攀西裂谷带内超基性碱性岩和层状辉长岩^(40)Ar-^(39)Ar年龄——以鸡街、大向坪和太和岩体为例

^(40)Ar-^(39)Ar Ages of the Ultrabasic Alklic Rock and Layered Gabbro inPanzhihua-Xichang Rift Zone: Examples from the Jijie,Daxiangping and Taihe Pluton

对分布在攀西古裂谷带内的禄丰县鸡街和大向坪超基性碱性环状杂岩体中霞辉岩,以及西昌太和层状辉长岩等两类岩石进行全岩^(40)Ar-^(39)Ar 坪年龄测定,结果表明鸡街岩体和大向坪岩体中霞辉岩年龄范围在214～193 Ma,相当于晚三叠世,属于印支期。总体上,超基性碱性环状杂岩的侵位时间略晚于含矿辉长岩;太和层状辉长岩^(40)Ar-^(39)Ar 坪年龄,由于过剩 Ar等原因的扰动,使其年龄值远远高于成岩年龄。暗示全岩或辉石单矿物等不适合作为攀西地区展状辉长岩定年的对象。

Because layered intrusion in Panxi paleorift have a large-scale economical V-and Ti-bearing magnetite deposits, some geochronological study has been done on it since the sixties, the dating techniques included K-Ar, Ar-Ar,Sm-Nd dating et al. The newer knowledge has been acquired by the results of dating. The present paper analyzes the age of the nephline-pyroxenite in ultrabasic ring alkalic complexes of Jijie, Daxiangping and the larered gabbro of Taihe, Xichang by 40Ar/ 39Ar method . These data shows the age of nephline-pyroxenite in ultrabasic ring alkalic complexes of Jijie and Daxiangping rang from 214- 193 Ma, which is consistant with the late Triassic epoch, belonging to Indosinian period. Generally speaking, the emplacement of ultrabasic ring alkalic complexes occurred later than that of the gabbro ore bearing. Wherever, because of the disturbance such as excess Ar etc, the 40Ar/ 39Ar plateau age far higher than its rock-forming age, which suggests the whole rock or pyroxene is not fit to be as the dating object in Panxi area.