Tectono-stratigraphic Features Of The Yanbian Group And Their Geotectonic Implications

The Grenville-aged orogen is a tie to link most of the continental blocks in Rodinia, which existed during the period from late Mesoproterozoic through early Neoproterozoic. The position of Yangtze Block in Rodinia have been warmly discussed in the recent years. More and more evidences suggest that the fold basement of Yangtze Block is an integral part of the Grenville-aged orogen. The Yanbian Group, which resulted from post-Grenville orogen, outcrops in the Panzhihua area, Sichuan province. Hence, the studies on the geological features and geotectonic implications of the Yanbian Group can provide some clues to refine the position of Yangtze Block in Rodinia.Based on the field working and lab analysis, the following conclusions were made:1. The anatomy of small-scale to meso-scale deformational structures have resulted in the reconstruction of the structural framework of the Yanbian Group. The statistical analyses of the fold hinge and cleavages developed in the Yanbian Group suggest the trend of the first stage penetrating structures of the Yanbian Group is EEN-WWS.2. Based on the new structural framework and the overlap relationships in every continuous outcrop, the new stratigraphic sequence of the Yanbian Group is put forward, which deeply changes the rock composition of every formation.3. The analysis of the geochemical and petrologic characteristics features shows that the assemblage of volcanic rocks is the series of middle ocean ridge basalt, ocean island basalt and ocean island andesite basalt, which implies that it is the relic of the ocean crust, i.e. typical ophiolites. The primitive study on the emplacement mechanism suggests that the volcanic rocks had underwent the stages of the trench accretion and the basement of forearc basin, which received the elastics of the Yanbian Group.4. Triangular diagram of the sandstone clastic compositions and the relationship diagram of major element suggest that the proto basin of the clastic rock of the Yanbian Group was a forearc basin, which was in an active continental margin.Based on the above conclusion, the regional expression of the Grenville-aged orogen in the Kangdian Area and orogenic architecture is also discussed, and the refining position of Yangtze Block in Rodinia is proposed...