The petrology and geochronology of the gabbro-dioritoid rocks from Veľké Železné (Nízke Tatry Mts., Western Carpathians)
Abstract: The gabbro-dioritoid rocks from Veľké Železné (Nízke Tatry Mts., Western Carpathians, Slovakia) were recently studied in order to better understand the age, origin, and evolution of the basic/intermediate magmas associated with Variscan granitic rocks. Their genesis was investigated from the points of view of petrology, whole-rock geochemistry (including Sr, Nd, and Pb isotopic characteristics), as well as U–Th–Pb zircon and apatite dating. The Famennian magmatic crystallization age of ca. 360 Ma (determined from zircon: 362.4 ± 2.9 Ma and apatite: 358.4 ± 2.8 Ma) is older than the Tournaisian–Visean ages for granite intrusions in the Tatric Unit. Geochemically, the studied rocks have an affinity to arc-related basalts, consisting of a metaluminous, magnesian, and high-potassium calc-alkaline character. Isotope data (i.e., (87Sr/86Sr)360 = 0.7035−0.7044 and εNd360 = +1.4 to +1.6) demonstrate that these gabbro-dioritoids were formed from the mantle-influenced, lower crustal and/or sub-continental lithospheric mantle (SCLM) sources, whereas the unsystematic increase of Pb isotope ratios indicate either the melting of an ancient Enriched mantle-II (EM-II) reservoir or the upper crustal assimilation and/or local fluid alteration. The data presented in this paper favour the origin of the studied gabbro-dioritoids at a continental arc, although we cannot rule out their genesis as a result of the subsequent slab break-off.
Exotic clasts of Upper Cretaceous Southalpine units (N Italy) point to uplift and erosion of uppermost Austroalpine (Eastalpine and Transdanubian) and E-Southalpine sources
Abstract: This study aims at identifying the source area(s) of two populations of exotic pebbles/cobbles present as driftwood dropstones in the upper Turonian to Coniacian pelagic layers of the Scaglia Rossa, as well as gravity flow deposits in the Santonian Sirone Conglomerate of the Lombardian Flysch. The clast assemblage indicates that the main source(s) were the structurally highest Austroalpine units of the Eo-Alpine orogenic edifice of the Eastern Alps and the Transdanubian Range; the erosion of such units produced Gosau-type gravels that, after local elaboration in high-energy settings, were resedimented into the Southalpine basins. Despite the affinities shown by the clast composition with the lithofacies of the Lombardian stratigraphic succession, origin from a central-Southalpine early orogenic retrobelt edifice can be reasonably excluded, since the onset of uplift and denudation of the Southern Alps occurred in the Late Oligocene. In Santonian times, a complementary source fed the Sirone Conglomerate and likely contributed the Kainach Gosau basin with clasts of Southalpine rocks. This source is inferred to have coincided with an emerging belt located in the eastern Southalpine domain, produced by transpression along the proto-Periadriatic Lineament. Ophiolitic detritus may have reached the Central Alpine and Southalpine areas during the Early Cretaceous; in contrast, the exhumation and uplift of the Koralpe–Wölz high-pressure belt and of its uppermost Austroalpine nappe cover at 89–84 Ma, likely separated the Southalpine retrobelt basins from ‘northern’ sources.
The Kolárovo gravity and magnetic anomaly body in a subcrop of the Danube Basin: A new geological interpretation
Abstract: We provide an analysis of the existing 2D and 3D gravimetric and magnetic interpretations of the well-known and significant Kolárovo gravity and magnetic anomaly, as well as present a new geological interpretation of its origin. It follows that the source of these anomalies is a high-density and highly magnetic crustal body with the following parameters: (a) density contrast is between +0.28 and +0.31 g cm−3, (b) magnetic susceptibility is ~22000×10−6 units of SI, (c) the depth of the upper boundary varies from ~4.5 to 6.0 km, (d) the depth of the center of the gravity body is between 8.7 and 12.5 km, and (e) the depth of the lower boundary moves in the interval from above 13 to 20 km. These factors and the inferred tectonic position of the Kolárovo body allow for its interpretation as a possible eclogite/ultramafite body. It occurs within a belt of magnetic and gravity anomalies tracing the Eo-Alpine high-pressure metamorphic complexes from the Eastern Alps to the Western Carpathians via the northern periphery of the Rába–Hurbanovo–Diósjenő fault zone. We assume that the position of the Kolárovo crustal body resulted from the Oligocene–Lower Miocene uplift of the East Alpine–West Carpathian junction caused by the compressional tectonic regime accompanied by crustal thickening, surface uplift, and erosion of units forming the present basement of the Danube Basin. Simultaneously, exhumation of the orogenic infrastructure occurred, which thus affected the Eo-Alpine metamorphic complexes, including the anomalous Kolárovo body. Subsequently, during the Middle–Late Miocene rifting and subsidence of the Danube Basin, the Kolárovo body was buried to its present position.
Inversion of deep-seated tectonics in the Central Depression of the Outer Carpathians (SE Poland)
Abstract: The deeply buried, northeastern segment of the fold-and-thrust belt of the Outer Carpathians is contoured by synorogenic sediments (Upper Oligocene–Lower Miocene) of tectonically multiplied thicknesses, which mask the deep-seated structures. Integration of archival mappings and profiles of deep wells with the new generation of geological-seismic cross-sections reveals the unconformable position of asymmetric folds and duplexes built of synorogenic sediments, resting upon the older flysch formations (Cretaceous–Lower Paleogene). These structures are cut by a system of dislocated, monovergent, imbricated overthrusts, deeply rooted in the outer zones of thrust folds. These zones are associated with deep-seated, high-amplitude (up to several kilometres), Meso–Paleozoic and Precambrian faults originated by subduction of the European Platform. As revealed by geological reinterpretation of MT-1 magnetotelluric soundings, the time/space identification of longitudinal, compressional sutures rotated by transversal, transpressional faults suggests a segmented model of subduction of the platform basement. Its coincidence with the reconstructed kinematic evolution of sedimentary covers justifies the origin of the inversion tectonics of the Central Depression of the Outer Carpathians as a result of the heterogenic structure of the consolidated basement.
