Geochronology and Genesis of Volcanic Rocks in Beitashan Formation at the Northern Margin of the Junggar, Xinjiang

详细信息   

• 责任者：Chai FengMei(Xinjiang Key Laboratory for Geodynamic Processes and Metallogenic Prognosis of the Central Asian Orogenic Belt ; Xinjiang University ; Urumqi 830049 ; China) ; Yang FuQuan
• 刊名：Acta Petrologica Sinica
• 出版年：2012
• 卷期：28(7)
• 关键词：火山岩 ; volcanic rocks ; 准噶尔盆地 ; Junggar Basin
• 页码：p.2183-2198
• 图表：illus.,3 tables,45 refs.
• 分类号：1001
• issnNo：ISSN1000-0569
• isbnNo：CN11-1922/P

摘要

LA-ICP-MS U-Pb zircon ages and geochemical data of whole rocks are reported for mafic volcanic rocks (basalts) from the Beitashan Formation at the northern margin of the eastern Junggar. The zircons with well-defined oscillatory zoning from augitophyre sample yielded mean ^{WEIGHT: normal; WORD-SPACING: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px">206}Pb/²³⁸U ages of 380.5±2.2Ma, which are

    

interpreted as the eruption age of the volcanic rocks of the Beitashan Formation. All basalt samples belong to subalkali tholeiite magma. They display obvious negative anomaly of Nb, Ta and Ti, obvious enrichment of LREE and LILEs (Ba, Sr, K, U and Pb) characteristics. They have positive ε_Nd(t) values (+6.84~+12.28) and low Sr isotopic compositions (initial ⁸⁷Sr/⁸⁶Sr values=0.703835~0.704337), indicating a deplete mantle source. The

    

regional geology and geochemical evidence indicate that these mafic volcanic rocks were generated at island arc tectonic setting and have similar magma sources. The primary magmas may have been derived from asthenosphere mantle and mantle wedge metasomatized by fluids and melts released from the subducted slab. During the cooling of magmas, they underwent crystallization differentiation of pyroxenes and plagioclase. The different volcanic rocks (eg. basalt, augitophyre, picrite and plagioclase-basalt) were likely resulted from different primary magma contents and differentiated in different magma chamber.