Banca de DEFESA: NITZSCHIA REGINA RODRIGUES DOMINGOS

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : NITZSCHIA REGINA RODRIGUES DOMINGOS
DATE: 08/01/2020
TIME: 09:00
LOCAL: Auditório do DGEF
TITLE:

Geophysical evidences of doming during the Pan-African/Brasiliano orogeny in the Seridó belt (Borborema Province, Brazil)

KEY WORDS:

Pan-African/Brasiliano orogeny; Borborema Province; Seridó belt; Gneiss domes; Potential field data.

PAGES: 166
BIG AREA: Ciências Exatas e da Terra
AREA: Geociências
SUMMARY:

The Seridó belt (SB) is a Neoproterozoic schist belt in the Borborema Province (NE Brazil). It was deposited, deformed and metamorphosed in the context of the Pan-African/Brasiliano orogeny. In this tectonic event, the crust was partially melted, particularly in the connection of the Patos shear zone with the SB, thus altering its rheological properties and, consequently, influencing its deformation. Among the occurrences of rocks associated with partial melting, the Santa Luzia anatetic dome (at c. 575 Ma) stands out. The aeromagnetic map of the SB shows an expressive long-wavelenght (˃25 km) regional anomaly in the south-central part of the area. This anomaly has sigmoidal shape and its central axis rotates from NNE-SSW to W near the Patos shear zone. Local anomalies with small wavelength (<25 km) and large amplitude (up to 2200 nT) overlap this regional anomaly. The limits of the magnetic anomalies often coincide with regional shear zones, thus revealing that the shear zones exert important tectono-structural control on the anomaly sources. Comparison with gravity data evidences that both types of anomalies share the same common anomalous sources, being these sources more magnetic and less dense than the surround crust. On the other hand, correlation with surface geology shows that the geophysical anomalies often occur in association with inhomogeneous magnetite-bearing migmatites and granites, which were formed from the melting of the SB basement rocks and magmatic injections. We perform two modeling approaches of the geophysical dataset: the first was a 3D automatic constrained inversion of the magnetic data and the second one was a 2.5D interpreter guided joint modeling of magnetic and gravity data along three profiles. In the latter modeling, we use also estimates of magnetic susceptibility and density measured in cores of a stratigraphic borehole in the region. Though the two modeling approaches are based on different assumptions and were performed independently, the obtained models are quite consistent. As a result of the integrated analysis of geophysical and geologic data, we evidence the existence of a regional domical structure in the south-central part of the SB. This large-scale dome, involving all the present upper crust of the SB, is composed by four elongated internal structures, geophysically modeled as four anomalous bodies, besides the surrounding material. Together, they form a crustal structure which show longer axis in the NE-SW direction that rotates to E-W direction following the Patos shear zone. The anomalous bodies are the geophysical expressions of rock volumes where the material resulting from the partial melting of the basement rocks and magmatic injections concentrate. The Santa Luzia dome is just a local small-scale dome of this crustal-scale structure. The metasediments of the Seridó Group occur along synforms surrounding the internal structures composing the regional dome. The formation of this crustal-scale dome is associated with the Pan-African/Brasiliano orogeny that occurred during the West Gondwana agglutination in the Neoproterozoic, thus evidencing that intense deformation concentrated in this region during the orogeny. In particular, because of the remarkable role of the Patos shear zone in shaping this crustal dome, it is reinforced the conception that the Patos shear zone was a very important tectonic limit in the African/Brasiliano orogeny.

BANKING MEMBERS:
Externo à Instituição - CARLOS JOSE ARCHANJO - USP
Externo à Instituição - VLADIMIR CRUZ DE MEDEIROS - SGB
Presidente - 349684 - WALTER EUGENIO DE MEDEIROS