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The Dinarides fold and thrust belt resulted from the collision of the Adriatic Microplate with Eurasia and shows an overall SW-vergent and in-sequence structural architecture. In the Paleocene the ophiolite-bearing internal Dinarides were exclusively affected by crustal shortening. The outward SW propagation of the deformation front reached the eastern Adriatic passive continental margin mainly composed of Mesozoic carbonate platform rocks in Mid-Eocene times. This led to high crustal Mid Eocene to Oligocene shortening and the formation of the external Dinarides. Two balanced crosssections across the external Dinarides show an along-strike contrasting deformation style observed in two orogenic segments separated by the 250 km long dextrally transpressive Split-Karlovac Fault: the southern segment dominated by SW-vergent forethrusts, and the northern segment dominated by NE-vergent backthrusts, located to the SE and NW from the Split-Karlovac Fault, respectively. So far, it is not known why the regionally rather uniform Mesozoic Adriatic carbonate platform sequence had undergone such contrasting along-strike deformation. To improve the understanding of the initiation of the NE-vergent backthrusts and to assess the amount of crustal shortening in the NW segment, a 2D kinematic forward model across the central Velebit Mt. was set up. The Velebit Mt. extends for about 130 km along the eastern Adriatic coast and form a SW-dipping monocline with topographic elevations reaching close to 1800 m. This faultrelated monocline is formed in the hanging wall of a NE-vergent backthrust system. The 2D kinematic forward model approach applied to a pre-deformed lithostratigraphic template scaled to reported stratigraphic thicknesses enabled us to test various geometries and temporal successions of fault activity not only for the Mid Eocene – Oligocene contraction, but also for the Mesozoic passive margin extension. Through an iterative trial-and-error method, we were able to reproduce the present-day deformed reference section across the Velebit Mt. and the Lika Plateau in its northeastern hinterland. Our best-fit balanced kinematic model suggests that the reactivation of Middle Triassic and Upper Jurassic basement-rooted half grabens played a key role in the initiation of the backthrusts. These half grabens were mainly reactivated by hanging wall shortcuts. This inversion of normal faults led to predetermination of the thin-skinned NE-vergent back thrusts, forming the upper part of a complex 68 km wide triangle structure. The structurally lower part comprised of a SW-vergent antiformal stack involving Paleozoic basement. We assessed a crustal shortening for the triangle structure of 47 km and a shortening of 98 km for the entire cross-section. Our results show that the differences in both the lithostratigraphic and Mesozoic halfgrabens along the eastern Adriatic passive margin played a crucial role in the Mid Eocene – Oligocene deformation of the external part of the Dinarides fold and thrust belt, which led to the contrasting along strike deformation styles to the NW and SE of the Split-Karlovac Fault.

The ongoing Petrinja earthquake sequence interests a structurally complex area characterized by the transition between the Dinarides and the Pannonian Basin structural units. The sequence mainshock (December 29, 2020 ; Mw = 6.4) struck in the vicinity of the Petrinja town and caused significant damage in the human and in the natural environments. The preliminary seismological and geodetic analyses indicated a dextral strike-slip NW-SE oriented fault as the event source. Numerous geologic surface deformation patterns have been identified in the aftermath of the main event, including collapsed sinkholes, liquefaction, different forms of landslides, and surface fractures which nature and causative process require further detailed studies. The aim of our contribution is to apply a multitude of different geophysical, geodetic and geologic methodologies to decipher the Petrinja seismogenic fault geometry in the light of its ongoing earthquake sequence. We will show how the different datasets converge in delineating the fault geometry and discuss their diverging aspects and implications. Our preliminary analyses on the geometric and kinematic characteristics of the mainshock (as well as those of the foreshocks and aftershocks) point to an important structural complexity. This aspect helps us to better understand the seismotectonic framework of the Petrinja seismogenic fault and other regional seismogenic faults of similar geologic and geodynamic setting.

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

Detailed outcrop-scale analysis of fault-slip data, in combination with data presented on published geological maps, were used for a reconstruction of the structural architecture and tectonic evolution of the Velebit Mt., the most prominent geomorphological structure in the central part of the External Dinarides in Croatia. The analysis of kinematic indicators recorded by major fault planes indicates the prevalence of dip-slip and top-to-NE motions, verifying that these faults are NE-verging thrusts rather than NE-dipping normal faults as previously thought. Consequently, we challenge earlier tectonic models that interpret the Velebit Mt. structure as a SW-vergent antiformal stack or thrust duplex formed above the major NE-dipping thrust system (TARI KOVAČIĆ & MRINJEK, 1994) or as a complex transpressional structure formed during the late-orogenic escape tectonic phase along an inherited crustal fault zone (GRANDIĆ et al., 2004 ; KORBAR, 2009). Instead, we use the concept of a passive roof duplex within a triangle structure. Thereby, the Velebit structure represents a stack of NE-verging backthrusts formed above a SW-vergent compressional duplex. Our interpretation was recently tested by BALLING et al. (2017) by construction of forward modelled balanced cross sections. Additionally, we analysed a large set of fault-slip data comprising more than 1000 measurements collected in the carbonate breccia exposed along the SW mountain slope at about 60 measurement sites. Curiously, the majority of recorded fault-slip data comprise structures with a normal sense of shear indicating orogen-perpendicular (NE-SW) to orogen-parallel (NW-SE) extension. According to the very good preservation and high frequency of occurrence, these extensional structures may have played an important role in formation of the extremely voluminous carbonate breccia exposed along the SW mountain slope. Accordingly, we propose that these structures resulted from a state of stress characterised by radial extension induced by gravitational collapse and spreading as a result of the uptilting of the SW-dipping Velebit monocline. Therefore, our interpretation is only partly in accordance with KORBAR (2009) who suggested that divergent extension and gravity gliding was a major mechanism in formation of the carbonate Jelar breccia in general.

