大陆碰撞造山与成矿过程:扎格罗斯和喜马拉雅造山带对比

大陆碰撞造山过程对理解板块构造登陆具有重要启示意义,但相关研究还存在较多问题。例如,几乎每个造山带都存在初始碰撞时限的争议,碰撞造山阶段存在多种划分方案,碰撞成矿作用的地球动力学机制不清楚等。通过综合对比研究扎格罗斯和喜马拉雅造山带构造-岩浆-成矿作用,发现碰撞造成的强烈挤压变形明显滞后于大陆初始碰撞时间。同时,碰撞过程还会出现滞后型弧岩浆作用。将这些碰撞初期出现的滞后型构造岩浆事件单独划分成一个碰撞造山阶段,称之为软碰撞阶段。由此,碰撞造山过程由软碰撞、硬碰撞和后碰撞3个阶段组成。其中,软碰撞阶段主要发育与低速率应变有关的变形构造和与俯冲大洋板片有关的岩浆事件;硬碰撞阶段主要为高速率应变的变形构造和大陆岩石圈俯冲诱发的岩浆事件;后碰撞阶段则会出现大量伸展构造来调节挤压应变,同时发育与大陆岩石圈拆沉、断离和撕裂有关的岩浆作用。软碰撞和硬碰撞阶段的挤压作用会造成铅锌矿床就位在褶皱逆冲带内,硬碰撞和后碰撞阶段发育的大型走滑断层控制斑岩型铜矿床的产出,后碰撞阶段出现的伸展构造赋存有金锑多金属热液矿床。碰撞造山带内保存有早期俯冲和后期碰撞阶段的新生地壳,为碰撞造山带金属成矿提供了物质来源。

Comparisons of the Collision Processes and Related Metallogenesis of Zagros and Himalaya Orogens

The study on continental collision process will shed light on plate tectonics within continent.However,there are some problems about the timing of the initial collision,such as the division about collisional phases and the dynamics of collisional metallogenesis.Comparing Zagros and Himalayan orogens in terms of their deformation,magmatism,and metallogenesis,it is noted that there is a time lag between intense collisional related shorting and initial collision.In the meanwhile,arc-like magmatic activity can also occur within collisional continental zone.It is suggested that the lag time between tectonic-magmatic activities and initiation of continental collision reflects the effects of a collision process involving the“soft”collision.Thus the collision processes can be divided into three phases,including soft collision,hard collision,and post collision.Among them,the soft collision phase is characterized by low-rate contractional deformation and magmatism related to subducted oceanic slab.In contrast,high-rate contractional deformation and magmatism related to subduction of continental lithosphere occur during the hard collision phase.There are lots of extensional structures during post collision phase,and magmatic activity of this phase is mainly induced by delamination,breakoff and tearing of the continental lithosphere.The hydrothermal Pb-Zn ore deposits occur in the fold and thrust belt during soft and hard collision phases.The porphyry Cu deposits are controlled by large strike-slip faults during hard and post collision phases,whereas the detachment-fault-related polymetallic deposits form related to crustal extension during post collision phase.The juvenile crust form during the early subduction phase and subsequent collisional phase,and supply metal for ore-forming system within continental collision zones.