黑龙江黑河地区晚侏罗世岩浆弧的火成岩记录:与蒙古-鄂霍茨克洋关系探讨

Records of the Late Jurassic Magmatic Arc in Heihe Area, Heilongjiang Province: Discussion on the Relationship with Mongolia-Okhotsk Ocean

黑龙江黑河北部的黑花山地区广泛发育中生代的侵入岩,但该侵入岩的形成时代、岩石组合、成因仍然不清.对黑花山地区侵入岩进行了野外、岩相学、岩石学、年代学、岩石地球化学等研究,以探讨该套岩石形成的时代、原因及大地构造背景.对两件二长花岗岩开展的LA-ICP-MS锆石U-Pb测年获得加权平均年龄分别为148.7±0.6 Ma、153.50±0.56 Ma,表明其形成于晚侏罗世.岩石组合主要为含有少量英云闪长岩(T1)、奥长花岗岩(T2)的T1T2G(狭义花岗岩)组合,即弧环境的侵入岩组合.上述岩石组合富硅、碱、高钾、过铝(A/CNK大于1)、低Fe2O3T.其在SiO2-K2O图上为高钾钙碱系列,硅镁图中为低铁钙碱(LF-LA)系列,Peacock指数为钙碱性或碱钙性,痕量元素蛛网图显示富集大离子亲石元素,亏损Nb、Ta、P、Ti、Y、Yb等元素.稀土元素配分模式为右倾型,轻稀土相对富集,(La/Yb)n=13.78~29.85,无负Eu异常或弱正Eu异常或弱的Eu负异常.花岗岩类具有高Sr低Y的特征,Sr/Y比值介于29.53~103.80,具有"C型"埃达克岩的特征.上述岩石组合及其特征均指示了弧火成岩的性质,结合构造环境判别认为该区晚侏罗世花岗岩类形成于蒙古-鄂霍茨克洋的南向俯冲有关的环境,岩浆可能源于兴安弧加厚下地壳的部分熔融作用.

The Mesozoic intrusive rocks are widely developed in Heihuashan area in the north of Heihe City,Heilongjiang Province,but the formation age,rock assemble age and genesis of the intrusive rocks are still unclear.In this paper,the intrusive rocks in Heihuashan area have been studied in the field,petrography,petrology,geochronology and petrochemistry,in order to discuss the formation age,petrogenesis and geotectonic background of these rocks,For two monzonitic granites,the weighted average ages of zircon U-Pb dating by LA-ICP-MS are 148.7±0.6 Ma and 153.50±0.56 Ma respectively,indicating that they were formed in the Late Jurassic.The intrusive rock assemblage of tonalite(T1),trondhjemite(T2),and granite(G)etc indicates a rock assembleage of T1 T2 G in arc environment.The above granitoids are rich in silicon,alkali,high potassium,peraluminium(A/CN K is greater than 1),and low in Fe2 O3 T.The rocks belong to high potassium calcium alkali series in the SiO2-K2 O diagram,low Fe-calcium alkali(LF-CA)series in SiO2-MgO diagram and calcium alkali or alkali calcium in SiO2-(Na2 O+K2 OCaO)diagram.The distribution pattern of rare earth element is right-leaning,with LREE relatively enriched and HREE depleted,giving(La/Yb)n=13.78-29.85 and no negative Eu anomaly or weak positive Eu anomaly or weak negative Eu anomaly.The granitoids are characterized by high Sr and low Y,with Sr/Y ratio ranging from 29.53 to 103.80,which are characteristic of"Ctype"adakites.The above rock assemblages and their characteristics all indicate the properties of arc igneous rocks.Combined with the tectonic environment,it is believed that the Late Jurassic granitoids in this area were formed in the southwardly subduction environment of the Mongolia-Okhotsk Ocean.The magma maybe derived from the partial melting of the thickening lower crust of Xing’an Arc.