Geodynamic Development of Eurasian Active Margin at Pre-collision Subduction and at Post-collision Closing of Tethys Ocean

Geodynamic development of Eurasian Active Margin is related to Phanerozoic collision and closure of Tethys Ocean coincided with northvergent movement and stressing of Afro-Arabian continent at the Eurasian margin.The collision coincided with subduction oceanic Slab under margin of continent at pre-collision stage revealed in formation of island arc,inter-arc backarc and minor ocean settings at pre-collision stage.After closure of ocean the subduction is terminated and pre-collision stage transferred in post-collision and orogenesis,caused by stressing Afro-Arabian continent at the Eurasian.Character of subduction determined the settings of pre-collision stage.The island arc setting is related with steady state subduction,interarc-backarc and minor ocean settings are controlled by steepening of subducting slab which caused invasion of mantle diapir extension and spreading the crust revealed in rifting in interarc-backarc and intensive spreading in minor ocean setting,whereas at island arc setting the mantle invasion and spreading did not occur.So,scale of mantle material participation in various settings determined character of volcanism and tectonics.The island arcs are characterized by calc-alkaline rhyo-dacite-andesite-basalt volcanism blocking tectonics,revealed in island uplifting and gold-base metal mineralization.The interarc-backarc settings revealed in tholeiite-olivine basaltic volcanism,rifting and Zn-Cu mineralization the minor ocean setting controlled by ophiolite volcanism ultimatic dunite-peridotite-magmatism and the most intensive spreading of lithosphere and copper-pyrite mineralization confirmed by volcano-petrogenic,metallogenic and tectonic indications and geochemical cryteria.Therefore,type of volcanism,magmatism and mineralization at precollision development are controlled by scale and influence of crustal-mantle participation.The post-collision stage of geodynamic development also is characterized by various scales of crustal mantle influence.Our studied region consists of pre-and post-collision stages,located in Iran,Caucasus,Turkey and Balcan-Carpathian is parth of the Eurasian active margin.At post-collision,as at pre-collision stages the volcanic-magmatic activity,tectonics and mineralization are depended on the crustial-mantle scale of influence and are controlled by volcano-petrogenic,metallogenic,as well as,tectonical and geochemical indicators.

阿尔金碰撞造山带西段的构造特征

根据阿尔金山西段前早古生代变质岩的岩石组成、沉积建造、变形变质作用改造历史、岩石地球化学特征等研究,将阿尔金碰撞造山带西段划分为3个构造单元:北阿尔金地块、中阿尔金地块(包括英格里克构造-蛇绿混杂岩带、肖鲁克·布拉克高压变质岩带和塔什萨依玉石矿高绿片岩相—低角闪岩相变质岩带)和南阿尔金地块(包括南阿尔金中—新元古界隆起带和阿尔金南缘复合构造-蛇绿混杂岩带)。提出该碰撞造山带经历了前长城纪古陆核形成阶段、长城纪—青白口纪不同基底联合阶段和早古生代洋陆转换阶段3个阶段的构造演化。

Crustal and Mantle Sources at Various Settings of Phanerozoic Geodynamic Development Expressed in Volcanism and Metallogeny of Eurasian Active Margin

Phanerozoic geodynamic development of the Tethys ocean revealed at Eurasian active margin is manifested in pre-and post-collision stages.The Phanerozoic crust was already divided into sialic and basaltic crusts and rigid upper mantle.The precious and nonferrous metals were redistributed between them.In the sialic crust,precious metals are concentrated: Au,Ag and Pb,in basaltic crust—zinc,the copper mainly rests in the mantle.Phanerozoic plate-tectonics was manifested in the following settings: island arc,inter/backarc and oceanic.Island arc setting correlates with steady-state subduction and controlled by calc-alkaline volcanism.At this stage,the sialic,basaltic crust and mantle material participate in volcanism,whereas the subducted slab plunged in mantle,the metallogenic indicators are Au,Pb,Zn and Cu.The stage of inter/backarc is related to steepening of subducting slab,because mantle diapir incursion provokes the rifting.At the initial stage and at stage of slackening rifting,when the sialic crust is not yet spread out from zone of volcanic activity,mineralization was represented by subalkaline trachydacites,shoshonite and alkali basaltic volcanism(volcanological indicators)and Au and Pb are participated with Zn and Cu in mineralization.The strengthening of steepening with mantle diapir incursion on higher level rifting spread out the sialic crust,volcanism on this stage is tholeiitic and mineralization is represented by zinc-copper-pyrite VMS(Volcanogenic Massive Sulphide)ores.The minor ocean setting is controlled by the most intensive spreading provoked by incursion mantle diapir at highest level,and spread out the basaltic crust as well,and volcanism belongs to ophiolites with dunite-peridotite magmatic activity.The mineralization was represented by copper-pyrite ores and single metallogenic indicator is the copper.The convergence of Eurasian and Afro-Arabian continents and closing of Tethys Ocean resulted in transferring the pre-collision stage in post-collision,characterized by trace elements Sb,W,Mo,Hg,as geochemical and metallogenic indicator of the postcollision setting.