Geology , petrography and geochemistry of the A-type granites from the Morro Redondo Complex ( PRSC ) , southern Brazil , Graciosa Province

The Morro Redondo Complex is one of the most important occurrences of the Graciosa A-type Province, southern Brazil. It consists of the Papanduva and Quiriri granitic plutons and a contemporaneous bimodal volcanic association. The Papanduva Pluton includes massive and deformed peralkaline alkali-feldspar granites with Na-Ca and Na-amphiboles and clinopyroxenes. The deformed types are the most evolved rocks in the province and carry rare ‘agpaitic’ minerals, some being described for the first time in granites from Brazil. The larger Quiriri Pluton comprises massive, slightly peraluminous, biotite syenoand monzogranites with rare Ca-amphibole. Biotite compositions are relatively homogeneous, whereas sodic amphiboles and clinopyroxenes show increasing Na and Fe3+ evolving paths. The Morro Redondo granites are ferroan, with high SiO2, alkalis and HFSE contents; the peralkaline types registering the highest fe#. LILE and HFSE abundances increase with the agpaitic index and the most evolved are HHP granites, with radiogenic heat production up to 5.7 μWm-3. Geothermobarometric estimates indicate emplacement under low pressures (~100 MPa), at temperatures up to 850-800 °C, and relatively reduced (QFM) and oxidized (+1 < ΔQFM < +3) environments for the Papanduva and Quiriri Plutons, respectively. In both cases, melts evolved to relatively high oxidation states upon crystallization progress.


INTRODUCTION
A-type magmatic provinces are widespread in the Earth's crust and have been formed since Archean times as a result of geodynamic processes associated to extensional tectonic environments.The diversity of rock types, with contrasting petrographic and geochemical signatures (e.g.Whalen et al. 1987, Eby 1992, Poitrasson et al. 1995, King et al. 1997, Schmitt et al. 2000, Litvinovsky et al. 2002, Gualda and Vlach 2007a, b, Nardi and Bitencourt 2009) is a particular feature of A-type magmatism.Although the nature of such diversity has been heavily discussed in literature, there is still no general consensus on the petrogenetic models and sources involved in their genesis (e.g.Martin 2006, Bonin 2007).The Graciosa Province, southern Brazil (Gualda and Vlach 2007a) is a typical example, where A-type granites and syenites from  http://dx.doi.org/10.1590/0001-37652014108312FREDERICO C.J. VILALVA and SILVIO R.F.VLACH two contrasted petrographic associations, namely alkaline and aluminous (subalkaline), as well as related K-rich dioritic, gabbroic and some volcanic rocks were emplaced during the final stages of the Brasiliano/Pan-African Orogeny, at the end of the Neoproterozoic.Such diversity provides an ideal setting to investigate the evolution, composition and geotectonic significance of A-type granitoids and associated rocks (Gualda and Vlach 2007a, b, c, Vlach and Gualda 2007, Vlach et al. 2011).
The Morro Redondo Complex (Góis 1995) is one of the largest and most important occurrences of A-type granites in the Graciosa Province.It crops out close to the Atlantic coast line between the states of Paraná and Santa Catarina, southern Brazil, and is made of granitic rocks of both alkaline and aluminous petrographic associations, along with a coeval bimodal volcanic association.Such characteristics make the complex an interesting site to the study of the petrographic variability of A-type rocks and their genetic relationships.In this contribution, we present and discuss general geologic, petrographic, magnetic susceptibility, as well as mineral and whole-rock chemical data for the granites of the Morro Redondo Complex, aiming to improve the knowledge of these rocks, to compare results with the available data from other occurrences of the province, and to establish a solid background for petrological studies currently in progress on the genesis and evolution of the Morro Redondo Complex, as well as the Graciosa Province as a whole.

GENERAL GEOLOGy
The A-type Graciosa Province was formed during an extensional (post-collisional sensu Liégeois 1998) tectonic environment related to the Gondwana amalgamation in south-southeast Brazil, during the final stages of the Brasiliano/Pan-African Orogeny, at ca. 580 -583 Ma (Vlach et al. 2011).The province encompasses several granitic and syenitic plutons, roughly circular to irregular in outline, intrusive into Archean and Neoproterozoic rocks of the Luiz Alves and Curitiba Microplates and the Paranaguá Terrain (Basei et al. 1992, Siga Jr et al. 1995), along an arc parallel to the present-day Atlantic coast line between the southeastern part of São Paulo and the northwestern portion of Santa Catarina states (Fig. 1a).Associated rocks include minor occurrences of K-rich diorites and gabbros, hybrid rocks and volcanics of a bimodal association.Contemporaneous volcano-sedimentary rocks are also described in the Campo Alegre, Guaratubinha and Corupá basins (Siga Jr et al. 2000, Almeida et al. 2012;Fig. 1a).
An important characteristic of the Graciosa Province is the coexistence of two distinct petrographic associations, either of alkaline or aluminous (subalkaline) affinity, which resemble many A-type provinces worldwide (e.g.Lameyre and Bowden 1982, Vlach et al. 1990, Pitcher 1993, Poitrasson et al. 1995, King et al. 1997, Litvinovsky et al. 2002, Qiu et al. 2004).The alkaline association is composed of metaluminous alkali-feldspar syenites to peralkaline hypersolvus granites, whereas the aluminous association comprises metaluminous to moderately peraluminous subsolvus syeno-and monzogranites.Detailed studies on the geology, petrography, mineralogy and geochemistry of the province can be found in Gualda and Vlach (2007a, b, c), Vlach and Gualda (2007) and references therein.
The Morro Redondo Complex extends to 25 km along N20°W and occupies ~250 km 2 between the cities of Tijucas do Sul and Garuva, states of Paraná and Santa Catarina, respectively, southern Brazil (Fig. 1b).It is intrusive into Archean granulites, gneisses and migmatites of the Luiz Alves Microplate.The eastern border is close to the N15° -25°W trending Rio Palmital-Serrinha Shear Zone (RPSSZ), the main limit between the Archean rocks (to the west) and the Neoproterozoic granitoid rocks of the Paranaguá Domain (to the east; Fig. 1a).
Granitic exposures are characterized by mountains with elevations of up to 1,600 m, alternated with remains of eroded plateaus, while flatlands with elevations around 700 -900 m define areas dominated by volcanic rocks (Fig. 2).Most of the outcrops are fairly weathered blocks and boulders, while expositions in mountain escarpments and waterfalls are scarce.Furthermore, these areas are covered by almost intact Atlantic Forest, with the exception of some parts in the western portion, where pines are exploited.Thick vegetation cover, rugged terrain and also very humid weather strongly limit access to the area and the sampling of fresh rocks, especially in the inner portions of the complex.
It was mapped only at the northernmost portion of the pluton.
4. Microgranitic facies: slightly inequigranular fine-grained alkali-feldspar microgranites, eventually with planar flow structures defined by euhedral amphibole crystals (Fig. 3d).They appear as centimetric to decametric dikes and other minor bodies which intrude the main granites of both the Papanduva and Quiriri plutons.

