西南天山托云中新生代火山岩盆地响岩的岩石成因研究

响岩代表了陆内火山岩省钠质碱性岩浆最终端的演化产物，揭示其成因机制对认识陆内火山岩省的岩浆演化过程具有重要意义。文章对出露在我国境内西南天山托云中新生代火山岩盆地的响岩开展了系统的矿物学、岩石学和地球化学研究，以揭示托云火山岩岩浆系列特征和岩浆演化过程。托云响岩以发育碱性长石、单斜辉石、铁橄榄石和角闪石斑晶为特征，在基质中可见霞石。在地球化学组成上，托云响岩以高的Na₂O含量(7.9%～8.6%)和K₂O含量(5.2%～6.3%)为特征，∑REE变化范围为408×10^-6～470×10^-6,稀土元素配分曲线具有明显的Eu异常，在原始地幔标准化的微量元素蛛网图上，样品显示出Ba、Sr、P、Ti的负异常和Nb、Ta、Zr、Hf的正异常特征。亏损的Nd同位素组成表明其成因与共生的碧玄岩有紧密的成因联系，经MELTS热力学模拟，响岩可由碧玄岩经碱性长石(36%)、单斜辉石(21%)、尖晶石(10%)、铁橄榄石(6%)和角闪石(5%)的分离结晶作用形成，进一步的EC-AFC模拟表明，响岩在形成过程中受到一定程...

Petrogenesis of the phonolite in the Tuoyun Mesozoic-Cenozoic volcanic basin, Southwestern Tianshan Mountains

Phonolite represents the final evolution product of the sodic alkaline magma in the continental volcanic province, and revealing its genetic mechanism is of great significance for understanding the magmatic evolution process of the continental volcanic province. A systematic mineralogical, petrological and geochemical study of the phonolite exposed in the Tuoyun Mesozoic-Cenozoic volcanic basin in the Southwestern Tianshan Mountains, China, has been carried out to reveal the magma series and magmatic evolution process of Tuoyun volcanic rocks. Tuoyun phonolite is characterized by the presence of alkali feldspar, clinopyroxene, fayalite and amphibole phenocrysts, and nepheline can be seen in the groundmass. In terms of geochemical composition, Tuoyun phonolite is characterized by high Na₂O (7.9%~8.6%) and K₂O (5.2%~6.3%). The total rare earth element ranges from 408×10^-6 to 470×10^-6, and the chondrite-normalized REE patterns have obvious Eu anomaly. In the primitive mantle-normalized trace element spider diagram, the samples show negative anomalies of Ba, Sr, P, Ti and positive anomalies of Nb, Ta, Zr and Hf. The depleted Nd isotopic composition shows that phonolite is genetically related to the associated basanite. Based on the MELTS thermodynamic simulation, the phonolite could be produced by the basanite through fractional crystallization of alkali feldspar(36%), clinopyroxene (21%), spinel (10%), fayalite (6%) and amphibole (5%). Further EC-AFC modeling exhibits that the phonolites has suffered crust contamination to some degrees(10%) during the evolution. The study shows that the Tuoyun volcanic rocks belong to the peralkaline series of basanite-phonotephrite-phonolite, and the phonolite represents the final evolution product of the peralkaline rock series in Tuoyun volcanic basin.