey o#-massive,nudd.

f

fo

r-ftyni:

ocrte-irtnrim

polmid

ithic+Pum

x,rL-

c,"

,brnk

fhjnc

lrnrie

bx

""ge.1

S.+l',.p"1

Thydrte

-

lntruslon

Jll'th;e

3 t . 3

q 2

l i g . l " ' r p " o a d r

l

o ' "

g ' a p ' r ;

o g o d ^ T o

o . r l ,

l d r a d

notebook J [,4cPhie

unpub

data)



DIAMOND RILL

LOG

project

RoSzllrv-..",f

Yi"<

Location

f4 i",p-

sactrb"o

l50-

5

co

ords

horeo

114 <D

pase

I

or

2

m

$rucrure

tos

E

grarnsrze

Q - m d

.? .1 T .T

mm

Samples

TS results

RL

M

INCL

Sca le

2oo

description

rosseo

v

R"

Allr-

date

1/

z/az_

l25(

..*^.178'-

78

-".1^.d

6.1

t5--4.-,

'l.'<',-t

3

,^ . \ .5--

a-a

f-t;.

4rever3<-

f."u

-

M

assi,,"

-"I+ie/ E-,w"

X1-

crcq.',

-.,r1^tt

,

\g-2n"1"

\-2^-

I.lJ

-

g)^.'.;.

tubr

b"-r".

L^

U _ . - - - - - - ' ] _ -

Llamclt;sh:c

^tlLy

ri-r-e.q

Jiff-""

orep;

Ll" f .L.s

"4". .

d- i l i . i f ' -d

p--,i. e-.

G^^.^

t;^t

-f,,b.

f"-.

|e-x{"."

Not

i^|e"se.

No

lilhi"'

"l<-o'r

-d

t z l 3 . z 3 ^ k ^ ; J

I

Fook

x

Massiv . , q-c lzd

{>q

"Lt - . , . r .

volc so.d"'1.

^*s-

4d-

u,nits

,,,,1h

'll^i.

"na{.,x-s"fprfal

Lx

-{

L,.it

bs.s.

C\asls'.

@

zo-zsZ,

l-3 n

-

r-

F:1 I

- -.p..1*'o-r5%,

-2

hh

+ig

PhJ' i '

- t t rrr

"

Motl-ix:

xia\s

5C7o

1'l'%.

tza2.

cs^ "1"^'5

.-.{l--LL

9a

\\ '

z < h

\ r

.

. t

tT,

, . \

c z

4

) .1

; -

* -

DI"

..-",

l5Z

t-t^^ {e\a-

F..PhJ;*,.

' ;

Fql?

\ro\..tq lu.{

alo.lo.5fit<

blo"k

=aA

ul.-f,l

\\..\

F q b

\ - ^

M"a;"--{t",ao, f.rd

5.,": [_.,-;.-

shrcel.

,ro.-o1

q,odeA

v"oL

=i"dn

t"d.

\ ] :

{ t t

f '

$ r

\ t



l \ " l

N-il

RI

|

, .

I

f-;----t

l ^ A l

l-r

-Fl

l r l

l . o l

f'l-l

f i , , l

l /

-

\ l

l * e

:

i r l

NT_l

I

Il

/. ' l

a

l-;%1

I

vz:r"

I

I

v

I

SYMBOLS

FOR

COHERENT

EXTURES

single

ine

symbols

or ow o moderate

phenocryst

bundance

double

ine

symbols

or abundant

henocrysts

smaller ymbols

or ine

grained henocrysts

larger

ymbols

or

coarse

rained henocrysts

additional

+"

symbolorcoarse,

henocryst-rich

granitoidexture

basalt,

oorly

o

moderately

orphyritic

basalt

phenocryst-rich

asalt

andesite,

oorly

o moderately

porphyritic

ndesite

phenocryst-rich

ndesite

dacite,

oorly

o

moderately

orphyritic

dacite

phenocryst-rich

acite

fine,

poorly

o

moderately

orphyritic

rhyolite

coarse,

oorly

o moderately

orphyritic

rhyolite

coarse,

henocryst-rich

hyolite

coarse hyolitic

orphyry

flow oliation

spherulites,ithophysae,lterationpots,

nodular evitrifcationexture

SYIVBOLS

OR VOLCANICLASTICEXTURES

.

