skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


  • NSF Public Access
  • Search Results
  • Integrating Experimental Investigations, Computational Modeling, and Petrochemical Data of Igneous Rocks: Quantifying Open-System Processes in Magma Storage and Transport Zones
Title: Integrating Experimental Investigations, Computational Modeling, and Petrochemical Data of Igneous Rocks: Quantifying Open-System Processes in Magma Storage and Transport Zones
Documenting the processes and timescales of magma formation and diversification and defining the locations, shapes, volumes, and phase states of magma storage and transport zones rely on data produced by novel analytical techniques and state-of-the-art experimental methods. Computational modeling effectively links these critical tools. The Magma Chamber Simulator (MCS) is an internally consistent thermodynamic open system model that uses experimental constraints from rhyolite MELTS (Gualda et al. 2012, Ghiorso & Gualda, 2015) to compute paths of open system magmas that evolve via processes including crystallization, magma mixing, cumulate/mush entrainment, and host-rock assimilation. MCS results yield elemental, isotope, mass, and thermal characteristics of melt ± crystals ± volatiles in "resident" magma, crustal wallrock (melt and solids), recharge magma, and entrained material. To model the petrochemical evolution of igneous rocks related by open-system processes, one typically runs 200+ models that vary initial compositions, pressures, and temperatures of magma, wallrock, etc. Comparison of model results with whole rock, mineral, and melt inclusion chemical data and other constraints (e.g., thermobarometry) yield interpretations about igneous processes at a range of scales—from how crust forms and evolves to processes responsible for in situ geochemical records of crystals—and allows assessment of epistemic and aleatoric uncertainties. Two examples of computational studies will illustrate MCS's utility and flexibility. (1) Modeling of historical basalts at Mt. Etna (Italy) provides evidence for variable degrees of melting of metasomatized mantle, followed by magma recharge and assimilation of partial melts of carbonate-flysch crust. (2) MCS models reproduce whole rock and mineral data of plagioclase-rich basalts at Steens Mountain (USA) through entrainment of gabbroic mush that likely formed in early stages of Columbia River Basalt magmatism. To enhance understanding of trans-lithospheric magma systems, future work on MCS will prioritize (i) building a post-processing environment that utilizes select statistical methods to inform "best-fit" models and to quantitatively assess uncertainty, and (ii) increasing modeling efficiency by adding automated modeling capabilities.  more » « less
Award ID(s):
2151038
PAR ID:
10629352
Author(s) / Creator(s):
; ; ;
Publisher / Repository:
AGU Fall Meeting 2024, held in Washington, D.C., 9-13 December 2024, Session: Volcanology, Geochemistry and Petrology / Experiment to Model to Interpretation: Insights into the Impact of Experimental Design on Models and Interpretation of Natural Systems Poster, Poster No. 3209, id. V11D-3209.
Date Published:
Format(s):
Medium: X
Location:
Washington DC
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; (, Journal of Petrology)
    null (Ed.)
    Abstract The Okataina Volcanic Centre (OVC), located in the Taupo Volcanic Zone, New Zealand, is a dominantly rhyolitic magmatic system in an arc setting, where eruptions are thought to be driven by mafic recharge. Here, Sr–Pb isotopes, and compositional and textural variations in plagioclase phenocrysts from 10 rhyolitic deposits (two caldera, one immediately post-caldera, four intra-caldera, and three extra-caldera) are used to investigate the OVC magmatic system and identify the sources and assimilants within this diverse mush zone. Plagioclase interiors exhibit normal and reverse zoning, and are commonly in disequilibrium with their accompanying glass, melt inclusions, and whole-rock compositions. This indicates that the crystals nucleated in melts that differed from their carrier magma. In contrast, the outermost rims of crystals exhibit normal zoning that is compositionally consistent with growth in cooling and fractionating melts just prior to eruption. At the intra-crystal scale, the total suite of 87Sr/86Sr ratios are highly variable (0·7042–0·7065 ± 0·0004 average 2SE); however, the majority (95 %) of the crystals are internally homogeneous within error. At whole-crystal scale (where better precision is obtained), 87Sr/86Sr ratios are much more homogeneous (0·70512–0·70543 ± 0·00001 average 2SE) and overlap with their host whole-rock Sr isotopic ratios. Whole-crystal Pb isotopic ratios also largely overlap with whole-rock Pb ratios. The plagioclase and whole-rock isotopic compositions indicate significant crustal assimilation (≥20 %) of Torlesse-like metasediments (local basement rock) by a depleted mid-ocean ridge mantle magma source, and Pb isotopes require variable fluid-dominant subduction flux. The new data support previous petrogenetic models for OVC magmas that require crystal growth in compositionally and thermally distinct magmas within a complex of disconnected melt-and-mush reservoirs. These reservoirs were rejuvenated by underplating basaltic magmas that serve as an eruption trigger. However, the outermost rims of the plagioclase imply that interaction between silicic melts and eruption-triggering mafic influx is largely limited to heat and volatile transfer, and results in rapid mobilization and syn-eruption mixing of rhyolitic melts. Finally, relatively uniform isotopic compositions of plagioclase indicate balanced contributions from the crust and mantle over the lifespan of the OVC magmatic system. 