Quiriri Pluton
The largest Quiriri Pluton occupies the central and southern parts of the complex, covering an area of ~190 km 2 (Fig. 1b).It is mainly composed of gray to red-colored biotite granites (2 ≤ M' ≤ 9) with well-developed quartz crystals.Distinct textural varieties were identified, but they could not be mapped properly due to the poor quality of outcrops and difficult accesses.The main facies, here named Q1, is widespread in the whole pluton.
Granites show massive structures and reddish, inequigranular, medium-grained textures (Fig. 4a).Alkali feldspar forms larger, red-stained, tabular crystals and dominates over whitish tabular plagioclase.Incipient magmatic flow structures and rapakivi-like textures are rarely seen.A similar variety, Q2, with typical gray colors (Fig. 4b), locally amphibole-bearing, appears close to the northwestern portion, while a third, red-colored, relatively plagioclase-poor facies crops out in the central area and locally in the northeastern part.It was named Q3 and carries primary biotite partially to completely replaced by chlorite and other hydrothermal minerals (Fig. 4c).Minor bodies and dikes of granite-porphyries with alkali-feldspar, plagioclase and quartz phenocrysts (up to 1.2 cm, cf.Fig. 4d) in a fine-grained matrix appear in some outcrops in the northwestern and northeastern areas.These are identified as Q4 facies.Granophiric intergrowths can be seen under hand lenses in some varieties of the Q3 and Q4 facies, while miarolitic cavities and vugs are ubiquitous.Simple pegmatite pods, aplite veins, as well as microgranular enclaves and both mafic and felsic schlieren-like structures, are typical of the main Q1 facies.Enclaves include typical felsic and FREDERICO C.J. VILALVA and SILVIO R.F.VLACH mafic fine-grained varieties of granitic (Fig. 4e) and dioritic compositions, respectively, and medium to fine-grained leucocratic varieties with plagioclase and interstitial mafic minerals similar to those found in the host granite (Fig. 4f).

Volcanic and subvolcanic rocks
Volcanic rocks occupy ~40 km 2 in the northwestern and central areas of the complex (Figs.1b and 2).General geologic and petrographic data are presented by Góis (1995) and Kaul (1997).Lithotypes are mainly porphyritic and microporphyritic rhyolites and alkali-feldspar rhyolites, with infrequent welldeveloped flow structures.They are peralkaline, with Na-Ca and Na-clinopyroxenes and amphiboles.A local occurrence of alkali-feldspar rhyolite with aenigmatite as flow-oriented microphenocrysts was found in the northwesternmost area.Thin basaltic flows occur between the rhyolite layers.These basalts are made of plagioclase (andesine-labradorite), augite, pigeonite (sometimes as cores in augite), apatite, magnetite and ilmenite and show intergranular to subophitic textures.Interstitial microgranophyric intergrowths and chlorite, biotite and Ca-amphibole pseudomorphs after pyroxene are sometimes recognized.Afanitic to porphyritic andesites and andesi-basalts with plagioclase (oligoclase-andesine), augite, biotite, magnetite, ilmenite and some quartz appear in very few outcrops.
Centimetric to metric basic dikes cross cut the Quiriri granites.Despite the fewness of field relationships, most of them appear to belong to the young Mesozoic (NW-SE and NE-SW) dike swarms of the Paraná Triple Junction (Coutinho 2008), nevertheless a few others appear to be synplutonic dikes.

Cross-cutting relationships and sequence of the magmatic events
Field structural relationships among the studied facies are very scarce and, therefore, the stratigraphy of the magmatic events is still a matter of debate.Rhyolite xenoliths are observed in the Papanduva main massive granites, while related peralkaline microgranitic dikes cut the Quiriri biotite granites.Such evidences suggest the main volcanism episode preceded, to some extent, the emplacement of the Papanduva main granites, whereas the late peralkaline microgranitic varieties were emplaced later than the Quiriri biotite granites.Nevertheless, it must be remembered that the building of a pluton may be very complex, involving the emplacement of several batches of magmas with contrasted rheological properties.Thus, the available information is not sufficient to draw a reliable scenario.

MATERIALS AND METHODS
This work presents, besides conventional field and petrographic data, magnetic susceptibility (MS) and mineral and whole-rock chemical data obtained from the intrusive rocks of the Morro Redondo Complex at the facilities of the Núcleo de Apoio à Pesquisa (NAP) GeoAnalítica-USP, Universidade de São Paulo, Brazil.
MS measurements were made with the GM Instruments SM-20 Portable Susceptibilimeter, considering a mean of 10 measurements per sample taken in appropriate outcrops during the field work and in rock slabs afterwards.
Mineral compositions were obtained by Wavelength Dispersive Spectrometry (WDS) microanalyses using a JEOL JxA-8600S Electron Microprobe under operating conditions of 15 kV and 20 nA for the column acceleration voltage and beam current.Pyroxenes, amphiboles, biotite, alkali feldspar and plagioclase were analyzed following the procedures described in Gualda and Vlach (2007b).The PROZA software (e.g.Bastin and Heijligers 1990) was employed for matrix effects corrections and data reduction.Mineral formulae and estimates of Fe 2+ /Fe 3+ ratios were calculated with the Mincal software (G.A.R. Gualda and S.R.F.Vlach, unpublished data, see also Deer et al. 1992, Droop 1987).Amphibole nomenclature follows Leake et al. (1997Leake et al. ( , 2004)); Fe 2+ and Fe 3+ were estimated with a variant of the method by Schumacher (1997), as discussed in Gualda and Vlach (2005).Clinopyroxene was classified according to Morimoto et al. (1988).
Whole-rock chemical analyses were determined using Inductively Coupled Plasma Atomic Emission Spectrometry/Mass Spectrometry (ICP-AES/MS) and x-Ray Fluorescence (xRF) instruments: major, minor and some trace-elements were quantified by ICP-AES and XRF, while most trace-elements were measured by ICP-MS, following the analytical protocols described by Mori et al. (1999) andNavarro et al. (2008), respectively.Radiogenic heat production per volume (A) was calculated using Th and U contents measured from the ICP-MS, after Rybach (1988): where K 2 O is given in wt.% and Th and U in ppm.A medium rock density (ρ) of 2.70 g/cm 3 was adopted.

