Late Ediacaran post-collisional magmatism in the Guéra Massif, South-Central Chad

ABSTRACT

The Guéra Massif of South-Central Chad is composed of collisional and post-collisional intrusive rocks related to the Central African Orogenic Belt. Collisional granites were emplaced at 595–590 Ma but there are a series of post-collisional intrusions that were emplaced at 570–560 Ma. The older granites have zircon U-Pb weighted-mean ages of 569 ± 6 Ma, 568 ± 7 Ma, and 568 ± 6 Ma, whereas the younger granites are 556 ± 7 Ma and 561 ± 6 Ma but all ages are within their maximum uncertainty. Both groups of post-collisional granites are peraluminous, ferroan, and alkali calcic to calc-alkalic but dioritic microgranular enclaves were observed within the older granites. The chemical variability of each group can be explained by fractional crystallization and it is likely that their parental magmas were derived by partial melting of the lower crust. The Nd isotopes of the older rocks (ε_Nd(t) = −9.5 to −1.2) are slightly less enriched than the younger rocks (ε_Nd(t) = −13.1 and −9.1). Moreover, the Nd isotopic compositions appear to indicate the existence of two isotopically distinct regions of the Guéra Massif with one centred on the Mongo (west) region and the other near the El Hidjer to Zan (east) region. The older group was emplaced during a period of crustal thinning after oblique collision and shearing related to the final suturing of the Congo-Saõ Francisco Craton and the Saharan Metacraton. The younger group was likely emplaced after a period of regional WNW-ESE directed crustal shortening. The punctuated nature of deformation/crustal relaxation cycles in the southern Saharan Metacraton suggests that there may have been many small terranes rather than larger cratonic blocks involved in the lithotectonic evolution of the Central African Orogenic Belt north of the Congo-Saõ Francisco Craton.

GRAPHICAL ABSTRACT

KEYWORDS:

• Saharan Metacraton
• post-collisional granite
• Late Ediacaran
• Chad
• Gondwana
• Central African Orogenic Belt

Acknowledgments

We are grateful to CPC-Taiwan for their assistance with field work logistics, and Hao-Yang Lee and Carol Chuang for their laboratory assistance. We thank Jean-Paul Liégeois, an anonymous reviewer, and Robert Stern for their constructive comments that helped to improve the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Highlights

• There are two groups post-collisional magmatism within the Guéra Massif

• The granitic rocks were emplaced at 570-560 Ma

• The rocks are peraluminous, ferroan, and alkali-calcic to calc-alkalic

• The granites were likely derived by partial melting of Proterozoic crust

Supplementary Material

Supplemental data for this article can be accessed here.

Additional information

Funding

This research was supported by funding provided by Ministry of Science and Technology (Taiwan) project 107-2628-M-003-003-MY3 to JGS.