Cratonic basins cover more than 10% of Earth's continental surface area, yet their origin remains enigmatic. In this thesis a suite of new and legacy geophysical and geological data are integrated to constrain the origin of the Parnaíba basin, a cratonic basin in Northeast Brazil. These data include a 1400 km long, deep (20 s two-way travel time) seismic reflection profile, five +/- 110 km offset wide-angle split-spread receiver gathers, gravity anomaly, and well data. In the centre of the basin, the depth to pre-Paleozoic basement is ~ 3.3 km, a zone of midcrustal reflectivity (MCR) can be traced laterally for ~ 250 km at depths between 17-25 km and Moho depth is ~ 42 +/- 2 km. Gravity and P-wave modelling suggests that the MCR represents the upper surface of a high density (2985 kg m³) and V_p (6.7 - 7.0 km s^-1) lower crustal body, likely of magmatic origin. Backstripping of well data shows a concave up decreasing tectonic subsidence, similar in form to that commonly observed in rift-type basins. It is shown, however, that the seismic and gravity data are inconsistent with an extensional origin. It is shown that an intrusive body in the lower crust that has loaded and flexed the surface of the crust, combined with sediment loading, provides a satisfactory fit to the observed gravity anomaly, sediment thickness and basin shape. A buried load model is also consistent with seismic data, which suggest that the Moho is as deep or deeper beneath the basin centre than its flanks and accounts for at least part of the tectonic subsidence through a viscoelastic stress relaxation that occurs in the lithosphere following load emplacement. Comparative analysis of the Michigan and Congo basins shows gravity data from these basins is also consistent with a lower crustal mass excess, while subsidence analysis shows viscoelastic stress relaxation may also contribute to their early subsidence histories. However, unlike Parnaíba, both of these basins appear to have been subjected to secondary tectonic processes that obscure the primary 'cratonic basin' subsidence signals. Parnaíba basin, therefore, offers an excellent record for the investigation of cratonic basin formation.

The Malay and Penya Basins, offshore Peninsular Malaysia, were formed during the early Oligocene as a result of regional dextral shear deformation caused by the indentation of India into Eurasia in the early Tertiary. Pre-existing basement inhomogeneities exerted a strong control on basin development. The Penyu Basin developed, initially, as isolated grabens and half-grabens at basement fault intersections, in response to roughly N-S extension. The major structures which include low-angle listric normal faults, pull-apart rhomb grabens and flower structures, suggest that "thin-skinned" crustal extension and strike-slip tectonics have played an important role in basin evolution. Basement faults in the Malay Basin are oblique (E-W trending) to the basin trend (NW-trending). The Basin developed by transtension of NW-trending sinistral shear zone, in which fault-bounded blocks rotate in response to the shear deformation, producing a series of E-trending half-graben depocentres. The Basins were subjected to transpressive inversion during the middle-late Miocene, as a result of rotation of the regional stress field, caused by progressive indentation of India into Eurasia. Subsidence analysis suggests that lithospheric stretching was the dominant process of basin formation. The high heat flows (85-100 mW m⁻²) are consistent with stretching factors, β, of 1.2 to 4.3. In the Malay Basin, uplift of the basin flanks preceeded subsidence during the rifting phase as a result of non-uniform stretching and lateral heat flow from the centre of the Basin. Both basins are undercompensated isostatically and characterised by low negative free-air gravity anomaly in the order of -20 mGal. Undercompensation suggests that the basins were formed, partly, by "thin-skinned" crustal extension which did not involve stretching of the subcrustal lithosphere.

