Alkaline rocks from continental Brazil

Earth-Science Reviews, 17 (1981) 135--154

135

Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

Alkaline Rocks From Continental Brazil H.H.G.J. ULBRICH and C.B. GOMES

Instituto de Geocigncias, Universidade de S~do Paulo, S~do Paulo, SP (Brazil)

ABSTRACT Ulbrich, H.H.G.J. and Gomes, C.B., 1981. Alkaline rocks from continental Brazil. EarthSci. Rev., 17: 135--154. The present literature review on Brazilian alkaline rocks stresses mainly the petrographic and geologic aspects. At least eight different rock associations are represented. Agewise, four groups are found among southern Brazilian outcrops: an older one, about 240 m.y. only, that is still poorly known; the massifs clustered around Jacupiranga, about 130 m.y. old; a few occurrences 100--110 m.y. old (Tunas, Itapirapua); and the youngest and most important one, with an age spread from about 80 m.y. to about 53 m.y. Recent research shows a clear tectonic control -- both on local and on regional scales -- of alkaline occurrences in southern Brazil. Alkaline magmatism was set off by pre-drift and drift activity and is, at its onset, geologically related to basaltic activity. Emplacement of many massifs is also locally controlled by old lineaments (e.g., in the Minas Gerais--Goi~s belt), as is emphasized by geophysical data. On a petrographic and chronologic basis, several alkaline provinces are distinguished in southern Brazil. Preliminary data on the Cambrian--Precambrian rocks from southern Bahia State (a province with undersaturated syenites and litchfieldites) and from cratonic areas in northern Brazil are also presented.

INTRODUCTION

Widespread attention has been paid, in the Brazilian literature as well as in international publications, to the striking suite of assorted alkaline rocks dotting large segments of the Precambrian basement in southern Brazil. The interest in those rocks has in the past been stimulated by European petrographers, mainly by Rosenbusch, Derby and colleagues, who assigned to new rock types the locality names from which t h e y were collected: jacupirangite from Jacupiranga, tinguaite from Tingu~, bebedourite and salitrite from Salitre. Since these descriptions from the 1880's and 1890's, a vast a m o u n t of literature has been added, especially in the last t w e n t y or so years, most of it dispersed in Brazilian publications and these are usually unavailable to foreign readers. To the classic localities in southern Brazil, dozens of newly discovered occurrences were added (Fig. 1), and it has alSO been shown that other alkali p r o v i n c e s - geologically still poorly k n o w n - are found in southern Bahia State (Fig. 1) and on the fringes of old Precambrian cratonic structures in northern Brazil (Fig. 2). Additions to our knowledge of alkaline 0012-8252 /81 /0000--0000/$ 05.00 © 1981 Elsevier Scientific Publishing C o m p a n y

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r o c k s c a m e m a i n l y f r o m studies o n a b s o l u t e age determinations, f r o m an intensive search for m i n e r a l i z a t i o n associated w i t h certain specific alkaline bodies, and f r o m s y s t e m a t i c regional studies w h i c h , in t o t o , d e v e l o p e d a g e o l o g i c frame o f reference into w h i c h the origin and e m p l a c e m e n t o f alkaline rocks, at least t h o s e o f s o u t h e r n Brazil, can be fitted. On the o t h e r hand, petrological generalizations o n a broad front can n o t as y e t be a t t e m p t e d ,

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since detailed petrological investigation of individual massifs is still at an early stage, with some notable exceptions (such as Ipor~, Itapirapu~, Jacupiranga, Poqos de Caldas and a few others). Stress will be laid in our review on geologic and petrographic aspects, within the scope of the available data. Within this context, information has been compressed mainly into tables, figures and graphs. Many maps of petrographically interesting localities are unavailable to foreign readers; most are reproduced here and may be completed with others easily accessible in the international literature, such as those of Polos de Caldas (Putzer, 1976), Jacupiranga (Melcher, 1966) and others (see Amaral et al., 1967). Rock names as cited here are mostly those of the original authors, corresponding roughly to a Rosenbusch or Johannsen-type classification. Obviously, much is still to be done to unravel the extraordinary geological phenomenon represented by the repeated and protracted invasion of alkaline masses into the Brazilian basement. It is hoped that this review will not only serve the uninitiated reader in his preliminary glimpse of Brazilian alkaline rocks, but also be o f use to the specialist.

138 ROCK A S S O C I A T I O N S

Available petrographic descriptions permit a preliminary classification of Brazilian alkaline rocks into several more or less well defined rock associations (data in Tables I and II; for locations, see Figs. 1 and 2). In m a n y cases, there are indications (e.g., of vertical as well as horizontal zonation) that surface evidence m a y not be sufficient to ascribe one or the other massif to a specific association. Certainly, a definitive investigation of trends and affinities will have to be postponed till comprehensive chemical data are accessible. The different types of rock association are as follows:

Type I. A saturated to undersaturated syenitic association, with alkali syenites, pulaskites and nepheline syenites (frequently associated with trachytes and phonolites) as predominant rock types. Examples are Banhad~o, Cabo Frio, Cana6ira, Itaflna, Ilha de Vit6ria, Lages, the Mendanha district, Morro de S~o Jo~o, Rio Bonito, Soarinho, Tangu~ and possibly also Tingu~. T h e described rocks and minerals are typical of miaskitic suites (S~brensen, 1974), though detailed mineralogical and chemical data are still lacking. Type II. A subsaturated, strongly peralkaline syenitic association, notably enriched in incompatible elements, with nepheline syenites and their corresponding aphanitic types (phonolites and tinguaites) as dominant rocks. The described rocks and minerals are those of agpaitic suites (S~rensen, 1974). The only known example is Poqos de Caldas. Type III. A mafic to ultramafic, alkali-saturated to peralkaline association, with glimmerites, dunites, peridotites and pyroxenites as important or dominant rocks. Associated rocks are sometimes more felsic types (alkali syenites, malignites and shonkinites) and also strongly undersaturated and peralkaline species (ijolites, melteigites). This is a petrographically very complex association and, as far as data become available, may have to be subdivided. Three lineages are represented. One shows dunites, peridotites and pyroxenites as main rock types and includes core carbonatites; examples are the massifs of the Minas Gerais--Goi~s belt (Arax~, Tapira, Serra Negra), Anit~polis, Jacupiranga and Juqui~ {Fig. 5). The second lineage is closely related to the first one, with glimmerites as the main silicate rocks, and carbonatites as dikes and plugs (Catal~o 1 in Goi~s, Ipanema in S~o Paulo). The third lineage also includes dunites and peridotites as important rock types but is devoid of carbonatites; most of the larger massifs of the Ipor~ Group in Goi~s belong to this category (with the possible exception of Morro do Engenho). Chemical data to attempt a differentiation between silicate rocks of carbonatite-bearing and carbonatite-free massifs, are still lacking. The carbonatite occurrences at Itapirapu~ and S~o Gotardo suggest that these massifs m a y also belong to type III associations, although present-day data indicate the predominance o f more leucocratic rocks.

139

Type IV. A mafic ultramafic alkali-gabbro association. Main rock types are the sometimes dominant pulaskites and nepheline syenites, together with essexites and theralites; also frequently present are intermediate types such as monzonites (Tunas). It is still too early to pinpoint possible chemical and mineralogical relationships between type III and type IV associations. Ilha do Monte de Trigo and Ilha de S~o Sebasti~o (Fig. 7) are other possible examples. Type V. An alkali basalt--trachyte--phonolite (tinguaite) association. It is of little geological importance, though widespread as dikes, sills and minor stocks and chimneys. Examples are Barra do Pirai, the Barra do Teixeira and Sete Quedas, Campos do Jordao, Jaboticabal, Mata Preto, Pantano, Piratini and Serra do Bueno. It is surprising that carbonatite occurrences are cited for the Mato Preto area (Table I). This association may in some cases be the volcanic counterpart of either the type I or type IV associations (e.g. in Paran~ State, where Banhad~o, Barra do Teixeira, Mato Preto and Sete Quedas are all related geologically and possibly also chemically). Type VI. An alkali granite--~lkali syenite association. Itatiaia (and possible also the related Passa Quatro Massif) is the only well-known Brazilian example where predominant saturated and slightly undersaturated rocks form a border zone to oversaturated core rocks. The possible "carbonatite" vein found within Itatiaia (Table I) is puzzling. Some of the massifs recently discovered in northern Brazil (Table II, Fig. 2) may also belong to this association. Type VII. A strongly undersaturated and peralkaline volcanic association, where dominant types are such rocks as leucitites, ugandites and analcitites, with or without accompanying undersaturated basalts and phonolites. Petrographic data are still very sparse. Possible examples are the Sacramento occurrence and the Santo Antonio da Barra district. Type VIII. An undersaturated, essentially persodic association, with alkali syenites--sodalite syenites--litchfieldites as main rock types. Only two described examples are known: Cana~ in Rio de Janeiro and Itajo do Col5nia in Bahia. Litchfieldites and some sodalite syenites also occur in Mapari and Catrimani, in northern Brazil (Table II, Fig. 2), and litchfieldites occur in Goi~s (the Folha de Peixe Precambrian rocks; Schobbenhaus Fflho, 1975). AGE GROUPS

Radiometric age determinations of Brazilian alkaline rocks were started in the 1960's (Amaral et al., 1967) and, by now, most of the known Brazilian occurrences have been dated by one or the other method. The outcrops of southern Brazil, in particular, 'have been thoroughly examined; individual

TABLE I Alkali massifs of southern Brazil and southern Bahia State Locality

AZkat£ne

oe=uppen~ea

Piratini,RS

£.

