摘要
青藏高原南部冈底斯班岩铜矿带的合矿斑岩具有埃达克岩的本质特征,是由俯冲到深部的新特提斯洋壳在榴辉岩相条件下部分熔融形成的。本文用冲江和拉抗俄两个矿区含矿斑岩的黑云母和斜长石斑晶测定了它们的^(40)Ar/^(39)Ar年龄,结果表明两个矿区虽然相隔百余千米,但形成时间非常一致。两个黑云母斑晶的坪年龄分别为13.5±1.0 Ma和13.42±0.10 Ma;两个斜长石斑晶分别给出了12.22±0.05 Ma和12.5±1.3 Ma的坪年龄。考虑到斜长石和黑云母对^(40)Ar/^(39)Ar系统较低的封闭温度,这些结果与辉钼矿给出的斑岩铜矿的Re-Os等时线成矿年龄(14Ma±)是一致的。根据含矿斑岩的产出位置和形成时间推测,印度板块沿雅鲁藏布江缝合带可能以高角度向亚洲大陆下俯冲进入岩石圈地幔。含矿斑岩和矿(化)带近EW向产出指示着斑岩岩浆上升侵位和铜矿化过程与高原达到最大高度的隆升过程是同步的。在此之后,高原的应力体制转变为EW向伸展,在重力作用下形成了一系列SN向塌陷构造—裂谷和正断层。
The ore-bearing porphyries of the Gangdese porphyry copper belt in the southern Tibet plateau possess the essential characteristics of adakite and formed from partial melting of subducted Tethyan oceanic crusts under eclogite facies conditions. This paper utilizes 40Ar/39Ar step-heating technique to date the ages of biotite and plagioclase phenocrysts of the ore-bearing porphyries sampled from Chongjiang and Lakange deposits. The analysis results indicate that the two copper-Molybdenum deposits have highly consistent mineralization ages despite of their more than 100 km apart each other. The two biotite phenocrysts yield plateau ages of 13. 5 ± 1. 0 Ma and 13. 42 ± 0. 10 Ma, respectively. Meanwhile the two plagioclase phenocrysts yield their plateau ages of 12. 22 ± 0. 05 Ma and 12. 5 ± 1. 3 Ma, respectively. Within analysis error range these age values are consistent with the mineralization age (14 Ma±) of the porphyry copper deposits based on molybdenite Re-Os isochon ages of the corresponding deposits. From the emplacement timing and location of the ore-bearing porphyries it is infered that the Indus plate was subducted in steep angle beneath the Asia continent along the Yaluzangbo suture and enter mantle lithosphere. The Ew-and NWW-striking occurrences of both ore-bearing porphyries and copper mineralization zones suggest that the porphyry emplacement and copper mineralization occurred under a SN-striking extension regime and were synchronous with the uplifting process in which the plateau reached its highest elevation. Hereafter, the stress regime of the plateau changed into EW-striking extention and a series of SN-striking collapse structures formed under gravity effect.
出处
《地质学报》
EI
CAS
CSCD
北大核心
2003年第2期245-252,共8页
Acta Geologica Sinica
