集宁岩群孔兹岩系的变质岩石学特征和沉积环境浅析

PETROLOGICAL FEATURES OF METAMORPHIC ROCKS IN THE KHONDALITE SERIES OF THE JINING ROCK GROUP AND THE SEDIMENTARY ENVIRONMENT ANALYSIS

基于在测区内先后开展的八幅矿调项目,通过对集宁岩群孔兹岩系岩石学、地球化学特征的分析和孔兹岩系变质原岩的恢复表明:集宁岩群孔兹岩系原岩主要为中酸性凝灰岩、泥(或页)岩、白云质泥灰岩、砂岩,是一套粒度极细的碎屑沉积岩。沉积物运距离长、沉积时水动力条件较稳定,说明集宁地区在前寒午纪时一度处于较稳定的还原条件下的克拉通盆地环境。物源区岩性应为中酸性火山岩(花岗闪长岩质),且地层厚度较大,说明在元古代早期,集宁附近曾经出露过大量中酸性花岗岩。部分麻粒岩的原岩为玄武岩,表明在元古代时期华北地台西部曾经有过一定规模的基性岩浆岩侵入事件,间接揭示出华北地台克拉通化痕迹。

Based on eight maps of mineral survey projects conducted early or late in the surveyed area, analysis of petrological and geochemical features of the Khondalite series of the Jining rock group, and restructuring of the protolith of metamorphic rocks in the Khondalite series suggested that the protolith was mainly of intermediate- acid tuff, mudstone （or shale）, dolomitic muddy limestone and sandstone, a set of very fine-grained elastic sedimentary rocks. The sediments had experienced a long distance of transport and deposited in relatively stable hydrodynamic conditions, indicating that the Jining area was once in a steady reducing cratonic basin environment. The lithology of source area should be acid volcanic rock （granodioritic） and the stratum thick, a reflection of tremendous intermediate-acid granites once outcropped near Jining in early Proterozoic. Some granulites have protolith of basalts, disclosing an occurrence of a remarkable basic magmatic intrusion in west of the North China Platform in Proterozoic, indirectly unveiling the trace of cratonization of the Platform.