Displays

The range of applicable contexts for dating fault-offset geomorphic features and seismically deformed sediment has been extended by recent developments in luminescence dating, in particular using the post-IR IRSL (Infra-Red Stimulated Luminescence) at 225 degrees centigrade for single grains of potassium feldspar. Sediments in desert contexts as well as coarse gravels deposited under high-energy fluvial conditions appear to provide consistent age estimates. At first order, single-grain K-feldspar post-IR IRSL-225 is reliable and accurate.

However, situations where a deposit is composed of grains that were well-exposed to light prior to burial is reworked at night or during a storm may pose a limitation. The degree that an earlier event may be distinguished from the final deposition depends on the luminescence characteristics of grains, the age difference between the two depositional events, and the proportions of grains each event provides to the target deposit. This effect may be referred to as “shadowing”.

We are developing new measurement protocols to help identify grains that were well-bleached, that is they were exposed to sufficient daylight to reduce their trapped charge population to a low level before deposition. We are applying IRSL photochronometry, a determination of light exposure duration, for each grain as part of the dating protocol. This is performed with multiple elevated temperature (MET) IRSL, isolating IRSL signals with different sensitivities to light. Age assessment can be based only on responses from grains that were well-bleached, reducing reliance on the assumption that shared apparent age is correctly identifies depositional age populations. The approach can provide age estimates for multiple past events and information about the environmental conditions that existed before final deposition.

How to cite: Rhodes, E. and Ivester, A.: Improving the robustness of single grain K-feldspar IRSL sediment age estimates from active tectonic contexts, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19294, https://doi.org/10.5194/egusphere-egu2020-19294, 2020

A driving motivator in many active tectonics studies is to learn more about the recurrence large and potentially destructive earthquakes, providing the means to assess the respective fault’s future seismic behavior. Doing so requires long records of earthquake recurrence. The lack of sufficiently long instrumental seismic records (that would be best suited for this task) has led to the development of other approaches that may constrain the recurrence of surface rupturing earthquakes along individual faults. These approaches take different forms, depending on the specific tectonic and geographic conditions of an investigated region.

For example, around the Mediterranean Sea, we frequently find bedrock scarps along normal faults. Assuming that bedrock (i.e., fault free-face) exposure is caused by the occurrence of sub-sequent large earthquakes, we may measure certain rock properties to constrain the time and size of past earthquakes as well as the fault’s geologic slip-rate. A now-classic example in this regard is the measurement of ³⁶Cl concentrations along exposed fault scarps in limestones.

For the presented study, we looked at another property of the exposed fault free-face, namely its morphologic roughness. We aim to identify whether fault free-face roughness contains information to constrain earthquake occurrence and fault slip-rates following the assumption that  sub-sequent exposure to the elements and sub-areal erosional conditions may leave a signal in how rough (or smooth) the fault free-face is (assuming a somewhat uniform pre-exposure roughness). Here, we present observations of fault free-face surface roughness for the Mt. Vettore fault (last ruptured in 2016) and the Rocca Preturo fault (The underlying models of fault free-face morphology were generated using the Structure-from-Motion approach and a large suite of unregistered optical images.). Employing different metrics to quantify morphologic roughness, we were indeed able to observe a) an increase in surface roughness with fault scarp height (i.e., longer exposure to sub-areal erosion causes higher roughness), and b) distinct (rather than gradual) changes in surface roughness, suggesting a correlation to individual exposure events such as earthquakes. Hence, fault free-face morphology of bedrock faults may serve as an additional metric to reconstruct earthquake recurrence patterns.

How to cite: Zielke, O., Benedetti, L., Mai, P. M., Rizza, M., Fleury, J., Pousse Beltran, L., Puliti, I., and Pace, B.: Discrete changes in fault free-face roughness: constraining past earthquakes characteristics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4032, https://doi.org/10.5194/egusphere-egu2020-4032, 2020

The Taiwan mountain range stands as one of the most active regions on Earth. With an overall shortening rate of ~40 mm/yr and an average erosion rate of ~4 mm/yr, this mountain range appears ideal to better understand the interactions between tectonics and surface processes, and how these shape active landscapes. Here we explore the geomorphic and sedimentary record of active deformation within the Southwestern Foothills of Taiwan, and we quantify from there the kinematics of active faults. In particular, we investigate the downstream portion of the meandering Tsengwen river - one of the largest rivers of this region - where we identify and correlate remnants of 7 terrace levels, progressively abandoned over the last ~5 kyr. The incision of these terraces is interpreted as being controlled to the first-order by folding and uplift related to underlying active faults. The evolution of the river is reconstructed from correlated terrace remnants, and our results indicate that the overall river sinuosity and gradient did not vary significantly during the past ~5 kyr in response to tectonics. Incremental tectonic uplift is retrieved from terrace incision corrected for sedimentation at the mountain front, and is used to derive the incremental shortening since terrace abandonment. Downstream, within the Coastal Plain, the Tsengwen river reaches its base level and aggrades. Sedimentary facies within boreholes of the Coastal Plain record vertical displacements relative to sea level, spatially consistent with potential blind active faults. When corrected for eustatic variations, these data allow for quantifying tectonic uplift rates within the Coastal Plain over the last ~20 kyr. Taken altogether, our quantitative analysis of the Tsengwen river record, from terrace incision to dowsntream aggradation, reveals that the most frontal active faults absorb a shortening rate of at least ~35 mm/yr, that is most of - if not all -  the shortening rate to the absorbed across the whole mountain range.

