云中山区界河口岩群单颗粒锆石年龄及地质意义

The age and significance of single-grain zircons in Jiehekou Gr. in the Yunzhong Mountain area

云中山区界河口岩群原岩主要为1套陆源碎屑岩夹镁铁质火山岩,经历了多次变形变质作用的叠加改造,变质程度达高角闪岩相,深熔作用强烈。整套岩石组合无底、无顶、无序,其与基底片麻岩之间(TTG)或是深熔渐变过渡,或是呈韧性剪切带接触。采自该岩群绿帘角闪二长变粒岩单颗粒锆石U-Pb法测年获得3组年龄值,即(2751±39)Ma、(2541±21)Ma和(2183±16)Ma,前者代表物源区的年龄,后两者代表2次深熔变质年龄。侵入该岩群的峪口眼球状黑云二长片麻岩单颗粒锆石U-Pb法测年获得(2493±38)Ma的成岩年龄,从而说明了云中山区界河口岩群形成时代为新太古代。发生在(2541±21)Ma强烈的区域性深熔作用,使基底片麻岩活化或重生,早期的信息大多已消失。界河口岩群与五台岩群年龄相当,推测界河口岩群与五台岩群并非是垂向上下关系,而是横向上的并列关系,现在所处的不同构造层次是弧-陆碰撞的造山过程中构造叠置形成,峪口片麻岩形成于后碰撞环境,其侵位形成的卵形构造局部斜切弧-陆碰撞所形成线状构造带。

Mesozoic Jiehekou Gr. is mainly composed of terrigenous clastic rocky mafic volcanic rocks,which have undergone several superposition of deformation and metamorphism,and the degree of metamorphism reaches high amphibolite facies,and the deep melting effect is strong. The entire set of rocks has no bottom,no top,and is disorder,and it is in contact with the base gneiss( TTG) or deep melting transition,or in a ductile shear zone.Results show that the age of the three groups are 2751 ± 39 Ma,2541 ± 21 Ma and 2183 ± 16 Ma,respectively. The former represents the source region of the leaf age, and the latter two represent the secondary deep melting deterioration age. The diagenetic age of 2493 ± 38 Ma was obtained by the U-Pb method of Yukou oval dolomitic gneiss with a single pellet of Yukou,which was invaded into the rock group,indicating the rock formation in the estuary Ancient times. Occurring with the 2541 ± 21 Ma strong regional deep melting effect,the base gneiss activation or rebirth,most of the early information has disappeared. The Jiehekou Gr. is similar to the age of the five groups. It is inferred that the Jiehekou Gr. and the Wutai rock group are not vertical and horizontal relations,but the horizontal relationship is parallel. The different tectonic levels are arc-land collision Orogenic formation in the process of orogeny formation,Yukou gneiss formation in the post-collision environment,and the formation of the oval-shaped oval-shaped local oblique arc-land collision formed by the linear structure zone.