Subsidence history, thermal maturity, and structural inversion of the Greater Caucasus-Kura-Adjara-Trialeti basin system of central-eastern Georgia

This study aims at defining the tectonic evolution of a portion of the Caucasian region, in Georgia, which experienced a complex pattern of deformation events throughout Mesozoic and Cenozoic times. An integrated approach was applied to unravel the thermo-tectonic history of three inverted sedimentary basins from burial to exhumation. Additionally, this dissertation provides examples of structural inversion of sedimentary basins in response to far-field transmission of compressional stresses away from collision zones, contributing to elucidate the dynamics of stress partitioning during continental collisions. The Adjara-Trialeti fold-and-thrust belt in south-western Georgia results from the structural inversion of a Middle Eocene continental back-arc rift basin opened as a consequence of the Northern Neotethys slab rollback. This study quantitatively defines the subsidence and exhumation history of the Adjara-Trialeti basin, constraining its Middle Miocene inception of structural inversion. The western Kura Basin is a flexural foreland basin trapped between the Lesser Caucasus to the south and the Greater Caucasus to the north. This study constrains successive and competing episodes of flexural subsidence during Oligocene-Miocene times, followed by partial inversion through thick- and thin-skinned tectonics in response to continued convergence between the adjacent, oppositely verging orogenic belts. The Greater Caucasus results from the structural inversion of a Jurassic continental back-arc basin, but the timing of its growth is still debated. An across-strike transect in its southern central domain was studied, indicating that this sector of the Greater Caucasus experienced two phases of structural inversion during Late Cretaceous-Paleocene and Late Miocene times. Overall, the dataset presented in this dissertation points to a complex and episodic history of incremental deformation, characterised by successive phases of extensional and compressional tectonics which developed in response to sequential terrane accretion at the southwestern margin of Eurasia since Late Cretaceous times, eventually determining the current configuration of the Arabia-Eurasia collision zone.

Tectonics of the wedge-top Epiligurian basins and implications for the syn-to-post orogenic evolution of the Northern Apennines fold-and-thrust belt (Italy)

This thesis has the aim to give an overview about the tectonic history of the Epiligurian units, which crop out in the axial portion of the Northern Apennines fold-and-thrust belt, from a structural and thermal point of view, through a multiscalar and multitecnique approach. I focused on a key example of Epiligurian wedge-top basin, (Marzabotto Basin) proceeding from macro-to-microscale approach. The study started from a remote sensing analysis of the lineaments and morphostructures which affected the study area to obtain the regional faulting pattern and an overview about the main tectonic structures, used as basis for the structural investigation at the mesoscale. On the basis of this, it was possible to reconstruct the succession of tectonic events that affected the Marzabotto Basin, consisting in: i) two sets of thrusts indicating a NE-SW and NW-SE shortening of the sedimentary succession; ii) NE-SW-left lateral transtensional faults related to a strike-slip tectonic phase; iii) three main sets of extensional structures which cut and displace the previous thrusts. Normal faults are related to the post-orogenic evolution and have been dated with U-Th method, getting an age of Middle-Late Pleistocene. From a thermal point of view, apatite fission-tracks and (U-Th)/He analyses of detrital minerals and thermal modelling on the middle-upper Eocene siliciclastic deposits allowed me to better constrain the local exhumation history and correlate it with the large-scale tectonic evolution of the Northern Apennines. In particular, the Marzabotto Basin experienced a complex burial-exhumation history, consisting in two cooling cooling phases related to the growth of the Northern Apennines belt (Oligo-Miocene in age) and a later cooling which tracks the accretion in the orogenic wedge concomitant with rollback-driven extension (late Miocene-Pliocene in age). In conclusion it is possible to affirm that the study shed new light on poorly constrained elements of fold-and-thrust belt.

Deep geometry of subduction below the Andean belt of Colombia as revealed by seismic tomography

In this study new tomographic models of Colombia were calculated. I used the seismicity recorded by the Colombian seismic network during the period 2006-2009. In this time period, the improvement of the seismic network yields more stable hypocentral results with respect to older data set and allows to compute new 3D Vp and Vp/Vs models. The final dataset consists of 10813 P- and 8614 S-arrival times associated to 1405 earthquakes. Tests with synthetic data and resolution analysis indicate that velocity models are well constrained in central, western and southwestern Colombia to a depth of 160 km; the resolution is poor in the northern Colombia and close to Venezuela due to a lack of seismic stations and seismicity. The tomographic models and the relocated seismicity indicate the existence of E-SE subducting Nazca lithosphere beneath central and southern Colombia. The North-South changes in Wadati-Benioff zone, Vp & Vp/Vs pattern and volcanism, show that the downgoing plate is segmented by slab tears E-W directed, suggesting the presence of three sectors. Earthquakes in the northernmost sector represent most of the Colombian seimicity and concentrated on 100-170 km depth interval, beneath the Eastern Cordillera. Here a massive dehydration is inferred, resulting from a delay in the eclogitization of a thickened oceanic crust in a flat-subduction geometry. In this sector a cluster of intermediate-depth seismicity (Bucaramanga Nest) is present beneath the elbow of the Eastern Cordillera, interpreted as the result of massive and highly localized dehydration phenomenon caused by a hyper-hydrous oceanic crust. The central and southern sectors, although different in Vp pattern show, conversely, a continuous, steep and more homogeneous Wadati-Benioff zone with overlying volcanic areas. Here a "normalthickened" oceanic crust is inferred, allowing for a gradual and continuous metamorphic reactions to take place with depth, enabling the fluid migration towards the mantle wedge.