阿尔金北缘喀腊大湾地区早古生代的中酸性火山岩为一套英安岩—流纹岩—粗面英安岩(少量)组合,在岩石地球化学上高SiO2、富碱(Na2O/K2O =0.4 ～22.2,Na2O+ K2O =2.49％ ～9.74％)、低钛,里特曼指数(δ)为0.20～5.52,铝饱和指数A/CNK为0.8～1.4,指示这是一套低钾—中钾钙碱性—碱性钾玄质(少量)火山岩,自北向南具有从准铝质Ⅰ型向弱过铝质—强过铝质S型花岗质岩浆过渡的特征.LREE、K、Ba、Th(U)、Pb、Zr富集以及Nb(Ta)、P、Ti的亏损指示其形成于与俯冲消减作用有关的活动大陆边缘环境.岩石地球化学研究表明,英安岩和流纹岩不存在分异演化关系,其源岩分别为变质(基性)火山岩和变质泥质岩.结合区域地质特征,认为该套中酸性火山岩形成于活动大陆边缘洋壳俯冲消减后期同碰撞—碰撞后的环境,是俯冲碰撞过程中陆壳巨量增厚,碰撞后伸展阶段中下地壳(或岩石圈)拆沉,幔源岩浆底侵,诱发趋于成熟的大陆边缘弧地壳在不同深度位置上发生部分熔融的产物.这一地质过程是对同一时期阿尔金北缘地区古大洋自北向南俯冲消减到米兰—金雁山地块之下的动力学机制的响应,也为判断阿尔金北缘红柳沟—拉配泉地区蛇绿混杂岩带早古生代的俯冲极性提供了佐证.%The Early paleozoic intermediate—felsic rock suit located in Kaladawan area consisting of mainly dacite,rhyolite and limited trachy dacite.They are geochemically characterized by high content of SiO2,high total alkali (Na2O + K2O =2.49％ ～9.74％,Na2O/K2O =0.4 ～ 22.2),low but variable TiO2 on the whole.Moreover Rittman values (δ) ranging from 0.2 to 5.52,alumina saturation index A/CNK (molecular proportion)ranging from 0.8 to 1.4 and corundum occurring in CIPW calculation which geochemically indicates that the dacite—rhyolite suite is attributed to low-K to med-K calc-alkaline rocks series and alkaline shoshonite series with a transition character that from metaluminous I-type to weakly—strongly peraluminous S-type granitics north—south through the Kaladawan aera.The remarkable enrichment of LREE,K,Ba,Th (U),Pb,Zr and distinct depletion of Nb (Ta),P,Ti,Sr,Rb inplys a closely subduction-related origin at active continental margin arcs.Petrological and geochemical features indicate that the dacites generated by dehydration partial melting of metaigeneous,the rhyolites derived from the dehydration partial melting of metapelites,and they could' nt be homologous magma evolution series.Combined with the field observational data,we presume that the intermediate—felsic rock suit is generated during syn-colllison and post-collision events of the late stage subduction in an active continental margin arc,they derived from partial melting at different depths of the grown crust below it which is due to low crustal (or lithospheric) delamination and asthenosphere mantle underplating caused by the thickening of continental crust during subduction and collision or stretching and thinning of the lithosphere in post-collision.Above all,the intermediate—felsic magmatic activity in Kaladawan area is a direct response to the southward subduction of ancient oceanic crust in Northern Altyn to the Milan—Jinyanshan Terrain during the Early Paleozoic period,and this also provides a definite evidence for confirming the polarity of Hongliugou-Lapeiquan ophiolite mélange zone in the North Altyn Mountain.
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