HR: 0800h
AN: T11D-0416    [Abstracts]
TI: Fault Framework and Kinematic Evolution of Mesozoic Intraforeland Inversion Structures, Central Neuquén Basin, Argentina
AU: * Grimaldi, G O
EM: grimaldi@tamu.edu
AF: Texas A&M University, MS 3115 TAMU, Dept of Geology & Geophysics, College Station, TX 77843-3115 United States
AB: Natural examples of basin inversion may be best analyzed using 3D seismic data. Detailed documentation of the complex fault framework and construction of curvature maps for fracture prediction may only be possible with the 3D seismic coverage over inversion structures. Whereas analog models show lateral variations in structural style and stratigraphic development during inversion, similar relationships have rarely been documented in natural inversion structures, which limits our understanding of the three-dimensional aspects of these features. A 3D seismic-reflection and borehole data set over a series of Mesozoic inversion structures in the Neuquén Basin of west-central Argentina was used to characterize, in full 3D, the structural and stratigraphic relationships associated with tectonic inversion structures that formed in this retroarc foreland setting. High-resolution time-structure maps, 3D visualization, seismic-attribute analysis (variance, time-dip, and amplitude), and structural restorations allowed the documentation of structural styles, fault linkage and propagation patterns, fold development, syn-inversion growth stratal patterns, and kinematic evolution. Inversion structures in the study area are characterized by two main fault systems. A deep fault system (that originally affected basement rocks and syn-rift strata during rifting) was selectively reactivated during inversion. Larger faults that formed during previous extension were preferentially reverse-reactivated during inversion, whereas smaller syn-rift faults were typically not reactivated. A shallower fault system, comprised of syn-inversion normal faults, formed at high angles to the reactivated, deep fault that generally bound the southern flank of the inversion structures. The shallower faults affected both post-rift and syn-inversion strata. The map patterns, location, and kinematic history of the shallower faults indicate that the hangingwall of the structure expanded during uplift and internally deformed as it accommodated to the shape of the curved footwall during oblique inversion. Similar styles of faulting are not reported in analog-model studies. Within the post-rift and younger section, a single through-going but curved fault defines the southern boundary of the inversion structures. This single fault changes into a series of fault segments, separated by accommodation zones, at depth. Fault systems in former syn-rift accommodation zones became linked into a through-going reverse fault during inversion. Folding and internal deformation were probably the dominant mechanisms that accommodated contraction during early and late stages of inversion. Initial fault lock-up at shallower stratigraphic and structural levels was due to the steep dips of the master fault at these levels, a condition that is not conducive to reactivation. During late stages of inversion, thick overburden inhibited further fault displacement and folding became the main mechanism for accommodating the contraction. Observations from this study suggest the need to incorporate more complex deformation scenarios, such as oblique inversion of curved (in plan view) faults and various hangingwall block deformation mechanisms, into scaled-model experiments.
DE: 8103 Continental cratons
DE: 8110 Continental tectonics: general (0905)
DE: 8169 Sedimentary basin processes
SC: Tectonophysics [T]
MN: Fall Meeting 2005