![Page 1: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/1.jpg)
Field methods in Archaean Field methods in Archaean geology: observations from geology: observations from
southern Africasouthern Africa
Axel HofmannAxel Hofmann
School of Geological Sciences, University of School of Geological Sciences, University of KwaZuluKwaZulu--Natal, Durban, South AfricaNatal, Durban, South Africa
![Page 2: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/2.jpg)
Archaean litho-tectonic units
• granitoid-greenstone terrains• high-grade gneiss terrains• cratonic rift and cover successions
Valley et al. 2006
![Page 3: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/3.jpg)
Geological map for southern Africa with main lithostratigraphic units
Kaapvaal Craton
Zimbabwe Craton
H. Jelsma
![Page 4: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/4.jpg)
Archaean provincesArchaean provinces
•• granitoidgranitoid--greenstone terrainsgreenstone terrains Belingwe
Barberton
![Page 5: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/5.jpg)
•• highhigh--grade gneiss grade gneiss terrainsterrains
Limpopo Belt
AncientGneissComplex
Archaean provincesArchaean provinces
![Page 6: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/6.jpg)
•• cratonic rift and cratonic rift and cover successionscover successions
Witwatersrand/PongolaSupergroups
Archaean provincesArchaean provinces
Manjeri Formation
![Page 7: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/7.jpg)
Cratonic rift and cover successionsCratonic rift and cover successions
• ≤ greenschist grade, relatively undeformed• unconformably overlie basement rocks• rift-related volcano-sedimentary
successions• epicontinental, passive-margin to foreland
basin sedimentary successions
![Page 8: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/8.jpg)
Frimmel, 2005
![Page 9: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/9.jpg)
Pongola SupergroupGold, 2007
![Page 10: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/10.jpg)
Granite
Quartzarenite
Basalt
![Page 11: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/11.jpg)
![Page 12: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/12.jpg)
![Page 13: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/13.jpg)
Schopf, 2006
![Page 14: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/14.jpg)
Nsuze Group, White Umfolozi Inlier
subtidal
intertidal
supratidal
![Page 15: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/15.jpg)
West Rand GroupBasement
![Page 16: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/16.jpg)
NsuzeMozaan
LST
LST
TST
TST
![Page 17: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/17.jpg)
NsuzeMozaan
LST
LST
TST
TST
![Page 18: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/18.jpg)
CentralRand
WestRand
MozaanGroup
NzuseBeukes and Cairncross, 1991
![Page 19: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/19.jpg)
Young et al., 1998
![Page 20: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/20.jpg)
Granitoid-greenstone terrains• greenstone belts
wrapped around or intruded by granitoids
• typically at greenschist to amphibolite facies metamorphic grade
• characterised by a large percentage of submarine mafic volcanic rocks
Ridley et al. 1997
![Page 21: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/21.jpg)
Palaeoarchaean GBs (e.g. Barberton GB)
![Page 22: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/22.jpg)
Barberton GBKromberg Fm (3.35 Ga)
![Page 23: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/23.jpg)
Neoarchaean GBse.g. Belingwe GB
![Page 24: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/24.jpg)
Belingwe GBZeederbergs Fm (2.70 Ga)
![Page 25: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/25.jpg)
Younging indicators
![Page 26: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/26.jpg)
cher
t H3c
alter
ed b
asalt
basa
ltHooggenoeg Formation, 3.47 Ga
Barberton GB
![Page 27: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/27.jpg)
Toggekry Formation, 3.53 Ga
Nondweni GB
![Page 28: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/28.jpg)
Metamorphism• mainly greenschist to
amphibolite facies
• one or more regional metamorphic events
• local contact metamorphism
• seafloor alteration in pre-3.0 Ga belts
Wilkins, 1997
![Page 29: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/29.jpg)
![Page 30: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/30.jpg)
Structure