~ e Rock

~sso-

(s)

ciated ores

types

Soather.

?g

Bpaz~Z

Trachyte,

none

tin~ite, phonolite Lage~,SC

65

Mato Preto,PR

67

Ne-syenite,

l~l~olite,

73

ghonolite

Jabotlcabal,Sg

64

Tingualte

Polos de Caldas,M~

53

Phonolitlc dikes Bulk of Nesyenltes and luJavrlte g~Ik of tlnguaites MarginalNesyenites and ring-dike tinguaites Early ankaratrites and as

74 BO

B7

Ribeiro(Ig71,P),Schobber~ha~ Filbo(1974,AP)

5beet-like irregular i n t ~ o n s , ~p to 12 k~ in intruding Pe~-Carboniferous s ~ d s t ~ e s .

LUflalOWn

Thee minor stocks, the largest one about 1.5 k~. in di- Train et a~.(Ig67, P}, e t e r , 25 km to the SE of B a ~ do T e Z ~ { ~ m Intrusions Cordani and Hasui 1968, localized at the fault contact between the PC Tr~s CBrre AP),Gomes e~ aZ.(1971, g),Figueiredo Filho gos granite and the Ag~ngui ~tasedi~nts. (lg77,P,personal co~ munication).

none

Caldasite veins (zircon-badGeleyite)~ ZrU-Moore (ZR-minerals, ~lybdenite, pyrite, fluorlte,u-minerals); Fe-Th-REE ore (mgnet Ite,bastnae~Ite, pyrT te,etc.~at depth, L~bearing fluOrite).

length,

Takeda(19sg,iv~)),Az~ral

un)~

carbo~tlte

Barrido Teixeira,PR

Over 30 small circular chimneys(diameter ra~)y over 500 m) , ~ i n l y int~dlng Gevoni~ C~eIeiras s~dstones, Alkaline ~ c k s also as lavas ~ d t u r f s a r o ~ d c h i ~ e y s ,

phonolite

61

References

Geological characteristics

er aZ.,(IgBl,AM).

A smll circular neck intruded into the PC Tr~s CBrregos batholith. ID km to the E,the petrographically related ~t~ Q ~ phonolite plug, Geologically related to this and f o r ~ r bodies is the nearby 8,~a~o massif, II km=, intrusive into Tr~s CBrregos granite, with Ne-syenites, alkali syenites, mallgnites,some ijolites and phonoIites (Kaefer and Algarte, 1972}.

Trein ~t al.(lg67,P), Cordani and Hasui (Ig68,AP),GemS ~t aZ. (Ig71,R).

S~II dike~ cutting lower Cretaceous Paran~ basalts.

Gemes and Valarelli (1970, AP).

An 800 kmz near-circular ~ s s i f , rbtruded mainly into PC basement, partly into Jurassic gotucatu sandstones;calde ra like str~cture,wlth marginal ring dike of early tingQa I t e s . l n t ~ i v e tinguaites and pho~olltes constitute 78]~ of exposures,nepheitne syenites Igmg%,phonolitic lavas 5%, volcanoclastlcs 3% and lujavrites and khibinites 0.5%.Ore deposition related to at least 2 cycles of hydrother~l alteration and breccia intrusion,affectlng~Inly the Inner tlngualtes,ln parts also later +ban some nephellne syenites (caldaslte veins).

Johannsen{IggB,p.155, C),Ellert(IgBg,P),Elleft et a~. 19gg, M ,

1 km ~ stock cut by trachytic dlkes,mstly covered by Recent alluvium, posslbIy related to nordmarkite outcrops of nemrbyl~/~oo~(~d=.

F~Itas(|ga7b,P),Araaral e~ a~.(1967, A), J.M.V.Coutinho (1977, personal comunicatlgn). A~ral er jZ.(1967,A), " Coutinho and Melcher ()973, MPC)

Ge,.r~es I--,o,cl,

Guimar~e$ and Dutra (Ig62,C , Amaral e~ aX.(Ig67,AM), Utsumi et aZ.(Igll,M),Gerski and Gerskl (lg74,MP), Bushee(Ig74,AMP). Pu~ zer (lg76, M).

sociated pyr~ c l a s t i c rockT.

Canan~la,SP

82

Pulaskite

unknown

llha do Monte de Trigo,SP

g0

Ne-syenite, theralite

none

Two separate stock-like intrusions taking up about 1.3 km~,cut by nu~rous dikes of lan~rophyres,rhomb porph 7ries, phonolites and several types of microsyenites.

llha de Sio Sebasti~o, gP(Fig.7)

81

Pulaskite,Nesyenite,theralite,essex ite,tinguaiTe, nordmarblte

none

Three stocks with concentric fractures,possibly with petrographic zoning+ Stocks,intrusiv~ into PC gnelsses,and later than basaltic dikes of Parana ancestry,are in turn cut by late trachytic, phonolitic and bostonitlc dikes.

Freitas(Ig47a,MP),Guimaraes(lgBO,C), Amaral e~ n!.(lg67,A),Hennies

Bj~rnberg and (1955, MP).

and Hasui(Ig68,

AMP],

Freitas(lg76,gP). Ellert

llha dos B~zios,SP

n.d.

Alkali syenite, nordmarkite

none

A stock-like intrusion,emplaced within PC gne~sses and hypersthene charnockites.An alkali syenite f)anked on 2 sides by nordmarkite borders. AS dikes,nordmarkite,syenite,bostonite,hedrumite,tlnguaite and teschenite. Possi bly related to S~o Seba~C£~o alkaline rocks.

llha da Vit~ria,SP

n.d.

Ne-syenite

none

S ~ l l intrusion into PC charnockitic rocks. Oikes of trachyte and microsyenites are abundant+Possibly related to SBo S~baec~o outcrops.

Gomes ~

Campos do Jord~o,SP

80

Tinguaite, shonklnite, n~nchiquite

none

A series of widely-spaced,scattered dikes within shield rocks, up to a ~ t e r thick.

PC

Malcherand Melcher (lg72,P), Hasui (unpublished)

Cabo Frio,RJ (Fig. 9d)

53

Pulasklte, nordnkgrkite, Me-syenite, trachyte

none

A 6-km~ stock-like intrusion into basement gneisses,with alkali and Ne-syenites as predominant rocks. Abundant late trachytic,phonolitic and lamprophyric dikes cutting both alkali rocks and gneisses.

Wright(IgOl,P),Gui~raes and Durra{ 1962,

~Z.CIg67,P)

C),Amaral et ~ . ( 1 9 6 7 ,

A),Lima(1974,1976,AMP), J.V.Valarelli(lg77,A, personal co~unicaticn).

Morro de S~o Jo~o (Casemir~ode Abreu),

73

Hornblende syenite, Ne-syenite, pseudoleucite syenite, ~alignite, tinguaite

unknow~

A 17-km~ circular stocK, intrusive into PC gneisses.Mag~ t i c breccias with malignite blocks also present. SO~ outcrops show strong hydrothe~l alteration (sericite, zeolltes,clays). Central corund~-bearing plug of trachytic breccia.

Guimaraes and Dutra (1962,C),Amaral e= ~2. (1967,AP},Lima(Ig76,A~ J.V.Valarelli (1977, A, personal communication).

Ita~na,RJ (Fig.gb}

65

Pulaskite, phonolite

unknown

A 6-km 2 elongated zoned stock, intrusive into PC gneisses. A she)l of pulaskite,often studded with pseudo)eucites,surrounds a core of phonolites and micro Nesyenites,all cut by magmatic breccias and late trachytic and phonolitic dikes.

Valenga(Igl4,P), (Ig76, AMP).

Itatiaia,RJ

66

Ne-syenite, pulaski te, quartz-alkali syenite, alkali granite

unknown

Guimar~es and Cutra (Tgl2,C),Ribeiro Filho (lg67,MP),Penalva(1961,

lingu~,RJ

BB

Ne-syenite, tinguaite, pho~llte

unknown

Zo~d body,220 km2,with Ne-syenites(in parts, pulaskite) as ~ i n rocks and a core of quartz-bearing alkali syenite and magmatic breccias,locally cut by a s~11 mass of alkali granite. Within PC gneisses,thenassif is cut by dikes of phonolite and pseudo~leucite tinguaite.A Th-REE -bearing carbonate vein,a few cm thick,was cited by Mau and Coutinho (1959) within Itatiaia massif. To the SW, the Paaea ~ ~ssif,petrographically similar. Subcircular massSf,lntrusive into PC gneisses,about 50 km~.Phonolites partly Intrusive,partly as lava sheets. Large pseudo-leucites present in m~ny tinguaites. Late dikes of lamprophyres,tinguaites and phonolites in both shield and alkaline rocks.

Lina

Graeff(IBB7,P), Derby (lBgl,P),Johannsen(193~ p.147,C),Amaral e~ ~i. (IgC7,A),Lima(Ig76,P).

TABLE I (continued) Locality

Age Rock (s) types

Associated

Geological characteristics

References

ores Tangu~.RJ (Fig. 9a)

67

Pulaskite, Ne-syenite, nordmarkite

Rio Bonito,RJ (Fig.gaB

69

Stock-like 5O-km~ intrusion.Associated are i r ~ g u l a r mas ses of mug~tie breccias and trachytes.Massif cuts P[ gneisses and is cut by ~honolitic and lamp~phyric dikes.

