IJG  Vol.3 No.5 , November 2012
Gravity and Aeromagnetic Studies of the Filabusi Greenstone Belt, Zimbabwe Craton: Regional and Geotectonic Implications
Author(s) Rubeni T. Ranganai*
ABSTRACT
The Filabusi greenstone belt (FGB), Zimbabwe craton, has been geologically remapped relatively recently but its regional tectonic setting and subsurface structure have, until now, remained unresolved. This paper presents gravity and aeromagnetic studies that have been undertaken to provide this important information, and also extend mapping to areas of poor exposure. Several new NNW-trending dykes and structures cutting across the greenstone belt have been revealed, as well as a major extension of one of the metakomatiitic-BIF units, the Shamba Range. ESE-trending dykes identified in the southeast appear on a regional scale to be part of the giant Okavango dyke swarm in northern Botswana. An ~3 km wide NNE-striking magnetic low occurs over the Irisvale-Lancaster shear zone (ILSZ) on the extreme west of the FGB where it roughly marks the boundary with the Bulawayo greenstone belt. Magnetic anomaly trends over ultramafic schists are consistent with strike-slip movement along the ILSZ, and together with the gravity anomalies, support northeasterly directed detachment of the adjacent Fort Rixon belt from the Bulawayo-Filabusi belt. The Bouguer gravity anomaly map shows that the FGB is characterised by a well defined positive anomaly up to 37 mGal, whose symmetry and extent confirm the postulated synclinal structure of the belt. Isolated oval shaped small gravity lows generally correlate with sub-/out-cropping K-rich post-volcanic granite plutons. 2.5D gravity models along three profiles across the greenstone belt show a simple “basin shape” with a possible maximum depth extent of only 4.5 km, compared to an estimated stratigraphic thickness of about 9.0 km. This suggests a truncation at shallow depth of the structurally repeated lithologies. Gravity data and models support the proposed FGB model; deposition of volcanics in an extensional, structurally determined, evolving basin. This autochthonous setting is consistent with other greenstone belts in the Zimbabwe craton and other parts of the world.

Cite this paper
R. Ranganai, "Gravity and Aeromagnetic Studies of the Filabusi Greenstone Belt, Zimbabwe Craton: Regional and Geotectonic Implications," International Journal of Geosciences, Vol. 3 No. 5, 2012, pp. 1048-1064. doi: 10.4236/ijg.2012.35106.
References
[1]   M. J. Bickle and E. G. Nisbet EG, Eds., “The Geology of the Belingwe Greenstone Belt, Zimbabwe: A Study of the Evolution of Archaean Continental Crust,” Geological Society of Zimbabwe, Special Publication 2, A. A. Balkema, Rotterdam, 1993.

[2]   J. F. Wilson, R. W. Nesbitt and C. M. Fanning, “Zircon Geochronology of Archaean Felsic Sequences in the Zimbabwe Craton: A Revision of Greenstone Stratigraphy and a Model for Crustal Growth,” In: M. P. Coward and A. C. Ries, Eds., Early Precambrian Processes, Geological Society, Special Publication 95, London, 1995, pp. 109-126.

[3]   T. G. Blenkinsop, A. Martin, H. A. Jelsma and M. L. Vinyu, “The Zimbabwe Craton,” In: M. J. de Wit and L. D. Ashwal, Eds., Greenstone Belts, Oxford Monograph on Geology and Geophysics, Clarendon Press, Oxford, 1997, pp. 567-580.

[4]   M. S. A. Horstwood, R. W. Nesbitt, S. R. Noble and J. F. Wilson, “U-Pb Zircon Evidence for an Extensive Early Archean Craton in Zimbabwe: A Reassessment of the Timing of Craton Formation, Stabilization and Growth,” Geology, Vol. 27, No. 8, 1999, pp. 707-710. doi:10.1130/0091-7613(1999)027<0707:UPZEFA>2.3.CO;2

[5]   H. A. Jelsma and P. H. G. M. Dirks, “Neoarchaean Tectonic Evolution of the Zimbabwe Craton,” In: C. M. R. Fowler, C. Ebinger and C. J. Hawkesworth, Eds., The Early Earth: Physical, Chemical and Biological Development, Geological Society, Special Publications 199, London, 2002, pp 183-211.

