Origin of Archean anorthosites: Evidence from the Bad Vermilion Lake anorthosite complex, Ontario

Ashwal, Lewis D.; Morrison, Donald A.; Phinney, W. C.; Wood, John R.

doi:10.1007/bf01166620

Cited by 60 publications

(29 citation statements)

References 19 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Previous studies have shown that there is no consensus on the composition of the melt from which they have crystallized and a variety of melt compositions have been proposed. These include aluminous tholeiite (Weaver et al 1981), tholeiite (Ashwal et al 1983) and komatiite (Ashwal 1993).…”

Section: Discussionmentioning

confidence: 98%

Chromitites from the Fiskenæsset anorthositic complex, West Greenland: clues to late Archaean mantle processes

Rollinson

Reid

Windley

2010

View full text Add to dashboard Cite

Chromitites in the late Archaean Fiskenaesset anorthosite complex are characterized by a most unusual mineral assemblage: highly calcic plagioclase, iron-rich aluminous chromites and primary amphibole. In particular, the chromite compositions are atypical of chromitites in layered igneous intrusions. However, rare occurrences of this mineral assemblage are found in modern arcs and it is proposed here that the late Archaean calcic anorthositic chromitites formed by the partial melting of unusually aluminous harzburgite in a mantle wedge above a subduction zone. This melting process produced a hydrous, aluminous basalt, which fractionated at depth in the crust to produce a variety of high-alumina basalt compositions, from which the anorthosite complex with its chromitite horizons formed as a cumulate within the continental crust. The principal trigger for the late precipitation of chromite is thought to have been the removal of Al from the basaltic melt through plagioclase crystallization, and the build-up of Cr through an absence of clinopyroxene. It is proposed that the aluminous mantle source of the parent magma was produced by the melting of a harzburgitic mantle refertilized by small-volume, aluminous slab melts. This process ceased at the end of the Archaean because the dominant mechanism of crust generation changed such that melt production shifted from the slab into the mantle wedge, thus explaining why highly calcic anorthosites are almost totally restricted to the Archaean.

show abstract

Section: Discussionmentioning

confidence: 98%

Chromitites from the Fiskenæsset anorthositic complex, West Greenland: clues to late Archaean mantle processes

Rollinson

Reid

Windley

2010

View full text Add to dashboard Cite

show abstract

“…Other features of the zoisite-celsian gneiss chemistry that are divergent when compared to typical anorthosite compositions include concentrations of P 2 O 5 and Zr approximately one order of magnitude higher than expected, as are concentrations of Y, Nb and U (Table 2) (i.e. Ashwal et al 1983;Kolker et al 1990). From the zircon petrography and geochronology it is known that some zircon was inherited, meanwhile identification of apatite in the accessory phases is compatible with the high P 2 O 5 concentrations documented.…”

Section: Zoisite-celsian Gneissmentioning

confidence: 95%

The chemistry of barium anomalies in the Berisal Complex, Simplon Region, Switzerland

Hetherington

Lundmark

Graeser

et al. 2007

Int J Earth Sci (Geol Rundsch)

View full text Add to dashboard Cite

The petrographic and geochemical features of two zoisite-celsian gneiss outcrops from the Berisal Complex, characterised by a syn-kinematic mineral assemblage that contains celsian and barium white micas and a maximum whole-rock BaO content of 8.36 wt%, are described. The outcrops are enclosed in a larger body of garnet-bearing two-mica augen-gneiss, which has intrusive contacts with the surrounding garnet-biotite-muscovite paragneiss, and also contains small outcrops of two-mica clinozoisite gneiss. The zoisite-celsian gneisses are strongly enriched in all alkaline-earth elements, are depleted in the alkali elements, and have high Zr/Hf and Nb/Ta ratios compared with the surrounding gneisses. The zoisitecelsian, two-mica clinozoisite, and garnet-bearing twomica augen-gneisses have Al/CNK molar ratios >1, and the zoisite-celsian gneisses are also enriched in Zr, Y, and Nb. Chondrite-normalised patterns for the rare earth elements (REE) show light REE enrichment, with a negative Eu anomaly. On the basis of field and geochemical data it is argued that the barium anomalies in the Berisal complex are the result of igneous fractionation of barium into anorthosite-dominated cognate inclusions within a larger volume of calcalkaline peraluminous melt. On the basis of U-Pb zircon ages, a conservative estimate for the age of magma crystallisation is placed at 460 ± 10 Ma, and thus was related to significant late Ordovician granitoid magmatism in Gondwana-derived microcontinents during collision between Avalonia-Cadomia and Gondwana.

show abstract

“…difficult to achieve by the two-stage processes outlined above (13). The extreme EuISm ratios may reflect a multistage (23) fractional crystallization process (13). Merrillite in mesosiderite gabbros is a late-stage phase, -probably crystallizing from interstitial melt, which may not have been completely trapped in the rock.…”

Section: Yblsm (Ci)mentioning

confidence: 99%

Mesosiderite Clasts with the Most Extreme Positive Europium Anomalies Among Solar System Rocks

Mittlefehldt¹,

Rubin

Davis

1992

Science

View full text Add to dashboard Cite

Pigeonite-plagioclase gabbros that occur as clasts in mesosiderites (brecciated stony-iron meteorites) show extreme fractionations of the rare-earth elements (REEs) with larger positive europium anomalies than any previously known for igneous rocks from the Earth, moon, or meteorite parent bodies and greater depletions of light REEs relative to heavy REEs than known for comparable cumulate gabbros. The REE pattern for merrillite in one of these clasts is depleted in light REEs and has a large positive europium anomaly as a result of metamorphic equilibration with the silicates. The extreme REE ratios exhibited by the mesosiderite clasts demonstrate that multistage igneous processes must have occurred on some asteroids in the early solar system. Melting of the crust by large-scale impacts or electrical induction from an early T-Tauri-phase sun may be responsible for these processes.

show abstract

Origin of Archean anorthosites: Evidence from the Bad Vermilion Lake anorthosite complex, Ontario

Cited by 60 publications

References 19 publications

Chromitites from the Fiskenæsset anorthositic complex, West Greenland: clues to late Archaean mantle processes

Chromitites from the Fiskenæsset anorthositic complex, West Greenland: clues to late Archaean mantle processes

The chemistry of barium anomalies in the Berisal Complex, Simplon Region, Switzerland

Mesosiderite Clasts with the Most Extreme Positive Europium Anomalies Among Solar System Rocks

Contact Info

Product

Resources

About