The Stillwater Complex: Integrating Zircon Geochronological and Geochemical Constraints on the Age, Emplacement History and Crystallization of a Large, Open-System Layered Intrusion

Wall, Corey J.; Scoates, James S.; Weis, Dominique; Friedman, Richard M.; Amini, Marghaleray; Meurer, W. P.

doi:10.1093/petrology/egy024

Cited by 126 publications

(63 citation statements)

References 135 publications

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“…Notably, the Main Anorthosite Layer shares many similarities with the Anorthosite zones in the Middle Banded Series of the Stillwater Complex as these anorthosites are older than the underlying rock sequences, which also host the J-M Reef. This was interpreted to suggest an out-of-sequence emplacement of the Stillwater Complex, which could also apply to the Fedorova-Pana Complex [42]. Geological relationships coupled with U-Pb dating of the Main Anorthosite Layer suggest that the layer crystallized coevally with the adjacent rocks of the ULH, but earlier than the LLH and other rocks from the lower portions of the West-Pana intrusion (Figures 2 and 8).…”

Section: U-pb Age Of the Main Anorthosite Layer And Crystallization Hmentioning

confidence: 92%

Section: U-pb Age Of the Main Anorthosite Layer And Crystallization Hmentioning

confidence: 95%

“…Considering the results of this study, the 2470 ± 9 Ma age for the gabbro-pegmatite from the LLH should be regarded as an upper temporal boundary for the crystallization of the intrusion (Figure 8). It appears, however, that this age most likely records the timing of late-to post-magmatic overprinting rather than the actual timing of emplacement, taking into account that high-precision dating of other large layered intrusions, such as the Bushveld or Stillwater Complexes, suggest a much shorter duration of magmatism, lasting for a few million years at most [15,42].…”

Section: U-pb Age Of the Main Anorthosite Layer And Crystallization Hmentioning

confidence: 99%

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The Main Anorthosite Layer of the West-Pana Intrusion, Kola Region: Geology and U-Pb Age Dating

Groshev

Karykowski²

2019

Minerals

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The West-Pana intrusion belongs to the Paleoproterozoic Fedorova-Pana Complex of the Kola Region in NW Russia, which represents one of Europe's most significant layered complexes in terms of total platinum group element (PGE) endowment. Numerous studies on the age of the West-Pana intrusion have been carried out in the past; however, all published U-Pb isotope ages were determined using multi-grain ID-TIMS. In this study, the mineralized Main Anorthosite Layer from the upper portion of the intrusion was dated using SHRIMP-II for the first time. High Th/U (0.9-3.7) zircons gave an upper intercept age of 2509.4 ± 6.2 Ma (2σ), whereas the lower portion of the intrusion was previously dated at 2501.5 ± 1.7 Ma, which suggests an out-of-sequence emplacement of the West-Pana intrusion. Furthermore, high-grade PGE mineralization hosted by the anorthosite layer, known as "South Reef", can be attributed to (1) downward percolation of PGE-enriched sulfide liquid from the overlying gabbronoritic magma or (2) secondary redistribution of PGEs, which may coincide with a post-magmatic alteration event recorded by low Th/U (0.1-0.9) zircon and baddeleyite at 2476 ± 13 Ma (upper intercept).

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Section: U-pb Age Of the Main Anorthosite Layer And Crystallization Hmentioning

confidence: 92%

Section: U-pb Age Of the Main Anorthosite Layer And Crystallization Hmentioning

confidence: 95%

Section: U-pb Age Of the Main Anorthosite Layer And Crystallization Hmentioning

confidence: 99%

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The Main Anorthosite Layer of the West-Pana Intrusion, Kola Region: Geology and U-Pb Age Dating

Groshev

Karykowski²

2019

Minerals

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“…The lack of systematic relationships between the thickness of the mafic and leucocratic portions of the units (e.g., [12]) is also observed at Karee, but can be related to the non-genetic relationship between the rocks in the Merensky Unit. Apparent out-of-sequence ages, derived from U-Pb dating of zircon and baddeleyite in the Bushveld Complex [3] and the Stillwater Complex, USA [93], have also been used. These minerals, however, crystallise very close to the solidus in the last pockets of melt [93].…”

Section: Evaluation Of the Role Of Intrusionmentioning

confidence: 99%

“…Apparent out-of-sequence ages, derived from U-Pb dating of zircon and baddeleyite in the Bushveld Complex [3] and the Stillwater Complex, USA [93], have also been used. These minerals, however, crystallise very close to the solidus in the last pockets of melt [93]. The temperature of zircon crystallization in the Stillwater Complex (Ti-in-Zircon method) overlaps with the temperature of the country rocks in the contact aureole [93] suggesting that these ages may reflect protracted cooling times rather than the first stages in the development of the rocks.…”

Section: Evaluation Of the Role Of Intrusionmentioning

confidence: 99%

The Merensky Cyclic Unit, Bushveld Complex, South Africa: Reality or Myth?