[6]   M. D. Prendergast, “The Bulawayan Supergroup: A Late Archaean Passive Margin-Related Large Igneous Province in the Zimbabwe Craton,” Journal of the Geological Society, Vol. 161, No. 3, 2004, pp. 431-445. doi:10.1144/0016-764902-092

[7]   M. D. Prendergast and M. T. D. Wingate, “Zircon Geochronology and Partial Structural Re-Interpretation of the Late Archaean Mashaba Igneous Complex, South-Central Zimbabwe,” South African Journal of Geology, Vol. 110, No. 4, 2007, pp. 585-596. doi:10.2113/gssajg.110.4.585

[8]   D. S. Bartholomew, “Base Metal and Industrial Mineral Deposits of Zimbabwe, and Gold Deposits of Zimbabwe,” Zimbabwe Geological Survey Mineral Resources Series No. 22 and 23, Harare, 1990.

[9]   S. D. G Campbell and P. E. J. Pitfield, “Structural Controls of Gold Mineralization in the Zimbabwe CratonExploration Guidelines,” Zimbabwe Geological Survey Bulletin 101, Harare, 1994.

[10]   N. Baglow, “The Geology of the Filabusi Granite-Greenstone Terrain,” Zimbabwe Geological Survey Bulletin 91, Harare, 1998.

[11]   S. D. G. Campbell, N. Baglow and P. E. J. Pitfield, “The Structural Framework of the Filabusi Greenstone Belt, and Its Relevance to Gold Mineralization,” Annals of the Zimbabwe Geological Survey, Vol. 15, 1990, pp. 29-38.

[12]   B. S. Kamber, R. Bolhar and G. E. Webb, “Geochemistry of Late Archaean Stromatolites from Zimbabwe: Evidence of Microbial Life in Restricted Epicontinental Seas,” Precambrian Research, Vol. 132, No. 4, 2004, pp. 379-399. doi:10.1016/j.precamres.2004.03.006

[13]   S. D. G. Campbell, P. M. Oesterlen, T. G. Blenkinsop, P. E. J. Pitfield and H. Munyanyiwa, “A Provisional 1:2,500, 000 Scale Tectonic Map and the Tectonic Evolution of Zimbabwe,” Annals of the Zimbabwe Geological Survey, Vol. 16, 1991, pp 31-50.

[14]   M. J. Bickle, E. G. Nisbet and A. Martin, “Archean Greenstone Belts Are not Oceanic Crust,” The Journal of Geology, Vol. 102, No. 2, 1994, pp. 121-138. doi:10.1086/629658

[15]   M. A. Hunter, M. J. Bickle, E. G. Nisbet, A. Martin and H. J. Chapman, “Continental Extensional Setting for the Archean Belingwe Greenstone Belt, Zimbabwe,” Geology, Vol. 26, No. 10, 1998, pp. 883-886. doi:10.1130/0091-7613(1998)026<0883:CESFTA>2.3.CO;2

[16]   R. T. Ranganai, K. A. Whaler and C. J. Ebinger, “Gravity Anomaly Patterns in the South-Central Zimbabwe (Archaean) Craton and Their Geological Interpretation,” Journal of African Earth Sciences, Vol. 51, No. 5, 2008, pp. 257-276. doi:10.1016/j.jafrearsci.2008.01.011

[17]   O. Gwavava and R. T. Ranganai, “The Geology and Structure of the Masvingo Greenstone Belt and Adjacent Granite Plutons from Geophysical Data, Zimbabwe Craton,” South African Journal of Geology, Vol. 112, No. 3-4, 2009, pp. 277-290. doi:10.2113/gssajg.112.3-4.277

