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Jl geol. Soc. Lond. Vol. 135, 1978, pp. 591-595, 1 table. Printed in Northern Ireland. Conference Report

Trace element studies of the origin of igneous rocks

W. J. Rea

TRACE ELEMENT STUDIES are increasingly im- subject of a paper by Harrison & Wood. portant in igneous petrogenetic investigations in as Mathematical modelling, using geochemical data, much as they place constraints on possible modes of now allows the quantitative assessment of petrogenetic origin of igneous rocks and also give evidence of the processes such as closed and open system fractiona- nature and composition of the mantle/crust systems tion, progressive and single stage partial melting, within which are generated and modified. crystal accumulation and mixing (Pearce). The The conference saw trace element studies applied to models, however require valid -liquid partition a wide range of igneous rock compositions, occurring coefficients for the trace elements concerned and there within a wide range of environments. Four papers is sometimes a substantial range in the available litera- were concerned with areas in which basalt lavas pre- ture values. The problem arises mainly because parti- dominate, i.e. Mull (Beckinsale et al.), the islands tion coefficients vary with physical conditions such as associated with the axial trough of the Red Sea (Hen- temperature (Harrison & Wood) and are also heavily derson & Parry), the East Scotia Sea (Saunders & dependent on melt structure which in turn reflects Tarney) where basalts are generated within an intra- chemical parameters such as asio~ and Primo. In this oceanic marginal basin and the South Shetland Islands sense the experimental determination of partition and Antarctic Peninsula (Weaver et al.) where differ- coefficients (Harrison & Wood) is particularly wel- ent periods of magma genesis have been related to come as is any increase in the variety of natural rock subduction and extension. Other papers dealt with systems for which natural partition coefficients have metabasalts from ophiolite complexes (Pearce), K-rich been determined. volcanics (Parker), diorites and granodiorites (Brown et al.), granites and charnockites (Petersen) and the Report of a joint meeting of the Mineralogical Society and the ultramafic to granitic rocks of the Fongen-Hyllingen Volcanic Studies Group, held during the Third Meeting of the Gabbro Complex (Esbensen). Geological Societies of the British Isles at Swansea University An important recent development in on 26 September 1977. The meeting was organised by Mr has been to extend the range of material which can be Ewen Home and Dr W. J. Rea. usefully analysed. For example, important petrogene- Wn_LtmM JOHN REA, Department of Geology, University tic information is now being obtained from altered and College of Wales, Llandinam Building, Aberystwyth, Dyfed metamorphosed igneous rocks using ratios based on SY23 3DB. trace elements such as Ti, Zr, Y, Nb, P, Ce, Sm, Yb, abundances of which appear to be unchanged by sec- Geocheml~ and petrogenesis ot the early TertiaO lava pile ondary processes (Pearce). Volcanic rock geochemis- of the Isle ot Mull, Scotland R.D. Beckinsale, R. J. Pank- try, which until recently was virtually synonymous with hurst, R. R. Skelhorn & J. N. Walsh lava geochemistry, has now expanded its scope to Major and trace element analyses and strontium isotope include pyroclasties, which are volumetrically ex- ratios are presented for twenty-four samples of lavas and tremely important at many volcanoes and which can plugs from the early Tertiary lava pile in Mull. The samples yield important petrogenetic information (Parker). were selected on the basis of petrographic freshness from a Developments in analytical techniques also have an large collection from outside the hydrothermally altered important influence on the direction of geochemical 'zone of pneumatolysis' which occupies the central region of and petrogenetic research. The rare earth elements the volcanic complex. Most of the analyses yield normative (REE), difficult to separate and analyse by classical hypersthene and we argue that these are essentially unaltered methods, can now be analysed, e.g. by neutron activa- magmatic compositions and do not result from alteration. The analytical data indicate that the samples may be divided tion analysis, and appear to give important petrogene- into three groups on the basis of major element chemistry, tic information, e.g. on plagioclase fractionation or initial 87Sr/86Sr ratios and correlations between lithophile ele- garnet melting and fractionation. Eight of the papers ment contents. Group I comprises an alkaline series (basalt- included REE data, Pearce presented mineral-liquid hawaiite-mugearite) with extremely low initial 87Sr/S6Sr partition coefficients for three rare earth elements and ratios (~<0.7030) and generally low lithophile element con- an experimental study of the partition of samarium tents. Apart from their alkalinity and high Sr and Zr contents between garnet and hydrous melt at 30 kb was the these samples have affinities with abyssal tholeiites. Group II Downloaded from http://jgs.lyellcollection.org/ by guest on September 29, 2021

