V O L C A N I C SUCCESSIONS

M O D E R N A N D A N C I E N T

A geological approach to processes, products and successions

R. A. F. CAS Department of Earth Sciences, Monash University

J . V . W R I G H T Consultant, Sheffield, England

i v

^^'«n London

A L L E N & U N W I N Boston Sydney Wellington

CONTENTS

?^IEFACE ix LIST OF TABLES xix

-' " / L

I H A P T E R O N E

miroduction to fades analysis ' zoleanic terrains 3

-lement 3 T/.roduction 4 L -.e facies concept " 5

- ;;cnption of facies ' : 6 1.3.1 Geometry 6 1.3.2 Lithology 8 - 3.3 Sedimentary structures 10 . 3.4 Sediment movement patterns 11

3.5 Fossils 11 -::e^ analysis and interpretation

- mportance of associations of facies 11 -.rr>- 12

- .- reading 12

"ER T W O

" ties of magmas relevant to . .^ai behaviour 15

- anent 15 rmas - an introduction to their asir\ 'and character 16

1 L I Classification 16 L i J! Alagmatic associations 19

2.2 Temperature 19 2.3 Density 20 2.4 Viscosity and yield strength 21 2.5 Factors controlling viscosity in magmas 23

2.5.1 Pressure . 24 2.5.2 Temperature 24 2.5.3 Volatile content 24 2.5.4 Chemical composition 26 2.5.5 Crystal content 26 2.5.6 Bubble content - 26

2.6 Strength 27 2.7 Fluid flow character .• ^ 27 2.8 Further reading - 30

C H A P T E R T H R E E

Volcaniclastic deposits: fragmentation and general characteristics 33

Initial statement 33 3.1 Introduction 33 3.2 Fragmentation due to magmatic

explosions 34 3.2.1 Explosive fragmentation from a

sealed, near-surface magma chamber or conduit 35

3.2.2 Explosive fragmentation of a vesiculating magma erupting from an open vent 36

3.3 Magma mixing as a means of triggering explosive eruptions 40

XI

xii CONTENTS

3.4.2 3.4.3

3.4.4

3.4.5

3.4 Phreatic or steam explosions and phreatomagmatic eruptions 3.4.1 Interaction with ground water

Interaction with surface water Lava flowing into water or over water-saturated sediment Pyroclastic flows moving into water or over water-saturated sediment Magma rising into a hydrothermal system

3.5 An introduction into the products of pyroclastic eruptions

3.5.1 Juvenile fragments 3.5.2 Crystals 3.5.3 Lithic fragments

3.6 Quench- or chill-shatter fragmentation 3.7 ITow fragmentation (autobrecciation)

and its products 3.8 Epiclastic fragmentation 3.9 Further reading

C H A P T E R F O U R

Lava flows -

Initial statement 4.1 Introduction

Size and form of subaerial lava flows Factors affecting the morphology of subaerial lavas

4.3.1 Effusion rate 4.3.2 Physical properties 4.3.3 Slope

Eruption of subaerial basaltic lavas Features of subaerial basaltic lava flows

4.5.1 Pahoehoe and aa lavas 4.5.2 Flood basalts 4.5.3 Plains basalts

Submarine basaltic lavas Subaerial basaltic lavas flowing into water Subaerial andesitic and dacitic lavas Eruption of subaerial rhyolite lava flows

4.10 Features of subaerial rhyolite lava flows 4.10.1 Shape 4.10.2 Lithology

4.2 4.3

4.4 4.5

4.6 4.7

4.8 4.9.

42 43 45

45

46

4.10.3 Surface features 85 4.10.4 Growth and internal structure 87

4.11 Subaqueous silicic lavas 88 4.12 Komatiites - peculiarities of the

Archaean 89 4.13 Further reading 91

C H A P T E R F I V E

47 their eruptions: an introduction

47 Initial statement 93 47 5.1 Introduction Q3 54 5.1.1 Pyroclastic fall deposits: 54 definition 94 54 5.1.2 Pyroclastic flow deposits:

definition 96 55 5.1.3 Pvroclastic surge deoosits' 56 definition 98 57 5.2 Eruptions producing pyroclastic falls 98

5.2.1 Explosive eruption columns 98 5.2.2 Ash clouds accompanying

pyroclastic flows 103 59 5.3 Pyroclastic fall denosits" tvoes and

description 104 59 5.4 Pyroclastic flow-forming eruntions 105 59 5.4.1 Lava-dome or lava-flow 60 collapse 107

