Tectonic Behavior Research Articles

Morphostructural evidence of crustal-scale, active along-strike segmentation of the Umbria-Marche Apennines, Italy

This paper discusses the response of topography and river networks to non-uniform lithology and tectonic forcing in the Umbria-Marche sector of the Apennines fold and thrust belt. We ruled out the role of variable erosion of rock types and interpret channel steepness data in terms of rock uplift, discovering a southward increase in the total amount of uplift. Such a trend appears as the large-scale response to uneven vertical motions of different sectors of the mountain ridge and foothills. The general coincidence between sector boundaries and transversal, NE-SW striking faults mapped by seismic interpretation in the outer zone of the fold and thrust belt, suggests that such faults extend to the SW, beneath the allochthonous thrust sheets of the mountainous area. Therefore, it may be inferred that such transversal faults represent long-lived, deeply rooted basement structures compartmentalizing both the axial and the outer zones of the fold and thrust belt. We suggest that differential uplift was essentially controlled by variable amounts of basement thrust displacement characterizing the compartmentalized belt. This interpretation deviates from a more conventional view that uplift of the central Apennines, particularly prominent in the south, is dynamically supported. Our results, besides shedding new light into the active tectonic behavior of a large portion of the Italian peninsula, also provide general insights into the surface response to the differential behavior of crustal blocks produced by along-strike segmentation of active mountain belts.

Quantitative and qualitative study of the Tawi basin: Inferences from Digital Elevation Model (DEM) using geospatial technology

The quantitative and qualitative analysis of the basin is fundamental to understand the structural and hydrological control of the basin. In the present study morphometric and morph tectonic parameters of the Tawi basin has been analyzed to infer the geological variation, topographic information, structural and complex tectonic behavior at a watershed scale. The assessment of several of drainage network and their relative parameters has been quantified by using the Digital Elevation Model (DEM) based analysis in the Geographic Information System (GIS) environment. Based on the quantitative analysis in terms of linear, aerial and relief it is well understood that the basin is inhomogeneous in nature, less structurally stable, very gentle to steep slopes, compounded by aggradational and denudational processes in large scale, exhibited by incompetent rocks and a portion of the basin is prone to flood particularly in the lower reaches. The quantified results show that in the various watersheds of the Tawi basin bifurcation ratio (Rb) varies from 0.001 to 6.80 and the mean bifurcation ratio (Rbm) varies from 2.58 to 4.11. The mean stream length (Lsm) in the various watersheds of Tawi basin varies from 0.019 to 60.26 km. The drainage density (Dd) of Tawi basin varies from 0 to 9.63 km/km2, and the value of the drainage texture (Td) varies from 3.76 to 13.38 km-1. The qualitative analysis based on the asymmetric factor (AF) of the Tawi basin shows that the watersheds W5 and W6 are moderately asymmetric, and W2 and W4 as strongly asymmetric in nature, whereas the hypsometric integral (HI) values reveal that watershed W1 is the most stable watershed with a highest HI value of 0.89, while the W7 is the least stable with a HI value of 0.28, providing a comprehensive understanding of the geomorphic dynamics in the Tawi basin.

Regional tectonic dynamics in Central Iran: Unveiling the interplay of fault systems through morphotectonic and seismological analyses in the Shotori mountains

Iran, located at the convergence of the Eurasian and Arabian tectonic plates, is a region of significant geologic and tectonic interest. This setting gives rise to complex tectonic dynamics that are crucial for understanding the seismicity and geological evolution of the area. This study provides novel insights into the tectonic dynamics of Central Iran, with a particular focus on the Shotori Mountains. Employing a combination of satellite imagery, earthquake catalog analysis, and field observations, we have studied the complex interactions among active fault systems in this part of Iran. Our investigation highlights the significant interactivity of these faults, especially at the convergence point of the Nayband strike-slip fault with the Esfandiar and Shotori thrust faults. This area is characterized by a high frequency of reverse mechanism earthquakes, primarily occurring in shallower crustal layers. A notable aspect of our findings is the identification of a distinct pattern of seismic activity linked to the interaction between different fault types. The Nayband shear zone, for instance, is critically responsible for right-lateral, oblique reverse faulting, and strike-slip events. This study also reveals a novel aspect of tectonic behavior in Central Iran: the correlation between strike-slip fault systems and their thrust terminations, influenced by the rotational dynamics of these faults. Our analysis suggests that the activation of strike-slip faults can precipitate the activation of their thrust terminations, a phenomenon particularly evident at their intersection points. This insight is crucial for understanding regional tectonic processes and could significantly impact seismic hazard assessments in Central Iran. Furthermore, the interaction between the Nayband strike-slip fault and its thrust terminations, such as the Shotori and Esfandiar faults, highlights areas of heightened tectonic activity. This study not only advances our understanding of the seismic and tectonic landscape of Central Iran but also has broader implications for regional tectonic studies and seismic risk management.

