东北准噶尔哈旦逊石炭纪弧岩浆及堆晶柱形成机制

为了阐明东北准噶尔弧岩浆形成机制和破译中地壳P波高速块体,对哈旦逊石炭纪侵入杂岩进行了锆石U-Pb年龄(324.8～323.1 Ma)和 δ18O及 εHf(t)、矿物化学、主微量元素和Nd-Sr同位素分析.其稀土元素分布模式上凹,从闪长岩(夹带角闪石岩堆晶)到二长花岗岩的主微量元素变异可以用两阶段分离结晶模拟.结果显...

Generation Mechanism of Carboniferous Arc Magma and Cumulate Column in Middle Arc Crust,Hadanxun of Northeast Junggar

Secondary-ion mass spectrometric U-Pb age(324.8-323.1 Ma)andδ¹⁸O and laser-ablation multi-collector ICP-MSε_Hf(t)of zircons,mineral chemistry and whole-rock geochemistry and Nd-Sr isotopes of the Carboniferous intrusive complex of Hadanxun were analyzed in this study in order to expound the mechanism of arc magma generation and decipher high P-wave velocity body in the middle crust of Northeast Junggar.Their rare earth element distribution patterns are concave-up.The major and trace element variations from diorite(with entrained hornblendite cumulate)to monzogranite,with decreasing Dy/Yb and primitive-mantle normalized NbN/TaN,can be reproduced with quantitative modeling of fractional crystallization of hornblendite(Stage 1)and feldspar-dominated minerals(Stage 2).They exhibit high Sr/Y,low Y and mean zirconδ¹⁸O of 6.42‰,suggesting derivation from subducting oceanic-slab.Al-in-hornblende barometer reveals that the hornblendite cumulate(population 1:26-22 km depth;population 2:20-18 km)constitutes high P-wave velocity body in the middle crust of Northeast Junggar.The Carboniferous intrusive complex of Hadanxun exhibits high positive zirconε_Hf(t)(weighted mean=12.99)and depletedε_Nd(t)(6.22-6.55)and(⁸⁷Sr/⁸⁶Sr)i(0.7037-0.7040),precluding oceanic crust and continental-crustal materials from Chinese Altay as source component.Thus,the Northeast Junggar was an intra-oceanic arc and the oceanic-plate subduction continued until the Carboniferous.