Sixth International Hutton Symposium on Granites and Related Rocks 2–6 July 2007, Stellenbosch, South Africa
FT2 Post-conference
Field trip to the Mesoarchaean Barberton Granite-Greenstone Terrain Jean-François Moyen Alexander F.M. Kisters Gary Stevens With the participation of Christiano Lana and Richard W. Belcher
June 2007
University of Stellenbosch, South Africa
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Cover photo: Top, view from the “Horseshoe hill” in Inyoni Shear Zone, looking North towards the Stolzburg pluton and the BGB. Bottom left, ca. 3.2 Ga shear zones in the 3.45 Ga Stolzburg pluton, near the granite–greenstone contact. Middle, Lit-par-lit intrusion of the Stolzburg pluton in a greenstone remnant, Theespruit River. Right, a dyke of ca. 3.1 Ga Boesmanskop syenite cutting banded gneisses in the Welverdiend Shear Zone (stop 3.6)
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Abbreviated program • Saturday, 7 July 2007: Fly from Cape Town to Johannesburg; drive to Badplaas. • Sunday, 8 July 2007: The lower part of Barberton Greenstone belt, and the granite– greenstone contacts in the ca. 3.55–3.45 Ga domain. • Monday, 9 July 2007: Structures and metamorphism in the ca. 3.45 Ga Stolzburg terrane; the ca. 3.1 Ga Boesmanskop syenogranitic complex. • Tuesday, 10 July 2007: The ca. 3.2 Ga plutons on the North-Eastern side of the Barberton Greenstone Belt. • Wednesday, 11 July 2007: The ca. 3.1 Ga granitic plutons in the South of the Barberton Granite–Greenstone Terrain. • Thursday, 12 July 2007: Drive back to Johannesburg.
Accommodation Forever Resorts – Aventura Badplaas Tel: +27 (0) 17 844 8000 Fax: +27 (0) 17 844 1391 E-mail:
[email protected]
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25°45'0"S
26°0'0"S
Machadodorp Carolina 26°15'0"S
Carolina
5.1 5.2
30°30'0"E
5.4
Heerenveen
Transvaal Supergroup
4.1
Rhg.
5.3
Warburton Karoo Supergroup 30°30'0"E
5.5
3.5
3.4
4.2
3.7
3.6
BMK
Stz.
Nelshoogte 4.3
Ko
4.4
3.3
0 2.5 5 Nelspruit
10
31°0'0"E
15
Barberton
20 Kilometers
4.6
4.7
Mbabane
Pigg's Peak
Josefsdal
4.5
eKulindeni
2.1
31°0'0"E
Oshoek
Sty.
2.2
Kom ati
Barberton Greenstone Belt
Kaap Valley
Sty: Steynsdorp Ths: Theespruit Stz: Stolzburg
3.2
2.3
Sw
A . nd S. ila R. az
Dalmein
Tjakastad
Ths. 2.4
Lochiel
eLukwatini
3.1
ma ti
30°45'0"E
BMK: Boesmanskop Bpl: Badplaas Rhg: Rooihoogte
Badplaas
Bpl. t rui sp ee Th
Schapenburg Mpuluzi
30°45'0"E
25°45'0"S
26°0'0"S
26°15'0"S
University University of Missouri Geoscience Australia Dionyz Stur State Institute of Geology Geoscience Research Institute University of Geneva University of Washington Seattle University of Missouri INGEIS Universität Stuttgart University of Puerto Rico Geol. Surv. NSW/ Monash University Geological Survey of Japan Geological Survey of Canada Ben Gurion University of the Negev Ben Gurion University of the Negev Université Toulouse III James Cook University University of Ottawa The Australian National University Université Clermont–Ferrand II Council for Geoscience, South Africa University of Stellenbosch University of Stellenbosch University of Stellenbosch University of Stellenbosch University of Stellenbosch
Surname
Nabelek Champion Kohut Clausen Annen Evans Whittington Lopez de Luchi Massonne Cavosie Quinn Nakajima Bédard Katzir Be’eri-Shlevin Nédélec Collins Benn Rapp Martin Belcher Stevens Moyen Kisters Sanchez–Garrido Taylor
Name
Peter David Milan Ben Catherine Bernard Alan Monica Hans-Joachim Aaron Cameron Takashi Jean Yaron Yaron Anne William J. Keith Robert P. Hervé Richard Gary Jean-François Alexander Cynthia Jeanne
[email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected]
Email
Excursion route v
Field trip participants
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Contents Abbreviated program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Excursion route . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . List of participants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
I
Introduction to the geology of the Barberton terrain 1. 2. 3.
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Stratigraphy of the Barberton Greenstone Belt . . . . . . . . . Main tectono-magmatic events . . . . . . . . . . . . . . . . . . Accretion stage of the BGGT at > 3.42 Ga (pre-D1 and D1 ) . . 3.1. An oceanic plateau. . . . . . . . . . . . . . . . . . . . . . 3.2. . . . modified by a subduction (?) event . . . . . . . . . . 3.3. Renewed (ultra)mafic activity . . . . . . . . . . . . . . . A subduction-collision-exhumation orogen at 3.29-3.21 Ga (D2 ) 4.1. Evidence for accretionary orogen in the BGGT . . . . . 4.2. Metamorphism associated with the ca. 3.2 Ga orogen . 4.3. Ca. 3.2 Ga magmatism . . . . . . . . . . . . . . . . . . 4.4. Evolution model . . . . . . . . . . . . . . . . . . . . . . The sheeted batholiths of the GMS suite (3.11 Ga) . . . . . . .
