Tectonics

A University of Hawaiʻi at Mānoa postdoctoral fellow took part in a world record for the deepest controlled-source electromagnetic (CSEM) survey of the seafloor. At 5,150 meters (approximately 3.2 miles) below sea level, the record-breaking survey happened above an oceanic trench in the Aleutian-Alaska Subduction Zone (AASZ) on June 6, 2019.
https://www.hawaii.edu/epscor/2019/08/06/record-breaking-survey-investigates-alaskan-ocean-trench/

The Proterozoic (middle-late) rocks of the Pakhal basin (6000 mts thick) situated in the south central part of the peninsular shield, extends through the state of Telangana, Madhya Pradesh and Maharashtra in a general NW-SE direction along the Pranhitha-Godavary valley. The sediments of the basin crop out as two mutually parallel NW-SE trending belts, with about a 40 kms wide stretch of Gandwana sediments separating them. These Proterozoic sediments are divisible broadly into the Pakhal super group, Penganga group and the Sullavai sandstone in that ascending order, each separated from the older unit by an angular unconformity. The Pakhal non-conformably rest over the Archaean basement. The Pakhal super group is divided into the Mallampally group, Mulug group and the Albaka sandstone. (Srinivasa Rao, 1984)

The Mallampally and Mulug group are represented by variable proportions of conglomerate arkose, shale, phyllite, dolomite and quarzite. The sediments were initially folded on NW-SE to NE-SW tending axes and later cross folded on East-West axis. In the south eastern part of the basin the sediments were metamorphosed leading to the development of staurolite, andalusite and garnet in the argillaceous and tremolite and actinolite in the carbonate units.

We present in this paper the results of a geophysical and geochemical survey of self potential, diffuse soil CO2 flux, soil temperature and gas permeability carried out in the Fondi di Baia craters on the western sector of Campi Flegrei caldera, one of the most hazardous active volcano in Italy. Work was aimed at highlighting the small-scale volcano-tectonic structures of this Holocene edifice and at evaluating its state of fracturing, in order to ascertain possible volcanic hazard for future vent reopening. The central sector of Campi Flegrei (Solfatara volcano-Pisciarelli) is indeed the one most affected by ground deformation and intense high-temperature fumarolic activity, nevertheless it cannot be ruled out a future vent opening along the western collapsed margin of the caldera, where Fondi di Baia craters are located. Our results show that the Fondi di Baia craters are characterized by a medium-high release of hydrothermal fluids through fractures that mimic the main volcano-tectonic structures of this portion of the caldera. Moreover, results indicate that, in case of a future volcanic reactivation, these previous structures could as well be possible paths for magma ascent. We provide a first estimate of the total flux of CO2 from Fondi di Baia diffuse degassing structure, quantified in 10.06 ± 1.07 t*d-1.

The numerous landslides which have developed in the mostly Cretaceous to Eocene turbiditic rocks of the Silesian Beskid are genetically and geometrically controlled by bedrock structural features, the Biała Wiseł-ka Landslide Complex being no exception. Its location is in the headwater area of the Wisła River, on the slopes of Mt. Barania Góra (1220 m a.s.l.). The bedrock is represented by flysch strata of the Silesian Nappe (Outer Car-pathian Fold-and-Thrust Belt), or, more specifically, the Upper Cretaceous turbiditic Upper Godula and Lower Istebna Beds of the Godula Thrust Sheet. The research work consisted in their mapping and structural analysis, facilitated by the use of a high-resolution digital elevation model based on LiDAR data. A comparative analysis enabled the determination of the relationships between landslides and the bedrock structure. The study results point to significant roles being played by the joint network, fault systems, the structural arrangement and the li-thology of rock strata in the initiation and evolution of the studied landslide complex. An additional result of the methods applied methods was the identification and characterization of previously unknown fault zones in the study area.

This paper presents the results of analysis of landslides distribution in the Sudetes (SW Poland). Our study was based on the analysis of the LiDAR-data digital elevation model and integrated with investigations of different factors for landslide development. The results of the study showed relationships between the spatial distribution of landslides and geology of their basement. For the areas built by Permo-Mesozoic and late Variscan sedimentary and volcanogenic rocks, the tectonic and lithological factors are predominant for landslide occurrences. The largest landslides have a tectonic affinity and represent a frontal type of geometry. The relationships between geological conditions and mass movements were also confirmed by the constructed landslide susceptibility map of the Sudetes.

