(U-TH)/HE THERMOCHRONOMETRY OF CONODONTS FROM THE NORTHERN CALCAREOUS ALPS, AUSTRIA

When attempting to understand the thermal and tectonic histories of orogens, carbonates present a unique problem. Carbonates can often predominate in many orogens and generally lack the mineral phases employed as thermochronometers creating large gaps in our understanding of these systems. However, a solution to this issue can be found in the use of apatite from conodont elements, which can be found reliably in Cambrian through Triassic age carbonates. Many studies have explored the use of biogenic apatite as a geo - thermochronometer, but work by Peppe and Reiners (2007) demonstrated the potential viability of (U-Th)/He dating of conodont elements. This work showed that conodonts behave similarly to magmatic apatite in terms of closure temperature and diffusion characteristics and produced ages in agreement with other thermochronometers, although data from certain localities was highly irreproducible. The purpose of this study is to employ and refine this novel thermochronometer in the Northern Calcareous Alps (NCA) of Austria, an orogenic system well suited to this task as it is composed largely of carbonates and also lacks good quantities of thermochronometric data. To this end, (U-Th)/He age determinations were conducted on a suite of Triassic age conodonts from the NCA. Sample suites tested were taken from two units, the Brenner Mesozoic and the Hochschwab, both allochthonous Triassic age carbonates thrust northward from the continental shelf. Preliminary age results correlate roughly to Apatite Fission Track and ⁴⁰Ar/³⁹Ar ages determined in the region, but one sample set yielded irreproducible ages. Two sample sets taken from the Hochschwab yield ages in agreement with Late Cretaceous to early Tertiary tectonic activities in the region. Brenner Mesozoic samples yielded older ages which may record late Cretaceous thrusting events. Further dating of a wider range of units and in a more comprehensive structural context (e.g., Brenner Mesozoic) will provide new constraints on tectonic and thermal events within the NCA and fill in the gap of data for this particular piece of the broader Alpine orogen.