Geological Implications of Unconformity between Upper and Middle Devonian,and 346.8 Ma Post-Collision Volcanic Rocks in Karamaili,Xinjiang
Wang Fuming
Liao Qunan
Fan Guangming
Cheng Wenjuan
Tian Jian
Chen Shuai
Wu Weiwei
Hu Chaobin
Abstract：A set of volcanic sedimentary formation outcrops in Wucaiwan,Karamaili area,eastern Junggar,composed of con-glomerate,sandstone characterized by molasse in its lower part,and intermediate-basic lava interbedded with intermediate-acidic tuff in its upper part.The volcanic sedimentary formation is categorized into the Lower Carboniferous Songkaersu Forma-tion in 1∶200 000 Karamaili Mountain report.The 1∶50 000 geological survey finds that a set of coarse conglomerate in the bottom high angle unconformably overlies the Early-Middle Devonian Karamaili Formation and contains plant fossil Prelepi-dodendron sp.of Late Devonian to Early Carboniferous.The volcanic rocks in the middle-upper part are intruded by post-collision granite of 341.1±4.0 Ma to 340.9±5.1 Ma,and its zircon U-Pb age is 346.8±3.3 Ma obtained by LA-ICP-MS.It indicates that the age of the volcanic sedimentary formation is Late Devonian-Early Carboniferous which might correspond to the Upper Devonian Keankuduke Formation in northern Junggar stratigraphic group.The volcanic rocks consist of basalt,basaltic andesite,and a handful of rhyolitic tuff,belonging to calc-alkaline and high K calc-alkaline series;and they are enriched in LILE and LREE ((La/Yb)N=2.97-6.66),depleted slightly in Nb,Ta,and depleted weakly in Zr,Ti in some samples,with Nb/U=7.43-20.88,Ce/Pb=3.17-12.45.These volcanic rocks show both intraplate and arc volcanic rock geochemistry characteristics,formed in post-collision extensional period after the closure of Karamaili Ocean before the Upper Devonian. This study determines the final amalgamation time of Karamali Ocean,an issue of wide concern.
Keywords：eastern JunggarKaramailiangular unconformitypost-collisionvolcanic rockKeankuduke Formation
Publication Date：2014-01-01
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：15( 1243-1257 )