592 W.J. Rea

contains hypersthene-normative basalts with more tholeiitic Trace element evidence for tim origin of tim diorite, and characteristics but (as in the case of the Skye Main Lava ~rite, of tim Choaet lmnlmtda, Gmmmey, Clmnml Series) the more evolved rocks are trachytes. This group is M. Brown, G. M. Power & C. Topley characterized by more normal levels of lithophile element concentrations and relatively high initial 87Sr/86Sr ratios of Within an area of 1 sq km even-grained diorite is transi- about 0.7055. Group III is less clearly defined and contains tional into acicular diorite and intruded by granodiorite and basalts that are generally sparsely olivine-phyric and in most all these appear to be older than an inhomogeneous diorite chemical respects fall between Group I and Group II-- which ranges from mesodiorite to leuco quartz diorite. Each including initial 87Sr/86Sr ratios (0.7033 to 0.7043). They rock-type has distinctive petrography and major element may represent mixtures of Group I and Group II type chemistry. Trace element distributions suggest that the series sources or magmas. Groups I and II appear to be similar, as a whole may not be explained in terms of crystal fractiona- respectively, to the relatively sodic iron-rich and the rela- tion. Of particular interest are trace element variations within tively potassic iron-poor silica enrichment trends disting- the inhomogeneous diorite and the acicular diorite as indi- uished in the Skye Main Lava Series. In the Group I magma cators of the probable origins of these rocks. series the behaviour of Y and Sr relative to other incompati- ble elements can only be explained by differential partial Trace element distributions in potassium-rich pumice and melting of a deep garnet-lherzolite mantle source. Fractional lava samples from Vuisini Volcano, central Italy R. J. crystallization has undoubtedly occurred at some stage during Parker the ascent of these magmas from the mantle, as indicated by the behaviour of Ni and Cr, but has not been a major factor A considerable amount of work has been carried out on in the production of evolved magma compositions. The the K-rich lavas from central Italy but the associated ignim- Group II magmas appear to have originated from a source brites and pyroclastics from this region have received little more enriched in lithophile elements, and a relatively shallow attention. Sparks (1975) has made detailed studies on the (<50 km) plagioclase-lherzolite mantle source is suggested tephrochronology and geology of Vulsini Volcano and six for these magmas because they have Sr/Ba ratios between major ignimbrite eruptions were identified and their eruption one and two orders of magnitude lower than those charac- sequence determined. Several smaller ignimbrites and pyro- teristic of Group I. Rb-Sr systematics suggest that the vertical clastic falls were also identified. Pumice clasts were subse- heterogeneity of the mantle which was largely responsible for quently collected (this work) from these ignimbrites and the chemical differences between these three groups may pyroclastics. A number of lava samples were also collected. have existed for a very long time prior to Tertiary The samples were examined for alteration effects such as magmatism. hydration/palagonitization of the pumice glass and samples showing these effects were discarded. Leucite is present in Petrogenetic studies ot metabasalts using immobile trace most of the lavas and in many of the pumice samples. In the element mtkm J.A. Pearce latter samples this mineral shows all degrees of alteration to analcime. The concentration of analcime in the pumice sam- The table below gives mineral-liquid partition coefficients for ples was determined by quantitative X-ray diffraction elements thought to be immobile during most weathering and (Parker, in press). Pure mineral separations of leucite and metamorphic processes. These coefficients, which are strictly analcime were also chemically analysed. These data were only valid for melts of tholeiitic basalt composition, will vary then used to correct the whole pumice major and trace according to melt composition, temperature and pressure. element geochemistry for this alteration. They can, however, be used with care to model the effects of The majority of the analysed lava samples from Vulsini fractional crystallization, crystal accumulation, magma mix- Volcano (this work and data in Appleton 1970) are charac- ing, progressive and sin#e-stage partial melting and mantle terised by SiO2 concentrations of 48-55 per cent, whereas the heterogeneities on some critical immobile element ratios. majority of analysed pumice samples fall in the range 55- Examination of these ratios in metabasalts from ophiolite 61 per cent SiO 2. Pumice samples from one of the ignim- complexes reveals that the reiative importance of source brites are characterised by SiO 2 levels of 48-49per cent. heterogeneities, fractional crystallization and crystal accumu- They are similar to low SiO 2 (48-50 per cent) lavas in their lation varies from complex to complex thus providing further major and trace element characteristics. This low SiO 2 ig- information on the environment of ophiolite formation. nimbrite is associated with a mixed magma ignimbrite which contains pumice samples from both high and low SiO 2 groups. OL CPX OPX PL HBL GT The pumice major and trace element trends, in conjunction Ti 0.01 0.35 0.12 0.05 1 0.35 with ignimbrite stratigraphic relationships, reflect a cyclic Zr 0.01 0.12 0.04 0.05 0.4 0.12 evolution towards more salic compositions for the six major Y 0.01 0.67 0.20 0.06 0.6 5 ignimbrite magmas. Pumice samples from individual ignim- Nb 0.01 0.1 0.01 0.01 0.8 0.1 brite eruptions may show distinct trends towards more salic Cr 0.5 3 1.5 0.01 4 6 compositions (increasing D.I.) indicating differentiation pro- Ce* 0.01 0.15 0.02 0.12 0.20 0.03 cesses operating on the scale of the individual ignimbrite Sm* 0.01 0.5 0.05 0.07 0.52 0.29 magma. These pumice samples show distinct Sr and Ba deple- Yb* 0.01 0.62 0.34 0.07 0.49 11 tion and Rb enrichment with increasing D.I. Sanidine is the Sc 0.5 3 1.5 0.02 3 10 dominant phenoeryst in these samples. This factor, when combined with sanidine partition coefficients from the litera- P'[" 0.07 0.01 0.01 0.01 0.3 0.15 ture, suggests that the observed trends for Sr, Ba and Rb are * Arth & Hanson (1975) controlled by fractionation of this mineral. Zr, Y and Th are ? Anderson & Greenland (1969) enriched in the more salic magmas, reflecting the incompati- Downloaded from http://jgs.lyellcollection.org/ by guest on September 29, 2021

