Timescales of crustal magma reservoir processes: insights from U-series crystal ages

Abstract

The dynamic processes operating within crustal magma reservoirs control many aspects of the chemical composition of erupted magmas, and crystals in volcanic rocks provide a temporally constrained archive of these changing environments. In this review, I compile 238 U-230 Th ages of accessory phases and 238 U-230 Th-226 Ra ages of bulk mineral separates of major phases. These data document that crystals in individual samples can have ages spanning most of the history of a volcanic centre. Age populations for accessory phases show protracted pre-eruptive crystal residence times but few crystals predate magmatic activity at a given centre. These data have been interpreted in the context of residence times of the host magmas or timescales of the storage of crystals within a largely crystalline portion of the reservoir system. In contrast, less than half of the bulk separate 238 U-230 Th-226 Ra ages for major phases are more than 10 kyr older than the eruption. Many of these apparently conflicting observations of ages of major and accessory phases can be reconciled within the context of a model where a crystal mush was remobilized during processes leading to eruption. Overall, the compiled data show that crystals contain rich archives of magmatic processes in crustal reservoirs, especially when combined with other crystal-scale geochemical data.

Repeated Rhyolite Eruption From Heterogeneous Hot Zones Embedded Within a Cool, Shallow Magma Reservoir

“…Zircons that record 10 3 –10 5 years of pre‐eruptive crystallization are a common feature of rhyolites (e.g., Costa, ; Reid, ). Xenocrysts, crystals disaggregated from the country rock, are not common in the LdM rhyolites nor generally in large silicic systems (Cooper, ). However, distinguishing zircons endemic to the erupted magma from those inherited from earlier, but related, magmatism (i.e., antecrysts) is commonly ambiguous (e.g., Chamberlain, Wilson, et al, ; Samperton et al, ; Wilson & Charlier, ).…”

Age of theLavaCreek supereruption and magma chamber assembly at Yellowstone based on40Ar/39Ar andU‐Pb dating of sanidine and zircon crystals

“…The ranges of zircon crystallization ages from silicic magmas that produce voluminous ignimbrites have been used to infer the dynamics and durations of magma reservoir evolution leading to supereruptions [see Lipman and Bachmann, 2015;de Silva and Gregg, 2014;Cooper, 2015 for recent reviews]. Physical models predict that shallow bodies of eruptible silicic magma with volumes like those associated with supereruptions (>450 km 3 ) are established incrementally during times of relatively high magmatic input (>0.005-0.01 km 3 yr 21 ) over intervals on the order of up to 10 4 -10 5 years depending on transient rates of magma recharge and the preexisting thermal state of the subvolcanic reservoir [Annen, 2009;Sch€ opa and Annen, 2012;Gelman et al, 2013;de Silva and Gregg, 2014].…”

The temporal evolution of chemical and physical properties of magmatic systems

“…By reviewing existing data on U-series crystal ages Cooper (2015) shows that accessory minerals, such as zircon, record protracted pre-eruptive residence times while approximately half of the major phases collected in eruptive products are less than 10 kyr older than the eruption. These data have been interpreted to result from the long-term storage of zircons in highly crystallized or solidified magma bodies, which are rapidly remobilized before eruption (Wilson & Charlier 2009;Charlier & Wilson 2010;Storm et al 2011).…”