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NEW LITHOSPHERE MODEL OF THE DINARIDES BASED ON THE FORWARD TELESEISMIC MODELLING

For a long time some considerations about a subduction of the Adriatic microplate beneath the Dinarides have been introduced. The Adriatic subduction in the geological history was documented in the literature, which took part from the Jurassic to the Paleogene. But, the absence of a lithospheric slab or “slab gap” has been considered in recent geological models, at least beneath the northern Dinarides (HANDY et al., 2015), based on some regional and global tomographic models (KOULAKOV et al., 2009) that pointed to a lack of the fast velocity anomaly beneath the northern Dinarides. However, new velocity models have revealed existence of shallow fast velocity anomaly in the northern Dinarides and deep fast anomaly in the southern Dinarides (ŠUMANOVAC  DUDJAK, 2016 ; ŠUMANOVAC et al., 2017). The anomaly was interpreted as a separation of the lower Adriatic lithosphere, which is detached from the crust, and steeply sinks beneath the Dinarides. A lithospheric slab sinking in the asthenosphere can be efficiently discovered by teleseismic tomography based on a fast velocity anomaly. The method has a good horizontal and a poor vertical resolution. However, good horizontal resolution depends on the space sampling, which means the study area should be uniformly covered by the receivers. Seismic arrays applied in the Koulakov and some other models do not satisfy this requirement. The study area was much better sampled by the array applied by ŠUMANOVAC et al. (2017) and significantly higher resolution has been achieved. The forward seismic modelling in the area of Dinarides has been applied to improve a reliability of the interpretation. A set of synthetic models was constructed and obtained inverse models were compared with the inverse model for observed data published by ŠUMANOVAC et al. (2017). In this model the shallow fast anomaly beneath the northern Dinarides clearly points to shallow descending Adriatic slab, but there are also several problems in the interpretation of the fast anomaly. The deep fast anomaly in the model (up to 450 km) in the southern Dinarides could not be unambiguously interpreted, because of the poor vertical resolution of the method, and the fast shallow anomaly is partially attenuated in the area of the northern Dinarides and gives an impression about the break in the lithospheric slab between the northern and southern Dinarides. Based on the seismic modelling, the analysis has showed the shallow Adriatic lithospheric slab stretches continuously beneath the entire Dinaridic mountain range (Fig. 1). The shallow Adriatic lithospheric slab in the northern Dinarides has been validated, but a cause of the deep southern fast anomaly does not have to be continuous deep Adriatic slab. A better fit of synthetic and observed inverse models has been obtained if the southern Adriatic slab has been considered as a discontinuous lithospheric slab, which consists of two parts. Accordingly, new geological model of the southern Dinarides has been constructed. Considering geological development a conclusion can be drawn the shallow Adriatic slab, stretching beneath the entire Dinaridic mountain range, is a consequence of the recent Adriatic subduction, and the deep part of the Adriatic slab in the southern Dinarides could be remnants of an older Adriatic subduction.

Dinarides, Subduction, Lithosphere model, Seismic modelling

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