by Lewis David Ashwal, Robert B. Trumbull, Susan Jane (Sue) Webb, Frederick Roelofse, Reiner Klemd

An ICDP project in the Bushveld Complex in South Africa will contribute to the following ICDP science themes: Large Igneous Provinces and Mantle Plumes; Natural Resources; Volcanic Systems and Thermal Regimes; and Deep Life. Drill sites are selected to provide vertical reference sections through the complex and also to test lateral variations across the complex. The reference sections will be curated at the National Core Facility operated by the South African Council for Geoscience. New ICDP cores will be complemented by existing core materials, including substantial donations from the South African mining industry (ca. 6000 m, value ca. 1.5 million US$). With a volume of 1 million km3, the Bushveld Complex is the world's largest known igneous body, and a LIP by itself. The complex contains subequal proportions of mafic and felsic igneous rocks, providing an opportunity to study relationships between mantle and crustal sources of magmatism in detail. The complex also contains fabulous mineral wealth, with resources of strategic and high-tech metals that are vital for the South African and global economies. Most of the 8 km-thick layered sequence of the Bushveld Complex is below the surface. Access by mining operations or fortuitous outcrop reveals only parts of the sequence in detail, and without vertical continuity. To understand how the Bushveld magmas accumulated and crystallized into layers, and how ores formed within them, requires studying a continuous vertical sequence including the roof and floor zones. Furthermore, some of the most interesting science topics require techniques or conditions such as oriented core, or fluid and biological sampling, which can only be provided by dedicated new drill holes. Coordinated studies of the drill cores, downhole experiments and fluid samples will address fundamental processes of crust and mantle melting to produce the Bushveld magma(s), the magma chamber processes that controlled melt evolution, development of mineral layering and ore formation, the geophysical and geodynamic aspects including crustal stresses and thermal gradient, and the nature of deep groundwater systems and microbial communities. The benefits of an ICDP project will be immediate and long-lasting. From the start, the drilling operations will be used as a training ground for technical and safety modules and workshops. The professionally logged and curated reference collection of the Bushveld Complex will be internationally available for research, teaching and for public outreach as a geologic heritage site.

• The objectives are focused into themes: Magma chamber processes, melt sources and magma evolution: How many separate melts were involved in filling the Bushveld magma chamber(s), from where were they derived, how much did they mix and how much left the system? How quickly was the complex assembled and how fast did it cool down? Interaction of mantle melts with the crust and the origin of felsic magmas: What is the proportion of mantle vs. crustal material in the mafic and felsic magmas? Are the two magma series related to each other and if so, how? Origin of ore deposits: How important were vertical transport processes in the magma through crystal settling and sinking of sulfide melts? What was the role of melt mixing or unmixing in ore formation? How important was metals transport and reworking by hydrothermal fluids? Geophysical properties and geodynamic processes: What isostatic effect did emplacement of Bushveld magmas have, what are the implications for elastic thickness of the lithosphere? How many magnetic reversals are recorded in the intrusion? What is the present state of stress and heat flow in the crust, and their variations with depth? Hydrogeology and the deep biosphere: What is the quantity and quality of deep groundwater in the Bushveld area and the effect of mining on these distributions and on hydraulic conductivity? Is there a geothermal potential? What is the nature of subsurface biomes, what are their energy sources and what role does water-rock interaction play thereby? How old are the deep microbe lineages, to what extent do near-surface and deep communities interact?

Bushveld, Deep Biosphere, Layered Intrusions, Lips, Ore Formation, South Africa

Latitude: -25.50000, Longitude: 30.10000