L i ~ (1976, AMP).

unknown

Zoned stock covering about 28.5 km).Pulaskite and local norGh.arkites are border facies,with a core of Ne-syenite, Intrusive into high-grade PC gneisses and granulites, Late trachytic,fhonolitic and lamprophyr~c dikes cut shield and massif rocks. Mag~tic breccias very rare,

Amaral et ~Z.(IBGT.A), ValenGa(Ig6D.P). Lima (1976. MP)

Fluorite veins

Irregular 3O-km z stOck,geologica}ly related to the T ~ ~ and 960 Bo.~o stocks.lntrusive into PC gneisses. About a third of outorofs is ~ g ~ t i c breccia with a trachytlc ~ t r i x , Late trachytic and lamprofhyric gneisses.

L i ~ (1976, Mr).

Fluorite veins in shield rocks,possibl~ aSSOCi ated to langua m a s s i f . -

Pulaskite. Ne-syenite, nordmarkite

Soarinho.BJ (Fig gab

n,d.

Alkali syenite, nordmarkite. ~nzonite, ~ngerite

Cana~.RJ (Fig.gel

n.d.

L i t c h f i e l d i t e , Disseminated corundum a l k a l i syenite

Mendanha dist r i c t , RJ

Sacramento.MG

~37

Ne-syenite, pulaskite, alkali syenite, phonolite

unknown

Ugandite?

unknOwn

To the 5 of T~ns~,district includes the Eerr~ ~ ~ , ~ n~e and G e ~ c ~ , the P£oo M~z~c~,and other localities, Poorly exposed.comprlses a series of s ~ l l intrusions of Ne-syenites and pulaskites, and various neck-like bodies of phonolite, among them a larger phonolitic chimney with breccias and tuffs, Intrusive into PC gneisses and granite. Trachyte. bostonite and phonolite dikes are plentiful, Ugandltic(? bentonitic of over 65 Barbosa et ire.

} lands, breccias amd turfs.outcropping as laterite;fresh ~ck in d r i l l cores at a depth m. Poorly known geologically. According to ~.(1970}.rock is akin to a micaceous kimber!

P i c r i t i c and foid-bearing known,

Morro d~s Droas,MG Taoira,MG

f~ntano,MG

78

Serra Negra,MG

82

gl

poorly

Ferreira e t a ) . (1965. MP),Amaral et ~ . ( ) 9 6 7 , A ) , L i ~ (Ig76,P)

Murta{ID65,P). Hasui (unpublished.A).Barbo-

sa et ~Z,(IgTO,CP),

Hasui and Cordani(Ig6a. AP}, Alves()gDO,P),Hasui and Cordani(196D,A),Barbosa Geisel Herz

Abatite,perowskite,pyrochlore.anatase, m gnetite(Nb,TI,Th,U.REE). vermiculite.

Alkaliolivine basalt Dunite.peridotite,jacupirangite,

none

S~ll volcanic chimney(about 50O m~),intruding low-grade slates of the Bambu~ G~up.

Hasui and Cordani(1968, A), Barbosa et =~(197~ P).

Disseminated Th-U mlneralizatlon; Pyrochlore.

Immediately to N of Salit~ stock,and separated from it by faults.Oval intrusion,about 8D km~.Dome-like structure of intruded PC BambuT Group around stock. Shonkinites and jacupirangites appa~ntly form th~n outer envelope to olivine rocks.Drilling detected fresh pyrochlore carbonatite.

Hasui and Cordani(lg6B. A),Barbosa et c:!.(1970, R).Souza Filho(Ig/~.P).

et ~Z.(1970,R),

Sobrlnho(1974.P),

(lg76,P).

carbonatite

S~o Gotardo,MG

alkali basalts(necks?);

A 35~km~ zoned circular stock,strongly doming quartzites and low-grade schists of PC Canastra Group.Some phonolites occur as lavas. Deeply weathered. Carbonatites found in d r i l l cores.

La~go(Ig54,MP), Guimar~es and Dutra (Ig62,E),

Jacupiran Dite.biotite pyroxenite (bebedourlieD.alkali syenite,phonolite,carbo natite.

shonkinite,

Arax~(Barrelro),MG

2O-km~ ~ s s i f . Core o6 alkali syenite within a border Lima (1974, Mr) zone of foliated l i t c h f i e l d i t e . Disseminated corundum near contacts and in surrounding PC m i g ~ t i t e s . Late trachyte dikes.Age unknown,but probably related to alkal i magmatismof SP-RJ coastal belt.

Two interconnected stocks,about 4O km ), intrusive

Urtite,melteigite,pulaskite, alkali gabbros, carbonatite

A suite of alkaline rocks and carbonatites found as large febbles within conglomerates of the Cretaceous Uberaba Fo~ation.Source as yet unknown and probably from a n ~ Iocality,slnce geologic arguments do not favor a link with other alkaline intrusions of the dis-

Hasui and Cordani(IgBD, A). Hasui and Hasano (IgD9.P).

20 km N of T~p~r~,a circular ~O-km~ stock, strongly doming the intruded PC Arax~ Group.Prin~ry rocks deeply weathered,ore superficially in residual crust, disseminate~ and as stockworks at depth.

Guimar~es(IgD7,f},Hasui and Cordani{Ig68,A},Da~ bosa et ~.{1970,R),Pu~

none

A series of snsll necks and dikes(c~o8 A)toe, c~Be~t~. P~t~) intruding low-grade schists of the PC BambuT G~up.Ol~vine-rich,pero~sk te and zeo re-bearing rocks,

Barbosa et aZ.(lgTD,P}, Hasui(A unpublishef),

unkno~

Rocks of a l k a l l ~ f f i n i t i e s outcrop over an area aof. several bundre~ km~,as dikes,stocks (over IOO are ~ady kno~),sillslchimneys,etc.and are collectively mapped as the Ipora Group.Great variety of petrographic types.The intrusions within PC Arax~ Group and Devonlan-Carboniferous conglo~rates,near city of Ipo r~, are G of the largest.The ~ s s i f c ~ g o 4oB BoYe presents a border zone with pyroxemites, peridetites, alkali gabbros.theralibes and essexites.and a dunitic co~.Ne*syenltes are subordi~te,5 km to SE,the smaller zpo~ M o ~ do Mayo)massif {Fig.D),about 24 km2, 14 km. from por~,the undated M~a Az~ tingua te d We (over 2 km in length ; Marques an~ Rippel,1970). The A ~ g ~ n k a dome,considered by so~ to be a syenitic massif, is interp~ted by Dietz et aZ,(1979) as a prob

Gul~r~es et az.(lgBD. P),Denni{Ig74,AMPC), Schobbenhaus Filho

Pyroxenite(jac~ pirangite), mlignite, car~onatite

unknOWn

Stockworks of pyrochlore in carbonatite;also apatlte, tltano-~gnebite (Nb,Th,U,REE,Ti).

in)o

Johannsen I93B,p.451, C), Hasui and Cordani{ g68,~

Alkali syenite, Apatite(francolite), Ne-syenite, perowski~e.~gnetite biotite fyroxen (Nb.Th,U,REE), ite(bebedeurit~), tinguaite, trachyte, carbo~tite

]ow-grade shales of the PC Dan}buT Group.Basement rocks strongly do~d.The larger stock to the SE presents w i n ly alkali and Ne-syenites,biotite pyroxenite and a s~Tl e l l i p t i c a l afatite-rich carbonatite (500 rex). Biotite pyroxenite is the main rock o f s ~ l l e r stock to the Ng. connected to the f o u r by trachyte outcrops, linguaires locally abundant, also as dikes.

Barbosa e t a~.(Ig70. R). Souza Filho {Ig74,MR).

zer(lg76.P).

Locally,barite, Serra do Buer~,GO

45?

Alkali olivine

basalt Ipor~.GO (Fig. 8)

78

Dunite,wherlite.

olivine pyroxenite,websterlte, theralite,essexite,Ne-syenite, lamprophyres

(ID75a.AR).

able as t r o b l eme.

Catal~o T.GO

Gli~rite, pyroxenite, perldetlte, carbonatite

Pyrochlo~,anatase, magnetlte,apatlte, locally derlte(Nb, REE,P,TI,Fe), vemicullte.

Circular stock. 27 km2 . intruding partly fenltized fC Arax~ mica schists.Oc~led structu~ of shield ~cks. Lateritic superficial mantle;unaltered rocks are phlo gopite gllmmerites and serpentiniled peridetites an~ pyroxenites,cut by carbonatlte (sovite)velns. Alkali syenites are subordinate.At depth.probably a carbonati t e plug capped by lO0-m thick(~etasomtic?) s i l e x l t e rock. 8 km to NW,the C~¢#)~o II dome;geochemlcal a n o ~

alles in residual mantle similar to those of Catal~o I.

Has~i and Cordani(lg68, A),Barbosa e~ aZ.(Ig70, R ,Valarelll(1971, P), Carvalho{ 974,MP).

TABLE I (continued) Locality

Santo Antonio da Barra(Rio Verde),GO

Age Rock (s) types

B5

Analcitite, analclte basalt,basanite, phonolite,lim burglte,mineT te,ugandite.-

Montes Claros de Goias, GO

89

Olivine pyroxenite,webster ire,No-syenite, essexite,theral ite,nordmarkit~

AmorinDpolis, ~gua E~ndada,GO

n.d.

