Maureen Feineman - Academia.edu (original) (raw)

Papers by Maureen Feineman

ICERI2019 Proceedings, 2019

Geological Society of America Abstracts with Programs, 2017

AGU Fall Meeting Abstracts, Dec 1, 2016

Geological Society of America Abstracts with Programs, 2017

ICERI2019 Proceedings, 2019

Volcanica

Thríhnúkagígur Volcano, Iceland, is a composite spatter cone and lava field characteristic of bas... more Thríhnúkagígur Volcano, Iceland, is a composite spatter cone and lava field characteristic of basaltic fissure eruptions. Lava drainback at the end of the eruption left ~60 m of evacuated conduit, and a 4 × 104 m3 cave formed by the erosion of unconsolidated tephra by the feeder dike. Field relationships within the shallow plumbing system provide three-dimensional insight into conduit formation in fissure systems. Petrographic estimates and the relative volumes of the cave and erupted lavas both indicate xenolithic tephra comprises 5–10 % of the erupted volume, which cannot be reproduced by geochemical mixing models. Although crustal xenolith entrainment is not geochemically significant, we posit that this process may be common in the Icelandic crust. The Thríhnúkagígur eruption illustrates how pervasive, poorly consolidated tephra or hyaloclastite can act as a mechanically weak pre-existing structure that provides a preferential pathway for magma ascent and may influence vent locat...

Contributions to Mineralogy and Petrology, 2020

Zircon is widely used to date metamorphic processes, particularly due to slow cation diffusion un... more Zircon is widely used to date metamorphic processes, particularly due to slow cation diffusion under crustal conditions. Here, we present laser-ablation depth profiling data that demonstrate rapid U diffusion in partially altered, high-pressure zircon. The zircons are hosted in metagabbros that underwent eclogite-facies (~ 550 °C, ~ 2.6 GPa) recrystallization during subduction of the Monviso meta-ophiolite. One metagabbro contains only newly grown zircons (50.2 ± 1.1 Ma); two coarser-grained samples exhibit thin metamorphic rims on igneous cores. Most profiles in the coarse-grained samples record discrete Pb C-rich and Pb*-, U-, Th-, and trace-element poor rims in the outermost ≤ 5 µm of each grain, but U shows apparent diffusion profiles that extend ~ 10-15 µm into zircon crystals and correlate with U-Pb date resetting. The data define three populations (cores, diffusively reset rims, and newly precipitated rims) that form two two-component mixtures, indicating that recrystallization was everywhere coupled with U addition. Data from fully equilibrated rims form a single age population (51.1 ± 0.4 Ma) within error of the newly grown zircon and compatible with ~ 1 My fluid-rock interaction timescales. We interpret the U profiles as evidence of inward U diffusion associated with fluid-induced resorption, and systematically exclude other mechanisms for their formation. However, calculated diffusivity estimates are > 20 orders of magnitude faster than predicted by experiments. The absence of zircon lattice damage, and the propagation of diffusion inward of a reaction front, indicates a link between fluid-saturated zircon alteration and fast U diffusion in zircon. Our results emphasize that-even at low temperature-zircon U-Pb systematics may be affected by parent and/or daughter diffusion over length scales large enough to affect laser-ablation or ion microprobe spot analyses.

Contributions to Mineralogy and Petrology

Here we present major element, trace element, and oxygen isotope data for garnet from an amphibol... more Here we present major element, trace element, and oxygen isotope data for garnet from an amphibolitized eclogite block from Ring Mountain, Franciscan Complex, California, USA. Garnetite veins 1–5 cm thick are laterally continuous up to 10 m within an Mg-rich blackwall zone of the eclogite block. Complex major and trace element zoning patterns reveal multiple stages of garnet growth in both the matrix and garnetite veins. Similarities in major and trace element zoning between matrix and vein garnet suggest that crystallization of the garnetite veins began toward the end of matrix garnet core growth, and continued throughout the garnet growth history of the rock. Oscillatory zoning in rare-earth elements suggests garnet growth in pulses, with matrix-diffusion-limited growth in between pulses. Oxygen isotope analyses of matrix and vein garnet have a range in δ 18 O values of 5.3–11.1 ‰. Differences in δ 18 O values of up to ~ 4 ‰ between garnet core and rim are observed in both the matrix and vein; garnet cores range from 9.8 to 11.1 ‰ (median 10.4‰), garnet mantles range from 8.3 to 10.0 ‰ (median 9.7 ‰), and garnet rims range from 5.8 to 7.8 ‰ (median 6.7 ‰). Late-stage vein crystallization appears as a garnet “cement” that fills in a network of small (typically 5–50 µm) garnet cores, and likely crystallized from an amorphous phase. The low δ 18 O values of this latest stage of garnet growth are consistent with interaction with serpentinites, and likely represent the physical incorporation of the eclogite block into the serpentinite matrix mélange.

