3D nanopetrography and chemical imaging of datable zircons by synchrotron multimodal X-ray tomography

摘要

Zircon is the most widely used mineral in petrochronology and provides key information about magmatic and crustal differentiation history of plutonic rocks, transport paths of clastic material ‘from source to sink’ and significantly contributes in the reconstruction of enigmatic planetary-scale tectonic episodes since the Archaean. However, detailed textural analysis of this accessory mineral has always been hampered by two-dimensional (2D) analytical limitations. With the advancements in X-ray nanotomography technology, it is now possible to non-destructively, yet digitally, cut, visualize, compare and quantify internal textures within zircons, their growth and zoning patterns and chemical distribution of trace elements in three dimensions (3D). We present a novel multimodal approach of using a synchrotron radiation nanobeam to perform 3D nanopetrography of < 100 µm zircons at ~100 nm resolution, demonstrating the capabilities of the technique by analysis of Paleoproterozoic zircons from the Central Finland Granitoid Complex. The integrated X-ray absorption, diffraction and fluorescence tomography revealed sector and oscillatory zoning patterns in 3D as well as differences in zoning pattern between trace elements, in addition to lattice parameters and inclusion composition within zircons. The multimodal synchrotron nanotomography elucidates the 3D nanopetrography and trace element composition of submillimeter-sized zircons in unprecedented detail.