Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 3 Solid Earth 1600 ppm Flu- Discussions ∼ , and M. Hand 2 , N. Phillips 2 nities in emplacement style to Large ffi respectively, according to the classification 252 251 3 , P. G. Betts 1,2 0.1 M km n and Eldholm, 1994), during which large volumes of > ffi C. The are A-type in composition (e.g. high Ga/Al ra- ◦ 50 M yr, , B. F. Schaefer < (Pa s). These physicochemical properties have led to the emplace- 1,2 η 100 km in length. Pigeonite inversion thermometers indicate eruption preserved), , represent the remnants of one of the most > 3 3.5 log 400 ppm Chlorine). These depolymerised the magma such that temperature- erentiation, material and heat transfer, and crustal growth (Reese et al., 1998; < ∼ ff 30 000 km This discussion paper is/has been under review for the journal Solid Earth (SE). Please refer to the corresponding final paper in SE if available. GEMOC, Earth and Planetary Sciences, Macquarie University, School of Geosciences, Monash University, Melbourne,School 3800, of Australia Geology and Geophysics, Adelaide University, Adelaide, SA, 5001, Australia > magma outpourings (e.g. Co mantle-derived are expelled onto the Earth’s surface in short geologic timescales 1 Introduction The viscosity of silicatetary magmas di is aZaranek critical and control Parmentier, on 2004).short the Large periods rate Igneous and of Provincesor scale (LIPs) time onto of represent during plane- relatively the which crustof significant ( Bryan volumes and of Ernst, material are 2008). emplaced in Most LIPs manifest as dominantly low-viscosity mafic neous system on a scalethe which planet. is The either Gawler not Range presentfelsic Volcanic or end Province poorly represents member preserved the of elsewhere eruptedprovinces. the on portion family of of the voluminous, rapidly emplaced terrestrial magmatic lobate flows temperatures of 950–1100 tios) and characterised byorine, elevated primary halogen concentrationscomposition-volatile ( non-Arrhenian melt viscosity modelling suggeststies they of had viscosi- ment of a Large RhyoliteBasaltic Provinces. Province, The which low has viscosity a of these felsic magmas has produced a unique ig- and lavas of the( Mesoproterozoic upper Gawler Range Volcanics (GRV) voluminous felsic magmatic eventssuggests preserved eruption on from Earth. a central Geophysical cluster interpretation of feeder vents which supplied large-scale Abstract 1 North Ryde, NSW, 2109,2 Australia 3 Received: 15 August 2010 – Accepted: 20Correspondence August to: 2010 M. – J. Published: Pankhurst 9 ([email protected]) SeptemberPublished 2010 by Copernicus Publications on behalf of the European Geosciences Union. A mesoproterozoic continental flood rhyolite province, the Gawler Ranges, Australia: the end member exampleLarge of Igneous the Province clan M. J. Pankhurst Solid Earth Discuss., 2, 251–274,www.solid-earth-discuss.net/2/251/2010/ 2010 doi:10.5194/sed-2-251-2010 © Author(s) 2010. CC Attribution 3.0 License. 5 20 25 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 2 M yr (Fanning et al., 1988). Significantly, 2 Ma; Fanning et al., 1988) upper Gawler < ) lavas with preserved outcrop extent of over 254 253 2 ± 250 m), chemically and isotopically laterally homoge- > 10%; Allen et al., 2008), and are absent (except for some mafic  across the central Gawler Craton (Allen and McPhie, 2002; Allen et al., 2 These volcanic rocks, which are a constituent of the last tectonothermal event to In this contribution we apply a combination of aeromagnetic and physicochemical The viscosity of natural silicate melts ranges over more than 10 orders of magnitude This contribution investigates a Continental Flood Rhyolite Province, and argues that interpreted lobe fronts insteeply the dipping southern and Gawler Ranges bimodal (McPhie orientations. et We al., consider 2008) this preserve to be consistent with flow complete terrain ( enclaves) in the lithologies investigated here. occur within the centralnetic data Gawler as Craton, a series are(wavelength of imaged 1–5 overlapping km) radiating in moderate-high lobes regional magnetic characterisedfeatures high-resolution by signal in a (Fig. mag- heterogeneous aeromagnetic 2). data Lobenetic and intensity fronts are and are texture. defined arcuate Recent by AMS a data combination obtained in of independent changes studies in from the mag- 12 000 km 2003, 2008; Fig. 1). TheDacite Eucarro are Rhyolite investigated and within Pondanna this Dacite study. membermagmatism The duration of is of the currently upper Gawler constrained Range tobasaltic Volcanics be and basaltic- comprise a volumetrically miniscule proportion of the 2 Morphology of the Upper GawlerThe Range upper Volcanics Gawler RangeA-type Volcanics (Blissett are et oneprising