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|Title:||Kinematics and mechanisms of upper-crustal deformation in the Eastern Cordillera, southern Central Andes, NW Argentina|
|Authors:||Santimano, Noela Tasca|
|Department:||Geography and Earth Sciences|
|Keywords:||Earth Sciences;Geography;Earth Sciences|
|Abstract:||<p>The Puna Plateau is the second highest continental plateau on Earth and is bordered by the Eastern Cordillera to the east. The growth of this plateau in a non-collisional tectonic setting is not well understood and requires an understanding of the deformation mechanisms and kinematics of its margins, notably the Eastern Cordillera. Deformation in the Eastern Cordillera is characterized by basement-involved folding and reverse faulting during the Tertiary and Quaternary. However, the orientation and kinematics of first-order structural elements of the Eastern Cordillera are not well known. This is addressed in this thesis by a comprehensive structural analysis of three key areas, La Poma, Southern Luracatao Valley and Cachi, in the Eastern Cordillera. Specifically, my structural analyses encompassed (1) field mapping and remote sensing of first-order fold structures and faults, (2) 3D modelling of these structures and (3) a detailed analysis of small-scale brittle shear faults (828 faults at 79 stations). Examination of first-order structures revealed that the Eastern Cordillera was affected by two deformation regimes: Non-cylindrical deformation, i.e., doming of upper crust, followed by cylindrical deformation, notably formation of km-scale folds with straight hinge lines in the hanging walls of orogen-parallel thrust and reverse faults. 3D modelling of these faults at La Poma and Luracatao Valley in the Eastern Cordillera revealed that west-dipping faults are consistently shallower than east-dipping ones. Displacement on shallow « 15°) west-dipping thrust faults in the La Poma area amounts to 2.4 kn1 and likely exceeds displacement magnitudes on east-dipping reverse faults. Analysis of brittle shear faults indicates that doming occurred during E-W shortening. This was followed by NE-SW -shortening on west-dipping thrust and reverse faults and later by NW-SE shortening on east-dipping reverse faults, which induced also a component of left-lateral displacement on N-S striking reverse faults. Brittle fault analysis indicates that shortening directions vary greatly in space and time and seem to depend rather on the local kinematic regime of first-order structures (domes, thrusts and reverse faults) than on far-field stresses related to plate boundary forces. Collectively, the structural analysis suggests that deformation was controlled by the local structural complexity of upper crust, including higher-order, pre-Andean mechanical anisotropies (such as aplitic dikes, foliation surfaces and cretaceous normal faults).</p>|
|Appears in Collections:||Open Access Dissertations and Theses|
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