PAPERS

Department of Geology

University of Queensland

Volume 11 Number 3

PAPERS

Department of Geology • University of Queensland

VOLUME 11 NUMBER 3

Cainezoic volcanic centres in southeastern Queensland, with special reference to the Main Range, Bunya Mountains, and the volcanic centres of the northern Brisbane coastal region. A. EWART and A. GRENFELL P. 1 - 57

Upper Mantle xenoliths and megacrysts and the origin of the Brigooda basalt and breccia, near Proston, Queensland. A.D. ROBERTSON, F.L. SUTHERLAND and J.D. HOLLIS P. 58 - 71

Cainozoic volcanic rocks in the Bundaberg-Gin Gin-Pialba area, Queensland P. 72 — 92 A.D. ROBERTSON

1

CAINOZOIC VOLCANIC CENTRES OF SOUTHEASTERN QUEENSLAND WITH SPECIAL REFERENCE TO THE MAIN RANGE, BUNYA MOUNTAINS AND THE VOLCANIC CENTRES OF THE NORTHERN BRISBANE COASTAL REGION

by A. Ewart and A. Grenfell

ABSTRACT Remnants of the Miocene-Oligocene volcanism occur as large eroded shield volcanoes, complex lava fields, ring complexes, and as localised domes, plugs, laccoliths, sills, and dykes. Descriptions are presented of the field and age relations, mineralogy, and chemistry of three major occurrences. The Main Range volcanic province extends approximately 120 km NNW-SSE, averaging 35 km in width, with a maximum thickness of 900 m. Two formations are recognised, the lower formation ranging between 24.0 — 25.6 Ma, and the upper formation between 18.1 — 24.0 Ma. The former consists of a mildly alkaline basalt-comendite association, and includes hawaiites, mugearites, benmoreites, and trachytes. The upper formation consists of hawaiites, alkali olivine basalts, mugearites, and rarer undersaturated lavas; the latter eruptives contain megacryst and xenolith suites dominated by spinel lherzolites , but including various clino­ pyroxenite types, some amphibole-bearing. Inclusion-bearing localities are documented.

The Bunya Mountains constitute an eroded shield volcano, originally exceeding 60 km in diameter, with a maximum thickness of approximately 700 km, and an age range of 22.0 to 23.7 Ma (possible extending to .29.4 Ma). Lavas are dominated by hawaiites {ne and ol normative), with minor tholeiitic andesites, benmoreites, and a single trachyte. Only sporadic megacryst/xenocryst occurrences are found. Volcanic occurrences within the coastal region north of Brisbane include the Maleny volcanic centre (25.2 — 33.7 Ma), consisting of Q-saturated, or near saturated, mafic lavas, with a maximum thickness of 180 m. Scattered megacrysts occur in the uppermost lavas. The region, however, also includes significant occurrences of comendites, biotite-rhyolites, and trachytes, outcropping as conspicuous domes, plugs, and laccoliths, and including the spec­ tacular Glass House Mountains. Ages range between 25.3 — 27.3 Ma.

INTRODUCTION

Southeastern Queensland is characterised by extensive late Oligocene-early Miocene volcanism (18 — 34 Ma), and in fact constitutes only a small segment of a belt of anorgenic Cainozoic volcanism that extends from far northeastern Queensland southwards, to Tasmania and through western Victoria to the south­ eastern corner of South Australia. The various volcanic centres throughout the whole region vary from large and complex shield volcanoes, to extensive basaltic lava fields, to small isolated plugs, sills, and laccoliths. The overall age range of the volcanism of the east Australian region is from Palaeocene to Recent, with the youngest centres occurring in northern Queensland and western Victoria. Rather young centres also occur in the Gayndah-Bundaberg region of central coastal Queensland. In a regional geo chronological study, Wellman & McDougall (1974a) dis­ tinguished two broad types of volcanic centres, namely central volcanic

Pap. Dep. Geol. Univ. Qd., 11(3): 1 -57, July, 1985. 2 provinces and lava field provinces. Their data show a systematic southward younging of the central provinces, but not of the lava fields. Sutherland (1981) has extended these interpretations by suggesting that both types of provinces do show migration paths when interpreted in terms of a model of northward drift of the Australian continent over several discrete mantle sources.

Southeastern Queensland Volcanic Centres (Text fig. 1)

The eroded remnants of three major shield volcanoes are recognised, namely the Tweed Shield, the Focal Peak Shield, and the Bunya Mountains. The extensive Main Range volcanic centres are generally regarded as a composite lava field province, and will be described in more detail in this paper. Additional smaller and more scattered centres occur, especially in the Fassifem Valley southwest of Brisbane, and north of Brisbane within the Noosa, Coolum, and Maleny-Glass Houses areas. The following notes summarise the essential features of those centres not being described further in this paper. All K-Ar dates quoted are based on the constants in Steiger & Jager (1977). Tweed Shield: This lies across the Queensland-New South Wales State border; a central elliptical-shaped intrusive complex (Mount Warning), some 5.5 by 8 km, consists of a core of trachyandesite, surrounded by a central syenite, which in turn is enclosed by an outer zone of laminated gabbros. These units are cut by a complex basalt-trachyte-syenite ring dyke, and a monzonite stock, together with minor dykes (mainly comendites). Surrounding the central complex is an outward dipping apron of lavas which comprises a lower mafic lava sequence, followed by a series of distinct rhyolite flows, pyroclastics, and plugs (the Binna Burra, Springbrook, and Nimbin rhyolites), overlain by an upper mafic lava sequence; these constitute the Lamington Volcanic Group. K-Ar dates give 20.5 to 23.6 Ma for the volcanic sequence, and 22.4 to 23.1 Ma for the intrusive complex. Further data are presented in Duggan & Mason (1978); Ewart et al. (1971; 1977); Webb et al. (1967), and Wellman & McDougall (1974b). Focal Peak Shield: This lies within a complex ring structure, some 14 km in diameter, marked by more-or-less peripheral rhyolite intrusions (including Mount Gillies), the massive Mount Barney granophyre, several syenitic intrusives, the gabbro-syenite intrusive of Focal Peak, doleritic cone sheets, and minor trachytic intrusives. Two distinct volcanic formations are associated with this centre: the Albert Basalt and the younger and rather complex Mount Gillies Rhyolite Formation. Focal Peak is interpreted as the major source of the former unit, with some additional eruptions from peripheral vents. K-Ar dates lie between 23.0 to 25. 6 Ma for the volcanic phase (Ross 1974, 1977; Stephenson 1956, 1959;Webber izZ.1967). Fassifern Valley: Within this area occurs an elliptical belt of numerous, mostly minor, silicic to intermediate extrusives and intrusives, the overall region of outcrop occupying some 90 x 30 km, and showing a prounounced N-S alignment. The southern end of this belt (part of which overlaps the Main Text fig. 1: Map of the southeastern corner of Queensland and the adjacent part of New South Wales showing the distribution of the main outcrop areas of Cainozoic mafic and silicic volcanism. Based on geological map “Moreton Geology” (1:500,000), Geological Survey of Queensland, 1980. 4

Range) extends into northern N.S.W., while its northern end is defined by the Flinders Peak trachyte. The Mount Alford ring complex (Stevens 1959, 1962) constitutes one prominent intrusive mass within the region. It consists of a central plug of micro­ diorite and subordinate granophyre intruded by dacite. The intrusion, between 3 to 4 km diameter, is cut by two series of dykes: a semicircular zone of rhyolitic ring dykes, and a second, non-arcuate set of cross-cutting rhyolitic, comenditic, and mafic dykes. K-Ar dates on three rhyolite dykes give 23.8 to 24.9 Ma (Ewart 1982). The Fhnders Peak area also constitutes a topographi­ cally prominent volcanic centre, containing a localised concentration of sills, dykes, and plugs. These are dominantly trachytes, but include subordinate rhyolite and mafic dykes. K-Ar dates on three trachytes range from 24.7 to 27.2 Ma (Webb et al. 1967; Ewart 1982).

SUMMARY OF PETROLOGICAL CHARACTERITSTICS OF SOUTHEASTERN QUEENSLAND CAINOZOIC LAVAS

The distribution of magma compositions, when measured in terms of SiO2 contents, is strongly bimodal (Text fig. 2), due to the relative abundance of rhyolites in addition to the dominant mafic lavas of broadly basaltic type. The histogram in text fig. 2 does not include data from the massive Mount Barney granophyre, which if included, would enhance even further the bimodality. It is also evident from text fig. 2 that the rhyolitic peak is superimposed on a broad band of trachytic compositions. The frequency of various compositions in text fig. 2 is not an accurate reflection of the volumes of these various lava types and its estimated that the mafic lavas prédominante volumetrically over the rhyolites by approximately 10:1. It is also important to note that the relatively high abun­ dance of rhyolites in southeastern Queensland is specific to this region, and is not found elsewhere through the east Australian Cainozoic province (Ewart, et al. 1985).

Mafic Lavas

These have silica contents dominantly in the range 45—50%, and range from nepheline, to olivine-hypersthene, to quartz-normative (Ewart et al. 1980). They are predominantly andesine-normative, with Mg/Mg + ZFe (atomic) ratios 0.3 to 0.6, K2O between 0.42 to 2.93%, and TiO2 from 0.8 to 3.6%. Phenocryst phases comprise olivine (Faig.75, sometimes with Cr-spinel inclusions), plagio­ clase (An25-68)’ less commonly augite. Groundmass mineral phases com­ prise augite, olivine (Fa33.77), feldspar (ranging from labradorite through to anorthoclase and sanidine), titanomagnetite, ilmenite, and apatite. Within many of the quartz-normative lavas, extensive development of subcalcic and pigeonitic pyroxenes occurs, and very rarely orthopyroxene; the term tholehtic andesite is used for lavas containing Ca-poor groundmass pyroxenes (Ewart et ¿zZ. 1980), and such lavas typically have SiO2 contents between approximately 52 to 57%. Megacrysts of aluminous augite, aluminous bronzite, olivine, ilmenite, and spinel sporadically occur in lavas from throughout the area. 5 6

Silicic Lavas

The rhyolites have been shown to have chemical, mineralogical, and isotopic characteristics which distinguish them from trachytic and peralkaline lavas of the region, and further indicate an independent petrogenesis for the rhyolitic magmas (Ewart 1982, 1985; Ewart et al. 1985). The rhyolites are typically high-silica potassic types (Table 1), and are characterised by well devel­ oped Eu anomalies ((Eu/Eu* = 0.42 - 0.05). Mineralogically, the following types may be recognised, based on pheno­ cryst assemblages: Rhyolites: (a) Sodic plagioclase + sanidine + quartz + Fe-biotite + allanite zt ilmenite — titanomagnetite (Binna Burra type), (b) Sanidine + quartz + fayalite + ferrohedenbergite + chevkinite + ilmenite (Fayalite rhyolite type, characteristic of the Mount Gillies rhyolites and also some of the Mount Alford rhyolites), (c) Sodic plagioclase + quartz + sanidine + ferrohypersthene + ilmenite (Ferrohy- persthene rhyolite type, characteristic of the Springbrook rhyolites, and some from Mount Alford).

Trachytes (non-peralkaline): (a) Sanidine + sodic plagioclase+ Fe-olivine +ferro­ augite -I- titanomagnetite + ilmenite (b) Sanidine + anorthoclase + ferroaugite — Fe-olivine -h titanomagnetite tilmenite.

Comendites: (i) Phenocrysts: Ca-poor anothoclase-sanidine — quartz t ferro­ hedenbergite (zoned to aegirine-augite) ilmenite, (ii) Groundmass: Ca-poor anorthoclase-sanidine -l- quartz -I- aegirine -I- fluor-arfvedsonite "L ilmenite Jz aenigmatite.

One of the most characteristic features shown by the mineralogy of the silicic magmas is the development of extreme Fe-enrichment within the Fe-Mg silicates, especially exemplified by the pyroxenes and olivines: a summary of the compositional ranges of these phases is illustrated in text figs 3 and 10, based on microprobe analyses of the various trachytic and rhyolitic lavas from the south­ eastern Queensland region.

THE MAIN RANGE

Introduction

Following current common usage, the Main Range is considered to be that segment of the Great Dividing Range linking the Bunya Mountains to the Queensland-New South Wales border. Important spurs are the Mistake Mountains and little Liverpool Range. A line from Laidley to Allora conven­ iently divides the volcanics of the Main Range into two subequal areas, here designated the northern Main Range and the southern Main Range. The Main Range rivals the Tweed Shield as the major Tertiary volcanic pro­ vince in southeastern Queensland. Continguous with, and east of, the Main 7

Text fig. 3: Composite plot, in terms of Mg, Fe + Mn, and Ca (atomic %) of phenocrystal pyroxenes (solid circles) and olivines (solid triangles) from the metalu- minous/peraluminous trachytes and rhyolites from the southeastern Queensland Cainozoic volcanic provinces, excluding the Main Range. Based on microprobe analyses.

Range proper lies an associated elliptical belt of predominantly acid intrusives. With its long axis trending approximately N 10°E — S lO’^W and with Mount Alford (Stevens 1959, 1962) located subcentrally, this elliptical intrusive zone is a feature of the Fassifem Valley in Queensland; it extends across the State border almost as far as Old Bonalbo in New South Wales. The Fassifern intru­ sives represent a segment of the belt of sporadic felsic volcanics which form a remarkably linear trend extending over 800 km from Fraser Island in Queens­ land to the Comboyne province in New South Wales. Where this volcanic zone bulges to incorporate the Fassifern intrusives, the major axis of the elliptical belt approximates closely the 8 - 12° W of S trail documented by Sutherland (1981) for the central volcano migration proposed in east Australia (Wellman & McDougall 1974a). Over the area encompassing the Great Dividing Range and the Darling Downs from 27° 15' S to the States’ border, late Oligocene-early Miocene lava flows in the Main Range constitute a volcanic pile which trends NNW — SSE for approximately 120 km at an average width of 35 km (Text fig. 4). The eruptives are largely basaltic, attaining a maximum total thickness of approximately 900 m and covering an area of about 4300 km^. Shallow lava dips (generally <3°, most commonly westwards) are typical. Extrusives extend back from the eastern escarpments to Pittsworth in the north, and to the vicinity of Warwick and Klllarney in the south. Although eruptives of the Tweed shield and the Main Range are roughly equal volumetrically and in area of exposure, this distinctly elongated outcrop pattern observed for the Main Range contrasts starkly with the essentially elliptical pattern (obviously centred on Mt Warning) displayed by the Lamington Volcanic Group. 8

Text fig. 4: Map of the Main Range showing the major features of the Tertiary volcanic geology. The intrusives depicted lie in the western sector of the Fassifern intrusive belt. Localities indicated are those referred to in the text. 9

Apart from eruptives of trachytic eomposition around Cooby Creek Dam (Stevens 1969) and rhyolitic flows in the Nutgrove Agglomerate Member (Cran- field & Schwarzbock 1974) at the southern end of the Bunya Mountains, inter­ mediate and/or acid lavas are not known in the northern Main Range volcanic pile. In contradistinction, lavas of a broad compositional spectrum occur in the southern Main Range, particularly in the east where the steep escarpment faces the Fassifern intrusives. Several thick trachyte horizons are interbedded with the mafic eruptives, and they are commonly dissected to display spectacular cliffs e.g. the residuals comprising The Steamers.