closer paced ymbolsor

dominant

rain

ize

and

grain

ype

pumice

r rel ict

umice

angular,

uveni le

ava lasts

fiamme/

vitriclast

r

relict itriclast

accretionaryapilli

angular,

olymict

ithic lasts

rounded,

olymict

ithic lasts

mudstonentraclast

sand-size

articles,

ranular

exture

m r r r i - c i z o n e r r i n l o c

distinct

lanar

tratifcation

diff se

planar

tratifcation

cross edding

micro-crossamination

pumice

lasts n sandmatrix

angular

olymict

ithic lasts ndmudstone

intraclastsn sandmatrix

ax:71

l r " o I

IBZ1

t a l

W7l

lr"

El

l o @ l

tr=t

- -

I

t . l

l . . l

sl

l v l l

l . . l

F--l

N

F

e . g .

l==-:; l

t - l

I

a':-.

l-'T:.ll

l : ,

l

ffi

ffi

w

i

'nz>a

jigsawjit

exture f f ne,moderately

porphyritic

hyolite

jigsawjit

exture f coarse,moderately

porphyritic

hyolite

jigsaw{it

exture f coarse

henocryst-

richandesite

pumice-clast-rich

eposit. oarse.moder-

ately

porphyritic

hyolitic

omposition

pumice-clast-rich

eposit, oarse,

phenocrysfrich

hyoliticomposition

pumice-clast-rich

eposit, oarse,

moder-

ately

porphyritic

acitic omposition

SYMBOLS

OR

JUVENILE-CLAST-RICH

EPOSITS

t = , I

t - ' - l

l \ / - l

| + l

T----------:----

l=

\\ //l

t "

-

|

|

-----

--1

t -

l r ^ l

g

I

Recomrnended ompos on and texturesymbos fof

graph

c logg ng of

vo

can c depos s

4



lmportant

extures

nd

structures

A small

number

of texturcs

ancl

structures

rreparticularly

important

n deciphering

enetic

rocesses

nd/or setting

ot

volcanic

eposits.

,arlv dentification

of these

eatures

hus

grcatly

accelcrates

rogress

orv:rrd

volcanologic:rl

ntcr-

pretations;

or

example

Porphyitic

exnu'e

lbund

ir.ravas, vr.r-volcanic

r.ttt'usions,

lavalike gnimbritesand clasts crivecl iom thesedeposit

rypes

1.1,

1.2) ;

Spherulixs,

ithop

usae

nd micropo

L itic texture

indicaring

high-temperaturc

evitrification

of coherent

volcanic

glass

(3,4,25.r-2);

Perlite

];rtdicatine

hydration

(or

quenching?)

f

cohercnt

volcanic

lass

5,27.2,

42.6-7);

Arcretionary

pilli-formcd

bv

subaeialexplosivc

ruptions

but

may be

rede

ositedand

reu'orhcd

7.6-8,

22.6,

38.1'

39.6,4o.r);

Flnwfoliations found

in l:rvas, 1'n-volcanic

ntrusions,

and heomorphic

nd lava-like

gnimbrires

8,

26.3-5):

Columxar

oints

-

found

in l:rv:rs, vn-volcrnic

ntrusions

and

primary

volcanicl:rsric

eposirs

mainly

pvroclastic)

hat

are

mpl. rced

ruL

9.

l -J .

26.1

2)r

Pillows

found

in lavas

emplacecl

subaqueously

and

intrusions

mplaced

nto

rvetsedinent

15,

16,

17);

Graded

edding

indicating

sedinrentation

lom nrass

f lows r

suspcrts ion

18.1,

0, 31.1,32. I ,34.2-3) ;

l lanar

hin

bcfut i ry

indi . r t ing

rr \PLn\ i ( ) r rr t r . tc t i r r t t

current

eposit ion

38.

,

38.8,

39.2,

39.5,

40.5-7

Crosstratifcation indicating ractioncurrentdepositiou

(38,

0.8,

I .3) .

