1

Magmatic dynamics and petrogenesis of eruptive deposits and 1

a shallow intrusive, Pa Bay, Akaroa Volcano, New Zealand 2 3

Anne A. Fulton1, 2 4 1University of Canterbury School of Geological Sciences, Christchurch, New Zealand 5 2Pomona College Geology Department, Claremont, CA, USA 6 7 8 Abstract 9

The magmatic and textural relationships between the deposits present in Pa Bay, a site of 10 parasitic Akaroa flank volcansim, were determined via geochemical and petrographic 11 analysis of field samples. No previous studies have identified such relationships in Pa Bay. 12 Scoria cone and fissure eruption deposits in the bay are cross-cut by an intrusive body; v 13 ariations within the intrusive body itself suggest magma mixing during and preceding the 14 time of emplacement. Major element geochemical data supported by thin section analysis of 15 phenocryst textures present evidence of an intrusive plug infilling the flank volcanic conduit 16 system as well as evidence of multiple episodes of magma mixing and mingling within the 17 shallow magma chamber. 18

19 1. Introduction 20

Banks Peninsula, located on the east coast of New Zealand’s South Island, is 21

principally made up of two intraplate composite shield volcanoes (Lyttleton and Akaroa) that 22

were active from 11 to 5.8 million years ago (Hampton & Cole, 2009). There have been 23

many physical and geochemical studies on Banks Peninsula volcanism (Hampton & Cole, 24

2009; Ring & Hampton, 2012; Timm et al., 2009; Johnson, 2012; Burgi, 2013; Metcalfe, 25

2013), but further insights into magmatic plumbing through geochemical and textural 26

relationships, especially on Akaroa’s flanks, are needed. 27

Lyttleton and Akaroa both have evidence of parasitic flank eruptions. Such eruptions 28

are primarily identified by fissure eruptions and scoria cones. Fissure and scoria cone features 29

are often dike fed and can provide insights on volcanic plumbing. Once a feeder dike reaches 30

the boundary between parent rock and volcanic cone, its further propagation is determined by 31

the stress field created by cone topography (Hintz & Valentine, 2012). Parasitic fissure 32

eruptions are usually formed from low viscosity lavas escaping through cracks in the flanks 33

of a central vent edifice that formed during inflation due to the filling of the volcano’s magma 34

chamber and gravitational influences (Winter, 2010). Scoria cones are monogenetic 35

volcanoes that are typically comprised of explosive scoria, fall deposits, and effusive lava 36

flows (Keating et al. 2008). They are most often basaltic with volumes of less than 1 km3; 37

they typically reach 200-300m in height and up to 2km in diameter (Keating et al., 2008, 38

2

Winter, 2010). Scoria cones are also frequently elongate along a fissure or larger on the 39

downwind side of the structure (Winter, 2010). 40

Pa Bay, on the NE coast of the peninsula, represents a particularly interesting outer 41

flank eruptive area on Akaroa (Figure 1). This is because, in addition to well-exposed scoria 42

and fissure deposits (Burgi, 2013), there is an intrusive body that could serve to provide 43

valuable tool in furthering understanding of the area’s plumbing system. The intrusive’s 44

relationship to the volcanic deposits is poorly understood. 45

This study aims to investigate Pa Bay volcanic deposits to determine their magmatic and 46

physical relationships and look for evidence of magmatic processes (i.e. mixing). It cannot be 47

determined solely from field observations and research to date whether intrusive and scoria 48

deposits originated from the same source. If they are from the same source, it could be 49

hypothesized that the scoria represents a less evolved magma than the intrusion due to 50

fractional crystallization in the magma body following fissure and scoria cone eruptions and 51

preceding intrusion emplacement. The Pa Bay deposits present an exciting opportunity to 52

look at magma chamber and shallow intrusive/extrusive dynamics within the volcanic 53

plumbing and petrogenic processes of Akaroa. 54

55

2. Pa Bay, Akaroa 56

2.1 Geologic Setting 57

The volcanism on Banks Peninsula has a complicated past. Lyttleton and Akaroa 58

volcanoes are mostly basaltic with some trachytic intrusives and dome structures (Hampton 59

& Cole, 2009). The basement in the area is made up of Mesozoic greywacke and some late 60