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II Field itinerary
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Saturday, 7 July
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Sunday, 8 July Komati river section, Songimvelo nature reserve . . . Contact of the Steynsdorp pluton . . . . . . . . . . . Contact of the Dalmein pluton . . . . . . . . . . . . Deformed intrusive breccia of the Theespruit pluton
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Monday, 9 July Stolzburg pluton contact . . . . . . . . . . . . . Felsic agglomerates in the Tjakastad schist belt Komatiite type locality . . . . . . . . . . . . . . The ca. 3.2 Ga Inyoni shear Zone (ISZ) . . . . Western slopes of Boesmanskop . . . . . . . . . Basal (?) contact of Boesmanskop pluton . . . Hypovolcanic facies of the Boesmanskop syenite
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Tuesday, 10 July Rooihoogte pluton . . . . . . . . The Nelshoogte pluton . . . . . . Nelshoogte pass . . . . . . . . . . Northern side of Nelshoogte pass Border of the Kaap Valley pluton
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Contents
Moodies conglomerates along the R40 . . . . . . . . . . . . . . . . . . . . . . . . . . . Panorama on the Fig Tree Valley . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wednesday, 11 July Pavements of the ca. 3.1 Ga Heerenveen granite . . . Intrusive breccias in the Heerenveen batholith . . . . . Synmagmatic shear zones in the Heerenveen batholith Schapenburg Greenstone remnant . . . . . . . . . . . . Eagle Heights . . . . . . . . . . . . . . . . . . . . . . .
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Thursday, 12 July
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III Articles The 3.2 Ga orogeny: structures and metamorphism 1. Kisters et al., 2003 . . . . . . . . . . . 2. Stevens and Moyen, in press . . . . . . 3. Moyen et al., 2006 . . . . . . . . . . . 4. Diener et al., 2005 . . . . . . . . . . . Petrology and geochemistry of the TTG suite . . . 5. Clemens et al., 2006 . . . . . . . . . . 6. Moyen et al., in press . . . . . . . . . Emplacement of the ca. 3.1 Ga GMS suite . . . . . 7. Belcher and Kisters, 2006 . . . . . . . 8. Westraat et al., 2005 . . . . . . . . . .
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List of Figures 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
Simplified geological map of the Barberton Greenstone belt . . . . . . . . Simplified log in the Barberton Greenstone Belt . . . . . . . . . . . . . . . 3.55-3.35 Ga history of the BGB . . . . . . . . . . . . . . . . . . . . . . . Intrusive relations of the Theespruit pluton with surrounding greenstones Distinct terranes in the BGB . . . . . . . . . . . . . . . . . . . . . . . . . Synthetic logs in the different terranes . . . . . . . . . . . . . . . . . . . . Delineation of tectonic terranes in the BGB . . . . . . . . . . . . . . . . . Emplacement model for the Nelshoogte pluton . . . . . . . . . . . . . . . Geodynamical model for the ca. 3.2 Ga evolution of the BGGT . . . . . . Extend of the ca. 3.1 Ga GMS suite . . . . . . . . . . . . . . . . . . . . . Road map, from Johannesburg to Badplaas . . . . . . . . . . . . . . . . . Geological map of the komati valley in Songimvelo Nature Reserve . . . . Log in the Onvewacht group . . . . . . . . . . . . . . . . . . . . . . . . . . Geological map of the Steynsdorp pluton and surroundings . . . . . . . . Geological and structural map of the core of the Steynsdorp anticline . . . Geological map of the Tjakastad schist belt and its contacts . . . . . . . . Geological map of the Inyoni Shear Zone . . . . . . . . . . . . . . . . . . . Metamorphic textures in Inyoni Shear Zone amphibolites . . . . . . . . . Summary of P–T estimates from the Inyoni Shear Zone . . . . . . . . . . Geological map of the Nelshoogte pluton . . . . . . . . . . . . . . . . . . . Strain pattern and intensity in the Nelshoogte pluton . . . . . . . . . . . Geological and structural map of the Heerenveen batholith . . . . . . . . Geological map of the Schapenburg Greenstone remnant . . . . . . . . . . Geological map of the North-Western edge of the Mpuluzi batholith . . . Conceptualized map of the outcrops aroud locality 5.5 . . . . . . . . . . .
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3 5 7 8 10 10 11 13 15 16 23 26 27 28 30 35 37 39 39 44 45 53 55 58 59
Part I Introduction to the geology of the Barberton Granite–Greenstone terrain
he meso-Archaean Barberton granitegreenstone terrain (BGGT) consists of two main components: the Barberton Greenstone Belt (BGB) proper, and the surrounding granitoids. The granitoids can further be subdivided into an early trondhjemite-tonalitegranodiorite (TTG) suite, that formed before or synchronous with the lower greenstone belt stratigraphy, and a younger, post-greenstone,
granite-monzonite-syenite (GMS) suite. Together, the belt and the TTGs define a regional dome-and-keel geometry, typical of many Archaean provinces.
T
Some recent papers from our group are reproduced in the appendix. They provide all the details and the data supporting the models discussed below, such that only an overview is given here.
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