Abstract
This study focuses on the eastern flank of the Santa Rita syncline (Dorr 1969DORR, J. V. N. II. Physiographic, stratigraphic and structural development of the Quadrilátero Ferrífero, Minas Gerais, Brazil . USGS/DNPM. Professional Paper 641-A., 1969. 110p.), with specific emphasis on the region known as Fábrica Nova. Important iron ore deposits are located on the flanks of this structure, such as Timbopeba, Alegria, São Luiz, Tamanduá, Almas and Fábrica Nova. The Santa Rita syncline is a fold with N-S axial direction and of subregional scale, with roots in the adjacent basement of the Santa Bárbara Complex and sectioned by the Água Quente thrust fault. The hypothesis of this study is that the structural framework of the region resulted from the superposition of at least three deformation phases on the Ouro Preto nappe. The Fábrica Nova mine, located in the central portion of the study area, is embedded in a synformal structure with a 100/20 trending axis named Fábrica Nova synform. The proposed model to explain the particular structural geometry of this region is based on the flanking folding mechanism (Passchier 2001PASSCHIER, C. W. Flanking structures. Journal of Structural Geology, v. 23, p. 951-962, 2001.). This mechanism may have been developed by E-W crustal shortening during the F4 tectonic deformation phase.
Keywords:
Geologia Estrutural; Quadrilátero Ferrífero; Sinclinal Santa Rita; Mina de Fábrica Nova
Resumo
O presente trabalho se concentra na aba leste do sinclinal Santa Rita, (Dorr 1969DORR, J. V. N. II. Physiographic, stratigraphic and structural development of the Quadrilátero Ferrífero, Minas Gerais, Brazil . USGS/DNPM. Professional Paper 641-A., 1969. 110p.), a partir da região conhecida como Fábrica Nova. Importantes depósitos de minérios de ferro estão localizados nos flancos dessa estrutura, como os de Timbopeba, Alegria, São Luiz, Tamanduá, Almas e Fábrica Nova. Esse sinclinal é uma dobra de escala sub-regional de direção axial N-S com raízes no embasamento adjacente do Complexo Santa Bárbara e seccionada pela falha de Água Quente. A investigação propõe a hipótese de que o arcabouço estrutural da região é resultante da superposição de pelo menos três fases de deformação sobre a nappe Ouro Preto. A mina de Fábrica Nova, localizada na porção central da área estudada, está inserida em uma estrutura sinformal de eixo 100/20, o sinforme de Fábrica Nova. Para a geometria particular dessa região, é proposto um modelo com base no mecanismo de dobramento por Flanking Folds (Passchier 2001PASSCHIER, C. W. Flanking structures. Journal of Structural Geology, v. 23, p. 951-962, 2001.). Esse mecanismo se daria através de um encurtamento crustal de direção E-W da fase de deformação F4.
Palavra-chave:
Geologia Estrutural; Quadrilátero Ferrífero; Santa Rita Syncline; Fábrica Nova de Minas; Fábrica Nova Syncline
1. Introduction
The area of this study is located along the eastern edge of the Quadrilátero Ferrífero (QFe) (Dorr 1969DORR, J. V. N. II. Physiographic, stratigraphic and structural development of the Quadrilátero Ferrífero, Minas Gerais, Brazil . USGS/DNPM. Professional Paper 641-A., 1969. 110p.) in the central portion of Minas Gerais state between the districts of Santa Rita Durão and Bento Rodrigues in a region known as Fábrica Nova (Fig. 1).
A summary geological map of the QFe and the location of the study area. Axial trace of Mangabeiras syncline (1), Moeda syncline (2), Dom Bosco syncline (3), Gandarela syncline (4), Vargem do Lima syncline (5), Santa Rita syncline (6), Mariana anticline (7), Furquim anticline (8), Ouro Fino syncline (9), Santo Antônio anticline (10) (model by Dorr 1969DORR, J. V. N. II. Physiographic, stratigraphic and structural development of the Quadrilátero Ferrífero, Minas Gerais, Brazil . USGS/DNPM. Professional Paper 641-A., 1969. 110p., Romano 1989ROMANO, A. W. Evolution tectonique de la région NW du Quadrilatère Ferrifère - Minas Gerais, Brésil. Nancy, France : Université de Nancy I, 1989. 259p. (Thèse Docteur)., Endo 1997ENDO, I. Regimes tectônicos do Arqueano e Proterozóico no Interior da Placa Sanfranciscana: Quadrilátero Ferrífero e áreas adjacentes, Minas Gerais. São Paulo: Instituto de Geociências da Universidade de São Paulo. 1997. 243p. (Tese de Doutorado) ., Almeida 2004ALMEIDA, L. G. Evolução tectônica da porção central do sinclinal Dom Bosco, Quadrilátero Ferrífero - Minas Gerais.Minas. Ouro Preto: Departamento de Geologia, Escola de Minas, Universidade Federal de Ouro Preto. 2004. 110p. (Dissertação de Mestrado)., Endo et al. 2004ENDO, I., SILVA, L. G., ZAVAGLIA, G., ROCHA, F. O. G., GUIMARÃES, M. L. V., ROSAS, C. F., LAGOEIRO, L. E., SANTOS, G. J. I. Arcabouço estrutural e modelo evolutivo do Sinclinal Gandarela, Quadrilátero Ferrífero, MG. In: CONGRESSO BRASILEIRO DE GEOLOGIA, 42. ARAXÁ, MG, 2004. (Resumo)., Endo et al. 2005ENDO, I., OLIVEIRA, A. H., PERES, G. G., GUIMARÃES, M. L. V., LAGOEIRO, L. E., MACHADO, R., ZAVAGLIA, G., ROSAS, C. F., MELO, R. J. Nappe Curral: uma megaestrutura alóctone do Quadrilátero Ferrífero e controle da mineralização. In: SIMPÓSIO NACIONAL DE ESTUDOS TECTÔNICOS, 10; INTERNATIONAL SYMPOSIUM ON TECTONICS, 4. Curitiba, p. 279-282, 2005. Boletim de Resumos Expandidos.).