The Karst Dinarides are a part of the Alpine-Dinarides mountain chain, situated along the NE Adriatic coast, and formed during a mid-Eocene to Oligocene contraction of a thick succession of predominantly carbonates Carboniferous to Eocene rocks. A very interesting, but yet poorly understood lithostratigraphic unit of the Karst Dinarides is a massive Cenozoic carbonate breccia found in their central part, known as Jelar or Velebit breccia. According to the basic geological maps it covers more than 1000 km2, forming several larger outcrop areas (the largest one, along SW slopes of Velebit Mt., covers almost 700 km2) and more than 400 smaller erosional outliers. Data of the thickness on the breccia are limited, indicating a wide range from very thin erosional remnants to more than 500 m thick sequences. Breccia is massive, mostly clast-supported, monomictic to polymictic, non-bedded, without gradation or any other visible arrangement. It contains exclusively carbonate clasts, ranging in size from less than I mm to several centimetres, only sporadically to meter-sized blocks. Clasts are predominantly angular, often tectonically fractured before deposition, and mostly derived from neighbouring rocks, while rare extraclasts originated from overlying, originally younger rocks. Matrix is carbonate, grey or yellowish to reddish, and contains small lithoclasts and recrystallized calcite without fossils or cements indicating a subaqueous deposition. This type of breccia is usually very tightly connected to cataclastic breccia, formed by an intense fracturing of neighbouring limestones (some areas designated on maps as Cenozoic carbonate breccia are predominantly represented by cataclastic breccia). Most of the studied contacts between the breccia and neighbouring carbonate rocks exhibit up to sev¬eral meters wide gradual transition from intact limestones and fractured limestones to cataclastic breccia and finally monomictic to polymictic breccia. In addition, at some outcrops small conglomerate bodies have been found within breccia, as well as karstified breccia and zones fractured by subsequent tectonics. Breccia could be found in different tectonic settings: the Velebit breccia s.s. covers the SW slopes of the Velebit Mt. in the hanging-wall of the SW-dipping Lika thrust fault, while other occurrences could be found along regional reverse faults, hinges of overturned anticlines or in the form of erosional remnants of previously much wider breccia sheets. Significantly, all these positions are characterized by NE-verging thrusts and folds, which are less common in the Dinarides. This fact contradicts to the traditional interpreta¬tion of the deposits as talus breccia shed from the front of inferred SW-propagating thrust faults. The breccia was probably formed by an intense in-situ fracturing, controlled by extension in apical parts of anticlines, resulting in disintegration of carbonate rocks into cm-sized clasts within km-wide zones, followed by a deposition by rockfall mechanisms into a complex system of deep fractures, while some clasts were transported by surficial processes. Breccia deposits were subsequently tectonized, diageneti- cally altered, intensely karstified and denuded during the long post-emplacement exposure, therefore result¬ing in a present day very complex appearance. Acknowledgment This work was supported by Croatian Science Foundation project IP-2014-09-9666.

This study was undertaken to obtain the thermochronological data to unravel the thermal history of the central part of the Karst Dinarides, exposed along the NE Adriatic coast in the Velebit Mt. and neighboring areas. The lower part of the sedimentary section (Upper Carboniferous to Triassic), covered by a succession of Mesozoic carbonates has been studied by an apatite fission track (AFT) and apatite and zircon (U-Th- Sm)/He thermochronology. The ZHe ages are between 80 and 70 Ma (full range is from 257 to 41 Ma), while the actinide content ranges from 133 to 874 ppm eU. No correlation between the ZHe ages and the eU content can be detected. Reproducibility of replicates is good for the majority of samples. The ZHe ages increase in the SE structural domains. AFT ages are younger than the corresponding stratigraphic ages and yield a single population of grain ages. Central ages range from 81 to 24 Ma1 with the vast majority clustering between 50 and 30 Ma. The mean track length varies from 14.4 to 11.9 pm, with the vast majority around 13 pm. Due to the rela¬tively low uranium content only six samples yielded the track numbers > 50. Considering samples, where the track number is sufficient and the track length > 12.9 pm with narrow distribution (SD < 1.6) we can assume that they experienced after the burial a slow cooling through the apatite partial annealing zone (PAZ ~60-120 0C). AFT ages plotted against their mean track lengths show a classic 3/4 boomerang trend, representing the progressive overprinting of an older component of tracks by a heating in a single dominant palaeothermal event. Older samples (> 60 Ma) have longer mean track lengths ; these decrease with a de¬creasing age (60-55 Ma), increase again in samples of 55-30 Ma. This trend may suggest rapid cooling at 50-30 Ma. The measured Dpars range from 2.5 to 1.5 pm, indicating that samples have a variable annealing kinetics. There is no correlation between the AFT ages and the elevation of the samples in general. AHe ages corrected for the alpha ejection showed the age range from 53 to 28 Ma, with eU contents that range from 7 to 88 ppm and the majority of ages are clustered around 30 Ma. No correlation between the AHe ages and the eU content can be detected. All AFT ages are younger than the corresponding ZHe ages and overlap within an uncertainty with the AHe ages, which is in agreement with the closure temperatures of these thermochronometers. Rapid exhu-mation started in the studied structural domains between 80 and 35 Ma, Le. between the Campanian and the end of Eocene, followed in some domains by a younger exhumation and cooling pulse. Acknowledgments. This study was funded by the project no. N307 475238 granted to Marek Lewandowski by the Polish Ministry of Science and Higher Education, and in part by the Croatian Science Foundation project IP-2014-09-9666. We thank Marta Mileusnic for her help during the field work.

