UnB - Instituto de Geociências - Produção Científica
RESUMOS/ABSTRACTS
THE CALDAS NOVAS AND SANTA CRUZ DOMES: STRUCTURAL EVOLUTION AND IMPLICATION FOR TECTONICS IN THE BRASÍLIA BELT, CENTRAL BRAZIL
LUIZ JOSÉ HOMEM D’EL-REY SILVA
In: Congresso Brasileiro de Geologia, 41, João Pessoa, 2002, SBG. Anais, 1: 341-341.
Palavras
chave: Analise estrutural, Análise Tectônica, CICLO BRASILIANO, NEOPROTEROZOICO, Domo de Caldas Novas, Domo de Santa Cruz
RESUMO
The three main lithotectonic domains of the Brasília Belt (the Goiás Magmatic
Arc, the Internal and the External zones) bend around an imaginary E-W axis
approximately coincident with the latitude of the Federal District, and stretch
along a NE-trending northern segment and along a SE-trending southern segment.
In despite of this concave-to-the-West arc-like geometry, detailed studies
carried out in the last decade have demonstrated that key areas in both segments
record a structural evolu
tio
n due to a WNW-ESE sub-horizontal maximum compressive stress
responsible for a D1-D2 progressive deforma
tio
n characterised by westward-dipping frontal ramps.
Nevertheless, a tectonic analysis carried out around two structural domes in the
inner part of the belt has revealed the importance of a younger event (D3)
for understanding the evolu
tio
n of the Brasília Belt. The Caldas Novas dome, situated in
the southern segment of the Internal Zone, and the Santa Cruz dome, situated in
the northern segment of the Magmatic Arc, near the Campos Verdes Emerald
District (NW of the Goiás State), are both mantled by quartzite comparable to
the Meso-Neoproterozoic, passive margin-like Paranoá Group, this one being
tectonically covered by a sequence of schists, other metasiliciclastics and
metavolcanics of a Neoproterozoic sequence (the Araxá Group) that filled a
back-arc basin mostly in the 950-800 Ma interval, although the
volcano-sedimentary record may be as young as ≈ 650 Ma. The two domes
display abundant evidence for a D1-D3 evolu
tio
n keeping quite similar characteristics: 1
– Event D1 developed a
pervasive, often mylonitic layer-parallel folia
tio
n (S1) and rare, isoclinal, dm-scale F1
folds. It was assisted by greenschist
facies metamorphism up to the garnet zone (mainly in the Araxá Group); 2
- Event D2, responsible for emplacement of the Araxá Group as a
nappe over the Paranoá Group, developed ESE-verging, dm- to dam-scale,
asymmetric F2 folds associated to a greenschist facies penetrative
axial planar folia
tio
n (S2) and contrac
tio
n faults; 3 - The
angular rela
tio
nship between S0//S1 and S2,
the vergence of (F1) F2 folds, and a penetrative,
WNW-trending, down-dip D1-D2 stretching linea
tio
n, all clearly define a D1-D2 regime
under a WNW-trending sub-horizontal maximum compression (s1)
resulting in upthrust to ESE, along low-angle, NW-dipping frontal ramps; 4
– Assisted by low-greenschist facies metamorphism, D3 is due to an
ENE-trending shortening responsible for open to tight, generally upright,
km-scale F3 folds, such as the domes. The Santa Cruz dome is a local
feature explainable by a very local combina
tio
n of stresses. However, because the Caldas Novas dome
displays the same D1-D3 kinematics reported in other areas
of the Araxá Group further to the south (e.g. the Araxá and the Passos
synforms, and other intervening large-scale F3 folds) D3
is most probably due to a regional event of ENE-shortening that affected
specifically the southern segment, late in the 650-600 Ma old continental
collision that imprinted final shape to the Brasília Belt.