Cretaceous volcanic deposits (Ring & Hampton, 2012). The 2012 paper by Ring & Hampton 61

concludes that Banks Peninsula volcanism was in a horst system crosscut by faults with the 62

magma plumbing system tracing these fault intersections. 63

In a primarily petrological study, Timm et al. (2009) concluded that upwelling 64

asthenosphere, made up of a combination of carbonated eclogite and peridotite is the source 65

of the Akaroa volcanic system. It is likely that the upwelling was caused by lithospheric 66

detachment/delaminations and related decompression that would have corresponded to 67

regional tectonics during the Miocene. 68

Akaroa is analogous with many other central stratovolcanoes exhibiting flank 69

eruptions, especially the modern example of Mt. Etna in Italy (Acocella & Neri, 2003). Etna 70

is part of a system similar to the above model proposed by Ring & Hampton (2012), and it 71

3

has multiple flank deposits that could be modern counterparts to Akaroa’s numerous parasitic 72

scoria cones. 73

Pa Bay flank deposits were first evaluated in a 2013 study by Burgi that made initial 74

characterizations via field mapping and facies analyses. The study identified deposits from 75

five parasitic cones thought to be from point source and fissure eruptions with Hawaiian, 76

Strombolian, and phreatomagmatic characteristics. Burgi’s study also documented the 77

presence of intrusives including dikes and the large crosscutting intrusive that is of interest in 78

the present paper. Other flank deposits identified on Akaroa include scoria cones in Okains 79

Bay and Pigeon Bay (Muller, 2012 & Shirley, 2012) with similar physical characteristics and 80

eruption styles to Pa Bay. Previous studies give valuable insights into Akaroa flank 81

volcanism, but geochemical analysis and data are still needed to gain a more complete 82

understanding of the system. 83

2.2 Field Description of eruptive deposits 84

In the vicinity of Pa Bay, there is evidence of a fissure eruption and several small 85

scoria cones of Hawaiian to Strombolian in nature (Burgi, 2013). The fissure deposits are 86

made up of welded and non-welded scoria, lapilli, and bombs up to 1 m in diameter. The 87

largest scoria cone in Pa Bay is near the central area of the bay where a large intrusive body 88

cross-cuts scoria deposits near the inferred vent location (Figure 2). This main scoria cone, 89

making up the south portion of the bay, is made up of proximal explosive deposits (blocks, 90

bombs and welded scoria) and layered medial ash and lapilli as seen in Figure 2. The cone 91

has a diameter of about 1 km and has been modelled to have reached heights of over 180 m 92

and a volume of about 0.05 km3 (Brennan, 2014). 93

2.3 Field Description of intrusive 94

A large crystal-rich intrusive body cross-cuts both the scoria cone deposits to the 95

south and the fissure deposits to the northwest of Pa Bay (Figure 3). Within the intrusive, 96

there are a variety of distinct textures, including dark “blobs” or enclaves up to about 1 m in 97

diameter in the section on the southeast shore and aligned vesicles in the section on the 98

northwest shore (Figure 3). 99

2.4 Contacts between deposits 100

On the south side of Pa Bay, the intrusive body cuts through the scoria cone very near 101

the central vent location (inferred via apparent dips in bedded scoria and lapilli, Figure 2). 102

The contact at this location is veneered and also interfingered in a narrow zone where the 103

deposits meet. The intrusive cuts through the cone and extends back into the hillside from the 104

exposed shoreline, and there is some scoria that remains adhered or “veneered” to the surface 105

4

of the intrusive where it has not completely eroded away (Figure 4). Also, directly at the 106

contact between vent facies and the intrusive, there is a small interfingering zone (up to 0.5 m 107

wide) where there are scoria clasts incorporated in the intrusive material (Figure 4). 108

Up the hill from the vent location, the intrusive splits off into a few small dikes that 109

propagate up through the scoria cone and eventually taper off. 110

On the north side of Pa Bay, the intrusive body has a seemingly linear contact with 111

the fissure deposits; however textural variations suggest the possibility of multiple injections 112

of intrusion that separated some of the fissure material, as seen in Figure 5. 113

114

3. Methods 115

Samples and photographic documentation of deposits and unit contacts were taken in 116

the field at Pa Bay, Banks Peninsula in February 2014. Sample locations were documented 117

with GPS. Samples were collected from scoria cone, fissure, and intrusive deposits in the 118

near-bay vicinity, and samples from three lava flows and more scoria cone were collected 119

inland about 0.5 km up the valley (Figure 1). The most suitable samples, representative of 120

their units and with little to no weathering, were analysed in hand sample then cut in 121

preparation for thin section and crushed and powdered for x-ray fluorescence (XRF) analysis. 122