component al., of the 1993) an felsic ca. extensive,Suite large 1595–1592 dominantly Ma (ca. igneous 1600–1575 Gawler Ma; province Range Fanningare (Allen et composed Volcanics et al., of and al., 1988). three coevalneous 2008) thick The dacite Hiltaba com- ( to upper Granite Rhyolite Gawler (67–74 wt% Range SiO Volcanics analysis to theRange Mesoproterozoic Volcanics, (1592 South Australia.tem We can demonstrate behave that like a aof mafic large viscosity-lowering large factors, felsic igneous notably magmatic eruption province sys- temperature given and an halogen appropriate content. combination parameters, and more rigorous testing of geological and geophysical observations. ally more crystal richerupt (e.g. at significantly Giordano lower etlava temperatures al., flows than analogous 2006). do to mafic those(Christiansen Further, magmas, of and felsic et flood thus magmas al., substantial provinces generally magmas 1984; are though, rare tend Haapala in to the et betration. geologic lower al., record viscosity Clemens than et 2007; magmas al. of Milner (1986)and comparable postulated elevated et silica halogen that concen- content al., this most could 1992). oftenphysicochemical be associated models due with to (e.g. A-type A-types. higher Giordano Recent felsic temperatures variables et advances for in felsic al., compositions 2008) now allows incorporating quantitative calculation a of large magma intensive number of tent, Alkali/Al ratio, water content, halogenet concentration al., and oxygen 1985, fugacity 1988, (Dingwell 1993;Virgo, Dingwell 1989; and Mysen, Virgo, 1988; 1990; Giordano WebsterThe et and viscosity al., De 2004b; of Vivo, Mysen 2002; felsicthat and Webster of magmas and mafic is Rebbert, magmas 1998). generally because many the orders former of are inherently magnitude more greater polymerised than and usu- its characteristics are a functionWe suggest of that the a inherent typical lowetry, duration, plate viscosity temperatures, margin of chemistry setting the and does magmasoutside magmatic not involved. the processes adequately conceptual of explain model the the for GRV, placing “normal” geom- it Silicic Large Igneous(Cashman Provinces. et al., 1998;tween Romano temperature et and al., compositional 2001) factors, and including represents silica a content, complex crystallite interplay con- be- often described as theels result exist, of mantle and plume debatecontrast, activity, continues Silicic and Large (Bryan although Igneous a andgenerally Provinces variety Ernst, accumulate are of as 2008 mod- rare, pulses and dominated overmargin by references longer processes explosive timescales, (Bryan, therein). eruptions, and 2007; Bryan occur In et as al., a 2002). result of plate (5–10 M yr; Jerram and Widdowson, 2005). These principally basaltic occurrences are 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ects of ff C, and the ◦ C (Creaser ◦ 200 ∼ C. Samples from this study were ◦ 256 255 5–10 km) magnetic signal interpreted as sub-volcanic features, ∼ C. Due to the remarkable chemical homogeneity of the single lavas over ◦ Following petrological work to confirm the primary nature of their textures and low 950–1050 and McPhie, 2002; Allen et al., 2003; Fanning et al., 1988; Giles, 1988). Fluorine and abundance of microphenocrysts withinunaltered the upper microcrystalline Gawler matrix, Range twelvehalogens) samples and Volcanics trace of were elements analysed usingprocessed a through for Bruker-AXS Bruker-AXS major, Spectra-plus S4 Software Pioneer minor at XRFtre the (including at Spectrometer Advanced James Analytical and Cook Cen- University. Thelimits standard for used both for F F and andpressing Cl Cl to was were FSL, the 0.02%. lower analytical detection run Pelletsblages were to (feldspar, kept minimize ferromagnesian in the phases risk a andmajor of desiccator rare (see Cl from quartz) Table contamination. the 2) and time Mineral and their of assem- trace abundances, element and results duplicate that of previous studies (Allen cooling was mostlypossible responsible that for eruptive the temperatureinvariably observed exceeded obtained spread from 1100 the (Fig. terminalto portions 3) have of and cooled the significantly lava therefore lobes with (Fig. it respect 2), to is which the are source. likely (Lindsley, 1983) support these observationsmate (Fig. for 3). the Hence eruptive we temperature∼ consider of the the upper best Gawler esti- Rangehundreds Volcanics to of be kilometres between (Creasercan make and the White, reasonable 1991;was assumption thoroughly Giles, that mixed the 1988; via magmatemperature Stewart, convection, throughout. system 1994), and Since feeding the we the therefore geothermometrygeothermometer volcanism maintained data (Lindsley, a range 1983) over