The thermal influence of a Miocene stratovolcano (Mátra Volcano) on its basement was studied by apatite and zircon (U–Th)/He thermochronometry. The pre-Miocene substratum of the volcano contains Mesozoic sedimentary units in addition to the nearby exhumed igneous Recsk Complex. The Oligocene emplacement age of the Recsk Complex is constrained by zircon U–Pb geochronology to be 29.6 Ma, which serves as a benchmark for the beginning of its thermal history. All measured apatite (U–Th)/He ages (19.9–5.9 Ma) and most of the zircon (U–Th)/He ages (26.2–17.7 Ma) are considerably younger than the emplacement age of the Oligocene Recsk Complex, implying thermal overprinting by the adjacent Miocene Mátra Volcano. The apatite and zircon He ages of the Oligocene complex increase from south to north, providing clear evidence of a northwards-weakening thermal overprint. The post-Oligocene thermal history of the basement was reconstructed via one-dimensional subsidence/thermal modelling. According to zircon He modelling, the thickness of the covering units above the Recsk Complex was estimated to be 1000–1500 m and the heat flux was c. 200 mW m −2 during the Miocene volcanism. Thermal modelling based on apatite He data suggests that the Miocene volcanism was followed by intensive erosion and the exposure of the Recsk Complex by the Late Miocene. Supplementary material: The locality, petrography and age yield of the dated samples of the Recsk Igneous Complex and details of the laser ablation inductively coupled plasma mass spectrometry dating of zircons from the Recsk Complex are available at: https://doi.org/10.6084/m9.figshare.c.4127444
Recent developments in geoanalytics have led to the rapidly increasing potential of sedimentary provenance analysis in paleogeographic reconstructions. Here we combine standard methods (petrography, zircon U-Pb geochronology, optical heavy-mineral identification) with modern techniques such as automated Raman-spectroscopic identification of heavy minerals and detrital apatite and titanite U-Pb geochronology. The resulting multi-parameter dataset enables the reconstruction of tectonic and paleogeographic environments to an as-yet unprecedented accuracy in space and time. The Paleogene siliciclastic formations of our study area, the Transylvanian Basin, represent an intensely changing sedimentary environment comprising three transgressive–regressive cycles on a simultaneously moving and rotating tectonic plate. We identified six major source components of the Paleogene sediments and outlined the paleo-drainage patterns for the three cycles, respectively. According to our data these components include: 1) pre-Variscan basement units of the nappes, 2) Variscan granitoids, 3) Permo-Triassic felsic volcanic rocks, 4) Jurassic ophiolites, 5) Upper Cretaceous granodiorites, and 6) Priabonian to Rupelian (37–30 Ma) intermediate magmatites, the latter representing newly recognized formations in the region. Abrupt paleographic changes can be directly deduced from the obtained dataset. The first phase of the Paleogene siliciclastic sequence is composed of mostly Southern Carpathian–derived sediments, to which Jurassic ophiolite detritus of the Apuseni Mts. was added during the second phase, while the siliciclastic material of the third phase represents mainly recycled material from the second phase. According to the detected diagnostic heavy-mineral associations, U-Pb age components and the positions of the potential source areas a set of provenance maps are presented.
Much of Earth’s carbon may have been stripped away from the silicate mantle by dense metallic-iron during core formation. However, at deep magma ocean conditions carbon becomes less siderophile and thus large amounts of it may be stranded instead in the deep mantle. Here, we describe the structure and compaction mechanisms of carbonate glass to deep mantle pressures. Our results, based on non-resonant inelastic X-ray scattering, X-ray diffraction and ab initio calculations, demonstrate a pressure-induced change in hybridization of carbon from sp2 to sp3 starting at 40 GPa, due to the conversion of [3]CO32- groups into [4]CO44- units, which is completed at ~112 GPa. The pressure-induced change of carbon coordination number from three to four increases possibilities for carbon-oxygen interactions with lower mantle silicate melts. sp3 hybridized carbon provides a mechanism for changing the presumed siderophile nature of deep carbon, becoming a possible source for carbon-rich emissions registered at the surface in intra-plate and near-ridge hot spots.
For a long time, the thermal history of northeastern (NE) Fennoscandia in the Phanerozoic and Precambrian remained unknown, since no thermochronological studies were carried out within the Kola Peninsula area. Two years ago, we developed the first model of tectono-thermal evolution of the Kola Peninsula territory for the last 1.9 Gyr using a set of newly obtained apatite fission-track (AFT) and Ar/Ar thermochronological data. However, the low-temperature history of the most ancient tectonic unit of the northeastern part of the Kola Peninsula—the Archean Murmansk craton—remained poorly constrained due to the lack of AFT data. In this paper, we present the first results of AFT studies of 14 samples representing intrusive and metamorphic Precambrian rocks, located within the Murmansk craton of NE Fennoscandia. AFT ages and track length distributions indicate a similar tectono-thermal evolution of Precambrian tectonic units in NE Fennoscandia over the last 300 Myr. The AFT ages are distributed between ca. 177 and ca. 384 Ma; their median value, ~293 Ma, confirms the presence of a previously identified hidden thermal event that took place at about 300 Ma. However, a detailed analysis of the AFT age distribution shows the presence of three statistically distinguishable age components: 180–190 Ma (C1), 290–320 Ma (C2) and 422 Ma (C3). We assume that the relatively young AFT ages of C1 may originate from apatite crystals with low thermal resistivity. Remarkably, this value coincides with the initial stage of the Barents Sea magmatic province activity during large-scale plume-lithospheric interaction, as well as with the assumed age of an enigmatic remagnetization event throughout the Kola Peninsula. C2 ages can be observed in both the gabbroic and non-gabbroic samples, whereas C3 ages can only be found in gabbro. It is supposed that C2 ages, similarly to the Central Kola terrane, correspond to a cooling event related to the denudation of a thick sedimentary cover, representing a continuation of the Caledonian foreland basin towards NE Fennoscandia. C3 ages may be associated with a thermal event corresponding to the Caledonian collisional orogeny.
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