摘要
大兴安岭南段黄岗梁火山-侵出隆起由火山灰流相的流纹质晶屑凝灰岩、侵出相的岩穹(流纹质碎斑熔岩)和浅成侵入相的斑状二长花岗岩构成,它们的SHRIMP锆石U⁃Pb定年结果分别为140.27±0.93 Ma、140.41±0.92 Ma和141.75±0.96 Ma,均属早白垩世初期岩浆活动的产物。3个岩相的同位素年龄在误差范围内一致,表明其间没有明显的间断,为粘稠的富晶岩浆(晶粥)连续作用的产物。这些火山-侵入杂岩属高钾钙碱性系列,主要为准铝质-过铝质岩石,它们的εNd(t)变化范围很小,为-0.43~-0.08,相应的二阶段模式年龄为0.98~0.96 Ga,表明其应起源于相同的源区。岩浆作用产物表现出从早到晚SiO_(2)和K_(2)O含量呈连续降低的趋势,不同岩相间成分上有一定的互补关系,暗示可能是由成分分带的岩浆房近于逐层排出/侵位形成流纹质晶屑凝灰岩和碎斑熔岩,残留岩浆充填到火山根部及火山机构周边的环状裂隙中冷却固结形成斑状二长花岗岩。该火山-侵入杂岩具有A型花岗岩特征,地球化学上均表现为富集Rb、Th、U等大离子亲石元素,强烈亏损Ti、Nb、Ta等高场强元素,具有明显负Eu异常,稀土元素配分图呈右倾的V字型,其可能是早白垩世软流圈上涌或者幔源镁铁质岩浆的底侵作用,诱发上覆地壳发生部分熔融形成的。
Huanggangliang volcanic⁃extrusive uplift in the southern Da Hinggan Mountains is composed of the rhyolitic crystalline tuff of the ash flow facies,the dome of the extrusive facies(rhyolite porphyroclastic lava),porphyritic monzogranite of the superficial intrusive facies.Their SHRIMP zircon U⁃Pb ages are 140.27±0.93 Ma,140.41±0.92 Ma and 141.75±0.96 Ma respectively,which were produced by magmatic activities in Early Cretaceous.The isotopic ages of the three lithofacies are consistent within the error range,indicating that there is no obvious discontinuity between the three lithofacies,and they are the products of continuous action of thick rich crystal magma(crystal mush).These volcanic⁃intrusive complexes belong to the high⁃K calc⁃alkaline series,and are mainly peraluminous and quasi⁃aluminous rocks,theirεNd(t)change little which range from-0.43 to-0.08,and the corresponding two⁃stage Nd model ages range from 0.98 to 0.96 Ga,suggesting that originated from the same source region.The contents of SiO_(2) and K_(2)O in magmatic products decreased continuously from early to late,and there is a certain complementary relationship between the compositions of different lithofacies,suggesting that rhyolitic crystalline tuff and rhyolite porphyroclastic lava may be discharged/emplaced layer by layer by magma chamber of composition zonation,and the residual magma is filled into the ring fissure of volcanic root and surrounding to form porphyritic monzogranite.The volcanointrusive complex have the characteristics of A⁃type granite,which are characterized by LILE(Rb,Th,U,etc.)enrichment and HFSE(Ti,Nb,Ta,etc.)strong depletion,and en⁃riched LREE patterns with strong negative Eu anomaly,and its genesis may be related to partial melting of the overlying crust induced by the upwelling of asthenosphere mantle or mafic magma underplating in the Early Cretaceous.
作者
苏荣昆
薛怀民
曹光跃
SU Rong-kun;XUE Huai-min;CAO Guang-yue(Institute of Geology,Chinese Academy of Geological Science,Beijing 100037,China;Beijing SHRIMP Center,Institute of Geology,Chinese Academy of Geological Science,Beijing 100037,China)
出处
《岩石矿物学杂志》
CAS
CSCD
北大核心
2022年第4期727-745,共19页
Acta Petrologica et Mineralogica
基金
中国地质调查局项目(DD20190001,DD20190370)。