relatively generally constant records cooling, we suggest that surface Pyroxene and feldspar geothermometry studiesupper of Gawler the Range Yardea Dacite Volcanicsand indicate record White, that temperatures 1991; the between Stewart,ties 950–1100 1994). within the New province temperature (Figs. data 2 from and a 3) range based of on new pigeonite locali- inversion geothermometry 3.1 Physicochemistry of the Upper Gawler Range Volcanics sulting in maximum values for calculatedtemperature viscosities estimates. at the lowest measured reasonable Recent advances inaround quantitative improvements in modelling experimental constraints ofdano (Giordano and et silicate Dingwell, al., 2003; melt Gior- 2004a,larly viscosity, b, for based 2006, magmas with 2008) largely depolymerising low allows agents, crystallite rigorous such content. as calculation halogens, These ofpropriate for models bulk viscosities, for incorporate compositions the particu- and the GRV. temperatures e contents We ap- are utilise used a to conservative provide approach a where minimum whole estimate rock for fluorine the de-polymerising agents, re- the belt. Thisdial, is implying not a the central source, case;(Fig. and above 2). thus and appears to below reflect sedimentary the cover primary the lava distribution lobes are ra- 3 Physicochemistry suggests an elliptical-shaped lobate architecture inemanate which from the a median central lines cluster, of whichmedium each is lobe wavelength characterised ( by a longerincluding wavelength, elliptical pipes/feeder vents and frozenical magma work chambers (Fig. interpreted 2). theintersection Previous apparent of geophys- the lobate Earth’s geometry surface1993). and of gentle the tilting If of lavas the the togeometry province geometry be (Rajagopalan – was et caused i.e. al., due they by to would the curve erosion in only, the all same the direction lobes no would matter have where the they same exist in contrasting with McPhieposed et southern al.’s areas, (2008) these interpretationupper lobes of Gawler correspond Range with a Volcanics mappable southwest (e.g.aeromagnetic single data Allen source. lobes suggest et that within al., the In the lobescover 2003), clearly ex- (Fig. whereas persist 2). to beneath younger the sedimentary The northeast total the preserved distribution of the upper Gawler Range Volcanics patterns at the termination of individual lobes, and a magma source to the northeast, 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | (Pa s) O may η 2 1% H 0.2 wt% fluo- 45% (Bagdas- ∼ ∼ 4.25 log > ∼ O and 2 20–25%, max 39%; Allen 3.25 and ∼ ∼ 400 ppm respectively (Table 1). C and an assumed pressure of 1.5 wt% H ◦ ∼ ∼ C for both the Eucarro Rhyolite and ◦ C). Calculated viscosities drop by sev- ◦ C exists, it is conceivable that viscosities ◦ 800 40% exhibit Newtonian behaviour. Since the 258 257 ∼ < 1600 ppm and ∼ (Pa s) for the upper Gawler Range Volcanics (Table 2, O. Creaser and White (1991) estimated water content η 2 2.5–3 log C or 1 wt% volatiles in solution equates to a viscosity decrease of ◦ ∼ nities (Fanning et al., 1988; Giles, 1988), and due to their absence of common Estimates of halogen contents are also likely to be minima. Fluorine is abundant Firstly, we may consider the actual abundance, and therefore influence, of volatiles to Temperature and major element data have been input to Giordano et al.’s (2008) Crystallite content has an important positive influence on magma viscosity ffi eruption (Aiuppa et al.,Cl 2002; and Holtz et water, al., both 1993). of which This contrasts are with highly the volatile behaviour and of would be expected to be variably imum water content ofThis 1 wt%, water consistent content with would8 the M increase Pa typical (Creaser further estimate and to obtained White,be 1991). from 2 considered wt% Hence LOI. to if our be conservative the a estimate reasonable pressure of minimum. was increasedin to all units sampled,tent implying with it studies was that elevatedand suggest throughout hence that the the F magma. majority is of This soluble loss is in through consis- silicate volatilisation melts would at not eruptive conditions have occurred before flow tops (Allen et al.,versely, 2003) we may could be lead over-estimating to the undervaluingLOI water of corresponds content the of broadly halogen these to influence. liquidsin H by Con- the assuming Yardea that Dacite byfeldspar comparing phenocrysts the at assemblages of a2 quartz, M temperature Pa plagioclase, with of experimentally and 900–1000 derived alkali data (Nekvasil, 1988). This estimate yielded a max- 4 Discussion A consequence of thetemperature Giordano of 100 et al.’saround (2008) one model order is of thatinput magnitude. parameters, an and Hence increase we the in now calculated explore