2018

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The Merensky Unit, Bushveld Complex, is commonly described using genetic terms such as "cyclic unit", typically without careful consideration of the connotations. We suggest that this contributes to the debate on processes forming the unit. This study integrates an extensive field study with detailed petrographic and textural analyses of the Merensky Unit to determine whether it is a "cyclic unit" sensu stricto. The study indicates that the bulk of the platinum-bearing chromitite-feldspathic orthopyroxenite developed through heterogeneous nucleation and in situ growth during multiple replenishment events. The overlying leuconorite developed above a gradational boundary, reflecting mixing following replenishment by a relatively more evolved magma. The bulk of this unit also formed in situ. The uppermost poikilitic anorthosite formed above a distinct boundary through a subsequent injection of a plagioclase-saturated magma, which crystallised in situ. Processes of gravitational settling and local remobilisation of crystals cannot be discounted from contributing to the development of the unit. The final textures throughout the unit developed through pervasive textural equilibration, with extensive fluid-mediated textural equilibration forming the megacrystic feldspathic orthopyroxenite. The evidence for at least five replenishment events indicates that the Merensky Unit is not a cyclic unit; therefore, the genetic term, "Merensky Cyclic Unit", is misleading and its use should be carefully considered in future work.

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Petrology and geochemistry of the Batchingou anorthositic suite rocks (Bana volcano‐plutonic complex, Cameroon Volcanic Line): Inference on their origin and relation with host granites

et al. 2022

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This study focusses on field mapping, petrographic description, and geochemical analyses of the Batchingou anorthositic suite rocks (Bana Plutono-volcanic Anorogenic Complex, Cameroon Volcanic Line). This suite consists of gabbroic (gabbro, gabbronorite, norite, and anorthosite) and charnockitic (mangerite, jotunite, enderbite, and monzogranite) rocks and intrude Ypresian granites (51 ± 1 Ma), within an elliptically shaped corridor of 1200 Â 600 m 2 . Gabbroic rocks evolved by crystal fractionation of olivine, hypersthene, augite, plagioclase, and ilmenite following the path: gabbro ! gabbronorite ! norite ! anorthosite. There is little or no crustal assimilation in this suite, contrarily to the charnockitic suite which likely evolved from a jotunite melt by assimilation of the Pan-African granito-gneissic basement rocks. Anorthosite has high Eu/Eu* (2.04-2.66), typical of anorthosites formed as cumulates. The La/Ta ratios (9.75-20.1 in gabbro, 21-45 in anorthosite and 23-76 charnockitic rocks), La/Yb N (4.2-19.5), Nb/U (22-90), and Nb/Th (5-23) suggest that the parental magma of the Batchingou anorthositic suite rocks is an alkaline basaltic melt deriving from a garnet-bearing asthenospheric mantle, but was variably modified during ascent by lithospheric spinel lherzolites and crustal rocks. The Batchingou gabbro has characteristics of evolved tholeiites and match the composition of the Laramie high-Al gabbro, whereas jotunite shows compositional affinity to ferrodiorites from Proterozoic anorthosite complexes. The gabbro Ni (19-39 ppm) and Cu (44-118 ppm) contents are low, indicating that their parental melt is not primitive. The Batchingou anorthositic suite differentiated from a different magma batch postdating the host granitoids and is similar to the anorthosite dykes of the Mboutou ring complex (Cameroon) and most of the ring complexes of the Aïr Province (Niger).

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The Stillwater Complex: Integrating Zircon Geochronological and Geochemical Constraints on the Age, Emplacement History and Crystallization of a Large, Open-System Layered Intrusion

Cited by 126 publications

References 135 publications

The Main Anorthosite Layer of the West-Pana Intrusion, Kola Region: Geology and U-Pb Age Dating

The Main Anorthosite Layer of the West-Pana Intrusion, Kola Region: Geology and U-Pb Age Dating

The Merensky Cyclic Unit, Bushveld Complex, South Africa: Reality or Myth?

Petrology and geochemistry of the Batchingou anorthositic suite rocks (Bana volcano‐plutonic complex, Cameroon Volcanic Line): Inference on their origin and relation with host granites

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