In general, the QFe is comprised of three major sets of rock units: the metamorphic complexes of Archean age, the metavolcanic-metassedimentary rock-type sequence of the greenstone-belt of Archean age, corresponding to the Rio das Velhas Supergroup, and the Paleoproterozoic supracrustal rocks of the Minas Supergroup and Itacolomi Group (e.g. Dorr et al. 1957DORR, J. V. N. II., GAIR, J. E., POMERENE, J. B., RYNEARSON, G. A. Revisão Estratigráfica Pré-Cambriana do Quadrilátero Ferrífero. Rio de Janeiro, DNPM/DFPM, 1957. 36p (Avulso. 81)., Dorr 1969DORR, J. V. N. II. Physiographic, stratigraphic and structural development of the Quadrilátero Ferrífero, Minas Gerais, Brazil . USGS/DNPM. Professional Paper 641-A., 1969. 110p., Cordani et al. 1980CORDANI, U. G., KAWASHITA, K., MULLER, G., QUADE, H., REIMER, V., ROESER, H. Interpretação tectônica e petrológica de dados geocronológicos do embasamento na borda sudeste do Quadrilátero Ferrífero, MG. Academia Brasileira de Ciências. v.52, n.4, p. 785-799, 1980., Schorscher et al. 1982SCHORSCHER, H. D., SANTANA, F. C., POLÔNIA, J. C., MOREIRA, J. M. P. Quadrilátero Ferrífero - Minas Gerais State: Rio das Velhas Greenstone Belt and Proterozoic rocks. In: INTERNATIONAL SYMPOSIUM ON ARCHEAN AND EARLY PROTEROZOIC EVOLUTION AND METALLOGENESIS, Salvador, 1982. Anais.... Salvador, SBG. p.43, 1982., Romano 1989ROMANO, A. W. Evolution tectonique de la région NW du Quadrilatère Ferrifère - Minas Gerais, Brésil. Nancy, France : Université de Nancy I, 1989. 259p. (Thèse Docteur)., Noce 1995NOCE, C. M. Geocronologia dos eventos magmáticos, sedimentares e metamórficos na região do Quadrilátero Ferrífero, Minas Gerais. São Paulo: Instituto de Geociências, Universidade de São Paulo, 1995. 128 p. (Tese de Doutorado)., Machado et al. 1996MACHADO, N., SCHRANK, A., NOCE, C.M., GAUTHIER, G. Ages of detrital zircon from Archean-Paleoproterozoic sequences: implications for greenstone belt setting and evolution of a transamazonian foreland basin in Quadrilátero Ferrífero, Southeast Brazil. Earth and Planetary Science Letters, v. 141, p. 259-276, 1996., Alkmim & Marshak 1998ALKMIM, F. F; MARSHAK, S., PEDROSA-SOARES, A. C., PERES, G. G., CRUZ, S. C. P., WHITTINGTON, A. Kinematic evolution of the Araçuaí - West Congo orogen in Brazil and Africa: Nutcracker tectonics during the Neoproterozoic assembly of Gondwana. Precambrian Research, v. 149, n. 1-2, p. 43-64, 2006.).
The regional structure of the QFe is the result of the superposition of two main tectonic events (Chemale Jr. et al. 1991CHEMALE, F. Jr., ROSIÈRE, C. A., ENDO, I. Evolução tectônica do Quadrilátero Ferrífero, Minas Gerais: um modelo. Pesquisas, v. 18, n. 2, p. 104-127, 1991.), namely the Transamazonian (2.1 – 2.0 Ga) and Brasiliano (0.8 – 0.6 Ga) orogenies. The first event produced the regional recumbent synclines and anticlines on the supracrustal rocks and the uplifting of gneissic-granite rocks arranged in structures like a nappe (Almeida 2004ALMEIDA, L. G. Evolução tectônica da porção central do sinclinal Dom Bosco, Quadrilátero Ferrífero - Minas Gerais.Minas. Ouro Preto: Departamento de Geologia, Escola de Minas, Universidade Federal de Ouro Preto. 2004. 110p. (Dissertação de Mestrado)., Endo et al. 2005ENDO, I., OLIVEIRA, A. H., PERES, G. G., GUIMARÃES, M. L. V., LAGOEIRO, L. E., MACHADO, R., ZAVAGLIA, G., ROSAS, C. F., MELO, R. J. Nappe Curral: uma megaestrutura alóctone do Quadrilátero Ferrífero e controle da mineralização. In: SIMPÓSIO NACIONAL DE ESTUDOS TECTÔNICOS, 10; INTERNATIONAL SYMPOSIUM ON TECTONICS, 4. Curitiba, p. 279-282, 2005. Boletim de Resumos Expandidos.), and the second caused the inversion, amplification, translation and crustal rotation of the synclines and anticlines around the dome structures.
The eastern edge of the QFe represents the border between the São Francisco craton and the Araçuaí Belt (e.g., Alkmim et al. 2006ALKMIM, F. F., MARSHAK, S. Transamazonian orogeny in the Southern São Francisco Craton Region, Minas Gerais, Brazil: evidence for Paleoproterozoic collision and collapse in the Quadrilátero Ferrífero. Precambrian Research, v. 90, n. 1-2, p. 29-58, 1998.), and its structure is conditioned by the Fundão-Cambotas (Endo & Fonseca 1992ENDO, I., FONSECA, M. A. Sistema de cisalhamento Fundão-Cambotas no Quadrilátero Ferrífero, MG: geometria e cinemática. Revista Escola de Minas, v. 45, n. 1/2, p.15-17, 1992.) and Água Quente thrust fault systems (Maxwell 1972MAXWELL, C. H. Geology and ore deposits of the Alegria district, Brazil. Washington: USGS/DNPM, 1972. 72p. (Professional Paper 341J) 72p., Ferreira Fº. 1999). The Santa Rita syncline (Fig. 1) is located within this system and, according to Dorr (1969)DORR, J. V. N. II. Physiographic, stratigraphic and structural development of the Quadrilátero Ferrífero, Minas Gerais, Brazil . USGS/DNPM. Professional Paper 641-A., 1969. 110p. and Maxwell (1972)MAXWELL, C. H. Geology and ore deposits of the Alegria district, Brazil. Washington: USGS/DNPM, 1972. 72p. (Professional Paper 341J) 72p., it is characterized as an asymmetric synform with a N-NE and N-S trending axis; it is open in the southern section and narrow in the northern section, with a subhorizontal plunge. The flanks are subparallels, and the overturned flank is sectioned by the Água Quente fault, which is of submeridian trace. The stratigraphic units on the overturned flank are thinner than its normal counterpart flank located to the west. Schists, phyllites, and ferruginous quartzites belonging to the Piracicaba and Sabará groups are present in the core.
