沙漠、戈壁和黄土表土岩石磁学特征及其对黄土磁化率机制的意义  

Rock magnetic properties of deserts,gobi and loess topsoils and their implications in models of magnetic susceptibility

作　　者：毛学刚[1,2] 赵丽娟 Mao Xuegang;Zhao Lijuan(School of Geographical Sciences/,Fujian Normal University,Fuzhou 350007,China;Institute of Geography,Fujian Normal University,Fuzhou 350007,China)

机构地区：[1]福建师范大学,地理科学学院,福建福州350007 [2]福建师范大学,地理研究所,福建福州350007

出　　处：《中国沙漠》2022年第2期183-193,共11页Journal of Desert Research

基　　金：福建省自然科学基金项目(2020J01141);国家自然科学基金(42130507)。

摘　　要：黄土高原黄土来自于其北部或西北部的沙漠和戈壁被广泛认可。本文选取西北地区典型的沙漠、戈壁和黄土表土样品,进行系统的岩石磁学研究。结果显示:沙漠和戈壁磁学特征相似,以磁铁矿占绝对优势,磁颗粒为多畴和假单畴,几乎不含超顺磁颗粒,磁性矿物总体含量高于黄土表土。黄土表土以磁铁矿为主,同时含有磁赤铁矿,磁颗粒以成壤过程中形成的超顺磁和单畴颗粒为主。虽然沙漠和戈壁细粒中亚铁磁性矿物相对比例明显高于粗粒,但粗粒组分含量大,对磁性稀释作用显著,全样总体表现为粗粒磁性特征。影响沙漠、戈壁和黄土磁化率的主导因素不同,沙漠和戈壁为磁性矿物含量主导型,磁性矿物总含量高,黄土表土为磁性矿物粒度主导型,超顺磁对磁化率贡献占主导。合理区分风速论和成土论两种磁化率机制,需准确判断成壤程度和氧化还原状态。因此,不同环境条件下磁化率的环境意义及古气候重建,需首先准确区分影响磁化率的主导因素。It is widely accepted that the loess on the Chinese Loess Plateau is derived from dust accumulation from the northern or eastern deserts and gobi.In the present study,typical samples of deserts,gobi and loess were collected and measured for rock magnetic measurements,and the mechanism of magnetic susceptibility was discussed as well.The results showed that the deserts and gobi samples were dominated by magnetite of multi domain(MD)and pseudo single domain(SSD)size with no ultrafine magnetic particles formed during pedogensis.The magnetic concentration of deserts and gobi was higher than loess topsoil.The loess topsoil was dominated by magnetite with presence of maghemite.Single domain(SD)and superparamagnetic domain(SP)size formed during pedogensis contributed considerably to the magnetic susceptibility of loess topsoil.Although the concentration of ferrimagnetic minerals was higher in the fine particles than the corresponding coarser ones,the magnetic properties of deserts and gobi samples displayed similarities to coarser particles,because the bulk samples were dominated by coarse particles.The magnetic susceptibility values of deserts,gobi and loess were similar but the critical factors could be different.The critical factor controlling the magnetic susceptibility of deserts and gobi was magnetic content due to high concentration of coarse magnetic particles.The critical factor controlling the magnetic susceptibility was magnetic domain size due to ultrafine particles formed during pedogensis.The pedogenic development and redox states could be used to distinguish pedogensis model and wind-vigour model of magnetic susceptibility.Therefore,the critical factors should be distinguished when interpreting different environments and reconstructing paleoclimate using the magnetic susceptibility.

关 键 词：黄土 磁化率 沙漠 成壤作用 

分 类 号：P56[天文地球—构造地质学]