北祁连山构造－火山岩浆演化动力学

DYNAMICS OF TECTONO-VOLCANO-MAGMATIC EVOLUTION FROM NORTH QILIAN MOUNTAINS,CHINA

笔者以区域构造－火山岩浆演化动力学为主线，从研究区域火山岩岩石学的角度探索北祁连山古板块构造体制与火山岩浆作用的关系，主要强调区域上不同特点火山岩的成因，其形成应直接与构造环境有关。作者的研究查明，从元古代末至泥盆纪，北祁连山经历了一个由大陆裂开→大洋化→洋盆扩张并俯冲消减→沟、弧、盆体系形成和完善→洋盆收缩闭合→碰撞造山的全过程，每一阶段均发育有相应岩石地球化学特征的海相火山活动。经确定有如下５种特定的火山岩浆产生环境：（１）元古代末－寒武纪大陆裂谷型火山作用，（２）寒武纪末－早奥陶世洋脊－洋岛型火山作用，（３）奥陶纪岛弧火山作用，（４）中－晚奥陶世弧后盆地火山作用，（５）晚奥陶世－志留纪海盆闭合期火山作用。作者的研究揭示，海底块状硫化物矿床的形成与拉张环境下火山岩浆的产生密切相关。因为海底循环的热卤水在此类矿床的形成中起着决定作用，而这种循环作用受与拉张环境相伴的局部高热流和海底火山活动所驱动。

The relation between paleo-plate tectonics and volcanic magmatism in North Qilina Mountains is explored in this paper on the basis of studies of regional volcanic petrology in view of dynamics of regional tectonics-volcnao-magmatic evolution.The main emphasis in this text is on the petrogenesis of various volcanic rocks,the origins of which can be related directly to their tectonic setting.It has been established by author's studies that from the end of Proterozoic era to Devonian period the North Qilina Mountains underwente complete total process:from continental rift→oceanization→spreading and subduction of ocean basin→formation and development of trench-arc-basin system→closing of ocean basin→collision orogenesis and in each stage there occurred respectively specific marine volcanism. On the basis of tectonic setting we can define five distinct environments in which volcanic magmas may be generated:1.Late Proterozoic-Cambrian continental rift volcanism,2.Late Cambrian-Early Ordovician mid-ocean ridge and ocean island volcanism,3. Ordovician island arc volcanism,4.Middle-Late Ordovician back-arc basin vocanism,5.Late Ordovician-Silurian volcanism during closing of ocean basin.Author's studies reveal that there is clearly a close correlation between the processes of volcanic magma generation in tensional tectonic settings and the formation of sea-floor massive sulfide deposits.Hot brine,which circulates through the sea-floor,plays a fundamental role in the formation of this type of ore deposits.The circulation is driven by the localized high heat fluxes and sea-floor volcanic activity associated with extension tectonic settings.