Dorr (1969)DORR, J. V. N. II. Physiographic, stratigraphic and structural development of the Quadrilátero Ferrífero, Minas Gerais, Brazil . USGS/DNPM. Professional Paper 641-A., 1969. 110p. argued that mesoscopic fold axes show subhorizontal plunge with axial trace parallel to the bedding direction in contrast. In turn Endo (1997)ENDO, I. Regimes tectônicos do Arqueano e Proterozóico no Interior da Placa Sanfranciscana: Quadrilátero Ferrífero e áreas adjacentes, Minas Gerais. São Paulo: Instituto de Geociências da Universidade de São Paulo. 1997. 243p. (Tese de Doutorado) . described fold axes with moderate plunging around 45º toward the E-SE. At the hinge of the Santa Rita syncline, the bedding shows steep dipping to the E bisected by penetrative regional schistosity, with an intersection lineation parallel to the corresponding mineral and stretching lineation plunging toward the E-SE (e.g. Ferreira Fº. 1999, Ferreira Fº. & Fonseca 2001FERREIRA, Fº F. A., FONSECA, M. A. Partição da deformação em regimes contracionais de antepaís: exemplo do sistema de falhas Água Quente. Revista Brasileira de Geociências, v. 31, n. 3, p.267-278, 2001.). This relationship between the linear fabrics predominates in the QFe region (Chemale Jr. et al. 1991CHEMALE, F. Jr., ROSIÈRE, C. A., ENDO, I. Evolução tectônica do Quadrilátero Ferrífero, Minas Gerais: um modelo. Pesquisas, v. 18, n. 2, p. 104-127, 1991., Alves 1991ALVES, J. A. C. Reconstrução estocástica da Mina São Luiz, Complexo Fazendão, MG, Dissertação de Mestrado. Ouro Preto: Departamento de Geologia, Escola de Minas, Universidade Federal de Ouro Preto, 1991. 120 p. (Dissertação de Mestrado)., Alkmim & Marshak 1998ALKMIM, F. F., MARSHAK, S. Transamazonian orogeny in the Southern São Francisco Craton Region, Minas Gerais, Brazil: evidence for Paleoproterozoic collision and collapse in the Quadrilátero Ferrífero. Precambrian Research, v. 90, n. 1-2, p. 29-58, 1998., Franco 2003FRANCO, A. S. P. Geometria e evolução tectônica do sinclinal Ouro Fino. Quadrilátero Ferrífero, MG. Ouro Preto: Departamento de Geologia, Escola de Minas, Universidade Federal de Ouro Preto. 102p., 2003. 102 p. (Dissertação de Mestrado), Almeida 2004ALMEIDA, L. G. Evolução tectônica da porção central do sinclinal Dom Bosco, Quadrilátero Ferrífero - Minas Gerais.Minas. Ouro Preto: Departamento de Geologia, Escola de Minas, Universidade Federal de Ouro Preto. 2004. 110p. (Dissertação de Mestrado)., Endo 1997ENDO, I. Regimes tectônicos do Arqueano e Proterozóico no Interior da Placa Sanfranciscana: Quadrilátero Ferrífero e áreas adjacentes, Minas Gerais. São Paulo: Instituto de Geociências da Universidade de São Paulo. 1997. 243p. (Tese de Doutorado) ., Endo et al.2005ENDO, I., OLIVEIRA, A. H., PERES, G. G., GUIMARÃES, M. L. V., LAGOEIRO, L. E., MACHADO, R., ZAVAGLIA, G., ROSAS, C. F., MELO, R. J. Nappe Curral: uma megaestrutura alóctone do Quadrilátero Ferrífero e controle da mineralização. In: SIMPÓSIO NACIONAL DE ESTUDOS TECTÔNICOS, 10; INTERNATIONAL SYMPOSIUM ON TECTONICS, 4. Curitiba, p. 279-282, 2005. Boletim de Resumos Expandidos.).
According to the models of Dorr (1969)DORR, J. V. N. II. Physiographic, stratigraphic and structural development of the Quadrilátero Ferrífero, Minas Gerais, Brazil . USGS/DNPM. Professional Paper 641-A., 1969. 110p. and Maxwell (1972)MAXWELL, C. H. Geology and ore deposits of the Alegria district, Brazil. Washington: USGS/DNPM, 1972. 72p. (Professional Paper 341J) 72p., the correct position of the Santa Rita syncline hinge has not been determined so far. Contemporary structures such as the Gandarela and Ouro Fino synclines, have hinges with E-SE plunges parallel to the intersection and mineral stretching lineations at approximately 100/45 (Franco 2003FRANCO, A. S. P. Geometria e evolução tectônica do sinclinal Ouro Fino. Quadrilátero Ferrífero, MG. Ouro Preto: Departamento de Geologia, Escola de Minas, Universidade Federal de Ouro Preto. 102p., 2003. 102 p. (Dissertação de Mestrado), Endo et al. 2004ENDO, I., SILVA, L. G., ZAVAGLIA, G., ROCHA, F. O. G., GUIMARÃES, M. L. V., ROSAS, C. F., LAGOEIRO, L. E., SANTOS, G. J. I. Arcabouço estrutural e modelo evolutivo do Sinclinal Gandarela, Quadrilátero Ferrífero, MG. In: CONGRESSO BRASILEIRO DE GEOLOGIA, 42. ARAXÁ, MG, 2004. (Resumo).). The bedding trace contour of the Minas Supergroup units of the Fábrica Nova region seems to indicate a "Z" type folding geometry (Fig. 3). If this hypothesis is correct, the syncline closure should occur in its southern section.
View of Fábrica Nova mine with the location of Santa Rita Durão district and Caraça region (Vale file).
2. Materials and Methods
This study was conducted in two phases. The first phase involved regional lithostructural mapping on a 1:5.000 scale, and the second stage included detailed mapping of the northern and southern pits of the Fábrica Nova mine (Fig. 2) on a 1:2.000 scale. The lithostratigraphic and structural data collected from this semi-detailed geological map enabled the proposal of a geological model for the Santa Rita syncline, especially with regard to the geometry of the Fábrica Nova region. The structural data collected during the mapping were launched in stereograms using GEOrient (v. 9.0) software.
Based on structural criteria proposed by Harland (1956)HARLAND, W. B. Tectonic facies, orientation, sequence, style and date. Geological Magazine. v. 93, p.110-120, 1956., Hansen (1971)HANSEN, E. Strain facies: minerals, rocks and inorganic material. Berlin: Springer Verlag, 1971. 209p., Robertson (1994)ROBERTSON, A. H. F. Role of the tectonic facies concept in orogenic analysis and its application to Tethys in the Eastern Mediterranean region. Earth-Science Reviews, v. 37, n. 3, p.139-213, 1994., Hsue (1995)HSUE, K. J. The geology of Switzerland : an introduction to tectonic facies. Princeton University Press, 1995. 250 p. (Monograph; ISBN 0691087873)., and Xypolias (2010)XYPOLIAS, P. Vorticity analysis in shear zones: a review of methods and applications. Journal of Structural Geology, v. 32. p.2072-2092, 2010., the study area was divided into two structural domains according to their structural styles, geometry, and fabric properties: eastern and western (Fig. 3).