Stratigraphy

Summary aspects of the Main Range stratigraphy are presented here; a detailed account of all new and redefined units will be published soon (Grenfell, in prep.). Volcanic rocks attaining a maximum total thickness of approximately 900 m along the Main Range comprise, in the southern sector, two formations of subequal thickness and extensive distribution, the Governors Chair Volcanics (lower) and the Superbus Basalt (upper). Correlative formations in the northern Main Range are the Meringandan Volcanics (of limited extent) and the Toowoomba Basalt, respectively. The Governors Chair Volcanics represent a typical mildly alkaline basalt — comendite association, with a complete gradation of lava types from basalt to comendite present. Conspicuous metaluminous and peralkaline trachyte hori­ zons which occur include the Wild Cattle, Steamers, Swanfels, Guymer, and Spicers Gap Trachyte Members. Although lavas dominate the volcanic rocks, basaltic agglomerate and trachytic tuff and ignimbrite are known. The Tregony Conglomerate Member represents an intercalated, discontinuous unit which constitutes an important marker over some 60 km in the southern Main Range; it is predominantly a fluviatile and lacustrine deposit, but with local facies varia­ tion to pyroclastic breccia. The thickest lava successions within the Governors Chair Volcanics occur in the extreme east of the southern Main Range, lensing westwards such that at least the evolved types characterizing this formation have pinched out beyond 152°20'E. Conformably overlying the Governors Chair Volcanics, the Superbus Basalt is exposed in most of the southern Main Range over an area of 1600 km^. The maximum thickness recorded is 440 m. Component lavas are predominantly hawaiite, with alkali olivine basalt, and mugearite; rare normatively undersatur­ ated (usually inclusion-bearing) lavas occur, including the Mount Mitchell neph­ eline benmoreite and the Middle Branch Creek leucite basanite, typically at or near the top of the volcanic succession. The Meringandan Volcanics in the northern Main Range comprise the Cooby Trachyte Member, the Gomaren Basalt Member, and porphyritic basalts (?) underlying these units. The maximum thickness recorded is 75 m; compon­ ent lithologies are predominantly hawaiite (including types transitional to muge­ arite) and melanocratic trachyte. The formation may be correlated with the Governors Chair Volcanics in the southern Main Range. 10

The Toowoomba Basalt conformably overlies the Meringandan Volcanics in the Cooby Creek area, and passes laterally into the Superbus Basalt in the sothern Main Range. Lithologies are dominated by hawaiite, with sporadic occurrences of inclusion-bearing nepheline hawaiite at or near the top of the succession. Basalt (5.5.) is uncommon. Intercalated tuff and lapilli tuff in the Toowoomba area are lithic types, predominantly basaltic but containing dis­ aggregated quartz fragments derived from Mesozoic sandstones underlying the Toowoomba Basalt.

K-Ar geochronology

Approximately one-third of some 65 pubhshed K-Ar ages referring to the belt of volcanic rocks extending from Fraser Island and the Bunya Mountains to the Tweed shield pertain to the Main Range extrusives and the Fassifern intru­ sives (Webb et al. 1967; McDougall & Wilkinson 1967; Wellman & McDougall 1974b; Green & Stevens 1975; Ewart 1982). A further 26 K-Ar dates have recently been performed for the Main Range province (Grenfell 1984); exclud­ ing two minimum ages and two determinations which may be anomalous due to excessive argon, these results are summarized here. Lower formation (=LF) eruptives and acidic Fassifern intrusives yielded ages in the range 25.6 to 24.0 Ma, volcanism terminating with the eruption of major leucotrachytic flows marking waning activity. A possible hiatus of ^0.5 Ma was then followed by recurrent activity, exclusively mafic. The ages of upper formation (=UF) lavas, plus inclusion-bearing mafic intrusives interpreted as equivalents, indicate a more protracted history of at least 5 Ma for the second major stage of volcanism. It is stressed, however, that most UF lavas (>99% by volume) were erupted during the first 2 Ma ('\>24.0 — 22.2 Ma); young ages <21.5 Ma were obtained from sporadic, inclusion-bearing lavas, in accordance with their stratigraphic position at or near the top of the succession. A spinel lherzohte-bearing nepheline hawaiite capping Gowrie Mountain yielded the youngest ages of 18.1 and 18.2 Ma. Comparable inclusion-bearing, undersatur­ ated lavas notably also post-date the main Tertiary sequences in central Queens­ land (Dr L. Sutherland, pers. comm.).

Eruptive centres

(1) Southern Main Range: Radiometrie ages, in conjunction with the spatial dis­ tribution of felsic eruptives in the southern Main Range (Text fig. 4) and the complete absence of silicic lavas in the Superbus Basalt, clearly indicate that at least the felsic members of the Governors Chair Volcanics were fed from scattered centres within the Fassifern intrusives. In particular, (i) the Kangaroo Mountain and Mount Castle trachytes were erupted from a centre located on or near Mount Fraser, (ii) the feeder to the Swanfels Trachyte Member undoub­ tedly is exposed in Hell Hole Gorge, and (iii) the major eruptive centre for flows in the Wild Cattle Trachyte Member apparently is buried under basalts in the vicinity of Lizard Point. Field and chemical evidence indicate that the Steamers Trachyte Member was erupted from the Focal Peak shield. 11

Although the exact stratigraphic positions of numerous mafic intrusives east of the escarpment remain to be clarified, available field and petrographic evidence indicates that at least some are LF equivalents. The absence of a single major eruptive focus (with central complex) located subcentrally within the Fassifern intrusive belt implies that the ultimate Miocene geometry of the Governors Chair Volcanics did not constitute a volcanic shield comparable with the Tweed and Focal Peak examples. The constructional land­ form involved, however, is interpreted to have been regionally domal in aspect, in response to the coalescence of extrusives from scattered felsic centres (com­ monly clustered locally). This composite volcanic mass was contiguous with the Focal Peak Shield to the south, the fossil form of the western flank of which is reflected in the attitude and distribution of the Steamers Trachyte Member (Text fig. 5). Mafic lavas which underlie exposures of the Tregony Conglomerate Member near Mount Hennessy and Mount Haldon demonstrate the existence, at least to the northwest, of an apron of basaltic lavas flanking the elliptical zone of felsic volcanicity through the Fassifern Valley. Dykes, localized along a zone perhaps 3 km wide extending for '\>30 km close to the present escarpment, apparently largely fed the Superbus Basalt; small volcanic cones probably punctuated the line of fissures. The lavas of this last major volcanic phase, exclusively basaltic, overlapped earlier felsic extrusives, drowning them to the west and probably to the east. The Miocene post-volcanic physiography is reconstructed geomorphologically as an elongated lava pile crested by a broad divide trending NW — SE and plunging very gently northwards. The lavas bridging Focal Peak and the Main Range subsequently have been stripped off a topographic high which was developed in the Mesozoic Woodenbong Beds, Kangaroo Creek Sandstone, and Walloon Coal Measures. Vigorous stream erosion in these Miocene elevated areas would have been increased by differential uplift of the Mount Barney granophyric mass. (2) Northern Main Range: The abrupt decrease in the degree of Tertiary volcanicity north of Mistake Mountains was apparently accompanied by a difference in style, while fissure eruptions largely account for UF lavas in the southern Main Range, equivalent lavas northwards (=Toowoomba Basalt) appear to have issued from scattered dykes and necks. Several basaltic feeders have been recorded (Richards 1920; Reid, 1922; McTaggart 1963; Cranfield et al. 1976; Protheroe 1981; Dudgeon 1982). Additional mafic feeders in the northern Main Range have recently been recog­ nized by Grenfell (1984), most notably at and near Gowrie Mountain (west of Toowoomba), just west of Mount Tabletop (east of the Toowoomba escarp­ ment), and at Mount Wyangapinni and nearby peaks (north of Pittsworth). Possible vents for member units of the Meringandan Volcanics have been noted by Stevens (1969).

Petrology

Analysed mafic lavas from the Main Range extend from strongly alkaline to weakly alkaline (Text fig. 6). Normatively, a spectrum of compositions ranging

basalt, howaiite (• Iherzodte-betring I DIVIDES; Saggerson and Williams (196M) □ mugearite Irvine and Baragar (1971) + benmoreite. trachyte (• Iherzoi te-bearing) Macdonald (1968) O comendite Kuno (1968)

Text fig. 6: Plot of total alkalis (Na20 + K3O, wt. %) versus silica (SiO2, wt. %) for lavas of the Main Range Group: (a) Governors Chair Volcanics and Meringandan Vol­ canics; (b) Superbus Basalt and Toowoomba Basalt. Open circles refer to basalts and hawaiites (filled circles indicate spinel lherzolite-bearing types); open squares to muge­ arites; crosses to benmoreites and trachytes; the diamond to comendite. The asterisk represents the Mount Mitchell nepheline benmoreite (spinel lherzolite-bearing). The divide labelled 1 is after Saggerson and Williams (1964); 2 after Irvine and Baragar (1971); 3 after Macdonald (1968); 4 after Kuno (1968). 14 from (silica) undersaturated to oversaturated exists (Text fig. 7). Felsic types are invariably Q-normative. Basalts (5.5.) are delineated on the basis of normative plagioclase more calcic than andesine i.e. \QQanl(ab + an} >50. Varieties recognized are basanite (ne >5%), alkali olivine basalt, and transitional basalt (Grenfell 1984). More evolved lavas follow the Coombs alkalic trend (Miyashiro 1978), and the types hawaiite, mugearite, and benmoreite are classified essentially according to the scheme of Coombs and Wilkinson (1969). Additionally, employing 66% SiO2 as a discriminatory boundary, the colour-indexed terms melanocratic and leucocratic provide convenient trachyte descriptors for the Main Range associ­ ation. Representative and averaged analyses are presented in Table 1. The eruption of LF lavas in the Main Range corresponds to the first of two major stages recognized in the development of the volcanic pile. System­ atic sequential eruptive patterns which are observed within the Governors Chair Volcanics can be summarized as: basalt hawaiite t. mugearite benmoreite + melatrachyte i hawaiite -> metaluminous leucotrachyte i peralkaline trachyte. Text fig. 8 illustrates the continuity of whole rock compositions. Relative volumetric abundances which have been estimated from member thicknesses and areal extents based on field mapping (Grenfell 1984) indicate proportions of 97:2:1 for mafic, benmoreite + melatrachyte, and leucotrachyte + rhyolite groups respectively (Steamers Trachyte Member excluded). Major elements indicate the transitional affinities of LF basaltic lavas, in accordance with a suite which is a representative of the mildly alkaline basalt — comendite association documented from both oceanic and continental environments. In support, Rb, Sr, Ba, Nb, Ce, Nd, V, and Cr levels are lower than typical alkali basalt values, whereas Na2O and K2O abundances and P2O5/Zr ratios typically exceed those for tholeiites. Evolved LF liquids are characteristically progress­ ively enriched in Rb, Zr, Pb, Th, Nb, Ce, Nd, and Y; on the other hand, extreme depletions of Sr, Ba, V, Cr, and Mg are observed in silicic eruptives. An important exception to this general pattern is the Swanfels Trachyte Member; its comparatively impoverished incompatible element levels extend across a compositional spectrum of rocks grading from metaluminous trachyte (SiO2 - 65.9%) to comendite (SiO2 = 74.3%). The second stage of volcanism involved the extrusion of exclusively mafic lavas throughout the length of the present Main Range, giving rise to the Super­ bus Basalt in the south and the Toowoomba Basalt in the north. Each upper formation is characterised by two series, distinct geochemically and geochrono- logically. The UFA series ('v24.0 — 22.0 Ma; >99% by volume) comprises pre­ dominantly hawaiitic lavas, with subordinate transitional and alkali olivine basalts, tuffs, mugearites, and rare subalkaline basalt; these eruptives are slightly more alkaline than the LF analogues. The UFB series lavas (21.4 — 18.1 Ma) have a moderately — to strongly-alkalic character {ne reaching 14.5%), with mg numbers in the range 51.0 — 73.7. They comprise olivine nephelinite, basanite and leucite basanite, hawaiite (predominant) and nepheline hawaiite, and nepheline benmoreite; intrusive equivalents in the southern Main Range include ocellar lamprophyres. Megacryst and xenolith suites which are domin­ ated by spinel lherzolite characterize these UFB series eruptives. Text fig. 7: Normative (C.I.P.W.) ne, di, ol, hy, and Q components of analysed mafic lavas ((56% SiO2) from the Main Range, Bunya Mountains and Maleny (plus Mount Mee) volcanic centres. Solid symbols are based on an assumed value of Fe2O3/Fe2O3 + FeO = 0.2 (or where the analysed values are less than, or equal to this value). Hollow symbols are based on analysed Fe2O3 and FeO (where the iron oxidation ratio is greater than 0.2). 16

Phenocryst mineral assemblages within basaltic members of the Governors Chair Volcanics are typically; (1) basalts (s.s.): ol tplag±Fe-Ti oxides (microphenocrystal). (2) hawaiites: o 1 + plag ± cpx ± Fe-Ti oxides (microphenocrystal). Rare phenocrysts in LF mugearites comprise andesine-oligoclase + ferroaugite + olivine ('\/Fa68) + (microphenocrystal) titanmagnetite and apatite; a distinctive amphibole of ferroedenitic/ferrorichteritic composition is common in the groundmass. Benmoreites and Type I melatrachytes are usually porphyritic in sodic plagioclase + ferroaugite/ferrohedenbergite + olivine ("\^Fa9Q) ± (micro­ phenocrystal) titanomagnetite and apatite. Phenocryst phases characterizing Type II melatrachytes are Ca-anorthoclase + ferroaugite + olivine ± (micro­ phenocrystal) titanomagnetite; Na-rich pyroxene + Na-Ca amphibole occur in the groundmass. Except for the Steamers Member, all trachytes in the formation are one-feldspar types; the leucocratic members carry phenocrystic calcic to Ca-poor anorthoclase + ferroaugite/ferrohedenbergite + fayalitic olivine + (microphenocrystal) titanomagnetite. Perkaline variants are character­ ized by Na-pyroxene + arfvedsonite i aenigmatite in the groundmass. Sparse phenocrysts in UFA series basalts and hawaiites comprise plagio­ clase (labradorite-andesine), ohvine, augitic-salitic clinopyroxene, and (micro­ phenocrystal) titanomagnetite. Associated mugearites (Superbus Basalt only) are chemically and mineralogically distinguishable from LF variants. The . Middle Branch Creek leucite basanite shows affinities with other leucite-bearing lavas of the eastern Austrahan Tertiary province. Mafic siUcates in its pegma- toidal phase comprise Ti-phlogopite, Ti-aegirine, and Ti-magnesioarfvedsonite. Despite the chemical overlap displayed by basic rocks of the Main Range Group, unmistable trends which correlate with the major hthostratigraphic units are evident from plots of major elements trace elements, Mg/Mg + ZFe vs. DI (Grenfell 1984). The plot of 100 Mg/Mg + SFe vs. DI is illustrated in text fig. 9. For Main Range Group lavas, a close parallel can be drawn with the (1) /zy-normative, (2) alkalic, and (3) basanitic trends recognized within the compositional spectrum of Anjouan lavas in the Comores Archipelago (Flower, 1973). It is emphasized, furthermore, that the eruption of LF lavas, followed by UFA then UFB series flows, represents broad shifts towards a progressively more alkaline chemical character in the Main Range volcanicity with time. Compilations of all available pyroxene and olivine analyses (phenocrysts, microphenocrysts, and groundmass) determined by electron microprobe are presented in text fig. 10 (data after Grenfell 1984). These data are grouped according to LF, UFA series, and UFB series lavas to conveniently illustrate geochemical diversity in terms of the pyroxenes crystallizing (compare e.g. Fodor et al. 1975). The dashed curve on each quadrilateral is the Skaergaard Ca-rich pyroxene trend (Brown and Vincent 1963); compositions enclosed by a dotted circle refer'to a rare (and rather unrepresentative) basanite occurrence in the Governors Chair Volcanics. Text fig. 8: Histogram showing the distribution of SiO2 (wt.% on a normalized, anhydrous basis) within lavas of the Main Range Group. 18

DIFFERENTIATION INDEX DI

Text fig. 9: Trends for LF, UFA series, and UFB series lavas as indicated by a plot of 100 Mg/Mg + ZFe versus differentiation index DI. Crosses and open symbols represent LF lavas (circles refer to basalts and hawaiites, squares to mugearites, crosses to ben­ moreites and trachytes, the diamond to comendite); filled circles and squares represent UFA series lavas (circles refer to basalts and hawaiites,squares to mugearites); filled circles with a horizontal line represent UFB series basalts and hawaiites, the asterisk refers to the Mount Mitchell nepheline benmoreite. 19

Text fig. 10: Compilation of all available pyroxene and olivine analyses in terms of Ca, Mg, and Fe + Mn (mol. %) for Main Range Group lavas, as follows: (a) Governors Chair Volcanics; (b) UFA series eruptives; (c) UFB series eruptives. Compositions enclosed by a dotted circle in (a) refer to a rare LF basanite. 20

Inclusions

In contrast to the paucity of occurrences of basaltic lavas containing megacrysts and ultramafic xenoliths elsewhere in southeastern Queensland (see Wass & Irving 1976; Ewart et al. 1980), such lavas occur sporadically through­ out the Main Range province. The inclusions may be locally very abundant. Spinel lherzolite xenoliths are undoubtedly the most common inclusions, with several occurrences in the area already documented e.g. Stevens (1965, 1969); Wass & Irving (1976); Protheroe (1981). Megacrystal kaersutite, ilmenite, and anorthoclase have been recorded from the Mount Mitchell nephel­ ine benmoreite (Green et al. 1974), together with clinopyroxene and spinel from Majuba Hill (Wass & Irving op. cit.}. Olivine, clinopyroxene, and ortho­ pyroxene in a flow at Muniganeen Trig., northwest of Toowoomba (Stevens 1969), presumably are xenocrystal. Table 2 records the inclusions found at the major localities within, or close to, the Main Range proper by Grenfell (1984). Relative abundances are denoted according to Wass & Irving {pp. cit.}. Crustal fragments not included in Table 2 comprise quartzites, presumably representing Mesozoic sandstones flooring the lava pile, plus rare granitic xenoliths (reaching 3 cm in diameter) of unknown source.

