RENolCONTI DELL,\ SOCIETA lTAUANA 01 MINERALOG IA E PETROLOGIA, 1988, \bI. 4}.2, pp. '4).,,4

Basic intrusion, charnockite.rapakivi granite plutonism aod crusta! depletion, S. W. Sweden

FREDERIK H. HUBBARD Depanment of Geolosy, Dundee University, Dundee, Scotland

AUSTRACT. - The southern segment of the South-West South-West Swedish Province by a series of Swedish Province (SWSP) of the Precambrian of the major thrust zones, it has characteristics Baltic Shield has features which distinguish it from the northern sesment of the same province and the peculiar to this region pf the Swedish Svecofennian sequences to the east. Repeated cycles of Precambrian. These include an abundance of syn and late·orogenic b..sic magma injection maimained meta-basic intrusions, the occurrence of high crusta! temperatures and led to progressive granulite fades assemblages within the general depletion of the rode! at, and adjacent to, the conduits. This is shown by the development of loc:::aI ~u1ile facies upper amphibolite facies terrain and zones in the seneral amphibolite facies terrain and the distinctive plutonic associations of alkaline occurrence of plutonic charnockite Jrulsses. granite and charnockite (e.g. QUENSEL P., The syn-orogenic: basic magmas caused depletion largely 1951; CALDENruS et al., 1966, MOHREN E., by the generation of hydrous solutions derived from dehydration of mafic minerals in the rountry rocks LARSSON W., 1968, HUBBARD F.H., 1975, ronsequent on the heat influx associated with the 1978). A Rb-Srisochron age of 1420Ma was intrusion. These hydrothermlll solutions metasomatised obtained by WELIN and GORBATSCHEV (1978) and migmatised the basic rocks, formed ap!ite from a composite charnock.ite and granite segregatioO$, or were exhausted to higher level. pIu ton (the Charnockite-Granite Association The late orogenic basic magmalism, which was associated with a shearing deformation, led to the of the Varberg region, HUSBARD F.H., 1975). development of granitic plutons which segregated during This piu ton was affected by post­ I15CCnt to leave residual-testite charnockile and released emplacement, hot shearing and thrusting and REE and RE-enriched alkali granites with. rapakivi the date may reflect isotope resetting during granite signature. While a COl volatile phase is indicated as importam this tectonic activity rather than the age of in the llte·tectonic episode, it is not evident as a faclor the intrusion. A similar age is, however, found in the earlier syntectonic crustal depletion. for amphibolites and granitoids in the Key words: Basic magma, depletion, dJarnockile, sranite. northern segment of the South-West Swedish Province (e.g. SKIOLD T. , 1976; DALY].S., PARK R.G., CUFF R.A. , 1979; SAMUELSSON L. , AHALL K.-L, 1985). The add plutonic rocks were emplaced in metamorphic Introduction sequences which show evidence of a long and The southern segment of the South West complex earlier development history. The Swedish Province (Fig. 1) occupies a impression gained is one of an old sequence somewhat enigmatic position in the hierarchy of crustal rocks which has undergone of development of the Precambrian rock extensive, and perhaps repeated, reworking. sequences of the Baltic Shield. Separated from Unfortunately no firm time scale has been the Svecofennian Province to the east by a established for the period preceding the late, major mylonite zone and its associated hot deformation and recrystallisation. granites and from the northern segment of the However, the rocks of south-west Sweden are ~44 HUBBARD EH . clearly old and may represent an Early DALY j.S. et al., 1983), they lack similar Proterozoic, or even Archaean, province with prominence in the southern segmenl. a history of Proterozoic reworking. The differences between the rock associations of General geology of the Varberg Region the South-West Swedish Province and those of the Svecofennian Province to the east may The best exposure of the rock sequences merely be a consequence of the exposure of of the southern segmenl of the South-West differing crustallevels but the possibility that Swedish Province is to be found around the the South-West Swedish Province is exotic town of Varberg, on the Kattegat coast south cannot be ignored. The rocks of south-west of Gothenburg (Fig. 1), and contiguous with Sweden most closely resemble those of the the limiting northen thrust zone. The geology Pee-Caledonian rocks of southern Norway is dominated by an intrusive plutonic complex (e.g. TORSKE T., 1985), which have a strong which comprises both charnockitic and non­ Sveconorwegian (GrenvilIian) signature charnockitic granitoid components in intimate thought, to some extent, to mark overprinting association - the Varberg Charnockite­ of a younger age on older rocks (PRlEM Granite Association (CGA) - (HUBBARD RN.A. et aI., 1973; VERSTEEVE A., 1975; F.H ., 197.5). The country-rocks to this TORSKE T., 1977; SMALLEY p,e. et al., 1983). association are, in large pare, upper While c. 1000Ma ages are fairly common in am phibolite facies grade granitic para-gneisses the northern segment of the South-West which have locally developed charnockitic Swedish Province (e.g. SAMUfJ..SSON 1., 1980; characters (HUBBARD F.H., 1978). Horizons

