• 责任者：Sun Lixin (Tianjin Center of Geological Survey ; CGS ; Tianjin 300170 ; China) ; Ren Bangfang
• 刊名：Geological Bulletin of China
• 出版年：2013
• 卷期：32(2/3)
• 关键词：花岗质片麻岩 ; granitic gneiss ; 铀—铅计时 ; U-Pb dating ; 内蒙古 ; Inner Mongolia
• 页码：p.327-340
• 图表：illus., 4 tables, 48 refs.
• 分类号：0802
• issnNo：ISSN1671-2552
• isbnNo：CN11-4648/P

The Xihnhaote block is distributed in the middle of the Hinggan-Mongolian orogenic belt in Inner Mongoha. Its meta- morphic basement was previously referred as part of ＂Baoyintu Rock Group＂, which is mainly composed of banded gneissic granites. This study shows that these banded gneissic granites are actually deformed granites. Two samples of banded gneissic granites were dated by LA-MC-ICP-MS zircon U-Pb technique. The zircons from these samples display clear oscillatory growth zoning in CL images, suggesting that they are ofmagmatic origin. The meta-granite （10TW53） from Sunitezuoqi area has a weighted mean ^207Pb/^206Pb age of 1516Ma±31Ma from the zircon cores and a weighted mean ^206Pb/^238U age of 451Ma±16Ma from the overgrown metamor- phic zircon rims. The zircon cores yielded εHf（t）values ranging from ＋2.8 to ＋8.5, with tDM model ages of 1.70-1.84Ga, suggesting their depleted mantle origin; the zircon mTts have εHf（t）values ranging from -6.5 to -12.7, with tDM model ages of 1.33-1.59Ga and tram model ages of 1.87-2.26Ga, which are similar to values of zircon rims. Another banded gneissic granite sanlple （10TW54） from this area displays a weighted mean ^207Pb/^206pb age of 1390Ma±17Ma from the zircon cores. They have positive εHf（t）values ranging from ＋0.4 to ＋11.9, suggesting a depleted mantle source and a juvenile crustal forming event. It is suggested that the Xilinhot block is a microcontinent with Precambrian basement and it underwent crustal growth in the Mesoporterozoic period and metamorphic refor- mation in the Caledonian period.