RENDlCONTJ OELUr. SOCIETA lTAUANA DI MINERALOGIA E PETROWGIA, 1988, Vol. 43·2, pp_ "'·'68

Evidence of magma mixing in the Itaporanga batholith, Northeastern

GORKl MAluANO, ALcIDES NOBREGA SIAL D~partm~nt of Geology, Fed~ ral Univ~rsity of P~mambuco, 50000, Recif~ , PE., Brazil

ABSTRACT. - Three very large high-K calc-alkaline ± 0.0003, probably representing the: emplacement ag~. balholiths (Bodoco, Serra da Lagoinha, and llaporanga) Hornblende and. biotite yielded 4lJAr/J9Ar age spectra intruded amphibolite facies metamorphics of the with well-defined plateau ag~s of ,. 580 Ma and c. 540 basement adjacent to the northern boundary of the Ma, r~spectively. They probably represent cooling ages Precambrian Cachoeirinha-Salgueiro Fold Belt, west of and their meaning is not well understood. and Parafba states, northeastern Brazil. These bodies were intruded syntectonically to the Fl Key wordJ: Magma mixing, Commingling, Hybrid. Fold d~formation with a final diapiric emplacement. In the Bell, Batholith. ltaporanga batholith, the beSI studied of these bodies, three petrographic fades were mapped. A hybrid zone, characterized by chemical and mechanical mixing, composes most of the outer portion of the batholilh, where int~nse interaction between granite, granodiorite Introduction and diorite mdrs took place, giving rise 10 migmatitic· like features. A commingling facies wh~re granite to Numerous granitic plutons and dikes pierce granodiorite and diorite units may be well individualized, the low-grade metasedimentary rocks of the is located towards the cemer of the batholith. Finally, Cachoeirinha-Salgueiro Fold Belt (CSF) and areas of porphyritic fades are mO!"~ abundant in the hybrid zone than in the commingling one. adjacent areas, in the western portions of the In the hybrid zon~ , diorile shows 50m~tim~5 pillow­ states of Paraiba and Pernambuco, like structures evidendng quenching, confirmed by the Northeastern Brazil (Fig. 1). presence of fine.grained fades and adcular apatite These granitoids intruded the multiple crystals. Cuspate COntacts between diorite dikes and deformed and poly-metamorphosed porphyritic granodiorites portray the viscosity contrast between these coexisting melts. Obstacles to mixing were Precambrian low-grade metasediments of the very often overcome, judging from the el

:": ." , EPlOOTE·8EARING CALC-AL KALlNE GR4N lTO IOS rE] CRETACEOUS SEDIMEN TARY COVER ~ CCO N CE'~AO TYPE I 0 SATURATEO PERALKALLN[ PLUroNS ;; GRANITOIDS WITH TROMOKJEMITlC AfflNI- ~~ (TIII\l NFO TYPE) ~ TIES (S ERRITA TYPE) 0 0" • OYERSATURATEO PERALKALINE PLUTOH! • • IIlIlJullI ICATiNGU[IRA TYPE ) CACt*OEIRINHA GRO\JP (SCHISTS,PHYL.LIT[S' ~ • ~ ~ •0 SHOSHONITIC GRANITOIOS(SOLlO'\o, TEIX[I- 0 • 0 RA, PART OF SALGU[II~O 841HOI,.ITH) • b!J SALQUEIRO GROUP (SCHISTS, GNEISSES) POTASSIC CALC:'ALKALlN[ GII4NITOI05 BASEMENT ROCKS (MAI N L Y GN[IS SE S \ITAPORANGA TYPE) 0 '" MIGMATITES) Fig.- 1. - Geological sketch of the Cachoeirinha-SaIgueiro Fold Bel!. Four different granitic groups IIf"e $hown (5,,, •. el al . 1987).

