Timing of uplift and evolution of the Lüliang Mountains, North China Craton

This study analyses evidence for reformed basin development and basin-mountain coupling associated with development of the Ordos Basin and the Lüliang Mountains, China. Gaining an improved understanding of the timing and nature of uplift and evolution of the Lüliang Mountains is important for the reconstruction of the eastern sedimentary boundary of the Ordos Basin (a major petroliferous basin) as well as for providing insight into the evolution and breakup of the North China Craton (NCC). Based on systematic sampling for fission track analysis, it is suggested that the main phase of uplift of the Lüliang Mountains occurred since later part of the Early Cretaceous. Three evolutionary stages of uplift and development are identified: slow initial uplift (120–65 Ma), accelerated uplift (65–23 Ma), and intensive uplift (23 Ma to present), with the majority of the uplift activity having occurred during the Cenozoic. The history of uplift is non-equilibrium and exhibits complexity in temporal and spatial aspects. The middle and northern parts of the Lüliang Mountains were uplifted earlier than the southern part. The most intensive episode of uplift activity commenced in the Miocene and was associated with a genetic coupling relationship with the eastern neighboring Cenozoic Shanxi Grabens. The uplifting and evolutionary processes of the Lüliang Mountains area since later part of the Early Cretaceous share a unified regional geodynamic setting, which was accompanied by uplift of the Mesozoic Ordos Basin and development of the neighboring Cenozoic Shanxi Grabens. Collectively, this regional orogenic activity is related principally to the far-field effects of both the compression sourced from the southwestern Tibet Plateau and westward subduction of the Pacific Plate in Cenozoic

Pressure dependence of He diffusion and fission-track annealing kinetics in apatite?: Experimental results

A number of preliminary experiments have been undertaken to test results reported by Wendt et al. (2002), concerning the dependancy of pressure on fission track annealing in apatite, and which implied a similar dependancy for He difusion in apatite

Experimental evidence concerning the pressure dependence of He diffusion and fission-track annealing kinetics in apatite

We offer this short note to document data we have collected regarding the pressure dependence of He diffusion and fission-track annealing kinetics in apatite. This work is a direct result of the provocative EPSL paper by Wendt et al. (2002). Should their data stand, so should many of their conclusions. For the record, we have communicated constructively with Anke Wendt and through her, her co-authors, and we have the singular goal of better understanding their data and the issues raised in their paper

Improved measurements of the fission-tracks annealing in apatite using c-axis projection

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Is Low‐Temperature Fission‐Track Annealing in Apatite a Thermally Controlled Process?

Abstract We report a new series of experiments to explore the phenomenon of low‐temperature annealing of fission tracks in apatite that feature a number of improvements over previous work. Grain mounts were preirradiated using 252Cf to increase confined track detection and allow briefer thermal neutron irradiation. We coirradiated and etched four apatite varieties (Durango, Fish Canyon, Renfrew, and Tioga) over five time steps equally spaced from 3.66 to 15 ln(s). A length standard was coetched with all experiments to ensure that subtle differences are within detection limits. Finally, we used a standard etching protocol, allowing the data to be comodeled with extensive high‐temperature data sets and recent analyses of induced tracks that underwent ambient‐temperature annealing over year‐to‐decade time scales. Ambient‐temperature annealing occurs at two different rates, with faster annealing at early stages that decreases to a slower rate that converges with empirical fanning linear or curvilinear models. The nature of this decrease varies among the apatite species examined, but no patterns could be determined. The fitted models make geological time‐scale predictions consistent with those based on high‐temperature data only and also make predictions consistent with reasonable inferred low‐temperature histories for all four apatite varieties. The empirical fanning curvilinear equation encompasses low‐temperature annealing at month‐to‐decade time scales, but low‐temperature annealing at shorter time scales may occur by a distinct mechanism. We consider but rule out annealing by radiation from short‐lived activated isotopes. We also reconsider the notion of the initial track length, and the appropriate length for normalizing confined track length measurements

Exhumation of the southern Pyrenean fold-thrust belt (Spain) from orogenic growth to decay

The deformation and exhumation history of an orogen reflects the interactions between tectonic and surface processes. We investigate orogenic wedge deformation, erosion, and sedimentation in the Pyrenees by (a) quantifying the spatiotemporal patterns of exhumation across the southern fold-thrust belt (FTB) with bedrock apatite fission track (AFT) thermochronology and (b) comparing the results with existing deformation, exhumation, and sedimentation chronologies. Eighteen new samples record exhumation during and after orogenesis between 90 and 10 Ma. Rocks from the range core (Axial Zone) record rapid exhumation that progresses east to west and north to south, consistent with patterns of tectonically driven uplift. Synorogenic sediments shed into piggyback basins on the southern fold-thrust belt during mountain building retain a detrital exhumation signal from the Axial Zone. In contrast, samples from other structural positions record exhumation of the thin-skinned Pyrenean thrust sheets, suggesting sediment burial and heating of sufficient magnitudes to reset the AFT system (>~3 km). In some locations, exhumation of these fold-thrust structures is likely an erosional response to thrust-driven rock uplift. We identify an exhumation phase ~25–20 Ma that occurs along the central and eastern Spanish Pyrenees at the boundary between thick- and thin-skinned portions of the wedge. We suggest that this distributed exhumation event records (a) a taper response in the southern orogenic wedge to sediment loading and/or (b) a shift to wetter, stormier climate conditions following convergence-driven uplift and full topographic development. A final exhumation phase between ~20 and 10 Ma may record the excavation of the southern fold-thrust system following base level lowering in the Ebro Basin