Effect of water on tholeiitic basalt phase equilibria: an experimental study under oxidizing conditions

Feig, Sandrin T.; Koepke, Jürgen; Snow, J. E.

doi:10.1007/s00410-006-0123-2

Cited by 287 publications

(214 citation statements)

References 94 publications

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“…Under the low pressure of 50 MPa, water is not changing the order of crystallization, in contrast to what is observed at higher pressure. The wellknown depression of plagioclase stability (plagioclase crystallizing after clinopyroxene) with increasing water content was observed in the experiments of Feig et al [2006] only at pressures !200 MPa. Moreover, water content also affects the mineral compositions.…”

Section: A3 Effect Of Watermentioning

confidence: 84%

“…FeTi oxides were not stable under the given redox conditions in the experiments of Feig et al [2006;submitted manuscript, 2008]; they are stable only at more oxidizing conditions. However, since the experimental system is primitive (FeO tot content of 6.5 wt%), it is expected that in a more evolved system, Fe-Ti oxides would be stable at lower temperatures, at least at the more oxidizing conditions in the hydrated regime.…”

Section: A2 Stability Of Oxidesmentioning

confidence: 99%

“…Moreover, water content also affects the mineral compositions. According to Feig et al [2006], the An content of plagioclase may increase about 10 to 15 mol% when increasing the water activity from 0 to 1 at a given temperature, while the Mg# of olivine and clinopyroxene is shifted to higher values (maximum of 5 to 10) due to the increased oxygen fugacity with water. Thus, the overall effect of water is to stabilize crystal mushes with moderate or high melt fractions to lower temperatures, and thereby shifting the An content of plagioclase and the Mg# of clinopyroxene and olivine to higher values.…”

Section: A3 Effect Of Watermentioning

confidence: 99%

“…[54] According to Feig et al [2006], at a given pressure, the orthopyroxene stability is increased by oxidizing redox conditions, and decreased with increasing water activities. Therefore, two orthopyroxene saturation curves are displayed in the phase diagram of Figure 14, one for reducing and one for oxidizing conditions, related to oxygen fugacities corresponding to QFM and QFM+2 at dry conditions, respectively.…”

Section: A5 Stability Of Orthopyroxene In a Primitive Systemmentioning

confidence: 99%

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Root zone of the sheeted dike complex in the Oman ophiolite

Nicolas

Boudier

Koepke

et al. 2008

Geochem Geophys Geosyst

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[1] In the Oman ophiolite crustal section, a contact zone between the gabbro unit and the volcanics and diabase sheeted dikes, called the root zone of the sheeted dike complex, has been recently mapped at a fine scale in a selected area. The Oman ophiolite is derived from a fast spreading ridge which had a melt lens located between the main gabbro unit and the root zone of the sheeted dike complex. With a few exceptions accounted for, this horizon has a fairly constant thickness, $100 m, and a crude internal pseudo-stratigraphy. At the base of the root zone are isotropic ophitic gabbros interpreted as a thermal boundary layer. This layer is transitional between the magmatic system of the melt lens, convecting at 1200°C, and a high-temperature (<1100°C) hydrothermal system, convecting within the root zone. Above this level, the isotropic gabbros have been, locally, largely molten due to an influx of seawater, at $1100°C, thus generating varitextured ophitic and pegmatitic gabbros. These latter gabbros constitute the upper part of the root zone and are associated with trondjhemitic intrusions as screens in the lower sheeted dikes. Diorites and trondjhemites were also generated by hydrous melting, at temperatures below 1000°C. The whole root zone is a domain of very sharp average thermal gradient ($7°C/m). At the top of the root zone, a new thermal boundary layer, with diabase dikes hydrated in amphibolite facies conditions, separates the preceding high-temperature convective system from the well-known greenschist facies (<450°C) hydrothermal system operating throughout the sheeted dike complex, up to the seafloor. The isotropic gabbros near the base of the root zone are intruded by protodikes with distinctive microgranular margins and an ophitic center. Protodike swarms are exceptional because, intruding a medium at $1100°C, they are largely destroyed by dike-in-dike intrusions and by hydrous melting. However, they demonstrate that this zone was generated by melt conduits issued from the underlying melt lens. Each dike of the sheeted dike complex is thus fed by one protodike. As this zone has been recently drilled by IODP in the eastern Pacific Ocean, a brief comparison is proposed.

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Section: A3 Effect Of Watermentioning

confidence: 84%

Section: A2 Stability Of Oxidesmentioning

confidence: 99%

Section: A3 Effect Of Watermentioning

confidence: 99%

Section: A5 Stability Of Orthopyroxene In a Primitive Systemmentioning

confidence: 99%

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Root zone of the sheeted dike complex in the Oman ophiolite

Nicolas

Boudier

Koepke

et al. 2008

Geochem Geophys Geosyst

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“…minerals and could not result in an early crystallization of magnetite of the three intrusions in the Panxi region. However, although small amounts of H 2 O may not change relative timing of minerals crystallization [48][49][50], involvement of H 2 O in magmas may significantly reduce the viscosity of magmas [51] to enhance flow differentiation. This is consistent with textural relationship observed in massive ores of the Panzhihua intrusion that tabular plagioclase grains are oriented along layering of the intrusion.…”

Section: Impact Of Co 2 and H 2 O On Relative Timing Of Magnetite Crymentioning

confidence: 99%

Volatile and C-H-O isotopic compositions of giant Fe-Ti-V oxide deposits in the Panxi region and their implications for the sources of volatiles and the origin of Fe-Ti oxide ores

Xing

Wang

Zhang

2012

Sci. China Earth Sci.

