河北大庙铁矿床黑云母^(40)Ar/^(39)Ar年龄及其地质意义  

New^(40)Ar/^(39)Ar geochronologic constraint on the age of Damiao Fe-Ti-P deposits,North China Craton and its geological significance

作　　者：周久龙[1] 罗照华[1] 贺怀宇[2] 孙静 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,北京100083 [2]中国科学院地质与地球物理研究所地球深部重点实验室,北京100029 [3]河北地质勘查局第四地质大队,河北承德067000

出　　处：《地学前缘》2012年第4期110-117,共8页Earth Science Frontiers

基　　金：国家自然科学基金项目(90814007);中国地质调查局地质调查工作项目(1212011121072);有色金属矿产地质调查中心危机矿山勘查理论项目(200699105-4)

摘　　要：文章以野外观察为基础确定了致矿侵入体,以岩相学特征确立了测年样品的代表性。在此基础上,选取大庙铁矿大乌素沟矿区浸染状铁矿石中的黑云母进行了40 Ar/39 Ar年龄测定,坪年龄为(395.8±3.7)Ma,反等时线年龄为(395.6±4.0)Ma(2σ;MSWD=0.9;n=8)。因此,大庙铁矿及其致矿苏长岩的形成年龄约为396Ma,相当于中泥盆世,而不是前人所认为的元古宙。新的测年结果与区域上近年来陆续识别出来的泥盆纪侵入岩类形成年龄一致,不仅表明华北克拉通的改造过程至少从泥盆纪就已经开始,而且暗示华北克拉通北缘仍有寻找其他"大庙式铁矿"的潜力。同时,文章提出,用成岩年龄作为成矿年龄时,需要有可靠的地质学和岩相学证据。The ore-bearing intrusion has been identified by field relationships in this paper and the dating sample is representative through petrographic characteristics.Based on the above,biotites were separated from the disseminated iron ore for 40Ar/39Ar dating.Perfect age plateau and inverse isochron-line were obtained,with the result of（395.8±3.7） Ma and（395.6±4.0） Ma（MSWD=0.9）,respectively.Thus this 40Ar/39Ar age（396 Ma） should represent the metallogenic epoch of Damiao ore deposits and the emplacement age of norite,which indicates that the former is the Middle Devonian rather than the Proterozoic as assumed previously.The new geochronologic result is consistent with that of the Devonian intrusions which were progressively recognized at the northern margin of North China Craton（NCC） recently,implicating that modification of the NCC was initiated in the Devonian at least and there are still exploration potential for＂Damiao-type＂ore deposits at the northern NCC.In addition,the authors point out that the reliable geological and petrographic evidences are required to justify the use of rock-forming age as the ore-forming age.

关 键 词：大庙式铁矿 斜长岩 苏长岩 40Ar/39Ar定年 成矿年代 华北克拉通 

分 类 号：P597.3[天文地球—地球化学] P618.31[天文地球—地质学]