苏鲁高压-超高压变质地体南缘高压与超高压变质带原岩的接触关系及其地质意义

苏鲁高压-超高压变质地体南缘高压与超高压变质带接触关系的确定对该地区构造格局的建立具有重要的意义。研究表明苏鲁高压-超高压变质地体南缘高压变质带内的锦屏群底部含砾岩层不整合覆盖于超高压变质带南部的朐山花岗片麻岩之上，含砾岩层中的砾石虽然经历了后期的塑性变形改造，但其地质特征仍展示出地层下部层位沉积砾石特有的性质。此外，同位素年代学研究揭示出朐山花岗片麻岩与锦屏群变质岩的原岩分别形成于859Ma和814Ma。这些都说明锦屏群变质岩与下伏朐山花岗片麻岩原岩之间的接触关系为角度不整合。在后期的构造运动过程中它们一起经历了高压-超高压变质变形作用，折返过程中锦屏群变质岩向北西西方向逆冲，形成叠加于不整合接触面的韧性剪切带。

Contact Relationship between the high-pressure and ultrahigh-pressure metamorphic belts in the southern Sulu high-pressure-ultrahigh-pressure metamorphic terrane and its geological significance

The determination of the contact relationship between the high-pressure (HP) and ultrahigh-pressure (UHP) metamorphic belts at the southern margin of the Sulu HP-UHP metamorphic terrane has great significance for establishing the tectonic framework of the area. The basal conglomeratic bed of the Jingping Group in the HP metamorphic belt at the southern margin of the Sulu HP-UHP metamorphic terrane unconformably overlies the Qushan granite-gneiss in the southern part of the UHP metamorphic belt. The gravels in the conglomeratic bed underwent late-stage plastic deformation but their geological characteristics still display the unique properties of sedimentary gravels in the lower part of the strata. In addition, isotope chronological study has revealed that the protoliths of the Qushan granite-gneiss and Jinping Group metamorphic rocks formed at 859 Ma and 814 Ma respectively, indicating that the contact between the Qushan granite-gneiss and Jinping Group metamorphic rocks is unconformable. They together underwent HP-UHP metamorphism-deformation in the process of the late-stage tectonic movement. During their exhumation the Jingping Group metamorphic rocks were subducted toward the WNW, forming a ductile shear zone on the unconformity.