The structural asymmetry and the vorticity were characterized according to the down-plunging view of the fold axis or the intersection lineation (Passchier & Williams 1996PASSCHIER, C. W., WILLIAMS, P. R. Conflicting shear sense indicators in shear zones; the problem of non-ideal sections. Journal of Structural Geology, v. 18, n. 10, p.1281-1284, 1996., Xypolias 2009XYPOLIAS, P. Some new aspects of kinematic vorticity analysis in naturally deformed quartzites. Journal of Structural Geology, v. 31. p. 3-10, 2009. and 2010XYPOLIAS, P. Vorticity analysis in shear zones: a review of methods and applications. Journal of Structural Geology, v. 32. p.2072-2092, 2010.). The characteristics of each domain are as follows:
The eastern domain encompasses the units of the Sabará Group (e.g. Gair 1958GAIR, J.E. The Sabará Formation. In: SYMPOSIUM ON STRATIGRAPHY OF MINAS SERIES IN THE QUADRILÁTERO FERRÍFERO, MINAS GERAIS, BRAZIL. BOLETIM SBG, v.7, n.2, p.68-69, 1958., Barbosa 1968BARBOSA, A. L. M. Contribuições recentes à geologia do Quadrilátero Ferrífero. Ouro Preto: Departamento de Geologia, Escola de Minas, Universidade Federal de Ouro Preto, 1968. (Boletim)., Renger et al. 1994RENGER F. E., NOCE C. M., ROMANO A. W., MACHADO N. Evolução sedimentar do Supergrupo Minas: 500 Ma de registro geológico no Quadrilátero Ferrífero, Minas Gerais, Brasil. Geonomos, v. 2, n. 1, p. 1-11, 1994., Almeida 2004ALMEIDA, L. G. Evolução tectônica da porção central do sinclinal Dom Bosco, Quadrilátero Ferrífero - Minas Gerais.Minas. Ouro Preto: Departamento de Geologia, Escola de Minas, Universidade Federal de Ouro Preto. 2004. 110p. (Dissertação de Mestrado)., Almeida et al. 2005ALMEIDA, L. G., CASTRO, P. T., ENDO, I., FONSECA, M. A. O Grupo Sabará no Sinclinal Dom Bosco, Quadrilátero Ferrífero: uma revisão estratigráfica. Revista Brasileira de Geociências, v. 35, n. 2, p. 177-186, 2005.) and the Santa Bárbara Complex (Dorr 1969DORR, J. V. N. II. Physiographic, stratigraphic and structural development of the Quadrilátero Ferrífero, Minas Gerais, Brazil . USGS/DNPM. Professional Paper 641-A., 1969. 110p., Herz 1970HERZ, N. Gneissic and igneous rocks of the Quadrilátero Ferrífero, Minas Gerais, Brazil . USGS/DNPM, 1970. 57 p. (Professional Paper 641-B).). The structural data obtained in this field suggests that the rocks of these units are folded as to form an antiform F2 with axis plunging toward to ESE.
The Minas Supergroup (Dorr 1969DORR, J. V. N. II. Physiographic, stratigraphic and structural development of the Quadrilátero Ferrífero, Minas Gerais, Brazil . USGS/DNPM. Professional Paper 641-A., 1969. 110p.) units comprise the western domain on an overturned stratigraphic position. The outline of these units forms a structure that resembles a boomerang geometry and a "Z" folding pattern associated with a clockwise vorticity. The Bento Rodrigues fault determines the boundary between these two structural domains.
Due to structural characteristics the western domain can be divided into two subdomains: IIa and IIb, which correspond to the northern and southern pits, respectively, of the Fábrica Nova mine (Fig. 3).
3. Results
The structural analysis was based on the structural framework from different observation scales (e.g. Williams 1985, Xypolias 2010). To better describe the structures, they were arranged into mesoscopic and macroscopic categories.
Mesoscopic Structures Bedding
The bedding was defined by the variation in the particle size of the quartz grains in the quartzites of the Moeda and Cercadinho formations and the Sabará Group as well as the alternating laminae rich in quartz and the hematite-magnetite-goethite in the itabirite of the Cauê Formation.
The bedding planes of quartzites of the Sabará Group in the eastern domain shows a NW-SE direction and dipping toward to NE at 056/54 (Fig. 6a). The bedding in the western domain was preserved in all of the units of the Minas Supergroup with a preferential NW-SE direction at the south and an E-W direction at the north of the domain, with a maximum of approximately 172/48 (Fig. 6b). The dispersion of the bedding orientation suggests the acting of the F4 folding phase with an axial trend at approximately 117/33. This fold, named Fábrica Nova synform, is characterized as an open, subcylindrical and asymmetric fold with plunge.
A schematic drawing of a sample from the Cercadinho Formation at a mesoscopic scale showing the superposition of two deformation phases represented by the S1 and S2 foliations with opposite vorticities. Plane view XZ strain axes.
a) S2 schistosity characterized by the preferential orientation of the mineral sericite and its counterclockwise vorticity relation to the S0 bedding. Outcrop FN-303, near Santa Rita Durão b) Asymmetric folds with "S" patterns mapped in the Fabrica Nova mine.
Structures of the First Deformation Phase (F1)
The structures that reflect this phase are represented by tight and asymmetric mesofolds, most likely associated with an S1 foliation oblique to the bedding. The rare asymmetric folds, relicts of this phase, have a "Z" pattern. In one of the few outcrops where the structures of this deformation phase were found, the bedding and S1 foliation relationship observed presents a clockwise vorticity in a "Z" pattern, which are preserved in the sericitic schist. In the silvery phyllite layer, the bedding and S2 foliation relationship exhibits a counterclockwise vorticity in an "S" pattern. The interference relationship is characterized by the superposition of the S2 regional schistosity folding the S1foliation with the same vorticity pattern as the F2 deformation phase (Fig. 4).
However, the original characteristics of this fabric were mostly obliterated by the subsequent deformation phases in most of the studied region.
