Laurentia-Kalahari collision and the assembly of Rodinia

The Llano Orogenic Belt along the present southern margin of Laurentia, reg arded as continuation of the Grenvillian Orogen along the eastern Laurentia n margin and exposed in basement uplifts in central and western Texas, reco rds an similar to 300-m.yr. history of orogenesis culminating in are-contin ent and continent-continent collision between similar to 1150 and 1120 Ma a nd continuing until similar to 980 Ma. The shape of the orogen and kinemati cs of the contractional deformation along the belt, together with the high- P metamorphic conditions attained, indicate that a previously unidentified craton served as an indentor. It is paleomagnetically acceptable for the Ka lahari Craton of southern Africa to have been opposed to this margin and wi thin similar to 1500 km of present-day central Texas at similar to 1100 Ma. Moreover, the Kalahari Craton is the correct size, and the structural and metamorphic evolution of the 1200-950 Ma Namaqua-Natal Orogenic Belt that w raps around its present southern margin is compatible with that craton havi ng been the indentor. The ocean basin that closed between the Laurentia and Kalahari Cratons would have been comparable to the present Pacific, with i sland arc/terrane accretion occurring during the Mesoproterozoic along oppo sing active convergent margins. The coeval 1.1 Ga Keeweenawan and Umkondo m agmatic provinces of Laurentia and Kalahari, respectively, are associated w ith rifts at a high angle to the Llano and Namaqua Orogens. The rifts are i nterpreted as the result of collision-generated extensional stresses within the two cratons. The voluminous mafic igneous rocks in both provinces, how ever, may reflect contemporaneous plume activity. Our reconstruction for 1. 1 Ga provides a testable model for the Llano Orogenic Belt of Texas and the Namaqua Orogenic Belt of southwestern Africa as opposite sides of a Himala yan-type collisional orogen, with the Natal Belt of southeastern Africa and the originally continuous Maudheim Belt of East Antarctica as a related In donesian-type ocean-continent convergence zone. This reconstruction leads t o a refinement of the paleogeography of Rodinia, with the Kalahari Craton i n a position isolated from both the East Antarctic and Rio de la Plata Crat ons by oceanic lithosphere. It also provides the first model for the assemb ly of that hypothetical early Neoproterozoic supercontinent. At least four separate cratonic entities appear to have collided along three discrete seg ments of the apparently anastomosing global network of "Grenvillian" orogen s: the type-Grenville Belt of eastern North America and counterparts in Sou th America, the Llano-Namaqua Belt, and the Eastern Ghats-Albany/Fraser Bel t of India-East Antarctica and Australia. Over the remarkably short interva l of similar to 200 m.yr., this first-order composite collisional event res ulted in the amalgamation of most of Earth's continental lithosphere and de fined the close of the Mesoproterozoic Era.