黑龙江多宝山地区晚三叠世岩浆活动对蒙古—鄂霍茨克洋南向俯冲的响应

近年来相继在嫩江多宝山地区发现了一系列晚三叠世岩浆岩。但该期岩浆活动的构造背景、成因机制及成矿作用迄今尚未得到很好的解读,这些问题对深入理解该地区构造演化、寻找多金属矿产具有重要意义。本文以多宝山矿区英云闪长岩、争光矿区闪长岩为研究对象进行系统的岩石学、地球化学及同位素年代学研究。锆石的LA-ICP-MS定年结果表明,多宝山英云闪长岩形成时代为(226.3±2.3) Ma,争光闪长岩形成时代为(229.3±3.1) Ma,两者在误差范围内一致,可能是同一岩浆房演化的产物。地球化学特征显示,多宝山英云闪长岩以高SiO₂(64.25%~66.44%)、Al₂O₃(16.54%~17.21%)、K₂O+Na₂O(8.16%~8.49%),低CaO(2.27%~2.95%)、MgO(0.99%~1.16%)、TiO₂(0.31%~0.36%)、P₅O₂(0.16%~0.17%)为特征;争光闪长岩以SiO₂(57.12%~58.5%)、Al₂O₃(14.59%~15.26%)、(Na₂O+K₂O)(5.34%~6.16%)、 TiO₂(0.83%~0.97%)、P₂O₅(0.15%~0.27%)及TFeO/MgO(1.12~1.25)相近为特征;多宝山英云闪长岩亏损Rb、Nb、Sm,富集Ba、U、Zr和Sr,Eu正异常明显(δEu=1.21~1.57),争光闪长岩Rb、Nb、Sm亏损,Ba、Th、Sr、Hf富集,Eu弱正异常(δEu=0.93~1.22)。二者富集轻稀土元素(LREE),亏损重稀土元素(HREE),稀土及微量曲线形态近似,显示同一源区的特征,原始岩浆起源于受俯冲流体交代的地幔楔的部分熔融,形成于与蒙古—鄂霍茨克洋板块俯冲有关的活动大陆边缘环境。多宝山矿集区晚三叠世钙碱性岩浆岩的确定指示蒙古—鄂霍茨克洋俯冲作用可影响到兴安地块东缘。综合区域晚三叠世矿床成矿时代及成矿背景,证实多宝山地区晚三叠世岩浆活动具有较强的银铜钼成矿能力,成矿潜力巨大。

Late Triassic magmatic activity in Duobaoshan area,Heilongjiang Province:Response to the southward subduction of the Mongol-Okhotsk Ocean

Late-Triassic magmatic rocks have been discovered in recent years in the Duobaoshan area of Nenjiang. So far, the tectonic setting, genesis and metallogeny of the magmatic activity have not been well understood, which significantly hindered our understanding of the regional tectonic evolution and prospecting for polymetallic deposits in this area. In this paper, we conducted systematic petrological, geochemical and geochronological studies of tonalite in the Duobaoshan deposit and diorite in the Zhengguang deposit. LA-ICP-MS zircon U-Pb dating yielded an age of (226.3±2.3) Ma for the Duobaoshan tonalite and (229.3±3.1) Ma for the Zhengguang diorite, indicating the two minerals, with similar formation age, are probably derived from the same magma chamber. The tonalite had elevated SiO₂ (64.25%-66.44%), Al₂O₃ (16.54%-17.21%), (K₂O+Na₂O) (8.15%-8.50%) and low CaO (2.27%-2.95%), MgO (0.99%-1.16%), TiO₂ (0.31%-0.36%) and P₅O₂ (0.16%-0.17%) contents comparable with the diorite whose major element contents were SiO₂ (57.12%-58.5%), Al₂O₃ (14.59%-15.26%), Na₂O+K₂O (5.34%-6.16%), TiO₂ (0.83%-0.97%), and P₂O₅ (0.15%-0.27%), with similar FeO/MgO (1.12-1.25) ratio. The Duobaoshan tonalite is characterized by depletions of Rb, Nb, and Sm, enrichments of Ba, U, Zr and Sr, and obvious positive Eu anomaly (δEu, 1.21-1.57). The Zhengguang diorite is characterized by depletion of Rb, Nb and Sm, enrichment of Ba, Th, Sr, Hf, and weak positive Eu anomaly (δEu, 0.93-1.22). Both tonalite and diorite are rich in light rare earth elements (LREE) and depleted in heavy rare earth elements (HREE), and have similar curve pattern on REE or trace element diagrams suggesting a common magmatic source. The magma probably derived from the partial melting of the mantle wedge metasomatized by the subduction fluid dehydrated from the downward moving Mongol-Okhotsk plate. The confirmation of the calc-alkaline magmatism in the Duobaoshan district indicates the subduction of the Mongol-Okhotsk oceanic plate can have remote influence, reaching as far as the eastern margin of the Xing’an Block. By compiling the metallogenic ages and background of the Late Triassic deposits in the study area, we can show that the Late Triassic magmatic activity in Duobaoshan area has great Ag-Cu-Mo mineralization ability and the study area has high exploration potential.