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Structural Analysis of the Itapucumi Group In Our reference: SAMES 895 P-authorquery-v8 AUTHOR QUERY FORM Journal: SAMES Please e-mail or fax your responses and any corrections to: E-mail: [email protected] Article Number: 895 Fax: +31 2048 52789 Dear Author, Please check your proof carefully and mark all corrections at the appropriate place in the proof (e.g., by using on-screen annotation in the PDF file) or compile them in a separate list. For correction or revision of any artwork, please consult http://www.elsevier.com/artworkinstructions. Any queries or remarks that have arisen during the processing of your manuscript are listed below and highlighted by flags in the proof. Location Query / Remark: click on the Q link to go in article Please insert your reply or correction at the corresponding line in the proof Q1 Please ensure that affiliation “a”, affiliation address, and corresponding author’s information are complete and accurate. Q2 The reference “Grant, 1990” occurs in the reference list but not in the body of the text. Please cite this reference or alternatively delete it. Q3 Please provide an update for reference “Ramos et al., in press”. Thank you for your assistance. SAMES895_proof ■ 8 September 2010 ■ 1/11 Journal of South American Earth Sciences xxx (2010) 1e11 Contents lists available at ScienceDirect Journal of South American Earth Sciences journal homepage: www.elsevier.com/locate/jsames 1 56 2 Structural analysis of the Itapucumí Group in the Vallemí region, northern 57 3 58 4 Paraguay: Evidence of a new Brasiliano/Pan-African mobile belt 59 5 60 6 Ginaldo Ademar da Cruz Campanha a,*, Lucas Warren b, Paulo César Boggiani a, 61 7 Carlos Henrique Grohmann a, Alberto Arias Cáceres c 62 8 63 9 a Instituto de Geociências da USP, 05508-080 Sao Paulo, SP, Brazil 64 b 10 Programa de Pós-Graduação em Geoquímica e Geotectônica do Instituto de Geociências da USP, Brazil 65 c 11 Industria Nacional de Cemento, INC, Paraguay 66 12 67 13 68 article info abstract 14 69 15 70 Article history: 16 The Neoproterozoic (Ediacaran) Itapucumí Group in northern Paraguay is composed of carbonate and 71 Received 21 October 2009 siliciclastic rocks, including ooid grainstones, marls, shales and sandstones, containing Cloudina fossils in 17 72 Accepted 20 April 2010 the eastern region. It is almost undeformed over the Rio Apa Cratonic Block but shows a strong defor- 18 mational pattern at its western edge. A detailed structural analysis of the Itapucumí Group was con- 73 19 Keywords: ducted in the Vallemí Mine, along with a regional survey in other outcrops downstream in the Paraguay 74 20 Western Gondwana River and in the San Alfredo, Cerro Paiva and Sgt. Lopez regions. In the main Vallemí quarry, the 75 Neoproterozoic 21 structural style is characterized by an axial-plane slaty cleavage in open to isoclinal folds, sometimes 76 Ediacaran e 22 Paraguay belt overturned, associated with N S trending thrust faults and shear zones of E-vergence and with a low- 77 23 Rio Apa block grade chlorite zone metamorphism. The structural data presented here are compatible with the 78 24 hypothesis of a newly recognized mobile belt on the western side of the Rio Apa Cratonic Block, with 79 25 Palavras-chave: opposite vergence to that of the Paraguay Mobile Belt in Brazil. Both belts are related to the Late Bra- 80 26 Gondwana Ocidental siliano/Pan-African tectonic cycle with a Lower Cambrian deformation and metamorphism age. The 81 Neoproterozóico deformation could be due to the late collision of the Amazonian Craton with the remainder of Western 27 82 Ediacarano Gondwana or to the western active plate boundary related to the Pampean Belt. The structural and 28 83 Faixa Paraguai lithologic differences between the western Itapucumí Group in the Vallemí and Paraguay River region 29 Bloco Rio Apa and the eastern region, near San Alfredo and Cerro Paiva, suggest that this group could be divided into 84 30 two lithostratigraphic units, but more stratigraphic and geochronological analyses are required to 85 31 confirm this possibility. 86 32 Ó 2010 Published by Elsevier Ltd. 87 33 88 34 89 35 resumo 90 36 91 37 O Grupo Itapucumí é constituído por rochas carbonáticas e siliciclásticas, caracterizadas pela presença de 92 38 grainstones com oóides, margas, folhelhos e arenitos de idade neoproterozóica (ediacarana), devido à 93 39 ocorrência do fóssil Cloudina na sua porção leste. Apresenta-se quase indeformado quando recobre o 94 40 bloco cratônico do Rio Apa, porém mostra um intenso padrão deformacional na sua porção ocidental. 