Geology and petrography of the graciosa granites (Southern Brazil)

GEOLOGY AND PETROGRAPHY OF THE GRACIOSA GRANITES (SOUTHERN BRAZIL)

GUILHERME A. R. GUALDA AND SILVIO R. F. VLACH

Instituto de Geociências, USP, São Paulo, SP

Presented by ANTONIO C. ROCHA-CAMPOS

The Serra da Graciosa region in eastern Paraná State (southern Brazil) concentrates important A-type granitic and syenitic massifs - the Graciosa Granites - that are part of the Serra do Mar Province. They are intrusive in Archean granulites of the Luiz Alves Craton and in Neoproterozoic gneisses of the Curitiba Microplate and formed during the post-orogenic stages of the Brasiliano Cycle.

In this study, we characterize the geology and petrography of the Graciosa Granites using information from field work, petrography and the interpretation of TM-Landsat images and aerogammaspectrometric maps. It was thus possible to differentiate rheologically independent areas formed by one or more intrusive units that are circumscribed by basement rocks. These are here defined as separate massifs.

Five massifs are identified among the Graciosa Granites. Both the Marumbi and the Anhangava Massifs have been identified previously. Until now the remaining three have been considered as a single massif - the Graciosa Massif. The presence of basement rocks inside the Graciosa Massif is portrayed in the works of Maack in the 1960's, and the structural independence of the three massifs is evident in satellite images and maps, as well as in the field. Therefore, we propose that the designation Graciosa Massif be discarded in favor of the following specific designations, from north to south: Capivari, Órgãos and Farinha Seca Massifs. The five massifs appear as ellipses oriented NE-SW and each occupies an area ranging from 34 to 100 km2.

A large variety of granitic and syenitic rock types is found. Amphibole alkali-feldspar granites make up both the Farinha Seca Massif and the easternmost part of the Órgãos Massif. The gradual variation from calcic to sodic amphibole reveals an affinity with an alkaline A-type association. In the northern and southernmost parts of the Anhangava Massif, ± olivine ± clinopyroxene ± amphibole ± quartz alkali-feldspar syenites and minor amphibole alkali-feldspar granites characterize a second alkaline association. Biotite syenogranites, monzogranites and alkali-feldspar granites, usually bearing calcic amphibole, are attributed to an aluminous A-type association. They are present in the central area of the Anhangava Massif, in the Capivari Massif, in most of the Órgãos Massif and in the Marumbi Massif. — ( December 8, 2000 )

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Publication Dates

• Publication in this collection
  05 Oct 2001
• Date of issue
  Sept 2001