Improved lithospheric seismic velocity and density model of the Korean Peninsula from ambient seismic noise data using machine learning

To accurately estimate physical properties and tectonic behavior in the near-surface, a reliable seismic property model is needed for realistic seismic modeling and earthquake location estimation. Recording ambient seismic noise (ASN) data and producing interferometric reflection images traditionally provides subsurface structure observation without an active source. However, due to low signal-to-noise ratio (SNR) and vertical resolution, interpreting upper mantle structures and inverting seismic models from noise data is difficult. To address this, machine learning (ML) techniques are applied to enhance vertical resolution and interpret geologically meaningful boundaries. Spectral enhancement with convolutional U-net generates higher resolution data by preserving temporal continuity. Unsupervised ML interprets lithospheric boundaries more robustly and objectively than manual horizon picking, and model-based seismic inversion integrates improved seismic data with prior full-waveform inversion (FWI) models. ML-based results improve inverted models, displaying more detailed geological structures and seismic property changes, surpassing seismic data limitations.

LA SUCCESSIONE OLIGOCENICA TRA OVADA E CASSINELLE (ALESSANDRIA) EVOLUZIONE PALEOGEOGRAFICA ED IMPLICAZIONI STRUTTURALI

Facies succession of the Oligocene terrigenous sequences from a seccar of Piedmont Tertiary Basin (between Ovada and Cassinelle, Alessandria) are here described and their significance discussed. The palaeogeographic evolution of the area results to be controlled by a synsedimentary tectonics. In the Early Oligocene, a generalised vertical mobility affected the region which, as a conse­quence, was splitted in some blocks with a differential tectonic behaviour by tensive lineaments; that is testified by a widesprcad continental facies characteristic of a high energy environment (lower pare of "Formazione di Molare"). Successively, ali the area subsided, and the sea transgressed over it (upper part of "Formazione di Molare"). During the Late Oligocene subsidence acted differentially along synse­dimentary faults and the deeper portions are individuated; which became location of relatively deep marine deposition ("Marne di Rigoroso"). The intense tectonic activity was responsible for the deposition of large conglomeratic and arenaceous bodies interbedded within the hemipelagic sequences (in the areas with precocious and intense drowning).

The Role of Salt Tectonics in the Energy Transition: An Overview and Future Challenges

In this paper we examine the role salt tectonics can play in a number of key energy transition technologies, namely, energy storage as gas in salt caverns (e.g. hydrogen and compressed air), CO2 storage, and geothermal energy. For each of these technologies we explore: i) fundamental concepts and driving forces; ii) how and why the properties of salt are of importance; and iii) the key salt-related technical challenges, potential future research directions, and technical approaches needed for large-scale development. We highlight how salt-bearing basins offer vast potential for development throughout the energy transition including, but not limited to: i) the likely demand for thousands of new hydrogen storage caverns inside salt bodies by 2050; ii) a likely early focus for porous media CO2 storage sites in basins strongly influenced by salt tectonics; and iii) enhanced geothermal energy potential in and around salt bodies. Effective exploitation of these resources will require a deeper understanding of the internal composition, geometry, and evolution of salt structures and their surrounding sediments, and potentially the development of more predictive models of salt tectonic behaviour. Critically, we see the need to integrate learnings of salt tectonics gained in the academic, mining, solution mining, and oil and gas communities, and apply a fresh perspective to answer research questions of relevance to the energy transition. Developing this new understanding will help optimise design, reduce geotechnical risk, and improve efficiency for energy transition technologies, thus indicating a strong future demand for salt tectonic research.