eruptive the viscosities consequences are of sensitive this. be to greater the than that recorded. Final degassing of the lava pile producing amygdaloidal ticularly halogen) estimates arefor conservative eruptive (Cl temperatures as iscould high not be as as included), low 1100 and as Fig. that 4). evidence for the Pondanna Dacite and Eucarro Rhyolite respectively. Given that the volatile (par- rine) are included in the models; resulting in viscosities of there is debate concerningstructure the (Zimova and specific Webb, role 2006, 2007), chlorine andfrom plays for our this in calculations. reason we Results depolymerising withheld of the chlorinebehaviour the data melt are combined modelling summarised encapsulating in non-Arrhenian Tablecompositions 2. appropriate The to the most upper significantat GRV, viscosities outcomes typical are are rhyolitic typical eruption that for temperatures for dry ( eral bulk compositions orders of magnitudePondanna (Table Dacite 2) (Fig. at 4), 950–1100 andtents there appropriate is for a the further Gawler viscosity Range decrease Volcanics when ( volatile con- and phenocryst abundance does not exceedet 40% al., (average 2003), this influencemal is and minimal, and chemical is controls. considered less important relative to ther- magmatic liquid viscosity model, chosen since it is calibrated for fluorine. Currently granitic hydrous phases,typically (e.g. between biotite) 1–2 wt%, and magmaticsidered their water low content low (1–2 wt%). during values emplacement of can be loss con- on(e.g. ignition Pinkerton (LOI) and Stevenson,sarov 1992), et particularly al., at 1994). concentrations magmas with Experimental crystallite concentrations workupper by GRV Lejeune observable and crystallite Richet content (1995) suggests is that low (excluding phenocryst abundance), These values are significantlyand higher 50–180 ppm than respectively those (Gaodegassing et of and al., typical hence 1998), felsic which should intrusionsextrusive have be not (300–515 expected equivalents. experienced to volcanic have Thea higher halogen upper contents Gawler than Range their Volcanics exhibit A-type chemical chlorine concentrations averaged 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 40 M yr; Bryan ≤ O contents reduced 2 C (Fig. 4). The role of fluo- ◦ 260 259 n and Eldholm, 1994; Courtillot et al., 2003; Jerram and 2 M yr) in comparison with other felsic LIPs ( ffi 10%) and basaltic andesites. Significantly, it is clear <  Perhaps then, the tectonic setting of the GRV has hallmarks of the voluminous,We (of- therefore envisage a spectrum of volcanic flood provinces which range from the The morphology of the volcanic province is characterised by an overlapping lobate The physico-chemical modelling suggests that a combination of elevated tempera- The second major source of uncertainty in the calculated viscosities is derived from 1600 Ma the province has been extensively eroded, and now we observe the remains mechanisms are controlled by their viscosity. ten A-type) felsic magmatism associated(e.g. with Hildreth the et evolution al., of 1991) the and Yellowstone the hotspot Parana-Etendeka plume (e.g.familiar, mafic Ewart dominated et end al., members 1998). (e.g.containing the appreciable Deccan volumes Traps, Siberia) of throughto felsic those the magmatism (Yellowstone, Gawler Parana-Etendeka) Rangevolumetrically system minor in ( whichthat magmatism is the overwhelmingly mode felsic with of rare, emplacement and possibly even magma transport and eruption equivalent small circle that relates toevent. Australia’s polar This wander leading suggests the emplacement of hotspot progression, geochemical and constraints. thereforea plume Betts regional activity, geodynamic et independent model al.Precambrian Australia. that (2009) appeals incorporate to these plume-modified observations orogenesis into in eastern lobes emanating from a centralvolcanoes zone (Thouret, is 1999). consistent Hence with emplacement thatvoluminous and observed upper eruption in Gawler of modern Range the shield Volcanics highgous may temperature, to be the considered plume to head beon processes physically a analo- associated comparable with scale CFBs.resent to Indeed, plume the they more derived are familiar preserved magmatismBetts analogues from et and al. independent have (2007) been chemicaltism argued use and across to palaeomagnetic the temporal Gawler rep- data studies. Craton, and Curnamona age province and progression Mount of Isa A-type Inlier magma- to define an would have probably been asions far of larger such volcanic expression a(Bondre of system the et system. are al., characteristic TheWiddowson, 2004; dimen- of 2005; Co “classic” White mafic andand large low Mckenzie, viscosities igneous 1995), enable provinces in large flow which lengths the of high lava. magma The flux radiating morphology rates of the of (if the distribution of similar aged granitic plutons is a useful proxy, see Fig. 1) what ∼ halogen loss. Morethey significantly, maintained the these Gawler conditions Rangeover throughout Volcanics such are such a anomalous short a time large inet ( al., volume, that 2002). and were erupted flow pattern that radiates fromvaries a between central 60 zone and (Fig.between 2). 