Geochemistry Features、Age And Geological Significance Of The Dyke Swarms At Yangyuchi Area In Northern Edge Of The Mid-Qilian Block

Intrusive rock can be emplaced in different crustal levels with the emplacement mechanism of complexity, it is often regarded as a direct geological mark of continental plate rigid and paleo stress state. At the same time, it is also an important sign of the lithosphere or crust mantle extension and paleo plate restoration. Dyke swarms as a representative of the primary magma, filling in volcanic or intrusive body supply channel, is used to invert the source area of the material composition and magmatic eruption history. Dyke swarms fill in some tectonic fissures and the special spatial distribution pattern can reflect the prevailing tectonic stress field. Meanwhile, the fissure filled by dyke swarms is a good channel for the rising of ore fluid and an effective prospecting mark. Dyke swarms at an orogenic cycle can be throughout and have a very important significancefor the reconstruction of the regional geological evolution.The dissertation identifies the spatial distribution of working area through field reconnaissance and sample collection, maps with large scale and sketches the tectonic contacts for a better area exposed. By understanding dyke swarm rock assemblages, and wall rock contact relationship, rock geochemical characteristics and isotopic geochronology, the dissertation analyzes the dyke swarm formation age and studies the dyke swarm tectonic environment and relationship with mineral resources comprehensively combined with the previous research data of dyke swarm. The dissertation gets several understandings.1. The dykes of research area are widely developed, mostly in the North West trending, of a bedding intrusive contact relationship with wall rock. They are all produced form the geological body of Ordovician and Ordovician before withdistribution of many kinds, basic, acidic and ultra-mafic.2. The geochemistry of the mafic dyke swarm is high potassium calcium alkaline basalt series. The acidic dyke swarm with per aluminous, rich silicon, petrochemical features of low magnesium, low calcium, potassium and sodium, belongs to the calcium alkaline dykes group.3. Zircons captured by dyke swarmsin research area are mostly concentrated in 460 Ma and 480 Ma ages, the crystalline rock age is concentrated in between 430Ma-440 Ma.The time period of the capture of zircon is the peak of the magma activity, and can correspond to the two periods of the magma activity in the region. Crystallization of dyke swarms into rock age are nearly the same, which formed in Lower Silurian, with a wide spectrum of dyke swarm formation times consistency, the dyke swarms in line with the characteristics of wide spectrum dyke swarms provides a chronological evidence.4.Dyke swarms formed in post collision stretching environment.Combined with chronological age characteristics, following Early Silurian period Qilian tectonic plate and the north Qilian plate subduction orogeny ended, the region gets into a relatively stable stage and gradually into the post collision(post orogenic stage, during this period the Qilian area is in the period of transition from subduction orogenic to collision orogenic.