Iron isotopic evolution during fractional crystallization of the uppermost <scp>B</scp>ushveld <scp>C</scp>omplex layered mafic intrusion

Bilenker, Laura; VanTongeren, J. A.; Lundstrom, Craig C.; Simon, Adam C.

doi:10.1002/2016gc006660

Cited by 35 publications

(19 citation statements)

References 48 publications

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“…This feature is obviously different from that in the Kilauea Iki lava lake in Hawaii and the Red Hill intrusion in Tasmania (Australia), both of which represent the magma differentiation in a closed system and have a negative correlation between δ 56 Fe whole rock and MgO (Sossi et al, ; Teng et al, ; Figure b). However, the nearly uniform δ 56 Fe whole rock of the Panzhihua intrusion is similar to that for the rocks along the ~2.5‐km‐thick Upper and Upper Main Zone of the Bushveld Complex (Bilenker et al, ; Figure b). Such a trend of δ 56 Fe whole rock in the Upper and Upper Main Zone was considered to reflect limited change of the Fe isotopic compositions of a multiply‐saturated magma; that is, the effect of the magnetite crystallization on the δ 56 Fe of the magma may have been minimized by competing crystallization of other Fe‐bearing cumulus phases, in particular, olivine and pyroxene.…”

Section: Discussionsupporting

confidence: 61%

“…The horizontal light blue shaded region represents the average of δ 56 Fe and 2 standard deviation errors (0.10 ± 0.08‰; 2SD, n = 146) of terrestrial basalts from Weyer and Ionov (), Dauphas et al (), and Teng et al (). (b) Variation of δ 56 Fe Whole Rock versus MgO (wt.%) for the samples in this study, as well as the Kilauea Iki lava lake in Hawaii (Teng et al, ), the Red Hill intrusion in Tasmania (Sossi et al, ), and the Upper and Upper Main Zones of the Bushveld Complex (Bilenker et al, ). The dashed lines indicate the change of Fe isotope composition with magma differentiation in closed systems: green line= Kilauea Iki; blue line = Red Hill intrusion.…”

Section: Resultsmentioning

confidence: 88%

“…Therefore, Fe isotopes can be fractionated to different extents in mafic magmatic systems with crystallization of specific mineral phases. Fe isotope systematics of the layered intrusions thus are sensitive to the crystallization sequence of Fe‐bearing minerals during differentiation of mafic magma (e.g., Bilenker et al, ; Chen et al, ; Liu, Zhou, Luais, et al, ; Schuessler et al, ; Sossi et al, ; Teng et al, ), providing important constraints on magmatic processes and formation of large amounts of Fe‐Ti oxides in layered intrusions.…”

Section: Introductionmentioning

confidence: 99%

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Iron Isotope Systematics of the Panzhihua Mafic Layered Intrusion Associated With Giant Fe‐Ti Oxide Deposit in the Emeishan Large Igneous Province, SW China

et al. 2019

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In order to investigate how Fe was enriched from parental high-Ti basaltic magma to form the stratigraphically thick Fe-Ti oxide ore at the bottom layers, we present a systematic study for Fe isotopic compositions of whole rocks and mineral separates (clinopyroxene, magnetite, and ilmenite) throughout the Panzhihua intrusion. Whole rock δ 56 Fe ranges from 0 ± 0.02‰ to 0.15 ± 0.04‰, consistent with the range of clinopyroxene (0.01 ± 0.02‰ to 0.16 ± 0.05‰). On the contrary, magnetite (Mt) separates have δ 56 Fe ranging from 0.17 ± 0.05‰ to 0.62 ± 0.02‰, showing a strikingly complementary trend with coexisting ilmenite (Ilm) separates (À0.52 ± 0.03‰ to À0.09 ± 0.02‰) along the profile. The calculated bulk δ 56 Fe of Fe-Ti oxides (Mt + Ilm), however, has a small range from 0.01‰ to 0.16‰, identical to those for clinopyroxene separates and whole rocks. The uniform δ 56 Fe of clinopyroxene may have resulted from the small Fe isotope fractionation between clinopyroxene and parental magma in early-stage magma differentiation before substantial crystallization of Fe-Ti oxides. The complementary trends of δ 56 Fe for Mt and Ilm along the profile and the uniform bulk δ 56 Fe of Fe-Ti oxides are better interpreted as in situ crystallization of Fe-Ti oxides from the interstitial liquid. Our Fe isotopic data and petrographic observations indicate that the thick Fe-Ti oxide ore layers in the lower zone of the Panzhihua intrusion may be attributed to in situ crystallization of Mt and Ilm from the interstitial, immiscible Fe-rich melt in the lower part of the magma chamber.Fe-Ti oxide ores and host rocks in the layered intrusions are generally composed of olivine, plagioclase, clinopyroxene, magnetite, and ilmenite in different proportions. In theory, heavy Fe isotopes are preferentially partitioned into phases with smaller coordination number (CN) or higher Fe 3+ /∑Fe than those with higher CN or lower Fe 3+ /∑Fe (Young et al., 2015). This explains why olivine, clinopyroxene, and ilmenite have similar or slightly lighter Fe isotopic compositions than the coexisting melt and why magnetite is isotopically heavier CAO ET AL.358

