关键词: 华北, 中元古界杨庄组, 岩石特征, 火山活动

Abstract: The Meso-and Neoproterozoic section of Jixian in Tianjin, China is highly worthy of integrated research, in which the Yangzhuang Formation takes the role of linking the old and new strata. The thickness of Yangzhuang Formation is small compared with the whole Proterozoic section, but it has multiple types of rocks with special origins. The main kinds of rocks include carbonate rocks, tuffite, siliceous rocks and quartz sandstone. Carbonate rocks are predominantly composed of intra-clastic dolostone, chert dolostone and sand-bearing dolostone. Tuffite is formed by the combination of volcanic ashes and carbonate mud. The thin-bedded siliceousrocks include chert and depositional quartz with textures of oolite and pebble. The quartz sandstone appears in the upper member of Yangzhuang Formation as thin-bedded strata with double peaks of grain size distribution. The petrology reveals that the sedimentary environment of the study area is carbonate tide-flat and shallow sea which is also strongly affected by the volcanic materials and wind-brought clastics during the period of Yangzhuang. The mentioned volcanic activity in Yangzhuang Formation is expected to propel the study of the Proterozoic chronology and tectono-sedimentary evolution of North China.

Key words: North China, Mesoproterozoic Yangzhuang Formation, petrology, volcanic activity