Late Paleoproterozoic K-feldspar pegmatite veins in Daqingshan area, North China Craton: SHRIMP age and Hf composition of zircons

This paper reports SHRIMP age and Hf isotope composition of zircons from a K-feldspar pegmatite vein in the Wulanbulang-Hademengou area of southern Daqing Mountain, North China Craton. Pegmatite veins widespread in this area cut early Precambrian geological bodies. Some K-feldspar grains show exsolution structures with formation temperatures from 750 to 800℃ in terms of ternary-feldspar geothermometry. The zircons are large and mostly equant. In cathodoluminescence images, they show banded or sector zoning in the center of the crystal and oscillatory zoning in the outer domain. Data are distributed on concordia with a weighted mean 207Pb /206Pb age of 1841±9 Ma(MSWD=1.5). They have εHf(t) and tDM1(Hf) values ranging from -10.4 to -6.6 and 2498 Ma to 2648 Ma, respectively. Combined with data available, some conclusions can be drawn as follows: ① the tectonic environment changed from compression to extension at least before 1.84 Ga in the Daqing Mountain area; ② the K-feldspar pegmatite veins were formed under the condition of high temperature; ③ the K-feldspar pegmatite veins were derived from the early Precambrian basement.