Megacrysts: The megacryst suite in the UFB series lavas comprises Ca-Tscher- makitic clinopyroxene (compositional range Ca37 gMg4g 7Fei3 5 — Ca4Q 5 ^842.8^^16.7)’ Al-orthopyroxene ('vCa3 7Mg77.2Fei9 q), anorthoclase, kaersutite, mica, and Mg-ilmenite. •

Xenoliths: Apart from accidental inclusions of obvious upper crustal origin, xenoliths present in the UFB series lavas are ultramafic and mafic types com­ prising peridotites, wehrlites, pyroxenites (both ‘anhydrous’ and kaersutite/ pargasite-b earing types), hornblendites, diorites, mafic granulites, and gabbro ids. Although both the Cr-diopside and Al-augite groups of Wilshire & Shervais (1975) are represented, the classification preferred is based sub­ stantially on that of Hollis (1980) and Sutherland and Hollis (1982). Contacts within inclusions from the key Australian localities of Bullenmerri and Lake Gnotuk near Camperdown in Victoria (Hollis op. cit.) which have been used to establish relationships between different types are not observed in the Main Range examples; nevertheless, the five main groups categorized by Sutherland & Hollis (pp. cit.} are represented. The nomenclature applied to xenoliths largely follows the recommen­ dations of the International Union of Geophysical Sciences (1973). Some (feldspathic ultramafic) spinel-plagioclase-augite-hypersthene inclusions with modal feldspar (10% which are strictly plagioclase websterites (lUGS 1973; see also Moorhouse 1959, p. 313) have been included, together with a single plagioclase-free occurrence, in the ultramafic-mafic granulite suite on a textural and mineralogical basis. Adopting this terminology, clinopyroxenite » websterite in abundance for the ultramafic suite. 21

Main Range xenolith groups, and their inclusion variants, are as follows: (1) Cr-diopside group spinel lherzolite (2) Green clinopyroxenite group spinel clinopyroxenite; clinopyroxenite. (3) Black peridotite-pyroxenite group (a) anhydrous types: wehrlite; olivine clinopyroxenite, clinopyroxenite (+ black spinel), and websterite. (b) poikilitic kaersutitic types: kaersutite pyroxenite. (c) metasomatized and related types: amphibole-spinel-olivine cUnopyroxenite; amphibole ("Lspinel) chnopyroxenite; hornblendite; titanomagnetite-apatite rock. (4) Diorite group meladiorite. (5) Granulite-gabbro group two-pyroxene mafic and ultramafic granulites; gabbro; coronitic hypersthene gabbro/microgabbro. Averaged pyroxene and olivine compositions for individual inclusions in the major ultramafic inclusion groups are compared in text fig. 11; corres­ ponding clinopyroxene data for granulite and gabbro inclusions are plotted in text fig. 12, while amphibole compositions (in terms of Ti, Mg, and Fe) for inclusions in the UFB series lavas are shown in text fig. 13 (all data after Gren­ fell 1984) in relation to fields delineated by other eastern Australian occur­ rences. Some mineralogical aspects of the major ultramafic groups for Main Range inclusions are summarized here. Cr-diopside group clinopyroxenes are Cr-diopsides and Cr-endiopsides (averaged Cr2O3 = 0.65%) of limited compositional range Ca44.4—49.0 Mg45 3_5Q 3Fe3 7_5 4. Coexisting orthopyroxenes are aluminous enstatites correspondingly restricted in composition to Cag 5_j ^Mggg.5—90.7 Feg 7_|Q 3. For all pyroxenes, mg289.9. Olivines are highly magnesian, with mg (=100Mg/Mg + SFe) 289.3; analyses reveal a narrow compositional span (Fa9.3 — 10.7)- Red-brown to brown Cr-spinels are TiO2-poor with M numbers (=10bMg/Mg -1- Fe^"*")) in the range 79.8 — 84.8. No relatively Fe-rich variants (Wilkinson & Binns 1977) have been detected in Main Range lherzolites. Some representative mineral analyses of these xenoliths are given in Table 3 and text fig. 14 (xenolith 4 and Harlaxton quarry xenolith), from the Harlaxton quarry. North Toowoomba. Host lavas are invariably normatively undersaturated, and they include types ranging from olivine nephelinite to nepheline benmoreite. Compositional parameters for the inclusion minerals show only Limited varia- Text fig. 11: Compositions (in mol.%) of pyroxenes and olivines in spinel lherzolite (represented by open circles), green clino-pyroxenite (filled squares), black peridotite­ pyroxenite (diamonds: filled, non-metasmatized; open, metasomatized) inclusions within lavas of the Main Range Group. Tie hnes join coexisting phases, except for spinel lherzolite (omitted for clarity). Text fig. 12; Compositions (in mol. %) of pyroxenes in granulite (represented by open triangles) and gabbroid (squares, hypersthene gabbros; filled triangles, gabbros) inclu­ sions within the UFB series lavas. Tie lines join coexisting phases. tions, however, which cannot be correlated with host rock petrochemistries. In fact, the chemical variability displayed between corresponding minerals of two discrete spinel lherzolite inclusions from the Malu quarry (northwest of Oakey) is approximately one-half that observed for the entire province. Representative pyroxene analyses for xenohths of the green chnopyroxen- ite inclusion group are given in Table 3 and text fig. 14 (xenolith 1). Pyroxene compositions have lower mg numbers, with ranges of 87.5 — 83.0 and 85.9 — 84.4 for clinopyroxene and orthopyroxene respectively, than for corresponding phases (mg2 89.9) in the Cr-diopside group. Cr2O3 levels are distinctly lower in the green clinopyroxenites. Averaged AI2O3 contents are 5.01 — 6.25% (clino­ pyroxenes) and 3.80 — 4.43% (orthopyroxenes). TiO2 varies from 0.41 — 0.72% in thediopsides/augites, and, since unmixing favours incorporation of TiO2 in the clinopyroxene phase, is predictably lowest (^0.4%) in those xenoliths whose clinopyroxenes display distinctly the most subcalcic chemistry ('\/Ca35Mg54Fe iq). Orthopyroxene compositions range from Caj.iMg84 9 24

Fei4 o to Ca2 9Mg8i 7Fei5 3, and are thus encompassed by corresponding phases in Victorian metapyroxenites (Hollis, 1980). Olivine has mg = 81.5. Spinel of olive-green colour is compositionally almost pleonastic, and has M = 75.7 in contrast to values 279.8 in spinel lherzolites, and 265.9 in other mafic- ultramafic inclusions. The Cr2O3 content lies below the microprobe detection limit. The black periodotite-pyroxenite group of inclusions essentially correlates with the Al-augite group of Wilshire & Shervais (1975) (=Ti-augite group of Wilkinson 1975) and Group II of Frey and Prinz (1978). Xenoliths are charac­ terized by black and vitreous augites t amphibole. Key localities in the Main Range are the quarry near Gowrie Mountain (some representative mineral analyses of which are presented in Table 3 and text fig. 14, xenoliths 2, 3 and 5-7), and the nepheline benmoreite exposure on Mount Mitchell. Compared with other ultramafic xenoliths, mineral assemblages characteristically are more Fe- and Ti-rich (mg <81 for ferromagnesians; TiO2 only rarely <0.7% in augites).

BUNYA MOUNTAINS

Introduction

These are interpreted as the eroded remnants of an old shield volcano, and appear as the northern extension of the Main Range, with which the Bunya lavas are broadly contemporaneous. The maximum diameter of the original shield is estimated to have exceeded 60km, while the maximum thickness of the succession may have exceeded 700 m, extending from approximately 400 m above sea level to 1,135 m at Mount Kiangarow, the highest point on the Bunya Mountains. Eruptions are most likely to have emanated from multiple vents within the summit region, and the numerous lava flows exhibit a generally outward radial dip from this broad summit region. No significant agglomeratic deposits have been recognised. Four K-ar dates published in Ewart (1982) lie between 23.2 to 23.7 Ma. These were obtained on samples ranging between the Mount Kiangarow summit to a lava flow exposed low down on the Dandabah-Dalby road (Text fig. 15), representing one of the lowest flows exposed on the southern flanks of the succession. Webb et al. (1967) report a slightly younger age of 22.6 Ma for a sample from Kumbia, on the lower northern flank of the Bunya Mountains. Two additional unpubhshed dates are also available (Dr. C.G. Murray, Geolog­ ical Survey of Queensland; pers. comm.). One from a lava 1 km north of the Dandabah camping reserve, representing the uppermost part of the sequence, gives 22.0 t- 0.3 Ma. The second sample from a lava below a laterite profile 8 km south of Nanango (on the northeastern extremity of the Bunya Mountains succession) gives a significantly older age of 29.4 to.3 Ma. A characteristic feature of this volcanic centre is the apparent extreme scarcity of sihcic eruptions; the most siliceous extrusive recognised is a single trachyte plug which has recently been reported in the southwestern flank of the volcano. An analysis of this trachyte, a vitreous sample, is presented in KEY. MAIN RANGE PROVINCE

amphibole megacrysts

o kaersutite in poikilitic amphibole pyroxenites

pargasite in metasomatized clinopyroxenite sample MLSlOH

kaersutite in camptonite sample CWNOl: c = clot; p = phenocryst core; r = phenocryst rim; c = grass

♦ coronitic kaersutite in hypersthene gabbro inclusion MLSIOG

Text fig. 13 : Compositions (in mol. %) in terms of Ti, Mg, and Fe of amphiboles in megacrysts and xenoliths of the UFB series lavas. Filled diamonds refer to amphibole megacrysts; open circles to poikilitic amphibole pyroxenites; filled circle to metaso­ matized chnopyroxenite; filled squares to kaersutite in camptonites (c = clot, p = phenocryst core, r = phenocryst rim, g = lava groundmass); the cross to coronitic kaersutite in a hypersthene gabbro. The long-dashed, dotted, and dashed curves outline fields of amphiboles from upper mantle rocks, lower crustal rocks, and megacrysts, respectively (after Sutherland & HoUis 1982). 26

Text fig. 14: Plots, in terms of Mg, Fe + Mn, and Ca (atomic %), of pyroxenes (solid circles), olivines (solid triangles), and amphibole (solid inverted triangles) occurring: (a) In seven separate xenoliths (xen 1 to 7) in the Gowrie Mountain quarry, west of Toowoomba. Plot (h) represents the groundmass phases in the host lava, (b) Xenoliths (plot (i) and groundmass phases (plot (j)) in the host lava from the Harlaxton quarry, Toowoomba. Text fig. 15: Map of the southern Bunya Mountains, along the summit road south of Dandabah, showing the location of analysed samples collected along the Dandabah- Dalby road. Sample numbers refer to the rock collection in the Department of Geology and Mineralogy, University of Queensland. 28

Table 4; the analysis suggests some selective Na loss associated with hydration. No other trachyte occurrences are currently recognised within the Bunya Mountains lava succession.

Petrology

Chemically, the lavas are predominantly ne— and oZ—normative, and within the classification used by Ewart et ¿zZ. (1980), are termed hawaiites. The normative chemistry, plotted in terms of ne, ol, hy, di, and Q, of all analysed samples is presented in text fig. 7 (based on both analysed and assumed Fe2 03/FeO values). In Table 4, analyses are presented for a series of samples collected along the road from the summit region (Dandabah) down the south­ ern slopes towards Dalby, representing a very general section through the volcanic succession in this part of the shield. These analysed sample localities are shown in text fig. 15. The major element data in Table 4 are recalculated water-free to facilitate more ready comparisons between samples. Towards the base of the sequence occur two relatively silicic flows, classed as potassic tholeiitic andesites (Ewart et al. 1980). These two flows are Q-normative, aphyric, and are distinguished mineralogically by the presence of groundmass pigeonitic pyroxenes. Apart from these two flows, the remaining analysed samples, all classed as hawaiites, are similar in their overall chemistry. The only possible overall trend is a general upward decrease in Mg, a feature also found in the Maleny volcanic sequence. In other respects, the lavas show the variable but relatively high TiO2 and K2O abundances which are characteristic of these continental anorogenic mafic volcanics. Bryan (1983) has also presented chemical data for samples collected on a traverse on or near the road across the Bunya Mountains, the results of which are very consistent with those presented in Table 4. The only notable differ­ ence is the reported occurrence of a trachyandesite (benmoreite) flow within the upper third of the sequence. Mineralogically, the hawaiite lavas are mostly only sparsely phenocrystal (Table 4) with plagioclase and olivine being normally present, with rare titan- omagnetite. Occasional plagioclase-phyric lavas occur in the summit region. Phenocrystal plagioclase ranges from An6i_4o (often exhibiting reverse zoning), and olivine from Fa24-47. Groundmass phases comprise feldspar which ranges from plagioclase (An67) continuously through to sandine (Or5g), olivine (Fa35_53), augite, titanomagnetite, ilmenite, and apatite. Anhedral flakes of groundmass phlogopite occur in the lowest lava sampled (No. 38784; see Ewart et al. 1980). In text fig. 16 and Table 5, a compilation of the com­ positions of the groundmass pyroxenes is presented. These exhibit very restricted ranges of Mg-Fe ratios and are dominantly calcic augites, consistent with the mildly undersaturated nature of the host lavas. Megacrysts of plagio­ clase (An37), olivine (Fa28-32)’ aluminous augite (including subcalcic types text fig. 16), and spinel (Table 5) have been identified in two samples, interest­ ingly from the lowest and highest parts of the volcanic succession. The mineralogy of the two aphyric tholeiitic andesites consists of plagio­ clase (An48, varying continuously to sanidine, Or54), Fe-rich augite, ferrifer- 29

Text fig. 16: Composite plots, in terms of Mg, Fe + Mn, and Ca (atomic %) of (plots (a) to (d)) the groundmass pyroxenes (solid circles), groundmass olivines (solid triangles), and phenocryst olivines (inverted solid triangles) in lavas from the Bunya Mountains, Mount Mee, and Maleny volcanic centres. Plots (e) and (f) show pyroxene megacryst compositions in Bunya Mountains and Maleny samples. 30

OUS pigeonite, olivine (Fa5g_77, in one sample), titanomagnetite, ilmenite, and apatite. The pyroxene and olivine compositions are plotted in text fig. 16b. The petrogenesis of the Bunya Mountains magmas, and in fact the mafic to intermediate lavas from other associated centres from southern Queensland, are discussed in detail by Ewart et al. (1980) and Bryan (1983) in terms of models of lower crustal and shallow level fractional crystallisation processes. Ewart et al. (1980) proposed a model of lower crustal fractionation, at esti­ mated temperatures of 1180—1200®C and pressures of 10—14kb. This model suggested trapping and re-equilibration of primary basaltic magmas at, or near the base of the crust, with some additional evolution occurring in shallower crust magma chambers. Bryan (1983) has shown, by means of materials balance calculations, the plausibility and likely importance of very low pressure frac­ tionation in the development of intermediate to siliceous magma compositions, such as those found in the Bunya Mountains. These calculations suggest that augite increasing in the later stages of fractionation, which is consistent with observed phenocrystal phases in the mafic lavas.