I' Imet.basit,

Okm

Fig. 1. - Location map (S.A ... study area; G .. Gothc:nburg; S. Stockholm; 0 .. Oslo; SWSP(S)·South-We$\ Swedish Province (southern segment); SWSP(N) .. South-We$t Swedish Province (northern segment); SOA .. Svcwfennian Orogenic A15ociation; cross panelD" Protogene woe granite$; dot panern .. Caledonide$) and geological sketch map of the Varberg area (black .. mela·basic rocks; VC, AGe and TC .. charnockite and sub-charDOCkite components and TG . the mator granite component of the Oumockite-Granite Association, CGA). BASIC INTRUSlON, CHARNOCKJTE..RAPAKlVI GRANITE PWIONISM AND CRUSTAL DEPLETION ETC. 5 4 .5 of more varied lithology, which include meta· occurring as enclaves, xenoliths and intrusive basic layers, occur within these rather sheets in the charnockites and as sub­ monotonous granitic gneisses. It is in these conformable sheets in the country rocks. compositionally-layered horizons that the Several generations of basic intrusion are structural complexity of the country rock indicated (Figs. 2, 3), which are all now

Fig. 2. - Folded metabuites cut by younger metabasile in depleted (charnockitic) granite gneiss. Triislovsliige.

Fig. }. - Agmatite of hornblendite blocks in scapolite·metabaggro. N. Honen.

~nciss is most clearly expressed. Metabasic represented by metamorphic derivatives. They rocks are a feature 01 both the plutonic may be grossly divided into those which complex and the surrounding country rocks; predate the granitoid plutonic activity and 546 HU88ARO F.H.