(ALMEIDA et al., 1967). Three bacholiths of phases, and well represented in a dike swarm this kind (Bodoco, Itaporanga, and Serra da near the town of Catingueira, Parafua, where Lagoinha batholith) intruded intermediate- to five dikes were emplaced paralld to the Patos· high-grade metamorphics of the basement Aurora lineament, probably during the early along the northern contact of the CSF. b) Late stages of the onset of the lineament. orogenic granitic rocks included the ­ Although the work of ALMEIDA et al. (1967) and Catingueira-types, the former composed was a marker in granite studies in northeastern essentially of biotite granites occurring Brazil, it lacked geochemical data which were associated with the ltaporanga-type granite, only recently provided by SIALet al. (I981a, being more abundant in areas of gneissic and 1981b) and SIAL (1984a, 1984b), when major migmatitic rocks. The mineralogical and trace elements, REE, and oxygen isotope composition of the Itapetim- and ltaporanga· data became available. types is very similar. The Catingueira-type is SIAL et al. (1981a, 1981b), studying the mainly represented by dikes of silica granitic rocks of the CSF and adjacent oversaturated alkaline rocks, with alkali­ migmatitic basement, used a geochemical pyroxene and amphibole as common mineral classification to distinguish four major groups EVIDENCE OF MAGMA MIXING IN THE ITAPORANGA BATHOUTIt, NORTHEASTERN BRAZIL 557

(Fig. I), northern border of the CSF, between its low· a) K calc-alkaline Group - the same as the grade metasedimentary rocks and the green Itaporanga-type of ALMElDA et al. (1967) schist- to amphiholite-grade rocks of the - emplaced in the basement migmatites, Serid6 Group, is limited in its NW portion northern and southern borders of the CSF. by a major sinistral strike-slip fault (Boqueirao b) Cale-alkaline G roup - the same as the dos Cochos Fault), which imposed to it a Concei(jao-type of ALMEIDA et al. (1967) tectonic foliation, better developed near the - emplaced in the CSF metasediments. fault zone (Fig. 2). This fault zone has c) Trondhjemitic Continental Group - approximately 700 m of outcrop width and includes portions of the Salgueiro batholith seems to have cut the batholith when it still and stocks which intruded the showed some degree of plasticity, as deduced Salgueiro Group Schists. from the predominance of ductile d) Peralkaline Group - the same as the deformation. This horn-like batholith is Catingueira-type of ALMEIDA et al. (1967) surrounded by a foliation probably generated - commonly associated with fault zones by shearing associated with ballooning during or ring structures. its final emplacement. This diapiric The peraIkaline bodies were studied by SIAL emplacement is characterized by folded border (1986) and FERRElRA and SIAL (1986) and zones, where schists of the CSF show found to surround the CSF, being divided overturned folds, and also where early folded into two major groups: (a) Silica oversatured apophyses of the porphyritic rocks represent peralkaline rocks located in the northeastern an early phase of the intrusion before the extremity of the fold belt (e.g. Catingueira, emplacement of the main body. Solidao, Teixeira) and (h) Silica saturated The foliation (ballooning + fluxion peralkaline bodies approaching the foliation) dips inwards the batholith, southwestern extremity of the belt (e.g. suggesting that the present level of exposure Triunfo, and ) (Fig. 1). may represent the root zone of the diapir. The main purpose of this work is to study The Cachoerinha Group schists show two preliminary geochemical data, associated with major foliations characterized by fine grained field observations in order to analyze the (F I) and coarse grained biotite (F2), the latter possibility of mixture of magmas as a major assumed to be syntectonic to the Brasiliano petrogenetic process in the Itaporanga (~Pan-African) cycle. The Itaporanga batholith, as a first step to further studies on batholith shows xenoliths with F2 foliation these porphyritic bodies in the CSF and parallel to the granite foliation, suggesting its elsewhere, in Northeast Brazil. emplacement as syn- to late-tectonic to the Brasiliano cycle. General geologic features Field evidence for magma mixing The Cachoeirinha-Salgueiro Fold Belt (CSF), also called the Pianco-Alto Brigida Mixing of magmas has been proposed as a System by BRITO NEVES (1975), who major petrogenetic process in the origin of described it as an ENE trending belt, located hybrid rock types in plutonic environments in the states of Pernambuco and Parailia, has (WALKER and SKELHORN, 1966; WIEBE, 1974 its northern limit on the Paralba lineament and 1980; VERNON , 1983; WHALEN, 1995; and the southern one on the Pernambuco WHALEN and GARlEPY, 1986) and in the lineament (Fig. I), comprising an area of voleanic associations (GROVE et al., 1982; approximately 40,000 Km2. The CSF is WHALEN and CURIE, 1984; HOOPER, 1985; composed of green schist to amphibolite fades KOYAGUCHI, 1986). The features observed in metamorphic rocks and several plutonic rocks where magma mixing took place, often intrusions. associated with crystal fractionation, The Itaporanga batholith, a porphyritic exhaustively discussed in an increasing diapiric igneous body, intrusive in the number of papers {VOCEL, 1982; WIEBE and 558 MARlANO G. • SlAL A.N.