PETROGRAPHy
Representative quantitative modal data for the granites are presented in Fig. 5.The Papanduva and Quiriri plutons are made of hypersolvus alkalifeldspar granites and subsolvus syenogranites, respectively.Moreover, a felsic microgranular enclave from the Quiriri Pluton plots as a monzogranite.Brief petrographic descriptions of these rocks are given below; additional microstructural relationships among the main rock-forming minerals will be presented in the mineralogical section.

Papanduva Pluton
The texture of the main massive facies is characterized by large tabular crystals of mesoperthitic alkali feldspar with well-developed quartz; amphiboles and pyroxene are interstitial and homogeneously distributed (Fig. 6a).Two contrasted amphibole generations are identified: an early-crystallizing green Na-Ca amphibole, which corresponds to the main mafic phase and a late-crystallizing blue Na-amphibole as interstitial isolated crystals and overgrowths.Also a latecrystallizing phase, compositionally zoned Naclinopyroxene appears as interstitial isolated euhedral crystals, fibro-radiated aggregates, and as ubiquitous mantles around amphibole.Zircon, chevkinite, fluorite, astrophyllite and some ilmenite, magnetite and titanite are accessory minerals.
Distinct deformational textures characterize the 'protomylonitic' and 'cataclastic' facies.Of importance, several of the observed textures depicted below suggest that deformation occurred mostly under sub-magmatic conditions, i.e. involving flow of melting and crystal mushes, assisted by crystal plastic deformation (Blenkinsop 2000, Passchier andTrouw 2005), rather than in solid-state conditions.FREDERICO C.J. VILALVA and SILVIO R.F.VLACH The deformed 'protomylonitic' facies shows textures defined by oriented and deformed ellipsoidal to irregular Na-amphibole, perthitic alkali feldspar and minor quartz megacrysts (2.0 -4.0 mm), the first displaying compositional zoning and the last undulose extinction.They are surrounded by a finegrained, saccharoidal matrix made of recrystallized quartz, slightly perthitic microcline and albite, joined by Na-clinopyroxene and accessory minerals (Fig. 6b).On the other hand, in the deformed 'cataclastic' facies, interstitial and deformed Na-clinopyroxene and amphibole crystals, coarse quartz surrounded by fine recrystallized grains, crystal microfractures (mainly in coarse alkali feldspar and quartz) filled by fine-grained, late-crystallizing aggregates of quartz and feldspar, along with bent mesophertitic alkali feldspar crystals are typical features (Fig. 6c).Fluorite, astrophyllite, titanite, aenigmatite and some ilmenite are common accessory minerals in both facies.Zircon and late magnetite appear only in the deformed 'cataclastic' facies, while combinations of late to post-magmatic 'agpaitic' Ti-, Zr-, and REEbearing rare silicates and oxides, such as narsarsukite, neptunite, elpidite and other (Na,K)-zirconosilicates, britholite, turkestanite, nacareniobsite, brookite and some as-yet unidentified minerals, are widespread in the deformed 'protomylonitic' facies, even in miarolitic cavities and vugs (Vilalva and Vlach 2010, Vilalva et al. 2013, Vlach and Vilalva 2007).
Hydrothermal alteration is ubiquitous in all petrographic facies except the grayish Q2 (Fig. 4).Related textures include: biotite crystals replaced by chlorite + epidote + magnetite; post-magmatic albite filling interstices between alkali feldspar crystals or as partial rims around plagioclase; sericitic or saussuritic plagioclase; and sericitic, red-clouded alkali feldspar (e.g.Figs.4c, d).The red-clouding phenomenon in feldspars occurs due to the precipitation of rosettes and needles of hematite from hydrothermal fluids into micro pores in the alkali feldspar surface, as a result of sub-solidus mineral-fluid replacement processes (e.g.Putnis et al. 2007).Indeed, in many outcrops, granite boulders show the red-staining concentrated in specific areas, which are always associated with epidote-filled microfractures.
Typical microgranular felsic enclaves are monzogranites with quartz, feldspars and chlorite pseudomorphs after biotite.Euhedral alkali feldspar, rounded quartz and minor plagioclase megacrysts, arguably xenocrysts from the host granite, are common (Fig. 7e).On the other hand, mafic microgranular enclaves are quartz-monzodiorites with biotite as the main mafic mineral, together with apatite, magnetite, A-TYPE GRANITES OF THE MORRO REDONDO COMPLEX and ilmenite.Leucocratic microgranular enclaves are made mainly (up to 80% volume) of euhedral tabular plagioclase (andesine).Interstitial chlorite, epidote, fluorite, titanite and magnetite have totally replaced the primary biotite and/or amphibole (Fig. 7f).

MAGNETIC SUSCEPTIBILITIES
Magnetic susceptibility measurement results are displayed as histograms in Fig. 8.Most values obtained for the Papanduva Pluton are lower than 1.0 x 10 -3 SI, with a mean and mode values of 0.42 x 10 -3 and 0.1 x 10 -3 SI (Fig. 8a).Exceptions are some samples from the deformed 'cataclastic' facies that yield values as high as 6.0 x 10 -3 SI, due to the presence of almost pure post-magmatic magnetite in micro-fractures or around Na-amphibole and pyroxene.Conversely, the Quiriri Pluton, albeit for some few measurements down to 0.04 x 10 -3 SI (Q2 facies), registers mean and mode values of 2.57 x 10 -3 and 2.3 x 10 -3 SI (Fig. 8b), up to 5-fold higher than those obtained for the Papanduva Pluton, as expected from their modal primary magnetite content.
The MS values of the peralkaline rocks from the Papanduva Pluton are amongst the lowest ever registered for rocks from the alkaline association within the Graciosa Province (typical values around 1.0 x 10 -3 SI).In contrast, values for Quiriri samples, as well as their range of variation, are very similar to those measured in the aluminous association elsewhere within the province (cf.Gualda and Vlach 2007a).