Santa F~,GO

Associated ores none

Geological characteristics

References

A series of volcanic rocks, of strong alkaline affiniHasui e~ ~.(Ig71,AMP), ties,outcropplng near city of Santo Antonio da Barra. Bez et ~L(IgZl,P),Schob Poor)y known geologicaTly,they belong to the Ipor~ benhaus FilhoI1975a,APR~ Group: analcitites,basalts,phonolites{Hasu~ e~ ~Z.,(IgPl); also tuffs,limburgite and minette lavas, capped by ugandites (Bez e~ ~.,1971}.Deerlying these rocks, a vulcanoclastic facies of Uberaba Formation with phonol ire pebbles (84 m.y.).

unknown

Oval zoned 2B-kmz stock of ~he Ipor~ Group, intrusive into fenitized Devonian Furnas sandstones and PC gneis sos. Two separate cores of serpentinized pyroxenitesT surrounded by more re]sic roeks;nordmarkites are restricted to SE part of massif. Lamprophyre dikes abundant. Close by, the ?~,'o~ set of dikes of basanite, trachyte and alkall basalt.

Dez(lgPO,P ,Figueiredo and Pena{I9 3,P .Schob-benhaus Filho(Ig7Sa,AR).

Trachyte, lamprophyres, alkali basalt

none

Two small vulcanic necks with breccias and ruffs. ~g~ ~oi~ presents rocks of lamprophyric composition. Probably related geologically to the Rio VerJ~ district.

Glaser et ,=?.(I970b,P).

n.d.

gunite,~herlIte, olivine cl~nopyroxenite,~lignite, mlssour~te

Oarnierite in residual laterite,verm~culite

zoned ultramaficintrusion,with a Tango core of serpen÷ tinized dunite.Deeply weathered. Malignite and gissou~ ire are subordinate rock types.Part of the Cretaceous Ipor~ Group, geologically related to other similar intrusions (?4o~ C Z ~ da ~ o ~ , e t c . ) .

gchobbenhausFilhoI1975~ R},Barbour{Ig76,MPC).

Morro do Engenho,gO

n,d,

Dunite, pyroxenite, alkali gabbro, No-syenite

Dernierite in l a t e r i t e

A zoned stock, covering several km~,with dunites as core rocks,surrounded by ~eridotites and pyroxenites. Alkali gaPbros and Ne-syenites are later border facies. Intrusive into shield rocks and Devonian Furnas sandstones.Mapped as part of the Ipor~ Group.

Chabanand Santos (1973, P),Schobbenhaus Filho {Igzgb,PR).

ASe

]oo-~lO

unknown

Elongated intrusion, 22 km% intrusive into PC Agungui Group.Site of intrusion possibly controlled by a NW-SE alignment of 5 collapse structures. Late magmatie breccias and dikes of trachyte and bostonite.

Amaral ~t ~L(1967, A), Trein e~ ~Z.(Ig67,MP),GO ~ s v~ ~Z.(Tg71,R), Fuck (Ig7g,MPC).

Magnetite segregations within syenites

Irregular elongated intrusion,4.5 km~.Centrally located feldspar-rich carbonatites[sdvites)as small dike lets and veins. Late ~ g ~ t i c b~ccias.Tinguaites a~ dikes.

Go~s and Cordani(lg65, A),A~ral et cZ.(Ig67,A), Gomes(lg7O,AMPC),Go~s aZ.(Ig71,R).

unknown

Pear-shaped zoned stock,5 kmD(including fenitized halo) intruded into PC granite.Gradations between fenites, pulaskites and Ne-syenites.Core is b i o t i t e pyroxenite, partly surrounded by i j o l i t e s a n d ~ I t e i g i t e s , a n d with a small central s~vite plug(a few m~).Late tinguaite dikes, 105 my.old.

T~Icher and Coutinho (IgDD,MP),Amaral et a~. (Ig67,AM),Carraro et ~ . (1967,MP).

Small dike cutting PC shield ~cks

Knecht(lgDO,PC), Amaral ~C ~.(1967, A)

13 km2,

Leinz(Ig4O,P),A~ral '~ ~7.(1967,A},Davino{197~ P),Aps and BornClg75,M~

~o~p:

m.y.

old.

Tunas,PR (Fig. 6)

110

Alkali syenite, pulaskite, Nosyenite, alkal i gabbro, ~nzonite,diorire

Itapirapu~,SP

IO3

~e-syenite, pulaskite, ~lignite, melteigite, carbonatite

129

No-syenite, puTaski~e, b i o t i t e pyro xenite+ijo] ~ ite,nmltelgite,carbonat ite

Anit~polis,SC

(IO5)

V~edade,SP

122

Shonkinite

Ipanema,SP

123

GIimmerite, pulaskite, lusitanlte, aeglrin~te, carbonatlte

Apatite, ~gnetite

Juqu~(Serrote),SP

127

Olivine pyro xenite,alkaT l i gabbros, No-syenite, ijolite, n~Iteig~te, pulasklte, carbonatite Tinguaite

Apatite, ~ g n e t i t e , pyroehlore; l o c a l l y , barite

Apatite mined in residual cap,later as disseminated phase in carbonatite.

(Fig. 5)

none

Maciel(Ig52,MP), A~ral et ~.(1967,A), Born (Ig71a,b, MPC).

Itanha~m,SP

130

Jacupiranga,gP

13O

Pyroxenite(ja cupirangite)T peridotite, No-syenite, ijolite, carbonatite

P~o de A~car,MT

gOP 238

Ne-syenite

unknown

See

Ne-syenite,

none

Representatives of a group of poorly known alkali intrusions.ltarantim is a large complex massif,covering several tens of km~,intrusive into PC migmatites,with alkali and Ne-syenites as dominant rocks. The rest are smaTl,scat tered masses of trachytes and alkali syenites, intrusiv~ into PC Jegui~ granulites.

none

N S elongated body,about ? kmLAlbite predominant over Fuji~ri{Ig67,MPC),Cor microcline in l i t e h f i e l d i t e , s o d a l i t e often a late mineral. dani et ~Z.(lg74,AR). Intrusive into PC Jequi~ Complex. Three separate ~ssifs,coverlng about 26 km2, elongated Souto(Ig72,MPC),Cordani along a N-S line. Intrusive into PC Jequi~ Complex. e~ aZ.(1974,AR).

Itabuna,

Itarantim, Gurup~_Mirim, Ita~are, llheus

Pig. l

]taju do ColGnia

665

Potiragu~

650

none

intruding fenitized PC schists and the Permian Tubarao sandstones.Deeply weathered surface,with scattoned magnetite and s i l e x i t e blocks,and disseminated apat ire in laterite.A core of g l i ~ e r i t e , w i t h late veins OF aegirinite and barren s~vite veins and dikes, surrounded by a broad fenitie halo,the inner portion of i t with apat ire and glimmerite veins.Shonklnite dikes cut shield ariaalkaline rocks.Quoted age is minimumage,since determined on biotite from shonkinite. Zoned stock,14 km:,intruDed into partly fenitized PC gneisses,with a ~ i n mass of olivine pyroxenites a~d alka l i mela-gabbros,and a zoned earbonatite core{~ km~),flan~ ed in part by an i j o l i t e - m e l t e i g i t e rim.Outer carbonatit~ is an apatite beforsite,inner one a banded ankerite-dolom ire carbonatite.Tinguaites and lamprophyre dikes cut inT trusive and shield rocks.

alkali syenite, trachyte

LitchfieTdite, sodalite syenite,tawite No-syenite, sodalite syenite

none

,~g,, gro,,p~ ~ncrdin~ =2 Fi~.4~ for ~t~te a b ~ e v i ~ i o ~ . ~e~ F±g. ~.

Dikes cutting shieTd rocks.ln the same area,scattered out crops of olivine sdvite dikes. -

A~ral et ~!.(1967,A), R.Ellert(Ig?7, personal communication) A 65-km~ oval shaped zoned intrusion,w~thin PC micaschists and granodiorite of A~ungui Group.Halo of fenites grades MeIoher(IgS4,MP), MeT into Ne-syenltes,in turn followed by pyroxenites and, at cher(Ig65,1966, MPC} , northern half,by peridotitie core.Southern part showswith Amaral et ~ . ( I g 6 7 , A } , in pyroxenite a crescent-shaped i j o l l t e area and a centra~gordani et c,I.{1971,R), apatite carbonatlte(sOvite)plug,O.25 km2,emplaced during AmaraIIin press,A). two intrusive phases. Poorly known,one of a series of alkali massifs of south- Putzer and Van Den Boon western Mato Grosso. Surrounded by recent deposits of Pa- {Ig6D,P),A~al et ::. raguay River. (IgDZ,A).Comte and Ha sui(IgTl,kP). Cordani ~t ~.(Tg?4,AR)

T A B L E II Preliminary data on alkaline o c c u r r e n c e s in northern Brazil a) L o c a ! ~ i e s State

a n d geologlaaZ

¢harae~erlstlc~

6f

occm,~nces

a~

the norchae~

border of ~he G u i a n a

eb£¢ld

o f ['ar~:

(]806 ~ SB, Rb/SP): ~ near-circular outcrop of Nastings~tic a l k a l i syenite, U km in diame ter,w~thin the PC Uatum~Group,Associated ores unknown (TUIXEIRA et a~.,IU/6,AP; MONTALVAO, 197U,R)T

Er*pea~P~

Caoho~ro (1BUG, Rb/Sr): ~solated outcrops of a l k a l i syenite, geological

c~aracteristics unknown(TA~

51NARI, I977, A, personal communication).

