【摘要】 为了厘清古太平洋板块俯冲动力学过程、牡丹江洋闭合残留效应及区域构造域的叠加关系,并对东北亚大陆边缘中生代构造演化框架进行精准重建。笔者通过对萝北黑龙江杂岩中新识别的中兴林场花岗质岩石开展野外地质、岩相学、锆石U-Pb年代学和全岩地球化学的系统研究,确定其形成时代和岩石成因,旨在查明岩脉形成时代并探讨其成因与地球动力学背景。研究结果表明,中兴林场花岗质岩石为黑云母花岗闪长岩,野外可见其呈岩脉侵入到黑龙江杂岩变质碎屑岩基质中。锆石LAICP-MS U-Pb定年结果显示中兴林场花岗闪长岩结晶于（103±1） Ma,表明黑龙江杂岩在早白垩世之前已经就位于松辽地块和佳木斯地块之间。中兴林场早白垩世花岗闪长岩属准铝质钙碱性系列,w （Na₂O）>3.2%,AI值<0.85,Ga/Al<2.6×10⁴,w （Zr）<250×10^-6,CIPW标准矿物不出现刚玉,表明其应为Ⅰ型花岗岩。花岗闪长岩的微量元素比值接近下地壳,Zr饱和温度属高温Ⅰ型花岗岩范畴,呈现平坦的重稀土配分型式,明显亏损Ti、P,存在微弱的Eu负异常,指示其岩浆来源于基性下地壳且经历了富钛矿物-磷灰石-斜长石等矿物的结晶分异。结合区域岩浆岩组合及构造特征,认为中兴林场早白垩世花岗闪长岩的形成与古太平洋板块俯冲有关的弧后伸展密切相关。更多还原

【Abstract】 To clarify the subduction dynamic process of the Paleo-Pacific Plate,the residual effects of Mudanjiang Ocean closure,and the superposition relationship of regional tectonic domains,and to accurately reconstruct the Mesozoic tectonic evolution framework of the Northeast Asian continental margin,systematic studies including field geology,petrography,zircon U-Pb geochronology and whole-rock geochemistry were carried out on the newly identified Zhongxing Forest Farm granitoids of the Luobei Heilongjiang Complex.The research determined the formation age and petrogenesis of the granitoids,aiming to find out the emplacement age of the dykes and discuss their petrogenesis and geodynamic setting.The results show that the Zhongxing Forest Farm granitoids are biotite granodiorites,which occur as dykes intruding into the metaclastic rock matrix of Heilongjiang Complex in the field.Zircon LA-ICP-MS U-Pb dating results indicate that the Zhongxing Forest Farm granodiorites crystallized at（103±1） Ma,revealing that the Heilongjiang Complex had been emplaced between the Songliao Block andthe Jiamusi Block prior to the Early Cretaceous.The Early Cretaceous granodiorites from the Zhongxing Forest Farm belong to the metaluminous calc-alkaline series,with w（Na₂O）> 3.2%,A/CNK <0.85,Ga/Al <2.6 × 10⁴,w（Zr） <250 × 10^-6 and no corundum in CIPW normative minerals,suggesting that they are I-type granites.The trace element ratios of the granodiorites are close to those of the lower crust,and their Zr-saturation temperatures fall into the category of high-temperature I-type granites.The granodiorites display a flat heavy rare earth element（HREE） distribution pattern,significant depletion in Ti and P,and a slight negative Eu anomaly,indicating that their magmas were derived from the mafic lower crust and experienced fractional crystallization of Ti-rich minerals,apatite,plagioclase and other minerals.Combined with the regional magmatic rock assemblages and tectonic characteristics,it is concluded that the formation of the Early Cretaceous granodiorites in the Zhongxing Forest Farm is closely related to the back-arc extension associated with the subduction of the Paleo-Pacific Plate.更多还原