LEGEND

OUAT ERNARV ALLUVIAl. DEPOSITS

B IO TITE ORA N OI)IORITE

1+++1 CONC E I~io T V PE OIlA N ITOII)$

liT LO " 'TIO RoeMS pORPKYRITIC lONE (GR ANITE, TO OTZ-MOtiZONITE , WI1 H It-FELDSPAR 'UG

K-OIOII'TE ~~~~~!I~N:tu;~:~=:W~~i~~~';J~s~~~lIsg:" SNT~'~:;:r·:~ETR~~srs,c~)

-A... s~ F OL I 4TION

....1- TECTONIC FOLIATION

~ f OLD AXIS

--l-- tOLD AXIS OF ANTIFOIIN

~ OVERTURN EO PLUNGI NG SY N FOIIN

....y... OVERTURNED DOUBLE PLUNGING JlNTlFORN

FRACT UR E

:':::; STRIKE-SLIP FAULT

"'A I I' IIOAD

P ... T H , •, ; "j'" Fig. 2. - Geological map of the: ltaporanga batholith, showing domains resulted from diffc:n:m degrees of interaction between fe:bic and mafie magmas. EVIDENCE OF MAGMA MIXING IN THE ITAPORANGA BATHOLlTH, NORTHEASTERN BRAZ IL 559

WILD, 1983; BARNES, 1983; WHAI...EN, 1986), Another conunon feature is the abundance led us to think this may have been· the case of mafic enclaves, some of them with with the Itaporanga batholith. This batholith crenuIated contocts (photo 2) and others, more is composed of granite, granodiorite, quartz regular, either angular or elliptical . According monzonite, monzonite, and diorite, and this to DIDlER (1987) these enclaves may represent compositional gradation may have resulted by proximity and distance of mixing site, interaction of granitic to granodioritic and respectively. dioritic magmas. Field evidence and Cuspate contacts between mafic portions preliminary chemical data will be discussed and the porphyritic granodiorite (photo 2), here in an attempt to analyze magma mixing and pillow-like structures developed by the as a major petrogenetic process in the mafic magma in contact with the cooler felsic Itaporanga batholith. one (photo 3), are evidence of viscosity and In order to have mixing of magmas several temperature differences between the two obstacles must be overcome. These obstacles magmas. Although differences in viscosity and are differences in viscosity, density, and temperature are obstacles to mixing, the temperature between the fdsic and mafic intense degree of interaction between mafk magmas, and also the very low diffusion rates and felsic magmas observed throughout this of chemical species in silicate liquids (VOGE.L zone suggests that these obstacles were et al., 1984). overcome. The Itaporanga batholith was divided into The syn- to late-emplacement of the three domains, based on possible mixture of Itaporanga batholith in relation to a major magmas. The hybrid zone, which varies in tectono-thermal event (the Brasiliano cycle) composition from granodioritic to quartz may have increased the possibility of monzodioritic, the porphyritic zone composed mechanical interaction between the two of granite to quartz monzonite and the magma types by favoring turbulent flow of commingling zone where dioritic rocks are in magmas, both in a liquid state (TURNER and close association with granitic, granodioritic CAMPBELL, 1986). Mechanical mixing may and monzonitic ones and identified as isolated also have being enhanced by a major strike­ units at outcroup scale (Fig. 2). slip fault which cuts the western portion of Hybrid zone . the obstacles to mixing the batholith, promoting homogeneization of mentioned above seem to have been the different magma types. suppressed in this portion of the batholith, Porphyritic zone . these portions may where a high degree of interaction between represent areas that crystallized before the felsic and mafic magmas is often observed, tectono-thermal event peak and had their giving rise to a migmatite-like structure (photo identities preserved without much mixing, or 1). In some of the outcrops mafic layers 10-50 pulses of felsic magma which crossed the cm wide are followed by felsic porphyritic magma chamber without much contamination ones, with approximately the same variation by the mafic magma. The degree of in width. K-feldspar megacrysts in the mafic interaction between diorite and granodiorite layers, as well as across the bOlll1dary between in the porphyritic zone was restricted to the mafic and felsic layers, are evidence of the presence of mafic enclaves. These enclaves are degree of chemical equilibrium (diffusion + commonly ellipsoidal showing sharp contacts, mechanically controlled) attained by these representing some distance from the mixing layers (photo 1). On the other hand, there are site (DIDIER, 1987). mafic layers without K·feldspar megacrysts, Commingling zone - in this portion of the suggesting recurrence of the mafic magma mapped area mafic (diorite) portions inside pulses, corroborated by biotite-rows in K­ the porphyritic granodiorite with sharp feldspar megacrysts. These biotite-rows contacts may be observed on the outcrop represent changes in temperature during K­ scale. Some of the malic portions show growth feldspar growth probably caused by more than of K-feldspar megacrysts, attesting that at one mafic pulse. least some degree of chemical equilibrium was 560 MARlANO G., SlAL A.N.

