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Proterozoic tectonic provinces of southern Africa
Precambrian Research, 25 (1984) 229--231
229
Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
PROTEROZOIC
TECTONIC PROVINCES OF SOUTHERN
AFRICA
C.W. STOWE, C.J.H. HARTNADY and P. JOUBERT
Precambrian Research Unit, Department of Geology, University of Cape Town, Private Bag, Rondebosch 7700 (South Africa) EXTENDED ABSTRACT Stowe, C.W., Hartnady, C.J.H. and Joubert, P., 1984. Proterozoic tectonic provinces of southern Africa. Precambrian Res., 25: 229--231. Recent investigations in southwestern Africa, i.e., the NW Cape Province and Namibia, require a consistent hierarchy of tectonic provinces, subprovinces (belts) and terranes in order to provide an adaptable framework (Table I and Fig. 1) for further progress in crustal evolution studies. The Proterozoic continental crust of southwestern Africa originated during three major orogenic cycles, known elsewhere in Africa as the Eburnean, Kibaran, and Pan-African episodes. The Early Proterozoic Kgalagadi privince is the equivalent southern African product of the Eburnean cycle, having formed mainly between 2100 and 1700 Ma ago. It is unfortunately partly concealed beneath extensive younger cratonic cover deposits in the central part of the subcontinent, west of the Archaean Kaapvaal, Zimbabwe and Limpopo provinces. We distinguish two major subprovinces. In western Zimbabwe, the Magondi belt consists of carbonate shelf and greywacke-slate "geosynclinal" deposits metamorphosed folded and thrust eastwards during the Magondi orogeny. On geophysical evidence, this belt appears to extend with an arcuate shape beneath younger cover in northeastern Botswana to include the enigmatic Mahalapye terrane at the western end of the Limpopo belt. The Kheis belt is a generally low-grade metamorphic, recumbently folded assemblage of siliciclastic wedges, extending from the northern Cape province into southern Botswana. It is intruded by granitoid batholiths of probable 1800 Ma age, and may incorporate the recently recognized Okwa terrane of the same approximate age in central Botswana. The Middle Proterozoic Namaqua province, extending for 2000 km across the southern flank of the Kaapvaal craton, consists of high-grade gneisses, 1100 Ma old charnockite/ granite plutons and older supracrustals that host large Cu--Zn--Pb massive sulphide ores. :Intense polyphase deformation culminated in the Gordonia subprovinee, a broad transcurrent shear orogeny adjacent to the Kaapvaal craton boundary, with a dextral shear displacement of at least 200 km. The wedge-shaped Richtersveld subprovince is a 2000 Ma old calc-alkaline assemblage separating the Gordonia subprovince from the Bushmanland subprovince. A subduction-related origin has been suggested for an obducted oceanic assemblage in the eastern Natal subprovince and for the Beattie magnetic and southern Cape conductivity anomalies south of the Bushmanland and Natal belts. The Late Proterozoic Damara province is redefined to include the Saldania belt (SW Cape) and the Gariep belt (NW Cape and SW Namibia). In addition the former Damara orogen of Namibia is now considered to be comprised of two rather different subprovinces, namely the Khomas belt and Swakop belt. Recent tectonic and geochronological studies in all of these belts suggest that their "Pan-African" orogenic evolution took place in two or more distinct stages or phases, the climax of the most recent phases
0301-9268/84/$03.00
© 1984 Elsevier Science Publishers B.V.
230 TECTONIC
MAJOR
DIVISIONS
OF
SOUTHERN
AFRICA
\
ZIMBABWE PROVINCE --20
°
• ". "~,~b'.' ~, ~'e. ~, .'OKWA • " • ." .,.:.C'~P •i ..... : ~...=~ T E R R A N E ° " " ." "
\
• " -..;.L. ,,-,-" ""
rUB~.~OVINCE
.