95 41 Análise estrutural detalhada foi realizada na mina Vallemí, norte do Paraguai, bem como reconhecimento 96 de outros afloramentos ao longo do rio Paraguai e na região entre San Alfredo, Cerro Paiva e Sargento 42 97 Lopez. Na mina principal em Vallemí, o estilo estrutural caracteriza-se pelo desenvolvimento de clivagem 43 ardosiana plano-axial de direção aproximada NeS em dobras abertas a isoclinais, por vezes com flanco 98 44 inverso e associadas a empurrões com vergência para E com desenvolvimento de metamorfismo de baixo 99 45 grau, na zona da clorita. Os dados estruturais levantados reforçam a hipótese da existência de uma nova 100 46 faixa móvel na margem oeste do Bloco Rio Apa, com vergência oposta à da Faixa Paraguai Meridional, 101 47 relacionada ao final do evento Brasiliano/Pan-Africano, com deformação e metamorfismo no Cambriano 102 48 Inferior. A deformação pode ser atribuída à colisão tardia entre o craton Amazônico e o restante do 103 49 Gondwana Ocidental, ou à borda de placa ativa associada à Faixa Pampeana. As diferenças estruturais e 104 50 em parte litológicas, entre as exposições da parte ocidental do Grupo Itapucumí, na região de Vallemí, das 105 51 106 52 * Corresponding author. Tel.: þ55 11 3091 3946; fax: þ55 11 3091 4258. Q1 107 53 E-mail address: [email protected] (G.A.daC. Campanha). 108 54 109 e Ó 55 0895-9811/$ see front matter 2010 Published by Elsevier Ltd. 110 doi:10.1016/j.jsames.2010.04.001 Please cite this article in press as: Campanha, et al., Structural analysis of the Itapucumí Group in the Vallemí region, northern..., Journal of South American Earth Sciences (2010), doi:10.1016/j.jsames.2010.04.001 SAMES895_proof ■ 8 September 2010 ■ 2/11 2 G.A.daC. Campanha et al. / Journal of South American Earth Sciences xxx (2010) 1e11 111 da parte oriental, nos arredores de San Alfredo e Cerro Paiva, conduzem à possibilidade do Grupo Ita- 176 fi 112 pucumí vir a ser dividido no futuro em duas unidades estratigrá cas distintas, o que requer estudos 177 fi fi 113 estratigrá cos e geocronológicos mais pormenorizados para uma conclusão de nitiva. 178 Ó 2010 Published by Elsevier Ltd. 114 179 115 180 116 resumen 181 117 182 118 Un análisis estructural detallado fue realizado en la Mina Vallemí en el norte de Paraguay. Afloran allí 183 119 litotipos del Grupo Itapucumí, de edad neoproterozoica, constituído por calcarenitas oolíticas, margas, 184 120 lutitas y areniscas. En la mina principal, la sucesión presenta deformación relativamente intensa, con 185 121 desarrollo de clivaje de plano axial y rumbo NeS. Se observan pliegues abiertos a isoclinales, a veces con 186 122 flanco invertido y asociados a cabalgamientos con vergencia al NE y E. Se registra asimismo meta- 187 fi 123 mor smo de grado bajo (zona de clorita). Los datos estructurales refuerzan la hipótesis de una nueva faja 188 124 móvil en el margen oeste del Bloque Río Apa, con vergencia opuesta a la del Cinturón Paraguay 189 meridional, este último relacionado al evento Brasiliano/Pan-Africano. Las diferencias estructurales y en 125 190 parte litológicas entre las exposiciones de la parte occidental del Grupo Vallemí y las de la parte oriental, 126 191 en los alrededores de Colonia San Alfredo, sugieren la posibilidad de que el Grupo Itapucumí pueda ser 127 subdividido en dos unidades litoestratigráficas distintas. Para llegar a una conclusión definitiva son 192 128 necesarios estudios estratigráficos y geocronológicos más pormenorizados. 193 129 Ó 2010 Published by Elsevier Ltd. 194 130 195 131 196 132 197 133 1. Introduction proto-Pacific margin. The main cratonic blocks involved are the 198 134 Amazonian, Rio Apa, São Francisco-Congo, Paranapanema (or Par- 199 135 The geology of northern Paraguay is dominated by extensive aná), Rio de La Plata, Pampia and Arequipa-Antofalla (Fig. 1). Recent 200 136 Phanerozoic sedimentary covers, including the Cenozoic Chaco review articles about this sector of Gondwana were published by 201 137 Basin and the Paleozoic Paraná Basin. The southern portion of the Rapela et al. (1998), Kröner and Cordani (2003), Rapela et al. (2007), 202 138 Rio Apa Cratonic Block outcrops between these sedimentary covers Ramos and Coira (2008), Cordani et al. (2009) and Cordani (2009). 203 139 in continuity with the exposures in the state of Mato Grosso do Sul, The Paraguay Fold Belt (Almeida, 1968; Alvarenga et al., 2000), 204 140 Brazil. The eastern side of the Rio Apa Block is flanked by the sometimes referred to as the ParaguayeAraguaia Belt or the 205 141 Paraguay Fold Belt and its correlated cratonic covers, represented Paraguay-Pampean Belt, is a curved belt around the Amazonian and 206 142 by the Corumbá and Cuiabá groups, while its southern region is Rio Apa cratonic blocks. It has undeformed or slightly deformed 207 143 covered by the Itapucumí Group. sedimentary covers over the cratons, passing to a marginal fold- 208 144 The Late Neoproterozoic to Cambrian tectonic evolution of this and-thrust belt with tectonic vergence towards the cratonic areas, 209 145 region is related to the amalgamation of Western Gondwana and its and it is characterized by low-grade metamorphism (Fig.
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