Photo 1. - MlglT\Atile·like structure in the hybrid zone a.aracteriud by intense interaction of mafic and porphyritic fclsic portions. _) K-fcldspar mcgacrysts in mafic layers, attc$ling that some: degree of chemical equilibrium between mafie and fdsic layers WIS attained.

PholO 2. - Malic enclaves with cuspal!: comacts, evidencing density contrast (hybrid zone), attained (photo 4). this portion of the batholith vary from quartz monzonite, [Q quartz monzodiorite, Petrography granodiorite, to granite, the latter being more Potphyritic zone· the rocks that compose common and attesting to a less intense or EVIDENCE OF MAGMA MIXING IN THE ITAPORANGA BATHOUTH, NORTHEASTERN BRAZIL 561

Photo J. - Pillow-like structure developed by the hotter mafk magma, in contact with cooler fdsk one.

Photo 4. - Mafk portion isolated and in sharp contact with fdsk portion (commingling zone). almost absent degree of mixing Quartz, and chlorite represent products of late plagiodase (An 10-30), microcline, biotite, ± hvdrothermal alteration . hornblende are the major mineral phases; . The evidence for mixing in this zone is sphene, allanite, apatite and zircon are mainly represented by mantled plagioclase common accessory phases, and calcite, sericite inclusions in the microcline megacrysts. These '62 MARlANO G., SlAt. A.N.

feldspar in the mafic portions suggests that the twO end-members eventually reached equilibrium.

Geochemistry Fifteen samples were analysed for major and selected trace elements by X-ray fluorescence techniques. Table 1 shows chemical analyses for different zones in the batholith. REE were analysed by induced coupled plasma, at the Geosollaboratory, Minas Gerais, for three samples from the same outcrop, representing respectively maSc, hybrid, and felsic members ... 00 ...... •• .. ' ...... • • I .. .. Co (F;g. }). Fig. }. - REE patterns for hybrid (cirdeJ, mafic The REE show small variations in the three (square), and fdsic (triangle) portions of the Itaporanga samples analyzed, with the hybrid sample bathotith. enriched in LREE in relation to mafic and felsic samples, and placed intermediate to plagioclase crystals may represent a syn-mixing mafic and felsic ones for the HREE (Fig. 3). growth. The discontinuity of the plagioclase The three samples analyzed show LREE mantle characterizes reaction with the matrix, enrichment related to HREE and flat negative pr,obably caused by dis~uilibrium during slopes, with the exception of the porphyritic ffilxmg. sample

