运用定量化结构分析方法揭示蚀变花岗斑岩的形成过程——以新疆莫阿特茂金岩体为例

Using quantitative textural analysis method to reveal the formation of altered granite porphyry:A case study from Maojin intrusions,Moate,Xinjiang

地球化学分析方法已广泛运用于火成岩成因的研究中,但对于一些蚀变较严重的岩石,有时仅通过地球化学分析难以还原岩浆固结的过程。火成岩定量化结构分析方法是通过对岩石中矿物的定量分析(诸如晶体粒度分布分析,晶体空间分布分析,以及晶体定向程度分析等),从而反演岩浆固结过程中发生的动力学过程。这种方法很好地避免了蚀变作用对还原岩体形成过程所产生的诸多影响。本文运用火成岩定量化结构分析方法,对新疆莫阿特茂金花岗斑岩体钻孔中10个样品的钾长石斑晶和石英斑晶分别进行分析。尽管这些样品普遍发生了碳酸盐化蚀变作用,定性观察中结构特征也比较均一,但是钾长石和石英斑晶的定量化结构数据及其在钻孔深度(约170 m)范围内的变化趋势显示,茂金花岗斑岩体可能至少由4次脉冲岩浆叠加形成,每股岩浆中心的CSD曲线小晶体缺乏,发生了粗化现象。由于脉冲式岩浆多次注入,导致的温度振荡加剧了矿物粗化。脉冲岩浆中心处斑晶体积含量的增加,可能与岩浆流动过程中对大晶体的影响有关,80 m深度以下脉冲岩浆接触带的斑晶体积含量明显增加,是由于机械压缩导致的。

Geochemical analysis method has been widely used for the study of igneous origin,but sometimes it is difficult to restore the process of consolidation of the magma only by geochemical analysis method for some serious altered rocks.Dynamic processes of magma consolidation can be inversed by quantitative textural analysis method through the quantitative analysis of minerals in the rock （such as crystal size distribution analysis,spatial distribution pattern analysis,and crystal alignment factor analysis）.Using this method can avoid the interference of alteration during the formation process restore of rock.In this study,we use quantitative textural analysis method of igneous to quantify the K-feldspar phenocrysts and quartz phenocrysts from 10 samples in the drilling through the granite porphyry of Maojin,Moate,Xinjiang.Although these samples generally occurred carbonate alteration,and textural characteristics seem homogeneous during qualitative observation,but according to the quantitative textural parameters and the trends within the scope of drilling depth of K-feldspar phenocrysts and quartz phenocrysts show that Maojin granite porphyry may potentially be fed by four pulses of magma,the CSDs at the center of each pulse show an absence of small crystals,where it occurs textural coarsening.Coarsening is greatly accentuated by temperature oscillations due to the multiple reinjections of the successive batches of magma.The modal abundance of phenocrysts at the center of each pulse of magma increases,may be associated with magma flow,which significantly affects large crystals.The modal abundance of phenocrysts at the contact zone between the pulses of magma below the depth of 80 m increases significantly,which is due to mechanical compaction.