The long-lasting convergence between the European and Adriatic plate led to the formation of the Dinar- ides fold and thrust belt. The Cretaceous deformation of the Internal Dinarides, composed by ophiolite-bar- ing nappes, is older than the mid Eocene deformation of the External Dinarides. The later consists mainly of shallow marine Mesozoic and Cenozoic carbonate platform rocks. Besides the overall younging trend of the start of the deformation from the internal to the external part, the Dinarides show a very prominent NW-SE “Dinaric” strike of the main folds and faults. However, a large-scale dextral strike-slip fault, the Split-Karlovac-Fault (SKF) striking N-S is interrupted this homogenous deformation pattern within the Ex¬ternal Dinarides. Within the most external part, the fault changed its strike to the “Dinaric” NW-SE strike and its kinematics turned to a pure top-SW thrusting. In close proximity to this change of fault kinematics, most of the heterogeneous 2 km thick mid-Eocene to late Oligocene sedimentary sequence is exposed - the Promina Beds. These beds are syn-tectonic and date the latest major deformation event within the Exter¬nal Dinarides and cover older Mesozoic and Cenozoic platform carbonate rocks in a progressive angular unconformity. Former sedimentological studies stated that the Promina Beds show an overall trend from deeper over shallow marine to fluvial depositional conditions, documenting the evolution from an under¬filled to an overfilled basin. The overall tectonic mechanism for the subsiding of the Promina Basin is a matter of debate, whether the accommodation space was created by a subsiding piggyback basin or in a flexural foreland basin setting. To validate one of the both tectonic settings, we have forward- and backward-modeled three balanced cross-sections on both sides of the SKF. Interestingly, the SKF marks a paleo-facies transition from a hiatus in the west to Permian evaporites in the east. The presence vs. absence of Permian evaporites led to areas of a contrasting style of deformation. The deformation in the western non-evaporitic segment of the SKF is characterized by a SW-vergent duplex system, which expands to the NW and is associated with a large- scale NE-vergent back thrust. In contrast, within the eastern segment the evaporites served as a main de¬tachment, which is used to tectonically double the entire carbonate platform by a SW-vergent nappe stack. Our results show, that the complex and contrasting hinterland deformation is related partly to the pres-ence of evaporites, leading to a nappe stack in the eastern segment, which produced a lithosphere flexure and enough subsidence. This favours the flexural foreland basin hypothesis for the origin of the Promina Basin, because most of the present-day outcropping sediments can be solely found in a close proximity to this eastern nappe stack. The Promina Beds solely contain carbonate platform rocks, proving that the catch¬ment did not substantial changed throughout time.

The Dinarides fold-and-thrust belt on the Balkan Peninsula records the long-lasting history of convergence between the European and the Adriatic plates. The Internal Dinarides are composed of composite ophiolite-bearing nappes, whereas the External Dinarides largely consist of Mesozoic and Paleogene shallow marine Adriatic Carbonate Platform (AdCP) rocks. Due to numerous paleontological studies the chronostratigraphic evolution of the AdCP is well known. However, kinematics, timing, and in some places even the geometry of Cenozoic deformation of the AdCP (i. e. the formation of the External Dinarides) are poorly constrained due to the lack of siliciclastic deposits suitable for dating of deformational events/phases. Consequently, neither exhumation rates nor deformation rates based on low-temperature thermochronology are yet known in this part of the Dinarides. However, the presence of different types of syn-depositional and tectonic breccia, in particular those outcropping over large areas on both sides of the Velebit Mts., could help in constraining the timing of Cenozoic deformational events. For this purpose, besides the definition of age and formation mechanisms of these breccia, their structural position is of crucial importance. To show the different structural postions we described the different breccia in the field and integrated them into a kinematic forward model of the Velebit Mts, an up to 1800 m high mountain range along the Adriatic coast. The geologically most viable, kinematically forward modelled cross-section is based on geological maps, dip data, four boreholes, an unpublished cross-section and fault kinematic data ; the latter revealing that the Velebit structure is controlled by a major NE vergent back thrust. In the northwestern part of the Velebit hinterland, a mostly monomict breccia conformably overlaying Jurassic and Cretaceous carbonates is widely exposed. Based on its structural position that is confined to the footwall of the major NE vergent back thrust and its petrographic characteristics, we interpret this breccia to represent tectonically reworked material mostly derived from lithologies in the footwall of the back-thrust. In contrast, the foreland-facing SW slope of the Velebit Mts. is characterised by the presence of mostly polymict breccia, known as Velebit breccia. Taking its structural position and its petrographic composition into account, this breccia is interpreted as consisting of prevailingly talus and fill-up deposits of a flexural foreland basin that formed during late Paleogene times due to the SW advancing nappe stacking. Our kinematic forward model suggests that both the cataclastic and the talus breccia must have formed at the same time, because their formation is directly related to shortening and uplift of the Velebit structure. Additionally, we found two types of much older intraformational breccia: Triassic intraformational breccia located in the hanging wall of Triassic normal faults and Cretaceous intraformational breccia, which is not associated to any local structure and hence only reflects pre-contractional emersion phase(s). Our study underlines that a precise distinction of the structural position and the formation mechanisms of seemingly monotonous, but genetically different carbonate breccia with respect to major km-scale faults and fault-related folds, are crucially important to gain an improved understanding of the kinematics and timing of deformation in carbonate-dominated thrust belt portions.