On analyzing GNSS displacement field variability of Taiwan: Hierarchical Agglomerative Clustering based on Dynamic Time Warping technique

We investigate the feasibility of using the Dynamic Time Warping (DTW) technique to cluster continuous GNSS displacements in Taiwan. Using the DTW distance as the measure for waveform similarity, we combine the DTW method with the Hierarchical Agglomerative Clustering (HAC) algorithm. This is in contrast to the conventional clustering approach that uses the Euclidean distance, considering the average long-term crustal motion, but inherently neglects full-waveform temporal variations. Here we apply the DTW-based HAC algorithm adopting DTW distance as the waveform similarity measure on 11 years worth of 3-D displacement data from 115 continuous GNSS network stations in Taiwan. We demonstrate the efficacy of the DTW-based HAC method in distinguishing the GNSS spatiotemporal variabilities that are consistent with the known, complex tectonic behavior of the region. An open-source Python package has been developed and made available to perform the HAC analysis.

Intraplate continental basalts over the past billion years track cooling of the mantle and the onset of modern plate tectonics

The temperature of the convecting mantle exerts a first-order control on the rheology, composition, and consequently, tectonic behavior of Earth's lithosphere. Although the mantle has likely been cooling since the Archaean eon, how mantle temperature has evolved thereafter is poorly understood. Here, we apply a statistical analysis to secular changes in the alkali index [AI = whole-rock (Na2O + K2O)2/(SiO2 − 35) as weight%] of global sodic intracontinental basalts, a proxy for the degree of mantle melting, to constrain the evolution of mantle potential temperature (TP) over the past billion years. Our results show that, during the early Neoproterozoic, TP remained relatively constant until the beginning of the Cryogenian (720 Ma), when mantle temperature dropped rapidly over the following ∼180 Ma. This remarkable episode of cooling records the onset of modern-style plate tectonics characterized by continuous deep subduction of the oceanic lithosphere, consistent with the widespread appearance of blueschists in the metamorphic rock record.

Stress Orientations and Driving Forces in the Indo-Burma Plate Boundary Zone

ABSTRACT The Indo-Burma range (IBR) is the forearc of an oblique subduction zone where the Indian slab obliquely converges with the Burma microplate. In this study, we consider earthquake focal mechanisms to help elucidate the tectonic behavior of the region. Toward this end, we examine the spatially variable stress orientations across the IBR and in the downgoing plate to better understand the associated plate driving forces and subduction dynamics. We combined earthquake focal mechanisms from 1 January 1950 until 31 December 2019 from a number of available catalogs and published studies, and divided the total of 189 events into spatial subdomains before performing stress inversions to document the spatial variability of the stress tensor. Generally, the maximum principal stress (S1) is oriented approximately north–south in all domains, subparallel to the subducting slab. The intermediate principal stress (S2) is plunging westward at variable angles. In contrast, the minimum principal stress (S3) is plunging to the east roughly following the dip of the subducting plate, indicative of down-dip tension in the slab. We do not observe a significant variation of the S1 orientation with depth, suggesting that north–south compression is due to the slab pushing northward through the mantle. Due to the well-defined slab-dip-parallel S3 direction for the megathrust and upper plate catalogs, the primary driving force of this subduction region is likely to be a net slab pull. Based on the seismic activity of the region, the consistency of focal mechanism-based stress and regional tectonic driving forces, as well as the S3 evidence for slab-pull forces, the possibility that the IBR can produce large earthquakes cannot be ruled out.