oA~,ep
EXPLANATION
~
~
1"oas~vEo WRffNCH
ZONE
''L'A°' ARCHAEAN
15 °
25 °
MERCATOR
30 °
pROJECTION
L having occurred at - 530 M a ago, the Precambrian--Phanerozoic boundary. Extensive Fig. 1. Major tectonic divisions of southern Africa: ( 1 ) N E limit of slaty cleavage/green,schist facies in Boland terrane; (2) E limit of penetrative dmaring; (3a) thrust faults at
base of Stinkfontein Fro.; (3b) faulting (strike/slip?) E of Aureus Mrs.; (4a) Naukluft Nappe Complex; (4b) Areb mylonite zone and southern overthrust belt limit, I-lakos-Auas terrane; (5) Okahandja lineament; (6a) Sesfontein thrust; (6b) Fransfontein/Xhorixas thrusts; (6c) Otavi valley fault zone; (Ta) S limit of high-grade Miami metamorphism; (7b) Urungwe klippe; (8) Ntingwe thrust zone; (9a) Doornberg strike-slip fault zone; (9b) Brakbos fault zone; (9c) Oremge Riwr ryncline; (gd) Lord Hill-Excelsior mylonite belt; (10a) Tantalite valley mylonite belt; (10b) Pofadder shear zone; (11) Intensely foliated (lag?) zone; (12a) Xade Complex; (12b) Tshane Complex; (12c) Kalai~ari line; (12d) Strydenberg fault zone; (13a) Dett inlier; (13b) Nyamandhlovu borehole; (14) Unconformity and thrust zones; (15a) Sunnyside shear zone; (15b) Palala shear zone; (16) Zoetfontein fault zone; (17) Limit of folded Matsap cover.
231 craton-vergent overthrust sheets, some incorporating deformed and disrupted complexes of oceanic metabasalt and serpentinised ultramafics, in addition to enigmatic sedimentary melange ( " m i x t i t e " ) deposits and voluminous metagreywacke terranes representing possible accretionary wedge/fore-arc basin assemblages, indicate the presence of a Late Proterozoic geosuture within the Khomas, Gariep and Saldania belts.
TABLE I Tectonic divisions Orogenic cycle
Province
Subprovince (belt)
Gondwanide Damara
Cape Saldanian
West Coast Gariep Khomas Pan-African
Swakop
Namaqua
Ghanzi-Chobe Zambezi Natal Bushmanland Gordonia
Kibaran $?t $?t
Kgalagadi Eburnian
Archaean
Zimbabwe Limpopo Kaapvaal
Richtersveld Rehoboth Kheis Magondi
Terrane
Boland Swartland Tygerberg -Port Nolloth Marmora Hakos-Auas Kuiseb Omaruru Ugab
Main deformation age (Ma) 270-- 225 530 610 610 700 550 500 530 570 530 530 82O 700-- 530 1218--1067 1213--1000
Aus
Kakamas Upington
1268--1050 1340--1000 2000--1100
Langeberg Okwa Urungwe Sinoia Deweras Mahalapye
1800--1740 1971--1810 2200--2050 2200--1760 2300--1900 3500--2600 3800--2600 3500--2900
229
Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
PROTEROZOIC
TECTONIC PROVINCES OF SOUTHERN
AFRICA
C.W. STOWE, C.J.H. HARTNADY and P. JOUBERT
Precambrian Research Unit, Department of Geology, University of Cape Town, Private Bag, Rondebosch 7700 (South Africa) EXTENDED ABSTRACT Stowe, C.W., Hartnady, C.J.H. and Joubert, P., 1984. Proterozoic tectonic provinces of southern Africa. Precambrian Res., 25: 229--231. Recent investigations in southwestern Africa, i.e., the NW Cape Province and Namibia, require a consistent hierarchy of tectonic provinces, subprovinces (belts) and terranes in order to provide an adaptable framework (Table I and Fig. 1) for further progress in crustal evolution studies. The Proterozoic continental crust of southwestern Africa originated during three major orogenic cycles, known elsewhere in Africa as the Eburnean, Kibaran, and Pan-African episodes. The Early Proterozoic Kgalagadi privince is the equivalent southern African product of the Eburnean cycle, having formed mainly between 2100 and 1700 Ma ago. It is unfortunately partly concealed beneath extensive younger cratonic cover deposits in the central part of the subcontinent, west of the Archaean Kaapvaal, Zimbabwe and Limpopo provinces. We distinguish two major subprovinces. In western Zimbabwe, the Magondi belt consists of carbonate shelf and greywacke-slate "geosynclinal" deposits metamorphosed folded and thrust eastwards during the Magondi orogeny. On geophysical evidence, this belt appears to extend with an arcuate shape beneath younger cover in northeastern Botswana to include the enigmatic Mahalapye terrane at the western end of the Limpopo belt. The Kheis belt is a generally low-grade metamorphic, recumbently folded assemblage of siliciclastic wedges, extending from the northern Cape province into southern Botswana. It is intruded by granitoid batholiths of probable 1800 Ma age, and may incorporate the recently recognized Okwa terrane of the same approximate age in central Botswana. The Middle Proterozoic Namaqua province, extending for 2000 km across the southern flank of the Kaapvaal craton, consists of high-grade gneisses, 1100 Ma old charnockite/ granite plutons and older supracrustals that host large Cu--Zn--Pb massive sulphide ores. :Intense polyphase deformation culminated in the Gordonia subprovinee, a broad transcurrent shear orogeny adjacent to the Kaapvaal craton boundary, with a dextral shear displacement of at least 200 km. The wedge-shaped Richtersveld subprovince is a 2000 Ma old calc-alkaline assemblage separating the Gordonia subprovince from the Bushmanland subprovince. A subduction-related origin has been suggested for an obducted oceanic assemblage in the eastern Natal subprovince and for the Beattie magnetic and southern Cape conductivity anomalies south of the Bushmanland and Natal belts. The Late Proterozoic Damara province is redefined to include the Saldania belt (SW Cape) and the Gariep belt (NW Cape and SW Namibia). In addition the former Damara orogen of Namibia is now considered to be comprised of two rather different subprovinces, namely the Khomas belt and Swakop belt. Recent tectonic and geochronological studies in all of these belts suggest that their "Pan-African" orogenic evolution took place in two or more distinct stages or phases, the climax of the most recent phases
0301-9268/84/$03.00
© 1984 Elsevier Science Publishers B.V.