m Al f'o .... n\il ... ItIC t ' ;t.CI~$ Dl HYDr i C f.CI~5 Cl Maf,c t ·.CI"" S

t:.L.t:.M . H i!-I-' Ill-f' 'n-I-' 110'1-1' 1::.3-1"' ,-, Ol-H 11l-H 161-H l'1::'-H 16Y-H ,-, 161- M 1'1::'-" ~ Q SlUO! 63.:' 01.Y 0 1.11 03 . ": 02.3 01> . 1 b0.b :'tI.:' :':. . 3 oll.Y :.ti • " ::..,..~ :'3.0 ::l2 . 1l :'0.1 1' 100: O.~O: If.tI~ 1:I . t!" .111 . 0" I:I . YO 1:1.:'1 1.2 1.0: 1.::1 " . YY 1 •. 2 101 . "'0 L' ;';> . 1 ,. . AI..203 10 . 111 1:'.1 lO.tI 1::'.'1' 1:' . :. 1'1 . 1 l'1.Y l:' . b Ib./ Ib . 1 1:',0: 14.4 l"1.tI 1/ .2 10 . ';1l ~ 1:.000:.:l 111 . ::'3 ,. , 1:1 . 11:1 1II . t!~ 1. 1 I:I.Y4 111 . :.2 L. 1.Y 1:I.t!1 1 • 'I , :.:! . O; , . , L. ":. '1 ~ 'co ;,,: . ~~ '1 . ":'1' '1 . 1· 3.:.::. 3.~" ":.1>0 ::.. '11 ::).Y2 b . O:l " . '1" ::' . 113 :..113 1 . 111 ] . 0::' b. :'1 • "0 If.lf3 If . HI "' . 1:11 If."o 'Llllt! II.lIIb II."V 11.14 lI . l:.! ,11. IIY 11. 1 101 11.1:" 11 . 12 \1.12 11.13 g ' Ob '-' 1.:' '-' ,. , 2.111 ,. , ":.0 :.! . 3 L' 0:. 1 :1 , 11 0:.16 :'.'1 2.b ,. , ~ \.:AO ~ . l 2 .tI O:: .t! 0! .2 2 . Y L' .. , 3.0 4.3 .i . 'I J.t! ,., :'.3 :..2 NAO!O :'.3 .'I.t! , , , 3 . Y , , 'I.CI 4. :.:0 3./ ••• , Z ...... ••• ...... ', " • 0: "..' ".3 K":O ,., :i.t! ,., , ., 3 . t! ,. . ••• ". t:! , .. ••• :i.t! ,., 3 . Y ".3 :;1.3 ~ HO!U'" iI. ::.Y 1l.::'4I 11.0'1' 11.0:' 1I.t!Y II.bO II . 'IY 11 . /:' 1I.t!" 1I.t!" lI.b:1 1l.:''I iI.:l3 11.]2 I!.t!b m 11":111- "'. 1 \I "'.141 1:I . 1:It! 1:1.11,'1' Ill. lilt! 11.114 0,0:i "' . 0Y 11 . 111:' 11.111 ".IIY 11.101'" 1I.1f'" "'.11" ".o!\I CoO: 11 . '111 11.0::' 11 . ::'11 1l . 41:1 11. 'IO! III.::IV 11 . :'0: II . :.!::) 11.:.":: II.O!:' 11. :'111 101.01 iI . '11l 11.42 11.2" ~ I'O!\.I::' If.;;:l 11 . 32 1:1 . 33 1:I . 0!::I 111 . 31 1II.20! III.'I~ ".3t:! "'.::..,. 111.34 "' ..:. 11.'1:" \1 . 3'" "' . till 11.'1'" 1 Of AI.. "'''' .b\l Y.,. ."'o .,..,.. Y:' "''''.01 "''''.0'' YY . /ti ",Y.:'Y 11111.111".'$ YY .ti:" Y<;I .b:) YY."'II YV'/'" "'''' . t:l3 Y"' . O:' "'''' .''V ~ ~

• 1 f(ACi:. ':'Lt:.Mt:.NrF ANAL YS':':."

., f'corpnlol r ,t. C fIlC''''' Dl Hyo ... ,C! faCl~' Cl Mat· ,c f".c'~s .~ t.I..E" 1-1" 0:-1" 111-1" Yl-f' lIH-f' 1:':;I-f' 103-f' lbl-I' 2H 1011'1 l,,:;,H 100tH I 1" 14:;1'1 101" ~ '" '" ~ no 1 / 11 loll Ibll 13it >0' ". 10:11 1211 1611 '" 1 0:1it ". 1 :,,11 11 lit ot'jl ~ ",. t!'ItI ." olll! :)tll! ::':111 m , .. ... 1011 '1'111 '" 1..:0 :':.111 bO'" 0:'''' 03'" ~ ...... 1.,.t!1I .. 1'12e 11'111 1411111 1 :'1" », 10!1it1it 1 "1II1it ", ltle& 111:'11 l"SII 2""'& lVoII 10: /11 'i0!1II 1] 1 (,j • co m ~ N r. 0:' F ".'$'11l :"ill! 3011 'Il lI ." :;'40 17:. 2111\! It!1I 'Ilitll ::IYII :;.::>11 ,.. O!t:I'" 0:4'" ", 30:'" " (211 2\1 2 1 32 O:t! ( O!'" ;':111 "11 n ,. 3" (0:11 2b " Utltl " .. " ------" ------_. ~ ------~ , no 30 13 22 H\l1 0:2 0:11 "" 2. u. n' ,. ,. ~ " " " " .. ~ 564 MARlANO G., SIAL A.N.

