沂沭断裂带高桥盆地早白垩世火山岩的地球化学及岩石成因

沂沭断裂带内高桥盆地早白垩世火山岩SiO₂含量为51.97%～68.94%；由玄武粗安岩、 粗面岩和流纹岩组成；都属于碱性岩。岩石富集Rb、 Ba、 K等大离子亲石元素和轻稀土元素；相对亏损Nb、 Ta、 Ti等高场强元素和重稀土元素；并具有富集的Sr-Nd-Pb同位素组成。钾质粗面岩具有高稀土Cr、 Ni含量、 La/Yb、Sr/Y和Th/U高比值；这类似于华北克拉通东南缘早白垩世富集岩石圈来源的基性岩（如方城玄武岩、 沂南辉长岩）；其可能主要来源于富集岩石圈地幔部分熔融。与之相比；钠质玄武粗安岩具有低Cr、 Ni含量 、 ⁸⁷Sr/⁸⁶Sr（t）、 Th/U和高ε_Nd（t）值；表明它可能由岩石圈地幔熔体与软流圈物质混合而成。沂沭断裂带高桥盆地火山岩形成于岩石圈伸展背景下；沂沭断裂带的活动可能诱使软流圈物质的上涌；导致岩石圈地幔升温发生部分熔融；并为软流圈物质的上升提供了通道。

Geochemistry and petrogenesis of the Early Cretaceous volcanic rocks in Gaoqiao Basin along the Yi-Shu fault zone

The Early Cretaceous volcanic rocks distributed in Gaoqiao Basin consists of basaltic trachyandesite, trachydacite and rhyolite, with SiO₂ contents varied between 51.97%～68.94%. They are belong to alkaline series, characterized by enriched LREE, LILEs(e.g. , Rb, Ba and K), and Sr-Nd-Pb isotopic compositions, and depleted HREE and HFSE(e.g. , Nb, Ta and Ti). The potassic trachyandesites exhibit high REE, Cr, Ni contents, and Sr/Y, La/Yb, Th/U ratios, which are the common features of the enriched lithospheric mantle-derived mafic rocks(e.g. , Fangcheng basalts, Yinan gabbros)in the southeast margin of the North China Craton. This implied that the trachyandesites originated from the partial melting of the enriched lithosphere mantle. The sodic basaltic-trachyandesite has low Cr, Ni, ⁸⁷Sr/⁸⁶Sr(t) and high ε_Nd(t), suggesting it is originated from enriched mantle sources with incorporation of depleted asthenosphere components. The Early Cretacous volcanic rocks in Gaoqiao Basin were formed under the lithosphere extension setting. The activities of the Yi-Shu fault zone induced and provided an advantage site for asthenosphere upwelling, resulting the melting of lithosphere mantle.