A mineralogical investigation of the Late Permian Doba gabbro, southern Chad: Constraints on the parental magma conditions and composition

J. Gregory Shellnutt, Tung Yi Lee, Chih Cheng Yang, Shin Tai Hu, Jong Chang Wu, Yoshiyuki Iizuka

Research output: Contribution to journalArticle

5 Citations (Scopus)

Abstract

The late Permian Doba (257 ± 1 Ma) gabbro was discovered at the base of an exploration well through the Cretaceous Doba Basin of Southern Chad. The gabbro is at least 250 m thick, has cumulus mineral textures and consists of plagioclase, clinopyroxene, orthopyroxene, Fe-Ti oxide, apatite and quartz. The composition of the silicate minerals (i.e. plagioclase, pyroxenes) from the lowest part of the intrusion tend to be more primitive (i.e. An59, Wo40-44En33-47Fs12-25) than the upper part (i.e. An41, Wo39-43En30-44Fs14-29) suggesting the magmatic system differentiated internally by crystal fractionation and crystal redistribution. Based on the chemistry of the pyroxenes, the parental magma was compositionally similar to a Ti-rich, within-plate continental tholeiite that had a bulk Mg# of ~44. The relative oxidation state of the magma was initially moderately reducing (i.e. ΔFMQ-0.3) and then became more reducing after a period of fractionation (i.e. ΔFMQ-1.2). The estimated initial magma temperature was at least 1100 °C. The within-plate composition suggests there was rifting-related magmatism near the boundary of the Saharan Metacraton that could be related to edge-driven mantle convection.

Original languageEnglish
Pages (from-to)13-20
Number of pages8
JournalJournal of African Earth Sciences
Volume114
DOIs
Publication statusPublished - 2016 Feb 1

Fingerprint

gabbro
Permian
magma
plagioclase
fractionation
crystal
tholeiite
mantle convection
silicate mineral
cumulus
orthopyroxene
clinopyroxene
apatite
rifting
magmatism
texture
oxide
quartz
Cretaceous
well

Keywords

  • Chad
  • Doba basin
  • Late Permian
  • Mineral chemistry
  • Saharan Metacraton
  • Tholeiitic basalt

ASJC Scopus subject areas

  • Geology
  • Earth-Surface Processes

Cite this

A mineralogical investigation of the Late Permian Doba gabbro, southern Chad : Constraints on the parental magma conditions and composition. / Shellnutt, J. Gregory; Lee, Tung Yi; Yang, Chih Cheng; Hu, Shin Tai; Wu, Jong Chang; Iizuka, Yoshiyuki.

In: Journal of African Earth Sciences, Vol. 114, 01.02.2016, p. 13-20.

Research output: Contribution to journalArticle

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