Aneta A. Anczkiewicz

Thermal history of the Podhale Basin in the internal Western Carpathians from the perspective of apatite fission track analyses

Abstract The thermal history of the Paleogene Podhale Basin was studied by the apatite fission track (AFT) method. Twenty four Eocene-Oligocene sandstone samples yielded apparent ages from 13.8 ± 1.6 to 6.1 ± 1.4 Ma that are significantly younger than their stratigraphic age and thus point to a post-depositional resetting. The thermal event responsible for the age resetting is interpreted as a combination of heating associated with mid-Miocene volcanism and variable thickness of Oligocene and potentially also Miocene sediments. Extending the mid-Miocene thermal event found in the Inner Carpathians into the Podhale Basin as a likely heat source suggests that the amount of denudation in the Podhale Basin determined only on the basis of heat related to the thickness of sedimentary sequence might have be significantly overestimated. Two samples from the western part of the basin that yielded 31.0 ± 4.3 and 26.9 ± 4.7 Ma are interpreted as having mixed ages resulting from partial resetting in temperature conditions within the AFT partial annealing zone. This observation agrees very well with reported vitrinite reflectance and illite-smectite thermometry, which indicate a systematic drop of the maximum paleotemperatures towards the western side of the basin.

Fission-track dating of apatite from the Góry Sowie Massif, Polish Sudetes, NE Bohemian Massif: implications for post- Variscan denudation and uplift

Six samples from the Gory Sowie Massif gneisses in the West Sudetes, analyzed for the purpose of apatite fission- track dating (AFT) yielded ages ranging from 43 to 57 Ma. No regional variation in the results was observed and the samples form a rather uniform population. From confined-track length measurements, short values between 8.8 and 9.6 µm were obtained. Track length distribution in four of the six samples is bimodal. This suggests residence in temperatures corresponding to the par- tial annealing zone until relatively recent times and subsequent rapid cooling to ambient conditions. We propose a mid-Tertiary rise in the geothermal gradient as a possible factor responsible for reheating the Gory Sowie Massif after it had cooled to temper- atures around 60 - 40 uC in the Oligocene. According to reverse-modelling results, the cooling began in the Cretaceous and there- fore correlates with the event reported from elsewhere in the northern part of the Bohemian Massif. As Lower Carboniferous sed- imentary rocks overlie the gneisses, the overburden which was responsible for keeping temperatures above 100 uC until early Ter- tiary was probably the Carboniferous-Permian Variscan molasse. The amount of the Cretaceous/early Tertiary denudation can be estimated to be 4 - 8 km. The recent, rapid cooling phase began 7- 5 Ma ago and is interpreted as the combined result of decrease of geothermal gradient and/or increased tectonic activity in the Sudetes as evidenced by the presence of the Pliocene, coarse-clas- tic Gozdnica formation.

THERMAL HISTORY OF LOWER PALEOZOIC ROCKS ON THE PERI-TORNQUIST MARGIN OF THE EAST EUROPEAN CRATON (PODOLIA, UKRAINE) INFERRED FROM COMBINED XRD, K-Ar, AND AFT DATA

The Upper Silurian–Lower Devonian section of the Dniester gorge in Podolia and samples from boreholes located S and N of this area were studied in order to reconstruct the thermal history of Lower Paleozoic sedimentary rocks in the Dniester segment of the Peri-Tornquist margin of the East European Craton which is the most eastern part of a major shale-gas target in Europe. X-ray diffraction data for illite-smectite from shales and carbonates indicate very advanced diagenesis and maximum paleotemperatures of ~200ºC, higher than interpreted from the ‘conodont alteration index’ (CAI) data. Diagenesis of the Devonian section is slightly less advanced than that of the underlying Silurian section, indicating that it is a regional feature and the result of burial. The regional distribution of the diagenetic grade based on illite matches well with the pattern established from the CAI data. K-Ar dating of illite-smectite from Silurian bentonites and shales gave a consistent set of dates ranging from 390 to 312 Ma. To explain such advanced levels of diagenesis and such K-Ar dates, the extension of the Carboniferous foreland basin (which today is only preserved to the NW of L’viv) toward the SE on the craton margin has to be assumed. The diagenetic zonation pattern of the Carboniferous coals supports this hypothesis. The Carboniferous cover may have been either sedimentary or partially tectonic (Variscan intracratonic duplexes) in origin and the thickness, necessary for the observed level of diagenesis, may have been reduced by an elevated heat flow along the major tectonic zone at the edge of the craton (TESZ). The presence of such cover is confirmed by completely reset Cretaceous apatite fission track (AFT) ages of the Silurian bentonites. The AFT dates also imply a Tertiary heating event in the area.The 10 Å clay mineral present in the dolomitic part of the profile (Silurian), both in bentonites and in other rocks, is aluminoceladonite or intermediate between illite and aluminoceladonite, while in the Devonian shale section only illite was documented. Chlorite is also common in the studied rocks and is at least partially authigenic. It is non-expandable in the samples from boreholes, while often expandable to variable extents in the samples from outcrops, which also contain goethite. Such variation in chlorite is attributed to contemporary weathering.

