Constraining long-term denudation and faulting history in intraplate regions by multisystem thermochronology: An example of the Sudetic Marginal Fault (Bohemian Massif, central Europe)

The Rychlebské hory Mountain region in the Sudetes (NE Bohemian Massif) provides a natural laboratory for studies of postorogenic landscape evolution. This work reveals both the exhumation history of the region and the paleoactivity along the Sudetic Marginal Fault (SMF) using zircon (U-Th)/He (ZHe), apatite fission track (AFT), and apatite (U-Th)/He (AHe) dating of crystalline basement and postorogenic sedimentary samples. Most significantly, and in direct contradiction of traditional paleogeographic reconstructions, this work has found evidence of a large Cretaceous sea and regional burial (to >6.5 km) of the Carboniferous-Permian basement in the Late Cretaceous (~95–80 Ma). During the burial by sediments of the Bohemian Cretaceous Basin System, the SMF acted as a normal fault as documented by offset ZHe ages across the fault. At 85–70 Ma, the basin was inverted, Cretaceous strata eroded, and basement blocks were exhumed to the near surface at a rate of ~300 m/Ma as evidenced by Late Cretaceous–Paleocene AFT ages and thermal modeling results. There is no appreciable difference in AFT and AHe ages across the fault, suggesting that the SMF acted as a reverse fault during exhumation. In the late Eocene–Oligocene, the basement was locally heated to <70°C by magmatic activity related to opening of the Eger rift system. Neogene or younger thermal activity was not recorded in the thermochronological data, confirming that late Cenozoic uplift and erosion of the basement blocks was limited to less than ∼1.5 km in the study area

Sulfur isotope measurement of sulfate and sulfide by high-resolution MC-ICP-MS

Author Posting. © Elsevier B.V. , 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Chemical Geology 253 (2008): 102-113, doi:10.1016/j.chemgeo.2008.04.017.We have developed a technique for the accurate and precise determination of 34S/32S isotope ratios (δ34S) in sulfur-bearing minerals using solution and laser ablation multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). We have examined and determined rigorous corrections for analytical difficulties such as instrumental mass bias, unresolved isobaric interferences, blanks, and laser ablation- and matrix-induced isotopic fractionation. Use of high resolution sector-field mass spectrometry removes major isobaric interferences from O2+. Standard–sample bracketing is used to correct for the instrumental mass bias of unknown samples. Blanks on sulfur masses arising from memory effects and residual oxygen-tailing are typically minor (< 0.2‰, within analytical error), and are mathematically removed by on-peak zero subtraction and by bracketing of samples with standards determined at the same signal intensity (within 20%). Matrix effects are significant (up to 0.7‰) for matrix compositions relevant to many natural sulfur-bearing minerals. For solution analysis, sulfur isotope compositions are best determined using purified (matrix-clean) sulfur standards and sample solutions using the chemical purification protocol we present. For in situ analysis, where the complex matrix cannot be removed prior to analysis, appropriately matrix-matching standards and samples removes matrix artifacts and yields sulfur isotope ratios consistent with conventional techniques using matrix-clean analytes. Our method enables solid samples to be calibrated against aqueous standards; a consideration that is important when certified, isotopically-homogeneous and appropriately matrix-matched solid standards do not exist. Further, bulk and in situ analyses can be performed interchangeably in a single analytical session because the instrumental setup is identical for both. We validated the robustness of our analytical method through multiple isotope analyses of a range of reference materials and have compared these with isotope ratios determined using independent techniques. Long-term reproducibility of S isotope compositions is typically 0.20‰ and 0.45‰ (2σ) for solution and laser analysis, respectively. Our method affords the opportunity to make accurate and relatively precise S isotope measurement for a wide range of sulfur-bearing materials, and is particularly appropriate for geologic samples with complex matrix and for which high-resolution in situ analysis is critical.Support was provided by National Science Foundations grants OCE-0327448 to P.R.C. and W.B. and OCE-0622982 to O.J.R. Support for L.A.B. was provided by the Woods Hole Oceanographic Institution Plasma Facility Development Grant (NSF-EAR/IF-0318137)

High-Ti muscovite as a prograde relict in high pressure granulites with metamorphic Devonian zircon ages (Běstvina granulite body, Bohemian Massif): Consequences for the relamination model of subducted crust.

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From Gondwana to Europe: The journey of Elba Island (Italy) as recorded by U–Pb detrital zircon ages of Paleozoic metasedimentary rocks

Elba Island, located midway between Corsica and mainland Italy, is a small but important fragment of the Adria Plate. It has a rich sedimentary record preserved in a stack of tectonic nappes of both continental margin and oceanic origin. Especially the detrital zircons in early Paleozoic to early Mesozoic metasedimentary rocks provide an archive of many important geological events in the island's history. Elba Island and Adria originated along the northern margin of Gondwana, but drifted north in Silurian times to become part of Europe. A large new dataset of LA-ICP-MS and SIMS U-Pb zircon ages allows us to trace this history. Three main stratigraphic units have been investigated. The oldest Porto Azzurro Unit was deposited in the early Cambrian and has zircon age distributions indicating a typical northern African provenance, most likely sourced from the Saharan Metacraton. The Ortano Unit has a simple, mostly unimodal Ordovician age distribution that is entirely dominated by metavolcanic rocks and their erosional products; a sample of the metavolcanic Ortano Porphyroids provided a SIMS U-Pb zircon age of 460. ±. 3. Ma. This phase of intense volcanism is related to the subduction of the Rheic Ocean beneath Gondwana, terminating with initial rifting and subsequent opening of the Paleotethys. This also marks the onset of the separation of a range of European terranes, including Adria and future Elba Island, from Gondwana. The Permo-Triassic Monticiano-Roccastrada Unit is the first to show a European provenance with the appearance of large amounts of Variscan and late to post-Variscan detritus. The presence of Variscan detrital zircons in the Permo-Triassic sediments is unexpected, since a Variscan age signature is so far not well recorded in the Adria Plate. This dataset is the most comprehensive detrital zircon dataset so far available for the Adria Plate and documents Adria's close affinity to Africa in the Lower Paleozoic, as well as its initial rifting within an active continental margin setting during the Ordovician and its final separation and independent evolution since late Palaeozoic times