TY  - JOUR
A1  - Cooke, R. A.
A1  - O'Brien, Patrick J.
A1  - Carswell, D. A.
T1  - Garnet zoning and the identification of equilibrium mineral compositions in high-pressure-temperature granulites from the Moldanubian Zone, Austria
Y1  - 2000
ER  - 
TY  - JOUR
A1  - O'Brien, Patrick J.
T1  - The fundamental Variscan problem : high-temperature metamorphism at different depths and high-pressure metamorphism at different temperatures
Y1  - 2000
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  - Cooke, R. A.
A1  - O'Brien, Patrick J.
T1  - Resolving the relationship between high P-T rocks and gneisses in collisional terranes : an example from the Gföhl gneiss-granulite association in the Moldanubian Zone, Austria
Y1  - 2001
ER  - 
TY  - JOUR
A1  - O'Brien, Patrick J.
A1  - Zotov, Nikolay
A1  - Law, Robin
A1  - Khan, M. Azam
A1  - Jan, M. Q.
T1  - Coesite in Himalayan eclogite and implications for models of India-Asia collision
Y1  - 2001
SN  - 0091-7613
ER  - 
TY  - JOUR
A1  - O'Brien, Patrick J.
T1  - Subduction followed by Collision : Alpine and Himalayan examples
Y1  - 2001
ER  - 
TY  - JOUR
A1  - O'Brien, Patrick J.
A1  - Kryza, R.
T1  - The Variscan basement of the Polish Sudetes
Y1  - 2001
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  - Guo, Jianbin H.
A1  - O'Brien, Patrick J.
A1  - Zhai, M. G.
T1  - High pressure granulites in the Sanggan area, North China craton : metamorphic evolution, P-T paths and geotectonic significance
Y1  - 2002
ER  -