[18]   P. H. G. M. Dirks and H. A. Jelsma, “Silicic Layer-Parallel Shear Zones in a Zimbabwean Greenstone Sequence: Horizontal Accretion Preceding Doming,” Gondwana Research, Vol. 1, No. 2, 1998, pp. 177-193. doi:10.1016/S1342-937X(05)70829-7

[19]   T. M. Kusky, “Tectonic Setting and Terrane Accretion of the Archean Zimbabwe craton,” Geology, Vol. 26, No. 2, 1998, pp. 163-166. doi:10.1130/0091-7613(1998)026<0163:TSATAO>2.3.CO;2

[20]   A. Hofmann and T. Kusky, “The Belingwe Greenstone Belt: Ensialic or Oceanic?” Developments in Precambrian Geology, Vol. 13, 2004, pp. 487-538.

[21]   V. K. Gupta, P. C. Thurston and T. H. Dusanowskj, “Constraints upon Models of Greenstone Belt Evolution by Gravity Modeling, Birch-Uchi Greenstones Belt, Northern Ontario,” Precambrian Research, Vol. 16, No. 4, 1982, pp. 233-255. doi:10.1016/0301-9268(82)90062-6

[22]   E. H. Stettler, J. H. de Beer, D. Eberle, J. Ludden and M. Mareschal, “Geophysics and Deep Structures,” In: M. J. de Wit and L. D. Ashwal, Eds., Greenstone Belts, Oxford monograph on geology and geophysics, Clarendon Press, Oxford, 1997, pp 339-375.

[23]   R. I. Gibson and P. S. Millegan, Eds., “Geologic Applications of Gravity and Magnetics: Case Histories,” Society of Exploration Geophysicists, Geophysical Reference Series 8, Tulsa, 1998.

[24]   P. Wellman, “Upper Crust of the Pilbara Craton, Australia: 3D Geometry of a Granite/Greenstone Terrain,” Precambrian Research, Vol. 104, No. 3-4, 2000, pp. 175-186. doi:10.1016/S0301-9268(00)00092-9

[25]   A. P. Peschler, K. Benn and R. W. Roest, “Insights on Archean Continental Geodynamics from Gravity Modelling of Granite-Greenstone Terranes,” Journal of Geodynamics, Vol. 38, No. 2, 2004, pp. 185-207. doi:10.1016/j.jog.2004.06.005

[26]   M. A. McLean and P. G. Betts, “Geophysical Constraints of Shear Zones and Geometry of the Hiltaba Suite Granites in the Western Gawler Craton, Australia,” Australian Journal of Earth Sciences, Vol. 50, No. 4, 2003, pp. 525541.

[27]   P. J. Treloar and T. G. Blenkinsop, “Archaean Deformation Patterns in Zimbabwe: True Indicators of TibetanStyle Crustal Extrusion or Not?” In: M. P. Coward and A. C. Ries, Eds., Early Precambrian Processes, Geological Society Special Publication 95, 1995, pp. 87-108.

[28]   M. J. De Wit, “On Archean Granites, Greenstones, Cratons and Tectonics: Does the Evidence Demand a Verdict?” Precambrian Research, Vol. 91, No. 1, 1998, pp. 181-226. doi:10.1016/S0301-9268(98)00043-6

[29]   W. B. Hamilton, “Archean Magmatism and Deformation were not Products of Plate Tectonics,” Precambrian Research, Vol. 91, No. 1, 1998, pp. 143-179. doi:10.1016/S0301-9268(98)00042-4

[30]   M. J. Van Kranendonk, R. H. Smithies and V. C. Bennett, Eds., “Earth’s Oldest Rocks,” Elsevier, Amsterdam, 2007.

