Z. geol. Wiss., Berlin 36 (2008) 6: 383 – 404, 11 Abb., 2 Tab.
The Pirituba calc-alkaline granitoid sequence (State of São Paulo, Brazil):
A differentiation of granodioritic crustal melts up to tourmaline granites
and pegmatites*
Die kalkalkalinen Granitoide der Pirituba Abfolge (Staat São Paulo, Brasilien):
Eine Differentiation granitischer Krustenschmelzen bis hin zu Turmalingraniten
und Pegmatiten
Suíte Pirituba de granitóides cálcio-alcalinos (Estado de São Paulo, Brasil):
Um exemplo da evolução de fusões crustais granodioríticas até turmalina granitos
e pegmatitos
GIULIO MORTEANI (Isen), JANINE P. TEUPPENHAYN (Bönen), JOHANN H. D. SCHORSCHER (São Paulo), JOSÉ B.
MADUREIRA FILHO (São Paulo), CHRISTINE PREINFALK (München)
DE
Key words: Boron, Brazil, fractionation, granites, isotopes, Mantiqueira, pegmatites, Perus, Pirituba, Rare Earths, Bor,
Brasilien, Fraktionierung, Granite, Isotope, Manitiqueira, Pegmatite, Perus, Pirituba, Seltene Erdelemente, Palavraschave: Boro, Brasil, fracionamento magmático, granitos, isótopos, Mantiqueira, pegmatitos, Perus, Pirituba, Terras
Rarass
Abstract
The here studied granitoids of Mairiporã, Taipas, Cantareira, Anhanguera, Pirituba and Perus belong to the Pirituba suite and intruded
in the area of São Paulo (Brazil) between 600 and 520 Ma at the end of the upper Proterozoic Brasiliano tectonothermal event into
the metavolcanics and metasedimentary rocks of the São Roque group. The São Roque group is part of the Ribeira fold belt of
Brasiliano age that borders the São Francisco craton to the east. 87Sr/86Sr initial ratios of 0.7231 ± 0.0003 for the Anhanguera and of
0.7209 ± 0.0011 for the Perus granitoids indicate for the respective magmas a crustal source. Both, the Perus granite and the
pegmatite are characterized by very high boron contents of about 5071 ppm to 19472 ppm, respectively. Tourmaline is the only
femic mineral in both rocks. The elevated boron contents demonstrate an involvement of boron-rich pelites of marine origin in the
anatectic magma genesis. For the Cantareira granitoid the 87Sr/86Sr initial ratio of 0.7100 ± 0.0088 suggests a crustal origin, too, but
with an admixture of a mantle component. The layering shown by both the Perus granite and the Perus pegmatite is produced by
differences in tourmaline content. Tourmaline crystallisation was driven by periodic changes in the boron concentration of the melt
and not by a late- to postmagmatic metasomatic tourmalinisation. For the Pirituba granitoid suite field evidence, major and trace
elements including REE and isotope data suggest a deep seated continuous evolution by differentiation from a granodioritic
composition towards the highly differentiated Perus syenogranite and pegmatite.
*
With this paper we would like to honour the memory of Professor G. Tischendorf honorary member of the Association of the Genesis of Ore
Deposits and author of many leading papers on the silicic magmatism and metallogenesis of the Erzgebirge.
Z. geol. Wiss. 36 (6) 2008
383
G. MORTEANI et al.
Zusammenfassung
Die hier untersuchten Granitoide von Mairiporã, Taipas, Cantareira, Anhanguera, Pirituba und Perus intrudierten im Gebiet
von São Paulo (Brasilien) in die Metavulkanite und Metasedimente der São Roque Gruppe am Ende des tektonothermalen
Oberproterozoischen Brasiliano Ereignisses im Zeitraum zwischen 600 und 520 Ma. Die Granitoide werden als Pirituba Abfolge
bezeichnet. Die São Roque Gruppe ist Teil des Brasiliano-Ribeira Faltengürtels, der den Ostteil des São Francisco Kratons begrenzt.
