Key Points Transverse-to-the-orogen faults may also participate in slip partitioning resulting from oblique subduction We implement a forward 3-D model of Andean subduction to simulate interseismic and coseismic deformation We constrain kinematics, slip rate, and seismic hazard associated with differently oriented regional faults
In the Kiggavik area (Nunavut, Canada), major fault zones along, or close to, where uranium deposits are found are often associated with occurrence of thick quartz breccia (QB) bodies. These bodies formed in an early stage (~1750 Ma) of the long-lasting tectonic history of the Archean basement, and of the Proterozoic Thelon basin. The main characteristics of the QB are addressed in this study; through field work, macro and microscopic observations, cathodoluminescence microscopy, trace elements, and oxygen isotopic signatures of the quartz forming the QB. Faults formed earlier during syn- to post-orogenic rifting (1850–1750 Ma) were subsequently reactivated, and underwent cycles of cataclasis, pervasive silicification, hydraulic brecciation, and quartz recrystallization. This was synchronous with the circulation of meteoric fluids mixing with Si-rich magmatic-derived fluids at depth, and were coeval with the emplacement of the Kivalliq igneous suite at 1750 Ma. These processes led to the emplacement of up to 30 m thick QB, which behaved as a mechanically strong, transverse hydraulic barrier that localized later fracturing, and compartmentalized/channelized vertical flow of uranium-bearing fluids after the deposition of the Thelon Basin (post 1750 Ma). The development and locations of QB control the location of uranium mineralization in the Kiggavik area.
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The description of folded/fractured reservoirs requires the understanding of mechanical behaviour of rocks during deformation. In folds, at the decametric scale, deformation is accommodated by flexural slip, faulting and formation of macroscopic fracture sets. The role of LPS has been recognized for years using magnetic fabric analysis which shows that in siliciclastic deposits the deformation is mainly accommodated by pretilting strain. This paper thus combines analyses of calcite twins, Anisotropy of Magnetic Susceptibility and Anisotropy of P-wave Velocity, together with petrological study to investigate the relationship between fold development and stress/strain. The results are compared to already available and newly collected mesoscale fracture and fault slip data. The Sheep Mountain anticline was chosen as a natural laboratory.Our results show a good agreement between calcite twinning and anisotropy of rocks properties, and with macroscopic fracturing on the other hand. Our study points toward a better description of deformation mechanisms of folded strata. A major result is the consistency of the record of deformation at microscopic and macroscopic scales, emphasizing that core scale data can be relevant to fold-scale structuring. This study yields important constraints for forthcoming modeling of stress distribution during fold development.
<p>Faults, joints and stylolites are ubiquitous features in fold-and-thrust belts commonly used to reconstruct the past fluid flow (or plumbing system) at the scale of folded reservoir/basins. Through the textural and geochemical study of the minerals that fills the fractures, it is possible to understand the history of fluid flow in an orogen, requiring a good knowledge of the burial history and/or of the past thermal gradient. In most of the case, the latter derives from the former, itself often argued over, limiting the interpretations of past fluid temperatures. We present the results of a multi-proxy study that combines novel development in both structural analysis of a fracture-stylolite network and isotopic characterization of calcite vein cements/fault coating. Together with new paleopiezometric and radiometric constraints on burial evolution and deformation timing, these results provide a first-order picture of the regional fluid systems and pathways that were present during the main stages of contraction in the Tuscan Nappe and Umbria-Marche Apennine Ridge (Northern Apennines). We reconstruct four steps of deformation at the scale of the belt: burial-related stylolitization, Apenninic-related layer-parallel shortening with a contraction trending NE-SW, local extension related to folding and late stage fold tightening under a contraction still striking NE-SW. We combine the paleopiezometric inversion of the roughness of sedimentary stylolites - that provides a temperature-free constraint on the range of burial depth of strata prior to layer-parallel shortening -, with burial models and U-Pb absolute dating of fault coatings in order to determine the timing of development of mesostructures. In the western part of the ridge, layer-parallel shortening started in Langhian time (~15 Ma), then folding started at Tortonian time (~8 Ma), late stage fold tightening started by the early Pliocene (~5 Ma) and likely lasted until recent/modern extension occurred (~3 Ma onward). The textural and geochemical (&#948;<sup>18</sup>O, &#948;<sup>13</sup>C, &#8710;<sub>47</sub>CO<sub>2</sub> and <sup>87</sup>Sr/<sup>86</sup>Sr) study of calcite vein cements and fault coatings reveals that most of the fluids involved in the belt during deformation are basinal brines evolved from various degree of fluid rock interactions between pristine marine fluids (&#948;<sup>18</sup>O<sub>fluids</sub> = 0&#8240; SMOW) and surrounding limestones (&#948;<sup>18</sup>O<sub>fluids</sub> = 10&#8240; SMOW). The precipitation temperatures (35&#176;C to 75&#176;C) appear consistent with the burial history unraveled by sedimentary stylolite roughness paleopiezometry (600 m to 1500m in the range) and geothermal gradient (23&#176;C/km). However, the western edge of the ridge recorded isotopically depleted past fluids of which corresponding precipitation temperature (100&#176;C to 130&#176;C) are inconsistent with local burial history (1500m). We interpret then pulses of eastward migration of hydrothermal fluids (>140&#176;C), driven by the tectonic contraction and by the difference in structural style of the subsurface between the eastern Tuscan Nappe and the Umbria-Marche Apennine Ridge. Allowed by an unprecedented combination of paleopiezometry and isotopic geochemistry, this fluid flow model illustrates how the larger scale structures control the fluid system at the scale of the range.</p>
By demonstrating that extensional inheritance plays a decisive role in the formation of orogens, recent studies have questioned the ability of a unique, complete Wilson cycle model to explain the diversity of collisional orogens. For 5 years, the OROGEN Research Project had therefore the ambition to challenge this classical Wilson cycle model. By focusing on the diffuse Africa-Europe plate boundary in the Biscay-Pyrenean-Western Mediterranean system, the project questioned the preconceived “Orogen singularity” assumption and investigated the role of divergent and convergent maturities in orogenic and post-orogenic processes. This work led us to rethink the development of collisional orogens in a genetic (or process-driven) way and to propose an updated version of the ” classical Wilson cycle”, the Wilson Cycle 2.0, and the ORO-Genic ID concept presented in this paper. The particularity of the Wilson Cycle 2.0 is to take into account the divergence and convergence maturity reached during extensional and orogenic processes in proposing different tectonic tracks associated with different ORO-Genic ID numbers. The ORO-Genic ID is composed of a letter (or track), corresponding to the maturity of divergence reached and a number corresponding to the maturity of convergence reached during the formation of the orogen. This new concept relies on the observed pre- and syn- convergent tectono- stratigraphic and magmatic record and deformation history and can be identified in using diagnostic criteria presented in this paper. It represents therefore a powerful tool that can be used to characterize the evolution and the architectural type of an orogenic system. Moreover, as a mappable concept, it can be easily used worldwide and can help us to explain differences in the style of deformation at crustal scale between orogens.