5.4.2 Eruption column collapse 108 62 5.5 Pyroclastic flow deposits: types and 62 description 110 64 5.5.1 Block- and ash-flow deposits 111 64 5.5.2 Scoria-flow deposits 111 64 5.5.3 Pumice-flow deposits or 65 ignimbrites 114 65 5.6 Origins of pyroclastic surges 114 71 5.6.1 Surges associated with 73 phreatomagmatic and 73 phreatic eruptions 114

5.6.2 Surges associated with flows 117 75 5.6.3 Surges associated with falls 120 76 5.7 Pyroclastic surge deposits: types and 79 descriptions 120 81 5.7.1 Base-surge deposits 120 81 5.7.2 Ground-surge deposits 125 83 5.7.3 Ash-cloud surge deposits 126

CONTENTS xi i i

4 W AciTt^tinnfirv laml i l 126 7.2 Fluidisation 1 79 PiM /\<. LI L l l v J l l c i l V l a j T i i i i 4 I) IGir ihpr rF^aHinQ" p,V I Ul l i i c i icauiiig, 126 7.3 Pyroclastic flow units and grading :

7.3.1 Thickness 86 87

( 11 A I ' l'ER SIX 7.3.2 Basal layers 7.3.3 Vertical grading

88 88

7.3.4 Gas segregation structures 90 i / ( ' ( / f I I I J/y 1 ULitlJLiV J l l l - l - U'C'jyL/oLvo

///( // ( / UpilUflb

129 7.3.5 Lateral grading 193 i / ( ' ( / f I I I J/y 1 ULitlJLiV J l l l - l - U'C'jyL/oLvo

///( // ( / UpilUflb 7.3.6 Compositionally zoned pumice

111 I t 1 11 'siHUMTienl 1 1 1 M 1111 .s I t i IV-11 i v . l i e

129 flow units 194

1 Introfli iction 129 7.4 Theoretical modelling of the transport 11, 1 1 I 111 V.yVJ L i e . L l V l l i

/» > T f r m i n H l fnll velocitv and muz/lc of pumice flows 194

VL H 'L11J 131 7.5 Form of moving pyroclastic flows:

r, \ 1 iHWHiinn—sTrombolian I I 1 1 1 t l VV CI 11 CI 11 C l v y i A A • • ^ * • '

133 head, body and tail deposits 197 6 3 1 Characteristics of the deposits 133 7.6 Pyroclastic surges as low particle

6.3.2 Mechanisms and dynamics 134 concentration flows 203

6.3.3 Classification 140 7.7 Energy sources and initiation of surges 203

6 •! Plinian 140 7.7.1 Base surges 203

6.4.1 General characteristics 141 7.7.2 Ground surges 204

6 4 2 Internal and lateral changes 144 7.7.3 Ash-cloud surges 205

6.4.3 Mechanisms and dynamics 148 7.8 Transportation and grain-support

i\ s Sub-nlinian I I l i e i l r l_/ 111 11U.1 1

151 processes in surges 205

(i () Ultranlinian 152 7.9 Depositional processes in surges 207 1 p , 1 F v_.' 1 1 1 n ^ l\ 1 \I u\c'AV\VAX\ 1) / V U l U C l i l l c l l l

153 7.10 Facies characteristics of surge deposits 209

(i S Surisevan and phreatoplinian 156 7.10.1 Geometry 209 | | | | 1 i P L I l l v P ^ y Cll 1 Ml * ^ AAA. -A* — 1

6.8.1 Surtseyan activity and deposits 157 7.10.2 Grainsize 209

6.8.2 Phreatoplinian activity and 7.10.3 Sorting 210

deposits 158 7.10.4 Shape and vesicularity 210

t-i X 3 Mechanisms 162 7.10.5 Composition 2̂ 11

1, 0 ni>;i'il silicic air-fall ash lavers I t / l y i c y l d l o l l i x - l e - £111 i c i i i c i i i i i i c i ^ A - i ' . '

163 7.10.6 Depositional structures 211

6.9.1 Whole-deposit grainsize 7.11 Surges compared with turbidity currents 217

populations 163 7.12 Pyroclastic surges and pyroclastic

0 .7 .Z occonuary i m c K c i i n i g ai iu flows - relationships 217

bimodalitv 164 7.13 Further reading 219

(. 10 Welded air-fall tuffs 165 6.10.1 Characteristics and examples 166 6.10.2 Conditions of formation 168 C H A P T E R E I G H T A in ̂ T h e r m a l facies model 172

C H A P T E R E I G H T

( i l l Further reading IP 1 I A vpivAAWA * — * ce

174 Ignimbrites and ignimbrite-forming eruptions 223

C H A P T E R SEVEN Initial statement ' 223

1 i.nichnrt and deoosition of subacrial 8.1 Enigma of ignimbrites 224

pyroclastic flows and surges 177 8.2 Occurrence, composition and size 225 pyroclastic flows and surges 8.3 Eruption sequence ana coiuimi c o i i d p » c 229

