Author name: Alexander A. Nemchin

High-Spatial-Resolution Geochronology

High-spatial-resolution isotope analyses have revolutionised U–(Th–)Pb geochronology. These analyses can be done at scales of a few tens of microns or less using secondary ion mass spectrometry or laser ablation inductively coupled plasma mass spectrometry. They allow determination of the internal age variation of uranium- and thorium-bearing minerals and as a consequence much greater understanding of Earth system processes. The determination of variation on the micron scale necessitates the sampling of small volumes, which restricts the achievable precision but allows discrimination of discrete change, linkage to textural information, and determination of multiple isotopic and elemental data sets on effectively the same material. High-spatial-resolution analysis is being used in an increasing number of applications. Some of these applications have become fundamental to their scientific fields, while others have opened new opportunities for research.

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Zircon as a Monitor of Crustal Growth

Zircon has long played a key role in crustal evolution studies as the preeminent U–Pb geochronometer. Recent advances in analytical capabilities now permit investigations of complex grains at high spatial resolution, where the goal is to link zircon ages to other petrographic and geochemical information. Zircon can provide time-stamped ‘snapshots’ of hafnium and oxygen isotope signatures of magmas throughout Earth’s history, even at the scale of individual growth zones within a single grain. This information is an invaluable help to geochemists trying to distinguish magmatic events that added new, mantle-derived material to the continental crust from those that merely recycled existing crust.

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