Kinematics and structural evolution of the Anziling dome-and-keel architecture in east China: Evidence of Neoarchean vertical tectonism in the North China Craton

The debate on the role of vertical versus horizontal tectonism in Archean cratons is intimately linked to the initiation of plate tectonics. The dome-and-keel architecture has been considered as a consequence of vertical tectonism. Although such a structural pattern is documented in some Mesoarchean and older cratons, such as the Kaapvaal and Pilbara cratons, whether it also occurs in Neoarchean cratons is poorly constrained. Determining the kinematics, structural evolution, and the timing of these structures is crucial in understanding how the tectonic behavior operated during the evolution of the early Earth. The North China Craton, especially its eastern part, is a Neoarchean continental block and preserves typical greenstone-granite rock assemblages. Detailed structural mapping reveals that the Anziling area (east China) is characterized by a typical dome structure without significant reworking by later deformation. The dome is in tectonic contact with a supracrustal rock assemblage that is now the dip-slip Shuangshanzi ductile shear zone. In the supracrustal rocks, compositional layers are folded into upright isoclinal folds. Meanwhile, along the shear zone, foliation varies from NNW to SW with sub-vertical dip. Mineral stretching lineations indicate a sinistral shear sense with a slightly oblique-slip component in the north, but show NWW-directed and SW-directed steep dip-slip shear in the west and south, respectively. Kinematic indicators imply that the granitic dome formed through a vertically upward movement accompanied by an uneven clockwise rotation. The supracrustal rocks sank downwards to form the regional keel structure. Structural data suggests that the Anziling area is a typical dome-and-keel structure. U-Pb zircon dating on pre-, syn-, and post-tectonic dykes indicate that the dome-and-keel structure formed at 2530−2500 Ma, and was intimately related to the emplacement of tonalite-trondhjemite-granodiorite granitoids. New data from this study suggest that until the late Neoarchean, the vertical tectonism was still a dominant tectonic regime that was operating in the eastern North China Craton.

Active Tectonics of Gülbahçe Fault Zone (GBFZ) by Using Geomorphic Indices, İzmir Province, Western Anatolia, Turkey

The Gülbahçe Fault Zone is a dextral strike-slip fault that extends for ~24 km on land and ~46 km under the sea, which consists of the significant southernmost active segments of İzmir Balıkesir Transfer Zone. In this study, the active tectonic behaviour of the Gulbahçe Fault Zone was evaluated by using of morphometric analysis of geomorphic indices. 30 sub-basins identified using ArcGIS ®10.5 (ESRI). All sub-basins were calculated by using mountain-front sinuosity (Smf), valley-floor width to valley height ratio (Vf), basin asymmetry factor (Af), basin shape indice (Bs), drainage density (Dd), and hypsometric integral (Hi) values. The obtained mean results of values are to define each sub-basin's relative tectonic activity (Iat). The Smf, Vf, Af, Bs, Dd, and Hi values range from 1.05 to 1.33; from 0.21 to 4.09; from 25 to 77; from 1.03 and 3.06; from 0.28 to 0.67, respectively. All the results were gathered under three classes, which sign high tectonics activity (Class 1), moderately active tectonic (Class 2), and low tectonics activity (Class 3). The results show that relative active tectonics indice value (Iat) was obtained between 1.33 and 2.33, indicating very high to moderately tectonic activity.

The Roman fish tanks of the Western Mediterranean basin as potential scenarios for research on sea-level changes

PurposeThis paper analyses Roman fish tanks, which have functional elements that could be used to research on palaeo-sea-levels. Thus, the conditions of 37 installations in the Western Mediterranean basin are reviewed to identify those that have the best environmental and constructive conditions to be analyzed.Design/methodology/approachThe methodology was largely based on the review of existing scientific bibliography dealing with sea-level variations from studies on historical constructions, existing historical documentation on Roman fish tanks on the Mediterranean coast, as well as the fieldwork carried out in fish tanks on the Mediterranean coasts.FindingsThe Roman coastal fish tanks located in the shoreline of the Western Mediterranean Sea have turned out to be an excellent indicator of sea-level changes. Nevertheless, current coastal retreat, erosion and storm surges are posing significant threats to their preservation, and they could be considered as a heritage at risk of disappearance. Moreover, variations in the tectonic behaviour of the different coastal sectors make it challenging to select these facilities as an indicator of the sea level.Originality/valueThe analysis of Late Holocene sea-level changes and palaeoenvironments from archaeological and biological evidences, although not without difficulties, is very convenient because it provides very precise data that cannot be obtained with other absolute dating methods. This approach is increasingly gaining popularity with researchers and is very innovative in its method of combining the results of several scientific disciplines.

