Post-caldera volcanism: in situ measurement of U–Pb age and oxygen isotope ratio in Pleistocene zircons from Yellowstone caldera

Abstract

The Yellowstone Plateau volcanic field, the site of some of the largest known silicic volcanic eruptions, is the present location of NE-migrating hotspot volcanic activity. Most volcanic rocks in the Yellowstone caldera (0.6 Ma), which formed in response to the climactic eruption of 1000 km 3 of Lava Creek Tuff (LCT), have unusually low oxygen isotope ratios. Ion microprobe analysis of both U^Pb age and N 18 O in zircons from these low-N 18 O lavas reveals evidence of complex inheritance and remelting. A majority of analyzed zircons from low-N 18 O lavas erupted inside the Yellowstone caldera have cores that range in age from 2.4 to 0.7 Ma, significantly older than their eruption ages (0.5^0.4 Ma). These ages and the high-N 18 O cores indicate that these lavas are largely derived from nearly total remelting of normal-N 18 O Huckleberry Ridge Tuff (HRT) and other pre-LCT volcanic rocks. A post-HRT low-N 18 O lava shows similar inheritance of HRT-age zircons. The recycling of volcanic rocks by shallow remelting can change the water content and eruptive potential of magma. This newly proposed mechanism of intracaldera volcanism is best studied by combining in situ analysis of oxygen and U^Pb isotope ratios of individual crystals. ß

Metamorphic growth and recrystallization of zircons in extremely 18O-depleted rocks during eclogite-facies metamorphism: Evidence from U–Pb ages, trace elements, and O–Hf isotopes

“…In this regard, the low d 18 O values of 0.1-3.7& for magmatic cores with the Neoproterozoic U-Pb age in this study can be interpreted to crystallize from low d 18 O granitic magmas, which were formed by remelting of high-T hydrothermally altered rocks in a rifting zone Wu et al, 2007;Zheng et al, 2007b;Zheng et al, 2008). This process was also used to explain the origin of low d 18 O igneous rocks in other areas (Taylor, 1977;Hattori and Muehlenbachs, 1982;Taylor, 1986;Bindeman and Valley, 2000;Bindeman et al, 2001Bindeman et al, , 2008.…”

A Pliocene ignimbrite flare-up along the Tepic-Zacoalco rift: Evidence for the initial stages of rifting between the Jalisco block (Mexico) and North America

“…The older sanidine crystals are probably derived from a Sierra Madre Occidental rhyolitic protolith and were preserved during partial melting to produce the Pliocene rhyolite. A similar scenario has been invoked for the formation of the Lava Creek Tuff rhyolite at Yellowstone by remelting of previously emplaced rhyolitic tuffs (down-dropped blocks), as inferred from δ 18 O and age analysis of zircons(Bindeman et al, 2001). Derivation of the Pliocene rhyolites by crustal partial melting and not crystal fractionation of intermediate lavas is supported by the paucity of intermediate composition lavas in the Tepic-Zacoalco rift during the Pliocene.This hypothesis is also consistent with the Sr trace element data(Table 4).…”

Fine-scale temporal recovery, reconstruction and evolution of a post-supereruption magmatic system

“…The 161 ka Kos Plateau Tuff eruption at Kos-Nisyros led to decompression-induced crystallisation within the remaining mush pile, and subsequent eruptions were hotter, drier and more reduced, likely resulting from mafic recharge (Bachmann et al 2012). In contrast, post-caldera activity at Yellowstone following the 639 ± 2 ka Lava Creek Tuff eruption was dominated by structural resurgence, then longer-term (hundreds of thousands of years) magma replenishment and recycling of modified and hydrothermally altered caldera fill or mush with the eruption of small volume domes from 516 to 473 ka (Bindeman et al 2001;Girard and Stix 2009). At another extreme, post-caldera activity may be expressed by a switch in magmatic expression.…”