First SHRIMP zircon U-Pb ages for Hutuo Group in Wutaishan: Further evidence for Palaeoproterozoic amalgamation of North China Craton

摘要

A felsic tuffaceous rock, obtained from a metamorphosed sequence of volcanics and sediments of the Hutuo Group, 8 km south of Taihuai in Wutaishan, contains two zircon populations. These record SHRIMP ~(207)Pb/~(206)Pb weighted mean ages of 2180 +- 5 Ma and 2087 +- 9 Ma, respectively. The older date is within error of the age of the Dawaliang Granite in Wutaishan and is considered to be derived from a similar crustal magmatic source. The younger date is within error of reported ages from metasediments and meta-volcanics of the Wanzi supracrustal rocks and the Nanying granitic gneisses in the adjacent Fuping Complex and is interpreted to be the age of volcanism in the Hutuo Group. These data establish that: (1) the Hutuo Group is Paleoproterozoic and not Archean in age and (2) the volcanism and sedimentation were coeval in the Wutai and Fuping complexes. Sedimentation was therefore widespread at this time and possibly reflects deposition along an evolving continental margin, most likely the western margin of the Eastern Block of the North China Craton. The age of 2087 +- 9 Ma for volcanism in the Hutuo Group means that it must have been deformed and metamorphosed after this time. This further supports the evidence, obtained from other recent studies, that the main tectonism in the Wutaishan area occurred at approx 1.8 Ga during the Luliang orogeny. This orogeny resulted in the collision of the Eastern and Western blocks of the North China Craton and formed part of a global supercontinental amalgamation event.