How to cite: Steer, P., Lefils, V., Simoes, M., Shyu, J. B. H., Rizza, M., and Siame, L.: Quantifying active deformation within the Southwestern Foothills of Taiwan, from incised fluvial terraces and sedimentary data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5237, https://doi.org/10.5194/egusphere-egu2020-5237, 2020

We report on the morphotectonic characteristics in the tectonically active Southern Ethiopia Rift (SER) based on the analysis of high-resolution topographic data (12m TanDemX) and satellite imagery. The study region is a wide zone of distributed extension at the transition from the SER and the Northern Kenyan Rift and reflects the long-term effects of episodic tectonic events in the landscape.  The uplifted footwall margins of the north-south trending and left stepping ēn ēchelon basins of the SER constitute Pan-African basement rocks in the southern and central part (Chew Bahir, Mali-Dancha and part of Beto) and tectonized Miocene basalts in the north (Sawula). As such this region is an ideal location to record the tectonic characteristics of a major transition zone between two rift systems. Some of the unsolved problems in this area concern the degree of tectonic activity, spatiotemporal variations in the amount of extension, and the nature of kinematic linkage between different faults. To examine these issues, we calculated morphometric indices of river catchments along major fault-bounded blocks as proxies for tectonic activity and combined this information with structural, seismicity, and climatic data. 
We determined basin asymmetry, hypsometric integral, mountain-front sinuosity, valley floor to valley-width-height ratio, basin shape, the range of basin form and mean slope; additionally, we calculated knickpoint distributions and channel-steepness index values from 89 sub-basins. Combined, the data suggest a significant north-south variation in extensional processes. For example, in the northern basins knickpoints are generally located in upstream areas near the channel heads. They are rare in the Mali-Dancha basin, whereas in the Chew Bahir basin a distinct distribution along the main channel is recognized from basin head to the mountain front. In the south the knickpoints are closest to the mountain front. This unique spatial arrangement of knickpoints in rivers draining the footwalls of extensional blocks in the north-south transect suggests a gradual, southward-directed shift in extensional deformation and recent tectonic activity. The normalized channel-steepness index value is generally small; however, it also exhibits a significant southward trend with higher values (i.e., tectonic activity). Additionally, the normalized channel steepness indices are higher at orthogonally interacting faults compared to neighbouring areas, suggesting strain localization. 
Our new results suggest a northward increase in the geomorphic maturity of the analyzed sub-basins from Chew Bahir (juvenile) to Sawula (mature), which is compatible with a northward decrease in tectonic activity and a dominance of erosional processes. This is consistent with published, northward-decreasing extension rates and the degree of regional seismicity. Furthermore, strain localization at interacting faults suggests kinematic linkage of the left-stepping bounding faults of the sub-basins.

How to cite: Erbello, A., Zeilinger, G., and R. Strecker, M.: North-South variation in tectonic activity along left-stepping extensional basins revealed by morphometric analysis: Gofa province, southwestern Ethiopia, East Africa, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6770, https://doi.org/10.5194/egusphere-egu2020-6770, 2020

In the 60’s, the formulation of the plate tectonic theory changed our understanding of the Earth dynamics. Aiming at explaining the earth first order kinematics, this primary theory of plate tectonic assumed rigid plates, a necessity to efficiently transfer stress from one boundary to another. 

If successful to explain, at first order, the plate-boundary evolutions, this theory fails when compared to the unpredicted but identified deformation located inside the plate-domains: the intraplate orogens. Indeed, the intraplate regions are thought to be slowly, if at all, deforming. Therefore, it is expected that intraplate regions do not show important finite deformation, that is to say, no mountains. Some intraplate regions, however, have important relief: the Snowy Mountains (Australia), the Ural Mountains (Russia) or the Massif Central (France) for examples. Traditionally, such regions are interpreted as old structures that are slowly eroded, interpretations that are most of the time weakly constrained. 

Our study is aiming at providing stronger constraints and then a better understanding of such challenging area that are the intraplate orogen domains. Because direct measurements of deformations (e.g. GNSS: Global Navigation Satellite System or InSAR: Interferometric Synthetic Aperture Radar) are most of the time below the precision level, it is necessary to derive this information from the landscape evolution. To do so, terrestrial cosmogenic nuclide (TCN) technics are a key method, allowing to constraint the temporal landscape evolution. Classically, two TCN-based approaches are used to quantify the landscape evolution rate: burial ages and watershed-wide denudation rates, based on measurement in quartz sediment of 10Be and 26Al concentrations, two radioactive cosmogenic isotopes.

Using the Massif Central (France) as study area, we show that this region is currently deforming.

From new geochronological constraints and a geomorphometric study, we propose that the region undergoes an active uplift encompassing the last c.a. 4 Ma. It can be explained by the combination of at least two phenomena: the first one is the uplift triggering event, that has yet to be clearly identified, and the second one: the erosional isostatic adjustment enhancing the first one and possibly continuing after the end of the first one. 