Oceanic seismotectonics from regional earthquake recordings: The 4–5°N mid-Atlantic ridge

Uncertainties in epicentral locations and hypocentral depths often prevent earthquakes from being associated with individual or group of faults in bathymetric data, thus limiting the understanding of tectonic behavior. Ocean bottom seismometers (OBSs) can overcome this problem, but they take significant efforts to build and deploy, so information from them covers only a minor part of the earthquake record of mid-ocean ridges. As an alternative, a combination of records from seismometers at regional distances and appropriate processing methods can yield location and depth estimates that are useful because they provide extensive data. We illustrate this with a study of magnitude of the seismicity in the 4–5°N Mid-Atlantic Ridge using data from seismometers in Brazil, Cape Verdes, and Africa coast. The seismicity occurred in swarms in 2012 (seven events), 2014 (five events), 2016 (62 events), and 2019 (eight events). We compare the seismicity with features using bathymetric data collected with a multibeam sonars, which reveal two detachment fault surfaces (“megamullions”), one close to the modern rift valley floor but offset by ~10 km from it. The located seismicity is shallow (best estimate less than 8 km below seafloor). The swarms occurred over two segments of the ridge and, in the 2016 case, clearly involved movements on widely distributed multiple faults, including faults on both sides of the valley. Although the methods used produce epicenters and hypocenters with uncertainties that are still larger than those of OBS experiments, they could provide a way to study whether seismicity is systematically deep in certain parts of the ridge where megamullions are observed.

Seismic faults triggered early stage serpentinization of peridotites from the Samail Ophiolite, Oman

Serpentinization of mantle peridotites has first order effects on the rheology and tectonic behavior of the oceanic lithosphere, on the global water cycle, and on the biosphere at mid-oceanic ridges. Investigating serpentinization of abyssal peridotites is limited by the scarce occurrences of peridotites at or close to the ocean floor at slow and ultra-slow ridge environments where peridotite is exposed by long-lived detachments. The processes controlling hydration of the upper mantle below a thick magmatic crust at fast spreading ridges are poorly constrained. Here we present results based on samples from cores drilled in peridotites from the Samail ophiolite obtained during the Oman Drilling Project. We describe an early generation of highly localized brittle faults ubiquitous through all the peridotite cores and investigate their relation to the main serpentinization event represented by mesh-textured serpentinites. We combine microstructural observations with mineral and bulk chemical analyses as well as oxygen isotope microanalyses obtained by secondary ion mass spectrometry (SIMS). Asymmetric wall rock damage, weakening of crystal preferred orientation (CPO) in small fault clasts, and intense fragmentation within the fault zones even in association with very small displacements suggest that the early stage faults represent seismic events and predate mesh formation. Hydration and mesh texture formation follows in the wake of this faulting. Serpentinization is associated with moderate enrichment of fluid mobile elements including B, Li, Rb and U, indicative of fluid rock interaction characterized by relatively low fluid/rock ratios. This is consistent with a scenario where serpentinization took place below a thick magmatic crust following an earthquake-induced permeability increase. The oxygen isotope compositions of mesh serpentine are consistent with off-axis serpentinization at temperatures in the range 200-250°C

Preservation of Modern and MIS 5.5 Erosional Landforms and Biological Structures as Sea Level Markers: A Matter of Luck?

The Mediterranean Basin is characterized by a significant variability in tectonic behaviour, ranging from subsidence to uplifting. However, those coastal areas considered to be tectonically stable show coastal landforms at elevations consistent with eustatic and isostatic sea level change models. In particular, geomorphological indicators—such as tidal notches or shore platforms—are often used to define the tectonic stability of the Mediterranean coasts. We present the results of swim surveys in nine rocky coastal sectors in the central Mediterranean Sea using the Geoswim approach. The entire route was covered in 22 days for a total distance of 158.5 km. All surveyed sites are considered to have been tectonically stable since the last interglacial (Marine Isotope Stage 5.5 [MIS 5.5]), because related sea level markers fit well with sea level rise models. The analysis of visual observations and punctual measurements highlighted that, with respect to the total length of surveyed coast, the occurrence of tidal notches, shore platforms, and other indicators accounts for 85% of the modern coastline, and only 1% of the MIS 5.5 equivalent. Therefore, only 1% of the surveyed coast showed the presence of fossil markers of paleo sea levels above the datum. This significant difference is mainly attributable to erosion processes that did not allow the preservation of the geomorphic evidence of past sea level stands. In the end, our research method showed that the feasibility of applying such markers to define long-term tectonic behaviour is much higher in areas where pre-modern indicators have not been erased, such as at sites with hard bedrock previously covered by post-MIS 5.5 continental deposits, e.g., Sardinia, the Egadi Islands, Ansedonia, Gaeta, and Circeo. In general, the chances of finding such preserved indicators are very low.

