FERROMAGNESIAN MINERALS /ROM the VOLCANIC SUITE of TENERIFE a Thesis Submitted for the Degree of Doctor of Philosophy of The

FERROMAGNESIAN MINERALS /ROM THE

VOLCANIC SUITE OF TENERIFE

A thesis submitted for the degree of Doctor of Philosophy of the University of London by Peter Wright Scott

October 1970. Dept. of Geology, Imperial College, London, S.W.7. ABSTRACT The Tenerife rocks have been classified as ankaramites, alkali basalts, trachybasalts, trachyandesites, trachytes and phonolites on the basis of their chemical and petrographic characteristics. Wet chemical and microprobe analyses and some optical data for olivines, pyroxenes, micas, garnets and sphene are presented; and, cell parameters for olivines, pyroxenes, garnet and sphene are also given. Olivine is restricted in its occurrence to the more basic rocks and is always forsterite rich (approx. Fo 80), although it may become more fayalitic in the groundmasses. A salitic clinopyroxene is present throughout the suite but aegirine is developed in the groundmass of some phonolites and in a nepheline-syenite boulder. The salites show only limited enrichment in hedenbergite with magmatic differentiation whilst the aegirines are enriched in diopside relative to hedenbergite. This is thought to be due to the limited amounts 2+ of Fe present in the "parental" magmas after the removal of varying proportions of olivine and kaersutite. Seven types of zoning have been recognised in the salites: normal, reversed, irregular, large scale oscillatory, minute scale oscillatory, hourglass, and a special "zoning" caused by the presence of green cores. The origin of most types of zoning can be explained by changes in conditions during crystallisation, but it appears unlikely that hourglass crystals have formed as suggested by Strong (1969).

A kaersutite of uniform composition occurs in most rock types although it becomes barkevikitic in the salic differentiates. It is thought to have formed as a stable cumulus phase at depth in magmas of intermediate composition but to have become unstable on being brought to the surface. The presence of magnesioarfedsonite and aenigmatite in the groundmass of some phonolites indicates crystallisation under low oxygen fugacities. A titaniferous, relatively magnesium-rich, biotite, and melanite and sphene are found in the phonolites as minor phenocrystal phases.

3 -

CONTENTS Page No. Acknowledgements. 5 SECTION 1. INTRODUCTION

1. Situation and physiography of Tenerife. 6 2. Previous Geological work on Tenerife. 7 3. Stratigraphy of the volcanic series. 7 4. Geological relationship to the other Islands and Africa. 11 5. Extent of the present work. 11

SECTION 2.

CLASSIFICATION AND PETROGRAPHY OF THE TENERIFE ROCKS. 1. Basis of classification. 14 2. Comments on chemical analyses of the volcanic rocks. 16 3. Petrography of the rock types. 17

SECTION 3. MINERALOGY

1. Olivine. 43 2. Pyroxene. 49 Intrbduction. 49 A. Crystallography. 49 B. General characteristics of pyroxenes from the individual rock types. 50 C. Variation in optical properties. 56 D. Chemical and Microprobe analyses. 57 E. X-Ray Diffraction Studies. 68 F. Zoning in the pyroxenes. 71 3. Amphibole. 93 A. Kaersutite. 93 B. Alkali amphiboles. 98 - 4 -

Page No. 4. Biotite. 101 5. Garnet. 104 6. Sphene. 107

SECTIOi•I

CONCLUSIONS. 172

Appendix 1.

Analytical and X--Ray techniques: 177

Appendix 2. Specimen localties. 182

Bibliography. 187

Enclosure. Simplified geological map of Tenerife..

Figures and tables are located at the end of each Section. 5

Acknowledgements.

I wish to thank Dr. G.D. Barley for the constant help, encouragement and supervision throughout the period of research, and P. 13uddaby and M.T. Frost for help and advice with microprobe, x-ray and computing techniques. Thanks are due to many post-graduate students and members of staff at Imperial College for helpful discussion and advice with experimental techniques, especially Dr. J. Nolan who allowed me to compare the pyroxene x-ray diffraction traces with those from his synthetic pyroxenes, and Dr. W.I. Ridley, who provided some separated pyroxene fractions and allowed access to his thin sections of rocks from the Las Canadas area. I am grateful to Mrs S. Bird for typing the thesis. My wife traced most of the diagrams, helped with the preparation of the photomicrographs and checked the final manuscript but, above all, she is to be thanked for encouragement and patience during the experimental and latter stages of preparation of the thesis. Receipt of an N.E.R.C. Research Studentship is acknowledged. -6--

SECTION 1

•INTRODUCTION

1. ------Situation and physiography of Tenerife The Canary Islands comprise seven major, and a few smaller islands situated off the west coast of Africa (fig. 1.). Tenerife is the largest of these islands, with an area of 2058 sq.Kms., and a maximum height above sea level of 3718 metres (Pico Teide).

In shape, Tenerife is roughly triangular, but is elongated in the north--east into the Anaga peninsula (fig. 2). This peninsula, and the north-western part of the island, the Teno peninsula, are formed of deeply dissected volcanic mountains, and, where they meet the sea, frequently form cliffs a few hundreds of metres high.

To the west of Anaga lies the plain of La Laguna, which further towards the west, rises to form the ridge of Cumbre de Pedro Gil. The sides of this ridge initially fall sharply, and then more gently to the sea forming the Oratava and Guimar valleys.

In the centre of the island is a wide semi-circular depression (2000 - 2500 metres above sea level) known as Las Canadas, which is bounded by a steep wall (Portillo and Tauce escarpmets) to the east, south and south-west. People have been known to compare this rugged desert area with the surface of the Moon. Rising out of Las Canadas to the north is the huge twin-peaked volcano of Pico Teide and Pico Viejo. To the north of this volcano the land falls fairly steeply to the sea, and to the west, this central part of the island is joined to the Teno peninsula by the Valle de Santiago. The top of the wall bounding Las Canadas falls uniformly to the sea at the south.

Water is scarce on the island but has great erosive power, cutting deep valleys, called "Barrancos", through the rock formations: -7

2. Previous Geological work on Tenerife.

There is an abundance of geological literature concerning Tenerife dating back to the early 18th Century. The majority is in 1,7nguages other than English. Much of the early literature deals with field relations of the volcanic formations, with obvious emphasis on the impresive Pico Teide and Las Canadas, sometimes followed by short petrographic descriptions of the rock-types. 11 considerable variation is found in rock nomenclature. Occasionally chemical analyses of rocks are presented, but only rarely have the minerals, in particular ferromagnesian minerals, been studied in any detail. Very little data is given concerning the properties of the minerals. Kunitz (1936) states analyses of two pyroxenes from Tenerife and these appear to be the first modern analyses of any mineral from the island.

Petrogra-chic descriptions, together with rock analyses, and some optical data on the minerals, are given by Jeremine (1933), Smulikowski (1937), and Smulikowski et al.(1946). Hausen (1956) gives a detailed review of literature concerning the geology of Tenerife, and quotes roc1,- analyses and optical properties of minerals from earlier sources, along with new data. The reader is referred to Hausen (1956) for a review of knowledge to that date.

Recent work, with the exception of Bravo (1955) and Ridley (1970) adds little to the knowledge of the mineralogy. A general account and most recent map of the geology is contained in Fuster et al. (1968). Ridley (1968) is concerned with the Las Canadas area. Geophysical data is contained in Macfarlane and Ridley (1968) and Bosshard (1969) and some ages of the rocks are given by Abdel-Monem et al. (1968). Plutonic nodules, found within the volcanic rocks, ore described by Borley et al. (1969).

3. Strati.gFaDhy- of the volcanic series. With the exception of a few recent sedimentary deposits, the rocks are entirely of volcanic origin. _8_

A brief stratigraphical description of the volcanic formations, from oldest to youngest is given below. It is based on divisions made by Fuster et al. (1968), Hausen (1956), and Ridley (1968) (Las Canadas area), and is augmented by the authorb own knowledge. Petrographical, mineralogical and geochemical characteristics described later are related to the formations as described here.

Ancient Series: These are the oldest rocks exposed on the island and are found on the Anaga and Teno peninsulas. The rocks comprising Ladera de Guimar, and a few isolated areas to the south are also grouped within this series. The latter areas either stand out as "Islands" (e.g. Roque del Conde) or are exposed by erosion in the floors of barrancos (e.g. Barranco del Rio). This series corresponds to an early shield building stage with abundant eruptions from a fissure complex traversing Tenerife, and embracing the island of Gomera as well. Abdel- Monem et al. (1968) date the lavas from 1-2 million years (Ladora'de Guimar) to 16 million years (northern side of Anaga). If these dates are correct, then the very similar rocks comprising this series. cover a time-span considerably greater than all tlie otlier formations together. Flows are mainly basaltic or ankaramitic, with subordinate pyroclasts, and they are cut by a network of mainly basic dykes.

Phonolitic intrusions into the Ancient 5eries:

Also intruded into the Ancient ,Series are some thick phonolitic dykes, sheets, and plugs. Hausen (1956) calls these "Phonolitic and trachytic differentiates of the same series, but they are distinct, in their occurrence, from any other formation. Fuster et al. (1968) considers these are feeding the more alkaline Canadas rocks which have since been eroded. Xenoliths are common in these intrusions.

Canadas Series:

After the shield building stage, activity became more localised towards the centre of the island, and the broad - 9

"Canadas volcano'' was built up. Ridley (1968, 1970) names this formation the "Vilaflor Complex". Outcrop of this series is restricted mainly to the southern Portillo and Tauce escarpments of Las Canadas, and the Tigaiga block; although Fuster et al. (1966) gives the older more basic lavas of this formation a much wider areal extent.

In the lower part of the series (Lower Canadas series) eruptions were mainly of basalt, trachybasalt, and mafic phonolite flows, interbedded with pyroclastics. It is difficult to distinguish the basaltic flows from those of the Ancient series.

The Upper Canadas Series is formed mainly of thick viscous phonolite flows with interbedded pyroclastics. The pyroclastics are mainly ignimbrites and eutaxites with some lapilli. The phonolitic intrusions of the Tauce escarpment and Roque de Garcia are thought to correspond to the outpouring of the phonolite lavas during this period (Ridley 1968).

Trachyte and Trachybasalt series:

This series is acsely related to, but late than, the Canadas Series, and the volcanic material is less alkaline. The emission centres are more dispersed, and the lavas lie unconformably on older material. Montana Gueza and other similar local centres are included in this group. The whole series covers a small areal extent. Lavas produced are trachytic or trachybasaltic, and there are pyroclastics near the emission centres.

Series 3 Basalts:

This basaltic formation, probably of a similar age to that of the Trachyte and Trachybasalt Series, covers a considerable areal extent. Very similar basaltic lavas emanated from many centres which are now represented by well preserved craters surrounded by lapilli and scoriae. Flows are generally thin, and the rock is fresh. - 10 -

Recent Salic Series:

1.1efore eruption produced this series collapse of the Canadas volcano took place. This produced the Portillo and Tauce escarpments. In the centre of the collapsed area the volcanoes of Teide and Viejo were then built up. This central volcanic activity produced as and pahoehoe lavas, which flowed until they reached the escarpments to the south and south-east (some were so viscous that they never reached the escarpments), or to the sea in the north. To the west, lavas flowed into the Valle de Santiago. Major activity took place from Teide and Viejo initially but was later accompanied by extensive flank activity (Ridley 1968). Flows range from trachybasalts to phonolites. Frequently they are partly or completely glassy. Pyroclastic material is mainly lapilli.

Recent Basic Series:

This series includes the historic and pre-historic emissions that have occurred at scattered points on the island. The basaltic lavas quite frequently flowed great distances from the centres. Varying amounts of pyroclastic material surround the centres.

Pumice deposits:

A considerable volume of pumice deposits are found in the southern part of Tenerife. It is difficult to relate these to any one series (they were probebly formed at varying times in the island's history), and they are thus grouped together here. The pumice fragments arc always trachytic or Phonolitic in character (Fuster et al. 1968).

Plutonic roc77s:

No major plutonic structures are found on Tenerife, but evidence, in the form of boulders and xenoliths, is present, which suLgesto that there may be plutonic rocks at depth. Von Fristch and Reiss (1868) describe an olivine dolerite and Gastesi (1967) describes gabbroic fragments found in underground workings. Nopheline syenite boulders have been found and mentioned by Jeremine (1933). These have also been described by Ibarrola and Viramonte (1967).

The present author has collected several xenoliths found within dykes and lavas ranging up to 15 cm. in diameter. These are ultrabasic, gabbroic or syenitic in composition and are described by Lorley et al. (1969).

4. Geological relationship to the other islands and Africa.

The other Canary islands all show similar volcanic formations to Tenerife, but each has its own minor variations. Volcanism again belongs to the alkaline olivine basalt - trachyte phonolite association. Ultrabasic and basic plutonic rocks arc found in the oldest formations of Gomera, La Palma, and Fuerteventura, and it is possible that the Canary Islands may have a common plutonic basement (Fuster et al. 1968a). Abdel-Nonem et al. (1967 and 1968) give ages which suggest that the islands become younger from east to west. Bosshard .(1969) st.7,tes that the crust in the western islands (Tenerife, Gomern, La Palma, and Hierro) is essentially oceanic and Gran Canaria is in the transitional zone between oceanic and continental. Lanzarote and Fuertevuntura are assumed. to be continental.

Two theories are possible concerning the origin of the Canary Islands. The first is that the islands originated on the Hid-Atlantic ridge and subsequently drifted into their present position: and the second, is that they are related to the forwation of the Atlas mountains in N.w. Africa. Bosshard (1969), from geophysical measurements, prefers the latter theory, and concludes that the islands formed along N.B. - „.1.T. faults as a probable result of shear and compres- sional forces during the Miocene in N.W. Africa.

5. Extent of the present work.

This thesis presents the results of a study of the ferromagnesinn minerals which, in part, make up the.volcnnic rocks of Tenerife. Samples collected by the author, during a six week stay on the island,and colleagues have been utilised. -12 -

The rocs, regardless of strrtigraphical position, are divided into types based on petrography and chemistry. The petrography of each of these is described in Section 2.

The ferromagnesian minerals studied are olivines, pyroxenes, amphiboles, micas and garnets. Special emphasis has been placed on the variation in chemistry of the pyroxenes and their zoning, using optical, chemical, microprobe and x-ray diffraction techniques. A minor study has also been made of sphene (titanite) although it is not a ferromagnesian mineral. All the mineralogical data and some discussion of the results, as applicable to the individual minerals are given in Section 3. General discussion and conclusions concerning the magmatic history of the Tenerife rocks are to be found in Section 4. Analytical techniques are described in Appendix 1. A simplified geological map based on that of Fuster et al. (1968) and Hausen (1956) can be found enclosed inside the back cover, and specimen localities of samples referred to in the text are given on the map and in Appendix 2. Fig 1

CANARY ISLANDS

O 0 o -0- LA PALMA Ef:sAte3I LANZAROTE D TE FUERTEVENTURA

GRAN CANARIA SPANISH SAHARA

HIERRO

Fig 2

TENERIFE

TN - 14

6ECTION 2

CLAIFICATIOK AND PETROGRAPHY OF THE TEI1ERIFE ROCKS

1. Basis of Classification

The nomenclature used here is simple and is based on that used by Le Iaitre (1962), Baker et al. (1964), and Baker (1969) for several other Atlantic islands, viz: alkali basalt - trachybasalt - trachyandesite - trachyte - phonolite. With the addition of an ankaamite term, to cover the cumulate basalts, all the rocks can be placed into one of these divisions using limits set by the Differentiation Index of Thornton and Tuttle (1960) (D.I. = sum of normative quartz + orthoclase + albite + nepheline + leucite + kalsilite), as follows: ankaramite < 20, alkali basalt 20-40, trachybasalt 40-65, trachyandesite 65-75, phonolite and trachyte > 75. The few petrographic breaks which are present in the series occur at the limits between two rock types. Broader variations in petrography occur throughout the suite. Unanalysed rocks were classified on the basis of these variations and breaks.

One disadvantage of this nomenclature is that it has been applied to almost saturated rocks (Gough Island. Le Maitre 1962), mildly undersaturated rocks (5t. Helena. Baker, 1969), and very undersaturated rocks (Tristan da Cuhna. Baker et al. 1964) Thus, while using this nomenclature, it is necessary to observe that chemically the Tenerife rocks are very undersaturated, having a comparable degree of undersaturation to rocks from Tristan da Cuhna.

The terms alkali basalt and trachybasalt are preferred to those of basanite and trachybasanite used by Ridley (1970), as the latter terms imply modal nepheline, which is absent. Alkali basalt is used as a general name in the sense of Yoder and Tilley (1962) to indicate a rock containing normative olivine and nepheline.

The term trachyandesite has been used before to describe alkalic rocks of intermediate composition, and despite criticisms - 15 -

of the name by Johannson (1938) arid Tilley and Muir (1964)i it continues to be used; Ridley (1970) calls such rocks plagioclase phonolites, as many; though not all, rocks of this composition from Las Canadas and elsewhere contain large plagioclase phenocrysts: All of these rocks can be described as trachyanesites and use of this name in a simple classification therefore seems justified. The name is unsatisfactory in that it has been applied to rocks which are both undersaturated to varying degrees, or saturated: Thus, while using the term here it should be remembered that the Tenerife trachyandesites are very undersaturated (Table 1).

Only lavas from Montana Guaza and a few lavas and dykes from the Ancient Series have been placed in the trachyte division. They have been called trachytes on account of their marked trachytic texture and lack of ferromagnesian minerals compared with the crystalline phonolites. The lavas from Montana Cuaza have been referred to as trachytes by previous workers (hausen, 1956. Fuster et al., 1968), and Fuster et al. (1968) also give details of other trachytes from the Trachyte and Trachybasalt Series. Chemically the trachytes are rather oxidised but they appear to be more phonolitic (table 1. No 12) in composition than the more usual saturated trachytes.

A summary of characteristics of each rock type, including the variations and breaks in petrography is given below: Ankaramite - Abundant large phenocrysts of olivine and pyroxene. Little feldspar. Alkali basalt - pyroxene, olivine and more rarely plagioclase and opaque phenocrysts. Groundmass contains the same minerals. Trachybasalt - Dominantly plagioclase phenocrysts with some pyroxene and olivine. Groundmass: plagioclase opaques, pyroxene, minor olivine. Trachyandcsite - Plagioclase and/or anorthoclase phenocrysts with more pyroxene and olivine. Groundmass: plagioclase, opaques, pyroxene. Nn olivine. - 16 -

Trachyte Variable grain size. Very abundant alkali feldspar. Some pyroxene and opaques. Phonolite Porphyritic varieties have anorthoclase, pyroxene, sphene and feldspathoid phenocrysts. Groundmass: alkali feldspar, alkali pyroxene, alkali amphibole, aenigmatite. Some partially or completely glassy.

2. Comments on chemical analyses of the volcanic rocks.

Chemical analyses of many of the rocks examined have been made by Drs. F.J. Abbott and C.D. Borley (Unpublished data), and these rocks, together with some analysed by Ridley (1970), have been classified using the nomenclature given above; 15 averaged analyses with their C.I.P.W. norms are given in table 1. Lnalysis No. 17 in this table is the average for nepheline syenite boulders from Tenerife given by Ibarrola and Viramonte (1967), and analysis No. 12 is from Fuster et al. (1968).

All the basaltic rocks are extremely undersaturated, • containing up to 15;' normative nepheline, and they all plot well wit',in the field of alkalic basalts on the alkali-silica diagram of Macdonald and Katsura (1964) for Hawaii (fig. 3). Only the ankaramites plot near the boundary between the tholeiitic and alhalic fields, probably due to the high proportion of pyroxene and olivine in these rocks. The undersaturated nature of the rocks continues throughout the series. Occasional analyses that give normative quartz have been discarded, as re-examination of thin and polished sections showed considerable oxidation of the rocks (G.D. Borley 1968. Personal communication). The phonolites approach the ternary phonolitic minimum in the system quartz - nepheline kalsilite. (Ridley 1970)

I.Tany phonolites, from the Recent Salic Series and some from the Canadas Series, are mildly peralkalinc, but the agpaicity index never exceeds 1.2 (Ridley 1970). The average index for phonolites of the Recent Salic Series is 1.09 and - 17 -

acmite and sodium metasilicate are present in the norm. The rocks are alw:s.ys partly glassy, and appropriate modal minerals, such as alkali pyroxene and alkali amphiboles or aenigmatite, are absent. In phonolites from the Canadas Series, however, alkali nyroxenes and amphiboles, and aenigmatite can be identified in some specimens, although the averaged analyses (Nos. 13 and 16) are not peralkaline.

.L11 the analyses have been plotted on a graph of the Thornton-Tuttle Differentiation Index against Si02 percentage (fig. 4), which shows their generally gradational character and the snarseness of points in the region DI 56-66. This gap" could be due to a sampling bias or a lack of abundance of rocks of this composition. These two factors would have to be eliminated, before it could be concluded that, differentiation did not produce a continuous series or, production of rocks of this composition was inhibited.

Ridley (1970) divides the rocks from Las Canadas according to their position on the DI- Si02 graph. These divisions, slightly modified, correspond broadly to the rock types from the whole island and they are marked in fig. 4. One of the main features shown by the analyses is the strongly alkalic, in particular sodic, nature of the phonolites (figs. and The traces on the F N - A 5 6). and Ca0 - Na20 - K20 ternary diagrams are identical to those from Las Canadas (Ridley 1970), but are extended at the basic end to accommodate the ankarariites, which are absent in Las Canadas.

Analyses and trends given by Hausen (1956), Fuster et al. (1968), and Ibarrola (1970) for Tenerife rocks compare with those given here.

3. Petroagraphy of the rock types.

The description of major rock types is followed by an account of a nepheline syenite boulder, and a brief description of the xenoliths. -3.8-

Ankara mites

The ankaramites contain abundant phenocrysts of clinopyroxene and olivine, up to 1 cm. across, in varying relative proportions (figs. 7 and 8). Occasionally smaller phenocrysts of euhedral titanomagnetitc are also present. The matrix is either fine-grained and equigranular, or coarser grained with a considerable variation in grain size: parts are almost glassy. In the latter type of groundmass well developed laths of labradorite are formed. Minerals constituting the groundmass, in varying proportions, are: olivine, clinopyroxene, plagioclase and opaques.

Olivine phenocrysts are forsteritic, and they are sometimes fragments of much larger crystals. These were presumably broken during movement of the crystal or the lava containing the crystal. Occasionally the sharp edges of the crystals are rounded. In many specimens groundmass and phenocrystal olivines are partly or completely altered to a green serpentine or red- brown iddingsite, the latter being by far the more common alteration product.

The pale purple clinopyroxene phenocrysts are always zoned, and, like the olivines are sometimes fragments of much larger crystals (fig. 9): the pattern of zoning in the fragments being cut off sharply. Rounded crystals and ragged edged crystals, containing abundant opaque inclusions around the borders, are common. Other larger inclusions of groundmass material, opaques, and olivine are frequent. (A more detailed description of the ferromagnesian minerals from all rock-types is given in Section 3).

True ankaramites are only found in the Ancient Series and Lower Canadas :Jeries. Also in these series semi-cumulate rocks, intermediate between the ankaramites and alkali basalts, ere found.

Alkali Easalts.

The alkali basalts show fairly constant mineralogical and textural features. Grainsize and the proportion of - 19 -

phenocrysto are the only significantly varying components. There are few differences between the basalts of the various formations.

Typically, the alkali basalts contain phenocrysts of subhedral to euhedral forsteritic olivine, pale purple to buff subhedral clinopyroxene and, occasionally, laths of plagioclase, subhedral to anhedral opaques, and kaersutite (fig. 10). The proportion of phenocrysts varies considerably, from semi- cumulate varieties, which grade into the ankaramites, to aphyric alkali basalts. The phenocrysts grainsize varies from several millimetres in diameter down to microphenocrysts. Completely aphyric alkali basalts are rare. Alkali basalts rich in plagioclase phenocrysts grade into the trachybasalts.

The olivine and pyroxene phenocrysts display similar features to those in the ankaramites, except that crystal fragments are considerably less common. The pyroxenes show a greater variety of zoning, hourglass zoning becoming common in some specimens (fig. 11). Occasionally the pyroxene crystals contain green cores (fig. 12). Pyroxene phenocrysts in less porphyritic varieties often group in clusters. In rocks from the Ancient Series the olivines are partly or completely altered to iddingsite, but in the younger rocks the olivines are fresh. Extinction angle measurements on plagioclase phenocrysts show that they arc zoned from An 60-65 in the centre to An 40-50 at the outer marGins. The kaersutite crystals almost always have a surrounding rim composed of opaques and optically orientated pyroxene crystals. The width of the rim varies and, in sonic cascs, a mass of opaques and pyroxene completely pseudomorph the amphibole. The pyroxenes, on occasions, completely enclose the opaques forming a single subhedral to euhedral crystal, with a mass of opaques in the centre (fig. 12 and 13). Pocks in which the kaersutite crystals or their pseudomorphs are found also tend to contain pyroxene phenocrysts with green cores. This correlation has also been found in rocks from Gran Canaria (T. Frisch 1969. Personal communication). -20 -

The groundmass minerals are plagioclase, pale purple pyroxene, olivine and opaques. Plagioclase and opaques are often in excess over the pyroxene and olivine. Occasional interstitial glass is sometimes present. Apatite has been identified as an accessory in many specimens.

Al3zali basalts from the Ancient Series and Canadas Series usually contain a higher proportion of phenocrysts than those from the younger formations. Aphyric varieties, which are slightly coarser grained than the groundmass of many lavas, frequently occur as dykes in the Ancient Series and Canadas Series.

Lavas from the Series 3 and Recent Basic Series are frequently more vesicular than the older alkali basalts. The younger rocks also tend to contain a higher proportion of feldspar and opaques in their groundmasses at the expense of the olivines and pyroxenes. A number of Series 3 basalts contain phenocrysts composed almost entirely of olivine and feldspar with little pyroxene.

Trachybasalts.

With an increase in phenocrystal and groundmass plagioclase, the alkali basalts grade into the trachybasalts. This is accompanied by a decrease in the modal content of olivine and, to a lesser extent, pyroxene. Several rocks from the Ancient Series and Lower Canadas Series, which contain almost equal amounts of olivine, pyroxene and plagioclase phenocrysts are intermediate between the alkali basalts and. trachybasalts.

Both aphyric and porphyritic trachybasalts can be recognised: the proportion of phenocrysts varying considerably. Very porphyritic varieties contain large (up to 1 cm,in length) plagioclase laths, often having a glomerophyric texture, with subordinate euhedral forsteritic olivine, subhedral pale purple pyroxene, and subhedral opaque phenocrysts (fig. 14 and 15). The plagioclase sometimes shows a rim of groundmass inclusions near the edges of the crystal. Extinction angle measurements show that the plagioclase is zoned from labradorite to andesine. - 21 -

The olivine is often altered to iddingsite, and the pyroxene is frequently zoned and sometimes contains inclusions of apatite.

Less porphyritic varieties contain only occasional small phenocrysts or microphenocrysts of plagioclase, pale purple zoned pyroxene, and opaques. The finer grained parts of all trachybasalts are composed dominantly of poorly twinned plagioclase and opaque minerals, with pyroxene and, more rarely, olivine (usually altered). The plagioclase laths tend to be larger than the other minerals, and the lack of good twinning suggests that they are more sodic than the corresponding phenocrysts. Occasionally the groundmass of porphyritic varieties is felted or glassy. Feldspar and opaque microlites can be identified in the glass. Apatite is an accessory.

Phenocrysts of pale blue hauyne are present in MA 29. The rock has a D.I. of 62.3 and appears to be intermediate between the trachybasalts and trachyandesites.

Occasional crystals of partly resorbed kaersutite, similar to those in the alkali basalts, occur. Kaersutite is especially abundant in MA 29.

Both phenocrystal and groundmoss feldspar is commonly flow orientated and often the rocks are very vesicular. Porphyritic trachybasalts appear to be restricted to the Canadas Series, Trachyte and Trachybasalt Series, and Recent Series. Aphyric varieties are frequently from the Series 3 Basalts. Fustcr et al. (1968) describes trachybasalts containing phenocrysts of anorthoclase. Chemically, these rocks are much more alkalic than the trachybasalts described here. Petrographi- cally they are trachyandesites.

Trachyandesites

The trachyandesites can be broadly divided into three types - those containing plagioclase phenocrysts; those with fewer phenocrysts, but of both plagioclase and anorthoclase; and aphyric varieties. Gradations between the types are found.

The first types are the plagioclase phonolites of Ridley (1970). -22 -

These occur as a number of flows from Viejo (Recent Salic Series), and occasionally in the Canadas Series (Portillo escarpment). Phenocrysts up to 5 mm. long, of zoned plagioclase (andesine-olgoclase), occasionally glomerophyric, are present. An outer rim of more allelic feldspar is sometimes formed. Other phenocrysts, usually smaller than the plagioclase, are pale purple to buff or pale green subhedral pyroxene, subhedral opaques, and kaersutite. Only rarely does the kaersutite appear to be stable in its final environment. The pyroxene crystals sometimes form in clusters (fig. 16).

The groundmass when coarse-grained, is composed mainly of flow orientated alkali feldspar and opaques, with a colourless or pale green pyroxene. Rare feldspathoids are found. Frequently the groundmass is rather glassy. Specimen TC 125 R contains small crystals of a pleochroic amphibole (elongate sections have a pale yellow and y medium brown.).

The less porphyritic trachyandesites contain phenocrysts of anorthoclase as well as plagioclase set in a matrix similar to that described above (fig. 17). In several specimens only occasional euhedral anorthoclase, euhedral pyroxene, and small subhedral opaque. phenocrysts are present.

Aphyric varieties have a more pronounced trachytic texture with an identical mineralogy to the other trachyandesites (fig. 18). They show gradational properties with the trachytes.

Trachytes

The only specimens examined that have been classed as trachytes are lavas from Montana Guaza (Trachyte and Trachy- basalt Series), and some small intrusions and flows within the Ancient Series. The trachyte from Montana Guaza is crammed with phenocrysts of anhedral alkali feldspar (2Va 45-50. Anorthoclase) up to 2 mm. long, but grade in size down to groundmass dimensions. The very fine groundmass, which is in part felted, contains abundant crystallites of feldspar. Well developed crystals of opaques, green pyroxene, and also a slightly pleochroic yellow -23-

mineral (extremes of pleochroism are: a pale orange yellow, y pale yellow) with moderate birefringence, can also be identified (fig. 19). The latter may be an alkali amphibole or astrophyllite. The feldspars are flow orientated.

Trachytes from the .ncient dories pre made up largely of interlocking alkali feldspar of very variable grain size, with a flow texture (fig. 20). Occasionally, some subhedral anorthoclase, pale green pyroxene, kaorsutite, opaques, sphene, or sodalite group minerals, stand out as phenocrysts. The finer grained parts of the roc?:. also contain a pale green pyroxene and opaques.

Phonolites.

The phonolites can be divided on the basis of petrography into three well defined types, each corresponding to a specific volcanic series. These are: a) Phonolite intrusions in the Ancient Series. b) Phonolite lavas and intrusions from the Canadas Series. c) Phonolites and glassy phonolites from the Recent Salic Series.

Chemical properties are similar, except that many phonolites from the Canadas Series and Recent Salic Series are peralkaline, whereas the intrusive phonolites from the Ancient Series are not. a). Phonolite intrusions in the Ancient Series.

Specimens of this type from Anagc contain large, up to 1 cm. ecross, anhedral phenocrysts of anorthoclase, along with smaller phenocrysts of pleochroic, zoned, subhedral pale purple or green pyroxene euhedral sphene, anhedral opaques and zoned kaersutite, sometimes partly resorbed (Pleochroism: a pale yellowish brown, p medium brown, y dark greenish brown) (fig. 21). There are also patches within the rock composed of a very pale brown isotropic mineral, occasionally with a sub- hexagcnal outline. This is probably altered analcite. Pyroxene and kaersutite frequently contain inclusions of apatite.

r:Tecimens PS9, Pb10, and Pal, all from a thick dyke, contain euhedral sodclite, and rounded crystals of a pale yellow - 24 -

brown andradite, which is surrounded by a rim composed mainly of opaque minerals (fig. 22).

Groundmass of these rocks are frequently very fine and sometimes partly glassy. They always contain, howeter;a very high proportion of feldspar.

PS 107 from Poque Higara (South Tenerife) contains only a few rounded phenocrysts of anorthoclase, almost completely resorbed phenocrysts of kaersutite, and occasional sphene and opaques. The groundmass consists of green pyroxene and aenigmatite, set within an interlocking mass of feldspars. b). Phonolite lavas and intrusions from the Canadas Series.

These are the only rocks, apart from the nepheline syenite boulders, to show in their mineralogy, the strongly undersaturatcd nature of the alkaline rocks.

Phenocrysts, when present, are most frequently of anorthoclase or pale green pyroxene. Other occasional phenocrysts arc: partially resorbed kaersutite, red-brown biotite, sphene, altered analcite (?), and minerals of the sodalite group (fig. 23). nicrophenocrysts of nepheline are abundant in some varieties (fig. 24).

In the very fine-grained groundmasses only a felted mass of feldspar and opaques can be recognised, and in some coarser grained varieties a mass of feldspar with trachytic texture, finer grained opaques and pyroxene, are found. However, other coarser grained varieties contain a bright green acmite-rich clinopyroxenc, pale pinkish or yellowish brown alkali amphibole, and aenigmatite, set within a mass of feldspar and opaques. The pyre:cone, amphibole and aenigmatite are quite often clustered around the uepholine microphenocrysts (fig. 24). The feldspars are flow orientated.

ps 36 and ML 36 contain abundant small pale yellow crystals, within the groundmass, of an unidentified mineral. The crystals are slightly pleochroic (a. colourless-very pale pink, y pale golden yellow), with a fairly high birefringence. The extinction angle varies but in elongate sections it tends - 25 -

to be low or almost parallel. c). Phonolites and glassy phonolites from the Recent Salic Series.

