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Methane (CH 4 ) in continental serpentinized peridotites (MSP) has been documented in numerous hyperalkaline (pH > 9) springs and gas seeps worldwide. With a dominantly abiotic origin, MSP is often associated with considerable amounts of hydrogen (H 2 ), produced by serpentinization. Both gases may fuel microbial activity in igneous rocks and may have played roles in the origin of life. MSP is also a natural CH 4 source for the atmosphere, not included in the global greenhouse-gas budget, yet. Here we document a new and major case of MSP, in the Dinaride ophiolite belt in Bosnia and Herzegovina. CH 4 is dissolved (83–2706 μM) in low temperature (13–30 °C), hyperalkaline (pH 10 to 12.8) waters in six sites, sampled through springs and boreholes. Four sites (Slanac, Vlajići, Kulaši and Lješljani) show CH 4 isotopic signatures typical of abiotic MSP (δ 13 C: −18.5 to −35.7‰; δ 2 H: −221 to −335.4‰); two sites (Vaićeva and Kiseljak) show a dominantly biotic signature (δ 13 C: −58.8 and −65.1‰; δ 2 H: −310.8 and −226.8‰), probably due to mixing with gas from coal-beds adjacent to the ultramafic rocks. H 2 concentration is highly variable (up to 348 μM), ethane, propane and butane reach 0.13 vol.% in total, and helium isotopic composition (R/Ra: 0.12 to 0.48) reflects a dominant crustal signature. The Lješljani site features the highest pH (12.8) and CH 4 emission (∼9 ton y −1 ) in peridotite-hosted hyperalkaline groundwater documented so far. Geological and geochemical data converge towards the hypothesis that, as proposed in similar cases, CH 4 was mainly generated by Sabatier reaction between H 2 (from serpentinization) and CO 2 (from C-bearing rocks, in tectonic contact with the ophiolite, or other CO 2 sources). CH 4 -H 2 -H 2 O disequilibria and Sabatier reaction constraints suggest that CH 4 is not formed in the hyperalkaline water, but in water-free or unsaturated rocks hosting opportune metal catalysts (e.g., chromitites). The amount of methane released to the atmosphere from individual springs is comparable to that of conventional biotic gas seeps/springs in sedimentary basins. [ABSTRACT FROM AUTHOR]

The geodynamic evolution of the Dinaride Mountains of southeastern Europe is relatively poorly understood, especially in comparison with the neighboring Alps and Carpathians. Here, we construct a new chronostratigraphy for the post-orogenic intra-montane basins of the Central Dinarides based on paleomagnetic and 40 Ar/ 39 Ar age data. A first phase of basin formation occurred in the late Oligocene. A second phase of basin formation took place between 18 and 13 Ma, concurrent with profound extension in the neighboring Pannonian Basin. Our paleomagnetic results further indicate that the Dinarides have not experienced any significant tectonic rotation since the late Oligocene. This implies that the Dinarides were decoupled from the adjacent Adria and the Tisza-Dacia Mega-Units that both underwent major rotation during the Miocene. The Dinaride orogen must consequently have accommodated significant shortening. This is corroborated by our AMS data that indicate post-Middle Miocene shortening in the frontal zone, wrenching in the central part of the orogen, and compression in the hinterland. A review of paleomagnetic data from the Adria plate, which plays a major role in the evolution of the Dinarides as well as the Alps, constrains rotation since the Early Cretaceous to 48 ± 10° counterclockwise and indicates 20° of this rotation took place since the Miocene. It also shows that Adria behaved as an independent plate from the Late Jurassic to the Eocene. From the Eocene onwards, coupling between Adria and Africa was stronger than between Adria and Europe. Adria continued to behave as an independent plate. The amount of rotation within the Adria-Dinarides collision zone increases with age and proximity of the sampled sediments to undeformed Adria. These results significantly improve our insight in the post-orogenic evolution of the Dinarides and resolve an apparent controversy between structural geological and paleomagnetic rotation estimates for the Dinarides as well as Adria.