宁芜盆地凹山和东山铁矿床中阳起石的激光^(39)Ar-^(40)Ar年代学研究  

Early Cretaceous mineralizations in Ningwu basin:Insight from actinolite ^(39)Ar-^(40)Ar laser dating results

作　　者：马芳[1] 蒋少湧[2] 薛怀民[3] 

机构地区：[1]北京大学地球与空间科学学院教育部造山带与地壳演化重点实验室,北京100871 [2]南京大学地球科学系成矿作用国家重点实验室,江苏南京210093 [3]中国地质科学院地质研究所,北京100037

出　　处：《矿床地质》2010年第2期283-289,共7页Mineral Deposits

基　　金：国家自然科学基金(40503006);中国地质调查局项目(1212010711814)的联合资助

摘　　要：文章通过对凹山和东山铁矿床中特征的组合矿物之一伟晶状阳起石进行激光39Ar-40Ar法定年,精确测定了玢岩铁矿的成矿时代。其中东山铁矿中新鲜阳起石(黑绿色)的39Ar-40Ar等时线年龄在126～129Ma之间,与赋矿围岩大王山组火山岩中角闪石的等时线年龄(127Ma)一致,证明成矿与成岩密切相关,成矿与成岩是同时期的产物。而凹山铁矿中蚀变阳起石(灰绿色)的39Ar-40Ar等时线年龄为(114±16)Ma。2种阳起石分别形成于成矿作用的不同阶段,黑绿色新鲜阳起石与磷灰石、磁铁矿同期形成,形成于岩浆向热液演化的高温阶段,在成岩和成矿之后的冷却过程中,矿体和潜火山岩体具有相同的闪石封闭温度(500℃±);而灰绿色蚀变阳起石形成于中期阳起石(透辉石)-钠长石-磷灰石-磁铁矿化矿体围岩蚀变阶段。Actinolite ^39Ar-^40Ar laser fusion technique was employed to determine the metallogenic epochs of the Ningwu porphyrite iron deposits. The ^39Ar-^40Ar isochron ages of the fresh actinolite （dark green） from the Dongshan iron deposit are from 126 to 129 Ma, which agree with the ^39Ar-^40Ar isochron age （127 Ma） of hornblende from the host volcanic rock of Dawangshan Group within the analytical errors, indicating that iron mineralization was associated with the Dawangshan Group volcanic rocks. The ^39Ar-^40Ar spectrum ages of altered actinolite （gray green） from the Washan iron deposit is （114 ±16） Ma. The two kinds of actinolites were formed at different metallization stages. The dark green actinolite was formed synchronously with apatite and magnet when the temperatures of the subvolcanic rock and the ore body fell to the hornblende closure temperature （ca. 500℃）. The gray green altered actinolite was formed at the middle stage of the actinolite （diopside）-albite-apatite-magnetic wall rock alteration.

关 键 词：地球化学 阳起石 激光39Ar-40Ar定年 玢岩铁矿 宁芜盆地 

分 类 号：P618.31[天文地球—矿床学]