Utjecaj mehaničke stratigrafije na deformacijski stil u središnjem dijelu Vanjskih Dinarida: studija kinematskim 2D modeliranjem

The External Dinarides fold-thrust belt formed during Mid-Eocene – Oligocene times by SW-propagating thrusting from the Internal Dinarides towards the Adriatic foreland. Although previously considered as structurally quite uniform, recent work of BALLING et al. (2021) reported along-strike contrasting deformation styles in two structural domains within this fold-thrust belt. The two structural domains with very contrasting deformation styles are separated by the N-S-striking dextral Split–Karlovac Fault, a 250 km long, transpressive transfer fault. The southeastern domain is characterized by a thin-skinned SW-vergent nappe stack in contrast to the northwestern domain, where a set of blind, thick-skinned top-SW thrust duplexes prevail underneath the passive NE-vergent backthrusts. To better understand possible causes that controlled these contrasting along-strike deformation styles, we firstly analysed a spatial-temporal along- and across-strike distribution of Paleo-Mesozoic lithofacies to both sides of the Split-Karlovac Fault. We further estimated the role of mechanical stratigraphy on deformation styles in this part of the fold-thrust belt. This analysis was used to construct a new 2D kinematic forward model across the northwestern backthrust-dominated domain. Our best-fit forward-modelled balanced cross section traversing the central Velebit Mtn. portrays a 75 km wide triangle zone. This zone took up at least 47 km of shortening during Eo-Oligocene times. It comprises a set of thin-skinned NE-vergent backthrusts detached in the upper Paleozoic basement atop a SW-vergent thickskinned antiformal stack detached in the lower Paleozoic Adriatic basement. The NE-vergent backthrusts likely nucleated at lateral facies boundaries related to extensional half grabens that locally formed during Permian to Middle Triassic and Late Jurassic phases of a passive margin extension. During the Eo-Oligocene shortening, the selective inversion of inherited Mesozoic half grabens boundary faults into the NE-vergent backthrusts in the northwestern domain led to the observed along-strike changes in the deformation style of the External Dinarides. Thus, our results indicate that both the variations in the mechanical stratigraphy and the pre-orogenic structural inheritance obtained during rifting and passive margin stages exert control on Eocene–Oligocene contractional structures within the central part of the External Dinarides

Utjecaj mehaničke stratigrafije na deformacijski stil u središnjem dijelu Vanjskih Dinarida: studija kinematskim 2D modeliranjem

The External Dinarides fold-thrust belt formed during Mid-Eocene – Oligocene times by SW-propagating thrusting from the Internal Dinarides towards the Adriatic foreland. Although previously considered as structurally quite uniform, recent work of BALLING et al. (2021) reported along-strike contrasting deformation styles in two structural domains within this fold-thrust belt. The two structural domains with very contrasting deformation styles are separated by the N-S-striking dextral Split–Karlovac Fault, a 250 km long, transpressive transfer fault. The southeastern domain is characterized by a thin-skinned SW-vergent nappe stack in contrast to the northwestern domain, where a set of blind, thick-skinned top-SW thrust duplexes prevail underneath the passive NE-vergent backthrusts. To better understand possible causes that controlled these contrasting along-strike deformation styles, we firstly analysed a spatial-temporal along- and across-strike distribution of Paleo-Mesozoic lithofacies to both sides of the Split-Karlovac Fault. We further estimated the role of mechanical stratigraphy on deformation styles in this part of the fold-thrust belt. This analysis was used to construct a new 2D kinematic forward model across the northwestern backthrust-dominated domain. Our best-fit forward-modelled balanced cross section traversing the central Velebit Mtn. portrays a 75 km wide triangle zone. This zone took up at least 47 km of shortening during Eo-Oligocene times. It comprises a set of thin-skinned NE-vergent backthrusts detached in the upper Paleozoic basement atop a SW-vergent thickskinned antiformal stack detached in the lower Paleozoic Adriatic basement. The NE-vergent backthrusts likely nucleated at lateral facies boundaries related to extensional half grabens that locally formed during Permian to Middle Triassic and Late Jurassic phases of a passive margin extension. During the Eo-Oligocene shortening, the selective inversion of inherited Mesozoic half grabens boundary faults into the NE-vergent backthrusts in the northwestern domain led to the observed along-strike changes in the deformation style of the External Dinarides. Thus, our results indicate that both the variations in the mechanical stratigraphy and the pre-orogenic structural inheritance obtained during rifting and passive margin stages exert control on Eocene–Oligocene contractional structures within the central part of the External Dinarides

Impact of mechanical stratigraphy on deformation style and distribution of seismicity in the central External Dinarides: a 2D forward kinematic modelling study