The Period of Granitoid Plutonic Activity Although rather severely disrupted by post­ emplacement hot shearing and thrusting the general form of the charnockite and granite complex of the Varherg region can be reconstructed with reasonable confidence due to the excellence of the outcropping along this coastal region (Fig. 4). The composite intrusion was emplaced during a period of shearing and shear folding, synchronous with a further basic magma influx into country rocks which already had well-established major structural and metamorphic patterns. The form of the pluton follows the general structural grain of the country rocks with the narrow, deeper, neck lying in a structural steep zone, which was concurrently being further accentuated by shearing. The lateral spread Fig. 4. - Idealised 5e(:tion of the Chamockitc:·Granite of the pluton at higher levels coincides with AS$odation. Fine dots .. charnockite cumulate (VC of a similar change in country rock structure. A Fig. I); coarse 001$ .. the active fractionatins zone (AGe of Fig. 1); heavy c;ros5eS" charnockitc and sub­ parallel distribution can be observed in the charnockite raiduum (Te of Fig. 1); fWit crosses .. the products of the accompanying basic activity. evolved granite (r G of Fig_ 1). This discontinuity of structural grain continued to play a fundamental role during those sub-sYhchronous with the emplacement the subsequent major thrusting which of the granitoids. The early group of meta­ established the northern limit of the southern basic rocks are amphibolites and garnet­ segment of the South-West Swedish Province. amphibolites and afe commonly linked with migmatisation. The younger group rocks, on The Charnockite-Granite Plutonic Activity the other hand, characteristically occur as garnet-pyribolite, although there are The plutonic granitoid association of the associated local developments of coarse garnet­ Varberg region has less well , and less amphibolite. completely, exposed counterparts throughout the province. In some instances, the granite has become detached from its charnockitic associates, in others, there is arrested The Pre-CGA Meta-basic Rocks development, as displayed at Varherg (the The earliest recognisable basic magmatism Charnockite-Granite Association or CGA of is that associated with the lithologically­ HUBBARD F. H ., 1975), where the granite­ layered gneiss/granulites within the granitic charnockite link remains intact, thus revealing gneisses, represented by tight, strongly the mechanism of formation. flattened, fold remnants. These may ~prese:nt The massive charnockite phases of these a volcanic component of the early supracrustal plutons are intcpreted as «cumulate-restites» system of the the gneiss complex. The from the fractionation of anatectic melt­ following cycle of basic magmatic activity was crystal aggregates derived from the local intrusive, polyphasai and syntectonic. granite-gneiss country rocks; the more Localised, crustai dehydration resulted from buoyant, less viscous, melt fraction rising to this, probably protracted, period of basic crystallise as K-feldspar megacrystic granite magma intrusion, with the basic bodies acting with the petrographic and chemical characters as water sinks during their sub-synchronous, of rapakivi granite (HUSBAlU) F.H., WHITLEY metamorphic transformation to amphibolite. ).E., 1978, 1979). The Varberg complex has BASIC INTRUSION, CHARN)CKlTE-RA~KlVI GRANlTI: PW10NISM AND CRUSTAL DEPLETION ETC. 547 the form of a narrow «neck» of charnockidc .. , ' ' .. , rocks surmounted by a flattened «cap» of , , R.I ..lld K-granlte magma granite, producing a mushroom-like section. ~ The charnockite neck has a complex structure. The flanks are composed of a generally homogeneous, sparsely feldspar-megacrystic, monzonitic' charnockite (the Varberg Arrut.d charnocklt. Charnockite or VC of HUBBARD F.H., 1975), locally with abundant xenoliths. The xenoliths of country rock in this intrusive charnockite are generally of granulite-facies grade; largely «charnocki tised» granite-gneiss. The nature Charnocklte IItall" dlv.lopm.nt of the xenoliths indicates that the pluton was with breakdown of emplaced into already depleted country rocks. ,,'~ eub-Iyetern Interface This depletion to granulite facies is largely ,'. localised to the conduit zones established by the early basic intrusions which instigated the depletion. The same conduits we re subsequently re-utilised by both the granitoid and the younger basic intrusions. Early buoyant rill with flow Central to the neck, an essentially similar IIparatlon of crYltal1 and rock forms the matrix to segregations of three m.'t In dilcrate aubtYltem' types: a) Veins, streaks and schlieren of coarsely feldspar-megacrystic rock of similar composition to the matrix, with charnockitic, or sub-charnocldtic, petrographies. (The term «sub-charnockitic» is here used to denote Rock ma .. dleagoragatlon rocks which maintain the dark quartz and through anat.)(I. feldspar characteristics of chamockite but in which much of the typical pyroxene of charnockite is exchanged for amphibole). Fig. 5. - Can oon of the proposed model for the b) Discrete masses of pink, coarse, segrega tion and potential separation of gunite from microcline porphyritic, leuco-granite. The charnockile. contacts with the enclosing charnockite are sharp. c) Granite masses, similar to b) above, from the diaphthoretic degradation of but with attached « tails» of coarse charnodcite associated with the later shearing charnockite or sub-charnockite comparable activity. with the segregations of type a). The nature and distribution of the These consititute the Apelviken-Getteron components of the complex suggest a Chamockite (AGe) of HUBBAJU) F.H. (1978). mechanism for the fractionation. Partial The major chamockite/sub-charnockite and melting led to loss of coherence in a mass of granite duplex rises from this central country rock undergoing foolSSed heating fractionating zone, repeating the form of the during shear deformation and mafic magma type c) segregations, but on a greatly expanded intrusion. Segregation of more melt-rich scale. At both scales, the transition from fractions during buoyant rise of the crystal ~ charnockite, through sub-charnockite, to melt amalgam would result in viscosity and granite is progressive and irregular. Sub­ density contrasts developing within the rising charnockite and granite can be observed in columns producing 'subsystems with the same outcrop, in a manner clearly distinct sufficiently distinct physical parameters for 548 HUBBARD F.H .

