TY  - JOUR
A1  - Kroner, Alfred
A1  - Wilde, S. A.
A1  - O'Brien, Patrick J.
A1  - Li, J. H.
A1  - Passchier, C. W.
A1  - Walte, N. P.
A1  - Liu, Dun Yi
T1  - Field relationships, geochemistry, zircon ages and evolution of a late Archaean to Palaeoproterozoic lower crustal section in the Hengshan Terrain of northern China
N2  - The Hengshan complex forms part of the central zone of the North China Craton and consists predominantly of ductilely-deformed late Archaean to Palaeoproterozoic high-grade, partly migmatitic, granitoid orthogneisses, intruded by mafic dykes of gabbroic composition. Many highly strained rocks were previously misinterpreted as supracrustal sequences and represent mylonitized granitoids and sheared dykes. Our single zircon dating documents magmatic granitoid emplacement ages between 2.52 Ga and 2.48 Ga, with rare occurrences of 2.7 Ga gneisses, possibly reflecting an older basement. A few granitic gneisses have emplacement ages between 2.35 and 2.1 Ga and show the same structural features as the older rocks, indicating that the main deformation occurred after similar to 2.1 Ga. Intrusion of gabbroic dykes occurred at similar to 1920 Ma, and all Hengshan rocks underwent granulite-facies metamorphism at 1.88-1.85 Ga, followed by retrogression, shearing and uplift. We interpret the Hengshan and adjacent Fuping granitoid gneisses as the lower, plutonic, part of a late Archaean to early Palaeoproterozoic Japan-type magmatic arc, with the upper, volcanic part represented by the nearby Wutai complex. Components of this arc may have evolved at a continental margin as indicated by the 2.7 Ga zircons. Major deformation and HP metamorphism occurred in the late Palaeoproterozoic during the Luliang orogeny when the Eastern and Western blocks of the North China Craton collided to form the Trans-North China orogen. Shear zones in the Hengshan are interpreted as major lower crustal discontinuities post-dating the peak of HP metamorphism, and we suggest that they formed during orogenic collapse and uplift of the Hengshan complex in the late Palaeoproterozoic (< 1.85 Ga)
Y1  - 2005
SN  - 1000-9515
ER  - 
TY  - JOUR
A1  - Möller, Andreas
A1  - O'Brien, Patrick J.
A1  - Kennedy, Allen
A1  - Kröner, Alfred
T1  - Linking growth episodes of zircon and metamorphic textures to zircon chemistry : an example from the ultra-high temperature granulites of Rogaland (SW Norway)
Y1  - 2003
ER  - 
TY  - JOUR
A1  - Möller, Andreas
A1  - O'Brien, Patrick J.
A1  - Kennedy, Allen
A1  - Kröner, Alfred
T1  - Polyphase zircon in ultrahigh-temperature granulites (Rogaland, SW Norway) : constraints for Pb diffusion in zircon
N2  - SHRIMP U-Pb ages have been obtained for zircon in granitic gneisses from the aureole of the Rogaland anorthosite-norite intrusive complex, both from the ultrahigh temperature (UHT; >900 °C pigeonite-in) zone and from outside the hypersthene-in isograd. Magmatic and metamorphic segments of composite zircon were characterised on the basis of electron backscattered electron and cathodoluminescence images plus trace element analysis. A sample from outside the UHT zone has magmatic cores with an age of 1034 ± 7 Ma (2{sigma}, n = 8) and 1052 ± 5 Ma (1{sigma}, n = 1) overgrown by M1 metamorphic rims giving ages between 1020 ± 7 and 1007 ± 5 Ma.In contrast, samples from the UHT zone exhibit four major age groups:(1) magmatic cores yielding ages over 1500 Ma(2) magmatic cores giving ages of 1034 ± 13 Ma (2{sigma}, n = 4) and 1056 ± 10 Ma (1{sigma}, n = 1)(3) metamorphic overgrowths ranging in age between 1017 ± 6 Ma and 992 ± 7 Ma (1{sigma}) corresponding to the regional M1 Sveconorwegian granulite facies metamorphism, and(4) overgrowths corresponding to M2 UHT contact metamorphism giving values of 922 ± 14 Ma (2{sigma}, n = 6). Recrystallized areas in zircon from both areas define a further age group at 974 ± 13 Ma (2{sigma}, n = 4).This study presents the first evidence from Rogaland for new growth of zircon resulting from UHT contact metamorphism. More importantly, it shows the survival of magmatic and regional metamorphic zircon relics in rocks that experienced a thermal overprint of c. 950 °C for at least 1 Myr. Magmatic and different metamorphic zones in the same zircon are sharply bounded and preserve original crystallization age information, a result inconsistent with some experimental data on Pb diffusion in zircon which predict measurable Pb diffusion under such conditions. The implication is that resetting of zircon ages by diffusion during M2 was negligible in these dry granulite facies rocks. Imaging and Th/U-Y systematics indicate that the main processes affecting zircon were dissolution-reprecipitation in a closed system and solid-state recrystallization during and soon after M1.
