Geochronological Constraints on the Paleoproterozoic 'Evolution of the North China Craton: SHRIMP Zircon Ages of Different Types of Mafic Dikes

摘要

Widespread magmatic and metamorphic events during the interval 2350-1650 Ma suggest that the North China craton (NCC) may have been involved in the evolution of the supercontinent Columbia. Metamorphosed and unmetamorphosed dikes have been characterized in terms of their geochemistry and geochronology. Dike suite 1 in the northern Wutai-Fuping terrane comprises amphibolite-facies assemblages and has a SHRIMP U-Pb zircon crystallization age of 2147 ± 5 Ma. Dike suite 2, distributed in the northern part of the Huai'an-Fengzhen terrane, has a two-pyroxene granulite assemblage, and yields a SHRIMP metamorphic zircon age of 1929 ± 8 Ma. Dike suite 3 in the Sanggan structural zone between the two terranes is composed of garnet two-pyroxene granu-lites, and has a SHRIMP zircon age of 1973 ± 4 Ma for the cores and 1834 ± 5 Ma for the rims, defining the time of crystallization and peak metamorphism, respectively. Dike suites 1 and 2 were possibly emplaced close to a continental margin and an arc respectively; whereas dike suite 3 was most likely post-orogenic. Zircon grains from an unmetamorphosed mafic dike in the north-central NCC yields a SHRIMP crystallization age of 1778 +- 3 Ma. We suggest that the metamorphosed mafic dike suites probably resulted from the amalgamation of the NCC in the Columbia supercontinent between 2080 and 1980 Ma (approx 2000 Ma), whereas the unmetamorphosed mafic dike swarms probably was emplaced during its break-up at 1780-1750 Ma. The metamorphosed dikes were likely uplifted and exhumed during a plume-driven upwelling event during 1830-1750 Ma, causing intrusion of (unmetamorphosed) dikes throughout the NCC.