How to cite: Malcles, O., Vernant, P., Ritz, J.-F., Fink, D., Cazes, G., Fujioka, T., Braucher, R., Chéry, J., and Camps, P.: Challenging Intraplate Orogens: from geomorphology to lithospheric dynamic. The French Massif Central Case study, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8547, https://doi.org/10.5194/egusphere-egu2020-8547, 2020

Clinoforms are aquatic sedimentary features commonly associated with strata prograding from a shallower water depth into a deeper water depth. They are very sensitive to changes in water depth, rapidly moving along the shelf in response to sea level changes.  By reconstructing the initial clinoform geometry of buried clinoforms, an estimate of the paleo water depth (PWD) can be made. When this is done for several subsequent clinoform sets the amounts and rates of bathymetric changes can be calculated.

Here we present a novel approach to estimate clinoform parameters and depositional depths for continental margin clinoforms using seismic reflections, wellbore and biostratigraphy data. Seismic interpretation of three relatively east-west regional full-stack seismic reflection data from the continental margin of the western Barents Sea revealed twelve Late Cenozoic horizons. The clinoform shapes have been restored by removing the effects of compaction and flexural isostasy (backstripping). This includes the effects of glacial/interglacial scenarios on horizons with strong glaciomarine seismic indications.

Based on the reconstructed clinoform geometries we use empirical relationships from literature between clinoform geometry and depositional depth to estimate PWD values. In these analyses it is possible to estimate the PWD of the upper rollover point and the toe point by measuring the bottomset height, foreset height and topset height. A sensitivity analysis study has also been done on several different scenarios, varying elastic thickness, decompaction and net to gross ratio. Comparison with biostratigraphic water depth estimates indicate that PWD estimates revealed from clinoform parameters give reliable results.

Any mismatch between the backstripped PWD values and the PWD values derived from the clinoform geometry can then be attributed to geological processes not included in the backstripping process. Among others, these could be explained by rifting, thermal effects in the lithosphere, faulting or eustatic sea level changes. This allows the quantification of the magnitude of these large-scale crustal processes through time.

We will demonstrate that this method can further constrain the PWD on the continental margin clinoform system and thus can help to improve the understanding of the interplay between sedimentary processes and large-scale crustal processes. Furthermore, the PWD estimates will be a reliable input for further analysis of source-to-sink and stratigraphic forward modeling studies as well as reservoir and source rocks prediction on the petroleum development and exploration.

How to cite: de Jager, G., Harishidayat, D., Emmel, B., and Johansen, S. E.: Dynamics and evolution of continental margin clinoform systems, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21495, https://doi.org/10.5194/egusphere-egu2020-21495, 2020

The movement of active faults due to inland earthquakes often involves surface displacement. In Japan, where many active faults are distributed, fault displacements are often accumulated and reflected on the current topography. For example, in a region where right-lateral strike-slip faults are distributed, it is possible to observe river topography systematically right-lateral strike-slip from the fault. Japan has many volcanoes as well as active faults, but in volcanic areas it is difficult to find evidence of fault activity accumulation in the terrain, and it is difficult to find fault traces on the surface. In this study, we performed geomorphological analysis using high-resolution DEM based on GIS in the southern part of Iwate prefecture where many volcanic rocks are distributed, and examined the relationship between river topography and active faults. The target area is mainly covered by Miocene to Pleistocene volcanic rocks. In this area, despite significant earthquakes occurring since 1896, there is little apparent surface displacement. An Mw 6.9 earthquake with surface displacement occurred in 2008 in this area. In this study, basic topographical measurements such as slope, aspect, dispersion of altitude, and stream density and stream-power indices were analyzed using 5mDEM in the target area. As a result, it was found that the SPI value tends to be higher in the area where surface displacement was observed in 2008. It is necessary to clarify the relationship between fault activity and topography by increasing the target area and conducting watershed analysis using SPI and other indices.

How to cite: Kawabata, D. and Kimura, H.: Slope analysis of active fault in volcanic areas using high-resolution DEM based on GIS, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13225, https://doi.org/10.5194/egusphere-egu2020-13225, 2020

Paleozoic orogenic belts developed between the basement rocks in the southern Korean Peninsula records important information to reconstruct the tectonic evolution of East Asia. Here we present SHRIMP and LA–(MC)–ICP MS U-Pb ages and Hf isotopes of detrital zircon grains from the Paleozoic metasedimentary successions that are incorporated into the major Phanerozoic orogenic belts (Okcheon and Hongseong-Imjingang Belts) in South Korea, providing new insights into provenances and tectonic evolution during the Paleozoic period. Based on the internal structures of the zircons from all the samples, they are mostly derived from igneous source rocks, showing two distinct spectra patterns in their presence/absence of Neoproterozoic ages. Our results suggest that (1) the presence/absence of the Grenville-age (ca. 1.3–0.9 Ga) detrital zircons and Hf data from the Early Paleozoic Joseon Supergroup in the Okcheon Belt suggest their derivations from different peripheral clastic provenances at least after the Early Cambrian, (2) ages and Hf isotope signatures of dominant Early Neoproterozoic and Silurian-Devonian detrital zircon populations from the Middle Paleozoic metasedimentary rocks in the Hongseong-Imjingang Belt reflect magmatic history involving juvenile input and crustal reworking, and (3) zircons from the Late Paleozoic Pyeongan Supergroup in the Okcheon Belt display dominant Paleoproterozoic and Carboniferous-Permian ages with Hf patterns showing vertical mixing trends between juvenile and recycled crustal material. These results, integrated with U-Pb and Hf isotope data from other parts of the Korean Peninsula and the Chinese cratons, will eventually help to understand the spatial and temporal relations of basins and orogenic belts in the Korean Peninsula, and will further provide important clues about Paleozoic evolution of the Korean Peninsula in relation to the tectonic history of East Asia.