Mt. Velebit is the most prominent geomorphological structure in the central part of the External Dinarides fold-thrust belt formed by contraction along the eastern margin of the Adriatic plate during Cenozoic convergence between the Adriatic and European plates. Detailed outcrop-scale analysis of fault-slip data were used in evaluation of existing tectonic models, reconstruction of the present-day structural architecture and tectonic evolution of the mountain. Our analysis shows the prevalence of dip-slip and top-to-NE motions along major Velebit’s faults, verifying that these faults are NE-verging thrusts and not NE-dipping normal faults as previously thought. Consequently, we also challenge earlier tectonic models that interpret the Mt. Velebit as a SW-vergent antiformal stack or thrust duplex formed above the major NE-dipping thrust system. Our data rather validate the concept of a passive roof duplex recently tested by Balling et al. (2017) by the construction of forward modelled balanced cross sections. Based on orientation and kinematic compatibility criteria of recorded fault-slip data, we separated six groups of conjugate fault sets used for assessing paleostress directions. Relative chronology between analysed sets and separated groups is partly defined. Presumably the oldest two groups contain fault sets with prevailing dip-slip and reverse motions: a first one is composed of antithetic NNW-striking sets that indicate the ENE–WSW trending contraction ; the second group contains a WNW-dipping set, which indicates WNW-ESE trending contraction. Structures of both groups strike parallel and slightly oblique to the structural grain and the mountain front. They are thus supposed to have formed during the major contractional tectonic phase in this part of the External Dinarides. Most of the recorded fault-slip data comprise structures with a normal sense of shear. These are separated into three groups: the most robust subgroup is composed of NW-striking antithetic fault sets indicating NE-SW trending extension ; a second group comprises NNE-striking antithetic sets, which show WNW–ESE extension, while a third group includes W-striking antithetic sets related to a N–S extension. Although separated into three kinematically homogeneous subgroups, these structures possibly resulted from one and the same state of stress, characterised by radial extension that according to good preservation and frequency of occurrence might play an important role in the formation of extremely voluminous carbonate breccia exposed along the SW slope of the mountain. The remaining group of faults comprises sets of subvertical, conjugate NW-striking dextral and NE-striking sinistral faults, which indicate N–S trending contraction. Outcrop- to map-scale overprinting relationships, suggest these to be the youngest brittle deformation structures in the study area. Acknowledgements. This research was financially supported by the Croatian Science Foundation, Grant no. IP-2014-09-9666. REFERENCES Balling, P., Tomljenović, B., Schmid, S.M., Ustaszewski, K. 2017. Contrasting deformation styles across the Split-Karlovac Fault (External Dinarides) induced by reactivation of pre-existing structures. In: Šarić, K., Prelević, D., Sudar, M. & Cvetković, V. (eds.): 13th Workshop on Alpine Geological Studies, Abstracts, Uni. Belgrade, Belgrade.

Mt. Velebit lies in the central part of external Dinarides formed by thrusting along the eastern margin of the Adriatic plate during Cenozoic convergence between the Adriatic and European plates. At present, the Adria–Europe convergence between Adriatic offshore area and Pannonian Basin amounts to 2–5 mm/yr and induces prevailingly a compressional stress regime across the external Dinarides, with predominantly N–S to NE–SW trending compression in the northwestern and southeastern parts, respectively. This stress partitioning is confirmed by the seismicity that is not uniformly distributed across the fold-thrust belt, being also variable in intensity and in kinematics of seismogenic sources as indicated by focal mechanisms of instrumentally recorded earthquakes. In the NW part of external Dinarides in Slovenia and in the Bay of Kvarner the ongoing seismo-tectonic activity is dominantly released along NW-striking Plio-Pleistocene dextral and dextral-reverse faults, which cut across the Eocene/Oligocene thrust faults (e.g. Moulin et al., 2016). On the other hand, in the Adriatic offshore and external Dinarides SE of Zadar, the ongoing seismicity is controlled by an orogen perpendicular NE–SW trending compression mostly accommodated by SW-verging Dinaridic thrust faults, only locally associated with strike-slip motions. The aforementioned parts of the external Dinarides are separated by Mt. Velebit, the most prominent geomorphological structure, which extends in NW–SE direction for ca. 140 km along the Adriatic coastline. Surprisingly, the mountain and its hinterland are characterized by conspicuously low instrumental seismicity, despite of a hypothetical NE-dipping Velebit thrust fault that is supposed to extend all along the SW front of the mountain (Herak and Bahun, 1979 ; Tari Kovačić and Mrinjek, 1994), and which is considered as a composite seismogenic source capable to generate earthquakes of M 6.5 (Kastelic et al. 2013). In order to characterise the ongoing seismicity and potential seismogenic sources of the Mt. Velebit area in more detail, a multidisciplinary seismological and tectonic project is undertaken (“VELEBIT: from Top to Bottom” ; http://www.pmf.unizg.hr/geof/znanost/seizmologija/velebit), among others addressing the questions about structural architecture, tectonic history and the present-day stress regime in this area. Here we present preliminary results of kinematic analysis of outcrop-scale shear joint/fault-slip data collected on more than 1400 locations in the Mt. Velebit area, aimed at the reconstruction of brittle deformation stages and related paleostress fields in the tectonic history of this area. Until now we have processed data collected in the NW part of the mountain (the Senj-Prizna section) measured in the Velebit breccia, a peculiar lithostratigraphic unit of post-Mid-Eocene age that crops out all along the SW mountain front. Based on orientation and kinematic compatibility criteria, we have separated six groups composed of conjugate fault/shear joint sets used for calculation of paleostress fields. Relative chronology between analysed sets and separated groups is only partly defined, and hence they are described here based on their kinematics and calculated paleostress fields. Two less frequent groups comprise fault/shear sets with prevailing dip-slip and reverse motions: a first one is composed of antithetic NNW-striking sets with prevalence of WSW-dipping planes and top-to-ENE motion that indicate the ENE–WSW trending compression ; a second one comprises WNW-dipping reverse fault/shear joint set which define WNW-ESE trending compression. Structures of both these groups strike parallel and slightly oblique to the structural grain and the mountain front in the NW part of the Velebit and thus are supposed to form during the major compressional tectonic phase in this part of external Dinarides. However, by far the most frequent fault-slip data are fault/shear joint structures indicating a normal sense of slip, separated so far into three groups based on their orientation: the most numerous group is composed of NW-striking antithetic fault/shear joint sets that indicate NE-SW trending extension ; a second group comprises NNE-striking antithetic fault/shear joint sets, which indicate the WNW–ESE trending extension, while a third group of normal fault/shear joints includes W-striking antithetic sets that define the N–S trending extension. However, although separated into three kinematically homogeneous groups, these structures possibly resulted from one and the same state of stress characterised by radial extension that according to extremely good preservation and frequency of occurrence of these structures might play an important role in the formation of the Velebit breccia. The remaining group of fault/shear joint structures comprises a subvertical conjugate pair composed of NW-striking dextral and NE-striking sinistral sets that indicate N–S trending compression. Based on overprinting outcrop- to map-scale relationships, this group of strike-slip faults is considered to be the youngest brittle deformation structures in the study area. In addition to this, we performed a detailed outcrop-scale analysis along the Lika and Brušane-Oštarije fault zones aimed at the collection of shear-sense indicators used for the reconstruction of the kinematic history of these faults. Our analysis shows the prevalence of dip-slip and top-to-NE motions along both faults, that together with the SW dipping direction defined by field observations and map-scale relationships shown on the 1:100’000 scale sheets of Basic Geological Map of Yugoslavia (Sokač et al., 1974 ; Šušnjar et al., 1973), led us to propose the working hypothesis, which presumes these are NE-verging thrusts/reverse faults and not the NE-dipping normal faults as previously thought. Consequently, we also challenge earlier tectonic models that interpret the Mt. Velebit structure as a SW-vergent antiformal stack or thrust duplex formed above the major NE-dipping thrust system. Rather we apply the concept of a passive roof duplex that was recently tested by Balling et al. (2017) by the construction of forward modelled balanced cross sections. The passive roof duplex model can explain, at least partly, the aseismic behaviour of the SW-dipping Velebit thrusts since they ride passively over the underlying duplex wedge envisaged at a depth between 10 to 15 km.