~ ~ TiO. ·oo o U' " 0 '.' u. coo to o .. ". ~ "".. • ,~

,~ ,00 ,., "' 1~O3 0 0 ~ 0 'U 0 u. 't.1> 0 o 0 0 8 0 .,. 0 0 '" 0 • 9 '" ~ ~ • ,~ ,,.

~ F"O) '.' tl arO ... 0 ... 0 o 0 ,.n o 00or • 0 ° 8 • '" 0 ". 0 t~ • " ~ "

~ ,., '.' '.' 00 ., <9 t!/.16 '.' 0 • 0 0 0 ° o ~ ",0 0 0 • " ~ '" " • • " " •

.- .. , PL O, - '00 0 '" C[]OcCO ." 0<1',. <00 0 0 8>0 ~ ." ..., 0 " " &S- 0,0' .., = " ",/" .." ." ~. - SIO, - - '" Sio..- -

Fig. 4. - Major dement variation diagrams. Symbols as in Fig. 3. EVIDENCE OF MAGMA MIX ING IN THE rt'r.PORANGA BATHOUTH, NOKl'HEASTERN BRAZIL. ,6,

Fig. 5. - Trace element vari.tion diagr.ms. Symbols u in Fig. 3. ages, and suggest a slow cooling compatible of the hybrid member, with the sum of square with a 'relatively deep level of emplacement. of residuals .. 1.0. This value shows good agreement with the data obtained through variation diagrams (Fig. 4), where addition of Discus.ion 55 to 65 percent of felsic to mafic magma was Field observadons suggested magma mixing observed to generate the hybrid compositions. to explain the complex chemical, and The HREE patterns (Fig. 3) also show that mechanical interactions between coexisting the hybrid component has an intermediate magma types. composition between felsic and mafic magmas. The intense interaction among the This behavior is not observed for the LREE lithologic types was tested using major patterns suggesting that a simple two end­ chemistry and the XLFRAC program of member magma mixing was not the only STORMER and N ICHOLLS (1978), where the process involved in the evolution of the felsic (granodioritic) magma was used as initial Itaporanga batholith and that mixing of magma and 45% of the mafic (dioritic) magma magmas may have occurred in association with was added to obtaining the hybrid other processes such as crystal fractionation. component. The hybrid composition obtained The absence of the Eu anomaly is explained was very dose to the chemical composition by the balance between feldspar and MARlANO G., SlAL A.N. hornblende. The relative enrichment in LREE The obstacles to mlxmg pointed out by compared. to HREE may have been caused VOGEL (1984), such as differences in viscosity, by the mineral association apatite, sphene and density, temperatures and the low diffusion allanite, frequently observed. in the lithologic rates of chemical species in silicate melts, seem types which compose the batholith. to have been overcome, since complete Microscopic observations showed hollowed graaation between porphyritic granodioritic acicular apatite, which suggests contrasting and fine grained. mafic dioritic rock is temperatures between the mafic and felsic observed throughout the batholith. magmas and a rapid cooling of the honer The present level of exposure, representing magma when in contact with the cooler one . the root zone of a diapiric intrusion associated Mantled plagioclase inclusions in the K­ with emplacement during a tectono-thermal feldspar megacrysts throughout the batholith, event (Brasiliano _ Pan-African Cycle). and a associated with biotite-rows in those widespread shearing event characterized by megacrysts, indicate that changes in a major sinistral strike-slip fault, which cut temperature were probably caused by the batholith when it had still a high successive pulses of mafic magma. The proportion of liquid provide us with extensive shearing observed throughout the uncommon degree of interaction between batholith may have an important role in the magmas of contrasting physk;a1 properties. mechanical interaction, contributing to the The agreement between a chemical balance formation of abundant hybrid composition. model and major elements mixing diagrams, The chemical equilibrium attained, associated with HREE patterns consistent demonstrated by growth of K-feldspar with a mixing model, suggests magma mixing megacrysts in the mafic portions, attests that as an important petrogenetic process, probably an interaction between the two magmas of occurring together with crystal fractionation contrasting compositions occurred when they during the evolution of the Itaporanga were in a liquid + crystal state (crystal-liquid batholith. mush), enhanced by a major shearing event. The inward dipping tectonic foliation AcknowkdgmmfS. - Were arc grateful \0 PADeT / within the batholith, associated with cuspate FINEP for financial support. Thank also go to CNPq, contacts between mafic enclaves and dikes and which provided one of us (CM) with a scholarship for their host porphyritic rocks observed in the graduate studies 11 the Uni versi ty of Georgia, USA, and hybrid zone attest, respectively, to a lower ANS with a grlUlt.in.aid for part of. this work. level of exposure of the diapiric intrusion and to the proximity of the mixing site (DlDIER, 1987).