How to cite: Jang, Y., Kwon, S., and Kim, S. W.: Detrital zircon U-Pb and Hf isotope studies of the Paleozoic successions in the Korean Peninsula: Implications for the provenances and tectonic evolution of the Phanerozoic orogenic belts, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4355, https://doi.org/10.5194/egusphere-egu2020-4355, 2020

This study aims to investigate the thermal history regarding the Late Miocene Formation of the Hengchun Peninsula with low-temperature thermal chronometry. The samples used in our study were from Lilungshan Formation, which included quartzite (conglomerates) and sandstones (matrix). Lilungshan Formation was an upper fan or feeder channel deposits in shelf environments. Measurements of paleocurrent indicate that these rocks were transported from the NW to the SE, which may represent its source area is a low-grade metamorphic orogenic belt (Yuli belt). In the Late Miocene, outcrops of Yuli belt were low-grade metamorphic rocks with low metamorphic temperatures. To do so, low-temperature thermal chronometry was applied to measure the time since the Lilungshan Formation cooling below the closure temperature. Apatite Fission-track thermochronology is used in this study, which is a radiometric dating method that refers to thermal histories of rocks within the closure temperature range of 110–135°C.

Our study indicates that the pooled age of apatite fission tracks of conglomerates is 3.3–5 Ma and the grain ages of sandstones are below 5 Ma. Those ages are lower than the formation age of Lilungshan Formation (NN11, > 5.6 Ma). In addition, the grain ages spectrum of sandstones is partial annealing, which implies that the conglomerate has suffered from the thermal event and rapidly brought to the earth’s surface within 4 Ma. This study also compares data of previous studies with regard to the fission tracks of conglomerates in Southern Taiwan and confirms the existence of thermal events. With the assumption that the thermal gradient of the accretionary prism is 40–45°C/km, we can suggest that Lilungshan Formation was located 3 km below the earth's surface in roughly 4 Ma.

Keywords: Hengchun Peninsula, Lilungshan Formation, Apatite Fission Track, thermal history, chronometry, Late Miocene

How to cite: Kao, S.-I., Chen, W.-S., and Chan, T. H.: Late Miocene thermal history of the Hengchun Peninsula, Southern Taiwan: Apatite Fission-Track data from the Lilungshan Formation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3289, https://doi.org/10.5194/egusphere-egu2020-3289, 2020

Along the northern coast of the South China Sea in southeastern China, marine terraces preserved on the widespread Cretaceous granite and recorded both Quaternary uplift and sea-level oscillation. However, because sediments or materials for dating are usually absent, it is difficult to date these paleo-shoreline, which cause great difficulties in early exploration. Fortunately, as great progress on terrestrial cosmogenic nuclide dating, it is possible to yield the exposure age of marine terrace and to calculate the uplift rate along coastal line. This study focuses on two typical sequences of preserved marine terraces lying on the coastal line adjacent the Taiwan Strait in southeastern China. These two sequences of marine terraces (denoted as NZS and HJC site, respectively) both locate on the footwall (uplifting wall) of normal NE-SW trending fault (the Coastal Normal Fault) but on separated blocks subdivided by a normal NW-SE fault. At least 5 terraces and 2 terraces developed on granite at HJC and NZS site, respectively. In particularly, T1 and T3 terrace at HJC site and T1 terrace at NZS site present typical abrasion wave-cut platform with preserved sea stacks. Hence, we collected both profile and surface quarts samples on these well-preserved marine terraces for ¹⁰Be exposure dating and yielded exposure ages of 51.0±1.9 ka, 66.2±2.9 ka in T1 and T3 terrace at HJC site, and 87.9±3.5 ka in T1 terrace at NZS site. After subtracting eustatic sea-level changes from the relative sea-level curve, we measure high uplift rates of 1.13 mm/a at HJC site and 1.04 mm/a at NZS site during late Pleistocene. The similar uplift rates in different faulting blocks suggest that surface uplift can be directly linked to NE-SW fault system. Low difference of uplift rate between tow site suggest relative vertical motion of tow faulting blocks could be adjust by NW-SE faults. The regional uplift with high uplift rates is likely corresponding to the major collision between Luzon arc and the Chinese continental margin. However, because the contribution of by isostasy, e.g. surface erosion or ice-volume variation in Quaternary, remains uncertain, the calculated uplift rate maybe overestimated.