Weathering, sedimentary and diagenetic controls of mineral and geochemical characteristics of the vertebrate-bearing Silesian Keuper

Abstract Mudstones and claystones from the southern marginal area of the European Upper Triassic, midcontinental Keuper basin (Silesia, southern Poland) were investigated using XRD, organic and inorganic geochemistry, SEM, K-Ar of illite-smectite, AFT, and stable isotopes of O and C in carbonates in order to unravel the consequent phases of the geological history of these rocks, known for abundant fossils of land vertebrates, and in particular to evaluate the diagenetic overprint on the mineral composition. The detected and quantified mineral assemblage consists of quartz, calcite, dolomite, Ca-dolomite, illite, mixed-layer illite-smectite, and kaolinite as major components, plus feldspars, hematite, pyrite, chlorite, anatase, siderite, goethite as minor components. Palygorskite, gypsum, jarosite and apatite were identified in places. The K-Ar dates document a post-sedimentary thermal event, 164 Ma or younger, which resulted in partial illitization of smectite and kaolinite. The maximum palaeotemperatures were estimated from illite-smectite as ~125°C. Apatite fission track data support this conclusion, indicating a 200-160 Ma age range of the maximum temperatures close to 120°C, followed by a prolonged period of elevated temperatures. These conclusions agree well with the available data on the Mesozoic thermal event, which yielded Pb-Zn deposits in the area. Organic maturity indicators suggest the maximum palaeotemperatures <110°C. Palygorskite was identified as authigenic by crystal morphology (TEM), and calcite by its accumulation in soil layers and by its isotopic composition evolving with time, in accordance with the sedimentary and/or climatic changes. Dolomite isotopic composition indicates more saline (concentrated) waters. Palygorskite signals a rapid local change of sedimentary conditions, correlated with algal blooms. This assemblage of authigenic minerals indicates an arid climate and the location at the transition from a distal alluvial fan to mudflat. Fe-rich smectite, kaolinite, and hematite were products of chemical weathering on the surrounding lands and are therefore mostly detrital components of the investigated rocks. Kaolinite crystal morphology and ordering indicates a short transport distance. Hematite also crystallized in situ, in the soil horizons. A large variation in kaolinite/2:1 minerals ratio reflects hydraulic sorting, except of the Rhaetian, where it probably signals a climatic change, i.e. a shift in the weathering pattern towards kaolinite, correlated with the disappearance of hematite. Quartz, 2M1 illite, and minor feldspars and Mg-chlorite were interpreted as detrital minerals. The documented sedimentation pattern indicates that in more central parts of the Keuper playa system, where an intense authigenesis of the trioctahedral clays (chlorite, swelling chlorite, corrensite, sepiolite) took place, illite and smectite were the dominant detrital clay minerals. Cr/Nb and Cr/Ti ratios were found as the best chemostratigraphic tools, allowing for the correlation of all investigated profiles. A stable decrease of these ratios up the investigated sedimentary sequence is interpreted as reflecting changes in the provenance pattern from more basic to more acidic rocks.

Multiple low-temperature thermochronology constraints on exhumation of the Tatra Mountains: New implication for the complex evolution of the Western Carpathians in the Cenozoic

The tectonothermal evolution of the highest mountain range in the Carpathian arc—the Tatra Mountains— is investigated by zircon and apatite fission track and zircon (U-Th)/He (ZHe) dating methods in order to unravel the disputed exhumation and geodynamic processes in the Western Carpathians. Our data in combination with geological evidences reveal a complex Cenozoic history, with four major tectonothermal events: (i) a very low grade metamorphism of the crystalline basement at temperatures >240°C due to tectonic burial during the Eo-Alpine collision in the Late Cretaceous (~80 Ma); (ii) exhumation and cooling of the basement to temperatures 150°C after burial to 5–9 km depths by the Paleogene fore-arc basin; (iv) final exhumation of the segmented basement blocks during Oligocene-Miocene (32–11 Ma) owing to lateral extrusion of the North Pannonian plate and its collision with the European foreland. The spatial pattern of thermochronological data suggests asymmetric exhumation of the Tatra Mountains, beginning in the northwest at ~30–20 Ma with low cooling rates (~1–5°C/Ma) and propagating toward the major fault bounding the range in the south, where the youngest cooling ages (16–9 Ma) and fastest cooling rates (~10–20°C/Ma) are found. Our data prove that the Tatra Mountains shared Cenozoic evolution of other crystalline core mountains in the Western Carpathians. However, the Miocene ZHe ages suggest that the Tatra Mountains were buried to the greatest depths in the Paleogene-Early Miocene and experienced the greatest amount of Miocene exhumation.