TY - JOUR
T1 - Just another drip
T2 - Re-analysis of a proposed mesoarchean suture from the Barberton mountain land, South Africa
AU - Van Kranendonk, Martin J.
AU - Kröner, Alfred
AU - Hoffman, J. Elis
AU - Nagel, Thorsten
AU - Anhaeusser, Carl R.
N1 - Funding Information:
MVK would like to extend his sincere thanks to Gary Stevens for an introductory field trip and for helping with access to the field area despite his awareness of my conflicting scientific ideas. Fred Daniels and staff at the Cradle of Life are acknowledged for their generous hospitality. Research was supported by a grant from the University of New South Wales . J.E.H. acknowledges grant from the Deutsche Forschungsgemeinschaft (DFG). M. Prause, S. Dowsett and J. Latham drafted some of the figures. This is contribution 491 of the Australian Research Council Centre of Excellence for Core to Crust Fluid Systems ( http://www.ccfs.mq.edu.au ).
PY - 2014/11
Y1 - 2014/11
N2 - Structural analysis of a proposed Mesoarchean suture located immediately to the southwest of the Barberton Greenstone Belt, South Africa - known as the Inyoni Shear Zone (ISZ) - reveals that the main, steeply dipping, NNE-striking fabric is distributed across only 1. km width, is late (D3), and clearly overprints two earlier sets of fabric elements (D1, D2) that were originally oriented at right angles to the direction of proposed collision. Dating of a S2 foliated meta-trondhjemite is interpreted to indicate that D2 deformation was at, or younger than, 3238.2. ±. 0.9 Ma. The D3 high strain fabric of the ISZ is localised around tightly folded, kilometre-scale supracrustal rafts, but dissipates in all directions away from the rafts, along and across strike. The kinematic asymmetry of S3 shear foliations changes across opposing limbs of tight, upright F3 folds of supracrustal rocks in the ISZ, indicative of simple shear related to buckle folding of more competent supracrustal rocks in a matrix of less competent granitic gneisses. F3 buckle folding was highly non-cylindrical on steep to subvertical axes that plunge to the south in the northern part of the zone and to the north in the southern part of the zone, with nests of vertically plunging sheath folds along amphibolite/metagranite contacts in the central area. High-pressure (HP), garnet-bearing amphibolites are restricted to close association with the vertical D3 sheath folds and do not extend along strike.Combined, the data indicate that the ISZ is not the product of west-directed subduction, as previously suggested. Rather, the strain and kinematic data indicate that the ISZ is just another drip of relatively cool, relatively rigid greenstones into hot, ductile granitic gneisses, formed during partial convective overturn of the upper (greenstone) and middle (granitic) crust. Uplift of the HP rocks was along a late (D4), brittle-ductile mylonite zone associated with emplacement of the c. 3.1. Ga Kees Zyn Doorns syenite.
AB - Structural analysis of a proposed Mesoarchean suture located immediately to the southwest of the Barberton Greenstone Belt, South Africa - known as the Inyoni Shear Zone (ISZ) - reveals that the main, steeply dipping, NNE-striking fabric is distributed across only 1. km width, is late (D3), and clearly overprints two earlier sets of fabric elements (D1, D2) that were originally oriented at right angles to the direction of proposed collision. Dating of a S2 foliated meta-trondhjemite is interpreted to indicate that D2 deformation was at, or younger than, 3238.2. ±. 0.9 Ma. The D3 high strain fabric of the ISZ is localised around tightly folded, kilometre-scale supracrustal rafts, but dissipates in all directions away from the rafts, along and across strike. The kinematic asymmetry of S3 shear foliations changes across opposing limbs of tight, upright F3 folds of supracrustal rocks in the ISZ, indicative of simple shear related to buckle folding of more competent supracrustal rocks in a matrix of less competent granitic gneisses. F3 buckle folding was highly non-cylindrical on steep to subvertical axes that plunge to the south in the northern part of the zone and to the north in the southern part of the zone, with nests of vertically plunging sheath folds along amphibolite/metagranite contacts in the central area. High-pressure (HP), garnet-bearing amphibolites are restricted to close association with the vertical D3 sheath folds and do not extend along strike.Combined, the data indicate that the ISZ is not the product of west-directed subduction, as previously suggested. Rather, the strain and kinematic data indicate that the ISZ is just another drip of relatively cool, relatively rigid greenstones into hot, ductile granitic gneisses, formed during partial convective overturn of the upper (greenstone) and middle (granitic) crust. Uplift of the HP rocks was along a late (D4), brittle-ductile mylonite zone associated with emplacement of the c. 3.1. Ga Kees Zyn Doorns syenite.
KW - Archean
KW - Barberton greenstone belt
KW - Metamorphism
KW - Partial convective overturn
KW - Suture
KW - Tectonics
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U2 - 10.1016/j.precamres.2014.07.022
DO - 10.1016/j.precamres.2014.07.022
M3 - Article
AN - SCOPUS:84906688165
SN - 0301-9268
VL - 254
SP - 19
EP - 35
JO - Precambrian Research
JF - Precambrian Research
ER -