Iniiial statement .. • 177 8.4 Source vents 233

/ . I Subaerial pyroclastic flows as high 8.4.1 Linear fissure vents 233

particle concentration flows 177 8.4.2 Ring fissure vents 234

xiv CONTENTS

8.4.3 Vent system for the Fish Canyon Tuff 235

8.4.4 Central vents . , 237 8.5 Co-ignimbrite breccias 237 8.6 Co-ignimbrite ash falls 242 8.7 Depositional facies model 244

8.7.1 Bandelier tuffs and model 244 8.7.2 Rio Caliente and Taupo

ignimbrites 246 8.7.3 Ignimbrite facies and

eruption rate Palaeocurrent indicators Secondary deposits

249 250 250

8.8 8.9 8.10 Welding and post-depositional processes 251

8.10.1 Welding 251 8.10.2 Vapour-phase crystallisation 258 8.10.3 Devitrification 258

8.11 Chemical analyses? 258 8.12 The great Taupo A D 186 eruption 260

8.12.1 Early air-fall phases 261 8.12.2 Taupo ultraplinian fall deposit 262 8.12.3 Taupo ignimbrite 264 8.12.4 Overview . 265

8.13 Further reading . , 265

C H A P T E R N I N E

Subaqueous pyroclastic flows and deep-sea ash layers • .

Initial statement 9.1 Introduction

Types of subaqueous pyroclastic flow 9.2.1 Subaqueous pyroclastic flow

deposits 9.2.2 Ash turbidites

Hot subaqueous pyroclastic flows and subaqueous welding of ignimbrites Submarine eruption of pyroclastic flows? A model for the passage of pyroclastic flows into subaqueous environments Deep-sea ash layers Subaqueous base surges? , Further reading

9.2

9.3

9.4

9.5

9.6 9.7 9.8

269

269 269 270

271 275

276

284

285 286 290 290

C H A P T E R T E N

Epiclastic processes in volcanic terrains

Initial statement 10.1 Introduction 10.2 Importance of erosion and sediment

transport in volcanic terrains 10.3 Epiclastic sediment transport

10.3.1 Sediment transport not dependent on an interstitial medium

10.3.2 Sediment transport involving ice as an essential interstitial medium

10.3.3 Sediment transport involving water as an essential interstitial medium

10.3.4 Sediment transport in which air is an essential interstitial medium

10.4 Further reading

C H A P T E R E L E V E N

Crystal-rich volcaniclastics -pyroclastic or epiclastic?

Initial statement 11.1 Introduction

Three types of ash and tuff Possible fragmentation and transportation modes for crystal-rich volcaniclastic deposits Factors influencing high crystal concentrations 11.4.1 Eruption of highly

crystallised magmas 11.4.2 Eruption-related crystal

concentration processes 11.4.3 Epiclastic crystal

concentration processes 11.5 Several 'crystal tuff deposits and

their interpretation 11.5.1 Crystal tuffs of pyroclastic

origins

11 11

11.4

293

293 293

294 297

298

305

308

329 330

333

333 333 334

335

337

337

338

340

341

341

CONTENTS XV

11.5.2 'Crystal tuffs' with mixed pyroclastic and epiclastic origins

11.5.3 Crystal-rich volcaniclastics of largely epiclastic origin

l i d (Ivcrview 11,7 Further reading ,

( I FXF TER T W E L V E

( liissification of modem and ancient volcaniclastic rocks of pyroclastic and epiclastic origins

343

345 347 347

liiiiial statement 1.1.1 Introduction 12.2 Modern pyroclastic deposits

12.2.1 Genetic classification 12.2.2 Lithological classification

12.3 Classification of lithificd, indurated and metamorphosed volcaniclastic rocks

12.4 Descriptive lithological aspects of ancient volcaniclastic rocks relevant to determining their genesis 12.4.1 Textural 12.4.2 Compositional

12.5 Use of the terms 'agglomerate', 'vulcanian breccia' and ' tuff in ancient successions

12.6 The consequences of redeposition on nomenclature

12.7 Nomenclature of quench-fragmented and autobrecciated volcaniclastics

12.8 Further reading

C H A P T E R T H I R T E E N

Modem volcanoes and volcanic centres

349

349 349 350 350 353

355

356 358 359

359

360

360 361

363

Initial statement 363 13.1 Monogenetic and polygenetic volcanoes 364

Basaltic shield volcanoes 365 13.2.1 Hawaiian shields 365 13.2.2 Icelandic shields • 367 13.2.3 Galapagos shields 369

