华北板块南缘中-新元古代地层沉积时限和古构造属性研究

The southern margin of the North China Plate is the key area of late Precambrian stratigraphic division and correlation between South China and North China, and the most probable patch area on 1200 to 1000 Ma lacuna of Meso-Neoproterozoic column of China. The Meso-Neoproterozoic depositional age, stratigraphic correlation and tectonic setting at southern margin of the North China Plate are still a matter of significant debate, where huge thick and completely preserved sedimentary records with minor magmatic activities are developed. New insights into aforementioned issues of southern margin of the North China Plate, especially Xu-Huai area, would be gave by geochemistry and geochronology of sediments rocks combining igneous rocks in this project. The depositional age and stratigraphic correlation would be limited jointly on the basis of C- and Sr-isotope stratigraphy of carbonate rocks, Detrital zircon U-Pb geochronology of sedimentary rocks and zircon U-Pb geochronology of igneous rocks. Using provenance tracing as main method, the basin origin, tectonic setting as well as its dynamics would be discussed by geochemical features of sedimentation combined with magmatism. there would be important significance to map late Precambrian chronostratigraphic framework of southern margin of the North China, to understand the Precambrian crustal growth and reworking history and to provide useful information about records the history of the assembly, accretion and breakup of supercontinent.

华北板块南缘是华南地区与华北地区晚前寒武纪地层衔接对比的关键地区，是填补中国中-新元古代地层柱中缺失的1200～1000Ma地层的最可能地区。华北板块南缘发育巨厚且保存完整的中-新元古代沉积记录和小规模的岩浆记录，地层沉积时限和区域对比以及大地构造演化一直未取得较为一致的意见。本项目计划选择徐淮地区为重点研究区，从沉积岩和岩浆岩的地球化学-年代学研究相结合的角度重新分析华北板块南缘中-新元古代地层沉积时限和古构造属性。其中用碳酸盐岩Sr、C同位素地层学、碎屑锆石年代学及岩浆岩年代学共同约束地层沉积时限及对比关系；以物源示踪研究为主线，沉积作用结合岩浆作用分析盆地成因类型、古构造属性及其演化。该研究将为华北南缘前寒武纪地层年代框架的建立和对比提供依据，对揭示华北板块南缘前寒武纪地壳演化及其对超大陆形成和解体的响应具有重要意义。

南华北克拉通是北华北克拉通缺失的1200～1000 Ma地层最有可能的填补地区，是华南地区与华北地区晚前寒武纪地层衔接对比的关键地区。南华北克拉通发育巨厚且保存完整的中、新元古代沉积记录和小规模的岩浆记录，本次工作着重以碎屑岩系的年代学、地球化学等研究约束沉积时限和沉积构造属性，能够为覆盖区地层预测、烃源岩评价和油气勘探等奠定地质基础。. 地层沉积时限研究证实南华北克拉通中、新元古界主体属于新元古界青白口系，西部豫西地区和东部徐淮地区的新元古界可对比。南华北新元古代盆地为被动大陆边缘裂谷盆地，有东、西两个沉积中心，古地理格局基本保持北高南低、西高东低，发育台地—台地边缘礁—缓斜坡碳酸盐岩沉积和滨岸陆源碎屑沉积，早期是陆源碎屑占优势的滨岸海滩环境，中晚期为开阔浅海、局限海碳酸盐岩缓坡—台地占优势。. 物源分析表明南华北克拉通中、新元古界及寒武系碎屑岩系的碎屑锆石谱图普遍存在垂向突变现象，物源为华北克拉通内部前寒武纪地质体；新元古代和寒武纪碎屑岩系中大量的1.6Ga—1.4Ga和1.3 Ga—1.0 Ga 碎屑锆石记录表明至少华北克拉通东缘和南缘曾有与Columbia超大陆裂解和Rodinia超大陆聚合有关的中元古代构造带，该中元古代构造带于新元古代时为华北克拉通东缘至南缘的主要物源供给区，至早古生代时所占比例明显减弱或完全缺失。. 四十里长山地区侵入新元古界—下古生界的中生代煌斑岩脉岩、花岗斑岩脉岩及正长岩类脉岩的侵位年龄分别为80.9±1.8Ma、86.1±1.0Ma和85.6±1.0Ma；脉岩组成晚白垩世双峰式侵入岩组合，形成于类似弧后盆地的板内伸展环境，与太平洋板块向欧亚大陆下的俯冲作用相联系。. 南华北新元古界—下古生界是值得深入探索的海相天然气新地层和新领域，原始干酪根属腐泥型，热演化程度达到高—过成熟阶段，包括6套区域性烃源岩层。马店组暗色泥页岩及泥质白云岩为最优的海相烃源岩，生排烃高峰期为早—中三叠世。生排烃高峰期原生包裹体特征评价马店组储层为工业气层或气显示层。