论文部分内容阅读
采用激光阶段加热40Ar/39Ar定年技术,选取柴北缘超高压变质带鱼卡地体超高压变质岩及其围岩的6个多硅白云母进行了Ar同位素分析,获得丰富年代学数据。榴辉岩和云母斜长角闪岩多硅白云母具有高Si、高Mg含量的特征,阶段加热给出复杂的表观年龄图谱,总气体年龄(708~534 Ma)和等时年龄(681~513Ma)都明显老于区内榴辉岩锆石U-Pb年龄,暗示样品含大量外来40Ar。相比之下,围岩花岗质片麻岩和白云母石英片岩多硅白云母具有相对低Si高Fe的特征,阶段加热给出平坦的40Ar/39Ar年龄谱,对应坪年龄分别为454和418Ma。构成年龄坪的数据点形成了线性关系良好的反等时线,并获得同坪年龄一致的等时年龄,能与区域地质年龄很好地吻合。坪年龄454Ma解释为花岗质片麻岩冷却到约400℃时的时间,同时也代表了鱼卡变质岩在经历了深俯冲超高压变质作用后,从上地幔折返抬升至中-上地壳深度的时限;片岩多硅白云母坪年龄418Ma纪录的则是区内一次强韧性剪切事件发生的时代。考虑到榴辉岩和斜长角闪岩原岩为变基性玄武岩类,其主要含钾矿物角闪石的Ar封闭稳定性较高,同时在超高压变质过程中,它们处在一个相对封闭和缺乏流体活动的极端地质环境,所以认为鱼卡榴辉岩多硅白云母外来40Ar来自原岩而非后期渗入的流体,属于“继承”40Ar的范畴。
Ar isotopic analysis of six ultrapowder metamorphic rocks and their surrounding rocks in the UHP metamorphic belt of the northern margin of the Qaidam basin by using 40Ar / 39Ar dating technology with laser stage heating has been carried out. Archenetic data have been obtained and rich chronological data have been obtained. Eclogite and mica amphibolite amphibolite with high Si, high Mg content characteristics of the stage heating gives a complex apparent age map, the total gas age (708 ~ 534 Ma) and isochron age (681 ~ 513Ma) are obviously older than the zircon U-Pb age of eclogite, suggesting that the sample contains a large amount of extrinsic 40Ar. In contrast, the peripheral rock granitic gneiss and muscovite quartz schist have the characteristics of relatively low Si high Fe, stage heating gives a flat 40Ar / 39Ar age spectrum corresponding to the age of 454 and 418Ma. The data points forming the age Ping formed a good linear relationship of the anti-isochronous line, and obtained the same age of the same isochron age, which can well coincide with the regional geological age. The 454 Ma age is interpreted as the time when the granitic gneiss cooled to about 400 ° C. It also represents that the metamorphic rocks from the Upper Mantle reverted to the mid-upper crust after experiencing deep-subducted UHP metamorphism Of the time limit; schist Mica Mica Ping 418Ma age record is a tough shear event in the region of the era. Considering that the eclogite and amphibolite precursors are basic basalts, the Ar-containing amphiboles of the major potash-bearing amphiboles have a high Ar closure stability and are relatively closed during the UHP metamorphism Lacking the extreme geological environment of fluid activity, it is considered that the 40Ar originating from the plutonic eclogites from the original rocks rather than from the fluid infiltrated later belongs to the category of “inheritance” 40Ar.