MINERALOGy
General microstructure and chemistry of the main granite-forming minerals are presented below.Representative chemical compositions of feldspars, amphiboles, clinopyroxenes and biotite are given in Table I.

Alkali Feldspar
Alkali feldspar from the Papanduva Pluton forms mesoperthitic, euhedral to subhedral crystals in the massive and microgranitic facies, and slightly perthitic megacrysts and fine-grained microcline in the deformed 'protomylonitic' and 'cataclastic' facies.Integrated compositions of mesoperthitic crystals and perthitic megacrysts, which should approach primary compositions, vary between Ab 35- 66 An 0-1 Or 65-34 and Ab 2-15 An 0 Or 99-85 , respectively (Fig. 9).They are slightly enriched in Fe 3+ when compared to alkali feldspars of peralkaline rocks from the Serra da Graciosa region within the province (Gualda and Vlach 2007b).Late to postmagmatic albite is also observed as interstitial pristine crystals or as swapped-rims around alkali feldspars in most samples.In the deformed 'protomylonitic' and 'cataclastic' facies, albite appears as granoblastic crystals in the matrix, as well as euhedral laths forming intergrowths with mafic minerals, which resemble the khybinitic texture of some undersaturated alkaline rocks (e.g.Gerasimovsky et al. 1974).In both cases, compositions are close to the ideal end-member (Ab 99-100 An 0-0.1 Or 1-0 , cf.Table I, Fig. 9), but the laths register slightly higher Fe 3+ contents (up to 1.7 wt.% Fe 2 O 3 ) than the most typical post-magmatic albite crystals (up to 1.3 wt.% Fe 2 O 3 ).
Alkali-feldspar from the Quiriri samples crystallizes as perthitic, euhedral to subheudral crystals, with well-developed chessboard textures.Their compositions vary around Ab 26-41 An 0-1 Or 74-58 (Table I, Fig. 9), and are similar to those observed in other plutons of the aluminous association elsewhere within the Graciosa Province (Gualda

Plagioclase
Primary sodic plagioclase occurs in the Quiriri Pluton as isolated euhedral to subhedral tabular crystals, sometimes in aggregates of 2 to 4 grains, often with post-magmatic partial albite rims and sericitic and saussuritic alterations at different intensities.They correspond to oligoclase, with compositions around Ab 73-87 An 24-11 Or 2-8 and normal to slightly oscillatory compositional zoning (Table I, Fig. 9).On the other hand, plagioclase from both felsic microgranular and leucocratic medium to fine-grained enclaves shows more calcic compositions, up to sodic-andesine (An 30-35 ), as qualitatively verified under the microscope.

Amphiboles
Sodic-calcic and sodic amphiboles are the main mafic phases in the Papanduva peralkaline granites.
They appear as isolated interstitial crystals, in aggregates of 3-4 grains or as elongated deformed FREDERICO C.J. VILALVA and SILVIO R.F.VLACH megacrysts in the deformed 'protomylonitic' facies.Most crystals display concentric to irregular patchy compositional zoning.Na-Ca amphibole (ferrorichterite) is found only in the massive facies, whilst sodic varieties are ubiquitous and correspond to both arfvedsonite and riebeckite, the latter being typical of the deformed 'cataclastic' and microgranitic facies.Compositional variations are defined by increasing Si, Fe 3+ , Na and K and decreasing Al, Fe 2+ and Ca contents from core to crystal rims.However, these variations do not span a wide compositional range as observed in other plutons of the Graciosa Province, since Ca-richer compositions are absent (Table I, Fig. 10a).Ca-amphiboles occur only in samples from the grayish Q2 facies of the Quiriri Pluton.They form rare, isolated, euhedral crystals partially replaced by chlorite, epidote, magnetite and fluorite.In some cases, only pseudomorphosed crystals are seen.Compositions correspond to ferrohornblende, edenite, and ferro-edenite, with Na contents (up to 2.4 wt.% Na 2 O) higher than those registered in similar plutons of the province (Gualda and Vlach 2007c).Zoning is very discrete, with some increasing in Na and K and decreasing in Ca and Al contents towards crystal rims (Table I, Fig. 10a).

Clinopyroxenes
Clinopyroxenes appear in samples of the Papanduva Pluton as interstitial yellow-greenish isolated crystals and in aggregates of several prismatic and/or fibrous grains.They comprise both late and post-magmatic phases and often appear as mantles around amphiboles.Concentric, patchy and irregular compositional zoning are common features.Some samples from the massive and deformed 'protomylonitic' facies present two other textural generations of pyroxene, recognized by their contrasted pleochroic schemes, one with dark-green, and another with orange to yellow pleochroic colors.The former is replaced by a yellow-greenish clinopyroxene whereas the latter appears as mantles around both phases in the deformed 'protomylonitic' facies.
The widespread yellow-greenish clinopyroxene corresponds to an aegirine or titanian aegirine (Aeg 81-99 Jd 5-0 WEF 15-0 ), with up to 7.0 wt.% TiO 2 .The dark-green variety is an aegirine-augite (Aeg 72 - 80 Jd 1 WEF 27-18 ) and the orange-yellowish phase corresponds to an almost pure aegirine (Aeg 93- 97 Jd 3-1 WEF 5-2 ) with relatively high Mn contents (up to 0.97 wt.% MnO, cf.Table I).The main compositional trend is defined by increasing Na and Fe 3+ and decreasing Ca and Fe 2+ contents from crystal cores to rims, in a relatively narrow range.Compositions plot along the Na (Aeg) -Fe 2+ +Mn (Hd) axis in the ternary plot Na (Aeg) x Mg (Di) x Fe 2+ +Mn (Hd) of Fig. 10b, most of them close to the Na (Aeg) apex, a compositional trait that highly contrasts with the observed evolutional trends in the whole Graciosa Province, marked by an initial decrease in Mg and increase in Fe 2+ + Mn, followed by a moderate increase in Na contents (Fig. 10b).Therefore, clinopyroxenes from the Papanduva Pluton correspond to the most evolved compositions observed elsewhere within the province, with high Na (9.7 -13.6 wt.% Na 2 O) and negligible Mg (lower than 0.2 wt.% MgO) contents.