Abstract The External Dinarides fold-thrust belt formed during Mid-Eocene–Oligocene times by SW-propagating thrusting from the Internal Dinarides towards the Adriatic foreland. Although previously considered as structurally quite uniform, recent work reported along-strike contrasting deformation styles in two structural domains within this fold-thrust belt. The two areas with very contrasting deformation styles are separated by the N–S-striking dextral Split-Karlovac Fault, a 250 km long, transpressive transfer fault. The southeastern domain is characterized by a thin-skinned SW-vergent nappe stack in contrast to the northwestern domain, where a set of blind, thick-skinned top-SW thrust duplexes prevail underneath the passive NE-vergent backthrusts. To better understand why the External Dinarides underwent such contrasting along-strike deformation, we reconsidered a temporal and spatial along- and across-strike distribution of Paleo-Mesozoic lithofacies to both sides of the Split-Karlovac Fault and estimated the role of mechanical stratigraphy on deformation styles in this part of the fold-thrust belt. Therefore, we constructed a new 2D kinematic forward model in the western backthrust-dominated domain. Our best-fit forward-modelled balanced cross section across the central Velebit Mtn. portrays a 75 km wide triangle zone. This zone took up at least 47 km of shortening during Eo-Oligocene times. It comprises a set of thin-skinned NE-vergent backthrusts detached in the upper Paleozoic atop a SW-vergent thick-skinned antiformal stack detached in the lower Paleozoic Adriatic basement. The NE-vergent backthrusts likely nucleated at lateral facies boundaries related to extensional half grabens that locally formed during Middle Triassic and Late Jurassic passive margin extension. During the Eo-Oligocene folding and thrusting, the selective inversion of inherited Mesozoic half grabens boundary faults into the NE-vergent backthrusts in the northwestern domain led to the observed along-strike changes in the deformation style of the External Dinarides. A seismotectonic analysis of instrumentally recorded earthquakes suggests contrasting seismic behaviour along the central and southern Velebit transects within the northwestern structural domain. The central Velebit Mtn. triangle structure appears to currently accommodate dominantly strike-slip motion, with reverse faulting being confined to east of the Split-Karlovac Fault. In contrast, seismicity along the southern Velebit cross section appears to be confined to the structurally lowermost parts of the triangle zone and the foreland, while it´s structurally higher parts are less seismically active. Also, a predominance of reverse faulting along this transect suggests ongoing accommodation of shortening in this part. Our results indicate that both the variations in the mechanical stratigraphy and the pre-orogenic structural inheritance obtained during rifting and passive margin stages exert control on contractional structures within the External Dinarides, including the distribution of present-day seismicity

Potential for the geological storage of CO2 in the Croatian part of the Adriatic offshore

Every country with a history of petroleum exploration has acquired geological knowledge of its sedimentary basins and might therefore make use of a newly emerging resource—as there is the potential to decarbonise energy and industry sectors by geological storage of CO2. To reduce its greenhouse gas emissions and contribute to meeting the Paris agreement targets, Croatia should map this potential. The most prospective region is the SW corner of the Pannonian basin, but there are also offshore opportunities in the Northern and Central Adriatic. Three “geological storage plays” are suggested for detailed exploration in this province. Firstly, there are three small gas fields (Ida, Ika and Marica) with Pliocene and Pleistocene reservoirs suitable for storage and they can be considered as the first option, but only upon expected end of production. Secondly, there are Miocene sediments in the Dugi otok basin whose potential is assessed herein as a regional deep saline aquifer. The third option would be to direct future exploration to anticlines composed of carbonate rocks with primary and secondary porosity, covered with impermeable Miocene to Holocene clastic sediments. Five closed structures of this type were contoured with a large total potential, but data on their reservoir properties allow only theoretical storage capacity estimates at this stage

Post-collisional mantle delamination in the Dinarides implied from staircases of Oligo-Miocene uplifted marine terraces

The Dinarides fold-thrust belt on the Balkan Peninsula resulted from convergence between the Adriatic and Eurasian plates since Mid-Jurassic times. Under the Dinarides, S-wave receiver functions, P-wave tomographic models, and shear-wave splitting data show anomalously thin lithosphere overlying a short down-flexed slab geometry. This geometry suggests a delamination of Adriatic lithosphere. Here, we link the evolution of this continental convergence system to hitherto unreported sets of extensively uplifted Oligocene–Miocene (28–17 Ma) marine terraces preserved at elevations of up to 600 m along the Dinaric coastal range. River incision on either side of the Mediterranean-Black Sea drainage divide is comparable to the amounts of terrace uplift. The preservation of the uplifted terraces implies that the most External Dinarides did not experience substantial deformation other than surface uplift in the Neogene. These observations and the contemporaneous emplacement of igneous rocks (33–22 Ma) in the internal Dinarides suggest that the Oligo-Miocene orogen-wide uplift was driven by post-break-off delamination of the Adriatic lithospheric mantle, this was followed by isostatic readjustment of the remaining crust. Our study details how lithospheric delamination exerts an important control on crustal deformation and that its crustal signature and geomorphic imprint can be preserved for millions of years

Post-collisional mantle delamination in the Dinarides implied from staircases of Oligo-Miocene uplifted marine terraces

Abstract The Dinarides fold-thrust belt on the Balkan Peninsula resulted from convergence between the Adriatic and Eurasian plates since Mid-Jurassic times. Under the Dinarides, S-wave receiver functions, P-wave tomographic models, and shear-wave splitting data show anomalously thin lithosphere overlying a short down-flexed slab geometry. This geometry suggests a delamination of Adriatic lithosphere. Here, we link the evolution of this continental convergence system to hitherto unreported sets of extensively uplifted Oligocene–Miocene (28–17 Ma) marine terraces preserved at elevations of up to 600 m along the Dinaric coastal range. River incision on either side of the Mediterranean-Black Sea drainage divide is comparable to the amounts of terrace uplift. The preservation of the uplifted terraces implies that the most External Dinarides did not experience substantial deformation other than surface uplift in the Neogene. These observations and the contemporaneous emplacement of igneous rocks (33–22 Ma) in the internal Dinarides suggest that the Oligo-Miocene orogen-wide uplift was driven by post-break-off delamination of the Adriatic lithospheric mantle, this was followed by isostatic readjustment of the remaining crust. Our study details how lithospheric delamination exerts an important control on crustal deformation and that its crustal signature and geomorphic imprint can be preserved for millions of years

O potresima u Hrvatskoj

U radu se ukratko opisuje seizmičnost Hrvatske i preliminarne analize zagrebačkog potresa od 22. ožujka 2020