Manycon.rponents

t.rd

extures le

nor stronglv

diagnostic

of

particular

origins.

fhe

most

frequendy

misinterpretecl

are;

WsicLes

Fornd

in

lavas, nrrusions

and

non-r.veldcd r

very

enselv

elded

vroclasticeposits

2.1-5,

20,17.2):

Pumice

nd

scorir

ploduced

in

abuntlance

v DarDcffusive

and

explosive

ruptions

(6.1-7,

20):

Gkss

hards

found

in hvaloclastite,

rimary

pyroclastic

deposits,

yn-eruptivc

esedimcnted

oIcaniclastic

rnd

volcanoserric

edimentarv

eposirs

7 1-3 12'4'23'30'LB);

Fiam

me

fottnd

n

diagenetically

ompacted,

on-rvcldecl,

primary

and

secondary

umiceous

deposits,

ncl n rvelded

primirry

pyroclastic eposirs

both

allout and

lorvdeposits)

(24.r-3,

6.5, 5.7,

6.2):

Pseudo-J)amme

found

n a rvide

valieryof cleformcd

nd

altered

olcanic

cposits

44.5).

A

s-m'ra 'y

o' the essent

a l

'eatures

oI

lhe sea-

f oor massve sul f ideenvironment

As presenrly

ur.rderstood,

,olcanic-hosted

massive ullide

mineralisation

orms

in

"rel:rtively

deep"

sca vater

rnd s at

least patially'

ssociated

vith volcanic

scquences.

lthoug}r

absolurc

vater

epthsare

not casilv

onstrainecl,

ppropriare

environments

rewell belorv

storm

wavebaseand

arehere

simpl1'

eferred o a.s

deep".

The seclimentarv

t.td

olcanic

proccsses

h:rt operate

n dcep

marine scttings

diffcr

from

those hat

operate

n shallorv

narineand subaerial

ettil.tgs.

Decpsubm:rrinc

olcat.ric

equences

onraindeposits

rom

both ntraba^sinal

nd cxtrabasinal

subaelial)

r basin-margin

(shallorv

narine) ruptive

centres,

nd rre

normallv nixtures

of

volcanic and

non-volcanicdeposirs.

l

he1, nclude

the

products

of botl.r

effusive anc{

explosivc

eluprions. Syn-

yolcanic ills, ykes ndcn'ptodomesmaybe ustascommon

:rs ava

lolvs. ntrusions

ud

lava lorvsare associ:rtcd

vith

hyaloclastite

nd

pepelite,and can

clevclop

pillorved and

lobate

orms.

Most clasticdeposits,

oth

volcrniclastic

nd

nor.r-volcanic,

reemplacecl

v lvarcr-supported

nasslor,vs

and

bv hllout

from suspension

n the

rvater olumn.

Water-

supported

mass lorvsare

a particularlv

mportant

neans bv

u'hich

subaerially

and shallorv

subaqueouslv

rupted

pyrocl:rsts re

transported

o deepsubmarine

depositional

settings, nd

bv v{ich

intrabasinal

v:rloclastite

s resedi-

menred.

oth svn-eruptive

nd

post-eruptive

olcaniclastic

mass-florv

epositscan

occut and

arc rtsuallv

associated

rvith

volcanicl:rstic

uc{stonend siltstonc

ormed

bv settling

from suspension .

tudies

fancient

equencesuggest

hat,

in general,

veldecl

umiccous

pvroclastic eposits

are

uncon-rnon

n belorv-rvavc-base

nvironrnents

nd restricted

ro speci:rl

ircutnstances

hatallor,v

ear

etention ndprimary

transport

n a deep

ubaqueous

etttng.

Non-volqrnjc

facies:rre wpically

intcrbedcled

vith the

rolcarr i .r , e. . rnJ l re

.peci . r l l l

ntpor t ' r t t t

n .onsrr l in i r rg

rhe depositional

environment

n cases

,vherehe

volcanic

licics aredominatedb1'very rhick n.rassivcavas,ntrusions

irnd/or

volcaniclastic

eposits.

