Cyclicity in the Main and Upper Zones of the Bushveld Complex, South Africa: Crystallization from a Zoned Magma Sheet

Tegner, Christian; Cawthorn, R. Grant; Kruger, F. J.

doi:10.1093/petrology/egl043

Cited by 162 publications

(127 citation statements)

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“…It is well known that there are compositional reversals of An content and Sr concentration for plagioclase, Fo content for olivine, Mg# value for clinopyroxene and Cr concentration for magnetite in different height levels of layered intrusions elsewhere, such as the Bushveld Complex (Cawthorn and Ashwal, 2009;Cawthorn and McCarthy, 1980;Tegner et al, 2006), the Sept Iles intrusion (Namur et al, 2010) and the Bjerkrein-Sokndal intrusion in Norway (Jensen et al, 1993). These compositional reversals are often attributed to the mixing of evolved magmas with new primitive magmas in magma chambers (Ashwal et al, 2005;Jensen et al, 1993;Namur et al, 2010), or evolved magmas with less differentiated magmas from the upper part of the magma chamber due to magma convection (Cawthorn and Ashwal, 2009;Cawthorn and McCarthy, 1980;Tegner et al, 2006). In general, mixing of evolved magmas with new primitive magmas would decrease P in the mixed magmas because P is highly undersaturated in primitive magmas.…”

Section: Two Compositional Reversals Of Apatite and Plagioclase In Thmentioning

confidence: 99%

“…The intrusion includes the marginal zone (MGZ), lower zone (LZ), middle zone (MZ, comprising MZa in the lower part and MZb in the upper part) and upper zone (UZ) (Pang et al, 2008(Pang et al, , 2009Zhou et al, 2005). Cumulus apatite is predominantly present in the MZb (Pang et al, 2008(Pang et al, , 2009) so that the apatite-rich MZb occurs above the major Fe-Ti oxide ore bodies in the LZ of the intrusion, similar to the occurrence of apatite-rich units in layered intrusions elsewhere (c.f., Namur et al, 2010;Tegner et al, 2006). The apatite-rich MZb is~500 to 600 m in thickness, which accounts for 25-30% of the~2-km-thick intrusion in terms of thickness (Pang et al, 2009;Zhou et al, 2005).…”

Section: Introductionmentioning

confidence: 99%

“…Occasionally, nelsonite layers that are composed of two-thirds Fe-Ti oxides, onethird apatite and minor olivine and plagioclase can form and interlayer with Fe-Ti-P-rich gabbro in the upper parts of layered intrusions, such as those in the Bushveld Complex in South Africa (Reynolds, 1985;Tegner et al, 2006) and the Sept Iles intrusion in Canada (Tollari et al, 2008). On the other hand, apatite-rich units often occur stratigraphically above major Fe-Ti oxide-rich layers in some mafic-ultramafic layered intrusions, such as those in the Skaergaard intrusion in Greenland Thy et al, 2009), the Bushveld Complex (Tegner et al, 2006;Von Gruenewaldt et al, 1985) and the Sept Iles intrusion (Namur et al, 2010(Namur et al, , 2012. Therefore, factors that control the crystallization sequence of Fe-Ti oxides and apatite from magmas are enigmatic and the role of P in the formation of major Fe-Ti oxide-rich layers of layered intrusions needs to be examined.…”

Section: Introductionmentioning

confidence: 99%

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Trace element compositions of apatite from the middle zone of the Panzhihua layered intrusion, SW China: Insights into the differentiation of a P- and Si-rich melt

Xing

Wang

2014

Lithos

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Section: Two Compositional Reversals Of Apatite and Plagioclase In Thmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Trace element compositions of apatite from the middle zone of the Panzhihua layered intrusion, SW China: Insights into the differentiation of a P- and Si-rich melt

Xing

Wang

2014

Lithos

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“…The rhythmic layering is similar to the magnetite-rich layers of the Main Zone and Upper Zone of the Bushveld Complex, South Africa [1], which hosts the largest magmatic Fe-Ti-V oxide deposit in the world. However, the magnetite-rich layers with >50% magnetite are only 20.42 m thick against a total thickness of up to ~6500 m of the Bushveld Complex [2]. Therefore, the magnetite-rich layers only make up a small proportion of the Bushveld complex and are thought to be a product of fractionation of magmas [1].…”

mentioning

confidence: 99%

“…In this paper, magnetite, clinopyroxene, plagioclase, and apatite were separated from different types of ores and host rocks of the Panzhihua, Hongge, and Baima intrusions. Volatile and C-H-O isotopic compositions of CO 2 and H 2 O that were trapped in these mineral separates are analyzed. The data set enables us to trace the source of volatiles and evaluate the role of fluids on the relative timing of magnetite crystallization.…”

mentioning

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

Bilenker

VanTongeren

Lundstrom

et al. 2017

Geochem Geophys Geosyst

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We present δ56Fe (56Fe/54Fe relative to standard IRMM‐014) data from whole rock and magnetite of the Upper and Upper Main Zones (UUMZ) of the Bushveld Complex. With it, we assess the role of fractional crystallization in controlling the Fe isotopic evolution of a mafic magma. The UUMZ evolved by fractional crystallization of a dry tholeiitic magma to produce gabbros and diorites with cumulus magnetite and fayalitic olivine. Despite previous experimental work indicating a potential for magnetite crystallization to drastically change magma δ56Fe, we observe no change in whole rock δ56Fe above and below magnetite saturation. We also observe no systematic change in whole rock δ56Fe with increasing stratigraphic height, and only a small variation in δ56Fe in magnetite separates above magnetite saturation. Whole rock δ56Fe (errors twice standard deviation, ±2σ) throughout the UUMZ ranges from −0.01 ±0.03‰ to 0.21 ±0.09‰ (δ56FeaverageWR = 0.10 ±0.09‰; n = 21, isotopically light outlier: δ56FeWR = −0.15‰), and magnetites range from 0.28 ±0.04‰ to 0.86 ±0.07‰ (δ56FeaverageMgt = 0.50 ±0.15‰; n = 20), similar to values previously reported for other layered intrusions. We compare our measured δ56FeWR to a model that incorporates the changing normative mineralogy, calculated temperatures, and published fractionation factors of Fe‐bearing phases throughout the UUMZ and produces δ56FeWR values that evolve only in response to fractional crystallization. Our results show that the Fe isotopic composition of a multiply saturated (multiple phases on the liquidus) magma is unlikely to change significantly during fractional crystallization of magnetite due to the competing fractionation of other Fe‐bearing cumulus phases.

show abstract

Cyclicity in the Main and Upper Zones of the Bushveld Complex, South Africa: Crystallization from a Zoned Magma Sheet

Cited by 162 publications

References 50 publications

Trace element compositions of apatite from the middle zone of the Panzhihua layered intrusion, SW China: Insights into the differentiation of a P- and Si-rich melt

Trace element compositions of apatite from the middle zone of the Panzhihua layered intrusion, SW China: Insights into the differentiation of a P- and Si-rich melt

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

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

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