亚热带第四纪沉积型红土与风化壳型红土的磁学特征对比

The Magnetic Characteristics Comparison of Sedimentary Red Clay and Laterite Weathering Crust in Subtropical China

对浙江新昌玄武岩、花岗岩风化壳红土和江西南昌第四纪沉积型红土剖面的磁学特征进行了分析,结果表明,同一气候区内风化壳红土的磁学特征受母质特征影响较大。随着风化强度的增加,强磁性的玄武岩风化壳磁化率先减小后增加,磁性矿物颗粒先变粗后变细,弱磁性的花岗岩风化壳磁化率逐渐增加,磁性矿物颗粒逐渐变细。第四纪沉积型红土剖面中,均质红土磁化率远大于网纹红土,磁性矿物颗粒亦较网纹红土层细。这些差别说明了第四纪沉积型红土剖面中均质红土与网纹红土不完全相同的物质来源。

Kind of red, loose or semi-cemented sediment was widely distributed in tropical and subtropical regions of China, called Quaternary Red Clay（QRC）. The causes and definitions of QRC were argued intensely.Depends on matrix, the QRC can be broadly divided into two types, Sedimentary Red Clay（SRC） and Laterite Weathering Crust（LWC）. The SRC, development on all kinds of Quaternary sediments, always got similar profile configuration. The layer of SRC profile, from top to bottom, was Homogeneous Red Clay（HRC） or Yellow-Brown Earth（YBE）, Vermicular Red Clay（VRC） and weathered gravel or bedrock; LWC was a kind of residual soil, formed by different types of bedrock weathering and widely distributed in tropical and subtropical regions. Representative LWC profile was generally contained weathered red soil, semi-weathered layer and bedrock. In this article, magnetic characteristics of basalt and granite weathering crust in Xinchang, Zhejiang Province, Quaternary SRC in Nanchang, Jiangxi Province were analyzed. The main characteristics of LWC are that, magnetic characteristics distinction of two kinds of weathering crust in the same climate zone was relatively large and the magnetic characteristics were determined by the matrix; Magnetisability of basalt weathering crust increased after a small decrease with the increasing weathering intensity; Magnetisability of granite weathering crust increased with increasing weathering intensity. Intense weathering made mineral particles tapering and antiferromagnetic minerals reduce in these two kinds of weathering crust. The main characteristics of sedimentary red clay were that, magnetisability of HRC was greater than VRC at least one order of magnitude. The content of antiferromagnetic mineral in VRC was much greater than the HRC. The content of Pseudo-Single Domain and Multidomain grain in VRC was much greater than the HRC. The magnetic characteristics change rule in SRC did not meet with the weathering rule prove that maybe HRC and VRC got different provenance in Quaternary sedimentary red clay profile.