How to cite: Liang, H., Zhang, K., Chen, Z., Huang, P., Li, Z., and Chen, Z.: Tectonic uplift rate in the northern coast of the South China sea: insight from the 10Be exposure dating of marine terrace in southeastern China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2653, https://doi.org/10.5194/egusphere-egu2020-2653, 2020

        Despite several tens of Pleistocene eustatic oscillations, it is surprised that only two marine sequences were preserved in the PRD (Pearl River Delta), the third biggest delta along the mainland China coast. The younger marine sequence (SQ1) has been consensus on the age of Holocene, i.e., MIS1, whereas the chronology of the older marine sequence (SQ2) is still in debate, i.e. belongs to MIS3 or MIS5. Those favor younger transgression suggest rapid uplift following the SQ2 deposited according to ¹⁴C and early luminescence dating, while the others argued that the current depth of SQ2 is affected by tectonic subsidence and better match the sea-level altitude in MIS5. To address this problem, it is significant to investigate a complete spatial distribution of SQ2 prior to dating. We applied 250 boreholes to acquire 5 Quaternary stratigraphic profiles throughout the PRD. These profiles reveal that the deposition area of SQ2 with current depth at -15 - -35m a.s.l. only reach the southern part of PRD, showing a much less area than SQ1. Sediments synchronous to SQ2 in the northern part of PRD present coarse grain in fluvial or piedmont environment, implying an erosional state. Preliminary OSL dating on SQ2 in boreholes in southern PRD yielded 85.5±5 ka, suggesting the SQ2 probably deposited in MIS5, here we infer to the high sea-level in MIS5a with altitude at ca. -20m. Moreover, we estimate the isostasy by erosion of granite highland in/around the PRD via hypsometric integral curve. We find that the modern average altitude of the highland is ca. 100-150m lower than the estimated isostatic altitude, suggesting tectonic subsidence in PRD. Overall, we interpret that the PRD was an eroding highland and keep subsiding since MIS5. Because of the topographic high, transgression occurred in MIS5 did not extend northward to modern delta area and led to absence of SQ2 in northern PRD. Subjected to tectonic subsidence, the once topographic high subsided beneath the modern sea-level but still higher the sea-level in MIS3. Marine sequence did not develop in PRD until transgression occurred in Holocene.

How to cite: Huang, P. and Liang, H.: Coupling of sea level changes and neotectonic activities in the Pearl River Delta─insight from stratigraphic profile and chronology, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6880, https://doi.org/10.5194/egusphere-egu2020-6880, 2020

We re-investigate the geological slip along the frontal Nameri Thrust, a local name for the Himalayan Frontal Thrust in the eastern Himalaya, India. Four levels of tectonically displaced and uplifted fluvial terraces preserved along the Kameng River were dated using the Optically Stimulated Luminescence (OSL) method. The OSL ages of the terraces bracket the timing of their abandonment post ~14, 11, 7.2 and 3 ka respectively. Considering the minimum timing of vertical uplift and height of the uplifted and incised bedrock strath beneath the lowermost river terrace T1, we use trigonometric method to infer a vertical uplift rate of ~0.44 mm/a on the Nameri Thrust during the Holocene Period. The mismatch in the geodetic convergence and the geological slip rates proposed for the Himalayan Frontal Thrust in the eastern Himalaya in earlier studies provoked us to re-evaluate the scenario of geological slip in the area. Our results suggest a contrasting estimate of geological slip rate as compared to the earlier studies. Though the results are indicative of a decrease in the Indo-Eurasian convergence in the eastern Himalaya in accordance with the recent GPS observations and models proposed for the region, we, however, suggest that the lower estimation in our study compared to that reported previously could be due to the use of different dating methods for the materials obtained for assigning chronology to the landforms and events. Since the ¹⁴C AMS radiocarbon dating method requires a contemporary organic component in the sediments to be dated, an overestimation of the dates is also possible if the sediment has mixed with old carbon, which makes it inferior to the OSL method in which the mineral grains are assumed to have been fully bleached before their burial. This makes the OSL method more reliable to date sediments since it does not encounter the ‘old-carbon’ error problem of overestimation of the ages. Two additional samples obtained to the south of the active mountain front yield southwardly-increasing luminescence ages of ~19 and 26 ka suggesting deposition of older sediments toward downstream by the Kameng River as a result of rampant incision in the upstream triggered by episodes of tectonic uplift prior to ~26 ka.

How to cite: Mishra, R. L., Jayangondaperumal, R., Pandey, A., Singh, V., and Srivastava, P.: New estimates of minimum geological convergence for the eastern Himalaya, India, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-248, https://doi.org/10.5194/egusphere-egu2020-248, 2019

The Western Kunlun Range is a mountain range located at the northwestern boundary of the Tibetan Plateau, facing the Tarim Basin. Our previous combined structural and morphological investigations of the mountain front, nearby the city of Pishan where a Mw 6.4 earthquake occurred in 2015, revealed the existence of a duplex uplifting Cenozoic strata, in which only the most frontal blind ramp is presently active and slips at a probable rate of 2 to 2.5 mm/yr. Located ~100 km further east along the mountain front, the Hotan anticline seems to present a different structure from surface geology, as older strata from Mesozoic and Paleozoic outcrop. Additionally, some authors proposed that the deformation would be here accommodated by a large blind basement thrust sheet, in clear contrast with the duplexes documented further west.