Most of these lavas are partially or completely glassy. The few completely crystalline varieties contain a groundmass of felted or semi-trachytic feldspar crystals (figs. 25 and 26).

Phenocrysts found within the glassy phonolites (Hyalo- phonolites of Ridley 1970) are mostly of anorthoclase and are occasionally abundant. Other, more rare, phenocrysts arc a pale buff to pale green euhedral pyroxene, a deep brown pleochroic biotite, and brown pleochroic kaersutite, which sometimes has a reaction rim of opaques. The glass varies in colour from very pale green, through colourless, to brown, and always contains crystallites of feldspar.

Some lavas are very vesicular whereas others are dense. The direction of flow can he seen, in the orientation of the anorthoclase phenocrysts., the bands of different coloured glass, and the orientated feldspar microliter.

Nepheline Syenitc.

One large nepheline syenite boulder (approx. 1 cu.metre) has been found on the Portillo escarpment. The rock appeared to be weathered and was rather porous. However all the minerals in the thin section are fresh.

Interlocking laths of anorthoclase and anhedral tabular nephelinc male up the bull- of the roe-- Clusters of green pleochroic (G. bright green, B. yellowish green, y pale yellow brown) aciaite-rich pyroxene, either as subhedral to anhedral crystals or as radiating fibres, are frequent, along with occasional subhedral pale brown amphibole, dark brown biotite, and sphenc (fig. 27). The amphibole and pyroxene sometimes form interlocking crystals. Occasional anhedral crystals of opaques ere found. Jercmine (1933) describes lavenite from a nephelinc syenite from Tenerife, but this mineral has not been identified in the present sample. - 26 -

Ibarrola and Viramonte (1967) describe and have analysed several specimens of nepheline syenite from Tenerife (table 1 No 17). Their descriptions are similar to the one given here, except that they record the presence of analcite in some specimens. They state that the amphibole is eckermannite.

Xenoliths.

The xenoliths can be divided into five types. Three of these namely dunite, pyroxenite and pyroxene-kaersutite rock are ultramafic in composition. Others are gabbros and syenites. In some alkali basalts from the Ancient Series and Lower Canadas patches of ankaramite can be found which grade into the normal alkali basalt. These are not regarded as xenoliths but as inhomogeneities within the rock. These patches do, however, illustrate the connection and gradational properties between the alkali basalts and ankaramites. They also act as an intermediate in containing segregations of crystals, along with the ankaramite flows and dykes, between the alkali basalts and dunitc or pyroxenite xenoliths. A much more detailed description of the xenoliths than that given below can be found in Dorley et al. (1969 and 1970. In preparation).

Dunite: These xenoliths are made up entirely of interlocking forsteritic olivine with occasional crystals of opaque oxides. The olivine shows typical stress features such as undulose extinction and translation lamellae. Alteration of olivine in the thin sections examined was only slight, but in the field many xenoliths appeared completely iddingsitised.

Pyroxenite: Pyroxenite xenoliths contain mainly pale purple interlocking clinopyroxene crystals along with, usually interstitial opaque oxides, and occasional olivine. The pyroxenes tend to enclose the olivine. One variety contains abundant apatite crystals of the same dimensions as the pyroxenes (ic 1-2 mm). The pyroxene crystals are often zoned and in several specimens the pyroxene has exaolved fine needles of an opaque mineral. -27 -

Pyroxene-kaersutite rock: Interlocking and, on occasions, intergrown pyroxene and kaersutite makeup the bulk of these xenoliths. Other minerals present are sphene, opaque oxides and interstitial feldspar. Small apatite crystals are found as inclusions in all of the minerals except feldspar. The pyroxenes are either a very pale purple to buff or green, and some crystals show complex zoning with both a buff and green colour in the same crystal. The kaersutite is brown, showing pleochroism from a pale yellow brown to dark brown and is zoned. i;oth pyroxene and kaersutite on occasions contain fine exsolution needles of an opaque phase.

Gabbro: Individual rounded and partly altered olivine crystals, along with individual crystals or clusters of anhedral pale pyroxene, and some opaque oxide anhedra, are surrounded by an interlocking mass of plagioclase. Pyroxene and olivine crystals can be up to a few millimetres in diameter. The pyroxene shows slight zoning. Patches within the gabbros are much finer grained and similar to the groundmass of alkali basalts.

Syenitu: These xenoliths, of variable grain size, contain abundant kaersutite along with pyroxene and sphene, all with a maximum diameter of 2-3 mm. Interstitial coarse plagioclase and/or finer grained feldspar with a little glass are also found. The brown kaersutite and pale purple, buff or green pyroxene are strongly zoned, and there appears to be a complex reaction relationship between the two minerals. Some finer grained varieties contain occasional euhedral crystals of sodalite. Interstitial carbonate is present in some specimens. A Na 0 2 FIG.3.. r Kill 16 o •• • • • • • • • • • • a • 14 • ALKALI — SILICA • • • os• DIAGRAM • *I • • • • • • • • •

• 12 • • • • • • • • e• • • • 10 •• • • e • • • •

a • • • 111.• % a • a • •• • • • ••• 6 I.• • • • • • 9 im • IA 60 • • • ••• • • • • • • • •• • • ALKALI C • 4 • FIELD • • •• • THOLE IIT IC • FIELD • • • is • • 2 • ••

45 50 55 60 SIB 2 e• F 10. 4. Si0 2 • • • ir • se. •• 60 • • I • • ToD• •• 8 •• ••• . • T RAC HYANDES ITES •• S. • 57 • •. •• el • PHONOLITES AND • • TRACHYTES 55 • • I •• • • 53 TRACHYBASALT$ •• • • • • 50 •• • ••• • • ••• • • 0 • • S • e• 46 •oto to • 45 * • •• •. • • • • .• ••• •• • • .1 • e • • is • _•. „0, • :- • 0 • e •e AN KARAMITES e 40 ALKALI B ASA LTS

75 20 40 60 65 $.0 OA.

FIG. S.

FeO ÷ Fe 0 2 3

Na20+ K 20 Mg 0

FIG. 6,

Na20 coo FIG. 7. PS116. ANKARAMITE. Olivine and pyroxene phenocrysts in fine-grained groundmass. Plane polarised light. x25.

FIG. 8. MA20. ANKARAMITE. Olivine and zoned pyroxene phenocrysts in fine-grained groundmass. Crossed nicols. x36

• bO -p 0 • H ••-1 0 +5 0 ts1 Co -d H a5 0 O E a) o F-1 5-i X +' o a) 0 0 • LIO .0 to •rl q-I 04 H 0 Q) H rd O 0 1.) U)Q) •H 4-) g -; J) O ;•1 H 0)5-i P4 0 al O 0 H Pi 0 —I- • 0 R .8-1 Pi U) x H O z0) •o c (11 cd H b.1) •H 0 • g rai 0 0

z 0 (15 0 ~r~

H ; H •ri Cl rte • II) Cs- 0 H •ri 0 H $-1 (1) o 4-) • • ED 4-) H cr, Ct Cd a) • 40 (1) P-I H F-1 H FIG. 11. 18-66. ALKALI BASALT. Hourglass and other zoned. pyroxene and opaque oxide phenocrysts in groundmass of opaques, pyroxene, feldspar and olivine. Crossed nicols. x 50

FIG. 12, MA8. ALKALI BASALT. One pyroxene phenocryst contains a green core, and two others include a mass of opaques. Olivine and opaque oxide microphenocrysts grade down to a groundmass of pyroxenes, opaques and feldspar. Plane polarised light x 85. 'I. ..., . • • — ... ••• • / I , eh t,• - ••••••••• •• Ao o ! • • , , '20 r.s.., i - — • ek,....i... - . - •• • • •', Ea.* f - ';'' ' ' -..- , ..-34-",:a.,„...... t.- • - • . .., "!" - .r,„ - ,i, f _ _._; ,_-•: ibAllir"' • (... "1.11' • ' •II- a• ' - 40,, It " •-.0 0.. - ‘ - • • ''. 0". , •!; •

* :. .ve.# •,•*. Nur v

*te C ..11 ft. st. .01" • fr**, • v FIG, 13. IiA8, ALKALI BASALT. A kaersutite crystal is almost comr_tc,,ly resorbed, leaving a mass of opaque oxides, pyroxene and a brownish semi-transparent mineral. This is surrounded bar a thin rim of pyroxene. Microprobe analyses made on the am,-1-'- and rimming pyroxene are given in tables 25 and 21 respeciv_ Two other pyroxene phenocrysts include a mass of opaque anhedra. Crossed nicols. x 40.

FIG. 14, PS112. RECENT TRACHYBASALT which swamped the village of Garachico in 1706. Large plagioclase and smaller olivine, pyroxene and opaque phenocrysts set in partly glassy matrix. Pla--) polarised light. x 30 FIG. l5. PS96. TRACHYBASALT. Large phenocrysts of plagioclase and pyroxene, and smaller opaques and oxidised olivines. Pyroxenes contain inclusions of apatite. Fine-grained groundmass of opaques, feldspar, pyroxene and altered olivine. Plane polarised light. x 40.

FIG. 16. P574. PLAGIOCLUE PHONOLITE (TRACHYANDESITE). One euhedral pyroxene along with feldspar phenocrysts set in a feldspar rich matrix. Crossed nicols. x 25. FIG. 17. 13-66. TRACHYANDESITE. Phenocrysts of feldspar pyroxene, and opaques. Field of view also includes part of a large kaersutite megacryst which is rimmed by opaque anhedra. The groundmass comprises mainly alkali feldspar. Plane polarised light. x 30.

FIG. 18. GB16. TRACHYATTDESITE. Phenocrysts of feldspar and microphenocrysts of blue hauyne and pyroxene set in a fine- grained matrix composed dominantly of flow orientated feldspar laths. Plane polarised light. x 35. FIG. 19. PS101. TRACHYTE from Montana GuazrJ. Abundant feldspar laths of varying size along with some pyroxene and opaques. Crossed nicolr3. x 40.

FIG. 20. MALL TRLCHYTE One pyroxene microphenocryst in a rock composed predominantly of alkali feldspar. Trachytic texture. Crossed nicols. x 45. FIG. 21. PS27. PHONOLITE intrusion from Ancient Series, Anaga Peninsula. Large clear anorthoclase and two smaller green pyroxene phenocrysts. Brown kaersutite is partly corroded and is surrounded by green pyroxene and opaque oxides. One small euhedral sphene touches the kaersutite. The groundmass is very fine-grained and predominantly feldspathic. Plane polarised light. x 35.

FIG. 22. P11. PHONOLITE intrusion from Ancient ,3eries, Anaga Peninsula. Phenocrysts of pyroxene, anorthoclase, partly altered kaersutite, sphene, opaques, colourless feldspethoid and andradite in a matrix composed largely of feldspar. The andradite partially includes an altered kaersutite. Plane polarised light. x 30 4. 411;1 FIG. 23. 9-66. PHONOLITE•from Canadas Series. Small phenocrysts of green pyroxene, biotite, opaques and anorthoclase in a very fine-grained crystalline matrix. Plane polarised light, x 40

FIG. 24. 1s85. PHONOLITE from Canadas Series; Microphenocrysts of nepheline in a groundmass of green pyroxene, pale brown amphibole, dark brown aenigmatite,and feldspar. Plane polarised light. x 100. FIG. 25. P';175. GLASSY PHONOLITE. Recent Salic Series. A large anorthoclase partly outside the field of view, and a small euhedral pyroxene are enclosed in a brown glass. Vesicles within the glass are elongated in the direction of flow. Plane polarised light. x 65.

FIG. 26. TC16. CRYSTALLINE PHONOLITE. Recent Salic Series. One kaersutite crystal rimmed with opaque anhedra along with a phenocryst of anorthoclase is set in a feldspar-rich matrix. Plane polarised light. x 50. FIG. 27, PfA69. Crystals of Biotite and pyroxene stand out against a background of alkali feldspar and nepheline. Plane polarised light. x 40. TABLE 1. Averaged analysis of Tenerife rooks

1 2 2 4 2 6 Z 8 2 10 11 12 II 14 11 16 43.40 42.06 43.34 45.43 45.16 48.31 49.31 48.86 54.15 54.61 54.55 61.00 60.15 58.00 56.93 60.32 59.44 SiO2 2.48 3.28 3.92 3.48 3.50 3.37 2.61 2.82 1.99 1.89 1.59 0.75 0.89 0.97 0.59 0.80 0.58 TiO2 9.90 9.51 14.31 14.12 15.35 15.38 18.55 17.91 18.91 18.44 19.51 18.00 18.79 18.93 20.25 19.27 19.36 A1203 Fe203 4.21 6.12 6.02 4.43 6.26 5.91 3.36 2.40 3.00 3.18 1.41 2.79 2.43 1.99 2.21 1.59 2.34 Fe0 8.17 7.00 6.89 7.78 5.74 5.18 4.64 6.46 3.18 3.10 3.74 0.39 0.89 1.99 0.98 1.09 0.74 MnO 0.20 0.13 0.21 0.21 0.19 0.23 0.21 0.20 0.28 0.21 0.19 0.18 0.23 0.20 0.17 0.20 0.17 15.91 15.70 7.25 8.48 6.80 4.06 3.25 3.67 2.17 2.12 1.82 1.07 0.47 0.77 0.47 0.45 0.59 Ca° 11..49 13.61 11.07 10.52 9.88 8.35 7.71 7.58 4.99 4.40 4.10 1.40 1.46 1.56 2.45 0.94 0.64 1.59 3.58 4.03• 5.29 5.32 5.53 6.92 6.77 8.37 7.48 7.96 9.07 7.44 7.81 8.94 1420 1.77 3.19 0.69 0.63 1.53 1.24 1.71 2.31 2.46 2.63 3.40 3.70 3.87 5.31 4.98 5.13 4.53 K20 5.63 5.97 0.32 0.13 0.53 0.61 0.84 0.99 0.74 0.81 0.38 0.37 0.26 0.16 0.13 0.12 0.03 0.22 P2o5 0.05 H2O ETC. 1.81 0.16 1.80 0.18 0.66 0.60 1.80 1.02 0.69 1.12 0.66 1.18 1.68 1.15 3.67 1.51 1.07 TOTAL 100.17 100.10 100.06 100.06 100.12 99.98 99.96 99.89 100.06 99.91 100.07 99.71 100.06 99.88 99.72 99.83 99.89 NORMS. OR 4.08 3.72 9.04 7.33 10.11 13.65 14.54 15.54 20.09 21.86 22.87 31.38 29.43 30.32 26.77 33.27 35.28 AB 9.44 1.26• 14.58 18.72 20.97 29.75 30.15 25.83 38.45 40.17 32.46 51.17 51.05 35.06 43.76 48.34 35.26 AN 17.84 16.14 20.21 18.80 18.74 11.40 19.47 16.28 10.49 9.00 4.24 _- 8.48 0.90 - BE 2.17 7.43 6.72 6.27 7.11 8.13 8.05 11.35 10.89 9.27 20.78 6.42 ::83 18.26 10.40 9.61 18.84 DI 29.40 39.61 24.55 23.42 19.29 18.34 11.09 13.06 9.27 8.16 11.81 4.28 2.53 5.800 2.53 01. 81 20:.7308 WO _ - _ - - - - - _ - - 0.97 - 0.10 - OL 23.87 16.37 5.76 10.09 5.60 1.13 3.32 6.09 1.17 1.2/ 1.59 0.48 MT 6.10 8.87 8.73 6.42 8.98 7.68 4.87 3.48 4.35 4.61 2.04 - 1.04 - 200. 1.85 - HT _ - 0.07 0.61 - - - - - 2.71 1.71 - 0.83 0.32 - IL 4.71 6.23 7.44 6.61 6.65 6.40 4.96 5.36 3.78 3.59 3.02 1.21 1.69 1.84 1.12 1.52 1.10 AP 0.75 0.30 1.24 1.42 1.96 2.31 1.72 1.89 0.89 0.86 0.61 0.37 0.30 0.28 0.07 0.51 0.12 AC - .. ------0.24 5.76 6.77 TN NO - o.28 0.33 0.38

D.I. 15.69 12.41 30.35 32.32 38.19 51.53 52.74 52.73 69.43 71.31 76.11 88.97 89.31 83.66 80.93 91.22 87.38 - 1.01 0.98 1.09 0.84 0.9R 1.09 P.I. •Peralkalinity index Na a K 9. Trachyandesite. Al Canadaa Series and Trachyte and Trachybasalt Series (4). (6) 10. Trachyandesite (Plagioclase Phonolite). Canadaa Series and Trachyte 1. Ankaramite. Ancient ;cries and Trachybasalt Series (S). P. Ankaramite. Canadaa jeriea (1) 11. Trachyandesite (Plagioclase Phonolite). Recent Salic Zeries (2). ancient Jeriea (12) 3. Alkali basalt. 12. Trachyte. Montana Guaza. Trachyte and Trachybasalt Series (Plaster 4. Alkali basalt. Canadaa jeries and Trachyte and Trachybasalt Serials (3) et al. 1968) (1). 5. -eries 3 naaalta. (18) 13. Phonolite. Canadaa .eries and Trachyte and Trachybasalt .aeries (11). G. Trachybasalt. Recent Basic :,erica (3). 14. Phonolite and Glaasy Phonolite. Recent Salic Series (24). /. frachybazalt. Canudas .aeries and Trachyte and Trachybasalt Series (7) 15. Phonolite. Intrusions into Ancient Series (2). Trachybasalt. ,tecent Salto Jeries. 16. Phonolite. Intrusiona at Rogue de Garcia and Tauce escarpment, Canadad Series (4). 17. Average analysis of nepheline ayenite (Ibarrola and Viramonte 1967).

In brackets is the number of analyses used to form the average. -43-

SECTION 3.

MINERALOGY

1. OLIVINE

Occurrence

Olivine is restricted to the ankaramites, alkali basalts and trachybasalts. It occurs as phenocrysts and in the groundmass. The modal percentage decreases from the ankaramites (up to 30), to the trachybasalts, when it can be less than lc/. The dunite xenoliths are composed almost entirely of olivine.

General features.

In hand specimen unaltered olivine phenocrysts are always a transparent pale greenish yellow. With alteration, this becomes initially translucent yellowish brown, and finally the opaque sometimes glistening, red brown of iddingsite.

Major characteristics of the mineral remain similar throughout the suite.

Phenocrysts: Unaltered crystals are clear, and colourless in thin section. A few inclusions of opaques are found. With the occasional exception of the opaque oxides, in the ankaramites and alkali basalts olivine appears to be the first mineral to have crystallised. In porphyritic trrchybasalts, the mineral relationships suggest that crystallisation of opaque oxides was followed by that of olivine and feldspar together, and then, pyroxeno.

The shape of the phenocrysts varies from completely euhedral to anhedral: crystals in the alkali basalts and trachybasalts have a tendency for development of more perfectly shaped crystals. Fragmental crystals are found in ankaramites and some semi-accumulate alkali basalts. These were presumably formed by break up of larger phenocrysts during movement. Many crystals exhibit a rounding of sharp edges, and ragged edges, which suggest that they have been partly resorbed (fig. 28). - kJ+ -

Hausen (1956) also notes these "Corrosion forms'. In a few rocks small skeletal phenocrysts and microphenocrysts, similar to some described by Dreyer and Johnston (1957) are present (fig. 28). According to these authors, such crystals have • grown rapidly in situ.

Rare crystals have translation lamellae and undulose extinction, indicating stress. These features are common in the dunite xenoliths.

Many large phenocrysts from the ankaramites and some from the alkali basalts contain an orange-brown oxidation rim surrounding the crystal, and this rim is sometimes surrounded in part by a further very narrow rim of normal olivine. This rim has different optical properties (i.e. extinction and birefringence) from that of the bulk of the crystal, and probably contains more fayalite. Pyroxene phenocrysts from the same specimens contain a similar thin rim of different composition, and both rims are probably produced during final crystallisation under low pressure and oxidising conditions after eruption or intrusion.

Major zoning, with a difference in optical properties between the centre and rim of phenocrysts (Tomkeieff'1939), does not appear to be present. This zoning has not been found during electron microprobe analysis of phenocrysts.

Alteration to iddingsite, or more rarely serpentine, occurs most often in rocks from the Ancient Series. Olivines from the Recent Series and Series 3 Basalts are always fresh.

Groundmass: Olivine occurs in minor quantites except in some ankaramites, and in some trachybasalts only occasional crystals can be recognised. Crystals are often slightly coarser than the remaining groundmass minerals and skeletal olivine can be found in some rocks. Alteration is very widespread.

Chemical composition derived from optical properties

Chemical compositions derived from optic axial angle measurements given by Hausen (1956) range from Fo90 to Fo55. - 45 -

The majority however correspond to Fo 80 5 (Compositions from Deer, Howie and Zussman. Vol. 1 1962). Hausen does not state whether measurements were made on phenocrystal or groundmass olivine. There appears to be no correlation between forsterite content, the rock type and the age of the rock.

A preliminary survey of the present specimens showed o that 2Vy was approximately 90 (- 10°) for all phenocrysts (2Vy = 90 corresponds to approximately Fo 86). Measurement of optic axial angles, as 2V approaches 90°, becomes increasingly difficult, and, in the case of olivine, unless accurate measurement can be made, serious errors arise in the composition (10 difference in 2V corresponds to approximately 2% forsterite).. Measurement of the p refractive index can be made relatively easily and errors are not so great. Values obtained, along with corresponding compositions from Bowen and 3chairer (1935) , are given in table 2. The olivines are all forsterite rich. From the specimens examined there appears to be no difference in composition between olivine from different rock types or with difference in age of the rocks. Variations in refractive index, due to zoning, were not apparent.

A wide range in composition of individual olivine crystals from the gabbroic xenoliths (Gastesi (1967), determined by optic axial angle measurements, was obtained. They average to approximately Fo80. Measurements on olivine from the host rock give similar or slightly more fayalitic compositions.

Electron Micro- crobeAnalyses. Results are given in table 3. All crystals analysed were free from alteration.

No significant change in composition of phenocrysts from one rock type to another is aprarent. Even microphenocrysts from the trachybasalts (Nos. PS 48 and TC 38) are still very rich in the forsterite molecule. True groundmass crystals, when analysed, contained more fayalite than the olivine from the corresponding phenocrysts. 24-66 shows a variation in composition between phenocrysts of different sizes, suggesting -46-

more than one period of crystallisation. However, an apparently small phenocryst may be a section, with small surface area, of a large one. In one crystal (MA 19 (3 and 4)), where loth the centre and rim were analysed, zoning is insignificant.

The small amounts of TiO and A120 in some analyses 2 3 may be real, but could also arise through slightly varying background count rates during the analysis. This, after compu- tation of results, would give an artificial, very small concentration. Door Howie and Zussman (1962 Vol. 1) state that the alumina in some olivine analyses is probably due to impurities in the analysed samples. Such impurities could not be present in an electron microprobe analysis. Manganese, calcium and nickel were, however, detected definitely in all crystals analysed. All three elements arc present in at least partial solid solution series with olivines.

:Electron microprobe analyses of three crystals from dunite xenoliths have a composition of Fo88, Fo86 and Fo82. Minor element concentrations (Ca, T•1n, Ni) are similar to those in table 3. (Borley et al. 1970. In preparation)

X-Ray Diffraction Studies

Cell 1w7srameters have been obtained for olivine phenocrysts from one ankaramite and three alkali basalts (table 4). General operating, and data refining procedure is explained in Appendi:c 1. The reflections used for refining the cell parameters, in increasing 2 G, are: 020(4), 021(4), 101(4), 111(1), 120(1), 121(4), 002(4), 130(4), 131(4), 112(4), 041(4), 210(4), 122(4), 140(3), 132(4), 150(3), 151(2), 222(4), 240(1), 241(3), 133(2), 152(1), 004(4), 062(4), 312(1), 322(2), 134(1), 174(1). Because of overlap, or poor development, all reflections wore not used for each refinement. The number, in brackets, refers to the number of specimens to which the reflection was applied. When calculated back from the refined parameters all reflections had a difference of less than 0.040 2& from the measured value.

The forsterite content of the olivines as calculated - 47 -

from the 130 reflection (Yoder and Sahama, 1957) and, when sufficiently developed to be measured, the 174 reflection (Jambor and rnith 1964), are also given in table 4. The cell parameters are in agreement with expected results from the olivines of approximate composition Fo80 (Jahanbagloo 1969).

Crysta]lisction trends.

As in alkaline olivine basalts from other provinces a considerable amount of olivine appears to have crystallised from the Tenerife magmas over a long period of time. This is reflected in the abundance and wide areal distribution of the ankaramites and allzali basalts within the Ancient and Lower Canadas ;aeries'. Younger alkali basalts and trachybasalts contain olivine in smaller quantities. Furthermore there is a complete absence of evidence for a reaction between olivine and the magma to form orthopyroxene.

Fractionation of olivine and pyroxene appears to have been operative in the formation of the ankaramites, and of olivine alone in the formation of the dunites, which are represented at the surface by xenoliths. The effect of fractionation of forsteritic olivine would deplete the magma in magnesium and, to a lesser extent, ferrous iron. Enrichment o1 olivine in ferrous iron, relative to the coexisting pyroxene (analyses given in table 13), shows that fractionation of olivine will have a greater effect on removal of ferrous iron from the magma than will the separation of pyroxene.

The presence of corrosion forms suggests that, after crystallisation, the olivine phenocrysts were not always stable. Reaction of olivine with its parental liquid, or a reaction with the new liquid surrounding the olivine after sinking of the crystal, may have taken place. Such a reaction could explain t:Je absence of olivine in the trachyandesites, trachytes and phonolites. Several olivine-liquid reactions have been observed in natural and synthetic basalts, and are given by -1+8-

O'Hara (1968). In undersaturated liquids these are of the form: undersaturated liquid + olivine diopside (+spinel). Ridley (1970) suggests that a similar reaction could be responsible for the occurrence of olivines in only the more basic rocks. Schairer et al. (1968) after a study of the nepheline diopside- anorthite join state that evidence of olivine resorption can be expected in nepheline bearing suites which are analogues of the synthetic systems. However, any reaction taking place here has not formed a mantle of any mineral (pyroxene would be expected) around the olivine. An increase in temperature after crystallisation of the olivine, possibly caused by separation into a hig'ier temperature environment, would also have.the effect of corroding the crystals; but, on subsequent cooling, over- growths, probably giving rise to zoning, may be expected. These are not apparent.

On comparison with other volcanic island;:, it is observed that on Tristan da Cuhna (Baker et al., 1964) and Tahiti (McBirney and Aoki, 1968), where the lavas are very undersaturated as in Tenerife, the occurrence of olivine is similarly restricted. However, on Gough Island (Le Maitre, 1962) and St. Helena (Baker, 1969), where the rocks are less undersaturated, olivine is present in all rock types. Also, there is no significant variation in the composition of the olivines from Tristan da Cuhna and Tenerife, but on Gough Island and St. Helena they become more fayalitic with differentiation, even in the trachybasalts. Thus, it appears that a compositional parameter, such as the degree of undersaturation, may affect the range of crystallisation and composition of the olivines produced. -49-

2. PYROXENE

Introduction

Pyroxene is the most widespread and abundant ferromagnesian mineral found within the Tenerife volcanic suite. It occurs in all rock types with the exception of the dunite xenoliths. The modal content varies from approximately 50% in some ankaramites (excluding pyroxenite xenoliths, where it is almost 100;'), to less than which is represented by the occasional crystal found in some glassy phonolites.

Two types of pyroxene have been identified; namely, salite (using the nomenclature of Poldervaart and Hess. 1951), and aegirine. The salite is found as phenocrysts in all rock types whereas aegirine is restricted to the groundmass of some phonolites and the nepheline syenite. Orthopyroxene and pigeonito, either as discrete crystals, or as exsolved phases from calcium rich clinopyroxenes, have not been found: this is a feature that is common to pyroxenes from many alkaline provinces (1:ennedy 1933. Poldervaart and Hess 1951. Wilkinson 1956. Doer, Howie and Sussman 1966, p126).

A. Crystallography

At several localities on the Anaga peninsula abundant perfectly formed pyroxene crystals (salite), up to 3 ems. in diameter, surrounded by a fine grained friable matrix, have been found, Bravo (1955) has described the field relations of similar concentrations of pyroxenes from Tenerife which have formed by various processes. Field evidence for the present crystals leads to the conclusion that they form the resistant part of an ankaramite which has been altered, presumably by weathering.

Most crystals are equidimensional, the others being elongated in the Z direction. Common forms produced arc the frontanaside pinacoids [100] and [010], vertical prism [110], and the bipyramid [111] (fig. 29). Some crystals have - 50 -

a simple twin with [100] as twin plane.

Small aegirine crystals, separated from the nephcline syenite, are long and prismatic.

B. General characteristics of pyroxenes from the individual roc;: types.

Brief descriptions are included in the petrography of the rock types (Section 2). A more detailed account of pyroxenes from the major rock types follows below. Quantitative optical properties including variations produced by zoning are given in tables 5 - 12. Refractive index determinations were carried out on suitably orientated grains, by the immersion method (Maximum error = ± .003). Optic axial angles (2V y) were determined using a Cooke, Troughton and Simms four axis universal stage, in sodium light 5893 .1) Only grains in which both optic axes could be measured were used and both positions of the optic axial plane were read (Fairburn and Podoisky. 1951) o (Maximum error - 2 ). Approximate extinction angles (Z y) were measured, without using a universal stage, on sections as near as possible parallel to [010]. Errors in the method will be large but constant variations were obtained when dealing with zoned crystals. No attempt has been made to deduce an accurate chemical composition from the measurements, and thus determination by a more accurate method is unnecessary.

Ankaramite: Large dull black salite pyroxene phenocrysts can constitute up to 50Y of the rock.

In thin section, the bulk of any phenocryst is colourless to very pale purple (pleochroism: a is slightly darker than (3 or y ), with slightly varying shades of purple corresponding to an irregular or oscillatory zoning pattern (fig. 9). Surrounding most crystals is a much darker purple rim (fig. 30), often containing abundant smell inclusions of opaque oxides - 51 -

either completely enclosed within the rim, or only partly enclosed by the pyroxene crystal (fig. 31). These oxides appear similar to, though sometimes smaller than, the adjacent groundmass opaques. The junction between the darker rim and the rest of the crystal is often very distinct.

Crystals are commonly euhedral to subhedral but some are completely anhedral with ragged edges. Occasional crystals exhibit simple twinning. Some phenocrysts, which are broken fragments of much larger crystals, contain the darker purple rim surrounding the complete broken fragment, but the inner pattern of zoning is cut off sharply (fig. 9). The inner pattern of zoning can sometimes be better observed in crossed polars by variation in birefringence colours. Under these conditions a very fine scale oscillatory zoning (minute scale oscillatory zoning) can often be seen superimposed on the more prominent zoning. Well developed hourglass zoned crystals are absent.

Cften crystals contain inclusions of groundmass material (fig. 43), and in some anhedral crystals the irregular shape of the pyroxene gives the appearance of having been corroded,(fig.32)the corroded area now being filled with groundmass material. Where inclusions and corroded areas are present, an adjacent darker purple colour of the pyroxene, similar to the outer rim of the crystals is found. Other inclusions are larger opaques and olivine.

Groundmass pyroxene crystals are often lath shaped and area darler- purple colour, of similar shade to that of the outer rim of phenocrysts. Coarser groundmass crystals are zoned. "Quench hourglass" structures (Strong. 1969) are common in groundmass pyroxenes from some rocks (fig. 33).

Alk;ai basalt: Phenocrysts visible in hand specimen are always a dull black, but separated fractions are not completely homogeneous. Most grains are a dark transparent purple brown but others are a transparent green. Occasional grains contain both colours -52-

This probably arises as a result of zoning.

Characteristics of the pyroxenes in thin section vary considerably. Differences, in part, follow the change in chemical composition and general petrography of the alkali basalts. In rocks containing fairly large and abundant phenocrysts, the pyroxene appears similar to that from the ankaramites, and the roc'z analyses tend towards the ankaramites. When pyroxene phenocrysts are scarce, small or absent rock analyses and petrography tend towards trachybasalts.

Pyroxene phenocrysts are very pale purple or almost colourless (pleochroism: a is slightly darker than f3 or ;ti) and on occasions contain green cores (extremes of pleochroism are, a : medium green, y: pale yellow green). Changes in shades of purple represent zoning within the crystal. Zoning which may be oscillatory (fig. 34), irregular (fig. 35), hourglass (figs. 36 and 37) or normal (i.e. an outer rim of different composition) (fig. 38), can sometimes be better observed in crossed polars. Hourglass zoning is extremely common in crystals from many alkali basalts, the actual hourglass part being the lighter purple. ninute scale oscillatory zoning can be superimposed on all other types of zoning, especially hourglass varieties (fig. 36).

The relationship between the pyroxenes with the green cores and kaersutite is explained in Section 2. These cores are of varying shades of green (fig. 12 and 39), yellow-green, or rather dirty buff colour, and on two occasions inclusions of partly resorbed kaersutite crystals, along with opaque oxides, have been found within a pyroxene containing a green core.

Crystal shape varies considerably but most phenocrysts are subhedral to euhedral. Many crystals, especially those exhibiting hourglass zoning are elongated in the Z direction. In several rocks small pyroxene phenocrysts are grouped in clusters (fig. 37) either alone, or with olivine phenocrysts. The pyroxene phenocrysts frequently contain inclusions of opaque oxides, olivine, occasional feldspar, and rarely, -53-

rounded inclusions of a sulphide mineral. Electron microprobe wavelength scans on the sulphide show the presence of only iron and sulphur.

Several pyroxene phenocrysts contain very fine needle- like lamellae of an opaque mineral, presumably exsolved from the host pyroxene (fig. 40). The lamellae form in two directions, (measurements of the acute angle vary from 36-840), giving a delicate lattice pattern over part of the phenocryst. Lamellae have been found in the darker parts of an hourglass zoned crystal, and in the centre of normal zoned crystals. The chemical nature of these lamellae could not be determined using the electron microprobe because of their very fine nature, and because only a small fraction of the lamellae, visible in thin section using transmitted light, were actually at the surface of a polished section.

