苏鲁造山带白垩系青山群流纹岩石泡构造的矿物学与地球化学特征：对石泡流纹岩成因的指示意义

石泡构造是酸性火山岩中的一种特殊原生构造，常见于流纹岩中。石泡构造成因的研究对认识流纹质岩浆性质和喷发环境都具有重要意义。然而，关于形成石泡构造的岩浆性质、形成机理及其影响因素的研究仍比较薄弱。本文以苏鲁造山带白垩系青山群流纹岩石泡构造为研究对象，通过矿物学、岩石学、地球化学等方法，对石泡构造的发育规律、石泡和石泡间胶结熔浆的矿物组成、元素变化进行了系统研究。结果表明，石泡构造流纹岩主要发育于溢流相上部亚相，石泡可划分为实心型和空心型两类。地球化学特征显示石泡流纹岩与流纹构造流纹岩属同源岩浆，石泡流纹岩经历了更高程度的分异作用。石泡构造流纹岩胶结熔浆中水含量高于下部流纹构造流纹岩的玻璃质，导致溢流相上部亚相挥发分逸出趋势相对明显，受限于富硅岩浆的高黏度，挥发分未能顺利逸出，在逸出点猝冷形成石泡壁，受瞬时应力作用和过冷程度影响，形成形态多样的空腔。随着结晶温度下降，空腔内部残余岩浆依次冷凝结晶形成玉髓或石英。石泡构造的形成意味着岩浆作用过程或者喷发环境水的加入，对于研究酸性岩浆的演化和火山喷发机制具有重要意义。

Mineralogical and geochemical characteristics of lithophysa structure of the Cretaceous Qingshan Group in Sulu orogenic belt: Implications for genesis of lithophysa rhyolite

Lithophysae is a special primary structure in acid volcanic rocks, commonly found in rhyolite. A study of genesis of lithophysa structure is significant for understanding the properties and eruptive environment of rhyolitic magma. However, research on the magmatic properties, formation mechanism and influencing factors of lithophysae formation are still limited. In this paper, considering the lithophysae of Cretaceous Qingshan Group rhyolite of Sulu orogenic belt as the research object, the development law of the lithophysae, the mineral composition and element changes of the lithophysae and the cementation slurry between the lithophysae have been systematically studied through mineralogy, petrology, geochemistry and other methods. The results indicate that the lithophysa rhyolite mainly develops in the upper subfacies of the overflow facies, and lithophysae can be divided into two types: solid type and hollow type. The geochemical characteristics show that lithophysa rhyolite and fluidal rhyolite belong to homologous magma, and lithophysa rhyolite has experienced a higher degree of differentiation. The water content in the cementation slurry of lithophysa rhyolite is higher than that of the glassy in the lower fluidal rhyolite, resulting in a relatively obvious trend of escape of volatiles in the upper subphase of the overflow phase. Due to the high viscosity of silicon rich magma, volatiles fail to escape smoothly, and a sudden cooling occurs at the escape point to form the lithophysa wall. Affected by instantaneous stress and degree of undercooling, various cavities are formed. As the crystallization temperature decreases, the residual magma inside the cavity condenses and crystallizes successively to form chalcedony and quartz. The formation of the lithophysae means the addition of water in the process of magmatism or eruption environment, which is of great significance for the study of the evolution of acid magma and the mechanism of volcanic eruption.