13.3 The source vents in flood basalt plateau and plains basalt provinces

13.4 Scoria cones (and pumice cones) 13.5 Maars, tuff rings and tuff cones 13.6 Pseudocraters and littoral cones 13.7 Stratovolcanoes

13.7.1 Morphometry 13.7.2 Output rates, repose periods

and life expectancy 13.7.3 Eruptions, characteristics

and deposits 13.7.4 Mass-wastage and epiclastic

processes 13.8 Intermediate-silicic multivent centres 13.9 Rhyolitic volcanoes or centres

13.9.1 Morphometry 13.9.2 Output rates, repose periods

and life expectancy 13.9.3 Eruptions, characteristics

and deposits 13.9.4 Caldera sediments and

domes: La Primavera 13.9.5 Other craters

13.10 Submarine spreading ridges and seamounts 13.10.1 Spreading ridges 13.10.2 Seamounts

13.11 Intra- or subglacial volcanoes 13.12 Further reading

C H A P T E R F O U R T E E N

Facies models for ancient volcanic successions

Initial statement 14.1 14.2

14.3

13.2

Introduction Facies geometry and facies -stratigraphic relationships: factors affecting them in ancient successions Factors affecting original lithological characteristics and depositional structures 14.3.1 Polyphase hydrothermal

alteration 14.3.2 Devitrification 14.3.3 Palagonitisation .

369 371 376 382 382 383

384

386

391 393 395 397

397

397

402 403

404 404 406 408 409

413

413 413

414

415

415 418 420

xvi CONTENTS

14.4

14.5

14.6 14.7

14.8

14.3.4 Hydraulic fracturing 14.3.5 Diagenesis 14.3.6 Metamorphism 14.3.7 Deformation 14.3.8 Relationship between

deformation and alteration Recognition of pumice in the rock record Facies as diagnostic indicators of palaeoenvironments and palaeoenvironmental conditions A suggested approach to facies analysis Facies models - what they represent and their uses Facies models for volcanic successions

420 15.4 421 15.5 422 15.6 422

422 15.7

423 15.8

14.8.1 14.8.2 14.8.3 14.8.4

14.8.5 14.8.6 14.8.7

14.8.8

Continental basaltic successions 427

14.8.9

Continental stratovolcanoes 427 Continental silicic volcanoes 429 Submarine basaltic rift volcanism 432 Oceanic basaltic seamounts 432 Marine stratovolcanoes 433 Submarine felsic volcanoes and volcanic centres Deep-marine facies derived from shallow marine-subaerial silicic volcanic centres 436 Intraglacial basaltic and rhyolitic volcanism 437

14.8.10 Precambrian volcanism 440 14.9 Summary 441 14.10 Further reading 442

C H A P T E R F I F T E E N

Volcanism and tectonic setting 445

Initial statement 445 15.1 An introduction to volcanism in the

modern global tectonic framework as a guide to the tectonic settings of ancient volcanic successions 446

15.2 Mid-oceanic ridge volcanism and the geology of the crust and lithosphere 446

15.3 Oceanic back-arc basin, interarc basin, marginal sea spreading

: • volcanism and its geological context 450

Intraplate oceanic volcanism 452 Intraplate continental volcanism 452 Continental rift volcanism 453 15.6.1 Narrow linear rift zones 453 15.6.2 Broad continental rift zones 455 Young island arc volcanism associated with oceanic trench subduction zones Microcontinental arc volcanism associated with oceanic trench subduction zones

15.9 Continental margin arc volcanism associated with oceanic trench subduction zones

15.10 Igneous rock-types as indicators of basement

15.11 Volcanism related to regional tectonic regimes and local stress field conditions 462

15.12 Igneous rocks as palaeostress indicators in the crust and lithosphere

15.13 An approach to evaluating the tectonic context of ancient successions

15.14 Further reading

435 A P P E N D I X 1

423 424

425 426

456

458

460

460

465

466 467

Methods used in studying modem pyroclastic deposits

1.1 Physical analysis 1.1.1 Thickness 1.1.2 Maximum grainsize 1.1.3 Grainsize distribution 1.1.4 Proportions of components 1.1.5 Crystal content of pumice 1.1.6 Density and porosity

1.2 Stratigraphic analysis

A P P E N D I X 11

Grainsize-textural classes of volcaniclastic rocks, some possible origins, and suggested diagnostic characteristics

REFERENCES • *

ACKNOWLEDGEMENTS . ,

INDEX

469

469 469 470 471 474 475 476 477

479

487

513

519