Well developed small pyroxene crystals are only present in the coarser grained groundmasses. Frequently the groundmass crystals are visibly darker in colour than the adjacent phenocrysts. "Quench hourglass" structures are common when the matrix is coarser grained (fig. 33).

Trachybasalt: Occasional phenocrysts up to 5 mm. in diameter are visible in the coarser grained porphyritic rock specimens.

In thin section the very pale purple or buff coloured subhedral to anhedral pyroxene phenocrysts are usually smaller than co-existing plagioclase and olivine (fig. 14). Zoning is not as strong as in pyroxenes from the more basic rocks, but hourglass, normal, and irregular zoning can be found. The pyroxene phenocrysts on occasions group in clusters along with, and including, opaque oxide microphenocrysts. In one extremely porphyritic variety (PS 96) abundant inclusions of apatite are found (fig. 15). Occasional crystals contain pale green cores. Less porphyritic trachybasalts contain only occasional unzoned pale purple or buff phenocrysts.

Fine-grained pyroxene in the groundmass of porphyritic -54-

and in completely aphyric varieties appears to be almost colourless, but in the coarser grained rocks it is pale purple. Estimation of the quantities of minerals in fine-grained rocs is difficult, but in several specimens the pyroxene appears to be not very abundant (<10}0).

Trachyandesite: Pyroxene occurs in relatively minor quantities in the trachyandesites (<105). In thin section phenocrysts are very pale purple to buff or pale green and generally subhedral to euhedral. Zoning is only occasionally present, rare crystals containing a pale green core and pale purple rim, or an hourglass structure (figs. 17 and 18).

Groundmass crystals are colourless or very pale green and tend to be elongate.

Trachyte: In thin section, the very small pale green pyroxene crystals found within the trachyte from Montana Guaza are anhedral, but elongated in one direction following the flow pattern of the feldspar (fig. 19). Modally this pyroxene makes up approximately 1;'. of the rock.

similar pale green pyroxene (maximum pleochroism is a : pale watery green.' : very pale yellowish brown) is found in the trachytes from the Ancient Series but, in addition, small euhedral or subhedral pale green phenocrysts are found (fig. 20). formal and hourglass zoning is present in some crystals.

Phonolite intrusions in the Ancient Series: small separated pyroxene grains from MA 7 are medium- dark green.

In thin section phenocrysts from 103 27, MA 7 and GB 4, are green, elongate, strongly pleochroic (a: pale watery green, 3: pale brownish green, y: pale yellow brown) subhedral and up to 1.5mm. in length. In some crystals zoning with a darker -55-

green rim is present. Small pyroxenes along with opaques also form rims around the kaersutite crystals (fig, 21). Green pyroxenes can be identified in the very fine-grained groundmass.

Specimens FS 9, PS 10 and PS 11, contain subhedral phenocrysts with green cores and pale purple or pale green rims (fig. 22). Occasionally zoning is more complex or the complete crystal is a pale purple. The kaersutite shows a poorly developed rim, if any, of pale green pyroxene. Elongate pale green crystals are found in the very fine-grained groundmass.

The fine-grained green pyroxene in the specimen from Roque Higara(PS 107) is strongly pleochroic (extremes are a: medium, y : pale brownish yellow) and elongate sections have a low extinction angle (ca. 10-15°). One larger crystal is zoned with a darker green rim. A mass of green pyroxene crystals once again rim a partially resorbed amphibole.

Phonolites from the Canadas Series, and Trachyte and Trachybasalt Series: Small (<1mm.) pyroxene phenocrysts when formed are pale green, slightly pleochroic in shades of green, occasionally zoned and subhedral to euhedral (fig. 25).

The very fine grained groundmass crystals are much brighter green and pleochroic (elongate sections have a: medium green.y: pale yellow green). They form either as discrete elongate crystals or in clusters of fine crystals often surrounding a nepheline microphenocryst (fig. 24). The extinction angle on elongate sections is small.

Phonolites from the Recent :Dane Series: Rare pale buff or pale green unzoned, euhedral phenocrysts up to lmmo across are found in crystalline varieties and in some glassy phonolites (fig. 25). Only occasional very fine-grained pale green or green crystals can be identified in the groundmass of crystalline varieties. -56-

Variation in optical properties.

The optical properties of the salite pyroxenes (trbles 5-12) are similar to those crystallising from other alkaline olivine basalt provinces as compiled by Wilkinson (1956), and also similar to more recent data for alkalic rocks from Oceanic islands given by Le Maitre (1962.Gough Island). Baker et al. (1964.Tristan da Cuhna), Bryan (1967. Clarion Island, Mexico), McBirney and Aoki (1968. Tahiti), and Baker (1969. St. Helena), although not all of these authors give chemical analyses of the pyroxenes. Curves given by Hess (1949), Carmichael (1960) and Brown and Vincent (1963), based on measurements of p refractive index and 2V , can be used to determine the chemical composition of pyroxenes in the quadrilateral Di - Hd - En - Fs. The curves, however, are based on pyroxenes crystallising from tholeiitic or a variety of magmas, and serious errors arise when pyroxenes crystallising from an alkaline olivine basalt magma are determined by this method. Pyroxenes from Tenerife and other alkalic areas plot on this basis in the fields of augite and ferroaugite but chemically all are salitic. Signi- ficant differences in minor element concentrations (eg. Ti and Al) occur between clinopyroxenes crystallising from alkaline olivine basalt and tholeiitic magmas, and this will cause the variation in optical properties. Only ninor variations are present in the optical properties of the pyroxene phenocrysts from different rock types and this is reflected in a similarly small range of chemical composition (Part D). However, large differences in 2V and Zr\l,' can be present within zoned crystals and this is paralleled by chemical variations across the crystal (Part F).

Pyroxene phenocrysts from the phonolites do show a slight increase in 2V y and z''y over those from other rock types and this is consistent with an increase in the proportion of acmite in the pyroxene. The properties of groundmass crystals from the phonolites and pyroxenes from the nepheline syenite are vastely different from the others and results fit with the high proportion of acmite in the pyroxene molecule - 57 - found from chemical and x-ray analysis (Parts D and E). Refractive index measurements on the aegirine from the nepheline syenite (a,: 1.755 - 1.765. y 1.795 - 1.805) indicate 70 - 80;' acmite in the pyroxene (Deer, Howie, and Zussman 1966. Tyler and King 1967).

D. Chemical and Microprobe analyses.

Ten complete chemical analyses are given in table 13 along with analyses of Kunitz (1936), Carmichael (1967) and Ridley (1970). An additional analysis (PS69) is, in part chemical (Fe203, FeD, MgO, MnO, CaO, Na20, K20), the remaining elements being the average of microprobe determinations (Si02, Ti02, A1203) (average of 12 analyses from table 14). Tables 14-22 are microprobe analyses of unzoned and zoned pyroxene phenocrysts and groundmass crystals. Analyses which are not referred to in part F (Zoning in the pyroxenes) were made on unzoned or only slightly zoned crystals and results are given in table 14. As far as possible determinations were made on centres of crystals, but analyses of different crystals from the same specimen sometimes vary considerably. Because of this variation, and as only a few analyses, at the most, were made on each specimen, averages have not been made. To carry out more analyses would take up considerably more operating time on the microprobe than was available, even assuming that a sufficient number of suitable crystals were present in the thin section. Also, when continuous crystallisation of any mineral takes place, a difference in compostion between individual crystals forming at different times would be expected; a chemical analysis is an average of this. The range in composition obtained under normal circumstances will reflect the crystallisation trend of the mineral forming from the magma. This can be seen in the relntive positions of different crystal analyses from the same specimen in in figs. 49 and 50 (Data from tables 13-23). When wide discrepancies exist the direction of variation follows the general trend in the crystallisation of the pyroxenes from the complete suite. -58-

Electron microprobe analyses of zoned crystals along with photographs or drawings of the crystals are given in Tables 15-22. Values for the ternary plots ?ado-En-Fs and Ac-Di-Hd for pyroxene analyses from the xenoliths (Borley et al. 1970) are given in Table 23.

Calculation of structural formulae and partitioning of pyroxene analycec into end-member molecules.

In the structural formulae, aluminium and titanium, in that order, have been added to silicon to make the sum of the Z sites equal 2.000. The structural formulae of the salitic pyroxenes, analysed using the microprobe, are quoted assuming all the iron as FeO, whereas in the same calculation for the aegirines Fe203 is used. Formulae were calculated by computer, using a program written by the author, with iron oxide as both Fe0 and Fe203. It is interesting to note that the sum of the cations (';': XYZ) in every formula where all Fe was calculated as Fe0 was greater than the theoretical sum of 4.00; by proportioning increasing amounts of Fe to Fe203 the sum was decreased and when all Fe was calculated as the sum was 7 Fe203 less than 4.00. Analyses which were exceptions showed special features such as high or low totals. These observations suggest that if an analysis is accurate and the variations due to the differing oxidation states of elements other than Fe are negligible, the corresponding concentration of the iron oxides when the total equals 4.00 may approximate to their actual amounts in the mineral. In an accurate analysis, the author can see no other factors likely to affect the result. A further study of this, using microprobe and chemical analyses, is necessary before definite conclusions can be made. However, 0 the aegirines, which should contain a very high ratio of Fe2 3 to Fe0 give a formula nearer XYZ = 4.00 with Fe as calculated from Fe203. The salitic pyroxenes with low Fe203 give the same with Fe calculated from FeO, and with an increase in the acmite 0 the formula becomes less perfect. molecule (ie Fe2 3) Pyroxene end-members, used in plotting the trends of - 59 -

crystallisation in the ternary systems Wo-En-Fs and Ac-Di-Hd, have been calculated as follows: for.the salitic pyroxenes, which are principally members of the diopside-hedenbergite 2+ series, Ca is taken as Wo, Mg as En, and Fe=Fe + Fe3+ + Mn (or from microprobe analyses Fe = Fe + Mn) as Fs. The salitic pyroxenes are positioned on Ac-Di-Hd as follows: 2 Na + K are taken as Ac, Mg as Di, and Fe + Fe3 + Mn (or Fe + Mn) less an amount of Fe3 (or Fe) equal to Na + K (to form Ac) for Hd. Potassium is included with Na for uniformity with other calculations made of end-members, although it is unimportant in the Tenerife pyroxenes. When Na is greater than Fe3, the latter has been used as a basic to form Ac, as this gives a more accurate representation of the acmite component within the pyroxene (this can be applied to chemical analyses only). The only Tenerife pyroxene containing Na in excess of Fe3+ is PS69 (table 13): the presence of excess Na is discussed later. Occasional analyses from other provinces, recalculated for comparative purposes, also contain excess Na over Fe3+.

The same calculation on the basis of Ac-Di-Hd cannot be made for the aegirine microprobe analyses as, frequently, Na exceeds Fe Mn, thus destroying the hedenbergite component, which would be made from Fe0 + MnO. The calculation has been made in the reverse order to give an approximation of the three components, as follows: Di is mcde from Mg with an equivalent amount of Ca and twice the amount of Si. The remaining Ca is allocated to an equivalent amount of Mn Fe along with twice the amount of Si to make Hd. The remaining Fe is allocated to Na with twice the amount of Si to make Ac. Al and Ti and some Si and Na will remain, but all of the major elements, commonly showing marked variations during crystallisation of pyroxenes from differentiating igneous suites (except all of the Na), have been allocated. The results of these calculations have been plotted on the same Ac-Di-Hd graph as the salitic pyroxenes, to show the extreme in pyroxene composition that can form, even though they have not been calculated in the same way. The nature of the pyroxene end-members formed by the Ti, -6o-

Al and remaining Si and Na is discussed later. These methods of calculation seem to give a reasonable graphical representation of the major components within the Tenerife pyroxenes, and the basic method used for the salites appears well established in recent literature. Other methods of end-member molecule calculation (Hess 1949, Yagi 1953, Yoder and Tilley 1962, Kushiro 1962, Edgar et al. 1969) have, with the possible exception of Yoder and Tilley (1962), very little following and several have been applied only to determine the specific variation in a single pyroxene component, and not to determine the overall type of pyroxene. Regardless of the order in which the molecules are calculated the salient features always stand out, and by calculating the aegirine microprobe analyses by the method given above, the maximum possible Di and Hd are formed at the expense of Ac, Tschermakb molecule, and jadeite. This must be remembered when comparisons are being made with pyroxenes from other provinces.

Chemical variations and trends shown by the analyses.

The features described below are the general variations between the separate rock-types and between phenocrystal and groundmass phases, regardless of the extensive zoning. The latter is described in detail in part F. The two types of pyroxene, salite and aegirine, are chemically well separated although both types can be found in the same rock (eg PS41. table 14).

An overall high concentration of alumina is present although it decreases in rocks more alkaline than the trachybasalts. Silica correspondingly increases with the decrease in alumina. Octahedral Al is always low, the major variation being in the tetrahedral sites. On occasions Ti has to be placed in the Z sites; this is particularly necessary in the aegirines. Titania consistently high in the salites, there being an increase in the pyroxenes from the ankaramites to alkali basalts followed by a decrease in the later differentiates: similar changes have been noted in other provinces by Yagi and Onuma (1967). - 61 -

The variation in titania is most marked on comparison of the microprobe analyses from the different rock types. The phenocrysts in the ankaramites probably accumulated in the magma chamber at higher pressures than pyroxene crystallising from the non-cumulate alkali basalts and trachybasalts. It has been found experimentally that the solubility of CaTiA1206 decreases with increase in pressure under dry conditions (Yagi and Onuma 1967) and this may have limited the amount of titania in the cumulate pyroxenes. High titania and alumina are common characteristics of salites crystallising from alkalic magmas (Kushire 1960. Verhoogen 1962). Titania in some aegirines is remarkably high.

In common with many rock analyses, much of the iron is in the ferric state. The proportion of iron increases slightly between phenocrystal pyroxenes from the ankaramites and alkali basalts, and magnesia correspondingly decreases. A similar small increase in iron and decrease in magnesia occurs in phenocrystal pyroxene as the rocks become more alkalic. Pyroxene phenocrysts and groundmass from the trachyte MA4A (table 14) are particularly rich in iron and depleted in magnesia. In microprobe analyses of groundmass crystals from a phonolite (11-66. table 14) slight enrichment in iron and soda and depletion in magnesia has taken place, but groundmass pyroxenes from phonolites PS41 and PS84 (table 14) show a considerable increase in iron and also soda, and the pyroxene correspondingly becomes aegirine. Lnalyses of the microphenocrysts in PS41 (PS41(1-3)) and other phonolites show only slight enrichment towards aegirine. In all analyses the proportion of manganese increases with iron.

Calcia remains fairly constant at 21-225 in salitic phenocrysts although it tends to decrease in those from later differentiates. It is low in the aegirines. The concentration of soda in the phenocrysts increases from less than 0.5 in some ankaramites to around 2.5 in microphenocrysts from some phonolites. Soda in the aegirines varies from approximately 6-12%.

Chemical analyses of groundmass pyroxenes from an -62 -

ankaramite (tRble 13. MA19G) and alkali basalt (MA6G) are similar to analyses of the phenocrysts from the same rock (PIA19P and 1.1A6P). One would expect groundmass crystals, forming at a lower temperature and later than the phenocrysts, to contain a higher proportion of the lower temperature pyroxene component, in this cese hedenbergite, and hence FeO, at the expense of diopside. This is only noticeable when the microprobe analyses of the centres of normal phenocrysts (excluding the special case of the green cores) are compared with the groundmass analyses (table 17. MA3(1),(2),(9), and.(11n. The groundmass crystals also contain more titania, alumina and less silica than the phenocrysts. Chemical variations due to extensive zoning in the phenocrysts will offset this effect in the chemical analyses.

Chemical and microprobe analyses matte on crystals from the same rock (table 13, 24-66, 49-66, MA19P, table 14 24-66 (1-4), 49-66, and table 15 MA19P(1-4)) give comparable results when taking into account the zoning, except that manganese oxide in chaical analyses 24-66 and MA19P (table 13) is much higher than corresponding microprobe analyses. The chemical analyses are possibly in error as, overall, the values from these appear anomalous.

Chemical analysis of PS69 was made, principally,to determine the amount of the hedenbergite molecule within the pyroxene. The microprobe analyses (table 14. PS69 (1-12)) show considerable variation in the content of most oxides. Comparison with the chemical analysis, which should be an approximate average of the microprobe analyses, show reasonable correlation for total iron, Mg0 and MnO, but Ca0 appears lower and Na20 higher in the chemical analysis. Potassium remained undetected in the microprobe analyses - wavelength scans were made on several crystals, potassium always being below the limits of detection - but 0.79K20 was recorded for the chemical analysis. This potassium might therefore be in the form of impurities such as alkali feldspar, whose nett effect on the analysis will be to increase Na and decrease Ca. The structural formula of -63-

the chemical analysis has been calculated using averaged values of TiO and A120 from the microprobe results. An SiO2' 2 3 appropriate plot on Ac-Di-Hd falls in the centre of the region occupied by the microprobe analyses. a The Alitic pyroxenes are members of the diopside- hedenbergite series. A gradual but limited change towards hedenbergite takes place as differentiation within the rock series proceeds. Pyroxenes from tables 13 and 14, and selected analyses from 15, 16, 17, 20, 21, 22, and 23 have been plotted in figs 49 and 50. The bulk of the analyses, including representatives from all rock types are found in a group on the diopsidic side of the salite field (fig. 49) (Poldervaart and Hess 1951). Occasional analyses from ankaramites plot in the field of diopside, and some phenocrysts, microphenocrysts and groundmass crystals, from trachytes and phonolites are richer in hedenbergite. These are more sodic salites. Analyses of the green cores found within some pyroxene phenocrysts show a continuation of the trend into ferrosalite: one of these analyses just crosses the limit (Ca45MG25Fe30) given by Wilkinson (1956) for common clinopyroxenes from an alkaline olivine basalt magma. Analyses of the green cores are explained in detail in Part F.

A limited increase in acmite along with hedenbergite, on differentiation, can be seen in the salitic pyroxenes as plotted in fig. 50A. Again, a strongly diopsidic group forming from the anharamites is followed by the bulk of the analyses in a group, from anItarami-ben, ba==.14)-07 4raahy13-ar=1.7.„ trachyandesites, and some phonolites. At the end of the sequence, including pyroxenes from the remaining phonolites and a trachyte, the crystallisation trend spreads out between two limits: the one towards acmite, with little or no increase in hedenbergite, and the other towards hedenbergite with only a limited increase in acmite. One crystal from a phonolite (PS41) shows the extension of the former, and analyses from the trachyte, MA4A, is an example of the latter. The trend towards hedenbergite can be further seen when analyses of the green cores are included - 64 -

(fig. 50B). Analyses of Kunitz (Kl. K2), which appear to be exceptionally low in alkalis have been disregarded.

The analyses of the aegirines represent a continuation of the trend towards acmite although no pyroxene has been found with 20-40c, c. A considerable spread from 44-80;' Ac is observed in pyroxenes from the nepheline syenite boulder, the chemical determination falling approximately in the middle of the range. The other two aegirines contain 80 Ac (fig. 50B). All the analyses tend to be positioned towards the acmite- diopside join rather than acmite-hedenbergite..

A closer examination of the pyroxene microprobe analyses from PS69 reveals the existence of two distinct aegirines. Optically this is not apparent. They are characterised mainly by their titanium content and are here named high - Ti and low - Ti aegirines. All other oxides also vary systematically: TiO Al 0 Fe 0 (total iron), Na 0 and to a lesser extent 2' 2 5' 2 3 2 SiO 2 are increased in the high-Ti aegirines and Mg0, Mn0 and Ca0 are increased in the low - Ti aegirines.

On comparison of the aegirines with others of similar soda content (eg Yagi 1953, Tyler and King 1967), the amount of total iron as Fe2O from the microprobe analyses, and 3 Fe20 3 from the chemical analysis, appears low. This is particularly apparent in the high - Ti varieties of PS69 and PS84, and is reflected in an excess of Na over total Fe (or Na over Fe3+) in the structural formula. Clearly calculation of the amount of the end-member acmite in these pyroxenes is not governed by Na, as is usual, but by Fe3+. It is for this reason that the calculations of Ac, Di and Hd have to be made in the reverse order. In the low - Ti aegirines titanium may be incorporated as CaTiA1206, the high charge of the titanium being balanced by substitution of Al in the Z cites in the normal way: but, occasionally insufficient Al is present. This is more marked in the high - Ti aegirines, where both Ca and Al appear to be present in insufficient quantities to accommodate all the Ti. In these pyroxenes the charge of the Ti must be balanced by the excess of Na, forming in terms of -65-

end-member molecules, a NaTi pyroxene. If the Ti is quadriValont this will still require some substitution of Al in the Z sites to maintain the charge balance.

Discussion and com.parison with pyroxenes from other provinces.

The Tenerife salites follow a similar crystallisation course to salites from other alkalic provinces (fig. 51) (eg. Gough Island, Le Maitre 1962. Black Jack Sill,Wilkinson 1957. Garbh ilean Sill,Murray 1954. Co. Limerick, Ashby 1946). The limited trend is towards replacement of diopside by heden- bergito with little or no change in the calcium content. This is in contrast to thoTeiTtLc clinopyroxenes where the calcium content is generally lower throughout the series from diopside to hedenbergite, and the initial trend is towards a depletion in calcium (eg. Skaergaard Intrusion, Brown and Vincent 1963. Bushveld Intrusion, Atkins 1969).

The aegirines are enriched in diopside relative to those from Sakhalin (magi 1953). However, analyses of some aogirines from Itapirapua, Brazil (Gomes et al. 1970) and Uganda (Tyler and King 1967) are also more enriched in diopside (fig. 52), and some aegirines from Cantal (Varet 1969) have a comparable diopside/hedenbergite ratio to those from Tenerife. Aegirine is only developed in the groundmass of some of the Tenerife phonolites. In the groundmass of others the pyroxene is a sodic saute. Similar features arc found in Cantal, which Veret (1969) relates to the peralkalinity of the rock: only the peralkaline phonolites contained aegirine.

The factors governing the crystallisation of minerals within a volcanic suite can be divided, and related to the formation of the phenocrysts and groundmass respectively. It is generally accepted that phenocrystal minerals will form under plutonic or sub-plutonic conditions at a higher pressure and probably temperature than those of the groundmass. The latter will crystallise at, or necr, atmospheric pressure and falling temperature as the lava or shallow intrusion solidifies. The composition and crystallisation trends of the same mineral, -66-

as phenocrysts, and within the groundmass, may vary considerably and, in these pyroxenes, this is reflected in the appearance of aegirine only in the groundmass of the phonolites. The usual absence of aegirine as a phenocryst mineral in volcanic rocks has been explained by Bailey (1969). He determined the stability of acmite in the presence of water, and found that at low pressures (ie. volcanic conditions) acmite melts at temperatures below that of other major constituents in phonolites. Thus, the mineral will only form at lower temperatures during the crystallisation of the groundmass. Tyler and King (1967) infer that the temperature of crystallisation is a major factor in determining the composition of the pyroxene in rocks from Uganda, and suggest that the diopsidic phenocrysts correspond to pre-extrusive and the acgirine groundmass to post-extrusive periods of crystallisation. A high temperature of crystallisation and the presence of sufficient calcium and magnesium must be inferred from the occurrence of pyroxene of salitic composition in the peralhalino glassy phonolites of the Recent Salic Series. The salitic microphcnocrysts and aegirine groundmass in PS41 (table 14) may be similarly related to the fall in temperature during crystallisation.

The change in composition of a clinopyroxene with differentiation can be towards enrichment in ferrous iron (hedenborgibe) or soda and ferric iron (acmite). Tholciitic clinopyroxenes commonly show extreme enrichment in hedenbergite with little or no increase in acmite, whereas pyroxenes in later differentiates of alkalic magmas can be enriched in the acmite or hedenbergite molecules (Aoki 1964). An increase in acmite, however, cannot take place until the liquid has built up a + 2+ sufficient concentration of Na and Fe3+ to replace Ca and Fc2+ in the pyroxene. Lc Maitre (1962) advances an hypothesis to explain this: the Fe203/Fe0 ratio in alkali basalts is higher than in tholciites and after abundant crystallisation of olivine much of the iron will be as Fe3+. Limited enrichment in hedenbergite mey however, occur. In later stages of differentiation, when the magma is sufficiently enriched in Na+, formation of a pyroxene rich in acmite will then be possible. -67-

2+ 2+ The limited Fig /Fe variation in pyroxenes from the Square 2+ Top Intrusion (Wilkinson 1966) is thought to be due to Fe in successive liquids becoming oxidised, and the short trend shown by these pyroxenes is parallel to the acmite-diopside join (fig. 52). In the Tenerife pyroxenes enrichment in acmite will be chemically most favourable in the peralkaline phonolites. Results of experimental studies on synthetic systems show that acmite crystallises only from a peralkaline liquid containing excess sodium silicate (ns)(Bailey 1969).

It is probable that in the Tenerife magmas the increase in hedenbergite in the pyroxene phenocrysts was limited by the high Fe 203/Fe0 ratio within the magma in the same way as visualised by Le Maitre for Gough Island and by Wilkinson for the Square Top Intrusion. After eliminating rocks noticeably oxidised by secondary processes, an overall higher Fe203/Fe0 ratio is present in Tenerife than on Gough Island. This may be due to crystallisation at a moderately high, or increasing partial pressure of oxygen. Aoki (1964) and Yagi (1966) have deduced that higher partial pressures of oxygen will favour the solid solution of acmite in pyroxenes. The Fe203/Fe0 ratio however is not necessarily dependent on the oxygen partial pressure. Increase of alkalis in the magma can have a similar effect on the ratio (Carmichael and Nicholls 1967). The enrichment of the aegirines in diopside at the expense of hedenbergite can likewise be explained by the highly oxidised state of the iron. Providing there is always a diopsidic component which can be incroporated into the pyroxene, the acmite-hedenbergite join will never be reached in pyroxenes crystallising from successively differentiated magmas. The presence of the diopside component is indicated by the salitic nature of the phenocrysts from the peralkaline glassy phonolites in the Recent Salle Series.

However, the green cores which are found in some pyroxene phenocrysts are further enriched in hedenbergite (see part F 2+ and fig. 50B), showing that under certain conditions more Fe was available for incorporation into the pyroxene. Phenocrysts containing these cores are associated with partly resorbed kaersutite, and the cores are thought to have formed at depth, -68-

during a similar stage in the crystallisation and fractionation history of the magma as the kaersutite.

The pyroxenes from the pyroxenite xenoliths (Barley et al. 1970) are similar in composition to phenocrysts from the basic roc7:zs (fig. 52) (table 23). Analyses 1P from a banded olivine-pyroxene xenolith is particularly close in composition to the cores of pyroxene phenocrysts in the ankaramites, indicating the probable genetic connection between the cumulate pyroxenes in the ankaramites and those in the pyroxenite xenoliths. Analysis 7P is of a green core, associated with kaersutite. The analysis plots along the extension towards hedenbergite shown by the other green cores.

E. X-Ray Diffraction Studies

Cell parameters have been determined for 11 salitic pyroxenes and one aegirine (table 24). Experimental techniques are explained in Appendix 1. All except two of the salites have been analysed chemically. The reflections used in refining the parameters, in increasing 24, were for the salites: 020, 021, 220, 221, 310, 311, 002, 221, 311, 330, 331, 421, 041, 150, 531, and for the aegirine: 220, 221, 310, 131, 002, 221, 331, 421, 150, 531, 440. Additional reflections were also used, when of sufficient intensity for accurate measurement. When calculated from the refined parameters almost all reflections had a difference of less than 0.04° 24 from the measured value; the remaining few gave a difference of less than 0.07° 29. It was noticed that the larger errors occurred in pyroxenes from the basic rocks, which are considerably more zoned than those of the later differentiates. The larger error may be a result of the zoning. The trace for MA7 was measured on three separate occasions and three sets of parameters refined. The second and third set were within the standard errors calculated by the program for the initial set of parameters.

Parameters obtained for the salites from the different -69-

rock types are similar. There is a tendency, however, for a, b, p, and a sin p to increase and for c to decrease through the series from ankaramites to phonolites, but almost the complete range of values is present within the pyroxenes from each rock type. The limited nature of the range compares with that of the chemical analyses.

Differences in the parameters between each specimen may be due to the change in composition of the pyroxene along the diopside-hedenbergite join, or because of differences in the concentration of the minor constituents, Na, Al, Ti, Mn and Fe3+ in the pyroxenes (table 13). The analyses are plotted on 2+ 2+ 2+ a Ca - Mg - Fe diagram in fig. 53 along with corresponding values for b and a sin p. According to Brown (1960) and Viswanathan (1966), b and a sin 0 should increase with increasing 2+ Mg - Fe substitution, and data for synthetic pyroxenes on diopside hedenbergite (Rustein and Yund 1969) shows that a 2+ 2+ and b increase with Fe substituting for Mg whereas c remains approximately constant. Over the limited range shown by the specimens very little change will be expected by an increase in Ca2+, and thus variation in the parameters should be 2+ primarily due to Fe - Mg2+ substitution, if the effect of minor elements is negligible. Clearly this is not so, as no uniform variation appears in fig. 53; but, there is a tendency for the specimens with a higher b and a sin p to contain more 2+ Fe . A similar slight increase in a with increase in Fe2+. is apparent from the data. Thus, the variation caused by 2+ 2+ substitution of the type Mg - Fe must be marked by the effect of the variation in concentration of minor elements.

The observed parameters are similar to those of Lewis (1967), and the chemical analyses of Lewis and in the present study are similar with respect to both major and minor elements; but, the Tenerife pyroxenes contain an overall slightly higher proportion of Fe203 than those of Lt. Vincent and Gough Island and more TiO2 than those of St. Vincent. However, the general conclusions reached by Lewis should be applicable to the Tenerife pyroxenes, ie. an increase in Al3+ gives a reduction -70-

in the b and a sin p parameter and an increase in c and the 4+ presence of Ti and Fe3+ may add to the effects of A13+. In the present samples the specimens with high A13+ show a reduction in a, b and a sin p and an increase in c, when compared with the specimens containing lower concentrations of the element. Specimen 7 (P7) with considerably more Ti than any others shows an apparent reduction in b when it is taken into account that it is the most Fe2+- rich specimen. The very low value of b in 5 (P191) can probably be attributed 4+ to Ti and Al3+, as it contains a higher proportion of these elements than in any other specimen, except for the titanium in 7.

Lewis observed that the St. Vincent pyroxenes contain more Fe3+ than those of the Skaergaard Intrusion (Brown 1960), andsuggostedthat this might be a contributing factor towards a decrease in b, The Tenerife specimens contain more Fe3+ than those of St. Vincent, and have lower b parameters in 2+ specimens of the same Ca - Mg - Fe composition. This may be 4+ attributed to the higher Fe3+ content; but as Ti is also higher in the Tenerife pyroxenes the direct effect of Fe3+ on the reduction of b values cannot be assessed. Experimental work of Sakata (1957), Coleman (1962) and Onuma et al. (1968) show that substitution of octahedral Ti, Al and Fe3+ and tetrahedral Al into diopside produce a decrease in b and a sin p and an increase in a and c (the magnitude of the variations caused by individual elements differs considerably but this appears to be the overall effect). These are the general modifications present in the cell parameters of the Tenerife pyroxenes when compared with those of other pyroxenes of similar 2+ Ca - Mg - Fe content, but containing less Ti, fa and Fe3+ (eg Brown 1960, Viswanathan 1966).

The trace for the aegirine PS69 was compared directly with those of synthetic pyroxenes made by Nolan (1969). Close correlation was obtained with pyroxenes high in acmite (Ac 70-80). From the aegirine analysis and curves of Nolan (1969), the expected b unit cell parameter is 8.840. The observed value is, however, less and will be a reflection of the presence of minor - 71 -

elements such as Ti and Al. These seem to cause a reduction of the b parameter as in the diopsidic pyroxenes.

F. Zoning in the pyroxenes

The -oresence of zoning has been mentioned in part B (General chcracteristics of the pyroxenes) where brief descriptions have been given of each type as it occurs in the rocks. Zoning is most widespread in the pyroxenes from the ankaramites and alkali basalts and it is from these rock types that most individual examples, described below, have been taken. Crystals from the trachybasalts, trachyandesites, trachytes and phonolites also exhibit some features of the zoning found in the more basic rocks, but it is in general much less prominent or absent. In the phonolite intrusions from the Ancient Series, however, pyroxene Dhenocrysts are frequently zoned but only the type here called normal zoning, and the zoning caused by pyroxene crystals containing green cores, is present.

Until the development of the electron microprobe, analysis of different components within a zoned mineral was very difficult: complete physical separation of the zones on the large scale necessary for analysis, unless there is a considerable difference in their chemical compositions, is alhost impossible. However Yagi (1953) has separated and analysed an aegirine- augite core and aegirine rim from a syenite, and Yagi (1966) has carried out the same with a pyroxene containing a soda- augite core and aegirine-augite rim. Other workers on pyroxenes fromalkalic magmas have separated zoned pyroxene into Fe-rich and Mg-rich fractions (eg. Wilkinson 1957, Wilkinson 1966, McBirney and Aoki 1968). In each case the separate analyses of the zoned crystals fall on the general trend of crystallisation of the pyroxenes determined by the bulk analysis of the mineral Iron the different rock types.

The microprobe analyses made here (tables 15-22) show a variation with zoning in both major and minor components of the pyroxene molecule. Othert but not always similar, results -72-

have been obtained by Preston (1966), Smith and Carmichael (1969), Strong (1969), Hargraves et al. (1970. Lunar Samples) Game (1970), Borley et al. (1970 In preparation) and Frisch and Schmincke (1970): the two latter reports are important here because they refer to pyroxenes from Tenerife and Gran Canaria, respectively.

