红海及周边地质构造特征与地球动力学演化

The geotectonic characteristics and geodynamic evolution of the Red Sea Rift and its adjacent areas

红海是地球上最年轻的大洋,其板块构造活动正处于威尔逊旋回的幼年期。红海南北两端分别连接着威尔逊旋回的胚胎期和终结期,即东非大裂谷和地中海。这一独特的地理位置和构造部位使其成为板块构造理论研究的圣地。本文通过对已有的地质、地球物理和地球化学资料进行综合分析,了解了红海地区的地形、重磁异常和沿脊的玄武岩地球化学组成等地质构造特征,探讨了红海裂谷的洋壳分布、地幔源区不均一性以及扩张演化历史等问题。红海地形中间深、南北两端浅,可以分为北、中北、中南、南等四段。重磁异常的条带主要出现在中南段,其他段不明显,因而限制了以往对红海扩张历史的认识。目前认为红海全段存在洋壳,红海两岸的沿岸悬崖是共轭扩张陆缘,呈向南开口的喇叭型扩张,而非对应红海岸线的梭子型。红海裂谷沿脊的地幔源区具有明显的不均一性,南段玄武岩显示E-MORB特征,表现为阿法尔地幔柱的影响。红海的发育经历了裂谷前火山作用(31~29Ma)、大陆张裂(29~13Ma)和洋底扩张(<13Ma)三个主要阶段。红海裂谷的形成演化与非洲大陆的裂解、阿法尔地幔柱的活动、新特提斯洋的闭合等密切相关,了解红海的地球动力学过程将为揭示区域大地构造演化以及板块运动规律提供依据。

The Red Sea is the youngest ocean on Earth, and it is currently in the juvenile ocean basin stage of the Wilson cycle. Its two ends are connected to the East African Rift in the south and the Mediterranean in the north, representing the embryonic and terminal stages, respectively. Due to its unique geographical and tectonic location, the Red Sea is an ideal location for the study of plate tectonics. Through comprehensive analysis of available geological, geophysical and geochemical data, we can reexamine the topography, gravity and magnetic anomalies, as well as the along-axis geochemistry of the basalts. This can help to determine the distribution of oceanic crust, the evolution history of the Red Sea Rift, and the heterogeneity of the mantle source. The Red Sea is deeper in the middle and shallower in the two ends, and it can be divided into four sections: the north, the central-north, the central-south and the south. The stripes of the gravity and magnetic anomalies are mainly observed in the central-south section instead of the other sections, which astricts the previous understanding of the Red Sea’s spreading history. It is currently believed that there is an oceanic crust throughout the entire Red Sea. The coastal escarpments on both sides of the Red Sea represent conjugate rifted continental margins that form a horn-shaped opening to the south, as opposed to the spindle-shaped spreading outlined by the coastline. The along-axis geochemical compositions of the basalts from the Red Sea Rift indicate the mantle source heterogeneity. Enriched MORBs were sampled from the southern section, suggesting the influence of the Afar plume. The Red Sea Rift has undergone three major stages of evolution: pre-rift volcanism(31~29 Ma), continental rifting(29~13 Ma), and oceanic spreading(<13 Ma). The formation and evolution of the Red Sea Rift are closely related to the breakup of Arabian plate from the African continent, the activity of Afar plume and the closure of New Tethys Ocean. The study of the geodynamic process of the Red Sea Rift provides a basis for understanding the geotectonic evolution and plate movement of the region.