Initiale 87Sr/86Sr Verhältnisse von 0.7231 ± 0.0003 im Anhanguera und von 0.7209 ± 0.0011 im Perus Granit zeigen, dass beide
Granite Magmen krustaler Herkunft darstellen. Sowohl der Perus Granit als auch der gleichnamige Pegmatit haben hohe Borgehalte, die zwischen 5071 und 19472 ppm liegen. Turmalin ist in beiden das einzige femische Mineral. Die hohen Borgehalte
zeigen, dass an der Entstehung der krustalen Schmelzen Bor-reiche Sedimente marinen Ursprungs beteiligt waren. Ein initiales
87Sr/86Sr Verhältnis von 0.7100 ± 0.0088 zeigt auch für die granitischen Gesteine der Cantateira Intrusion eine krustale Herkunft
jedoch mit einer Beteiligung des Mantels. Der Lagenbau, wie er sowohl für die Granitoide von Perus als auch für die Perus Pegmatite
typisch ist, ist durch unterschiedliche Turmalingehalte bedingt. Die Kristallisation des Turmalins wird durch periodische Schwankungen im Bor-Gehalt der Schmelze und nicht durch spät- bis postmagmatische Turmalinisierung gesteuert. Geländebeobachtungen,
Haupt- und Spurenelementdaten, einschließlich der SEE Bestimmung und Isotopendaten zeigen innerhalb der Pirituba Abfolge
eine kontinuierliche Differentiation eines tief sitzenden Magmenkörpers, der mit einer granodioritischen Zusammensetzung beginnt
und mit dem hoch differenzierten Syenogranit und Pegmatit von Perus endet.
Resumo
Os granitóides de Mairiporã, Taipas, Cantareira, Anhanguera, Pirituba e Perus aqui estudados pertencem à Suíte Pirituba e intrudiram
as rochas metavulcânicas e metassedimentares do Grupo São Roque, nessa parte do Estado de São Paulo (Brasil), entre 600 e 520
Ma, no final do evento tectono-termal Brasiliano. O Grupo São Roque è parte do Cinturão Móvel Ribeira, de idade Brasiliana, que
bordeja o Cráton do São Francisco a leste. As razões iniciais de 87Sr/86Sr de 0,7231 ± 0,0003 para os granitóides Anhanguera e de
0,7209 ± 0,0011 para os de Perus indicam fontes crustais para os respectivos magmas. O granito e o pegmatito Perus são
caracterizados por teores muito altos de boro de em torno de 5071 ppm e 19472 ppm, respectivamente. Em ambas as rochas a
turmalina é o único mineral fêmico presente. Os elevados teores de boro apontam para a participação de pelitos marinhos ricos em
boro na gênese por anatexia desses magmas. Para os granitóides Cantareira, as razões iniciais de 87Sr/86Sr de 0,7100 ± 0,0088
também sugerem uma origem crustal, porém, em mistura com uma componente do manto. O bandamento magmático presente em
ambos, no granito e no pegmatito Perus, resultou de diferenças nos teores e na distribuição da turmalina. A cristalização da turmalina
deveu-se a variações periódicas nas concentrações do boro – e não a uma turmalinização magmática tardia até pós-magmática,
metassomática. Para os granitóides da Suíte Pirituba, evidências de campo, dados de elementos maiores e traço, incluindo ETR, e
dados isotópicos, sugerem uma origem crustal profunda e evolução contínua, por diferenciação, de uma composição granodiorítica
para o sienogranito Perus e o pegmatito Perus a este conectado, ambos altamente diferenciados.
1.
Introduction and problem
The studied granodioritic to granitic intrusions of
Cantareira, Mairiporã, Taipas, Anhanguera, Pirituba and
the Perus tourmaline granite and pegmatite belong to the
Pirituba granite suite as defined by HASUI & HAMA (1972)
and are found at about 12 km NNW of the centre of São
Paulo City (São Paulo State, Brazil). Major and trace
whole rock chemistry including REE and isotope data will
be used to produce evidence for a continuous evolution
leading from a granodioritic magma, represented by
the intrusions of Mairiporã, Cantareira, Taipas and
Anhanguera, to the highly differentiated Perus tourmaline
granite and pegmatite. Special emphasis will be given
to the role of boron in the genesis of the prominent
magmatic banding of the Perus granitoids and pegmatite.
On the basis of the tectonic setting, the predominant
granodioritic composition and Sr isotope data it will
be discussed if the Pirituba granitoids, like most of the
384
granitoids in the Mantiqueira province, are the product
of an anatectic process of Brasiliano age that was driven
by basaltic underplating of the Paleoproterozoic crust.
This study did give the last chance to study in some
detail the Perus tourmaline granite and its pegmatitic
facies because the construction of a highway that will
bypass the city of São Paulo destroyed most of the
outcrops.
2.
Geology and petrography
The Cantareira, Mairiporã, Taipas, Anhanguera, Pirituba
and the Perus granitoids are found in the upper Proterozoic metasedimentary and metavolcanic rocks of the São
Roque group (Fig. 1a). The São Roque group is part of
the Mantiqueira Province or Ribeira (Sudeste, Paraiba)
fold belt, a fold belt of Brasiliano (upper Proterozoic) age,
whose major features developed during the collision of
Z. geol. Wiss. 36 (6) 2008