火山岩磁化率特征及其影响因素:以准东石炭系巴塔玛依内山组为例

以准噶尔盆地东部石炭系巴塔玛依内山组火山岩为例,通过测量分析不同岩性类型火山岩磁化率,确定研究区主要类型火山岩的磁化率特征,总结磁化率的影响因素。结果表明,研究区内基性火山岩的平均磁化率为11.705×10~(-3)SI,中性火山岩的平均磁化率为6.325×10~(-3)SI,酸性火山岩的平均磁化率为0.345×10~(-3)SI,磁化率可以有效区分这三种具有不同磁性矿物组合的岩石类型。研究区火山岩受成岩作用改造强烈,其磁化率受矿物组成、成岩方式、结构构造及岩石蚀变等因素的综合影响。进一步研究发现,钙质、硅质等逆磁性矿物不同程度地交代辉石和角闪石等强磁性矿物斑晶,且作为填隙物的主要成分充填于岩石孔缝中,是致使研究区中基性火山岩整体磁化率明显偏低的主要原因。

Magnetic susceptibility characteristics of volcanic rock and their influencing factors: a case study of Carboniferous Batamayineishan Formation in eastern Junggar Basin

In order to determine the magnetic susceptibility characteristics and to summarize the influencing factors, the authors collected samples of various volcanic rocks and measured them for magnetic susceptibility from the Carboniferous Batamayineishan Formation in the eastern Junggar Basin. The average susceptibilities are 11.705×10-3 SI, 6.325×10-3 SI, and 0.345×10-3 SI for basic, intermediate, and acid volcanic rocks, respectively. The magnetic susceptibility can effectively differentiate the three types of volcanic rocks with different magnetic mineral assemblages. The volcanic rocks in the study area are strongly influenced by diagenesis, and the magnetic susceptibilities are affected by mineral compositions, diagenesis mode, texture and structure,and rock alteration. Further study shows that calcareous, siliceous and other diamagnetic minerals metasomatically replaced the strong magnetic minerals such as pyroxene and hornblende phenocrysts in the rocks at different extent and filled in the apertures as the main interstitial materials, which is the major reason that results in the obviously low susceptibilities of the basic-intermediate volcanic rocks in the study area.