Strengthening the link between geochronology, textures and petrology

Abstract

Time must be integrated with other geologic parameters such as pressure–temperature ( P- T), composition or structural–textural information in order to quantify the dynamics of geologic processes like mountain building, faulting, metamorphism or magmatism. In the past, this connection was weak due to large sample sizes required in geochronology; however, recent developments open up exciting new possibilities. Texturally controlled in situ dating of minerals utilizing UV–laser ablation 40Ar/ 39Ar or Rb–Sr microsampling facilitates the crucial link between ages and textures at high spatial resolution. In situ U–Pb ages of accessory minerals can now be linked to the corresponding P- T evolution via their characteristic trace elemental signatures, indicative of mineral reactions in rocks. Garnet dating by Sm–Nd, and more recently Lu–Hf, can greatly benefit from both laser ablation inductively coupled plasma mass spectrometry (ICPMS) screening and improved leaching strategies, improving the link between time and P- T. Such integrated approaches can yield the duration and rates of deformation in shear zones, the rates of burial and exhumation of subducted rocks or the duration of entire metamorphic loops, to name a few. Potential for further development is identified in diverse areas. Dating of carbonate minerals related to brittle faulting using U–Pb could provide previously unavailable constraints on rates and duration of brittle deformation in the Earth’s upper crust. In situ Rb–Sr dating applicable to micas could become available using either laser ablation dynamic reaction cell-ICPMS or microbeam accelerator mass spectrometry. Other future developments and trends, and their limitations, are discussed briefly.