Latest Zircon U-Pb Age of the Baiyingaolao Formation Volcanic Rocks in the Keyihe Area of North-Central Da Hinggan Mountains

Objective Mesozoic volcanic rocks are mainly distributed in the Da Hinggan Mountains.The Baiyingaolao Formation is the main stratum in this area and has been considered to be formed in the Late Jurassic.Many scholars have researched these Mesozoic volcanic rocks in this area,which have been much debatable（Zhang Xiangxin et al.,2017）.A series of studies focusing on the Baiyingaolao Formation volcanic rocks in the middle-south section of

The Middle Devonian Bimodal Association of Volcanic Rocks in the Northern Area of East Junggar, Xinjiang

The Middle Devonian volcanic rocks in the northern area of East Junggar, located between the Ertix andUlungur rivers of northern Xinjiang, may be divided into basic and acid ones. It is evident that a compositionalgap exists between the two groups so that the volcanic rocks are not in line with a calc-alkaline series becausethe intermediate rocks are absent in the area. The fact shows that the volcanic rocks are a typical bimodal asso-ciation. The formation of the bimodal association of volcanic rocks in the area was closely related to continen-tal rifting or continental extension in the Middle Devonian. In such a tectonic setting, magmas were first pro-duced by partial melting of the mantle. Where crustal thinning was greater, the magmas ascended and eruptedon the surface directly so that the basic volcanic rocks formed, but olivine and/or partial pyroxenefractionation occurred in the magmas during their ascent through the thinning crust. On the other hand, wherecrustal thinning was less, ascending mantle-derived magmas reached the lower crust and accumulated there, re-sulting in partial melting of the lower crust and thus giving rise to the contaminated magma which was consoli-dated as acid volcanic rocks on the surface.

Petrology and Geochronology of Monzonite Porphyry Intruding in Xiong'er Volcanic Rocks in Xiaoshan Area, Western Henan Province

Xiong’er volcanic rocks cover an area of more than6×104 km2 along the southern margin of North China Craton.The Xiong’er group has been divided,from bottom to top,into the Dagushi,Xushan,Jidanping and

New Zircon SHRIMP U-Pb Ages of the Langjiu Formation Volcanic Rocks in the Shiquanhe Area,Western Lhasa Terrane and their Implications

Objective The potassic and ultrapotassic rocks relating to the India-Eurasia collision and continual plate convergence are widely distributed in the Lhasa terrane. These rocks are very important to understand the deep processes of the India-Eurasia collision and the uplift and evolution of the Tibetan Plateau. Although high-potassic volcanic rocks are also exposed in the western Lhasa terrane, their formation time is still uncertain for the lack of reliable dating. We carried out zircon U-Pb geochronological study on the Langjiu Formation volcanic rocks, which are part of the Early Cretaceous Zenong group volcanic rocks based on 1：250000 scale Shiquanhe regional geological survey report, in the Shiquanhe area of the western Lhasa terrane. These new age data not only offer chronological basis for the regional stratigraphic correlation and classification, but also provide an essential opportunity for revealing signatures of magmatic pulses hidden in the deep crust of the Lhasa terrane.