华北克拉通西南缘汝阳群沉积时代及其地质意义：来自碎屑锆石U-Pb年龄的证据

汝阳群分布在华北克拉通西南缘,位于河南-陕西-山西交界地区,主要为一套未变质的碎屑岩及碳酸盐岩地层,不整合于熊耳群火山岩系之上,其上被洛峪群整合覆盖。长期以来,其地质时代一直存有较大的争议。本文通过对汝阳群下部白草坪组4个石英砂岩样品中的碎屑锆石进行LA-ICP-MS U-Pb年龄测定,获得的²⁰⁷Pb/²⁰⁶Pb年龄分布范围为3 000～1 800 Ma,主要集中在2 600～2 400 Ma之间(约占67%),年龄主峰值为2 550～2 500 Ma,说明其沉积物质主要来源于新太古代末以及古元古代的地质体。其中,最年轻锆石的²⁰⁷Pb/²⁰⁶Pb谐和年龄值分别为1 817±22 Ma、1 838±23 Ma、1 924±17 Ma和1 829±28 Ma,说明汝阳群沉积时代不老于1 800 Ma,与其上覆洛峪群中近期获得1 611±8 Ma的年龄相吻合,因此其形成时代应为中元古代早期。

Depositional age and geological implications of the Ruyang Group in the southwestern margin of the North China Craton:Evidence from detrital zircon U-Pb ages

The Ruyang Group distributes in the southwestern margin of the North China Craton, mainly locating in the border of Henan-Shaanxi-Shanxi Province.The Group, covering on the Xiong'er Group with angular unconformity and being overlain consistently by the Luoyu Group, is mainly composed of unmetamorphosed clastic and carbonate strata.In this paper, the authors reports LA-ICP-MS U-Pb ages from four quartz sandstones of the Baicaoping Formation of the Ruyang Group.The youngest ²⁰⁷Pb/²⁰⁶Pb ages are1 817±22 Ma, 1 838±23 Ma, 1 924±17 Ma and 1829±28 Ma, respectively.Those ages combined with the high-precise dates 1 611±8 Ma in the Luoyu Group overlying on the Ruyang Group indicate that the Ruyang Group should be early Mesoproterozoic.The²⁰⁷Pb/²⁰⁶Pb ages of the detrital zircon range from 3 000 Ma to 1 800 Ma, with 67% between 2 600 Ma to 2 400 Ma and the main peak of ages(2 550～2 500 Ma), meaning that sedimentary materials mainly sourced from Paleoproterozoic geologic bodies.