MALENY MAFIC VOLCANIC SEQUENCE

Introduction

The lavas of the Maleny-Mapleton region overlie the Mesozoic sediments and volcanics of the Nambour Basin and the older rocks of the D’Aguilar Block, and partly conceal the boundary between the two. The lava flows covered and preserved a dissected topography, and the basalt cover on the Maleny-Mapleton plateau varies in thickness from approximately 1 to 180 m. The thickest parts of the sequence occur where the lavas infilled a pre- basalt valley near the present location of Montville. Elsewhere, the basalt cover is between 15 to 60 m thick and covers the dissected sub- basalt topography which has a relief of about 60 m. the base of the lavas is usually between about 245—260 m above sea level (Evans 1976). The basalt capping on Mount Buderim, to the east of the Maleny-Mapleton plateau, is interpreted to repre­ sent an extension of the Maleny lavas, with an inverted topography resulting from basalt infilling a pre-basalt valley. One physiographic feature that is exhibited by the basaltic sequence on Maleny-Montville plateau is the occurrence of amphitheatre-headed valleys, due to the erosional effects on alternating resistant and non-resistant basaltic horizons. The individual flows are generally relatively thin (less than 10 m), although locally exceeding 15 m; these thicker flow units are typically charac­ terised by columnar jointing. Each flow is massive at the base, with a vesicular top. At the base of the succession, the vesicles are zeolite-infilled, predomin­ antly by natrolite and chabazite. A well developed feature is the common occurrence of prominent red paleosols separating flow units, these being espec­ ially conspicuous in weathered road cuttings. The paleosols are subhorizontal when seen in a single road cutting, but in fact have amplitudes up to 15 m when traced over a somewhat wider area. The frequency and occurrence of 31

these highly oxidised paleosol horizons suggest considerable time intervals between flow outpourings, and the possibility of protracted volcanism.

Age

Evans (1976) provided three whole rock ages for the mafic lavas, ranging from 28.1 to 33.7 Ma. The oldest and youngest of these dates are internally consistent in terms of their relative stratigraphic positions. An additional date of 25.2 Ma was obtained on anorthoclase megacrysts, occurring in one of the stratigraphically highest mafic flows (Ewart 1982; see sample 3784.3 in Table 6). This last date indicates that the Maleny volcanism overlapped that forming

the Glass House Mountains (see later). The dates do, however, suggest a rela­ tively long period of volcanism for the Maleny centre, spanning over 8 Ma. Owing to the relatively high percentages of non-radiogenic argon in other analysed Maleny samples, it has so far proved impossible to confirm the wide range of dates.

Petrology

Chemical analyses of a series of samples from a traverse between Skenes Creek and Montville, and along the Maleny-Landsborough Road, are presented in Table 6. A plot of all available analyses in terms of normative ol-hy-di-(^ is presented in text fig. 7. It is evident that the Maleny mafic lavas exhibit a rather narrow range of composition in terms of silica saturation, most analyses plotting in proximity to the ol-hy boundary (i.e. plane of silica saturation). The lavas are andesine normative, with variable but mostly moderately high TiO2 and K2O contents. There is, furthermore, a tendency for the stratigraphically lowest flows to be more Mg-rich than those occurring higher in the sequence. Phenocryst phases comprise olivine (Fa22-55)5 minor plagioclase (An55_4Q, with rims zoned to anorthoclase), and less commonly augite. The higher phenocrystal olivine contents tend to correlate with higher whole rock Mg values. The more Mg-rich phenocrystal olivines, occurring most extensively within the lower parts of the volcanic succession, are characterized by the occurrence of small (typically <20m) euhedral inclusions of Cr-bearing spinels. These exhibit a wide range of compositional variability between grains, which is attributed to post-eruption solid state alteration of original chromites during cooling; this is supported by the application of the Cr-spinel-olivine geother­ mometer, the results of which give subsolidus temperatures (Ewart et al. 1980). The occurrence of Cr-spinels is rare in lavas in southeastern Queensland, outside those of the Maleny centre. Groundmass mineralogy comprises plagioclase (varying from An53 sodic plagioclase compositions to sanidine), rare olivine (Fa3|_44), augite (which 32 extends to subcalcic compositions in the most K2O-deficient lavas), titano- magnetitie, ilmenite, and apatite. Plots of the olivine and groundmass pyroxene compositions are presented in text fig. 16, and pyroxene analyses in Table 7. In view of the quartz saturated, or near saturated, chemistry of the Maleny lavas, it is noteworthy that no reaction rims are observed on the olivines, nor has the presence of any groundmass Ca-poor pyroxene been recorded. Ewart et al. (1980) thus classed the Maleny lavas as hawaiites. Megacrysts occur within lavas in the uppermost part of the sequence. Phases identified include andesine (Angg 9Or5 g to An47 50r4 j), anortho­ clase (Or29.4An7 4 to Or4Q qAng q), aluminous low Ca augite, ortho-pyroxene (Mg77 5Fei9 gCag 9), and ilmenite. Plots of the pyroxene megacryst compo­ sitions are given in text fig. 16, and analyses in Table 7. To the south of the Maleny and Glass House Mountains volcanic centres occurs a series of localised basaltic outcrops in the Mount Mee area (Text Fig. 17). No age data are available. Only a single sample has been here investigated (Table 6). The whole rock analysis indicates it to be ne-normative (Text fig. 7), and thus quite distinct from the Maleny lavas. It is also andesine-normative. Phenocryst phase include plagioclase (An4i_4g, with reversely zoned rims extending to Angg), and olivine (Fag 1.39). Groundmass minerals are plagio­ clase (An^Q, ranging through to sodic sanidine), olivine (Fa36_45), augite (Text fig. 16;Table 7), Fe-Ti oxides, and apatite.

THE GLASS HOUSE MOUNTAINS, COOLUM, AND NOOSA AREAS (Text fig. 17)

Introduction

These areas contain prominent dome-like intrusions/extrusions of trachytes, comendites, and rhyohtes. The most spectacular are those belonging to the Glass House Mountains, comprising a localised group of eroded dome­ shaped hills, and conical peaks, possibly in part laccohthic. Additional sills and dykes also occur in the same area. These are intruded into essentially horizon­ tally bedded Late Triassic Early Jurassic sandstones and shales (the Lands- borough Sandstone). Each of the prominent volcanic hills represents a separate centre of intrusion. Bryan & Stevens (1973) have described Mount Ngungun, which is characterised by near vertical columnar jointing in all observed exposures. These authors suggest that it originally represented a cumulo-dome, although remnants of the enclosing volcanic cone, if it ever existed, have been removed by erosion. The lower Miocene physiographic surface, between 120—210 m in altitude, is recognised in the Maleny plateau, to the north of the Glass House Mountains, where it is capped by mafic lavas (previously described) and has a gentle easterly dip. Probable erosional equivalents occur west of the Glass House Mountains, and as the majority of the peaks of the Glass Houses reach elevations above this inferred Miocene surface, it is concluded that the intrus­ 33 ions reached the lower Miocene surface and built up volcanic cones (Stevens 1971; Evans 1976). The lower lying outcrops of comendite (e.g. Trachyte Range) are interpreted as sills. No associated pyroclastics have been recognised, but if present, would be expected to have been removed by erosion. Three volcanic types are recognised in the Glass Houses: metaluminous trachyte, peralkaline trachyte, and comendite (Table 8). Porphyritic anortho­ clase trachytes (metaluminous) occur at Mounts Beerburrum and Miketee- bumulgrai; these trachytes are dark blue-grey when fresh, but very readily oxidise to brown coloration. Mount Beerwah, the highest of the Glass House peaks (556 m), is a peralkaline trachyte. A minor intrusive mass east of Mount Tibrogargan is a non-porphyritic, fayalite-bearing trachyte (metaluminous), while dykes of pale grey porphyritic, anorthoclase trachytes (metaluminous) crop out on the old Gympie road. The remaining Glass House peaks (Ngungun, Tibrogargan, Saddleback, Trachyte Range, Conowrin, The Twins, Coochin, and Tibberoowuccum) are comendites. Four K-Ar dates are available for the Glass House Mountains: Mount Ngungun, 25.3 Ma (whole rock); Trachyte Range, 25.5 Ma (whole rock); Mount Beerburrum, 25.6 Ma (feldspar); Mount Beerwah, 27.3 Ma (feldspar) (Webb et al. 1967; Ewart 1982). These indicate a slightly older age for Mount Beerwah, but do also indicate overlap of volcanicity between the Glass House Mountains and at least the younger lava phases of the Maleny volcanic centre. Approximately 50 -60 km north and NNE of the Glass House Mountains, in the Coolum to Noosa region, occur five prominent isolated dome and plug- hke structures, comprising three comendites (Mounts Coolum, Cooran, and Cooroora), and two biotite-bearing rhyolites (metaluminous; Mounts Peregian and Tinbeerwah). The two rhyolites are considered to represent laccoliths, as is Mount Coolum (see below). Only Mount Coolum is dated, giving 25.3 Ma (whole rock, Webb et al. 1967), which is identical to the Glass House Mountains.

Mount Coolum

This is, so far, the only dome-like structure in the region that has been systematically mapped (Murphy 1972). It is an isolated dome-like hill, bounded on all sides by either precipitous cliffs or very steep slopes. It is roughly elliptical in plan, with a disused quarry situated at its base on the eastern side of the dome, and several incised gullies eroded on the upper slopes. It is intruded into the Late Triassic-Early Jurassic Landsborough Sandstone, which has an approximately 10° easterly dip in this area; in proximity to Mount Coolum, however, the sediments are deformed with resulting dips of up to 40° radially outwards from the dome. In fact, only a veneer of Landsborough Sandstone is interpreted to remain over sill-like extensions of the Mount Coolum comendite around the base of the dome (Text figs 18 and 19). The comendite has also been observed to be underlain by sandstone in an exposure in the quarry. Occurring in a cave at the foot of the cliff situated to the northwest of the quarry is a block of hornblende diorite porphyry, inter­ 34

Text fig. 17: Map of the Glass House Mountains to Noosa region to show the locations of the main volcanic areas referred to in the text. 35

Text fig. 18: Geological map of Mount Cooluni showing the outcrop area of comendite, and the dips of the columnar jointing. After Murphy 1972. Contours in feet. 36 preted as a xenolith from a late Jurassic sill intrusion into the Landsborough Sandstone; it is similar to other intrusions occurring elsewhere in the Coolum region. One of the most striking features of Mount Coolum is the occurrence of columnar jointing, the dips of which range predominantly between 0 to 20® (including those exposed in cliff faces), the dip azimuths forming a complete radial pattern (Murphy 1972). Around the base of the dome, however, the dips of the columns are much steeper, ranging between 70—90®, as seen in the quarry. Near vertical dips are also seen near the summit, in the northwestern sector of the dome. Flow lamination is also visible in many areas of comendite outcrop, some­ times best seen microscopically. This is due to preferred orientation of elongate feldspar laths, and alternating feldspar-rich and amphibole-rich layers. Field measurements suggest a vertical, or near-vertical magma flow (with circumfer­ ential orientation) near the upper surfaces of the dome, while around the lower peripheral region (e.g. the quarry), flow is interpreted to have been near horiz­ ontal (Text fig. 19; Murphy 1972). The interpretation is that Mount Coolum represents a shallow laccolithic intrusion (Text fig. 19), which explains the absence of associated flows of pyroclastics. It is assumed that vertically developed columnar jointing would have, been present within the original uppermost surface of the intrusion, but has subsequently been removed by erosion. At present, only a veneer of sand­ stone still remains around the periphery of the dome. The localised area of vertical jointing near the summit would thus have represented an original irregularity in the uppermost intrusive surface.

Petrology

Whole rock analyses, including trace elements, are presented in Table 8, and microprobe analyses of selected mineral phases are given in Tables 9 and 10. The comendites are all characterised by a molar excess of alkalis over alumina, resulting in at least normative ac. Some samples, such as that from Mount Cooran, are only just peralkaline. Nevertheless, all samples exhibit characteristic mineralogy, particularly in the presence of sodic amphiboles, and less commonly, sodic pyroxenes. These peralkaline lavas from the region north of Brisbane also exhibit typical geochemical characteristics expected in such types, most notably their very depleted abundances of Mg, Ca, Mn, P, Ba, Sr, Ni, Cr, and V, coupled with very strong enrichments in Rb, Zn, Nb, and Zr (noting the absence of zircon in these lavas). These chemical features can be contrasted (Table 8) with the rhyolites from Mounts Tinbeerwah and Peregian, both peraluminous (which may, at least in part, be accentuated by devitrification within these rocks). These rhyolites are quite clearly less depleted in elements such as Mg, Ca, Ba, and Sr, and characteristically less enriched in Zr, Zn, Nb, Ce, and Rb. Compared with the rhyolites elsewhere in southeastern Queensland (see averaged data in Table 8), the Tinbeerwah and Peregian rhyolites are geochemically most similar 37

DIAGRAMMATIC CROSS-SECTION

I Tc I comendite I R-J» I Landsborough Sandstone I I hornblende diorite porphyrite Column dips — Magma flow

Text fig. 19: Interpretative section of Mount Coolum, along the Section A-B shown in fig. 18, to show the inferred laccohthic structure, and directions of magma Oow^after Murphy(1972) to the hypersthene-rhyolites of the Springbrook and Mount Alford areas (although mineralogically distinct). The Glass House Mountains’ mafic trachytes are metaluminous (those from Miketeebumulgrai, Beerburrum, and east of Tibrogargan), whereas the siliceous trachyte from the old Gympie road is just peraluminous. These trachytes are all distinctly potassic, with strongly enriched Ba, Zr, and Ce con­ centrations, and strongly depleted Cr, Ni, and V abundances. These trachytes differ markedly from the peralkaline quartz trachyte of Mount Beerwah which exhibits the same geochemical characteristics shown by the more sUiceous comendites. Mineralogically, the non-peralkaline trachytes are characterised by pheno­ crystal calcic anorthoclase, extending to potassic oligoclase and sanidine com­ positions (Text fig. 21); in the Miketeebumulgrai, Beerburrum, and old Gympie road trachytes, these form particularly conspicuous phenocrysts. Additional phenocryst and microphenocryst phases (Table 9) include ferroaugite (extend­ ing to ferrohedenbergite) and fayalitic olivine (Text fig. 20; the latter phase completely pseudomorphed by iddingsite in the Miketeebumulgrai and Beer­ burrum trachytes), plus titanomagnetite. The groundmass of these trachytes normally includes the same phases with interstitial quartz. The peralkaline lavas commonly exhibit sparsely distributed phenocrysts and microphenocrysts of an alkali feldspar (Text fig. 21), bi-pyramidal quartz (although these are very uncommon in the Mount Coolum comendite), whereas sodic amphibole only occurs very rarely as a well defined, euhedral to Text fig. 20: Plot of the pyroxene (solid circles) and olivine (solid triangles) compo­ sitions occurring in the Glass House Mountains trachytes and comendites. Plots (a) to (c) expressed in terms of Mg, Fe + Mn, and Ca (atomic %). Plots (d) and (e), which show relative Na-enrichment trends, are expressed in terms of Mg, Fe + Mn — Na, and Na (atomic %). subhedral microphenocrystal phase. Groundmass minerals are dominated by low-Ca anorthoclase-sanidine, quartz, and sodic amphibole belonging to the fluor-bearing riebeckite-arfvedsonite solid solution series. Aegirine is sub­ ordinate to amphibole in all comendites described here, while aenigmatite occurs erratically as a minor groundmass phase. Analyses of these Fe-silicates are listed in Tables 9 and 10. Ilmenite occurs within certain of the Glass House peralkaline lavas (Table 9), the compositions of which are notable for their relatively high Zn, and depleted Mg levels. The amphiboles and pyroxenes are pure, or almost pure Fe-endmember compositions, most of the amphiboles lying close to fluor-arfvedsonite. The Na-enrichment in the pyroxenes is illus­ trated in text fig. 20, where the aegirines occurring in the peralkaline lavas are compared with the ferroaugites and ferrohedenbergites in the non-peralkaline Glass House trachytes, these latter showing very little tendency for Na-enrich- ment. The roles of a AI2O3 and fo2 in the control of Na-enrichment in these pyroxenes have been discussed by Ewart (1981). 39

Text Fig. 21; Plots, in terms of Ab, An, and Or (mol. %), of the feldspars occurring in the Glass House non-peralkahne trachytes ((a) to (d)), the comendites from the Noosa region ((e), (f)), the Glass House Mountains (g) to (i), and the Mount Beerwah peral­ kaline trachyte ((j)). All composition, except those in plot (b), refer to phenocryst and microphencryst phases.