them to develop as discrete units. The more Discus.ion buoyant subsystems, by aggregating on contact with kindred units, wou1d accumulate The intrusion of basic magma is of to large size and could potentially separate importance in initiating and maintaining from their more sluggish crystal·rich.residues. metamorphism as it provides an efficient Internal crystal accumulation during the rise means of transporting heat into, and through, of the segregations, would result in the the crust. It also strongly influences the development of sluggish crystal-rich tails to distribution, arx:l the mix, of volatiles within the rising masses, with greatly reduced an aHected crusta! seedon. T OURET J.L. R. viscosity/buoyancy contrast relative to their (1971) identified the importance of the surroundings. The consequent «braking hydration involved in the conversion of basic effect,. could lead to retention of the intrusions to amphibolites for dehydration of

Fig. 6. - Mingling of bll$ic and acid (charoockite) magmas. Nu. cumulate-residues with separation of the crustal rocks and the devdopment of granulite buoyant, lower viscosity, granite melt fades. Current theories on the processes of fractions. The segregations described for the granulite fades metamorphism fall into two centre of the neck are interpreted as main groups; those which em'l'asise the representing stages in these development importance of a massive influx 0 CO2 (e.g. processes as they affected magma-enriched FROST B.R., FROST C O ., 1987) and those fractions which were unable to coalesce with which emphasise the importance of crustal the major mass. The cartoon of Fig. 5 melting (e.g. FYFE W., 1973). Anyone, or a summarises the proposed development scheme combination, of three processes may lead to and can be rdated to both the small and the the formation of depleted granulite terrains; large scale bodies. Concentration of available C0z-streaming, partial melting o r water in solution in the silicate melt phase is recrystallisation of original dry rocks (e.g. in accord with the charnockitic, or sub­ L AMB W., VAllEY]., 1984). charnockitic, nature of the crystal cumulate In the Varberg area of the southern segment restites, and the lack of evidence of reaction of the South-West Swedish Province, the between the granite and its « dry» charnocki tic direct association of crustal depletion with host. influxes of basic magma is evident. The direct BASIC INrRUSlON, CHARNOCKIT£.RAPAXJV1 GRANITE PWlQNISM AND CRUSTAL DEPLETION En:. 549

L,.IOCClO/ NlZO+KZ O)