Both thin section preparation and XRF analysis were carried out by University of Canterbury 123

lab technicians. XRF analyses to obtain major element chemistry were performed on a Philips 124

PW2400 Sequential Wavelength Dispersive X-ray Fluorescence Spectrometer at international 125

standards following the methods of Hartung (2011). XRF major element data were 126

interpreted using IgPet 2012, and data sets from previous studies of Akaroa (Dorsey, 1988; 127

Johnson, 2012; Metcalfe, 2013) were considered in some analyses. 128

Once they were prepared, thin sections were analysed on a Zeiss petrographic 129

microscope for mineralogic and textural descriptions, and photomicrographs were taken with 130

a Leica petrographic microscope. Then, to obtain accurate mineral and textural percentages, 131

point counts were carried out with a PELCON Automatic Point Counter and associated 132

software. Point counts were taken at 1mm increments with 350 to 500 points counted on 133

each thin section. 134

Field and photographic interpretations were also taken into account for analysing unit 135

relationships and contacts. 136

137

4. Results 138

4.1 Thin section data 139

5

Apart from the more evolved valley lava flows, all sample thin sections exhibit typical 140

basaltic mineral assemblages, including plagioclase microphenocrysts, granular pyroxenes 141

and tiny magnetites within the groundmass, plus plagioclase, clinopyroxene, and olivine 142

phenocrysts (Winter, 2010). The thin sections from the valley lava flows (F12PB5, F12P6S) 143

both have heavily trachytic texture and few phenocrysts or vesicles (Figure 6, f.). 144

There are distinct textural and mineralogical differences between mafic enclave and 145

host intrusion material. The thin sections from the enclaves (PB1.114, PB1.214) exhibit 146

weakly trachytic texture in the groundmass, and they have a variety of unusual textures in 147

plagioclase phenocrysts. Such textures include reaction rims, evidence of resorbtion, and 148

small melt inclusions (Figure 6, a., b.). The enclave thin sections also contain several in-filled 149

vesicles or amygdules with radiating calcite crystals (Figure 6, c.). In contrast, thin sections 150

from the host intrusion and the intrusion at the northwest side of the bay (PB0214, F9PBTW) 151

have pilotaxitic texture and more pyroxene and olivine within the groundmass. Additionally, 152

the enclaves contain less feldspar (primarily plagioclase) and fewer vesicles than their host 153

material (Table 1.). Also, the majority of the enclave plagioclase phenocrysts have resorbed 154

rims and small melt inclusions, while few of the plagioclase phenocrysts within the host 155

intrusion show resorbed rims, but many exhibit oscillatory zoning that is not present in the 156

enclaves (Figure 6, d., e.). 157

Apparent textural and mineralogical differences exist between intrusion, scoria cone 158

and fissure samples. In general, the intrusion samples contain less volume percent 159

groundmass and more volume percent feldspar (dominantly plagioclase) than the scoria cone 160

samples (Tables 1 & 2). The samples of scoria from the fissure eruption on the northwest side 161

of the bay (12PB34, F9PBBM) are highly vesicular and contain large proportions of 162

phenocrysts. The scoria cone sample from the valley (F12PB6) has the largest proportion of 163

phenocrysts of all samples, especially in regard to plagioclase. 164

4.2 Geochemical data 165

All Pa Bay samples plot as picrite basalt, while valley lava flows (only plotted in 166

Figure 4 (i)) range between hawaiite and mugearite (Figure 7). All analysed samples have 167

low silica content (44-51 wt. %). 168

Overall chemical similarities exist between fissure, scoria cone, and intrusive deposits 169

(Figure 8). There are significant differences within the intrusion between the enclaves and the 170

host material; the enclaves are more mafic than their host material (higher wt. % MgO and 171

lower wt. % SiO2). Chemical differences also exist between welded and unwelded scoria 172

6

(F9PBLT, F9PBBM, 13PB34) and lava flow (F12PB2 & F12PB03) samples within the scoria 173

cone deposits (Figure 4). 174

See Table 3 for all major element geochemical data. 175

176

5. Discussion 177

Since the fissure, scoria cone and intrusion deposits are chemically similar, despite 178

being texturally diverse, it is likely that they came from a similar magma source. The 179

significantly more silicic and alkaline nature of the valley lava flows, as well as their heavily 180

trachytic textures, confirm a separate eruptive source, which was likely the main Akaroa vent. 181