120 km, The 30 with length and single scalefelsic of lobe 120 km single large fronts lobes and igneous across. associated province terminal is The lobes of protracted great denudation importance history to of note. the Since Gawler emplacement at those of tholeiitic basalts atrine is eruption double temperatures in such of a 950 a system depolymerising because agent it in increases itself water (e.g. solubilitycompositions Dingwell as et are well al., as exceedingly 1985). acting rare as Suchand low in viscosities Fallick, in the 1997), felsic geologic particularly record in (e.g. volcanic topaz piles ; that Taylor have experienced degassing and lowest reasonable eruptive temperatureprobable estimates in eruptive order viscosities. tolected constrain from Temperature the within calculations maximum the are frontalatures part are based of likely on individual to lobes samples recordsignificant or maximum in col- at cooling. terms the of lobe Hence uncertainty front this in where parameter the temper- is viscosities one obtained. oftures the during least eruption coupledthe with eruptive high viscosities fluorine and of moderate the H upper Gawler Range Volcanics to values approaching our estimates for theand total any volatile content increase must indecrease be content in regarded total of as viscosity. these conservative species minima, will be accompaniedthe by estimates a of eruptive concomitant temperature. The calculations are therefore informed by the degassed within and between units during eruption (Aiuppa et al., 2002). Therefore, 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | (Pa s)) η 3 log < C), elevated halo- ◦ C to 1100 ◦ 950 ∼ 262 261 This study was supported by an ARC Linkage Grant LP454301 to Hand, , compositionally zoned lava of Mesoproterozoic age, Geol. Soc. Am. Bull., 114, 3 (Pa s): a range closer to those viscosities exhibited by basalts ( η 675 km > flows, J. Geophys. Res.-Solid, 103, 27281–27289, 1998. topaz rhyolites from the236, Thomas 1984. Range and Spor Mountain, Utah, Am. Mineral., 69, 223– an undervalued component ofPaper, large Geol. igneous Soc. provinces Am., and 362, 97–118, volcanic 2002. rifted margins, Special Rev., 86, 175–202, doi:10.1016/J.Earscirev.2007.08.008, 2008. Deccan Volcanic Province, India, B.2004. Volcanol, 66, 29–45, doi:10.1007/S00445-003-0294-X, Australia: implications for Mesoproterozoic continental reconstructions,501, Terra doi:10.1111/J.1365-3121.2007.00778.X, Nova, 2007. 19, 496– canics, in: The geologyJ. of F., Preiss, South W. Australia, V., and Volume1993. Parker, 1, A. The J., Precambrian, Department edited of by: Mines and Drexel, Energy, Adelaide, 106–124, Bubble-Bearing rhyolite Melts, Phys. Earth Planet. In., 83, 83–99,Williams, 1994. H. A., Chalmers, N.in C., eastern and Precambrian Hills, Australia, Q.: Tectonics, 28, Mesoproterozoic Tc3006, plume-modified doi:10.1029/2008tc002325, orogenesis 2009. felsic Igneous Province inAustralia, western J. Laurentia: Volcanol. Geoth. The2008. Res., 1.6 Ga 172, Gawler 132–147, Range Volcanics, doi:10.1016/J.Jvolgeores.2005.09.027, South istry of widespreadSouth felsic Australia, volcanic Aust. J. units Earth in Sci., 50, the 97–112, Mesoproterozoic 2003. Gawler Range Volcanics, A 1592–1609, 2002. as an indicator of volcanic29, dynamics: 1559, The doi:10.1029/2002gl015032, 2001 2002. eruption of Mount Etna, Geophys. Res. Lett., Cashman, K., Pinkerton, H., and Stephenson,Christiansen, J.: E. Introduction H., to Bikun, special J. section: V., Sheridan, Long M. lava F., and Burt, D. M.: Geochemical evolution of Bryan, S. E. and Ernst, R. E.: Revised definition of large igneous provinces (LIPs), Earth-Sci. Bryan, S. E., Riley, T. R., Jerram, D. A., Stephens, C. J., and Leat, P. T.: Silicic volcanism; Bryan, S.: Silicic Large Igneous Provinces, Episodes, 30, 20–31, 2007. Bondre, N. R., Duraiswami, R. A., and Dole, G.: Morphology and emplacement of flows from the Betts, P. G., Giles, D., Schaefer, B. F., and Mark, G.: 1600–1500Blissett, Ma A. hotspot H., track in Creaser, eastern R. A., Daly, S. J., Flint, R. B., and Parker, A. J.: Gawler Range Vol- Betts, P. G., Giles, D., Foden, J., Schaefer, B. F., Mark, G., Pankhurst, M. J., Forbes, C. J., Bagdassarov, N. S., Dingwell, D. B., and Webb, S. L.: Viscoelasticity of Crystal-Bearing and