安徽月山岩体的^(40)Ar/^(39)Ar年龄及与其有关的成矿时代估计

^(40)AR/^(39)AR DATING FOR THE YUESHAN DIORITE, ANHUI PROVINCE AND THE ESTIMATED FORMATION TIME OF THE ASSOCIATED ORE DEPOSIT

安徽月山岩体是长江中下游钢铁成矿带中的一个重要含矿岩体.我们对该岩体的角闪石和黑云母进行了^(40)Ar/^(39)Ar年龄测定.角闪石的未扰动年龄谱给出岩体侵位年龄为136Ma.根据黑云母的扰动年龄谱,估计岩体从浸位到矿化(晚期热液作用)的时间间隔不少于9Ma.月山岩体的年龄测定结果以及前人对长江中下游其它含铜岩体的年龄测定结果表明,该区所有铜矿化岩体均形成于136Ma前,且产出于沿江构造单元内.此外,月山岩体的研究还表明,对中酸性岩的年龄测定,封闭温度高的角闪石是较理想的样品,在解释与矿化有关或热液作用发育的岩体的黑云母K-Ar结果时,必须持慎重态度.

: 40Ar/39Ar determination of an amphibole and two biotite samples of the Yueshan diorite, Anhui province, offers a good example in which emplacement age of the intrusion and information on formation time of the ore deposit associated with the pluton are both obtained by using 40Ar/39Ar spectra. Undisturbed spectra for amphibole give an emplacement age of 136 Ma for the intrusion. Disturbed spectra for biotite samples provide information on the duration between emplacement of the pluton and the late stage hydrothermal alteration. Age determined for the Yueshan diorite together with previous results on ages of copper associated plutons indicate that all copper associated plutons were formed at about 137 Ma ago and in a limited tectonic subunit, that is a long the Yangtze River.