The palaeomagnetism of the main zone of the eastern Bushveld Complex

Hattingh, P. J.

doi:10.1016/0040-1951(86)90205-2

Cited by 33 publications

(15 citation statements)

References 16 publications

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“… b References: (1) Cornell et al , 1996; (2) Evans et al , 1997; (3) Beukes et al , 2002; (4) Reischmann , 1995; (5) Morgan and Briden , 1981; (6) Walraven et al , 1990; (7) Hattingh , 1986a; (8) Hattingh , 1986b; (9) Hattingh , 1989; (10) Hattingh and Pauls , 1994; (11) Kamo et al , 1996; (12) Hargraves , 1970; (13) Hart et al , 1995; (14) Compston and McElhinny , 1975; (15) McElhinny and Opdyke , 1964; (16) Bates and Jones , 1996; (17) Layer et al , 1988; (18) Morgan , 1985; (19) Jones et al , 1975; (20) McElhinny and Cowley , 1978; (21) Cornell et al , 1998; (22) Onstott et al , 1986b. …”

Section: Discussionmentioning

confidence: 99%

Paleomagnetism of a lateritic paleoweathering horizon and overlying Paleoproterozoic red beds from South Africa: Implications for the Kaapvaal apparent polar wander path and a confirmation of atmospheric oxygen enrichment

Evans

Beukes²,

Kirschvink

2002

J. Geophys. Res.

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[1] The Olifantshoek Group in southern Africa contains Paleoproterozoic red beds that are exceptionally well preserved, lying unconformably atop a regionally extensive lateritic paleoweathering profile. We studied the basal unit of this succession, known as the Gamagara or Mapedi Formation, and the lateritized substrate (so-called ''Drakenstein'' or ''Wolhaarkop'' paleosol) on which it developed. Two ancient magnetic components are observed. One (INT), usually with a distributed unblocking spectrum between 300°and 600°C but occasionally persisting to >675°C, is directed shallowly southward or northward. A mesoscale fold test at South Sishen Mine indicates that this component was acquired during deformation; similarity of the direction to previous results suggests that it was acquired at $1240 Ma, during early Namaqua orogenesis. Combining our INT results with existing data from the Namaqua eastern zone (NEZ), we calculate the NEZ pole at (44.9°N, 021.5°E, K = 23.2, A 95 = 12.8°, Q = 5). The most stable component from our data set (HIG), always persisting as a nonzero endpoint to demagnetization at >665°-680°C, is observed in 32 samples from South Sishen and Beeshoek Mines. Directed moderately east-downward (Sishen) or west-upward (Beeshoek), this component predates the mesoscale fold at Sishen. More importantly, a conglomerate test at Beeshoek indicates that HIG was acquired prior to Paleoproterozoic deposition of the Gamagara/Mapedi Formation. The concordance between directions from the paleoweathering zone and immediately overlying red beds indicates that HIG is a primary magnetic remanence for the basal Gamagara/Mapedi (BGM) Formation. The dual-polarity BGM paleomagnetic pole (02.2°N, 081.9°E, dp = 7.2°, dm = 11.5°, Q = 6) lies neatly between previous Kaapvaal poles with ages of $2220 (Ongeluk lavas) and 2060 Ma (Bushveld complex). Our data thus support recent correlations of the Gamagara/Mapedi Formation with pre-Bushveld sediments of the Pretoria Group. A preBushveld age for BGM is also consistent with its substantial distance from a new, albeit less reliable, paleomagnetic pole from the $1930-Ma Hartley lavas, higher within the Olifantshoek succession (12.5°N, 332.8°E, K = 18.6, A 95 = 16.0°, Q = 3). Our conglomerate test at Beeshoek confirms previous allegations that the intense hematitization observed in the Drakenstein-Wolhaarkop paleosol occurred during Paleoproterozoic weathering under a highly oxygenated atmosphere.

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Section: Discussionmentioning

confidence: 99%

Paleomagnetism of a lateritic paleoweathering horizon and overlying Paleoproterozoic red beds from South Africa: Implications for the Kaapvaal apparent polar wander path and a confirmation of atmospheric oxygen enrichment

Evans

Beukes²,

Kirschvink

2002

J. Geophys. Res.

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“…However, the interpretation of magnetic data in the BIC is complicated by the presence of strong remanent magnetization both in the mafic cumulate rocks and in younger dykes. Fortunately, the palaeomagnetic and petrophysical properties of the BIC have been well studied (Hattingh 1986a,b,c, 1989; Hattingh & Pauls 1994).…”

Section: Introductionmentioning

confidence: 99%

Palaeomagnetism and⁴⁰Ar/³⁹Ar geochronology of mafic dykes from the eastern Bushveld Complex (South Africa)

