GEOCHEMICAL CHARACTERIZATION OF A RECONSTRUCTED 1110 MA LARGE IGNEOUS PROVINCE

This work offers the best estimates for the paleoposition of the Indian and Amazonian cratons along with conjoined Kalahari-SF/Congo reconstruction. 1110 Ma Large Igneous Province (LIP) fragments in the Kalahari craton, southern Africa (Umkondo LIP); Dronning Maud Land, Antarctica; Bundelkhand portion of Indian craton (Mahoba dolerite dykes); Congo craton (Huila-Epembe dolerite dykes); and Amazonia (Rincon del Tigre-Huanchaca LIP) have been reconstructed as a single LIP with plume centre beneath the NW part of the Kalahari Craton. This 1110 Ma mafic magmatism is dominantly tholeiitic, ranging from basalt to andesitic basalt in composition, generated over a range of mantle melting depths [(Gd/Yb)N =1.2 to 2.3], exhibit low to high contamination with crustal components (negative Nb anomalies, eNd (0 to -12), and elevated Th/Yb). The data fall into two Groups based on TiO₂ content, with Group 1

(low Ti) of andesitic basalt composition, and Group 2 (high Ti) exhibiting a basaltic affinity. Group 1 magmas were generated in the spinel lherzolite field followed by significant contamination likely during passage through metasomatised lithospheric mantle in crustal magma chambers. A greater melting depth reaching into the garnet lherzolite field is proposed for the Group 2 magmas. The majority of Group 2 units are located in the Kalahari and Congo cratons, and this reflects onset of deeper melting closer to the interpreted plume axis in our reconstruction. In this context, we are looking both for variation from plume centre region to distal regions and also sectorial variations. We are also considering the location of feeders that are linked to high Ti and low Ti magmas. Given the idea of a lateral injection of magmas into radiating swarms, we consider here the distal magmas actually originate in the plume centre region in mid-crustal magma chambers from which the magma has been laterally injected.