Seven types of zoning have been recognised in the pyroxenes from Tenerife and are called normal, reversed, large scale oscillatory, minute scale oscillatory, irregular, hourglass, and the zoning caused by pyroxenes containing green cores. The latter is essentially reversed zoning but is described separately below as its origin is probably different from the other reversed zoning. Wilkinson (1957) divided the zoning present in pyroxenes from a teschenite sill according to the variation in 2Vy. The relationships he obtained are as follows: 2V(core) > 2V(margin)(Normal zoning) 2V(core) < 2V(margin)(Reversed zoning), repetition of certain 2V values (Irregular or Oscillatory zoning). With the addition of hourglass zoning these relationships can be applied directly to the pyroxenes from the Tenerife basic rocks, and consistent results are obtained which can be related to the same chemical changes (tables 6-8). However, it is preferable that the term "normal zoning" should refer to the zoning found most frequently and expected within crystals forming from an igneous melt under usual conditions, taking into account experimental results:cg., in the case of pyroxenes from the diopside-hedenbergite series, the outer margin of the crystal should be enriched in hedenbergite, and pyroxenes crystallising in the acmite-diopside- hedenbergite series should have an outer margin enriched in acmite. These two, examples apply to the Tenerife pyroxenes from the basic rocks and phonolitos respectively, and in the former a decrease in 2Vy occurs from the core to margin, whereas the latter produces an increase. Thus a strict classification on the basis of 2V can be misleading.

In the classification given below an attempt has been made to make it applicable to pyroxenes in general. The uniform -73- features of this zoning as related to Tenerife are given in brackets, and may not necessarily occur in zoned pyroxenes from other suites.

1. Normal zoning. The zoning is concentric and two or more well defined zones or a gradation are present, the outer zones being enriched relative to the core in a pyroxene component commonly found concentrated in later differentiates of the series: eg. in zoned pyroxenes from Sakhalin (Magi 1953) the margin contains a higher proportion of aegirine than the core (The outer margin is a darker colour than the core and 2V(core) > 2V(margin) in pyroxenes from the basic rocks, but in pyroxenes from the phonolites 2V(core) < 2V(margin).

2. Reversed zoning: The complete opposite 1. is present. (This occurs in pyroxenes with the green cores often found in alkali basalts and other rock types, although 2V(core) > 2V(rim). Apart from this it is very uncommon).

3. Large Scale Oscillatory zoning: The zoning is concentric with a repetition of bands with alternating normal and reversed zoning relative to each other, This occurs on a relatively large scale and a small finite number of bands can be counted (A repetition in shades of purple is present in pyroxenes from the basic rocks).

4. Minute Scale Oscillatory zoning: An infinite number of very narrow bands form, usually, a concentric pattern (In plane polarised light this zoning is often not visible, but in crossed nicols near, and at the extinction position changes in polarisation colours are observed. It is usually superimposed on other types of zoning following their general pattern).

5. Irregular zoning: Isolated and irregularly shaped patches of the crystal have different compositions. (In the basic roci:s areas of no crystal have different shades of purple and the darker purple corresponds to a lower 2Vy). - 74 -

6. Hourglass zoning: The actual hourglass part has a different composition from the rest of the crystal. The junction between the zones is well defined: (The hourglass part has a paler purple colour and higher 2Vy).

(7. Zoning produced by the green cores: The pyroxene crystal contains a green or greenish buff core which grades outwards into a pale purple rim 2V(core) > 2V(margin))

More than one of these types can be present in a crystal and it is common in the ankaramites and alkali basalts for an oscillatory or irregularly zoned crystal to contain a thin outer rim of normal zoning.

Preliminary to the carrying out of microprobe analyses on the different parts of zoned crystals, wavelength scans were made on a few selected zoned pyroxenes in order to determine the elements present, and the nature of the variations which might be expected. Results of this work and the scans obtained are nut reproduced here, as virtually all of the qualitative and semi-quantitative data obtained is rendered superfluous by the presentation of the analyses. The results from the analyses arc in agreement with that expected from the scans.

Normal zoning.

This is the most common type of zoning. 11 difference in both optical and chemical properties exists between the core and margin of the crystal. Frequently in the basic rocks a pale purple pyroxene phenocryst is surrounded partly or completely by a darker purple rim of varying thickness. The core of the crystal may have a separate pattern of zoning (fig. 1+2), but the change in colour is most marked at the rim: the depth of colour at the rim is similar to that of the groundmass pyroxenes. This rim has a lower 2Vy (table 6) and higher extinction angle (Z y) (table 12) than the core of the crystal. Its thickness varies from considerably less than a tenth of the diameter of the crystal to almost a third, but is usually very narrow in - 75 -

comparison with the bulk of the crystal. As stated in part B, inclusions of opaques, similar to those in the groundmass, are sometimes found within these rims, but not in the rest of the crystal.

Normal zoning in pyroxenes from the phonolites is only rarely seen by a small change in the green colour across the crystal; commonly only a small variation in the extinction position or birefringence is observed and a sharp break between the zones is absent. 2Vy increases at the margin of the crystal (table 9). GD4 and TC18312).

Analyses of crystals exhibiting normal zoning are found in tables 15 (all analyses), 17 (MA3(9-10)), 19(18-66(6-7)), and 22(PS27(1-2)). In addition, in table 16, MA17(5) is the outer darker zone of a crystal which has oscillatory zoning, and in table 17, NA3 (4 and 6) and MA3 (5 and 7) are analyses made on two successively darker outer zones in an irregularly zoned crystal, with analyses MA3 (1 and 2) being made on the core.

The analyses show that in the pyroxenes from the basic rocks, the outer rim contains more Ti, Al and Fe and less Mg and Si than the core. In MA3 (table 17) this is illustrated even further with an initial outer zone (MA3 (4 and 6)), containing more Ti, Al and Fe and less Mg and Si than the core (MA3 (1 and 2)), followed by another very thin rim (MA3 (5 and 7)), darker in colour and surrounding the crystal. This rim contains even more Ti, Al and Fe and less Mg and Si than the core. Analysis of a groundmass crystal (MA3 (11)) is similar to that of the outermost zone.

The zoned crystal from the phonolite (PS27 (1 and 2)) contains only a small variation in Si, Al and Ti but there is more Fe, En and Na and less Mg and Ca in the outer zone than in the core. The change in composition from the inner to outer zone follows the trends of crystallisation for the whole suite with respect to the variation in diopside, hedenbergite and acmite (fig. 54). An increase in hedenbergite with no increase 76 -

in acmite takes place in pyroxenes from the basic rocks; whereas the pyroxene from the phonolite shows an increase in acmite with constant hedenbergite: The plot on Wo - En - Fs (fig. 54) is rather misleading as it shows an apparent increase in Wo as well as Hd from the inner to outer zone in the pyroxenes from the basic rocks. This is because replacement of Mg2+ 2+ by Fe in the pyroxene structure is net the only substitution taking place: the decrease in P7g2± is always greater than 2+ the increase in Fe . The amount of octahedrally coordinated A13+ remains approximately constant in the inner and outer zones; ie. the proportion of Tschermak's molecule remains 4+ constant. Thus the increrse in Al3+ and Ti in the outer zone 4+ will be due to more Ti substituting in the Y position which necessitates more A13+ substituting in the Z position for Si4+ in order to maintain the charge balance. In end-member pyroxenes this means an increase in CaTiA1206 whereas CaAl2Si06 remains constant; and overall, an increase in CaTiA1206 and CaFc6i r 2 O takes place in the outer zone at the expense of CaMgSi206, all other component remaining constant. However, the purple colour of titanaugites and titansalites may be due to TO+ (Burns 1970), and thus, as a darker colour is present at the rim of the crystal a higher proportion of TO+ is indicated. This will still require more Al3+ in the outer zone but less than if all the Ti is quadrivalent. If a considerable proportion of Ti is trivalent then correspondingly more Fe ma:: be oxidised to Fe3+ to balance the charges, but this cannot be determined from the microprobe results.

Loam traverses (ie. movement of the specimen slowly under the electron beam) to selected elements have been made on MA19 (fig. 41, table 15) across the junction of the inner and outer zones. Results show that the junction between the zones is sharp, corresponding to the colour change observed in thin section. An increase in Fe, Ti, Al and Ca, and a decrease in Mg and Si is present in the outer zone. Oscillatory zoning on a small scale is also observed in the outer darker purple zone. Similar changes with the oscillations are recorded for Fe, Ti and Al, which show variations in the - 77 - opposite direction to Mg and Si. In thin section, under crossed nicols, it can be seen that minute scale oscillatery zoning is present in the outer zone, superimposed on a less well defined coarser oscillatery zoning. It is the latter and not the minute scale oscillatery zoning which has been picked up during the traverses.

As this zoning is concentric it is obvious that initial crystallisation of the core produced the bulk of the crystal. After this, in the case of the ankaramites and semi-cumulate alkali basalts, accumulation of the phenocrysts occurred. A change in either the physical conditions or chemical nature of the crystal/liquid mixture must have ensued before crystallisation of the outer zone or zones. In MA19, other ankaramites and some allzali basalts, pyroxene phenocrysts with a narrow well-defined outer zone of darker purple predominate, the outer zone occasionally including small opaque anhedra similar to that of the groundmass. The analysis of the outer zone in MA3 corresponds closely to that of a groundmass pyroxene. Thus it is probable that the thin outer zone formed at approximately the same time as the groundmass crystals, i.e. during or after extrusion or during cooling after emplacement in the case of intrusion; and thus at a lower temperature and pressure than the rest of the phenocryst. More Fe was available for incorporation in the pyroxene and apparently there was also more Ti and Al. The increase in Al may have been due to a decrease in the available silica in the magma from which the groundmass crystallised. laishiro (1960), Verhoogan (1962) and Le Bas (1962) show that it is the silica content of a liquid which appears to be the controlling influence on the incorporation of Ti and Al into the pyroxene structure. But it is possible, under certain circumstances, for the concentration of titania to have a similar effect. Yagi and Onuma (1967) state that with increase in pressure the amount of CaTiA1206 in diopside decreases. Thus in the cores of pyroxene phenocrysts, the amount of titanium substitution may be limited by the prevailing pressure. If the temperature of formation of pyroxene and - 78 - olivine phenocrysts is high, crystallisation of an opaque phase will be inhibited; there appears to be little or no early formed opaque phase in the ankaramites, and cumulate olivine, and the cores of pyroxene phenocrysts are devoid of opaque inclusions. Thus, the amount of titania in the magma may increase with separation of olivine and pyroxene phenocrysts. Further evidence is provided in that the cores of pyroxenes forming from non-cumulate alkali basalts are richer in Ti than those from the ankaramites. More Ti will be available which, as well ns entering the opaque phase, may cause an increase in the amount crystallising in the outer zone of normal zoned crystals.

The crystals which have more than one rim of normal zoning (eg. nA3) will have a more complex history of formation, and crystallisation of the outer zones will take place with conditions always changing in the same direction. Crystallisa- tion of one zone may take place before extrusion, followed by a further outer zone richer in Ti, Al and Fe, after extrusion.

Phenocrysts from the phonolite PS27 do not exhibit a well defined colour change across the crystal with zoning: where a colour change is visible it is gradual. The specimen is from a comparatively large intrusion, and thus zoning could be produced by continuous crystallisation of the pyroxene during emplacement and cooling, allowing the separation of material successively richer in acmite.

Reversed Zoning

In the pyroxenes from the basic rocks more Fe, Ti and Al and less Ng and Si in the core relative to the rim, along with a darl-.er purple colour will be expected in a crystal showing reversed zoning. There should be an increase in 2Vy from core to margin. Pyroxenes frcm the later differentiates, however, will contain more Fe and Na, and less Mg and Ca in the core, and a decrease in 2Vy from core to margin will be observed. Three optic axial angle measurements on pyroxenes frcm phonolites show this reversal in zoning (table 9), but two of these are - 79 - crystals with green cores and a pale purple rim, characteristic of some pyroxenes in the alkali basalts, are described separately below, along with the other green cores: the remaining measurement TC126R, is within experimental error. One example from an alkali basalt/trachybasalt (MA22(table 6)) has a slightly higher 2Vy and correspondingly paler colour at the margin of the crystal This may be attributable to a reversal in zoning but, again, the difference between zones is very small.

Two analyses have been made on a pyroxene crystal from a phonolite in the Upper Canadas Series (table 22. MA28 (1-2)) which shows a small reversal in zoning. The crystal has a uniform green colour, but small variations are present in the extinction position from core.to rim. There is more Ti, Al, Fe and Ha, and less Si and Mg, and slightly less Ca in the core than in the remainder of the crystal. The variation in the end-member pyroxene components are shown in fig..54 along with the analyses made on the cores of two other unzoned phenocrysts from the same specimen (table 14. MA28 (1 and 2)). The other phenocrysts plot nearest the analyses of the outer part of the zoned phenocryst; thus, it is the core which is the anomoly. It is richer in acmite relative to the margin.

No general conclusions can be drawn regarding the crystallisation of pyroxenes in the phonolites from just one example of reversed zoning, but a few other phenocrysts in the same specimen show a variation in the extinction position across the crystal, which may be similarly interpreted. The analysis of the rock shows it to be slightly peralkaline Na K/Al = 1.01, but the pyroxene is diopside rather than acmitic; thus crystallisation will have taken place at an overall high temperature. The core of the crystal may have formed at a slightly higher partial pressure of oxygen, favouring the crystallisation of a pyroxene richer in acmite (Magi 1966).

?'ell developed examples of reversed zoning, with darker purple cores, have not been found in pyroxenes from the basic rocks. However,.theoretically an extension of the large scale -8o-

oscillatory zoning (see below) is possible, where crystallisation of one zone high in Fe, Ti and Al takes place, followed by one other zone, forming under different pressure and temperature conditions, containing lower concentrations of the elements. But, such a crystal on reaching the surface would still be rimmed by normal zoned material.

Large Scale Oscillatory zoning.

In this type of zoning "large scale" has a purely relative meaning in order to distinguish this type from the minute scale oscillatory zoning: the zoning is still on a microscopic scale. It occurs mainly in phenocrysts from the ankaramites but occasional examples can be found in alkali basalts and other rock types. In the ankaramites this zoning is present in the cores of some normal zoned crystals and perfect examples have bands of varying shades of purple concentrically arranged around the centre of the crystal; but, more usually the shape is far less uniform and oscillatory zoning becomes irregular. The change in colour and composition between the zones can be well defined or gradual, and minute scale oscillatory zoning may be superimposed on the larger scale type.

Table 16 contains four analyses (MA17(1-4)) made on the core of a phenocryst with oscillatory zoning. MA17(5) is the outer darker purple zone and MA17 (6-7) are analyses of groundmass crystals. Beam traverses for selected elements were made along the straight line joining the analysed points (fig. 42). As in normal zoning the darker purple zones (MA17 (2 and 4)) contain more Ti, Al and Fe, and less Mg and Si than the paler coloured areas (MA17 (1 and 3)). The outer zone (MA17(5)) shows only a further small increase in Fe and Ti, and decrease in Si and Ng, when compared with the rest of the crystal. Al is lower in this outer rim. The tendency for increase in Fe, Ti and Al and decrease in Mg and Si in the groundmass crystals characteristic with a late formed outer rim, is not apparent in this specimen. This may indicate that conditions governing the crystallisation of the groundmass were nearer - 81 -

that of the phenocrysts. The traces of the beam traverses show in general the same compatibility and incompatibility of the elements as the analyses. In fact, the increase in Fe, Ti and Al and decrease in Mg and Si in the areas with a darker purple colour is characteristic of all the types of zoning. As in the normal zoning, when the increases occur, they are Fe2+/3+ A13+ in the Z rites, Ti44-/3+ in the Y rites and in the Y sites at the expense of Si4+ and Mg21-. If the Ti is trivalent then to maintain charge balance the increase in Fe may be in the ferric ion, as in the normal zoning.

It is thought that crystallisation of the bulk of each pyroxene and olivine crystal took place in the magma chamber prior to accumulation. Segregation of olivine and pyroxene phenocrysts occurred to form the monomineralic xenoliths - the minerals may not have crystallised at the same time - but in all the ankaramites both minerals coexist as phenocrysts, indicating that at least during part of their crystallisation history they formed and accumulated simultaneously. It is, however, strange that whereas the core of the pyroxene is extensively zoned the olivine is not; but the substitutions that can take place in pyroxenes are much more varied than in olivine, and pyroxenes are thus probably sensitive to small changes in the pressure and temperature conditions under which the minerals were crystallising; the olivines being only noticeably affected by major variations in these factors. The variation in pressure and temperature necessary for the formation of a zone of slightly differing composition may be caused by movement of the crystal in the magma. A small decrease in temperature will allow an increase in the CaTiA1206 components at the expense of diopside - The liquidus of the systems CaNgSi206 CaTiA1206 (magi and Onuma 1967) and CaMgSi206 CaFeSi206 (Schairer and Yoder 1962) both decrease with increase 2+ in Ti, Al and Fe - and an increase in pressure will tend to limit the incorporation of more CaTiA1206 (Magi and Onuma 1967).

Oscillations in the zoning are observed in the trace across the outer zone of MA19 (fig. 41) and in the trace made -82-

on the outer pale purple zone of a crystal with a green core (fig. 46). As with the major oscillatory zoning described above Fe, Ti and Al increase together and in the opposite direction to Mg and Si. Variations here must be due to changes in the pressure and/or temperature during final crystallisation at or near the surface. Variations are not likely to be great and thus the pyroxene must be very sensitive to small changes. Factors such as an irregular movement of the magma towards the surface may cause a sufficient change or pause for the crystallisation of a zone of slightly differing composition; or, if the outer zone had not formed on extrusion, the crystal may be subjected to varying temperature conditions during flow of the lava.

Minute scale oscillatory zoning

This zoning is moot easily recognised in thin sections of pyroxene phenocrysts which are almost at the extinction position (figs. 36, 38, and 44C), the junction between zones being diffuse, and an overall extinction of the crystal not being attained. It is, however, occasionally recognised in plane polarised light (fig. 44A enlarged area), when it is more distinct. Variation in the depth of colour in plane polarised light does not occur but a sharp line delimits each zone. On occasions zones are further defined by the presence of very small opaque anhedra (fig.44A enlarged area). The width of each zone varies considerably but it is always smaller, by several orders of magnitude, than the large scale oscillatory zoning. The zoning also appears to be more noticeable when sections are thicker than normal (i.e. feldspars show yellow- orange red birefringence colours). In crystals with normal zoning the oscillatory bands are often only prominent in the outer zone (fig. 38), but frequently a complete pattern of minute scale oscillatory zoning is superimposed on hourglass phenocrysts (fig. 36,44c and 55). The pattern of zoning follows the external shape of the phenocryst and, in the case of hourglass crystals, individual bands tend to pass from one part of the hourglass to the other with an abrupt change in -83-

direction. They form an acute angle at the junction between the hourglass and the remainder of the crystal.

The zoning may be caused by successive crystallisation of material varying slightly in composition on an extremely small scale, in the same way as the large scale oscillatory zoning; but, beam traverses made with the microprobe across the zoning give inconclusive results. Small variations were recorded for certain elements (eg. Al), but traverses made with the beam offset e(i.e. to determine any change in the background) gave similar traces. However, with such narrow zones, the electron beam may be too coarse to resolve the separate areas and, if present, differences in elemental concentrations will be small.

The occasional presence of opaque anhedra along the line between some of the narrow bands indicates that, even if no compositional variation is present, these anhedra were included or adsorbed onto the surface of the specimen as crystallisation took place. A pause in the crystallisation of the pyroxene may have occurred to allow this to happen. The sharp line visible will thus be a plane surface on which crystallisation was taking place but had temporarily ceased. Thus, crystallisation may have been intermittent or pulsating and not a continuous process. A sharp line delimiting the zones will be visible in the section only if the section is cut perpendicular to the surface. 3cctions cut at an acute angle to the surface will show a diffuse junction between zones in the same way that a twin plane appears diffuse in sections which cut it at low angles. Reflection and/or refraction of the light beam on the surface will cause light to pass through the specimen which is otherwise at extinction. The surface available for reflection and/or refraction will increase as the section thickness becomes greater, thereby making the zoning more conspicuous in thicker sections.

If the zoning is caused in this way then, strictly speaking, the phenomenon should not be referred to as "zoning". However, compositional differences may still be present and -84- each band is, in fact, a "zone", being distinct from the next.

Irregular zoning.

It is easy to visualise that a crystal, forming under similar conditions to the large scale oscillatory zoned varieties, may be broken during movement or partly resorbed by an increase in temperature. So that when more material crystallises and surrounds the fragment, an irregular pattern is produced. Many of the Dyroxene phenocrysts in the ankaramites and semi- cumulate alkali basalts are, at least in part, irregularly zoned. The darker purple colours correspond, as in the normal and large scale oscillatory zoning, to higher proportions of Fe, Ti and Al and less Mg and Si. However, different phenocrysts from the same specimen only occasionally have the same or similar patterns of zoning. Each crystal therefore has its own separate history of formation and possibly originated some distance from, what is now, its adjacent phenocryst.

/dialyses of an irregularly zoned crystal are given in table 17 (14A3 (1-8)). Analyses 4 and 6, and 5 and 7 have been discussed in the section on normal zoning, and are made on outer zones which have formed later than the core of the crystal. The true core (i.e. the part believed to have formed first) contains 1:.co Ti, Al, and Fe, and more Mg and Si (analyses and 2) than the remainder of the crystal. Numbers 3 and 8 were made on the irregular zoning element. These areas are of a slightly darker purple than the almost colourless core and surround patches containing groundmass material. The analyses correspond closely to 4 and 6, which have formed later and, presumably, at a lower temperature and pressure than the core.

It is thought that the darker purple patches in the centre of 1•A3 formed at the same time as the initial outer zone (4 and 6), after the core was partially resorbed. This would then allow crystallisation to take place on areas "inside" the crystal which, in thin section, would appear to be in the centre. This stage of crystallisation did not completely fill the resorbed patches and the remaining "empty holes" were later filled during crystallisation of the groundmass. - 85 -

Many other crystals in this and other ankaramites contain patches of groundmass crystals surrounded by darker purple areas of pyroxene which are either partly or completely enclosed within the core of the phenocryst. This can also be explained by partial resorption of the phenocryst. Resorption appears to have taken place preferentially on certain faces or at areas of weakness (eg. where cleavages or partings intersect).

Hourglass zoning

Hourglass zoning is common in pyroxene phenocrysts from many alkali basalts (fig. 36, 37, 44 and 45), and several trachybasalts and trachyandesites. It is almost completely absent in phenocrysts from the ankaramites, semi-cumulate alkali basalts and phonolites. Variations in the depth of colour in plane polarised light occur, the hourglass part (1 in table 8) being the paler colour. Varying birefringence colours are also observed. In addition, hourglass structures are found frequently in the groundmass pyroxenes from ankaramites and alkali basalts (fig. 33). It is common for hourglass phenocrysts to have a completely concentric pattern of minute scale oscillatory zoning superimposed on them, the individual bands passing from one part of the hourglass to the next (fig.55). In several sections the two hourglass parts are joined (fig. 44B), but in others they are not. Thus, it is probable that geometrically the hourglass is made up of twc pyramids or cones, one inverted on top of the other, joined at their apices. Inverted pyramids are indicated instead of cones, because presumed basal sections do not show a rounded cross-section of the zoning. This is in agreement with the shape assumed for some hourglass pyroxenes by Scott (1914) and L7trong (1969) but not found by Preston (1966). The bases of the pyramids, however, are not rectangular; they appear to follow the external shape of the cross-section. The hourglass structure is best seen in sections cut parallel to the c-crystallographic axis (presuming the longest axis is c), and the bases of the pyramids are parallel to (001). Sections -86-

approximately parallel to (010) (fig. 44A), in twinned crystals have the twin plane dividing the hourglass into two parts. The junction between the two zones is fairly sharp but, occasionally, the hourglass is penetrated a small distance by the darker purple zone, following a band of minute scale oscillatory zoning.

Consistent results are obtained for optic axial angle (2VT is lower in the darker coloured areas) and extinction angle measurements (2, y is lower in the hourglass part)(tables 8 and 12). The same variations are observed in crystals exhibiting normal zoning.

Microprobe analyses have been made on four crystals with visible hourglass zoning (table 18 (1-12),(13-18), (20-21); table 19 (1-5)), and on a further one which is a basal section of an hourglass zone (table 18 (22-23)). The latter gives the appearance of having normal zoning, but the outer margin is much thicker than usual and most other phenocrysts in the same section are hourglass crystals. Some crystals in other specimens, which appear to be normally zoned may, in fact, be basal sections of hourglass crystals; but chemical variations in both types of zoning are similar.

The chemical variations are identical to those observed and described above for the normal, large scale oscillatory and irregular zoning, namely; more Fe, Ti and Al, and less Mg and Si are present in the darker purple zone, i.e. the actual hourglass part contains less Fe, Ti and Al and more Mg and Si than the remainder of the crystal. Moreover, where several analyses have been made on the hourglass part, they are almost identical (eg. table 18. PS118(1,2,7,8,9 and 10)), whereas analyses made on the darker zone vary slightly. As with the other types of zoning (normal, irregular and large scale oscillatory) octahedral A13+ remains fairly constant between zones, in comparison with the variations in tetrahedral A131- 4+ Fe2113+ and Si and octahedral Mg, and Ti3V4+. Consequently there is little variation in the CaAl2Si06 component, the predominant differences between the zones being caused by -87-

increases in the content of the titanium and iron bearing end- member pyroxenes at the expense of diopside.

Beam traverses for the major elements (except Ca) have been made across the junction of the hourglass crystal in fig. 44A (see fig. 44A). The same variations as in the microprobe analyses were observed, the junction between the zones being very sharp; the overall sloping trace for silicon is probably due to a general drift in the specimen current, and hence count-rate, during the traverse.

A summary of previous work on the hourglass structure in pyroxenes is given by Strong (1969), who successively eliminates all except one of Farquar's (1960) ten hypotheses as to the origin of the hourglass structure. The remaining theory Strong accepts mainly on the basis of analytical evidence. This evidence indicates that the different sectors will have formed at different times, impurities in the magma being adsorbed onto the surface impeding the growth of certain crystal faces. Changes in conditions of crystallisation then cause the adsorbed material to leave the surface allowing filling of the remaining sectors. Strong assumes that small skeletal hourglass crystals in the groundmass are formed as a result of rapid crystallisation from the magma, in the same way that olivines (Drover and Johnston, 1957) and apatites (Wyllie et al. 1962) can form.

Certain features of the pyroxenes observed in this present study seem to cast doubt on the theories of Strong, even though analytical results strongly support the two-fold development of the phenocrystal hourglass structure. The theory for the formation of the quench hourglass groundmass pyroxenes is accepted here only with certain reservation. Actual skeletal pyroxenes are very rare; the quench crystal is invariably completed, with deposition of infilling material in the form of pyroxene of slightly different composition (assumed from optical characteristics). This makes a perfect miniature of the hourglass phenocryst. Thus, the same factors may determine the growth of the smaller structure as well as the phenocrystal .88-

hourglass pyroxenes. The boundary between the zones; however, is usually curved, whereas in the well deVeloped phenocrysts definite angular relationships are established; but this may be an apparent feature due to relative size; The part which appears to have formed first in the quench crystals is the hourglass sector; drawings of Strong (fig; 1) indicate the reverse.

If the hourglass sector of a phenocryst formed initially and infilling of the remaining faces occurred at a later date, one would expect to see occasional examples which are incomplete leaving an hourglass "skeleton" or partly infilled zone. Strong makes no mention of these features, and an examination of the present specimens did not reveal incomplete hourglass phenocrysts. This infilling, however, may have taken place relatively early in the crystallisation history of the rock, although, if this were so, differences in the chemical composition of the zones would be less than that observed.

The chemical variation is identical and of similar magnitude to that shown by other types of zoning (eg. normal, large scale oscillatory and irregular) and is logical evidence, as recognised by Strong, for assuming that the hourglass port formed first, in the same way as the cores of phenocrysts from ankaramites. This was then followed, at a later date, by crystallisation of the remainder of the phenocryst equivalent to the outer darker purple rim of a normal zoned pyroxene. This is further shown in that the analyses of the hourglass sector (eg table 18, PS118 (1,2,7,8,9 and 10)) arc almost identical, whereas the remaining sectors tend to contain more Fc, Ti and Al and less Mg and Si (eg table 18. PS118 (5 and 6)) towards the margin of the crystal than nearer the core (eg table 18. PS118 (5 and 4)).

The minute scale oscillatory zoning seems to indicate that simultaneous growth of both zones took place. This concentric zoning appears to cross from one part of the hourglass structure to the next, with only angular changes in direction following the external morphology of the crystal. This would _89_

indicate that the zoning is a feature of the growth of the crystal, and the hypothesis given above concerning this zoning shows it to be a form of "growth rings", each "zone" representing a short pause in the crystallisation. But, it is strange if crystallisation of the hourglass sector took place first, that these "growth rings" should appear to completely surround all sectors.

Experimental work on the hourglass structure in silicates is being undertaken, according to Farquar (1960), but the present author is unaware of any published results. Hourglass structures, however can be found by crystallisation from aqueous solutions and several are mentioned by Buckley (1951). They can form by parallel growth of both zones with adsorption of impurities or air bubbles onto certain faces; but, the relative rates of growth are also upset.

In conclusion it seems that, whereas the evidence for the formation of the hourglass structure in pyroxenes studied by Strong (mainly from Comores Island) points towards non- simultaneous growth, the evidence from Tenerife pyroxenes is less substantial. In fact, if each band of minute scale oscillatory zoning is formed at the same time around the complete crystal, it seems difficult for the hourglass to form in the way suggested by Strong. He states that because chemical differences between sectors encompass more than one element, one cannot assume that the hourglass structure resulted from adsorption of only one ion on a particular face; but, it is surely possible that preferential adsorption and incorporation 4+ of ions such as Si4+ or Ti may cause an overall disequilibrium in the pyroxene. This will necessitate increased concentrations of ions of other elements to maintain charge balance or fill vacant sites in that sector.

One feature, which appears to have been overlooked, is the condition under which hourglass crystals preferentially form, since all zoned crystals are not of the hourglass variety. In Tenerife the ankaramites are devoid of hourglass phenocrysts but in some alkali basalts almost every phenocryst has an -90-

hourglass structure. In the latter rocks pyroxene is the predominant phenocrystal phase, followed by plagioclase, but there are only subordinate small olivine phenocrysts. Pyroxenes are almost always euhedral. It seems that in these rocks pyroxenes crystallised unhindered for a relatively long period in time.

Pyroxene phenocrysts containing green cores

These phenocrysts occur in several alkali basalts and in one phonolitic intrusion from the Ancient Series. They are found most frequently in the Ancient and Canadas Series. A core of green, yellow-green or greenish-buff is enclosed by a buff or pale purple rimof varyir4 thickness( figs. 12 and 46). Occasionally a further rim of normal zoning is developed. The shape of the core, on rare occasions, follows the external morphology of the crystal but, more usually it is rounded. Patches of green within a pyroxene crystal sometimes occur. The association of these crystals with kacrsutite has been mentioned in Section 2. Irregular patches of green within pale coloured pyroxene crystals are observed in some of the syenitic xenoliths: again there is an association of this with kaersutite. Optically 2Vy and Z y decrease from core to margin (tables 7 and 12), unless there is a further outer rim where Z y initially decreases and then increases with the normal zoning.

Hausen (1956) in some of his basaltic rocks describes zoned pyroxene phenocrysts containing green cores and assumes that they arc richer in soda: kaersutite is also present in the same rocks. Frisch and Schmincke (1970) have found a similar reversal in zoning in xenoliths from Gran Canaria, but the colour change is not apparent. Other green cores within pyroxene phenocrysts have been attributed to the presence of a chrome-diopside phase (eg. Huckenholtz 1966). Wavelength scans using the microprobe have been made on the present samples but chromium remained undetected.

Microprobe analyses of both zones from seven crystals, - 91 -

contained in three sections, are given in tables 20, 21 and 22. In each case there is more Fe and Na and less Mg and Ca in the green core than in the remainder of the crystal. The variations in Si, Ti and Al are not consistant, but a decrease in Si is always accompanied by an increase in Al. A more significant variation in octahedral Al occurs in this zoning than in other types, and in analyses of two outer zones all the Al has to be placed in the tetrahedral sites along with some Ti.

The main feature of this zoning is the increased amount of hedenbergite and to a lesser extent acmite in the core (fig. 56), although the relative hedenbergite and acmite contents of the cores vary considerably. This gives a reversal to that observed in the normal zoning. The overall increase in hedenbergite and acmite for PS10 reflects the phonolitic nature of the rock. Two analyses of groundmass crystals from MA8 are nearer in composition to the outer margins than the cores, with the exception of the most diopsidic pair of analyses. The core of the latter is a buff colour and not the green of other crystals. An analysis of a pyroxene surrounding a partially resorbed amphibole is also similar to that of the outer margins (table 21. MA8 (7)). Beam traverses across one crystal (fig. 46) show the same variation in chemistry as the analyses, with respect to Fe, Mg and Na: little variation in Ca is recorded. Ti and to a lesser extent Al are lower in the core but Si appears similar in both zones. A feature of these traces is the uniform concentration of all elements across the core, in comparison with the oscillatory zoning of the other parts. This may indicate uniform conditions during crystallisation of the core. Ls with other types, the junction between the zones appears sharp.

Frisch and Schmincke (1970) state that the reversal in zoning in pyroxenes from Gran Canaria may be due to increasing partial pressure of oxygen, producing more Mg in the outer rim, as shown experimentally in magnetite bearing assemblages from

the system Fe0 - MgO - SiO2. In the present study, however, -92-

the composition of the outer parts of the crystal is the same as that commonly found in the pyroxenes; it is the increase in Fe and Na at the core which produces the reversal in zoning. The association of these pyroxenes with partly or completely resorbed kaersutite indicates that the origin of these cores may, in some way, be connected with the amphibole. Kaersutite always appears as xenocrysts or megacrysts (Ridley 1970) in the alkali basalts and most other rocks, and is almost invariably partially or completely resorbed.