Allen, S. R., McPhie, J., Ferris, G., and Simpson, C.: Evolution and architecture of a large Allen, S. R., Simpson, C. J., McPhie, J., and Daly, S. J.: Stratigraphy, distribution and geochem- Allen, S. R. and McPhie, J.: The Eucarro rhyolite, Gawler Range Volcanics, South Australia: Aiuppa, A., Federico, C., Paonita, A., Pecoraino, G., and Valenza, M.: S, Cl and F degassing Acknowledgements. Schaefer and Betts. We acknowledgeyou the to contribution landowners of in PIRSAand support the Graham in Gawler Hutchinson this for Ranges project. analyticalthis for support. Thank manuscript, access whom Thank and improved you support. the to paper reviewers considerably. of Thank previous you versions to of Kevin Grant References a large volume felsicrepresents igneous an province, end- and member suggest of the that Large the Igneous Gawler Province Range clan. province gen concentrations and low-moderate waterstructure. content The resulting low in viscosity a magmawhich depolymerised erupted emanated melt from large-scale a lobate central flows, clusternism of representing to feeder a produce vents viable a from emplacement floodandesites. mecha- Rhyolite The Province with volume volumetrically andto insignificant areal that basalts extent of and preserved of mafic suchgeologic Large a record, Igneous flood Provinces, and rhyolite whichthe is are are form directly present often analogous throughout of attributed the mantle to plumes. upwelling We of therefore anomalously present hot a mantle viable in mechanism for sustaining The calculated viscosities of5.0 the log upper Gawler Rangethan Volcanics that range of between typical 3.4– obtained felsic melts by (Giordano considering et elevated al., temperatures 2008). ( This viscosity range has been 5 Conclusions 5 5 30 25 20 15 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ects ects ff ff system and fac- 2 on the Solubility of 5 -SiO 3 O usive eruptions: Palae- 2 ff O 2 and P 3 O 2 ect of fluorine on viscosities in the O-FeO-Fe ff 2 ect of F on the density of haplogranite ff ects of F, B ff 264 263 ; implications for phonolites, trachytes and rhyolites, Am. Mineral., 2 SiO 3 O 2 O-Al 2 n, M. F. and Eldholm, O.: Large Igneous Provinces – Crustal Structure, Dimensions, and ffi Formation, North-Western Namibia, B. Volcanol., 54, 200–219, 1992. oflow data on anVolcanol. Geoth. extensive Res., felsic 172, lava 148–161, in doi:10.1016/J.Jvolgeores.2006.11.011, 2008. the Mesoproterozoic Gawler Range Volcanics, J. doi:10.1016/J.Lithos.2004.09.009, 2005. Study at High Viscosities, J. Geophys. Res.-Solid, 100, 4215–4229, 1995. Water in Haplogranite Melts Compared492–501, to 1993. Natural Silicate Melts, Contrib. Mineral. Petr., 113, logical constraints on the processes and products of flood volcanism, Lithos, 79, 385–405, cambrian Res., 40–41, 407–427, 1988. Planet. Sc. Lett., 208, 337–349, doi:10.1016/S0012-821x(03)00042-6, 2003. stocks in Namibia:plume, Topaz-bearing Lithos, A-type 97, granites 174–192, related doi:10.1016/J.Lithos.2006.12.002, 2007. to continental riftinging and the mantle Genesis andstone Plateau Contamination Volcanic of Field, J. Basaltic Petrol., and 32, 63–138, Rhyolitic doi:10.1093/petrology/32.1.63, Magma 1991. Beneath the Yellow- zoic evolution of thePrecambrian Gawler Res., 40–41, Craton, 363–386, South 1988. Australia, through U-Pbical zircon composition geochronology, ofCosmochim. the Acta, continental 62, 1959–1975, crust 1998. as revealed by studies in East China, Geochim. and Di Muro,ment A.: for metaluminous, Andoi:10.1016/J.Chemgeo.2006.01.007, peraluminous expanded 2006. and non-Arrhenian peralkaline model liquids, for Chem. silicate Geol., meltPlanet. 229, Sc. viscosity: Lett., 42–56, 271, A 123–134, doi:10.1016/J.Epsl.2008.03.038, treat- 2008. Goboboseb Mountains and Messumdence Igneous of Complex, early Namibia, cretaceousParana-Etendeka Part CFB, tristan J. I: plume Petrol., Geochemical 39, melts 191–225, evi- and 1998. the role of crustal contamination in the of water and fluorine5159–5168, doi:10.1016/J.Gca.2004.08.012, on 2004b. the viscosity of silicic magmas, Geochim. Cosmochim. Acta, 68, tors controlling relative viscosities ofActa, fully 52, polymerized 395–403, silicate 1988. melts, Geochim. Cosmochim. melt, Am. Mineral., 78, 325–330, 1993. and comparisondoi:10.1016/J.Chemgeo.2004.08.032, with 2004a. basalts, phonolites, and rhyolites, Chem. Geol., 213, 49–61, on density and viscosity, Chem. Geol., 70, 86, 1988. Earth’s mantle, Earth Planet. Sc. Lett., 205, 295–308, 2003. canism from the middle Proterozoic of South Australia, Geology, 19,system 48–51, Na 1991. 