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北苏鲁仰口地区出露超高压的变辉长岩。锆石阴极发光图像和其内部矿物包体激光拉曼测试的联合研究结果表明,变辉长岩锆石具有弱发光效应的岩浆韵律环带的核和被改造的强发光效应的边。岩浆韵律环带的核部保存大量而复杂的矿物包体,包括普通辉石(cpx)+斜方辉石(Opx)+斜长石(Pl)+石英(Qtz)+黑云母(Bt)+钛铁矿(Ilm)+磷灰石(Ap);边部保存的矿物包体则相对较少,包括普通辉石(Cpx)+斜方辉石(Opx)+斜长石(Pl)+磷灰石(Ap)。尽管岩浆韵律环带核部的稀土元素总含量比被改造的锆石边部明显偏高,但二者稀土元素配分模式具有明显的相似性,主要表现为轻稀土相对亏损,而重稀土明显富集,相应的(La/Yb)_N=0.00015～0.00039,并具有明显的负Eu异常(Eu/Eu~*=0.20～0.26)、相对明显的正Ce异常(Ce/Ce~*=71.5～147.4)和较高的Th/U比值(1.97～2.69)。上述特征表明,仰口地区变辉长岩中的锆石均为继承性的岩浆锆石,而没有新生的变质锆石、LA-(MC)-ICP-MS锆石原位U-Pb定年和Lu-Hf同位素分析结果表明,两件锆石样品Y1和Y2的年龄数据所构成的不一致线显示了十分接近的上交点和下交点年龄。其上交点年龄分别为785±15Ma(2σ)和784±12Ma(2σ),应代表原岩的形成时代,表明变辉长岩的原岩与Rodinia超大陆裂解的岩浆事件存在密切的成因关系;而下交点年龄分别为226±24Ma(2σ)和228±26Ma(2σ),与苏鲁其它类型超高压岩石中含柯石英锆石微区记录的变质年龄十分吻合,应代表变辉长宕的超高压变质时代。岩浆结晶锆石的核部具有明显偏高的。~(176)Lu/~(177)Hf(0.00044～0.00291)和~(176)Yb/~(177)Hf(0.0165～0.1168)比值,而~(176)Hf/~(177)Hf比值变化于0.281956～0.282048之间,相应的ε_(Hr)(t)=-8.5～-14.0,t_(DM2)=2.03～2.32Ga,表明仰口地区变辉长岩的原岩起源于古元古代时期的富集地幔或发生部分熔融的下地壳残留体。被改造的岩浆结晶锆石的边部边具有明显偏低的~(176)Lu/~(177)Hf(0.00029～0.00060)和~(176)Yb/~(177)Hf(0.0112～0.0200)比值,而~(176)Hf/~(177)Hf(t)比值变化于0.281953～0.282002之间,相应的ε_(Hf)(t)=-10.2～-11.9,t_(DM2)=2.12～2.21Ga。与岩浆结晶锆石核部相比,被改造的岩浆锆石边部的~(176)Lu/~(177)Hf、~(176)Yb/~(177)Hf、~(176)Hf/~(177)Hf(t)比值和ε_(Hf)(t)和t_(DM2)值的变化范围更小,表明中-新三叠纪的超高压变质作用使岩浆结晶锆石边部的Lu-Hf同位素体系发生调整,更趋向于均一化。
North Sulu Yangkou exposed UHP gabbro. The results of a joint study of zircon cathode luminescence images and the laser mineralization Raman test show that the gabbro zircons have a weak luminescence effect in the core of the magmatic rhythmic zone and the edge of the strong luminescence effect that was modified. The core of the magmatic rhythm conserves a large number of complex mineral inclusions, including cpx + Opx + Pl + Qtz + Bt + Ilm + apatite (Ap); and the marginal preserved mineral inclusions are relatively few, including Cpx + Opx + plagioclase (Pl) + Phosphorus Graystone (Ap). Although the total content of rare earth elements in the nuclei of the magmatic rhythmic zone is obviously higher than that of the modified zircons, the REE patterns have obvious similarities, mainly due to the relative depletion of light rare earths and the significant enrichment of heavy rare earths (La / Yb) _N = 0.00015 ~ 0.00039, with obvious negative Eu anomalies (Eu / Eu ~ * = 0.20 ~ 0.26) and relatively obvious positive Ce anomaly (Ce / Ce ~ * = 71.5 ~ 147.4) ) And higher Th / U ratio (1.97 ~ 2.69). The above characteristics show that the zircons in the gabbro from Yangkou area are all inherited magmatic zircons without new metamorphic zircons, in-situ U-Pb dating of LA- (MC) -ICP-MS zircons, and Lu The -Hf isotopic analysis shows that the inconsistency line formed by the age data of the two zircons, Y1 and Y2, shows a very close upper and lower intersection age. The dating points of the upper strike point are 785 ± 15Ma (2σ) and 784 ± 12Ma (2σ) respectively, which should represent the age of the protolith formation, indicating that there is a close genetic relationship between the protolith of the gabbro and the magmatic events of the Rodinia supercontinent. While the lower crossover points are 226 ± 24Ma (2σ) and 228 ± 26Ma (2σ), respectively. They coincide well with the metamorphic age recorded by the kerogenite zircons in other ultrahigh-pressure rocks in the Sulu region, Era of metamorphism. The core of magmatic crystalline zircons is significantly higher. ~ (176) Hf (0.00044 ~ 0.00291) and ~ (176) Yb / ~ (177) Hf (0.0165 ~ 0.1168) The corresponding ε_ (Hr) (t) = -8.5 ~ -14.0 and t_ (DM2) = 2.03 ~ 2.32Ga, indicating that the original rocks of the Yangsikou gabbro origin originated from the Paleoproterozoic Enriched mantle or partially melted lower crust remnants. The marginal edges of the altered magmatic zircons have significantly lower ratios of ~ (176) Lu / ~ (177) Hf (0.00029 ~ 0.00060) and ~ (176) Yb / ~ (177) Hf (0.0112 ~ 0.0200) , While the ratio of Hf / ~ (177) Hf (t) varied from 0.281953 to 0.282002 and the corresponding ε_ (Hf) (t) = -10.2 ~ -11.9 and t_ (DM2) = 2.12 ~ 2.21Ga . Compared with the magmatic zircon nuclei, the ~ (176) Lu / ~ (177) Hf, ~ (176) Yb / ~ (177) Hf and ~ (176) Hf / (177) Hf (t) ratio and ε_ (Hf) (t) and t_ (DM2) values show a smaller range, indicating that the Meso-Neo-Triassic UHP metamorphism caused the Lu- Hf isotope system adjustment, more tended to be uniform.