Conference Agenda

The Cenozoic exhumational evolution of the Southern Patagonian Andes and its potential tectonic and climatic controls remain poorly constrained. Here, we integrate 21 new and 73 published bedrock thermochronological ages with 3D thermo-kinematic modelling (Pecube) to quantify exhumation pulses in the Torres del Paine area. This approach is used to identify temporal and spatial variations in exhumation rates before and after the start of Late Miocene glaciation. Our new AHe and ZHe ages range from 1.3 ± 0.7 Ma to 6.8 ± 1.6 Ma and from 13 ± 2.5 Ma to 86.3 ± 29.2 Ma, respectively. ZHe ages decrease westward with the youngest ages (~13 - ~19 Ma) being restricted to the deeply exhumed retroarc, which is in accordance with previous studies.

Our numerical modelling results indicate that the distribution of observed thermochronologic ages can be explained by an up to 120 km-wide, parabolic-shaped exhumation pattern. The maximal exhumation rates of 1 ± 0.2 mm/yr operated between 24 ± 2 Ma and 10 ± 2 Ma. We link these results to rock uplift above the mid-crustal ramps in the retroarc. Furthermore, our models show that after a short period of quiescence (1–2 Myr), average exhumation rates increase again at 10–7 Ma to values of 0.5 ± 0.1 mm/yr, which we relate to the onset of Late Miocene fluvio-glacial erosion. This timing of significant glacial erosion is, compared to previous studies (<7–5 Ma), early, but coincides with earliest (~10 Ma), even though sparse, evidence for glaciation.

The Early Cretaceous to Paleogene intracontinental Salta rift basin in NW Argentina consists of multiple branches, radiating from the central Salta-Jujuy high. One of these branches is the ENE–WSW striking Lomas de Olmedo sub-basin. Syn- and post-rift sediments of the Salta Group reach a thickness of 5 km at the sub-basin’s depocenter. To the east, the majority of the Salta Group is undeformed and located in the subsurface. However, to the northwest, the Salta Group is increasingly folded and reaches full exposure in the Cianzo syncline, about 20 km east of Humahuaca. The SW–NE striking Hornocal fault cuts the Cianzo syncline to the north and is interpreted as a normal Cretaceous syn-rift fault that was inverted during Cenozoic deformation. Miocene oblique reverse displacement along the Hornocal fault is indicated by structural mapping and unpublished fission track data.

We are applying low-temperature (U-Th-Sm)/He thermochronology to constrain the timing and magnitude of multi-phase Cretaceous-Cenozoic deformation and exhumation within the Lomas de Olmedo basin. We use zircon (U-Th-Sm)/He cooling ages to constrain Cretaceous-Paleogene rift shoulder exhumation. Apatite (U-Th-Sm)/He thermochronology is used to study the reactivation of the Hornocal fault during the Cenozoic contractile phase, related to the Andean orogeny. First results show predominantly Late Miocene to Pliocene cooling ages for apatite (U-Th-Sm)/He aliquots within the Cianzo syncline, indicating recent exhumation along the Hornocal fault. This is consistent with regional data and suggests a major phase of deformation occurring in this part of the Central Andes during the Late Miocene to Pliocene.

We investigated a suite of metabasite blocks from serpentinite and shale matrix mélanges of the Califonia Coast Ranges. Our new dataset consists of ⁴⁰Ar/³⁹Ar dates of amphibole and phengite and U-Pb dates of metamorphic zircon. Combined with published geochronology, including prograde Lu-Hf garnet ages from the same blocks, we can reconstruct the timing and time scales of prograde and retrograde metamorphism of individual blocks. In particular we find that exhumation from amphibole-eclogite facies conditions occurred as a single episode at 165–157 Ma, with an apparent southward younging trend. It was initially uniform (when comparing individual blocks) and fast (with cooling rates up to ~140 °C/Ma). In the blueschist facies, exhumation slowed and became less uniform among blocks. Considering the subduction zone system, the high-grade exhumation temporally correlates with a magmatic arc pulse (Sierra Nevada) and the termination of forearc spreading (Coast Range Ophiolite). Our findings suggest that a geodynamic one-time event led to exhumation of amphibole-eclogite facies rocks. We propose that interaction of the Franciscan subduction zone with a ridge led to extraction of the forearc mantle and exhumation of subducted rocks into the blueschist facies. We also show that the Franciscan subduction zone did not undergo significant cooling over time.