The phenocrystal alkali feldspars he between anorthoclase and sodic sanidine, there frequently being a marked compositional variation within individual samples of 10 to 30mol % (Text fig. 21). The following lists the actual compositional ranges observed (microprobe data) within the peralkaline trachyte and comendites here described: The compositions tend to fall into sodic and potassic groups, a feature quite widespread in east Australian comendites (Ewart 1985), and in the Mount Cooroora sample, the two distinct compositional types occur in the one sample, as discrete microphenocrysts. The potassic compositions provide a possible petrogenetic link to the non-peralkaline rhyolites occurring widely in the southeastern Queensland region (Ewart 1985). Averaged rim compositions of the phenocrysts tend to converge between Or35_4Q. The Tinbeerwah and Peregian rhyolites contain two feldspars, a sodic plag­ ioclase (An|5_i9 (Tinbeerwah); An 16-29 (Peregian)) and sanidine (Or52-57 40

Sample* Anorthoclase Phenocrysts/Microphenocrysts

Range (Or, mol.%) Mean (Or, mol.%)

38606 31-47 37.3 38672 26-51 38.1 38666 16-50 31.2 42980 (a) 27-34 31.7 (b) 40-55 46.0 42979 42-58 50.1 38605 22-40 . 29.7

* Localities in Table 8

(Tinbeerwah); 0149.57 (Peregian)). These are similar to the feldspars observed in other non-peralkaline rhyolites of the region, as shown by the comparative plots of data in text fig. 11 (although andesine xenocrysts (An35_37) also occur in the Tinbeerwah rhyolite). Other phenocryst phases present are Fe-Ti oxides and fluor-biotite, the compositions of the latter being illustrated in text fig. 23, and presented in Table 10. The petrogenesis of the various silicic magma types of eastern Australia is extensively discussed by Ewart (1982, 1985) on the basis of chemical, miner­ alogical, and isotopic data. The trachytic and rhyolitic magmas are shown to have evolved along separate petrogenetic lines, the isotopic data indicating that the rhyolites are likely to have evolved as localised crustal melts (followed by crystal fractionation). The trachytic and most of the peralkaline magmas are interpreted to have developed via very efficient crykal-liquid fractionation pro­ cesses from mafic parental magmas, although localised wall rock assimilation is likely for some centres. It is also possible that some comenditic magmas could have evolved by continued crystal fractionation from rhyolites. Although the chemical, mineralogical, and isotopic data do strongly support the role of crystal-liquid fractionation processes iri controlling the chemistry of the silcic magmas, it should be noted that conventional mass balance calculations do not readily provide highly precise solutions to the derivation of, for example, the comendites from trachytic and basaltic parents,.particularly solutions which are also internally consistent with trace element data. Further discussion is provided in the above noted references.

ACKNOWLEDGEMENTS

The authors wish to thank Drs C.G. Murray and N.C. Stevens for helpful comments on the manuscript. 41

Text fig. 22: Plots, in terms of Ab, An, and Or (mol. %), of the coexisting phenocryst feldspars occurring in the Mount Peregian and Tinbeerwah rhyolites. These are com­ pared to composite plots of the phenocrystal feldspar compositions occurring in rhyolites from the Tweed, Focal Peak, and Alford volcanic centres. 42

Text fig. 23: Plots, in terms of Mg, Fe + Mn, and Al (atomic %), of the biotite pheno­ cryst occurring in the Mount Peregian and Tinbeerwah rhyolites. These are compared with the compositions of Fe-rich biotite phenocrysts occurring in the Binna Burra rhyolites, from the Tweed shield volcano. 43 a n d

3 . 5 5 2 . 8 3 0 . 1 4 0 . 4 0 0 . 6 9 0 . 2 8 5 . 1 0 4 . 7 5 4 . 4 6 1 6 1 5 . 5 7 1 7 1 3 . 0 6 3 . 2 3 7 7 5 0 6 4 ( 2 . 4 6 ) 9 9 . 8 7 < 1 ( 1 1 2 9 1 1 8 1 4 5 1 5 6 0 1 2 7 6 t o t a l

V o lc a n ic s )

T r a c h y t e

0 . 2 1 1 . 0 9 1 . 7 2 1 . 8 7 3 . 7 4 3 . 0 3 8 . 7 9 4 . 1 7 4 . 9 2 2 9 5 . 9 1 5 . 0 9 1 5 5 5 . 3 7 5 3 5 7 7 6 6 7 9 9 . 6 0 3 4 C h a ir ( 2 . 0 9 ) 6 1 4 O r ig in a l 6 3 7 1 2 2 4 3 6

S w a n f e ls

n d 5 9 b a s is . 1 . 3 6 1 0 . 0 1 0 . 0 5 2 . 6 8 0 . 0 5 0 . 1 0 4 . 7 5 4 . 2 9

9 5 1 4 1 0 . 3 3 7 0 7 2 7 6 . 3 8 4 8 h a w a iit e s

< 1 2 6 . 2 1 5 1 2 1 5 ( 0 . 8 7 ) 9 9 . 8 5 GROUP <

2 1 7 4 2

d e t e c t e d . ( G o v e r n o r s

(com endite)

( t r a c h y t e )

n o t ( e x c lu d in g

n d

3 0 . 0 1 2 . 1 7 0 . 2 5 0 . 8 5 0 . 0 4 4 . 4 3 0 . 1 0 4 . 9 0 = 1 2 . 4 2 7 4 . 8 3 a n h y d r o u s 1 3

1 3 1 9 7 2 6 9 6 0

1 6 . 6 ( 1 RANGE ( 0 . 7 5 ) < 1 1 2 5 1 2 4 p h a s e 6 7 2

p h a s e 1 0 0 . 0 0

M e m b e r n d

a n

Volcanics).

Volcanics):

m elatrachytes o n

0 . 1 3

1 . 4 5 6 . 3 2 . 3 3 3 . 5 0 0 . 5 3 0 . 1 3 4 . 3 8 5 . 0 9 0 . 0 9 11 1 2 3 3 6 5 3 4 1 4 . 5 5 1 0 4 1 3 0 6 7 6 7 . 8 2

MAIN

( 1 • 6 9 1 ( 2 . 5 2 ) 9 9 . 6 3 e v o v le d < 1 2 9 8 e v o lv e d

1 0 0 %

leucotrachytes

T y p e

THE

m o s t p r e s e n t e d , 1 .4 1 le a s t 3 . 5 1 0 . 4 6 0 . 8 7 0 . 0 6 0 . 1 7 3 4 . 4 6 2 1 3

0 . 1 2 4 . 9 2

1 3 . 7 1 7 0 . 3 1 1 1

Conglom erate 6 1 1 6 7 5 5 4 6 4 t o t a l (M eringandan 1 2 .1

( 2 . 5 2 ) 9 9 . 7 1 ( 1 (M eringandan

1 2 5 8 6 9 1 0 9 6 9 5

OF a ls o

t o

a r e

M e m b e r : M e m b e r :

T r e g o n y M e m b e r 3 . 5 1 0 . 5 4 2 . 6 2 0 . 2 5 5 . 3 8 5 . 8 8 0 . 8 0 0 . 1 8 1 4 . 2 8

M e m b e r 1 0 1 5 . 2 5 V o lc a n ic s : V o lc a n ic s : 8 4 6 1 . 3 0 8 5 1 0 8 8 7 0

1 0 . 3 ( 1 9 9 . 4 6 ( 2 . 6 0 ) 1 4 6 ( 1 4 8 9 9 7 8 9 8 LAVAS

c la s t , ( Z H j O ) n o r m a liz e d

C h a ir C h a ir

B a s a lt

3 . 4 4 2 . 4 7 2 . 8 6 0 . 1 6 T r a c h y t e T r a c h y t e 0 . 1 6 0 . 6 8 0 . 4 0 4 . 7 0 4 . 8 2 1

9 8 . 6

FOR 5 1 8 4 1 2 1 4 . 6 7 7 8 6 8 a r e 6 5 . 6 3 T r a c h y t e ( 1

2 2 4

( 2 . 7 9 ) 9 9 . 8 1 1 3 2 7 1 4 6 4 5 ( i g n i t i o n

M e m b e r )

G o m a r e n C o m e n d it e C o o b y o n G o v e r n oG r o s v e r n o r s S w a n f e ls S w a n f e ls

a n a ly s e s

3 . 4 7 8 7 .1 1 0 . 8 6 4 . 7 1 0 . 6 4 3 . 0 8 0 . 2 7 4 . 6 3 4 . 9 9 0 . 2 0 1 1 1 5 . 2 8 5 5 6 1 . 8 7

( 1 6 7 8 2 6 8 9 9 . 6 7 ( ( 2 . 4 0 ) 2 7 1 7 3 1 1 3 5 7 4 3 1 0 : 1 3 : 1 5 : 1 2 : A l l 1 6 : 1 4 : 1 1 : lo s s

ANALYSES

2 .8 1 2 4 1 . 6 9 5 . 2 1 2 . 8 0 1 . 2 2 0 . 1 4 5 . 1 7 4 . 3 3 5 . 5 8 7 6 . 4 2 6 5 8 5 2 5 2 1 7 . 5 2 5 3 . 5 2 2 4 8 4 7 1 1 2 ( 2 . 6 2 ) 9 9 . 6 5 5 0 9 5 7 8

1 .2 5 1 . 3 1 0 . 2 3 3 . 0 3 5 . 0 5 5 . 0 3 0 . 6 2 6 6 . 3 6 4 . 2 9 9 2 6 . 5 1 5 . 8 9 5 6 . 9 3 5 5 7 6 6 5 5 9 ( 3 ( 2 . 6 5 ) 9 9 . 5 9

7 5 4 1 2 7 3 0 7 7 3 4

h a w a iit e s

h a w a iit e s

5 4 8 . 2 3 9 . 2 6 2 . 3 6 2 . 0 6 0 . 1 7 0 . 7 4 7 . 8 0 3 . 7 2 3 . 3 2 5 . 7 1 4 . 4 6 REPRESENTATIVE 1 0 4 7 . 8 8 8 5 1 1 6 1 3 9 2 8 h a w a iit e s 4 6

( 2 . 2 3 ) 5 0 3 8 5 8 3 0 6 3 2 7 1 5 1 1 0 0 . 0 2

h a w a iit e s 2 1

a n d a n d

2 3 AND

3 1 .5 1 8 . 4 5 0 . 1 6 a n d 2 . 4 9 7 . 9 8 7 . 9 7 0 . 5 4 3 . 1 2 3 . 1 8 4 3 . 3 1 5 . 4 2 3 1 3 4 5 4 2 5 4 9 . 1 9 3 4 determ inations)

3 1 7 2 3 6 ( 3 . 6 2 ) 9 9 . 8 7 1 9 0 1 5 5 m elatrachytes a n d 1 0 7 7

b a s a lts

b a s a lts I

3 .

2

b a s a lts

b a s a lts

m u g e a r it e s

3

3 1 . 7 3 3 9 . 4 7 9 . 0 4 2 . 8 0 3 . 6 4 3 . 7 2 9 . 8 6 3 0 . 8 0 0 . 1 8

b a s a lt s benm oreites T y p e

4 . 8 3 7 2 6 7 8 2 9

4 9 1 4 . 1 0 4 4 . 6 5 1 7 3 3 1 3 9 8 5 5 9 2 6 7 ( 2 . 3 0 ) 9 9 . 6 1 2 7 0 1 8 0

fluorescence S e r ie s ) :

S e r ie s ) : AVERAGED

S e r ie s ) :

7 . 4 6 S e r ie s ) : 1 . 5 0 1: 7 . 1 2 0 . 1 5 0 . 5 7 6 . 5 6 2 . 6 2 4 . 4 0 3 . 5 2

3

2 . 8

1 6 . 0 0 2 5 0 . 1 0 x - r a y 2 5 2 5 3 2 5 4 2 9 (UFA (UFB ( 3 . 1 0 )

m u g e a r it e s

2 4 6 1 2 0 3 3 0 6 5 0 1 5 3 1 0 0 . 0 9 —

4 V o lc a nV ic o s lc : a n ic s : V o lc a n ic s : V o lc a n ic s : (UFA

(UFB

B a s a lt B a s a lt

TABLE 1 1 . 2 5 0 . 7 1 7 . 9 3 2 . 3 8 3 . 5 3 7 . 9 2 4 . 3 4 0 . 1 8 6 . 1 0 3 2 . 7 C h a ir C h a ir C h a ir C h a ir 1 5 . 6 6 2 1 4 9 . 9 9 ( p . p . m . 2 6

2 8 5 2 B a s a lt B a s a lt : 3 3

B a s a lt

2 2 6 1 1 9 ( 3 . 0 3 ) 9 9 . 9 5 2 9 7 4 8 7

1 6 6

e le m e n t s

G o v e r n oS r u s p e r b u s T o o w o oT m o o b w a oG o m o v b e a r n oS r u s p e r b uG s o v e r nG o r o s v e r n o r s

S u p e r b u s

( o r ig in a l)

2 ; 7 : 8 : 6 : 9 : 3 : 1 : 5 : A n a ly s is 4 : A I 2 O . 3 F e O F e 2 O 3 N a 2 O T iO 2 M n O M g O ^ 0 5 Z H 2 O 2 ’ S iO 2 C a O K 2 O R b B a P b S r Z r N b ’ T r a c e T h C e N d Y V C r 44

— . ST R i I u (9341).

e -S Warwick ______

=

------W s A A 3

a

C

(9342);

C I C C CASS MEGACRYSTS

tlelidon

g. §■ A- =

H

C A S SCR (9243): PS

______

------

Oakey S R 2 a S A

=

O

S,

R SA S aS group Granulite- gabbro

(9242);

I .s e -sS ite group) (Dior-

Toowoomba C

I P2 =

T

LOCALITIES

J g§ i s 9343);

______

group

CRSS (sheet l i Eo sg.

INCLUSION

Esk

= Queensland.

