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Previous issue date: 2014-12-18 === Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico - CNPq === Atrav?s de fun??es de receptor migradas e empilhadas (phase-weightedstack),
investigou-se a arquitetura crustal da Prov?ncia Borborema. Para isso,
foram utilizados telessismos de ondas ? registrados em 64 esta??es
sismogr?ficas distribu?das no Nordeste brasileiro, depois de aplicar um conjunto
de modifica??es no algoritmo de empilhamento para corrigir inconsist?ncias
detectadas no algoritmo original e melhorar sua efici?ncia computacional. A
Prov?ncia Borborema representa a por??o mais oeste de um or?geno
Neoproterozoico, que experimentou extens?o no Mesozoico, o que levou ?
forma??o de um grande n?mero de bacias intracontinentais do tipo rifte, e,
posteriormente, ? deriva continental. O Cenozoico foi marcado por processos de
soerguimento topogr?fico, que poderia estar relacionado com vulcanismo, o que
possibilitou a forma??o do Planalto da Borborema. Devido ? limitada
compreens?o a respeito da arquitetura crustal da Prov?ncia, as rela??es de
causa e efeito entre a topografia superficial, a extens?o Mesozoica e o
soerguimento Cenozoico n?o s?o claras. O empilhamento de fun??es de
receptor evidencia as convers?es ?? no limite entre a crosta e o manto,
mostrando crosta espessa, entre 36 e 40 km na por??o sul do Planalto e crosta
entre 30 e 32 km nas regi?es ao redor, incluindo o norte do Planalto. Essa mesma
abordagem tamb?m revelou a presen?a de uma descontinuidade entre 9 e 18
km de profundidade, que tende a desaparecer em dire??o ao sul do Planalto, ?
medida que a crosta se torna espessa. Dessa forma, argumenta-se que a crosta
fina na Prov?ncia Borborema ? o resultado de processos de estiramento crustal
durante o Mesozoico e que a descontinuidade intracrustal observada consiste
num detachment de baixo ?ngulo, que atuou na acomoda??o da distens?o. A
crosta espessa na por??o sul do Planalto seria, ent?o, um bloco com reologia
mais resistente, que resistiu a deforma??o durante o Mesozoico, enquanto a
crosta fina sob o norte do Planalto seria proveniente de uma bacia pret?rita, cuja
crosta foi afinada durante o Mesozoico e soerguida durante o Cenozoico. === The crustal architecture of the Borborema Province was investigated
through migration and stacking of receiver functions (phase-weighted-stack). The
stacks were developed from teleseismic ?-waves recorded at 64 seismological
stations distributed throughout Northeast Brazil, after applying a number of
modifications to the stacking algorithm that corrected inconsistencies in the
original algorithm and improved its computational efficiency. The Borborema
Province is the westernmost portion of a Neoproterozoic orogen that experienced
extension in the Mesozoic, leading to the formation of a number of intracontinental
rift basins and, eventually, to the continental drift. The Cenozoic was
marked by topographic uplift of the Province, perhaps related to coeval episodes
of volcanism, which resulted in the formation of the Borborema Plateau. Due to
limited understanding of the crustal architecture of the Province, the causal
relationships between surface topography, Mesozoic extension, and Cenozoic
uplift are poorly understood. The receiver function stacks highlight ?? conversions
from the crust-mantle boundary that demonstrate a thick crust between 36 and
40 km in the southern Plateau, and crust between 30 and 32 km in the regions
around, including the northern Plateau. The receiver function stacks also
revealed the presence of a discontinuity between 9 and 18 km depth that tends
to fade away towards the southern Plateau as the crust thickens. It is argued that
the thin crust in the Borborema Province is the result of crustal stretching during
Mesozoic times, and that the intracrustal discontinuity marks the location of a lowangle
detachment zone that accommodated extension within the crust. The thick
crust in the southern Plateau would then be a rheologically strong block that
resisted deformation during the Mesozoic, while the thin crust beneath the
northern Plateau would be a portion of a formerly depressed crust that
experienced uplifted during the Cenozoic.
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