The geology and geochemistry of the Sterkspruit intrusion, Barberton Mountain Land, Mpumalanga province
Date
1997
Authors
Conway, Gavin, Patrick
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Journal ISSN
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Abstract
The Sterkspruit Intrusion, in the south-western portion of the Barberton
greenstone belt, is a sill-like body containing rocks of gabbroic to dioritic
composition. It is hosted by a sequence of komatiitic basalts and komatiites of
the Lower Onverwacht Group. The intrusion is considered unique in this area in
that it lacks ultramafic components and has no affinities with the surrounding
mafic- to- ultramafic lavas. The gabbroic suite also contains an unusual
abundance of quartz, and the chill margin shows an evolved quartz-normative,
tholeiitic parental magma. Based on petrographic and geochemical evidence,
the intrusion can be subdivided into four gabbroic zones and a quartz diorite,
which is an end product of a differentiating magma. The chill margin records an
MgO content of 4.8%, an Mg# of 42, an Si02 value of 52.5% and a normative
plagioclase composition of An44. The sill-like nature of the body, indicated by
geochemical trends, and the steep sub-vertical layering, point to a body that
has been tilted along with the surrounding lavas. This constrains the relative
age of the body to be older than the emplacement of the Kaap Valley and
Nelshoogte Plutons, which caused the regional deformation observed in the
Nelshoogte Schist Belt. A sequence of tholeiitic to andesitic basalts from the
Kromberg Formation in the Upper Onverwacht Group, have compositions which
can be correlated with the Sterkspruit Intrusion. It is possible that this body
represents a subvolcanic magma chamber, which acted as a feeder to tholeiitic
lavas higher up in the volcanic sequence. The Sterkspruit Mafic Dyke Swarm
intruded the southern Nelshoogte Schist Belt and displays intra-dyke chemical
variation.
Description
Thesis (M.Sc.)--University of the Witwatersrand, Science Faculty (Geology), 1997.
Keywords
Geology--South Africa--Barberton, Geochemistry--South Africa--Barberton
Citation
Conway, Gavin Patrick (1997) The geology and geochemistry of the Sterkspruit intrusion, Barberton Mountain Land, Mpumalanga province, University of the Witwatersrand, Johannesburg, <http://wiredspace.wits.ac.za/handle/10539/21899>