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Magma replenishment, and the significance of poikilitic textures, in the Lower Main Zone of the western Bushveld Complex, South Africa

Andrew A. Mitchell, Hugh V. Eales and F. Johan Krueger
Magma replenishment, and the significance of poikilitic textures, in the Lower Main Zone of the western Bushveld Complex, South Africa
Mineralogical Magazine (August 1998) 62 (4): 435-450

Abstract

Petrographic and compositional variations in the Lower Main Zone (LMZ) of the western Bushveld Complex indicate changing regimes of magma replenishment. The lowermost unit of the LMZ, designated N-I, is an enigmatic sequence of leuconoritic cumulates, characterized primarily by up-sequence increases in both orthopyroxene Mg# and whole-rock Sr isotope initial ratio. The Sr isotope profile of N-I is ascribed to injection and progressive integration of small influxes of fresh magma with high (Main Zone-type) Sr isotope initial ratios. The basal Fe-enrichment in N-I, on the other hand, is ascribed to a separate, later mechanism involving the downward migration of late-stage Fe-rich liquids. The overlying two units, N-II and G-I, delineated chiefly in terms of basal Mg-enrichment of orthopyroxene, are ascribed to injections of fresh magma into the chamber. Poikilitic orthopyroxene grains in the basal parts of both N-II and G-I suggest entrainment and partial resorption of plagioclase grains from the semi-crystalline resident material into which the fresh magma was intruded.


ISSN: 0026-461X
EISSN: 1471-8022
Serial Title: Mineralogical Magazine
Serial Volume: 62
Serial Issue: 4
Title: Magma replenishment, and the significance of poikilitic textures, in the Lower Main Zone of the western Bushveld Complex, South Africa
Affiliation: University of Durban-Westville, Department of Geology, Durban, South Africa
Pages: 435-450
Published: 199808
Text Language: English
Publisher: Mineralogical Society, London, United Kingdom
References: 40
Accession Number: 1999-018408
Categories: Igneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. strat. cols., 1 table, geol. sketch map
S35°00'00" - S27°00'00", E16°30'00" - E33°00'00"
Secondary Affiliation: Rhodes University, ZAF, South AfricaBernard Price Institute for Geophysical Research, ZAF, South Africa
Country of Publication: United Kingdom
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute.
Update Code: 199907
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