古—中元古代哥伦比亚超大陆裂解的动力学过程及效应

The breakup geodynamic process and effects of the Paleo-Mesoproterozoic Columbia supercontinent

超大陆的聚合与裂解是板块构造运动的自我表达形式,其聚合过程伴随有全球性俯冲、碰撞造山活动,而裂解过程则发育大规模基性岩浆事件。哥伦比亚超大陆是地球地质历史时期第一个真正意义上的全球性超大陆,其主体于2.1~1.8Ga完成聚合,并于1.3 Ga最终裂解。相较于其他年轻的超大陆,哥伦比亚超大陆的古地理重建模型还存在较大的不确定性,这限制了对其裂解动力学过程及效应的认识。本文以全球古—中元古代基性岩浆事件对比为主线,综合已有研究成果及全球岩浆岩地球化学数据,提出古—中元古代多期地幔柱活动主导了哥伦比亚超大陆的不彻底裂解,影响了当时大陆地壳的化学成分和地形高度。高度分异的大陆地壳与低地形导致由陆壳物质风化剥蚀进入海洋的营养物质的通量大大降低,进而限制了海洋生物的初级生产力,最终阻碍了哥伦比亚超大陆至罗迪尼亚超大陆过渡时期的生命演化进程。

The assembly and breakup of supercontinents is the self-expression of plate tectonics.The assembly stage is accompanied by global-scale subduction and collisional orogeny,while the fragmentation stage produces large-scale mafic magmatic events.The Columbia supercontinent was the first true supercontinent in Earth's history,and its main body coalesced between 2.1~1.8 Ga and finally broke apart at 1.3 Ga.Compared with the other younger supercontinents,the paleogeographic reconstruction model of the Columbia supercontinent still remains quite uncertain,which profoundly influences our understanding of the geodynamic processes and effects of its breakup.In this study,based on the correlation of global Paleo-Mesoproterozoic mafic magmatism events,integrated with the published work and analysis of global igneous rock geochemical data,we proposed that multiple Paleo-Mesoproterozoic mantle plume events resulted in the incomplete breakup of the Columbia supercontinent,which significantly affected the geochemical compositions and topographic height of the continental crust at that time.Highly differentiated continental crust and low topographic height together greatly reduced the flux of nutrients into the ocean by weathering and denudation of continental crust materials,thus limiting the primary productivity of marine organisms,and ultimately stalling the evolution of life during the transition period from the Colombian supercontinent to the Rodinia supercontinent.