On its way to the surface, the Pa Bay intrusive body accumulated a dynamic history. 182

The presence of texturally and chemically distinct mafic enclaves within parts of the intrusion 183

(Figure 3) and complicated textures present in plagioclase phenocrysts within various areas of 184

the intrusion suggest shallow mingling and mixing. Clynne (1999) documented mafic, 185

undercooled enclaves with reacted phenocrysts at Lassen Peak, California. These enclaves 186

were formed when hot, mafic magma was quenched upon injection into a more silicic magma 187

body (Clynne, 1999). The Pa Bay enclaves appear to be very similar and therefore suggest a 188

similar origin process. Enclaves at both locations have plagioclase phenocrysts with reaction 189

textures, mainly comprised of resorbed rims (Figure 3). All plagioclase phenocrists in the 190

Lassen andesitic inclusions have some degree of reaction that is from partial melting of 191

crystals that were introduced into a hotter liquid that required a more calcic equilibrium 192

plagioclase composition (Clynne, 1999). All plagioclase phenocrysts within the Pa Bay 193

enclaves also show similar degrees of reaction with resorbed rims and some embayments 194

(Figure 6, a.). Plagioclase textures provide the best evidence and constraints on shallow 195

magma mixing and can indicate multiple heating and cooling events, changes of pressure, etc. 196

(Cashman & Blundy, 2013; Viccaro et al. 2010; Clynne, 1999). 197

Oscillatory zoning has also been linked to complex magma mixing and movement and 198

is present within phenocrysts from other areas of the Pa Bay intrusive (Figure 6, e.). 199

Compositional zoning results from kinetic effects and/or changes in bulk chemistry or magma 200

chamber parameters (Vicarro et al., 2010). The magma chamber dynamics that cause the 201

zoning could be injections of hotter, more juvenile magmas into a cooling chamber (Winter, 202

2010), which was likely the case in the source chamber for the Pa Bay intrusive. 203

A magma chamber with extensive mixing and primitive injections would be an open 204

system that produces linear trends in geochemical Harker diagrams; curved trends correspond 205

to simple fractional crystallization (Cashman & Blundy, 2013). A case of strict, binary end-206

7

member mixing will produce perfectly linear X-Y trends, but this model is too simple to 207

explain most systems (Winter, 2010). Based on the available geochemistry data, there are 208

roughly linear trends within the intrusive (Figure 9) that could be a result of late stage mixing 209

and mingling within the shallow magma chamber. However, this study does not have quite 210

enough data points to accurately determine a definite geochemical trend within the intrusions, 211

but it can be assumed, given more samples and data, that there would indeed be a trend 212

indicating complicated magma mixing. After taking geochemistry into account, field and 213

phenocryst textures still provide the clearest constraints on Pa Bay magma dynamics. 214

Johnson (2012) presents curved trends for his and previous Akaroa geochemical 215

samples that represent large-scale magma evolution of Akaroa, which appears to be 216

dominated by simple fractional crystallization. The Pa Bay intrusive represents a small subset 217

of Akaroa’s plumbing on an outer flank where many complicated processes were occurring 218

on a comparatively small scale. 219

Many modes of evidence including the presence of enclaves in only one section of the 220

intrusive and the presence of distinctly aligned vesicles in another section (Figure 3) point to 221

complicated magma interactions and suggest multiple emplacement events. The contact on 222

the northwest side of Pa Bay includes several areas of chemically and texturally distinct 223

deposits (Figure 5) and has been interpreted to represent a series of several intrusive 224

injections into the welded fissure deposits. The variety of textures and chemical variations 225

within the intrusion also support the idea that it was not emplaced in a single event from a 226

single batch of magma. Awdankiewicz (2005) found a scoria cone in southwest Poland with a 227

volcanic plug that was formed over at least two or three magma emplacements that each 228

solidified separately in late episodes of volcanic activity after the central vent was inactive. 229

