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Structural controls of kimberlite and lamproite emplacement

Authors
Journal
Journal of Geochemical Exploration
0375-6742
Publisher
Elsevier
Publication Date
Volume
53
Identifiers
DOI: 10.1016/0375-6742(94)00033-8
Disciplines
  • Earth Science
  • Geography

Abstract

Abstract In this article we review the regional and local structural controls on the emplacement, in the crustal environment, of kimberlites and lamproites after the generation of the magmas at depth. We find that there is good evidence that they are related to major deep faults or shears (mobile zones) that traverse the entire crust and may even traverse the lithosphere. Kimberlite and lamproite emplacement is favoured by transcurrent or extensional reactivation of these. The transcurrent reactivation may be a part of continental rifting. The extensional reactivation forms characteristic linear grabens (aulacogens). The emplacement of the kimberlites and lamproites appears to predate or, especially, postdate the peak tectonism, but this last point may be largely apparent because any sedimentation associated with the tectonism will tend to cover syn- or pre-tectonic intrusives. The kimberlites and lamproites within or adjacent to the mobile zones preferentially occur at intersections between conjugate zones or along internal and splay faults and shears which have a dilational or a conjugate orientation. The orientation of these depends upon kinematics of the transcurrent movement at the time of emplacement. Intrusives in the aulacogens are preferentially sited in the hanging wall of the major graben forming zone and tend to occur along oblique transfer structures which in turn are usually old basement shears or faults and may extend into the basement. The sedimentary cover may obscure the deep basement structures of aulacogens to such an extent that they may be seen only as widely spaced fault braids, fractures or joints in the cover. Diamondiferous kimberlites occur when the above structures form on Archean basement, whereas diamondiferous lamproites appear to be favoured by old reworked basement. In both cases the lithosphere should be abnormally thick.

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