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西秦岭造山带北部的秦岭杂岩中新识别出麻粒岩相岩石,它们由角闪二辉麻粒岩和石榴夕线黑云片麻岩组成,并具有强烈的混合岩化特征.本文选择3个麻粒岩相岩石和1个深熔浅色体样品进行SHRIMP、LA-ICPMS锆石和独居石的U-Pb年代学分析,一个麻粒岩相变泥质岩样品中的锆石给出了加权平均年龄为(430±4)Ma(MSWD=0.88),另一个麻粒岩相变泥质岩的独居石给出了(433±4)Ma(MSWD=0.27)的加权平均年龄,两者在误差范围内一致,结合岩相学观察及锆石特征,认为其代表了变泥质岩麻粒岩相变质时代;角闪二辉麻粒岩中的变质锆石分别给出了(424±3)Ma(MSWD=0.45)和(402±3)Ma(MSWD=1.4)的2个加权平均年龄值,结合岩相学特征,认为前者代表麻粒岩相的变质年龄,而后者可能为麻粒岩相变质作用之后的退变质作用改造的时代;混合岩中浅色体中的锆石给出了(426±2)Ma(MSWD=0.3)加权平均年龄,代表了深熔脉体的结晶年龄.因此,与东秦岭造山带相似,西秦岭造山带北部同样记录了早古生代晚期麻粒岩相变质作用及深熔作用,其形成于商丹洋向北俯冲的岩浆弧背景还是与早古生代的碰撞造山有关仍需进一步确定.
The granulite facies rocks are newly identified in the Qinling complex in the northern part of the West Qinling orogenic belt and consist of hornblende two-pyroxene and pomegranate diagenetic gneisses with intense mixed petrified characteristics. U-Pb chronological analysis of SHRIMP, LA-ICPMS zircons and monazite samples from three granulite facies rocks and one deep-melt light-colored rock specimen, zircons from a granulite-facies argillaceous sample The weighted average age was (430 ± 4) Ma (MSWD = 0.88), and the other monazite monzogranite monazite gave a weighted average age of (433 ± 4) Ma (MSWD = 0.27) They are consistent within the error range, and combined with petrographic observation and zircon characteristics, they are considered to represent metamorphic granulite granulite facies metamorphism. The metamorphic zircons in the amphibole- ± 3) Two weighted average age values of Ma (MSWD = 0.45) and (402 ± 3) Ma (MSWD = 1.4) combined with petrographic characteristics suggest that the former represents the metamorphic age of granulite facies and the latter may be (426 ± 2) Ma (MSWD = 0.3) weighted average ages of zircons from the light-colored bodies in the mixed rocks, representing the depth of retrograde metamorphism after the metamorphism of the granulite facies metamorphism Therefore, similar to the East Qinling orogenic belt, the northern part of the western Qinling orogenic belt also recorded late Early Paleozoic granulite facies metamorphism and deep-melting. The magmatic arc formed in the northward subduction of the Shangdan Ocean is also related to Early Paleozoic collision orogenic related still need to be further identified.