70, 80–87, 1985. External Consequences, Rev. Geophys., 32, 1–36, 1994. constraints, Am. Mineral., 71, 317–324, 1986. Milner, S. C., Duncan, A. R., and Ewart, A.: Quartz Latite Rheoignimbrite Flows of the Etendeka McPhie, J., DellaPasqua, F., Allen, S. R., and Lackie, M. A.: Extreme e Lindsley, D. H.: Pyroxene thermometry, Am. Mineral., 68, 477–493, 1983. Lejeune, A. M. and Richet, P.: Rheology of Crystal-Bearing Silicate Melts – an Experimental- Jerram, D. A. and Widdowson, M.: The anatomy of Continental Flood Basalt Provinces: geo- Holtz, F., Dingwell, D. B., and Behrens, H.: E Giles, C. W.: Petrogenesis of the ProterozoicGiordano, Gawler D. Range and Dingwell, Volcanics, D. South B.: Non-Arrhenian Australia, multicomponent Pre- melt viscosity: a model, Earth Haapala, I., Frindt, S., and Kandara, J.: Cretaceous Gross SpitzkoppeHildreth, and W., Klein Halliday, A. Spitzkoppe N., and Christiansen, R. L.: Isotopic and Chemical Evidence Concern- Gao, S., Luo, T. C., Zhang, B. R., Zhang, H. F., Han, Y. W., Zhao, Z. D., and Hu, Y. K.: Chem- Giordano, D., Russell, J. K., and Dingwell, D. B.: Viscosity of magmatic liquids: A model, Earth Fanning, C. M., Flint, R. B., Parker, A. J., Ludwig, K. R., and Blissett, A. H.: Refined Protero- Giordano, D., Mangiacapra, A., Potuzak, M., Russell, J. K., Romano, C., Dingwell, D. B., Ewart, A., Milner, S. C., Armstrong, R. A., and Duncan, A. R.: Etendeka volcanism of the Giordano, D., Romano, D. B., Dingwell, D. B., Poe, B., and Behrens, H.: The combined e Dingwell, D. B., Knoche, R., and Webb, S. L.: The e Giordano, D., Romano, C., Papale, P., and Dingwell, D. B.: The viscosity of trachytes, Dingwell, D. B. and Virgo, D.: Viscosities of melts in the Na Dingwell, D. B., Brearley, M., and Virgo, D.: The dual role of ferric iron in liquid silicates: E Dingwell, D. B., Scarfe, C. M., and Cronin, D. J.: The e Creaser, R. A. and White, A. J. R.: Yardea Dacite; large-volume, high-temperature felsic vol- Courtillot, V., Davaille, A., Besse, J., and Stock, J.: Three distinct types of hotspots in the Co Clemens, J. D., Holloway, J. R., and White, A. J. R.: Origin of an A-type granite; experimental 5 5 30 25 20 30 15 25 10 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 2 -SiO 3 O 2 O, Chem. 2 -Al -H 3 2 O 2 -SiO 4 O-Fe O 2 2 ciency for stagnant lid ffi O and Cl-solubilities in F- 2 ects of chlorine and fluorine on ff 265 266 ect of chlorine on the viscosity of Na ff -Fe-O, Am. Mineral., 74, 58–76, 1989. 2 Li, Na, K, Ca 0.5, Mg 0.5) melts, Chem. Geol., 174, 115–132, 2001. -SiO = 3 (X O 8 2 O 3 O-Al 2 icate melts, consequences ofchloride magma melt at evolution, Mt. and Somma-Vesuvius, implications Am. Mineral., for 87, exsolution 1046–1061, of17543–17585, 2002. hydrous 1995. temperature-dependent viscosity cooledspheres, from Earth Planet. above Sc. with Lett., 224, implications 371–386, doi:10.1016/J.Epsl.2004.05.013, for 2004. planetary litho- enriched silicate liquids; implications for volatileMineral. saturation Petr., of 132, topaz 198–207, rhyolite 1998. magmas, Contrib. magmatic convergence and the origins of topaz granite, Terra Nova, 9, 105–108, 1997. Crustal growth, PhD, Adelaide University, Adelaide, 1994. the viscositydoi:10.1016/J.Gca.2006.12.002, of 2007. aluminosilicate melts, Geochim. Cosmochim. Acta, 71, 1553–1562, 24, 769–778, 1993. convection with dislocationPlanet., viscosity: 103, 13643–13657, Application 1998. to Mars andhydrous Venus, XAlSi J. Geophys. Res.- melts, Am. Mineral., 91, 344–352, 2006. Magmas at Sub-Liquidus Temperatures, J. Volcanol. Geoth. Res., 53, 47–66,case 1992. history from the Gawler Range Volcanic Province, South Australia, Explor. Geophys., felsic melts, Am. Mineral., 73, 956–965, 1988. Geol., 88, 223–243, 1990. nosilicate melts; relationships amongsystem temperature, Na composition, and oxygen fugacity in the White, R. S. and Mckenzie, D.: Mantle Plumes and FloodZaranek, Basalts, J. Geophys. S. Res.-Solid, 100, E., and Parmentier, E. M.: The onset of convection in fluids with strongly Webster, J. D. and De Vivo, B.: Experimental and modeled solubilities of chlorine in aluminosil- Webster, J. D. and Rebbert, C. R.: Experimental investigation of H Thouret, J. C.: Volcanic geomorphology – an overview, Earth-Sci. Rev., 47, 95–131, 1999. Taylor, R. P. and Fallick, A. E.: The evolution of fluorine-rich felsic magmas: source dichotomy, Stewart, K. P.: High temperature felsic volcanism and the role of mantle magmas in Proterozoic Zimova, M. and Webb, S. L.: The combined e Reese, C. C., Solomatov, V. S., and Moresi, L. N.:Romano, Heat C., Poe, transport B., e Mincione, V., Hess, K. U., and Dingwell, D. B.: The viscosities of dry and Zimova, M. and Webb, S.: The e Rajagopalan, S., Zhiqun, S., and Major, R.: Geophysical investigations of volcanic terrains: A Pinkerton, H. and Stevenson, R. J.: Methods of Determining the Rheological Properties of Nekvasil, H.: Calculation of equilibrium crystallization paths of compositionally simple hydrous Mysen, B. R. O.: Interaction