Structures of the Second Deformation Phase (F2)
The S2 regional schistosity is a penetrative planar fabric characterized by the preferential orientation of minerals such as sericite (Fig. 5a), hematite, and quartz. In the eastern domain, the S2 schistosity has an attitude of approximately 066/55 (Fig. 6c). In the western domain, the arrangement of the mapped units clearly expresses a folded system in which the S2schistosity shows an attitude of approximately 082/43 (Fig. 6d). The attitude of the axis of this fold (B4) is 104/40. The F2 folds, which have been mostly mapped in the Fábrica Nova mine, are tight folds with an axis plunging slightly to the ESE and a major attitude of approximately 119/21 in the northern pit (subdomain IIa; Fig. 6e) and 093/17 in the southern pit (subdomain IIb; Fig. 6f). These folds are asymmetric with "S" patterns, furthermore, they have wavelengths and amplitudes on the order of a few meters (Fig. 5b). A box-fold pattern can be observed in subdomain IIa and is interpreted as the manifestation of the superposition of the F2 folds over the F1 folds with opposite vorticities. The "S" folds in this system are better preserved than the "Z" folds, attesting to the superposition of the deformation phases. The intersection between the S0 bedding planes and the S2 schistosity is the predominant fabric in the itabirites of the Fábrica Nova mine. This structure shows moderate plunging to the ESE with average attitudes of approximately 094/22 (Fig. 6g). The mineral lineation, characterized by the preferential orientation of the mica and hematite crystals, shows an orientation parallel to the L2 intersection lineation (S0xS2) and B2 fold axis, with moderate plunging to the ENE of approximately 080/25 (Fig. 6h).
Structures of the Third Deformation Phase (F3)
The structural framework of phase F3 consists of open folds with an E-W axis featuring wavelengths and amplitudes of decametric dimensions that primarily outcrop in the Fábrica Nova mine.
The S3 foliation is a disjunctive cleavage of the E-W direction and the subvertical plunges that dips or to the north or to the south with an attitude of approximately 018/80 (Fig. 7a) and are attributed to the third deformation phase. The open F3 mesofolds or undulations of the bedding that show an axis with moderate plunging to the ENE and kink folds with an axial plane that dips to the south are also attributed to this phase. Among the structures of this phase, a mesofold occurring in the western portion of the Fábrica Nova northern pit stands out. This fold is an open antiform with a wavelength of approximately 200 meters and an amplitude of a few tens of a meter whose axis exhibits an attitude of 081/43 (Fig. 7b). The core of this fold is formed by silvery phyllites of the Cercadinho Formation.
Structures of the Fourth Deformation Phase (F4)
The F4 deformation phase was responsible for the final arrangement of the Fábrica Nova region, and its manifestation is represented in the Fábrica Nova synform, a fold with an ESE plunging axis and a boomerang-like geometry in plain view. The structures of this phase are primarily represented by S4 crenulation cleavages observed in itabirites of the Cauê Formation and in schists of the Sabará Group. The general direction of the S4 cleavage is N-S with an average attitude of 280/72 (Fig. 7c). Tight folds with steep axial plane and N-S trending axis are also attributed to this deformation phase.
Structures of the Fifth Deformation Phase (F5)
The records of the fracture system in the Fábrica Nova mine demonstrate the occurrence of two preferential directions, orthogonal to each other. These directions are N10-20E and N80-90 W (Fig. 7d).
Macroscopic Structures Bento Rodrigues Fault: General Aspects and Kinematics
The major fault of the Fábrica Nova region, hereafter called the Bento Rodrigues fault, bisects the entire mapped area, from south of Bento Rodrigues village, crossing the border east of the Fábrica Nova mine to north until Santa Rita Durão village. In the southern portion of the map, west of Bento Rodrigues, the fault trace has an NNW-SSE direction. In the central portion, near the Fábrica Nova mine, the fault trace changes its orientation to E-W, bearing toward NNE-SSW in the northern portion of the mapped area. This structure is related to the F2deformation phase, which corresponds to the development of the S2 regional schistosity and the apparent thrust of the Santa Bárbara Complex over the Minas Supergroup.
Unlike what was proposed by Dorr (1969)DORR, J. V. N. II. Physiographic, stratigraphic and structural development of the Quadrilátero Ferrífero, Minas Gerais, Brazil . USGS/DNPM. Professional Paper 641-A., 1969. 110p., Maxwell (1972)MAXWELL, C. H. Geology and ore deposits of the Alegria district, Brazil. Washington: USGS/DNPM, 1972. 72p. (Professional Paper 341J) 72p., Chemale Jr. et al. (1991)CHEMALE, F. Jr., ROSIÈRE, C. A., ENDO, I. Evolução tectônica do Quadrilátero Ferrífero, Minas Gerais: um modelo. Pesquisas, v. 18, n. 2, p. 104-127, 1991., and Ferreira Fº (1999), the fault kinematics seems to be essentially of a dextral strike-slip character with a small reverse component. The fault trajectory shows a deflection to the left relative to the bedding trace, thereby providing an extension of the layer that results in the generation of an extensional megaboudin structure. These mine-scale tectonics lead to the thinning and disappearance of the units from the Moeda and Batatal formations in the frontal portion of the Fábrica Nova mine pit.
Folds and Folding: Geometry and Relationships
Two subregional-scale folds occur in the Fábrica Nova region: the Fábrica Nova synform from the F4 deformation phase and the Bento Rodrigues anticline (Fig. 8). In addition, a tight antiform in the eastern section of the northern pit of the Fábrica Nova mine exists, known as the Alto Pai Miguel antiform. The axial-plane foliations that might be genetically associated with these folds were not clearly or convincingly observed.
A summary geological map of the Fábrica Nova area indicating the position of the axial traces of the Bento Rodrigues anticline (BRA), the Fábrica Nova synform (FNS) and the Alto Pai Miguel antiform (PMA).
The Fábrica Nova synform is an open fold a few kilometers in size, characterized by the rotation of the primary structures and tectonic foliations located in the northern pit of the Fábrica Nova mine (subdomain IIa) and its surroundings (Fig. 8). Only the stratigraphic units of the Minas Supergroup are involved in this fold. The axis of this fold has a moderate plunge to E-SE. The western flank in the southern portion has bedding attitudes of approximately 080/20, reaching values of 107/36 in the western portion of the northern pit domain and 200/60 in the northern portion.
The Bento Rodrigues anticline is a reclined fold a few kilometers in size, composed by the gneisses of the Santa Bárbara Complex followed by the quartzites and schists of the Sabará Group (Fig. 8). On the eastern flank, which represents the normal stratigraphic succession, the bedding and S2 foliation relationship shows counterclockwise vorticity and "S" asymmetric folds, whereas in the western flank, which has an overturned character, the relationship shows clockwise vorticity with "Z" asymmetric folds. The hinge of this anticline is located on the inner portion of the Fábrica Nova synform hinge and bounded to the east by the Bento Rodrigues fault.