1.0 • ~ . • '~• 0.' • ..• • 1>1> I> I> •

A ,

-O.~

-1.0 SI02 40 ,0 60 10 80

Fig. 7. - Lime/alkali vs. SiOl diawam. Filled triangles,. younger basic intrusions; open triangles ,. older basic intrusions; filled circles and $Cjuares,. charnockite and sub-charnockite members of CCA, respectively; open squares ,. evolved gcanile. Since there is considerable da,a point overlap for the CCA data, only representative points arc included. connection of the charnockitic rocks with content (5i02 range:o 42.8-47.1 wt.%) and crustal melting is demonstrated by the do not define a clear fractionation trend on Charnockite-Granite Association (CGA) and the plot. The younger basic rocks (Bas2), on the synchronous existence of basic and acid the other hand, have an extended silica range magma is shown by evidence of magma (5 iO~ = 44 .2-55.6) and display well a calc· mingling (Fig. 6). alkaline to calcic trend in Fig. 7. The Basl The mean chemical comjX)sitions of the rocks are ferrogabbroic Ootunitic) in character major rock types of the region are presented whereas the Bas2 suite are aluminous with an in Table 1 and their general mineralogical anorthositic fractionation locally evident. compositions in Table 2. The lime/alkali vs. The acid plutonic rocks are divided, in silica plot for the intrusive rocks (Fig. 7) Table 1, into the recognised components of provides petrochemical support fo r the field the Charnockite-Granite Association. The and petrographic sub-division of the basic Varberg Charnockite (VC) data represent the intrusions into two distinctive groups. The monzonitic residual charnockite phase from older basic rocks (Basl) vary little in silica the evolving system. Two data sets are HUBMRD F.H. provided from the internal segregating zone, the Apelviken-Getteron Charnockite (AGC), which emphasise the close compositional similarity of the relatively fine-grained charnockitic matrix [AGC(f)] and the coarse· grained segregating sub-charnockitic masses [AGC(c)]. Both range in composition from quartz·monzonite to adamellite. The adamellitic Tronningenas Charnockite (TC) data relate to the charnockitic and sub­ charnockitic «tail » to the main granite segregation, the Torpa Granite (TG). In the lime/alkali vs. silica diagram of Fig. 7. all the components of the CGA lie along a well­ defined alkaline fractionation trend. The close fit and rational compositional progression of the CGA components along the trend regression line show that the rocks all belong to a coherent consanguineous igneous suite. The extreme mismatch of the trends of the fractionated basic rocks and the addic rock association makes it extremdy unlikely that they derive from a common parent by assimilation-fractional crystallisation (AFC) processes. Also, there is no compositional evidence to suggest that a mixing regime was important in the development of either rock .. " Co tU ZtS-Tlny suite. Fig. 8. - Elemenl spidergram, normalised 10 primordial The suite of xenoliths found in the intrusive mantle (normalisina values from WOOD D.A., 1979). charnockites of the CGA suggests that Open circles . granite gneW; filled circles . chamockitic granile gneiss; stiW1ed field . variation within CGA granulite fades assemblages were already a componenu. feature of the country rocks. This depletion episode may reasonably be ascribed to the of massive CO2 infusion. The features syntectonic period and, in particular, to the described are more readily attributed to the associated, repeated, basic magmatism. One activity of migrating hydrous solutions, indicated mechanism of depletion is developed from metamorphic dehydration of dehydration through amphibol.itisation of the biotite and hornblende at the elevated basic rock. The transformation of the temperatures engendered by the basic amphibolite fades country rock granite magmatic activity. These metasomatised the gneisses to granulite facies equivalents entailed basic intrusions, were exhausted to higher depletion in Si02, K20 and Th (HUBBARD levels and/or gave rise to the ductless aplite F.H., 1978; CoNSTABLEJ.L., HUBBARD F.H., bodies recognised to occur in the area 1981) but no significant changes in REE (QUENSEL P., 1951; HUBBARO F.H., 1975). concentrations (Fig. 8). This is more The fluid incrusion evidence from the rocks consistent with volatile-flushing depletion of the CGA, on the other hand, shows the than partial melting, although there is presence of abundant CO2 during this later evidence of some limited anatexis. However, event. The quartz of the charnockite the quartz grains of the granulite fades components contains 75-95% CO~ gneisses uncharacteristically contain no CO2 inclusions, the granite 60-70%, associated, fluid inclusions but only brine (ToURET J.L.R., but not mixed, with concentrated brine 1971). There is, therefore, no direct evidence inclusions. This confirms the dissociation in BASIC INTRUSION, CHARNOCKITE·RAPAKIVI GRAN ITE PLUTONISM AND CRUSTAL DEPLETION ETC.. 55l both dme and mechanism of the in situ country rock depletion and the CGA-type of magma generation and fractionation, as well I as the differing hydration-s tates of the crustal CiU' rocks affected. The change in type of the basic magmas active during the shearing-related, late-tectonic period to a mott fractionated sequence (Fig. 7), with a calc-alkaline/calcic trend, is also significant. , Conclusions , I The rocks of the southern segment of the I, co..... 2 I South-West Swedish Province display crustaJ , I I Hilt CO depletion processes of diffettnt types; always , 2 I linked with the accession of mantle-derived ,IGran ullt' Granullt' I basic magmas. I ~",O : The intrusion of hot magma into the , already high grade metamorphic rocks of , ~ CO2 : the crustal segment now exposed at Varberg ______J ...... 1I____ - produces local prograde metamorphism from Metabcult, upper amphi1x>lite to granulite facies , Hilt largely by mineral dehydration reactions. The expelled water caused metamorphic / metasomatic transformation of the basic Undtrpln'lf G.bbro magmatic rocks to amphibolite and garnet­ amphibolite, subsynchronous with their emplacement. The formation of. ductless aplite may also relate to this hydrous volatile phase. Bas.ltlc Magma The immobility of LREE in the granite from Mantlt gneisses during their transformation in situ to Fig. 9. - Schematic SYllOptiC representation of the charnockitic granite gneiss (Table 1 and Fig. mood for basic intrusion, charoockite.granite plutonism and crustal depletion, south·west Sweden. 8) restricts the probability of extensive partial melting during this depletion. There is no evidence remaining of a significant COO2-rich vapour phase to infiltrate and concentration of CO2 in the volatiles at that deplete the country rocks would be expected time. (MYSEN B.O., 1976; MYSEN B.O. et aJ. , High temperatures were maintained, or 1976). In the case of the Varberg complex, regained, during the late-orogenic period of however~ the fluid inclusion data suggest that shearing deformation by the intrusion of a the excess CO2 from the chamockite remains further suite of basic magmas aJong the dissolved in the evolved granite magma whose established conduit zones. These fractionated quartz grains crystallised with 60-70% CO2 magmas introduced a CO2,rich volatile phase inclusions . This implies low polymerisation in to the evolving system, which became the granite melt and maintenance of high concentrated in the developing anatectic melt. temperature and pressure (MYSEN B.O., Buoyant rise of crustal rocks, disaggregated 1976). The crystallisation of the granite in by partial melting, led to the segregation and close association with the charrockite suggests fractionation processes described to produce that the granite magma was not H 20- LILE-depleted charnockite and LILE­ sarurated. The H20-saturated granite solidus enriched alkaline gr.uU,e (Table 1). During the lies below the temperatures (700-800°C) evolution of the acidic pIu tons, release of a indicated by the contemporary basic magma "2 HUBBARD EH.