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Section: Discussionsupporting

confidence: 61%

Section: Resultsmentioning

confidence: 88%

Section: Introductionmentioning

confidence: 99%

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Iron Isotope Systematics of the Panzhihua Mafic Layered Intrusion Associated With Giant Fe‐Ti Oxide Deposit in the Emeishan Large Igneous Province, SW China

et al. 2019

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“…Isotopic data for magnetite samples in δ 56 Fe vs. δ 18 O space. The dashed orange box denotes the range for magmatic (igneous) Fe and O isotope values as established byTaylor (1967Taylor ( , 1968,Heimann et al (2008),Weis (2013),and Bilenker et al ( , 2017. Stars denote δ 56 Fe vs.…”

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confidence: 99%

Kiruna-Type Iron Oxide-Apatite (IOA) and Iron Oxide Copper-Gold (IOCG) Deposits Form by a Combination of Igneous and Magmatic-Hydrothermal Processes: Evidence from the Chilean Iron Belt

Simon¹,

Knipping²,

Reich³

et al. 2018

Metals, Minerals, and Society

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Iron oxide copper-gold (IOCG) and Kiruna-type iron oxide-apatite (IOA) deposits are commonly spatially and temporally associated with one another, and with coeval magmatism. Here, we use trace element concentrations in magnetite and pyrite, Fe and O stable isotope abundances of magnetite and hematite, H isotopes of magnetite and actinolite, and Re-Os systematics of magnetite from the Los Colorados Kiruna-type IOA deposit in the Chilean iron belt to develop a new genetic model that explains IOCG and IOA deposits as a continuum produced by a combination of igneous and magmatic-hydrothermal processes. The concentrations of [Al + Mn] and [Ti + V] are highest in magnetite cores and decrease systematically from core to rim, consistent with growth of magnetite cores from a silicate melt, and rims from a cooling magmatic-hydrothermal fluid. Almost all bulk δ 18 O values in magnetite are within the range of 0 to 5‰, and bulk δ 56 Fe for magnetite are within the range 0 to 0.8‰ of Fe isotopes, both of which indicate a magmatic source for O and Fe. The values of δ 18 O and δD for actinolite, which is paragenetically equivalent to magnetite, are, respectively, 6.46 ± 0.56 and -59.3 ± 1.7‰, indicative of a mantle source. Pyrite grains consistently yield Co/Ni ratios that exceed unity, and imply precipitation of pyrite from an ore fluid evolved from an intermediate to mafic magma. The calculated initial 187 Os/ 188 Os ratio (Osi) for magnetite from Los Colorados is 1.2, overlapping Osi values for Chilean porphyry-Cu deposits, and consistent with an origin from juvenile magma. Together, the data are consistent with a geologic model wherein (1) magnetite microlites crystallize as a near-liquidus phase from an intermediate to mafic silicate melt;(2) magnetite microlites serve as nucleation sites for fluid bubbles and promote volatile saturation of the melt;(3) the volatile phase coalesces and encapsulates magnetite microlites to form a magnetite-fluid suspension; (4) the suspension scavenges Fe, Cu, Au, S, Cl, P, and rare earth elements (REE) from the melt; (5) the suspension ascends from the host magma during regional extension; (6) as the suspension ascends, originally igneous magnetite microlites grow larger by sourcing Fe from the cooling magmatic-hydrothermal fluid; (7) in deep-seated crustal faults, magnetite crystals are deposited to form a Kiruna-type IOA deposit due to decompression of the magnetite-fluid suspension; and (8) the further ascending fluid transports Fe, Cu, Au, and S to shallower levels or lateral distal zones of the system where hematite, magnetite, and sulfides precipitate to form IOCG deposits. The model explains the globally observed temporal and spatial relationship between magmatism and IOA and IOCG deposits, and provides a valuable conceptual framework to define exploration strategies.