The Alto Pai Miguel antiform is a reverse fold of a hectometric scale located in the eastern portion of the Fábrica Nova mine (Fig. 8). The core of the structure is composed of rocks from the Cercadinho Formation that outcrop in that area. Originally, these rocks were interpreted as belonging to the Batatal Formation arranged by a thrust fault. The correct modeling of this structure is of utmost importance because it will be reflected in the modeling of the mine.
4. Discussions and conclusions
The proposed model suggests that the Santa Rita syncline is a reclined fold of a subregional scale, with a WNW-ESE axial direction and roots in the adjacent basement of the Santa Bárbara Complex. The inverse flank of this syncline is bisected by the Água Quente thrust fault. This fold was generated during the Transamazonian event approximately 2,125 Ma ago and consists of a reclined synclinorial fold resulting from the refolding of the normal flank of the Ouro Preto nappe (e.g. Almeida 2004). The hinge zone is located in the Caraça region (Fig. 2) with axes that exhibit moderate-to-steep ESE plunging. The flanks are subparallel and the stratigraphic units are thinner in the overturned flank compared with its normal flank counterpart located to the west. Schists, phyllites, and ferruginous quartzites belong to the Piracicaba and Sabará groups are located in the core of the fold. The southern portion of the inverse flank of the Santa Rita syncline is sliced by a complex thrust fault system that Barbosa (1968)BARBOSA, A. L. M. Contribuições recentes à geologia do Quadrilátero Ferrífero. Ouro Preto: Departamento de Geologia, Escola de Minas, Universidade Federal de Ouro Preto, 1968. (Boletim). called Ouro Fino nappe. After these tectono-metamorphic events, a phase of mafic and ultramafic magmatism occurred during the pre-Brasiliano age.
The Fábrica Nova mine is embedded in a Fábrica Nova synform structure with axes oriented at 100/20. The direction of the bedding of the units that comprises the west flank behaves consistently and homogeneously as a homocline, which was slightly disturbed by undulations from the F3 deformation phase. The east flank bedding, in turn, was strongly disturbed by folding partially associated with two shortening fields due to F3 and F4 deformation phase, respectively, in the N-S and E-W direction. In addition, the brittle tectonic structures that form the sedimentary basin of the Cata Preta Formation (e.g. Castro et al. 1998CASTRO, E. C., FERREIRA, J. E., CASTRO, P. T. A. Formação Cata Preta: uma nova unidade litoestratigráfica, definida em rochas cenozóicas, no extremo leste do Quadrilátero Ferrífero. In: CONG. BRAS. GEOL., 40, 1988. Belo Horizonte. Anais... Belo Horizonte: SBG, 1998. p. 81., Lipski 2002LIPSKI, M. Tectonismo cenozóico no Quadrilátero Ferrífero, Minas Gerais. Ouro Preto: Departamento de Geologia, Escola de Minas, Universidade Federal de Ouro Preto. 2002. 171 p. (Dissertação de Mestrado)) might have contributed to the rotation of the basement structures.
The relationships between the structures from the F4 deformation phase are the most complex because they do not directly respond to the regional E-W shortening field and are not laterally or regionally replicated. Cover deformation mechanisms induced by a basement-involved structures can behave actively (e.g Wilcox et al. 1973WILCOX, R. E., HARDING, T. P., SEELY, D. R. Basic Wrench Tectonics. The American Association of Petroleum Geologists of Bulletin, v. 57, n. 1, p.74-96, 1973., Naylor et al. 1986NAYLOR, M. A., MANDL, G., SIJPESTEIJN, C. H. K. Fault geometries in basement-induced wrench faulting under different initial stress states. Journal of Structural Geology, v.8, n. 7, p. 737-752, 1986., Brink et al. 1996BRINK, U. TEN, S., KATZMAN, R., LIN, J. Three-dimensional models of deformation near strike-slip faults. Journal of Geophysical Research, v. 101, n. B7, p.16.205-16.220, 1996., Erslev 1991ERSLEV, E. A. Trishear fault-propagation folding. Geology, v.19, p.617-620, 1991., Narr & Suppe 1994NARR, W., SUPPE, J. Kinematics of basement-involved compressive structures. American Journal of Science, v. 294, p. 802-860, 1994., Erslev & Mayborn 1997ERSLEV, E. A., MAYBORN, K. R. Multiple geometries and modes of fault-propagation folding in the Canadian thrust belt. Journal of Structural Geology, v. 19, n. 3-4, p. 321-335, 1997., Tindall 2000TINDALL, S. E. The Cockscomb Segment of the East Kaibab Monocline: taking the structural plunge. Geology of Utah's Parks and Monuments. Utah Geological Association Publication 28, 2000.) or passively (e.g Passchier 2001PASSCHIER, C. W. Flanking structures. Journal of Structural Geology, v. 23, p. 951-962, 2001., Grasemann & Stüwe 2001GRASEMANN, B., STÜWE, K. The development of flanking folds during simple shear and their use as kinematic indicators. Journal of Structural Geology, v. 23, p. 715-724, 2001., Exner et al. 2004EXNER, U., MANCKTELOW, N. S., GRASEMANN, B. Progressive development of s-type flanking folds in simple shear. Journal of Structural Geology v. 26, p. 2191-2201, 2004.).
Kinematic indicators and the structural symmetry of the F4 deformation phase are compatible with the deformation mechanism and partitioning related to the flanking fold model described and established by Passchier (2001)PASSCHIER, C. W. Flanking structures. Journal of Structural Geology, v. 23, p. 951-962, 2001. (Fig. 9).
A model of planar fabric deflection along and around the zone surrounding a cross-cutting element (CE) (Passchier 2001PASSCHIER, C. W. Flanking structures. Journal of Structural Geology, v. 23, p. 951-962, 2001.). In the case of Fábrica Nova, the CE is a crustal discontinuity represented by an ultramafic dike.
In the case of Fábrica Nova, the cross-cutting element to the regional fabric element is the crustal discontinuity that feeds the mafic rock dikes in the NW-SE direction present in this segment of the QFe (Fig. 10). Based on this mechanism, the structures of the F4 deformation phase can be understood as the manifestation of the deformation partitioning process around the major discontinuity and second-order subsidiary structures in response to the crustal shortening in the EW direction.