~u~u~ (102U ± 2U, K/Ar): IU-km~ i n t r u s i o n , on the Serra de AcaraT, at the boundary with the

Republ i c of Guyana. Nepheline syenites are dominant rocks, poorly known geologically (IUULER e~ ~E., Ig7s, AP; TEIXEIRA e t a~., I976, A).

Maw~ona{ (not dated); probabTy also related to a Precambrian a l k a l i magmatic cycle of northeastern ParS. Two oval shaped intrusions w i t h i n the PC Vila Nova Group the largest covering about UU km~ the smaller one about U km~. Deeply weathered; l a t e r i t e s show high anomalles in Cr,V,Zr, Ni and Ta. Petrography unknown(ultramafic alkaline and related rocks probably dominant)IISSLER ~C aZ., ~gTS,P). Ma~e~ (not dated): a c i r c u l a r topographic high w i t h i n shield rocks, close to the former l o c a l i t y . Deeply weathered,laterite with hlgh COntents of Cr,V,Ta and especially Ti(dominant rocks probably u l t r a mafic) ([SSLER et aZ.,]g7U,P). A~ap~ F e d e r a l T e r r i t o r y :

(7335 ± 39, 1C80 + 63, 1537 ± 38, a l l Rb/Sr}: three small c i r c u l a r stocks (diameters from 200 to 50U meters).Dominant types are nepheline syenites, a l k a l i syenites and )itchfieldites. Associated ores unknown (LIMA et a~.,197A, PR; ISCLCR ¢t a~.,Ig75,AP).

Mapari

Rorai~a Federal Territory;

(IOU, Rb/Sr): oval shaped stock, about 2 km~, w i t h i n shield focus, w~tU sodalite-nepheline syenites and l i t c h f l e l d i t e s as dominant rocks; phonolite dikes p l e n t i f u l . Probab)y related to a cycle of basic t h o l e i i t i c maBmatism (Apotei Formation) as a late dlf~erentiated phase (SANTOS and SALAS, I974, P; ISSLER et a/.,1U75,AP; BASEl and TEIXEIRA, 1975, A).

Ca~ti~arl

State OU Amazonas Se~ssa~°"ions In°t dated): close to the city of Sao Gabrlel da Uachoeira, a set of 3 circular deures, the largest covering about 16.5 km~. Possibly, carbonatites and a series of associated a l k a l i rocks. High anomalies of Nb pyrochlore), Zr, Ce, La, etc. in l a t e r i t e s (ISSLCR e~ aZ., I975, P). b) L6oa~it~e~ State

and ~eo~ogCoal

characteristic~

of ooe~rcne~

at th~ northern border of the Guapor~ orato~

oU Hato G r o s s o :

Canc~md (I175 ± 15, Rb/Sr; 11U9 ± 57, K/Ar): a large intrusion of a l k a l i syenite(mainly,nordmarkites);

oval shape, 21 km Uy IU km. Strong geocbemica] anomalies of personal communication).

T i , Zr, Nb, eta. (UASEI,)U77, AP,

State oU Amazona~:

Swru,durf do~e (1260, Rb/Sr): a large dome-like structure, 700 km~, affecting the PU Tries Pires and BeneficenCe Grouu$, l o c a l l y pierced by a series of plugs, necks an4 dikes of nepheline syenites, a l k a l i syenites and l u s i t a n i t e s , and capped in ~laces by some trachyte and phonollte flows. Poorly known geologically, but t e n t a t l v e l y associated with the Canam~ syenitic intrusion (IWANUUH, 1976, AP).