To further document potential lateral variations in the structural style and how they may affect the kinematics of active deformation along the mountain front of the Western Kunlun, we carry out a structural and morphological analysis of the Hotan anticline. We build structural cross-sections based on seismic reflection profiles, and calculate the incremental uplift recorded by dated fluvial terraces to quantify shortening rates over the last ~300 kyr. Our analysis reveals that a duplex structure, located below the basement thrust sheet, presently accommodates active deformation at a rate of 0.5 to 2.5 mm/yr, with a preferred rate of ~1.6 to 2.3 mm/yr. In more detail, uplifted terraces reveal that all ramps of the duplex are active in the case of the Hotan anticline, while only the most frontal ramp is documented as active in the case of the Pishan anticline further west. These results indicate that the style and rate of active shortening are rather homogeneous all along the mountain front, in contrast with the first impression provided by surface geology. Moreover, the discrepancy between surface geology and active morphology reveals progressive structural changes over geological times, from a blind basement ramp to duplexes. However, in the details, active deformation still remains segmented as its partitioning on the various ramps of the duplexes is variable along strike.

How to cite: Guilbaud, C., Simoes, M., Barrier, L., Van der Woerd, J., Baby, G., Li, H., Pan, J., Tapponnier, P., and Harlet, D.: Investigating lateral variations in the kinematics of active deformation along the Western Kunlun mountain front (Xinjiang, China): structural and morphological analysis of the Hotan anticline, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10132, https://doi.org/10.5194/egusphere-egu2020-10132, 2020

We present an updated tectono-stratigraphic development model of the Megalopolis Basin (MB), which is an intra-montane basin, located in the actively extending domain of the Hellenic Arc, based on re-interpretation of borehole data, field mapping and stratigraphic – sedimentological reconnaissance. The Megalopolis basin develops on the hanging-wall of the W. Mainalo Fault System, which accommodates the deformation associated with the exhumation of the PQ metamorphics in the window of Assea, east of the MB. During the early stages of basin development, NNW-SSE normal faults controlled its eastern margin. These interacted with and gradually dismembered the ENE-WSW ones that were related to pre-Pliocene extension.

The establishment of ENE-WSW Quaternary extension in the southern Peloponnese is associated with major, range-bounding NNW-SSE faults, such as the Sparta F. that controls the eastern margin of the Taygetos horst. Fault growth and consequent uplift of the Taygetos horst affected the southern reaches of the Megalopolis Basin, through the development of an intra-basinal high (Leontari horst) that split the southern portion of the MB in two sub-basins, while the activity on the faults on the eastern margin of the MB ceases. The switching-off of the eastern margin was taken over by the faults that control the western margin of the MB, such as the prominent NNW-SSE, east-throwing Ellinitsa Fault and the Lykaion Fault System; the latter is a rather elusive structure, owing to the nature of the affected formations (erodible Pindos clastics) and dense forest cover that obscure fault exposures.

The successive stages of fault evolution are reflected in, and largely control, the sedimentation type(s) in the MB. The initial Pliocene lacustrine conditions were gradually replaced by extensive fluviatile sedimentation (Megalopolis Fm), which interfingers with more focused, lacustrine deposits in the basin centre (Marathousa Fm.), when the Pleistocene Megalopolis Lake developed. The subsequent deposition of the (mainly) fluvial Apiditsa and Ellinitsa formations, follows the gradual starvation of sediment feeding from the E-ESE, (which fed the Megalopolis Fm) and marks the onset of fault activity in the southern and western parts of the MB. The establishment of the modern Alfeios drainage, initially deposited floodplain sediments, subsequently to cut into them and form terraces, following episodic(?) drops of its base-level, owing to alternating climatic conditions and/or surges of fault activity. Finally, the breaching of the basement salient in the NNW (Karytaina gorge), led to the establishmnent of the present-day base level, with Alfeios cutting into its more recent deposits.

This research was conducted under the auspices of the Ephoreia of Paleoanthropology and Speleology, Greek Ministry of Culture, and was supported by the European Research Council (CROSSROADS).

How to cite: Kranis, H., Skourtsos, E., Davis, G., Karkanas, P., Tourloukis, V., Panagopoulou, E., and Harvati, K.: Switch-on, switch-off: Plio-Quaternary evolution of the Megalopolis Basin (Southern Greece), through structural overprinting, interaction and fault migration, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19950, https://doi.org/10.5194/egusphere-egu2020-19950, 2020

We present investigations of a major Miocene fault system crossing the city of Vienna by using sedimentological, geophysical, remote sensing and numerical age dating methods. The fault zone is located at the western edge of the Vienna Basin, a c. 55 km wide and c. 200 km long rhomb-shaped pull-apart basin, separating the mountain ranges of the Alps and Carpathians. At its western edge a major sidewall fault, the Leopoldsdorf Fault System  vertically offsets alpine units by up to 5 km. In this study, we focus on Pleistocene fluvial sediments of the Danube deposited along this fault zone. Distribution and facies provide suitable conditions to speculate on Quaternary fault activity. Fluvial gravels rest on top of fine-grained, marine sediments of the Miocene. Quaternary uplift preserved these sediments in the form of terraces that were extensively covered by Pleistocene aeolian deposits (i.e. loess). Later, solifluction affected those fine-grained sediments and obliterated the terrace steps resulting in a relative homogenously inclined top as well as a flat accumulation zone at the toe of the slope. Age brackets of Quaternary deposits are provided from redeposited quartz gravels using cosmogenically produced ²⁶Al and ¹⁰Be as well as luminescence ages of the loess-like cover sediments.

The high resistivity contrast of the coarse-grained sediments to the underlying fine-grained marine sediments and the overlying loess deposits provided excellent conditions to infer the geometry of the fluvial deposits. Accordingly, we used electrical resistivity tomography and data derived from driller’s lithologic logs to constrain possible vertical offset of terraces. Possible surface ruptures were discussed by utilizing data from LiDAR-based high-resolution digital elevation models.