R S E S? of

XENOLITHS a s RANGE

------

i 5 •£ MAIN C follows:

peridotite-pyroxenite

as 2: University

Black ------

sheets

i S 5 I TABLE ______series Mineralogy,

& s & R

i S A

------

1:100,000 Geology & «

(Green cpx

i enite grouli of

A C ACS A ^■1 A A A AR AR C C A C AR C C A C Os 1 1 group) ------______(Cr- diop.

Topographic

Department

rate. and

-

R

National

hawaiite benmoreite

hawaiite

hawaiite ______

.

nephelinite basanite LAVA the

______

______collection.

______

______to scarce;

=

rock

NUMBER HOST sample 43600 hawaiite 43604 43601 43564 nepheline olivine leucite nepheline camptonite S 43597 43589 hawaiite hawaiite 43606 hawaiite 43624 hawaiite hawaiite 43614 nepheline 43616 basanite nepheline 43605 hawaiite 43603 43615 43619 hawaiite 43608 hawaiite 43607 43578 43591 basanite hawaiite 43536 basanite 43537

’ refer

the

to

’ ,

common; (head)

refer

neck)

Mt = references ______’ ______

Ck C

and grid (West)

Creek Creek

Creek Creek Creek

(flow/?neck) (flow/?neck) (plug) (intrusive) (flow) (flow/?neck) (sUl) (flow) (plug) qty (plug) (flow) (flow/neck) (plug) (flow/neck) (flow/ (neck) (flow/?neck) (neck) (flow)

to

Gowrie knob

numbers Tabletop Whitestone

qty

Mountain

Hill Mountain s

Branch

63 ’

Falls Falls

Mile Mile

qry

Mt Mt O ttle

near

abundant;

82749

Wyangapinni Mitchell

388985 399960 174855 160371 473912 472910 491775 491775 022483 473874 840560 8565 045290 = 976543 999519 5 723438 840560 622435 670332

Prefixes Sample ’ LOCALITY ^Owen E Harlaxton H Malu GRID T Council T Near Majuba Mt Gowrie Gowrie T Qty Pittsworth Hirstglen H Mt W Wild W T T T T T H Near Middle Seven W W W Seven A ' 0 W W Teviot Teviot “ 45

1.11 - 0.07 0.03 -

10.31 19.01 0.12 0.13 28.28 99.28 14.70

100.31 Spinel 54.84

1.61 0.44 0.22 6.20 - 6 99.71 1.35 0.07 0.03 0.07 14.02

99.55 LAVAS. 25.04 50.67 magnetite; Opx

OCCURRING =

XENOLITHS

15.46

Mag

HOST

2.65 8.03 2.68 Xenolith 0.14 4.79 5.62 spinel; - 0.40

0.06 - 99.29 13.39 47.87 PHASES Cpx

THE

21.96

chrome 1.96 2.33 0.11 8.67 Ilmenite; 6.57 9.02 -

(olivines).

- -

= 99.50 = 1.09 LHERZOLITE 47.41 13.31 17.93 3

Cpx FROM

=

Ilm

Cr-Sp AND

99.73 99.56 0.08 5.68 PYRRHOTITE

2.65 1.30 11.63 13.92 0.07 0.06 - - - homogeneous. GIVEN 5

97.54

12.08 10.33

Cations Amph

olivine;

2 AND =

39.74

ALSO

and

1.30 7.06 3.47 9.57 0.17 6.44

Oliv optically 1.28 Xenolith

0.09 - 4 99.69

99.34 13.25 18.02 48.60 = Cpx ARE orthopyroxene;

SPINEL, 0 TOOWOOMBA),

=

OF

3.31

8.31 0.06 0.12 Opx - 0.42

11.28 - - 56.72 pyrrhotite, 99.92

100.25 10.24 21.08 PHASES (haersutite); Cr-Sp

(spinels);

(WEST 24

8.85 1.10 = AMPHIBOLE,

- 0.05 - - 0.37 - 9.84 0.12

4 49.64 100.84 40.71 QUARRY

Oliv 100.73

amphibole

Nickeliferous = clinopyroxene;

= QUARRY Cations

=

0.13 3.97 5.54 0.16 0.92 6.37 GROUNDMASS 2 Xenolith 0.05 0.31 0.13 0.81 99.89 OLIVINE,

99.80

32.94 54.93 Opx Pyrr Cpx Amph and

MOUNTAIN

32

2.61

0.38 0.09 6.62 1.94 0.86 = 0.90 0.10 99.74

MOUNTAIN 99.55 15.24 20.88 1.44 51.29

0 Cpx

GOWRIE

PYROXENE, ______

3

TOOWOOMBA.

1.57 8.36 7.75 2.50 0.13

5.50

1.09 OF - -

99.78 100.03 14.05 18.40 48.43 Cpx Xeno- lith GOWRIE

metal.

(pyroxenes); NORTH

THE as 4

8.33

0.43 0.10 0.05 - 18.31 IN 99.65 - - 0.69 0.09 56.79

98.81 14.86 Spinel

listed

2 FROM 25.80

(MICROPROBE) and

Cations

8.61 7.94 1.34 3.19 0.13 5.74 S 0.06 0.09 99.70 QUARRY 99.38

17.98 1.26

48.39 Cpx Xenolith and

13.58 analysed 6;

9242/856564 9242/978543

7.46 XENOLITHS 1.77 = 3.58 7.22 0.14 4.24

Ni ANALYSES 99.77 0.13 0.06

0 99.41 0.78 47.67 13.44

Cpx

on

and

20.74

sheet): sheet):

HARLAXTON

Fe 3.93 9.41 0.24 0.15 9.84 0.48

1.50 0.06 0.31 0.15 1 29.91 100.49

Opx 100.44 Cu. SEPARATE THE

AVERAGED

calculated 54.35

(1:100,000 (1:100,000 3:

1.22

0.13 5.01 5.06 0.42 6.16 0.50% ______

FROM Xenolith 0.48 0.12 FeO 99.91 SEVEN 100.03

16.93 1.10 52.22

Cpx Ref. Ref.

IN and

TABLE

17.34 Grid Grid Includes

SiO2 AI2O3 MgO CaO K2O 2 (1) TiO2 FeO MnO L (2) (3) Na^O Cr2O3 NiO Fe2O3 Fe2O3 FeO

46

0.07 0.08 0.56 0.06 4.27 99.40 4.75

51.70 38.38 99.87 42.66 Ilm LAVAS

PHASES

1.65 0.73 0.55 <2) 0.04 - spinel; HOST 18.75

71.75 2.62 96.09 30.95 homogeneous. 43.90 99.19

Mag Groundmass LHERZOLITE

THE

Ilmenite;

chrome

AND = =

optically 1.56 3.11 0.11

2.48 PYRRHOTITE 0.46 - 0.19

22.31 FROM 50.17 7.54 14.17 Ilm

99.62 5.30 99.87

Cpx TOOWOOMBA Cr-Sp

(olivines).

AND 3

=

GIVEN

olivine;

pyrrhotite,

= - - 9.38

0.21 0.13 - 0.35 9.92 57.40 11.49 20.48 99.98 2.35 Cr-Sp 100.22 TOOWOOMBA), QUARRY, SPINEL,

ALSO

Oliv Cations

OF Z

orthopyroxene;

ARE -

and 9.86 0.02 0.64

Nickeliferous - - - 0.03 0.40 0.07 40.60

4 10.43 48.85

= Oliv (WEST Opx 100.40 100.46

=

(haersutite); 0

AMPHIBOLE,

HARLAXTON PHASES

Pyrr

0.05 0.04 3.88 0.30 0.12 0.12 0.66 6.74 0.43 6.15 55.40 33.17 Opx 100.25 100.32 Xenolith QUARRY

(spinels);

amphibole

OLIVINE,

24 =

clinopyroxene;

Magnetite;

= = =

0.81

0.06 1.70 0.43 0.04 6.66 1.25 1.48 2.58 51.76 14.46 99.91 GROUNDMASS Cpx

Cpx Amph Mag MOUNTAIN

Cations

Z

99.76

PYROXENE,

21.26

2.92

0.52 - - 4.30 21.86 - - 1.08 and

OF 66.07 44.49 96.75 23.98 99.15

Mag GOWRIE

32

=

TOOWOOMBA,

0

THE

Groundmass 2.24

5.47 0.12 ______0.64 0.23 -

21.33 48.39 8.02 13.05 6.19 99.49 2.03 99.69 Cpx FROM NORTH

metal. IN (MICROPROBE)

(pyroxenes);

as

4

=

------4.18 - listed 56.35 99.11 QUARRY Pyrr^^^

QUARRY XENOLITHS

and ANALYSES cations

2

38.08

1.20

0.12 _ - 0.12 - 0.83 0.26 16.12 22.05 17.02 and

99.81 6.60 Spinel 100.47 MOUNTAIN analysed

6;

9242/856564 9242/978543

7 SEPARATE

=

Ni

58.21 0

HARLAXTON AVERAGED

and on

_ 1.21 2.62 sheet): sheet): 0.34 0.04 0.08 0.20 6.30 0.08

THE SEVEN GOWRIE

15.30 25.70 99.96 Fe Opx Xenolith 12.94 100.22

IN

Cu.

50.71

FROM

calculated :100,000

(continued):

_____ (1 (1:100,000 3 1.58 8.12 1.34 0.10 - 0.14

0.50% 17.53 48.06

8.35 5.36 99.07 3.32 99.40 Cpx FeO

Ref. Ref.

and OCCURRING

TABLE

13.85 Includes Grid Grid

XENOLITHS

(2) (3) (1) 2 Fe2O3 2 SiO2 FeO MgO NanO K2O NiO S Fe2O3 FeO AI2O3 CaO Cr2O3 MnO TiO2 47

3 . 4 7 1 .4 5 1 .2 1 2 . 1 7 1 . 4 ^ ^ ^ - 3 . 5 4 - 0 . 9 0 0 . 1 3 5 6 . 8 6 4 . 1 2 1 9 9 . 6 9 6 0 . 6 0 1 5 . 5 6 ( 6 . 1 9 ) 6 4 7 7

3 5 4 8 4 < 1 9 8 1 6 5 3 6 3 8 2 8 1 1 1 5 S lo p e s W e s t e r n T r a c h y t e 4 2 9 9 5 9 2 4 4 / 5 2 0 2 6 3

MAJOR

1 . 3 3 8 . 5 7 3 . 1 3 0 . 5 5 0 . 1 6 8 . 8 8 4 . 1 3 3 . 2 0 7 . 6 2

2 . 0 4 )

3 0 . 5 - 4 MOUNTAINS, 3 3 5 5

1 4 . 1 8 4 8 . 2 3 3 3 1 0 - ( 9 9 . 5 1 2 2 . 1 1 0 5 2 3 4 1 8 9 5 3 8 2 6 9 1 9 5 1 6 5 B a s e 9 2 4 4 / 3 8 7 8 4 YA

6 2 7 1 9 3

BUN INCLUDED.

2 . 5 4 2 . 2 5 5 . 5 3 3 . 9 5 7 . 1 3 6 . 3 6 0 . 1 7 1 . 4 0 2 . 2 2

2 . 6 9 )

6 . 5 0 .1 0 .1 5 4 1 4 . 7 6

5 3 . 6 9

THE ( 9 9 . 5 0 4 6 . 2 1 7 5 5 5 1 1 1 4 6 0 1 7 3 3 5 9 4

4 0 8 ALSO

3 8 7 8 3 OF IS 9 2 4 4 / 6 4 0 2 1 7

0 .1 1 .1 1 1 . 4 4 2 . 1 4 5 . 2 7 3 . 0 0 3 . 7 0 0 . 2 0 5 . 5 2

4 . 0 9

2 . 7 2 ) 1 . 0 - 6 . 7

1 5 . 9 4 SLOPES 5 7 . 5 8 __ - 6 3 SLOPES

( 5 7 . 2 8 8 1 7 0 1 8

1 2 3 2 3 5 6 5 4 6 3 3 1 0 0 . 5 1 4 3 0 FREE

3 8 7 8 2 9 2 4 4 / 6 4 1 2 2 2

WATER

WESTERN

SOUTHERN

1 . 7 4 2 . 1 4 ) 0 . 1 4 1 . 9 9 6 . 9 6 6 . 3 3 5 . 0 4 0 . 7 7 5 . 1 0

4 . 0 8 4 0 . 1 5 1 6 . 9 2 5 0 . 9 2

5 1 7 7 ( 7 9 3 6 . 1 - 2 8 9 6 1 3 4 3 3 8 4 8 0 6 6 8 1 0 0 . 5 6 THE 1 0 1

1 0 0 % ) 3 8 7 8 1 THE 9 2 4 4 /

6 4 3 2 2 2

(TO

FROM

FROM _

1 . 9 3 8 . 5 4 3 . 5 9 5 . 1 6 0 . 1 4 0 . 5 8 0 . 3 4 6 . 8 7 6 . 7 8 3 . 1 8 )

2 . 8 8 8

2 3 1 6 . 3 0 n d 4 9 . 7 7 1 4 2 6 ( 9 9 . 4 5 - 1 5 4 1 6 0 2 3 3 3 9 6 1 0 6 1 2 0 1 3 8

3 8 7 8 0 9 2 4 4 / 6 4 4 2 2 5

_

s lo p e s ;

TRACHYTE

2 . 9 6 )

1 6 . 5 2 .3 5 . 5 1 3 . 6 7 2 . 0 4 0 . 1 4 0 . 9 5 6 . 1 1 0 . 4 3 6 . 7 7 8 . 3 8 3 7 A COLLECTED 2 4 1 6 . 2 2 4 3 4 9 . 7 7

( 9 9 . 5 5 - 1 7 5 1 0 4 2 0 0 4 3 9 RECALCULATED 2 6 1 5 5 1 4 4 1 2 7

3 8 7 7 9 9 2 4 4 / 1 5 ) . 6 4 4 2 2 5

s o u t h e r n

ARE

_ LAVAS

F ig .

OF

3 . 9 9 ) 3 . 9 1 1 . 6 7 0 . 1 4 0 . 7 3 3 . 2 3 1 7 . 9 7 2 4 . 3 4 6 . 2 2 5 . 7 2 5 4 (s e e lo w e s t 5 5 7 0 1 7 . 5 7

4 8 . 4 9

( 9 9 . 5 6 2 6 . 4 7 5 4 1 1 2 5 4 3 2 8 8 3 8 8 1 2 7 t o

3 8 7 7 8 9 2 4 4 / 6 4 4 2 3 4 _ ANALYSES

DALBY

R o a d ,

ANALYSES

p r e s e n t .

TO 1 . 4 8 3 . 5 4 3 . 3 2 6 . 8 3 0 . 1 8 0 . 7 8

4 . 7 2 4 . 1 2

2 . 4 0 )

2 3 0 . 5 - 4 7 3 1 0 . 0 3 1 6 . 6 9

4 8 4 8 . 3 2 2 9 ( 2 8 . 5 1 3 6 2 7 7 5 9 4 4 4 7 4 0 1 2 1 0 0 . 0 9 D a lb y 1 3 7

determ inations) a ls o 3 8 7 7 7 9 2 4 4 / _

ELEMENT 6 4 3 2 3 5

a lo n g

ELEMENT LEADING b i o t i t e

2 . 7 0 )

1 . 5 9 3 . 1 5 0 . 1 6 6 . 9 5 9 . 3 2 0 . 8 0 4 . 8 6 4 . 1 8 4 . 0 2 5 4 . 5 3 1 6 . 6 8 6 8 4 7

4 8 . 2 8 ( 3 8 - 2 5 . 6 1 3 4 2 8 0 4 2 6 _ 5 8 0 3 9 1 8 1 0 0 . 1 0 fluorescence 0 . 1 % t r a v e r s e 1 3 3

3 8 7 7 6

ROAD TRACE

9 2 4 4 / 6 4 3 2 3 5

x - r a y

q u a r t z ;

-

AND

3 . 0 6 1 . 2 7 3 . 6 6 6 . 8 1 0 . 1 7 7 . 1 9

5 . 1 7

4 . 5 7 0 . 5 9

2 4 1 8 . 1 5 4 9 . 3 6 3 9 5 5 1 9 . 4 3 2 1 5 ( 4 . 2 7 ) - _ 4 6 5 2 D a n d a b a h 1 0 5 SUMMIT 3 0 4 2 0 3 6 4 2 1 4 1 1 0 0 . 5 4

T o p 3 8 7 7 5 9 2 4 4 / 0 . 3 %

Phenocrysts

6 1 1 2 4 8 ( p . p . m . - MAJOR

THE

4 : %) )

s a n id in e :

( v o l.

