Characterizing Carbonates from the Sheep Pass Formation, Nevada Using Laser Ablation ICP-MS

Abstract:

Laser ablation plasma mass spectrometry allows for rapid high spatial resolution sampling, which is favorable for geochemically variable samples such as carbonates. This method also allows characterization of samples through the evaluation of elements, element ratios, and isotope ratios. Pairing LA ICP-MS with paragenetic studies provides the ability to geochemically characterize physically distinguishable fluid events that formed new phases. This is particularly useful for analysis of vein filling minerals, which can then be attributed to a tectonic or magmatic event. Coupling elemental analyses with U-Pb dating allows us to not only date the timing of mineralization and its associated tectonic activity, but also to better characterize the fluids in order to understand where they came from and what they may have interacted with. A suite of carbonates from the basal member of the Sheep Pass Formation in east-central Nevada was analyzed using LA ICP-MS, yielding U-Pb ages that are in agreement with both the ages found using ID TIMS and the known age of that member. An age was also attained for fluorite from a vein that cuts the dated Sheep Pass member. This age is distinctly younger than the lacustrine carbonates and is consistent with evidence that the major bounding faults of this basin have experienced multiple phases of movement.