湖南宁乡钾镁煌班岩中火山微球粒的初步研究

本次研究从钾镁煌斑岩中挑选出上万个微球粒进行了系统研究。微球粒有三种：无磁性无色透明一半透明浅贡色、棕褐色至不透明黑色；弱磁性－强磁性黑色；强磁性钢灰色铁质。除微球粒外，还有岩浆溅射碎片和炉渣状溅射碎片等火山尘。微球粒具有火山喷发条件下可出现的多种多样的表面结构和内部结构。其化学成分主要为（１）贫铁型，富Ｓｉ、Ｍｇ、Ｃａ、Ｐ，贫Ｔｉ、Ｍｎ、Ｋ；（２）富铁型，富ＳＩ、Ｔｉ、Ｍｎ、Ｋ，贫Ｃａ、Ｍｇ、Ｐ

A Preliminary Study of Volcanic Microspherolites from Lamproite, Ningxiang County,Hunan Province

A large number of microspherolites selected from Ningxiang lamproite, Hunan Pro-vince, South China, were examined and analysed by several approaches. In terms of their physical properties and chemical compositions, three groups of microspherolites can be distinguished. They are considered as volcanic microspherolites although those from sedimentary rocks and ocean floor are traditionally attributed to cosmic dusts. The microspherolites are described as of the following three groups:(1)nonmag-netic group, which is colorless and transparent, pale-yellow and semitransparent to dark yellow and opaque; (2) magnetic group, which is dark in color; (3)strong magnetic group, which is steel grey and dominated by iron. In addition, some volcanic dusts,such as magmatic splashed fragments and blocks, can also be observed. The features of microspherolites are varied, and their facies and textures show evidently that they are products of volcanism. Chemical compositions of these microspherolites vary in a wide range, from iron deficiency to iron dominance: (I)Fe-poor type, which is rich in Si, Mg, Ca and P,but poor in Ti, Mn and K; (2) Fe-rich type, which is high in Si, Ti, Mn and K,but poor in Ca, Mg and P; (3) Fe-high type, which is dominated by Fe. Lamproite microspherolites are characterized by diversity both in chemical composilion and in physical properties. It is concluded that liquation took place in the magma chamber after the emplacement of lamproite magma in the deep crust, and afterwards microspherolites were formed as a result of rapid cooling and quenching during volcanic eruption.