Trace element studies of the origin of igneous rocks 593

ble nature of these elements and their resulting concentration Fe/Mg series comprise charnockites, whereas low Fe/Mg in residual magma liquids. series include hbl-bi granites; Sr-isotope studies, however, reveal similarities in terms of low initial Sr-ratios and abso- An experimental study o! samarium partition between garnet lute ages. and liquid Wendy J. Harrison & B. J. Wood Study of the charnockites and related anorthosite-norite series reveals a sequence of non-fractionating, inflexional The partitioning of Sm between garnet and hydrous melt REE patterns with constant La/LuN about 5 and increasing has been studied at 30 kb in the systems Mg3A12Si3012-H20 abundances from La N 15 to 130. A modal ratio of and Ca3A12Si3012-H20. The partition coefficient K D plag:opx: cpx/hbl: ap of 60: 30: 9:1 results in a non- (= C~m/C~m) was determined at low Sm concentrations (< fractionating bulk REE partition coefficient Dx/1 of about 50 ppm) using the radioisotope Sm TM and a 0-track mapping 0.33. Fractional crystallization (Rayleigh law) of this model technique. The partition coefficient is temperature dependent liquid indicates 80 per cent solidification to produce the in both systems. It increases from 0.11 (1200°C) to 0.19 (at observed increase in REE abundances of charnockite relative 1500°C) in the system Mg3AIESi3012-H20 and from 0.64 to norite. (1200°C) to 0.96 (1400°C) in the system Ca3A1ESi3012-H20 A positive Eu-anomaly in the anorthosite-norite series at 30 kb. The differences between the two systems reflect shows decreasing tendency with evolution. Primitive charnoc- differences in the sizes of the garnet sites into which Sm 3÷ kites also possess Eu excess (Eu/Eu* = 2) which implies that substitutes. they do not represent pure residual liquids. In more evolved charnockite member, the Eu content decreases and develops Rare F.au~ and other trace dement rdatiommhips in volcanic a large negative anomaly. Deformed plagioclases surrounded rocks trom the Red Sea Islands P. Henderson & S. J. Parry by unstrained K-feldspar and quartz in primitive charnockites support the view that Eu-surplus may reflect plagioclase Towards the SSE end of the Red Sea occur the volcanic excess as the result of incomplete separation between early islands of Jebel at Tair, the Zubair group and the Hanish- plagioclase and magma. Zukur group. These islands are associated with the axial The granite series is divided into various stages reflecting trough, are Recent in age, and range from true tholeiites at decreasing REE fractionation. The Red granite shows ex- Jebel at Tair, through transitional basalts in the Zubair tremely high LREE fractionation, and a marked levelling for Islands group, to alkali basalts on the Hanish-Zukur group. intermediate and HREE. La/Sm N is 7-10 and the pattern Trace-element analyses of groundmass fractions show a displays no Eu anomaly. A second stage comprises the larger relation with magma type. At one extreme, the tholeiite of TranevSg and Holum granites which show reduced La/Sm N Jebel at Tair has a chondrite normalised La/Lu of about 3 ratios about 3. Their REE patterns, however, continuously and relatively high concentrations of Co (---45 ppm) and Sc decrease from La to Lu and display a La/LuN of 13-14 (-~ 40 ppm) and at the other, a trachyandesite of the Hanish- suggesting that HREE fractionation occurred. A small nega- Zukur Islands has (La/LU)cN = 11 and low transition element tive Eu-anomaly is also present. The following stage includes contents (Sc 9 ppm; Co 4 ppm). In samples from the Zubair the Lyngdal granite with La/LuN of 8-10 and a significant group there is a good correlation between Sc and Co con- negative Eu-anomaly about 0.70. tents, suggesting that olivine and clinopyroxene fractionation The granites form a succession in which increasing REE controlled the sequence of liquid compositions. On the basis fractionation apparently follows decreasing Eu-depletion. of published partition coefficients, a fractional crystallization Absolute and relative ages furthermore indicate that more of about 50 per cent of an original melt is required to fractionated members are older than less fractionated ones, produce the observed transition element variation. and thus suggest a partial fusion origin of presumably garnet- The Zubair samples also show nearly constant La/Lu con- bearing source materials rather than fractional crystallization centration ratios despite a threefold variation in rare earth of residual liquids. element (REE) contents. The data suggest that olivine frac- Experimental studies indicate that partial fusion of garnet- tionation was dominant in controlling the liquid composition. lherzolite under hydrous conditions may produce a This is supported by the major element data. The Hanish- granodioritic liquid, which fits the composition of the early Zukur samples have very similar REE distributions to those and more strongly fractionated Tranevhg granite. Other low of the Zubair group, but are in contrast to those of Jebel at Fe/Mg granite members are believed to reflect progressive Tair. It is unlikely that the rocks of the three island groups fusion products. Anorthosite kindred rocks, here including were derived from the same parent magma. The absence of high Fe/Mg-charnockites, are generally agreed to originate an Eu anomaly in any of the samples shows that no signific- from basic magmas derived from an upper mantle source. ant plagioclase fractionation was involved in their geneses. The presented REE data accordingly point towards coexis- The REE data suggest that the rocks of these islands were tence of contrasting magma suites showing basic and acid produced by relatively small amounts of partial melting of affinity--possibly derived from upper mantle sources--that probably lherzolitic source material. lead to the formation of granitic melts. This agrees with the Sr-isotope data and may possibly be explained by partial fusion of a common parental material at different invariant REE patterns relating to the petrogenesis o! granites and charnoekites in SW Norway J.S. Petersen points. Trace element distn'bution during extreme differentiation in The Rogaland igneous province in SW Norway includes the Fongen-Hyllingen gabbro complex, Trondheim Region, several post-kinematic granitic intrusions, some of which Norway K.H. Esbensen show affinity to anorthosite rock kindreds. Geochemical studies suggest a bimodal grouping into separate magmatic The synorogenic, layered Fongen-Hyllingen gabbro com- series, characterized by contrasting Fe/Mg ratios. High plex, central Norwegian Caledonides, displays a composite Downloaded from http://jgs.lyellcollection.org/ by guest on September 29, 2021