Mining, Metallurgy & Exploration

American Mineralogist, May 1, 2020

This is a preprint, the final version is subject to change, of the American Mineralogist (MSA) Ci... more This is a preprint, the final version is subject to change, of the American Mineralogist (MSA) Cite as Authors (Year) Title. American Mineralogist, in press.

Geochemistry, Geophysics, Geosystems

Many of Earth's volcanoes experience well-defined states of "quiescence" and "unrest,"

Earth and Planetary Science Letters, 2012

Geostandards and Geoanalytical Research, 2016

Trace element concentrations and Li isotope ratios have been analyzed in olivine-hosted melt incl... more Trace element concentrations and Li isotope ratios have been analyzed in olivine-hosted melt inclusions found in tephras from Volcan Jorullo, a monogenetic cinder cone of the Michoacan-Guanajuato Volcanic Field, Mexico. The melt inclusions range from basalt to basaltic andesite in composition, with K2O and incompatible trace element concentrations increasing with SiO2 content. Lithium concentrations range from 2 ppm in the most primitive inclusions to 12 ppm in the most evolved. Some of the lava flows from Jorullo contain abundant granitic xenoliths, and most contain plagioclase xenocrysts, suggesting that the lavas have assimilated some amount of crustal material. Lithium concentrations in the lava flows are 10-12 ppm, while the Li concentration in a granitic xenolith from one of the flows is 29 ppm. We interpret the basaltic melt inclusions containing 2 ppm Li to represent the primitive melt, while the higher Li in the more evolved melt inclusions and the lava flows results from assimilation of granitic country rock. The positive correlation between Li/Y and Eu/Eu* in the melt inclusions supports this theory of Li enrichment by crustal assimilation. The delta7Li in the melt inclusions ranges from typical arc lava values of 1.1±1.10/00 in the most primitive (low-Li) melt inclusions to extremely light values down to -9.2±0.90/00 in the more evolved (high-Li) melt inclusions. The significance of these data lies in determining whether the light Li in the evolved melt inclusions represents the initial composition of the contaminated melt itself, or if the Li isotope ratios in these inclusions have been altered by post-entrapment processes such as diffusive exchange with olivine or with the evolving melt through the olivine host. Lithium is known to diffuse quite quickly, and furthermore 6Li has been shown to diffuse more quickly than 7Li, which could result in kinetic fractionation of Li in the melt inclusions post-entrapment. However, it is puzzling that the most evolved melt inclusions, which were presumably the last melt inclusions to be trapped prior to or during eruption, have the most fractionated delta7Li. Lithium isotopic analysis of granitic xenoliths collected from the lava flows will determine if the country rock can provide a direct source of light Li. We propose that the high mobility of Li combined with high concentrations of Li in crustal rocks relative to basalts may combine to make Li an ideal tracer of crustal interaction even in relatively primitive lavas.

Volcan El Jorullo (1759 to 1774) was produced in one of two historical eruptions within the Micho... more Volcan El Jorullo (1759 to 1774) was produced in one of two historical eruptions within the Michoacan- Guanajuato Volcanic field (MGVF) in the western Trans Mexican Volcanic Belt. Although direct observations of the eruption were sparse compared to the nearby 20th century Paricutin eruption, detailed geological, petrological and geochemical studies begun by Luhr and Carmichael (CMP 90, 1985) and continued by ourselves and others have uncovered a complex (and non-linear) sequence of melting, ascent, differentiation, assimilation and eruption. Collectively these betray a much larger spatial and temporal variability in magma storage and migration conditions than one might anticipate for a one-time volcanic event in a volcanic field fed sufficiently with magma to have produced nearly 1000 similar volcanic cones in the Holocene and Pleistocene. This presentation will summarize primarily ongoing geochemical work (mostly in the past decade) since the seminal Luhr and Carmichael study. We show that melts supplied to Jorullo were a mixture of those generated from an arc-fluid fluxed mantle and the lower crust and that magmas carry a signature of two distinct assimilation events (one deep, one probably shallow). Further, conditions of magma accumulation, differentiation, storage and transport were sufficiently heterogeneous to produce spatial and temporal variations in lava compositions erupted in at least 8 distinct effusive events that collectively formed the compound Jorullo flow field. We suggest that there are direct feedbacks between what, where and how various magma compositions were erupted at Jorullo and contrast these conditions to those at Paricutin, at which an apparently simpler sequence of events prevailed (e.g., McBirney et al CMP 95, 1987)