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“…Previous Fe isotope studies on other LMI revealed complex Fe isotope systematics in neighbouring minerals within cumulate layered intrusive rocks Liu et al, 2014), yet without any systematic variations, and even in the case of the Bushveld Complex, without notable isotope fractionation (Bilenker et al, 2017). Here, we measured Fe isotope compositions in cumulate rocks with known variable whole-rock Hf isotope systematics that relate to magma mixing, which vary with intrusion depth (Nebel et al, 2013a).…”

Section: Introductionmentioning

confidence: 78%

Incremental Growth of Layered Mafic-Ultramafic Intrusions Through Melt Replenishment Into a Crystal Mush Zone Traced by Fe-Hf Isotope Systematics

et al. 2020

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Layered mafic-ultramafic intrusions (LMI) are among the largest igneous bodies on Earth, and represent aggregations of large volumes of mantle-and some crustalderived melts. Melts are emplaced over time-intervals of less than 1 million years, predominantly through multiple pulses of injections into pre-existing melt-crystal slurries. The dynamic interaction of physical processes, including density-driven separation and mixing of different components, within a solidifying magma chamber leads to such extreme chemical diversity between cumulate rock units that no unified model currently explains all aspects of the genesis of these intrusions. Here we present whole-rock stable Fe isotope data (expressed in variations as δ 57 Fe relative to IRMM-014) for samples of drill core taken from the stratified paleo-magma chamber of the Upper Zone of the late-Archean Windimurra Igneous Complex, Western Australia. Variations from near chondritic (δ 57 Fe ∼ + 0) to heavy (δ 57 Fe∼ + 0.2) values show a co-variation with initial radiogenic Hf isotope data that is unique to the Windimurra Upper Zone. The systematic isotopic variations from the roof to the base of the Upper Zone are best explained by an intricate sequence of events that included fractional crystallization and physical mixing. We propose that melt freshly sourced from the mantle was injected into and inflated a pre-existing crystal-melt mush comprising the upper Middle Zone. Reestablishment of crystal layering after replenishment introduced a chemical stratification with the formation of what became the Upper Zone and a crystal-interstitial melt ratio decreasing from roof to base. Basal, vanadiferous magnetitite horizons crystallized from Fe out of the liquid-in-residence. Variable degrees of perturbation and chaotic stirring of crystals with imperfect mixing of new and old components was followed by rapid crystal settling and subsequent cumulate stratification. Such melt rejuvenation, proposed here to be the cause for a newly established Upper Zone, leaves no unique petrologic fingerprint and forges a range in hybrid magma compositions throughout the Upper Zone rather than one single parental melt. This incremental growth of the intrusion

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Iron isotopic evolution during fractional crystallization of the uppermost Bushveld Complex layered mafic intrusion

Cited by 35 publications

References 48 publications

Iron Isotope Systematics of the Panzhihua Mafic Layered Intrusion Associated With Giant Fe‐Ti Oxide Deposit in the Emeishan Large Igneous Province, SW China

Iron Isotope Systematics of the Panzhihua Mafic Layered Intrusion Associated With Giant Fe‐Ti Oxide Deposit in the Emeishan Large Igneous Province, SW China

Kiruna-Type Iron Oxide-Apatite (IOA) and Iron Oxide Copper-Gold (IOCG) Deposits Form by a Combination of Igneous and Magmatic-Hydrothermal Processes: Evidence from the Chilean Iron Belt

Incremental Growth of Layered Mafic-Ultramafic Intrusions Through Melt Replenishment Into a Crystal Mush Zone Traced by Fe-Hf Isotope Systematics

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