Non-r'olcanic

sedimentary

flciesm:rinlvcomplise

urbidites

ndhe

mi-pelagicmudstone,

together

vith

rninor biogcnic,

iochenical

and chernical

scdimentarl.

deposits.

Fossils

n intercalated

sedimcntary

faciesmlr. also

providc

independenrconstraints

on

the

rvater

eprhof

tl.re eposit ional

etting.

n general,he

non-

volcanicscdimentan'

ncies

ack irbLLndalrr

r large raction

su'ucturcs,

uch as cross

bedding,scouls,

or channels.

lntroductiono the \lountReadVocanics

Tl.reN4ount

ReadVolcanics,

'estctn

Tasnania, cottsist

of

compositionallr '

rnd texturally

diverse,

Middlc to

Late

Cambrian

lavas urd volcanicl:rstic

ocks

(Corbctt

1992).

The volcanics

havebcen affected

by

regionaldeformation

and meramorphism,

nd

locallyhvdrorherm:rl

ltcratiot.r

s

intensc.

l

hesevolcanics

ale famous

r,vorldwide

or the

abundance

nd ricbness

fdeposits f

massivculf ides

hat

ther-contain

(e.g.

Mount

L,vell,

Hercules,Roseberl',

Que

River,Hellver

Solorron

1989, -arge

1992)(

Fig. l0).

Thel. present

a considerable

ut tvpical

challenge

or

mapping,

exturalnterplet:rtion

ndvolcanic

acies nalysis.

Thc

Mounr Read

Volcanics ornprise

hc lollowing

Iithostratigraphic

nits:

he Ccnrral

VolcanicConplex,

the

V'estcrn

olcano-scd

mentarv equences,

heEastern

uartz-

porphvlit ic

equenccnd

heTvndall roup

Corbett

992)

t 5



10). Lavas nd svn volcanic

nmrsions

oi

rhe Mounr

.olcanics

are prcdoninandl

rhlolires

ano

oac(es,

local l r

bund.rntndesi tes

Dd

asaks.hrr

conform{)

on

eeochclr l ical

r r i r t ion

diegrams

ci 1.

1992).

The princip.rl o)canic

aclesn

rhe \4ount

ReadVolcanics

( \J.Phie

nd rulcn 1992) l

h . . x d . '

J i

. t .

t - r " r ' - . o . r m . , n

,

VolcanicComplexand occurat rlrnv localiries

volcano-sedimcnr:rry

cqucnces;

tbpostr:

n*t

manr npcs

of

uvrniJc

l : rst , r ich,olcanic la* ic

masslorv

ne sdominared

y poor.ll

or non-rcsicul.rr,

larrchstsand

clated <,

hcsubrqueous

mphccncnt

lavr

flo*s .rnd ava

domes: hc

odrer conrains

bundanr

pumice c lasrs

roduced

bv sLrbaer i r l

r shal lorv

xplosi e n,prions

nd redcposired

nro

deeper

seft ingsi

ot ni. ittr"s;tm Iargclvcontunnablc,enlnrccd

mired ui rh

qct,

unconsol idarcd

osr

<,rming

eperire

nd silL onplcxcs.

Thescvolcanic

acics

re nrerbedded

irh sediment,

rry frcicsconprising

aminared

r massivc,

lacxmuosrone

and

eraded

beddcd sandstonc

urbidi res of

mixed

volc,nicand

neras€diment ry

Precanhr ian

bascmcnt

provenancc.liddie

tiambrian

rrilobircs

and other

m.rrnre

loss;lsarc

sparselv

isrributed n

the se<limcntarl

acics

(Corben

199- l ) .

Circn

this selecr ion

f facics i th

*hich

to rvork,an

attempr hes

b,cen nadc

o reconstLucr

he

Cambr ian

facics

rchi tecmrc

f dre

Mount Rerd blcanics

Fig.1t) .

The

bcst conelarion

iamcr.oLk

br reconstr.ucting

icics

.r rchi recnrrc

s pr<,v ided

y volcanic

facics

drar aLe

e r u p t e d

n l : r r qc

v c , l um c s ,

e p o r i t c d

r . r p i d l y ,

a n d

ridcsprcad.