From the rounded shape of these green cores and their widely varying composition in individual specimens, it is thought that thoso cores are xenocrystal in the same way as the kaersutite. The kaersutite has become unstable producing usually a pyroxene and opaques, but the green cores have been partially resorbed by the magma. Varying stages of resorption will produce the rounded shape and chemical variation between different crystals. Resorption ceased with crystallisation of the normal pyroxene around the remaining core. As stated in part D., these cores indicate that during part of the history of crystallisation and fractionation of the Tenerife parent magma, conditions were such that formation of a pyroxeno richer in hodunbergite and to a certain extent, acmite, was favoured. -93-

3. AMPHIBOLE

Two amphiboles, one calciferous and the other alkali- rich have been found and are described here. The former is kaersutite which occurs as phenocrysts and xenocrysts in all the major rock types except the anknramites, trachytes and most phonolitcs. It is most abundant in the trachyandesitcs where, on occasions, it appears semi-cumulate, and is common in some alkali basalts, trachybasalts, and phonolite intrusions from the Ancient Series. Ridley (1970) describes and has analysed a knersutite mogacryst from the Anaga peninsula and Borley et al. (1970) gives a description and microprobe analyses of kaersutites from xenoliths. This amphibole has been called barkevikite, basaltic hornblende, or hornblende by other workers on Tenerife, an understandable error as kaersutite can only be positively identified by chemical analysis.

An alkali amphibole occurs in the groundmass of some phonolitos along with aegirine and aenigmatite. It has been suggested that this is katophoritic in composition by Smulikowski et al. (1946) and Ridley (1970). Microprobe analysis on one very small crystal from a phonolite intrusion shows it to be a magnesioarfedsonite. A foyaite (nepheline syenite) inclusion within a phonolite of Smulikowski ct al. (1946) is said to contain arfcdsonitc and Ibarrola and Viramonte (1967) describe nepheline syenite blocks containing eckermannite. The author described, in Section 2, two very fine-grained unidentified minerals occurring in small quantities. These may be other alkali amphiboles, and it is possible that detailed collection and examination of the peralknline phonolites and nepheline syenitc inclusions may reveal the presence of several other alkali amphiboles. The fine-grained nature of the phonolites makes, however, such a task extremely difficult, if not impossible.

A. KAERbliTIT2,.

General characteristics: The kaersutite crystals are always brown and are usually - 94 -

strongly pleochroic (a. pale yellowish brown, R. medium brown, y, dark (sometimes greenish) brown). When unaltered, crystals are euhedral to subhcdral, and occasionally simply twinned. In the presant thin sections crystals up to 5 mm.,in diameter are found, but Ridley (1970) has analysed a megacryst and Bravo (1955) has also found larger crystals of amphibole (presumably kaersutite).

Optically the mineral appears similar in all rock types. The only noticeable differences arc the degrees of corrosion and the relative abundance of the mineral. There is a tendency for the mineral to be a darker brown in the phonolites but a more reddish brown in other rock types. Marked colour changes show zoning in crystals from the phonolite intrusions in the Ancient Series. The extinction angle is always low (<10°) or approximately parallel to the cleavage, but Hausen (1956) o and Smulikowski et al. (1946) give values as high as 28 , and Smulikowski et al. (1946) give two optic axial angle measure- o o ments of 50 and 74 (2Va). The kaersutite almost always appears unstable in its present environment. The only specimens where it is not partially or completely corroded are PS92, PS93 (fine- grained trachybasnit/trachyandesite from Viejo. Recent Series), and PS119 (intrusive alkali basalt/trachybasalt). In PS9 and PS10, from the outer parts of an 8 metre Wide dyke, the kaersutite is also largely unaltered; but in PS11, from the same dyke, it is often enclosed by a single crystal of opaque oxide or the opaque pseudomorphs the amphibole. In other rocks the kaersutite shows all stages of corrosion from an initial mass of small opaques surrounding the amphibole, to a mass of opaques, pyroxene and a little feldspar completely pseudomorphing the mineral (figs. 13, 26 and 57). On occasions an elongate semi-transparent dark brown mineral is also formed.

Analyses: Microprobe analyses of 12 crystals from nine rocks are given in table 25. In addition an analysis of a megacryst by Ridley (1970) is reproduced. With the exception of the megacryst, the formulae have been calculated on the basis of 23 oxygen atoms, -95-

as favoured by Borg (1967) for amphibole analyses where h20 has not been determined, and the analysis totals approximately 985. As with the pyroxene microprobe analyses, the sum of the cations in the structural formulae with Fe calculated from Fe0 was higher than that calculated with Fe as Fe203. The formulae calculated with Fe from Fe0 is given here as they are generally closer to R1 and overall totals for the X, Y and Z sites are nearer ideality.

The haersutites are very low in silica, over two atoms of A13+ per formula unit being present in the Z sites. On occasions insufficient Al is present to fill the vacant Z sites: this is quite common in analyses of kaersutite (cf. Wilkinson 1961. Aoki 1963. Leake 1968). The deficiency in the Z sites has not been made up, but it is likely that some Fe3+ or Ti will be tetrahedrally coordinated. Analysis R1 shows a relatively high Fe0/Fe 0 ratio in comparison with many of the salitic 2 3 pyroxones.

On the basis of the classification by Wilkinson (1961) for titanium rich amphiboles of this type, all of the analyses with the possible exception of PS10(3) are kcersutites. 2+ 2+ Wilkinson characterised kaersutite by a lower Fe /Mg ratio 2+ (Mg >2atoms per formula unit) than barkevikite, and TiO2 near or greater than 5%. Kaersutite and not basaltic hornblende 2+ 3+ (oxyhornblende) is indicated by the high Fe /Fe ratio in Ri. On this basis PS10(3) is a barkevikite but the analysis is of an outer zone, the inner zone being kaersutite (PS10(2)); thus illustrating the continuous chemical variation between the two minerals. Analyses from all the phonolites tend towards barkevikite in composition. Wilkinson (1961) states that magmatic differentiation of nepheline bearing igneous suites should be accompanied by a change from kaersutite in more basic rocks, towards a barkevikitic composition in later differentiates.

Kaersutites from the alkali basalts, trachybnsalts, and trachyandesites are very uniform in composition and also compare with the chemical analysis (R1). Those occurring in the phonolites, however, are poorer in titania and magnesia but -96-

richer in iron. There also tends to be more manganese and less calcium in kaersutites from the phonolites. Further enrichment in iron at the expense of magnesium is found between the inner and outer zones of one crystal from a phonolite (PS10(2 and 3)). There is also more manganese and less titania and calcium in the outer zone. Analyses of xenolithic and xenocrystal kaersutite of Borley et al. (1970) show no marked differences from the analyses given here, except that in the xenoliths reversed zoning, with respect to iron and magnesium, is apparent. It is interesting to note that the kaersutites with reversed zoning are from a xenolith contained in the same dyke from which PS10 was taken. This dyke contains abundant xenoliths and petrographic characteristics of dyke and xenoliths indicate a very complex history of crystallisation of the amphiboles and pyroxenes.

Discussion:-

Petrological evidence from Tenerife and elsewhere along with experimental results indicates that crystallisation and fractionation of kaersutite may occur at depth. This iG refledted in the presence of kaersutite rich xenoliths, megacrysts, and abundant large crystals in some trachyandesites, giving a semi- cumulate rock. Borley et al. (1970) give evidence for and suggest a crystal cumulus origin for most of the Tenerife xenoliths, and Le Maitre (1969) examines several possible hypotheses but similarly concludes that kaersutite bearing xenoliths from Tristan da Cuhna originated by accumulation of phases crystallising at depth. Binns (1969) assumes intra- telluric crystallisation and separation of.kaersutite megacrysts from Arnidale, Australia, and Aoki (1970), suggests that the kaersutite bearing inclusions in Iki Island,Japan have been produced from alkali basalt magmas under hydrous conditions in the lower parts of the crust.

.experimental results of Yoder and Tilley (1962) show that an amphibole is precipitated from olivine tholeifte, high alumina basalt, alkali basalt, and hawaiite at pressures between 1.4 and 10 Kbars. (water saturated) and temperatures lower than -97-

900 - 1050°C. More recently Green and Ringwood (1968) have obtained similar results for tholeiite and basaltic andesite compositions, the amphiboles crystallising being similar in many respects to the present kaersutites (i.e. subsilicic, soda-rich, calcium amphiboles); and Kushiro (1970) crystallises a pargasitic (?) amphibole from a hydrated peridotite (Lherzolite) at approximately 1015°C between 8 and 18 Kbars. Thus, it seems probable that kaersutite would crystallise and separate from a basaltic or intermediate liquid of the right composition (high in titania and low in silica) under magmatic conditions and under pressure.

The kaersutite, however, is always corroded to varying extents, the products being principally pyroxenes and opaques. Similar alteration has been observed by Uchimizu (1966), Frisch and Schmincke (1970), and Le Maitre (1969). The latter assumes this to be a near surface effect reflecting the fact that amphibole is not a stable phase even in hydrous basaltic melts at pressures less than 1.4 Kbars. Undoubtedly this instability has also caused the resorption of the amphibole on Tenerife. Yagi, in the discussion of Frisch and Schmincke (1970), states that heating experiments on some kaersutite indicates that the amphibole is decomposed to a mixture of pyroxene plus magnetite at temperatures higher than Ca 900°C (presumably at atmospheric pressure). Thus the extent of resorption may be limited in more alkaline liquids solidifying at lower temperatures. Le Maitre assumes unaltered kaersutite in some rocks to be due to relatively rapid chilling,. In the present samples, this may be true for PS92 and PS93 which are fairly fine-grained lavas, and also for PS9 and PS10 assuming the presence of abundant xenoliths is due to the speed of emplacement, along with chilling by the wall rock. However the presence of unaltered kaersutite in PS119, which is a fairly coarsely crystalline basic intrusion, seems unexplainable.

Finally, Ridley (1970) assumes that in the majority of occurrences onAtlantic Islands, the mineral has a connate origin, and that it may be important in the modification of undersaturated liquids. Borley et al. (1970) goes further and -98-

states that subtraction of kaersutite from liquids of intermediate composition could lead to an abrupt increase in the silica content of residual liquids; giving the apparent 'gaps in the chemical analyses between Differentiation Index 55-65 (between trachybasalts and trachyandesites); and, could also aid in the production of a peralkaline magma.

B. ALla.LI AMPHIBOLES.

The possible occurrence of several alkali amphiboles in different phonJites and nepheline syenite inclusions has been mentioned above.

General characteristics:

The amphibole analysed (table 25. PS84) is from the groundmass of a peralkaline phonolite intrusion in the Upper Canadas Series (Tauce Escarpment) and occurs with aegirine. The same or similar mineral occurs in the very fine-grained groundmass of several other phonolite lavas and intrusions from the same series. It is associated with aegirine and, sometimes, aenigmatite. The pale brown or pinkish-brown mineral is pleochroic (extremes are (P684). a: pale watery brown. pale yellow brown), and has a low birefringence. o Extinction angles on elongate sections are approximately 20 . One larger crystal in PS84 is zoned and the crystal analysed has aV 59°. In many lavas the mineral forms in clusters of prismatic crystals in a similar way to the aegirines and aenigmatite.

Microprobe analyses:

Characteristics of the amphibole (table 25. PS84) are relatively low alumina, and high titania, calcia, soda and potash. The structural formula has been calculated on the basis of 23 oxygen atoms with all iron as FeO. As with several of the kaersutites a deficiency in the Z sites is present even after all Al3+ has been included. On comparison with analyses and end-member molecules given in Deer, Howie and Zussman (1963. Vol.2), the mineral appears to be a magnesio- -99-

arfedsonite. The latter name is preferred to the katophorite- magnesiokatophorite solid solution because of the low alumina (only 0.4 atoms per formula unit substitute for Si) and high alkali content of the amphibole. The mineral is chemically similar to some magnesioarfedsonites described by Sutherland (1969) from fenites.

Crystallisation:

The stability of alkali amphiboles of similar, though more iron-rich, composition to the present magnesioarfedsonite (i.e. riebeckite-arfedsonite solid solution) has been determined by Ernst (1962). Results show that for alkali amphiboles forming under low fluid pressure (i.e. in lavas and associated intrusion) at magmatic temperatures, the oxygen fugacity must be low (approximately that of the magnetite-wustite buffer). Ernst, however, states that as the iron-rich alkali amphiboles are stable only at low temperature they should not occur in lavas, even when the fugacity is low. But, the presence of magnesium might raise the maximum temperature of stability (cf. Sutherland 1969. P131) and allow an alkali amphibole to crystalline from a phonolitic magma.

Bailey (1969) has also deduced that an arfedsonitic amphibole can only be stable in peralkaline liquids under low fugacities of oxygen but that the assemblage acmite-arfedsonite, which is observed in PS84, may indicate a higher fugacity or a lower degree of peralkalinity of the magma. However, the presence of aenigmatite in several phonolites is a reflection of crystallisation under low fugacity of oxygen; synthetic aenigmatite forming in experiments of Ernst (1962) only with fugacities controlled by the magnetite-wustite and wustite-iron buffers and low fluid pressures. It is thus concluded for the present phonolitos that oxygen fugacities were low; but, where aenigmatite is absent as in PS84, fugacities may have been slightly increased. Bailey (1969) also notes the possibility that, when aegirine forms as rims around an alkali amphibole or vice versa, a fluctuation in the fugacity may be present. A similar but rare occurrence, and only of aegirine rimming amphibole, is found - 100 -

in the nepheline syenite boulder (PS69), and may be interpreted as indicating a small increase in fugacity during crystallisation. No such relationship is, however; apparent in the groundmass of the phonolites; and the author prefers the alternative suggested by Nash and Wilkinson (1970); that the assemblage aegirine- alkali amphibole (and possibly, in some cases aenigmatite) is in equilibrium over a small but limited oxygen fugacity - temperature interval in the Tenerife phonolites. -101 -

4. BIOTIT,!;

General characteristics

Biotite occurs in minor quantities as microphenocrysts in several phonolites form the Canadas and Recent Salic Series (fig. 23). Occasional crystals are always found in glassy phonolites from the Recent Salic Series. The mineral is strongly pleochroic in shades of brown (a : orange brown to light brown. 7 ; dart red-brown to dark brown or almost black), and forms as discrete crystals which are generally euhedral. Several crystals are also found within the nepheline syenite boulder (1.---169). The mineral is usually very fresh but occasionally shows slight alteration and contains opaque anhedra as inclusions.

Microprobe analysis:

Six analyses of biotite from two phonolites and the nepheline syenite are given in table 26. A microprobe analysis made by Carmichael (1967) (TC19) of biotite from a glassy phonolite, which is identical to PS75, is also included. Close similarities between TC19 and PS75 show that consistent results are obtained from identical specimens which have been independently prepared, and analysed using different microprobes and different standards. As H 0 cannot be determined, the structural formulae have been 2 calculated on the basis of 22 oxygens and iron has been calculated from Fe0.

The most striking feature of the biotites is the high concentration of titania. Some of this may be tetrahedrally coordinated, as a deficiency in the Z sites remains, even after all the aluminium is included with silicon. Variations in magnesium and iron between the different samples is present, PS69 being the most iron-rich and lowest in magnesium, although overall the biotites tend towards the magnesium rich or phlogopite end of the annite - phlogopite series. Potash is also enriched in PS69. Calcia is less than 0.05;/ in all analyses. A small quantity of barium has been found by Carmichael in TC19, but the element has not been determined in specimens analysed by the author. -102 =6

Discussion.

Little data is available in the literature concerning the crystallisation of biotites from alkaline volcanic rocks, and analyses of biotites from rocks comparable to the Tenerife phonolites are lacking. However; these biotites show some similarities with those from nepheline syenites (Foster 1960), in which Ti is variable (in several of the biotites TiO is 2 greater than 4.0(:::), and octahedral Al is low; but all of the Tenerife biotites are more rich in magnesium and; regardless of the oxidation state of iron, plot well outside the field for biotites from nepheline syenites. Foster bases the plot on the Mg - (Fe21-+Mn) (All-Fe34-+Ti) relation in the octahedral group. Analyses of Carmichael (1967) from salic rocks (all are saturated with respect to silica except the Tenerife specimen TC19) are high in titania and all Al has to be incorporated in the Z cites. McBirney and Aoki (1968) hove analysed a titaniferous biotite TiO 2) from Tahiti. It occurs in a more basic undersaturated rock (theralite) than the Tenerife specimens but, curiously, is more enriched in iron.

The stabilities of the end-member biotites, phlogopite and annite, has been studied by Yoder and Eugister (1951+) and Eugster and Wones (1962), respectively. Combining their results, and assuming that the melting point of the phonolites will not be unlike that given by Barker (1965) for a nepheline syenite, it appears that for biotite to crystallise as a stable phenocrystal phase in a phonolite, the following conditions are necessary: 1. low partial pressure of oxygen, 2, high magnesiuw/ferrous iron ratio, 3. high water pressure. The absence of biotite as a groundmass phase and the presence of slightly altered phenocrysts is probably due to the decrease in water pressure on eruption. The mineral is altered only in the more crystalline phonolites. In the glassy varieties the apparently fresh biotite is probably a reflection of the rapid chilling of the roc's-. Evidence, from the presence of alkali amrhibole and aenigmatite in other phonolites, indicates the -103 -

general low partial pressure of oxygen under which the phonolites crystallised. The presence of a relatively high amount of magnesium is seen in the salitic nature of the coexisting pyroxene phenocrysts and the high diopside/hedenbergite ratio in thu aeL;irLies. 5. GARfET.

General characteristics:

Yellow brown melanite garnets up to 3 mm. in diameter are common in one phonolite intrusion from Anaga (specimens PS9, 10 and 11). Similar garnets have been found at other localities by Von fristdhand Reiss (1868), Smulikowski et al. (1946) and Hausen (1956). Their occurrence appears to be restricted to phonolites from the Ancient Series.

In thin section the present crystals are pale yellow brown and rounded (fig. 22). They contain several inclusions of small sphenes and tend to be associated with kaersutite, often partially enclosing amphibole phenocrysts. Each crystal is surrounded by a narrow rim, composed of small opaque anhedra and other very fine-grained material, except when it abuts against a kaersutite phenocrysts. The garnet is completely isotropic and unzoned.

Chemical analyses and Cell Size:

Four microprobe analyses are given in tal)le 27. Analyses 1 and 2 were made on the centre and outer area respectively of the same crystal. Zoning is not apparent and analyses from all three crystals are similar. The totals of each analysis are approximately 1007!, with iron calculated as

Fe203, indicating a high andradite content. In order to estimate the amount of Fe0 present the iron has been proportioned as follows: the structural formula is calculated with all iron as Fe203' and the Z sites filled with Si + Al. The remaining Al + Ti along with most of the Fe3+ is used to make the sum of the Y sites 4.00. The remaining Fe is given to the X sites 2+ and assumed to be Fe . The percentage of Fe203 and Fe0 is then calculated and used to give the formulae quoted in table 27. By proportioning the iron in this way a more accurate representation, on recasting into end-member molecules, can be obtained; and, as expected; Fe0 is very low in comparison to Fe203.

The end-member molecules have been calculated by the method of ,.ickwood- (1968). Clearly the garnet is an andradite -105 -

but also contains almost 20% grossular. The method of calculation, however, seems to be biased against the formation of the titanium- garnet, schorlomite. This is also apparent in analyses of Ti- rich garnets given by Deer,Howie, and Zussman (1962 Vol.1) and calculated by Richwood. The garnet is called melanite on account of the relatively high titanium content. Deer, Howie and Zussma:a (Vol. 1 1962) state that garnets with 1-5% TiO2 are usually called melanites, and garnets of similar composition to those analysed here are called melanitesby Howie and Wolley (1968).

The cell edge, determined from the powder diffraction pattern is 12.004 (1.002)R. Cu radiation was used and a least squares refinement was made using 27 reflections (a at low angles and resolved a and m 1 2 at higher angles). The value is fairly low in comparison with many other melanites and is probably due to the lower TiO 2 content and the presence of a high proportion of grossAlar. The cell edge increases with increasing TiO2 but the presence of other garnet end-members, with smaller unit cells, will cause e reduction in the value determined. Howie and Wolley (1968) note the effect of grosoular on the shortening of the cell edge in melcmites and, when this was corrected for, the cell sizes approximated to that of the synthetic andradite- schorlomite series.

Crystallisation of the melanite:

Experimental results of Huckenholtz (1969) and Huckenholtz et al. (1969) demonstrate that andradite having a Ti-bearing component in solid solution (i.e. melanite) can crystallise as a primary phase from a ptronolitic magma at or near atmospheric conditions. However, this will be influenced by the chemical composition of the magma. Oxidising conditions are necessary along with a probably low Na20 content to prevent the formation of an acmitic pyroxene.

stated previously, the general crystallisation history and origin of the specimens (13139, 10 and 11) containing the melanite apnears very complex. However, several features point towards the fairly late crystallisation of the mineral at low -106-

pressures. The garnet partly includes kaersutite crystals, some of which are altered, and, although the xenoliths contain abundant pyroxene and amphibole, melanite is absent. In contrast to the pyroxene, amphibole and feldspar, the garnet is unzoned. Its presence within the rock, and not in intentices, shows that it is a primary crystallisation product of the magma, unlike similar garnets of Nash and Wilkinson (1970) and Varet (1967 and 1969).

The rounded appearance vnd surrounding rim indicate that the garnet may also not be completely stable in its final environment. The concentration of Na 0 may have increased 2 before intrusion and final crystallisation, and caused slight decomposition of the melanite. -107 -

6. SPHEUE.

Sphene occurs as a minor phenocrystal phase in the phonolite intrusions from the Ancient Series. In other phonolites and trachytes the mineral is present as an accessory. In thin section it is typically euhedral showing rhombic cross sections (fig. 21), and some crystals have varying degrees of pleochroism from pale buff to orange yellow. Petrographic relationships show that the mineral forms early in the crystallisation history of any phonolitic assemblage.

While separating the pyroxene fraction from MA7 by magnetic methods a fraction rich in light golden-yellow sphene was obtained. The mineral was easily purified by removal of the remaining feldspar, and the cell parameters have been determined by powder diffraction methods on the resulting material. Two partial microprobe analyses have been made to substantiate the data (table 28).

In general, substitution by other elements for calcium, titanium, silicon or oxygen in the structure of sphene is limited; but varieties rich in rare earths and other elements have been reported. Sahama (1946) and more recently Deorcgowie and Zussman (1962. Vol.1) give reviews of the chemical substitutions that can tae place. Limited substitutions, predominantly of iron and aluminium are found in the present samples. As the total for the elements analysed is approximately 96, the presence of other species is indicated. Water and fluorine (Sahama 1946) are always present in the sphene structure, and up to and slightly over 1% may be found. Slow wavelength scans revealed the presence of the rare earth elements, lanthanum, cerium, praseodymium and, possibly samarium and gadolinium. Relative intensities show cerium and than lanthanum to be the most abundant.

The reflections used in refining the cell parameters and measured 20's (corrected against silicon internal standard) are given in table 29. In addition, the relative intensities and the 2(3. for each reflection, calculated back from the 1o8 -

parameters, arc produced. In all except two reflections differences between 2e (observed) and 2e (calculated) were less than 0.04° 2e. The strongest reflection at 27.54° was not used as it is not singularly indexed. The parameters are + within -0.01 R (a, b and c) and - 0.15° ((3) of values given by Bragg (1937). Fig 28

Olivine— Skeletal phenocrysts (-0 . 5 -- and microphenocrysts

Scale in mm. <-0 . 7-- ---,

0 I ivine -

Corroded phenocrysts

.(-----2 . 0 ----,

Fig 29

Pyroxene — Y C ry s tallography - 110 -

FIG, 30. P61. Euhedral pyroxene phenocryst from an ankaramite containing a n=ow darker rim of normal zoning. Plane polarised light. x 30.

PS FIG 31. X14. (.pLque oxide inclusions within outer zone of normal zoned pyroxene crystal. Plane polarised light. x 120 FIG 32

30-66 ANK ARAMITE. CORRODED PYROXENE.

FIG 33

GROUNDMASS HOURGLASS PYROXENES

PS 4

PS 62

PS 3

PS 17 ALL CRYSTALS < 0.1 MM. LONG - 112 -

FIG. 34. 34-66. Pyroxene phenocryst from an alkali basalt showing irregular and large scale oscillatory zoning. crossed nicols, x 35.

FIG. 35. TC37. Pyroxene phenocryst from an alkali basalt showing irregular zoning. Crossed nicols. x 55. OTT X '9TOOTU prISSOIO 'seuTATT0 pure seuoxoxgd Jo ao4sriTo uTLI4Tm 4si:doouolid auexo.ad pouoz ssuiSanoH •0170,1 'Lc -Dia

OTT x *9T00Tu possoao *aatIlo 0114 o4 selliBanog oti4 Jo 4aud ouo taoas sassed TioTtim BuTuoz .L.To4 ITETT oso aulos o4nuTm aqq. a4og *4-res3ct Tunrce uc WOJJ 4s.Raoouotid auoxo.1/cd pouoz esITE9JnoH *v171701, .9C .Dia

LT FIG. 38. 24-66. Broken pyroxene phenocryst with normal zoning from alkali basalt. Well developed minute scale oscillatory zoning in the outer zone. Crossed nicols. x 35.

FIG. 39. 35-66. Pyroxene crystal with green core from alkali basalt. Plane polarised light. x 100. FIG. 40. 23-66. Exsolution of opaque lamellae in pyroxene phenocryst. Plane polarised light. x 250.

41-48 MAY BE FOUND BETWEEN TABLEb 15-22.

0 ry FIG. 49. Hd

Chemical variation in the salitic pyroxenes

0 Chemical Analyses

• Microprobe Analyses

X Green Cores

O Xenoliths

FIG. 51:11%.

Chemical variation in the salitic pyroxenes Ac o Chemical Analyses

Microprobe Analyses

PS41

etc ii--11-66 --s • • ,MA4A • PS2

10 • • * O. ,, \ • or, 0 • \ PS 0 / S. 456 ::4-7", -- , Po 41 • 6)0 ; : : P PS75 • • \c, 0 0 0 • • , 5 • % 0. t• ••Cill • • 0

• 05 • •

• *

10 20 30 Di lid FIG• 50B.

Chemical variation in the pyroxenes

. Microprobe analyses ( PS 69) PS 84 1 PS 41 )

o Chemical analysis

x Green cores

Xenoliths

M11.1.M. , Spread of salite analyses

Di 20 40 60 FIG. 51.

J — Black Jack Sill. Wilkinson 1951

G — Gough Island. Le Maitre 1962

E — Garbh Eilean. Murray 1954

S — Skaergaard. Brown and Vincent 1963

L — Co. Limerick. Ashby 1946

---- Tenerife Wo ••=111-1•.M. FIG. 52.

M — Morotu, Sakhalin. Yagi 1953

I — Itapirapua, Brazil. Gomes 1970

P _ Pantellerites. Carmichael 1962

6 _ Gough Island. le Maitre 1962

S_ Square Top. Wilkinson 1966

C_ Cantal. Varet 1969

Tenerife

Di Hd FIG. 53.

c 2+ a sin II in brackets

/8197 (9458) 2 4 cem 8.895 (9.369) 5* 8-881 (9.360 ;32. 1) 8* / 1 8-925 (9.383) 8.893 9 (9.359 8.1111. / (9.369) 7 \ 8-902 \ (9.374)

Mg24-• FIG. 54.

Normal and reversed zoning • core Wo o rim

07/8

• 8 reversed MA19 MA 2 8

Ac /PS 2 7 10 28 reversed

Z2gr

PS 56_0 • 18 —66 MA 19 o-

MA 3

Di \/ >Hd 5 10 15 20 25 30 FIG. 55.

Idealised Hourglass Twinned Py roxe ne Crystal with Minute

Scale Oscillatory Zoning.

Sectio n parallel to 010 opprox through centre of crystal

FIG. 56. ( OVERLEAF )

FIG. 57.

Partially resorbed kaersutite crystal. Fl 6.56. Ph enocrysts containing green cores • core Wo • rim 55 • groundmass MA8

o pyroxene rimming amphibole MA8

10 15 20 25 30 35 PS I c' 0

0.-51 0- - PS 5 8

io 0

5 MA 0

\/ V V Hd D i< 15 20 25 30 35 40 45 50 - 125 -

TABLE 2.

Refractive index of olivine phenocrysts.

Specimen p RI. Fo (1..002) MA19 Ancient series 1.697 78. Ankaramite MAll Ancient series 1.684 84. Ankaramite MA6 Ancient series 1.686 83 Alkali basalt PS115 Ancient series 1.697 78. Alkali basalt MA23 Lower Canadas series 1.691 81 Ankaramite/alkali basalt 24-66 Lower Canadas series 1.690 81. Alkali basalt 31-66 Series 3 Basalt. 1.693 80 Ankaramite/alkali basalt HA37 Series 3 Basalt 1.686 83 Alkali basalt TC10 Series 3 -Basalt 1.685 84 Alkali basalt TC34 Series 3 Basalt 1.689 82 Alkali basalt 49-66 Recent Basic series 1.690 81 Alkali basalt

TABLE 3

MICROPROBE ANALYSES OF OLIVINES

HA19 HA19 HA19 HA19 MA17 HA17 mAl7 mA8 Tc37 TC37 24-66 24-66 HA22 TC34 T034 ps48 Tc38 (1) (2) (3) (4) (1) (2) (3) (1) (2) (1) (2) (1) (2)

SiO 2 38.1 38.6 36.4 39.6 35.4 38.6 38.o 38.8 39.4 39.5 39.6 37.8 39.2 38-9 39.o 38.4 38.8 TiO ND ND 2 ND ND ND ND ND 0.05 0.04 0.04 0.05 0.06 0.01 0.06 0.05 0.0 0.0 Al 0 2 3 ND ND ND ND ND ND ND 0.04 0.01 0.04 o.o6 0.0 0.03 0.03 0.05 0.0 0.0 XFeO 21.9 16.3 16.5 :12.2 37.6 20.8 21.2 19.5 17.0 17.0 _15;5 23.7 17.3 21.8 20.0 19.3 20.9 Mg0 39.9 44.7 44.5 44.3 25.8 40.4 40.8 42.9 43.4 43.8 44.4 37.8 43.6 40.2 41.7 40.4 39.9 MnO 0.3 0.2 0.2 0.2 0.7 0.3 0.3 0.2 0.3 0.2 0.2 0.5 0.3 0.3 0.3 0.4 0.4 NiO 0.2 0.2 0.2 0.2 0.2 0.1 0.2 ND 0.2 0.2 ND ND 0.2 0.1 0.1 0.1 0.1 Ca0 0.4 0.3 0.2 0.3- 0.6 0.3 0.3 0.2 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 TOTAL 100.7 100.3 101.0 101.8 100.3 100.5 100.8 101.7 101.5 101.1 100.1 100.2 100.9 101.6 101.5 98.9 100.4

STRUCTURAL FORMULA ON BASIS OF 4 OIYOENS

si 0.98 0.98 0.99 0.99 1.00 0.99 0.98 0.98 0.99 0.99 1.00 0.99 0.99 0.99 0.99 1.00 1.00 Al - - - - 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Ti ------0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Fe 0.47 0.35 0.35 0.36 0.89 0.1+5 0.46 0.41 0.38 0.36 0.33 0.52 0.36 0.47 0.43 0.142 0.45 Mg 1.54 1.69 1.67 1.65 1.08 1.55 1.57 1.62 1.63 1.64 1.67 1.48 1.64 1.53 1.57 1.56 1.53 Mn 0.01 0.01. 0.004 0.01 0.02 0.01 0.01 0.01 0.01 0.01 0.004 0.01 0.01 0.01 0.01 0.01 0.01 Ni 0.004 o.004 0.004 0.004 0.004 0.003 0.003 - 0.003 0.004 0.004 0.003 0.001 0.002 0.002 Ca 0.01 0.01 0.01 0.01 0.02 0.01 0.01 041 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01

x 2.03 2.06 2.03 2.03 2.01 2.02 2.05 2.05 2.03 2.02 2.01 2.02 2.02 2.02 2..02 2.00 2.00

Fo% 76 83 8 82 55 78 77 80 81 82 84 74 82. 77 79 79 77

All iron quoted as Fe0 ND Not determined HA19(1) Ankaramite. Ancient Series. Groundmass crystal Tc37(2) Alkali basalt Ancient Series Centre of large phenocryat.

MA19(2) 11 Centre of small phenocryst. 24-66(1) Alkali basalt Canadae Series Centre of large phenocryat.

MA19(3) 11 Is 11 Centre of largo phenocryst. 24-66(2) St " Centre of small phenocryst.

mA19(4) 11 Rim of large phenocryat. HA22 Alkali basalt/trachybasalt. Canadae Series Centre of broken MA17(1) Ankaramite Ancient Series Oroundmass crystal. phenocryst. Centre of phenocryat. mAl7(2) 11 Centre of small phenocryat. TC34(1) Alkali basalt. Series 3.

11 A 11 a 14 II 11 11 Tc34(2) mA17(3) Centre of large phenocryat. P348 Tracbybasalt. Series 3. Microphenocryat. mA8 Alkali basalt Ancient Series Centre of phenocryst. Tc37(1) Alkali basalt Ancient Series Centre of small phenocryst Ts38 Traebybasalt. Series 3 or Ancient Series? Hicrophenocryet. - 127 -

TABLE 4

Cell parameters of olivine composition composition Specimen a _b c from from 130 174_ MP19 Ancient series 4.770 10.250 6.005 Fo 83 Ankaramite t.001 t.002 -.002 MA6 Ancient series 4.770 10.251 6.007 Fo 78 Fo 79 Alkali basalt t.002 t.003 t.002 31-66 Series 3 Basalt 4.775 10.262 6.008 Fo 75 Ankaramite/alkali basalt -...002 ±.002 -.002 MA37 Series 3 Basalt 4.769 10.257 6.007 Fo 82 Fo 8o Alkali basalt ±.002 t.002 1-.001

Standard error calculated from the program. - 123 -

TABLE 5.

