太行山和华北其它地区中生代岩浆作用的锆石U-Pb年代学和地球化学特征及其岩浆成因和地球动力学意义

Zircon U-Pb geochronology and geochemistry of the Mesozoic magmatism in the Taihang Mountains and other places of the North China craton, with implications for petrogenesis and geodynamic setting

华北克拉通东部中生代岩浆岩的主要特征是岩石类型复杂(从辉长质到二长花岗质),显示高钾钙碱性、高Sr-Ba、高Sr/Y和La/Yb比值和高度富集的Sr-Nd同位素成分。锆石SHRIMP定年表明,太行山地区岩浆作用发生在138-127Ma之间。该年代结果与东亚其它地区已经发表的锆石年代数据揭示了中生代岩浆作用的发展具有从日本岛(和朝鲜半岛;210Ma),到胶辽半岛(180Ma),再到大别山-太行山(138Ma)的年轻化趋势。这暗示华北中生代岩浆作用可能与古太平洋板块的俯冲有关,但华北中生代岩浆岩似乎没有明显的向内陆方向的成分变化极性,可能与古太平洋板块在地幔过渡带的水平俯冲有关。地球化学数据表明,华北中生代岩浆岩可能主要形成于壳幔岩浆混合作用和随后的分离结晶过程,而不是形成于基性下地壳部分熔融作用。

The Mesozoic rocks from eastern North China Craton (NCC) range in composition from gabbroic to monzogranitic, showing high-K calc-alkaline to shoshonitic affinity, high Sr-Ba and high Sr/Y, La/Yb, and highly enriched Sr-Nd isotopic compositions. SHRIMP zircon dating for four plutons from the Taihang Mountains, westernmost NCC, yields ages of 138 similar to 127 Ma, which, along with published ages for magmatic rocks from other parts of eastern East Asia, reveal a northwestward younging trend of calc-alkaline magmatism from Japan island chain (and Korean peninsula; 210 Ma), through Jiaodong and Liaodong Peninsula (180 Ma), and to the Taihang orogen (138 Ma). This suggests the genesis of the Mesozoic rocks in the NCC was linked to the subduction of the paleo-Pacific plate, rather than to the Triassic collision between the Yangtze block and NCC. The lack of a regular variation in compositions from the coastal areas to interiors of eastern China as is shown by the magmatic rocks in the Basin and Range is probably related to the 'flat subduction' of the paleo-Pacific slab beneath the NCC. Moreover, they probably originated from mixing between mafic magmas from enriched mantle sources and crust-derived granitic melts, followed by fractionation, rather than from melting of mafic lower crust as previously suggested by many others.