Dados da Submissão

Título

STRUCTURAL ANALYSIS OF THE ALEGRIA SYNFORM - EASTERN BORDER OF THE QUADRILÁTERO FERRÍFERO: EVIDENCE FOR A LARGE DEXTRAL DRAG FOLD

Texto do resumo

The eastern border of the Quadrilátero Ferrífero is an area of great geological interest due to its interpretation as the boundary between the São Francisco Craton and the Araçuaí Belt. This region has a complex deformational history with structuring conditioned by the Água Quente Fault System (AQFS), which plays a crucial role in local deformation. The AQFS accommodates deformation in the form of a system of imbricated thrusts, consisting of frontal (N-S) and oblique (W-E) faults, which are partitioned into domains conditioned by the presence of the Serra do Caraça (SC), which acts as a barrier against deformation, reorienting and rotating fault traces. The present study aimed to conduct structural analysis of the Alegria Synform, through systematic geological-structural mapping, stereographic analysis, and geometric and kinematic interpretation. From a lithostratigraphic point of view, the study area comprises the rocks of the Minas Supergroup, mainly itabirites, schists, quartzites, and phyllites. The work was conducted in the mining complexes of Alegria, focusing on pit regions and their surroundings. A total of 3,256 field station were collected, collecting over 6,600 georeferenced planar and linear measurements with GPS and taken with a Brunton compass (Clar notation). In this study, traditional techniques used for structural mapping in polydeformed terrains were adopted, highlighting foliation (Sn) and mineral stretching lineation (Le) as main structural features. The applied methodology includes extensive bibliographic review, initial field inspection, data collection, local and regional geological-structural profile construction, laboratory investigations, stereographic analyses, geometric and kinematic interpretation. This latter step was carried out according to modern structural concepts, resulting in the development of a geostructural evolution model for the Alegria Synform. The results reveal foliation Sn and mineral stretching lineation (Le) as the main structural features, observed in virtually all mapped lithotypes. The foliation Sn has an orientation N-S in the southern Alegria mine and rotates dextrally until it is approximately E-W in the northern mine, with modal attitudes of 97/31 and 163/62, respectively. Additionally, various types of folds were observed, exhibiting centimetric to metric proportions and intrafolial morphologies, with broken flanks or asymmetrical with intact flanks. S-C structures, drag folds, and various kinematic indicators were also observed. To analyze the geometric variability of foliation, structural domains were defined through Structural Contour Maps. The Structural Contour Maps aim to establish locations where the foliation presents a similar structural pattern and thus individualize regions with kinematic characteristics equivalent to the geometry of frontal (N-S) and lateral (E-W) ramps. The structural framework outlined by foliation Sn and lineation Le explains the Alegria Synform as a large dextral drag fold, resulting from a ductile to ductile-brittle thrust system, with mass transport from E to W. In this region, the Serra do Caraça act as a structural buttress and plays an important role in the deformation pattern, causing the regional N-S foliation to rotate and reorient according to the E-W direction.

Palavras Chave

Progressive deformation; Structural geology; Structural model; Água Quente Fault