Strain ratio: Rf based on the Passchier model (2001)PASSCHIER, C. W. Flanking structures. Journal of Structural Geology, v. 23, p. 951-962, 2001.. The fabric element "HE" represented by the top surface of the Cauê Formation and "CE" denotes the cross-cutting element represented by the direction of the crustal discontinuity filled by mafic and ultramafic rocks.
When considering this subregional deformation mechanism using the flanking fold as a model to understand the Fábrica Nova structural framework, the strain ratio (Rf) can be measured considering
i) the angular relationship of the direction of the layers in the short and long flanks and
ii) the angular relationship between the crustal discontinuity, the transverse element direction, and the direction of the short flank layers (Passchier 2001). The Rf value is approximately 18.7 (Fig. 10).
5. Acknowledgments
The authors thank both management departments of the VALE mining company for their collaboration: Mine Planning of Short-Term Extraction - GAQAS and Mineral Exploitation of Ferrous Management - GAEMF. The first author is grateful to the Brazilian federal agency CAPES for their scholarship and the colleagues from the Geology Department of the Federal University of Ouro Preto - UFOP for their support and also everyone that somehow contributed to accomplish this study.
6. References
- ALMEIDA, L. G. Evolução tectônica da porção central do sinclinal Dom Bosco, Quadrilátero Ferrífero - Minas Gerais.Minas. Ouro Preto: Departamento de Geologia, Escola de Minas, Universidade Federal de Ouro Preto. 2004. 110p. (Dissertação de Mestrado).
- ALMEIDA, L. G., CASTRO, P. T., ENDO, I., FONSECA, M. A. O Grupo Sabará no Sinclinal Dom Bosco, Quadrilátero Ferrífero: uma revisão estratigráfica. Revista Brasileira de Geociências, v. 35, n. 2, p. 177-186, 2005.
- ALKMIM, F. F., MARSHAK, S. Transamazonian orogeny in the Southern São Francisco Craton Region, Minas Gerais, Brazil: evidence for Paleoproterozoic collision and collapse in the Quadrilátero Ferrífero. Precambrian Research, v. 90, n. 1-2, p. 29-58, 1998.
- ALKMIM, F. F; MARSHAK, S., PEDROSA-SOARES, A. C., PERES, G. G., CRUZ, S. C. P., WHITTINGTON, A. Kinematic evolution of the Araçuaí - West Congo orogen in Brazil and Africa: Nutcracker tectonics during the Neoproterozoic assembly of Gondwana. Precambrian Research, v. 149, n. 1-2, p. 43-64, 2006.
- ALVES, J. A. C. Reconstrução estocástica da Mina São Luiz, Complexo Fazendão, MG, Dissertação de Mestrado. Ouro Preto: Departamento de Geologia, Escola de Minas, Universidade Federal de Ouro Preto, 1991. 120 p. (Dissertação de Mestrado).
- BARBOSA, A. L. M. Contribuições recentes à geologia do Quadrilátero Ferrífero. Ouro Preto: Departamento de Geologia, Escola de Minas, Universidade Federal de Ouro Preto, 1968. (Boletim).
- BRINK, U. TEN, S., KATZMAN, R., LIN, J. Three-dimensional models of deformation near strike-slip faults. Journal of Geophysical Research, v. 101, n. B7, p.16.205-16.220, 1996.
- CASTRO, E. C., FERREIRA, J. E., CASTRO, P. T. A. Formação Cata Preta: uma nova unidade litoestratigráfica, definida em rochas cenozóicas, no extremo leste do Quadrilátero Ferrífero. In: CONG. BRAS. GEOL., 40, 1988. Belo Horizonte. Anais... Belo Horizonte: SBG, 1998. p. 81.
- CHEMALE, F. Jr., ROSIÈRE, C. A., ENDO, I. Evolução tectônica do Quadrilátero Ferrífero, Minas Gerais: um modelo. Pesquisas, v. 18, n. 2, p. 104-127, 1991.
- CORDANI, U. G., KAWASHITA, K., MULLER, G., QUADE, H., REIMER, V., ROESER, H. Interpretação tectônica e petrológica de dados geocronológicos do embasamento na borda sudeste do Quadrilátero Ferrífero, MG. Academia Brasileira de Ciências v.52, n.4, p. 785-799, 1980.
- DORR, J. V. N. II. Physiographic, stratigraphic and structural development of the Quadrilátero Ferrífero, Minas Gerais, Brazil . USGS/DNPM. Professional Paper 641-A., 1969. 110p.
- DORR, J. V. N. II., GAIR, J. E., POMERENE, J. B., RYNEARSON, G. A. Revisão Estratigráfica Pré-Cambriana do Quadrilátero Ferrífero. Rio de Janeiro, DNPM/DFPM, 1957. 36p (Avulso. 81).
- ENDO, I. Regimes tectônicos do Arqueano e Proterozóico no Interior da Placa Sanfranciscana: Quadrilátero Ferrífero e áreas adjacentes, Minas Gerais. São Paulo: Instituto de Geociências da Universidade de São Paulo. 1997. 243p. (Tese de Doutorado) .
- ENDO, I., FONSECA, M. A. Sistema de cisalhamento Fundão-Cambotas no Quadrilátero Ferrífero, MG: geometria e cinemática. Revista Escola de Minas, v. 45, n. 1/2, p.15-17, 1992.
- ENDO, I., SILVA, L. G., ZAVAGLIA, G., ROCHA, F. O. G., GUIMARÃES, M. L. V., ROSAS, C. F., LAGOEIRO, L. E., SANTOS, G. J. I. Arcabouço estrutural e modelo evolutivo do Sinclinal Gandarela, Quadrilátero Ferrífero, MG. In: CONGRESSO BRASILEIRO DE GEOLOGIA, 42. ARAXÁ, MG, 2004. (Resumo).
- ENDO, I., OLIVEIRA, A. H., PERES, G. G., GUIMARÃES, M. L. V., LAGOEIRO, L. E., MACHADO, R., ZAVAGLIA, G., ROSAS, C. F., MELO, R. J. Nappe Curral: uma megaestrutura alóctone do Quadrilátero Ferrífero e controle da mineralização. In: SIMPÓSIO NACIONAL DE ESTUDOS TECTÔNICOS, 10; INTERNATIONAL SYMPOSIUM ON TECTONICS, 4. Curitiba, p. 279-282, 2005. Boletim de Resumos Expandidos.
- ERSLEV, E. A. Trishear fault-propagation folding. Geology, v.19, p.617-620, 1991.