    more » « less
  2. ; ; (, Geochemistry, Geophysics, Geosystems)
    Abstract This study is motivated by the observed variability in trace element isotopic and chemical compositions of primitive (Si52 wt %) basalts in southwest North America (SWNA) during the Cenozoic transition from subduction to extension. Specifically, we focus on processes that may explain the enigmatic observation that in some localities, basalts with low Ta/Th, consistent with parental melts in a subduction setting, have signatures consistent with continental lithospheric mantle (CLM). In locations with the oldest CLM (Proterozoic and Archean), Cenozoic basalts with low Ta/Th have well below zero. We model channelized magma transport through the CLM using simple 1D transport models to explore the extent to which diffusive and reactive mass exchange can modify Nd isotopic compositions via open system melt‐wallrock interactions. For geologically reasonable channel spacings and volume fractions, we quantify the reactive assimilation rates required for incoming melt with a different than the wall‐rock to undergo a substantial isotopic shift during 10 km channelized melt transport. In the presence of grain boundaries, enhanced diffusion between melt‐rich channels and melt‐poor surrounding rock contributes to isotopic equilibration, however this effect is not enough to explain observations; our models suggest a significant contribution from reactive assimilation of wall‐rock. Additionally our models support the idea that the observed covariability in Ta/Th and in Cenozoic basalts cannot be attributed to transport alone and must also reflect the transition from subduction‐related to extension‐related parental melts in SWNA. 
    more » « less
  3. ; ; ; (, Journal of Petrology)
    Abstract The nearly continuous volcanic eruption record at Mt. Etna dating back ~700 years provides an excellent opportunity to investigate the geochemical evolution of a highly active volcano. Of particular interest is elucidating the cause of selective enrichment in alkali elements (K and Rb) and 87Sr/86Sr observed in various episodes of past activity. More recently, this alkali enrichment trend started to manifest in the 17th century and accelerated after 1971, and was accompanied by an increase in the volume, frequency, and explosivity of eruptions. Explanations for this signature include recharge of alkali-enriched magmas and/or crustal contamination from the subvolcanic basement. This study quantitatively examines the role of crustal contamination in post-1971 Etnean magma compositions via hundreds of open-system phase equilibria and trace element calculations based upon whole-rock major oxides, trace elements, 87Sr/86Sr ratios, and mineral compositional data. Available pre-1971 petrochemical data are satisfactorily reproduced by fractional crystallization of a high whole-rock MgO (12–17 wt.%), Ni (135–285 ppm), and Cr (920–1330 ppm) parental magma composition that is documented in Etna's ~4-ka fall-stratified deposit. Observed post-1971 whole-rock and glass trends and phase equilibria are reproduced via modeled assimilation of a skarn and flysch mixture, lithologies that represent the uppermost 10 to 15 km of sedimentary rocks beneath Etna. Notably, models show that K2O (wt.%) and Rb (ppm) behave incompatibly during partial melting of skarn/flysch. Additionally, the observed elevation of 87Sr/86Sr in post-1971 samples is consistent with the addition of radiogenic Sr from wallrock partial melts. In best-fit models, which yield observed post-1971 K2O, Rb, and 87Sr/86Sr trends, ~17% anatectic melt is assimilated and there may be a subordinate stoped wallrock component of ≤2% (percentage is relative to the starting mass of pristine magma). Previous work has shown that metasomatized spinel lherzolite and garnet pyroxenite can be melted in different proportions to reproduce long- and short-term changes observed in Etna’s geochemical products. We propose that the alkali enrichment signature observed after 1971 can be fully explained through the combination of mantle heterogeneity and crustal contamination. In particular, up to ~20% crustal input coupled with mantle heterogeneity of primitive melts explains the geochemical signals quite well. The influence of crustal contamination on post-1971 lavas is, in part, the result of frequent recharge of magmas that thermally primed the middle to upper crust and enhanced its partial melting. 