During extension of the continental lithosphere, rift basins develop. These are often initially offset, and must interact and connect in order to create a continuous rift system that may ultimately achieve break-up. When simulating extensional tectonics and rift interaction structures, analogue and numerical modellers often apply a continuous extension rate along the strike of a rift or rift system. Yet in nature extension velocity variations occur plate boundaries as a natural consequence of tectonic plates moving apart about a pole of rotation, resulting in rotational extension, associated rift propagation and structural gradients. We ran analogue models to assess rift interaction structures forming in orthogonal extension settings versus rotational extension settings. Our experiments show that these contrasting extension boundary conditions lead to different large-scale structures. Rotational extension causes significant changes in rift maturity between rift segments, delays rift interaction zone development, and makes rift segments propagate in opposite directions. Still local features in a rotational extension system can often be regarded as evolving in an orthogonal extension setting. We find that various degrees of rift underlap produce three basic modes of rift linkage structures. Low underlap distance experiments develop rift pass structures. With increasing underlap distance, transfer zone basins develop. High degrees of underlap tend to result in en echelon sub-basins. Our results match with data from previous modelling efforts and natural examples. We furthermore propose a large-scale tectonic scenario for the East African Rift System, based on rotational extension, which may also be applicable for other large-scale rift systems.

This study concerns the tectonics of the Western Afar Margin (WAM), situated between the Ethiopian Plateau and Afar Depression in East Africa. The WAM represents a developing passive margin in a highly volcanic setting, offering unique opportunities for studying (magma-rich) continental break-up. Earthquake analysis reveals that the margin still deforms under a ca. E-W extension regime (a result also derived from recent field data), whereas extension in Afar is ca. SW-NE. Adding GPS data highlights the current rotational opening of Afar. This tectonic setting is however recent and local, related to the rotation of the Danakil microcontinent (since 11 Ma). Otherwise the rotation of Arabia dominates regional tectonics since 25 Ma, predicting SW-NE extension along the WAM. The (now reactivated) large-scale en echelon fault patterns along the margin indeed capture this early phase, indicating the multiphase history of the margin. Furthermore, the WAM shows large-scale flexure towards Afar. Fault mapping and earthquake analysis highlight that recent faulting is dominantly antithetic (dipping away from the rift and bounding remarkable marginal grabens), although a large but older synthetic escarpment fault system is present too. Analogue models confirm that marginal flexure initially develops large escarpments, and the currently active structures only occur later on. Moreover, these experiments do not develop marginal grabens under oblique extension conditions. Instead, oblique extension creates the large-scale en echelon fault arrangement typical of the WAM. These results indicate that the margin’s recent structural architecture could only form after a shift to orthogonal extension, supporting the multiphase extension scenario.

Fluid flow, fluid pressure and water-rock interaction are important controls on fault activity. However, the relation between fluid flow and fault activity is often difficult to quantify because of a lack of data on the timing and duration of past flow events. Here we present a new approach to quantify the history of hydrothermal activity in fault zones that combines low-temperature thermochronology, subsurface temperature data and inverse thermal modelling. We present case studies from the Basin and Range Province, the Alps and the Roer Valley Graben that provide new insights on episodic fluid flow and its links with deformation and seismic activity

We reinvestigated parts of the northern Austroalpine margin, collected structural data to interpret the kinematic relationship between the marginal slice (“Cenoman-Randschuppe” = CRS) and the Allgäu-/ Lechtal thrust sheets, and propose a revised model for the tectonic evolution of the northern front of the northwestern Northern Calcareous Alps (NCA).

During Cretaceous (N)NW directed (Eoalpine) thrusting, the Lechtal thrust sheet (including its frontal slice, the “Falkensteinzug” = FSZ) was emplaced onto the Allgäu thrust sheet in the Albian, deduced from (i) the Albian age of the youngest sediments below the Lechtal thrust (Tannheim- and Losenstein Fms.) and (ii) Cenomanian deposits unconformably overlying the eroded northern Lechtal thrust sheet (Branderfleck Fm.). The future CRS was, at that time, in the foreland of the upper Lower Cretaceous Alpine orogenic wedge. Sinistral W-E striking transform faults cut across this foreland, decoupling CRS and FSZ from the main body of the NCA, enabling an independent evolution of the CRS from the lower Upper Cretaceous onwards. Subsequent Upper Cretaceous and younger (Mesoalpine) shortening leads to incorporation of Rhenodanubian Flysch (RDF), and Helvetic units into the Alpine nappe stack; the Allgäu thrust representing the NCA basal thrust. Growth strata within thrust-sheet-top deposits (Branderfleck-Fm.) give evidence for refolding of thrust sheet boundaries.