- ERSLEV, E. A., MAYBORN, K. R. Multiple geometries and modes of fault-propagation folding in the Canadian thrust belt. Journal of Structural Geology, v. 19, n. 3-4, p. 321-335, 1997.
- EXNER, U., MANCKTELOW, N. S., GRASEMANN, B. Progressive development of s-type flanking folds in simple shear. Journal of Structural Geology v. 26, p. 2191-2201, 2004.
- FRANCO, A. S. P. Geometria e evolução tectônica do sinclinal Ouro Fino. Quadrilátero Ferrífero, MG. Ouro Preto: Departamento de Geologia, Escola de Minas, Universidade Federal de Ouro Preto. 102p., 2003. 102 p. (Dissertação de Mestrado)
- FERREIRA, Fº F. A., FONSECA, M. A. Partição da deformação em regimes contracionais de antepaís: exemplo do sistema de falhas Água Quente. Revista Brasileira de Geociências, v. 31, n. 3, p.267-278, 2001.
- GAIR, J.E. The Sabará Formation. In: SYMPOSIUM ON STRATIGRAPHY OF MINAS SERIES IN THE QUADRILÁTERO FERRÍFERO, MINAS GERAIS, BRAZIL. BOLETIM SBG, v.7, n.2, p.68-69, 1958.
- GEORIENT v. 9.0 packages. Structural Geology - Mapping/GIS Software for Microsoft Windows. Disponível <http://sur.ly/o/holcombe.net.au/software%2Frodh_software_georient.htm/AA001290>. Acesso em 18.fev.2015, 12:14
» http://sur.ly/o/holcombe.net.au/software%2Frodh_software_georient.htm/AA001290 - GRASEMANN, B., STÜWE, K. The development of flanking folds during simple shear and their use as kinematic indicators. Journal of Structural Geology, v. 23, p. 715-724, 2001.
- HANSEN, E. Strain facies: minerals, rocks and inorganic material. Berlin: Springer Verlag, 1971. 209p.
- HARLAND, W. B. Tectonic facies, orientation, sequence, style and date. Geological Magazine. v. 93, p.110-120, 1956.
- HERZ, N. Gneissic and igneous rocks of the Quadrilátero Ferrífero, Minas Gerais, Brazil . USGS/DNPM, 1970. 57 p. (Professional Paper 641-B).
- HSUE, K. J. The geology of Switzerland : an introduction to tectonic facies. Princeton University Press, 1995. 250 p. (Monograph; ISBN 0691087873).
- LIPSKI, M. Tectonismo cenozóico no Quadrilátero Ferrífero, Minas Gerais. Ouro Preto: Departamento de Geologia, Escola de Minas, Universidade Federal de Ouro Preto. 2002. 171 p. (Dissertação de Mestrado)
- MACHADO, N., SCHRANK, A., NOCE, C.M., GAUTHIER, G. Ages of detrital zircon from Archean-Paleoproterozoic sequences: implications for greenstone belt setting and evolution of a transamazonian foreland basin in Quadrilátero Ferrífero, Southeast Brazil. Earth and Planetary Science Letters, v. 141, p. 259-276, 1996.
- MAXWELL, C. H. Geology and ore deposits of the Alegria district, Brazil. Washington: USGS/DNPM, 1972. 72p. (Professional Paper 341J) 72p.
- NARR, W., SUPPE, J. Kinematics of basement-involved compressive structures. American Journal of Science, v. 294, p. 802-860, 1994.
- NAYLOR, M. A., MANDL, G., SIJPESTEIJN, C. H. K. Fault geometries in basement-induced wrench faulting under different initial stress states. Journal of Structural Geology, v.8, n. 7, p. 737-752, 1986.
- NOCE, C. M. Geocronologia dos eventos magmáticos, sedimentares e metamórficos na região do Quadrilátero Ferrífero, Minas Gerais. São Paulo: Instituto de Geociências, Universidade de São Paulo, 1995. 128 p. (Tese de Doutorado).
- PASSCHIER, C. W. Flanking structures. Journal of Structural Geology, v. 23, p. 951-962, 2001.
- PASSCHIER, C. W., WILLIAMS, P. R. Conflicting shear sense indicators in shear zones; the problem of non-ideal sections. Journal of Structural Geology, v. 18, n. 10, p.1281-1284, 1996.
- RENGER F. E., NOCE C. M., ROMANO A. W., MACHADO N. Evolução sedimentar do Supergrupo Minas: 500 Ma de registro geológico no Quadrilátero Ferrífero, Minas Gerais, Brasil. Geonomos, v. 2, n. 1, p. 1-11, 1994.
- ROBERTSON, A. H. F. Role of the tectonic facies concept in orogenic analysis and its application to Tethys in the Eastern Mediterranean region. Earth-Science Reviews, v. 37, n. 3, p.139-213, 1994.
- ROMANO, A. W. Evolution tectonique de la région NW du Quadrilatère Ferrifère - Minas Gerais, Brésil. Nancy, France : Université de Nancy I, 1989. 259p. (Thèse Docteur).
- SCHORSCHER, H. D., SANTANA, F. C., POLÔNIA, J. C., MOREIRA, J. M. P. Quadrilátero Ferrífero - Minas Gerais State: Rio das Velhas Greenstone Belt and Proterozoic rocks. In: INTERNATIONAL SYMPOSIUM ON ARCHEAN AND EARLY PROTEROZOIC EVOLUTION AND METALLOGENESIS, Salvador, 1982. Anais.... Salvador, SBG. p.43, 1982.
- TINDALL, S. E. The Cockscomb Segment of the East Kaibab Monocline: taking the structural plunge. Geology of Utah's Parks and Monuments. Utah Geological Association Publication 28, 2000.
- XYPOLIAS, P. Vorticity analysis in shear zones: a review of methods and applications. Journal of Structural Geology, v. 32. p.2072-2092, 2010.
- XYPOLIAS, P. Some new aspects of kinematic vorticity analysis in naturally deformed quartzites. Journal of Structural Geology, v. 31. p. 3-10, 2009.
- WILCOX, R. E., HARDING, T. P., SEELY, D. R. Basic Wrench Tectonics. The American Association of Petroleum Geologists of Bulletin, v. 57, n. 1, p.74-96, 1973.
- WILLIANS, P. F. Multiply deformed terrains problems of correlation. Journal of Structural Geology, v. 7, n. 3/4, p.269-280, 1985.
Publication Dates
-
Publication in this collection
Apr-Jun 2015
History
-
Received
03 Apr 2014 -
Accepted
23 Mar 2015