Mass-fl

*en9laced

puniccous roLcanicla-stic

i . , . -

; .

r r - " r eJ

. | r g r

n g n i

r J c , r l ,

; , .

(

L f , ; o n .

e

the obvious

irst choicc.

Someexamples

n the founr

Rerd

\blcania

have

bcenuaced

br over 12

km along

xrike and

relcal

rhe presencc

of svn volcanlc

laulrs

drat crcarcd

importan.scdimenr rapsand cnv;ronrnentsa\ourable t)

sutfldc

mnrer.rlnarion.

Fg l0

Dsl rbJlono l rh- .

r

c

pa

r fos l ra tg .aphc,c 'maiorsandra lor

T 3 : s - a 1 i j .

c e p . r ss n r h e C a r b ' a . L t o L r r F e a C V o . a n c s c l w e s l 4 t r l

-asman

a U.J l€d I

on C.r |e l t

( i9921



The volc.rnc hosr c,lucnces

o o"o

tu*ivcsulndc rleposiLs

in

t lLeNlount

ReadVolcrnics,

Hclhcr end Rosebetl

Hcrcules,

rc

'carurciLn uranl ofthc

plrtes

l igs

12, 3).

fhe

I Iel lver eposit

sa n picalmound

snlc

Kuroko

'pe),

; - J .

r .

.

l i . . ' l o o "

n , i ,

.

r r r ' l ' d < p o

r r r r r n :

I6 millrcn

tonnes r.rding 11'i)

crd. 13on inc,0.49;

coPPer,

I60

ppn

silver nd 2.-]ppm gold

(\{cA.rdu

rnd Dronscikl

1990).

he m:sivc srltilc

lndr is oc.rted

enveen.riom Jl

scquencc

of feldspar-phlrit :rndcsnichv.ts. \'rrh nlnor

volcaniclastic

nia, and

r hrngnrgrvrllscclucnce

l pillow

brsah

nd bL,rck

udsrone

Fig.

2).

lnmedi.rtelv one

strikc,

rhc

ore posnion s

rcprcscnLedv co.rrrc,

olvmict,

rolcanic

l i rhic

r ich, m.rss-f lo* mplaccd

brecci.r nd

lamrnrtcd

volcrnicl.rsticmLrdsronc

rd s.rndstonc

V'rtcrs

ancl

ihl lece 9j)2). hem.rssive

tLl l ideodvis nderlain

,1

, r '

l - r

r r o 1 r , ' e

r ' . 1 -

. n ' "

. r

e r i t

o l

'

:

, r " r r ' t .

ard

rel.rrecltringcr

minerJis.rtion

Gcmmell:ld

Lrge 19921.

TheRoscben eposits.r25 ni lLiononne assivesulr ide

ort b odi, grading .2o n

e.rd, l .E(,, z inc,

0.6r1 ' i ,opper.

t " p p . . . l \ c ' , r

4

r . 1 , r

. . J .

L c J . t . . i ,, . , n ' i . , . ,

numl 'er of sheet ikc

orc lcnscs ostcd n ", .^s, ' . " ,

hn;nrrcd,

puniceous, hlol i t ic s,rndstonend siLrsronc,

abovc

li,onell ofverv thick,

rnasslos cmplrccdpum,cc

Lreccia

Al len

ndCas1e90, IcPhic.rndAl lcn992l.Thc

liontrll

sequc cc

s,rlrtrcdend ocalivstronglv elirn,ed o

quartzsc, ic i tcnd chlori te chist ont: ining iseminrrcd

p.r'ritc.'l

c hangnrgrvallcquentc

s donrnrared y

'.rri.rblv

crysr.rl-rich

r pLrmiceous

oLcrnicl.rsticandstonc, nd

in

placcs

nclLrdeshin r l tervals fblack

ntLtdstone

l ig.

l3).

Both $cse deposns.rnd

rhen in thc N{ount

lcrd

Volcanicsere dcscribed

l Largc

19921

nd in rehted

p:rpcrs n rhc

t:lonnnt Geolog SpecirL

sue

(19921

on

''iustrrlirn

volcanic'hosred :rs

vcsulfide eposirs nd hc

l

volcanic nvironmcnr.