T A B L E III R e f e r e n c e s cited in Tables I and II ALVES,B.P.,1960.Dep~, Nae.Pvod.Min.~D~.F~.P~od.M~n.;B01.lO8,1-48; APARAL,G.,1947.P~e,&J~pOSi~ on Ca~bona~eee,Pogos de Caidas,Brazll(in press);AMARAL,G. BUSBEE,J.;CORDANI,U.G. ;KAWASHITA,K.and REYNOLDS,J .H. ,lgBT.Geo~h~'~.Co*~ehlm.Ae~a,31:117-14Z; APS,V.and BORN,if, ,1U75.CeoLe ~ a Z . ,37:BS-34;BARBOSA,U.;BRAUN, O.P.G.and DYER,R.U.,lg70.L~p¢. N=e.P~d.MCn.,D~v.~om.pvod.M~n,,B01,136: 1-336; GARBOUR,A.P.,I976.I~Gt.Geoc.~nC.,USP;"LivreDoc~ncia" Thesis{unpubllshed);UA L SEI,H.A.S.and TEIXEIRA,W.,197U.An,XConf.Cec~.Inte~aCanae, l:4S3-#73; BEZ,L.,1B7U.XXIYCOnge,B~.GeoZ,,Bol.]:g61-364 (Abs.); BEZ,L,;GUIMAP~ES,J. and 6UIMARAES,D.,IB71.An.XXV Congr.B~.Ceol..,Z:lZl-lUG; UJ~UUUG,A.d.C.and ELLERT,R.,1955.An,Acad.b~.CCIne. Z7:lUB-187; BORN,H.,1U71a.I~eC.Geoe~ne.,USP, D. Ue. Thesis (unpublished). BO~,H.,1971b.AmXXV Congr.gvaG.GeoL,l:BBg-BBU; BUSHEE,J,,lg74.oniv,cazuflo~£a at Ber~Ie¥,Ph.O.Dissertation(unpublished);CARRARO,C. C.;ISSLER,R.B. and FOR~SO,M.L.L.,1967.U~I~.Fed.E~o ~z~do do suGPubl.Esp.16:~'B5; CARVALHO,W.T.,Ig74.A~.XXVIIZCo~gv.B~e.Geo~.,S:107-1Bg; CHABA~,N. and SANTOS,J,F.,IU73.XXVZ7 Co~r.B~.~eoE,,1:B7-SG(Abs. ); COMTE,D. and HASUI,Y.,lB71.Ree.Bz~e,GeOC.,I :33-~3; COROANI,U.G.and HASUI,Y.,IUG8.An.XXII C~gr. Bvae. ~eo~,, 149-153; CORDANI,U.G.;UURNAT,M,;TEIXEIRB,W.an~KINOSGITA,H,,IgTg.A,,XXVZIICo~gr,B~.OeoL,U:BS3-259; CORDANI,U.G,;GIRARBI,V.A.V,;GOMES,U.G.; LELLIS~H.S;MELCHER,C.C.and MELPI,A.j,,IU71.An.XXV C~v.B~.GeoZ.,I:IU3; CUUTINHO,J.M.V,andMELCBER,G.C.,Ig73,Rrv.B~.~o~,,3:2~3-?S~; OANNI,J,C.M.,IB7U.Un~e. Pa~s-Sud, C~n~re d'O~e~,D.Sc.Thesls; DAVINO,A.,1974.~neC.Geo~.,USP, UOI.6:I29-144; DERBY,O.A.,189I.C~t.Jo~,Geo~.5oo.~n, B7:UUI"265; DIETZ,R.S.; FRENCH,B.and OLIVE[RA,M,A.M.,IU73.XXVZIC~gr.~z~e. Geo~.,t:10~-IOg(Abs.); ELLER?,R,,1969.BOL~ae.EiLCC.Let.,USP,~eOZOgCa,IB:5-63; ELLERT,R.;CUUTINHO,J.M.V. and UJ~RRBER@,A.J.S.,IBUB. In: ELLERT,R.,IBsg; FERREIRA,E.O.; ANGEIRAS,A.~.and ARAUJO,G.G.,IgBB.De~C.Nac.~od,M~n.,~V.GeoLMBn.,Av.gG:I'dB;FIBUEIRE~,A.J.A. and PENA,B.S.,Ig73.XXrH Co~r.B~e,Geol.,Bol.l:lU3-1OS(Abs.); FRUITAS,R.O.,Ig47a.~L~a~.~Y~.CGLe~.,U~P,GeoZ~a, 3:]-209; FREITAS,R.O.,Ig47b.BOI.Fac.~C~.C~ Let,,USP,Geo~o~a,g; FRCITAS,R.O.,Ig7U.In~,Geo~@Ieo,Bol.I:I"17~; FUC~,R.B.,197U.Ine~.~oc~nc,,usP,U.Sc.Thesis(unpubli~hed); FUJIMORI,S.,IBU7.Dep~, Nap. p~d,~n,,Z)~g.?om.Prod.~n.,Notas Pre1~m.e Est.,IU1; 6EISEL SOBRINBO,E,,1974.C~,~O,~.N~oZe~,UOI.IO:I-IU; ~ASER,I.;ALMEIDA,J.P.and BEZ,L,,Ig7Oa. XX~¢ C~gr, B~.GeOL ,Go1.1:338-340(Abs,); CLASER,I.;BEZ,L.;MARQUES,V.J,and RIPPEL,C.,1970b.xxzvCo~v.B~a.Geo~.,Uo1.~:39; GOMES,C.B.,IBTO.BoZ.I~t.Gaoe,Ae~n., usG 1:77-197; GOMES,C.U.andCORDANI,U.G.,1965,An.Acad.h~e. OC~ne.,37:U97°501; GDMES,U.B.andVALARELLI,J.V.,Ig7U.XXIVCon~v.B~.GeoL,Bo~.]:33S-336(AbS.);U~ MES,C.B.;DAMASCBNO,E.C.;MELCHUR,G.C.and BO~,H.,1967.XXZ CO~r.B~.Geo~,, 65-66 (Abs.); GDMES,C.U.;BITTENCOURT,I.;CORDAMI,U.G.;D~SCBNO,E.C.;MELCHER, G,C. and MELFI,A.J.,IglI.An. XXV Co~z..~.~o~,,1:99; GORSKI,V.A.and ~RSKI,E.,1974,Co~.~c.~n,#UO~e~,Uol.13:i-g3; GRAEFF,F.,188/.Ne~s J~vb,~n~L,2:222-26~ GUIMARAES,D.,Ig57.pep~.~a~.P~d.~m,~,~om.Prod.~n.,Bol.lO3:l'37; GUIMAR~E$,O.,IUBU.Osp~.Nao.P~od.~'n.,D~U.~,P~d.~n.,UoI.I07:I-41O; CUIMARAUS,D. and DUTRA,C.V., 1UC2.Dept.Nao.P~d.M~n,,Dgp,~.P~od.~n.,Bo1.11U:4S-7U; GUINAPJ~EU,6.;GLASER,I.and MAUQUES,J.,IUUU.M~r,Met~.,48:11-I~; HASUI,Y.andCUUOANI,U.G IUUG.An.XXZI Co~r.B~. GeoL,13U-1~3; HASUI,Y.andHASANO,S.,I969.An.Aoad.b~a, CC~n~.,Bl:lBU'154; HASUI,Y.; DYER,R,C,and IWANUC~,W.,IB71.An,XXV C~gv. ~ e . ~aoZ,,~:BBg-BsU; HENNIEU,W.T.and HASUI,Y.,19UG.An.XXIICongr.5~.GeoZ.,14U-148; HERZ,N.,1976.U.S.GeoLS~e~,P~o~.P~pe~,uBg'E,Gp; ISSLER,R.S.;LIMA,M.I.C.; MONTALVAO,R.M.G.and SILVA,G.G.,1976.An.X ~onf.GeoZ.ln~er~wC~,1:103-1UB; IWANOCH,W.,IgTC.XXIX Co~v.Bvae,~eoZ., 196(Abs.); JOHANNSEN,A.,IggB,A d~eez~pt£~ pec~g~hu of the ~ e ~ ~cke. Vol.IV.Th~ ~Cv, of ChCga~op~aa, Chicago,l-523. IC~EFUR,L.Q.and ALGARTE,J.P. ,IBT2.An.XXVJ CoM~r.B~e.GeoEI,I:UI-6~.KNECHT,Th., 196~S~B~Ge~8~l`U:7l-7U;LAMEG~,A~R`'1954~DeP~ac~d.MCn~o~M~n.~N~tas Urelim.e Est.,79:|-12; kEINZ,V.,194O.DepC.N,Z~,P~d.~n.,DgV.F~,P~d. M~n,,B01.88:7-52~ LIMA,P.R.A.dos S,, 1974.~n,XXVII Congr.B~.Geo~,,Bo~,l:17U-181; LI~IA,P.R.A.dos S,,Ig7U.Se~a ~ Betud~e C~o~g~e.,Unlv. Fed,Uural Rio de Janeiro,Deut.Geoci~ncias, 205-U~B; CI~L~'M~C~;N~NTALVAU~R~M~G~;ISSCUR'R~U~;~LIVUIRA,A~U~;BASU],M~A~U.;ARA~J~J~F~V~andSILVA,G.6.,IUlB.P~je~o R ~ , V o l . 6,1/I-I/12U; MACIEL,P.,IB52.Soo,B~e,~eo~.,Uoi.l:3-14; MARQUUS,V.J.andRIPPEL,C.,IUTO.xX!V Conrr.B~s. GeoZ.,1:121 (Abs.);~U,N.andCUUTINHO,J.M.V.,IgU9,Soc. B~e.~eoZ.,Bol.8;UI-UB; MULCHER,G.C.,IBU4.L~p~.Na¢.P~d,M~n.,~p.CmoZ,M~,.,No~aS P~lim.e Est.,#A:I-21; MULCHER,G.C.,196U.BoZ.~.~Z,O~,Cet.,pgp,~o~og~a, 21:1-73; MELCHER,G.C.,IU66.C~O~tI~# - ~utrZe O , F , ~ Cr~c~-~ d.(e~tor#):lUg-IBl ,John Wiley & SaneLtd.N~ York; M~ELUHUR,GIC.and CObq'INHO,J.M.V., IUG6. SOO.~r~.Geo~.,UOI.15:59"93;'MELUHER,G.C.and MELCHER,U.A.,Ig7B,XX~ICO~gr,BZ~,GeOL,UOI.I:ZI6-BJ7 (Abs,); ~NTALUAO,R.M,G.,Ig7U.Re~.B~,GeOe,,U:230-2U5; MURTA,R.L.L.,1965.An.a~d.b~.C~o.,37;BB3-470; PENALVA,F.,19U7.BoL~aO.~Z,CC.~et.~U~,~eo~og~a,UU:Bu-Igu; PUTZER,H.,IUIU.~eraZZoge~Se~eP~n~en ~n S~r~ka,Sc~ei~e~bar~'ec~e,Stuttgart,316 p.; PUTZER,H,andBO(04,vanden G.,IUUU.C~o~.~.flB:423-44~; RIBEI~O,H.,Ig?1,1~er~n~a,Gee~og~a,4:SU-71; RIBEIRO FILHO,E.,IU67.BOL~ao.E~I.C~.Ca¢.,USP,GeOZO~a,BU:S-U3; SANTOS,J.O.S.and SALA$,H.T.,197A.XXFIIZCo,gv.B~e.c~oZ.,1:412-413 (~)S.);SGBOBBENHAUU FILHO,C.,Ig74. Depr.Gac,PeodJB~n.,1-UB; SCBOBBENMAUSFILHO,C.,IU75a.DepC,N~.~d.~n,,]-76; SCMOUBUNHAUSFILHO,C.,197Ub,~epc.#ae.~d.M~n,,i-74; ~UTO,P.G,,i97U.l~t,~eo¢ ' ~ n ~ , USP, M.S.Thesls, 1-U5; BOUZUFI LHG,J. G.C.,1974.Com.N~. ~ . Nuele~, UOI.9: 1-41 ; TAKB~,F.K., I g4B.~ept. Ea~. G~o~.C~¢ogr., Santa Catarlna;TEI XEI RA,W.;U_A SEI,M.A.S.and TA$SINARI,C.C.G.,IU7C.XX/X C~.B~,G~o~., 193 (AbS,);TREIN,E.; MARINI,O.J.and FUCK,R.A,,19U7.BoZ.~aI~.C~oo,,Ug/~G:326-347; UTSUMI,O.; GLIVEIRA,A.G.;PARISI,C.A.and WILLIAM,D.D,,1971.XX~ Co~r.a~e.ceoL,Bol,Usp.U:7-13; VALARELLI,J.V.,IgTI,I~t.G~oc~e~,,UGP,"LIv~ Doc~n¢la" Thesis (unp~UIisBed);VALEN~A,J.G.,IgUg.An.A~.b~.C£~na.,41:U41 (AbS.);VALEN~A,J.G.,IU74.gX~IIIOo~g~.B~,~o~.,UOI.I:4UT"431 (BUS.); WgiGHT,F.G.,1901,~e~e~k'e Mgne~Lpe~v.~.,N.F.UO; U33-BSU, 273-3~O.

144

data are presented in Fig. 3, and a cumulative diagram is shown in Fig. 4. S o m e ages have been considered as t e n t a t i v e - especially those of Bahia and northern Brazil -- and interpreted with caution (for a critical discussion of ages, see age references in Tables I, II and III, and especially Amaral et al., 1967; Cordani, 1973; and Herz, 1977). In southern Brazil, at least four well
~

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Fig. 3. A g e d i a g r a m o f i n d i v i d u a l a l k a l i n e m a s s i f s f r o m s o u t h e r n Brazil. L i s t o f r e f e r e n c e s : Z -- A m a r a l et al. ( 1 9 6 7 ) ; 2 -- C o m t e and Hasui ( 1 9 7 1 ) ; 3 = A m a r a l ( 1 9 7 4 ) ; 4 = C o r d a n i and Hasui (1968); 5 = Gomes and Cordani (1965); 6 = Hasui and Cordani (1968); 7 = H a s u i e t al. ( 1 9 7 1 ) ; 8 = S c h o b b e n h a u s Filho (1975a); 9 = Danni (1974); 10 = Bushee ( 1 9 7 4 ) ; 11 = H e n n i e s a n d H a s u i ( 1 9 6 8 ) ; 1 2 = S c h o b b e n h a u s F i l h o ( 1 9 7 4 ) ; 13 = L i m a ( 1 9 7 6 ) ; 14 = J . V . V a l a r e l i i ( 1 9 7 7 , pers. c o m m . ) ; 1 5 = G o m e s a n d Valarelli ( 1 9 7 0 ) ; 1 6 = U . G . C o r d a n i ( 1 9 7 7 , pers. c o m m . ) ; 1 7 = Y. H a s u i ( 1 9 7 7 , pers. c o m m . ) . F o r r e f e r e n c e s s e e T a b l e III.

