The mode of emplacement of the Honningsvåg Intrusive Suite, Magerøya, northern Norway

• Published in: Geological Magazine
• Main Author: ROBINS, BRIAN
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 1998
• Subjects: Geology; Norway; Honningsvåg; Magerøya; Northern Norway
• Online Access: http://dx.doi.org/10.1017/s0016756898008395; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0016756898008395

The Honningsvåg Intrusive Suite consists of several layered mafic/ultramafic intrusions and a transgressive body of igneous breccia that appears to represent a magma conduit. It is emplaced into a Silurian, flysch-type sedimentary sequence that is thermally metamorphosed to spotted slate, cordierite–andalusite or pyroxene hornfels and agmatitic migmatite. Folds and flattened reduction spots in the hornfelses suggest that emplacement took place after Caledonian deformation and development of a slaty cleavage. Tectonic rotation subsequent to emplacement has led to exposure of the Honningsvåg Intrusive Suite in a natural cross-section corresponding to ∼10 km of crustal depth. Basaltic magma was initially emplaced as a several-kilometre-tall pipe that crystallized to form Intrusion 1. A second magma chamber was initiated alongside this pipe and subsequently expanded laterally into a sill-like magma body as batches of olivine-saturated basalt were added. A later magma chamber, represented by Intrusion 4, developed largely within the cumulates forming the upper part of Intrusion 2 and appears to have been accompanied by opening of a broad inclined feeder into which blocks and slabs of older cumulates collapsed. The resulting igneous breccias of Intrusion 3 are chaotic and largely clast-dominated in the lower part of the conduit, but enclosed slabs are matrix supported and orientated parallel to an originally subhorizontal banding in the feldspathic peridotite matrix in the upper part. The core of the breccia body has a troctolite matrix and contains blocks of older breccia, suggesting re-opening of the conduit, either during the crystallization of Intrusion 4 or possibly during the development of chambers represented by the younger layered intrusions. The cumulates in Intrusion 4 subsided sufficiently to invert marginal parts of the Layered Series before a further magma chamber was initiated in its roof rocks. The last major magma chamber opened alongside Intrusion 5 and extended upwards as a pipe or broad dyke to the ...