TY - JOUR
T1 - Age, lithology and structural evolution of the c. 3.53 Ga Theespruit Formation in the Tjakastad area, southwestern Barberton Greenstone Belt, South Africa, with implications for Archaean tectonics
AU - Van Kranendonk, M. J.
AU - Kröner, A.
AU - Hegner, E.
AU - Connelly, J.
N1 - Funding Information:
MVK thanks Thinus Cloete for help with fieldwork logistics and for an introductory fieldtrip through the Barberton Mountain Land in 1998. A.K. acknowledges mass spectrometric analytical facilities in the Max-Planck-Institut für Chemie in Mainz. Zircon analyses of sample 160932 were carried out on the Sensitive High Resolution Ion Microprobe Mass Spectrometer (SHRIMP II) operated by a consortium consisting of Curtin University of Technology, the Geological Survey of Western Australia and the University of Western Australia with the support of the Australian Research Council. We thank M.T.D. Wingate for assistance during SHRIMP analysis. A.K. also appreciates financial support from the Institute of Geoscience Research (TIGeR), Curtin University of Technology, Perth. Paul Evins and two anonymous reviewers provided comments that helped clarify parts of the manuscript. This paper is published with the permission of the Executive Director of the Geological Survey of Western Australia and is contribution no. 436 of the Geocycles Cluster of Mainz University, funded by the State of Rhineland-Palatinate, Germany.
PY - 2009/4/15
Y1 - 2009/4/15
N2 - A field and petrographic re-assessment of rocks from the Theespruit Formation near Tjakastad, southwestern Barberton Greenstone Belt, is combined with new zircon U-Pb ages and whole-rock Sm-Nd isotopic results to reveal several important inconsistencies with a previous thrust-accretion model for this area. It was found that faults previously interpreted as 'thrusts' are extensional, 'thrust slices of basement orthogneiss' are little deformed quartz-feldspar porphyries or sheared felsic volcaniclastic sedimentary rocks, and 'sedimentary diamictites' are felsic agglomerates. These observations, combined with consistent facing directions of bedding, the recognition of distinct stratigraphic variations across strike, and U-Pb zircon dates from 13 felsic metavolcanic samples, all suggest that the Theespruit Formation is a moderately strained, coherent stratigraphic succession deposited at c. 3530 Ma and affected by extensional shear deformation at c. 3230 Ma. A 3453 ± 6 Ma population of zircons analysed previously from an amphibolite-facies Theespruit Formation felsic schist is interpreted as being of metamorphic, rather than detrital, origin, and arising from heat associated with felsic plutonic rocks that stitch the Theespruit Formation to the overlying Komati Formation at ca. 3450 Ma, 220 Ma earlier than the proposed thrusting event. Crown
AB - A field and petrographic re-assessment of rocks from the Theespruit Formation near Tjakastad, southwestern Barberton Greenstone Belt, is combined with new zircon U-Pb ages and whole-rock Sm-Nd isotopic results to reveal several important inconsistencies with a previous thrust-accretion model for this area. It was found that faults previously interpreted as 'thrusts' are extensional, 'thrust slices of basement orthogneiss' are little deformed quartz-feldspar porphyries or sheared felsic volcaniclastic sedimentary rocks, and 'sedimentary diamictites' are felsic agglomerates. These observations, combined with consistent facing directions of bedding, the recognition of distinct stratigraphic variations across strike, and U-Pb zircon dates from 13 felsic metavolcanic samples, all suggest that the Theespruit Formation is a moderately strained, coherent stratigraphic succession deposited at c. 3530 Ma and affected by extensional shear deformation at c. 3230 Ma. A 3453 ± 6 Ma population of zircons analysed previously from an amphibolite-facies Theespruit Formation felsic schist is interpreted as being of metamorphic, rather than detrital, origin, and arising from heat associated with felsic plutonic rocks that stitch the Theespruit Formation to the overlying Komati Formation at ca. 3450 Ma, 220 Ma earlier than the proposed thrusting event. Crown
KW - Archean
KW - Barberton greenstone belt
KW - Tectonics
KW - Theespruit Formation
UR - http://www.scopus.com/inward/record.url?scp=62349130694&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=62349130694&partnerID=8YFLogxK
U2 - 10.1016/j.chemgeo.2008.11.006
DO - 10.1016/j.chemgeo.2008.11.006
M3 - Article
AN - SCOPUS:62349130694
VL - 261
SP - 115
EP - 139
JO - Chemical Geology
JF - Chemical Geology
SN - 0009-2541
IS - 1-2
ER -