E le m e n t s ALONG

R f .

TABLE 0 . 2 %

( o r i g i n a l )

Z H 2 O S iO 2 B a F e 2 O 3 F e O Z R b N i M n O M g O N a 2 O K 2 O S r Z r Z n N b Y T h C r V M o d e s A u g it e ( 1 : 1 0 0 , 0 0 0 T i O 2 A I 2 O 3 C a O ^ 0 5 T r a c e C e Plagioclase M a g n e t it e ( 1 ) O liv in e G r i d 48 0.08 9.22 0.86 0.14 0.17 0.16 15.99 98.51 56.11 16.71 99.43 38772(1)

phases 25.00

1.63 8.53 6.83 0.19 2.35 0.96 0.53 0.07 6.43 13.45 48.80 19.27 100.26 38772<1> 100.49 Megacryst

PYROXENES,

0.85 0.13 7.10 0.63 4.67 1.57 5.69 0.34 0.08 17.71 17.15 51.28 38784 LAVA 100.10

99.93

1.76 8.94 2.87 0.20 0.48 MEGACRYST 2.69 6.52 0.06 0.13

14.67 20.58 50.13 99.82 38784 100.09 MOUNTAINS

AND

)

BUNYA

0.36 0.85 0.33 3.12 0.13 0.47 10.85 34.98 49.39 34.56 100.01 38783 THE 100.06

(spinels)

IN

GROUNDMASS 24

=

OF

2 1.81 1.00 0.41 0.42 1.42 10.86 19.26 15.46 49.88 99.10 14.18 99.24 32, 38783

-

0

OCCURRING

2.35 1.47 (MICROPROBE) 0.82 0.32 0.44 -

(9244/557315) 33.61 10.13

SPINEL, 99.19 33.61 99.19

38782 (pyroxenes); Pyroxenes

4

=

Kiangarow

ANALYSES

0.45 0.97 2.78 0.60 cations - 0.76 18.54 15.79 10.28

MEGACRYST 99.20

15.11 99.30 Groundmass 38782 2

A Mount

6,

=

0 AND

49.81 50.05 AVERAGED

lookout,

5: 0.21 2.84 3.38 0.74

8.47 _____2.45 0.04 10.68 21.95 11.52 48.70 100.06 38776 100.31 (assuming

summit

TABLE

FeO

from

2.61 2.00 0.54 9.77 0.24 and 8.90 0.97 0.04 0.08

20.85 13.52 50.80 100.45 38775 100.55 sample

Fe2O3

Hawaiite

SiO2 2 ()) FeO FeO L Fe2O3 TiO2 CaO Na2O NiO Calculated AI2O3 MnO MgO Cr2O3 49 2

1 . 8 4 2 . 0 2 5 . 1 7 8 . 2 7 3 .3 0 . 1 2 0 . 5 2 1 . 0 6 . 9 7 6 . 3 3

4 . 1 6 0 MEE 1 6 . 3 9 4 8 . 2 1 2 9 2 6 ( 2 . 7 5 ) 3 1 5 2

1 0 0 . 2 1 1 2 7 1 1 2 1 2 1 1 1 9 5 2 1 2 5 1 4 5 0 9 4 4 3 / 4 2 9 6 7 7 8 1 0 6 4 MT MEE.

(2)

o

2 . 2 1 0 . 7 1 2 . 6 6 4 . 9 3 3 . 9 6 5 . 0 4 2 . 9 2 6 . 2 4 0 . 1 9 1 . 0 3 . 5 0 . 2 5 0 . 1 2 4 1 7 . 0 6 9 6 8 2 3 7 3 7 6 2 5 4 . 0 7 MOUNT ( 3 . 3 4 ) 3 7

1 1 5 1 0 0 . 2 1 3 5 4 3 9 2 5 4 0 3 7 8 4 3 9 4 4 4 / 8 3 4 5 2 7 AND

7 . 1 5 1 . 5 7

3 . 8 3 2 . 7 4 7 . 0 0 0 . 5 3 4 . 1 4 0 . 1 9 4 . 7 0

1 . 0 3 0 . 1 0 .1 9 9 . 8 1 1 6 . 9 9 5 1 . 1 7 2 4 1 9 3 4 5 6 9 8 3 3 - ( 2 . 7 2 ) 3 6 5 1 4 2 5 1 1 1 3 0 2 3 9 CENTRE T o p 3 7 8 9 3 9 4 4 4 / 8 9 3 4 7 9

1 . 6 5 3 . 5 3 0 . 6 5 5 . 5 1 7 . 0 9 3 . 8 2 6 . 8 7 2 . 4 2 0 . 2 0

2 0 . 3 ( 1 ) 0 . 1 9 3 1 6 . 6 5 2 7 4 6 2 0 9 9 . 9 4 5 1 . 6 2 ( 3 . 1 2 ) 2 2 - - 1 9 3 1 1 0 4 6 5 1 1 2 1 2 2 6 7 0 VOLCANIC FREE. 9 4 4 4 /

3 7 8 9 4 8 8 6 4 8 3 M o n t v i l l e

WATER

1 . 1 6 MALENY 2 . 0 2 3 . 2 6 6 . 9 3 0 . 1 7 6 . 9 7 0 . 4 0 4 . 0 9 7 . 6 2

2 .1 2 . 0 0 . 1 5 . 0 0 . 1 1 5 . 3 2 5 2 . 0 7 1 4 3 6 2 7 C r e e k , ( 3 . 3 0 ) 2 2 1 0 0 . 1 7

1 1 5 1 7 5 1 4 6 2 7 5 2 3 3 3 5 4 1 6 9 3 7 9 0 4 THE 9 4 4 4 / 8 7 8 4 9 7 1 0 0 % )

S k e n e s

(TO

FROM

0 . 1 6 0 . 5 4 2 . 2 2 7 . 4 0 3 . 4 9 6 . 1 3 3 . 3 9 1 . 3 2 6 . 5 8 p r e s e n t .

2 . 4 3 . 0 p r e s e n t . 2 2

5 3 2 8 1 5 . 4 0 5 3 . 3 8

2 8 ( 3 . 2 8 ) - - - 1 9 5 1 1 5 1 6 9 1 2 7 1 0 0 . 3 1 2 9 0 3 8 0 5 3 0 9 4 4 4 / CENTRE 3 7 9 0 3

a ls o 8 7 1 4 9 8 a ls o

LAVAS

2 . 4 5 3 . 4 5 7 . 1 7 1 . 8 8 6 . 2 6 0 . 1 7 3 . 6 8 0 . 5 9 4 . 3 8 2 . 6 0 . 1 0 .1 0 . 5 0 . 1 1 5 . 7 8 5 4 . 2 1 9 9 . 4 2 2 3 3 0 4 8 MAFIC ( 2 . 5 8 ) 3 3 RECALCULATED

1 1 4 1 2 8 1 0 8 1 2 0 4 9 6 3 2 0 4 5 0

9 4 4 4 / VOLCANIC

3 7 8 9 9 8 7 9 4 8 7 OF

orthopyroxene orthopyioxene

7 . 7 6 7 . 5 1 1 . 4 0 2 . 1 3 7 . 2 5 0 . 4 6 0 . 1 6 3 . 1 8 3 . 4 2

MALENY

2 0 .1 5 . 0 1 5 . 3 0 5 1 . 4 4 2 1 3 6 2 2 ANALYSES - 2 3 ( 3 . 3 0 ) - 1 0 0 . 0 1 1 1 5 1 2 5

5 8 1 2 0 5 2 3 8 3 5 0 2 0 8 B a s e 3 7 9 0 5 ANALYSES 9 4 4 4 / 8 7 3 4 9 5 m egacrystic

m egacrystic

0 . 1 %

0 . 2 %

ELEMENT

1 . 8 5 a n d 2 . 3 3 0 . 6 5 6 . 5 4 0 . 1 2 5 . 3 9 3 . 9 9 5 . 7 9 4 . 9 8 5 . 0 - - a n d 6 5 . 0 3 1 7 5 1 6 . 1 5 3 8 7 8 ELEMENT 5 2 . 2 1 5 7 ( 3 . 1 5 ) 3 2 . 4

R d . 1 1 6 1 1 7 4 0 5 2 8 0 1 0 0 . 5 6 5 0 8

T o p 3 8 6 9 0 determ ined) 9 4 4 4 / 9 1 8 3 7 7

MAJOR

a n d e s in e

a n d e s in e TRACE

1 .8 1 8 . 0 1 0 . 5 5 1 . 6 9 8 . 5 2 7 . 9 9 0 . 1 3 3 . 2 9 0 . 3 0 p lu s

2 . 6 2 . 0 0 . 5 p lu s

1 5 . 1 5 1 3 2 3 5 2 . 5 5 2 2 9 9 . 5 0

1 1 .1 ( 2 . 0 0 ) - - AND 1 9 6 1 3 4 1 2 7 1 2 2 1 4 9 3 8 0 2 8 8

9 4 4 4 / Landsborough

3 8 6 8 8 fluorescence 9 4 1 3 6 1

ROCK

X - r a y

M a le n y ,

1 . 7 0 8 . 0 6 0 . 7 1 anorthoclase 8 . 1 4 7 . 6 7 0 . 1 3 0 . 3 4 1 . 8 7 3 . 3 9

anorthoclase

8 . 0 2 1 1 0 . 1 2 8 1 5 . 0 2 5 2 . 9 7 1 5 . 6 - ( 2 . 2 8 ) - 2 1 1 6 7 1 4 8 1 0 7 1 4 8 3 1 2 1 0 0 . 4 7 4 0 2 1 3 2 B a s e 3 8 6 8 7 WHOLE 9 4 4 4 / 9 4 0 3 6 0 ( p . p . m . ;

6 :

M egacrystic

M egacrystic

( v o l. % )

E le m e n t s

R e f . TABLE

1 5 % 0 . 3 %

( o r ig in a l)

S Í O 2 A I 2 O 3 F e O T Í O 2 N a 2 O K 2 O Z H 2 O M n O T e 2 O 3 M g O C a O E R b ^ 0 5 B a N b Y M o d e s A u g it e S r Z r Z n C e PlagioclaseO liv in e (1:100,000) T r a c e T h C r V G r id N i M a g n e t it e ( 1 ) ( 2 ) 50 8.14 2.34 0.09 1.76 0.51 0.05 2.70 0.21 rim 99.62 13.74 20.24 99.39 10.24 49.85 42967 Pyroxenes

MEE

core

MT 7.35 3.33 2.64 0.15 0.17 2.32 0.49 0.05 9.72 13.83 20.65 99.94 49.23 100.20 mass 42967 Ground

1.83 8.46 0.06 0.66 0.19 1.27 4.31 _ 15.01 17.70 99.50 99.68 50.19 10.11 37843 PYROXENES

1.04 0.11 1.98 0.23 0.18 3.41 0.35 53.83 12.61 100.73 100,63 37894 Megacrysts LAVAS MEGACRYST

11.68

AND

1.22 0.99 5.23 8.22 MAFIC 9.32

0.74 0.14 0.17 50.78 17.01 100.08 100.20 37894 MEE

15.70 27.93

1.64 1.59 9.86 2.64 0.54 0.19 0.02 12.82 20.26 99.65 99.49 50.09 MOUNT GROUNDMASS 11.29

37893 OF

AND

1.55 8.01 1.50 0.11 2.29 0.20 0.40 9.41 14.57 20.52 51.00 100.16 100.00 37894 MALENY

CENTRE

THE (MICROPROBE)

IN 0.23 0.33 1.18

9.89 0.09

1.66 1.29 18.75 14.99 99.50 99.62 51.21 10.95 37904 VOLCANIC

ANALYSES

pyroxenes

4)

1.74 0.41 8.66 2.65 0.11 1.79 0.21 9.30 OCCURRING - 19.87 14.07 99.48 49.97

10.27 MALENY 37899 cations

Groundmass AVERAGED

Z

7: 1.97 6, 7.40 0.19 0.29

0.42 1.49 2.48

______9.17 14.62 20.26 99.48 99.28 50.36 =

37905 (0

TABLE

Fe2O3

2.26 0.31 0.46 0.43 1.72 0.09 - and 17.71 13.08 99.41 50.23 99.37

13.47 38687

• FeO

13.12

Z FeO S Calculated Fe2O3 FeO CaO Na2O Cr2O3 NiO SiO2 MnO MgO TiO2 AI2O3 51

M t 1 .5 6

0 . 1 9 2 . 7 5 0 . 0 6 0 . 0 4 0 . 2 6 6 . 3 0 0 . 0 1 0 . 0 4 2 0 . 0 8 4 . 4 0 1 2 . 3 7 1 7 6 2 4 5 9 9 . 3 7 7 1 . 3 1 o f 3 3 5 3 2 0 2 2 0 2 1 5 1 7 0

9 4 4 4 / 1 5 2 5 B e e r- b u r r u m 3 8 6 0 3 R id g e N 9 5 2 1 9 5

4

1 . 3 4 0 . 0 1

0 . 0 5 0 . 0 1 1 . 0 8 0 . 1 5 0 . 5 4 0 . 0 7 0 . 5 0 4 . 9 9 5 . 8 2 2 1 2 . 3 2 1 1 2 8 Q u a r r y 7 3 . 3 0 3 4 1 6 5 1 2 5 2 3 5 9 0 0 1 9 0 1 3 8 1 0 0 . 1 8 9 4 4 4 / 3 8 6 0 6 P e a c h e sR te d r

9 4 5 2 9 0

4

1 .0 5 0 .0 1 0 . 0 1 0 . 0 5 2 . 1 4 1 . 2 2 5 . 6 3 0 . 1 4 0 . 0 2 0 . 2 0 4 . 0 9 1 4 T i b r o - 1 1 . 4 9 5 2

5 8 1 6 4 1 4 0 2 9 5 4 2 5 3 6 0 9 9 . 6 0 7 3 . 5 5 1 9 6 0 9 4 4 4 / M t 3 8 6 9 6 g a r g a n RHYOLITES

9 4 4 2 1 4

es

t

4

REGION

d i AND

e n

1 .3 3 0 . 0 7 0 . 0 3 0 . 1 8 0 . 0 2 0 . 0 2 0 . 2 0 5 . 6 0 0 . 8 8 0 . 0 2 4 . 6 7 1 3 . 6 5 3 2 7 3 . 4 5 1 9 4 1 8 0 7 2 1 4 1 3 1 5 1 9 0 9 7 0 1 0 0 . 1 2 9 4 4 4 / 3 8 6 9 7 C o m T w in s NOOSA

9 1 4 1 7 5

4 TO

0 .0 1 0 . 1 5 2 . 0 3 4 . 7 1 2 . 0 2 5 . 6 5 0 . 1 3 0 . 1 8 0 . 3 7 0 . 1 2 1 1 ( 1 2 5 ( 0 . 0 1 1 1 . 4 6 4 7 3 8 3 1 5 COMENDITES. 3 6 5 2 2 0 4 4 5 4 3 5 7 2 . 4 6 9 9 . 2 9

2 2 4 5 9 4 4 4 / 3 8 6 7 2 N g u n g u n Q u a r r y 9 3 8 2 4 6 COOLUM

4

1 . 2 4 0 . 2 6 0 . 0 1 2 . 7 4 1 0 . 0 3 0 . 0 6 0 . 0 7 6 . 8 6 0 . 1 2 0 . 2 2 4 . 4 0 1 6 5 2 1 4 . 1 9 4 2 3 4 5 2 5 5 2 7 7 2 1 8 9 9 . 5 1 6 9 . 3 1 4 1 0 1 1 0 0 MOUNT TRACHYTES, 9 4 4 3 / 3 8 6 6 6

S a d d le - b a c k

9 2 6 1 1 9 OF

3 MOUNTAINS

THE

------1 . 1 8 2 . 0 3 0 . 2 6 0 . 0 6 7 . 6 6 0 . 0 4 4 . 8 5 0 . 0 2 0 . 0 8 0 . 2 2 0 . 2 0 1 1 1 1 6 . 9 1 2 7 5 6

B e e r- 3 3

1 5 5 1 5 8 2 0 5 2 3 0 ( 9 9 . 1 2 6 5 . 6 1 AND

1 2 7 5 9 4 4 4 / 3 8 6 0 5 M t w a h HOUSE

8 8 5 2 5 1

(Peralkaline) ..