In a typical thin-skinned fold-and-thrust belt, deformation should decrease towards the thrust front, whereas within the NCA it increases. An Austroalpine thrust front controlled by transform faults could cause an increase in deformation towards the most external NCA, and explain the absence of the Arosa zone between Allgäu and Vienna. Such faults would most probably also cut out Lower Austroalpine units. Therefore, RDF and CRS are juxtaposed; the latter found in the tectonic position of the Arosa zone.

Quantitative uncertainty analysis and 2D and 3D modelling of the subsurface, as well as their visualization form the basis for decisions in exploration, nuclear waste storage and seismic hazard assessment. Methods such as cross-section balancing are well established and yield plausible kinematic scenarios, however without a quantitative measure of the uncertainty of structures at depth. On the other hand, new probabilistic modeling approaches emerge, which provide quantitative uncertainties of existing structures, however without providing information on their time evolution. We combine classical cross-section balancing (2D, kinematic modelling) with 3D probabilistic modelling to bridge between these approaches and develop a more powerful workflow than the stand-alone tools offer. We apply this approach to the Subalpine Molasse, the fold-and-thrust belt of the northern Alpine Foreland. Low relief, vegetation and urbanization cause outcrop conditions that are typical for fold-and-thrust belts, with seismic and well data available as well as data from mining. We provide a first 3D structural model of the region and derive constraints on geometry and kinematics in fold-and-thrust belts. Our study shows that cross-section balancing and 3D geometric and probabilistic modelling can be used to iteratively improve the structural model, while probabilistic modelling reveals areas of high structural uncertainties.

The Southern Chotts and Jeffara Basins are situated in Central Tunisia within the Saharan domain of North Africa. The Southern Chotts Basin hosts reservoirs within the Triassic, Permian and Ordovician units that contain significant hydrocarbon accumulations and the Jeffara Basin contains outcrop analogues of the same hydrocarbon-bearing formations. Late Hercynian shortening influences the deposition and geometry of the Permian and Triassic units through the formation of topographic highs. This phase affects the reservoir properties observed at the surface and consequently how they can be predicted at depth.

The integration of outcrop, subsurface (seismic and well) and satellite data indicate that a period of shortening occurred during the Late Permian to Early Jurassic. Furthermore, fracture data collected shows evidence of layer parallel shortening consistent with compressional deformation. This shortening is characterised at the scale of hundreds of meters by fault-related folds and by E-W striking folds in the Palaeozoic and early Mesozoic units at basin scale. The Triassic and Jurassic units are constrained in the synclines between the main topographic highs (Tebaga de Medenine and Telemzane Arch) highlighting the strong influence this late Hercynian event has on the distribution of these deposits.

The permeability of the Palaeozoic reservoirs in these basins are primarily controlled by natural fractures. The compressional drivers interpreted within these units aid the prediction of fractures in the subsurface. These predictions combined with well data and seismic attributes are integrated into an innovative fracture model of the reservoirs and quantifying the contribution of the fractures to reservoir flow.

A significant amount of the ongoing shortening between the Eurasian and Arabian plates is accommodated within the Zagros Fold-Thrust Belt. However, the spatial and temporal distribution of active shortening within the belt especially in the NW part is not well constrained yet. To overcome this, we have mapped uplifted river terraces along the Greater Zab River that crosses the belt and dated them with luminescence dating. We then used kinematic modeling of the fault-related folding belt to calculate long-term slip rates during Late Pleistocene-Holocene. Our results show active faulting and folding in the area. The Zagros Mountain Front Fault accommodates about 0.9 mm/yr of fault normal slip, while another basement thrust further to the SW accommodates less than 0.4 mm/yr. Horizontal slip rates related to detachment folding of the Safin, Sarta, and Girda Baski anticlines are 0.3 mm/yr, 0.6 mm/yr, and 0.3 mm/yr, respectively. Basement thrusting and thickening of the crust are restricted to the NE part of the Zagros belt. This is also reflected in the regional topography and the distribution of uplifted terraces. In the southwestern part the deformation is limited mainly to folding and thrusting of the sedimentary cover above the Triassic basal detachment. In the NE, itis associated with slip on basement thrusts.