594 W.J. Rea rock series in which the cumulus assemblages in the lower inferred (Ce/Yb) n is approx. 1-2 while the extreme quartz- Fongen series (approx. 4000 m) begin with chromite-olivine bearing syenites (before the entry of allanite) show cumulates and olivine-plagioclase cumulates followed by var- (Ce/Yb). = 8.8. ious sedimentary determined facies of two-pyroxene (+ This inferred magmatic differentiation is considered to olivine) gabbros with subsequent re-entry of abundant have taken place by fractional crystallization in a completely olivine, joined later by Fe/Ti-oxides and finally apatite as closed system with generally increasing Prho acting as the index liquidus phases. The upper Hyllingen series (approx. dominating controlling factor reflecting the synorogenic crys- 3000 m) continues this evolution towards late differentiates tallization regime. consisting of non-layered monzonites and final quartz- bearing alkali-syenites. In the uppermost parts of this Hyl- lingen series important changes in the liquidus assemblages The geocbemblry of Mesozoic-Cenozoic volcanism in the comprise: South Shetland Islands and the Antarctic Peninsula S.D. Weaver, A. D. Saunders, J. Tarney & R. J. Pankhurst Calc-alkaline volcanism on the Antarctic Peninsula extends 1. Reaction with melt by Ca-poor pyroxene resulting in back for at least 180 Ma. Mesozoic volcanics on the west Ca-amphibole, which gradually becomes a primary phase, coast of the Peninsula are dominantly basaltic, distinctly ending as ferrohastingsite. more sodic and have lower K, Rb, Ba, Th and Ce/Y com- 2. Disappearance of olivine due to oxidation at a composi- pared with the silicic east coast volcanics. These features are tion Fo 17. consistent with the subduction of Pacific Ocean lithosphere 3. Appearance of alkali feldspar and quartz (together with along the western margin of the Peninsula, an increase in albite, which constitutes the final stage of the plagioclase Benioff zone depth from west to east and corresponding reaction series) as primary precipitate phases; zircon and increase in the proportion of garnet in the source regions of later sphene together with hedenbergite, oxides and stilp- the subduction-related magmas. nomelane are important mafic constituents. In the Tertiary, subduction and magmatism ceased prog- 4. Allanite constitutes the latest incoming liquidus phase. ressively from south to north and the pacific and Antarctic plates became coupled as sections of spreading ridge arrived at the continental margin. Subduction continued at the north- ern end of the Peninsula and early Tertiary volcanics on the Throughout the entire Fongen-Hyllingen series a brown South Shetland Islands are intermediate in character between primary intercumulus Ti-carrying amphibole is an important island-arc tholeiite and talc-alkaline types, having low K, Rb, component of all rock types except in these final differen- Ba, and slightly LREE-enriched patterns (normalised Ce/Yb tiates where it grades into the primary ferrohastingsitic am- about 2). Plio-Pleistocene volcanism on the South Shetlands phibole. has a more incompatible element-enriched, more distinctly The rhythmically layered rock series, which are the prime calc-alkaline nature. characteristic of the complex, are intraformationally in- The South Shetland ensialic block is now separated from terspersed with non-layered, medium- to