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采用激光阶段加热40Ar/39Ar技术,对柴达木盆地北缘锡铁山榴辉岩退变质作用形成的榴闪岩和斜长角闪岩之角闪石进行了定年分析。09NQ44Amp来自榴闪岩,各阶段表观年龄(以现代空气氩40Ar/36Ar比值295.5扣除非放射性成因40Ar)构成了单调下降的阶梯状年龄谱。在反等时线图解上,2~4阶段数据点和5~18阶段数据点分别构成了两条等时线,等时年龄分别为427.6±10Ma和425.1±2.6Ma,对应的初始40Ar/36Ar比值则分别为435.2±6.1和705.3±13。角闪石09NQ43Amp来自榴辉岩强烈退变质作用形成的斜长角闪岩,40Ar/39Ar阶段加热分析也获得单调下降的年龄谱,在反等时线图解上其数据点3~6阶段和7~16阶段分别构成了两条等时线,等时年龄分别为418.9±2.9Ma和418.1±2.1Ma,对应的初始40Ar/36Ar比值则分别为493.7±2.8和685.8±34.3。等时线截距值高于现代大气40Ar/36Ar比值,表明角闪石中含过剩40Ar。同时,由低温和中-高温阶段加热数据点分别构成两条等时年龄基本一致,截距值却明显不同的等时线,表明在角闪石热力学性质不同的源区,存在两期明显不同且未混合的初始捕获Ar组分。等时年龄425~418Ma代表的是锡铁山榴辉岩角闪岩相退变质作用发生的时间。等时线图解法虽然有效的校正了角闪石中的过剩40Ar,但仅根据表观年龄图谱和等时线图谱还无法清晰判断过剩40Ar在角闪石中的赋存状态,有待进一步探讨。
40Ar / 39Ar technique was used to analyze the hornblende of amphibolite and amphibolite formed by the degenerated metamorphism of the Xieshe eclogite in the northern margin of the Qaidam basin. 09NQ44Amp came from the amphibolite. The apparent ages of all stages (40Ar / 36Ar with a ratio of 40Ar / 36Ar to the non-radiogenic 40Ar deduced from the modern air argon) constitute a monotonically decreasing staircase age spectrum. On the anti-equi-time plot, two isochronal data points from stage 2 to stage 4 and from stage 5 to stage 18, respectively, have isochronal ages of 427.6 ± 10 Ma and 425.1 ± 2.6 Ma, respectively, corresponding to the initial 40Ar / 36Ar The ratios were 435.2 ± 6.1 and 705.3 ± 13, respectively. Amphibole 09NQ43Amp came from the amphibolite that formed by the strong retrogressive metamorphism of eclogites. The 40Ar / 39Ar stage heating analysis also obtained a monotonically decreasing age spectrum. In the anti-equi-time plot, the data points 3 to 6 and 7 The two isochronals were formed in ~ 16 stages, respectively, with isochron age of 418.9 ± 2.9Ma and 418.1 ± 2.1Ma, respectively. The corresponding initial 40Ar / 36Ar ratios were 493.7 ± 2.8 and 685.8 ± 34.3, respectively. The isochronal intercept is higher than the 40Ar / 36Ar ratio of the modern atmosphere, indicating that the amphibole contains 40Ar excess. At the same time, heating data points from low temperature and middle-high temperature stage respectively constitute two isochronous age groups which are basically the same in age but distinct in intercept value, indicating that there are two distinct periods in source regions with different amphibole thermodynamic properties And unmixed initial capture Ar component. Isochronous age of 425 ~ 418Ma represents Xiyishan eclogite amphibolite metamorphism occurred time. Although the isochronism diagram effectively corrects the excess 40Ar in amphibole, the occurrence of excess 40Ar in amphibole can not be clearly judged based on the apparent age and isochord maps, which needs further study.