[31]   J. F. Wilson, “A craton and Its Cracks: Some of the Behaviour of the Zimbabwe Block from the Late Archaean to the Mesozoic in Response to Horizontal Movements, and the Significance of Some of its Mafic Dyke Fracture Patterns,” Journal of African Earth Sciences, Vol. 10, No. 3, 1990, pp. 483-501. doi:10.1016/0899-5362(90)90101-J

[32]   C. W. Stowe, “Wrench Tectonics in the Archaean Rhodesian Craton,” Transactions of the Geological Society of South Africa, Vol. 83, No. 2, 1980, pp. 193-205.

[33]   N. Baglow, “The Epoch Nickel Deposit, Zimbabwe,” In: C. R. Anhaeusser and S. Maske, Eds., Mineral Deposits of Southern Africa, Geological Society of South Africa, Johannesburg, 1986, pp 359-376.

[34]   J. F. Wilson, D. L. Jones and J. D. Kramers, “Mafic Dyke Swarms in Zimbabwe,” In: H. C. Halls and W. F. Fahrig, Eds., Mafic Dyke Swarms, Geological Association of Canada Special Paper 34, 1987, pp. 433-444.

[35]   R. J. Blakely, “Potential Theory in Gravity and Magnetic Applications,” Cambridge University Press, Cambridge, 1995.

[36]   P. R. Milligan and P. J. Gunn, “Enhancement and Presentation of Airborne Geophysical Data,” AGSO Journal of Australian Geology & Geophysics, Vol. 17, No. 2, 1997, pp. 63-75.

[37]   S. W. Letros, D. W. Strangway and J. Geissman, “Apparent Susceptibility Mapping in the Kirkland Lake Area, Ontario, Abitibi Greenstone Belt,” Canadian Journal of Earth Sciences, Vol. 20, No. 4, 1983, pp. 548-560. doi:10.1139/e83-052

[38]   H. J. Broome, “Generation and Interpretation of Geophysical Images with Examples from the Rae Province, Northwestern Canada Shield,” Geophysics, Vol. 55, No. 8, 1990, pp. 977-997.

[39]   A. Martin, “The Geology of the Belingwe-Shabani Schist Belt,” Rhodesia Geological Survey Bulletin 83, Salisbury, 1978.

[40]   J. B. Moody, “Serpentinisation: A Review,” Lithos, Vol. 9, No. 2, 1976, pp. 125-138. doi:10.1016/0024-4937(76)90030-X

[41]   F. S. Grant, “Aeromagnetics, Geology and Ore Environments, I. Magnetite in Igneous, Sedimentary and Metamorphic Rocks: An Overview,” Geoexploration, Vol. 23, No. 3, 1985, pp. 303-333. doi:10.1016/0016-7142(85)90001-8

[42]   R. T. Ranganai and C. J. Ebinger, “Aeromagnetic and LANDSAT TM Structural Interpretation for Identifying Regional Groundwater Exploration Targets, South-Central Zimbabwe Craton,” Journal of Applied Geophysics, Vol. 65, No. 2, 2008, pp. 73-83. doi:10.1016/j.jafrearsci.2008.01.011

[43]   R. T. Ranganai, “Geophysical Investigations of the Granite-Greenstone Terrain in the South-Central Zimbabwe Archaean Craton,” Ph.D. Thesis, University of Leeds, Leeds, 1995.

[44]   C. V. Reeves, “The Geophysical Mapping of Mesozoic Dyke Swarms in Southern Africa and Their Origin in the Disruption of Gondwana,” Journal of African Earth Sciences, Vol. 30, No. 3, 2000, pp. 499-513. doi:10.1016/S0899-5362(00)00035-X

[45]   F. Jourdan, G. Feraud, H. Bertrand, A. B. Kampunzu, G. Tshoso, B. Le Gall, J. J. Tiercelin and P. Capiez, “The Karoo Triple Junction Questioned: Evidence from Jurassic and Proterozoic 40Ar/39Ar Ages and Geochemistry of the Giant Okavango Dyke Swarm (Botswana),” Earth and Planetary Science Letters, Vol. 222, No. 3, 2004, pp. 989-1006. doi:10.1016/j.epsl.2004.03.017

[46]   O. Gwavava, “A Regional Gravity Study of the Limpopo Belt and Mechanisms of Isostatic Compensation in the Region,” Ph.D. Thesis, University of Zimbabwe, Harare, 1990.

