The Bjerkreim-Sokndal Layered Intrusion, Rogaland, SW Norway: Evidence from marginal rocks for a jotunite parent magma
1997; Elsevier BV; Volume: 39; Issue: 3-4 Linguagem: Inglês
10.1016/s0024-4937(96)00021-7
ISSN1872-6143
Autores Tópico(s)Geochemistry and Geologic Mapping
ResumoThe Late-Proterozoic Bjerkreim-Sokndal Layered Intrusion (BKSK) consists of andesine anorthosite, leuconorite, troctolite, norite, gabbronorite, jotunite, mangerite, quartz mangerite and charnockite. The sequence of appearance of cumulus minerals and their compositions suggest a parent magma that was evolved, had plagioclase (±olivine) on the liquidus, was sufficiently TiO2-rich for hemo-ilmenite to crystallise early, and low in CaO and CaOAl2O3 compared to basalts as reflected by the sodic plagioclases and the delayed appearance of cumulus augite. Fine- to medium-grained jotunites found along the northern contact of the BKSK consist of plagioclase (An45–53), inverted pigeonite (Mg# = 55-50), sparse augite (Mg# = 69-59), Fe-Ti oxides, K-feldspar, quartz and apatite. They are basic to intermediate rocks with relatively high FeOtotal, high TiO2, low MgO/MgO + FeO, moderate Al2O3 and low CaO and normative diopside. The jotunites have compositions that are consistent with the parental magma for the lower part of the BKSK Layered Series, and are interpreted as being marginal chills. Similar, but slightly more differentiated, jotunite magmas were subsequently emplaced into the BKSK and the surrounding region as broad dykes and small plutons. Jotunite is a minor rock type in most massif-type anorthosite provinces but may have an important petrological significance.
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