【作者】 王亚飞；

【导师】 杜杨松；

【作者基本信息】 中国地质大学（北京） ， 矿物学、岩石学、矿床学， 2009， 硕士

【摘要】 宁芜盆地娘娘山组火山岩为盆地内中生代最后一期火山喷发形成的火山岩,其喷发方式与岩浆性质与前几组火山岩均有明显不同。本文对娘娘山组火山岩,尤其是第二亚旋回火山岩中的蓝方石响岩进行了详细的岩相学、地球化学和矿物学研究,取得了以下成果和认识。1、娘娘山组火山岩主要岩石类型为假白榴石响岩及蓝方石响岩,另有少量响岩质熔结凝灰岩、熔结角砾岩和粗面岩等;2、两亚旋回火山岩碱质含量变化趋势不同,假白榴石响岩更富钾,而蓝方石响岩更富钠。两亚旋回响岩均强烈富集轻稀土和大离子亲石元素,相对亏损重稀土元素,稀土元素配分曲线和微量元素蛛网图相似,表明二者源区相同;3、矿物化学及背散射电子探针分析结果表明,“蓝方石”与“黝方石”之间的关系可能为大的蓝方石斑晶内含有大量形状不规则的黝方石和方钠石,而“蓝方石”内黄铁矿和磁黄铁矿可能是“包裹体”而非“析离体”;4、蓝方石响岩的Rb-Sr全岩+单矿物内部等时线年龄为120±9Ma;5、利用矿物-熔浆温压计估算了蓝方石响岩结晶时的温压条件,并与相应的相图相验证,同时结合斑晶、加大边和基质中不同矿物的成分变化,反演了蓝方石响岩结晶过程中熔浆成分及物理化学条件的变化;6、稀土元素模拟和综合地球化学分析结果表明,娘娘山组火山岩既不可能由龙王山组、大王山组火山岩经主要斑晶矿物斜长石、角闪石和辉石平衡分离结晶作用形成,也不可能由“正常”的扬子地壳部分熔融而来,而更可能由富含大离子亲石元素源区部分熔融形成的岩浆经结晶分异作用及陆壳的同化混染作用而形成,且以结晶分异为主。更多还原

【Abstract】 The volcanic rocks of the Niangniangshan (NNS) Formation formed by the latest eruption of the Mesozoic volcanic activities in the Ningwu Basin are evidently different in volcanic eruption type and magmatic character from those of the Longwangshan (LWS), Dawangshang (DWS), and Gushan (GS) Formations formed in the early 3 volcanic eruptions. A detailed petrographical, mineralogical and petrochemical study has been carried out and contributes to the following achievements.1. The main rock types of the NNS Formation are psedoleucite phonolite formed in the 1st subcycle of eruption and hauyne phonolite in the 2nd subcycle, as well as minor phonolitic ignimbrite, rhyakkumulate, and trachyte;2. The psedoleucite phonolite is rich in potassium. In contrast, the hauyne phonolite is rich in sodium. However, both are significantly rich in LREE and LILE, relatively poor in HREE and HFSE, and greatly similar in chondrite-normalized REE patterns and TE spiderdiagrams, which may imply their same magma source region;3. The mineral chemical and thermodynamic data combined with BSE image and related diagrams support the occurrence of a large amount of irregular nosean and sodalite scattered in hauyne phenocrysts and the existence of pyrite and pyrrhotite in hauyne phenocrysts as inclusions rather than schlierens;4. Hauyne phonolite is dated at 120±9 Ma using the whole-rock plus single minerals isochron method and represents product of the early Cretaceous volcanic eruption;5. Hauyne phonolite crystallization P-T conditions have been determined using the mineral-liquid thermobarometers and are consistent with the corphase diagrams;6. The REE simulation and comprehensive geochemical analysis results indicate that the NNS Formation volcanic rocks cannot be formed by eruption of magma with composition of the LWS and DWS volcanic rocks through fractionation of the predominant phenocrysts includeing plagioclase, amphibole and pyroxene in them, or by partial melting of the "normal" Yangtze crust, but more probably by partial melting of pre-enriched mantle source followed by crystal fractionation with slight crustal contamination.更多还原