Biotite
Biotite is the typical mafic mineral in samples from the Quiriri Pluton.It occurs as interstitial crystals with orange to brownish pleochroism.Compositions are nearly homogeneous, with Fe/(Fe+Mg) cationic ratios and Al IV varying between 0.56 -0.70 and 2.1 -2.5, respectively (Table I, Fig. 10c).Crystals in the mafic microgranular enclaves are slightly more magnesian, with Fe/(Fe+Mg) ratios between 0.47 and 0.61.Most compositions are equivalent to those commonly registered in biotites from anorogenic alkaline suites (cf.Abdel-Rahman 1994).They partially overlap the compositions of biotite in plutons of the Serra da Graciosa Region (Gualda and Vlach 2007b)  are more magnesian than biotite from the Mandira (Santos and Vlach 2010) and Guaraú Massifs (R.P. Garcia and S.R.F.Vlach, unpublished data) from the Graciosa Province (Fig. 10c).
A remarkable compositional feature of the studied biotite, as well as from most occurrences in the province, is that it does not follow the Feavoidance model of Muñoz (1984), and variable positive correlations are observed between F and Fe contents.In fact, the calculated x F and x Mg molar fractions, when plotted against each other, define a field in which this model does not play a major role (Mason 1992, Charoy andRaimbault 1994).

WHOLE-ROCK GEOCHEMISTRy
Major and trace-element compositions of representative granite samples of Papanduva and Quiriri plutons, for which a complete FRx and ICP data set is available, are presented in Table II.Additional data may be requested from the first author.Moreover, some previous data are also presented by Kaul and Cordani (2000) for granites and Góis (1995) for granites and volcanic rocks.In the latter, an alkaline nature for the rhyolites, with varieties of both comendites and panterellerites, and a calc-alkaline to alkaline nature for basalts, andesi-basalts and andesites were pointed out.Most of the major and trace-element geochemical signatures of the granites from Morro Redondo Complex are typical of A-type or intraplate granites from other occurrences in the Graciosa Province and elsewhere (Collins et al. 1982, Pitcher 1993, Whalen et al. 1987, Vlach and Gualda 2007, Nardi and Bitencourt 2009, Frost and Frost 2011).They are alkali-rich (8.7 ≤ Na 2 O + K 2 O ≤ 9.3 wt.%), ferroan (Frost et al. 2001, Frost andFrost 2011) evolved rocks that exhibit a narrow compositional range, with 74 ≤ SiO 2 ≤ 78 wt.%.In the normative haplogranitic Or-Ab-Qz ternary (Fig. 11), built according to the projection scheme of Blundy and Cashman (2001) to consider Anbearing compositions, these rocks plot close to the granitic minimum at considerably low pressures.The ternary also depicts the relatively Qz-poor and plagioclase-rich nature of the aluminous samples from the Quiriri Pluton.

Plutons
Selected geochemical diagrams are shown in Fig. 12 to emphasize the main contrasts between the alkaline and aluminous (subalkaline) granites.The fe# numbers are ≥ 0.96 and between 0.87 and 0.91, while molecular ASI (Alumina Saturation) and AI (Agpaitic) indexes vary between 0.76 -0.94, 1.04 -1.28 and 1.00 -1.04, 0.88 -0.91 in the peralkaline and in the main peraluminous granites from the Papanduva and Quiriri plutons, respectively.In the former, these indexes show a distinct larger range of variation, as well as a very good positive correlation.It is noteworthy that in the Quiriri Pluton, the hornblende-bearing granite (facies Q2), as well as the felsic enclave hosted in the main Q1 granites have lower fe# (0.82 and 0.83, respectively) and AI, while the granite porphyries (facies Q4) present fe# values similar to the peralkaline granites (0.99 -1.00) as well as a somewhat higher AI.As expected, the peralkaline granites register lower CaO contents, as well as Al 2 O 3 /Fe 2 O 3 and K 2 O/Na 2 O molecular ratios than the main aluminous ones.These ratios correlate positively in the peralkaline samples.
Typical chondrite-normalized trace-element patterns are displayed in Fig. 13.Compared with the Quiriri main peraluminous Q1 granites, which present relatively monotonous patterns, the Papanduva peralkaline granites are relatively enriched in the alkaline metals, Zn, Ga, Th, Nb, Zr, Hf, y, M-HREE, and depleted in the alkaline-earth metals, P and Ti.The relative enrichment in HFSEs of the peralkaline granites is significant, with Zr, Nb, y, REE T abundances of up to 2430, 88, 320 and 996 ppm, respectively.In the Quiriri Pluton, the felsic enclave, with lower fe#, as well as the granite porphyries, with higher fe#, tend to present greater incompatible element abundances.Correlations between selected trace elements contents with the Agpaitic Index are depicted in Fig. 14.This plot reinforces the findings reported above and, of importance, depicts the wide variation range and the well-marked positive correlation of most of the LIL and HFS elements with AI as registered in the chemical signature of the peralkaline granites.
Total REE+y contents vary between ca.250 and 1150 ppm and are between ca. 1 and 3 orders of magnitude higher than those for chondrite (Fig. 15).Thompson (1982), plus Li, Zn and Ga after McDonough and Sun (1995).Symbols as Fig. 5.

107
A-TYPE GRANITES OF THE MORRO REDONDO COMPLEX granites, the patterns for the main peraluminous Quiriri granites show a higher fractionation of the LREE over HREE and within the LREEs and the HREEs, with La N /yb N , La N /Nd N and Dy N /Lu N ratios between 10 -22 and 3 -16, 3.1 -3.8 and 1.7 -3.5 and 1.1 -1.5 and 0.7 -1.9, respectively.Eu negative anomalies are a typical feature in all the investigated samples, with Eu/Eu* [Eu* = (Sm N *Gd N ) 0.5 ] between 0.11 -0.15 and 0.21 -0.28 for the Papanduva and Quiriri plutons, respectively.Altogether, geochemical signatures of the Quiriri Pluton are very akin with other peraluminous rocks from the aluminous association in the Graciosa Province (e.g.Gualda andVlach 2007a, Vlach andGualda 2007, cf. Fig. 12).However, with the exception of the felsic enclave, rocks with SiO 2 < 74.4 wt.% are lacking in this pluton (cf.Table II).On the other hand, the peralkaline alkalifeldspar granites of the Papanduva Pluton include the most evolved peralkaline rocks that constitute the alkaline association in the province.Boynton (1984).Symbols as in Fig. 5.