• Strata are steeply dipping and commonly tightly to isoclinally folded due to polyphase deformation. – granitoid doming/diapirism– folding and thrusting– transcurrent shearing
![Page 31: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/31.jpg)
Jackson et al. 1987
Structure
![Page 32: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/32.jpg)
C. Anhaeusser
![Page 33: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/33.jpg)
S2
S3
![Page 34: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/34.jpg)
![Page 35: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/35.jpg)
Clemens et al. 2006
![Page 36: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/36.jpg)
Campbell and Pitfield, 1994
Midlands GB
![Page 37: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/37.jpg)
Granitoid composition
• multiphase, composite granitoid batholiths, plutons and stocks
• tonalitic to granitic in composition
• pre-, syn- or post-tectonic
van Kranendonk 2004
![Page 38: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/38.jpg)
C. Anhaeusser
Granitoid composition
pre-tectonic syn-tectonic post-tectonic
![Page 39: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/39.jpg)
C. Anhaeusser
pre-/ syn-tectonic pluton
![Page 40: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/40.jpg)
C. Anhaeusser
post-tectonic pluton
![Page 41: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/41.jpg)
Steynsdorp pluton, 3.51 Ga Theespruit Fm, 3.54 Ga
Granitoid-greenstone contact relationships
• intrusive contact• unconformable contact• tectonic contact
![Page 42: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/42.jpg)
C. Lana
![Page 43: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/43.jpg)
Greenstones and basement unconformities
Ridley et al. 1997
Bleeker 200?
Belingwe Greenstone Belt, ZimbabweYellowknife Supergroup, Canada
![Page 44: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/44.jpg)
Belingwe GB
basement gneiss Manjeri Fm
![Page 45: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/45.jpg)
Belingwe GB: Manjeri – Reliance contact
Kusky and Vearncombe 1997
![Page 46: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/46.jpg)
Greenstones and thrusts
• correct identification and interpretation of thrust planes is fundamental for an understanding of the tectonic evolution of greenstone belts
Kusky and Vearncombe 1997
![Page 47: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/47.jpg)
Stowe, 1968
Shurugwi greenstone belt, Zimbabwe
![Page 48: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/48.jpg)
de Wit 2004
![Page 49: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/49.jpg)
Terabayashi et al. 2003Hickman and van Kranendonk 2004
![Page 50: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/50.jpg)
High-grade gneiss terrains
• granitoid gneisses intrusive into or tectonically interleaved with supracrustal rocks
• upper amphibolite- to granulite-facies metamorphic grade
• complex, polyphase deformation and high-grade metamorphism
![Page 51: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/51.jpg)
High-grade gneiss terrains
• A geological history is inferred from establishing a record of depositional, structural and metamorphic events on the basis of various structural, mineralogical and cross-cutting relationships.
• Of importance is the correct identification of supracrustal gneisses and their protoliths. This may be tricky, as intensely deformed and metamorphosed metasomatised volcanic rocks may resemble sedimentary rocks.
![Page 52: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/52.jpg)
Passchier et al. 1992
![Page 53: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/53.jpg)
Nutman et al. 1984, in Nisbet, 1987 Myers, 2001
Protolith identification, Isua greenstone belt
![Page 54: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/54.jpg)
![Page 55: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/55.jpg)
pillow basalt
carbonate alteration in pillow basalt
calc-silicate gneiss
![Page 56: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/56.jpg)
pillow basalt
pillow basalt, silicified
quartz-muscovite schist
![Page 57: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/57.jpg)
carbonated lapillistone
ultramafic lapillistone
marble
![Page 58: Field methods in Archaean geology: observations from southern …archenv.geo.uu.nl › pdf › hofmann Field methods.pdf · 2009-10-14 · Field methods in Archaean geology: ... Axel](https://reader035.vdocuments.net/reader035/viewer/2022070803/5f032c287e708231d407e5ee/html5/thumbnails/58.jpg)
komatiite
silicified komatiite
banded fuchsitic quartzite