Document Type

Dissertation

Date of Award

1974

Keywords

Geology, Brazil, Mar Mountains

Degree Name

Doctor of Philosophy (PhD)

Department

Geological Sciences

First Advisor

William D. MacDonald

Second Advisor

Thomas W. Donnelly

Third Advisor

Hugh E. Hunter

Abstract

Detailed geologic mapping in the Serra do Mar region of eastern São Paulo, Brazil, enables the definition of two northeasterly trending Precambrian lithologic complexes in heretofore undifferentiated crystalline complex rocks. These two complexes are the Suzano Complex and the Itatinga Complex, separated one from the other by the large Cubatão fault zone.

The Suzano Complex is divided into three formations: the Oropó schist, the Iupeba gneiss, and the Paranapiacaba gneiss. The Itatinga Complex is divided into four formations: the Biritiba-Mirim migmatite, the Jurubatuba migmatite, the Itapanhaú gneiss, and the Guarujá migmatite. Numerous late and post-tectonic granitic bodies occur intrusive into both complexes.

Metamorphic grade increases from northwest to southeast. In the Suzano Complex the beginning of the sillimanite-almandine-orthoclase subfacies of the amphibolite facies of the Barrovian-type facies series of metamorphism is achieved. In the Itatinga Complex migmatites and nebulites are representative of the highest temperature ranges of the amphibolite facies.

Post-metamorphic amphibolite bodies in the Cubatão fault zone reach the sillimanite-almandine-orthoclase subfacies of the amphibolite facies. Relict granulitic rocks in the Itapanhaú gneiss of the Itatinga Complex represent the highest grade rocks of the study area in the hornblende-orthopyroxene-plagioclase subfacies of the granulite facies of regional metamorphism.

The analyses of feldspar compositions in intrusive plutons indicate that there is no significant difference in the compositions of feldspars of the late and post-tectonic granites. The negative results obtained in the analyses preclude correlations within and between plutons and may suggest a common source for the granitic magma.

Four northeast trending structural provinces are defined in the region based on the analysis of minor structures: the Suzano Block, the Jurubatuba Block, the Itapanhaú Block, and the Santo Amaro Block. They are separated one from the other respectively by three major faults and cataclastic zones: the Cubatão fault zone, the Freires cataclastic zone, and the Bertioga cataclastic zone. Tilting and rotation of the structural provinces occurred along these weakness planes.

Faults and cataclastic zones mapped in the northern portions of the study area are thought to be splays related to a large easterly trending fault zone in the valley of the Tietê River. This fault zone may represent the extension of the Taxaquara fault (Hennies et al, 1967), mapped in regions west of the present study area. The Taxaquara fault and its extension are the only easterly trending lineaments in the area, cutting across the regional northeasterly structural trends.

The Taxaquara fault can be extended eastward across the study area, to the coast, to join with the “42.5° fracture zone” (Francheteau and Le Pichon, 1972) in the São Paulo embayment. The Taxaquara fault, the “42.5° fracture zone,” the Novo Redondo “fracture zone” in the Cuanz Basin off the coast of Angola, Africa, and an unnamed structural and geochronological boundary in Angola are thought to have once formed a single ancient lineament along which rifting of South America and Africa occurred. It is proposed that this lineament be referred to as the Ubatuba lineament.

North and south of the Ubatuba lineament rifting of the continents was probably controlled by reactivated ancient faults of northeast trend, such as the Cubatão fault, the Freires cataclastic zone and the Bertioga cataclastic zone.

The formation of the Serra do Mar is linked to structural processes active during continental rifting, beginning in Cretaceous time. An outline of the tectonic history of a rifted continental margin is presented.

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