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vol.74 issue3The third order sequence stratigraphy of the Itararé Subgroup (late Paleozoic) across Paraná BasinFacies and sequence stratigraphy of the Itararé and Guatá Subgroups (late Paleozoic), Northern Paraná Basin, Brazil author indexsubject indexarticles search
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Anais da Academia Brasileira de Ciências

Print version ISSN 0001-3765On-line version ISSN 1678-2690

An. Acad. Bras. Ciênc. vol.74 no.3 Rio de Janeiro Sept. 2002

http://dx.doi.org/10.1590/S0001-37652002000300019 

EXTRUSION-RELATED EXTENSIONAL SIGNATURES UNDER HIGH-PRESSURE NAPPE COMPRESSIONAL REGIME*

CARLOS H. G. CARVALHO AND MARIO C. CAMPOS-NETO

Instituto de Geociências, USP, São Paulo, SP.
Presented by ANTONIO C. ROCHA-CAMPOS

 

The Neoproterozoic nappe system exposed south of the São Francisco Craton underwent a minimum of 200 km of near-horizontal northeastward displacement. This nappe system comprises the south-southeast sector of Brasília Belt and piles up three tectonic settings (from top to bottom): the roots of a neoproterozoic magmatic arc (Socorro-Guaxupé Nappe); high-pression metassedimentary nappes (Três Pontas-Varginha, Carmo da Cachoeira, Aiuruoca-Andrelândia, Pouso Alto and Carvalhos klippe); parautochthonous medium-pressure nappes and duplexes.

In the southeast of Aiuruoca-Andrelândia Nappe, a brittle-ductile sinistral shear zone (Liberdade Shear Zone) limits the southern Alagoa Migmatites and may represent a lateral ramp for the eastern Lima Duarte Nappe. Close to Alagoa (MG), this shear zone turns E-W, breaking the nappe hind portion, in a southward normal-ductile movement.

North of this shear zone, the garnet-sillimatite bearing metassedimentary sequence lays over a gnaissic-diatexitic basement and is highly sliced by strata-like tourmaline-bearing granites. In the metassediments, main foliation S2 is transposed by a normal-fault related thick protomilonitic S2' foliation. In the gnaisses, southward transport is marked by shear-sense indicators such as S-C foliations and quartz sigmoids. A low-temperature, late brittle thrust system, overlaps the extensional structures.

Heading north, the end of this structural-metamorphic domain is marked by an antiform in gnaissic diatexites. A normal fault with average northeastward dip limits the fold and juxtaposes upper kianite-staurolite bearing micaxists. From this limit, the structural pattern of Aiuruoca-Andrelândia Nappe is homogeneous, with sin-metamorphic ductile shear-sense indicators to E-NE.

The alternating of extensional structures in a general compressive regime and in the hind portion of high-pressure nappe, is associated with the extrusion process and with the search, in the collisional orogen, of isostatic balance. — (December 14, 2001).

 

* Supported by FAPESP 00/11390-4 and 98/15624-8.

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