TABLE 1 Mean major oxide and trace element compositions for the ma;or rock units from Varberg. Maior oxides in wt%, trace elements in ppm. REE by INAA, othen by XRFS. Total iron as FC20J' VC .. Varberg Chamockite; AGC(j) and AGC(c) = Ape/viken·Cetter6n Chamockite fine·grained matrix and coarse segregations respectively; re = Triinningeniis Chamockite; YG = Torpa Granite; GC = Granite Gneiss; ecc = Charnockitic Granite Gneiss; Ba!l "" early basic introsions; Bas2 = later basic intrusion

AGelf) AGeCc) ro 00 BASI IASl ", ", "" " • .. • • " " 5,02 58.6 St . 4 63. 4 , 70.6 • , ..., SII.7 T,Ol ... .., .., ...., ., " ., ".., , , L' .01. 1203 IS .3 13.1 H .] 15.5 1(. 1 , 16.1 16.8 ' .:Ol , u u L. ,• 10.l .,.. ., ., ...., ...., " ., ...., " ., ., "" ... .., ..,... L', ..,.. . , ... ••• ... 'c.." .., ... •• ... 11. 2 11. 2 11. 20 ...... ,.. .., .., ••• u ... .., .., •••• u .., ... L' ... "P2.0S . ••• ., ., , ., ., ., . •• ·. .. "~ " " "." '"" '" ,.." ,.." .. ".. 2'"161 1522'" 14 72 UP'" 11'"40 U t1 m ... ". '" ". " ... •" '"" " " " '".. " " '". ". '" '" '" .. ".. , " " .." " .. " " " '" " "Th ", , ", ", " ", " , , ,,. .. , .., , "• , •, , , ,. m '" '"" ... '"" ". " " " '"" ,." .. .. " " " "• ", ", ", ~ ", , "• ", ", , • , " , , ,• ", , •, '" , , , , , , , '"" TABLE 2 The geneml mineral assemblage ofthe rock units. Rock unit ablm:vitltion! are as in Table 1. Within each unit the minerals are grouped into felsic, mafic and accessory minerals and are arranged in rough descending order of abund4nce within each group. pl :o plagioclase; pl* = antiperthitej mp = microperthite; mi = microcline; qz =quartz; by =bypersthenej di = diopside; hb = hornblende; bi = biotite; gt _ garnetj ap _ apatite; zi _ zircon; JP = sphene

