Lead contents of S-type

ORIGINAL PAPER
Lead contents of S-type granites and their petrogenetic significance
Fritz Finger •David Schiller
Received:8October 2011/Accepted:15May 2012/Published online:5June 2012ÓSpringer-Verlag 2012
Abstract An evaluation of Pb and Ba contents in S-type granites can provide important information on the pro-cesses of crustal partial melting.Primary low-T S-type granites,which form mainly by fluid-absent muscovite melting,may acquire a significant enrichment in Pb when compared to higher-T S-type granites for a given Ba con-tent.We consider the following factors are responsible for this enrichment:Muscovite is a major carrier of Pb in amphibolite facies metapelites,and thus large quantities of Pb can be liberated upon its breakdown.The typical restite assemblage of Qz ?Bt ?Sil ±Pl ±Grt ±Kfsp that forms during low-T,fluid-absent muscovite melting can take up only minor amounts of this Pb.This is because the crystal/melt Pb distribution coefficients for these restite minerals are low to very low.Only K-feldspar is moder-ately compatible for Pb,with a crystal/melt distribution coefficient of *3,but its modal content in restites is usually low.At the same time,the restite assemblage will retain much Ba owing to the very high Ba uptake in both biotite and K-feldspar,which is an order of magnitude higher than for Pb.Thus,during a low-T anatectic event involving a low degree of crustal melting,Pb (as an incompatible element)can become strongly enriched in the partial melt relative to Ba and also relative to source rock values.In the case of higher-T anatexis and larger partial melt amounts,the Pb becomes less enriched and the Ba less depleted or even enriched relative to source rock values.During fractional crystallization of a S-type granite
magma,Ba behaves strongly compatibly and Pb weakly compatibly.The concentrations of both elements decrease along the liquid line of decent.Owing to this sympathetic fractionation behavior,the primary,source-related Pb–Ba fingerprint (with weak or strong Pb enrichment)remains in evolved S-type granites.This facilitates a distinction between primary low-T S-type granites,which are related to muscovite melting,and secondary low-T S-type granites that evolve through fractional crystallization from a higher-T parental magma.We show in this paper that a simple logarithmic Pb versus Ba diagram can be a valuable aid for interpreting the petrogenesis of S-type granite suites.Keywords S-type granites ÁBa and Pb contents ÁCrustal
melting
Introduction
S-type granites are commonly interpreted as magmas derived from the partial melting of quartz-and feldspar-bearing metasedimentary crust (Chappell and White 1974).Nevertheless,to paraphrase Read (1948),there are S-type granites and S-type granites.Some of them form at relatively low-T anatectic conditions of 700–780°C in equilibrium
with biotite-and sillimanite-bearing restite (Patin
˜o Douce and Harris 1998).Others form at higher temperatures of *800–900°C in equilibrium with cordierite-,garnet-,and/or orthopyroxene-bearing restite (Clemens and Wall 1981;Clemens and Vielzeuf 1987;White 2001;Rene et al.2008).In tectonic research,S-type granites play an important role as ‘‘geological windows.’’They provide information on the composition and the tectonothermal state of the middle and lower crust regions in orogens,given that one can determine the granite-forming conditions from geochemical
Communicated by J.Blundy.
F.Finger (&)ÁD.Schiller
Department of Materials Engineering and Physics,University of Salzburg,Salzburg,Austria e-mail:friedrich.finger@sbg.ac.at
Contrib Mineral Petrol (2012)164:747–755DOI 10.1007/s00410-012-0771-3
and petrographic data(Chappell and White1992;Henk et al.2000).Unfortunately,this is not an easy task,since S-type granite compositions are not only a function of source compositions and melting conditions,and can be modified through a variety of processes during magma ascent and cooling(e.g.,fractional crystallization or restite unmixing).Zirconium and LREE whole rock contents of granites have been shown to provide,with some limitations, useful estimates of liquidus temperatures for individual granite samples(Watson and Harrison1983;Montel1986; Miller et al.2003).However,these thermometers,which are based on the solubility behavior of zircon and monazite in melts,do not indicate whether,for instance,a low-T granite is primary(i.e.,formed through low-T melting)or a product of fractional crystallization and cooling(i.e.,a derivative of a former higher-T crustal melt).The same holds true for attempts to estimate magma temperatures from TiO2con-tents(Sylvester1998).
