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浙东早白垩世英坑火山–侵入杂岩的地球化学特征及其成因意义
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Abstract:
英坑火山–侵入杂岩由流纹岩和石英二长斑岩组成，是浙江沿海晚中生代岩浆活动的典型代表。本文对英坑火山–侵入杂岩开展了系统的岩相学、全岩地球化学成分分析，旨在探讨火山–侵入杂岩的成因联系和岩浆演化过程。地球化学分析结果显示，英坑火山岩和侵入岩都具有A/CNK < 1.1，高铝(Al2O3 = 13.64~15.09 wt.%)，高全碱(Na2O + K2O = 8.98~9.34 wt.%)特征，哈克图解显示流纹岩与石英二长斑岩具有良好的线性关系，并且流纹岩的Al2O3、CaO、MgO、FeOT、TiO2、P2O5含量都比侵入岩的低，流纹岩相较于石英二长斑岩(DI, 90.64~90.70)具有更高的分异指数(DI, 95.80~96.16)，这说明火山岩经历了更高程度的结晶分异作用。研究表明，本区火山岩与侵入岩具有相似的地球化学特征，为古太平洋板块俯冲导致的岩石圈减薄的背景下经历了壳幔组分混合和不同程度分离结晶作用的同期岩浆活动的产物。
The Yingkeng volcanic-intrusive complex, composed of rhyolite and quartz monzonite porphyry, is a typical representative of the Mesozoic magmatic activity along the coastal region of Zhejiang. This study conducts a systematic petrographic and whole-rock geochemical analysis of the Yingkeng volcanic-intrusive complex, aiming to explore the genetic relationship and magmatic evolution process of the volcanic-intrusive rocks. The geochemical analysis results show that both the Yingkeng volcanic rocks and intrusive rocks have characteristics of A/CNK < 1.1, high alumina (Al2O3 = 13.64~15.09 wt.%) and high total alkali content (Na2O + K2O = 8.98~9.34 wt.%). The Harker diagrams reveal a strong linear correlation between rhyolite and quartz monzonite. Additionally, the rhyolite contains lower concentrations of Al2O3, CaO, MgO, FeOT, TiO2, and P2O5 compared to the intrusive rocks, and exhibits a higher differentiation index (DI, 95.80~96.16) than the quartz monzonite (DI, 90.64~90.70). This suggests that the volcanic rocks underwent a higher degree of crystallization differentiation. The results show that the volcanic rocks in this area have similar geochemical characteristics to the plutonic rocks, and are the products of the contemporaneous magmatic activity that underwent the mixing of crust-mantle components and different degrees of separation crystallization under the background of lithospheric thinning caused by the subduction of the Paleo-Pacific plate.
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