REFERENCES Summary and conclusions Au.1ElDA F.F.M., LWNARDOS, D E, O.H., VALENCA J. The porphyritic, K-rich calc-alkaline (1967) - R~iew on Rranitic rocks of Northeast South Itaporanga batholith shows strong fi eld AmerU:a. IUCSfUNESCO Symposium, Rccife, 41 p. BARBOSA O. (1970) - Geolcgia «onomica da part~ da evidence for coexistence aoo mingling of rtgiao do mt.iio s"o Francisco. Div. Fom. Prod. magmas of contrasting compositions. Frozen­ Mineral, DNPM, Bol. 40, Rio de Janeiro. in magma mixing testimonies are observed BARNES CC. (198)) - P~trolcgy and upwa,J :{onation of throughout the batholith as pillow-like the Wooky Cm!ie btltholith, Kla_tb Mountains, Ollifomia. Jour. Petrol. Vol. 24, Pan 4, p. 49'·'37. structures, cuspate contacts between mafic BRITO NEVE$ B .B. (19n) . Rqjo1lltli=o geoteclonica dikes and the porphyritic granodiorite, do Precambriano noJ"tkstino. Unpublished Ph . D. inclusions of biotite-rows in K-feldspar dissertation, Univ. SIO Pauio, 198 p. megacrysts attesting to at least two growth DII)IEl!.}. (1987) - Contribution of tnclttvt studin to the undentanding 0/ origin and ~lution ofgranitie _gmas. stages, and migmatite-like structures Ceologische Rundschau, 76/1, pp. 41 -'0. developed as the result of close interaction FERREJRA V.P., SIAL A.N. (1986) . The ptralkalic between felsic and mafic magmas. magmatirm in the Pm:ambrian Cachotrinha-Salgu~iro EVIDENCE OF MAGMA MIXING IN THE ITAPORANGA BATHOUTH, NOKI'HEASTERN BRAZIL 567

