U-Pb baddeleyite dating of intrusions in the south-easternmost Kaapvaal Craton (South Africa) : revealing multiple events of dyke emplacement

Abstract: This study presents U-Pb baddeleyite ages for five dolerite dykes and one sill in the Mesoarchean granitic basement of south-easternmost Kaapvaal Craton in northern KwaZulu-Natal, South Africa. The oldest dyke is ENE-trending, and is dated to 2729 ± 5 Ma. One ENE- and two SE-trending dyke are dated to 2580 ± 3 Ma, 2574 ± 5 Ma and ˃2517 ± 5 Ma (minimum age for the latter given by the 207Pb/206Pb date for the “oldest” fraction), respectively. These are interpreted to belong to a common ca. 2577 Ma event of dyke emplacement. A dolerite sill was dated to 2423 ± 7 Ma and an ENE-trending dyke to 2168 ± 5 Ma. The ENE-trend is shared among all dated generations, and their trends are interpreted to largely be controlled by basement structures pre-dating the younger generations of dykes. The 2729 Ma dyke can be correlated to the 2724 Ma age of the Phokwane Formation and the 2733 Ma age of the Mohle Formation (Hartswater Group, Ventersdorp Supergroup), extending Ventersdorp volcanism into the southeastern part of the Kaapvaal Craton. The ca. 2577 Ma generation represents a new magmatic event on the Kaapvaal Craton. It bears a temporal similarity to the ca. 2575 Ma Great Dyke on the Zimbabwe Craton. However, different trends and a distance of over 800 km between these units argues against a Kaapvaal-Zimbabwe connection at 2575 Ma in their present-day positions. The ca. 2423 and 2168 Ma intrusions also represent new magmatic events in this part of the Kaapvaal Craton, although similar ages have been reported for the Westerberg Sill and Hekpoort volcanics. Based on these new temporal constraints, the data in this study supports a juxtaposition of Kaapvaal and Pilbara in Vaalbara, at 2729 Ma. The new 2168 Ma age in this study can be temporally linked to magmatic events in the Superior and Wyoming cratons, and is supportive of the Kaapvaal, Superior and Wyoming cratons being in close proximity at these times.