Fundamentals of detrital zircon fission-track analysis for provenance and exhumation studies with examples from the European Alps

Abstract

Fundamental aspects of detrital zircon fission-track analysis in provenance and exhumation studies include etching of fission-tracks in zircon, decomposition of grain-age distributions, detection of major bedrock age components, and reproducibility of results. In this study, we present new detrital zircon fission-track data of sediment samples from eight Italian rivers, draining the European Alps and previously published data from the Rhône delta in southeastern France. These samples are used to demonstrate that variable etching rates in detrital zircon, which have been shown elsewhere to necessitate a multi-etch procedure during sample preparation, are not a significant problem for zircons from the Alps. Etching response in zircon is a function of radiation damage, principally caused by α-decay. Spontaneous fission-track density can be used as a proxy for total radiation damage. We use spontaneous track density, fission-track cooling age, and uranium content to define a "window of countability" for detrital zircon. We also show that detrital zircon fission-track results are reproducible, by comparing results from modern sediments from the same river drainage. The results also compare well with the known distribution of bedrock cooling ages in each drainage. On a regional scale, our data illustrate that a few samples can provide an overview of the fission-track age pattern of a whole orogen, which is useful for exhumation and provenance studies.

Fission-track Analysis of Detrital Zircon

“…Field-based estimates of the zircon fission-track closure temperature are shown from Harrison et al (1979), Zaun and Wagner (1985), Hurford (1986), Brandon and Vance (1992), Foster et al (1996), and Bernet (2002). Kamchatka (Garver et al 2000); Appalachian rivers (Meyer and Garver, 2000); Southern Alps (Garver and Kamp 2002); Indus River (Cerveny et al, 1988); Mississippi River (Meyer and Garver, 2000), Himalaya rivers (Brewer, unpublished); European Alps (Bernet et al 2004b). Radial plot with best-fit peaks.…”

“…If detrital samples of the same stratigraphic age are collected and compared to each other, than it is useful to look for reoccurring peak-age groups (i.e. label P1, P2, P3 and so on, see Table 1 in Bernet et al 2004b; also see Sircombe and Hazelton 2004). If samples with different depositional ages from a stratigraphic section are presented, than P1, P2, P3 etc.…”

“…per sample that are then etched for different lengths of time (see Naeser et al 1987;Garver et al 2000b;Bernet et al 2004b), but in cases where the grain-age distribution is very large (i.e. grain ages span 1000 m.y.)…”

“…Meyer and Garver 2000). The reason for the different etch times is that a detrital sample contains a mixture of zircons with different amounts of radiation damage, and therefore different chemical reactivity (or "etchabilities" -discussed below -see Naeser et al 1987;Garver et al 2000a;Bernet et al 2004b). Nevertheless, in most provenance and exhumation studies, grain ages between a few million and several hundred millions of years can be dated (Fig.…”

Uplift, denudation, and their causes and constraints over geological timescales

“…The more commonly adopted dating methods use single grains and include U-Pb zircon, zircon fission track analysis, and 40 Ar/ 39 Ar dating of micas In all approaches, it is implicit that the mineral system has been closed after erosion. Bernet et al (2004) give an overview of the application of zircon fission track analysis to provenance studies, using samples from both the source region and modern sediments carried in rivers from the same drainage system. Carter and Moss (1999) combined detrital zircon fission track analysis with zircon U-Pb dating, to exploit the different temperature sensitivity of these two dating systems.…”