Produção Nacional
ANÁLISE ESTRUTURAL E DEFORMACIONAL EM ZONAS DE CISALHAMENTO DE BAIXO MERGULHO E TRANSCORRENTES ASSOCIADAS A ZONA DE SUTURA ALTEROSA, NA REGIÃO DE CRISTINA E ITAJUBÁ - MG
2006; Sociedade Brasileira de Geologia; Volume: 36; Issue: 3 Linguagem: Inglês
10.25249/0375-7536.2006363413425
ISSN2177-4382
AutoresIramaia Furtado Braga, Hans Dirk Ebert,
Tópico(s)Geological formations and processes
ResumoThe region or Cristina and Itajubá-MG, located south of São Francisco Craton, comprises paragneisses of the Piracaia Complex, granulites and ortogneisses of the Paraisópolis Complex which are overthrusted on metassediments of the Andrelândia Group and its basement (Amparo/São Gonçalo do Sapucaí Complex), metamorphosed in the amphibolite facies. Ductile fabrics record two main tectonic events. A thrusting event (Dn) generated the regional Sn, which shows foliation with NW-SE strike and low dips to SW, in association with down dip stretching lineations. Dn is attributed to the collision of the São Paulo Block (Socorro-Guaxupé Terrane) to ENE onto the São Francisco Plate during the Brasilia Orogeny (630-610 Ma), whose limit, the Alterosa Suture Zone (ASZ), is marked in that area by the Lourenço Velho SZ. Sn also shows a progressive sinistral inflection to a almost vertical NE-SW orientation along the Maria da Fé and Cristina strike slip shear zones. These amphibolite to granulite facies shear zones are consistent with the SW-NE compressive tectonic regime and are interpreted as lateral ramps of the Dn event. A Strike-slip/transpressive deformation (Dn + 1) formed, in lower amphibolite facies, the mylonitic foliation Sn + 1, that occur along NE-SW trending dextral shear zones within the transpressive Rio Paraíba do Sul Belt, with is related to the younger Ribeira collision (590-560 Ma). The strain analysis using Fry and Rf/phy methods revealed oblate strain elipsoids, with predominance of pure shear component of over simple shear. Simple shear predominates only in samples close to the SLSZ, where kinematic markers indicate top movement to NE and constitutes an important zone of mass transport . The obliquity between the largest axis of the strain e1lipse in relation to the foliation in planes XZ and YZ indicates non-coaxial deformation in both kinematic planes. The analyses of the strain ratio on these sections indicates that the quartz exerted strong rheologic importance for shear zone development, better accomodating the regional strains in relation to feldspars, that does not show substantial strain variation among samples with low and high deformation.
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