ANALYSES

4

1 . 6 9 0 . 0 1 0 . 1 5 0 . 6 6 0 . 2 4 0 . 0 9 0 . 8 2 5 . 8 2 5 . 8 7 0 . 4 9 0 . 8 0 GLASS 9 . 9 G y m - 1 4 1 8 . 0 4 5 3 5 9 R d

1 1 5

1 1 0 9 5 0 3 7 0 9 9 . 5 8 6 4 . 9 0 1 2 5 1 1 8 5 MOUNTAINS 9 4 4 3 / 3 8 6 6 8

O ld p ie 9 1 4 1 3 1 ELEMENT

M t . 1 . 2 6 1 . 6 7 5 . 5 5 3 . 8 6 0 . 1 3 2 . 0 7 5 . 4 6 0 . 1 2 0 . 3 6 0 . 2 7 0 . 3 2

- 1 1 5 6 5 1 6 . 9 8 5 2 1 1 . 2 3 4 1 4 1 1 3 4 TRACE 1 5 6 6 1 . 5 7 9 9 . 6 2 6 0 0 - 5

o f 1 1 5 2

9 4 4 4 / g a r g a n 3 8 6 0 6 E. T i b r o - GLASSHOUSE 9 6 6 2 1 6

determ ination) AND

THE

0 . 1 1 5 . 3 1 1 . 3 4 1 . 6 9 3 . 1 6 2 . 0 5 5 . 8 1 0 . 4 1 0 . 1 3 0 . 8 4 0 . 4 9 1 5 B e e r - 9 7 9 8 1 5 . 6 2 5 2 5 4 9 1 1 . 3

8 0 1 6 7 6 9 5 9 9 . 8 5 5 6 0 6 2 . 8 9 MAJOR 9 4 4 4 / M t

b u n u m 3 8 6 0 2 FROM 8 : 9 5 0 1 8 2 fluorescence

3 .6 1

1 . 9 0 2 . 1 7 5 . 3 1 0 . 6 3 1 . 5 9 0 . 6 9 0 . 6 2 0 . 1 2 5 . 8 0 0 - 1 9 6 . 6 3 1 6 . 6 5 - X - r a y M ik e t e e - 1 5 TABLE 9 2 5 0 - 2

5 0 7 3 5 1 0 0 1 2 0 9 5 0 6 0 . 1 2 9 9 . 4 0 1 4 5 9 4 4 3 / M t b u m u lg r a i 3 8 6 6 9 T r a c h y t e s 8 9 6 1 2 3 ( p . p . m .

d e t e c t e d

E le m e n t s

R e f .

n o t

O

=

q

N i (1:100,000)— V G r id T h A I 2 6 3 F e O K H 2 O + H o O - R b B a Z n P b N b Y S iO o F e 2 O 3 N a 2 O C e T iO o M n O M g O C a O P l b s T o t a l S r Z r T r a c e ______52 - 2

3 . 2 7 0 . 0 5 0 . 2 6 0 . 6 8 0 . 9 4 0 . 0 2 0 . 1 8 0 . 6 0 5 . 2 0 4 1 2 2 0 7 6 1 2 . 2 3 3 4 2 0 5 1 7 6 . 5 7 4 1 T y p e t o 1 9 5 2 2 8 1 0 0 . 0 0 2 0 6

B e a r in g S.E.

5

O t h e r

_

Hypersthene

o f

- 1 (Recalculated

0 . 0 2

1 . 1 6 2 0 . 1 5 0 . 0 3 0 . 1 7 0 . 6 8 3 . 4 2 0 . 7 2 6 5 . 3 2 3 5 7 4 2 2 2 0 9 6 1 2 . 3 0 7 6 . 0 2 T y p e 1 1 9 9 . 9 9 1 4 5 1 6 5 1 6 8 3 8 7 F a y a lit e RHYOLITES

R h y o lit e s

b a s is ) _

Com positions

AND

Ferrohedenbergite B u r r a

-

REGION T y p e

1 1 0 . 0 1 5 . 3 1 0 . 7 7 0 . 4 6 0 . 0 3 0 . 4 4 0 . 0 7 3 . 6 0 0 . 0 1 1 1 0 . 5 1 2 . 5 7 4 4 7 6 . 7 2 9 9 . 9 9

1 3 7 1 4 7 4 7 1 4 4 5 8 6 0 9 5 < A v e r a g e d Q u e e n s la n d a n h y d r o u s B in n a

_ 2 NOOSA

COMENDITES,

TO

2 . 0 1 3 1 . 1 0 0 . 0 4 0 . 3 8 0 . 0 9 0 . 4 8 0 . 7 8 3 . 6 2 4 . 9 0 0

1 < 0 . 0 1 5 1

2 7 1 3 . 4 8 2 9 P e re - 2 2 7 3 . 6 9 3 2 5 2 1 7

5 1 4 3 2 1 5 2 4 6 1 0 0 . 5 7 M t 3 8 6 2 9 9 5 4 4 / g ia n ------_ 0 8 5 6 8 2 COOLUM

1 TRACHYTES,

OF R h y o l i t e s

MOUNT

3 . 5 3 0 . 4 1 1 . 2 9 0 . 5 4 0 . 8 4 0 . 0 4 0 . 1 4 0 . 0 6 0 . 1 8 4 . 6 5 - 9 2 4 T i n - 2 7 7 5 . 6 1 4 3 1 2 . 9 6 4 5 6 9 5 2 1 2 2 4 1 1 1 2 6 3 1 2 9 1 0 0 . 2 5

_ b e e r w a li 9 4 4 5 / M t 4 2 9 8 2 THE

9 7 9 8 0 9 MTS

ANALYSESAND

4 0 . 0 2 - 1 .2 1 1 . 6 5 0 . 0 4 0 . 5 4 0 . 0 7 _ - 4 . 1 7 0 . 1 8 0 . 0 2 4 . 9 0 1 2 . 2 6 5 4 7 4 . 5 7 4 9 1 0 < 1 9 9 . 6 3 2 2 5 2 7 5 5 3 3 3 8 9 2 7 0 ELEMENT 1 4 5 0

Q u a r r y C o o r o o r a 9 4 4 5 / 4 2 9 8 0 GLASSHOUSE

MOUNTAINS 8 4 2 8 3 2

OF

TRACE

------N.E.

AND

7 - 1 . 5 3 1 . 2 9 - 0 . 0 3 0 . 1 4 0 . 1 4 4 . 5 5 - 0 . 2 0 0 . 6 9 2 4 . 5 8 C o o r a n 4 1 2 7 0 . 0 5 1 0 1 2 . 3 8 7 4 . 6 0 GLASSHOUSE 1 5 5 1 4 0 1 9 0 determ ination) 2 7 9 4 5 7

1 0 0 . 1 8 1 1 6 0 REGION Ck)mendites M t 9 4 4 5 / 4 2 9 7 9 MAJOR 8 1 3 8 7 0 THE

FROM

fluorescence

4

3 0 . 2 4 C o o lu m (continued): 5 5

1 . 6 3 1 . 1 9 0 . 0 7 0 . 1 4 0 . 0 3 0 . 0 3 4 . 8 9 4 . 4 5 0 . 9 8

- 9 9 . 7 7 - < 1 3 4 5 4 5 4 2 0 7 4 . 5 2 1 1 . 6 0 - 8 1 2 5 1 7 9 1 4 0 1 1 9 0

M t - X - r a y 3 8 6 3 0 9 5 4 4 /

0 8 6 6 1 8 TABLE ( p . p . m .

d e t e c t e d

E le m e n t s

R e f .

n o t

=

S iO 2 A I 2 O 3 F e 2 O 3 F e O H 2 O - R b S r Z r Z n Y (1:100,000) C a O T o t a l B a P b N b C e C r V - T i O 2 M n O M g O N a 2 O K 2 O P 2 O 5 H 2 O + T r a c e T h N i G r id . ------53

- R d

3 . 5 3 0 . 0 4 1 . 0 6 _ 9 9 . 6 5 5 0 . 5 2 9 9 . 3 0 ( 4 ) 4 6 . 4 1 4 3 . 2 4 P e a c h 3 8 6 0 6 e s t e r

I lm e n it e s

B e e r - 3 . 9 3

0 . 0 2 1 . 0 8 _ 4 3 . 4 7 9 9 . 6 1 ( 3 ) 1 0 0 . 0 0 5 0 . 5 2 4 7 . 0 1 M t w a h 3 8 6 0 5

N g u n -

1 . 4 3 6 . 4 5

2 . 9 2 9 9 . 7 1 2 6 . 6 3 0 . 2 3 0 . 3 6 _ 2 . 6 1 2 2 . 4 3 5 1 . 5 9 1 1 . 6 9 9 7 4 6 M t 3 8 6 7 2 g u n OXIDES (ilm enite).

2

______=

Aegirine-augites FE-TI 0 . 8 1 B e e r - 5 . 3 5 0 . 6 3 0 . 0 1 0 . 1 7

2 . 8 5 9 . 5 6 2 7 . 6 9 5 0 . 8 0 1 8 . 5 0 1 1 . 0 4 9 9 . 7 2 9 7 3 7 M t w a h 3 8 6 0 5 AND C a t io n s

B e e r - 0 . 0 9

COMENDITES

_ 0 = 3 , 2 1 9 . 7 0 3 0 . 6 7 7 6 . 1 7 4 8 . 5 7

0 . 3 5 0 . 6 9 0 . 0 8 - 9 7 . 4 3 ( 2 ) 1 0 0 . 5 0 M t b u r r u m 3 8 6 0 2

AND PYROXENES

OF

M ik e t e e -

(m agnetite); 0 . 0 9

_

1 9 . 2 4 0 . 5 8 0 . 6 6 0 . 1 2 - 7 6 . 3 0 3 1 . 3 2 4 8 . 1 2 9 7 . 3 6 ( 1 ) 1 0 0 . 5 0 2 4 M t b u m u lg r a i 3 8 6 6 9

= M a g n e t it e s

TRACHYTES

C a t io n s

0 . 1 1

(MICROPROBE) _ 1 4 . 1 4 0 . 6 6 0 . 5 5 0 . 1 5 - 7 9 . 9 5 2 9 5 . 5 6 4 0 . 4 5 4 3 . 5 5 9 9 . 6 0

3 8 6 8 6 HOUSES

3 2 ,

=

Z n O O

; GLASS

% Z n O

0 . 0 3 ANALYSES

- _ - - - 2 . 0 0 2 . 5 4 0 . 2 8 0 . 0 8 6 6 . 6 1 3 0 . 3 4 Tibrogargan

0 . 9 8 % THE F a y a lit e 3 8 6 8 6 1 0 1 . 8 8 1 . 2 7

M t

o f

E. (pyroxenes) FROM

I n c lu d e s 4 I n c lu d e s

1 . 0 5 1 . 9 5 0 . 7 1 4 . 2 1 0 . 3 5 AVERAGED = 0 . 5 3 n . d . 1 9 . 3 7 2 5 . 1 4 2 3 . 3 9 4 8 . 9 9

1 0 0 . 5 5 3 8 6 8 6 1 0 0 . 3 5 9 :

S C a t i o n s

TABLE B e e t - 0 . 4 9 6 , 1 .3 1 1 . 1 2 0 . 8 0

5 . 6 2

0 . 5 0 n . d . 2 1 . 8 7 4 9 . 2 0 1 9 . 8 5 9 9 . 5 8 2 0 . 6 9 = 9 9 . 4 5

M t b u r r u m 3 8 6 0 2 0

Ferroaugites

Z n O F e 2 O 3 ______

Z n O

M ik e t e e - 0 . 4 9

1 . 1 5 1 . 1 7 0 . 7 1 5 . 8 7 0 . 5 2 2 1 . 4 2 n . d . 4 9 . 3 7 a n d 1 9 . 9 1 2 0 . 3 7

9 9 . 4 4 9 9 . 5 6 M t . b u m u lg r a i 3 8 6 6 9 0 . 3 7 % 0 . 3 5 %

F e O

I n c lu d e s I n c lu d e s

S iO 2 1 T i O 2 A I 2 O 3 F e O N a 2 O Z r O 2 M n O 2 F e O M g O C a O F e 2 O 3 C a lc u la t e d ______54 9.04 0.27 5.49 0.72 3.38 0.32 10.26 14.00 Mt 19.87 99.14 38629 Peregian

35.79

97.64

Tin- 0.61 0.81 5.61 8.70 0.34 3.24 4.34

34.96 99.83 26.09 15.13 98.39 Mt beerwah 42982

THE

THE 1

- 0.22 1.45 1.03 1.23 9.76 1.28 2.95 0.02 98.74 48.79 32.85 99.99 42980 FROM

FROM

Cooroora

0.4

Mt 1.05 1.39 2.36 0.16 0.03 0.63 0.45 0.33 0.04 9.49 98.25 32.39 49.93 97.25 42980 BIOTITES

2

AND

2.41 1.33 1.17 1.65 1.54 0.06 8.20 0.06

0.4 0.12 AENIGMATITE

34.34 99.19 47.89

98.48 42979 AND Cooran

LAVAS,

Mt 2.11 0.51 9.21 1.34 0.03 0.06 0.47 2.60 0.29 0.72 33.10 49.49 98.89 100.00 42979 TINBEERWAH

AMPHIBOLES

n.d. COOROORA 1.03 1.13 1.17 8.86 1.24 0.03 2.32 0.24 0.98 AND

98.06 32.15 99.04 49.89 Saddle- 38666 back AND

SODIC

Rd

OF

n.d. 1.55 0.81 0.06 1.38 0.47 7.90 0.78 2.32 0.60 PERECIAN 34.15 98.49 49.45 99.47

Peach- ester 38606 COORAN,

MTS.

OF

7

(MCROPROBE)

8.35 0.6 0.02 0.84 6.71 - - - 1.22 - 39.85 42.15 99.81 38672(1) GLASSHOUSE,

RHYOLITES THE

0.05 0.58 0.66 34.00 1.19 2.38 7.59 1.35 1.33 2.17 n.d. 49.25 ANALYSES 99.64

100.55 38672 OF

Ngungun

0.71 0.03 0.27 1.46 0.58 1.49 8.49 1.34 2.06 n.d. determined 98.62

LAVAS 49.15 33.91 99.49 Mt 38672 AVERAGED not

=

10:

n.d. n.d. 0.74 0.13 1.17 0.01 2.13 5.31 5.61 1.60 2.44 98.72 45.66 34.82 99.62 38672 TABLE PERALKALINE

34.27 0.09 0.56 0.85 0.53 1.16 2.00 7.86 1.26 2.44 n.d. 49.30 99.29______Mt. 100.32 Beerwah 38605

Cl

O

F, Aenigmatite

FeO AI2O3 F 2 Less ()) SÍO2 ZrO2 TÍO2 CaO Na2O K2O Cl for MgO MnO 55

REFERENCES

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