HIGH SPATIAL RESOLUTION PETROCHRONOLOGY BY LA- ICP-TOF-MS: A NEW TOOL FOR QUANTIFYING THE TEMPORAL EVOLUTION OF CONTINENTAL CRUST

Recent advances in laser ablation systems and mass spectrometers have enabled the high-speed acquisition of high spatial resolution 2-D and 3-D ‘images’ of elemental and isotopic variations in a range of materials. With some notable exceptions, most applications of this potentially transformative technique have been in the field of biological imaging, and have not yet found widespread application in the field of earth science. Here we combine two recently developed technological advances to demonstrate the ability of this technique to produce petrochronologic data at the micron-scale on accessory minerals (e.g., U/Pb on zircon, monazite, titanite), and rock-forming minerals (e.g., Rb/Sr on mica) and assess the potential applications of these methods to studies of the temporal, geochemical, petrological evolution of continental crust. Analytical instrumentation consists of a newly developed “TwoVol3” laser ablation chamber installed on an NWR193 laser ablation system (Elemental Scientific Lasers) connected to a “Vitesse” time-of-flight inductively coupled plasma mass spectrometer (Nu Instruments). In Laser-based imaging applications, there is a key balance between the speed of acquisition and the required spatial resolution that places practical limits on the area that can be mapped and/or the spatial resolution with which differences in elemental concentrations can be detected. We present data demonstrating that the ultrafast washout (~1 ms), nm-scale stage precision, and the across-chamber <1% elemental reproducibility of the “TwoVol3” cell coupled with the ultrafast acquisition rate of the "Vitesse" increases the limits by which high-resolution, multi-element/isotopic maps can be generated in a given period of time. Together, these instrument attributes enable the routine production of petrochronology images of accessory minerals at a rate of up to 1000 pixels per second at detection limits in the ppm range. This technique has potential to revolutionize the way we collect and interpret petrochronology data at the micron-scale to interpret detailed records of earth history.