The Yellowstone hotspot in space and time: Nd and Hf isotopes in silicic magmas

doi:10.1016/j.epsl.2006.04.030

Earth and Planetary Science Letters

Volume 247, Issues 1–2, 15 July 2006, Pages 143-156

https://doi.org/10.1016/j.epsl.2006.04.030 Get rights and content

Abstract

Over the course of its 16 m.y. history, the Yellowstone hotspot has produced silicic magmas exhibiting systematic, and often sympathetic, variations in isotopic and chemical composition, temperature and frequency of eruption. Nd and Hf isotopic ratios vary systematically from initial eruptions at ∼ 16 Ma, contemporaneous with basaltic volcanism in eastern Oregon and Washington, to the present day Yellowstone Volcanic Plateau. Nd and Hf isotopic ratios co-vary and span the range of most terrestrial samples, reflecting mixing of mantle and crustal sources. Earliest erupted silicic magmas were hot (in excess of 1050 °C), relatively less evolved and have isotopic ratios within the range of contemporaneous Columbia River flood basalts. The transit of the hotspot across the lithospheric boundary between the western accreted oceanic terrain and the Precambrian craton at 15 Ma is marked by shifts in ε_Nd from + 4 to − 11 and in ε_Hf from + 10 to − 10. The duration of the transit yields a crustal magma source diameter of ∼ 70 km. In the interval from 14 to 9 Ma, ε_Nd systematically increases from − 11 to − 7, recording a minimum increase in the mantle component from 5% to 30%. The mantle component could be twice as great, depending upon the isotopic composition of crust and mantle reservoirs. In this same interval, peak temperatures of ∼ 1000 °C occurred at 9 Ma. The last 8 m.y. are characterized by less frequent eruption of lower temperature (830–900 °C) and more compositionally evolved magmas.

Introduction

Hotspots provide a window into the earth's interior and yield information on the differentiation of the earth, the persistence of long-lived geochemical heterogeneities in the Earth's mantle, and geodynamic processes that recycle outer portions of the earth into its interior. Additionally, because hotspots originate at sublithospheric depths, they play an important role in plate tectonic theory and provide key reference points in assessment of relative plate motions. Hotspots are distinguished by their anomalous thermal character, a pronounced geoidal anomaly, a linear space- and time-transgressive volcanic history, and often, a geochemically distinct volcanic record.

The Yellowstone hotspot (YHS) is of interest because it is located on a continent and offers the opportunity to examine the interrelationship of coupled mantle and crustal igneous processes. Among continental hotspots, the Yellowstone hotspot is amenable to study because it is young, active, and the relative plate motion between the North American plate and the localized mantle heat source is sufficiently rapid so as to leave a well-defined hotspot trace. In addition, the Yellowstone plateau has been the locus of some of the most voluminous production of silicic magma on the planet in the Quaternary.

The YHS has been the focus of investigation for several decades and there continues to be disagreement as to its origin and evolution. Fundamental questions remain including whether or not the hotspot is the result of a mantle plume, and if so, where the plume first impinged on the North American lithosphere. The nature of the source of silicic magmas is speculative, and the mass and thermal contributions from the mantle are poorly constrained, although they are critical factors in crustal growth and maturation. A question of particular importance is whether large silicic provinces represent new material from the mantle or the recyling of older continental material. The ages of volcanic events and their distribution bear on the debate about the relative roles of plate motion and crustal extension in governing the apparent migration rate of the hotspot. In order to address these questions we have measured Nd and Hf isotopic ratios in glass from silicic tuffs erupted over the past 16 m.y. history of the hotspot.