Agu Fall Meeting Abstracts, Dec 1, 2004

One of the most striking common features of subduction zones worldwide is the appearance of the v... more One of the most striking common features of subduction zones worldwide is the appearance of the volcanic front at a height of approximately 120 km above the subducting slab. The water-rich compositions of the lavas erupted at the volcanic front suggest that melting is initiated by dehydration of hydrous phases in the slab, primarily amphibole. However, the location of the front is offset considerably from the predicted origin of fluids due to amphibole dehydration at ˜80km slab depth. The lateral offset at the surface varies with subduction angle, but generally the predicted site of fluid release is ˜20-70 km trench-ward of the actual volcanic front. Many of the proposed mechanisms for generating this offset involve stalling the fluid in the mantle such that it is drawn down and/or back into the mantle wedge due to viscous flow in the solid mantle. For example, the fluid may re-crystallize as phlogopite and pargasitic amphibole in the portion of the mantle that is viscously coupled to the subducting slab. These newly formed hydrous minerals have higher breakdown pressures than glaucophane, the dominant hydrous mineral in the slab, and could explain the offset to deeper apparent depths of dehydration. However, processes that rely upon solid mantle flow are very slow. For a slab descending at 100mm/yr, 5x105 years are required to descend 40 km vertically ( ˜50 km along-slab). Such long periods of time spent in transport in the mantle are seemingly contradicted by strong U-series isotopic disequilibria in arc lavas. Although special circumstances may be evoked in order to allow U-series disequilibria to be extended in time, it is also possible that reaction rates in the cold descending slab are sluggish to the point that fluids are not released at the expected depth of 80 km, but instead are retained to greater depths where increasing temperatures allow reactions to proceed. In this scenario, the fluids would then be able to proceed relatively quickly to the region of melting, preserving their isotopic disequilibria.

ICERI2019 Proceedings, 2019

Geological Society of America Abstracts with Programs, 2017

AGU Fall Meeting Abstracts, Dec 1, 2016

Geological Society of America Abstracts with Programs, 2017

ICERI2019 Proceedings, 2019

Volcanica

Thríhnúkagígur Volcano, Iceland, is a composite spatter cone and lava field characteristic of bas... more Thríhnúkagígur Volcano, Iceland, is a composite spatter cone and lava field characteristic of basaltic fissure eruptions. Lava drainback at the end of the eruption left ~60 m of evacuated conduit, and a 4 × 104 m3 cave formed by the erosion of unconsolidated tephra by the feeder dike. Field relationships within the shallow plumbing system provide three-dimensional insight into conduit formation in fissure systems. Petrographic estimates and the relative volumes of the cave and erupted lavas both indicate xenolithic tephra comprises 5–10 % of the erupted volume, which cannot be reproduced by geochemical mixing models. Although crustal xenolith entrainment is not geochemically significant, we posit that this process may be common in the Icelandic crust. The Thríhnúkagígur eruption illustrates how pervasive, poorly consolidated tephra or hyaloclastite can act as a mechanically weak pre-existing structure that provides a preferential pathway for magma ascent and may influence vent locat...