RADIOGENIC HEAT PRODUCTION
Radiogenic heat is generated by the decay of radioactive isotopes 40 K, 232 Th, 235 U and 238 U and is directly related to the chemical and thermal evolution of the crust (e.g.Jaupart and Mareschal 1999, 2010, Bea 2012).Heat energy enhances hydrothermal circulation and high heat producing (HHP) granites are often associated with ore deposits and geothermal anomalies.Representative heat productions per unit volume (A) due to intrusive rocks of the Morro Redondo Complex are presented in Table II.

CRySTALLIZATION CONDITIONS
The quantification of intensive parameters related to the emplacement and crystallization of the magmas that formed the A-type granites of the Morro Redondo Complex, and the Graciosa Province as a whole, is not an easy task, due to the lack of appropriate mineral assemblages, compositions and/or the intense late to post-magmatic transformations (e.g.Vlach andGualda 2007, Anderson et al. 2008).
Notwithstanding, a qualitative assessment may be drawn, as detailed below.
LITHOSTATIC PRESSURE AND TEMPERATURES Gualda and Vlach (2007a) emphasize that geological and petrographic evidences indicate that the emplacement of plutons from the Graciosa province are incompatible with confining pressures higher than ca.200 MPa, an observation which is also in accordance with available gravimetric data (Hallinan et al. 1993).The scenario does not diverge for the Morro Redondo Complex, where the association of coeval plutonic and volcanic rocks, the presence of vugs, miarolitic cavities, volcanic xenoliths, as well as of granophyric inter-growths in the granites, point to crystallization in shallow crustal levels.Our Ab-Or-Qz normative data also supports this inference (Fig. 11).
The assemblage biotite + hornblende + titanite + Fe-Ti oxides (+ quartz + alkali feldspar + plagioclase) in samples from the Quiriri Pluton allows for the application of the geobarometer Al-in-hornblende of Anderson and Smith (1995), calibrated with the plagioclase-hornblende thermometry of Holland and Blundy (1994).Pressure estimates vary between 60 and 120 MPa, with a mean value of 80 (± 20) MPa (Fig. 17a), which seems to be a reasonable result, in agreement with estimated confining pressures for other shallow alkaline massifs and complexes elsewhere (e.g.Larsen and Sørensen 1987, Potter et al. 2004, Mann et al. 2006).However, this value may be underestimated, since plagioclase compositions in the Quiriri Pluton are relatively sodic (An 8-27 ) and so, the expected Al IV contents in hornblende would be lower than those observed in calibrated experiments (Anderson and Smith 1995).
Zircon and apatite saturation temperatures were estimated for Quiriri samples following Watson and Harrison (1983, see also Hanchar and Watson 2003and Miller et al. 2003) and Harrison and Watson 1984 (see also Pichavant et al. 1992).Results are presented in Table II.All samples are within the calibrated range specified by Miller et al.

109
A-TYPE GRANITES OF THE MORRO REDONDO COMPLEX (2003), with a M factor [ = (Na+K+2Ca)/(Al•Si), in cations] between 1.36 and 1.46.Evaluated temperatures range from 794 to 860 °C, with a mean of 807 °C (Fig. 17b).Most samples gave temperatures close to 800 °C, a value significantly lower than temperature estimates obtained for similar plutons from the Graciosa Province (Gualda and Vlach 2007a) and A-type granites elsewhere (e.g.Poitrasson et al. 1995, King et al. 1997, King et al. 2001), in the range 850 -900 °C.Apatite saturation temperatures are always higher (800 -897 °C), with a mean of 834 °C.The felsic enclave has zircon and apatite saturation temperatures of 847 and 897 °C, respectively (Fig. 17b).Holland and Blundy (1994) vs. Al-in-hornblende barometric estimates (P in MPa) of Anderson and Smith (1995).Uncertainty lines in T and P in each estimative represents 1σ precision error.(b) Zirconium-Saturation Thermometry estimates (T Zr °C) of Watson and Harrison (1983) vs. Apatite Saturation Thermometry estimates (T ap °C) of Harrison and Watson (1984).Symbols as in Fig 5 .Plagioclase-hornblende equilibrium temperatures were computed according to Holland and Blundy (1994), based on the reaction edenite + albite ↔ richterite + anorthite (see Anderson 1996).Estimated temperatures range from 629 to 655 °C, with a mean of ~643 (± 4) °C (Fig. 17a).They should be, however, interpreted with caution, given the high fe# values of Ca-amphiboles in the Quiriri Pluton, a feature that also prevents the use of the amphibole geothermometer of Ridolfi et al. (2010).Although qualitative, these temperatures estimates partially overlap those derived from the plagioclase -alkali feldspar solvus (500 -650 °C, Fig. 9) and are consistent with the expected close-to-solidus temperatures in such granitic systems.
In peralkaline rocks like those from the Papanduva Pluton, any estimates of zircon or apatite saturation temperatures may result in meaningless values (e.g. Watson 1979, Keppler 1993, Miller et al. 2003).Although some authors argue that the crystallization of mineral phases such as Naamphiboles and pyroxenes may allow magmas to turn saturated in Zr (cf.Watson 1979, Hanchar andWatson 2003), and others even consider zircon saturation temperatures as reasonable estimates (e.g.Shellnutt and Iizuka 2011), in peralkaline systems, even if zircon is a crystallizing phase and the M parameter is within the calibration range of Watson and Harrison (1983), Zr does not necessarily behave FREDERICO C.J. VILALVA and SILVIO R.F.VLACH as an essential structural trace element, since it may be also incorporated in significant amounts by other essential or accessory minerals.Furthermore, the positive correlation between AI and Zr contents in our samples indicates that Zr solubility increased with peralkalinity.Therefore, the calculated zircon saturation temperatures for zircon-bearing samples of the Papanduva Pluton (880 -970 °C, mean ~930 °C) appear to be in disagreement with several evidences from peralkaline volcanic systems worldwide (cf.Macdonald 2012 and references therein); nevertheless they are not out of the expected range for some 'dry' A-type granites (e.g.Clemens et al. 1986, White et al. 2005).
Qualitative estimates of the solidus temperature for the Papanduva Pluton can be obtained from the mineral assemblage.Because of the presence of ferrorichterite and arfvedsonite, as well as aenigmatite as an important magmatic accessory phase, maximum solidus temperatures are suggested to fall within the interval between 700 -750 °C (e.g.Ernst 1968, Thompson and Chisholm 1969, Scaillet and MacDonald 2001), which is in agreement with alkali feldspar solvus estimates, between 650 -750 °C (Vilalva 2007).