Letts

Torsvik

Webb

et al. 2005

Geophysical Journal International

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S U M M A R YWe report palaeomagnetic and 40 Ar/ 39 Ar age data for dykes that intrude the ∼2 Ga eastern Bushveld Igneous Complex (BIC). The dykes were previously assumed to be of Karroo age (Jurassic ∼ 180 Ma) based on their NE-SW orientation. Palaeomagnetic data (pole position 8.7 • N, 22 • E; dp/dm = 18/20.6 • ), however, clearly demonstrate that these dykes are Precambrian in age, either ∼1.9 Ga and close to the Early Proterozoic Bushveld age, or 1649 ± 10 Ma based on 40 Ar/ 39 Ar plagioclase laser fusion ages from one of the dykes. Both normal and reverse polarity dykes are identified, and a positive reversal test together with a semi-conclusive contact test attests to a primary magnetization. If the 40 Ar/ 39 Ar age represents a primary cooling age then palaeomagnetic poles from South Africa (Kalahari) at ∼1.9 to ∼2 Ga and ∼1650 Ma are virtually identical, and suggest an apparent polar wander loop; alternatively, the Kalahari Craton drifted from high southerly (>50 • ) to high northerly latitudes (or vice versa) during this interval. Conversely, if we assign a ∼1.9 Ga age for dyke emplacement as suggested from a comparison with Kalahari palaeomagnetic poles (e.g. Waterberg-Soutpansberg pole), the ∼1650 Ma 40 Ar/ 39 Ar age must relate to a thermal disturbance that did not erase the primary magnetic signature.

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“…Apparent polar-wander path for the Kalahari craton for the period 2050-1800 Ma. MD: Mashonaland sills (this study); BC crt: Critical Zone, Bushveld Complex (Hattingh, 1986~); BC Main: Main Zone, Eastern Bushveld Complex ( Hattingh 1986b); BC west: Main Zone, Western Bushveld Complex (Hattingh 1986a); LA: Limpopo metamorphics A (Morgan 1985); GPA: Group A (this study); SDN: Sebanga dykes ( N bearing) (this study ;Mushayandebvu 1991;Jones et al 1975); SDsP Sebanga dykes (shallow P bearing) (as for (SDN); B, C, E, F, K and L: virtual geomagnetic poles from sites within the Limpopo Belt in satellite dykes of the Great Dyke (Jones et al 1975). the N-bearing Sebanga dykes and the remanences of the bodies of Group A predate the Mashonaland sills then the pole swung northwards to mid-latitudes and westwards before returning to low latitudes. If, however, the remanences in these bodies post-date that in the sills it is possible that the APWP does swing northwards after sill emplacement, as suggested by McElhinny et ul.…”

Section: Discussionmentioning

confidence: 99%

A palaeomagnetic investigation of the Mashonaland dolerites, north-east Zimbabwe

Bates

Jones

1996

Geophysical Journal International

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S U M M A R YEarlier palaeomagnetic work on the Mashonaland dolerite sills and dykes (1830-t 230 Ma) showed that they record a geomagnetic field reversal. 28 new sites have been sampled in sills (26) and dykes (2) in north-east Zimbabwe. Detailed alternating-field demagnetization (AFD) is more effective in removing secondary components of remanence than thermal demagnetization (TD) and enables an assumed primary remanence to be isolated at 16 sill sites. Combined with earlier results there are 11 sill sites with a positive inclination (P) (D=287", I=53", k=40) and 18 with a negative inclination (N) (D = 114", I = -47", k = 35). The data lead to a positive class-B reversal test. Field tests suggest that the N remanence is the younger and that the period of Mashonaland igneous activity spanned a reversal of the Earth's magnetic field from P to N. The areal distribution of polarity is not random: sills with only P remanence are found in the more elevated central region of the Mashonaland Igneous Province, whilst predominantly N-bearing sills occupy the lower surrounding terrain.

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The palaeomagnetism of the main zone of the eastern Bushveld Complex

Cited by 33 publications

References 16 publications

Paleomagnetism of a lateritic paleoweathering horizon and overlying Paleoproterozoic red beds from South Africa: Implications for the Kaapvaal apparent polar wander path and a confirmation of atmospheric oxygen enrichment

Paleomagnetism of a lateritic paleoweathering horizon and overlying Paleoproterozoic red beds from South Africa: Implications for the Kaapvaal apparent polar wander path and a confirmation of atmospheric oxygen enrichment

Palaeomagnetism and⁴⁰Ar/³⁹Ar geochronology of mafic dykes from the eastern Bushveld Complex (South Africa)

A palaeomagnetic investigation of the Mashonaland dolerites, north-east Zimbabwe

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The palaeomagnetism of the main zone of the eastern Bushveld Complex

Cited by 33 publications

References 16 publications

Paleomagnetism of a lateritic paleoweathering horizon and overlying Paleoproterozoic red beds from South Africa: Implications for the Kaapvaal apparent polar wander path and a confirmation of atmospheric oxygen enrichment

Paleomagnetism of a lateritic paleoweathering horizon and overlying Paleoproterozoic red beds from South Africa: Implications for the Kaapvaal apparent polar wander path and a confirmation of atmospheric oxygen enrichment

Palaeomagnetism and40Ar/39Ar geochronology of mafic dykes from the eastern Bushveld Complex (South Africa)

A palaeomagnetic investigation of the Mashonaland dolerites, north-east Zimbabwe

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Palaeomagnetism and⁴⁰Ar/³⁹Ar geochronology of mafic dykes from the eastern Bushveld Complex (South Africa)