Early Permian Cumulates in Northern Margin of North China Craton and Their Tectonic Significances

Shao Jian; Tian Wei; Zhang Jiheng

doi:10.3799/dqkx.2015.131

Abstract：Understanding about genesis of the Early Permian basic-ultrabasic rocks in the northern margin of North China craton are varied,with one of the influential viewpoints suggesting that they are related with activities of “Andes-type continental mar-gin”,which is discussed in this paper based on researches of the cumulates in east Hebei Province.Early Permian basic-ultrabasic cumulates controlled by Fengning-Longhua lithospheric faults are distributed discontinuously in the northern margin of North China craton.The SHRIMP Zircon U-Pb ages from cumulates are 280-300 Ma.Petrographic studies confirm that the complexes consist of a suite of cumulates including dunite,pyroxenite,amphibolite,gabbro,diorite,anorthosite,and so on,which in turn can be further divided into layered and circular ones,both with obvious cumulate texture.Mineralogical stud-ies show that hornblende,pyroxene,and phlogolite in cumulates all are characterized by mantle sourced components of high Mg and high Cr.Sr/Ba ratio of cumulates with different components does not change with their melting degrees,showing that cumulates possess a fractional crystallization trend.Similar REE patterns and transition group elements reveal their consanguin-ity.Comparison of cumulates of the Late Paleozoic with those of the Early Mesozoic from the concerned area indicates that these Early Permian cumulates have characteristics of an initial-rift magma,which offers the earliest evidence of the transforma-tion from the stable to the active one of continental crust of North China craton.Viewed from broader regions,activities of this period in this area are driven by deeper geodynamics.