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The Panzhihua, Hongge, and Baima Fe-Ti-V oxide deposits in the Panzhihua-Xichang (Panxi) region are hosted in large layered mafic-ultramafic intrusions. The layered intrusions intrude either the Neoproterozoic Dengying Formation, composed mainly of limestone, or the Paleoproterozoic Hekou Formation, composed of meta-sedimentary-volcanic rocks. It remains unclear if the wall rocks have been involved during the fractionation of magmas and have affected the sequence of crystallization of Fe-Ti oxide. Volatiles and their C-H-O isotopic compositions of magnetite, apatite, clinopyroxene, and plagioclase of different types of ores from the three intrusions are analyzed using a technique of stepwise heating mass spectrometer to evaluate the role of wall rocks in the formation of Fe-Ti oxide ores. Volatiles released from magnetite are composed mainly of H 2 O and CO 2 , whereas the other minerals are composed mainly of H 2 O, CO 2 and H 2 . At 800-1200°C temperature interval, the average  13 C values of CO 2 of all the minerals from the three intrusions range from 7.7‰ to 13.5‰ and the average  18 O CO 2 values from 19.1‰ to 19.5‰, which are scattered in a mixed field with basalt and the two types of wall rocks as end-members, indicating that CO 2 from the wall rocks may have been involved in the magmas from which the three intrusions formed. At 400-800C temperature interval, both  13 C values (13.7‰ to 17.9‰ on the average) and  18 O values (16.2‰ to 19.2‰ on the average) of CO 2 of all the minerals are lower than those for 800-1200C temperature interval, and much closer to the values of the wall rocks. Abundant H 2 O released at the 400-800C temperature interval has relatively low   D values ranging from 90‰ to 115‰, also indicating the involvement of fluids from the wall rocks. The average bulk contents of volatiles released from magnetite of the Hongge, Baima, and Panzhihua intrusions are 4891, 2996, and 1568 mm 3 STP/g, respectively, much higher than those released from other minerals in total, which are 382, 600, and 379 mm 3 STP/g, respectively, indicating that magnetite crystallized from magmas with much more volatiles than other minerals. This can be interpreted as that crystallization of clinopyroxene and plagioclase in the early fractionation of magmas resulted in volatiles such as H 2 O that were eventually enriched in the residual magmas and, at the same time, fluids from the wall rocks may have been involved in the magmas and were trapped in magnetite, which crystallized later than clinopyroxene and plagioclase. Three giant Fe-Ti-V oxide deposits in the Panxi (Panzhihua-Xichang) region, SW China, are hosted in the Panzhihua, Hongge, and Baima layered mafic-ultramafic intrusions. These intrusions are unique in that large amounts of massive and semi-massive ores occur in the lower parts of the intrusions, whereas rhythmic layering composed of vari-

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Comb layering monitors decompressing and fractionating hydrous mafic magmas in subvolcanic plumbing systems (Fisher Lake, Sierra Nevada, USA)

McCarthy

Müntener

2016

JGR Solid Earth

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Understanding the dynamics of volcanic eruptions requires constraints on the processes of melt extraction in shallow magma reservoirs. This study focuses on the formation of intraplutonic igneous layering known as comb layers and orbicules within the Fisher Lake Pluton, Sierra Nevada. Comb layers are mineralogically and texturally diverse, ranging from plagioclase‐amphibole comb layers to plagioclase‐pyroxene and olivine comb layers. The majority of individual layers are related to the initiation of plagioclase nucleation and growth on preexisting host rocks and remobilized xenoliths. We use simple phase diagrams to illustrate the formation of comb layers through crystal fractionation along conduit walls and xenoliths, with plagioclase as the liquidus phase. Near‐adiabatic ascent of water‐undersaturated melts through the crust will lead to superheating and crystal resorption, which upon saturation of volatiles at shallow depth can induce heterogeneous nucleation of plagioclase. The rarity of orbicules and comb layers worldwide suggests that adiabatic decompression of crystal‐poor, moderately hydrous melts through the crust is rare. Most melts in intermediate/silicic volcanoes crystallize in multiple reservoirs within the crust prior to emplacement at shallow depth as crystal‐bearing melts. Comb layers and orbicules preserve evidence of multiple melt injections where a sequence of texturally and mineralogically similar comb layers and orbicules reflect the timescale of an individual melt pulse. Short timescales on the order of months to years for the growth of these sequences are estimated using experimental plagioclase growth rates and are interpreted as representing the lifetime of a melt injection within a long‐lived, subvolcanic melt extraction zone.

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Effect of water on tholeiitic basalt phase equilibria: an experimental study under oxidizing conditions

Cited by 287 publications

References 94 publications

Root zone of the sheeted dike complex in the Oman ophiolite

Root zone of the sheeted dike complex in the Oman ophiolite

Volatile and C-H-O isotopic compositions of giant Fe-Ti-V oxide deposits in the Panxi region and their implications for the sources of volatiles and the origin of Fe-Ti oxide ores

Comb layering monitors decompressing and fractionating hydrous mafic magmas in subvolcanic plumbing systems (Fisher Lake, Sierra Nevada, USA)

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