内蒙古大青山地区新太古代晚期岩浆作用:来自锆石SHRIMP U-Pb定年的证据

本文报道了华北克拉通西部大青山地区新太古代晚期变质深成侵入岩的锆石SHRIMP年龄。本文涉及的3个样品取自大青山的石拐南部,岩性为黑云母二长花岗质片麻岩、紫苏石英闪长质片麻岩和闪长质片麻岩。根据矿物组合,黑云母二长花岗质片麻岩和紫苏石英闪长质片麻岩遭受高角闪岩相-麻粒岩相变质,闪长质片麻岩遭受角闪岩相变质。锆石具核-幔-边或核-边结构。岩浆锆石年龄为2484±7Ma、2494±12Ma和2495±10Ma,考虑到岩石遭受后期构造热事件强烈改造,岩浆锆石发生不同程度变质重结晶,振荡环带变得模糊,年龄很可能偏年轻,岩浆锆石真实的形成年龄应更大一些,形成于新太古代晚期。2个样品记录早期变质锆石年龄为2441±7Ma和2481±10Ma;2个样品记录晚期变质锆石年龄为1847±35Ma和为1919±73Ma。结合前人工作,可得出如下结论:1)石拐地区存在新太古代晚期二长花岗岩、石英闪长岩和闪长岩等不同类型变质深成侵入岩。新太古代晚期岩浆作用在整个大青山地区很可能广泛发育,古元古代晚期孔兹岩带是在太古宙基底之上或其邻区发展起来的。2)与大青山地区其它古元古代早期以前的地质体类似,新太古代晚期变质深成侵入岩普遍遭受古元古代早期和晚期构造热事件叠加改造。

Late Neoarchean magmatism identified in Daqingshan, Inner Mongolia: SHRIMP zircon U-Pb dating

This paper reports SHRIMP zircon U-Pb dating results of Late Neoarchean granitoids in Daqingshan, western North China Craton. Three samples dated in this study are taken from the south of Shiguai, include biotite monzogranitic gneiss, hypersthene quartz dioritic gneiss and dioritic gneiss. Based on mineral association, the biotite monzogranitic gneiss and hypersthene quartz dioritic gneiss underwent upper amphibolite-granulite facies metamorphism whereas the dioritic gneiss underwent amphibolite facies metamorphism. The zircon grains commonly show core-mantle-rim or core-rim textures. Dating on magmatic zircon domains yielded ages of 2484±7Ma, 2494±12Ma and 2495±10Ma, which is younger than real ages of the magmatic zircon because of later metamorphic recrystallization, and may be formed at Late Neoarchean. The rocks also recorded metamorphic zircon ages at 2441±7Ma to 2481±10Ma and 1847±35Ma to 1919±73Ma, respectively. Combined early work, main conclusions can be drawn as follows: 1) There are different types of Neoarchean magmatic rocks, including monzogranite, quartz diorite and diorite, in the south of Shiguai, Late Neoarchean magmatism may extensively occur in the entire Daqingshan area. Late Paleoproterozoic khondalite Belt was developed on Archean basement or its adjacent area. 2) Similar to other geological bodies of the Early Paleoproterozoic in the Daqingshan area, the Late Neoarchean intrusive rocks commonly underwent tectono-thermal events at the early and late Paleoproterozoic, respectively.