Study Of Qixiangzhan Silicic Lava Flows Of Tianchi Volcano In Changbaishan Area

Qixiangzhan silicic lava flows of the Tianchi volcano, Changbai Mountains, locate in the north of the Tianwengfeng. It is erupted from Qixiangzhan parasitic crater. Previous workers mainly studied Qixiangzhan silicic lava flows as the part of Tianchi volcano. But the emplacement mechanism of the silicic lava flows is poorly known. Through careful investigation in the field, the emplacement of silicic lava flows is discussed. On the basis of the analysis of petrography, mineralogy and major element of the profiles by means of optical microscope and electron probe microanalyser (EPMA) , the author studys the internal textures of the lava flows, especially its mineralogical and geochemical characteristics. Furthermore, the comparison is carried out between Qixiangzhan volcanic rocks and pantellerite from Pantelleria Volcano, Italy. Some new ideas and conclusions are obtained:1. The lava flows include the thick layers and thin layers, and the well-developed flow banding is present. The obsidian appears on the top and the bottom of lava flow unit.2. The petrological textures of lava flows consist of porphyritic texture, glomeroporphyritic texture, spherulitic texture, and the groundmass typically consists of microlites and glass.3. The chemical compositions of rock-forming mineral from the Qixiangzhan volcanic rocks have been determined by EPMA and systematically studied. This indicates that sanidine, hedenbergite, fayalite, arfvedsonite, ferrorichterite, quartz and ilmenite predominates in the lava flows.4. The comparison between the comendite from Qixiangzhan Tianchi Volcano and the pantellerite from Pantelleria Volcano, Italy, indicates that the comendite from Qixiangzhan is characterized by the enrichment in Si,Al,K,Mg,Ca and P, and the depletion in Fe,Na,Mn and Ti.