TY - JOUR
T1 - A structural transect across the coastal mobile belt in the Brazilian Highlands (latitude 20°S)
T2 - The roots of a Precambrian transpressional orogen
AU - Cunningham, Dickson
AU - Alkmim, Fernando F.
AU - Marshak, Stephen
N1 - Funding Information:
The authors are grateful to Hanna Jordt-Evangelista for her careful advice and criticism of the manuscript. Helpful reviews by N. Machado, R. Strachan and R. Bauer led to improvement of the manuscript. D.C. is especially grateful to André Danderfer for his friendship, useful scientific discussions and logistical help. This work was supported by NSF International Programs Grant No. 9301292 awarded to Cunningham and Marshak.
PY - 1998/11/1
Y1 - 1998/11/1
N2 - We present results of a detailed structural analysis from a 250 km-long, east-west-trending transect crossing the Coastal Mobile Belt, a part of the Precambrian orogen which lies between the eastern edge of the Sao Francisco craton and the Atlantic coast. The region exposes amphibolite-granulite grade metamorphic rocks and migmatites which formed at mid-lower crustal depths during the Brasiliano orogeny (0.63-0.52 Ga). This event marked the closure of the northernmost Adamastor Ocean and collision between the Sao Francisco and Congo Cratons during West Gondwana assembly. Brasiliano deformation resulted in W-vergent structures including thrust faults which accommodated kilometer-scale transport of crystalline basement, overturned kilometer-scale folds, sheath folds and penetratively developed gneissosity and schistosity. Isolated relics of an older folded fabric occur locally and may represent Transamazonian (2.2-2.0 Ga) deformation. The orogen is kinematically partitioned with the eastern 175 km dominated by moderately- to steeply dipping north-trending dextral strike-slip and oblique-slip faults and associated flower structures, whereas the western 75 km is dominated by W-vergent shallowly- to moderately east-dipping thrust faults. The boundary between these two provinces may mark a Brasiliano suture. Throughout the transect, quartzite and metasedimentary belts form strongly deformed zones between massive crystalline basement thrust sheets. The granulite-cored Serra do Caparau massif, the highest mountains in South America outside of the Andes and Guyana shield, occupies a restraining bend between two Brasiliano dextral shear zones. The W-vergent Coastal Mobile Belt formed contiguously with the E-vergent Pan-African West Congo orogen now exposed along the conjugate margin of Africa. Thus an important late Precambrian boundary between structurally linked but kinematically opposed structural provinces must lie hidden in the extended offshore continental margins of either continent. Cretaceous opening of the South Atlantic and separation of the West Congo belt from the Coastal Mobile Belt may have been structurally influenced by this boundary.
AB - We present results of a detailed structural analysis from a 250 km-long, east-west-trending transect crossing the Coastal Mobile Belt, a part of the Precambrian orogen which lies between the eastern edge of the Sao Francisco craton and the Atlantic coast. The region exposes amphibolite-granulite grade metamorphic rocks and migmatites which formed at mid-lower crustal depths during the Brasiliano orogeny (0.63-0.52 Ga). This event marked the closure of the northernmost Adamastor Ocean and collision between the Sao Francisco and Congo Cratons during West Gondwana assembly. Brasiliano deformation resulted in W-vergent structures including thrust faults which accommodated kilometer-scale transport of crystalline basement, overturned kilometer-scale folds, sheath folds and penetratively developed gneissosity and schistosity. Isolated relics of an older folded fabric occur locally and may represent Transamazonian (2.2-2.0 Ga) deformation. The orogen is kinematically partitioned with the eastern 175 km dominated by moderately- to steeply dipping north-trending dextral strike-slip and oblique-slip faults and associated flower structures, whereas the western 75 km is dominated by W-vergent shallowly- to moderately east-dipping thrust faults. The boundary between these two provinces may mark a Brasiliano suture. Throughout the transect, quartzite and metasedimentary belts form strongly deformed zones between massive crystalline basement thrust sheets. The granulite-cored Serra do Caparau massif, the highest mountains in South America outside of the Andes and Guyana shield, occupies a restraining bend between two Brasiliano dextral shear zones. The W-vergent Coastal Mobile Belt formed contiguously with the E-vergent Pan-African West Congo orogen now exposed along the conjugate margin of Africa. Thus an important late Precambrian boundary between structurally linked but kinematically opposed structural provinces must lie hidden in the extended offshore continental margins of either continent. Cretaceous opening of the South Atlantic and separation of the West Congo belt from the Coastal Mobile Belt may have been structurally influenced by this boundary.
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U2 - 10.1016/S0301-9268(98)00077-1
DO - 10.1016/S0301-9268(98)00077-1
M3 - Article
AN - SCOPUS:0032462113
SN - 0301-9268
VL - 92
SP - 251
EP - 275
JO - Precambrian Research
JF - Precambrian Research
IS - 3
ER -