Optic Axial Angle and p Refractive Index measurements on pyroxene phonocrysts. R.I. measurements made on centres of phenocrysts gouged out of rock specimens. R.I. for MA 7 determined using separated mineral fractions. Spec. No. Rock type p R.I. 2V y(") MA 11 Ankaramito 1.707 51 MA 19 n 1.699 53 20 11 1.707 52 MA 24 n 1.711 51 TC 10 Alkali basalt 1.705 50 TC 34 11 1.711 50 TC 36 n 1.703 51 TC 37 11 1.712 50 TC 39 11 1.716 55 GB 11 n 1.715 49 MA 31 h 1.716 52 12-66 n 1.716 3o 18-66 n 1.712 54 23-66 11 1.707 52 24-66 n 1.706 54 28-66 11 1.709 53 29..66 17 1.715 51 30-66 U 1.708 52 31-66 n 1.712 51 34-66 n 1.713 52 35-66 n 1.714 53 38-66 n 1.703 53 49-66 n 1.717 54 MA 22 Trachybasalt 1.709 51 7-66 U 1.715 53 TC 44.. Bomb from cinder cone 1.713 55 n M TC 44C 71 M 1.717 55 8-66 Pyroclastic material 1.719 56 MA 7(GB4) Phonolite 1.720-1.724 65-71 - 129 -

TArALE 6

pptic axial angle measurements on individual pyroxene crystals with normal zoning

Specimens are from Pnkaramites, alkali basalts, and trachybasalts.

Spec. Ho. Colour 2Vy_(°)

core rim core Rim

18-66 pale purple - darker purple 52 49 37 18-66 pale purple - darker purple 55-47 (hourglass) 39 MA 11 pale purple - darker purple 53 52 45 42 MA 31 pale purple - darker purple 52 45 PS 104 v. pale purple - darker purple 52 44 PS 104 v. pale purple - darker purple 53 46 PS 51 pale purple - darker purple 55 48 PS 51 pale purple darker purple 60 54 Ps 81 uniform very pale purple 51 47 MA 22 darker purple - purple 51 53 TC 210R pale buff 6o 58 MA 19 pale purple - darker purple 54 50 MA 19 groundmass, darker purple average 50 PS 118 pale purple 58 55 PS 96 v. pale purple 53 46 PS 96 v. pale purple 53 50 PS 96 v. pale purple 53 50 PS 103 v. pale purple 54 51 -130 -

TABLE 7, Optic axial angle measurements on individual pyroxene crystals with green cores from alkali basalts

Spec. No. Colour 2V 'y ( ° ) core rim core Intermediate rim 34-66 green-pale purple-darker purple 57 54 52 MA 14 pale green-v. pale buff 55 45 PS 58A pale green-v. pale purple 64 47 PS 31 green-pale purple 65 41 PS 58 green-pale purple 61 41 PS 31 dirty buff-pale purple 54 48

TABLE 8. Optic axial angle measurements on individual pyroxene crystals with hourglass zoning from alkali basalts and ankaramites

Spec. lo. Colour 2V (°)

1Yr 2 1 2 Gri 11 pale purple - darker purple 50 48 MA 17 pale purple, darker purple 47 46 MA 10 pale purple - darker purple 53 48 18-66 normal and hourglass zoning 55 47 pale purple core - darker rim rim 39 - 131 -

TABLE 9

Optic axial angle measurements on individual pyroxene phenocry8tS from phonolitos

Spec. No. Colour 2Vy (°)

core rimcore intermediate rim_..... TC 89R pale green 63 GB 4 green 65 71 TC 126R pale green 6o 58 TC 223R v. pale buff 59 TC 1831 green 58 63 PS 105 pale green 64 PS 10 green - pale purple 73 56 PS 10 green - pale purple 72 55 PS 45A pale green 61 PS 45L pale green 61 PS 47 pale green 63 -132 -

TABLE 10.

Oatic axial angle measurements on pyroxenes from trachyandesites and trachytes

c o 1To Roch_type (°)

PS 74 trachyandesite (phonocrysts) 63 PS 93 trachyandesite (phenocrysts) 59 PS 105 trachyte (phenocryst) 64 PS 101 trachyte (groundmass) 63

TABLE 11.

Range of extinction angle values for pyroxenes

ey (0) AnIcaramites phenocrysts 43 - 5o Alkali basalts phenocrysts 40 - 58 Trachybasalts phcnocrysts 43 - 53 groundmass > 50 Trachyandesites phenocrysts 49 - 59 Trachytes Phonolitos phonocrysts 49 - 57 groundmass (aegirine) > 70 Nopheline Syenite (aegirine) > 8o -133- TABLE 12

Extinction angle measurements on individual zoned pyroxene crystals , y. o Spec.. Rock typg.. Colour z ( ) No/ core rim core rim Normal zoning MA17 ankaramite pale purple - darker purple 44 50 MA20 ankaramite pale purple - darker purple 44 49 ps56 alkali basalt pale purple - darker purple 44 49 mA3 alkali basalt pale purple darker purple 41 43 MA20 ankaramite pale purple - darker purple 43 48 Crystals with green cores. PS58 alkali basalt green pale purple 62 52 PS58 alkali basalt green pale purple 50 45 PS58 alkali basalt green-pale buff-pale purple 63 58 64 ps9 phonolite green - pale purple 55 1+9 hourglass zoning I -----, 2 1 ------c,„....1.j 1---' 1. 2. 1. 2. PS118 alkali basalt pale purple --darker purple 50 56 PS118 alkali basalt pale purple - darker purple 46-49 52-53 ps56 alkali basalt pale purple - darker purple 47 57 Ps56 alkali basalt pale purple--darker purple 50 57 GB11 alkali basalt pale purple - darker purple 47 58 GB11 alkali basalt pale purple - darker purple 50 58 MA3 alkali basalt pale purple - darker purple 46 49 TC37 alkali basalt pale purple - darker purple 45 47 Tc4 alkali basalt v. pale purple 43 48 TC33 trachybasalt v. pale purple 47 52 TC32 trachybasalt v. pale purple 48 52 Tc45 trachyandesite v. pale purple 49 59 GB8 trachyandesite pale buff-darker buff purple 48 52

TABLE 13 CHEMICAL ANALYZES OY PTROXESES 24-66 Ilmkk itaILL23 all mall E1212 tam Eat ELL° WILP1 p6 11111 26 El . 12 48.28 46.43 50401 48.40 46.46 49.46 53.24 53.17 (53.2) 46.73 45.21 8102 48.96 47.28 48.29 46.99 47.56 47.22 47.81 47.47 2.74 2.07 346 2.4(9) 2.72 5.54 2.62 1.43 0.91 0.88 1.67 3.78 Ti02 2.16 1.86 2.69 2.55 1.57 2.08 2.14 7.04 0.9(8) 6.52 4•91 4•45 2.77 1.85 1.35 5.37 5.67 81 4.08 5.49 6.29 7.80 5.35 5.96 5.45 5.46 5.52 23 1.94 2.3 2.66 3.24 P0203 3.08 3.24 3.88 3.54 2.77 3.40 3.17 4.12 3.86 2.28 17.89 3.85 3.02 1 3.45 4.66 5.92 9.6 6.42 7er0 4.14 3.42 3.83 3.30 3.64 4.41 4.02 3.37 3.81 4.30 3.70 3.91 6.91 5.88 7.07 12.95 12.64 13.09 13.76 12.95 12.3 13.52 12.76 MgO 13.39 14.12 12.44 12.64 15.45 12.61 15.06 14.93 13.40 12.98 2.00 0.33 0.66 0.84 Ha) 1.85 0.72 0.15 1.02 1.56 0.94 0.92 0.15 0.69 0.95 0.15 0.25 0.26 0.44 20.6 Ca0 22.36 22.71 20.25 21.89 19.81 21.26 22.24 21.34 21.73 21.94 3.84 21.24 20.14 21.51 20.55 21.17 22.24 22.93 0.61 0.76 12.48 0.59 0.83 0.92 1.07 1.24 1.2 0.19 0.26 Ha20 0.76 0.68 0.92 0.91 0.78 0.62 0.73 0.79 0.06 0.12 0.00 0.31 0.79 120 0.07 0.00 0.38 0.00 0.09 0.14 101.17 100.23 100.53 (100.0) 100.27 TOTAL 100.85 99.52 99.12 100.83 99.80 99.37 100.38 100.13 99.41 100.13 95.85 100.33 100.70 100.29 FORMULA ON BASIS or 6 caroms 1.836 1.758 1.706 si 1.821 1.772 1.792 1.735 1.794 1.785 1.760 1.770 1.781 1.729 2.01 1.800 1.736 1.954 1.957 1.990 0.164 0.046 0.043 0.010 0.238 0.252 Al 0.179 0.228 0.208 0.265 0.206 0.215 0.240 0.230 0.219 0.271 0.200 0.215. 0.004 0.042 Ti 0.049 -

Al 0.015 0.071 0.074 0.028 0.049 0.008 0.025 0.038 0.04 0.085 0.030 0.073 0.036 0.049 Ti 0.060 0.052 0.076 0.076 0.058 0.072 0.044 0.061 0.060 0.102 0.12 0.076 0.106 0.072 0.039 0.024 0.025 0.043 0.065 F.3 0.086 0.091 0.110 0.099 0.077 0.096 0.089 0.115 0.109 0.064 0.53 0.107 0.084 0.054 0.063 0.072 0.097 0.092 2 F• 0.129 0.107 0.120 0.102 0.113 0.139 0.125 0.104 0.120 0.134 0.12 0.121 0.215 0.182 0.142 0.180 0.300 0.222 0.203 Mg 0.742 0.789 0.697 0.695 0.856 0.705 0.837 0.823 0.749 0.720 0.12 0.722 0.708 0.728 0.758 0.712 0.686 0.758 0.718. Ma. 0.048 0.019 0.004 0.026 0.040 0.024 0.024 0.004 0.018 0.013 0.03 0.005 0.008 0.008 0.016 0.020 0.026 Ca 0.891 0.912 0.816 0.866 0.789 0.855 0.888 0.847 0.873 0.875 0.16 0.810 0.806 0.855 0.808 0.831 0.826 0.897 0.927 Na 0.055 0.050 0.067 0.065 0.056 0.045 0.044 0.052 0.057 0.055 1.02 0.042 0.062 0.066 0.076 0.089 0.088 0.014 0.019 0.003 0.019 0.004 0.003 0.006 0.007 0.014 0.04

2.000 2.000 2.000 2.000 2.000 2.000 2.000 2.000 2.000 2.000 2.01 2.000 2.000 2.000 2.000 2.000 2.000 2.000 2.000 IT 2.015 2.035 1.980 2.003 2.021 1.988 2.057 2.021 2.011 2.015 2.18 1.978 1.990 1.995 1.972 1.974 2.000 2.031 2.024

Wo 47.0 47.5 46.7 48.4 42.1 47.0 45.2 44.7 46.8 48.4 45.9 44.3 46.8 45.2 45.8 44.9 45.4 47.8 En 39.2 41.1 39.9 38.9 45.6 38.8 42.6 43.5 40.1 39.9 40.9 38.9 39.8 42.4 39.2 37.3 38.4 37.0 Fs 13.8 11.4 13.4 12.7 12.3 14.2 12.2 11.8 13.1 11.7 13.2 16.8 13.4 12.4 15.0 17.8 16.2 15.2

Ac 5.5 5.0 7.2 7.0 5.2 4.7 4.1 5.0 5.7 5.9 69 4.4 6.1 6.8 7.9 9.0 8.7 1.3 1.9 Di 73.8 78.4 75.1 75.4 78.8 73.1 77.9 78.7 75.2 77.3 15.5 75.6 69.8 74.9 78.7 72.4 67.8 70.4 70.9 Hd 20.7 16.6 17.7 17.6 16.0 22.2 18.0 16.3 19.1 16.8 15.5 20.0 24,1 18.3 13.4 18.6 23.5 28.3 27.2 24-66 Phenocrysts. Alkali basalt dyke. Canada. Sari's. MA60 Oroundaass. Alkali basalt. Ancient Striea. 31-66 Phenocrysts. Alkali basalt. Series 3 basalts. PS69 Nephsline syenite boulder. (9) aaaaa ge of 12 microprobe analysts. 49-66 Phenoorysts. Alkali basalt. Recent Cinder Cone. P191 Phonocrysts. Alkali basalt. Ridley (1970) MA23 Phenocrysts. Alkali basalt. Lower Canadas Series. P7 Phenocrysts. Trachybasalt. Ridley (1970). Canada. Series. MA11 Phenocrysts. Ankaramits. Ancient Series. P6 Phenocrysta. Trachybasalt. Ridley (1970). Canada. Series. MA15 Phenocrysts. Ankariaite. Ancient Series. P40 Phenocrysts. Phonolite slaiy(1970). Recent Salic Series. MA19P Phenocryats. Ankaramits. Ancient Series 9183 Phenocrysts. Glassy phonolite. Ridley(1970). Recent Salio Seriea. MA196 Groundaass. Ankaramite. Ancient Series. 26 Phenocrysts. Glassy yhonallt• (TC19) Carmichael (1967) Recent Salle Serie. MEP Phenocrysta. Alkali basalt. Ancient Series. SiO2 by differtnos. 11 Tephrite Kunits (1936) 12 Syenite baits (1936) TABLE 14 Microprobe analyses of individual pyroxene crystals

24-66 24-66 24-66 24-66 24-66 49=66t 122i Eia 1222 Tc38 Tc38 Lal P.374 rs74 P374 PS74 _ILI_ _LLI_ _ill_ (4) (5) iLL -2.1 -ill (2) ill (4 ) Si02 47.8 48.2 48.4 46.8 46.9 45.5 44.6 45.4 43.9 46.3 43.7 47.2 51.2 51.3 51.2 51.9 2.1 2.1 2.6 2.8 3.5 2.9 3.3 3.8 4.4 2.0 0.5 0.6 0.7 0.3 TiO2 2.3 2.0 4.4 4.8 5.1 7.6 8.1 8.0 7.6 6.4 9.3 5.5 1.7 1.8 2.0 1.2 Al203 5.3 4.7 - - .. .. - - - Fe205 ------no 7.5 7.5 7.6 7.7 7.6 7.5 7.5 7.2 8.0 8.1 8.8 8.0 8.3 7.1 8.3 8.2 MgO 13.6 14.3 13.9 13.6 13.3 12.4 12.4 12.7 12.7 12.6 11.3 12.8 12.8 14.0 12.9 13.3 MO 0.2 0.2 0.2 0.2 0.2 0.1 0.2 0.1 0.1 0.2 0.2 0.5 0.8 0.7 0.7 0.7 Ca0 22.2 21.9 21.9 22.3 22.2 22.8 22.4 23.3 23.3 22.2 22.4 22.6 21.5 22.2 22.0 22.2 0.5 0.5 • 0.5 0.6 1.1 1.0 1.1 1.0 Na20 0.4 0.4 0.5 0.5 0.5 0.7 - 0.6 0.8 120 ND ND ND ND ND ND ND TB ND ND ND 0.0 0.0 0.0 0.0 0.0 TOTAL 99.3 99.2 99.0 98.0 98.3 99.2 99.2 100.1 99.5 100.3 100.7 99.4 97.9 98.7 98.9 98.8 FOR}IPLL ON BASIS OF 6 =WEDS Si 1.80 1.82 1.83 1.80 1.79 1.72 1.69 1.71 1.67 1.74 1.64 1.79 1.96 1.94 1.94 1.97 Al 0.20 0.18 0.17 0.20 0.21 0.28 0.31 0.29 0.33 0.26 0.36 0.21 0.04 0.06 0.06 0.03 Ti ------..," -

Al 0.03 0.03 0.03 0.02 0.02 0.06 0.05 0.06 0.01 0.02 0.05 0.04 0.04 0.02 0.03 0.02 Ti 0.07 0.06 o.o6 0.06 0.08 0.08 0.10 o.08 0.09 0.11 0.13 0.06 0.02 0.02 0.02 0.01 Fe 0.23 0.24 0.24 0.25 0.24 0.24 0.24 0.23 0.26 0.26 0.28 0.25 0.27 0.22 0.26 0.26 Mg 0.76 0.80 0.78 0.78 0.75 0.70 0.70 0.71 0.72 0.70 0.64 0.72 0.73 0.79 0.73 0.75 Mn 0.01 0.01 0.01 0.01 0.01 0.00 0.01 0.00 0.00 0.01 0.01 0.02 0.03 0.02 0.02 0.02 Ca 0.90 0.88 0.88 0.91 0.91 0.92 0.91 0.94 0.95 0.89 0.90 0.92 0.88 0.90 0.90 0.90 Na 0.03 0.03 0.04 0.04 0.04 0.04 0.04 0.03 0.05 0.05 0.05 0.06 0.06 0.07 0.05 0.08 X

2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 XY 2.03 2.04 2.04 2.07 2.05 2.04 2.05 2.05 2.08 2.04 2.06 2.07 2.05 2.04 2.04 2.04

W. 47.4 45.6 46.1 46.7 47.6 49.5 49.0 50.0 49.2 47.8 49.2 46.2 46.1 46.6 47.1 46.6 Ea 40.0 41.5 40.8 40.0 39.3 37.6• 37.6 37.8 37.3 37.7 35.0 37.7 38.2 41.0 38.2 38.9 Fs 12.6 12.9 13.1 13.3 13.1 12.9 13.4 12.P 13.5 14.5 15.8 14.1 15.7 12.4 14.7 14.5 7.8 Ac 3.0 2.8 3.9 3.8 4.0 4.3 4.2 3.2 5.1 5.1 5.4 6.1 7.8 6.8 7.9 Di 76.0 76.2 75.7 75.0 75.0 74.5 73.7 75.6 73.5 72.2 68.8 72.7 70.9 76.7 72.3 72.8 lid 21.0 21.0 20.4 21.2 21.0 21.2 22.1 21.2 21.4 22.7 25.8 21.2 21.3 16.5 19.8 19.4 Pyroxines are oolitic unless :stated otherwise TC38(1-2) Microphonocrysta. lrachybasslt. 24-66 (1-5) Phenocryats. Alkali basalt. PS92 khonocryot. Trachybasalt/trachyandesite. 49-66 PS74 (1-4) illenocrysts. Trachyandeeite. Phenocryat. Alkali basalt. TC34 Small phenocryat. Alkali basalt.

MA22 Phenocryst. Trachybasalt

TC53 Phenocryat. Trachybasalt. TABLE 14 (continued) GB8 Gh8 GE8 13-66 NA4A NA4A 9-66 9-66 9-66 9-66 9-66 1-66 1-66 (1) (2) ill (1) (2) (1) (2) (3) (4) (5) (1) (2) SiO 43.4 48.4 2 51.7 48.2 47.6 47.8 52.8 52.5 52.0 52.6 50.9 50.3 51.3 TiO. 1.1 1.5 2.7 3.1 0.9 1.0 0.8 4 0.7 0.9 0.7 0.7 0.9 0.7 A1 0 2.5 3.4 2 3 5.8 9.1 4.2 3.9 1.1 1.1 1.6 1.1 1.4 1.7 1.6 Fe203 ------Fe0 8.5 9.0 8.3 7.8 13.3 14.1 8.7 8.9 8.6 8.5 7.9 12.9 12.8 '1g0 13.6 13.1 13.1 11.9 9.3 8.6 13.7 13.3 13.8 13.8 14.1 10.0 10.1 MnO 0.5 0.4 0.3 0.4 1.0 1.1 0.9 1.0 0.9• 1.0 1.3 1.4 CaO 23.1 22.7 22.6 22.8 21.4 21.6 22.1 22.1 21.7 22.5 201.619.9 20.2 Na20 0.8 0.7 0.7 0.6 1.6 1.5 1.4 1.4 1.4 1.2 1.2 2.6 2.5 K 20 0.0 0.0 0.0 0.0 ND ND ND ND ND ND 0.0 0.0 0.0 TCTAL 101.8 99.0 101.1 99.1 100.1 99.6 101.5 101.0 100.9 101.4 98.7 99.6 100.6 FORMULA ON BASIS OF 6 OXYGENS Si 1.91 1.84 1.78 1.66 1.86 1.86 1.96 1.96 1.94 1.95 1.93 1.94 1.95 Al 0.09 0.15 0.22 0.34 0.14 0.14 0.04 0.04 0.06 0.05 0.06 0.06 0.05 Ti - 0.01 - 0.01

Al 0.02 - 0.03 0.07 0.05 0.04 0.01 0.01 0.01 - 0.02 0.02 Ti 0.03 0.03 0.07 0.09 0.03 0.03 0.02 0.02 0.03 0.02 0.01 0.03 0.02 Fe 0.26 0.29 0.2o 0.25 0.43 0.46 P.27 0.28 0.27 0.26 0.25 0.42 0.41 Ng 0.75 0.74 0.73 0.68 0.53 0.50 0.75 0.74 0.76 0.76 0.80 0.57 0.57 Mn 0.02 0.01 0.01 0.01 0.03 0.04 0.03 0.03 0.03 0.03 0.03 0.04 0.04 Ca 0.91 0.93 0.90 0.93 o.88 0.90 0.88 o.88 0.87 0.89 0.88 0.82 0.83 Na 0.05 0.05 0.05 0.04 0.12 0.12 0.10 0.10 0.10 0.09 0.09 0.19 0.18 K------

Z 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 XY 2.04 2.05 2.05 2.07 2.07 2.09 2.06 2.06 2.07 2.05 2.09 2.07

Wo 46.9 47.2 47.4 49.7 47.1 47.4 45.6 45.6 45.1 45.9 44.9 44.3 44.9 En 38.7 37.6 38.4 36.4 28.3 26.3 38.9 38.3 39.4 39.2 40.8 30.8 30.8 Fs 14.4 15.2 14.2 13.9 24.6 26.3 15.5 16.1 15.5 14.9 14.3 24.9 24.3

Ac 4.9 4.8 5.0 4.3 12.1 12.0 9.5 9.5 9.4 8.6 8.3 18.4 17.6 Di 72.8 71.2 73.0 72.3 53.5 50.0 71.4 70.5 71.7 72.3 74.1 55.4 55.9 Hd 22.3 24.0 22.0 23.4 34.4 38.0 19.1 20.0 18.9 19.1 17.6 26.2 26.5

GB8(1-3) Fhenocrysts. Trachyandesite 13-66 Fyroxene inclusion in amphibole xenocryst. Trachyandesite. MA4A (1) Nicrophenocryst (2) Groundmass. Trachyte. 9-66(1-5) Microphenocrysts. Phonolite. 1-66(1-2) Nicrophenocrysts. Phonolite.

TALE 14 (continued)

MA28 M428 PS:. 2111 Ps l P545A P545A 11-66 11-66 11-66 PS41 P541 PS41 PS41 Ps84 (1) (2) 1)( (2) (1) Sal (3) Ili (2) ill al - SiO2 52.2 51.2 45.4 49.1 52.0 52.4 52.4 49.7 50.9 50.3 51.5 50.6 50.9 51.9 50.8 TiO2 0.9 1.1 3.0 0.9 0.4 0.9 0.7 .1.7 1;2 1.0 0.9 '1.2 1.9 1.8 7.2 L1203 1.4 2.1 8.0 3.7 0.9 1.5 1.3 4.2 3.5 2.5 1.8 2.6 1.8 1.9 0.9 Fe203 .. .. - - . - .. - - - . - 28.2 23.6 140 8.8 9.0 9.2 12.7 8.8 9.0 8.2 11.5 12.5 12.5 8.9 9.4 10.3 .. . Ng0 13.3 12.7 11.0 9.5 12.8 13.2 14.1 9.5 9.8 9.0 13.2 12.5 11.4 1. 7 2.1 Na0 1.0 0.9 0.2 0.9 0.9 0.6 0.7 0.8 0.8 0.9 0.9 0.8 0.5 Ca0 22.6 22.3 22.8 20.4 22.2 21.9 22.0 21.7 21.3 21.6 22.5 22.3 20.0 4.5 Z.: Na20 1.1 1.2 0.9 1.9 1.0 1.2 0.9 1.6 1.7 1.6 1.0 1.2 2.5 11.0 11.6 120 ND ND ND 0.0 0.0 ND ND ' 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1 TOTAL 101.3 100.5 100.5 99.1 99.0 100.9 100.3 100.7 101.7 99.4 100.5 100.6 99.8 101.5 100.8 FORMA ON BASIS or 6 OITGENS Si 1.94 1.92 1.71 1.90 1.97 1.95 1.96 1.88 1.91 1.94 1.93 1.90 1.93 1.95 1.91 Al 0.06 0.08 0.29 0.10 0.03 0.05 0.04 0.12 0.09 0.06 0.07 0.10 0.07 0.05 ::54 Ti ... • • - .. •

Al 0.01 0.06 0.07 0.01 0.02 0.02 0.07 0.07 0.05 0.01 0.02 0.01 0.03 Ti 0.02 0.03 0.09 0.03 0.01 0.03 0.02 0.05 0.04 0.03 0.03 0.04 0.05 0.05 0.15 F. 0.27 0.28 0.29 0.41 0.28 0.28 0.25 0.37 0.39 0.40 0.28 0.30 0.33 0.80 0.67 Mg 0.74 0.71 0.62 0.55 0.73 0.73 0.78 0.54 0.55 0.51 0.74 0.70 0.64 0.10 0.12 Mn 0.03 0.03 0.01 0.03 0.03 0.03 0.02 0.03 0.03 0.03 0.03 0.02 0.03 0.02 0.02 Ca 0.90 0.90 0.92 0.85 0.90 0.87 0.88 0.88 0.86 0.89 0.90 0.90 0.81 0.18 0.16 ha 0.08 0.08 0.06 0.14 0.07 0.08 0.06 0.12 0.13 0.12 0.08 0.09 0.18 0.80 0.84 0.00

Z 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 KY 2.04 2.04 2.06 2.08 2.03 2.04 2.03 2.06 2.07 2.03 2.07 2.07 2.05 1.98 1.96

wo 46.4 46.9 50.0 46.2 46.4 45.6 45.6 48.3 47.0 48.6 46.2 46.9 44.8 16.4 16.5 En 38.1 37.0 33.7 29.9 37.6 38.2 40.4 29.7 30.0 27.9 37.9 36.4 35.3 9.1 12.4 Fa 15.5 16.1 16.3 23.9 16.0 16.2 14.0 22.0 23.0 23.5 15.9 16.7 19.9 74.5 71.1

Ac 7.7 7.8 6.5 14.1 6.1 7.7 5.7 12.8 13.4 12.8 76.6 8.8 16.0 bo bo Di 71.2 69.7 67.4 55.6 64.1 70.2 74.3 57.4 56.7 54.2 70.5 68.6 64.0 11 15 Ed 21.1 22.5 26.1 30.3 29.8 22.1 20.0 29.8 29.9 33.0 21.9 22.6 18.0 9 5

MA28(1-2) .Phenocrysts, Phonolite. PS41(1-3) Microphenocrysts. Phonolite; PS9 'Phenocryst. Phonolite. PS41(4) Graundmass aegirine. Phonolite. P527 Phenocryat. Phonolite. PS84 Grouadaaas aegirine. Phonolite PS75 Phenocryst. Glaaay phonolite. PS45A(1-2) Phenocrysts. Glassy pbonolite. 11-66(1-3) Ground=ass. Phonolite. TABLE 14 (continued)

PS69 PS69 Ps69 PS69 PS69 ps69 ps69 ps69 ps69 Ps69 Ps69 ps69 (11) (1) -ii/ -L2/ -Li/ -12/ (6) _VI (8) _LI/ (10) (12) SiO2 50.6 51.3 50.6 50.8 50.9 51.5 50.8 50.7 50.8 50.7 51.2 50.9 TiO2 0.9 3.6 3.1 1.4 4.9 3.8 1.5 1.7 1.1 1.2 4.2 1.5 A1203 0.8 1.0 1.2 0.8 1.2 0.9 0.7 0.7 0.7 0.8 0.9 0.7 Fe 203 21.4 27.1 24.2 24.7 25.9 26.4 25.0 24.3 23.3 23.6 25.4 24.3 Fe0 - - -. - .. - - - - Mg0 5.5 1.8 3.3 3.5 1.7 1.5 3.o 3.o 3.9 3.7 1.7 3.2 Mn0 1.4 0.7 0.8 1.2 0.7 0.6 1.1 1.2 1.2 1.2 0.8 1.1 Ca0 13.3 3.7 9.0 8.6 3.6 2.7 7.1 7.3 10.2 8.8 2.6 7.9 Na 0 2 6.2 12.0 10.1 9.0 12.0 12.2 9.3 9.4 7.7 8.5 11.9 9.3 K 0 2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 ND ND ND ND ND TOTAL 100.1 101.2 102.3 100.0 100.9 99.6 98.5 98.3 98.9 98.5 98.7 98.9 FORMULA ON BASIS OF 6 OXYGENS. Si 1.93 1.93 1.89 1.94 1.92 1.96 1.96 1.96 1.95 1.96 1.96 1.96 Al 0.04 0.05 0.05 0.04 0.05 0.04 0.03 0.03 0.03 0.04 0.04 0.03 Ti 0.03 0.02 0.06 0.02 0.03 0.01 0.01 0.02 - 0.01

Al------Ti - 0.08 0.03 0.02 0.10 0.11 0.03 0.02 0.01 0.04 0.12 0.03 Fe 0.61 0.77 0.68 0.71 0.73 0.76 0.73 0.71 0.67 0.69 0.73 0.70 Mg 0.31 0.10 0.13 0.20 0.10 0.09 0.18 0.17 0.22 0.21 0.10 0.18 Mn 0.05 0.02 0.03 0.04 0.02. 0.02 0.04 0.04 0.04 0.04 0.03 0.04 Ca 0.54 0.15 0.36 0.35 0.15 0.11 0.29 000 0.42 0.36 0.10 0.33 Na 0.46 0.88 0.73 0.67 0.88 0.90 0.70 0.71 0.57 0.64 0.88 0.69 K 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - - - - -

2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 XY 1.97 2.00 2.01 1.99 1.98 1.99 1.97 1.95 1.94 1.98 1.96 1.97

Wo 35.8 14.4 28.8 26.9 15.0 11.2 23.4 24.6 31.1 27.7 10.4 26.4 En 20.5 9.6 14.4 15.4 10.0 9.2 14.5 13.9 16.3 16.2 10.4 14.4 Fa 43.7 76.0 56.8 57.7 75.0 79.6 62.1 61.5 52.6 56.1 79.2 59.2

Ac 44 83 6o 63 82 88 69 68 55 62 '88 64 Di 32 11 20 21 12 10 19 18 24 22 12 20 Ed 24 6 20 16 6 2 12 14 21 16 0 16

PS69(1-12) Ground=aan aor-irine nepheline syenite.

MA 19. NORMAL ZONING. X 30

Continued overleaf

P5 56

1 0 mm

NORMAL ZONING.

135 56(1) Core

TS 56(2) Margin 0 (1.) ---)

X C 0 (1)

0 0 73 U

0 C U

0 d

0 - 11+0 - TABLE 15 PYROXENE - NORMAL ZONING Analysed areas marked in fig. 41 (opposite) MA19 MA19 MA19 MA19 PS56 PS56 (1) (2) (3) (4) (1) (2) 46.9 42.2 SiO2 50.5 45.6 50.9 47.1 2.5 4.9 TiO2 1.0 2.6 0.9 2.5 Al203 4.3 7.4 4.4 6.9 6.9 9.8 Fe0 5.6 7.2 5.6 7.2 7.1 8.5 MgO 15.3 12.2 15.2 12.9 13.5 11.6 MnO 0.1 0.1 0.1 0.1 0.2 0.2 CaO 22.0 22.4 21.9 22.9 22.1 22.2 o.6 Na20 0.5 0.4 0.5 0.4 o.6 0.0 0.0 K20 ND ND ND ND TOTAL 99.3 97.9 99.5 100.0 99.8 100.0 FORMULA ON BASIS 6 OXYGENS Si 1.87 1.74 1.88 1.76 1.76 1.60 Al 0.13 0.26 0.12 0.24 0.24 0.40 Ti

Al 0.06 0.08 0.07 0.07 o.o6 0.04 Ti 0.03 0.07 0.03 0.07 0.07 0.14 Fe 0.17 0.23 0.17 0.23 0.22 0.27 Mg 0.85 0.70 0.84 0.72 0.75 0.66 Mn 0.00 0.00 0.00 0.00 0.01 0.01 Ca 0.87 0.92 0.87 0.92 0.89 0.90 Na 0.03 0.03 0.03 0.03 0.05 0.05

Z 2.00 2.00 2.00 2.00 2.00 2.00 XY 2.01 2.03 2.01 2.04 2.05 2.07

uo 46.o 49.8 46.3 49.2 47.6 48.9 45.0 37.8 44.7 38.5 40.1 35.9 Fs 9.0 12.4 9.0 12.3 12.3 15.2

Ac 2.9 3.2 3.0 3.2 5.1 5.3 Di 83.4 75.3 83.2 75.8 76.5 70.2 Hd 13.7 21.5 13.8 21.0 18.4 24.3 FIG 41. MA 19. Normal zoning.

A B C

Ti Ti

asVV 'TM

0 o I 14

a FIG, 42

lit.A 17. LA '"CIF.: SCALE osciLr_iaTCRY ZONINij7.