Contributions to Mineralogy and Petrology, 2020

Zircon is widely used to date metamorphic processes, particularly due to slow cation diffusion un... more Zircon is widely used to date metamorphic processes, particularly due to slow cation diffusion under crustal conditions. Here, we present laser-ablation depth profiling data that demonstrate rapid U diffusion in partially altered, high-pressure zircon. The zircons are hosted in metagabbros that underwent eclogite-facies (~ 550 °C, ~ 2.6 GPa) recrystallization during subduction of the Monviso meta-ophiolite. One metagabbro contains only newly grown zircons (50.2 ± 1.1 Ma); two coarser-grained samples exhibit thin metamorphic rims on igneous cores. Most profiles in the coarse-grained samples record discrete Pb C-rich and Pb*-, U-, Th-, and trace-element poor rims in the outermost ≤ 5 µm of each grain, but U shows apparent diffusion profiles that extend ~ 10-15 µm into zircon crystals and correlate with U-Pb date resetting. The data define three populations (cores, diffusively reset rims, and newly precipitated rims) that form two two-component mixtures, indicating that recrystallization was everywhere coupled with U addition. Data from fully equilibrated rims form a single age population (51.1 ± 0.4 Ma) within error of the newly grown zircon and compatible with ~ 1 My fluid-rock interaction timescales. We interpret the U profiles as evidence of inward U diffusion associated with fluid-induced resorption, and systematically exclude other mechanisms for their formation. However, calculated diffusivity estimates are > 20 orders of magnitude faster than predicted by experiments. The absence of zircon lattice damage, and the propagation of diffusion inward of a reaction front, indicates a link between fluid-saturated zircon alteration and fast U diffusion in zircon. Our results emphasize that-even at low temperature-zircon U-Pb systematics may be affected by parent and/or daughter diffusion over length scales large enough to affect laser-ablation or ion microprobe spot analyses.

Contributions to Mineralogy and Petrology

Here we present major element, trace element, and oxygen isotope data for garnet from an amphibol... more Here we present major element, trace element, and oxygen isotope data for garnet from an amphibolitized eclogite block from Ring Mountain, Franciscan Complex, California, USA. Garnetite veins 1–5 cm thick are laterally continuous up to 10 m within an Mg-rich blackwall zone of the eclogite block. Complex major and trace element zoning patterns reveal multiple stages of garnet growth in both the matrix and garnetite veins. Similarities in major and trace element zoning between matrix and vein garnet suggest that crystallization of the garnetite veins began toward the end of matrix garnet core growth, and continued throughout the garnet growth history of the rock. Oscillatory zoning in rare-earth elements suggests garnet growth in pulses, with matrix-diffusion-limited growth in between pulses. Oxygen isotope analyses of matrix and vein garnet have a range in δ 18 O values of 5.3–11.1 ‰. Differences in δ 18 O values of up to ~ 4 ‰ between garnet core and rim are observed in both the matrix and vein; garnet cores range from 9.8 to 11.1 ‰ (median 10.4‰), garnet mantles range from 8.3 to 10.0 ‰ (median 9.7 ‰), and garnet rims range from 5.8 to 7.8 ‰ (median 6.7 ‰). Late-stage vein crystallization appears as a garnet “cement” that fills in a network of small (typically 5–50 µm) garnet cores, and likely crystallized from an amorphous phase. The low δ 18 O values of this latest stage of garnet growth are consistent with interaction with serpentinites, and likely represent the physical incorporation of the eclogite block into the serpentinite matrix mélange.

Mining, Metallurgy & Exploration

American Mineralogist, May 1, 2020

This is a preprint, the final version is subject to change, of the American Mineralogist (MSA) Ci... more This is a preprint, the final version is subject to change, of the American Mineralogist (MSA) Cite as Authors (Year) Title. American Mineralogist, in press.

Geochemistry, Geophysics, Geosystems

Many of Earth's volcanoes experience well-defined states of "quiescence" and "unrest,"

Earth and Planetary Science Letters, 2012

Geostandards and Geoanalytical Research, 2016

Trace element concentrations and Li isotope ratios have been analyzed in olivine-hosted melt incl... more Trace element concentrations and Li isotope ratios have been analyzed in olivine-hosted melt inclusions found in tephras from Volcan Jorullo, a monogenetic cinder cone of the Michoacan-Guanajuato Volcanic Field, Mexico. The melt inclusions range from basalt to basaltic andesite in composition, with K2O and incompatible trace element concentrations increasing with SiO2 content. Lithium concentrations range from 2 ppm in the most primitive inclusions to 12 ppm in the most evolved. Some of the lava flows from Jorullo contain abundant granitic xenoliths, and most contain plagioclase xenocrysts, suggesting that the lavas have assimilated some amount of crustal material. Lithium concentrations in the lava flows are 10-12 ppm, while the Li concentration in a granitic xenolith from one of the flows is 29 ppm. We interpret the basaltic melt inclusions containing 2 ppm Li to represent the primitive melt, while the higher Li in the more evolved melt inclusions and the lava flows results from assimilation of granitic country rock. The positive correlation between Li/Y and Eu/Eu* in the melt inclusions supports this theory of Li enrichment by crustal assimilation. The delta7Li in the melt inclusions ranges from typical arc lava values of 1.1±1.10/00 in the most primitive (low-Li) melt inclusions to extremely light values down to -9.2±0.90/00 in the more evolved (high-Li) melt inclusions. The significance of these data lies in determining whether the light Li in the evolved melt inclusions represents the initial composition of the contaminated melt itself, or if the Li isotope ratios in these inclusions have been altered by post-entrapment processes such as diffusive exchange with olivine or with the evolving melt through the olivine host. Lithium is known to diffuse quite quickly, and furthermore 6Li has been shown to diffuse more quickly than 7Li, which could result in kinetic fractionation of Li in the melt inclusions post-entrapment. However, it is puzzling that the most evolved melt inclusions, which were presumably the last melt inclusions to be trapped prior to or during eruption, have the most fractionated delta7Li. Lithium isotopic analysis of granitic xenoliths collected from the lava flows will determine if the country rock can provide a direct source of light Li. We propose that the high mobility of Li combined with high concentrations of Li in crustal rocks relative to basalts may combine to make Li an ideal tracer of crustal interaction even in relatively primitive lavas.