fine-grained, the Antarctic Peninsula by Bransfield Strait, an asymmetric homogeneous granular rocks displaying grading relationships graben-like structure of extensional origin with a quasi- to the layered facies. These rocks fit in the general cumulate oceanic crustal structure. Extension in Bransfield Strait prob- stratigraphy; the pertinent phases which in the adjacent ably began within the last 4 million years following the cumulates are the liquidus phases generally make up the cessation of subduction at the South Shetland trench. The main part of these rocks together with a minor, but important active and recently active volcanoes of Deception, Bridgman content of the brown amphibole. Their textures show abso- and Penquin Islands are situated in Bransfield Strait. The first lutely no evidence that accumulative processes were responsi- two lie on a line of seamounts; whereas Penquin Island is ble for their formation; some sort of rapid crystallization off-axis on the fault-bounded margin of the Strait. Dexeption from the contemporary magma is inferred. These 'average lavas are a fractionated sequence from olivine-tholeiite to rocks' together with the final differentiates have been the rhyodacite. Bridgman lavas are highly feldsparphyric quartz- subject of a geochemical investigation under the working tholeiites. Both volcanoes have Sra7/Sr~ in the range 0.7034- hypothesis that they reflect the evolution of the contempor- 0.7035, high Na/K, K/Rb, Zr/Nb and low K, Rb and Rb/Sr. ary magma. An evolution which closely parallels that of REE patterns are essentially parallel with normalised Ce/Yb basaltic volcanic rock series appears. Major element patterns of about 2. Modelling suggests that the incompatible are consistent with a tholeiitic differentiation showing moder- element-enriched Deception basalts formed by a smaller ate iron enrichment grading into an alkaline affinity. degree of melting (c. 3 per cent) than the Bridgman lavas (c. K20/Na20 reaches unity in the final granites. 10 per cent) and that the mantle sources were similar but Trace-element distribution patterns follow these trends: with some small inhomogeneity with respect to K and Rb the large cations (K, Ba, Rb and Cs) are all markedly suggesting the presence or absence of phlogopite. Penguin enriched in the final differentiates, as are the large, multiva- basalts are slightly ne-normative with high Na/K, K/Rb, lent cations (Nb, Hf, Zr, U and Th). Th/U increases with Zr/Nb, low K, Rb, Rb/Sr, 51"87/S1 "86 of 0.7039 and normalised differentiation, as does Nb/Ta; Zr/Hf, however, shows no Ce/Yb of about 4. They were formed by a small degree of significant trend. The REE shows a prominent enrichment melting of a mantle source containing garnet. relative to homogeneous, non-cumulate marginal gabbros, In many respects, Deception and Bridgman lavas have believed to represent a best approximation to the initial affinites intermediate between basalts of mid-ocean ridge and magma. A progressive LREE enrichment relative to HREE calc-alkaline type. They appear to be related to mantle illustrates the alkaline affinity of the extreme differentiates diapirism (back-arc spreading), which separated the South and indicates an influence of amphibole fractionation. Initial Shetland Islands block from the Antarctic Peninsula. Downloaded from http://jgs.lyellcollection.org/ by guest on September 29, 2021