Harris and Inger(1992),Inger and Harris(1993),and Nabelek and Bartlett(1998)have suggested ways of inferring the melting conditions in the source terranes of granitic suites,based on the large ion lithophile(LIL) elements Rb,Cs,Sr,and Ba and their covariation trends. We suggest here that Pb is another useful element in this context.Like Rb,Cs,and Ba,the Pb is found mainly in the K-sites of micas and K-feldspar(Wedepohl1974),which makes it suitable for modeling processes of crustal partial melting.Surprisingly,Pb has been little considered in granite geochemistry.The aim of this paper is to show that Pb contents and Pb/Ba ratios of S-type granites are useful geochemical parameters that may help to assess melting conditions in the middle and lower continental crust. Temperatures of S-type granite magmas
Crustal partial melting can theoretically occur at tempera-ture conditions as low as*600–650°C,which are the minimum-temperature melt conditions of the Qz-Ab-Or system with H2O in excess(Tuttle and Bowen1958). However,in nature,such very low-T partial melts are vol-umetrically insignificant,because no or only very limited amounts of free H2O are available in the source regions (Clemens and Watkins2001).There is a wide consensus today that S-type granite-forming processes generally require temperatures significantly higher than650°C,and that melting rates are determined mostly by the amounts of H2O provided throughfluid-absent melting of mineral assemblages involving micas(Clemens and Vielzeuf1987).
The onset offluid-absent melting in fertile metase-dimentary sources(i.e.,rocks that contain quartz,plagio-clase,muscovite,and biotite)normally takes place at temperatures in the range of700–750°C with the reaction Ms?Qz?Pg=melt?Sil±Kfs or the reaction Ms? Bt?Qz?Pg=melt?Grt?Sil±Kfs(Vielzeuf and Holloway1988).The resulting low-T melts are typically very felsic,as Fe and Mg have low solubilities in granitic liquids at these conditions(Scaillet et al.1995).Due to the generally low degrees of crustal partial melting at T\800°C(Clemens and Vielzeuf1987),low-T S-type melts will not always be able to segregate from the source and rise to higher crustal levels.If they do,which may be facilitated by tectonic squeezing,they commonly form leu-cogranitic-pegmatitic intrusive systems,often with a tour-maline mineralization(Inger and Harris1993;Nabelek and Bartlett1998).
Two other prominentfluid-absent melting reactions relevant for the formation of S-type granites at higher-T (*800–900°C)are Bt?Sil?Qz?Pg=melt?Crd ?Grt±Kfs and Bt?Qz?Pg=melt?Opx±Grt±Kfs(Le Breton and Thompson1988;Vielzeuf and Hollo-way1988;Vielzeuf and Montel1994).Due to the higher anatectic temperatures,considerably higher degrees of mel-ting(20–40%)are normally associated with these biotite breakdown reactions(Clemens and Vielzeuf1987;Stevens et al.1997).During ascent and on cooling,these magmas may eventually undergo differentiation resulting in lower-T felsic residual melts.Such low-T residual(leuco) granites have low Zr and REE contents similar to primary low-T granites,indicating magma temperatures around 700–750°C.The challenge is to develop criteria to distin-guish between the two possibilities of primary versus sec-ondary low-T S-type granite formation.Pb contents and Pb/ Ba ratios appear to provide a possible key to this problem.
Chappell et al.(2004)introduced a fundamental subdi-vision of granitic rocks into low-temperature and high-temperature suites,based on whether magma temperatures were high enough to attain a state of zircon under saturation. S-type granites are,in general,assigned to the low-tem-perature group on this general temperature classification for granites,but Chappell et al.(2004)also pointed out the necessity to further subdivide S-type granites into relatively lower-T and relatively higher-T subtypes.Our tentative subdivision of low-T and higher-T S-type granites takes this proposal into account and is therefore not in conflict with the work of Chappell et al.(2004).However,to avoid any misunderstanding,we stress,here once more,that our ‘‘higher-T S-type granites’’do not belong to and should not be mixed up with the zircon-undersaturated high-tempera-ture granite suites defined by Chappell et al.(2004).
Pb contents and Pb/Ba ratios of S-type granites Literature data show that most S-type granites have Pb contents between20and40ppm.Taking for instance the
two large S-type granite provinces of the Lachlan Fold Belt and the European Variscides,we note that more than90% of the Lachlan S-type granites and about80%of the Variscan S-type granites have Pb contents that fall within this range(Fig.1).Pb contents of\20ppm occur in about 5%of the Lachlan S-types and about20%of the Variscan S-types.It is important to note that granites with Pb con-tents[40ppm are rare in both terranes.
