The application of zircon cathodoluminescence imaging, Th-U-Pb chemistry and U-Pb ages in interpreting discrete magmatic and high-grade metamorphic events in the North China Craton at the Archean/Proterozoic boundary

Two distinct Late Neoarchean to Early Paleoproterozoic magmatic events are recognized at the northern margin of the Eastern Block of the North China Craton based on interpretation of zircon structure, cathodoluminescence signature, Th-U-Pb chemistry and age. The first event is represented by emplacement of the Chaihe trondhjemite and Xianjinchang tonalite with magmatic zircon core ages ranging from 2559-2553 +/- 7 Ma, respectively. These rocks experienced a subsequent high-grade metamorphic event, constrained by partial recrystallization of primary magmatic zircon and growth of new zircon rims, between 2517 and 2490 Ma. A second magmatic episode, generated by partial melting of crustal rocks during this metamorphic event. is represented by the Hongshilazi syenogranite with an age of 2502 +/- 11 Ma. The short time interval between initial magmatism and high-grade regional metamorphism signifies they were related to the same major tectonothermal event. When considered along with evidence of a similar sequence of events at this time similar to 800 km to the south in eastern Hebei and the previously-established similar to 2500 Ma age of granulite-facies metamorphism in mafic rocks across the craton, it is proposed that a large mantle plume developed beneath the North China Craton at the close of the Archean. (C) 2008 Elsevier B.V. All rights reserved.