Strukturno-geološkim istraživanjima načinjenim tijekom 2013.–2015. godine prikupljeni su i u GIS bazu podataka arhivirani podaci o orijentaciji i prostornom rasporedu pukotina i rasjeda s 276 lokacija raspoređenih u 11 istraživačkih poligona u NP Sjeverni Velebit i okolnom području. Istraživanja su provedena u cilju odredbe glavnih pukotinskih i rasjednih setova, njihove relativne starosti i proračuna režima paleonaprezanja u kojima su nastali, kao doprinos rekonstrukciji tektogeneze i morfogeneze Velebita. Među pukotinama bez vidljivih pokazatelja pomaka izdvojena su četiri dominantna seta. Najdominantniji set je pružanja SZ–JI, odnosno paralelno s pružanjem slojeva u krilima Apatišanske i Štirovačke antiklinale. S obzirom na pružanje i prostorni raspored, taj set pukotina odgovara onom koji očekivano nastaje u zonama maksimalne zakrivljenosti antiklinala te dijelom i u njihovim krilima u završnom stadiju boranja zbog lokalne koncentracije vlačnih naprezanja u konveksnim dijelovima bora. Ovaj set pukotina je u pravilu otvoren i zjapeći pa doprinosi izraženijoj koroziji i dubokom okršavanju karbonatnih stijena. Izdvojena su i dva dijagonalna i jedan poprečan pukotinski set u odnosu na pružanje Apatišanske i Štirovačke antiklinale za koje se pretpostavlja da su nastali već u početnom stadiju boranja naslaga i to dijagonalno, odnosno paralelno pružanju najvećeg vektora regionalnog režima kompresijskog naprezanja. Po kriteriju kinematske kompatibilnosti, među pukotinama s vidljivim pokazateljima pomaka izdvojene su smične pukotine nastale u kompresijskom, ekstenzijskom i transpresijsko–transtenzijskom režimu paleonaprezanja. Postanak smičnih pukotina u kompresijskom režimu naprezanja s najvećim vektorom poprečnim na pružanje Apatišanske antiklinale pretpostavljen je tijekom glavne tektonske faze u ovom dijelu Dinarida krajem eocena, dok za smične pukotine nastale u režimu paleonaprezanja koji obilježava radijalna ekstenzija nije pouzdano utvrđeno jesu li nastale kao posljedica sinorogenetske ekstenzije, gravitacije ili postorogenetske ekstenzije koja je moguće uslijedila nakon glavne kompresijske faze u ovom dijelu Dinarida. Podaci o sustavu pukotina i rasjeda prikupljeni u suradnji s djelatnicima i uz financijsku potporu NP Sjeverni Velebit također su korišteni i u analizi i rekonstrukciji paleonaprezanja za cjelokupno područje Velebita, u kombinaciji s podacima prikupljenim terenskim istraživanjima koja je financirala Hrvatska zaklada za znanost projektom IP-2014-09-9666.

The deformation was predated and post-dated by two phases of contraction. The Oligo-cene - Early Miocene phase of contraction took place during the final stages of the Dinaric colli- sion and was related to the onset of deposition in the basin. The post-Middle Miocene phase of contraction inverted the basin fill by reactivat-ing the earlier basal listric detachment. This event is correlated with the regional indenta-tion of the Adriatic continental unit.

The southern part of the Adriatic offshore in Croatia was only partially covered with vintage 2D seismic data, mostly near to the coast line and in the vicinity of larger islands. Recently, however, two independent seismic acquisitions have been conducted by INA (2012) and Spectrum (2013) that beside significantly better imaging of structures, resulted in coverage of previously unexplored parts of the South Adriatic basin, thus providing a new insight into structural styles and tectonics in this part of the Mediterranean. First studies show that compressional structures, which predominate in coastline and hinterland area of the fold-thrust belt of the Dinarides gradually turn towards the west into prevailing halokinetic structures controlled by deformation of Triassic salt. In the southern part of the study area the most prominent halokinetic structures are aligned along the NW-SE trending South Adriatic Ridge (SAR) formed ahead of the SW-verging fold-thrust belt of the Dinarides. The SAR comprises a set of salt anticlines and intervening synclines that gradually increase in height towards the NW and merge into the belt of salt diapirs concentrated around the Palagruža High. Onset of anticlines growth in the SAR took place, at least locally, already during Jurassic, and continued to growth during Cretaceous, Oligo-Miocene and locally even in Pliocene times. In the Central Adriatic, compressional tectonics with prevailing southwest-verging thrusting provoked intensive salt flowage that locally resulted in diapirism, salt extrusion, piercing and collapse structures. Almost as a rule, halokinetic structures are associated with fractures and normal faults well developed in younger Mesozoic carbonate and Cenozoic clastic sequences and are used as pathways for gas and fluid migration, clearly documented by numerous gas chimneys and bright spots developed above and around these halokinetic structures.

