Geologic reconnaissance of the island of Velika Palagruža (central Adriatic, Croatia)

Velika Palagruža (Pelagosa) is the largest island of the Palagruža archipelago (central Adriatic Sea, Croatia). Despite its minute size the island bears a certain geological interest being the only exposed piece of land in the central part (Mid-Adriatic ridge) of the common Adriatic foreland of the Apenninic and the Dinaridic orogenic domains. The litho-, bio-, and chemostratigraphic (strontium and sulphur isotopes) characteristics of the sedimentary units, along with tectono-structural and geomorphic characteristics of the island, are described in this paper. The oldest Žalo unit is composed of highly deformed siliciclastics containing gypsum, and carbonates of Middle Triassic (Ladinian) age. This unit represents a transitional fl uvial-to-shallow marine, occasionally evaporitic environment, typical of the Middle Triassic rifting phase of the Adriatic microplate. Soft and strongly deformed Žalo unit deposits are found along a probably still active, WNW&ndash;ESE striking, subvertical, oblique-slip fault that crosses the entire length of the island. The Žalo unit is probably in diapiric contact with the Lanterna unit, poorly defi ned as Late Triassic, and characterized by dolomite with chert and dolomite breccia, presumably deposited in a transitional platform-to-basin environment of an evolving Adriatic basin. The Lanterna unit deposits are capped by Miocene biocalcarenites of the Salamandrija unit over an almost perpendicular discordance, possibly representing an unconformity, suggesting that an early deformational phase preceded a Miocene marine transgression. Talus, landslide deposits, and humic soil make up the cover of the bedrock sedimentary succession, and they represent the ultimate phase of emersion of the island, which probably occurred during Pliocene(?) to Quaternary times. An active neotectonic regime of the central Adriatic is evidenced by present-day seismicity, while recent uplifting of the island is shown by the presence of remnants of pebbly palaeobeach deposits, marine (erosional) straths, and cyanobacterial supratidal encrustations (pelagosite) currently observed at various elevations above mean sea level. </span

Geologic reconnaissance of the island of Velika Palagruža (central Adriatic, Croatia)

Velika Palagruža (Pelagosa) is the largest island of the Palagruža archipelago (central Adriatic Sea, Croatia). Despite its minute size the island bears a certain geological interest being the only exposed piece of land in the central part (Mid-Adriatic ridge) of the common Adriatic foreland of the Apenninic and the Dinaridic orogenic domains. The litho-, bio-, and chemostratigraphic (strontium and sulphur isotopes) characteristics of the sedimentary units, along with tectono-structural and geomorphic characteristics of the island, are described in this paper. The oldest Žalo unit is composed of highly deformed siliciclastics containing gypsum, and carbonates of Middle Triassic (Ladinian) age. This unit represents a transitional fl uvial-to-shallow marine, occasionally evaporitic environment, typical of the Middle Triassic rifting phase of the Adriatic microplate. Soft and strongly deformed Žalo unit deposits are found along a probably still active, WNW&ndash;ESE striking, subvertical, oblique-slip fault that crosses the entire length of the island. The Žalo unit is probably in diapiric contact with the Lanterna unit, poorly defi ned as Late Triassic, and characterized by dolomite with chert and dolomite breccia, presumably deposited in a transitional platform-to-basin environment of an evolving Adriatic basin. The Lanterna unit deposits are capped by Miocene biocalcarenites of the Salamandrija unit over an almost perpendicular discordance, possibly representing an unconformity, suggesting that an early deformational phase preceded a Miocene marine transgression. Talus, landslide deposits, and humic soil make up the cover of the bedrock sedimentary succession, and they represent the ultimate phase of emersion of the island, which probably occurred during Pliocene(?) to Quaternary times. An active neotectonic regime of the central Adriatic is evidenced by present-day seismicity, while recent uplifting of the island is shown by the presence of remnants of pebbly palaeobeach deposits, marine (erosional) straths, and cyanobacterial supratidal encrustations (pelagosite) currently observed at various elevations above mean sea level

The diversity and geodynamic significance of Late Cambrian (ca. 500 Ma) felsic anorogenic magmatism in the northern part of the Bohemian Massif: A review based on Sm-Nd isotope and geochemical data

International audienceCa. 500 Ma orthogneisses and bimodal suites are widespread along the northern part of the Bohemian Massif (central European Variscides) and are interpreted to document intense magmatism during a continental break-up episode along the northern periphery of Gondwana. Based on geological setting, and geochemical and isotopic evidence, these felsic igneous rocks record the generation of: (1) magmas of pure or predominantly crustal derivation, represented by minor extrusives and much more voluminous orthogneisses similar to S-type granitoids; (2) subordinate magmas of exclusively mantle origin (ranging from within-plate alkali trachytes to oceanic plagiogranites) corresponding to felsic derivatives of associated basalts; and (3) magmas of hybrid origin, produced either as a result of large degrees of contamination of mantle-derived magmas ascending through the crust, or alternatively, generated by partial melting of mixed sources, such as interlayered sediments and mafic rocks or graywackes containing a juvenile component. The high-temperature dehydration melting process responsible for the generation of the most abundant rock-types necessitated the advection of mantle heat, in a context of continental lithosphere extension, as documented by broadly coeval basaltic magmatism at the scale of the igneous province. The large volumes of felsic magmas generated during the 500-Ma anorogenic event are interpreted to result from the combination of a hot extensional tectonic regime with the widespread availability in the lower crust of fertile lithologies, such as metagraywackes. This in turn reflects the largely undifferentiated nature of the crustal segment accreted some 50–100 m.y. earlier during the Cadomian orogeny