MA 17. Ankarami.L. Pyroxenc crystal showing large scale oscillatory zoning and an outer rim of normal zoning. Plane polarised light. x 25

Beam traverses for Ca, Mg, Fe, Ti, Al, Si, Na and Mn along the line indicated are shown overleaf. MA 17. Ankaraaite. Pyroxene crystal showing large scale oscillatory zoning and an outer rim of normal zoning. Plane polarised light. x 25

Beam traverses for Ca, Mg, Fe, Ti, Al, Si, Na and Mn along the line indicated are shown overleaf. - 143 - TABLI 16 PYROXENE - LARGE SCALE OSCILLATORY ZONING MA17(1-5) Oscillatory zoned phenocryst. See fig. 4 2 (opposite) MA17(6-7) Groundmass pyroxenes. MA17 MA17 MA17 MA17 -MA17 nu'? mAl7 (1) (2) •(3) (4) (5) (6) (7) sio., 48.7 47.2 49.0 47.7 47.5 46.5 50.4 1.8 2.6 3.1 2.9 2.2 TiO2 1.8 2.9 6.8 5.2 6.o 3.8 Al203 5.3 6.4 5.4 Fe0 6.3 7.8 6.6 7.7 8.1 7.9 7.6 Mg0 14.0 12.7 14.1 12.9 12.8 13.1 14.5 Mn0 0.1 0.2 0.1 0.2 0.2 0.1 0.1 Ca0 23.3 22.9 23.2 23.0 23.1 22.1 22.3 Na2O 0.4 0.5 0.4 0.5 0.5 0.5 0.4 K2O ND ND ND ND ND ND ND TOTAL 99.9 100.6 100.6 101.4 100.5 99.1 101.3 FORMULA ON BASIS OF 6 OXYGENS Si 1.82 1.76 1.81 1.76 1.78 1.76 1.85 Al 0.18 0.24 0.19 0.24 0.22 0.24 0.15 Ti

Al 0.05 0.04 0.04 0.06 0.01 0.03 0.01 Ti 0.05 0.08 0.05 0.07 0.09 0.08 o.o6 Fe 0.20 0.24 0.21 0.24 0.25 0.25 0.23 Mg 0.78 0.71 0.78 0.71 0.72 0.74 0.79 Mn 0.00 0.01 0.00 0.01 0.01 0.00 0.00 Ca 0.93 0.92 0.92 0.91 0.93 0.90 o.88 Pa 0.03 0.04 0.03 0.03 0.03 0.03 0.03

Z 2.00 2.00 2.00 2.00 2.00 2.00 2.00 NY 2.04 2.04 2.03 2.03 2.04 2.03 2.00

No 48.7 48.9 48.2 48.7 48.7 47.6 46.3 En 40.8 37.8 40.8 38.o 37.7 39.2 41.6 Fs 10.5 13.3 11.0 13.3 13.6 13.2 12.1

Ac 3.1 4.2 3.0 3.1 3.0 3.0 2.9 Di 79.6 74.0 78.8 74.0 73.5 74.7 77.5 Hd 17.3 21.8 18.2 22.9 23.5 22.3 19.6

°11)1$141, 014',',/,13' kOrfeligf, )1'P

rv.."0,4\ifivts...561,14,1„,,440\tultsy,thos*„10.46,04,,,,,,06,,,A,00.k..cs,a100,..4,4010004,4040410torev\„,0%.406,,,....„.,„„14,1,4.4.0A,44vs

1001#00014010041* A 44444141/44,0414040001049100#P1 t ArAii/4?!.*41sP)

Cl kiltdAehi1k,\11*'Orkr.i4f41116NNPA4440404„iie'r'4*VA*1..6%* ri 'llettli•ioria01,4tYM14 . •

r i vicolvM"44‘41/4Afrky,IMN4100 hiMiWol‘i: 4„ks,t.,,...L v, i ' A l s1 r 71,41. IV SWANS004.1)05',141,601iptt414,$,IwkiikeeNtO.MAW./44'0%.4 , 1/4. .t4WITAAWAININ VAPAII\1 ,i1/444,tispapeklii , '''‘APAsyvbsiv111"ty'''' olv„t.,4,..4,0m s\,,,viti'vv...,,,,A, / •+vv,"..„ . .,...,..,i, '*.ivt,,,:ts.,,",q)\.„Ni....

YI 1.1IPIIViii1it1lltNIVI*114610AMOf101441110114tI MiAf41,//011ilyS/Ote1061006%000,0040:01000111*111

1111;411:1,171410410*1)°11 141010041L,Y40A1/11 1ttikirN il IN\IN41.iNti;011 1/1104/( 044/0110\1k060*1:1

FIG 42. MA 17 OSCILLATORY ZONING. FIG. 43

MA3. Ankaramite. Pyroxene crystal showing irregular and normal zoning. A wide outer zone (analyses 4 and 6) is surrounded by a further very thin zone (analyses 5 and 7). Crossed nicols. x 28.

PIA 3 (9) . ICOR& or C.R"/ STAL AL N 3 60). (zipi of sArig c2•-/S1-

NOT ILLUSTRATED

IA" • ' CIrs- ki 7 r"! ;irk.

MA3. Ankaramite. Pyroxene crystal showing irregular and normal zoning. A wide outer zone (analyses 1+ and 6) is surrounded by a further very thin zone (analyses 5 and 7). Crossed nicols. x 28.

MA 3(9). CORE O.F ca•is -rpL L NA 3 (to) of STA

NOT ILLUSTRATED TABLE 17. PYROXENE - IRREGULAR ZONING MA3(1-8) Crystal with irregular zoning. See fig. 43 (opposite) MA3(9-10) Crystal with normal zoning. See fig. 43 (opposite) MA3(11) Groundmass pyroxene MA3(1) MA3(2) MA3(3) MA3(4) MA3(5) MA3(6) MA3(7) MA3(8) MA3(9) MA3(lo) MA3(11) SiO2 51.6 52.4 49.7 47.6 45.6 49.5 48.9 48.4 51.4 46.9 43.8 TiO2 1.2 1.0 1.7 2.2 3.6 2.2 2.6 2.1 1.3 3.5 4.8 A1203 3.0 2.6 3.9 5.4 6.3 4.9 4.0 5.2 3.2 6.2 7.8 FeO 5.1 4.8 5.7 6.9 9.•3 6.4 8.5 6.7 4.8 8.5 9.1 MgO 15.9 16.2 15.0 13.9 11.8 14.9 13.6 14.2 15.9 13.0 11.8 Mn0 0.1 0.1 0.1 0.1 0.2 0.1 0.2 0.1 0.1 0.1 0.2 CaO 23.5 23.6 23.2 23.3 22.8 23.5 22.7 22.9 23.5 22.8 22.4 Na20 0.3 0.3 0.3 0.3 0.5 0.3 0.4 0.3 0.3 0.4 0.5 K20 ND ND ND ND ND ND ND ND ND ND ND TOTAL 100.7 101.0 99.6 99.7 100.1 101.8 100.9 99.9 100.5 101.4 100.4 FORMULA ON BASIS OF 6 OXYGENS Si 1.89 1.91 1.85 1.79 1.73 1.81 1.82 1.81 1.89 1.74 1.66 Al 0.11 0.09 0.15 0.21 0.27 0.19 0.18 0.19 0.11 0.26 0.34 Ti - - - -

Al 0.02 0.02 0.02 0.03 0.01 0.02 - 0.04 0.03 0.01 0.01 Ti 0.03 0.03 0.05 0.06 0.10 o.o6 0.07 o.o6 0.04 0.10 0.14 Fe 0.16 0.15 0.18 0.22 0.29 0.20 0.27 0.21 0.15 0.26 0.29 Mg 0.87 0.88 0.83 0.78 0.67 0.81 0.75 0.79 0.87 0.72 0.67 Mn 0.00 0.00 0.00 0.00 0.01 0.00 0.014 0.00 0.00 0.00 0.01 Ca 0.92 0.92 0.93 0.94 0.93 0.92 0.91 0.92 0.92 0.91 0.91 Na. 0.02 0.02 0.02 0.02 0.04 0.02 0.03 0.03 0.02 0.03 0.04 K------

2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 XY 2'.02 2.02 2.03 2.05 2.05 2.02 2.04 2.05 2.03 2.03 2.07

Wo 47.2 47.2 47.9 48.5 48.9 47.6 46.9 48.0 47.4 48.1 48.4 En 44.6 45.1 42.8 40.2 35.3 42.0 38.7 41.1, 44.9 38.1 35.6 Fs 8.2 7.7 9.3 11.3 15.8 10.4 14.4 10.9 7.7 13.8 16.0

Ac 1.9 1.9 2.0 2.0 4.1 2.0 2.9 3.0 2.0 3.1 4.1 Di 84.5 85.5 82.2 78.0 69.1 80.2 72.8 79.0 85.3 73.5 69.1 13.6 12.6 15.8 20.o 26.8 17.8 24.3 18.0 12.7 23.4 26.8 - 14? - FIG. 44

A. PS118 Alkali basalt. Twinned hourglass pyroxene crystal. Analyses 1-12 table 18. Plane polarised light x 13. Beam traverses across the junction between the two zones along along the line indicated are shown overleaf.

Enlarged area of PS118.A. Showing minute scale oscillatory zoning and inclusions of small opaque anhedra between some zones. Plane polarised light x 8o A. PS118 Alkali basalt. Twinned hourglass pyroxene crystal. Analyses 1-12 table 18. Plane polarised light x 13. Beam traverses across the junction between the two zones along along the line indicated are shown overleaf.

Enlarged area of PS118.A. Showing minute scale oscillatory zoning and inclusions of small opaque anhedra between some zones. Plane polarised light x 8o TABLE 18 PYROXENH - HOURGLASS ZONING

PS118(1-12) Hourglass crystal A. See fig 44A (opposite) PS118 PS118 PS118 PS118 PS118 PS118 PS118 P3118 PS118 PS118 PS118 PS118 (1) (2) (3) (L) , (5) , (6) (7) (8) (9) (10) (11) (12) 3i0, 47.9 48.4 45.6 '46.1 444 44.3 47.2 47.8 47.8 48.0 44.1* 4 44.9 TiO2 2.9 2.9 3.9 3.6 4.4 4.3 2.9 2.9 2.9 2.8 4.4 4.7 A1203 5.5 5.6 8.4 8.1 8.5 8.1 5.7 5.9 5.3 5.3 8.8 8.7 Fe0 7.5 7.5 8.1 8.0 8.4 * 8.0 7.3 7.3 7.6 7.5 8.3 8.1 MgO 13.3 13.1 12.0 12.1 11.6 11.8 13.4 13.4 13.5 13.5 10.8 10.8 Mn0 0.1 0.2 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.2 0.2 0.2 CaO 22.5 22.5 22.1 22.1 21.8 22.1 22.6 22.7 22.6 22.5 22.3 22.4 Na 0.6 20 0.5 0.5 o.6 0.5 0.6 0.6 0.6 o.6 0.5 0.6 0.6 K 0 ND ND 2 ND ND ND ND ND ND ND ND ND ND TOTAL 100.2 100.7 100.8 100.7 99.4 99.3 99.8 100.7 100.3 100.4 99.5 100.4 FORMULA ON BASIS OF 6 OMENS Si 1.79. 1.80 1.70 1.72 1.67 1.68 1.77 1.77 1.79 1.79 1.67 1.69 Al 0.21 0.20 0.30 0.28 0.33 0.32 0.23 0.23 0.21 0.21 0.33 0.31 Ti

Al 0.03 0.05 0.07 0.08 0.05 0.04 0.02 0.03 0.02 0.03 0.07 0.07 Ti 0.08 0.08 0.11 0.10 0.13 0.12 0.08 0.08 0.08 0.08 0.13 0.13 Fe 0.23 0.23 0.25 0.25 0.27 0.26 0.23 0.23 0.24 0.23 0.26 0.25 Mg 0.74 0.73 0.67 0.67 0.65 0.67 0.75. 0.74 0.75 0.75 0.61 0.60 Mn 0.00 0.01 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.01 0.01 0.01 Ca 0.90 0.90 0.88 0.88 0.89 0.90 0.91 0.90 0.91 0.90 0.91 0.90 Na 0.04 0.04 0.04 0.04 0.05 0.05 0.04 0.04 0.04 0.04 0.05 0.05

Z 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 XY 2.02 2.04 2.02 2.03 2.05 2.04 2.03 2.02 2.04 2.04 2.04 2.01

Wo 48.1 48.1 48.9 48.9 48.9 49.2 48.1 48.1 47.9 47.6 50.8 51.1 En 35.6 39.1 37.2 37.2 35.7 36.6 39.7 39.6 39.5 39.7 34.1 34.1 Fa 12.3 12.8 13.9 13.9 15.4 14.2 12.2 12.3 12.6 12.7 15.1 14.8

Ac 4.1 4.1 4.4 4.4 5.4 5.4 4.1 4.1 4.0 4.0 5.7 5.8 Di 76.3 75.3 72.8 72.8 69.9 72.0 76.5 76.3 75.8 75.8 69.3 69.8 Ed 19.6 20.6 22.8 22.8 24.7 22.6 19.4 19.6 20.2 20.2 25.0 24.4 )(

855 6239 -ri co

6128 6329 3141 3047

2589 5786

709

5947

2696 2565 — 2615

5917 5813 >IC

mrf CD FIG. 44 (continued)

Ps 1/813 HouRcILsS5 70NiNGT ,

B. PS118. Hourglass pyroxene crystal, analyses 13-18. Unzoned crystal, analysis 19, table 18. Crossed nicols. x 27. FIG. 44 (conti,,,zca)

PC „AR. HOURGLASS ZONING .

B. PS118. Hourglass pyroxene crystal, analyses 13-18. Unzoned crystal, analysis 19, table 18. Crossed nicols. x 27. TABLE 18 (continued) PS118 PS118 P3118 p3118 PS118 P3118 p3118 PS118 PS118 PS118 PS118 (13) (14) (15) (16) (17), (18) (19) (20) (21) (22) (23)

SiO2 48.7 46.1 45.2 46.1 48.4 49.o 46.5 48.9 46.8 47.8 45.0 TiO2 2.8 4.4 4.3 4.1 2.7 2.7 3.6 2.8 3.5 2.5 4.o A1203 5.5 7.9 7.6 7.5 5.4 5.2 6.6 5.1 6.7 5.5 7.7 Fe0 7.5 7.9 8.1 7.9 7.4 7.4 7.8 7.5 7.5 7.6 8.1 Mg0 13.4 11.9 11.6 11.5 12.6 13.0 11.6 12.8 12.1 13.7 12.1 1•:n0 0.2 0.1 0.1 0.2 0.2 0.2 0.1 0.2 0.1 0.2 0.1 CO 22.5 22.5 22.7 22.7 22.8 22.5 22.5 22.4 22.5 22.4 22.6 Na20 0.5 0.6 0.6 0.6 0.6 '0.6 0.6 0.6 0.6 0.5 0.6 ND ND ND K20 ND ND ND ND ND ND ND ND TOTAL 101.1 101.4 100.2 100.6 100.1 100.6 99.3 100.3 99.8 100.2 100.2 FORMULA ON BASIS OF 6 OXYGENS Si 1.80 1.71 1.70 1.73 1.81 1.82 1.76 1.82 1.76 1.79 1.69 Al 0.20 0.29 0.30 0.27 0.19 0.18 0.24 0.18 0.24 0.21 0.31 Ti

Al 0.04 0.05 0.04 0.06 0.05 0.05 0.06 0.05 0.06 0.03 0.03 Ti 0.08 0.12 0.12 0.12 0.08 0.08 0.10 0.08 0.10 0.07 0.11 Fe 0.23 0.25 0.25 0.25 0.23 0.23 0.25 0.24 0.24 0.24 0.26 Mg 0.74 0.66 0.65 0.64 0.70 0.72 0.65 0r71 0.68 0.77 Mn 0.01 0.00 0.00 0.01 0.01 0.01 0.00 0.01 0.00 0.01 0.00 Ca 0.89 0.89 0.92 0.91 0.91 0.90 0.91 0.89 0.90 0.90 0.91 Na 0.04 0.04 0.04 0.05 0.04 0.04 0.05 0.04 0.04 0.04 0.04 K z 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 XY 2.03 2.01 2.02 2.04 2.02 2.03 2.02 2.02 2.02 2.06 2.03

Wo 47.6 49.4 50.5 50.2 49.2 48.4 50.3 48.1 49.4 46.9 49.2 En 39.6 36.7 35.8 35.4 37.8 38.7 35.9 38.4 37.4 40.1 36.8 Fs 12.8 13.9 13.7 14.4 13.0 12.9 13.8 13.5 13.2. 13.o 14.0

Ac 4.1 4.4 4.4 5.5 4.3 4.2 5.6 4.2 4.4 3.9 4.3 Di 75.5 72.5 72.2 71.1 74.5 75.0 72.2 74.0 73.9 75.5 72.3 Hd 20.4 23.1 23.4 23.4 21.2 20.8 22.2 21.8 21.7 20.6 23.4

PS118(13-18) Hourglass crystal B. See fig 44B (opposite) P3118 (19) Unzoned crystal. See fig 44B (opposite) PS118(20-21) Hourglass crystal. See fig 44C (overleaf) PS118(22-23) Basal section of hourglass crystal. See fig 44D (overleaf) p5118C. HOurkGrLASS ZONING-

PS 118. HOURGLASS CRYSTAL X50

PS 118 - BASAL SECT ION OF HOURGLASS CRYSTAL.

Twin plane

1.5 mm . F 1 6 44 .6 soolvi ca- ‘-kontecLrk)zz

PS 118. HOURGLASS CRYSTAL k 50

PS 118 - BASAL SECTION OF HOURGLASS CRYSTAL.

Twin plane

< 1.5 mm

c0 0 %.0 H .2, • ri H r-i H ra C., III - H (0 1 1 CJ i 0) • Co ca ,C) O k 0 b0 U) C..; 0 O co O O ca - I CS X in • ' •

, •H U\ u H O. c) r-I rd 0 e) co P4 - k i . )

c0 ,-1) - H 0 +> L--- ,S) .- H • -P 1 CO Cr' H , I

. o

tro t illustrated vp 0 4-1 0 H co-1 4-1 F.. 0 0 0 0 ;..1 faCt ci 0 U) • . 1 .1.) c... ..-i P4 c; g onveLr . / O S • oo g LO 1Z ; 1 H H 4 CJ O k 0 C.; CO F-i 0 • › O P. .1-1 I • 1 C) X U) CO 0 0 • a) a O'N ) • . a 0 1 H cr\ C.) 2 ›. (I) 0 H co 4-1 C) c; C) 1 • 0 3

CD H 4) $-1 0 ri o 0 bC •

0 :-.6. (6- ) !Tot illustrated 0 ci-1 +3 14 -p 0 0 ci • -P $. C;) g ta0 U) a) 0 • 4 •

TABLE 19 PYROXENE - HOURGLASS ZONING 18-66(1-5) Hourglass crystal. See fig. 45. (opposite) 18-66(6-7) Crystal with normal zoning. See fig. 45 (opposite) 18-66 18-66 18-66 18-66 18-66 18-66 18-66 (1) (2) (3) (4) (5) (6) (7)

SiO2 47.2 46.9 43.2 43.7 46.0 47.5 42.5 4.7 TiO2 2.5 2.7 4.1 3.7 2.6 2.5 5.6 11.4 A1203 6.6 6.8 10.1 9.8 6.5 Fe0 7.6 7.5 8.2 8.3 7.4 7.7 8.2 MgO 13.3 13.1 31.3 11.3 13.5 12.9 11.2 Mn0 0.1 0.1 0.1 0.2 0.1 0.2 0.1 CaO 22.3 22.5 22.4 22.6 22.5 22.8 22.3 0.6 Na20 0.5 0.5 0.6 0.5 0.5 0.6 0.0 K20 ND ND ND ND ND 0.0 TOTAL 100.1 100.1 100.0 100.1 99.1 99.8 101.0 FORMULA ON BASIS OF 6 OXYGENS Si 1.77 1.76 1.63 1.65 1.74 1.78 1.59 Al 0.23 0.24 0.37 0.35 0.26 0.22 0.41 Ti

Al 0.06 0.06 0.08 0.09 0.03 0.03 0.09 Ti 0.07 0.08 0.12 0.10 0.07 0.07 0.13 Fe 0.24 0.24 0.26 0.26 0.24 0.24 0.26 Mg 0.74 0.73 0.63 0.64 0.76 0.72 0.63 Mn 0.00 0.00 0.00 0.01 0.00 0.01 0.00 Ca 0.89 0.90 0.90 0.91 0.92 0.92 0.90 Na 0.04 0.04 0.04 0.04 0.03 0.05 0.04

Z 2.00 2.00 2.00 2.00 2.00 2.00 2.00 XY 2.04 2.03 2.03 2.05 2.05 2.04 2.05

,10 47.6 48.1 50.3 50.0 47.9 48.6 50.3 En 39.6 39.1 35.2 35.2 39.6 38.2 35.2 Fs 12.8 12.8 14.5 14.8 12.5 13.2 14.5

Ac 4.1 4.1 4.5 4.4 3.o 5.2 4.5 Di 75.5 75.3 70.8 70.3 76.0 74.2 70.8 Hd 20.4 20.6 24.7 25.3 21.0 20.6 24.7

WITH 4f(EiN co(-Li. —er

P5 58 (1-2) PYROX ENE WITH GREEN CORE.

PLANE POLARISED LIGHT X90.

Continued overleaf

CRYSTALS WITH GREEN CORES.

PS 58(3)

ps 58(5)

PS 58 (4)

3.0mm

. • 1

P5 58 (1-2) PYROX ENE WITH GREEN CORE.

PLANE POLARISED LIGHT X90.

Continued overleaf

CRYSTALS WITH GREEN CORES.

PS 58 (3)

PS 58(5)

PS 58 (4)

3.0mm - 156 - TABLE 20

PYROXENE - CRYSTALS WITH GREEN CORES Analysed crystals shown in fig. 46 (opposite) Ps58 Ps58 Ps58 Ps58 Ps58 Ps58 (1) (2) (3) (4) (5) (6)

SiO2 43.7 47.0 44.9 48,1 42.5 43.1 TiO2 2.0 2.4 2.5 2.0 1.7 2.5 A1203 7.2 4.7 7.8 4.8 6.9 5.7 FeO 12.7 7.9 10.7 7.5 13.6 7.8 MgO 9.1 14.7 10.8 14.5 9.4 14.2 Mn0 0.4 0.2 0.3 0.2 0.4 0.2 Ca0 22.3 22.8 22.6 23.0 21.9 22.8 Na20 1.4 0.4 0.9 0.4 1.5 0.5 K20 ND ND ND ND ND ND TOTAL 98.8 100.1 100.5 100.5 97.9 96.8 FORMULA ON BASIS OF 6 OXYGENS Si 1.71 1.77 1.71 1.80 1.70 1.69. Al 0.29 0.21 0.29 0.20 0.30 0.27 Ti 0.02 0.04

Al 0.05 0.06 0.01 0.03 Ti 0.06 0.05' 0.07 0.06 0.05 0.03 Fe 0.42 0.25 0.34 0.23 0.45 0.26 Mg 0.53 0.82 0.61 0.81 0.56 0.83 Mn 0.02 0.01 0.01 0.01 0.01 0.01 Ca 0.94 0.92 0.92 0.92 0.94 0.96 Na 0.10 0.03 0.07 0.03 0.12 0.03

Z 2.00 2.00 2.00 2.00 2.00 2.00 XY 2.02 2.08 2.08 2.07 2.16 2.12

wo 49.2 46.o 48.9 46.7 48.o 46.6 En 27.7 41.0 32.5 41.1 28.6 40.3 Fs 23.1 13.0 18.6 12.2 23.4 13.1

Ac 10.3 2.8 7.3 2.9 11.7 2.7 Di 54.6 75.9 63.5 77.1 54.9 75.5 Hd 35.1 21.3 29.2 20.0 33.4 21.8 .. 157

FIG. 46. (continued)

PS58. Crystal with green core. Lnalyses 1 and 2, table 20. Crossed nicols. x 90. Beam traverses across the crystal along the line indicted are shown opposite. PS58. Crystal with green core. Analyses 1 and 2, table 20. Crossed nicols. x 90. Beam traverses across the crystal along the line indicted are shown opposite. Al

Q P

PS 58. Pyroxene crystal Na with green core.

FIG 46. P

FIG 41.

MA 8— Pyroxenes with green cores •

0.5mm

0•6MM

1.5mm TABLE 21 PYROXENE - CRYSTALS WITH GREEN CORES mA8 MA8 MA8 MA8 MA8 MA8 MA8 MA8 MA8 (1) (2) 1.12. iLl 121 (6) al (8) 121 SiO, 45.5 42.3 46.7 45.4 48.8 50.2 44.8 48.5 44:3 4.1 TiO2 1.6 4.5 1.0 4.1 2.2 1.8 3.7 2.6 4.2 4.9 8.2 Al2o3 6.6 8.7 5.7 7.5 6.2 7.9 Fe0 12.8 9.0 16.6 7.4 7.5 6.5 7.7 7.7 8.6 MgO 9.0 11.2 5.5 12.9 12.8 13.6 12.6 14.1 12.1 Mn0 0.5 0.1 1.1 0.2 0.1 0.1 0.2 0.2 0.2 CaO 21.8 22.5 20.8 22.9 21.9 23.0 22.7 22.7 22.7 0.8 0.4 o.4 0.6 Na20 1.4 o.6 1.8 0.4 0.5 0.0 0.0 0.0 0.0 K20 0.0 0.0 0.0 0.0 0.0 TOTAL 99.2 98.9 99.2 100.8 100.3 99.8 100.1 101.1 100.8 FORMULA ON BASIS OF 6 OXYG EMS si 1.77 1.63 1.84 1.70 1.81 1.87 1.69 1.80 1.67 Al 0.23 0.37 0.16 0.30 0.19 0.13 0.31 0.20 0.33

Ti .11m. ME el&

Al 0.07 0.03 0.11 0.03 0.08 o.o6 0.04 0.01 0.04 Ti 0.05 0.13 0.03 0.12 0.06 0.05 0.10 0.07 0.12 Fe 0.42 0.29 0.55 0.23 0.23 0.20 0.24 0.24 0.27 Mg 0.52 0.64 0.33 0.72 0.71 0.76 0.71 0.78 0.68 Mn 0.02 0.00 0.04 0.01 0.00 0.00 0.01 0.01 0.01 Ca 0.91 0.93 0.88 0.92 0.87 0.92 0.92 0.90 0.92 Na 0.11 0.05 0.14 0.03 0.05 0.03 0.04 0.03 0.05

K dna dna 41•10

Z 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 XY 2.10 2.07 2.08 2.06 2.00 2.02 2.06 2.04 2.09

Wo 48.7 5o.o 48.9 48.9 48.1 48.9 48.9 46.6 48.9 En 27.8 34.4 18.3 38.3 39.2 40.5 37.8 40.4 36.2 Fs 23.5 15.6 32.8 12.8 12.7 10.6 13.3 13.o 14.9

Ac 11.4 5.4 15.2 3.2 5.3 3.1 4.2 2.9 5.2 Di 54.2 68.8 35.9 75.0 75.6 79.2 74.0 75.7 70.8 Hd 34.4 25.8 48.9 21.8 19.1 17.7 21.8 21.4 24.0

MA8(1-6) Phenocrysts with green cores. See fig 47 opposite. mA8(7) Pyroxene rimming partially resorbed amphibole. See fig 13. mA8(8-9) Groundmass pyroxene.

• licsi&R.Stfr a •TiVi3i4 z! .msr44. (lilt' -AS.

.4 Polo xe ofi S 7.7. rtise.43

• .

,t) #

y - • , • s . t,

.•

MA 2 8 .

REVERSED ZONING

C PS 10 .

CRYSTAL WITH

GREEN CORE

tblittlE• fitrt prtmanA.11%

fIG 4L,

A 10, . '• _ • ' •

•

6, Ai

'n1 ' -.. v 111 , % "". ;Sr

•

M A 28.

REVERSED ZONING.

PS 10.

CRYSTAL WITH

GREEN CORE - 162 - TABLE 22 ZONED PYROXENES FROM PHONOLITES PS27(1-2). Normal zoning. See fig.48A (opposite) MA28(1-2). Reversed zoning. See fig. 48B (opposite) PS10(1-2). Crystal with green core and pale purple rim. See fig.48C (opposite) PS 27 PS27 MA28 MA28 PS10 PS10 (1) (2) (1) (2) (1) (2)

SiO2 48.9 49.1 49.2 51.4 46.2 46.3 Ti02 1.0 0.9 1.9 1.2 1.2 1.7 A1203 3.8 3.5 3.4 2.2 6.7 6.7 FeO 11.6 12.4 10.3 9.1 14.9 12.4 MgO 10.4 9.2 12.1 12.8 7.7 9.5 MnO 0.6 1.0 1.0 1.0 0.9 0.5 CaO 21.7 20.3 21.7 22.3 22.0 23.0 Na20 1.6 2,2 1.5 1.2 1.5 0.9 K20 0.0 0.0 0.0 0.0 ND ND TOTAL 99.6 98.6 101.1 101.2 101.1 101.0 FORMULA ON BASIS OF 6 OXYGENS Si 1.87 1.90 1.85 1.92 1.78 1.76 Al 0.13 0.10 0.15 0.08 0.22 0.24 Ti

Al 0.04 0.06 - 0.02 0.09 0.06 Ti 0.03 0.03 0.05 0.03 0.04 0.05 Fe 0.37 0.40 0.32 0.28 0.48 0.40 Mg 0.60 0.53 0.68 0.70 0.44 0.54 Mn 0.02 0.03 0.03 0.03 0.03 0.02 Ca 0.89 0.84 0.88 0.89 0.91 0.94 Na 0.12 0.17 0.11 0.09 0.12 0.07 X- - - - -, -

Z 2.00 2.00 2.00 2.00 2.00 2.00 KY 2.07 2.06 2.07 2.04 2.11 2.08

Wo 47.4 46.7 46.1 46.8 48.9 49.5 En 31.9 29.1+ 35.6 36.9 23,7 28.4 Fs 20.7 23.9 18.3 16.3 27.4 22.1

Ac 12.1 17.7 10.7 8.9 12.6 7.3 Di 60.6 55.2 66.o 69.3 46.3 56.2 lid 27.3 27.1 23.3 21.8 41.1 36.5 - 163 -

TABLE 23 PYROXENES FROM XENOLITHS Analyses are given in Borley et al. (1970)

1P 2P 3P 4P 5Pa 5Pb 6P 7P 8P Ac 4 4 3 7 7 8 9 15 7 Di 83 79 77 74 65 66 66 38 63 Hd 13 17 20 19 28 26 25 47 30

Wo 44 50 50 50 49 49 50 47 49 En 46 39 39 36 32 34 33 20 32 Fs 10 11 11 14 18 17 17 33 19

1P (GB1) Banded olivine and pyroxene rock. 2P (PS122) Pyroxenite. 3P (PS106) Pyroxenite. 4P (PS20) Pyroxene-kaersutite rock. 5P (PS16) Pyroxene-kaersutite rock. 6P (PS16) Pyroxene-kaersutite rock. 7P (PS11) Syenite (green core of pyroxene) 8P (PS23) Syenite. - 164 -

TABLE 24 Pyroxene cell parameters.

j..1( Specimen oR bP cp a sin0 Ca2+ Mm2+ Fe2+ MA19P 9.745 8.893 5.283 73.81 9.359 48.o 45.3 6.71x (ankaramite) 1.004- -.003 -.004 -.04 MA6P 9.753 8.895 5.276 73.90 9.369 50.1 43.0 6.92 (alkali basalt) -.005 ±.003 -.004 -.o5 24-66 9.753 8.892 5.284 73.90 9.369 50.5 42.1 7.43 (alkali basalt) 1.004 ±.003 1.003 .1.04 31-66 9.743 8.897 5.275 73.87 9.358 50.4 43.7 5.94 (alkali basalt) 1.004 -.003 -.004 -.o4 P191 9.742 8.881 5.288 73.92 9.361 49.0 43.7 7.35 (alkali basalt 1.004 -.003 1.003 -.o4 P194 9.758 8.887 5.277 73.92 9.376 - - (alkali basalt) -.003 -.002 -.002 -.03 P6 9.751 8.909 5.266 73.96 9.369 48.4 41.3 10.36 -.003 (trachybasalt) -.002 1.004 .03 P7 9.755 8.902 5.28o 73.95 9.374 46.6 41.o 12.47 (trachybasalt) 1.003 1.002 -.002 ±.03 MA7(PS27) 9.757 8.904 5.283 74.00 9.378 - - (phonolite) -.004 1.003 1.004 1.04 8 P183 9.76o 8.925 5.266 74.03 9.383 48.2 41.4 10.4 (phonolite) -.003 -.003 -.003 -.03 P4o 9.749 8.911 5.271 73.94 9.369 47.4 44.3 8.39 (phonolite) 1.002 -.002 1.002 1.03 PS69 9.679 8.822 5.301 72.77 9.245 - - (nepheline 1.006 -.003 1.004 1.05 syenite)

Refers to numbers in fig. 53 and text. - 165 - TAUPE 25

Microprobe analyses of amphiboles R1 PS58 MA8 PS56 MA22 P292 PS92 GB8

SiO2 39.2 38.6 38.7 39.9 39.1 39.4 39.3 39.0 TiO2 5.9 6.1 5.9 5.6 6.8 7.4 7.3 5.8 A1203 12.7 13.7 13.3 13.1 12.8 12.0 12.0 11.6 Fe203 4.0 Fe0 6.5 11.1 11.3 10.4 10.4 11.1 11.2 13.1 MgO 13.1 13.3 12.6 14.2 13.3 12.8 12.7 12.4 Mn0 0.1 0.1 0.2 0.1 0.1 0.5 0.4 0.3 Ca0 12.4 12.4 12.0 11.9 12.3 11.9 12.1 11.8 Na20 3.6 2.7 2.9 2.6 2.6 2.7 2.7 2.9 1(20 1.5 0.8 1.0 1.0 o.8 1.0 0.9 1.0 H2O 1.4 TOTAL 100.4 98.8 97.9 98.8 98.2 98.8 98.6 97.9 FORMULA ON BASIS OF 23 OXYGENS (except R1) Si 5.81 5.68 5.76 5.84 5.77 5.82 5.81 5.86 Al 2.19 2.32 2.24 2.16 2.22 2.09 2.08 2.06

Al 0.01 0.06 0.09 0.10 - - - - Ti 0.67 0.68 o.66 o.61 0.75 0.82 0.81 0.65 Fe3 o.45 ------2 Fe 0.80 1.37 1.41 1.27 1.29 1.37 1.38 1.64 Mg 2.89 2.91 2.80 3.09 2.93 2.82 2.80 2.78 Mn 0.01 0.01 0.02 0.02 0.02 0.06 0.06 0.04