The long-lasting convergence between the European, African and Adriatic Plates led to the deformation of the Dinarides fold and thrust belt. This orogen is subdivided into the internal and external Dinarides. The internal part is composed by composite ophiolitic nappes, whereas the external part consists of several thrust sheets of mainly Mesozoic to Paleogene shallow marine Adriatic Carbonate Platform rocks. The presence of Mid-Eocene to Mid-Miocene syntectonic deposits defines the time interval of SW directed folding and thrusting. Here Triassic and Late Cretaceous evaporitic intercalations serve as main detachment horizons in the external Dinarides, resulting in a NW-SE strike, which can be traced from Slovenia to Albania. However, the exact amount of total shortening and its Neogene component is unknown. To tackle this issue we balanced two unpublished cross-sections across external Dinarides. Furthermore, we investigated several Miocene wedge-top basins with respect to their substratum. These restricted intra-montane basins were filled with up to 500 m of lacustrine limestones. Field observations show that these basins are not fault bounded and passively uplifted by much deeper faults. This is supported by the analysis of longitudinal river profiles, which show that major knickpoints in this area are immobile and are hence rather related to erosional contrast between different lithologies. This, in turn, implies that the basin boundaries underwent insignificant deformation. Our balanced sections strongly support the assumption that the total amount of shortening within the study area is highly variable alongstrike. In the northern profile we assessed a total shortening of ~60 km (38%), whereas in the southern profile a minimum shortening of ~130 km (88%) was estimated. The high variation of shortening amounts is strongly affected by the presence of a largescale dextral transpressive strike-slip fault, the Split-Karlovac Fault. This fault also seems to actively accommodate seismogenic strain. This is suggested by the pronounced seismic moment release that spatially coincides with the SE end of the Split-Karlovac Fault. The fact that the great majority of earthquakes along the southern profile show reverse faulting mechanisms, implies that the strain field remained unchanged since the onset of folding and thrusting in Paleogene times.

U periodu od 05. do 09. srpnja 2016. održana je stručna geološka ekskurzija na temu tektonskog tektonske evolucije Jadranske karbonatne platforme te stvaranja slijeda naslaga kroz mezozoik i paleogen. Geološka ekskurzija bila je organizirana za studente diplomskog studija Instituta polytechnique LaSalle Beauvais (Francuska) pod pokroviteljstvom AAPG, Institut polytechnique LaSalle Beauvais, France, Rudarsko-geološko-naftnog fakulteta Sveučilišta u Zagrebu te Nacionalnog parka Sjeverni Velebit. Kroz pet dana ekskurzije studenti su upoznati s tektonskom evolucijom i litostratigrafskim razvojem naslaga unutrašnjih i vanjskih Dinarida odnosno na tipskim lokalitetima na Medvednici, Velebitu te Istri.

U radu su predstavljeni novi podaci o P-T evoluciji i vremenu metamorfizma u Slavonskim planinama. Za detaljnije informacije kontaktirati na drbalen@geol.pmf.hr

U okviru diplomskih radova „Geološko kartiranje i rekonstrukcija geološke građe okolice Skrada“ te „Petrološke i stratigrafske značajke stijena okolice Skrada“ detaljno je istražena geološka građa središnjeg dijela Gorskog kotara, okolice Skrada. Glavni cilj istraživanja bio je litološki i stratigrafski definirati stijene na istraživanom području i njihove strukturne odnose. Na temelju rezultata dobivenih geološkim kartiranjem i laboratorijskim istraživanjem, konstruirana je geološka karta u mjerilu 1:20.000 s pripadajućim geološkim profilima i geološkim 3D modelom.