The Pa Bay intrusive appears to have a similar origin. Due to its vicinity to the inferred vent 230

in central Pa Bay and the lack of mixing or alteration at its contacts with scoria deposits, it is 231

most likely that the intrusive is a basaltic plug that in-filled the scoria cone’s conduit system 232

after it had ceased eruptive activity. Once the fissure eruption and central Pa Bay scoria cone 233

were no longer active, or possibly some time later, another few batches of magma were 234

remobilized and injected subvolcanically, cross-cutting the vent area and other deposits, 235

forming a plug that was later exposed with the eventual erosion along Akaroa’s coast. The 236

intrusion section with the mafic enclaves represents one pulse of injection from a mingled 237

magma, and the other intrusion sections, including the area with vesicle flow alignment and 238

the northwest contact, represent additional pulses of magma injection. 239

8

It is common for magma mixing to occur due to the replenishment of a magma 240

chamber by an injection of primitive parent magma from lower in the crust or mantle 241

(Winter, 2010). Such mixing and recharge processes can then trigger eruptions or sub 242

volcanic emplacement (Sparks et al., 1977; Murphey et al., 2000). In fact, several other 243

studies have cited primitive magma injection as the catalyst for mixing, the formation of 244

phenocryst textures, and the movement and emplacement of magma (Cashman & Blundy, 245

2003; Clynne, 1999; Vicarro et al., 2009). Then, following this model, the Pa Bay intrusive 246

may have been emplaced via several pulses of late-stage volcanic activity prompted by 247

multiple recharge events in the shallow magma chamber. Once magma was mobile, intrusion 248

emplacement would have been controlled by structural discontinuities within the greater 249

volcanic edifice. Specifically in Pa Bay, the intrusion filled the already existing scoria cone 250

conduit system, creating a volcanic plug. 251

252

6. Conclusions 253

Pa Bay is a much more complicated example of volcanic flank activity than 254

previously known. It not only contains evidence of a fissure eruption and formation of scoria 255

cones, but it also contains an intrusive plug that, upon careful analysis, reveals a complex 256

magma plumbing history. 257

It is proposed that fissure deposits and the central Pa Bay scoria cone were formed 258

during a basaltic parasitic eruption on Akaroa that produced explosive and effusive products, 259

transitioning from Hawaiian to Strombolian eruption style over time. Once volcanic activity 260

ceased, some magma remained stored at a shallow level. Subsequently, after an unknown 261

period of time, batches of hotter, more primitive degassed magma were injected into the 262

shallow chamber, prompting mingling and mixing and remobilizing the stagnant magma in 263

the process. This resulted in the emplacement of an intrusive plug through the scoria cone 264

conduit system via several pulses of magma. A later Akaroa main vent eruptive period then 265

produced the lava flows present up the valley from Pa Bay. 266

267

7. Further Work 268

The ability to analyse trace element data could unveil more subtle differences between 269

samples. Microprobe analysis on plagioclase phenocrysts would provide higher resolution 270

understanding of magma mixing and plumbing interactions. To gain a deeper understanding 271

of the relationships between scoria cone and intrusive deposits further geochemical and 272

9

textural analyses are needed of additional samples. Also, modelling of the intrusive is needed 273

to illustrate the mechanisms of Pa Bay’s plumbing system. 274

275

Acknowledgements 276

I would like to thank Sam Hampton and Darren Gravley for their guidance and 277

insights on this project. Much appreciation goes to Rob Spiers for preparing thin sections, 278

Stephen Brown for running the XRF samples, and Kerry Swanson for help with the 279

photographic microscope. Without the resources and opportunities from the Frontiers Abroad 280

program and the University of Canterbury, and without access to the land of Adam and 281

Crystal Thacher, this project would not have been possible. A special thank you goes out to 282

all the other FA students with whom I had the privilege of working and getting to know. 283

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FIGURES 374

375 Figure 1. 376 377

378 Figure 2. 379 380

13

381 Figure 3. 382 383 384

385 Figure 4. 386

14

387 Figure 5. 388

15

389 Figure 6. 390

16

391 Figure 7. 392

17

393 Figure 8. 394

18

395 Figure 9. 396

19

FIGURE CAPTIONS 397

398

Figure 1. Map of Pa Bay with sample sites and sample names designated by orange triangles. 399

The sites to the bottom left are the deposits up the valley (SW) from the main bay area. Inset 400

shows Pa Bay’s location on Banks Peninsula. 401

402

Figure 2. (A) crystal-rich intrusion, (B) proximal welded scoria deposits, (C) fall-dominated 403

medial scoria deposits, (D) conglomerate. The white dashed line estimates the vertical extent 404

of the scoria cone deposits that are then overlain by loess. Black dashed lines trace out 405

apparent dips in scoria deposits, indicating the likely centre vent location. 406