Volcan El Jorullo (1759 to 1774) was produced in one of two historical eruptions within the Micho... more Volcan El Jorullo (1759 to 1774) was produced in one of two historical eruptions within the Michoacan- Guanajuato Volcanic field (MGVF) in the western Trans Mexican Volcanic Belt. Although direct observations of the eruption were sparse compared to the nearby 20th century Paricutin eruption, detailed geological, petrological and geochemical studies begun by Luhr and Carmichael (CMP 90, 1985) and continued by ourselves and others have uncovered a complex (and non-linear) sequence of melting, ascent, differentiation, assimilation and eruption. Collectively these betray a much larger spatial and temporal variability in magma storage and migration conditions than one might anticipate for a one-time volcanic event in a volcanic field fed sufficiently with magma to have produced nearly 1000 similar volcanic cones in the Holocene and Pleistocene. This presentation will summarize primarily ongoing geochemical work (mostly in the past decade) since the seminal Luhr and Carmichael study. We show that melts supplied to Jorullo were a mixture of those generated from an arc-fluid fluxed mantle and the lower crust and that magmas carry a signature of two distinct assimilation events (one deep, one probably shallow). Further, conditions of magma accumulation, differentiation, storage and transport were sufficiently heterogeneous to produce spatial and temporal variations in lava compositions erupted in at least 8 distinct effusive events that collectively formed the compound Jorullo flow field. We suggest that there are direct feedbacks between what, where and how various magma compositions were erupted at Jorullo and contrast these conditions to those at Paricutin, at which an apparently simpler sequence of events prevailed (e.g., McBirney et al CMP 95, 1987)

Agu Fall Meeting Abstracts, Dec 1, 2004

One of the most striking common features of subduction zones worldwide is the appearance of the v... more One of the most striking common features of subduction zones worldwide is the appearance of the volcanic front at a height of approximately 120 km above the subducting slab. The water-rich compositions of the lavas erupted at the volcanic front suggest that melting is initiated by dehydration of hydrous phases in the slab, primarily amphibole. However, the location of the front is offset considerably from the predicted origin of fluids due to amphibole dehydration at ˜80km slab depth. The lateral offset at the surface varies with subduction angle, but generally the predicted site of fluid release is ˜20-70 km trench-ward of the actual volcanic front. Many of the proposed mechanisms for generating this offset involve stalling the fluid in the mantle such that it is drawn down and/or back into the mantle wedge due to viscous flow in the solid mantle. For example, the fluid may re-crystallize as phlogopite and pargasitic amphibole in the portion of the mantle that is viscously coupled to the subducting slab. These newly formed hydrous minerals have higher breakdown pressures than glaucophane, the dominant hydrous mineral in the slab, and could explain the offset to deeper apparent depths of dehydration. However, processes that rely upon solid mantle flow are very slow. For a slab descending at 100mm/yr, 5x105 years are required to descend 40 km vertically ( ˜50 km along-slab). Such long periods of time spent in transport in the mantle are seemingly contradicted by strong U-series isotopic disequilibria in arc lavas. Although special circumstances may be evoked in order to allow U-series disequilibria to be extended in time, it is also possible that reaction rates in the cold descending slab are sluggish to the point that fluids are not released at the expected depth of 80 km, but instead are retained to greater depths where increasing temperatures allow reactions to proceed. In this scenario, the fluids would then be able to proceed relatively quickly to the region of melting, preserving their isotopic disequilibria.