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GEOPHYSICAL MODELLING OF THE MOLOPO FARMS COMPLEX IN SOUTHERN BOTSWANA; IMPLICATIONS FOR ITS EMPLACEMENT WITHIN THE 2 GA LARGE IGNEOUS PROVINCES OF SOUTHERN AND CENTRAL AFRICA

2010; Geological Society of South Africa; Volume: 113; Issue: 4 Linguagem: Inglês

10.2113/gssajg.113.4.381

1996-8590

A. S. D. Walker, R.M. Key, Gaud Pouliquen, Gus Gunn, J. SHARROCK, I. McGEORGE, M. KOKETSO, J. Elizabeth Farr,

Geomagnetism and Paleomagnetism Studies

Research Article| December 01, 2010 GEOPHYSICAL MODELLING OF THE MOLOPO FARMS COMPLEX IN SOUTHERN BOTSWANA; IMPLICATIONS FOR ITS EMPLACEMENT WITHIN THE ~2 GA LARGE IGNEOUS PROVINCES OF SOUTHERN AND CENTRAL AFRICA A.S.D. WALKER; A.S.D. WALKER British Geological Survey, Keyworth, Nottingham, United Kingdom, NG12 5GG, e-mail: asdw@bgs.ac.uk Search for other works by this author on: GSW Google Scholar R.M. KEY; R.M. KEY British Geological Survey, West Mains Road, Edinburgh, United Kingdom, EH9 3LA, e-mail: rmk@bgs.ac.uk Search for other works by this author on: GSW Google Scholar G. POULIQUEN; G. POULIQUEN Geosoft Europe Limited, Wallingford, United Kingdom, OX10 0AD, e-mail: gaud.pouliquen@geosoft.com Search for other works by this author on: GSW Google Scholar G. GUNN; G. GUNN British Geological Survey, Keyworth, Nottingham, United Kingdom, NG12 5GG, e-mail: agg@bgs.ac.uk Search for other works by this author on: GSW Google Scholar J. SHARROCK; J. SHARROCK Gondwana Ventures (Pty) Limited, P.O. Box 20241, Francistown, Botswana, e-mail: gondwana@botsnet.bw Search for other works by this author on: GSW Google Scholar I. McGEORGE; I. McGEORGE MSA Geoservices, P.O. Box 2258, Gaborone, Botswana, email: ian@msageoservices.com Search for other works by this author on: GSW Google Scholar M. KOKETSO; M. KOKETSO Department of Geological Survey, Private Bag 14, Lobatse, Botswana, e-mail: mkoketso@gov.bw Search for other works by this author on: GSW Google Scholar J. FARR J. FARR Wellfield Consulting Services (Pty) Limited, P.O. Box 1502, Gaborone, Botswana, e-mail: jfarr@wellfield.co.bw Search for other works by this author on: GSW Google Scholar Author and Article Information A.S.D. WALKER British Geological Survey, Keyworth, Nottingham, United Kingdom, NG12 5GG, e-mail: asdw@bgs.ac.uk R.M. KEY British Geological Survey, West Mains Road, Edinburgh, United Kingdom, EH9 3LA, e-mail: rmk@bgs.ac.uk G. POULIQUEN Geosoft Europe Limited, Wallingford, United Kingdom, OX10 0AD, e-mail: gaud.pouliquen@geosoft.com G. GUNN British Geological Survey, Keyworth, Nottingham, United Kingdom, NG12 5GG, e-mail: agg@bgs.ac.uk J. SHARROCK Gondwana Ventures (Pty) Limited, P.O. Box 20241, Francistown, Botswana, e-mail: gondwana@botsnet.bw I. McGEORGE MSA Geoservices, P.O. Box 2258, Gaborone, Botswana, email: ian@msageoservices.com M. KOKETSO Department of Geological Survey, Private Bag 14, Lobatse, Botswana, e-mail: mkoketso@gov.bw J. FARR Wellfield Consulting Services (Pty) Limited, P.O. Box 1502, Gaborone, Botswana, e-mail: jfarr@wellfield.co.bw Publisher: Geological Society of South Africa First Online: 09 Mar 2017 Online ISSN: 1996-8590 Print ISSN: 1012-0750 © 2010 Geological Society of South Africa South African Journal of Geology (2010) 113 (4): 381–400. https://doi.org/10.2113/gssajg.113.4.381 Article history First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation A.S.D. WALKER, R.M. KEY, G. POULIQUEN, G. GUNN, J. SHARROCK, I. McGEORGE, M. KOKETSO, J. FARR; GEOPHYSICAL MODELLING OF THE MOLOPO FARMS COMPLEX IN SOUTHERN BOTSWANA; IMPLICATIONS FOR ITS EMPLACEMENT WITHIN THE ~2 GA LARGE IGNEOUS PROVINCES OF SOUTHERN AND CENTRAL AFRICA. South African Journal of Geology 2010;; 113 (4): 381–400. doi: https://doi.org/10.2113/gssajg.113.4.381 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySouth African Journal of Geology Search Advanced Search Abstract The Molopo Farms Complex is an extremely poorly exposed, major, ultramafic-mafic layered intrusion straddling the southern border of Botswana with South Africa. It lies within the south-western part of the ~2.0 Ga large igneous province of southern and central Africa that includes the better known Bushveld Complex. Integrated interpretation of regional gravity data and new high-resolution airborne magnetic data have constrained the geometry of the Molopo Farms Complex in southern Botswana as a strongly faulted, polyphase intrusion compartmentalised by regional ductile shear zones. Previous models showing that the Complex was emplaced in at least two discrete stages are supported. Ultramafic rocks were initially emplaced as a semi-coherent lopolithic sheet up to about 4 km in thickness cutting across Transvaal Supergroup strata that had already been folded into open eastwest trending dome and basin structures with wavelengths of about 4 km. Steeply dipping, dyke-like ultramafic bodies adjacent to, and within major shears are inferred to be solidified feeders to the main lopolithic part of the MFC. It is likely that the initial ultramafic sheet was emplaced at a high crustal level (<3 km depth) into an attenuated Transvaal Supergroup sequence. This lack of a thick hanging wall sequence is thought to be significant for the emplacement of the succeeding mafic sheets. The ultramafic sheet thermally altered its wall rock and also created a complex fracture system in its hanging wall rocks. Differentiation within the ultramafic sheet produced basal harzburgites overlain by bronzites and possibly mafic sheets. Later mafic/basic sheets and dykes, again fed along shear-controlled, steeply dipping zones, spread into the fracture network created by the initial emplacement of the ultramafic lopolith to form a distinctive spider's-web pattern on high-resolution airborne magnetic maps. It is proposed that either post-emplacement regional folding or gravitational collapse of the basal ultramafic lopolith produced a major basin with a ~40 km eastwest diameter, north of the Jwaneng-Makopong Shear Zone and smaller basin to the southeast. The newly postulated, steeply dipping ultramafic/mafic feeders, as well as the ultramafic lopolith and areas with anomalous nickel values in soils are considered to be prospective for PGE-bearing magmatic nickel-copper sulphide mineralisation. Magmatic rocks dated at about 2.0 Ga are a common feature, not only of the Kaapvaal Craton, but of all the African cratonic blocks south of the Equator. Reactivated intracratonic faults and shears appear to control emplacement of individual magmatic complexes although a sub-continental thermal anomaly unconfined by lithospheric plate boundaries is a likely driving force for the widespread magmatism. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.