一阶反转曲线(FORC)图的原理及应用实例

自然样品中的磁性矿物携带着丰富的环境演化信息．然而在一般情况下，自然样品的磁性是其含有的诸多磁性矿物的综合反映．为了分离这些磁信息，近年来发展了一种新的岩石磁学方法：一阶反转曲线（FORC）图．该方法不但可以确定磁性矿物矫顽力的分布以及磁性矿物颗粒之间磁相互作用的强弱，而且还可以帮助区分磁性矿物的种类和磁畴状态．本文首先详细介绍该方法的基本原理和其物理意义，在此基础上，给出了一个应用FORC图确定含铝的钛磁铁矿玄武岩样品中磁性矿物在加热过程发生转变的研究实例．在两个温度下的FORC图密度分布差的结果表明，这种新方法可以灵敏地检测样品中微弱的磁性矿物改变，因此在岩石磁学、环境磁学和古地磁学研究中具有很好的应用前景．

The first-order reversal curve (FORC) diagram: Theory and case study

The magnetic minerals in natural rocks can record variations in paleoenvironment.However,the magnetic properties of samples represent signals from the assemblage of various magnetic minerals and grain sizes of the measured samples.To circumvent this problem,the first-order reversal curve(FORC)diagram was designed recently to decode the magnetic properties of bulk samples.The FORC diagram can provide the distributions of both the coercivity spectrum and the magnetic interaction field.Moreover,it may also identify different magnetic minerals and characterize their domain status.In this paper,we firstly introduced the theory of the FORC diagram and its physical explanations.We then applied the method in detecting the thermal alteration of a basalt sample,which contains aluminum-substituted titanomagnetite.In order to further enhance the signal related to the thermal alteration upon heating,we constructed the difference of two FORC diagrams measured at two temperatures for the first time.The results show that the difference of two FORC diagrams is rather sensitive,and can diagnose even subtle changes in magnetic minerals upon heating.