between water and melt in the system CaAl Mysen, B. O. and Virgo, D.: Redox equilibria, structure, and properties of Fe-bearing alumi- 5 5 30 25 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 1 order of magnitude C) ◦ ∼ 2.2 wt% total volatiles and a ∼ ∗ C with ◦ F ppm Cl ppm erence between rhyolitic and basaltic viscosities ff 268 267 (Pa s) – for the Upper Gawler Range Volcanics with 7.86.05.8 7.24.5 5.55.0 5.3 3.23.8 4.0 1.8 4.6 3.4 950 1100 950 1100 950 1100 0.5 0.7 1.5 0.1 0.2 0.1 10.3 9.7 5.4 800 70.913.3 67.6 13.8 50.0 15.0 η Eucarro Pondanna Tholeiitic O in accordance with Giordano et al. (2006) tholeiitic basalt input Rhyolite Dacite Basalt 2 Pa s) ( Detection Limit 200GRER01GRER03 200 GRER07GRER09 1400Pondanna Dacite 290 380 GRYD18 1960GRYD19 1920 680 310 GRYD20 360 GRYD23GRYD24 1470GRYD25 1670GRYD28 330 1340GRYD29 430 1390 390 1290 290 1840 310 1790 360 1770 460 490 Eucarro Rhyolite η OO 7.5 6.5 7.0 6.0 800 800 2 2 0.02 wt% H 3 = 5 O 3.2 3.4 2.0 2 2 ∗∗ O 2 O O 5.7 5.2 0.2 2 2 2 7 orders of magnitude di 1 wt% H 2 wt% H SiO TiO Al FeO(T)MnOMgOCaONa K P 2.8F 0.1Viscosity 0.1(all 4.3 in log 0.9Dry 0.1 11.0 1.1 1.1 0.2 0.20 8.0 11.5 0.23 0.00 Temperature (all in wt%) ∼ O 2 Calculated viscosities – log Measured (XRF) halogen concentrations for the Eucarro Rhyolite and Yardea Dacite. 0.50 wt% H = “Virtually dry” input used Typical, theoretical composition used ∗ ∗∗ Table 2. between calculated Gawlertypical Range tholeiitic Volcanics basalt at composition at 1100 typical eruptive temperature. reference to aal. typical (2008). (theoretical) Note the tholeiite composition using the equations of Giordano et at their respective typical eruptive temperatures, compared with the Table 1. Note values areduring likely eruption. to be minimum measurements due to devolatilisation and degassing Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | N Craton Gawler 2 . ig F

., al 270 269 t km e st 200

hur k an 0.370.99 0.19 0.45 0.26 0.85 0.2 0.51 51.07 50.23 50.39 49.98 YD030 (single crystal) Creaser and White (1991) P 1. e 3 North Cover successions Archaean basement Hiltaba Granite Suite Gawler Range Volcanics Mesoproterozoic sedimentary rocks Palaeoproterozoic supracrustal rocks O 0.27 0.06 0.32 0.13 2 2 O 2 ur 2 Al FeOMnOMgO 18.96CaO 0.92Na 9.69 17.72 30.99 18.02 1.63 11.53 4.96 0.94 9.81 17.60 30.74 1.32 12.34 4.56 TiO Mineral AugiteSiO Pigeonite Augite Pigeonite Total 99.95 100.02 99.69 99.85 ig F Single crystal pyroxene analyses from YD030 (data points are 10 µm apart) compared Simplified geological map of the Gawler Craton. Fig. 1. Table 3. with data from Creaser and White (1991), all in wt%. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ite (1991) Fs Wh 100 art (1994) Augite compositions ew St Pigeonite compositions 90 Creaser and thermal boundary Poly 80 Hd 70 60 272 271 50 40 30 C for the upper Gawler Range Volcanics. ◦ 1 atm Di 20 40 C and 1110 30 ◦ % 10 20 Mol Mol Sample sites superimposed onto reduced to the pole greyscale aeromagnetic image Graphical pyroxene geothermometer after Lindsley (1983). Pigeonite and augite data 10 Figure 3. Pankhurst et al. 0 En Fig. 3. from Creaser and White (1991),between Stewart 900 (1994) and this study indicate magmatic temperatures of the Gawler Rangeregions Volcanics. of The similar lobeclosely magnetic morphology follow texture of the defined theimaged modern by lava undercover arcuate outcrop (NE flows of shapes. distribution can Lake be (inset) Gairdner). The observed in (preserved) as the flow SW fronts and these shapes are also Fig. 2. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | O contents 2 2 2 2 2 2

1200

Pondanna Dry Pondanna

Eucarro Dry Eucarro

Pondanna 1 wt% H O H wt% 1 Pondanna Pondanna 2 wt% H O H wt% 2 Pondanna Eucarro 1 wt% H O H wt% 1 Eucarro Eucarro 2 wt% H O H wt% 2 Eucarro Tholeiite (0.5 % H O) H % (0.5 Tholeiite Upper GRV 1000 ο 274 273 Temperature ( C) Temperature 800

typical

& rhyolites rhyolites

600

8 6 4 2 0

18 16 14 12 10 Viscosity (log Pa s) Pa (log Viscosity η Photograph (sample YD23, crossed polarized light) of pigeonite crystal within unal- Viscosity vs. Temperature plot illustrating calculated palaeo-viscosities of Pondanna Fig. 5. tered microcrystalline matrix displayinglamellae classic indicating “Christmas high tree temperatures (especially texture”; for a dacite-rhyolite result compositions). of exsolution Dacite and the Eucarro Rhyolite using measured fluorine and 0.02, 1 and 2 wt% H Fig. 4. for these units. Amodeled typical for comparison. theoretical tholeiitic Thetemperatures basalt results and composition elevated indicate halogen (see that content Tableof a decrease 2) the combination the has Gawler viscosity of Range also of unusually Volcanics been melts towards high typical of magmatic values the of composition basalts.