During recent investigations the most complete succession of Kimmeridgian deeper marine deposits has been documented at the slopes of Mt. Poštak, where it is visible that deposits from the Lemeš locality correspond to the upper part of the complete succession. Therefore new informal stratigraphic unit Poštak is proposed composed of three members: Rastičevo, Dimići and Lemeš. Deposits underlying Poštak unit are of the Oxfordian age, and are composed of thick-bedded light brown oncoid-peloid-bioclastic limestones composed of algal-balls oncoids, rounded intraclasts, peloids, gastropods, bivalves, small benthic foraminifera and abundant micrite matrix. These limestones were accumulated in the low-energy shallow subtidal. (A) Lower part of the Poštak unit, the Rastičevo member, is composed of alternation of light-brown thick-bedded limestones with rare bivalve and echinoderm bioclasts and thin intraclastic-peloid-skeletal intercalations. These deposits of probably Lower Kimmeridgian age were deposited in newly formed intraplatform trough connected to the open sea. (B) Middle part of the Poštak unit, the Dimići member, is characterized by alternation of light grey and greenish-grey limestones with radiolaria and dark grey, thin-bedded to laminated, mostly recrystallized radiolarian limestones enriched in organic contents. They usually comprise numerous greybrown chert layers and/or nodules with numerous radiolarians infilled by microquartz. Frequent fractures, fissures and microstylolites are commonly infilled by dark organic matter. Laminated limestones have significantly higher total organic contents than interbedded thicker light grey and greenish-grey limestone beds. These middle Kimmeridgian rocks were deposited in deepest parts of the intraplatform trough, and therefore are spatially restricted. (C) Upper part of the Poštak unit, the Lemeš member, is composed of well-bedded light grey to light brown limestones with rare chert nodules. They contain calcitized radiolaria, ammonites, aptichi, pelecypods, gastropods, echinoids, planktonic foraminifera, rare belemnites and finely dispersed or within stylolites and fissures concentrated organic matter. Towards the younger parts of the unit there are gradually more and more layers comprising material transported from the contemporaneous shallow-marine environments, and these layers are becoming thicker. Limestones of Lemeš member were deposited during the gradual infilling of the intraplatform trough, but planktonic fauna, especially relatively frequent layers with ammonites of Upper Kimmeridgian to Lower Tithonian age, and indicate still preserved connection with the open sea. Overlying Tithonian deposits are not present at the Poštak Mt., since Poštak unit limestones are in tectonic contact with the Lower Cretaceous deposits – wide contact zone is infilled by polymictic carbonate breccia corresponding to Velebit (‘Jelar’) breccia. According to the detailed geochemical investigation the fine-grained, laminated limestones of Dimici member have an excellent generation potential and represent very good to excellent oil-prone source rocks. Organic matter content is between 0.35 and 11.9%, in average 2.97% TOC. Petroleum potential is good (between 1.17 and 67.00 mg HC/g rock, in average 18.25 mg HC/g rock). Organic facies AB/B (after Jones, 1984, 1987) is determined. It is characterized with high organic matter content, excellent hydrocarbon potential and high transformation ratio. Type II kerogen dominates. Occasionally, the type I kerogen is present as well. According to microsolubility and strong yellow to yellow-orange fluorescence effect, organic matter is a mixture of algal, bacterially degraded kerogen and migrated bitumen. Amorphous organic matter gradually changes from lamalginite to bituminite I and finally to organo-bituminous-mineral groundmass, i.e. to matrix bituminite. Solid bitumen is incorporated in all structural types. Phytoplankton is represented by prasinophycean phycomata and dinoflagellate cysts. Throughout the geological columns quantitative variations in cyanobacterial and liptinite/liptodetrinite content are microscopically observed. Variations in C27 and C29 regular sterane were documented as well. Bitumen reflectance is in the range from 0.15 to 0.30% Ro (asphaltite group). Organic facies AB/B is characterized with high organic sulfur content (up to 10%). Stable carbon isotope values are in range from 13C -27.79 to -24.65‰ in kerogen and from -29.53 to -25.55‰ in bitumen. According to maturity parameters (Tmax, PI, TAI, fluorescence color, vitrinite reflectance, bitumen reflectance, biomarker maturity parameters M/H, 22S/(22S+22R), Rc, Rm(MDR), 20S/(20S+20R), Ts/Tm), the organic facies AB/B, i.e. the source rocks of Poštak area generally reach onset of oil generation.

During the Late Oxfordian and Early Kimmeridgian the intraplatform Lemeš trough was formed in the area of todays Lika, Western Bosnia and Herzegovina and Northern Dalmatia, which had continuous connection with the open sea. Deeper marine 'Lemeš Beds' were described in 1909 by Schubert from the Lemeš pass on the Svilaja Mt. During recent investigations the most complete succession of Kimmeridgian deeper marine deposits has been documented at the slopes of the Poštak Mt., where it is clear that deposits from the Lemeš locality correspond to the upper part of the complete succession. Therefore, a new informal lithostratigraphic unit named Poštak is proposed ; composed of three members: Rastičevo, Dimići and Lemeš. The Rastičevo member is composed of alternation of light-brown thick-bedded limestones with rare bivalve and echinoderm bioclasts and thin intraclastic-peloid-skeletal intercalations. These deposits of probably Lower Kimmeridgian age were deposited in newly formed intraplatform trough connected to the open sea. The Dimići member is characterized by alternation of light grey and greenish-grey limestones with radiolaria and dark grey, thin-bedded to laminated, mostly recrystallized radiolarian limestones enriched in organic contents. These middle Kimmeridgian rocks were deposited in the deepest parts of the intraplatform trough, and therefore are spatially restricted. The Lemeš member is composed of well-bedded light grey to light brown limestones with rare chert nodules. Limestones of Lemeš member were deposited during the gradual infilling of the intraplatform trough, but planktonic fauna, especially relatively frequent layers with ammonites of the Upper Kimmeridgian to Lower Tithonian age indicate still preserved connection with the open sea. The objective of this work is detail organic geochemical characterization of the Dimići member. Based on the integration of analytical data performed on more than hundred samples organic facies AB/B (after Jones, 1987) is recognized. Organic facies is characterized with high organic matter content (from 0.35 to 11.9%, in average 2.97% TOC), excellent hydrocarbon potential (between 1.17 and 67.00 mg HC/g rock, in average 18.25 mg HC/g rock) and high transformation ratio. Type II kerogen dominates in the organic-rich laminated limestones. Occasionally, the type I kerogen is present as well. Organic matter is a mixture of algal, bacterially degraded kerogen and migrated bitumen. Amorphous organic matter gradually changes from lamalginite to bituminite I and finally to organo-bituminous-mineral groundmass, i.e. to matrix bituminite. Solid bitumen is incorporated in all structural types. Phytoplankton is represented by prasinophycean phycomata and dinoflagellate cysts. Throughout the geological sections quantitative variations in cyanobacterial and liptinite/liptodetrinite content are microscopically observed. Variations in C27 and C29 regular sterane were documented as well. Bitumen reflectance is in the range from 0.15 to 0.30% Ro (asphaltite group). Organic facies is characterized with high organic sulfur content (from 6 to 10%). Stable carbon isotope values are in range from 13C -27.79 to -24.65‰ in kerogen and from -29.53 to -25.55‰ in bitumen. These values are common in the Jurassic rocks and are generally attributed to the specific algal and bacterial lipids, as well as to the developed water anoxia. The Upper Jurassic fine-grained, laminated limestones have an excellent generation potential and represent very good to excellent oil-prone source rocks. According to maturity parameters (Tmax, PI, TAI, fluorescence color, vitrinite reflectance, bitumen reflectance, biomarker maturity parameters M/H, 22S/(22S+22R), Rc, Rm(MDR), 20S/(20S+20R), Ts/Tm), the organic facies AB/B generally reached onset of oil generation. Migrabitumen, which fill fissures, cavities and pores in the rocks, is classified as the natural asphalt, being the product of early generation from sulfur and organic rich kerogen. Deposition of these dark organic-rich laminated limestones with cherts occurred in the low energy environments within intraplatform trough. Water stratification and bottom waters euxinia were occasionally disturbed by inflow of the open sea water masses. The laminated organic matter in a form of lamalginite was deposited in calm, stable environment with developed water mass stratification under oxygen–depleted conditions. In relatively disturbed unstable conditions organic matter deposited as lamalginite became decomposed and bacterially degraded, leading to a gradual transition into bituminite I and finally into organo-bituminous-mineral groundmass, matrix bituminite. According to available geological data original dimensions of the Lemeš trough, in which the source rock was deposited, can not be reasonably estimated. Preserved volume of Dimići member is low, discovered on a small number of sites with respect to presumed total area of the trough sediments. Deposits are subsequently significantly tectonically disintegrated and are recently found in several structural units separated by thrust and strike-slip faults with displacements in tens of kilometers. In order to estimate the real perspective of further hydrocarbon exploration in this area and evaluation of petroleum systems, based on proven source rock characteristics and source rock-bitumen correlation, the results should be verified and supplemented by geophysical measurements and potential exploration drillings.