VOLCANIC

FACIES:

f;.,1

ru

F=l

E

F r

' l

S.henra i .

la . .s a c l r ectJre l

s lDnar ne . tan .

s .q len .es s . f as the

.1 . . t

F leadV.c i . . s

t re . re rn ia rn : ra o ca i . as lc n i iss I . r de t .s ls rc c . r .sean-e . r - .dh laocrs l : .1 'o r . . ra as.a a t : i lo r .

i t r r l . m s a r d l h . k . i a b . , a r L . l : o ' p - n . D r e . . E l h a t c r o t i l t l . r l n a ' ( e r s 1 0 'c . r c : 1 . .

- h e r e

a r e . o n s . e '

: r .

, -E .na

\ ra .a r i ]

s

n re :1 re l r .ocn . rs 01 a 3

l i ( s s s a r . l

. . . : . as : . . ls a . l

. . . . . ta . e :

1 ,1 d

. . r

l r .n r V.Pi r e a .c A . r r

i

1992)

NON.VOLCANICFACIES:

si l ic ic -

lavas,i l ls

nd

malic

I

in situ autoclaslic

- intermedialer

breccia

resedimented

yaloclastite

pumiceous

olcaniclastic

andstone/breccia

mudslone

lurbidi tes

contacl

1 7



Plates Graphicog Hellyerlral igraphy

3 5

33.3,33

3 3 7

3 3 4

452

)

l

J

Solthwel lSub roup

verylhck,mass

e o

graded

rhyo

etvolcanr th

c breccra

and

congromerate ack

pyrt

c

and

grey

m.caceous

udstone

Que

River

Shale

Helyer

Basal l

massve

nd owbasa,

nya

oclastte

brecca,

peperte

massve

dacte auloc

aslrc r€cc

a

potym

t votcanic

brecoa,

grad€d

olcanic

andstone

massve

su ide

1 2 4

1 45 - 1 4

428

2 9 1

3 3 5

3 7 5

4 2 7

I

t

I

434,43

5

,

J o

01

h.

se. : .n

. ,strared

ere

s

,rr0l

-

' fe ldspar

phyr ic

equence'

rnassve, ledspar

hync

andes ia l toclastc

recc i

mrnor

oymn

vocan

p

ow

basa , basa c hya

cas l le

Anima Creek Greylvacke

grad€d,

m caceoLrsandstone

I

seq .n .e

.1n .1Fc

' j

na3s e

s 'de or b . .1 , / wes tern

asn-ana he

l . r ia

Ba5ed

or

i l i a ' . r s

anC la a . - .

l j 9 r2 )

ard C . , t re

a fd Kom, ,sha.

t98g)

1/16

2 64mm



Pla les :

1 0 1

4 2 2

4 2 4

4 3 1

Graphic g

Hercules-Rosebery

trat igraphy

Mount

BlackVolcan

s

massre riyo ie

and

dacte.

altocast brecc

4 5 1

4 6 3 . 4 6 4

6 3 . 6 4

4 6 5 , 4 6 6

F

-3

S

np fed

, :ph .

, ' l .e

i , i i :

:hc{ncss c l1 re . .c t . ^ l ra t . . l . . . s

''hangingwall

pyroc

asrtcs

very hrckiy eddec.

rysta.

a.d/or

um

e

rch

sandstone

L

I

{

t

l

3 3 4

467

hosl ock

mass

e od fi se y bedded

pumiceaus

a.dstone

and

bfeccra

lootwallpyroc

ast cs"

very

h cky b€dded,

massve

o

weakry raded

eldspa'

bearng

pumce

r€cca: assve

aote

andautoclastc

recc

,"o

ca. c saai a

aa

r0 :na

-2 r

1r

Bas . on 3 E€-

_1. r ' ]

cs l lseberr ' rnas: e sL .e . r . - . ra s r , . . T l re

l ia

- .1

l -3a l ) ._d

l , ' l . f ' . . a . .

A

e .

119- .2 )

ti

fi=

/ (

t

(

$

__R"\

-

fLvl

1/16 2 64mm

I

I

volcanic texture part-1

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