PT  - JOURNAL ARTICLE
AU  - DEMPSTER, T. J.
AU  - PRESTON, R. J.
AU  - BELL, B. R.
TI  - The origin of Proterozoic massif-type anorthosites: evidence from interactions between crustal xenoliths and basaltic magma
AID  - 10.1144/gsjgs.156.1.0041
DP  - 1999 Jan 01
TA  - Journal of the Geological Society
PG  - 41--46
VI  - 156
IP  - 1
4099  - http://jgs.lyellcollection.org/content/156/1/41.short
4100  - http://jgs.lyellcollection.org/content/156/1/41.full
SO  - Journal of the Geological Society1999 Jan 01; 156
AB  - Plagioclase-rich reaction zones occur around numerous aluminous crustal xenoliths within a suite of Palaeogene sub-volcanic basic sheets on the Isle of Mull, NW Scotland. The xenoliths consist of a glassy core, containing mullite needles, generated from the melting of pelitic source rocks. Thick plagioclase mantles grew at the interface between the aluminous liquid and the enclosing basaltic magma and provide a high-level analogue for the petrogenesis of Proterozoic massif-type anorthosites. Similar interactions between mantle-derived basic magmas ponded at the base of the crust and relatively Al-rich lower crustal lithologies would result in the precipitation of large volumes of plagioclase. Anorthosite massifs were then emplaced at higher crustal levels as crystal-rich mushes within relatively juvenile Proterozoic crust. The model negates the need to crystallize large volumes of mafic minerals prior to the production of plagioclase-saturated liquids, and also accounts for the significant influence of crustal sources on the isotopic signatures of all members of the anorthosite suite.