How to cite: Salcher, B., Otto, J.-C., Neuhuber, S., Lüthgens, C., Grupe, S., Payer, T., and Fiebig, M.: Geophysical and Geological investigations of a major Miocene fault system within the city of Vienna: evidence for active tectonics , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10608, https://doi.org/10.5194/egusphere-egu2020-10608, 2020

The “Seewinkel” region is the eastern most part of Austria located east of Lake Neusiedl, Austria’s largest lake. The area is located in the western part of the Little Hungarian Plain and is characterized by extremely low relief and abundant shallow lakes and pans. The general geological setting shows Quaternary fluvial sediments with minor aeolian cover in places, above Pannonian (Miocene, Tortonian) limnic fine-grained sediments. Recent seismic data show the existence of abundant brittle faults in the subsurface, related to the formation of the Pannonian Basin.

We model the thickness of the Quaternary sediments in this hardly exposed area, to gain insight into their deposition, the influence of pre- and post-tectonic structures and to improve our understanding of the uppermost groundwater storey. This study combines existing borehole data (mainly from OMV, Geological Survey of Austria, Gruppe Wasser Ziviltechnikergesellschaft für Wasserwirtschaft GmbH and Amt der Burgenländischen Landesregierung) and observations from construction sites with high-resolution airborne laser scanning (ALS) topographic data to model the thickness of the Quaternary sediments in an Open-Source geographic information systems (GIS) environment.

The Quaternary fluvial sediments pinch out towards northwest, being virtually zero close to the eastern shore of Lake Neusiedl, and increase in thickness towards east, reaching almost 30 m at the Austrian/Hungarian border. This tendency is mimicking the thickness trend of the underlying Pannonian sediments and most probably is related to the still ongoing regional subsidence in the Little Hungarian Plain.

How to cite: Zemann, P., Draganits, E., Hodits, B., Schiel, B., Berka, R., and Weissl, M.: Modelling the base of fluvial Quaternary sediments in the “Seewinkel” area (Austria), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19543, https://doi.org/10.5194/egusphere-egu2020-19543, 2020

A breccia is a rock made up of angular clasts. Its formation can be the result of several types of geological processes (sedimentary, tectonic, hydraulic, magmatic, etc.). The aim of this study is to understand the formation and the preservation of sedimentary breccias with a significant thickness (several tens to hundreds of meters) in extensional environments, by comparing the Bas-Agly Basin, in the eastern French Pyrenees, to a recent analogue (Pleistocene-Holocene deposits of the Chora Sfakion region, SW Crete). In both cases, the breccias mainly consist of carbonate elements.

Our preliminary results show that:

- Along the coast of the Chora Sfakion region, sedimentary breccias are preserved at the front of a major normal fault scarp over a distance of ca. 20 km. Their formation results from a destabilization of the topographic slope triggered by the activity of the fault. The breccias were preferentially developed at the expense of dolomitic layers that underwent intense fracturation during an older deformation phase. Breccia deposition was related to processes of aerial or sub-aquatic landslides. Relatively fine-grained unsorted breccias are found close to the main fault whereas larger blocks and olistoliths are found farther away and down-slope, attesting for large mass slides. Preservation of the breccias has been favoured by subsidence at the front of the fault.

- The sedimentary breccias of the Bas-Agly Basin bear characteristics that are broadly comparable to those of Crete. With respect to the Cretan case, the Bas-Agly deposits, which consist of breccias alternating with fine sediments, represent a more distal part of the system. However, the age of the breccias in the Bas-Agly Basin is widely debated, with estimates ranging from the Late Jurassic to the Eocene. Depending on the actual age, the tectonic environment could have been quite different, e.g. extensional or compressional. Thus, it is crucial to know the real age of these rocks. In order to solve this issue, we initiated a geochronological study, using in-situ U-Pb dating by LA-ICP-MS and focusing on the carbonate matrix of the breccias. This approach has proven successful and yielded ages consistent with the proposed extensional environment.

In summary, extensional tectonics appear to favour both the production and the preservation of large volumes of sedimentary breccias, which, therefore, may be considered as a marker of this tectonic regime. Whether compressional tectonics could produce a similar situation is a topic of ongoing research.

Keywords: breccias, sedimentary, syntectonic, extension, Crete, Pyrenees, U-Pb dating

How to cite: Kernif, T., Nalpas, T., Gautier, P., Bourquin, S., and Poujol, M.: Formation and preservation of syntectonic sedimentary breccias in extensional environments (Crete and Pyrenees) and in-situ U-Pb constraints for the age of breccias in the Bas-Agly Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9024, https://doi.org/10.5194/egusphere-egu2020-9024, 2020