407

Figure 3. The extent of the intrusive based off of observed (yellow, solid lines) and inferred 408

(dashed lines) contacts with scoria cone deposits. The inset on the left highlights the mingling 409

zone within the intrusive with mafic enclaves outlined in red. The inset on the right 410

demonstrates the flow alignment of vesicles (traced by the dashed lines) within the intrusive 411

on the north side of Pa Bay. 412

413

Figure 4. Southern contact between the intrusion and proximal scoria cone deposits. Scoria 414

remains veneered on the surface of the intrusion where it has yet to erode away, as seen in 415

insets (i) and (ii). Some interfingering at the contact can be seen in inset (ii) as well as a clast 416

of scoria incorporated into the intrusive material. 417

418

Figure 5. Contact between the intrusive (left) and fissure deposits (right) on NW side of Pa 419

Bay. The inset shows a scoria clast within the fissure deposits. Dotted white lines outline the 420

contact and suggest multiple injections of intrusive through cracks in the area. 421

422

Figure 6. Examples of thin section textures. (a.) Plagioclase phenocryst in XPL from a mafic 423

enclave (sample PB1.114) with a resorbed rim, reaction rim and fine melt inclusions. (b.) 424

Clinopyroxene phenocryst in XPL from a mafic enclave (sample PB1.114) exhibiting 425

extensive resorbtion and some recrystallization. (c.) Amygdule in PPL from a mafic enclave 426

(sample PB1.214) that now contains secondary calcite. (d.) Plagioclase phenocryst in XPL 427

from the intrusion on the south side of the bay (sample PB0214) showing resorbtion, reaction 428

rim, and an embayment. (e.) Another Plagioclase phenocryst in XPL from the intrusion on 429

the south side of the bay (sample PB0214) with distinct oscillatory compositional zoning. (f.) 430

20

Trachytic texture in the thin section from sample F12PB5, a mugearite lava flow up the 431

valley. 432

433

Figure 7. Total alkali-silica diagram (based off of Cox-Bell-Pankhurst 1979) of geochemistry 434

for all Pa Bay samples including: fissure deposits (red dots), scoria cone deposits (green 435

triangle), intrusive deposits (blue squares), and lava flows from up the valley (magenta 436

diamonds). 437

438

Figure 8. Harker Diagrams of Major element data. Red dots indicate fissure deposits, blue 439

squares indicate intrusive deposits, and green triangles indicate scoria cone deposits. 440

441

Figure 9. Selected major element variation diagrams compared to wt. % SiO2. Black lines 442

represent the line of end member mixing between the host intrusion (PB0214) and the mafic 443

enclaves (PB0114). The lines are representative of only strict binary mixing. Blue squares 444

represent intrusive samples, red dots represent fissure samples, and green triangles represent 445

scoria cone samples. Labels within the diagrams correspond to sample numbers. 446

447 TABLES 448 449

Sample Description %Feldspar %Olivine %Clinopyroxene %Groundmass %Vesicles %Other PB1.114 “blobs” 1.7 6.9 5.7 82.9 2.3 0.6 PB1.214 “blobs” 2.9 9.8 5.9 74.6 6.8 0 PB0214 Host

intrusion 6.2 6.2 4.5 67.1 14.8 1.2

F9PBTW NW bay intrusion

12.4 16.1 4.3 64.1 2.9 0.2

Table 1. 450 451

Sample Description %Feldspar %Olivine %Clinopyroxene %Groundmass %Vesicles %Other F12PB2 NW bay

lava 2.4 8.8 0.6 85.6 2.6 0

F12PB3 NW bay lava

3.2 9.2 0.9 85.0 1.7 0

F12PB5 Valley lava 0.2 1.0 0.4 95.4 2.8 0.2 F12P6S Valley lava 1.6 0.2 0 97.6 0.6 0 F12PB6 Valley

scoria 17.4 9.0 1.6 67.4 3.4 1.2

12PB34 Bay scoria 1.0 3.9 3.2 49.9 41.8 0.2 F9PBBM Bay scoria 1.5 9.6 9.6 51.9 35.6 0.2

Table 2. 452 453 454

21

455 Table 3. 456 457 458 TABLE CAPTIONS 459

Table 1. Intrusion thin section volume percentages derived from point count data. 460

461

Table 2. Extrusive (including scoria cone and fissure deposits) thin section volume 462

percentages derived from point count data. 463

464

Table 3. Major geochemical data for samples taken from Pa Bay. 465