Both the S-type granites of the Lachlan Fold Belt and the Variscan S-types(with few exceptions)are commonly regarded as having formed through higher-T crustal melt-ing(800–900°C)in conjunction with biotite breakdown reactions(Clemens and Wall1981;Finger et al.1997; 2009;White2001;Chappell et al.2004;Rene et al.2008; Zˇa´k et al.2011).During ascent and cooling,the magmas may have been modified to varying degrees by differenti-ation processes.In particular,the Variscan granites com-prise significant volumes of secondary(=fractionated) low-T S-types in some places(e.g.,Erzgebirge,Fich-telgebirge,Devon,and Cornwall:Hecht1998;Fo¨rster et al. 1999;Chappell and Hine2006).These show mostly a combination of low Ba contents(\200ppm)and low Pb contents(\30ppm).
For comparison,we have plotted in Fig.1the Pb and Ba contents of such S-type granites,which are regarded in the literature as forming mainly fromfluid-absent muscovite melting(±incipient biotite melting),generally at low degrees of melting.Typical and well-studied examples of these primary low-T S-type granites are the Tertiary Himalayan granites(Inger and Harris1993;Dietrich and Gansser1981;Visona and Lombardo2002;Harrison et al. 1999),the Proterozoic Harney Peak granite complex in Dakota(Duke et al.1992;Shearer et al.1986,1987; Nabelek et al.1992),the Devonian Phillips pluton in Maine(Pressley and Brown1999),and a certain group of S-type granites in the Variscan Bohemian Massif,Czech Republic,termed the Destna/Lasenice granites(Rene et al. 2008).Arguments for a low-T origin(\800°C)of these S-type granites are stated in the above-cited papers and include low biotite contents,low contents of Zr and LREEs (low zircon and monazite saturation temperatures),the presence of much inherited zircon and monazite,and the observation of specific trends in Ba,Rb,Sr covariation diagrams,which can be best modeled in terms offluid-absent muscovite melting(±incipient biotite melting).
Figure1shows that these primary low-T S-type granites mostly have Pb contents greater than40ppm,sometimes even attaining Pb concentrations as high as80–100ppm. As mentioned earlier,most Lachlan and Variscan S-type granites contain less that40ppm Pb.Although there is a certain degree of overlap of the Pb contents in the range between20and50ppm,the Pb–Ba diagram(Fig.1)pro-vides a surprisingly clear separation between the primary low-T S-type granites and the Variscan and Lachlan S-type granites,due to the fact that the Pb contents in both groups tend to decrease sympathetically with Ba.As will be dis-cussed below,the latter feature is most likely related to magma evolution by fractional
crystallization.
Discussion
Behavior of Pb during fractional crystallization
of a S-type granite
To assess the behavior of Pb during fractional crystalliza-tion,we selected some examples of S-type granite suites that have been described in the literature as involving strong magma modification through fractional crystalliza-tion.These data are plotted on Pb–Ba diagrams(Fig.2). The examples chosen include the Dartmoor granite from southern England with cumulative and evolved felsic magma types(Darbyshire and Sheppard1985;Chappell and Hine2006),the Adlethan/Koetong S-type granites and the Lake Boga pluton from the Lachlan Fold Belt(Chap-pell and White1998;Mills et al.2008),the Bergen pluton from the Erzgebirge,Germany(Fo¨rster et al.1999)and the South Mountain Batholith,USA(Dostal and Chatterjee 2010).In addition,we have plotted cumulative and frac-tionated magma types of the Harney Peak granite system (Shearer et al.1987;Duke et al.1992).
In all six cases,positive covariation trends for Pb and Ba can be observed.These trends exhibit a strong Ba frac-tionation from several hundred ppm down to a few tens of ppm.The degree of Pb fractionation is comparably minor (i.e.,D Pb/D Ba&0.1).The fractionation trends are always roughly parallel to the line that delineates thefield of primary low-T S-type granites(Fig.1).This means that the primary,source-related Pb versus Bafingerprint of a S-type granite parental magma(low-T or higher-T)will still be visible in cumulative(i.e.,Ba,Pb enriched)or residual (i.e.,Ba,Pb depleted)derivatives of that magma.In other words,fractionation trends of higher-T S-type granite suites will be positioned on the left side,that is,in the low Pb sector of the Pb–Ba diagram(examples1–5in Fig.2), whereas fractionation trends of primary low-T S-type granite systems will be positioned in the high Pb sector of that diagram(example6in Fig.2).