Wybrane problemy geologii strukturalnej w południowo-wschodniej części polskiego segmentu Karpat zewnętrznych Punkt 1. Witryłów - pofałdowe dajki klastyczne. Zapis późnej deformacji tektonicznej płaszczowiny skolskiej. Prezentowane stanowisko oligoceńskich warstw menilitowych znajduje się w skarpie wąwozu, w dolinie Sanu. Warstwy czertów, piaskowców i mułowców przecięte są tu dajkami klastycznymi o składzie odpowiadającym niżejległym piaskowcom kliwskim. Dajki klastyczne oraz planarne struktury tektoniczne widoczne w odsłonięciu tj. spękania ciosowe, nasunięcia oraz uskoki stanowią doskonały przykład zapisu schyłkowej, progresywnej deformacji pryzmy akrecyjnej w płaszczowinie skolskiej. Prowadzący: Natalia Radzik, Piotr Strzelecki, Anna Świerczewska, Antek Tokarski. Punkt 2. Dołżyca - strefa nasunięcia wstecznego w mikrotektonicznym obrazie wstęg deformacyjnych. Zaprezentowany zostanie zróżnicowany zapis mikrotektoniki wyrażony we wstęgach deformacyjnych wzdłuż doliny Solinki. Omawiana strefa to miejsce kontaktu centralnego synklinorium karpackiego i strefy przeddukielskiej w obrębie płaszczowiny śląskiej. Prezentowany zapis ma charakter wczesnej deformacji i dotyczy gruboławicowych piaskowców o zróżnicowanej pozycji stratygraficznej i strukturalnej. Zaprezentowane zostaną implikacje dla rozwoju strukturalnego, warunków pogrzebania oraz właściwości zbiornikowych skał wynikające z charakteru badanych wstęg. Prowadzący: Piotr Strzelecki, Natalia Radzik, Anna Świerczewska, Antek Tokarski. Punkt 3. Kamieniołom „Krywe” - problematyka osuwisk strukturalnych w paśmie Otrytu Przykład dużego konsekwentnego osuwiska translacyjnego powstałego w obrębie gruboławicowych piaskowców otryckich warstw krośnieńskich przewarstwionych wkładkami szarych łupków marglistych (oligocen). Osuwiska tego typu są charakterystyczne dla południowych stoków pasma Otrytu a powierzchnie poślizgu rozwijają się przede wszystkim w przewarstwieniach łupkowych. Prezentowane osuwisko jest przykładem wpływu struktury podłoża skalnego (spękań i uskoków) na rozwój ruchów masowych w Karpatach. Zaprezentowany zostanie również ciekawy przekrój poprzeczny przez spiętrzony w wyniku ruchów grawitacyjnych jęzor osuwiskowy. Prowadzący: Jacek Rubinkiewicz, Rafał Sikora, Aleksander Biel.

ABSTRACT The rate at which transient knickpoints propagate through a landscape fundamentally controls the rate of geomorphic response to tectonic and climatic perturbation. Here we present knickpoint retreat rates upstream of active faults for 19 bedrock catchments in Turkey and 11 bedrock catchments in Italy where we have very good constraints on both the magnitude and timing of the tectonic perturbation and where climate histories are well documented. We show that the knickpoints have average retreat rates of between 0.2 and 2 mm/yr for catchments with drainage areas between 6 and 65 km2 and we test whether differences in rock mass strength and catchment size are sufficient to explain this range in retreat rates. Our analysis suggests that even accounting for these two variables, knickpoint propagation velocities differ markedly, and we show that channels crossing faults with higher throw rates have knickpoints that are retreating faster. The dependence of knickpoint retreat velocity on throw rate is at least as important as catchment drainage area. These results indicate, counterintuitively, that landscapes forced by large amplitude tectonic perturbations will have shorter response times than those perturbed by smaller amplitude changes. The link between the knickpoint propagation velocity and throw rate is largely (but not completely) explained by channel narrowing in areas of high uplift rate. Channel steepening upstream of the active faults may explain all of the residual dependency of knickpoint retreat rate on fault throw rate, but only if the slope exponent, n, in the standard stream power model is greater than 1.3. However, we cannot rule out a role for sediment supply in driving enhanced knickpoint retreat rate in addition to the well-documented channel narrowing effect. Finally, we find that mean knickpoints retreat rates in Turkey are only half of those in Italy, for catchments of equivalent size, crossing faults with similar throw rates. This difference in fluvial response time is accounted for by long-term differences in the ratio of precipitation to infiltration in the two areas over the last 1 My.