145 Ii

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JACUPIRANGA ITANHAI~M ANITAPOLIS IPANEMA PIEDAOE

SALITRE SERRANEGRA 20- PANTANO MORRODASBROAS TAPIRA POLOSDE CAI..DAS CAMPOSDOJORD~,O i, DES~O SEBASTI~,O 15- LDOMONTE DE TRtGO CANANEIA 8ARRA DOTEIXEIRA MATO PRETO LAGES I0- PIRATINI ITATIAIA MFNDANHA RIO BONITO TtNGUA TANGUA 5 ITAONA CABO FRIO

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AGE, MILLION YEARS Fig. 4. Cumulative age diagram of alkaline massifs in southern Brazil. Data are from Fig. 3.

second age group clusters around 130 m.y., and most of its representatives outcrop near Jacupiranga (the "Jacupiranga node" of Herz, 1977); if ages are confirmed, then some Paraguayan occurrences may also be added to this group. A Barremian hiatus ensues and alkaline activity was only resumed locally during Aptian and Albian times, in Paran~--S~io Paulo states (Tunas, Fig. 6 and Itapirapua) and probably also as closing magmatic injections at Anit~polis. Alkaline activity diminishes during Cenomanian times, to be resumed vigorously during the Late Cretaceous. Most of southern Brazil's alkaline rocks fall within this fourth group, especially those massffs and occurrences constituting the Minas Gerais--Goi~ belts and the S~o Paulo-Rio de Janeiro coastal belt. Geologically and petrographically, however, representatives of these age groups are very dissimilar. Spread of ages is n o w very ample but is not a result of analytical errors. Thus, there are reasons to believe that Pogos de Caldas was emplaced during a minimum time interval of at least 20 m.y. (Bushee, 1974). The S~o Paulo--Rio de Janeiro coastal belt shows ages from isolated massifs from about 80 m.y. to about 53 m.y. Moreover, occurrences in Brazilian islands indicate that alkaline magmatism may still be in progress off the Brazilian coast (Abrolhos, 42--52 m.y.; Fernando de Noronha, 22--2 m.y.; Martin Vaz, about 0.8 m.y.; Trindade,

146

N

x•sye ~

pheli n e enite

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0.51

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Fig. 5. The Juqui~ alkaline massif (after Born, 1971). BC and CC = border and core carbonatite, respectively. For additional information, see Table T.

Fig. 6. The Tunas alkaline massif (after Fuck, 1972). For additional information, see Table I.

147

~selo

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nepheline syenites

Fig. 7. The Ilha de S~o Sebasti~o alkaline massifs (after Hennies and Hasui, 1968; see also references in Table I). The system of transversal and ring faults, visible in air and satellite photos, is intruded by late dike rocks (Y. Hasui and W.R. Paradella, 1977, pers. comm.).

average age of 2.5 m.y.; see Cordani, 1970; Herz, 1977, and bibliography therein). On the other hand, some younger ages determined for occurrences of the Minas Gerais--Goi~s belt (around 45 m.y. for Sacramento and Serra do Bueno) are suspect and probably a result of argon loss. Obviously, the results found during preliminary investigations of rocks from southern Bahia (Fig. 1, Table I) set those occurrences far apart from any age group known in southern Brazil. It is still too early to draw any conclusions about alkaline occurrences in northern Brazil (Fig. 2, Table II); there are, however, indications of at least two very different events, one of them very old (a petrologic companion to the widespread and intense granitic reworking of old basement rocks?), the other one a Cretaceous volcanic to subvolcanic phenomenon. GEOLOGIC SETTING AND ALKALINE PROVINCES

Regional geologic arguments indicate very definite relationships between major structural units and the emplacements of alkaline masses in southern Brazil. Essentially, alkaline magmatism is here related to large geologic

148 phenomena, starting in Late Jurassic time and ultimately correlatable, in one way or the other, with continental break-up and drift (e.g., Herz, 1977). Five old cratonic areas are recognized in South America (the Guyana, Guapor~, S~o Francisco, S~o Luis and La Plata shields or cratonic masses), already well accreted by Late Precambrian times (in most instances, much older than that) and fringed by some newer Precambrian--Cambrian belts, such as the Ribeira and Brasilia folded belts (Fig. 1). Outcrops of these cratonic areas are separated b y large sedimentary protobasins (the Paran~, Parnalba and Chaco syneclises, Figs. 1 and 2). The tectonic stability of eastern South America lasted till the end of the Jurassic. Large areas underwent subsidence from then on (e.g., the Paran~ and Parnaiba syneclises) and new faulting developed smaller continental basins; vertical displacements up to the Late Cretaceous or Early Tertiary, as evidenced by sediment accumulation, are as 5000 m (for a summary, see Almeida, 1972; Almeida et al., 1973). New tectonic activity in southern Brazil is associated from its very beginning with basaltic magmatism which appears first as dikes and sheets and then as enormous outpourings covering most of the Paran~ Basin and other surrounding areas. The oldest fissure eruptions occurred at a b o u t 147 m.y. in Santa Catarina State, while the youngest have an age of a b o u t 119 m.y.; bulk activity was concentrated between 120 and 130 m.y. (Cordani and Vandoros, 1967). This is also roughly the age of emplacement of alkaline mafic--ultramafic rocks in the "Jacupiranga n o d e " which, according to Herz (1977), may represent the location of a diffuse hot spot at one of a series of triple junctions: t w o of its arms now form the present northeast and south arms o f the S~o Paulo e m b a y m e n t (Fig. 1), while the third failed arm runs inland and is n o w covered b y Paran~ basalts, possibly representing the site of maximum accumulated flow thickness (Herz, 1977, p. 106). Similarly, Anit~polis to the south may be an alkaline remnant pinpointing the early activity o f a second h o t spot. At any rate, initial localization of the Jacupiranga alkaline emplacements, and of somewhat earlier swarms of basalt dikes, was controlled by the presence of the Ponta Grossa arch (Fig. 1). Initial alkaline activity was resumed after a brief interval of quiescence, again localized along the structural heights of the Ponta Grossa arch (Tunas and Itapirapua, Fig. 1). It has been noted that Brazilian coastal basins (e.g., that of Santos, within the S~o Paulo embayment, Fig. 1) progressively developed a marine character during the Aptian, a b o u t 110 m.y. ago, showing agewise, the first existence of the South Atlantic Ocean (Herz, 1977 and bibliography therein). This date is contemporaneous with the Tunas emplacement. The series of alkaline massifs dotting the S~o Paulo--Rio de Janeiro coastal area, altogether increasingly younger in the northeast, have been interpreted as the traces o f a h o t spot as drift further enlarged the oceanic area (Herz, 1977); Almeida, (1976) showed that most massifs occur within a system of NE trending rift valleys or close to their limiting faults, sometimes also associated with NE-trending normal faults. To the south, it is the Rio Grande do Sul arch (Fig. 1) which, although

149

less active magmaticaUy, determines the late emplacement of the Piratini alkaline occurrences (Almeida, 1971). The supersaturated character of the Itatiaia Massif is puzzling; its emplacement apparently precedes a Tertiary graben-faulting within an ENE-trending minor uplift of the Ribeira belt off the Ponta Grossa arch (Almeida, 1971). The Brasilia folded belt is the site of emplacement of the Minas Gerais-Goi~s belt of mafic--ultramafc alkaline massifs (Fig. 1), most of which have cores of carbonatites. Newer data show that the localization of these massifs is strongly controlled by older structural features (Hasui et al., 1975; F.F.M. Almeida and Y. Hasui, 1977, pers. comm.). In the first place, the whole a r e a - from Tapira to Catal~o I I - is the site of a well-marked gravimetric regional high, the superficial evidence of which has been called the Alto Parnaiba Uplift; its northeastern flank is punctuated by many volcanic necks and possibly diatremes, while uganditic and similar rocks are found along its southwestern margin and the largest massifs crop out on its central area. Locally, all major alkaline occurrences are aligned along old linear structures, sharply defined on magnetometric maps. They constitute a family of parallel, NW-trending lineaments, in evidence since Late Precambrian times, each of which may control the intrusion of one or more alkaline masses. Its northernmost representative, for instance, controls the emplacement of the Catal~o I and II and Serra Negra--Salitre massifs, with the Coromandel kimberlite somewhat to the north of it (Fig. 1). In the same area, magnetometry reveals a few NNW-trending lineaments, which on geologic grounds are believed to be younger. Some alkaline massifs are localized at the intersection of both sets. To the northwest of the Minas Gerais--Goi~ occurrences, the map shows a remarkable alignment of the larger intrusions of the Ipor~ Group (Figs. 1 and 8, Table I), whose location is controlled by one or many NNW-trending lineaments; geophysical data in this case are still lacking. The so-called central Paraguay arch, an anticlinal structure separating the Chaco from the Paran~i syneclises, is the site of relatively old (220--100 m.y.) alkaline emplacements at the western border of the Paran~i Basin. Data are still too scanty to d e f n e properly petrographies and ages. Very little can be said tectonically about the site of emplacement of alkaline occurrences in southern Bahia and northern Brazil. It is interesting to note, however, that the pattern is again repeated on a broad scale: there is a geographic relationship between alkaline sites and cratonic borders, which no doubt reveals a geologic conditioning by older tectonic events of a still unknown nature. Petrographies, ages and regional arguments are now used to define the ten petrographic provinces shown below (Turner and Verhoogen, 1960, p. 75). An evaluation of data for northern Brazilian rocks is as yet not possible. (1) The Rio Grande do Sul province, the only example of which is Piratini (79 m.y.), uniquely determined by age and geologic setting, and characterized by a type 5 petrography.

