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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

Published online by Cambridge University Press:  06 May 2015

J. GREGORY SHELLNUTT ,
TUNG-YI LEE ,
CHIH-CHENG YANG ,
SHIN-TAI HU ,
JONG-CHANG WU ,
KUO-LUNG WANG  and
CHING-HUA LO
J. GREGORY SHELLNUTT*
Affiliation:
National Taiwan Normal University, Department of Earth Science, 88 Tingzhou Road Section 4, Taipei 116, Taiwan
TUNG-YI LEE
Affiliation:
National Taiwan Normal University, Department of Earth Science, 88 Tingzhou Road Section 4, Taipei 116, Taiwan
CHIH-CHENG YANG
Affiliation:
Chinese Petroleum Corporation-Taiwan, Exploration and Development Research Institute, Wen Fa Road, Miaoli 36042, Taiwan
SHIN-TAI HU
Affiliation:
Chinese Petroleum Corporation-Taiwan, Exploration and Development Research Institute, Wen Fa Road, Miaoli 36042, Taiwan
JONG-CHANG WU
Affiliation:
Chinese Petroleum Corporation-Taiwan, Exploration and Development Research Institute, Wen Fa Road, Miaoli 36042, Taiwan
KUO-LUNG WANG
Affiliation:
Academia Sinica Institute of Earth Sciences, 128 Academia Road Section 2, Taipei 115, Taiwan
CHING-HUA LO
Affiliation:
National Taiwan University, Department of Geosciences, P.O. Box 13–318, Taipei 106, Taiwan
*
†Author for correspondence: [email protected]
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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 40Ar–39Ar step-heating geochronology yielded a Late Permian plateau age of 257 ± 1 Ma. The major and trace elemental geochemistry shows that the gabbro is tholeiitic in composition and has trace element ratios (i.e. La/YbN > 7; Sm/YbPM > 3.4; 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. ISr = 0.70495 to 0.70839; ɛNd(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. ISr = 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.

Keywords

Late PermianSaharan Metacraton40Ar–39Ar datingDoba basinChad
Type
Original Articles
Information
Geological Magazine , Volume 152 , Issue 6 , November 2015 , pp. 1073 - 1084
Copyright
Copyright © Cambridge University Press 2015 

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