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The exhumation history of basement areas is poorly constrained because of large gaps in the sedimentary record. Indirect methods including low temperature thermochronology may be used to estimate exhumation but these require an inverse modeling procedure to interpret the data. Solutions from such modeling are not always satisfactory as they may be too broad or may conflict with independent geological data. This study shows that the input of geological constraints is necessary to obtain a valuable and refined exhumation history and to identify the presence of a former sedimentary cover presently completely eroded. Apatite fission-track (AFT) data have been acquired on the northern part of the Ardenne Massif close to the Variscan front and in the southern Brabant, in particular for the Visean ash-beds. Apatite fission-track ages for surface samples range between 140 ± 13 and 261 ± 33 Ma and confined tracks lengths are ranging between 12.6 ± 0.2 and 13.8 ± 0.2 μm. Thermal inversion has been realized assuming that (1) samples were close to the surface (20–40 °C) during Triassic times, this is supported by remnants of detrital Upper Permian–Triassic sediments preserved in the south of the Ardenne and in the east (border of the Roer Graben and Malmédy Graben), and (2) terrestrial conditions prevailed during the Early Cretaceous for the Ardenne Massif, as indicated by radiometric ages on paleoweathering products. Inversion of the AFT data characterizes higher temperatures than surface temperatures during most of the Jurassic. Temperature range is wide but is compatible with the deposition on the northern Ardenne of a significant sedimentary cover, which has been later eroded during the Late Jurassic and/or the Early Cretaceous. Despite the presence of small outliers of Late Cretaceous (Hautes Fagnes area), no evidence is recorded by the fission-track data for the deposition of a significant chalk cover as highlighted in different parts of western Europe. These results question the existence of the London-Brabant Massif as a permanent positive structure during the Mesozoic.

Quartz overgrowths from Keuper sandstones of the Paris basin were examined using cathodoluminescence (CL) microscopy and spectroscopy coupled with a scanning electron microscope (SEM). With the use of standard cold CL equipment, it was observed that the emission of authigenic quartz is much less intense than that of detrital quartz grains, but a reversal of intensity was observed with scanned CL in the 200-800 nm range. The main CL emission band of diagenetic quartz is at 330-340 nm in the UV range, with other bands in the visible range. The determination of trace element distributions in authigenic quartz by in situ analyses and by SIMS imagery reveals the correlation of the 330-340 nm emission band with the highest Al and Li contents. The cathodoluminescence emission of diagenetic quartz in the UV range appears to be influenced by the coupled substitution of Al and Li into the crystal. Two explanations are suggested: (1) Al, Li, or both serve as activators, and (2) the incorporation of Al and Li causes lattice defects that lead to an enhancement of the intrinsic luminescence. Trace element analyses and fluid-inclusion studies revealed that quartz overgrowths precipitated from a fluid that partially originated from an Li-enriched primary brine derived from eastern Triassic evaporites of the Paris basin. The specific CL emission band in the UV range can be linked to the diagenetic environment. The chemistry of the fluids appears to be the essential parameter, whereas precipitation temperatures do not influence the occurrence of such emissions.

Cathodoluminescence (CL) spectrometry represents a promising technique for the analysis of trace-element concentrations and distributions in minerals. However, a higher precision and a standardization of the recording conditions are required to use CL spectral data quantitatively. A significant step towards a more quantitative treatment of CL spectra is presented in this study. A procedure to correct the spectra for the various efficiencies as a function of the wavelength of the CL detector is proposed using low-pressure mercury-vapor and quartz-iodine lamps. CL spectra presented in this study are thus corrected for the system response. Apatite CL spectra, which are commonly composed of two broad bands centered at 3.5 and 2.2 eV, are deconvoluted to isolate component bands and determine their areas. The crystallographic control by prismatic or basal sections of apatite on spectral intensities is significant and only prismatic sections should be used. Signal decrease associated with electron bombardment (electron beam aging) is exponential and appears drastic in the first hundred seconds but continues even after 15 minutes of beam bombardment. All observed CL bands could be correlated with a specific activator [rare earth elements (REE) or manganese]. The 3.5 eV band is composed of three bands at 3.59 eV, 3.29 eV, and 2.87 eV. Ion microprobe results and comparison between CL and photoluminescence data support [Ce.sup.3+] activation for the origin of these bands. The relationship between CL band intensity and REE concentration measured by ion microprobe analysis demonstrates that CL also can provide semi-quantitative data for [Gd.sup.3+], [Ce.sup.3+], [Dy.sup.3+], and [Sm.sup.3+] when recording conditions are strictly controlled.