150

Miscellaneous porphyritic rocks

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(2) The Anit~polis province (129 m.y.), in the southern part of the Ponta Grossa arch, with a possible intrusive span of over 20 m.y., characterized by carbonatites and a type 3 petrography. It may represent the site of a former triple junction (Herz, 1977). (3) The Tunas province, early examples of which are Tunas (type 4 petrography) and Itapirapua (type 3 association?), with ages from 100 to 110 m.y. Both massifs are localized on a domal flexure of the Ponta Grossa arch, which is also responsible for tensional northwest fractures, filled by early basaltic dikes (Algarte, 1972). Other examples are the Banhad~o syenitic stock (type 1 petrography and unknown age) and the Barra do Teixeira, Mato Preto, Ponta Grossa and Sete Quedas volcanic occurrences (with type 5 petrography and possible ages between 67 and 73 m.y.). The area is so well defined structurally and so far from other similar outcrops that it is here tentatively considered aaa separate province with a rather discontinuous and protracted magmatic history. (4) The Jacupiranga province, possibly the site of a triple junction (Herz, 1977), mostly with a type 3 petrography and an age peak at about 130 m.y. Examples are Ipanema, Itanha~m, Jacupiranga, Juqui~ and possibly also

151

Piedade. Carbonatites are found in all occurrences, except at Piedade. Shankinites are widespread as late dikes. (5) The littoral province of S~o Paulo and Rio de Janeiro states, where stocks and minor occurrences of leucocratic rocks represent a type 1 petrography (Fig. 9). Ages vary widely, from older to the southwest (about 82 m.y., Canan6ia, S~o Sebasti~c ~ to younger to the northeast (about 53 m.y., Cabo Frio). Herz (1977) interprets the succession of rocks within this province as the trace of a hot spot piercing platform rocks during drift, which may also manifest itself off the Brazilian coast (Cordani, 1970; Herz, 1977). Some minor occurrences (e.g., the Campos do Jord~o and Jaboticabal occurrences) are probably but offshoots of magmatic activity within this province. (6) The Polos de Caldas agpaitic province. Petrography, mineralogy and ore suites, on the one hand, and distance from other alkaline centres, on the other hand, set Polos de Caldas apart from other occurrences. Although agpaitic rocks are predominant by far, there are within the massif some miaskitic representatives (syenites with sphene and Ca-pyroxene) attesting to a complicated chemical evolution. (7) The mafic--ultramafic, carbonatite-bearing, province of the Minas

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Fig. 9. Alkaline massifs froth the S~o Paulo--Rio de Janeiro littoral belt (after maps in Lima, 1976). For additional information, see Table I .

152

Gerais--Goi~s alkaline belt. Type 3 petrographies characterize the main massifs (notably enriched in Ti, Zr, Nb, P, REE, sometimes also U and Th) while accessory occurrences flanking them are of little geologic importance (Serra do Bueno, Morro das Broas with type 5 petrographies; Sacramento, with strongly undersaturated rocks). Kimberlite pipes and diatremes were also found and are probably the sources for diamond placers in the area. Magmatism peaked at about 80 m.y. (the ages of Sacramento and Serra do Bueno are, within this context, probably anomalous). (8) The Goi~s province of mafic--ultramafic associations, usually without carbonatites (only cited in the Morro do Engenho Massif). Most occurrences belong to the Ipor~ Group and show a type 3 petrography. Ages cluster around 85 m.y. (9) A Mato Grosso--Paraguay alkaline province, mainly with type 1 associations (Fecho dos Morros, P~o de Agt'lcar) and apparently also with type 4 petrographies (Cerro Cor~, Cerro Charar~). Preliminary dates seem to indicate a protracted magmatic history (from P~o de Aq~car, 238 m.y., to at least 129 m.y.). This province may, in fact, be petrographically and genetically very complex: for instance, recent mapping discovered at Pedro Juan Caballero, Paraguay, a (sSvitic?) carbonitite plug within a circular structure (Berbert and Triguis, 1973). (10) The Cambrian--Precambrian Bahi a province, mainly with type 8 and type 1 petrographies. It is interesting to note that no age counterparts are found in southwest Africa (Cordani, 1973), in contrast with ages and geologic structures in corresponding basement rocks. Some massifs are difficult to evaluate. The Lages occurrence, for instance, stands isolated: it may be a late manifestation of an alkaline magmatism that formerly produced Anit~polis. Similarly, the Itatiaia Massif may be considered an extreme case of the mostly miaskitic association of the S~o Paulo--Rio de Janeiro littoral belt, or m a y b e - as its interesting type 6 petrography does suggest -- an independent unit. CONCLUSIONS AND SUGGESTIONS F O R F U R T H E R WORK

The present review shows clearly, on the one hand, the great complexity and wide-ranging petrographic and geological variety of the Brazilian alkaline occurrences. On the other hand, it also shows that present-day lack of data hampers any attempt at a valid or definitive petrological interpretation. What is the precise relationship between the opening of the South Atlantic Ocean and the emplacement of the associated contemporaneous alkaline rocks? What types of geological controls determine the appearance of dozens of occurrences in weU-defined linear belts? How are alkaline magmas generated within the mantle? What are the relationships between the Cretaceous basaltic outpourings and the alkaline occurrences? Are the older alkaline rocks (e.g., the Precambrian plutons in southern Bahia) to be interpreted in the light of the more modern occurrences, i.e., as magmas emplaced within

153

stable platforms eventually subjected to drifting mechanisms? In some cases, interpretative speculations, some of which are cited here, may already show the way towards a better understanding of these phenomena. But in most cases, proper answers to questions such as these have to await the arrival of more data, especially a sounder knowledge of the geological setting and the chemical and mineralogical characteristics of the alkaline rocks.

ACKNOWLEDGEMENTS

Discussions with our colleagues F.F.M. de Almeida, U. Cordani, J.M.V. Coutinho, R. Ellert, H. Born and especially Y. Hasui helped to improve our understanding of Brazilian alkaline rocks. Thanks are due to F.F.M. de Almeida, Y. Hasui, R. Ellert, G. Amaral and J.V. Valarelli for permission to use unpublished data. One of the authors (H.H.U.) gratefully acknowledges financial support from FAPESP (Geol. 76/658) and CNPq (Proc. 2222.0289/ 77). REFERENCES Algarte, J.P., 1972. A influ~ncia dos arqueamentos crat6nicos no condicionamento das alcalinas nos Estados de S~o Paulo e Paran~. An. XXVI Congr. Brasil. Geol., 1 : 65--69. Almeida, F.F.M. de, 1971. Condicionamento tect6nico do magmatismo alcalino mesoz6ico do Sul do Brasil e do Paraguai oriental. An. Acad. Brasil. Ci~nc., 43: 855--836. Almeida, F.F.M. de, 1972. Tectono-magmatic activation on the South American platform and associated mineralization. XXIV Int. Geol. Congr., Section 3 : 339--346. Almeida, F.F.M. de, 1976. The system of continental rifts bordering the Santos Basin, Brazil. An. Acad. Brasil. Ci~ne., Suppl., 48: 15--26. Almeida, F.F.M. de, Amaral, G., Cordani, U.G. and Kawashita, K., 1973. The Precambrian evolution of the South American cratonic margin south of the Amazon River. In: A.E.M. Nairn and F.G. Stehli (Editors), The Oceanic Basins and Margins, 1. Plenum Press, New York, N.Y., pp. 411--446. Amaral, G., Bushee, J., Cordani, U.G., Kawashita, K. and Reynolds, J.H., 1967. Potassiu m - a r g o n ages of alkaline rocks from southern Brazil. Geochim. Cosmochim. Acta, 31 : 117--142. Berbert, C.O. and Triguis, J.A., 1973. Carbonatito de Pedro Juan Caballero, Paraguai. XXVI Congr. Brasil. Geol., 1 : 77--78 (Abstr.). Born, H., 1971. Complexo alcalino de Juqui~. An. XXV Congr. Brasil. Geol., 1: 223-225. Bushee, J., 1974. Potassium--Argon Ages of Some Alkaline Rocks from Southern Brazil. Dissertation, University of California at Berkeley, Calif., 145 pp. Comte, D. and Hasui, Y., 1971. Geochronology of eastern Paraguay by the Potassium-Argon method. Rev. Brasil. Geoci~nc,., 1 : 33--43. Cordani, U.G., 1970. Idade do vulcanismo no Oceano Atl~ntico Sul. Univ. S~o Paulo, Inst. Geoci~nc., Astron., 1 : 9--75. Cordani, U.G., 1973. E v o l u ~ o Geol6gica Pr~-Cambriana da Faixa Costeira do Brasil entre Salvador e Vit6ria. Thesis. Univ. S~o Paulo, Inst. Geoci~nc. (unpublished). Cordani, U.G. and Vandoros, P., 1967. Basaltic rocks of the Paran~ Basin. In: Problems in Brazilian Gondwana Geology. Univ. Fed. Paran~, Inst. Geol., pp. 207--231.

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[Received Septemper 4, 1980]