Section snippets

The Yellowstone hotspot

Numerous lines of evidence support a hotspot origin for the Yellowstone system including extraordinarily high heat flow, a pronounced 1000 km diameter geoid anomaly, and a parabola of active seismicity and tectonism in the Yellowstone Plateau/Eastern Snake River Plain [1], [2]. The pronounced topographic decline to the west of the Yellowstone Plateau that defines the Snake River Plain can be modeled as the response of cooling lithosphere that has additional loading from injection of

Analytical methods

We analyzed glass from 54 representative YHS metaluminous rhyolite ash-fall tuffs ranging in age from 15.9 to 0.4 Ma for ¹⁴³Nd/¹⁴⁴Nd. The isotopic ratios of 5 proximal silicic volcanic units along the hotspot track were analyzed for comparative purposes. These units include: basal vitrophyre of the ∼ 16.4 Ma ash-flow tuff of Double H Mountains, a peralkaline tuff in the McDermitt volcanic field; basal vitrophyre from an early unit of the ∼ 16 Ma Jarbidge Rhyolite; the rhyolite of Birch Creek; and

Temporal variation in isotopic ratios

Results of isotopic analysis of YHS glass for present day ratios of ¹⁴³Nd/¹⁴⁴Nd and ¹⁷⁶Hf/¹⁷⁷Hf are provided in Table 1. The temporal pattern of isotopic variation in Nd and Hf in silicic magmas of the YHS is illustrated in Fig. 3. At ∼ 16 Ma, silicic ash fall tuffs exhibit ε_Nd values of + 3 to + 4, within the range of contemporaneous Columbia River flood basalts [7]. Two distinct glasses from the younger Rattlesnake Tuff (7.05 Ma), erupted from the Harney Basin in central Oregon, yield similar ε_Nd

Model for generation of hybrid melts

We propose a model for the generation of silicic magmas at the Yellowstone hotspot that involves the advection of mantle-generated basalt magma into the lower crust that undergoes partial melting producing a hybrid magma that may fractionate and is subsequently erupted at the locus of the hotspot. The evidence for such a process lies in Nd isotopic ratios in silicic magmas (ε_Nd = − 10 to − 5) that are significantly elevated relative to the Precambrian continental crust and hence require a

Discussion

The age and isotopic relations of YHS silicic magmas are consistent with a mantle plume model for the hotspot. Evidence includes the broad distribution of silicic volcanism contemporaneous with mafic volcanism in the same region early in the history of the hotspot. Silicic magmas were being produced as early as 16.5 Ma, and silicic fallout tuffs, including those with sources west of the Sr .706 line such as sample buf94-614 (15.4 Ma), occur in sedimentary interbeds of the Columbia Plateau flood

Summary

Nd and Hf isotopes provide a continuous record of production of silicic magmas from the YHS from 16 Ma to the present. The silicic magmas result from hybridization of partially fused lower crust and mantle-derived basaltic magma, with a minimum mantle contribution ranging between 20% and 40%. From the isotopic record it is possible to trace the hotspot from early in its history in the accreted terranes west of the Precambrian craton onto the craton to its present location beneath the

Acknowledgements

BPN wishes to thank the inhabitants of the Radiogenic Isotope Geochemistry Laboratory at the University of Michigan for their hospitality and assistance during her sabbatical initiation into the nuances of Nd and Hf isotopes. Ongoing discussions with H. E. Cathey, R. B. Smith, M. Jordan and W.P. Leeman have been most beneficial. We very much appreciate careful reviews of versions of the paper by W. Leeman, D. Geist, A. Grunder, A. Glazner and P. Ihinger. Analytical support was provided by

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We present a detailed review of the petrological and geochemical aspects of rhyolite and associated silicic volcanic rocks (up to 20 vol% of all rocks) reported to date from twelve well known Phanerozoic continental mafic Large Igneous Provinces (LIPs). These typically spread over ≤10⁴ km² (rarely 10⁵ km² for Paraná-Etendeka) area and comprise ≤10⁴ km³ of extrusive silicic rocks, erupted either during or after the main basaltic eruption within <5 Myr, with some eruption(s) continuing for ≤30 Myr. These rhyolites and associated silicic volcanic rocks (60−81 wt.% of SiO₂) are mostly metaluminous to peraluminous and are formed via (i) fractional crystallization of parental mafic magma with negligible crustal contamination, and (ii) melting of continental crust or assimilation and fractional crystallization (AFC) of mafic magma with significant crustal contribution. Rhyolites formed by extensive fractional crystallization are characterized by the presence of clinopyroxene phenocrysts, exhibit steep negative slopes in bivariate major oxides plots and weak to no Nb-Ta anomaly; these typically have temperature >900 °C. Rhyolites formed by significant crustal contribution are characterized by strong negative Nb-Ta anomalies, absence of clinopyroxene phenocrysts, and are likely to have a magma temperature <900 °C. Geochemical signatures suggest rhyolite melt generation in the plagioclase stability field with a minor fraction originating from lower crustal depths. A large part of the compositional variability in rhyolites, particularly the Sr-Nd-Pb-O isotope ratios, suggests a significant role of continental crust (upper crustal melting or AFC) in the evolution of these silicic rocks in the continental mafic LIPs.
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The Yellowstone hotspot in space and time: Nd and Hf isotopes in silicic magmas