Trace element studies of the origin of igneous rocks 595

The origin and evolution of basalts from an intra-oceanic basalts have greater large ion lithophile (LIL) element (Rb, marginal basin in the East Scotia Sea: a trace element Ba and Sr) abundances, slightly higher Sr-isotope ratios study A.D. Saunders & J. Tarney (0.7028-0.7034) and higher Ce~/Yb~ ratios (0.9--1.43) than MORB; they appear to have been derived from a less depleted mantle source. In many respects, the Scotia Sea The South Sandwich spreading centre is a fast spreading basalts are similar to some transitional basalts from the axis behind the intra-oceanic South Sandwich island arc. mid-Atlantic ridge (e.g. Iceland). Intra- and inter-dredge Major and trace element, rare-earth element and Sr-isotope variations may be accounted for in terms of variable degrees data on 4 suites of basalts dredged from the spreading axis of melting of a common mantle source, though one in which have revealed small but significant differences between these pyroxene was refractory during the formation of dredge 20, basalts and those from major mid-ocean ridges (e.g. the 22 and 23 basalts, in order to increase progressively the mid-Atlantic ridge) elsewhere in the world. On major ele- Ce/Yb ratios. The dredge 24 basalts may be derived from a ment grounds alone, however, such distinctions cannot be similar source, but with substantial degrees of partial melting made. Dredges 20, 22 and 23 are subalkaline olivine involving refractory olivine. It is suggested that the geochem- tholeiites similar to mid-ocean ridge basalts (MORB) al- ical differences observed between the Scotia Sea basalts and though K20 contents are rather higher than in MORB. MORB are of little value for discriminating marginal basin Dredge 24 comprises a fractionated suite of quartz-normative crust from oceanic crust in studies of ophiolite complexes basalts with low abundances of Ti, Zr, Nb, Y and REEm because of the susceptibility of K, Rb, Ba and Sr to both similar to island-arc tholeiites. However, the Scotia Sea halmyrolysis and hydrothermal alteration.

References

ArCOEaSON, A. T. & GREE~, L. P. 1969. Phosphorus origin of the early Precambrian crust of northeastern fractionation diagram as a quantitative indicator of crys- Minnesota. Geochim. cosmochim, acta 341, 325--62. tallization differentiation of basaltic liquids. Geochim. PARKER, R. J. 1978. Quantitative determination of anal- cosmochim. Acta 33, 493-505. cime in pumice samples by X-ray diffraction. Mineralog. APPLm'ON, J. D. 1970. The petrology of the potassium-rich Ma g. 42, 103-6. lavas of the Roccamonfina Volcano, Italy. Thesis, Ph.D., SPARKS, R. S. 1975. Stratigraphy and geology of the ignim- Univ. of Edinburgh (unpubl.). brites of Vulsini Volcano, central Italy. Geol. Rdsch. 64, As'm, J. G. & HASSON, G. N. 1975. Geochemistry and 497-522.