SHRIMP U-Pb zircon geochronology of the Fuping Complex: implications for formation and assembly of the North China Craton

The Fuping Complex, located within the central zone of the North China Craton, is composed of amphibolite to granulite facies orthogneisses, interleaved with minor supracrustal rocks at similar metamorphic grade. The oldest components recognised are hornblende gneiss enclaves within the predominant biotite orthogneiss which have a SHRIMP U-Pb zircon age of 2708 +/- 8 Ma. We consider these enclaves to represent fragments of similar to2.7 Ga continental materials incorporated in the biotite gneiss. The biotite gneiss has a SHRIMP U-Pb zircon age of 2513 +/- 12 Ma, interpreted to be time of magmatic crystallisation of the igneous precursor, based on the igneous characteristics of the zircons. This indicates a major magmatic episode at 2.52 Ga in the Fuping Complex, identical to the age of felsic volcanism within the low-grade Wutai Complex which crops out immediately to the west. A gneissic granite that intrudes the biotite gneisses has a poorly-defined Pb-207/Pb-206 age of 2045 +/- 64 Ma. This is within error of the age of 2097 +/- 46 Ma obtained from a fine-grained gneiss interlayered with amphibolite of the Wanzi Supracrustal Suite (WSS), interpreted to be volcanic in origin. Zircons from both these samples have strong oscillatory zoning and provide the first indication of a Palaeoproterozoic magmatic event in the area, again similar in age to magmatic events recently recognised in the adjacent Wutai Complex. These data indicate a comparable history for the Fuping and Wutai Complexes and support geochemical evidence that they had a common origin and formed part of a Late Archaean are, affected by later Palaeoproterozoic re-activation. Low-uranium zircons without oscillatory zoning, separated from a sample of biotite gneiss, yield data clustered at 1817 +/- 26 Ma, which is interpreted to reflect a period of new zircon growth during a major metamorphic event. These data support the recently-proposed tectonic model that amalgamation of the North China Craton occurred due to collision of the Eastern and Western Blocks along the central zone at similar to1.8 Ga ago. (C) 2002 Elsevier Science B.V. All rights reserved.