Abstract

Introduction

Section snippets

The Yellowstone hotspot

Analytical methods

Temporal variation in isotopic ratios

Model for generation of hybrid melts

Discussion

Summary

Acknowledgements

J. Volcanol. Geotherm. Res.

J. Volcanol. Geotherm. Res.

Earth Planet. Sci. Lett.

Geochim. Cosmochim. Acta

Earth Planet. Sci. Lett.

Geochim. Cosmochim. Acta

Earth Planet. Sci. Lett.

Chem. Geol.

Earth Planet. Sci. Lett.

The track of the Yellowstone hot spot: volcanism, faulting, and uplift

Magmatism and extension: the thermal and mechanical effects of the Yellowstone hotspot

J. Geophys. Res.

A captured island chain in the Coast Range of Oregon and Washington

J. Geophys. Res.

Isotopic and geochemical constraints on the origin and evolution of the Columbia River basalt

J. Petrol.

Origin of the Columbia River basalts; melting model of a heterogeneous plume head

Earth Planet. Sci. Lett.

Ages of the Steens and Columbia River flood basalts and their relationship to extension-related calc-alkalic volcanism in eastern Oregon

Geol. Soc. Amer. Bull.

Genesis of flood basalts and Basin and Range volcanic rocks from Steens Mountain to the Malheur River Gorge, Oregon

Geol. Soc. Amer. Bull.

Mantle dynamics and genesis of mafic magmatism in the intermontane Pacific northwest

J. Geophys. Res.

Geochronology of age-progressive volcanism of the Oregon High Plains: implications for the plume interpretation of Yellowstone

J. Geophys. Res.

Helium isotope ratios in Yellowstone and Lassen Park volcanic gases

Geophys. Res. Lett.

Geothermal gases of the mud volcano area, Yellowstone National Park

EOS Trans. Am. Geophys. Union

Intensive sampling of noble gases in fluids at Yellowstone. I. Early overview of the data; regional patterns

Geochim. Cosmochim. Acta

Yellowstone hotspot; a continental mantle plume

EOS Trans. Am. Geophys. Union

Tephrostratigraphy of ash fall tuffs from the Yellowstone hotspot in sedimentary interbeds of the Columbia River Basalt Group

Geol. Soc. Amer. — Abstr. Prog.

Crystal fractionation and recharge (RFC) in the American Bar Flows of the Imnaha Basalt, Columbia River basalt group

J. Petrol.

Physical state of the western U.S. upper mantle

J. Geophys. Res.

Beneath Yellowstone: evaluating plume and nonplume models using teleseismic images of the upper mantle

GSA Today

Upper mantle P wave velocity structure of the eastern Snake River Plain and its relationship to geodynamic models of the region

J. Geophys. Res.

Upper-mantle origin of the Yellowstone hotspot

Geol. Soc. Amer. Bull.

Tomographic images of the Yellowstone Hotspot structure

EOS Trans. Am. Geophys. Union

Linear Vent Area of the Soldier Meadow Tuff, an ash-flow sheet in northwestern Nevada

Geol. Soc. Amer. Bull.

Stratigraphy and geochronology of Miocene volcanic rocks in northwestern Nevada

The High Rock caldera complex; nested “failed” calderas in northwestern Nevada

EOS, Trans. Am. Geophys. Union

Laser fusion 40Ar/39Ar dating of the type Steens Mountain Basalt, southeastern Oregon and the age of the Steens geomagnetic polarity transition

EOS, Trans. Am. Geophys. Union

Peralkaline ash flow tuffs and calderas of the McDermitt volcanic field, southeast Oregon and north central Nevada

J. Geophys. Res.