Zircon U-Pb geochronology of Baoyintu beds in the northwestern margin of the North China Craton

The Baoyintu Inlier is located at the northwestern margin of the North
China Craton (NCC). Here we present LA-ICP-MS and SHRIMP U-Pb data for
zircons extracted from samples of monzogranitic orthogneiss and units in
the beds. The 1679±13 Ma date for the orthogneiss demonstrates that Late
Palaeoproterozoic rocks do exist in the inlier. The ca. 1413 Ma minimum
age of detrital zircons in metasedimentary rocks shows that the maximum
age of the Baoyintu beds is Mesoproterozoic. The age distribution of
detrital zircons in the structurally lowest exposed part of the beds form
clusters at ca. 2680, 2450, 1800 and 1560 Ma, which partly correspond to
tectonic-magmatic–metamorphic events previously recognised in the NCC. A
structurally higher unit in the beds yields age peaks at ca. 1640 and 1500
Ma limiting the maximum age of the beds at ca. 1500 Ma. Amphibolite with a
dolerite protolith from the upper unit also shows evidence for
metamorphism during ca. 877-851 Ma.