扬子克拉通太古代崆岭群角闪岩相与麻粒岩相岩石的岩石磁学研究

MAGNETIC PETROLOGY OF ARCHEAN AMPHIBOLITE-GRANULITE FACIES ROCKS FROM YANGTZE CRATON, SOUTH CHINA

提供了扬子克拉通太古代基底崆岭群２０件代表性岩石样品的密度与磁性参数的测量结果．结果表明，变碎屑岩与ＴＴＧ（英云闪长－奥长花岗－花岗间长质）片麻岩（１３个样品）的磁化率与饱和剩磁普遍大于斜长角闪岩和辉长岩．前者的磁化率与饱和剩磁平均值分别为１２１３×１０（－６）ＳＩ与１９．９４Ａ／ｍ，而后者的则为８０２×１０（－６）ＳＩ与１０．７７Ａ／ｍ．变碎屑岩与ＴＴＧ片麻岩呈明显的亚铁磁性状态；斜长角闪岩和辉长岩则以顺磁性或顺磁性与亚铁磁性混合状态分布为主．热磁分析结果表明，变碎屑岩与ＴＴＧ片麻岩的剩磁载体以磁铁矿与磁赤铁矿为主；斜长角门岩和辉长岩则明显含有磁黄铁矿与次要的磁铁矿．变碎屑岩与ＴＴＧ片麻岩的磁性具有很强的非均一性．推断崆岭群中的变碎屑岩为麻粒岩相变质级，视深度相当于大陆下地壳；而斜长角闪岩的变质级明显低于变碎屑岩，可能为角门岩相，视深度相当于中地壳．变碎屑岩与ＴＴＧ片麻岩磁性的强非均一性可能与该区后期广泛发生的混合岩化作用密切相关。

Densities and various magnetic parameters were measured for 20 representative rock samples of differing lithologies from the Archean Kongling amphibolite to granulite-facies terrain of the Yangtze Craton. Metaclastic sedimentary rocks and tonalitic-trondhjemitic-granodioritic-grantic(TTG) gneisses show values of susceptibility κand saturation isothermal remanent magetization J(rs) that are higher than those of amphibolites and gabbros. The former has κ=1213× 10(-6)SI and J(rs)= 19.94 A/m and shows clear ferromagnetic characteristics, while the latter has κ=802×10(-6)SI and J(rs)=10.77A/m and is dominated by a mixed paramagnetic and ferromagnetic behavior. Thermal magnetic analysis indicates that magnetite and maghemite of hard magnetism are the major carries of remanent magnetism in the metaclastic sedimentary rocks and TTG gneisses. In contrast, the amphibolite and gabbro contain significant amounts of magetite of soft magnetism and pyrrhotite. Magnetism of metaclastic sedimentary rocks and TTG gneisses is highly inhomogeneous, comparison with magnetic characteristics of rocks from other amphibolite to granulite facies terrains indicates that the Kongling metaclastic sedimentary rocks were subjected to granulite facies metamorphism and formed in the lower crust depth. The amphibolite underwent lower grade metamorphism of probably high-amphibolite facies and were produced apparently in the middle crust. The high inhomogeneity of metaclastic sedimentary rocks and TTG gneisses might have been associated with later, widespread migmatization of the region.