ABSTRACT

The North China Craton (NCC), which underwent multiple subduction and lithospheric destruction during the Mesozoic, is well known for hosting some of the world-class gold deposits. In many cases, Mesozoic mafic dykes are associated with the gold deposits, although there has been no systematic studies aimed to integrate the characteristics of these dykes in different regions of the NCC. Here we investigate diabase and lamprophyre dyke suites in the Xiaoqinling region along the southern margin of the NCC, and compile the published geochronological, geochemical and isotopic data for regional mafic dykes and gold deposits from the major gold belts including Jiaodong, Xiaoqinling and central NCC. Zircon U-Pb data show the mafic dykes in Xiaoqinling were emplaced in two episodes at 219–227 Ma and 121–137 Ma, and their εHf(t) values (ranging from −2.1 to 3.8 and −13.6 to 1.6 respectively) suggest increasing input of lithospheric materials in the Early Cretaceous dykes. The compiled geochemical data on the mafic dykes from different regions in the NCC show that the magmatic evolution involved olivine and clinopyroxene fractional crystallization with limited crustal contamination and subduction-related fluid metasomatism. The geochemical and isotopic signature suggests multiple sources for the parent magma of the mafic dykes ranging from convective asthenospheric mantle to ancient lithospheric mantle, with the magma source characterized by enriched mantle (EM2 or EM2+ EM1), and that signatures might be potential for gold mineralization. Further, most dykes are coeval and cospatial with gold deposits in the NCC. The geochronological data show that small amount of both Mesozoic dykes and gold deposits formed in Triassic whereas the peak formed in Cretaceous following slab roll back of the Pacific plate subducting from the east during 145–110 Ma. We envisage that the tectonic extension associated with Pacific slab subduction contributed to the magmatism and gold mineralization in the NCC.

摘要

华北克拉通（NCC）在中生代经历了多次俯冲和岩石圈破坏，以拥有一些世界一流的金矿床而闻名。在许多情况下，中生代铁镁质岩脉与金矿床有关，尽管还没有系统的研究旨在将这些岩脉的特征整合到NCC的不同区域。在这里，我们调查了沿NCC南部边缘的小秦岭地区的辉绿岩和煌斑岩脉组，并汇编了已发布的有关主要铁矿带（包括胶东，小秦岭和NCC中部）的区域基性岩脉和金矿床的地质，地球化学和同位素数据。锆石U-Pb数据显示，小秦岭的铁质岩脉在219-227 Ma和121-137 Ma的两个时期中均被侵染，其εHf（t）值（范围为-2）。1到3.8和-13.6到1.6）提示白垩纪早期岩石圈物质的输入增加。来自NCC不同地区的铁镁质岩脉的汇编地球化学数据表明，岩浆演化涉及橄榄石和斜辉石的部分结晶，地壳污染和俯冲相关的流体交代作用有限。地球化学和同位素特征表明，镁铁质岩浆母岩浆有多种来源，从对流软流圈地幔到古代岩石圈地幔，其岩浆源以富集的地幔（EM2或EM2 + EM1）为特征，这些特征可能是金矿化的潜力。 。此外，大多数堤坝与NCC中的金矿床同生并同空间。地质年代学数据表明，在三叠纪形成了少量的中生代堤和金矿床，而在145-110 Ma期间，太平洋板块从东部俯冲下来后，白垩纪形成了一个峰值。我们设想与太平洋板块俯冲有关的构造扩展导致了ＮＣＣ的岩浆作用和金矿化。