Lower crustal attenuation in northeastern Tibetan Plateau from ML amplitude

This study investigated the crustal attenuation structures of Sg and Lg waves of the northeastern Tibetan Plateau. We collected ML amplitude data recorded at 168 permanent stations between 1985 and 2016 and 11 temporary broadband stations between 2014 and 2016. Detailed Q0 variation maps of Sg and Lg waves were obtained by applying ML amplitude tomography. The average Q0 values of the Sg and Lg wave were 440 and 220, respectively. Relatively high attenuation anomalies of both waves appeared in the central and eastern regions of the Bayan Har Block and the east edge of the Qiangtang Block, which may be related to partial melting, high geotemperature, and strong tectonic processes. High attenuation anomalies were also found in the Qilian Orogenic Belt and Hetao Graben, which may be related to their active tectonic behavior and densely distributed faults. The relatively low attenuation anomalies of both waves were revealed in the Alax and Ordos blocks, Qaidam, Tarim, Qinghai Lake, and Gonghe basins, which can be explained by the tectonically stable properties and ancient composition of geological elements. These results indicate that the path between the highly attenuated lower crust of the Bayan Har Block and the Qilian Orogenic Belt is obstructed by three adjacent low attenuated areas (i.e., the Qilian, Qinghai Lake, and Gonghe basins); thus, it appears unlikely that a crustal flow channel from the interior of the Tibetan Plateau to the Qilian Orogenic Belt will form.

Data‐Driven Two‐Fault Modeling of the Mw 6.0 2008 Wells, Nevada Earthquake Suggests a Listric Fault Rupture

AbstractStructural fault complexity at depth affects seismic hazard, earthquake physics, and regional tectonic behavior, but constraining such complexity is challenging. We present earthquake source models of the February 21, 2008, Mw 6.0 Wells event that occurred in the Basin and Range in the western USA, suggesting the rupture of both the shallow and deep parts of a listric fault. We use a large data set including 150 local seismic waveforms from the USArray combined with high‐quality Interferometric Synthetic Aperture Radar and teleseismic waveforms. Rather than imposing an a priori fault geometry in the source inversions, as is often done in the literature, we use a data‐driven approach whereby all the faulting parameters and number of faults are determined by the data alone. We find a two‐fault normal faulting solution comprising: (i) a shallow (centroid depth ∼4.6 km) sub‐event with Mw 5.3 and fault dip of ∼77°; and (ii) a deeper (centroid depth ∼8.8 km), larger Mw 6.0 sub‐event on a fault with shallower dip angle (∼41°). Our preferred two‐fault model is consistent with aftershocks and with the tectonics of the region. The local USArray waveforms used in the modeling are key to detect the rupture of both shallow and deep parts of the possible listric fault. The lack of such dense and uniform coverage of earthquakes in other regions on Earth may explain why the full seismic rupture of listric faults may have gone undetected in the past. Thus, earthquake slip on whole listric faults may be more common than previously thought.

The role of slab geometry in the exhumation of cordilleran-type orogens and their forelands: Insights from northern Patagonia