Ca 1.97 1.96 1.91 1.87 1.94 1.88 1.92 1.91 Na 1.14 0.76 0.83 0.75 0.74 0.76 0.77 0.83 K 0.28 0.15 0.20 0.19 0.15 0.18 0.17 0.18 OH 1.38 ------7 8.00 8.00 8.00 8.0o 7.99 7.91 7.89 7.92 Y 4.83 5.03 4.98 5.09 4.99 5.07 5.05 5.11 x 3.39 2.87 2.94 2.81 2.83 2.92 2.86 2.92 Microprobe analyses except Rl. Total iron as Fe0 R1 Ridley 1970. Megacryst Kaersutite (formula on basis of 24 oxygens) PS58 Kaersutite. alkali basalt. MA8 Kaersutite. alkali basalt PS56 Kaersutite. a]kali basalt. MA22 Kaersutite. alkali basalt PS92 Kaersutite. trachybasalt GB8 Kaersutite. trachyandesite TAELE 25 (continued)

13-66 PS10 PS10 PS10 PS27 PS27 ps84 (1) (2) (3)

5102 37.5 38.6 38.4 37.5 37.6 38.7 50.9 TiO2 5.7 3.4 3.o 1.9 5.o 4.o 3.1 Al203 14.5 13.1 13.3 12.7 13.4 12.6 2.6 Fe203 ------Fe0 10.4 18.1 18.4 24.6 16.3 16.9 12.2 Mg0 12.8 9.2 8.8 5.2 9.1 9.5 15.1 Mn0 0.4 0.5 0.6 1.4 0.4 0.6 1.0 Ca0 12.6 11.6 11.7 10.8 11.2 11.3 5.5 Na20 2.3 2.6 2.8 2.7 3.1 3.1 6.4 K20 1.1 1.5 1.5 1.9 1.1 1.2 1.3 H20 ------TOTAL 97.3 98.6 98.5 98.8 97.2 97.9 98.1 FORMULA ON BASIS OF 23 OXYGENS Si 5.60 5.89 5.88 5.93 5.78 5.92 7.41 Al 2.40 2.11 2.12 2.07 2.22 2.08 0.44

Al 0.16 0.24 0.27 0.30 0.20 0.20 - Ti 0.64 0.38 0.35 0.23 0.57 0.46 0.34 Fe3______- 2 Fe 1.30 2.31 2.36 3.27 2.10 2.16 1.48 Mg 2.86 2.10 2.01 1.23 2.08 2.16 3.28 Mn 0.05 0.07 0.08 0.18 0.06 0.08 0.12

Ca 2.02 1.90 1.93 1.8/+ 1.85 1.85 0.86 Na 0.67 0.77 0.84 0.84 0.93 0.92 1.80 K 0.21 0.30 0.30 0.39 0.22 0.23 o.40 OH ------z %op 8.00 8.00 8.00 8.00 8.00 7.85 Y 5.01 5.10 5.07 5.21 5.01 5.06 5.22 X 2.90 2.97 3.07 3.07 3.00 3.00 3.06 13-66 Kaersutite. trachyandesite. PS10(1)Kaersutite. Phonolite PS10(2)Kaersutite. phonolite. Core of zoned crystal. PS10(3)Kaersutite. phonolite. Outer zone of PS10(2). PS27 Kaersutite. phonolite. (see fig. 48A) PS27 Kaersutite. phonolite. (see fig. 48A) ps84 Magnesioarfedconite)phonolite. - 167 - TABLE 26 MICROPROBE ANALYSES OF BIOTITES. 9-66 9-66 9-66 PS75 PS75 PS69 TC19 (1) (2) (3) (1) (2)

SiO2 37.3 36.9 37.3 37.o 36.7 38.2 36.4 6.88 TiO2 6.7 6.9 6.7 7.2 7.1 4.8 A1203 12.8 12.8 12.6 12.6 12.5 11.5 12.1 Fe0 13.4 13.6 13.6 15.1 14.5 15.6 14.8 Mg0 16.2 16.1 16.1 13.5 13.0 12.4 13.4 MnO 0.5 o.6 o.6 0.5 0.5 1.1. 0.40 Ca0 0.0 0.0 0.0 0.0 0.0 0.0 0.02 Na20 1.1 1.1 1.0 0.9 0.9 0.7 1.11 k20 8.5 8.8 8.8 8.3 8.2 9.5 8.54 TOTAL 96.5 96.8 96.7 95.1 93.4 93.8 93.815 FORMULA ON BASIS OF 22 OXYGENS Si 5.50 5.44 5.49 5.56 5.55 5.61 5.57 Al 2.21 2.21 2.19 2.23 2.25 2.15 2.18

Al ------Ti 0.75 0.76 0.74 0.82 0.82 0.57 0.79 Fe 1.64 1.67 1.67 1.89 1.85 2.07 1.89 Mg 3.54 3.54 3.54 3.04 2.95 2.92 3.05 Mn 0.06 0.07 0.07 0.06 0.06 0.10 0.05

Ca 0.00 0.00 0.00 0.00 0.00 0.00 0.00 No 0.30 0.30 0.28 0.28 0.26 0.20 0.33 Ii 1.60 1.64 1.66 1.59 1.60 1.92 1.67

7.71 7.65 7.68 7.79 7.8o 7.76 7.75 Y 5.99 6.04 6.02 5.81 5.68 5.66 5.78 N 1.90 1.94 1.94 1.87 1.86 2.12 2.00

Includes Ba0 = 0.16 9-66 (1-3) Microphenocrysts phonolite. PS75(1-2) Crystals within phonolitic glass. PS69 Small crystal in nepheline syenite. TC19 Biotite crystals from phonolitic glass (Carmichael 1967) - 168 -

TABLE 27. Microprobe analyses of Melanite Specimens PS9 and PS10. Phenocrysts from a phonolite dyke within the Ancient Series. The method of proportioning iron is given in the text.

12_ - 3 4 SiO2 34.9 34.7 34.6 34.7 TiO2 3.0 3.0 3.5 3.1 A1203 5.3 5.1 4.5 5.0 Fe203 23.3 23.4 24.1 23.6 FeO 1.1 1.0 0.9 1.2 MgO 0.2 0.3 0.3 0.3 Mn0 1.9 1.9 1.7 1.9 Ca0 31.0 31.0 31.3 30.9 TOTAL 100.7 100.4 100.9 100.7 FOEMULA ON BASIS OF 24 OXYGENS Si 5.75 5.75 5.70 5.72 Al 0.25 0.26 0.30 0.28

Al 0.77 0.73 0.58 0.70 Ti 0.37 0.38 0.44 0.39 Fe3+ 2.89 2.91 2.99 2.94

Fe2+ 0.15 0.14 0.12 0.16 Mg 0.06 0.06 0.06 0.06 Mn 0.21 0.21 0.20 0.21 Ca 5.48 5.50 5.54 5.48

z 6.00 6.00 6.00 6.00 Y 4.03 4.02 4.01 4.03 x 5.90 5.91 5.92 5.91 -169-

TABLE 27 (continued)

1 2 3 4

Andradite 71.8 72.8 75.3 72.1 Pyrope 1.0 1.1 1.1 1.0 Spessartine 3.6 3.6 3.4 3.6 Grossular 19.4 19.2 18.2 19.7 Almandine 2.1 1.4 0.2 1.7 Schorlomite 2.1 1.9 1.8 1.9 % Cations allocated 98.3 98.0 97.2 99.7 Remainder Ti .025 .027 .033 .027 2+ Remainder 10 .003 .006 .011 .006 -170 -

TABLE 28. Microprobe Analyses and Cell Parameters of Sphene. Specimen PS 27 (MA7,GB4). (See fig. 48A)

1 2

SiO,L 29.2 29.3 TiO2 36.8 36.1 A1203 1.45 1.36 HFe0 1.20 1:46 MgO 0.03 0.01 MnO 0.05 0.08 Ca0 27.5 27.0 Na20 0.04 0.07 TOTAL 96.27 95.38

Total Fe as FeO

Cell Parameters a 6.559 ±.005 R b 8.709 t .003 2 c 7.450 t .005 2 119.86 .03°

Standard errors calculated by least squares program - 171 -

TABLE 29 Unambiguously indexed reflections used in refining sphene cell - parameters.

hkl 29(012) 2&(Cu) Wavelength Intensity observed calculated a or al 111 17.95 17.95 a 50 112 25.97 26.09 a 5 202 29.80 29.77 a >100 131 34.32 34.31 a 95 022 34.57 34.57 a 65 132 39.39 39.36 a1 25 112 39.71 39.71 a 16 040 41.48 41.47 a 5 24 312 42.84 42.82 a1 223 43.32 43.30 a1 7 313 46.55 46.54 a1 10 133 48.48 48.50 a 3 310 49.11 49.18 a 4 042 50.50 50.51 a1 18 202 52.42 52.38 a 14 240 52.91 52.91 a1 16 333 55.76 55.76 a1 38 133 61.96 61.95 a1 15 153 65.62 65.61 a1 27 351 69.71 69.70 a1 10 12 262 72.22 72.24 a1 -172 -

SECTION 40

CONCLUSIONS

Discussion and conclusions with regard to the properties of individual ferromagnesian minerals and the conditions under which they crystallised have been made in the relevant parts of Section 3. Some further general discussion is necessary here,, the data from studies on individual minerals being coordinated, and correlated with those obtained by other workers, and used as a basis for considering the origin and evolution of the Tenerife magmas.

Ridley (1970) suggested that the parental magma in Tenerife and probably other Canary Islands was of basanite (nepheline normative alkali basalt) composition, evidence for this being seen in the abundance of alkali basalts erupting at different times throughout the Canary Archipelago. In Tenerife the volcanic activity appears to have been cyclical, each new cycle commencing with eruptions of basaltic magma, and continuing with eruptions of the salic members of the suite. Olivine and pyroxene and, possibly, some oxides would be the first minerals to crystallise from such a magma at depth and, after settling, would give rise to crystal/liquid mixtures which are represented at the surface now by ankaramitic lavas, and by dunite and pyroxenite xenoliths; at depth, accumulate rocks such as wehrlites might be present. On the island of Gomera, which contains rocks closely similar to the Tenerife formations a basal complex containing abundant wehrlites occurs (Bravo 1961+). The wehrlitic roclzs are likewise interpreted as cumulates.

The dimensions of the pyroxene and olivine phenocrysts in the ankaramites arc incompatible, under normal circumstances, with post-eruptive crystallisation from a lava or shallow intrusion, and the well defined normal zoning in the pyroxenes can be interpreted as indicating crystallisation of the bulk of the crystal prior to extrusion, followed by formation of the outer zone on final solidification of the lava. The oxidation rims around some olivine phenocrysts may also represent a - 173 -- post-eruptive effect; the phenocrysts haVing crystallised at depth: The pyroxene phenocrysts contain significant amounts of and experimental work on the substitution of titanium TiO2' in diopside (Yagi and Onuma 1967) shows that above 10 Kbars under dry conditions the amount of CaTiA1206 soluble in diopside decreases almost to zero. Therefore, the pressure during crystallisation of the olivine and pyroxene phenocrysts from the ankaramites may not have been much in excess of 10 Kbars, if dry conditions prevailed. The increased amounts of titania in pyroxenes from the alkali basalts and in the outer rims of normal zoned crystals, in comparison with the amounts contained in the cores of crystals from ankaramites may be a reflection of the low pressure under which the former pyroxenes crystallised; but experimental results show that a lower temperature of crystallisation will have a similar effect to a low pressure (Yagi and Onuma 1967. 1969). The high proportion of tetrahedral to octahedral aluminium in the pyroxenes also reflects a prodominently high temperature, as opposed to high pressure crystallisation (Aoki and Kushiro 1968), as pyroxenes formed under very high pressure (eclogites and mantle phases) contain all their aluminium in octahedral coordination. It seems that results of the present study are not at variance with conclusions of Ridley (1970) that a basaltic magma in Tenerife began to crystallise (olivine and pyroxene) at between 13-20 Kbars, and Borley et al. (1970) that over the pressure range 9-10 Kbars (the upper limit may be higher) and at a temperature above 10150C clinopyroxenite xenoliths have formed (assuming crystallisation under approximately the same conditions for the pyroxenite xenoliths and the phenocrysts in the ankaramites).

Irregular and large scale oscillatory zoning in large pyroxene phenocrysts and corroded crystals is probably a reflection of movement during or after formation of the crystal. Sinking of a crystal into a region of higher temperature or an area of different composition, or a change in total pressure in the magma could lead to partial resorption of a phenocryst or crystallisation of a zone of different composition; and, with relative upward and downward, or intermittent movement, large scale oscillatory zoning might be produced. In contrast, olivines coexisting with the pyroxenes are unzoned but corrosion forms arc sometimes present. As suggested in Section 3.2, olivines may be less sensitive than pyroxenes to changes in conditions during crystallisation, only a drop in temperature 2+ 2+ or a change in the Fe /Mg ratio of the magma affecting their composition. Thus, it may be that the zoning in the pyroxenes is a reflection of changes in elemental concentrations (eg. Ti, Al, Fe3+) or changes in pressure; but, changes in the former 2+ independent of changes in the Fe /Mg2+ ratio are unlikely. This points to a final conclusion that crystallisation of zones of slightly different composition in the cores of these pyroxenes might simply have been caused by changes in pressure during crystallisation. However, it is still conjectural whether the changes in pressure alone were of sufficient magnitude to cause the observed differences in zonal composition.

Lbundant kaersutite appears to have crystallised at depth and experimental results, discussed in Section 3.3, show that an amphibole of kaersutite composition can crystallise from some magmas of basaltic.or intermediate composition over a fairly wide pressure range, but it appears to be unstable at surface pressures. The abundance of large, partially resorbed kaersutite crystals in the trachyandesites and the presence of megacrysts and kaersutite-rich xenoliths indicates that the mineral may have been a major cumulus phase in some liquids of intermediate composition. Pyroxene also crystallised with kaersutite to form the ultramafic xenoliths containing varying proportions of kaersutite and clinopyroxene (Borley et al. 1970), and the occurrence of pyroxene crystals with green cores in some rocks containing kaersutite indicates another connection between the two minerals. It is probable that the green cores of these pyroxenes, like the kaersutite, crystallised at depth. These cores are the representatives of a pyroxene trend towards enrichment in the hedenbergite molecule; but the outer rims of the crystals are the more usual salitic pyroxene. It is -175-

thought that the limited trend towards the hedenbergite enrichment shown by the salitic pyroxenes waa due to the initially high oxidation state of iron in the primary magma; and removal of 2+ Fe by separation of large quantities of olivine during early stages of differentiation (Le Maitre 1962) would have accentuated enrichment of the residual liquids in Fe3+. However the presence of the green cores shows that the iron in the residual liquids was not always so highly oxidised, and it is suggested that early crystallisation and separation of abundant olivine was not 2+ completely effective in the removal of Fe . A limited enrichment in hedenbergite is thought possible but, clearly, the green cores go beyond this limit. These green cores could have crystallised and separated under pressure from a magma of intermediate composition, before crystallisation of kaersutite from the same magma, the pyroxene becoming enriched in hedenbergite and, to a certain extent, acmite. Following a slight drop in temperature 2+ crystallisation of kaersutite with a high Fe /Fe3+ ratio might have taken place, and the effect on the liquid of removal of this mineral would have been in part, similar to that of separating olivine; i.e. to further deplete the residual liquids in ferrous iron. Pyroxenes crystallising subsequently from these liquids would show only limited enrichment in hedenbergite.

From its occurrence, kaersutite appears to have separated predominantly from liquids of intermediate composition, although its presence, in rocks varying in composition from alkali basalts to phonolites, suggests that it might have crystallised at depth from a wider range of compositions. However, the mineral shows little change in composition throughout the sequence alkali basalt, trachybasalt and trachyandesite, and changes in composition slightly only when it appears in the phonolites. In the more basic rocks, therefore, kaersutite may be purely xenocrystal, along with the green cores of the pyroxenes; but it is probable that it is present as a primary phase in the more salic rocks such as the phonolites in which it tends towards barkevikite in composition.

Finally, it is apparent, from the occurrence and characteristics of the ferromagnesian minerals, both in the major rock - 176 -

types and xenoliths, that crystallisation and separation of large amounts of olivine, Iyroxene and kaersutite took place in various magmas at depth. By considering the effects of removal of olivine and pyroxene from the assumed alkali basalt parent magma, and of kaersutite from a "residual" intermediate magma, the differentiation process which produced the variety of rock types observed can largely be understood. The effects of separating olivine and pyroxene from the parental alkali basalt magma would be to deplete the residual liquids in calcium, magnesium and iron (predominantly ferrous iron), and by further separation of plagioclase (an important phenocrystal phase in the trachybasalts) the residual liquid would be even more depleted in calcium (Ridley 1970). Separation of kaersutite from intermediate residual liquids would have had various effects on the residual salic liquids, one of which might have been a sharp increase in silica, thereby producing the observed "gap" in the chemical analyses between the trachybasalts and trachyandesites (Borley et al. 1970). Seprration of kaersutite would also further deplete the residual salic liquid in magnesium and ferrous iron, and though to a lesser extent, in ferric iron (see above); an increased Na 20/K20 ratio might also have been produced in the residual liquid (Barley et al. 1970). Borley et al. also suggests that the subtraction of an aluminian kaersutite together with anorthoclase (present as a cumulus phase in some syenitic xenoliths) would considerably deplete residual liquids in alumina whilst enriching them in soda, and thus the liquids may tend towards peralkalinity. The residual liquids should group close to a eutectic composition, and RidleY_(1970) has shown that the phonolites of the Recent Salle Series and, to a certain extent, those from the Canadas Series, group around the ternary phonolitic minimum in the system quartz-nepheline-kalsilite. -177-

Appendix 1.

Analytical and X-Ray Techniques.

1. Mineral Separation.

The parent rocks were crushed, washed to remove dust, and small fractions were then sieved off.

Following removal of magnetite by a hand magnet, the required minerals were separated by a combination of heavy liquid flotation, and magnetic separation using a Frantz Isodynamic Separator. Final impurities were removed by hand- pickirig.

When both phenocryst and groundmass pyroxenes were required, the phenocrysts were first removed, after which, the groundmass material was recrushed to facilitate separation of the fine-grained pyroxene.

2. Chemical Analysis.

Samples of approximately 200-300 mgms. were generally used.

silica was determined by the combined colorimetric gravimetric method of Jeffrey and Wilson (1960), and alumina by the classical "difference" method. "Rapid" methods of analysis were used for titanium, manganese, total iron, sodium and potassium. The ammonium metavandate method of Wilson (1955) was used to determine ferrous iron. Calcium and magnesium were determined by atomic absorption°

As only 200 mgms. of pyroxene from PS69 were obtained, approximately 80 mgms. were used to determine calcium, magnesium, total iron, and manganese by atomic absorption, and titanium, sodium, and potassium by "rapid methods". 8o mgms. were used to determine ferrous oxide, and the remaining material was used for x-ray diffraction studies.

A rock of known chemical composition was analysed in each "batch" of mineral analyses to serve as a check on precision. -178-

3. Electron Microjorobe Techniques.

All electron microprobe data was obtained using a Cambridge Scientific Instruments "Geoscan", a fully focusing two spectrometer instrument with which two elements may be determined simultaneously.

Sample preparation: Uncovered thin sections of rocks, between 40-50 microns in thickness, were polished. These thin sections were then examined optically in transmitted and reflected light. Suitable crystals, or parts of crystals, for analysis were picked out and either drawn or photographed, in transmitted light. Crystals chosen for analysis were, where possible, flat without pitted surfaces. Where small crystals or the outer rims of large ones were to be analysed, the areas picked were those where the edges were not bevelled.

Following microscope examination the sections and standards were simultaneously carbon coated to make them conducting; they were then ready for analysis.

Standards: The standards used were natural analysed minerals or synthetic minerals that were assumed to be stoiciometric in composition. The synthetic minerals were grown by Dr. White, of the Crystal Growth Laboratory, Imperial College. A list of the stand,Irds and the elements they were used to determine is given below:

Element sought Standard used Sodium Analysed jadeite. nagnesium Synthetic spinel (MgA1204) or synthetic forsterite (Mg2SiO4). Aluminium Analysed jadeite or synthetic spinel (MgA1204). Silicon Analysed wollastonite, analysed jadeite, or synthetic forsterite (Mg2SiO4). Potassium Synthetic potassium tantalate (KTa0 ). 3 Calcium Analysed wollastonite. -179-

Titanium Synthetic rutile (Ti02). Chromium Synthetic(Cr203). Manganese Analysed rhodonite. Iron Synthetic yttrium iron garnet (Y Fe 0 ). 3 5 12 Kielce]. Synthetic M.O.

Operating procedure: a). Mineral analysis. An excitation potential of 15KV was used for all analyses. The electron beam was focused to a size of approximately 2 microns and the specimen current was set between .03 - .07 [ia. Care was taken to ensure that the count rates were not too high, thus alleviating the necessity to make dead-time corrections. Count rates of under 7,000 counts/sec were accepted.

The analysing crystals were potassium acid phthalate (KAP) for magnesium, aluminium and sodium, lithium fluoride for iron, manganese, nickel, chromium, titanium, and calcium, and pentaerithritol (PET) for potassium. Silicon was determined using either the KAP or PET crystal. A minimum of 4 - 5 counts of 10 seconds duration were made on standard and specimens, the specimens being moved very slightly under the beam after each count. Thus each analysis corresponds to an analysis of a few square microns. b). Wavelength scans. Wavelength scans with the electron beam stationary on a specimen, were made with an excitation potential of 15 or 20 KV. Beall size and specimen current was as above.

When comparisons were to be made of intensities in the elemental lines (e.g. the differences of composition in a zoned pyroxene), the scans were made consecutively with identical machine and recorder conditions. c). Specimen traverses under the electron beam. General machine and operating conditions were the same as those for analysis. The elemental line required was positioned by reference to a standard. The specimen holder was set to - 180 -

move in a pre-determined direction at a speed of 3 or 30 microns/ minute. Counts of 10 seconds duration were made at various times during the traverses, and noted at the appropriate points on the chart-recorder. Traverses, with the spectrometers offset 2° from the elemental line, were frequently made, to confirm that the variations across the specimens were due to differences in concentrations of the elements present, rather than any other factors.

Length of recording often varied for the same traverse. This could be accounted to two factors: cne, the slightly varying speed of the traversing motor, and two, the inability to accurately superimpose the traverses.

Data processing: Raw intensity data (actual counts) was corrected for absorption, atomic number effect, and fluorescence by means of a computer program (Mark 2 version) written by Mason, Frost and Reed (1969) for the I.B.M. 7094.

The program calculates absorption by the Philibert method (Philibert 1963), with the modification proposed by Duncur-ib and Shields (1966), and refined by Heinrich (1967). The atomic number effect is calculated as suggested by Duncumb and Reed (1968), and fluorescence calculated by the method due to Reed (1965).

It was assumed that analysis had been made for all elements in the mineral except oxygen, which would make up the total. Thus, the "Difference" method of calculation was used.

Reliability of Results: If the standard drift (i.e. difference in counts on the standard before, and after the specimen counts) was greater than 35 for any element, then the analysis was not accepted. Determination of the element was repeated. In many analyses the drift was less than lY for all the elements.

A mineral of known composition, within the standard block, was determined with each set of analyses. When analysis -181 -

of this mineral compared favourably with the accepted analysis, then the set of analyses were thought to be correct.

Determinations of separate oxidation states of the elements, and determination for water cannot be made in a microprobe analysis, and therefore the sum of the oxides of the elements present will not necessarily be 100Y. For example, if iron is quoted as FeO, the analysis of an acmite-rich pyroxenc should total considerably less than 100:, because much of the iron will be in the trivalent state. Factors, such as this, were taken into account when deciding if an analysis was acceptable.

Presentation of results: Analyses are quoted correct to 0.1;:. The method is insufficiehtly accurate for results to be stated, with any confidence to a greater degree of precision. Structural formulae are likewise only given to 0.01%. The structural formulae have, however, been calculated from the analyses using values to 0.01;:-, and thus may vary by I 0.01 from formulae calculated using the quoted analyses.

4. X-Ray diffractometer techniques.

The minerals were mixed with a little silicon, powdered, and examined as micro-cavity mounts on an etched glass microscope slide. All measurements were made with a Philips X-Pay Diffrac- tometer using filtered copper radiation at 40 KV and 20 ma. 1 o Traverses were made at a scan speed of /4 2 Gimin. and recorded so that 1° 26 was represented by either 1 inch or 2 ems. of chart paper. The centres of well defined, unambiguously indexed. peaks were found by measuring both sides of the peak at half peak height. The value for the centre of the peak thus obtained was corrected by reference to the silicon peaks. When resolved, the al peak was determined (X= 1.54050) but at low angles a was measured (;\= 1.5418).

Cell refinements were made by using a least squares program by Burnham (1962), modified for Fortran IV by moT. Frost, Department of Geology, Imperial College. Weighting was given to the higher angle reflections -182 -

AER2211?1 ,: " Specimen Localities

The localities of specimens referred to in tables and figures or in the text are listed below, and are positioned as near as possible on the enclosed simplified geological map. The TC, GB and -66 series were collected by Dr.G.D.Borley, the TC-R scrio's of Dr.W.I.Ridley, and the MA series by Dr.M.J.Abbott. The author collected the PS series.

PS3. Alkali basalt. Ancient Series. Lava 3 Km. north of San Andres, Anaga. PS4. Alkali basalt. Ancient Series. Dyke 3 Km. north of San Andres, Anaga. PS9-11 Phonolite intrusion. Ancient Series. 8 metre wide dyke. 200 metres west of Igueste, Anaga. PS14. Ankaramite. Ancient Series. 200 metres west of Igueste, Anaga. PS22. Euhedral pyroxenes from weathered ankaramite. Ancient Series 2 Km. west of Igueste, Anaga. PS27 (GBL)WA7). Pbonolite intrusion. Ancient Series. Large intrusive sheet 4.5 Km north of San Andres, Anaga. PS31. Alkali basalt. Ancient Series. Lava 6 Km. north of San Andres, Anaga PS41. Large phonolite boulder within pyroclastics. Montana de Guajara. Canadas Series. PS45A Glassy phonolite. Recent Salic Series. Lava, eastern flank of Teide (approx 3000 metres elevation). ps47. Glassy phonolite. Recent Salic Series. Lava, eastern flank of Teide (approx 2750 metres elevation). Trachybasalt. Series 3 basalt. Lava. Dip slope of Las Canadas, east of Las Pilas. ps51. Alkali basalt. Historic flow. Mete Fuentes, east of Las Canadas. PS56. Alkali basalt. Ancient Series. Dyke,Punta del Fraile,Teno. PS58. Alkali basalt. Ancient Series. 7 metre wide dyke. 6 Kms. west of Duenavista, Teno. i83

PS58A Specimen from same dyke as PS58. PS61. Ankaramite. Ancient Series. Dyke, La Asomada, 2.5 Km. west of Lantiago del Teide,HTeno. PS62. Alkali basalt.. Ancient Series. Dyke 0.5 metre wide at top of Lac Pichacos. 3Km west of Santiago del Teide. PS69. Nepholine syenite boulder. Loose block in wall of Las Canadas to north of Las Pilas. PS74. Plagioclase phonolite (Trachyandesite). Recent Salic Series. Lava crossing road below MnEOBlanca. PS75. Glassy phonolite. Recent Salle Series. 1 Km east of PS74. PS81. Alkali basalt. Ancient Series. Barranco de las Gambuesas, Arafo. PS84. Phonolite intrusion. Canadas Series. Tauce Escarpment, Las Canadas. Ps85. Phonolite Canadas Series. Lava. Tauce Escarpment, Las Canadas. ps86. Phonolite Canadas Series. Lava. Tauce Escarpment, Las Canadas. Ps92. Trachybasalt/trachyandesite. Recent Series. Lava. Pico Viejo. Ps93. Trachybasalt/trachyandesite. Recent Series. Lava. Pico Viejo. Ps96. Trachybasalt. Canadas Series. Dyke below La Angostura, Wall of Las Canadas. PS101. Trachyte. Trachyte and Trachybasalt Series. Vontana Guaza. PS103.Alkali basalt. Ancient Series. Lava on ridge to south of Roque Higara. PS104.Alkali basalt. Ancient Series. Ridge to south of Roque Higara. PS105.Trachyte. Ancient Series. Ridge to south of Roque Higara. PS107. Phonolite. Ancient Series. Intrusion. Roque Higara. PS112. Trachybasalt. Historic lava which swamped Garachico. PS115.Alkali basalt. Lncient Series. Lava below Mna. Izana. PS116.Ankaramite. Ancient Series. 1 Km. N.E. of Mna Izana. PS118.Alkali basalt. Ancient Series. Lava. La Crucita. PS119.Alkali basalt. Ancient Series. Dyke. Roque Acebe. TC2. Trachybasalt. Recent Series. Cinder Cone. Puerto de la Cruz. TC4. Alkali basalt. Series 3 Basalt. 1 Km. east of Realjo Alto. -184-

TC8. Trachybasalt. Series 3 Basalt. 2 Km. west of Oratava. TC10. Alkali basalt. Series 3 Basalt. Between Oratava and Realjo Alto. TC16. Phonolite. Recent Salle Series. Near 34 Km. post Las Canadas. TC19. ,Glassy Phonolite, Recent Salle Series. Las Canadas. TC21. Glassy Phonolite. Recent Salic Series. Near 39 Km. post Las Canadas. TC32. Trachybasalt. Series 3 Basalt. El Ampero, near Icod. TC33. Trachybasalt. Series 3 Basalt. 6 Km. west of Icod. TC34. Alkali basalt. Series 3 Basalt. Near Tanque. TC36. Alkali basalt. Ancient Series. Lava 5 Km. north of Santiago del Teide. TC37. Alkali basalt. Ancient Series. Dyke cutting TC36. TC38. Trachybasalt. Series 3 Basalt. Santiago del Teide. TC39. Alkali basalt. Ancient Series. Santiago del Teide. TC40. Alkali basalt. Series 3 Basalt. 1 Km. east of El Portillo. TC44A. Alkali basalt. Bomb from Cinder Cone. Series 3 Basalt. Nna. Colorada. TC44C. Alkali basalt. Bomb from Cinder Cone.Series 3 Basalt. Mna. Colorada. TC45. Trachyandesite. Canadas Series. Roque ChiMaque. TC89R Phonolite. Canadas Series. Las Canadas. TC126R. Phonolite. Canadas Series. TC183R. Phonolite. Canadas Series. Las Canadas. TC210R. Alkali basalt. Las Canadas. TC223R. Phonolite. Las Canadas. GB4. See PS27. GB8. Trachyandesite. Recent Salic Series. 4 Kms. N.W. along track from Boca de Tauce. GB11. Alkali basalt. Series 3 Basalt. 11 Km. Post, west of El Tanque. GB16. Trachyandesite. Canadas Series. 1 Km. west of Icor. MA3. Alkali basalt. Ancient Series. 3 Km. north of San Andres, Anaga. MA4A. Trachyte. Ancient Series. 3 Km. north of San Andres, Anaga. MA6. Alkali basalt. Ancient Series. 5 Km. north of San Andres, Anaga, MA7. See PS27 ML8. Alkali basalt. Ancient Series. 7 'Km. north of San Andres, Anaga. -185-

MA10. Alkali basalt. Ancient Series. Las Palmas, near Buenavista, Teno. MAll. Ankaramite. Ancient Series. 1.5 Km. north of Puerto del Santiago, Teno. MA14. Alkali basalt. Ancient Series. 1.5 Km. north of Puerto del Santiago, Teno. MA15. Ankaramite, Ancient Series. Santiago del Teide, Teno. MA17. Ankaramite. Ancient Series. 3 Kms. north of Santiago del Teide, Teno. MA19. Ankaramite. Ancient Series. 2 Kms. west of Buenavista, Teno. MA20. Ankaramite. Ancient Series. 2 Kms. west of Buenavista, Teno. MA22. Alkali basalt/trachybasalt. Canadas Series? Fasnia. MA23. Ankaramite/alkali basalt. Canadas Series? Fasnia. MA_24. Ankaramite. Canadas Series? Fasnia. ML28. Phonolite. Canadas Series. Arica Viejo. MA29. Trachybasalt/trachyandesite. Canadas Series or Trachyte and Trachybasalt Series. Granadilla. MA31. Alkali basalt. Series 3 Basalt. 3 Kms. south of Granadilla. MA36. Phonolite. Canadas Series. San Miguel. MA37. Alkali basalt. Series 3 Basalt. San Miguel. 1-66. Phonolite. Trachyte and Tradhybasalt Series. Montana Chasogo. 7-66. Trachybasalt. Canadas Series. Portillo escarpment, Las Canadas. 8-66. Pyroclastic material. Canadas Series. Portillo escarpment. 9-66. Phonolite. Canadas Series. Fortino escarpment. 11-66. Phonolite. Canadas Series? El Roque near San Miguel. 12-66. Alkali basalt. Series 3 Basalt? West of San Miguel. 13-66 Trachyandesite. Series 3 Basalt? West of San Miguel. 18-66. Alkali basalt. Series 3 Basalt? Adeje. 23-66. Alkali basalt. Canadas Series. Las Canadas. Top of Portillo escarpment. 24-66 Alkali basalt. Canadas Series. Las Canadas. Top of Portillo escarpment. 28-66. Alkali basalt. Series 3 Basalt. Barranco Hondo. 29-66. Alkali basalt. Series 3 Basalt. Barranco Hondo. 30-66 Alkali basalt. Series 3 Basalt. Barranco Hondo. -186-

31-66. Alkali basalt. Series 3 Basalt. Barranco Hondo. 34-66. Alkali basalt. Ancient Series. Dyke 1 Km. east of Bajamar. 35-66. Alkali basalt. Ancient Series. Dyke 1 Km. east of Ba,-1,apar. 49-66. Alkali basalt. Historic flow. S.E. of wall of Las Canadas. - 187 -

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