It remains to be discussed,whether the geochemical trends depicted in Fig.2,interpreted here and in the original publications(op.cit.)to represent fractional crys-tallization,are consistent with available crystal/melt dis-tribution coefficients for Ba and Pb.Trends of strongly decreasing Ba concentrations in S-type granite suites are commonly ascribed to fractional crystallization involving K-feldspar and biotite.Ba is known to strongly partition into these two minerals(crystal/melt distribution coeffi-cients of around20are reported in the literature;Icenhower and London1995,1996;Blundy and Wood2003;Ren 2004).However,it is under debate whether an early crystallization and fractionation of K-feldspar is a likely scenario for granitic rocks(Clemens et al.2009).For many S-type granite melts,voluminous early crystallization of K-feldspar(together with plagioclase,quartz,and
biotite)
is basically feasible,because these commonly form at near minimum-melt compositions of the Q-Ab-Or system (Chappell 2004).Early K-feldspar crystallization may also be facilitated by the fact that water-undersaturated crustal melting shifts the granitic minimum toward the Or apex (Holtz et al.1992),so that K-feldspar should precipitate as H 2O activity increases.
The highest crystal/melt distribution coefficients repor-ted for Pb and K-feldspar are around 4and thus signifi-cantly lower than for Ba (Nash and Crecraft 1985).Quartz,biotite,and plagioclase can take up no or only little Pb (Nash and Crecraft 1985).Fractionation of a granitic assemblage (Kfs ?Pl ?Qz ?Bt)should therefore pro-duce a steep positive covariation of Ba and Pb in a cumulate–residual melt system with D Pb \D Ba,which is consistent with the trends in Fig.2.Behavior of Pb during crustal melting
Muscovite in amphibolite facies metapelites can accumu-late fairly large amounts of Pb,because Pb partitions into muscovite more readily than into biotite.This affinity of Pb for muscovite has already been mentioned in early work of Hietanen (1969)and Haak et al.(1984),and is confirmed by own data (Table 1).Consequently,one can expect that
large amounts of Pb are liberated when muscovite-rich sources undergo low-T crustal melting.Most of it will probably enter the melt phase,as the coexisting restite mineralogy (Qz ?Bt ?Sil ±Grt ±Pl ±Kfsp)is inca-pable of incorporating much Pb.Restitic biotite will retain large amounts of Ba (Icenhower and London 1995)and will also constitute a major trap for Rb and Cs (Nabelek and Bartlett 1998).However,restitic biotite will take up only little Pb,even if full trace element equilibrium with the melt is attained.Most published crystal/melt distribu-tion coefficients for Pb and biotite are in the range of 0.1–0.6(Nash and Crecraft 1985;Ewart and Griffin 1994)and thus an order of magnitude lower than for Ba in biotite.Plagioclase can incorporate only small amounts of Pb (Bindeman et al.1998),and sillimanite and quartz com-monly contain no appreciable Pb (Nash and Crecraft 1985;Ewart and Griffin 1994).K-feldspar is a potential carrier of Pb (see above).However,since K-feldspar normally would not constitute a voluminous restite component in an ana-tectic scenario,the Pb can be expected to behave generally incompatibly during crustal melting.This means that,if melt proportions are low,Pb can become significantly enriched in a granitic partial melt relative to both Ba and source rock values.Strong enrichment of Pb is also likely in melts formed in disequilibrium batch melting situations involving muscovite breakdown.Since muscovite com-monly contains considerable amounts of Ba as well,such disequilibrium batch melts will probably be characterized by both high Pb and relatively high Ba contents.Higher degrees of crustal melting associated with biotite break-down (or the introduction of external fluid)will generally lead to a lower degree of Pb enrichment in the melt.Pb and Ba contents in source rocks of S-type granites Figure 3shows Pb and Ba contents of metapelites and metagreywackes,the relevant source rocks for S-type granite magmas.The data sets come from very different regions (Namibia,Himalaya,Maine,Bohemian Massif,Dakota)and refer to sedimentary series of different ages and geological environments.Nevertheless,all data
sets
Table 1LIL element and Pb contents of muscovite and biotite fractions separated from a mica schist from the Bohemian Massif
(Pancir
ˇ,Kralovy Hvost,Czech Republik)Muscovite
Biotite Whole rock Rb 144280156Ba 1,9961,038816Pb 602121Cs
3
41
17
The muscovite fraction shows a much higher content of Pb than the biotite fraction.Measurements by XRF on pressed pellets
have in common that Pb contents are low for most samples (mostly3–30ppm)and contents of Ba are moderate to high(mostly300–1,000ppm).These values thus define the common source rockfield for S-type granites in a Pb–Ba diagram.Evidently,a high degree of partial melting of metapelite or metagreywacke will result in primary melt compositions that plot in or close to thisfield.Likewise, primitive S-type granite magmas with high restite contents would plot close to source rock compositions.Note that *70%of the Lachlan S-type granites have Pb–Ba coor-dinates that are indistinguishable from those of common metapelites and metagreywackes,which is consistent with the restite-rich nature of many of the Lachlan S-type granites(Chappell et al.1987;White2001).The Variscan granites appear to be,in general,more strongly differen-tiated and many of them plot outside of the metapelite/ metagreywackefield.
