Research Highlights
Burgess, S. D., Coble, M. A., Vazquez, J. A., Coombs, M. L., and Wallace, K. L., 2019, On the eruption age and provenance of the Old Crow tephra. Quaternary Science Reviews, v. 207, p. 64-79.
The authors investigated the Old Crow tephra found in eastern Beringia utilizing U/Pb, U/Th, and (U-Th)/He zircon geochronology as well as titanomagnetite geochemistry to determine provenance and eruption age. The authors found that the eruption occurred at 202.9 +/-9.5 ka from an Aleutian source distinct from the Emmons Lake Volcanic Center. This work introduces a new Old Crow tephra eruption age during the MIS 7 interglacial period which disagrees with previous MIS 5e deposition ages, and highlights the need for more studies investigating Pleistocene chronology in eastern Beringia.
Blackburn, T., Simon-Tov, S., Coble, M.A., Stock, G., Brodsky, E., and Hallet, B., 2019, Composition and formation age of the amorphous silica coating glacially polished surfaces: Geology, v. 47, no. 4, p. 347–350.
Amorphous silica layers deposited on bedrock were investigated to determine the timing and nature of their deposition during glaciation in Yosemite National Park, California. The authors found that the amorphous coatings precipitated from chemical weathering of silicate bedrock beneath glaciers during the last glacial maximum at 30-10 ka. This work helped to recognize that glacial polish is comprised of subglacial chemical precipitates which may preserve the timing of formation as well as the compositions of subglacial waters.
Drabon, N., Byerly, B.L., Byerly, G.R., Wooden, J.L., Wiedenbeck, M., Valley, J.W., Kitajima, K., Bauer, A.M., Lowe, D.R., 2022. Destabilization of Long‐Lived Hadean Protocrust and the Onset of Pervasive Hydrous Melting at 3.8 Ga.
Detrital zircon trace and rare earth element geochemistry as well as Hf and O isotopes were investigated from a new Hadean locality, containing 4.1-3.3 Ga detrital zircons from the 3.31 Ga Green Sandstone Bed, Barberton Greenstone Belt. Zircons older than 3.8 Ga show evidence for a long-lived protocrust with a relative absence of juvenile additions to zircon-bearing magmas, whereas after 3.8 Ga zircon Hf isotopes indicate a more muted protocrust signal with evidence for relatively juvenile melt components. These results mirror results from other Archean terranes and indicate a global onset of crustal instability and recycling between 3.6 and 3.8 Ga, with implications for the formation of early Earth crust and onset of plate tectonics.
Anderson, N.L., Singer, B.S., and Coble, M.A., 2019, Repeated rhyolite eruption from heterogeneous hot zones embedded within a cool, shallow magma reservoir: Journal of Geophysical Research: Solid Earth, v. 124, no. 3, p. 2582–2600.
The Laguna del Maule volcanic field, central Chile, was investigated in this study to determine the timing and conditions of zircon crystallization in a large, shallow, silicic magma body. By measuring zircon trace elements and U-Th ratios, the authors determined the magma reservoirs produces two episodes of rhyolitic volcanism at 23-19 and 8-2 ka. Zircon crystallization occurred over 160 kyr, over which time several hundred cubic kilometers of magma were emplaced. Their results indicate most of the volume of the reservoir existed in a relatively cold, near-solidus state during zircon crystallization, yet smaller hot zones were likely distributed throughout the reservoir containing extractible magma mush which produced the rhyolite eruptions.
Benson, T.R., Coble, M.A., Rytuba, J.J., and Mahood, G.A., 2017, Lithium enrichment in rhyolite magmas of intracontinental calderas: Nature Communications, v. 8, p. 270.
In this study the authors demonstrated that lake sediments within intracontinental rhyolitic calderas have the potential to host large lithium clay deposits, a material of great economic value due to the rising demand for lithium-ion batteries. Quartz-hosted melt inclusions from rhyolitic ignimbrites and lavas erupted through felsic continental crustal material were found to contain Li concentrations similar to those observed in rare-metal granites (>1000 ppm), whereas rhyolites erupted through thinner mafic crust have considerably less Li enrichment. Over 100 large Cenozoic calderas have been identified in western North America, of which the largest and youngest are likely to host large volumes of Li clay resources.
Rubin, A.E., Cooper, K.M., Till, C.B., Kent, A.J., Costa, F., Bose, M., Gravley, D., Deering, C. and Cole, J., 2017, Rapid cooling and cold storage in a silicic magma reservoir recorded in individual crystals: Science, v. 356, p.1154-1156.
U-Th and trace element concentrations in zircon were investigated from the Taupo Volcanic Zone, New Zealand, to determine the thermal history zircon crystallization. The authors found that zircons resided in the magmatic system for 1,000- 100,000 years, however they experienced magmatic temperatures of >650-750 C for only years to centuries. The results of this study indicate magma reservoirs likely exist in a “cold,” near-solidus state for most of their lifetimes, punctuated by periods of rapid heating and remobilization prior to eruptions.