宁芜地区中生代富钾和富钠火山岩的源区特征:岩石学和地球化学证据

发布时间：2018-03-14 15:16

本文选题：火山岩　切入点：安山玢岩　出处：《岩石学报》2017年02期 　论文类型：期刊论文

【摘要】：宁芜中生代火山盆地广泛产出早白垩世中基性火山岩,钾质岩石主要为龙王山组英安岩、粗安岩,钠质火山岩主要为大王山组玄武粗安岩、粗安岩、英安岩以及钠质安山玢岩类。钠质辉石安山玢岩的锆石U-Pb年龄为128.9±1.9Ma,为早白垩世产物。稀土元素球粒陨石标准化配分曲线均表现为一致的平缓右倾型式,Eu负异常不明显,富集大离子亲石元素,亏损高场强元素,具Nb、Ta的负异常。钾质龙王山组火山岩总体Cs、Rb、Ba、Th、U等LILE含量较钠质大王山组火山岩和钠质安山玢岩高,并具有较高的Si、K,较低的Ca、Mg,高Rb/Sr,高Isr(0.70521~0.70857);钠质火山岩具有较低的Si、富Na、高Sr、低I_(sr)(0.70544~0.70768),Mg~#相对较高。钠质辉石闪长玢岩斑晶中有斜长石的矿物结构和成分不平衡现象,锆石Hf同位素特征为ε_(Hf)(t)=-6.2~+0.6,变化较大,指示岩浆混合过程。地幔源区可能是由中元古代俯冲板块释放出流体发生交代作用后形成的富集地幔,钾质火山岩地幔源区交代矿物可能以金云母为主,崆岭群TTG片麻岩为其地壳端元。而钠质火山岩地幔源区交代矿物可能以角闪石和单斜辉石为主,中元古上溪群变质基性岩或新生下地壳基性岩为其地壳端元。
[Abstract]:In the early Cretaceous Mesozoic volcanic rocks, the potash rocks are mainly composed of Longwangshan formation, trachyandesite and sodium volcanic rocks, which are mainly composed of Black Tortoise trachyandesite and trachyandesite of the Dawangshan formation. The zircon U-Pb age of sodium pyroxene andesite porphyrite is 128.9 卤1.9 Ma. it is the product of early Cretaceous. The standardized distribution curves of chondrites of rare earth elements all show that the flat right-dip type of EU negative anomaly is not obvious. It is enriched in large ion lithophile elements, depleted in high field strength elements, and has negative anomalies of NB Ta. The total LILE content of volcanic rocks of the potassium Longwangshan formation is higher than that of sodium Dawangshan formation volcanic rocks and sodium anandesite porphyrite, and the total LILE content of the volcanic rocks of the kalium Longwangshan formation is higher than that of sodium dawangshan formation. It also has higher Si-K, lower Ca-Mg, higher RB / Sr, higher Isrn 0.70521 + 0.70857, and lower Si-rich, Na-rich, high-Sr-0.705440.70768 Mg#. The mineral structure and composition of plagioclase in porphyrite porphyry of sodium pyroxene are unbalanced, and the mineral structure and composition of plagioclase are out of balance in the porphyrite porphyrite of sodium pyroxene, and the mineral structure and composition of plagioclase are unbalanced in the porphyry of sodium pyroxene, and the mineral structure and composition of plagioclase in the porphyry of sodium pyroxene are not balanced. The isotopic characteristics of zircon HF are 蔚 ~ (-1) HflT ~ (-2) -6.2 ~ 0.6, indicating the magmatic mixing process. The mantle source region may be a enriched mantle formed by the metasomatism of the fluid released from the Mesoproterozoic subduction plate. The metasomatic minerals in the mantle source of the potash volcanic rocks may be mainly phlogopite, while the TTG gneiss of the Kongling group are the end elements of the crust, while the metasomatic minerals in the mantle source of the sodium volcanic rocks may be mainly amphibole and clinopyroxene. Metamorphic basic rocks of Mesoproterozoic Upper Stream Group or Neo-Lower crustal basic rocks are the end elements of their crust.
【作者单位】：桂林理工大学地球科学学院;北京大学地球与空间科学学院;合肥工业大学资源与环境工程学院;
【基金】：国家自然科学基金项目(41530206) 桂林理工大学科研启动费资助项目联合资助
【分类号】：P588.14

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