With a decreasing degree of partial melting,melt com-positions will move progressively away from the meta-pelite/metagreywackefield,in the direction of lower Ba and higher Pb contents.We have tried to quantify these effects using the geochemical models introduced by Harris and Inger(1992)for Himalayan S-type granite formation. Taking their model parameters forfluid-absent muscovite melting of a metapelitic source(fractional melting, F=0.11)and crystal/melt distribution coefficients for Pb from Nash and Crecraft(1985)(set4,consistent with Harris and Inger1992),a C L/C0enrichment factor of2.9 would result for Pb(Fig.3).The corresponding C L/C0 value for Ba is0.2(see Table5in Harris and Inger1992).
The muscovite?biotite melting model of Harris and Inger(1992)(fractional melting,F=0.33)leads,as expected,to a lesser degree of enrichment in Pb(C L/C0= 2.1).Additionally,a third melting vector is displayed in Fig.3,which refers to a scenario of high-T anatexis of a metapelite(F=0.5),in which neither biotite nor K-feldspar exists in the restite in significant quantities.This situation would lead to a roughly twofold enrichment of Pb and Ba in the granitic partial melt,since both elements would behave incompatible in this case.The three partial melting vectors depicted in Fig.3clearly show that Pb contents and Pb/Ba ratios of S-type granite partial melts vary widely under different anatectic conditions,whereby high enrichment factors for Pb are obtained in low-T anatectic situations with low partial melt amounts.This latter fact is probably one of the main reasons,why primary low-T S-type granites have,in general,higher Pb contents and Pb/Ba ratios than higher-T S-type granites.
Additionally,it must be taken into account that the source rocks of S-type granites also have a relatively wide range of Pb contents(Fig.3),and that this will also influence the Pb contents of(local)partial melts.Musco-vite-rich schists,which are predestined for the production of low-T crustal melts,might commonly have elevated Pb contents,owing to the high Pb uptake capability of the muscovite.For instance,we have found that muscovite-rich schists in shear zones of the Bohemian Massif some-times have extremely high Pb concentrations(up to 100ppm;unpublished University of Salzburg data).The ability of the muscovite to concentrate Pb may thus con-stitute a second important reason for the elevated Pb con-tents of primary low-T S-type granites.
Petrogenetic significance of the Pb–Ba diagram
Our work suggests that the Pb–Ba diagram can help to identify primary low-T S-type granites,which formed through low-degree source melting(mainly muscovite melting),and to discriminate these from higher-T S-type granites,as well as from secondary low-T S-type granites formed by fractionation(Fig.1).However,this is not the only petrogenetic information that the Pb–Ba diagram can provide.As discussed above,fractional crystallization of a homogenous S-type granite magma will commonly pro-duce a series of derivative magmas that will plot along a steep subvertical trend in the Pb–Ba diagram(D Pb/ D Ba&0.1;Fig.2).On the other hand,source heteroge-neities and different anatectic conditions are likely to result in sets of partial melts with a comparably greater Pb var-iation relative to Ba(Fig.3).Geochemical data for leu-cosomes from high-grade metasedimentary series(Jung et al.2000)confirm this rule.