REDOx CONDITIONS
Mineral assemblages and mafic silicate compositions observed in the Quiriri Pluton point to relatively oxidizing crystallization conditions.The paragenesis biotite ± Ca-amphibole + quartz + titanite + magnetite ± ilmenite indicates ƒ O2 conditions close to or higher than the TMQAI [titanite -magnetite -quartz -amphibole (Fe-tremolite)ilmenite] buffer (Noyes et al. 1983, Wones 1989), for which precise thermodynamic parameters were not well established yet.The fe# number [ = Fe/(Fe + Mg), cations] of biotite and amphiboles leads to a similar conclusion.The equilibrium: a annite(Btss) + 0.5 O 2 = a sanidine (AFss) + a magnetite (Mtss) + H 2 O where a stands for the activity of the indicated component in the main mineral solid solutions, was studied and calibrated by Wones (1981).It indicates that for a given ƒ H2O , the higher the oxidation state is, the lower the expected annite content within biotite will be, as the equilibrium will shift to the right.Similar reasoning can be applied to the fe# values observed in Ca-amphiboles (e.g.Anderson and Smith 1995).Using this equilibrium and a large data set including independent ƒ O2 determinations and fe# numbers in biotite from magnetitebearing Mesoproterozoic granites from Laurentia (USA), Anderson et al. (2008) estimated Δ QFM values as a function of the biotite fe# number.Our compositions, mostly with 0.6 ≤ fe# ≤ 0.7, give Δ QFM ≈ +1, a value one or two units lower than the estimates based on the TMQAI equilibrium (Vlach and Gualda 2007).The fe# numbers measured in Ca-amphibole, down to 0.4, point also towards relatively high oxidizing conditions (Anderson and Smith 1995).
The stability of Na-Ca and Na-amphiboles in the peralkaline Papanduva granites suggest relatively reduced crystallization conditions, between the MW (Magnetite -Wüstite) and QFM (Quartz -Fayalite -Magnetite) buffers (Ernst 1968, Stolz 1986, Marks et al. 2003, Pe-Piper 2007).Such conditions turn progressively more oxidizing as crystallization proceeds and the occurrence of aenigmatite in an antipathetic relation with Fe-Ti oxides, a typical feature of several samples from the Papanduva Pluton, suggests crystallization inside the 'no-oxide field', an area in the T -ƒO 2 space where aenigmatite, aegirine and quartz coexist in the absence of Fe-Ti oxides, located above the QFM buffer in supersaturated rocks (Nicholls and Carmichael 1969, see also Vilalva 2007).Moreover, the relative stability of Na-amphiboles and aegirine depends on ƒ O2 , ƒ H2O , and the availability of Na meta and di-silicates hypothetical molecules in the melt, as described by the equillibrium: A-TYPE GRANITES OF THE MORRO REDONDO COMPLEX 4 riebeckite + 4 (Na 2 SiO 3 ) + 2 (Na 2 Si 2 O 5 ) + 3 O 2 = 20 aegirine + 4 H 2 O and a similar one relating aegirine to arfvedsonite (Bailey 1969, see also Deer et al. 1978).This reaction shows that in aenigmatite-absent rocks, the late to post-magmatic crystallization of aegirine, as isolated crystals or mantles around amphiboles, is favored in more oxidizing environments, limited by QFM and HM buffers (Bailey 1969, Vilalva 2007).