/oldlHlt, NOH«au Brazil: g~hmrical arp«n. Rev. VEP.NON R.H. (19SJ)· Rntite, x~oliths, microgranitoid Bras. Geoc., v. 16 (I), pp. 7J·8'. enclalJt!1 in VIlni~ . Journal of the Proc. of the Royal GROVE T.L., GERUCH D.e., SANOO T.W. (1982) . Sce. of New South Wales, 116, pp. 77·IOJ. Origin 0/ caic-llliuJline m1t!S lallas at Mt!dicine LIke VOGEL T.A. (1982) . Magma mixing in the llCidic'Nsic voicano by fractional, animilation, and mixing. Contr. complex 0/ AninIlmun:Nn: implications on the evolution Mineral. Petrol. SO. pp. 160· ]82. 0/ shallow magma chamkn Contrib. Mineral. Petrol., HOOPER P.R. (198')· A care 0/ simpkmagma mixing in 79, pp. 411·42J. the Columbia Rivt!r Basalts Group: the WHbur CTt!ek, VOGE L T.A., YOUNKER L.W., WtLBAND J.T., Lapwoi, and Asotin/fcws, Saddk Mountains Formation. KAMPMUI!1.l.ER £. (1984) . Magmll mixing: the Maneo Contr. Mineral. Petrol. 91, pp. 66-7). Juite Isk o/Slt~, Scotland. Contrib. Mineral. Petrol., KOYAGuclll T. (1986) . TeJttural and compositionai 82, pp. 2}l·241. nI;u,.ce /or mafl1Ja mixing tIIId in mecNnisms, Abu WAUC.ER G.P.L., SKEUIOIlN R.R (1966) . Some vobnk rroup, s()1I~tmI Japan. Contrib. Mineral. IlllocilltionJ 0/ llCidic IlnJ NUC ifJft!Ous rockJ. Earth· Petrol., 9J, pp. JJA,. Science Rev. 2, pp. 9J·I09. SIAL A.N. (19841)· paJrao Ttffrmal dt wtQpof dt oxivnio WHAliNJ.B. (198')· The McGerrinpje plutoniccompltx, t!17I gmnitoides do t!Spaco Cv:hoeirinN, Nordeste do GIlJ~, QueM: nlidntce 0/ mIlgmll mixing and Brasd. Anais XXXlIl Congr. Bras. Geel., Soc. Bras. hybridization. Current Research, Pan A, Geol. Survey Geel., Rio de Janeiro, pp. 271(}.2722. of Canada, Paper 8' lA, p. 79}.800. SIAL A.N. (1984b) . Litogroquimicll ck ekmentos terras WHALEN J.B. (1986) • GeochemiJtry 0/ tht maftc Ilnd raras na .carocterizacao ck granitoide$ do espaco voicllnic components 0/ tht TopSllih igneouJ suite, uchoeirinha, Nordeste BrasH. Anais XXXIII Congr. westt!l1l Ntw/oundlllnd. Current Research, Part. B. Bras. Gee!., Soc. Bras. ~l., Rio deJaneiro, p. 2696 Geol. Survey of Canada, Paper 86· 18, pp. 121·130. ·2709. WHALEN ).B., CURRlE K.L. (1984) . Tht TopSlli/s igneous SIAL A.N. (1986) . Granite types in Northeast BrlUH: terrant Wt!1tem Ntw/oundumd: tl/idence /or mllgpta currmt know/df#. Rev. Bras. Geoc. V. 16(1), pp. mixing. Contrib. Mineral. Petrol., 87, pp. }l9·J27. '4·72. WHALEN ).B., GARJEPY C. (1986) . Pt/Togent!Sis 0/ the SIAL A.N., LIMA £.S., PEsSOA D.A., CASTRO C., McGerringk pllllon;c compkx, GIlSPC, Quch«: a VII~"OEL H.S. (1981a) . GeoquimiCIl ck dois stocks I=liminry rqxwt. Current Research, Part A. Geol. gNnodioritieos tk Sm"ita (PE): elemt!ntQJ maioft!S. Univ. Survey of Canad., Paper 86·IA, pp. 26,·274. Fed. de PernambuC(), Dept. Geol., Estudos e WlEBE R.A. (1974) • Coexisting intermt!dillte Ilnd Nsk PesquiSls, v. 4, p. 27·52. magmaJ, Ingoish, Cape BTt!ton Island. Journal of SIAL A.N., PEsSOA D.A., LIMA E.S, CASTRO C., Geology, 82, pp. 74·87. VILLAROEL H.S., SoRBA G.S., RoORIGUES CA SILVA WmBE R.A. (1980)· Comminglingo/contrasttd magmas M.R. (198Ib)· Petrologfll e geoquimica do Ntolito ck in the plutonic tnllironment: eJtampks from the Nain Bodoco e stocks ck Serrita, Pt!I1Iambuco. Atas X Simp. anoHhosific compltx. Journ. GeoI. 88, pp. 197·209. Geel. Nordeste, Soc. Bras. Geol., , pp. J88·401. WIEBE R.A., Wn.o T. (19SJ)· Fractionlll crystalli~ation TURNER J.S., CAMPBEU. LH. (1986) . C01fVC(;tion and and mllgma mixing in the Tigalak layered intrusion, tM mixing in magma cNmkn. EarthScience RevieW$, V. Nllin Ilnorthosifi(: complex, Labrador. Contrib. Mineral. 2J, pp. 2"·J'2. Petrol. 84, pp. J27·}44.