Abstract In cordilleran-type orogens, subduction geometry exerts a fundamental control on the tectonic behavior of the overriding plate. An integrated low-temperature, large thermochronological data set is used in this study to investigate the burial and exhumation history of the overriding plate in northern Patagonia (40°–45°S). Thermal inverse modeling allowed us to establish that a ∼2.5–4-km-thick section originally overlaid the Jurassic–Lower Cretaceous successions deposited in half-graben systems that are presently exposed in the foreland. Removal of the sedimentary cover started in the late Early Cretaceous. This was coeval with an increase of the convergence rate and a switch to a westward absolute motion of the South American Plate that was accompanied by shallowing of the subducting slab. Unroofing was probably further enhanced by Late Cretaceous to early Paleogene opening of a slab window beneath the overriding plate. Following a tectonically quiescent period, renewed exhumation occurred in the orogen during relatively fast Neogene plate convergence. However, even the highly sensitive apatite (U-Th)/He thermochronometer does not record any coeval cooling in the foreland. The comparison between Late Cretaceous and Neogene exhumation patterns provides clear evidence of the fundamental role played by inter-plate coupling associated with shallow slab configurations in controlling plate-scale deformation. Our results, besides highlighting for the first time how the whole northern Patagonia foreland was affected by an exhumation of several kilometers since the Late Cretaceous, provide unrivalled evidence of the link between deep geodynamic processes affecting the slab and the modes and timing of unroofing of different sectors of the overriding plate.

New insights on the relative sea level changes during the Late Holocene along the coast of Paros Island and the northern Cyclades (Greece)

Geomorphological and archaeological indicators of former sea levels along the coast of Paros enabled us to determine and date six distinct sea level stands and the relative sea level (rsl) changes between them, as well as plot the rsl curve for the last 6,300 years. The Late Holocene history of the rsl change in Paros began with the sea level at 4.90 ± 0.10 m below mean sea level (bmsl) dated to the Late Neolithic period (4300 BC-3700 BC). The next sea level at 3.50 ± 0.20 m bmsl is dated to the Geometric and Archaic period of the Cyclades (1050 BC-490 BC) and most probably lasted during the Hellenistic period (323-146 BC). The sea level at 2.40 ± 0.25 m bmsl is dated to the Roman period (146-400 AD) and the next sea level at 1.35 ± 0.20 m bmsl to the Venetian period of the Cyclades (1207-1537). The sea level at 0.80 ± 0.10 m bmsl is dated to after the Venetian period, during the Ottoman rule of the island (1537-1821). The youngest sea level stand at 0.45 ± 0.10 m is attributed to the recent change in the sea level after the late 19th c. onward. The separation between glacio-hydro-isostatic signals and the observed rsl change on Paros Island, in an area of seismic quiescence, demonstrates a significant tectonic component in the rsl changes. Moreover, the sea level stands deduced from Paros in comparison with those from the northern Cyclades indicate a uniform tectonic behaviour of the entire northern and central section of the Cyclades plateau.

The effect of galactic chemical evolution on terrestrial exoplanet composition and tectonics

The increasing exoplanet catalogue of terrestrial to super-Earth sized rocky planets has necessitated approaches to address their surface conditions, degassing, tectonics, and habitability. One of the key unknowns is the spectrum of compositional endmembers, particularly in geophysically critical elements such as Fe (relative to Si), and heat producing elements (HPEs), including U, Th and K. The fractional distribution of these elements determines core size, gravity, and internal temperatures, which govern the geodynamics of rocky planets. Whilst the relative proportions of these elements can vary enormously in solar-system bodies, on long timescales, galactic chemical evolution (GCE) predicates the availability of these elements for building rocky planets. Existing models demonstrate a systematic dilution of heat producing elements over time, and an increase in Fe/Si due to increased Type Ia supernova activity since galaxy formation. Here we test the consequences of these trends for terrestrial planet behaviour. We assume an Earth-type planet – i.e., planets that accreted similarly to Earth, and inherited elements in a similar partitioning ratio as Earth to the Sun. We varied their Fe/Si ratios, and thus core size, and use a mineral physics package to calculate internal structures, physical properties, and gravity. Planets forming early in the Milky Way's history tend to have low Fe/Si ratios, and thus small cores, although elevated HPE budgets. The configuration of convection in planets that have large mantle fractions relative to the Earth tends to focus stress in the lithosphere and promote tectonic activity. Together with lower gravity, and thus weaker surface faults, plate tectonic behaviour is enhanced in small-core planets. In contrast, planets forming currently have higher Fe/Si, core size, higher gravity, and a lower propensity to plate tectonics. Our results imply a high-propensity for plate tectonics on Earth-sized planets early in galactic history, with the tendency for tectonics diminishing as the galaxy evolved.