Y1  - 2002
ER  - 
TY  - JOUR
A1  - Kröner, Alfred
A1  - Wilde, Simon A.
A1  - Zhao, Guochun
A1  - O'Brien, Patrick J.
A1  - Sun, Min
A1  - Liu, Dun Yi
A1  - Wan, Yusheng
A1  - Liu, S. W.
A1  - Guo, Jianbin H.
T1  - Zircon geochronology and metamorphic evolution of mafic dykes in the Hengshan Complex of northern China: Evidence for late Palaeoproterozoic extension and subsequent high-pressure metamorphism in the North China Craton
N2  - Magmatic and metamorphic zircons have been dated from ductilely deformed gabbroic dykes defining a dyke swarm and signifying crustal extension in the northern part of the Hengshan Complex of the North China Craton, These dykes now occur as boudins and deformed sheets within migmatitic tonalitic, trondhjemitic, granodioritic and granitic gneisses and are conspicuous due to relics of high-pressure granulite or even former eclogite facies garnet + pyroxene-bearing assemblages. SHRIMP ages for magmatic zircons from two dykes reflect the time of dyke emplacement at similar to 1915 Ma, whereas metamorphic zircons dated by both SHRIMP and evaporation techniques are consistently in the range 1848-1888 Ma. The Youngest granitoid gneiss yet dated in the Hengshan has an emplacement age of 18 2 17 Ma. These results complement recent geochronological studies from the neighbouring Wutai and Fuping Complexes, to the SE of the Hengshan, showing that a crustal extension event Occurred in the late Palaeoproterozoic. This preceded a major high-pressure collision- type metamorphic event in the central part of the North China Craton that occurred in the Palaeoproterozoic and not in the late Archaean as previously thought. Our data support recent suggestions that the North China Craton experienced a major, craton-wide orogenic event in the late Palaeoproterozoic after which it became cratonized and acted as a stable block.
Y1  - 2006
U6  - https://doi.org/10.1016/j.precamres.2006.01.008
SN  - 0301-9268
ER  - 
TY  - JOUR
A1  - Kröner, Alfred
A1  - O'Brien, Patrick J.
A1  - Nemchin, A. A.
A1  - Pidgeon, R. T.
T1  - Zircon ages for high pressure granulites from South Bohemia, Czech Republic, and their connection to Carboniferous high temperature processes
Y1  - 2000
ER  - 
TY  - JOUR
A1  - Li, J. H.
A1  - Kröner, Alfred
A1  - Qian, X. L.
A1  - O'Brien, Patrick J.
T1  - Tectonic evolution of an early Precambrian high-pressure granulite belt in the North China Craton
Y1  - 2000
ER  - 
TY  - JOUR
A1  - Kroner, Alfred
A1  - Oberhänsli, Roland
A1  - Mezger, Klaus
A1  - Teklay, M.
T1  - Geochemistry, Pb-Pb single zircon ages and Nd-Sr isotope composition of Precambrian rocks from southern and eastern Ethiopia: implications for crustal evolution in east Africa
Y1  - 1998
ER  -