辽东早元古代碳酸盐岩的地质地球化学特征

辽东半岛早元古宙坳拉槽内靠近优地槽一侧,分布着一套复杂碳酸盐岩系,其下部和海底拉斑玄武岩呈沉积接触,或薄互层状共存,与火山凝灰岩互层。底部碳酸盐岩主要为钙型,向上过渡为钙镁型碳酸盐,其中含有数层由海底喷气作用形成的硅质岩,上部的硅质条带状碳酸盐岩中含有条带状、条纹状喷气沉积的硫化物。碳酸盐岩系顶部为厚层质纯镁质碳酸盐岩,局部含巨厚层状菱镁矿。岩系中碳酸盐岩、硅质岩、金属硫化物的稀土特征和铁锰指数具有一致性。铅同位素研究表明它们源于下地壳。有证据显示:碳酸盐岩系是在一定水深条件下由沉积作用形成的。这和碳氧同位素碳研究的结果吻合。种种特征表明这套复杂的碳酸盐岩系具有其独特性,可能暗示着一种特殊的碳酸盐岩形成方式。

THE CEOLOGICAL AND GEOCHEMICAL CHARACTERICS OF CARBONATE IN EARLY PROTEROZOIC AULACOGEN IN LIAODONG

The complex carbonate suite,appearing upset"S"shape, distributed along the trasition belt from miosyncline to eugeosync line in Liaodong early pro-terozoic aulacogen.It occure in transition belt environment that the basement is quite active in aulacogen. The lower part of the sequence is composed of Ca-carbonate,interbedded with basic volcanic rock.tuffaceous sediment rock, formed complex thin bedded structure.The middle part consist of thick,pure dolo-carbonate,there are several silicilith beds that formed by the exhalation on the ocean bottom in it,and a companied with sulphide mineralization. The upper part of the sequence is a thick Mg-carbonate and terminated at ma-gnesite to top of the suite. The REE features and Fe-Mn indices show that the carbonate have consistency with silicilith and sulphide, the results of lead isotope stand for that the origin is deep,and the carbon-oxygen isotope figure show that the carbonate have a special genesis.