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2017-10-04T19:45:16Z No. of bitstreams: 1 JulianaAparecidaGoncalvesLopes_DISSERT.pdf: 6908423 bytes, checksum: adf870a414cc76ebcff90a78b5a86557 (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2017-10-10T23:17:13Z (GMT) No. of bitstreams: 1 JulianaAparecidaGoncalvesLopes_DISSERT.pdf: 6908423 bytes, checksum: adf870a414cc76ebcff90a78b5a86557 (MD5) / Made available in DSpace on 2017-10-10T23:17:13Z (GMT). No. of bitstreams: 1 JulianaAparecidaGoncalvesLopes_DISSERT.pdf: 6908423 bytes, checksum: adf870a414cc76ebcff90a78b5a86557 (MD5) Previous issue date: 2017-08-01 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico (CNPq) / A an?lise quantitativa da subsid?ncia tect?nica contribui para identifica??o dos mecanismos que formam as bacias sedimentares, uma vez que a configura??o tect?nica desempenha uma fun??o principal na evolu??o destas bacias. A Bacia Potiguar, localizada na Margem Equatorial Brasileira, apresenta sua evolu??o relacionada a processos de rifteamento complexos, implementados durante a abertura do Oceano Atl?ntico no Jur?ssico/Cret?ceo. Esses processos foram respons?veis pelo desenvolvimento de um rifte emerso abortado, e um rifte submerso, que evoluiu at? a ruptura crustal e forma??o da margem continental transformante. N?s aplicamos a t?cnica de backstripping para quantificar a subsid?ncia tect?nica durante as fases rifte e p?s-rifte da Bacia Potiguar, e analisar a varia??o espacial da subsid?ncia durante os dois eventos tect?nicos, sucessivos e distintos, respons?veis pela evolu??o da bacia. Os par?metros necess?rios para aplica??o desta metodologia foram obtidos por meio de linhas s?smicas 2D e dados de po?os explorat?rios. As curvas de subsid?ncia tect?nica apresentam per?odos com taxas de subsid?ncia moderadas (at? 300 m/Ma), que correspondem a evolu??o do Rifte Potiguar emerso (~141 a 128 Ma). A partir de 128 at? 118 Ma, as curvas apresentam taxas de subsid?ncia nulas para o rifte emerso, enquanto que, altas taxas de subsid?ncia tect?nica (acima de 300 m/Ma) foram registradas no rifte submerso. Durante a fase p?s-rifte, que ocorre a partir de 118 Ma, as taxas de subsid?ncia tect?nica diminu?ram exponencialmente para valores menores que 35 m/Ma, provavelmente relacionadas ? subsid?ncia termal. As taxas de subsid?ncia tect?nica nos v?rios setores do Rifte Potiguar durante as diferentes fases de rifteamento indicam falhamentos mais intensos na parte sul da falha de Carnaubais, ao longo das principais falhas de borda, e na regi?o sudeste do rifte submerso. Durante a fase p?s-rifte, as taxas de subsid?ncia tect?nica aumentam da por??o emersa para a submersa at? a regi?o da quebra da plataforma. As taxas mais altas de subsid?ncia do p?s-rifte (at? 35 m/Ma) est?o concentradas na regi?o central da por??o submersa, e podem estar relacionadas a processos litosf?ricos relacionados ? ruptura da crosta continental e espalhamento oce?nico. A varia??o nas taxas de subsid?ncia e no padr?o das curvas de subsid?ncia nos permitiu interpretar a assinatura tect?nica registrada pelas sequ?ncias sedimentares da Bacia Potiguar durante sua evolu??o. No rifte emerso, as curvas apresentaram taxas de subsid?ncia de at? 300m/Ma durante uma longa fase de rifteamento (13 Ma), o que confirmou o desempenho de um regime distensional nesta por??o. No rifte submerso, as curvas apresentaram taxas de subsid?ncia acima de 300 m/Ma em um intervalo de tempo mais curto (5 a 10 Ma), t?picas de bacias formadas por um regime transtensional. / The quantitative analysis of the tectonic subsidence sheds light on basin-forming mechanisms, since tectonic plate motions play the main role in the genesis of sedimentary basins. The Potiguar Basin, located in the Brazilian Equatorial Margin, presents an evolution related to a complex rifting process, implemented during the Atlantic Ocean opening in the Jurassic/Cretaceous. Different driving mechanisms were responsible for the onset of an aborted onshore rift and an offshore rift, which evolved to crustal rupture and formation of a continental transform margin. Therefore, we applied the backstripping method to quantify the tectonic subsidence during the rift and post-rift phases of the Potiguar Basin and to analyze the spatial variation of subsidence during the two successive and distinct tectonic events responsible for the basin evolution. The parameters required to apply this methodology were extracted from 2D seismic lines and exploratory well data. The tectonic subsidence curves present periods with moderate subsidence rates (up to 300 m/My), which correspond to the evolution of the onshore Potiguar Rift (~141 to 128 Ma). From 128 to 118 Ma, the curves show null subsidence rates in the onshore Potiguar Basin, whereas high subsidence rates (over 300 m/My) occurred in the offshore rift. The post-rift phase had begun at ca. 118 Ma (Aptian), when the tectonic subsidence drastically slowed down to less than 35 m/My, probably related to thermal subsidence. The tectonic subsidence rates in the various sectors of the Potiguar Rift during the different rift phases indicate more intense faulting in the southern portion of the onshore rift, along the main border faults, and in the southeastern portion of the offshore rift. During the post-rift phase, the tectonic subsidence rates increased from onshore to the offshore portion until the continental slope. The highest rates of post-rift subsidence (up to 35 m/My) are concentrated in the central region of the offshore portion, and may be related to lithospheric processes related to the continental crust rupture and oceanic seafloor spreading. The variation in subsidence rates and the pattern of subsidence curves allowed us to interpret the tectonic signature recorded by the sedimentary sequences of the Potiguar Basin during its evolution. In the onshore rift, the curves presented subsidence rates up to 300 m/My during a long-term rift phase (13 Ma), which confirmed an extensional regime in this portion. In the offshore rift, the curves presented high subsidence rates over 300 m/My in a shorter period (5 to10 My), typical of basins formed in a transtensional regime.