Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
8911287 | Journal of Volcanology and Geothermal Research | 2018 | 67 Pages |
Abstract
Rhyolitic volcanism in the Yellowstone Volcanic Field has spanned over two million years and consisted of both explosive caldera-forming eruptions and smaller effusive flows and domes. Effusive eruptions have been documented preceding and following caldera-forming eruptions, however the temporal and petrogenetic relationships of these magmas to the caldera-forming eruptions are relatively unknown. Here we present new 40Ar/39Ar dates for four small-volume eruptions located on the western rim of the second-cycle caldera, the source of the 1.300â¯Â±â¯0.001â¯Ma Mesa Falls Tuff. We supplement our new eruption ages with whole rock major and trace element chemistry, Pb isotopic ratios of feldspar, and paleomagnetic and rock magnetic analyses. Eruption ages for the effusive Green Canyon Flow (1.299â¯Â±â¯0.002â¯Ma) and Moonshine Mountain Dome (1.302â¯Â±â¯0.003â¯Ma) are in close temporal proximity to the eruption age of the Mesa Falls Tuff. In contrast, our results indicate a period of volcanism at ca 1.45â¯Ma within the Yellowstone Volcanic Field, including the eruption of the Bishop Mountain Flow (1.458â¯Â±â¯0.002â¯Ma) and Tuff of Lyle Spring (1.450â¯Â±â¯0.003â¯Ma). These high-silica rhyolites are chemically and isotopically distinct from the Mesa Falls Tuff and related 1.3â¯Ma effusive eruptions. The 40Ar/39Ar data from the Tuff of Lyle Spring demonstrate significant antecrystic inheritance, prevalent within the upper welded ash-flow tuff matrix, and minimal within individual pumice. Antecrysts are up to 20â¯kyr older than the eruption, with subpopulations of grains occurring every few thousand years. We interpret these results as an indicator for the timing of magmatic pulses into a growing magmatic system that would ultimately erupt the Tuff of Lyle Spring, and which we more broadly interpret as the tempo of crustal accumulation associated with bimodal magmatism. We propose a system whereby chemically, isotopically, and temporally distinct, isolated small-volume magma batches are periodically generated and erupted in a low magmatic flux state, which is punctuated by larger volume caldera-forming eruptions.
Related Topics
Physical Sciences and Engineering
Earth and Planetary Sciences
Geochemistry and Petrology
Authors
Tiffany A. Rivera, Ryan Furlong, Jaime Vincent, Stephanie Gardiner, Brian R. Jicha, Mark D. Schmitz, Peter C. Lippert,