论冀东地区太古宙迁西群的解体
DISINTEGRATION OF THE ARCHEAN QIANXI GROUP IN EASTERN HEBEI
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摘要: 作者通过大量野外地质调查和室内综合研究提出;冀东太古宙迁西群是由80%以上的长英质片麻岩,不足20%的上壳岩所组成。其中长英质片麻岩主要是英云闪长岩—花岗闪长岩—花岗岩组合的深成花岗杂岩;上壳岩包括层状火山—沉积岩、脉岩及基性侵入体两大类,它们均以规模不等和形态各异的包体,赋存于花岗杂岩之中。由于强烈变质和变形作用,包体被拉长并与花岗杂岩相间排列,形成沿纵横方向变化不定的“构造成分层”。因此,以往迁西群的层序划分,实际上是”构造成分层”的组合和归并,并不具有真正的地层层序的实际意义,应该予以彻底解体。Abstract: On the basis of a lot of field geological surveys and stratigraphical, petrological and petrochemical studies, it is indicated that the Archean Qianxi Group in eastern Hebei is composed of over 80% felsic gneiss and less than 20% supracrustal rocks. Felsic gneiss is mainly represented by a plutonic granite complex of the tonalite-granodiorie-granite association. The supracrustal rocks include two parts: (1) stratified volcanic rocks, volcano-sedimentary rocks and sedimentary rocks, and (2) old dyke rocks and basic stratified intrusions, which generally occur as inclusions of small sizes and diverse shapes in the granite complex. Owing to strong metamorphism and deformation, these inclusions have been stretched to different degrees and are arranged alternately with the granite complex, thus forming "structural (or deformed)-composional layers" that change erratically both longitudinally and laterally. Therefore the stratigraphic sequence of the Qianxi Group defined previously is actually the product of combination and incorporation of "structural-compositional layers" rather than real stratigraphic sequence, so should be disintegrated.