月球陨石NWA 11801中火山玻璃的特征与成因

Characteristics and petrogenesis of volcanic glasses in lunar meteorite NWA 11801

对月球陨石NWA 11801开展了详细的岩石矿物学研究,发现了24颗玻璃,其中9颗玻璃成分相近。其主量元素Mg、Al、Ca和Fe的成分及微量元素Mn、Cr等的成分都分布在一个较小的范围内,且MgO/Al_(2)O_(3)=1.31~1.54,落在月球火山玻璃范围(>1.25),故这9颗玻璃为火山玻璃。然而,它们在结构上具有一定变化,其内部微晶的数量和形态表现出差异性,这些差异性是由于冷却环境不同造成的。因此,9颗火山玻璃的结构和成分特征表明,它们可能是同一岩浆喷发形成,但喷出后玻璃形成的环境温度条件不同。另外,在其中一颗火山玻璃中发现了橄榄石斑晶,橄榄石呈自形晶且Fo值(76.4 mol%~78.2 mol%)较高,可能表明这些橄榄石来自于月球内部,记录了月球岩浆结晶和演化的过程。

A detailed petrological and mineralogical study of lunar meteorite NWA 11801 has found 24 glasses,nine of which have similar compositions.The chemical composition of nine glasses are similar,and their elements(for example major elements of Mg,Al,Ca,Fe and trace elements of Mn,Cr,etc)are distributed in a small area.They have MgO/Al_(2)O_(3)=1.31-1.54,which falls in a range of lunar volcanic glasses(MgO/Al_(2)O_(3)>1.25),so nine glasses are volcanic glasses.However,they have certainly discrepancy in the structure,the number and morphology of the internal microcrystals of volcanic glasses,these differences are caused by different cooling environment.Therefore,the features of structure and composition of nine volcanic glasses indicate that they may be from the same source of magma eruption and form in the different cooling environment.In addition,olivine phenocrysts are found in a volcanic glass.The olivines are euhedral with a high Fo value(76.4 mol%-78.2 mol%),indicating that olivines come from the interior of the moon and record the crystallization and evolution of lunar magma.