2. Estado del arte de la tecnología orientada a objetos
2.3. Esfuerzo unificado
2.3.2. Lenguaje unificado de modelado
The Andean segment covered by this study is remarkable for the apparent absence of regional-scale, continuous fault systems. However, as Figure 6.2 illustrates, from the systematic measurement of individual fault planes it is possible to trace major fault systems across the entire orogenic belt. These discontinuous fault-systems are composed of networks of interconnected fault planes.
Figure 6.10 illustrates how the fault systems present in the Main Cordillera can be correlated with more evident, continuous structures which controlled the
emplacement of Mesozoic plutons in the Coastal Cordillera, to the west of the study area.
Arc-oblique structures have been identified in several Andean segments (e.g., Salfity, 1985; Chernicoff et al., 2002; Acocella et al., 2011) and their activity can be traced back at least to the Triassic, when they were active as master and transfer faults of NW- to NNW-oriented rifts (Mpodozis and Ramos, 1989; Ramos, 1996; Giambiagi
Chapter 6 – Structural evolution of the Andean Main Cordillera of Central Chile et al., 2003a; Niemeyer et al., 2004; Sagripanti et al., 2014). Some authors (e.g., Ramos, 1994) have suggested that the geometry of the Triassic rifts, in turn, was controlled by NW-trending suture zones formed during the Proterozoic and Palaeozoic as a result of the accretion of continental blocks to the south-western margin of Gondwana.
Figure 6.10. Main fault systems identified by this study in the Main Cordillera of central Chile (from Figure 6.2), and their correlation with similar oblique structures recognized by previous works in the Paleozoic and Mesozoic rocks of the Coastal Cordillera. Background geology simplified from SERNAGEOMIN (2002).
6.7 Conclusions
The internal architecture of the inverted Abanico Basin in the Main Cordillera of central Chile is dominated by NE- and NW-striking fault systems, oblique to the continental margin and to the axes of the Meso-Cenozoic magmatic arcs. The
correlation of the fault systems recognized in this study with older structures present in the rocks of the Coastal Cordillera suggests that they reflect reactivation of long- lived basement structures, which penetrate deep into the lithosphere. Field evidence
shows some of them were active as normal faults in the late Eocene – Oligocene, during the deposition of the Abanico and Coya-Machali formations (Fig. 6.3). Fault plane kinematics demonstrates that most of these faults were reactivated as strike-slip ± reverse faults during tectonic inversion in the middle Miocene – early Pliocene (Fig. 6.4). Reactivation during tectonic inversion was associated with hydrothermal fluid flow, based on the widespread epidote, chlorite, tourmaline, quartz, calcite, actinolite and Cu-Fe sulfides precipitation on the fault planes (Fig. 6.4). The age of tectonic inversion was confirmed with three 40Ar/39Ar ages on syn-tectonic
hydrothermal minerals.
The kinematic and dynamic analysis of fault-slip data shows that structural reactivation during tectonic inversion was concentrated around major plutons and porphyry Cu-Mo deposits (Figs. 6.8, 6.9). In these areas the fault-slip dataset is consistent with reactivation during E- to ENE-directed compression. This suggests feedback between magmatic and hydrothermal activity, fluid pressure, and the reactivation under compression of the structural architecture inherited from the extensional period. In the margins of the inverted Abanico Basin, compression was accommodated by reverse faulting (sub-vertical σ3), while in the central part of the basin, where the rock column is considerably thicker and the topography higher, a strike-slip regime (sub-vertical σ2) was predominant during Miocene-early Pliocene tectonic inversion.
Chapter 7 – Discussion
Chapter 7
Discussion
“The valleys, by which the Cordillera are drained, follow the anticlinal or rarely synclinal troughs, which deviate most from the usual north and south course; or still more commonly those lines of faults or of unequal curvature (that is, lines with the strata on both hands dipping in the same direction, but at a somewhat different angle) which deviate most from a northerly course.” (Darwin, 1846).
The results of this work show that the structural architecture and evolution of the Andes of central Chile is dominated by long-lived, arc-oblique fault systems
inherited from the Andean basement which, as noted by Darwin (1846), deviate from the usual N-S trend of Andean structures in central Chile and Argentina. They
interact with younger, arc-parallel faults formed during the Meso-Cenozoic. The Cenozoic geologic history is characterized by two main tectonic stages: stage one during which an extensional regime was dominant within the arc, and a second stage associated with tectonic inversion in a contractional to transpressional regime. Arc- oblique and arc-parallel structures were active during both tectonic episodes, with different kinematics controlled by their orientation and the prevailing stress field.