Project

Discipline

Geodynamic evolution; U-Pb thermochronology; Geochronology; Northern Andes; Diffusion

Lead
Le but principal de cette étude est d’améliorer la compréhension et la méthodologie de la thermochronologie U-Pb de haute température, en l’appliquant à des minéraux accessoires extraites de roches cristallines, et en modélisant les données U-Pb pour générer des histoires thermiques pour des températures >350°C. Les techniques thermochronologiques contribuent d’importantes connaissances aux processus géologiques. La plupart de ces techniques sont sensibles à des températures faibles (<350°C).
Lay summary
Buts i) Améliorer la thermochronologie de haute température U-Pb en l’appliquant à des minéraux accessoires extraites de roches cristallines Mésozoiques, et en modélisant les données U-Pb pour générer des histoires thermiques pour des températures plus élevées que 350°C. ii)  Tester l’hypothèse que l’isotope fils (Pb) est émis des minéraux accessoires par diffusion volumétrique, en fonction de la température. iii) Déterminer les durées d’extension continentale qui ont mené au rifting et à la génération de la lithosphère océanique de la Téthys Occidental.   Innovation i) Combiner des datations U-Pb de cristaux d’apatite, rutile et de titanite (ID-TIMS) avec des datations in-situ (LA-MC-ICP-MS) sur les mêmes minéraux, qui peuvent être utilisés pour reconstruire des histoires thermiques théoriques, et evaluer l’exactitude de ces reconstructions. ii) Reconstruire des histoires thermiques par inversion numérique des âges et des tailles des grains. iii) Appliquer cette méthodologie à des roches Phanérozoiques, pour lesquelles l’obtention d’âges précis sur des minéraux pauvres en Pb radiogénique, représente un défi analytique.

Direct link to Lay Summary

Last update: 02.04.2013

Active participation

Self-organised

Number	Title	Start	Funding scheme

The main aim of this study is to advance understanding and methodology of high-temperature U-Pb thermochronology, by applying it to accessory phases extracted from young (Mesozoic) crystalline rocks, and inverting U-Pb age data to generate continuous thermal history paths at temperatures higher than 350°C.This project will advance research into U-Pb thermochronology of titanite, apatite and rutile separated from Phanerozoic crystalline rocks, by combining i) ID-TIMS dates of a range of grain sizes, ii) laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) intra-grain dates, and iii) cathodoluminescence, back-scattered electron imaging and LA-ICP-MS trace element mapping to qualitatively and quantitatively constrain crystal heterogeneity, respectively.Thermochronological techniques have significantly contributed to our understanding of geological processes since the early 1970’s because they are capable of accurately quantifying variations in temperature, with time. Most techniques are sensitive to low temperatures (<350°C), and thus are limited to investigating the thermal histories of the upper crust. This study represents an important contribution to Earth Sciences because:i)High temperature (>350°C) U-Pb thermochronology provides earth scientists with a tool to generate continuous t-T paths for the lower and middle crust, which will significantly increase our understanding of a) how lower crustal rocks exhume to the surface (e.g. pure or simple shear during extension?), b) the tectonic stability of lower crust and cratons, and c) the tectonic history of active margins over long time periods (e.g. 500 Ma), during which they may have experienced numerous terrane collision events and a substantial quantity (e.g. >15km) of exhumation.ii)This will be the first study to combine ID-TIMS and LA-MC-ICP-MS ages of apatite, which can be used to derive theoretical thermal history paths, and assess the accuracy of those paths. Furthermore, corroboratory data from both techniques would confirm that Pb is lost by thermally activated diffusion, confirming the use of apatite U-Pb ages as thermochronometers.The Northern Andes will be used as the study region because they represent a superb natural laboratory to test the U-Pb thermochronological method. The tectonic history of the region has been extensively studied by the principal applicant and other authors, and numerous 40Ar/39Ar and lower temperature thermochronological constraints have been published. Previous studies that utilised the U-Pb thermochronological method applied it to Precambrian rocks. This study will be the first to apply it to Phanerozoic rocks, and will therefore face the challenge of generating sufficiently precise U-Pb ages from minerals with low ratios of radiogenic to common Pb.