MAGNETIC STRUCTURE OF THE CONTINENTAL CRUSTAL CROSS-SECTION IN THE CENTRAL NORTH CHINA CRATON: IMPLICATIONS FOR DEEP GEOLOGICAL STRUCTURE AND GEODYNAMICAL PROCESSES
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摘要: 为探讨华北克拉通中部地壳的磁性结构与深部地质过程之间的相互关系，测量了五台-集宁地壳剖面４４件岩石样品的磁性参量及磁滞回线．结合岩石学、地球化学及磁卫星资料的综合研究结果表明，整个断面具有明显的磁性分带结构特征．上地壳、中地壳与下地壳上部岩石饱和磁化强度（Ｊｓ）的平均值分别为５８．７Ａ／ｍ、６８１．２Ａ／ｍ与１０６８．０Ａ／ｍ，而饱和等温剩磁ＪＳＩＲＭ为４．１Ａ／ｍ、７７．９Ａ／ｍ和１３８.４Ａ／ｍ.磁性与变质相及成分对应分析显示，断面内的磁性结构主要受变质作用控制（尤其是变酸性岩与变基性岩）．Ｊｓ值的变异系数Ｖｃ，上地壳为６２．２％、中地壳为６２．５％、下地壳为１４３．７％，而ＪＳＩＲＭ值的变异系数则分别为７０７％、８６．１％、１６５.４％．中一下地壳之间Ｖｃ值的差异远大于上一中地壳，显示了地壳深部磁性强度的非均一分布特征．本区中一下地壳岩石的磁化强度明显高于秦岭造山带北缘的登封群与太华群，这一差异可能与两区地壳深部热结构的明显差异相关．结合磁卫星长波长磁异常分析推测，地壳断面中基性麻粒岩的磁性代表了区域下地壳的磁化强度，如果地壳深部的剩余磁性以热粘滞剩磁（ＴＶＲＴ）为主，则可估算出...Abstract: The saturation magnetization （Js） and saturation isothermal remanentmagnetization （JSIRM） are measured for 44 samples from the Wutai-Jining crustalcross-section in central North China Craton. Results show that rock magnetismprimarily depends on metamorphic grade and less depends on lithology. Thegreenschist-, amphibolite- and granulite-factes rocks have average saturationmagnetization （Js） of 58.7A/m, 686.2A/m and 1068.0A/m, respectively, and their JSIRMare 4.lA / m, 77.9A / m and 138.4A / m, respectively. Variation coefficients （Vc） of Jsincreases from 62.2% in the upper crust through 62.5% in the middle crust to 143.7%in the lower crust. Similarily, JSIRM increases from 70.7 through 86.1, to 165.4%. Thisdocuments considerably greater heterogeneity in the lower crust compared to the upperand middle crust. Combination with longwavelength magnetic anomalies from Magsatinfers that the Jining terrain is responsible for lower crustal magnetization in the region.If thermal viscous remanent magnetization （TVRM） is dominate component ofremanent magnetization, the total magnetization of lower crust in the central NorthChina craton may reach 4.85A / m. The value is comparable to the magnetizationof the lower crust from shield areas in other parts of the world.
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