Zircon SHRIMP U-Pb data and regional contrasts of geochemical characteristics of Linzizong volcanic rocks from Konglong and Dinrenle region, middle Gangdese belt

This study reports the whole-rock geochemical and zircon U-Pb geochronological data of Linzizong Volcanic Succesion (LVS) outcropped in Konglong-Dingrenle region of the middle Gangdese belt. Zircon U-Pb dating results indicate that acidic detritus crystal ignimbrite (LZ06022-2) collected from bottom layer of the Nianbo Formation yields an age of 59.64 +/- 0.72 Ma, and that andesitic crystal tuff (LZ06017-4) sampled from bottom layer of the Dianzhong Formation was emplaced around 69.97 +/- 0.72Ma. This is the oldest age for LVS. Combing with previously reported volcanism, geochemical and chronological date, it is revealed that the volcanic activity characteristics are different from early to late and east to west of the Gangdese. First, the eruptive patterns of volcanism of Linzizong volcanic successions mainly include extrusive and explosive facies. The volcanic explosivity index is getting weaker from early to late, which means the eruptive patterns change from explosion facies-dominated of the early Dianzhong Fromation to extrusion facies of the late Pana Formation. Second, under the time evolution the volcanic activity changes from intensive to weak. In the early, the east area is more intensive than the middle and west area. But, in the interim, the west area is more intensive than the other. To the late stage, the volcanic activity of whole Gangdese is weak. The volcanism of the Nianbo Formation is the most intensive, frequent and long lasting in the middle belt of LVS. The early stage of LVS is mainly basic, middle stage and late stage is prevailed by neutral and acidic rock types. Respectively, the total alkali content is increasing, and the rock series also change from calc-alkaline to high potassic calc-alkali to shoshonite. Third, LVS has the characteristics of epicontinental arc volcanic rocks, and it is the product of India-Asian continent collision. The starting time of collision for the west, middle and east area is different. In the contrast, the middle belt is slightly earlier than that of the eastern and western part.