... 1970; Lowe 1975; Owen 1987; Collinson 1994). As clay-rich sediments become buried they consolidate and become more cohesive, with a corresponding increase in tensile strength. It is within this regime that clastic dykes and sills are able to intrude. ...

The tectono-sedimentary evolution of asymmetric extensional systems driven by the activity of major normal faults or detachments associated with footwall exhumation is often characterized by a sequence of slower, faster, and ultimately again slower subsidence rates in the center of hanging wall half-grabens during their synkinematic and postkinematic evolution. We have studied this specific evolution by the means of 3-D stratigraphic numerical modeling that accounts for the variability of the sediment and water flux combined with climatic and sea level variations, and sediment compaction. The model setup is constrained by observations from the Pannonian back-arc basin of central Europe. Our modeling predicts the formation of low-order tectonic and higher-order sea level and climate-driven transgressive-regressive sedimentary cycles. Furthermore, we model and analyze the autocyclic nature of the depositional systems. Retrograding-prograding cycles are visible on the proximal flank of the half-grabens by their different spatial and temporal expressions, while depocenters record large water depth variations linked to the specific and episodic activity of normal faults and their migration with time. The application to a system of multiple half-grabens in the Pannonian Basin, which are activated in different locations, at different times and with different kinematics, demonstrates a complex interplay between direct sediment sourcing and the sediments' ability to bypass trapping subbasins and paleo-reliefs created by eroded footwalls. Plain Language Summary The formation and evolution of sedimentary basins is of prime interest as they record different Earth processes. The understanding of rifting mechanics and associated evolution of extensional sedimentary basins is also important for the assessment of their potential for georesources including freshwater. The spatial and temporal variabilities of vertical movements in asymmetric extensional systems control landscape evolution coupled to sedimentary and climatic processes. This paper aims to quantify the effect of tectonics and climatic variations on the overall architecture of such basins. Our numerical modeling demonstrates the low-order tectonic and higher-order sea level and climate-driven influence on the sedimentary transport routes and overall architecture. The application of our model in the Pannonian Basin of central Europe shows how tectonic inheritance control sedimentary transport routes.

Extensional basins often show along-strike variability in terms of fault geometries, basement structures, subsidence, and thermal evolution. This is particularly pronounced when extension reactivates preexisting suture zones with opposing dip directions, that is, opposite polarities, which creates wide strike-slip transfer zones. We have studied this extensional variability by means of thermomechanical lithospheric-scale 3-D numerical modeling. We conducted a series of experiments to model the extension of a thick lithosphere simulating a young orogenic area containing segmented suture zones inherited from former opposing subduction polarities, implemented as rheologically weak inclined layers with opposite dips. Numerical experiments demonstrate that the initial subduction sutures are reactivated by two long-lived lithospheric-scale detachment faults, which remain active until the onset of oceanic spreading. The opposite polarity of these faults causes their migration toward each other by asymmetric mantle lithosphere extension and thermal accretion. Crustal kinematics shows the formation of extensional detachment faults and high-offset listric normal faults. These structures undergo gradual tilting during their footwall exhumation, while the rheological weak suture layers are redistributed beneath the crust. The results demonstrate an active interaction along the strike of the system between the two opposite dipping weak zones, where fault segments mechanically interact. During extension, the maximum horizontal fault offset switches the apparent sense of shear in the separating strike-slip transfer zone. This kinematics explain the rapid change in the sense of shear in major strike-slip transfer zones or transform faults, such as observed during the extension of the Pannonian back-arc basin.