ROC k Un H Gen.ra l M.neral A ••••b lag. GO .,. ". pi ; O • • hi.. "''', H . p l O, q ~ .b ".] l i. OOC , .p; >0 . ">. di. Dr" , ." p l O, ql ; >" h b; Dr •. b i, ~i , ... AGe: p ."i" , 1,10. ".oH • "> . b i; ore." • .,. "i. , " .. ; .. TO ." p i " , " >0 , hy ; Dr • . O' , ." ".. ; ". " ", ". ro ai , ", pI: O. , hb; Dr., ., . ".. ., . s .. . 1 ,', ,, ~ ; >0 . d i. hy; ore, .,. S... Z q z ; " , >,. >0. gl, Dr" e.. .,. " , ". cryst allisation and the granulite fades volatile phase associated with the basic magma metamorphism of the country rocks. The influx was water-poor and carbon dioxide- BASIC INTRUSION, CHARNOCK1T&RAPAK1VI GRANITE PWTONISM AND CRUSTAL DEPLETION ETC. 553

rich, suggesting that there had been d~per HUBBARD F.H., W/OTLEY).E. (1978)· Rapakivi Vilniu, level crystallisation of amphibole to «fix» anorthosite and chIIlmockitic plutollism. Nature, 271 , water. In addition, the crustal rocks affected pp. 439·440. must already have been water-depleted. Under H UBBARD F.H., WIUTLEY ).E. (1979) . REE in chamockite and associated rocks. Lithos, 12, pp. 1· t I. «normal» conditions, following the model of LAMa W., VALLEY). (1984) . Metamorphism of reduced FROST B.R. and FROST C.D. (1987), the granulites in 10w.COJ vapour-free enrivonments. granite generated by basic magma-triggered Nature, 312, pp. '6·,8. a-?atexis would be water-saturated, pass to MOl/REN E., LARSSON W. (1968) . Beskritlning till kartblaikt Laholm. Sv~riges GeoL Unders., S ~r AI, higher levels before crystallising and be 197, pp. 1·42. dissociated from its cumulate-restite MYSEN B.O . (1976) _ The ro~ 0/volatikl ill silicau mefl1: charnockites. solubility 0/ carbon dioxitk and water in feldspar, After the main orogenic activity, which pyl"Oxene and foldspathoid melts to JOKB and 1625°C.Am. J. Sci., 276, pp. 969-996. established the general character of the MYSEN B.O., EGGUR D.H., SEITZ M.C., HOu,oWAY metamorphic regime of the southern segment JR. (1976) . Carbon dioxUk in Jilit:au melts and cryJlais. of the SWSP, basic magmas continued to be 1. Solubility _asurements. Am., )., Sci., 276, pp. generated in the mantle, formed a petrological 4"·479. PRIEM H.N.A., BoELkIJK N.A.l.M., HEBEDA E.H., crustal underplate, and crystallised VUDURMAN E.A.TI/., VERsc/mu RH. (1973)· Rb· amphiboles. From this evolved, fractionated, Sr in~tigatiom on Precambrian granites, granite gneism sub-crustal magma source, CO2"rich, H20- alld acidic metavolcanics in central Telema,k: poor, hot magma leaked into the crusts during metamorphic ~tting of Rb-Sr whok nxlt systems. late shearing tectonism to generate the Norges Geol. Unders., 289, pp. 37-B. QUENSEL P. (19'1)· Thecbamocki~smesofthe VarMz charnockite-granite associations from the district 011 the south·fUn/m>l coast of S~ . Ark. already depleted crust now exposed in south­ Mineral., Gee!., I, pp. 229·333. west Sweden. The model proposed IS SAMUELSSOH L. (1980) - Ma;or featurt"S of ~ Proterozoic symbolically represented in Figure 9. of the Gotebo'l rPgion SweIkn. Geol. Foren. Stockh. Filth., 102, pp. 141 ·144. SAMUELSQON L, AttALl. K.-I. (198') . Proterrnoic REFERENCES development of Bohusliin, south·wes/m>l Sweden. In Tobi A.C., TooretJR.L. 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