TY - JOUR
T1 - Paleoproterozoic orogenesis in the southeastern Gawler Craton, South Australia
AU - Reid, A.
AU - Hand, M.
AU - Jagodzinski, E.
AU - Kelsey, D.
AU - Pearson, N.
PY - 2008/1
Y1 - 2008/1
N2 - Integrated structural, metamorphic and geochronological data demonstrate the existence of a contractional orogen preserved in the ca 1850 Ma Donington Suite batholith along the eastern margin of the Gawler Craton, South Australia. The earliest structures are a pervasive gneissic foliation developed in the Donington Suite and interleaved metasedimentary rocks. This has been overprinted by isoclinal and non-cylindrical folding, and zones of pervasive non-coaxial shear with north-directed transport, suggesting that deformation was the result of orogenic contraction. SHRIMP U-Pb zircon data indicate that a syn-contractional granitic dyke was emplaced at 1846±4 Ma. Overprinting the contractional structures are a series of discrete, migmatitic high-strain zones that show a normal geometry with a component of oblique dextral shear. U-Pb zircon data from a weakly foliated microgranite in one such shear zone give an emplacement age of 1843±5 Ma. Rare aluminous metasedimentary rocks in the belt preserve a granulite-grade assemblage of garnet+biotite+plagioclase+K-feldspar+silicate melt that formed at ∼600 MPa and ∼750 C. Peak metamorphic garnets are partially replaced by biotite+sillimanite+cordierite assemblages suggesting post-thermal peak cooling and decompression, and are indicative of a clockwise P-T evolution. Chemical U-Th-Pb electron microprobe ages from monazites in retrograde biotite yield a minimum estimate for the timing of retrogression of ca 1830 Ma, indicating that decompression may be linked to the development of the broadly extensional shear zones and that the clockwise P-T path occurred during a single tectonothermal cycle. We define this ca 1850 Ma phase of crustal evolution in the eastern Gawler Craton as the Cornian Orogeny.
AB - Integrated structural, metamorphic and geochronological data demonstrate the existence of a contractional orogen preserved in the ca 1850 Ma Donington Suite batholith along the eastern margin of the Gawler Craton, South Australia. The earliest structures are a pervasive gneissic foliation developed in the Donington Suite and interleaved metasedimentary rocks. This has been overprinted by isoclinal and non-cylindrical folding, and zones of pervasive non-coaxial shear with north-directed transport, suggesting that deformation was the result of orogenic contraction. SHRIMP U-Pb zircon data indicate that a syn-contractional granitic dyke was emplaced at 1846±4 Ma. Overprinting the contractional structures are a series of discrete, migmatitic high-strain zones that show a normal geometry with a component of oblique dextral shear. U-Pb zircon data from a weakly foliated microgranite in one such shear zone give an emplacement age of 1843±5 Ma. Rare aluminous metasedimentary rocks in the belt preserve a granulite-grade assemblage of garnet+biotite+plagioclase+K-feldspar+silicate melt that formed at ∼600 MPa and ∼750 C. Peak metamorphic garnets are partially replaced by biotite+sillimanite+cordierite assemblages suggesting post-thermal peak cooling and decompression, and are indicative of a clockwise P-T evolution. Chemical U-Th-Pb electron microprobe ages from monazites in retrograde biotite yield a minimum estimate for the timing of retrogression of ca 1830 Ma, indicating that decompression may be linked to the development of the broadly extensional shear zones and that the clockwise P-T path occurred during a single tectonothermal cycle. We define this ca 1850 Ma phase of crustal evolution in the eastern Gawler Craton as the Cornian Orogeny.
UR - http://www.scopus.com/inward/record.url?scp=42649134056&partnerID=8YFLogxK
U2 - 10.1080/08120090801888594
DO - 10.1080/08120090801888594
M3 - Article
AN - SCOPUS:42649134056
SN - 0812-0099
VL - 55
SP - 449
EP - 471
JO - Australian Journal of Earth Sciences
JF - Australian Journal of Earth Sciences
IS - 4
ER -