The southwestern margin of Iberian (SWIM) marks the transition between the Mediterranean Alpine Orogenic Belt and the Atlantic Azores–Gibraltar Fracture Zone, near the diffuse segment of the Africa (Nubia)-Eurasia (Iberia) plate boundary. The Gulf of Cadiz Contourite System (GCCS) has been build-up by the circulation of the Mediterranean Outflow Water (MOW) on the continental middle slope. This work aims to understand how the tectonic structures controlled the development, evolution and morphology of the GCCS. This has been accomplished with the analysis of high quality regional 2D seismic reflection profiles. Four sedimentary basins were mapped in the study area – the Algarve, Doñana, Sanlucar and Cadiz basins – developed in the foreland of the Betic-Rif Orogen. Three major tectonic structures – the Gil Eanes Fault (GEF), Cadiz Fault (CF) and the Albufeira-Guadalquivir-Doñana Basement High (AGDBH) – were identified on the SWIM. The NW-SE-oriented GEF and the NE-SW to ENE-WSW-oriented CF were identified as dextral strike-slip faults. The AGD is an E-W to ENE-WSW elongated morphostructural high that marks the southern boundary of the Algarve Basin. Based on their location and orientation they were interpreted as being inherited structures from the Mesozoic rift system. Based on the described regional structures, the SWIM was divided into four tectonic domains (A, B, C and D) with different structural and seismological characteristics. Contourite depositional and erosional features show different characteristics – distinct size, extension, configuration and depositional architecture - for each of the  tectonic domains recognised. Tectonic-controlled subsidence led to the development of an accommodation space, forming the main depositional sector in the GCCS (Domain C). Contrariwise, where the margin suffered uplift, the accommodation space was limited and the contourite depositional features are not very extensive (Domain D). The presence of structural obstacles (e.g. AGDBH, paleo-slope) is another important factor in the drift evolution: mounded geometries were only observed where important structural obstacles conditioned the current circulation (Domain B, C and D). Where the seafloor is gentle with smooth relief, spread-out MOW circulation occurs, forming sheeted drifts related to weak and wide non-focused bottom-currents (Domain A). This work demonstrates the influence that the inherited tectonic structures and the margin paleo-topography has on the development of the contourite system. Furthermore, we propose that tectonics also control the dimensions and types of the contourite depositional features.

Acknowledgements: D.D. thanks the Portuguese Foundation for Science and Technology (FCT) for a PhD scholarship (reference SFRH/BD/115962/2016). This research has been conducted under the framework of ‘The Drifters Research Group’, Department of Earth Sciences, Royal Holloway University of London (UK). This project is partially funded by a Joint Industry Project supported by TOTAL, BP, ENI, ExxonMobil, TGS and Wintershall and partially supported through the CGL2016-80445-R (AEI/FEDER, UE), CGL2015-66835-P and CTM2016-75129-C3-1-R.

How to cite: Duarte, D., Roque, C., Hernández-Molina, F. J., Ng, Z. L., Magalhães, V. H., Llave, E., and Sierro, F. J.: Tectonic domains of the Betic Foreland System, SW Iberian Margin: Implications for the Gulf of Cadiz Contourite System, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1033, https://doi.org/10.5194/egusphere-egu2020-1033, 2019

Abstract:

Giant subduction earthquakes (M_W 8 to 9) are usually characterized by heterogeneous slip distributions, including regions of very pronounced slip that are commonly known as asperities. However, it is a matter of ongoing debate whether asperities constitute persistent geologic features or if they rather represent transient features related to the release of elastic strain accumulated in areas of seismic gaps. Recent giant earthquakes along the coast of north-central Chile, such as the 2010 Maule (M8.8), 2015 Illapel (M8.3), and 2014 Iquique (M8.2) events, were all associated with the rupture of single or multiple seismic asperities. Here we compare permanent deformation and seismic-cycle deformation patterns and rates along the 2015 Illapel earthquake rupture zone (~30° to 32°S) spanning orbital to decadal time scales. To decipher permanent deformation features manifested in the upper plate of the subduction system we identified and correlated the elevations of Late Pleistocene marine terraces using TanDEM-X digital topography and previously published terrace ages. We focused on terraces related to the Marine Isotope Stages (MIS) 5 and 9 (~124 ka and ~320 ka) due to their excellent preservation and lateral continuity. We furthermore compared deformation rates based on these uplifted terraces and compared them with published co-seismic slip and interseismic locking models of the Illapel earthquake. Uplift rates derived from the MIS-5 marine terraces range between 0.08 and 0.35 m/ka, while uplift rates based on MIS-9 terraces range between 0.38 to 0.96 m/ka. The higher uplift rates are found at the northern part of the Illapel rupture and these areas correlate to crustal structures (e.g. Puerto Aldea Fault). We observed a direct correlation between MIS-5 and MIS-9 uplift rates and co-seismic slip in the northern parts of the rupture while there was no clear correlation in the south at the central and southern parts of the rupture zone. The comparison between the spatial distribution of locked areas and uplift rates provided only a weak correlation for the MIS-9 terraces at the southern part of the rupture. Our results suggest that the northern part of the IIIapel rupture zone may accumulate permanent deformation during megathrust earthquakes. In contrast, accumulation of deformation at the southern part of the rupture may be controlled by activity in the neighboring seismotectonic segment. Broad warping patterns of marine terraces might reflect changes in boundary conditions at interplate depths, such as subduction of seamounts or other oceanic bathymetric features. This analysis highlights the temporal and spatial variability of deformation at convergent plate margins over multiple time scales.

How to cite: Freisleben, R., Jara-Muñoz, J., Melnick, D., and Strecker, M.: Comparing permanent deformation and seismic asperities in the 2015 Illapel earthquake rupture zone, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10637, https://doi.org/10.5194/egusphere-egu2020-10637, 2020