Relief is often classified as polyphasic phenomena, which show multiple tectonic overprints and produce unique physiographic characteristics of the certain part of Earth’s surface. Analysis of three-dimensional properties and origin of landscape often implies multidisciplinary quantitative approach connecting active tectonics processes with climate and erosion features trough available data from field of geology, seismology, geochronology, and tectonic geomorphology, etc. In this work, identification of neotectonic and recent active faults in Bilogora Mt. of NE Croatia was performed by combined DEM based morphometric analysis and structural analysis of 2D seismic sections, supplemente by 2D mapping with GPR. Bilogora Mt. area is a Pliocene-Quaternary transpressional morphostructure or a positive flower structure (Prelogović et al., 1998) genetically linked with tectonic evolution of the Drava depression and its SW prolongation (Bjelovar sub-depression). According to our data this structure is related to tectonic inversion of NW-striking Drava basin boundary fault (DBBF), from initially normal into later dextral strike-slip fault. Bilogora Mt. area is predominantly composed of highly deformed clastic Pliocene-Quaternary sediments of the 3rd depositional megacycle of the SW Pannonian Basin in Croatia (Velić et al., 2002 ; Saftić et al., 2003). Recent tectonic activity in the area is confirmed by moderate seismicity (VI°-VIII° MCS, 3, 5≤ML≤5, 6). Fault plane soulutions in the northwestern part indicate NE-SW directed Shmax and NE- to S-SW-dipping seismogenic structures characterized by strike-slip and reverse motions (Herak et al., 2009). Computer-based morphometry using DEM (10m resolution) was performed by ESRI ArcMap 9.3.1. software with available extensions (CalHypso, Spatial Analyst, ArcHydro 1.1, and StPro.) and Matlab software. Study area, divided into 131 drainage basins, was analyzed by relief and basin morphometry (elevation and slope distribution, hypsometry, asymmetry factor), and longitudinal stream profile morphometry (maximal concavity, distance from the source, concavity factor, steepness index, and concavity index). Morphometry results points to several drainage basins affected by recent on-going tectonics. These drainage basins and streams are located: i) between towns of Koprivnica and Pitomača in the NW part, and ii) between towns of Virovitica and Daruvar in SE part. Furthermore on-going tectonics was cross-checked by a set of 2D seismic sections and boreholes using Schlumberger Petrel Seismic to Simulation software. As a result, 3D structural depth model was constructed, with 6 stratigraphic horizons and fault planes active during the Neogene and Quaternary times. Morphometrically recognized on-going tectonics in the NW part of Bilogora Mt. area correlate well with subsurface fault-related folds formed in hangingwalls of normal-inverted and newly formed reverse faults, displacing the base Pliocene-Quaternary horizon and propagating towards the surface. Pliocene and Quaternary vertical offset along these faults varies between 20 and 490 m, indicating slip rate of 0.1 mm/year. By application of empirical geometrical fault-scaling relationships of Wells and Coppersmith (1994), we estimate that some of analyzed faults could generate earthquakes with magnitudes up to 6.86, which are greater than historically reported. The same faults could generate maximal vertical surface displacement < 1.46 m per seismic event. Landscape response to ongoing tectonic activity was additionaly studied by 2D mapping with Malå ProEx Georadar (RTA antenna with 50 MHz) at 6 selected locations. At three locations in the NW part, a vertical offset of very shallow stratigraphic horizons are confirmed to reach 0.5 m, and also confirmed the most recent tectonic activity by even surface-braking faults.

With GPS-derived shortening rates of c. 3-5 mm/a, the Adria-Europe convergence zone across the fold- and-thrust belt of the Dinarides (Balkan Peninsula) is a slowly deforming plate boundary by global standards. We have analysed the active tectonics and instrumental seismicity of the northernmost segment of this fold-and-thrust belt at its border to the Pannonian Basin. This area hosts a Maastrichtian collisional suture formed by closure of Mesozoic fragments of the Neotethys, overprinted by Miocene back-arc extension, which led to the exhumation of greenschist- to amphibolite-grade rocks in several core complexes. Geological, geomorphological and reflection seismic data provide evidence for a compressive or transpressive reactivation of extensional faults after about 5 Ma. The study area represents the seismically most active region of the Dinarides apart from the Adriatic Sea coast and the area around Zagreb. The strongest instrumentally recorded earthquake (27 October 1969) affected the city of Banja Luka (northern Bosnia and Herzegovina). Fault plane solutions for the main shock (ML 6.4) and its largest foreshock (ML 6.0) indicate reverse faulting along ESE-WNW-striking nodal planes and generally N-S trending pressure axes. The spatial distribution of epicentres and focal depths, analyses of the macroseismic field and fault-plane solutions for several smaller events suggest on-going shortening in the internal Dinarides. Our results therefore imply that current Adria-Europe convergence is widely distributed across c. 300 km, rendering the entire Dinarides fold-and-thrust belt a slowly deforming plate boundary.