[47]   K. Fisk and M. T. Hawadi, “The National Gravity Dataset of Zimbabwe,” Zimbabwe Geological Survey Bulletin No. 103, Harare, 1996.

[48]   H. Moritz, “Geodetic Reference System 1980,” Bulletin of Geodesy, Vol. 58, No. 3, 1984, pp. 388-398. doi:10.1007/BF02519014

[49]   W. H. F. Smith and P. Wessel, “Gridding with Continuous Curvature Splines in Tension,” Geophysics, Vol. 16, 1990, pp. 222-227.

[50]   R. T. Ranganai and O. Gwavava, “Gravity Modelling of Late Archaean Chilimanzi and Razi plutons, Zimbabwe craton,” 23rd Colloquium of African Geology CAG23 Abstracts, Johannesburg, 2011, p. 344.

[51]   D. M. Robertson, “Potash Granites of the Southern Edge of the Rhodesian Craton and the Northern Granulite Zone of the Limpopo Belt,” In: L. A. Lister, Ed., Symposium on Granites, Gneisses and Related Rocks, Geological Society of South Africa, Special Publication 3, Salisbury, 1973, pp 265-276.

[52]   I. J. Won and M. Bevis, “Computing the Gravitational and Magnetic Anomalies Due to a Polygon: Algorithms and Fortran Subroutines,” Geophysics, Vol. 52, No. 2, 1987, pp. 232-238.

[53]   C. Subrahmanyam and R. K. Verma, “Gravity Interpretation of the Dharwar Greenstone-Gneiss-Granite Terrain in the Southern Indian Shield and Its Geological Implications,” Tectonophysics, Vol. 84, No. 2-4, 1982, pp. 225245. doi:10.1016/0040-1951(82)90161-5

[54]   R. C. A. Minnitt and C. R. Anhaeusser, “Gravitational and Diapiric Structural History of the Eastern Portion of the Archean Murchison Greenstone Belt, South Africa,” Journal of African Earth Sciences, Vol. 15, No. 3-4, 1992, pp. 429-440. doi:10.1016/0899-5362(92)90026-9

[55]   J. R. Ridley, J. R. Vearncombe and H. A. Jelsma, “Relations between Greenstone Belts and Associated Granitoids,” In: M. J. de Wit and L. D. Ashwal, Eds., Greenstone Belts, Oxford monograph on geology and geophysics, Clarendon Press, Oxford, 1997, pp. 376-397.

[56]   A. F. M. Kisters and C. R. Anhaeusser, “Emplacement Features of Archaean TTG Plutons along the Southern Margin of the Barberton Greenstone Belt, South Africa,” Precambrian Research, Vol. 75, No. 1-2, 1995, pp. 1-15. doi:10.1016/0301-9268(95)00003-N

[57]   H. A. Jelsma, P. A. van der Beek amd M. L. Vinyu, “Tectonic Evolution of the Bindura-Shamva Greenstone Belt (Northern Zimbabwe): Progressive Deformation Around Diapiric Batholiths,” Journal of Structural Geology, Vol. 15, No. 2, 1993, pp. 163-176. doi:10.1016/0191-8141(93)90093-P

[58]   J. H. de Beer and E. Stettler, “Geophysics and the Deep Structure of the Barberton Belt: A review,” 11th SAGA Biennial Technical Meeting and Exhibition, Swaziland, 16-18 September 2009, pp. 2-6.

 
 
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