    more » « less
  4. ; (, Contributions to Mineralogy and Petrology)
    Crystal mush systems, often referenced in the context of large silicic magma bodies, involve the reactivation of a near- solidus crystal mush by heat input from mafic injections. This model suggests that interstitial melt is extracted from the mush, leading to the generation of high-silica rhyolites and granites. Such processes have been well-documented in various tectonic settings and contribute to both large-scale eruptions and the formation of granitic plutons. However, in the Mineral Mountains, Utah, the zircon and whole rock geochemical record indicate a different scenario. The presence of sector-zoned zircons and the absence of highly evolved central domains indicative of extraction from a mush suggest rapid magma generation from partial melting of solid granitoids rather than from a long-lived crystal mush. Fractional crystallization and equilibrium partial melting models support derivation from the granitoid bodies, rather than from a common shared parental rhyolitic magma or from coeval basalts. The proposed model, presented here, for rhyolite formation in the Mineral Mountains involves episodic injections of mafic magma into the crust, leading to localized partial melting of different granitoid lithologies. Partial melting up to 30% can produce isolated, ephemeral pools of high-silica melt, which crystallize zircons rapidly and ascend to form rhyolitic domes. This process is distinct from the long-lived crystal mush model, explains the lack of intermediate compositions, and the confinement of mafic eruptions to lower elevations. By integrating geochemical data, zircon morphology, and fractionation modeling, this study provides a comprehensive framework for understanding the magmatic processes at play in the Mineral Mountains. 
    more » « less
  5. ; (, Geosphere)
    Bulk-rock data are commonly used in geochemical studies as a proxy for melt compositions in order to understand the evolution of crustal melts. However, processes of crystal accumulation and melt migration out of deep-crustal, crystal-rich mush zones to shallower storage regions raise questions about how faithfully bulk-rock compositions in plutons approximate melt compositions. This problem is particularly acute in the lower crust of arcs, where melt reservoirs are subject to periodic melt extraction that leaves behind a cumulate residue. Here, we examine bulk-rock data from the perspective of high-Sr/Y plutonic rocks in the lower crust of a well-exposed Early Cretaceous cordilleran-arc system in Fiordland, New Zealand. We test the validity of using high-Sr/Y bulk-rock compositions as proxies for melts by comparing bulk-rock compositions to melts modeled from >100 major- and trace-element analyses of 23 magmatic clinopyroxene grains from the same samples. The sampling locations of the igneous clinopyroxenes and encompassing bulk rocks are distributed across ~550 km2 of exhumed lower crust and are representative of Mesozoic lower-crustal arc rocks in the Median batholith. We confirm that bulk-rock data have characteristics of high-Sr/Y plutons (Sr/Y >50, Na2O >3.5 wt%, Sr >1000 ppm, and Y <20 ppm), features that have been previously interpreted to indicate the presence of garnet as a residual or fractionating phase. In contrast to bulk rocks, igneous clinopyroxenes have low Sr (<100 ppm), high Y (25–100 ppm), and low molar Mg# [100 × Mg/(Mg + Fe)] values (60–70), which are consistent with derivation from fractionated, low-Sr/Y melts. Chondrite-normalized rare-earth-element patterns and Sm/Yb values in clinopyroxenes also show little to no evidence for involvement of garnet in the source or in differentiation processes. Fe-Mg partitioning relationships indicate that clinopyroxenes are not in equilibrium with their encompassing bulk rocks but could have been in equilibrium with melt compositions determined from chemometry of coexisting igneous hornblendes. Moho-depth calculations based on bulk-rock Sr/Y values also yield Moho depths (average = 69 km) that are inconsistent with Moho depths based on bulk-rock Ce/Y, contact aureole studies, Al-in-horn- blende crystallization pressures, and our modeled clinopyroxene crystallization pressures. These data indicate that most Mesozoic high-Sr/Y bulk rocks in the lower crust of Fiordland are cumulates formed by plagioclase + amphibole + clinopyroxene accumulation and interstitial melt loss from crystal-rich mush zones. Our data do not support widespread fractionation of igneous garnet nor partial melting of a garnet-bearing source in the petrogenesis of these melts. We speculate that melt extraction and the production of voluminous cumulates in the lower crust were aided by unusually high heat flow and high magma addition rates associated with an Early Cretaceous arc flareup. We conclude that bulk-rock compositions are poor proxies for melt compositions in the lower crust of the Median batholith, and geochemical modeling of these high-Sr/Y bulk rocks would overemphasize the role of garnet in their petrogenesis. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email