The Pb–Ba diagram thus seems to constitute a useful ‘‘process plot’’for S-type granite petrogenesis.For instance,if a S-type granite pluton or suite shows mainly a horizontal data spread in the Pb–Ba diagram(e.g.,the Bhutan pluton,Fig.4),then this can be interpreted as a source-controlled pattern.We presume that fractional crystallization has hardly modified this suite.The preser-vation of source-controlled chemical variations implies that the plutonic system was not or only poorly(at best par-tially)homogenized during its magmatic evolution.Con-versely,if an S-type granite suite yields widely uniform Pb and Ba contents(e.g.,the Phillips pluton,Fig.4),or if an S-type granite suite exhibits a narrow,well-defined frac-tional crystallization trend(e.g.,the South Mountain plu-ton,Fig.2),then this hints at a stage of effective magma equilibration in the plutonic system.Alternatively,a monotonous rock type and uniform melting conditions in the source region could be responsible.
A Pb–Ba plot for the Himalayan Makalu granite system (Fig.4)exhibits a large Ba variation,which is most likely governed by fractional crystallization.However,the trend is ill defined,due to a large scatter in the Pb values.We consider that this kind of data distribution reflects a com-bination of source-controlled magma heterogeneities and
fractional crystallization.This view accords with the pet-rogenetic interpretations given for the Makalu granite (Visona and Lombardo2002).
Lastly and importantly,it should be emphasized that the Pb–Ba diagram should never be used alone and that one should always carefully check to see whether the petro-genetic interpretations deduced from this diagram are in agreement with other geochemical and geological information.
Late-to post-magmatic Pb mobility
S-type granites with an extremely high degree of frac-tionation(Ba\20ppm)and/or a strong autometasomatic overprint(expressed by albitization,greisenization,or topaz mineralization)may sometimes show unusually high Pb contents,most probably due to alteration at highfluid–rock ratios.Gu et al.(2011),for instance,report Pb con-tents of up to162ppm for topaz granites from NW China. If such alteration remains unrecognized,it could lead to serious genetic misinterpretations of the data patterns in the Pb–Ba diagram.Likewise,caution is recommended for metamorphosed and sheared granites,as Pb can be mobile in metamorphicfluids(Wedepohl1974).
Conclusions
Lead is one of the few elements that behave generally incompatibly during crustal melting.Unlike the LIL ele-ments Cs,Rb,and Ba,which are strongly retained in restitic biotite(Nabelek and Bartlett1998)and therefore often behave compatibly during low-T crustal melting,the Pb can become significantly enriched in low-T S-type granite melts,particularly if the proportion of partial melting remains low.A second important point is that muscovite,a major constituent of metapelitic sources,can accumulate relatively high Pb contents.These two factors can probably explain why primary low-T S-type granites that form mainly in conjunction withfluid-absent musco-vite breakdown are commonly characterized by high Pb contents of40–100ppm and by high Pb/Ba ratios. Unfractionated higher-T S-type granites,whose formation is coupled with biotite breakdown reactions and higher degrees of melting,commonly show a lesser enrichment of Pb relative to source rock values and a lesser depletion or even an enrichment of Ba.
If fractional crystallization occurs,this can reduce the Pb contents of the residual melts and mask the original Pb characteristics of the parental magmatic system.However, since Ba and Pb appear to sympathetically decrease during fractional crystallization,the original Pb–Ba systematics of the primary magmas can still be estimated.On this basis, primary low-T granites(and their derivatives)can be dis-criminated from fractionated(=secondary)low-T granites spawned through the differentiation of higher-T parental melts.
The Pb–B a diagram,as introduced in this paper,con-stitutes a useful means for the petrogenetic interpretation of S-type granites,the more so as both elements can be easily and reliably determined by standard XRF methods.In combination with other geochemical parameters(e.g., Harris and Inger1992;Sylvester1998;Miller et al.2003; Chappell and Hine2006),a Pb–Ba diagram can provide help to assess whether chemical variations in a suite of S-type granites are mainly due to source heterogeneities and varying partial melting conditions or to fractional crystallization.
Acknowledgments This paper benefited from discussions with B.W.Chappell during his stay in Salzburg in summer2011.We are grateful to him for allowing us using his unpublished geochemical data base for S-type granites from the Lachlan Fold Belt.Igor Broska is thanked for kindly providing us with data tables for Variscan granites from the Carpathians.Discussions with M.Rene´,K.Verner, and J.Zˇak regarding the origin of some Czech granites
were。