V036-04
New Frontiers in Microanalytical Noble Gas Geochronology and Thermochronology
Monday, 14 December 2020: 08:42
Virtual
Kip V Hodges, Arizona State University, Tempe, AZ, United States, Matthijs C Van Soest, Arizona State University, School of Earth and Space Exploration, Tempe, AZ, United States, Chris McDonald, Arizona State University, School for Earth and Space Exploration, Tempe, AZ, United States, Cameron M Mercer, NASA Goddard Space Flight Center, Greenbelt, MD, United States and Hayden Miller, Arizona State University, School of Earth and Space Exploration, Tempe, United States
Abstract:
The adaptation of ultraviolet laser microsampling technologies to
40Ar/
39Ar dating studies in the mid-1990’s launched a new era of microanalytical thermochronology. Many successful studies undertaken over the next decade and a half by researchers worldwide provided us with an unprecedented understanding of the distribution of radiogenic Ar within minerals popular for thermochronology, and we began to understand how the complexity of Ar systematics in these minerals sometimes challenge simple conceptual approaches to thermochronology. Despite these advances, the number of laser ablation
40Ar/
39Ar thermochronology studies has fallen dramatically in recent years. Our purpose here is to encourage a renaissance in this technique, and an expansion of the use of the laser ablation microprobe (UVLAMP) to include (U-Th)/He thermochronometry.
We show examples of how ArF excimer (193 nm) laser microprobes are currently being used at Arizona State University for both 40Ar/39Ar and (U-Th)/He studies. Most of our work in the 40Ar/39Ar realm at present is focused on impact melt materials, especially those collected during the Apollo missions. We show how the laser microprobe offers a dramatic improvement over incremental heating studies in establishing 40Ar/39Ar dates of specific melt components in these complex rocks. Our UVLAMP 40Ar/39Ar research on terrestrial samples is focusing on dating tectonite fabric-forming minerals, what we might call “tectochronology” rather than “petrochronology”. We show how such studies are now much easier and the results are more informative than during the early days of UVLAMP studies as a consequence of recent improvements in mass spectrometry technologies. Finally, we show examples of UVLAMP (U-Th)/He dating studies of apatite and zircon crystals using methods first developed at ASU. Such work is now routine in our laboratories. In conjunction with laser ablation U/Pb geochronology on the same crystals, this technique has proven especially useful for detrital studies.