230 TECTONIC
MAJOR
DIVISIONS
OF
SOUTHERN
AFRICA
\
ZIMBABWE PROVINCE --20
°
• ". "~,~b'.' ~, ~'e. ~, .'OKWA • " • ." .,.:.C'~P •i ..... : ~...=~ T E R R A N E ° " " ." "
\
• " -..;.L. ,,-,-" ""
rUB~.~OVINCE
.
oA~,ep
EXPLANATION
~
~
1"oas~vEo WRffNCH
ZONE
''L'A°' ARCHAEAN
15 °
25 °
MERCATOR
30 °
pROJECTION
L having occurred at - 530 M a ago, the Precambrian--Phanerozoic boundary. Extensive Fig. 1. Major tectonic divisions of southern Africa: ( 1 ) N E limit of slaty cleavage/green,schist facies in Boland terrane; (2) E limit of penetrative dmaring; (3a) thrust faults at
base of Stinkfontein Fro.; (3b) faulting (strike/slip?) E of Aureus Mrs.; (4a) Naukluft Nappe Complex; (4b) Areb mylonite zone and southern overthrust belt limit, I-lakos-Auas terrane; (5) Okahandja lineament; (6a) Sesfontein thrust; (6b) Fransfontein/Xhorixas thrusts; (6c) Otavi valley fault zone; (Ta) S limit of high-grade Miami metamorphism; (7b) Urungwe klippe; (8) Ntingwe thrust zone; (9a) Doornberg strike-slip fault zone; (9b) Brakbos fault zone; (9c) Oremge Riwr ryncline; (gd) Lord Hill-Excelsior mylonite belt; (10a) Tantalite valley mylonite belt; (10b) Pofadder shear zone; (11) Intensely foliated (lag?) zone; (12a) Xade Complex; (12b) Tshane Complex; (12c) Kalai~ari line; (12d) Strydenberg fault zone; (13a) Dett inlier; (13b) Nyamandhlovu borehole; (14) Unconformity and thrust zones; (15a) Sunnyside shear zone; (15b) Palala shear zone; (16) Zoetfontein fault zone; (17) Limit of folded Matsap cover.
231 craton-vergent overthrust sheets, some incorporating deformed and disrupted complexes of oceanic metabasalt and serpentinised ultramafics, in addition to enigmatic sedimentary melange ( " m i x t i t e " ) deposits and voluminous metagreywacke terranes representing possible accretionary wedge/fore-arc basin assemblages, indicate the presence of a Late Proterozoic geosuture within the Khomas, Gariep and Saldania belts.
TABLE I Tectonic divisions Orogenic cycle
Province
Subprovince (belt)
Gondwanide Damara
Cape Saldanian
West Coast Gariep Khomas Pan-African
Swakop
Namaqua
Ghanzi-Chobe Zambezi Natal Bushmanland Gordonia
Kibaran $?t $?t
Kgalagadi Eburnian
Archaean
Zimbabwe Limpopo Kaapvaal
Richtersveld Rehoboth Kheis Magondi
Terrane
Boland Swartland Tygerberg -Port Nolloth Marmora Hakos-Auas Kuiseb Omaruru Ugab
Main deformation age (Ma) 270-- 225 530 610 610 700 550 500 530 570 530 530 82O 700-- 530 1218--1067 1213--1000
Aus
Kakamas Upington
1268--1050 1340--1000 2000--1100
Langeberg Okwa Urungwe Sinoia Deweras Mahalapye
1800--1740 1971--1810 2200--2050 2200--1760 2300--1900 3500--2600 3800--2600 3500--2900