Rapid magma evolution constrained by zircon petrochronology and 40Ar/39Ar sanidine ages for the Huckleberry Ridge Tuff, Yellowstone, USA

Abstract

Understanding the time scales of magmatic differentiation, storage, and eruption of largevolume silicic magmas is a primary goal of igneous petrology. Within the Huckleberry Ridge Tuff (HRT; Idaho, USA), representing the earliest and largest caldera-forming eruption associated with Yellowstone volcanic activity, zircon morphological zoning patterns coupled to strongly correlated changes in Ti-in-zircon thermometry and trace element indicators of progressive differentiation provide a proxy record for the evolution of the HRT member B magma body. Tandem in situ and isotope dilution U-Pb dating of single zircon crystals demonstrates an absence of pre-Pleistocene xenocrysts, but reveals the presence of antecrysts recycled from pre-caldera rhyolites in the HRT magma. The petrochronologic interpretation of autocrystic zircon thermal, chemical, and temporal characteristics suggests that HRT member B differentiated over ~10 k.y. prior to eruption at 2.0794 ± 0.0046 Ma as defi ned by new astronomically calibrated, single-crystal total fusion 40 Ar/ 39 Ar sanidine analyses. This refi ned eruption age demonstrates that the transitional polarity preserved by HRT member B does not record the Reunion subchron, but rather a separate, younger geomagnetic event. Our novel approach places the thermal and chemical regime of silicic magmas within a temporal context and demonstrates the rapid evolution of a large volume of silicic magma.

Precise ages of the Réunion event and Huckleberry Ridge excursion: Episodic clustering of geomagnetic instabilities and the dynamics of flow within the outer core

“…7). Four concordant plateaus ranging in age from 2.084 ± 0.005/0.006 to 2.097 ± 0.004/0.006 Ma were generated from what we interpret to be antecrysts, thereby confirming the observations of Rivera et al (2014) and Gansecki et al (1998), but at a scale that the latter study could not resolve owing to large single-crystal uncertainties. is in excess of the single data point uncertainties which range from 10.4 to 96.6 kyr (2σ ) (Fig.…”

“…Lanphere et al (2002) suggested that there is a small amount of excess Ar present in HRT sanidine, which results in total fusion ages that are older than the eruption age. Rivera et al (2014) suggest that sanidine and Ages calculated relative to 28.201 Ma Fish Canyon sanidine (Kuiper et al, 2008) using decay constants of Min et al (2000). Preferred age for each sample is given in bold font.…”

“…1), arguing that members A and B record the Réunion event as defined by the Geologic Time Scale 2004 (Gradstein et al, 2004), and that member C was erupted some 20 kyr later. However, Rivera et al (2014) determined 40 Ar/ 39 Ar and U-Pb ages from the HRT that are significantly younger than those of Ellis et al (2012). The average of several imprecise unspiked K-Ar dates from normally magnetized lavas at Gamarri, Ethiopia, led Kidane et al (1999) to propose that they also record the Réunion event at about 2.07 ± 0.10 Ma (Fig.…”

“…Data of Gansecki et al (1998) has been filtered to remove xenocrysts, analyses with <90% 40 Ar * , and grains that were not completely fused (see text for details). The 40 Ar/ 39 Ar and U-Pb ages from Rivera et al (2014) for the Huckleberry Ridge tuff are mean values of the youngest modes of populations of single crystal sanidine and zircon dates. Magnetic polarity of lava indicated by: open bars reversed; filled bars normal; striped bars transitional.…”

Stratigraphic continuity and fragmentary sedimentation: the success of cyclostratigraphy as part of integrated stratigraphy

“…The consistency between U -Pb and astronomical dating has been substantiated by single crystal U -Pb zircon dating of several ash layers in the tuned Monte dei Corvi and La Vedova sections of northern Italy (Wotzlaw et al 2014). Single crystal 40 Ar/ 39 Ar dating of Pleistocene silicic volcanics that incorporate an astronomically calibrated age of the FCs neutron fluence monitor yield eruption ages that achieve concordance or near concordance with CA-ID-TIMS 238 U/ 206 Pb zircon latecrystallization dates (Rivera et al 2013(Rivera et al , 2014Singer 2014). The use of these (or similar) radio-isotopic dating methods also nears or achieves concordance with independently determined astronomical ages for the same units, extending from the Pleistocene to the Cretaceous (Smith et al 2010;Meyers et al 2012;Wu et al 2013a;Ma et al 2014;Sageman et al 2014).…”