TECTONIIC CONTROL OF LARGE SCALE TOPOGRAPHY OF THE EXTERNAL DINARIDES

The External Dinarides of Croatia are largely composed of platform carbonates transferred from the Adria to Eurasia during Tertiary subduction. The homogeneity of carbonate lithologies, and the lack of silicate minerals in these rocks has led to a ubiquitous karst topography, which hinders fluvial processes. Instead, erosion in the External Dinarides is almost entirely limited to chemical dissolution. Since the low topography of the Dinarides does not appear to have a strong climate forcing effect, the relatively homogenous distribution of precipitation results in similarly uniformly distributed erosion; therefore, large scale (wavelength of 10’s of km) topographic variation is either controlled by the contrasting erodibility of various carbonate lithologies, or active tectonics. We analyzed a suite of samples distributed across both topographically high and low elevations with the microprobe and ICP-MS and found that the weight percent Ca in every sample was that of pure calcite. We then expanded our investigation by incorporating spectral analysis of ASTER imagery across the entire external Dinarides, with similar results. We conclude that the large scale topography in the External Dinarides is not the result of lithologic heterogeneity, and instead controlled by tectonics.

Our results have several implications which bear directly on Peri-Adriatic mountain building. Significant uncertainty persists regarding the Tertiary evolution of the Adria micro-plate, with the majority of literature regarding tectonics on its eastern (Dinaric) margin complete by Eocene. However, several recent lines of evidence indicate that the External Dinarides are much younger and currently active. Our conclusion of tectonic topography, which is supported by the spatial correlation between seismicity and relief, is in agreement with the later hypothesis. Moreover, our conclusion suggests that the spatial distribution of late Tertiary shortening can be correlated with extant high relief.