CONCLUSIONS AND FINAL REMARKS
The Morro Redondo Complex, one of the largest complexes in the Graciosa Province, is composed of high-SiO 2 rocks from the alkaline and aluminous associations of A-type granites that form two contrasting plutons namely Papanduva and Quiriri, as well as coeval acid and basic to intermediate volcanic rocks.Scarce field evidence suggests that granites were emplaced slightly after the volcanics, and at least some peralkaline rocks were emplaced after the main aluminous ones.
The Papanduva Pluton is made of hypersolvus aegirine ± arfvedsonite -alkali-feldspar granites with massive and deformational structures, the latter including 'cataclastic' and 'protomylonitic' facies, and low magnetic susceptibilities that formed in relatively reduced environments.Textural relationships between mafic and felsic minerals indicate that they followed an agpaitic crystallization sequence (e.g.Sørensen 1997, Andersen et al. 2010), in which main and accessory mafic phases appear after quartz and alkali feldspar.
The granites of the Papanduva Pluton are among the most evolved peralkaline rocks within the Graciosa Province, showing Agpaitic Indexes up to ca. 1.3, the highest Na and Fe 3+ contents in Na-amphiboles and clinopyroxenes, as well as the highest LILE and HFSE abundances.These correlate positively with the peralkalinity grade (as measured by the Agpaitic Index), a geochemical signature that led to the crystallization of rare 'agpaitic' assemblages in the more evolved facies, as evidenced by the Ti-, Zr-and REE-rich unusual accessory mineralogy, formed during late to post-magmatic stages.It is worth mentioning that several among these minerals, including aenigmatite, neptunite, narsarsukite, Na-K zirconosilicates, nacareniobsite, turkestanite, as well as to date poorly studied and/or unidentified minor phases (Vilalva and Vlach 2010, Vilalva et al. 2013, Vlach and Vilalva 2007) are described for the first time in peralkaline granites from Brazil.Such mineralogical and textural features, along with geochemical data, indicate that the more evolved the liquids are, the higher the Agpaitic Index will be, as well as the Na 2 O, Fe 2 O 3 T , LILE and HFSE abundances.
The Quiriri Pluton has the largest area extent and comprises slightly peraluminous (1.05 < ASI < 1.20), subsolvus biotite ± hornblende syenogranites, as well as granite porphyries with higher magnetic susceptibilities, formed under relatively oxidizing conditions.Similar to other rocks of the aluminous association within the Graciosa Province (Gualda andVlach 2007a, Vlach andGualda 2007), Quiriri granites have homogeneous compositions, with relatively lower fe# numbers and Fe 2 O 3 T /Al 2 O 3 molecular ratios and higher Ca and alkaline earth metals, and are characterized by relatively Caand Al-rich mafic mineral paragenesis defined by annitic biotite ± hornblende + titanite ± allanite + magnetite + ilmenite + fluorite (+ apatite + zircon).Consequently, biotite and hornblende show discrete chemical variations, contrary to what is observed in amphiboles and clinopyroxenes from the peralkaline Papanduva granites.Furthermore, a remarkable feature of many samples from the Quiriri Pluton is the hydrothermal alteration which can be locally pervasive and in which some sulfides are seen.
Both plutons register relatively high heat productions.The highest A values (of up to 5.7 μWm -3 ), are found in the deformed 'protomylonitic' granites of the Papanduva Pluton and approach those tipically found in HHP granites elsewhere.Such FREDERICO C.J. VILALVA and SILVIO R.F.VLACH characteristics reflect the geochemical signatures of the studied granites and are features mostly attributed to inheritance from their source rocks, enhanced later by magmatic fractionation processes.
Geological and petrographic evidence indicates that both plutons were emplaced at shallow crustal levels.Semi-quantitative pressure estimates for the hornblende-bearing Quiriri samples are about 100 MPa.Estimated close-to-liquidus zircon and apatite saturation temperatures for the Quiriri main granites vary between 800 and 850 °C, while for a felsic monzogranitic enclave within these rocks they range from ca. 850 to 900 °C, the higher values found through apatite saturation estimates.The presence of ubiquitous minute apatite inclusions in zircon crystals (F.C.J. Vilalva et al., unpublished data) suggest that this phosphate may be a liquidus phase, while zircon is coeval or slightly late.Altogether, these temperature estimates are somewhat lower than those observed in similar granites from the Serra da Graciosa region (Gualda and Vlach 2007a).Considering the close-to-solidus temperature calculated for the main Quiriri granites at ~650 °C, melts crystallization range was about 200 -250 °C.Given the peralkaline nature of the Papanduva melts, it is difficult to attribute confidence to zircon saturation temperature estimates (up to 970 °C).Based on some data from alkaline rhyolite occurrences and laboratory experiments (Macdonald 2012, Scaillet andMacdonald 2001), we suggest a crystallization interval between ~800 and 600 °C for the peralkaline melts.
Ti-in-quartz temperatures (Wark and Watson 2006) in representative samples result in mean values of about 740 and 830 (± 20) °C for the main granites and felsic enclave from the Quiriri Pluton and 715 (± 20) °C for the Papanduva Pluton (our unpublished data).Except for the felsic monzogranitic enclave, such temperatures appear to be underestimated when compared with the saturation temperature estimates for the aluminous granites, as in fact, quartz was expected to be a relatively early crystallizing phase, considering the involved textures, rock compositions and emplacement pressures.
The peralkaline melts crystallized arguably under ƒO 2 conditions close to or slightly below the QFM buffer, some of them within the 'no-oxide' field of Nicholls and Carmichael (1969).Amphibole and clinopyroxene compositional variations, as well as the development of aegirine mantles around amphibole, indicate the crystallization followed an oxidizing path, ending close to the HM buffer in the post-magmatic stage, a common feature of most peralkaline occurrences in the Graciosa Province (e.g.Vlach and Gualda 2007).Conversely, melts that formed the Quiriri granites crystallized under more oxidizing conditions (Δ QFM ≥ 1), close to the TMQAI buffer (Noyes et al. 1983, Wones, 1989), with evolution also following an oxidizing path.

Figure 2 -
Figure 2 -SRTM 3D digital model for the Morro Redondo Complex and surrounding areas based on contour lines equidistant at 5 meters through mathematical interpolation using the software Global Mapper.P: Papanduva Pluton, Q: Quiriri Pluton, V: main outcrops of the associated bimodal volcanic rocks, LA: Luiz Alves Microplate, E: Estrela high-K calc-alkaline granite (Paranaguá Terrain).
GRANITES OF THE MORRO REDONDO COMPLEX

Figure 8 -
Figure 8 -Histograms (absolute frequency) showing the magnetic susceptibility (MS) variation for representative samples of the Papanduva (a) and Quiriri (b) Plutons.

Figure 9 -
Figure 9 -Average compositions of core, intermediate zone and rim for alkali feldspar and albite, and individual chemical analysis of plagioclase in the An-Ab-Or molecular ternary plot for representative samples of the Quiriri (a) and Papanduva (b) Plutons.Available chemical data for feldspars from other plutons of the Graciosa Province are shown for comparison (c): plutons of the alkaline (1) and aluminous (2) associations in the Serra da Graciosa region(Gualda and Vlach 2007b).Solvus curves for Ptotal = 100 MPa, according to the model afterFuhrman and Lindsley (1988).Inset ternary plots in (a) and (c) show compositions of coexistent plagioclase and alkali feldspar crystals.Symbols as in Fig.5.

Figure 11 -
Figure 11 -Normative compositions for selected samples of the Quiriri and Papanduva Plutons in the haplogranitic Or-Ab-Qz ternary system.Units are weight fractions.Silica-feldspar cotetics from Blundy and Cashman (2001).Symbols as in Fig 5.

Figure 14 -
Figure 14 -Variation diagrams showing the behavior of selected LIL (a) and HFS (b) elements vs. AI for samples of the Quiriri and Papanduva Plutons, Morro Redondo Complex.

Figure 16 -
Figure 16 -Histogram showing typical values for the radiogenic heat production (A) for selected samples from the Quiriri and Papanduva plutons, Morro Redondo Complex.

TABLE II (continuation)
A-TYPE GRANITES OF THE MORRO REDONDO COMPLEX