Granite diapirism in Archaean rocks

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Abstract
This contribution is an extended abstract of a paper published elsewhere. It is included as an introduction to the published discussion which was stimulated by Professor Stephansson’s lecture. IN A RECENT PAPER the author suggested a classification of igneous intrusions ( Stephansson 1975 ). The term batholith is proposed for a large composite body of granitic diapirs and narrow septa of supracrustal rocks in a region of orogenic deformation. The diapirs may be of the same or different composition and have a characteristic feature of piercing a root of older rocks. The Svecofennian of central Sweden has been divided into a number of batholiths and subprovinces where metasediments, metavolcanics and migmatites predominate over the intrusions in the subprovinces. The batholiths consist of mostly granitoid intrusions of deep-seated type. The Vdala-Uppland batholith is the largest and most characteristic in form of the batholiths in central Sweden. It has an almost circular outcrop within a belt of synorogenic granites and foliated granitic gneisses which concentrically surround a core of less deformed quartz diorites and granodiorites. The division of central Sweden into batholiths and subprovinces and the distribution of granite diapirs within each batholith is supported by gravity data. The variation in the tectonic appearance of diapirs in orogenic zones results from a number of factors. Depending on the characteristics of the diapir, e.g. size, structure, contact with surrounding rocks these are divided into epi-, meso- and catatectonic diapirs ( Stephansson 1975 ). Most of the intrusions in the Vdala-Uppland batholith are of catatectonic type and their

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