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Late Permian mafic rocks identified within the Doba Basin of southern Chad and their relationship to the boundary of the Saharan Metacraton

John Gregory Shellnutt, Tungyi Lee, Chihcheng Yang, Shintai Hu, Jongchang Wu, Kuolung Wang and Chinghua Lo
Late Permian mafic rocks identified within the Doba Basin of southern Chad and their relationship to the boundary of the Saharan Metacraton
Geological Magazine (November 2015) 152 (6): 1073-1084

Abstract

The Doba gabbro was collected from an exploration well through the Cretaceous Doba basin of southern Chad. The gabbro is composed mostly of plagioclase, clinopyroxene and Fe-Ti oxide minerals and displays cumulus mineral textures. Whole-rock (super 40) Ar- (super 39) Ar step-heating geochronology yielded a Late Permian plateau age of 257+ or -1 Ma. The major and trace elemental geochemistry shows that the gabbro is tholeiitic in composition and has trace element ratios (i.e. La/Yb (sub N) >7; Sm/Yb (sub PM) >2.4; Nb/Y>1; Zr/Y>5) indicative of a basaltic melt derived from a garnet-bearing mantle source. The moderately enriched Sr-Nd isotopes (i.e. I (sub Sr) =0.70495 to 0.70839; epsilon Nd(T)=-1.0 to -1.3) fall within the mantle array (i.e. OIB-like) and are similar to other Late Permian plutonic rocks of North-Central Africa (i.e. I (sub Sr) =0.7040 to 0.7070). The enriched isotopic composition of the Doba gabbro contrasts with the more depleted compositions of the spatially associated Neoproterozoic post-Pan-African within-plate granites. The contrasting Nd isotope composition between the older within-plate granites and the younger Doba gabbro indicates that different mantle sources produced the rocks and thus may mark the southern boundary of the Saharan Metacraton.


ISSN: 0016-7568
EISSN: 1469-5081
Coden: GEMGA4
Serial Title: Geological Magazine
Serial Volume: 152
Serial Issue: 6
Title: Late Permian mafic rocks identified within the Doba Basin of southern Chad and their relationship to the boundary of the Saharan Metacraton
Affiliation: National Taiwan Normal University, Department of Earth Science, Taipei, Taiwan
Pages: 1073-1084
Published: 201511
Text Language: English
Publisher: Cambridge University Press, London, United Kingdom
References: 51
Accession Number: 2016-001996
Categories: Igneous and metamorphic petrologyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables, geol. sketch maps
N08°00'00" - N15°00'00", E15°30'00" - E22°00'00"
Secondary Affiliation: Chinese Petroleum Corporation, TWN, TaiwanAcademia Sinica, Institute of Earth Sciences, TWN, TaiwanNational Taiwan University, TWN, Taiwan
Country of Publication: United Kingdom
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 201601
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